Gilroy City Council
July 29, 2024

10.4.3 Critical Facilities
Critical facilities as defined for this plan will continue to be operational during a drought. Critical facility elements such as landscaping may not be maintained due to limited resources, but the risk to the Santa Clara County OA’s critical facilities functions is low.

10.4.4 Environmental Impact
Environmental losses from drought are associated with damage to plants, animals, wildlife habitat, and air and water quality; forest and range fires; degradation of landscape quality; loss of biodiversity; and soil erosion. Some of the effects are short-term and conditions quickly return to normal following the end of the drought. Other environmental effects linger for some time or may even become permanent.

Wildlife habitat, for example, may be degraded through the loss of wetlands, lakes, and vegetation.

However, many species will eventually recover from this temporary aberration. The degradation of landscape quality, including increased soil erosion, may lead to a more permanent loss of biological productivity. Although environmental losses are difficult to quantify, growing public awareness and 162 United States Geological Survey. (2000, December). Land Subsidence in the United States. https://water.usgs.gov/ogw/pubs/fs00165/#:~:text=Thepercent20sitepercent20ispercent20inpercent20thepercent20Sa npercent20Joaquinpercent20Valley,resultedpercent20inpercent20permanentpercent20subsidencepercent20andperc ent20relatedpercent20groundpercent20failures.

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concern for environmental quality has forced public officials to focus greater attention and resources on these effects.

Santa Clara County Tree Mortality Exposure
Large numbers of trees have died in California since the beginning of the 2012-2016 drought. Most of these trees were stressed from higher temperatures and a shortage of water, making them more vulnerable to insects and diseases. California’s pattern of tree mortality corresponds with global trends that are linked to increasingly dry and hot climatic conditions. Prolonged periods of drought, combined with the increased infestation of native bark beetles, have contributed to the death of millions of trees on federal, state, and private lands across the state. Removal of these dead trees can be costly and challenging, which can add to the financial impacts of drought. “Many trees in California’s forests were turning rust colored as another year of drought and bark beetles or other insects led to higher tree mortality. Trees were stressed from inadequate water and could not produce enough sap or pitch to defend themselves against insects.” Drought Impact Reporter Dashboard
October 19, 2022
The following figures show the areas where the state is focused for removal of dead trees. The Tier 1 Tree Mortality High Hazard Zones (see Figure 52) represent areas of tree mortality in direct proximity to assets determined to be important to life and property (including communications, transportation, recreation, communities, and utilities). These areas were designated by state and local governments as being in greatest need of dead tree removal, pursuant to the California Governor’s Emergency proclamation on October 30, 2015.

The Tier 2 Tree Mortality High Hazard Zones, shown in Figure 53, are defined by watersheds that have elevated tree mortality as well as significant community and natural resource assets.

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Figure 53: Tier 1 Tree Mortality High Hazard Zones162 F 163
Figure 54: Tier 2 Tree Mortality High Hazard Zones163 F 164
163 California State Geoportal. (2022 June 2). California High Hazard Zones (Tier 1). https://gis.data.ca.gov/maps/a71a85136b0b414ea734fdfbe3d7674a/explore?layer=0&location=37.231739%2C121.694821%2C9.99 164 California State Geoportal. (2022 June 2). California High Hazard Zones (Tier 2). https://hub.arcgis.com/maps/e50b7577426c4367a518b80b38e9b5d8/explore?location=37.371146%2C121.549960%2C10.88

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10.4.5 Economic Impact
Drought causes the most significant economic impacts on industries that use water or depend on water for their business, most notably, agriculture and related sectors (forestry, fisheries, and waterborne activities). In addition to losses in yields in crop and livestock production, drought is associated with increased insect infestations, plant diseases, and wind erosion. Water- and lake-related recreational activities including, but not limited to, fishing, swimming, rafting, and canoeing are valuable for the local and regional economy, particularly when the lake/reservoir is located in a rural area with limited other recreational/tourism opportunities. Drought can lead to other losses because so many sectors are affected losses that include reduced income for farmers and reduced business for retailers and others who provide goods and services to farmers.

This leads to unemployment, increased credit risk for financial institutions, capital shortfalls, and loss of tax revenue. Prices for food, energy, and other products may also increase as supplies decrease. When a drought occurs, the agricultural industry faces risk of economic impact and damage. During droughts, crops do not mature, resulting in smaller crop yields, undernourishment of wildlife and livestock, decreases in land values, and ultimately financial losses to farmers.164F 165 Agriculture production has been a
significant and growing factor in Santa Clara County, especially as agricultural effects on the economy start to normalize (after a period of decline).

Evaluation of direct effects (i.e., excluding indirect and induced spending benefits) can occur based on information conveyed in USDA reports. According to the 2017 Census of Agriculture, 890 farms were present in Santa Clara County, encompassing 288,084 acres of total farmland. The average farm size was 324 acres.

Santa Clara County farms had a total market value of products sold of $310.2 million ($293.7 million in vegetable crops including nursery and greenhouse; and $18.4 million in cattle, layers, and horses, and related products), averaging $348,524 per farm.

A prolonged drought can affect a community’s economy significantly. Increased demand for water and electricity may result in shortages and higher costs of these resources. Industries that rely on water for business may be impacted the most (e.g., landscaping businesses). Although most businesses will still be operational, they may be affected aesthetically—especially the recreation and tourism industry. Moreover, droughts within another area could affect food supply/price of food for residents within the Santa Clara County OA.

10.5 Future Trends in Development
Land use planning is also directed by general plans adopted under California’s General Planning Law.

Municipal planning partners are encouraged to establish General Plans with policies directing land use and dealing with issues of water supply and protection of water resources. These plans increase capability at the local municipal level to protect future development from impacts of drought. All planning partners reviewed their general plans under the capability assessments undertaken for this effort.

Deficiencies revealed by these reviews can be identified as mitigation actions to increase capability to deal with future trends in development.

To confront the challenges of increasing drought vulnerability, several efforts are underway to address water needs in the OA. Santa Clara Valley Water District is investing in locally reliable, sustainable and efficient water supplies such as recycled and purified water. Santa Clara County has adopted a modified Water Efficient Landscape Ordinance to guide future landscape and water management practices to promote long-term water efficiency.
165 National Integrated Drought Information System. (n.d.). Agriculture. https://www.drought.gov/sectors/agriculture

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10.6 Scenario
Drought is a cyclic part of the climate of California. Continuation or exacerbation of the current situation across the State (i.e., an extreme, multiyear drought associated with record-breaking rates of low precipitation and high temperatures) is the worst-case scenario for Santa Clara County. Low precipitation and high temperatures increase possibility of wildfires throughout the County, increasing need for water when water is already in limited supply. Surrounding counties, also under drought conditions, could increase their demand for the water supplies on which Santa Clara County also relies, triggering social and political conflicts. The higher density population of the Bay Area increases the likelihood of such conflicts. Additionally, the longer drought conditions last in or near the Santa Clara OA, the greater the effect on the local economy; water-dependent industries especially will undergo setbacks. According to the USGS, “Climate change exacerbates droughts by making them more frequent, longer, and more severe.”165F
166

10.7 Issues
Important issues associated with drought in the OA include the following:
 Identification and development of alternative water supplies.  Utilization of groundwater recharge techniques to stabilize the groundwater supply.  The probability of increased drought frequencies and durations due to climate change.  The promotion of active water conservation even during non-drought periods.  Monitoring of implementation and benefits of the Long-Term Reliable Water Supply Strategy projects, Water Conservation Implementation Plan projects, and water system capital improvement upgrades.
 Application of alternative techniques (groundwater recharge, water recycle, local capture and reuse, desalination, and transfer) to stabilize and offset Sierra Nevada snowpack water supply shortfalls.
 Regular occurrence of drought or multiyear droughts that may limit the Operational Area’s ability to successfully recover from or prepare for more occurrences-particularly noteworthy due to longevity of the current ongoing drought.

Table 61: EMAP Consequence Analysis: Drought
Subject Ranking Impacts/Drought
Health and Safety of
Persons in the Area of the
Incident
Minimal to
moderate
Drought impact tends to be agricultural; however,
because of the lack of precipitation that leads to drought, water supply disruptions can occur, which can affect
people. The impact is expected to be minimal.

Responders Minimal With proper preparedness and protection, the impact on the responders is expected to be minimal.

Continuity of Operations Minimal There is minimal expectation for utilization of the COOP. 166 U.S. Geological Survey. (n.d.). Droughts and Climate Change. https://www.usgs.gov/science/scienceexplorer/climate/droughts-and-climate-change

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Subject Ranking Impacts/Drought
Property, Facilities, and
Infrastructure
Minimal to
severe
Impact on property, facilities, and infrastructure could be minimal to severe, depending on the length and intensity of the drought. The structural integrity of buildings and buckling of roads could be affected.

Delivery of Services Minimal The impact on the delivery of services should be nonexistent or minimal.

Environment Minimal to
severe
The impact on the environment could be severe. Drought
can severely affect farming, ranching, wildlife, and plants due to the lack of precipitation.

Economic Conditions Minimal to
moderate
Impacts on the economy will be dependent on how
extreme the drought is and how long it lasts.

Communities that depend on water recreation could be
tested, as well as agricultural.

Public Confidence in
Jurisdiction’s Governance
Minimal Confidence could be an issue during periods of extreme drought if planning is not in place to address intake needs and the loss of agricultural crops.

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11 Climate Change

11.1 General Background
Definitions
 Climate Change: changes in average weather conditions that persist over multiple decades or longer1.
 Climate Mitigation: action taken to curb climate change by reducing or preventing the emission of greenhouse gases.
 Climate Adaptation: action taken to protect the community from the impacts of a changing climate.  Adaptative Capacity: an estimate of the community’s current ability to deal with the projected impacts of climate change.

Climate, consisting of patterns of temperature, precipitation, humidity, wind and seasons, plays a fundamental role in shaping natural ecosystems and the human economies and cultures that depend on them. Climate change is defined as “changes in average weather conditions that persist over multiple decades or longer. Climate change encompasses both increases and decreases in temperature, as well as shifts in precipitation, changing risk of certain types of inclement weather events, and changes to other features in the climate system.”16F
167 A key indicator of climate change is the increase of global temperatures.

Multiple temperature records from all over the world have shown a warming trend. The Intergovernmental Panel on Climate Change (IPCC) has stated that the warming of the climate system is unequivocal.167F 168
The 2022 global average surface temperature was 1.55 °F warmer than the 20th-century average of 57.0 °F and about 1.90 ˚F warmer than the pre-industrial period (1880-1900). In fact, the ten warmest years on record have all occurred since 2010, with the last nine years of 2014-2022 among the ten warmest years.168F
169 2022 ranked as the sixth-warmest year on record since 1880.169F170 Although this temperature change may seem small, it means a significant increase in accumulated heat worldwide which is driving regional and seasonal temperature extremes, reducing snow cover and sea ice, intensifying heavy rainfall, and changing habitat ranges for plants and animals—expanding some and shrinking others.170F 171
167 Globalchange.gov. (No Date). Glossary. https://www.globalchange.gov/climate-change/glossary 168 The Intergovernmental Panel on Climate Change. (n.d.). Summary for Policymakers. https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_SummaryForPolicymakers.pdf 169 https://www.noaa.gov/news/2022-was-worlds-6th-warmest-year-on-record 170 National Oceanic and Atmospheric Administration. (2023, January 12). 2022 Was World’s 6th -Warmest Year on
Record. https://www.noaa.gov/news/2022-was-worlds-6th-warmest-year-on-record 171 National Oceanic and Atmospheric Administration. (2023, January 18). Climate Change: Global Temperature. https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature#SnippetTab

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Figure 55: Global Temperature 1880-202217 F
172
The global warming temperature trend and its related impacts are caused by an exponential increase of greenhouse gas emissions including carbon dioxide, methane, nitrous oxide, and fluorinated gases.

Emissions of these gases come from a variety of sources, such as the combustion of fossil fuels for energy and transportation, agricultural production, changes in land use and volcanic eruptions. According to the U.S. Environmental Protection Agency (EPA), carbon dioxide concentrations measured about 280 parts per million before the industrial era began in the late 1700s and reached 414 parts per million in 2021, a 48% increase.172F
173 See Figure 54. In addition, the concentration of methane has more than doubled since pre-industrial times, and nitrous oxide is being measured at a record high of 334 parts per billion.173F 174
172 NASA. (n.d.). World of Change: Global Temperatures. https://earthobservatory.nasa.gov/world-of-change/globaltemperatures 173 Environmental Protection Agency. (n.d.) Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases. https://www.epa.gov/climate-indicators/climate-change-indicators-atmospheric-concentrations-greenhousegases#:~:text=Carbon%20dioxide%20concentrations%20have%20increased,is%20due%20to%20human%20activitie s
174 Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock, eds. (2017). Climate science special report: Fourth National Climate Assessment, volume I. U.S. Global Change Research Program. https://science2017.globalchange.gov/.

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Figure 56: Global Carbon Dioxide Concentrations Over Time174F 175
Scientists can place this rise in carbon dioxide in a longer historical context through the measurement of carbon dioxide in ice cores. According to these records and illustrated in Figure 55, carbon dioxide concentrations in the atmosphere are the highest that they have been in 650,000 years.175F 176
The major scientific agencies of the United States and the world—including NASA, NOAA, and the Intergovernmental Panel on Climate Change (IPCC)—agree that long-term climate change is occurring.

There is broad scientific consensus (97 percent of scientists) that the current, unprecedented climatewarming trends are very likely due to human activities.176 F 177 Unless emissions of greenhouse gases are
substantially reduced, this warming trend is expected to continue.

11.1.1 Climate Change Indicators
Climate change will affect the people, property, economy, and ecosystems of the Santa Clara County Operational Area (OA) in a variety of ways. Some of these impacts are already being felt. Widespread, pervasive impacts to ecosystems, people, settlements, and infrastructure have resulted from observed increases in the frequency and intensity of climate and weather extremes, including temperature extremes on land and in the ocean, heavy precipitation, drought, and fire weather.17F 178 Rising global
temperatures have also been accompanied by other more localized changes in weather and climate. 2022 serves as a good example of this.
175 Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock, eds. (2017). Climate science special report: Fourth National Climate Assessment, volume I. U.S. Global Change Research Program. https://science2017.globalchange.gov/.
176 NASA. (2023). Carbon Dioxide. https://climate.nasa.gov/vital-signs/carbon-dioxide/ 177 NASA. (n.d.). Scientific Consensus: Earth’s Climate is Warming. https://climate.nasa.gov/scientific-consensus/ 178 The Intergovernmental Panel on Climate Change. (n.d.). Summary for Policymakers. https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_SummaryForPolicymakers.pdf

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The OA started the year in the drought, experienced record high temperatures in the summer that reached as high as 109 degrees Fahrenheit in San José and ended with the start of multiple atmospheric rivers which brought record rainfall and flooding.

California’s number of extreme heat events (including both days and nights) has increased. In particular, there has been an increase in nighttime temperatures. Scientists have demonstrated that nighttime temperatures are more sensitive to the greenhouse gases which cause climate change178 F 179. This example
helps demonstrate the consequence of climate change that are already being felt throughout the region.

The planet’s oceans and glaciers have also experienced changes: oceans are warming and becoming more acidic, ice caps are melting, and sea levels are rising.179F 180,
180F
181 Sea level along the U.S. coastline is
projected to rise, on average, 10 to 12 inches in the next 30 years (2020–2050), which will be as much as the rise measured over the last 100 years (1920–2020). This has already put some coastal homes, beaches, roads, bridges, and wildlife at risk. As a coastal county, sea-level rise is one of the most concerning impacts of climate change facing the OA. At the time of the development of this plan, NASA reports the following trends18F
182:
 Carbon Dioxide: Increasing trend, currently at 419 parts per million as of February 2023.  Global Temperature: Increasing trend, increase of 1.6 ºF since 1880.  Arctic Ice Minimum: Decreasing trend, 12.6% per decade.  Land Ice: Decreasing trend, Antarctica is losing approximately 150 billion tons a year and Greenland is losing about 270 billion tons per a year.
 Sea Level: Increasing trend, 3.8 inches per year.

Climate change impacts are most frequently associated with negative consequences, for example, warmer average temperatures could increase air conditioning costs and affect the spread of diseases like Lyme disease but could also improve conditions for growing some crops. More extreme variations in weather are also a threat to society. More frequent and intense extreme heat events can increase illnesses and deaths, especially among vulnerable populations, and damage some crops. While increased precipitation can replenish water supplies and support agriculture, intense storms can damage property, cause loss of life and population displacement, and temporarily disrupt essential services such as transportation, telecommunications, energy, and water supplies.182F
183 The most important effect for the development of this plan is that climate change will have a measurable impact on the occurrence and severity of natural hazards.

11.1.2 Projected Future Impacts
The Fourth National Climate Assessment Report for the United States183F 184 indicates that impacts resulting
from climate change will continue through the 21st century and beyond. Evidence of human-caused climate change is overwhelming and continues to strengthen. 179 California Office of Environmental Health Hazard Assessment. (2019, February 11). Extreme Heat Events. https://oehha.ca.gov/epic/changes-climate/extreme-heat-events 180 National Oceanic and Atmospheric Administration. (2023, January 12). 2022 Was World’s 6th -Warmest Year on
Record. https://www.noaa.gov/news/2022-was-worlds-6th-warmest-year-on-record 181 U.S. Geological Survey. (2022, March 1). Global and Regional Sea Level Rise Scenarios for the United States. https://www.usgs.gov/publications/global-and-regional-sea-level-rise-scenarios-united-states 182 NASA. (n.d.). Ice Sheets. https://climate.nasa.gov/vital-signs/ice-sheets/ 183 Environmental Protection Agency. (n.d.). Climate Change Indicators: Weather and Climate. https://www.epa.gov/climate-indicators/weather-climate
184 U.S. Global Change Research Program. (n.d.). Fourth National Climate Assessment. https://nca2018.globalchange.gov/

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The impacts of climate change are intensifying across the country and represent a real threat to Americans’ physical, social, and economic well-being are rising. These impacts are projected to intensify, however how much they intensify will depend on actions taken to reduce global greenhouse gas emissions and to adapt to the risks from climate change now and in the coming decades.184F 185
The California Climate Adaptation Planning Guide (APG) outlines the following climate change impact concerns for the Bay Area Region communities185F
186:
 Increased temperature
 Reduced precipitation
 Sea level rise – coastal inundation and erosion
 Public health – heat and air pollution
 Reduced agricultural productivity
 Inland flooding
 Reduced tourism
According to the Fourth U.S. National Climate Change Assessment, after the third climate assessment where there were more than twice as many high temperature records as low temperature records broken between 2001 and 2012, global high temperature records continued to be broken in 2014, 2015, and 2016. Heavy rainfall events and large forest fire incidents are becoming more frequent and more severe.

Long-term impacts, like a continued decline in arctic ice and increase chronic drought, are expected.

Cal-Adapt,186F
187 a resource for public information on how climate change might impact local communities, based on the most current data available, has projected increases in temperature within the OA in particular. Table 62 shows the expected increases in average maximum temperatures and Table 63 addresses the number of extreme heat days per year. The increase in average surface temperatures can also lead to more intense heat waves that can be exacerbated in urbanized areas by what is known as the urban heat island effect.

Table 62: Average Maximum Temperature – Santa Clara County187F 188
Baseline (1961–1990)
Medium Emissions (RCP 4.5) High Emissions (RCP 8.5)
Mid-Century End-Century Mid-Century Mid-Century
30-year
average

68.6 oF 72.0 oF 73.1 oF 72.8 oF 76.0 oF
30-year range 68.4–68.8 oF 70.5–73.5 oF 71.0–75.7 oF 70.9–75.0 oF 73.2–80.5 oF 185 U.S. Global Change Research Program. (n.d.). Fourth National Climate Assessment, Chapter 1: Overview. https://nca2018.globalchange.gov/chapter/1/
186 Cal OES. (June 2020). Climate Adaptation Planning Guide. https://www.caloes.ca.gov/wpcontent/uploads/Hazard-Mitigation/Documents/CA-Adaptation-Planning-Guide-FINAL-June-2020-Accessible.pdf 187 Cal-Adapt. (n.d.). Explore and analyze climate data from California’s Climate Change Assessment. https://caladapt.org/ 188 Cal-Adapt. (n.d.). Annual Averages. https://cal-adapt.org/tools/annual-averages

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Table 63: Number of Extreme Heat Days Per Year
(Heat Is above 92.7 oF) Santa Clara County18F
189
Baseline (1961-1990)
Medium Emissions (RCP 4.5) High Emissions (RCP 8.5)
Mid-Century End-Century Mid-Century End-Century
30-year
average
4 days/yr. 12 days/yr. 17 days/yr. 17 days/yr. 31 days/yr. 30-year range 0–16 days/yr. 0–32 days/yr. 2–44 days/yr. 1–61 days/yr. 0–101 days/yr.

Although the California Climate Adaptation Planning Guide projected reduced precipitation in the region, recent Cal-Adapt projections show significant increases in Santa Clara County’s average annual precipitation levels (see Table 64).

Table 64: Average Annual Precipitation – Santa Clara County189F 190
Baseline (1961-1990)
Medium Emissions
(RCP 4.5)
High Emissions
(RCP 8.5)
Mid-Century End-Century Mid-Century End-Century
30-year
average

23.8 inches 26.0 inches 26.0 inches 26.3 inches 9.1–68.6 inches
30-year range

8.2–51.5
inches

9.2–54.5
inches

9.0–51.3
inches 29.2 inches 8.6–63.6 inches
Climate change projections contain inherent uncertainty, largely derived from the fact that they depend on future greenhouse gas emission scenarios. Generally, the uncertainty in greenhouse gas emissions is addressed by the presentation of differing scenarios: low-emissions to high-emissions scenarios. In lowemissions scenarios, there is an effort to limit greenhouse gas emissions leading to emissions starting to decline close to mid-century. In high-emissions scenarios, greenhouse gas emissions continue to increase at current rates through the end of the century. Different climate scenarios can also be described in terms of likelihood and confidence. Likelihood refers to the statistical probability of the effect described occurring. Confidence refers to how valid that result is likely to be, based on available data and its consistency with current literature. There will always be some level of uncertainty when estimating future conditions. Uncertainty in outcomes is addressed by averaging a variety of climate change model outcomes or providing a range of outcomes. Despite this general uncertainty, climate change projections present valuable information to help guide decision-making. 189 Cal-Adapt. (n.d.). Extreme Heat Days & Warm Nights. https://cal-adapt.org/tools/extreme-heat 190 Cal-Adapt. (n.d.). Annual Averages. https://cal-adapt.org/tools/annual-averages

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Figure 57: Impacts of Climate Change on Human Health190F 191

11.1.3 How Climate Change Impacts Hazard Mitigation
An essential aspect of hazard mitigation is estimating the likelihood of hazard events. Traditionally, the probability of a hazard event occurring has been expressed as a statistical projection based on records of past events. This approach assumes that the likelihood of hazard events occurring remains essentially unchanged over time. Thus, averages based on the past frequencies of floods, for example, are used to estimate future flooding frequencies: if a river has flooded an average of once every five years for the past 100 years, then it can be expected to continue to flood an average of once every five years.

For hazards that are affected by climate conditions, the assumption that future behavior will be equivalent to past behavior may not be valid given that climate conditions are changing. As flooding is generally associated with precipitation frequency and quantity, for example, the frequency of flooding will not remain constant if broad precipitation patterns change over time. 191 California Department of Public Health. (February 2017). Climate Change and Health Profile Report – Santa Clara County.
https://www.cdph.ca.gov/Programs/OHE/CDPH%20Document%20Library/CHPRs/CHPR085SantaClara_County2- 23-17.pdf

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Specifically, as hydrology changes, storms currently considered to be a one percent annual chance flood event (100-year flood) might strike more often, leaving communities at greater risk of flooding. The risks of landslide, severe storms, extreme heat events and wildfire are all affected by climate patterns as well.

For this reason, an understanding of climate change is pertinent to efforts to mitigate natural hazards.

Information about how climate patterns are changing provides insight on the reliability of future hazard projections used in mitigation analysis. This section summarizes current understandings about climate change in order to provide a context for the recommendation and implementation of hazard mitigation measures.

Table 65: Potential Direct and Related Climate Change Impacts in the Operational Area Direct Impacts Related Impacts
Rising temperatures  Heat wave
 Changes in wind patterns19F
192
 Drought
 Reduced snowpack
 Increased extreme events, including severe storms and wildfires  Shifting human health and disease patterns.
 Sea Level Rise
 Permanent inundation of previously dry land
 Larger area impacted by extreme high tide
 Increased coastal erosion
 Saltwater intrusion into freshwater systems
Changes in precipitation192F
193  Changed seasonal patterns
 Flooding
 Saturated earth
 Reduced snowpack
 Drought
The links between these climate change indicators and most of the natural and other hazards of concern profiled in this MJHMP are direct but less clear for other hazards as illustrated in Table 66 and discussed later in this section.
192 Columbia Climate School. (2021, January 6). Will Global Warming Bring a Change in the Winds? https://news.climate.columbia.edu/2021/01/06/westerly-winds-climate-change/ 193 Columbia Climate School. (2021, January 6). Will Global Warming Bring a Change in the Winds? https://news.climate.columbia.edu/2021/01/06/westerly-winds-climate-change/

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Table 66: Climate Change Impacts on Natural and Other Hazards Negative Impact on Natural and Other Hazards
Climate Change
Indicator
Natural Hazards Other
Dam and Levee
Failure
Drought
Earthquake
Flood
Landslide
Inclement
Weather
Tsunami
Wildfire
Sea Level Rise
Terrorism
Technological
Incidents
Power Outages
Epidemic/Pandemic
Fog
Rising temperatures X X X X X X X X X
Heat wave X X X X X X X
Changes in wind
patterns193F
194

X X X X X X X
Drought N/A X X X
Reduced snowpack X X X
Increased extreme events,
including severe storms
and wildfires

X X X N/A X
Shifting human health and
disease patterns
X
Sea Level Rise X X X X X N/A X X
Changes in precipitation194F
195 X X X X X X X X X
Changes in seasonal
patterns

X X X X X X X X X
Flooding X N/A X X X X
Saturated earth X X X X X
194 Columbia Climate School. (2021, January 6). Will Global Warming Bring a Change in the Winds? https://news.climate.columbia.edu/2021/01/06/westerly-windsclimate-change/

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11.2 Responses to Climate Change
Communities and governments worldwide are working to address, evaluate and prepare for climate changes that are likely to impact communities in coming decades. Climate change discussions encompass two separate but inter-related considerations: mitigation and adaptation. The term “mitigation” can be confusing because its meaning changes across disciplines:
 Mitigation in restoration ecology and related fields generally refers to policies, programs or actions that are intended to reduce or to offset the negative impacts of human activities on natural systems. Mitigation can be understood as avoiding, minimizing, rectifying, reducing, or eliminating, or compensating for known impacts.195F
196
 Mitigation in climate change discussions is defined as “reducing emissions of and stabilizing the levels of heat-trapping greenhouse gases in the atmosphere.”196F 197 The goal is to stabilize the
climate and avoid significant human interference.
 Mitigation in emergency management is typically defined as the effort to reduce loss of life and property by lessening the impact of disasters.197F
198
In this section, mitigation is used as defined by the climate change community. In the other sections of this plan, mitigation is primarily used in an emergency management context. The IPCC defines adaptation as “the process of adjustment to actual or expected climate and its effects.” Mitigation and adaptation are related, as the world’s ability to reduce greenhouse gas emissions will affect the degree of adaptation that will be necessary. Moreover, some initiatives and actions can both reduce greenhouse gas emissions and support adaptation to likely future conditions. The ability to adapt to changing conditions is often referred to as adaptive capacity, which is “the ability of systems, institutions, humans and other organisms to adjust to potential damage, to take advantage of opportunities, or to respond to consequences.”198F 199
Societies across the world are facing the need to adapt to changing conditions and to identify ways to increase their adaptive capacity. Some efforts are already underway. Farmers are altering crops and agricultural methods to deal with changing rainfall and rising temperature; architects and engineers are redesigning buildings; planners are looking at managing water supplies to deal with droughts or flooding.

Adaptive capacity goes beyond human systems, as some ecosystems show a remarkable ability to adapt to change and to buffer surrounding areas from the impacts of change. Forests can bind soils and hold large volumes of water during times of plenty, releasing it through the year; floodplains can absorb vast volumes of water during peak flows; coastal ecosystems can hold out against storms, attenuating waves and reducing erosion. Other ecosystem services—such as food provision, timber, materials, medicines, and recreation—can provide a buffer to societies in the face of changing conditions. Ecosystem-based adaptation is the use of biodiversity and ecosystem services as part of an overall strategy to help people adapt to the adverse effects of climate change. This includes the sustainable management, conservation and restoration of specific ecosystems that provide key services. 196 Environmental Protection Agency. (n.d.). Types of Mitigation Under CWA Section 404. https://www.epa.gov/cwa404/types-mitigation-under-cwa-section-404-avoidance-minimization-and-compensatorymitigation#:~:text=The%20White%20House%20Council%20on%20Environmental%20Quality%20%28CEQ%29,rectif ying%2C%20reducing%20over%20time%2C%20and%20compensating%20for%20impacts. 197 NASA. (N.D.). Responding to Climate Change. https://climate.nasa.gov/solutions/adaptation-mitigation/ 198 Federal Emergency Management Agency. (2017, November). Fact Sheet, Planning for a Resilient Community. https://www.fema.gov/sites/default/files/documents/fema_planning-resilient-communities_fact-sheet.pdf 199 Intergovernmental Panel on Climate Change. (n.d.). Annex II, Glossary. https://www.ipcc.ch/site/assets/uploads/2018/02/WGIIAR5-AnnexII_FINAL.pdf

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One type of mitigation measure that is also important to acknowledge is nature-based solutions (NBS).

FEMA defines NBS as sustainable planning, design, environmental management, and engineering practices that weave natural features or processes into the built environment to promote adaptation and resilience19F
200. These actions usually have multiple benefits such as reducing flood risk, reducing urban heat, adding recreation space, protecting nature spaces like shorelines and wetlands, and improving water quality in addition to fighting climate change. They may be more cost-effective than traditional grey infrastructure projects and are often more palatable by the public due to their hard to quantify benefits like additional recreation space, community beautification, increased property values, and better public health.

The immediacy of some of these benefits can also increase public support for NBS when compared to less clear, long-term benefits of other climate adaptation measures. Many communities within the OA have taken an interest in NBS, also known as green infrastructure, and actively engage in and encourage implementation of NBS separately or in conjunction with traditional infrastructure projects. Further information is included in Volume 2.

A coordinated response to climate change is necessary to implement effective risk reduction measures across the OA. Initiatives including the Silicon Valley 2.0 Climate Change Preparedness Tool, the Santa Clara County Climate Collaborative and Climate Resilience Tool, and local climate action and adaptation plans reflect the OA’s commitment to assessing and implementing climate mitigation and adaptation actions. Assessment of the current efforts and adaptive capacity of the planning partners participating in this hazard mitigation plan are included in the jurisdiction-specific Annexes in Volume 2.

11.3 Vulnerability Assessment – Hazards of Concern
The following sections provide information on how each identified hazard of concern for this planning process may be impacted by climate change and how these impacts may alter current exposure and vulnerability to these hazards for the people, property, critical facilities, and the environment in the OA.

11.3.1 Earthquake
Climate Change Impacts on Earthquake
Currently, the impact, if any, of climate change on earthquakes is not well understood. “Climate-related stress changes might or might not promote an earthquake to occur, but we have no way of knowing by how much.”20F
201 Some scientists say that melting glaciers could induce tectonic activity. As ice melts and water runs off, tremendous amounts of weight are shifted on the earth’s crust. As newly freed crust returns to its original, pre-glacier shape, it could cause seismic plates to slip and stimulate volcanic activity, according to research into prehistoric earthquakes and volcanic activity. NASA and USGS scientists found that retreating glaciers in southern Alaska may be opening the way for future earthquakes.201F
202 Other researchers are studying whether the stress of alternating periods of drought and heavy precipitation in the Sierra Nevada could potentially be felt on faults in or near the range and whether the increased pumping of groundwater in the Central Valley during times of drought could have an effect on the seismicity on the adjacent San Andreas Fault.20F 203
200 FEMA. (May 2023). Nature-Based Solutions. https://www.fema.gov/emergency-managers/riskmanagement/nature-based-solutions 201 NASA. (2019, October 29). Can Climate Affect Earthquakes, Or Are the Connections Shaky? https://climate.nasa.gov/news/2926/can-climate-affect-earthquakes-or-are-the-connections-shaky/ 202 NASA. (2004, August 2). Retreating Glaciers Spur Alaskan Earthquakes. https://www.nasa.gov/home/hqnews/2004/jul/HQ_04252_glaciers.html 203 NASA. (2019, October 29). Can Climate Affect Earthquakes, Or Are the Connections Shaky? https://climate.nasa.gov/news/2926/can-climate-affect-earthquakes-or-are-the-connections-shaky/

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Secondary impacts of earthquakes could be magnified by climate change. Soils saturated by repetitive storms or heavy precipitation could experience liquefaction or an increased propensity for slides during seismic activity due to the increased saturation. Dams storing increased volumes of water due to changes in the hydrograph could fail during seismic events.

Exposure, Sensitivity, and Vulnerability
Because impacts on the earthquake hazard are not well understood, increases in exposure and vulnerability of the local resources are not able to be determined. In general, everywhere that is susceptible to earthquake-induced liquefaction may be more susceptible if saturated with water due to climate change conditions when an earthquake occurs.

11.3.2 Wildfire
Climate Change Impacts on Wildfire
Wildfire risk is determined by climate variability, local topography, and human intervention. Climate change has the potential to affect multiple elements of the wildfire system: fire behavior, ignitions, fire management, and vegetation fuels. The frequency of extreme wildfires which burn over 25,000 acres is also expected to increase by nearly 50 percent across the state by 2100 according to the state’s Fourth Climate Change Assessment. Under both high- and medium-emissions scenarios, the change in acres burned in Santa Clara County is likely to increase until 2050 and then decrease by the end of the century.

Fire season for the OA is also expected to begin earlier in the year and last longer203F 204. The Cal-Adopt
projections204F
205 demonstrating how wildfire risk in the areas surrounding the OA is expected to increase over the next century is shown in Table 67.

Hot, dry spells create the highest fire risk. Increased temperatures may intensify wildfire risk by warming and drying out vegetation. Changes in climate patterns may impact the distribution and perseverance of insect outbreaks that create dead trees and vegetation, increasing the amount of available fire fuel. Wetter periods followed by a drought can result in increased dry vegetative ready to be burned. When climate alters fuel loads and fuel moisture, forest susceptibility to wildfires changes. Climate change also may increase winds that spread fires.

Table 67: Wildfire – Projected Santa Clara County Acres Burned 204 County of Santa Clara Office of Sustainability. (n.d.). Climate Change Projections in Santa Clara County. https://siliconvalleytwopointzero.org/climateprojections/wildfire 205 https://cal-adapt.org/tools/wildfire
Baseline (1961–1990)
Medium Emissions (RCP 4.5) High Emissions (RCP 8.5)
Mid-Century End-Century Mid-Century End-Century
30-year
average
6212.0 acres 6848.3 acres 6897.2 acres 6957.8 acres 6613.5 acres 30-year range
6143.0–
6366.3 acres
6512–7295.2
acres
6459.2–7388.5
acres
6570.1–7599.1
acres
6158.9–7378.2
acres

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Exposure, Sensitivity, and Vulnerability
Population and Property
While previous Cal-Adapt projections showed wildfire risk in the areas surrounding the OA decreasing over the next century, current projections show increased risk to wildfire, with increases in annual acres burned. Table 68 indicates the population and buildings at risk in the moderate, high, and very high FHSZs. Should the risk increase as Cal-Adapt projects, these totals are likely to increase also. WUI fires are an increased concern of the OA. While not all OA residents may experience increased risk to wildfire directly, secondary impacts, such as smoke and poor air quality will impact many more. These impacts are likely to be felt disproportionally. Vulnerable populations, including the elderly, low-income populations, and people with disabilities, will face some of the greatest negative impacts. Long-term impacts to public health, including mental health, will also be important to consider as the frequency and severity of wildfires increase.

Table 68: Population and Buildings at Risk – Santa Clara County Moderate FHSZ High FHSZ Very High FHSZ
Buildings Population Buildings Population Buildings Population 995 3,714 2,599 9,622 9,547 33,167
Critical Facilities
The risk to critical facilities would increase with the overall increased risk of wildfires. Key infrastructure including utilities, water, gas, electric, and communications infrastructure can be damaged during a wildfire. Secondary impacts, like increased power outages, transportation delays or disruptions, and smoke, are also likely to impact the operations of critical facilities.

Environment
It is possible that the exposure and vulnerability of the environment will be impacted by changes in wildfire risk due to climate change. Natural fire regimes may change, resulting in more frequent or higher intensity burns. While the California ecosystem is adapted to some fire, these types of events and fuel conditions represent risk beyond the norm for the local environment. These changes may alter the composition of the ecosystems in areas in and surrounding the OA including destroying vulnerable fish and wildlife habitats.

Economy
Recent fires destroyed residences, burned thousands of acres, forced people to evacuate. Costs involved included personal and business losses, lost economic activity, and the cost of containing a wildfire.

Seasonal agricultural workers and workers outside on poor air quality days are most likely to experience increased negative impacts or disruptions to their work due to increase wildfire events. Transportation infrastructure could also be impacted.

11.3.3 Inclement Weather
Climate Change Impacts on Inclement Weather
Climate change presents a challenge for risk management associated with inclement weather. While only slight changes in annual rainfall is expected in the OA, there is an increased risk that this rainfall will occur during an extreme precipitation event. These severe storms will be an essential to replenish fresh water supplies particularly during times of drought however, they may result in increased flooding. The number of weather-related disasters during the 1990s was four times that of the 1950s and led to 14 times as much in economic losses.

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Historically, the County has experienced just two extreme precipitation events per year. Depending on the emissions scenario, the OA is predicted to experience 3-5 events per year by the end of the century.205F 206
The type of inclement weather event may also change. Fewer snow events and additional rain events are predicted.

Climate projections such as found in the CMRA tool show an increasing number of days over 95 and over 100 degrees through mid to late century, in both lower and high emission scenarios. Projections also anticipate higher maximum temperatures averaged over a 5 day period, which indicates there may also be extended periods of extreme heat.

Extreme cold events are less common in the OA. The Temperature Minimum explorer as part of the ClimRR climate tool, shows the minimum temperature increasing through mid- to end-century. Current projections suggest that climate change may reduce vulnerability to extreme cold in the OA.

It is not fully understood how climate change may impact high wind events. Climate change is expected to contribute to more severe weather in the future. However, the Wind Explorer in the ClimRR tool shows little difference in wind miles per hour between mid-and end-century. Further investigation may be needed to fully understand how climate change may impact high winds in the OA.

Exposure, Sensitivity, and Vulnerability
Population and Property
Population and property exposure and vulnerability would be unlikely to increase as a direct result of climate change impacts on the inclement weather hazard. Inclement weather events may occur more frequently, but exposure and vulnerability will remain the same. Secondary impacts, such as the extent of localized flooding, may increase, impacting greater numbers of people and structures.

Critical Facilities
Critical facility exposure and vulnerability would be unlikely to increase as a result of climate change impacts on the inclement weather hazard; however, critical facility owners and operators may experience more frequent disruption to service provision. For example, more frequent and intense storms may cause more frequent disruptions in power service.

Environment
Exposure and vulnerability of the environment would be unlikely to increase; however, more frequent storms and heat events and more intense rainfall may place additional stressors on already stressed systems.

Economy
Climate change impacts on the inclement weather hazard may impact the local economy through more frequent disruption to services, such as power outages.

11.3.4 Drought
Climate Change Impacts on Drought
Due to a warmer climate, droughts could become more frequent, more severe, and longer lasting. As stated in the National Climate Resilience Toolkit, “higher surface temperatures brought about by global warming increase the potential for drought. Evaporation and the higher rate at which plants lose moisture 206 Santa Clara County. (February 2023) Draft Unincorporated Santa Clara County Climate Vulnerability Assessment.

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through their leaves both increase with temperature. Unless higher evapotranspiration rates are matched by increases in precipitation, environments will tend to dry, promoting drought conditions.206F 207
Drought is one of the most expensive hazards due to its impacts across sectors, particularly the agricultural industry. Valley Water indicates that it poses a severe threat to their normal operations due to the region’s dependency on imported water and increased demand for water across the region. The OA could likely experience what stresses other regions globally have started to experience:
 Growing populations
 Increased competition for available water
 Poor water quality
 Environmental claims
 Uncertain reserved water rights
 Groundwater overdraft
 Aging urban water infrastructure
California is particularly well-aware of the potential negative impacts of prolonged drought. Until storms in early 2023, the entire state, including the entire OA, was in severe to extreme drought. DWR has noted impacts of climate change on statewide water resources by charting changes in snowpack, sea level, and river flow. As temperatures rise and more precipitation comes in the form of rain instead of snow, these changes will likely continue or grow even more significant.

Cal-Adapt indicated in early 2023 that Santa Clara County should expect future April snowpack levels to be reduced by up to 25 inches from the baseline (1961-1990) by 2099.207F 208 These future projections may or
may not be adjusted following the area’s recent record-breaking snowpack levels. In addition to snowpack resources, the OA’s water supply is derived from groundwater and surface water resources. Increased incidence of drought may cause a drawdown in groundwater resources without allowing for the opportunity for aquifer recharge. Under the HadGEM-ES simulation, a high-emissions scenario, an extended drought is predicted for California from 2025–2075.208F 209
Exposure, Sensitivity and Vulnerability
Population and Property
Population exposure and vulnerability to drought are unlikely to change as a result of climate change given that the entire OA is already exposed to this hazard. Greater numbers of people may need to engage in behavior change, such as water saving efforts, significant life or health impacts are unlikely so long as water supplies can be managed to account for the additional strain. Property exposure and vulnerability may increase as a result of increased drought resulting from climate change, although this would most likely occur in non-structural property such as crops and landscaping. It is unlikely that structure exposure and vulnerability would increase as a direct result of drought, although secondary impacts of drought, such as wildfire, may increase and threatenstructures. 207 U.S. Climate Resilience Toolkit. (n.d.). Drought.
https://toolkit.climate.gov/topics/water/drought#:~:text=Higher%20surface%20temperatures%20brought%20about%2 0by%20global%20warming,environments%20will%20tend%20to%20dry%2C%20promoting%20drought%20condition s.
208 Cal-Adapt. (n.d.). Snowpack. https://cal-adapt.org/tools/snowpack/ 209 Santa Clara County. (February 2023) Draft Unincorporated Santa Clara County Climate Vulnerability Assessment.

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Critical Facilities
Critical facility exposure and vulnerability are unlikely to increase as a result of increased drought resulting from climate change; however, critical facility operators may be sensitive to changes and need to alter standard management practices and actively manage resources, particularly in water-related service sectors. Water-related infrastructure may experience disruptions.

Environment
The vulnerability of the environment may increase as a result of increased drought resulting from climate change. Ecosystems and biodiversity in the Bay Area are already under stress from development and water diversion activities. Prolonged or more frequent drought resulting from climate change may further stress the ecosystems in the region, which include many special status species.

Economy
Increased incidence of drought could increase the potential for impacts on the local economy including the agricultural and recreational sectors, the wine industry, and related tourism activities. Crop-related losses would be expected to be particularly high given a severe drought.

11.3.5 Dam and Levee Failure
Climate Change Impacts on Dam and Levee Failure
Dams and levees are engineered barriers designed to retain surface water based on assumptions including information on a river’s flow behavior (depicted on a hydrograph). Safeguards are built into these structures but there is increased risk associated with hazard events that surpass what the impacted dam or levee was designed to withstand. Substantial increases in rainfall or/or snowmelt in an area can have significant effects on the hydrograph used for the design of a dam or levee. If the hydrograph changes, it is conceivable that the dam or levee can lose some or all of its designed margin of safety, also known as freeboard.

In the case of dams, if freeboard is reduced, dam operators may be forced to release increased volumes early in a storm cycle in order to maintain the required margins of safety. Such early releases of increased volumes can increase flood potential downstream. According to the California Department of Water Resources (DWR), flood flows on many California rivers have been record-setting since the 1950s. This means that water infrastructure, such as dams and levees, have been forced to manage flows for which they were not designed. The California Division of Dam Safety (DSOD) has indicated that climate change may result in the need for increased safety precautions to address higher winter runoff, frequent fluctuations of water levels, and increased potential for sedimentation and debris accumulation from changing erosion patterns and increases in wildfire events. According to the DSOD, climate change also will impact the ability of dam operators to estimate extreme flood events.209F 210
Dams are constructed with safety features known as “spillways.” Spillways are put in place on dams as a safety measure in the event of the reservoir filling too quickly. Spillway overflow events, often referred to as “design failures,” result in increased discharges downstream and increased flooding potential.

Although climate change will not increase the probability of catastrophic dam failure, it may increase the probability of design failure.

In the case of levees, a reduction in freeboard caused by a changing hydrograph means that a levee may no longer protect an area against the design-storm standard for which it was originally built. This means that risk to the area that a levee is protecting from inundation will increase. 210 California Department of Water Resources. (n.d.). Climate Change Basics. https://water.ca.gov/WaterBasics/Climate-Change-Basics

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Exposure, Sensitivity and Vulnerability
Population and Property
While the exposure and vulnerability of population and property are unlikely to change significantly as result of climate change alone, the likelihood of failure of water infrastructure (dams and levees) is generally expected to increase because of more frequent exposure to extreme events.210F 211 Dam failures
may experience increase overtopping or breaches due to extreme precipitation events, even if the overall precipitation in the OA is expected to decrease.

This problem is exacerbated because of the age of many of the dams in the OA and the increasing population living in potential inundation areas. It should be noted that dams, and those levees in the OA that are accredited, are mapped in a FEMA special flood hazard area where flood insurance applies. If a levee loses its accreditation, additional people and property can be considered exposed to increased flood risk. There are a number of ongoing projects in the OA which would impact the existing FEMA flood layers including the Lower Berryessa Flood Protection Project, Permanente Creek Flood Protection Project, Upper Berryessa Creek Flood Protection Project, and Sunnyvale East and West Channels.21F 212
These projects may reduce the local risk to riverine flooding.

Critical Facilities
Dam owners and operators are sensitive to the risk and may need to alter maintenance and operations to account for changes in the hydrograph and increased sedimentation. Critical facility owners and operators in levee failure inundation areas should always be aware of residual risk from flood events that may overtop the levee system.

Environment
The exposure and vulnerability of the environment to dam and levee failure may change as a result of climate change. Cascading hazards, as discussed throughout this plan, could have a notable impact on the environment. For example, if there is a long period of drought caused by climate change prior to a dam failure, it could reduce the land’s ability to hold water resulting in increased runoff and damage.

Such a scenario could result in additional disaster events, such as landslides and mudslides.

Ecosystem services may be used to mitigate some factors that could increase the risk of design failures, such as increasing the natural water storage capacity in watersheds above dams. The use of nature-based solutions or green stormwater infrastructure systems could also help with stormwater collection around the dam.

Economy
Changes in the dam failure hazard related to climate change may affect the local economy. More frequent flooding events due to dam failure would negatively impact the local economy. Economic impacts may also result from changes to the levee failure hazard if accreditation is lost.

11.3.6 Flood
Climate Change Impacts on Flood
Climate change is expected to impact both precipitation-driven riverine and surface flooding as well as coastal flooding in the OA. High frequency flood events (e.g., 10-year floods) in particular will likely 211 Mallakpour, I., AghaKouchak, A., & Sadegh, M. (2019). Climate‐induced changes in the risk of hydrological failure of major dams in California. Geophysical Research Letters. https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2018GL081888 212 Silicon Valley 2.0. Memorandum SV2.0 Tool Update – Flood Hazar Layer Map Updates. (June 2021). https://siliconvalleytwopointzero.org/downloads/SiliconValley2.0_Flood-Hazard-Layer-Map-Update-Memo.pdf

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increase with a changing climate. What is currently considered a 1-percent-annual-chance (100-year flood) also may strike more often, leaving many communities at greater risk.

Climate change is already impacting water resources, and resource managers have observed the following:
 Historical hydrologic patterns can no longer be solely relied upon to forecast the water future.  Precipitation and runoff patterns are changing, increasing the uncertainty for water supply and quality, flood management and ecosystem functions.
 Extreme climatic events will become more frequent, necessitating improvement in flood protection, drought preparedness and emergency response.

The amount of snow is critical for water supply and environmental needs, but so too is the timing of snowmelt runoff into rivers and streams. Rising snowlines caused by climate change will allow more mountain areas, such as the Sierra Nevada watersheds, to contribute to peak storm runoff. Changes in watershed vegetation and soil moisture conditions will likewise change runoff and recharge patterns. As stream flows and velocities change, erosion patterns will also change, altering channel shapes and depths, possibly increasing sedimentation behind dams, and affecting habitat and water quality. Intense dry periods followed by wet periods will result in additional flooding. With potential increases in the frequency and intensity of wildfires due to climate change, there is potential for more floods following fire, which increase sediment loads and water quality impacts.

Use of historical hydrologic data has long been the standard of practice for designing and operating water supply and flood protection projects. For example, historical data are used for flood forecasting models and to forecast snowmelt runoff for water supply. This method of forecasting assumes that the climate of the future will be similar to that of the period of historical record. However, the hydrologic record cannot be used to predict changes in frequency and severity of extreme climate events such as floods. Scientists project greater storm intensity with climate change, resulting in more direct runoff and flooding. Going forward, model calibration must happen more frequently, new forecast-based tools must be developed, and a standard of practice that explicitly considers climate change must be adopted.

Exposure, Sensitivity, and Vulnerability
Population and Property
Population and property exposure and vulnerability may increase as a result of climate change impacts on the flood hazard. Runoff patterns may change, resulting in flooding in areas where it has not previously occurred. People experiencing homelessness are particularly susceptible to the impacts of climate change, including flooding.

Critical Facilities
Critical facility exposure and vulnerability may increase as a result of climate change impacts on the flood hazard. Runoff patterns may change, resulting in risk to facilities that have not historically been at risk from flooding. Additionally, changes in the management and design of flood protection for critical facilities may be needed as additional stress is placed on these systems. Planners will need to factor a new level of safety into the design, operation, and regulation of flood protection facilities such as dams, bypass channels and levees, as well as the design of local sewers and storm drains.

Environment
The exposure and vulnerability of the environment may increase as a result of climate change impacts on the flood hazard. Changes in the timing and frequency of flood events may have broader ecosystem impacts that alter the ability of already stressed species to survive. The destruction due to fire or sea level rise of habitats with important flood protection ability may impact the vulnerability of the OA.

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Economy
If flooding becomes more frequent, there may be impacts on the local economy. More resources may need to be directed to response and recovery efforts, and businesses may need to close more frequently due to loss of service or access during flood events. Flood damage to essential utilities will also present a major concern for the local economy.

11.3.7 Landslide
Climate Change Impacts on Landslide
Climate change may impact storm patterns, increasing the probability of more frequent, intense storms with varying duration. Increase in global temperature is likely to affect the snowpack and its ability to hold and store water. Warming temperatures also could increase the occurrence and duration of droughts, which would increase the probability of wildfire, reducing the vegetation that helps to support steep slopes.

All of these factors would increase the probability for landslide and/or mudslide occurrences.

Exposure, Sensitivity, and Vulnerability
Population and Property
Population and property exposure and vulnerability would be unlikely to increase as a result of climate change impacts on the landslide hazard. Landslide events may occur more frequently, but the extent and location should be contained within mapped hazard areas or recently burned areas.

Critical Facilities
Critical facility exposure and vulnerability would be unlikely to increase as a result of climate change impacts on the landslide hazard; however, critical facility owners and operators may experience more frequent disruption to service provision as a result of landslide hazards. For example, transportation systems may experience more frequent delays if slides blocking these systems occur more frequently.

Towers supporting power lines and bridges could also collapse during a landslide event. In addition, increased sedimentation resulting from landslides may negatively impact flood control facilities, such as dams and levees.

Environment
Exposure and vulnerability of the environment would be unlikely to increase as a result of climate change, but more frequent slides in river systems may impact water quality and have negative impacts on stressed species.

Economy
Changes to the landslide hazard resulting from climate change are unlikely to result in significant impacts on the local economy. The economy of the OA is considered to be highly adaptive to landslide risk.

11.3.8 Tsunami
Climate Change Impacts on Tsunami
The impacts of global climate change on tsunami probability are unknown. Some scientists say that melting glaciers could induce tectonic activity, inducing earthquakes, which could result in tsunamis. Other scientists have indicated that underwater avalanches (also caused by melting glaciers), may also result in additional tsunamis. Even if climate change does not increase the frequency with which tsunamis occur, it may result in more destructive waves. As sea levels continue to rise, tsunami inundation areas would likely reach further into communities than current mapping indicates.

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Exposure, Sensitivity, and Vulnerability
As land area likely to be inundated by tsunami waves increases, exposure and vulnerability to the tsunami hazard may increase for population, property, critical facilities, and the environment. Changes to the tsunami hazard from climate change may result in more direct economic impacts on a greater number of businesses and economic centers, as well as the infrastructure systems that support those businesses.

Population and Property
The population and property identified in the tsunami inundation areas are mostly likely to experience the most detrimental impacts of a tsunami event. This area is described in Figure 61. While most of the OA is unlikely to experience these impacts, vulnerable populations are at the highest risk of these impacts, including the homeless, elderly, children, and even the historically underserved communities.

Based on the National Structure Inventory, 14 commercial buildings and 2 industrial buildings are potentially vulnerable to tsunami. A tsunami has the potential to cause over $6 million in damages to these buildings.

If sea level rise increases the tsunami inundation area, then the population and property at risk will increase.

Critical Facilities
The risk to critical facilities would be similar to that of the flood risk. Key infrastructure including utilities, water, gas, electric, and communications infrastructure can be damaged during a tsunami. Destructive waves can damage buildings, homes, and businesses. Severe flooding, and other impacts, like power outages, transportation disruptions, are also likely to impact the operations of critical facilities.

Environment
A tsunami has the potential to cause detrimental impacts on the OA’s environment. This may include uprooted trees and plants and destroyed animal habitats such as nesting sites for birds. Tsunami’s may result in the disappearance or abrupt erosion of beaches. During a tsunami event hazardous material infrastructure and pipelines may become damaged, causing the contamination of the environment with oil, raw sewage, and poisonous pollutants.

Economy
The cost of repair after a tsunami can impacts the economy. The tourism industry may be impacted as historic coastal properties and popular coastal businesses are damaged. Critical facilities and other important assets may be damaged by temporary inundation, resulting in loss of services such as power or wastewater treatment. Local tax revenue may decline as areas that were previously occupied by houses and businesses that may permanently close or have difficulty repairing.

11.3.9 Extreme Temperatures
Climate Change Impacts on Extreme Temperatures
Extreme temperatures are a serious consequence of climate change. Extreme heat is of particular concern to the OA. Climate change is expected to bring longer, more frequent, and more severe extreme heat events to the region.21F
213 By 2100, the area can expect 6 to 10 heat waves a year. Also, by the end of the century according to a medium emissions model, there will also be an estimated 2-44 days per year 213 County of Santa Clara Office of Sustainability. (N.D.). Climate Change Projections in Santa Clara County – Extreme Heat. https://siliconvalleytwopointzero.org/climateprojections/extremeheat

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defined as extreme heat days – or days where the maximum temperature is above 92.7 °F.213F 214 Extreme
heat days followed by warm nights are dangerous because they don’t allow time for the population, landscapes, and the built environment to cool off. This can result in increased mortality, health issues, and wildfire risk.

Exposure, Sensitivity and Vulnerability
Population and Property
Extreme temperature days can directly harm human health. While flooding is the most common natural disaster, extreme temperatures are the deadliest. Extreme heat can result in a variety of heat-related illness from mild heat stress to fatal heat stroke. Mental health stress and other illnesses can also increase. Vulnerable populations, including the elderly, children, and people with pre-existing conditions will be disproportionally impacted by extreme heat. Societally inequities, such as the distribution of minority populations in areas more exposed to the urban heat island effect, can be exasperated by extreme heat conditions.

Critical Facilities
The impacts to critical facilities from extreme heat can range from barely noticeable to profound. More and more the value of using building materials that can reduce or withstand the impacts of extreme temperatures is being acknowledged. When building materials are pushed beyond their temperature thresholds, they are at risk of failure. Transportation infrastructure may also be damaged or destroyed, including asphalt, rail tracks, and cars. There is increased demand on energy utilities as the need for air conditioning rises. Back-up generators or alternative cooling methods such as community resilience hubs may be necessary if power supplies are insufficient to cool the community.

Environment
Extreme temperatures, especially hotter temperatures, can wreak havoc on unprepared ecosystems.

They are responsible for reducing biodiversity, resulting in numerous species death. Water supplies are also strained during extreme temperature events. Climate change also alters the range, biogeography, and growth of microbes which could result in additional foodborne and waterborne illnesses.214F 215
Economy
The economy will be impacted by the increase in extreme heat days. Extreme heat is associated with loss of productivity, increased chances of mortality, and increased of a workplace accident. A study from UCLA found that workers comp claims occurred more frequently on hotter days for both indoor and outdoor workers. An estimated 15,000 injuries occur per year in California and the financial cost may be between $750 million to $1.25 billion per year.215F
216 It also costs power more to maintain normal operations, such as keep the air conditioning running in an office. Some industries, such as construction, simply may not be able to function in too hot an environment. Research indicates that overall, economic growth declines and crop yields drop during periods of extreme heat. 214 Cal-Adapt. (N.D.) Extreme Heat Days & Warm Nights. https://cal-adapt.org/tools/extreme-heat/ 215 California Department of Public Health. (February 2017). Climate Change and Health Profile Report Santa Clara County.
https://www.cdph.ca.gov/Programs/OHE/CDPH%20Document%20Library/CHPRs/CHPR085SantaClara_County2- 23-17.pdf
216 UCLA Luskin. (June 2021). High Temperatures Increase Workers’ Injury Risk Whether They’re Outdoors or Inside. https://luskin.ucla.edu/high-temperatures-increase-workers-injury-risk-whether-theyre-outdoors-orinside#:~:text=A%20UCLA%20study%20published%20today%20shows%20that%20hot,from%20California%E2%80 %99s%20workers%E2%80%99%20compensation%20system%2C%20the%20nation%E2%80%99s%20largest.

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11.3.10 Sea Level Rise
Climate Change Impacts on Sea Level Rise
In addition to impacts on the identified hazards of concern, climate change presents risks related to sea level rise. Sea level rise will cause currently dry areas to be permanently inundated. The scope of temporary inundation from extreme tide events and storm surge also will also expand. Within the OA, the cities of Palo Alto, Mountain View, Sunnyvale, Milpitas, and San José are expected to experience the most impacts from sea level rise.216 F
217 Multiple possible sea level rise scenarios are presented in Table 69. Although the exact extent and timing of sea level rise is still uncertain, assessing potential areas at risk provides important information appropriate for planning purposes.

Table 69: Silicon Valley 2.0 Santa Clara County Sea Level Rise Projections and Inundation Layers SV 2.0 Tool Scenarios OPC 2018 Projections Permanent Sea Level Rise 100-year Storm Surge (+47”) Timeframe Scenario Risk
Tolerance
Projection
(in)
Inundation Layer Used in
Tool (in)
Projection
(in)
Inundation Layer Used in
Tool (in)
Baseline Current n/a 0 none 47 48
Mid-Century
Medium Top of likely
range

13.2 12 60.2 66
High 1 in 200 22.8 24 69.8 66
Late-Century
Medium Top of likely
range

40.8 36 87.8 84
Medium-High 1 in 20 52.8 52 99.8 96
High 1 in 200 82.8 84 129.8 131
217 County of Santa Clara Office of Sustainability. (n.d.). Climate Change Projections in Santa Clara County. https://siliconvalleytwopointzero.org/climateprojections/slr

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Exposure, Sensitivity, and Vulnerability
The following assessment was conducted using data provided by the San Francisco Bay Conservation and Development Commission. A sea level rise of 48 inches above current mean higher high water was assumed.

Population
Sea level rise will increase the population exposed to both permanent and temporary inundation.

Currently, approximately 0.94 percent of the OA population is estimated to reside in areas subject to sea level rise impacts. The vast majority of these individuals reside in Palo Alto. Table 70 shows exposed population by jurisdiction.

Table 70: Estimated Population Residing in Sea Level Rise Inundation Areas Jurisdiction Estimated
Population
Estimated Population
Exposed
% of Population
Exposed
Campbell 43,442 0 0.0%
Cupertino 60,646 0 0.0%
Gilroy 59,472 0 0.0%
Los Altos 31,809 0 0.0%
Los Altos Hills 8,452 0 0.0%
Los Gatos 33,526 0 0.0%
Milpitas 80,248 0 0.0%
Monte Sereno 3,450 0 0.0%
Morgan Hill 45,037 0 0.0%
Mountain View 82,097 60 0.07%
Palo Alto 68,523 9,373 13.68%
San José 1,014,125 6,275 0.62%
Santa Clara (city) 127,608 0 0.0%
Saratoga 31,039 0 0.0%
Sunnyvale 154,808 2,421 1.56%
Unincorporated
County 90,253 36 0.04%
Total 1,934,535 18,165 0.94%
Property
The majority of losses from sea level rise are related to residential structures, closely followed by commercial and industrial. The majority of these assets are in Sunnyvale, San José, and Palo Alto.

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Table 71: Structure Type in Sea Level Rise Inundation Areas Jurisdiction Residential Commercial Industrial Agricultural Religious Government Education Total Campbell $0 $0 $0 $0 $0 $0 $0 $0
Cupertino $0 $0 $0 $0 $0 $0 $0 $0
Gilroy $0 $0 $0 $0 $0 $0 $0 $0
Los Altos $0 $0 $0 $0 $0 $0 $0 $0
Los Altos Hills $0 $0 $0 $0 $0 $0 $0 $0
Los Gatos $0 $0 $0 $0 $0 $0 $0 $0
Milpitas $0 $0 $0 $0 $0 $0 $0 $0
Monte Sereno $0 $0 $0 $0 $0 $0 $0 $0
Morgan Hill $0 $0 $0 $0 $0 $0 $0 $0
Mountain View $0 $128,886,000 $83,412,000 $1,034,000 $836,000 $6,966,000 $18,923,000 $240,057,000 Palo Alto $1,415,492,000 $525,812,000 $209,418,000 $4,075,000 $21,582,000 $15,911,000 $206,524,000 $2,398,814,000 San José $489,324,000 $562,847,000 $634,429,000 $4,243,000 $47,844,000 $13,429,000 $16,031,000 $1,768,147,000 Santa Clara
(city) $0 $0 $0 $0 $0 $0 $0 $0
Saratoga $0 $0 $0 $0 $0 $0 $0 $0
Sunnyvale $314,344,000 $755,253,000 $774,439,000 $377,000 $238,000 $5,129,000 $0 $1,849,780,000 Unincorporated
County $0 $998,000 $0 $0 $0 $0 $0 $998,000.00
Total $2,219,160,000 $1,973,796,000 $1,701,698,000 $9,729,000 $70,500,000 $41,435,000 $241,478,000 $6,257,796,000

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Table 72: Structure and Contents Value in Sea Level Rise Inundation Areas Jurisdiction Structures
Exposed
Estimated
Value of
Exposed
Structures
Estimated
Value of
Exposed
Contents
Estimated
Total Value
% of Total
Replacement
Value
Campbell 0 $0 $0 $0 0.0%
Cupertino 0 $0 $0 $0 0.0%
Gilroy 0 $0 $0 $0 0.0%
Los Altos 0 $0 $0 $0 0.0%
Los Altos
Hills 0 $0 $0 $0 0.0%
Los Gatos 0 $0 $0 $0 0.0%
Milpitas 635 $468,554,661 $386,407,648 $854,962,309 4.5% Monte
Sereno 0 $0 $0 $0 0.0%
Morgan Hill 0 $0 $0 $0 0.0%
Mountain
View 102 $1,012,240,021 $1,110,560,396 $2,122,800,417 8.5% Palo Alto 4,014 $2,069,879,805 $1,642,022,511 $3,711,902,316 14.4% San José 912 $2,573,152,965 $2,275,265,284 $4,848,418,248 2.3% Santa Clara
(city) 450 $1,273,778,027 $1,228,024,465 $2,501,802,492 5.8% Saratoga 0 $0 $0 $0 0.0%
Sunnyvale 355 $2,632,745,163 $3,074,816,827 $5,707,561,990 13.3% Table 73: Structure and Contents Value in Sea Level Rise Inundation Areas, Unincorporated Santa Clara County
Jurisdiction Structures
Exposed
Estimated Value of
Exposed Structures
Estimated Value of
Exposed Contents
Estimated Total
Value
Unincorporated
County 1 $262,260 $131,130 $393,390
County + All
Cities 6,469 $10,030,612,900 $9,717,228,260 $19,747,841,162 Critical Facilities
There are 72 critical facilities located in OA areas subject to impacts from sea level rise.

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Table 74: Critical Facilities in Sea Level Rise Inundation Areas Jurisdiction Essential
Facilities Transportation Utilities Community Assets
Hazardous
Materials Total
Campbell 0 0 0 0 0 0
Cupertino 0 0 0 0 0 0
Gilroy 0 0 0 0 0 0
Los Altos 0 0 0 0 0 0
Los Altos Hills 0 0 0 0 0 0
Los Gatos 0 0 0 0 0 0
Milpitas 0 0 0 0 0 0
Monte Sereno 0 0 0 0 0 0
Morgan Hill 0 0 0 0 0 0
Mountain View 1 0 0 1 2 3
Palo Alto 9 12 3 5 9 29
San José 2 7 1 5 7 20
Santa Clara (city) 0 1 0 0 0 1
Saratoga 0 0 0 0 0 0
Sunnyvale 1 2 0 1 11 14
Unincorporated
County 0 0 0 1 0 1
Total 13 26 4 13 29 72
Environment
All sea level rise inundation areas are exposed and vulnerable to impacts. Important coastal habitat may be lost as sea level rise permanently inundates areas, or it may be damaged due to extreme tide and storm surge events. Saltwater intrusion into freshwater resources may occur, further altering habitat and ecosystems and threatening the water supply. Protective ecosystem services may be lost as land area and wetlands are permanently inundated.

Economy
Sea level rise will impact the local economy. The tourism industry may be impacted as historic coastal properties are inundated. Critical facilities and other important assets may be damaged by temporary inundation, resulting in loss of services such as power or wastewater treatment. Coastal businesses may relocate to other areas rather than face high costs from increased risk of storm surge and costs associated with managed retreat. Local tax revenue may decline as areas that were previously occupied by houses and businesses are permanently inundated.

Future Development
The land area of the OA will be reduced as sea level rise permanently inundates areas. This will have significant impacts on land use and planning in local communities. Local General Plans in the OA will guide this future development.

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11.4 Issues
This assessment of climate change led to identification of the following issues throughout the Santa Clara County OA:
 Planning for climate change related impacts can be difficult due to inherent uncertainties in projection methodologies.
 Average temperatures are expected to continue to increase in the OA, which may lead to a host of primary and secondary impacts, such as an increased incidence of heat waves.  Expected changes in precipitation patterns are still poorly understood and could have significant impacts on the water supply and flooding in the OA.
 Some impacts of climate change are poorly understood such as potential impacts on the frequency and severity of earthquakes, thunderstorms, and tsunamis.  Heavy rain events may result in inland stormwater flooding after stormwater management systems are overwhelmed.
 Permanent and temporary inundation resulting from sea level rise has the potential to impact significant portions of the population and assets in the OA.

Table 75: EMAP Consequence Analysis: Climate Change
Subject Ranking Impacts/Climate Change
Public Minimal to
Severe
Residents across the OA will be impacted by climate change.

Noticeable impacts will include changes in temperature, increased frequency and severity of natural hazards, and the permanent inundation of part of the community due to sea level rise. Even residents outside of areas immediately impacted by hazard events will experience secondary effects such as smoke, a reduction in air quality, disruption of services, and transportation delays or disruptions.

Responders Minimal to
moderate
Responders will be relied upon when a disaster event occurs. They may need to consider climate change and the changing likelihood of future events when allocating resources towards certain hazards.

However, overall, since climate change is a long-term challenge with occurs over many years, there is unlikely to be significant changes needed to responder’s immediate response and recovery efforts.

Continuity of
Operations
(including
continued
delivery of
services)
Minimal to
Severe
The impacts on continuity of operations depends largely on facility and critical infrastructure location, hazard location, frequency, and severity, and human interference. Certain types of infrastructure, such as wastewater treatment plants which could be inundated by sea level rise or power utilities in high-risk wildfire areas, are more likely to be disrupted or destroyed. Delivery of services may also be slowed or stopped in impacted areas. Since climate change occurs over time, there is the opportunity for at-risk facilities and organizations to develop continuity of operations plans which address the increased risks associated with climate change.

Property,
Facilities, and
Infrastructure
Minimal to
Severe
The localized impact to properties, facilities, and infrastructure could be severe. Sea level rise impact estimates are one of the best examples of how climate change could directly relate to the complete loss of property, facilities, and infrastructure. Increased frequency and severity of other hazard events will likely result in damage, destruction, or disturbances to other structures and infrastructure across the OA.

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Subject Ranking Impacts/Climate Change
Environment Minimal to
Severe
California’s ecosystem has adapted to some of the impacts of climate change including wildfires. However, the increased frequency and severity of hazard events could strain the adaptative capacity of an ecosystem already stressed by increased human development.

Climate change could result in changes to the watershed, water supply, destroy or damage fish and wildlife habitats, destroy crucial flood protective habitats near the ocean, and increase the spread of invasive spices and the death of trees and vegetation.

Economic
Conditions
Minimal to
Severe
Climate change may impact the local economy in multiple different ways. Increased severe hazards events will test the financial resilience of the OA. Certain sectors, including agriculture and tourism, are likely to experience the worse impacts of climate change. Disturbances to transportation, communication, power, and water infrastructure due to climate change can also have a significant impact on the economy.

Impacts largely depend on how effectively the population and built environment can respond to changing climate conditions.

Public
Confidence in
the Government
Minimal to
Severe
Climate change is at the forefront of the national discussion on natural disasters. The public often has intense opinions on the subject. In general, climate change adaptation measures are widely supported in the OA. Solutions which consider short-term benefits, such as planting trees which increase shade and enhance the community’s curb appeal while at the same time reducing the urban heat island effect, are likely to be the most supported. Consistent messaging, accurate and timely public information, and clear reasoning for climate change adaptation measures will increase public’s confidence in the government.

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12 Dam and Levee Failure
Definitions
 Dam: Any artificial barrier, together with appurtenant works, which does or may impound or divert water, and which is or will be either 25 feet or more in height from the natural bed of the stream or watercourse at the downstream toe of the barrier, as determined by the department, or from the lowest elevation of the outside limit of the barrier, as determined by the department, if it is not across a stream channel or watercourse, to the maximum possible water storage elevation or has or will have an impounding capacity of 50 acre-feet or more.40  Levee: A man-made structure, usually an earthen embankment, designed and constructed to prevent inland flooding from major storm events and extreme waterlevels.  Emergency Action Plan: A formal document that identifies potential emergency conditions at a dam and specifies actions to be followed to minimize property damage and loss of life. It contains procedures and information to help the dam owner issue early warning and notification messages and inundation maps to show emergency management authorities the critical areas for action in case of an emergency.
 High Hazard Dam: Dams where failure or improper operation will probably cause loss of at least one human life.
 Extremely High Hazard Dam: California’s Division of Safety of Dams (DSOD) has classified some High Hazard Dams as Extremely High Dams. These are expected to cause considerable loss of human life or would result in an inundation area with a population of 1,000 ormore.

12.1 General Background
Dams and levees are designed to mitigate flood events but sometimes floods larger than the estimated risk occur which can cause a partial or total failure. Other causes of dam and levee failure vary.

12.2 Causes of Dam and Levee Failure
A dam failure occurs when the barrier constructed does not obstruct or restrain water as designed, which can rapidly result in a large area of completely inundated land. Levees, though similar, are embankments built to prevent the overflow of a river or stream.

12.2.1 Causes of Dam Failure
Dam failures can be catastrophic to human life and property downstream. Dam failures in the United States typically occur in one of four ways:
 Overtopping of the primary dam structure, which accounts for 34 percent of all dam failures, can occur due to inadequate spillway design, settlement of the dam crest, blockage of spillways, and other factors.
 Foundation defects due to differential settlement, slides, slope instability, uplift pressures, and foundation seepage can also cause dam failure. These account for 30 percent of all dam failures.  Failure due to piping and seepage accounts for 20 percent of all failures. These are caused by internal erosion due to piping and seepage, erosion along hydraulic structures such as spillways, erosion due to animal burrows, and cracks in the dam structure.

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 Failure due to problems with conduits and valves, typically caused by the piping of embankment material into conduits through joints or cracks, constitutes 10 percent of all failures.

The remaining six percent of U.S. dam failures are due to miscellaneous causes. Many dam failures in the United States have been secondary results of other disasters. The prominent causes are earthquakes, landslides, extreme storms, massive snowmelt, equipment malfunction, structural damage, foundation failures, and sabotage.

The most likely disaster-related causes of dam failure in the OA are earthquakes, excessive rainfall, and landslides. Poor construction, lack of maintenance and repair, and deficient operational procedures are preventable or correctable by a program of regular inspections. Terrorism and vandalism are serious concerns that all operators of public facilities must plan for; these threats are under continuous review by public safety agencies.

12.2.2 Causes of Levee Failure
A levee breach occurs when part of a levee gives way, creating an opening through which floodwaters may pass. A breach may occur gradually or suddenly. The most dangerous breaches happen quickly during periods of high water. The resulting torrent can quickly swamp a large area behind the failed levee with little or no warning. When a levee system fails or is overtopped, severe flood damage can occur.

Earthen levees can be damaged in several ways. Strong river currents and waves can erode the surface.

Trees growing on a levee can blow over, leaving a hole where the root wad and soil used to be.

Burrowing animals, such as the California ground squirrel, the salt marsh harvest mouse, or the western burrowing owl can create holes that enable water to pass through a levee. If severe enough, any of these situations can lead to a zone of weakness that could cause a levee breach. In seismically active areas, earthquakes and ground shaking can cause a loss of soil strength, weakening a levee and possibly resulting in failure. Seismic activity can also cause levees to slide or slump, both of which can lead to failure.

No levee provides protection from events for which it was not designed, and levees require maintenance to continue to provide the level of protection they were designed and built to offer. Maintenance responsibility belongs to a variety of entities including local, state, and federal government and private landowners.

12.3 Hazard Profiles
Levees and dams serve different purposes. Though both can be made with the same materials, their relationship to water is different. Levees run parallel to water while dams lie across. A levee’s primary focus is to reduce flood risk and protect life and property. Dams also serve risk management functions but deliver other infrastructure benefits for communities and industry. The aging dam infrastructure in the OA is notable. Table 76 shows that the Lake Ranch Dam was built in 1877 and ten dams were built in the 1930s.

12.3.1 Past Dam Failure Events
According to the 2018 State of California Multi-Hazard Mitigation Plan, there have been ten dam failures in the state since 1950. The most recent dam emergency occurred in February 2017 at Oroville Dam in northern California’s Butte County when it was on the verge of overflow. The concrete spillway was damaged by erosion and a massive hole developed. The auxiliary spillway was used to prevent overtopping of the dam and it experiences erosion problems also. Evacuation orders were issued out of concern about a potential large uncontrolled release of water from Lake Oroville. Such a release was ultimately prevented, and evacuees returned to their homes.

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Table 76: Dams Classified as a High Hazard or an Extremely High Hazard Risk 217F 218,
218F
219
Name National
ID #
Hazard
Class Owner Dam Type
Dam
Height
(feet)
Crest
Length
(feet)
Reservoir
Capacity
(acrefeet)
Year
Built
Inundation
Map
Closest
City
Almaden CA00289 Extremely
High SCVWD Earth 110 500 2,000 1936 Yes San José
Almaden Valley CA00661 High San José
Water Co. Earth 38 1,100 27 1955 Yes San José
Austrian 622.013 Extremely
High
San José
Water Co. Earth 185 700 6,200 1950 Yes Los Gatos
Calero 72.003 Extremely
High SCVWD Earth 90 840 9,850 1935 Yes San José
Cherry Flat CA00158 Extremely
High
City of San
José Earth 60 230 500 1936 Yes San José
Coyote CA00287 Extremely
High SCVWD Earth and Rock 140 980 22,541 1936 Yes Gilroy Coyote Percolation
(Steel flashboard dam
being replaced with
an inflatable rubber
dam)
CA00286 High SCVWD Steel
Flashboard 24 204 72 1934 Yes San José
DeBell CA00686 High City of Gilroy Earth 53 580 120 1952 Yes Gilroy Ed R. Levin CA00890 Extremely
High
County of
Santa Clara Earth 38 470 150 1968 Yes Milpitas
Elmer J. Chesbro CA00806 Extremely
High SCVWD Earth and Rock 95 690 8,086 1955 Yes Morgan Hill 218 National Inventory of Dams. (n.d.). Dams of the Nation. https://nid.sec.usace.army.mil/#/ 219 California Department of Water Resources. (n.d.). California Dam Breach Inundation Maps. https://fmds.water.ca.gov/maps/damim/

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Name National
ID #
Hazard
Class Owner Dam Type
Dam
Height
(feet)
Crest
Length
(feet)
Reservoir
Capacity
(acrefeet)
Year
Built
Inundation
Map
Closest
City
Felt Lake CA00670 Extremely
High
Stanford
University
Board of
Trustees
Earth 67 590 900 1930 Yes Palo Alto
Foothill Park CA00868 High City of Palo
Alto
Earth 86 600 67 1988 Yes Palo Alto
Guadalupe CA00290 Extremely
High
SCVWD Earth 142 695 3,460 1935 Yes San José
Higuera CA00687 Extremely
High
Wells Fargo
Bank
Earth 44 525 65 1953 Yes Milpitas
James J. Lenihan,
“Lexington Reservoir”
CA00293 Extremely
High
SCVWD Earth 208 810 21,430 1953 Yes Los
Gatos
Kuhn CA00683 Extremely
High
Private Entity Earth 67 312 85 1947 Yes San José
Lake Ranch CA00676 High San José
Water Co.

Earth 38 160 215 1877 Yes San José
Leroy Anderson
(inactive)
CA00294 Extremely
High
SCVWD Earth 235 1,430 91,300 1950 Yes Morgan
Hill
North Fork CA00299 Extremely
High
Pacheco
Pass Water
District
Earth 100 600 6,150 1939 No Hollister
Rinconada Reservoir CA00295 High SCVWD Earth 40 240 46 1969 Yes Campbell Stevens Creek CA00292 Extremely
High
SCVWD Earth 132 1,080 3,074 1935 Yes Cupertino
Uvas CA00807 Extremely
High
SCVWD Earth 118 1,100 10,000 1957 Yes Morgan
Hill
Vasona Percolating CA01516 Extremely
High
SCVWD Earth 34 1,00 410 1935 Yes Los
Gatos
San Mateo County Dam with an Inundation Area extending into the OA.

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Name National
ID #
Hazard
Class Owner Dam Type
Dam
Height
(feet)
Crest
Length
(feet)
Reservoir
Capacity
(acrefeet)
Year
Built
Inundation
Map
Closest
City
Searsville CA00669 Extremely
High
Stanford
Board of
Trustees
Masonry 68 260 1,840 1890 Yes Palo Alto

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Historically, overtopping caused two of the state’s nine dam failures; the others were caused by seepage or leaks. One failure, the 1963 Baldwin Hills Dam Failure in Los Angeles County, resulted in three deaths because the leak turned into a washout. The historical record indicates that California has had about 45 failures of non-federal dams. The failures occurred for a variety of reasons, the most common being overtopping. Other reasons include shortcomings in the dams or an inadequate assessment of surrounding geomorphologic characteristics.

One dam failure event was recorded in the OA in 2017. After a series of slow-moving storms fronts, despite attempts to release water through at outlet at the bottom of the dam, the man-made Anderson Reservoir in Morgan Hill reached its peak capacity and water overtopped Anderson Dam, resulting in flooding downstream along Coyote Creek. The flooding was estimated to have cause $100 million in damages and displaced 14,00 residents219 F
220
.

12.3.2 Dam Location and Extent
According to the USACE National Inventory of Dams (NID), there are 44 regulated dams in the OA (Figure 57). Extremely high hazard dams are indicated in red, high hazard dams are indicated in orange, and dams with a significant hazard are shown in green. Low hazard dams are not mapped.

The DSOD has certified all these dams and has designated all of them with a Condition Assessment of “Satisfactory.” In addition, these dams all have the emergency action plan (EAP) required for all dams that do not have a low downstream hazard potential designation20F 221
. The EAP requirements include an
early warning system and operational procedures that may be used, such as reducing reservoir levels and reducing downstream flows, as well as procedures for notifying affected residents and agencies responsible for emergency management. The Searsville Dam, an Extremely High Hazard Dam located in San Mateo County, has an inundation area that could impact parts of the City of Palo Alto. This dam has been added to Table 76.

The Anderson Dam, located three miles east of U.S. 101 in Morgan Hill, was discussed in the 2019 MJHMP but on February 24, 2020, the Federal Energy Regulatory Commission ordered that Anderson Lake should be drained due to earthquake risk. At the time of writing this update, work on the $576-million Anderson Dam Seismic Retrofit Project continues. The project is expected to be complete by 2031.

Dam Inundation Mapping
The most significant issue associated with dam failure involves the potential impact on properties and populations in the inundation zones. As listed in Table 76, all but two of the dams have an approved inundation map. Flooding because of a dam failure would significantly impact these areas. Figure 58 shows dam inundation depth grids within the County.
220 San José Spotlight. (2022, June 1). Valley Water settles with San José residents over 2017 flood. San José flood victims get multimillion-dollar settlement - San José Spotlight (sanjosespotlight.com) 221 California Legislative Information. (n.d.). Water Code, Division 3, Dams and Reservoirs. Chapter 8. https://leginfo.legislature.ca.gov/faces/codes_displayexpandedbranch.xhtml?tocCode=WAT&division=3.&title=&part= &chapter=&article=&nodetreepath=4

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Figure 58: Location of Dams Impacting Santa Clara County21F 222
222 California Department of Water Resources, Division of Safety of Dams. (n.d.). Dam Breach Inundation Map Web Publisher. https://fmds.water.ca.gov/webgis/?appid=dam_prototype_v2

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Figure 59: Dam Inundation Depth Grids

12.3.3 Levee Location
Currently, there are 89 levees listed by the United States Army Corps of Engineers (USACE) in Santa Clara County,2F
223 a significant increase from the seven levees listed in 2017. As shown in Figure 59, most of these structures are located in the South San Francisco Bay area. 223 National Levee Database. (n.d.). Levees of the Nation. https://levees.sec.usace.army.mil/#/

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Figure 60: Levees in Santa Clara County23F
224
The Santa Clara Valley Water District (SCVWD) owns and maintains most of these levees. It manages approximately 100 miles of levees in Santa Clara County. About 50 miles provide 100-year flood protection and nearly 18 miles were constructed in partnership with the Corps. Other levee sponsors include U.S. Fish and Wildlife Service (USFWS) (12), the City of Palo Alto (2) Caltrans District 4, and the Alameda County Flood Control District with Santa Clara County (1). Table 77 provides information about levees in the County.

Most of the levees have not been screened by the USACE for risk. Of the seven that have been screened, three are considered to be low risk, three are considered moderate risk and one review is labeled “No Verdict.” Of the 89 levees, a total of 14 have been accredited by FEMA and recognized on a Flood Insurance Rate Map (FIRM). One levee is designated as a Provisionally Accredited Levee (PAL).

This designation may be used for a levee system that FEMA has previously accredited as providing base flood hazard reduction on an effective FIRM, and for which FEMA is awaiting data and/or documentation that will show the levee system is compliant with 44 CFR 65.10. 224 National Levee Database. (n.d.). Levees of the Nation. https://levees.sec.usace.army.mil/#/

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Table 77: Levees in Santa Clara County 24F
225

FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Coyote Creek, Santa
Clara – LB
Santa Clara SCVWD 6.72 9,477 1,879 $1.59B Low A A
Coyote Creek, Santa
Clara – RB
Santa Clara SCVWD 4.9 26,188 4,721 $3.47B Moderate A A
Coyote Creek, Santa
Clara – RB Bypass
Alameda,
Santa Clara
SCVWD 1.67 1,247 21 $219M No Verdict N A
Cunningham Flood
Detention Facility
Certification Project
Santa Clara SCVWD 4.32 20,689 3,588 $3.08B Not Screened A N Cunningham Flood
Detention Facility
Certification Project 2
Santa Clara State 4.5 32,882 6,174 $3.64B Not Screened A N Guadalupe River - LB Santa Clara SCVWD 8.48 30,391 3,364 $3.85B Moderate A A Guadalupe River - RB Santa Clara SCVWD 6.9 24,361 2,335 $3.21B Moderate A A King & Lyons Alameda and
Santa Clara
Alameda
County
Flood
Control

3.5 3,497 62 $449M Low PAL A
Los Gatos Creek Santa Clara Caltrans
District 4
.41 92 27 $29.9M Not Screened A N
Santa Clara County
Levee 1
Alameda,
Santa Clara
Local 1.33 0 0 0 Not Screened N N
225 National Levee Database. (n.d.). Levees of the Nation. https://levees.sec.usace.army.mil/#/

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FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 10
Santa Clara USFWS 0.68 0 1 0 Not Screened N N
Santa Clara County
Levee 11
Santa Clara USFWS 2.28 0 0 0 Not Screened N N
Santa Clara County
Levee 12
Santa Clara SCVWD 0 0 4 $212M Not Screened N N
Santa Clara County
Levee 13
Santa Clara City of Palo
Alto

0.62 0 0 0 Not Screened N N
Santa Clara County
Levee 14
Santa Clara Local 1.06 0 0 0 Not Screened N N
Santa Clara County
Levee 15
Santa Clara SCVWD 1.13 1,632 298 $436M Not Screened N N Santa Clara County
Levee 16
Santa Clara USFWS 8.66 0 0 0 Not Screened N N
Santa Clara County
Levee 17
Santa Clara SCVWD 1.39 140 21 $248M Not Screened N N
Santa Clara County
Levee 18
Santa Clara USFWS 1.67 0 0 0 Not Screened N N
Santa Clara County
Levee 19
Santa Clara SCVWD 1.42 2,181 727 $450M Not Screened N N Santa Clara County
Levee 20
Santa Clara SCVWD 0.19 269 89 $134M Not Screened N N
Santa Clara County
Levee 21
Santa Clara SCVWD 1.97 1,512 420 $364M Not Screened N N Santa Clara County
Levee 22
Santa Clara USFWS 3.24 0 0 0 Not Screened N N
Santa Clara County
Levee 23
Santa Clara SCVWD 1.56 1,722 628 $401M Not Screened N N

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FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 24
Santa Clara USFWS 1.24 0 0 0 Not Screened N N
Santa Clara County
Levee 25
Santa Clara USFWS 0.43 0 0 0 Not Screened N N
Santa Clara County
Levee 26
Santa Clara SCVWD 2.86 0 0 0 Not Screened N N
Santa Clara County
Levee 27
Santa Clara USFWS 0.66 0 0 0 Not Screened N N
Santa Clara County
Levee 28
Santa Clara SCVWD 4.01 0 0 0 Not Screened N N
Santa Clara County
Levee 29
Santa Clara SCVWD 3.05 5,409 1,719 $1.08B Not Screened N N Santa Clara County
Levee 3
San Mateo,
Santa Clara
SCVWD 7.56 17,748 6,351 $4.45B Not Screened N N
Santa Clara County
Levee 30
Santa Clara SCVWD 1.31 3,389 750 $628M Not Screened A N Santa Clara County
Levee 30.2
Santa Clara - 1.21 4,107 1,315 $777M Not Screened N N
Santa Clara County
Levee 31
Santa Clara USFWS 1.01 0 0 0 Not Screened N N
Santa Clara County
Levee 32
Santa Clara - 0.66 0 0 0 Not Screened N N
Santa Clara County
Levee 33
Santa Clara - 0.11 0 2 $1.09 Not Screened N N
Santa Clara County
Levee 34
Santa Clara USFWS 1.8 0 0 0 Not Screened N N
Santa Clara County
Levee 35
Santa Clara SCVWD 5.7 21,352 715 $6.03B Not Screened A N

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FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 36
Santa Clara SCVWD 5.19 0 0 0 Not Screened N N
Santa Clara County
Levee 37
Santa Clara SCVWD 2.76 32,113 5,873 $10.6B Not Screened A N Santa Clara County
Levee 37 North
Santa Clara - 8.89 0 0 0 Not Screened N N
Santa Clara County
Levee 38
Santa Clara SCVWD 3.78 0 0 0 Not Screened N N
Santa Clara County
Levee 4
Santa Clara - 0.08 0 0 0 Not Screened N N
Santa Clara County
Levee 40
Santa Clara SCVWD 1.26 8,031 43 $169M Not Screened N N
Santa Clara County
Levee 41
Santa Clara SCVWD 3.7 2,454 208 $951M Not Screened A N
Santa Clara County
Levee 42
Santa Clara SCVWD 3.52 11,654 4,092 $2.99B Not Screened N N Santa Clara County
Levee 43
Santa Clara SCVWD 0.02 0 0 0 Not Screened N N
Santa Clara County
Levee 44
Santa Clara - 0.26 0 0 0 Not Screened N N
Santa Clara County
Levee 45
Santa Clara SCVWD 3.56 0 0 0 Not Screened N N
Santa Clara County
Levee 46
Santa Clara SCVWD 1.11 5,616 53 $641M Not Screened N N
Santa Clara County
Levee 47
Santa Clara - 0.54 0 0 0 Not Screened N N
Santa Clara County
Levee 48
Santa Clara City of Palo
Alto

0.29 865 33 $82M Not Screened N N

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FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 49
Santa Clara USFWS 0.41 0 0 0 Not Screened N N
Santa Clara County
Levee 5
Santa Clara - 0.21 0 0 0 Not Screened N N
Santa Clara County
Levee 50
Santa Clara - 1.44 0 0 0 Not Screened N N
Santa Clara County
Levee 52
Santa Clara USFWS 2.5 0 0 0 Not Screened N N
Santa Clara County
Levee 53
Santa Clara - 0.03 0 0 0 Not Screened N N
Santa Clara County
Levee 54
Santa Clara SCVWD 1.83 8,645 688 $1.54B Not Screened A N Santa Clara County
Levee 55
Santa Clara City of Palo
Alto

0.33 2 2 $3.93M Not Screened N N
Santa Clara County
Levee 56
Santa Clara - 0.72 0 0 0 Not Screened N N
Santa Clara County
Levee 57
Santa Clara - 0.36 0 0 0 Not Screened N N
Santa Clara County
Levee 58
Santa Clara - 1.78 0 0 0 Not Screened N N
Santa Clara County
Levee 6
Santa Clara SCVWD 1.51 6,548 1,840 $1.2B Not Screened N N Santa Clara County
Levee 61
Santa Clara SCVWD 1.58 2,370 382 $247M Not Screened N N Santa Clara County
Levee 62
San Benito,
Santa Clara
SCVWD 2.41 41 14 $24.4M Not Screened N N
Santa Clara County
Levee 64
Santa Clara SCVWD 1.06 50,774 1,610 $10.2B Not Screened N N

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FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 65
Santa Clara - 1.39 12,714 2,494 $2.6B Not Screened N N
Santa Clara County
Levee 67
Santa Clara - 0.88 180 48 $82.7M Not Screened N N
Santa Clara County
Levee 7
Santa Clara - 0.2 0 0 0 Not Screened N N
Santa Clara County
Levee 72
Santa Clara SCVWD 0.86 0 5 $2.27M Not Screened N N
Santa Clara County
Levee 73
Santa Clara SCVWD 0.94 475 186 $97.6M Not Screened N N
Santa Clara County
Levee 74
Santa Clara - 0.62 413 128 $63.7M Not Screened N N
Santa Clara County
Levee 75
Santa Clara SCVWD 1.09 181 21 $100M Not Screened N N
Santa Clara County
Levee 79
Santa Clara - 0.87 6,131 1,840 $917M Not Screened N N
Santa Clara County
Levee 8
Santa Clara - 0.56 0 0 0 Not Screened N N
Santa Clara County
Levee 80
Santa Clara - 0.72 47 7 $1.87M Not Screened N N
Santa Clara County
Levee 81
Santa Clara SCVWD 0 0 0 Not Screened N N
Santa Clara County
Levee 82
Santa Clara SCVWD 0 0 0 Not Screened N N
Santa Clara County
Levee 83
San Benito,
Santa Clara
SCVWD 2.65 149 19 $22.5M Not Screened N N
Santa Clara County
Levee 84
Santa Clara SCVWD 0.54 1,647 759 $253M Not Screened N N

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FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 85
Santa Clara - 0.87 1,767 551 $246M Not Screened N N
Santa Clara County
Levee 86
Santa Clara SCVWD 1.88 0 0 0 Not Screened N N
Santa Clara County
Levee 88
Santa Clara SCVWD 0.75 1,517 244 $633M Not Screened N N Santa Clara County
Levee 89
Santa Clara SCVWD 1.04 9,275 2,261 $1.97B Not Screened A N Santa Clara County
Levee 9
Santa Clara SCVWD 3.41 12,080 1,617 $2.79B Not Screened N N Santa Clara County
Levee 90
Santa Clara SCVWD 0.81 2,052 344 $191M Not Screened N N Santa Clara County
Levee 92
Santa Clara SCVWD 0.21 5,982 295 $4224M Not Screened N N Santa Clara County
Levee 93
Santa Clara - 1.3 13 5 $238M Not Screened N N
Santa Clara County
Levee 96
Santa Clara - 0.5 273 5 $27.7M Not Screened N N
Uvas Creek - LB Santa Clara SCVWD 2.19 14,505 4,377 $1.72B Low A A *Accredited Levee column abbreviations: accredited (A), not accredited (N), and Provisionally Accredited Levee (PAL). **USACE Rehab column abbreviations: active (A) and not active (N).

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12.3.4 Frequency of Dam and Levee Failure
Dam and levee failure events are infrequent and usually coincide with events that cause them, such as earthquakes, landslides and excessive rainfall and snowmelt. There is a “residual risk” associated with dams that remains after safeguards have been implemented. The residual risk is associated with events beyond those that the facility was designed to withstand. However, the probability of occurrence of any type of dam failure event is low in today’s regulatory and safety oversight environment.

Further information on the impact of climate change on the probability of dam failure is included in Section 11.

Probability in OA: Unlikely

12.3.5 Severity
FEMA categorizes the downstream hazard potential of a dam into three categories in increasing severity:

Low, Significant, and High. The state’s Division of Safety of Dams (DSOD) adds a fourth category of "Extremely High." The OA has dams in all four categories; this plan focuses on the Extremely High Hazard and High Hazard dams.

Table 78: Potential Downstream Hazard from Dams25F
226
Hazard
Potential Potential Downstream Impacts to Life and Property Number of Dams in the OA Low No probable loss of human life and low economic and environmental losses. Losses are expected to be principally limited to the owner’s property.
13 Significant No probable loss of human life but can cause economic loss, environmental damage, impacts to critical facilities, or other significant impacts.
4 High Expected to cause loss of at least one human life. 6 Extremely High Expected to cause considerable loss of human life or would result in an inundation area with a population of 1,000 or more. 18 12.3.6 Warning Time for Dam Failure
EAPs are critical in identifying areas downstream from dams requiring warning and evacuation in the event of dam failure. Warning and evacuation time can dramatically influence the number of persons at risk and the number of fatalities per dam failure.
226 California Department of Water Resources. (2021, September). Downstream Hazard. https://water.ca.gov/- /media/DWR-Website/Web-Pages/Programs/All-Programs/Division-of-Safety-of-Dams/Files/Publications/Division-ofSafety-of-Dams-Definitions-for-Downstream-Hazard-and-Condition-Assessment.pdf

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Advance Warning of Failure
Warning time for dam failure varies depending on the cause of the failure. In events of extreme precipitation or massive snowmelt, evacuations can be planned with sufficient time. In the event of a structural failure due to earthquake, there may be no warning time.

Time for the Failure to Occur
A dam’s structural type also affects warning time. Earthen dams do not tend to fail completely or instantaneously. Once a breach is initiated, discharging water erodes the breach until either the reservoir water is depleted, or the breach resists further erosion. Concrete gravity dams also tend to have a partial breach as one or more monolith sections are forced apart by escaping water. The time of breach formation ranges from a few minutes to a few hours.26F
227
Time after Failure for Notification
Time available to notify those in the impacted area will depend on the dam’s distance from it and the river flow. The warning and protective action process is divided into the following three time periods:
 Warning delay time is the period between when a threat is first detected, or when an emergency manager is first notified of the threat and when an emergency manager issues a first alert/warning.
 Warning diffusion time is the period after the first alert/warning is issued and the time that people receive that alert/ warning.
 Protective action initiation time is the period after people receive the first alert/ warning and when they initiate protective action. In this time period, most people take a range of actions to prepare to implement a protective action and may receive subsequent warning messages.27F 228
Santa Clara County and its planning partners have established protocols for emergency warning and response through the County’s adopted emergency operations plan28F 229. The SCVWD Dam Safety
Program maintains the operation of its dams and works with Santa Clara County Emergency Management to provide copies of the most recent dam EAPs and inundation maps and uses this information to plan notification needs for downstream areas in the event of a failure.

12.3.7 Warning Time for Levee Failure
As with dam failure, warning time for levee failure depends on the cause of the failure. A levee failure caused by structural failure can be sudden and occur with little to no warning. If heavy rains are impacting a levee system, communities located in the immediate danger zone can be evacuated before a failure occurs. If the levee failure is caused by overtopping, the community may or may not be able to recognize the impending failure and evacuate. If a levee failure occurs suddenly, evacuation may not be possible. 227 Starosolszky, O. and Melder, O.M. (2014, April 23) Hydrology of Disasters: Proceedings of the World Meteorological Organization Technical Conference Held in Geneva, November 1988. https://books.google.com/books?id=DSFpAwAAQBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=o nepage&q&f=false
228 U.S. Army Corps of Engineers. (2019 April 30). A Guide to Public Alerts and Warnings for Dam and Levee Emergencies. https://www.publications.usace.army.mil/Portals/76/Users/182/86/2486/EP%201110-2-

17.pdf?ver=2019-06-20-152050-550
229 Santa Clara County. (2017, January). County of Santa Clara Emergency Operations Plan. Emergency Operations Plan (EOP) - Office of Emergency Management - County of Santa Clara (sccgov.org)

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12.4 Exposure
Exposure to the dam failure hazard was assessed by use of GIS spatial analysis, overlaying the inundation areas with data from the underlying population, buildings, and critical facilities. The consistency of the data available to support this risk assessment varied greatly within the OA. The level of analyses varied based on available data.

12.4.1 Population
The estimated total population living in the inundation area of an Extremely High Hazard, or a High Hazard dam is 32.17% of the total county population.

12.4.2 Property
Table 79 summarizes the estimated property exposure in the inundation area of an Extremely High Hazard or a High Hazard dam. These estimates were determined using a combination of Hazus and GIS data.

Table 79: Estimated Exposure and Value of Structures in the Dam Failure Inundation Area Exposure County Total
Inundation Area 162.90 square miles
Number of Buildings Exposed 168,271
Percentage of Exposed Buildings in the County 31.43%
Exposed Value in the County $131,358,283,000
Total Percentage of Exposed Value in the County 34.48%

12.4.3 Environment
The environment would be exposed to a number of risks in the event of dam failure. The inundation could introduce many foreign elements into local waterways. This could result in destruction of downstream habitat and could have detrimental effects on many species.

12.5 Vulnerability
The vulnerability of people, property, critical facilities, and the environment was evaluated for the combined dam failure inundation area. Countywide summaries are provided below.

Change in conditions: no change in vulnerability
 Growth in population and building is slow and not concentrated in areas at particular risk to dam failure.
 No new dams have been constructed in the OA.
 Dams with significant or high hazard potential are required to have an EAP.  Dam safety programs include inspection, maintenance, and ongoing monitoring of dams to ensure stability and proper functioning of dams.

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 DSOD and dam owners such as SCVWD periodically undertake special engineering studies to ensure that its dams are compliant with the latest design guidelines and regulations to minimize seismic risks to its dams.
• Although vulnerability to dams is not increasing, risk to people and structures in dam inundation remains high. In the unlikely even of a failure, the high volume and velocity of resulting flood waters can have devastating impacts downstream.

12.5.1 Population
All populations downstream from dam failures that are incapable of escaping the area within the allowable time period are vulnerable. Those that particularly vulnerable includes the elderly and children, people with medical conditions, people who are visually impaired and/or have vision loss, people with public transportation needs, people with non-visible disabilities, people with limited English proficiency. The vulnerable population also includes those who would not have adequate warning from a television or radio emergency warning system or cell phone alert or people who may unable to get themselves out of the inundation area. The potential for loss of life is affected by the capacity and number of evacuation routes available to populations living in areas of potential inundation. Those who are located closest to the dam would have the least warning time.

Table 80 shows the number of households and population within potential dam inundation areas in each city in the OA. These values were obtained using Hazus 6.0 dasymetric census blocks that were within a dam inundation boundary.

Table 80: Population in Dam Inundation Area
Jurisdiction Population Households
Campbell 32,482 13,326
Cupertino 840 284
Gilroy 27,185 7,752
Los Altos 3,242 1,097
Los Altos Hills 0 0
Los Gatos 5,721 2,523
Milpitas 14,242 4,315
Morgan Hill 25,469 8,296
Monte Sereno 0 0
Mountain View 17,931 7,215
Palo Alto 8,200 3,318
San Jose 396,703 137,686
Santa Clara 51,519 18,932
Saratoga 350 111
Sunnyvale 30,143 11,832
Unincorporated 8,955 2,629
Total 622,982 219,316

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12.5.2 Property
Vulnerable properties are those closest to the dam inundation area. These properties would experience the largest, most destructive surge of water. Low-lying areas are also vulnerable since they are where the dam waters would collect. Dam inundation areas can be extensive depending on the volume of water contained by the dam. Table 81 shows the value of buildings exposed to potential dam inundation within the OA. This does not take into account any damage functions based on depth of flooding, it is only a summary of building values within the potential inundation zone.

12.5.3 Critical Facilities
Typical vulnerabilities of critical facilities impacted by dam failure include road failure with road segments and bridges washed out creating isolation issues., This includes all roads, railroads, and bridges in the path of the dam inundation. Those that are most vulnerable are those that are already in poor condition and would not be able to withstand a large water surge. Utilities such as overhead power lines, cable and phone lines could also be damaged from the rushing water. Other critical facilities buildings can become flooded and inoperable. Loss of these utilities could create additional isolation issues for the inundation areas. Emergency response could also be delayed. The analysis in Santa Clara County shows the following facilities could be impacted by dam failure:
 Highway bridges: 352
 Rail bridges: 67
 Light rail bridges: 6
 Light rail facilities: 36
 Wastewater treatment facilities: 1
 Schools: 158
 Fire stations: 24
 Hospitals: 7
 Communication Facilities: 6
 Electric Power Facilities: 7

12.5.4 Environment
The environment would be vulnerable to multiple risks in the event of dam failure. The inundation could introduce foreign elements into local waterways, resulting in destruction of downstream habitat and detrimental effects on many species of animals, especially endangered species such as coho salmon. The extent of the vulnerability of the environment is the same as the exposure of the environment.

Reservoirs held behind dams affect many ecological aspects of a river. River topography and dynamics depend on a wide range of flows, but rivers below dams often experience long periods of very stable flow conditions or saw-tooth flow patterns caused by releases followed by no releases. Water releases from dams usually contain very little suspended sediment; this can lead to scouring of riverbeds and banks.

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Table 81: Value of Exposed Structures in the Dam Inundation Area by Jurisdiction Jurisdiction Residential Commercial Industrial Agricultural Religious Government Educational Total Campbell $4,338,205,000 $1,534,627,000 $418,973,000 $13,221,000 $90,790,000 $14,829,000 $216,448,000 $6,627,093,000 Cupertino $160,643,000 $6,496,000 $2,027,000 $0 $675,000 $1,054,000 $5,339,000 $176,234,000 Gilroy $2,768,627,000 $1,566,395,000 $507,771,000 $19,205,000 $24,057,000 $66,266,000 $204,184,000 $5,156,505,000 Los Altos $687,482,000 $6,339,000 $12,817,000 $0 $4,831,000 $0 $19,788,000 $731,257,000 Los Altos Hills $0 $0 $0 $0 $0 $0 $0 $0
Los Gatos $758,943,000 $615,193,000 $67,764,000 $251,000 $32,366,000 $28,170,000 $107,868,000 $1,610,555,000 Milpitas $1,497,684,000 $626,566,000 $811,058,000 $156,000 $23,605,000 $1,175,000 $31,025,000 $2,991,269,000 Monte Sereno $0 $0 $0 $0 $0 $0 $0 $0
Morgan Hill $4,114,421,000 $1,308,828,000 $773,853,000 $17,254,000 $96,415,000 $46,581,000 $161,812,000 $6,519,164,000 Mountain View $2,615,045,000 $1,500,804,000 $562,361,000 $3,282,000 $67,756,000 $19,574,000 $57,915,000 $4,826,737,000 Palo Alto $1,478,921,000 $420,664,000 $27,422,000 $464,000 $5,489,000 $0 $157,677,000 $2,090,637,000 San José $46,073,871,000 $17,490,269,000 $7,035,829,000 $96,030,000 $748,644,000 $925,107,000 $4,665,413,000 $77,035,163,000 Santa Clara
(city) $6,161,892,000 $3,784,586,000 $2,203,267,000 $22,795,000 $175,731,000 $44,789,000 $123,534,000 $12,516,594,000 Saratoga $66,875,000 $202,000 $5,927,000 $0 $0 $0 $0 $73,004,000 Sunnyvale $4,084,357,000 $1,325,027,000 $745,125,000 $303,000 $36,082,000 $15,642,000 $110,192,000 $6,316,728,000 Unincorporated
County $2,183,239,000 $1,458,486,000 $315,766,000 $406,032,000 $40,527,000 $83,070,000 $200,223,000 $4,687,343,000 Total $76,990,205,000 $31,644,482,000 $13,489,960,000 $578,993,000 $1,346,968,000 $1,246,257,000 $6,061,418,000 $131,358,283,000

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12.6 Cascading Hazards
Dam and levee failures can lead to cascading hazards including landslides, bank erosion, and destruction of downstream habitat. It could also impact future drought events by releasing stored water resources.

12.7 Regulatory Oversight for Dams
Responsibility for dam safety in the OA is distributed among federal agencies, state agencies, the SCVWD and private dam owners.

12.7.1 National Dam Safety Act
Potential for catastrophic flooding due to dam failures led to passage of the National Dam Safety Act (Public Law 92-367). The goal of this FEMA-monitored effort is to identify and mitigate the risk of dam failure so as to protect the lives and property of the public. The National Dam Safety Program is a partnership among the states, federal agencies, and other stakeholders that encourages individual and community responsibility for dam safety. Under FEMA’s leadership, state assistance funds have allowed all participating states to improve their programs through increased inspections, emergency action planning, and purchases of needed equipment. FEMA has also expanded existing and initiated new training programs. Grant assistance from FEMA provides support for improvement of dam safety programs that regulate most of the dams in the United States.29F 230

12.7.2 U.S. Army Corps of Engineers Dam Safety Program
The USACE is responsible for safety inspections of some federal and non-federal dams in the United States that meet size and storage limitations specified in the National Dam Safety Act. The USACE has inventoried dams; surveyed each state and federal agency’s capabilities, practices, and regulations regarding design, construction, operation, and maintenance of dams; and developed guidelines for inspection and evaluation of dam safety.230F
231

12.7.3 Federal Energy Regulatory Commission Dam Safety Program The Federal Energy Regulatory Commission (FERC) cooperates with a large number of federal and state agencies to ensure and promote dam safety. More than 3,000 dams are part of regulated hydroelectric projects in the FERC program. Two-thirds of these are more than 50 years old. As dams age, concern about their safety and integrity grows, so oversight and regular inspection are important.

FERC inspects hydroelectric projects on an unscheduled basis to investigate the following:
 Potential dam safety problems
 Complaints about constructing and operating a project  Safety concerns related to natural disasters
 Issues concerning compliance with the terms and conditions of a license 230 Federal Emergency Management Agency. (n.d.). Dam Safety. https://www.fema.gov/emergency-managers/riskmanagement/dam-safety 231 U.S. Army Corps of Engineers. (n.d.). Dam Safety Program. https://www.usace.army.mil/Missions/CivilWorks/Dam-Safety-Program/

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Every five years, an independent consulting engineer, approved by the FERC, must inspect and evaluate projects with dams higher than 32.8 feet (10 meters), or with a total storage capacity of more than 2,000 acre-feet.

FERC monitors and evaluates seismic research in geographic areas such as California where there are concerns about possibly seismic activity. This information is applied in investigating and performing structural analyses of hydroelectric projects. FERC also evaluates the effects of potential and actual large floods on the safety of dams. During and following floods, FERC visits dams and licensed projects, determines the extent of damage, if any, and directs any necessary studies or remedial measures the licensee must undertake. The FERC publication Engineering Guidelines for the Evaluation of Hydropower Projects (2021) guides the FERC engineering staff and licensees in evaluating dam safety. The publication is frequently revised to reflect current information and methodologies.

FERC requires dam licensees to prepare EAPs and conducts training sessions on how to develop and test these plans. The EAPs outline an early warning system if there is an actual or potential sudden release of water from a dam due to failure. The plans include operational procedures that may be used, such as reducing reservoir levels and reducing downstream flows, as well as procedures for notifying affected residents and agencies responsible for emergency management. These plans are frequently updated and evaluated to ensure that everyone knows what to do in emergency situations.231F 232

12.7.4 State of California
One of the earliest state regulatory programs was enacted in California in the 1920s. California’s Division of Safety of Dams (DSOD) monitors dam maintenance and safety at the state level. When a new dam is proposed, DSOD engineers and geologists inspect the site and the subsurface. Upon submittal of an application, DSOD reviews the plans and specifications prepared by the owner to ensure that the dam is designed to meet minimum requirements and that the design is appropriate for the known geologic conditions. After approval of the application, DSOD inspects all aspects of the construction to ensure that the work accords with the approved plans and specifications. After construction, DSOD inspects each dam annually to ensure performance as intended and to identify developing problems. DSOD periodically reviews stability of dams and their major appurtenances in light of improved design approaches, requirements, and new findings regarding earthquake hazards and hydrologic estimates in California.23 F 233
Finally, on June 27, 2017, SB 92 required an EAP for all dams that do not have a low downstream hazard potential designation.23F
234
An EAP is a dam owner’s formal plan that identifies potential emergency conditions at a dam and specifies actions to be followed to minimize loss of life and property damage. It includes information that dam owners use to notify local emergency management officials and state and federal dam safety regulators. The EAPs must do all of the following:
 Be based upon an inundation map approved by DWR pursuant to Section 6161 of the state’s Water Code.
 Be developed by the dam’s owner in consultation with any local public safety agency that may be impacted by an incident involving the dam, to the extent a local public safety agency wishes to consult.
232 Federal Energy Regulatory Commission. (2015, July). Chapter VI, Emergency Action Plans. https://cmsstage.ferc.gov/sites/default/files/2020-04/chap6.pdf 233 California Department of Water Resources. (2021, June 1). Dam Safety and the Importance of the Division of Safety of Dams with Andy Mangney. https://water.ca.gov/News/Blog/2020/June/DSOD-Andy-MangneyQA#:~:text=DSOD%20also%20conducts%20independent%20reviews%20of%20applications%20for,in%20light%20of %20improved%20design%20approaches%20and%20requirements. 234 California Legislative Information. (2021). Government Code Title 2, Division 1, Chapter 7. https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?sectionNum=8589.5&lawCode=GOV

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 Adhere to FEMA guidelines, and include, at a minimum, all of the following:
▪ Notification flowcharts and contact information
▪ The response process
▪ The roles and responsibilities of the dam owner and impacted jurisdictions following an incident involving the dam
▪ Preparedness activities and exercise schedules
▪ Inundation maps approved by the Department of Water Resources pursuant to Section 6161 of the Water Code
▪ Any additional information that may impact life or property

12.7.5 Santa Clara Valley Water District
The SCVWD Dam Safety Program includes four main components234F 235:
 Periodic Special Engineering Studies
The SCVWD periodically undertakes special engineering studies to ensure that its dams are compliant with the latest design guidelines and regulations to keep pace with the growing body of knowledge surrounding earthquakes. In addition to seismic studies, the SCVWD periodically conducts other special engineering studies to minimize the risks to its dams. Though not required by the regulatory agencies, the water district has proactively expanded this potential failure mode analysis approach to the remainder of our dams.
 Surveillance and Monitoring
Instrumentation placed in and on the dam furnishes data for water district engineers to determine if the structure is functioning as intended. SCVWD continuously monitors the conditions of its dams and uses automated instrumentation at five dams. The equipment can collect, check, record, and archive the collected data and alert staff when parameters exceed set threshold limits.
 Dam Inspections and Maintenance
SCVWD routinely inspects and monitors the condition of each dam and provides an annual surveillance report to the DSOD and each year they also jointly inspect each of its dams with DSOD.
 Emergency Response and Preparedness
At the core of the Dam Safety Program’s emergency response and preparedness is its postearthquake dam evaluation program team. After significant earthquakes, trained personnel inspect the dams for any signs of damage or potential for failure. SCVWD works with various agencies on emergency action planning and training exercises each year. Under the Dam Safety Program, SCVWD is developing updated maps which estimate what areas could flood in the highly unlikely event of a dam failure.
235 Santa Clara Valley Water District. (n.d.). Dam Safety Program. https://www.valleywater.org/flooding-safety/damsafety-program

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12.7.6 Regulatory Oversight for Levees
Regulatory oversight depends on whether the levee is accredited or not. The USACE has recently updated its guidance for evaluating, designing, and constructing levees. Engineer Manual (EM) 1110-2- 1913. The document has been available for review and publication was expected at the end of December 2022.

Federal Emergency Management Agency (FEMA)
FEMA does not evaluate the performance of a levee system—this is the responsibility of the levee owner.

FEMA is responsible for establishing levee system evaluation and mapping standards for an accredited levee, determining flood insurance risk zones, and reflecting these determinations on FIRMs.

State of California
The Department of Water Resources (DWR), Division of Flood Management inspects the levees annually and prepares a report which addresses vegetation, animal control, slope stability, erosion, and vehicle traffic.

12.8 Future Trends in Development
Land use in the OA is directed by general plans adopted under state law and local regulations. The safety elements of the general plans establish standards and plans for the protection of the community from hazards. Dam and levee failure are currently not addressed as stand-alone hazards in the safety elements, but flooding is. Municipalities participating in this MJHMP have established comprehensive policies regarding sound land use in identified flood hazard areas. Most of the areas vulnerable to the more severe impacts from dam and levee failure intersect the mapped flood hazard areas. Flood-related policies in the general plans will help to reduce the risk associated with dam and levee failure hazard for all future development in the OA.

12.9 Scenario
An earthquake in the region could lead to liquefaction of soil around a dam. This could occur without warning during any time of the day. A terrorist or other intentional attack also could cause a catastrophic failure of a dam that impacts the OA. While the probability of dam failure is very low, the probability of flooding associated with changes to dam operational parameters in response to climate change is higher.

Dam designs and operations are developed based on hydrographs with historical record. If these hydrographs experience significant changes over time due to the impacts of climate change, the design and operations may no longer be valid for the changed condition. This could have significant impacts on dams that provide flood control. Specified release rates and impound thresholds may have to be changed.

This would result in increased discharges downstream of these facilities, thus increasing the probability and severity of flooding.

12.10 Issues
There is often limited warning time for dam failure. These events are frequently associated with other natural hazard events such as earthquakes, landslides, or inclement weather, which limits their predictability and compounds the hazard. Important issues associated with dam failure hazards include the following:
 Federally regulated dams have an adequate level of oversight and sophistication in the development of an EAP for public notification in the unlikely event of failure. However, the protocol for notification of downstream citizens of imminent failure needs to be tied to local emergency response planning.

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 Mapping for federally regulated dams is required and available; however, mapping for nonfederal-regulated dams that estimates inundation depths is needed to better assess the risk associated with dam failure from these facilities. Moreover, although mapping is required for federally regulated dams, development downstream of dams and upgrades to older dams may have altered inundation areas; however, these inundation maps may not have been updated for significant periods of time. Encouraging property owners of dams to update EAPs and inundation maps will ensure availability of the most accurate data to assist emergency planners and local officials.
 Most dam failure mapping required at federal levels requires determination of the probable maximum flood. While the probable maximum flood represents a worst-case scenario, it is generally the event with the lowest probability of occurrence. For non-federal-regulated dams, mapping of dam failure scenarios that are less extreme than the probable maximum flood but have a higher probability of occurrence can be valuable to emergency managers and community officials downstream of these facilities. This type of mapping can illustrate areas potentially impacted by more frequent events to support emergency response and preparedness.  The concept of residual risk associated with structural flood control projects should be considered in the design of capital projects and the application of land use regulations.  Addressing security concerns and the need to inform the public of the risk associated with dam failure is a challenge for public officials.
 Limited financial resources for dam maintenance during economic downturns result in decreased attention to dam structure operational integrity because available funding is often directed to more urgent needs. This could increase potential for maintenance failures. Dam failure inundation areas are often not considered special flood hazard areas under the NFIP, so flood insurance coverage in these areas is not common.

12.11 Consequence Analysis
When a dam fails, the stored water can be suddenly released and have catastrophic effects on life and property downstream. The amount of warning time depends largely on the nature of the failure. Homes, bridges, and roads may be demolished in minutes. The impact of the event may be felt for an extended period of time. Residents near a significant or high-hazard dam should become familiar with the dam’s emergency action plans if one is available. EAPs written for dams include procedures for notification and coordination with law enforcement and other governmental agencies; information on the potential inundation area; plans for warning and evacuation; and procedures for making emergency repairs.

The information in Table 82 provides the consequence analysis of the potential for detrimental impacts of dam failure done for accreditation with the Emergency Management Accreditation Program (EMAP).

Table 82: EMAP Consequence Analysis: Dam Failure
Subject Ranking Impacts/Dam Failure
Health and Safety of
Public in the Area of
the Incident
Severe The localized impact is expected to be severe for the inundation area and moderate to minimal for other affected areas.

Responders Minimal The impact on responders is expected to be minimal with proper training. The impact could be severe if there is a lack of training.

Continuity of
Operations (including
continued delivery of
services)
Minimal Temporary relocation may be necessary if inundation affects government facilities.

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Subject Ranking Impacts/Dam Failure
Property, Facilities,
and Infrastructure
Minimal to
severe
The localized impact could be severe for facilities and infrastructure in the inundation area of the incident. The farther away from the incident area, the more likely the damage will lessen, from moderate to minimal.

Delivery of Services Minimal to
severe
Delivery of services could be affected if there is any disruption to the roads and/or utilities due to the inundation. Minimal to severe, depending on area size and location affected.

Environment Severe The impact will be severe for the immediate area. The impact will lessen as distance increases from the immediate incident area.

Economic Conditions Minimal to
severe
Impacts on the economy will greatly depend on the scope of the inundation and the amount of time it takes for the water to recede.

Public Confidence in
the Government
Minimal to
severe
The public’s confidence will vary, depending on the perception of whether the failure could have been prevented, the warning time, and the time it takes for response and recovery.

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13 Flood
Definitions
 Flood: The inundation of normally dry land.
 Floodplain: The land area along the sides of a river that becomes inundated with water during a flood.
 1-Percent-Annual-Chance (100-Year) Floodplain: The area flooded by the flood that has a 1- percent chance of being equaled or exceeded in a given year. The 1-percent-annual-chance flood is the standard used by most federal and state agencies.  0.2-Percent-Annual-Chance (500-Year) Floodplain: The area flooded by the flood that has a 0.2- percent chance of being equaled or exceeded in a given year.  Regulatory Floodway: Channel of a river or other water course and adjacent land areas that must be reserved for discharge of the base flood without cumulatively increasing water surface elevation more than a designated height. Communities must regulate development in these floodways to ensure no increases in upstream flood elevations.
 Return Period: The average number of years between occurrences of a hazard (equal to the inverse of the annual likelihood of occurrence).
 Riparian Zone: The area along the banks of a natural watercourse.

13.1 General Background
Flooding is a temporary condition in which normally dry land is partially or completely inundated. There are number of ways in which flooding can happen. The water levels in bodies such as streams, rivers, lakes, and reservoirs can exceed the water body’s banks, causing water to overflow into nearby areas.

Heavy precipitation can overwhelm the ability of soil to absorb water or local storm drains to carry it away, causing water to build up on the surface. Water from oceans and bays can inundate shoreline areas during exceptionally high tides or be pushed ashore by the winds of an intense storm during coastal floods. Flooding may also occur from infrastructure failure, such as a burst water tank or pipe. Dam inundation, a specific type of infrastructure failure flood that occurs when a dam partially or completely fails, is discussed separately under Dam Failure. Flooding is California’s second most frequent disaster after wildfire.

A floodplain is the area adjacent to a river, creek, or lake that becomes inundated during a flood.

Floodplains may be broad, as when a river crosses an extensive flat landscape, or narrow, as when a river is confined in a canyon.

When floodwaters recede after a flood event, they leave behind layers of rock and mud. These gradually build up to create a new floor of the floodplain. Floodplains generally contain unconsolidated sediments (accumulations of sand, gravel, loam, silt, and/or clay), often extending below the bed of the stream.

These sediments provide a natural filtering system, with water percolating back into the ground and replenishing groundwater. These are often important aquifers, the water drawn from them being filtered compared to the water in the stream. Fertile, flat reclaimed floodplain lands are commonly used for agriculture, commerce, and residential development.

Connections between a river and its floodplain are most apparent during and after major flood events.

These areas form a complex physical and biological system that not only supports a variety of natural resources but also provides natural flood and erosion control. When a river is separated from its

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floodplain with levees and other flood control facilities, natural, built-in benefits can be lost, altered, or significantly reduced.

Coastal communities face additional unique flooding hazards. This includes storm surge, waves, and erosion. Coastal flooding can be especially dangerous when high waters combine with the power of waves. Storm surge refers to the abnormal rise in seawater level during a storm. It can cause major coastal and inland flooding. Waves are generated by wind blowing across water. During a storm, wind speeds tend to be higher and last longer, creating larger, more powerful waves. These waves can cause significant damage to anything they impact along the coast. In this case, erosion refers to the wearing away of beaches, dunes, or bluffs by the forces of waves, flowing water, and/or winds. This process can quickly change the appearance of a coastline.

13.1.1 Measuring Floods and Floodplains
Flood frequency and severity are calculated using a number of variables. Flood studies determine the likelihood that a certain river discharge (flow) level will occur in a given year. For example, the 100-year flood has a 1-percent chance of being equaled or exceeded in any given year. For many years, federal agencies referred to the flood frequency statistics in terms of reoccurrence internals (i.e., the “100-year” or “500-year” flood). However, these measurements reflect statistical averages only; it is possible for two or more floods with a 100-year or higher recurrence interval to occur in a short time. The same flood can have different recurrence intervals at different points on a river. In recent years, the terminology has changed to the annual exceedance probability (i.e., 1%, 0.2% chance of occurring) to clear up this confusion.235F
236 The “annual flood” is the greatest flood event expected to occur in a typical year.

The extent of flooding associated with a 1-percent annual probability of occurrence (the base flood or 100-year flood) is the standard regulatory boundary for many organizations. Also referred to as the special flood hazard area (SFHA), this boundary is a convenient tool for assessing vulnerability and risk in flood-prone communities. Many communities have maps that show the extent and likely depth of flooding for the base flood. Corresponding water-surface elevations describe the elevation of water that will result from a given discharge level which is important to understand for floodplain management and community development in order to mitigate risk to new and existing structures.

13.1.2 Floodplain Ecosystems
Floodplains can support ecosystems that are rich in plant and animal species. A floodplain can contain 100 or even 1,000 times as many species as a river. Wetting of the floodplain soil releases an immediate surge of nutrients: those left over from the last flood, and those that result from the rapid decomposition of organic matter that has accumulated since then. Microscopic organisms thrive and larger species enter a rapid breeding cycle. Opportunistic feeders (particularly birds) move in to take advantage. The production of nutrients peaks and falls away quickly, but the surge of new growth endures for some time. This makes floodplains valuable for agriculture. Species growing in floodplains are markedly different from those that grow outside floodplains. For instance, riparian trees (trees that grow in floodplains) tend to be very tolerant of root disturbance and very quick growing compared to non-riparian trees.236F 237
236 U.S. Geological Survey. (2018, June 7). The 100-Year Flood. https://www.usgs.gov/special-topics/water-scienceschool/science/100-yearflood#:~:text=The%20USGS%20and%20other%20agencies%20often%20refer%20to,and%20this%20corresponds% 20to%20a%205-year%20recurrence-interval%20flood.
237 International Union of Forest Research Organizations. (n.d.). Riparian and Coastal Ecosystems. https://www.iufro.org/science/divisions/division-8/80000/80100/80105/

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13.1.3 Effects of Human Activities
Because they border water bodies, floodplains have historically been popular sites to establish settlements. Human activities tend to concentrate in floodplains for a number of reasons: water is readily available; land is fertile and suitable for farming; transportation by water is easily accessible; and land is flatter and easier to develop. But human development in floodplains frequently interferes with the natural function of floodplains. It can affect the distribution and timing of drainage, thereby increasing flood problems. Urbanization can create local flooding problems by altering or confining drainage channels.

This increases flood potential in two ways: it reduces the stream’s capacity to contain flows, and it increases flow rates or velocities downstream during all stages of a flood event. River debris, such as the dumping of waste and rubbish, can decrease the conveyance of the river channels. Mining and other industries can change water patterns. Sometimes, humans intentionally make changes, through structural flood control measures such as dams, levees, and embankments.

13.1.4 Federal Flood Programs
FEMA Regulatory Flood Zones
FEMA Flood Zones are geographic areas FEMA has defined according to their levels of flood risk. These areas are determined via statistical analyses of records of river flow, storm tides, and rainfall; information obtained through consultation with the community; floodplain topographic surveys; and hydrologic and hydraulic analysis. These zones are described in terms of high-, moderate-, and low-risk. The “low-risk” area does not mean “no-risk.” Anywhere it rains, it can flood. About 25-percent of NFIP claims come from properties in a low-risk flood zone. Everyone is in a flood zone, but not everyone is in a Special Flood Hazard Area (SFHA). The SFHA is the high-risk area, or the land area covered by floodwaters during the base flood where communities that participate in the NFIP must enforce floodplain management regulations and where mandatory purchase of flood insurance applies for federally backed mortgages. A structure within a 1-percent annual chance floodplain (the SFHA) has a 26-percent chance of undergoing flood damage during the term of a 30-year mortgage.

FEMA Flood Zones are further defined as follows:
 Zones A1-30 and AE: SFHAs that are subject to inundation by the base flood, determined using detailed hydraulic analysis. Base Flood Elevations are shown within these zones.  Zone A (Also known as Unnumbered A-zones): SFHAs where no Base Flood Elevations or depths are shown because detailed hydraulic analyses have not been performed.  Zone AO: SFHAs subject to inundation by types of shallow flooding where average depths are between 1 and 3 feet. These are normally areas prone to shallow sheet flow flooding on sloping terrain.
 Zone VE, V1-30: SFHAs along coasts that are subject to inundation by the base flood with additional hazards due to waves with heights of 3 feet or greater. Base Flood Elevations derived from detailed hydraulic analysis are shown within these zones.  Zone B and X (shaded): Moderates flood hazard areas between the limits of the base flood and the 0.2-percent-annual-chance (or 500-year) flood.
 Zones C and X (unshaded): Areas of minimal flood hazards outside the SFHA with an elevation higher than the 0.2-percent-annual-chance flood.

Modern visualizations can help residents understand their flood risk. DFIRMS identify locations of specific properties in relation to SFHAs; base flood elevations (1-percent annual chance) at specific sites; magnitudes of flood within specific areas; undeveloped coastal barriers where flood insurance is not available; and regulatory floodways and floodplain boundaries (1-percent and 0.2-percent annual chance floodplain boundaries). FEMA’s National Flood Hazard Layer is a compilation of GIS data including a

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nationwide digital Flood Insurance Rate Map and updated data, like a LOMA (Letter of Map Amendment) or LOMR (Letters of Map Revision) which amend the FIRM.

Risk changes over time. These flood maps are not designed to incorporate future conditions including climate change, sea-level rise, and changes in development. Additional studies are necessary when significant changes occur in order to keep up with changing conditions.

Risk Mapping, Assessment, and Planning
FEMA’s Risk Mapping, Assessment and Planning (Risk MAP) program develops non-regulatory guidance documents. Risk MAP supports community resilience by providing data, building partnerships, and supporting long-term hazard mitigation planning.237F
238 Each Risk Map product is tailored to the needs of the individual community and may involve different steps, processes, and end results. A “whole community” approach is used throughout the development of these products and the public is provided multiple opportunities to participate. The resulting products are intended to help property owners, community planners, emergency management officials, and others make risk-informed planning and development decisions. Additionally, at the end these products should help local officials identify mitigation opportunities that will work for their communities.

There are currently no Risk MAP products available for the Operational Area (OA). However, through Risk MAP FEMA is looking to conduct flood hazard studies for all the populated coastlines in order to update their FIRMs and Flood Insurance Studies (FISs) so communities have access to the best available data on their coastal flood risk.238F
239
National Flood Insurance Program
The NFIP makes federally backed flood insurance available to homeowners, renters, and business owners in participating communities. A federal disaster declaration is not necessary for an NFIP payout.

Insurance can also cover significantly more than FEMA’s Individuals and Household Program, which is sometimes available post-disaster. The average NFIP Claims Payment for California between 1996 and 2019 was $18,400.239 F
240 Most homeowner’s insurance does not cover flood insurance. Flood insurance is an important measure of a community’s resiliency to the flood hazard.

For most participating communities, FEMA has prepared a detailed Flood Insurance Study (FIS). The study presents water surface elevations for floods of various magnitudes, including the 1-percent annual chance (100-year) flood and the 0.2-percent annual chance (500-year) flood. Base flood elevations and the boundaries of the 100- and 500-year floodplains are shown on Flood Insurance Rate Maps (FIRMs), which are the principal tools for identifying the extent and location of the flood hazard. FIRMs are the most detailed and consistent data source available, and for many communities they represent the minimum area of oversight under their floodplain management program. Santa Clara County also has DFIRMs. This means the FIRM data is accessible to residents, local governments, and stakeholders online at FEMA’s Map Service Center and National Flood Hazard Layer websites. 238 Federal Emergency Management Association. (2021, November 4). Risk Mapping, Assessment and Planning (Risk MAP). https://www.fema.gov/flood-maps/tools-resources/risk-map 239 Federal Emergency Management Association. (2021, November 4). Risk Mapping, Assessment and Planning (Risk MAP). https://www.fema.gov/flood-maps/tools-resources/risk-map 240 Federal Emergency Management Association. (2022). Historical Flood Risks and Costs. https://www.fema.gov/data-visualization/historical-flood-risk-and-costs

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Participants in the NFIP must, at a minimum, regulate development in the SFHA in accordance with NFIP criteria. The minimum criteria for NFIP participation include, but are not limited to240 F 241:
 Require permits for all proposed construction or other development in the community to determine whether such construction or development will be place in flood-prone areas.  Review proposed development to assure that all necessary permits have been received.  Require the elevation of new and substantially improved residential structures to above the base flood level.
 Require the elevation or dry floodproofing (making watertight) new or substantially improved nonresidential structures in Zone A.  With limited exception, prohibit encroachments, including fill, new construction, substantial improvements, and other development within the adopted regulatory floodway.  Adhere to additional requirements to protect buildings in coastal areas from the impacts of waves, high velocity, and storm surge.

Table 83 lists each participating municipal jurisdiction’s date of entrance into the NFIP and the effective date for its current FIRM.

Table 83: NFIP Status in the Operational Area
Community NFIP Community # NFIP Entry Date Current Effective FIRM
City of Campbell 060338 06/30/1976 02/19/2014
City of Cupertino 060339 05/01/1980 05/18/2009
City of Gilroy 060340 08/01/1980 05/18/2009
City of Los Altos 060341 07/16/1980 05/18/2009
Los Altos Hills 060342 01/02/1980 05/18/2009
Los Gatos 060343 01/17/1979 02/19/2014
City of Milpitas 060344 07/16/1980 02/19/2014
City of Monte Sereno 060345 05/18/2009 02/19/2014
City of Morgan Hill 060346 06/18/1980 05/18/2009
City of Mountain View 060347 08/15/1980 05/18/2009
City of Palo Alto 060348 09/19/1984 10/16/2012
City of San José 060349 08/02/1982 02/19/2014
City of Santa Clara 060350 07/16/1980 02/19/2014
City of Saratoga 060351 01/17/1979 02/19/2014
City of Sunnyvale 060352 05/15/1978 05/18/2009
Unincorporated County 060337 08/02/1982 02/19/2014
241 Federal Register. (2021). Request for Information on the National Flood Insurance Program’s Floodplain Management Standards. https://www.federalregister.gov/documents/2021/10/12/2021-22152/request-for-informationon-the-national-flood-insurance-programs-floodplain-management-standardsfor#:~:text=The%20minimum%20NFIP%20requirements%20for%20participating%20communities%20include%2C,im pacts%20of%20waves%2C%20high%20velocity%2C%20and%20storm%20surge.

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Building codes are an important part of developing resilient communities. All community’s that participate in the NFIP must adhere to the NFIP floodplain management criteria, including adopting a flood damage prevention ordinance. The California Department of Water Resources (DWR) has developed a 2020 model ordinance which reflects NFIP requirements and California Building Standards Code (CCR Title 24). Communities that did not use this ordinance may make amendments to their existing regulations.

This ordinance reflects the fact that the flood provisions of CCR Title 24 meet or exceed the minimum requirements for buildings and structures.241F
242
“Substantial improvement” refers to any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds 50 percent (or less, if defined as so in the jurisdiction’s floodplain management ordinance) of the market value of the structure before the start of construction of the improvement. “Substantial damage” means any damage of any origin sustained by a structure that would cause the cost of restoring the structure to its before damage condition to equal or exceed 50 percent of the market value of the structure before the damage occurred. The repairs to a substantially damaged structure are considered a substantial improvement and that structure would be required to meet current NFIP standards in order to protect it from future flood losses. These kind of post-disaster policies and procedures are further described in Volume 2, as applicable.

All participating planning partners are currently in good standing with the provisions of the NFIP. In California, the DWR is the coordinating agency for floodplain management. The DWR works with FEMA and local governments by providing grants and technical assistance, evaluating community floodplain management programs, reviewing local floodplain ordinances, participating in statewide flood hazard mitigation planning, and facilitating annual statewide workshops. Compliance is monitored by FEMA regional staff and by the DWR. Maintaining compliance under the NFIP is an important component of flood risk reduction. All planning partners that participate in the NFIP have identified actions to maintain compliance and good standing. Details about participation in the NFIP are further described the individual annexes in Volume 2 of this plan.

Risk Rating 2.0
FEMA recently updated the pricing methodology for the NFIP through Risk Rating 2.0. This new methodology builds on years of investment in flood hazard information by leveraging new technology and best practices such as private sector data sets, catastrophe models, and evolving actuarial science to develop rates that are actuarily sound, equitable, easier to understand, and better reflective of risk.24F 243
Previously, rates were based on relatively static measurements, emphasizing a property’s zone on the FIRM. Now, FEMA is able to incorporate additional flood risk variables into their rating calculations. This includes flood frequency, multiple flood types – river overflow, storm surge, coastal erosion, and heavy rainfall – and distance to water source, along with such property characteristics as elevation, numbers of floors, and the cost to rebuild. This reflects a significant change to their rating system. It is intended to make flood insurance more equitable. Before, policyholders were lower-valued homes were paying more than their share of the risk while policy holders with higher-valued homes were paying less than their share. With Risk Rating 2.0, FEMA is able to distribute premiums across all policyholders based on home value and a property’s unique flood risk.243F
244
Risk Rating 2.0 rates went into effect for new policies in October 2021. All remaining policies renewed on or after April 1, 2022, utilize the new rating methodology as well. The FEMA estimated first-year premium changes for existing NFIP policies in Santa Clara County is displayed in Figure 60: Risk Rating 2.0:

Project Premium Changes for Santa Clara County.
242 California Department of Water Resources. (n.d.). National Flood Insurance Program. https://water.ca.gov/nfip/ 243 Federal Emergency Management Association. (2022, April 18). Risk Rating 2.0: Equity in Action. https://www.fema.gov/flood-insurance/risk-rating
244 Federal Emergency Management Association. (2022, April 18). Risk Rating 2.0: Equity in Action. https://www.fema.gov/flood-insurance/risk-rating

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Figure 61: Risk Rating 2.0: Project Premium Changes for Santa Clara County24F 245
The Community Rating System
The community rating system (CRS) is a voluntary program within the NFIP that encourages floodplain management activities that exceed the minimum NFIP requirements. Flood insurance premiums are discounted to reflect the reduced flood risk resulting from community actions meeting the following three goals of the CRS:
 Reduce flood damage to insurable property.
 Strengthen and support the insurance aspects of the NFIP.  Encourage a comprehensive approach to floodplain management.

For participating communities, flood insurance premium rates are discounted in increments of 5 percent.

For example, a Class 1 community would receive a 45 percent premium discount, and a Class 9 community would receive a 5 percent discount. (Class 10 communities are those that do not participate in the CRS; they receive no discount.) Previously, properties outside of the SFHA received smaller discounts: a 10-percent discount if the community is at Class 1 to 6 and a 5-percent discount if the community is at Class 7 to 9. Now, under Risk Rating 2.0, the discount is applied uniformly to all policies throughout the participating community regardless of whether the structure is located in the SFHA.

The CRS classes for local communities are based on 19 creditable activities in the following categories:
 Public information
 Mapping and regulations
245 Association of State Floodplain Managers. (2021, September). Data Visualization Dashboards for FEMA’s Risk Rating 2.0 Projected Premium Change Analysis. https://floodsciencecenter.org/projects/data-visualizationdashboards-for-fema-risk-rating-2-0-projected-premium-change-analysis/

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 Flood damage reduction
 Warning and response
Figure 61 shows the nationwide number of CRS communities by class as of October 2022, when there were 1,353 communities receiving flood insurance premium discounts under the CRS program.

Figure 62: CRS Communities by Class Nationwide as of October 2022245F 246
CRS activities can help to save lives and reduce property damage. Communities participating in the CRS represent a significant portion of the nation’s flood risk; over 70 percent of the NFIP’s policy base is located in these communities. Communities receiving premium discounts through the CRS range from small to large and represent a broad mixture of flood risks, including both coastal and riverine flood risks.

Table 84: CRS Community Status in the Operational Area246F 247
Community NFIP
Community #
CRS Entry
Date
Current CRS
Classification
% Premium
Discount,
SFHA/non-SFHA
Cupertino 060339 10/01/2005 7 15/5
Gilroy* 060340 05/01/2007 8 10/5
Los Altos 060341 10/01/1991 8 10/5
Milpitas 060344 10/01/1991 7 15/5
Morgan Hill 060346 05/01/2003 7 15/5
246 Federal Emergency Management Association. (2022, October). Community Rating System. https://www.fema.gov/floodplain-management/community-rating-system 247 FEMA. (2023). Community Rating System. https://www.fema.gov/floodplain-management/community-ratingsystem

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Community NFIP
Community #
CRS Entry
Date
Current CRS
Classification
% Premium
Discount,
SFHA/non-SFHA
Mountain View 060347 05/01/2002 8 10/5
Palo Alto 060348 10/01/1991 6 20/10
San José 060349 10/01/1991 7 15/5
Santa Clara (city) 060350 05/01/2002 7 15/5
Sunnyvale 060352 10/01/1998 7 15/5
*Gilroy CRS rating is 8 as of 5/1/2007. Starting 10/1/2023, the rating will be a 7 with a percentage premium discount of 15% of SFHA and 5% for non-SFHA.

Santa Clara Valley Water will lead the development of a separate Floodplain Management Plan specifically dedicated to meeting the CRS planning requirements, allowing planning partners that participate in the CRS program to maintain or enhance their CRS classifications. Relevant information from this Hazard Mitigation Plan will be incorporated into the Floodplain Management Plan.

13.2 Hazard Profile
The following information is extracted from the Santa Clara County Flood Insurance Study247F 248:
 The mountains and foothills in northern Santa Clara County are the sources of the watercourses that flow through the north portion of the OA. Near San José, the major waterways include Los Gatos, Guadalupe, and Alamitos Creeks flowing out of the Santa Cruz Mountains; Coyote Creek and a host of tributaries, including Upper Penitencia and Silver Creeks, flowing out of the Diablo Range; and Fisher Creek with headwaters on the western side of the Coyote Creek Valley. The 75-mile-long Coyote Creek is the primary natural drainage facility for the eastern side of the Santa Clara Valley.
 Permanente and Stevens Creeks, which flow north through the OA near Mountain View, are the primary runoff drainage channels in that area. In addition to providing flood control, these creek beds provide gravel lenses that penetrate the impervious underground clay layers. These lenses allow rain runoff to percolate down to replenish the underground water supply.  The principal watercourses in the south portion of the OA are Llagas, Uvas, and Coyote Creeks.

Edmundson (Little Llagas), Church, Center, Tennant, Maple, and Foothill Creeks also flow through the area. The area is unusual in that creeks originate in both the Diablo Range, to the east, and the Santa Cruz Mountains, to the west. Waters originating in the area are conveyed to Monterey Bay via the Pajaro River.
 Drainage-ways in the OA are a combination of natural channels (creek beds) and channels altered by human activity.
 Drainage patterns in the OA have been altered by urbanization, and the runoff, which has increased, is a greater flood threat than in previous years. The construction of water-conservation flood retention facilities has also altered the drainage pattern.  A variety of conditions cause flooding in the Santa Clara County OA. In smaller drainage basins, flooding is usually the result of intense storms. In larger basins, flooding results from storms of long duration. Shallow overland flooding often occurs due to the small capacity of the creeks. 248 Federal Emergency Management Association. (2014, February 19). Flood Insurance Study Santa Clara County. https://www.milpitas.gov/_pdfs/FISReport.pdf

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13.2.1 Types of Flood-Related Hazards
Flooding in the Santa Clara County OA typically occurs during the rainy winter season. Four types of flooding primarily affect the County: stormwater runoff, riverine, flash floods, and tidal floods.

Stormwater Runoff Floods
Stormwater runoff is generated from rain and snowmelt events that flows over land or impervious surfaces, such as parking lots and roads, without being absorbed.248F 249 Stormwater flooding is a result of
local drainage issues and high groundwater levels. Locally, heavy precipitation, especially during high lunar tide events, may induce flooding within areas other than delineated floodplains or along recognizable channels. If local conditions cannot accommodate intense precipitation through a combination of infiltration and surface runoff, water may accumulate and cause flooding problems.

Flooding issues of this nature generally occur within areas with flat gradients, and generally increase with urbanization, which speeds accumulation of floodwaters because of impervious areas249F 250. Pump stations
may be unable to pump stormwater during a large precipitation event due to insufficient channel capacity or submergence of the pump station, rendering it inoperable. Shallow street flooding can occur unless channels have been improved to account for increased flows. Numerous areas within the County undergo stormwater flooding that contributes to street and structure inundation.

Urban flooding is by increased water runoff due to urban development and drainage systems. Drainage systems are designed to remove surface water from developed areas as quickly as possible to prevent localized flooding on streets and within other urban areas. These systems utilize a closed conveyance system that channels water away from an urban area to surrounding streams, and bypasses natural processes of water filtration through the ground, containment, and evaporation of excess water. Because drainage systems reduce the amount of time surface water takes to reach surrounding streams, flooding in those streams can occur more quickly and reach greater depths than prior to development within that area.250F
251
Riverine Floods
Riverine flooding is overbank flooding of rivers and streams. Natural processes of riverine flooding add sediment and nutrients to fertile floodplain areas. Flooding in large river systems typically results from large-scale weather systems that generate prolonged rainfall over a wide geographic area, causing flooding in hundreds of smaller streams, which then drain into the major rivers. Shallow area flooding is a special type of riverine flooding. FEMA defines shallow flood hazards as areas inundated by the 100-year flood with flood depths of only 1 to 3 feet. These areas are generally flooded by low-velocity sheet flows of water. Two types of flood hazards are generally associated with riverine flooding:
 Inundation: Inundation occurs when floodwater is present, and debris flows through an area not normally covered by water. These events cause minor to severe damage, depending on velocity and depth of flows, duration of the flood event, quantity of logs and other debris carried by the flows, and amount and type of development and personal property along the floodwater’s path.  Channel Migration: Erosion of banks and soils worn away by flowing water, combined with sediment deposition, causes migration or lateral movement of a river channel across a floodplain.

A channel can also abruptly change location (termed “avulsion”); a shift in channel location over a large distance can occur within as short a time as one flood event. 249 Environmental Protection Agency. (2023, February 2). National Pollutant Discharge Elimination System (NPDES) Stormwater Program. https://www.epa.gov/npdes/npdes-stormwater-program 250 FEMA. (1997, January). Multi Hazard Identification and Risk Assessment: The Cornerstone of the National Mitigation Strategy. https://babel.hathitrust.org/cgi/pt?id=pst.000032338492&view=1up&seq=5 251 Environmental Protection Agency. (n.d.). Flow Alteration. https://www.epa.gov/caddis-vol2/flow-alteration

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Natural stream channels in rural parts of the Santa Clara County OA typically can accommodate average rainfall amounts and mild storm systems; however, severe floods occur in years of abnormally high rainfall or unusually severe storms. During those periods of severe floods, high-velocity floodwaters carry debris over long distances, block stream channels, and create severe localized flooding.

Flash Floods
The National Weather Service defines a flash flood as a rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level. Such floods generally begin within 6 hours of the rain event that causes them. Ongoing flooding can intensify to flash flooding in cases where intense rainfall results in a rapid surge of rising flood waters.251F 252
Flash floods can tear out trees, undermine buildings and bridges, and scour new channels. In urban areas, flash flooding is an increasingly serious problem due to removal of vegetation and replacement of ground cover with impermeable surfaces such as roads, driveways, and parking lots. The greatest risk from flash floods is occurrence with little to no warning. Major factors in predicting potential damage are intensity and duration of rainfall, and steepness of watershed and streams.

Coastal Floods
Coastal flooding of normally dry land by the coastline is caused by abnormally high tides, storm surge, and persistent onshore winds and waves. Rising and falling water levels, breaking waves, and shifting sands are common sights along the shore. Typically, they are a normal part of life on the coast, however when they strengthen intensity they can threaten life, property, and livelihoods of coastal populations.

Coastal floods come with a unique range of concerns including storm, waves, and erosion. All of these can contribute to extensive damage to homes, businesses, and infrastructure. The flooding of bay adjacent SFHAs is likely in the Santa Clara County OA, particularly where land is at or slightly above sea level. Areas mapped as Zone V and Zone VE are considered at high-risk from coastal flooding and are subject to stricter building requirements because of the likelihood of damage from strong waves.

High Tide Floods
It no longer takes a strong storm or hurricane to flood coastal areas. Tidal floods are characterized by inundation of normally dry lands by the coast, often caused by extreme high tide events that result in shallow flooding of low-lying coastal areas. Colloquially known as “King Tides,” these tides exceed the highest water level reached at high tide on an average day and normally occur once or twice per year.

King Tide events are the leading cause of flooding by bay waters.

Tidal flooding is becoming increasingly exacerbated by sea level rise as a result of climate change or tectonic activity.25F
253 Average daily water levels are rising along with the oceans. As a result, high tides are reaching higher and extending further inland than in the past. Additional information regarding the impacts and exposure of the OA to sea level rise is presented in Section 11, Climate Change. 252 National Weather Service. (n.d.). Flood Related Hazards. https://www.weather.gov/safety/flood-hazards 253 National Oceanic and Atmospheric Administration. (n.d.). Flooding on a Sunny Day? Here’s How. https://oceantoday.noaa.gov/flooding-sunny-day/

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13.2.2 Principal Flooding Sources
FEMA’s Flood Insurance Study for Santa Clara County assessed over 50 creeks, channels, and water bodies, including the following principal flooding sources253F 254:
 Adobe Creek
 Alamitos Creek
 Alviso Slough
 Arastradero Creek
 Arroyo Calero
 Barron Creek
 Berryessa Creek
 Calabazas Creek
 Canoas Creek
 Concepcion Drain
 Coyote Creek
 Daves Creek
 East Little Llagas Creek
 East Penitencia Creek
 Evergreen Creek
 Fisher Creek
 Fisher Creek Overbank
 Flint Creek
 Fowler Creek
 Guadalupe River
 Guadalupe Slough
 Hale Creek
 Lions Creek
 Llagas Creek
 Llagas Overbank
 Los Gatos Creek
 Lower Penitencia Creek
 Matadero Creek
 Miguelita Creek
 Miller Slough
 North Morey Creek
 Permanente Creek
 Permanente Diversion
 Purissima Creek
 Quimby Creek
 Ronan Channel
 Ross Creek
 Ruby Creek
 San Francisco Bay
 San Francisquito Creek
 San Joaquin River
 Santa Teresa Creek
 San Tomas Aquino Creek
 San Tomas Aquino Creek
Reach 2
 Saratoga Creek
 Silver Creek
 Smith Creek
 South Babb Creek
 South Morey Creek
 Stevens Creek
 Sunnyvale East Channel
 Sunnyvale West Channel
 Thompson Creek
 Upper Penitencia Creek
 Upper Penitencia Creek Reach 2
 Upper Penitencia Creek Reach 2
Overflow
 Uvas Creek
 West Branch Llagas Creek
 West Little Llagas Creek
 Wildcat Creek
Understanding watershed conditions can help clarify the OA’s vulnerability to flooding. A watershed is the area of land that drains to a common waterway. Every watershed has unique qualities that affect its response to rainfall. Stormwater discharge is influenced by the watershed’s soil type, geology, typography, vegetation, shape, and land use.254F
255 The Santa Clara County OA contains five watersheds25F256:
 Coyote Watershed is the OA’s largest watershed, with 322 square miles. It contains Coyote Creek, which is the longest creek in the county.
 Guadalupe Watershed drains the Guadalupe River and its tributaries through downtown San José.
 Lower Peninsula Watershed is a small-creek watershed that feeds tidal wetlands along the San Francisco Bay’s southwest shoreline.
 Uvas-Llagas Watershed is mainly agricultural land and natural areas. This is the only watershed in the county in which waterways flow southward.
254 Federal Emergency Management Association. (2014, February 19). Flood Insurance Study Santa Clara County. https://www.milpitas.gov/_pdfs/FISReport.pdf
255 USGS. (2019, June 8). Surface Runoff and the Water Cycle. https://www.usgs.gov/special-topics/water-scienceschool/science/surface-runoff-and-water-cycle 256 Santa Clara Valley Water District. (n.d.). Watersheds of Santa Clara Valley. https://www.valleywater.org/learningcenter/watersheds-santa-clara-valley

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 West Valley Watershed is the smallest watershed in the county, covering 85 square miles of numerous small creeks.

Figure 63: Watersheds in the Operational Area256F
257

13.2.3 Past Events
Based on NOAA’s National Centers for Environmental Information, 141 flood events in the OA were recorded between 1950 and 2022, as summarized in Table 85: History of Flood Events, . These events include flash floods, lakeshore floods, coastal floods, and flooding from heavy multi-day rain events.

Since 1954, 10 presidential-declared flood events in the OA have caused in excess of $4.468 billion in property damage throughout the region.

According to the USDA’s Risk Management Agency, Santa Clara County received $13,131,222 in payments for insured crop losses on 5,031 affected acres as a result of excessive moisture and flood events between 2003 and 2022. Table 86: Crop Insurance Claims Paid from Excessive Moisture and Flood, 2003-2022 summarizes these payments. The highest damaging year was 2016. Additionally, 39 flood-related federally declared disasters or emergencies have occurred in California since 1953. This equates to a major flood event impacting the state around once every 2 years. 257 Santa Clara Valley Water District. (2023). Watersheds of Santa Clara Valley. https://www.valleywater.org/learningcenter/watersheds-santa-clara-valley

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Table 85: History of Flood Events257 F
258,
258F
259
Date Declaration # Type of Event Estimated Damage
2/5/1954 15 Flood & Erosion Not available
12/23/1955 47 Flood Coyote Creek, Stevens Creek, Matadero Creek, San Francisquito Creek, and
Guadalupe River flooded
4/4/1958 82 Heavy Rainstorms and
Flood
Penitencia Creek, Guadalupe River, San
Tomas Aquinas Creek, Stevens Creek,
Permanente Creek, Matadero Creek, and
San Francisquito Creek flooded. $20 million,
plus $4 million agricultural damage
3/6/1962 122 Floods Not available
10/24/1962 138 Severe Storms and
Flooding
$4 million in regional flooding
2/25/1963 145 Severe Storms, Heavy
Rains and Flooding
Not available
1/16/1973 None Severe Storms and
Flooding
$86,207 in damage
1/7/1982 651 Severe Storms, Flood,
Mudslides and High
Tide
$273 million, 256 homes and 41 businesses
destroyed; 6,259 homes and 1,276
businesses damaged.
2/9/1983 677 Coastal Storms,
Floods, Slides and
Tornadoes
$523 million
2/21/1986 758 Severe Storms and
Flooding
$407 million; 1,382 homes and 185
businesses destroyed; 12,447 homes and
967 businesses damaged.
2/11/1992–
2/14/1992
None Severe Storms and
Flooding
$20,000 in damage
1/13/1993 None Severe Storms and
Flooding
$112,000 in damage
1/10/1995 1044 Severe Winter Storms,
Flooding, Landslides,
Mud Flows
$741 million total; 11 deaths
3/12/1995 1046 Severe Winter Storms,
Flooding Landslides,
Mud Flow
Approx. $1.1 billion total; damage to homes:
major 1,322; minor 2,299; destroyed 267.
12/10/1996 None Flood Not available
1/01/1997 None Flash Floods Not available
258 National Oceanic and Atmospheric Administration. (2017). Storm Events Database. https://www.ncdc.noaa.gov/stormevents/
259 Association of Bay Area Governments. (2010). Data and Research. https://abag.ca.gov/our-work/resilience/dataresearch

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Date Declaration # Type of Event Estimated Damage
1/4/1997 1155 Severe Storms,
Flooding, Mud and
Landslides
$1.8 billion total; 23,000 homes; 2,000
businesses damaged or destroyed.
1/25/1997 None Flash Flood Not available
2/3/1998 None Flash Flood Not available
2/7/1998 None Flash Flood Not available
2/8/1998 None Flash Flood Not available
2/9/1998 1203 Severe Winter Storms
and Flooding
$550 million; 17 deaths
2/13/2000 None Flash Flood Mainly on Coyote Creek
10/13/2009 None Heavy Rain and
Flooding
$400,000
1/18/2010–
1/20/2010
None Heavy Rain and
Flooding
Localized flooding, roads closed, damage
estimate not available.
12/23/2012 None Heavy Rain and
Tornado
Localized flooding, levee overtopped in East
Palo Alto.
2/28/2014 None Heavy Rain and
Flooding
Flooding of urban areas, small streams and
creeks, and a few localized mud and
rockslides.
12/2/2014 None Flood Not available
12/3/2014 None Flood Not available
12/11/2014 None Heavy Rain and
Flooding
Flooding and mudslides
2/06/2015 None Heavy Rain and
Flooding
Multiple off ramps from I-280 flooded.
10/28/2016 None Flood Not available
12/10/2016 None Flood Not available
2/7/2017 None Flash Flood Not available
2/9/2017 None Flood Not available
2/14/2017 4301 Severe Winter Storms,
Flooding, and
Mudslides
34 of 57 CA Counties declared for flooding
events that occurred from January 3 to
January 12, 2017
2/20/2017 None Flood, Flash Flood Not available
2/21/2017 None Flood Not available
1/8/2018 None Flood Not available
1/9/2018 None Flood Not available
1/25/2018 None Flood Not available
3/1/2018 None Flood Not available
4/6/2018 None Flood Not available
11/22/2018 None Flood Not available
11/23/2018 None Flood Not available
11/29/2018 None Flood Not available

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Date Declaration # Type of Event Estimated Damage
12/17/2018 None Flood Not available
1/6/2019 None Flood Not available
1/16/2019 None Flood Not available
1/17/2019 None Flood Not available
2/4/2019 None Flood Not available
2/13/2019 None Flood Not available
2/14/2019 None Flood Not available
2/27/2019 None Flood Not available
5/15/2019 None Flood Not available
11/26/2019 None Flood Not available
12/1/2019 None Flood Not available
12/2/2019 None Flood Not available
1/16/2020 None Flood Not available
1/27/2021 None Flood Not available
3/10/2021 None Flood Not available
12/27/2022–
1/31/2023
4683 Severe Winter Storms,
Flooding, Landslides,
and Mudslides
Damage estimates are ongoing at the time of
this writing. Damage was sufficient for a
Presidential Disaster Declaration.

Note: N/A = Not Applicable.

Table 86: Crop Insurance Claims Paid from Excessive Moisture and Flood, 2003-2022259F 260
Crop Year Commodity Acres
Affected Indemnity Amount
2003 None None None
2004 None None None
2005 All Other Crops 79 $13,144
2006 All Other Crops 83 $6,937
2007 None None None
2008 None None None
2009 None None None
2010 None None None
2011 Walnuts, Cherries, Processing Apricots 910 2,706,413 2012 Cherries 239 $113,052
2013 None None None
2014 Cherries 18 $29,015
260 United States Department of Agriculture. (n.d.). Cause of Loss Historical Data Files. https://www.rma.usda.gov/Information-Tools/Summary-of-Business/Cause-of-Loss

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Crop Year Commodity Acres
Affected Indemnity Amount
2015 Cherries, Processing Apricots, All Other Crops 322 $1,053,095 2016 Cherries, Processing Apricots 1,059 $4,279,020
2017 Cherries, Processing Apricots 119 $69,405
2018 None None None
2019 Cherries, Cultivated Wild Rice, All Other Crops 1,725 $3,975,874 2020 Cherries, Processing Apricots, All Other Crops 245 $337,118 2021 Cherries, Grapes 80 $122,467
2022 Cherries 152 $425,682
Total 5,031 $13,131,222

13.2.4 Location
Flooding that has occurred in portions of the OA has been extensively documented by gage records, high water marks, damage surveys, and personal accounts. This documentation was the basis for the 2014 FIRMs generated by FEMA for the Santa Clara County OA. The 2014 current effective Flood Insurance Study is the sole source of data used in this risk assessment to map the extent and location of the flood hazard, as shown in Figure 63: Mapped Flood Hazard Areas in the Operational Area.

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Figure 64: Mapped Flood Hazard Areas in the Operational Area

13.2.5 Frequency
Recurrence intervals and average annual numbers of events in the Santa Clara County OA were calculated based on data from 1996 to 2022 in NOAA’s Storm Events Database. Santa Clara County has experienced one hundred fourteen significant events since 1996 classified as “flood” in the database.

Smaller floods may occur more frequently and be categorized as a different event type, typically “flash flood” or “winter storm.” Based on these data, floods have a 158 percent chance of occurring in any given year, flash floods have a 33 percent chance, and coastal floods have a 4 percent chance. The total estimated percent chance of occurrence for any type of flood in a given year is 100 percent, meaning that flooding will likely continue to be an annual hazard.

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The frequency and magnitude of floods will likely be influenced by climate change. Climate change may cause an increase in the number of intense rainfall events, resulting in increased flood risk. Sea level rise, which may exacerbate the risk of flooding in shore areas, is also of concern.

Further information on the impact of climate change on the probability of flooding is included in Section 11.

Probability in OA: Occasional

13.2.6 Severity
The principal factors affecting flood damage are flood depth and velocity. The deeper and faster flood flows become, the more damage they can cause. Shallow flooding with high velocities can cause as much damage as deep flooding with slow velocity. This is especially true when a channel migrates over a broad floodplain, redirecting high velocity flows and transporting debris and sediment. Another element that characterizes the community’s flood threat is length of time floodwaters remain above flood stage.

Although jurisdictions can implement mitigation and take preventative actions to significantly reduce severity and threat of flood events, some type of residual risk will always exist (i.e., risk of a hazard event occurring despite technical and scientific measures applied to reduce/prevent it). Threats associated with residual risk could include failure of a reservoir, a dam breach, or other infrastructure failure, or a severe flood event that exceeds flood design standards or drainage capacity.

Flood severity is often evaluated by examining peak discharges. Table 87 lists peak flows used by FEMA to map the floodplains of the OA as found in the effective Santa Clara County Flood Insurance Study.

Table 87: Summary of Peak Discharges Within the Operational Area260F 261
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
Adobe Creek
 Above Railroad (At El Camino Real) 1,350 2,500 2,700a 2,700a  At East Charleston Road 1,400a 1,400a 1,400a 1,400a
 At East Meadow Drive 1,350 1,350 1,350 1,350
 At Edith Road 1,000 1,830 2,140 2,700
 At El Monte Avenue 690 1,340 1,700 2,370
 At corporate limits 890 1,650 1,920 2,400
 At Foothill Expressway 1,070 2,120 2,320 2,690
 At Middlefield Road 1,020a 1,020a 1,020a 1,020a
 At Moody Road 590 1,150 1,430 1,930
 At Old Altos Road 960 1,760 2,050 2,490
 At Pine Lane 1,110 2,150 2,360 2,730
261 Federal Emergency Management Agency. (2014, February 19). Flood Insurance Study. https://map1.msc.fema.gov/data/06/S/PDF/06085CV002B.pdf?LOC=65c0f78954006b048e415150264ffe4b

6.5 p. 425 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 276
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 At Railroad 1,350 1,450a 1,450a 1,450a
 At U.S. Highway 101 1,660 1,780 1,780 1,780
 At Van Buren Road 1,060 1,890 2,220 2,810
 Below Alma Street 1,450 1,700 1,700 1,750
 Below Purissima Creek 1,040 1,980 2,200 2,510
Alamitos Creek
 Downstream of confluence with
Arroyo Calero
2,150 5,180 6,750 11,000
 Downstream of confluence with Golf
Creek
3,530 7,020 8,680 12,700
 Downstream of confluence with
Greystone Creek
2,940 6,200 7,800 11,800
 Downstream of confluence with
Randol Creek
2,660 5,800 7,380 11,400
 Upstream of confluence with Arroyo
Calero
1,430 3,580 4,750 7,900
 Upstream of confluence with
Guadalupe River
3,630 7,180 8,860 12,900
Alamitos Creek By-Pass Channel b B 3,250 b
Alamitos Creek Overflow Area b B 140 b
Arastradero Creek
At Page Mill Road 140 300 360 460
Arroyo Calero
 Downstream of confluence with Santa
Teresa Creek
1,020 1,820 2,180 3,010
 Upstream of confluence with Alamitos
Creek
1,180 1,980 2,330 3,110
 Upstream of confluence with Santa
Teresa Creek
660 1,120 1,320 1,770
Arroyo De Los Coches
 At confluence with Berryessa Creek b B 1,420 b
Barron Creek
 At El Camino Real 270 270 270 270
 At Foothill Expressway 176 364 453 640
 At Foothill Expressway 320 630 760 1,100
 At Laguna Avenue 180b 180b 180b 180b
 At Lower Fremont Road 96 208 268 390
 At mouth 320 430 430 430
 At Ramona Street 320 430a 430a 430a

6.5 p. 426 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 277
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 At Railroad 320 675 675 675
 At Upper Fremont Road 32 77 98 143
 Downstream of El Camino Real 270 270 270 270
 Upstream of Barron Creek Diversion b B 740 b
 Upstream of Fabian Way b B 250 b
 Upstream of Laguna Avenue b B 1,603 b
 Upstream of Railroad 320 820 920 1,080
Berryessa Creek
 At confluence with Calera Creek b B 3,600a b
 At confluence with Sierra Creek 1,230 2,250 2,580 1,230  At confluence with Tularcitos Creek b B 2,500a b
 At confluence with Wrigley Ditch b B 2,000a b
 At Morrill Avenue 1,230 1,7001 1,750a 1,230
 At Piedmont Road b B 1,600 b
 Downstream of confluence with
Arroyo De Los Coches
b B 2,000a b
 Downstream of Montague
Expressway
800a 800a 800a 800a
Calabazas Creek
 Above Prospect Road b B 1,800 b
 Above Railroad and Prospect Creek b B 1,140 b
 At Coffin Road 3,000 4,100 4,600 5,800
 At El Camino Real 2,090d 2,290d 2,340d 2,360d
 At Grant Road 1,200 1,600 1,800 2,300
 At Interstate Highway 280 1,950 2,490 2,700 3,360
 At Junipero Serra 2,000 2,700 3,100 3,900
 At Kifer Road 2,600 3,600 4,000 5,200
 At Lawrence Expressway 2,100 3,000 3,300 4,200
 At Rainbow Drive Below La Mar
Court
750 1,070 1,310 1,370
 Below Miller Avenue 1,670 2,050 2,210 2,670
 Below Tantau Avenue/Upstream of
Pruneridge Avenue
1,700a 1,900a 1,950a 2,000a
 Downstream of confluence with
Rodeo Creek
1,170 1,700 1,950 2,610
 Downstream of Prospect Road 7501 1,000e 1,180e 1,220e  Downstream of U.S. Highway 101 2,760d 3,200f 4,780f 5,510f  Through box culvert at Miller Avenue 1,400a 1,550a 1,600a 1,600a

6.5 p. 427 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 278
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Upstream of Benton Street 2,100d 2,170a 2,170a 2,200a  Upstream of Kifer Road 2,550d 2,820d 3,000d 3,340d
 Upstream of Lawrence Expressway 2,050d 2,310d 2,370d 2,540d  Upstream of Pomeroy Avenue 2,190d 2,200d 2,200d 2,200d  Upstream of U.S. Highway 101 2,760d 3,020d 3,200d 3,550d  Upstream of State Highway 237 3,010d 3,420d 5,000d 5,100d Calera Creek
 At confluence with Berryessa Creek b B 920 b
 Upstream of Interstate Highway 680 b B 850 b
Canoas Creek
 At Blossom Hill Road 1,320 1,390 1,400 1,420
 At Capitol Expressway 1,850 1,910 1,960 2,000
 At confluence with Guadalupe River 1,900a 1,950a 1,970a 2,000a  At Cottle Road 480 500 510 530
 At Santa Teresa Boulevard 780 810 830 850
 Upstream of Nightingale Drive 1,990 2,250 2,350 2,500 Concepcion Drainage
 At Alto Verde Lane 22 51 68 102
Coyote Creek
 At Interstate Highway 280 3,880 10,180 12,630 14,700
 At U.S. Geological Survey gage near
Edenvale
4,050 10,940 13,670 14,700a
 At U.S. geological Survey gage near
Madrone
4,500 12,000 15,000 24,000
 Downstream of Anderson Reservoir 4,500 11,000 15,000 23,500  Downstream of confluence with
Berryessa Creek
7,300 10,500 12,800 15,000
 Downstream of confluence with Silver
Creek
6,200 10,300 12,500 15,000
 Downstream of Silver Creek
Diversion
4,000 10,680 13,330 14,700
 Upstream of confluence with Fisher
Creek
4,410 12,010 14,830 16,400a
 Upstream of confluence with Silver
Creek
3,790 9,920 11,400a 11,400a
 Upstream of Silver Creek Diversion 4,000 10,680 13,330 14,700

6.5 p. 428 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 279
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
Daves Creek
 At Los Gatos Creek 130 230 270 370
East Little Llagas Creek
 Approx. 1,500 ft. upstream of
Sycamore Avenue
b B 2,211 b
 At confluence of Church Creek b B 5,355 b
 At confluence of San Martin Creek b B 3,712 b
 At U.S. Highway 101 700 1,200 1,300 1,700
 At Tenant Creek confluence b B 2,881 b
 Upstream of Seymour Avenue 330 430 460 490
East Penitencia Creek
 Downtown of Trimble Road 280 340a 340a 340a
 Upstream of confluence with Lower
Penitencia Creek
480 970h 1,080h 1,280h
 Upstream of Trimble Road 280 400 450 540
Fisher Creek
 At confluence with Coyote Creek 700a 700a 700a 700a
 At Kalana Avenue 470 960 1,130 1,500
 At Miramonte Avenue 300 600 710 930
 At Richmond Avenue 450 700 700 700
 At Willow Springs Road 270 460 560 810
 Downstream of Bailey Avenue 1,000 1,810 2,160 2,950
 Upstream of Bailey Avenue 620 900 900 900
 Upstream of Railroad 1,260 2,310 2,560 3,530
Fisher Creek Overbank
 500 feet downstream of Richmond
Avenue
250 630 900 1,540
 At Bailey Avenue 220b 680 970 1,670
Guadalupe River
 At Blossom Hill Road 3,500 8,500 11,500 19,000
 At Coleman Avenue 7,000 13,500a 15,500a 15,500a
 At Hedding Street 7,500 9,800a 9,800a 9,800a
 At Hobson Avenue 7,000 11,400a 11,400a 11,400a
 At Interstate Highway 280 6,000 7,000a 7,000a 7,000a
 At Malone Road 5,600 11,500 11,900a 11,900a
 At Railroad 5,800 10,900a 10,900a 10,900a

6.5 p. 429 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 280
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Downstream of confluence with
Canoas Creek
5,500 11,000 12,800 12,800
 Downstream of confluence with Los
Gatos Creek
7,000a 10,000a 10,000a 10,000a
 Downstream of confluence with Ross
Creek
4,500 9,000 12,500 20,000
 Downstream of State Highway 17 7,500 12,000a 13,000a 17,000a  Upstream of confluence with Canoas
Creek
4,500 9,500 12,000a 12,000a
Hale Creek
 At Berry Avenue 510 1,020 1,120 1,580
 At confluence with Permanente Creek 710 880 900 960
 At Cuesta Drive/North Springer Road 595 750 760 810
 At Foothill Expressway 460 970 1,060 1,490
 At Interstate Highway 280 101 218 284 440
 At Rosita Avenue 595 700a 700a 700a
 At Summer Hill Avenue 177 370 472 735
Lions Creek
 Upstream of West Branch Llagas
Creek
b b 1,840 b
Llagas Creek
 At Rucker Avenue 4,900i 9,700i 10,200i 12,700i
 At Railroad 2,200 3,900 5,300 8,500
 Downstream of Buena Vista Creek 5,200 10,400 11,000 11,500a  Downstream of Chesbro Reservoir 900 3,100 3,900 6,000  Downstream of East Little Llagas
Creek
5,000 9,800 10,400 12,900
 Downstream of Hayes Creek 1,800 3,800 4,800 7,500
 Downstream of Leavesley Road 5,200d 5,200d 5,200d 5,200d  Downstream of Live Oak Creek 5,500 9,700 9,800 10,300  Downstream of Machado Creek 1,400 3,600 4,500 7,000
 Downstream of Panther Creek 5,300 9,700a 9,800a 10,100a  Downstream of Princevalle Drain b b 18,800 b
 Downstream of West Branch Llagas
Creek
b b 17,800 b
 Upstream of East Little Llagas Creek 2,500 4,300 5,400 8,600  Upstream of Jones Creek b b 18,800 b
 Upstream of Panther Creek 5,200 9,400a 9,400a 9,400a

6.5 p. 430 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 281
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
Los Gatos Creek
 At Leigh Avenue 1,680 6,510 7,440 11,340
 At Meridian Avenue 1,770 6,620 7,570 11,500
 At Park Road 1,580 6,140 6,990 10,630
 At State Highway 17 1,540k 6,370 7,300 11,200
 Below Lexington Dam 1,610 5,850 6,650 9,630
 Below Vasona Dam 1,550 6,100 6,950 10,600
 Upstream of confluence with
Guadalupe River
2,130 7,000 7,980 11,900
Lower Penitencia Creek
 At Capitol Avenue 740 1,200 1,210 1,220
 At confluence with Berryessa Creek 2,550 3,700 3,700 3,700  At Nimitz Freeway 1,750a 3,500a 3,500a 3,500a
 At Redwood Avenue 850 1,150j 1,150j 1,150j
 At South Main Street 7003 1,120j 1,120j 1,120j
 Downstream of confluence with
Berryessa Creek
2,550 2,600a 2,600a 2,600a
 Downstream of confluence with East
Penitencia Creek
800 1,670 2,150 2,840
 Downstream of Trimble Road 320 1,060h 1,510h 1,620h
Madrone Channel
 At East Dunne Avenue b b 600 b
 Upstream of East Little Llagas Creek b b 1,200 b
Matadero Creek
 Above confluence with Arastradero
Creek
194 392 506 690
 Approximately 270 feet upstream of
U.S. Highway 101
b b 2,800 b
 At Alma Street 1,380 2,000a 2,000a 2,000a
 At corporate limits 402 795 970 1,300
 At El Camino Real 1,100 2,100 2,280 2,690
 At Louis Road 1,380 1,500b 1,500b 1,500b
 At Middlefield Road 1,380 1,900b 1,500b 1,900b
 At Railroad b b 2,435 b
 At U.S. Highway 101 1,660 1,775 1,775 1,775
 Below confluence with Arastradero
Creek
325 660 790 1,030
 Downstream of Foothill Expressway b b 1,900 b

6.5 p. 431 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 282
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Downstream of Park Boulevard b b 2,700 b
 Downstream of U.S. Highway 101 b b 3,100 b
 Upstream of Railroad 1,220 2,170 2,520 2,810
Mayfield Slough
At Embarcadero Road 10.00 b 10.5 10.8
Miller Slough
 At U.S. Highway 101 b b 760 b
Middle Road Overflow Area
 At convergence with Llagas Creek b b 39 b
 At divergence from West Little Llagas
Creek
b b 658 b
North Morey Creek
 Upstream of Lions Creek b b 485 b
Pajaro River
 At U.S. Highway 101 b b 30,500 b
Permanente Creek
 At confluence with Hale Creek 780l 1,650l 1,780l 1,980l  At El Camino Real 1,150 1,310 1,310 1,310
 At Railroad 1,270 1,470 1,600 1,600
 Downstream of confluence with Hale
Creek
1,000a 1,000a 1,000a 1,000a
 Downstream of East Charleston Road 1,390n 1,400a 1,400a 1,400a  Downstream of Miramonte Avenue 370 760 890 1,030
 Downstream of Permanente Road 760 1,260 1,480 1,960
 Downstream of Portland Avenue 1,340 2,050 2,050 2,050  Downstream of U.S. Highway 101 1,350 1,400a 1,400a 1,400a  Upstream of confluence with Hale
Creek
440l 840l 980l 1,110l
 Upstream of Interstate Highway 280 1,250 2,160 2,570 3,480  Upstream of Portland Avenue 1,340 2,220 2,700 3,440
 Upstream of Tributary, 700 feet
upstream of Highway 280
860 1,460 1,720 2,310
 Upstream of U.S. Highway 101 1,350 2,250f 4,000f 7,100f Permanente Diversion
 At confluence with Stevens Creek 1,230 1,280 1,390 1,550  At Grant Road 1,200 1,240a 1,340a 1,490a
 Downstream of Carmel Terrace 1,075a 1,075a 1,075a 1,075a

6.5 p. 432 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 283
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Downstream of Diversion Structure 1,190 1,610 1,610 1,610 Prospect Creek
 Upstream of confluence with
Calabazas Creek
b b 635 b
Purissima Creek
 At corporate limits 147 320 402 588
 At Interstate Highway 280 37 82 104 153
 At Viscaino Road 88 182 227 320
San Francisco Bay
At confluence of Guadalupe Slough
and Coyote Creek
b b 10.8 b
At crossing of Railroad and Alviso
Slough
b b 11.3 B
At Milpitas b b 11.4 B
At Mountain View 10.2 b 10.7 11.0
At Palo Alto 9.9 b 10.5 10.8
At Sunnyvale 3.7 b 10.7 B
San Francisquito Creek
 At Alma Street 4,350 7,050 8,280 9,850a
 At U.S. Geological Survey gage 4,050 6,700 7,860 10,500  Downstream of Chaucer Road 4,350 6,000a 6,000a 6,200a  Downstream of Middlefield Road 4,350 6,350a 6,690a 7,410a  Near Pasteur Drive 4,200 6,850 8,070 10,400
 Upstream of Middlefield Road 4,350 7,100 8,330 9,850a San Francisquito Creek – Overflow
 At Chaucer Street b b 563 B
 At Middlefield Road b b 752 B
 Combined Middlefield/Chaucer
Overflows
b b 1,080 B
San Thomas Aquino Creek
 At Cabrillo Avenue 2,560f 2,920f 2,920f 2,920f
 At confluence with Saratoga Creek 5,900 8,300 9,100 11,000  At El Camino Real 3,570 3,610 3,610 3,610
 At Homestead Road 3,450f 3,450f 3,450f 3,450f
 At Pruneridge Avenue 3,460 3,820f 3,820f 3,820f
 At Saratoga and Los Gatos Roads 620 990 1,140 1,480
 At Stevens Creek Boulevard 3,300 3,820f 3,820f 3,820f

6.5 p. 433 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 284
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 At U.S. Highway 101 5,900 8,300 9,100 11,000
 At U.S. Highway 237 5,900 8,300 9,100 11,000
 Downstream of Railroad 5,900 8,300 9,100 11,000
 Upstream of Westmont Avenue 2,000 2,900 3,200 4,077o
 Near Bicknell and Quito Roads 670 1,050 1,230 1,580
 Near Old Adobe and Quito Roads 730 1,150 1,350 1,720
Saratoga Creek
 At confluence with San Tomas
Aquino Creek
2,700 3,750 4,100 4,800
 At El Camino Road 2,700 3,750 4,100 4,800
 At Herriman Avenue 1,550 3,020 3,750 4,630
 At Homestead Road 2,700 3,750 4,100 4,800
 At Kiely Boulevard 2,700 3,750 4,100 4,800
 At Stevens Creek Boulevard 2,500 3,500 3,900 4,600
 At U.S. Geological Survey gage at
Springer
1,350 2,750 3,490 4,450
 At Railroad 1,760 3,230 3,950 4,800
 Downstream of Benton Street 2,700 3,750 4,100 4,800
 Downstream of Kiely Boulevard 2,700 3,750 4,100 4,800  Downstream of Warburton Avenue 2,700 3,750 4,100 4,800 Silver Creek
 At confluence with Coyote Creek 2,550 2,650 2,670 2,750  At intersection of King and McKee
Roads
2,000a 2,000a 2,000a 2,000a
 At Interstate Highway 680 2,210 2,400 2,400 2,400
 At Ocala Avenue 1,530 2,000p 2,000p 2,000p
 Downstream of confluence with
Thompson Creek
2,080 3,200 3,600 4,300
 Downstream of Cunningham Avenue 1,420p 2,150p 2,580p 2,600p  Downstream of confluence with
Miguelita Creek
2,300 2,300 2,300 2,300
 Downstream of confluence with North
Babb Creek
1,500a 1,500a 1,500a 1,500a
 Downstream of confluence with South
Babb Creek
1,940 2,600 2,700 2,700
Smith Creek
 At Railroad 200 370 440 610
 At Wedgewood Avenue 160 300 350 480

6.5 p. 434 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 285
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Below Smith Creek Drive 125 230 280 390
South Babb Creek
 At Clayton Road 390 760 890 1,150
 At confluence with Silver Creek 200a 200a 200a 200a
 Downstream of White Road 390a 390a 390a 390a
 Upstream of Clayton Road B b 890 B
 Upstream of Lochner Drive 400 550a 550a 550a
 Upstream of White Road 400 570a 570a 570a
South Morey Creek
 Upstream of Lions Creek B b 420 B
Stevens Creek
 At Crittenden Lane 2,350g 2,350g 2,350g 2,350g
 At Homestead Road 1,110m 4,530 5,570 7,470
 At Interstate Highway 280 1,110m 4,460 5,460 7,310
 At Stevens Creek Boulevard 1,110m 4,430m 5,430 7,240
 At U.S. Geological Survey gaging
station No. 262
1,200 2,800 5,400 7,000
 At U.S. Highway 101 3,030 5,550 5,750 5,950
 Downstream of Interstate Highway
280
1,110 4,460 5,460 7,310
 Downstream of Junipero Serra 1,550 3,200 5,580 7,650
 Downstream of Stevens Creek Dam 1,140 4,440 5,280 6,940  Downstream of Railroad 2,750 5,350g 5,350g 5,350g
 Upstream of Junipero Serra 1,500 3,150 5,500 7,500
 Upstream of Permanente Diversion 1,750 3,600 6,000 8,200  Upstream of Railroad 2,750 6,110 7,360 9,610
Sunnyvale East Channel
 Downstream of Caribbean Drive B b 1,100 B
Sunnyvale West Channel
 Downstream of Highway 237 B b 360 B
Tennant Creek
 Approximately 1,250 feet upstream of
Hill Avenue
B b 420 B
 Downstream of Maple Avenue B b 650 B
 Upstream of confluence with East
Little Llagas Creek
B b 2,015 B

6.5 p. 435 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 286
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
Thompson Creek
 2,000 feet downstream of Aborn
Road
1,440 2,550 3,000 3,700
 At Aborn Road 1,440 2,350 2,700 3,250
 At Quimby Road 1,480 1,900a 1,900a 1,900a
 Downstream of Yerba Buena Creek 1,060 1,750 1,950 2,400 Upper Penitencia Creek
 At Capitol Avenue 1,350a 1,350a 1,350a 1,350a
 At confluence with Coyote Creek 1,110 1,110 1,110 1,110  At Gridley Street 1,460 3,050 3,600 4,950
 Upstream of North Jackson Avenue 1,350a 1,350a 1,350a 1,350a  At King Road 960a 960a 960a 960b
 At Mabury Avenue 1,050a 1,050a 1,050a 1,050a
 At Upper Penitencia Road 1,460 2,810a 2,950a 2,950a
 At U.S. Geological survey gage at
Dorel Road
1,400 2,940 3,600 5,170
Uvas Creek
 At confluence with Bodfish Creek B b 10,910 B
 At confluence with Little Arthur Creek B b 8,500 B
 At downstream face of Watsonville
Road Bridge
B b 10,360 B
 At Thomas Road B b 14,000 B
 At Railroad B b 5,2003 B
 At U.S. Highway 101 B b 8,0003 B
 At Uvas Road B b 7,800 B
 Downstream of Hecker Pass Road B b 13,550 B
 Downstream of Santa Teresa
Boulevard
B b 14,000 B
Uvas Creek – East Overbank Above Highway 101
 Approximately 1,200 feet above U.S.

Highway 101
Q b 2,200 B
 At U.S. Highway 101 Q b 1,100 B
Uvas Creek – East Overbank Above Railroad
 At downstream limit of flooding Q b 3,200 B
 At upstream limit of flooding Q b 2,100 B
Watson Road Overflow Area
 At convergence with Llagas Creek B b 447 B

6.5 p. 436 of 750
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 287
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 At divergence from West Little Llagas
Creek
B b 97 B
West Branch Llagas Creek
 Downstream of divergence from West
Branch Llagas Creek – East Split
B b 160 B
 Upstream of divergence from West
Branch Llagas Creek – East Split
B b 1,400 B
West Branch Llagas Creek – Lower Split
 At Day Road Interceptor (NRCS
PL566)
Q b 1,200 B
West Branch Llagas Creek – Middle Split
 Downstream of Highland Avenue Q q 80 Q
West Branch Llagas Creek – Upper Split
 Upstream of Highland Avenue Q q 200 Q
West Little Llagas Creek
 1,000 feet upstream of Wright
Avenue
A a 1882 A
 At Fourth Street A a 9002 A
 At U.S. Highway 101 A a 1,080b A
 Downstream of Edmundson Avenue A a 1,269 A
 Downstream of Monterey Highway A a 8132 A
 Downstream of Railroad A a 4602 A
 Upstream of Llagas Avenue A a 1,702b A
 Upstream of Monterey Highway A a 1,936 A
 Upstream of Seymour Avenue A a 1,770b A
Wildcat Creek
 Above Portos Drive 480 810 960 1,230
 At Saratoga and Los Gatos Roads 310 500 570 740
 Below Douglas Lane 430 710 840 1,070
a Decrease in flow rate based on capacity restrictions. b Data not available/computed.
c Discharge decrease due to Barron Creek Diversion.
d Flow rate accounts for upstream channel spills.
e Slow rate reflects upstream capacity restriction.
f Flow influenced by spill from adjoining watercourse.
g Flow reduction due to bridge or channel capacity restriction. h Increase in flow rate due to spills from neighboring subbasins. i Flow rate reduction due to attenuation in the floodplain. j Reduction in flood rate due to storage behind railroad. k Flow rate reduction due to attenuation in
reservoirs.
l High flows affected by Permanente Diversion.
m Decrease in flow rate due to storage along
channel.
n High flows diverted to Stevens Creek.
o Logarithm extrapolation.
p Flow rate reduction due to storage in Lake
Cunningham.
q Flooding due to spill—drainage area not
applicable.

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13.2.7 Warning Time
Advanced warning is essential for quick and effective response to a flood threat. Because of the sequential pattern of weather conditions needed to cause serious flooding, occurrence of a flood without warning is unusual. Warning times for floods can be between 24 and 48 hours. Flash flooding can be less predictable, but populations in potential hazard areas can be warned in advance of flash flooding danger.

NWS issues watches and warnings when forecasts indicate rivers may approach bank-full levels. Flood extent or severity categories used by NWS include minor flooding, moderate flooding, and major flooding, based on property damage and public threat261F
262:
 Minor Flooding: Minimal or no property damage, but possibly some public threat or inconvenience.
 Moderate Flooding: Some inundation of structures and roads near streams. Some necessary evacuations of people and/or transfer of property to higher elevations.  Major Flooding: Extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.

When a watch is issued, the public should prepare for the possibility of a flood. When a warning is issued, the public is advised to stay tuned to a local radio station for further information and be prepared to take quick action if needed. A warning means a flood is imminent, generally within 12 hours, or is occurring.

Local media broadcast NWS warnings. Thresholds for flood warnings have been established on some of the major rivers in Santa Clara County, based on available stream gage information. Current stream flows are gathered from the following USGS stream gauges in the county26F 263:
 USGS 11153000 Pacheco Creek, Dunneville, CA
 USGS 11153650 Llagas Creek, Gilroy, CA
 USGS 11164500 San Francisquito Creek, Stanford University  USGS 11169025 Guadalupe River along Highway 101, San José, CA  USGS 11169500 Saratoga Creek, Saratoga, CA
 USGS 11169800 Coyote Creek, Gilroy, CA
 USGS 11173200 Arroyo Hondo, San José CA

13.3 Cascading Impacts
One of the most problematic cascading impacts of flooding is bank or coastal erosion, which in some cases can be more harmful than the actual flood. This is especially true in the upper courses of rivers with steep gradients, where floodwaters may pass quickly and without much damage, but scour the banks, edging properties closer to the floodplain or causing them to fall in.

Flooding is also responsible for hazards such as landslides or mud flows when high flows over-saturate soils on steep slopes, causing them to fail. In California, there are significant ties between wildfire, floods, and subsequently landslides as one hazard cascades into the next. 262 National Weather Service. (n.d.). Severe Weather 101 – Floods. https://www.nssl.noaa.gov/education/svrwx101/floods/faq/ 263 U.S. Geological Survey. (2023). Current Conditions for California: Streamflow. https://waterdata.usgs.gov/ca/nwis/current/?type=flow

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Hazardous materials spills are also a secondary hazard of flooding if storage tanks rupture and spill into streams, rivers, or storm sewers. Debris of any kind could impact water quality and change the natural flow of water. This could potentially increase the risk next time there is a storm event.

Floods could also cause dam failure, or overtopping. The risk of dam failure is described more in Section 12. This risk is of particular concern because it may create a flood substantially larger than the original flood. Depending on the topography of the area downstream of a dam failure event, the floodwaters could remain constrained in a narrow canyon area, preventing them from slowing down before the reach urbanized flatter terrain.263F
264 Furthermore, while floodwaters will travel down and absorb into the ground in flat areas, the water will also pick up sediment and debris as it travels. The sediment and debris in the water may pose additional risks.

13.4 Exposure
The Level 2 Hazus protocol was used to assess flood risk in the OA. The model used census data at the block level and FEMA floodplain data, which has a level of accuracy acceptable for planning purposes.

Where possible, the Hazus default data was enhanced using local GIS data from local, state, and federal sources.

13.4.1 Population
Population counts of those living in the floodplain within the OA were generated by estimating percent of residential buildings in each jurisdiction within the 1-percent-annual-chance flood hazard areas and multiplying this by total population within the OA. This approach yielded an estimated population in the OA of 176,882 living within the 100-year floodplain (9.14% percent of the total OA population).Table 88 lists population estimates by jurisdiction living in the 10-percent, 1-percent and 0.2-percent annual chance flood hazard areas. The City of Gilroy, City of Santa Clara, Sunnyvale, San José, Campbell, Milpitas, and Morgan hill have the highest percentage of population exposed to 1% annual flood hazard, Table 88: Population Within the 10-Percent, 1-Percent, and 0.2-Percent Annual Chance Flood Hazard Areas
Jurisdiction
10-Percent Annual
Chance Flood Hazard
Area
1-Percent Annual
Chance Flood Hazard
Area

0.2-Percent Annual
Chance Flood Hazard
Area
Population
Exposeda
% Total of
Population
Population
Exposeda
% of Total
Population
Population
Exposeda
% of Total
Population
Campbell 2446 5.63 3685 8.48 4608 10.61
Cupertino 0 0.00 1311 2.16 1740 2.87
Gilroy 5,742 9.65 10,361 17.42 13,398 22.53
Los Altos 0 0.00 0 0.00 11 0.03
Los Altos Hills 0 0.00 0 0.00 0 0.00
Los Gatos 273 0.81 1,216 3.63 1,485 4.43
264 Santa Clara Valley Water District. (2017, October). Local Hazard Mitigation Plan. https://s3.us-west1.amazonaws.com/valleywater.org.us-west-1/s3fs-public/2021- 05/R14163%20%202017%20FINAL%20LOCAL%20HAZARD%20MITIGATION%20PLAN%20v.%2004-09- 21%20(04-12-21).pdf

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Jurisdiction
10-Percent Annual
Chance Flood Hazard
Area
1-Percent Annual
Chance Flood Hazard
Area

0.2-Percent Annual
Chance Flood Hazard
Area
Population
Exposeda
% Total of
Population
Population
Exposeda
% of Total
Population
Population
Exposeda
% of Total
Population
Milpitas 2,691 3.35 5,335 6.65 9,457 11.78
Monte Sereno 0 0.00 0 0.00 0 0.00
Morgan Hill 1,758 3.90 2,979 6.61 3,412 7.58
Mountain View 1,687 2.05 4,063 4.95 6,525 7.95
Palo Alto 617 0.90 629 0.92 4,534 6.62
San José 52,257 5.15 111,750 11.02 190,009 18.74
Santa Clara (city) 10,239 8.02 16,644 13.04 35,182 27.57 Saratoga 587 1.89 1,487 4.79 1,790 5.77
Sunnyvale 2,786 1.80 13,969 9.02 21,284 13.75
Unincorporated
County 2,241 2.48 3,453 3.83 4,579 5.07
Total 83,324 4.31 176,882 9.14 298,014 15.40

13.4.2 Property
Exposed Value
Table 89, Table 90, and Table 91 summarize the estimated value of exposed buildings in the OA. This methodology estimated $8.7 billion worth of exposure to the 10-percent-annual-chance flood, representing 2.3 percent of the total replacement value of the OA, $22.4 billion worth of building-andcontents exposure to the 1-percent-annual-chance flood, representing 9.1 percent of the total replacement value of the OA, and $40 billion worth of building-and-contents exposure to the 0.2-percentannual-chance flood, representing 10.56 percent of the total.

Table 89: Value of Structures in the 10-Percent Annual Chance Flood Hazard Area Jurisdiction
Estimated Value within the Floodplain % of Total
Replacement
Structure Contents Total Value
Campbell $46,559,000 $43,284,000 $140,698,000 1.60
Cupertino $0 $0 $0 0.00
Gilroy $96,223,000 $165,308,000 $574,813,000 4.86
Los Altos $0 $0 $0 0.00
Los Altos Hills $0 $0 $0 0.00
Los Gatos $16,191,000 $22,610,000 $109,895,000 1.14
Milpitas $44,056,000 $47,811,000 $224,231,000 1.40
Monte Sereno $0 $0 $0 0.00
Morgan Hill $30,975,000 $18,233,000 $67,576,000 0.63
Mountain View $22,645,000 $33,678,000 $140,380,000 0.83

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Jurisdiction
Estimated Value within the Floodplain % of Total
Replacement
Structure Contents Total Value
Palo Alto $7,892,000 $163,325,000 $91,985,000 0.45
San José $1,187,925,000 $2,015,872,000 $6,140,963,000 3.56 Santa Clara (city) $178,713,000 $233,150,000 $766,887,000 2.77 Saratoga $21,643,000 $16,633,000 $51,942,000 0.56
Sunnyvale $41,315,000 $68,059,000 $216,544,000 0.74
Unincorporated County $67,392,000 $67,064,000 $255,548,000 1.25 Total $1,761,529,000 $2,895,027,000 $8,781,462,000 2.30 Table 90: Value of Structures in the 1-Percent Annual Chance Flood Hazard Area Jurisdiction
Estimated Value within the Floodplain % of Total
Replacement
Structure Contents Total Value
Campbell $91,932,000 $80,508,000 $257,047,000 8.48
Cupertino $24,021,000 $18,081,000 $59,916,000 2.16
Gilroy $225,196,000 $420,220,000 $1,346,610,000 17.42
Los Altos $1,351,000 $710,000 $2,234,000 0.00
Los Altos Hills $0 $0 $0 0.00
Los Gatos $30,840,000 $42,934,000 $168,827,000 3.63
Milpitas $115,342,000 $137,652,000 $548,317,000 6.65
Monte Sereno $0 $0 $0 0.00
Morgan Hill $115,482,000 $81,114,000 $259,011,000 6.61
Mountain View $75,707,000 $109,233,000 $416,222,000 4.95 Palo Alto $18,739,000 $40,559,000 $157,789,000 0.92
San José $3,271,469,000 $5,761,915,000 $15,986,581,000 11.02 Santa Clara
(city)
$360,286,000 $476,086,000 $1,462,841,000 13.04
Saratoga $100,151,000 $73,527,000 $226,648,000 4.79
Sunnyvale $208,800,000 $260,543,000 $832,836,000 9.02
Unincorporated
County
$157,862,000 $178,277,000 $682,246,000 3.83
Total $4,797,178,000 $7,681,359,000 $22,407,125,000 9.14

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Table 91: Value of Structures in the 0.2-Percent Annual Chance Flood Hazard Area Jurisdiction
Estimated Value within the Floodplain % of Total
Replacement
Structure Contents Total Value
Campbell $127,488,000 $110,733,000 $355,863,000 4.04
Cupertino $36,263,000 $29,154,000 $94,619,000 0.66
Gilroy $319,375,000 $641,660,000 $2,015,006,000 17.03
Los Altos $1,791,000 $948,000 $3,090,000 0.04
Los Altos Hills $0 $0 $0 0.00
Los Gatos $39,193,000 $56,508,000 $212,717,000 2.21
Milpitas $191,075,000 $242,248,000 $934,245,000 5.84
Monte Sereno $0 $0 $0 0.00
Morgan Hill $161,794,000 $109,502,000 $350,641,000 3.25 Mountain View $119,699,000 $166,238,000 $669,226,000 3.95 Palo Alto $76,861,000 $100,127,000 $367,056,000 1.81
San José $5,656,110,000 $10,606,664,000 $28,947,287,000 16.79 Santa Clara
(city)
$812,021,000 $1,177,901,000 $3,760,129,000 13.60
Saratoga $127,579,000 $96,493,000 $289,244,000 3.09
Sunnyvale $351,074,000 $419,774,000 $1,361,761,000 4.64 Unincorporated
County
$225,387,000 $262,239,000 $929,177,000 4.53
Total $8,245,710,000 $14,020,189,000 $40,290,061,000 10.56

13.4.3 Critical Facilities and Infrastructure
Table 92, Table 93, and Table 94 summarize the critical facilities and infrastructure in the 10-, 1-, and

0.2-percent-annual-chance flood hazard areas. Details are provided in the following sections.

Toxic Release Inventory Reporting Facilities
Toxic Release Inventory (TRI) facilities are known to manufacture, process, store, or otherwise use certain chemicals above minimum thresholds. If damaged by a flood, these facilities could release chemicals that cause cancer or other human health effects, significant adverse acute human health effects, or significant adverse environmental effects.264F 265 During a flood event, containers holding these
materials can rupture and leak into the surrounding area, disastrously affecting the environment and residents. Seventy-eight facilities within the 1-percent-annual-chance flood zone are TRI reporting facilities.
265 Environmental Protection Agency. (n.d.). Flooding. https://www.epa.gov/natural-disasters/flooding

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Table 92: Critical Facilities in the 10-Percent Annual Chance Flood Hazard Area Jurisdiction
Number of Facilities in the Floodplain
Essential
Facilities Transportation Utilities Community Assets
Hazardous
Materials Total
Campbell 0 1 0 1 0 2
Cupertino 0 0 0 0 0 0
Gilroy 1 8 0 1 0 10
Los Altos 0 0 0 0 0 0
Los Altos Hills 0 0 0 0 0 0
Los Gatos 0 6 0 0 0 6
Milpitas 2 2 0 1 1 6
Monte Sereno 0 0 0 0 0 0
Morgan Hill 0 0 0 1 0 1
Mountain View 0 0 0 1 2 3
Palo Alto 0 1 0 0 3 4
San José 17 50 1 19 37 124
Santa Clara (city) 3 2 0 2 9 16
Saratoga 0 3 0 0 0 3
Sunnyvale 1 1 0 0 2 4
Unincorporated
County 0 32 0 3 0 35
Total 24 106 1 29 54 214
Table 93: Critical Facilities in the 1-Percent Annual Chance Flood Hazard Area Jurisdiction
Number of Facilities in the Floodplain
Essential
Facilities Transportation Utilities Community Assets
Hazardous
Materials Total
Campbell 1 1 0 2 0 4
Cupertino 0 2 0 1 0 3
Gilroy 5 15 0 5 1 26
Los Altos 0 0 0 0 0 0
Los Altos Hills 0 0 0 0 0 0
Los Gatos 0 7 0 2 0 9
Milpitas 3 10 0 2 1 16
Monte Sereno 0 0 0 0 0 0
Morgan Hill 0 1 0 1 0 2
Mountain View 1 1 0 3 3 8

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Jurisdiction
Number of Facilities in the Floodplain
Essential
Facilities Transportation Utilities Community Assets
Hazardous
Materials Total
Palo Alto 0 1 0 0 4 5
San José 35 87 0 38 48 208
Santa Clara (city) 5 2 3 4 18 32
Saratoga 0 7 0 1 0 8
Sunnyvale 4 2 0 2 3 11
Unincorporated
County 4 49 0 3 0 56
Total 58 185 3 64 78 388
Table 94: Critical Facilities in the 0.2-Percent Annual Chance Flood Hazard Area Jurisdiction
Number of Facilities in the Floodplain
Essential
Facilities Transportation Utilities Community Assets
Hazardous
Materials Total
Campbell 1 1 0 2 0 4
Cupertino 0 4 0 1 0 5
Gilroy 7 16 0 6 1 30
Los Altos 0 0 0 0 0 0
Los Altos Hills 0 0 0 0 0 0
Los Gatos 0 8 0 2 0 10
Milpitas 4 11 0 3 3 21
Monte Sereno 0 0 0 0 0 0
Morgan Hill 1 1 0 1 0 3
Mountain View 2 1 0 4 3 10
Palo Alto 2 3 1 0 5 11
San José 52 125 7 60 62 306
Santa Clara (city) 8 7 2 7 51 75
Saratoga 1 11 0 1 0 13
Sunnyvale 7 2 0 3 6 18
Unincorporated
County 4 54 0 4 0 62
Total 89 244 10 94 131 568

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Utilities and Infrastructure
It is important to determine who may be at risk if infrastructure is damaged by flooding. Roads or railroads that are blocked or damaged can isolate residents and can prevent access throughout the OA, including for emergency service providers needing to get to vulnerable populations or to make repairs. Bridges washed out or blocked by floods or debris also can cause isolation. Water and sewer systems can be flooded or backed up, causing health problems. Underground utilities can be damaged. Dikes can fail or be overtopped, inundating the land that they protect. The following sections describe specific types of critical infrastructure.

Roads
The following major roads in the OA pass through the 1-percent-annual-chance flood zone and thus are exposed to flooding:
 US 101
 Interstate 280
 Interstate 680
 Interstate 880
 State Route 9
 State Route 17
 State Route 82
 State Route 85
 State Route 87
 State Route 152
 State Route 237
Some of these roads are built above the flood level, and others function as levees to prevent flooding.

Still, in severe flood events these roads can be blocked or damaged, preventing access to some areas.

Infrastructure Lifelines
Flooding events can significantly impact critical infrastructure lifelines such as highways, bridges, airports, water and wastewater facilities and communication facilities. An analysis showed that there are 629 infrastructure lifelines (241 are bridges) that are in or cross over the 1-percent-annual-chance flood zone and 928 infrastructure lifelines in the 0.2-percent-annual-chance flood zone.

Water and Sewer Infrastructure
Water and sewer systems can be affected by flooding. Floodwaters can back up drainage systems, causing localized flooding. Culverts can be blocked by debris from flood events, also causing localized urban flooding. Floodwaters can get into drinking water supplies, causing contamination. Sewer systems can be backed up, causing wastewater to spill into homes, neighborhoods, rivers, and streams.

Levees
SCVWD constructed flood protection levees in the north, central, and southern portions of the county, some of which provide 1-percent-annual-chance flood protection. The levees along Uvas Creek, King Creek, Lyons Creek, and Coyote Creek participate in Corps’ Levee Program. Levees along the Guadalupe River do not participate. SCVWD does not believe the majority of levees could withstand intensities of a 1-percent annual chance flood. Additionally, coastal flooding from San Francisco Bay circumvents levees near the Bay. Moreover, current flood levels do not account for potential sea level rise, which would exacerbate vulnerability and further reduce the ability of the levees to prevent or reduce flooding.

The presence and effects of levee systems in the Santa Clara County OA are not reflected on the FIRM, meaning that areas, structures, and populations vulnerable to failures of those levees cannot be determined. Levee failures could place large numbers of people and great amounts of property at risk.

Unlike dams, levees do not serve any purpose beyond providing flood protection and (less frequently) recreational space for residents. A levee failure could be devastating, depending on severity of flooding and amount of land development present. In addition to damaging buildings, infrastructure, trees, and other large objects, levee failure can result in significant water quality and debris disposal issues. Severe erosion is also a consideration.

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13.4.4 Environment
Loss estimation platforms such as Hazus are not currently equipped to measure environmental impacts of flood hazards. The best gauge of vulnerability of the environment would be a review of damage from past flood events. Loss data that segregates damage to the environment was not available at the time of this plan. Capturing this data from future events could be beneficial in measuring the vulnerability of the environment for future updates. Habitats that are expected to be impacted by riverine flooding are shown in Table 95.

Table 95: Habitats Expected to Be Impacted by Riverine Flooding265F 266
Habitat Type FEMA 100-Year Storm
Riverine Flooding
Bay Wetlands: Coastal Salt Marsh and Coastal Brackish Marsh 1,695 acres (84%) Freshwater Wetland 2,350 acres (64%)
Grassland 3,176 acres (2%)
Riparian and Riverine 546 acres (19%)
Freshwater Lake and Pond 1,792 acres (57%)
Chaparral and Scrubland 358 acres (0.3%)
Coastal Scrubland 9 acres (0.2%)
Coniferous Forest 20 acres (0.2%)
Hardwood Forest 314 acres (0.5%)
Oak Woodland 1,341 ac (0.7%)
Redwood Forest 40 ac (0.3%)
Note: Given that vulnerability to riverine flooding is currently determined by FEMA Flood Insurance Rate Maps (FIRMS), it is possible that the flooding near the Bay could be occurring from either storm surge or riverine flooding.

Specific strategies for each will be required once source confirmation is made. Habitats with vulnerability of less than 1% were not considered highly vulnerable.
266 County of Santa Clara Office of Sustainability and Climate Action. (2015, August). Silicon Valley 2.0 Climate Adaptation Guidebook.
https://sustainability.sccgov.org/sites/g/files/exjcpb976/files/documents/1_150803_Final%20Guidebook_W_Appendic es.pdf

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Figure 65: 100-Year Floodplain Area Land Cover26F
267

13.5 Vulnerability
Changes in Conditions: No change in vulnerability
 The areas vulnerable to 1% and 0.2% flood events have as mapped in FIRMs have not changed.  Population growth and building growth in the OA have been slow.  Flooding can occur in localized areas not identified in special flood hazard areas (SFHAs) during heavy rain. These are more difficult to anticipate in advance and areas at risk may not yet have been recognized.
 New development may alter local drainage patterns and change flood potential. 267 County of Santa Clara Office of Sustainability and Climate Action. (2015, August). Silicon Valley 2.0 Climate Adaptation Guidebook.
https://sustainability.sccgov.org/sites/g/files/exjcpb976/files/documents/1_150803_Final%20Guidebook_W_Appendic es.pdf

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 Warming temperature from climate change may alter the frequency and intensity of storms and increase the associated runoff.

13.5.1 Population
Vulnerable Populations
A geographic analysis of demographics using the Hazus model identified populations vulnerable to the flood hazard as follows:
 Economically Disadvantaged Populations: It is estimated that 2.76 percent of the people within the 100-year floodplain are economically disadvantaged, defined as having household incomes of $20,000 or less.
 Population over 64 Years Old: It is estimated that 20,723 persons or 11.7 percent of the population in the census blocks that intersect the 100-year floodplain are over 64 years old.  Population under 16 Years Old: It is estimated that 38,185 persons or 19.9 percent of the population within census blocks located in or near the 100-year floodplain are under 18 years of age.

Commuters and visitors are also vulnerable to the flood hazard, in part because they may not be as familiar with evacuation routes and areas that typically flood. Commuters whose workplaces or major transportation routes are in or near the 1-percent-annual-chance flood zone may be especially vulnerable.

The most at-risk members of society often experience the greatest losses from disasters. Socially vulnerable populations often live in high-risk floodplains due to lack of affordable housing, historical inequitable land use and housing practices, and other societal barriers. Disasters can exacerbate preexisting racial and social disparities. According to Plan Bay Area 2050, homes in Equity Priority Communities may be over 50% more likely to experience flooding from sea level rise.267F 268
Estimated Impacts on Persons and Households
Impacts on persons and households in the OA were estimated for the 10-, 1-, and 0.2-percent-annualchance flood events through the Level 2 Hazus analysis. Table 96 summarizes the results.

Table 96: Estimated Flood Impact on Persons
Jurisdiction
Number of Displaced Persons Number of Persons Requiring Short-Term Shelter
10%
Annual
Chance
Flood
1%
Annual
Chance
Flood

0.2%
Annual
Chance
Flood
10% Annual
Chance
Flood
1% Annual
Chance
Flood

0.2%
Annual
Chance
Flood
Campbell 2,297 3,796 5,047 106 204 232
Cupertino 0 1,078 1,543 0 199 284
Gilroy 5,343 9,782 13,209 304 443 581
Los Altos 0 11 21 0 1 1
Los Altos Hills 0 0 0 0 0 0
268 Plan Bay Area. (2021, October). Final Plan Bay Area 2050. https://www.planbayarea.org/finalplan2050

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Jurisdiction
Number of Displaced Persons Number of Persons Requiring Short-Term Shelter
10%
Annual
Chance
Flood
1%
Annual
Chance
Flood

0.2%
Annual
Chance
Flood
10% Annual
Chance
Flood
1% Annual
Chance
Flood

0.2%
Annual
Chance
Flood
Los Gatos 571 980 1140 48 53 85
Milpitas 4,288 8,115 13,191 304 451 592
Monte Sereno 0 0 0 0 0 0
Morgan Hill 1,424 2,700 3,304 32 32 38
Mountain View 1,505 4,056 6,842 51 244 336
Palo Alto 313 392 3,872 58 72 137
San José 54,856 115,365 192,561 3,879 7,005 11,625
Santa Clara (city) 10,888 17,583 35,621 456 678 1,161
Saratoga 454 1,738 2,022 44 67 73
Sunnyvale 3,054 12,386 21,405 85 448 730
Unincorporated
County
1,965 3,522 4,839 90 123 149
Total 86,958 181,504 304,617 5,457 10,020 16,024
Public Health and Safety
Floods and their aftermath present numerous threats to public health and safety:
 Unsafe food: Floodwaters contain disease-causing bacteria, dirt, oil, human and animal waste, and farm and industrial chemicals. Their contact with food items, including food crops in agricultural lands, can make that food unsafe to eat. Refrigerated and frozen foods are affected during power outages caused by flooding. Foods in cardboard, plastic bags, jars, bottles, and paper packaging may be unhygienic with mold contamination.  Contaminated drinking and washing water and poor sanitation: Flooding impairs clean water sources with pollutants. The pollutants also saturate into the groundwater. Flooded wastewater treatment plants can be overloaded, resulting in backflows of raw sewage. Private wells can be contaminated by floodwaters. Private sewage disposal systems can become a cause of infection if they or overflow.
 Mosquitoes and animals: Floods provide new breeding grounds for mosquitoes in wet areas and stagnant pools. The public should dispose of dead animals that can carry viruses and diseases only in accordance with guidelines issued by local animal control authorities.

Leptospirosis—a bacterial disease associated predominantly with rats—often accompanies floods in developing countries, although the risk is low in industrialized regions unless cuts or wounds have direct contact with disease-contaminated floodwaters or animals.  Mold and mildew: Excessive exposure to mold and mildew can cause flood victims—especially those with allergies and asthma—to contract upper respiratory diseases, triggering cold-like symptoms. Molds grow in as short a period as 24 to 48 hours in wet and damp areas of buildings and homes that have not been cleaned after flooding, such as water-infiltrated walls, floors, carpets, toilets, and bathrooms. Very small mold spores can be easily inhaled by human bodies and, in large enough quantities, cause allergic reactions, asthma episodes, and other respiratory problems. Infants, children, elderly people, and pregnant women are considered most vulnerable to mold-induced health problems.

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 Carbon monoxide poisoning: In the event of power outages following floods, some people use alternative fuels for heating or cooking in enclosed or partly enclosed spaces, such as small gasoline engines, stoves, generators, lanterns, gas ranges, charcoal, or wood. Built-up carbon monoxide from these sources can poison people and animals.  Hazards when reentering and cleaning flooded homes and buildings: Flooded buildings can pose significant health hazards to people entering them. Electrical power systems can become hazardous. Gas leaks can trigger fire and explosion. Flood debris—such as broken bottles, wood, stones, and walls—may cause injuries to those cleaning damaged buildings. Containers of hazardous chemicals may be buried under flood debris. Hazardous dust and mold can circulate through a building and be inhaled by those engaged in cleanup and restoration.  Mental stress and fatigue: People who live through a devastating flood can experience longterm psychological impact. The expense and effort required to repair flood-damaged homes places severe financial and psychological burdens on the people affected. Post-flood recovery can cause, anxiety, anger, depression, lethargy, hyperactivity, and sleeplessness. There is also a long-term concern among the affected that their homes can be flooded again in the future.

Current loss estimation models such as Hazus are not equipped to measure public health impacts such as these. The best preparation for these effects includes awareness that they can occur, education of the public on prevention, and planning to deal with them during responses to flood events.

13.5.2 Property
Structures and Contents
Hazus calculates losses to structures from flooding by looking at depth of flooding and type of structure.

Using historical flood insurance claim data, Hazus estimates the percentage of damage to structures and their contents by applying established damage functions to an inventory. The analysis is summarized in Table 97, Table 98, and Table 99 for the 10-, 1-, and 0.2-percent-annual-chance flood events, respectively.

Table 97: Loss Estimates for 10-Percent-Annual-Chance Flood Jurisdiction Structures
Impacteda
Estimated Loss Associated with Flood % of Total
Replacement
Structure Contents Total Value
Campbell 278 $46,559,000 $43,284,000 $140,698,000 1.60
Cupertino 0 $0 $0 $0 0
Gilroy 382 $96,223,000 $165,308,000 $574,813,000 4.86
Los Altos 0 $0 $0 $0 0
Los Altos Hills 0 $0 $0 $0 0
Los Gatos 17 $16,191,000 $22,610,000 $109,895,000 1.14
Milpitas 234 $44,056,000 $47,811,000 $224,231,000 1.40
Monte Sereno 0 $0 $0 $0 0
Morgan Hill 373 $30,975,000 $18,233,000 $67,576,000 .63 Mountain View 112 $22,645,000 $33,678,000 $140,380,000 .83 Palo Alto 40 $7,892,000 $163,325,000 $91,985,000 .45
San José 4,541 $1,187,925,000 $2,015,872,000 $6,140,963,000 3.56

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Jurisdiction Structures
Impacteda
Estimated Loss Associated with Flood % of Total
Replacement
Structure Contents Total Value
Santa Clara
(city)
918 $178,713,000 $233,150,000 $766,887,000 2.77
Saratoga 74 $21,643,000 $16,633,000 $51,942,000 .56
Sunnyvale 245 $41,315,000 $68,059,000 $216,544,000 .74
Unincorporated
County
104 $67,392,000 $67,064,000 $255,548,000 1.25
Total 7,318 $1,761,529,000 $2,895,027,000 $8,781,462,000 2.30 Note: Values shown are accurate for comparison of results in this plan. See Section 6 for discussion of data limitations.
a
Impacted structures are those with finished floor elevations below the flood event water surface elevation. These structures are the most likely to receive significant damage in a flood event.

Table 98: Loss Estimates for 1-Percent-Annual-Chance Flood Jurisdiction Structures
Impacteda
Estimated Loss Associated with Flood % of Total
Replaceme
nt
Value Structure Contents Total
Campbell 478 $91,932,000 $80,508,000 $257,047,000 2.92
Cupertino 61 $24,021,000 $18,081,000 $59,916,000 .42
Gilroy 1,116 $225,196,000 $420,220,000 $1,346,610,000 11.38 Los Altos 0 $1,351,000 $710,000 $2,234,000 .03
Los Altos Hills 0 $0 $0 $0 0.00
Los Gatos 131 $30,840,000 $42,934,000 $168,827,000 1.76 Milpitas 797 $115,342,000 $137,652,000 $548,317,000 3.43 Monte Sereno 0 $0 $0 $0 0
Morgan Hill 722 $115,482,000 $81,114,000 $259,011,000 2.4 Mountain View 414 $75,707,000 $109,233,000 $416,222,000 2.46 Palo Alto 70 $18,739,000 $40,559,000 $157,789,000 .79
San José 12,496 $3,271,469,000 $5,761,915,000 $15,986,581,000 9.27 Santa Clara
(city)
1,999 $360,286,000 $476,086,000 $1,462,841,000 5.29
Saratoga 276 $100,151,000 $73,527,000 $226,648,000 2.42 Sunnyvale 1,520 $208,800,000 $260,543,000 $832,836,000 2.84

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Jurisdiction Structures
Impacteda
Estimated Loss Associated with Flood % of Total
Replaceme
nt
Value Structure Contents Total
Unincorporated
County
346 $157,862,000 $178,277,000 $682,246,000 3.33
Total 20,366 $4,797,178,000 $7,681,359,000 $22,407,125,000 5.87 Note: Values shown are accurate for comparison of results in this plan. See Section 6 for discussion of data limitations.
a
Impacted structures are those with finished floor elevations below the flood event water surface elevation. These structures are the most likely to receive significant damage in a flood event.

Table 99: Loss Estimates for 0.2-Percent-Annual-Chance Flood Jurisdiction Structures
Impacteda
Estimated Loss Associated with Flood % of Total
Replacement
Structure Contents Total Value
Campbell 666 $127,488,000 $110,733,000 $355,863,000 4.04 Cupertino 83 $36,263,000 $29,154,000 $94,619,000 0.66
Gilroy 1,469 $319,375,000 $641,660,000 $2,015,006,000 17.03 Los Altos 0 $1,791,000 $948,000 $3,090,000 0.04
Los Altos Hills 0 $0 $0 $0 0.00
Los Gatos 147 $39,193,000 $56,508,000 $212,717,000 2.21 Milpitas 1,197 $191,075,000 $242,248,000 $934,245,000 5.84 Monte Sereno 0 $0 $0 $0 0
Morgan Hill 837 $161,794,000 $109,502,000 $350,641,000 3.25 Mountain View 732 $119,699,000 $166,238,000 $669,226,000 3.95 Palo Alto 495 $76,861,000 $100,127,000 $367,056,000 1.81 San José 22,052 $5,656,110,000 $10,606,664,000 $28,947,287,000 16.79 Santa Clara
(city) 4,635 $812,021,000 $1,177,901,000 $3,760,129,000 13.60 Saratoga 357 $127,579,000 $96,493,000 $289,244,000 3.09 Sunnyvale 2,478 $351,074,000 $419,774,000 $1,361,761,000 4.64 Unincorporated
County 541 $225,387,000 $262,239,000 $929,177,000 4.53
Total 35,689 $8,245,710,000 $14,020,189,000 $40,290,061,000 10.56 Note: Values shown are accurate for comparison of results in this plan. See Section 6 for discussion of data limitations.
a
Impacted structures are those with finished floor elevations below the flood event water surface elevation. These structures are the most likely to receive significant damage in a flood event.

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Key results are as follows:
 There would be up to $8.7 billion of flood loss from a 10-percent-annual-chance flood event in the OA. This represents 2.3 percent of the total replacement value for the OA.  There would be up to $22.4 billion of flood loss from a 1-percent-annual-chance flood event in the OA. This represents 5.87 percent of the total replacement value for the OA.  There would be $40.29 billion of flood loss from a 0.2-percent-annual-chance flood event in the OA. This represents 10.56 percent of the total replacement value.

Structures permitted or built in the OA before the initial FIRM date are called “pre-FIRM” structures, and structures built after the FIRM date are called “post-FIRM.” The insurance rate is different for the two types of structures. Generally, it can be assumed that unmitigated pre-FIRM structures are more vulnerable to flooding than post-FIRM.

Flood-Caused Debris
Left over debris from flooding can be costly to remove and have significant consequences if not dealt with properly. The Hazus analysis estimated the amount of flood-caused debris within the OA generated by flooding, as summarized in Table 100. The model breaks debris into three general categories; Finishes (dry wall, insulation, etc.), Structural (wood, brick, etc.), and Foundations (concrete slab, concrete block, rebar, etc.).

Table 100: Estimated Flood-Caused Debris
Annual Flood
Chance
Finishes (Tons) Structure (Tons) Foundation
(Tons)
Total Debris
(Tons)
10% AnnualChance Flood24,095 3,963 3,847 31,905
1% AnnualChance Flood82,351 8,119 7,945 98,415

0.2% AnnualChance Flood162,896 14,307 14,287 191,490
Flood Insurance
Flood Insurance Statistics
Table 101 lists flood insurance statistics that help identify vulnerability in the OA. All 16 municipal planning partners participate in the NFIP, with 12,159 flood insurance policies providing $3.6 billion in insurance coverage. According to FEMA statistics, 1,556 flood insurance claims were paid between November 1978 and February 23, 2023, for a total of $22,996,576, an average of $14,779 per claim.

Properties constructed after a FIRM has been adopted are eligible for reduced flood insurance rates.

Such structures are less vulnerable to flooding since they were constructed after regulations and codes were adopted to decrease vulnerability. Properties built before a FIRM is adopted are more vulnerable to flooding because they do not meet code or are located in hazardous areas. The first FIRMs in the OA were available in 1975.

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Table 101: Flood Insurance Statistics268 F
269
Jurisdiction
Date of
Entry
Initial
FIRM
Effective
Date
# of Flood
Insurance
Policies
as of
2/23/2023
Total
Coverage
Total
Annual
Premium
Claims,
11/1978
to
2/23/2023
Value of
Claims
paid,
11/1978 to
2/23/2023
Campbell 06/30/1976 28 8,541,000 16,222 1 $0
Cupertino 04/18/1975 64 20,042,400 64,687 20 $812,171
Gilroy 06/04/1976 100 46,698,600 140,441 33 $287, 117
Los Altos 09/24/1976 101 31,769,400 79,333 13 $5,896
Los Altos Hills 11/26/1976 34 11,036,000 26,775 16 $45,641 Los Gatos 02/27/1976 66 20,606,800 39,411 17 $51,957
Milpitas 03/28/1975 1,025 288,494,700 1,062,641 69 $27,829 Monte Sereno 05/18/2009 9 3,150,000 5,123 4 $41,974
Morgan Hill 06/18/1980 309 93,061,100 285,955 74 $603,444 Mountain View 09/19/1975 344 117,867,000 263,363 8 $8,501 Palo Alto 09/06/1989 2,377 655, 737, 600 2,601,795 474 $8,936,790 San José 04/09/1976 4,872 1,351,586,300 4,412,960 626 $10,284,648 Santa Clara
(city)
02/11/1977 683 222,286,800 643,583 29 $264,753
Saratoga 11/28/1975 67 22,554,900 58,630 17 $53,676
Sunnyvale 12/05/1975 527 183,134,600 543,354 10 $68,655 Unincorporated
County
06/20/1978 276 74,048,500 410,772 130 $1,654,709
Unknown - 1,440 382,986,000 1,555,609 15 135,932
Total 12,322 $2,877,864,100 $12,210,654 1,556 $22,996,576 This data likely has some limitations. The “Unknown” category was not included in the 2016 dataset used in the 2017 Hazard Mitigation Plan. It also reflects a decrease in policies since the 2017 plan in every jurisdiction except Los Altos, which gained a total of 18 policies, for a total of 5,000 less policies in force across the OA. It is unclear if this is due to the rising cost of flood insurance, voluntary suspension of flood insurance, or another reason.

NFIP Participation
As participating communities, each jurisdiction within the OA was required to adopt floodplain management criteria via local regulations that meets NFIP minimum standards. Multiple communities have adopted regulations that exceed these standards. Further detail is included in each annex in Volume II and in the following table. The special districts and fire department that participated in this plan update are not eligible to participate in the NFIP.
269 FEMA Region IX on 2/23/2023

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Table 102: Date of Floodplain Management Regulation Adoption Jurisdiction Adoption Date
City of Campbell January, 2014
City of Cupertino June, 2016
City of Gilroy January, 2017
City of Los Altos March, 2009
City of Milpitas November, 1995
City of Morgan Hill September, 2017
City of Mountain View April, 2023
City of Palo Alto 2004
City of San Jose April, 2009
City of Santa Clara June, 2023
City of Saratoga 1996
City of Sunnyvale November, 1994 – anticipated update Oct. 2023 County of Santa Clara April, 2009
Town of Los Altos Hills November, 2001
Town of Los Gatos 2003
Repetitive Loss and Severe Repetitive Loss
A repetitive loss property is defined by FEMA as an NFIP-insured property that has experienced any of the following since 1978, regardless of any changes in ownership:
 Four or more paid losses in excess of $1,000.
 Two paid losses in excess of $1,000 within any rolling 10-year period.  Three or more paid losses that equal or exceed the current value of the insured property.

A severe repetitive loss property is further defined as follows:
 Four or more paid losses in excess of $5,000 each, with the cumulative amount of such claim payments exceeding $20,000.
 At least two separate claim payments made, with the cumulative amount of the building portion of such claims exceeding the market value of the building.  At least two of the above referenced claims occurred within any rolling 10-year period and must be more than 10 days apart.

Repetitive loss properties make up only 1 percent of flood insurance policies in force nationally, yet they account for 25 to 30 percent of the nation’s flood insurance claim payments. According the draft 2023 State of California Hazard Mitigation Plan, 34.8 percent of the repetitive properties in the state are located outside of the SFHA. The government has instituted programs encouraging communities to identify and mitigate the causes of repetitive losses. The key identifiers for repetitive loss properties are the existence of flood insurance policies and claims paid by the policies. This doesn’t include properties which have flooded repeatedly but don’t have insurance. Over 50 percent of severe repetitive loss structures nationally are estimated to be without NFIP coverage.

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FEMA-sponsored programs, such as the CRS, require participating communities to identify repetitive loss areas. A repetitive loss area is the portion of a floodplain holding structures that FEMA has identified as meeting the definition of repetitive loss. Identifying repetitive loss areas helps to identify structures that are at risk but are not on FEMA’s list of repetitive loss structures because no flood insurance policy was in force at the time of loss.

FEMA’s list of repetitive loss properties identifies four such properties in the OA as of February 23, 2023.

The breakdown of the properties by jurisdiction is presented in Table 103. With the potential for flood events annually, all of the mapped floodplain is considered to be susceptible to repetitive flooding.

Table 103: Repetitive Loss Properties
Jurisdiction
Number of
Repetitive
Loss
Properties
Type of Repetitive
Loss Properties
Number of
Severe
Repetitive
Loss
Properties
Type of Severe
Repetitive Loss
Properties
Cupertino 3
Single Family (1)
Other Nonresidential (2) - -
Los Gatos 1 2–4 Family (1) - -
Morgan Hill 2 Single Family (2) 4
Single Family (2)
Business (1)
Other Nonresidential (1)
Palo Alto 4
Single Family (3)
Other Nonresidential (1) 1 Business (1)
San José 6 Single Family (6) 1 Single Family (1)
Sunnyvale 1 Other Nonresidential (1) - -
Unincorporated
County 8 Single Family (8) 3 Single Family (3)
Unknown 1 2-4 Family (1) - -
Total 25
Single Family (20)
Other Nonresidential (4)
2-4 Family (2)
9 Single Family (6)
Business (2)
Other Nonresidential (1)
Note: Based on FEMA Region IX Report of Repetitive Losses, 2/23/2023.

Substantial Improvement/Substantial Damage
In order to be a part of the NFIP, participating jurisdictions commit to implementing substantial improvement / substantial damage provisions of their floodplain management regulations after an event.

According to FEMA, these terms are defined as:
 Substantial Improvement means any reconstruction, rehabilitation, addition or other improvement to a structure, the total cost of which equals or exceed 50 percent of the market value of the structure before the state of construction of the improvement.  Substantial damage means damage of any origin sustained by a structure whereby the cost of restoring the structure to its before damaged condition would equal or excel 50 percent of the market value of the structure before the damage occurred.

Multiple jurisdictions within the OA have adopted higher standards, including a repetitive loss or cumulative damage. These higher standards are described further in Volume II in addition to additional information on how these provisions are implemented.

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Table 104: Substantial Damage/Substantial Improvement Implementation Jurisdiction Responsible Party Higher Standard?
City of Campbell Floodplain Administrator No
City of Cupertino Building Official Yes
City of Gilroy Floodplain Administrator Yes
City of Los Altos Floodplain Administrator, Building
Official
No
City of Milpitas City Manager, Floodplain
Administrator
Yes
City of Morgan Hill Floodplain Administrator Yes
City of Mountain View Floodplain Administrator or
designee
Yes
City of Palo Alto Floodplain Administrator No
City of San Jose Floodplain Manager, other
departments/divisions including
public works as necessary
No
City of Santa Clara Floodplain Administrator, Building
Official
No
City of Saratoga City Manager or designee, usually
someone from Public Works or
Community Development
No
City of Sunnyvale Floodplain Administrator, Building
Official
No
County of Santa Clara Yes
Town of Los Altos Hills Floodplain Administrator No
Town of Los Gatos Floodplain Administrator No

13.5.3 Critical Facilities and Infrastructure
Percentage of damage and functional down-time estimates were not generated for critical facilities and infrastructures in the flood scenarios. However, a count of facilities within the flood hazard boundaries was obtained using the Hazus facility inventory (Tables 92-94). Replacement values provided in Hazus were used to estimate the flood loss potential to critical facilities exposed to the flood risk. The Hazus critical facility results are presented in Table 105, Table 106, and Table 107.

Table 105: Estimated Damage to Critical Facilities and Infrastructure from the 10% Annual Chance Flood
Type of Critical Facility Number of
Facilities Affected Estimated Replacement Cost
Essential Facilities 24 $236,048,440
Transportation 106 $474,684,230
Utilities 1 $1,030,643,100
Community Assets 29 Not Available

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Type of Critical Facility Number of
Facilities Affected Estimated Replacement Cost
Hazardous Materials 54 Not Available
Total/Average 214 $1,741,375,770
Note: N/A = Not Applicable.

Table 106: Estimated Damage to Critical Facilities and Infrastructure from the 1% Annual Chance Flood
Type of Critical Facility Number of
Facilities Affected Estimated Replacement Cost
Essential Facilities 58 $871,412,940
Transportation 185 $959,350,260
Utilities 3 $1,070,055,100
Community Assets 64 Not Available
Hazardous Materials 78 Not Available
Total/Average 388 $2,900,818,300
Note: N/A = Not Applicable.

Table 107: Estimated Damage to Critical Facilities and Infrastructure from the 0.2% Annual Chance Flood
Type of Critical Facility Number of Facilities
Affected Estimated Replacement Cost
Essential Facilities 89 $3,478,003,120
Transportation 244 $1,348,101,860
Utilities 10 $2,057,661,430
Community Assets 94 Not Available
Hazardous Materials 131 Not Available
Total/Average 568 $6,883,766,410
Note: N/A = Not Applicable.

These tables indicate that a significant number of important assets are currently located within the 10-, 100-, and 500-year floodplains. A breakdown of the number of critical facilities at risk for each jurisdiction can be found in Table 92 through Table 94. Flooding could impact response facilities such as fire and policies stations which may directly damage facilities and equipment within buildings, as well as impact their ability to provide response activities in the immediate aftermath of a flood. Several schools are also in flood hazard zones. Transportation networks such as roadways and railways may be damaged or become temporarily impassable during a flood, which may provide further difficulty for people displaced from their homes and seeking shelter. Numerous other community facilities included in the community assets category are also in hazard zones, which indicates a variety of community support services may disrupted by flooding. Facilities with hazardous materials on site may be compromised by flooding, which may result in contamination of floodwaters and dispersal of harmful materials. The City of San Jose, the City of Gilroy, and the unincorporated county have the highest number of critical facilities and infrastructure at risk to flooding.

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13.5.4 Environment
Flooding is a natural event, and floodplains provide many natural and beneficial functions. Nonetheless, flooding can impact the environment in negative ways. Migrating fish can wash into roads or over dikes into flooded fields, with no possibility of escape. Pollution from roads, such as oil, and hazardous materials can wash into rivers and streams. During floods, these can settle onto normally dry soils, polluting them for agricultural uses. Human development such as bridge abutments and levees, and logjams from timber harvesting can increase stream bank erosion, causing rivers and streams to migrate into non-natural courses.

Additionally, while the vulnerability assessment typically focuses on human vulnerability to flood events, the opposite is also worth noting. Floodplains have many natural and beneficial functions; however, due to negative impacts of floods, many structural and other measures have been devised to limit how far a floodplain can extend. Disruption of natural systems can have long-term consequences for entire regions; however, this potential impact has only recently been noted. Some well-known, water-related functions of floodplains include the following269 F
270:
 Natural flood and erosion control.  Filter nutrients and impurities from runoff.  Provide flood storage and conveyance.  Process organic wastes.  Reduce flood velocities.  Moderate temperatures of water.  Reduce flood peaks.  Groundwater recharge.
 Reduce sedimentation.  Promote infiltration and aquifer recharge.  Surface water quality maintenance.  Reduce frequency and duration of low surface flows
Areas within the floodplain that typically provide these natural functions are wetlands, riparian areas, sensitive areas, and habitats for rare and endangered species. In the northern end of the county, wetlands (both Bay Wetlands and Freshwater Wetlands) will be impacted by flooding adjacent to the coastline. In the southern end of the county, flooding of the Pajaro River watershed would impact Grassland, Riparian, and Freshwater Wetland habitats.270F 271 Riparian habitat would be impacted throughout
the county; however, this habitat type is naturally adapted to withstand some degree of seasonal flooding.

13.5.5 Economic Impact
Locations of flooding will experience the heaviest economic impact. Within these areas, renovations of commercial buildings may be necessary, disrupting associated services. Additionally, significant damage within agricultural areas may occur with destruction of crops and other agricultural products. The tourism industry may also be affected by major flood events, as popular vacation areas tend to overlap flood hazard zones. Finally, flooding can cause extensive damage to public utilities and disruptions to delivery of services. Loss of power and communications may occur; and drinking water and wastewater treatment facilities may be temporarily out of operation.
270 FEMA. (2022, April 1). Benefits of Natural Floodplains. https://www.fema.gov/floodplain-management/wildlifeconservation/benefits-natural 271 Santa Clara Valley Water District. (2017, October). Local Hazard Mitigation Plan. Microsoft Word - R14163 2017 FINAL LOCAL HAZARD MITIGATION PLAN v. 04-09-21 (amazonaws.com)

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13.6 Future Trends in Development
Pre-pandemic, Santa Clara County had been one of the state’s fastest growing counties, averaging a

1.21-percent increase in population per year from 2005 through 2015. The Silicon Valley job market grew, and many young tech employees elected to live in an urban environment rather than commute from the suburbs. The area has not recovered economically since the pandemic. The population decreased slightly from 2021 to 2022, and employment levels for almost all major areas of the economy were still below pre-pandemic levels at last indication.271F
272 Almost 90,000 tech industry employees were laid off in 2022 alone. The Silicon Valley housing market has cooled, but not crashed. A decrease in population and employment, particularly in high-income industries, may reduce the amount of new development in the SFHA. The Santa Clara County Planning Department Website did not show any significant development being proposed in the SFHA in the unincorporated areas of the county at the time of this writing. It is unclear if these trends will continue over the next five years.

Any areas of growth could be impacted by the flood hazard if located within the identified hazard areas.

The planning partners have appropriate policies, plans, and programs in place to address future growth within flood hazard areas. The SCVWD intends to discourage development within vulnerable areas and/or to encourage higher regulatory standards on the local level. Additionally, all municipal planning partners are participants in the NFIP and have adopted flood damage prevention ordinances which regulate development in high-hazard areas. All municipal planning partners also have general plans that address frequently flooded areas in their safety elements. All partners have committed to linking their general plans to this hazard mitigation plan. More information on planning partners’ development is available in Volume 2 of this plan.

With around 60 percent of communities in the OA participating in the CRS program, there is incentive to adopt consistent, appropriate, higher regulatory standards in areas with the highest degree of flood risk.

Additionally, there are many active regional partners involved in land use planning and risk reduction in the Bay Area. Plan Bay Area 2050 is the nine-county San-Francisco Bay Area plan for long-term development. This plan includes 35 strategies for housing, the economy, transportation, and the environment. It maintains urban growth boundaries in order to curb urban sprawl and identifies other strategies to reduce risk from flooding. The 2015 Stronger Housing, Safer Communities report led by ABAG developed a series of strategies for developing safe, smart growth in the Bay Area, including recommendations for flood protection measures.

The County of Santa Clara’s Office of Sustainability and Climate Action has also developed the Silicon Valley 2.0 Climate Adaptation Guidebook which provides additional recommendations and examples.

Jurisdictions in the OA can expand upon these and other resources to make risk-informed land use and flood mitigation decisions in light of future growth.

13.7 Scenario
Historically, floods have regularly affected the Santa Clara County OA. The OA can expect noteworthy flooding about once a year, with a flash flood every 2 to 3 years. Duration and intensity of heavy winter rains and atmospheric river events that cause flooding may increase due to climate change. The floodplains mapped and identified for the Santa Clara County OA will continue to take the brunt of these floods. OA residents prepare themselves for flooding by seeking and receiving information, and by pursuing mitigation. Impacts of flood events should decrease as the OA continues to promote and implement hazard mitigation and preparedness.
272 Silicon Valley Indicators. (n.d.). Data about Silicon Valley’s Economy and Community Health. https://siliconvalleyindicators.org/

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The worst-case scenario would be a series of heavy rains or storm events during an atmospheric river event, particularly if the rains also occur at high tide. These rains could flood numerous areas within a short time. This could overwhelm the response and floodplain management capability within the OA, as the OA would be subject immediately to flash flooding and coastal flooding, with subsequent influences on the County’s streams. Major roads could be blocked, preventing critical access for many residents and critical functions. High in-channel flows could cause water courses to scour, possibly washing out roads and creating more isolation problems. In the event of multi-basin flooding, Santa Clara County would not be able to make repairs quickly enough to restore critical facilities and assets.

13.8 Issues
Important issues associated with floods in the OA include the following:
 The extent of the flood-protection currently provided by flood control facilities (dams, dikes, and levees) is not known due to the lack of an established national policy on flood protection standards.
 The levee system within the OA is not consistently adequate to mitigate effects of a 1-percent annual chance flood.
 The risk associated with the flood hazard overlaps the risk associated with other hazards such as earthquake, landslide, mud slides and fishing losses. This provides an opportunity to seek mitigation alternatives with multiple objectives that can reduce risk for multiple hazards.  There is no consistency of land-use practices and floodplain management scope within the OA.  How climate change will affect flood conditions in the OA is uncertain.  More information is needed on flood risk to support the concept of risk-based analysis of capital projects.
 There needs to be a sustained effort to gather historical damage data, such as high-water marks on structures and damage reports, to measure the cost-effectiveness of future mitigation projects.  Ongoing flood hazard mitigation will require funding from multiple sources.  There needs to be a coordinated hazard mitigation effort between jurisdictions affected by flood hazards in the OA.
 Floodplain residents need to continue to be educated about flood preparedness and the resources available during and after floods.
 The concept of residual risk should be considered in the design of future capital flood control projects and should be communicated with residents living in the floodplain.  The promotion of flood insurance as a means of protecting private property owners from the economic impacts of frequent flood events should continue.  Existing floodplain-compatible uses such as agricultural and open space need to be maintained.

There is constant pressure to convert these existing uses to more intense uses within the OA during times of moderate to high growth.
 The economy affects a jurisdiction’s ability to manage its floodplains. Budget cuts and personnel losses can strain resources needed to support floodplain management.

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Table 108: EMAP Consequence Analysis: Flood
Subject Ranking Impacts/Flood
Public Minimal to
severe
The localized impact is expected to be severe for persons living within the inundation area. Residents of the SFHA are most at risk from flooding. Flooding can result in injury, loss of life, and the loss of property and livelihood. Daily life of residents, visitors, and commuters would be disrupted,
particularly if evacuations are necessary. Flood waters could carry containments which impact public health. Water that is slow to recede could act as a habitat for disease-carrying insects. The public would be exposed to risk during flood clean-up, including mold. Vulnerable populations may be disproportionally impacted by a flood event and have unique response and recovery needs. There may long-term public health consequences of a flood event.

Responders Minimal to
moderate
Responders may be responsible for supporting evacuations, closing roads, assisting injured members of the public, and managing the overall incident. Depending on the event,
responders may play a significant role in locating and
assisting survivors after the flood. During the course of their duties, responders will likely face increased risk of personal injury. They may be directly exposed to the flood water, including any containments.

Continuity of
Operations (including
continue delivery of
services)
Minimal to
severe
Temporary relocation may be necessary if inundation affects government facilities. Delivery of services could be affected if there is any disruption to facilities, roads, and/or utilities due to the inundation or cascading impacts.

Property, Facilities, and
Infrastructure
Minimal to
severe
The localized impact could be severe for property, facilities and infrastructure that are inundated. Additional damage or disruption could be caused by debris, road closures, and stormwater issues. Water and wastewater treatments plants may be overloaded.

Environment Minimal to
severe
Flooding can provide benefits to environment. However, it also can potentially expose the environment to containments, hazardous materials, silt, and debris. Flooding can damage or destroy natural habitats and wildlife like fish caught up in the flood water can die. Floods can additionally cause erosion, landslides, and changes to the watershed.

Economic Conditions Minimal to
severe
Impacts on the economy will greatly depend on the scope of the inundation and the amount of time it takes for the flood water to recede. A major flood event could be costly. There would be emergency response needs, disaster cleanup,
delays and disruption in services and transportation, and potential closure to local businesses due to direct flood losses or lack of employees or customers.

Public Confidence in
the Government
Minimal to
severe
The public’s confidence will vary, depending on the perception of the warning time, the information shared, and the time it takes for response and recovery. Accurate and timely
distribution of information before, during, and after the event will influence public trust.

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14 Landslide/Mass Movement
Definitions
 Landslide: The movement of masses of loosened rock and soil down a hillside or slope. Slope failures occur when the strength of the soils forming the slope is exceeded by the pressure, such as weight or saturation, acting upon them.
 Mass Movement: A collective term for landslides, debris flows, and sinkholes.  Mudslide (or Debris Flow): A river of rock, earth, organic matter, and other materials saturated with water. Mudslides develop in the soil overlying bedrock on sloping surfaces when water rapidly accumulates in the ground, such as during heavy rainfall or rapid snowmelt. Water pressure in the pore spaces of the material increases to the point that the internal strength of the soil is drastically weakened. The soil’s reduced resistance can then easily be overcome by gravity, changing the earth into a flowing river of mud or “slurry.”

14.1 General Background
The U.S. Geological Survey defines landslides to include a wide range of ground movement, such as rock falls, deep failure of slopes, and shallow debris flows. Although gravity acting on an over-steepened slope is the primary reason for a landslide, there are other contributing factors.

Landslides and mudslides can be initiated by storms, earthquakes, fires, volcanic eruptions, or human modification of the land. They can move rapidly down slopes or through channels and can strike with little or no warning at avalanche speeds, posing a serious hazard to properties on or below hillsides.

When landslides occur—in response to such changes as increased water content, earthquake shaking, addition of load, or removal of downslope support—they deform and tilt the ground surface. The result can be destruction of foundations, offset of roads, breaking of underground pipes, or overriding of downslope property and structures.

The USGS defines land subsidence as the loss of surface elevation due to the removal of subsurface support. In California, the two principal causes for land subsidence are aquifer compaction due to excessive groundwater pumping and decomposition of wetland soils exposed to air after wetland conversion to farmland.

14.1.1 Landslide Types
Landslides are commonly categorized by the type of initial ground failure. Common types of slides are shown in Figure 65. The most common is the shallow colluvial slide, occurring particularly in response to intense, short-duration storms. The extent of landslides can range from mild to severe and are dependent on several factors, including the type of event. The largest and most destructive are deep-seated slides (greater than 10 to 15 feet deep), although they are less common than other types.

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Figure 66: Common Types of Landslides
Mudslides (or debris flows) are rivers of rock, earth, organic matter, and other soil materials saturated with water. They develop in the soil overlying bedrock on sloping surfaces when water rapidly accumulates in the ground, such as during heavy rainfall or rapid snowmelt. Water pressure in the pore spaces of the material increases to the point that the internal strength of the soil is drastically weakened. The soil’s reduced resistance can then easily be overcome by gravity, changing the earth into a flowing river of mud.

A debris avalanche (see Figure 66) is a fast-moving debris flow that travels faster than about 10 miles per hour (mph). Speeds in excess of 20 mph are not uncommon, and speeds in excess of 100 mph, although rare, can occur. The slurry can travel miles from its source, growing as it descends, picking up trees, boulders, cars, and anything else in its path. Although these slides behave as fluids, they pack many times the hydraulic force of water due to the mass of material included in them. They can be among the most destructive events in nature.

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Figure 67: Typical Debris Avalanche Scar and Track27F
273
Landslides also include the following:
 Rock Falls: Blocks of rock that fall away from a bedrock unit without a rotational component.  Rock Topples: Blocks of rock that fall away from a bedrock unit with a rotational component.  Rotational Slumps: Blocks of fine-grained sediment that rotate and move down slope.  Transitional Slides: Sediments that move along a flat surface without a rotational component.  Earth Flows: Fine-grained sediments that flow downhill and typically form a fan structure.  Creep: A slow-moving landslide often only noticed through crooked trees and disturbed structures.
 Block Slides: Blocks of rock that slide along a slip plane as a unit down a slope.

14.1.2 Landslide Modeling
Two characteristics are essential to conducting an accurate risk assessment of the landslide hazard:
 The type of initial ground failure that occurs, as described above  The post-failure movement of the loosened material (“runout”), including travel distance and velocity
All current landslide models—those in practical applications and those more recently developed—use simplified hypothetical descriptions of mass movement to simulate the complex behavior of actual flow.

The models attempt to reproduce the general features of the moving mass of material through measurable factors, such as base shear, that define a system and determine its behavior. 273 California Department of Conservation. (n.d.). Hazards from “Mudslides” …Debris Avalanches and Debris Flows in Hillside and Wildfire Areas. https://www.conservation.ca.gov/cgs/Pages/Publications/Note_33.aspx

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Due to the lack of experimental data and the limited current knowledge about the behavior of the moving flows, landslide models use simplified parameters to account for complex aspects that may not be defined. These simplified parameters are not related to specific physical processes that can be directly measured, and there is a great deal of uncertainty in their definition. Some, but not all, models provide estimates of the level of uncertainty associated with the modeling approach.

Run-out modeling is complicated because the movement of materials may change over the course of a landslide event, depending on the initial composition, the extent of saturation by water, the ground shape of the path traveled and whether there is additional material incorporated during the event.273F 274

14.1.3 Landslide Causes
Mass movements are caused by a combination of geological and climate conditions, as well as encroaching urbanization. Vulnerable natural areas are affected by residential, agricultural, commercial, and industrial development and the infrastructure that supports it. The following factors can contribute to landslide: change in slope of the terrain, increased load on the land, shocks and vibrations, change in water content, groundwater movement, frost action, weathering of rocks, and removing or changing the type of vegetation covering slopes.

Excavation and Grading
Slope excavation is common in development of home sites or roads on sloping terrain. Grading can result in slopes that are steeper than the pre-existing natural slopes. These steeper slopes can be at an increased risk for landslides. The added weight of fill on slopes can also result in an increased landslide hazard. Small landslides can be common along roads, in either the road cut or the road fill. Landslides below new construction sites are indicators of the potential impacts stemming from excavation.

Drainage and Groundwater Alterations
Water flowing through or above ground is often the trigger for landslides. Any activity that augments the amount of water flowing into landslide-prone slopes can increase landslide hazards. Broken or leaking water or sewer lines can be especially problematic, as can water retention facilities that direct water onto slopes. However, even lawn irrigation and minor alterations to small streams in landslide-prone locations can result in damaging landslides. Ineffective stormwater management and excess runoff can also cause erosion and increase the risk of landslide hazards. Drainage can be affected naturally by the geology and topography of an area. Development that results in an increase in impervious surface impairs the ability of the land to absorb water and may redirect water to other areas. Channels, streams, flooding, and erosion on slopes all indicate potential slope problems.

Road and driveway drains, gutters, downspouts, and other constructed drainage facilities can concentrate and accelerate flow. Ground saturation and concentrated velocity flow are major causes of slope problems and may trigger landslides.

Changes in Vegetation
Removing vegetation from very steep slopes can increase landslide hazards. Areas that have experienced wildfire and land clearing for development may experience long periods of increased landslide hazard. In addition, woody debris in stream channels (both natural and man-made from logging) may cause the impacts from debris flows to be more severe. 274 McDougall, S. (2016). 2014 Canadian Geotechnical Colloquium: Landslide runout analysis — current practice and challenges. Canadian Geotechnical Journal. 54(5): 605-620. https://doi.org/10.1139/cgj-2016-0104

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14.1.4 Landslide Management
While small landslides are frequently a result of human activity, the largest landslides are often naturally occurring phenomena with little or no human contribution. The sites of large landslides are typically areas of previous landslide movement that are periodically reactivated by significant precipitation or seismic events. These naturally occurring landslides can disrupt roadways and other infrastructure lifelines, destroy private property, and cause flooding, bank erosion, and rapid channel migration.

Landslides can create immediate, critical threats to public safety. Engineering solutions to protect structures on or adjacent to large active landslides are often extremely or prohibitively expensive. Despite their destructive potential, landslides can serve beneficial functions to the natural environment. They supply sediment and large wood to the channel network and can contribute to complexity and dynamic channel behavior critical for aquatic and riparian ecological diversity. Effective landslide management should include the following elements:
 Continuing investigation to identify natural landslides, understand their mechanics, assess their risk to public health and welfare, and understand their role in ecological systems.  Regulation of development in or near existing landslides or areas of natural instability through the Santa Clara County Code and City ordinances.
 Preparation for emergency response to landslides to facilitate rapid, coordinated action among Santa Clara County, local cities, and state and federal agencies, and to provide emergency assistance to affected or at-risk citizens.
 Evaluation of options including landslide stabilization or structure relocation where landslides are identified that threaten critical public structures or infrastructure.

14.1.5 Land Subsidence Effects
Subsidence is one of the most diverse forms of ground failure, ranging from small or local collapses to broad regional lowering of the earth’s surface. The causes of subsidence, mostly associated with human activities, are as diverse as the forms of failure, and include dewatering (oxidation) of peat or organic soils, dissolution in limestone aquifers, first-time wetting of moisture-deficient low-density soils, natural compaction, liquefaction, crustal deformation, subterranean mining, and withdrawal of fluids (groundwater, petroleum, geothermal).

The compaction of susceptible aquifer systems caused by excessive groundwater pumping is the single largest cause of subsidence in California. The second largest cause of subsidence in California is the oxidation (decomposition) of organic soils.274F
275 Alteration to the Sacramento-San Joaquin Delta in the late 1800s through the creation of levees and ground water pumping is known as the single largest human alternation of the Earths’ surface topography, but it left over 5,200 square miles of areas susceptible to subsidence, primarily from decomposition of organic carbon in the peat soils.275F 276
275 U.S. Geological Survey. (2018, October 18). Decomposition of Organic Soils in the Sacramento-San Joaquin Delta. https://www.usgs.gov/centers/land-subsidence-in-california/science/decomposition-organic-soils-sacramentosan-joaquin 276 U.S. Geological Survey. (2018, November 29). Land Subsidence Along the California Aqueduct in West-central San Joaquin Valley, California. https://www.usgs.gov/publications/land-subsidence-along-california-aqueduct-westcentral-san-joaquin-valley-california

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Aquifer Compaction
Aquifer compaction due to groundwater pumping affects both manmade infrastructures and natural systems. The greatest effects are on infrastructure that traverses a subsiding area. In the San Joaquin Valley, the main problems reported are related to water conveyance structures. Many water conveyance structures, including long stretches of the California Aqueduct, are gravity driven through the use of very small gradients; even minor changes in these gradients can cause reductions in designed flow capacity.

Managers of the canals, such as the California Department of Water Resources, the San Luis DeltaMendota Authority, the Bureau of Reclamation, and the Central California Irrigation District, have to repeatedly retrofit their canals to keep the water flowing, even at reduced amounts. Subsidence also affects roads, railways, bridges, pipelines, buildings, and wells.

Compaction of an aquifer system may permanently decrease the aquifer’s capacity to store water. Even when water levels rise, sediments can remain compacted; most compaction that occurs as a result of historically low groundwater levels is irreversible.

Additionally, as the topography of the land changes by varying amounts in different places, low areas, such as wetlands, change size and shape, migrate to lower elevations, or even disappear. Rivers may change course or erosion/deposition patterns to reach a new equilibrium.

Decomposition of Wetland Soils
The Sacramento-San Joaquin Delta of California was once a great tidal freshwater marsh. It is blanketed by peat and peaty alluvium deposited where streams that originate in the Sierra Nevada, Coast Ranges, and South Cascade Range enter San Francisco Bay. In the late 1800s, levees were built along the stream channels, and the land thus protected from flooding was drained, cleared, and planted. The leveed tracts and islands help to protect water-export facilities in the southern Delta from saltwater intrusion by displacing water and maintaining favorable freshwater gradients. However, the decomposition of organic carbon in the peat soils causes land subsidence in the Delta and increases stresses on the levees. Ongoing subsidence behind the levees, where the land has been drained, exposed to the atmosphere, and planted, increases stresses on the levee system, making it less stable.

This threatens to damage agricultural and developed lands and degrade water quality in the massive water-transfer system.

14.2 Hazard Profile

14.2.1 Past Events
Losses from landslides are typically lower than those from flooding. However, in the El Niño storms of early 1998, the USGS documented $150 million in losses due to approximately 300 landslides in the Bay Area and Santa Clara County. The slides ranged from a 25-cubic-meter failure of engineered material to reactivation of the 13 million-cubic-meter Mission Peak earth flow complex in Alameda County.

Landslides have occurred in conjunction with earthquakes and heavy rains events in Santa Clara County.

Table 109 lists known landslide events that affected Santa Clara County between 1980 and 2023. Other landslides around the Bay Area near the OA, particularly in the Santa Cruz Mountains, are documented by the California Geological Survey.276F
277
277 California Geological Survey. (2011). Susceptibility to Deep-Seated Landslides in California. https://www.conservation.ca.gov/cgs/Documents/Publications/Map-Sheets/MS_058.pdf

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Table 109: Landslide Events in Santa Clara County27F
278,
278F
279,
279F
280,
280F
281,
281F
282
Dates of Event Event Type FEMA
Declaration Location Losses/Impacts
12/19/1981 to
1/08/1982
Severe storms, flood,
mudslides, high tide
651 San Francisco
Bay area
Prolonged heavy rains and saturated soils caused
numerous slope failures and mud flows on steep and
unstable slopes throughout the San Francisco Bay area.
1/21/1983 to
3/30/1983
Coastal storms, floods, slides,
tornadoes
677 San Francisco
Bay area
A landslide restricted Clayton Road to one lane just east of the community of Alum Rock. Another, on the east side of Milpitas, resulted in vertical and horizontal offset of a roadway.
4/24/1984 Morgan Hill Earthquake None Calaveras fault
east of San
José.

This 6.2 magnitude earthquake caused minor landslides
throughout the region.
10/17/1989 Loma Prieta Earthquake 845 San Andreas
fault near Loma
Prieta.

Landslides and rockslides in Santa Clara County on steep slopes in the Santa Cruz Mountains blocked roads,
damaged structures, and caused at least two deaths.
1/03/1995 to
2/10/1995
Severe winter storms,
flooding, landslides, mud
flows
1044 San Francisco
Bay area
Minor landslide damage in Santa Clara County was
attributed to heavy rains and saturated soils.
2/13/1995 to
4/19/1995
Severe winter storms,
flooding, landslides, mud
flows
1046 San Francisco
Bay area
Minor landslide damage in Santa Clara County was
attributed to heavy rains and saturated soils.
278 Association of Bay Area Governments. (2011). 2011 Bay Area Hazard Mitigation Plan. https://abag.ca.gov/2011-bay-area-hazard-mitigation-plan 279 U.S. Geological Survey. (1987). The Morgan Hill, California, Earthquake of April 24, 1984. U.S. Geological Survey Bulletin 1639. https://pubs.usgs.gov/bul/1639/report.pdf
280 U.S. Geological Survey (1989). The Severity of an Earthquake. https://pubs.usgs.gov/gip/earthq4/severity_text.html 281 NOAA. (2023). Storm Events Database. https://www.ncdc.noaa.gov/stormevents/ 282 California Department of Conservation. (n.d.). Reported California Landslides Database. https://www.conservation.ca.gov/cgs/landslides

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Dates of Event Event Type FEMA
Declaration Location Losses/Impacts
2/02/1998 to
4/30/1998
Severe Winter Storms and El
Nino Rainstorm
1203 San Francisco
Bay region
$7.6 million in Santa Clara County landslide damage
occurred mostly in the northern county, along the range front of the Santa Clara Valley. $6.1 million in damage was attributed to reactivation of three local landslides. The rest was attributed to small debris flows along road cuts or narrow canyon walls. In Alum Rock, the Penitencia Creek landslide caused extensive damage to water and sewer
lines and closed roads. Another landslide closed Clayton Road east of Alum Rock area. The third, near Old
Piedmont Road on the east side of Milpitas, had a
displacement near the toe of about 20 cm.
1/10/2017 Debris Flow, Heavy Rain None Santa Clara,
Montalvo
The third and final system in a string of Atmospheric River events between January 2 to 11. This system resulted in widespread roadway flooding and debris flows across the CWA. Black road at Gist Road is impassable due to major mudslide or rockslide.
1/18/2017 Debris Flow, Heavy Rain None Santa Clara,
Redwood
Estates
Three storm systems swept through the region between
January 18-23. The first occurred on January 18 as a cold front moved through. Heavy rain, widespread flooding, and debris flows were observed. Mud/rock/dirt slide blocking one lane heading towards Highway 17 from Bear Creek
Rd.
2/07/2017 Debris Flow, Heavy Rain None Santa Clara,
Los Gatos
An atmospheric river swept through the Bay Area
beginning on the night of Feb 6. This system produced
widespread roadway flooding, debris flows, and strong
winds. Mud slide reported at 18500 Limekiln Canyon Road. 2/09/2017 Debris Flow, Heavy Rain None Santa Clara,
Los Altos Hills
A cold front passed over the area Thursday Feb 9. There were strong winds ahead of the front and heavy rains
associated with the frontal passage that produced roadway flooding and debris flows. Mud/dirt/rockslide blocking south bound lanes Skyline Dr at Alpine.

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Dates of Event Event Type FEMA
Declaration Location Losses/Impacts
2/09/2017 Debris Flow, Heavy Rain None Santa Clara,
Saratoga
A cold front passed over the area Thursday, Feb 9. There were strong winds ahead of the front and heavy rains
associated with the frontal passage that produced roadway flooding and debris flows. Second mudslide in area and a tree down partially blocking 23600 SR9 near SavannahChanelle Vineyard. 2/20/2017 Debris Flow, Heavy Rain None Santa Clara,
Los Gatos
Potent AR brought copious amounts of rain to the region causing widespread flooding, debris flow, accidents, and over topping of reservoir spillways. Highway 17
southbound shut down due to a rockslide just north of
Lexington Reservoir.
1/06/2019 Debris Flow, Heavy Rain None Santa Clara,
Los Gatos
A vigorous cold front swept through California on January 5th bringing widespread rainfall and gusty winds. Unstable air behind the frontal passage and sufficient low level shear allowed shallow thunderstorms to develop over the coastal waters, some of which contained rotating cells. Two
waterspouts developed and made landfall as tornadoes on the 6th. Additionally, heavy rainfall and strong winds
caused roadway flooding, minor debris flows, and
numerous downed trees across the region. This storm
system caused two fatalities; one caused by a downed tree in Berkeley and another man died in Santa Rosa Creek
due to rising waters. Mud slide reported at Cats/Lexington south side on Hwy 17.
1/17/2019 Flood, Heavy Rain None Santa Clara,
Saratoga
A moderate to strong atmospheric river impacted much of California in the middle of the month. A weak surface low developed off the coast on January 15th bringing moderate to heavy rainfall to portions of the region. Over the next 24 to 36 hours a second strong low pressure system moved to the north and east bringing heavy rain, destructive winds, high surf, flooding, and thunderstorms to the Bay Area.

Numerous reports were received of downed trees and
power lines. Winds were recorded between 60 and 100
mph. Downed trees resulted in two fatalities. Mud/dirt/rock at Mt Eden Rd and Orchard Meadow Dr blocking most of
roadway.

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Dates of Event Event Type FEMA
Declaration Location Losses/Impacts
2/04/2019 Debris Flow, Heavy Rain None Santa Clara,
Redwood
Estates
A mid/upper low with a very cold airmass moved through in early February bringing snow to lower elevation peaks
across the region prompting a rare Winter Weather
Advisory. Junipero Serra Peak received around a foot of snow. Rainfall just ahead of this system also brought
roadway flooding and minor debris flows. Mud, rock, and debris covered Hicks Road resulting in a multiday closure.

Highway 35 closed due to sinkhole.
2/10/2019 Debris Flow, Heavy Rain None Santa Clara,
Bells Station
A cold front moved through the region into February 10th lowering snow levels below 1500 ft, per the Bodega Bay
Profiler. The areas peaks saw another dusting to several inches of snow as a result with Mount Hamilton recording almost 6 inches. Additionally, showers ahead of the front the previous evening caused some minor roadway
flooding. Mud and rocks in slow lane on WB HWY 152.
2/11/2019 Landslide None Santa Clara 160 meters east of intersection of Hicks Road and Pheasant Road. Mud, rock, and debris covered Hicks Road resulting in multiday closure
2/13/2019 Debris Flow, Heavy Rain None Santa Clara,
Robertsville
An atmospheric river with an associated cold front moved through the region from February 12th to the 15th bringing widespread flooding and debris flows. Multiple mainstem rivers flooded prompting evacuations from local officials.

Strong wind gusts caused downed trees, power outages,
and structural damage. Additionally, a tree fell on a car causing one fatality and one serious injury on Highway 17 while another downed tree caused a serious multi-car
traffic accident that resulted in another fatality as well as major injuries. The areas peaks received upwards of 10
inches of rainfall and widespread wind gusts of 50 to 60 mph were observed. Mount Saint Helena recorded wind
gusts of 80 mph. Mudslide blocking both lanes of Hicks Rd in south San José.

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Dates of Event Event Type FEMA
Declaration Location Losses/Impacts
2/13/2019 Flood, Heavy Rain None Santa Clara,
Saratoga
An atmospheric river with an associated cold front moved through the region from February 12th to the 15th bringing widespread flooding and debris flows. Multiple mainstem rivers flooded prompting evacuations from local officials.

Strong wind gusts caused downed trees, power outages,
and structural damage. Additionally, a tree fell on a car causing one fatality and one serious injury on Highway 17 while another downed tree caused a serious multi-car
traffic accident that resulted in another fatality as well as major injuries. The areas peaks received upwards of 10
inches of rainfall and widespread wind gusts of 50 to 60 mph were observed. Mount Saint Helena recorded wind
gusts of 80 mph.

Mud in NB lane of CA-9 1 mile south of Redwood Gulch.
2/14/2019 Debris Flow, Heavy Rain None Santa Clara,
Saratoga
An atmospheric river with an associated cold front moved through the region from February 12th to the 15th bringing widespread flooding and debris flows. Multiple mainstem rivers flooded prompting evacuations from local officials.

Strong wind gusts caused downed trees, power outages,
and structural damage. Additionally, a tree fell on a car causing one fatality and one serious injury on Highway 17 while another downed tree caused a serious multi-car
traffic accident that resulted in another fatality as well as major injuries. The areas peaks received upwards of 10
inches of rainfall and widespread wind gusts of 50 to 60 mph were observed. Mount Saint Helena recorded wind
gusts of 80 mph. Mud slide blocking lanes at SR 9 and
Booker Creek Rd.

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Dates of Event Event Type FEMA
Declaration Location Losses/Impacts
1/27/2021 Debris Flow, Heavy Rain None Santa Clara,
Coyote
A plume of moisture from the tropical Pacific brought an Atmospheric River to the Bay Area January 26–29. This
system generated heavy rain rates causing flooding and
debris flows over area burn scars as well as 15 to 20
inches of rain in the Santa Lucia Mountains. Mudflows near the River Fire burn scar in Monterey County caused
damage to homes, covered roadways, and trapped animals
at local ranches. Debris flows near the Dolan Fire burn scar caused an entire section of Highway 1 near Rat Creek to collapse into the Pacific Ocean. This was an unusually cold system for an Atmospheric River resulting in lower snow levels and allowing for accumulating snow as low as 1300 feet in elevation. Additionally, strong south to southeast winds gusted to 60-70 mph across area peaks with Mt
Diablo reaching 80 mph. Valley locations were gusting up to 40 mph. Numerous trees fell across the region including into homes and onto cars. Multiple power outages were
also reported. It is estimated that the storm caused millions of dollars in damage across Santa Cruz County.

Mud/dirt/rocks in roadway at Metcalf Rd and Monterey
Hwy.
3/10/2021 Flood, Heavy Rain None Santa Clara,
San José
A cold upper low moved through the region in early March bringing widespread showers and isolated thunderstorms
to the Greater Bay Area. This system caused roadway
flooding, debris flows, lightning, and small hail. Snow was also reported on some of the area’s peaks throughout the region as snow levels dropped down to 2,000 ft. A
mudslide occurred along the River Fire burn scar in
Monterey County sending mud and debris into nearby
homes. Roadway flooding northbound 280 & 87 due to
heavy rain.

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Dates of Event Event Type FEMA
Declaration Location Losses/Impacts
3/10/2021 Hail None Santa Clara,
San José
International
Airport
A cold upper low moved through the region in early March bringing widespread showers and isolated thunderstorms
to the Greater Bay Area. This system caused roadway
flooding, debris flows, lightning, and small hail. Snow was also reported on some of the area’s peaks throughout the region as snow levels dropped down to 2,000 ft. A
mudslide occurred along the River Fire burn scar in
Monterey County sending mud and debris into nearby
homes. Image on social media showing small hail near the San José International Airport.

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Figure 68: A Santa Clara County Debris Flow Triggered by Winter Storms Following the Loma Fire, 201728 F
283
According to the Santa Clara Valley Water District,283F 284 Santa Clara County has experienced as many as
13 feet of subsidence caused by excessive pumping of groundwater in the early 1900s. The SCVWD was created in the early 1930s to protect groundwater resources and minimize land subsidence. To reduce the demand on groundwater and minimize subsidence, the SCVWD uses a combination of imported surface water (from the State Water Project and San Francisco’s Hetch-Hetchy system), recycled water, and groundwater. Figure 68 shows the history of land surface elevation, groundwater elevation, and the estimated population of Santa Clara County from 1900 up to 2020. The SCVWD started importing water in the 1960s when the groundwater elevation reached its lowest elevation. 283 Swanson, B. (n.d.). A Santa Clara County debris flow triggered by winter storms following the Loma Fire, 2017 [Photograph]. California Geologic Survey.
284 SCVWD. (n.d.). Subsidence. https://www.valleywater.org/your-water/where-your-watercomes/groundwater/subsidence#:~:text=Land%20subsidence%20is%20a%20settling%20of%20the%20Earth%27s,J ose%20to%20southern%20San%20Francisco%20Bay%20were%20impacted.

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Figure 69: SCVWD Historic Groundwater Conditions284F
285

14.2.2 Location
In general, landslide hazard areas are where the land has characteristics that contribute to the risk of the downhill movement of material, such as the following:
 A history of landslide activity or movement during the last 10,000 years.  A steep slope.
 Stream or wave activity, which has caused erosion, undercut a bank, or cut into a bank to cause the surrounding land to be unstable.
 Recent wildfires, as debris flows often occur in areas that experienced wildfires the previous year.285F
286
 Recent construction, construction debris, or erosion due to construction.  The presence of an alluvial fan (geologic features built by runoff spreading out in a wide fan-like area), indicating vulnerability to the flow of debris or sediments. 285 Santa Clara Valley Water District. (2021). Imported Water: Vital to Santa Clara Valley [Photograph]. https://www.valleywater.org/your-water/where-your-water-comes/imported-water 286 USGS California Water Science Center. (2018, October 31). Post-Fire Flooding and Debris Flow. https://ca.water.usgs.gov/wildfires/wildfires-debris-flow.html

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 The presence of impermeable soils, such as silt or clay, which are mixed with granular soils such as sand and gravel.

The best available predictor of where movement of slides and earth flows might occur is the location of past movements. Past landslides can be recognized by their distinctive topographic shapes, which can remain in place for thousands of years. Most landslides recognizable in this fashion range from a few acres to several square miles. Most show no evidence of recent movement and are not currently active. A small proportion of them may become active in any given year, with movements concentrated within all or part of the landslide masses or around their edges.

The recognition of ancient dormant mass movement sites is important in the identification of areas susceptible to flows and slides because they can be reactivated by earthquakes or by exceptionally wet weather. Also, because they consist of broken materials and frequently involve disruption of groundwater flow, these dormant sites are vulnerable to construction-triggered sliding.

The California Landslide Hazard Identification Act directs the State Geologist to identify and map hazardous landslide areas for use by municipalities in planning and decision-making on grading and building permits. Three factors that characterize landslide hazard areas include significant slope, weak rocks, and heavy rains. This program focuses on urban areas and growth areas that exhibit these characteristics. The OA includes both high- and low-risk landslide areas.

The Association of Bay Area Governments Resilience Program286F 287 provides more detailed mapping for the
Bay Area through use of USGS Summary of Distribution of Slides and Earth Flows (1997) and Map Showing Principal Debris-Flow Source Areas (1997). The County of Santa Clara overlaid these data on its jurisdictional boundaries to develop Geological Hazard Zones to suggest areas specific geologic hazards may be present. Additional geologic reports are required for construction in areas where a specific geologic hazard may be present.
287 Association of Bay Area Governments. (n.d.). Resilience. https://abag.ca.gov/our-work/resilience

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Figure 70: Deep-Seated Landslide Susceptibility in Santa Clara County

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14.2.3 Frequency
There are over 75,000 active and dormant landslides mapped in the Bay Area and other natural hazards such as earthquakes, heavy rain, floods, or wildfires continue to trigger landslides so there will likely be more landslide activity in the OA on an annual basis.287F 288 In the OA, landslides typically occur where
landslides and earth flows have occurred in the past. These previous locations may not show any evidence of recent movement and may not be currently active, but some portion of them may become active in any given year from natural hazard events. As shown in Table 109, damage from the El Niño rainstorm event in 1998 was mainly attributed to reactivation of landslide locations and because of sequential severe storms that saturated steep, vulnerable soils. Landslide events occurred during the severe storms of 1983, 1995, and 1998. Atmospheric rivers that occurred along the west coast in 2021 and 2022 also caused landslide events in California. As more frequent storms hit the west coast and wildfires become more frequent due to climate change, there will likely be increased landslide incidents.

Until better data is generated specifically for landslide hazards, this severe storm frequency is appropriate for the purpose of ranking risk associated with the landslide hazard. Subsidence is hard to predict. Given that it is a generally slow and gradual process which develops over time including in areas like the San Joaquin River Delta, it can be assumed the OA is at continuous risk from this hazard.

Further information on the impact of climate change on the probability of landslide/mass movement is included in Section 11.

Probability in OA: Occasional

14.2.4 Severity
Landslides destroy property and infrastructure and can take the lives of people. Slope failures in the United States result in an average of 25 to 50 lives lost per year and are estimated to cost society billions of dollars in damages. Landslides can pose a serious hazard to properties on or below hillsides. When landslides occur—in response to such changes as increased water content, earthquake shaking, addition of load, or removal of downslope support—they deform and tilt the ground surface. The result can be destruction of foundations, offset of roads, breaking of underground pipes, or overriding of downslope property and structures.

14.2.5 Warning Time
The speed of mass movements may range from inches per year to many feet per second, depending on slope, material, and water content. Some monitoring methods can provide an idea of the type of movement and the amount of time prior to failure. It is also possible to determine what areas are at risk during general time periods. Assessing geology, vegetation and predicted precipitation can help in predictions. Landslide early warning systems (LEWS) have gained more attention from researcher, government officials, and other decision makers in recent years.28F 289 The San Francisco Bay region was
once home to the to the first public debris-flow hazard advisory in the United States however, it had to be shut down due to lack of resources. There is currently no practical warning system for individual landslides. The current standard operating procedure is to monitor situations case-by-case and respond after the event has occurred. Warning signs for landslide activity include the following:
 Springs, seeps, or saturated ground in areas that have not typically been wet before 288 Santa Clara Valley Water District. (2017). Local Hazard Mitigation Plan. https://www.valleywater.org/floodingsafety/local-hazard-mitigation-plan 289 Guzzetti, F., & Gariano, S. L., & Peruccacci, S., & Brunetti, M. T., & Marchesini, I., & Rossi, M., & Melillo, M. (2020, January). Geographical Landslide Early Warning Systems. Earth-Science Reviews. https://www.sciencedirect.com/science/article/pii/S0012825219304635

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 New cracks or unusual bulges in the ground, street pavements or sidewalks  Soil moving away from foundations
 Ancillary structures such as decks and patios tilting and/or moving relative to the main house  Tilting or cracking of concrete floors and foundations  Broken water lines and other underground utilities
 Leaning telephone poles, trees, retaining walls or fences  Offset fence lines
 Sunken or down-dropped roadbeds
 Rapid increase in creek water levels, possibly accompanied by increased turbidity (soil content)  Sudden decrease in creek water levels though rain is still falling or just recently stopped  Sticking doors and windows, and visible open spaces indicating jambs and frames out of plumb  A faint rumbling sound that increases in volume as the landslide nears  Unusual sounds, such as trees cracking or boulders knocking together

14.3 Cascading Impacts
Landslides can cause secondary effects such as blocking access to roads, which can isolate residents and businesses and delay transportation. This could result in economic losses for businesses. Other potential problems resulting from landslides are power and communication failures. Vegetation or poles on slopes can be knocked over, resulting in possible losses to power and communication lines.

Landslides also have the potential of destabilizing the foundation of structures, which may result in monetary loss for residents. The damage of destruction of culverts, levees, dams, or other flood mitigation infrastructure during a landslide can result in increased likelihood and damage from flooding. They also can damage rivers or streams, potentially harming water quality, fisheries, and spawning habitat.

14.4 Exposure

14.4.1 Population
Population could not be examined by landslide hazard area because the boundaries of census block groups do not coincide with the hazard area boundaries. However, population was estimated using the building count from the National Structure Inventory multiplied by the most recent average household size from the U.S. Census Bureau. Using this approach, the estimated population living in a moderate to high landslide risk area is 182,752. Table 110 shows the population residing in landslide hazard areas by city.

Table 110: Population Exposed to Landslide Hazard
Jurisdiction Population in hazard
area
% of Total City
Population
Campbell 629 1.45
Cupertino 4,530 7.47
Gilroy 2,578 4.33
Los Altos 1,082 3.40

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Jurisdiction Population in hazard
area
% of Total City
Population
Los Altos Hills 2,986 35.33
Los Gatos 7,527 22.45
Milpitas 2,217 2.76
Monte Sereno 575 16.67
Morgan Hill 4,583 10.18
Mountain View 337 .41
Palo Alto 620 .90
San Jose 39,694 3.91
Santa Clara 614 .48
Saratoga 6,639 21.39
Sunnyvale 611 .39
Unincorporated 16,158 17.90
County Total 91,379 4.72

14.4.2 Property
There are 506,562 acres of land in the OA in a moderate to high landslide risk area. There is also a high number of existing structures and personal vehicles in the OA with an estimated value of $23 billion.

Table 111 shows the number and replacement value of structures exposed to the landslide risk and Table 112 shows the land by acreage exposed to moderate to high landslide hazard in the OA.

Table 111: Exposure and Value of Structures in Moderate to High Landslide Risk Areas Jurisdiction
Estimated Value within the Landslide Risk Area % of
Total
Replace
ment
Value Structure Contents Vehicle Total
Campbell $119,347,275 $93,490,164 $17,091,000 $229,928,440 1.45 Cupertino $642,077,740 $352,803,132 $46,269,000 $1,041,149,872 7.47 Gilroy $426,639,497 $241,668,405 $24,615,000 $692,922,903 4.33 Los Altos $183,084,928 $112,059,655 $11,295,000 $306,439,583 3.40 Los Altos Hills $551,842,500 $29,164,233 $30,159,000 $611,165,733 35.33 Los Gatos $1,329,885,950 $802,145,351 $97,668,000 $2,229,699,302 22.45 Milpitas $280,013,499 $146,512,485 $22,212,000 $448,737,984 2.76 Monte Sereno $102,860,017 $52,144,778 $6,264,000 $161,268,795 16.67 Morgan Hill $636,319,187 $339,329,715 $46,368,000 $1,022,016,903 10.18 Mountain View $50,017,254 $26,790,401 $6,714,000 $83,521,656 0.41 Palo Alto $278,075,584 $207,755,004 $33,669,000 $519,499,589 0.90 San José $5,567,073,749 $3,165,037,570 $450,567,000 $9,182,678,320 3.91

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Jurisdiction
Estimated Value within the Landslide Risk Area % of
Total
Replace
ment
Value Structure Contents Vehicle Total
Santa Clara
(city) $84,759,092 $49,960,448 $14,184,000 $148,903,541 0.48 Saratoga $1,136,966,663 $661,435,350 $78,399,000 $1,876,801,014 21.39 Sunnyvale $104,153,879 $87,361,931 $8,604,000 $200,119,810 0.39 Unincorporated
County $2,611,823,403 $1,557,860,929 $220,905,000 $4,390,589,332 17.90 Total $14,104,940,226 $7,925,519,558 $1,114,983,000 $23,145,442,784 4.72 Table 112: Acreage in Moderate to High Landslide Hazard Areas Jurisdiction
Moderate to High Hazard Area
Area (acres) % of Total
Campbell 143.29 3.7%
Cupertino 2616.51 36.3%
Gilroy 3880.9 36.6%
Los Altos 247.32 5.9%
Los Altos Hills 2321.63 40.0%
Los Gatos 2954.63 39.6%
Milpitas 1572.02 18.1%
Monte Sereno 222 21.4%
Morgan Hill 1996.03 24.2%
Mountain View 105.14 1.3%
Palo Alto 4605.85 27.7%
San José 24693.71 21.3%
Santa Clara (city) 121.54 1.0%
Saratoga 2999.47 36.7%
Sunnyvale 144.7 1.0%
Unincorporated County 457938.24 75.9%
Total 506562.98 60.7%

14.4.3 Critical Facilities and Infrastructure
Table 113 summarizes critical facilities exposed to the landslide hazard in moderate, high, and very high risk areas. No loss estimation of these facilities was performed due to the lack of established damage functions for the landslide hazard. A significant amount of infrastructure, under the Infrastructure Lifeline category, can be exposed to mass movements:

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 Roads: Access to major roads is crucial after a disaster event. Landslides can block roads, causing neighborhood isolation and transportation delays. This can result in economic losses for businesses.
 Bridges: Landslides can damage road bridges. Mass movements can knock out bridge abutments or significantly weaken the soil supporting them, making them hazardous for use.  Power Lines: Power lines are generally elevated above steep slopes; but the towers supporting them can be subject to landslides. A landslide could trigger failure of the soil underneath a tower, causing it to collapse and ripping down the lines.

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Table 113: Critical Facilities and Infrastructure in Moderate to Very High Landslide Risk Areas Jurisdiction Essential Facilities Transportation Utilities Community Assets
Hazardous
Materials Total
Campbell 0 5 0 1 0 6
Cupertino 0 10 0 2 0 12
Gilroy 0 0 0 1 0 1
Los Altos 1 3 0 0 0 4
Los Altos Hills 2 10 0 0 0 12
Los Gatos 3 12 0 0 0 15
Milpitas 0 5 0 0 0 5
Monte Sereno 0 0 0 0 0 0
Morgan Hill 1 1 0 0 0 2
Mountain View 0 9 0 0 0 9
Palo Alto 0 5 1 3 0 9
San José 11 110 1 10 0 132
Santa Clara (city) 0 11 0 1 0 12
Saratoga 5 14 0 3 0 22
Sunnyvale 0 2 0 0 0 2
Unincorporated County 12 73 4 30 0 119
Total 35 269 6 49 0 359

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14.4.4 Environment
Environmental problems as a result of mass movements can be numerous. Landslides that fall into streams may significantly impact fish and wildlife habitat, as well as affecting water quality. Hillsides that provide wildlife habitat can be lost for prolong periods of time due to landslides. Some habitat types support more diverse species than others. In California, riparian areas contain the greatest diversity of species. For an area such as Santa Clara County, where steeps slopes, landslide potential, and other related geologic hazards are prevalent, erosion control is important to minimize the related adverse effects of a mass-movement event.289F
290

14.5 Vulnerability
Change in conditions: Increase in vulnerability
 As shown in section 14.2.1, an increasing number of landslide events have been documented since 2017.
 There has been a recent increase in the number of heavy rainfall events. Increased precipitation contributes to saturated soils which may stimulate landslide movement.  Landslide risk is highest in the foothills. Roads here are often narrow, or may have limited access such as dead-end spur roads. This makes ingress and egress difficult if roadways become blocked by slides.

14.5.1 Population
All of the estimated 91,379 persons exposed to high landslide risk areas are considered to be vulnerable.

Los Altos Hills, Los Gatos, and Saratoga have the highest percentage of population residing in areas at high risk to landslides. Increasing population and the fact that many homes are built on view property atop or below bluffs and on steep slopes subject to mass movement, increases the number of lives endangered by this hazard. Landslides losses don’t tend to be as heavily felt by socially vulnerable populations as other hazards. Everyone that lives in high-risk areas is at risk. There has been little research on human vulnerability to landslide as most research focuses on structural vulnerability however, some studies suggest that human behavior can play an important role in predicting potential losses.290F
291 While the size and timing of some landslides mean that injury or death is highly likely, advanced warning and immediate action (such as moving to a higher floor) can sometimes make all the difference. Education and outreach could help mitigate this risk to the public.

Some landslides onset too quickly for protective action to be taken, which can affect all demographic groups. However, residents who are older, those who are young, those who are visually or hearing impaired, or those who have mobility difficulties due to physical impairments may be particularly at risk to landslide. In cases where warning time is possible prior to a landslide, people with limited English proficiency may have difficulty receiving or understanding warning from a television, radio emergency warning system or cell phone alert to take appropriate action. 290 County of Santa Clara. (1994). Santa Clara County General Plan. https://stgenpln.blob.core.windows.net/document/GP_Book_A.pdf 291 Pollock, W. & Wartman, J. (2020, October 4). Human Vulnerability to Landslides. National Library of Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7567151/

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14.5.2 Property
Although complete historical documentation of the landslide threat in the OA is lacking, the mountainous terrain surrounding the Santa Clara Valley indicates potential for landslides. Loss estimations for the landslide hazard are not based on modeling utilizing damage functions, because no such damage functions have been generated. Instead, loss estimates were developed representing 10 percent, 30 percent, and 50 percent of the replacement value of exposed structures. This allows emergency managers to select a range of economic impact based on an estimate of the percent of damage to the general building stock. Table 114 shows the general building stock loss estimates in the aggregate of all landslide risk areas.

Table 114: Loss Potential Based on All Building Stock in Aggregated Landslide Areas Jurisdiction Exposed Value
Estimated Loss Potential from Landslide
10% Damage 30% Damage 50% Damage
Campbell $229,928,440 $22,992,844 $68,978,532 $114,964,220 Cupertino $1,041,149,872 $104,114,987 $312,344,962 $520,574,936 Gilroy $692,922,903 $69,292,290 $207,876,871 $346,461,452 Los Altos $306,439,583 $30,643,958 $91,931,875 $153,219,792 Los Altos Hills $611,165,733 $61,116,573 $183,349,720 $305,582,867 Los Gatos $2,229,699,302 $222,969,930 $668,909,791 $1,114,849,651 Milpitas $448,737,984 $44,873,798 $134,621,395 $224,368,992 Monte Sereno $161,268,795 $16,126,880 $48,380,639 $80,634,398 Morgan Hill $1,022,016,903 $102,201,690 $306,605,071 $511,008,452 Mountain View $83,521,656 $8,352,166 $25,056,497 $41,760,828 Palo Alto $519,499,589 $51,949,959 $155,849,877 $259,749,795 San José $9,182,678,320 $918,267,832 $2,754,803,496 $4,591,339,160 Santa Clara
(city) $148,903,541 $14,890,354 $44,671,062 $74,451,771 Saratoga $1,876,801,014 $187,680,101 $563,040,304 $938,400,507 Sunnyvale $200,119,810 $20,011,981 $60,035,943 $100,059,905 Unincorporated
County $4,390,589,332 $439,058,933 $1,317,176,800 $2,195,294,666 Total $23,145,442,784 $2,314,544,278 $6,943,632,835 $11,572,721,392

14.5.3 Critical Facilities and Infrastructure
There are 398 critical facilities exposed to the landslide hazard to some degree. A more in-depth analysis of the mitigation measures taken by these facilities to prevent damage from mass movements should be done to determine if they could withstand impacts of a mass movement.

Several types of infrastructure are exposed to mass movements, including transportation, water and sewer and power infrastructure. Highly susceptible areas of the OA include mountain roads and transportation infrastructure. At this time all infrastructure and transportation corridors identified as exposed to the landslide hazard are considered vulnerable until more information becomes available.

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14.5.4 Environment
Landslides and other mass movements impact the environment through changing the earth’s topography; diverting or reducing the quality of rivers, streams, and groundwater; destroying forests and vegetation; and the destruction of natural habitats particularly around at-risk water bodies. Erosion from landslide can significantly degrade the potability water and its capacity to serve as a habitat for fish and other wildfire.

Landslides are difficult to predict. The environment most vulnerable to landslide hazard is the same as the environment exposed to the hazard.

14.6 Future Trends in Development
Santa Clara County has been one of the state’s fastest growing counties from 2010-2020, but more recently has experienced a decrease in population. It can be assumed the OA will continue to grow, though at a slower pace. Mass movements are becoming more of a concern as development moves outside of urban centers and into areas less developed in terms of infrastructure. The planning partners are equipped to handle future growth within landslide hazard areas. Landslide risk areas are addressed in the safety elements of local general plans. All planning partners have committed to linking their general plans to this hazard mitigation plan. This will create an opportunity for wise land use decisions as future growth impacts landslide hazard areas.

Additionally, the State of California has adopted the International Building Code (IBC) by reference in its California Building Standards Code. The IBC includes provisions for geotechnical analyses in steep slope areas that have soil types considered susceptible to landslide hazards. These provisions assure that new construction is built to standards that reduce the vulnerability to landslide risk. California real estate disclosure laws will also help ensure the public is aware of their risk.

14.7 Scenario
Major landslides could occur in the OA as a result of soil conditions that have been affected by severe storms, groundwater, or human development. The worst-case scenario for landslide hazards in the OA would generally correspond to a severe storm such which includes heavy rain and causes flooding in the OA. Landslides are most likely during late winter when the water table is high. After heavy rains from November to December, soils become saturated with water. As water seeps downward through upper soils that may consist of permeable sands and gravels and accumulates on impermeable silt, it will cause weakness and destabilization in the slope. As rains continue, the groundwater table rises, adding to the weakening of the slope. Gravity, poor drainage, a rising groundwater table and poor soil exacerbate hazardous conditions. An intense storm could cause saturated soil to move, resulting in landslides.

Continued heavy rains and flooding will complicate the problem further. As emergency response resources are applied to problems with flooding, it is possible they will be unavailable to assist with landslides occurring all over the OA. In this scenario, it is probable that private and public property, including infrastructure, could be affected. Members of the public could be injured or killed. Road obstructions caused by mass movements would create isolation problems for residents and businesses in sparsely developed areas. Mass movements could affect bridges that pass over landslide prone ravines and knock out rail service through the OA. Landslides carrying vegetation such as shrubs and trees may cause a break in utility lines, cutting off power and communication access to residents. The impacts to the immediate vicinity of a landslide would be severe while the impacts to the OA would depend on what public infrastructure, including transportation routes, are involved.

14.8 Issues
Important issues associated with landslides in the OA include the following:
 There are existing homes in landslide risk areas throughout the OA. The degree of vulnerability of these structures depends on the codes and standards the structures were constructed to.

Information to this level of detail is not currently available.

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 Future development could lead to more homes in landslide risk areas.  Mapping and assessment of landslide hazards are constantly evolving. As new data and science become available, assessments of landslide risk should be reevaluated.  The impact of climate change on landslides is uncertain. If climate change impacts atmospheric conditions, then exposure to landslide risks is likely to increase.  Landslides may cause negative environmental consequences, including water quality degradation.
 The risk associated with the landslide hazard overlaps the risk associated with other hazards such as earthquake, flood, and wildfire. This provides an opportunity to seek mitigation alternatives with multiple objectives that can reduce risk for multiple hazards.

Table 115: EMAP Consequence Analysis: Landslide/Mass Movement Subject  Ranking  Impacts/Landslide/Mass Movement
Public  Minimal to
moderate
The public is at risk from injury, loss of life, and loss of property from a landslide, debris flow, or other mass
movement event. Because of the localized nature of these events, the damage would be severe in the immediate
vicinity and less impactful further away from the site.

Responders  Minimal  Responders may be called upon in the event of a landslide/mass movement event. They may be asked to
assess the situation, rescue survivors, divert traffic, and manage the overall incident.

During the course of their duties, they may be exposed to an increased risk of personal injury. Responders
responding to another hazard event could also be at risk from a landslide caused by an event like an earthquake’s aftershock or flood.

Continuity of
Operations (including
continued delivery of
services)
Minimal to
moderate
Continuity of operations and continued delivery of
services would depend on if a facility was in the
immediate vicinity of the landslide/mass movement event.

There also may be transportation delays if key roadways are impacted.

Property, Facilities, and
Infrastructure
Minimal to
severe
Landslides are a serious hazard to property, facilities, and infrastructure. They can result in damage and destruction to property through the destruction of foundations, offset of roads, destruction of bridges, breaking of underground pipes, or overriding of downslope property and structures.

Environment  Minimal to
moderate
Landslides and other mass movement events can alter
the earth’s topography, change water courses and water
quality, remove forests and vegetation, destroy natural habitats, and cause erosion. Landslide areas are prone to repeated slides.

Economic Conditions  Minimal to
moderate
Impacts to the economy will depend on the location of the event. Disruptions to impacted facilities, critical
infrastructure, or transportation routes could have a longterm effect on the local economy.

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Subject  Ranking  Impacts/Landslide/Mass Movement
Public Confidence in
the Government
Minimal to
severe
The public’s confidence will depend on the government’s ability to manage and properly message the event.

Prompt and accurate information will influence public
trust.

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15 Tsunami
Definitions
 Tsunami: A series of traveling ocean waves of extremely long wavelength usually caused by displacement of the ocean floor and typically generated by seismic or volcanic activity or by underwater landslides.
 Seiche: A standing wave in an enclosed or partially enclosed body of water such as bays and lakes. Seiches are typically caused when strong winds and rapid changes in atmospheric pressure or an earthquake push water from one end of a body of water to the other.

15.1 General Background

15.1.1 Tsunami
A tsunami consists of a series of high-energy waves that radiate outward like pond ripples from an area where a generating event occurs. Earthquakes may produce displacements of the sea floor that can set the overlying column of water in motion, initiating a tsunami, depending on the magnitude of the earthquake and the type of faulting. Landslides, including from glaciers melting, and underwater volcanos are also sources of these events.

Tsunamis are typically classified as local or distant. Locally generated tsunamis have minimal warning times, leaving few options except to relocate to high ground. They may be accompanied by damage resulting from the triggering earthquake due to ground shaking, surface faulting, liquefaction, or landslides.

Distant tsunamis may travel for hours before striking a coastline, giving a community a chance to implement evacuation plans. In the open ocean, a tsunami may be only a few inches or feet high, but it can travel with speeds approaching 600 miles per hour. Tsunami waves arrive at shorelines over an extended period. Figure 70 shows likely travel times across the Pacific Ocean for a tsunami generated along the California coastline near the San Francisco Bay Area.

As a tsunami enters the shoaling waters near a coastline, its speed diminishes, its wavelength decreases, and its height increases greatly. The first wave usually is not the largest. Several larger and more destructive waves often follow the first one. As tsunamis reach the shoreline, they may take the form of a fast-rising tide, a cresting wave, or a bore (a large, turbulent wall-like wave). The bore phenomenon resembles a step-like change in the water level that advances rapidly (from 10 to 60 miles per hour).

The configuration of the coastline, the shape of the ocean floor, and the characteristics of advancing waves play important roles in the destructiveness of the waves. Offshore canyons can focus tsunami wave energy and islands can filter the energy. The orientation of the coastline determines whether the waves strike head-on or are refracted from other parts of the coastline. A wave may be small at one point on a coast and much larger at other points. Bays, sounds, inlets, rivers, streams, offshore canyons, islands, and flood control channels may cause various effects that alter the level of damage. It has been estimated, for example, that a tsunami wave entering a flood control channel could reach a mile or more inland, especially if it enters at high tide.

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The first visible indication of an approaching tsunami may be recession of water (draw down) caused by the trough preceding the advancing, large inbound wave crest. Rapid draw down can create strong currents in harbor inlets and channels that can severely damage coastal structures due to erosive scour around piers and pilings. As the water’s surface drops, piers can be damaged by boats or ships straining at or breaking their mooring lines. The vessels can overturn or sink due to strong currents, collisions with other objects, or impact with the harbor bottom.

Figure 71: Potential Tsunami Travel Times in the Pacific Ocean, In Hours291 F 292
Conversely, the first indication of a tsunami may be a rise in water level. The advancing tsunami may initially resemble a strong surge increasing the sea level like the rising tide, but the tsunami surge rises faster and does not stop at the shoreline. Even if the wave height appears to be small, 3 to 6 feet for example, the strength of the accompanying surge can be deadly. Waist-high surges can cause strong currents that float cars, small structures, and other debris. Boats and debris are often carried inland by the surge and left stranded when the water recedes.

At some locations, the advancing turbulent wave front will be the most destructive part of the wave. In other situations, the greatest damage will be caused by the outflow of water back to the sea between crests, sweeping all before it and undermining roads, buildings, bulkheads, and other structures. This outflow action can carry enormous amounts of highly damaging debris with it, resulting in further destruction. Ships and boats, unless moved away from shore, may be dashed against breakwaters, wharves, and other craft, or be washed ashore and left grounded after the withdrawal of the seawater. 292 National Oceanic and Atmospheric Administration. (n.d.). Estimated Tsunami Travel Times to Coastal Locations. https://www.ncei.noaa.gov/maps/ttt_coastal_locations/

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15.1.2 Seiche
A seiche is a standing wave in an enclosed or partially enclosed body of water, such as San Francisco Bay.

Seiches are typically caused when strong winds and rapid changes in atmospheric pressure or an earthquake push water from one end of a body of water to the other. The largest seiche that was ever measured in the San Francisco Bay, following the 1906 earthquake, was 4 inches high. The Bay Area has not been adversely affected by seiches.29F
293 However, the OA may see seiches on creeks if there was a local earthquake event. These kinds of seiches could have devastating environmental impacts.

15.2 Hazard Profile

15.2.1 Past Events
According to the 2023 California State Hazard Mitigation Plan,293F 294 over 80 tsunamis have been observed
or recorded along the coast of California in the past 150 years. The National Centers for Environmental Information294F
295 has recorded the California coastline being impacted by tsunami wave events on six dates since 2005: November 15, 2006, February 27, 2010, March 11, 2011, September 16, 2015, January 1, 2022, and January 15, 2022. Together these events caused approximately $55 million in property damage and cost one life. The Santa Clara County OA has never been impacted by a tsunami. The closest tsunami to affect the OA was the tsunami event on March 10, 2011, that occurred in Japan and traveled across the Pacific Ocean to create wave surges that damaged coastal areas in nearby Santa Cruz and Monterey Counties. These counties were included in FEMA-1968-DR-CA declaration. The largest impact of this tsunami experienced in the San Francisco Bay was at Berkeley Marina, where the tsunami caused about $50,000 in damages.

15.2.2 Location
Although the OA has not been significantly impacted by tsunami or seiche events before, the recent tsunamis due to disaster events around the world – including earthquakes and an underwater volcano eruption - has underscored how vulnerable the California coastline is to this type of hazard. Following these events, there have been a number of new studies and reports expanding on the State of California’s understanding of its exposure to tsunami risk. Cal OES, in conjunction with the University of Southern California and FEMA, developed Tsunami Hazard Areas Maps to assist cities and counties in identifying their tsunami hazard for tsunami response planning utilizing the best available scientific information. The risk areas are not defined in terms of human-created geographic features, however, according to the 2022 California Geological Survey Tsunami Hazard Area Map295 F 296 – County of Santa
Clara, approximately the area of the OA around the San Francisco Bay including parts of Sunnyvale, San José, Palo Alto, and Mountain View are in the Tsunami Hazard Area.

While only a relatively small portion of the OA may be directly impacted by a tsunami wave, additional tsunami impacts could be felt in the OA along area creeks that would rise with floodwaters from a San Francisco Bay tsunami caused by a local earthquake.
293 Alameda County Community Development Agency. (2022, March 17). Safety Element of the Alameda County General Plan. https://www.acgov.org/cda/planning/generalplans/documents/SafetyElementupdateapprovedbyBOS31722-FINAL.pdf 294 California Office of Emergency Services. (2023). Hazard Mitigation Planning. https://www.caloes.ca.gov/office-ofthe-director/operations/recovery-directorate/hazard-mitigation/state-hazard-mitigation-planning/ 295 National Centers for Environmental Information. (n.d.). Storm Events Database. https://www.ncdc.noaa.gov/stormevents/
296 California Department of Conservation. (2022, October 7). California Tsunami Maps and Data. https://www.conservation.ca.gov/cgs/tsunami/maps

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Figure 71 shows potential tsunami inundation areas on the southern portion of the San Francisco Bay and Coyote Creek, which is the northern portion of the Santa Clara County OA.

Figure 72: Tsunami Hazard Area

15.2.3 Frequency
The frequency of tsunamis is related to the frequency of the events that cause them, so it is similar to the frequency of seismic, volcanic activities, or landslides around the Pacific Basin. Generally, four or five tsunamis occur every year in the Pacific Basin.

It is unclear what impact future conditions such as climate change may have on the frequency of tsunami events. It is possible that increased severe flood events, wildfires, and warming conditions could impact

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the frequency of landslides, which are one known sources of tsunamis. However, they make up only a relatively small percentage of the root causes of tsunamis. Earthquakes are the most common cause of tsunamis. Current data indicates that there is not a statistically significant impact of climate change as we know it on earthquakes. This doesn’t necessarily mean that climate change does not have impact.

Current science may simply lack the capability to distinguish a direct correlation between these hazards.

For example, earthquakes can be triggered by changes to the amount of stress on a fault. According to NASA’s Jet Propulsion Laboratory at the California Institute of Technology, changing conditions, such as surface water levels, due to hazards such as flooding and droughts may impact earthquakes, but we have no way of knowing by how much. It is unlikely that the OA would notice a significant change in the frequency of tsunami events due to climate change.

Further information on the impact of climate change on the probability of tsunamis is included in Section 11.

Probability in OA: Unlikely

15.2.4 Severity
Tsunamis are a threat to life and property to anyone living or visiting near the ocean. The full extent of a tsunami event can be severe, and is often measured by magnitude, similar to earthquakes. The higher the magnitude, the more severe and destructive the tsunami may be.

From 1950 to 2007, 478 tsunamis were recorded globally. Fifty-one of these events caused fatalities, to a total of over 308,000 coastal residents. The overwhelming majority of these events occurred in the Pacific basin. Recent tsunamis have struck Nicaragua, Indonesia, and Japan, killing several thousand people.

Property damage due to these waves was nearly $1 billion. The San Francisco Bay faces the greatest threat from distant tsunamis originating in areas such as Alaska, Washington, and Japan.

It is general consensus that the Santa Clara County OA would not likely see significant impacts from a tsunami originating in the Pacific Ocean, given the area’s primarily inland location. The extent of the damage would be limited to the immediate area. Boats, docks, and property near the bay may suffer some impacts if they were to be hit directly. Additionally, the OA would likely see minor tsunami impacts on creeks from a local earthquake event, with any floodwaters flowing up creeks impacting people visiting the creeks. A local earthquake tsunami can occur any time, and the resulting floodwater waves can carry damaging debris.

Some studies suggest that future conditions such as climate change are likely to increase the severity of tsunamis. Sea-level rise is one of the main reasons why. These additional impacts will most severely be experienced in low-elevation Pacific islands however, all coastal communities are at risk of the dangers associate with sea-level rise. Scientists studying the probability of an Alaska-Aleutian subduction zone earthquake and the subsequent impact to southern California supported the conclusion that rising sea levels can increase tsunami impacts. If the sea continues to rise as predicted, someday the impacts of a small tsunami will be similar to a large tsunami of today. The risk to the OA may change over time.

15.2.5 Warning Time
Typical signs of a tsunami hazard are earthquakes and/or sudden and unexpected rise or fall in coastal water. The large waves are often preceded by coastal flooding and followed by a quick recession of the water. Tsunamis are difficult to detect in the open ocean; with waves less than 3 feet high. The tsunami’s size and speed, as well as the coastal area’s form and depth, affect the impact of a tsunami; wave heights of 50 feet are not uncommon. In general, scientists believe it requires an earthquake of at least a magnitude 7 to produce a tsunami.

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The Pacific tsunami warning system evolved from a program initiated in 1946. It is a cooperative effort involving 26 countries along with numerous seismic stations, water level stations and information distribution centers. The National Weather Service296 F 297 operates two regional information distribution
centers. One is located in Ewa Beach, Hawaii, and the other is in Palmer, Alaska. The Ewa Beach center also serves as an administrative hub for the Pacific warning system.

The warning system only begins to function when a Pacific basin earthquake of magnitude 6.5 or greater triggers an earthquake alarm. When this occurs, the following sequence of actions occurs:
 Data is interpolated to determine epicenter and magnitude of the event.  If the event is magnitude 7.5 or greater and located at sea, a TSUNAMI WATCH is issued.  Participating tide stations in the earthquake area are requested to monitor their gages. If unusual tide levels are noted, the tsunami watch is upgraded to a TSUNAMI WARNING.  Tsunami travel times are calculated, and the warning is transmitted to the disseminating agencies and thus relayed to the public.
 The Ewa Beach center will cancel the watch or warning if reports from the stations indicate that no tsunami was generated or that the tsunami was inconsequential.

This system is not considered to be effective for communities located close to the tsunami because the first wave would arrive before the data were processed and analyzed. In this case, strong ground shaking would provide the first warning of a potential tsunami.

15.2.6 Extent
The extent of Tsunami can be measured through the new tsunami intensity scale which was proposed by Papadopoulos and Imamura in 2001. This intensity scale defines the ranges of anticipated intensities of Tsunami as:

Table 116: Tsunami Intensity Scale297F
298
Category Description
I. Not Felt a) Not felt even under the most favorable
circumstances.
b) No effect.
c) No damage.

II. Scarcely Felt a) Felt by a few people on board in small vessels.

Not observed in the coast.
b) No effect.
c) No damage.

III. Weak a) Felt by most people on board in small vessels.

Observed by a few people in the coast.
b) No effect.
c) No damage.
297 National Weather Service. (n.d.). Pacific Tsunami Warning Center. https://www.tsunami.gov/?page=history 298 UNESCO. (n.d.) The New Tsunami Intensity Scale. https://neamtic.ioc-unesco.org/images/Neamtic/PDF/intensityscale.pdf

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Category Description
IV. Largely Observed a) Felt by all on board in small vessels and by few people on board in large vessels.
b) Few small vessels move slightly onshore.
c) No damage.

V. Strong a) Felt by all on board in large vessels and
observed by all in the coast. Few people are
frightened and run to higher ground.
b) Many small vessels move strongly onshore, few
of them crash each other or overturn. Traces of
sand layer are left behind in grounds of favorable
conditions. Limited flooding of cultivated land.
c) Limited flooding of outdoor facilities (e.g.
gardens) of near-shore structures.

VI. Slightly Damaging a) Many people are frightened and run to higher ground.
b) Most small vessels move violently onshore, or
crash strongly into each other, or overturn.
b) Damage and flooding in a few wooden
structures. Most masonry buildings withstand.

VII. Damaging a) Most people are frightened and try to run in higher ground.
b) Many small vessels damaged. Few large vessels
oscillate violently. Objects of variable size and
stability overturn and drift. Sand layer and
accumulations of pebbles are left behind. Few
aquaculture rafts washed away.
c) Many wooden structures damaged, few are
demolished or washed away. Damage of grade 1
and flooding in a few masonry buildings.

VIII. Heavily Damaging a) All people escape to higher ground, a few are washed away.
b) Most of the small vessels are damaged, many
are washed away. Few large vessels are moved
ashore or crashed each other. Big objects are
drifted away. Erosion and littering in the beach.

Extensive flooding. Slight damage in tsunami
control forest, stop drifts. Many aquaculture rafts
washed away, few partially damaged.
c) Most wooden structures are washed away or
demolished. Damage of grade 2 in a few masonry
buildings. Most RC buildings sustain damage, in a
few damage of grade 1 and flooding is observed.

IX. Destructive a) Many people are washed away.
b) Most small vessels are destroyed or washed
away. Many large vessels are moved violently
ashore, few are destroyed. Extensive erosion and
littering of the beach. Local ground subsidence.

Partial destruction in tsunami control forest, stops
drifts. Most aquaculture rafts washed away, many
partially damaged.
c) Damage of grade 3 in many masonry buildings,
few RC buildings suffer damage grade 2.

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Category Description
X. Very Destructive a) General panic. Most people are washed away. b) Most large vessels are moved violently ashore,
many are destroyed or collided with buildings.

Small boulders from the sea bottom are moved
inland. Cars overturned and drifted. Oil spill, fires
start. Extensive ground subsidence.
c) Damage of grade 4 in many masonry buildings,
few RC buildings suffer damage grade 3. Artificial
embankments collapse, port water breaks
damaged.

XI. Devastating Lifelines interrupted. Extensive fires. Water backwash drifts cars and other objects in the sea.

Big boulders from the sea bottom are moved
inland. Damage of grade 5 in many masonry
buildings. Few RC buildings suffer damage grade
4, many suffer damage grade 3.

XII. Completely Devastating Practically all masonry buildings demolished. Most RC buildings suffer at least damage grade 3.

15.3 Cascading Impact
One additional direct impact a tsunami wave may have on the Santa Clara County OA is through floating debris that can cause damage to any affected areas. The removal of this debris would also take OA time and resources.

Another cascading hazard includes tsunami-triggered fires. This refers to fires that burn after a tsunami event in spilled oil, debris, cargo, vehicles, vegetation as well as residential, commercial, or industrial buildings. These fires could result in injury, death, damage, and contamination of the environment by releasing potentially toxic gases and smoke into the air.

Inundation of wastewater treatments plants, three out of four which sit close to the mapped Tsunami Inundation Area, would also be of concern. This could release raw sewage, waste chemicals, and chemicals used in the treatment of wastewaters into the OA.

15.4 Exposure and Vulnerability
Changes in conditions: no change in vulnerability
 No changes in conditions leading to the occurrence of a tsunami have changed.  Development is not taking place in the potential tsunami hazard, so vulnerability is not increasing.

15.4.1 Population
The population of the Santa Clara County OA is located outside of a tsunami inundation area; therefore, no population exposure exists for the tsunami hazard. No residential properties were identified in the potential tsunami evacuation zone. Minimal risk may be present to employees or recreational visitors to the two parks in the area.

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15.4.2 Property
Based on the National Structure Inventory, 14 commercial buildings and 2 industrial buildings are potentially vulnerable to tsunami. These buildings have a total value of $6.7 million. Limited additional information is currently available about these facilities to determine additional impacts.

15.4.3 Critical Facilities and Infrastructure
Critical facilities and infrastructure in the Santa Clara County OA that are located within the tsunami inundation area include 5 ports, 3 railroad bridges, 4 highway bridges, 2 parks, and 1 open space.

Port location data was obtained from Hazus but little additional information about the function or these facilities and potential impacts from interruption or loss of operation. Two highway bridges are located on McCarthy Blvd near the northern border of Milpitas and San Jose. These are located near the outer edge of the potential inundation area and alternative routes are nearby. Another is located in Mountain View, also on the outer-most edge of the hazard area where alternate routes are available. A forth is in San Jose in the Alviso area, across the Guadalupe River which also has alternate routes. Two of the Southern Pacific railway bridges are also in the Alviso area, which is near the outer edge of the hazard zone. However, one bridge on this rail line is located closer to the shoreline and may experience more severe effects from a tsunami.

15.4.4 Environment
Waterways originating from southern portion of San Francisco Bay would be exposed to the effects of a tsunami or seiche; inundation of water and introduction of foreign debris could be hazardous to the environment. All wildlife inhabiting the area is exposed. Erosion and the destruction of naturally occurring marine habitats would be a concern. All of San Francisco Bay is in the Tsunami Hazard Area. The vulnerability of aquatic habit and associated ecosystems would be highest in low-lying areas close to the southern portion of San Francisco Bay coastline.

Tsunami waves and seiches can carry destructive debris and pollutants that can have devastating impacts on all facets of the environment. Millions of dollars spent on habitat restoration and conservation in the OA could be wiped out by one significant tsunami. There are currently limited tools available to measure these impacts. However, it is conceivable that the potential financial impact of a tsunami or seiche event on the environment could equal or exceed the impact on property. Community planners and emergency managers should take this into account when preparing for the tsunami hazard and considering future development.

15.5 Future Trends in Development
Land along the coast in the OA which could be impacted by a tsunami is primarily already developed or preserved as green space. Most of the land is classified as parks, including CPAD open space, Williamson Act parcels, and conservation easements according to the Plan Bay Area 2050. Additionally, the Tsunami Hazard Area in the OA is within flood hazard areas that are already regulated under floodplain management regulations. However, current FEMA flood maps do not consider tsunami flood risk. Additional data is needed to understand tsunami risk. FEMA has produced the website, “Thinking Beyond Flood Maps – Using FEMA’s Coastal Data to Reduce Risk and Build Resilience” as well as other non-regulatory products to support coastal communities’ development. FEMA also participates in the National Tsunami Hazard Mitigation Program (NTHMP), which is administered by NOAA. The NTHMP works to reduce the impacts of tsunamis through collaboration, communication, and financial and technical support. The Mitigation and Education component provides recommendations to reduce tsunami risk. Additionally, NOAA, through the National Weather Service, sponsors the NWS TsunamiReady Program which helps communities minimize the risk posed by tsunamis through better

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risk assessment, planning, education, and early warning systems. Resources like these provide planning partners and developers with the tools needed to ensure any future development is at reduced risk from tsunami events.

15.6 Scenario
The worst-case scenario that may directly impact the OA is a local tsunami or seiche event originating in the San Francisco Bay triggered by a seismic event. This event could occur anytime and could be particularly severe given the limited warning time. There is potential for loss of life and injury. Property and business in the Tsunami Hazard Area could impacted. The series of floodwater waves that would occur would carry damaging debris and cause environmental impacts deep into the OA. These environmental impacts may be the longest impacts felt after the event, particularly if complex debris, crude oil, legacy contaminants, or other pollutants get into the nearby coastal marine environments or onshore. This could potentially have a long-term impact on the immediate local economy.

The largest kind tsunami event that may indirectly impact the OA would be a catastrophic earthquake and tsunami along one of the faults near California. For example, in anticipation of a full rupture along the 800-mile-long Cascadia Subduction Zone (CSZ) which lies off the northwest coast of the United States, the State of California is preparing for impacts of a magnitude 9.0 earthquake and the resulting tsunami waves, aftershocks, and flooding. Historical evidence suggests that an event of this magnitude will occur within the next 200 years. It is assumed this will be a “no-notice” event. If the CSZ experiences a full fault rupture, it will have a significant impact on surrounding areas, including other counties, states, and countries. According to the California Cascadia Subduction Zone Earthquake and Tsunami Response Plan, there may be over a thousand deaths, 1,500 injured, and 28,000 structures damaged or destroyed in northern coastal California alone. The cascading impacts of this event would also be substantial. It can be assumed if this were to occur, there would be an immediate need for support from first responders, volunteers, NGOS, and public health and medical services from outside the affected area. The 20 hospitals in Santa Clara County and mass care sheltering venues would need to be prepared to support survivors, including the injured. There would also be a noticeable impact to the daily life of OA residents, including potential disruption to critical infrastructure such as transportation, energy, telecommunications, utility systems, and public health and medical systems. The region, the State, and the Nation may face long-term economic repercussions.

The Science Application for Risk Reduction (SAFRR) Tsunami Scenario298F 299 includes additional information
on potential tsunami scenarios on the California pacific coast. This, and other resources, were consulted when developing the consequence analysis in Table 117: EMAP Consequence Analysis: Tsunami.

15.7 Issues
Important issues associated with tsunamis in the OA include the following:
 As tsunami warning technologies evolve, the tsunami warning capability within the OA will need to be enhanced to provide the highest degree of warning.
 With the possibility of climate change, the issue of sea level rise may become an important consideration as probable tsunami inundation areas are identified through future studies.

Special attention will need to be focused on the vulnerable communities in the tsunami zone and on hazard mitigation through public education and outreach. 299 U.S. Geological Survey. (2013). The SFARR Tsunami Scenario. https://www.usgs.gov/publications/safrr-scienceapplication-risk-reduction-tsunami-scenario

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Table 117: EMAP Consequence Analysis: Tsunami
Subject Ranking Impacts/Tsunami
Public Minimal to
Moderate
Home and property owners within the Tsunami Hazard
Area are most at risk of impacts from a tsunami event.

Impacts to the public include potential for injury or loss of life, destruction and or/loss of lands and property, and contamination of water due to flooding. Flood water can pose health risks even after the initial wave. Post-tsunami cleanup would also have to be done appropriately to
reduce exposure to pollutants in water, debris, and moldy structures. Educating the public in advance on their
tsunami risk and ways to mitigate their risk will enhance the public’s ability to respond and recover.

Responders Minimal First responders, such as fire and police, would be relied upon to respond to this event. The impact on responders is expected to be minimal with proper training. The impact could be severe if there is a lack of training. It is important responders are aware and on the lookout for the
secondary effects of tsunamis.

Continuity of
Operations (including
continue delivery of
services)
Minimal Temporary relocation may be necessary in the unlikely event inundation affects government facilities. Delivery of services could be impacted if there is any disruption to the roads and/or utilities due to the inundation.

Property, Facilities, and
Infrastructure
Minimal to
moderate
Potential damages include damage or loss of properties, temporary impacts to transportation routes, debris build up, and potential stormwater system and wastewater
overload. Communication systems could also be limited.

The localized impact could be significant for facilities and infrastructure in the inundation area of the incident. The farther away from the incident area, the more likely the damage will lessen, from moderate to minimal.

Environment Minimal to
severe
The impact to the environment could be severe,
depending on the size and unique characteristics of a
tsunami. There may be significant and complicated debris removal required including a diverse array of pollutants spilling into the environment. Marine habitats may be
damaged by contaminants, which may have a short or
long-term impact on the environment and health of the
coastal ecosystem. The shoreline may erode. The
environmental impacts may not be limited to waterways.

Debris, toxins, airborne ash after a tsunami-related fire, and more could enter the surrounding land and air.

Economic Conditions Minimal to
severe
Impacts on the economy will greatly depend on the scope of the inundation and the amount of time it takes for the water to recede as well as any leftover debris or
contaminants. Secondary hazards experienced will also
impact the economy’s recovery. Industries such as fishing, tourism, and environmental recreation may experience
more significant impacts.

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Subject Ranking Impacts/Tsunami
Public Confidence in
the Government
Minimal to
severe
The public’s confidence will vary, depending on the
perception of whether the failure could have been
prevented, the warning time, and the time it takes for
response and recovery. Proactive preparation in advance of a tsunami event and effectively implementing response plans will support confidence in government.

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16 Other Hazards of Interest
Definitions
 Terrorism: The unlawful use or threatened use of force or violence against people or property with the intention of intimidating or coercing societies or governments. Terrorism is either foreign or domestic, depending on the origin, base, and objectives of the terrorist or organization.  Weapons of Mass Destruction: Chemical, biological, radiological, nuclear, and explosive weapons associated with terrorism.
 Active Threat: An active threat is a situation involving an individual or individuals using or threatening to use deadly physical force on others in a confined and populated area.  Cyber Threat: Any circumstance or event with the potential to adversely impact organizational operations (including mission, functions, image, or reputation), organizational assets, or individuals through an information system via unauthorized access, destruction, disclosure, modification of information, and/or denial of service.
 Technological Hazards: Hazards from accidents associated with human activities such as the manufacture, transportation, storage, and use of hazardous materials.  Epidemic/Pandemic: An epidemic is a sudden increase in the number of cases of a disease above what is normally expected in that population in a specific area. A pandemic is an epidemic that occurs over a broad geographic region, usually nationally or globally.  Fog: visible cloud water droplets that are low-lying and influenced by nearby bodies of water, topography, and wind conditions.

16.1 General Background
In addition to the hazards of concern presented in the preceding sections, four other hazards of interest, which were addressed in the 2017 Plan, are also included in this MJHMP:

1. Intentional criminal, malicious acts, including acts of terrorism, cyber threats, and active threats.

2. Technological incidents that arise accidentally from human activities such as the manufacture, transportation, storage, and use of hazardous materials; transportation accidents; pipeline failure and release; and utility failure.

3. Epidemics and pandemics of human disease.

4. Fog
Although they may not be traditionally profiled in hazard mitigation plans like some of the other hazards in the plan, they are included for the following reasons:
 This plan takes a proactive approach to disaster preparedness to protect the public safety of all citizens.
 Preparation for and response to an event involving these hazards of interest will involve many of the same staff, critical decisions, and commitment of resources as a natural hazard.  The multi-hazard mitigation planning effort is an opportunity to inform the public about all hazards, including those beyond the natural hazards of concern.
 The likelihood of an event involving one of these hazards of interest in the Santa Clara County OA is greater than some of the identified natural hazards in this plan.

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The sections below provide short profiles of each of the four other hazards of interest. No formal risk assessment was performed and mitigation actions for these hazards are not mandatory under 44 CFR Section §201.6(c)(2)(i). The “Identified Needs” identified at the end of this section shall serve in the place of a formal action plan. All planning partners for the MJHMP should be aware of these hazards and take steps to reduce the risks they present whenever it is practical to do so.

16.1.1 EMAP Consequence Analysis
The planning team decided to include one comprehensive analysis for all of the other hazards of interest. The analysis results are provided in Table 118.

Table 118: EMAP Consequence Analysis: Other Hazards of Interest Subject Ranking Impacts
Public Severe
Impact of the immediate area could be severe, especially in the event of intentional hazards. Impact for less affected areas could be moderate to light.

Responders Severe
Impact to responders could be severe for unprotected
personnel and moderate to light for prepared personnel. In the event of some hazards, responders may be specifically targeted.

Continuity of Operations
(including continued
delivery of services)
Moderate
There is some expectation of execution of the COOP. This will vary depending on the severity of the event. Services may need to be conducted at a secondary and secure
location.

Property, Facilities, and
Infrastructure Severe
Critical facilities are often targeted, making impacts
potentially severe. Utilities, technology, transportation systems, and infrastructure are most likely to be damaged or impacted.

Environment Severe
Surrounding environment of targeted or impacted areas can be severe. The greatest impact will be to trees, bushes, foliage, crops, and wildlife.

Economic Conditions Minimal to
Severe
Impacts to the economy will greatly depend on the severity of the event, and any damages sustained such as utilities and roads. In a localized event damages may be minimal, but economic impacts can become severe when the event is more widespread.

Public Confidence in the
Government
Minimal to
Severe
Response and recovery will be in question if not timely and effective.

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16.2 Intentional Hazards

16.2.1 Terrorism and Weapons of Mass Destruction
Terrorist activities are those that involve an illegal use of force or violence against people and property in violation of criminal laws of the United States with the intent to intimidate, coerce, or ransom. FEMA states that acts of terrorism include the use of weapons of mass destruction, including biological, chemical, nuclear, and radiological weapons; arson, incendiary, explosive and armed attacks; industrial sabotage and intentional hazardous materials releases; agro-terrorism; and cyber-terrorism29F 300. The threat
of violence is also a component of terrorism. The following are potential methods used by terrorists that could affect the Santa Clara OA as a direct target or collaterally:
 Bombings; improvised explosive devices  Conventional firearms/mass shootings  Suicide attacks  Secondary attacks
 Chemical or biological weapons  Cyber-terrorism
 Radiological dispersal device  Agro-terrorism
 Vehicle/aircraft attacks  Kidnappings/assassinations  Conventional firearms/mass shootings  Nuclear weapons (fission or thermonuclear)
The Federal Bureau of Investigation (FBI) categorizes two types of terrorism in the United States30F 301:
 International Terrorism: Violent, criminal acts committed by individuals and/or groups who are inspired by, or associated with, designated foreign terrorist organizations or nations (statesponsored).  Domestic Terrorism: Violent, criminal acts committed by individuals and/or groups to further ideological goals stemming from domestic influences, such as those of a political, religious, social, or environmental nature.

The effects of terrorism can include injuries, loss of life, property damage, or disruption of services such as electricity, water supplies, transportation, or communications. Effects may be immediate or delayed.

Terrorists often choose targets that offer limited danger to themselves and areas with relatively easy public access. Foreign terrorists look for visible targets where they can avoid detection before and after an attack, such as international airports, large cities, major special events, and high-profile landmarks.

Cal OES and local governments have identified high profile targets for potential terrorists within their jurisdictions. Large business centers, high visibility tourist attractions, transportation providers, and critical infrastructure in Santa Clara County may become a target for terrorism and can present security challenges of an ongoing nature. Multiple incidents can happen simultaneously, and typically require a multi-agency, multijurisdictional response.
300 FEMA. (n.d.) Terrorism.
https://www.fema.gov/pdf/areyouready/terrorism.pdf#:~:text=Terrorism%20is%20the%20use%20of%20force%20or% 20violence,States%20for%20purposes%20of%20intimidation%2C%20coercion%2C%20or%20ransom. 301 Federal Bureau of Investigation. (n.d.) Terrorism. https://www.fbi.gov/investigate/terrorism

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Those involved with terrorism response, including law enforcement, fire and rescue, public health and public information staff, are trained to deal with the public’s emotional reaction swiftly as response to the event occurs. The area of the event must be clearly identified in all emergency alert messages to prevent those not affected by the incident from overwhelming local emergency rooms and response resources therefore reducing service to those actually affected. The public will be informed clearly and frequently about what government agencies are doing to mitigate the impacts of the event. The public will also be given clear directions on how to protect the health of individuals and families.

Table 119 provides a hazard profile summary for terrorism-related hazards. Most terrorist events in the United States have been involved detonated and undetonated explosive devices, tear gas, pipe bombs, and firebombs.

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Table 119: Event Profiles for Terrorism301 F
302
Hazard Application Modea Hazard Durationb
Static/Dynamic
Characteristicsc
Mitigating and
Exacerbating Conditionsd
Conventional
Bomb
Detonation of
explosive device on
or near target;
delivery via person,
vehicle, or projectile.

Instantaneous; additional
secondary devices, or
diversionary activities
may be used,
lengthening the duration
of the hazard until the
attack site is determined
to be clear.

Extent of damage is
determined by type and
quantity of explosive.

Effects generally static other
than cascading
consequences, incremental
structural failure, etc.

Overpressure at a given standoff is
inversely proportional to the cube of the
distance from the blast; thus, each
additional increment of standoff provides
progressively more protection. Terrain,
forestation, structures, etc. can provide
shielding by absorbing and/or deflecting
energy and debris. Exacerbating
conditions include ease of access to
target; lack of barriers and shielding;
poor construction; and ease of
concealment of device.

Chemical
Agent
Liquid/aerosol
contaminants
dispersed using
sprayers or other
aerosol generators;
liquids vaporizing
from puddles/
containers; or
munitions.

Hours to weeks,
depending on the agent
and the conditions in
which it exists.

Contamination can be
carried out of the initial
target area by persons,
vehicles, water, and wind.

Chemicals may be corrosive
or otherwise damaging over
time if not remediated.

Air temperature can affect evaporation of
aerosols. Ground temperature affects
evaporation of liquids. Humidity can
enlarge aerosol particles, reducing
inhalation hazard. Precipitation can
dilute and disperse agents but can
spread contamination. Wind can
disperse vapors but also cause target
area to be dynamic. The micrometeorological effects of buildings and terrain can alter travel and duration of
agents. Shielding in the form of
sheltering in place can protect people
and property from harmful effects.
302 Federal Emergency Management Agency (2003). Integrating Manmade Hazards into Mitigation Planning. https://gema.georgia.gov/document/publication/howto7pdf/download

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Hazard Application Modea Hazard Durationb
Static/Dynamic
Characteristicsc
Mitigating and
Exacerbating Conditionsd
Arson/
Incendiary
Attack
Initiation of fire or
explosion on or near
target via direct
contact or remotely
via projectile.

Generally minutes to
hours.

Extent of damage is
determined by type and
quantity of device,
accelerant, and materials
present at or near target.

Effects generally static other
than cascading
consequences, incremental
structural failure, etc.

Mitigation factors include built-in fire
detection and protection systems and
fire- resistive construction techniques.

Inadequate security can allow easy
access to target, easy concealment of
an incendiary device, and undetected
initiation of a fire. Non-compliance with
fire and building codes, as well as failure
to maintain existing fire protection
systems, can substantially increase the
effectiveness of a fire weapon.

Armed Attack Tactical assault or
sniping from remote
location, or random
attack based on fear,
emotion, or
mental instability.

Generally minutes to
days.

Varies based on the
perpetrators’ intent and
capabilities.

Inadequate security can allow easy
access to target, easy concealment of
weapons, and undetected initiation of an
attack.

Biological
Agent
Liquid or solid
contaminants
dispersed using
sprayers/ aerosol
generators or by
point or line sources
such as munitions,
covert deposits, and
moving sprayers.

Hours to years,
depending on the agent
and the conditions in
which it exists.

Depending on the agent used
and the effectiveness with
which it is deployed,
contamination can be spread
via wind and water.

Infection can spread via
humans or animals.

Altitude of release above ground can
affect dispersion; sunlight is destructive
to many bacteria and viruses; light to
moderate wind will disperse agents but
higher winds can break up aerosol
clouds; the micro-meteorological effects
of buildings and terrain can influence
aerosolization and travel of agents.

Agro-terrorism Direct, generally
covert contamination
of food supplies or
introduction of pests
and/or disease
agents to
crops and livestock.

Days to months. Varies by type of incident.

Food contamination events
may be limited to specific
distribution sites, whereas
pests and diseases may
spread widely. Generally, no
effects on built environment.

Inadequate security can facilitate
adulteration of food and introduction of
pests and disease agents to crops and
livestock.

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Hazard Application Modea Hazard Durationb
Static/Dynamic
Characteristicsc
Mitigating and
Exacerbating Conditionsd
Radiological
Agent
Radioactive
contaminants
dispersed using
sprayers/ aerosol
generators, or by
point or line sources
such as munitions.

Seconds to years,
depending on material
used.

Initial effects will be localized
to site of attack; depending
on meteorological conditions,
subsequent behavior of
radioactive contaminants
may be dynamic.

Duration of exposure, distance from
source of radiation, and the amount of
shielding between source and target
determine exposure to radiation.

Nuclear Bomb Detonation of
nuclear device
underground, at the
surface, in the air, or
at high altitude.

Light/heat flash and
blast/shock wave last for
seconds; nuclear
radiation and fallout
hazards can persist for
years.

Electromagnetic pulse
from a high- altitude
detonation lasts for
seconds and affects only
unprotected electronic
systems.

Initial light, heat, and blast
effects of a subsurface,
ground or air burst are static
and determined by the
device’s characteristics and
employment; fallout of
radioactive contaminants
may be dynamic, depending
on meteorological conditions.

Harmful effects of radiation can be
reduced by minimizing the time of
exposure. Light, heat, and blast energy
decrease logarithmically as a function of
distance from seat of blast. Terrain,
forestation, structures, etc. can provide
shielding by absorbing and/or deflecting
radiation and radioactive contaminants.

Intentional
Hazardous
Material
Release (fixed
facility or
transportation)
Solid, liquid, and/or
gaseous
contaminants
released from fixed
or mobile containers
Hours to days. Chemicals may be corrosive
or otherwise damaging over
time. Explosion and/or fire
may be subsequent.

Contamination may be
carried out of the incident
area by persons, vehicles,
water, and wind.

Weather conditions directly affect how
the hazard develops. The micrometeorological effects of buildings and terrain can alter travel and duration of
agents. Shielding in the form of
sheltering in place can protect people
and property from harmful effects. Noncompliance with fire and building codes, as well as failure to maintain existing fire
protection and containment features, can
substantially increase the damage from
a hazardous
materials release.
a. Application Mode: Application mode describes the human acts or unintended events necessary to cause the hazard to occur. b. Duration: Duration is the length of time the hazard is present. For example, a chemical warfare agent such as mustard gas, if un- remediated, can persist for hours or weeks under the right conditions.

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c. Dynamic or Static Characteristics: These characteristics of a hazard describe its tendency, or that of its effects, to either expand, contract, or remain confined in time, magnitude, and space. For example, the physical destruction caused by an earthquake is generally confined to the place in which it occurs, and it does not usually get worse unless aftershocks or other cascading failures occur; in contrast, a cloud of chlorine gas leaking from a storage tank can change location by drifting with the wind and can diminish in danger by dissipating over time. d. Mitigation and Exacerbating Conditions: Mitigating conditions are characteristics of the target and its physical environment that can reduce the effects of a hazard. For example, earthen berms can provide protection from bombs; exposure to sunlight can render some biological agents ineffective; and effective perimeter lighting and surveillance can minimize the likelihood of someone approaching a target unseen. In contrast, exacerbating conditions are characteristics that can enhance or magnify the effects of a hazard. For example, depressions or low areas in terrain can trap heavy vapors, and a proliferation of street furniture (trash receptacles, newspaper vending machines, mailboxes, etc.) can provide hiding places for explosive devices.

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16.2.2 Active Threat
Active Shooter
Active shooter attacks are typically motivated by the desire to maximize human casualties. They are differentiated from other attack types by the indiscriminate nature of the victims, who often are targets of opportunity. Active shooter attacks range from “lone wolf” shooters who act alone and without any organizational affiliation to organized groups acting in concert to achieve a specific objective. Active shooter tactics sometimes employ a blend of lone shooters and multi-person teams as part of a larger assault.

Active shooters may use small arms, light weapons, or a combination of the two depending on the type of attack. Small arms are revolvers, automatic pistols, rifles, shotguns, assault rifles, light machine guns, etc.

Light weapons are medium caliber and explosive ordinance, grenade launchers, rocket propelled grenades, etc. Attackers can increase their likelihood of success by using a wider array of weapons, including improvised explosive devices.

Biological Attack
Biological hazards include disease-causing microorganisms and pathogens, such as bacteria and viruses, which multiply within a host and cause an infection. Some bacteria and viruses can spread from one individual to another. Infections typically occur as a result of airborne exposure, skin contact, or ingestion. In general, exposure to bacteria and viruses can occur through inhalation (as is the case with airborne B. anthracis spores, which cause anthrax), ingestion of contaminated food or water (the case with E. coli, which causes gastrointestinal infection), contact with infected individuals, or contact with contaminated surfaces (which may be harboring, for example, viruses that cause influenza). Domestic and transnational threat groups have considered targeting heating, ventilation, and air conditioning systems of large commercial buildings.

Anthrax has been used as a weapon for nearly 100 years and is one of the most likely agents to be used in a biological threat. Its spores are easily found in nature, can be produced in a lab, and can last for a long time. It can be released quietly and without anyone knowing. Microscopic spores can be put into powders, sprays, food, and water. Due to their size, victims may not be able to see, smell or taste them.302 F
303 Terrorists may release anthrax spores in public places. In 2001, letters containing powdered anthrax spores were sent through the U.S. mail, causing skin and lung anthrax in 22 people. Five people died, all due to lung anthrax.30F
304
If a biological attack were to occur in the Santa Clara County OA, a large number of personnel could be impacted. Buildings in the impacted area and transportation infrastructure might be closed for investigation and cleanup. These areas would not be accessible until cleanup is completed, which would impact the businesses. Hospitals could become overwhelmed with people coming in fearing contamination. Residents and businesses may need to shelter in place in the area of the attack. 303 Centers for Disease Control and Prevention. (n.d.) The Threat of an Anthrax Attack. https://www.cdc.gov/anthrax/bioterrorism/threat.html
304 Chan, C. & Pan, E. (n.d.). Anthrax in the air? San Francisco Department of Public Health. https://www.sfcdcp.org/wp-content/uploads/2017/12/SFDPH.Anthrax_in_the_Air._SF_Med._Society_article.pdf

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Chemical Attack
Chemical weapons are poisonous vapors, aerosols, liquids, and solids that have toxic effects on humans, animals, and plants. A chemical attack is the spreading of toxic chemicals with the intent to do harm. A wide variety of chemicals could be made, stolen, or otherwise acquired for use in an attack. Harmful chemicals that could be used in an attack include:304 F 305
 Chemical weapons (warfare agents) developed for military use;  Toxic industrial and commercial chemicals that are produced, transported, and stored in the making of petroleum, textiles, plastics, fertilizers, paper, foods, pesticides, household cleaners, and other products; and
 Chemical toxins of biological origin such as ricin.

Exposure pathways include inhalation, skin contact, ingestion, or injection. Depending on the severity of exposure, impacts may include temporary illness or injury, permanent medical conditions, or death. An attack using chemicals can come without warning. Signs of a chemical release include difficulty breathing; choking or eye irritation; losing coordination; nausea; or a burning sensation in the nose, throat, and lungs.305F
306
A chemical release in the Santa Clara County OA could lead to closure of streets and major transportation routes (including bridges) for extended periods of time, causing transportation delays and traffic. Many homes and businesses would also be impacted as they would need to be evacuated for an extended period of time. There could also be impact on the environment and/or natural resources that would require cleanup. Hazardous material response teams and fire-rescue would be needed to respond to the incident and coordinate cleanup efforts.

Radiological Attacks
The radiological accident hazard has been identified in the State hazard mitigation plan with a low probability. Terrorist acts involving radiological or nuclear materials (e.g., radiological dispersion device or an improvised nuclear device) is presented as an example of potential radiologic releases but not discussed further.

Explosive Devices
Improvised explosive device (IED) attacks are a favored method of terrorist groups around the world. The evolution in explosive materials and firing devices and their ease of concealment and delivery have increased the effectiveness of this hazard. IED attacks are typically motivated by the desire to maximize human casualties. The intention may also be to create fear in the community. Explosive incidents account for 70 percent of all terrorist attacks worldwide. These types of attacks range from small-scale letter bombs to large-scale attacks on specific buildings.

IEDs generally consist of TNT equivalent explosives (e.g., black or smokeless powder) in a container (e.g., galvanized pipe, paint can, etc.). These propellants are easily purchased on the commercial market.

IEDs may also contain added shrapnel to induce greater casualties or shaped charges that direct the force of the explosive toward the target. Devices may be hidden in everyday objects such as briefcases, flowerpots, or garbage cans, or on the person of the attacker in the case of suicide bombers. The most commonly used container is galvanized pipe, followed by PVC pipe. 305 Department of Homeland Security. (n.d.). Chemical Attack Fact Sheet: Warfare Agents, Industrial Chemicals, and Toxins. https://www.dhs.gov/publication/chemical-attack-fact-sheet 306 Federal Emergency Management Agency. (n.d.). Chemicals and Hazardous Materials Incidents. https://www.ready.gov/hazmat#during

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When shrapnel is added to the device, the type of shrapnel varies—bullets and other small pieces of hardware are common, as are glass and gravel.

An attack using IEDs or other explosive device in the Santa Clara County OA has potential large-scale consequences that may require multi-agency and multijurisdictional coordination. Depending on the location of the attack, businesses and other venues may be closed for investigation and due to damage. If the attack occurred in or near residences, evacuations and/or sheltering may occur.

Fire as a Weapon
The use of fire for criminal, gang, and terrorist activities, as well as targeting first responders, is one of numerous increasingly complex approaches to terrorism. This tactic can include arson, improved incendiary devices (IIDs), deliberate forest fires, and more. Human-causes are the leading cause of wildfires in California. Between the last plan update and 2022, the annual acres burned due to arson caused wildfires ranged from 483 acres (2022) to 44,609 acres (2020).306F 307 Fire, and incendiary devices
such as Molotov cocktails, have been used more frequently recently both during civil disturbances and in an attempt to break up otherwise peaceful protests. IID incidents have also increased. Between 2019 and 2020 alone, IID incidents targeting government facilities increased 210%, incidents targeting critical infrastructure facilities increased 141%, and incidents targeting commercial facilities increased 113 percent.307F
308

16.2.3 Hazard Profile
Past Events
The South Bay Area has not experienced a major regional terrorism event. According to the Cal OES Terrorism Response Plan, California has had a long history of defending the public against domestic and foreign terrorists. Domestic terrorist groups in California have been focused on political or social issues, while the limited internationally based incidents have targeted the state’s immigrant communities due to foreign disputes. Advanced technologies and communication have allowed these groups to become more sophisticated and better organized, with remote members linked electronically.

In California, most terrorist events have involved explosives, followed by incendiaries and firearms, as shown in Figure 72. During a recent three-month period, the Bomb Squad from the Santa Clara County Sheriff’s Office was called out three times:308F
309
 September 5, 2022: Explosive Material Mitigation: The Bomb Squad was called to the scene of a man that was attempting to manufacture homemade explosives causing an explosion at his home. The explosion took off the suspect’s right hand and caused serious trauma to his lower face. Bomb Technicians deployed bomb disposal robots to extract the explosive material and precursor chemicals from the trailer to facilitate a controlled demolition and render the scene safe.  October 31, 2022: Suspected IED Mitigation: The Bomb Squad was called for a suspicious item suspected of being an IED that was abandoned on the side of the roadway. The item was made to look like an IED but was not viable.
307 Cal Fire. (December 2022). Arson Caused Wildfires – Acres Burned. https://34c031f8-c9fd-4018-8c5a4159cdff6b0d-cdn-endpoint.azureedge.net/-/media/calfire-website/images---misc/arson-acres-burned2022.jpg?rev=83a9dd360a794b6cb627bdf7371f2791&hash=7F588C79EC88FF533701B966B2E0138A 308 Cybersecurity & Infrastructure Security Agency. (n.d.). Fire As A Weapon. https://www.cisa.gov/sites/default/files/publications/Fire%20as%20a%20Weapon%20Action%20Guide_Final%20508 %20%2804.12.21%29v.2_1.pdf
309 Santa Clara County Sheriff’s Office. (2023). Military Equipment Use Report, 6-Month Report. Military Equipment Use 6-Month Report_FINAL DRAFT (2.15.23).pdf (sccgov.org)

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 November 15, 2022: Suspected IED Mitigation: The Bomb Squad was called to a Lockheed Martin Facility in Santa Clara for a reported IED in the shipping and receiving room. The item was made to look like an IED but was not viable.

Other agencies responded to two other incidents involving explosives.  March 1, 2023: Explosive Material Mitigation: The City of San José bomb squad was called to a South San José home as part of an investigation into someone possessing explosives and illegal drugs.
 February 7,2020: Suspected Terrorist Attack: Assailants in a vehicle opened fire on a Sikh police officer patrolling in Morgan Hill, California, United States. A Santa Clara County Sheriff’s Deputy was injured in the assault. No group claimed responsibility for the attack.” These are not the first incidents in the OA. One other example includes an attack in 2014 at a PG&E Corporation’s Metcalf transmission substation in San José when an unknown person entered an underground vault and cut telephone cables. Within half an hour, snipers opened fire on a nearby electrical substation. Shooting for 19 minutes, the persons were able to knock out 17 giant transformers that funnel power to Silicon Valley. Electric-grid officials were able to reroute power around the site and requested power plants in Silicon Valley to produce more electricity, but it took utility workers 27 days to conduct repairs and make the substation functional. The Wall Street Journal reported the incident at the time was called “the most significant incident of domestic terrorism involving the grid that has ever occurred.” There have been no arrests or persons charged for the incident.309F 310
Figure 73: Weapon Types Used in Terrorist Events in California310F 311
310 Smith, Rebecca. (February 2014). Assault on California Power Stations Raises Alarm on Potential for Terrorism; April Sniper Attack Knocked Out Substation, Raises Concern for Country’s Power Grid. Assault on California Power Station Raises Alarm on Potential for Terrorism - WSJ
311 Global Terrorism Database. (n.d.). Database Search Results. https://www.start.umd.edu/gtd/search/Results.aspx?charttype=bar&chart=target&search=california

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Terrorist attacks can occur anywhere in the Santa Clara County OA. Past targets in California have included businesses, private citizens, government, educational institutions and many more. In California, as shown in Figure 74, businesses are the most frequent targets, accounting for 28 percent of all terrorist attacks in the state.

Figure 74: Targets of Terrorist Attacks in California31F 312
Severity
The severity of terrorist attacks ranges from inconsequential when the attack fails, to catastrophic. The effects of terrorism can include injuries, loss of life, property damage, or disruption of services such as electricity, water supplies, transportation, or communications. Effects may be immediate or delayed.

Terrorists often choose targets that offer limited danger to themselves and areas with relatively easy public access. Foreign terrorists look for visible targets where they can avoid detection before and after an attack, such as international airports, large cities, major special events, and high-profile landmarks. In recent months, there has been a rise in physical attacks against utility infrastructure in North Carolina and the Pacific Northwest.312F
313 Attackers targeted substations and used guns, fire, metal chains, and other weapons during their attack. As of this writing, the FBI is currently investigating. 312 Global Terrorism Database. (n.d.). Database Search Results. https://www.start.umd.edu/gtd/search/Results.aspx?charttype=bar&chart=target&search=california 313 Oregon Public Broadcasting. (December 2022). String of electrical grid attacks in Pacific Northwest is unsolved. https://www.opb.org/article/2022/12/08/string-of-electrical-grid-attacks-in-pacific-northwest-are-unsolved/

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Warning Time
For this hazard, warning time relates to warnings to local law enforcement from federal authorities and other law enforcement agencies as well as warnings to the public. In dealing with terrorism, the unpredictability of human beings must be considered. While education, heightened awareness, and early warning of unusual circumstances may deter terrorism, intentional acts that harm people and property are possible at any time. Public safety entities must react to the threat, locating, isolating, and neutralizing further damage and investigating potential scenes and suspects to bring criminals to justice.

People with a desire to perform such acts may seek out targets of opportunity that may not fall into established lists of critical areas or facilities. First responders in the Santa Clara County OA train to respond not only to organized terrorism incidents, but also to random acts by individuals who may choose to harm others and destroy property. The Intelligence Unit of the Santa Clara County Sheriff’s Office is comprised of a Sergeant and a Deputy that are assigned to the FBI’s Joint Terrorism Task Force (JTTF) and the Northern California Regional Intelligence Center (NCRIC) respectively with the goal of helping safeguard the Santa Clara County community by conducting terrorism investigations, sharing criminal intelligence and threat assessment information with regional partners, and by processing and assessing Suspicious Activity Reports (SARs) submitted by local law enforcement and the public.

AlertSCC is the County of Santa Clara’s official emergency alert and warning system for the most up-todate information on emergencies and disasters happening in the area.

Critical Facilities, Infrastructure, and the Environment Critical facilities, infrastructure, and the environment are common targets of terrorist attacks. The environment may be impacted depending on the size and location of the terrorist attack. Human-caused fires pose a serious threat, as well as hazardous materials release.

Future Trends in Development
Terrorist attacks in urban areas would cause significantly more harm, injury, death, or property damage than it would rural areas. As the Santa Clara OA continues to develop, the target area for terror attacks expands as does the number of potential victims of an attack.

Cascading Impacts
A completed terror attack on critical facilities and infrastructure and the environment could involve multiple other hazards including power outage, utility failure, and hazardous materials release.

16.2.4 Cyber Threats
A cyber threat is an intentional and malicious crime that compromises that digital infrastructure of a government, person, or organization, often for financial or terror-related reasons. Such attacks vary in nature and are perpetrated using digital mediums or sometimes social engineering to target human operators. Generally, attacks last minutes to days, but large-scale events and their impacts can last much longer. As information technology continues to grow in capability and interconnectivity, cyber threats become increasingly frequent and destructive. In 2014, internet security teams at Symantec and Verizon indicated that nearly a million new pieces of malware—malicious code designed to steal or destroy information—were created every day.31F
314
314 Symantec. (2015). Protection from Advanced Threats with Symantec Insight and SONAR. Broadcom. https://docs.broadcom.com/doc/protection-from-advanced-threats-with-insight-sonar-en.

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Cyber threats can vary in their severity, based on the systems affected by an attack, the warning time, and the ability to preempt an attack.314F
315 They also differ by motive, attack type and perpetrator profile.

Motives range from the pursuit of financial gain to political or social aims. Types of threats include using viruses to erase entire systems, breaking into systems and altering files, using someone’s personal computer to attack others, or stealing confidential information. Municipalities and private businesses within the Santa Clara County OA are susceptible to the most current and common cyber-attacks, such as socially engineered Trojans, unpatched software, phishing attacks, network-traveling worms, and advanced persistent threats. Many of these attacks are engineered to automatically seek technological vulnerabilities. Possible cyberterrorist targets include the banking industry, power plants, air traffic control centers, and water systems. The spectrum of cyber risks is limitless, with threats having a wide range of effects on the individual, community, organizational, and national threat.315F 316
“[The cyber threat] has exploded. It has become more diffuse, more sophisticated, more dangerous than ever before.”
Lisa O. Monaco, Deputy Attorney General (DAG)
Address at Annual Munich Cybersecurity Conference (Feb. 17, 2021)316F 317
This risk assessment includes cyberattacks and cyberterrorism. The terms often are used interchangeably, though they are not the same. While all cyberterrorism is a form of cyberattack, not all cyberattacks are cyberterrorism.

Cyberattack
Public and private computer systems are subject to a variety of cyberattacks, from blanket malware infection to target attacks on system capabilities. Cyber-attacks seek to breach IT security measures designed to protect an individual or organization. The initial attack if followed by more severe attacks for the purpose of causing harm, stealing data, or financial gain.

One of the most common cyber threats is malware. Malware refers to malicious software that a cybercriminal or hacker has created to disrupt or damage a legitimate user’s computer. It is often spread via an unsolicited email attachment or other legitimate-looking download. Types of malware include the following:
 Viruses: A self-replicating program that attaches itself to clean file and spreads throughout a computer system, infecting files with malicious code.
 Trojans: Programs disguised as legitimate software where the victim is tricked into uploading trojans onto their computer where they cause damage or obtain sensitive and/or valuable data.  Spyware: This malicious software is designed to enter your computer or other device, gather data about you, and forward it to a third-party without your consent. In December 2022, a U.S. lawmaker predicted spyware hacks of U.S. government employees could be in the hundreds, including diplomats.317F
318
315 Cybersecurity & Infrastructure Security Agency. (n.d.). Cyber Threats and Advisories. https://www.cisa.gov/topics/cyber-threats-and-advisories 316 Federal Emergency Management Agency. (2022). Cybersecurity. https://www.ready.gov/cybersecurity#:~:text=1%20Accessing%20your%20personal%20computers%2C%20mobile% 20phones%2C%20gaming,services.%205%20Impacting%20transportation%20and%20the%20power%20grid. 317 U.S. Department of Justice. (2022 July). Comprehensive Cyber Review. https://www.justice.gov/media/1232936/dl?inline=
318 Center for Strategic & International Studies. (2023). Significant Cyber Incidents. https://www.csis.org/programs/strategic-technologies-program/significant-cyber-incidents

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 Ransomware: Ransomware is a type of malware used by cyber actors to extort owners of computer systems. Since 2013, ransomware attacks are becoming increasingly common. On April 22, 2021, an apparent ransomware attack on the Santa Clara Valley Transportation Authority (VTA), paralyzed many of the agency’s computer systems for days.318F 319 The hacker group claimed
that it stole 150 gigabytes of data from the transit authority and threatened to post it publicly if VTA does not “cooperate.”
 Malvertising: Malware downloaded to a system when the victim clicks on an affected ad.

Other types of cyber threats include the following:
 Phishing: Malicious email messages that ask users to click a link or download a program.

Phishing attacks may appear as legitimate emails from trusted third parties.  Man in the Middle Attack: Man-in-the-Middle is a type of cyber threat where a cybercriminal intercepts communication between two individuals in order to steal data.  Denial of Service Attacks: These attacks that focus on disrupting service by flooding computer networks and servers with traffic until the network can no longer function.  Advanced Persistent Threat (APT): An attack in which the attacker gains access to a network and remains undetected. APT attacks are designed to steal data instead of cause damage.

With millions of threats created each day, the importance of protection against cyberattacks becomes a necessary function of everyday operations for individuals, government facilities, and businesses. The increasing dependency on technology for vital information storage and the often automated method of infection means higher stakes for the success of measurable protection and education.

Cyberterrorism
Cyberterrorism is the use of computers and information, particularly over the internet, to recruit others to an organization’s cause, cause physical or financial harm, or cause a severe disruption of infrastructure service. Such disruptions can be driven by religious, political, or other motives. Like traditional terrorism tactics, cyberterrorism seeks to evoke very strong emotional reactions, but it does so through information technology rather than a physically violent or disruptive action. Cyberterrorism has three main types of objectives:319F
320

1. Organizational: Cyberterrorism with an organizational objective includes specific functions outside of or in addition to a typical cyber-attack. Terrorist groups today use the internet daily for recruitment, training, fundraising, communication, or planning. Organizational cyberterrorism can use platforms such as social media as a tool to spread a message beyond country borders and instigate physical forms of terrorism. Additionally, organizational goals may use systematic attacks as a tool for training new members of a faction in cyber warfare.

2. Undermining: Cyberterrorism with undermining as an objective seeks to hinder the normal functioning of computer systems, services, or websites. Such methods include defacing, denying, and exposing information. While undermining tactics are typically used due to high dependence on online structures to support vital operational functions, they typically do not result in grave consequences unless undertaken as part of a larger attack. Undermining attacks on computers include the following:
319 The Mercury News. (2021, April 22). VTA Targeted in Apparent Ransomware Attack, Hackers Threaten to Release Trove of Data. https://www.mercurynews.com/2021/04/22/cyberattack-targets-vta-unclear-if-personalinformation-breached/ 320 INFOSEC. (2012, December 21). Cyberterrorism Defined (as distinct from “Cybercrime”). https://resources.infosecinstitute.com/topic/cyberterrorism-distinct-from-cybercrime/

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a. Directing conventional kinetic weapons against computer equipment, a computer facility, or transmission lines to create a physical attack that disrupts the reliability of equipment. b. Using electromagnetic energy, most commonly in the form of an electromagnetic pulse, to create an electronic attack against computer equipment or data transmissions. By overheating circuitry or jamming communications, an electronic attack disrupts the reliability of equipment and the integrity of data.
c. Using malicious code directed against computer processing code, instruction logic, or data.

The code can generate a stream of malicious network packets that disrupt data or logic by exploiting vulnerability in computer software, or a weakness in computer security practices.

This type of cyber-attack can disrupt the reliability of equipment, the integrity of data, and the confidentiality of communications.

3. Destructive: The destructive objective for cyberterrorism is what organizations fear most. Using computer technology and the internet, the terrorists seek to inflict destruction or damage on tangible property or assets, and even death or injury to individuals.

16.2.5 Hazard Profile
Past Events
Previous cyberattacks have occurred against the local government, critical infrastructure, and businesses in the OA. For example, in 2021, Santa Clara Valley Transportation Authority experienced a ransomware cyberattack, with the intention of obtaining data and disrupting essential services.

The location of Silicon Valley within the OA also makes the area a significant target to major cyberattacks on businesses. In 2022, Nvidia, a major chip manufacturer based in Santa Clara, experienced a cyberattack in which valuable data was stolen. The attackers demanded a ransom to protect Nvidia’s data.

Location
Cyberattacks are local in nature. They can occur from anywhere.

Severity
A cyberattack, even a successful one, could have a minor impact on the victims or it could be catastrophic, depending on the situation.

Warning Time
The severity and timing of cyber threats are impossible to predict. There may be no warning. Some cyber incidents take weeks, months, or even years to be discovered and identified.320F 321
Critical Facilities, Infrastructure, and the Environment Critical facilities and infrastructure are common targets of cyberattacks. There is not expected to be significant environmental impacts.
321 Federal Emergency Management Agency. (2022). Cybersecurity. https://www.ready.gov/cybersecurity#:~:text=1%20Accessing%20your%20personal%20computers%2C%20mobile% 20phones%2C%20gaming,services.%205%20Impacting%20transportation%20and%20the%20power%20grid..

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Future Trends in Development
Future development is unlikely to be significantly influenced by cyber-attacks. However, cyberattacks that could impact larger populations could cause significantly more harm, injury, death, or property damage.

Expanding the local economy also presents additional targets for cyber-attacks.

Cascading Impacts
Cyberattacks can have many cascading impacts depending on the target, timeframe, and success of the attack. As stated in the 2018 State of California Hazard Mitigation Plan, “Computer system failures have the potential to result in cascading hazards such as energy outages, hazardous materials release, oil spills, transportation accidents, or dam failure.”321F
322

16.3 Technological Incidents
Technological hazards are associated with human activities such as the manufacture, transportation, storage, and the use of hazardous materials. Incidents related to these hazards are assumed to be accidental with unintended consequences. Given the complex system of transportation networks, the large population, and the number of businesses in California, incidents occur on a regular basis throughout the state, as reported by the news media. Technological hazards can be categorized as follows:
 Hazardous materials incidents
 Transportation incidents
 Pipeline and tank hazards
 Utility failure
Hazardous Materials Incidents
A hazardous material is any substance that is flammable, combustible, corrosive, poisonous, toxic, explosive, or radioactive. Hazardous materials are present across the United States in facilities that produce, store, or use them. For example, water treatment plants use chlorine on-site to eliminate bacterial contaminants, and dry-cleaning businesses may use solvents that contain perchloroethylene.

Even the natural gas used in homes and businesses is a dangerous substance when a leak occurs.

Hazardous materials are transported along interstate highways and railways daily. The following are the most common types of hazardous material incidents:
 Fixed-Facility Hazardous Materials Incident: This is the uncontrolled release of materials from a fixed site capable of posing a risk to health, safety, and property. It is possible to identify and prepare for a fixed-site incident because laws require those facilities to notify state and local authorities about what is being used or produced at the site.  Hazardous Materials Transportation Incident: This is any event resulting in uncontrolled release during transport of materials that can pose a risk to health, safety, and property.

Transportation incidents are difficult to prepare for because there is little if any notice about what materials could be involved should an accident happen. These incidents can occur anywhere, although most occur on major federal or state highways or major rail lines. In addition to materials such as chlorine that are shipped throughout the country by rail, thousands of shipments of radiological materials (mostly medical materials and low-level radioactive waste) take place via ground transportation across the United States.
322 California Office of Emergency Services. (2018). 2018 State of California Hazard Mitigation Plan. https://www.caloes.ca.gov/office-of-the-director/operations/recovery-directorate/hazard-mitigation/state-hazardmitigation-planning/

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 Many incidents occur in sparsely populated areas and affect few people. However, hazardous materials have been involved in accidents in areas with much higher population densities, as shown in Figure 74.

Figure 75: Highly Populated Areas with Hazardous Material Incidents Within Santa Clara County32F
323
 Pipeline Hazardous Materials Incident: Numerous natural gas pipelines, heating oil, and petroleum pipelines run through the Santa Clara County OA and surroundings. These are used to provide these products to utilities in the region and to transport the materials from production facilities to end users.

Federal regulations govern the transportation of hazardous materials in all modes of transportation: air, highway, rail, and water (Title 49, Code of Federal Regulations; Transportation, Code of Federal Regulations, Hazardous Materials Regulations). Title 49 CFR lists thousands of hazardous materials, including gasoline, insecticides, household cleaning products, and radioactive materials. California regulated substances that have the greatest probability of adversely impacting the community are listed in state code (Title 19, Division 2, Chapter 4.5, Sections 2735-2785; Hazardous Material Management Plan/Hazardous Material Inventory).

Even though information for 2022 is not complete, it appears that the total number of hazardous material incidents in Santa Clara County has decreased in the last few years. The number of injuries and fatalities has also decreased. The total incidents are outlined in Table 120. 323 National Pipeline Mapping System. (n.d.). NPMS Public Viewer. https://pvnpms.phmsa.dot.gov/PublicViewer/

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Table 120: Santa Clara County Hazardous Materials Spills 2019–202232F 324
Year Total
Incidents
Type
Injuries Fatalities Petroleum Chemical Sewage Railroad Railroad Derailment
Vapor Other
2019 196 22 13 27 24 4 9 4 11 12
2020 153 76 11 17 20 2 3 19 10 7
2021 157 70 13 20 20 2 7 18 9 11
2022 87 42 8 14 13 3 3 13 6 8
Santa Clara County has four Certified United Program Agencies that administer hazardous materials, hazardous waste, and underground storage tank programs within their jurisdictions:
 Hazardous Materials Compliance Division of the Santa Clara County Department of Environmental Health (for all areas of Santa Clara County other than the cities of Santa Clara, Gilroy, and Sunnyvale)  Santa Clara City Fire Department
 Gilroy Building, Life, and Environmental Safety to Community Development Department, Fire Prevention Division  Sunnyvale Department of Public Safety
Participating Agencies are local fire agencies that coordinate their activities under a memorandum of understanding with Santa Clara County Department of Environmental Health:
 Milpitas Fire Department
 Mountain View Fire Department
 Palo Alto Fire Department
 Santa Clara County Fire Department
324 California Office of Emergency Services. (n.d.). Spill Release Reporting. https://www.caloes.ca.gov/office-of-the-director/operations/response-operations/firerescue/hazardous-materials/spill-release-reporting/

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Transportation Incidents
Transportation incidents are those involving air, road or rail travelers resulting in death or serious injury.

The potential for transportation accidents that block movement through the OA is significant, as is the likelihood of hazardous material incidents resulting from a traffic or rail accident.

The Bay Area has a number of airports, including the San Francisco International Airport, Oakland International Airport, and San José International Airport, as well as San Martin Airport and Reid Hillview Airport, which are smaller municipal airports that enhance the potential for an air disaster. Major transportation routes in the OA include the following:
 Major highways include Interstates 880 (Nimitz Freeway) and 280; U.S. Highway 101 and Highway 237; and State Routes 87, 85, and 17.
▪ The 49 miles of light rail serving Santa Clara County is operated by the Santa Clara Valley Transportation Authority (VTA), which oversees public transit services in the county. The Santa Clara VTA is continuing development for Phase II of its BART Silicon Valley Extension.

The project is planning four stations: 28th Street/Little Portugal Station, Downtown San José Station, Diridon Station, and Santa Clara Station. Construction of Phase II is estimated to carry 54,600 passengers each weekday to destinations throughout the Bay Area by 2040.324F 325
 Amtrak has a train station in San José at Santa Clara University.  The Santa Clara Depot, in the City of Santa Clara, is served by the Caltrain from San Francisco and the Altamont Corridor Express from Stockton.
 The Great America station in the City of Santa Clara hosts Amtrak’s Capitol Corridor trains and Altamont Corridor Express trains. The station is close to Levi’s Stadium and California’s Great America.
 There are 15 Caltrain stations in the OA. Caltrain is a commuter rail between San Francisco, San Mateo, and Santa Clara counties.
 The Santa Fe railroad has a right of way that parallels U.S. Highway 101 through the eastern edge of the county.
 Daily commuter traffic is very high in the OA due to Silicon Valley’s dense-employment population.

Pipeline Hazards
Approximately 300,000 miles of gas transmission pipelines and 170,000 miles of hazardous liquid pipelines move their products throughout the United States every day. Transmission pipelines connect urban areas, and only occasionally traverse highly populated areas. Numerous natural gas pipelines, heating oil, and petroleum pipelines run through the Santa Clara County OA and surroundings (see Figure 76).
325 Valley Transportation Authority. (n.d.). VTA’s BART Silicon Valley Phase II. https://www.vta.org/projects/bart-sv/phase-ii

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Figure 76: Gas and Hazardous Liquids Pipelines in Santa Clara County325F 326
Pipeline Systems and Risks
Around 1945, the United States invested in the development of a nation-wide system of pipelines for the purpose of transporting natural gas and petroleum products. Most of these materials are moved by hazardous liquid and gas transport operators through a system of pipelines ranging in diameter from 20 to 42 inches. These pipes reach from the material origin wells to their destination in refineries that further process the material. Although pipelines are the safest and most reliable way to transport natural gas, crude oil, liquid petroleum products, and chemical products, there is still an inherent risk due to the nature of the hazardous materials.

Transmission pipelines are those that transport raw material for further refinement. These pipes are large and far reaching, operating under high pressure. Distribution pipelines are those that provide processed materials to end users. Distribution pipelines serve homes and businesses and thus are located where people live and work. These are smaller in diameter, some as small as a half an inch, and operate under lower pressure. Because of the extensive reach of the distribution system, incidents have the potential to be far reaching. For example, a pipeline leak may release material into a migration pathway, such as a sewer line, and reach an ignition source far from the location of the actual leak. Due to the far-reaching underground and unpredictable nature of the pipeline failure hazard, it is difficult to gauge the extent to which the hazard affects the Santa Clara County OA. Minor pipe leaks may remain undetected for years until identified during renovation, excavation, or maintenance. In some scenarios, such leaks may go undetected until the severity has increased, resulting in a noticeable smell or, in the worst-case scenario, an explosion.

Incident causes are grouped as follows:
 Corrosion: Incidents caused by galvanic, atmospheric, stray current, microbiological, or other corrosive action.
 Excavation Damage: Incidents resulting directly from excavation damage by operator’s personnel (oftentimes referred to as "first party" excavation damage), by the operator’s contractor (oftentimes referred to as "second party" excavation damage), or by people or contractors not 326 National Pipeline Mapping System. (n.d.). NPMS Public Viewer. https://pvnpms.phmsa.dot.gov/PublicViewer/

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associated with the operator (oftentimes referred to as "third party" excavation damage). This cause type also includes those incidents determined to have resulted from previous damage due to excavation activity.
 Incorrect Operation: Incidents caused by operating, maintenance, repair, or other errors by facility personnel, including but not limited to improper valve selection or operation, inadvertent over pressurization, or improper selection or installation of equipment.  Material/Weld/Equipment Failure: Incidents in main or service pipe, or in welds, joints, or connections joining main pipe or service pipe due to faulty manufacturing procedures; defects resulting from poor construction, installation, or fabrication practices; and in-service stresses such as vibration, fatigue, and environmental cracking. also included are incidents resulting from equipment failures such as: malfunction of control/relief equipment (valves, regulators, or other instrumentation); failures of the body of equipment, vessel plate, or other material; and all other equipment-related failures.
 Natural Force Damage: Incidents resulting from earth movement, earthquakes, landslides, subsidence, lightning, heavy rains/floods, washouts, flotation, mudslides, scouring, temperature, frost heave, frozen components, high winds, or similar natural causes.  Other Outside Force Damage: Incidents caused by non-excavation-related outside forces, such as fire or explosion; damage by vehicles or other equipment; nearby industry; failures due to mechanical damage; and intentional damage including vandalism and terrorism.

The greatest risk to the public regarding pipelines is the unintended release of a material being transported through the system. These materials are hazardous and have the capability to severely impact the surrounding environment, population, and property. These impacts may lead to severe injury or death. Combustible material transported through these pipelines may ignite or explode. Hazardous liquids may contaminate water systems. Families that rely on the transported material to heat their households may experience disruption of service. Pipeline failures also have the potential to negatively impact the economy, causing business interruptions or severely damaging vital infrastructure.

Depending on the pipeline material, age of the system, and transported product, pipelines may experience one or more general types of corrosion. Table 121 identifies corrosion types and a description of each.

Table 121: Corrosion Type
Corrosion
Type Description
External External corrosion occurs due to environmental conditions on the outside of the pipe.

Internal Corrosion on the internal wall of a natural gas pipeline can occur when the pipe wall is exposed to water and contaminants in the gas, such as O2, H2S, CO2, or chlorides.

Atmospheric Atmospheric corrosion occurs on a steel surface in a thin wet film created by the humidity in the air in combination with impurities.

Stress
Cracking
Stress corrosion cracking is the initiation of cracks and their propagation, possibly up to complete failure of a component, due to the combined action of tensile mechanical loading and a corrosive medium.

Pipeline material plays an important role in the possibility of experiencing a pipeline failure. The main causes for both hazardous liquid and gas transmission pipelines failure are corrosion, material or welding

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failure, or damage due to excavation.326F
327 Plastic pipes installed for natural gas distribution systems from the 1960s through the early 1980s may be vulnerable to cracking, resulting in gas leakage and potential hazards to the public. Hundreds of thousands of miles of plastic pipe have been installed, with a significant amount installed prior to the mid-1980s. While distribution systems may widely vary in terms of construction material, nearly all transmission pipeline systems are constructed from high-strength steel treated with an anti-corrosive chemical.327F
328
Pipeline incidents may lead to severe injury or death. Combustible material transported through these pipelines may ignite or explode. In the case of a spill, the released product becomes a hazard by dispersing in the environment, contaminating water bodies, soil, and potentially affecting people and wildlife. Families that rely on the transported material to heat their households may experience disruption of service. Pipeline failures also have the potential to negatively impact the economy, causing business interruptions or severely damaging vital infrastructure.

Pipelines are monitored by system control and data acquisition systems that measure flow rate, temperature, and pressure. These systems transfer real-time data via satellite from the pipelines to a control center where valves, pumps, and motors are remotely operated. If tampering with a pipeline occurs, an alarm sounds. The ensuing valve reaction is instantaneous, with the alarm system isolating any rupture and setting off a chain reaction that shuts down pipeline pumps and alerts pipeline operators within seconds.

Pipeline Oversight
Pipelines are regulated in California by the Office of the State Fire Marshal Pipeline Safety Division.

CERCLA, the Emergency Planning and Community Right-to-Know Act, and California law require responsible parties to report hazardous material releases if certain criteria are met. CERCLA requires that all releases of hazardous substances exceeding reportable quantities be reported by the responsible party to the National Response Center. If an accidental chemical release exceeds the Right-to-Know Act applicable minimal reportable quantity, the facility must notify state emergency response commissions and local emergency planning committees for any area likely to be affected by the release and provide a detailed written follow-up as soon as practicable. Information about accidental chemical releases must be made available to the public.

The California Public Utilities Commission (CPUC) serves as the state regulation authority regarding pipeline operations. The CPUC conducts operation and maintenance compliance inspections and accident investigations. It reviews utilities’ reports and records, conducts construction inspections, conducts special studies, and acts in response to complaints and inquiries from the public on issues regarding gas pipeline safety. The CPUC also endorses the system safety approach embodied in federal government regulations.

The U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA) is responsible for providing federal regulatory oversight of transmission pipelines. The agency’s Integrity Management Program is a transmission pipeline program started in 2000. This program focuses on regulations for transmission pipelines in high consequence areas, such as pipelines passing through high population centers or particularly sensitive ecological areas. 327 Pipeline Association for Public Awareness. (2023). Pipeline Safety Facts and Statistics. https://pipelineawareness.org/safety-information/pipeline-safety-factsstatistics/#:~:text=According%20to%20government%20and%20industry,failure%2C%20human%20error%20and%20 corrosion.
328 Pipeline and Hazardous Materials Safety Administration. (2023, May 4). Pipeline Safety: Gas Pipeline Leak Detection and Repair. https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2023- 05/Gas%20Pipeline%20Leak%20Detection%20and%20Repair%20NPRM%20-%20May%202023.pdf

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The Integrity Management Program specifies how pipeline operators must identify, prioritize, assess, repair, and validate the integrity of their pipelines through comprehensive analysis.

PHMSA’s 2005 Distribution Integrity Management Program Phase One report found a lack of risk-based assessment in managing distribution pipeline systems. A guidance document was developed to assist operators in deciding what actions are needed to comply with standards of the distribution integrity management program.328F
329
In 2002, PHMSA released control guidelines for gas leakage. The guidelines included a regulatory classification for leakage severity, as shown in Table 122.

Table 122: Leak Classifications
Grade Description Examples Action Criteria
1 A leak that represents an
existing or probable
hazard to persons or
property and requires
immediate repair or
continuous action until the
conditions are no longer
hazardous.

Any leak which, in the
judgment of operating
personnel at the scene is
regarded as an immediate
hazard.

Escaping gas that has
ignited.

Any indication of gas which
has migrated into or under a
building or into a tunnel.

Any reading at the outside
wall of a building or where
gas would likely migrate to
an outside wall of a building.

Any leak that can be seen,
heard, or felt and which is in
any location that may
endanger the general public
or property.

Requires prompt action to protect
life and property. Action may
require one or more of the
following:
 Implementing a company
emergency plan
 Evacuating premises
 Blocking off an area
 Rerouting traffic
 Eliminating sources of ignition
 Venting the area
 Stopping the flow of gas by
closing valves or other means
 Notifying police and fire
departments
2 A leak that is recognized
as being non-hazardous
at the time of detection,
but requires scheduled
repair based on probable
future hazard.

Any leak which, under
frozen or other adverse soil
conditions, would likely
migrate to the outside wall of
a building (Note: This type of
Grade 2 leak must be
repaired ahead of seasonal
freeze/thaw conditions).

Any leak which, in the
judgment of operating
Leaks should be repaired or
cleared within one calendar year
but no later than 15 months from
the date they were reported. In
determining the repair priority,
criteria such as the following
should be considered:
329 Pipeline and Hazardous Materials Safety Administration. (2005). Gas Distribution Integrity Management Program (DIMP) Integrity Management for Gas Distribution: Report of Phase 1 Investigations.https://www.phmsa.dot.gov/pipeline/gas-distribution-integrity-management/dimp-integrity-managementgas-distribution-report-of-phase-1-investigations-2005

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Grade Description Examples Action Criteria
personnel at the scene, is of
sufficient magnitude to
justify scheduled repair.
 Amount and migration of gas
 Proximity of gas to buildings
and subsurface elements
 Extent of pavement
 Soil type and soil conditions
such as frost cap, moisture,
and natural venting
3 A leak that is nonhazardous at the time of
detection and can be
reasonably expected to
remain non-hazardous.

Because petroleum gas is
heavier than air and will
collect in low areas
instead of dissipating, few
leaks can safely be
classified as
Grade 3.

Any reading under a street
in areas without wall-to-wall
paving where it is unlikely
the gas could migrate to the
outside wall of a building.

These leaks should be reevaluated during the next
scheduled survey, or within 15
months of the date reported,
whichever occurs first, until the
leak is re-graded or no longer
results in a reading.

Source: PHMSA, 2002

16.3.2 Hazard Profile
Past Events
PHMSA records of natural gas pipeline events in the State of California do not include any events in Santa Clara County. The Bay Area has not experienced a hazardous materials release event with a regional impact. Hazardous material releases are often localized due to the limited release of such events.329F
330
Location
All technological hazards including hazardous materials incidents, transportation incidents, pipeline hazards, and power failure are local in nature, but may cross jurisdictional lines.

Severity
The impact of leaks or spills of hazardous materials on the environment depends on the scale of the incident, the materials involved and the location of the spill. Spills along the California coast are well documented.

Warning Time
There is rarely any warning time before a leak or spill of hazardous materials. Explosions or fires associated with pipeline incidents can occur instantly and escalate quickly. 330 California Office of Emergency Services. (2018). 2018 State of California Hazard Mitigation Plan. https://www.caloes.ca.gov/office-of-the-director/operations/recovery-directorate/hazard-mitigation/state-hazardmitigation-planning/

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Critical Facilities and Infrastructure
It is unlikely that an oil spill will have a direct impact on most critical facilities and infrastructure. An important exception would be an oil spill near the intake of a water treatment plant, a power plant that uses water for cooling, or an industrial facility that uses water in its processing.

Environment
The impact of leaks or spills of hazardous materials on the environment depends on the scale of the incident, the materials involved and the sensitivity of the spill location. Spills can impact air quality, waterways, fish, and wildlife as well as damage habits.

Future Trends in Development
The anticipated additional development in the county’s urban areas, which are already near the pipelines (see Figure 75), will increase the number of people and businesses exposed to this hazard.

Cascading Impacts
Cascading impacts associated with the pipeline hazard include:
 Urban structure fires;
 Public health consequences for pipeline failures; and  Potential significant environmental impacts both long and short term, depending on the pipeline location.

16.3.3 Utility Failure, Power Outages, and Public Safety Power Shutoff Utility Failure
Utility failure is defined as any interruption or loss of utility service due to disruption of service transmission caused by accident, sabotage, natural hazards, or equipment failure. A significant utility failure is defined as any incident of a long duration, which would require the involvement of the local and/or state emergency management organizations to coordinate provision of food, water, heating, cooling, and shelter. Widespread outages can occur without warning or as a result of a forecasted event.

Generally, warning times are short in the case of utility failure. In cases where a failure is caused by natural hazards, greater warning time is possible.

Except for the cities of Palo Alto and Santa Clara, Pacific Gas and Electric (PG&E) is responsible for operating and maintaining the electrical transmission and distribution system in the OA. The utility supplies electricity to an approximate population of 1.7 million residential and business customers in 1,260 square miles of the OA. PG&E has both overhead and underground lines throughout the OA. The Silicon Valley Clean Energy Authority was created to help generate electricity from clean sources in the OA and currently serves 270,000 residents and businesses.

Wastewater and potable water utility restoration are essential to community continuity and recovery.

Interruption of these services may have cascading economic and environmental impacts.

Utility failure can cause cascading impacts including:
 Chemical accidents can occur after power is restored to industrial facilities. Power interruptions at chemical handling plants are of particular concern because of the potential for a chemical spill during restart (EPA, 2001).
 Without proper procedures for backup of data and systems, the loss of data, systems, and telecommunications is a risk incurred by utility failure. Data and telecommunications provide a primary method for service to the community by the government and the private sector. A loss of

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data or a system could result in loss of emergency dispatch capabilities, emergency planning services, infrastructure monitoring capabilities, access to statistical data, and loss of financial and personnel records. Loss of communication capability by first responders could have negative impacts on public safety. Backup systems such as amateur radio operators may be required during disaster to augment communications capabilities. Power outages can also lead to instances of civil disturbance, including looting.

Power Outages
Power outages are defined as any electrical system failure due to an unplanned disruption of service transmission caused by natural hazards, cyber-attacks, transportation accidents, accidental constructionrelated damage, sabotage, equipment failure or an intentional interruption through rolling blackouts or power shutoffs.

A significant outage is an incident of a long duration, which would require the involvement of the local and/or state emergency management organizations to coordinate provision of food, water, heating, cooling, and shelter. Widespread outages can occur without warning or as a result of a forecasted event.

Generally, warning times are short in the case of utility failure. In cases where a failure is caused by natural hazards, greater warning time is possible. In the OA, electric power is provided to the cities by ten utilities, as shown in Table 123.

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Table 123: Electric Providers in Santa Clara County30F
331
Jurisdiction
Commercial
Energy of
California
Freedom
Energy
Hudson
Energy
Pacific
Gas and
Electric
Company
Palo Alto
Utilities
Pilot
Power
Group
Public
Power &
Utility of
Maryland
San José
Clean
Energy
Silicon
Valley
Power
StateWise
Energy
Campbell 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Cupertino 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Gilroy 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Los Altos 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Los Altos
Hills

14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Los Gatos 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Milpitas 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Monte
Sereno

14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Morgan Hill 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Mountain
View

14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Palo Alto 1.30% 1.30% 1.30% 1.30% 90.88% 1.30% 1.30% 1.30% 1.30% 1.30% San José 12.52% 12.52% 12.52% 12.52% 12.52% 12.52% 12.52% 12.38% 12.52% 12.52% Santa Clara 49.92% 50.08%
Saratoga 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% Sunnyvale 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 14.29% 331 Find Energy LLC. (2022 August 9). Santa Clara County, California Electricity Rates and Statistics. https://findenergy.com/ca/santa-clara-county-electricity/#citycoverage

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16.3.4 Hazard Profile
Public Safety Power Shutoff
In 2012, the California Public Utilities Commission (CPUC) ruled that the California Public Utility Code gives electric utilities the authority to shut off electric power to protect public safety, since power supply systems have the potential to ignite wildfires.

These shutoffs typically end within 24 hours after the weather conditions have subsided but may extend beyond the 24-hour timeframe, depending on conditions. An extended power outage due to a power shutoff, is likely to have the same impacts on a community as described above for an unplanned power outage.

Past Events
The California Public Utilities Commission collects and compiles data on public safety power shutoffs Their records from 2019 through October 2021 show that the number of days with power shutoffs anywhere in the system has increased each year (see Table 124).

Table 124: Power Shutoffs Statewide31F
332
Year
Calendar Days
with a Power
Shutoff
Anywhere in
California
Power Shutoff Duration
Shortest Longest
2019 26 0 days, 1 hr., 19 min. 5 days, 21 hr., 0 min.
2020 31 0 days, 0 hr., 16 min. 5 days, 10 hr., 32 min.
2021 (through 10/22/21) 42 0 days, 2 hr., 52 min. 4 days, 18 hr., 38 min.

Location
Each power shutoff is linked to a specific circuit, but on many days, multiple circuits experience shutdowns, resulting in widespread power outages. Power loss from other causes is typically limited to local areas but could also affect larger regions.

Severity
The severity of power loss of any type relates to the number of days without power and the situation of the population and businesses without power. A 16-minute power loss is not significant to most, but to a person with a critical electrical medical device the loss would be severe. A loss of power for four days would be considered severe by all.
332 Union of Concerned Scientists. (2022, February 2). California Utilities Shut Off Power for Fewer People, But Too Many Are Still in the Dark. https://blog.ucsusa.org/mark-specht/california-utilities-shut-off-power-for-fewer-people-buttoo-many-are-still-in-the-dark/

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Warning Time
Warning time for power outages will depend on the cause. An outage caused by hitting a distribution line or by an accident at a substation will occur without warning. However, an outage caused by weather conditions may come with some advance notice. Public safety power shutoffs are intended to provide adequate warning time.

Critical Facilities and Infrastructure
The impact of power outage on the facilities themselves is likely to be minimal but disruption of critical services would be significant.

Environment
The impact of power outage on the environment is unlikely but not impossible.

Future Trends in Development
In a growing community, more people and more businesses mean more are inconvenienced and/or negatively impacted by power outages.

Cascading Impacts
A county or city in the dark because of a power outage or shutdown could see an increase in crime.

Other impacts could include the following:
 Individuals would not have use of power-dependent medical equipment.  Chemical accidents can occur after power is restored to industrial facilities. Power interruptions at chemical handling plants are of particular concern because of the potential for a chemical spill during restart.32F
333
 Disrupting communications.
 Without proper procedures for backup of data and systems, the loss of data, systems, and telecommunications is a risk incurred by power outages. Data and telecommunications provide a primary method for service to the community by the government and the private sector. A loss of data or a system could result in loss of emergency dispatch capabilities, emergency planning services, infrastructure monitoring capabilities, access to statistical data, and loss of financial and personnel records. Loss of communication capability by first responders could have negative impacts on public safety. Backup systems such as amateur radio operators may be required during disasters to augment communications capabilities.  Closing retail businesses, grocery stores, gas stations, ATMs, banks, and other services.  Causing food spoilage and water contamination.
 Discomfort for those living without heat or without cooling during the outage.  Power outages can also lead to instances of civil disturbance, including looting. 333 Environmental Protection Agency. (2021, February). Risk of Chemical Accidents During Process Startup. https://www.epa.gov/sites/default/files/2021-02/documents/ncistartupsafety-enforcementalert.pdf

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16.4 Epidemic and Pandemic
An outbreak occurs when there are more cases of a particular disease than expected in each area, or among a specific group of people, over a particular period of time. Epidemic has a similar definition, but generally refers to when a larger number of people or larger geographic area are experiencing an outbreak. In an outbreak or epidemic, it is presumed that the cases are related to one another or that they have a common cause.3F
334 A pandemic then refers to an epidemic which has spread over a large area such as an entire country, or even a continent, usually affecting a larger number of people.

The Santa Clara County Department of Public Health is responsible for protecting and improving the health of the community within the OA. The public health department responds to public health related emergencies and disasters and supports field responders at medical and rescue incidents. The OA has numerous health care facilities within its borders, including the following:
 The Stanford Health Care-Stanford Hospital in Stanford  El Camino Hospital in Mountain View
 Santa Clara Medical Center, in Santa Clara
 Good Samaritan Hospital in San José
 Kaiser Permanente San José Medical Center
 Lucile Packard Children’s Hospital at Stanford
The following sections describe commonly recognized human health hazards that are a concern in the OA.

COVID-19
In late 2019, patients were reported exhibiting symptoms of an abnormal flu-like illness. The initial outbreak rapidly expanded across the world over the next few months and became known as COVID-19, a respiratory disease caused by SARS-CoV-2, a type of coronavirus. The disease spreads from personto-person, usually through close contact such as when someone in conversational distance coughs, sneezes, speaks, sings, or breathes.34F
335 The disease can also spread through the air in congested areas where people tend to conjugate and through touching surfaces contaminated by the virus.

Symptoms of COVID-19 include fevers, chills, and sore throat. Other symptoms include muscle aches, severe fatigue or tiredness, headache, new and persistent cough, shortness of breath, and loss or change of sense of taste or smell. Symptoms usually begin within 5-6 days from the time of exposure.

However, some people with the disease remain asymptomatic. It is believed that some asymptomatic people may have been able to transmit the disease to others, but further research is needed. Everyone is able to be infected although older people, people with pre-existing conditions, and people who are pregnant are more likely to be infected or have a serious infection.

By March 4, 2020, Governor Gavin Newsom declared a State of Emergency to make additional resources available, formalize emergency actions already underway across multiple state agencies and departments, and help the state prepare for broader spread of COVID-19. The proclamation came as the number of positive California cases rose and following one official COVID-19 death. Since then, cases 334 Center for Disease Control and Prevention. (n.d.). Lesson 1: Introduction to Epidemiology. https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section11.html 335 World Health Organization. (December 2021). Coronavirus disease (COVID-19): How is it transmitted? https://www.who.int/emergencies/diseases/novel-coronavirus-2019/question-and-answers-hub/q-a-detail/coronavirusdisease-covid-19-how-is-ittransmitted?gclid=EAIaIQobChMI_oSJxvnq_gIVFdiGCh2sYQe4EAAYASAAEgJByfD_BwE

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continued to rise and over 1.1 million people died of COVID-19 in the United States alone. Measures were implemented to reduce the rapid spread including social distancing, mandatory testing, and isolation and quarantine policies.

Figure 77 illustrates the course of COVID-19 in Santa Clara County from onset through January 2023. As this plan is being prepared, the California COVID-19 State of Emergency ended on February 28, 2023, and the COVID-19 national emergency and public health emergency is scheduled to end on May 11, 2023.

Figure 77: Santa Clara COVID Cases 2020–202335F
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Almost 7,000 cases of COVID-19 per day were recorded across the county at the peak of the pandemic, as shown in Table 125, but the percentages of each city’s population that were infected ranged from 9.6% in Monte Sereno to 37.3% in Gilroy.
336 Santa Clara County Public Health. (2023). COVID Cases and Deaths Dashboard. https://covid19.sccgov.org/dashboard-cases-and-deaths

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Table 125: COVID-19 Cases Countywide and by City of Residence36F 337
County/City Cases Population Rate City Cases Population Rate Santa Clara
Countya
496,338 1,885,508 26.3% Monte Sereno 331 3,492 9.5%
Campbell 10,005 42,470 23.6% Morgan Hill 13,696 43,876 31.2% Cupertino 8,523 60,614 14.1% Mountain
View
13,885 80,993 17.1%
Gilroy 20,715 55,525 37.3% Palo Alto 10,714 67,019 16.0% Los Altos 4,913 30,588 16.1% San José 285,709 1,026,658 27.8% Los Altos
Hills
1,231 8,517 14.5% Santa Clara 27,388 126,209 21.7%
Los Gatos 6,805 30,922 22.0% Saratoga 4,540 30,886 14.7% Milpitas 17,293 77,457 22.3% Sunnyvale 27,079 152,323 17.8% a Countywide total (includes city cases).

The spread and scope of COVID-19 was more than sufficient for it to be declared a pandemic. The only comparable outbreak in modern times could be the 1918 flu pandemic which affected an estimated one third of the world’s population. The two pandemics shared similar characteristics; their exact origins are unknown, it took multiple years for the diseases to run their course, and they required significant local, regional, and global efforts to respond and recover from.

Today, COVID-19 still represents a series threat however, some of that threat has been mitigated by the development of COVID testing capabilities and vaccines. COVID vaccines have been shown to effectively decrease the severity and likelihood of infection. COVID-19 is expected to be endemic, meaning that it will remain present in certain parts of the world with relatively low spread except for occasional outbreaks.

For this reason, it will continue to be a challenge that public health professionals will have to prepare for and respond to. There are still many unknowns about the disease as well. One significant threat is being referred to as “long COVID” or Post-COVID Conditions (PCC). Some people who develop the disease are experiencing long-term symptoms that continue or develop after the initial infection. These symptoms can include a wide range of problems including tiredness, fatigue, fever, difficulty breathing, coughing, difficulty thinking of concentrating, and more. While scientists work to develop effective treatment, the public, government, and private sector should be aware of this poorly understood condition.37F 338
Disease Outbreaks
In addition to COVID-19, there have been other major disease outbreaks within Santa Clara County since 2018 (see Table 126).38F
339
337 Santa Clara County Public Health. (2023). COVID Cases and Deaths Dashboard. https://covid19.sccgov.org/dashboard-cases-and-deaths
338 Centers for Disease Control and Prevention. (December 2022). Long COVID. https://www.cdc.gov/coronavirus/2019-ncov/long-termeffects/index.html?s_cid=11841:%2Blong%20%2Bcovid:sem.b:p:RG:GM:gen:PTN:FY23 339 California Office of Emergency Services. (2023). California State Hazard Mitigation Plan – Part 3. https://www.caloes.ca.gov/wp-content/uploads/Hazard-Mitigation/Documents/California-SHMP_PublicReview_Vol1- Part3.pdf

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Lyme Disease
Lyme disease is caused by certain bacteria (called Borrelia burgdorferi) that can spread from the bite of an infected western blacklegged tick. Lyme disease may start as a mild illness that begins 3 to 30 days after a tick bite and might easily be mistaken for other common illnesses like a cold or flu. Signs and symptoms also can include a red, painless rash that may spread over time. If Lyme disease is not treated, it might develop into more severe health problems.39F
340
Valley Fever
Valley fever (also called coccidioidomycosis or “cocci”) is a disease caused by a fungus that grows in the soil and dirt in some areas of California and the southwestern United States. People and animals can get sick when they breathe in dust that contains the Valley fever fungus. This fungus usually infects the lungs and can cause respiratory symptoms including cough, fever, chest pain, and tiredness.340F 341
West Nile Virus
West Nile Virus (WNV) is a mosquito-borne disease that was first detected in the United States in 1999. WNV first appeared in California in 2003, and by 2004, WNV had spread to all 58 counties. In 2022, there was one human case, 26 dead birds and 23 mosquito samples taken.341F 342
Risk of infection is reduced through the coordinated efforts of local and state public health and vector control agencies. People can protect themselves from WNV by taking precautions to prevent mosquito bites.342F
343
Table 126: Disease Outbreaks Identified in Santa Clara County, 2018–202234F 344
Disease Outbreaks 2018 2019 2020 2021 2022
COVID-19 x x x
Lyme Disease x x
Valley Fever x x x x x
West Nile Virus x x x x
Other Diseases of Concern
Influenza
Epidemics of the flu typically occur in the fall and winter. Because flu seasons fluctuate in length and severity, a single estimate cannot be used to summarize influenza-associated deaths. Figure 78 depicts the weekly percentage of emergency department visits for influenza-like illness in Santa Clara County by influenza season. The most recent reports are for February 22, 2023. 340 California Department of Public Health. (n.d.) Lyme Disease. https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/LymeDisease.aspx 341 California Department of Public Health. (n.d.). What is Valley Fever? https://www.cdph.ca.gov/Programs/CID/DCDC/pages/Coccidioidomycosis.aspx 342 California Department of Public Health. (n.d.) 2022 West Nile Virus Activity in California. West Nile. https://westnile.ca.gov/
343California Department of Public Health. (n.d.) West Nile Virus. https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/WestNileVirus.aspx 344 California Department of Public Health. (n.d.) Diseases and Conditions. https://www.cdph.ca.gov/Pages/allDiseases.aspx

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Figure 78: Weekly Percentage of Emergency Department Visits for Influenza-Like Illness in Santa Clara County, 2019, to February 22, 202334F
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H1N1
In April 2009, the World Health Organization (WHO) issued a health advisory on an outbreak of influenzalike illness caused by a new subtype of influenza A (A/H1N1) in Mexico and the United States. The disease spread rapidly, and in June the WHO declared an H1N1 pandemic, marking the first global pandemic since the 1968 Hong Kong flu. In October, the U.S. declared H1N1 a national emergency. In August 2010, the WHO declared an end to the pandemic globally. H1N1 viruses and seasonal influenza viruses are co-circulating in many parts of the world. It is likely that the 2009 H1N1 virus will continue to spread for years to come, like a regular seasonal influenza virus.

H5N1/H7N9
The highly pathogenic H5N1 avian influenza virus is an influenza A subtype that occurs mainly in birds, causing high mortality among birds and domestic poultry. Outbreaks of highly pathogenic H5N1 among poultry and wild birds are ongoing in a number of countries.

H5N1 virus infections of humans are rare, and most cases have been associated with direct poultry contact during poultry outbreaks. Rare cases of limited human-to-human spread of H5N1 virus may have occurred, but there is no evidence of sustained human-to-human transmission. Nonetheless, because all influenza viruses have the ability to change and mutate, scientists are concerned that H5N1 viruses one day could be able to infect humans more easily and spread more easily from one person to another, potentially causing another pandemic.
345 Santa Clara County Public Health. (2023). Influenza Report. https://publichealthproviders.sccgov.org/diseases/influenza/influenza-report

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While the H5N1 virus does not now infect people easily, infection in humans is much more serious when it occurs than is infection with H1N1. More than half of people reported infected with H5N1 have died.

Infections in humans and poultry by a new avian influenza A virus (H7N9) continue to be occasionally.

The last outbreak was in 2017 in China. Another case was reported in Malaysia. While mild illness in human cases has been seen, most patients have had severe respiratory illness, and some have died.

Source investigation by Chinese authorities is ongoing. Many of the people infected with H7N9 reportedly have had contact with poultry. However, some cases reportedly have not had such contact. Close contacts of confirmed H7N9 patients are being followed to determine whether any human-to- human spread of H7N9 is occurring. No sustained person-to-person spread of the H7N9 virus has been found at this time. However, based on previous experience with avian flu viruses, some limited human- to-human spread of this the virus would not be surprising.

As of the time of this writing, there is currently an outbreak of avian flu in birds. Over 58 million birds have been impacted, primarily in North and South Dakota345F
346. Santa Clara County has not reported any cases
of avian influenza. The first case of influenza A (H5N1) in humans was reported in the U.S. in April 2022.

Despite the unlikely transmission of the bird flu to humans, the CDC still recommends preventative measures for those exposed to infected birds. No cases of H7N9 have been detected in people in the United States.

Smallpox
Smallpox is a sometimes-fatal infectious disease. There is no specific treatment, and the only prevention is vaccination. Symptoms include raised bumps on the face and body of an infected person. The oldest evidence of smallpox was found on the body of Pharaoh Ramses V of Egypt who died in 1157 BC.

Outbreaks have occurred from time to time for thousands of years, but the disease is now eradicated after a successful worldwide vaccination program. The last case of smallpox in the United States was in 1949. The last naturally occurring case in the world was in Somalia in 1977. As of the publication of this document, there are no cases of smallpox in the world. Currently only two locations in the world have samples of smallpox: The Center for Disease Control (CDC) in Atlanta and the Ivanovsky Institute of Virology in Russia.

After the disease was eliminated, routine vaccination among the general public was stopped. Therefore, any cases of smallpox in the world would be considered an immediate international emergency. In 2003, the Wisconsin Division of Public Health conducted an investigation of state residents who became ill after having contact with prairie dogs. The cases appeared in May and June of 2003, and symptoms in the human cases included fever, cough, pox-like rash and swollen lymph nodes. CDC laboratory test results indicated that the cause of the human illness was Monkeypox, an orthopox virus that could be transmitted by prairie dogs. This outbreak, and the potential use of smallpox as a weapon of bioterrorism, brought the fear of smallpox back to the forefront of the population. A detailed nationwide smallpox response plan created at the end of 2002 is designed to quickly contain a potential outbreak and vaccinate the population.
346 U.S. Department of Agriculture. (May 2023). 2022-2023 Confirmations of Highly Pathogenic Avian Influenza in Commercial and Backyard Flocks. https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-diseaseinformation/avian/avian-influenza/hpai-2022/2022-hpai-commercial-backyard-flocks

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Viral Hemorrhagic Fevers
Viral hemorrhagic fevers (VHFs) are a group of illnesses caused by several distinct families of viruses.

VHF describes a multisystem syndrome (multiple systems in the body are affected). Characteristically, the overall vascular system is damaged and the body’s ability to regulate itself is impaired. These symptoms are often accompanied by hemorrhage (bleeding); however, the bleeding itself is rarely life- threatening.

While some types of hemorrhagic fever viruses can cause relatively mild illnesses, many cause severe, life-threatening disease.

The viruses that cause VHFs are distributed over much of the globe. However, because each virus is associated with one or more particular host species, the virus and the disease it causes are usually seen only where the host species live. Some hosts, such as the rodent species carrying several of the New World arenaviruses, live in geographically restricted areas. Therefore, the risk of getting VHFs caused by these viruses is restricted to those areas. Other hosts range over continents, such as the rodents that carry viruses that cause the Hantavirus pulmonary syndrome in North and South America, or the rodents that carry viruses that cause hemorrhagic fever with renal syndrome in Europe and Asia.

Ebola
The 2014 Ebola virus outbreak was unprecedented in geographical reach and impact on health care systems across the globe. This was the largest and deadliest Ebola virus outbreak ever recorded. It was the first time the West African countries of Guinea, Liberia, Sierra Leone, Nigeria, Mali, and Senegal saw the virus. Ebola is more common in Central African countries, such as the Democratic Republic of Congo and Sudan, where it was first discovered in 1976. It was also the first time that Ebola made it to the United States and Europe, prompting world-wide preparedness and response efforts. The outbreak was closely monitored, and traveler screenings were developed for those returning from West Africa.

In August 2014 two U.S. healthcare workers returned to the United States for treatment for Ebola. The case that most impacted the health care system in the United States was a patient diagnosed with Ebola in Dallas, Texas who died due to Ebola in October 2014. The nurse who provided care for him later tested positive for Ebola. This caused responses across the country from hospitals, emergency medical teams, fire departments and public health agencies to enhance isolation precautions, develop emergency policies, train with personal protective equipment, and conduct multi-agency emergency exercises in case the spread of Ebola became a pandemic.

Before the 2014 outbreak, only 2,200 cases of Ebola had been recorded and 68 percent were fatal.

Twenty percent of new Ebola infections were linked to burial traditions in which family and community members wash and touch dead bodies before burial. In Guinea, 60 percent of Ebola infections were linked to traditional burial practices.

Plague
Plague is a potentially fatal infectious disease of animals and humans caused by the Yersinia pestis bacterium. People usually get plague from being bitten by a flea that is carrying the plague bacterium or by handling an infected animal. Today, modern antibiotics are effective against plague, but if an infected person is not treated promptly, the disease is likely to cause illness or death.

Plague is an ancient disease but outbreaks throughout the world continue. Major plague epidemics occurred in the middle of the sixth century in Egypt, Europe, and Asia; during the 14th century in Europe, following caravan routes; in the 18th century in Austria and the Balkans; and in the late 19th century worldwide (but mostly in China and India). Manchuria in 1910–1911 witnessed about 60,000 deaths due to pneumonic plague with a repeat in 1920–1921. A minor outbreak occurred as recently as the summer of 1994 in Surat, India, closely following an earthquake in September 1993. Globally, the WHO reports 1,000 to 3,000 cases of plague every year.

In North America, plague is found in certain animals and their fleas from the Pacific Coast to the Great Plains, and from southwestern Canada to Mexico. The last urban plague epidemic in the United States

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occurred in Los Angeles in 1924–25. Since then, human plague in the U.S. has occurred as mostly scattered cases in rural areas (an average of 10 to 15 persons each year per the CDC). Most human cases in the United States occur in northern New Mexico, northern Arizona, southern Colorado, California, southern Oregon, and far western Nevada.

Zika Virus
Zika is a disease transmitted by yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus). An Aedes mosquito can only transmit Zika virus after it bites a person who has this virus in their blood. The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild, with symptoms lasting for several days to a week after being bitten by an infected mosquito. People usually do not get sick enough to go to the hospital, and they rarely die from the Zika virus. For this reason, many people might not realize they have been infected. However, Zika virus infection during pregnancy can cause a serious birth defect called microcephaly (abnormally small head and brain), as well as other severe fetal brain defects. Once a person has been infected, he or she is likely to be protected from future infections. Zika virus is not spread through casual contact but can be spread by infected men to their sexual partners. There is a growing association between Zika and Guillain-Barré Syndrome, a disease affecting the nervous system.

The mosquitos that carry Zika are not native to California and from 2015 to the publishing of this document, there has been no local mosquito-borne transmission of Zika virus in California.346F 347 However,
infestations have been reported in multiple counties in California. Most cases were documented in people who were infected while traveling outside the United States. The CDC maintains a list of countries where zika has been reported. Required reporting for Zika in California began in 2016. These numbers may be underestimated given multiple factors, including the fact many people are asymptomatic. Currently, the represent a decrease in cases in Santa Clara County. Thirty-six cases were reported from 2015 to 2016, 14 in 2017, 8 in 2018, 3 in 2019, and no cases since.

16.4.2 Hazard Profile
Location
These diseases are a worldwide threat, occasionally increasing in severity in some locations. Areas with higher concentrations of vulnerable populations are more likely to experience a serious outbreak.

Severity
The severity can range from very localized, in just case of just a few infected, to severe with widespread infection and complications. Widespread sickness and loss of life have resulted from the COVID-19 Pandemic. The most recent totals available as this plan is being written show a total of 496,338 confirmed cases and 2,714 deaths in Santa Clara County.

Warning Time
The first human cases of the diseases discussed in this MJHMP appeared with very little warning, as did the start of recent outbreaks. Air travel radically increases the speed at which disease spreads around the world. Today’s communication does provide warning to local communities of diseases which could be a problem for them in the future.
347 The Mercury News. (2016, March). Four Zika virus cases reported in Bay Area. https://www.mercurynews.com/2016/03/03/four-zika-virus-cases-reported-in-bay-area/

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Critical Facilities and Infrastructure
No direct impact is expected on the facilities, but the operation of medical-related facilities can and have been overwhelmed. The operation of critical infrastructure can be impacted by employee absence due to illness.

Environment
Epidemic, pandemic, and vector-borne diseases can be directly or indirectly tied to environmental impacts. Air pollution in California dropped suddenly during the COVID-19 lockdown between March 19 and May 7, 2020. Changes in the environment, due to human stressors or climate change, may increase vector-borne diseases and drive disease emergence in wildlife which could be transmitted to humans.347F 348
Future Trends in Development
Future development in Santa Clara County is not anticipated to have any direct impact on the risk of epidemic/pandemic disease. There could be an indirect impact from the development of buildable lands in that the population that could be exposed to this hazard would be increased. However, no direct impact is expected.

Cascading Impacts
In general, cascading impacts are not anticipated. A widespread pandemic like COVID-19 could threaten global supply chains and the local economy due to disruptions, delays, and shutdowns due to preventative employee health measures and lack of healthy workers.

16.5 Fog
The National Weather Service describes nine types of fog.348F 349 Fog in the Santa Clara County OA has
different origins depending on the time of year. In summer, fog forms when warm, moist, and stable air is blown across a cooler surface (land or water). The air temperature falls until the dew point is reached and condensation occurs. Fog typically occurs in the Bay Area in June, July, and August. It is usually foggy in the morning, with fog burning off as the temperatures rise.

In winter, fog typically originates from the Great Valley. Radiation (ground) fog forms in the moist regions of the Sacramento River Delta and arrives to the region via Suisun and San Pablo Bays and San Francisco Bays on cool easterly winds. While this type of fog is less frequent than summer fog, appearing one winter and not again for years, it is typically denser and more likely to lead to significantly reduced visibility.349 F
350
The fog typical for the San Francisco Bay Area is known as advection fog. This type of fog forms when warm, moist, and stable air is blown across a cooler surface (land or water). The air temperature falls until the dew point is reached and condensation occurs. Fog typically occurs in the Bay Area in the June, July, and August. It is usually foggy in the morning, with fog burning off as the temperatures rise. 348 Semenza JC, Rocklöv J, Ebi KL. (May 2022). Climate Change and Cascading Risks from Infectious Disease. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9334478/
349 National Oceanic and Atmospheric Administration. (n.d.). National Weather Service Glossary. https://w1.weather.gov/glossary/index.php?word=fog
350 L.A. Times. (n.d.). Inside the return of Tule fog in California’s Central Valley. https://www.latimes.com/projects/return-tule-fog-california-central-valley

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16.5.1 Hazard Profile
Past Events
The National Oceanic and Atmospheric Administration Storm Events Database reports 5 events of dense fog since the last plan update. Dense fog means the visibility was limited to a quarter of a mile or less.

However, this database does not account for the more common fog events in the OA, which typically occur in the morning when the temperatures are cool, and the relative humidity is high.

Location, Frequency, and Warning Time
Fog can occur almost anywhere during any season and is classified based on how it forms, which is related to where it forms. Certain seasons are more likely to have foggy days or nights based on a number of factors, including topography, nearby bodies of water, and wind conditions. Fog can form overnight. Local National Weather Service offices issue a Dense Fog Advisory when widespread dense fog develops. The California Department of Transportation (Caltrans) has implemented a fog detection and warning system that uses speed and visibility detectors to assess road conditions, traffic management software to process data and control the field devices, and changeable message signs to provide information to the traveling public.350F
351
Severity
Heavy fog is particularly hazardous when it reduces visibility to ¼ mile or less. Although fog seems like a minor hazard, it can have significant impacts. Severe fog incidents can close roads, cause vehicle accidents, cause airport delays, and impair the effectiveness of emergency response. The California Highway Patrol records and news reports describe highway accidents, many with serious injuries or deaths, due to low visibility in dense fog. Many of those accidents involve chain reaction crashes including recent crashes in Santa Clara County. Financial losses associated with transportation delays caused by fog have not been calculated in the United States, but it is likely to be substantial.

Critical Facilities and Infrastructure
Critical facilities and infrastructure in the Santa Clara County OA would only be impacted indirectly by the fog hazard.

Environment
In the context of the MJHMP Update, fog is considered to be a hazard, but fog plays a key role in California’s ecosystems and agricultural sector.

Future Trends in Development
As more lands are developed in the Santa Clara County OA and more people use the area’s highways, the fog hazard’s impact will increase.

Cascading Impacts
Potential cascading impacts of dense fog involve delays in response to all other hazard events in the vicinity and relate to highway accidents, some of which could involve hazardous materials. 351 Berman, M., Liu, J., and Justison, L. (2009). Caltrans Fog Detection and Warning System. https://rosap.ntl.bts.gov/view/dot/27652

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Scenario
The worst-case scenario for the fog hazard is probably the situation today. The negatives of delays, inconvenience, and potential traffic accidents are clear. Increases in temperatures in the Santa Clara County OA and likely related decreases in fog could have a more long-term negative impact on the environment and agriculture.

16.6 Identified Needs
This assessment of the other hazards of interest led to identification of the following needs throughout the Santa Clara County OA:
 Continue regular and redundant emergency preparedness training for field level responders (police, fire, and public works) and public information staff in order to respond quickly in the event of a disaster associated with the identified hazards of interest. Enhance awareness training for all local government employees to recognize threats or suspicious activity in order to prevent an incident from occurring.
 Continue all facets of hazardous materials team training and response through commitment of resources from the Environmental Health Department, local fire departments, and potential funding through homeland security budgets.
 Continue to improve response times for public safety throughout the Santa Clara County OA so as to reduce exposure to human-caused incidents. Maintain appropriate staffing levels of public safety personnel to address vulnerabilities identified in this section.  Continue to implement the hazardous materials business plan with enhancements, as warranted by the type of uses in the Santa Clara County OA and innovative technologies in preventing hazardous materials incidents.
 Continue to work proactively with industrial businesses regarding placards and labeling of containers, emergency plans and coordination, standardized response procedures, and notification of the types of materials being transported through the Santa Clara County OA. On at least an annual basis, conduct random inspections of transporters as allowed by the business; install mitigating techniques at critical locations; implement routine hazard communication initiatives; enhance security along the transportation corridors; and continuously look to the use of safer alternative products to conduct all business and transportation operations.  Participate in regional, state, and federal efforts to gather terrorism information at all levels and keep public safety officials briefed at all times regarding any local threats. Further develop response capabilities based on emerging threats.
 Commit support to the Bay Area Urban Area Security Initiative by dedicating fire, emergency medical services, emergency management grant managers, and police personnel to the program as funded with Homeland Security grants.
 Participate in the Cal OES Disaster Resistant California annual conference and other training sessions sponsored by regional, state, and federal agencies.  Use Crime Prevention Through Environmental Design in future planning efforts as well as enhancing existing infrastructure and buildings to prevent or mitigate human-cause incidents.

Crime Prevention Through Environmental Design is an urban planning design process that integrates crime prevention with neighborhood design and community development. The process is based on the theory that the proper design and effective use of the built environment can reduce crime and the fear of crime and improve the quality of life. It creates an environment where the physical characteristics, building layout, and site planning allow inhabitants to become key agents in ensuring their own security.

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 Participate in regional training exercises per the requirements of Homeland Security Presidential Directive #8 in support of national preparedness. These training exercises may be sponsored by the U.S. Department of Homeland Security San José office, the Bay Area Urban Area Security Initiative, local government offices of homeland security, grant funds through Cal OES, or FEMA.

Training exercises test and evaluate the ability to coordinate the activities of local and state government first responders, volunteer organizations and the private sector in responding to terrorism and technological hazards. The trainings enhance interagency coordination, provide training to staff, test response and recovery capabilities, and implement the Standardized Emergency Management System, the National Incident Management System, and the California and national mutual aid systems.
 Work with the private sector to enhance and create business continuity plans to be followed in the event of an emergency.
 Review existing automatic aid and mutual aid agreements with other public safety agencies to identify opportunities for enhancement.
 Identify, relocate, or construct a redundant Emergency Operations Center in a location away from hazards.
 Maintain an emergency services information line that the public can contact 24 hours a day during an emergency to ask questions of emergency staff.  Coordinate with all school districts in the OA and individual cities to ensure that their emergency preparedness plans include preparation for human-caused incidents.  Encourage local businesses to adopt information technology and telecommunications recovery plans.
 Promote 72-hour self-sufficiency through the United Neighborhoods of Santa Clara County and other neighborhood associations, emergency preparedness efforts through local governments, emergency preparedness websites of local governments, civic organizations and the private sector, public outreach, and other means. Ensure inclusion of program information for people with disabilities and others with access and functional needs.  Prepare and present the human-caused hazard risk and preparedness program to the public through meetings, town hall gatherings, and preparedness fairs and outreach.  Maintain any and all citizen advisory groups and periodically e-mail emergency preparedness information including human-caused hazard preparedness instructions and reminders.  Support disease prevention through vaccination and personal emergency and disaster preparation to help reduce the impacts of human health hazards.  Integrate medical and response personnel in a unified command to provide care when needed in response to human health hazards.
 Adequately train and supply medical and response personnel.  Carry out up-to-date and functional all-hazard contingency planning.  Develop a system for informing the public with a unified message about the human health hazard.  Provide health agencies and facilities with surge capacity management and adaptation to the rising number and needs of the region.

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16.7 Related Plans
The following plans also address issues related to the “other hazards,” including response priorities.

Santa Clara County Operational Area Emergency Operations Plan and Annexes
The Santa Clara County OA Emergency Operations Plan is an all-hazards document describing the OA’s Emergency Operations organization, compliance with relevant legal statutes, other guidelines, and critical components of the Emergency Response System. The Emergency Operations Plan consists of threat summaries based on a Santa Clara County OA hazard analysis. This hazard analysis was conducted by Santa Clara County OEM staff, providing a description of the local area, risk factors and the anticipated nature of situations that could occur in the Santa Clara County OA. The Emergency Operations Plan is activated during extraordinary emergency situations associated with large-scale disasters or emergencies affecting the Santa Clara County OA.

Santa Clara County Public Health Department Plan
This Santa Clara County Public Health Department Plan outlines the efforts to prepare for response to a disaster that has a medical/health component. The Countywide Medical Response System plan is focused on the goal of terrorism preparedness, and addresses topics such as risk communications, decontamination, personal protective equipment, mass prophylaxis, education, training, and exercises.

Each topic identifies participating agencies, including fire, law enforcement, hospitals, emergency management, schools, the medical examiner, mental health services, and many others. The plan further enumerates a list of responsibilities to the Countywide Medical Response System for each identified agency, as well as a list of public health commitments through the system that will assist those agencies.

Hazardous Materials Business Plans
Hazardous materials business plans are implemented by Certified Unified Program Agencies within their jurisdictions, along with local fire departments to protect human health and the environment from hazardous materials incidents.

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17 Mitigation Strategy

17.1 Goals and Objectives
Hazard mitigation plans must identify goals for reducing long-term vulnerabilities to identified hazards (44 CFR Section 201.6(c)(3)(i)). A guiding principle, a set of goals and measurable objectives for this plan were reviewed and approved by the larger Planning Team based on data from the preliminary risk assessment and updates to mitigation priorities since the previous MJHMP. The guiding principle, goals, objectives, and actions in this plan all support each other. Goals were selected to support the guiding principle. Objectives were selected that met multiple goals. Actions were prioritized based on the action meeting multiple objectives.

17.1.1 Guiding Principle
A guiding principle focuses the range of objectives and actions to be considered. This is not a goal because it does not describe a hazard mitigation outcome, and it is broader than a hazard-specific objective. The guiding principle for this hazard mitigation plan is as follows:

To equitably reduce risk and increase resilience by establishing and promoting a comprehensive mitigation program and efforts to protect the Whole Community and environment from identified natural and humaninduced hazards.

17.1.2 Goals
The following are the mitigation goals for this plan:

1. Actively develop community awareness, understanding, and interest in hazard mitigation and empower the Operational Area to engage in the shaping of associated mitigation policies and programs.

2. Minimize potential for loss of life, injury, social impacts, and dislocation due to hazards.

3. Minimize potential for damage to property, economic impacts, and unusual public expense due to hazards.

4. Minimize likelihood and impact of hazards causing environmental damage or damaging open space/nature preserves in the County and preserving ecological connectivity in the region and by working with residents to help build community capacity to respond and adapt to hazards and emergencies.

5. Effectively deliver essential information to the whole community that promotes personal preparedness and includes advice to reduce personal vulnerability to hazards.

6. Encourage programs and projects that promote community resiliency by maintaining the functionality of critical Operational Area resources, facilities, and infrastructure.

7. Pursue feasible, cost-effective, grant eligible, and environmentally sound hazard mitigation measures.

8. Increase adaptive capacity to reduce risk from hazard impacts that stem from a changing climate.

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9. Remove barriers for local governments to access mitigation funding (broad vs. specific) and reduce the administrative pain points to recipient agencies during the project deployment and auditing phases.

The effectiveness of a mitigation strategy is assessed by determining how well these goals are achieved.

17.1.3 Objectives
Each selected objective meets multiple goals, serving as a stand-alone measurement of the effectiveness of a mitigation action, rather than as a subset of a goal. The objectives also are used to help establish priorities and have been reviewed and approved by the Mitigation Strategy Working Group, and the larger Planning Team. The objectives are as follows:

1. Establish and maintain partnerships in the identification and implementation of mitigation measures in the Operational Area.

2. Implement hazard mitigation programs and projects that protect life, property, and the environment.

3. Develop and provide updated information about threats, hazards, vulnerabilities, and mitigation strategies to state, regional, and local agencies, as well as private sector groups, communitybased organizations, and non-profits.

4. Improve understanding of the locations, potential impacts, and linkages among threats, hazards, vulnerability, and measures needed to protect life, property, and the environment.

5. Encourage the incorporation of mitigation best management measures into plans, codes, and other regulatory standards for public, private, and non-governmental entities within the Operational Area.

6. Inform the public on the risk exposure to natural hazards and ways to increase the public’s capability to prevent, prepare, respond, recover, and mitigate impacts of these events.

7. Advance community and natural environment sustainability and resilience to future impacts through preparation and implementation of state, regional, and local projects.

8. Reduce repetitive property losses from all hazards.

9. Where feasible and cost-effective, encourage property protection measures for vulnerable structures located in hazard areas.

10. Improve the process on how public agencies select systems that provide warning and emergency communications for a broad array of agencies. This includes improving the selection process and ensuring warning and emergency communications processes are effective and accessible.

11. Partner with educational institutions that provide research, case studies and the like to help bolster agency communication that demonstrates the value of hazard mitigation.

17.2 Mitigation Alternatives
Catalogs of natural hazard mitigation alternatives were developed that present a broad range of alternatives to be considered for use in the OA, in compliance with 44 CFR (Section 201.6(c)(3)(ii)). One catalog was developed for each natural hazard of concern evaluated in this plan. The catalogs present alternatives that are categorized in two ways:
 By who would have responsibility for implementation:
▪ Individuals (personal scale).
▪ Businesses (corporate scale).

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▪ Government (government scale).
 By what the alternative would do:
▪ Manipulate the hazard.
▪ Reduce exposure to the hazard.
▪ Reduce vulnerability to the hazard.
▪ Increase the ability to respond to or be prepared for the hazard.

Hazard mitigation actions recommended in this plan were selected from among the alternatives presented in the catalogs. The catalogs provide a baseline of mitigation alternatives that are backed by a planning process, are consistent with the established goals and objectives, and are within the capabilities of the planning partners to implement. Some of these actions may not be feasible based on the selection criteria identified for this plan. The purpose of the catalog was to provide a list of what could be considered to reduce risk of the flood hazard within the OA. Actions in the catalog that are not included for the partnership’s action plan were not selected for one or more of the following reasons:
 The action is not feasible.
 The action is already being implemented.
 There is an apparently more cost-effective alternative.  The action does not have public or political support.

The catalogs for each hazard are presented in Table 127 through Table 134.

Table 127: Alternatives to Mitigate the Dam and Levee Failure Hazard What Alternative
Would Do Personal Scale Corporate Scale Government Scale Manipulate the
Hazard
None. Remove dams.

Remove levees.

Harden dams.

Remove dams.

Remove levees.

Harden dams.

Reduce Exposure to
the Hazard
Relocate out of dam
failure inundation
areas.

Replace earthen
dams with
hardened
structures.

Replace earthen dams with
hardened structures.

Relocate critical facilities out of
dam failure inundation areas.

Consider open space land use
in designated dam failure
inundation areas.

Reduce
Vulnerability to the
Hazard
Elevate home to
appropriate levels.

Flood-proof
facilities within
dam failure
inundation areas.

Adopt higher floodplain
standards in mapped dam
failure inundation areas.

Retrofit critical facilities within
dam failure inundation areas.

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What Alternative
Would Do Personal Scale Corporate Scale Government Scale Increase the Ability
to Respond to or Be
Prepared for the
Hazard
Learn about risk
reduction for the dam
failure hazard.

Learn the evacuation
routes for a dam failure
event.

Educate yourself on
early warning systems
and the dissemination
of warnings.

Educate
employees on the
probable impacts
of a dam failure.

Develop a
continuity of
operations plan.

Map dam failure inundation
areas.

Enhance emergency
operations plan to include a
dam failure component.

Institute monthly
communications checks with
dam operators.

Inform the public on risk
reduction techniques.

Adopt real-estate disclosure
requirements for the re-sale of
property located within dam
failure inundation areas.

Consider the probable impacts
of climate in assessing the risk
associated with the dam failure
hazard.

Establish early warning
capability downstream of listed
high hazard dams.

Consider the residual risk
associated with protection
provided by dams in future
land use decisions.

Table 128: Alternatives to Mitigate the Drought Hazard
What Alternative
Would Do Personal Scale Corporate Scale Government Scale Manipulate the
Hazard
None. None. Groundwater recharge
through stormwater
management
Reduce Exposure to
the Hazard
None. None. Identify and create
groundwater backup
sources.

Reduce Vulnerability
to the Hazard
Drought-resistant
landscapes.

Drought-resistant
landscapes.

Water use conflict
regulations.

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What Alternative
Would Do Personal Scale Corporate Scale Government Scale Reduce water system
losses.

Modify plumbing
systems through water
saving kits.

Reduce private water
system losses.

Reduce water system
losses.

Distribute water saving
kits.

Increase the Ability to
Respond to or Be
Prepared for the
Hazard
Practice active water
conservation.

Practice active water
conservation.

Public education on
drought resistance.

Identify alternative
water supplies for times
of drought and create
mutual aid agreements
with alternative
suppliers.

Develop drought
contingency plan.

Develop criteria
“triggers” for droughtrelated actions.

Improve accuracy of
water supply forecasts.

Modify rate structure to
influence active water
conservation
techniques.

Table 129: Alternatives to Mitigate the Earthquake Hazard What Alternative
Would Do Personal Scale Corporate Scale Government Scale Manipulate the
Hazard
None. None. None.

Reduce
Exposure to the
Hazard
Locate outside of hazard
area (off soft soils).

Locate or relocate
mission-critical
functions outside
hazard area where
possible.

Locate critical facilities
or functions outside
hazard area where
possible.

Reduce
Vulnerability to
the Hazard
Retrofit structure (anchor
house structure to
foundation).

Build redundancy for
critical functions and
facilities.

Harden infrastructure.

Provide redundancy for
critical functions.

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What Alternative
Would Do Personal Scale Corporate Scale Government Scale Secure household items that
can cause injury or damage
(such as water heaters,
bookcases, and other
appliances).

Build to higher design.

Retrofit critical buildings
and areas housing
mission-critical
functions.

Adopt higher regulatory
standards.

Increase the
Ability to
Respond to or Be
Prepared for the
Hazard
Practice “drop, cover, and
hold.”
Develop household
mitigation plan, such as
creating a retrofit savings
account, communication
capability with outside, and
72-hour self-sufficiency
during an event.

Keep cash reserves for
reconstruction.

Become informed on the
hazard and risk reduction
alternatives available.

Develop a post-disaster
action plan for your
household.

Adopt higher standard
for new construction;
consider “performancebased design” when
building new structures.

Keep cash reserves for
reconstruction.

Inform your employees
on the possible impacts
of earthquake and how
to deal with them at
your work facility.

Develop a continuity of
operations plan.

Provide better hazard
maps.

Provide technical
information and
guidance.

Enact tools to help
manage development
in hazard areas (e.g.,
tax incentives,
information).

Include retrofitting and
replacement of critical
system elements in
capital improvement
plan.

Develop strategy to
take advantage of postdisaster opportunities.

Warehouse critical
infrastructure
components such as
pipe, power line, and
road repair materials.

Develop and adopt a
continuity of operations
plan.

Initiate triggers guiding
improvements (such as
<50% substantial
damage or
improvements).

Further enhance
seismic risk
assessment to target

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What Alternative
Would Do Personal Scale Corporate Scale Government Scale high hazard buildings
for mitigation
opportunities.

Develop a postdisaster action plan
that includes grant
funding and debris
removal components.

Table 130: Alternatives to Mitigate the Flooding Hazard What Alternative
Would Do Personal Scale Corporate Scale Government Scale Manipulate the
Hazard
Clear storm drains and
culverts.

Use low-impact
development techniques.

Clear storm drains
and culverts.

Use low-impact
development
techniques.

Maintain drainage system.

Institute low-impact
development techniques on
property.

Dredging, levee construction,
and providing regional
retention areas.

Structural flood control, levees,
channelization, or revetments.

Stormwater management
regulations and master
planning.

Acquire vacant land or
promote open space uses in
developing watersheds to
control increases in runoff.

Reduce
Exposure to the
Hazard
Locate outside of hazard
area.

Elevate utilities above
base flood elevation.

Use low-impact
development techniques.

Locate critical
facilities or functions
outside hazard area.

Use low-impact
development
techniques.

Locate or relocate critical
facilities outside of hazard
area.

Acquire or relocate identified
repetitive loss properties.

Promote open space uses in
identified high hazard areas
via techniques such as:
planned unit developments,
easements, setbacks,

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What Alternative
Would Do Personal Scale Corporate Scale Government Scale greenways, sensitive area
tracks.

Adopt land development
criteria such as planned unit
developments, density
transfers, clustering.

Institute low impact
development techniques on
property.

Acquire vacant land or
promote open space uses in
developing watersheds to
control increases in runoff.

Reduce
Vulnerability to
the Hazard
Raise structures above
base flood elevation.

Elevate items within
house above base flood
elevation.

Build new homes above
base flood elevation.

Flood-proof structures.

Build redundancy for
critical functions or
retrofit critical
buildings.

Provide floodproofing when new
critical infrastructure
must be located in
floodplains.

Harden infrastructure, bridge
replacement program.

Provide redundancy for critical
functions and infrastructure.

Adopt regulatory standards
such as freeboard standards,
cumulative substantial
improvement or damage, lower
substantial damage threshold;
compensatory storage, nonconversion deed restrictions.

Stormwater management
regulations and master
planning.

Adopt “no-adverse impact”
floodplain management
policies that strive to not
increase the flood risk on
downstream communities.

Increase the
Ability to
Respond to or
Be Prepared for
the Hazard
Buy flood insurance.

Develop household plan,
such as retrofit savings,
communication with
outside, 72-hour selfsufficiency during and
after an event.

Keep cash reserves
for reconstruction.

Support and
implement hazard
disclosure for sale of
property in risk
zones.

Produce better hazard maps.

Provide technical information
and guidance.

Enact tools to help manage
development in hazard areas
(stronger controls, tax
incentives, and information).

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What Alternative
Would Do Personal Scale Corporate Scale Government Scale Solicit cost-sharing
through partnerships
with others on
projects with multiple
benefits.

Incorporate retrofitting or
replacement of critical system
elements in capital
improvement plan.

Develop strategy to take
advantage of post-disaster
opportunities.

Warehouse critical
infrastructure components.

Develop and adopt a continuity
of operations plan.

Consider participation in the
Community Rating System.

Maintain and collect data to
define risks and vulnerability.

Train emergency responders.

Create an elevation inventory
of structures in the floodplain.

Develop and implement a
public information strategy.

Charge a hazard mitigation
fee.

Integrate floodplain
management policies into
other planning mechanisms
within the OA.

Consider the probable impacts
of climate change on the risk
associated with the flood
hazard.

Consider the residual risk
associated with structural flood
control in future land use
decisions.

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What Alternative
Would Do Personal Scale Corporate Scale Government Scale Enforce National Flood
Insurance Program.

Adopt a Stormwater
Management Master Plan.

Table 131: Alternatives to Mitigate the Landslide/Mass Movement Hazard What Alternative
Would Do Personal Scale Corporate Scale Government Scale Manipulate the
Hazard
Stabilize slope (dewater,
armor toe).

Reduce weight on top of
slope.

Minimize vegetation
removal and the
addition of impervious
surfaces.

Stabilize slope (dewater,
armor toe).

Reduce weight on top of
slope.

Stabilize slope (dewater,
armor toe).

Reduce weight on top of
slope.

Reduce Exposure
to the Hazard
Locate structures
outside of hazard area
(off unstable land and
away from slide-run out
area).

Locate structures outside
of hazard area (off
unstable land and away
from slide-run out area).

Acquire properties in
high-risk landslide areas.

Adopt land use policies
that prohibit the
placement of habitable
structures in high-risk
landslide areas.

Reduce
Vulnerability to the
Hazard
Retrofit home. Retrofit at-risk facilities. Adopt higher regulatory standards for new
development within
unstable slope areas.

Armor/retrofit critical
infrastructure against the
impact of landslides.

Increase the
Ability to Respond
to or Be Prepared
for the Hazard
Institute warning system
and develop evacuation
plan.

Keep cash reserves for
reconstruction.

Educate yourself on risk
reduction techniques for
landslide hazards.

Institute warning system
and develop evacuation
plan.

Keep cash reserves for
reconstruction.

Develop a continuity of
operations plan.

Produce better hazard
maps.

Provide technical
information and
guidance.

Enact tools to help
manage development in
hazard areas: better

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 407
What Alternative
Would Do Personal Scale Corporate Scale Government Scale Educate employees on
the potential exposure to
landslide hazards and
emergency response
protocol.
land controls, tax
incentives, information.

Develop strategy to take
advantage of postdisaster opportunities.

Warehouse critical
infrastructure
components.

Develop and adopt a
continuity of operations
plan.

Educate the public on
the landslide hazard and
appropriate risk
reduction alternatives.

Table 132: Alternatives to Mitigate the Inclement Weather Hazard What Alternative
Would Do Personal Scale Corporate Scale Government Scale Manipulate the
Hazard
None. None. None.

Reduce Exposure
to the Hazard
None. None. None.

Reduce
Vulnerability to
the Hazard
Insulate house.

Provide redundant
heat and power.

Insulate structure.

Plant appropriate trees
near home and power
lines (“Right tree, right
place” National Arbor
Day Foundation
Program).

Relocate critical
infrastructure (such as
power lines)
underground.

Reinforce or relocate
critical infrastructure
such as power lines to
meet performance
expectations.

Install tree wire.

Harden infrastructure such as
locating utilities underground.

Trim trees back from power
lines.

Increase the
Ability to
Respond to or Be
Prepared for the
Hazard
Trim or remove trees
that could affect power
lines.

Trim or remove trees
that could affect
power lines.

Create redundancy.

Support programs such as
“Tree Watch” that proactively
manage problem areas
through use of selective

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What Alternative
Would Do Personal Scale Corporate Scale Government Scale Promote 72-hour selfsufficiency.

Obtain a NOAA
weather radio.

Obtain an emergency
generator.

Equip facilities with a
NOAA weather radio.

Equip vital facilities
with emergency power
sources.
removal of hazardous trees,
tree replacement, etc.

Increase communication
alternatives.

Modify land use and
environmental regulations to
support vegetation
management activities that
improve reliability in utility
corridors.

Modify landscape and other
ordinances to encourage
appropriate planting near
overhead power, cable, and
phone lines.

Provide NOAA weather radios
to the public.

Table 133: Alternatives to Mitigate the Tsunami Hazard
What Alternative
Would Do Personal Scale Corporate Scale Government Scale Manipulate the
Hazard
None. None. Build wave abatement
structures (e.g., the
“Jacks” looking
structure designed by
the Japanese).

Reduce
Exposure to the
Hazard
Locate outside of hazard
area.

Locate structure or
mission critical functions
outside of hazard area
whenever possible.

Locate structure or
functions outside of
hazard area whenever
possible.

Harden infrastructure
for tsunami impacts.

Relocate identified
critical facilities
located in tsunami
high hazard areas.

Reduce
Vulnerability to
the Hazard
Apply personal property
mitigation techniques to your
home such as anchoring
Mitigate personal
property for the impacts
of tsunami.

Adopt higher
regulatory standards
that will provide higher

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 409
What Alternative
Would Do Personal Scale Corporate Scale Government Scale your foundation and
foundation openings to allow
flow through.
levels of protection to
structures built in a
tsunami inundation
area.

Utilize tsunami
mapping once
available, to guide
development away
from high-risk areas
through land use
planning.

Increase the
Ability to
Respond to or
Be Prepared for
the Hazard
Develop and practice a
household evacuation plan.

Support/participate in the
Redwood Coast Tsunami
Working Group.

Educate yourself on the risk
exposure from the tsunami
hazard and ways to minimize
that risk.

Develop and practice a
corporate evacuation
plan.

Support/participate in the
Redwood Coast Tsunami
Working Group.

Educate employees on
the risk exposure from
the tsunami hazard and
ways to minimize that
risk.

Create a probabilistic
tsunami map for the
OA.

Provide incentives to
guide development
away from hazard
areas.

Develop a tsunami
warning and response
system.

Provide residents with
tsunami inundation
maps.

Join NOAA’s Tsunami
Ready program.

Develop and
communicate
evacuation routes.

Enhance the public
information program to
include risk reduction
options for the
tsunami hazard.

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Table 134: Alternatives to Mitigate the Wildfire Hazard What Alternative
Would Do Personal Scale Corporate Scale Government Scale Manipulate the
Hazard
Clear potential fuels on
property such as dry
overgrown underbrush
and diseased trees.

Clear potential fuels
on property such as
dry underbrush and
diseased trees.

Clear potential fuels on
property such as dry
underbrush and diseased
trees.

Implement best
management practices on
public lands.

Reduce Exposure
to the Hazard
Create and maintain
defensible space around
structures.

Locate outside of
hazard area.

Mow regularly.

Create and maintain
defensible space
around structures and
infrastructure.

Locate outside of
hazard area.

Create and maintain
defensible space around
structures and infrastructure.

Locate outside of hazard
area.

Enhance building code to
include use of fire resistant
materials in high hazard
area.

Reduce
Vulnerability to
the Hazard
Create and maintain
defensible space around
structures and provide
water on site.

Use fire-retardant
building materials.

Create defensible
spaces around home.

Create and maintain
defensible space
around structures and
infrastructure and
provide water on site.

Use fire-retardant
building materials.

Use fire-resistant
plantings in buffer
areas of high wildfire
threat.

Create and maintain
defensible space around
structures and infrastructure.

Use fire-retardant building
materials.

Use fire-resistant plantings in
buffer areas of high wildfire
threat.

Consider higher regulatory
standards (such as Class A
roofing).

Establish biomass
reclamation initiatives.

Increase the
Ability to
Respond to or Be
Prepared for the
Hazard
Employ techniques from
the National Fire
Protection Association’s
Firewise Communities
program to safeguard
home.

Identify alternative water
supplies for firefighting.

Support Firewise
community initiatives.

Create /establish
stored water supplies
to be utilized for
firefighting.

More public outreach and
education efforts, including
an active Firewise program.

Possible weapons of mass
destruction funds available
to enhance fire capability in
high-risk areas.

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 411
What Alternative
Would Do Personal Scale Corporate Scale Government Scale Install/replace roofing
material with noncombustible roofing
materials.

Identify fire response and
alternative evacuation
routes.

Seek alternative water
supplies.

Become a Firewise
community.

Use academia to study
impacts/solutions to wildfire
risk.

Establish/maintain mutual
aid agreements between fire
service agencies.

Create/implement fire plans.

Consider the probable
impacts of climate change
on the risk associated with
the wildfire hazard in future
land use decisions.

17.3 Santa Clara County 2023 Mitigation Action Plan
An action plan is a detailed document that identifies specific steps required to achieve a particular goal.

The document breaks down the goal into actionable and measurable tasks that can be easily followed and tracked. These actions are determined by the risk of natural hazards impacting a community and the identifying solutions. The purpose of an action plan is to define specific steps necessary for achieving a certain goal, including required resources and a timeline for completing tasks.

The 2017 Santa Clara County MJHMP included action items for the entire Operational Area. The participants did not choose to continue to identify area-wide actions and opted for actions by jurisdiction only. The area-wide actions were integrated as appropriate in the Santa Clara County Annex and their status is summarized in Volume II Section 13. Each individual jurisdictions and special districts information can be found in each annex in Volume 2.

The planning partners utilized the following criteria to prioritize action items into the categories of high, medium, or low.
 High Priority— A project that:
▪ Meets multiple goals and objectives (i.e., multiple hazards); ▪ Addresses multiple hazards;
▪ Has benefits that exceed cost;
▪ Has funding secured or is an ongoing project;

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 412
▪ Meets eligibility requirements for Hazard Mitigation Assistance grants; ▪ Can be completed in the short term (1 to 5 years);
▪ Addresses immediate short-term impacts of climate change; ▪ Benefits underserved and/or socially vulnerable populations; AND ▪ Considers the Multi-Benefit Criteria utilized by the Santa Clara County Climate Collaborative, including equity, long-term value, ecosystem benefit, community benefit, and crossjurisdictional alignment.  Medium Priority— A project that:
▪ Meets multiple goals and objectives;
▪ Addresses multiple hazards;
▪ Has benefits that exceed costs;
▪ Has funding has not been secured, but that is grant eligible under Hazard Mitigation Assistance grants or other grant programs;
▪ Project can be completed in the short term (1-5 years), once funding is secured. Medium priority projects will become high priority projects once funding is secured; ▪ Addresses immediate short-term impacts of climate change; ▪ Benefits underserved and/or socially vulnerable populations; AND ▪ Considers the Multi-Benefit Criteria utilized by the Santa Clara County Climate Collaborative, including equity, long-term value, ecosystem benefit, community benefit, and crossjurisdictional alignment.  Low Priority— A project that:
▪ Will mitigate the risk of at least one hazard;
▪ Has benefits that do not exceed the costs or are difficult to quantify:
▪ Does not have secured funding;
▪ Is not eligible for Hazard Mitigation Assistance grant funding; ▪ Has a timeline for completion that is long term (greater than 5 years). Low priority projects may be eligible for other sources of grant funding from other programs; ▪ May address impacts of climate change;
▪ May benefit underserved and/or socially vulnerable populations; AND ▪ Considers the Multi-Benefit Criteria utilized by the Santa Clara County Climate Collaborative, including equity, long-term value, ecosystem benefit, community benefit, and crossjurisdictional alignment.

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 413
Table 135 County of Santa Clara 2023 Action Items
Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC-1* Maintain, implement, and update as
appropriate, the County
unincorporated CWPP, while
expanding the planning scope to
integrate all of the Operational
Area’s jurisdictions. Create
defensible space programs on a
county-wide basis. Using the 2023
Santa Clara County CWPP as a
guide, implement fuel management
and fuel reduction treatment
throughout the county specifically
adjacent to areas classified as high
and extreme risk to structures to
reduce the potential for catastrophic
wildfire.

Wildfire Santa Clara County
Fire Department- orFireSafe Council
SCCFD
General
Budget;
County OEM
General
Budget;
HMGP;
PDM; EMPG
Ongoing Low

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 414
Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC-2* CAL FIRE, South County Fire, and
the Santa Clara County Fire
Department should prepare for
coordinated wildfire response
operations through the
development of a Wildfire Annex to
the County's Emergency
Operations Plan. In August 2020 in
response to the SCU Lightning
Complex, the Wildfire Annex was
used to shed light into the response
and recovery activities that
unfolded.

Wildfire County OEM SCCFD
General
Budget;
County OEM
General
Budget;
HMGP;
EMPG
Short-term Low
SCC-4* Continue to promote programs that
mitigate vegetation fire, such as
diseased tree removal, creating
defensible space, and FireWise
community programs. In
accordance with the 2023 CWPP,
promote public education and
outreach to engage citizens in
helping to reduce risk around
individual property, particularly in
areas with larger drive times from
fire response. Utilize Fire Safe
Councils free chipping programs,
teach Firewise landscaping
techniques, and organize
community cleanup and green
waste removal in high risk areas to
reduce ignitability.

Wildfire Santa Clara County
Fire Department
SCCFD
General
Budget;
County OEM
General
Budget;
South
County Fire
General
Budget;
HMGP; and
EMPG
Ongoing Low

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 415
Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC-8* Develop, update, and maintain GIS
inventories of essential facilities, atrisk buildings and infrastructure and prioritize mitigation projects. Ideas
for Implementation: • Identify critical
facilities at risk from natural hazards
events. • Develop strategies to
mitigate risk to these facilities, or to
utilize alternative facilities should
natural hazard events cause
damage to the facilities in question.
• Identify bridges at risk from flood
or earthquake hazards.

All Hazards, Flood,
Earthquake, Wildfire
ISD (GIS) County ISD
Budget,
County
OEM
Budget,
Emergency
Management
Performance
Grant
Program,
HMGP;
PDM;
FMA; EMPG
Longterm/Ongoing
Medium
SCC-9* Maintain the WebEOC system so
that it is up to date. For example,
review the WebEOC vendor's Road
Map, assess the vendor
technology's fitness relative to the
needs of the County's situational
awareness process and IT
infrastructure; consider upgrading
to a new system if necessary.

All Hazards, Wildfire,
Flood, Inclement
Weather – Heavy
Precipitation/Atmospheric
River, Inclement Weather
– High Winds
ISD (GIS) County ISD
Budget,
County
OEM
Budget,
Emergency
Management
Performance
Grant
Program,
HMGP;
PDM;
FMA; EMPG
Short-term Medium

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 416
Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC10*Participate in statewide effort to
collaborate on spatial data
standardization, data sharing
platform, common operating
procedures.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
TSS (GIS) County ISD
Budget,
County
OEM
Budget,
Emergency
Management
Performance
Grant
Program,
HMGP;
PDM;
FMA; EMPG
Ongoing Medium
SCC11*Develop and provide the Indoor
Mapping, Evacuation Routing to
Emergency Response Personnel.

All Hazards, Wildfire TSS (GIS) County ISD
Budget,
Emergency
Management
Performance
Grant
Program,
HMGP;
PDM; FMA;
EMPG
Long-term Medium

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 417
Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC13A*Identify county facilities vulnerable
to earthquakes and develop
appropriate actions.

Identify county facilities vulnerable
to earthquakes (may include
building age, soft story structures,
building materials more vulnerable
to earthquake damage). Consider
options to retrofit, relocate or
consider alternate methods to
minimize earthquake damage and
maintain response functionality.

Earthquakes ISD (GIS) County ISD
Budget Fleet
and Facilities
Budget
Emergency
Management
Program,
HMGP;
PDM; FMA;
EMGP
Long-term Medium
SCC13B*Identify the most seismically
vulnerable bridges on county roads.

Establish priorities for repair,
retrofit, or other efforts to harden
bridges against earthquake damage
to maintain transportation
functionality and facilitate
emergency response.

Earthquakes ISD (GIS) County ISD
Budget Fleet
and Facilities
Budget
Emergency
Management
Program,
HMGP;
PDM; FMA;
EMGP
Long-term Medium

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 418
Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC15*Deploy plume modeling software
and enable OEM staff to manage
data input to assess hazardous
materials atmospheric risk. Due to
the COVID-19 global pandemic
there has been no progress on this
ongoing capability.

All Hazards, Wildfire,
Climate Change,
Inclement Weather –
High Wind
County Fire, Consumer
and Environmental
Protection Agency
(Department of
Environmental Health)
County ISD
Budget,
County
OEM
Budget;
County
Public
Health
Budget;
SCCFD;
EMPG; the
State
Homeland
Security
Grant
Program
Long-term Medium
SCC18*Miguelito Road Repairs for two road
sections (located in east side of
San Jose): Section 1, located near
the intersection of Camino Vista
Way and Miguelito Road, would
replace the current soldier pile wall
with a new retaining wall and
repave the roadway. Section 2,
located near the intersection of Rica
Vista Way and Miguelito Road,
would repair the slope failure.

All Hazards, Landslide Roads and Airports County
Roads and
Airports
Budget;
County OEM
Budget;
HMGP;
PDM; FMA
Long-term Medium

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 419
Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC21*Alma Bridge Road Slide Repair
(located in Los Gatos): Project site
is 0.75 mile south of the Los Gatos
Rowing Club @ Lexington
Reservoir
Dam Failure,
Landslide
Roads and Airports County
Roads and
Airports
Budget;
County OEM
Budget;
HMGP;
PDM; FMA
Long-term Medium
SCC23*Review and implement selected
recommendations detailed in the
Loma Fire Watershed Emergency
Response Team Final Report,
October 25, 2016 (CA-SCU006912). Potential actions may include, but are not limited to
deployment of an early warning
system, infrastructure
improvements, establishment of a
Firewise community program,
waterway clearance, general
watershed restoration, etc.

Wildfire County OEM County
Roads and
Airports
Budget;
County OEM
Budget;
HMGP;
PDM; FMA
Long-Term Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC24*Review critical facilities and capital
projects for mitigation project
potential- including, but not limited
to: water drainage, power
production maintenance/ upgrades,
etc.

Review flood risk assessment of
critical facilities at risk to 100 and
500 year flood. Initiate further study
to determine appropriate methods
to reduce flood risk, which might
include stormwater capture or
drainage, use of permeable
surfaces, changes to landscaping,
flood control structures, relocation,
or alternatives.

All Hazards
Flood
Fleet and Facilities County
Roads and
Airports
Budget,
County OEM
Budget,
County Fleet
and Facilities
Budget,
County
Roads and
Airports
Budget,
County
Planning &
Development
Budget;
HMGP;
PDM; FMA;
EMPG; the
State
Homeland
Security
Grant
Program
Short-term Medium

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 421
Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC25*Provide technical information and
guidance to public on individual risk
identification using information
sharing/ GIS platforms.

Use GIS tools such as StoryMaps
or other GIS platforms or web
applications for public education
and outreach. Provide a method for
residents to understand where they
are in relation to potential hazards,
and educate them on what actions
they can take to reduce their
personal risk.

All Hazards, Wildfire,
Drought, Climate
Change, Flood
ISD (GIS) County ISD
Budget,
County OEM
Budget,
SCCFD;
EMPG; the
State
Homeland
Security
Grant
Program
Short-term High
SCC26*Develop strategy to take advantage
of post disaster opportunities
through the development of
Disaster Recovery Planning,
Disaster Cost Recovery Planning,
etc.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
County OEM County OEM
Budget;
SCCFD;
County
Finance
Agency
Budget;
EMPG; the
State
Homeland
Security
Grant
Program;
HMGP
Long-term Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC27*Develop and adopt a COOP for
County Departments, as
appropriate.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
County OEM County OEM
Budget;
SCCFD;
County ISD;
EMPG; the
State
Homeland
Security
Grant
Program;
HMGP
Short-Term Medium
SCC28*Maintain existing data and gather
new data needed to define risks
and vulnerabilities impacting the
County. New data should be
integrated into County policies,
including but not limited to
stormwater management, postdisaster recovery, real estate disclosures, environmental
protection, climate change, fire
suppression, and seismic activity.

All Hazards, Climate
Change, Wildfire,
Earthquake
County OEM County OEM
Budget;
SCCFD;
County ISD;
EMPG; the
State
Homeland
Security
Grant
Program;
HMGP
Ongoing Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC29*Maintain existing data and gather
new data needed to define risks
and vulnerability impacting the
County. New data should be
integrated into County plans,
including but not limited to the
County's General Plan, Capital
Improvement Plan, Stormwater
Plan, Habitat Conservation Plan,
Community Wildfire Protection
Plan, Forest Management Plan,
Climate Action Plan, Emergency
Operations Plan, Threat & Hazard
Identification & Risk Assessment,
Post-Disaster Recovery
Framework, Continuity of
Operations Plan, and Public Health
plans.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
County OEM County OEM
Budget;
SCCFD;
County ISD;
EMPG; the
State
Homeland
Security
Grant
Program;
HMGP;
BRIC
Ongoing Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC30*Develop a Debris Collection and
Management Plan.

Earthquake, Wildfire,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/ /High Winds,
Dam/Levee Failure,
Flood, Landslide/Mass
Movement
County Roads and
Airports
County OEM
Budget;
SCCFD;
County ISD;
County
Roads &
Airports
Budget;
County
Public Health
Budget;
EMPG; the
State
Homeland
Security
Grant
Program;
EMPG
Short-term High
SCC32*Integrate the hazard mitigation plan
into other plans, ordinances, and
programs that dictate land use
decisions within the community.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
County OEM County OEM
Budget,
SCCFD
Budget,
County
Planning &
Development
Budget
Ongoing Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC33*Development and implement a
program to capture perishable data
significant events (e.g. high water
marks, locations of poor draining
following heavy rain, roadways or
culverts that have been damaged in
flood events, damage from high
wind events, preliminary damage
estimates, damage photos) to
support future mitigation efforts
including the implementation and
maintenance of the hazard
mitigation plan.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
County OEM County OEM
Budget,
SCCFD
Budget,
County

ISD/GIS
Budget,
County
Finance
Agency
Budget
Long-term Medium
SCC34*Actively participate in the plan
maintenance protocols outlined in
Volume 1 of the hazard mitigation
plan.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
County OEM County OEM
Budget,
HMGP,
BRIC
Ongoing Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
SCC35*Coordinate with the private sector
on prioritization of critical facilities
before and during restoration of
utility services.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
County OEM County OEM
Budget
Ongoing Medium
1 Address gaps in data and missing
information within this Annex for the
next plan update.

All Hazards, Earthquake,
Wildfire/Wildfire
Smoke/Air Quality,
Inclement Weather –
Heavy
Precipitation/Atmospheric
River/Extreme
Temperatures/High
Winds/Space Weather,
Drought, Climate
Change, Dam/Levee
Failure, Flood,
Landslide/Mass
Movement
All Departments General
fund,
Short term Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
2 Maintain a coordinated, multilingual public awareness campaign to educate and engage the public
about hazard risk, preparedness,
and safety to provide real-time
health related information during
extreme heat and poor air quality
warning days and information on
cooling center, resiliency hubs,
emergency shelters, and other
preparedness and post disaster
resources for the region.

Inclement Weather –
Extreme Temperatures,
Wildfire/Wildfire
Smoke/Air Quality
County OEM General fund Ongoing Medium
3 Consider nature-based solutions
such as a goal to plant 1,000 trees
annually Countywide in areas to
address issues such as urban heat
islands, low tree canopy, poor air
quality and stormwater
management. Work with local
governments, agencies, and
nonprofit partners to build a
comprehensive urban forest.

Inclement Weather –
Extreme Temperatures,
Flood
Office of Sustainability General
fund, BRIC
Medium-term Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
4 In coordination with SCVWD, host
regular workshops and classes on
water conservation, including
providing information on droughttolerant landscaping, available rebates for water retrofits, and
water efficiency strategies in new
buildings. Distribute outreach
materials for water conservation.

Drought County OEM? General
Fund
Medium-term Medium
5 Work with local jurisdictions in dam
inundation zones to ensure
residents and businesses are
aware of the potential risk, and that
dam inundation mitigation
strategies are integrated into local
planning efforts. Work with local
jurisdictions to identify vulnerable
populations and unique information
needs to communicate their risk.

Use GIS mapping for risk analysis
and communication as appropriate.

Dam/Levee Failure County OEM General
Fund
Medium
Term
Medium

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Action
Item
Number
Action Item Description Hazard(s) Mitigated
Lead Position, Office,
Department, or
Division Responsible
for Implementation
Potential
Funding
Sources
Expected
Timeline for
Completion
Priority
6 Identify facilities to serve as
warming or cooling centers/shortterm severe weather shelters in an effort to reduce loss of life. Assist
vulnerable populations by
facilitating and also notifying them
about warming centers (a shortterm emergency shelter that operates when temperatures or a
combination of precipitation, wind
chill, wind and temperature become
dangerously inclement).

Extreme Heat, Extreme
Cold, High Wind, Heavy
Rain
County OEM General
Fund
Medium
Term
Medium
7 Identify areas with above ground
utilities at risk to damage from high
wind and evaluate feasibility of
pursuing funding for
undergrounding of utilities.

Consider areas where powerlines
may be near areas with high wildfire
risk.

High Wind, Wildfire County OEM General
Fund
Medium
Term
Medium

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17.4 Financial Capabilities
Determining current and/or potential funding sources is an important step of the mitigation planning process. By exploring, identifying, and evaluating alternative sources now, planning partners are positioned to select and implement actions which are financially obtainable.

This plan is written in accordance with federal guidelines in order to ensure participants remain eligible for certain mitigation funds. Under the Code of Federal Regulations (CFR) Title 44, Part 201.6 (44 CFR §201.6), Local Mitigation Plans, local governments must have a Federal Emergency Management Agency (FEMA)-approved plan in order to apply for and/or receive hazard mitigation project grant funds for hazard mitigation programs including:
 Hazard Mitigation Grant Program (HMGP)
 HMGP Post Fire Program (HMGP-PF)
 Building Resilient Infrastructure and Communities (BRIC)  Flood Mitigation Assistance (FMA)
 Safeguarding Tomorrow Revolving Loan Fund Program
It is important to consider a variety of funding streams. Mitigation actions can and should be funded through multiple different avenues. Funding opportunities may include federal agencies; state, local, and tribal programs, as applicable; or private funding. Potential Federal, State, and Local funding opportunities are described below.

17.4.1 Federal
FEMA’s Hazard Mitigation Assistance (HMA) grants fund eligible mitigation measures to reduce future disaster losses. Eligible applicants include state agencies, local governments, special districts, federally recognized tribes, and private non-profit organizations.

California’s Office of Emergency Services (Cal OES) administers hazard mitigation assistance grants on behalf of FEMA. Cal OES supports outreach to inform eligible jurisdictions of available grants, reviews applications, and provides technical assistance. Cal OES is also responsible for submitting applications to FEMA by FEMA’s stated deadline. When eligible entities are interested in applying for these funds, the State Hazard Mitigation Officer (SHMO) can provide additional guidance and education about available grants and the grant application process.

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Table 136: FEMA Mitigation Funding Sources
Program Timeframe Description Lead Agency
or Agencies Resource(s)
Hazard Mitigation
Grant Program
(HMGP / 404
Mitigation)
Post-disaster -
application period
opens on the date of
the presidential
declaration.

Provides funding to state, local, tribal,
and territorial governments to develop
hazard mitigation plans and implement
mitigation products to reduce or
eliminate future disaster losses. Eligible
project types including planning and
enforcement, flood protection,
retrofitting, and construction. An
approved hazard mitigation plan is
required to receive funding. Because
the State of California has an enhanced
HMP, the State is eligible for additional
HMGP funds, up to 20% of the federal
share of disaster assistance provided
after a federally declared disaster.

FEMA https://www.fema.gov/grants/mitigation
/hazard-mitigation
https://www.fema.gov/grants/mitigation
/hazard-mitigation-assistance-guidance
HMGP Post Fire
(HMGP-PF)
State’s first FMAG
declaration of the fiscal
year to 6 months after
the end of that fiscal
year
Helps communities implement hazard
mitigation measures after wildfires
disasters. Funding depends on the 10-
year national average assistance
provided under Fire Management
Assistance Grants (FMAG)
declarations for States.

FEMA https://www.fema.gov/grants/mitigation
/hazard-mitigation-assistance-guidance
https://www.fema.gov/sites/default/files
/2020-07/fema_DRRA-1204-policy.pdf
Fire Management
Assistance
Grants (FMAG)
Post-Fire Management
Assistance Declaration
Available to states, local and tribal
governments for the mitigation,
management, and control of fires on
publicly or privately owned forests or
grasslands.

FEMA https://www.fema.gov/sites/default/files
/documents/fema_fmagppg_063121.pd
f
Public Assistance
406 Program
Post-federal disaster
declaration
Public Assistance funded mitigation
measures for disaster-damaged
facilities. Limited to eligible counties
and eligible damaged facilities, as well
FEMA https://www.fema.gov/pressrelease/20220328/fema-hazardmitigation-grants-404-and-406

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Program Timeframe Description Lead Agency
or Agencies Resource(s)
as only the parts of the facility that are
damaged. Designed to reduce the
potential of future losses through a
similar disaster to the same eligible
facility.

Flood Mitigation
Assistance (FMA)
Annual Funding for cost-effective measures to
reduce or eliminate the long-term risk
of flood damage to buildings,
manufactured homes, and other
structures insured under the National
Flood Insurance Program (NFIP).

FEMA https://www.fema.gov/grants/mitigation
/floods
Building Resilient
Infrastructure and
Communities
(BRIC)
Annual Provides funding to states, local
communities, tribes, and territories to
implement mitigation projects. This
program is designed to support
capability- and capacity-building,
promote partnerships, and enable large
projects. It emphasizes nature-based
solutions, community lifelines, and
benefitting underserved communities.

Each State has allocated funds as well
as a nationally competitive fund.

FEMA https://www.fema.gov/sites/default/files
/documents/fema_bric-policy-fp-008-
05_program_policy.pdf
https://www.fema.gov/sites/default/files
/documents/fema_riskmap-naturebased-solutions-guide_2021.pdf https://www.fema.gov/sites/default/files
/documents/fema_fy-22-mitigationaction-portfolio.pdf
Pre-Disaster
Mitigation (PDM)
Congressionally
appropriated
Makes funding available for state, local,
tribal, and territorial governments to
plan for and implement sustainable
cost-effective measures designed to
reduce the risk to individuals and
property from future natural hazards.

Previously replaced by the BRIC
program, the Consolidated
Appropriations Act of 2022
reauthorized PDM for FY22.

FEMA https://www.fema.gov/grants/mitigation
/pre-disaster

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Program Timeframe Description Lead Agency
or Agencies Resource(s)
Rehabilitation of
High Hazard
Potential Dam
(HHPD) Grant
Program
Annual Provides technical, planning, design,
and construction assistance in the form
of grants for rehabilitation of eligible
high hazard potential dams. The dam
must be located in a jurisdiction with a
FEMA-approved plan that includes dam
risks.

FEMA https://www.fema.gov/emergencymanagers/risk-management/damsafety/rehabilitation-high-hazardpotential-dams https://www.fema.gov/sites/default/files
/documents/fema_hhpd-fact-sheet_05-
19-2020.pdf
National Flood
Insurance
Program (NFIP)
Ongoing Eligible property owners, renters and
businesses who purchase flood
insurance through the NFIP may be
eligible for funds to repair their
property. Increased Cost of
Compliance (ICC) claim benefits may
be available for compliance activities
including elevation, flood-proofing,
relocation, and demolition.

FEMA https://www.fema.gov/flood-insurance
Planning partners may soon have access to additional mitigation funds through FEMA’s new Safeguarding Tomorrow Revolving Loan Fund Program. The Safeguarding Tomorrow through Ongoing Risk Mitigation (STORM) Act became law on January 1, 2021, and authorized FEMA to provide grants to eligible entities including the State of California for the development of a revolving loan fund for hazard mitigation initiatives.

Once established, this revolving loan fund will provide low interest loans to jurisdictions to reduce vulnerability to natural disaster, foster resilience, and reduce disaster suffering. These loans may be used as the non-federal cost match for other HMA grant applications. The first application for STORM is currently open as of the time of this writing.

FEMA funds should not be the only source of mitigation funding a community considers. Other federal resources are described in Table 137.

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Table 137: Additional Federal Funding Sources
Program Timeframe Description Lead Agency
or Agencies Resource(s)
Community Development
Block Grant – Disaster
Recovery (CDBG-DR)
Congressionally
Appropriated
Grants to states and local governments to
develop viable communities (e.g., housing,
suitable living environment, expanded economic
opportunities) and recover from federally
declared disasters. Principally for low- and
moderate-income areas.

U.S.

Department of
Housing and
Urban
Development
(HUD)
https://www.hud.gov/progr
am_offices/comm_plannin
g/cdbg
CDBG-Mitigation (CDBGMIT)Congressionally
Appropriated
Supports a range of mitigation activities focused
on reducing or eliminating the long-term impacts
of future disasters.

HUD https://www.hud.gov/progr
am_offices/comm_plannin
g/cdbg-dr/cdbg-mit
Section 108 Loan
Guarantee Program
Upon request Provides low-cost, long-term financing for economic development and community
development projects, including improvements
to increase resilience.

HUD https://www.hudexchange.
info/programs/section108/section-108-programeligibilityrequirements/#overview Natural Resources
Conversation Services
(NRCS)
Ongoing Can provide funding and technical assistance to communities to address threats to watersheds,
including conducting damage assessment and
evaluating potential solutions.

U.S.

Department of
Agriculture
(USDA)
https://www.nrcs.usda.gov
/
Urban Waters Small
Grants Program
Every two years Program that protects and restores urban waters by improving water quality through
activities that also support community
revitalization and other local priorities.

U.S.

Environmental
Protection
Agency (EPA)
https://www.epa.gov/urban
waterspartners/urbanwaters-smallgrants#:~:text=Overview% 20Since%20the%20incept
ion%20of%20the%20Urba
n%20Waters,with%20indiv
idual%20award%20amou
nts%20of%20up%20to%2
0%2460%2C000.
https://www.epa.gov/sites/
default/files/2016-
10/documents/uwsg_flyer
_october2016.pdf

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Program Timeframe Description Lead Agency
or Agencies Resource(s)
Clean Water State
Revolving Fund (CWSRF)
Annual Provides low-cost financing for a range of water infrastructure projects.

EPA https://www.epa.gov/cwsrf
https://www.epa.gov/nps/f
unding-resourceswatershed-protection-andrestoration
WaterSmart Annual Funding opportunity to support adequate and safe water supplies through water conservation,
water management, and restoration projects.

Bureau of
Reclamation
https://www.usbr.gov/wate
rsmart/
Partners for Fish and
Wildlife
Ongoing Financial and technical assistance to private
landowners, corporations, local governments,
and universities interested in pursuing
restoration projects affecting wetlands and
riparian habitats.

U.S. Fish and
Wildlife
Service (FWS)
https://www.fws.gov/progr
am/partners-fish-andwildlife
National Coastal
Resilience Fund
Annual Funds nature-based solutions designed to
improve the resilience of coastal communities
and ecosystems.

National Fish
and Wildlife
Foundation
https://www.nfwf.org/progr
ams/national-coastalresiliencefund?activeTab=tab-1
Flood Risk Management
Program (FRMP)
Upon request Program designed to focus the policies,
programs, and expertise of the Corps toward
reducing overall flood risk. USACE works with
local government partners to coordinate flood
risk management within the context of shared
responsibility, including helping communities
understand their flood risk, communicate flood
risk to the public, and develop solutions.

U.S. Army
Corps of
Engineers
https://www.iwr.usace.arm
y.mil/Missions/Flood-RiskManagement/Flood-RiskManagementProgram/Partners-inSharedResponsibility/State-andLocal/

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Program Timeframe Description Lead Agency
or Agencies Resource(s)
Community Wildfire
Assistance
Ongoing Technical and funding assistance for wildfire
mitigation measures and training.

Department of
Interior Bureau
of Land
Management
https://www.blm.gov/sitepage/programs-publicsafety-and-fire-fire-andaviation-regionalinformation-montanadakotas-3 Emergency Management
Performance Grant
(EMPG)
Annual Grant designed to support state, local, tribal,
and territorial emergency management
agencies in the implementation of the National
Preparedness System and the National
Preparedness Goal of a secure and resilient
nation. FY23 EMPG program also included an
emphasis on the national priorities of equity;
climate resilience; and readiness.

DHS/FEMA https://www.fema.gov/gran
ts/preparedness/emergen
cy-managementperformance
Emergency Watershed
Protection
Ongoing Program that offers technical and financial
assistance to help local communities relieve
imminent threats to life and property caused by
natural disasters that impair the watershed.

USDA https://www.nrcs.usda.gov
/programs-initiatives/ewpemergency-watershedprotection Watershed and Flood
Prevention Operations
(WVFPO) Program
Ongoing Provides technical and financial assistance to
help plan and implement watershed projects.

USDA https://www.nrcs.usda.gov
/programsinitiatives/watershed-andflood-preventionoperations-wfpoprogram#:~:text=The%20 Watershed%20Protection
%20and%20Flood%20Pre
vention%20%28WFPO%2
9%20Program,Watershed
%20and%20Flood%20Pre
vention%20Operations%2
0%28WFPO%29%20Prog
ram%20OVERVIEW

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17.4.2 State
The State of California proactively invests in hazard mitigation and climate adaptation in order to develop more resilient communities. Open grants can be found online through the California Grants Portal. Table 138 lists some of the state-led funding sources available or likely to become available.

Table 138: State Mitigation Funding Sources
Program Timeframe Description Lead Agency
or Agencies Resource(s)
Prepare California As Funded Initiative to advance local capabilities through funding additional staff and covering the nonfederal cost share for mitigation actions.

Cal OES https://www.caloes.ca.gov/
office-of-thedirector/operations/recove
ry-directorate/hazardmitigation/preparecalifornia/
Earthquake Brace + Bolt
(EBB) Program
TBD Grants for qualified homeowners with eligible
houses in higher-earthquake-risk areas to
seismically retrofit their house.

California
Earthquake
Authority
https://portal.earthquakea
uthority.com/DiscountsGrants/Brace-and-BoltGrants#:~:text=CEA%20of fers%20two%20brace%20
%2B%20bolt%20grant%2
0programs,help%20CEA
%20policyholders%20pay
%20for%20a%20seismic
%20retrofit.

Proposition 84 Ongoing The California Safe Drinking Water, Water Quality and Supply, Flood Control, River and Coastal
Protection Bond Act (Proposition) makes new
funding available for flood protection and water
management programs.

Multiple http://bondaccountability.r
esources.ca.gov/p84.aspx
http://bondaccountability.r
esources.ca.gov/PDF/Pro
p1E/PROPOSITION_84_f
act.pdf

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Program Timeframe Description Lead Agency
or Agencies Resource(s)
Integrated Regional Water
Management Grant
Program
Ongoing A collaborative grant program that covers
planning, project implementation, and
disadvantaged communities and tribes in order to
implement water management solutions on a
regional scale.

Department of
Water
Resources
https://water.ca.gov/Progr
ams/Integrated-RegionalWater-Management
Urban Community
Drought Relief Funding
As Funded Offers financial assistance to address drought impacts, including drought resilience planning,
climate resilience activities, and water
conservation activities.

Department of
Water
Resources
https://water.ca.gov/Water
-Basics/Drought/UrbanDrought-Grant
https://water.ca.gov/-
/media/DWRWebsite/WebPages/WaterBasics/Drought/Files/Urba n-Community-DroughtRelief/FrequentlyAskedQu
estions.pdf
Wildfire Prevention Grants Annual Funding for eligible applicants to conduct hazardous fuels reduction activities, wildfire
prevention planning, and wildfire prevention
education.

CAL FIRE https://www.fire.ca.gov/wh
at-we-do/grants/wildfireprevention-grants
Wildfire Resilience Block
Grants
As Funded Provides technical and financial assistance for forest management including reducing the risk of
wildfires.

CAL FIRE https://www.fire.ca.gov/wh
at-we-do/natural-resourcemanagement/wildfireresilience#ResilienceGran tAnchor

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Program Timeframe Description Lead Agency
or Agencies Resource(s)
Listos California Funded for
2023
Local resilience grants for community-based
organizations throughout the state to provide
disaster training and resources to vulnerable and
diverse populations.

Cal OES https://www.grants.ca.gov/
grants/2022-23-listoscalifornia-statewide-grantls-program-rfp/ https://news.caloes.ca.gov
/cal-oes-released-2023-
funding-opportunities-forlistos-california-campaign/
California Climate
Investments
Ongoing Over 70 programs that fund various projects
related to climate change and climate resilience.

More than 20
state agencies
https://www.caclimateinve
stments.ca.gov/allprograms
Resilient California Ongoing Resources for climate resilience including grant programs.

Governor’s
Office of
Planning and
Research
https://resilientca.org/topic
s/investing-in-adaptation/
Integrated Climate
Adaptation and Resiliency
Program (ICARP)
Ongoing Three grant programs designed to support
mitigation and climate adaptation through
adaptation planning, climate resilience efforts, and
preparing for the impacts of extreme heat.

Governor’s
Office of
Planning and
Research
https://opr.ca.gov/climate/i
carp/
Climate Smart Land
Management Program
Funded for
2023
New grant opportunity to implement projects and
develop plans that increase climate action on
California’s natural and working lands
Department of
Conservation
https://www.conservation.
ca.gov/dlrp/grantprograms/Pages/ClimateSmart-Land-ManagementProgram.aspx

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17.4.3 Local
Local capability to fund mitigation actions can come from a variety of sources. Some sources local jurisdictions may have access to include:
 Capital improvements project funding.
 Taxes levied for specific purposes.
 User fees for water, sewer, gas, or electric services.  Stormwater utility fees.
 General obligation bonds.
 Special tax bonds.
 Private activity bonds.
 Development impact fees for homebuyers or developers.  Public or private partnerships.

The individual resources of each participating planning partner are discussed in each annex in Volume 2.

17.5 Action Plan Prioritization
The planning partners utilized the following criteria to prioritize action items into the categories of high, medium, or low.
 High Priority— A project that:
▪ Meets multiple goals and objectives (i.e., multiple hazards); ▪ Addresses multiple hazards;
▪ Has benefits that exceed cost;
▪ Has funding secured or is an ongoing project;
▪ Meets eligibility requirements for Hazard Mitigation Assistance grants; ▪ Can be completed in the short term (1 to 5 years);
▪ Addresses immediate short-term impacts of climate change; ▪ Benefits underserved and/or socially vulnerable populations; AND ▪ Considers the Multi-Benefit Criteria utilized by the Santa Clara County Climate Collaborative, including equity, long-term value, ecosystem benefit, community benefit, and crossjurisdictional alignment.  Medium Priority— A project that:
▪ Meets multiple goals and objectives;
▪ Addresses multiple hazards;
▪ Has benefits that exceed costs;
▪ Has funding has not been secured, but that is grant eligible under Hazard Mitigation Assistance grants or other grant programs;

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▪ Project can be completed in the short term (1-5 years), once funding is secured. Medium priority projects will become high priority projects once funding is secured; ▪ Addresses immediate short-term impacts of climate change; ▪ Benefits underserved and/or socially vulnerable populations; AND ▪ Considers the Multi-Benefit Criteria utilized by the Santa Clara County Climate Collaborative, including equity, long-term value, ecosystem benefit, community benefit, and crossjurisdictional alignment.  Low Priority— A project that:
▪ Will mitigate the risk of at least one hazard;
▪ Has benefits that do not exceed the costs or are difficult to quantify:
▪ Does not have secured funding;
▪ Is not eligible for Hazard Mitigation Assistance grant funding; ▪ Has a timeline for completion that is long term (greater than 5 years). Low priority projects may be eligible for other sources of grant funding from other programs; ▪ May address impacts of climate change;
▪ May benefit underserved and/or socially vulnerable populations; AND ▪ Considers the Multi-Benefit Criteria utilized by the Santa Clara County Climate Collaborative, including equity, long-term value, ecosystem benefit, community benefit, and crossjurisdictional alignment.

17.5.1 Benefit-Cost Review
One of the criteria used to prioritize proposed mitigation actions was a benefit-cost review. This review was not of the detailed benefit-cost analysis required by FEMA for project grant eligibility under Hazard Mitigation Assistance grants. A less formal approach was used because some projects may not be implemented for up to 10 years, and associated costs and benefits could change dramatically in that time.

Therefore, a review of the apparent benefits versus the apparent cost of each project was performed.

Parameters were established for assigning subjective ratings (high, medium, and low) to the costs and benefits of these projects.

Cost ratings were defined as follows:
 High—Existing funding will not cover the cost of the project; implementation would require new revenue through an alternative source (for example, bonds, grants, and fee increases).  Medium—The project could be implemented with existing funding but would require a reapportionment of the budget or a budget amendment, or the cost of the project would have to be spread over multiple years.
 Low—The project could be funded under the existing budget. The project is part of or can be part of an ongoing existing program.

Benefit ratings were defined as follows:
 High—Project will provide an immediate reduction of risk exposure for life and property.  Medium—Project will have a long-term impact on the reduction of risk exposure for life and property, or project will provide an immediate reduction in the risk exposure for property.

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Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 17: Mitigation Strategy 442
 Low—Long-term benefits of the project are difficult to quantify in the short term.

Using this approach, projects with positive benefit versus cost ratios (such as high over high, high over medium, medium over low, etc.) are considered cost-beneficial and are prioritized accordingly.