Draft
SEA-LEVEL RISE ANALYSIS AND VULNERABILITY
ASSESSMENT FOR POINT ARENA COVE
Technical Report
Prepared for October 2023
City of Point Arena
Draft
SEA-LEVEL RISE ANALYSIS AND VULNERABILITY
ASSESSMENT FOR POINT ARENA COVE
Technical Report
Prepared for October 2023
City of Point Arena
Services provided pursuant to this Agreement are intended solely for the use and benefit of the City of Point Arena.
No other person or entity shall be entitled to rely on the services, opinions, recommendations, plans or specifications provided pursuant to this agreement without the express written consent of ESA, 575 Market Street, San Francisco CA 94105.
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Petaluma, CA 94954
707.795.0900
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D202201148.00
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TABLE OF CONTENTS
Page
1. Introduction.................................................................................................................. 1
1.1 Background .......................................................................................................... 1
1.2 Study Purpose ...................................................................................................... 2
1.3 Scope of Study ..................................................................................................... 2
2. Project Setting ............................................................................................................. 5
2.1 Study Area............................................................................................................ 5
2.2 Community Outreach and Engagement................................................................ 6
2.3 Community Assets................................................................................................ 6
3. Historic and Existing Conditions ............................................................................. 11
3.1 Historic Storms and Documented Impacts.......................................................... 11
3.1.1 Analyzing Historic Water Levels............................................................... 12
3.1.2 Observations from the January 5, 2023, Storm Event ............................. 15
3.2 Existing Flooding ................................................................................................ 16
3.2.1 Tides and Water Levels ........................................................................... 17
3.2.2 Waves...................................................................................................... 18
3.2.3 Creek Flooding......................................................................................... 19
3.3 Extreme Event Flooding ..................................................................................... 22
3.3.1 FEMA....................................................................................................... 22
3.3.2 USGS Coastal Storm Modelling System (CoSMoS) ................................ 24
3.3.3 USGS 100-year Coastal Total Water Levels............................................ 26
3.3.4 ESA’s Estimated Extreme Coastal Flooding ............................................ 27
3.3.5 ESA’s Estimated Extreme Fluvial Flooding.............................................. 28
3.4 Influence of Filled Park Area on Flooding ........................................................... 30
3.5 Local Sediment Processes ................................................................................. 31
3.5.1 Sediment Transport ................................................................................. 31
3.5.2 Historic Erosion........................................................................................ 31
4. Future Conditions with Sea-Level Rise.................................................................... 33
4.1 Relevant State Sea-Level Rise Guidance........................................................... 33
4.1.1 California Strategic Plan to Protect California’s Coasts and Oceans 2020-2025 (Ocean Protection Council).................................................... 33
4.1.2 State of California Sea-Level Rise Guidance (Ocean Protection Council).................................................................................................... 33
4.1.3 Sea-Level Rise Policy Guidance (California Coastal Commission).......... 34
4.2 Sea-Level Rise Projections................................................................................. 34
4.3 Future Hazard Mapping ...................................................................................... 36
4.3.1 Future Coastal Flooding........................................................................... 36
4.3.2 Future Fluvial Flooding ............................................................................ 39
4.3.3 Combined Coastal and Fluvial Flooding .................................................. 42
4.3.4 Future Erosion ......................................................................................... 43
5. Vulnerability Assessment ......................................................................................... 47
5.1 Methodology ....................................................................................................... 47
5.1.1 Exposure to Hazard ................................................................................. 47 Table of Contents
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5.1.2 Sensitivity to Hazard and Adaptive Capacity............................................ 48
5.1.3 Overall Vulnerability ................................................................................. 49
5.2 Point Arena Cove Vulnerabilities ........................................................................ 49
6. References ................................................................................................................. 53
7. List of Preparers ........................................................................................................ 55 List of Figures
Figure 1 Study Vicinity ........................................................................................................ 2 Figure 2 Study Area............................................................................................................ 5 Figure 3 Identified City Assets near Point Arena Cove ....................................................... 8 Figure 4 Identified City Assets within the Project Area ....................................................... 9 Figure 5 Assets Along Point Arena Cove Pier .................................................................... 9 Figure 6 Large Waves Destroy Pier During January 1983 Storm Event ........................... 11 Figure 7 Cobble and Storm Debris Covering Arena Cove Parking Lot (January 6, 2023) 12 Figure 8 Non-Tidal Residuals (2008 – Present Day) ........................................................ 13 Figure 9 Non-Tidal Residuals (2008 – Present Day), Associated Wave Characteristics, and Recent Large NTR Events (red)...................................... 13 Figure 10 Overtopping During January 5, 2023 Storm ....................................................... 15 Figure 11 Non-Tidal Residuals and Associated Wave Characteristics: January 5, 2023 Storm............................................................................................................... 16 Figure 12 Sea-Level Rise Trend from Arena Cove Tide Gauge ......................................... 17 Figure 13 Wave Buoys Used in Analysis ............................................................................ 18 Figure 14 Offshore and Nearshore Wave Characteristics from 1981-Present Day............. 19 Figure 15 Modeled Point Arena Watershed........................................................................ 20 Figure 16 Creek Overflow During January 10, 2023 Precipitation Event ............................ 21 Figure 17 Riverine Flooding Extent and Depth During January 10, 2023 Precipitation Event ............................................................................................................... 22 Figure 18 FEMA Floodplain Classification .......................................................................... 23 Figure 19 FEMA FIRM for the City of Point Arena .............................................................. 24 Figure 20 Existing Flood Inundation for a 100-year Storm Event........................................ 25 Figure 21 USGS Total Water Levels for Return Periods 1-yr to 500-yr .............................. 26 Figure 22 Total Water Levels for Return Periods 1-yr to 100-yr.......................................... 27 Figure 23 Estimated Coastal Inundation During the January 5, 2023 Storm and a 100- Year Storm Event ............................................................................................ 28 Figure 24 Existing Riverine Flooding Depth and Extent for a 2-year Storm........................ 29 Figure 25 Existing Riverine Flooding Depth and Extent for a 10-year Storm...................... 29 Figure 26 Existing Riverine Flooding Depth and Extent for a 100-year Storm.................... 30 Figure 27 Sea-Level Projections for Arena Cove................................................................ 35 Figure 28 Future Inundation for a 100-year Storm with 0 to 6.6 Feet of Sea-Level Rise .... 37 Figure 29 Total Water Level Return Period for Present and Future Conditions with Sea-Level Rise ................................................................................................ 38 Figure 30 Existing and Future Coastal Flood Hazard Zones .............................................. 39 Figure 31 Predicted Peak Flows (cfs) in the Point Arena Watershed Under Future Climate Conditions .......................................................................................... 40 Figure 32 Existing and Future Fluvial Flooding Extent and Depths for the 2-, 10-, and 100-year Storm Events.................................................................................... 41 Figure 33 Combined Coastal-Fluvial Flooding for a 100-year Storm: Existing and Future Conditions with 6.7ft of Sea-Level Rise................................................ 42 Figure 34 Cobble Berm Profile Evolution with Sea-Level Rise ........................................... 44 Table of Contents
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Figure 35 Potential Erosion Hazard Zones with Sea-Level Rise......................................... 45 Figure 36 Potential Shoreline Erosion with Sea-Level Rise................................................ 46 Figure 37 Components of Vulnerability............................................................................... 49 List of Tables
Table 1. Point Arena Cove Assets...................................................................................... 7 Table 2. Arena Cove Surveyed Assets............................................................................... 7 Table 3. Recent Extreme Storms at Point Arena (2008 – Present Day)........................... 14 Table 4. Tidal datums at Arena Cove (#9416841)............................................................ 17 Table 5. Summary of Existing Extreme Event Flows ........................................................ 28 Table 6. Watershed Average Percent Change in Future Extreme Rainfall....................... 39 Table 7. Hazard Exposure Scoring................................................................................... 48 Table 8. Hazard Sensitivity Scoring.................................................................................. 48 Table 9. Hazard Adaptive Capacity Scoring ..................................................................... 49 Table 10. Arena Cove Asset Vulnerabilities........................................................................ 50 Table of Contents
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Sea-Level Rise Analysis and Vulnerability Assessment for Point Arena Cove 1 ESA / D202201148.00 Technical Report October 2023
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1. INTRODUCTION
Though coastal communities are historically well-accustomed to occasional hazards such as flooding, wave overtopping, and erosion, climate change is forecast to increase exposure to coastal hazards. For coastal areas with intersecting river systems, the combined chance of marinefluvial flooding intensifies the risks of inundation and damage even more so. Identifying, preparing for, and adapting to the threats posed by sea-level rise will be one of the greatest challenges of the century. Local governments, agencies, and districts will be faced with significant challenges in continuing to provide basic services while adapting to the new paradigm posed by sea-level rise. Coastal communities in northern California are particularly vulnerable given their exposure to large storm systems that originate from the Pacific Ocean. The consequences of failing to adapt to vulnerabilities is potentially quite significant for society, public health, and the natural environment.
This document provides an informed assessment of the vulnerabilities of assets in the Arena Cove portion of Point Arena, focused on the developed area at the apex of the cove. The intent is that this information on exposures and vulnerabilities will support development of an informed and effective plan to adapt to these hazards.
1.1 Background
The City of Point Arena is a small coastal community in Mendocino County of approximately 450 residents within a 1.2-square mile area (Figure 1). It is home to Point Arena Cove and Pier and the Point Arena-Stornetta Lands of the California Coastal National Monument. The Pier serves both the commercial and recreational fishing communities, and the Cove provides the only water access for several miles, and the best small craft access between Noyo and Bodega (about 80 nautical miles). The City of Point Arena, a general law city incorporated in 1908, is located entirely in the Coastal Zone and is subject to the regulations of the California Coastal Act (1976).
The City is taking a proactive approach to determine potential impacts of sea-level rise on City assets and assess its vulnerability.
1. Introduction
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SOURCE: Imagery (Maxar) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 1
Study Vicinity
1.2 Study Purpose
The City of Point Arena was recently awarded a grant from the California Coastal Commission (CCC) to assess the City’s exposure and vulnerability to sea-level rise related coastal hazards, including the potential effects of climate change on Arena Creek. The City seeks to conduct a vulnerability assessment to map coastal flooding and erosion hazards for existing and future conditions with sea-level rise, which will be used to inform an update to the Community Health and Safety Element of the City’s Local Coastal Program (LCP). The study will serve as a first step in evaluating the risk of the City’s assets, both natural and built resources and facilities, located near the coast. The study will also provide a basis for future studies that may develop and evaluate adaptation strategies to address said vulnerabilities. The goal for this study is to provide a realistic assessment of existing and future hazards that will incrementally advance the policy for local planning documents.
1.3 Scope of Study
The scope of the study included the following:
1. Data gathering: Gather and document data pertinent to City assets, historic ocean and creek flooding events, and projected future sea-level rise.
1. Introduction
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a. Inventory assets that are likely to be in the extreme coastal hazard zone. b. Engage with community members to collect in-person accounts of historic and current coastal conditions and extreme events (including the recent events such as January 5, 2023).
c. Summarize current scientific guidance for sea-level rise projections and policies.
2. Coastal hazards: Map coastal flooding and erosion hazards for existing and future conditions with sea-level rise using available hazard mapping and simplified methods. a. Determine likely landward extent of a 100-year event with over 6 feet of sea-level rise. b. Compare results of available hazard mapping with anecdotal evidence from recent or historic extreme events.
c. Work with the City to define a set of sea-level rise planning scenarios. d. Perform an exposure analysis to determine what critical infrastructure is most vulnerable to sea-level rise and when.
3. Arena Creek flooding: Conduct an initial coarse hydrologic and hydraulic analysis of Arena Creek to establish baseline conditions and consider how these conditions might change with future climate change.
a. Determine the likely precipitation rates for mean and extreme conditions, using nearby systems that include rain and flow gauges.
b. Develop a hydraulic model and run up to nine flow scenarios to map potential future conditions.
4. Community engagement: Engage with community members throughout the development of the vulnerability assessment to obtain and understand local stakeholder observations, perspectives, and priorities.
5. Policy recommendations: Provide coastal hazard-related policy recommendations that the City may consider for inclusion in its updates to the Community Health and Safety Element of the General Plan (GP) and LCP.
1. Introduction
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2. PROJECT SETTING
This section provides a synopsis of the study area as well as the City assets within it.
2.1 Study Area
This report focuses on the impacts of sea-level rise to the City of Point Arena, specifically Point Arena Cove (Figure 2) and City assets therein. As previously mentioned, Point Arena Cove is home to a pier, a boat launch, and recreational water and beach access for residents and tourists alike. The west-facing Cove is characterized by a cobble beach fronted by rocky reef and surrounding 150-foot-tall bluffs. Point Arena Creek flows into the ocean just south of the parking lot, adjacent to land fill north of the southern bluff.
SOURCE: Imagery (NOAA NGS 2023) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 2
Study Area
During large precipitation and storm events, the Cove is susceptible to both marine and fluvial flooding. This study endeavors to summarize the magnitude and extent of both flooding sources as well as other coastal hazards, such as erosion.
2. Project Setting
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2.2 Community Outreach and Engagement
ESA conducted community outreach and engagement in partnership with City staff on February 1 and 2, 2023. Initial outreach consisted of a community meeting on February 1st with approximately 20 attendees; subsequent outreach included interviews with individual stakeholders. The February 1st stakeholder meeting included an overview of the project goals and objectives, anticipated project timeline, state sea-level rise guidance, and coastal hazard processes and sea-level rise projections. ESA requested community input on asset identification, observations of historic flooding and erosion, and insights regarding other factors pertinent to vulnerability.
General community observations and priorities included the following (note community input has been grouped into categories for ease of reference):
• Erosion: Community members confirmed that the bluffs south of the community picnic area have been eroding due to wave undercutting.
• Overtopping:
– Waves overtop the revetments and flood the parking lot approximately every 2 to 3 years, and the degree of overtopping has been significantly worsening approximately every 5 years.
– When waves overtop the northern revetment, they reflect off of the northern bluff and will continue behind the Coast Guard Boathouse during large storm events (like the one on January 5th, 2023)
– Westerly and southwesterly swells tend to cause the most damage to infrastructure. • Recreational Assets: Community members confirmed the frequent usage of the Cove for surfing, picnicking, tide pooling, vehicular and maritime access to the shore. • Ecological Assets: Attendees mentioned that there used to be more fish (trout and steelhead, specifically) in the Creek and reaffirmed the importance of the Point Arena mountain beaver.
2.3 Community Assets
ESA staff visited the Cove in February of 2023 and met with City staff, City Council, and community members to discuss observations of historic flooding and identification of community assets potentially vulnerable to existing and future flooding with sea-level rise. Based on this meeting as well as prior meetings with City staff, ESA identified a number of assets within the project area with the potential to be affected by existing and future coastal hazards with sea-level rise (see Figures 3 - 5). The identified assets have been grouped into categories below (Table 1) for ease of reference; however, some assets (e.g., the beach) may in fact span one or more categories.
2. Project Setting
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TABLE 1. POINT ARENA COVE ASSETS
Pier
Boat ramp
Storage
Floating platform
Harbor office
Boat Lift
Public restrooms
Fish cleaning stations
Pier
Shoreline Armoring
Revetment Seawall
Developed Areas
Parking lot Event/overflow parking Private property (e.g., restaurants and shops)
Historic Coast Guard
Boathouse
Utilities
Electric (e.g., vaults) Gas lines Sewer (e.g., manholes and pump station)
Water
Wastewater
Recreational
Picnic area Beach (north and south) Surf breaks (north and south) Ecological
Point Arena mountain beaver Wetlands Lagoon and creek Bioretention basins The Point Arena mountain beaver is a federally listed endangered subspecies found only in the vicinity of Point Arena and the southwest Mendocino County coast (USFWS 1998). Community members have indicated a handful of observations of the Point Arena mountain beaver on the hillslope on the south side of Arena Creek. Community members also identified an approximate wildlife corridor zone that is potentially used by species including the Point Arena mountain beaver. Note that the areas shown in Figure 3 are approximate and do not represent regulatory habitat zones or actual biological surveys. USFWS is currently initiating a 5-year review of the endangered status of the Point Arena mountain beaver (USFWS 2023).
ESA surveyed a portion of the assets identified above to ascertain an approximate estimate of existing asset elevations. Elevations of the surveyed assets are noted in Table 2 below and are referenced later in this report.
TABLE 2. ARENA COVE SURVEYED ASSETS
Asset Surveyed Elevation(s) (ft NAVD)
Pier 23
Parking lot 12 – 16
Creek 8 – 12 (thalweg to bank)
Beach 4.5 – 17
Seawall 16 – 18 (top)
Electric vaults 13
Sewer pump station 16 – 17
Sewer manholes 17
NOTES: Surveyed elevations have been rounded to the nearest whole digit and are not intended for design purposes.
2. Project Setting
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SOURCE: ESA 2023, Imagery (Maxar) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 3
Identified City Assets near Point Arena Cove
2. Project Setting
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SOURCE: ESA 2023; Imagery (Maxar) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 4
Identified City Assets within the Project Area
SOURCE: SHN City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 5
Assets Along Point Arena Cove Pier
2. Project Setting
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3. HISTORIC AND EXISTING CONDITIONS
3.1 Historic Storms and Documented Impacts
The Point Arena community is no stranger to weathering large storms. Numerous news articles and blog posts1 may be found documenting the damage that has occurred to the nearby infrastructure over the last century. One particular storm on January 26, 1983 destroyed the pier and a fish house and severely damaged several other pieces of infrastructure within the Cove (see Figure 6). Other frequently documented impacts from large storms include overtopping of the revetment, flooding and deposition of cobble/gravel from the beach into the parking lot (Figure 7), and inundation into nearby private and retail buildings, among others.
SOURCE: “The Great Disaster at Arena
Cove” by Nicholas King
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 6
Large Waves Destroy Pier During January
1983 Storm Event
1 https://acornpartnersineducation.org/programs-events/students-protecting-the-coast/acorn-naturalist-guide/ naturalist-guide-point-arena-town-history/; http://kenjonesfishing.com/2015/04/point-arena-pier/; https://www.mendotraintony.com/mendocino-coast-ravaged-by-1983-storm/; https://mendofever.com/2023/01/09/city-of-point-arena-declares-a-local-emergency/
3. Historic and Existing Conditions
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SOURCE: Paul Andersen City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 7
Cobble and Storm Debris Covering Arena Cove
Parking Lot (January 6, 2023)
3.1.1 Analyzing Historic Water Levels
ESA obtained 1- and 6-minute water level measurements from the Arena Cove NOAA tide gauge and calculated non-tidal residuals (NTRs or residuals) for each dataset to determine the timing and magnitude of historic storm events within the Cove. NTRs are the “extra” water level that remains after the predicted water levels (tides) are subtracted from the observed water levels. In other words, NTRs are the result of waves, surge, and other events that are otherwise unaccounted for by the tidal predictions.
Figure 8 below illustrates the results of the NTR calculations for the period of record (limited by the available 1-min data, which began in 2008). The blue lines indicate the 1-minute water level, NTRs, and difference between the 1- and 6-minute data, and the orange lines indicate the 6- minute water level and NTRs. The orange dots on Figure 9 show the coincident wave height, period, and direction for significant NTR events greater than 3 feet using the 1-min water level data. This indicates that the most extreme local NTR water levels at Arena Cove (i.e., NTR greater than about four feet) are associated with long period swells with offshore peak wave directions with a strong west component (i.e., ~260 to 300 degrees).
3. Historic and Existing Conditions
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SOURCE: Water level data (NOAA) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 8
Non-Tidal Residuals (2008 – Present Day)
SOURCE: Water level and wave data (NOAA) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 9
Non-Tidal Residuals (2008 – Present Day), Associated Wave Characteristics, and Recent Large NTR Events (red)
3. Historic and Existing Conditions
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Although noisier, the 1-min water level data provides a better synopsis of the actual water surface elevation fluctuations during extreme conditions than the 6-minute water level data, which is primarily used to represent still water level or tide conditions. The unique location of the tide gauge in Arena Cove makes it a valuable tool for observations of wave driven water level changes, commonly described as wave setup, or mor specifically, dynamic wave setup.
Based on ESA’s analysis, several recent significant storm events were noted on December 17-18, 2018; January 17-18, 2019; and January 5-8, 2023. Two tsunamis were also observed on March 11, 2011 and January 15, 2022. The NTRs for these events ranged from 1 to 6 feet. The full range of storm events, including date, NTR, and associated wave characteristics, are noted in Table 3 below.
TABLE 3. RECENT EXTREME STORMS AT POINT ARENA (2008 – PRESENT DAY) NDBC 46014 NDBC 46059
Date NTRa (ft) Hs (ft) Tp (s) Dp b (deg) Date NTR (ft) Hs (ft) Tp (s) Dp (deg) 1/5/2008 5.2 30 17 N/Ac 2/23/2008 4.3 33 13 N/A
2/24/2008 4.5 25 15 N/A 1/18/2010 4.2 N/A N/A N/A
1/19/2010 4.2 26 17 N/A 1/24/2010 3.3 N/A N/A N/A
1/25/2010 3.3 21 17 N/A 11/1/2010 4.2 27 19 N/A
11/2/2010 4.3 24 19 N/A 3/10/2011
(tsunami)
5.5 10 14 N/A
3/11/2011
(tsunami)
5.4 8 N/A N/A 3/31/2012 3.7 27 15 N/A
12/11/2015 4.6 30 17 280 12/10/2015 4.7 35 16 295
1/21/2017 5.2 30 19 275 1/20/2017 5.3 40 18 300
12/16/2018 4.9 26 16 285 12/16/2018 4.9 28 19 290
1/17/2019 4.8 25 16 270 1/16/2019 4.8 40 19 275
11/27/2019 3.1 37 15 300 11/26/2019 3.2 28 15 340
1/10/2021 3.2 20 17 300 1/10/2021 3.3 29 18 280
10/25/2021 4 24 16 300 10/24/2021 4.2 N/A N/A N/A
1/15/2022
(tsunami)
4.3 11 15 300 1/14/2022
(tsunami)
4.3 12 14 295
1/5/2023 6 33 17 250 1/4/2023 6 38 16 260
1/7/2023 3.7 20 16 260 1/7/2023 3.5 20 15 275
1/13/2023 4 22 19 245 1/12/2023 4 24 16 280
NOTES:
a NTRs noted are the maximum recorded during the event. b Degrees begin with 0 in the north and run clockwise.
c Wave period and direction were not available for the entire record. Wave direction was not recorded at either gauge until 2015.
SOURCE: Water level and wave data (NOAA), calculations (ESA)
3. Historic and Existing Conditions
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3.1.2 Observations from the January 5, 2023, Storm Event Of the significant storm events noted above, ESA was onsite to observe the most recent storm on January 5, 2023, which resulted in significant flooding of the Cove (see Figure 10). During the event, large waves overtopped the seawall and inundation extended across the majority of the parking lot, carrying cobble and large logs with the wave boar. Wave crests were also observed to nearly reach the bottom of the pier. In addition, the power in the Cove was lost, and because there was no backup generator, neither the boat hoist on the pier nor the sewer lift station were operable.
SOURCE: Louis White (ESA) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 10
Overtopping During January 5, 2023 Storm
ESA performed post-storm analysis to obtain the water levels, NTRs, and wave characteristics for the event (Figure 11). NTRs were noted as high as 3 to 6 feet above predicted water levels (for the 6-minute and 1-minute averages, respectively). Offshore wave heights reached peaks ranging from 302 to 383 feet, coming from a predominantly westerly direction (Figure 11). Nearshore wave heights closer to the Cove reached approximately 17 feet at an 18 to 20 second period with 2 Point Arena Buoy, 46014 NDBC 19 nautical miles north of Point Arena. Available:
https://www.ndbc.noaa.gov/station_page.php?station=46014 3 West California Buoy, 26059 NDBC 357 nautical miles west of San Francisco. Available:
https://www.ndbc.noaa.gov/station_page.php?station=46059
3. Historic and Existing Conditions
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a direction of about 250 to 270 degrees (Figure 11).4 Based on offshore and nearshore wave heights, ESA computed a total water level of approximately +30 feet NAVD for the January 5, 2023 event.
SOURCE: Water level and wave data (NOAA) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 11
Non-Tidal Residuals and Associated Wave
Characteristics: January 5, 2023 Storm
3.2 Existing Flooding
This section provides a synopsis of the existing conditions for the three main flood sources (tides, waves, and the creek) within Point Arena Cove. Existing hydrologic conditions are important to understand because they form the foundation for projected changes with sea-level rise. 4 CDIP MOP MO-149 https://cdip.ucsd.edu/mops/?moplist=Mendocino_County&xitem=info&mop=M0149
3. Historic and Existing Conditions
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3.2.1 Tides and Water Levels
Point Arena experiences mixed semidiurnal tides, or two daily high tides and two daily low tides of differing elevations. These daily tides also vary with the spring-neap tidal cycles, which occur approximately twice a month.
Coastal engineers use vertical datums, or defined reference surfaces, to estimate the relative elevation of the tides and water levels to the land around it. Measuring the water levels over prolonged periods provides a baseline for understanding typical water levels and how they may change over time. For this study, ESA used the closest NOAA tide gauge: Arena Cove (Station #9416841), located in the middle of the Cove. Tidal datums for the gauge are shown in Table 4.
TABLE 4. TIDAL DATUMS AT ARENA COVE (#9416841)
Tidal datum Abbreviation ft NAVD
Maximum Observed Tide (observed on February 6, 1998) MOT 8.53 Highest Astronomical Tide HAT 7.48
Mean Higher High Water MHHW 5.73
Mean High Water MHW 5.06
Mean Tide Level MTL 3.04
Mean Sea Level MSL 3.00
Mean Low Water MLW 1.01
Mean Lower Low Water MLLW -0.14
NOTES: The tidal datums listed above are from the most recent tidal epoch: 1983-2001.
SOURCE: NOAA Tides and Currents 2020
The record for the Arena Cove tide gauge dates back to 1978. The relative sea level trend recorded over this period (Figure 12) is 0.86 mm/year, which is equivalent to 0.28 ft over 100 years.
SOURCE: NOAA City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 12
Sea-Level Rise Trend from Arena Cove Tide Gauge
3. Historic and Existing Conditions
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3.2.2 Waves
The study area is exposed to large swell and large storm seas. The majority of the wave exposure comes from the north Pacific, with swell primarily from between the west and northwest directions. Strong winds and seas can also arrive from these directions as well as the south through southwest. Swells from the southern hemisphere also reach the study area and occasionally with relatively high power (very long wave lengths associated with long travel distances), although they are generally smaller than the north Pacific swells. Based on input from local community members (see Section 2.2), the most damaging storms have come from the westsouthwesterly direction.
Offshore and nearshore wave characteristics for the study area (e.g., significant wave height, peak wave period, dominant wave direction, and wave power) are shown in Figure 14 below.
Additional information can be obtained from the closest wave buoys (Figure 13):
• Nearshore (CDIP M0149)5
• Point Arena (NBDC 46014)6
• West California (NDBC 46059)7
SOURCE: Imagery (Earthstar Geographics) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 13
Wave Buoys Used in Analysis
5 https://cdip.ucsd.edu/mops/?moplist=Mendocino_County&xitem=info&mop=M0149 6 https://www.ndbc.noaa.gov/station_page.php?station=46014 7 https://www.ndbc.noaa.gov/station_page.php?station=46059
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SOURCE: Wave data from NOAA and CDIP City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 14
Offshore and Nearshore Wave Characteristics from
1981-Present Day
3.2.3 Creek Flooding
ESA conducted an initial hydrologic and hydraulic analysis of Arena Creek to assess current flood challenges and how riverine flooding will change under future climate change conditions.
The following sections describe the methodology and provide an overview of existing flooding conditions based on a recently observed storm event (January 10, 2023) with high rainfall.
Methodology
The Point Arena watershed (Figure 15) was simulated in HEC-HMS 4.10, a software used to simulate complete hydrologic processes for watersheds, to determine flows for mean and extreme flood conditions. The Point Arena watershed was first delineated using USGS StreamStats.8 8 StreamStats is a USGS web application used to delineate drainage areas and estimate basin characteristics on userselected sites on streams. Accessed at https://streamstats.usgs.gov/ss/. 0 10
20 30
40 50
Sig Wave Height (ft)
NDBC-46059 (Depth: 15220 ft)
NDBC-46014 (Depth: 1680 ft)
MOP-M0149 (Depth: 49 ft)
0 5
10 15
20 25
Tp (sec)
0 100
200
300
400
Dp (Deg)
1980 1985 1990 1995 2000 2005 2010 2015 2020
Date & Time (PST)
10 2
10 4
10 6
Wave Power (ft.lb/sec/ft)
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SOURCE: NOAA 2017 LiDAR City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 15
Modeled Point Arena Watershed
The watershed was modeled using the Soil Conservation Service (SCS) Unit Hydrograph method to compute a runoff hydrograph. The SCS Unit Hydrograph method is based on the concept of a unit hydrograph, which represents the response of a watershed to a unit amount of rainfall over a specific duration. Key inputs to the SCS Unit Hydrograph method are the curve number and percent imperviousness. The curve number is an empirical parameter used for predicting direct runoff and infiltration from excess rainfall and is a function of land use and soil type. Soil data was retrieved from the USGS Web Soil Survey while land use data was retrieved from the 2019 National Land Cover Database (NLCD 2019). Percent imperviousness represents the percentage of the watershed that consists of impervious surfaces such as roads, roofs, and other paved surfaces and was derived using the NLCD 2019 dataset. Higher curve number values and percent imperviousness values represents higher runoff potential which will increase peak flows.
Peak flows obtained from HEC-HMS were simulated using the HEC-RAS 6.3.1 hydraulic model.
ESA developed a two-dimensional (2D) hydraulic model to evaluate the flood extents of mean and extreme events. The 2D model allows for a more accurate representation of complex flow patterns and hydraulic interactions with topographic features. The terrain for the 2D hydraulic model was derived using a 2017 FEMA LiDAR flight (OCM Partners, 2023). Cell-spacing for the grid was set to 10-feet. Base Manning’s roughness, an empirical parameter used to define resistance to flow, for the hydraulic model was set to 0.05, while calibrated regions were used to assign a Manning’s roughness of 0.016 for impervious surfaces such as Port Road and the Point
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Arena parking lot and a Manning’s roughness of 0.13 for densely vegetated areas such as those along Port Road.
Modeled Creek Flooding Event (January 10, 2023)
Observations of creek flooding occurred most recently during a high precipitation event on January 10, 2023. The event caused severe creek flooding and overflow onto Port Road, the sole access road leading into and out of the Cove (see Figure 16). Observations from this event were used to verify the results of the fluvial model as described below.
SOURCE: Paul Andersen 2023 City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 16
Creek Overflow During January 10, 2023 Precipitation Event The January 10, 2023 rainfall event peak flow was estimated using the hydrologic model in HECHMS and routed in HEC-RAS. No rain gauges with recent data exist within the immediate vicinity of Point Arena. Therefore, the Boonville rain gauge, located approximately 20 miles east of Point Arena and managed by the California Department of Water Resources, was chosen instead. A scaling factor equivalent to the ratio of the mean annual precipitation of the Point Arena basin to the mean annual precipitation of the Boonville rain gauge was used to amplify the precipitation data for the January 10, 2023 rainfall event. The corresponding peak flow was then estimated in HEC-HMS and simulated in HEC-RAS. The flood extents were then compared to observed flooding from the storm event to verify the HEC-HMS inputs and peak flow. Flood extents for the January 10, 2023, rainfall event are shown in Figure 17.
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SOURCE: Imagery (Maxar) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 17
Riverine Flooding Extent and Depth During
January 10, 2023 Precipitation Event
3.3 Extreme Event Flooding
Several sources are available with which to estimate the magnitude and extent of an existing 100-year storm (i.e., a storm with a 1% annual chance of occurrence): the Federal Emergency Management Agency (FEMA) and the U.S. Geological Survey (USGS). The following subsections briefly describe and provide local results for each source as well as results for analyses performed by ESA.
3.3.1 FEMA
FEMA develops Flood Insurance Studies (FISs) and Flood Insurance Rate Maps (FIRMs) for the purpose of informing the public of flood risks, to inform building policy in risk-prone areas, and to control the chance of damage to property. FEMA FIRMS typically show colored zones indicating the extent of the 1% (100-year) and 0.2% (500-year) annual chance flood events. These events can happen as a result of flooding from coastal flood sources (ocean water levels and waves), precipitation flood sources (high freshwater runoff), or a combination of both (as is the case for Arena Cove).
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Within the flood hazard zone (also known as the 100-year floodplain), FEMA further categorizes zones of relative hazards in terms of the wave height and flow rate (see Figure 18). The zones are intended to relate the potential damage that may occur within the floodplain as a result of the intensity of flooding. It is important to note that FEMA only considers existing conditions and does not account for long-term coastal erosion or sea-level rise in its mapping.
SOURCE: CDWR 2020 City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 18
FEMA Floodplain Classification
The latest FIRM for Point Arena Cove, dated July 18, 2017, is shown in Figure 19 and includes a coastal “VE” zone and a fluvial “A” zone. The coastal VE zone specifies a base flood elevation (BFE) of 32 feet NAVD, which for coastal areas is the 100-year total water level (i.e., elevation of the 100-year wave runup elevation). This implies that any assets located seaward of the orange line in Figure 12 and at or below this elevation are already exposed to flood inundation during a 100-year event. No elevation is specified for the A zone. The FEMA mapping is approximate landward of the orange line, with the landward hazard zone based on the creek flood source.
Based on historic and recently observed events (see Figure 10), it would appear that the FEMA FIRM underpredicts the extent of the 100-year floodplain and high-velocity hazards actually extend further into the developed area.
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SOURCE: FEMA 2017 City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 19
FEMA FIRM for the City of Point Arena
3.3.2 USGS Coastal Storm Modelling System (CoSMoS)
The USGS’s Coastal Storm Modeling System (CoSMoS) (Barnard 2019) provides storm-induced coastal flood and erosion hazard mapping for both current and future conditions, including a range of storm scenarios (i.e., return periods). Though the online mapping provides flood depths, the map is most useful for visualizing flood inundation (depicted in blue) and wave runup (depicted as small green dots) extents.
Figure 20 shows the existing coastal flood hazard with a 100-year event, essentially the same scenario as the FEMA maps. Flood depths are indicated by the blue shading with darker shading indicating greater depth (see legend). The shaded areas indicate water depths that persist for several minutes, and do not include the shorter bursts of high velocity wave runup extending farther landward and higher. The extent of wave runup is located by the green dots, which extend landward of the shaded flood areas.
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Note that FEMA considers flooding to extend to the limits of wave runup, which can also cause structural damage and scour. Hence the ‘green dots’ on the CoSMoS map should be compared to the flood limits in the FEMA map. Compared to both the FEMA FIRM as well as ESA’s analysis (see Section 2.3.4 below), the extent of wave runup modeled by CoSMoS may be over-estimated in this case given the local topography (i.e., cove surrounded by steep bluffs).
SOURCE: USGS City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 20
Existing Flood Inundation for a 100-year Storm Event
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3.3.3 USGS 100-year Coastal Total Water Levels
A recent study by the USGS (Shope et al. 2022) computed total water levels every 100 meters for the entire West Coast and a range of return periods (1-year through 500-year). These values supersede those provided in CoSMoS (see Section 3.3.2). Three USGS transects intersect Point Arena Cove: transect ID 12692, 12691, and 12690, noted in the below figure as “north, “middle”, and “south”. Figure 21 shows USGS’s total water level estimates for each transect and the full range of return periods. The 100-year total water level, as estimated by the USGS analysis, is in the range of +23 to +31 feet NAVD. The largest of the USGS estimated total water levels is comparable with the BFE estimated by FEMA (+32 feet NAVD) though lower than the 100-yr total water level estimated by ESA (+33 feet NAVD, see section 2.3.4).
SOURCE: USGS 2022 City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 21
USGS Total Water Levels for Return Periods 1-yr to 500-yr
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3.3.4 ESA’s Estimated Extreme Coastal Flooding
To perform a more site-specific analysis, ESA also calculated total water levels (TWLs) for a range of return periods under existing conditions (Figure 22). The TWLs were calculated from a 63-year time series (1960-present day) of coincident wave and water levels used by FEMA for their coastal flood analysis (FEMA 2014). Based on ESA’s analysis, the 100-year total water level is approximately +33 feet NAVD for existing conditions.
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 22
Total Water Levels for Return Periods 1-yr to 100-yr
ESA used in-person observations from the January 5, 2023 storm event to calibrate the total water level calculations above and to map the approximate inundation extent of a 100-year storm (Figure 23). Compared to the FEMA and CoSMoS 100-year landward flood extents, ESA’s estimates were closer to CoSMoS’ modeled landward extents of inundation, which is more extensive than FEMA’s.
100-year =
33 ft NAVD
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SOURCE: Imagery (NOAA
NGS 2023)
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 23
Estimated Coastal Inundation During the January 5, 2023 Storm and a 100-Year Storm Event
3.3.5 ESA’s Estimated Extreme Fluvial Flooding
The 2-year, 10-year, and 100-year flows were obtained from HEC-HMS 4.10 using the frequency storm method, which transforms precipitation depths for a given storm duration into a design hydrograph. The extreme event flows are summarized in Table 5.
TABLE 5. SUMMARY OF EXISTING EXTREME EVENT FLOWS
Extreme Event Flow (cfs)
2-year 279.7
10-year 618.4
100-yr 1068.3
The extreme event flows were modeled in HEC-RAS as a quasi-unsteady-state simulation. The maximum flows were applied at the upstream end of the model domain and were held constant during the simulation period. A constant tailwater elevation equivalent to MHHW plus one foot was selected at the downstream end of the model domain. During extreme rainfall events, it was assumed that the cobble beach berm is scoured out. Surface differencing between the 2017 FEMA LiDAR and a previous 2016 USGS LiDAR dataset revealed that the 2017 FEMA LiDAR depths in the downstream creek channel were several feet lower than that of the 2016 USGS LiDAR data. Additionally, the cobble beach berm elevations that were surveyed in March 2023 are not present within the 2017 FEMA LiDAR, indicating that the LiDAR data was flown when the Point Arena creek was in a scoured state. Figures 24-26 map the flood extents for the existing extreme events.
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SOURCE: Imagery (Maxar) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 24
Existing Riverine Flooding Depth and Extent for a 2-year Storm SOURCE: Imagery (Maxar) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 25
Existing Riverine Flooding Depth and Extent for a 10-year Storm
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SOURCE: Imagery (Maxar) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 26
Existing Riverine Flooding Depth and Extent for a 100-year Storm
3.4 Influence of Filled Park Area on Flooding
Note that the presence of the filled “park” area on the south bank of Arena Creek, which is an elevated area overlooking the beach and the parking, and which includes a picnic area, appears to greatly influence the direction of fluvial flooding onto the parking area. The park is an artificially filled area, which was developed when the parking area of the cove was constructed by filling the historic lagoon with material. Based on observations of the creek flows and flooding, the park feature deflects creek flows to the north toward the parking area. The parking lot was constructed at a very low elevation in the lagoon floodplain, and thus is already vulnerable to regular flooding.
The park area tends to enhance the flooding by deflecting all flows toward the parking and forcing the creek to flow through a narrow corridor. The reaction to the creek flooding has been to construct a short berm separating the parking and the creek, but coastal wave events move cobble and beach sediments into the creek mouth, which tends to also block the fluvial flows. We hypothesize that under historical conditions, where the lagoon was much wider with a back-beachlagoon interface along a longer reach, the lagoon would fill during rain-driven fluvial events and then would drain through a channel that would route across the beach along the tall hillside and bluff. Lagoons in California that are “perched” above the tides, such as at Arena Creek, tend to intermittently blow out and drain across the beach (Behrens et al. 2015). Lagoons with coarse cobble beaches also tend to have more permanent “overflow” channels draining the lagoon over the beach when the water level in the lagoon exceeds the low point of the beach berm.
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3.5 Local Sediment Processes
The following sections discuss coastal sediment transportation processes within the study area.
These processes are important to understand because they influence how the coastline has historically responded to sea-level rise and extreme events and therefore how it might respond to sea-level rise in the future.
3.5.1 Sediment Transport
The section of coastline within the study area is characterized by a cove with cobble/gravel beaches, rocky offshore reefs, and surrounding steep bluffs. Sediment sources for the Cove are the creek, which delivers sediment during large precipitation events, erosion of the adjacent bluffs, and onshore transport via waves. Sediment sinks for the Cove are offshore transport via waves and anthropogenic removal of beach sediment by local residents after storms wash them onto the Cove parking lot.
3.5.2 Historic Erosion
Data concerning historic coastal erosion rates is generally difficult to come by. For this study, ESA used information from a Philip Williams & Associates (PWA, now ESA) report that analyzed the effects of sea-level rise on coastal erosion throughout the State of California (2009).
Much of the historical data from the PWA report was sourced from two USGS shoreline change reports (Hapke et al. 2006, Hapke and Reid 2007) that included long-term erosion rates for sandy and cliff-backed shorelines (i.e., bluffs). Historic shoreline change rates within the project area ranged from -0.07 to -0.16 meters per year (-0.23 to -0.52 feet per year); however, information for the Cove itself was limited to two shoreline stretches on the northern side of the Cove. For reference, historic erosion rates just south of the Cove ranged from -0.13 to -0.15 meters per year (-0.43 to -0.49 feet per year), which is comparable to other adjacent and similarly-oriented shorelines in the larger area.
Anecdotal observations of erosion of the filled park area on the south side of Arena Creek by community members indicate that fill comprising the park area has eroded significantly over the past decade. No estimates of erosion rates are available for this location.
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4. FUTURE CONDITIONS WITH SEA-LEVEL
RISE
The following section summarizes state sea-level rise guidance, regional sea-level rise projections, and available coastal hazard maps for projected future conditions with sea-level rise over the next century.
4.1 Relevant State Sea-Level Rise Guidance
Pertinent policies and guidance concerning sea-level rise projections and planning in the State of California are outlined below. The following is not an exhaustive list, and it is important to note that such policies are often being updated due to frequent updates in climate science as more data is collected and future projections based on historic data are revised.
4.1.1 California Strategic Plan to Protect California’s Coasts and Oceans 2020-2025 (Ocean Protection Council)
The California Ocean Protection Council published the California Strategic Plan to Protect California’s Coasts and Oceans 2020-2025 (OPC 2020)9. Objective 1 of the plan states:
“Objective 1.1Build Resiliency to Sea-Level Rise, Coastal Storms, Erosion, and Flooding “1.1.1: Ensure California’s coast is resilient to at least 3.5 feet of sea-level rise by 2050, as consistent with the State’s Sea-Level Rise Guidance Document as appropriate for a given location or project. This target will be modified periodically based on the best available science and updates to the State’s Sea-Level Rise Guidance Document.” This objective calls for coastal development to be adapted to withstand 3.5 feet of sea-level rise, with the adaptation implemented by 2050. Note that the 2050 date is a goal for implementation of the adaptation, in anticipation of future sea levels reaching 3.5 sometime after that date.
4.1.2 State of California Sea-Level Rise Guidance (Ocean Protection Council)
The OPC adopted sea-level rise guidance in March of 2018 that updated the previous state guidance based on advances in climate science. The OPC guidance provides a synthesis of sealevel rise science and projected rates for the state of California, steps for local governments and state agencies to incorporate sea-level rise science into permitting, planning, and investment decisions, and preferred adaptation approaches. The vulnerability assessment and adaptation 9 https://www.opc.ca.gov/webmaster/ftp/pdf/2020-2025-strategic-plan/OPC-2020-2025-Strategic-Plan-FINAL20200228.pdf
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strategy recommendations in this report are intended to be consistent with the sea-level rise projections and adaptation strategy recommendations within the OPC’s sea-level rise guidance.
4.1.3 Sea-Level Rise Policy Guidance (California Coastal Commission)
This document provides guidance for incorporating sea-level rise considerations into planning and design of projects and policy documents for areas along the California coast within the jurisdiction of the CCC. The most recent update (2018) to the guidance adopted the sea-level rise projections presented in the OPC (2018) California Sea-Level Rise Guidance (high emission scenarios only). The target audience are applicants and agencies preparing Coastal Development Permit applications and Local Coastal Program updates. The guidance includes useful and fundamental concepts for application of the sea-level rise projections and development of adaptation strategies. Chapter 7, “Adaptation Strategies,” discusses four adaptation strategies:
accommodate, protect, hybrid, and retreat. This report and ESA’s recommendations herein are intended to be consistent with the CCC’s Sea-Level Rise Policy Guidance.
4.2 Sea-Level Rise Projections
Projections of global sea-level rise are well-documented and investigated, with recent research projecting sea-level rise on the order of 2 to 10 feet by 2100 in California (e.g., Cayan et al. 2009, Griggs et al. 2017). This research has been used to develop a series of policy guidance documents by the State of California that have recommended including specific amounts of sea-level rise in project planning and design, which were described in section 3.1 (Relevant State Sea-Level Rise Guidance).
While large-scale (global- or state-level) sea-level projections have existed for several decades, smaller scale (e.g., region- or county-scale) estimates have only become readily-available in recent years. This is partly because of advances in techniques to downscale global climate models for parts of the California coast, and also because of an effort to consider local rates of vertical land motion (VLM). Projections of sea-level rise vary along the coast of California due to the regional oceanic effects as well as VLM. Beside varying geographically, the projections also vary based on the selection of future global emissions scenarios (e.g., greater levels of carbon emissions relate to higher sea-level rise). The following paragraphs provide a general summary of the sea-level rise science that has been developed for California, specifically within the study area region.
Climate models show strong agreement on the amount of sea-level rise that is likely to occur by 2050 and start to diverge after 2050 based on the range of potential emissions scenarios. The OPC 2018 Sea-Level Rise Guidance provides probabilistic projections of sea-level rise and categorizes them into recommended low risk aversion, medium-high risk aversion, and extreme risk aversion projections.
These risk aversion categories are intended to be selected based on a project’s apparent level of tolerable risk and its ability to adapt to future sea-level rise. The low and medium-high risk
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aversion scenarios are probabilistic projections where “low” represents the upper bound of the “likely range” (approximately 17% probability of exceedance) and “medium-high” represents a 1-in-200 chance (0.5% probability of exceedance). The extreme risk aversion (or H++) is a single scenario that does not have an associated likelihood of occurrence but is considered a high-end scenario associated with catastrophic melting of the West Antarctic Ice Sheet (OPC 2018).
Figure 27 presents a graphical plot of the sea-level rise projections for the Arena Cove tide station through the year 2100. Note that the curves accelerate over time, and that sea-level rise is expected to continue well beyond the end of the century. The OPC provides projections up to the year 2150; however, the uncertainty increases for projections beyond the year 2100 due to a limited number of models that project sea-level rise beyond the end of the 21st century.
SOURCE: data (OPC 2018) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 27
Sea-Level Projections for Arena Cove
Due to the current uncertainty associated with models beyond the year 2100 as well as the likely removal of the extreme risk aversion scenario based on recent study (Sweet and others 2022), ESA applied the medium-high risk aversion projections from OPC’s 2018 guidance up to the year 2100 for this study: The corresponding amounts of sea-level rise used are 1.8, 3.3, and 6.7 feet for 2050, 2070 and 2100, respectively. Note that lower-cost facilities that are not as sensitive to coastal hazards or have greater adaptive capacity may be evaluated relative to the low-risk aversion curve: For example, it may not be desirable or practicable to locate a coastal trail or picnic table or lawn above and landward of the higher sea level projections but rather to relocate or reconstruct these features as needed.
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4.3 Future Hazard Mapping
ESA considered several existing hazard models in addition to performing its own analysis. The results for potential future flood and erosion hazards are shown separately below. Though the results are separated by hazard type below, it is important to remember that flooding and erosion are intricately connected and that the actual future flood and erosion extents may be more or less than what is noted below. Similarly, combined fluvial and marine flooding may lead to exacerbated flood conditions if or when extreme marine and fluvial events occur simultaneously.
4.3.1 Future Coastal Flooding
The primary existing model for future coastal inundation with sea-level rise is the USGS’s CoSMoS (Barnard 2019). The model predicts future coastal flooding under a range of sea-level rise (0ft to 16.4ft) and storm scenarios (0-year to 100-year). Figure 28 below shows the results from CoSMoS for 0ft, 1.6ft, 3.3ft, and 6.6ft of sea-level rise with a 100-year storm. Note that CoSMoS does not model the exact amounts of sea-level rise that are prescribed by OPC; however, these scenarios shown below are approximate to those listed for the OPC medium-high risk sea-level rise projections. As Figure 28 depicts, the majority of the project area is inundated under present conditions, and flooding continues to move further up the valley with increasing sea levels.
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SOURCE: USGS CoSMoS, Point Blue City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 28
Future Inundation for a 100-year Storm with 0 to 6.6 Feet of Sea-Level Rise
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While the CoSMoS results provides a reasonable assessment of future hazards at a broader scale, it is not intended for site specific analysis and does not provide a great level of detail when it comes to potential future flood depths. As such, ESA performed its own analysis of the potential future total water levels with future sea-level rise (see Figure 29). Based on ESA’s analysis, future extreme flooding (i.e., the 100-year flood) may be expected to increase by approximately 14 feet (e.g., from +33 to +47 feet NAVD) with up to 6.7 feet of sea-level rise by the end of the century.
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 29
Total Water Level Return Period for Present and Future
Conditions with Sea-Level Rise
To map the potential future flood zone in the Cove with sea-level rise, ESA assumed a Bruun shoreline transgression (i.e., that the shoreline will shift inland and upwards with sea-level rise, see section 4.3.4). While ESA notes that armoring is present within the Cove and may be maintained/upgraded to adjust with sea-level rise, using a Bruun shoreline transgression allows for a more conservative estimate of potential future flooding under more natural shoreline conditions, which may be a good indicator after failure of the armoring. An additional setback of 10 feet was also applied to account for the likely beach width.
Figure 30 depicts the results of this mapping, where the future flood line indicates a potential future beach crest (if no armoring were present). As Figure 30 depicts, much of the Cove is already within the 100-year flood hazard zone. Given the topography of the Cove (i.e., a valley surrounded by steep bluffs), future flooding is restrained to the most low-lying areas. This means that as the sea level rises, flooding will simply move up the valley, deepening the existing flood levels and allowing for high velocity areas to move further inland as well.
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SOURCE: Imagery (NOAA NGS
2023)
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 30
Existing and Future Coastal Flood Hazard Zones
4.3.2 Future Fluvial Flooding
Future climate conditions scenarios were analyzed for design events with projected changes in extreme rainfall for a high emissions trajectory (RCP 8.5) for time horizons 2050 (2035- 2064), 2070 (2055-2084), and 2100 (2070-2100). Future extreme rainfall was quantified by performing a frequency analysis assuming a generalized extreme value distribution using 30 years of downscaled climate model projections centered around the future years of interest (CMIP5, 2013).
The increase in design event rainfall, averaged over the watershed, is summarized in Table 6.
The relative percent increase in extreme rainfall was used to scale the design event rainfall depths in the hydrologic model to derive peak flow values, which were then routed in the hydraulic model for each scenario shown in Table 6. Figure 31 shows the simulated flow hydrographs for design events under future climate conditions. In general, for a given flood return period, the peak flow rate increases over time.
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TABLE 6. WATERSHED AVERAGE PERCENT CHANGE IN FUTURE EXTREME RAINFALL Emission
Scenario
Time
horizon
Recurrence
Interval
% Change relative to historic
period (1950-2005)
Model mean Model range
High (RCP 8.5) 2050
2-year 11.5% -0.1% - 55.9%
10-year 10.4% -0.1% - 30.3%
100-year 7.5% -17.4% - 42.1%
High (RCP 8.5) 2070
2-year 14.7% -11.1% - 55.1%
10-year 15.2% -0.1% - 36.8%
100-year 14.2% -18.0% - 43.8%
High (RCP 8.5) 2100
2-year 19.0% -0.1% - 49.9%
10-year 19.9% -11.3% - 46.8%
100-year 20.3% -17.3% - 70.4%
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 31
Predicted Peak Flows (cfs) in the Point Arena Watershed Under Future Climate Conditions
Figure 32 maps the flood extents for the 2-, 10-, and 100-year storms, comparing the existing conditions to those predicted for the 2100 time horizon. As the figures depict, the area of potential future flooding does not significantly increase between the existing and future conditions, but rather, the depth of flooding increases (e.g., the darker blue color indicating greater flood depth).
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SOURCE: Imagery (Maxar) City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 32
Existing and Future Fluvial Flooding Extent and Depths for the 2-, 10-, and 100-year Storm Events
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4.3.3 Combined Coastal and Fluvial Flooding
The wave and creek flood maps are plotted together on the same map in Figure 33. Similarly to the modeled creek flooding, the extent of the combined coastal-fluvial flood inundation does not significantly increase with sea-level rise and increased precipitation. This is largely due to the steep topography of the Cove area, which channels the overtopped coastal flooding as well as flooding from the creek into the roadway. Instead, it is anticipated that the flood depths and velocities will increase with climate change.
Note that where the wave and creek flood maps are overlain, an increase in the 100-year water level is implied. Quantifying this increase is beyond the scope of this study but may be worthwhile if more detailed mapping is accomplished. Note that this map indicates more severe flooding than the effective FEMA map (Figure 19).
SOURCE: Imagery (NOAA
NGS 2023)
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 33
Combined Coastal-Fluvial Flooding for a 100-year Storm:
Existing and Future Conditions with 6.7ft of Sea-Level Rise
4. Future Conditions with Sea-Level Rise
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4.3.4 Future Erosion
Shoreline Evolution with Sea-Level Rise
Future sea-level rise is expected to create a permanent rise in ocean water levels that will shift the water’s edge landward. Higher water levels will result in larger waves that break closer to the shoreline and higher wave runup. In general, the higher water levels and associated waves are expected to increase beach and bluff erosion and result in narrower beaches depending on sand supply. That said, beaches and bluffs will likely respond to sea-level rise differently. A rise in sea levels will likely cause beach systems to shift landward and upward, as the waves erode the shore and sediment deposits in the surf zone, essentially rebuilding the surf zone sea floor at the higher sea level10 (see Figure 34). This may erode, modify, or cover City assets, depending on proximity to the shoreline and height above sea level.
This migrating shore condition will not occur in all locations. For example, areas with erosion resistant barriers (like seawalls and the bluffs at Point Arena) will not erode fast enough to provide space for beaches but rather may supply beach material that will migrate offshore or along shore to other beaches: The cove area of Point Arena may accumulate cobble and other sediments over time, depending on the backshore conditions.
Increased sediment loads from the rivers (i.e., if rainfall frequency or intensity increases) or localized erosion of bluffs; however, depending on amount of sea-level rise, the characteristics of the backshore (e.g., armored or natural), and the soil composition, these sediment delivery processes may or may not be enough to keep pace with projected rising seas. In general, allowing shores to migrate landward and up with sea level rise is most likely to extend the life of these features. Indeed, this constructive response to sea level rise (aka resilience) is one reason that Natural Shore Infrastructure is gaining State11 and Federal12 interest. 10 This process of shore ‘transgression’ is often referred to as the ‘Bruun Rule’ owing to the geometric shore response conceptual model developed by Brunn (1962)
11 ‘CA Gov’t Code Chapter 3 ARTICLE 5. Authority for and Scope of General Plans 65302. (g)(4)(C)(v) The identification of natural infrastructure that may be used in adaptation projects, where feasible. Where feasible, the plan shall use existing natural features and ecosystem processes, or the restoration of natural features and ecosystem processes, when developing alternatives for consideration. For purposes of this clause, “natural infrastructure” means using natural ecological systems or processes to reduce vulnerability to climate change related hazards, or other related climate change effects, while increasing the long-term adaptive capacity of coastal and inland areas by perpetuating or restoring ecosystem services. This includes, but is not limited to, the conservation, preservation, or sustainable management of any form of aquatic or terrestrial vegetated open space, such as beaches, dunes, tidal marshes, reefs, seagrass, parks, rain gardens, and urban tree canopies. It also includes systems and practices that use or mimic natural processes, such as permeable pavements, bioswales, and other engineered systems, such as levees that are combined with restored natural systems, to provide clean water, conserve ecosystem values and functions, and provide a wide array of benefits to people and wildlife.’ 12 US Army Corps of Engineers, Engineering Research and Development Center Engineering With Nature (EWN) https://ewn.erdc.dren.mil/wp-content/uploads/2021/04/ASBPA-1130-1150_Natural_Infrastructure_Altman.pdf
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City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 34
Cobble Berm Profile Evolution with Sea-Level Rise
Future Erosion Hazard Zones
There are a number of acceptable methods for predicting future erosion; however, the unique geomorphology of the Cove does not lend itself to a specific one. Most methods rely upon historic erosion rates and then amplify the historic rate by a certain percentage to account for accelerated erosion with sea-level rise. In the case of the Cove, the dual geomorphologies (i.e., bluff and beach), ESA reviewed several existing models that project future erosion hazard zones that are also readily available or applicable within the parameters of this study13.
Figure 35 shows bluff erosion forecast by the Pacific Institute team (PWA (formerly ESA) 2009) as well as USGS’ CoSMoS modeling for the bluffs on both sides of the developed Arena Cove.
Because the Pacific Institute and USGS models focus on bluff erosion, ESA performed an analysis of potential shoreline erosion within the Cove itself (Figure 36). ESA’s analysis considered erosion of the existing shoreline (including the armored shoreline as it is presently located as well as the cobble berm seaward of the lagoon). A basic Bruun transformation14, which presumes the shore migrates up and landward in proportion to sea level rise and the overall slope of the surf zone (e.g., Figure 34), to model potential future erosion within the Cove. 13 ESA has developed methods to address shore response to sea level rise etcetera for a range of conditions but the application of these models is beyond the scope of this project. These models are particularly useful when evaluating alternative adaptation plans which may include a range of strategies such as armoring, beach nourishment and retreat.
14 This process of shore ‘transgression’ is often referred to as the ‘Bruun Rule’ owing to the geometric shore response conceptual model developed by Brunn (1962).
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SOURCE: USGS (CoSMoS) and
PWA 2009; Imagery
(Maxar)
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 35
Potential Erosion Hazard Zones with Sea-Level Rise
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In general, we expect that unarmored shore would move landward with sea-level rise along with the adjacent bluffs. A more detailed analysis is needed to provide erosion projections than can be accomplished with the scope of this study.
SOURCE: USGS (CoSMoS); Imagery (NOAA NGS
2023)
City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 36
Potential Shoreline Erosion with Sea-Level Rise
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5. VULNERABILITY ASSESSMENT
Vulnerability may be defined as “the degree to which natural, built, and human systems are at risk of exposure to climate change impacts…”.15 As the definition implies, vulnerability is a function of a resource’s exposure, sensitivity, and adaptive capacity to a given hazard or stressor. This section provides an overview of the vulnerability analysis methodology as well as a summary of the City’s assets that are vulnerable to the coastal hazards identified in section 4.
5.1 Methodology
Assets within the study area (see Figure 2) were analyzed to determine their potential exposure to the flooding and erosion hazards as well as the sensitivity and adaptive capacity of the assets to the potential hazard. Sensitivity and adaptive capacity scoring were developed based on ESA’s judgement and with input from the City and community members. The results of this analysis are summarized in Table 10.
5.1.1 Exposure to Hazard
To assess exposure to hazards, the ESA compared an asset’s proximity to the erosion and inundation areas noted in section 4. For flood hazards, ESA evaluated an asset’s proximity to the combined fluvial and marine 100-year flood zone (section 4.3.3) as well as the freeboard (i.e., elevation) above or below the floodplain. For the erosion hazards, ESA evaluated an asset’s proximity to potential future shorelines, assuming no armoring is present. Armoring was not included in the erosion hazard mapping in an effort to conservatively evaluate future vulnerabilities.
A hazard exposure grade of Low, Medium, or High (Table 7) was assigned to characterize each asset’s exposure to hazards. This grade was assigned after quantifying the asset’s exposure and is dependent on both timeframe (e.g., if an asset could potentially flood in the near-term it would have a higher hazard exposure grade than one that could flood in the long-term) and the potential level of severity posed by the type of hazard zone (i.e., erosion versus long-term effects of infrequent flooding). For example, future erosion by 2050 is considered “high” exposure because it would cause significant damage to structures and infrastructure in the near-term, while exposure to erosion in 2070 is considered “medium” exposure and erosion by 2100 is considered “low” exposure because the risk is later in the century. Exposure to 100-year flooding by 2050 is considered “medium” exposure because while the risk is a near-term risk, it is still a lowlikelihood event (i.e., 1% annual chance of occurrence annually). 15 California Governor’s Office of Planning and Research (OPR), 2018. Defining Vulnerable Communities in the Context of Climate Adaptation. Las accessed March 8, 2023 via https://opr.ca.gov/docs/20180723-Vulnerable_ Communities.pdf.
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TABLE 7. HAZARD EXPOSURE SCORING
Timeframe
Anticipated Amount of Sea-Level
Rise (ft) Under CCC/OPC
Medium-High Risk Scenario Future Erosion
Future 100-year Combined
Coastal-Fluvial Flooding
Existing 0 High High
Short-term (2050) 1.8 High Medium
Mid-term (2070) 3.3 Medium Low
Long-term (2100) 6.7 Low Low
5.1.2 Sensitivity to Hazard and Adaptive Capacity
Sensitivity is an asset’s level of impairment when flooded or affected by erosion or waves. In general, assets that are highly sensitive would lose their primary function if exposed to any degree of flood or erosion whatsoever. If assets can maintain their primary function(s) during inundation, they would have low sensitivity. If assets would lose only part of their function, it is considered, for the purposes of this assessment, moderately sensitive. For example, one of the sensitivities of impacts to roadways is the disruption of vehicular access critical for the provision of emergency services, which would mean the asset has a high sensitivity.
Similar to the hazard exposure scores, a hazard sensitivity grade is determined for each asset.
Table 8 presents the grading scheme.
TABLE 8. HAZARD SENSITIVITY SCORING
Score Considerations
Low The given hazard would have no or a low impact on the asset, and the primary function of the asset could be maintained.
Medium The given hazard would cause minor damage or disruption.
High The given hazard would cause major damage or disruption.
For the purposes of this study, adaptive capacity is defined as the asset’s ability to cope with and recover from impacts. In general, assets that have low adaptive capacity would take a long time or be unable to recover if exposed to any degree of flood or erosion whatsoever. If assets are operational as soon as water recedes, they would have high adaptive capacity. For example, in many cases once waters recede off parking lots, vehicular access is restored with little damage to the roadway itself, which would mean the asset has a high adaptive capacity. Note, adaptive capacity is inversely correlated with vulnerability (i.e., low adaptive capacity leads to higher vulnerability). Table 9 presents the adaptive capacity scoring scheme.
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TABLE 9. HAZARD ADAPTIVE CAPACITY SCORING
Score Considerations
High The asset would be able to rebound from the impact quickly (e.g., high adaptive capacity).
Medium The given hazard would cause temporary operational interruption.
Low The given hazard would cause long-term operational interruption. The asset would require a significant effort to rebound from the impact (e.g., low adaptive capacity).
5.1.3 Overall Vulnerability
The overall vulnerability for each asset was determined based on the combination of an asset’s vulnerability components (Figure 37):
Vulnerability = (Exposure + Sensitivity) – Adaptive Capacity The vulnerability summaries are indications of the degree of potential vulnerability, not rankings or priorities.
SOURCE: ESA 2023 City of Point Arena Sea-Level Rise Vulnerability Assessment Figure 37
Components of Vulnerability
5.2 Point Arena Cove Vulnerabilities
Table 10 below presents the results of the vulnerability analysis for the assets that were noted in section 2.3. Note that for the purposes of this study, the individual pier assets have been grouped together and placed under the general “developed areas” asset category.
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TABLE 10. ARENA COVE ASSET VULNERABILITIES
Asset Hazard Exposure
Timeframe
Exposure
Score Consequences of Exposure Sensitivity Score
Adaptive
Capacity Score
Overall
Vulnerability
Shoreline Armoring
Revetment Present High Overtopping and more frequent interaction with larger waves may degrade the existing structure.
Medium Medium Medium
Seawall Present High Overtopping and more frequent interaction with larger waves may degrade the existing structure
Medium Medium Medium-High
Developed Areas
Pier Present High Higher sea levels decrease the negative freeboard, allowing larger waves to more frequently batter the structure and potentially reach the decking or degrade the stability of the pilings and attached equipment.
High Low High
Parking lot Present High Parking and access (including for emergency purposes) will be temporarily cutoff until inundation recedes. Erosion of the cobble berm and lagoon area may cause more extensive
inundation of the parking lot during large storm events as the lagoon area moves further landward.
Medium Medium Medium-High
Event/overflow
parking
2070 Medium Increased coastal and fluvial flooding may render the overflow parking lot unusable during extreme events in the mid- to longterm.
Low Medium Low-Medium
Historic Coast Guard
Boathouse
Present High According to community observations, the CG building has historically experienced inundation during large storm events.
Larger waves and higher future sea levels will likely undermine the building foundation and cause direct structural damage, rendering the building unusable and a potential hazard to landward buildings if waves relocate portions of the structure further inland.
High Low High
Private Property Present High According to community observations, the lower buildings within the Cove frequently experience flooding at present. Larger waves and higher future sea levels will increase the frequency and extent to which inundation is experienced. This may cause more frequent closures and the need for repairs or floodproofing for buildings to remain inhabitable and operable.
High Medium Medium-High
Utilities
Electric Present High Electric utilities (especially those located belowground) will experience more frequent inundation from sea-, creek-, and groundwater-rise. Power (potentially supporting
communications and emergency services) may be cut off during storm events. High winds in January 2023 downed power lines resulting in an inability to operate the boat lift, raise the floating dock, maintain power to the sewer lift station, and more.
High Medium Medium-High
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TABLE 10. ARENA COVE ASSET VULNERABILITIES
Asset Hazard Exposure
Timeframe
Exposure
Score Consequences of Exposure Sensitivity Score
Adaptive
Capacity Score
Overall
Vulnerability
Sewer pump station Present High If inundated, the sewer pump station may become inoperable, causing the system to back up or spill over. Inoperable during power outages.
High Medium Medium-High
Sewer manholes Present High Sewer manholes may not be able to convey waste, causing the system to back up or spill over.
High Low High
Recreational
Picnic area / Park 2050 High Erosion of the fronting bluff may undermine the picnic area. Low High Low-Medium Beaches Present High Erosion and more frequently flooding of the beaches will decrease both the space and duration over which beachgoers can effectively enjoy the area. The existing armoring may cause additional squeezing16 of the shoreline.
Medium Medium Medium-High
Surfing Present Low Although higher water levels may allow for bigger waves to travel closer to shore, the “reef breaks” are best during low to mid tide levels could break less frequently with higher water levels. SLR may increase wave reflection off of the bluffs, which will change the quality of the surf breaks.
Low Medium Low-Medium
Ecological
Beaver habitat Present High Higher sea levels (and therefore saline water) may intrude further inland with sea-level rise. Larger and more extreme events may cause more intense flooding of the lagoon and creek systems, potentially altering the suitability of the habitat for the Point Arena mountain beaver.
Medium Medium Medium-High
Wetland habitat Present High Higher sea levels (and therefore saline water) may intrude further inland and more frequently with sea-level rise. With adequate space to migrate inland, wetland habitats may be able to recover. Without adequate migration space, wetland habitats will eventually be squeezed out.
High Medium Medium-High
Bioretention basin Present High More frequent and larger overtopping from coastal and fluvial flooding may damage the retention structure and prevent it from naturally recovering without anthropogenic interference.
Medium Medium Medium-High
16 With ongoing beach erosion and sea-level rise and without any other mitigating measures, fixing the shoreline location with a seawall or revetment will eventually lead to the loss of the beach seaward of the structure(s).
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6. REFERENCES
Barnard, P.L., Erikson, L.H., Foxgrover, A.C., Finzi Hart, J.A., Limber, P., O’Neill, A.C., van Ormondt, M., Vitousek, S., Wood, N., Hayden, M.K., and Jones, J.M., 2019. Dynamic flood modeling essential to assess the coastal impacts of climate change. Scientific Reports, Volume 9, Article #4309, 13 pp., http://dx.doi.org/10.1038/s41598-019-40742-z.
Behrens, D.K., Brennan, M., Battalio, B., 2015, A quantified conceptual model of inlet morphology and associated lagoon hydrology, Shore and Beach, 83(3), pp. 33-42.
California Coastal Commission (CCC), 2018, Sea-level Rise Policy Guidance: Interpretive Guidelines for Addressing Sea-level Rise in Local Coastal Programs and Coastal Development Permits, adopted on August 12, 2015; update adopted November 7, 2018.
Cayan et. al., 2009. Cayan, D., Tyree, M., Dettinger, M., Hidalgo, H., Das, T., Maurer, E., Bromirski, P., Graham, N., and Flick, R., 2009, Climate Change Scenarios and Sea Level Rise Estimates for California 2008 Climate.
CMIP5. 2013. Downscaled CMIP3 and CMIP5 Climate Projections: Release of Downscaled CMIP5 Climate Projections, Comparison with Preceding Information, and Summary of User Needs. U.S. Department of the Interior, Bureau of Reclamation, Technical Service Center, Denver Coorado, 116 p., available at: https://gdo-dcp.ucllnl.org/downscaled_ cmip_projections/dcpInterface.html#About.
FEMA, 2014, Intermediate Data Submittal #3: Nearshore Hydraulics, Mendocino County, California, FEMA Region IX, California Coastal Analysis and Mapping Project / Open Pacific Coast Study, Prepared by BakerAECOM, August 2014.
Griggs, G., Árvai, J., Cayan, D., DeConto, R., Fox, J., Fricker, H.A., Kopp, R.E., Tebaldi, C., Whiteman, E.A. (California Ocean Protection Council Science Advisory Team Working Group), 2017, Rising Seas in California: An Update on Sea-Level Rise Science, California Ocean Science Trust, April 2017.
Hapke et. al. 2006. National Assessment of Shoreline Change, Part 3: Historical Shoreline Change and Associated Coastal Land Loss Along Sandy Shorelines of the California Coast.
U.S. Geological Survey Open-File Report 2007-1219. Last accessed on March 3, 2023 via https://pubs.usgs.gov/of/2006/1219/of2006-1219.pdf.
Hapke, C.J. and Reid, D. 2007. National Assessment of Shoreline Change, Part 4: Historical Coastal Cliff Retreat along the California Coast. U.S. Geological Survey Open-File Report 2007-1219Last accessed on March 3, 2023 via https://pubs.usgs.gov/of/2007/1133/of2007- 1133.pdf.
OCM Partners, 2023: 2017 FEMA Lidar: California Region 9, https://www.fisheries.noaa.gov/inport/item/58428.
6. References
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Ocean Protection Council (OPC), 2018, State of California Sea-Level Rise Guidance, prepared by the California Natural Resources Agency and the California Ocean Protection Council, adopted March 14, 2018.
Ocean Protection Council (OPC), 2020, Strategic Plan to Protect California’s Coast and Ocean 2020-2025, prepared by the California Natural Resources Agency and the California Ocean Protection Council, adopted February 26, 2020.
Philip Williams & Associates, Ltd. (PWA), 2009. California Coastal Erosion Response to Sea Level Rise Analysis and Mapping. Prepared for the Pacific Institute. March 11, 2009. PWA REF. #1939.00.
Shope, James B.; Erikson, Li H.; Barnard, Patrick L.; Storlazzi, Curt D.; Serafin, Katherine; Doran, Kara; Stockdon, Hilary; Reguero, Borja; Mendez, Fernando; Castanedo, Sonia; Cid, Alba; Cagigal, Laura; Ruggiero, Peter (2022). “Characterizing storm-induced coastal change hazards along the United States West Coast.” Scientific Data. Vol. 9, Issue 224. http://doi.org/10.1038/s41597-022-01313-6.
U.S. Fish and Wildlife Service (USFWS), 1998, Point Arena Mountain Beaver (Aplodiontia rufa nigra (Rafinesque)) Recovery Plan, Region 1, Portland, Oregon, 71 pp. Accessed online September 18, 2023: https://ecos.fws.gov/docs/recovery_plan/980602.pdf.
U.S. Fish and Wildlife Service (USFWS), 2023, Endangered and Threatened Wildlife and Plants; Initiation of 5-Year Status Reviews of 47 Species in California, Nevada, and Oregon, Notice of initiation of reviews; request for information, Department of the Interior, Fish and Wildlife Service, Federal Register, Vol. 88, No. 158, August 17, 2023. Accessed online September 18, 2023: https://www.govinfo.gov/content/pkg/FR-2023-08-17/pdf/ 2023-17728.pdf#page=1.
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7. LIST OF PREPARERS
The following ESA staff contributed to the work described in this report:
Louis White, PE
Bob Battalio, PE
Meagan Flier, EIT
Yashar Rafati, PhD, PE
Phong Ly, EIT
James Gregory, PE
ESA also acknowledges the review and guidance of the City of Point Arena staff, including Scott Perkins and Paul Andersen, City Council members, and the Point Arena community members during site visits, meetings, and workshops.
7. List of Preparers
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