Attachment I
Coastal Hazards Report
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Memo
SUBJECT PROJECT
Coastal Hazards Analysis Bay Bridge Pump Station
Replacement Project (5-67)
TO DATE
Orange County Sanitation District October 2023
Introduction
This memorandum summarizes the analysis for coastal hazards for the Bay Bridge Pump Station (BBPS) Replacement Project, Newport Beach, Orange County, California. The Orange County Sanitation District (OC San) proposes to replace the existing BBPS with a new pump station and force main infrastructure. The existing BBPS is over 50 years old, outdated, and no longer meets structural, electrical, and maintenance standards. The Project includes replacing the existing pump station and force mains with a new pump station, replacement force mains, a new electrical building, a new emergency generator building, and an odor control structure.
The new pump station will include a trench-type wet well and a dry well for housing the pumps, motors, and other mechanical equipment. As shown on Figure 1, the pump station site also includes an electrical building, a generator building, and an odor control structure. The proposed electrical building includes the electrical equipment, instrumentation, control equipment, and restroom. The electrical building has a finished floor elevation of 15.50 feet NAVD88 and is elevated from the grade level. The entrance to the underground pump station dry well is also elevated to the same elevation of the electrical building finished floor at 15.5 feet NVAD88. The generator room finished floor is 14.17 feet NAVD88 and the generator will be mounted on a 2-ft-high belly fuel tank. The odor control structure finished floor is 14.00 feet NAVD88. The new force main will be installed beneath the Newport Bay Channel and would not be affected by coastal processes and is not included in the analysis.
This memorandum summarizes the potential impacts on the BBPS resulting from anticipated sea level rise, coastal geologic instability, and flooding per the requirements of the Newport Beach Local Coastal Plan Policies LUPs 2.8.1-1, 2.8.-2 and 2.8.1-4 and per Section 30253 of the Coastal Act.
Site Characteristics and Land Use
The Project site is located within a fully developed and urbanized area north of East Coast Highway. The existing BBPS is approximately 4,800 square feet, occupied by a single-story pump station building. The perimeter of the pump station building is surrounded by concrete masonry walls on all sides with two entrance gates. The existing facility is located on a parcel that is surrounded to the north, east, and west by a recreational vehicle storage area.
Seven acres of the site are planned for a mixed-use development. Surrounding land uses include residential, commercial, and commercial recreational marine uses. Within the vicinity of the Project, East Coast Highway, also known as State Route 1 is a 7 to 8 lane roadway including a bridge that crosses the Newport Bay Channel.
Bayside Drive is located to the east of the Project and is a 4 lane, designated secondary road.
Sea Level Rise Evaluation and Flooding
Several analyses have been conducted to understand the potential for anticipated Sea Level Rise (SLR) to impact the BBPS and whether the facility is at risk.
In 2019, OC San prepared the Resiliency Study SP-152 (Resiliency Study) which examined the potential climate change impact, including SLR on OC San facilities throughout its service area. The Resiliency Study used SLR projections from the Rising Seas Report and California’s Fourth Assessment (Hall 2018) as representing the state 13-165
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of science for SLR for the Orange County area. Relying on Hall 2018, OC San used SLR increases of 1.54 feet for 2050 and 3.71 feet for the year 2070 (Hazen 2019) to determine the potential risk of SLR in 2050 and 2070.
Using the 2050 and 2070 projections, the Resiliency study did not identify the BBPS site as having a significant risk associated with SLR in Year 2050 or 2070 (Hazen 2019).
The design also considers the most conservative SLR reference from the State of California’s Sea Level Rise Guidance (California Ocean Protection Council 2018) and Critical Infrastructure at Risk: Sea Level Rise Planning Guidance for California’s Coastal Zone (California Coastal Commission 2021). According to the State of California’s Sea Level Rise Guidance (California Ocean Protection Council 2018), the H++ scenario SLR for Los Angeles are 2.6 feet by 2050, 6.4 feet by 2080, and 9.9 feet by 2100. According to the State Sea-Level Rise Guidance, under the H++ SLR scenario, 2.7 feet of SLR can be expected by 2050, 6.6 feet by 2080, and 10.2 feet by 2100 (California Coastal Commission 2021). The life expectancy of the new pump station will be around 50 years and the 6.6 feet SLR of Year 2080 based on California Coastal Commission 2021 will be used for evaluation.
The SLR is evaluated based on the mean high water (MHW). The MHW is 4.50 feet NAVD88 for Newport Beach Bay Per NOAA Tides & Currents. The Our Coast Our Future (OCOF) map with projection of 6.6-ft SLR above MHW is shown on Figure 2. A portion of the existing site is shown inundated based on the 2080 SLR of 6.6-ft SLR Above MHW (11.10 feet NAVD88). The BBPS design took a conservative approach of designing to a minimum floor elevation of 14.00 feet NAVD88 as shown on Figure 1. Using this minimum floor elevation, construction of the new BBPS would avoid SLR impacts for the anticipated life of the facility.
Per comments received from the City of Newport Beach on August 3, 2023, a maximum bay water elevation of
7.7 feet NVAD88 was evaluated for SLR. The 6.6-ft SLR above the maximum bay water elevation leads to 14.3 ft NVAD88 elevation. The electrical room and the entrance to the underground pump station are at 15.5 ft NVAD88, hence, the electrical equipment and underground pump station will be protected from SLR. The generator room finished floor is 14.17 feet NAVD88, however, the generator will be mounted on a 2-ft-high belly fuel tank and the generator panels will be mounted 3.5 ft above finished floor. Therefore, the generator and panels will be located higher than 14.3 ft NVAD88 elevation and protected from SLR.
The odor control area finished floor is at 14 ft NVAD88. The liquid odor control is not critical process for the facility, however, measures have been incorporated to protect from SLR. For example, the foul air fan and carbon scrubber will be mounted on equipment pads and the equipment will be higher than SLR elevation of 14.3 ft NVAD88. In addition, flood barrier/shield can be used for odor control area pedestrian door and temporary measures such as sand bags can be used for roll up gate. Waterproofing admixtures such as Dry-Block or Eucon Blocktite systems will be used for the odor control area structure block walls to protect the facilities from flooding.
Per the discussion above, the BBPS critical process will be protected from SLR based on either MHW or maximum bay water level elevation.
Flooding & Tsunami
According to the Federal Emergency Management Agency (FEMA) 2019 FIRM map, the Project is not located within the 100 year flood hazard zones (Figure 3). As analyzed in the 2020 Recirculated Environmental Impact Report (Michael Baker International 2020), less than significant impacts are anticipated in the event of the 100- year flood.
The Project site is located within the designated tsunami zone (California Department of Conservation 2022).
During design of the BBPS, the engineers used the American Society of Civil Engineer’s (ASCE) Tsunami Design 13-166
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Zone (TDZ) to determine the Maximum Considered Tsunami (MCT). In the event of a tsunami, the Project site could be expected to see some minor flooding and the run up elevation at the Project site is 7.24 feet above MHW or 11.74 feet NAVD88 (Figure 4 and 5). Figure 4 shows that in the event of tsunami, the parking areas may be expected to see minor flooding. However, because the minimum floor elevation of the new BBPS would be 14.00 feet NAVD88, the new facilities would not be subjected to inundation.
Furthermore, onsite drainage is routed to the BBPS. The pump station is designed to operate even if the site is inundated. Therefore, the risk of flooding the pump station is minimal.
Ground Improvements and Shoring
The Project site is located in an area of potential liquefaction. To mitigate the potential for liquefaction, static settlement, and differential settlement, the new pump station will be excavated over 35 feet deep such that the impacts from liquefaction are not anticipated. The ground improvement plan for the overall pump station site can be referenced to the Geotechnical Design Report enclosed in the permitting package. Deep excavation will require shoring and design is exploring several techniques including, but not limited to slurry diaphragm wall, secant pile wall shoring, solid sheet pile wall, or a combination of shoring techniques.
Erosion and Shoreline Loss
The location of the BBPS is located within a developed area and is not located at the shoreline or at the bank of the Newport Bay Channel. The Project site is not subject to erosion and shoreline loss. The BBPS would not be subjected to erosion or shoreline loss as a result of waves or wave run up. The Project does not include, and does not require shoreline protection.
Summary and Conclusion
The BBPS Project has been analyzed with regards to postal coastal hazards, including SLR, flooding, tsunami, and geologic stability. The new BBPS will be located in a developed area, including the location of the existing BBPS. The new BBPS is designed to ensure that the facilities would not be subjected to the SLR and tsunami impacts.
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References:
Michael Baker International. 2020. Bay Bridge Pump Station and Force Mains Replacement Project (Project No. 5-67) 2020 Recirculated Environmental Impact Report. May 2020.
Arcadis. 2022. Preliminary Design Report Project No. 5-67 Bay Bridge Pump Station Replacement.
California Coastal Commission. 2021. Critical Infrastructure at Risk: Sea Level Rise Planning Guidance for California’s Coastal Zone. Final Adopted Guidance. November 17, 2021.
California Department of Conservation. 2022. Orange County Tsunami Hazard Areas. Website located at https://www.conservation.ca.gov/cgs/tsunami/maps/orange. Retrieved June 17, 2022 California Ocean Protection Council. 2018. State of California’s Sea Level Rise Guidance. March 14, 2018.
Hall, Alex, Neil Berg, Katharine Reich. (University of California, Los Angeles). 2018. Los Angeles Summary Report. California’s Fourth Climate Change Assessment. Publication number: SUM-CCCA4-2018-007 Hazen. 2019. Climate Resiliency Study. Final Report. SP-152. November 27, 2019.
Our Coast Our Future Mapping Tool. 2022. Website located at: https://ourcoastourfuture.org/ retrieved June 10, 2022
NOAA Tides & Currents Datums for Newport Beach. Website located at:
https://tidesandcurrents.noaa.gov/datums.html?datum=NAVD88&units=0&epoch=0&id=9410580&name=NEWPO RT+BEACH%2C+NEWPORT+BAY+ENTRANCE&state=CA retrieved August 22, 2023
Enc. [Enclosures]
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