San Francisco Bay Area Coastal Study

Transcription

1 San Francisco Bay Area Coastal Study California Coastal Analysis and Mapping Project September 2012

2 San Francisco Bay Counties California Coastal Analysis and Mapping Project This publication is an initiative of the Mitigation Division of FEMA Region IX. San Francisco Bay Area Coastal Study and Mapping Overview The Federal Emergency management Agency (FEMA) is performing new detailed coastal engineering analyses of the shoreline and coastal areas within the nine counties of: Alameda Contra Costa Marin Napa San Francisco San Mateo Santa Clara Solano Sonoma The new coastal study will revise and update the flood and wave data for the coastal Flood Insurance Study reports and Flood Insurance Rate Maps for each of the above counties. FEMA s coastal study and mapping efforts benefit from new technologies and coastal data, including the latest 2010 detailed topographic data collected as part of the California Coastal Mapping Program. The coastal flood hazard analyses use regional-scale storm surge and wave models of San Francisco Bay. These models produce time-series output of water levels, open ocean swells, and wind-driven waves at over eight thousand points along the complex San Francisco Bay shoreline. Input parameters to the regional-scale models include ocean tide levels, lower Sacramento River discharges, wind and pressure fields, and various river andcreek discharges. The model output from the regional models is used to estimate wave runup and overtopping along the Bay s myriad of shoreline structures and steep shorelines, as well as overland wave propagation over beaches, marshes, and inland developed areas. These onshore analyses will form the basis for potential revisions to the Base Flood Elevations (BFEs) and Special Flood Hazard Areas (SFHAs) within the coastal areas of the nine Bay Area counties. Coastal High Hazard Areas (Zone VE) will be mapped when supported by flood hazard modeling results. The US Army Corps of Engineers is also conducting coastal analyses within San Francisco Bay, and these studies will be evaluated for compatibility with FEMA s study and mapping goals. Following FEMA s due process and statutory requirements, the BFE s will be finalized in revised Flood Insurance Study reports and on the Flood Insurance Rate Maps. FEMA is coordinating with Federal and State entities, we well as regional and local stakeholders. FEMA will continue to coordinate with these stakeholders as the study and mapping efforts progress. Next Steps, Stay Informed and Engaged After FEMA s review and approval of the coastal flood hazard analysis, it will commence with the floodplain mapping on a county-by-county basis. FEMA will schedule a Flood Risk Review meeting with each Bay Area county during this phase of the study. The goal of the Flood Risk Review meeting is to enhance the communities understanding of the available flood risk datasets, to discuss study methods and results, and to provide information on increasing risk awareness and stimulating mitigation actions that can reduce risk. To stay up to date with the San Francisco Bay Area Coastal Study, and the companion Open Pacific Coast study, sign up for the quarterly e-bulletin, Coastal Beat, that will include schedule updates, technical articles and facts of interest, and relevant information as the study progresses. Visit for additional coastal study information. Stay informed and engaged in FEMA s coastal studies by signing up for RSS feeds from this site to receive updates delivered directly to your inbox. FEMA welcomes your feedback, questions and comments. San Francisco Bay Area Coastal Study Mapping Timeline 2 San Francisco Bay Area Coastal Study California Coastal Analysis and Mapping Project FEMA 3

3 National Flood Insurance Program Discovery Map: Los Angeles County

4 Coastal Flood Issues in the San Francisco Bay Area Types of Flooding Annual High Tide Inundation ( King Tides ) How it works: King Tides are abnormally high predictable astronomical tides that occur approximately twice per year within San Francisco Bay. King Tides are the highest tides that occur each year and typically exceed 7 ft Mean Lower Low Water (MLLW) at the Presidio tide station. Example Events: King Tides occur every year during the winter, typically during the months of December, January, and February. Types of Impacts: Nuisance flooding; inundation of low-lying roads, boardwalks, and waterfront promenades; can exacerbate coastal and riverine flooding. Location of Impacts: HWY 101 off-ramp at Mill Valley, Sausalito waterfront, and Richardson Bay shoreline in Marin County; Embarcadero waterfront (Pier 14) and Marina area in San Francisco; and Bay Bridge Toll Plaza frontage road and Jack London Square in Alameda County. El Niño Winter Storms How it works: During El Niño winters, atmospheric and oceanographic conditions in the Pacific Ocean produce severe winter storms that impact the San Francisco Bay region. Pacific Ocean storms follow a more southerly route and bring intense rainfall and storm conditions to the Bay area. Riverine and coastal flooding often coincide and produce upstream flooding. Tides are elevated by approximately 0.5 to 1.0 feet above normal along the coast and wind setup can elevate water levels even further locally. Example Events: Winters of ; ; ; Types of Impacts: Severe inundation of low-lying roads, boardwalks, and waterfront promenades; combined riverine and coastal flooding; wave damage to coastal structures. Location of Impacts: Throughout the Bay, particularly along developed shorelines and tidally influenced creeks and sloughs prone to high tide flooding. Extreme High Tide Inundation How it works: When Pacific Ocean storms coincide with high tides, storm surge due to meteorological effects can further elevate San Francisco Bay water levels to produce extreme high tides. El Niño conditions along the California coast can also contribute to storm surge and produce extraordinarily high water levels. Example Events: January 27, 1983 (8.66 ft MLLW); December 3, 1983 (8.65 ft MLLW); February 6, 1998 (8.38 ft MLLW); January 8, 2005 (8.14 ft MLLW); December 31, 2006 (8.09 ft MLLW). Types of Impacts: Severe inundation of low-lying roads, boardwalks, and waterfront promenades; can exacerbate coastal and riverine flooding and cause upstream flooding; can interfere with stormwater outfalls. Location of Impacts: Throughout the Bay, particularly along developed shorelines and tidally influenced creeks and sloughs prone to high tide flooding. Wind Wave Events How it works: Strong winds due to Pacific Ocean storms or strong thermal gradients produce strong winds that blow across the Bay. When the wind blows over long reaches of open water large waves can be generated that impact the shoreline and cause damage. Example Events: Pacific Ocean winter storm events; pre-frontal southerly winds; northerly thermal winds. Types of Impacts: Wave damage along the shoreline, particularly to coastal structures such as levees, docks and piers, wharfs, revetments; backshore inundation due to wave overtopping of structures and ponding. Impacts can be exacerbated by high tides which limits wave dissipation over mudflats and marsh. Location of Impacts: Exposed shorelines with expansive wind fetches, particularly along the East Bay shoreline. 6 San Francisco Bay Area Coastal Study California Coastal Analysis and Mapping Project FEMA 7

5 Points of Contact Role Name Phone Number FEMA Study Manager Kathy Schaefer (510) Study Project Manager Kris May (510) North Bay Technical Lead Brad Hall (916) Central Bay Technical Lead Krista Conner (215) South Bay Technical Lead Darryl Hatheway (619) Outreach Coordinators Wendy Chang (510) Lisa Messano (510) GIS Manager James Johnston (510) For more information on the California Coastal Analysis and Mapping Project (CCAMP) visit: Contact: Kathy Schaefer FEMA Study Manager FEMA MAP Front and Back Cover Photos: Copyright Kenneth & Gabrielle Adelman, California Coastal Records Project,