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<br /> <br />More extensive, longer-duration flooding: As sea levels rise there is the potential that <br />storm events will flood larger areas for longer periods of time and that there will be new <br />overtopping and overbank flooding of riverine systems that that do not currently cause <br />flooding. <br />Shoreline erosion and overtopping: Sea level rise can cause shoreline protection, such as <br />levees, berms and revetments, to be damaged or fail to due to increased tidal and wave <br />energy. There is also the potential that shoreline protection will be overtopped during <br />storm events when there are extreme tide levels and wind-driven waves, flooding inland <br />areas, including homes and community services that are currently protected. <br />Elevated groundwater and increased salinity intrusion: As sea levels rise, groundwater <br />and salinity levels are also predicted to rise. This will cause damage to below grade living <br />spaces, finished basements, and electrical/mechanical equipment that is below or at-grade. <br />In addition, increasing groundwater levels may increase liquefaction susceptibility, and <br />require the use of pumping of storm water for flood management, which will increase both <br />operations and maintenance costs. <br />Permanent inundation: Sea level rise can cause areas that are not currently exposed to <br />regular high tide inundation to be flooded, resulting in the need to either protect or move <br />people and infrastructure, and the loss of trails, beaches, vistas, and other shoreline <br />recreation areas. In addition, increased tidal scour due to increased tidal prism in riverine <br />systems can trigger changes in channel geometry and sediment transport processes. <br /> <br />5.6.3 Flood Hazard in the Bay Area <br /> <br />5.6.3.1 Current Flooding <br />The magnitude of flood used as the standard for floodplain management in the United <br />States is a flood having a probability of occurrence of one percent in any given year, also <br />known as the 100‐year flood or base flood. The most readily available source of <br />information regarding the 100‐year flood is the system of Flood Insurance Rate Maps <br />(FIRMs) prepared by FEMA. These maps are used to support the National Flood Insurance <br />Program (NFIP) and show 100‐year floodplain boundaries for identified flood hazards. <br />These areas are also referred to as Special Flood Hazard Areas (SFHAs) and are the basis <br />for flood insurance and floodplain management requirements under the NFIP. FIRMs also <br />show floodplain boundaries for the 500‐year flood, which is the flood having a 0.2 percent <br />chance of occurrence in any given year).