Alameda County California is located along the east coast of San Francisco Bay. Numerous creeks convey flow from the western most ridges in the County west through urbanized communities into San Francisco Bay. These creeks collectively drain approximately 232 square miles of the western most portion of Alameda County. Potential sources of flooding for developed lower lying areas between the county's western ridges and San Francisco Bay include coincident elevated stages in the Bay together with heavy precipitation. Rising sea levels and higher rainfall intensity in the future pose increased flooding risks to this area. The Alameda County Flood Control District authorized a study of the primary tidally influenced outfalls to the Bay to identify flood elevations and floodplain extents for current and future conditions with seal level rise. Additionally, the study included development of conceptual level mitigation alternatives for each outfall and identification of criteria to be used to assess impacts and performance of each alternative. The performance assessment of design alternatives required application of the following types of hydrodynamic modeling tools: • Delft 3D modeling of San Francisco Bay under current and future sea level rise scenarios to observe potential future tidal impacts to the study area and establish boundary conditions for the creek assessments. • One dimensional HEC-RAS unsteady flow modeling of tidally influenced creeks along the Bay to identify current and future design flood elevations accounting for sea level rise and to assess impacts and performance of alternatives to reduce the risk of flooding.
Proposed improvements are designed to provide up to 100year flood protection accounting for future sea level rise and include tide gates, diversions, levees, floodwalls, and pump stations. The results of this study will be used to inform the Alameda County Flood Control Districts Capital Improvement Plan
