Reso 2025-151 Environmental Hazards Element General Plan

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S A N L E A N D R O G E N E R A L P L A N E N V I R O N M E N T A L H A Z A R D S 7-10 Flooding Flood hazards in San Leandro are associated with overbank flooding of creeks and drainage canals, dam failure, tsunamis, and rising sea level. Overbank Flooding At one time, flooding along creeks and streams was relatively common in San Leandro. These hazards were greatly reduced during the 1960s and 1970s when the Alameda County Flood Control and Water Conservation District (ACFCWCD) channelized the lower portions of San Leandro Creek and constructed flood control ditches in the southern part of the City. Today, ACFCWCD manages a network of channels, levees, storm drains, pump stations, culverts, and dikes intended to reduce flood hazards throughout the county. Although the channels were effective, they did not eliminate flood hazards entirely. During the last 50 years, urbanization in the watersheds has increased impervious surface area, which has resulted in faster rates of runoff and higher volumes of stormwater in the channels. Maps published by the Federal Emergency Management Agency (FEMA) indicate that a 100-year storm (e.g., a storm that has a one percent chance of occurring in any given year) could cause shallow flooding in parts of western San Leandro. Areas within the 100-year flood zones (shown in Figure 7-4) include land adjacent to San Leandro Creek, San Lorenzo Creek, and the Estudillo Canal; land along flood control channels in the vicinity of Bayfair Center and Bonaire Park; and coastal areas surrounding Oyster Bay Regional Shoreline, the San Leandro Shoreline Park, and Heron Bay. Other types of flood hazards, including coastal flooding and ponding, have also been mapped in the city. Resolution No. 2025-151 Exhibit A 10 of 84