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planrting and system maintenance, the Tri Valley now experiences minimal flood damage compared with other areas of California. Currendy, flood-producing rainfall occurs during the winter months in the Pleasanton area. Storm runoff is concentrated rapidly by the network of tributaries through the hills which discharge into Arroyo Mocho, Arroyo del Valle and other tributaries to the Arroyo de la Laguna. The tributaries have carved well-defined courses through the hills but upon reaching the flat valley, the channels become shallow and inadequate for higher frequency flows. The main flooding problem is currendy caused by the low capacity of the lower reaches of Arroyo de la Laguna, which causes backwater flooding in its tributary channels. When substantial rainfall does occur, the runoff is rapid and heavy, causing stream-flows to exceed the normal stream courses' capacities and inundates large areas of the flat valley floor. Flooding is not limited to occasions of intense precipitation, however. Flooding may occur following low-intensity precipitation spread over several days, as occurred in storms of 1955 and 1958. Flood Hazard Zones The Federal Emergency Management Agency (FEMA) maps flood hazards throughout the country, including Pleasanton. These flood hazard maps, known as Flood Insurance Rate Maps, or FIRMS, are used to identify flood-prone areas, with the most susceptible areas designated as special flood hazard zones. The Federal Insurance Administration (FIA) of the Federal Emergency Management Agency (FEMA) administers the National Flood Insurance Program, available nationwide. This program provides insurance coverage for events that are not covered by traditional homeowner's policies. By partnering with private insurance companies, FIA makes insurance available to many people who would otherwise be unprotected. Figure V-7 shows the areas that are subject to 100-year and 500-year flooding. While about 1,900 acres are in the 100-year FEMA flood plain, about 3,425 acres are in the 500-year flood plain. Flood Control Efforts Special Drainage District 7 of the Alameda County Flood Control and Water Conservation District (Zone 7) is responsible for providing flood control and water resources to the Tri Valley, which includes the Cities of Pleasant on, Dublin and Livermore. To ensure controlled drainage of the Valley's surface water runoff, Zone 7 currendy manages 39 miles of flood control channels ranging from concrete-lined channels to natural creeks. Streambed channelization along Arroyo de la Laguna, Alamo Canal, Arroyo Mocho, Hewlett Canal, Chabot Canal, Pleasanton Canal, and Tassajara Creek has substantially reduced the possibility of extensive flooding, especially by reducing the time of ponding. A major dam on Arroyo Del Valle controls flooding on that waterway. Public Safety 082906, clean V-19 City Council 8/29/2006