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COMPREHENSIVE EMERGENCY MANAGEMENT PLAN channel improvements required of development projects during the past several years have significantly reduced this type of flood hazard. As a result of good planning and system maintenance. the Livermore-Amador Valley has experienced minimal flood damage compared with other areas of Califomia. Currently, 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 currently 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 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 Livermore-Amador Valley, which includes the Cities of Pleasanton, Dublin and Livermore. To ensure controlled drainage of the Valley's surface water runoff, Zone 7 currently 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. In September 2002, Zone 7 began the development of the Stream Management Master Plan (SMMP). This plan balances flood protection with water supply, water quality, habitat and environment and recreation and trails objectives for the Valley. Aviation Hazards Although not located within the Pleasanton Planning area, the Livermore Municipal Airport affects land uses in Pleasanton in the form of noise and safety impacts. In addition, the Hacienda Business Park operates a very limited and temporary heliport near Owens and Chabot Drives. Flight paths to and from the heliport are directly over 1-580. The Valley Care Medical Center also operates a heliport at its hospital on Santa Rita Road. The heliport is operated on an as-needed basis for emergency medicar transportation. (Pleasanton General Plan's Safety Element, 1996). ANNEX G - Local Hazard Mitigation Annex Updatedl~12/05 8