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Published: 1994

Total Pages: 336

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The lower basin of the Santa Ana River is located in Orange County, California, and is 30.5 miles in length. Flood protection for the lower basin is provided by prado Dam and Reservoir. When completed in 1941, Prado Dam was designed to control a 200-year flood. However, recent projections have shown that Prado Dam now offers only a 70-year flood protection based upon the following factors: urbanization in the drainage area, additional historical data on rainfall and runoff, and advances in predicting future flood potential. According to Santa Ana River hydraulic studies, the existing lower basin channel is inadequate to convey a large flood flow safely to the ocean. Existing flood control improvements built by local interests have reduced damages from small floods. As part of these channel improvements there are 11 existing vertical concrete drop structures. However, these improvements fail to provide protection for the highly urbanized lower Santa Ana river floodplain. About 2 million people live and work in this floodplain. Since additional channel right-of-way is not available because of urbanization, increased channel capacity can only be achieved by additional depth of flow. The increased channel flow will require drop structures designed for higher unit discharges. An improved channel design will require the removal or modification of the existing drop structures in order to implement a new drop structure configuration.