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Orange County Coastal Regional Sediment Management Plan
APPENDIX D – DAM BYPASSING
PRADO BASIN SEDIMENT MANAGEMENT DEMONSTRATION PROJECT
Orange County Water District
2011
Proponents
The Orange County Water District is the local lead agency for the proposed Prado Basin
Sediment Management Demonstration Project. The Orange County Water District was formed
in 1933 by a special act of the California State Legislature to protect Orange County’s rights to
water in the Santa Ana River. The Orange County Water District’s primary responsibility is
managing the vast groundwater basin under northern and central Orange County that supplies
water to more than 20 cities and water agencies, serving more than 2.3 million Orange County
residents. Water conservation at Prado Dam, located in Riverside County, is a major source of
water for Orange County Water District’s groundwater recharge efforts in Orange County.
The U.S. Army Corps of Engineers (USACE) is the federal lead agency for the proposed
project. As operator and manager of the Prado Dam, USACE is responsible for evaluating
requests to use federal land in the Prado Basin and to determine whether such requests are: (1)
compatible with the federal Project, laws, regulations and policies and (2) when such use will be
in the interest of the Government and/or the public.
Purpose
The purpose of the proposed project is to explore practical and beneficial methods to restore the
flow of sediments trapped behind, and upstream, of Prado Dam to habitats and beaches
downstream. The Santa Ana River Watershed is the largest in Southern California, covering
2,450 square miles. Flow from 92 percent of the watershed (2,255 of 2,450 sq.mi.) is controlled
by Prado Dam. Since 1941 approximately 50,000 acre feet (af) of storage below elevation 563
has been lost due to sediment deposition in the Basin. On average, 735 af (1.19 million yd 3 ) of
sedimentation occurs each year.
Upon the completion of Prado Dam in 1941, the sediment transport mechanics of the Santa Ana
River watershed were dramatically altered. Once sediment-laden water enters the Prado Basin
the velocity of the water decreases, sediment settles out of the water and then relatively clean
water is released through Prado Dam. Water that is discharged from Prado Dam has the
capacity to pick up existing sand and sediment below the dam and transport the material to the
coast. Because the Dam is cutting off the replacement source of sediment, the river below the
Dam is “sand starved”. The presence of the Dam has severely altered the flow of sediments
downstream, affecting natural habitats and decreasing replenishment of beach sands. The
Everest International Consultants, Inc. D.2