To protect both upper and lower Mainstem project communities, Seven Oaks Dam, a 550-foot-high and 2,980-foot long rockfill dam with a gross capacity of 145,600 acre feet, has been constructed in the upper Santa Ana Canyon. The dam will reduce the Reservoir Design Flood inflow of 85,000 cfs, to a controlled outflow of 7,000 cfs, to provide 350-year flood protection.
The project is operated in tandem with Prado Dam, also located on the Santa Ana River 38 miles (61.1 km) downstream, to provide flood protection to Orange County, California.
Seven Oaks Dam accounts for about $534 million of the total $2.09 billion project cost. The Dam is made of 38 million cubic yards of soil, rock and clay that will form ten mostly vertical zones. These zones will help control the water while protecting the integrity of the dam. The pervious material acts as drain-channeling water out of the dam, while zones of impervious material keeps the water out. The Dam is designed to resist an earthquake measuring 8.0 on the Richter scale.
Seven Oaks Dam is operated and maintained by the project sponsors; The Orange County Flood Control District, The San Bernardino County Flood Control District and Riverside County Flood Control and Water Conservation District.
The Seven Oaks Dam Reservoir Regulation is performed by the Orange County Flood staff.
Seven Oaks Dam Testing
The outlet works of Seven Oaks Dam were subjected to Hydraulic Testing in the winter of 2011. Led by the US Army Corps of Engineers with assistance from local sponsors (the counties of Orange, Riverside and San Bernardino), the test program demonstrated that the outlet works were capable of discharging flows of up to 6200 cubic feet (46,376 gallons) of water per second. Photos from the testing program are presented below:
Seven Oaks Dam Project Features
Cost: $534 million
Construction contract was awarded in the Year 1994, Construction began in May 1994 with completion date of November 15, 1999.
550-foot high, earth-rockfill dam, 2,980 feet long
Gross reservoir capacity of 145,600 acre-feet
Reduces peak inflow of 85,000 cfs to a peak outflow of 7,000 cfs
Property acquisition including 1,500 acres property acquired for Endangered Species Preserve
Relocate Edison powerhouse, flume & transmission line, spreading basins and water wells
Endangered Species Preserve Program Underway
Status: 100% complete; Turnover to Local Sponsor for Operation: October 1, 2002