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 40.3 miles (64.9 km) downstream, to provide flood protection to Orange County, California.

Seven Oaks Dam accounts for about $464 million of the total $1.4 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 deigned 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 Control Division staff.

• Cost: $464 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