The Santa Ana River Mainstem Project is located along a 75-mile reach of the Santa Ana River in Orange, Riverside and San Bernardino counties. The plan for flood control improvements includes three principal features:
Lower river channel modification for flood control along the 30 miles of the Santa Ana River from Prado Dam to the Pacific Ocean.
Construction of Seven Oaks Dam (about 38 miles upstream of the existing Prado Dam) with a gross reservoir storage of 145,600 acre-feet.
Enlargement of Prado Dam to increase reservoir storage capacity from 217,000 acre-feet to 362,000 acre-feet.