Prado Dam is a flood control and water conservation project, which was in operation since its completed construction date of April 1941 by the U.S. Army Corps of Engineers, Los Angeles District. Recently, the project has undergone some modifications to expand its capacity to provide additional capacity for storage of flood waters and sediments by enlarging the existing Prado Dam and Reservoir, and to take advantage of the increased downstream channel capacity by also increasing the release capacity of the outlet works. The modification of this project was authorized by Congress and was based on the plan recommended by the Los Angeles District of the U.S. Army Corps of Engineers. The modification of raising the dam's embankment and constructing the new outlet works was completed in June 2008.
The project is located at the upper end of the Lower Santa Ana River Canyon, which is a natural constriction controlling 2,255 square miles (5,840 square kilometers) of the 2,450 square mile (6345 square kilometer) Santa Ana River watershed. The dam is located on the Santa Ana River approximately 30.5 miles (49 kilometers) upstream of the Pacific Ocean. The dam embankment is located in Riverside County, California approximately 2 miles (3.2 kilometers) west of the City of Corona. Portions of the reservoir are in both Riverside and San Bernardino Counties. Authorization for the project is contained in the Flood Control Act of June 22, 1936 (PL 74-738).
Prado Dam provides flood control and water conservation storage for Orange County, California. It is the downstream element of the Santa Ana River flood control system. The purpose of the project is to collect runoff from the uncontrolled drainage areas upstream along with releases from other storage facilities. Generally, when the water surface elevation in the reservoir pool is below the top of the buffer pool elevation (498.0 feet NGVD during the flood season, 505.0 feet NGVD during the non-flood season), water conservation releases are made. These releases are coordinated with the Orange County Water District and are based upon the capacity of their groundwater recharge facilities and agreements with other agencies. If the water surface in the reservoir exceeds the top of the buffer pool, flood control releases commence. The objective of the flood control operation is to drain the reservoir back to the top of the buffer pool as quickly as possible without exceeding the capacity of the channel downstream.
Modifications to Prado Dam were recently completed where the main embankment has been raised from 566 feet, NGVD to elevation 594.4 feet, NGVD. A new outlet works was also constructed to allow for increased release capabilities from the dam. The new outlet works has a maximum controlled release capacity of 30,000 cfs (850 cms), which cannot yet be fully utilzied due to the ongoing construction of the Corps of Engineers' Santa Ana River project (Reach 9 Project) to improve the downstream channel. When the Reach 9 Project has been completed, the downstream channel capacity immediately downstream of the dam will increase to over 30,000 cfs (850 cms). These improvements will enable the dam to take full advantage of the improved channel capacity downstream and will greatly incrase the level of flood protection to the communities of Orange County that are located within the Santa Ana River flood plain.
When the water surface elevation in the reservoir reaches 543.0 feet, NGVD uncontrolled releases from the spillway will commence. The spillway is also planned for modification in the future where it will be raised 20 feet, up to elevatin 563 feet, NGVD. The Interim Water Control Plan will be implemented during this time to reflect oepration of the dam using the new outlet works features while the spillway remains at elevation 543.0 feet, NGVD.
The Interim Water Contorl Planfor Prado Dam was approved in May 2003.