Location and Description
Prado Dam is a single purpose flood risk reduction project located in Riverside County on the Santa Ana River about two miles west of the city of Corona near the head of Santa Ana Canyon. Its primary purpose is to reduce the risk of damage from floods for the metropolitan areas in Orange County, Calif., and for the highly developed urban and agricultural areas of the Santa Ana Coastal Plain.
Modifications to Prado Dam in response to increased population and infrastructure in the area include construction of the State Route 71 Dike extension to the main embankment in January 2001, raising the embankment and constructing new outlet works in October 2008, and constructing the Corona National Housing Tract Dike and the Corona Sewer Treatment Plant Dike in November 2008. The drainage area above the dam is 2,233 square miles.
The original construction of the project, which includes an earth fill embankment, outlet works and concrete spillway, was completed in May 1941.
Dam Safety Issues
The primary objective of the Corps’ Dam Safety Program is to maintain public safety by making sure dams owned and operated by the Corps are safe, and the risks to the public are minimized. An integral part of the program is the risk-informed screening process. Dams are classified based upon confirmed or unconfirmed dam safety issues, the combination of life or economic consequences should failure occur and the probability of failure. This process enables us to prioritize dam safety actions to correct deficiencies, which include interim risk reduction measures to be undertaken while further investigations are conducted and remedial actions are implemented.
Prado Dam received a Dam Safety Action Class III, or DSAC III, rating in December 2009 based on a Screening Portfolio Risk Analysis, or SPRA, completed in July 2009. A DSAC III rating is given to dams where the dam is significantly inadequate, or the combination of life, economic or environmental consequences with probability of failure is moderate to high.
Prado Dam received a DSAC III rating because of the potential for:
· Embankment seepage and piping.
· Overtopping of the dam in the vicinity of the existing spillway.
As a result of Prado Dam’s DSAC III rating, the Corps has implemented the following Interim Risk Reduction Measures, or IRRMs:
· Inspection by Special Dam Inspection Team when trigger elevation of 528 ft has reached.
· Update the Emergency Action Plan annually.
- Coordinate with local interests and downstream agencies to discuss the predicted failure modes identified in the SPRA report and their associated risks.
- Conduct an orientation seminar dam safety exercise.
- Updating flood maps to derive downstream inundation mapping for various events including dam failure under different failure modes. It is anticipated that this IRRM will be completed by 2020.
Public Safety is Number One Priority
Public safety is our number one priority. While we cannot completely eliminate risk, we can reduce it. Our screening and classification of Prado Dam does not mean that failure is taking place. It means we have identified dam safety issues that don’t meet industry standards and the risk to public safety is unacceptable. Routine inspections and operation of the dam will continue and emergency action plans have been developed in coordination with local emergency management officials. Currently, there is no evidence to suggest an emergency situation exists or is about to occur.
The U.S. Army Corps of Engineers owns and operates 694 dams that serve a variety of purposes, including navigation, flood damage reduction, water supply, irrigation, hydropower, recreation, environmental enhancement and combinations of these purposes. As part of our responsibility in managing these dams, the Corps has a comprehensive Dam Safety Program that has public safety as its primary objective. Corps dams are routinely inspected and continually evaluated for safety in compliance with the Federal Guidelines for Dam Safety issued in 1979 and Engineering Regulation ER 1110-2-1156, Safety of Dams – Policy and Procedures.