Location and Description
Painted Rock Dam is a flood risk reduction project located on Gila River in Maricopa County about 70 miles southeast from Phoenix, Ariz.
Painted Rock Dam is an earthfill embankment dam and includes an embankment, spillway, outlet works and two saddle dikes.
The Painted Rock Dam was constructed between 1957 and 1959.
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.
Current Status
Painted Rock Dam received a Dam Safety Action Class III, or DSAC III, rating in March 2009 based on a Screening Portfolio Risk Analysis, or SPRA, completed in May 2008. 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.
Painted Rock Dam received a DSAC III rating because of the potential for:
· Partial failure from undercutting concrete spillway crest during the Project Maximum Flood
· Seepage and piping through the foundation
As a result of Painted Rock Dam’s DSAC III rating, the Corps has implemented the following Interim Risk Reduction Measures, or IRRMs:
- Inspect and monitor per the most recent version of the Instruction for Reservoir Operations Center Personnel (Orange Book), increasing the frequency of inspection and monitoring with increasing pool elevation, and deploy a Special Dam Inspection Team when the pool elevation reaches the trigger elevation. This IRRM would reduce the probability of failure by assisting emergency managers in detection and evaluation of potential seepage and piping and potential failures. Inspection of sinkhole and its potential impact on the foundation seepage, and the erodibility of the spillway rock and sill will be emphasized.
- Update the Emergency Action Plan on an annual basis to aid in notification of the Special Dam Inspection Team and local interests and agencies.
- Flood mapping based on the capacity of the downstream channel, including channel breakouts for floods lower than the maximum flood event
- Incorporate early notification for inspection into the Instruction for Reservoir Operations Center Personnel (the “Orange Book”) for water year 2012 and emergency action sub plan.
What’s next?
· Coordination with local interest to outline dam safety issues and the associated failure modes, including discussion of the SPRA process, SPRA findings for Painted Rock Dam, IRRM, study schedule and proposed future meetings. This coordination will include a flood emergency exercise to be scheduled with the potentially affected emergency management offices within the agencies.
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 Painted Rock 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.
Background
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.