Painted Rock Dam

Painted Rock Dam is a major flood control project in the Gila River Drainage Basin constructed and operated by the U.S. Army Corps of Engineers, Los Angeles District. The construction of this flood control project (as set forth in House Document 331, 81st congress, 1st session) was authorized by the Flood Control Act of May 17, 1950 (PL 81-516) and the Flood Control Act of December 22, 1944 (PL 78-534). The project construction was initiated on 25 July 1957 and completed on 18 January 1960 at a cost of $13,670,000 (excluding cost of lands and severance damages).

Painted Rock Flood Control Project is located on the Gila River, in the southwest part of Maricopa County in the State of Arizona about 20 miles northwest of Gila Bend, Arizona. Gila Bend is a town located on the U.S. Highway No. 80 approximately 78 miles southwest of Phoenix, Arizona. There is a sharp bend in the Gila River north of Gila Bend, wherein the river changes its course from flowing due south to flowing northwesterly. Painted Rock Dam is physically located at the end of this northwesterly flowing river reach. Immediately downstream of Painted Rock Dam, the Gila River changes it course from flowing northwesterly to a southwesterly direction. The dam site is in a gap between the Painted Rock Mountains and the Gila Bend Mountains where the river is confined to a relatively narrow channel. It is the last dam on the Gila River before its confluence with the Colorado River.

Painted Rock Dam has a drainage area of 50,800 square miles. The principal tributaries to the Gila River include the Verde, Salt, San Francisco, Santa Cruz, San Pedro, New, Agua Fria, and Hassayampa Rivers, Santa Rosa Wash, and San Simon Creek. More than half of the storm runoff coming into the Painted Rock Reservoir is unregulated inflow. The regulated inflow coming from the upstream projects includes: (1) releases made by the Salt River Project System which is comprised of seven reservoirs on the Salt and Verde Rivers; (2) releases made by the Coolidge Dam on the upper Gila River operated by the San Carlos Indian Project; and (3) releases made by the New Waddell Dam on the Agua Fria River operated by the Central Arizona Project. The purpose of the Painted Rock Flood Control Project is to provide protection for downstream communities by collecting the storm runoff from the upstream drainage areas, providing temporary flood storage space in the reservoir, and making flood releases at a rate which does not exceed the downstream channel capacity. The current downstream channel capacity is limited to approximately 10,000 cfs. The current Water Control Manual for Painted Rock Dam was approved in June 1962. The revision to the approved Water Control Manual is currently underway.

The 3 outlet gates are normally set to a 0.5 foot opening to bypass low flows. During the initial stages of a flood event, a debris pool will be built. Flood releases will begin when the water surface elevation rises above elevation 550 feet m.s.l. in the reservoir. Painted Rock Dam is operated on a prediction basis which establishes the rate of release of floodwaters from the dam based on upstream and downstream conditions. Relevant factors which control operations at Painted Rock Dam include: prior rainfall and runoff, forecasted precipitation (short-term and long-term), ground conditions (e.g., saturation, snowpack, etc.) and forecasted runoff, the current level of Painted Rock Reservoir and current inflow to the reservoir, current level of inflow to and outflows from upstream dams, expected operation of upstream dams, the status and expected operation of dams on the main stem of the Colorado River, and current relationship between reservoir outflow and downstream damages. When the water surface rises to elevation 661 feet m.s.l., uncontrolled spillway flows will begin. During the initial spillway flows, releases from the outlet gates are adjusted so that the combined spillway flow and the outlet gates outflow will not exceed downstream channel capacity. If the uncontrolled releases exceed the downstream channel capacity, the controlled releases from the outlets are shut off.