Painted Rock Dam

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.


Operational Objectives   Regional Flood Risk Management  
Completion Date   February 1960  
Stream System    Gila River Lower Colorado River
Drainage Area    50,800 sq. mi. Extends into New Mexico and Mexico
Significant Upstream Flood Control Facilities   9 major dams Salt River Project (6 dams), Bureau of Indian Affairs - Tat Momolikot Dam & Coolidge Dam (San Carlos Reservoir), Central Arizona Project - New Waddell Dam
DSAC Rating   3
Elevation  NGVD 1929 + 2.06 feet =  NAVD 1988
  Streambed at dam   524.0 ft 526.1
  Entrance invert elevation   530.0 ft 532.1
  Debris pool   550.0 ft 552.1
  Spillway crest   661.0 ft 663.1
  Spillway Design Surcharge   696.3 ft 698.4
  Top of dam   705.0 ft 707.1
  Debris pool   482 acres  
  Spillway crest 52,112 acres  
  Spillway Design Surcharge   81,474 acres  
  Top of dam   89,600 acres  
  Debris pool   3,148 af  
  Spillway crest   2,336,169 af  
  Spillway Design Surcharge   4,669,103 af  
  Top of dam   5,414,025 af  
  Allowance for sediment (50-year)2,4   200,000 af  
Dam Type: Rolled Earthfill    
  Height above original streambed   181 ft  
  Top length   4,796 ft  
  Top width   20 ft  
West Dike top length   450 ft  
Spillway (rebuilt in 1994) Type: Detached broadcrested weir
  Crest length   610 ft  
  Spillway Design Surcharge   35.3 ft  
  Spillway Design freeboard   8.7 ft  
Outlets Works Location Right Abutment
 Controlled Gate Type Hydraulically operated Tainter Gates    
  Gates - Number & size   3 - 10' W x 18' H ft  
  Entrance / Exit invert elevation   530.0 / 519.8 ft 532.1 / 521.9
  Number and size   1 - 25 ft, diameter  
  Length   925 ft  
  Maximum Scheduled Release @ spillway crest   22,500 cfs, maximum average  
  Maximum Physical Release capacity @ spillway crest4   30,480 cfs  
Reservoir Design Flood3        
  Duration (Inflow)   18 days  
  Total volume   2,800,000 af  
  Maximum water surface elevation   660.5 ft 662.6
  Inflow peak   300,000 cfs  
Spillway Design Flood3        
  Duration (Inflow)   18 days  
  Total volume   7,680,000 af  
  Maximum water surface elevation   696.3 ft 698.4
  Inflow peak   620,000 cfs  
  Outflow peak   436,500 cfs  
Historic Maximums   (Date)    
Maximum Water Surface Elevation (6 ft spillway surcharge)   667.05    (2-26-1993) ft 669.15
Maximum Water Impoundment (114% of flood control volume)   2,811,274    (2-26-1993) af(1985 Survey) 669.15
Maximum Inflow      (2-XX-1993) cfs  
Maximum Outflow   25,886    (2-26-1993) cfs  
1. 1993 Landsat Survey (1995 recomputation incorporating previously unrecognized volume low in basin)
2. Design Memorandum No. 1, Hydrology, August 1954
3. Design Memorandum No. 3, General Design for Painted Rock Reservoir, March 1955
4. Design Memorandum No. 6, Embankment, Spillway & Outlet Works, November 1956