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Rapid Valley Unit
Photo of Pactola Dam and Reservoir
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Pick Sloan Missouri Basin Program
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Rapid Valley Unit History (64 KB) (pdf)
General Description| Plan| Development| Benefits
General Description

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The Rapid Valley Unit of the Pick-Sloan Missouri Basin Program consists of Pactola Dam and Reservoir located on Rapid Creek about 15 miles west of Rapid City, South Dakota. There are 8,900 acres of privately developed land and the associated irrigation diversion and supply works in the Rapid Valley Water Conservancy District. The land is situated along Rapid Creek immediately downstream from Rapid City for a distance of about 20 miles and is provided a supplemental irrigation water supply from Pactola Reservoir. The reservoir provides the major supply of water for Rapid City, including Ellsworth Air Force Base, and flood protection along Rapid Creek. Fish and wildlife benefits also are provided, along with water-based recreation opportunities.

Pactola Reservoir supplements the supply of stored water available from Deerfield Reservoir (Rapid Valley Project). Thus a full water supply is provided for irrigation and municipal purposes.

Facility Descriptions

Pactola Dam is a zoned earthfill structure, 230 feet high, 40 feet wide at the crest, and 1,255 feet long. It has an open-cut channel spillway in the left abutment with a 240-foot uncontrolled concrete crest and a design capacity of 38,400 cubic feet per second. The outlet works consist of a concrete horseshoe-shaped tunnel through the left abutment with two high-pressure slide gates. There are two dikes to the left of the spillway having a total crest length of 2,100 feet. Pactola Reservoir has a total storage capacity of 99,000 acre-feet, of which 43,000 acre-feet is exclusive flood control storage, regulated by the Corps of Engineers. Conservation storage amounts to 55,000 acre-feet; dead and inactive storages total 1,000 acre-feet. Water surface area at spillway crest level is 1,232 acres.

Operating Agencies

Pactola Dam and Reservoir are operated and maintained by the Bureau of Reclamation on a pooled storage basis with Deerfield Reservoir (Rapid Valley Project). Water became available from Pactola Reservoir on May 1, 1958.

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Prior to the gold rush of 1876, Indians hunted in the Black Hills, adjoining foothills, and surrounding prairie lands. The gold rush brought a great influx of people to the area, and subsequent clashes between the Indians and the newcomers resulted in deeding the Black Hills area to the Federal Government. Rapid City was founded in 1876. The first railroad reached Rapid City in 1886, and extensive development soon followed.


Interest in developing the water resources of Rapid Creek was accentuated by realization that additional sources of water were necessary to meet the irrigation and municipal water needs of the general area. In 1948, landowners in the Rapid Valley Water Conservancy District and adjoining areas petitioned the Bureau of Reclamation to construct Pactola Dam and Reservoir for storage of irrigation water. In 1949, the city commissioners of Rapid City submitted a resolution to Reclamation requesting storage in a proposed Pactola Reservoir for municipal uses, including water for Ellsworth Air Force Base. Reclamation undertook a thorough investigation of potential dam and reservoir sites and irrigation and municipal water needs.


The Rapid Valley Unit was included in the plan for development of the Missouri River Basin as outlined in Senate Document 191, 78th Congress, and authorized by the Flood Control Act of 1944 (Public Law 534). This approved the general comprehensive plan set forth in Senate Document 191 and House Document 475 as revised and coordinated by Senate Document 247, 78th Congress, 2nd session.


Construction of Pactola Dam began November 25, 1952, and was completed on August 15, 1956.

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Supplemental stored water is available to the 8,900 acres of irrigated land within the Rapid Valley Water Conservancy District. Under present conditions, the integrated irrigation-dryland farms produce corn, alfalfa, small grains, and pasture. The principal products contribute to a stable feed supply for stock cow herds and fattening of cattle.

Municipal and Industrial

The major portion of the municipal water needs for Rapid City, including the Ellsworth Air Force Base, is provided from storage in Pactola Reservoir.

Recreation, Fish & Wildlife

Numerous facilities associated with outdoor recreation are provided at Pactola Reservoir, including picnic grounds, campgrounds, and boat ramp developments, in addition to a visitor center and scenic overlooks. The recreation areas are administered by the Forest Service. The combined cold and warm water fishery at the reservoir is maintained by the South Dakota Department of Game, Fish, and Parks.

For specific information on recreation at Pactola Reservoir, click on the name below:

Pactola Reservoir
Flood Control

Pactola Reservoir provides flood protection benefits to Rapid City and to agricultural lands and rural and suburban developments along Rapid Creek. Pactola Reservoir has an exclusive flood control capacity of 43,057 acre-feet and a surcharge capacity of 41,892 acre-feet for a total flood capacity of 84,949 acre feet and, as of 1998, has prevented $2.9 million in flood damages.

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Last updated: Apr 05, 2013