General
The Rapid Valley Project consists of Deerfield Dam and Reservoir, located on Castle Creek, a tributary of Rapid Creek, about 25 miles west of Rapid City, South Dakota. There are various irrigation diversion and supply works in the Rapid Valley Water Conservancy District, and 8,900 acres of privately developed land that are provided supplemental irrigation water from Deerfield Reservoir. The reservoir also provides a supplemental supply of water for Rapid City, including Ellsworth Air Force Base. Fish and wildlife benefits are provided, along with water based recreation opportunities. Pactola Reservoir (Rapid Valley Unit) supplements the supply of stored water available from Deerfield Reservoir. Thus, a full water supply for irrigation and municipal purposes is provided.
History
The area in and around Rapid Valley, except for that served by the Iowa Canal Extension, has had irrigation in some form for many years. Until 1930, there was usually a sufficient flow in Rapid Creek to take care of irrigation needs. After 1930, the water supply became inadequate for full irrigation development. Only those crops that could be grown without full water requirement were planted on most farms, the exception being lands with full water rights.
Construction
A modification of Deerfield Dam to safely pass a revised inflow design flood was started in 1982. The work includes raising the dam by 38 feet, and the existing spillway will be replaced by a new one. Construction was started on July 7, 1942, by the Farm Security Administration and was later continued by the Civilian Conservation Corps and the Civilian Public Service Camp under the Works Projects Administration during World War II. The facilities were completed by the Bureau of Reclamation in 1947. Minor construction cleanup work, and disposal of excess equipment were accomplished in 1949. Water first became available from Deerfield Reservoir storage on May 1, 1948.
Plan
Deerfield Dam, a zoned earthfill structure, has a structural height of 133 feet, a crest length of 825 feet, and a crest width of 35 feet. The side-channel spillway, located in the right abutment, is concrete lined with an uncontrolled crest 190 feet long and a capacity of 16,700 cubic feet per second. The outlet works consist of a 5-foot-diameter concrete conduit through the dam base, extending to a 39-inch-diameter steel pipe contained within a 6.5-foot horseshoe-shaped concrete conduit. The steel pipe has a discharge capacity of 275 cubic feet per second. Small releases for fish and wildlife needs can be made through a 6-inch-diameter pipe which parallels the 39-inch- diameter pipe. The reservoir has a capacity of 15,700 acre-feet and a 414-acre water surface area. Conservation storage is 15,200 acre-feet; dead and inactive storage totals 600 acre-feet. Deerfield Dam and Reservoir are operated and maintained by the Bureau of Reclamation on a pooled storage basis with Pactola Reservoir, which is located downstream from Deerfield Dam on Rapid Creek.
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