General

The Shadehill Unit of the Pick-Sloan Missouri Basin Program consists of Shadehill Dam and Reservoir, located about 12 miles south of Lemon, South Dakota in the northwestern part of the State, and immediately downstream from the confluence of the North and South Forks of the Grand River. The reservoir stores irrigation water for 6,700 acres. There were 2,664 acres of land that were irrigated in 1992. Associated diversion facilities divert directly from the reservoir or from the Grand River downstream from the dam. The reservoir also provides benefits for flood control, fish and wildlife conservation, recreation, and silt detention.

History

Early History

The early settlers in this area were cattlemen who established widely separated ranches on the open range. Major settlement took place from 1900 to 1910, after the railroad was extended into the region. Favorable crop yields and prices stimulated farming operations, and most of the lands which appeared suitable for tillage were brought under cultivation. Recurring years of deficient precipitation, combined with submarginal quality of much of the cultivated land, contributed toward the abandonment of much of the crop land for tillage.

In 1938, following urgent requests by local residents as result of several extreme drought years, the Bureau of Reclamation made an inspection of the Shadehill Unit area which led to the initiation of further investigations.

Investigations

Investigations leading to the development of the Shadehill Unit began in 1931. In the course of studies made by the Corps of Engineers, a topographic survey was made of the reservoir site on the Grand River immediately downstream from the confluence of the North and South Forks. This was followed by a reconnaissance survey by the Bureau of Reclamation in 1938-39 to determine the quality of available water and conduct limited field investigations. In 1941, while the Indian Service was preparing plans for the construction of Blue Horse Dam, approximately 30 miles downstream from Shadehill Dam, the Bureau of Reclamation was making further studies for a reservoir at the Shadehill site. It was jointly agreed that the Shadehill Unit would be the preferable initial development as it offered a greater probability for rapid conversion to irrigation. The Indian Service would participate in the cost and receive part of the stored water for use on reservation land.

A water supply and quality study of the Grand River and detailed engineering field surveys of the dam and reservoir site were carried out from 1945 to 1948. Land classification surveys of potentially irrigable lands that could receive irrigation water service from Shadehill Reservoir were also undertaken during this period.

Authorization

The unit was authorized by the Flood Control Act of December 22, 1944, Public Law 534, which 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, 2d session.

Construction

Construction of Shadehill Dam began April 19, 1949, and was completed August 15, 1951. The first impoundment of water was made on July 1, 1950.

Operating Agency

Shadehill Dam and Reservoir are operated and maintained by the Bureau of Reclamation.

BENEFITS

Irrigation

A full supply of irrigation water is available from Shadehill Reservoir to 6,700 acres of land under the administration of the West River Conservancy Sub-District. The integrated irrigated-dryland farms produce alfalfa, corn, and livestock.

Flood Control

Flood control benefits are provided by the the exclusive flood control capacity of 217,708 acre-feet and surcharge capacity of 111,203 acre-feet for a total flood capacity.

Recreation and Fish and Wildlife

Facilities provided for outdoor recreation around the reservoir include picnic sites, campgrounds, swimming beaches, areas for seasonal use cabins, and a marina. All recreational areas and facilities, including the fishery, are administered by the South Dakota Department of Game, Fish, and Parks.

Plan

Shadehill Dam

Shadehill Dam and Reservoir are operated and maintained by the Bureau of Reclamation. The dam and associated dikes are rolled-fill earth structures. The dam has a crest length of 12,843 feet and a maximum structural height of 145 feet. The two dikes have a total length of 1,360 feet with a maximum structural height of 83 feet. The reservoir has an active capacity of 81,443 acre-feet.

The uncontrolled service spillway is a reinforced concrete conduit, 13.5 feet in diameter, with a morning-glory inlet, and was designed to accommodate a maximum flow of 5,700 cubic feet per second.

The controlled outlet works are a horseshoe-shaped concrete conduit with a capacity of 600 cubic feet per second. The original outlet works was modified in 1960 to provide a 600-cubic-foot-per-second-capacity outlet extension to the Grand River. This modification provides additional flood control capacity and permits flood control releases to the Grand River when the reservoir water level is below the crest of the spillway.

An open-cut unlined emergency spillway with a bottom width of 1,500 feet and capacity of 127,000 cubic feet per second is located immediately upstream from the left abutment. The spillway discharges into Flat Creek, a tributary of the Grand River downstream from Shadehill Dam. The drainage basin area above Shadehill Dam is about 3,120 square miles.

Overview

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Other

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