Oahe

The Oahe Dam is a large earthen dam on the Missouri River, just north of Pierre, South Dakota, United States. The dam creates Lake Oahe, the fourth-largest man-made reservoir in the United States. The reservoir stretches 231 miles (372 km) up the course of the Missouri to Bismarck, North Dakota. The dam's power plant provides electricity for much of the north-central United States. It is named for the Oahe Indian Mission established among the Lakota Sioux in 1874.

The project provides flood control, hydropower generation, irrigation, and navigation benefits. Oahe Dam is one of six Missouri River mainstem dams, the next dam upstream is Garrison Dam, near Riverdale, North Dakota, and the next dam downstream is Big Bend Dam, near Fort Thompson, South Dakota.

In September and October 1804, the Lewis and Clark Expedition passed through what is now Lake Oahe while exploring the Missouri River.

The Oahe Dam was authorized by the Flood Control Act of 1944, and construction by the United States Army Corps of Engineers began in 1948. The world's first rock tunnel boring machine (TBM) was invented in 1952 by James S. Robbins for the Oahe Dam project,[2] which marked the beginning of machines replacing human tunnelers.[3] The earth main dam reached its full height in October 1959. It was officially dedicated by President John F. Kennedy on August 17, 1962, the year in which it began generating power. The original project cost was $340,000,000.

Tours of the powerplant are given daily, Memorial Day through Labor Day.

Tours are currently suspended due to Covid-19 Outbreak.

As a result of the dam's construction the Cheyenne River Indian Reservation lost 150,000 acres (61,000 hectares) bringing it down to 2,850,000 acres (1,150,000 ha) today. Standing Rock Reservation lost 55,993 acres (22,660 ha) leaving it with 2,300,000 acres (930,000 ha). Much of the land was taken by eminent domain claims made by the Bureau of Reclamation. Over and above the land loss, most of the reservations' prime agricultural land was included in the loss. The regions where the populations were resettled had soil with a higher clay content, and resources such as medicinal plants were less prevalent.[4]

The loss of this land had a dramatic effect on the Natives who lived on the reservations. Most of the land was unable to be harvested (to allow the trees to be cut down for wood, etc.) before the land was flooded over with water.[5] One visitor to the reservations later asked why there were so few older Natives on the reservations and was told that "the old people had died of heartache" after the construction of the dam and the loss of the reservations' land.[6] As of 2015, poverty remains a problem for the displaced populations in the Dakotas, who are still seeking compensation for the loss of the towns submerged under Lake Oahe, and the loss of their traditional ways of life.[7]

Huff Archeological Site is a fortified Mandan village site on what is now the bank of Lake Oahe. It is designated a National Historic Landmark, but is endangered by erosion pressure from the lake.

Excessive precipitation in the spring, along with melting snow from the Rocky Mountains forced the dam to open the release gates (not the spillway), releasing 110,000 cu ft/s (3,115 m3/s) in June with another 50,000 cu ft/s (1,416 m3/s) through the power plant totaling 160,000 cu ft/s (4,531 m3/s).[8] The previous release record was 53,900 cu ft/s (1,526 m3/s) in 1997.