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| Angostura Dam | |
|---|---|
| Name | Angostura Dam |
| Location | near Lewiston, North Dakota, Mercer County, North Dakota |
| Status | Operational |
| Opening | 1951 |
| Owner | U.S. Army Corps of Engineers |
| Dam type | Earth-fill embankment |
| Height | 162 ft (49 m) |
| Length | 9,800 ft (2,987 m) |
| Reservoir | Lake Oahe |
| Plant capacity | 40 MW |
Angostura Dam Angostura Dam is a multipurpose earth-fill embankment dam on the Missouri River in southwestern North Dakota, built for flood control, water supply, navigation, and hydroelectric power. Constructed and operated by the U.S. Army Corps of Engineers as part of mid-20th century river basin development, it created a major reservoir and altered regional Missouri River basin flow regimes. The structure and its reservoir have become focal points for Bureau of Reclamation projects, regional tribal interests, and state-level transportation and recreation planning.
Planning for the project originated in the context of the Flood Control Act of 1936, the Pick-Sloan Missouri Basin Program, and post-Great Depression public works initiatives championed by the New Deal and later federal policy. The site selection process involved studies by the U.S. Geological Survey, consultations with Standing Rock Sioux Tribe and Mandan, Hidatsa and Arikara Nation representatives, and coordination with the North Dakota State Water Commission. Groundbreaking occurred in the late 1940s amid concurrent construction of other basin projects such as Garrison Dam and Oahe Dam. The facility was completed and dedicated in 1951, with subsequent modifications influenced by lessons from the 1951 Floods and evolving standards from the Federal Power Commission.
The design combined an earth-fill embankment with a reinforced spillway and outlet works modeled after contemporary projects like Garrison Dam and Fort Peck Dam. Engineering firms working under contract coordinated with the U.S. Army Corps of Engineers Omaha District for geotechnical surveys, borrow material sourcing, and seismic assessments referencing standards from the American Society of Civil Engineers. Construction methods incorporated heavy equipment from manufacturers such as Marion Power Shovel Company and Caterpillar Inc., and workforce programs drew labor from nearby communities including Bismarck, North Dakota and Mandan, North Dakota. River diversion employed cofferdam techniques similar to those used at Fort Peck Lake.
The embankment rises approximately 162 feet above the streambed and extends nearly 9,800 feet along the crest, with zoned fill sections using compacted clay and rock. The spillway structure features reinforced concrete ogee sections and radial gates supplied to Corps specifications; flow capacity was calculated using hydrologic analyses influenced by Hortonian runoff studies and data from the U.S. Weather Bureau. Outlet works include penstocks leading to a powerhouse with generating units rated to provide peaking capacity; hydraulic equipment listings referenced standards from the Hydropower Reform Coalition and turbine manufacturers such as Francis turbine designs common to mid-century installations.
The impoundment created by the dam forms a large reservoir that altered the regional Missouri River hydrograph, affecting tributaries like the Heart River and local aquifers monitored by the U.S. Geological Survey. Reservoir operations balance flood control curves established under the Pick-Sloan Plan with irrigation and municipal water demands from communities such as Beulah, North Dakota and Hazelton, North Dakota. Sedimentation rates have been tracked using protocols promoted by the International Association of Hydrological Sciences, while evaporation losses are estimated with methodologies from the National Oceanic and Atmospheric Administration and Western Regional Climate Center.
The hydroelectric facility was installed to provide renewable baseload and peaking power to the regional grid, coordinated with the Western Area Power Administration and state utilities including Minnkota Power Cooperative. Generating units employ medium-head turbines feeding transformers to step up voltage for transmission via lines interconnected with networks serving Bismarck and links to Eastern Interconnection systems. Power sales and operational scheduling historically complied with licensing frameworks overseen by the Federal Energy Regulatory Commission and contractual arrangements with municipal and cooperative utilities.
The reservoir has become a regional hub for boating, fishing, and wildlife viewing, drawing visitors from Bismarck, Mandan, Minot, North Dakota, and neighboring South Dakota communities. Recreation management involves collaboration between the U.S. Army Corps of Engineers and state parks agencies, and species monitoring engages the U.S. Fish and Wildlife Service and tribal natural resource programs. Environmental impacts have included loss of native riparian habitat, altered fish migration affecting species assessed by the International Union for Conservation of Nature, and cultural-site inundation of places important to the Mandan and Arikara peoples. Mitigation efforts have involved habitat rehabilitation projects supported by the Environmental Protection Agency and ecosystem restoration initiatives inspired by the Missouri River Recovery Program.
Day-to-day operations are administered by the U.S. Army Corps of Engineers Omaha District with maintenance contracting to regional firms and periodic inspections guided by criteria from the Federal Emergency Management Agency and the Association of State Dam Safety Officials. Routine programs include structural monitoring, spillway gate maintenance, sediment management, and hydropower turbine overhauls planned in coordination with the North Dakota Department of Water Resources. Emergency action planning follows templates developed after the Teton Dam failure to ensure coordination with county emergency managers in Mercer County, North Dakota and adjoining jurisdictions.
Category:Dams in North Dakota Category:United States Army Corps of Engineers dams