Anderson Ranch Dam

Coordinates: 43°21′27″N 115°26′55″W / 43.35750°N 115.44861°W / 43.35750; -115.44861
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Anderson Ranch Dam
View from southwest in August 2009
Anderson Ranch Dam is located in the United States
Anderson Ranch Dam
Location in the United States
Anderson Ranch Dam is located in Idaho
Anderson Ranch Dam
Location in Idaho
CountryUnited States
LocationElmore County, Idaho
Coordinates43°21′27″N 115°26′55″W / 43.35750°N 115.44861°W / 43.35750; -115.44861
Construction began1941[1]
Opening date1950; 74 years ago (1950)
Operator(s)U.S. Bureau of Reclamation[2]
Dam and spillways
ImpoundsSouth Fork of Boise River
Height456 feet (139 m)[2]
Length1,350 feet (411 m)[2]
CreatesAnderson Ranch Reservoir
Total capacity503,500 acre-feet (0.621 km3)[2]
Catchment area960 square miles (2,490 km2)[2]
Surface area4,815 acres (19.5 km2)[2]
Normal elevation4,190 ft (1,280 m) AMSL
Power Station
Commission date1951 (1986)[1]
Turbines2 x 20 MW[1]
Installed capacity40 MW
Columbia River Basin
Columbia River Basin

Anderson Ranch Dam is an earth rockfill type dam in the western United States, on the South Fork of the Boise River in southwestern Idaho. In Elmore County northeast of Mountain Home, it is several miles north of U.S. Route 20 and operated by the U.S. Bureau of Reclamation.

When completed 74 years ago in 1950, Anderson Ranch was the tallest dam of its type in the world.[3] Its primary purpose is to provide irrigation water for agriculture, with a secondary purpose of hydroelectric power. Its generating capacity was increased from 27 to 40 MW in 1986.[1][2] Its reservoir has a spillway elevation of 4,196 feet (1,280 m) above sea level.

The construction of the dam began in 1941 and experienced numerous challenges with materials, fuel, and labor shortages during World War II. Work was halted for over nine months beginning in late December 1942. The Reclamation Act of 1902 had racial exclusions on labor which were strictly adhered to until Congress changed the law in 1943. This allowed Japanese American internees to work on Reclamation projects; Anderson Ranch utilized internees from the Minidoka War Relocation Center, northeast of Twin Falls.[1]

The South Fork of the Boise River originates in the Smoky Mountains north of Fairfield. Its watershed includes portions of the Smoky Mountains, Soldier Mountains, Boise National Forest, and Sawtooth National Forest. Below the dam, the South Fork flows northwestward into the reservoir behind the concrete Arrowrock Dam, completed in 1915.

The Bureau of Reclamation and Idaho Water Resource Board are working on raising the dam by six feet (1.8 m), resulting in approximately 29,000 acre-feet (35,800,000 m3) of new storage space.[4] The design is scheduled for completion in the summer of 2024.[5]


  1. ^ a b c d e National Park Service - history - Anderson Ranch Dam & Powerplant, Idaho - accessed 2012-02-09
  2. ^ a b c d e f g Anderson Ranch Dam Archived 2011-07-16 at the Wayback Machine, NPDP Dam Directory
  3. ^ "". Archived from the original on 2011-11-12. Retrieved 2012-02-10.
  4. ^ [1] U.S. Bureau of Reclamation, Anderson Ranch Dam Raise - accessed 2022-07-18
  5. ^ [2] U.S. Bureau of Reclamation, Anderson Ranch Dam Raise Milestones - accessed 2022-07-18

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