Yellowtail Dam

Yellowtail Dam
View of the dam face looking upstream
Location of the Yellowtail Dam in Montana
Country	United States
Location	Big Horn County, Montana
Coordinates	45°18′24″N 107°57′29″W / 45.30667°N 107.95806°W / 45.30667; -107.95806Coordinates: 45°18′24″N 107°57′29″W / 45.30667°N 107.95806°W / 45.30667; -107.95806
Construction began	1961
Opening date	1967
Construction cost	$110 million
Owner(s)	U.S. Bureau of Reclamation
Dam and spillways
Type of dam	Concrete arch-gravity
Impounds	Bighorn River
Height	525 ft (160 m)
Length	1,480 ft (450 m)
Width (crest)	22 ft (6.7 m)
Width (base)	147 ft (45 m)
Dam volume	1,545,664 cu yd (1,181,745 m3)
Spillways	1 main + outlet works
Spillway type	Concrete tunnel, 2x radial gates
Spillway capacity	92,000 cu ft/s (2,600 m3/s)
Reservoir
Creates	Bighorn Lake
Total capacity	1,381,189 acre·ft (1.703672 km3)
Catchment area	19,600 sq mi (51,000 km2)
Surface area	17,300 acres (7,000 ha)
Power station
Hydraulic head	495 ft (151 m)
Turbines	4x 62.5MW Francis
Installed capacity	250 MW
Annual generation	510,564,280 KWh

Yellowtail Dam is a dam across the Bighorn River in south central Montana in the United States. The mid-1960s era concrete arch dam serves to regulate the flow of the Bighorn for irrigation purposes and to generate hydroelectric power. The dam and its reservoir, Bighorn Lake, are owned by the U.S. Bureau of Reclamation.

The project was the result of negotiations between the federal government and the Crow Nation, the tribe of Native Americans that lived on the surrounding Crow Indian Reservation, and was originally envisioned as a shared facility that would provide profits for both sides. Eventually, the land was sold to Reclamation, although much of the reservoir, which extends 72 miles (116 km) upstream into Wyoming, lies in the reservation. The dam was authorized in 1944 and groundbreaking was in 1961; it was completed in 1967 after six years of construction. Today aside from its original purposes the dam serves for recreation both above and below the structure. Regulation of the Bighorn provided by the Yellowtail Dam has transformed the lower river into one of Montana's premier trout streams. However, there has been significant controversy surrounding the allocation of water in the reservoir between Montana and Wyoming, and the ecological damage wrought on 184 miles (296 km) of river both above and below the dam.

In the early 20th century, the population of the Yellowstone River valley of southern Montana, of which the Bighorn River is the largest tributary, was growing rapidly and so was the acreage of irrigated land – however, the system was vulnerable to floods and droughts. In 1905, the federal government conducted the first feasibility studies for a dam on a stretch of the Bighorn within the Crow Indian Reservation, some 45 miles (72 km) southeast of Billings, Montana. The leaders of the Crow Nation, which owned the land, agreed to building a dam there because electricity generated there would provide income for the tribe.