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The Lower Teton Division of the Teton Basin Project was authorized for the purpose of storing water of the Teton River in eastern Idaho. Storage space would provide for supplemental and primary irrigation water, power production, flood control, and enhancement of fish and wildlife and recreation. Major features of the first phase of the Lower Division included Teton Dam and Reservoir, Teton Power and Pumping Plant, a switchyard, Fremont discharge and pump canal, Enterprise-East Teton feeder pipeline and canal, and 27 water replacement wells.
Teton Dam, after being basically completed in November 1975, failed on June 5, 1976, and was completely inoperative after that date.
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Teton Reservoir, formed by construction of Teton Dam, was to provide a supplemental water supply to 111,210 acres of land in the Fremont-Madison Irrigation District, local and downstream flood control benefits, water to operate a 16,000-kilowatt powerplant, and major recreation developments. Ground-water pumping in dry years would supplement the water supply when surface flows were fully appropriated. The reservoir also would have provided a full water supply to approximately 37,000 acres of land under the second phase of the project. The second phase would have required separate authorizing legislation.
Teton Dam was located on the Teton River, a tributary of Henrys Fork of the Snake River in Fremont County of eastern Idaho. The dam, located 3 miles northeast of Newdale, Idaho, was a 305-foot-high zoned earthfill structure with a crest length of 3,100 feet including spillway, and a crest elevation of 5,332.0 feet. Total impoundment capacity was 288,250 acre-feet, with an active capacity of 200,000 acre-feet. A three-gated, chute-type spillway was located on the right abutment, along with an auxiliary outlet works and access shaft. The main river outlet was located in a tunnel in the left abutment.
The power and pumping plant were located in a steel-framed building at the base of the left abutment of the dam. The powerplant consisted of two 10,000-kilowatt generators with provision to install a third unit in the future. Pumping plant facilities included six pumping units, two rated at 7.35 cubic feet per second and four at 14.7 cubic feet per second. The rated head was 323 feet. Water from the pumping plant was to be delivered into the Fremont Pump Canal.
Shortages of irrigation water occur frequently in the Henrys Fork Valley. During a series of dry years such as occurred in the 12-year period from 1931 through 1942, shortages occurred in each of the 12 years in the Ashton area and in 10 of the 12 years in the St. Anthony-Rexburg area.
The Teton River is subject to flooding caused by ice jams in the early spring even though the discharge is quite low at that time. These ice jams occur frequently and occasionally raise the water surface elevation to flood heights.
Channel capacity in the lower reaches of the Teton River is about 2,000 cubic feet per second and general inundation occurs at 4,000 cubic feet per second. The maximum flood of record occurred on February 11 and 12, 1962, when unseasonably warm weather and rain rapidly melted snowpacks on the valley floor and foothills, and ice-jammed channels raised the peak flow to 7,000 cubic feet per second at the St. Anthony gage. Much of Sugar City and Rexburg and the lands between these towns were inundated. The previous flood of record was in 1893, with a peak discharge of 5,830 cubic feet per second. Floods in 1894 and 1918 are believed to have been larger than the 1893 flood, but no estimates were made of peak discharges.
Twenty reservoir sites were investigated and surveyed by the Reclamation Service (now Bureau of Reclamation) in the Henrys Fork area during 1902-1905. Henrys Lake, Island Park, Grassy Lake, and sites on the Teton River were among those considered.
Field investigations were undertaken in the 1930`s and 1940`s on several damsites in the Upper Teton Basin. These sites were not considered feasible either because of unfavorable geological conditions or excessive cost per acre-foot of storage. Also, minimal flood control protection would result from smaller upstream reservoirs. A reconnaissance report dated October 1961 recommended that detailed studies begin immediately on the Lower Division, including Teton Dam and Reservoir, and that future studies on the Upper Division should be initiated when local interest and economic conditions indicated that a project was justifiable. In March 1962, a report on the Lower Teton Division was issued showing feasibility of the project which was later authorized for construction.
Construction of the Lower Teton Division of the Teton Basin Project was authorized by the Act of September 7, 1964 (78 Stat. 925, Public Law 88-583). The authorized purposes of the Teton Basin Project were irrigation and hydroelectric generation and, as incidents to these purposes, to enhance recreational opportunities and provide for the conservation and development of fish and wildlife resources.
Construction of Teton Dam began in February 1972 and was basically completed in November 1975. At the time of dam failure on June 5, 1976, the two scheduled electrical generating units had been installed and were almost ready for testing. The pump units also were installed but were not ready for operation. First phase construction of the Fremont discharge and pump canal and the Enterprise-East Teton feeder pipeline and canal was partially completed.
Failure of Teton Dam
On June 5, 1976, the Teton Dam structure failed and was rendered completely inoperative. Reservoir elevation at the time of failure was 5,301.7 feet; the reservoir was filling at about 3 feet per day. At full reservoir capacity of 288,250 acre-feet, the water surface elevation would have been 5,320.0 feet.
The failure of Teton Dam resulted in the loss of 11 lives and millions of dollars in property damage.
The Bureau of Reclamation had been issued a permit from the Idaho Department of Water Resources for the development of groundwater as a part of the Teton Basin Project. Five of the wells had been developed at the time of dam failure. These five wells, with a total capacity of 80.88 cubic feet per second, are being used by the Fremont-Madison Irrigation District for irrigation of lands within their service area.
The loss of wildlife habitat associated with the construction of Teton Dam and Ririe Dam led to the establishment of the Tex Creek Wildlife Management Area. In 1976 and 1977, the U.S. Army Corps of Engineers and the Bureau of Reclamation purchased 11,000 acres of critical big game winter range in the Tex Creek area just east of Idaho Falls, Idaho. The Idaho Department of Fish and Game eventually assumed additional critical acreages. Also, a cooperative agreement with the Bureau of Land Management resulted in the inclusion of 9,600 additional acres of land, and today, the Tex Creek Wildlife Management Area encompasses more than 28,700 acres. The entire area is managed for wildlife, with emphasis on big game habitat.