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Riverton Unit
Photo of Bull Lake Dam and Reservoir
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Pick Sloan Missouri Basin Program
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Riverton Unit History (86 KB) (pdf)
General Description| Plan| Development| Benefits
General Description

The Riverton Unit is located in central Wyoming in Fremont County on the ceded portion of the Wind River Indian Reservation. The unit lands lie in the Wind River Basin and to the north of the river. Direct flow water from Wind River and stored water from Bull Lake Creek are used to provide irrigation service to approximately 71,000 acres as of 1996.

Unit features are Bull Lake Dam, Pilot Butte Dam, Wind River Diversion Dam, and Pilot Butte Powerplant, together with approximately 100 miles of main canals, 300 miles of laterals, and 644 miles of drains.

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The unit receives its water supply from the Wind River and its tributaries. The principal storage is provided by Bull Lake Reservoir on Bull Lake Creek. Supplemental storage is provided by Pilot Butte Reservoir, an offstream reservoir supplied with water diverted from Wind River by the Wind River Diversion Dam. Water released from Bull Lake Reservoir flows through Bull Lake Creek to the Wind River where it augments the natural flow of that stream. Water for unit lands is delivered through the Wyoming Canal, which leads from Wind River Diversion Dam to Pilot Butte Reservoir and beyond to the distribution system. Pilot Canal flows in a generally easterly direction from Pilot Butte Reservoir, servicing lands lying south of those supplied by the Wyoming Canal.

Facility Descriptions
Bull Lake Dam and Reservoir

Bull Lake Dam is a modified homogeneous earthfill dam 81 feet high and containing 820,000 cubic yards of material. The spillway is a concrete chute 100 feet wide, controlled by three automatic radial gates. The capacity of the spillway is 11,000 cubic feet per second. The capacity of the outlet works is 4,000 cubic feet per second. Bull Lake Dam creates a reservoir of 152,000 acre feet.

Pilot Butte Dam and Reservoir

Pilot Butte Reservoir is located 10 miles below Wind River Diversion Dam. It is formed by three earthfill embankments constituting Pilot Butte Dam. The main embankment is 63.6 feet high and has a volume of 135,000 cubic yards. To complete the reservoir, two other embankments were required, one 25 feet high containing 51,000 cubic yards of material, and the other 12 feet high containing 19,000 cubic yards of material. The reservoir has an active capacity of 31,600 acre-feet.

Wind River Diversion Dam

Located 32 miles northwest of Riverton, Wyoming, Wind River Diversion Dam is a concrete gravity structure with an embankment wing, a hydraulic height of 19 feet, and a concrete volume of 17,200 cubic yards. The spillway is a concrete ogee weir with a capacity of 40,000 cubic feet per second. The diversion dam serves as the headworks to the Wyoming Canal with a capacity of 2,200 cubic feet per second.

Pilot Butte Powerplant

The Pilot Butte Powerplant is located at the drop from the Wyoming Canal to Pilot Butte Reservoir. The plant has two generating units which operate under a maximum head of 105 feet with a total capacity of 1,600 kilowatts. The plant was shut down on June 15, 1973, because of high operation and maintenance costs and penstock problems. The penstock was replaced, and the units were placed back in service in June 1990. Power was distributed over 76 miles of transmission lines.

Canal Distribution and Drainage Systems

There are two main canals in the unit. Wyoming Canal is 62.4 miles long and has a capacity of 1,800 cubic feet per second. Pilot Canal is 38.2 miles long with a capacity of 1,000 cubic feet per second. About 74 :percent of the total length of these two canals is lined.

A total of 300 miles, 125 miles of lined canal and 85 miles of pipeline, make up the system of laterals. The drainage system extends 644 miles, of which 382 miles are closed pipelines.

Operating Agencies

The unit is operated and maintained by the Midvale Irrigation District.

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Since the unit lands were largely included in the Wind River Indian Reservation during the earliest days of western development, settlement came comparatively late. On March 3, 1905, the Congress passed an act ratifying an agreement with the Indians of the Wind River Reservation, ceding lands north of Wind River to the United States. Provisions were made for the disposal of these lands under the homestead, townsite, coal, and mineral land laws.


The first reference to the area as a possible irrigation project is found in the third annual report of the Reclamation Service. The reconnaissance was presumably made in July 1904. On February 20, 1906, the State of Wyoming was granted a permit to make a survey for the development of irrigable land. Following the survey by the State, a private company began construction of an irrigation project in the fall of 1906. Wyoming Canal No. 2 was placed in operation in 1908, and in 1915 the irrigation works for the Riverton Valley had been completed. In 1916-1917, the Bureau of Reclamation conducted investigations on the higher lands of the project, involving a greater cost per acre, for the Office of Indian Affairs. All the vacant land within the project was withdrawn from entry and construction was begun on the project as an Indian irrigation project.


The project was authorized for construction by the Secretary of the Interior on June 19, 1918, under the terms of the Indian Appropriation Act for fiscal year 1919, approved by the Congress on May 25, 1918. By the act of June 5, 1920, the project was placed under the jurisdiction of the Bureau of Reclamation. On September 25, 1970, Public Law 91-409 reauthorized the project as the Riverton Unit of the Pick-Sloan Missouri Basin Program.


Actual construction began on the main canal in January 1920. Construction of the Wind River Diversion Dam was started in July 1921 and was completed in 1923.

In 1925, water was delivered to project lands. Further construction was carried out in the 1930`s and following the end of World War II. The construction period for Bull Lake Dam was during 1936-1938. Coincidental with construction of canals and laterals to serve new lands in recent years, major work in draining land already irrigated has been carried out.

Rehabilitation and Betterment

The unit is being modified to include relief to water users, construction, betterment of works, land rehabilitation, water conservation, fish and wildlife conservation and development, flood control, and silt control on the entire unit. Unit modifications consist mainly of addition of sediment excluders at the Wyoming Canal headworks, repair of Wind River Diversion Dam, lining for main canals, lining and pipe for laterals, drains, and fish and wildlife facilities.

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Principal crops are alfalfa, beans, alfalfa seed, sugar beets, barley, oats, wheat, sunflower seeds, and potatoes.

Recreation, Fish & Wildlife

Bull Lake Reservoir offers boating and good trout fishing. Ocean Lake, an offstream reservoir located in the center of the irrigated lands about 15 miles northwest of Riverton, is not a storage reservoir, but was created as a result of operation of the unit. Pilot Butte Reservoir, about 10 miles below Wind River Diversion Dam, is also a popular recreation area.

Lake Cameahwait
Ocean Lake
Pilot Butte Reservoir

Flood Control

Bull Lake, with an active capacity of 151,737 acre-feet has greatly reduced flooding on Bull Lake Creek and contributes to the abatement of floods on the Wind River. Total damages reduced by Bull Lake Reservoir since construction has totaled $2.6 million as of 1998.

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Last updated: Apr 05, 2013