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Helena Valley Unit
Helena Valley Dam, Montana
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Pick Sloan Missouri Basin Program
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General Description| Plan| Development| Benefits

General Description

Helena Valley Unit of the Pick-Sloan Missouri Basin Program is in central Montana, adjoining the city of Helena, and 3.5 miles west of Canyon Ferry Dam on the Missouri River. The principal purposes of the unit are irrigation and municipal water for the city of Helena. Features of the development are a tunnel, dam and regulating reservoir, canal, pumping plant, and other facilities to furnish water to about 17,000 acres of land and for municipal use.

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The Helena Valley Unit water supply is discharged from Canyon Ferry Reservoir, 17 miles east of Helena on the Missouri River. Helena Valley Pumping Plant, below Canyon Ferry Dam, lifts water by turbine-driven pumps to Helena Valley Tunnel. This water flows by gravity through the 2.7-mile tunnel under the Spokane Hills into Helena Valley. Helena Valley Canal conveys the water around the south, west, and north sides of the valley, terminating in a wasteway into Lake Helena. Helena Valley Reservoir, with an active capacity of 5,897 acre-feet, is located at mile 11 of the Helena Valley Canal. This reservoir regulates pumped water and supplies water through a two-level outlet works to the municipal works constructed by the city of Helena.

Facility Descriptions
Helena Valley Pumping Plant

Helena Valley Pumping Plant, 500 feet downstream from Canyon Ferry Dam, houses two 5,000-horsepower Francis type hydraulic turbines; each turbine is connected directly to a 150-cubic-foot-per-second centrifugal pump; the two pumps lift a total of 300 cubic feet per second of water to the inlet end of the Helena Valley Tunnel. Water is supplied to the pumping plant by a 10-foot diameter welded steel penstock pipe from Canyon Ferry Dam. A portion of the water from the reservoir is pumped up to the tunnel through a 75-inch-diameter discharge line; the remainder is discharged into the Missouri River. A 10-foot-long reducer section at the upstream end connects the penstock pipe to the 13-foot diameter conduit liner pipe in Canyon Ferry Dam. A 60-ton fixed-wheel gate in the upstream face of Canyon Ferry Dam regulates the flow of water into the penstock. An exposed manifold provides for future installation of a small powerplant. A 92-inch butterfly valve is located in each of the two branches for the turbines.

Helena Valley Tunnel

The Helena Valley Tunnel passes through a high range of hills on the left bank of the Missouri River, 14 miles east of Helena, Montana. The gravity flow tunnel conveys water in a westerly direction through the Spokane Hills which separate Helena Valley and the Missouri River. The water is pumped into the tunnel from Canyon Ferry Reservoir by two hydraulic turbine-driven pumps. The tunnel is concrete lined, horseshoe shaped, 7 feet in diameter, and 2.7 miles long. The tunnel capacity is 300 cubic feet per second with water depth at 5.5 feet. The invert at the tunnel inlet end is 73.41 feet above Canyon Ferry Reservoir maximum water surface elevation and 211.16 feet above the horizontal centerline of the pumps.

Helena Valley Dam, Reservoir, and Canal

Water flowing from Helena Valley Tunnel at mile 2.8 discharges into the 300-cubic-foot-per-second Helena Valley Canal. The canal is 31.7 miles long, with 10.2 miles unlined and 21.5 miles lined. At mile 11, the canal discharges into a 10,451-acre-foot-capacity regulating reservoir. Helena Valley Dam, which forms the reservoir is an earthfill structure 94 feet high, with a crest length of 2,650 feet. A 600-foot-long dike extends from the left abutment of the dam.

The reservoir has 5,897 acre-feet of conservation storage for irrigation and municipal water. An outlet built into the dam supplies municipal water to the city of Helena. The 350-cubic-foot-per-second outlet to the Helena Valley Canal is located in the dike. Between the reservoir and mile 17, the canal provides facilities for future supplemental service to 10 irrigation ditches which have been diverting water from Prickly Pear Creek; between miles 17 and 22, facilities are provided for supplemental service to existing ditches diverting water from Prickly Pear and Tenmile Creeks. The canal terminates at Lake Helena, which occupies the lower part of the valley.

The reservoir area upstream from the dam has been earth blanketed to reduce seepage from the reservoir, and pressure relief wells have been installed near the downstream toe of the dam. These measures have not been totally effective and other measures are being considered to relieve the uplift pressures on the downstream toe of the dam.

Lateral and Drainage System

The lateral system is 64.8 miles long, which includes 51.9 miles unlined, 12.7 miles lined, and 0.2 mile of pipe. The drainage system is 56.5 miles long, including 26.6 miles of open drains and 29.9 miles of pipe drains.

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Helena was established in 1864, following the discovery of gold in Last Chance Gulch, and was a thriving gold camp by 1865. Many of the miners, disappointed in their quest for gold, took up homesteads in the valley.

The water from Prickly Pear, Tenmile, Silver, and McClellan Creeks was appropriated for irrigation purposes concurrently with the land claims, and shortages of water were noted as early as 1866. In 1883, the Water Corporation of Prickly Pear Valley was formed by people claiming water rights out of Prickly Pear Creek.

From 1910 to 1920, Lewis and Clark County was rather heavily settled. As agriculture yields and prices dropped rapidly after 1919, farm bankruptcies, foreclosures, and attractive industrial opportunities in other sections of the country induced people to leave the area.


In 1905-1906, a preliminary investigation by the Reclamation Service proposed diversion of Madison River waters to supply irrigable land in the Helena Valley by a canal. In 1912, The Montana Reservoir and Irrigation Co., now a subsidiary of the Montana Power Company, developed an irrigation system to serve an area similar to that planned by Reclamation and erected pumping plants on the north and south shores of Lake Helena. The Montana Reservoir and Irrigation Co. contract expired in 1942, but the company operated the pumps and served the land on the same basis beyond that time. Reconnaissance investigations of the Helena Valley Basin by the Bureau of Reclamation were reported in 1940 and 1943. Various reservoir sites and other alternatives were investigated. The recommended plan involved pumping irrigation water from Canyon Ferry Reservoir. This plan was outlined in Senate Document 191, 78th Congress, 2d session.


The unit was authorized by the Flood Control Acts of December 22, 1944, and July 24, 1946.


Construction of facilities was begun in 1957 and completed in 1958.

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Full irrigation development provides for more intensive land use and greater diversification through the production of potatoes, alfalfa, grain, and irrigated pasture. Livestock production has been supplemented by fattening cattle, sheep, and hogs, and increased production of dairy and poultry products.


Recreation in the area consists of both Helena Valley Reservoir and Canyon Ferry Lake. Campsites are available, as well as boating, fishing, and other activities.

For specific information on a recreation site, please visit the individual dam pages, located above under Related Facilities.

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Last updated: Aug 03, 2010