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of the Interior
The Big Flat Unit of the Missoula Valley Project is in west-central Montana about 7 miles west of the city of Missoula. The unit lands are parallel and adjacent to Clark Fork River, which is known locally as the Missoula River. The project furnishes irrigation water from the Bitterroot River for about 800 acres of land. The principal project feature is Big Flat Canal and headworks.
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Water is diverted from the Bitterroot River at a point 5 miles southwest of Missoula into the Big Flat Canal, which conveys the water to the project lands. The canal headworks are located on the canal about 488 feet below the point of diversion.
The Big Flat Canal is 9.3 miles long and extends about 5 miles to the upper end of the irrigable area and about 4 miles within the irrigable area. One mile of concrete bench flume has been constructed on the upper 5 miles of the canal. The canal has an initial capacity of 39 cubic feet per second to the headworks and 25 cubic feet per second below the headworks. Two miles of laterals complete the distribution system.
The Big Flat Irrigation District operates and maintains the project.
Irrigation has been practiced in the Missoula Valley since the founding of the city of Missoula in 1864. Many years ago, a canal diverted water from the south bank of the Clark Fork River, about 3 miles above the present dam of the Montana Power Company at Bonner. The canal followed down the south side of the canyon, and around the southeast corner of Missoula. When the Chicago, Milwaukee, St. Paul, and Pacific Railroad was built into the valley in 1909, this canal was purchased and the right-of-way was used for a roadbed. Another canal diverted from Rattlesnake Creek and crossed through the center of Missoula to irrigate the area west of the city. As the city grew, the canal had to be abandoned. Other canals diverted from Grant Creek and Butler Creek to irrigate parts of the valley; however, recent dry years and increased diversion of water from the headwaters has made use of these creeks impracticable for farming.
Investigation of the Big Flat Unit was started in 1939 at the request of local interests. Surveys were made by the Works Progress Administration, assisted by the Montana State Water Conservation Board. The Bureau of Reclamation classified the lands and prepared cost estimates.
Construction of the Missoula Valley Project was found feasible by the Secretary of the Interior on October 20, 1943, and approved by the President on May 10, 1944, under authority of the Water Conservation and Utilization Act of August 11, 1939 (53 Stat. 1418, Public Law 76-398) as amended. The authorized project purpose is irrigation.
Construction of the project began on June 7, 1945, and was completed in 1949.
Suburban development for rural homesites in the northern portion of the project area has increased in recent years. Subdividing is expected to continue. Hay, grain, and pasture are the principal crops within the irrigated areas.