Nilan Water Users Association
The Nilan Water Users Association obtains water from Nilan Reservoir, an off-stream reservoir located about 6 miles west of the town of Augusta in the Elk Creek drainage. The Elk Creek drainage is also at times referred to as the South Fork Sun River. Water is diverted mainly from Ford Creek to supply the reservoir. Nilan Reservoir covers about 500 surface acres, stores 10,090 acre-feet of water and was built in 1951. The dam is 54 feet high. This project is operated by the Water Users in cooperation with the State of Montana Department of Natural Resources and Conservation. It operates separately from the Sun River Project. Water from the reservoir is used to irrigate about 4,500 acres in the Elk and Smith Creek drainages below Nilan Reservoir and in the Willow Creek drainage upstream from Willow Creek Reservoir. Both the Elk Creek and Willow Creek drainages receive return flows from this project.
Broken O Ranch
The Broken O Ranch is a large private water user in the Sun River watershed. The majority of the water used by the Broken O is diverted directly from the Sun River with smaller amounts diverted from tributaries, Elk and Dry creeks. Floweree Canal, Broken O's largest supply canal, has a rockfill diversion structure on the Sun River located 25 river miles downstream from Gibson Dam and about 2.5 miles upstream from where Highway 287 crosses the Sun River north of Augusta. The inlet for the Floweree Canal is immediately across from where the outlet canal from Willow Creek Reservoir enters the Sun River. Another major diversion is located on the river below U.S. Highway 287. Portions of the Broken O Ranch also receive water from the Greenfields Irrigation District and Nilan Water Users Association. Excluding the acreage served by those irrigation projects, the Broken O has about 9,840 irrigated acres. The capacity of the Floweree Canal is approximately 185 cubic feet per second.
Rocky Reef
The Rocky Reef Ditch Company is a smaller irrigation project on the Sun River formed in 1916. The project irrigates approximately 500 acres and includes a diversion on the Sun River and a 2.2-mile long ditch. The diversion structure is a rockfill dam located approximately two miles northwest of the town of Fort Shaw and about one mile downstream from where Big Coulee enters the Sun River.
Sun River Ditch
Sun River Valley Ditch Company Dam with concrete blocks in place
The Sun River Valley Ditch Company irrigation project is located at the lower end of the drainage, between the towns of Sun River and Vaughn. Most of the irrigated land can be observed while traveling along Montana Highway 200 between Vaughn and the junction where U.S. Highway 89 diverges to Fairfield and Choteau. The Company has an adjudicated water right established in 1868 that is the second oldest on the Sun River.
The diversion dam is on the Sun River about two miles upstream from the town of Sun River. This structure consists of a wide concrete apron that forms a low dam about two feet high. When the river flow is low, concrete blocks are placed on the apron to increase water height. This structure backs water up into an upstream side channel where the irrigation canal headgates are located. There is no storage of water for this project.
The main canal is 12 miles long and has a capacity of 75 cubic feet per second. The canal can also receive supplementary flows of at least 20 cubic feet per second from Mill Coulee Creek. The canal empties into Muddy Creek about ½-mile upstream of the town of Vaughn.
