The Turnbull Hydroelectric Project would consist of two separate generating facilities located on canal drops within the Bureau of Reclamation’s Sun River Project. The Sun River Project is a federal irrigation project constructed west of Great Falls, MT in the 1930s. The two generating facilities are Upper Turnbull and Lower Turnbull. These projects would utilize water released for irrigation from Pishkun Reservoir. Released water flows exclusively within manmade canals, which incorporate concrete drop structures designed to control water flow across steep topographic gradients. The Turnbull hydroelectric project proposes to bypass two of these drop structures by directing canal flow into penstocks, through generating facilities, and then returning water to the canal system at the bases of the drop structures.
The project would not alter the amount or timing of irrigation water stored or released from any reservoir and would not change any point of irrigation use, but would merely utilize existing flows to generate power. The Greenfields Irrigation District would continue to control Pishkun Reservoir irrigation releases and water use.
The project would interconnect with the Northwest Energy electrical grid just north of Fairfield, MT. The total amount of new transmission line required to interconnect would be about six miles.
Hydroelectric Project Operations
All proposed projects will operate in a run-of-river mode, i.e. power generation will automatically adjust to the amount of water being delivered in the canal system. The project use of water is entirely non-consumptive. The lower canal flow will equal the flow in the upper canal. When a power plant is offline, all water will spill over into the existing drop structure, thus bypassing the project entirely.
All project facilities are located within or immediately adjacent to existing right-of-way used for access and maintenance of Greenfields Irrigation District canals. The project will not affect storage, release or timing of irrigation flows in any part of the canal system, but will merely utilize existing flows to generate power. The projects utilize canal flow and are not located near nor will they affect any natural waterways. For these reasons, and since all areas proposed for new construction have been previously disturbed and are used regularly for routine maintenance of the canal system, the environmental impact associated with the hydroelectric development will be minimal. Furthermore the proposed project structures will be small and low profile and will have virtually no visual impact.
Beneficial Water Use
The proposed hydroelectric projects are designed to produce 25,300 MW-HRS of energy annually. This amount of energy is equivalent to approximately 50,000 barrels of oil.
Because it is based on irrigation delivery, power generation from the proposed projects will help meet peak summer demands for power. The hydroelectric projects constitute an additional beneficial use of water but will not affect existing beneficial water uses.
The Federal Energy Regulatory Commission has issued licenses for development of both generating facilities. The project developers have executed a power purchase agreement with NorthWestern Energy and have received a financing commitment based on a USDA rural development program loan guarantee.
Construction is scheduled to begin in July 2010 and will be kicked off with a ground breaking event in mid July.