The Federal Energy Regulatory Commission on April 27 issued a final environmental impact statement related to a November 2013 application from Twin Lakes Canal Co. for an original license for the construction, operation, and maintenance of the 10-MW Bear River Narrows Hydroelectric Project.
The project would be located on the main stem of the Bear River in Franklin County, Idaho, about 9 miles northeast of the city of Preston. The project would occupy 658 acres of land, 243 acres of which is federal land administered by the U.S. Department of the Interior, Bureau of Land Management (BLM), and would generate an average of 48,531 megawatt-hours (MWh) of energy annually. The primary project purposes are water storage for irrigation and hydroelectric power generation.
The Bear River Narrows Project would involve the construction of these new facilities: a dam, spillway, reservoir, intake structure, penstock, powerhouse, substation, transmission line, access roads, and recreation facilities. The new, 690-foot-long, 109-foot-high, earthen dam would be constructed with an overlayment of roller compacted concrete (RCC) and a crest at elevation 4,734 feet above mean sea level.
A 4.5-mile-long reservoir would be created by the dam with a surface area of 362 acres at the normal maximum elevation of 4,734 feet and a useable storage volume of 5,000 acre-feet between elevation 4,718 feet and elevation 4,734 feet. A 48-foot-wide, 16-foot-long, 20-foot-high concrete intake structure would be constructed in the reservoir with a bar screen trashrack with 1.5-inch clear space openings, an invert opening elevation of 4,630 feet, and a top opening elevation of 4,650 feet.
A new, 600-foot-long, 14-foot-diameter, spiral, welded steel penstock would lead from the intake structure, through the dam, to the Bear River Narrows Project powerhouse. The proposed 80-foot-wide, 52-foot-long, 24-foot-high powerhouse would be constructed downstream of the dam with a concrete substructure and steel superstructure housing: two generating units, each with a 7,020-horsepower (5,250 kW) vertical Francis-type turbine and a 5,000-kW (5,555 kilovolt-amperes at a 0.86 power factor) generator; one 120-inch-diameter butterfly bypass valve with a 66-inch orifice; and 48-inch-diameter cone bypass valve.
A transformer substation would be located near the proposed powerhouse. A 0.74-mile-long, 46-kilovolt, three-phase transmission line would be constructed from the substation to the point of interconnection with the nearby PacifiCorp transmission line.
Construction of the proposed project is expected to be complete approximately 3.5 years after issuance of a license for the project. The initial filling of the reservoir would occur in the fall and winter and is expected to be completed within 5 to 6 months. The proposed project would provide a downstream minimum flow equal to the minimum flow requirement at PacifiCorp’s upstream Oneida development of 250 cubic feet per second (cfs) plus leakage from Oneida dam (estimated at 1 cfs) at all times, including during construction. Once the project is constructed, it would use unallocated water available in the Bear River during the period from October 1 to April 15 (outside of the irrigation season) to initially fill the reservoir to elevation 4,734 feet.