Thompson Falls Upstream Fish Passage Facilities Design Development

GEI assisted PPL Montana in development of upstream fish passage facilities at the Thompson Falls Hydroelectric Project. This 92.6 MW project has full-year daily average streamflows ranging from 9800 cfs (2001) to 28,000 cfs (1997), and peak annual discharge can exceed 100,000 cfs. Maximum static head is 62 feet.

Target species to be passed upstream include bull trout, west-slope cutthroat trout, and other non-anadromous species. Behavior of these non-anadromous species was not well-defined, GEI conducted radio-telemetry studies (2004-2005) to determine tailrace fish behavior downstream of the dam. Identification of fish holding locations, through a range of project discharges, is necessary to determine the optimum site for an upstream passage facility. Behavioral findings and the fishway site recommendation were presented in a January 2006 Letter Report.

GEI initiated a feasibility study to identify the optimum type of upstream fish passage facility in February 2006, which will result in selection of a preferred alternative by July 2006. Study alternatives include a full-height fish ladder, a lock-type trap and haul facility, and a lift-type trap and haul facility.

A 2006 radio-telemetry study will focus on whether a newly-developed spill gate operating schedule can maintain tailrace hydraulic conditions (through a range of spill discharges) which will optimize fish holding adjacent to the proposed fishway site.

Preliminary design of the preferred upstream passage facility alternative (from the feasibility study) will commence in August 2006. Preparation of plans and specifications, followed by construction, will occur in 2007-2010. Total costs will exceed $2 million.