Mitigation for the Construction and Operation of Libby Dam

food sources, as evidenced by the loss of species and total numbers since impoundment
(Voelz and Ward 1991). Hauer and Stanford (1996) found a significant reduction in insect
production for nearly every species of insect during a 13-14 year interval in the Kootenai
River. These losses can be directly attributed to hydropower operations. Benthic macroinvertebrate
densities are one of the most important factors influencing growth and density of
trout in the Kootenai River (May and Huston 1983).
Large gravel deltas have formed at the mouths of several tributaries of the Kootenai
River (Quartz, O’Brien and Pipe Creeks) due to the loss of high spring flows. These deltas
have reached proportions that are potential barriers to migrating fish such as bull trout,
westslope cutthroat trout, burbot, and mountain whitefish at low river levels below Libby
Dam (Graham 1979; Marotz et al. 1988).
A mix of mitigation techniques is necessary to offset losses caused by dam
construction and operation. A cooperative mitigation and implementation plan developed by
Montana Fish, Wildlife & Parks, the Kootenai Tribe of Idaho and the Confederated Salish
and Kootenai Tribes documents the hydropower related losses and mitigation actions as
called for by the Northwest Power Planning Council’s Fish and Wildlife Program (MFWP,
CSKT and KTOI 1998). This plan identifies several actions that do not require modification
of Dam operation to be successful. These include aquatic habitat improvement, fish passage
improvements, off-site mitigation, fisheries easements, and conservation aquaculture and
hatchery products.
The Libby Creek watershed is the second largest tributary between Kootenai Falls
and Libby Dam, and has an area of 234 square miles. Libby Creek provides critical
spawning and rearing habitat and a migratory corridor for the threatened bull trout, and
resident redband trout. The U.S. Fish and Wildlife Service’s Bull Trout Recovery Plan
designates Libby Creek as part of the Kootenai River and Bull Lake Critical Habitat Sub-
Unit (USFWS 2002). Libby Creek has been degraded by past management practices,
including road building, hydraulic and dredge mining, and riparian logging. These past
activities likely disrupted the natural equilibrium within Libby Creek that resulted in
accelerated bank erosion along a number of meander bends causing channel degradation.
This resulted in poor fish habitat that likely reduced the productivity and carrying capacity
for resident salmonids within Libby Creek. Currently the stream channel is over-widened
and shallow with limited pool habitat (Sato 2000). Many of the problems related with the
unstable conditions within the Libby Creek watershed are a result of land management
activities that occurred in the upper watershed, and therefore restoration activities should first
focus on the upper watershed (Sato 2000).
Grave Creek is a fourth order tributary to the Tobacco River, with a watershed area
of approximately 55 square miles. Grave Creek is one of the most important bull trout
spawning streams in the Montana portion of the Kootenai River (see Chapter 1), and has
been designated as critical habitat within the U.S. Fish and Wildlife Service’s Bull Trout
Recovery Plan (USFWS 2002). Grave Creek is also currently on the Montana Water
Quality Limited Segment List as an impaired stream. The State of Montana has proposed
122