4 minute read
Dunn Creek Confluence Habitat Restoration
Kootenai River, Libby, Montana, United States
Following the construction of Libby Dam in 1972, the Kootenai River downstream of the dam continues to be impacted by altered hydrology, changes in nutrient, wood, and sediment loading, and changes in water quality. These changes have altered riparian processes and affected aquatic and terrestrial habitat, resulting in a degraded ecosystem relative to historical conditions. The U.S. Army Corps of Engineers (USACE) Seattle District (NWS) developed a comprehensive design, which was implemented in 2015, to improve salmonid habitat in the Kootenai River downstream of Libby Dam by partially mitigating for the loss of wood recruitment (i.e., accumulations of large wood, or log jams) to the river below the dam. The project area is located in the reach of the Kootenai River between Libby Dam and the Fisher River, approximately three miles downstream of the dam. The purpose of this project is to rehabilitate—and to the extent possible, restore—natural processes related to large woody debris in the reach.
Producing Efficiencies
The accumulation of large wood, commonly known as log jams, in forested stream ecosystems contributes to the ecosystems’ health, especially as regards invertebrate and fish habitat and sediment retention. In the case of Kootenai River, the reach downstream of Libby Dam lacks sediment and wood due to the existence of the dam. Existing large wood complexes are older and have degraded; as a result, they have ceased to function at an optimal level and limit the river’s ecosystem function potential. As a pilot project, engineered log jams (ELJs) were constructed to restore, in part, the function of wood in the river downstream of Libby Dam.
Using Natural Processes
The ELJs were constructed in a manner that will allow the structures to “rack” large and small woody debris—sourced from upstream of the dam—that will be placed in the river downstream of the dam and upstream of the project. The ELJs were constructed to be self-maintaining in light of the lack of bedload movement and recruitment. They were engineered to sustain one-hundred-year flood events from Libby Dam.
Broadening Benefits
There was an opportunity to take advantage of the need to protect important cultural resources at the mouth of Dunn Creek, which are Confederated Salish and Kootenai Tribes sites. There was also a desire to improve fish and riparian habitat in the same general vicinity and create a project to accommodate both needs while also considering interests of other stakeholders—including anglers. The project is part of a larger suite of projects intended to increase riparian and riverine functionality downstream of Libby Dam.
Promoting Collaboration
USACE NWS at Libby Dam worked with several local stakeholders, including the Montana Chapter of Trout Unlimited; Montana Fish, Wildlife and Parks; U.S. Forest Service, Lincoln County; and Kootenai Tribe of Idaho to develop a conceptual plan for projects on USACE property on the Kootenai River.
