The Confederated Salish and Kootenai Tribes are addressing impacts from nutrient and sediment inputs from Coleman Coulee and Moiese Wasteway irrigation return flows by constructing a series of treatment wetlands. Geum Environmental Consulting, Inc. designed the treatment wetlands and assisted with construction oversight of wetland grading and installation of the wetland plants.
Coleman Coulee is a natural drainage-way that also conveys irrigation return flows into Mission Creek, a tributary of the Flathead River. The Moiese Wasteway conveys irrigation return flows through a natural ephemeral drainage. Both Coleman Coulee and the Moiese Wasteway contribute sediment and nutrients into Mission Creek and ultimately the Flathead River. Phase I of the constructed wetland project in 2008 focused on treating flows from Coleman Coulee by creating approximately 5 acres of wetland. Phase II of the project in 2010 focused on treating flows from the Moiese Wasteway by creating approximately 11 acres of wetland.
In both project areas, wetland complexes were constructed by creating connected cells that fit the natural topography. Drop structures between wetland cells were constructed using bioengineering materials, and are intended to become partially vegetated over time.
A diverse mix of sedges, rushes, and bulrushes in the form of herbaceous plugs, prevegetated coir mats, and containerized plants; were installed throughout the wetland cells in both project areas to encourage quick establishment of dense wetland vegetation.
Once fully vegetated, these wetland cells will help filter and retain sediments and nutrients by slowing water velocities, thereby allowing sediments to drop out of the water, and increasing water retention time and evapotranspiration rates as water is routed through the series of wetland cells.
The Confederated Salish and Kootenai Tribes are monitoring water quality at both wetland sites. In addition to the expected improved water quality effects in the area, the wetlands are also providing habitat for migratory birds and waterfowl.