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Aaron Prussian, US Forest Service, aaronprussian@fs.fed.us (Presenter)
Ashley McFarland, University of Idaho Extension, amcfarland@uidaho.edu
Kajsa Stromberg, Idaho Department of Environmental Quality, Kajsa.Stromberg@deq.idaho.gov

 

Forest roads are often identified as contributing to impaired water quality in mountainous watersheds because of their ability to capture and redirect hillslope flow and deliver sediment to streams. As such, management agencies often treat all roads and stream crossings as equally influential on streams. However, the effects of forest roads on water quality and patterns of sediment delivery may be variable and not well understood in many cases. In 2010, the GRAIP model was used to evaluate 60% of the forest roads in a Coeur d’ Alene River tributary that does not meet water quality standards for sediment. Only 10% of the surveyed roads delivered sediment to streams and sediment delivery occurred through 6% of drainage features. Two types of drainage features delivered three-quarters of the sediment contribution from roads: non-engineered features and stream crossing culverts. One third of the stream crossing culverts were direct conduits of water and sediment from roads into streams. One-quarter of surveyed culverts were also found to substantially increase the risk of catastrophic failure and sedimentation, while another quarter was found to block fisheries migration. Roads also extended the stream channel network by over 10% by capturing and redirecting water into new flowpaths. Our results suggest the connection between roads and streams is highly variable and localized, and highlights the need to use more advanced techniques designed to specifically identify the interactions of roads and streams. Finally, these techniques can be used to efficiently plan and implement projects to reduce sediment loads in streams.