Lab 4 – Watershed Crossings Assessment
Forest roads potentially impact freshwater fish habitat through the rerouting of water, the triggering of shallow rapid landslides, and the delivery of fine sediments to the stream. Fine sediments can wash down from forest road impacted streams into fish spawning streams and clog up the coarser spawning ground substrates, severely impacting the survival of incubating fish. Additionally, fine sediments can fill in fish habitat rearing pools, resulting in shallower depths, higher water temperatures and less habitat area for juvenile rearing in the summer. The impacts make forest roads a potential factor limiting fish production throughout the Pacific Northwest.
Forest road density and fish stream crossing density are two metrics that can serve as proxies of the potential for forest roads to impact streams. There is more fine sediment produced as road densities increase and there is a higher probability of road sediment entering streams as road/stream crossings increase.
In this lab I completed a GIS assessment of potential forest road conditions in the Stillaguamish River watershed, sub-watersheds, and catchments. Specifically, I will calculated road density as miles of forest road per square miles of area for watershed, sub-watersheds and catchments, and I calculated road crossing density as number of road crossings per miles of fish bearing streams within a watershed, sub-watersheds and catchments. Upon completion I created an ArcGIS Story Map to tell the story of my GIS Assessment of potential forest road impacts in the Stillaguamish watershed.