Geospatial Inventory and Assessment of Sediment from Unpaved Roads
Doyle L. Crosswhite, The Nature Conservancy; Ethan Inlander, The Nature Conservancy, and Matt Van Eps, Watershed Conservation Resource Center
Abstract:
The Kings River watershed, in Northwest Arkansas, is uniquely diverse both geographically and ecologically and is the last unimpounded tributary of the White River hosting thirty endemic species. Sedimentation is a principal stressor and unpaved roads are a significant source of suspended sediment in the Kings River watershed. Sedimentation impacts aquatic habitats by filling interstitial spaces of gravel stream beds, interfering with the gills and suffocating eggs of fish, amphibians, and benthic insects.
We evaluated 60.6 miles of unpaved roads within the 54 mi2 Dry Fork Creek, a subwatershed of the Kings. Road density was 1.1 mi/mi2. We developed a GIS/GPS based inventory of road conditions and estimated sediment loads entering streams using the U.S. Forest Service Water Erosion Prediction Project (WEPP) road model.
Our inventory was used to develop plans for improving unpaved roads and reducing sediment delivery to streams. We collected GIS line features such as surface substrate type and ditch conditions, and point features like bridge locations, culverts, and cross-drains.
The annual sediment load entering the stream network from the erosion of publicly owned, unpaved roads for the Dry Fork Creek watershed was estimated to be 1,089 tons. The estimated sediment loading ratio from public unpaved roads is 20 ton/mi2 for the Dry Fork Creek watershed.
These results were used to prioritize the worst road segments for remediation. We held a training workshop for county road crews to demonstrate BMPs at priority sites.
Keywords: erosion, sediment, roads, watershed, GIS, GPS
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