Erosion Analysis of the Road Network In the Lake Tahoe West Collaborative Restoration Project

The Lake Tahoe West Collaborative Restoration Project study area contains 181 km or roads, 33.5 km of which are paved. Many of the unpaved roads are closed and covered with vegetation. An analysis of road surface erosion and sediment delivery using GIS topographic tools and the Water Erosion Prediction Project WEPP:Road Batch interface estimated that the current road network was delivering 55 Mg of sediment per year. Closing unpaved roads that are currently trafficked will reduce erosion by 20 percent. Traffic supporting thinning operations will on the average, increase sediment delivery by 19 times on those road segments used for access, for the years in which the thinning operations are active. However, following active use for harvest, those estimated loads would rapidly return to the current values. Consequently, the increased sediment delivery associated with harvesting operations could be approximated by multiplying the estimated delivery by the fraction of time that the roads are actually used for harvest (for example, if the roads are likely to be opened for harvest 2 years out of 20, then the increase might double current loads from those road segments). These calculations do not account for potential sediment reduction benefits for harvest because of reduced impacts from wildfires, nor the reduction in erosion following wildfire because of the potential deposition of eroded sediments on the road surface. Furthermore, it is important to note that the sediment from the Lake Tahoe West road network is estimated to be less than 1% of that from the hillslopes.