DEVELOPMENT OF A HILLSLOPE-EROSION-POTENTIAL INDEX FOR SEDIMENT TRANSPORT IN THE YUBA RIVER BASIN

As part of the Upper Yuba River Studies Program, the feasibility of introducing wild Chinook salmon and steelhead to the Yuba River above Englebright Dam near Marysville, Calif., is being investigated. The Yuba River Basin is heavily influenced by historical hydraulic mining, draining 3,480 km2 on the west slope of the Sierra Nevada. This investigation requires determining how sediment transport influences salmonid habitat in the upper basin, and habitat and flood risk in the reaches below the dam under various management scenarios that enable fish passage. A conceptual model was developed showing the erosional processes in this basin; a distributed parameter watershed model, Hydrological Simulations Program–Fortran (HSPF) is being used to quantify the conceptual model and to examine the influences of land use and climate on sediment transport within the basin and on sediment yield into Lake Englebright. An understanding of the contribution of hillslope erosion to total basin sediment movement is needed for the simulation of sediment transport. A spatially distributed index of hillslope erosion potential was developed using an evaluation of the relative contribution of various factors to the delivery of hillslope material < 2 mm in diameter to the channels. Factors considered were slope, geology, historical mine sites, mass erosion, streams, vegetation cover, a soil erodability index from the national soils database (STATSGO), modeled potential evapotranspiration, and road density. The relative influence of each factor was estimated on the basis of field observations, a mass erosion inventory, and aerial photos; the estimated influences were used to develop an equation in GIS to produce a map of erosion potential for model input. The distribution of the hillslope-erosion-potential index is consistent with field observations, reflecting the dominant features and processes that control erosion in this basin, and thus supports the conceptual model.