Truckee River basin assessment: Sediment source analysis in support of TMDL delineation

In accordance with Section 303(d) of the Clean Water Act, the Lahontan Regional Water Quality Control Board (LRWQCB) of the California Department of Environmental Protection has ascertained that the Truckee River and a number of its tributaries in California are water quality limited for sediment, nutrients, total dissolved solids and chloride. The water quality of the river system has been impacted by a variety of sources, including forest management, urban and recreational development, hydromodification and other alterations of wetland and fisheries habitat. The Desert Research Institute is actively conducting research to investigate the cumulative effects of management activities to watershed and channel conditions of the Truckee River basin. To determine chronic sediment sources, the study features aerial photographic analyses and utilization of a spatially-distributed. GIS-based model complemented by a field monitoring network. Analyzing and comparing historical and recent air photos allows for a gross estimation of the magnitude and rate of sediment discharges from sub-watersheds stemming from both natural and anthropogenic influences. Estimation of runoff and sediment from landscape units within sub-watersheds is accomplished through use of the Annual Agricultural Nonpoint Source (AnnAGNPS) model. Input to the model includes land use, topography and slope, soil type, vegetation type and density, and climate data; these parameters allow for estimation of actual and projected sediment loads within the basin. Field monitoring of suspended sediment conducted during the period of snowmelt runoff serve as a validation tool for the model. Results from the analyses facilitate the prioritization of restoration needs within the basin.