USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Tahoe Stormwater Particle Assessment and Management for Urban and Roadway Runoff

Principal Investigators:
Alan Heyvaert and Jim Thomas, Desert Research Institute
John Reuter, University of California, Davis

Proposal [pdf]

Final Report [pdf]

Project Summary

Lake Tahoe has long been renowned for its exceptional clarity, which decreased over time with development and urbanization in the basin (Goldman 1988). Although urban areas in the Tahoe Basin occupy a relatively small amount of the total watershed, they contribute a substantial portion of pollutant loadings that have caused clarity loss in the lake. It is estimated that 72% of the total loading for fine sediment particles (FSP) derive from urban areas, while 38% of total phosphorus and 16% of total nitrogen derive from this same source (LRWQCB and NDEP, 2011). Since fine particles (<16 µm) and nutrients both contribute to clarity reductions in Lake Tahoe (Jassby et al., 1999; Swift et al., 2006), these are the focus of current pollutant reduction strategies, with an emphasis on reduction in FSP loading (LRWQCB and NDEP, 2008). However, the characterization of these particles in relation to other water quality parameters and in relation to effective methods for particle removal in stormwater runoff from roadways and urban areas are not well understood. Evaluating processes responsible for FSP and nutrient removal will allow these factors to be considered in the design of erosion control projects and BMPs to help reduce fine sediment and nutrient loading to Lake Tahoe.

Overall BMP effectiveness in the Lake Tahoe Basin has been reviewed and synthesized in a number of documents (e.g., Reuter and Miller 2000, Reuter et al. 2001, Strecker et al. 2005, 2NDNATURE 2006). Although some BMPs have been extensively monitored for their performance in the Lake Tahoe Basin, these studies tend to be the exception. In particular, the fine sediment particles (<16 µm) that significantly affect lake water clarity have not been well studied, and a better understanding is needed of their characteristics and of the processes involved in fine sediment removal with typical treatment methods. Even at the national level, information on how these fine soil particles in stormwater runoff are trapped and processed in BMPs is largely unavailable (International Stormwater BMP Database). The success of both the Lake Tahoe TMDL and the Tahoe Environmental Improvement Program (EIP) will depend upon a more detailed understanding of the transport and fate of these fine particles within BMPs for effective water quality planning, prioritization for new BMP installations, quantification of BMP effectiveness, and for general BMP design, operation and maintenance.

Given the significant expected cost associated with nutrient and FSP load reductions needed in the Tahoe Basin, and the fact that this effort will occur over a decadal timeframe (Lahontan and NDEP 2008), it is relevant to examine the characteristics of urban runoff water treatment associated with fine sediment particles and other important water quality characteristics, such as turbidity, total and size fractionated suspended solids and phosphorus loading. This information will be needed for improved management models and to determine the effectiveness of fine sediment removal by processes and unit operations that target this removal in different types of BMPs.