Skip to main content
ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #210505
Title: Fine-Sediment Loadings to Lake Tahoe

Author
item Simon, Andrew

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2007
Publication Date: 6/1/2008
Citation: Simon, A. 2008. Fine-Sediment Loadings to Lake Tahoe. Journal of the American Water Resources Association, 44(3): 618-639.

Interpretive Summary: Fine-sediment entering Lake Tahoe from surrounding watersheds is the leading cause of a 35-year trend of decreasing water clarity. In an effort to quantify and ultimately control the delivery of this material to the lake, it was first necessary to determine total fine-sediment loadings as well as the contributions from channel sources. Data needed to be in the format of numbers of particle as opposed to tonnes so that results could be used by scientists at the University of California, Davis to simulate changes in lake clarity. Historical flow and sediment-transport data from a number of gauging stations and recent samples of flow and sediment concentrations measured in numbers of particles were combined with extensive evaluations of channel-stability conditions to provide basinwide estimates of fine-sediment loadings to the lake. An average, annual estimate of fine-sediment (<0.063 mm) loadings to the lake of 5,206 T/y was calculated. A total of 7.79E+19 particles in the 5-20 u m fraction were calculated to enter Lake Tahoe in an average year with the Upper Truckee River accounting for almost 25% of the total. An average, annual fine-sediment loading from streambank erosion of 1,305 T/y was calculated. This represents about 25% of the average, annual fine-sediment load delivered to the lake from all sources.

Technical Abstract: Over the past 35 years, a trend of decreasing water clarity has been documented in Lake Tahoe, attributable in part to the delivery of fine-grained sediments emanating from upland and channel sources. The overall objective of the research reported here was to determine the amount of fine sediment delivered to Lake Tahoe from each of the 63 contributing watersheds. The greatest contributors of fine sediment happened to be those with measured data, not requiring extrapolation. In descending order they are: Upper Truckee River (1010 T/y), Blackwood Creek (846 T/y), Trout Creek (462 T/y) and Ward Creek (412 T/y). Summing estimated values from the contributing watersheds, provided an average, annual estimate of fine-sediment (<0.063 mm) loadings to the lake of 5,206 T/y. A total of 7.79E+19 particles in the 5-20 u m fraction were calculated to enter Lake Tahoe in an average year with the Upper Truckee River accounting for almost 25% of the total. Contribution of fine sediment from streambank erosion were estimated by developing empirical relations between measured or simulated bank-erosion rates with a field-based measure of the extent of bank instability along given streams. An average, annual fine-sediment loading from streambank erosion of 1,305 T/y was calculated. This represents about 25% of the average, annual fine-sediment load delivered to the lake from all sources. The two largest contributors, the Upper Truckee River (639 T/y) and Blackwood Creek (431 T/y), account for slightly more than 80% of all fines emanating from streambanks, representing about 20% of fine sediment delivered to Lake Tahoe from all sources.