HR: 1330h
AN: H42E-1123    [PDF]
TI: Assessing Suspended-Sediment Transport Rates at the Regional Scale: Lake Tahoe Basin
AU: * Heins, A
EM: aheins@ars.usda.gov
AF: University of Nottingham, School of Geography, University Park,, Nottingham,, UK NG7 2RD United Kingdom
AU: Simon, A
EM: asimon@ars.usda.gov
AF: USDA-ARS National Sedimentation Laboratory, 598 McElroy Drive,, Oxford,, MS 38655 United States
AB: In recent years, suspended-sediment transport has received increased attention due to a greater emphasis being placed on water quality issues. Secchi-disk data has shown a trend of decreasing water clarity in Lake Tahoe over the past 35 years that can be partly attributed to delivery of fine sediment from channel and upland sources. In an effort to quantify the magnitude and sources of suspended sediment into Lake Tahoe, the USDA-ARS National Sedimentation Laboratory with support from the U.S. Army Corps of Engineers initiated a study to examine these issues. Historical flow and sediment-transport data from more than 30 gages were used to determine bulk suspended-sediment loads and yields for sites around the lake. Eighteen index stations were used to make comparisons between sediment production and delivery from individual watersheds and between different sides of the lake. Fine-grained sediment transport was determined for 20 sites based on relations derived from particle-size distributions across the range of measured flows. Suspended-sediment loads and yields vary over orders of magnitude from year to year, from west to east and north to south across the basin. Median annual suspended-sediment loads for index stations range from about 2200 tonnes/yr (T/y) from the Upper Truckee River to 3 T/y from Logan House Creek. Based on the historical data, the largest annual contributors of sediment are in decreasing order, Upper Truckee River (2200 T/y), Blackwood Creek (1930 T/y), Second Creek (1410 T/y), Trout Creek (1190 T/y), Third Creek (880 T/y) and Ward Creek (855 T/y). Data from Second and Third Creeks may be somewhat misleading though because of a short period of data collection in the case of the former, and the fact that data collection occurred during major construction activities and following storm-induced debris flows in these basins. Analysis of suspended-sediment transport ratings with longer periods of record show that sediment loads from northeastern streams have significantly decreased across the entire range of flows. Suspended-sediment yields were used to compare suspended-sediment contributions from different watersheds of varying size and location. Western and northern streams produce the highest yields. Sediment yields from northern streams have been decreasing since the early 1970's while those from the Upper Truckee River have also decreased albeit at a slower rate than in Third and Incline Creeks. In other parts of the basin, temporal trends of decreasing loads per unit area and unit water were subtler. No statistically significant trend of increasing suspended-sediment loads or yields was identified as reported recently by other workers. Fine-grained loads show a similar pattern as total loads with the greatest contributors being the Upper Truckee River (1010 T/y), Blackwood Creek (844 T/y), Trout Creek (462 T/y) and Ward Creek (412 T/y). In terms of fine-grained loadings per unit area, a slightly different picture emerges. Blackwood, Third, and Ward Creeks, all disturbed streams have the greatest fine-grained suspended-sediment yields at 21.5, 20.2, and 16.4 T/y/km2. In comparison, the Upper Truckee River produces 7.1 T/y/km2; General Creek, 2.8 T/y/km2; and Logan House Creek, 0.4 T/y/km2. Overall, the contribution of channel materials to sediment loads varies widely throughout the Lake Tahoe basin. Watersheds disturbed by human intervention produced orders of magnitude more sediment than stable, undisturbed watersheds. Undisturbed channels tend to have greater amounts of their sediment load emanating from upland areas.
DE: 1824 Geomorphology (1625)
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2003 Fall Meeting