HR: 0800h
AN: H51E-0416    [Abstracts]
TI: Road Sediment Production and Delivery in the Southern Sierra Nevada, California
AU: * Korte, A
EM: amkorte@cnr.colostate.edu
AF: Department of Forest, Rangeland and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523-1472 United States
AU: MacDonald, L H
EM: leemac@cnr.colostate.edu
AF: Department of Forest, Rangeland and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523-1472 United States
AB: Unpaved roads are a major source of sediment in many forested watersheds, but there are relatively few data on road sediment production rates and even fewer data on the delivery of road-related sediment to the stream network. The primary goals of this study are to: (1) quantify sediment production rates from different road surfaces; (2) determine the key controls on road sediment production rates; and (3) quantify the extent to which roads are connected to the stream channel network. The study is part of the Kings River Experimental Watershed study (KREW) in the southern Sierra Nevada Mountains in east-central California. Elevations range from 1485 m to 2420 m, and most of the precipitation falls as snow. Sediment production was measured with sediment fences from 36 road segments and 9 undisturbed swales over the 2003-2004 wet season, and from 41 road segments and 18 undisturbed swales over the 2004-2005 wet season. The road segments are stratified into native-surface roads, ditches adjacent to paved roads, gravel roads, and mixed-surface roads. A detailed survey on 13 km of roads has identified and characterized individual road segments, and the connectivity of each segment to the stream network. Precipitation for the 2003-2004 wet season was 700 mm or 70% of the long-term mean. Native surface roads had the highest mean sediment production rate at 0.44 kg m-2, while the mixed-surface roads averaged 0.10 kg m-2 and the gravel roads generated only 0.06 kg m-2. No sediment was produced from the ditches adjacent to the paved roads or the undisturbed hillslopes. In the second wet season precipitation was well above average and the initial results indicate that sediment production rates were 2-4 times higher than in the first wet season. The preliminary analysis of the road survey data indicate that 54% of the road segments had either no sediment plume or a plume less than 20 m in length. Thirty-three percent of the road segments had sediment plumes longer than 20 m but did not connect to a stream channel; only 13% of the road segments had plumes that extended to within 10 m of a stream channel. The results indicate that native-surface roads are an important and highly variable sediment source, but much of this sediment is unlikely to reach the stream network.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1815 Erosion
DE: 1826 Geomorphology: hillslope (1625)
DE: 1834 Human impacts
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: Fall Meeting 2005