HR: 08:30h
AN: H51H-03    [Abstracts]
TI: Prediction of Sediment Transport and Patch Dynamics in a Steep, Rough Stream
AU: * Yager, E
EM: yager@seismo.berkeley.edu
AF: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720
AU: Dietrich, W E
H51H-03 AF: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720
AU: Kirchner, J W
H51H-03 AF: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720
AU: McArdell, B W
H51H-03 AF: Natural Hazards Group, WSL Swiss Federal Research Institute, Birmensdorf, CH-8903 Switzerland
AB: Steep streams (gradients of 3-20%) comprise a large portion of mountainous drainage networks. However, flow and sediment transport in these channels are highly variable processes that are poorly understood. Large, relatively immobile grains cause spatial fluctuations in the flow and the transport of finer, more mobile sediment. In addition, the local availability of the more mobile grains may be limited due to a stochastic sediment supply. Most transport equations do not include such variability and therefore over-predict flux in steep streams by several orders of magnitude. Thus, it is currently difficult to determine the effects of flow and sediment supply on steep-channel morphology such as grain-size patches and steps. The response, in size and composition, of more mobile patches to changes in sediment flux is relatively unknown. We previously developed a transport equation that that accounts for the stress borne by large, relatively immobile grains and the limited availability of the more mobile sediment. Our transport equation generally predicted flux to within an order of magnitude when tested in a steep, laboratory flume. To further test our theory, we measured flow (discharge, depth, and velocity), and bed properties in the Erlenbach torrent (gradient of 10%) in Switzerland. Here, calibrated hydrophones (acoustic sensors) record bedload transport rates at minute intervals. We also installed tracer particles that ranged in size from 11 to 128 mm. We surveyed tracer positions after six events and measured changes in the thickness and area of grain-size patches after four events. The mobile particle size increased with flow and although the largest event mobilized all tracer sizes, the boulder steps remained in place. Gravel and cobble patches were dynamic and exchanged sediment with upstream sources. Patch extent (area and thickness), however, remained relatively constant with flow and sediment flux. Thus, for moderate events, patches may be in equilibrium with the current step morphology, flow and sediment supply. We use this unique dataset to test and modify our sediment transport equation for field conditions.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1847 Modeling
DE: 1856 River channels (0483, 0744)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: Fall Meeting 2005