HR: 08:45h
AN: H41G-04    [Abstracts]
TI: Relations Between Sediment Transport and Storage During Aggradation and Degradation in a Gravel Bed River
AU: * Smith, B J
EM: bsmith8@interchange.ubc.ca
AF: USDA Forest Service, Pacific Southwest Research Station, 1700 Bayview Dr., Arcata, CA 95521 United States
AU: * Smith, B J
EM: bsmith8@interchange.ubc.ca
AF: Humboldt State University, 1 Harpst St, Arcata, CA 95521 United States
AU: Lisle, T E
EM: tel7001@humboldt.edu
AF: USDA Forest Service, Pacific Southwest Research Station, 1700 Bayview Dr., Arcata, CA 95521 United States
AU: Hilton, S
EM: shilton@fs.fed.us
AF: USDA Forest Service, Pacific Southwest Research Station, 1700 Bayview Dr., Arcata, CA 95521 United States
AU: Sutherland, D G
EM: dsutherland@fs.fed.us
AF: USDA Forest Service, Pacific Southwest Research Station, 1700 Bayview Dr., Arcata, CA 95521 United States
AB: Sediment routing models typically transfer sediment through a channel network using fixed values of transport capacity. However, transport capacity is dynamic at the sediment pulse time scale. The purpose of this research is to develop relations between transport capacity and volume of sediment in storage (transport-storage or T-S relation) that would replace fixed values of transport capacity applied to channel segments within sediment routing models. The form and stability of T-S relations were studied in a series of flume experiments and compared to a T-S relation observed in a single reach (1 km) in a steep (3%) gravel-bed river in northern California. Flume experiments were designed to simulate cycles of aggradation and degradation, similar to those documented at the field site. T-S relations for full cycles of aggradation and degradation showed hysteresis. For a given storage volume, higher output rates were observed during channel degradation than aggradation due to opposite longitudinal trends in transport and changes in bed texture that increased bed mobility during early stages of degradation before armoring intensified. The stability of T-S relation was examined by conducting flume experiments with variations in sediment feed, initial channel armor development, adjustment to sediment supply before and after equilibrium was reached, and sequential episodes of aggradation and degradation. Results of these experiments showed that the T-S relation during aggradation is stable and is not sensitive to initial channel armor or equilibrium status. In contrast, the form of the T-S relation during degradation is sensitive to sediment feed rate during degradation and whether equilibrium was reached before sediment feed was reduced and degradation began. Transport rates during channel degradation were correlated with local stored sediment volume and a reach scale measure of the concentration of finer particles on the bed surface. Multiple aggradation-degradation cycles increased residual storage volume, but did not affect the slope of T-S relations. Results from these flume experiments were used to constrain the form of the T-S relation developed from limited field data. Collectively, this set of flume experiments provides insight into the form of a T-S relation under full aggradation-degradation cycles within a single reach, as well as the application of T-S relations to a drainage network.
DE: 4558 Sediment transport
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting