HR: 1340h
AN: H53C-1257    [Abstracts]
TI: Modeling pool response to sediment pulses
AU: * Harrison, L R
EM: lharrison@umail.ucsb.edu
AU: Keller, E A
EM: keller@geol.ucsb.ed
AB: Distinct sediment pulses following wildfires, landslides and releases from dam reservoirs exert a strong influence on channel morphology. Recent theoretical, experimental and field studies have found that large sediment inputs are often transported as a single pulse that is either translated or dispersed, depending on the grain size of the ambient bed material and the pulse itself. Our ability to route the sediment pulse down the channel requires an understanding of the dominant transport mechanism (translation, dispersion) as well as the reach-scale patterns of erosion and deposition due to pools, bars and riffles. The goal of this work was to determine the processes involved in reach-scale channel adjustment following a pulse of sand over a coarse bed, using detailed measurements of three-dimensional flow and sediment transport patterns. We designed experiments on flume channels at the Sierra Nevada Aquatic Research Laboratory that included alternate pool-riffle sequences, thus greatly improving our approximation of natural conditions. Results found substantial translation as well as dispersion of the topographic high point of the pulse. On a reach-scale the patterns of erosion and deposition closely follow the hydraulics. The pulse was transported through the riffles and the bar-pool topography showed the most significant channel change. As the pulse was mobilized, the pool thalweg was reestablished and significant lateral dispersion occurred, resulting in substantial bar growth in areas of flow separation. The bars became relatively stable zones of sediment storage within the channel that did not undergo subsequent erosion, while the pool head, center and tail were gradually eroded to ambient conditions. These experimental results will be used to evaluate current theoretical models and develop a process-based understanding of pool response to sediment pulses. Findings from this work will significantly improve our ability to include reach-scale patterns of erosion and deposition when routing sediment pulses through river systems.
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1886 Weathering (1625)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting