HR: 0800h
AN: H51E-0811    [Abstracts]
TI: Trapping of fine-grained sediment in a gravel-bed river by large woody debris: a physical modeling study
AU: * Skalak, K J
EM: kskalak@udel.edu
AF: University of Delaware, Department of Geological Sciences, Newark, DE 19716, United States
AU: Wilcock, P
EM: wilcock@jhu.edu
AF: Johns Hopkins University, Dept. of Geography & Environmental Engineering, Baltimore, MD 21218, United States
AU: Pizzuto, J
EM: pizzuto@udel.edu
AF: University of Delaware, Department of Geological Sciences, Newark, DE 19716, United States
AB: We used a physical model to investigate the processes of erosion, transport, and storage of fine-grained sediment in a gravel-bed river with abundant large woody debris (LWD) accumulations. Fine-grained sediment storage specifically refers to deposits of mud and sand located in the channel margins and near-bank regions. We have termed these fine-grained channel margin (FGCM) deposits. Extensive field surveys of the study area indicate that these near-bank deposits are principally controlled by the presence of LWD, which obstructs a portion of the main flow and creates regions of reduced velocity, allowing for the deposition of mud and sand. The specific experimental question we addressed in these experiments is: what is the behavior of water and sediment behind a porous obstruction in the nearbank region of an open channel? We focused on the relative roles of discharge, slope, suspended sediment concentration, and the configuration of the LWD, which are the primary variables controlling the quantity and distribution of fine sediment in the study area. We conducted several types of experiments: 1) a series of experiments to define sediment transport behavior in the absence of simulated LWD in a straight, prismatic channel, 2) experiments to explore most favorable configuration of simulated LWD that conform to field observations, 3) experiments to investigate the formations and geometry of the deposit as controlled by sediment supply with constant discharge and LWD, and 4) a series to investigate the erosion and deposition of the features after they have been formed. We developed quantitative, predictive relationships between the volume of mud stored and the governing variables (i.e. hydraulics, sediment supply, and characteristics of the LWD).
DE: 1800 HYDROLOGY
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1825 Geomorphology: fluvial (1625)
DE: 1847 Modeling
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting