HR: 1340h
AN: H23G-1728 [WITHDRAWN]    [Abstracts]
TI: The Effect of Open-Framework Gravels in Hyporheic Braided River Sediments on Ground Water Flow Velocity
AU: * Engstrom, D
EM: dale.engstrom@umontana.edu
AF: Department of Geosciences, University of Montana, Missoula, MT 59812, United States
AU: Woessner, W W
EM: willim.woesner@umontana.edu
AF: Department of Geosciences, University of Montana, Missoula, MT 59812, United States
AU: Gannon, J
EM: jim.gannon@umontna.edu
AF: Division of Biological Science, University of Montana, MIssoula, MT 59812, United States
AB: Preserved networks of interconnected, clast-supported, large diameter pore spaces provide conduits for rapid ground water transport. These conduits are found within near-horizontal beds of coarse open-framework sediments naturally deposited and modified by braided rivers. The pore networks provide highly conductive pathways that dominate water flux in fluvial bars and bar complexes and become interconnected at scales of 10's to even 1000's of meters. They are here hypothesized to provide rapid flow through extensive hyporheic exchange networks in the braided river-flood plain setting. At two field sites in the Nyack floodplain in Montana, coarse, open-framework gravel beds have been determined to exist within braided river bar sediments, duplicating what others have found in other braided river settings. A number of small vertical-interval techniques were used to detect ground water velocities and hydraulic conductivities developed in closely-spaced wells along the flow-lines. Geophysical techniques, including borehole GPR and electrical resistivity tomography, are being used to image braided bar architecture for comparison with the hydrologic findings, and to extend the characterization of the sediments beyond the wells. The demonstrated integration of the geologic, geophysical and hydrologic results allows the detection of the link between sedimentological conditions and hyporheic exchange mechanisms in the braided river setting.
DE: 1820 Floodplain dynamics
DE: 1825 Geomorphology: fluvial (1625)
DE: 1830 Groundwater/surface water interaction
DE: 1835 Hydrogeophysics
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
SC: Hydrology [H]
MN: 2007 Fall Meeting