HR: 16:30h
AN: H24F-03    [Abstracts]
TI: Ground Water / Surface Water Exchange: Streambed Versus a Channel Bar
AU: * Shope, C L
EM: chris.shope@dri.edu
AF: University of Nevada, Reno Desert Research Institute, Div. of Hydrologic Sciences 2215 Raggio Parkway, Reno, NV 89512, United States
AU: Constantz, J E
EM: jconstan@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Cooper, C A
EM: clay.cooper@dri.edu
AF: Desert Research Institute, Div. of Hydrologic Sciences 2215 Raggio Parkway, Reno, NV 89512, United States
AU: McKay, W A
EM: alan.mckay@dri.edu
AF: Desert Research Institute, Div. of Hydrologic Sciences 2215 Raggio Parkway, Reno, NV 89512, United States
AB: The streambed is important in controlling exchange of water, solutes, and heat between streams and ground water. Processes such as sedimentation, erosion, and fluctuations in diurnal temperatures can have significant effects on the streambed hydraulic conductivity, which in turn affects fluid velocities across the streambed. The objectives of this study are to quantify the difference in flux magnitude and direction within and around a channel bar. The focus of this presentation is to compare fluxes in channel bar sediments with fluxes in the streambed to determine the effect of the upper boundary conditions on sediment fluxes. A network of piezometers was installed on and around a channel bar located within the Truckee River, a dense 6th order river network, located primarily in northwest Nevada. Instruments used were temperature loggers, pressure transducers, and stage recorders. Several methods were simultaneously utilized to quantify water and heat fluxes and to interpret the hydrodynamic processes through the streambed sediments. Numerical simulations are being completed to quantify the spatial and temporal fluid flux and heat transport in relation to varied hydraulic parameters such as variable river stage, geometry, and hydraulic conductivity. In general, we have found that surface water exchange to the streambed occurs at the upstream portion of bed features and streambed discharge dominates at the downstream bed feature. This exchange is evidenced at the channel bar as well as localized riffles and point bars adjacent to the channel bar. We found that at least two separate hydraulic conditions are evident during our study. The range in water levels between the piezometers was altered from approximately 1.25 m to a minimum of 0.10 m and the mean potentiometric surface increased by 1 m. These variations are geomorphic responses due to a flood event, inundating the channel bar, and a channel restoration project both upstream and downstream of the study area. These alterations have caused a reversal in the vertical head gradient (VHG) in some locations by up to 0.14. There also appears to be a critical stage height that alters the flux direction or magnitude. In conclusion, stage boundary conditions coupled with streambed features significantly contribute to the exchange direction. Sedimentation and erosion from restoration activities and streambed evolution also impacted fluid flux patterns due to their impact on streambed surface hydraulic conductivity patterns.
DE: 0483 Riparian systems (0744, 1856)
DE: 1825 Geomorphology: fluvial (1625)
DE: 1830 Groundwater/surface water interaction
DE: 1878 Water/energy interactions (0495)
SC: Hydrology [H]
MN: 2007 Fall Meeting