HR: 14:25h
AN: H23G-04    [Abstracts]
TI: Modeling Hyporheic Flux Along a Second-Order Semi-arid Stream: Red Canyon Creek, Wyoming
AU: * Lautz, L K
EM: lklautz@syr.edu
AF: Dept. of Earth Sciences, Syracuse University, Syracuse, NY 13244 United States
AU: Siegel, D I
EM: disiegel@syr.edu
AF: Dept. of Earth Sciences, Syracuse University, Syracuse, NY 13244 United States
AB: Models of near-stream hyporheic exchange flows are difficult to prepare because geomorphic stream features and adjacent subsurface characteristics both affect groundwater-surface water interaction. Inverse models of the results of in-stream tracer tests characterize net short time-scale hyporheic exchange along reaches, but not the actual physical processes driving the exchange. In contrast, numerical groundwater flow models simulate near-stream and hyporheic flow driven by hydraulic gradients from a physical process perspective. In this paper, we present a three-dimensional MODFLOW model of hyporheic exchange along a lower riparian reach of Red Canyon Creek, Wyoming. We calibrated the model results to hydraulic head measurements from $>$ 30 monitoring wells, piezometers, in-stream mini-piezometers, and to changes in stream discharge measured by in-stream tracer tests. We also simulated hyporheic flow paths with MODPATH (a particle-tracking package), from which we obtained residence times of water parcels in the hyporheic zone. Hydraulic gradients around in-stream flow obstructions, such as beaver dams, and through meander bends, cause most near-stream hyporheic exchange (residence time $<$30 days). Hyporheic residence times $<$10 days occur only along flow paths around beaver dams. We also simulated stream solutes moving into the subsurface with MT3D, a solute transport package, and operationally defined the hyporheic zone as places where solute concentrations were equal to or greater than 10% of the stream water concentration after a 10-day model simulation. The results of this modeling agreed with MODPATH; solutes move both horizontally and vertically from streams into the subsurface behind debris dams, which create hydraulic steps in the subsurface and surface flow systems.
DE: 1824 Geomorphology (1625)
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting