HR: 10:20h
AN: H12B-01 INVITED     [Abstracts]
TI: Contaminant Transport Hydrology Of Surface/Ground Water Interactions
AU: * Medina, M A
EM: miguel.medina@duke.edu
AF: Duke University, Department of Civil and Environmental Engineering, Durham, NC 27708-0287 United States
AU: Kazezyilmaz-Alhan, C M
EM: cmk5@duke.edu
AF: Duke University, Department of Civil and Environmental Engineering, Durham, NC 27708-0287 United States
AU: Lin, Y
EM: yi.chang.lin@duke.edu
AF: University of Massachusetts, Department of Civil and Environmental Engineering, Amherst, MA 01003 United States
AB: The crucial role of surface/ground water interactions in determining contaminant concentration distributions both in streams and ground water has only recently been recognized. In particular, in pool and riffle or meandering types of streams, long tails and small peaks are observed in the stream tracer data, which reflects the influence of surface/subsurface flow on solute concentration. Bencala and Walters (1983) first presented a comprehensive transient storage model for streams to explain the effects of surface storage and the hyporheic zone in stream concentration. We complement these surface/subsurface modeling efforts by incorporating the transient storage zone in a conjunctive stream-aquifer model. The core of this conjunctive model is MODFLOW which computes the ground water flow in the aquifer, while DAFLOW computes unsteady stream flow with diffusion wave routing technique and MOC3D computes the solute transport in ground water. In addition, an explicit finite difference package for solute transport in streams is developed, which solves one-dimensional transient storage equations. Results show that the conjunctive stream-aquifer model with transient storage can handle well the bank storage effect under a flooding event. The application of the model over a stream network shows that the stream-aquifer interaction acts as a strong source or sink along the stream. The existing transient storage model lumps the surface storage and hyporheic zone together in a single storage zone. Therefore, in order to further improve it, we develop a model that represents the movement of water through the hyporheic zone in order to explain the physics of water exchange between the surface water and the porous media in a mechanistic manner. For this purpose, we include the advection and dispersion processes into the transient storage zone, and we consider the hyporheic zone as a transient porous media from surface water to ground water. A new parameter, storage thickness, is introduced to represent the interface between the hyporheic zone and the channel, through which the water exchange takes place. This improved model not only includes the surface/subsurface water interaction directly through transient storage, but also represents the movement of stream water through the porous media with the advection and dispersion terms in the storage zone equation. We apply this new model to a hypothetical problem, and we also simulate the Uvas Creek experiment, comparing our results to observations reported by Bencala and Walters (1983).
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting