HR: 11:50h
AN: H12B-07    [Abstracts]
TI: Systematic Groundwater/Stream Interactions Resulting From Regional Hydrogeologic Change
AU: * Urbano, L D
EM: lurbano@memphis.edu
AF: University of Memphis, Department of Earth Sciences, Memphis, TN 38152 United States
AU: Waldron, B
EM: bwaldron@memphis.edu
AF: University of Memphis, Ground Water Institute, Memphis, TN 38152 United States
AB: The analysis of groundwater/stream (gw/sw) interactions requires a clear understanding of the underlying hydrogeology. While much research has investigated the affects of more accessible hyporheic zone, there are still many unknowns regarding the influence of regional-scale gw/sw interactions on local hyporheic exchange fluxes. In an effort to isolate the effects of the regional hydrogeology we investigate gw/sw interactions at the edges of subcropping confining units, where unconfined aquifers transition confined conditions, using theoretical numerical modeling. The models predict substantial fluctuations in groundwater discharge to the streams in these regions. The predicted groundwater discharge patterns are tested by detailed downstream measurements of stream flow in the Loosahatchie River, TN, which traverses the gently dipping, confining unit subcrops of the eastern flank of the Mississippi Embayment. The theoretical model predicts two distinct zones of groundwater discharge fluctuation relative to the location of the subcrop. The first zone, immediately upstream of the subcrop, shows increasing groundwater discharge to the already gaining stream. In the second zone, immediately downstream of the subcrop, groundwater discharge to the stream drops abruptly to near zero, but the stream remains gaining. Downstream of this, the groundwater discharge begins to recover till it approaches its original rate. Measurements from the Loosahatchie River were taken during a period of low flow when flow in the stream was dominated by groundwater. They confirm the discharge increase in the upstream zone, and show a decrease in discharge in the second zone, but, much greater than the one predicted by the models; the stream becomes a loosing stream in this reach. This discrepancy is likely due to the simplified stream representation (a constant head boundary) in the models. The models and measurements show a clear region of significantly and systematically fluctuating gw/sw interactions that can serve as a laboratory for future research into the importance of hydrogeology on stream flow and geomorphology.
DE: 1829 Groundwater hydrology
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting