ANALYTICAL MODEL FOR SATURATEDlUNSATURATED HYPORHEIC ZONE FLOW DUE TO ALLUVIAL WELL DEPLETIONS

ABSTRACT: Water exchange between a stream and an underlying aquifer is an important groundwater/surface water interaction. Pumping from groundwater resources that are hydraulically interactive with adjacent streams induces a water flux from the stream to the aquifer. Analytical and numerical models for pumping wells hydraulically interacting with partially penetrating streams assume continuous hydraulic connection and saturated flow between the stream and aquifer, specifying the stream as a constant head boundary. However, pumping next to a stream may cause part of the area between the streambed and aquifer to become unsaturated, and the flux from the stream to the underlying aquifer then becomes constant. This research presents an analytical solution for drawdown and stream depletion that accounts for unsaturated flow. The effect of unsaturated flow on the total flux from surface water to groundwater will be investigated using the proposed analytical solution. KEY TERMS: stream/aquifer interaction; hyporheic zone; unsaturated flow; drawdown; stream depletion