Effects of Varying Stream Channel Conductance on Siting New Pumping Wells in an Aquifer

In regions of the world where growing population and changing climates are threatening water supplies, accurate modeling of potential human impacts on water resources is becoming more important. Stream depletion, the reduction of surface water flow due to the extraction of groundwater from a hydraulically connected aquifer, is a direct way that development can alter water availability. Thus, the accurate modeling of stream depletion is an important step in siting new groundwater wells. Proper estimation of stream depletion requires appropriate parameterization of aquifer and streambed hydraulic properties. Although many studies have conducted numerical investigations to determine stream depletion at specific sites, they typically do not use measured streambed hydraulic conductivity (K3), but rather assume a representative value. These assumptions are inaccurate for natural systems because Kr varies spatially along the stream channel. In this work, we investigate how stream depletion is affected by spatially-variable conductance, given by C = wKr/br, where C is conductance, w is the width of the stream, Kr is the streambed hydraulic conductivity, and br is the thickness of the streambed. The conductance of the model stream channel is varied along the flow axis with regions of relatively high conductance along the straight sections and regions of relatively low conductance along the bent sections. This was done to better represent the conductance patterns in a natural system. It was found that altering the value of conductance along the stream channel can affect stream depletion estimations to a significant degree. For example, if attempting to determine the optimal placement of a pumping well in an aquifer to minimize its effect on the stream, modeling stream depletion with conductance values that vary along the stream channel will alter favorable well locations. The numerical simulations show that in situations such as the one described, accounting for the natural variations of conductance will be necessary to develop an accurate model of a stream-aquifer system.