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Lackey, Gregory D ¹ ; Neupauer, Roseanna M ² ; Pitlick, John ³

¹ Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado
² Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado
³ Department of Geography, University of Colorado, Boulder, Colorado

Extracting groundwater from an aquifer has the potential to reduce the flow rate of a hydraulically connected stream or river. This phenomenon is known as stream depletion and it occurs as a result of artificially lowered hydraulic head in an aquifer underlying a stream. In water scarce regions of the United States, pumping wells causing stream depletion can potentially endanger aquatic habitats and infringe on neighboring water rights. These factors have made the accurate modeling of stream depletion an important step in the process of siting new groundwater wells. Stream depletion estimations depend heavily on appropriate parameterization of the modeled aquifer and streambed hydraulic properties. Many studies have estimated stream depletion using numerical models, however, streambed conductance, the ease by which water can travel through the streambed, is often assumed or calibrated for. This assumption of a homogeneous stream channel is not accurate for a true system. Flow patterns in a stream deposit an assortment of sediments inconsistently across the streambed. These geomorphological influences result in stream channel conductance values that are highly variable along the length of the stream channel. In this work, we investigate how stream depletion estimations are impacted by spatially-variable streambed conductance. Natural patterns of streambed heterogeneity are investigated by varying the stream channel conductance along the flow axis. Regions of relatively high and low conductance values were modeled along the straight and bent sections of the stream, respectively. It was found that variations of streambed conductance along the stream channel impacted stream depletion estimations to a significant degree. Therefore, if the goal of a model is to determine the optimal placement of a pumping well in an aquifer to minimize its effect on the stream, the modeler should account for heterogeneous streambed conductance because these variations will alter favorable well locations. The numerical simulations show that accounting for the natural variations of streambed conductance will be necessary in order to develop an accurate model of a stream-aquifer system.