Quantification of Stream Depletion Due to Aquifer Pumping Using Adjoint Methodology: A Case Study

摘要

Water availability for humans and the environment faces increasing threats from expanding populations and potential reduction in supply due to changes in climactic patterns. In light of these threats, the need to minimize stream depletion, defined as the depletion of flows in streams and rivers caused by groundwater pumping, becomes paramount. Stream depletion associated with pumping wells has been quantified by both analytical and numerical approaches; however, methods for identifying the stream depletion caused by new wells remain inefficient and require separate simulations for each potential well location. In this work, we develop adjoint equations of a coupled groundwater and surface water system that can be solved to calculate stream depletion. We use MODFLOW with the stream package to solve the adjoint equations, and, unlike previous work, we allow the head and resulting flow in the river to change as a result of depletion. With only one simulation of the adjoint equations, stream depletion can be calculated for a well at any location in the aquifer, making it an efficient method for siting future wells. A case study is presented comparing the stream depletion calculated using adjoint methodology with that found using traditional methods.