Drawdown and stream depletion produced by pumping in the vicinity of a partially penetrating stream

Commonly used analytical approaches for estimation of pumping-induced drawd own and stream depletion are based on a series of idealistic assumptions ab out the stream-aquifer system. A new solution has been developed for estima tion of drawdown and stream depletion under conditions that are more repres entative of those in natural systems (finite width stream of shallow penetr ation adjoining an aquifer of limited lateral extent). This solution shows that the conventional assumption of a fully penetrating stream will lead to a significant overestimation of stream depletion (> 100%) in many practica l applications. The degree of overestimation will depend on the value of th e stream leakance parameter and the distance from the pumping well to the s tream. Although leakance will increase with stream width, a very wide strea m will not necessarily be well represented by a model of a fully penetratin g stream. The impact of lateral boundaries depends upon the distance from t he pumping wen to the stream and the stream leakance parameter. In most cas es, aquifer width must be on the order of hundreds of stream widths before the assumption of a laterally infinite aquifer is appropriate for stream-de pletion calculations. An important assumption underlying this solution is t hat stream-channel penetration is negligible relative to aquifer thickness. However, an approximate extension to the case of nonnegligible penetration provides reasonable results for the range of relative penetrations found i n most natural systems (up to 85%). Since this solution allows consideratio n of a much wider range of conditions than existing analytical approaches, it could prove to be a valuable new tool for water management design and wa ter rights adjudication purposes.