Analysis of pumping-induced stream-aquifer interactions for gaining streams

This paper presents analytical solutions that can be used to evaluate stream infiltration and baseflow reduction induced by groundwater pumping in nearby aquifers. Critical time, infiltration reach, and travel times can also be calculated to determine the hydraulic connectivity between the well and the stream. The critical time indicates the earliest time of reversal of hydraulic gradient occurring along the stream - aquifer interface, the infiltration reach is the stream segment where stream water recharges the aquifer, and the shortest travel time for the stream water particle to get into a pumping well is along the meridian line. The transient features of the two stream depletion components, baseflow reduction and stream infiltration, are evaluated separately. The rate of baseflow reduction can be greater than the rate of stream infiltration for a stronger gaining stream. However, for a given distance between the stream and well, a higher pumping rate or a weaker gaining stream results in higher rate of stream infiltration, although the total depletion rate is the same for different pumping rates or varied hydraulic gradient of the baseflow. When a steady-state condition is assumed for a transient flow, the rate and volume of stream infiltration can be overestimated; this overestimation can be very significant in the early stage of pumping.