Electric‐analog and digital‐computer model analysis of stream depletion by wells

Electric‐analog or digital‐computer models are used to compute the effect of ground‐water withdrawal or recharge on streamflow. The results can be generalized on a map showing lines of equal elapsed time. The lines indicate the time of recharging or discharging that is needed to affect the streamflow by a given fraction of the amount pumped or injected. The generalization is based on the similarity in shape of the relations between pumping time and stream depletion for (1) semi‐infinite homogeneous aquifers drained by a straight, fully penetrating stream, and (2) complex heterogeneous aquifers. Response curves from a model reflect the combined effect of stream sinuosity, irregular impermeable boundaries, areal variation in aquifer properties, and imperfect hydraulic connection between the stream and aquifer. The elapsed‐cime lines are identified by sdf (stream depletion factor) values. These values can be calculated from observations made on an electric‐analog model and then may be used in a digital‐computer program for determining the effects of ground‐water pumping or recharge on streamflow.