SEASONAL IMPACTS OF PUMPIMG ON A NEARBY STREAM

Ground-water pumping from aquifer systems that are hydraulically connected to streams depletes streamflow. The amplitude and timing of stream depletion depends on the stream depletion factor (SDFi) of the pumping wells, which is a function of aquifer hydraulic characteristics and the distance from the wells to the stream. Wells located at different locations, but having the same SDFi and the same rate and schedule of pumping, will deplete streamflow equally. Wells with small SDFi deplete streamflow approximately synchronously with pumping. Wells with large SDFi deplete streamflow at approximately a constant rate throughout the year, regardless of the pumping schedule. For large values of SDFi, artificial recharge that occurs on a different schedule from pumping can offset streamflow depletion effectively. The requirements are 1) that the pumping and recharge wells both have the same SDFi, and 2) that the annual total quantities of recharge and pumping be equal. Ground-water recharge can be managed to offset the impacts of new ground-water developments, allowing for changes in the timing and source of withdrawals from a basin without injuring existing users or instream flows.