The effects of groundwater interception on stream flow

Water supply wells located at distance from surface streams may reduce stre am flow by interception of groundwater. The wells do not cause drawdown bel ow the stream channel, and consequently, do not induce leakage. Rather, the wells withdraw groundwater that would otherwise discharge into the stream. Modeling was conducted to evaluate concepts of stream depletion by groundw ater interception. A hypothetical basin model was constructed with dimensio ns and parameters resembling western basins. Three aquifer scenarios were m odeled: isotropic, anisotropic and leaky. Simulations were conducted for 20 to 30 year time periods. Infiltration recharge was applied seasonally. Pum ping wells were located at 1,400 ft, 5,000 ft, and 10,000 ft from a river b oundary, and pumped seasonally and continuously at 300 gpm. Modeling result s show stream depletion occurred in all simulations. After a lag time to re ach a steady condition, the average rate of stream depletion became equal t o the time-average pumping rate in the well. Resistance to flow created a d ampening effect on stream depletion. With greater resistance to flow, oscil lation in stream depletion due to seasonal pumping was reduced and the time to a steady condition was increased. The resistance to flow increased with distance from the stream and with lower hydraulic conductivity.