Effects of aquifer anisotropy on the migration of infiltrated stream water to a pumping well

Pumping of groundwater near a stream can induce infiltration of stream water into the surrounding aquifers. Analysis of the migration of the infiltrated stream water to the pumping well is important to better understand stream-aquifer interactions. The paper analyzes the effects of aquifer anisotropy on the migration process of infiltrated stream water to a partially penetrating well. MODFLOW is used to simulate the transient groundwater velocity fields, and MODPATH is used to record the locations of water particles. Pathlines were plotted over a cross section to show the hydraulic connectivity between the well and the stream for various levels of aquifer anisotropy. Travel times, infiltration rates, and fractions of pumped river water were determined to characterize the migration process. Generally, the movement of the infiltrated stream water is slow; the water can take several months to arrive at a well located a short distance from a stream. Results suggest that the rate of produced stream water at the well is higher for the anisotropy K_h/K_z= 10 and 20 (ratio of horizontal to vertical hydraulic conductivity) than for K_h/K_z< 10, or > 20. On the other hand, when K_h/K_z is between 20 and 100, the first water particle that gets to the pumping well needs a shorter travel time than that for other K_h/K_z values. A gaining stream can significantly reduce the rate of stream infiltration and produced stream water. Areal recharge provides an additional source to the well, thus reducing the rate of stream infiltration as well as the rate of produced stream water.