Effects of stream-aquifer disconnection on local flow patterns

Disconnected stream-aquifer systems are becoming increasingly common because of lowering groundwater tables. This work focuses on the pathways and rates of infiltration and seepage as streams transition from fully connected to disconnected conditions. HYDRUS-2D simulations show for a connected stream, water infiltrates vertically then moves laterally below the top of the preflooding capillary fringe height, finally causing an upward displacement of antecedent water into the vadose zone. This contradicts the commonly held assumption that stream water moves laterally for some distance into the stream bank, forming a wedge above the antecedent water. Even for shallow disconnections (<1 m), there is an increase in infiltration losses from the stream, elimination of postflooding seepage, and increased lateral and vertical mixing of stream water and antecedent pore water.