Observed and Simulated Movement of Bank‐Storage Water

Abstract

AbstractDetailed hydrologic and water‐chemistry data were collected that document the movement of bank‐storage water during March 7‐April 17, 1990, in an alluvial aquifer adjacent to the Cedar River, Iowa. Hydrologic data included 745 daily ground‐water‐level measurements from 27 observation wells. Water‐chemistry data indicate that bank‐storage water had smaller specific conductance and larger concentration of atrazine than ambient ground water. To quantify the movement of the bank‐storage water, a two‐dimensional ground‐water flow model was constructed, and the resulting calibrated model accurately simulated observed conditions. Analysis of water chemistry and model results indicate that a 2‐meter rise in the river stage caused bank‐storage water to move horizontally at least 30 meters into the aquifer and vertically about 4 meters below the river bottom, whereas the remaining 30 percent moved laterally through the riverbank. The model also showed that bank storage caused the ground‐water flux to the river to increase by a factor of five during the first three weeks of base flow after runoff and that it required about five weeks for bank‐storage water to discharge from the alluvial aquifer after the peak river stage. These results quantitatively demonstrate the importance of bank storage as a source of recharge to the alluvial aquifer and as a source of water to the river during early base‐flow conditions.