U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Comparison of Simulated and Observed Movement of Bank-Storage Water Adjacent to the Cedar River, Iowa

Abstract

A ground-water flow model was constructed to describe quantitatively the movement of bank-storage water in an alluvial aquifer adjacent to the Cedar River, Iowa, during March 7-April 17, 1990, at the Palisades study area. The results from this two-dimensional model were compared to hydrologic and water-chemistry data. Hydrologic data consisted of 745 daily ground-water-level measurements made in 27 wells during March 8-April 5, 1990. These 745 measurements were used for model calibration and for comparing measured and simulated hydraulic heads and gradients. Water-chemistry data indicate that bank-storage water had a lower specific conductance and higher concentration of atrazine compared to the ambient ground water. Analysis of water chemistry and model results indicate that bank-storage water moved about 30 meters into the aquifer at a depth of 6 meters below land surface. The model also showed that 70 percent of the total bank-storage water moved through the river bottom while the remaining 30 percent moved laterally through the riverbank. The flux of bank storage-water both into and out of the river bottom is largest near the river's edge and decreases substantially with distance from the river's edge to the center of the river. The model showed that it would take about 5 weeks for bank-storage water to discharge from the alluvial aquifer after the peak river stage.