Simulation of an urban ground-water-flow system in the Menomonee Valley, Milwaukee, Wisconsin using analytic element modeling

A single-layer, steady-state analytic element model was constructed to simulate shallow ground-water flow in the Menomonee Valley, an old industrial center southwest of downtown Milwaukee, Wisconsin. Project objectives were to develop an understanding of the shallow ground-water flow system and identify primary receptors of recharge to the valley. The analytic element model simulates flow in a 18.3 m (60 ft) thick layer of estuarine and alluvial sediments and man-made fill that comprises the shallow aquifer across the valley. The thin, laterally extensive nature of the shallow aquifer suggests horizontal-flow predominates, thus the system can appropriately be modeled with the Dupuit-Forchheimer approximation in an analytic element model. The model was calibrated to the measured baseflow increase between two USGS gages on the Menomonee River, 90 head measurements taken in and around the valley during December 1999, and vertical gradients measured at five locations under the river and estuary in the valley. Recent construction of the Milwaukee Metropolitan Sewer District Inline Storage System (ISS) in the Silurian dolomite under the Menomonee Valley has locally lowered heads in the dolomite appreciably, below levels caused by historic pumping. The ISS is a regional hydraulic sink which removes water from the bedrock even during dry weather. The potential effect on flow directions in the shallow aquifer of dry-weather infiltration to the ISS was evaluated by adjusting the resistance of the line-sink strings representing the ISS in the model to allow infiltration from 0 to 100% of the reported 9,500 m³/d. The best fit to calibration targets was found between 60% (5,700 m³/d) and 80% (7,600 m³/d) of the reported dry-weather infiltration. At 60% infiltration, 65% of the recharge falling on the valley terminates at the ISS and 35% at the Menomonee River and estuary. At 80% infiltration, 73% of the recharge terminates at the ISS, and 27% at the river and estuary. Model simulations suggest that the ISS has an greater influence on the shallow ground-water flow in the eastern half of valley as compared to the western half. Preliminary three-dimensional simulations using the numerical MODFLOW code show good agreement with the single-layer simulation and supports its use in evaluating the shallow system. Copyright ASCE 2004.