Hydrogeologic Controls on Springs in the Mukwonago River Watershed, SE Wisconsin: Final Report to the Wisconsin Department of Natural Resources

Background/Need: The health of wetlands is essential for maintaining overall environmental health as wetlands play an integral role in the storage of water after flood events, recharge and discharge to the local aquifer, balancing of baseflow and the regulation of water quality (Carter, 1986). The effects of urbanization on the natural environment, and on wetlands in particular, can be profound. By increasing the coverage of impervious surfaces as well as the demand for round water, urbanization can result in long-term damage to wetland systems. As development of high capacity wells and surface construction in the Mukwonago River watershed continues, managers involved with conservation recognize that maintaining spring discharge and water levels in the wetland is essential to preserving the integrity of these aquatic habitats. There is a critical need to evaluate potential effects of increased pumping and decreased recharge that may accompany continued suburban development.

Objectives: The goals of this project were to asses the hydrogeologic controls on ground water discharge to the Mukwonago River watershed’s springs and wetlands and to develop a numerical ground water flow model to assess development impacts.

Methods: In this study we used water level and stream flow measurements along with major ion and strontium isotope analyses to estimate sources and amounts of ground water from bedrock aquifers that may mix with shallow waters before discharging to springs and wetlands in the watershed. We developed a numerical ground water flow model that captures the essential interactions among subsurface hydrostratigraphic units and surface discharge features, which in turn allows assessment of the impact of ground water pumping to the system.