Simulation of regional groundwater flow and groundwater/lake interactions in the Central Sands, Wisconsin

A multiscale, multiprocess modeling approach was applied to the Wisconsin Central Sands region in central Wisconsin to quantify the connections between the groundwater system, land use, and lake levels in three seepage lakes in Waushara County, Wisconsin: Long and Plainfield (The Plainfield Tunnel Channel Lakes), and Pleasant Lakes. A regional groundwater-flow model, the Newton Raphson formulation of the U.S. Geological Survey modular finite-difference flow model groundwater-modeling package (MODFLOW-NWT), centered on the lakes, was used to extend regional surface-water boundaries to provide boundary conditions for two focused inset models, in the hydrologic simulation modeling package (MODFLOW 6), at higher resolution around the lakes. Land use and groundwater use were simulated at a regional scale using the Soil Water Balance model, which provided recharge and water-use boundary conditions for the MODFLOW models. Agricultural irrigation is the primary groundwater use in the area. Land and groundwater-use scenarios representing no irrigation, current (2018) irrigation, and potential future irrigation were simulated with the groundwater-flow model and the lake levels over a 38-year representative climate period.