Using the New Rome Formation as a geologic weighing lysimeter for water management in Wisconsin’s sand plain

This project tested the concept of using geologic weighing lysimeters (GWLs) to estimate components of the water balance in parts of Wisconsin’s central sand plain where the New Rome Formation (NRF), a regional aquitard, occurs. As described in the proposal body, additions or subtractions of water at the land surface are transmitted as pressure changes beneath the aquitard, and relatively simple measurements of these pressure changes can be translated into estimates of recharge and evapotranspiration at the field scale or larger. Such a method is attractive because it is completely independent of crop, cover, and soil types and is based on hydraulic response rather than on plot measurements or energy-balance theory. It therefore provides an independent check on these more common methods. In addition to testing the method, we also tested and documented physical properties of the NRF, a potentially significant regional aquitard. The “sand plain” of central Wisconsin is an economically important agricultural region that depends heavily on irrigation from high-capacity wells for crop production. There is evidence that groundwater drawdown and increased evapotranspiration associated with this water use is reducing lake levels and streamflows in local surface water resources, and that climate change might be amplifying these impacts. As a result, there have been conflicts between farmers who use groundwater for irrigation, local property owners and environmental groups concerned about environmental degradation, and regulatory officials charged with approving new high-capacity wells. Results of this work will help inform these issues. Objectives: 1) To test the concept that geologic weighing lysimeters (GWLs) can be used to estimate groundwater recharge and evapotranspiration over large areas of Wisconsin’s central sand plain. 2) To refine our understanding of the hydrogeologic properties and function of the NRF, a widespread aquitard underlying parts of the central sand plain.