Wells_Content Page_Central Sands Lakes Study Modeling

Central Sands Lakes Study Modeling

The DNR collaborated with USGS Upper Midwest Water Science Center to develop a state-of-the-art modeling approach and used an established numerical groundwater flow model (MODFLOW) as a tool to evaluate how groundwater withdrawals, land use changes and climate affect lake levels. To inform the model, we used inputs such as: groundwater and surface water quantity data; hydrologic and geologic information; and precipitation, evaporation and transpiration estimates.

The CSLS model provided the amount of reduction to lake levels due to groundwater withdrawals. The DNR’s key findings regarding modeling include:

  • Precipitation has the largest effect on how much water reaches the water table, with more recharge in wetter years and less recharge in drier years.
  • While precipitation largely controls recharge, land use and irrigation have smaller but persistent impacts on recharge.
  • Differences in precipitation and evapotranspiration patterns, land use, soil types and many other factors can lead to different recharge rates – even on nearby fields.
  • Our groundwater modeling results indicate current levels of irrigated agriculture cause lake level reductions, but by a different amount on each lake.
  • Lake level drawdowns from any one individual well are very small, but the drawdown from dozens or hundreds of wells combined can accumulate into a significant impact.

Map of the Groundwater Model Domain

The CSLS model domain (dark blue boundary) encompassed most of the Central Sands Region. This area differs from the Central Sands Region so that the boundaries of the groundwater model line up with major hydrologic features, such as the Wisconsin River to the west, the Tomorrow/Waupaca River to the northeast and the Fox River to the southeast. To allow for more specific evaluation of the three study lakes (Plainfield, Long and Pleasant Lakes), we added more detail to the model in the areas near the lakes where we have additional information and where we want to better understand the groundwater and lake interactions.

Proposed regional groundwater model domain for the Central Sands Lakes Study.
Regional groundwater model domain for the Central Sands Lakes Study.

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