US Long-Term Ecological Research Network
Numerical analysis of groundwater and lake systems with application to the Trout River basin, Vilas County, Wisconsin
This study is designed to investigate three-dimensional steady-state and transient interactions between lakes and groundwater and to assess impacts of climate change on lake and groundwater systems in northern Wisconsin. Relevant source codes, executable file, and input and output files from the simulations are included in two accompanying floppy diskettes. Chapter I provides general background and introductory material. Chapter 2 introduces the lake package developed for the U.S. Geological Survey’s MOD FLOW code and demonstrates its use through steady-state and transient simulations for a hypothetical problem involving a lake and two streams. This package was developed to incorporate lake level fluctuations when estimating transient groundwater fluxes into and out of a lake. Chapter 3 investigates the influence of lake position on groundwater fluxes. Results show greater groundwater flows for lakes located lower in a watershed than for lakes located upgradient. It is demonstrated that (I) high intensity groundwater recharge can cause groundwater flow reversals and the formation of a stagnation point downgradient of a flow-through lake, which causes a net increase in groundwater inflow and (2) high intensity groundwater recharge affects upper flow-through lakes more than those located lower in the watershed. Chapter 4 investigates the impacts of climate change on lake and groundwater systems in the Trout River Basin in northern Wisconsin. A regional steady-state threedimensional flow model was calibrated to hydrologic conditions in 1991. By comparing simulations of the baseline condition and four hypothetical scenarios (representing+ 10\%, +5\%, -5\%, -10\% changes in precipitation, evaporation, and groundwater recharge), the impacts of climate change are assessed. Results suggest that water budgets, lake levels, and groundwater heads will be affected differently.Small and shallow lakes in recharge areas will be affected the most whereas drainage lakes (Trout Lake and Allequash Lake) will be affected the least.
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