Wisconsin's Role in Great Lakes Restoration - American Water ...

Simulation of Groundwater / Lake-Water Interaction at Shell Lake, Washburn County,
WI
Paul F. Juckem, U.S. Geological Survey, Middleton, WI, pfjuckem@usgs.gov
Randy J. Hunt, U.S. Geological Survey, Middleton, WI, rjhunt@usgs.gov
Dale M. Robertson, U.S. Geological Survey, Middleton, WI, dzrobert@usgs.gov
William J. Rose, U.S. Geological Survey, Middleton, WI, wjrose@usgs.gov
Charles P. Dunning, International Atomic Energy Agency, Vienna, Austria c.dunning@iaea.org
Daniel T. Feinstein, U.S. Geological Survey, Middleton, WI, dtfeinst@usgs.gov
Shell Lake, the largest seepage lake (no stream outlet) in Wisconsin, experienced large-scale
flooding during the late 1990s and early 2000s. In 2002, the City of Shell Lake obtained a
permit to construct a pipeline to divert water from the lake to lower the lake level, and from
November, 2003 to July, 2005 the City diverted three billion gallons of water. As part of the
permit, the City was required to evaluate the effects of this diversion on the water levels of
Shell Lake and adjacent lakes; this was addressed through a cooperative study with the U.S.
Geological Survey.
As part of this study, nested monitoring wells were installed around the lake and the lakeaquifer
system was simulated with a MODFLOW model that incorporated several packages to
simulate the lakes (LAK7), streams (SFR7), and overland runoff to the lakes (UZF1). Geologic
core samples and measured hydraulic heads indicated a complex geology and groundwater
flow system near the lake, with limited groundwater / lake-water interaction. The lake is
approximately 40 feet above nearby down-gradient streams, and hydraulic heads along the
up-gradient shoreline illustrate both groundwater discharge to the lake and underflow beneath
the lake. Simulation of the flow system was performed using hydraulic conductivity fields that
were estimated by use of pilot points and associated regularization using the parameter
estimation code PEST. Simulated flow patterns matched field data, and transient results
indicate that the diversion caused the water level of Shell Lake to decline by approximately 3
feet by the end of 2005. Results of this study will be used by the City and Wisconsin Dept. of
Natural Resources to evaluate potential future diversions and are now being used to help
understand changes in lake water quality.
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