Doug Cherkauer's Research
Determining ground-water recharge rates in southeastern Wisconsin. The Southeastern Wisconsin Regional Planning Commission (SEWRPC) contracted with the USGS and Wisconsin Survey (WGNHS) to develop a ground-water flow model for southeast Wisconsin. They, in turn, contracted with me and my students to give them a measure of the spatial distribution of recharge rates to use as input. We calculated rates for about 250 subwatersheds using a regression model we had developed on a grant from the Wisconsin Ground Water research program (Sajjad Ansari’s MS thesis). It links the annual average rate of recharge to soil permeability, land slope, land cover and the depth to the water table within the watershed. Several students (Heidi Yantz, Paul Lenaker, Craig LaCosse among them) used GIS to obtain all the necessary inputs for the calculations. We’ve checked the accuracy of the values by simulating streamflow at a number of USGS gaging stations using the distributed-parameter watershed model PRMS (Precipitation Runoff Modeling System). PRMS generates a ground-water discharge to the stream (baseflow) which can then be compared to the calculated recharge rate for an area of interest. In subwatersheds where there are no net extractions of ground water by wells, then baseflow and recharge are essentially identical. The checking has shown that our empirical method is accurate to within + 20%.
The work has shown that recharge in the region ranges from 0 to 16 in/yr, but that most areas fall within the range of 4 to 8 in/yr. Articles are in the final stages of review at Ground Water which describe both the empirical method and how to utilize PRMS to extract ground-water recharge.
Development of a ground-water flow model for Fond du Lac County, WI. As part of the DNR’s Source Water Assessment Program, they contracted with the WGNHS and us to create a fully three-dimensional flow model for the county. It would allow generation of capture zones for all the municipal wells in the area, including those for Fond du Lac, Waupun, Ripon and many more communities
Doug Carlson worked on the project for the year after he completed his dissertation and put together as detailed a model as the existing geologic information allows. He then calibrated it quite nicely and the model is now fully functional. The primary thing we learned from the process is that the hydrogeology of Fond du Lac Co. is extremely complex. The eastern part of the county has both the Silurian dolomite and deeper sandstone aquifer, but the Silurian (and the underlying Maquoketa shale) pinch out to the west. There the sandstone is unconfined and interactive with surface water systems. Carbonate units, which are protected from weathering by the overlying Maquoketa to the east, have been exposed in the west and have very different conductivities. At the base of the Paleozoic aquifers, the Precambrian surface has over 500 feet of relief (partly due to faulting) in the area. In fact, there are locations in the county where the rock subcropping beneath glacial deposits is the Precambrian. On top of that, Bob Taylor and alumni John Jansen and Pat Jurcek (among others) have demonstrated that there is considerable saline water at the base of the Paleozoic system.
The model incorporates a pretty good rendition of the stratigraphy, but it has not included the faulting or the saline water. There’s a lot more work to be done.
Assessment of ground water/surface water interactions at a Nature Conservancy (TNC) site in Vilas County. Several years back, TNC was given a site of roughly 2000 acres on the Michigan border. It had been in the hands of a single family since the early 1900s. It has never been developed, except for some dirt roads. The site is the hydrologic headwaters for the area. It contains 7 large lakes and numerous smaller ones plus associated wetlands. Two streams drain these surface water bodies and the ground water system of the site. But all water leaving the site originates on the site as precipitation.
We (Joy Loughry, Jon Tortomasi and I) installed an array of monitoring wells around the site in summer, 2001. Joy is working on defining the whole flow system for her thesis. Tim Grundl and I took the Field Methods class up there (October, 2002). We sampled wells and did quite a bit of stream gaging and electrical resistivity soundings and are now developing a clearer picture of the subsurface geology and the ground-water flow system. Class members will be presenting the results at the Wisconsin Ground Water Assoc. meeting in April, 2003.