AN APPROACH FOR EVALUATING THE HYDROGEOLOGY OF NATIONAL FOREST UNITS IN NORTHERN WISCONSIN

Understanding relationships among groundwater, surface water, ecology, and climate is critical for successful long-term management of multiple-use forests. The Wisconsin Geological and Natural History Survey, US Geological Survey, and US Forest Service are undertaking a cooperative multi-year study of the Chequamegon-Nicolet National Forest in Northern Wisconsin. The Forest contains five geographically distinct management units which together comprise over 1.5 million acres including over 600 lakes, 2,000 miles of streams, and 347,000 acres of wetlands. The climate is humid (about 32 in/yr precipitation) and the geology generally consists of glacial deposits, ranging from absent to over 100 ft thick, over crystalline bedrock. Groundwater is a critical resource throughout the Forest, providing base flow to springs, streams, and wetlands and water supply for domestic, commercial, and agricultural use.

We are developing a baseline understanding of the hydrogeology of this vast area by focusing on one management unit at a time through a 5-year timeframe. Study activities in each management unit include the following:

• Construction of a database of existing information, including locations of many wells, spring locations, streamflow measurements, geologic mapping, previous studies, and related information
• Estimation of groundwater recharge using a Soil Water Balance (SWB) approach considering climate, topography, land cover, and soil characteristics
• Evaluation of aquifer properties using existing geologic mapping, specific-capacities values reported on well construction reports, and results of previous studies
• Development of a two-dimensional groundwater flow model using the analytic-element GFLOW code
• Use of the GFLOW model to produce water-table maps and simulation of specific management scenarios such as climate change
• Collection and analysis of groundwater samples for major ions and environmental isotopes
• Focused research on subwatersheds in order to understand groundwater/surface water relationships

Results of this work will be used by Forest managers and others to inform management decisions in this multi-use environment.