Tuesday, April 13, 2010: 4:00 p.m.
Continental B (Westin Tabor Center, Denver)
The USGS has constructed a regional groundwater-flow model of the Lake Michigan Basin and surrounding areas as part of the National Water Availability and Use Pilot project for the Great Lakes Basin. The work is part of a recently initiated series of framework studies aimed at evaluating the state of the resource from water-use and ecological standpoints. The transient, 20-layer, two-million-node SEAWAT model incorporates multiple aquifers and pumping centers with cones of depression that extend into deep saline waters. The model simulates the exchange of water between surface-water bodies and shallow sequences of heterogeneous glacial deposits which, in turn, overlie stratified, dipping bedrock of the Wisconsin Arch and Michigan Structural Basin. These hydrogeological elements pose challenges for the model setup, the handling of variable density conditions, and calibration. The final model provides a multi-state framework for quantifying the regional sources and sinks of groundwater (including recharge, pumping, and groundwater exchange with surface-water bodies — all elements of the groundwater budget that change with time) and for mapping the direction and magnitude of flows in a series of aquifers (including the locations of groundwater divides at different depths on both sides of Lake Michigan and their movement in response to pumping). Modeling results are distilled into water-availability measures for the Lake Michigan Basin which show the long-term effect of pumping on the resource, including the effect on groundwater exchange with Lake Michigan itself. Of particular value are sustainability indicators designed to evaluate shallow and deep pumping under variable climatic conditions in terms of 1) the fraction of available natural groundwater inflow diverted to water-use demand and 2) the percent of natural groundwater outflow diverted from surface-water bodies. For the Lake Michigan Basin