T. C. WINTER'S CONTRIBUTION TO THE ANALYSIS AND UNDERSTANDING OF INTERACTIVE LAKE-GROUNDWATER SYSTEMS

Over thirty years ago, Thomas C. Winter showed in his dissertation, "The hydrologic setting of lakes in Minnesota and adjacent states with emphasis on the interaction of lakes and ground water" (1976), that lakes form an integral and active part of near-surface groundwater flow systems. Lakes form flow system boundaries and shape hydraulic potential gradients around them. Winter’s numerical simulation experiments (the "TCW" models) extended previous concepts by Hubbert, Toth, Freeze and Witherspoon, and others specifically to the lake environment. Unlike these earlier mathematical models, which incorporated groundwater discharge points as areas with zero dimensions, the TCW model considered lakes as two-dimensional discharge features with unique boundary geometries and boundary conditions, depending on the lake configuration and potential of the groundwater flow field around the lake. Winter also showed that the configuration of the free hydraulic surface, the water table, profoundly controlled interaction with local and deeper groundwater flow systems. Winter critically examined the prevailing hypothesis at the time that the water table would be a subdued reflection of the land surface topography, and in doing so, defined the concept of the stagnation point and focused recharge. Fundamentally, Winter discovered how the stagnation zone mostly controls leakage from lakes and lake hydraulic connection to deeper flow systems.

Winter realized early-on that detailed and accurate hydrologic budgets of the lake and lake watershed needed to be done to test the results of his seminal heuristic models. To this end, he instrumented field sites representing a range of climatic and geologic lake settings across the Nation. He viewed lake-groundwater interaction as part of a total and integrated hydraulic system, and his studies included geology of near-surface unconsolidated deposits, aquifer flow in potential fields, lake-groundwater chemistry, lake evaporation, and limnology. Tom Winter’s integrative approach of coupling rigorous field studies to numerical modeling approaches now forms the template for how scientists throughout the world study the hydrology of lakes.