Green Bay is a large freshwater estuarine system that drains one-third of the Lake Michigan basin. The International Joint Commission designated southern Green Bay as an area of concern (AOC) in the 1980s due to ecosystem degradation including eutrophication, harmful algal blooms (HABs), hypoxia, lost or altered habitat, and reduced water quality. Restoration studies have found excessive nutrient loading and release of toxic materials, primarily produced in farmlands and industrial units, to be major drivers of Green Bay environmental/ecological issues. The Green Bay geomorphology and restricted mixing is a barrier to the efficient transport of sediments (as well as the accompanying nutrients and contaminants), acting as a retention basin for Lake Michigan. The purposes of this research were to: a) use the existing database of hydrodynamic, wave, and sediment field data to develop a three-dimensional (3D) predictive model of sediment transport in Lake Michigan, with an emphasis in Green Bay; b) use the sediment transport model to contribute to understanding ecological and environmental problems in the bay, and to recommend long-term solutions to those problems; and c) analyze summer patterns of circulation, wave action, current and wave-induced bottom shear stress, thermal structure, and sediment transport in Lake Michigan, with special attention to Green Bay.

Green Bay is the largest freshwater estuarine system on earth, drains one-third of the Lake Michigan basin and delivers one-third of the lake’s phosphorus load. Southern Green Bay is a designated area of concern (AOC) due to ecosystem degradation that includes eutrophication, harmful algal blooms (HABs), hypoxia, lost or altered habitat, and reduced water quality. While marine estuaries are subject to tidal influence and saltwater intrusion, this freshwater estuary is subject to lake intrusion of freshwater with different quality parameters. Understanding the simultaneous effects of tributary flows and lake intrusions is crucial to comprehend the dynamics of freshwater estuaries. A single hydrodynamic, wind-wave, and sediment transport model was developed for the lake and its estuary. This approach provides fine resolution in the estuary and simulates directly the combined effects of tributary flows and lake intrusions. The approach overcomes open-boundary limitations of nested models, and of whole-lake models that lack sufficient resolution or wind-wave and sediment transport simulation. The model confirms findings of previous studies and demonstrates how the circulation, thermal regime, wave action, and sediment transport in the estuary depend on meteorological forcing, tributary flows, and lake intrusions. The stage is set to apply this approach to study biogeochemical processes in lakes and estuaries.