HIGH VERTICAL-RESOLUTION HYDRODYNAMIC MODELING OF MISSISQUOI BAY TOWARDS A BETTER UNDERSTANDING OF WATER QUALITY AND THE EFFECTS OF CAUSEWAYS

Missisquoi Bay, a uniformly shallow (<4 m) and eutrophic region in the northeast quadrant of Lake Champlain bordering Vermont and the Province of Quebec, has been experiencing nearly annual cyanobacterial blooms during the summer months. These blooms and the eutrophic status are a result of anthropogenic inputs (both current and historical) of phosphorus into the bay. Earlier investigations as well as public beliefs suggested that the rock-filled causeway (located at the southwestern section of the bay) was limiting the flushing of pollutants out of the bay. ASA’s 1997 numerical model that was focused on this topic (and based on roughly a single month’s worth of data), indicated just the opposite. Over a decade later, the VT EPSCoR RACC program (2012-2015), collected between 2-3 orders of magnitude more data over the entire bay. It is the aim of this modelling effort to calibrate a new atmospherically-coupled, 3D flexible-mesh, high vertical-resolution, hydrodynamic model of the Restricted Arm (encompassing Missisquoi Bay, Inland Sea, and Malletts Bay), with these data sets. This validated model is used to investigate the impacts on circulation dynamics and residence time of the partial or complete removal of the Missisquoi Bay causeway. Since the model covers a much broader region, we will also seek to quantify the effects of partial to complete removal of the three other remaining causeways within the Restricted Arm.