Implementation of a Wetting and Drying Model in Simulating the Androscoggin/Kennebec Plume and the Circulation in Casco Bay

Casco Bay, located on the west Maine coast, is characterized by a complex series of peninsulas, numerous small islands, and some intertidal zones. Previous studies suggested that Casco Bay is a source region of toxic algal bloom and such events are closely related to variations of sea surface salinity (Keafer, 2005). The Androscoggin/Kennebec estuary is less than 20km to the east. Discharges from the two rivers combined reach ~ 1.3xl010 m3 annually and the resultant plume is a key factor that drives salinity variability in Casco Bay. A comprehensive coastal ocean model is used to simulate the Androscoggin/Kennebec plume and the circulation in Casco Bay from 2004 to 2005. The model results compare favorably with moored observations from GoMOOS buoy C and ship survey data. Wind and tidal forcing determine the spread of the plume in the bay. A wetting and drying (WAD) scheme is adapted to enhance the model ability to solve the detail conditions in shallow areas. By comparing the run without WAD, significant differences are presented. It suggests that the WAD scheme enhances the mixing and entrainment processes near the estuary, which results in stronger tidal intrusion into the estuary and thicker plume near the estuary mouth