Abstract
Due to climate change, the strength and frequency of heavy rainfall and flooding events have been changing along with the associated use of protective measures such as diversions directing river water to coastal areas. Bonnet Carre Spillway (BCS) is the flood control structure on Mississippi River protecting the City of New Orleans from flooding by diverting about 250,000 cfs from the river into Lake Pontchartrain (LP). For the first time ever BCS was operated for three years in a row in 2018, 2019 and 2020. It was also operated twice in the same year for the first time in 2019. It is important to understand the transport of this excess freshwater through LP into the Mississippi Sound estuarine system, the physical processes driving this transport, the extent of freshwater impact and how rapidly conditions change. In this study, we develop a COAWST-based modeling system that covers a study area including the LP basin system, Mississippi Sound, Mobile Bay and the continental shelf of Mississippi Bight. The river forcing includes discharge of Mississippi River as well as other local rivers including those of the LP system. The atmospheric forcing is provided by NOAA’s High-Resolution Rapid Refresh model. With a multi-nested approach, the model resolves the channels (i.e. Pass Manchac, Rigolets and Chef Menteur Pass) in between Maurepas, Pontchartrain and Mississippi Sound allowing us to study circulation and exchange in and between different water bodies of the system. The freshwater flow into LP via BCS crevasse is added so that the modeling system may be setup to study diversion operation scenarios. This modeling approach will help us better understand the dynamics and physical drivers of freshwater transport in this region and the impact of incoming freshwater on HAB formations, onset of Hypoxia, oyster habitat, etc.
