Presenter: Salme Cook (United States Geological Survey)

Description:
Climate change, population growth and sea level rise have put increased pressure on the Delaware Bay Estuary and greater Delaware River Basin to provide water resources, including drinking water for approximately 13 million people (~4% of the US population). Salinity intrusion threatens industrial, agricultural, and freshwater intakes, and influences aquacultural resources and fisheries. This work aims to understand how storm events (i.e., hurricanes, subtropical storms, and nor’easters) and local bathymetric features affect salinity intrusion, specifically the location of the salt front, within the Delaware Bay estuary. We use the COAWST numerical modeling system to perform simulations that incorporate river discharge from the Delaware River at Trenton, the Schuylkill River, and the Chesapeake & Delaware canal, with subtidal, low frequency signals forced at the mouth of the estuary, and bulk atmospheric forcing providing the local wind field. The model was run for a drought year (2016) and a wet year (2019) to investigate the role of storms during different bulk hydrodynamic conditions. Results show good agreement with observed time series of water level and salinity and represent both the spring-neap and long-term seasonal patterns of the calculated daily average salt front (~0.45 PSU). Results show that the movement of the salt front depends upon the location and duration of the storm systems, moving over one mile a day in some cases. As river discharge wanes in the summer and the salt front advances, it stalls out at several locations along the thalweg, suggesting an interaction between turbulent mixing and bathymetry. These bathymetric sill-like features are shown to suppress movement of the salt front and delay intrusion events.  Understanding the mechanisms that drive the salt front can aid in better water resource management in the region, especially during periods of drought.