Salt dispersion in Delaware Bay estuary

Delaware Bay is a coastal plain estuary located in the east coast of the United States and provides recreation, transportation, fishery and water resources. The physical characteristics of an estuary significantly influence the function and value of these resources. For example increased salt intrusion associated with channel deepening may be a threat to potable water supplies and increase diseases to shelf-fish. It is then relevant to understand these physical characteristics and the processes that govern them. This graduate work focused on some hydrodynamic aspects of Delaware Bay, in particular, the transport of salt, stratification and the role of the cross-channel dynamics. Numerical simulations and observations were the tools employed to develop this work. The Regional Ocean Modeling System (ROMS) was used to set up a model of the bay. The observations consisted of a mooring array in the middle reach of the bay, equipped with ADCPs and CT sensors at different depths. Additionally, four cross-channel tidal surveys were performed in the same location of the mooring array. The results indicate that the net salt transport due to tidal flows ($F7t$) is of the same order of magnitude as the salt transport due to the estuarine exchange flow ($F7e$). Furthermore, $F7t$ is intensified during neap periods, presenting a spring-neap variability that is opposite to previous parameterizations. We concluded that this spring-neap variability is caused by the action of the cross-channel flows on the salinity field that enhances the tidal period variability of salinity ($s7t$) during neap tides, and brings the along-channel velocity and salinity out of quadrature. The lateral flows, acting on the cross-channel salinity gradient, tend to stratify the water column on the flood and destratify the water column during the ebb. This tidal period variability competes, and often overcomes, the along-channel straining. Consequently stratification in Delaware Bay is often enhanced during the flood and reduced during the ebb, contrary to the classic model of tidal straining. This demonstrates that the cross-channel dynamics has an important influence on the salt transport and stratification in this system and may have other important consequences on processes such as sediment transport.