Inflows/outflows at the transition between a coastal plain estuary and the coastal ocean

A series of numerical experiments were performed to study the dynamics at the transition region between a wide (Kelvin number between 2 and 3.6) coastal plain estuary and the adjacent coastal ocean. In particular, the separate effects of modifying the seaward discharge within the estuary, the coastal ambient flow, the coastal ocean bottom slope, and the initial salinity gradient were investigated. The numerical experiments were carried out in a flat-bottom estuary with a N-S orientation that is connected to the ocean in the E-W direction. Results show that increased seaward discharge at the estuary upstream boundary reduces volume inflow and increases volume outflow through a cross-section at the estuary mouth. A southward coastal ambient flow is responsible for increased volume inflow, for keeping estuarine outflow within a few kilometers from the coast, for increasing surface flow divergence at the estuary mouth, and for hindering inflow that originates to the south of the estuary. When the coastal ambient flow is suppressed, the bottom slope of the coastal ocean causes negligible effects to volume transports, to the dynamcal balances, and to the shape and extent of inflows/outflows compared to results over a flat bottom. These effects of the bottom slope become non-negligible but are still minor when the coastal ambient flow is active. A pulse of buoyant water at the estuary upstream boundary causes, after the discharge stops, increased volume inflow with respect to other experiments. Increased salinity gradients produce enlargements to the deformation radii, the volumes exchanged, and the regions directly influenced by inflows and outflows.