On the wind-induced exchange between Indian River Bay, Delaware and the adjacent continental shelf

Abstract

The structure of the wind-induced exchange between Indian River Bay, Delaware and the adjacent continental shelf is examined based on current measurements made at the Indian River Inlet which represents the only conduit of exchange between the bay and the coastal ocean. Local wind measurements and sea levels from stations located along the open coast and in the interior of the bay are also obtained. Coastal sea level fluctuations are coherent with winds over periodicities of 2–10 days, with the highest response corresponding to winds aligned along two bands, one broadly centered around the general orientation of the Middle Atlantic Bight coastline between New Jersey and Virginia (040°T), and the other narrowly focused on the direction perpendicular to the local coastline (090°T). Currents in the inlet are also highly coherent with the wind along these two directions, but the high coherence is limited to time scales between 2 and 5 days. Within those time scales the currents in the inlet show largely depth-independent fluctuations which are highly coherent and in quadrature phase with the coastal sea level fluctuations, indicating that the subtidal exchanges in those time scales are principally accomplished by the remote wind effects on the shelf through the impingement of coastal sea level fluctuations at the entrance to the inlet. This coastal pumping effect produces unidirectional inflow throughout the water column under coastal set-up conditions, and outflow occurs under coastal set-down conditions. There is indication that a weaker, but still significant mode of bi-directional exchange also exists in the inlet, with currents in the upper layer fluctuating in opposite directions relative to those in the lower layer.