Impacts of Cross-Shore Winds, Waves, and Sand Ridges on Inner Shelf Circulation

Abstract

Understanding of circulation on inner continental shelves needs to be advanced to accurately predict the transport and connection between the shelves and nearshore. The circulation over the storm-dominated Fire Island Shelf, New York and a series of in situ shoreface connected sand ridges was investigated through high-resolution field observations, numerical simulations of hydrodynamics, and principal component analyses. The along-shelf subtidal flows were more energetic than the cross-shelf subtidal flows. Alongshore winds were driving the along-shelf subtidal flow and the variability of water levels. The cross-shelf subtidal flows were dominantly onshore near the seabed and offshore near the surface: the processes significant in this two-layer exchange were cross-shore winds which were commonly overlooked in literature, alongshore winds through Coriolis, and bottom friction. The ridges were significant in changing the magnitude and even the direction of the pressure gradients and associated flows. Wave impacts including water level changes, Stokes drift, vortex force, and breaking became significant in the inner shelf and the nearshore during wave-energetic events. Depending on the directions of waves and winds, waves caused to accelerate or decelerate and even reverse the wind-induced flow. In case of more shore-normal waves, the cross-shore Stokes drift became more significant; its interaction with Earth's rotation and flow vorticity generated significant Stokes-Coriolis impacts and vortex force, respectively, in the alongshore. With results applicable to other shelf settings, this study advanced the understanding of spatial and temporal variations of flows along and across inner shelves under varying forcing conditions.