Wind contributions to current forcing in a tidal inlet: A case study at Oregon Inlet, NC

Abstract:

The influence of local and regional winds on tidal inlet hydrodynamics are investigated using 40 days of field observations collected at Oregon Inlet, NC, in the Spring of 2019. The component of winds oriented in the direction of the inlet channel is strongly correlated with observed water level gradients through the inlet that vary over sub-tidal timescales. Both the wind component and the water level gradient are well correlated to the residual (non-tidal) current within the inlet that varies over the same timescales. The contributions of wind to the net current are examined with a force balance and results suggest that the total hydrodynamics adjustments due to winds are comparable in magnitude to the tidal forcing. The magnitude of the wind-induced current exceeds the magnitude of the astronomically forced tidal current about 1/3 of the time and exceeds 50% of the tidal current about 2/3 of the time. The force balance also decouples the two mechanisms of wind influence, indicating that the sub-tidal current primarily results from the wind induced pressure gradient, with local wind drag modifying the sub-tidal current by 1-5%, generally in the same direction as the pressure gradient. The strong influence of winds on the net current suggests that models for sediment transport in the inlet should include wind induced pressure gradients across the inlet, and that local wind drag can largely be ignored. This work was supported by a DOD SMART Fellowship and the U.S. Army Corps of Engineers.