The effects of wind‐generated currents on velocity asymmetry in tidal basins with varying geometries

Abstract

Geomorphologic characteristics of tidal basins have been shown to control tidal asymmetry and associated sediment transport potential in coastal regions. In this study, we examine how winds modulate horizontal velocity asymmetry patterns in shallow tidal basins. Numerical modelling experiments for a series of idealized basins in which planform shape and bathymetry were varied, reveal that an increase in wind speed promotes more extreme horizontal velocity asymmetry (larger velocity asymmetry values) without substantially altering the overall spatial pattern of velocity asymmetry throughout the domains. The wind forcing primarily influences mean and peak flow velocities, with a limited effect on tidal harmonics. Changes to the velocity asymmetry patterns are most evident for wind speeds of 6 m/s and greater, and for wind directions parallel to the main axes of the basins’ tidal channels. However, the velocity asymmetry is strongly depth‐dependent. Shallow intertidal basin regions are characterized by a downwind‐directed increase in velocity asymmetry, whereas deeper subtidal channels display asymmetry changes in the opposite direction. Additionally, the timing and duration of a wind event are found to influence the velocity asymmetry patterns. Wind events coinciding with flooding tides result in the most noteworthy differences between the relative size of the peak flood‐ and ebb‐directed currents inside the shallow basins, for wind event durations of both 3 and 6 h.