Wave Enhanced Overtides in an Idealized Tidal Inlet System

Abstract

AbstractTidal water levels and currents in the shallow water environments of the inner shelf are subject to nonlinear interactions that produce higher frequency harmonics known as overtides, which contribute to the residual transport of scalars. The primary hydrodynamic overtide generating mechanisms (advection, nonlinear continuity and bottom friction) are well known. Yet, other mechanisms may exist in coupled systems characterized by wind waves and barotropic tides. This work uses process‐oriented coupled tides‐waves numerical simulations of an idealized barrier beach domain to study the effect of varying tidal range and wave conditions (height, period, direction) to investigate new mechanisms of overtide generation. Harmonic analysis of results from 92 simulations indicates that an increase in wave height amplifies overtide current velocities in both the alongshore and cross‐shore directions, while changes in wave period and wave direction have a lesser effect. A maximum increase of ∼140% in overtide current velocity magnitudes was observed in domain‐wide averages from a tides only to a coupled tides‐waves simulation. Decomposition of the depth‐averaged momentum balance of the tides only and tides‐waves simulations identify bottom stress, pressure gradient, and bottom wave streaming enhancing overtide generation. Accelerations from wave‐enhanced pressure gradients and bottom wave streaming produce a shoreward bottom current and an offshore directed return flow that persist throughout a semidiurnal tidal cycle, interacting with tidal currents to enhance asymmetries between flood and ebb.