Wave Breaking and Turbulence at a Tidal Inlet: Shoals, Currents, & Winds

Abstract

Field measurements of waves, currents, winds, and turbulence collected from surface drifters at New River Inlet (NC) are used to characterize wave breaking. Breaking regions are identified along drifter tracks by three separate metrics: decreases in wave energy flux, wave breaking counts from images, and elevated turbulent dissipation rates. Break points are used to evaluate the conventional depth breaking parameter, γ, and to develop a new breaking parameter, γ_u, which includes the effects of currents. The new breaking parameter has a more consistent critical value across all conditions because it successfully accounts for enhanced breaking with opposing currents and depressed breaking with following currents. In addition, turbulent dissipation rates correlate better with γu than with γ when currents are present. A TKE (turbulent kinetic energy) budget is discussed where the change in TKE is due to the balance between wave breaking and turbulent dissipation. Net energy input and change in TKE are well-matched but the magnitudes are offset. This suggests that other terms in the balance such as transport of TKE, generation of MKE (mean kinetic energy), and bubble dynamics are important to the overall energetics of the inlet. Offshore of the inlet, away from the shoals and currents, whitecaps are common, and the turbulent dissipation rates are correlated with windspeed, consistent with previous studies.