Vertical Structure of the Turbulent Dissipation Rate in the Surfzone

Surfzone turbulence is generated at the surface by breaking surface gravity waves and near the bed from the vertical shear of strong mean currents. Surfzone turbulence vertically mixes momentum, sediment, tracers, and biota. However, the vertical structure of surfzone turbulence and the relative contributions of these two sources is not well understood. Turbulence is often quantified using the turbulent dissipation rate. Previously, the vertical structure of the dissipation rate has been indirectly examined using a single fixed Acoustic Doppler Velocimeter (ADV) along with tidal changes in water level and bathymetry evolution. In October 2008, a vertical array of 3 ADVs will be deployed for 2 weeks in the surfzone to study the vertical structure of the dissipation. The rapidly-sampled ADVs together with an algorithm that converts from frequency to wavenumber spectra is used to estimate the dissipation. Breaking-wave and bottom-boundary-layer dissipation scalings will be examined to determine the relative importance of surface and bottom turbulence sources under different wave, tide, and current conditions. Supported by ONR and NSF