Video‐imaged surf zone wave and roller structures and flow fields

Abstract

The measurement of mean water levels, roller geometries, and phase ensemble‐averaged velocity and turbulence intensity fields under spilling and plunging waves breaking in a two‐dimensional laboratory surf zone is presented. The velocities were measured using digital correlation image velocimetry, while water levels and roller geometries were determined through gray scale filtering of video images. The phase ensemble‐averaged horizontal and vertical components of velocity and turbulence intensities are measured throughout the entire flow domain, including the wave roller area, by utilizing the aerated areas as part of the flow structure. The time‐averaged horizontal velocities (undertow), turbulence intensities, and turbulent kinetic energies are determined by averaging across the wave phase. Turbulence magnitudes are found to compare favorably with existing laser Doppler anemometry measurements below the wave trough level, where such measurements have generally been confined because of aeration contamination effects. The significantly higher velocity and turbulence intensity magnitudes measured above the trough level in the present experiments highlight the novel nature of the present investigation for describing flow regimes in the surf zone.