BOTTOM BOUNDARY SHEAR STRESSES ON A MODEL BEACH

Resumen

The maximum amplitude of shear stress in the bottom boundary layer of water waves was evaluated with a Preston probe inclined on a 1 12 5 slope beach Near bottom velocity profiles were obtained in laminar and developing turbulent flow conditions from which the experimental boundary layer thicknesses were evaluated Agreement between experimental bottom velocities and those calculated from Airy theory deteriorate with decreasing depth on the beach resulting m lower shear stress values than predicted by linear theory The measured boundary layer thickness on the slope exceeds the predicted for horizontal bottom, increasing shoreward to some critical depth outside the breaker zone from where it decreases shoreward The influence of roughness on the shear stress distribution is considerable m the "offshore" region, but becomes negligible near the breaker zone On a smooth bottom the coefficient of friction agrees with Kajiura's expression.