Apparent Roughness in Wave–Current Flow: Implication for Coastal Studies

High turbulence intensities generated by waves in the wave bottom boundary layer affect the mean current velocity and should be taken into account for calculation of currents in the presence of waves. This influence of the wave-induced turbulence on the mean current can be schematized by introducing an “apparent” bed roughness, which is larger than the physical bottom roughness. Apparent bed roughness is defined here as roughness that provides the same depth-mean velocity for current alone configuration as for the wave–current flow. A one-dimensional vertical “k–l” turbulence closure model that allows detailed time dependent flow modeling has been applied for apparent roughness computations. The domain of variable parameters is chosen according to the Israeli near-shore conditions. An approximate expression for apparent bed roughness calculations as a function of wave and current parameters based on this turbulence closure model is derived. Simulation of flow patterns on the Tel Aviv coast using the three-dimensional Costal and Marine Engineering Research Institute flow model and implementing apparent roughness maps, calculated by the approximate expression, has been performed.