Model for the Computation of Time-Steady Nearshore Currents

BACKGROUND: Under the assumptions of longshore uniformity, monochromatic and unidirectional waves, one-dimensional (1-D) models have predicted the steady depth-integrated longshore current with reasonable accuracy in the regions of intense breaking (e.g., Bowen 1969; Longuet-Higgins 1970; Kraus and Larsen 1991). The addition of random wave fields with directional spread (Battjes 1974; Thornton and Guza 1986) produce similar results but indicate a difference in the magnitude of the horizontal mixing terms. It is, however, necessary to also predict the vertical structure of time-steady currents in the surf zone to reliably compute sediment transport rates. Indeed, concentrations of sediment are found to be orders of magnitude larger in the near-bed boundary layer where fluid velocities are, in general, smaller than the depth-averaged value. It is, therefore, of practical importance to predict the vertical variation of nearshore currents.