Time-averaged model for longshore current and sediment transport in the surf and swash zones

A numerical model based on the time-averaged continuity, cross-shore momentum, longshore momentum and energy equations for the case of longshore uniformity is developed to predict the cross-shore variations of the mean and standard deviation of the free surface elevation and depth-averaged cross-shore and long-shore velocities under obliquely-incident irregular breaking waves. Iterative finite-difference approximations are used to solve these governing equations. The suspended sediment volume per unit horizontal area is estimated using the computed energy dissipation rates due to wave breaking and bottom friction. The longshore suspended sediment transport rate is estimated as the product of the longshore current and suspended sediment volume. The developed model is compared with available field data and with the time-dependent model of Kobayashi and Karjadi (1996). The model is also compared with the laboratory data for spilling and plunging breaker tests after analyzing the extensive measured data to get meaningful results for comparison. The calibrated model is in fair agreement with the data except that this time-averaged model cannot predict wave runup, low frequency waves, shear waves and bed load. The longshore suspended sediment transport rate is shown to be approximately proportional to the square of the longshore current. The developed model is computationally very efficient and well suited for future comparisons with extensive data sets.