FIELD INVESTIGATION OF SEDIMENT TRANSPORT IN THE SWASH ZONE

Concurrent measurements of swash flow velocity and sediment transport were obtained from a natural beach to develop a means for predicting s ediment transport in the swash zone. Twenty-seven swash events were mo nitored and the sediment load of each event was correlated to the flow velocity for both the wave uprush and backwash. The sediment load dis played a strong relationship with the time-averaged velocity cubed, co nsistent with equations for both bedload transport and total load tran sport under sheet flow conditions. Validation of the energetics-based model of Bagnold (1963, 1966) revealed different constants of proporti onality for wave uprush and backwash, with the uprush value being appr oximately twice that obtained for the backwash. Similarly, validation of a modified Shields parameter (to account for the effect of a slopin g bed) also indicated different coefficients. The physical explanation for the different constants of proportionality is that neither sedime nt transport model adequately accounts for the disparate nature of the two phases of the swash cycle. (C) 1998 Elsevier Science Ltd. All rig hts reserved.