Sand and stone transport under breaking irregular waves and currents

Five tests were conducted in a wave basin with a recirculation system in the Large-scale Sediment Transport Facility (LSTF) of the US Army Engineer Research and Development Center to study sediment transport due to waves and currents. These five tests are explained where the fine sand beach is assumed to be impermeable. The analyzed data are presented for the subsequent comparison with the cross-shore numerical model CSHORE. The effects of external currents on the wave-induced longshore current and sediment transport in the surf zone are examined using the five tests and CSHORE which is extended to include the alongshore pressure gradient term in the longshore momentum equation and to allow oblique waves in the wet and dry zone on a beach. Analytical solutions for the case of current only are derived from the combined wave and current model and the sediment transport model in CSHORE. The cross-shore variations of the wave setup, root-mean-square wave height, mean cross-shore and longshore velocities, and total longshore sediment transport rate are predicted fairly well for the five tests with no and favorable pressure gradients. The cross-shore variation of the suspended sediment volume per unit area is predicted only qualitatively partly because of the large scatter of the sediment volumes estimated from the measured sand concentrations. The calibrated and verified CSHORE is used to compute cases of adverse and time-varying pressure gradients and extrapolate the experimental results for wider applications. The adverse alongshore pressure gradient is shown to reverse the longshore current in the outer surf zone. The tidal effect on longshore sediment transport is predicted to be minor if the tide generates the alongshore pressure gradient varying with time sinusoidally.;Permeability is important for rubble mound structures and gravel beaches. A probabilistic hydrodynamic model for the wet and dry zone on a permeable structure is developed to predict irregular wave action on the structure above the still water level. The model is based on the time-averaged continuity and momentum equations for nonlinear shallow-water waves coupled with the exponential probability distribution of the water depth. The model predicts the cross-shore variations of the mean and standard deviation of the water depth and horizontal velocity. The model is compared with four test series in which measurement was made of the wave overtopping rate and probability as well as the water depth, velocity and discharge exceeded by 2% of incident 1,000 waves. The agreement is mostly within a factor of 2. Damage progression of a stone armor layer is predicted by modifying a formula for bed load on sand beaches with input from the hydrodynamic model. The damage progression model is compared with three tests that lasted up to 28.5 hours. The numerical model tends to underpredict the eroded area above the still water level (SWL) as well as the deposited area below SWL at the beginning of each test. The agreement tends to improve with the damage progression. This may be related to stone units placed in unstable manners on the initial profile. The model predicts the temporal progression of the eroded area quite well. CSHORE predicts both sand transport on impermeable beaches and stone transport on permeable structures within the error of a factor of 2.