This paper describes a study of alongshore sediment transport rate based on three‐dimensional hydraulic model experiments performed with regular and irregular waves. Deep‐water wave conditions, wave heights through the surf zone, wave‐breaking angles, longshore current velocity distribution, and the bed‐load and suspended‐load sediment transport distributions are measured simultaneously to form a coherent data set. An expression is developed linking sediment transport rate to wave steepness, beach slope, relative grain size, and breaking angle. The expression compares well with published field data.

Alongshore sediment transport rate

The total rate of longshore sediment transport was measured by streamer traps at 29 locations along the southeast coast of the United States and the Gulf Coast of Florida. The rate was also measured concurrently by traps and by short-term impoundment at Indian Rocks Beach, west-central Florida. Data on beach profiles, breaking wave conditions, and sediment properties were taken together with the transport rate. The measured total rates of longshore sediment transport were compared to predictions obtained with published empirical formulas, most of which have been calibrated mainly by sediment tracer measurements made on the (high-wave energy) Pacific coast. Transport rates measured in this study by the streamer sediment traps and the short-term impoundment along low-wave energy coasts were considerably lower than the rates predicted by empirical formulas. The empirical predictions appear to be unrealistically high for the low-wave energy settings investigated in this study. The linear relationship between wave energy flux factor and the total rate of longshore sediment transport contained in the commonly used CERC predictive formula is supported by the streamer trap measurements. However, a lower value of the empirical coefficient, 0.08 instead of the 0.78 recommended by the Shore Protection Manual, was determined by the trap data for low-energy coasts. The total rates of longshore sediment transport predicted by the KAMPHUlS (1991) formula which includes the influences of wave period, beach slope, and sediment grain size were about 3 times lower than the CERC predictions and closer to the measured values.

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Total Longshore Sediment Transport Rate in the Surf Zone: Field Measurements and Empirical Predictions

A review and assessment of longshore sediment transport equations for coarse-grained beaches

Calculation of littoral sand transport rate

A bed-load model, based on a generalization of Bagnold's (1954) constitutive equations together with the assumption of similarity profiles for velocity and concentration, was proposed for sediment transport by waves by Sleath (1994). This model is now extended to wave/current flows and applied to three different situations: (a) oscillatory flows with superimposed currents, (b) net transport produced by progressive waves over a flat horizontal bed, and (c) longshore transport induced by waves approaching a beach. In all three cases the model gives reasonable agreement with experiment. In the case of longshore transport the model produces almost the same formula as that of the Coastal Engineering Research Center (1977), apart from additional terms for density and grain size.

Sediment transport by waves and currents

A series of mobile bed model tests of a prototype circular sand island was performed to determine scale effects. It was found that scale effect was largely a function of mobility number with some secondary effects of Reynolds number, bedform and critical profile depth. It was concluded that a model series using prototype sand grain size is necessary at this time to effect successful extrapolation to prototype.

R.B. Nairn

Papers

Calculation of littoral sand transport rate

Scale effects in large coastal mobile bed models