Miles, J.R., 2013. Wave shape effects on sediment transport.

Waves approaching the shoreline become skewed in the shoaling region and asymmetrical in the surf zone. The different velocity distributions associated with these waves affects sediment suspension, transport, and ultimately beach morphology evolution. An intra-wave model of sediment suspension was constructed in which a given velocity time series is used to predict sediment concentrations based on a Bagnold type u-cubed model for stirring, balanced by settling. The model was validated against field data gathered at Sennen (Cornwall, UK), where simultaneous high frequency (8 Hz) measurements of sediment concentration and velocity were made in the surf zone of a macro-tidal, intermediate beach. The model was run for a range of hypothetical velocity time series associated with different wave shapes, grain sizes and wave periods. Results indicate that asymmetric waves, skewed waves, and skewed-asymmetric wave velocity profiles lead to increased wave-averaged suspended sediment concentrations, and increased onshore transport rates when compared to sine waves of similar velocity range. Skewed-asymmetric waves give rise to almost twice as much transport as skewed or asymmetric waves alone. Finer grained sediments, and shorter period waves give higher mean sediment concentrations and transport rates. In conditions when sine waves result in little net transport (coarse grains or long wave periods), the evolution of wave shape to skewed and/or asymmetric can directly give rise to a net onshore transport. Wave shape (sine, skewed and/or asymmetric) is therefore identified as a key controlling variable in predicting suspended sediment concentrations and transport rates in the nearshore.