Longshore sand transport rates — A simple model for the East Anglian coastline

Abstract

A model has been developed for the East Anglian coast which predicts the potential longshore sand transport rates for seven 25 km-sections of coastline. Daily vector-averaged wind data from a single site on this coast are used in empirical equations to calculate the offshore waveheights. Wave refraction diagrams with the offshore topography for each section provide the angle of incidence of waves on the beach and the ratio of the incident wave's energy per unit crest length to the offshore wave energy per unit crest length. Six-second period waves are considered, with a cosine-squared directional spread of energy about the average wind direction. Wind data for the years 1964–1976 inclusive were input into the model and average annual potential sand transport rates computed for each 1 km-length of beach in each section. Variability between each 1 km was high and averages of not less than 5 km were normally used. Annual variability was considerable, reflecting the annual variability of winds. Potential transports were compared with the results of the cliff erosion studies and beach profiles from the East Anglian Coastal Research Programme. Generally there was good agreement when “continuity of sand” along the coastline was considered. Two sites were found where the computed potential rates were unreasonable in view of the general system, reflecting weaknesses of this model technique. At sites where the potential transport rates were considerably in excess of the rates likely to occur from sand continuity considerations, the beaches were found to be dominantly shingle. Technical details of the operation of this model are given in an Appendix.