A simple general expression for longshore transport of sand, gravel and shingle

•Derivation of simple general expression for computation of longshore transport along sand, gravel and shingle beaches•Comparison of results with formula of Kamphuis and CERC•Verification with measured short-term and long-term longshore transport values

Longshore transport of sand, gravel and shingle has been studied using field and laboratory data over a wide range of conditions. A detailed model (CROSMOR) for cross-shore and longshore sediment transport has been used to determine the effects of wave period, grain size, beach/surf zone slope and type of waves (wind waves or swell waves). The longshore transport was found to be proportional to wave height to the power 3.1 (≈ H3.1), to grain size to the power − 0.6 (≈ d50− 0.6) and to beach slope to the power 0.4 (≈ tanβ0.4). Regular swell waves yield much larger (factor 1.5) longshore transport rates than irregular wind waves of the same height. It is proposed to take this effect into account by a swell correction factor. Based on all results, a new simple and general (dimensionally correct) expression for longshore transport of sand, gravel and shingle beaches with grain sizes between 0.1 and 100 mm has been derived. Short-term and long-term field data of sand, gravel and shingle have been used for verification. In most cases the predicted longshore transport rates are within a factor of 2 of the measured values. The CERC and Kamphuis formulas have also been tested.