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.