Annual variation in the net longshore sediment transport rate

Abstract

The annual variation in the net longshore sediment transport rates at three South African and at one North African site is investigated. The net rates at these sites, given in the first table, show large variations. It was found that measurements of longshore transport rates should be conducted continuously for 5–8 years in order to obtain an accurate value (within 10%) of the true long-term mean net longshore transport rate. A second table was drawn up, which can be applied to determine the range in which the true mean rate will fall if measurements were done over a shorter period than the recommended 5–8 years. It is reasonable to expect that the conclusions are widely applicable, especially for exposed sites. It is recommended that an accurate assessment of the long-term mean net longshore transport rate at a site can best be made cost-effectively by doing limited site-specific measurements, calibrating the best longshore transport formula for the particular site, and predicting the transport rates using a representative wave climate.