Critical Examination of Longshore Transport Rate Magnitude

Abstract

Inconsistencies in the field data and predictions of longshore sediment transport (LST) rates associated with the CERC and Bagnold formulae are discussed. Practical errors in direct application of the formulae can result in overprediction of LST by a factor of up to 1.8. The degree of wave-averaging affects LST prediction by factors of 1.5 to 2.5. Use of the formulae with hindcast wave data results in overprediction of LST by factors of 2 to 5. Consideration of non-linear effects contradict laboratory findings that relate LST to wave steepness or surf similarity. Reasonable errors in field measurements potentially yield errors in the LST formulae by factors of 2 to 4. The functional dependence on wave height of the CERC and Bagnold formulae is validated by consideration of long-term shoreline change at long shore-normal structures.