Longshore transport of fine-grained sediment

An approximate formula is derived for the longshore transport of fine-grained sediment due to waves. This formula yields the cross-shore distribution of the unit discharge of suspended sediment mass as a function of wave and sediment properties, and bottom slope. The derivation is conveniently divided into two parts, one for the surf zone from the shoreline to the breakerline, and the other for the zone seaward of the breakerline, nominally up to the depth of closure. Suspended sediment concentration at any position is assumed to be determined exclusively by a local balance between erosion or entrainment of bottom sediment and settling of the eroded material. The formula has been applied to limited laboratory basin data on longshore current and suspended sediment concentration, as well as some suspended sediment measurements off Lian Island bordering the Yellow Sea in China. Improvements to the approach are contingent upon a better physical understanding of the way in which bottom mud is eroded and transported over the profile.