Scour near structures in coastal seas

Scour is herein considered to be the lowering of the bed in the vicinity of a structure due to local accelerations and decelerations of the near-bed velocities and the associated turbulence (vortices) leading to an increase of the local capacity for transportation of sediment. Once a scour hole is formed, flow separation will take at the edge of the hole and a mixing layer will develop increasing the turbulence intensities and stimulating further scour of the bed (selfintensiffing process). Excessive scour close to the structure may ultimately lead to instability/failure of the structure. Herein, scour by currents, waves and combined waves and currents is considered. Jet scour related to high-velocity flows under, through and over structures is not reviewed.