On the Risk of Erosion of Cohesionless Sea Floors

Sea floor erosion caused by currents in natural or man-made channels such as coastal inlets and coastal navigation canals is in many cases a serious problem. Erosion is of course also the first step in the natural littoral processes that are forming the coastlines of the continents. While the problem of incipient motion of the particles of a cohesionless sea floor usually has been approached from a deterministic point of view it should be realized that this phenomenon actually must be of a stochastic nature due to the turbulence of the flowing water and the more or less random composition of the bed material. By developing expressions for the time-mean velo- city profile near the bed, the hydrodynamic lift and drag forces acting on the individual particles and a criterion of incipient motion, an entrainment function similar to the one proposed by Shields is derived.