Discrete Particle Model for Bedload Sediment Transport in the Surf Zone

Abstract

Predicting the evolution of nearshore bathymetry from the highest uprush of the swash offshore to the location of wave breaking is a difficult problem of significant importance, with economic, legal, engineering, scientific, and military implications for coastal environments. Despite the apparent accessibility of the phenomena of interest, namely, the motion of sand under the forcing of waves and currents, the predictive capability of existing models for nearshore evolution is poor. A detailed study of the forces exerted on individual sand grains is undertaken in an effort to elucidate sediment transport mechanisms in the surf zone. New results indicate that fluid acceleration is a particularly important feature of surf zone transport; likewise, the processes of particle size segregation and the role of particle shape are newly explored. The study methodology employs computer simulations that describe the collective and individual motions of discrete particles immersed in a Newtonian fluid having essentially arbitrary density and viscosity. In this study all particle properties are those of quartz sand, and the fluid properties correspond to saltwater at 20°C. Such discrete-particle models, having a basis in molecular dynamics studies, have a broad range of applications in addition to the sedimentological one of interest here; for example, similar methodologies have been applied to traffic flow, schooling fish, crowd control, and other problems in which the particulate nature of the phenomenon is of critical importance.