Grains in motion: A review

This review paper aims to present a practical, integrated procedure for the prediction of sediment transport rates in both the continental and marine environment, based on the settling velocity of particles. Such studies have important applications in diverse fields such as civil and coastal engineering, sedimentology and environmental geology, where they can assist in flood control and the prevention of contaminant dispersal by wind and water, as well as the siltation of dams and harbours. The formation of placer deposits including gold, diamonds and other heavy minerals is also controlled by sediment transport processes, so that these studies can form the basis for more efficient exploration programs. The first part of the paper discusses some basic principles important in sediment transport, followed by an overview of published methods to determine the settling velocity of differently shaped particles, including natural grains. The application of settling velocity to predict the entrainment threshold of sediments on plane, horizontal and inclined beds by unidirectional currents and oscillatory waves is then discussed, which finally leads to the determination of sediment transport rates over plane and rippled beds. The validity of this approach to natural conditions is tested against published field data where possible. Other, widely used methods are also critically discussed, pointing out severe problems in current sampling technology and the calculation of bedload transport in natural environments