Grains in motion: A review

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.