ABSTRACT
Most rivers transport sediment for some or all of the time. Over timescales of events (floods), seasons and years, erosion and deposition of sediment alters the channel cross section and affects channel roughness. Sediment deposition reduces reservoir capacity, erosion of the bed can lead to instability of the watercourse, and scour can undermine hydraulic structures. Estuaries and coastlines are subject to constant sediment movements, leading to long-term accretion or erosion. Thus, the study of sediment transport is of fundamental importance in river and coastal engineering. In this chapter, the basic concepts of sediment transport are introduced and some of the most widely used prediction formulae are described. The treatment is limited to cohesion-less transport in unidirectional flow, which is the transport of sand and gravels by rivers and tidal currents. Firstly, the principal characteristics of sands and gravels and the modes of transport in water are described. Next the concepts of threshold of movement, the entrainment function and suspended sediment transport are introduced and equations developed. This leads to the calculation of the necessary parameters associated with the prediction of sediment transport and the presentation of sediment transport equations for bed load, suspended load and total load. Examples are given of how to calculate their values for both tidal and river flow situations. Finally, the accuracy and limitations of the transport equations and the further complexities to be found in estuaries and along coastlines are discussed. This chapter also provides some of the background knowledge required for the study of river engineering, which is presented in Chapter 15. Worked examples and problems for solution are also given in the text.
