CHAPTER 4
SEDIMENT TRANSPORT
4.1 INTRODUCTION
This chapter describes key terms and several methods of computing sediment transport in
alluvial channels. Since a significant portion of understanding sediment transport processes
centers on correct use of the terminology, the first two sections deal with definitions and
general concepts. The chapter also includes the derivation of the basic suspended bed
sediment transport equation to illustrate the significant physical processes of sediment
entrainment into the flow. Three classic sediment transport formulae are then discussed to
illustrate the application of sediment transport theory.
Simple sediment transport equations, in the form of power functions, are also presented in
this chapter. The power function equations are well suited for quick estimates of sediment
transport capacity and are easily adapted to field measurements. The Yang sand and gravel
total load equations are also suggested as a basic approach for hand calculation. In
addition, an overview of selected sediment transport equations is presented. The overview
suggests the range of applicability of these equations (based on bed-material size), and
provides references to those equations not discussed in detail in this chapter. Finally, a step-
wise application procedure for sediment transport calculations is outlined.
Numerous sediment transport formulae have been developed with a wide range of laboratory
and field conditions. Appendix B includes the results of testing several widely used sediment
transport equations using a large compilation of river data.
4.2 DEFINITIONS
In this section the basic terms for describing sediment load in alluvial channels are
summarized.
Bed layer: The flow layer, several grain diameters thick (usually taken as two grain diameters
thick), immediately above the bed.
Bed load: Sediment that moves by rolling or sliding along the bed and is essentially in contact
with the stream bed in the bed layer, i.e. contact load.
Bed material: The sediment mixture of which the stream bed is composed.
Bed material discharge (load): That part of the total sediment discharge which is composed of
grain sizes found in the bed, i.e. bed load (contact load) plus suspended bed material
discharge (load). The total transported bed material discharge (or bed sediment discharge) is
assumed equal to the transport capacity of the flow.
4.1
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