3.6 SEDIMENT DISCHARGE MEASUREMENT
In this section the basic terms and methods of measuring sediment discharge (sediment
load) are described. In Chapter 4, the theory, equations, and methods of computing bed
material transport are described.
There are many terms that have developed over time to describe the many aspects of the
transport of sediment by water. Sediment transport is the time rate of a quantity of sediment
(by weight) moving past a cross-section of the stream. It is a discharge. Because it is
measured by weight (often as tons), discharge is often referred to as sediment load. Other
terms associated with sediment transport are suspended sediment discharge, bed load, bed
material load, bed material discharge, and wash load.
The many terms describing sediment transport result from using or misusing and mixing
terms that describe (1) the source of the sediment (bed material load and wash load), (2)
mode of particle movement (suspended bed material load and bed load) and (3)
measurement of sediment discharge (measured sediment discharge and unmeasured
sediment discharge). The terms are defined in Chapter 4, (Section 4.2) and illustrated in
Figure 3.20 from HEC-20 (Lagasse et al. 2001).
Composed of particles
Composed of particle
finer than those found in
sizes found in the bed
appreciable quantities in
that move by surface
the bed. Washload moves
found in the bed that
creep, sliding, saltation
in suspension and is
are transported in
or rolling within the
provided by bank and
BED MATERIAL LOAD
TOTAL SEDIMENT LOAD
Figure 3.20. Definition of sediment discharge (load) components (Lagasse et al. 2001).