Environmental Engineering Reference
In-Depth Information
and sediment inputs they are inadequate to describe the sediment trans-
port process. Under such conditions the process of sediment transport can
best be described by numerical modelling.
Irrigation canal networks form a complicated hydraulic system as they
have to handle the motion of water and sediment as well as the mutual
interaction of both motions. The sediment transported by the flowing water
causes changes in the bed and on the sides of the canals and these changes
will also influence the water movement. Hence, sediment transport and
water flow are interrelated. However, the time scales of the flow of water
and the sediment transport are different in canals and therefore, the two
processes will be discussed separately to specify their particular properties
and characteristics.
The objective of these lecture notes is a description of the recently
developed and tested sediment transport concepts in irrigation canals and,
therefore, only those hydraulic aspects necessary for a better understand-
ing of the sediment transport will be discussed in Chapter 2. This chapter
will present a synopsis of the main hydraulic principles in open canals
together with a short description of the dimensionless numbers used
in the sediment concepts and a classification of flow types including
uniform and non-uniform flow theories. Also the basics of the flow
distribution above hydraulically rough and smooth boundary layers will
be reviewed.
Before discussing the concepts of sediment transport the main proper-
ties of sediment will be given. Sediments are fragmented material formed
by the physical and chemical disintegration of rocks and they can be
divided into cohesive and non-cohesive sediments. Non-cohesive sedi-
ments do not have physical-chemical interaction and their size and weight
are important in view of their behaviour. The total sediment transport
in rivers and canals can be divided in suspended load and bed load (see
Figure 1.1).
Wash Load
(direct erosion material)
Total Suspended
Load
Total Sediment
Transport
Suspended
Bed-Material
Bed Load
(from bed)
Figure 1.1. Classification of
sediment transport.
Chapter 3 will present the main characteristics of sediments including
density and porosity; particle size and size distribution; shape and fall
velocity and the main dimensionless parameters used in the sediment
transport theories.
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