The Sediment Transport Model and its Applications - Sediment Transport in Irrigation Canals: A New Approach - page 187

expressed in terms of either the ratio between the actual incoming sedi-
ment load and the sediment transport capacity of the canal (equilibrium
concentration) or the ratio between the actual median sediment size and
the design value of the median diameter (0.15 mm):

actual sediment load
equilibrium sediment load (108 ppm)

Relative sediment load = (7.3)

actual median sediment
design median sediment size (d 50 =

=

Relative sediment size

0 . 15 mm)
(7.4)

The changes in the sediment concentrations and diameter are kept
within the limitations of Galappatti's model as presented by Ghimire
(2003), Ribberink (1986), Wang et al. (1986) and Paudel (2010). Their
research results are discussed in Chapter 5 and include two specific
limitations: firstly, concerning the deviation of the mean concentration
from the mean equilibrium concentration and secondly, the fall velocity
of the sediment w s / u ∗ should be much smaller than unity.
In view of the fact that the total incoming sediment load during the
simulation period is different for each relative sediment load, a relative
deposition value will be used to describe the deposition in the entire
canal. The relative deposition is expressed in terms of the ratio of the total
sediment deposited and the total amount of sediment entering the canal,
both during the simulation period. It is expressed as:

total deposition in canal
total volume of incoming sediment load

Relative deposition = (7.5)

The deposition in an irrigation canal depends on many factors; one
is formed by the characteristics of the incoming sediment. Any deviation
from the equilibrium concentration at a certain place and time will result
in a relatively larger sediment load and a greater deposition in the entire
canal. Table 7.3 shows the total amount of sediment deposited as a function
of the relative sediment load after 90 days for the design flow of 25.75 m 3 /s
and according to Brownlie's predictor.

Table 7.3. Total amount of sediment deposition as a function of the relative discharge
according to Brownlie's sediment predictor.

Relative sediment load 1.0 1.25 1.5 2.0

Total volume of sedimentation (m 3 ) 0 1889 5062 11392