The Sediment Transport Model and its Applications - Sediment Transport in Irrigation Canals: A New Approach - page 209

in sediment deposition. The analysis of a weir at 2 500 m from the intake
shows that for an actual incoming concentration less than the equilibrium
concentration there is no sedimentation in the canal.
The previous discussions show that for discharges smaller than the
design discharge the equilibrium concentrations are smaller than the con-
centration for the design discharge (55 ppm). These smaller values have
been used to evaluate only the effect of the structure. Therefore the equi-
librium concentrations of the canal have been determined for various
discharges without the influence of the weir and this concentration has
been used as the incoming concentration for a simulation with the weir at
the end of the first canal section. The effect of the structure on the depo-
sition will be more pronounced when the sediment-carrying capacity of
the canal decreases for smaller inflow discharges. The model simula-
tions show some deposition in the canal, which started from the weir in
an upstream direction. The values are very small, about 5-10% of the
incoming sediment load, and the deposition height is also relatively small,
but nevertheless observable. This phenomenon can also be observed in
the previously presented examples, but it is very small and much smaller
than the sedimentation due to the suspended load.
Figure 7.29 gives the sedimentation over the first 300 m in front of the
weir for an incoming concentration smaller than the equilibrium concen-
tration and for a discharge of 74% of the design discharge. The described
tendency is very clear during the first days after the start of the simulation.
For longer periods and for larger discharges the effect becomes smaller.

9.85

9.84

9.83

9.82

9.81

9.80

9.79
2200 2250 2300 2350 2400 2450 2500 2550

Figure 7.29. Sediment
deposition in the canal section
300 m upstream of the weir
as a function of time.

Distance from intake (m)

0 days 15 days

30 days 90 days

Figure 7.30 shows the sediment volumes deposited in the canal for
a weir width of 10 m at the end of a canal section of 2 500 m for the
various discharges (74, 80, 90, 100%) and for an incoming concentration
equal to the equilibrium concentration at t 0 (23, 32, 42 and

54 ppm respectively). The deposited volumes due to the structure are small

= 0 and x =