Hydraulic Design of Irrigation Canals - Sediment Transport in Irrigation Canals: A New Approach - page 258

Table C.4. Reduction of the boundary shear
stresses in non-straight canals.

Slightly sinuous 10%

Moderate sinuous 25%

Very sinuous 40%

C.7 SEDIMENT TRANSPORT CRITERIA

The velocity in a canal should be large enough to prevent siltation of
suspended sediment. The conveyance of suspended sediment through the
whole system assumes a concentration of very fine particles in suspension,
which is almost evenly distributed over the vertical of the turbulent water.
De Vos (1925) has stated that the relative transport capacity ( T / Q )is
proportional to the average energy dissipation per unit of water volume.

T
Q ∝

ρ w ∗ g ∗ v av ∗ S (C.27)

where:
T/Q = relative transport capacity

density of water (kg/m 3 ) ρ w =

acceleration due to gravity (m/s 2 )

g =

v av = average velocity (m/s)

bottom slope (m/m)
From energy considerations follows that sediment particles will be
transported by the water in case:

S =

ρ w ∗ v av ∗ S v av ∗ S

w ≤ or w ≤ (C.28)

ρ s − ρ w

where:
w

=

fall velocity (m/s)

ρ s = density of the sediment particles (i.e. 2600 kg/m 3 )

ρ w = density of the water (kg/m 3 )

relative density
To convey sediment in suspension the hydraulic characteristics of the
canal system should remain constant or should not decrease in downstream
direction. This means that ρ w ∗

=

S (W/m 3 ) should be constant or

g ∗ v av ∗

non-decreasing in downstream direction.
In a wide canal the average velocity can be expressed by v av = C ∗

S ) 0 . 5 , in which C is a general smoothness factor. From this velocity

( y ∗