SETRIC, a Mathematical Model for Sediment Transport in Irrigation Canals - Sediment Transport in Irrigation Canals: A New Approach - page 166

start from the upstream

compare concentration
with d/s sub-section
and compute new BL

subsection upstream of
a section

Y N

u/s boundary? N

control
structure?

N

last
subsection?

Y N

check for the
consistency

Y

compare concentration
with d/s sub-section
and compute new BL

no change in BL

get new BL

Y

compare concentration
with d/s sub-section
and compute new BL

check for the
consistency

no change in BL

get new BL

BL = Bed level

siphon or
sluice?

control
structure?

Y Y

A section may be defined by:
• control structures
• off-takes
• change in canal geometry
• change in roughness
Consistency:
• bed erosion will not take place if the concentration downstream
of that point is not increasing and vice versa
Constraints:
• no change in bed level at upstream boundary
• no change in bed level upstream and downstream of a structure
except for weir and flumes where deposition up to crest level is possible
• no change in sediment concentration within the control consistency

N N

check for crest flushing
adjust computed BL

check for the
consistency

no change in BL get new BL

Figure 6.2. Flow diagram for SETRIC for calculating the water flow in main and lateral canals during a time step (after
Paudel, 2002).

Sediment aspects
The sediment is characterized by:
- Sediment concentration (ppm) at the most upstream boundary of the
main canal; no change of the inflowing sediment concentration during
one simulation period;
- Sediment size by the mean diameter d 50 ;
- No sediment deposition in the structures, the sediment inflow is equal
to the sediment outflow;
- Variations of the roughness conditions over time are incorporated in
the model; sedimentation during the irrigation season will induce
the development of bed forms, which depend on the flow condi-
tions (different flow conditions will produce different types of bed
form). The total equivalent friction factor is computed for every
time step and for each flow condition in each cross section of the
schematization;