SETRIC, a Mathematical Model for Sediment Transport in Irrigation Canals - Sediment Transport in Irrigation Canals: A New Approach - page 164

level, or at bifurcations or confluences have to be simulated by the
model. The distribution of water and sediment at bifurcations will
depend on the local flow pattern at the branches.

6.1.4 General description of the mathematical model
The mathematical model SETRIC simulates the water flow, sediment
transport and changes of bottom level in an open irrigation network with a
main canal and several secondary canals with or without tertiary outlets.
Various flow conditions along the canal network and during the irrigation
season can be simulated. Figure 6.1 shows the flow diagram for calcu-
lating the change of the bottom level in a canal reach during one time
step. Flow diagrams of the computer program SETRIC for the water flow
and sediment transport calculations in a canal reach are shown in Figures
6.2 and 6.3. The specific module for downstream controlled irrigation
systems will be discussed in Section 6.2.
The background for the hydraulic and sediment transport computations
was described in the previous chapters. The general framework of the
computer program consists of:

Hydraulic aspects
- The water flow can be modelled as a sub-critical, quasi-steady, uniform
or gradually varied flow (backwater as well as drawdown curves). The
water profiles for the subcritical, gradually varied flow include: H2,
M1, M2, C1, S1 and A2;
- The water flow is in open canals with a rectangular or trapezoidal
cross section; only friction losses are considered: no local losses due
to changes in the bottom level, cross section or discharge will be taken
into account. Seepage losses are also not included in the model;
- The canal sections are characterized by the following geometrical
dimensions:
• length ( l ) presents the length of a canal reach ( m );

• bottom width ( B );

• side slope m (1 vertical : m horizontal);

• the roughness is defined by the equivalent roughness coefficient

( k s ); the model computes the total friction factor from the composite
roughness of the cross section (See Appendix F);

• the distance is measured along the canal axis; coordinates give the

location of a canal reach; the most upstream boundary is defined as
x

= 0m;

• bottom slope ( S o in m/m);

•

bottom elevation above a reference level (datum) at the beginning of
each canal section ( z b ).