Introduction - Sediment Transport in Irrigation Canals: A New Approach - page 6

Dahmen (1994) pointed out that an irrigation network should be
designed and operated in such a way that the required flow passes at the
design water level; no erosion of the canal bottom and banks occurs and
no deposition of sediment in the canal takes place. The design of a canal
requires a set of equations related to the water-sediment flow to provide
the unknown variables of the bottom slope and cross section. The geom-
etry of an irrigation canal that carries water and sediment will be the end
result of a design process in which the flow of water and the transport of
sediments interact. Chapter 4 outlines the main aspects of various design
methods of irrigation canals, including the regime method, the tractive
force and the permissible velocity approaches and the rational procedure.
Méndez (1998) developed the SETRIC model to improve the under-
standing of sediment transport in irrigation canals under changing flow
conditions, sediment load and roughness conditions and for various oper-
ational and maintenance scenarios. SETRIC is a one-dimensional model,
where the water flow in the canal has been schematised as quasi-steady
and gradually varied. The one-dimensional flow equation is solved by
the predictor-corrector method and Galappatti's (1983) depth integrated
model has been used to predict the actual sediment concentration at any
point under non-equilibrium conditions. Galappatti's model is based on
the 2-D convection-diffusion equation. The mass balance equation for
the total sediment transport is solved by Lax's modified method, assum-
ing steady conditions for the sediment concentration. The model including
the various calculation steps are presented in Chapter 6. For the prediction
of the equilibrium concentration the following sediment predictors have
been evaluated and the model uses the Brownlie, Engelund-Hansen and
Ackers-White methods. These sediment transport concepts are extensively
discussed and presented in Chapter 5 and Appendix A.
The SETRIC model can be applied to evaluate designs of an irriga-
tion network and to analyse the alternatives, but it can also be used as a
decision support tool in the operation and maintenance of a system and/or
to determine the efficiency of sediment removal facilities in an irrigation
system (Depeweg et al., 2002; 2003 and 2004). In addition the model can
be helpful for the training of engineers to enhance their understanding of
sediment transport in irrigation canals. Some examples of the application
of SETRIC for the design and evaluation of irrigation canals are provided
in Chapter 7.
In recent years SETRIC has been used to evaluate a large irrigation
system in Nepal (Paudel, 2002) and to assess its suitability to predict non-
equilibrium sediment transport (Ghimire, 2003). A special study analysed
the applicability and versatility of the SETRIC model in an irrigation canal
for different conditions of operation and sediment inputs (Sherpa, 2005).
Also, a one-dimensional convection diffusion module has been devel-
oped to calculate the flow and sediment transport in both equilibrium and
non-equilibrium conditions (Timilsina, 2005).