INFORMED USE AND POTENTIAL PITFALLS OF CANAL MODELS

Numerical models of unsteady flow in canals are used in the design, an alysis, and operation of irrigation-canal systems. Their informed use requires knowledge of the potential pitfalls and sources of error. The re are three model parameters that influence errors in the model outpu t: the distance step DELTAx, the time step DELTAt, and a weighting fac tor theta. The influence of the Courant number on the accuracy of the results is studied. Calibration of topographical and hydraulic paramet ers and verification of the model are important steps in the successfu l implementation of canal models, Two tests are presented that can be used to check the accuracy and stability of the programs. The first is a mass-conservation test, and the second is a ramp-discharge test. Th e results of these tests on several commercially available programs ar e presented. The intricacies of model calibration, model interpretatio n, and performance parameters are also discussed.