COMMENTS ON MODELING ALLUVIAL RIVERS

Abstract

The main criterion of modeling is how well it serves to support the right decisions. Predic- tive capability depends not only on correct simulation of sedimentation phenomena, but also on the nature of the decision which has to be supported. A code for simulating sedi- ment phenomena consists of its uncontested hard core and the protective belt, comprising the auxiliary hypotheses, assumptions and parameters. Calibration of complex models by integrated effects is ambiguous because the same effects can be obtained by different sets of parameters, the errors sometimes canceling out each others. Increasing the complexity of a model can improve its simulation capability, but introduces increasing data error. Long term prediction of river phenomena is limited because of the chaotic response of the highly non linear relationships. In the light of the above difficulties, a pragmatic approach to river modeling is suggested, based on site-specific simulation rather than on generally valid codes.