Five common mistakes in fluvial morphodynamic modeling

• More widespread use of fluvial morphodynamic models calls for more awareness of common mistakes.
• Numerical simulations show the effects of omitting sediment transport deviations due to bed slopes.
• Numerical simulations show the effects of inputs that impose morphodynamic patterns beforehand.
• Lack of data is no valid reason for preferring 1D morphodynamic models over 2D or 3D models.

Recent years have seen a marked increase in the availability of morphodynamic models and a proliferation of new morphodynamic codes. As a consequence, morphodynamic models are increasingly developed, used and evaluated by non-experts, possibly leading to mistakes. This paper draws attention to five types of common mistakes. First, new morphodynamic codes are developed as extensions of existing hydrodynamic codes without including all essential physical processes. Second, model inputs are specified in a way that imposes morphodynamic patterns beforehand rather than letting them evolve freely. Third, detailed processes are parameterized inadequately for application to larger spatial and temporal scales. Fourth, physical and numerical phenomena are confused when interpreting model results. Fifth, the selection of modeling approaches is driven by the belief that complete data are a prerequisite for modeling and that the application of 2D and 3D models requires more data than the application of 1D models. Examples from fluvial morphodynamics are presented to illustrate these mistakes.