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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 modelling approaches is driven by 2 the belief that complete data are a prerequisite for modelling and that the application of 2D and 3D m o d e l s r e q u i r e s m o r e d a t a t h a n t h e a p p l i c a t i o n o f 1 D m o d e l s. E x a m p l e s f r o m f l u v i a l morphodynamics are presented to illustrate these mistakes.

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The Dutch River Waal, a branch of the Rhine, has been trained for centuries to mitigate the effects of ice-jams and improve navigation. The works, started in 1850, involved river straightening and narrowing by a series of transverse groynes. Besides fulfilling their goal, the groynes also created the need to raise flood protection works and caused undesirable channel incision. This study assesses the effectiveness of training the river with a longitudinal wall instead of with groynes. The investigation analyzes the long-term response of the historical river with a two-dimensional depth-averaged (2DH) morphodynamic model. The results show that the wall would create two parallel channels, one becoming deeper and the other one shallower. The former would be as suitable for navigation as an equally-wide channel obtained with groynes. The latter would contribute in conveying water during high flow events and improve the river ecology. Training the river with a wall would also lessen channel incision. The best performance is obtained if the wall is built on the channel centerline, starting just upstream of a point bar top.

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