Numerical simulations of the effects of vegetation on flow and morphology are helpful to understand the behaviour of natural rivers and to predict the developments of rehabilitated rivers. However, some fundamental problems remain in modelling these interactions. This paper describes the application of two-dimensional and three-dimensional numerical models to natural and rehabilitated river systems, i.e. the Rhine (the Netherlands), Allier (France) and Volga (Russia). The results show that vegetation has a pronounced effect on flow patterns and morphological developments in rivers. This can be subdivided in remote effects and local effects. Further analysis of the model results shows a fundamental shortcoming in the mathematical modelling of the effects of vegetation on the local sediment transport capacity. Traditional approaches to modelling vegetation roughness yield erroneous results in combination with common sediment transport equations. Therefore, research focuses on the development of new model approaches to accurately simulate the influence of vegetation on flow and morphology.@en