Benchmark study of numerical model grids to study historic floods of the river Rhine

Up until now, structured curvilinear grids are commonly used for hydraulic modelling. However, this grid type has several disadvantages such as staircase representations along closed boundaries and unnecessary high resolution in sharp inner bends. A so called ‘flexible mesh’ can overcome these limitations, since different shapes of grid cells can be used. However, model performance is not directly clear. Several different grid types are compared based on model performance and computation time. This shows that an unstructured grid with curvilinear grid cells in the summer bed and triangles in the floodplains is the most appropriate mesh for 2DH hydraulic modelling. A curvilinear grid in the summer bed ensures high resolution in the channel cross direction, while less grid cells are needed compared to a complete triangular grid. This has a beneficial effect on computation time.