Until now, structured curvilinear grids are commonly used for hydraulic modelling to discretize the model domain within the finite difference and finite volume framework (e.g. From the six grids studied, the hybrid grid with curvilinear grid cells in the main channel and triangular grid cells in the floodplain is recommended for hydraulic modelling since computation time is low, while model output shows sufficient accuracy.Ĭurrently, sophisticated two dimensional horizontal (2DH) models are used to get a detailed and accurate representation of water levels, flood patterns and potential flood prone areas which help to define flood protection measures. The analysis shows that unstructured grids are affected most by the calibration which is reflected in the wide spreading of calibrated friction values. Bathymetry accuracy and numerical friction, both as a result of grid resolution, and numerical viscosity as a result of grid shape play a vital role. This enabled us to draw conclusions on the choice of optimal usage of the grids in engineering studies. Therefore, calibration was performed such that simulated water levels resembled measured water levels by adjusting the main channel friction. The spread in simulated water levels was found to be rather large with a maximum deviation of 78 cm. We studied simulated water levels using the six grids, considering equal main channel friction, which enabled to study the isolated effects of grid shape and size. As a case study, we use the Waal River (with main channel and floodplains).
In this study structured, unstructured and hybrid grids with a high and low resolution were compared. Grid shape (curvilinear/structured versus triangular/unstructured) and grid size affect model output.