Unveiling the Implications of Schematisation Choices in Fluvial Flood models : Dike breach induced floods in Betuwe Tieler en Culemborgerwaarden

Flood modelling software is constantly updated, and new software is developed. This research showed the impact of several schematization choices on model results in D-HYDRO Large differences between simple weir flow equations for dike breach flow and the more accurate D-HYDRO calculations are found. Sensitivity factors in D-HYDRO make river flow direction very important. Alternative river schematisations, other that a detailed 2D grid are found to produce largely different results. This research has unveiled considerable limitations of the Verheij-vdKnaap equation for breach growth and has introduced viable alternatives. These alternatives include a flow velocity factor and are therefore sensitive to breach initiation moment and the underlying hydraulic conditions in the breach. In the distribution of water, fixed weirs reduce the flow velocity over elevated elements and can largely delay a flood wave compared to elevated grid cells. The effects of fixed weirs and waterways on flood simulation results are largely dependent on their own size, the magnitude of the flood wave and the flooded area. This research can be used as a guide for modelers to improve the accuracy of current flood models and to make the right schematization choices for their modelling goals in future fluvial flood models.