Comparing Various Methods of Building Representation for 2D Flood Modelling In Built-Up Areas

Floods in built-up areas are among the most catastrophic natural hazards mainly due to the high value properties existing in these areas. The most vulnerable areas are the riverine areas with mild terrain which are often encountered in the coastal zone. Due to the mild terrain and the complicated topography caused by buildings, roads and infrastructure, a two-dimensional modelling is required for a realistic simulation of the flood evolvement. In this paper the flood simulation is performed by a recently devised fully dynamic numerical model, the FLOW-R2D, which is based on the two-dimensional Shallow Water Equations solved by the Finite Difference Method and the McCormack numerical scheme. The performance of the model is tested for three alternative representations of the resistance caused by buildings, namely, the reflection boundary, the local elevation rise, and the local increase of the Manning roughness coefficient. The model was run for three different hydrographs and produced time series of water depths and flow velocities in the entire computational domain of the inundated area for each hydrograph. The results of the model for the three alternative building representations and different building alignments were compared with the experimental data available from experiments reported in recent papers. Based on the comparison between numerical and experimental results it was concluded that the reflection boundary method proved to be the most successful building representation for the application of FLOW-R2D. Finally, the data requirements and the required density of the digital terrain model were discussed in relation to the building representation methods.