Comparing 2D capabilities of HEC-RAS and LISFLOOD-FP on complex topography

This study evaluates and compares two-dimensional (2D) numerical models of different complexity by testing them on a floodplain inundation event that occurred on the Secchia River (Italy). We test 2D capabilities of LISFLOOD-FP and HEC-RAS (5.0.3); implemented using various grid size (25-100m) based on 1m DEM resolution. As expected, best results were shown by the higher resolution grids of 25m for both models, which is justified by the complex terrain of the area. However, the coarser resolution simulations (50 and 100m) performed virtually identical compared to high-resolution simulations. Nevertheless, spatial distribution of flood characteristics varies; the 50 and 100m results of LISFLOOD-FP and HEC -RAS misestimated flood extent and water depth in selected control areas (built-up zones). We suggest that the specific terrain of the area can cause ambiguities in large-scale modelling, while providing plausible results in terms of the overall model performance.