Flood risk management based on 2D TELEMAC computations: an example with Swiss hazard map

A case study in Switzerland is considered, where hazard/flood maps are established as part of the planning of flood protection measures. Due to the commune’s location within a flat plain divided by a railway dike, it could be shown that the settlements an d infrastructures are much more endangered by floods than originally thought. Using the theme “land cover” of the digital cadastral survey , a digital terrain model (DTM) and bathymetry data, break lines were generated to build a triangular mesh . Culverts, tubes and bridges are a n important element of hazard mapping, as they can alter or create new flow paths not only as common bottlenecks in the channel ( overflow), but also outside in flooded settlement areas where pedestrian/road underpasses and tunnels a re present However, the modelling of culverts and tubes has revealed that they are no longer suitable from a certain size of the channel, as the flow passes by the point which define s the culvert. Thus, several workarounds were tested to improve the relia bility of the culverts/tubes Recorded floods have shown that buildings are not necessarily an impermeable obstacle for the flowing water. An approach was developed to consider buildings as floodable as well as impermeable, as it could be observed that lar ger building complexes may by traversed by floods and alter the flow paths in this way. If these aspects are taken into account, an informative hazard map may be established