Sensitivity of Transport Model to Hydraulic Model for Flood Risk Assessment of Road Infrastructures

Urban inundations cause large impacts to road infrastructures which are especially important during emergencies because the resilience of a community relies upon fast connection to shelters and critical facilities (e.g. hospitals, fire stations). Moreover, during riverine floods the inundation propagates in the urban environment mostly following the road network where the majority of injuries and fatalities take place (as pedestrians or as a drivers).

The overarching objective of the research is the increase of preparedness to floods in urban areas by raising risk awareness of citizens, land planners and civil protection in order to increase flood resilience.This works aims at understanding the sensitivity of transport model and human vulnerability to the resolution of the flood maps. Three different hydraulic approaches are compared: a quasi-2D model adopted for official flood hazard maps, a full 2D model (TELEMAC-MASCARET system) with a 30 m resolution (e.g. like common global DTMs) and a full 2D model with a mesh resolution able to capture single buildings and roads (LiDAR-derived 1 m resolution). A transport model allows the mathematical modelling of transportation systems by representing the stretches of roads (links, and their nodes), users, and users` routing. Changes in time and distance between origin and destinations as a result of flooding are analysed by coupling a network model with flood hazard, using a transport network disruption model.

The human vulnerability is based on a dimensionless stability threshold, based on subject characteristics (height and level of critical submergence) and inundation parameters (i.e. Froude number), which allows the determination of dangerous conditions for pedestrians in flooded roads.

The methodology is applied to a district of Florence (Italy) which is classified at high risk of flood and is placed at the crossing of two streams and in a crucial road junction for the area. The results in terms of road accessibility, service areas and citizens vulnerability are compared and discussed for the three different hydraulic approaches to provide support for decision makers and civil protection rescuers.