Towards the simulation of flood evacuation in urban scenarios: Experiments to estimate human motion speed in floodwaters

Studies on flood risk assessment at urban scale are becoming increasingly oriented towards the use of evacuation simulation models for population's safety. However, such tools generally simplify human dynamics in floodwater conditions and need data to quantify proper individual's speed. Novel information on the above dynamics is here presented. A group of over 200 volunteers has been engaged in evacuation laboratory experiments carried out into an open channel. Results allow to estimate the pedestrian's isolated motion speed as a function of depth D [m] (in the range 20–70 cm) of floodwater, in both “walking” and “running” conditions. To this aim, experiments were carried out in still water. For each walking conditions and floodwater depth, correlations have been obtained between evacuation speed and age, individuals’ height, mass and body mass index. The existence of significant motion speed differences, depending on D, is underlined. In addition, general trends in evacuation speed reduction depending on the specific flood force per unit width M have been investigated and confirmed. It is also clarified how human physiology and kinematics (i.e. knee articulation) can induce specific speed-affecting effects depending on D. Such quantitative differences in motion discourage the use of fire or general-purpose databases for flood simulations, while such experimental data could be used as input for evacuation models to describe different evacuees’ walking types in evacuation procedure.