Hydrodynamics of pedestrians' instability in floodwaters

Abstract

Abstract. People safety is the first objective to be fulfilled by flood risk mitigation measures and according to existing reports on the causes of casualties, most of the fatalities is due to inappropriate behaviors like walking or driving in floodwaters. Currently available experimental data on people instability in floodwaters suffer of a large scatter primarily depending on the large variability of physical characteristics of the subjects. This paper introduces a dimensionless mobility parameter θP for people partly immersed in flood flows, which accounts for both flood and subject characteristics. The parameter θP is capable of identifying a unique threshold of instability depending on Froude number thus overcoming the scatter of existing experimental data. Moreover, a 3D numerical model describing a detailed geometry of a human body and reproducing a selection of critical pairs of water depth and velocity is presented. The numerical results in terms of hydrodynamic forces and force coefficients are analyzed and discussed. Both the mobility parameter θP and the numerical results hint the crucial role of Froude number and relative submergence as the most relevant dimensionless numbers to interpret the loss of stability. Finally, the mobility parameter θP is compared with an analogous dimensionless parameter for vehicles instability in floodwaters, providing a new contribution to support flood risk management and people education.