New criterion for the stability of a human body in floodwaters

Extreme flood events often lead to heavy casualties, with flood risk to humans varying with the flow conditions and the body attributes. Therefore, it is important to propose an appropriate criterion for the stability of a human body in floodwaters in the form of an incipient velocity. In this study, two formulae for the incipient velocity of a human body for sliding and toppling instability were derived, based on a mechanics-based analysis, and with both formulae accounting for the effect of body buoyancy and the influence of a non-uniform upstream velocity profile acting on the flooded human body. More than 50 tests were conducted in a flume to obtain the conditions of water depth and velocity at instability for a model human body, with the experimental data being used to calibrate two parameters in the derived formulae. Finally, the proposed formulae were validated in detail against existing experimental data for real human subjects, with different stability thresholds being obtained for children and adults in terms of assessing their stability related to floodwaters.