Author(s): Junqiang Xia; Roger A. Falconer; Xuanwei Xiao
Keywords: Human stability; Incipient velocity; Theoretical analysis; Flume experiments; Floodwater
Abstract: An extreme flood event often leads to serious loss of human life, and the risk to human subjects in a floodwater varies both in time and place across a flood-prone area, and also changes with different body shapes and weights. The variation in the hazard degrees for human subjects in floodwaters needs to be estimated in the flood risk management. However, existing criteria of human stability usually neglect the effects of body buoyance and non-uniform velocity profile of incoming flow. Therefore, it is important to propose an appropriate criterion of human stability in floodwaters, and the criterion is usually represented by the concept of incipient velocity in practice. In the current study, different forces acting on a human subject have been analysed, with the corresponding expressions for these forces being presented, and with the formulas of incipient velocity being derived respectively based on two different instability mechanisms. The derived formulas account for the effect of body buoyance through calculating the human body volume under different water depths, and also consider the influence of non-uniform velocity profile on human instability. About 50 runs of flume experiments were then conducted to obtain the conditions of water depth and corresponding velocity at human instability, using a vivid scaled model human body. The experimental data from these studies were then used to determine two parameters in the derived formula for each instability mechanism. Finally, the derived formulas were validated in detail by the current experimental data obtained from the scale ratios and other experimental data using the real human subjects, and the validation results indicated that the proposed formulas can be used to assess the risk to human subjects in floodwaters.