A comparative study on pedestrian flow through bottlenecks between flood evacuation and land evacuation

In a flood, people may be forced to evacuate in water until reaching a secure shelter. Understanding the characteristics of pedestrian flow in water is therefore of utmost importance. Some researchers studied individual walking speed in water, whereas it is still rare to study pedestrian and evacuation dynamics, e.g., characteristics of pedestrian flow through a bottleneck. In this paper, evacuation experiments through bottlenecks are conducted in 0.60-m-deep water, with 97 volunteers with an average age of 21.7 years participating. The results are compared with those on land. It is shown that the flow rate in water is lower than that on land, with a difference varying with bottleneck width b as ΔJ=0.60b−0.04ped/s. The average specific flow rate in water is 0.43ped/(m·s) lower than that on land. Based on the relation of time headway–width, density–width, and speed–width, threshold widths for the flow transition from "interrupted" to "flowing" stages are 1.3 m in water and 1.0 m on land respectively. Compared with that on land, during "interrupted" stage in water, stop behavior is more frequent, the speed near the exit is 0.22 m/s lower, and the speed-up point is closer to the exit. During "flowing" stage, continuity of the pedestrian flow at exit is inferior in water compared to that on land, a 0.2–0.3 m wider exit is required in water to achieve similar continuity on land. These findings may provide valuable insights into emergency management during flood evacuation.