Experimental study of the stability of pedestrians exposed to urban pluvial flooding

Abstract

Populations in urban environments are extremely mobile throughout the day and in various weather conditions; accounting for this pedestrian mobility and security becomes of high importance. Research into the security and stability of the pedestrian environment under exposure to critical water flows provides an essential knowledge base with which the associated hazard unto them can be critically evaluated. This research seeks to analyse degrees of hazard in relation to persons exposed to high volume rain events in urban areas. Several human trials of critical urban flows were conducted in order to determine the stability limits of pedestrians, crossing through a water flow in a real scale physic model. Additionally, the critical first step from a dry footpath into fast flowing water is considered and an assessment of the tested subjects' emotional responses when entering and crossing flooded roadways was carried out. Results from this study are compared with various proposed human stability criteria as well as alternatives proposed in other written works. The presented study offers a stability threshold focused on shallow depths and high velocity conditions, the most common urban flooding conditions. Keywords: Urban flood risk; hazard; drainage system; pedestrian stability. 11When designing drainage systems, the dual drainage concept should be considered (Djordjevic 12 et al. 1999; Nasello and Tucciarelli 2005; Concha and Gómez 2009; Nanía et al. 2015 Table 3. 150Critical storm events do not occur in a regimented manner, they can occur at any time of day. 188 High hazard: The tested subject lost stability completely. 189 Medium hazard: The tested subject showed a great difficulty in carrying out the complete 190 protocol. The subject needed to make a great effort. Slowness, stumbles, slips and a loss of one 191 or both shoes were other issues to consider a case as a medium hazard. 192 Low hazard: Small or inestimable instabilities were observed. The tested subject was able to 193 carry out the complete protocol without any inconvenience. 201In a total of 2345 assessed test cases, the number of high hazard scenarios, determined through a 202 complete loss of stability, amounted to 38, 1.6% of the total cases. This may seem as a very low number 203 of cases, however, the assessment of a high hazard situation was very rigorous and only account for 204 instances where there was a complete loss of stability and fall (Figure 8). There were multiple instances 205 where subjects lost balance but were able to recover their footing and continue without having fallen. 206These scenarios are classified as medium hazard as no fall occurred. 220The answers regarding the main points are summarized and listed below: 221(1) Discomfort caused by the safety equipment: All the respondents agreed that the comfort of the 222 safety equipment was good enough and it did not prevent to them from carrying out the tests 223 naturally. 224(2) Duration of the tests: The tests duration was adequate according to mo...

Further improvement in a criterion for human stability in floodwaters

“…The toppling stability thresholds for adults and children were illustrated respectively by the thin broken curve and the thick solid curve in Figure . Figure presents the observed datapoints of water depth and flow velocity for people at toppling instability, covering the laboratory measurements of Abt et al, ; Karvonen et al, ; Takahashi et al, ; Yee, ; Russo et al, ; Martínez‐Gomariz et al, .…”

“…Figure shows that the calculated results generally agree well with the observed data obtained from the tests conducted in laboratory flumes (Abt et al, ; Jonkman & Penning‐Rowsell, ; Karvonen et al, ; Takahashi et al, ; Yee, ), whereas the proposed stability guideline for adult is higher than the data sets of Russo et al () and Martínez‐Gomariz et al (), and this can be partly attributed to the fact that their experiments were conducted under the condition of low depth and high velocity. In addition, the specific characteristics of the experimental campaign (safety equipment, costume, footwear, ground surfaces, etc.)…”

Hydrodynamics of pedestrians' instability in floodwaters

“…Further experiments on human subjects should investigate the instability conditions in super-critical flow regimes, which have been currently addressed only by Jonkman and Penning Rowsell (2008) and recently by Martinez-Gomariz et al (2016). The evaluated force coefficients, which are a dimensionless measure of the forces, are strongly similar for the different human subjects and can be adopted in concep-tual models, which usually account for standard values for cylinders.…”

“…Further studies should better investigate the role of the friction coefficient for the occurrence of instability (Martinez-Gomariz et al, 2016), which might be crucial especially for super-critical flow regimes. Moreover, the effect of different physical (i.e.…”

“…A large scatter exists within the same dataset and, to a more significant degree, when all datasets are combined (Cox et al, 2010;Russo et al, 2013). In fact, instability conditions are strongly affected by diverse "non-hydraulic" parameters (Martinez-Gomariz et al, 2016), including the physical characteristics of the sub-jects (i.e. weight and height), their level of training, clothing and experimental conditions.…”