Vehicles instability criteria for flood risk assessment of a street network

Abstract

Abstract. The mutual interaction between floods and human activity is a process, which has been evolving over history and has shaped flood risk pathways. In developed countries, many events have illustrated that the majority of the fatalities during a flood occurs in a vehicle, which is considered as a safe shelter but it may turn into a trap for several combinations of water depth and velocity. Thus, driving a car in floodwaters is recognized as the most crucial aggravating factor for people safety. On the other hand, the entrainment of vehicles may locally cause obstructions to the flow and induce the collapse of infrastructures. Flood risk to vehicles can be defined as the combination of the probability of a vehicle of being swept away (i.e. the hazard) and the actual traffic/parking density, i.e. the vulnerability. Hazard for vehicles can be assessed through the spatial identification and mapping of the critical conditions for vehicles incipient motion. This analysis requires a flood map with information on water depth and velocity and consistent instability criteria accounting for flood and vehicles characteristics. Vulnerability is evaluated thanks to the road network and traffic data. Therefore, vehicles flood risk mapping can support people's education and management practices in order to reduce the casualties. In this work, a flood hazard classification for vehicles is introduced and an application to a real case study is presented and discussed.

Criterion of vehicle instability in floodwaters: past, present and future

“…For stationary vehicles (brakes applied), incipient motion for sliding occurs when drag force exerted by the incoming flow exceeds the frictional force, which is the product of the [32]. Thus, the mode of sliding instability on a flat surface occurs when .…”

Assessing the risk of vehicle instability due to flooding

“…The present study selected the stability model developed by Arrighi, Castelli, and Oumeraci (2016) and Arrighi, Huybrechts, et al (2016), because it is considered one of the most robust methodologies of those proposed in scientific literature (Bocanegra et al, 2020) for these reasons: (i) the equations that it contemplates have a solid theoretical basis; (ii) it considers the Froude number, which is a very important and widely used parameter in many formulations; (iii) it allows vehicles' watertightness and nonwatertightness conditions to be taken into account; (iv) it enables stability to be determined for any vehicle type.…”

“…From the balance of horizontal forces that acts on type i car located on a plane at a slope of zero, and based on the diagram provided in Figure 1, Arrighi, Castelli, and Oumeraci (2016) and Arrighi, Huybrechts, et al (2016)) defined the following mobility parameter θ vi : where ρ c is the car's mean density, ρ is water density, h c is the distance between the chassis and the ground, H is the undisturbed water depth, β is the angle of flow incidence, and H v , L , and l are car height, car length, and car width, respectively.…”

“…Geometry of the car used to determine mobility parameter θ v . Source : Arrighi, Castelli, and Oumeraci (2016) and Arrighi, Huybrechts, et al (2016) …”

“…Mobility parameter θ vi was calculated by Arrighi, Castelli, and Oumeraci (2016) and Arrighi, Huybrechts, et al (2016) with the experimental data reported by Shu et al (2011) and Xia et al (2011, 2014), which included measures taken in seven car models on scales 1:14, 1:18, and 1:43. The obtained results allowed critical mobility parameter θ vcr to be obtained, which can be established by the equation below, where Fr is the Froude number, which requires data only about water depth H and velocity U .…”