Author(s): Junqiang Xia; Roger A. Falconer; Binliang Lin; Guangqian Wang
Keywords: Flash floods; People safety; Vehicles safety; Hazard degree; Hydrodynamic model; Numerical assessment
Abstract: Flash flood is one of extremely dangerous disasters due to a short timescale, a limited opportunity for issuing warnings, and a high average mortality. Many of past extreme flood events were accompanied by flash floods, and they are one of the main sources leading to severe loss of human life among natural disasters. Flash floods also can cause great loss of properties, such as the damage to vehicles in the 2004 Boscastle flood, UK. Therefore, it is important to assess the safety degrees of people and vehicles during flash floods using a numerical model. In the current study, an assessment algorithm of people and vehicles safety degrees is integrated with an existing 2D hydrodynamic model capable of simulating flash floods, in which the curves between water depths and corresponding critical velocities for child and adult, developed by the previous researchers, are used to assess the degree of people safety, and a new incipient velocity formula is used to evaluate the degree of vehicles safety. The developed model was then applied in two real case studies, including the Boscastle flood in the UK and the Malpasset dam-failure flood in France. According to the analysis of the model predictions, the following conclusions can be obtained: (i) simulations from the Boscastle flood indicate that vehicles in the car park would be flushed away by the flow with high velocity, which corresponded with the fact that vehicles were flushed by the flood, and indirectly testified the prediction accuracy of the incipient formula for vehicles; (ii) simulations from the Malpasset dam-failure flood show that the adopted method for the assessment of people safety was applicable, and some local people inhabited below the dam would be swept, which corresponded well with the report of casualties.