Incipient velocity for partially submerged vehicles in floodwaters

Vehicles parking in urban areas can often cause various hazards to people and buildings when they are swept away by flash floods. Therefore, it is necessary to investigate the appropriate criteria of vehicle stability in floodwaters. Different forces acting on partially submerged vehicles have been analysed, with a mechanics-based formula of incipient velocity being derived. Experiments were conducted to obtain the conditions of water depth and corresponding velocity at the threshold of vehicle instability for three typical types of die-cast model vehicles. The data were used to determine two key parameters. Incipient velocities for partially submerged prototype vehicles in floodwaters were estimated using two different approaches, including the predictions using the scale ratios and computations based on the formula. These critical conditions using the scale ratios compare well with the calculations using the derived formula, and the derived formula was also validated by the visually-observed data of swept vehicles in flash floods.