Distributive Assessment of Vehicle Damage in Flash Floods Caused by Unplanned Urban Development Using PCSWMM

In the spring of 2019, during preparations for the grand Iranian celebration of Nowruz, a massive flash flood struck “Darvazeh Quarn” in Shiraz, Iran. The flood was triggered by the diversion of a river from its natural course and the inadequate capacity of the drainage channel designed to handle floodwaters at the entrance of Shiraz City. Consequently, floodwaters from the upstream catchment area surged into a crowded parking lot filled with people and vehicles, resulting in significant damage to vehicles and the loss of lives. To analyze the event, a 1D/2D simulation was conducted using PCSWMM to determine the maximum values of depth and velocity. These values were then utilized to calculate the required stability index for vehicles and create a risk map. In this research, the stability or instability condition of cars was determined by employing the curve presented in the Australian Rainfall & Runoff (AR&R) Guideline using the hydrodynamic index of D.V ≤ 0.3. To ascertain the damage values, the HAZUS-MH depth-damage curve was applied. The existing damage models only consider damage based on flood depth, neglecting the impact of velocity in flash floods. To address this gap, the AR&R curve was first extended up to one meter and then integrated with the HAZUS-MH curve. This integration allowed the algorithm proposed in this study to calculate damage values across different depth and velocity ranges. By leveraging the distributive flood risk map produced using the relevant tools in PCSWMM software and considering the parking lot’s capacity, the study estimated that the maximum damage to small cars would be 12%.