Author(s): Lea Dasallas; Barry Evans; Dion Todd; Hamish Kampman; Markus Pahlow; Thomas Cochrane
Linked Author(s): Lea Dasallas
Keywords: Urban Flooding Stability Function Transport Flood Risk Analysis Emergency Evacuation Planning
Abstract: Many urban areas are experiencing an increasing frequency of flooding due to climate change. Densely developed and impervious catchments, particularly areas with steep topography, are susceptible to high-velocity surface runoff during floods. Emergency management strategies, such as planning for safe evacuation routes, are considered a cost-effective approach to minimise the danger posed by these events. In the past, mainly flood depth was considered as a transport route obstruction when planning for evacuations. This approach neglects the floodwater velocity component, which has been shown to have a large impact on the risk during evacuation. Here, a combined depth-velocity stability function is employed and the effect on risk for the transport network during urban pluvial flood events is assessed. A 1D-2D hydraulic model is utilised to simulate the flood depth and velocity for a 24-hour 250-year recurrence interval rainfall hyetograph with a nested storm profile for central Wellington, New Zealand. Network area analysis is used to generate and compare the no-flood, depth-only, and depth-velocity risk maps for the Wellington evacuation hubs. The risk assessment highlights that a depth-only risk-based assessment underestimates the number of cells identified as posing risk to vehicles by approximately 38% and pedestrians by 80% during the peak of the flood event, highlighting the importance of including velocity within the risk assessment, and emphasising the susceptibility of pedestrians in particular to risks associated with flow velocities. The combination of the depth-velocity stability function, 1D-2D hydraulic modelling and network analysis introduced here can help to improve risk management and evacuation planning for urban areas.
Year: 2025