Research Exposes Challenges In Flood Evacuation Planning

New UC research has highlighted the underestimated relevance of water velocity in flood evacuation planning, a danger highlighted by the flooding in Valencia in 2024.

The study, led by Te Whare Wānanga o Waitaha | University of Canterbury (UC) Engineering academics Professor Tom Cochrane, Associate Professor Markus Pahlow and postdoctoral fellows Dr Lea Dasallas and Dr Barry Evans indicates that depth-only risk assessments under-report hazardous conditions during peak flooding events, potentially misjudging risks to vehicles and pedestrians.

“Most flood evacuation models currently consider water depth alone, ignoring the critical role of velocity,” says Professor Cochrane. “Recent flooding in Valencia, Spain, demonstrated the destructive power of velocity, with cars swept through streets, highlighting the immense risk to life.”

Without accounting for velocity, current models may fail to provide adequate evacuation information, leaving some unable to reach evacuation hubs and underestimating the potential risks evacuees could be subjected to during a flood event.

The research initially focused on an urban area where steep terrain and paved surfaces make footpaths and roads particularly vulnerable during extreme rainfall events.

“Our modelling showed that these areas can be at heightened risk for certain flood scenarios when floodwaters move at dangerous speeds,” Professor Cochrane says.

Associate Professor Pahlow emphasised the relevance of considering both flow depth and velocity: “High flow velocities significantly increase risks to people and infrastructure. Depth-only assessments fail to capture the full picture, especially during the peak of flood events, when risks are most severe.

“For pedestrians, even moderate water depths can become life-threatening when combined with high flow velocities. In contrast, vehicles can better withstand high flow velocities but are more susceptible to water depths than pedestrians.”

The research highlights the urgent need to integrate both water depth and velocity – together with the behavioural aspect of evacuees – into flood-evacuation planning to ensure safer routes and better-informed emergency responses.

“This approach can save lives by providing more accurate risk assessments and ensuring communities are better prepared,” Professor Cochrane says.

“As climate change drives more frequent and severe extreme rainfall events, cities should look into adapting their flood risk management strategies. Our findings not only expose vulnerabilities in urban transport networks but also provide a framework for enhancing community resilience.”

The UC study contributes to a broader global effort, supported by the European Union’s Horizon Europe project Mitigating environmental disruptive events using people-centric predictive digital technologies to improve disaster and climate resilience (Minority Report), to address the impacts of climate change and improve disaster preparedness worldwide.

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