Dangers of shallow, fast-moving, flood waters highlighted
Tuesday, 3 February 2026
Researchers are warning Wellington Hospital and other essential services in the capital are in increasing danger of being cut off during heavy rainfall, and are calling for cities across New Zealand to rethink flood planning.
Most public flood maps focus almost entirely on how deep water gets, not how quickly it flows. However, new research out of the University of Canterbury using central Wellington as a case study shows that when water speed is included in models, areas classified as high risk for pedestrians increase by more than 80% and medium-risk areas more than triple - meaning many streets that look safe in shallow floods are actually dangerous.
The research team modelled an extreme rainfall event under future climate conditions, overlaying flood risk maps onto the transport network to test whether people could still reach essential services during the peak of a major flood.
They looked at access to hospitals, public transport hubs and key bottlenecks in the central city. When water speed was added to the models, previously “safe” roads and intersections emerged as high-risk zones, especially in areas where streets effectively acted as channels for fast-moving water, which could be powerful enough to knock people off their feet or sweep vehicles away. Important routes to Wellington Hospital, public transport and other essential services would be in danger of being cut off.
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In some scenarios, nearly all walking routes to key services were deemed unsafe during the flood’s peak. Vehicle access was also significantly reduced, particularly where steep terrain and narrow routes created choke points.
“These are places people still try to drive through or walk across,” lead researcher Dr Lea Dasallas said. “But once you account for velocity, it becomes clear that those routes are much more dangerous than they appear.
“When flood velocity is included in the assessment, the areas classified as high risk for people walking increased by more than 80%. Medium-risk pedestrian areas, including for children and older people, more than tripled.”
As storms intensified, relying on outdated flood assessment methods could increase the risk of injury or loss of life, particularly in cities with steep catchments and dense transport networks, meaning cities needed to rethink how they planned for floods and shift from static flood maps to dynamic models that showed how water moves through transport networks in real time.
Dasallas said the goal of their research was to improve urban resilience. “We want to help councils, emergency managers and the public make more informed decisions before and during flood events.
“That could mean more targeted road closures, clearer public warnings, and better planning for access to hospitals and emergency services that would be based on how water actually behaves, not just how deep it gets.”