2024 – Response of levee infrastructure to Cyclone Gabrielle, Hawke’s Bay, New Zealand, and Lessons Learned to Inform Future Flood Management.

Tim Morris, Dominic Fletcher, Jamie Yule

In February 2023 the Hawke’s Bay Region, located on the East Coast of New Zealand’s North Island, was severely impacted by Cyclone Gabrielle. Flooding resulted in approximately thirty levee breaches with flood depths to about 7 m and sediment deposits to house roof line in some areas.

Other consequences across the region included eight deaths and many billions of dollars damage. Example losses included many houses written off, damage to infrastructure including major road bridges destroyed, loss of levees, the Redclyffe electrical substation, rail lines, as well as damage to horticulture and other businesses. In select locations future land use changes will be implemented because of the event.

To set the scene, the paper will overview hydrological aspects of the event. Flood defence infrastructure performance and the impact on levees from an extreme event that was well beyond original designer expectations (overdesign event performance) is discussed, as is embankment response to overtopping flows. Forensic assessment on how materials performance failure mechanisms occurred is provided.