Cyclone Gabrielle River Breach Rapid Repair
On February 15th, following Cyclone Gabrielle, 280 m of stopbank breached when the Waipawa River reverted to its historical course causing widespread damage across rural farmland and severely impacting critical infrastructure in the area. RDCL collaborated with local authorities and contractors through the design and construction process to repair the stopbank and restore river function.
RDCL developed a flexible design philosophy based on evolving ground conditions, site hydrology, and available materials. Geotechnical and geophysical investigations were carried out in parallel with the early design stages allowing the ground model to be refined as new information became available. Open communication between local authorities, contractors, and consultants enabled fast, informed decision making that resulted in a robust and fit-for-purpose solution.
A Potential Failure Mode Analysis (PFMA) highlighted risks associated with soft, erodible foundation materials and the potential for localised overtopping due to the existing stopbank geometry. The project drew on a combination of geotechnical investigations, groundwater assessments, and geophysical surveys — including ERT and MASW — to build a detailed understanding of subsurface conditions. Investigations confirmed a ground profile of soft silt and sand over coarse gravels with high groundwater pressures, underlain by bedrock at depths of at least 10 metres. The final design addressed these challenges through low-energy batter slopes, a wider embankment footprint, and a simplified alignment.
Geophysical: Multi-Channel Analysis of Surface Waves (MASW), Electrical Resistivity Tomography (ERT).
