Investigating an underwater pipeline to withstand a major earthquake and keep delivering Wellington’s water supply

Cross Harbour Pipeline Investigations

New Zealand’s capital lies between two great tectonic plates and sits atop one of the most active geological faults: the Wellington Fault.

The city’s water supply relies on pipelines that cross the Fault in several locations. In a major earthquake these pipelines are expected to sustain significant damage, resulting in extensive parts of Wellington going without water for up to 100 days.

When it was discovered that the Harbour Bores project was unviable, we investigated ‘Plan B’: the Cross Harbour Pipeline (CHP). If progressed, this solution would significantly improve the disaster and operational resilience of Wellington’s water supply by providing an alternative pipeline route that doesn’t cross the Fault and is designed to remain in service after a one in 2,500-year earthquake.

Because the CHP would be located within a seismically active environment, there is still a risk of damage from other natural hazards once it's built. To quantify these effects an innovative design approach was required that involved significant geotechnical work and assessment of over 700 pipeline routes to select the most resilient route and design. We had the best people on the job and the majority NZ-based design team were joined by international experts from the UK, Los Angeles, and Calgary in Canada.