Hydrogeological Investigations of New Zealand’s Longest Twin Tunnels

PDP was engaged by Aurecon (on behalf of NZTA) to investigate and report on the hydrogeological aspects for the Waterview Tunnel – the country’s longest road tunnel featuring twin 2.4 km tunnels beneath Auckland, each carrying a three-lane motorway at depths of up to 45 metres. 

A key feature of our involvement was leading one of New Zealand’s most extensive long-duration pumping tests, involving over 200 monitoring piezometers. Our team developed a comprehensive monitoring and testing programme to better understand groundwater inflows, aquifer responses, and potential dewatering impacts. In situ testing included more than 50 packer permeability tests and over 150 rising and falling head tests, providing valuable data across the project area.We also delivered groundwater quality assessments, including analysis for potential concrete corrosion, biofilm formation, and landfill leachate migration. Advanced groundwater modelling was undertaken to evaluate tunnel inflows and the influence of dewatering on settlement, water quality, and baseflow to Oakley Creek. Our work helped shape design decisions, consent conditions, and long-term risk mitigation strategies – ensuring safe delivery of Auckland’s longest twin tunnel link.