The Waiwhetū aquifer beneath Lower Hutt provides up to 70% of Wellington’s drinking water during summer, extracted from bores located in the Waterloo area. The region’s water supplier, Wellington Water Ltd, is undertaking a borefield redevelopment programme, including a revision of the existing conceptual and numerical groundwater models used for water resource planning and operations. This project represents the fifth revision of the Hutt Aquifer Model (HAM5) and has been developed in collaboration with Greater Wellington Regional Council, GNS, and Earth in Mind Ltd.

HAM5 comprises a Database model, a calibrated numerical model that integrates available groundwater information. This model then acts as the foundation for additional probabilistic predictive scenarios using innovative tools for uncertainty analysis. The scenarios incorporate changes in sea level, riverbed morphology, and groundwater abstraction. HAM5 has been built with a flexible modelling approach, allowing for spatial and temporal refinement of model inputs and outputs. It has been designed for rapid model customisation to assist with scientific investigations in the future.

HAM5 will be a valuable tool for Wellington Water Ltd and Greater Wellington Regional Council to provide a safe and sustainable water supply to the Wellington region. The model will enable the future development of tools for water supply operations and active management of risks to this vital drinking water source.


  • Three-dimensional geological modelling using Leapfrog software
  • Numerical groundwater modelling using MODFLOW 6
  • Development of customised model builds using python scripting approaches
  • Predictive scenario analysis, including climate change effects
  • Uncertainty analysis and history matching using PEST tools
  • Delineation of Source Water Risk Management Areas


  • Wellington Water Ltd


  • 2021 – ongoing

Explore More Projects

How can we help?

Get in touch with a Tonkin + Taylor representative today. Our friendly and knowledgeable team make it easy to find the right solution to suit your specific needs.

Get In Touch