Omāroro Reservoir

Critical Water Storage for the Capital


Wellington Water


Te Whanganui-a-Tara (Wellington), Aotearoa/New Zealand

Year Completed


Project Value

NZ $70M

Holmes worked alongside contractor Heb to produce an alternative design for the Omāroro reservoir in 2019. This offering was ultimately successful, and the detailed design was completed for this critical Wellington Water project over the second half of 2020.

The Holmes structural and geotechnical design team created efficiencies through a number of means, saving the asset owner millions of dollars in capital expenditure. The alternative design drew on a thorough assessment of soil-structure interaction to demonstrate performance under service, ultimate and maximum credible earthquake events. This was particularly important for the reservoir as it is buried in its final state and a lifeline asset. We reduced material use and accommodated the contractors preferences by not adopting key elements of the original design.

We sought input from Wellington Water during the design process, and adapted aspects of the specification to suit their longer term needs. A simple example is the adoption of certain roughness requirements on the tank floor to reduce risk of slips for personnel inspecting or cleaning in future.

The team completed construction staging checks for precast walls and for different backfilling scenarios. Our structural modellers and civil designers performed a number of staged construction modelling exercises to assist the Heb team in communicating with their own staff and with external stakeholders. This enhanced safety outcomes and overall understanding for both project contributors and other interested parties.

With permanent works design complete, the team continues with temporary works, construction monitoring and technical support through 2021.

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