Omāroro Reservoir

In collaboration with HEB, Holmes developed a smarter, more sustainable design for Wellington Water’s Omāroro reservoir.

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 contractor’s 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.

The alternative design significantly reduced material use and culminated in savings of around 500 tonnes of reinforcing steel (approx. 50% reduction), 2500 m3 of concrete (approx. 30% reduction) and 15- 20 thousand cubic metres of earthworks compared to the original design. By reducing materials volumes, we proudly saved the client $9M in capital expenditure, and around 20% in embodied carbon compared to the original design.

Throughout the project, our team conducted extensive 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 approach enhanced safety outcomes and overall understanding for both project contributors and other interested parties.