Preliminary design is currently under way on a 3km long wastewater tunnel under Hobson Bay in Auckland, New Zealand, in preparation for a call for tenders in the middle of next year.
Extensive geotechnical studies are currently being undertaken, which will last until July 2004. Detailed design and tendering of work will then take place between August 2004 and June 2005. Preliminary design is being carried out by Auckland-based Tonkin & Taylor Ltd.
According to the current schedule of works, tunnel construction should take place between July 2005 and April 2007, followed by the removal of the existing system.
The expected diameter will be about 3.4m, and will be bored through the East Coast Bays Formation of the Waitemata Group, comprising a thick succession of interbedded sandstones and siltstones. The method of construction will probably be TBM or roadheader, but the final decision will rest with the selected contractor, who will also choose whether the lining will be pre-cast or cast in-situ.
The new tunnel will run 35m below sea level and 80m below Orakei ridge – a new pumping station will also be built at Orakei. Residents and landowners are currently being consulted on the new proposals.
The estimated US$28M project, financed by the client Watercare, will replace an existing pipeline, which is more than 90 years old. Although it would be cheaper to refurbish the current system, the proposed tunnel will have a greater capacity and reduce the risk of storm-related overflows into Waitemata Harbour.
The current pipeline, which is visible from the shoreline, will be removed upon completion of the new deep tunnel, thus visually improving Hobson Bay.
Related Files
Map showing the existing sewer network and future deep tunnel alignment at Hobson Bay in Auckland, New Zealand
