Torbay/Browns Bay Wastewater Sewer upgrade
Project overview
Large pipe installed to give increased capacity
Minimising the impact
Fitting the jigsaw together
North Shore City Council is upgrading a major sewer between Torbay and Browns Bay as part of Project CARE, our 20-year programme to improve beach water quality.
The sewer, which runs through a tunnel under the headland between Waiake Beach and Browns Bay, needs to be enlarged to cater for existing flows and future growth in the northern East Coast Bays area.
The $5 million project will see the existing sewer replaced with a larger pipe.
The work is a critical part of the council’s Project CARE to reduce the number of wet weather sewage overflows onto North Shore City beaches, by repairing and improving our sewerage network.
Work is expected to begin on the project in October 2006 and take about a year to complete.
The existing 40-year-old sewer inside the tunnel is corroded and currently running at capacity. It needs to be enlarged to cater both for increased flows during wet weather, and for future growth.
The 750metre long tunnel runs typically about 25 to 40 metres beneath the headland between Waiake and Browns Bay. It was constructed by hand in 1965 and the excavated material used to build Manly Esplanade as it stands today.
Large pipe installed to give increased capacity
During the latter half of 2005 our engineering staff investigated several options for upgrading the sewer, including construction of a new tunnel parallel to the existing one.
However the most feasible and cost-effective solution is to temporarily divert existing sewage flows from the tunnel and replace the existing pipe with a new, larger one.
The existing 500mm diameter pipe and the surrounding backfill will be removed from the tunnel and a one metre diameter pipe will be installed in its place.
The void around the pipe will then be filled with cement grout to hold the sewer pipe in position and protect it. The grout will be pumped into the tunnel from both ends and from four shafts drilled down to it from Clifton Rd, Ridge Rd, and Sharon Rd. All work will be carried out within the existing tunnel profile.
During the project sewage will be temporarily diverted from the existing pipe via a temporary pumping station and a pipeline over the ridge to Browns Bay.
The diversion pipeline will largely run beneath the road and will be installed by directional drilling to minimise the impact on the community. Several manholes will be needed along the route.
A section of the pipe will be fixed to the surface of Lotus Walk and the pathway will therefore need to be closed for the duration of the project.
It is inevitable that a project of this magnitude will cause some disruption and inconvenience to the community.However our engineering staff will draw on our experiences of other major works, such as the installation of the new trunk sewers in Browns Bay, to ensure that any impacts are minimised and those residents most directly affected kept up to date with developments.
Construction sites will be required at both ends of the tunnel and will be set up at the southern end of Waiake Reserve and the northern end of Manly Esplanade for the duration of the project.
It is likely that there will be some noise from these sites, and some additional traffic movements. Construction hours will be limited to 7am to 7pm Monday to Saturday.
Four boreholes will be drilled from small worksites on Clifton Rd, Ridge Rd, and Sharon Rd down to the tunnel, both for ventilation and for pumping in the cement grout to fill the tunnel. These will be located to cause the least disruption to neighbouring properties, and traffic and pedestrian access to all properties will be maintained at all times.
A chamber will be constructed at Waiake Reserve for the temporary pumping station. The pumps, which will operate 24 hours a day, will be underground to minimise any noise.
Lotus Walk will be closed to the public for the duration of the project in the interests of safety. An alternative route will be available between Sharon Rd and Manly Esplanade via Clifton Rd and Canaan Way.
We thank you for your patience while we undertake this important part of Project CARE.
The work on the tunnel is the next step in an overall programme to improve the performance of our wastewater system in the northern bays area.
We have just completed a major project in Browns Bay to install enlarged sewers, which have the extra capacity to provide temporary storage needed for increased flows during wet weather. The Browns Bay pumping station was also upgraded to cater for increased flows from future growth.
Once the Torbay Tunnel is finished the next stage of Project CARE will be to upgrade the section of sewer between the tunnel and the new Browns Bay beach front sewer. That project is expected to start in about two year’s time.
Water
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