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The Lyttelton Harbour Wastewater Project will improve water quality in the harbour for current and future generations to enjoy

Lyttelton Harbour
Wastewater Project
digs into final phase

Lyttelton Harbour/Whakaraupo is Christchurch’s summer playground, and in the warmer months you’ll see water sports enthusiasts sharing the blue-green waters with recreational fishermen, swimmers and the occasional rare Hector’s dolphin.

And thanks to the $53 million Lyttelton Harbour Wastewater Project, the harbour is a step closer to being a healthier place to swim and fish, as the routine discharge of treated wastewater into the harbour comes to an end. Under the new scheme, all of Lyttelton Harbour’s waste-water will be redirected to the main Christchurch wastewater treatment plant in Bromley.

Christchurch City Council city services general manager David Adamson says the Lyttelton Harbour Wastewater Project will improve wastewater services in Lyttelton, Governors Bay and Diamond Harbour. “This is a really important project for our city and ultimately will improve water quality in Lyttelton Harbour,” Mr Adamson says.

Pipelines, pump stations and
buffer tanks

The project has been constructed in four stages, starting with pipeline installation in the roof cavity of the Lyttelton road tunnel, installation of two submarine pipelines to connect outlying settlements to Lyttelton, construction of a terminal pump station, and conversion of three existing wastewater treatment plants (WWTPs) at Diamond Harbour, Governors Bay and Cashin Quay into pump stations.

A brand-new pump station is now pumping all the wastewater from Governors Bay through a new submarine pipeline to Lyttelton

The fourth and final phase involves the installation of a pipeline connecting the Lyttelton wastewater scheme to the Christchurch wastewater scheme. 

Stages 1 and 2 are all but complete and work is well underway on stages 3 and 4, with the entire project planned for completion and commissioning in early 2020. Council engaged contractors McConnell Dowell to carry out stages 1 and 2 while Fulton Hogan is leading stages 3 and 4 of the project.

Design challenge

Council’s senior project manager Hunter Morton says connecting a brand-new wastewater system to Christchurch’s existing system comes with a unique set of challenges, requiring innovative solutions from the project team.

“As we are connecting a significant number of properties to an existing wastewater system, there are a number of limiting factors based on the existing infrastructure on the Christchurch side of the Port Hills,” Mr Morton says.

“As with most systems, capacity issues can arise during heavy rainfall events. The challenge is how to connect to an existing system without overwhelming that system during a heavy rain event,” he adds. “To get around this issue, the conversion of the WWTPs includes the reuse of the existing wastewater treatment assets to create buffer tanks for backup storage during storm events.”

All three WWTP conversions are being fitted out with splitter boxes so that when a significant flow comes into the station, the extra flow heads off into a buffer to ensure the system doesn’t get overwhelmed.

The stage 4 pipeline is a gravity pressure main, which acts like a pump station, but with the use of gravity and automatic valves. Lyttelton Harbour’s wastewater is pumped up through the tunnel and then transfers into a gravity pipeline at 90 m above sea level.

Lyttelton Harbour Wastewater Project master map

Mr Morton says the flow in this pipeline is controlled by a set of automatic valves close to the terminal end of the pipe. “This way, we can control the velocity through the pipe to ensure no accumulation of sediment.” 

Construction

Stage 3 of the project involves the conversion of existing WWTPs at Governors Bay, Diamond Harbour and Cashin Quay into pump stations and the construction of a brand-new pump station on Simeon Quay. These pump stations will be the powerhouses to pipe Lyttelton Harbour’s wastewater through the Lyttelton Tunnel and on to the city’s main treatment plant.

Mr Morton says that while stage 3 is well underway, it hasn’t been without some challenges. “The ‘class 1’ material deep under the proposed Governors Bay pump station was tested and failed to show strength properties to be able to have full confidence in the in-situ soils, resulting in the need for a significant redesign of the foundations to isolate the station from the poor ground,” he says.

“Thanks to the team effort between our designer and contractor, we were able to support the fast turnaround of a complex design and minimise impact on the commissioning of the Governors Bay pump station.”

Over at the Diamond Harbour station, demolition works revealed unstable rock hidden directly behind the existing concrete walls. This required rock anchors to be installed to protect construction staff at the site, as well as protecting the station from future damage from falling rocks.

An increasingly visible project

With marine works now complete, the project team are moving full steam ahead to complete key onshore targets. This is the more visible stage of the build process, with major works happening in Lyttelton’s Simeon Quay and across the hill in the
 Heathcote Valley.

The Heathcote Valley pipeline involves installing 4.5 km of underground pipeline from the Heathcote end of the road tunnel along Port Hills Road, Mauger Drive and along State Highway 74 to the Alport Place pump station in Woolston.

A 4.5 km pipeline will run through the Heathcote Valley

“Work on this phase began in March with crews from our contractor Fulton Hogan working simultaneously in different locations to minimise the length of disruption to residents and local businesses,” says Mr Morton. 

“As with any project, communicating with our residents is important, so in addition to regular works notices, we created a monthly enewsletter to share news and updates with stakeholders and the community. We were able to reach out to people affected and listen to their concerns, then go back to the project team to find a workable solution.”

These efforts weren’t without reward – Fulton Hogan and their subcontractors were delighted to receive a surprise delivery of homemade muffins from a resident one morning. They worked hard to keep access open for this particular family, allowing access from their house. “It’s always so rewarding to receive positive feedback from our community,” Mr Morton says.

A feat of engineering

While navigating a busy residential area has its challenges, one of the more difficult feats of engineering is yet to come. Once the Heathcote Valley pipeline passes through the residential area, it continues under some paddocks until it reaches the Heathcote River.

From here, it starts to get technical with specialist directional drilling teams planning to work around the clock to install a section of pipeline deep under the Heathcote River and along Ferry Road.

“One of the more difficult feats of engineering will involve installing the section of pipeline deep under the Heathcote River by using directional drilling technology to create a tunnel some 10 m deep and dragging more than 535 m of pipeline through the space,” explains Mr Morton. “Despite the scale of this project, people won’t see much of the constructed work as most of the assets will be underground.”

Once completed, this pipeline will be connected to the existing pump station in Woolston and allow all of Lyttelton Harbour’s wastewater to be pumped through to the Christchurch wastewater treatment plant in Bromley.

Lyttelton Harbour’s wastewater will be connected to the Christchurch wastewater scheme via an existing pump station in Alport Place in Woolston

Safeguarding the harbour’s future

The Lyttelton Harbour Wastewater Project is part of Christchurch City Council’s commitment to restoring the cultural and ecological health of Lyttelton Harbour – part of a major environmental plan for the area.

The council is working with Environment Canterbury, Te Hapu o Ngati Wheke, Te Runanga o Ngai Tahu, Lyttelton Port Company and harbour communities to improve water quality in Lyttelton Harbour as part of the Waka-Ora Healthy Harbour Plan. The plan sets out ways local authorities and the wider community can help ensure a better future for the harbour.

Work will be carried out to tackle issues such as erosion, sedimentation and pollution of waterways, and efforts will be made to improve the biodiversity of native land and marine species, from shellfish and sea grass to dolphins, penguins and birds.

The Lyttelton Harbour Wastewater Project is a practical solution to improving the health of the harbour for current and future generations to enjoy.


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