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Water and jobs to flow as Northland culvert replacement aims to help ecology flourish

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Restoring the natural marine environment around State Highway 10 south of Mangonui, is a key part of a project which will see a 50-year-old culvert replaced with a bridge designed to increase tidal flows.

a major culvert under a State Highway 10 causeway at Papakawau which would allow Back River to once again flow directly into Mangonui Harbour

The current Papakawau Culvert on State Highway 10 south of Mangonui, as seen from above.

Restoring the natural marine environment around State Highway 10 south of Mangonui, is a key part of a project which will see a 50-year-old culvert replaced with a bridge designed to increase tidal flows.

“We always strive to deliver good environmental outcomes as part of the design, construction and operation of our infrastructure projects and this was a particular driver for the team working on this one,” says Waka Kotahi National Infrastructure Delivery Manager Andy Thackwray.

The $5m Papakawau Culvert Replacement project, is funded through the Government’s shovel ready Crown Infrastructure Partners (CIP) programme. Work will begin on Monday September 20 and is expected to take approximately six months.

It’s set to create employment opportunities for Northlanders with our contractor Fulton Hogan looking to use local quarry and traffic management companies.

The project’s vision is rehabilitation of Aputerewa Creek’s upper estuary ecological function.

“The reinstatement of the channel and installation of a bridge will increase and re-establish more natural tidal flows and contribute to the ecological function, including fish passage, of the upper estuary and creek system,” says Andy Thackwray.

“This will provide habitat suitable for fish and infauna within the new channel and opportunities for sustainable fishing.”

The current culvert has a diameter of just 450mm and was installed into the causeway during the 1970s. As a result of it being too small, the natural tidal flow was restricted and the quality of the marine environment in this area has declined over time.

“The new bridge will be larger than the culvert allowing more water through under the roadway. It will be built by installing two large concrete walls, excavating the channel between them and installing a concrete deck on the top and bottom.”

The first two months of construction will be focussed on relocating services and the construction of a small temporary diversion road to the east of SH10. (See map below).

Papakawau detour map

Papakawau detour map

This road will take both lanes of traffic while we build the bridge, in order to minimise disruption.

Temporary speed limits may be in place and road users are asked to drive carefully and follow all signage.

“At times the project team may need to work very early in the morning or later into the evening, due to working with tidal restrictions for the bridge construction, but they’re excited about the opportunity to work on a project which will have a lasting impact,” says Andy Thackwray. 

Waka Kotahi will be working closely with the Northland Regional Council to address marine sediment which has accumulated around the causeway on SH10 near Paewhenua Island. This work will include dredging, removing mangroves and ongoing maintenance.

 

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