Steps help native fish avoid the rush hour

Heb Construction's environment manager Fiona Mountfort sizes up a fish ladder inside a culvert. Photo / Greg Bowker

When cars and trucks cruise along Auckland's new Hobsonville motorway from 2012, fish and eels should be splashing happily up a network of "ladders" being built in culverts beneath them.

The contraptions, series of rectangular plastic blocks screwed to the bases of about 20 culverts under the motorway and an associated two-lane northern extension of State Highway 16, are designed to break water flows and provide resting platforms for fish such as native kokopu or inanga on their journeys upstream.

They are being built by Transport Agency contractor Heb Construction to the specifications of a freshwater biologist.

They were required as part of Auckland Regional Council resource consents for the $220 million motorway project, which began a year ago as part of the 48km western ring route between Manukau and Albany.

Downstream watercourses are also being reshaped and their banks planted out, to provide shady pools for fish to laze in, before or after their journeys through the culverts.

Members of the local iwi, Ngati Whatua Nga Rima o Kaipara, helped a project landscape team catch hundreds of fish and eels from streams where 15km of culverts have since been installed, and to release them into other watercourses for the construction period.

Exceptions were koi carp and gold fish, which were destroyed to prevent further degradation of water quality for the native fish.

Transport Agency northern highways manager Tommy Parker said workers had also noticed dotterels nesting in risky locations inside the construction zone, which runs 6km along a motorway route between Upper Harbour Bridge and Massey North, and 2.2km from the end of State Highway 16 to Brigham Creek Rd.

That followed extensive efforts by Heb to ensure staff were aware of the project's effect on the environment.

Wildlife experts were alerted, and the dotterel eggs were rescued and taken to Auckland Zoo, where they were hatched.

Mr Parker said the agency recognised that building motorways was disruptive, and wanted to be good neighbours regardless of its obligations to follow resource consent guidelines.

"The fish ladders are a good example of that," he said.

"We consulted extensively with the community and local iwi about our plans for protecting the waterways around the Hobsonville deviation project."

Meanwhile, the first of seven bridges to be completed across the motorway has been opened on Trig Rd, for Whenuapai traffic, to allow earth to be dug out to a depth of 11m beneath it.

Traffic at the eastern end of the project will be moved on Sunday to permanent westbound lanes of the new motorway for a short distance between Upper Harbour Bridge and Buckley Ave, to allow another bridge to be built for local access.

At the western end, where the new motorway will join SH16, traffic using a large temporary roundabout will be transferred on Sunday, December 13 to a new bridge which will become part of Hobsonville Rd.