Westchester Drive Link Road

9 April 2013

When Wellington’s newest road - an extension to Westchester Drive - opens in a few weeks’ time, the community will not only be able to check out the new northern suburbs link but see how stormwater run-off will be treated to protect Stebbings Stream.

Construction worker next to a roadside swale.

One of the new Westchester Drive roadside swales

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The road, which will make it quicker and easier for Churton Park and Stebbings Valley residents to get on and off State Highway 1, includes three grass-covered swales and four purpose-built interceptors to help filter road run-off.

Mayor Celia Wade-Brown will open the new 800-metre road, which links Lakewood Avenue and Middleton Road, at 11am on Saturday 20 April. Between 10am and 3pm, people will be able to walk through and take a good look. It will open for general use and vehicles at 7am the next day, Sunday 21 April.

The Council’s City Networks Manager, Stavros Michael, says most of the stormwater is being piped into roadside swales - shallow, sloping hollows designed to slow the flow of water and replicate nature.

“Oil and other pollutants such as rubber and brake linings get trapped as the water flows down through the grass and then across rock ‘rip-rap’ before being channelled into the stream, which runs alongside the road.

Where it wasn’t possible to use swales, we have put in special interceptors to make sure the water going into the stream is as clean as possible,” he says. Stebbings Stream flows into Porirua Stream and on into Porirua Harbour.

Work on the new road and footpath has taken two years. It involved major earthworks, the construction of two new bridges, a roundabout, new retaining walls and barrier fences. New services including water and sewage mains and ducting for power, gas and telecommunications have also been installed.

Rather than the stream disappearing underground in places - through culverts - which was the original plan, it has instead been bridged to better protect the stream and stream life.

Planting is an important part of the project. Steeper slopes have been hydro-seeded with a mix of grasses. Blackberry and other weeds have been removed and over the next few months nearly 4000 native plants will be going in to help restore the stream banks and adjoining roadside areas.

The new road will reduce through-traffic in Churton Park, ease peak-hour congestion in Johnsonville, and potentially allow for future, more direct bus routes.