Pipes bridge the gap

SUPPLY SECURITY: Hunua 4 project manager Andy Spittal says installing the 1.6 metre-diameter, 12mm-thick steel pipes while the second Manukau Harbour bridge is under construction will minimise traffic disruption. Official construction of the project is scheduled to start in 2012.

Pipes capable of carrying 3000 litres of water a second are now being installed under the girders of the second Manukau Harbour bridge.

The 1km "under the bridge" section is part of Watercare Services' $245 million Hunua 4 pipeline project.

Construction on the pipeline won't start until 2012 but the bridge section is being done now so residents won't be disrupted twice.

The pipeline will run for about 30km - from Redoubt North Reservoir to Murphys Rd then under Thomas, Boundary, Reagan and Puhinui roads and across Pukaki Creek to Mangere.

From there it will pass under Kirkbride, Mountain and Coronation roads, under the new harbour bridge to Onehunga and on to Epsom.

Hunua 4 project manager Andy Spittal says the new pipeline is being installed to cater for future demand and to secure the water supply, particularly in Manukau city and the airport precinct.

"The issue is more of security, not capacity. As of now there are water supply risks that exist because of the degree of reliance on existing reticulation infrastructure," Mr Spittal says.

"To shut the older supply lines down for more than a few hours is impossible.

"Hunua 4 duplicates significant sections of the existing Hunua 1, 2, and 3 supply lines.

"Once Hunua 4 is working Watercare can take the other water mains out of service to carry out essential maintenance."

Hunua 4 will be connected to the local network in six key locations across Manukau city to meet future demand in growth areas such as Flat Bush and the airport precinct.

Watercare is planning to lodge consents for the project early next year and start construction in 2012.

But Mr Spittal says they've brought forward $15 million to build the section on the second harbour bridge "so we don't doubly disrupt traffic or residents in the area".

"We are closely co-ordinating with New Zealand Transport Agency so that pipelaying plans work in with the upgrades of road networks - like the planned upgrade of the intersection at Kirkbride Rd," he says.

Watercare plans to use "trenchless technology" for the intersection at Kirkbride Rd.

The same tunnelling technology will be used across Pukaki Creek and where the pipeline crosses the motorway and railway.

But for most parts of the route, Hunua 4's pipes will be laid under the road using an open trenching method with trenches of 4 metres deep and 3 metres wide on average.

With 30 metres to 50 metres of trench open at any one time, each construction area is expected to be about 200 metres long.

The pipeline is scheduled for full commissioning in 2016.