Whakarongo city's preferred site

00:00, Sep 12 2012

Palmerston North has changed where it plans to encourage residential growth because a previously favoured area is at risk of liquefaction damage in earthquakes.

The Pioneer Highway on the outskirts of the city has been given the thumbs down, and Whakarongo is now the priority.

A consultant's report to the city council on the extent of the potential liquefaction problems at "City West" says the possible costs of construction techniques needed for developing the area could cast doubt on its potential for housing.

The council's planning and policy committee has recommended that land at Whakarongo be developed first.

Both areas were identified two years ago as preferred residential growth areas.

Liquefaction is where ground-shaking leads to water rising to the surface.


Last year a GNS desktop review identified that City West, an area on both sides of Pioneer Highway extending out to Longburn-Rongotea Rd and No 1 Line, was susceptible to liquefaction and lateral spreading in an earthquake. The risks were moderate to high.

Earthquakes strong enough to start triggering liquefaction have been recorded in Palmerston North three times in the past 150 years.

The report does not rule out the possibility the land could be developed using mitigation techniques to protect houses and services.

Last month, a Tonkin and Taylor study based on new information from a series of bore holes, penetration tests and shear tests confirmed the widespread presence of sand and silty soils susceptible to liquefaction.

Policy planner Daniel Batley said the area could still be developed, but site specific studies would be needed at the subdivision stage to identify what building techniques would be needed to help make houses safe.

Any development would also have to comply with changes made to the Building Act when new recommendations came out of analysis of the Christchurch earthquakes. The costs of building to meet those likely new requirements were not known.

There were fewer difficulties with developing Whakarongo, an area bounded by Napier Rd, James Line up to the Kelvin Grove cemetery, and following a straight line across to Stoney Creek Rd.

The liquefaction risks were negligible for most of the area, and flooding was not likely to be a problem.

If the full council agrees at the end of the month, the process of notifying a change to the District Plan to zone the land residential can begin.

Whakarongo would yield about 700 sections, ensuring the city has enough greenfields housing sites to last 11 years, or more, if current low demand continues.

The council wants to manage the costs of providing services to new residential areas by focusing on one at a time.

But it faces the risk that landowners in the City West area might want to go ahead with rezoning anyway.

One of the key landowners, Pioneer City West Ltd, has already lodged a private plan change with the council, but it is on hold.

The company could ask the council to publicly notify that plan change at any time.

However, Mr Batley said Pacific City West planned to do its own studies focused on the risks for housing before deciding what to do about its plan change.

The focus of the council-commissioned report is on roads and services.

Manawatu Standard