Sinking land could take years to settle

AARON LEAMAN
Last updated 05:00 19/06/2014
Sinking subdivision
PETER DRURY/ Fairfax NZ
SINKING FEELING: The owners of a Wimbledon Cl house say the land around their brick house has dropped by up to 60cm over the past seven years. Their backyard is flooded every time it rains.

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Properties affected by severe subsidence in a western Hamilton suburb could take decades to settle, a geologist has warned.

Homeowners in Wimbledon Close and Twickenham Place are appealing to Hamilton City Council for help after the land around their houses began sinking - in some cases by up to 60cm.

Thornton Estate developed the subdivision, with engineering reports indicating subsidence would be an issue due to peaty soil. However, council staff have said they were surprised by the level of subsidence and estimate up to 10 properties could be adversely affected.

GNS Science engineering geologist Sally Dellow said peaty soil was open and loose "so the moment you put any weight on it, it will start to compress".

Dellow said at some point the land would stop sinking but the timing depended on the depth of the peat and how much it had compressed already.

"Sixty centimetres of subsidence is pretty excessive, even 10cm is enough to start severing connections to things like water, stormwater and wastewater services," she said.

"It's not an issue that's easily resolved. Depending on the thickness and compressibility of the peat, subsidence might go on for a hundred years."

Council building control manager Phil Saunders said testing at one property indicated the peaty soil would compress another 5cm over the next three years before stabilising.

Council staff briefed elected members on the subsidence problem during a closed-door meeting on Tuesday.

"It is our intention to make contact with any potentially affected owners as soon as possible to ensure they are provided with up-to-date information that assists them to understand the reasons for the subsidence and how they are able to mitigate any damage to their services," Saunders said.

"Any affected property owners will be contacted and it is our aim to engage with the owners to ensure they are informed and understand what, if any, effect subsidence has on their property."

Saunders confirmed a Wimbledon Cl resident first contacted council about subsidence problems four years ago.

The council had since commissioned a geo-tech engineer to provide further information.

"It is important to understand that although your property may be subject to subsidence, this does not mean that your building structure will be damaged," Saunders said.

aaron.leaman@fairfaxmedia.co.nz

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