A swath of properties built on peaty soil in a western Hamilton suburb are sinking, causing flooding and major damage to houses.
Some residents in the area want to know how the subdivision in Nawton could have been allowed to be built without safeguards and are demanding help from the Hamilton City Council.
The Waikato Times spoke to homeowners in Wimbledon Close and Twickenham Place, some of whom fear their homes could be unsaleable after their sections began sinking by up to 60 centimetres.
One of the worst-affected properties borders the swampy Farnborough Drive Reserve behind Wimbledon Close and floods every time it rains.
Councillors will be briefed on the subsidence issue at a closed-door meeting today but an internal memo reveals council staff have already sought legal advice on any potential liability.
Council city planning and environmental services general manager Brian Croad said the sinking land was "a highly complex issue" and staff were offering support and advice to homeowners.
Twickenham Place resident Adrian Waterhouse said subsidence problems had caused his garage floor to crack, some doors to stick, and a gap to develop in one of his downpipes.
"The footpath outside our house was replaced because the land sank and caused it to crack but the problem is a lot more noticeable in Wimbledon Close," Waterhouse said. "We bought this house 12 years ago and I first started noticing problems seven or eight years ago.
"I contacted the council and they told me to ring my builder and his advice was there's nothing wrong but the land is definitely sinking. You only need to look at the letterbox to see how the land has dropped away."
Waterhouse said the land behind him frequently flooded before it was developed into sections. "It was a fair dinkum bog. I remember they had to bring in a lot of topsoil before they could build there."
Other residents showed the Waikato Times around their properties, highlighting downpipes that no longer reached the ground, cracked and sunken driveways, and sodden, spongy lawns. One homeowner said she was looking to the council for help and believed cracked ceilings in her home were evidence her house had moved.
A Wimbledon Close resident, who declined to be named, said council staff had visited his property to survey the damage.
He was adamant the buck stopped with council.
"We built here in 2007 and we've had problems ever since.
"It was the council that issued the permits for these homes and it's up to them to fix it," he said.
"We paid $415,000 for this house but we wouldn't be able to sell it.
"The council might try to fix the problem but the land will only sink again and we'll be in the same situation.
"We want the council to relocate us away from here."
The man estimated the land around his house had sunk by 60cm, saying his backyard flooded whenever it rained.
His concrete driveway was so badly damaged, he had to put sand and concrete pavers over it.
Councillor Dave Macpherson said the subsidence issue was far more widespread than first thought and he believed the council should have acted earlier to remedy the problem.
"The underlying land is peat, it is low-lying and it is right alongside a wetland area - a recipe for problems without proper ground preparation by the developer," Macpherson said.
In such areas, developers were usually required to "pre-load" the ground for a long time and to provide special drainage arrangements, plus decent piling and flood protection.
"A lot of this has been lacking here, only the houses themselves are properly piled.
"Roads, street gutters, footpaths and manholes are all out of sync, and this is in a new subdivision."
Macpherson said council staff had known about the problem for at least four years.
Council building control manager Phil Saunders said council had received formal approaches from two homeowners in Wimbledon Close worried about subsidence - one had mitigated the problem and the other was still getting advice from the council.
Saunders said the houses in the subdivision had been built on deep piles after engineering reports indicated subsidence would be an issue in the area.
The council was surprised by the level of subsidence and estimated up to 10 properties could be affected.
"The engineering report says subsidence will occur but it doesn't say to what level.
"We haven't seen subsidence to this level in the city anywhere else," Saunders said.
Tauranga-based land surveyors and engineers Shrimpton and Lipinski surveyed the area.
Croad said staff wanted to take a proactive approach in helping residents but believed the council had assessed and approved the subdivision in accordance with the right procedures.
"What this shows is some of the concerns might be more widespread than we were aware of.
"Probably now we will have a closer look and we will invite those people that do have a concern to contact us and we will go from that point," Croad said.
Hamilton West MP Tim Macindoe, speaking from Britain, said his office had been approached by a resident seeking help.
Staff from his office visited the property owner along with council staff.
Macindoe said he wanted to work with councillors to find a solution.
- Waikato Times