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Houses affected by land subsidence being monitored

Uncertainty still hangs over 18 city properties that remain significantly at risk and impacted by land subsidence caused by the major rain event at the start of the month.

People living in two of those properties had to find alternative accommodation and are not yet back in their homes.

More than 30 properties have been affected to varying degrees by the two to three days of rain that drenched the city and much of the rest of the district.

Gisborne city received more than 230 millimetres of rain during the event.

Gisborne District Council has listed the affected homes in three tiers.

Eighteen properties are in Tier 1, where land subsidence is within eight metres of the house,

Eight properties are in Tier 2, where there has been no immediate threat to property.

Six properties are in Tier 3 (six properties) where there's no immediate threat but a need for ongoing monitoring and advice.

Council chief scientist Murry Cave said there were houses at risk on all 18 Tier 1 properties.

“They are particularly at the western end of Clifford Street, areas either side of Hospital Hill, at the top of Ballance Street and through to Gaddums Hill.

“Most are more elevated properties but there are some below them that are also at risk.”

The council yesterday gave the all clear on a property in Clifford Street, which reduced the Tier 1 number from 19 to 18. The family living there were able to return to their home.

“The two uninhabitable properties are in Ballance Street,” Dr Cave said.

Consulting engineers Tonkin and Taylor inspected those yesterday.

“If they say it's safe for the people living there to return to their homes, then they will be allowed to do so.

“One is occupied by a man living alone and the other has multiple people living in it.”

Dr Cave has described the land subsidence situation in the wake of the storm as “a reasonably large scale event”.

“It's not an Abbotsford (Dunedin, 1979, when 69 houses were destroyed by a single landslip).

“This involves multiple landslides as a result of a rather complex weather event, with two to three days of pretty solid rain causing these problems.”

It would be up to the Earthquake Commission (EQC) and the insurance companies to determine the seriousness of the situation on the 18 individual properties, said Dr Cave.

“We at the council will maintain a watch on all those properties, and we will be updating the EQC regularly.

“I expect that most of the affected properties will be recoverable.

“But I can see the need for quite extensive geo-technical reinstatement work to be done to fully secure them again.”

Dr Cave said the Tier 2 and 3 properties were mostly near waterways.

“They have been affected by stream and riverbank erosion and slumping of the bank. There's no actual threat to the dwellings on those properties.

“We are also assessing landslides in rural areas and the risk to the roading network and properties where those land subsidences have occurred.

“There has also been a landslide dam created in the Glenroy area that we are monitoring and a potential one in the headwaters of the Waimata River.

“Risk assessments are also being carried out on both of those situations.”