Rockfall in Sumner a warning for residents and the city council

16:00, Jan 25 2013

Even before the earthquakes, Sumner residents knew that the dramatic cliffs surrounding them posed dangers. Rocks were commonly dislodged after rain and in drying summers - usually small rocks but capable of killing were they to fall on a person's head.

In the earthquakes they did kill and destroy and damage houses, a tragic reality with which residents, the Government and the Christchurch City Council are having to cope.

The difficulty of the parties in reaching a common position is one of the stories of the recovery and the fall of a van-sized rock into a Sumner house on Wednesday night is evidence of how urgent their challenge is.

Plainly the ground-disturbed Port Hills, even without quakes, are capable of spewing forth huge rocks that could shatter lives and buildings.

That lives were not lost in Wednesday's fall was because the hit house had been red-zoned and its residents had moved elsewhere.

Some houses, red-zoned because of rock danger, are still occupied as their owners negotiate an exit. Some houses, red-zoned and designated unsafe for occupation, by way of a notice posted under section 124 of the Building Act, are illegally occupied and no moves are being made to evict their residents. Houses with either classification provide risky accommodation.


Were the parties co-operating on a path leading to the abandonment of those dangerous houses, the issue would not be in the headlines so frequently. But the determination of some of their owners to stay put and the willingness of the city council to help them to do so risks a long, messy and dangerous row.

At worst, lives will be lost. At best, lives will be at risk for years, while ratepayers and the council fund rockfall mitigation work on uninsured and patchily serviced properties.

Had city councillors required that the section 124 notices be enforced and that services be withdrawn from red-zoned homes, the mess it now finds itself in would have been avoided. Endangered householders would have been forced to move on.

That is what the Government wants, and it has common sense and science on its side.

Houses condemned because they are in the path of potential rockfall have been subjected to detailed and lengthy investigation by experts and peer reviewed. The ground the houses are on and the rocks above them have been mapped, as have the probable trajectories of the rocks if they fell. Few, if any, other pieces of land anywhere in the world have been so intensively studied.

Mitigation measures, such as fences and bunds, have been considered but ruled out because of their doubtful ability to halt rocks dislodged with mighty force by earthquakes and the expense of their construction and upkeep.

That careful and far from cheap investigation gives the lie to the claim of some affected householders that they are being forced out on the basis of shoddy evidence. It also shows that the council's indulgence of them is misguided. It might garner councillors a handful of votes at the October election and silence some of their critics, but it keeps families in the path of destructive nature.

Not that the stay-put householders are out on a wholly irrational limb. Their love for their houses is understandable as they are usually positioned in dramatic surroundings with views. As well, the owners bought with the knowledge that cliffs and hillsides towered above them and that danger was thereby posed. Moreover, some of the landowners are prepared to pay for protective fences or ditches and provide detailed arguments for the safety of their properties. Others simply say they are prepared to take the risk of staying on.

Such cocking a snoot is admirable in principle but unsustainable in practice. It endangers the lives and wellbeing of not only the householders but their families and visitors. It forces the continued council servicing of properties probably alone in a street and to part-fund doubtful remediation. It prevents Christchurch from being completely rebuilt to minimise seismic danger.

That can be done if we learn from the mistakes of our forebears and outlaw such things as the building of houses under cliffs and below boulder-strewn hills.

The Press