$11m homes at risk as cliff crumbles
Owners of two homes seeking to erect 38-metre sea wall to contain damage
Owners of multimillion-dollar clifftop Auckland homes are taking extreme measures to try to delay “cliff failure” threatening their land.
Properties on a 2km stretch on Belmont’s Seacliffe Ave between Takapuna and Devonport are dealing with the effects of erosion, according to a report to Auckland Council from specialists Davis Coastal Consultants.
The report said residents’ options to try to stop ongoing damage to their sites from what Davis called “cliff failure” included building palisade walls, drilling drains through the cliff face to clear surface water, placing mesh and soil nails, and planting the cliff head.
The exposed, north-facing Waitemata sediment cliffs with little vegetation are between St Leonards Beach and Narrow Neck Beach below Seacliffe Ave and Hamana St, which form one road.
Weak siltstone and sandstone is tumbling from the grounds and cliff faces, falling around 30m at some points onto the foreshore.
The Herald has reported on many parts of the country – and especially in Auckland, Taranaki and the Bay of Plenty – where shoreline cliffs have been eaten away to the point where homes are threatened.
This naturally occurring process is being slowly compounded by rising seas driven by climate change, with New Zealand’s sea level projected to be about 30cm higher by mid-century – and up to a metre higher by 2100.
So the owners of two properties, worth a combined $11m, now want to build a 38-metre sea and retaining walls at the cliffside of the beach to hold back the damage.
The council has notified Allen and Barbara Peters’ application to attempt to deal with erosion at their properties, which have unimpeded views of the Hauraki Gulf.
Submissions on the walls can be made by February 9 but Gary Taylor of the Environmental Defence Society called for it to be rejected, saying the structure would be “a pretty horrendous intrusion”.
The Peters’ homes at 66 and 68 Seacliffe Ave were built above the cliffs where, in the 1970s, a massive slip dumped about 1000 cubic metres of metal, earth, rock and vegetation onto the foreshore. That fall included concrete rubble and steel beams.
Pictures accompanying their application show rusted metal, rock and even entire, mature pohutukawa growing near the bottom of the cliff beneath the homes.
Those man-made elements were a failed attempt 40 years ago to deal with erosion but came crashing down onto the beach.
“The dominant feature of the talus [debris pile] is the significant volume of old steel beams and concrete rubble that extends around the seaward extent of the material. The debris is understood to originate from materials imported to undertake adhoc cliff protection works, in response to fears of cliff instability in the 1970s,” the Davis report said.
In the years after the slip, residents of four adjacent properties at 62 to 68 Seacliffe Ave installed a palisade wall at the head of the cliffs for protection.
Allen and Barbara Peters’ properties had a palisade wall, built in 2002, because of “a historic slope failure”.
The new proposal is for a rock masonry seawall and a landward retaining wall behind it.
Council valuations list 66 Seacliffe Ave at $7.5m and 68 Seacliffe Ave at $3.5m.
“The cliffs along the subject coastline are undergoing constant retreat,” Davis’ environmental assessment said. “The large historic cliff failure that resulted in the talus deposit on the foreshore is clear evidence of this process at work. Recent failures along the adjacent coastline are evident.
“The process of erosion and cliff retreat is a natural process. However, there is development at the head of the cliffs and this ongoing retreat poses a threat to the property.”
A seawall would armour the cliff against incoming wave energy to deal with erosion, the report said, and needed to be high and big enough to retain the wave forces.
Because the collection of twisted metal and the pohutukawa is itself being threatened — soon the tree will be washed away — the materials will be left lying on the beach.
Although the proposed wall would change the quality and character of the natural landscape and introduce man-made elements into a sensitive environment, it would have positive effects, the Davis report said.
“This includes hiding or screening the debris/talus, protecting the bank and pohutukawa trees and generally improving the visual and sensory/experiential quality of the environment,” the council was told.
No decision will be made on the non-complying application until after the February 9 close-off date for public submissions. A council officer said the seawall structure was not reclamation but an attempt to build around the existing fallen materials.
The Peters could not be reached.