Cliff properties checked after death

A swimming pool hangs over the edge of the cliff between Waiake Beach and Browns Bay. Photo / Paul Estcourt

The Auckland Council is inspecting clifftop North Shore properties to see if residents' stormwater drainage contributed to a fatal rockfall.

About 40 sections will be checked after part of the cliff-face at Rothesay Bay crumbled on Saturday, killing Inna Rudyy-Collie, who was walking with her two dogs.

Council building control manager Ian McCormick said stormwater treatment was one of several avenues of the investigation into the tragedy.

"We're going door-to-door, looking at private stormwater controls to ensure that there's nothing there ... exacerbating what would be a normal erosion of that cliff-face.

"It's a precautionary thing that we're doing to make sure we've got a complete understanding of how that cliff-face is behaving."

The findings will make up part of a geotechnical report on the Rothesay Bay cliff which is expected to be completed this week and will be part of the coronial inquiry into Mrs Rudyy-Collie's death.

Mr McCormick said he did not believe that stormwater run-off had caused Saturday's collapse, but a thorough investigation was needed to rule it out.

"We don't believe so at this stage, but we'd like to cover all the bases as part of the assessment we are doing. We're looking at all the properties along the full length of the cliff."

Homeowners who stripped their properties of trees or vegetation could destabilise the cliff by removing roots which bound the soil and rocks.

The council could not force residents to plant more trees on the coastal clifftop.

But it would tell them if their actions might be leading to erosion.

Mr McCormick also observed at least two residential drainpipes at Rothesay Bay which discharged stormwater straight on to the rocks.

"The ones I saw did not seem to have changed the behaviour of the cliff-face, but they [residents] shouldn't be doing it."

The installation of the pipes could lead to degradation of the clifftop, and the discharge could gouge channels and destabilise the rock.

Council chief operating officer Patricia Reade urged beachgoers to stay 10m from the cliff, especially at high tide when walker were forced closer to the face.

While the rockfall was typical of the natural erosion on Auckland's east coast, the council is considering a wider investigation of the city's cliff-faces after the accident.

Auckland's east coast cliffs have been eroding at a rate of two to six a century for the past 10,000 years.

This is a much faster rate than the west coast, where erosion is negligible in comparison.

The east coast erosion is partly due to increased development, but also the geological conditions - most of the cliff-face is made of soft and brittle sandstone and mudstone.