A huge landslide came down at Bushy Knoll, Tiniroto on July 22 and a further collapse is likely in heavy rain, Gisborne District Council's principal scientist says.
A huge landslide came down at Bushy Knoll, Tiniroto on July 22 and a further collapse is likely in heavy rain, Gisborne District Council's principal scientist says.
Drone surveys undertaken by Gisborne District Council’s principal scientist Dr Murry Cave have shown two landslides in the region are likely to fail again.
A drone map of the Te Kuri o Pāoa/Young Nick’s Head landslide has revealed significant ongoing risks at multiple sites along the cliff face.
Two Sundays ago it was discovered a large landslide had come down, and a warning went out for people, including boaties, to stay away from the area.
The warning remains after Cave flew a drone over the cliffs to map the landslide.
“It was clear from this that there would be an ongoing risk from the landslide and a more detailed assessment would be required,” he said in a statement.
A drone map of the recent landslide on Young Nick's Head has revealed significant ongoing risks at multiple sites along the cliff face.
Cave said there had been several failures around the region in the last month.
The Bushy Knoll landslide in Tiniroto was also likely to fail again in heavy rain, he said.
The drone survey showed around 30,000cu m (more than 70,000 tonnes) of saturated, unstable debris made up the landslide, which came down on July 22.
“If the rain is heavy enough to trigger a further collapse of this landslide, it could generate a debris flow that could travel downstream for a considerable distance,” Cave said.
“The most immediate risk that has been identified is to the bridge on Elmers Road, which has very little freeboard [clearance above high water level] and was damaged during Cyclone Gabrielle.”
Cave’s assessment of the landslide included looking at aerial photography, which showed the land failure started with Cyclone Gabrielle and progressed after each bad weather event over the past 18 months before it collapsed on July 22.
“The slopes in this area are quite steep and the ground remains very wet, like it does elsewhere in the region. This means that the landslide is very likely to fail again.”
Cave said the council would continue to monitor the landslides, “particularly after heavy rain”.
He asked that anyone who has observed active slope failures or unusual signs of movement on their land (for example, open cracks forming or hollows developing where these have not been observed previously) contact Gisborne District Council so any possible risk can be assessed.
