Mr Lyndon Sanders1, Mr Jason Barnett1
1Tonkin Consulting, Adelaide, Australia
In 2018, Tonkin was engaged by the District Council of Robe to assess landslide risk along cliffs near the Robe township.
Traditional landslide risk assessment relies on accessing the top and base of cliffs but this comes with serious risks of falls from cliff tops and dangerous sea conditions.
Tonkin used a drone to capture high quality video of the cliffs supplementing a physical inspection from coastal walking trails. The drone allowed around stability assessment of 1.5 km of cliff in less than a day.
The video included low level oblique views of the undercut cliffs and high level (aerial) views. The footage was reviewed immediately after flight, allowing rapid preliminary assessment of the risks to be made by a principal geotechnical engineer. Advice to Council on the same day saw Council immediately close access to some parts of the cliff tops. Other risk mitigation measures are being implemented.
Post-processing of the drone footage integrated its data with a Digital Terrain Model so that comparison with future surveys will allow quantitative assessment of the rate of coastal recession, a critical input into Council’s Coastal Access Management Strategy.
Drones are not the whole answer, however. While inspecting the cliff top, signs of ongoing sinkhole development were observed near the known ‘Blowhole’. This required improved risk management and would not have been detected by drone flights alone.
We expect that, combined with expert analysis, drone surveys will form an inexpensive input into future landslide risk and shoreline recession assessments.
Lyndon Sanders’ involvement with coastal stability includes the 2000 study of the City of Onkaparinga coastline, stability assessments at the Head of the Bight viewing platforms, in Robe, Hallett Cove and various other sites. He has been involved in riverbank stability assessment along the River Murray, River Torrens, Onkaparinga and Gawler Rivers, and worked on DEWNR’s Riverbank Collapse Risk Assessment Technical Committee. His paper ‘Examples of Landslides in the Adelaide Metropolitan Area’ includes coastal landslides.
Jason uses alternative technologies in specialist inspections, including landslides and storagetank internals. Jason combines video recordings with GIS to present data intuitively, reliably and cost-effectively.