Aerial surveys urged for Australia's road slope risks

Civil Geotechnical Consultants has called for high-precision aerial assessments to become standard practice for identifying slope hazards along Australia's roads, warning that current methods can miss risks on high-risk corridors.

The warning comes as engineers and public authorities face growing pressure from landslides, rockfalls and other slope failures linked to heavier rainfall and more extreme weather. Geoscience Australia says rainfall or seepage can saturate slope material and trigger landslides. The Bureau of Meteorology and CSIRO have also reported that the intensity of short-duration extreme rainfall has increased by at least 10 per cent in some parts of Australia in recent decades.

Most road authorities still assess slope danger from road level using manual inspections, photographs and sketches. That can leave the upper sections of a slope out of view, making it harder to spot unstable rock, erosion or other signs of failure before an incident occurs.

Ian Thompson, Director and Geotechnical Engineer at Civil Geotechnical Consultants, said the limits of ground-based inspections can affect both safety decisions and public spending.

"When you assess a slope from the road, you often can't physically see the top of it, so you're making educated guesses about what's up there. If you don't find a hazard, you never understand the risk. If you find it but get it wrong, you're either underestimating the risk or spending public money on a risk that may not exist," Thompson said.

The RSK-owned consultancy says aerial surveying should strengthen, not replace, existing inspection methods. It argues that drone-based surveys can give engineers a clearer picture of unstable terrain before failures force road closures or emergency works.

Weather pressure

The issue has growing financial and operational implications for governments and road owners. Insurers incurred AUD $2.19 billion in claims from declared extreme-weather events in 2023-24, according to the Insurance Council of Australia, and the country ranks second globally for weather-related losses per head of population.

For transport networks, slope failures can shut roads, delay freight, isolate communities and increase risks for motorists and maintenance crews. In remote and regional areas, even a single closure can have outsized effects where alternate routes are limited or non-existent.

Civil Geotechnical Consultants says it has been developing drone-based three-dimensional slope modelling in Australia since 2019. The method is designed to let engineers quickly survey a high-risk site, identify hazards that are not visible from the ground and create a baseline model against which future changes can be measured.

Thompson said the process can also help after severe weather, when authorities need to inspect roads and reopen them within tight disaster-recovery timeframes.

"We can fly a site in an hour or two and build a three-dimensional model with high precision," Thompson said.

"That kind of detailed rock-face mapping used to take three days with a geologist and a compass. Drone technology delivers much better information that governments and road owners can use to make safety decisions.

"At CGC, we're seeing more extreme weather events, and we're seeing them more often. Each year brings more disaster-related events, which means more slope failures, more risk and more assessments - and those events are reaching further south and further inland than they used to," Thompson said.

Broader use

Beyond roadside slopes, the same aerial assessment methods are also being used for other infrastructure and construction tasks. The firm applies the approach to measure earthworks volumes, track construction progress, assess cuttings and embankments, monitor movement after heavy rain and inspect structures including bridges.

After a rockfall, detailed aerial data can also be used to measure how far debris has travelled. That information can help authorities decide where to place exclusion zones, fencing or warning signs based on measured evidence rather than roadside visual estimates.

The consultancy employs more than 35 engineers across Brisbane, Cairns, the Gold Coast, Melbourne, the Sunshine Coast and Townsville. It works with local and state government bodies and contractors on road and rail projects, and holds the Queensland Department of Transport and Main Roads GE3 qualification for major geotechnical work.

Thompson said the greatest risks are concentrated in familiar parts of the network.

"The highest-risk places are the ones you would expect: steep, uneven, high rainfall and not a lot of infrastructure investment," Thompson said.