Geotechnical Engineering Office’s Lawrence Shum also says his team will test landslide prediction model this rainy season
Hong Kong authorities will use drones under a pilot project to create a catalogue of hundreds of thousands of natural slopes in the city for safety, following the identification of three large-scale, high-risk sites.
Lawrence Shum Ka-wah, deputy head of the Geotechnical Engineering Office (GEO) on Hong Kong Island, said on Monday that his team would also test a landslide prediction model this rainy season after the city recorded the largest rockfall incident in nearly a century at Shau Kei Wan in 2023.
The three high-risk sites are areas near Jardine’s Lookout in Wan Chai, Violet Hill in Tai Tam Country Park and Tai Wo Ping near Beacon Hill at the foot of Lion’s Rock.
“It does not mean that landslides will occur at these three areas, but they have been identified for hazard assessment and necessary mitigation works,” he said.
Shum said 181 landslides occurred in Hong Kong last year, down from the annual average of about 300, as the city had experienced 5 per cent less rainfall and fewer rainstorms.
He noted that 20 per cent of the landslides in the past 60 years had occurred on natural hillsides with no prior history of such incidents, thus posing considerable risks and affecting critical infrastructure.
Shum said that the office aimed to expand its Smart Slope Register catalogue of man-made slopes to include all natural terrain, which he estimated to be a six-digit figure.
“This is expected to be completed within a year,” he said.
The register would record basic geospatial data, the history of failures and affected facilities for each natural terrain, to help the office assess whether they posed significant risks and should be prioritised for mitigation measures.
Measures that could be put in place include constructing rigid or flexible barriers to intercept debris to provide a buffer and protect facilities while allowing time for evacuation.
He said the office would introduce the use of drones for data collection under the government’s pilot “sandbox” scheme for unmanned aircraft, which aims to help authorities in testing airspace operations and infrastructure while developing policies and regulatory guidelines for the industry.
He estimated that the slope catalogue project would increase the office’s workload by a third and its estimated expenditure on landslides would also climb from about HK$1.1 billion (US$140.7 million) per year to around HK$1.5 billion.
Under the “sandbox” scheme, the office will use drones with remote sensing technology for real-time surveillance and data collection in areas such as construction management, slope monitoring and emergency response.
“After heavy rain, drones can inspect affected areas to assess conditions,” Shum said.
Drones could go on automated flight missions along predefined routes at scheduled intervals to monitor man-made slopes, disaster mitigation and large areas of natural terrain.
The office will also test its landslide prediction model this rainy season, which the Hong Kong Observatory said usually fell between April and September.
The model analyses rainfall data, landslide reports and man-made slope data to identify causes and the relationship between rainfall and landslides to predict the number of reported landslides during heavy rainstorms, Shum said.
A 16-hour black rainstorm pounded Hong Kong in September 2023, triggering landslides in Shau Kei Wan, Shek O and Redhill Peninsula, which exposed illegal work or unauthorised construction on slopes.
Shum said an analysis of the landslide above Yiu Hing Road in Shau Kei Wan showed that it was the largest recorded rockfall incident in nearly a century, with a source area close to 2,000 square metres, which was “highly uncommon” in the city.
The review showed that the massive natural terrain had granite rock slopes and “sheeting joint structures” that were infiltrated by overflowing water from the natural stream and catchwater, reducing stability and triggering the landslide, Shum said.