The close proximity of steeply sloping terrain to buildings and infrastructure in Hong Kong, coupled with seasonal torrential rainfall, inevitably brings with it the risk of casualties due to landslides. Since 1977, the Geotechnical Engineering Office (GEO, known as Geotechnical Control Office before 1991) has been conducting studies and works to reduce landslide risk in Hong Kong.
Until 2010, the work (which was implemented under a Landslip Preventive Measures Programme) focused on substandard man-made slopes that posed the greatest landslide risk in Hong Kong. Given more than 30 years of sustained efforts, the landslide risk arising from man-made slopes has been reduced considerably. On the other hand, the landslide risk arising from natural hillside is rising due to the encroachment of more urban development or redevelopment on steep hillsides and is now comparable with the risk associated with man-made slopes.
In 2010, the GEO launched a rolling Landslip Prevention and Mitigation Programme (LPMitP) to systematically deal with the landslide risk associated with both man-made slopes and natural hillside. Under the LPMitP, the most deserving man-made slopes and natural hillside catchments are selected for studies each year in accordance with a risk based priority ranking system. The necessary landslip prevention and mitigation works, as identified by the studies, for man-made slopes and natural hillside catchments under Government's maintenance responsibility are implemented under the LPMitP. For private slopes found to be liable to become dangerous, statutory actions are taken against the responsible private owners by the Buildings Department through the Buildings Ordinance to ensure its rectification.
Apart from in-house resources, the GEO also engages consultants in landslip prevention and mitigation studies and the letting and administration of contracts for the subsequent works. GEO let an average of about 10 consultancy agreements and 13 works contracts on landslip prevention and mitigation each year. So far, GEO had spent about $23.6 billion on landslip prevention and mitigation studies and works; about 5,897 Government man-made slopes were upgraded, studies for about 6,032 private man-made slopes were completed and mitigation measures for 281 natural hillside catchments were implemented.
It is Government's policy to improve the environment and to make slopes look as natural as possible in their surroundings. Hence, apart from maintaining the highest standard of slope safety, the GEO is committed to provide landscape treatments to all man-made slopes upgraded and natural hillside mitigation measures implemented under the LPMitP. Existing trees are preserved and vegetation is used as cover to slopes and mitigation measures as far as practicable. Where the use of hard cover is unavoidable, landscape measures are implemented to minimize its visual impact. A number of technical guidelines on good practice in slope landscaping works have been published by the GEO. The most comprehensive guidance document is GEO Publication No. 1/2011 – Technical Guidelines on Landscape Treatment for Slopes.. To improve the technology in greening, the GEO has been researching into the use of vegetation in landslip prevention and mitigation works and experimenting with new techniques of providing erosion control measures and vegetation covers to steep slopes. The results of the research provide useful knowledge for establishing robust, cost-effective and eco-friendly vegetation covers for man-made slopes and natural hillside mitigation measures.