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Preventive measures to meet landslide challenges

Severe Typhoon Utor has come and gone. Fortunately, despite heavy rainstorms, it did not cause severe casualties, serious flooding or landslides. Nonetheless, we have never lowered our guard against the potential hazards caused by heavy rainfall. The black rainstorm in May this year served to remind us that we should remain vigilant at all times against sudden flooding. During the rainstorm, 26 landslide reports were received, and the two incidents at the worksite on Anderson Road in Sau Mau Ping were of particular concern to the public. While it was fortunate that the incidents occurred in the early morning and no one was injured, they reminded us that we should always be prepared for danger and take preventive measures as early as possible.

I noted that the Geotechnical Engineering Office (GEO) of the Civil Engineering and Development Department started an investigation immediately after the incidents that day. Preliminary findings show that one of the possible causes of the landslides is that the amount of rainwater flowing on the ground at the Anderson Road worksite exceeded the capacity of the site drainage system. As the investigation report usually takes six months to complete, the Head of the GEO immediately reminded all works departments to urge contractors to keep the storm drains clear during site formation works so as to prevent the occurrence of similar incidents.

Currently, some 40 000 government man-made slopes listed in the Catalogue of Slopes have been assigned to the relevant government departments for maintenance. In April each year before the rainy season, all departments concerned will complete the routine inspection and maintenance of government man-made slopes, including clearing drains and repairing slope surfaces. Professional geotechnical engineers will inspect the slopes every five to 10 years and give advice on slope maintenance and improvement works.

We have several decades of experience behind our landslip prevention and mitigation work. You may recall that after a number of fatal landslide disasters in the 1970s, the Government established the GEO in 1977 to deal with slope safety. In the same year, the GEO launched the Landslip Preventive Measures Programme (LPMP) to progressively stabilise substandard government man-made slopes affecting developed areas and major roads in accordance with the landslide risks.

Thanks to over 30 years of continuous efforts, the LPMP was completed at the end of 2010. The overall landslide risk of man-made slopes has been reduced to less than 25 per cent of the 1977 level, in line with the international best practices of risk management. On the day of the black rainstorm in May, 154 millimetres of rainfall per hour was recorded in the developed areas, which is the highest level ever recorded in Hong Kong. Had it not been for the slope stabilisation and maintenance work over the past decades, more landslides or even more serious incidents would have occurred that day.

Owing to the rapid growth of our population and the hilly terrain of our territory, more and more development or redevelopment projects will be located near steep natural hillside catchments, which may impose a higher landslide risk that requires vigorous action in the long term. In addition, extreme weather and unpredictable rainstorms brought by climate change have made the prevention and mitigation work all the more challenging. In view of this, the GEO implemented the Landslip Prevention and Mitigation Programme (LPMitP) in 2010 to further the maintainance of natural hillside catchments and stabilise man-made slopes under a risk-oriented management approach and reduce the risk of landslides.

Since our efforts have been focused on stabilising the high risk man-made slopes over the past 30 years or so, carrying out risk mitigation works on natural hillsides presents a new challenge for us. As the urban areas continue to sprawl towards the rural hillsides, we have to manage these natural hillsides with known potential risks in a systematic way. Given that it is both impractical and costly to carry out large-scale slope stabilisation works on natural hillsides, we have adopted more cost-effective risk mitigation measures, such as erecting debris traps and barriers, to reduce the landslide risks of natural hillside catchments.

Having taken into account various factors including the availability of resources, the capacity of the industry and the adverse impacts of mitigation works on the public and the environment, we plan to stabilise 150 government man-made slopes, conduct safety-screening studies for 100 private man-made slopes, and carry out risk mitigation works for 30 natural hillside catchments this year.

Since 1977, we have stabilised some 5 000 substandard government man-made slopes, conducted safety-screening studies for about 5 400 private man-made slopes, and carried out risk mitigation works for some 52 natural hillside catchments. Moreover, the GEO works with the Hong Kong Observatory to monitor rainfall and issue timely landslip warnings. According to records, over 90 per cent of fatal landslide incidents occurred when landslip warnings were in force, which fully demonstrates that the warning system is indeed very reliable. We hope that you will all ensure your own safety and stay away from hillsides when landslip warnings are in force.

Lastly, I would like to inform you that My Blog will be suspended for two weeks during the summer holiday. See you again on September 8.

18 August, 2013