Landslide danger shifts with rise in rural homes
The encroachment of urban Hong Kong deeper into rural areas has forced a strategy rethink by the billion-dollar-a-year government department whose job it is to keep the city safe from landslides.
And Hong Kong's chief slope protector says natural hillsides, rather than man-made slopes, are now the focus.
The Geotechnical Engineering Office (GEO), which operates under the Civil Engineering and Development Department, was set up in 1977 after a series of fatal landslides in 1972 and 1976.
Its main taks are to mitigate the risk from existing man-made slopes and natural hillsides, to ensure new developments comply with slope safety and to educate the public about the city's hilly terrain.
Since 1977, it has spent HK$15.5 billion on slope stabilisation works and its current annual budget is HK$1 billion.
'As we make progress in upgrading man-made slopes, we reduce the risks they present, but sooner or later, the risk from hillsides will catch up,' said the GEO's head, Chan Yun-cheung. 'So since 2010, we have committed more than half our resources to hillsides.'
The shift to upgrading natural slopes was a direct result of population growth which had pushed urban development farther out, he said.
Official government figures show that by 2039, Hong Kong will be home to 8.89 million people, up from about 7.1 million.
Chan said hillsides regularly 'fail', that is collapse and cause landslides. But because 'most were far away from people, you could allow them to fail'.
'But the city has grown, the population has grown, so what previously did not matter, matters now,' he said. 'So to be fair, that chunk of money must now be divided into two parts: one for hillsides affecting developments and one for man-made slopes.'
The GEO upgrades about 400 man-made slopes a year, while about 30 hillsides get the same attention.
'A hillside is much bigger than a man-made slope so you're talking about hectares of terrain,' Chan said.
'We cannot afford to soil-nail [a technique used to stabilise man-made slopes] the whole hillside because it will be too disruptive to the natural terrain.'
Instead concrete or flexible steel barriers are erected to catch the main flow.
'But we won't prevent landslides from happening; we mitigate it, we can't stop it.
'There will always be some risk and landslides are one way that hillsides evolve. This is nature.'
On average Hong Kong experiences about 300 landslides per year but this can be skewed by weather.
In 2008, on Lantau Island alone there were 2,300 landslides due to extremely heavy rainfall throughout the year.
The number of landslides reported last year in Hong Kong, far below the annual average of 300 for the past two decades