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SCMP Reporter

Twenty-four slopes on Lantau Island have been stabilised in an environmentally friendly way by the Civil Engineering and Development  Department.
It  spent about HK$75 million on a project to upgrade slopes along South Lantau Road from Mui Wo to Pui O between December 2001 and October 2004.
The project aims to decrease the landslide risk to the local community and the threat of traffic disruption, as happened when several landslides occurred along the road in the early 1990s.
On Saturday, floods hit North Lantau Highway as torrential rain triggered landslides on the hill opposite the Caribbean Coast complex.
Terence Chan Chun-fai,  the department's chief geotechnical engineer,  said the project aimed to make man-made slopes look as natural as possible.  'And the project is a success, as we found plant diversity increased on the slopes.'
Work included the cutting  and filling of slopes in 24 locations.
Technicians cut steep slopes back to lower their angle,  and place inserts  to stabilise the soil. Toe-wall planters  for trees and shrubs are placed on some slopes.
Mr Chan said the old way to cut a slope involved covering it with cement or building a retaining wall, which left a surface  that could not accommodate vegetation.
Now 'if the slope is too steep, we use a hard surface [to cover it] and plant some creepers on it to keep it green', he said.
When filling  slopes, the department extracts all loose material and replaces it with rocks, which are then  packed down  to make the slope   strong.  It is then topped off with soil and planted  with  trees and shrubs.
The department planted 20 to 30 species of vegetation, which included about 11,600 trees and 52,000 shrubs.
Billy Hau Chi-hang,  an assistant professor with the department of ecology and biodiversity at Hong Kong University, conducted four biology surveys on the slopes during the past year and found the number of plant species in those areas had increased to about 190.
He  said the increase was due to the local species of vegetation growing after the department had planted  various other species.
The trees and shrubs also attracted various insects to the area.
Professor Hau said the new, greener way to upgrade slopes was much better than the traditional way, as cement slopes had no ecological value.
'The different species [of trees an shrubs] also ensure there are flowers blooming on the slopes throughout the year,' he said.



Green route to Lantau slope stabilisation