LAND, PUBLIC WORKS AND UTILITIES
exercises are carried out yearly to remove over 250 000 cubic metres of silt from drains and watercourses, to keep them free-flowing and their pollution level low.
The department also operates an Emergency Storm Damage Organisation. The organisation is run by staff working on a rotational basis and is supported by the department's own labour force and contractors. Its operation ensures that emergency situations are dealt with efficiently.
Geotechnical Control
The Geotechnical Engineering Office (GEO) of the Civil Engineering Department was established after the landslip disasters of the 1970s, and the control of geotechnical aspects of construction works, in the interest of public safety, continues to be one of its foremost duties. Checks were made on 7 000 design proposals during the year.
Work to upgrade unsatisfactory old slopes to modern safety standards is continuing. Private sector resources are now being employed to accelerate the Landslip Preventive Measures Programme. During 1993, landslip preventive works were completed on 90 slopes and retaining walls, at a cost of $70 million, within the programme. Preliminary studies were carried out on 1200 slopes and retaining walls, and detailed geotechnical investigations were finished on 100 slopes and retaining walls. Work was completed on the extension to the Mid-Levels boulder fence above Conduit Road, together with the in situ stabilisation of large boulders in the boulder field behind the fence, at a cost of $5.6 million. Upgrading work on the slopes of an old landfill borrow area at Fung Shing Street, Ngau Chi Wan, was also completed at a cost of $7 million.
The GEO operates the Landslip Warning System and a 24-hour emergency service to provide advice to protect public safety when landslips occur. Exceptionally heavy rainfall on June 16 resulted in about 100 landslip incidents, one of which involved a fatality. GEO staff attending these incidents gave advice on immediate measures to reduce danger, as well as on permanent remedial measures.
The GEO's public education campaign continued, to increase awareness of the importance of slope maintenance and the responsibility of land owners to maintain their slopes.
A revised edition of Geoguide 1: Guide to Retaining Wall Design was produced. Publication of the document will provide upgraded technical standards in this area. The GEO also published a document on granular and geotextile filters with the same objective.
The Hong Kong Geological Survey prepared 1:20 000 scale geological maps for the Tung Chung, Tai O and Cheung Chau districts. Compilation of memoirs relating to the Northeast New Territories and Lantau Island neared completion during the year, with publication scheduled for 1994. Work also started on the compilation of a comprehensive publication on the geology of Hong Kong.
A programme of systematic land inspections continued to identify old fill slopes and retaining walls, using aerial photography. Following publication of engineering geology maps and reports on the North Lantau development area, work commenced on a study of potential hazards related to slopes in the Tung Chung Valley. New geophysical techniques were introduced to assist with developing the stratigraphic model for offshore sediments. Other geophysical surveys were completed in Tolo Harbour, North Lantau and North Lamma. These will help to identify geological structures and buried marble in development
areas.
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