LAND, PUBLIC WORKS AND UTILITIES
204
Operation and maintenance of drainage system
With the commissioning of each additional item of infrastructure there is a consequential increased commitment in operations and maintenance. At present, the sewage treatment facilities are being operated to provide grit removal and screening for sewage of some 1.3 million cubic metres per day and to provide full biological treatment for sewage of another 350 000 cubic metres per day. Sludges produced from both sewage treatment works and water treatment works at Sha Tin are dumped at sea by the 1 400 cubic metre-capacity purpose-built vessel Sha Tin Prince which commenced operation in March 1991. The environmental effect of such dumping is carefully monitored.
The department also operates an all-the-year-round emergency storm damage organisation. This organisation is run by staff working on a rotational basis and is supported by the department's direct labour force and contractors. Its operation ensures that emergency situations, even outside normal working hours, can be dealt with efficiently. Effective maintenance of the drainage infrastructures is an essential part of the total effort to reduce the risk of flooding as well as to ensure the proper and effective disposal of foul water. Since the establishment of the department, the approach to operation and maintenance of the public drainage system has progressively shifted from crisis management to preventive maintenance. Resources have been deployed to carry out regular inspection, cleansing, repair and improvement of the drainage system, especially at identified drainage black spots. The results are promising and although the public drainage system has become larger and more complex with urbanisation, the number of drainage complaints, chokage and flooding show steadily declining trends. The department now maintains 2 850 kilometres of watercourses, drains and sewers, increasing at the rate of 50 kilometres per year. Some 90 000 cubic metres of silt are removed from drains and watercourses each year to keep their pollution level low and keep them free-flowing.
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 6 494 design proposals in 1992.
The GEO also operates the Landslip Warning System and a 24-hour emergency service to provide advice on landslips. An exceptionally heavy rainfall event occurred on May 8, 1992, which resulted in more than 350 landslip incidents, two of which involved fatalities. GEO staff attended all of these incidents giving advice on immediate measures to prevent further danger as well as on permanent remedial measures.
In June 1992 arrangements were made for members of the public to gain access to the government's catalogue of slopes and to obtain information about the results of the squatter area studies undertaken by GEO.
During 1992, landslip preventive works were completed on 33 slopes and retaining walls requiring the expenditure of $62.3 million in the Landslip Preventive Measures Programme and substantial remedial works were carried out to three major landslips. Preliminary studies were carried out on 1 602 slopes and retaining walls and detailed geotechnical investigations were finished on 53 slopes and retaining walls. In addition, the inspection of a number of boulder and rock outcrop features along Seymour Cliffs in the Mid-Levels was undertaken, with preventive stabilisation works completed on 45 features, at a cost of $2.6