Information Paper for
Provisional Legislative Council Panel on Planning, Lands and Works
Meeting on 15 January 1998
1.In April 1995 and April 1996, the Administration presented information papers on flood control to Members of the Legislative Council. This paper provides an update of progress of flood control projects and measures.
2.In previous years, flooding problems had been concentrated in the northern and north-western districts of the New Territories (NW and NNT) which are low-lying areas and natural flood-plains. The problem had also been exacerbated due to intensive development on the flood-plains and the lack of maintenance of some of the streams which have become dumping grounds for rubbish, construction debris and livestock wastes. However, drainage conditions in the NW and NNT have gradually improved as flood control works are making steady good progress in these areas. Since the Legislative Council was informed of progress in April 1996, there has not been any extensive flooding in the NW and NNT despite the record-breaking rainfalls in June and July 1997, although some local flooding, such as Ting Kok Road and the Mei Chung Court, has occurred due to blockage of the drains by construction debris and illegal structure(bridge) across the stream course.
3.In recent years, severe flooding also occurred in urban areas, most notably in West Kowloon, where the stormwater drainage systems were built decades ago, and were of design capacities lower than current standards. The drainage system has also become inadequate because of ageing and intensified infrastructural development. The problem is further aggravated by silting and the presence of other obstructions in the drainage systems, and blockage of gullies by rubbish and debris.
4.To resolve the flooding problem, the Drainage Services Department (DSD) has started a 3-tier plan which comprises:
Long Term Structural Measures
LONG TERM STRUCTURAL MEASURES
Short Term Improvement and Management Measures
Planning and Legislative Measures
5.Long term structural measures include river training projects which will provide comprehensive river channel systems, and village flood protection schemes for low lying flood prone villages. The programme of works for these projects, totalling an estimated $6 billion, is summarised in the attached Tables 1-3. In the urban area, we shall carry out a 3-stage West Kowloon Stormwater Drainage Improvement Project to upgrade the drainage system in the area. Details of the programme are given at Table 4 and described in paragraph 12 below.
River Training Projects
6.As mentioned in paragraph 2 above, the NW and NNT are the two major flood prone areas. Major river training projects are underway in these two areas to alleviate the flooding problem. These are summarized at Tables 1, 2 and 3. Further details are given in the following paragraphs.
7.The most critical flood mitigation project in the NNT is the 3-staged Shenzhen River Regulation Project, which is a joint venture project between the Shenzhen Municipal Government and the Hong Kong Special Administrative Region Government. Stage I Works had been completed in April 1997, and Stage II Works are now progressing in full swing scheduled for commissioning by 2000. Planning for Stage III Works is already in hand, with construction scheduled for completion in 2004. Upon completion of Stage I works, the flooding situation in the low lying areas around Lo Wu has been minimized and confined to local low-lying areas.
8.In the North-western New Territories, construction of Yuen Long Main Drainage Channel (60CD, Contract A) is nearly completed. We are also progressing well with the construction of the lower reaches (60CD, Contract B) and the middle reaches of Kam Tin Main Drainage Channel (43CD, Contract C). We aim to complete these new drainage channels by the end of 1998, by which time they will bring significant relief to the flooding problem of Yuen Long Town and the low lying areas along Kam Tin River.In the Northwestern New Territories we are progressing well with the construction of Yuen Long Main Drainage Channel (60CD, Contract A), the lower reaches (60CD, Contract B) and the middle reaches of Kam Tin Main Drainage Channel (43CD, Contract C). We aim at commissioning these new drainage channels by the end of 1998, by which time they would bring significant relief to the flooding problem of Yuen Long Town and the low lying areas along Kam Tin River. Planning and design for another 25 km of new river channels are underway including the upper reaches of Kam Tin River, Ngau Tam Mei drainage channel and some smaller channels.
9.In the Northern NT, the training of Indus River and Beas River (53CD and 87CL) will commence in phases by the end of 1998. The programme has taken into consideration the need to complete these river training projects in sequence with the Shenzhen River Regulation Project.
10.The Rural Drainage Rehabilitation Scheme (64CD&91CD) aims to rehabilitate and improve six stream-courses in the NT. Works include improving the secondary drainage systems in the upper part of the drainage basins that are urgently needed to supplement the main drainage channels. The first package of works is scheduled to commence in early 1998.
Village Flood Protection Schemes
11.These schemes will protect low-lying villages that are at levels below the drainage channels by collecting water in flood storage pond and pumping it into the drainage channelsThese schemes will protect low-lying villages that are at levels below the drainage channels. Typically an earth bunds is constructed around the villages to protect them from flood overflowing the river banks, while rainfall runoff within the earth bunds is directed to a flood storage pond and subsequently pumped into the drainage channels. Currently there are five flood protection schemes under construction in the New Territories to protect 12 low lying villages at Tai Tau Leng/Tsung Pak Long (72CD), Sha Po Tsuen (71CD), San Tin (35CD), Chau Tau (35CD) and Ha Mei San Tsuen (473CL). They are scheduled to complete in 1998 and 1999. Another eight schemes in the North-western NT are at various stages of planning and detailed design.
West Kowloon Stormwater Drainage Improvement Project
12.To upgrade the drainage system in West Kowloon, a 3-stage West Kowloon Stormwater Drainage Improvement Project will be carried out to increase the drainage capacity of the existing system. Stage I will commence in early 1998 for completion in 2002 to upgrade the critical sections of the drainage system. The flooding situation will be improved after the completion of Stage I. Stage II will commence in 1999 for completion in 2004. After completion of Stage I and Stage II, the stormwater drains in the area will be able to cater for rainstorms of return period of 20 years. The system will be further upgraded under Stage III which is targeted for completion by 2007, upon completion, the drainage system will carry storms of return periods of 50 years.
SHORT TERM IMPROVEMENT AND MANAGEMENT MEASURES
13.These measures include local drainage improvement works, maintenance activities to identify and remove drain blockages and surveillance activities to ensure that the capacity of the drainage system is preserved.
Rural Planning and Improvement Strategy
14.Most of the local drainage improvement works in the New Territories is carried out under the Rural Planning and Improvement Strategy programme. Under this programme, there are at present 55 minor stormwater drainage projects estimated at a total cost of $278 million. So far, 27 projects have been completed, 8 are under construction, and the remaining 20 are under planning and design. To expedite project delivery, we shall implement some projects under a design and construction consultancy commencing early 1998.
Preventive Maintenance Works
15.DSD has a preventive maintenance programme to inspect, desilt and repair the stormwater drain system. This is to ensure that the problematic drains are inspected on a regular basis especially before and during the rainy season. Any blockage found will be cleared and defects rectified immediately. The total length of river channels, main water courses, culverts and stormwater drains in Hong Kong is about 2,000 km. Under this preventive maintenance programme, we inspect at least 800km of these drains, and spend about $100 million on the necessary maintenance works annually. In addition, a special programme of inspecting flood control installations, including flood water pumping stations and local flood warning systems, is conducted each year to ensure that they will be fully operational in times of rainstorm.
16.We are taking special short term actions to ensure that the existing stormwater drainage system in the West Kowloon area is able to function as effectively as possible. These measures include completion of the Hinterland Drainage Improvement Works by the Territory Development Department in June 97, installing 60 additional gullies by the Highways Department to in-take surface runoff, Close Circuit Television Vision survey and cleansing of drains underneath Nathan Road and its environs in 1997, and inspection and desilting of major multi-cell box culverts in the area. This desilting exercise will be completed before the start of 1998 rainy season.
Blockage of Gully Inlets
17.Many local flooding incidents are caused not by inadequacy of the stormwater drains, but by blockage at the inlets to the drainage system. This is often the result of rubbish blocking the gully and drainage inlets. More effort is being made with the assistance of the Urban Services Department and the Regional Services Department to keep road gullies and catchpits clear of rubbish.
Construction Site Activities
18.We have established that some localized flooding is caused by construction site activities. Problems arise as a result of construction waste blocking the drains, inadequate temporary drainage arrangements, temporary works obstructing flow in the drainage system, or damage to the drains. Before the rainy season each year, reminders are sent to engineers, authorised persons, consultants and contractors in charge of construction sites requesting their co-operation in exercising strict control of their construction activities.
19.Over the last three years, DSD has identified 108 blackspots across the territory where there have been frequent floods in the past. Special efforts are being made to find solutions and draw up plans to remove these flooding blackspots. Remedial measures are being implemented and progress is closely monitored. So far, we have been able to remove 24 flooding blackspots as a result of effective short term improvement or management measures. Although ultimate removal of the remaining blackspots will depend on completion of the long term structural measures described in paragraphs 5 to 12 we will continue our effort to mitigate the effects of the flooding at these locations.
Nullah Decking Study
20.The Nullah Decking Feasibility Study commenced in July 96 and is still on going. The Consultants have completed Working Papers on all 31 chosen nullahs in the territory. Due to flood control consideration, decking would not be recommended where it would cause drainage problems and increase difficulties in future operation and maintenance. Consultation with District Boards is currently being carried out for those nullahs on which decking is recommended.
PLANNING AND LEGISLATIVE MEASURES
21.Planning and legislative measures are non-structural means to prevent flooding problem by drawing up long term visions and programmes to cater for future growth and development of each region. These measures include:
Drainage Master Plan Studies
Land Use Planning and Drainage Impact Assessment
Land Drainage Ordinance
Drainage Master Plans
22.In 1996, a major initiative commenced was the preparation of Drainage Master Plans (DMP) covering all flood prone areas of the territory. These studies will review the condition and performance of the existing stormwater drainage systems in a comprehensive manner, including all reported flooding incidents. On the basis of these studies, both long term and short term measures to upgrade the system to cope with current and future development pressures will be worked out. In addition, a computerized asset management system will be developed to facilitate future maintenance of the stormwater drainage system. A total of seven DMP studies will be carried out. The areas covered by these studies and their respective time frame are shown at figure 1 attached.
23.The first 5 DMP studies are in progress. The first study, namely the Northwest New Territories DMP Study, and the second study, namely the Northern Hong Kong DMP Study, will be completed in January and February 1998 respectively. Major proposals put forward under the first study covering the NWNT included raising the banks of existing main river channels, adding new drainage channels to divert stormwater flow from the flood-prone catchments and upgrading various pipeline identified to be of inadequate capacity. The second DMP study covered the northern Hong Kong Island where the catchments consist of natural hillsides and a coastal strip of highly urbanised areas. The study revealed that the existing drainage systems, particularly those in the urban area, are of inadequate capacity and have put forward the option of diverting stormwater from the upland catchments via a tunnel directly into the sea. This has advantage over works to enlarge major culverts in the built-up area. The sixth study will commence shortly in early 1998, and the last study will start mid 1998.
Land Use Planning and Drainage Impact Assessment
24.Urbanization and infrastructure development have significant adverse impact on the drainage system. To minimize such impact, we provide drainage advice when land use plans are prepared or revised to ensure that the overall land use proposal is compatible with land drainage requirement. We also require proponents of major infrastructures to carry out Drainage Impact Assessments to identify and mitigate any adverse impact to drainage in the area as part of the project. An Advice Note setting out procedures has been issued to private sector development proponents and Authorized Persons. A similar instruction has been issued to Government departments covering public sector projects.
Land Drainage Ordinance
25.The Land Drainage Ordinance enacted in 1994 empowers the Drainage Services Department to gain access through private land to carry out drainage maintenance works and remove obstructions along main watercourses in gazetted Drainage Authority Areas. Five Drainage Authority Areas covering the major flood prone basins in the NT have been gazetted, of which four have been approved and one is under consideration due to objections. The Drainage Services Department has been maintaining and enhancing the capacities of these main watercourses, of which the frequency and severity of flooding has been reduced.
26.The Administration will continue with its efforts to implement the above projects and measures and reduce the risk of flooding to the community.
Drainage Services Department