Shouldering our core responsibility to safeguard the general public against flooding, the Department endeavours to ensure that our drainage system remains in good condition and up-to-date.

Overview

During the past year, the Department continued its efforts to improve the drainage system in Hong Kong and to guard against flooding. We implemented a series of projects to increase the flood prevention level of different districts, reviewed and updated the Drainage Master Plans (DMPs), and devised strategies to cope with the city's changing drainage needs.

In the urban areas, a series of improvement works totalling $10.3 billion that cover the construction of drainage tunnels in Hong Kong West, Tsuen Wan and Lai Chi Kok and works of underground stormwater storage scheme in Happy Valley, are well under way. The above-mentioned tunnels, when completed, will intercept stormwater from the upper catchments and raise the flood prevention level in various urban areas including Tsuen Wan, West Kowloon and the northern Hong Kong Island. Flood protection level in the Wong Nai Chung Road, Tin Lok Lane, Lap Tak Lane and Morrison Hill Road districts will be enhanced upon completion of stormwater storage scheme in Happy Valley. Elsewhere in Wong Tai Sin, the improvement works of Kai Tak River have commenced in phases and are progressing satisfactorily.

In the New Territories, another $13.7 billion programme of flood prevention works, launched since 1997, is in progress. Such works include the training of rivers of more than 100 kilometres and flood protection schemes in 27 villages. (Details of the major flood control projects are listed in Appendix A and their locations in Appendix B.) In order to meet the recent development needs of the Liantang-Heung Yuen Wai Boundary Control Point, our Department together with Shenzhen Water Affairs Bureau will jointly implement the Shenzhen River Regulation Project Stage IV.

A comprehensive, territory-wide DMP has been completed. In order to cope with the latest developments in the community and also the changes in the weather pattern and the effects, our Department has commenced to conduct the review studies for the DMPs of different districts in phases. Further to the completion of review studies for DMP in Yuen Long, North District and Happy Valley in 2011, we embarked on a 30-month review studies for DMP in West Kowloon and East Kowloon; they are in progress and aim for completion in mid-2014. Review studies for DMP in Tai Po will start in end of 2012; for Shatin and Sai Kung, similar review studies are scheduled to start in early 2013.

Prevention is better than cure. During maintenance and routine operation in 2011-12, our staff carried out regular preventive maintenance works, such as inspection, desilting and maintenance, all of which covered more than 2017 kilometres of drains and watercourses, costing some $104 millions. (Details are shown in Appendix C.)

Our endeavour to improve drainage system, coupled with the completion of various flood prevention projects, resulted in the removal of all remaining major flooding blackspots in Hong Kong. Nevertheless, we still have 15 blackspots of less severity. We will keep on closely monitoring these locations during rainy periods and expect to clear them all when we complete other improvement projects.

Flood Prevention in the New Territories

Low-lying topography, insufficient drainage facilities, coupled with rapid urban development in the New Territories, have always been our main concerns. In mapping out preventive strategies, we consider the afore-mentioned factors plus prolonged heavy rain in the past and the damages caused.

Since the late 1990s, our Department has constructed about 79 kilometres of drainage channels to better collect and convey stormwater. The completion of 27 village flood protection schemes has meant greater protection for some 30000 residents in 35 villages, covering about 240 hectares of low-lying areas. Our efforts in this regard will continue.

The drainage improvement works at Lung Yeuk Tau and Kwan Tei River were completed in 2011. Such works have raised the capacity of the watercourses, making them capable of withstanding rainstorms with a return period of 10 years. During construction, we encountered extensive unforeseen underground utilities obstruction. With combined efforts from our staff members and our contractor, we managed to complete the scheduled improvement works before the wet season of 2011.

Other parts of the New Territories, such as Tai Po and Fanling, shared the same shortcomings, which are inadequate drainage system and low-lying topography. Our drainage improvement works at Kau Lung Hang are progressing smoothly, and are expected to be commissioned in 2012. Elsewhere in Tai Po's Lam Tsuen River and Tung Tze Road, such works are also progressing satisfactorily.

The 30^th Anniversary of Shenzhen River Regulation

The governments in Hong Kong and Shenzhen established the Joint Working Group of Shenzhen River Regulation 30 years ago in April 1982. Since then, working parties from both sides have co-operated closely to resolve the flood problems in the vicinity of Shenzhen River, benefitting local residents. The good partnership built over these years between the two regions and the encouraging results have become a model for future cross-boundary infrastructure projects.

Shenzhen-Hong Kong Co-operation Model

The Shenzhen River Regulation's Joint Working Group (JWG) co-ordinates efforts from both the Hong Kong SAR and the Shenzhen Municipal Governments in regulating the river and abating the river's pollution problems. Working parties from both governments jointly formulated and implemented strategies and remedial measures. A Technical Sub-group and an Environmental Sub-group are established under the JWG to assist in the planning and implementation of flood prevention measures in Shenzhen River as well as managing the river's floating refuse and pollution abatement issues too.

Regulation of Shenzhen River, Stage IV

(Liantang-Heung Yuen Wai Section)

The Shenzhen River Regulation Project is to be implemented in four stages. Stages I, II, III, were completed in 1997, 2000 and 2006 respectively, having successfully trained 13.5 kilometres of the Shenzhen River from Deep Bay to Ping Yuen River.

To alleviate flooding risk in the river's unregulated upstream section, and to pave the way for the construction of the Liantang-Heung Yuen Wai Boundary Control Point and also with the development of northern New Territories, the two governments, represented by our Department and the Shenzhen Water Affairs Bureau, will go ahead to implement the regulation project's Stage IV.

The section to be trained under Stage IV is about 4.5 kilometres long, which is further upstream of the trained river section under Stage III and lies between the confluence of Ping Yuen River and the north-east of Pak Fu Shan. The scope of works in this Stage IV includes widening river channel, constructing river embankment and a flood retardation basin, all with a view to improving its flood prevention level to cope with possible rainstorm with a return period of 50 years.

An ecological river concept will be adopted for Stage IV. The alignment of the proposed river will follow the existing river as much as possible instead of using the traditional straightening method. The cross-sections of the river will mostly be in trapezoidal shapes, with grasscrete panels on the sloping surfaces of the river embankments; while rip-raps or in-situ natural river bed materials, rather than concrete bedding, will be used for the new river beds.

The existing river bends will be improved and kept as 'river marshlands' to provide suitable ecological habitats. The largest existing river bend will be designed as a 'flood retardation basin', not only to greatly enhance the river's ecological value but also to help store floodwater during heavy rainstorms; thus the downstream water level will be under control.

Upon completion, the project will alleviate the flood problem of the adjacent areas and at the same time enhance the ecological value of the concerned section of Shenzhen river. Advanced works for Stage IV commenced in February 2012, six months after the start of the detailed design study for the main regulation works. This will be followed by major site works, scheduled to start in mid-2013 and is aimed for completion in 2017. The project's cost is to be shared between the two governments; for Hong Kong, the bill will amount to about $800 million.

Flood Prevention in Urban Areas

Urban areas necessitate different flood prevention approaches due to a much higher population density. To minimise traffic disruption caused by road works, we devise stormwater storage schemes, pumping stations and flow diversion through drainage tunnels.

On Hong Kong Island, the Happy Valley Underground Stormwater Storage Scheme was activated in September 2011 subsequent to funding approval by the Legislative Council's Finance Committee. We expect to complete the entire project in phases from 2015 to 2018 before the rainy season in 2018. This storage scheme will relieve flooding in the Wong Nai Chung Road, Tin Lok Lane, Lap Tak Lane and Morrison Hill Road districts.

In the northern part of the Island, works on the 11-kilometre long Hong Kong West Drainage Tunnel is progressing well. Tunnel excavations were completed in February 2012 and subsequent works are continuing. When the tunnel is completed in the third quarter of 2012, most of the stormwater from the upper catchment in the mid-levels, from Tai Hang to Kennedy Town, will be intercepted and be diverted for discharge to the sea near Cyberport. This will reduce the volume of rainwater flowing downstream to areas including Sheung Wan, Central, Admiralty and Wan Chai.

In Kowloon, the main project is the Kai Tak River Improvement Works which will increase the drainage capacity of the Kai Tak River. At present, flooding occurs during heavy rainstorms along Choi Hung Road especially at its junction with Shatin Pass Road, seriously affecting traffic flow in Wong Tai Sin and the adjacent districts. Views from the public gathered in 2010 and 2011 at our 'Build Our Kai Tak River' engagement exercise underlined public aspirations to revitalise Kai Tak river to a natural green river corridor and to keep the river open as much as possible. Our Department acted on these public views and our proposed works will not only improve the river's drainage capacity but also enhance the living environment and landscaping in the area. There will be a scenic and leisure park for public enjoyment, and efforts will be made to foster closer connection with the adjacent neighbourhoods.

Construction works for Kai Tak River's upstream section, from Po Kong Village Road to Tung Kwong Road, commenced in October 2011 and will be completed in phases from 2015 to 2017. Such works include reconstruction and rehabilitation of the river's upstream section totalling about 600 metres in length, construction of a 400-metre-long box culvert alongside the river, relocation of some existing water mains and sewers. Ancillary works such as landscaping and in-situ reprovisioning of the current footbridge near Tung Tai Lane will also be carried out. Meanwhile, design for the improvement relating to the river's midstream section is in progress. This section's construction works will be carried out concurrently with portion of the upstream section.

Elsewhere in Kowloon, our Department's other improvement projects are in Lai Chi Kok and Tsuen Wan where drainage tunnels are being built. The Lai Chi Kok Drainage Tunnel, measuring 4.9 metres in diameter and 3.7 kilometres in length and costing around $1.7 billion, will alleviate flooding risk not only in that district but also in Cheung Sha Wan and Shum Shui Po areas. Works being carried out in this main tunnel are to involve compressed air operations under a pressure up to 4.2 bar, which is unprecedented in Hong Kong. Another feature of the construction is the use of state-of-the-art slurry shield boring machine that had helped complete the tunnel boring in December 2011. The entire project will be completed in the third quarter of 2012.

For the Tsuen Wan Drainage Tunnel, measuring 5.1-kilometre long, 6.5-metre wide and costing around $1.3 billion, its anticipated completion in the second quarter of 2013 will relieve flood risk in both Tsuen Wan and Kwai Chung districts. In February 2012, excavation of tunnel was completed while excavation works for connection adits are progressing well.

Bold New Initiatives

Happy Valley Underground Stormwater Storage Scheme

The Happy Valley Recreation Ground is earmarked for an underground stormwater storage scheme. It will be the third stormwater storage scheme in Hong Kong; the first one in Tai Hang Tung, completed in 2004 to address flood problems in Mong Kok, and the second is the Sheung Wan Stormwater Pumping Station, completed in 2009 to address flood problems in Sheung Wan. Under the Happy Valley scheme, an underground storage tank with a capacity of 60000m³ will be built with pumping facilities and a box culvert. Advance works for this storage scheme, including the drainage works in Pitch No. 8 of the Happy Valley Recreation Ground and access manhole construction in Wong Nai Chung Road, commenced in October 2011. Tender for the main construction is to be invited in April 2012, with works to commence in mid-2012. Construction will be carried out in two phases. Upon completion of Phase 1 in early 2015, residents of Happy Valley and the adjacent neighbourhoods will be assured of improved flood protection. When Phase 2 is completed in early 2018, the flood protection level will be further enhanced to the ultimate design level.

This ambitious flood prevention scheme was awarded 'Winner of 2012 IWA Project Innovation Awards - East Asia Regional Awards' (Planning Category), organised by the International Water Association for its practical approach and innovativeness. The project has also been fully recognised by the international water engineering industry.

Drainage Master Plan (DMP) Studies and Review

Since 1994, this Department has completed eight stormwater DMP studies and three drainage studies. In 2008, we commenced to conduct review studies for the DMP of different districts in phases. Review studies for DMP in Yuen Long, North District and Happy Valley were completed in 2011. Review studies for DMP in West Kowloon and East Kowloon began in January 2012 while similar studies for DMP in Tai Po, Shatin and Sai Kung are to start by end of 2012 and early 2013 respectively.

Review Studies of West Kowloon and East Kowloon Drainage Master Plans

To enhance Kowloon's sustainable development and to keep up with the large-scale projects namely the West Kowloon Culture Centre, the Kai Tak Development Plan, the Guangzhou-Shenzhen-Hong Kong Express Rail Link, the Kwun Tong Line Extension, Shatin to Central Link and the Central-Kowloon Route plus others, our Department is now conducting a comprehensive review and an evaluation of the existing drainage system. We will recommend improvement measures when the studies are finished within 30 months.

In conducting our review studies, we will apply one and two dimensional hydraulic mathematic models to simulate the interactions between rivers, drainage pipes/culverts and overland flows. We will also adopt the topographical data from the Light Detection and Ranging in the models to accurately assess the overall hydraulic performance of the drainage system. The review studies will also assess, among other aspects, the adverse effect of siltation, utilities intrusions, dry weather flow interceptors as well as climate change on the system. Measures to further improve the flood protection level in Kowloon will be recommended upon completion of the review studies.