Since 1997, DSD has been implementing a $12 billion flood prevention programme in the NT, including more than 100 km river training works and 27 village flood protection schemes. The drainage improvement works in Tai Po Town area and Ho Chung River at Sai Kung were completed in 2009. In urban areas, a $9.6 billion programme of drainage improvement works to raise the flood protection level in the concerned catchments including the construction of Hong Kong West, Tsuen Wan and Lai Chi Kok drainage tunnels are now in satisfactory progress. These major flood control projects are listed in Appendix A, whereas locations of the projects are shown in Appendix B.

Wing Lok Street in Sheung Wan is a low-lying area where flooding had occurred in the past under severe rainstorms and high tide conditions in Victoria Harbour. To solve the flooding problem in Sheung Wan, DSD had constructed stormwater intercepting drains and pumping station to pump stormwater of the low-lying area to the sea. Since the commissioning of Sheung Wan Floodwater Pumping Station in March 2009, no flooding case in Sheung Wan low-lying area has been reported.

Apart from continuing with the implementation of planned flood protection projects, DSD is actively reviewing new flood protection needs. The Drainage Master Plan (DMP) Studies for Yuen Long and the Northern NT were completed in 1998 and 1999 respectively. The majority of the improvement works and river training works recommended in the Studies have been completed. However, in view of changes in land uses and new developments planned within the areas, DSD commissioned a DMP Review for Yuen Long and North Districts in March 2008. Taking into account of the major changes in land uses, new development proposals and town planning, numerical models for evaluating the hydraulic performance of the major rivers/channels are being set up. Further drainage improvement works for major rivers, upstream channels and the local flooding spots would be proposed by the Study which is expected to be finalized in late 2011.

In respect of operation and maintenance, DSD continues to carry out preventive measures including inspection, desilting and repair works for drainage systems. In 2009-10, over 2,077 km of drains and watercourses were inspected and about $111 million was spent on such maintenance works. DSD always puts efforts in resolving issues related to problematic road gullies, stormwater intakes, drains and watercourses and inspects them on a regular basis especially before and during the rainy season. The operation and maintenance works carried out in the past years on flood prevention are shown in Appendix C.

The year 2009 was drier than usual. The annual rainfall of 2,182 mm was about 8 per cent below the normal yearly rainfall of 2,382 mm. In 2009, no Black Rainstorm Warning Signal was issued while only 20 and 2 times of Amber and Red Rainstorm Warning Signals were issued respectively. Special Announcement on Flooding in northern New Territories was issued for 4 times in the year.

Under the influence of a stronger than normal sub-tropical ridge, the weather was hotter than usual in August, September and October.  It was also wetter than usual in September with a total rainfall of 486.3 mm, which was about 69 percent above normal.

Typhoon Koppu brought unsettled weather to Hong Kong and Typhoon Signal No. 8 was hoisted from the evening of 14 September to morning of 15 September. Rainfall of more than 70 mm was generally recorded over the territory. Owing to the coastal low-lying nature and storm surge effect, Wing On Street in Tai O was flooded in the early morning of 15 September 2009. Home Affairs Department (HAD) had activated the “Early Alerting System, Emergency Relief and Services for Serious Flooding in Tai O” during the typhoon event. HAD, Fire Services Department and Hong Kong Police Force staff were deployed on site to assist evacuation of Tai O villagers. DSD district staff was mobilised to carry out clearing work at channels and drains.

Low-lying topography, insufficient drainage facilities and rapid urban development in the NNT and the NWNT were the main reasons in the past causing flooding during prolonged heavy rain and tropical cyclones. Since the late 1990s, DSD had already constructed about 77 km drainage channels to better collect and convey stormwater; and a number of village flood protection schemes to protect villages in low-lying areas. The completed 27 village flood protection schemes have protected 35 low-lying villages from flooding. Over 240 hectares of low-lying village area accommodating a population of 30,000 people are being protected.

Flood Prevention in Other NT Areas
As some NT locations other than NWNT and NNT such as Tai Po and Sai Kung are still suffering from the risk of flooding due to deficiency in drainage system or natural low-lying topography, DSD is also implementing drainage projects to improve the drainage systems in areas such as Lam Tsuen River and Tung Tze Road in Tai Po to cope with the developments. In addition, the improvement works at Tai Po Town area and Ho Chung River of Sai Kung were completed in 2009.

Flood Prevention in Urban Areas
Due to limited space and dense population in urban areas, DSD has adopted different approaches for drainage improvement works in order to upgrade flood protection level. These approaches include the use of stormwater storage, pumping or flow diversion through drainage tunnels to minimise the extent of works that may cause disruptions to traffic or conflicts with underground utilities. In recent years, DSD has reviewed the drainage systems in the urban area of northern Hong Kong Island, West Kowloon, and Tsuen Wan/Kwai Chung and proceeded to construct drainage tunnels to enhance the regional flood protection level. The drainage improvement works of Kai Tak Nullah in Wong Tai Sin will be implemented in stages starting from 2010 to increase the overall drainage capacity of the nullah thereby alleviating the flooding risk.

West Kowloon
Major stormwater drainage works in West Kowloon include Tai Hang Tung flood storage tank, Kai Tak stormwater transfer tunnel and about 42 km stormwater drains. A total cost of $2.3 billion of these works has already been completed in stages since 2004. During the heavy rain on 7 June 2008, the Tai Hang Tung flood storage tank, Kai Tak stormwater transfer tunnel and the associated new drains had worked together and prevented extensive flooding and inconvenience caused to the public in Mongkok area.

To address the flooding problem in Lai Chi Kok, DSD is constructing the Lai Chi Kok Drainage Tunnel (LCKDT) at a total cost of $1.7 billion. The works commenced in late 2008 and is scheduled for completion in 2012. The LCKDT is 4.9 m in diameter and comprises two segments – a Branch Tunnel and a Main Tunnel, of a total length of 3.7 km. The Branch Tunnel runs along Ching Cheung Road from Chak On Estate to Butterfly Valley. It comprises six intakes for intercepting runoff from the upper rural areas. The flow is then discharged via the Main Tunnel which runs southwards from Butterfly Valley to Victoria Harbour.

The tunnels are being constructed by a state-of-the-art slurry shield Tunnel Boring Machine (TBM). Boring for the Branch Tunnel started in March 2010 and works are in steady progress.

Hong Kong Island
Since the commissioning of Sheung Wan Floodwater Pumping Station in March 2009, no flooding case in Sheung Wan low-lying area has been reported.

On the other hand, other Northern Hong Kong Island areas are still subject to flooding risk due to possible rapid overland flows from hillside slope during severe rainstorms. To reduce the overall flooding risk in the northern part of Hong Kong Island, DSD has commenced the construction of Hong Kong West Drainage Tunnel (HKWDT).

HKWDT is our major initiative to enhance the flooding protection in Northern Hong Kong Island. Upon project completion, the 11 km long tunnel will intercept stormwater from the upper catchment at the mid-levels from Tai Hang to Kennedy Town and discharge it to the sea near Cyberport, thus reducing the volume of rainwater flowing to the downstream low-lying areas including Sheung Wan, Central, Admiralty and Wan Chai. This tunnel project also includes 34 intakes located in Mid-levels and 8 km long connection adits. The design-and-build contract commenced in late 2007 for completion in 2012-13.

The drainage tunnel is being constructed by two TBMs of 7 m and 8 m diameters from the east and west sides of the tunnel. It is expected that the excavation of main tunnel will be completed in early 2011.

The construction of intakes will be proceeded in phases. The intake construction works, comprising intake structure, drop shaft and adit, at 20 intake locations have been commenced.

Reducing Flooding Blackspots
A systematic approach to identify flooding blackspots in the territory was established in 1994. With the progressive completion of major flood prevention projects, the number of flooding blackspots has been reduced substantially. In particular, all major or regional blackspots identified were removed in 2010. Currently there are 18 flooding blackspots. We are implementing drainage improvement works for 14 flooding blackspots while formulating the flood relief measures for the remaining 4 flooding blackspots. We are closely monitoring these locations during heavy rainstorms and expect the majority of these blackspots to be removed after the completion of the drainage improvement works.

Shenzhen River is the boundary river between Shenzhen and Hong Kong. From 1995 to 2007, Shenzhen and Hong Kong have jointly completed the Stages 1, 2 and 3 of the Regulation of Shenzhen River project to alleviate the flooding problems in the surrounding areas. The regulated Shenzhen River, with a total length of about 13.5 km, includes the section between its junction with Ping Yuen River to the estuary of Shenzhen River.

To alleviate the flooding problems in the unregulated upstream section of the Shenzhen River, and to match with the construction of the Liantang/Heung Yuen Wai Boundary Control Point and the development of the northern New Territories, Shenzhen and Hong Kong will jointly implement the Regulation of the Shenzhen River Stage 4 project. The project will be jointly implemented by the Hong Kong Drainage Services Department and the Shenzhen Water Affairs Bureau.

The section of the Shenzhen River to be trained under Regulation of Shenzhen River Stage 4 project is about 4.5km long, which is further upstream of the trained river section under Stage 3 project between the confluence of Ping Yuen River and the north-east of Pak Fu Shan. The scope of the Stage 4 project includes widening of river channel, construction of river embankment and construction of a flood retardation basin, with a view to improving the flood prevention capacity to withstand 50-year rainstorm.

An ecological river concept will be adopted in designing the Regulation of Shenzhen River Stage 4 project. The alignment of the proposed river will follow the existing river as much as possible, instead of using the traditional method of straightening the river. 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 will be used for the new river beds instead of using concrete bedding.

Meanwhile, the existing river bends will be kept and improved as river marsh lands to provide suitable ecological habitats for the Shenzhen River. The largest existing river bend will be designed as a flood retardation basin, which will greatly enhance the ecological value of the Shenzhen River, and at the same time temporarily store floodwater during heavy rainstorms to control the downstream water level.

Upon completion, the project will alleviate the flooding problem in the vicinity, and also enhance the ecological value of the adjacent areas. The river training works is scheduled to commence in 2012 for completion in 2017. The Hong Kong’s share of the project cost is estimated to be about HK$800 million.