Hong Kong West Drainage Tunnel

Why does flooding occur in the Northern Hong Kong Island, especially in low-lying areas around Sheung Wan, Central, Wan Chai and Admiralty, during heavy rains?

The majority of the drainage systems of Hong Kong Island were built decades ago. With ongoing urbanisation, large areas of natural ground are turned into hard paved areas, the volume of the surface runoff increases dramatically during heavy rains. The capacity of the existing drainage systems in the low-lying areas are no longer adequate to cope with large quantity of stormwater. During heavy rains, stormwater overflow main drain directly to the road surface causing flooding of low-lying areas. To alleviate the flooding in Northern Hong Kong Island and thus minimizing public inconveniences as well as economic loss during heavy rains, Drainage Services Department has implemented the Hong Kong West Drainage Tunnel Project since November 2007 and was completed in August 2012.

What are the benefits for the construction of the Hong Kong West Drainage Tunnel?

The Project consists of building a main drainage tunnel of about 11km long extending from Haw Par Mansion at Tai Hang to Cyberport, 34 intakes and a total of about 8km adits connecting the intakes with the drainage tunnel. The drainage tunnel intercepts stormwater collected from Mid-Levels, and discharges it into the sea directly and thus bypassing the existing drainage systems downstream. This can relieve the discharge load of the existing drainage systems at the low-lying urban areas and improve the overall flood protection standard, thus minimizing the risk of flooding in Northern Hong Kong Island.

Are there any measures to minimize impacts to the environment during the construction of the Hong Kong West Drainage Tunnel?

Minimizing impacts to the environment during construction is one of our key tasks. The main drainage tunnel and most of the intakes were constructed underground by using Tunnel Boring Machines and Raise Boring Machines respectively. With adoption of these environmentally friendly methods the construction period can be greatly reduced. Moreover, it can avoid prolonged and extensive excavation works in the low-lying urban area, especially the commercial and financial centres in the areas of Central, Admiralty and Wan Chai, thus minimizing traffic disruption, environmental impacts and disturbances to the public.

What measures will the Contractor adopt to avoid bringing out mud and dirt onto public roads by construction vehicles?

Every construction vehicle must have its wheels properly washed before leaving the construction site. The Contractor has assigned workers at site exits to monitor the situation. Moreover, our resident engineers and supervisors will strengthen site supervision to make sure this requirement of wheel-washing has been enforced.

Why a temporary pier has to be built at Cyberport?

The temporary pier is to provide a loading and unloading point for transportation of equipment of the Tunnel Boring Machines, precasted tunnelling segments and excavated materials by sea, thus minimizing the traffic impacts on the nearby road networks. Upon completion of the whole Project, the temporary pier was handed over to South Island Line(West), SIL(W), Project of MTRC for transportation of material by sea. The temporary pier was completely dismantled and the original coastline was restored in end 2014.

Are there any short-term measures being carried out by the Drainage Services Department to relieve the present flooding problems before the completion of the Project?

The Drainage Services Department strives the best to ensure the existing drainage systems are functioned properly. We conduct desilting on a regular basis, especially before rainy seasons, to ensure the drainage systems are free from obstructions to reduce the risk of flooding. In times of adverse weather, our direct labour force will be deployed to flooding blackspots to carry out necessary emergency relief works to tackle the flood hazards. We will also maintain close contact with relevant government departments.

When Red Rainstorm Warning Signal or Tropical Cyclone Signal 8 is hoisted, an Emergency Control Centre will be activated within DSD to monitor flooding and maintain close contact with relevant government departments.

How can the Project alleviate the flooding problem of Northern Hong Kong Island?

Further to the Hong Kong West Drainage Tunnel Project in 2012, a much better flood protection level of Northern Hong Kong Island, especially in areas around Sheung Wan, Central, Admiralty, Wan Chai, Causeway Bay and Happy Valley is achieved. Flooding problem is much alleviated.