Drainage Services Department adopts innovative concept to relieve flooding (with photos)
The Drainage Services Department has adopted an innovative concept to alleviate flooding by building drainage tunnels to intercept excessive rain water from the mid-levels and discharge it into the sea directly, hence bypassing the downstream urban areas.
The department today (December 20) awarded two contracts with a total contract sum of HK$3,875 million for building the Hong Kong West drainage tunnel and Tsuen Wan drainage tunnel. The two projects aim to solve flooding problems in the northern part of Hong Kong Island, Tsuen Wan and Kwai Chung.
The Director of Drainage Services, Mr Wong Chee-keung, said at the contract signing ceremony, “After the completion of the two drainage tunnels, the flooding risk in Tsuen Wan, Kwai Chung and the northern part of Hong Kong Island, in particular areas in Central, Sheung Wan and Wan Chai, can be greatly relieved. The general standard of flood protection in these areas can be substantially raised.”
Mr Wong pointed out that the current urban drainage systems were designed and constructed decades ago according to the then flood protection standard. With urban development and the extension of paved areas, the surface runoff has increased significantly, thus overloading urban drainage systems. The risk of flooding has increased correspondingly during heavy rainstorms.
He said that the traditional way to treat flooding by enlarging drainage systems would entail extensive road works and cause serious traffic congestion. The adoption of rain water intercepting tunnels, which intercepts excessive water from the mid-levels and discharges it directly into the sea, could reduce the amount of rain water flowing into urban areas.
Mr Wong said, “The main benefit of the innovative intercepting concept is that we only use tunnel boring machines to construct the drainage tunnels. Prolonged and extensive pipe-laying works in the urban area is not required. Thus the inconvenience to the public will be minimal and the downstream areas will have a better level of flood protection.”
The tunnel scheme has also adopted innovative designs such as vortex drop shafts and de-aeration chambers to effectively divert the floodwater into the tunnel.
The $2,752 million contract for the Hong Kong West drainage tunnel comprises the construction of an 11-kilometre-long main tunnel with diameter varying from 6.25 metres to 7.25m from Tai Hang to Pokfulam, the eastern and western portals, 34 intakes, about 8km of connecting admit tunnels and ancillary works.
The Tsuen Wan drainage tunnel contract amounts to $1,123 million. It comprises the construction of a 5.1km drainage tunnel with an internal diameter of 6.5m, three intake structures each at Wo Yi Hop Road, Lo Wai and Tso Kung Tam and one outfall at Yau Kom Tau.
The Hong Kong West drainage tunnel project began on November 30, 2007, for completion in 2012.The Tsuen Wan Drainage Tunnel project will start on December 28, 2007, for completion in 2011.
Ends/Thursday, December 20, 2007
Issued at HKT 15:30
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