1.                       INTRODUCTION


1.1                   Background


1.1.1               Surface water falling within the northern catchments of Hong Kong Island is intercepted by a series of drainage pipes and culverts running through the urban area that ultimately discharge at several locations into Victoria Harbour. The existing system is overloaded and flooding and hazardous overload water flows can occur in extreme conditions. However, much of the catchment[1] is outside the urban area and the objective of the drainage improvement scheme studied here is to intercept surface water before it enters the urban area and direct it to a discharge outlet on the west-side of Hong Kong island. This will reduce the flows entering into the lower catchment and reduce flooding frequency in the urban area.


1.1.2               Current investigations were preceeded by the Stormwater Drainage Master Plan Study (CE 91/95). The Hong Kong West drainage tunnel and lower catchment improvement formed an element of the earlier study and a Preliminary Project Feasibility Study Report (PPFS) was carried out on these elements. A Preliminary Environmental Review (PER) formed Appendix F of the PPFS issued in March 1999. The environmental chapter of the PPFS (1999) concluded that "Overall, after construction, there will be general improvement in environmental quality due to the improvement of the drainage system". The environmental improvement will, primarily, result from the reduction of flooding and hazardous flow within the urban area. The PER did not identify any insurmountable environmental issues, but concluded that further assessment would be needed in the next phase of its implementation.


1.1.3               The CE91/95 study identified a tunnel alignment running from a tunnel portal close to the site of the Haw Par Mansion in Tai Hang and following a sinuous route beneath urban areas in Jardines Lookout and Mid Levels. A discharge portal at the west end of Hong Kong Island at Pokfulam, north of the Cyberport site was identified. Intakes were identified on drainage paths intersecting the alignment to intercept flows and direct them to the tunnel. It was envisaged that the tunnel would be formed using a tunnel boring machines (TBM). Due to the proximity to Country Parks it was determined that the project would be classified as a Designated Project (DP) falling under the requirements of the EIA Ordinance.  The CE 25/2002 (DS) investigation commenced in October 2002 and includes this EIA Study.


1.2                   Agreement No. CE25/2002 (DS) Drainage Improvement in Northern Hong Kong Island - Investigation


1.2.1               In October 2002, DSD commissioned Black & Veatch Hong Kong Ltd. (B&V) to undertake the Drainage Improvement in Northern Hong Kong Island - Hong Kong West Drainage Tunnel and Lower Catchment Improvement - Investigation Study to review and develop the previous work. This requires a review of the extent, alignment, profile and sections of the lower catchment drainage improvement works and drainage tunnels, as well as the number and locations of intake shafts, emergency exits and the associated drainage structures. Site investigations, surveys, physical-modelling tests, impact assessments, studies and preliminary designs are also undertaken as part of the Assignment. The Project consists a drainage tunnel and associated structures such as drop shafts, intake shafts, portals and stilling basin.  This EIA is prepared for the Project and forms part of the Investigation Assignment.

[1]           The catchment is enclosed by the ridgelines running between Jardines Lookout in the east through Mount Butler, Mount Cameron, Mount Gough and the Peak.