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.