2.1.1
Improvement works at the three rivers
were recommended in the “Stormwater
Drainage Master Plan Study in Sai Kung, East Kowloon and Southern Lantau”
(DMP Study). The total length of Sai
Kung River is approximately 1.3km from upstream grassland flowing through Sai
Kung town centre before entering into the Inner Port Shelter (Sai Kung Hoi).
The concerned section is 150m long which is located at the mid section of the
Sai Kung River. The proposed Sha Ha Diversion Box Culvert will connect the Sai
Kung River at upstream and the box culvert constructed by Civil Engineering and
Development Department (CEDD) at downstream.
2.1.2
The Pak Kong River runs alongside the
Hiram’s Highway before entering a road crossing under the Hiram’s Highway to
Pak Sha Wan. The total length is approximately 1.32km and the concerned section
is 600m long located at the downstream end of the river as stated in the
Project Brief. During the public
consultation, the local residents in Pak Kong objected the drainage improvement
works in Pak Kong because of the need for resumption of village houses along
both sides of the river bank. The local residents requested during the public
consultation to minimise the extent of works as far as possible and they would
accept a higher flooding risk instead of resumption of houses. As agreed with
the local residents, this project will only re-construct two bottlenecks in Pak
Kong River and stabilise an existing channel slope adjacent to Hiram’s Highway.
2.1.3
The Ho Chung Channel runs alongside Ho
Chung Road before passing under the Hiram’s Highway to Pak Sha Wan in the
south. The total length is approximately 1.6km and the concerned section is
650m long located at the downstream area.
2.1.4
The major items of the drainage
improvement works are summarised in Table
2.1 below.
Table
2.1 Summary of Project Elements
|
Works Programme
|
Dec 2005 to April 2008
|
|
Major Elements in Sai Kung River and Sha Ha
Diversion Culvert
|
|
(a)
Open Trapezoidal Channel
|
Length = 150m
|
Depth = 3m – 3.5m
|
|
|
Bank width = 16m – 24m
|
Bed width = 5m
|
|
|
Gabion walls with rip-rap bases and natural substrates
|
|
(b)
Diversion Box Culverts
|
Length = 280m
|
3 cells 3m(W) x 3m(H)
|
|
(c)
Low Flow Pipes
|
Length = 12m
|
3 x 600mm diameter
|
|
|
|
|
|
Major Elements in Pak Kong River
|
|
(a)
Channel Widening
|
Length = 100m
|
Depth = 3m (approx.)
|
|
|
Bank width = 13m
– 18m
|
Bed width = 7m – 18m
|
|
|
To be reinstated by gabion blocks and concrete
retaining wall
|
|
(b)
Reprovision of crossings
|
2 numbers (1 vehicular crossing and 1 pedestrian
crossing)
|
|
|
|
|
|
Major Elements in Ho Chung Channel
|
|
(a)
Open Trapezoidal Channel
|
Length = 300m
|
Depth = 3.8m – 5m
|
|
|
Bank width = 17m
– 42m
|
Bed Width = 17m – 34m
|
|
|
Gabion walls with rip-rap bases and natural
substrates
|
|
(b)
Rectangular Channel
|
Length = 350m
|
Depth = 5m
|
Width = 17m – 25m
|
|
(c)
Reprovision of crossings
|
4 numbers (1 vehicular crossing and 3 pedestrian crossings)
|
|
(d)
Floodwall
|
Length = 300m
|
Height = 1m
|
|
|
|
|
|
|
|
2.1.5
It is noted that natural lowland and
estuarine river habitats are relatively rare habitats in Hong Kong, and are
known to provide habitats for a diversity of aquatic organisms. The detailed design of the drainage
improvements should reflect the potential ecological value of the existing
rivers, and natural features of the rivers should be retained wherever
possible. The following
ecological-friendly design has been incorporated as basic principles:
(a)
Riverbeds should not be lined with
concrete: the natural stream bed and substrate should be retained.
(b)
Riverbanks should not be lined with
concrete: soft engineering materials should be utilised as far as
possible.
(c)
Natural features of the rivers (such
as pool/riffle sequences) should be retained and incorporated wherever
possible.
(d)
Compensatory planting should be
provided to mitigate the loss of natural riparian vegetation.
2.1.6
Environmental benefits and
dis-benefits, alternative drainage options, considerations and constraints for
the proposed drainage improvement works at each river were evaluated. Public
consultation was also undertaken with local residents, village representatives,
the Rural Committee Members, the District Council and green groups. Comments
from relevant parties have been addressed and incorporated into the design of
the three layouts for the drainage improvement works.
2.2.1
With the existing drainage system at
its current capacity level, there is a risk of flooding during heavy rainstorms
in Sai Kung. The potential consequences of such flooding include:
(i)
Flooding
will persist in Sai Kung Town Centre, downstream area of Ho Chung and Pak Kong
River.
(ii)
Development
in Sai Kung, Pak Kong and Ho Chung will be hindered. The existing drainage
system will not provide the flood protection standard required for future
development. Further development will
increase the frequency, severity and extent of flooding.
(iii)
Damage
to properties, blockage of roads and accesses, nuisance to the public and risk
to lives will remain.
2.2.2
If the Project does not proceed, these
risks to the community in Sai Kung and Ho Chung will continue and some future
development may need to be compromised. There are no simple, small-scale works
that can be implemented to reduce these risks. The only effective solution to
provide adequate flood relief is to implement the drainage improvement works
identified in this Project. For Pak Kong, due to the reduction in scope of the
works, the flooding risk will remain.
2.3.1
The construction programme of the
Project will commence in December 2005 and is expected to complete by April
2008.
2.4.1
Concurrent projects with likely
interaction with this Project are identified. The potential cumulative impacts
have been addressed in the relevant sections of the EIA Report. The
construction programmes of the concurrent projects are based on the available
information at the time of the submission of this Report.