14.1
Environmental
Sensitive Areas Protected
14.1.1
A total of 300 domestic buildings, 26 schools, 1 hospital
and 1 Homes for the Ages, population is approximate 119,000, are within the
influence zone of the project boundary during the construction stage. The assessment predicates that 3 schools
and 8 domestic buildings and 1 Home for the Ages, population is approximate
3,300, would only be affected by cumulative construction noise after
implementation of mitigation measures such as the use of quiet plant,
application of noise barrier and the adoption of regular noise monitoring
during construction. Notwithstanding the above, the exceedances of the noise
level are marginal. Therefore a
substantial number of the population (population is approximate 115,700) will
be protected during construction stage.
14.1.2
Further
it is estimated that with 2 domestic buildings at Eastern Portal, 12 domestic
buildings at Western Portal and 1 building along the adit with vertical shaft
at W3 (population is approximate 5,400) would be subject to exceedance of the
ground borne noise during the period 2300 to 0700. However, it has demonstrated that after
restricting the TBM or blasting operation in non-restricted period for
tunnel/adit section (i.e.
14.1.3
With
appropriate mitigation measures and precautions in place, the adjacent
sensitive receivers, water bodies, habitats and historical buildings/structures
will be protected during both construction and operation of the project. Table 14.1 summarises the respective
impacts and the corresponding measures taken to mitigate the impacts
Table 14.1 Summary
of Mitigation Measures to be Implemented During the Construction and Operation
Stages of the Project
|
Types of Impact |
Affected
Location |
Mitigation
Measures |
|
Loss of woodland /shrubland |
Eastern Portal, Western Portal and all intakes |
- Minimise the land
intake by adoption of environmental friendly design and construction method - Reservation of existing
woodland, shrubland and stream as far as possible. - Good site
practice - On-site
compensatory planting |
|
Loss of Stream habitat |
Eastern Portal, Western Portal and all intakes |
- Provision of
temporary by-pass for water flow during construction. - Section of
temporary loss to be reinstated after construction. |
|
Eastern Portal |
- Provision of low
flow channel and step chute inside the stilling basin structure to maintain
existing aquatic habitats. |
|
|
Eastern Portal, Intakes PFLR1(P) , W12(P) and P5(P) , MB16, E5(B)(P) and TP789(P) |
- Survey of the
site and translocation of frogs including Hong Kong Cascade Frogs and Lesser
Spiny Frogs |
|
|
Air borne noise impact |
All construction sites |
- Use of quiet
plant |
|
Intakes W5(P) and W8 |
- Use of
cantilevered-type noise barriers when noise level exceeds the limit |
|
|
Eastern Portal, intakes E7(P), WO(P), E5(A)(P),
GL1(P), MB16, P5(P), W10 and W12 |
- Use of movable
barrier when noise level exceeds the limit |
|
|
Eastern Portal |
- Use of full noise
barrier enclosure at mud pit area - Use of partial
enclosure at loading and unloading bays |
|
|
BR7(P), E7(P), E5(A)(P), W5(P), W8 and W12 |
- Pre-drilling
followed by chemical splitting to replace use of excavator mounted breaker |
|
|
Eastern Portal, DG1(P), E7(P), RR1, W0(P), W5(P) and
W8 |
- No construction
activity is recommended during the examination period. |
|
|
Ground borne noise impact |
Eastern Portal, Western Portal |
- Limit the TBM
operation time |
|
Horizontal adit with vertical shafts W3 and W5 |
- Restriction of
rock breaking operation if the measured noise levels exceeds the limit. |
|
|
Construction dust impact |
All locations |
- Adoption of good
housekeeping and effective dust suppression measures. |
|
Western Portal |
- Delivery of
excavated spoil by barge to avoid land transport |
|
|
Water quality impact |
All locations |
- Adoption of good
housekeeping and site management practices to control site run-off, spillage
of chemical, on-site effluent generation. |
|
Western Portal |
- Erection of silt
curtain in the waters during construction of the temporary berth, placing of rock
armour panel at the seabed and outfall structure - All construction
for the basin shall be carried out inside the temporary cofferdam which is a
temporary watertight enclosure to prevent dispersion of sediment. - The Western
Portal is designed with provision of stilling basin and armour rock panels on
the seabed. Such provisions will
reduce the flow discharge velocity from outlet and hence the disturbance to
seabed. |
|
|
At all intakes |
- Bar screens are
provided to screen off large stone, tree branches and other debris - Sand trap at the
bottom of the intake drop shaft to retain coarser particles/ sand |
|
|
Main tunnel and adits |
- Regular cleansing
to remove debris, sand and leaves prior to onset of heavy rainstorm - Deployment of
marine vessel to collect floating debris/leaves on an as-needed basis |
|
|
Waste generation |
All locations |
- By implementation
of waste management plan through good site practices for the achievement of
waste minimization at source, waste
recycle and reuse. |
|
Cultural heritage impact |
Eastern Portal and Intake W3 |
- Condition of condition
survey to the historical buildings ( - Provision of a
buffer zone between the work site and the respective buildings. |
|
Landscape and Visual impacts |
All locations |
- Preservation of
the existing landscape and visual resources as much as possible by minimising
the land intake - To provide
compensatory planting and design the landscape design to blend in the
surrounding environment. - Erection of
decorative hoarding around the works site during construction - To arrange
landscaping works and reinstatement works immediately after completion of the
civil works. |
14.2
Environmental Friendly
Designs and Problems Avoided
14.2.1
The principle of design of
the proposed works is to avoid environmental impacts as far as practical. The minimisation will be the key design
principle only when avoidance is not possible. Bearing this in mind, the tunnel
alignment for this project is selected with the shortest tunnel length. The benefit of the design is to reduce
the volume of spoil/excavated material to be generated as far as possible. Since the tunnel is designed to have life span of 120 years and have minimum
operation and maintenance requirements, it will turn to be an environmental
advantage.
14.2.2
The location of the intake
structures, tunnel portals and outfall locations are mainly in disturbed areas
which have lower ecological value such that lesser habitats and vegetation will
be affected and hence the least environmental impacts will be generated.
14.2.3
Some environmental friendly
designs have been incorporated into the drainage system to mitigate potential
impact to the surrounding environmental.
These include provision of low flow channel, basin and
step chute within the diversion
structure at Eastern Portal to maintain existing aquatic habitats as far as
possible. The expansion section of
the stilling basin at Western Portal will attenuate the flow velocity significantly
and hence to prevent scouring and erosion of seabed. In addition, the protection of the
seabed at the immediate downstream of the outfall will be enhanced by placement
of rock armours over the seabed.
14.2.4
At the locations of intakes
points and tunnel portal, the areas will be landscaped such as to blend it into
the surrounding environments. Most
of the structures are either be constructed underground or screened by
planting, reducing the visual impact to the nearby sensitive receivers. For those intakes structures located
inside existing sitting out or garden areas, the area on the top of the
structure will be designed for the use of the public as far as possible such
that loss of amenity areas will be minimal.
14.3
Environmental
Benefit of the Project
14.3.1
The primary objective of
the proposed drainage tunnel is to improve the flood protection level for the
low lying areas on
14.3.2
The drainage tunnel will
convey the uphill runoff via its intake structures and adit system for disposal
into the sea off the western cost of