2.7.1
Key Project Requirements
CLP proposes to
establish 3 x 132 kV supply circuit from the existing Pui O Substation on south
Lantau Island, via Chi Ma Wan Peninsula via Adamasta Channel towards Cheung
Chau North and Cheung Chau South Substations as shown in Figure 2.1. The preferred option of circuit
alignment includes the following five sections:
(i)
Section 1: Pui
O Substation to Pui O Beach using underground cable (3 x 132kV circuits of
approximate length 2350m);
(i)
Section 2: Pui
O Beach to Tai Long Wan east using cable tunnel (3 x 132kV circuits of
approximate length 3000m), including a reclamation area of 180 m2 by the side of
Pui O Wan for the works area of the proposed tunnel portal;
(i)
Section 3: Tai
Long Wan to Cheung Chau Sai Tai Road using submarine cable (3 x 132kV circuits,
each cable of approximate length 2300m);
(i)
Section 4:
Cheung Chau Sai Tai Road to Cheung Chau South Station using underground cable
(2 x 132kV circuits of approximate length 100m); and
(i)
Section 5:
Cheung Chau Sai Tai Road to Cheung Chau North Station using underground cable
(1 x 132kV circuit of approximate length 1250m).
2.1 Site LocationSite Location and Route Selection
Prior to conducting this EIA Study, a detailed
Route Options Assessment was carried out by MCL. Four
options for the cable routes were investigated and the evaluations, merits and
demerits of each are given in the Final Report for “132kV Supply to Cheung Chau - Route Options
Assessment”, April 2000. The four options essentially were:
Option I: Overhead
transmission lines in Pui O and Chi Ma Wan Peninsula; submarine cables across
Adamasta Channel; underground cables in Cheung Chau.
Option IIa: Overhead transmission lines in Pui O;
submarine cables from Pui O to Cheung Chau; underground cables and overhead
transmission lines in Cheung Chau.
Option IIb: Underground cables in Pui O; submarine
cables from Pui O Beach to Cheung Chau; underground cables in Cheung Chau.
Option III: Underground
cables in Pui O; cable tunnel in Chi Ma Wan Peninsula; submarine cables across
Adamasta Channel; underground cables in Cheung Chau.
In the
aforementioned Route Options Assessment, a number of factors including
environmental and ecological impacts, landscape and visual character, statutory
requirements, land requirements and ease of maintenance were considered in the
evaluation process to allow a decision to be made on the optimum alignment
option. In addition to which the alignment options were circulated to various
Government departments including Environmental Protection Department,
Agricultural, Fisheries and Conservation Department, Planning Department, Lands
Department, Electrical & Mechanical Services Department, Civil Engineering
Department for comment.
A set of
evaluation criteria covering environmental issues, statutory requirements,
traffic impacts, programme, cost, etc. were established taking into account the
comments received from various Government departments. The evaluation process
identified Option III, which included a cable tunnel across the Chi Ma Wan
peninsula, as the preferred option.
Detailed
evaluation of
alignment options as given in the previously approved Route Options Assessment
is given in Annex 1.
Justifications
for selecting the cable tunnel option as given in the previously approved Route
Options Assessment Report are summarised below:
It was identified there would be
no visual impacts resulting from the majority of the preferred alignment which
is either underground, under water or inside a cable tunnel. The only visual impact would be from the
tunnel portals on the two sides of Chi Ma Wan Peninsula. For the construction of the northern portal
located on the south side of Pui O Beach, a temporary works area will be
required for the construction of the portal. The southern portal will be facing
Adamasta Channel on the rocky coast of Chi Ma Wan Peninsula. The visual impact
of the portal to the public is insignificant.
Landscape and Ecology
Similar to visual impacts, the
only areas along the proposed alignment which cause landscape and ecological
impacts are at the two tunnel portals.
As the areas involved are relatively small, the landscape and ecological
impacts were considered to be minimal.
Construction Impacts
The potential construction
impacts in environmental terms are air and noise both of which will only be
short term and non-persistent. During
the operational phase, effects of the electricity circuits on adjacent areas
along the alignment will be minimal.
Marine Traffic
The construction of the
submarine cables across Adamasta Channel will create the least hazard to the
marine traffic using the Channel among all other alternatives. Moreover, the duration of the cable laying
work is not expected to be long. With
proper scheduling of the work the associated risk could be kept well within an
acceptable limit.
Fisheries
The proposed alignment will have
the minimum disturbance on fisheries among all other alternatives and the
duration of the works is expected to be short.
Statutory Requirements and Procedures
The construction of the submarine
cables across Adamasta Channel and the small scale temporary works area at the
northern portal will require gazetting of the work under Foreshore and Seabed
(Reclamation) Ordinance. The coverage of this temporary works area is the
smallest amongst the options considered.
Land Requirements
The cable route is either aligned
in public roads or government lands and thus no resumption or clearance of land
is required.
Summary
The selected option has
demonstrated that it is the optimum for upgrading the existing supply circuits
from Pui O to Cheung Chau. In this EIA Study, the environmental impacts have
been assessed to show the project can be constructed with no residual impacts.
2.2 Project Description
CLP
proposes to establish 3 x 132 kV supply circuit from the existing Pui O
Substation on south Lantau Island, via Chi Ma Wan Peninsula via Adamasta
Channel towards Cheung Chau North and Cheung Chau South Substations. The
proposed circuit alignment includes the following five sections as shown in Figure 2.2:
(i)
Section 1: Pui O Substation to Pui O Beach using
underground cable (3 x 132kV circuits of approximate length 2350m);
(ii)
Section 2: Pui O Beach to Tai Long Wan east using
cable tunnel (3 x 132kV circuits of approximate length 3000m), including a small temporary works platform of 550180 m2 by the side of Pui
O Wan to be used as the works area for the proposed tunnel portal;
(iii)
Section 3: Tai Long Wan to Cheung Chau Sai Tai Road
using submarine cable (3 x 132kV circuits, each cable of approximate length
2300m), including a
temporary landing area of about 200 m2 by the side of Tai Long Wan
for transporting the tunnel boring machine off-site at once the excavation
works are completed;
(iv)
Section 4: Cheung Chau Sai Tai Road to Cheung Chau
South Station using underground cable (2 x 132kV circuits of approximate length
100m); and
(v)
Section 5: Cheung Chau Sai Tai Road to Cheung Chau North
Station using underground cable (1 x 132kV circuit of approximate length
1250m).
The proposed alignment will start
from Pui O Substation with underground cables along South Lantau Road and Chi
Ma Wan Road to the proposed tunnel portal on the south side of Pui O Beach. The
alignment will continue in a cable tunnel leading to the other end at Tai Long
Wan East. The cables will be spread out by means of a number of small sections of underground cables in the Tai
Long Wan portal area.
For the worst case scenario 9a total of nine number of submarine cables will could be laid to Cheung Chau south
across the navigation fairway of the Adamasta Channel. It is more likely that the cables will be
laid using 3 triple-core cables. The minimum distance between the cables is 50m
in the worst in the
worst case where nine9 separate cables are laid and will be 150m when three3 triple-core cables are laid. The selection factors forthat
governs the selection of using 3
triple-core orf 9 single cables depend oninclude weight of cables, capital cost of cables,
installation works and the allowance
for the
bending
radius. The distance
across the channel between the landfalls in the deepest section on Tai Long Wan
and Cheung Chau is about 2300m and the water depth is around 10m. Two 132kV
circuits will be connected to Cheung Chau South Substation via underground
cables laid along Sai Wan Promenade.
The remaining single 132 kV
circuit will be laid underground along Chueng Chau Sai Tai Road, Tai Hing Tai
Road, Praya Street, Pak She Praya Street and connected to Cheung Chau North
Substation.
2.3 Transmission Methods for the Proposedand
Alternative Route Considerations
DifferentAs indicated in the
foregoing section, as part of the Route Options Assessment, different
transmission methods and alternative route optionshave been established giving due considerations to
land use, technical feasibility, safety, health and environmental aspects. The
preliminary route proposal as stated below had been circulated to Environmental
Protection Department, Agricultural, Fisheries and Conservation
Department,Planning Department, Lands
Department, Territory Development Departments and other relevant government
departments and concerned parties including District Office/Islands and Green
Lantau Association for comments.
The following are thewere evaluated and tThe following
subsection provides general
descriptions of the implementation
works required for constructing the proposed route. options and
transmission methods being considered.
2.3.1 Overhead
Transmission Lines
‘Overhead
transmission lines’ is one of the most common transmission methodsare commonly used for
land cables. For the proposed 3 x 132kV circuits, overhead transmission lines can be used inare proposed for the
section of the route on the Chi Ma Wan Peninsula on thefor those
sections from Pui O Substation to Tai Long Wan East and Ha Keng.
.
The overhead lines will be supported on 18m high
H-poles at maximum intervals of 180m. The poles will be
provided at closer distancewith a maximum interval of 180m between two poles.
The poles may be closer to suit the topography
and at locations where the alignment changes direction. The required horizontal
separation between two 132 kV circuits is 30m. Conductors will be installed at
11.7m above ground on the H-H-poles. The transmission
lines between poles, including the sag at 75°C, shallwill maintain
a minimum of 6.7m above ground and 3.7m above any existing vegetation.
The foundations for the H-poles are generally 1.2m
x 1.2m (plan) by 3m deep concrete footings. Access roads leading to the support
locations for the construction of the foundations and erection of the poles can
be eliminated if helicopters are employed for carrying out the works. The extent of vegetation
and tree clearance required is therefore Trees to be cleared will
therefore be limited to those atlimited to any trees at the site of
support locations. Notwithstanding, pole locations will be selected to
avoid mature trees wherever possible.Wherever possible, the design tenet will be to
select pole locations which avoid mature trees.
2.3.12 Underground Cables
Electricity cables laid underground by means of open
excavation are also widely
used in Hong Kong. Trenches from 800 towill be either 800mm or 1200mm wide and
approximately 1000 mm deep arewill be required for layingto lay the proposed 132kV
cables.
Typically, the first two sets of cables to be laid
underground will require a minimum horizontal spacing of 600mm, whilst the
required separation offor the third set of cables to the first two
sets is approximately 2 to 3m.
Other trenchless techniques such as directional drilling
for laying underground cables are also practicable. These methods can apply to areas where
existing underground utilities are thoroughly investigated and identified as
not conflicting with the proposed cable alignments.commonly adopted. With
these methods, the disturbance to residents and existing traffic to residents and existing traffic
caused by the associated construction work will be reduced to the a minimum.
2.3.23 Cable Tunnel
Using tunnel to accommodateBy accommodating the
transmission lines in a
tunnel through the Chi Ma Wan Peninsulawill minimise the
encroachmentof the cable routes on Lantau South
Country Park.
However, its construction costPark will be minimised. Construction costs when compared to other options, such as overhead
transmission lines and underground cables is more expensive.are greater, although
environmental benefits and visual impacts are reduced.
The
construction methods forTwo methods for constructing the tunnel in
the anticipated hard rock conditions can could be considered as both are practical. These are:-
·
Drill and Blast Method; and
·
Tunnel Boring Machine (TBM) Construction
Drill and blast is the traditional, though
relatively slow, method of constructing tunnels in rock. The vibration and
noise disturbance would result in severe limitations on the extent and power
permitted for the blasting. This could reduce progress rates toas slow as
30m per week.
TheBy Ccomparingson on the performance
of TBMs to
drill and blast, the former is usually considered to be better although this is governed
by the hardness and mass of the rock, the power of the machine and the layout
of the cutting tools. A review of similar tunnels work wide isconstruction requirements has
shown that a rate of around 90m per week can be achieved once the crews have become
familiar with the operation of the machine and to associated ancillary equipment.
The
proposedsize
of the tunnel is approximately 3m in diameter as shown in Figure 2.3.It will be divided
longitudinally into two compartments by a partition wall. Each compartment will be linked together by
emergency access provided in every 50m. Apart fromIn addition to the major
electrical and mechanical installation, the tunnel will be equipped with a ventilation system to
provide cooling for the cables
and to the atmosphere within
the tunnel. Fire detection systems will also be provided to
detect the presence of fire in the tunnel so that for safety reasons.
evacuation of the tunnel can be initiated.
It is recommended that cables within the tunnel should be maintained with an appropriate separation to avoid the inter-circuit thermal effect. This would be:
·
Typical cable to cable horizontal axial spacing:
300mm (cables in air or in stabilized sand);
·
Typical circuit to circuit horizontal axial spacing:
900mm (cables in air or in stabilized sand); and
·
Typical circuit to circuit vertical spacing:
300mm.
2.3.34 Submarine Cables
For submarine cables, the key essential
issues will beissues
to be addressed are the method of laying the cables, connections to landfall,
the depth of burial and nature of fill. Submarine cables areIt is understood that for
protection to the cables (from hazards such as anchor drag) submarine cables
will normally be laid
at depths of at least 3 metres below seabed. For 132kV cables, each single cable will need(or triple-core cable) needs
a separation distance of
approximately 50m. The depth of burial shouldmust bein a sufficient cushion thickness
to give adequate protection to the cables against damage. The thicknessdamage and should be
designed with
consideration ofgiving
due regard to vulnerability to damage, chance and consequences of damage.
The permanent protection for the submarine cables
will depend on assessment of the chances andthe potential consequences
of the load and the cost of protection. Man–made hazards such as anchor drop,
anchor drag, and sunken vessels, grounding vessels and trawl boards; natural
hazards such as seabed movements; waves, currents and vortex induced
oscillations shouldwill need to be considered in the
assessment. by
the contractor. The permanent protection proposed for this section
of the route is concrete slabs, 2m x 3m x 0.3mTo indicate the
location of the cables and to avoid damage during maintenance dredging a layer
of concrete slabs, 2m x 3m x 0.3m will be laid over the alignment. These will be placed either by crane
from a barge (using GPS) or by diver and will eventually be covered by natural
sedimentation patterns.
There are various methods available for laying
submarine cables. One advanced technique is by using a
‘burying machine’ which will excavate a trench and at the same time leave a cable
in it.lay the
cable. The cables are fed from a barge towed along the cable alignment by
steel wires. There will be no joints in
the cables laid by this technique.
technique and no need for digging
trenches or backfilling.
Prior to laying the submarine cables, detailed
investigations arewill be required by the cContractor to determine
seabed levels, rock head levels, mud thickness, existing utility alignments in
seabed, object protrusions above the seabed such as sunken vessels and or metal
objects.Hydrographic
surveys are required to collect data of waves, tidal patterns, currents, winds
etc.
2.4
Preferred Route Option and Construction
Method
2.4.1 Preferred Route Option
The Study of the Route Options Assessment has
assessed four different alignment options with a mixture of transmission
methods including overhead transmission lines, underground cables, submarine
cables and cable tunnel for the installation of 3 x 132kV electricity circuits
from Pui O Substation at Lantau south to Cheung Chau (refer to Figure 2.1).
These alternative alignments have been circulated
to various Government departments for comments. A set of evaluation criteria covering environmental issues,
statutory requirements, traffic impacts, programme, costs etc. are established
taking into account the comments received.
The evaluation process has identified the adoption of cable tunnel to
cross Chi Ma Wan as the preferred option.
2.4.1
Construction Method
(a)
Underground cables willare expected to be laid
using open trench excavation method. The length of each trench is assumed not
exceed 50m and no other trenches will be dug simultaneously within a 150m
distance along the same road;
(b)
CableThe cable tunnel willbe
preferably be constructed
using a TBM as this is
faster, has less environmental impact in terms of vibration and noise. It does not require large volume of water to
cool the working face, according to the tunnel designer as the preferred form
of TBM uses recirculation of water and chillers to cool the cutting face. This minimises the by TBM method.volume of wastewater generated
which requires treatment prior to disposal. The choice of TBMmethod or
the conventional drill & blast technique wouldwill
depend on the final decision of the project cContractor.TBM is the favoured
option (although the Contractor may choose an alternative) for excavating the
tunnel.
An initial tunnel drive (approx. 100m long) would be excavated from the portal
using blasting or machine breaking for the erection of the TBM. Restrictions on
the blasting, if blasting was adopted, would be similar to the blasting for the
portal formation. NIn addition to which it should be noted that the
form of construction does not require o storage of
explosives overnight but rather daily delivery is expected for this
Project, but rather daily delivery. The control on the use
of explosives is under the Dangerous Goods Ordinance (Cap. 295) and n No further assessment has been carried out for this
aspect of construction.
(c)
Submarine cables towill be laid byare expected to be laid using the
direct burying method and only one submarine cable will bewith only one single cable (or
triple-core cable) being laid during each operation. Thenumber of
submarine power cables for this project shall be either 9 or 3 but it cannot be
confirmed at this stage. It will depend on the recommendation of the submarine
cable supplier. However, the worst case scenario of 9 numbers of nine separate submarine cables has
been investigated in this EIA Report. The submarine cables will be covered by concrete
slabs of approximate dimensions Dredging may2m(W) x 3m(L) x 0.3m(D) to indicate the
location of the cable and to provide protection during dredgingas an
indication of the location of the cablesas an indication protection
layer. They will
be placed close to the surface of the seabed. The concrete slabs will gradually
be affected by natural sedimentation patterns in the area and covered, thereby
re-establishing the base stratum. Manual excavation by divers will be
required at both landfalls whenwhere the water istoo shallow.
At the Cheung Chau Typhoon Shelter the cables will
need to be passed through the breakwater which will require a section of 4.9m
wide and 0.75m high to be broken out, a concrete sleeve put in place and the
breakwater reinstated. The
level of the concrete sleeve is expected to be at the same level of the
submarine cables (ie 3m below seabed).
The proposed
partial
demolition of the northern end of the South Breakwater of Cheung Chau Typhoon
Shelter has been circulated to CED during the route options assessments.preliminary design of
the concrete sleeve at the breakwater has been discussed with CED and Specific procedures for the partial demolition of
the Pthe roceduredetails of the partial demolition of the breakwater will need to be be agreed by the contractor with with CED (although agreement in principle has been given) during the detailed design stage prior to the works commenceing on-site. The
cables can will then be passed through the
breakwater from the submarine section to typhoon shelter section, by hand using
qualified
qualified divers for such work.
2.5
Schedule Programme
The
construction programme for the proposed project has been outlined in Table 2-1 below and depicted in Figure 2.4. The level of the
concrete sleeve is expected to be at the same level of the submarine cables (ie
3m below seabed). The preliminary
design of the concrete sleeve at the breakwater has been discussed with CED and
the details of the design will be agreed with CED during the detailed design
stage.
|
Task |
No. of
Weeks |
Period |
|
Tunnel Section |
120 |
Jul 02 –
Oct 04 |
|
Mobilisation
and Site Clearance |
4 |
Jul 02 – Aug 02 |
|
Site
Formation at Pui O and Tai Long Wan |
20 |
Aug 02 – Dec 02 |
|
Tunnelling |
37 |
Dec 02 – Sep 03 |
|
Lining,
Ancillary Building etc. |
41 |
Sep 03 – Jun 04 |
|
Fitting
Out and Statutory Submission |
18 |
Jun 04 – Oct 04 |
Submarine Section
|
48 |
May 03 –
Apr 04 |
|
Seabed
Survey |
10 |
May 03 – Aug 03 |
|
Mobilisation |
13 |
May 03 – Aug 03 |
|
Removal
of Breakwater |
10 |
Aug 03 – Oct 03 |
|
Cable
Laying |
13 |
Nov 03 – Jan 04 |
|
Testing
and Commissioning |
8 |
Feb 04 – Mar 04 |
|
Reinstate
Breakwater |
8 |
Mar 04 – Apr 04 |
Underground
Section
|
133 |
Feb 02 –
Aug 04 |
|
South
Lantau Road |
26 |
Jul 02 – Jan 03 |
|
Chi
Ma Wan Road |
133 |
Feb 02 – Aug 04 |
|
Cheung
Chau Island |
26 |
Jan 03 – Jul 03 |
Testing &
Commissioning for the Whole Route
|
8 |
Aug 04 –
Oct 04 |
|
Testing
and Commissioning |
8 |
Aug 04 – Oct 04 |
|
Works
Completed |
0 |
Oct 04 – Oct 04 |
Installation
of the proposed 132kV supply circuit from Pui O to Cheung Chau is planned to
commence in mid 2002 for completion inby the end of 2004.
2.6 Cumulative Impacts
Based on the available information, it is understood
that the following projects could potentially interface with this proposed 3 x
132kV supply circuits installation depending on the timing and phasing of the
projects:Assignment. These include:
·Highways Department’s Contract Agreement No. CE
47/96 – RPIS Minor Rural Improvement Works Package 5 IS-032 Improvement of Chi
Ma Wan Road, Lantau Island (Phase I);
·
Highways Department’s Contract Agreement No. CE
47/96 – RPIS Minor Rural Improvement Works Package 5 IS-032 Improvement of Chi
Ma Wan Road, Lantau Island (Phase I);
and
·
Reclamation of Sai Wan Typhoon Shelter and
Associated Engineering Works at Cheung Chau by Territory Development
Department; and
Reclamation of Sai Wan Typhoon Shelter and
Associated Engineering Works at Cheung Chau by Territory Development Department
Department; and
·
220DS
– Outlying Islands Sewerage Stage 1 Phase 1B - Outfall Replacement and Sewage
Sludge Dewatering Facilities Upgrading at Cheung Chau Sewage Treatment Plant;
As this installation of the proposed underground cables will be executed under the project “RPIS Minor Rural Improvement Works Package 5 IS-032 Improvement of Chi Ma Wan Road, Lantau Island (Phase I)”, the construction activities of the Chi Ma Wan Road widening will not be implemented simultaneously at the same location as that of laying the power cables. In addition, the tunnel portal at Pui O is located over 500m from the section of Chi Ma Wan Road to be widened. As a result, no cumulative impacts are anticipated.
Territory
Development Department (TDD)
has submitted a project profile for a Study Brief fromto EPD for the project
“Reclamation of Sai Wan Typhoon Shelter and Associated Engineering Works at
Cheung Chau”.
The tentative construction programme for this project will commence in early
2003 and be completed in 2005. However, the EIA Study is atChau (CE 66/2000)”. The
construction works are expected to commence in mid 2004 for completion in 2006.
This means that there will be no the preliminary stage and it is thus more
appropriate that the EIA study for the reclamation works at Sai Wan takes on
board the findings of this EIA Report with respect to cumulative impacts.interface with the cable laying
of this Project which is scheduled to be constructed between November 2003 and
January 2004. Therefore, no cumulative impact with the project CE 66/2000 is
expected.
For the project of 220DS, it has
been confirmed that the completion date for the construction works will be in
early May 2002. Therefore, no cumulative impacts are expected.
As there is no
fixed schedule fFor the maintenance dredging for Cheung Chau
typhoon shelter, it is recommended confirmed that the Phase 1
maintenance works is planned to commence in December 2001 for completion in
April 2002 and the Phase 2 maintenance works is planned to commence in late
2002 for completion in early 2003 (say December 2002 to April
2003).consideration
be given to programming any such works to avoid overlap with the cable laying
works. After
these two maintenance works, no further works are planned in the next few
years. Therefore there is no interface
with this Project and no cumulative impacts are expected.
No other concurrent projects in the vicinity of the project area have been identified during the construction programme for this Project and as such no cumulative impacts are anticipated.