Contents
1.1 Background
1.2 Purpose
of this Report
1.3 Organisation
of this Report
2.1 Need
for the Temporary Staging
2.2 Preliminary
Layout of Temporary Staging and Pile Configuration
2.3 Method
and Sequence of Construction / Removal of the Temporary Staging
3 Assessment of Potential Environmental Impacts
3.1 General
3.2 Air
Quality
3.3 Noise
3.4 Water
Quality
3.5 Marine
Ecology
3.6 Fisheries
3.7 Landscape and Visual
4 Summyar
of Environmental Assessment of Current Temporary Staging Scheme
5 Comparison
of TEmporary Staging Schemes
1
Introduction
1.1
Background
The
"Tuen Mun - Chek Lap Kok Link" Project (hereinafter referred to as
"the Project") comprises a dual 2-lane highway connecting the
proposed Tuen Mun Western Bypass at the southern coast of Tuen Mun Area 40 and
the Hong Kong International Airport (HKIA) and Tung Chung. The Project comprises the following key
components:
(i)
Construction of a dual 2-lane road tunnel (in two
tubes) of approximately 5.0km long between Tuen Mun and the proposed Hong Kong
Boundary Crossing Facility (HKBCF) located at northeast of the HKIA;
(ii)
Construction of approximately 4.2 km of seawalls and
reclamation of approximately 35.6 ha of the Government foreshore and seabed at
Tuen Mun Area 40 and Lantau for the tunnel portals and the associated roads;
(iii)
Construction of an approximately 1.6km long dual
2-lane viaduct between HKBCF and North Lantau Highway (NLH) and the associated
roads at Tai Ho;
(iv)
Construction of a toll plaza at Tuen Mun Area 46 and
the associated roads at Tuen Mun;
(v)
Construction of administration building, ventilation
buildings and other ancillary buildings to facilitate ventilation and tunnel
control operation serving the proposed road tunnel and toll plaza above; and
(vi)
Ancillary works including site formation, slope
drainage, utilities, footbridge, noise barriers, retaining walls, berths and
temporary pontoon.
An
Environmental Impact Assessment (EIA) study for the Project was conducted in
accordance with the EIA Study Brief No. ESB-175/2007 and was based on the
available information obtained during preliminary design stage. The EIA study
concluded that the Project would be environmentally acceptable with the
implementation of recommended mitigation measures.
The
EIA Report (Register No.: AEIAR-146/2009) was approved on 23 October 2009 under
the Environmental Impact Assessment Ordinance (EIAO). Following the approval of
the EIA Report, an Environmental Permit (EP) was granted on 4 November 2009 (EP
No: EP-354/2009) for the construction and operation of the Project. A variation of environmental permit was
approved with an Environmental Permit (EP No: EP-354/2009/A) issued by the Director
of Environmental Protection (DEP) on 8 December 2010. Another
application for variation of environmental permit (VEP) (EP-354/2009/B) was granted on 28 January 2014.
The
need for temporary staging for the construction of the Southern Connection
viaducts, which has not been taken into account during the investigation phase
EIA, arose during the Design and Construction Stage of the Project. An Environmental Assessment for the
Temporary Staging for Construction for the Southern Connection was prepared ([1])
and the Environmental
Protection Department (EPD) has confirmed no adverse comments on the reference
scheme in October 2012. The reference
scheme comprises a temporary access bridge parallel to the alignment of the
permanent bridge and viaducts structure.
During the
construction design, the scheme for the temporary staging was revised under
which 38 isolated staging platforms with one temporary landing platform will be
constructed. This Environmental Review (ER) serves
to assess the environmental consequence during the installation, operation and
removal of the current temporary staging scheme and to identify additional
mitigation measures necessary for the minimisation of the associated impacts. It
should be noted that the scheme of temporary staging is not classified as a
Designated Project under Schedule 2
of the EIAO. It is also not being considered as
material change to a Designated Project under Item 6 of the EIAO-TM.
1.2
Purpose
of this Report
This
ER aims to assess the potential environmental impacts caused by the current temporary
staging scheme and to recommend additional mitigation measures and EM&A
works for the temporary staging work, if necessary.
1.3
Organisation
of this Report
The remainder
of the report is organized as follows:
·
Section 2 discusses the need for the temporary staging
as well as the preliminary design and scale of the temporary staging.
·
Section
3 reviews the relevant environmental baseline, investigation as well as
assessment carried out for the approved EIA. The potential environmental impacts for
each of the relevant environmental aspects covered under the approved EIA are
identified and evaluated. Additional mitigation measures and environmental
monitoring and audit (EM&A) would be proposed, if necessary.
·
Section 4 provides a summary of the ER findings on the
current temporary staging scheme.
·
Section 5 provides a comparison of environmental
impacts of the reference scheme and the currently proposed scheme.
2
The
Temporary Staging
2.1
Need
for the Temporary Staging
Temporary
staging is required to provide a stable working platform and transfer of
materials for the piling work in connection of the viaduct construction between
HKBCF and North Lantau. The proposed temporary staging scheme comprises
a series of isolated staging platforms.
Such design scheme can facilitate the transfer of material and hence
save time for the construction work.
In addition, the use of isolated working platforms can minimise
obstructions to the navigation channel/marine traffic around the works area and
minimise propeller wash in shallow waters offshore.
The
temporary staging works also require construction of one temporary landing
platform along the seawall as temporary storage and for transfer of material
from land to the isolated staging platforms. The temporary landing platform will also
be used as the yard for the fabrication of reinforcement cages for bored piling
works.
2.2
Preliminary
Layout of Temporary Staging and Pile Configuration
The
preliminary layout plan of the proposed temporary staging platforms is shown in
Figure 2.1, which corresponds to the permanent bridge
pile layout. The temporary staging
consists of 38 isolated staging platforms (spaced from approximately 35m to
approximately 195m apart, centre to centre) with one landing platform near the
North Lantau Highway. It should be
noted that the staging platforms will be constructed in stages as shown in Figures 2.2-6 so that the 38 staging platforms will not
be present at the site together at any one time. The typical pile configurations and
details of the isolated staging platforms are provided in Figure 2.7. The isolated platforms would be
supported by pipe piles of 1,168 to 1,200mm in diameter with a truss of 3,000mm
tall between the piles on both sides of the isolated platforms. The width of the pile deck for the isolated
platforms ranges from ~21m to ~80 m wide and supported by pairs of parallel
arrays of pipe piles on both sides and/or in the middle. The pipe piles would be the only
structures which are submerged underwater in any occasion while the bottom of
the truss may also be submerged underwater during high tide.
The
landing point of the isolated platforms comprises one temporary landing platform
to be formed along the seawall near the NLH as shown in Figure 2.8. Design drawings of the landing platform
are shown in Figures 2.9-10 . This platform will be removed and the
seawall will be reinstated upon completion of the TM-CLKL construction works.
2.3
Method
and Sequence of Construction / Removal of the Temporary Staging
In
general, works will start from both sides of the Southern Connection, ie from
the HKBCF reclaimed area and the NLH.
Construction of the temporary staging has commenced in early November 2013
in stages ([2])
and will be maintained
for operation until the construction of the permanent bridge structure is
completed in around mid-2016 (ie around 31 months). The removal of the temporary staging
will take another 2 months.
2.3.1
Method of Construction
Method of
Construction (Isolated Staging Platform for Marine Bored Pile / Pier Columns
Construction) (At Piers of Viaducts A, B, C, D and E)
The
isolated staging platforms are planned to be constructed in five stages as shown
in Figures 2.2-6.
The 38 isolated platforms will not be present at the same time. The actual number of isolated platforms
will range from 10 to 24 during the five stages.
1. Flat-top barge mounted with 120 / 150 tons
crawler crane will be towed by tug boat to the proposed pipe pile locations.
2. Drive the pipe piles down into the seabed by
vibratory hammer lifted by crawler crane until the termination criteria are
reached according to working drawings.
3. Pre-fabricated structural components of
temporary working platform will be transported either by flat-top barge or
derrick lighter to pier locations.
4. Pairs of prefabricated steel trusses will be
installed on top of driven pipe piles.
5. Prefabricated deck panels will be
placed on top of steel trusses.
6. Upon completion of temporary staging platform
of individual piers, the flat-top barge and derrick lighter will move to
another pier location for temporary platform erection with repeated procedures
from 1 to 5.
Method of
Construction (Temporary Landing Platform at Viaduct D near NLH)
One
temporary landing platform will be constructed at Viaduct D near NLH which comprises
onshore rockfill platform retained by seawall blocks/in-situ concrete and offshore steel platform supported on driven
pipe piles into seabed.
1. Onshore rock amours on top of sloping
seawall which conflict with the proposed platform will be temporarily removed.
2. 4 layers of sea wall blocks will be placed
underneath water on the toe of the existing Grade 700 rockfill at onshore area
to acts as retaining structure for later on backfilling of rockfill on top of
sloping seawall.
3. Cast
in-situ concrete block on top of sea wall blocks for both retaining
structure and supports for steel platform towards the sea side.
4. Laying geotextile on top
of the existing rock surface.
5. Backfill the sloping
seawall with rockfill materials up to circa +5.1 mPD.
6. 300mm thick of reinforced concrete pavement
will be constructed on top of the backfilled rockfill materials.
7. A crawler crane mounted with vibratory
hammer will position near edge of aforesaid rockfill platform and a row of
25nos. 1000mm diameter pipe piles at 6m c/c will be driven down into seabed to
support the steel deck on top.
8. Structural steel members will be placed on
top of pipe piles and welded in position.
9. Type III sheetpile to be placed on top of supporting members with
welding connections.
Construction
Sequence for Removal of Temporary Staging Platforms
1. Remove all welding connections between sheetpile deck and supporting structural members
2. Lift the sheet pile deck unit piece by piece
3. Sheet pile deck units to be delivered off
site via staging platforms and seawall access track.
4. Remove welding joints between open frames
and pipe piles.
5. Cut the frame and lift it up by crawler
crane and place it on either flat-top barge or the temporary staging platforms.
6. Frame will be dismantled into manageable
pieces and delivered off site via marine routes or land access via access track
at Siu Ho Wan.
7. All pipe piles will be extracted by
vibratory hammer.
Construction
Sequence for Removal of Onshore Landing Platform
1. Demolish the 300mm thick reinforced concrete
pavement by backhoe with breaker and delivery of the inert debris off site for
reuse in other construction site via marine routes by derrick lighter or via
land access by dump truck.
2. Remove the rockfill material and delivery
off-site by derrick lighter with grab.
3. Remove the geotextile placed on the top of
the existing rock surface.
4. Lifting the cast-in and
seawall block and delivery off-site by derrick lighter.
5. Reinstate the seawall profile as per the
original.
3
Assessment
of Potential Environmental Impacts
3.1
General
This
section provides an assessment of the potential environmental impacts from the
construction, operation and removal of the temporary staging platforms, based on
the findings of the approved EIA as well as the latest update design for the
temporary staging. This section
covers most aspects under the approved EIA, except for the aspects described in
Table 3.1 which are deemed irrelevant
/ negligible for the temporary staging works.
Table 3.1 Environmental
Aspects Included/Excluded in this Assessment
|
Environmental Aspects |
Included/ Excluded |
Justifications |
|
Air Quality |
Included |
·
Potential impact from the temporary staging works,
including fugitive dust and gaseous emissions. |
|
Noise |
Included |
·
Potential construction noise impacts due to
installation, operation and removal of the temporary staging platforms |
|
Water
Quality |
Included |
·
Potential impact from the temporary staging works,
including sediment plume impacts from the installation, change in flow regime
and propeller wash during operation etc. |
|
Marine
Ecology |
Included |
·
Potential impact from the temporary staging works,
including direct loss of habitats and indirect impacts caused by changes in
water quality, underwater noise and marine traffic etc. |
|
Fisheries |
Included |
·
Potential impact due to temporary loss of seabed
habitat and fishing grounds as well as indirect impacts caused by changes in
water quality. |
|
Landscape
and Visual |
Included |
·
Potential impact from the temporary staging works
due to potential blockage of view. |
|
Terrestrial
Ecology |
Excluded |
·
Marine Works ·
At least 300m away from nearby woodland, shrubland
and grassland |
|
Cultural
Heritage |
Excluded |
·
Marine Works ·
No area of marine archaeological potential was
identified in the approved EIA ·
At least 330 m away from the nearest cultural
resources; the nearest cultural resources are a shrine (TH-1) and a grave
(G5) on the hillside of the NLH |
|
Waste Management |
Excluded |
·
Marine works ·
No excavation/dredging required ·
No marine mud disposal is required ·
Material for temporary staging platforms will be
reused in other construction site after removal |
|
Land
Contamination |
Excluded |
·
Marine works ·
No excavation required |
|
Landfill Gas
Hazard |
Excluded |
·
Marine works far away from any landfill sites |
It
is anticipated that the works for the temporary staging platforms will be
carried out concurrently with the construction of the Southern Connection as
well as the other section of the TM-CLKL project and the HKBCF reclamation. Cumulative environmental impacts, in
particular on water quality, marine ecology, fisheries and landscape and
visual, are expected.
3.2
Air
Quality
3.2.1
Review of Approved EIA
Fugitive
dust impact is one of the major concerns during the construction of the TM-CLKL
in the approved EIA. The approved
EIA states that no significant dust impact from the cumulative effect of the
TM-CLKL, HKBCF and HKLR is expected at the air sensitive receivers (ASRs)
around the Southern Connection viaducts during the construction of the
TM-CLKL. Standard mitigation
measures for construction sites specified in the Air Pollution Control
(Construction Dust) Regulation would be implemented. Construction phase EM&A is
recommended as well. The gaseous
emission from construction plant is considered minor and was not elaborated in
detail in the approved EIA.
3.2.2
Identification and Evaluation of Potential Impacts
It
is anticipated that the construction and operation of temporary staging platforms
would be concurrent with the nearby bridge and piles construction for the
Southern Connection. The
installation of the temporary staging platforms would not involve any open
excavation. Therefore, a significant
fugitive dust issue is not expected from the installation of the temporary
staging platforms. During the use
of the temporary staging platforms for construction of the Southern Connection
viaducts, potential fugitive dust impact is expected to be minimal since the
surface of the temporary staging platforms would be mostly consisted of
metal. Additional cumulative fugitive
dust impact is not anticipated. It
is thus anticipated that impacts related to the temporary staging works would
be no greater than those considered to be acceptable within the approved EIA
Report and as such no additional nor different mitigation measures would be
considered necessary than those presented within the approved EM&A Manual.
The
use of vessels and plant for the installation and removal of temporary staging platforms
as well as the construction of the Southern Connection viaducts may induce
minor gaseous emission near the works area. The increase in the numbers of vessels
and plant involved only contribute to a small portion of plant and equipment
needed for the construction of the Southern Connection and the HKBCF
reclamation. The proposed plant
inventory is given in the Table 3.2. It is worth to note that plant which
work at the navigation channel along bridge section E are generally over 800 m
away from the nearest ASR (ASR8 Pak Mong Village House) (see Figure 3.1), while the rest of the plant would be in
most of the time over 450m away from this ASR. In view of such separation distance from
the nearest ASR and the small increase in the proportion of the number of
vessels and plant required, the potential air quality impact due to the gaseous
emissions from vessels and plant would be minimal and would be no greater than
those considered to be acceptable within the approved EIA Report. As such, no additional, nor different,
mitigation measures would be considered necessary than those presented within
the approved EM&A Manual.
3.2.3
Recommendations of Additional Mitigation Measures and
Environmental Monitoring
No additional
mitigation measure and EM&A for air quality would be required.
3.3
Noise
3.3.1
Review of Approved EIA
Only
one noise sensitive receiver (NSR) at Northern Lantau is identified for
construction phase of the TM-CLKL. The NSR is a village house at Pak Mong
near Tai Ho Wan (NSR1 of the approved EIA Report) (see Figure 3.1).
The maximum predicted construction
noise levels at NSR1 for the whole construction sequence is predicted to be 74dB(A), which complies with the Daytime Construction Noise
Criteria of 75dB(A). The maximum
construction noise level is predicted during the construction of bridge piles
on land around the landing point of the Southern Connection viaducts at NLH. No mitigation measure is recommended for
the construction of the TM-CLKL. Nevertheless,
EM&A for noise is recommended at NSR1 to ensure that there would not be any
unacceptable noise impact.
3.3.2
Identification and Evaluation of Potential Impacts
The
installation, operation and removal of the temporary staging platforms would
generate noise. Table 3.2 provides the plant inventory
of the associated works which has been confirmed to be practicable. The closest NSR is NSR1 Pak Mong Village
House which is located more than 450m away from the temporary staging
works. Based on the plant inventory
shown in Table 3.2, the predicted
cumulative noise level due to the temporary staging works at NSR1 is 62.6 dB(A) (see Table 3.3).
Table 3.2 Tentative
Construction Plant Inventory for the Temporary Staging and Corresponding Sound
Power Level
|
Power Mechanical Equipment (PME) |
No. of items |
TM Ref/ Other Ref |
Unit Sound Power Level (SWL), dB(A) |
On-time % |
Total SWL |
|
Plant work for Isolated Platform construction along viaducts A, B, C,
D and E1 to E2 |
|||||
|
Derrick
Lighter |
2 |
CNP 061 |
104 |
100% |
107 |
|
Tugboat |
1 |
CNP 221 |
110 |
10% |
100 |
|
Flat-top
Mounted with Crane |
1 |
CNP 048 |
112 |
100% |
112 |
|
Vibratory
Hammer |
1 |
EPD/PME/18 |
115 |
100% |
115 |
|
Generator |
1 |
CNP 102 |
100 |
100% |
100 |
|
Welding
Machine |
2 |
(a) |
100 |
100% |
103 |
|
Flat-top
barge |
1 |
CNP 061 |
104 |
100% |
104 |
|
|
|
|
|
Total SWL |
118 |
|
Plant work from the Navigation Channel along Bridge Section E3 to E13 |
|||||
|
Derrick
Lighter |
2 |
CNP 061 |
104 |
100% |
107 |
|
Tugboat |
1 |
CNP 221 |
110 |
10% |
100 |
|
Flat-top
mounted with crane |
2 |
CNP 048 |
112 |
100% |
115 |
|
Vibratory
Hammer |
2 |
EPD/PME/18 |
115 |
100% |
118 |
|
Generator |
3 |
CNP 102 |
100 |
100% |
105 |
|
Welding
Machine |
6 |
(a) |
100 |
100% |
108 |
|
|
|
|
|
Total SWL |
120 |
|
Plant work for landing platforms along the NLH |
|||||
|
Derrick
Lighter |
3 |
CNP 061 |
104 |
100% |
109 |
|
Tugboat |
1 |
CNP 221 |
110 |
10% |
100 |
|
Vibratory
Hammer |
1 |
EPD/PME/18 |
115 |
50% |
112 |
|
Generator |
1 |
CNP 102 |
100 |
100% |
100 |
|
Air
Compressor |
1 |
CNP 003 |
104 |
50% |
101 |
|
Flat-top
barge |
1 |
CNP 061 |
104 |
50% |
101 |
|
|
|
|
|
Total SWL |
114 |
|
Note: (a)
Reference from East Rail Extension - Sheung Shui to Lok Ma Chau Spur Line EIA
(Application No. EIA-044/2000) which was approved for public inspection but
later rejected upon consideration of public comments. The same SWL reference was also quoted
in the Harbour Area Treatment Scheme (HATS) Stage 2A Environmental Impact
Assessment Study – Investigation (AEIAR-121/2008). |
|||||
Table 3.3 Prediction
of Noise Level at NSR1
|
Activities |
SWL, dB(A) |
Distance, m |
Noise Level at NSR1, dB(A) (a) |
|
Plant work
for Isolated Platform construction along viaducts A, B, C, D and E1 to E2 |
118 |
450 |
60 |
|
Plant work
from the Navigation Channel along Bridge Section E3 to E13 |
120 |
800 |
57 |
|
Plant work
for landing platforms along the NLH |
114 |
450 |
56 |
|
|
|
Total |
62.6 |
|
Note: (a)
Including +3 dB(A) façade correction |
|
|
|
The
EIA predicted that the construction noise level will reach 74 dB(A) at NSR1 during the peak construction period of the
Southern Connection. Adding the
predicted noise contributed by the temporary staging works, the overall
predicted noise level at NSR1 will still comply with the criterion of 75 dB(A). It is
worth to note that the above calculation has assumed that the construction of
the temporary staging would be carried out concurrently with the land-based
piling work closest to the NSR, which is considered very conservative and would
unlikely happen. The installation
of the temporary staging is expected to proceed far beyond the shore, probably
over 500m from the NSR when the based piling work closest to the NSR
begins. Hence, it is expected that
the noise contribution from the temporary staging works is negligible and the
cumulative impact would be no greater than those considered to be acceptable
within the approved EIA Report.
During
operation of the temporary staging, construction activities of the permanent
structures of the Southern Connection would be the only source of noise from
the works which has been assessed by the construction noise assessment in the
approved EIA Report. As discussed
above, the construction
noise level will reach 74 dB(A) at NSR1 during the
peak construction period of the Southern Connection and will not exceed the
criterion of 75 dB(A).
Given
the above, no additional nor different mitigation measures would be considered
necessary than those presented within the approved EM&A Manual.
3.3.3
Recommendations of Additional Mitigation Measures and
EM&A
No additional
mitigation measures and EM&A for noise are required.
3.4
Water
Quality
3.4.1
Review of Approved EIA
According
to the approved EIA, the construction of the TM-CLKL as well as the HKBCF and
HKLR would involve extensive marine works, including various marine piling,
foundation works, dredging as well as reclamation filling. The worst-case scenarios for each of the
three consecutive years of construction of the three projects have been
assessed, based on the more conservative assumption of the construction
sequence (sequence A, with higher total sediment loss). Mitigated scenario for a less
conservative (and more realistic) construction sequence (sequence B, with lower
total sediment loss and the use of leading seawall to confined sediment), has
also been assessed. Based on the
water quality modelling results, with the application of the integrated
protection measures (as given in Sections
6.7.4.17 and 6.7.4.18 of the
approved EIA Report) and also the (1+1) silt curtain system, the major zone of
influence is mainly limited to areas within 500m from the reclamation sites,
where there is limited specific sensitive use of the waters within this
radius. Yet, marginal suspended
solids (SS) exceedances of WQO at the airport water intake (WSR 25), artificial
reef site at the north-east of the airport (WSR 41) as well as coral site near
the River Trade Terminal (WSR 47b) are still predicted. The use of silt curtain at cooling water
intake at WSR 25, the reprovision of artificial reef at WSR 41 as well as the
translocation of coral at WSR 47b would be implemented and no significant water
quality impact is expected.
The
water quality impact due to the operation of the three projects has been
assessed in the approved EIA based on the model prediction. It is predicted that the water quality
conditions in North-western waters would not be affected by the projects in an unacceptable
manner and the predicted changes, especially for physicochemical parameters
like DO, salinity and temperature, are small and within the ranges of natural
variations experienced in the study area.
Residual impacts during the operational phase would be low and
considered acceptable.
EM&A for water quality
for both construction and operation phase of the project has been recommended.
3.4.2
Identification and Evaluation of Potential Impacts
Sediment
Plume Impact from the Installation of the Temporary Staging Platforms
The
installation of temporary staging platforms will involve marine piling, which
may result in localized elevation in SS.
The marine piles would be installed in stages as shown in Figures 2.2-2.6, thus the SS elevation during the
piling works would be highly localized and minimal. Since the construction of permanent
marine bridge piles for the Southern Connection would be commenced when the
installation of temporary staging is still in progress, cumulative water
quality impact, particularly for suspended solids, from the construction of
permanent piles would be expected. As
given in Figure 1b of Appendix 05 of the approved EIA, the
contribution of suspended solid from the construction of permanent pile (1017)
has been taken into account in the construction phase sediment plume modelling
exercise (2012 scenario). The water
quality modelling results of the 2012 construction phase scenario indicated
that, the construction of permanent piles of Southern Connection as well as
other marine works under TM-CLKL, HKBCF and HKLR would not result in
significant elevation in SS level near the Southern Connection. The predicted SS elevation at the
nearest WSR (WSR22c Tai Ho Wan Outlet (outside) (Near coral site) is minimal
(maximum 0.2 mg/L) and complies well with the relevant assessment criteria (ie
3.6, 5.1, 8.1 and 5.5 mg/L for surface, mid-depth, bottom and depth-averaged
level, respectively, for the dry season period; 2.3, 3.3, 6.0 and 2.7 mg/L for
surface, mid-depth, bottom and depth-averaged level, respectively, for the wet
season period). The predicted SS
elevation at other receiver points in Tai Ho Wan (WSR22a and WSR22b) is even
lower. No other WSR was identified
within 1 km of the Southern Connection (and the temporary staging platforms). It is anticipated that the elevation in
SS level contributed from the installation of temporary staging platforms would
be even less significant than the level resulted from the construction works
for the permanent piles of the Southern Connection. In addition, coral translocation was
undertaken in October 2013 before commencement of the Southern Connection
construction which would help to reduce the indirect water quality
impacts to corals at Tai Ho Wan. Given the above, it is expected that
there would not be significant cumulative impact from the installation of the
temporary staging platforms at the nearby receivers at Tai Ho Wan. Unacceptable cumulative water quality
impacts at other WSRs further away are also not anticipated in view of the
localized nature of the impact from the installation of the temporary staging
platforms.
The
construction of temporary rockfill platform from the NLH side would require
removal of rock armour along sloping seawall. The removal and reinstatement of rock
armours would not create significant SS impact since the fine content in the
rock materials would be negligible. Loss of fines during the seawall removal
and reinstatement work is therefore not expected.
Change
in Flow Regime and the Associated Change in Water Quality due to the Temporary
Staging
The
marine piles of the temporary staging platforms may also affect the tidal flow
across the channel during its operation. The piles will be the only structure
submerged in water during most of the time, except during high tide when part
of the supporting truss will also submerge in water.
Evaluation
Approach and Justifications
Under the approved EIA, the change in flow regime
during the construction phase has not been elaborately assessed
for the following
reasons:
·
The
change in flow regime during construction phase is considered limited and is
less a significant issue when compared with the SS impact resulted from the
marine dredging and filling of the nearby concurrent projects; and
·
The worst case scenario
for the change in flow regime should be the
operation phase (where all reclamation and bridge piles are in place),
which has been considered in the operation
phase modelling scenario.
To
assess the potential change in flow regime as well as the associated change in
water quality from the temporary staging, reference has been made to the
operation phase water quality modelling results under the approved EIA
(referred as "operation phase modelling results" hereafter). It is considered appropriate,
conservative and acceptable in adopting the operation phase modelling results
of the approved EIA for assessing the worst-case potential change in flow
regime and water quality from the temporary staging platforms in view of the
followings:
·
The
worst-case scenario for change in flow regime and the associated impact on
water quality arise from TM-CLKL is assessed in the operation phase modelling
scenario;
·
All
reclamation and bridge piles (except for the temporary staging platforms) which
are expected to be in place during the lifespan of the temporary staging platforms
have been covered in the operation phase modelling scenario;
·
The
effect on flow regime due to the partially formed reclamation and bridge piles
nearby during the lifespan of the temporary staging platforms is expected to be
less than that of the completed reclamation and bridge piles considered in the
operation phase modelling scenario;
·
The
reclamation for the Logistic Parks and the Tung Chung Future Development near
Tai Ho Wan affect the tidal flow at Tai Ho Wan and the potential contribution
on the change in flow regime by the temporary staging platforms is expected to
be less than that of the two pieces of reclamation;
·
Adopting
the operation phase modelling scenario is deem conservative and acceptable for
assessing the worst-case potential change in flow regime and water quality from
the temporary staging platforms since (1) the intermediate case during the
construction of HKBCF and TM-CLKL would exert less significant effect on flow
regime, and (2) the obstruction in tidal flow due to the temporary staging platforms
is expected to be minimal when compared with the effect of the reclamation for
the Logistic Parks and the Tung Chung Future Development.
To support the
above analysis, Table 3.4 compare the
coastline configuration near the Project Area and Figure 3.2 shows the coastline
configuration assumed in the operation phase modelling scenario.
Table 3.4 Comparison of Coastline
Configurations
|
|
Operation Phase Modelling Scenario |
Start of the
Construction of the Temporary Staging Platforms |
Near End of
Construction of the Temporary Staging Platforms |
|
HKBCF
Reclamation |
Fully
formed |
Partly
formed southern seawall only |
Southern
seawall formed with some reclamation formed inside |
|
Less
/ smaller reclamation than operation phase modelling scenario |
Less
/ smaller reclamation than operation phase modelling scenario |
||
|
TM-CLKL
Southern Connection |
Fully
formed, with smaller spacing between piles |
No
marine pile formed yet |
Fully
formed piles, with larger spacing |
|
Less
obstruction in flow than operation phase modelling scenario |
Less
obstruction in flow than operation phase modelling scenario |
||
|
Other
Reclamation / Works nearby |
Fully
formed reclamation of Logistic Parks and Tung Chung Future Development
respectively |
Some
pipe piles installed for temporary staging near the navigation channel and
near the coastline of Tai Ho Wan No
reclamation for Logistic Parks and Tung Chung Future Development |
Fully
formed temporary staging No
reclamation for Logistic Parks and Tung Chung Future Development |
|
No
obstruction in flow by reclamation but some minimal obstruction by pipe piles |
No
obstruction in flow by reclamation but some obstruction by pipe piles (by 242
nos. of pipe piles) |
Figure 3.2 Coastline
Configurations Assumed in the Operation Phase Modelling Scenario
Regional
Effect on Tidal Flow
The
operation phase hydrodynamic modelling carried out under the approved EIA shows
that though the reclamation for the HKBCF and TM-CLKL Southern Connection as
well as the permanent piles at the Southern Connection viaducts would result in
change in tidal flow at the Western Waters (as indicated in Table 6.17 of the approved EIA Report),
the change in water quality at water sensitive receivers is not
significant. As shown in Appendix D7C of the approved EIA Report,
the water quality parameters are generally in compliance with the WQO (and with
sufficient margin of safety), except for the total inorganic nitrogen at WSR 07
(Black Point Cooling Water Intake, over 7km away from the proposed temporary
staging platforms) where exceedance
is already predicted at the baseline level. While the change in water quality due to
the reclamation for the HKBCF, TM CLKL Southern Connection and the permanent
piles for Southern Connection viaducts is not significant, the predicted water
quality near the Southern Connection viaducts would also be satisfactory during
the operation phase. The three
receiver points (WSR22a/b/c) at Tai Ho Wan are only minimally affected.
When
compared with the scale of works (and associated change in flow regime) under
the TM-CLKL, HKBCF and HKLR, those of the temporary staging platforms are
deemed minimal. As calculated in
the direction perpendicular to the Tung Chung Navigation Channel, the whole
cross section from Tai Ho Wan to the north eastern tip of the Airport Island
(indicated by the red line shown in Figure 3.2) would be around 3.62km. The projection of the HKBCF Island and
the TM-CLKL Southern Landfall would together cover 1,533m of the cross section,
which indicated that the HKBCF Island and the TM-CLKL Southern Landfall would
contribute to a change of 42.35% of the cross section of the tidal
channel. Based on the pile
configuration assumed under the Appendix
D3 of the approved EIA Report, the total blockage due to the permanent
piles of the Southern Connection viaducts would be 171.6m (based on the assumed
pile configurations for TM-CLKL Southern Connection viaducts stated in Appendix D3 of the approved EIA Report),
which contribute to an additional 4.74% reduction of the cross section. As discussed previously, such a
significant change (42.35%+4.74% = 47.09%) in the cross section of the tidal
channel due to the HKBCF and the TM-CLKL Southern Connection, though may result
in some level of change in flow regime, would not contribute to any significant
change in water quality at all identified WSRs or any additional exceedance in
WQO (TIN exceedance at WSR 07 Black Point Cooling Water Intake is predicted at
the base case scenario, thus not considered as "additional
exceedance").
It
should be highlighted that the reclamation for Logistic Parks and Tung Chung
Future Development has not been taken into account in the above calculation
since both reclamation areas do not lie exactly on the same cross section
considered above (indicated by the red line shown in Figure 3.2). Yet it is reasonable to expect the
reclamation for Logistic Parks and Tung Chung Future Development would have
contributed a notable effect on the flow regime at the tidal flow channel and
Tai Ho Wan.
In
comparison, the change in cross section of the tidal channel would be minimal
by the temporary staging platforms even under the worst case scenario during
which 24 platforms will present at the site (please refer to Figure 2.3). Based on the current design, the diameter
of the pile would be 1.168 to 1.2m.
Assuming that parallel arrays of piles of the staging platform would
approximately overlap with each other at most of the sections along the current
flow direction (see Figure 3.3), the
additional cross section blocked by the piles would be approximately 93.4m during
the critical construction period (see Table
3.5). This represents
approximately 2.6% of the cross section of the tidal channel between Tai Ho Wan
and the north eastern tip of the Airport Island. The same was assumed for the calculation
of pile friction in the Appendix D3
of the approved EIA Report. It
should also be noted that the temporary staging platforms would not encroach
into the Tung Chung Navigation Channel, where water depth is deep and the major
tidal current flow through. The arrays
of piles along the extensions at the northern side (where water is deeper) of
the temporary staging platforms would generally be quite parallel to the flow
direction (as indicated in Figure 2.1 and Figure 3.3). Such arrangement would minimize the
overall blockage arisen from piles at the extensions.
When
compared with the cumulated decrease of cross-section from the TM CLKL as well
as the HKBCF (42.35%), the additional change (2.6%) due to the temporary
staging platforms would be minor. Also, as the temporary staging platforms
are located at the shallower part of the channel, where current flow is slower,
the overall change of current flow due to the temporary staging platforms would
be even less significant. Besides,
based on the latest update design on the Southern Connection, the spans between
permanent piers would be generally greater than those assumed under the
computational modelling in the approved EIA, such that the temporary increase
in current flow blockage due to the temporary staging platforms would be partly
offset and the expected deviation from the result of computational modelling
would be less significant. It
should also be noted that the cross section covered by the pipe piles of the
temporary staging platforms has also been covered by the reclamation for the
Logistic Parks and the Tung Chung Future Development assumed in the operation
phase modelling scenario. It is
therefore expected that the obstruction in tidal flow and the potential change
in flow regime by the two reclamation areas would be significantly more than
that resulted from the pipes of the temporary staging platforms. The reduction in the obstruction of the
tidal flow channel due to the 'absence" of the two reclamation areas
during the entire lifespan of the temporary staging platforms would provide
some allowance, which could offset part (if not all) of the change in flow
regime by the temporary staging platforms. In view of the marginal decrease of cross
section area due to the temporary piles (after consideration the offsetting),
significant change in the flow regime at the channel over that predicted in the
approved EIA is not expected. The
associated change in water quality is expected to be minimal as well. In view of the significant separation, aggravation
of the predicted WQO exceedance of TIN at WSR 07 (Black Point Cooling Water
Intake) is not anticipated. Table 3.6 shows the change in flow
regime and water quality predicted under the operation phase water quality
modelling as well as the expected flow and water quality performance of the
temporary staging platforms.
Table 3.5 Calculation
of Additional Section Blockage
|
Feature |
Arrays of Pile
Parallel to flow direction |
Total Width (m) |
Assumptions |
|
12
nos. of Isolated Platforms E3 to E13 |
43 |
50.2 |
·
Piers
E4 to E13 each has four rows of piles parallel to the flow direction; ·
Total
number of arrays of pile at E4 to E13 parallel to flow direction = 4 rows of
pile/pier x 10 piers = 40 arrays of pile ·
Pier
E3 has three rows of piles parallel to the flow direction ·
Total
number of arrays of pile at E3 parallel to flow direction = 3 arrays of pile ·
Total
arrays of pile = 40 + 3 = 43 ·
Diameter
of pile is 1.168m ·
Total
width = Diameter of pile x Total number of arrays of pile = 43 x 1.168m =
50m. |
|
Other
12 Isolated Platforms at Viaduct A, B, C and D |
36 |
43.2 |
·
Each
pier has three rows of piles parallel to the flow direction; ·
Total
number of arrays of pile parallel to flow direction = 3 rows of pile/pier x 12
pier = 36 arrays of pile ·
Diameter
of pile is 1.2m ·
Total
width = Diameter of pile x Total number of arrays of pile = 36 x 1.2 = 43.2m. |
|
Total |
|
93.4 |
|
Table 3.6 Summary of Change in Flow
Regime and Associated Change in Water Quality for the Temporary Staging and the
Nearby Projects
|
Development |
Reduction in Cross Section in Tidal Channel |
Change in Flow Regime |
Associated
Change in Water Quality |
|
Artificial
Island of HKBCF and TM- CLKL Southern Landfall |
1,533m
(42.35%(a)) |
Change
in flow regime considered acceptable. |
Change
in water quality considered minimal. No additional exceedance predicted. |
|
Permanent
Bridge Piles for Southern Connection |
171.6m
(4.74%(a)) |
||
|
Piles
for the Temporary
Staging |
93.4m
(2.6%(a)) |
Additional
change in flow regime considered minor and acceptable. |
Additional
change in water quality considered negligible. Compliance at WSRs is expected. |
|
Note: (a)
Percentage change compared with the base case
scenario of the approved EIA, ie without TM-CLKL, HKBCF and HKLR. |
|||
The assessment
for the regional effect on tidal flow due to the temporary staging platforms is summarized
below:
·
General
compliance of WQO at all WSRs, except for WSR 07, was predicted under the
worst-case scenario for change in flow regime and the associated impact on
water quality (which is the operation phase modelling scenario) assessed in the
approved EIA;
· The additional blockage of the tidal
flow channel by the temporary staging platforms is relatively small when
compared with the cumulative impact by the HKBCF and the bridge piles of the
TM-CLKL Southern Connection;
·
The
reclamation for the Logistic Parks and the Tung Chung Future Development which
has been considered in the operation phase modelling scenario, would exert some
effect on the flow regime nearby, and its absence during the entire lifespan of
the temporary staging platforms would provide some allowance for offsetting the
reduction in tidal flow channel due to the temporary staging platforms; and
·
The
additional blockage of the tidal flow channel by the temporary staging platforms
would be minimal when compared with the cumulative impact by the HKBCF and the
bridge piles of the TM-CLKL Southern Connection. The minimal additional blockage of the
tidal flow channel is expected to only result in minor change in flow regime,
as compared with the contribution by the HKBCF and the bridge piles of the
TM-CLKL Southern Connection. The
predicted change in water quality from the operation phase modelling assessment
is minimal despite the greater change in flow regime. Similarly, the potential change in water
quality is expected to be minimal in
view of the minor change in flow regime.
Localised
Effect at Tai Ho Wan
It
is anticipated that the potential change in flow regime would be highly localized,
particularly at the nearshore area of North Lantau where more platforms will be
constructed. Stagnation of water at
this area may be resulted from the reduced current flow, potentially results in
accumulation of floating refuse and depletion of dissolved oxygen. As discuss previously, an embayment area
is formed in between the two reclamation areas for Logistic Parks and Tung
Chung Future Development at the outer Tai Ho Wan. Similar stagnation of water may be
resulted from the formation of embayment.
As judged by dimension of the embayment formed, the potentially affected
area in outer Tai Ho Wan would be much larger than that of the temporary
staging platforms. Also, the level
of change in local flow by the temporary staging platforms is expected to be
less significant than that caused by the two reclamation areas, since the
change is induced by array of separate pipe piles instead of solid reclaimed
landmass. As shown in the results
of the operation phase modelling scenario, the water quality at the WSRs in Tai
Ho Wan (WSR22a/b/c) would full comply with the WQO requirement. In view of the smaller affected area as
well as the lower level of change, it is therefore expected that the potential
change in flow regime and the associated change in water quality from the use
of temporary staging platforms would also be acceptable.
As
some small patches of the coral communities are identified at the seawall
section along the footprint of the temporary staging ([3]), change in flow regime and water
quality may affect these coral communities (Figure 3.4). Coral colonies feasible for translocation
were translocated to the receptor site at Yam Tsai Wan of North Lantau in
October 2013 before commencement of the Southern Connection construction in
accordance with the Detailed Coral Translocation Methodology submitted under Condition 2.6 of the EP-354/2009A. As some coral colonies are not feasible
for translocation, water quality monitoring is recommended to be carried out at
the location of the coral communities (indicated as "SR4a" on Figure 3.1, easting and northing: 815247E,
818067N). Baseline monitoring was
carried out for 4 weeks before the commencement of all marine works under the
Southern Connection on 31 October 2013.
The impact monitoring has been undertaking since commencement of the
Southern Connection construction and will be undertaken for the entire lifespan
of the temporary staging works. Post-construction
water quality monitoring will also be carried for at least 4 weeks after the
complete removal of temporary staging. The monitoring methodology (including
parameters, monitoring equipment, in-situ measurements) follows that of other
SR (sensitive receiver) stations. Other
water sensitive receivers are much further away and are not expected to be
affected by the localized effect in flow regime of the temporary staging platforms. No other additional water quality
monitoring is required. In case
elevated SS or turbidity is identified during the water quality monitoring, the
source of pollution shall be tracked down and be removed as soon as
possible. In case depletion of dissolved
oxygen is identified, artificial aeration should be arranged at the identified
coral community in the vicinity of SR4a (Figure 3.4). With the implementation of the proposed
monitoring and corresponding measures, the potential change in water quality
associated with the change in flow regime due to the temporary staging platform
is expected to be acceptable and no unacceptable water quality impact is
expected.
The
flow regime within the highly landlocked Tai Ho Wan would also be of particular
concern. The narrow opening,
together with two other small box culverts (the locations of the two small box
culverts are shown in Figure 3.1) at the Tai
Ho Wan Section of the NLH largely separates the Tai Ho Wan water from the
external water and any change in flow pattern at the external water would not
affect the Tai Ho Wan water directly.
Since the opening and the two small box culverts are the only
connections with the external water, the flow regime within the Tai Ho Wan is
dominated by the flow across the narrow opening (as well as the inflow from
nearby watercourse), which itself is driven by the water level inside and
outside the opening. While the
temporary staging platforms would affect the flow pattern at the outside of the
opening, the change of flow pattern could exert only very limited effect on the
water level (which is typically dominant by the tidal condition). In addition, the box culvert which is
located within the footprint of the temporary landing platform will be extended
in order to maintain the existing function of the culvert to allow water flow
between Tai Ho Wan and the external waters (please refer to Figure 2.9 for the location of the box culvert and its
extension). It is therefore
expected that the temporary staging platforms would not result in significant
change in flow regime in the Tai Ho Wan water.
Besides,
the pipe piles of the temporary staging platforms may allow the accumulation of
floating refuse at the nearby water, resulting in deterioration of water
quality. Inspection for the
accumulation of floating refuse will form part of the regular site inspection
and collection of floating refuse will be carried out on a need basis to remove
any trapped floating refuse as soon as possible. The collection of floating refuse will be
carried out from the shore, from the temporary staging platforms or from low
draft vessels. In view of the low
water depth near the works area, the use of vessels for collection of floating
refuse will be carried out at high tide, to ensure sufficient clearance from
the seabed to the vessels and avoid any excessive disturbance of seabed from
the movement of the vessels.
Brief
Summary
In
conclusion, it is expected that during the construction and operation of the
temporary staging platforms, the additional marine piles would only result in
minimal change in flow regime and water quality additional to the level
predicted under the operation phase of the approved EIA. Additional exceedance in WQO due to the
temporary staging platforms is not expected and no unacceptable water quality
impact is expected. In view of the
significant distance between the temporary staging platform and WSR07 as well
as the small scale of the temporary staging works (when compared with other
nearby works), significant deterioration of water quality at WSR07 due to the
proposed temporary staging works is not anticipated. The flow pattern and water quality at
Tai Ho Wan are not expected to be significantly affected by the temporary
staging platforms in view of its land-locked geographic settings. The potential of accumulation of
floating refuse identified and regular site inspection as well as collection of
floating refuse would be provided to ensure the avoidance of the potential
water quality impact.
3.4.3
Potential Water Quality Impacts from Other Construction
Activities Associated with the Temporary Staging
The
temporary staging would be the platform for all the required construction works
to be carried out for the construction of the Southern Connection, including
but not limited to:
·
Transportation
of workers, machineries and construction materials;
·
Loading
and unloading of vehicles and barges;
·
Positioning
of cranes and other machineries for the construction of the Southern Connection;
·
Transportation
and lifting of parts of the viaducts and main crossing; and
·
Bored piling
for the construction of the permanent piles.
Construction
site runoff would be generated from various construction activities as well as
during rainstorm which may contain high level of suspended solid from the temporary
staging platforms. If uncontrolled,
the construction site runoff may enter the marine environment and result in
adverse water quality impact.
Standard measures and good site practices stipulated in ProPECC PN 1/94 "Construction Site
Drainage" should be followed as far as practicable. In particular, temporary drainage system
such as surface channel will be provided on the temporary staging platforms to
divert and collect the surface runoff from daily operation and the first flush
during a rainstorm. The runoff will
be properly treated prior to discharge into the sea. Wastewater generated from construction
works such as bored / drilling water will be collected, treated, neutralized
and de-silted through silt trap or sedimentation tank prior to discharge into
sea. As such, unacceptable water
quality impact from runoff containing high level of suspended solid is not
anticipated to occur.
The
following types of chemical wastes may be generated during the construction
activities on the temporary staging platforms:
·
Used
paints, engine oils, hydraulic fluids and waste fuel; and
·
Spent
cleansing fluids / mineral oils from machineries.
Chemical
wastes will be disposed of via a licensed waste
collector to a facility licensed to receive chemical waste in accordance with
the Waste Disposal
(Chemical Waste) (General) Regulation. As such, there will not be any planned
discharge of chemical wastes to the surrounding waters. To
reduce the possibility of chemicals entering surrounding
waters, chemical waste will
be handled with care in accordance with the Code of Practice on the Packaging,
Handling and Storage of Chemical Wastes. For example, chemical wastes will be stored
by containers which are suitable for the substance
they are holding, resistant to corrosion, maintained in a good condition, and
securely closed. The storage area
will also be covered to prevent rainfall entering (water collected within the
bund must be tested and disposed of as chemical waste, if necessary). In addition, precautionary measures to prevent
spillage of oil and chemicals as well as response actions to be taken in the
event of accidental spillage are presented in the Spill Response Plan (SRP) which
has been developed in accordance with Clause 2.7 of the Environmental Permit
(EP-354/2009/B). The Contractor
will strictly follow mitigation measures stipulated in the SPR in order to
reduce the possibility of spillage as well as the potential water quality
impacts. Given the above, it is expected
that no unacceptable water quality impacts will be caused by the use of
chemicals during the construction of the temporary staging platforms.
Concrete
batching would be carried out offsite and be transported onsite via concrete
lorry mixers. Concrete dump truck
will be loaded onto the barge. The
barge will then move to the construction location and the concrete inside would
be pumped directly from the concrete pump truck to the location where marine
piers are being constructed. The
Contractor will ensure all equipment used are well-maintained
and would not result in accidental leak of concrete to the marine
environment. In addition, concrete
lorry mixers and concrete dump trucks would be washed at a designated bunded
area where the washout will be pumped out to a proprietary wastewater treatment
unit with pH adjustment provided on the temporary landing platform and concrete delivery barges. The
effluent quality of treated water will also be monitored to confirm compliance
with discharge limits as per the respective Water Pollution Control Ordinance (WPCO)
discharge license before discharged.
Unacceptable water quality impact associated with concrete batching,
transportation and storage onsite is thus not anticipated. With the implementation of the
appropriate mitigation measures, adverse water quality impact arise from the
construction site runoff from the temporary staging is not anticipated.
The
construction materials as well as machineries would be delivered by sea to the temporary
staging platforms. At the
platforms, goods will be loaded /unloaded from barges by cranes lifting. Goods to be loaded to / unloaded from
barges include construction machineries, tools, plant, construction
material and construction waste. Following
industrial standards required for crane lifting in Hong Kong will minimize the
risk of accidental dropping of goods during lifting. Since the amount of goods to be loaded /
unloaded by cranes lifting is small and relatively intact, significant water
quality impact due to any accidental dropping of these goods into the sea would
be unlikely. The barging location at
the staging platforms will allow sufficient clearance for the barges from the
seabed and disturbance of the seabed due to the movement of the barges is
therefore not expected. During
construction of the temporary staging platforms, there will be 38 numbers of
isolated platforms to be constructed in stages with three individual work
fronts at any one time. It is
anticipated that the installation works will involve four flat-top barges, four
derrick barges and two tug boats. It
should also be noted that the construction of the landing platforms, which
involve the use of one flat-top barge, three derrick barges and one tug boat,
will also be undertaken concurrently with the staging platform
construction. During operation of
the temporary staging (ie during construction of the permanent structures), the
number of barges present within the working area at any one time will be below
18. Since the number of works
vessel present within the working area at any one time is low, significant
blockage of current flow by the draft of the works vessel is not expected
during both the construction and operation of the temporary staging. In addition, potential water quality
impacts due to disturbance of the seabed sediment by propeller wash is not
expected to be unacceptable given the low number of vessels involved as
presented above and the localised nature of the sediment disturbance. Also, coral translocation was undertaken
in October 2013 before commencement of the Southern Connection construction which
would help to reduce the indirect water quality impacts to corals at Tai Ho Wan,
which is the nearest WSR to the works area.
With
the implementation of standard good site practice and the provision of
temporary drainage system on the temporary staging platforms, unacceptable water
quality impact is not anticipated to arise from the construction and operation
of the proposed temporary staging platforms.
3.4.4
Potential Water Quality Impacts from the Removal of
the Temporary Staging Platforms
The
removal of the temporary staging platforms will involve cutting of the pipe
pile 1m below the existing seabed level.
The cutting of the metallic pipe pile will be carried out by industrial
divers using underwater flame cutter.
To allow cutting of the pipe pile 1m below the existing seabed level, a
small area of sediment will be displaced around the pipe pile manually by the
divers. It is anticipated that
small and localized elevation of suspended solid may arise from the
displacement of the marine sediment by the divers. Yet such elevation in suspended solid
will be transient and the disturbed sediment will be settled within a
relatively short period of time. No
unacceptable water quality impact from this operation is expected. Since the marine construction required
for the permanent piles will be completed during the removal of the temporary
staging platforms, cumulative water quality impact from the nearby marine
construction is not anticipated.
The minor depression of seabed would be left and allow the seabed to
reinstate naturally.
Additional
water quality impact from the installation, operation and removal of the
temporary staging has been assessed and predicted to be minimal. Cumulative
impact from the temporary staging platforms and the nearby works is expected to
be acceptable.
3.4.5
Recommendations of Additional Mitigation Measures and
EM&A
Additional
mitigation measures for water quality proposed include:
·
Regular
inspection for the accumulation of floating refuse and collection of floating
refuse if required;
·
Provision
of temporary drainage system for collection of construction site runoff to
allow appropriate treatment before discharge into the sea; and
·
Wastewater
generated from construction works such as bored / drilling water will be
collected, treated, neutralized and de-silted through silt trap or
sedimentation tank before disposal.
Minimization
of the flow blockage due to piles of the temporary staging platforms and minimization
of propeller wash in shallow water have been taken into account during the
detailed design of the temporary staging platforms. The following factors have been
considered:
·
Maximizing
span between piers;
·
Minimising
number of piles; and
·
Locate
temporary piles behind each other along the current flow direction.
One
additional water quality monitoring station for EM&A is proposed at the
coral communities in the proximity of the temporary staging (station SR4a as
shown in Figure 3.1), as some coral colonies are not feasible to
be translocated. The monitoring had
covered the 4 weeks period before the commencement of all marine works under
the Southern Connection, and will cover the whole period when the temporary
staging is in its lifespan as well as 4 weeks after the complete removal of the
temporary staging platforms. In
case elevated SS or turbidity is identified during the water quality
monitoring, the source of pollution will be tracked down and be removed as soon
as possible. In case depletion of
dissolved oxygen is identified, artificial aeration will be arranged at the
identified coral community in the vicinity of SR4a (Figure 3.4).
Inspection for accumulation of
floating refuse will be carried out during the regular site inspection. Collection of floating refuse will be
arranged on a need basis. Other
details of the water quality monitoring should be in line with the requirements
for monitoring at SR (sensitive receiver) stations stated in the EM&A
manual.
In
order to further reduce the potential impacts from propeller wash, the
possibility of reducing the volume of vessel traffic within the works area will
be explored. For example, the works
vessel stationed at Viaducts A, B, C and D could potentially be re-positioned
without the use of tug boat by adjustment of the anchor position.
3.5
Marine
Ecology
3.5.1
Review of Approved EIA
The
findings of the ecological survey conducted under the approved EIA indicated
that the benthic species present at the area along the proposed alignment are
generally similar throughout the North-western Waters. In addition, infauna diversities at the
area along the proposed alignment are similar to other areas in the
North-western Waters and are relatively low compared to other regions in Hong
Kong (Section 8.9.2.17 of the
approved EIA Report). According to
the coral survey (spot check dive and rapid ecological assessment) carried out
for the approved EIA, the coral coverage along the alignment of the Southern
Connection viaducts was found to be low and the diversity of the coral was
found to be low as well (Sections
8.9.4.7- 8.9.4.10 of the approved EIA Report). The cetacean line-transect survey also
indicated that with the exception of a rare sighting in which two Chinese White
Dolphins (CWD) was made near Tung Chung, CWD were largely absent to the east of
airport platform and near Tai Ho Wan, as indicated in Appendix F1 of the approved EIA Report (Section 8.9.1.6).
During
the construction of the TM-CLKL, the major ecological impacts to marine
ecological resources include:
·
Permanent loss of approximately 47ha of seabed for northern
and southern reclamation and pier construction as well as 390m of sloping seawall and 210m of vertical seawall at Tuen Mun.
·
Indirect impacts due to the change in water quality,
namely SS elevation, oxygen depletion and release of contaminants, due to marine dredging,
filling and viaduct pier works.
·
Increased acoustic
disturbance to marine life due to piling works for the
viaduct piers, dredging and reclamation works.
·
Injury/mortality or disturbance
from construction phase vessel traffic
to marine life, specifically the CWD.
With
the implementation of mitigation measures proposed for the marine works, the
potential water quality impact as well as the associated impact to the marine
ecology would not be significant. The
implementation of other mitigation measures, including acoustic decoupling,
dolphin exclusion zone, vessel speed limit and restrictions, etc. would also
help to reduce the potential acoustic disturbance to marine life due to piling
works for the viaduct piers, dredging and reclamation works, as well as
injury/mortality or disturbance from vessel traffic. EM&A for marine ecology has been
recommended.
3.5.2
Identification and Evaluation of Potential Impacts
As discussed in the earlier
Section 3.4, the potential change
in water quality due to the installation, operation and removal
of the temporary staging platforms would be minimal. It is expected that the potential
indirect impact to marine ecology due
to the change in water quality would be minimal
as well.
Soft
Substrate Benthic Communities and Corals
The installation of temporary staging
would result in direct disturbance to the bottom sediment and the associated
marine life at the Southern Connection viaducts. Yet in view of the coverage by the
temporary piles (each pile would only cover 1.07 m2
([4]) or 1.13 m2 ([5]) of seabed and the total covered area
would be about 269 m2 or 0.03ha ([6])), as well as the low diversity and
common species at the affected area, ecological impact due to the direct
disturbance from the temporary staging would be minimal. The direct loss of subtidal marine
habitat due to the temporary staging platforms is relatively negligible when
compared with the impact resulted from the rest of the TM-CLKL (loss of
approximately 47ha of seabed). No
significant increase in cumulative impact on subtidal marine habitat is
expected from the construction and operation of the temporary staging.
The disturbance of rock armour at the landing
platform may potentially affect the attached coral communities on the rock
armour. According to the results of
coral survey conducted under the approved EIA, no coral community was found
along the alignment of the four landing positions of the viaducts of the
Southern Connection (survey stations E1-E10). The coral survey results at the survey
station C6 and C7 near the landing position in the east indicated that there is only limited level of coral communities
(gorgonian [1 colonies per 2 m2] and ahermatypic coral [1 colonies
per 1m2] for C6; gorgonian [1 colonies per m2] and
ahermatypic coral [1 colonies per 2m2] for C7). Findings from further dive surveys
undertaken at Tai Ho Wan in December 2012, January and October 2013 ([7])
confirmed the existence
of coral communities with low coverage and low diversity on the rock armour (Figure 3.4). Based on the engineering design, disturbance
to approximately 260m long of rock armour seawall is required for the
construction of the landing platforms.
Potential direct impact to the coral communities attached to the
affected rock armour would be expected.
In view of the extent of potential direct impact, limited level of coral
communities expected to be affected by the removal of rock armour as well as
the completion of coral translocation, it is expected that direct impact to
coral communities would be limited as well. The temporary loss of intertidal marine
habitat due to the landing platforms is relatively negligible when compared
with the impact arises from the rest of the TM-CLKL. No significant increase in cumulative
impact on intertidal marine habitat is expected from the construction and
operation of the temporary staging platforms.
Chinese
White Dolphin
The
piling works required for the installation of the temporary staging platforms would
not involve the use of bored and percussive piling as well as any rock socket
formation, which may produce significant level of underwater noise that may
affect marine life, especially CWD.
As indicated by the findings of the cetacean line-transect survey
conducted under the approved EIA (refer to
Appendix F1 of the approved EIA Report), the water around the Southern
Connection viaducts is of little usage by CWD. Based on the latest Final Report of
Monitoring of Marine Mammals in Hong Kong Waters (2012-13), the distribution
pattern of CWD at water near the Southern Connection remains similar to that of
Appendix F1 of the approved EIA
Report. The CWD usage near Tai Ho
Wan remains low as shown in Figures 3.5 and 3.6. In addition, recent land-based
theodolite tracking of CWD undertaken as part of the baseline marine bored
piling monitoring of the EM&A programme confirmed the low usage of CWD with
no sightings recorded along the alignment of the Southern Connection Viaduct
Section during 30 survey days from early September to mid-October. As required under the approved EIA,
acoustic decoupling should be carried out for all noisy equipment, such as
compressors and generators on barge to minimize the transmission of vibration
from the barge to the marine environment.
Based on the same logic, the transmission of vibration from the
temporary staging platforms to the marine environment should be reduced by the
application of the similar acoustic decoupling measures at the noisy equipment
during the entire lifespan of the temporary staging. A 250m dolphin exclusion zone will also
be implemented during the construction and decommissioning of the temporary
staging platforms and the temporary landing platform. With the implementation of the
precautionary and mitigation measures, it is expected that the potential acoustic
disturbance to CWD due to the whole lifespan of the temporary staging would be
minimal.
Figure
3.5 Distribution of CWD Sightings in Central North Lantau from
2005-2009 (Source: Appendix F1, Approved EIA of TM-CLKL)
Figure
3.6 Distribution of CWD Sightings in North Lantau from April 2012 –Mar
2013 (Source: Monitoring of Marine Mammals in Hong Kong Waters (2012-2013))
The presence
of piles of the temporary staging platforms may affect the movement of CWD
within the area. Considering the low
usage of CWD within the
works area, temporary nature of the piles and a maximum of 242 piles that
occupy 2.6% of the whole cross section of the tidal channel (indicated by the
red line shown in Figure
3.2) will present at the site at any one time, it is not expected that
the presence of the piles will lead to any unacceptable impact to the movement
of CWD. It should also be noted
that ~1,100 piles will be installed under the reference staging scheme which will
occupy 3.79% of the concerned tidal channel. As such, potential impact to CWD
movement is considered greater under the reference than the current schemes.
Regarding the
potential disturbance to CWD as a result of marine traffic caused by the temporary
staging, a comparison of the estimated volume of marine traffic that will be
caused by the current temporary staging scheme and the reference scheme is
presented in Tables 3.7a-b. It is expected that the volume of
marine traffic, in terms of total estimated distance travelled by the vessels
during the construction, operation and decommissioning stages of the temporary
staging, would be lower for the current scheme than the reference schemes. Summary of key findings regarding the
estimated total marine traffic volume is listed below:
During construction and decommissioning of the temporary
staging:
·
The
estimated volume of marine traffic is higher for the reference scheme due to
its continuous nature as more steel structures would be required to be transported
and removed from the site during the construction and decommissioning stages,
respectively.
During operation of the temporary
staging:
·
The
estimated volume of marine traffic required for the delivery of bored pile
casings and disposal of sediments and spoils is the same between the reference
and current schemes.
·
The
estimated volume of marine traffic required for delivery of concrete and
passengers, which are mainly within the works area, is expected to be lower for
the reference scheme which could rely on the continuous staging for such land delivery. However, it should be noted that the
reference scheme would still require to delivery 50% of the concrete through
off-site marine route due to constraint on land traffic capacity at the
temporary vehicular bridge.
Overall, the estimated volume of marine traffic within the works area is
expected to be lower for the reference scheme than the current scheme.
·
The
estimated volume of marine traffic required for delivery of reinforcement cages
is expected to be lower for the current scheme as it only involves short
distance of marine traffic within the works area between the isolated platforms
and the temporary landing platform where the fabrication of reinforcement cages
will be undertaken. For the reference
scheme under which there is no landing platform for fabrication on site, the
reinforcement cages are required to be fabricated offsite and transported to
the works area. As such, the estimated
volume of marine traffic off the works area is higher for the reference scheme
than the current scheme.
Overall, the
volume of marine traffic within the works area, where the usage by CWD is noted
to be low, is expected to be higher for the current scheme. However, the volume of marine traffic
outside the works area, which involves the larger North Lantau area more
frequently used by the CWD, is expected to be higher for the reference
scheme. Given the above and the higher
estimated total volume of marine traffic of the reference scheme (ie
considering both marine traffic within and outside the works area), it is
expected that the disturbance to CWD as a result of marine traffic caused by
the current scheme would be no worse than that of the reference scheme.