1.
Introduction
Under the Environmental Impact Assessment Ordinance, the Environmental Impact Assessment (EIA) Report (Register
No. AEIAR-196/2016) prepared for the “Tung Chung New Town Extension” has been approved by the Environmental
Protection Department (EPD), and an Environmental Permit (Permit no.
EP-519/2016) has been issued for the project.
Pursuant to Condition 2.16 of the Environmental Permit, Silt Curtain Deployment Plan
should be submitted prior to the commencement of reclamation related to marine
works at Tung Chung East. The plan
includes the construction programme and detail on the design, operation,
maintenance, regular patrol and monitoring of the silt curtain to be deployed
during the construction.
Accordance with condition 2.5 of the EP,
Qualified Ecologists had been appointed to form part of the ET and carry out
work relating to ecological aspects. The Qualified Ecologists had been
consulted in preparation of this Plan.
2. Silt Curtain Deployment Programme
A brief programme
showing the major reclamation works
and their related
works is enclosed in Appendix A. In general, perimeter silt curtain has to be deployed to enclose
the works area as far as practicable. The minimum length of overlapping silt
curtain and the width of gap between 1st and 2nd layer of silt curtain is 150m
and 100m respectively. Where the marine works are not enclosed by
perimeter silt curtain, localized silt
curtain around the marine works shall be deployed to enclose the works area
before start of the marine works. Additional localized silt curtain (frame type
silt curtain) will also be deployed when placing sand with fine content of
>5% to 10% onto the seabed (see Appendix
C1 and Appendix C2). Some
indicative phases of silt curtain deployment are presented as follows:
1.
Protective silt curtain (floating
single silt curtain type) will be deployed before commencement of construction
works in order to minimize potential water quality impacts that may be caused
by vessel’s movements during site
investigation works at shallow water
area (see Appendix C3 for the Silt Curtain Layout).
2.
Installation of Perimeter Silt
Curtain during DCM trial for DCM Trial Embankment
(at the works area near Tai Ho Wan) (see Appendix C4 for the Silt Curtain
Layout).
3.
Installation of Perimeter Silt
Curtain during reclamation filling for DCM Trial
Embankment (at the works area near Tai
Ho Wan) (see Appendix C5 for the Silt Curtain Layout).
4.
Perimeter silt curtain (floating
single silt curtain type) will be deployed during all reclamation works (see Appendix C6 for the Silt Curtain Layout).
In case the silt curtain layout has to be
updated due to potential work constraints or
marine safety, the proposed silt
curtain layout shall be reviewed and agreed by the Environmental Team and the Independent Environmental
Checker as sufficient to control the potential
water quality impact due to the associated marine works before implementation.
3.
Design of Silt Curtain
The floating single silt curtain consists of
a layer of geotextile tied on 300-500mm diameter sub-buoys. The geotextile
extended to the seabed level secured by steel chain ballast. The buoys will be
further positioned by nylon ropes tied on nearby existing structures. Sufficient length of geotextile will be provided
such that the silt
curtain can be extended from the water surface to the seabed during high tide
condition. The minimum overlapping length between the different sheet is 150m.
Silt curtain (Model DSP15) with curtain depth of 7.4m (D=7.4m) and curtain
strength 15 ton/m (Canvas (15ton/m)) is deployed in this project.
Job reference and typical section of the proposed silt
curtain is attached in Appendix B.
4. Silt Curtain Installation
i)
Link up 300-500mm buoys together by a net
ii)
Tie up
top end of the geotextile to the buoys net and the bottom end with steel chain
ballast before transportation.
iii)
Transport the silt curtain to the location for
fixing via a marine pontoon.
iv)
Refer to the Environmental Permit
No. EP-519/2016 Clause 2.27, a dolphin exclusion zone of 250m shall be
implemented around the reclamation site during the installation or redeployment
of the perimeter silt curtain. Before the start of the installation work, Qualified
Ecologists with dolphin monitoring experience shall scan the exclusion zone for
at least 30 minutes. If dolphins are observed in the exclusion zone, the
installation work shall be delayed until the dolphins left the area.
v)
Workers tie
the buoys to the water and then slowly put the geotextile with the steel chain
ballast into sea.
vi)
Put the buoys to the water and then
slowly put out the geotextile with the steel chain ballast into sea.
vii)
In order to maintain the position
of the silt curtain especially at location with strong current, place concrete sinkers
to the seabed if required
and tie the silt curtain to
the sinkers with nylon strings by divers.
If dolphins are observed within the
exclusion zone during the installation work, the relevant part of the work
shall cease until the dolphins left the area.
Once the perimeter silt curtains are installed or re-deployed, the Dolphin Watching
Plan shall be implemented as part of the EM&A programme.
5. Operation, Maintenance,
Regular Patrol and Monitoring of Silt Curtain
i)
On-board supervisors will be
assigned to check the condition of the silt curtain before commencement of
works every day. Completed
inspection checklists will be kept on site for record purpose. Refer Appendix D for the sample of Silt Curtain Daily Inspection Checklist. Diver inspection will be arranged after adverse weather
and when necessary.
ii)
For the tentative arrangement of
silt curtain under adverse weather (e.g. Red or Black Rainstorm, Typhoon Signal No. 3 or above etc.), the
silt curtain will not be temporary removed during adverse weather. However, related works will be
suspended immediately if silt curtain is found any damaged. Immediate
inspection of silt curtain after adverse weather is necessary. Working procedures include (1) lift up the silt
curtain for water by derrick barge, (2) sew (double-line sew) a new piece of geotextile to the
existing geotextile to cover the damage area, (3) ensure sufficient overlapping length
(150m) & width
of gap (100m) and (4) diver inspection shall be carried out if
necessary to inspect the installation and decommission of silt curtain to
ensure proper installation and functioning of the silt curtain according to the
design drawings. Nearby marine works will resume after repairing of the damaged silt curtains.
iii)
Refuse around the silt curtain will
be collected at regular intervals on a daily basis so that water behind the
silt curtains will be kept free from floating
debris.
iv)
Sufficient spare geotextile will be
kept on site for replacing of damaged silt curtains. The spare geotextile shall
be kept in place to avoid direct contact with water and sunlight.
Reporting Mechanism
When
insignificant defect of silt curtain gap less than one unit length of the silt
curtain (around 20m), BKSCTJV Inspection team will inform BKSCTJV Marine and
Environmental Department, and arrange resource to carry out repairing work.
As the major works conducted near to the
perimeter silt curtain are marine DCM works and sand placing works. All the DCM
barges are under confinement by an additional primary and secondary silt
curtain. Meanwhile, a frame-type silt curtain will be installed around the grab
when placing sand onto the seabed. Therefore, with these protective measures,
it is considered that sufficient protection to the marine quality is provided.
When
significant defect of silt curtain gap greater than one unit length of the silt
curtain (around 20m), the following reporting mechanism should be implemented:-
1.
Once JV Inspection team identified the defect, they
will take immediate photos and then send to JV Marine
Department and Environmental Department,
2.
JV Environmental Department reporting to PM, ET and IEC,
including the anticipated time to repair completion,
3.
Request advice from PM, ET and IEC on whether any works should
be suspended or slowed down, etc, shall be discussed.
%20final%20submission_files/image008.jpg)
6.
Removal of Silt Curtain
Prior to removal of silt curtains, all marine
works for which the silt curtains are deployed shall be stopped and visual
inspection of the water quality within the area protected by silt curtains
shall be conducted to confirm no sediment plume remaining within the works area
before commencing silt curtain removal.
Floating silt curtains shall be removed by
detaching the chain connecting the silt curtain to the anchors. Care should be
taken to protect the silt curtain skirt from damage as it is dragged from the
water. The remaining anchors shall be individually connected to the crane by
divers and carefully lifted off the seabed for recovery onto the barge to
minimize the disturbance to the seabed.
Silt
curtain removal schedule
As all reclamation works below +2.5mPD are completed at VS1, SS1/MES and all reclamation area
respectively and no marine works will be conducted in such area, it is
scheduled to remove the silt curtain as below:
|
Silt curtain removal schedule
|
Location of silt curtain removal
|
Date (tentative)
|
|
Stage 1
|
SS1/MES, VS1
|
Q2 of 2023
|
|
Stage 2
|
All reclamation area
|
Q2 of
2023 (Subject to site condition)
|
For more details, please refer to
Appendix C7 – Silt
Curtain Layout for the Perimeter Silt Curtain after completion of reclamation
works.
Silt curtain shall be removed in
accordance with the Silt Curtain Deployment Plan and contract requirement and
subject to obtaining the acceptance from the Project Manager and relevant
authorities including Environmental Protection Department.
%20final%20submission_files/image002.jpg)
%20final%20submission_files/image004.jpg)
%20final%20submission_files/image006.jpg)
%20final%20submission_files/image010.jpg)
%20final%20submission_files/image012.jpg)
%20final%20submission_files/image014.jpg)
%20final%20submission_files/image016.jpg)
%20final%20submission_files/image018.jpg)
%20final%20submission_files/image020.jpg)
%20final%20submission_files/image022.jpg)
%20final%20submission_files/image024.jpg)
%20final%20submission_files/image026.png)
%20final%20submission_files/image030.png)
%20final%20submission_files/image031.png)
%20final%20submission_files/image033.jpg)
%20final%20submission_files/image035.png)
%20final%20submission_files/image037.png)
%20final%20submission_files/image039.png)