Revision Summary

 

Revision Number

Date of Report

Amendment

1

21 May 2018

First submission

2

7 Nov 2018

Updated to include silt curtain arrangement of the DCM trial embankment (at the works area near Tai Ho Wan) and sand filling

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Contents

1.     Introduction. 6

2.     Silt Curtain Deployment Programme. 6

3.     Design of Silt Curtain. 7

4.     Silt Curtain Installation. 7

5.     Operation and Maintenance of Silt Curtain. 8

6.     Removal of Silt Curtain. 9

 

 

 

APPENDIXES

Appendix A. 10

Construction Programme. 10

Appendix B. 12

Design and Job Reference of Silt Curtain. 12

Appendix C. 15

Layout of Silt Curtain. 15

Appendix C1. 16

Localized Silt Curtain Arrangement for Dredge Barge with Closed Grab. 16

Appendix C2. 18

Localized Silt Curtain Arrangement for Derrick Barge with Closed Grab. 18

Appendix C3. 20

Silt Curtain Layout for Protective Silt Curtain before Commencement of Construction Works  20

Appendix C4. 22

Silt Curtain Layout during DCM trial for DCM Trial Embankment (at the works area near Tai Ho Wan) 22

Appendix C5. 24

Silt Curtain Layout during Reclamation Filling for DCM Trial Embankment (at the works area near Tai Ho Wan) 24

Appendix C6. 26

Silt Curtain Layout for the Perimeter Silt Curtain during all Reclamation Works. 26

Appendix D.. 28

Silt Curtain Inspection Checklist 28

Appendix E. 30

Implementation Schedule of the Major Environmental Mitigation Measures. 30


 

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 and Maintenance 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.

 

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.


 

 

 

Appendix A

Construction Programme


 

 

 

Appendix B

Design and Job Reference of Silt Curtain


 

 

 

 

Appendix C

Layout of Silt Curtain

 

 

 

 

 

 

 

 

Appendix C1

Localized Silt Curtain Arrangement for Dredge Barge with Closed Grab

 

 

 

Appendix C2

Localized Silt Curtain Arrangement for Derrick Barge with Closed Grab

 


 

 

 

Appendix C3

Silt Curtain Layout for Protective Silt Curtain before Commencement of Construction Works

 

 

 

Appendix C4

Silt Curtain Layout during DCM Trial for DCM Trial Embankment (at the Works Area Near Tai Ho Wan)

 

 

 

Appendix C5

Silt Curtain Layout during Reclamation Filling for DCM Trial Embankment (at the Works Area Near Tai Ho Wan)

 

 

Appendix C6

Silt Curtain Layout for the Perimeter Silt Curtain during all Reclamation Works

 

 

Appendix D

Silt Curtain Inspection Checklist

 

 

Appendix E

Implementation Schedule of the Major Environmental Mitigation Measures