2. CONSIDERATION OF ALTERNATIVES2-1 2.1 Introduction 2.2

Agreement No. CE 52/2007 (HY) EIA ReportTuen Mun – Chek Lap Kok Link – Investigation Section 2 – Consideration of Alternatives

Report R/48 Issue 3 – August 2009

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2. CONSIDERATION OF ALTERNATIVES..........................................................2-1

2.1 Introduction ..............................................................................................2-1

2.2 Alignment Option Review and Selection ..................................................2-1

2.3 Construction Alternatives.......................................................................2-20



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2. CONSIDERATION OF ALTERNATIVES

2.1 Introduction

2.1.1.1 Several options and alternatives have been considered in the development,refinement and selection of the scheme of the TM-CLKL to be taken forward forenvironmental assessment and preliminary design. This section of the reportprovides the details of the alignment options considered and the constraints andconsiderations assessed in adopting the recommended scheme.

2.1.1.2 In addition, as part of this process, the various construction methodology optionsavailable have been reviewed in order to determine the most effective means ofbuilding the Project. The review has taken into account engineering feasibility,site conditions, programme constraints and environmental considerations.Details of the construction method alternatives are also provided below.

2.2 Alignment Option Review and Selection

2.2.1 Background

2.2.1.1 In 2005, Highways Department (HyD) commissioned an engineering feasibilitystudy (FS), namely Tuen Mun Chek Lap Kok Link and Tuen Mun WesternBypass – Feasibility Study (Agreement No. CE 28/2005 (HY)), to evaluate thetechnical feasibility and impacts of the Project. The FS recommended that theTM-CLKL shall be a dual 2-lane road with a total length of about 9 km with about4 km long submarine tunnel and 5 km long elevated structure.

2.2.1.2 However, the subsequent site selection study for the HKBCF, completed in 2007,proposed to integrate the TM-CLKL southern landfall reclamation with theHKBCF reclamation to the northeast of Chek Lap Kok. This arrangement wasdeemed to provide a cost-effective connection between the two Projects and wasadopted for the TM-CLKL alignment study.

2.2.2 Development of Previous Alignment Options for TM-CLKL

2.2.2.1 In the former FS, the FS Consultants developed and assessed a number ofalignment options for the TM-CLKL. The FS Consultants initially consideredfive alignment options for the main crossing, as shown in Figure 2.1, with threeconnection options at the northern end at Tuen Mun and five connection options atthe southern end at Chek Lap Kok Airport Island / North Lantau, before short-listing two main alignment options, as shown in Figure 2.2, for detailedassessment.

2.2.2.2 Both the above mentioned short-listed options included an artificial island at TaiMo To. Option CLKL-2 comprised an immersed tube (IMT) tunnel between theartificial island and an area of proposed reclamation adjacent to the east side of theTuen Mun River Trade Terminal, whereas Option CLKL-5 comprised an IMTtunnel between the artificial island and an area of proposed reclamation protrudingfrom Butterfly Beach. The toll plaza for the tunnel was proposed to be located onthe artificial island for both options.



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2.2.2.3 Option CLKL-2 would have required the diversion of various submarine utilities,including CLP 132kV power cables, HGC and NWT telecommunication cablesand a China Gas proposed gas main. On the other hand, Option CLKL-5 wouldhave affected Butterfly Beach and Butterfly Beach Park, which in turn would havelikely attracted significant objections from local residents. The FS Consultants,therefore, consulted the concerned utility undertakers, who indicated that thesubmarine cables are for supplying power to the Airport and they have programmefor installing two more sets of 132kV cable from Tuen Mun to the Airport island.From the programming point of view, CLP and NWT advised that they wouldrequire 3 years for the diversion of their cables in order to maintain their servicesat all times during the diversion works. The FS Consultants considered that therequired time duration could be accommodated in the overall implementationprogramme for TM-CLKL. Furthermore, with regard to the cost of the diversionworks, under the license agreement for the submarine utilities, the cost would beborne by the utility undertakers. Apart from the above, Option CLKL-5 wouldhave affected Butterfly Beach and Butterfly Beach Park, which in turn would havelikely attracted significant objections from local residents. Moreover, OptionCLKL-5 would have other adverse impacts: a) vehicular emission from theviaduct section and tunnel portal at Northern Landfall would affect the nearbyASRs along Tuen Mun Area 40 seafront; b) the reclamation area is close to anexisting seawater intake; c) more sediments would be excavated and disposed; d)highly significant landscape and visual impacts resulting from the reclamation tothe residents of seafront premises near Butterfly Beach; e) moderate air and noiseimpacts during the construction stage would affect the nearby residents. The FSConsultants, therefore, recommended Option CLKL-2 as the preferred alignmentoption for TM-CLKL. This alignment formed the base reference scheme in theEIA Study Brief (ESB 175/2007).

2.2.2.4 For the section of the alignment to the south of the artificial island, the alignmentof TM-CLKL depended on the alignment of the HZMB North Lantau HighwayConnection (NLHC). In respect of the NLHC sea viaduct option, the TM-CLKLwould head southwest and connect with NLHC off the southeast coast of ChekLap Kok, while for the NLHC land tunnel option, the TM-CLKL would headsouth, and connect with NLH and the proposed Road P1 at Tai Ho Wan.

2.2.3 Development of HZMB Hong Kong Boundary Crossing Facilities

2.2.3.1 In 2007, HyD commissioned a FS, namely Hong Kong – Zhuhai - Macao BridgeHong Kong Boundary Crossing Facilities Site Selection Study – Feasibility Study(Agreement No. CE 7/2007 (CE)), to identify possible locations and layouts forthe HKBCF. The above FS recommended that the HKBCF be located on an areaof new reclamation off the northeast coast of Chek Lap Kok, as shown in Figure2.3. Furthermore, the FS, also, recommended that the artificial island forsouthern landfall of TM-CLKL should be integrated with the proposedreclamation for the HKBCF, as also shown in Figure 2.3, which in turn affectedthe layout of the preferred alignment option for TM-CLKL recommended underthe FS (Agreement No. 28/2005 (HY)).



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2.2.3.2 The recommendation to locate the HKBCF off the northeast coast of Chek LapKok, also, affected the layout of the NLHC, in so far as the NLHC land tunneloption became obsolete and, at that time, the NLHC sea viaduct option wasredirected to land at the HKBCF (and was also renamed the Hong Kong LinkRoad (HKLR)). The most up to date HKLR alignment comprises a combination ofmarine and land viaduct, tunnel and at-grade road. The HKBCF was linked toNLH by the southern section of TM-CLKL, as shown in Figure 2.3.

2.2.3.3 The development and assessment of the previous alignment options forTM-CLKL, under Agreement No. CE 28/2005 (HY), did not take account of theproposal to locate the HKBCF off the northeast coast of Chek Lap Kok, nor did ittake account of the proposal to integrate the artificial island for TM-CLKL withthe proposed reclamation for the HKBCF. As such, it was necessary for thisAssignment to develop and consider new alignment options which took fullaccount of the HKBCF.

2.2.3.4 Ideas regarding the previous connection options were incorporated into the newalignment options. Furthermore, the previous preferred alignment OptionCLKL-2 which was used to apply for the EIA Study Brief and included in EIAStudy Brief ESB 175/2007 issued in December 2007 was also included in theoption evaluation process under this Assignment in order to reinforce the previousrecommendation under Agreement No. CE 7/2007 (CE) of integrating theartificial island for TM-CLKL with the proposed reclamation for the HKBCF.

2.2.4 Initial Alignment Options

2.2.4.1 The Initial Alignment Options are described below, and comprise two NorthernConnection Options at Tuen Mun, two Southern Connection Options at Lantauand three Main Crossing Options. The options for the north, south and maincrossing are shown on Figures 2.4, 2.5 to 2.5a, and 2.6 respectively.

2.2.4.2 There are quite a number of key constraints that needed to be taken into account indeveloping and assessing the options and these include:

Geological Conditions Across Urmston Road;

Construction Practicality;

Marine Borrow Pits and Mud Disposal Pits;

Contaminated Mud Pit at South of the Brothers;

Requirements of Safe Navigation of Vessels;

Marine Restricted Zones around the Airport Island;

Tuen Mun Immigration and Sham Shui Kok Anchorages;

Existing Submarine Utilities;

Designated Area of North Shore Lantau;

Connection for Hong Kong – Zhuhai – Macao Bridge Hong KongBoundary Crossing Facilities;



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Runways & Associated Airport Height Restriction (AHR);

Sky Pier and the East Fire Rescue Station;

Aeronautical lights (ie. Aviation beacons);

Meteorological Equipment;

Premises at Tuen Mun Area 40;

River Trade Golf at Tuen Mun Area 46;

Fireboat Station and the associated berth at Tuen Mun River TradeTerminal;

Butterfly Beach and Butterfly Beach Park;

Future Tung Chung East and West Developments;

Tuen Mun River Trade Terminal;

Operations of Helicopters;

Airport Development and Facilities;

Developments at North Lantau;

Marine Accesses;

Existing and Proposed Drainage / Sewerage Networks;

Crematorium, Columbarium, Funeral Services Centre in Tuen Mun Area46; and

Existing graves near Tuen Mun Area 46.

Northern Connection Options at Tuen Mun

2.2.4.3 As discussed above, Option CLKL-2 was recommended as the preferredalignment option in the former FS. Therefore, the development of the NorthernConnection Options all focussed on optimising the connections betweenTM-CLKL, TMWB and the local road network and minimising reclamation.Two options, Options N1 and N2 have been evaluated in detail and are shown inFigure 2.4 and described below.

Northern Connection Option N1

2.2.4.4 Option N1 has a permanent reclamation adjacent to Tuen Mun River TradeTerminal to form the northern landfall for the submarine tunnel. From thesubmarine tunnel, this option heads north eastward, passes over the land ofsawmills (2 nos.) and an open space car park under short-term tenancy (STT) onviaduct and crosses over the re-aligned Lung Mun Road. Before connecting to theTMWB, there is a combined toll plaza northeast of the River Trade Golf where atoll plaza has been proposed to allow tolling for travelling solely on TM-CLKL orTMWB or both.



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Northern Connection Option N2

2.2.4.5 Option N2 avoids the sawmills in Tuen Mun Area 40 and the proposedCrematorium, Columbarium, Funeral Services Centre in Tuen Mun Area 46.Permanent reclamation is required east of the sawmills to form the northernlandfall for the submarine tunnel. From the tunnel portal, this option headsnorthward east of Butterfly Beach Laundry and crosses over Lung Mun Road onelevated structure, before turning north eastward and connecting with TMWB. Atoll plaza is proposed on the reclamation.

Southern Connection Options at North Lantau

2.2.4.6 The development of the Southern Connection Options has mainly focussed on theconnections between TM-CLKL, HKBCF and NLH. Two southern connections,a viaduct scheme, Option S1 (as shown in Figure 2.5), and a tunnel scheme,Option S1a (as shown in Figure 2.5a) have been assessed. Both options requirethe realignment of NLH and Cheung Tung Road to accommodate the link roadconnections. They also take account of the latest developments and modificationsto the layout of the HKBCF.

Southern Connection Option S1

2.2.4.7 Option S1 is based on the preferred alignment option recommended in the formerFS, but takes into account of the current recommended scheme for the HKBCF.From the HKBCF, this option heads south eastward on elevated structure acrossthe Tung Chung Navigation Channel and the waters west of the proposedcontaminated mud pits at south of the Brothers, before crossing the AirportExpress Railway and connecting with NLH between the Future Tung Chung EastDevelopment and the proposed Lantau Logistics Park. This option also providesconnection with the HKIA via the connection roads at the HKBCF. This optionmay also connect with the future Lantau Road P1 at Tai Ho Wan.

Southern Connection Option S1a

2.2.4.8 Option S1a is a tunnel option which requires permanent reclamation at thesouth-east side of the proposed HKBCF to form a landfall for the submarinetunnel. From the submarine tunnel, this option, similar to Option S1, heads southeastward towards another landfall located at west of the proposed contaminatedmud pits at south of the Brothers, before crossing the Airport Express Railway andconnecting with NLH between the Future Tung Chung East Development and theproposed Lantau Logistics Park.

2.2.4.9 Similar to Option S1, this option also provides connection with the HKIA via theconnection roads of the HKBCF and future Lantau Road P1.



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Main Crossing Options

2.2.4.10 The three Main Crossing Options presented below utilise the space between TaiMo To, the HKBCF and Chek Lap Kok. They also take account of the latestdevelopments and modifications to the layout of the HKBCF. The three optionsall comprise a submarine tunnel assumed for the EIA to be constructed by tunnelboring machine (TBM) method as opposed to an immersed tube (IMT) tunnel.The engineering and environmental advantages of the TBM solution compared toan IMT tunnel is described in Section 2.3.1 below. An overview of the MainCrossing Options is shown in Figure 2.6.

Main Crossing Option M1

2.2.4.11 Option M1 is based on the recommended alignment option recommended in theformer FS, but takes account of the current recommended scheme for the HKBCF.From the HKBCF, this option heads north eastward across the waters between theHKBCF and Tai Mo To on elevated structure, before passing onto an area ofreclamation adjacent to Tai Mo To that forms the Southern Landfall for the mainsubmarine tunnel crossing. From this landfall, the submarine tunnel heads northwestward crossing the proposed sand borrow area and passing under UrmstonRoad.

2.2.4.12 Option M1 can connect with any of the Northern Connection Options and any ofthe Southern Connection Options described above. Therefore, the toll plaza ofTM-CLKL may be located either at Tai Mo To or Tuen Mun for this particularoption.


2.2.4.13 Option M3 follows the recommended scheme of the HKBCF FS, except that thetoll plaza is located in Tuen Mun. From the HKBCF, this option heads northwardin submarine tunnel under the waters west of Tai Mo To, before crossing theproposed sand borrow area and passing under Urmston Road. The SouthernLandfall comprises an area of reclamation combined with the reclamation for theHKBCF alongside the eastern edge of the HKBCF.

2.2.4.14 Similar to Option M1, Option M3 can connect with any of the NorthernConnection Options and any of the Southern Connection Options described above.


2.2.4.15 Option M4 follows the option recommended in the HKBCF FS, except the tollplaza is located in Tuen Mun. The HKBCF FS recommended that such optionshould be considered in the subsequent investigation assignment, hence OptionM4 is included in this evaluation. From the HKBCF, this option headsnorthward in submarine tunnel under the waters northeast of Chek Lap Kok,before passing under Urmston Road. The Southern Landfall comprises an area ofreclamation combined with the reclamation for the HKBCF alongside the westernedge of the HKBCF. This option affects the proposed sand borrow area the least.



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It also provides direct connections with HKIA. The route to the SouthernConnection Options requires a longer detour across the HKBCF. Similar toOptions M1 and M3, Option M4 can connect with any of the Northern ConnectionOptions and any of the Southern Connection Options described above.

2.2.5 Detailed Evaluation Methodology

2.2.5.1 In order to fully evaluate the Initial Alignment Options for TM-CLKL describedabove with a view to identifying the Recommended Scheme to be taken forwardto the subsequent preliminary design and impact assessments, etc, a comparativeassessment was undertaken. The comparison comprised a preliminary desk-topassessment and was undertaken based upon the following criteria sets, which werealso divided into sub-sets as required:

(i) Transport and Operation Planning;

(ii) Marine Impact;

(iii) Engineering;

(iv) Environmental Impacts;

(v) Planning and Lands Issues; and

(vi) Public Perception.

2.2.5.2 The environmental impacts criteria were further divided as per Table 2.1 below:

Table 2.1 Detailed Environmental Evaluation Criteria

Environmental Parameter Rating Principle

Air quality and noise impactOptions with less potential noise and air qualityimpacts during both the construction and operationphases will be rated higher.

Water qualityOptions causing less impact on water quality andhydrodynamics during the construction andoperation phases will be rated higher.

Ecology and fisheries

Options causing less effect on the Chinese WhiteDolphin and its habitat and less potential impact tofisheries and other marine and terrestrial ecologyresources during the construction and operationphases will be rated higher.

Waste managementOptions which generate smaller amounts of disposalmaterials and maximise the use of public fill forconstruction/reclamation works will be rated higher.

Landscape and visualOptions which result in less landscape and visualimpacts during the construction and operationstages will be rated higher.



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2.2.5.3 Each of the main criteria groups were weighed to reflect their relative importanceand each option assessed, compared and ranked from these different perspectives.The robustness of the detailed evaluation exercise and selection of theRecommended Scheme was subjected to sensitivity testing.

2.2.5.4 The environmental assessment of the initial alignment options are presentedbelow.

2.2.6 Environmental Assessment of the Initial Alignment Options

Northern Connection Options

Air Quality and Noise Impacts

2.2.6.1 Two of the northern options land in the industrial area between the River TradeTerminal and Butterfly Beach. The closest residential properties are located atButterfly Estate to the east and are more than 1km away from the proposedoptions. The buildings in the vicinity of the landings comprise industrial andoffice facilities which will be sensitive to air quality impacts but not noise. Assuch, construction and operational noise impacts for the schemes will not presentto be an issue.

2.2.6.2 The key air sensitive receivers in the area are clustered at the west end of theindustrial area north of the River Trade Terminal (RTT). These sensitivereceivers are relevant to all the northern alignment options and have the potentialto be subject to construction impacts and vehicular emissions during theoperational phase.

2.2.6.3 Option N1 would comprise a large reclamation adjacent to the RTT and then anelevated viaduct section towards the toll plaza and Lung Mun Road connection.In terms of construction impacts, the majority of the works would be marine basedand the works for the viaduct piers which are close to the ASRs will be relativelyminor. However, the road alignment under this option comes out of tunnelcloser to the RTT and the other ASRs than the other option and as such the tunnelportal, ventilation building and the viaduct connection have the potential forgreater impacts, particularly the Pillar Point Fire Station and Fire Boat Station.The combined toll plaza, with its higher emissions from slow moving and idlingvehicles, would also be close to the Butterfly Beach Laundry. Overall, OptionN1 was ranked “Fair” for Air Quality and Noise.

2.2.6.4 Option N2 is similar to Option N1 in that it would comprise a reclamation area forthe tunnel portal and a viaduct section heads northwards and to the east ofButterfly Beach Laundry, crossing over Lung Mun Road on elevated structure,before turning north eastward and connecting with TMWB. While thisalignment would be closer to Butterfly Beach and the high density residential areaof south Tuen Mun, these properties would still be over about 1km away and notASRs for this project. However, as this alignment makes landfall at the easternend of the industrial strip, the majority of the ASRs potentially affected by OptionN1, are also more than 500m away from the portal and viaduct section. The key



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ASR is the Butterfly Beach Laundry, although the proposed toll plaza would beslightly further away in this option as it is located in the reclamation. While thepotential impacts are the same, given the increased distance from the ASRs,Option N2 was ranked higher for Air Quality and Noise as “Good”.

Water Quality

2.2.6.5 In respect of water quality impacts, the key issue for the northern landing optionsis the need for and size of any reclamation. Both options comprise relativelysimilar levels of reclamation, with Option N1 comprising 16.5ha and Option N2comprising 19.1ha.

2.2.6.6 Option N1 presents a reclamation which has been reduced in size when comparedwith Option N2 as the toll plaza is proposed to be located on land and not on thereclaimed land. The alignment would also be shifted westwards closer to theRTT reclamation so as to minimise the land reclamation needed. Reducing thesize of the reclamation is preferable from a construction impact perspective(reduced dredging and quantities of waste sediment generated) and also reducesdirect loss of ecological habitat. Operationally, the elongated reclamation wouldprotrude slightly outside of the 10m depth contour but somewhat in the wake ofthe RTT. As such, while significant effects on tidal flows and large scale waterquality are unlikely, localised acceleration in the flows at the end of thereclamation could occur. The reclamation, however, could also affect wave actionon Butterfly Beach which might have a knock-on effect with respect to thecleanliness of the beach and siltation. There would also be the opportunity for theaccumulation of floating debris in the niche between the new reclamation and theRTT. Based upon this above, Option N1 was ranked “Fair” for Water Quality.

2.2.6.7 Option N2 would have a larger reclamation overall due to the location of the tollplaza in this area. This larger size means that, irrespective of the TBM tunnelconstruction, greater dredging and seabed disturbance would occur for Option N2as compared to Option N1. In terms of flows, as with Option N1, there could besome acceleration in the flows at the end of the reclamation, although large scalewater quality impacts are unlikely to be affected. Unlike Option N1, however,Option N2 would create a large embayed area between the reclamation and theRTT and floating debris and local water flushing could be a problem. Thereclamation could also affect wave action on Butterfly Beach which might have aknock-on effect with respect to the cleanliness of the beach and siltation. Due tothe potential for slightly larger impacts on Water Quality, Option N2 was ranked“Poor”.

Ecology and Fisheries

2.2.6.8 In terms of the marine environment, several important ecology sensitive receiversare present within the broad study area. These include sites of conservationimportance (e.g., the Sha Chau and Lung Kwu Chau Marine Park), importanthabitats (e.g., prime habitat for the Chinese White Dolphin) and several species ofconservation interests (e.g., horseshoe crabs at Lung Kwu Tan). Butterfly Beach isalso just over a kilometre away and the area is a key location for the fishing



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industry, although direct impacts to the highly mobile fish resources would not beexpected. Options which disturb the marine environment have the potential toimpact the water quality and ecological sensitive receivers in the area. As such,options which would require reclamation could result in construction impactsassociated with dredging and also operational impacts associated withobstructions to tidal flows (and secondary effects therefore on water quality andmarine ecology) and direct loss of seabed habitat.

2.2.6.9 The terrestrial environment of the Tuen Mun landing area is mostly disturbedurbanised area (heavy / special industrial use) or contains habitats of relativelylow ecological values (e.g., plantation woodland and fire-disturbed grassland).These habitats are unlikely to support significant species of ecological concern.The main area of ecological value comprises the Siu Lang Shui SSSI butterfliesoverwintering site but this is some distance (~1.7km) northwest of the landingarea.

2.2.6.10 Both Options N1 and N2 would require permanent reclamation works for thetunnel portal and, in respect of Option N2, the toll plaza as well. These marineworks have the potential to cause marine ecological impacts during both theconstruction and operational stages. The land works for both options would belocated in already disturbed areas dominated by disturbed areas, currentlyoccupied by the River Trade Golf, and of low ecological value. The marineworks for Option N2 would be larger than for Option N1 increasing the potentialfor impacts and also resulting in more direct seabed loss. In addition, thereclamation for Option N2 would be located close to Butterfly Beach potentiallyaffecting the ecology in this area. As such, Option N1 was ranked “Fair” andOption N2 ranked “Poor”.

Waste Management

2.2.6.11 As mentioned above, all the northern options land just east of the RTT in a largelydeveloped area with industrial land use. Based upon the land use in this area,there is potential for contaminated land issues which could affect Options N1 andN2.

2.2.6.12 Both Options N1 and N2 all pass through the potentially contaminated landassociated with the works areas adjacent to the coast on viaduct and whilequantities would be relatively small and likely to restricted to surface deposits,this material would need to be managed carefully to avoid secondary impacts.Both options would require marine sediment removal as part of the works to formthe reclamations. The approximate amount of material to be dredged would be1.46Mm3 and 1.71Mm3 (bulk volume with 30% bulk factor) for Options N1 andN2 respectively. While the quantity of sediment is higher for Option N2 giventhe larger reclamation works, this option has less land excavation works thanOption N1 as the toll plaza is located in the reclaimed land. On balance, bothoptions were deemed to be similar and based upon the amount of marine dredgedmaterial generated by each and the potential for interface with contaminated land,both were ranked “Poor” for waste management.



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Landscape and Visual

2.2.6.13 Under Option N1, the sources of landscape and visual impacts will include thereclamation works (16.5ha) at seafront near RTT and the toll plaza at the site ofRiver Trade Golf. The proposed works will cause permanent loss of 16.5haseawater body near Pillar Point and the impact is considered as substantial. Theproposed works will cause permanent loss of the temporary River Trade Golfwithin the planned Crematorium, Columbarium, Funeral Services Centre and openspace. However, as the River Trade Golf is under STT, its sensitivity is consideredas medium. Therefore, the impact on River Trade Golf is moderate. Besides,proposed works will slightly affect nearby urbanized vegetation and planting. Theproposed works will moderately affect an inshore water landscape near PillarPoint; and would slightly affect Pillar Point miscellaneous urban fringe landscapeand Pillar Point industrial urban landscape. The proposed works will be visible tosmall populations of workers near RTT (closest viewing distance: close to 100m),high populations of recreational users at Butterfly Beach (closest viewing distance:close to 1.5km) and high populations of residents at Butterfly Estate and nearbyestates (closest viewing distance: close to 1.5km). Given the relatively longviewing distance (1.5km) of the recreational and residential VSRs, it is consideredthat the visual impact is moderate. Based on the moderate to substantial landscapeimpacts and moderate visual impacts, Options N1 was ranked “Poor”.

2.2.6.14 In terms of Option N2, the sources of landscape and visual impacts would includereclamation works (19.1ha) and the tunnel portal for the northern landing pointconnecting to the proposed TMWB at the seafront near the RTT. The proposedworks would cause permanent loss of 19.1ha seawater body near Pillar Point andthe impact is considered as substantial. The proposed works would moderatelyaffect landscape resources of nearby urbanized vegetation and planting. Theproposed works would moderately affect and inshore water landscape near PillarPoint; and would slightly affect Pillar Point miscellaneous urban fringe landscapeand Pillar Point industrial urban landscape. The proposed works would also bevisible to small populations of workers near RTT (closest viewing distance: closeto 200m), high populations of recreational users at Butterfly Beach (closestviewing distance: close to 1km) and high populations of residents at ButterflyEstate and nearby estates (closest viewing distance: close to 1km). Given thelarge scale of proposed work and medium viewing distance (1km), the visualimpact would be considered to be substantial. Based on the substantial landscapeand visual impacts, Options N2 was, also, ranked “Poor”.

2.2.6.15 Based on the above, the Northern Connection Options were scored for theEnvironmental Impacts criteria set as summarised in Table 2.2 below.



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Table 2.2 Northern Connection Options Scores – Environmental Impacts

OptionSub-Criterion

N1 N2

Air quality and noise impact 60 80

Water quality 60 40

Ecology and fishery 60 40

Waste management 40 40

Landscape and visual 40 40

2.2.6.16 Environmentally, Option N1 resulted in the higher score of the two options.Option N1 is also the more favourable option after taking into account otherparameters including traffic performance and impact, operation and maintenanceissues, construction practicability and safety and cost and programme.

Southern Connection Options

Air Quality and Noise Impact

2.2.6.17 There are two possible options on the south, Options S1 and S1a, the formercomprising a viaduct landing at Tai Ho Wan and the latter a tunnel option thatmakes landfalls adjacent to Tai Ho Wan and the south-east of proposed HKBCFtogether a viaduct landing at Tai Ho Wan. In terms of existing sensitivereceivers, both areas are generally unpopulated but with some village housespresent at Pak Mong Village on the western edge of Tai Ho Wan. Theresidential area of Tung Chung new town is about 2km from the viaductalignment and the closest slip road connections associated with both options.Both options have the potential to affect future development at the potentialLantau Logistics Park, possible Lantau Logistics Park Extension or othercompatible uses and the proposed Future Tung Chung East Development becauseof the viaduct.

2.2.6.18 The potential sources of noise and air impacts for Option S1 would be from theopen section of the southern viaduct and would be an issue for the villagers at PakMong and the future sensitive receivers in the Future Tung Chung EastDevelopment and the potential Lantau Logistics Park, although the number ofsensitive receivers is likely to be small and the additional impacts given thebackground of the NLH are not expected to be significant. Construction phaseimpacts on the villagers at Pak Mong, some 500m away, are also not expected tobe significant given the baseline environment. As such, Option S1 was ranked“Good”.

2.2.6.19 In terms of Option S1a, the alignment is largely in tunnel, the only potentiallyaffected area is at Siu Ho Wan which is close to the portal and where the tunnelventilation building will be located and also the connecting slip roads. Theconcentrated pollutant emissions from the tunnel ventilation could have the effect



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of contributing to the overall air pollution in the area but this should be balancedagainst the fact that there are no air and noise sensitive receivers present in thetunnel portal area. Another potential sources of noise and air impacts for OptionS1a would be from the open section of the southern viaduct and would also be anissue for the villagers at Pak Mong and the future sensitive receivers in the FutureTung Chung East Development and the potential Lantau Logistics Park, althoughthe number of sensitive receivers is likely to be small and the additional impactsgiven the background of the NLH are not expected to be significant. Constructionphase impacts on the villagers at Pak Mong, some 500m away, are also notexpected to be significant given the baseline environment. Therefore, Option S1awas also ranked “Good”.

Water Quality

2.2.6.20 Option S1 presents the scheme recommended by the Feasibility Study andconsists of a viaduct section between the TM-CLKL tunnel portal/HKBCF and theconnection with the North Lantau Highway. However, the spans of the bridgeswould be at least 60m and less than 50 piers would be expected. However, theviaduct spans over the main navigation channel where the water depth is deeperand flows stronger and the piers would, therefore, be located in an area of lowwater speeds. As such, no significant effects on tidal flows would be expectedfrom the bridge piers. There would be the potential for some constructionimpacts during dredging for the piers, however, the works would be relativelyminor and temporary, with only 0.03Mm3 (bulk volume with 30% bulk factor)being dredged. On this basis, Option S1 was ranked as “Good” for WaterQuality.

2.2.6.21 For Option S1a, part of the viaduct of Option S1 is replaced with the IMT tunnelwhich is about 1.4km long. Operationally, as the tunnel requires reclamations(totally about 14.0ha) at either end of the alignment for the tunnel portals, thisoption will effectively form a barrier across the Tung Chung Bay, with only asmall channel left open in between the 2 reclamations. It would be predicted,therefore, to have significant effects on the hydrology of the area and the flushingof the Tung Chung Bay and Airport Channel. There would also be direct seabedand habitat loss as a result of the reclamations. During construction, this optioncould create potentially greater construction impacts due to substantially increaseddredging works close to Tai Ho Wan, the San Tau Beach SSSI in Tung ChungBay and the horseshoe crab habitats. A quantity of 0.6Mm3 of sediment wouldbe expected to be dredged for the IMT tunnel and the reclamation. Therefore,during construction, there would be seabed disturbance and water quality issueswhich could, importantly, affect the Tai Ho Wan flushing culvert. Based uponthe potential water quality impacts during both the operational and constructionstages, Option S1a was ranked “Very Poor” for Water Quality.


2.2.6.22 Ecologically, the area contains many ecologically sensitive receivers. Tai HoWan represents a sensitive ecological resource, comprising the Tai Ho StreamSSSI, mangroves and seagrass stands, numerous fish species and the brown fish



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owl has been noted in this area. Intertidally, mangroves, seagrass and horseshoecrabs are located in Tung Chung Bay and the San Tau Beach SSSI to the west ofthe proposed alignments. The terrestrial ecology of the area close to the NorthLantau Highway and other developments is low and the areas generally disturbed.However, further up the hillside, natural woodland, grassland and shrublandhabitats exist and the boundary of the North Lantau Country Park is within about200m of the NLH corridor.

2.2.6.23 The land connection of Option S1 occurs at Tai Ho Wan, with elevated slip roadsdirectly connecting with the North Lantau Highway in the transport corridor. Assuch, there are not expected to be any impacts on the sensitive Tai Ho Wan, norany significant vegetation removal as a result of this option. While there wouldbe construction noise impacts which in some settings could cause disturbance towildlife, given the existing noise from the NLH and AEL, the temporaryconstruction impacts would not be expected to be significant. There would besome disturbance to the seadbed and a relatively small loss of marine habitat as aresult of the pier construction. Generally, the potential impacts to both marineand terrestrial ecology would be expected to be small and therefore, Option S1was ranked “Good”.

2.2.6.24 Option S1a would require an IMT tunnel which would need dredging andpermanent reclamations at either end of the alignment and as such, this optionwould have greater disturbance to the marine environment and the potential fortemporary impacts at least to Tai Ho Wan (via the flushing culvert), Tung Chungand the horseshoe crab habitats. Notwithstanding the permanent habitat losses,while the habitats temporarily disturbed would be expected to regenerate in time,this could take up about 3-5 years. Terrestrially, Option S1a would be the sameas Option S1 with the slip roads connecting directly with the North LantauHighway in the transport corridor and, therefore, avoids Tai Ho Wan and thevegetated hillside. Based upon the potential marine impacts, Option S1a wasconsidered less preferable than Option S1 from an ecology perspective and ranked“Poor”.

Waste Management

2.2.6.25 Waste management issues for Option S1 would be relatively minor and limited tothe dredging for the viaduct piers and the excavation in the transport corridors toaccommodate the new slip roads. The amount of marine sediment to be removedwould be in the region of 0.03Mm3 (bulk volume with 30% bulk factor). Thesmall amounts of the sediment would not be expected to be contaminated and torequire disposal in confined disposal mud pits. As such, Option S1 was ranked“Good”.

2.2.6.26 Option S1a would generate substantially more material, largely in the form ofdredged sediment for the IMT tunnel and reclamations. The sediment generatedwould be a quantity of 0.6Mm3 (bulk volume with 30% bulk factor). Based uponthis, Option S1a was ranked “Poor”.



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2.2.6.27 In terms of Option S1, the sources of landscape and visual impacts would includethe sea viaduct in open seascape from the south portal on the proposed HKBCF tothe Southern Connection and the viaduct. These would substantially affect theseawater body north of Tai Ho Wan, moderately affect the roadside planting alongNorth Lantau Highway and slightly affect the vegetation at Tai Ho and Pak Mong.The affected landscape character areas would include inshore water landscapesnear Tai Ho and the North Lantau transportation corridor landscape. The proposedworks would be mainly visible to high populations of visitor and workers of theHKIA (closest viewing distance: close to 1.8 km), high populations of residents atTung Chung New Town (closest viewing distance: close to 1.8km), lowpopulations of residents of Tai Ho (closest viewing distance: close to 400m), highpopulations of users of North Lantau Highway (closest viewing distance: close to10m), medium populations of hikers in country parks in North Lantau (closestviewing distance: close to 800m), the proposed Lantau Logistics Park (closestviewing distance: close to 800m), possible LLP Extension or other compatibleuses (closest viewing distance: close to 700m) and the Future Tung Chung EastDevelopment (closest viewing distance: close to 250m). Mitigation measuresthat would likely be required would include minimised construction area, the useof appropriate (visually unobtrusive and non-reflective) building materials andcolours in built structures and screen planting. With the implementation ofmitigation measures, the view would still be changed from an open seaview topartial blockage. Therefore, it is considered that the visual impact on differentVSRs is moderate to moderate/substantial. Based on the moderate landscapeimpacts and moderate to moderate/substantial visual impacts, Option S1 wasranked “Fair”.

2.2.6.28 For Option S1a, the alignment would largely be in tunnel and, as such, the sourcesof landscape and visual impacts would be restricted to the portals at the HKBCFand the Southern Connection and also a short section of viaducts connection toNLH. These would substantially affect the seawater body north of Tai Ho Wan,moderately affect the roadside planting along NLH and slightly affect thevegetation at Tai Ho and Pak Mong. The affected landscape character areas wouldinclude inshore water landscapes near Tai Ho and the North Lantau transportationcorridor landscape. The proposed works would be mainly visible to highpopulations of visitor and workers of the HKIA (closest viewing distance: close to1.8 km),low populations of residents of Tai Ho (closest viewing distance: close to400m), high populations of users of North Lantau Highway (closest viewingdistance:close to 10m), medium populations of hikers in country parks in NorthLantau (closest viewing distance: close to 800m), the proposed Lantau LogisticsPark (closest viewing distance: close to 800m), possible LLP Extension or othercompatible uses (closest viewing distance: close to 700m) and the Future TungChung East Development (closest viewing distance: close to 250m). Therewould be another permanently loss of about 14.0ha seawater body in between theHKBCF and Tai Ho Wan. Mitigation measures that would likely be requiredwould include minimised construction area, the use of appropriate (visuallyunobtrusive and non-reflective) building materials and colours in built structures,



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planting above the portals and screen planting along the Lantau Highway. Basedon the substantial landscape impacts and moderate visual impacts, Option S1a wasranked “Poor”.

2.2.6.29 Environmentally, Option S1 was preferred as it would potentially cause lessimpact on the marine environment and generate less waste. Option S1 was, also,the more favourable when taking into account all other parameters, being rankedsignificantly better for transport and operation planning, planning and land issuesand engineering.

Main Crossing Options

Air Quality and Noise Impact

2.2.6.30 All three main crossing alignments would comprise long tunnels for the majorityof their lengths and are only in the open when they connect to the HKBCF and tothe north portal. In addition, there are no air or noise sensitive receivers in thevicinity of the alignments. As such, air quality and noise impacts are not a keyissue for these main crossings, given that the dominant factor will be the HKBCFitself. However, all options would require a ventilation building at each end ofthe tunnel, which would contribute to the air pollution in the broad study area.On balance, all options were considered to be equal and were ranked “Good”.

Water Quality

2.2.6.31 The Main Crossing Option M1 is similar to the alignment recommended by theprevious FS Study and included in the EIA Study Brief and would comprises asmall reclamation of about 13.7ha at Tai Mo To for the tunnel portal. Thealignment would then connect to a further reclamation area of about 14.6haconnected to the HKBCF via a small stretch of viaduct which would cross an areaof stronger flows. As the tunnel would be constructed by TBM, no dredging ordisturbance to the seabed is required and, as will be the case for the other twooptions also, therefore, will not cause any water quality impacts during either theconstruction or operational stages. In addition, given that the Option M1reclamation would be located in relatively shallow water adjacent to the Brothers,no significant impacts on local tidal flows or the flows in Tung Chung Bay wouldbe anticipated from this reclamation on its own, with the HKBCF reclamationbeing the dominant factor. However, the mud depth in this area is thicker andthis would result in increased dredging. The amount of material to be removedfor the purposes of the reclamation at Tai Mo To would be about 3.0Mm3.

2.2.6.32 In total, Option M1 would require 28.3ha of reclamation to accommodate thetunnel portals and connections roads, in addition to an extra stretch of viaduct.While no effects on the overall flows in the area would be expected from OptionM1 works, given that the HKBCF will be dominant, it would cause more seabedloss and disturbance than the other options and as such, was ranked “Poor”.



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2.2.6.33 The second Main Crossing Option M3 would have the reclamation connected tothe HKBCF on the eastern side and, therefore, would avoid the need for a separatetunnel landing reclamation. The area of reclamation needed for Option M3would be 19.1ha. Given its size, the HKBCF reclamation would likely affect thetidal flows in the study area and along the North Lantau coastline and couldpossibly increase flows through the Airport sea channel leading to increasederosion which could affect the seagrasses and mangroves in Tung Chung Bay.However, the contribution of the main combined TM-CLKL reclamation forOption M3 would be unlikely to increase the magnitude of any HKBCF impactsand could present a net decrease in construction impacts than if the reclamationswere constructed and operated separately as with Option M1. However, in thedesign assessed, in order to accommodate an alignment gradient of 5% as it exitsfrom the tunnel to the portal, an elongated nib of reclamation would be required tothe north. As this nib extends to the 10m contour, it would have a possiblysignificant impact on flows between Chek Lap Kok and Tai Mo To and possiblycause a redistribution of the larger scale flows.

2.2.6.34 Based upon this, while the area of reclamation as compared to Option M1 wouldbe smaller and as such construction phase impacts would be less, given thepotential operational implications of the nib, Option M3 was also ranked “Poor”.

2.2.6.35 Main Crossing Option M4 would be similar to Option M3 but assumes that theconnection with the HKBCF would be made on the west instead of the east. Thesize of the reclamation needed and the need for a nib would be comparable toOption M3 and as such the predicted construction and operational impacts wouldalso be expected to be about the same. Based on this, Option M4 was ranked thesame as Option M3 at “Poor”.


2.2.6.36 The location of the main crossing options contains important ecological sensitivereceivers including habitats and species of conservation importance. TheChinese White Dolphin (CWD) is the single most important species in the studyarea and the one that has the potential to be impacted, both by the TM-CLKL andcumulatively. The proposed alignments of the main crossing options would bewithin the prime habitat for the local population of CWD. The potentialdisturbance and habitat degradation/destruction could represent a significant threatto the long-term sustainability of this species and options which minimisepotential impacts on this species were favoured.

2.2.6.37 The area is also a fishing ground and protection of other species includinghorseshoe crabs, which are occasionally found close the Brothers, and corals ofwhich some have been noted in the area, were also an issue when comparing theoptions. As such, while all options require reclamation of about the same size,the method of construction will have a notable effect on the potential impacts tothe marine environment and options which can reduce the amount of dredgingrequired will be preferable.



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2.2.6.38 Besides the 14.6ha reclamation attached to the HKBCF, Option M1 would alsohave an extra area of reclamation for the tunnel portal at Tai Mo To which wouldincrease the direct habitat loss by 13.7ha for marine ecology and fisheries. Inaddition, the area around the Brothers has increased in importance for the CWD inrecent years and is currently highly utilised by this key species. As mentionedabove the area around The Brothers is also habitat for horseshoe crabs andoccasional corals. As such, construction impacts and direct loss of habitat in thisarea would be of concern and this option was ranked “Very Poor” accordingly.

2.2.6.39 Main Crossing Options M3 and M4 would be very similar. Both reclamationconnect to the HKBCF and would be away from the CWD habitat at The Brothers.While there would be direct habitat loss and construction impacts, the effects oncorals and benthos would be similar for both the options and less than for OptionM1. As such, both Options M3 and M4 were ranked “Fair” from an ecologyperspective.

Waste Management

2.2.6.40 All three main crossings would comprise a long tunnel formed by TBM. Thelengths of the tunnels would vary slightly. Due to the different lengths, theamount of material generated by each would be about 1.09Mm3 for Option M1,1.48Mm3 for Option M3 and 1.39Mm3 for Option M4 in bulk volume with 30%bulk factor.

2.2.6.41 For the reuse of excavated alluvium, it is necessary to use a slurry treatment plant(STP) to separate the slurry and the alluvium generated from the TBM tunnellingand then the alluvium could be used as public fill. On the basis of the similaramount of waste that would be generated, Options M1, M3 and M4 were allclassed as “Fair”.


2.2.6.42 In terms of Main Crossing Option M1, the sources of landscape and visualimpacts would include reclamation works at Tai Mo To and the sea viaduct to/from the airport and HKBCF. The proposed works would cause a permanentchange to the island landscape of Tai Mo To and permanent loss of the inshorewater landscape near Tai Mo To which is of high sensitivity. Therefore,landscape impacts would be considered to be substantial. The proposed workswould be mainly visible to high populations of visitors and workers at the HKIA(closest viewing distance: 2.8km), high populations of residents at Tung ChungNew Town (closest viewing distance: 4km), high populations of residents at TuenMun (closest viewing distance: 4.4km), the proposed Lantau Logistics Park(closest viewing distance: close to 2.8km), possible LLP Extension or othercompatible uses (closest viewing distance: close to 2.7km) and the Future TungChung East Development (closest viewing distance: close to 3.5km). Mitigationmeasures that would likely be required would include minimised construction area,the use of appropriate (visually unobtrusive and non-reflective) building materialsand colours in built structures and screen planting. With the implementation ofmitigation measures, the view would still be changed from an open seaview to



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partial blockage by the marine viaduct. Therefore, the visual impact would beconsidered as moderate to substantial. Based on the substantial landscape andmoderate to substantial visual impacts and the permanent change of Tai Mo Toisland landscape, Option M1 was ranked “Very Poor”.

2.2.6.43 For Option M3, the sources of landscape and visual impacts would includereclamation works at HKBCF. The proposed works would cause permanent lossof the seawater body near HKBCF which is of high sensitivity. Therefore, it wasconsidered that the landscape impact would be substantial. The proposed workswould be mainly visible to high populations of visitor and workers of the HKIA(closest viewing distance: 2km), high populations of residents at Tung ChungNew Town (closest viewing distance: 4km), high populations of residents at TuenMun (closest viewing distance: 6km), the proposed Lantau Logistics Park (closestviewing distance: close to 2km), possible LLP Extension or other compatible uses(closest viewing distance: close to 1.9km) and the Future Tung Chung EastDevelopment (closest viewing distance: close to 2km). Mitigation measures thatwould likely be required would include minimised construction area, the use ofappropriate (visually unobtrusive and non-reflective) building materials andcolours in built structures and screen planting. With the implementation ofmitigation measures, the visual impact would be considered as insubstantial toslight. Based on the substantial landscape and insubstantial to slight visual impacts,Option M3 was ranked “Fair”.

2.2.6.44 The sources of landscape and visual impacts for Main Cross Option M4 wouldinclude reclamation works at HKBCF. The proposed works would causepermanent loss of the seawater body between the HKBCF and the HKIA which isof high sensitivity. Therefore, it is considered that the landscape impacts would besubstantial. The proposed works would be mainly visible to high populations ofvisitor and workers of the HKIA (closest viewing distance: 20m), highpopulations of residents at the Tung Chung New Town (closest viewing distance:2km), high populations of residents at Tuen Mun (closest viewing distance: 6km),possible LLP Extension or other compatible uses (closest viewing distance: closeto 2.3km) and the Future Tung Chung East Development (closest viewing distance:close to 2.4km). Mitigation measures that would likely be required wouldinclude minimised construction area, the use of appropriate (visually unobtrusiveand non-reflective) building materials and colours in built structures and screenplanting. With the implementation of mitigation measures, the view would still bechanged from open seaview to partial blockage by the marine viaduct. Therefore,the visual impact is considered as moderate to substantial. Based on thesubstantial landscape and moderate to substantial visual impacts, Option M4 wasranked “Poor”.

2.2.6.45 Based on the above, the Main Crossing Options were scored for theEnvironmental Impacts criteria set as summarised in Table 2.4 below.



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Table 2.4 Main Crossing Options Scores – Environmental Impacts

OptionSub-Criterion

M1 M3 M4

Air quality and noise impact 80 80 80

Water quality 40 40 40

Ecology and fishery 20 60 60

Waste management 60 60 60

Landscape and visual 20 60 40

2.2.6.46 Options M3 and M4 were ranked better than Option M1 environmentally, largelybecause of the need for the second reclamation at Tai Mo To for Option M1 whichincreased construction and operational marine impacts. The overall weightedscores for all parameters favour Main Crossing Option M3 which was preferableon the basis of engineering programme, transport connectivity and trafficperformance and impact.

2.2.7 Alignment Selection

2.2.7.1 Following the detailed evaluation of the alignment options based on all the criteriadetailed in Section 2.2.5 above, the highest rankings are given to NorthernConnection Option N1, Southern Connection Option S1 and Main CrossingOption M3 in the base assessment. This overall conclusion did not conflict withthe results of the environmental assessment, the environmentally preferredalignment being a combination of Option N1, Option S1 and Option M3.

2.2.7.2 In order to test the robustness of the detailed evaluation, sensitivity tests wereundertaken based upon one relevant criteria set having its overall weightingboosted by 50% (multiplier 1.5) or by 100% (multiplier 2.0). In both cases, thehighest scores remained for Option N1, Option S1 and Option M3 and were,therefore, consistent with the overall conclusion.

2.2.7.3 Thus, according to the outcome of the option assessment and the associatedsensitivity tests, combined alignment N1, S1 and M3 was selected as therecommended option for further assessment under the Assignment.

2.3 Construction Alternatives

2.3.1 Tunnel Construction

2.3.1.1 The key options for constructing the main tunnel connecting the northern landfallat Tuen Mun and the southern landfall at the HKBCF are either by tunnel boringmachine (TBM) or immersed tube (IMT) tunnel.



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TBM

2.3.1.2 Based on the internal traffic envelope and ventilation requirements, the twin boredTBM tunnels is envisaged to have an external diameter of approximate 14.0m.The tunnels will be constructed in parallel configuration with a typical separationof about one times the diameter of the tunnel or 14.0m.

2.3.1.3 The twin bored tunnel of external diameter of approximate 14.0m with centralseparation of about 14.0m will be constructed by Tunnel Boring Machine (TBM)launched from Tuen Mun side and retrieved from reclamation beside the HKBCF.Cross passages connecting the twin tunnels will be provided at regular intervals.Generally ground freezing method will be employed for the cross passageconstruction.

2.3.1.4 The TBM moves forward as it excavates the tunnel by extending the pushingjacks at the back. When the advancement of the machine reaches distance of thelength of a ring, the excavation stops and the pushing jacks are retrieved, aconcrete circular ring in form of a numbers of segments were then put together atthe tail of the shield. The pushing arms are once again extended in full contactwith the concrete ring just erected and excavation is resumed. The cycle ofexcavation and ring erection is repeated as the TBM is advanced to form the liningof the tunnel.

2.3.1.5 The TBM tunnel would require the extension of the northern and southern landfallreclamations in order to provide the necessary tunnel cover as the tunnel ascendsto the portals. In order to provide safe tunnel construction by TBM, soil cover ofabout 14.0m will be provided to the tunnel at the ends of the reclamations. Thisresults in the reclamations requiring protruding nibs at both ends. In the north,while significant effects on tidal flows and large scale water quality are unlikely,localised acceleration in the flows at the end of the reclamations could occur.The reclamation, however, could also affect wave action on Butterfly Beachwhich might have a knock-on effect with respect to the cleanliness of the beachand siltation. In the south, the nib would have potential impacts on flowsbetween Chek Lap Kok and Tai Mo To and possibly cause a redistribution of thelarger scale flows.

2.3.1.6 The major advantages of employing TBM for the construction of submarinetunnel across Urmston Road are summarized as follows:

TBM scheme involve limited dredging operation;

No need for diversion of 132kV cable and telecommunication cablesconnecting Tuen Mun and Chek Lap Kok Airport Island;

No impacts on existing navigation channel Urmston Road;

Minimum ecology impact of Chinese White Dolphin; and

Construction of TBM tunnel does not depend on the weather and can beoperated with day and night shifts



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2.3.1.7 The major concern of TBM is the possible risk to human health and safety ofexposure to hyperbaric environment on rare occasions. Maintenance of the TBMcutterhead is required from time to time particularly for changing worn ordamaged cutter discs. Cutterhead tools can be changed within the spokes of thecutterhead under atmospheric conditions. Notwithstanding, the possibility existsduring emergency situation for entering the excavation chamber under hyperbariccondition if such operations cannot be carried out within the cutterhead spokes.

IMT

2.3.1.8 The proposed immersed tube tunnel (IMT) is in the form reinforced concreterectangular box structure of dimensions 9.6m high x 33.2m wide and is designedto accommodate 2 x 2 lanes.

2.3.1.9 An immersed tube tunnel consists of numbers of prefabricated tunnel elements arefirst fabricated in the casting basin. After the tunnel elements are constructed, theyare floated to the site, installed one by one, and connected to one another underwater. There will be around 32 nos. tunnel elements and each element is about120m long. An immersed tunnel is generally installed in the trench that has beendredged previously in the bottom of the sea. The space between the trench bottomand the invert of the tunnel was filled with sand foundation. As constructionproceeds, the tunnel is backfilled. The completed tunnel is covered with aprotective layer over the roof.

2.3.1.10 The major advantages of employing immersed tube for the construction ofsubmarine tunnel across Urmston Road are summarized as follows:

Shallow soil cover (about 2-3m) making the gradients of road more gentleand have a better connection to the approach tunnels on both ends; and

The extents of reclamations are smaller as compared with TBM tunneloption; andCross passages can be more easily provided within the internal tunnelstructure

2.3.1.11 The major concerns of IMT construction for TM-CLKL include environmentaland ecological impact due to extensive dredging of seabed, location andavailability of land required for casting basin, risk due to deep sea divingoperation under high currents and low visibility conditions, impact on marinetraffic of existing navigation channels especially Urmston Road during towing andsinking operations and diversion of 132kV cable and telecommunication cablesconnecting Tuen Mun and Chek Lap Kok Airport Island.

Selected Method

2.3.1.12 The TBM tunnel will have significant environmental advantages over the IMTtunnel scheme. For the IMT tunnel construction, dredging for the tunnel trenchwould be required, which would be about 140-210m wide and about 17-30m deep(from seabed) and this would be required for the full submarine tunnel alignment.The total amount of marine sediment to be dredged for the IMT tunnel



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construction is approximately 11.5Mm3 bulk volume (with 30% bulk factor).During the construction phase, the need for dredging would disturb the seabedresulting in temporary losses of marine habitat and would, also, release sedimentinto the water column increasing the risk of impacts to water quality and marinelife. As the alignment for the tunnel passes though fisheries, Chinese WhiteDolphins, coral and other marine life habitats, avoiding such impacts through theuse of TBM is a notable environmental advantage.

2.3.1.13 Based upon the notable environmental advantages during the construction phaseand the engineering justification, the TBM method is preferred and selected.

2.3.2 Reclamation Methods

Seawalls

2.3.2.1 The project involves extensive reclamation, with 16.5ha required for the northerntunnel landfall and 19.1ha required for southern landfall to the cope line (or21.1ha and 25.4ha, respectively, for the footprint area to the bottom of the seawallwhere it intersects the seabed). Three types of seawall are proposed for theseareas as follows:

vertical blockwork seawall, where berthing of vessels is required;

vertical wave absorption seawall:

sloping seawalls elsewhere, to provide better wave dissipation.

2.3.2.2 There are several ways to construct the seawall foundation but each have differentengineering and environmental implications. The key construction methods arelisted below and further details on each provided in the following sections:

stone column method;

deep cement mixing;

sand compaction piles; and

fully dredged.

Stone Column Method

2.3.2.3 This method can be applied when the increases to the overall bearing capacity andstrength of the treated layer are needed. The stone columns are installed with avibratory probe and the void created as the probe is removed is filled with rock.The formed columns allow transfer of the load from the fill layer to firmer stratum.The extraction of the probe has the possibility of causing minor sediment plumesdue to the adherence of fine clay material to the outside. However, it is expectedthat the presence of a sand capping layer, covering the area as a pre-treatment toprovide sufficient ground stability for the construction equipment, would filtermost of this material and, as such, the sediment plumes should be minimal.



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2.3.2.4 Notwithstanding, this technique is not deemed suitable for treatment of softmarine deposits as are present in the study area. The technique when applied inmarine site conditions is slow and, therefore, expensive and furthermore hasdifficulty in providing an adequate level of quality that can be checked withtransparent methods. In addition, the volume of stones placed in each column isnot able to be accurately measured and the stone consumption over depth in eachcolumn is unable to be checked. Hence, there is a great risk of leaving poorlytreated zones which may lead to excessive settlements or instability for thereclamations and the structures on them.

Deep Cement Mixing

2.3.2.5 The deep cement mixing method requires that cement is used to mix with themarine deposits to improve the shear strength of the bearing stratum and to reducethe consolidation settlement of the bearing stratum under load.

2.3.2.6 Cement slurry is mixed with the sediment by a rotating paddle inside a metalcasing. When the mixing system reaches the seabed and is no longer contained,the injected cement has the potential to leak into the environment. Leakage ofcement slurry in the last section of the column formation can be as much as 5% ofthe application, and could affect water quality in terms of suspended solids andlocal changes to pH, potentially leading to an increase of ammonia toxicity tosensitive species such as juvenile fish. The waters in the study area are oftennitrogen enriched and the water quality objective (WQO) of 0.021 mg/l forun-ionised ammoniacal nitrogen level could be exceeded by the leaked cementeven though any impact would likely be localised to the leakage area.

2.3.2.7 On the other hand, the reliability of this method can be variable as the strength ofthe soil-cement pile will be influenced by factors such as sediment type,consistency of soil/cement mixing and the curing environment. Other constraintsinclude the fact that it is difficult to control the quality of the works and establishthe diameter of the pile formed which would require lengthy field trials and, also,the technique would be very costly compared to other methods. As such,notwithstanding that the overall impacts on the water quality are likely to be smalland localised, this method is not proposed.

Sand Compaction Pile

2.3.2.8 Sand Compaction Pile (SCP) refers to the construction of a column of dense sandthrough the full thickness of the sediment and broadly follows the followingmethod:

Possibly following the laying of a sand blanket, a steel tube, typicallyvarying in diameter from 0.4 to 0.8 m, is pushed into the sediment to therequired depth. Insertion of the tube can be assisted by vibration at thetop of the tube and air/water injection at the base of the tube. The tube isblocked during insertion and there is no boring or removal of spoil as thetube is inserted;



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When the steel tube has reached the required level it is withdrawn a shortdistance and at the same time sand is forced out of the base of the tube bycompressed air;

The level of the sand in the tube is monitored to ensure that the tubealways contains sand and that the sediment around the tube is not allowedto collapse below the tube;

The tube is then pushed back into the sand and vibrated back on top of thesand that has been deposited in the ground below the tube in order toincrease the diameter of the sand column by pushing it out against thesediment and increasing the density of the sand at the same time; and

When the desired diameter has been achieved (determined from the knownvolume of sand placed in the column) more sand is added to the tube andthe process of sand placement and compaction is repeated. The processis continued until the sand compaction pile has reached the desired level.

2.3.2.9 The composite pile formed would increase strength and result in a decrease inconsolidation settlement and lateral displacement. This method, also, requiresthe shortest period for sediment stabilisation and improvement of strength of theground conditions and, as such, is used in the stabilisation of foundation soilsupporting structures offshore.

2.3.2.10 Though the dredged volume when using SCP will be decreased by 70% whencompared with the fully dredged method, the use of SCP will increase theconstruction cost by three times and may cause an overall delay of the programmeby 30 months.

2.3.2.11 Furthermore, in view of the fast track of the construction works and the lack oflocal experience on the construction of SCP in Hong Kong, the adoption of SCPwould very likely increase the risk of unpredictable construction difficulties andhigh construction cost.

2.3.2.12 Setting aside the time and cost factors, SCP is technically not applicable for use inthe southern landfall reclamation where excessive upheaval of the existing seabedinduced by the SCP installation could adversely affect the use of the seawall forberthing both during construction and operationally. The existing seabed at thesouthern landfall is approximately -4mPD to -11mPD, and the thickness of themarine deposits is about 14m. Using this technique, the seabed would heave byabout 4m after installation of the SCPs, and such upheaval would adversely affectthe operation of barges both during construction and in future if the heavedmaterials are not dredged away. Doing so, however, will inevitably increase thequantity of material for disposal and potential water quality impacts.

2.3.2.13 In view of the prolongation to the construction programme, increase inconstruction cost, inability of a total avoidance of dredging marine deposits andother factors mentioned above, the use of SCP is not recommended to form theseawall foundation at either landfall.



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Fully Dredged for Seawall Foundation

2.3.2.14 Complete removal of marine deposits by dredging and backfill with sand/rock fillfor seawall foundation is a commonly used method in Hong Kong because it isconsidered to be a robust engineering solution to ensure the stability of seawall forprotection of the reclaimed land behind.

2.3.2.15 The fully dredged method has the following advantages from an engineeringperspective:

avoids long term settlement and deformation of the seawall; and

is the most rapid technique where programme constraints are present.

2.3.2.16 During dredging works fine material will be displaced and may be carrieddownstream of the works area. The extent of the suspended sediment plume willdepend on the rate of release, the particle size of the dredged material and itscharacteristic settling velocity, the prevailing currents and hydrodynamicconditions. It is proposed that grab dredgers be used for this activity, and thiswill result in instantaneous sediment plumes, formed throughout the water columnas the grab is pulled to the surface.

2.3.2.17 Based on a comparison of the methods above, the fully dredged option for theformation of the seawall foundations has the potential to release the mostsuspended solids into the water column and would be the least environmentallyfavourable option.

Selected Method

2.3.2.18 Based upon the above, from an engineering perspective, both the Stone ColumnMethod and the Deep Cement Mixing have been rejected as unsuitable for use inthe Project. Also, as the use of the SCP technique will result in an overall delayof the programme by 30 months compared with the fully dredged method, doesnot give the same level of ground strength and would result in sediment heave atthe southern landfall, this method is not proposed to form the foundations for thelandfall reclamation seawalls. The comparison between the various constructionmethods for seawall foundation are summarized in Table 2.5 below:



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Table 2.5 Summary of Comparison between various construction methodsfor seawall foundation

Stone ColumnMethod

Deep CementMixing

SandCompaction

PilesFully Dredged

Total Cost High Very High High Low

ConstructionPeriod Slow Slow Slow Fast

Dredging No No Partially Dredged Fully Dredged

Remarks As mentionedin section2.3.2.4, thereare someengineeringdifficultiesencountered forinstallation ofstone columninto the softmarine deposits.Hence themethod is notfeasible

It is veryexpensivewhencompared withother method.Also, there isno local trackrecord in HongKong for themethod

It is expensive,long constructionperiod anddredging isunavoidable dueto sediment heave.Also, there is nolocal track recordin Hong Kong forthe method.

Low cost andshortconstructionperiod whencompared withothers. Feasiblesolution forseawallfoundation.

2.3.2.19 The fully dredged method, being the only remaining feasible solution, is, therefore,selected.

Land Formation

2.3.2.20 The main purposes of the reclamations for the TM-CLKL are to provide land forthe launching and receiving shaft for the TBM as well as providing minimum soilcover of 14.0m to facilitate the safe operation of the TBM. The reclamationswill, also, contain the portal and tunnel approach roads.

2.3.2.21 Reclamation can be formed using either fully dredged or non-dredged methods.

Non-dredged Method

2.3.2.22 For the most common non-dredged method, the marine deposits are left in placeand band drains installed to accelerate primary consolidation so that thereclamation can be constructed more rapidly. If the highly compressed marineand alluvial deposits are not dredged, these layers would consolidate under theweight of the fill material and this would result in settlement of the reclaimed land.The consolidation process is slow and in order to speed this up, band drains can beinstalled to drain the pore water. The band drains are installed through the fulldepth of the compressible layer and cut off at the sand drainage layer at the top.



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Surcharge in the form of soil embankment is then placed on the land after theband drains have been installed.

2.3.2.23 While a cost-effective process, the time required for consolidation of the marinedeposits can present severe constraints on the construction programme.

2.3.2.24 Environmentally, this process has notable advantages of avoiding the constructionphase impacts associated with dredging and the associated potential water quality,marine ecological and waste management implications that results. Theextraction of the band drain device has the potential to cause minor sedimentplumes due to the possible adherence of fine clay material to the outside, but thesand drainage layer would be expected to filter most of the material and, as such,the sediment plumes should be minimal.

2.3.2.25 Other non-dredged methods include those which may be applicable to seawallconstruction such as stone column method, sand compaction pile (SCP) and deepcement mixing (DCM), the details of which are described in the foregoingsub-sections. However, these methods are either not deemed suitable for thetreatment of the marine deposits in the study area, or the reliability of which canbe variable as discussed above. Moreover, the use of SCP is more applicable tothe strengthening of seawall foundation rather than general reclamation.

Fully Dredged Method

2.3.2.26 For the fully dredged method, the marine deposits will be removed by dredging,and the post reclamation settlements can be reduced significantly. It is suitablefor the reclamation requiring short construction period and provides goodfoundation for the structure above.

2.3.2.27 As with the fully dredged seawalls, any dredging works for the land formationwould also result in the loss of suspended solids into the water body and, as theworks would be extensive and undertaken over a notable time period, unmitigatedimpacts could be significant. However, depending on the progress of the seawall,a partially completed seawall or leading edge of seawall could act as a barrier toreduce the losses of dredged sediment. Notwithstanding, the potentialenvironmental impacts will be more significant than those from the non-dredgedmethod and, as such, would not be environmentally preferred.

Selected Method

2.3.2.28 Given the notable environmental advantages of the non-dredged method of landformation, this has been proposed for the majority parts of both the northern andsouthern landfalls. The use of band drains and surcharging are preferred over theother alternative non-dredged methods which have been dismissed on engineeringgrounds.

2.3.2.29 However, at the southern portion of the northern landfall and the northern portionof the southern landfall, deep excavation will be required for constructing theTBM shafts and the deeper section of the cut-and-cover tunnel. This wouldinevitably have removed the marine deposits located above the proposed



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structures and, therefore, the fully dredged method is proposed in conjunctionwith the seawall construction.

2.3.3 Piling Methods

2.3.3.1 Piling activities will be required for the viaduct piers of the southern sectionlocated within the sea channel between the southern reclamation and north Lautaushoreline.

2.3.3.2 The type of piling method to be used will have a bearing on the potential impactsto cetaceans, specifically the Chinese White Dolphin (CWDs), that resides thestudy area. Cetaceans use two functional classes of sound, these areecholocation and communication. Echolocation is used for orientation, navigation,prey detection and learning about the surrounding environment, whilstcommunication is used for intra-species signalling (Richardson, 1995). CWDsvocalise through the production of clicks, rapid click sequences (screams) andwhistles (Wursig, 1995a). Noise is transmitted efficiently through water andcetaceans are known to be able to detect submarine noise over several kilometresfrom the source (Richardson, 1995). Sounds introduced into the marineenvironment have the potential to interfere with the dolphins ability to detect callsfrom other individuals, echolocation pulses or other natural sounds (Richardson,1995). Noise can also lead to a disruption of dolphin behaviour. Disruption offeeding, resting and social interactions have all been attributed to elevated sounds(Richardson, 1995). Elevated noise of sufficient intensity can also damage thehearing sensitivity which may be either acute or chronic (Richardson, 1995).

Percussive Piling

2.3.3.3 Percussive piling creates loud, impulsive sounds that have the potential tophysically injure or disturb dolphins. Most of the energy from pile drivingoccurs below 20 kHz, with a peak at about 200 to 1,500 Hz (1/3 octave spectra)(Nedwell and Howell 2004). The lower acoustic frequencies of pile driving canbe transmitted for as far as about 40 km in water deeper than several meters(David 2006), so the impacts can in some cases be quite long-range.

2.3.3.4 Because most pile driving results in considerable energy into the single kHz digits,it has the potential to be a serious issue for dolphins. This is the range wheresmall cetaceans, such as humpback dolphins, produce most of theircommunication sounds, and are most acoustically-sensitive, although they alsomay produce sounds to frequencies as high as 200 kHz and beyond (Goold andJefferson 2004). Loud sounds are, also, known to cause (short-term) behaviouralreactions such as increased swimming speed and also interfere withcommunication and induce physiologic impairment in cetaceans (Richardson,1995; Jefferson, 2000a; Wursig et al., 2000). Certain research in relation tomarine piling for wind farms (Madsen et al. (2006)) suggests that pile driving isthe noisiest and most disturbing part of the process and that it could causebehavioural disturbance and even hearing impairment. Other research (David(2006)) speculates that pile driving could mask strong bottlenose dolphinvocalizations at 9 kHz within 10-15 km and weak vocalizations up to 40 km.



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However, this was not based upon direct behavioural or physiologicalinformation.

2.3.3.5 However, there is not much detailed information on reactions of marine mammalsto pile driving. Harbour seals (Phoca vitulina) may vacate areas of pile driving(for example, Rodkin and Reyff 2004), but in the Arctic, Blackwell et al. (2004)found that a related species, the ringed seal (Phoca hispida) appeared to ignore thepile-driving work that was being conducted from a nearby artificial island. Thelatter case, however, may represent an example of habituation, as the Arctic hasextensive oil drilling and extraction operations.

2.3.3.6 Intensive monitoring of CWD behaviour during percussive pile driving forconstruction of the aviation fuel receiving facility (AFRF) at Sha Chau in 1996,did, however, show that dolphin density was lower for the period of piling (andother activities) but recovered once construction of the AFRF has been completed(Jefferson 2000; Würsig et al. 2000). There were, also, probable impacts ondolphins swimming speed, patterns and dive times (Jefferson 2000).

2.3.3.7 Although percussive piling does produce high-intensity noise impacts capable ofinducing physical injury, the piling duration is usually shorter than would berequired for bored piling.

2.3.3.8 Notwithstanding, the use of percussive piling may result in at least temporaryabandonment of habitat (see Jefferson 2000), forcing animals to spend time inlower-quality habitats which in turn may result in lowered fitness, reducedreproductive output, or reduced survival.

Bored Piling

2.3.3.9 Noise created by bored piling methods tends to be a less intensive continuousnoise, rather than the pulsed high power sounds emitted through percussive piling.Bored piling usually creates a steady sound that is less disruptive to dolphins thanthe pulsed or burst sounds associated with activity such as percussive piling(Wursig et al., 2000). Dolphins are known to habituate to low-level sounds such asthose produced through bored piling (Greene and Moore, 1995).

2.3.3.10 However, bored piling work generally takes a longer time period to drive the piles,thereby lengthening the overall time period of impact and likely resulting inchronic lower level impacts as opposed to the an acute high-energy noise impactof percussive piling. The programming for the southern viaduct piling isapproximately 14 months.

2.3.3.11 Almost no work has been done on its effects on dolphins or porpoises, but it isreasonable to assume that it may also cause behavioural disturbance, although it isgenerally accepted that the impacts would be much less severe than for percussivepiling.

2.3.3.12 Notwithstanding the longer construction period, based upon the potential for lesssevere impacts to this key species and, together with the engineering preferencesabove, bored piling techniques have been selected for the viaduct works.



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Selected Method

2.3.3.13 Due to the heavy loads imposed by the relatively long spans of the viaduct, theviaduct piers will be required to sit on piles founded on rock. In order tominimise the number of piles located in the sea channel, large diameter piles ofdiameter between 1.5m and 2.5m will be required. Piles of this size will be toolarge to be driven and will need to be constructed by bored methods. Therefore,percussive piling will not be used for construction of the piles supporting theviaduct.

2.3.4 Sand Filling Methods

2.3.4.1 Sand filling is required for the land formation at the southern landfall, and thesand can be deposited using either a pelican barge or a bottom dumping hopperbarge. Land formation at the northern landfall uses public fill.

2.3.4.2 Since pelican barges will used for the transportation of marine sand imported fromChina, they are preferred for the marine sand filling in the Project to avoid doublehandling of the material. Hopper barges will be used for transportation of thepublic fill from local storage site to the project area.

2.3.4.3 It should, also, be noted that the pelican barge would not “rainbow” in the sameway as a trailer. A pelican barge has a conveyor belt extending from the centralpart of the barge to the front edge and during the unloading process, the material istransferred from the body to the front edge and then merely drops down. Theconveyor belt can, therefore, at the most cast the material out for a very smalldistance only. This process may be better described as “dropping” and does notcompare to the fluidised and pumped sand and water mixture that is commonlydescribed as “rainbowing”. As such, the potential environmental impacts of theuse of pelican barges in terms of sediment losses would be similar to that of thebottom dumping hopper barge.

Documents

2. CONSIDERATION OF ALTERNATIVES2-1 2.1 Introduction 2.2