1 INTRODUCTION

1.0.0.1 Ove Arup & Partners Hong Kong Limited (Arup) have been appointed by the Highways Department to undertake Agreement No. CE109/98 - Deep Bay Link - Investigation and Preliminary Design. This Environmental Impact Assessment Report is a part of the overall investigation and preliminary design work and is submitted under the Environmental Impact Assessment Ordinance for the Project.

1.0.0.2 This Report consists of three volumes. Volume 1 contains the main body text. Volume 2 includes the Figures and Volume 3 contains the Photographs and Appendices. For Chapter 9 Cultural Heritage, all figures are included in Volume 1 for reference.

1.1 Background

1.1.0.1 Deep Bay Link (DBL) is a proposed expressway/trunk road of dual-3 lane standard with hard shoulders providing a strategic link between the proposed Shenzhen Western Corridor (SWC) at its landing point at Ngau Hom Shek and a proposed interchange with the Yuen Long Highway (YLH) and the proposed Route 10-North Lantau to Yuen Long Highway (R10-NLYLH) at Lam Tei.

1.1.0.2 In January 1998, the Transport Department (TD) issued a Client Project Brief (CPB) requesting the Planning Department (PlanD), on behalf of the Highways Department (HyD) to conduct a Preliminary Project Feasibility Study (PPFS) on the feasibility of constructing the DBL. The CPB pointed out the following:-

(a) The need for DBL has been established in the "Review of Hong Kong's Capacity to cope with Additional Traffic Movement associated with the Proposed New Cross-Border Transport Links (Crosslinks) Study" in 1996. As proposed in the Crosslinks Study, DBL would serve as the strategic link between the SWC and Hong Kong's highway network.

(b) According to the Crosslinks Further Study Stage 1, the expected traffic throughput and volume to capacity ratio (v/c) at DBL are as follows:

(c) The DBL should be commissioned as soon as possible, in any case not later than 2005.

1.1.0.3 In June 1998, PlanD, on behalf of HyD, commenced the PPFS and the associated Preliminary Environmental Review (PER) to establish the feasibility of the project and to meet the necessary procedural requirements in the Public Works Programme process. The PPFS Report was completed in May 1999.

1.1.0.4 Subsequently, HyD submitted a project profile (No. PP-036/1998) and an application (No. ESB-025/1998) for an Environmental Impact Assessment (EIA) study brief under section 5(1) of the EIAO on 11 December 1998. This has led to this EIA study.

1.1.0.5 Currently a target completion date of mid-2006 has been established using all reasonable endeavour. DBL is proposed to be a dual-3 lane trunk road linking Ngau Hom Shek to an interchange with the YLH and the proposed R10 at Lam Tei.

1.2 Description of Project

1.2.0.1 DBL is a 5.4-km expressway/trunk road connecting R10 and the Shenzhen-Hong Kong Western Corridor across the boundary at Deep Bay near Ngau Hom Shek. Two major interchanges have been included in the project, the Lam Tei Interchange will connect DBL to R10 and YLH while the Hung Shui Kiu (HSK) Interchange will connect traffic to the Hung Shui Kiu New Development Areas (HSKNDA) (Former HSK Strategic Growth Area HSKSGA). Figure 1.1 (A to D) shows the location and general layout of the proposed DBL which also gives the project scope of this EIA in relation to other projects.

1.2.0.2 The original proposed scope of the Project includes:

(a) A dual 3-lane expressway/trunk road with bridge structures linking the proposed SWC at Ngau Hom Shek to an interchange with the YLH and the proposed R10 -NLYH at Lam Tei. The carriageway would be designed to expressway standard between the cross boundary control facility area and the interchange with the YLH. The remaining section from the cross-boundary control facility area up to the HKSAR Boundary would be designed so as to take into account the design of the SWC as appropriate and the security measures required;

(b) An interchange of the DBL with the YLH and the proposed R10-NLYLH at Lam Tei. The location of the interchange has to tie in with the recommendations of the on-going R10-NLYLH Study;

(c) An interchange south of the cross-boundary control facilities to connect with the possible Tuen Mun Western Bypass (not confirmed yet at this stage) and the road networks of the HSK NDA recommended under the Planning and Development Study on North West New Territories (NWNT Study);

(d) All cross boundary control facilities required by various departments, including Hong Kong Police Force, Customs and Excise Department, Immigration Department, Department of Health, Agriculture, Fisheries and Conservation Department and other concerned parties within the cross-boundary control facility area;

(e) A northbound and a southbound vehicle holding area for goods vehicles with capacities to be determined;

(f) An option to provide a toll plaza for DBL, pending the decision on whether DBL should be tolled;

(g) Associated civil, structural, geotechnical, landscape and drainage works, street lighting, traffic aids (including sign gantries), noise barriers, fire hydrants, traffic control and surveillance system, security control system and E&M works; and

(h) Reprovisioning and modification works to San Wai Sewage Treatment Works, if affected, and any associated compensatory land.

1.3 Changes in the Project Scope

1.3.0.1 At the 4th Plenary of the Hong Kong/Guangdong Cooperation Joint Conference on 25th July 2001, the two Governments agreed the principle of co-locating the boundary facilities for immigration and customs clearance procedures in the Shenzhen Territory. The scope of the DBL project was therefore modified, with the following items deleted from the original project scope:

(i) boundary control facilities as described in item (d) above;

(ii) vehicle holding areas as described in item (e) above;

(iii) toll plaza and associated facilities as described in item (f) above; and

(iv) facilities to allow for the change over of left-hand driving and right-hand driving

1.3.0.2 A Ha Tsuen Interchange was added to the original scope. The tentative construction programme for DBL is given in Table 1.1 at the end of this Chapter.

1.4 Objective of the EIA Study

1.4.0.1 The purpose of this EIA study is to provide information on the nature and extent of environmental impacts arising from the construction and operation of the proposed designated projects and related activities taking place concurrently. This information will contribute to decisions by the Director of Environmental Protection on:

(i) the overall acceptability of any adverse environmental consequences that are likely to arise as a result of the proposed project;

(ii) the conditions and requirements for the detailed design, construction and operation of the proposed project to effectively mitigate against adverse environmental consequences wherever practicable; and

(iii) the acceptability of residual impacts after the proposed mitigation measures are implemented.

1.4.0.2 The objectives of the EIA study are as follows:

(i) to describe the proposed project and associated works together with the requirements for carrying out the proposed project;

(ii) to identify and describe the elements of the community and environment likely to be affected by the proposed project and/or likely to cause adverse impacts to the proposed project, including both the natural and man-made environment;

(iii) to identify and quantify emission sources and determine the significance of impacts on sensitive receivers and potential affected uses;

(iv) to identify and quantify any potential losses or damage to flora, fauna and wildlife habitats;

(v) to identify any negative impacts on sites of cultural heritage and to propose measures to mitigate these impacts;

(vi) to identify and quantify any potential landscape and visual impacts;

(vii) to propose the provision of infrastructure or mitigation measures so as to effectively minimize pollution, environmental disturbance and nuisance during construction and operation of the proposed project;

(viii) to identify, predict and evaluate the residual (i.e. after practicable mitigation) environmental impacts and the cumulative effects expected to arise during the construction and operation phases of the proposed project in relation to the sensitive receivers and potential affected uses;

(ix) to identify, assesses and specify methods, measures and standards, to be included in the detailed design, construction and operation of the proposed project which are necessary to effectively mitigate these environmental impacts and reducing them to acceptable levels;

(x) to investigate the extent of side-effects of proposed mitigation measures that may lead to other forms of impacts;

(xi) to identify constraints associated with the mitigation measures recommended in the EIA study; and

(xii) to design and specify the environmental monitoring and audit requirements, to ensure the implementation and the effectiveness of the environmental protection and pollution control measures adopted.

1.5 Approach of Assessment

1.5.0.1 The assessment approach was based on the EIAO-TM which generally included:

1.5.1 Description of the Environment

1.5.1.1 the characteristics of the environment were described for identification and prediction of environmental impacts. Baseline environmental surveys were carried out to determine the existing environmental conditions on the site and in all environs likely to be affected by the proposed project. This information formed the basis for predicting and evaluating the impacts. Reference was also made to the results from past studies (e.g. Yuen Long Highway Widening EIA) and on-going studies (e.g. technical information from Shenzhen Western Corridor, HSKNDA and Route 10 for assessment of future impact).

1.5.2 Impact Prediction

1.5.2.1 The guidelines on assessment methodologies are given in Annexes 12 to 19 of EIAO-TM. Part of the subject areas were made use of quantitatively predictive tools for the prediction of future impacts including traffic air quality impact, construction and traffic noise impact. These predictions were based on internationally recognized methods and had been applied in similar situations in previous EIA studies namely:

• CALINE4 dispersion model approved by United States Environmental Protection Agency (USEPA) was used to assess traffic air emissions impact (refers to Section 2.5)
• Calculation of Road Traffic Noise (CRTN) adopted by UK Department of Transport was used to assess traffic noise impact (refers to Section 3.3.2)
• Technical Memorandum on Noise from Construction Work other than Percussive Piling (GW-TM) under Noise Control Ordinance

1.5.2.2 These methodologies have been generally accepted for use in assessing environmental impacts and comparison of prediction results with EIAO-TM standards. There are some limitations of methodologies such as the accuracy of the predictive base data for future e.g. traffic flow forecasts and weather conditions, the definition of worst-cases and the assumptions of dispersion process.

1.5.3 Impact Evaluation

1.5.3.1 An evaluation of the anticipated changes and effects were made with respect to the criteria described in Annexes 4 to 10 of EIAO-TM.

1.5.4 Impact Mitigation

1.5.4.1 The methodologies proposed for mitigation gave priority to avoidance of impacts as in the alignment selection and engineering design given in Sections 1.7 to 1.8.

1.5.4.2 The assessment methods were aimed to (i) identify and evaluate mitigation measures in order to avoid, reduce or remedy the impacts; (ii) assess the effectiveness of mitigation measures; and (iii) define the residual environmental impacts, which are the net impacts remaining with the mitigation measures in place.

1.5.4.3 The assessment methodologies were allowed for the assessment and evaluation of the cumulative environmental effects. This is outlined in Section 1.9 and detailed in individual technical chapters.

1.6 The Scope

1.6.0.1 The scope of this EIA study covers the items mentioned in Sections 1.2 and 1.3, and the project is collectively identified as a designated project under Part I A.1 of Schedule 2 of the EIAO. The Environmental Impact Assessment Study Brief No. is ESB-025/1998.

1.6.0.2 There is no other designated project identified under the scope of this Project. The project has no impact on agriculture and hence agricultural impact is not assessed in this EIA Report

1.7 Considerations on Alignment Options

1.7.0.1 This section describes the previous considerations given to DBL alignment alternatives. Several initial studies have been carried out prior to this EIA in order to arrive the currently proposed alignment.

1.7.0.2 The demand for travel by people and transport of goods across the boundary between Hong Kong and the Pearl River Delta of the Mainland had found continued to grow as the two economies become further integrated in recent years. In order to accommodate this rapid traffic growth and to further facilitate the socio-economic linkages between Mainland and Hong Kong, a new cross-boundary road link was put forward by the Shenzhen authority - the Shenzhen-Hong Kong Western Corridor (SWC) across Deep Bay from Shekou, Shenzhen.

1.7.0.3 As a response to this proposal, an initial study was carried out by the Planning Department in September 1995 and completed in May 1996. The initial study considered a number of route corridors and landing points for the bridges and undertook an initial environmental appraisal of the Deep Bay Link.

1.7.0.4 The initial study set off a 3-Stage further study named "Feasibility Study for Additional Cross-border Links" and Deep Bay Link was one of the studied cross-border link. The study analyzed the strategic level planning requirement and consisted of:

Stage 1 to investigate the cross-boundary demand for which concluded the need for Deep Bay Link;

Stage 2, to investigate the environmental and ecological impacts, land use planning issues, financial and economic assessments, as well as preliminary engineering feasibility, the early planning such as consideration of different route options, was included in this stage.

Stage 3, to undertake the engineering feasibility of the Deep Bay Link, which is this Study and this EIA Report.

1.7.0.5 The Environmental Assessment Technical Report of Stage 2 provided the backbone for the strategic planning level review and the environmental option studies of this EIA Report. Environmental study findings regarding Deep Bay Link are summary in the following sections.

1.7.1 Landing Point for SWC and the Broad Corridor for the DBL

1.7.1.1 The Environmental Assessment Technical Report provides the initial assessment of the DBL routing and the landing point of SWC. The report determined that there were three feasible alternatives for the landing point, namely:

i) the landing point at Pak Nai (southern alignment),

ii) the landing point at Sheung Pak Nai (central alignment) and

iii) the landing point at Ngau Hom Shek (northern alignment).

1.7.1.2 These landing points and associated specific DBL alignment have been termed the southern, central and northern alignments respectively as shown in Figure 1.2. The southern and central landing points would result in the DBL being in tunnel, while the northern option would results in DBL being at grade on an alignment around the north of the Castle Peak range.

1.7.1.3 The results of a comprehensive option assessment of these three landing points showed that the southern (Pak Nai) and the central (Sheung Pak Nai) options scored very low in respect of environmental, and cost and programme factors, with the central option ranking lower than the southern route largely due to the severe ecological impacts (see Appendix 1A for an account of ecological resources in different parts of Deep Bay) on the Sheung Pak Nai headland and the high cost of tunnel. The northern option, landing at Ngau Hom Shek and passing at-grade through the Ha Tsuen area to Lam Tei, was demonstrated to provide the overall best solution taking into account the three factors.

1.7.2 Refinement of Ngau Hom Shek Landing Option

1.7.2.1 Further to the identification of best land point - the northern alignment landing at Ngau Hom Shek, considerations were given to review the various alternatives for the inland routing.

1.7.2.2 A supplementary study was carried out prior to this DBL EIA to consider a tunnel alignment of DBL based upon the landing point at Ngau Hom Shek. The study comprised an option assessment of three alternatives:

• Option 1 Northern Alignment (At-grade Scheme): at-grade alignment with cross-boundary facilities at Ha Tsuen
• Option 2 Tunnel Scheme: tunnel alignment with the cross-boundary facilities to the north on the coastline at Ngau Hom Shek
• Option 3 Cavern Scheme: tunnel alignment with the cross-boundary facilities within a cavern system beneath Castle Peak Hills

1.7.2.3 The options 2 and 3 are presented in Figure 1.3 and option 1 is shown in Figure 1.2. The assessment of the alternatives had been undertaken using a numerical "scaling" and "weighting" system based upon four key criteria, namely environment, land, engineering and cost and programme. Each criteria category had been assigned a "weighting proportion" which denotes the relative percentages of the items as a fraction of the weighting value as a whole. The output of this methodology provided a numerical ranking of the options and thereby provides an indication of preference. Sensitivity tests, based upon different weighting sets, had also been undertaken to evaluate the outcome of emphasis being placed on different criteria.

1.7.2.4 Results of this previous option assessment showed that the Option 1 Northern Alignment (At-Grade Scheme) would not fragment the key ecological area along the Deep Bay coastline and overall habitat loss of the alignment was restricted to foothills, village and agricultural habitats which are already disturbed and fragmented and of limited ecological importance. Thus, any impacts were considered minor.

1.7.2.5 Option 2 Tunnel Scheme, however, had its alignment and cross-boundary facilities accommodated on the narrow coastal strip of Deep Bay, causing moderate to severe impacts with the opportunity to mitigate habitat loss being limited and thus is ranked less favorably than Option 1.

1.7.2.6 Option 3 Cavern Scheme would be no habitat loss associated with the cross boundary facilities and a notable length of the alignment would be in tunnel. Thus, overall this option would have less ecological impact than the at-grade option.

1.7.2.7 Air pollution from the Option 1 would be evenly spread over the length of the road, although the number of sensitive receivers potentially affected will be greater than from the tunnel or cavern options. Concentrated portal ventilation systems for the tunnel/cavern options will result concentrated pollutants around the portals and the ventilation shafts and AQOs could be exceeded in these locations.

1.7.2.8 Similar, noise mitigation to Option 1 would be required along the at-grade sections of the tunnel and the cavern options. However, the tunnel and cavern options would affect a smaller number of sensitive receivers overall. Thus, Option 1 was scored worse than the other two alternatives.

1.7.2.9 Water quality impacts due to storm runoff and accidental spills both during construction and operation of the project have been considered in the evaluation. These impacts could affect the local stream courses and the water body in Deep Bay but it had been that assumed that in case of all options, mitigation will reduce any pollution to acceptable levels and all options are considered equal in terms of the potential for impacts.

1.7.2.10 The proposed HSKNDA was a notable sensitive area associated with the DBL. For all options, however, the southern section of the alignment, together with the interchange for proposed HSKNDA access and the interchange with the R10-NYLH at Lam Tei, was common to all options. This area was adjacent to the proposed HSKNDA and thus, any environmental impacts and the mitigation required to reduce them to acceptable levels would be effectively equal for all the options.

1.7.2.11 The option assessment also included the evaluation of impacts on land, engineering feasibility and cost and programme implications. The comparison of land criteria had largely been based upon the level of difficulty associated with the resumption of private lots. The cavern option affected the least number of lots but encroaches on the Castle Peak Firing Range which, thus, the difficulty of obtaining this land was expected to be higher than the two other options. Both the cross-boundary facilities associated with the at-grade option would affect a significant number of lots but the at-grade option being considered as creating more resumption difficulties that the tunnel. In respect of engineering, due to the known poor geology in this area both the tunnel and cavern options would be very difficult and risky to construct, requiring specialist construction techniques and equipment, which also had significant cost and programme implications. The tunnel option was likely to take over a year longer than the at-grade option and cavern a further 4-5 years cost HK$2.5 and 5 billion extra respectively. These factors presented as severe constraint for the tunnel options.

1.7.3 Selection of At-Grade Alignment

1.7.3.1 The previous option assessment study concluded that the Option 1 Northern Alignment(At-grade Scheme) was the overall best option, at times by a notable margin, having significant engineering, cost and programme benefits. The ecological impacts associated with this option are not severe and the air and noise impacts could likely be mitigated to acceptable levels. This option was noted to have a wider area of influence on the proposed HSKNDA but the critical area was the southern section of alignment which was common to all alternatives.

1.7.3.2 The sensitivity tests also showed that engineering, cost and programme factors all heavily handicap the tunnel and particularly the cavern option, which had the additional constraint of encroaching on the Castle Peak Firing Range. The implications of these factors on the scoring of the cavern option was marked and failed to offset its advantages, such as low environmental implications, even when the bias is towards this criteria. In all cases the cavern option was ranked a definite third. The location of the large cross-boundary facilities on the ecologically sensitive coastal strip at Ngau Hom Shek was also a constraint for the tunnel option.

1.7.3.3 The Option 1 Northern Alignment (At-Grade Scheme), which was the basis of this EIA, had demonstrated that it provided the overall best solution taking into account all the factors.

1.8 Alignment Considerations in this Project

1.8.0.1 The previous assessments for the alignment option selection were evaluated with the presence of boundary control facilities (with the boundary control area and vehicle holding areas). Followed the policy decision (Section 1.3) at the 4th Plenary of the Hong Kong/Guangdong Cooperation Joint Conference on 25th July 2001, the boundary control facilities has been moved to Shenzhen and no longer required in the current proposed alignment. The findings of the previous option assessments were re-visited in this context.

1.8.0.2 For the choice of landing point, the key factors were the conservation of the ecological sensitive areas along Deep Bay. The landing point at Ngau Hom Shek (Option 1 Northern Alignment) would still be the best option because it could reduce the fragmentation of the key ecological areas namely Ha Pak Nai, Pak Nai SSSI, Sheung Pak Nai and Mai Po along the Deep Bay coastline.

1.8.0.3 In consideration of the alignment routing from Ngau Hom Shek to Route 10 portal, this Project has evaluated the various physical constraints, effect on different types of sensitive receivers, possibility of depressed road and tunnel alignment, and optimization of design of reduce pollution and different foundation construction methods. The key outcomes are described in the following sections. The final environmental outcomes and benefits for the proposed DBL alignment are concluded in Chapter 13.

1.8.1 Constraints in the Routing of Alignment

1.8.1.1 This Project has considered different alignment options within the study envelope. Figure 1.5 identifies the constraints and considerations around the study area. Within the narrow array of the alignment, there are a number of potential constraints identified:

Physical Constraints

• Castle Peak Hills, Yuen Tau Shan
• Yuen Long Highway
• Castle Peak Road
• West Rail
• Light Rail Transit
  

Landuse Constraints

• Proposed Hung Shui Kiu New Development Area (Formerly known as Hung Shui Kiu Strategic Growth Area)
• Existing villages and residents of relatively high density (Lam Tei, To Yuen Wai, Choi Yuen Tsuen, Nai Wai, Tsing Chuen Wai, San Sang Tsuen, Ha Tsuen, etc)
• Existing San Wai Sewage Treatment Works
• Castle Peak Firing Range

Engineering, Functional and Connection Requirements

• Connections to Hung Shui Kiu NDA
• Connections to Yuen Long Highway
•  Connections to Route 10
• Connections to Ha Tsuen

Burial Grounds

• Existing Permitted Burial Ground Nos. 21, 22, 23, 24, 25, 06, 55, 57, 58 (from Route 10 portal to Ngau Hom Shek)

Ecologically Sensitive Areas and SSSI
 

• Pak Nai SSSI, Sheung Pak Nai, Ha Pak Nai
• Fishponds and stream courses along Ngau Hom Shek coastline
• Mangrove strips and other coastal habitats at Ngau Hom Shek
• Observed egretries at Ngau Hom Shek

Sites of Archaeological Interest and Cultural Heritage Importance

• Fu Tei Ha Archaeological Site
• Tsing Chuen Wai Archaeological Site
• Tuen Tsz Wai Archaeological Site
• Tseung Kong Wai So Kwun Tsai Archaeological Site
• Ngau Hom Shek Archaeological Site
• Nai Wai
• Sun Fung Wai
• Mui Fat Tsz Temple
• Ling To Monastery

1.8.1.2 While putting all the constraints on the map, it is clear that the proposed DBL alignment have been chosen to pass through the gaps between numerous constraints and optimized among various conflicts. A number of alignment options have been studied with different constraints and assumption changes. The process is best summarized in Figure 1.4.

1.8.2 Design Optimization

1.8.2.1 Beside the constraints, considerations have also been given to improve the environmental quality of the proposed alignment. The size of Lam Tei Interchange is much reduced by adopting competent design of slip roads and connections of Yuen Long Highway. In general, a number of sensitive receivers in Lam Tei area would be subject to reduced noise and air quality impacts as a result of the more compact interchange layout under the current I&PD scheme as compared with the previous PPFS scheme. The shorter ramps would result in less traffic noise and air emission to the Lam Tei area. Higher elevation and more gentle gradient (1% compared with up to 4% in the PPFS scheme) of the proposed DBL mainline would also result in reduced noise and air quality impacts to the low-rise village type sensitive receivers in the area. Traffic speeds are reduced as the trade-offs.

1.8.2.2 In the view of the above, the elevated alignment would present the best option for DBL in balancing various constraints.

1.8.3 Considerations on Depressed Road and Tunnel Alignment for DBL

1.8.3.1 The former assessments have reviewed the major tunnel alignments as for the long tunnel and cavern under Castle Peak Hills. This EIA further investigated the possibility of individual road segments between Hung Shui Kiu to Route 10 in the preferred option for the application of tunnel and depressed road alignment to reduce environmental impacts.

1.8.3.2 The desirable gradient for a mainline like Deep Bay Link is limited to 3% as required by the Transport and Planning Design Manual (TPDM). A depressed road passing underneath Castle Peak Road and climb up again to pass over YLH for connection to Route 10 Lam Tei Tunnel will be around 5.25% which is very steep.

1.8.3.3 The desirable gradients of these ramps are 4% and the maximum that is acceptable to TD is 6%, some of them are already 6% for the current viaduct scheme. With a depressed road system, the gradients of these slip roads have to exceed 10%, which is not acceptable by TD. This is illustrated in Figure 1.7.

1.8.3.4 A mainline passes under Castle Peak Road will also pass underneath LRT, where there are very stringent requirements that is difficult to meet. One requirement will be such that the cover will be very large, ie the road level will be very much below the at-grade rail level, thus the gradient of the mainline will be further adjusted.

1.8.3.5 To comply with TPDM, changing lanes within a depressed carriageway or tunnel is not allowed. The weaving distance from 1 lane to another plus the taper length are quite long, hence a bifurcation or an interchange should be around 400m away from a tunnel portal depending on the traffic figures. This requirement is different from a viaduct option and is a fundamental and big constraint to the road design.

1.8.3.6 A depressed carriageway is bounded by wall on both sides, the sight distance is limited at curves and for tight radius curves, the sight distance will not satisfy the requirements of the TPDM. This can only be mitigated either by using a large radius or a non traffic corridor within the depressed carriageway (ie a strip of road similar to a hard shoulder but may have to be provided at the fast lane). Due to the land constraints, this is not quite feasible for this project and is not cost effective.

1.8.3.7 Part of the depressed carriageway has to be constructed by cut and cover method. The excavation may be very deep and extensive temporary shoring works will be necessary. For shallow excavation sheet piling will be used, and for deep excavation, diaphragm walls or contiguous bored pile wall have to be used. These systems are costly and time consuming and it is consider that it cannot meet the programme of the project.

1.8.3.8 The layout of HSK NDA was planned with several roads connecting to DBL which are elevated. A depressed road system is not feasible to connect these HSK roads due to the gradient and headroom problem. In particular when a desirable sight distance is required, the radius of any tunnels, subways or submerged roads will be large and is therefore space consuming.

1.8.3.9 Ventilation is required for the depressed carriageway system, and usually ventilation buildings will be provided at the tunnel portals at either end. The air quality will be concentrating at these areas and may have adverse effect to some part of the area. For this particular project, it seems that it is difficult to locate a suitable space that is suitable for a tunnel portal with a ventilation building.

1.8.3.10 A tunnel is always more risky than a viaduct during operation and construction. A fire occurs within a tunnel is always many time more dangerous than it happens on an open highway. Due to the fact that a tunnel is enclosed and suffocation is always the major problem which will not occur on an open highway.

1.8.3.11 A large team of patrol and operator is required for the normal operation and safety of the tunnel is required and the operating cost is costly. Together with the operating cost (mostly for ventilation and lighting) and maintenance cost, the recurrent cost can be very high. That is why tolling is required for tunnel, which in fact is to subsidise the operating cost rather than the construction cost, although it is equally more expensive than a flyover. When the toll level is high, the route is not attractive to traffic any more.

1.8.3.12 Depressed road and tunnel alignments are considered not suitable for Deep Bay Link.

1.8.4 Considerations on Foundation Construction Methods

1.8.4.1 The northern section of DBL at the interface with SWC traverses a coastal drainage sub-catchment that drains direct to Deep Bay. This section of DBL is to be constructed predominately on viaduct with localised sections of at grade construction determined by the hilly topography.

1.8.4.2 Considerations were given to the potential water quality impacts to Deep Bay mudflats during construction associated with the proposed bored piling operation from one pair of piers located approximately 15m to the northwest of Deep Bay Road.

1.8.4.3 The excavated material in forming a bored pile would likely have a high water content contaminated with suspended solids. Discharge of contaminated water from excavated material may be hard to control and may have the potential to contaminate  the mudflats. The following options were put forward for consideration:

• Adoption of a different piling methods including driven H-piles (hydraulically driven) and pre-bored H piles.
• Increasing the viaduct span to reduce the number of columns.

Review of Piling Methods and their Potential Environmental Impacts

General Considerations on the Foundation Selection

1.8.4.4 The viaduct of SWC and DBL are both long span structures with typical spans of around 75m. The typical vertical loading of these structures would be in the order of 50MN. The use of deep foundation (piles) is therefore needed. The selection of the most suitable type of foundation depends on the load carrying capacities, ability to cope with the difficult terrain, resistance to lateral loads, environmental impacts, safety, speed of construction, cost, durability and constructability. By considering all these factors, large diameter bored pile was considered to be the most suitable foundation type for the route. A balance between engineering and environmental considerations were arrived as described as follows:

Driven H-Pile

1.8.4.5 This involves the driving of the pile by percussive action. This method avoids the need for removal of excavated material and there is no risk of spillage. However, driven piles have a rather small load carrying capacity of around 3.8MN each and hence would require a large number of piles per pile cap and prolonged piling time and associated impacts.

1.8.4.6 One of the main concern would be H-pile might not be able to achieve the required depth for the bridge structure in this DBL due to its constraints and geology. H-piles driven by vibratory hammer would have problem reaching the required depth. However, this is subject to confirmation by the detailed geological site investigation.

1.8.4.7 The environmental concern with driven H-piles including those driven by hydraulic hammer is the noise and vibration impact to noise sensitive receivers. Strict control would be required to control noise limiting piling to just 3 hours per day. This combined with the greater number and slower progress rate per pile would have a prolonged implication on nearby residents. Further the percussive noise from the operation is likely to have a disturbing effect on fauna, driving away wildlife from the surrounding area. However, it is noted that such noise impact could be controlled by intensive mitigation measures or sophisticated piling method e.g. impulsive pile driver by compressed air-operated machines, complete enclosure of the piling rig, use of resilient packing and dolly, use of acoustic shrouding and damping, etc.

1.8.4.8 Another area of concern is the secondary effect from pile driving which is the strong vibration induced and propagated through the ground. The vibration is likely to have significant effect on the local ecology as well as the nearby residents.

Bored Pile

1.8.4.9 This is constructed by installing casing and removing the soil within the casing by grabbing. The grabbed material is muddy slurry and if dumped onto the ground can cause contaminated runoff. However, if the excavated material is disposed direct to a series of skips or tanks, the potential impact would be minimal. The process is tedious and requires storage space for containers but since only one pile would be done at a time for these two pile caps, a clean and controlled process could be handled if properly supervised. The small amount of muddy water leaking from the grab onto the ground can be effectively contained and collected by specific measures. One method is to excavate a trench where the water and slurry would collect. Water in the trench would dissipate into the ground water avoiding impact to the streamcourse or the Deep Bay mud flats. Another possible method would be the use of sheetpiles to enclose the whole of the site, particularly fencing off the site from the nearby stream course. Careful arrangement of the site using sandbag bunds and cutoff channels to prevent cross contamination of general runoff and runoff from the working area would be required.

1.8.4.10 It is noted that many instances of bored piling causing site contamination are due to contractor's preference to expedite construction by dumping the excavated material direct to the ground adjacent to the pile and using a backhoe to load onto trucks later. At Deep Bay this can readily be controlled by incorporation of appropriate clauses in the particular specification preventing this working method and requiring the contractor to provide method statements for approval that prevent contamination.

Pre-bored H-pile

1.8.4.11 It uses percussive action to drill down the hole while taking a temporary casing down with it. The soil is removed by blowing compressed air into the bore thereby blowing the soil from the bore. A steel H-pile is then lowered into the bore and backfilled using tremie concrete. The action of removing the soil is necessarily uncontrolled and as a result muddy water from the bore gets spread around the site. The contractor would use sheeting at the top of the bore to prevent widespread dispersal. This is not wholly effective in preventing dispersal of excavated material or the discharge of muddy water. As far as possible the discharged water would be collected and conveyed to a settlement tank prior to discharge.

1.8.4.12 As the capacity of each pre-bored H-pile is much smaller than that for bored pile, one would need a number of H-piles to replace each bored pile. Overall, in terms of controlling muddy run-off, this piling technique is considered to be slightly inferior to that of bored pile.

Proposed Precautionary Measures

1.8.4.13 It is proposed that bored pile foundation be used for these two concerned pier locations. The recommended precautionary measures against runoff of silt onto Deep Bay are shown in Figures 4.3 and 4.5. First, a row of interlocking sheetpiles would be installed to essentially fence off the area from the nearby stream course. Second, a series of treatment/settlement tanks would be arranged on site to handle the excavated materials, carry out treatment before discharging the water. Obviously, a testing program on the quality of the treatment water would have to be implemented on site as well. The layout of the treatment/settlement tanks, along with the piling arrangement are shown in Figure 4.3 for information.

1.8.4.14 Details of the proposed mitigation measures are presented and discussed in the Water Quality Chapter.

Suggested Contractual Arrangements

1.8.4.15 Quite often good intent in design may not effectively transferred into good practice on site because inevitably the contractor would try to get away with doing the minimum of works to minimize their cost. This is particularly true for the implementation of environmental measures. It is therefore suggested that the proposed measures stated in Water Quality Chapter should be properly designed and formed part of the contract and reflected in the tender drawings. In this way, the works are priced and paid for accordingly, giving a much better chance of its full implementation on site.

Increasing the Viaduct Span to Reduce the Number of Piled Supports

1.8.4.16 The consideration of various span lengths across the Deep Bay coastal area has been part of the SWC EIA study. The consideration of the first span from the landside joining between DBL and SWC are summarized below:

1.8.4.17 The viaduct at this section of DBL in Ngau Hom Shek already has adopted a long span of 75m between piers, which is greater than the standard spans of some 45m. The selection of a 75m span was selected based on a number of considerations including environmental and structural configuration.
1.8.4.18 A longer span bridge requires a larger column than the short span bridge. This was considered in the SWC EIA through the water quality modelling where a 75m was agreed to be optimal. It was found that a greater span with larger columns had greater impact on the upstream flow conditions where the velocities decreased and sedimentation increased.

1.8.4.19 A longer span also requires a much deeper deck section with a greater area of the bridge exposed to wind significantly increasing wind loading. Also the deeper and longer the deck, the greater the vertical load at the columns supports and associated seismic (horizontal) load. The cumulative effect of these extra loads will require a larger foundation. More piles will be necessary and would affect more of the mudflats.

1.8.4.20 According to the investigation by the consultant between HKSAR and China, the precast segmental launching method has been agreed to be the most cost-effective method for this bridge deck construction. But for a segment of 8m deep for a 150m span, it will be extremely difficult for transporting and launching. A special machine or system more extensive than the typical may need to be mobilised to the site. This machine or system may affect a larger area of the mudflat or generate more noise compared with a shorter span bridge. The designers on the Shenzhen side have advised the longest viaduct they can adopt is 75m and a mismatch between the Hong Kong and Shenzhen side viaducts, would detract from the overall appearance.

1.8.4.21 Considering locally increasing the 75m long span at the shore, this will detract from the SWC's appearance by creating odd span lengths with different deck depths at the shore. In addition the deep segments required by a long span require a completely different set up of fabrication machinery to be devised and this is considered not cost effective.

1.8.4.22 To summarise increasing the span locally or for the entire SWC is not considered to have any benefit in terms of minimising water quality impacts and actually increase water quality impacts. Further, uneven span lengths from locally lengthened bridge span would detract from the appearance of the bridge and have adverse landscape and visual impacts. The greatly increased depth of the deck will also present a much greater obstruction to birds.

Conclusion

1.8.4.23 It can be seen that the alternative piling methods have adverse implications with respect to the environment. Percussive piling methods although they remove the risk of contaminated runoff affecting Deep Bay have significant impacts with respect to noise and vibration. The increased noise and vibration would have more widespread effect of driving wildlife away from their habitat. This effect would be prolonged due the longer construction period.

1.8.4.24 It is considered that potential runoff contamination from the bored piling operation could be effectively mitigated, as discussed above, with lesser impact the general site formation works. Bored piles are therefore recommended.

1.8.4.25 Considering increasing the spans at the Deep Bay coastline, this not considered to have any practical benefit in reducing disturbance to the topography or the potential for reducing water quality impacts. The recommended column spacing is 75m.

1.9 Considerations on Cumulative Effect from Other Major Projects in the Vicinity

1.9.0.1 There are several major projects in the vicinity that would have influence on DBL and its surrounding receivers. Their respective construction programmes in relation to DBL are as follows:

Project Anticipated Programme
Deep Bay Link 2003-2006
Shenzhen Western Corridor* 2003-2005
Yuen Long Highway Widening* 2003-2005
Hung Shui Kiu New Development Area* 2004-2010
Route 10 Northern Section* 2004-2007
San Wai Sewerage Treatment Works* 2004-2007

* The programme is tentative only and subject to review by the respective study.

1.9.0.2 The time-table indicated here is only for the purpose of evaluating any likely cumulative impacts with DBL in this EIA Report. The actual implementation programme will be subject to their individual study and government's decision.

1.9.1 Shenzhen Western Corridor (SWC)

1.9.1.1 The northern end of DBL will be connected to the Shenzhen Western Corridor (SWC) at Ngau Hom Shek. SWC is a proposed highway carrying a dual-3 carriageway crossing Deep Bay to connect HKSAR and Shenzhen on the Mainland side. Implementation of SWC project is synchronised with the implementation of DBL.

1.9.1.2 The SWC EIA study is currently under-preparation. The key issues to address include potential coastal/seaside impacts to Deep Bay, particularly the ecological impacts and the water quality impacts. While in this DBL EIA Report, landside impacts for DBL alignment are addressed.

1.9.1.3 The demarcation line between DBL and SWC is indicated in Figure 1.1A. The same project proponent Highways Department is responsible for the two adjoining projects. There would be likely construction phase and operational phase cumulative impacts in Ngau Hom Shek Area in this case.

1.9.2 Yuen Long Highway Widening

1.9.2.1 Yuen Long Highway (YLH) is a dual two-lane highway serving as a trunk route between Tuen Mun and Yuen Long. It will be widened to dual three-lane standard under the project "Widening of Yuen Long Highway between Lam Tei and Shap Pat Heung Interchange" and its related EIA Report was approved under the EIAO in May 2002. DBL will be connected to YLH via Lam Tei Interchange.

1.9.2.2 According to the current programme, the widening works will be carried out in parallel with the works for DBL. There would be likely construction phase and operational phase cumulative impacts along the YLH with DBL slip roads joining in terms of air and noise impacts. It is assumed in this report the relevant recommended mitigation measures for YLH will be fully implemented.

1.9.3 Route 10 - Northern Section

1.9.3.1 Route 10 - Northern Section (Route 10) is a proposed dual three-lane highway between Lam Tei and Lantau. The project will include construction of a 1.7 km long suspension bridge crossing Ma Wan Channel, a 1.65 km long tunnel at Tai Lam Chung and interchanges with Tuen Mun Road and a 4.1 km long tunnel at Lam Tei and interchanges with Deep Bay Link and Yuen Long Highway.

1.9.3.2 The project is divided into two sections i.e. the Southern Section from North Lantau to So Kwun Wat and the Northern Section from So Kwun Wat to Lam Tei. The southern end of DBL is planned to be connected to Route 10 Northern Section via Lam Tei Interchange.

1.9.3.3 Cumulative impacts during construction phase and operational for areas near the R10 tunnel portal and toll plaza in conjunction with DBL are likely. It is understood that the construction schedule for Route 10 Northern Section would be revised to a later time. For the assessment of cumulative impact in this Report, the original schedule 2004-2007 is assumed the worst case for the purpose of the environmental impact assessment.

1.9.4 Hung Shui Kiu New Development Area (HSKNDA)

1.9.4.1 The Hung Shui Kiu New Development Area (formerly known as Hung Shui Kiu Strategic Growth Area) is located in the Tuen Mun -Yuen Long Corridor and centred on a newly proposed KCRC West Rail station. It is planned to accommodate residential developments and ancillary GIC facilities, education facilities, commercial developments, container back-up area, and other regional infrastructures.

1.9.4.2 The initial Recommended Outline Development Plan (RODP) of HSKNDA was brought to public consultation in late 1999 to early 2000. The assessment carried in this DBL EIA is based on this RODP. Alternative options to cope with likely changes in HSKNDA layout are also evaluated. Any likely residual constraints imposed by DBL are identified for further consideration in the planning stage of HSKNDA. Figure 1.8 shows the layout plan of HSKNDA RODP.

1.9.4.3 For the purpose of this assessment, an alternative layout was included for air and noise assessments. The alternative layout included the following revisions:

• the Government Quarters site in Area 2C and the school sites in Area 2D was swapped; and
• the secondary school and the Indoor Recreation Centre at the side of the West Rail viaduct was swapped.

1.9.5 San Wai Sewerage Treatment Works

1.9.5.1 The San Wai Sewerage Treatment Works (SWSTW) is located in Government Land Allocation GLA-TYL 214 assigned to Drainage Services Department. It is proposed to upgrade and expand the San Wai Sewage Treatment Works (STW) and the Ha Tsuen Pumping Station to cope with the population increase in the North West New Territories (NWNT). Localized impact during construction phase is likely and however receivers are farther away from influence from DBL. Cumulative construction and operational stage impact to the San Wai STW due to the proposed DBL project is not anticipated.

1.10 Scenario Without Deep Bay Link

1.10.0.1 Due to the continued growth of cross-boundary traffic, particularly freight traffic, there are considerable demands from the public to increase boundary-crossing capacities. The existing boundary crossings at Lok Ma Chau, Man Kam To and Sha Tau Kok operate with a permit system and at present there is a restriction on the number of permits issued due to traffic congestion. Despite this control, severe congestion still occurs at the existing crossing and the increased volume of cross boundary traffic will only cause further deterioration in the coming years. Increasing the capacities of existing crossings would likely cause high traffic loading to existing roads for which refitting of mitigation measures may be difficult or not possible. The current situation has already raised the concerns from Shenzhen Authorities that severe traffic congestion often occurs in the city centre of Shenzhen. Deep Bay Link in this case provides an alternative pathway for cross-boundary traffic under proper environmental measures.

1.10.0.2 Baseline conditions of the affected areas for Deep Bay Link are evaluated in individual technical chapters. The areas are mostly rural in nature with mixed landuses such as villages, abandoned agricultural land, container storage areas, open storage areas, workshops as well as medium-rise residential developments. It is observed the general area along Deep Bay Link (Lam Tei, Hung Shui Kiu, Ha Tsuen and Ngau Hom Shek has been under development pressure. Fishponds and agricultural land are progressively turned to container storage areas. There would be increasing population, increasing needs for container storage and workshop sites, decreasing the areas of agricultural land.

1.10.0.3 Without DBL, these areas currently affected by Deep Bay Link would likely be affected by these development pressures. Traffic would be increased and heavily rely on existing village/local roads, Yuen Long Highway and Castle Peak Road, The associated air and noise pollution impact could not be controlled further due to the limitation of existing roads. Habitat loss and degradation would be driven by developmental pressure.

1.10.0.4 The overall environmental quality would be deteriorated if no proper planning is in place. While Deep Bay Link will be one of the main components of the overall NWNT development, it would provide a linkage support to future sustainable planning development which help to improve the future environment.

Table 1.1                  Tentative Construction Programme for DBL