(ACE Paper 43/2001)
This paper presents the alignment options considered for the Shenzhen Western Corridor (SWC) and the Deep Bay Link (DBL). It also discusses the advantages and disadvantages of each option and explains the reasons for adopting the recommended options for preliminary design.
2. The alignments of the SWC and the DBL were first proposed under the Feasibility Study for Additional Cross-border Links Stage 2 completed in early 2001. The proposals were based on the SWC being a bridge structure and the Hong Kong boundary crossing facilities being located along the DBL.
3. It has now been agreed that both the HKSAR and Shenzhen authorities will each responsible for the respective section of the SWC, and to co-locate the boundary crossing facilities at Shekou in Shenzen. Therefore, it is opportune to review all available alignment options to examine whether the previous proposals remain valid.
Shenzhen Western Corridor
4. The landing point of SWC on the Mainland side is Dongjiaotou, Shekou. A landing point located further away from the Shenzhen city centre is chosen in order to divert traffic from the congested existing crossings. Moreover, traffic forecasts indicate much of the cross boundary traffic would be heading to the Pearl River Delta Region which is to the west of Shenzhen city centre. At Shekou, the SWC could be conveniently connected to the highway network leading to other parts of Southern China. As much area of Shekou is already developed, the most suitable landing point would be the reclaimed land at Dongjiatou which could provide adequate space for the cross boundary facilities.
5. The crossing may be in the form of a tunnel or a bridge (see Figure 1). The Hong Kong landing point may also be at a number of locations.
6. A bridge option will involve a number of piers at Deep Bay and at the HKSAR landfall. The construction of the pier foundation at Deep Bay will involve dredging and excavation and will therefore affect the water quality, and hence the ecology. The piers will also affect the hydrodynamics of Deep Bay in the operational phase and the erosion and sedimentation patterns of Deep Bay.
7. As the coastal areas of Yuen Long are designated archaeological sites, a bridge landing with piers will affect these areas.
8. While the above effects of a bridge option have been considered, mitigation measures have also been identified. The mitigation measures will involve the use of closed grabs and silt curtains during dredging and excavation. The obstruction by the bridge piers can be compensated by dredging a small amount of sediment along the bridge alignment to restore the flushing capacity of Deep Bay. As for the piers at the landing, they affect only localized areas and archaeological rescue operation can be undertaken prior to construction of the foundation.
9. The HKSAR landing of the crossing under the bridge option can be located at three different points, namely, Sheung Pak Nai, Ngau Hom Sha and Ngau Hom Shek (see Figure 2). As the landing point at Shekou is at Dongjiaotou, areas further north or south of these three points along the coast will require a longer bridge. More piers will be required to cater for the longer length and this will increase the adverse effect on the water flow of Deep Bay. Moreover, it will be difficult to provide connections to the existing road network from a landing point further north or south of these points because of the terrain (tunnel required through Castle Peak) or constraints posed by existing and planned developments (Tin Shui Wai/ proposed Hung Shui Kiu New Development Area). Landing points further north will also be closer to the Mai Po Ramsar Site and Lau Fau Shan oyster farms. To the south, Chinese White Dolphins have been observed not far from Sheung Pak Nai and construction in that area is not recommended.
Sheung Pak Nai
10. The Sheung Pak Nai area is less than 500m away from the Pak Nai SSSI. Construction works at this landing will inevitably affect the SSSI. There are also a number of fishponds at the coastal areas which may be affected by a bridge landing. The fishponds have contribution to the ecology of the area and any disturbance is undesirable. The bridge alignment associated with this option is also closer than the other options to areas where Chinese White Dolphins had been observed.
Ngau Hom Sha
11. A bridge landing at this point will affect a number of coastal fishponds. The fishponds have contribution to the ecology of the area and any disturbance is undesirable. This landing option will also be close to the core area of the Ngau Hom Shek Archaeological Site which should not be disturbed by excavation as advised by the Antiquities and Monuments Office. The core area has been identified to have high archaeological potential where even a rescue operation prior to construction is not recommended.
Ngau Hom Shek
12. This landing point option affects the least number of fishponds among the options. Moreover, the bridge alignment associated with this option is the shortest of the three and hence there will be the least number of piers in Deep Bay waters. The site is about 2km from the Pak Nai SSSI and about 5km from Mai Po Ramsar Site. It therefore has the least effect on either of the sites out of the three landing point options.
13. Ngau Hom Shek is therefore considered as the preferred landing point for the bridge option for the SWC.
14. The tunnel can be constructed by immersing precast tunnel sections into a dredged trench to be backfilled by sand (immersed tube tunnel). However, extensive dredging will be required to form the trench, to provide a firm base for the tunnel to rest on and to form channels for the transportation of precast units. The dredging will affect the water quality and the ecology of Deep Bay during construction stage adversely. Associated backfilling works are also expected to exacerbate the problem. The landing area of the tunnel has to be at Ngau Hom Sha and Ngau Hom Shek in order to provide a safe curvature. This landing will disturb the Ngau Hom Shek Archaeological Site which is of cultural heritage significance.
15. The tunnel can also be constructed in the form of a drill-and-blast tunnel where the tunnel is formed by excavating or blasting through a suitable geological stratum. This form has the benefit of not requiring dredging and backfilling and in this regard, it is preferable to the immersed tube tunnel. Owing to the greater depth required for this tunnel form, the southern portal of the tunnel can be formed south of the Ngau Hom Shek Archaeological Site without disturbing the area.
16. A tunnel option in this instance, regardless of its form, has features that present adverse environmental impacts. It will be necessary to rely on a substantial ventilation outlet at the landing area to cope with the length of the crossing. This point source of air pollution will be difficult to mitigate for the sensitive receivers in the vicinity. Construction of a tunnel will also generate a large amount of excavated material, the disposal of which will also be a problem.
17. To facilitate the landing of a tunnel, of either form, at Dongjiaotou, the reclamation will need to be extended further outwards into Deep Bay. The extent will be some 500m for the immersed tube tunnel and over 1km for the drill-and-blast type. This additional provision of reclaimed land will likely bring about more adverse impact on the water quality of Deep Bay.
18. Of the two forms of tunnel construction, the drill-and-blast type is the construction method with less significant environmental implications. However, because of its greater depth, the tunnel has to extend through the foothills to provide a flat enough gradient for the traffic. The foothills to the west of Yuen Long are considered by the indigenous Yuen Long villagers to be of high 'fung shui' significance. The alignment is also under a traditional burial ground for burials of deceased villagers. During consultation, the villagers indicated that they strongly opposed to tunnelling through the hills and under burial grounds. In this regard, the drill-and-blast scheme will face strong local opposition which will not be easy to overcome.
19. Another point that may be noted is that the construction of tunnel options requires longer construction periods at higher costs. The longer construction period is at variance with the plan to implement this cross-boundary route as soon as possible to relieve congestion at existing crossings and to minimize the construction impact.
20. An overall assessment of the available options of the crossing is one of the subjects being studied in the on-going SWC - Investigation and Planning Study. It will also be presented in the EIA Report as a deliverable of the Study. Preliminary assessment, however, indicates that a bridge crossing has benefits over the two forms of tunnel crossing for this project.
Deep Bay Link
21. The Deep Bay Link is the route connecting SWC with Yuen Long Highway. It therefore acts as a link to integrate SWC with the existing HKSAR road network. The connection with Yuen Long Highway is chosen to be at Lam Tei so that an interchange can be located to facilitate traffic movements to access conveniently Tuen Mun Road, Route 3 - Tai Lam Tunnel and the proposed Route 10 Northern Section. The corridor between Ngau Hom Shek and Lam Tei can allow the DBL alignment to be fitted to the west of the proposed Hung Shui Kiu (HSK) New Development Area (NDA) without cutting through it. The Castle Peak acts as a constraint to locating the DBL further west especially in view of the unsuitability of using a tunnel (discussed later).
22. The location of DBL next to the HSK NDA enables it to act as a connection between the NDA and the existing road network especially for the use of heavy goods vehicles. This connection enables vehicles to or from the container back-up areas at HSK to access the SWC or elsewhere in Hong Kong without having to travel through the internal roads of the NDA. In this way, the traffic of the internal roads of the NDA can be reduced significantly and a better living environment can be provided for the residents.
23. The original DBL alignment proposed under the Feasibility Study for Additional Cross-border Links Stage 2 is to adopt an open carriageway and the route will cut through Burial Ground No. 55 (This alignment is shown as 'the original alignment option' in Figure 3). This arrangement will require removal of many graves and extensive slope works. In view of the unacceptability of mass relocation of graves to villagers and the undesirability of extensive cutting of the hills, alternative options are considered especially for the section affecting the burial ground.
24. The DBL alignment joining the SWC landing point and Yuen Long Highway at Lam Tei may follow a few options within the corridor discussed above, namely, Long Tunnel, Short Tunnel and Viaduct options (see Figure 3).
25. Owing to the need to connect to Yuen Long Highway, the section of DBL at Tuen Mun has to remain above ground to maintain headroom over Castle Peak Road, West Rail and Light Rail. As such, the arrangement of this section for all options is the same.
26. Some facilities have to be provided along DBL to enable the route to serve as a cross boundary route. These facilities include:
a vehicle weighing station operated by HK Police
a recovery vehicles base for the operation of the route
a turn-around route as close to the coast as possible for vehicles to turn back
27. The original alignment of the DBL includes an area for the boundary control facilities. As agreed with the Mainland side, the cross boundary facilities for the Hong Kong and Shenzhen will be co-located on the Shenzhen side. Therefore the provision for the cross boundary facilities has been deleted in the currently proposed alignment of DBL.
28. In this option the DBL is a tunnel with the northern portal at the coastal area. To enable a direct connection to be made with Yuen Long Highway via the Lam Tei Interchange, as well as the future Route 10 Northern Section, the southern portal has to be located at the southern end of Yuen Tau Shan.
29. A long tunnel will keep the route away from view for over half of the length of the DBL and therefore has minimal visual impact on the proposed HSK NDA and local residents.
30. While this option presents low environmental impacts on sensitive receivers, it cannot deliver a number of essential requirements of the route. It is not possible to operate a weighing facility or turn-around route inside the tunnel because weaving of vehicles is not allowed in tunnels due to traffic safety reasons. Providing them at Ngau Hom Shek will require a roundabout and connecting sliproads which will disturb the Ngau Hom Shek Archaeological Site. If they are provided at Tuen Mun near the southern portal, they will be too far from the coast to satisfy the requirement that they are located as close to the boundary as possible on traffic and security grounds.
31. The long tunnel also cannot provide the required connections to HSK NDA. Vehicles from the NDA will have to access the southern portal in order to reach the SWC. Sliproads of sizeable radii will be required. These sliproads cannot be provided because of the lack of sufficient space near the southern portal. It is unlikely that space can be made available by reducing the size of the NDA to accommodate these sliproads as the development of the NDA has to be based on a fixed area and target population.
32. The long tunnel will need to be constructed through the foothills which are regarded as of vital 'fung shui' significance by the local villagers. This scheme will therefore attract very strong opposition and will be difficult to implement. The disposal of excess excavated materials in the construction of a long tunnel will also be a problem.
33. In order to accommodate the operational facilities and to provide connections to HSK NDA, an open highway is proposed where the alignment is mostly on viaduct. It is necessary to adopt an elevated route instead of a ground level route between the foothills adjacent to Castle Peak Firing Range and the crossing with West Rail to maintain safe gradients for the traffic.
34. Noting that the route is close to the HSK NDA near the Permitted Burial Ground No. 55 of Yuen Tau Shan, and that the distance cannot be increased without affecting numerous graves, a short tunnel is proposed to be routed through Yuen Tau Shan under the burial ground. This scheme minimizes the visual, air quality and noise impacts at an area where a number of sensitive receivers (schools and residential blocks) will be located under the HSK NDA development.
35. During public consultation, the short tunnel proposal was strongly opposed by Yuen Long villagers as they considered that the tunnel would destroy the good 'fung shui' of Yuen Tau Shan.
36. This option shifts the tunnel section eastwards so that it becomes an elevated viaduct clear of the Yuen Tau Shan burial ground. This alignment places the route closer to HSK NDA. The Territory Development Department is prepared to replan the NDA to accommodate such shift and to ensure that the visual, air quality and noise impacts on future sensitive receivers will be acceptable. Discussions are under way with concerned parties to firm up the agreement.
37. In view of the strong local objections to the original alignment option, and the long tunnel and short tunnel options, the viaduct option is proposed to be adopted. We will implement suitable mitigation measures to address the environmental impacts and coordination with HSK NDA project proponents.
38. Another point that may be noted is that the construction of tunnel sections, especially the long tunnel option, requires longer construction periods at higher costs. The longer construction is at variance with the plan to implement this cross-boundary route as soon as possible to relieve congestion at existing crossings and to minimize the construction impact.
39. An overall assessment of the available options of the DBL is one of the subjects being studied in the on-going DBL - Investigation and Preliminary Design Study. It will also be presented in the EIA Report as a deliverable of the Study.
40. The assessment of various options will be further explored and presented in the respective EIA Studies to be submitted under the EIAO in 2002.