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Advisory Council on the Environment

Shenzhen Western Corridor

(ACE-EIA Paper 17/2002)
For advice

Purpose

1. This paper presents the key findings and recommendations of the Environmental Impact Assessment (EIA) report for the Shenzhen Western Corridor (SWC) submitted under Section 6(2) of the Environmental Impact Assessment Ordinance (EIAO). The Highways Department (HyD) and their consultants will make a presentation.

Advice Sought

2. Members' views are sought on the findings and recommendations of the EIA report. The Director of Environmental Protection would take into account the comments from the ACE and the public when he makes his decision on the approval of the EIA report under the EIAO.

Need for the Project

3. The existing three vehicular boundary crossings between the Hong Kong Special Administration Region (HKSAR) and Shenzhen Special Economic Zone are nearly saturated. To relief the present congestion at the existing crossings and to cope with the expected growth in cross-boundary traffic, both the HKSAR and Shenzhen Governments propose to provide a fourth vehicular boundary crossing, i.e. the SWC between the western districts of both cities.

Description of the Project

4. The proposed SWC is a dual 3-lane highway spanning across Deep Bay linking Dongjiaotou in Shenzhen and Ngau Hom Shek at the north-western territory of the HKSAR (Figure 1 MSWORD). It will be an elevated bridge structure of about 5.1km long. The section of the highway within the HKSAR waters, about 3.2 km long, will be provided under this Project and will be connected to the local highway network via the future Deep Bay Link.

5. The proposed SWC is a Designated Project under Item A.1, Schedule 2 of the EIAO (i.e. a road which is an expressway, truck road, primary distributor road or district distributor road including new roads, and major extensions or improvements to existing roads). Construction of this Project is scheduled to commence in 2003 for road opening by the end of 2005.

Alignment Selection

6. Four alignment options with different built forms viz. straight-type bridge, curved-type bridge, immersed tube-type tunnel and drill and blast-type tunnel have been evaluated on environmental, engineering, programme, marine, cost, public perception, land and traffic factors in the EIA Report. Emphasis has been placed on the environmental factors and sensitivity tests were also conducted to test the recommended option. The results indicated that the bridge options are preferable than the tunnel options on environmental grounds. In comparing the straight and curved bridge, the EIA recommends the s-curve bridge alignment as the preferred option.

Specific Environmental Aspects to Highlight

7. The key environmental issues identified for this project are: water quality, ecology, fisheries, air quality, noise and mud disposal.

Water Quality

8. During construction, the potential water quality impacts on Deep Bay arise mainly from the dredging works for the construction of the bridge piers. They could be effectively minimized by:

  1. surrounding each bridge pier by cofferdams to contain the sediment plumes during pier construction;
  2. using closed grabs to remove sediments inside the cofferdams to prevent escape of dredged sediments during transit onto barges, and.
  3. installing silt curtains, as a secondary defense, to prevent escape of sediments, if any.

9. With the first two measures in place, the maximum increase of suspended solid levels would occur near the Mai Po Nature Reserve Area in the Hong Kong waters at about 11.9 mg/L or 17.3% increase (i.e. less than 30%, under WQO requirement) over the background value. This impact has taken into account the potential cumulative water quality impacts from the reclamation and dredging activities on the Mainland side.

10. During operation, the potential water quality impacts arise mainly from the stormwater runoff from road surface and the spillage of chemicals onto the Deep Bay mudflats due to vehicular accidents on the SWC. For road surface runoff, a twice-weekly cleaning programme using vacuum air highway-sweepers is proposed to remove the road sludge. The HyD will also monitor the effectiveness of the cleaning programme during the first year of operation.

11. Regarding accidental spillage of chemicals, the potential risks of accidents involving dangerous goods vehicles will be reduced through the enforcement of the stringent requirements for the conveyance of dangerous goods by vehicles under the proposed Dangerous Goods (Amendments) Ordinance. It is scheduled for enactment before the SWC is open to traffic at the end of 2005. As a second-tier mitigation, the EIA report has proposed an emergency response framework based on which the future Management Authority of the SWC would take the lead to develop a detailed emergency response plan with due consideration to the need to protect the ecologically sensitive Deep Bay environment. The HyD would also look into the viability of incorporating an interceptor in the bridge drainage system at the detailed design stage to further reduce the amount of accidental spillages into Deep Bay.

Ecology

12. A detailed 12-month ecological field survey was conducted in 1998-1999 under the previous Crosslinks EIA study. Further fieldwork was carried out under this SWC EIA from August 2001 to June 2002 to fill the information gap or update the survey data.

13. With the purpose of minimizing the impacts on the ecological sensitive areas of Deep Bay, several design features have been incorporated in the EIA study, including increasing the pier spacing to 75m, adopting submerged pile caps, restricting cable-stayed structures away from the intertidal zone, bridge deck height and no suspended power-lines on the bridge, etc.

14. During the construction stage, the cumulative temporary direct habitat loss will be 2.7 ha. in the subtidal zone, and 0.75 ha in the intertidal zone, due to construction activities and the use of a temporary bridge. The EIA report makes reference to the disturbance zone concept adopted in the Spurline EIA and estimates that the potential temporary loss of feeding ground for the Black-faced Spoonbills (BFS) would be 0.24ha. This 0.24ha. represents 1.6% of the intertidal feeding habitat for BFS along the south shore of Deep Bay. Previous studies have confirmed that the south shore of Deep Bay is less important to the BFS than the core feeding sites at the intertidal mudflat, fishponds and Gei Wai in the Inner Deep Bay area.

15. Apart from the temporary loss of feeding habitat, the bridge construction will also result in a loss of 0.25ha. of mangrove trees and affect about 0.001ha. of seagrass. The EIA report proposes to:

  1. compensate the loss of mangroves by planting 2 droppers near the site of impact for each tree felled;
  2. relocate the affected seagrass to an area to be identified in Pak Nai;
  3. clear the oyster beds 50m from both sides of the bridge to enhance its feeding capability for the waterbirds; and
  4. clean up and restore the profile of the mudflat after construction

16. During the operational phase, the EIA estimates that the Project will result in a permanent loss of seabed and mudflat on the HKSAR side of Deep Bay of about 0.2ha. in the subtidal zone and 0.024 ha. in the intertidal zone. This amount represents only a very tiny fraction of the total 11,500 ha. of Deep Bay seabed and the over 1,000 ha. of mudflat along the 15km south shore of Deep Bay.

17. As to the potential permanent loss of feeding ground for the BFS, the EIA report estimates that such loss would be around 0.099ha, including both direct and indirect losses. For the fact that the feeding function of 0.139 ha. of tideline will be restored by clearing the oyster beds 50m on both sides of the bridge, the EIA report estimates that there would be a net 0.04 ha. of tideline feeding ground restored for the BFS.

18. Extensive literature review on global experience finds no evidence to indicate bird collision with bridges is a major cause of fatalities that concern researchers. Observations of birds using the intertidal section of drainage channels beneath the Route 3 flyover and the field study of bird responses, including BFS, to the Lotus Bridge between Macau SAR and Zhuhai indicated that bridges present no barrier effect on birds.

19. The EIA estimates that the increase of sedimentation rates at Mai Po and Ramsar Site due to this Project will be about 0.3 to 0.5 mm/year as compared with the prevailing rates of 13 to 28.2 mm/year.

20. As an addition package of measures to enhance the long-term goodness of the Deep Bay ecosystem, the EIA report proposes a plan to restore the function of about 24 ha of Gei Wai at Mai Po (Nos. 16 & 17, as shown in Figure 2 MSWORD) as bird feeding ground by dredging of sediments to recover the level of the bottoms of water channels connecting the Gei Wai and Deep Bay. This area would be over 20 times the temporary peripheral feeding ground loss for all birds including the BFS in the SWC construction phase.

21. This plan will be completed before the commencement of the SWC construction works and the restored function is estimated to stand against the prevailing natural sedimentation for over a decade. The report also proposes a programme to locate and remove exotic mangrove species & weeds in Inner Deep Bay so as to restore the mudflat.

Fisheries

22. The EIA finds that the commercial fisheries resources located within and around the assessment area are neither abundant nor of high value. The potential losses in capture fisheries, about 0.196 ha of sea areas, would be small compared to the overall resources in HKSAR. The permanent loss of 16 ha of potential oyster farming sites within the works area would constitute a 2.1% reduction in the overall potential area for oyster beds within Deep Bay.

Air Quality

23. With the implementation of mitigation measures including watering twice daily and limiting the construction vehicle travel speed on unpaved site areas to not more than 10 km/hour, the cumulative dust impact during construction at all air sensitive receivers (ASRs) will be mitigated to within the EIAO-TM criteria. The predicted 1-hour and 24-hour TSP levels, after mitigation, at the worst affected ASRs - village houses at Ngau Hom Shek, are 435 μg/m3 and 214 μg/m3 respectively which are within the respective limits of 500μg/m3 and 260μg/m3.

24. The EIA has considered the cumulative operational impacts due to traffic emissions from the adjacent road networks and stack emissions from major emission sources in both the HKSAR and Shenzhen areas. Using conservative vehicular emission factors, the predicted highest 1-hour average and 24-hour average NO2 level at the worst affected ASR - villages houses at Ngau Hom Shek, are 82% and 95% respectively of the corresponding AQO.

Noise

25. With the use of quiet plant, on-site movable barriers, purpose-built site hoarding and limiting the number of equipment, construction noise at nearby noise sensitive receivers (NSRs) can be controlled to within the EIAO-TM criteria, with the worst affected NSRs - villages houses at Ngau Hom Shek, at 75 dB(A).

26. With the low-noise surfacing adopted as a standard provision under the current policy for high speed roads, the predicted noise levels at the nearby NSRs are found in the range of 65 to 70 dB(A) and no adverse traffic noise impacts are expected.

Mud Disposal

27. Construction of the bridge piers and the enhancement measures at Mai Po would involve dredging of marine sediments that need to be disposed of. The EIA estimates that the bridge pier construction would generate about 34,500m3 and 22,500m3 of dredged mud for open sea disposal and confined marine disposal respectively. The amount of dredged mud at Mai Po would be about 8,800m3 for confined marine disposal.

Environmental Monitoring & Audit (EM&A)

28. An EM&A programme has been put forward in the EM&A manual submitted in the EIA report. The EM&A requirements will be enforced as Environmental Permit conditions.

Public Consultation

29. The HyD has made the EIA report, EM&A manual and Executive Summary available for public comment under the EIAO on 11 September 2002. Members will be briefed about any comments received from the public at the meeting.

Environmental Protection Department
September 2002


 

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