3. REVIEW OF RELATED EIA STUDIES
3.1.1 The Planning Department has previously conducted two studies on the additional Cross-border Links. From 1995 to 1996, the first study, titled "A Review of Hong Kong's Capacity to Cope with Additional Traffic Movement Associated with New Cross-Border Transport Links" (abbreviated as "Crosslinks Study"), was carried out. In 1999, the second study, titled "Feasibility Study for Additional Cross-Border Links, Stage 2: Investigations on Environment, Ecology, Land Uses Planning, Land Acquisition, Economic/Financial Viability and Preliminary Project Feasibility/Preliminary Design" (abbreviated as "Crosslinks Stage 2 Study"), was carried out.
3.1.2 The Crosslinks Study investigated a number of broad route corridors and landing points for bridge crossings, and also carried out an initial environmental assessment. The conclusions included a response plan detailing the outline highway network and recommendations for further detailed studies. As a result of this work, the Crosslinks Stage 2 Study was commissioned.
3.1.3 The Mainland authorities conducted EIA studies to assess environmental issues associated with the proposed project. The "Shenzhen Western Corridor (Shenzhen Bay Bridge) Environmental Impact Assessment Report" was completed in 1998 by the China Greening Environment Development Centre, affiliated with the State Environmental Protection Administration. The "Environmental Impact Assessment Report of the Shenzhen Western Corridor Reclamation and Foundation Treatment Engineering" was completed in 1999 by the Shenzhen Environmental Science Research Institute.
3.1.4 This section provides a review of the environmental assessments conducted previously in the two Hong Kong studies, focusing on environmental issues relating to the Shenzhen Western Corridor. A review of the two Mainland studies is included in Appendices 3A and 3B.
Bridge Crossings and Outline Highway Network
3.2.1 The Crosslinks Study carried out in Hong
Kong between 1995 and 1996 examined two proposed bridge crossings, the Shenzhen
Western Corridor and the Lingdingyang Bridge. To support these proposed bridge
crossings, an outline highway network was envisaged.
Environmental Assessment of Options
3.2.2 The environmental assessment conducted for the Crosslinks Study investigated different initial options. Engineering overview of the alternative forms of crossing option was considered in the study. The three alternative forms were bored tunnel, immersed tube tunnel and bridge.
· Bored tunnel: There were heavily faulted and fractured rock underlying the marine deposits (up to 35 m in depth). This would cause difficult to the construction of tunnel. The length of tunnel would be increased in order to keep a shallow gradient to reduce emissions in the tunnel. It would not be possible to connection with Deep Bay Coastal Road because of the depth of the tunnel. The final length of the tunnel would be about 8 km to make the connections. Advanced Tunnel Boring Machines (TBM) and a drill and blast technique were identified as the possible construction methods.
· Immersed tube tunnel: The length of the immersed tube would be about 5 km and would be at the limit of current practice for immersed tube tunnel. To provide transition structures from immersed tube to open retained structure, reclamation at each landing point would be required. A small island would also be required at the mid point for ventilation extraction. The potential impacts to water flows were addressed and should be avoided. Construction of an immersed tube tunnel would require extensive dredging of marine deposits resulting in significant impacts to marine ecology. Also, there would be problems in fabrication, transportation and placement of immersed tube tunnel units in the shallow water region.
· Bridge : Foundation conditions, span spacing
and height of bridge were the criteria for the bridge design. There would be no
significant difficulties for construction of bridge foundation. A 10% reduction
in the cross-sectional area of water was expected. Assessment of the resulting
hydrodynamic conditions and re-distribution of marine deposits was recommended.
Increased span length would minimise the impacts from the construction and
operation of the bridge. It was identified that impacts arising from
construction activities on ecology, water quality and navigation in Deep Bay
would be less than those from an immersed tube tunnel.
3.2.3 For the Shenzhen Western Corridor, three prospective landing points, shown on Figure 3.1 in Hong Kong were examined. These are:
· Ngau Hom Shek
· Ha Pak Nai
· Tsang Tsui
3.2.4 The following sections highlight key findings regarding the Shenzhen
Western Corridor and the prospective landing points.
Water Quality Impacts
Prospective Landing at Ngau Hom Shek
3.2.5 The prospective landing point at Ngau Hom Shek is located within the ecologically sensitive area of Deep Bay. This option was predicted to pose potentially adverse effects on water quality that is already under severe stress. Local circulation of marine water, sediment transport and deposition patterns could also be affected. The severity of the impact would depend on the extent of reclamation required to provide landfall and on the construction methods employed. Impacts on water quality may in turn affect marine ecology in the area.
3.2.6 The Crosslinks Study examined the construction and operation of a bridge crossing. The option of an immersed tube tunnel crossing had not been appraised, but was considered to be difficult due to the nature and depth of soft bed materials, as well as other engineering constraints. The Study concluded that whether the crossing would be via bridge or tunnel, the potential for severe adverse impacts on the existing hydrodynamic regime and the Deep Bay ecosystem exists.
3.2.7 Futian (in Shenzhen), the Mai Po Marshes, the inter-tidal mudflats areas at the mouth of the Shenzhen River were identified in the Crosslinks Study to be key areas that would be particularly sensitive to changes in the ecosystem. In addition, it was noted that disturbance to the oyster cultivation operations in the Lau Fau Shan area could lead to adverse socio-economic impacts on residents in the North West New Territories and Shenzhen Special Economic Zone. Commercial fishing activities in this area could also be adversely affected by changes to the existing aquatic regime.
3.2.8 Measures to mitigate these impacts essentially included the relocation of the landing point further south, and the provision of the landing point on already formed land.
Prospective Landing at Ha Pak Nai
3.2.9 The Crosslinks Study found that water quality impacts associated with this landing option may not be as harsh as those predicted for the Ngau Hom Shek landing point, but potential problems would still require considerable efforts to resolve.
3.2.10 Providing the landing point on already
formed land would mitigate some of the impacts.
Prospective Landing at Tsang Tsui
3.2.11 No insurmountable impact was predicted for this prospective landing point. In particular, the altering of circulation in Deep Bay was not considered to be severe.
3.2.12 Again, providing the landing point on already formed land would mitigate some of the impacts.
Waste Disposal
Prospective Landing at Ngau Hom Shek
3.2.13 The Crosslinks Study noted that disposal of construction waste and spoil would be a key concern. It was estimated that approximately 2 million cubic meters of spoil might be generated from the construction of the entire route of the tunnel option, including the highway network
Prospective Landing at Ha Pak Nai
3.2.14 The volume of spoil from all the road and bridge works was estimated to be approximately 1 million cubic meters.
Prospective Landing at Tsang Tsui
3.2.15 The volume of spoil from all the road and bridge works was estimated to be approximately 3 million cubic meters.
Air Quality Impacts
3.2.16 The Study noted that air quality would be a key issue, and had examined potential concerns associated with the operational phase of the highway network linked to each prospective landing point. The coastal route associated with the Tsang Tsui landing was found to pose less impact.
Noise Impacts
3.2.17 Noise impacts were not identified as a key issue in strategic terms. No insurmountable impact was predicted for the operational phase of the highway network linked to each prospective landing point.
Ecological Impacts
Prospective Landing at Ngau Hom Shek
3.2.18 The ecological impacts to Deep Bay were in relation to the water quality impacts. Also, loss of fish ponds may potentially occur near Ngau Hom Shek and Ha Pak Nai.
Prospective Landing at Ha Pak Nai
3.2.19 For this landing option, water quality impacts to Inner Deep Bay may not be as harsh as those predicted for the Ngau Hom Shek landing point. However, the highway network linked to this landing point may affect a country park area and stream courses in Tuen Mun.
Prospective Landing at Tsang Tsui
3.2.20 No insurmountable impact was predicted. Beaches at the landing point may however be lost.
Visual and Landscape Issues
Prospective Landing at Ngau Hom Shek
3.2.21 The Study found that visual impacts from the construction phase of this landing point would be severe but not highly visible due to the rural nature of the location. The cuttings made through the villages of San Sang San Tsuen and San Sang Tsuen in addition to Tai Lam Chung would be considered to be severe both in terms of visual impact during construction and landscape impact once construction was completed. For the operational phase, the landing point would require substantial treatment with soft landscaping to blend the structures into the surroundings.
Prospective Landing at Ha Pak Nai
3.2.22 Findings and recommendations for this landing point option were similar to those for the Ngau Hom Shek landing point.
Prospective Landing at Tsang Tsui
3.2.23 Visual impacts from the construction phase of this landing point were found to be relatively minor. Visual and landscape issues associated with the operational phase were not considered to be key concerns.
Conclusions and Recommendations of the Crosslinks Study
3.2.24 The Crosslinks Study confirmed that, due to the continual growth of cross-border traffic between Hong Kong and the Mainland, there would be a need for additional border-crossing capacity in order to meet traffic demand.
3.2.25 The landing of the Shenzhen Western Corridor could be between Ngau Hom Shek and Pak Nai, or even farther south towards Tsang Tsui.
Pak Nai was preferred, as it could minimise the potential environmental impacts.
3.2.26 Further detailed environmental study, especially in terms of quantifying impacts on water quality, air quality and noise climate would be necessary.
3.2.27 Also, further investigations to assist in
project planning and route selections, as well as highway engineering
feasibility were recommended.
3.3.1 In accordance with the recommendations of the Crosslinks Study, the Crosslinks Stage 2 Study was conducted. The Crosslinks Stage 2 Study noted that the Pak Nai landing point, recommended in the Crosslinks Study, and the Sheung Pak Nai landing point scored very low with regard to environmental, engineering, and cost and programme factors in a comprehensive option assessment of the three proposed landing points. Based on the results of the comprehensive option assessment, the third landing point, Ngau Hom Shek, was adopted for detailed assessment and the Preliminary Project Feasibility Study. An environmental assessment was carried out as part of Stage 2 work. The following sections highlight key issues identified from the assessment of the Shenzhen Western Corridor.
Water Quality Impacts
3.3.2 The Deep Bay Model, calibrated and validated under Deep Bay Water Quality Regional Control Strategy Study - Agreement No. CE 17/95, was used in the Crosslinks Stage 2 Study to predict hydrodynamic and water quality impacts from the bridge alignments in Deep Bay. The proposed Deep Bay Crossings are directly relevant to the present Study.
3.3.3 The assumptions made in the Crosslinks Stage 2 Study on the Deep Bay Crossings bridge alignment were:
· the main span consisted of three openings of 110 m, 140 m and 110 m, with a total length of 360 m;
· four twin leaf pears with two blocks of 3 x 3 piles each with a width of 2. m were used for the main span;
· ship protection islands for main span with a width of 40m were considered;
· secondary spans were designed to be supported by Y-shaped piers at a 50-m spacing, and the piers consisted of two blocks of 2 x 2 piles with a width of 1.8 m; and
· reclamation on the Shenzhen side was included in the assessment.
3.3.4 The situations with and without a bridge across Deep Bay were simulated. For the case with the bridge, two alternative alignments were examined: a northern alignment landing at Ngau Hom Shek, and a southern alignment landing at Pak Nai. Major findings from the Crosslinks Stage 2 Study are summarised as follows:
· Both bridge alignments would pose very little impact on the instantaneous tidal flows and salinity patterns in the vicinity of the bridge.
· In terms of minimising impacts on tidal flows and salinity patterns in Deep Bay, no obvious difference between the two alignment options was found.
· The reduction in the accumulated tidal fluxes was predicted to be about 1%.
· Regarding the northern alignment in particular, the potential water quality impacts due to the presence of the bridge were found to be similar for both the wet and dry season cases, and the changes in water quality landward of the bridge alignment were predicted to be small.
· The use of driven piles for bridge pier construction would not cause any adverse environmental impacts, and silt curtains should be installed surrounding the works area to provide further control in sediment dispersion.
· The small-scale dredging work that would be required to construct the landing point on the Mainland side of Deep Bay was predicted to generate sediment plume. The modelling results showed that if no mitigation measures are taken, the sediment lost to suspension in the water of the works area would likely exceed the (Hong Kong) Water Quality Objectives for suspended solids (SS) concentration, but impact remote from the work area would be minor.
· The reported addressed dredging to restore the flow patterns in Deep Bay and stated that siltation rates in Deep Bay would be much the same as the baseline situation should flow conditions be restored to baseline conditions. The seabed levels in Deep Bay were expected to be stable. Future maintenance dredging may not be required after the restoration of flow patterns in the bay by mitigation dredging.
3.3.5 The Crosslinks Stage 2 Study recommended the following measures to mitigate water quality impacts:
· increasing the bridge spans;
· dredging along the bridge alignment, if required, to restore the original flow area and to reduce energy loss due to bed friction;
· deploying silt curtains for all dredging activities, and for the construction of seawall at the landing point on the Shenzhen side; and
· completing the seawall at an early stage of the reclamation and prior to the carrying out of dredging, in order to minimise sediment loss to Deep Bay waters.
Air Quality Impacts
3.3.6 The PATH model (Pollutants in the Atmosphere and their Transport over Hong Kong) was used in the Study to assess regional air quality impacts that may result from changes in road traffic emissions following the implementation of the Crosslink scheme. Levels of nitrogen dioxide, ozone and respirable suspended particulates were calculated and compared with baseline conditions as well as the Air Quality Objectives.
3.3.7 The year 2020, a scenario with the worst case total traffic emissions, was used in the simulation for situations with and without the bridge, and for a range of meteorological conditions.
3.3.8 Modelling results showed that with the bridge constructed, the levels of nitrogen dioxide, ozone and respirable suspended particulates would increase only slightly in the region. Overall, the proposed bridge would not pose any significant effect on air quality over the main urban areas of Hong Kong. Impact would be mainly localised around the bridge and the associated road-links. Also, with the bridge constructed, the concentrations of air pollutants around main arterial roads in the north eastern area of Hong Kong would be reduced, as traffic is partially shifted to the west.
3.3.9 The Study concluded that Crosslink traffic would only pose minimal effect on air quality; therefore, air pollution from vehicles should not be a constraint for the scheme. For assessing local impacts, further assessment was recommended.
Noise Impacts
3.3.10 A semi-quantitative noise assessment was carried out in the Study to identify broad implications of the scheme. Assessments results showed that on-site impacts could be effectively mitigated by appropriate measures. A vertical noise barrier on the bridge, 5 m in height and 300 m off-shore from the landing point, was recommended. Also, a more detailed assessment was recommended to further examine on-site impacts as well as off-site impacts that may result from the consequential effects of Crosslink traffic on the roads of Hong Kong.
3.3.11 The Study concluded that traffic noise would not pose any insurmountable issues, and should not be a constraint for the scheme.
Ecological Impacts
3.3.12 The ecological assessment examined the quality of habitats, species, and size/abundance of habitats/organisms that may be affected by the scheme. In addition, the duration of impacts, reversibility of impacts, magnitude of environmental changes, and effective mitigation measures were addressed.
3.3.13 The following are protected habitats and sites of concerns in the Deep Bay area:
· Ramsar Site at Mai Po
· Mai Po Marshes SSSI and Nature Reserve
· Inner Deep Bay SSSI
· Futian Nature Reserve (in Shenzhen)
· Mai Po Village SSSI
· Tsim Bei Tsui SSSI
· Tsim Bei Tsui Egretry SSSI
· Mangroves, intertidal mudflats, fish ponds, gei wai and reedbeds around Inner Deep Bay
· Mangroves, oyster rafts, fish ponds, egretry and natural coast at Ngau Hom Shek
· Seagrass beds, mangroves, mudflats, fish ponds, orchards, streams, natural coast and Pak Nai SSI at Sheung Pak Nai
· Seagrass beds, mangroves, mudflats, orchards, streams and natural coast at Pak Nai
· Seagrass beds, mangroves, mudflats, egretry, fish ponds, orchards, streams and natural coast at Ha Pak Nai
3.3.14 Species of concern identified in the Study included waterbirds,
especially migratory species, breeding herons and egrets, rare mammals,
invertebrates, seagrass and horseshoe crabs.
3.3.15 It was noted that the sensitive areas in Inner Deep Bay are large in size, containing extensive and diverse natural and semi-natural habitats that are known to be important. The mangrove area is the largest in Hong Kong, and one of the largest in South China. The area also contains one of the largest reedbeds in South China. As such, Inner Deep Bay is of critical importance to tens of thousands of birds, as well as for supporting the abundance of wildlife in the region, both fauna and flora. Similarly, the sensitive areas in Ngau Hom Shek, Sheung Pak Nai, Pak Nai and Ha Pak Nai are also important habitats in their own respect.
3.3.16 Evaluation of ecological impacts from the construction and operation of the Shenzhen Western Corridor concluded that:
· marine habitat loss and fragmentation would be minor;
· intertidal habitat loss and fragmentation would be minor to moderate;
· terrestrial habitat loss and fragmentation would be minor;
· water quality degradation would be minor to moderate;
· marine disturbance would be minor to moderate; and
· terrestrial disturbance would be minor to moderate.
3.3.17 The Crosslinks Stage 2 Study also concluded that adverse ecological impacts could be mitigated to acceptable levels by implementing appropriate measures.
3.3.18 For the construction phase of the Shenzhen Western Corridor, the following mitigation measures were recommended:
· Marine habitat loss and fragmentation could be mitigated by creating artificial reef at some of the bridge piers.
· Intertidal habitat loss and fragmentation could be mitigated by designing the bridge to pass over the intertidal zone without touching down, prohibiting access to the intertidal zone, and compensatory planting of mangroves.
· Terrestrial habitat loss and fragmentation could be mitigated by on-site compensatory habitat creation (of shrubland or woodland) as necessary using native species, compensatory planting of bamboo and native trees for egretry loss, avoiding the disturbance of egretries during the breeding season (from March to August), and keeping construction activities strictly confined.
· Water quality degradation could be mitigated by careful selection of construction methods and control measures, timing of work including avoidance of earth-moving activities during wet season, and run-off control for land-based works.
· Marine disturbance could be mitigated by the establishment and enforcement of dolphin exclusion zone, acoustic decoupling, implementing bubble curtains if percussive piling or blasting is to be carried out, the use of closed grab and silt curtain during dredging, and careful scheduling of works.
· Terrestrial disturbance could be mitigated by scheduling noisiest work activities outside the winter season.
3.3.19 For the operational phase of the Shenzhen Western Corridor, the following mitigation measures were recommended:
· Water quality degradation could be mitigated by implementing run-off treatment system in the drainage network on the bridge.
· Terrestrial disturbance could be mitigated by the use of noise barriers between the highway and the lowland/coastal habitats to the west of the alignment.
3.3.20 The Study recommended further careful consideration of construction methods and mitigation measures for keeping construction phase water quality impacts and terrestrial/marine disturbance to acceptable levels.
Conclusions and Recommendations of the Crosslinks Stage 2 Study
3.3.21 The Crosslinks Stage 2 Study identified a number of environmental concerns relating to the proposed project. Unmitigated potential impacts were assessed as being unacceptable and appropriate mitigation measures were developed.
3.3.22 Assessment of mitigated impacts indicated that most residual impacts could be reduced to acceptable levels by the implementation of recommended mitigation measures.
3.3.23 More detailed evaluation would be required in the Environmental Impact Assessment for the proposed project to determine cumulative impacts.