4. CONSIDERATION OF DIFFERENT ALIGNMENT OPTIONS

4.1 Introduction

4.1.1 The objective of this section is to investigate the alignment options for the proposed SWC. Alternative tunnel and bridge alignment options were evaluated and ranked according to the method given in Appendix 4A. Assessment involved consideration on traffic, engineering, environmental, marine, land, implementation programme, public perception and cost issues. The option with the highest score in the evaluation was chosen as the recommended alignment option for the Shenzhen Western Corridor.

4.2 Alignment Options

Landing Point Options

4.2.1 The landing point of SWC at Shenzhen side would be located on reclaimed land at Dongjiaotou (東角頭) in Shekou.

4.2.2 The following Hong Kong side landing points for SWC were considered and compared: (refer to Figure 4.1)

· Sha Kong Tsuen

· Ngau Hom Shek

· Ngau Hom Sha

· Sheung Pak Nai

Landing Point at Sha Kong Tsuen

4.2.3 Sha Kong Tsuen is the most easterly point of the proposed landing point sites. The SWC if connected to Sha Kong Tsuen from Dongjiaotou will be orthogonal to Deep Bay. For a bridge option, bridge piers can be orientated orthogonal to the water current but the bridge is slightly longer than at Ngau Hom Shek alignment.

4.2.4 Sha Kong Tsuen is closer to Lau Fau Shan with comparatively more abundant oyster beds along the coastline. Construction work there is likely to create higher impacts to these oyster beds than at other landing points. There are also fishponds along the coastline and the nearby Deep Bay Road. The only valley that can allow a road to pass through is heavily populated and also currently occupied by a very active container yard. Large land resumption and resettlement would have to be carried out if this alignment is adopted.

4.2.5 There are two archaeological sites, namely Sha Kong Tsuen Archaeological site and Sha Kong Miu Archaeological site, in the vicinity. An SWC alignment landing at Sha Kong Tsuen would need to avoid impacting the Sha Kong Miu (Temple).

4.2.6 The available space provided would not be suitable to accommodate a trunk road to connect SWC with Yuen Long Highway (YLH) and Route 10. A road in this case would be very close to Tin Shui Wai, and would have adverse environmental impacts as well as traffic impacts.

4.2.7 In addition to the above factors, the alignment option via Sha Kong Tsuen would encroach on the Hung Shui Kiu New Development Area and TDD would not favour such encroachment.

4.2.8 In conclusion, landing point at Sha Kong Tsuen was discarded in view of the above problems.

Landing Point at Ngau Hom Shek

4.2.9 The SWC is also orthogonal to Deep Bay if connected at this site to Dongjiaotou. The length of the route is also the shortest among the landing point options. There is a valley immediate south of Deep Bay Road such that the connection road (i.e. DBL) could utilise this valley to go southward.

4.2.10 Ngau Hom Shek is located east of the Castle Peak Firing Range (CPFR). The connection road, DBL, is not allowed to encroach into the CPFR under any circumstances. The number of fishponds along the coastline is the least in Ngau Hom Shek, and hence the impact would be the least.

4.2.11 Neither the Mai Po Ramsar Site nor the SSSI at Sheung Pak Nak is close to this site. It is also far away from areas where dolphins have been sighted.

4.2.12 The valley is the only area in the vicinity that it is not identified as a permitted burial ground. There is no grave along this valley although the cut slopes could affect a few graves.

4.2.13 There is no historical building in this area. The private lots and population to be cleared would be minimal. There are only a few houses to be cleared and the majority of the private lots here are used as storage yards and are inactive due to inconvenient traffic through Deep Bay Road.

4.2.14 The connection to DBL is excellent which could satisfy all the requirements from relevant government bodies such as TD, HyD, Police, TDD and DSD etc. In particular, TDD required that DBL should provide connections to HSK NDA.

Landing Point at Ngau Hom Sha

4.2.15 The site is about 1km west of the valley between BG YL/57 at Ngau Hom Shek. Hence a straight linkage to the road at the southern section is not possible. A fairly large area to accommodate a horizontal bent is necessary if the road is to be at-grade or elevated. If the turning is underground or if retaining walls are provided, the sight line is the critical factor for providing the horizontal alignment. A very large radius (as large as 1,000m) may be required depending on the design speed or the width of hard shoulder.

4.2.16 Ngau Hom Sha is located just east of the Castle Peak Firing Range (CPFR). A direct link with the south (i.e. HSK NDA) would need to be in the form of a tunnel since the hill is very high at this location.

4.2.17 Along the coastline here, there are more fish ponds than Ngau Hom Shek. The number of private lots and population are also slightly more.

4.2.18 The landing point is very close to the core site of the Ngau Hom Shek Archaeological site as identified by AMO.

4.2.19 The boundary of the permitted burial ground area YL/57 extends from Ngau Hom Shek to abut the boundary of the CPFR at this area. Hence there is no land between the burial ground and the CPFR to allow for an at-grade road to pass the hill to the south. A tunnel option through the CPFR is potentially hazardous. A tunnel through the permitted burial ground was objected by local villagers at consultations with the rural committees.

Landing Point at Sheung Pak Nai

4.2.20 A small area of Sheung Pak Nai is classified as Site of Special Scientific Interest (SSSI) with high ecological value. Any construction work there is prone to affect the environment, in particular ecology. A link connecting Dongjiaotou and HKSAR at this place would be skewed to the coastline thus making the link longer.

4.2.21 To avoid disruption to the SSSI and also the CPFR, any alignment with landing point near Sheung Pak Nai has to be in the form of a deep tunnel.

4.2.22 This site is the most westerly site of all sites mentioned above. Although the water in this area is shallow, it is closer to the area where the Chinese White Dolphin have been observed.

Option A - Bridge Option (Straight Type) Landing at Ngau Hom Shek

4.2.23 This option proposes a bridge connecting Shenzhen at Dongjiaotou and Hong Kong at Ngau Hom Shek. Figure 4.2 shows the horizontal and vertical alignments. This alignment is the shortest of the four landing options and relatively straightforward. The alignment beyond the Boundary of HKSAR entirely follows the proposed alignment in the Mainland FS Report dated July 2001 and it is the most preferred option by Mainland. The plan and elevation of this option is shown in Figure 4.3.

4.2.24 At the northern and southern navigation channels, cable-stayed bridge has been proposed to provide a landmark view to the Deep Bay that was also recommended by Mainland. The tentative layout of the bridge is shown on Figure 4.4

4.2.25 The geological cross section for this alignment, based on limited ground investigation data, is shown in Figure 4.5.

Option B - Bridge Option (Curved Type) Landing at Ngau Hom Shek

4.2.26 This option is more or less the same as alignment option A. This alignment is shown on Figure 4.6. The curved shape of the alignment was proposed from the point of aesthetic view. Although the length of the alignment is slightly longer, the curved feature may enhance this option visually. The vertical alignment is the same as option A. The plan and elevation of this option is shown in Figure 4.7.

4.2.27 Similar to option A, cable stayed bridge has been proposed for both the northern and southern navigation channels as shown in Figure 4.4

4.2.28 The geological cross section is also similar to option A, as shown in Figure 4.5.

Option C - Tunnel Option (Immersed Tube Type) Landing at Ngau Hom Sha

4.2.29 Immersed tube tunnel was proposed for this tunnel alignment landing at Ngau Hom Sha. The tunnel would have to climb up to the land and reach the valley in YL/57 with a maximum gradient of 3%. The tunnel portal would be located slightly south of Deep Bay Road just above the ground surface. Due to required sight distance, the radius within the tunnel is large (around 1000m) and due to the required gradient, it has to utilise the area between Deep Bay Road and the hill identified as Permitted Burial Ground YL/57.

4.2.30 To connect the HSK NDA, which is a requirement, the road has to curve around the valley through the BG YL/57 via the Ha Tsuen Interchange. The alignment is shown on Figure 4.8.

4.2.31 The tunnel box would be composed of 4 cells in which two cells would be used for ventilation purpose. As shown in Figure 4.9, the cross-section of the ventilation cells required is comparable to the carriageway cells as the length of the tunnel is approx. 5.5km which is almost four times the length of the Western Harbour Crossing.

4.2.32 The geological cross-section for this alignment, based on limited ground investigation data, is shown in Figure 4.10. Apart from navigation consideration, the foundation system was also considered in determining the vertical alignment of the tunnel. Although it is possible to found a significant length of the tunnel within the soft marine mud, due to no net increase in vertical effective stress from the tunnel, it is still geotechnically preferred to found the tunnel beneath the marine mud. There are four main reasons for this:

· The top of the partially dredged mud would be heavily disturbed and softened to different degree along the alignment. The subsequent placing of the tunnel box would cause uneven settlement at the different units.

· Extremely difficult to achieve a good blanket before placing the tunnel units, leading to permeation of clay and hence uncontrolled settlement.

· Inadequate bearing capacity from the marine mud during construction when the tunnel units have to be temporarily supported by footings.

· Further ground investigation, using both marine boreholes and marine CPT, would be required at the detailed design stage to better define the vertical alignment if this option is chosen. At both ends where the tunnel has to rise to road levels, it would be necessary to replace the dredged marine mud with marine sand fill or rockfill in order to achieve the desired alignment.

Option D - Tunnel Option (Drill and Blast Type) Landing at Sheung Pak Nai

4.2.33 This option is similar to option C but drill and blast construction method was proposed for this option. The tunnel would be located further down in rock thus requiring this construction method, and hence it is very deep for the section within Deep Bay. It has to climb up to the land and reach the portal near Ha Tsuen with a maximum gradient of 3%.

4.2.34 To allow for sight distance, the turning radius for the tunnel would be very large (1000m). To provide adequate gradient (less than 3%) the road has to utilise the entire area south of Deep Bay Road. To connect HSK NDA, the road would be aligned to connect the Ha Tsuen Interchange.

4.2.35 Due to the substantial length of the tunnel, a ventilation tunnel is required for the whole alignment and more than two ventilation buildings may be required. The tentative cross-sections are shown on Figure 4.11.

4.2.36 For drill and blast tunnel excavation, it is preferred to locate the tunnel within competent rock of Grade III to Grade II to avoid extensive temporary stabilisation. The proposed vertical alignment is illustrated in Figure 4.12 against the preliminary geological profile established based on limited ground investigation at this stage, see Figure 4.13. Towards both ends where the tunnel has to rise to meet ground level, the tunnel will inevitably need to go through less competent rocks. In such case, careful staging and specifically planned excavation techniques with primary support requirements are essential.

4.2.37 At the HKSAR end, it is possible to achieve the excavation mostly within decomposed rock of varying degree of decomposition. At certain location, the ground cover above the tunnel would be insufficient for the drill and blast technique. In such cases, different construction technique would have to be employed.

4.2.38 At the mainland end, it would have to pass through sediments and eventually marine deposits near the reclamation. Obviously, the use of drill and blast would not be appropriate here. It is envisaged that this section would be constructed by cut and cover techniques. Various environmental factors would have to be considered in coming up with the appropriate cut and cover method if this option were to be chosen.
Machine Bored Tunnel

4.2.39 The road width of SWC per carriageway is 15.05m crossing of 3 traffic lanes each 3.75m wide (to meet Mainland requirement), a hard shoulder 3.3m wide and a marginal strip 0.5m wide. For a tunnel option of SWC, with one tunnel for each carriageway, 1.5m wide elevated walkway would be required on each side of the tunnel. This would add up to a total width of 18.05m. The maximum diameter for tunnel boring machines is about 14m, which is less than the 18.05m minimum required for SWC. Therefore, agreement with the Mainland Authorities to further reduce the total width of the tunnel cross section would be required for the use of this machine bored tunnel option.

4.3 Evaluation Of Alignment Options On Environmental Aspect

Noise Impact

4.3.1 The impacts due to noise generated by the alignment options during construction and operational phases of the SWC project are presented. Details of the rating scale are included in Appendix 4A.

Operational Noise

4.3.2 Operational traffic noise impacts from each of the options were assessed. Sensitive receivers and their respective assessment points were identified to evaluate the potential impacts. Mitigation measures would be proposed if exceedance of the EIAO-TM noise criteria was predicted, so as to minimise any adverse potential noise impacts.

(1) Unmitigated Scenario

Option A - Bridge Option (Straight Type)

4.3.3 The predicted noise levels ranged from 64 to 74 dB(A). Exceedance of up to 4 dB(A) was predicted at some of the receivers. It was estimated that about 52% of dwellings would be within the EIAO-TM noise criterion of 70 dB(A). The source of exceedance would be solely due to the traffic noise of the proposed SWC alignment during operation.

Option B - Bridge Option (Curved Type)

4.3.4 The predicted noise levels also ranged from 64 to 74 dB(A). Exceedance of up to 4 dB(A) was predicted at some of the receivers. It was estimated that about 52% of dwellings would comply with the EIAO-TM noise criterion. The source of exceedance would also be due to the traffic noise of the proposed SWC alignment during operation.

Option C - Tunnel Option (Immersed Tube Type)

4.3.5 Predicted noise levels ranged from 64 to 83 dB(A). Exceedance of about 10-12 dB(A) was predicted at the assessment points (8036, 8038, 8048, 8049 and 8050) in close proximity to the proposed alignment. It was estimated that approximately 43% of dwellings would comply with the EIAO-TM noise criterion. Noise impact was attributed to the proposed SWC alignment.

Option D - Tunnel Option (Drill and Blast Type)

4.3.6 Noise impact was not predicted at the sensitive receivers because of the hilly and terrain nature of the existing area surrounding the tunnel option. None of the dwellings would be affected and the noise criterion would be fully complied.

4.3.7 No traffic noise modelling result was given for Option D since the alignment of this option would be underground and noise impact on the nearby sensitive receivers was not expected.

(2) Mitigated Scenario

4.3.8 Since exceedances were found at some of the sensitive receivers under Options A, B and C, mitigation measures were proposed to minimise the adverse impact.

Option A - Bridge Option (Straight Type)

4.3.9 Low noise surfacing was proposed for the roads with vehicle speed limit greater than 70km/hr. All proposed low noise surfacing should be designed according to the design guidelines/practice notes issued by HyD Guidance Note No. RD/GN/011B. With low noise surfacing in place, noise levels would be reduced to within the EIAO-TM standard. Hence, the level of impact should be low.

Option B - Bridge Option (Curved Type)

4.3.10 Same type of mitigation measure as Option A was also proposed. The predicted noise level would be the same as Option A and within the EIAO-TM standard. The level of impact was also expected to be low.

Option C - Tunnel Option (Immersed Tube Type)

4.3.11 Low noise surfacing was also proposed for the roads with vehicle speed limit greater than 80km/hr. In addition, mitigation measures in the form of 3m and 5m high vertical barriers were proposed at the cut-and-fill slope. With these mitigation measures in place, noise levels would be reduced to within the EIAO-TM standard. The level of impact was expected to be moderate.

Option D - Tunnel Option (Drill and Blast Type)

4.3.12 Mitigation measure would not be required as minimal impact was predicted. The noise level would be similar to background noise level.

4.3.13 Table 4.1 summarises the traffic noise impacts under unmitigated and mitigated scenarios for the sensitive receivers.

4.3.14 From the predicted noise levels, Option C showed a higher level of noise impact during operation than both Options A and B if no mitigation was provided. With mitigation measures in place, noise impact could be kept within the EIAO-TM noise criterion for all options.

Construction Noise

4.3.15 Potential noise impact would be emanated from using powered mechanical equipment (PME) for different activities during the construction phase. The magnitude and duration of noise impact during construction for each of the option is discussed below. Mitigation measures were recommended to prevent and reduce potential noise impacts from such activities.

Option A - Bridge Option (Straight Type)

4.3.16 Highest noise impact was expected during the fabrication yard activity among all types of the construction activities. The calculated sound power level (SWL) was about 127 dB(A) for this activity which involves the fabrication of precast segments and batching plant operations with a duration of about 9 months.

4.3.17 To reduce the potential construction noise impacts, mitigation measures are required and the followings have to be considered:

· Use quiet plants and working methods;

· Use quiet plants and movable noise barriers;

· Reduce the numbers of plants operating in critical areas close to NSRs; and

· Use noise screening structures or purpose-built noise barriers along the site boundary.

4.3.18 Provided that proper mitigation measures were in place, construction noise would not result in adverse impact on nearby sensitive receivers.

The impacts would also be transient.

Option B - Bridge Option (Curved Type)

4.3.19 The calculated SWL were also the same as Option A and the highest potential noise impact was also expected to occur during the fabrication of precast segments and batching plant operations with the same construction period of about 9 months. Recommended mitigation measures would also be the same as that of Option A mentioned above.

4.3.20 Provided that proper mitigation measures were in place, construction noise would not cause adverse impact on nearby sensitive receivers.
Option C - Tunnel Option (Immersed Tube Type)

4.3.21 Construction of the cut-and-cover tunnel section and at-grade approach road would involve using a large amount of PME, generating noise impacts on nearby sensitive receivers. Construction of the at-grade approach road would generate the most noise impact. The calculated SWL was about 128 dB(A) for this activity for a period of about 16 months.

4.3.22 Considering the longer duration of this noisy construction activity compared to the noisy ones of both Options A and B, Option C would have greater construction noise impacts on the sensitive receivers.

4.3.23 To lessen the construction noise impacts, mitigation measures should be provided as for Options A and B mentioned above.

Option D - Tunnel Option (Drill and Blast Type)

4.3.24 The highest noise emanating activity would be the drilling and blasting activity for the tunnel construction. The calculated SWL for drilling and blasting per each tunnel was about 128 dB(A), and the activity would last for about 40 months.

4.3.25 Since the construction site is rather distant to the sensitive receivers when compared with the other options, in addition to the topographical feature which acts as natural barrier, noise impact was expected to be minimal.

4.3.26 Recommended mitigation measures would be the same as those of the other three options. However, as there would be ventilation shafts provided for this tunnel option, potential noise sources would be emanated from the fan systems. Therefore, other mitigation by incorporating silencer and acoustic louvers into the exhaust system should also be provided to reduce the noise impact.

4.3.27 Table 4.1 summarises the construction noise impacts of the four options.

Evaluation of Noise Impacts Arising from Various Options

4.3.28 The impacts of operational traffic noise and construction noise from the four options are summarised in Table 4.1.

4.3.29 Since the impact of operational traffic noise is long-term while the construction noise is transient in nature, much weighting was given to the traffic noise impacts in determining the overall ratings.

4.3.30 Since Option C (Tunnel option - immersed tube) would have longer duration of construction noise impact from the noisiest activity and higher operational traffic noise impact when no mitigation measures were provided, it was concluded that this option would pose the greatest noise impact on the nearby sensitive receivers.

4.3.31 Overall, Option D scored the highest rating while Option C the lowest. Both Options A and B had the same score. The assessment was based on the information available during the early stages of options development. The preferred option was further assessed under Section 6.

Table 4.1: Evaluation of Noise Impact to Sensitive Receivers

Air Quality Impact

4.3.32 Impacts due to air emissions generated by the alignment options during construction and operation stages after practical mitigation measures were considered. Details of the rating scale are described in Appendix 4A.

Operational Phase Air Quality Impact

4.3.33 The Traffic Impact Assessment Update (Final) Report (May 2001) of Agreement No. CE 109/98 Deep Bay Link Investigation and Preliminary Design predicted year 2021 peak hour traffic flow on each direction of SWC to be approximately 3800 vehicles per hour and the percentage of heavy vehicle to be about 66% for both directions.

4.3.34 With reference to the vehicle emission factors in the Fleet Average Emission Factors - EURO3 Model provided by EPD, the fleet average emission factors of year 2011 (the last future year forecast) were taken in this assessment as conservative estimates for year 2021. This did not take into account the possible improvement in the fleet average emission factors between year 2011 and year 2021.

4.3.35 Using the above assumptions, vehicle emissions of nitrogen oxides (NOx) were estimated for the four alignment options and are tabulated in Table 4.2. To provide a fair comparison between the four alignment options, the alignment length for each option was taken as the length from the connection point of SWC at Mainland China to a point on Deep Bay Link about 1km inland from Ngau Hom Shek.

Table 4.2: Comparison of Total Peak Hour NOx Emissions from Different Alignment Options

4.3.36 As shown in Table 4.2 above, the total NOx emission of the tunnel options (Options C and D) are higher than the bridge options (Options A and B) by 13% to 17%. The NOx emissions estimated above in Table 4.2 do not take into account the higher vehicle emission rates due to changes of road gradient. The changes of road gradient for the tunnel options are larger, in particular for Option D, compared with the bridge options. Even higher total NOx emissions would therefore be expected for the tunnel options when compared with the bridge options.

4.3.37 The air quality impacts at sensitive receivers due to vehicle emissions from SWC would depend on the total NOx emission from SWC as well as the dispersion pattern of the air pollutant from the source of pollution to the sensitive receivers. For the bridge options, most of the road alignment would be very much exposed. Traffic emissions from SWC would be spread all along the SWC alignment. Whereas for the tunnel options, most of the traffic emissions from SWC would be emitted from the tunnel portals and/or ventilation shafts at the two ends of the SWC alignment. In other words, the pollution loading for the bridge options would be distributed over the whole length of SWC alignment, whereas for the tunnel options the pollution loading would be concentrated at a few localised spots as well as the approach section of the tunnel.

4.3.38 For the bridge options (Options A and B), more than 80% (out of the alignment length of 6.3 km listed in Table 4.2) of the SWC alignment would be over Deep Bay with no air quality sensitive receivers in close proximity. The major air quality sensitive receivers on Hong Kong side were those scattered village houses in Ngau Hom Shek along the Deep Bay Link alignment on land side (about 1 km out of the alignment length of 6.3 km listed in Table 4.2). For compliance with the Air Quality Objectives at nearby sensitive receivers, buffer distance in the order of 20m from the road alignment would be expected. Requirement on buffer distance would be subject to detailed cumulative air quality modelling.

4.3.39 For tunnel Option C, the portal of the tunnel on Hong Kong side is near Ngau Hom Sha. About 80% (out of the alignment length of 7.1 km listed in Table 4.2) of the SWC alignment would be the tunnel section. The major air quality sensitive receivers on Hong Kong side were those scattered village houses in Ngau Hom Shek and Ngau Hom Sha in close proximity to the tunnel portal and the approach section to the tunnel. In view of the large volume of air pollutant that would be emitted from the tunnel portal and/or ventilation shaft, the impact distance of this tunnel option would be much larger (could be up to more than 100m) around the tunnel portal and/or ventilation shaft when compared with the bridge options. The actual impact distance would depend on the ventilation design of the tunnel. Air quality impact was also expected along the tunnel approach section. The length of this approach section is about 1.5 km (out of the alignment length of 7.1 km listed in Table 4.2), which is longer than the land side alignment length of 1 km for Options A and B.

4.3.40 For tunnel Option D, the portal of the tunnel on Hong Kong side is further inland to the south-east of Ngau Hom Shek. More than 95% (out of the alignment length of 7.4 km listed in Table 4.2) of the SWC alignment would be the tunnel section. In view of the longer length of the tunnel section when compared with Option C, higher emissions of air pollutant from the tunnel portal and/or ventilation shaft would be expected. The impact distance from the tunnel portal and/or ventilation shaft would thus also be larger. Nevertheless, the tunnel portal would be further away from air quality sensitive receivers compared with Option C. The nearest air quality sensitive receivers were the scattered village houses at Ngau Hom Shek about 500m away. The actual impact distance would depend on the ventilation design of the tunnel.

4.3.41 In some situations, road tunnels would collect and transfer the vehicle emissions away from sensitive receivers in close proximity of the road alignment and hence are beneficial to those sensitive receivers. However, for the SWC, since most of the road alignment (about 80%) is above Deep Bay with no air quality sensitive receivers around, the road tunnel would instead collect and bring the vehicle emissions closer to the sensitive receivers on the land side. This is not desirable and higher operational air quality impact would be expected for the tunnel options when compared with the bridge options.

4.3.42 In summary, more than 80% of the air pollutants emitted from the bridge options (Options A and B) would be dispersed and diluted over the atmosphere above Deep Bay. Whereas for the tunnel options (Options C and D), the air pollutants generated within the tunnel section would be collected and exhausted at the two ends of the tunnels in the proximity of air quality sensitive receivers. Unless proven air pollution control system for road tunnel becomes available on the market to reduce pollutant emissions from the tunnel section of Options C and D, adverse air quality impact would be expected around the tunnel portal and/or ventilation shaft.

Construction Phase Air Quality Impact

4.3.43 The major potential air quality impacts during the construction phase of SWC would result from dust arising from construction activities including site clearance, excavation and filling, open site erosion, and handling and transportation of construction and demolition material. The proposed works area for the four alignment options are similar but the intensity of the construction activities could be quite different.

4.3.44 The peak hour incoming and outgoing construction traffic flows for the four alignment options were estimated and listed in Table 4.3 below. Construction traffic was expected to travel to and from the works area at Ngau Hom Shek through Fung Kong Tsuen Road to Ping Ha Road. The construction traffic flow also gives a good indication of the intensity of land-based dust generating activities for the four alignment options.

Table 4.3: Comparison of Peak Hour Construction Traffic for Different Alignment Options

4.3.45 As shown in Table 4.3, the construction traffic flows for the tunnel options (Options C and D) are higher than those for the bridge options (Options A and B). Comparing with the construction traffic flows for the bridge options (Options A and B), the construction traffic flow for Option C and Option D would be about 28% and 156% higher respectively. The large difference between Option D and the other options is mainly related to the large volume of material generated from the drill and blast operations for the tunnel construction.

4.3.46 Besides the works area and the access roads, intensive construction activities would also be carried out along the at-grade section of the road alignment. Among the four alignment options, Option C includes a long section of at-grade approach road that would be in close proximity to many existing sensitive receivers in the area. Relatively higher construction dust impact associated with the construction of at-grade road would therefore be expected for Option C.

4.3.47 Based on the above, the construction dust impacts of Options C and D would be higher than those of Options A and B. Option C would require the construction of a longer at-grade road section, Option D would require tunnel construction by drill and blast, and the need to handle and transport a large volume of construction and demolition material.

Overall Rating of Air Quality Impact

4.3.48 With reference to the discussion above on the operational phase and construction phase air quality impacts for the four alignment options, the rating of the air quality impact is summarised in Table 4.4 below. The overall impact and rating tabulated in Table 4.4 below have taken into account that operational impact would be a longer-term impact and thus have more bearing on the overall impact.

Table 4.4: Rating of Air Quality Impact for Different Alignment Options

4.3.49 As shown in Table 4.4, the overall impact of Options A and B is moderate and the overall impact is high for Options C and D. In summary, the bridge options (Options A and B) would be better options when compared with the tunnel options (Options C and D) in air quality point of view.

Water Quality Impact

4.3.50 Water quality impacts due to the construction and operation of each alignment option were considered. Ratings were given to the alignment options based on a 5-point scale, with higher scores for the options with less impact. The interpretation of the rating scale is described Appendix 4A.

Option A - Bridge Option (Straight Type)

4.3.51 The proposed SWC bridge will be supported by a number of piers. The spacing for typical span of the proposed SWC bridge within Hong Kong and Mainland boundaries would be 75m. There are in total of about 78 pairs of bridge piers for the whole alignment. Dredging may need to be carried out for pier construction. Increases in suspended solids levels and turbidity, and potential release of contaminants from the sediment into the water column during the dredging operations would affect the water quality and aquatic environment in the vicinity of the dredging sites. Spreading of sediment plumes by tidal currents to regions further away from the dredging sites may cause adverse impacts to the marine ecology in Deep Bay. The mud flats and oyster beds near the landing points on both the Hong Kong and Shenzhen sides are likely to be affected by the dredging activities.

4.3.52 In the Deep Bay Water Control Zone, the Water Quality Objective (WQO) for suspended solids (SS) specifies that the increase in suspended solids due to waste discharge shall be less than 30% of the natural ambient level or the discharge shall not cause the accumulation of suspended solids which may adversely affect the aquatic communities. Uncontrolled release of the dredged sediment into the water column is likely to cause exceedance of the WQO. Disturbance to the seabed and release of a large amount of sediment during the uncontrolled dredging operation could increase the SS concentrations to such a limiting level causing WQO exceedance.

4.3.53 For the straight type bridge option (Option A), the bridge piers would be constructed in the form of bored piles and dredging would be confined within the bored pile casing. Release of sediment particles may only occur during the transfer of the dredged sediment to the barge. The potential release of sediment could be controlled through the use of closed grab and installation of silt curtains surrounding the working area. As a result, there should not be significant disturbance to the seabed sediment and the construction impacts in terms of sediment loss should be localised and were therefore not expected to be significant.

4.3.54 One concern is the need for disposal of the dredged sediment arising from pier construction. The dredged sediment should be disposed of in an environmentally acceptable manner. Sediment disposal may cause water quality impacts in the dumping sites and would cause reduction in the storage capacity of the dumping sites. It was however anticipated that the volume of dredged sediment to be generated from pier construction would be relatively small for this option. The effect on the dumping sites and the associated water quality impacts would not be significant.

4.3.55 Construction site runoff and sewage generation would also be the potential sources of water pollution. Adoption of the guidelines for the handling and disposal of construction discharges outlined in ProPECC Note PN1/94 on Construction Site Drainage as part of the construction site management practices would minimise the potential impacts.

4.3.56 During the operational phase, the presence of bridge piers may reduce the flushing capacity and therefore impact upon the water quality in Deep Bay. The erosion and sedimentation patterns in Deep Bay may also be altered due to changes in hydrodynamic patterns. When the flushing capacity is restored, the effect on erosion and sedimentation patterns due to the bridge in Deep Bay would be minimal.

4.3.57 Road surface runoff, which may be contaminated with silt and grit, and oily wastes, would potentially affect the water quality of Deep Bay during the operation of the SWC bridge. In general, the first flush flow contains most of the contaminants. The subsequent overland flow would be uncontaminated. Road drainage systems with the installation of silt traps along the bridge would be provided to treat the road surface runoff prior to discharging into the Deep Bay waters. The drainage pipes which discharge the surface runoff would be suitably designed to minimise the impact to the mud flats near the landing points.

4.3.58 The identified water quality impacts that may arise during the construction and operational phases of the proposed straight type bridge option could be minimised through implementation of mitigation measures. This option is not likely to cause unacceptable water quality impacts and the overall water quality impacts would be low.

Option B - Bridge Option (Curved Type)

4.3.59 The major water quality issues for this option are the same as those for the straight type bridge option. However, the curved type bridge option would involve a slightly longer bridge alignment. The preliminary engineering design determined that the length of the s-curve alignment would increase by about 21m when compared to the straight type bridge option. Due to the small increase in bridge length, there would be no need to have additional bridge pier. With a 75m span spacing for typical span, the total number of bridge piers is the same as the straight type bridge option of about 78 pairs. Same as the straight type bridge option, dredging would be confined within the bored pile casing and cofferdams. There would not be significant disturbance to the seabed sediment and construction impacts in terms of sediment loss are not likely to be significant.

4.3.60 Construction site runoff and sewage generation could be mitigated to acceptable levels through implementation of control measures and good management practices. It is expected that the amount of polluted road runoff would be slightly increased during the operational phase of this option due to the increased road surface area. However, the increased amount would be insignificant for an additional 21m of bridge section.

4.3.61 The effects on the discharge capacity for this option would be similar to the straight type bridge option. As the potential impacts for this option can be mitigated through implementation of mitigation measures, this option is not much different from the straight type bridge option. The water quality impacts for this option would be low.

Option C - Tunnel Option (Immersed Tube Type)

4.3.62 The construction of immersed tube tunnel usually adopts the cut and cover method. This would require extensive dredging of marine sediment along the SWC alignment across the Deep Bay. To provide a consolidated foundation for placing the immersed tube units, sediment dredging would be carried out along the proposed alignment across Deep Bay with a length of about 5 km and a width of approximately 100 m. Dredging a transportation channel for delivering the precast tunnel units would also be required due to the shallow water depth of Deep Bay. The mud flat and oyster beds near the landing points on both the Hong Kong and Shenzhen sides would be completely removed during the dredging of the tunnel trench. A large amount of dredged sediment would need to be disposed of for this option. This may cause secondary impacts to the water body near the dumping sites and quickly deplete the capacity of the dumping sites. The Government policy on waste minimisation encourages limiting the dredging and disposal of marine mud. This option is obviously not in line with the Government policy.

4.3.63 Due to the need for extensive dredging, this option may result in significant impacts on the water quality and marine ecology in Deep Bay. The large scale dredging may require several dredgers working at the same time in order to meet the tight construction programme. Provision of sand foundation and rock blanket requires sand and rock filling along the tunnel alignment for protection of the tunnel units. As the bed rock near the landing point on the Shenzhen side is at a low level, a large amount of sand fill would be required in this region to support the tunnel units. Loss of fines during the filling activities would be significant leading to adverse water quality impacts. Control of dispersion of sediment/fines in large working areas is difficult and high frequency of WQO exceedance for SS may occur. As Deep Bay is a very sensitive water body, extensive dredging and filling in Deep Bay would not be environmentally acceptable.

4.3.64 This option may also cause impacts to the local streams as it requires a longer land section for connection to the Deep Bay Link. Construction site runoff and sewage generation may have a higher potential to cause impacts on the local streams. The coastal section of this option on the Hong Kong side would run in close proximity to the Pak Nai SSSI. Extensive dredging during marine works as well as site runoff that generated from the land based construction sites could adversely affect the nearby water quality sensitive receivers, which are of significant ecological values. This option was considered to have the greatest potential water quality impacts.

4.3.65 The tunnel is a confined environment. Road surface would not be affected by rainstorms to generate contaminated road surface runoff. In case of an accident, release of chemicals would be within the tunnel area and would not release into the surrounding water environment. The potential water quality impacts for the tunnel option during the operational phase is expected to be minimal. However, the overall water quality impacts for this option would be severe due to extensive dredging.

Option D - Tunnel Option (Drill and Blast Type)

4.3.66 Construction of tunnel by drilling and blasting would have lower potential impact on the water quality in Deep Bay compared to other options in terms of sediment loss to the marine environment during the construction phase as the works would be carried out under the seabed. However, additional reclamation at the Mainland side would be needed for the tunnel to climb up to the landing point at Dongjiaotou where the mud flat would be completely removed during dredging. A large amount of dredged sediment would need to be disposed. This may cause secondary impacts to the water body near the dumping sites and quickly deplete the capacity of the dumping sites. Due to the need for dredging, this option would result in significant impacts on the water quality and marine ecology in Deep Bay.

4.3.67 A significant amount of drilled materials would be generated from this option. The materials are likely to be marine deposits, which should not be contaminated. Open sea disposal of the marine deposits may cause secondary water quality impacts in the water near the dumping sites and accelerate the reduction in the capacity of the dumping sites.

4.3.68 This alignment runs very close to the Pak Nai SSSI. The drilling and blasting activities in the regions near the Pak Nai SSSI, mud flats and local streams should be suitably designed and operated so as to minimise the potential impacts to these sensitive receivers.

4.3.69 Due to the confined nature of the tunnel option, there would be no road surface runoff during the operational phase of the project. Spillage of chemicals during an accident would be controlled within the tunnel area. Release of chemical spills into the Deep Bay waters is unlikely. The potential water quality impacts for this tunnel option during the operational phase was expected to be minimal. However, the overall water quality impacts for this option would be high due to the additional reclamation at the Mainland side.

Comparison of the Proposed Options

4.3.70 The potential water quality impacts associated with each of the options are summarised in Table 4.5. The key environmental issues related to the bridge option for both the straight type and curved type would be the construction of pier, construction site runoff, sewage generation, road surface runoff, accidental spillage of chemicals and reduction in flushing capacity leading to the water quality changes in Deep Bay. These potential impacts, however, would be minimised through implementation of effective mitigation measures. With all the mitigation measures in place, the bridge option was not expected to generate unacceptable water quality conditions in Deep Bay.

4.3.71 The immersed tube type tunnel option would involve extensive dredging and filling activities. Impacts on mud flats, oyster beds and water quality in Deep Bay during the construction phase would be severe and this option is not likely to be environmentally acceptable although the impacts during the operational phase should be low.

4.3.72 There would be dredging and filling activities at the Mainland side for the drill and blast type tunnel option. The water quality impact during reclamation would be high. Road surface runoff and release of chemicals into the Deep Bay waters during an accident would not be a critical concern for this option. The impact on water quality in Deep Bay during operational phase for this option was expected to be low. Disposal of the drilled materials may cause secondary impacts but it is expected to be not significant when suitable control mechanisms are in place.

4.3.73 In order to compare the effects on hydrodynamic conditions in Deep Bay between the bridge option and tunnel option, model simulations were performed to determine the reduction in flushing capacity for the two options. The factors which may affect the hydrodynamic conditions for the two options in the operational phase of the Project are:

4.3.74 The modelling results showed that the reduction in flushing capacity for the tunnel and bridge options were 7% and 3.5% respectively. Detailed of the modelling methodology are presented in Section 7.5 and the relevant assessment is presented in Section 7.7.120 to Section 7.7.133. The additional reclamation for the tunnel option would cause a reduction in flushing capacity 2 times higher than that for the bridge option. This in turn would affect the water quality and sedimentation conditions in Deep Bay. With the ramp in place, the sedimentation rates at Maipo and Ramsar sites would further increase by 0.6 to 1 mm/yr when compared to the bridge option. In view of the higher potential impacts, the tunnel option is less preferable.

4.3.75 The recommended ratings for the proposed options are presented in

Table 4.5: Comparison of the Proposed Options

Table .6: Recommended Rating for the Proposed Options – Water Quality Impacts

4.3.76 In summary, the bridge option with relatively lower water quality impacts in the construction phase was found to be preferable over the tunnel option. The operational phase water quality impacts associated with the bridge option could be controlled through implementation of suitable mitigation measures.

Table 4.7 presents the mitigation measures to minimise water quality impacts associated with the bridge option.

Table 4.7: Mitigation Measures to Minimise Water Quality Impacts

Ecology Impact

4.3.77 The intertidal, terrestrial and subtidal ecology impacts due to construction and operation of each alignment option were assessed and rated in this section. Ratings were given to the alignment options based on a 5-point scale, with higher scores for the options with less impact. Ratings were weighted according to the relative conservation implication of impacts to the intertidal zone (50% of the total rating), terrestrial zone (30% of the total rating), and sub-tidal zone (20% of the total rating). The interpretation of the rating scale is described in Appendix 4A.

Option A - Bridge Option (Straight Type)

4.3.78 The proposed SWC bridge will be supported by piers, and would have a cable-stayed portion at the southern navigation channel. Localised dredging would be required for construction of each pier, and then pre-cast sections of bridge deck would be placed on top of the piers. As noted above in Section 4.3, increases in suspended solids levels and turbidity, and potential releases of contaminants from dredged sediments into the water column during the dredging operations would affect the water quality and aquatic environment near the dredging sites. Spreading of sediment plumes and contaminants by tidal currents to areas distant from the dredging sites may cause adverse impacts to the marine ecology in Deep Bay. The mudflats near the landing points on both the Hong Kong and Shenzhen sides are likely to be affected by the dredging activities.

4.3.79 In the Deep Bay Water Control Zone, the Water Quality Objective (WQO) for suspended solids (SS) specifies that any increase in suspended solids shall be less than 30% of the ambient level or the discharge shall not cause accumulation of suspended solids which could adversely affect aquatic communities. As noted in Section 4.3 of this report, uncontrolled release of dredged sediments into the water column would probably cause exceedance of this WQO.

4.3.80 Option A bridge piers would probably be constructed using bored piles, with dredging confined within the bored pile casing. Release of sediment particles would only be expected to occur during transfer of dredged sediments to barges. Release of sediments would be controlled through the use of closed grabs combined with installation of silt curtains around the working area. As a result sediment distribution through the open water column would not be expected to be significant, therefore construction impacts due to sediment loss should be localised and acceptable.
4.3.81 Disposal of dredged sediments arising from pier construction is also an ecological concern that must be addressed through environmentally acceptable sediment disposal. Sediment disposal could cause water quality impacts and could reduce the sediment storage capacity at the disposal sites. However, a relatively small volume of dredged sediment would be generated by pier construction in Option A, therefore the effects on the dumping sites and water quality near them would be insignificant.

4.3.82 Construction site runoff and sewage generation could also cause water pollution. Off-site pre-casting would decrease the amount of site runoff and sewage production. Adoption of the guidelines for the handling and disposal of construction discharges outlined in ProPECC Note PN1/94 on Construction Site Drainage as part of the construction site management practices would minimise the potential impacts.

4.3.83 During the operation phase the presence of bridge piers may cause reduction in tidal exchange, which would affect water quality in Deep Bay. Erosion and sedimentation regimes in Deep Bay could also be affected by changes in hydrodynamics due to bridge piers. The change would not be severe, and only minimal water quality impacts and effects on erosion and deposition regimes in Deep Bay would be expected.

4.3.84 Road surface runoff would be expected to contain silt, grit, and hydrocarbon wastes. This could degrade the water quality of Deep Bay during the operation of the SWC bridge. Silt traps would be installed along the bridge to treat runoff prior to discharge into Deep Bay waters. The drainage pipes which discharge the surface runoff would be designed to minimise physical impacts to the mudflats in the intertidal zone. Spills of chemical substances on the road surface could contaminate Deep Bay waters during the operation phase. Mitigation of such accidents would require development and implementation of a contingency plan.

4.3.85 The identified potential water quality impacts due to the construction and operation phases of the Option A bridge could be minimised through implementation of mitigation measures. Because Option A is not likely to cause unacceptable water quality impacts it would also be expected to cause low or undetectable impacts upon the intertidal and subtidal ecology in the assessment area. The exception to this would be chemical spills, which would require special control or mitigation measures.

4.3.86 Construction of the Option A bridge would result in permanent removal of an area of intertidal and subtidal seabed from Deep Bay that could total approximately 0.13ha, or 0.0013% of the total Deep Bay seabed area. Some 80% of the total seabed loss would occur in the subtidal zone, with the remaining 20% in the intertidal zone (estimated 2500m of alignment in subtidal zone versus 600m in intertidal zone). The subtidal seabed supports marine organisms that are little studied in Hong Kong, thus their conservation status is largely unknown. The intertidal seabed supports vegetation of conservation concern (mangroves and seagrasses), invertebrate and vertebrate organisms that attract foraging birds, and invertebrates of conservation concern (horseshoe crabs). Migratory and resident birds using the mudflat include species of local and regional conservation concern (ardeids) and at least one species of global conservation concern (Black-faced Spoonbill).

4.3.87 Terrestrial ecology impacts would result primarily from disturbance to the Ngau Hom Shek egretry. The alignment would pass near the egretry location, thus it is doubtful that the egretry would be occupied during the construction phase. Birds could recolonise the egretry during the operation phase. If the egretry were abandoned during construction, this would cause a potential loss of nesting opportunities for up to 10 pairs of herons and/or egrets over the 3 year construction period. (Note that the mean number of nests, based upon Bird Watching Society data,from 1998-2001 was 9.5, and 10 nests were recorded during the field survey for the present EIA study.) This effect was not considered severe because the impact would not be permanent, the affected population represents some 1% of the total number of nesting heron and egret pairs in Hong Kong, and there is a nearby egretry at Pak Nai where alternative nesting habitat is available. Other terrestrial impacts are considered to be of limited conservation concern because of the highly fragmented and disturbed condition of the habitats.

Option B - Bridge Option (Curved type)

4.3.88 The ecology and biodiversity conservation issues for Option B are largely the same as those for Option A. If the Option B curved type bridge required more piers, the increased impacts from sediment resuspension and seabed loss would be proportional, as would the amount of dredged material requiring disposal. Similar to Option A, construction impacts arising from sediment re-suspension in Option B are not likely to be significant. Impacts to marine waters due to construction site runoff and sewage generation could be mitigated to acceptable levels through implementation of control measures and good management practices.

4.3.89 The amount of contaminated surface runoff from the road surface would be slightly increased during the operational phase due to the increased road length. This would be mitigated through the use of sediment and grease traps.

4.3.90 Option B impacts on tidal exchange might be slightly higher as a result of the increased number of piers. This could be mitigated by periodic dredging of accumulated sediments from between piers to restore tidal exchange capacity if and when needed.

4.3.91 Terrestrial impacts of Option B are identical to those from Option A.

4.3.92 Potential impacts from Option B are either insignificant or can be mitigated by implementing mitigation measures. The impacts on subtidal, intertidal and terrestrial ecology would be low. The exception to this would be chemical spills, which would require special control or mitigation measures.

Option C - Tunnel Option (Immersed Tube Type)

4.3.93 Immersed tube tunnels are normally constructed using the cut-and-cover method, which would require dredging of marine sediments over an area of approximately 50 ha. The intertidal mudflat and associated seagrasses and mangroves on the Hong Kong and Shenzhen sides would be removed during the dredging of the tunnel trench. Large quantities of dredged sediments would require disposal in Option C, possibly causing secondary impacts to marine waters near the disposal sites and reducing the capacity of the disposal sites.

4.3.94 The need for extensive dredging could cause significant impacts on the water quality and marine ecology in Deep Bay. Large-scale dredging could require several dredgers working simultaneously. Provision of sand foundations and rock blankets for protection of the tunnel units would require sand and rock filling, sometimes to great depths. Because the bedrock near the landing point on the Shenzhen side is deep, a large amount of sand fill will be required to support the tunnel units. Loss of fines during filling would lead to water quality degradation. Control of dispersion of sediment/fines in large working areas is difficult, and a high frequency of WQO SS exceedance might occur. Deep Bay is a sensitive water body, therefore extensive dredging and filling would not be environmentally acceptable.

4.3.95 Indo-Pacific Hump-backed Dolphins have been recorded at low frequencies and in small numbers in waters off-shore from Black Point, i.e. the mouth of Deep Bay. . The Option C alignment would encroach upon areas used by dolphins. Increased sedimentation from dredging or filling works would potentially affect dolphin foraging in the areas near Sheung Pak Nai.

4.3.96 Option C would cause severe impacts to three or more streams because of the longer terrestrial section connecting to Deep Bay Link. Construction site runoff and sewage generation would be expected to have a greater potential impact on local streams and associated fauna. The terrestrial alignment on the Hong Kong side would run nearer to the Pak Nai SSSI, possibly affecting mangroves and seagrasses. Extensive dredging marine habitats and increased potential for site runoff from the terrestrial construction sites could adversely affect the ecological value of affected streams. Option C has the greatest potential marine and terrestrial water quality impacts (see Section 4.3) and terrestrial habitat impacts, therefore the greatest potential impacts on subtidal, intertidal and terrestrial ecology.

4.3.97 Because the tunnel would be a confined environment precipitation on the road surface would not generate contaminated runoff. Accidental spills of chemicals would be confined to the tunnel area and would not affect the surrounding marine water environment. Therefore, potential operation phase water quality impacts of Option C would primarily come from reduction of flushing rate caused by the section connecting the seabed and the Mainland landing point. However, construction phase water quality impacts would be severe, and would lead to severe ecological impacts.

Option D - Tunnel Option (Drill and Blast Type)

4.3.98 Construction of Option D would have the least potential impact upon Deep Bay water quality in terms of sediment resuspension because construction of all but the northernmost 1.6km of the alignment would be carried out under the seabed. However, a significant amount of drilled materials would still be generated. The materials are likely to be marine deposits, which are not expected to be contaminated. Disposal of the marine deposits might cause secondary water quality degradation near the disposal sites, and would reduce the capacity of the disposal sites. The northernmost 1.6km of the alignment would cause construction phase impacts similar to Option C.

4.3.99 This alignment lies near Pak Nai SSSI, therefore construction could degrade seagrasses and mangroves at the SSSI. Blasting in the vicinity of Sheung Pak Nai could adversely affect dolphins that have been sighted at low frequencies and in small numbers in the mouth of Deep Bay. Dolphins are particularly sensitive to sound generated by underwater blasting, therefore the impacts of tunnel construction upon dolphins could be severe.
4.3.100 Because the tunnel option is isolated from marine waters, there would be no road surface runoff during the operation phase. Chemical spills would be confined to the tunnel area, therefore contamination of Deep Bay waters would be unlikely. Marine water quality impacts for this option would be minimal, but freshwater streams and fishponds would be adversely affected.

Comparison of the Proposed Options

4.3.101 The potential subtidal, intertidal and terrestrial ecological impacts of each of option are summarised in Table 4.8. The key ecological issues for both Option A (straight) and Option B (curve) would be habitat degradation resulting from construction of piers, construction site runoff, sewage generation, road surface runoff, accidental spillage of chemicals and reduction in flushing capacity leading to the water quality and hydrodynamic (sediment erosion or deposition) changes in Deep Bay. With the exception of seabed loss due to pier construction these potential impacts would be mitigated. Excessive sediment accumulation on Inner Deep Bay mudflats has been highlighted as a primary conservation concern at the Mai Po and Inner Deep Bay Ramsar Site, therefore this potential impact would require special attention. With all the mitigation measures in place (particularly compensation dredging to remove accumulated sediments from between bridge piers to retain baseline tidal exchange volumes), it is predicted that neither bridge option is likely to generate unacceptable water quality degradation or habitat loss or degradation in Deep Bay.

4.3.102 Option C (immersed tube) option would require extensive dredging and filling. The impacts on water quality and subtidal/intertidal habitats during the construction phase would be significant. Terrestrial impacts on freshwater streams and fishponds are also predicted to be severe. Option C is not likely to be environmentally acceptable in spite of the fact that impacts during the operation phase are expected to be low.

4.3.103 Option D (drill and blast) would require some dredging and filling on the Mainland side. Blasting could adversely affect dolphins that infrequently use the area in small numbers. The only practicable mitigation measure to avoid impacts to dolphins is exclusion of dolphins from the vicinity of blasting. This would be expected to have unacceptable programme implications for the construction project. Road surface runoff and release of chemicals into the Deep Bay waters during an accident would not be a key issue except at the tunnel portals. Terrestrial impacts on freshwater streams and fishponds are predicted to be severe. The Option D impacts on water quality in the HKSAR side of Deep Bay during the construction and operation phases were expected to be the lowest of all options. However, water quality impacts on the Mainland side would be high due to additional reclamation. Disposal of the drilled materials may cause secondary impacts but those were expected to be insignificant if control mechanisms were implemented.

4.3.104 The recommended ratings for the proposed options are presented in Table 4.9.

Table 4.8: Comparison of the Proposed Options

Table .9: Recommended Rating for the Proposed Options Ecology Impacts

Fisheries Impact

4.3.105 The marine capture fisheries, oyster culture, and pond fisheries impacts due to construction and operation of each alignment option were assessed and rated in this section. Ratings were given to the alignment options based on a 5-point scale, with higher scores for the options with less impact. The interpretation of the rating scale is described Appendix 4A.

Option A - Bridge Option (Straight Type)

Marine Capture Fisheries and Oyster Culture

4.3.106 The proposed SWC bridge will be supported by piers, and would have a cable-stayed portion at the southern navigation channel. Localised dredging would be required for construction of each pier, and then pre-cast sections of bridge deck would be placed on top of the piers. As noted above in Section 4.3, increases in suspended solids levels and turbidity, and potential releases of contaminants from dredged sediments into the water column during the dredging operations would affect the water quality and aquatic environment near the dredging sites. Spreading of sediment plumes and contaminants by tidal currents to areas distant from the dredging sites may cause adverse impacts to the capture fisheries in Deep Bay. The oyster beds near the landing points on both the Hong Kong and Shenzhen sides would likely be affected by the dredging activities, and some oyster beds on both sides would require relocation. As noted in Section 4.3 of this report, uncontrolled release of dredged sediments into the water column would probably cause exceedance of the Water Quality Objective (WQO) for suspended solids (SS) in the Deep Bay Water Control Zone.

4.3.107 Option A bridge piers would probably be constructed using bored piles, with dredging confined within the bored pile casing. Release of sediment particles would only be expected to occur during transfer of dredged sediments to barges. Release of sediments would be controlled through the use of closed grabs combined with installation of silt curtains around the working area. As a result sediment distribution through the open water column would not be expected to be significant, therefore construction impacts due to sediment loss should be localised and acceptable.

4.3.108 Disposal of dredged sediments arising from pier construction is also a capture fisheries concern that must be addressed through environmentally acceptable sediment disposal. Sediment disposal could cause water quality impacts, thereby affecting capture fisheries near the disposal site(s). However, it is anticipated that a relatively small volume of dredged sediment would be generated by pier construction in Option A, therefore the effects on the dumping sites and water quality near them would be insignificant.

4.3.109 Construction site runoff and sewage generation could also cause water pollution. Adoption of the guidelines for the handling and disposal of construction discharges outlined in ProPECC Note PN1/94 on Construction Site Drainage as part of the construction site management practices would minimise the potential impacts.

4.3.110 During the operation phase the presence of bridge piers may cause reduction in tidal exchange, which would affect water quality in Deep Bay, thereby affecting capture fisheries and oyster culture. Implementation of mitigation dredging to remove accumulated sediments from between the bridge piers could restore tidal exchange capacity, thereby minimising water quality impacts in Deep Bay and minimising impacts upon capture fisheries.

4.3.111 Road surface runoff would be expected to be contaminated with silt, grit, hydrocarbon and metal wastes. This could degrade the water quality of Deep Bay during the operation of the SWC bridge. Silt traps would be installed along the bridge to treat runoff prior to discharge into Deep Bay waters. This would minimise most impacts to capture fisheries. Potential contamination of oyster beds by metals transported in highway runoff is a concern in the baseline situation where most highway runoff in the catchment flows to Deep Bay. The proposed bridge would not change that situation, but drainage from the highway to Deep Bay would be more direct, thereby allowing less natural assimilation of metals prior to reaching Deep Bay.

4.3.112 Most identified potential water quality impacts due to the construction and operation phases of the Option A bridge can be minimised through implementation of mitigation measures. Because Option A is not likely to cause unacceptable water quality impacts it would also be expected to cause low or undetectable impacts upon the capture fisheries and oyster production in the assessment area.

4.3.113 Construction of the Option A bridge would require removal of some oyster beds and rafts from their current locations. The oyster beds could not be reoccupied after completion of the construction and the oyster rafts would be relocated.

Pond Fisheries

4.3.114 Construction and operation of the Option A bridge would not require permanent loss of fish ponds, therefore there would be no impact upon pond fisheries.

Option B - Bridge Option (Curved type)

4.3.115 The capture fisheries, oyster culture and pond fisheries issues for Option B are largely the same as those for Option A. If the Option B curved type bridge required more piers, the increased impacts from sediment resuspension and seabed loss would be proportional, as would the amount of dredged material requiring disposal. Similar to Option A, construction impacts arising from sediment re-suspension in Option B are not likely to be significant. Impacts to capture fisheries and oyster culture due to construction site runoff and sewage generation could be mitigated to acceptable levels through implementation of control measures and good management practices. There would be no impacts to pond fisheries.

4.3.116 The amount of contaminated surface runoff from the road surface would be slightly increased during the operational phase due to the increased road length. This would be mitigated through the use of sediment and grease traps.

4.3.117 Option B impacts on tidal exchange might be slightly higher as a result of the increased number of piers. This could be mitigated by periodic dredging of accumulated sediments from between piers to restore baseline water quality by restoring tidal exchange capacity.

4.3.118 Potential impacts from Option B would either be insignificant or could be mitigated by implementing mitigation measures.

Option C - Tunnel Option (Immersed Tube Type)

Marine Capture Fisheries and Oyster Culture

4.3.119 The cut-and-cover construction method employed for Option C would require dredging of marine sediments over an area of approximately 50 ha. This would generate sediments that would adversely affect both capture fisheries and oyster beds on the Hong Kong and Shenzhen sides. Many oyster rafts and beds on both sides would be removed to enable dredging of the tunnel trench. Large quantities of dredged sediments would require disposal in Option C, possibly causing secondary impacts to capture fisheries near the disposal sites.

4.3.120 The need for extensive dredging could cause significant impacts on water quality in Deep Bay, thereby adversely affecting capture fisheries and oyster culture. Large-scale dredging could require several dredgers working simultaneously. Provision of sand foundations and rock blankets for protection of the tunnel units would require sand and rock filling, sometimes to great depths. Because the bedrock near the landing point on the Shenzhen side is deep, a large amount of sand fill will be required to support the tunnel units. Loss of fines during filling would lead to water quality degradation. Control of dispersion of sediment/fines in large working areas is difficult, and a high frequency of WQO SS exceedance might occur. Deep Bay is a sensitive water body, therefore extensive dredging and filling would not be environmentally acceptable.

4.3.121 Extensive marine dredging and increased potential for site runoff from the terrestrial construction sites could adversely affect the ecological value of affected streams that discharge to Deep Bay. Option C has the greatest potential marine water quality impacts (see Section 4.3), therefore the greatest potential impacts on capture fisheries and oyster culture.

4.3.122 Because the tunnel would be a confined environment precipitation on the road surface would not generate contaminated runoff. Accidental spills of chemicals would be confined to the tunnel area and would not affect the surrounding marine waters. Therefore, potential operation phase water quality impacts of Option C would primarily come from reduction in flushing rate caused by the section connecting the seabed and the Mainland landing point. However, construction phase water quality impacts would be severe, and would lead to severe fisheries and oyster culture impacts.

Pond Fisheries

4.3.123 Pond fisheries would be affected by Option C construction because the alignment crosses several ponds. The construction works area would affect other ponds in the Sheung Pak Nai area. While the total area of fishponds to be lost would be small, the impacts of Option C upon pond fisheries would exceed those expected from either Option A or Option B.

Option D - Tunnel Option (Drill and Blast Type)

Marine Capture Fisheries and Oyster Culture

4.3.124 Construction of Option D by drilling and blasting would have the least potential impact upon Deep Bay water quality in terms of sediment resuspension because construction would be carried out under the seabed. Underground construction would also minimise impacts upon oyster culture beds and rafts. Option D would have the least potential impact upon capture fisheries and oyster culture. However, a significant amount of drilled materials would be generated. The materials are likely to be marine deposits, which are not expected to be contaminated. Disposal of the marine deposits might cause secondary water quality degradation through sedimentation near the disposal sites, thereby adversely affecting capture fisheries.

4.3.125 Because the tunnel option is isolated from marine waters, there would be no road surface runoff during the operation phase. Chemical spills would be confined to the tunnel area, therefore contamination of Deep Bay waters would be unlikely as would indirect impacts upon fish and oysters.

Pond Fisheries

4.3.126 Fishponds at Sheung Pak Nai would be permanently lost within the alignment corridor. Other ponds would be temporarily occupied during the construction phase. The Option D alignment would have the greatest adverse impact upon pond fisheries.

Comparison of the Proposed Options

4.3.127 The potential capture fisheries, oyster culture, and pond fisheries impacts of each of option are summarised in Table 4.10. The key issues for both Option A (straight) and Option B (curve) would be degradation of marine waters and displacement of oyster rafts and beds resulting from construction of piers, construction site runoff, sewage generation, road surface runoff, accidental spillage of chemicals and reduction in flushing capacity leading to water quality changes in Deep Bay. With all the mitigation measures in place (particularly compensation dredging to remove accumulated sediments from between bridge piers to retain baseline tidal exchange volumes), it is predicted that neither bridge option is likely to generate unacceptable water quality degradation or habitat loss or degradation in Deep Bay.

4.3.128 Option C (immersed tube) would require extensive dredging and filling. The impacts on water quality and oyster culture during the construction phase would be significant. Fishponds would be permanently lost along the alignment, and temporarily lost in the works areas. Option C is not likely to be environmentally acceptable due to severe construction phase impacts in spite of the relatively low operation phase impacts.

4.3.129 Option D (drill and blast) would require neither dredging nor filling, thus minimising impacts to capture fisheries and oyster culture. Road surface runoff and release of chemicals into the Deep Bay waters during an accident would not be a key issue. However, impacts on fishponds are predicted to be most severe under Option D. The Option D impacts on water quality in Deep Bay during the construction and operation phases were expected to be the lowest of all options. Disposal of the drilled materials may cause secondary impacts but those were expected to be insignificant after implementing control mechanisms.

4.3.130 The recommended ratings for the proposed options are presented in Table 4.11.

Table 4.10: Comparison of the Proposed Options

Table 4.11: Recommended Rating for the Proposed Options Capture Fisheries, Oyster Culture, and Pond Fisheries Impacts

Waste

4.3.131 The waste management implications due to construction and operation of each of the alignment options were considered. Ratings were given to the alignment options based on a 5-point scale, with higher scores for the options with less impact. The interpretation of the rating scale is presented in Appendix 4A.

Options A and B - Bridge Option (Straight Type and Curved Type)

4.3.132 The construction activities for the straight type bridge option and the curved type bridge option would be basically the same. A wide variety of wastes would be generated during the construction phase of the SWC bridge. The types of waste may include:

· site clearance waste;

· excavated materials;

· marine dredged materials;

· construction and demolition (C&D) waste

· chemical waste; and

· general refuse.

4.3.133 The site clearance waste would mainly be generated from the preparation of the works area at Ngau Hom Shek and road improvement works at the Fung Kong Tsuen Road to provide access to the works area during the construction phase of the project. The waste would generally consist of natural vegetation such as scrub and grass and may include the materials from clearance of village house and temporary structures.

4.3.134 Excavated materials may be generated during the preparation of the works area and generally consist of soil and rock. These materials could be reused and off-site disposal of the excavated materials may not be required.

4.3.135 The construction of bridge piers for this option may require dredging of marine sediment at the pier locations. As the bridge piers would be constructed on bored pile foundations, only the sediment within the bored pile casing would be dredged away for off-site disposal. It is therefore expected that the amount of dredged sediment would not be large for the bridge option. Disposal of sediment should be in compliance with the Waste Disposal Ordinance.

4.3.136 C&D waste would mainly arise from the construction of the bridge sections and demolition of the existing structures. The waste may include wood from formwork and falsework, scrap metals, plastics, material and equipment wrapping, surplus concrete and grouting, and damaged and surplus construction materials.

4.3.137 The chemical waste that would be generated from the construction activities may include spent hydraulic and mineral oils, used engine oils, waste fuel, cleaning fluids from mechanical machinery, spent solvents and acid/alkali, and scrap batteries. Disposal of chemical waste should be in compliance with the Waste Disposal (Chemical Waste)(General) Regulation.

4.3.138 General refuse that would be generated from the work site mainly consists of paper and food waste. The storage of general refuse may cause odour problem and attract pests. The storage area should be cleaned on a regular basis. A licensed waste collector should be employed to collect the refuse for disposal so as to minimise potential environmental impacts.

4.3.139 The waste to be generated during the operational phase of the SWC bridge would be general refuse such as light debris, cigarette butts, paper clippings, leaves and metal dust. The amount of general refuse would be small and would not be a major concern.

4.3.140 All the potential wastes that would be generated from the construction and operation of the SWC bridge could be controlled through the implementation of waste management plan. The waste management hierarchy would include minimisation of waste at source and good practices, reuse and recycle of materials to avoid disposal, and treatment and disposal in accordance with the relevant regulations.

4.3.141 The curved bridge option has the longer bridge section and involves more bridge piers when compared to the straight type bridge option. Although the amount of construction materials and waste that would be generated from the construction and operational activities for the curved type bridge option would be slightly larger, the potential impacts would be mitigated to acceptable levels by the implementation of waste management plan. The rating scales for the two bridge types should be the same. The potential environmental impacts associated with the waste generation from both the straight type bridge option and curved type bridge option would be minimal.

Options C and D - Tunnel Option (Immersed Tube Type and Drill and Blast Type)

4.3.142 Most of the waste types for the tunnel option would be similar to those for the bridge option. The waste types may include site clearance waste, excavated materials, marine sediment, C&D waste, chemical waste and general refuse. The key concern for the tunnel option is the generation of a large amount of sediment from the dredging and drilling operations.

4.3.143 The at grade section for the immersed tube type tunnel option would increase the amount of site clearance waste, which mainly consists of scrub and grass, and the materials from clearance of village house and temporary structures. The site clearance waste that would be generated from the drill and blast type tunnel option would be from the tunnel portal area. The amount of site clearance waste would be comparatively smaller.

4.3.144 Excavated materials for the tunnel option would mainly consist of soil and rock. The drill and blast type tunnel option generates a larger amount of excavated materials during the excavation of the tunnel section on land. These materials should be reused and recycled on site or off site to minimise the need for disposal or dumping.

4.3.145 Extensive amount of marine sediment would be dredged away from the existing seabed along the tunnel alignment for the immersed tube type tunnel option. Similarly, the drilling operations for the drill and blast type tunnel option would also remove a very large quantity of marine sediment from the region below the seabed. Off-site disposal of the dredged/drilled sediment would be required. The quality of the sediment to be disposed of should be analysed in order to determine the disposal option. It is worth noting that the Government policy on waste minimisation encourages to limiting on dredging and disposal of marine mud. The requirement for disposal of a large amount of sediment for the tunnel option is not in line with the Government policy.

4.3.146 C&D waste would mainly be generated from the construction of tunnel portals, viaducts and demolition of the existing structures. The waste may include wood from formwork and falsework, scrap metals, plastics, material and equipment wrapping, surplus concrete and grouting, and damaged and surplus construction materials. The chemical waste and general refuse management implications for the tunnel option would be similar to those for the bridge option.

4.3.147 During the operational phase of the tunnel, the waste to be generated would include spent lubricant and solvents from the operation and maintenance of ventilation systems. In addition, general refuse such as light debris, cigarette butts, paper clippings, leaves and metal dust would also be generated.

4.3.148 Most of the potential wastes that would be generated from the tunnel construction and operational activities could be controlled through the implementation of waste management plan. However, disposal of a large amount of dredged/drilled sediment would cause impacts to the dumping facilities. For the open sea or confined marine disposal, sediment disposal may cause water quality impacts in the receiving water at the dumping facilities. The capacity of the dumping facilities would be significantly affected in order to accommodate a large amount of sediment. New dumping pits would need to be opened causing disturbance to the seabed conditions.

4.3.149 The potential impacts due to waste management for both the immersed tube type tunnel option and the drill and blast type tunnel option would be similar. Implementation of waste management plan would minimise the impacts. However, the need for disposal of a large amount of sediment for the tunnel option is a major disadvantage. The impacts for two types of the tunnel option would be moderate.

4.3.150 The recommended ratings for the proposed options are presented in Table 4.12.

Table 4.12: Recommended Rating for the Proposed Options - Waste

Cultural Heritage Impact

4.3.151 The cultural heritage impacts due to construction and operational phases of each of the alignment options were considered. Ratings were given to the alignment options based on a 5-point scale, with higher scores for the options with less impact.

Options A and B - Bridge Option (Straight Type and Curved Type)

4.3.152 The land sections of the straight type bridge option and curved type bridge option would be the same. Main archaeological sites identified in vicinity of the bridge option were Ngau Hom Shek Archaeological Site and Tseung Kong Wai So Kwun Tsai Archaeological Site.

4.3.153 Permitted burial areas namely BG Nos. YL/57 and YL/58 were identified adjacent to the alignment. Some clan and blood graves were found close to the alignment.

4.3.154 The bridge options would directly (total destruction or removal) and indirectly (impact due to construction or operation) affect a number of graves of the Tang and other clans distributed along the alignment in three locations. Among these, there were some large multiple joint graves and some graves dating back to the 19th century. In addition, the relocation of these graves would damage the wholeness and integrity of the clan cemetery to a certain degree.

Options C and D - Tunnel Option (Immersed Tube Type and Drill and Blast Type)

4.3.155 Main archaeological sites identified in vicinity of the tunnel option included the Ngau Hom Shek Archaeological Site, Fu Tei Au Archaeological Site and Tseung Kong Wai So Kwun Tsai Archaeological Site. Some artefacts were also found in the Fu Tei Au Archaeological Site.

4.3.156 Comparing to Options A and B, the number of the potentially affected burials in these two options would be smaller, the distribution of the burial sites was more scattered, the graves were less historically important, and the relocation of the graves should be easier.

4.3.157 Archaeological sites were first reported in the vicinity of Ngau Hom Shek and Ngau Hom Sha in the 1930s, and the Archaeological Map of Hong Kong published by Government in 1972 showed two sites within the area. A few other sites were noted there by William Meacham in 1976. A test excavation by the AMO was conducted in 1978 on a hill spur and a large quantity of Late Neolithic stone working material was unearthed. The territory-wide survey commissioned by Government in 1982 reported four sites in the area, only two of which at Ngau Hom Shek were deemed to have any remaining archaeological potential. The second territory-wide survey of 1997 found only sparse material in the area.

4.3.158 All of the sites thus far discovered were in hill slope or ridge top environments. It was not expected that a considerable depth of deposit would be encountered in any of these sites. However, the horizontal spread of artefacts may cover quite a large area. Some other areas may also have considerable archaeological potential but these could only be confirmed by thorough further archaeological survey.

4.3.159 The recommended ratings for the proposed options are presented in Table 4.13.

Table 4.13: Recommended Rating for the Proposed Options - Cultural Heritage Impacts

Hazard to Life

4.3.160 Hazard impact for each alignment option was considered only if there were overnight storage of explosives and the storage location was in close vicinity of populated areas during the construction phase. Potential hazard consequent from certain operational activities due to the alignment options was considered in the assessment.

4.3.161 Ratings were given to the alignment options based on a 5-point scale, with higher scores for the better options. The interpretation of the rating scale is described in Appendix 4A. In considering that the potential hazard to life during the operational stage of the project would be higher than that during the construction stage, A percentage distribution of 70% and 30% were applied to the ratings for operational stage and construction stage.

4.3.162 The proposed alignments include 2 bridge options (straight type and curved type) and 2 tunnel options (immersed tube type and drill and blast type). Explosives would be required during the construction stage for the drill and blast type tunnel. It is likely that the remaining three options would not involve explosive operation and therefore would not be a concern. Even for the case that explosives would be required for the remaining three options, the amount of explosives would be small and the explosives could be delivered to the site each day to avoid overnight storage on site.

4.3.163 For the drill and blast tunnel option, explosive storage would likely be located in the vicinity of the proposed tunnel portal. There are a number of village developments located near the storage location. These include the following:

· Ha Tsuen Village

· Tseung Kong Wai Village

· Kau Lee Uk Tsuen

· San Sang San Tsuen

4.3.164 The above listed villages are about 300 m away from the storage location. These villages are mainly low rise buildings and are not densely populated. The on-site storage of explosives may still pose potential risks to the people in these villages. High hazard impact would be expected from the drill and blast type tunnel option.

4.3.165 The working environment for the tunnel option would be a confined space. In case of fire and smoke emission inside the tunnel during the construction operations, this would pose a high risk to the workers. Preventive measures to avoid fire generation inside the tunnel units should be strictly implemented and smoking should be prohibited to minimise the potential hazard.

4.3.166 The tunnel option has a lower rating when compared to the bridge option in terms of hazard to life during the construction stage. The drill and blast type tunnel option has the lowest rating as overnight storage of explosives may be required. The two bridge options would have similar potential risks to human life and therefore should be in the same ranking.

4.3.167 During the operational stage, the major concern would be the occurrence of vehicle accidents, fire and smoke emission, and accidental spillage of chemicals causing hazard to life. The main difference of the tunnel option from the bridge option is the confined environment. The escape routing and supply of fresh air/venting of smoke during an accident would be a limitation for the tunnel option. Therefore, the tunnel option would pose a higher hazard to life. The long tunnel section (more than 5km) increases the exposure period of the tunnel users to vehicle emissions. This may affect the health of the tunnel users. The recommended ratings for the alignment options are summarised in Table 4.14.

Table 4.14: Recommended Rating for the Proposed Options - Hazard to Life

Landscape and Visual Impact

4.3.168 This section assesses the four options of the SWC alignment in terms of landscape and visual impact. The landscape is defined by an area within 500 metres of the proposed works boundary, including 500m from the demarcation line between SWC and Deep Bay Link. The visual study area is defined by the visual envelope of the Project.

4.3.169 Generally, this portion of the SWC and the SWC/DBL interface comprised of several significant Landscape Resource areas:

(1) Mangrove vegetation associations located along the coastline;

(2) The rural village character of Ngau Hom Shek;

(3) The agricultural land located between Ngau Hom Shek and Ngau Hom Sha; and

(4) The prominent natural ridgeline located behind Ngau Hom Shek.

4.3.170 From a visual impact perspective, the SWC and the SWC/DBL interface would affect several key Visual Resources:

(1) Coastal Protection Area and Agricultural area around Ngau Hom Shek and stretching south to Ngau Hom Sha;

(2) The Greenbelt and Conservation Area adjacent to Ngau Hom Shek;

(3) The coastal mud flats; and

(4) The sea.

Methodology

4.3.171 The Landscape and Visual Impacts were considered separately where:

(1) Landscape impact assessment should assess the source and magnitude of developmental effects on the existing landscape elements, character and quality in the context of the site and its environs, and ;

(2) Visual impact assessment should assess the source and magnitude of effects caused by the proposed development on the existing views, visual amenity, character and quality of the visually sensitive receivers within the context of the site and its environs.

Landscape Impact

4.3.172 The assessment of the potential impacts of a proposed scheme on the existing landscape comprised two distinct sections :

· Baseline survey, and ;

· Potential landscape impacts assessment.

Baseline Survey

4.3.173 A baseline survey of the existing landscape character and quality was undertaken from site and desk-top surveys. Landscape elements considered include :

· Local topography ;

· Woodland extent and type ;

· Other vegetation types ;

· Built form ;

· Patterns of settlement ;

· Land use ;

· Details of local materials, styles, streetscapes, etc. ;

· Prominent watercourses ;

· Cultural and religious identity.

4.3.174 Proposed developments either within the study area or adjacent to it were also considered. The baseline survey would form the basis of the landscape context by describing broadly homogenous units of character. The landscape was rated into low, medium or high depending not only on the quality of elements present but also their sensitivity to change and local or regional importance. The quality of the landscape is not only related to its visual amenity.

Landscape Assessment

4.3.175 The assessment of the potential landscape impacts of the proposals would result from :

· Identification of the sources of impact, and their magnitude, that would be generated during construction and operation of the scheme ;

· Identification of the principal landscape impacts, primarily in consideration of the degree of change to the baseline conditions. The impacts were considered systematically in terms of the landscape elements, the site and the its context.

4.3.176 The overall landscape impact was a product of the following factors :

· The landscape character and its quality;

· Source, nature and magnitude of potential impacts;

· The degree of change caused by each of the impacts to the existing landscape;

· Tolerance of the landscape to absorb the change;

· Significance of this change in consideration of the local and regional areas and other developments;

· Cumulative effects on the landscape of this and neighbouring proposals; and

· Identification of plant species of significant value which should be conserved.

4.3.177 The degree of landscape impact was rated into highly significant, significant, moderate, slight and insignificant. The impacts may be beneficial or adverse.

Visual Impacts

4.3.178 The assessment of the potential visual impact of the scheme comprised two distinct parts:

· Baseline survey; and

· Visual impact assessment.

Baseline Survey

4.3.179 The baseline survey of all views towards the proposals was undertaken by identifying:

· The visual envelope or visual zone within which the proposed development may be contained either wholly or partially with in views. This must also include indirect effects such as offsite construction activities; and

· The visually sensitive receivers within the visual envelope whose views would be affected by the scheme. The potential receivers were considered as three groups:

· views from residences - the most sensitive of receivers due to the high potential of intrusion on the visual amenity and quality of life;

· view from workplaces - less sensitive than above due to visual amenity being less important within the work environment;

· views from public areas - including all areas apart from the above, e.g., public parks, recreation grounds, footpaths, roads, etc. Sensitivity of this group depends on the transitory nature of the receiver, e.g. sitting in a park or travelling on a highway. Also considered was the degree of view or glimpsed views; and

· views of the drivers and passengers passing along the SWC.

4.3.180 The sensitivity of each group was also influenced by its location and direction of view relative to the scheme. Both present and future visually sensitive receivers would be considered.

Visual Impact Assessment

4.3.181 The baseline survey would form the basis of the visual character and quality of the site. The assessment of the potential visual impacts would result from :

· identification of the sources of visual impacts, and their magnitude, that would be generated during construction and operation of the scheme;

· identification of the principal visual impacts primarily in consideration of the degree of change of the baseline conditions.

4.3.182 The impact assessment would relate to the visual receiver group and their existing and potential views subsequent to the scheme development. The visual impact would result from consideration of the following:

· Character of existing view;

· Quality of existing view;

· Context and location of the visually sensitive receiver;

· Visual receiver group sensitivity;

· Degree of change to existing views;

· Other views available to visual receiver group; and

· The cumulative effects on views of this and other neighbouring developments.

4.3.183 The degree of visual impact was rated as significant, moderate, slight and insignificant. The impacts may be beneficial or adverse.

Mitigation Measures

4.3.184 The identification of the visual and landscape impacts would highlight those sources of conflict requiring landscape design solutions to reduce the impacts, and, if possible, blend the development and associated activities, in with the surrounding landscape. These mitigation measures should take into account factors including :

· Woodland, tree and shrub planting of new or disturbed slopes, amenity strips and areas central reservations and adjacent to any new structures ;

· Earth mounding and screening, structural or vegetated ;

· Highlighting unacceptable impacts and considering alternative scheme proposals ;

· Treatment of structural forms ;

· Hard landscape, furniture and other landscape ;

· Significant landscape elements.

4.3.185 This would result in the formation of landscape mitigation measure proposals which would alleviate the previously identified landscape and visual impacts as far as possible.

Criteria & Ratings

4.3.186 The definition of criteria and interpretation of the rating scale is described in Appendix 4A.

Existing Landscape Context

4.3.187 The four Landscape Resource areas (or character areas) are discussed below.

Mangrove vegetation associations located along the coastline

4.3.188 The mangroves identify the coastal edge interface of the land and the sea. In addition to being an important ecological resource they are also an important landscape resource, especially when viewed in association with the adjacent landscape. The mangroves create a unique landscape character forming a natural edge to the adjacent rural landscape.

The rural village character of Ngau Hom Shek

4.3.189 The rural village type character of Ngau Hom Shek and adjacent areas was a significant landscape resource by way of its existing vegetation and small water ponds.

The agricultural land located between Ngau Hom Shek and Ngau Hom Sha

4.3.190 As above, the landscape significance of this area lied within its existing vegetation and water ponds.

The prominent natural ridgeline located behind Ngau Hom Shek

4.3.191 The prominent natural ridgeline and its associated natural vegetation (although with few trees) was located within the Greenbelt and Conservation area adjacent to Ngau Hom Shek.

Existing Visual Context

Coastal Protection Area and Agricultural area around Ngau Hom Shek and stretching south to Ngau Hom Sha

4.3.192 This coastal protection area is an area of significant scenic beauty. It is generally defined by the coastal edge to the west and the adjacent ridgeline to the east . Its rural / agricultural character is defined by the mixed association of water ponds, market gardens including orchards, natural vegetation including significant quantities of trees, and small scale dwellings. This is seen with a backdrop of vegetated slopes of the Castle Peak Greenbelt and Conservation area.

The Greenbelt and Conservation Area adjacent to Ngau Hom Shek.

4.3.193 These sinuous and undulating foothills and ridges create a very interesting and scenic visual resource. They are covered with natural vegetation including woodland, scrubland and grassland. Their attractiveness is highlighted by their proximity to the shoreline. They create a dramatic effect in combination with the narrow coastal strip and the sea.

The coastal mud flat

4.3.194 The coastal mud flats and oyster farms create an interesting visual resource. Seen in association with and in contrast to the seascape they contribute to create an interesting Arcadian landscape

The sea

4.3.195 The sea is a valuable visual resource. It serves as a foil or backdrop to the landscape features and offers visual relief.

Landscape Impacts Assessment (sub-factor 1)

Option A (Straight Bridge Options)

4.3.196 The elevated road and bridge option with the straight alignment generally minimises impacts upon the landscape since much of the structure is elevated on columns and piers. Retention of existing landform and vegetation can be maximised. The effect upon the existing landscape within the study area would be limited to the piers and columns (and the construction zone required) and the overshadowing created by the structure.

Option B (Curved Bridge Option)

4.3.197 Similar to Option A the curved elevated road and bridge option minimises impacts upon the landscape and allows maximum retention of existing landform and vegetation. The effects on the existing landscape will be limited to the piers and columns (and the construction zone required) and the overshadowing created by the structure. The curved alignment of the road / bridge is likely to be more sympathetic to the landform at either end, and have a less man-made appearance than the straight alignment in Option A.

Option C (Tunnel Option)

4.3.198 This option requires an additional 800 metres of at grade road to be constructed within the Coastal Protection Area. This will involve slope cutting works to almost its entire length and on both its sides. In addition, the construction of a cut and cover tunnel would also have highly significant impacts upon the landscape (although the potential for mitigation of this area is more favourable). A portal structure would also be required again significantly affecting the landform. The area is densely vegetated and much of this will require to be felled.

Option D (Tunnel Option)

4.3.199 This option incorporates a drill and blast tunnel joining the DBL at a point approximately 700 metres east of Ngau Hom Shek. This option would have highly significant landscape impacts but these would be limited to a small area around the portal structure. In addition, locating the tunnel entry at this area would mean that a significant portion of DBL would not be required to be constructed. This would result in a natural and relatively sensitive valley (located between the proposed portal structure and Ngau Hom Shek) being retained in its existing condition. The proposed portal structure would be located within a steep sided and narrow valley and the impacts from this option would require substantial slope cutting to the area immediately surrounding the road and portal structure.

Visual Impacts Assessment (sub-factor 2)

Option A

4.3.200 Option A would have a highly significant visual impact. It is envisaged that the bridge structure would be seen from a number of sensitive visual receivers (although these would be limited to a relatively small number of residence in villages located along the adjacent coast). The bridge would offer spectacular views of Deep Bay and the hinterland surrounding either end of the bridge, for drivers and passengers using the SWC.

Option B

4.3.201 Option B would also have a highly significant visual impact, and would be visible from the same set of visually sensitive receivers (although these would be limited to a relatively small number of residence in villages located along the adjacent coast). The magnitude of the impact would be similar, but the curved alignment in Option B would generally create a visually more sympathetic and interesting appearance, and would be slightly favoured over Option A in this regard. Option B would similarly offer spectacular views of Deep Bay and the hinterland surrounding either end of the bridge, for drivers and passengers using the SWC, however the curved alignment B would result in a more dynamic and interesting view, and result in less glare to drivers due to the changing perspective.

Option C

4.3.202 Option C road and tunnel option would have significant visual impact to those villages within and immediately adjacent to the proposed development. The extensive slope works close to residential properties would result in significant changes in landform profile and disruption of the landscape pattern. The portal structure would also be exposed, especially to the village and farmers located to the north, and together with the slopes would represent large-scale man-made elements in a small-scale semi-rural environment. The road would also be highly visible from any person in a position. The view for drivers and passengers constrained within the length of the tunnel would be of very poor quality, and not a fitting celebration of the gateway into / out of Hong Kong.

Option D

4.3.203 This option would have the least visual impact of the options. Its primary source of impact would be the portal structure and adjacent slope cuttings. However, these are located within what could be described as a hidden valley and would be exposed to few visual receivers. As with Option C, the view for drivers and passengers within the length of the tunnel would be of very poor quality.

Potential for Mitigation (sub-factor 3)

Option A (Straight Bridge Option)

4.3.204 The potential for landscape mitigation is high. Much of the immediately surrounding area could be planted with compensatory planting and the landform would not be significantly altered. Some water ponds could be maintained. In addition, areas of significant vegetation could be retained (such as the mangroves). However, from a visual mitigation perspective, the option has fairly low potential. Some localised screen planting could be introduced around adjacent receivers. The resultant combined mitigation potential could be classified as moderate only.

4.3.205 The bridge and elevated road structure would be highly visible to the surrounding area. Its height (minimum 25 meters) and massive length stretching into Deep Bay would create highly significant visual impacts. Mitigation would be limited to treatment of the road and bridge structures themselves. The bridge would represent a gateway feature into / out of Hong Kong, and with appropriate design could become a significant landmark and cultural feature within the Deep Bay area and in the context of cross border communication.

Option B (Curved Bridge Option)

4.3.206 The potential for landscape mitigation to this options is similarly high, with extensive compensatory planting, no significant alteration of the landform, and retention of some water ponds and areas of significant vegetation (such as the mangroves). From a visual mitigation perspective, the option also has fairly low potential, with the bridge and elevated road structure being highly visible to the surrounding area. Again, some localised screen planting could be introduced around adjacent receivers.

4.3.207 Its height (also minimum 25 meters) and massive length stretching into Deep Bay would create highly significant visual impacts. Mitigation could be limited to treatment of the road and bridge structures themselves. This bridge option would also represent a gateway feature into / out of Hong Kong, and with appropriate design could become a significant landmark and cultural feature within the Deep Bay area and in the context of cross border communication. The curved alignment is likely to be more attractive and elegant in appearance, and would be favoured over the straight alignment of Option A. The resultant combined mitigation potential was also classified as moderate, but was considered to be greater than Option A.

Option C (Tunnel Option)

4.3.208 The long, additional length of road, its substantial width, the slope cutting required and the portal structure would result in highly significant landscape impact. However, with sensitive landscape design techniques employed the potential to mitigate these impacts would be high to moderate. From a visual impact point of view, potential mitigation could also be classed as moderate. This potential could be higher if not for the substantial additional length of road required. The resultant combined mitigation potential could therefore be classified as moderate.

Option D

4.3.209 The limited area affected by this option and the fact that the portal location would be subject to few visual receivers means that both landscape and visual mitigation potential for this option would be high.

Summary Ranking

4.3.210 Table 4.15 represents a summary of the landscape and visual impacts and the potential for mitigation for each of the options.

Table 4.15: Summary of Rating for Sub-factors on Landscape and Visual Impacts

4.4 Evaluation Of Alignment Options On Engineering Aspect

Highway Alignment

4.4.1 The horizontal alignments and vertical profiles of all four options A to D have been designed to fully satisfy the Transport Planning and Design Manual (TPDM) requirements. Horizontal alignments and vertical profiles are given in Figures 4.4, 4.6, 4.8 and 4.12.

4.4.2 Based on the setting out information of the carriageway horizontal and vertical alignments of the four options, a comparison was made between the alignments of the options based on the following quantitative rating method.

4.4.3 For each alignment option, the individual segments of straight lines, circular curves and spiral curves along the carriageway centreline were identified and the lengths, radii and gradient of the segments were measured.

4.4.4 The methodology for assessing the performance of each alignment option was based on the procedures contained in the Appendix 4A.

Alignment option A - Bridge Form (Straight Type)

Table 4.16: Evaluation on Horizontal Alignment

Table 4.17: Evaluation on Vertical Alignment

0. Note: US = Upward slope, DS = Downward slope

Table 4.18: Evaluation on Horizontal Alignment

Table 4.19: Evaluation on Vertical Alignment

Note: US = Upward slope, DS = Downward slope

Alignment option C – Tunnel Form (Immersed Tube Type)

Table 4.21: Evaluation on Vertical Alignment

Alignment option D – Tunnel Form (Drill & Blast Type)

Table .23: Evaluation on Vertical Alignment

4.4.5 The rating method was in accordance with Appendix 4A - The endorsed Working Paper on Method to Rank Alignment Options. Table 4.24 shows the rating for the four alignment options due to the geometry of the highway alignment.

Table 4.24: Summary of Ratings of Horizontal and Vertical Alignments to Each Option

Drainage Impact

4.4.6 DSD drainage records showed no major drainage services in the areas of the alignment options. The impact to existing drainage system due to the alignment options would be minimal for all options.

4.4.7 The impact to the surface water drainage in the area, however, would be affected by the structures of the highway, particularly if there are abutments, retaining walls or depressed roads that cut across the existing stream courses. Ditches, cut-off channels and appropriate stormwater drains would need to be provided in such case in order to convey upstream overland flow or surface runoff from the highway.

4.4.8 The assessment of drainage impact due to each of the alignment options was based on the impact to the surface water drainage, as the impact to existing drainage system would be minimal.

4.4.9 For options A and B, the whole SWC alignment would be on elevated structure and the bridge substructure would only have negligible obstruction to surface water flow. The drainage impact of these two options was therefore considered to be minimal, with score of 5 points for each option.

4.4.10 For option C, there would be a long length of at-grade road between the tunnel portal near Ngau Hom Sha and the connection point with DBL near Ngau Hom Shek. The disruption to the surface water flow by the at-grade road, which would partly be on embankment and partly through cut slopes, would be significant. The drainage impact of option C was therefore considered to be high, with a score of 2 points.

4.4.11 For option D, there would be a small length of at-grade road near the tunnel portal at Ngau Hom Shek. The drainage impact of this options was considered to be low, with a score of 4 points.

Utilities Impact

4.4.12 This section presents the findings on existing utilities that would have potential conflicts with the four alignment options.

4.4.13 After examination of the utilities drawings obtained from various utilities authorities/undertakers, it was found that the following utilities would be affected by at least one of the four alignment options:

· water mains from WSD

· power cables from CLP

· street lighting cables from HyD

· telephone cables from PCCW

4.4.14 Since different degree of extent of impact would be imposed by each of the four alignment options, each of the above-mentioned items of affected utilities is discussed in the following paragraphs (refer to Figure 4.14). The approximate affected lengths of the utilities and the overall scores for each alignment option are summarised in Table 4.25.

(1) Existing water mains from WSD

· Along the Deep Bay Road in Ngau Hom Shek, an existing 200mm-diameter fresh water pipeline was found in the vicinity of the site. For both types of bridge options (i.e. Options A and B), no significant impacts would be imposed because the positions of the columns would be located well away from the water mains reserve. However, the at-grade section near the interface with Deep Bay Link would affect 30m of fresh water mains reserve.

· For Option C, a 30-metre wide cut & cover tunnel section and a 1200m long at-grade section would be built as an approach road to the tunnel, cutting across the existing Deep Bay Road at Sheung Pak Nai and the hill to the east of Ngau Hom Sha. This section would have impacts on existing water mains.

· For Option D, the top surface of the drill and blast tunnel section passing under Deep Bay Road would be about -5.0mPD, which is 10m below the ground level (+5.8mPD) of the Deep Bay Road. This would provide enough cover for the underground water mains passing above it. Thus, no impacts would be imposed.

(2) Existing CLP power cables

· In the study area, most of the CLP's services were found to be 11kV power lines. These lines were either overhead power lines or underground cables. A few 33kV subsurface cables and 400kV overhead lines with pylons could also be found in the area.

· Along the Deep Bay Road, an existing 11kV overhead line with poles crossing the SWC at Ngau Hom Shek was observed. Since the proposed levels of SWC for both Options A and B at this section would be approximately +19mPD, and the existing road level is +5.8mPD, the headroom between the bridge deck and the ground would be sufficient to maintain this line. However, about 280m of LV and 220m of 11kV cables would be affected by the at-grade section near San Wai STW.

· As for Option C, as mentioned in (1), the cut and cover tunnel section crossing existing Deep Bay Road would affect the underground LV and 11kV power cables there.

· Option D would also have no significant impact on existing power cables at Ngau Hom Sha for the same reason as mentioned in (1). However, about 280m of LV and 220m of 11kV cables would be affected by the at-grade section near San Wai STW.

(3) Street lighting cables from HyD

· Records provided by CLP Engineering Limited showed street lighting along all existing roads, including carriageways, primary access roads and village access roads.

· Existing street lighting cables and 10m-height lighting columns along the verge of Deep Bay Road at Ngau Hom Shek were observed, as shown in Figure 4.14. The soffit level of the bridge would be approximately +16mPD for both Options A and B, and the level of Deep Bay Road at that section would be about +5.8mPD.

· At Sheung Pak Nai, street lighting along Deep Bay Road would be affected by the cut and cover tunnel section of Option C crossing Deep Bay Road.

· Option D, being an underground tunnel section in Ngau Hom Shek, would have no significant impact on existing street lighting installation.
(4) Telephone cables from PCCW

· Figure 4.14 shows an existing PCCW telephone cable along Deep Bay Road at Ngau Hom Shek and Sheung Pak Nai. Again, the viaduct structure above Deep Bay Road of both Options A and B would provide adequate headroom for emergency and maintenance works.

· For Option C, the cut and cover tunnel section on the land would have significant impact on the telephone duct along Deep Bay Road as well as the telephone cables serving the villages alongside.

· Similar to the reason stated in (1), Option D would have no impact to the telephone cables underneath Deep Bay Road.

Table 4.25: Summary of Utilities Impact due to Alignment Options

Construction Practicability

4.4.15 The different options would encounter different types and degree of difficulties during construction, apart from the cost and programme issues. In this section, considerations related to construction practicability are discussed. The following sub-factors were considered:

(1) Degree of temporary works

(2) The need of special plants and specially trained skilled labour

(3) Additional land required for construction

(4) Interfacing at both ends of the crossing

4.4.16 The key considerations are essentially the same for the two bridge options and hence no distinctions were made in the discussion in Section 3.4.3 between the two bridge forms.

Option A & B - Bridge Forms

4.4.17 The construction of the bridge foundation would require significant temporary works. At this stage, it is expected the foundation to be large diameter bored piles and found on competent bedrock. To construct the piles, a temporary platform would be required for the crew, power units and the lifting crane. Other items such as temporary casing, reinforcement cage and other equipment could be delivered using barges at an appropriate time to minimise the working space of the temporary platform. A temporary bridge would be constructed alongside the proposed bridge to facilitate the transportation of concrete and the removal of the excavated materials. This temporary bridge would be dismantled and the associate piles would be removed using a heavy-duty vnibrator when construction is completed.

4.4.18 The construction of this type of bridge, mostly in the form of viaduct with a small cable-stay element, is quite common in Hong Kong. No special plants would be required.

4.4.19 With access from both marine and land, it is envisaged that no additional land during construction would be required, apart from the casting yard. However, it is envisaged that the casting yard would be in Mainland, due to cheaper cost there.

Option C - Tunnel Form (Immersed Tube Type)

4.4.20 Significant dredging to remove the soft marine mud would be necessary before installing the precast tunnel units. At several locations, the depth of dredging would be notably lower than the founding level of the tunnel and hence backfilling using rockfill or sand fill would be required. All these operations were considered to be difficult and required skilled labour. One particular concern would be the possibility of trapped marine mud at the bottom of the backfill materials. The trapped marine mud would be disturbed and soft and would give rise to settlement problem to the tunnel. Subject to the cost optimisation exercise, the precast tunnel unit was expected to be large and heavy (>10,000 tonnes). In order to tow the units into position in Deep Bay, it would be necessary to dredge out a marine trench in the relatively shallow water for temporary access.

4.4.21 The tunnel units would need to be precast in a casting basin. Unlike the relatively simple casting yard required for the segments in the bridge options, the casting basin for the units of the immersed tube tunnel would require significant site formation to suit the transportation need. Typically, the basin would be excavated to approximately -8mPD in order to connect to the launching channel. Previously in Hong Kong, the Shek O Quarry at the SE side of Hong Kong had been used for the casting of the units for both the Western Harbour Crossing (WHC) and the Western Immersed Tube (WIT). Negotiation with the quarry operators would be required if the same location were to be used for casting units for this tunnel. In view of the significantly longer tunnel length than that of the WHC and WIT (both approximately 1.3km), the casting basin may have to be extended in order to cope with the required output.

4.4.22 Both skilled labour and special equipment are demanded in this option. Due to the curved alignment, the units would have to be uniquely cast. There is still limited experience in towing large units such as these with non-symmetrical geometry and hence model testing may be required to determine the safe working loads for the tow hawsers and winch ropes. The subsequent placing of units, levelling, position adjustment by jacking, backfilling of sand beneath the tunnel units and the use of divers all require skilled labour throughout the construction process.

4.4.23 To interface with DBL, the alignment would have to pass through high ground at Ngau Hom Shek. It is envisaged this to be constructed using a permanent cut slope of up to 25m and approximately 300m long. Obviously the construction of such an extensive rock slope would involve many other considerations such as environmental and visual but in terms of construction difficulties, the lack of proper access would probably require a temporary access road. At the same time, the removal of materials would put significant pressure on the existing roads leading to Lau Fau Shan.

Option D - Tunnel Form (Drill and Blast Type)

4.4.24 As pointed out in the Desktop Review Report of Site Investigation Records (Arup 2001), there has been limited ground investigation (i.e. 19 boreholes) into the rock strata. From those 19 boreholes, it was revealed that the granite in most of the boreholes appears to be comparatively weak, possibly a result of heavy sharing as suggested by the description of Lamprophyre and Gneiss. Also, the presence of numerous dykes has been noted which again gives credence to the presence of a significant fault zone or zones within the area. The proposed alignment has been planned, as far as possible, to follow the top of the fresh rock interpreted from the few boreholes actually located along the alignment. However, with the degree of faulting and the quality of the sheared granite observed in the borehole logs, it could be expected that this alignment would encounter many weak zones which would then require particular attention during the drill and blast operations. In the weaker rock zones, fibre reinforced shotcrete would be required and rock bolting was envisaged for most section of the alignment.

4.4.25 During tunnel excavation, the conditions would be continuously changing in terms of the type of rock, seepage conditions and stability. The excavation method, sequencing, temporary supports and stabilisation measures would have to be dealt with differently and would hence required skilled labour throughout.

4.4.26 The drill and blast tunnelling method would require additional land close to the tunnel exit during construction for stockpiling the excavated materials. With the existing road network, it would be difficult to cope with the several hundred trucks of excavated materials per day to keep up with the advances of both tunnels. The demand for temporary land usage close to the site would therefore be high, which in turn, would cause further considerations, particularly environmental.

Summary of Ratings for Construction Practicability Factor

4.4.27 Ratings were given to the alignment options under each of the above sub-factors based on the above assessments. The interpretation of the rating scale is described in Appendix 4A. The rating for each selected alignment option under f4 Construction Practicability factor was calculated by summing the individual ratings for each of the above sub-factors and spread on a 5-point scale by dividing the sum with the no. of sub-factors.

Table 4.26: Score on Construction Practicability Factor

Construction Traffic Management

Overview

4.4.28 The impact of each design option has been assessed according to the methodology as described in the Working Paper on Method to Ranking Alignment Options. Examination of options primarily focused on junction capacity assessment.

4.4.29 The amount of construction traffic required would depend heavily on the type of construction method and schedule chosen for each design option. Calculation was made on the traffic requirement for each and every activity during various construction stages. Based on this information, the critical path in traffic term was then established for different design options. For each option, construction traffic on the critical path would be added to the base case traffic forecasts.

4.4.30 According to the information on construction plant inventory and construction phases, the critical path was found to be in year 2004 for Bridge Options as well as Tunnel Option (Immersed Tube Type), and year 2006 for Tunnel Option (Drill and Blast Type). This implies the base case traffic forecasts for Bridge Options and Tunnel Option (Immersed Tube Type) would be year 2004 whilst that of Tunnel Option (Drill and Blast Type) would be year 2006.

4.4.31 Information on construction plant and construction phases also indicates that the amount of construction traffic required during peak hours would be approximately 18 vehicles per direction for Bridge Options, 23 vehicles for Tunnel Option (Immersed Tube Type) and 46 vehicles for Tunnel Option (Drill and Blast Type) respectively.

Base Case Situation

4.4.32 Traffic surveys were carried out in order to assess existing traffic conditions during peak hours. By applying appropriate growth factors to the surveyed data, calculation was made for base case peak hour traffic forecasts under each design option.

4.4.33 Four junctions in the immediate area of impact have been identified for capacity assessment. From the analysis, two of the junctions (Ping Ha Road/Lau Fau Shan Road/Tin Wah Road and Ping Ha Road/Tin Ying Road/Hung Tin Road) would require junction improvement schemes prior to the SWC construction. The other two junctions (Tin Ying Road/Tin Wah Road and Ping Ha Road/Fung Kong Tsuen Road) would be able to cope with traffic demands satisfactorily.

Impacts of Design Options

4.4.34 It is envisaged that construction traffic for all four design options would access Fung Kong Tsuen Road from Yuen Long Highway via Hung Tin Road, Tin Ying Road and Tin Wah Road. Analysis revealed that the contribution of construction traffic, of any design option, would be small compared to total traffic along this route. On Tin Ying Road, which would be the longest section on this route, the contribution of construction traffic would be approximately 5% for the two Bridge Options, 6% for Tunnel Option (Immersed Tube Type) and 10% for Tunnel Option (Drill and Blast Type).

4.4.35 With appropriate improvement schemes, the two problem junctions identified in paragraph 4.4.33 above would be able to accommodate not only background traffic but also construction traffic for all design options. Based on existing layouts, the other two junctions would however operate with sufficient capacity for any design option. According to the analysis, the impacts on key junctions caused by Bridge Options and Tunnel Option (Immersed Tube Type) would likely be low. However, the impacts resulting from Tunnel Option (Drill and Blast Type) may be slightly higher than the other three options. This is partly attributed to the additional materials required for this design option. More significantly, however, the base case traffic forecasts under this option would be year 2006. Unlike the other options, the base year traffic forecasts for Tunnel Option (Drill and Blast Type) would need to take account of traffic growth between years 2004 and 2006 as well.

4.4.36 Similarly, the construction traffic impacts on road capacity in the adjacent areas would be negligible, although traffic conditions under the Tunnel Option (Drill and Blast Type) may be marginally worse than the other options. Analysis indicated that all the roads (on the construction traffic routes) between the works area and Yuen Long Highway would operate within capacity under every design option.

4.4.37 There would be adequate pedestrian facilities along the proposed construction traffic routes near the works area. At the key junctions, there would be sufficient segregation between pedestrians and vehicular traffic. Pedestrian safety would unlikely be affected by construction traffic from any design option.

4.4.38 Given the small proportion of construction traffic in the overall vehicle composition, its impacts on traffic-related environmental issues are likely to be insignificant. Furthermore, vehicle stop-start situations would improve once the implementation of junction improvement schemes is in place.

4.4.39 The proposed construction traffic routes have been carefully chosen to minimise adverse impacts to the local community. It would provide a fast route to Yuen Long Highway without, for the most part, running close to local residential areas. Most of the roads on this preferred route were classified as district distributors, according to The Annual Traffic Census 2000 published by Transport Department. These roads would have a higher road capacity than alternative route choices in the nearby areas. Impacts of construction traffic on local community would be small, irrespective of the design options.

4.4.40 In conclusion, the impacts of construction traffic on the surrounding areas would be low under both Bridge Options and Tunnel Option (Immersed Tube Type). According to the 5-point rating scale in the Working paper on Method to Ranking Alignment Options, it was considered appropriate to give 4 points (low impact) to these three options. From construction traffic's point of view, Tunnel Option (Drill and Blast Type) would be less desirable than the other options. This is mainly because the critical path for this option lies in year 2006, where its base case traffic volume would be higher than that of the other options. Moreover, more construction traffic would be required by this option than the other construction methods being considered. By applying the 5-point rating scale to Tunnel Option (Drill and Blast Type), the reasonable mark would be 3 points (moderate impact). Bridge Options are best options, in traffic perspective, as they are most likely to give rise to the least traffic impacts on the surrounding areas.

Traffic Operation

4.4.41 Traffic operation for both the tunnel and bridge options for the Shenzhen Western Corridor (SWC) would not differ substantially as both options should follow the safe practice recommended by the Transport Planning and Design Manual (TPDM). However, the Bridge Option was considered a more desirable alternative for several reasons.

4.4.42 According to the current standard adopted in TMCA/HyD, within tunnels, a light recovery vehicle assumed to be travelling at 60km/h has to reach the incident scene within two minutes. Hence, should a tunnel be more than 4km, this requirement could not be met even if the recovery bases are located right at both ends of the tunnels. Relaxation of the requirement has to be obtained from the Transport Department (TD). On viaducts, the allowable light recovery vehicle travelling time is 12 minutes. As SWC is approximately 5.5km in length, this requirement could be met for both bounds of the traffic with a single light recovery base. In addition, above ground highways are generally more easily visible and can be reached even by helicopters in case of accidents. The tunnel option is therefore much less desirable than the viaduct option during emergency.

4.4.43 In general, the bridge option is also more favourable due to its flexibility. The alignment could be designed such that different configurations may be accommodated with regard to different traffic patterns. A viaduct could also be modified more easily should future expansion be required. In addition, Categories 1, 2 and 5 vehicles and overheight vehicles are disallowed inside tunnels. Furthermore, due to the associated cost, hard shoulders are normally provided on viaducts but not inside tunnels. The bridge option would therefore be safer in this aspect.

4.4.44 Maintenance of tunnels is normally carried out during night-time through full closure of one tube. Contra-flow operation has to be allowed for the tunnels. Although the SWC will be 3-lane which would allow the middle lane to be closed, having two-way traffic within a constrained area would still be considered undesirable. On the other hand, the two-way traffic would be at least separated by a median for the Bridge Option and maintenance of the bridge could be carried out by mere lane closure.

4.4.45 However, the cable-stayed spans could be sensitive to wind loads, rendering special wind management strategies necessary. In which case, the bridge would be closed when wind load exceeds a certain threshold. The occurrence of high wind loads is a random event which cannot be predicted in contrast with normal tunnel closure for maintenance. In this respect, tunnel operation excels the bridge operation.

4.4.46 In terms of cost of traffic operation, the Tunnel Option would be more expensive as more standard highway furniture including lane use signals, variable speed limit signs, vehicle detectors, closed-circuit televisions and public address have to be deployed. Should directional signs be required, they would have to be in place prior to the tunnels rendering the signing strategy undesirable and not in accordance with the TPDM requirements. In addition, crossovers and as discussed above, more vehicle recovery bases would be necessary.

4.4.47 Overall, it was considered the bridge operation would be rated as 4 (good performance) in the 5-point rating scale whereas the tunnel operation would be rated as 2 (poor performance).

4.5 Evaluation Of Alignment Options On Marine Aspect

Loss of Navigational Water Space

4.5.1 This factor is associated with the impact due to reduction in the effective water area required for the safe navigation of vessels as a result of the construction and operation of the SWC. The intensity of the impact would implicitly be a function of the characteristics and density of the vessels adjacent to the alignment, and the level of obscuring of the navigation path.

4.5.2 As noted in previous Metocean and Ship Impact Issues Working Paper (Ref: 001) navigation within Deep Bay is severely constrained by available water depths. For the purposes of this assessment, only the SWC between chainages 0 - 4000m was considered as navigable, the area to the east of this chainage being shallow mudflats.

4.5.3 Vessel movements within Deep Bay are principally associated with the developing terminal facilities at Shekou south-west of the SWC alignment. Vessels crossing the alignment are either small fishing vessels, less hindered by draft restrictions, or small coastal vessels travelling to/from small ports sited within Shenzhen River. These larger vessels cross the SWC at approximately right angles, with their navigation constrained by the limits of the deeper channel. Up to 80 vessel movements per day to these ports has been estimated by Mainland authorities.
Option A

4.5.4 It is presently anticipated that the two main navigation channels associated with the SWC would be bridged by cable stay spans in excess of 140m in width. These requirements are in line with International requirements for safe passage and there would be limited reduction in the navigable waterspace required for larger vessels traversing the SWC. The landmark cable stay spans would assist in the clear definition of the main navigation channels. Figure 4.4 associated with the Bridge Option - Main Spans - General arrangement illustrates bridge piers of less than 8m in width at generally 75m centres. This span width is adequate for the safe passage of fishing boats and would ensure the structure is relatively "porous" to the movement of small craft, providing that the crew maintains a proper lookout. A 75m pier spacing would result in approximately 53 spans within the 4000m navigable width of the SWC, a "blockage" of much less than 425m in width.

Option B

4.5.5 The curve developed in Option B ensures that the navigation channels are crossed at an angle closer to the perpendicular than for Option A, the straight alignment. However this improvement, while beneficial, would not be of a significantly great magnitude to impact the ranking of this bridge option in comparison with a straight alignment. Furthermore, the chainage of the structure is very similar to that of the straight alignment.

Option C

4.5.6 An immersed tube tunnel would be set at sufficient depth to allow the unhindered passage of vessels traversing above the SWC alignment. The sole impact would be focussed near the Mainland landfall where the alignment rises from tunnel to connect with the new reclamation. This section of tunnel would extend approximately 650 - 700m from the edge of the proposed reclamation.

Option D

4.5.7 This would be reviewed in a similar manner to Option C.

Summary

4.5.8 The ranking of Loss of Navigable Waterspace, on the basis of the ranking methodology in Appendix 4A, with the minimum impact developing a score of 5, any impact twice that having a score of 0 (2 x 450m = 900m), and linearly interpolating in between, may be summarised as:

· Option A - Rating = 5, (minimum loss of navigable waterspace of options considered, 450m);

· Option B - Rating = 5, (minimum loss of navigable waterspace of options considered, 450m);

· Option C - Rating = 2, (5 x (900-700)/(900-450) = 2.2), and

· Option D - Rating = 2 (5 x (900-700)/(900-450) = 2.2).

Loss of Anchorage Space

4.5.9 This factor is associated with the loss of designated mooring areas which would require relocation as a result of the planned alignment options. The comparison was made by evaluating the potential loss of anchorage area as a result of the various options.

4.5.10 There are no anchorages within the HKSAR component of the SWC, however two anchorages are present within Mainland waters. A dangerous goods tanker anchorage (of approximately 44ha) would be straddled by the alignment, while a cargo anchorage (of approximately 57 ha) would be to the south-west of the alignment.

Option A

4.5.11 The SWC would clip the northern half of the tanker anchorage. The remaining section of anchorage would lie close to the bridge, and its relocation to another site would be recommended. As well as the reprovisioning of this facility the development of the northern navigation channel would result in the cargo and tanker anchorage being bisected. This would effectively require the reprovisioning of both facilities within another area.

Option B

4.5.12 Given the low level of curve and deviation from a straight alignment this option may be evaluated in a similar manner to Option A.

Option C

4.5.13 Tunnel option C would pass further to the south than the bridge options. The alignment would bisect the tanker anchorage and pass close to the north of the cargo anchorage. The location of a submerged tube tunnel would require the establishment of a no anchoring zone in the area above and adjacent to the tunnel. This, together with the works required for the landfall, would effectively subdivide this anchorage into two small unusable waterspaces. The reprovisioning of the tanker anchorage would be required.

Option D

4.5.14 While the deep tunnel option would not impose restrictions on anchoring on the waterspaces it would pass under, the landfall would impact the north-west corner of the tanker anchorage. A reduction in usable waterspace of approximately 20% would be imposed on this anchorage.

Summary

4.5.15 The ranking of Loss of Anchorage Space, on the basis of the ranking methodology in Appendix 4A, with the minimum impact developing a score of 5, any impact twice that having a score of 0, and linearly interpolating in between, may be summarised as:

· Option A - Rating = 0, (loss of anchorage = 44 + 57ha = 101ha, > twice minimum considered);

· Option B - Rating = 0, (loss of anchorage = 44 + 57ha = 101ha, > twice minimum considered);

· Option C - Rating = 2, (loss of anchorage = 44ha, = 5 * (44-11)/(101-11) = 1.8), and

· Option D - Rating = 5, (minimum loss of anchorage of options considered, 20% x 57ha = 11ha).

Disruption during Construction

4.5.16 This factor examined the potential impacts during construction from marine-based construction plants at the site and the location of working areas adjacent to existing facilities. The impact may be reviewed, in part, by assessing the most disruptive situation which would occur at any time, and the duration of such disruption. To review the impact of construction it was first necessary to briefly review the marine construction operations:

Option A

4.5.17 Bridge would most probably be constructed, within the navigable water area, by the use of driven or bored piles, and the installation of precast pile caps and piers, with some in-situ concrete. It is likely that the deck sections would be installed in large lifts, using such technology as the Versatruss system (www.vtruss.com), or in a series of more conventional lifts of deck segments onto launching gantries. Work would be expected to proceed on many fronts with simultaneous piling, pier and deck installation across the full length of the route.

Option B

4.5.18 As Option A

Option C

4.5.19 Immersed tue would require the preparation of a dredged trench, excavated down to sound material. Stable back slopes would also be dredged, and this dredged channel would itself be used as the principal access and installation channel for the installation of precast units. It is anticipated that trailer suction hopper dredgers would be used for this work. The installation operation for the units themselves would impose significant, but temporary, impacts across the width of the navigation channels.

Option D

4.5.20 The development of an immersed tube would concentrate all activities at the extremities of the alignment. For marine aspects this would require the construction of a landfall on the Mainland side, and the removal of spoil from the tunnel section. It is unknown at present whether barges would be used to remove this material out of Deep Bay, or they would be used within the ongoing reclamation works. Assuming removal offsite was adopted, barging points and waiting areas would be required to support these operations.
Summary

4.5.21 The following ranking is proposed, on the basis of the ranking methodology in Appendix 4A:

· Option A - "2 high impact";

· Option B - "2 high impact";

· Option C - "3, moderate impact", and

· Option D - "4, low impact".

Risk to Marine Traffic

4.5.22 Traffic impacts associated with the construction and operation of the alignment options could pose risk to marine traffic. This factor addressed both the volume of marine traffic developed during construction, and the anticipated compression and risk brought about by the development of the alignment following construction. It was necessary to identify the traffic impacts developed by construction, (rather than the on-site disruption reviewed above) and the future impacts on the traffic flows.

4.5.23 In developing the assessment for this option this factor was nominally weighted on a basis of 25% construction traffic impact, and 75% permanent impact.

Option A

4.5.24 As noted above, the construction of a bridge would require multiple workfronts across the alignment supported by barges, tugs and fast launches, where waterdepths allow. This would generate significant local impacts which must be managed with local control measures. While the marine activity associated with construction would be high, the level of traffic in the area passing across the alignment would be low. Hence impacts on craft within the area would likely be limited.

4.5.25 Once complete the bridge would have two principal navigation spans for larger craft, and approach spans sufficient for the safe passage of smaller vessels. Permanent traffic impacts were anticipated to be small.

Option B

4.5.26 As Option A.

Option C

4.5.27 Construction issues would focus on the activity developed by formation of the trench for the immersed tube tunnel and the passage of these vessels and dumping of material at spoil grounds outside Deep Bay. During the installation of units themselves a small flotilla of tugs and barges would be used to escort and position the units.

4.5.28 Following completion of the works there would be no impact on marine traffic, except the compression of traffic developed by the navigation restrictions imposed by the landfall works on the Mainland side.

Option D

4.5.29 The construction of the tunnel options would generate a large number of vessel movements associated with spoil removal, however local traffic impacts would be limited to the western edge of the bay. Following completion of the works there would be no impact on marine traffic excepting the compression of traffic developed by the navigation restrictions imposed by the landfall works on the Mainland side.

Summary

4.5.30 The following ranking was adopted, on the basis of the ranking methodology in Appendix 4A:

· Option A - "3 moderate risk";

· Option B - "3 moderate risk";

· Option C - "4 low risk", and

· Option D - "4, low risk".

Risk of Structure against Ship Collision

4.5.31 This factor reviewed the risk to the proposed structures of the alignment options due to collision by marine crafts after incorporation of practical ship collision protection measures where necessary.

Option A

4.5.32 As identified in the review of navigation waterspace spans and navigation channels would be designated with due allowance to the constraints of the local vessels navigation. However, while spans may be developed on the basis of international guidelines, there would still be the possibility of impact; and in particular the impact on the deck structure from the masts or booms of over-height vessels. Potential mitigation measures for ship impact have been developed in the Ship Impact Working Paper (Ref: 008).

Option B

4.5.33 As Option A

Option C

4.5.34 As identified in Figure 4.9 associated with the Tunnel Option (Immersed Tube Type), Typical Cross Section, a rock blanket and anchor release bands would be included within the design of the immersed tube to protect it from potential damage from vessels. While these engineering measures have proved effective for past tunnels in Hong Kong, they would need to be supported by control measures to prohibit anchoring in the waterspaces above the alignment.

Option D

4.5.35 A deep tunnel would not pose ship impact risks, although the landfall structures may have a marginal hazard.

Summary

· Option A - "3 moderate risk";

· Option B - "3 moderate risk";

· Option C - "4 low risk", and

· Option D - "5, minimal risk".

Overall Summary

4.5.36 Following assessment of the options, the following summary was developed:

Table 4.27: Summary of Marine Impact Evaluation

4.6 Evaluation Of Alignment Options On Land Aspect

4.6.1 The Land Use Impact Assessment assessed the impact of the four proposed alignment options based on the existing land use, planning land use and future development potential of the assessment area.

4.6.2 In the meetings with the Mainland Authorities, it was understood that the landing point at Shenzhen side would be on the reclaimed land at Shekou and it could be relocated as there would be no other available land that could accommodate the combined Boundary Crossing Facilities. Hence, all the four alignment options were proposed starting at the reclamation area at Mainland side and the land use impact on the Mainland side was excluded from this assessment.

Effect on Existing Land Use

4.6.3 The number of affected private and government land lots were counted for each of the alignment options. For equitable comparison purpose, demarcation line of Option D was considered as the common line for counting the number. of affected land lots for all the four options.

4.6.4 Number of affected land lots due to each alignment option are listed in the Tables 4.28 to 4.30.

Table 4.28: Affected Land Lots due to Alignment Option A and B (refer to Figure 4.15)

Table 4.29: Affected Land Lots due to Alignment Option C (refer to Figure 4.16)