4.5
Evaluation
of Baseline Data for the Lok Ma Chau Fish Ponds
4.5.1
Based on the data presented in Sections 4.3 and 4.4 of
this Chapter, it is clear that the Lok Ma Chau fish ponds are of high
ecological value. Establishment of the baseline value is addressed primarily
with reference to habitat characteristics, rather than solely on the number of
individual birds using the area. It is clear from a comparison of the data
presented in Appendix A4.3 on numbers of key target species in certain fish
ponds (exact fish ponds detailed in Appendix G) at Lok Ma Chau prior
to clearance, and the number of birds present after clearance (Baseline Report,
Appendix 4.1), that the baseline value is variable, especially when one
compares pre and post clearance.
4.5.2 During the 2000-01 winter (widespread clearance and drainage) numbers for Black-faced Spoonbill, Grey Heron, and Great Cormorant all showed a clear increase in the average number of individuals per visit during the winter months (see graphs in Appendix A4.3). Numbers of Great Egret were highest during the 98-99 winter, when there were high numbers roosting within the area. Numbers the following winter, when no such roosting was observed, were far lower, and increased again in the 00-01 winter.
4.5.3
The increase is especially marked for Black-faced
Spoonbill, for which none were recorded during the 98-99 winter, but an average
of 16.2 birds per visit were recorded during the 00-01 winter.
4.5.4
The reasons for these increases are thought to include
the reduction in levels of human disturbance, and the greater availability
of food, particularly for piscivorous species such as ardeids and Black-faced
Spoonbills, and for the latter species, an increasing wintering population in
Deep Bay.
4.5.5
The numbers of large waterbirds present within the Lok
Ma Chau area during the winter of 00-01 are not representative of commercial
fishponds, and as such are not considered a valid baseline when predicting post
enhancement targets for the mitigation wetlands. It is therefore proposed that
the baseline for the present EIA study, for calculation of required
compensation, is taken as the average number of individuals per pond recorded
during 98-99 to 99-00. For those ponds within the resumption area but for which
no data are available from the 98-99 and 99-00 winters, it is assumed (except
for those ponds within the exclusion zones and areas of reduced
density) that their value is directly comparable.
4.6
Identification of Potential Impacts
During Construction
4.6.1
The main
operations involved in the construction of the railway, stations and associated
structures are described in Chapter 2 of this report. This section highlights
the main impacts on habitats and their associated species, from the
construction of the railway, as required in Clause 3.5.2 (vii) of the Study
Brief.
4.6.2
Direct
temporary on-site loss of habitats during the construction phase are likely to
have significant impacts on all habitats other than those which are already
highly degraded or artificial. Habitat loss will occur as a result of the land
used for the construction of the track, supporting structures, stations, access
roads and storage areas for materials and equipment etc. However, the actual
operation phase footprint (i.e. land directly and permanently altered by the
project) will be relatively small in most cases, limited to the width of the
rail track, the Lok Ma Chau station footprint, and the construction of
Emergency Access Points (EAPs), Ventilation Buildings (VBs) and the Kwu Tung
Station Box.
4.6.3
The greatest impact on ecologically valuable habitats is
the loss of fish ponds at Lok Ma Chau, primarily as a result of the construction
of the proposed station and border crossing. More limited impacts will arise
from the presence of the viaduct across fishponds between Lok Ma Chau and
Chau Tau. The total impact in the Lok Ma Chau area amounts to the loss of
9.5 ha of fishponds (Table 4.27). However, as will be explained in the
calculation of required compensation, the narrow strip of fishponds alongside
the Shenzhen River represents an already disturbed area that is rarely used
by large waterbirds and is therefore excluded from the calculation of habitat
compensation requirements (Figure
4.3). As the line will be entirely underground throughout its traverse
of Long Valley there will be no habitat loss in this location.
4.6.4
Other habitat losses indicated in
Table 4.27 are much smaller in area and these habitats are considered less
ecologically valuable than fish ponds (see Section 4-4 of this report). Much of
the woodland impacted will be replaced through landscaping measures (see
Chapter 12, Landscape and Visual Impact Assessment).
Table 4.27
Long-term habitat loss
due to permanent structures and the viaduct “shadow”
|
Section |
Sheung Shui |
Long Valley |
Kwu Tung/Pak Shek Au |
Chau Tau |
Lok Ma Chau |
Total loss (ha) |
Total present within 500 m*1 |
% Loss within 500 m |
|
Structures causing habitat loss |
Eastern Ventilation Building |
_ |
East EAP/ Kwu Tung Station Box/West EAP |
West Ventilation Building, Railway Storage Yard |
Viaduct columns + shadow,
Viaduct EAP/LMC Station |
|||
|
Fung shui wood |
0.00 |
0.00 |
0.00 |
0.00 |
0.02 |
0.02 |
17.81 |
0.11 |
|
Lowland secondary forest |
0.00 |
0.00 |
0.00 |
0.00 |
0.02 |
0.02 |
15.11 |
0.13 |
|
Plantation forest |
0.00 |
0.00 |
0.08 |
0.00 |
0.06 |
0.14 |
32.89 |
0.42 |
|
Orchard |
0.00 |
0.00 |
0.52 |
0.00 |
0.00 |
0.52 |
10.91 |
4.77 |
|
Active dry agric. land |
0.00 |
0.00 |
0.09 |
0.00 |
0.00 |
0.09 |
34.41 |
0.26 |
|
Active wet agric. land |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
14.25 |
0.00 |
|
Inactive wet agric. land |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.64 |
0.00 |
|
Inactive dry agric. land |
0.00 |
0.00 |
0.28 |
0.27 |
0.00 |
0.55 |
19.42 |
2.83 |
|
Managed wetland |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
2.36 |
0.00 |
|
Active fish pond |
0.00 |
0.00 |
0.00 |
0.00 |
0.40 |
0.40 |
44.12 |
0.91 |
|
Inactive fish pond |
0.00 |
0.00 |
0.00 |
0.13 |
9.10 |
9.23 |
48.03 |
19.22 |
|
Bloodworm Pond |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
2.72 |
0.00 |
|
Marsh |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
1.67 |
0.00 |
|
Water courses |
0.00 |
0.00 |
0.00 |
0.04 |
0.00 |
0.04 |
56.97 |
0.07 |
|
Grass/shrub mosaic |
0.00 |
0.00 |
0.00 |
0.00 |
0.02 |
0.02 |
8.05 |
0.25 |
|
Wasteland |
0.00 |
0.00 |
0.00 |
0.06 |
0.00 |
0.06 |
43.52 |
0.14 |
|
Developed areas |
0.20 |
0.00 |
1.85 |
1.10 |
0.02 |
3.17 |
426.22 |
0.74 |
Note: All values are in ha.
*1 See Table 4.1.
4.6.5
Habitat
fragmentation can take a number of forms. Habitats may be fragmented simply by
two parts of an area being divided by an access route. The degree of use and
construction of the linear feature dividing the habitat into two parts is the
most important factor. Visual fragmentation of open habitats may result in the
sum of the two 'newly created' parts being of less value to, for example,
flocking winter waders, than was the area before a road or railway line was
constructed. This is because the fragmentation does not impede bird movement,
rather it makes the two new areas of habitat of less value as individual units
in terms of attracting large flocks which act vigilantly in keeping a watch for
potential predators.
4.6.6
Ecologically
valuable habitats may be fragmented by the direct effects of habitat physical
barriers formed by the track and associated structures (Van der Grift and
Kuijsters, 1998). This can have detrimental effects on the remaining habitats
through vegetation composition and structural changes at habitat edges,
inhibition of dispersal of species and increased susceptibility to disturbance
and perdition.
4.6.7
Direct
fragmentation effects are reduced by the proposal to place the eastern section
of the Spur Line underground and the western section on a viaduct. Only for a
short section to the west of Chau Tau (200m) will there be a ramp forming a
physical barrier at ground level.
4.6.8
The
habitats where the ramp will be formed at Chau Tau are already highly
fragmented and of low to moderate ecological value. Direct fragmentation
effects of the project are, therefore, restricted to those arising as a
consequence of the station construction. These will be significant but, unlike
effects of (for example) a railway constructed at grade, will not extend to
creating a physical barrier to movement.
4.6.9 In addition to direct habitat loss, the Spur Line will cause disturbance impacts to Species of Conservation Importance in adjoining areas, even though these will not be physically affected by development. These impacts include active disturbance (arising from noise or other human activities) and passive disturbance resulting from birds’ avoidance of structures (principally the station and the railway viaduct). Operational effects of disturbance are limited to the area around Lok Ma Chau Station and the viaduct between the station and Chau Tau. There will be no disturbance effects as a consequence of the underground section of the line (which includes all of Long Valley. Disturbance effects during construction will be somewhat wider and will affect areas to the east and west of Long Valley where ground stabilisation under the Rivers Sutlej prior to bored tunnelling, and the construction of the EAP respectively will be carried out.
4.6.10
The wetlands which will be constructed
as compensation for wetland losses under the Main Drainage Channel project for
San Tin (ERM 1999a) and Lok Ma Chau Boundary Crossing Expansion (Binnie 1999)
are very close to the existing Lok Ma Chau Boundary Crossing and hence will
suffer from disturbance impacts from this source. Accordingly, the potential
impact on these constructed wetlands from the Spur Line involves only loss of
habitat and not disturbance. This impact has been included in the calculation
of habitat loss under the Spur Line, albeit a very minor impact from one
viaduct column.
4.6.11
General disturbance effects are widely recognized and have been documented in
the past (e.g. Hockin et al. 1992).
Such effects may include the complete avoidance of an area (which is therefore
comparable to habitat loss) and reduced densities (e.g. where only certain
less-sensitive or accustomed individuals use the area). Other less-obvious
disturbance effects may include reduced habitat quality through reduced feeding
efficiency (e.g. because of a need for increased vigilance), which may in turn
lower survival rates or breeding output. Noise may also interfere with breeding
behaviour, through for example obscuring bird song which may then reduce
breeding densities (Reijnen et al.
1995, 1996). Care must therefore be taken in interpreting the observation of a
species close to a disturbance source as being evidence that there is no
disturbance effect. On the other hand, the observation that there is a
disturbance effect, may not necessarily mean that this results in a population
impact, as animals may, for example, move to alternative areas if suitable
habitat is in excess (i.e. populations are not at carrying capacity).
4.6.12
Species affected
by disturbance are
likely to be most birds and mammals, particularly the larger species. Such
species are likely to be disturbed by loud noises, moving objects and the
presence of people. Stationery objects such as buildings and trees, are also sources
of disturbance as these may obscure flight lines and views of potentially
approaching predators. Many species will therefore avoid approaching such
structures.
4.6.13
According
to Hill et al. (1997) the severity
and overall impact of disturbance (at least on birds) is likely to depend on
the following factors:
i) intensity
of disturbance;
ii) duration
and frequency of disturbance (continuous, infrequent, regular, variable);
iii) proximity
of source;
iv) seasonal
variation in sensitivity of affected species;
v) presence
of people associated with the source;
vi) whether
animals move away, but return after disturbance ceases;
vii) whether
important numbers are affected;
viii) whether
there are alternative habitats available nearby;
ix) whether
rare, scarce or especially shy species are affected.
4.6.14
In
particular, disturbance impacts are normally greatest when they are close and
frequent. Although, some species can adapt to regular disturbances from noise
and moving machinery, the close proximity of people is rarely adapted to. Thus,
species tend to show increasing responses across a gradient of severity, from
passive-low-level and continuous to active-high-level continuous (Hockin et al. 1992).
4.6.15 Although no information on the specific disturbance effects of railways is known to be available there are numerous international references documenting cases of impacts from road disturbance. Such impacts tend to be fairly low when compared to industrial, urban and residential sources where people are highly visible or where disturbance sources are unpredictable. In the case of the Spur Line, the low frequency of trains (compared with road traffic) and the noise mitigation measures that are included in the design, will reduce the disturbance impacts within the Long Valley area. In addition the design and alignment of the railway has specifically taken into account disturbance to wildlife and aimed to reduce ecological impacts, as described in Chapter 2 of this report.
4.6.16 Although there are no scientific studies of the impacts of railway disturbance in Hong Kong, anecdotal observations suggest that some wetland Species of Conservation Importance occurring along the Spur Line route are not highly susceptible to railway disturbance. Observations by team members of birds alongside the East Rail line south of Tai Po Market and at Lo Wu indicate that at least some egrets adapt to the presence of trains passing by. Breeding numbers at an egretry alongside the KCRC at Tai Po Market do not appear to be affected by normal operational use of the railway and station, and although this egretry was established after the station came into use, the effects of construction activity on an active egretry are unknown (Young and Cha 1995).
4.6.17 In spite of the anecdotal evidence presented above and the relatively few studies that have been carried out in Hong Kong, there is some evidence of disturbance impacts. The Town Planning Board Guidelines for Application for Developments within the Deep Bay Area (TPB PG-NO. 12B) acknowledges that, on the basis of scientific studies undertaken during the Fish Pond Study, reduced bird usage occurs on fish ponds that are adjacent to or in the vicinity of open storage, industrial uses, dispersed village developments and roads. Consequently the Board recommends that mitigation for such disturbance impacts should be undertaken.
4.6.18 The use by birds of habitats close to major highways was also shown to be limited due to noise disturbance in the EIA for the Expansion of the Lok Ma Chau Boundary Crossing (Binnie 1999).
4.6.19 In conclusion, given the amount of circumstantial evidence it must be assumed that some degree of disturbance impacts will occur as a result of the operation of the railway. The main species groups that will be affected will be sensitive species, such as flock-feeding waterbirds, larger herons and egrets and birds of prey. These are some of the most threatened and important species using the wetland habitats within the vicinity of the Spur Line. Mitigation to be implemented along the Spur Line (for noise reduction and ecological habitat compensation) will therefore be designed to minimize the disturbance impacts and provide suitable compensation habitat for sensitive species.
4.6.20 As described above, the sensitivity of different species to disturbance will vary. An assessment of the predicted impacts of disturbance on each of the bird Species of Conservation Importance that regularly occur in significant numbers has therefore been carried out. This assessment interprets the findings of the above literature review in relation to the context of the present Spur Line development by additionally taking account of:
• Observations by the ecological study team along Hong Kong's existing rail network.
• Disturbance impacts observed during the course of development projects within the Deep Bay area, in particular monitoring of the Shenzhen River Regulation Works between Lok Ma Chau and Mai Po, during construction.
• Disturbance impacts observed from the operation of the Lok Ma Chau (road) Boundary Crossing during ecological survey in connection with the proposed improvement of the Boundary Crossing Plaza, and during ecological surveys for the San Tin Main Drainage Channel EIA.
• Field experience of the ecological study team, who are highly familiar with the distribution of birds in the Deep Bay area and have undertaken studies of waterbird ecology in fishponds (including fieldwork for the Planning Department Fish Pond Study).
• Existing noise levels in the vicinity of the Spur Line and anticipated noise levels from the construction and operation of the Spur Line.
4.6.21 The Spur Line is designed to achieve noise levels of 50dB(A) at night-time in rural areas of Lok Ma Chau at the nearest sensitive receivers to the track (approximately 15m away). Permitted noise levels increase to 60dB(A) during the day-time. This noise level of 50 dB(A) is considerably lower than the noise levels expected at a similar distance from a major highway such as Fanling Highway. There will be no airborne noise from the tunnel boring construction or during railway operation along the tunnel section of the Spur Line. Construction of the structures such as EAPs, Ventilation Buildings, Launching Shaft and Recovery Shaft are located in areas of low ecological importance and the temporary construction noise from these works is unlikely to have an impact on the local ecological resources.
4.6.22 Noise levels have been predicted during the construction and operation of the Lok Ma Chau Boundary Crossing. During construction, levels of 57 to 74dB(A) are expected at noise sensitive receivers (NSRs) (mainly residences in the area) from various construction plant. Mitigation measures are being implemented to reduce the noise level to the guideline level of 60dB(A) (in accordance with Deep Bay Guidelines for the Special Measures Zone) as far as possible. During operation of the road, noise levels are predicted to be 60 to 70dB(A) at various sensitive receivers (BBV 1999). These levels fall within the acceptable limits for traffic within the area. Thus, against this background, the operational noise from the railway will be insignificant and there will be no discernible increase in noise levels as a consequence of railway operation.
4.6.23 During operation of the Spur Line in the above ground section of the railway, i.e. Lok Ma Chau, noise levels will exceed Acceptable Noise Levels (ANLs) at some NSRs which are very close to the railway line, in the absence of mitigation measures. A variety of mitigation measures is being considered to reduce noise levels to ANLs, which are described in the Noise Chapter of this report.
4.6.24 Although the additional Hong Kong information is not truly quantitative or amenable to rigorous statistical analysis, or adequate for application in respect to other development proposals, it is sufficient to provide a basis for predictive assessment with respect to this particular project.
4.6.25 Thus, disturbance impacts have been calculated by defining distances from the edge of the disturbance source to the furthest point of:
• an avoidance zone, i.e. where a particular species is precluded from using the area; and
• a zone of reduced density, i.e. where the numbers of a species are lower than they would be in the absence of disturbance either because it occurs in lower numbers (more tolerant individuals) and/or for a shorter period of time (for example during periods of reduced human activity). In this analysis, it is assumed that the overall utilisation of the zone of reduced density is 50% of that in undisturbed areas (0% at the border with the avoidance zone and 100% of density at the border with the undisturbed areas).
4.6.26 These distances have been estimated for construction and operation phase impacts and for disturbance impacts in the fishpond area around San Tin / Lok Ma Chau (which take into account the predicted avoidance effects of the large station structure). Disturbance impacts in other habitats are not considered because they are unlikely to be significant due to existing disturbance sources and the low ecological value of these habitats.
4.6.27 These predicted disturbance impacts have been calculated on the assumption that there will be minimal visual human disturbance from the station (i.e. people within the station will not be highly visible from outside) and take into account basic mitigation measures, including screening of the area with landscaping measures.
4.6.28 The results of this assessment are presented in Table 4.28.
4.6.29 In calculating the areas of impact for each species around the station for the purposes of defining the necessary mitigation, the area of defined distance bands around the station were calculated as shown in Figure 4.3 and Table 4.29. These areas take into account the 100 m bands along the west side of Lok Ma Chau Boundary Crossing, which is considered to be already highly disturbed and large birds will rarely use this area; and the 100 to 200 m band for which a reduced density of birds is assumed (Figure 4.3). On the east side of the Lok Ma Chau Boundary Crossing, the fishponds are already highly disturbed by the Boundary Crossing traffic. The additional disturbance from the viaduct is included in the area values shown in Table 4.29 taking into account the disturbance bands indicated in Table 4.28.
Table 4.28
Predicted disturbance
impacts of the railway and station on
Species of Conservation
Importance regularly occurring at Lok Ma Chau
(except where stated only those species
found in the Lok Ma Chau / San Tin area during the 2000 to 2001 baseline survey
are included)
|
Species |
Lok Ma Chau station complex and viaduct section |
Viaduct track sections only |
Overall disturbance sensitivity |
||
|
Exclusion distance (m) |
Max distance of reduced density (m) |
Exclusion distance (m) |
Max distance of reduced density (m) |
||
|
Globally
Threatened Species |
|
|
|
|
|
|
Black-faced Spoonbill |
100 |
200 |
100 |
150 |
High |
|
Greater Spotted Eagle ** |
200 |
500 |
# |
# |
Very high |
|
Imperial Eagle ** |
200 |
500 |
# |
# |
Very high |
|
Regionally
Important Species |
|
|
|
|
|
|
Great Cormorant |
100 |
150 |
# |
# |
High |
|
Grey Heron |
100 |
200 |
100 |
150 |
High |
|
Great Egret |
100 |
200 |
100 |
150 |
High |
|
Little Egret |
20 |
100 |
30 |
100 |
Moderate - High |
|
Chinese Pond Heron |
20 |
30 |
0 |
100 |
Moderate |
|
Common Teal |
50 |
100 |
50 |
100 |
Moderate - High |
|
Eurasian Coot |
20 |
50 |
25 |
50 |
Moderate |
|
Black-winged Stilt |
50 |
50 |
50 |
75 |
Moderate - High |
|
Red-billed Starling |
50 |
100 |
40 |
75 |
Moderate |
|
Restricted
Range In Hong Kong |
|
|
|
|
|
|
Northern Hobby |
100 |
100 |
50 |
100 |
High |
|
Declining
in Hong Kong |
|
|
|
|
|
|
Black-naped Oriole |
50 |
50 |
- |
- |
Moderate |
|
Locally
Important Species |
|
|
|
|
|
|
Cinnamon Bittern |
20 |
20 |
50 |
75 |
Low |
|
Pintail Snipe* |
30 |
30 |
0 |
60 |
Moderate |
|
Swinhoe's Snipe* |
30 |
30 |
0 |
60 |
Moderate |
|
Common Snipe* |
30 |
30 |
0 |
60 |
Moderate |
|
Richard's Pipit |
20 |
30 |
20 |
50 |
Low |
|
Bluethroat* |
20 |
30 |
0 |
50 |
Low |
|
Common Stonechat* |
20 |
30 |
0 |
50 |
Low |
|
Zitting Cisticola* |
20 |
30 |
0 |
50 |
Low |
Notes
* The predicted impacts for these species are for the station site and
the at-grade section of the line. Since these species will also use freshwater
wetlands, there is no exclusion distance for the elevated sections of the line
where these species are expected to use the area under the line to some extent.
# Species not predicted to be affected.
- Species absent.
Predicted impacts take into account basic mitigation measures,
including the creation of wetland habitats with reedbeds and the planting of
trees and bamboo as screening.
Table 4.29
Habitats and Areas within defined bands around
Lok Ma Chau station and beneath Viaduct
|
|
Habitat Type |
|
|
Inactive
Fishponds |
Active
Fishponds |
|
|
Station
Footprint and area affected directly below viaduct |
9.2 |
0.4* |
|
Distance band from station
platform and from viaduct east of LMC Boundary Crossing (m) |
|
|
|
Up to 100m |
8.6 |
1.25 |
|
100 to150m |
5.7 |
1.7 |
|
100 to 200m |
10.8 |
2.6 |
* This area of 0.4ha is already
within the 100m disturbance band of Lok Ma Chau Boundary Crossing and is
therefore included in the exclusion area in the calculation of impacts due to
Spur Line.All areas in ha.
Dust Deposition on Vegetation
4.6.30
Unmitigated
construction operations, if allowed to take place, would be likely to create
significant levels of dust, e.g. due to the use of haul
roads, and wind blown dust in works areas which
can be deposited on nearby habitats. This can cause vegetation damage, which
can, in turn, have secondary affects on associated fauna (such as insects and
birds). In severe cases dust deposition can also affect animals, such as
nesting birds directly. Impacts from dust deposition as a result of
construction operations are, however, likely to be temporary and reversible and
standard mitigation measures will be implemented which will negate harmful dust
emissions.
4.6.31 Dust and exposed earth from construction operations may also enter watercourses through run-off, particularly during heavy rainfall periods. This can lead to high turbidity from soil particles and eutrophication as a result of nutrient enrichment (as phosphates, which are normally the limiting nutrient in freshwater systems, are bound to soil particles). Aquatic macrophytes may be reduced or lost completely as a result of reduced light penetration due to the increased turbidity from soil particles and increased free-floating algae populations following eutrophication. Severe eutrophication can also lead to oxygen depletion and the impoverishment of aquatic animal communities and, in turn, other animals, such as waterbirds, that feed on them. In addition, construction of the footbridge across the Shenzhen River will lead to sediment in the river being disturbed during cofferdam construction for the bridge piers. Such disturbed sediment will have a similar effect to that of increasing turbidity in the river.
4.6.32
However,
as reported under the habitat evaluation section, the water quality in existing
watercourses is poor and their ecological quality is low. Ecological
degradation of these habitats may not, therefore, occur if pollutant levels in
site run-off are not significantly above those of the water-courses, or if the
run-off volume is relatively low. Additional sediment inputs including those
arising from construction within the Shenzhen River, and potential associated
additional nutrients loads may, however, have off-site impacts on the Deep Bay
mudflats and coastal waters. Mitigation measures must be put in place to
prevent adverse impacts on the ecological resources of Deep Bay.
4.6.33
Mitigation
measures are designed to strive towards minimal pollution of water-courses from
the construction and ongoing operation of the railway, station and footbridge
across the Shenzhen River, following the precautionary principle. These issues
are dealt with in more detail in the Water Chapter of this report.
Toxic Pollutants from Construction Operations
4.6.34 During construction, there is potential for some areas that are contaminated with chemicals and toxic pollutants from storage activities to be disturbed during excavation. It is essential that measures are taken to minimise run-off from these sites during construction and avoid contaminated material entering water courses.
4.6.35 Spills and run-off from construction sites can contain high levels of toxic pollutants (such as oil) which can cause direct mortality of plants and animals (in severe cases), sublethal impacts (e.g. by reduced breeding success) or indirect effects through impacts on food resources etc. Watercourses and soils alongside or under the viaduct sections of the track may therefore become contaminated. Where soils and sediments are contaminated long-term effects may occur. For example, soil contamination under and adjacent to the viaducts sections may inhibit vegetation reestablishment and planned habitat compensation restoration and creation measures. Contamination of watercourses may have off-site effects on ditches, rivers and the valuable estuarine waters and mudflats of Deep Bay. During the construction of the footbridge across Shenzhen River, there is a potential for concrete washings to enter the river, which would have an adverse effect on ecology downstream. Measures that should be put in place to prevent this impact are described in the Water Chapter of this report.
4.6.36
Bioaccumulation
may also occur where toxic substances are passed up the food chain in
increasing concentrations. As a result top-level predators such as some reptiles, mammals and birds
of prey can be particularly susceptible to bioaccumulation of toxins.
4.6.37 During construction, areas of land will be cleared for use as Works Areas. During this period, areas of ground, which are currently undisturbed, will be compacted for use as storage areas, vehicle movement or other purposes. Wetland areas into which rain quickly infiltrates, will becomes hardened and rainfall will wash off, taking sediment with it, to be deposited on land adjacent to the compacted site, or in watercourses. The wetland function of these area may therefore be lost temporarily. Although the impact is temporary, extensive compaction over a long period will make habitat restoration more difficult because of the need to re-establish the soil base for a wetland area.
Hydrological
Disruption
4.6.38 A hydrology impact assessment has been carried out for the bored tunnel construction works across Long Valley and is described in detail in Chapter 3. The assessment has shown that the potential impact on groundwater levels is minimal due to the use of specialised equipment to minimise water ingress during the tunnelling operation. The Earth Pressure Balance Machine (EPB TBM) is designed to maintain a pressure at the working face to balance pressure from the surrounding ground. A small volume of water and biodegradable foam is used to form a paste which is brought back into the tunnel and up to the launching shaft area by a conveyor belt system. There will be minimal exchange of materials with the groundwater, minimising effects on the groundwater system. Contingency plans have been described for potential impacts on groundwater levels and ground settlement through monitoring programmes and, if necessary, reinstatement of settled levels.
Vibration
4.6.39 There will be no discernible vibration effects on, or immediately below the surface (i.e. within the biosphere) as a consequence of the tunnel, either during construction or operation of the Spur Line. This is evident from measurements made during Contract DB320 for KCRC West Rail tunneling at Tsuen Wan. No measurable vibration was detected during the tunnel construction.
