4.
TERRESTRIAL ECOLOGICAL ASSESSMENT
4.1.1
This chapter assesses the impacts of the Project
upon terrestrial ecology. The Project
consists of the provision of a drainage tunnel and collecting system for
Northern Hong Kong Island as well as a discharge outlet at Cyber Port. The discharge outlet includes a stilling basin to release
the surface runoff collected from the Hong Kong Island catchment
to the Lamma Channel.
4.1.2
The objective of this assessment is to identify
existing ecological resources in the Study Area, evaluate any impacts of the
Project at both construction and operation phases, and, where required, to
propose mitigation measures to minimize adverse impacts. The assessment follows the criteria and guidelines
as stated in Annexes 8 and 16 of the EIAO TM and the EIA Study Brief No.
ESB-070/2001.
4.1.3
The assessment is mainly focused on the
above-ground intake structures along the proposed Hong Kong West Drainage
Tunnel. The outlet structures of the
tunnel and the impacts on the receiving water body are covered by the chapter
for marine ecological assessment in this report.
4.1.4
The nature and scope of the Project are described
in Chapter 2 of this Report.
In accordance with the EIA Study Brief No. ESB-070/2001, this section
identifies and assesses the terrestrial ecological
impact associated with the Designated Project described in Chapter 2.
4.1.5
Alternative alignments and design options were
studied at the early stage of this assignment.
Findings in the study are summarized in Section 2.4 of this report.
The alignment and design option proposed in this report, as compared
with other alignments and design options, has minimum predicted impact.
4.1.6
There are no scheduled concurrent designated
projects (DP) in the vicinity of the proposed tunnel portals, intakes or tunnel
alignment during the construction and operation phases.
4.2.1
The
Technical Memorandum on Environmental Impact Assessment Process (TM-EIAO) was
used as a guideline for this Project.
Other relevant environmental legislation, guidelines and references
include:
·
EIA Study Brief No. ESB-070/2001;
·
Environmental Impact Assessment Ordinance (Cap.
499)
·
Hong Kong Planning Standards and Guidelines
(HKPSG) Chapter 10;
·
Forests and Countryside Ordinance (Cap. 96) and
its subsidiary legislation the Forestry Regulations;
·
Wild Animals Protection Ordinance (Cap. 170);
·
Country Parks Ordinance (Cap. 208) and
associated subsidiary legislation;
·
Ecological Baseline Survey For Ecological
Assessment (EIAO Guidance Note No. 7/2002);
·
Town Planning Ordinance (Cap. 131), in
particular, Town Planning Board Guidelines for Application
·
United Nations Convention on Biodiversity
(1992);
·
PRC relevant Regulations and Guidelines,
including Class 1 and Class 2
protected species in China and China Plant Red Data Book listing
species of conservation importance.
4.3.1
The
assessment area for terrestrial ecology included all areas within 500 m from
the site boundary of the works areas.
4.3.2
A
four-month ecological baseline survey programme was conducted from August to November 2003
to fulfill the requirements as detailed in EIA study brief ESB-070/2001. Results of the
ecological baseline survey are described in Appendix B. The ecological baseline surveys recorded
ecological data within the assessment area and established the ecological
profile for impact assessment.
4.4.1
Major
habitats recorded within the study area include natural woodland, shrubland, fung shui woodland, urban
plantation (including road, village, construction site, grave site and
recreational park) and stream/nullah. The ecological values of these habitats are evaluated and ranked in Appendix B (see Table 11-15 in Appendix B). The overall
ecological values are summarized in the table below for easy reference.
Table
4.1 Evaluation
of habitats within the study area
|
Habitat |
Overall Ecological Values |
|
Natural Woodland |
Medium to high |
|
Shrubland |
Low to Medium |
|
Fung Shui Woodland |
High |
|
Urban Plantation |
Low |
|
Stream/nullah |
Low to Medium |
*Please refer to Tables 11-15 in Appendix B for further details of the evaluation.
4.4.2
Four
floral species of conservation concern were recorded within the study
area. Species protected by Hong Kong
Forestry Regulations include one shrub, Pavetta
hongkongensis, one tree fern Sphaeropteris lepifera and one fern Angiopteris fokiensis. One tree species Artocarpus
hypargyreus protected in China is common in Hong
Kong. All of these species are located
outside the works area of the proposed project.
The rare plant species Ulmus parvifolia recorded in fung shui wood is native to north China but considered an exotic
locally. Therefore it is not included
with the four floral species of conservation concern in Table 4.2 below:
Table
4.2 Evaluation
of floral species of conservation concern
|
Species |
Growth Form |
Location |
Protection
status |
Distribution |
Rarity |
|
Pavetta hongkongensis |
Shrub |
TP789, HKU1 |
Protected under Forestry Regulations in Hong Kong |
Widely distributed in Hong Kong |
Occasionally seen in Hong Kong |
|
Artocarpus hypargyreus |
Tree |
HKU1 (and other woodland) |
Category III nationally
protected species in China, also listed as ‘vulnerable’ in the China Plant
Red Data Book. |
Widely distributed in Hong
Kong |
Occasionally
seen in Hong Kong |
|
Sphaeropteris lepifera |
Tree fern |
W5 |
Protected under Forestry
Regulations in Hong Kong |
Hong Kong Island |
Rare |
|
Angiopteris fokiensis |
Fern |
W5 |
Protected under Forestry
Regulations in Hong Kong |
Hong Kong Island and Tai Mo
Shan |
Rare |
4.4.3
Fauna
of conservation concern recorded during field surveys included Belly-banded
Squirrel, Black Kite, Buzzard, Greater Necklaced Laughing Thrush, Hong Kong
Cascade Frog (upstream of PFLR1(P) and W12(P)), Lesser Spiny Frog (P5(P)) and
Greater Short-nosed Fruit Bat (two bats roosted at a Chinese Fan Palm near W12(P))
(Table 4.3).
4.4.4
Hong
Kong Cascade Frog is protected under Wild Animals Protection Ordinance (Cap
170) and Lesser Spiny Frog is considered threatened in China due to a decline
in populations of the species throughout its range (Fellowes et al.
2002). Both species are considered of
potential global concern (ibid.).
4.4.5
All
bats are protected under WAPO in Hong Kong and Greater Short-nosed Fruit Bat is
considered a local conservation concern (Fellowes et al. 2002). Belly-banded Squirrel is protected under WAPO.
4.4.6
Black
Kite and Buzzard are State Class 2 Protected Animals of China and both are
listed in Appendix 2 of CITES (Wang 1998).
Black Kite is considered of potential global concern by China
authorities (ibid.) but is not listed by IUCN World Conservation Union
under any category of threat. Greater
Necklaced Laughingthrush is a rare resident and inhabits thick shrubland and
forest in Hong Kong (Carey et al. 2001).
All birds are protected under WAPO in Hong Kong.
Table
4.3 Fauna
species of conservation concern
|
Common Name |
Latin name |
Location |
Protection Status |
Distribution |
Rarity |
|
Greater short-nosed fruit bat |
Cynopterus
sphinx sphinx |
Two individuals roosted at a Chinese
Fan Palm near W12(P) |
Wild Animals Protection Ordinance (Cap
170) |
Widespread localities in the New
Territories and Hong Kong Island |
Uncommon to common in Hong Kong |
|
Belly-banded Squirrel |
Callosciurus
erythraeus styani |
Found in the woodland habitats adjacent
to BR3(P)-BR4(P), BR5(P)-BR7(P), HKU1(P), W11(P), W10, W12(P) and PFLR1(P) |
Wild Animals Protection Ordinance (Cap
170) |
Scattered localities in the New
Territories and Hong Kong Island |
Uncommon in Hong Kong |
|
Black Kite |
Milvus
lineatus |
Record on all transects. |
Wild Animals Protection Ordinance (Cap
170) Class II Protected Animal in PRC CITES Appendix II |
Distribute widely in Hong Kong. |
Common in Hong Kong |
|
Buzzard |
Buteo buteo |
Record at
Western Outlet Portal (Transect L) |
Wild Animals Protection Ordinance (Cap
170) Class II Protected Animal in PRC CITES Appendix II |
Distribute widely in Hong Kong. |
Common/uncommon in Hong Kong |
|
Greater Necklaced Laughing Thrush |
Garrulax
pectoralis |
DG1(P) |
Wild Animals Protection Ordinance (Cap
170) |
Distribute widely in Hong Kong |
Rare in Hong Kong |
|
Hong Kong Cascade Frog |
Amolops
hongkongensis |
45 m and 60 m upstream of PFLR1(P) and
W12(P) respectively |
Wild Animals Protection Ordinance (Cap
170) |
Distribute widely in Hong Kong Island
and the New Territories, not found on Lantau or other islands |
Common in Hong Kong |
|
Lesser Spiny Frog |
Paa exilispinosa |
P5(P) |
Not
protected |
Distribute widely in Hong Kong |
Fairly common in Hong Kong, considered
potential global concern |
4.5.1
The significance of ecological impacts is evaluated based
primarily on the criteria set forth in Table 1, Annex 8 of the TM-EIAO:
·
habitat
quality;
·
species
affected;
·
size/abundance
of habitats/organisms affected;
·
duration
of impacts;
·
reversibility
of impacts; and
·
magnitude of environmental changes.
4.5.2
Impacts are generally ranked as "minor",
"moderate" or "severe", although in a few cases a ranking
of "minimal" (less than "minor") may be given. The ranking of a given impact will vary based
on the criteria listed above. For
example, an impact might be ranked as "minor" if it affected only
common species and habitats, or if it affected only small numbers of
individuals or small areas, whereas it might be ranked as "severe" if
it affected rare species or habitats, large numbers of individuals or large
areas. The major factors giving rise to
a ranking are explained in the text. As
noted in Annex 16 of the TM-EIAO, a degree of professional judgment is involved
in the evaluation of impacts.
4.5.3
The Project consists of the
provision of a drainage tunnel (Hong Kong West Drainage
Tunnel) and
collecting system for Northern Hong Kong Island as well as a discharge outlet
at Cyber Port. The discharge outlet includes
a stilling basin to release the surface runoff arising from the Hong Kong
Island catchment to Lamma
Channel. The tunnel is approximately 10 km in length, starting at
4.5.4
The construction activities at tunnel portals and intake
shafts are detailed in Chapters 2
and 7. Works would include site preparation and
clearance, excavation, intake structures and tunnel portal structure
construction, utilization of ancillary equipment at tunnel portals to support
tunnel construction, material handling and rock drilling at portals and
intakes, and blasting underground if unavoidable. For the western portal at Kong Sin Wan, a
temporary berthing point will be constructed for transportation of excavated
spoil during the tunnel construction and delivery of supporting TBM (tunnel boring machines) materials and equipment by
marine access.
4.5.6
The
35 intake structures would be constructed on existing stormwater
flow paths (mostly existing drainage culverts) to collect surface water. Each would include three major components: a
diversion structure on the ground surface, a drop shaft from the ground surface
to the level of the tunnel, and a horizontal adit at
the base of the shaft to take the flow into the tunnel. By the application of “Raise Boring” at most
of the intake locations, the adit and the drop shaft
would be constructed from the tunnel beneath rather than from the ground
surface. The intake diversion structure
would be the only ground surface structure visible at each intake point, which
is mostly less than or around 100 m2 in area. A works area larger than the diversion
structure would be needed to accommodate works equipment. The intake point works areas range from 150 m2
to 1,500 m2, but most would be below 1,000 m2. The construction works for intake points are
small-scale. Even the maximum tentative
construction programme for the deepest intake point
is less than 12 months, and the ground surface works would take even less time.
4.5.7
The Eastern Portal (Figure 2.3-8) is
also the biggest water flow receiving point of the tunnel. It would
be established adjacent to an existing
watercourse at the southern end of a car park immediately east of the Haw Par
Mansion on the south side of Tai Hang Road.
Construction activities in the works area will include:
l
initial excavation/breaking to establish the portal;
l
excavation and construction of the stream diversion
structure;
l
assembly and operation of the tunnel boring machine
(TBM);
l
handling of the spoil;
l
supply of materials for construction of the stream diversion
structure and tunnel; and
l
establishment and later removal of site offices.
4.5.8
A
much larger works area, in particular the existing car park, is therefore
needed at Eastern Portal but will avoid rare plant Ulmus
parvifolia and the fung shui woodland habitat.
4.5.9
The western portal will be an engineered structure
specifically designed to discharge tunnel flow into the sea while maximizing
dissipation of the flow’s energy (Figure 2.3-35). The Portal will also be the second
site for
assembly and operation of TBM,
where a TBM will start construction
of the tunnel alignment working from the western portal in an easterly
direction (The TBM at Eastern Portal would work in an westerly direction).
4.5.10
The portal will be constructed on an existing reclaimed area
beneath the northern access road to Cyberport
and the works area would cover mostly an engineering slope and the reclaimed
land.
Habitat loss
4.5.11
Since the proposed drainage pipes would be installed as
tunnels between the intake points the alignment itself would not cause habitat
loss. Habitat loss would therefore
mainly result from the construction of the 35 intake points and the two portals
and is considered permanent, while habitat loss at works areas is considered
temporary as these sites would be reinstated after the construction has been
completed. Habitat loss was calculated
by overlaying the existing alignment on the habitat map using ArcView GIS version 3.2a.
4.5.12
The proposed project would cause a permanent loss of 0.16 ha
of woodland, 0.70 ha of urbanised/disturbed, 0.04 ha
of shrubland habitats and 85 m of natural stream, the temporary habitat loss would include 0.53 ha of woodland, 1.56 ha of urbanised/disturbed land, 0.11 ha of shrubland, 91 m of natural stream, and 384 m of nullah
(Table 4.4). As all the
ground surface structures would be located outside the Pok
Fu Lam Country Park and Lung Fu Shan Country Park, none of these habitat losses
would occur inside any of the country parks.
Eastern Portal
4.5.13
The
Eastern Portal would have a works area of about 6,876 m2, which is
only second to Western Portal in size. A
considerable portion (1,375 m2 in total, see Table 4.4) of this works area is urbanized/disturbed habitat (an
existing car park). There would be a loss of over 1,000m2 of this
habitat but the impact is ranked as minimal as similar habitat (i.e. urbanized/disturbed)
would be reprovided. There is a stand of woodland
inside the works area of which the majority (4,481 m2) is in the
temporary works area and only a small fraction (37m2) in the
permanent works area. The woodland
within the temporary works area would not be affected, so there would be only 37
m2 of permanent woodland loss and no temporary woodland loss. This is confirmed in the landscape chapter of
this report that within the temporary works area no tree would be felled and
only one tree would be transplanted. The impact on woodland loss in Eastern
Portal is thus ranked as minor. Compensation for the permanent woodland loss
would be provided.
4.5.14
The total loss of stream habitat is
limited in the present Project
(91 m
temporary loss in total and 85 m permanent loss in total). The majority of the permanent loss would result from the modification of
a section of stream course immediately upstream from the Eastern Portal location
(54 m in length, about 68% of 85m of the total stream habitat permanent loss). This
stream was semi-natural and partially channelised.
Currently, this stream flows in its natural stream bed until it reaches the car
park immediately east of the Haw Par Mansion where the stream flow is collected
by underground drains which replace the natural stream bed. The tunnel portal and the section of stream
to be modified are located just upstream from the car park. The modification is essential for adjusting
the flow rate before the stream flow enters the drainage tunnel. The width of the channel would expand
progressively in this section (Figure 2.3-8). In
non-flood situations, the flow would still go into the drains beneath the car
park. But when the water depth exceeds a
threshold level, the excess would flow into the tunnel opening. The stream was surveyed for aquatic
fauna. According to the results of
ecological baseline surveys in Appendix
B, no rare or protected species was recorded within the works area at this
site. Some common stream organisms
including macrobenthic stream fauna were recorded and
Mosquito fish was the only fish species recorded. In addition, recorded herpetofauna, butterfly
and dragonfly species were also common and widespread in Hong Kong, and of low
conservation concern. Although no species
of conservation concern were found at the Eastern Portal stream, the streambed
is natural and a relatively large section of the stream habitat would be lost
and consequently this impact is ranked minor to moderate and mitigation is
recommended. There is also another 39m of the stream lied within the works area
boundary. However, the engineers have confirmed that the section would not be disturbed
during construction. Therefore, different from the case in intake points (see
below), this section is not considered as temporary loss.
Western Portal
4.5.15
The
Western Portal has the largest works area among all construction sites of the
Project, i.e. over 8,000 m2.
But the entire works area is on urbanized/disturbed habitat (an
engineered slope and reclaimed lands).
These are the only habitat types on the site and they are considered low
in ecological value. No other habitats would be affected or disturbed. The
impact is ranked as minimal as similar urbanized/disturbed habitat would be reprovided. No
mitigation is needed for the Western Portal. However, this site provides an
opportunity for compensation planting and is one of the largest compensation
areas for the project (619 m2).
Intake Points
4.5.16
Among the 35 intake points, urbanised/disturbed
habitat is the
predominant habitat type to be affected, and 18 take points would encroach
only one type of land
habitat, i.e. urbanised/disturbed habitat. Only 16 intake points would encroach
woodland habitats. There are
also 2 intake points (including one from the 16 intake
points affecting woodland, i.e. this intake point would encroach both shrubland and woodland habitats) would encroach shrubland habitat. Woodland habitats affected are
mainly located alongside roads (Figures
4.1a-c).
Impacts of loss of urbanised/disturbed and shrubland
habitat are not considered as severe due to the limited ecological value,
low wildlife abundance and small affected area of these habitats.
Woodland
4.5.17
Among the 35 intake points, 16 would include
woodland
habitats within the works area boundaries and constitute
temporary and permanent woodland loss. Indeed, subject to the judgments by
on-site engineers, most of the potentially affected woodlands might not be encroached
during construction. Only 14 out of the 16 intake points would confirmedly
result in a total of 1,559 m2 of permanent woodland loss. Due to the limited size of
woodland to be permanently lost, and the temporary nature of the impact on most
of the woodland to be affected, the construction impact on terrestrial habitats is ranked as minor.
However, due to the ecological value of woodland habitat, mitigation is
required to compensate the impact of woodland loss. The four plant species protected in Hong Kong or in China and
recorded during the study are located outside the site formation area and the
temporary works area of the proposed intake points. One exception is the single tree of Artocarpus hypargyreus
recorded at HKU1. If this tree would be
affected by construction works, it will be transplanted. The fung shui wood and the ‘rare’ species Ulmus
parviflora will not be affected by the project.
Therefore, potential impacts of the project to the these
plant species are minimal.
Stream/nullah
4.5.18
Besides
in the Eastern Portal, the intake
points will
also cause loss of natural streams, but the loss is very small (31m
out of the total 85m permanent loss of
stream habitat, and all 91 m of the
total
temporary loss). These permanently lost
sections of streams (31m) are
scattered among 5 intake
locations (Table 4.4) and all
are close to roads, residential buildings, or existing drainage facilities. They would be modified into channels as
part of the diversion structure of the intake points. Sections of streams lied within
the temporary work areas are potentially disturbed by the construction works,
depending upon the final works plan at these intake points. To adopt a
conservative approach, all these sections of streams are considered temporarily
lost. Dragonflies
and amphibians were only recorded at a few of the proposed intake points.
Dragonfly nymphs and amphibian larvae usually live in unpolluted aquatic
habitats. Most of the proposed intake
points are however located on concrete nullahs with poor water quality. These are of low ecological importance as
dragonfly or amphibian habitats.
4.5.19
Two amphibian species of conservation concern, Hong Kong
Cascade Frog and Lesser Spiny Frog, were recorded within the study area. Hong Kong Cascade Frogs were only found at 45
and 60 m upstream of PFLR1(P) and W12(P) respectively,
but not at the proposed works area of PFLR1(P) and W12(P). Lesser Spiny Frogs and their tadpoles were
recorded in the proposed work area of P5(P). The stream at P5(P)
has been modified to a concrete nullah, and is not the natural habitat of
this species. Construction works at PFLR1(P), W12(P) and P5(P) will not affect important
habitats of Hong Kong Cascade Frog and Lesser Spiny Frog.
4.5.20
The impact of loss/modification of stream and nullah in the study area is
ranked minor. Compensation of these scattered stream
habitat losses
is thus not required. However mitigation measures for temporary
stream loss (e.g. reinstatement and by-pass channels) and translocation of
frogs, in particular Hong Kong Cascade Frog and Lesser Spiny Frog, are needed. It is also necessary to translocate tadpoles, if any are present, at the same time.
4.5.21
Frogs are not very mobile animals and are usually found at
habitats with some moisture. The
dependence of frogs on humid environments means they are largely
habitat-restricted. Site formation may result
in mortality of frogs due to their strong site fidelity. Those frogs that leave the works areas and
search for new habitats may risk death due to desiccation. Although the project will mostly affect frog
habitats of low ecological importance, precautionary mitigation measures are recommended to minimize
the residual impact at the 7 intake points where frogs were found. Precautionary mitigation measures are discussed in Section 4.6.1.
Shrubland
4.5.22
Among the 35 intake points, only two would encroach shrubland habitat. Potential impacts to loss of shrubland are considered
minor due to the limited area to be lost (1,092 m2 temporary loss and 400 m2
permanent loss from 35 intake points) (Table 4.4) and absence of
rare/protected species potentially affected.
Urbanised/disturbed
4.5.23
This
is the predominant habitat type to be affected in both the two portals and almost
all intake points (32 out of the 35 intake points). At 18 intake
points, urbanised/disturbed habitat would even be the only habitat type other than stream and nullah to be permanently encroached. A total of over 7,000 m2 permanent
loss and over 15,000m2 temporary loss would result from the Project.
(Table 4.4). Two rare fern species Tree Fern Sphaeropteris lepifera and Fern Angiopteris fokiensis were
found during field surveys near Intake Point W5(P) (Figure 4.1-c), they were however located in recreational park
outside the works areas for the Project and there would be no impact on the
ferns. Potential impacts to loss of urbanised/disturbed
area are considered minimal
due to the
low ecological value of this habitat and similar habitat would be reprovided.
Dependent
fauna
4.5.24
The impact of the habitat loss to fauna depends on the
habitat requirements of fauna in the study area and the quantity and quality of
lost habitats.
4.5.25
The areas of terrestrial habitat
loss during the construction phase are
small (temporary 0.53 ha and permanent 0.16 ha of woodland, temporary 0.11 ha
and permanent 0.04 ha of shrubland) and are scattered over 35 intake points and 2 portals. Therefore, habitat loss at each intake point
will only account for small proportion of the daily home range of highly mobile
animals such as avifauna (particularly raptors) and Belly-banded Squirrel. Loss of habitats is mainly confined to
roadside or urbanized/disturbed locations, which are generally of low
ecological importance as wildlife habitats.
The impact from the loss of habitats to terrestrial fauna is ranked
minor. However, in order to minimize
residual impact, it is recommended that habitats temporarily lost to
construction work should be re-instated after completion of construction works.
Construction Noise and disturbance
4.5.26
Noise and visual disturbance may occur during site formation
and construction, potentially affecting the distribution and behavior of fauna
of the adjacent habitats. Due to the
temporary and localized nature of the disturbance, and the disturbed nature of
affected habitats, potential impacts to fauna from this source are ranked as
minor.
4.5.27
Construction works at W12(P) would
not remove the roosts of Greater short-nosed Fruit Bats. However, due to the
proximity of the roost to the works area (around 10m), it is possible that the
roosting bats may leave the Chinese Fan Palm when construction work commences. Since Chinese Fan Palm is common on Hong Kong
Island, the bats could find new roost easily.
For example, Chinese Fan Palm was recorded at various locations within the Study Area,
including
Urban Plantation habitat within Area A (where the bat roost will be affected) and Area C, and Woodland within Area B and Area D. Another
10 Chinese Fan Palms were seen near the intake point W12(P),. Therefore
alternative bat roosts are available over a wide range of areas and the bats
can find new roost easily. The impact to
this bat species is therefore also
ranked minor.
4.5.28
Ecological impacts to the surrounding country parks including
Pok
Fu Lam Country Park and Lung Fu Shan Country Park are
minimal as all of the intake points and works areas are located outside the
country park boundaries.
Surface Runoff
4.5.29
Streams are breeding habitats for amphibians and dragonflies,
and mortality of nymphs/larvae may result from
sedimentation. Most of the watercourses affected by this Project are concrete
nullahs carrying polluted water. However some natural streams within the Study
Area will also be affected by the Project.
To prevent
sedimentation in streams, site runoff should be collected and properly treated before discharging
to the nearby drainage system. With good site practice,
the impact to aquatic fauna from this source is ranked minor.
Construction Dust
4.5.30
Indirect construction impacts on habitat, and flora and fauna
include dust generated during construction which may affect growth of
vegetation and distribution of fauna.
Avifauna may temporarily avoid nesting at locations affected by dust
generated during construction. Due to
the temporary, reversible, localized and small scale of the impacts, dust
impacts to flora and fauna are considered minor.
4.5.31
The construction stage impacts are summarised
in Table 4.5.
Table 4.4 Estimated habitat loss
|
|
Habitat Loss (Permanent) (m2) |
Habitat Loss (Temporary) (m2) |
|
|||||||
|
Intake point |
Woodland |
Urbanised/ Disturbed |
Shrubland |
Natural Stream (m)** |
Woodland |
Urbanised/ Disturbed |
Shrubland |
Natural Stream (m)** |
Nullah (m)*** |
Woodland to be reinstated (m2) |
|
E5(A)(P) |
|
54 |
|
|
|
244 |
|
|
|
496 |
|
E5(B)(P) |
|
208 |
|
|
|
272 |
|
|
|
|
|
MB16(P) |
|
99 |
|
|
|
339 |
|
|
14 |
305 |
|
MBD2 |
|
158 |
|
|
|
773 |
|
|
26 |
269 |
|
E7(P) |
|
572 |
|
|
|
138 |
|
|
|
543 |
|
THR2(P) |
55 |
262 |
|
8 |
251 |
380 |
|
8 |
|
437 |
|
HR1 |
114 |
64 |
|
|
458 |
77 |
|
|
20 |
147 |
|
GL1(P) |
|
211 |
|
|
|
186 |
|
|
|
148 |
|
DG1(P) |
|
106 |
|
|
|
355 |
|
|
|
313 |
|
W0(P) |
|
154 |
|
|
|
1321 |
|
|
|
0 |
|
BR3 |
10 |
|
246 |
|
153 |
|
747 |
35 |
|
691 |
|
BR4(P) |
106 |
|
|
|
349 |
|
|
|
|
247 |
|
W1(P) |
296 |
46 |
|
|
881 |
356 |
|
|
70 |
774 |
|
BR5(P) |
102 |
|
|
|
451 |
|
|
9 |
16 |
295 |
|
BR6(P) |
163 |
65 |
|
|
470 |
98 |
|
|
20 |
56 |
|
BR7(P) |
|
107 |
|
|
29 |
143 |
|
|
13 |
318 |
|
W3(P) |
|
239 |
|
|
|
593 |
|
|
51 |
450 |
|
B2(P) |
74 |
25 |
|
|
239 |
48 |
|
|
|
297 |
|
MA13(P)&MA14(P) |
152 |
|
|
|
766 |
|
|
|
10 |
688 |
|
MA15(P) |
258 |
41 |
|
|
390 |
281 |
|
|
21 |
243 |
|
MA17(P) |
|
48 |
|
|
|
202 |
|
|
|
0 |
|
M3(P) |
|
131 |
|
|
|
490 |
|
|
8 |
470 |
|
TP789(P) |
|
132 |
|
3 |
|
199 |
|
6 |
|
256 |
|
TP5 (P) |
|
99 |
|
2 |
|
398 |
|
10 |
|
180 |
|
TP4(P) |
|
100 |
|
|
63 |
346 |
|
|
20 |
320 |
|
W5(P) |
|
63 |
|
|
|
233 |
|
|
9 |
0 |
|
RR1(P) |
|
153 |
|
|
|
207 |
|
|
|
0 |
|
W8 |
|
101 |
|
|
|
49 |
|
|
|
0 |
|
P5(P) |
|
25 |
154 |
|
|
28 |
345 |
|
14 |
336 |
|
W10 |
|
50 |
|
|
|
341 |
|
|
|
0 |
|
W11 |
102 |
17 |
|
|
389 |
264 |
|
|
35 |
443 |
|
HKU1(P) |
6 |
151 |
|
|
41 |
401 |
|
|
20 |
396 |
|
PFLR1(P) |
121 |
27 |
|
10 |
367 |
202 |
|
23 |
|
405 |
|
W12(P) |
|
97 |
|
8 |
|
314 |
|
|
18 |
45 |
|
Eastern Portal* |
37 |
1043 |
|
54 |
|
332 |
|
|
|
0 |
|
West Portal |
|
2396 |
|
|
|
6019 |
|
|
|
619 |
|
Total (m2) |
1596 |
7043 |
400 |
85 |
5296 |
15628 |
1092 |
91 |
384 |
10,187 |
|
Total (ha) |
0.16 |
0.70 |
0.04 |
0.01 |
0.53 |
1.56 |
0.11 |
0.01 |
0.04 |
1.02 |
*There would be 4,481 m2 of woodland and 39m natural
steam habitat within the temporary works area of Eastern Portal, which however will not be affected as confirmed by the engineers of the Project.
**natural stream =
equal to or more than 50% natural substrate
***nullah = >50% concrete/man-made substrate, underground
drains were not counted.
Table
4.5
Construction stage impacts
|
Impacts |
Receiver |
Habitat
quality |
Species
affected |
Size/abundance
of habitats/organisms affected |
Duration of
impacts |
Reversibility of
impacts; |
Magnitude of environmental
changes |
Severity |
Mitigation
Recommended |
|
Habitat loss |
Eastern Portal |
||||||||
|
Eastern Portal Woodland |
Medium to high |
Terrestrial fauna, including common species and
species conservation importance (Black Kite) |
Small, 37m2 |
Permanent
within site formation boundary. Temporary
within works area. |
Permanent loss, irreversible. Temporary loss to be reinstated. |
Minor |
Minor |
Yes (see Section 4.6 below) |
|
|
Natural stream/nullah |
Low to medium |
Mosquito fish Gambusia sp. (the only fish
species recorded), and common stream macrobenthic, |
Moderate, 54m. Limited
species affected |
Moderate |
Minor to Moderate |
Yes (see Section 4.6 below) |
|||
|
Urbanised/ disturbed |
Low |
Terrestrial fauna, including common species and
species of conservation importance (Black Kite) |
Moderate, over 1,000 m2 Limited
species affected |
Minor |
Minimal |
No |
|||
|
Western Portal |
|||||||||
|
Urbanised/ disturbed |
Low |
Terrestrial fauna, including common species and
species of conservation importance (e.g. Black Kite and Buzzard) |
High over 8,000 m2 Limited
species affected |
Permanent
within site formation boundary. Temporary
within works area. |
Permanent loss, irreversible. Temporary loss to be reinstated. |
Minor |
Minimal |
No |
|
|
All intake
points |
|||||||||
|
Woodland |
Medium to high |
Terrestrial fauna, including common species and
species of conservation importance (e.g. Black Kite and Greater Necklaced
Laughing Thrush) |
Small size affected |
Permanent
within site formation boundary. Temporary
within works area. |
Permanent loss, irreversible. Temporary loss to be reinstated. |
Minor |
Minor |
Yes (see Section 4.6 below) |
|
|
Natural stream/nullah |
Low to medium |
Common amphibian species and two spp. of conservation concern (i.e. Hong Kong Cascade Frog and Lesser Spiny
Frog) |
Small size affected |
Minor |
Minor |
Yes for the seven intake points where frogs were
found during the field surveys. |
|||
|
Shrubland |
Low to medium |
Common species of terrestrial fauna |
Small size affected |
Minor |
Minor |
No |
|||
|
Urbanised/ disturbed |
Low |
Common species of terrestrial fauna |
Small size affected |
Minor |
Minimal |
No |
|||
|
Construction
noise and
disturbance |
Wildlife
species on adjacent habitats |
NA |
Terrestrial fauna, including common species and
species of conservation importance (e.g. Greater short-nosed fruit bats and
Belly-banded Squirrel) |
Low abundance of fauna |
Temporary |
reversible |
Minor |
Minor |
No other than good site practice |
|
Construction
dust |
Vegetation
Wildlife
species on adjacent habitats |
NA |
Terrestrial fauna, including common species and
species of conservation importance (e.g. Greater short-nosed fruit bats and
Belly-banded Squirrel) |
Low abundance of fauna |
Temporary |
reversible |
Minor |
Minor |
No other than good site practice |
|
Surface
runoff |
Aquatic
fauna |
Low to medium |
Common species of aquatic fauna and dragonflies |
Low abundance of aquatic fauna |
Temporary |
Reversible, |
Small scale earth works at intake points. At eastern
portal major earth works inside the tunnel and at the end of the stream
course. |
Minor |
Yes (see Section 4.6 below) |
4.5.32
Except the intake points themselves, all other structures of
the drainage tunnel will be underground and the operation will not pose any
observable impact to the surrounding habitats and the associated flora and
fauna. Low flow channel or dry weather flow channel is
designed to cater for the flow in dry season and normal wet season such that
the ecology at the downstream can be maintained. There will be no operation phase impact on stream/nullah
habitats. The potential operational
impact on habitat and terrestrial and aquatic fauna is therefore ranked as
minimal.
4.6.1
The
construction methods applied in the present Project would help avoid the
majority of the environmental impacts, and in turn the ecological impacts,
encountered in other similar projects.
Bored drilling method would be used to build the drainage tunnel. This method, in which the only locations with
ground surface works would be the two end points, is much more environmental
friendly than the cut-and-cover method, in which ground surface works are
needed along the entire alignment of the tunnel. More details of the horizontal boring
construction method are given in Section
7.11.
4.6.2
The
construction of connecting channels to each intake point is a major task during
the construction phase in addition to building the tunnel. Instead of drilling from the ground surface
at intake locations towards the tunnel as in some other projects, in the
present Project the drilling of the connecting channels would start from the
newly constructed drainage tunnel.
Except when the drilling work is reaching the intake locations, no
ground surface works/facilities are needed at the majority of the intake
points. This would reduce the
disturbance impacts (including noise and human activities) during the
construction phase. This method will
minimize the extent of excavated materials from the surface level at the intake
point locations and to the greatest extent minimize the risk of water quality
impacts from site runoff during construction.
4.6.3
During the detailed design stage, the following issues should
also be considered as possible to further minimise the impacts:
·
Adjustment of site boundary to minimise temporary loss of natural stream habitat during construction.
·
Adjustment of site boundary to minimise use of woodland as temporary works area. In particular, the woodland habitat in
temporary works area of the Eastern Portal will be avoided, thereby greatly
reducing the area of temporary loss of woodland habitat.
·
Minimizing felling of large trees. A tree survey was conducted at the intake
points/portal areas especially for those encroaching woodland habitats. Among the 563 existing trees with diameter
at breast height (dbh) > 95mm within the works
area, it is estimated that 410
trees will be retained, while about 63 trees will be felled, mostly
composing of common native pioneer trees and fruit trees.
·
About 90 trees within the works areas will be
transplanted. The single Artocarpus hypargyreus
recorded within the temporary works area of HKU1 would also be transplanted if
found to be in the path of the works.
4.6.4
Standard site practices including the following, should be
enforced to minimise the disturbance to the
surroundings:
·
Treat any damage that may occur to large
individual trees in the adjacent area using materials and methods appropriate
for tree surgery.
·
Reinstate work sites/disturbed areas immediately
after completion of the construction works, in particular, through on-site
tree/shrub planting along the woodland and shrubland section within the
temporary works area. Tree/shrub species
to be planted should be the same as those in the surrounding area. Only native species should be planted.
·
Regularly check the work site boundaries to
ensure that they are not exceeded and that no damage occurs to surrounding
areas.
4.6.5
The permanent loss of 0.16 ha of woodland due to site
formation and temporary loss of 0.53 ha of woodland within the works area would
be mitigated by on site compensatory planting.
While loss of woodland at the temporary works area at the Eastern Portal
would be avoided, reinstatement of the temporary works area together with
planting a mixture of tree species at most of the temporary works areas at
various intake points and the Western Portal would be adequate for compensating
loss of woodland (refer to last column of Table
4.4 and Table 10.5 of Chapter 10). As tree planting doubles as a landscape mitigation measure,
and at some intake points the space available for planting would not be enough
to fully compensate the woodland loss from the same location, trees will also
be planted at some other intake points where there would be no woodland loss
from the Project. This could help increase the compensation ratio. A total of 1.02
ha would be
planted with woodland species, reaching almost a 1.5:1 ratio for compensatory
planting (approximately
1.5 tree would be planted for the loss of one tree). Tree/shrub species used should be based on
those in the surrounding areas, including those shown in Table 4.6, which are commonly recorded during
the baseline surveys.
Table 4.6 Plant/shrub species for
compensatory planting
|
Species |
Growth
Form |
Species |
Growth
Form |
|
Ficus microcarpa |
Tree |
Cinnamomum camphora |
Tree |
|
Litsea monopetala |
Tree |
Litsea
glutinosa |
Tree |
|
Choerospondias axillaris |
Tree |
Schefflera octophylla |
Tree |
|
Gordonia axillaris |
Tree |
Ilex asprella |
Shrub |
|
Cratoxylum cochinchinense |
Tree |
Psychotria rubra |
Shrub |
|
Celtis tetrandra subsp. sinensis |
Tree |
Litsea rotundifolia |
Shrub |
|
Artocarpus hypargyreus |
Tree |
Rhodomyrtus tomentosa |
Shrub |
|
Machilus spp. |
Tree |
Rhaphiolepis
indica |
Shrub |
4.6.6
The
majority of the permanent stream habitat loss would come from the modification
of a section of stream course (54 m) immediately upstream from the Eastern
Portal and mitigation at this site is required. The tunnel portal is located at
the end of the natural section of the stream (Figure
2.3-8). The modification is essential for adjusting
the flow rate before the stream flow, which is the largest stream along the
tunnel alignment, enters the drainage tunnel.
The width of the channel would expand progressively in this
section. In non-flood situations, the
flow would continue into an existing underground drain beneath the car
park. But when the water depth exceeds a
threshold level, the excess flow would go into the tunnel opening. Although only limited aquatic fauna were
found in this stream during the ecological field survey (Mosquito fish was the
only fish species found, see Appendix B),
the stream course remains natural and has potential to develop a more diverse
fauna. The aim of the mitigation is
mainly to provide living space within the modified section for aquatic
communities to develop. A low-flow
channel would be provided within the channelised
section to maintain a deeper water depth in the expanded channel, in particular
during dry season (Figures 4.2 and 4.3). And there would be a
basin at the end of the channelised section. Both structures could provide living space
for aquatic life within the channelised section. Furthermore, step chute in the form of a
series of descending water pools would be constructed between the low flow
channel and the undisturbed stream course.
There would also be openings for aquatic fauna between each chute step
(pool). These could work like a “ladder”
to help avoid isolating the aquatic fauna in the channelised
section from natural habitats.
4.6.7
Measures are also needed to
maintain the flow of all
affected streams/nullahs during
the construction stage. Temporary
bypasses should be provided if the stream/nullah
flows will be cut off by the construction works. After the construction works are finished,
sections of temporary loss should be reinstated. Construction materials, wastes, and equipment
should be cleared from the sites.
4.6.8
Surveys of amphibians at Eastern Portal, PFLR1(P),
W12(P), MB16, E5(B)(P), TP789(P) and P5(P) prior to commencement of
construction is recommended. Frogs, including Hong Kong Cascade Frog and Lesser
Spiny Frog, and tadpoles found at the works areas of these
proposed intake points will be collected and translocated
to nearby streams that will not be affected by the project before commencement of construction. These procedures should be performed by
experienced herpetologists. A detailed
translocation proposal will be submitted during the detailed design stage.
4.6.9
Measures should be taken to avoid site runoff entering
into streams/nullahs and
thus affecting freshwater and marine habitats. In addition, site runoff should also be properly treated (by silt traps and grease traps) before
discharging to the nearby drainage system to reduce the potential of suspended solid, organics and other contaminants entering the local stream and marine environment.
4.6.10
Construction
phase mitigation measures are summarized in Table 4.7 below.
Table 4.7 Construction
phase mitigation measures
|
Impacts |
Mitigation
Recommended |
|
Habitat loss |
Adjustment
of site boundary to minimise temporary works area and loss of natural habitats. Minimizing
felling of trees and transplantation. On site compensatory planting
of native species. Provision of living
space, low flow channel and step chute within the modified section at the
Eastern Portal. Provision
of temporary by-pass for water flows. Sections of temporary loss of stream as well as work sites/disturbed areas to be reinstated immediately after
completion of construction. Construction materials, wastes, and equipment
should be cleared from the sites. Translocation
of frogs. |
|
Disturbance & Surface runoff |
Good
site practice. Treat
any damage that may occur to large individual trees in the adjacent area. Regularly
check the work site boundaries. Prevention
of sediment and runoff to streams habitats, desilting runoff. |
4.6.11
No mitigation measure is required as the ecological impact is
considered minimal.
4.7.1
The residual ecological impacts include net loss of 85 m of stream course as a result of the construction and operation of the
proposed project. This impact is
considered acceptable
due to the small area involved, the scattered distribution of the loss and the low quality of the affected stream
habitat.
4.8
ENVIRONMENTAL AUDIT AND
MONITORING
4.8.1
Besides the EM&A for site practices, no specific EM&A programme for terrestrial ecology would be required for the
Project.
4.9.1
Major habitats recorded within the study area include natural
woodland, shrubland, fung shui
woodland, urban plantation and stream/nullah.
The proposed construction would cause permanent losses of 0.16 ha of woodland, 0.70 ha of urbanised/disturbed land, 0.04 ha of shrubland habitats and 85 m of natural stream, and temporary losses of 0.53 ha of woodland, 1.56 ha of urbanised/disturbed land, 0.11 ha of shrubland, 91 m of natural stream, and 384 m of nullah. This project
will cause limited terrestrial ecological impacts. The proposed construction methods will avoid
or minimise impacts to the extent possible. Remaining impacts are addressed by
mitigation. Mitigation would
be implemented to provide living space within the modified stream section for aquatic communities to develop. With the recommended
mitigation measures in place, the residual ecological impacts are considered
acceptable. Permanent loss of 85m scattered stream habitats would constitute residual
ecological impact which is considered acceptable due to the small area
involved, the scattered distribution of the loss and the low naturalness of the
stream sections concerned.
Carey, G.J., Chalmers, M.L., Diskin, D.A., Kennerley, P.R.,
Leader, P.J., Leven, M.R., Lewthwaite, R.W.,
Melville, D.S., Turnbull, M. and Young, L. 2001. The Avifauna of Hong Kong.
Hong Kong Bird Watching Society, Hong Kong.
Fellowes J.R., Lau, M.W.N., Dudgeon, D. Reels, G.T.,
Ades, G.W.J., Carey, G.J., Chan, B.P.L., Kendrick, R.C., Lee, K.S., Leven,
M.R., Wilson, K.P.D. and Yu, Y.T. 2002. Wild animals to watch: Terrestrial and
freshwater fauna of conservation concern in Hong Kong. Memoirs of the Hong
Kong Natural History Society 25: 123–160.
Wang, S. 1998. China Red Data Book of Endangered Animals: Mammalia. Science
Press, Beijing.