This
section presents the results of the assessment of ecological value of the
habitat and the potential impacts from the construction and operation of the drainage
system of the Project (Drainage Improvement in Tsuen Wan and Kwai Chung – Tsuen
Wan Drainage Tunnel - Investigation), on ecological resources in the Study
Area. Field surveys covering a period of
4 months (August to November 2003) were undertaken to establish the baseline
ecological conditions of the Study Area. The methodology and results of the literature
review and baseline surveys
are presented in Appendix F. Measures
required to mitigate identified adverse impacts are recommended, where appropriate.
A number of international conventions and local
legislation and guidelines provide the framework for the protection of species
and habitats of ecological importance. Those related to the Project are:
·
Country
Parks Ordinance (Cap 208);
·
Forests
and Countryside Ordinance (Cap 96);
·
Wild
Animals Protection Ordinance (Cap 170);
·
Animals
and Plants (Protection of Endangered Species) Ordinance (Cap 187);
·
Town
Planning Ordinance (Cap 131);
·
·
The
Technical Memorandum on Environmental Impact Assessment Process under the
Environmental Impact Assessment Ordinance (EIAO TM);
·
United
Nations Convention on Biodiversity (1992); and
·
PRC
Regulations and Guidelines.
The Country Parks
Ordinance provides for the designation and management of
The Forests and
Countryside Ordinance prohibits felling, cutting, burning or destroying of
trees and growing plants in forests and plantations on Government land. The subsidiary Forestry Regulations prohibit the picking, felling or possession of
listed rare and protected plant species. The list of protected species in Hong
Kong which comes under the Forestry
Regulations was last amended on 11 June 1993 under the Forestry (Amendment) Regulation 1993 made under Section 3 of the Forests and Countryside Ordinance.
Under the Wild
Animals Protection Ordinance, designated wild animals are protected from
being hunted, whilst their nests and eggs are protected from destruction and
removal. All birds and most mammals
including all cetaceans are protected under this Ordinance, as well as certain
reptiles, amphibians and invertebrates. The Second Schedule of the Ordinance
that lists all the animals protected was last revised in June 1992.
The purpose of the Animals
and Plants (Protection of Endangered Species) Ordinance is to restrict the
import and export of scheduled species. The Ordinance is primarily related to
controlling trade in threatened and endangered species and restricting the
local possession of them.
The Town Planning
Ordinance provides for the designation of areas such as “Coastal Protection
Areas”, “Sites of Special Scientific Interest (SSSIs)”, “Green Belt” and
"Conservation Area” to promote conservation or protection or protect
significant habitat.
Chapter 10 of
the HKPSG covers planning
considerations relevant to conservation. This chapter details the principles of
conservation, the conservation of natural landscape and habitats, historic
buildings, archaeological sites and other antiquities. It also addresses the issue of
enforcement. The appendices list the
legislation and administrative controls for conservation, other conservation
related measures in
Annex 16 of the EIAO TM sets out the general approach
and methodology for assessment of ecological impacts arising from a project or
proposal, to allow a complete and objective identification, prediction and
evaluation of the potential ecological impacts. Annex 8 recommends the criteria that can be used for evaluating
ecological impacts.
The Peoples’ Republic of China (PRC) is a Contracting
Party to the United Nations Convention on
Biological Diversity of 1992. The
Convention requires signatories to make active efforts to protect and manage
their biodiversity resources. The
Government of the Hong Kong Special Administrative Region has stated that it
will be “committed to meeting the environmental objectives” of the Convention
(PELB 1996).
The PRC in 1988 ratified the Wild Animal Protection Law of the PRC, which lays down basic
principles for protecting wild animals. The Law prohibits killing of protecting
animals, controls hunting, and protects the habitats of wild animals, both
protected and non-protected. The Law
also provides for the creation of lists of animals protected at the state
level, under Class I and Class II. There
are 96 animal species in Class I and 156 in Class II. Class I provides a higher level of protection
for animals considered to be more threatened.
The Study Area was defined as the area within 500 m of
either side, and along the full stretch of the alignment of the Tunnel Option
No. 3 the shortest tunnel alignment (discussed in Section 2 and recommended in the Option Selection Report, and
endorsed by the Drainage Services Department), as well as the intake and
outfall structures. Following a
literature review of available ecological data characterising the Study Area,
reconnaissance surveys were undertaken in August 2002 to update and field check
the validity of the information gathered in the review. A number of more focused baseline field
surveys were then carried out to determine the existing ecological
conditions. The surveys were designed to
fill any identified data gaps in order to facilitate a compliant assessment of
the Project’s impacts upon ecology and the development of appropriate
mitigation measures. Special attention
was paid to those areas which will be directly impacted by the proposed
construction areas. The baseline surveys
cover a 4-month period from August to November 2003.
The following baseline surveys were identified as being
required:
·
Habitat and vegetation surveys;
·
Dragonfly and butterfly surveys;
·
Herpetofauna survey including night survey;
·
Bird survey;
·
Mammals survey including night survey;
·
Stream fauna survey; and
·
Intertidal survey.
Details
of the baseline field
survey methodology are presented in Appendix F.
This section presents a summary of the findings of the
baseline field surveys performed during the period August to November
2003. The results of the literature
review and baseline field surveys are presented in full in Appendix F. The baseline ecological conditions
were evaluated based on the criteria laid out in Annex 8 & 16 of the EIAO
TM.
Most of the Study Area located below and immediately above
the catchwater running along the southern boundary of
Table 7.1 Habitat Types
recorded within the Study Area
|
Habitat type |
Size |
Ecological
Value |
Notes |
|
|
79.1 ha |
Moderate |
Species
of conservation interest recorded included Emerald Dove, Rhesus Macaque,
Black Kite, Chinese Pond Heron and Little Egret. |
|
|
181.2 ha |
Low to Moderate |
Species
of conservation interest recorded included Japanese Pipistrelle, Pallas Squirrel
Common Buzzard. |
|
Grassland |
89.4 ha |
Low |
Species
of conservation interest recorded included Red Admiral and Japanese
Pipistrelle |
|
Village-Orchard |
40.5 ha |
Low
to Moderate |
Neither rare nor protected
species were recorded during the survey. |
|
Stream/Channel |
7.54 ha
(ca. 5km) |
|
|
|
Intake I-1
Channel |
|
Low
|
Man-made
channel with smooth channel bed and lack of pool areas |
|
Sam Dip
Tam Stream |
|
Moderate |
Residential
sewage inputs were found in the middle course of the-stream, above the
proposed Intake I-2. Species of
conservation interest recorded included Hong Kong Newt, Chinese Pond Heron,
Little Egret and White-throated Kingfisher |
|
Tso Kung
Tam Stream |
|
Moderate |
Residential sewage inputs
were found just upstream to the proposed location for Intake I-3. Species of conservation interest recorded
included Little Egret, Striated Heron, Plumbeous Redstart. |
|
All Other Streams/Channels within the Study Area |
|
Low to Moderate |
Species
of conservation interest recorded included Hong Kong Cascade Frog |
|
Urbanised/Disturbed Area |
165.4 ha |
Low |
Species of conservation
interest recorded included Arundina graminifolia and Common Rat
Snake. The Common Rat Snake was
recorded near the proposed Intake I-2. |
|
Intertidal
Habitat (Artificial/Disturbed Seashore) |
1
km |
Low |
The
Outfall O-1 will be located on the highly disturbed habitat with low species diversity
and richness (only 6 species of intertidal fauna were recorded during
baseline surveys). All recorded faunal
species were common and widespread in |
The proposed
Species of conservation interest recorded within the Study
Area during the surveys included orchid Arundina
graminifolia, Japanese Pipistrelle Pipistrellus abramus, Rhesus
Macaque Rhyacornis fuliginous, Pallas Squirrel Callosciurus
erythraeus styani, Striated Heron Butorides striatus, Chinese Pond
Heron Ardeola bacchus, Little Egret Egretta garzetta, Black Kite Milvus
lineatus, Common Buzzard Buteo buteo, Emerald Dove Chalcophaps
indica, White-throated Kingfisher Halcyon smyrnensis, Plumbeous
Redstart Rhyacornis fuliginous, Common Rat Snake Ptyas mucosus,
Hong Kong Newt Paramesotriton hongkongensis, Hong Kong Cascade Frog Amolops
hongkongensis, Red Admiral Vanessa indica and Freshwater crab Cryptopotamon
anacoluthon.
Only three species of conservation interest (Common Rat
Snake, Striated Heron and Plumbeous Redstart) recorded in the vicinity of the
proposed surface structures during the surveys. The two bird species Striated
Heron (usually foraging in coastal mangrove and occurring in wooded stream
mainly during winter) and Plumbeous Redstart (winter visitor, occurring in
rocky stream) were recorded close to Intake I-3. Common Rat Snake was recorded close to Intake
I-2.
The proposed drainage tunnel is approximately 5.13 km long
running below ground with 4 surface structures, including 3 intake structures
and an outfall. The potential ecological
impact arising from the drainage improvement works, based on the results of the
recent baseline surveys, revised layout drawings and construction methods of
Tunnel Option No. 3 the shortest tunnel alignment (discussed in Section 2
and recommended in the Option Selection Report, and endorsed by the Drainage
Services Department), may arise from the construction and operational phase
impacts detailed below.
·
Direct habitat loss and habitat fragmentation
resulting from land take for the construction activities for the surface
structures of the proposed drainage tunnel;
·
Direct impacts to inactive/less
mobile/habitat-specific wildlife nesting/inhabiting the affected area and
surrounding habitats, and associated impacts to wildlife including restriction
of wildlife utilisation (ie transit, feeding and roosting), degradation of
habitat quality/ ecological function, as a result of temporary and permanent
loss, isolation and fragmentation of ecological habitat, and noise, construction
activities;
·
Direct and indirect impacts to watercourses,
including deterioration of water quality, silty run-off and sedimentation
effect, as a result of construction activities and discharge; and
·
Impacts to the surrounding habitat due to
physical disturbance of this habitat including construction activities,
increased human activities, inappropriate storage or dumping of construction
material, or hill fire.
·
Potential hydrological disruption to the natural
downstream habitats and aquatic fauna; and
·
Impacts to the hydrology and water quality of
the coastal habitats in the vicinity of the outfall.
Apart from the potential ecological
impacts, potential conflicts of the land use of the proposed
The proposed drainage tunnel will be constructed 7 m to
200 m below the existing ground level. The major impacts on the ecological
resources will be the construction of surface structures including the 3
stormwater intakes (Intakes I-1, I-2 and I-3) and an outfall structure (Figures
7.1 to 7.6).
In general, the construction of the proposed drainage tunnel
including temporary and maintenance access, sand/boulder trap, intake and
outfall structures (including vertex chamber and drop shaft), site formation,
excavation, hand digging, drilling and blasting works (at Intakes I-2 and I-3),
will lead to the loss of existing habitats, particularly stream/channel,
plantation, village-orchard, intertidal habitat (artificial/disturbed seashore)
and urbanised/disturbed areas, as well as the effect of habitat fragmentation
and isolation.
The details of the construction sequences, methods and
programme are presented in Section 2.
Most of the works at Intake I-1 including the construction
of maintenance works area and spiral access ramp will be undertaken on sloping
area which mainly involve slope cutting works, installation of soil nails,
construction of retaining walls, site formation and excavation, pilings. All of the areas to be affected by Intake I-1
were identified as low quality, man-made and highly disturbed habitats
including man-made channel with smooth concrete bottom, plantation and
urbanised/disturbed habitat (Figure 7.1 and Table
7.2). Neither rare nor
protected species will be affected, and no aquatic fauna were recorded in the
vicinity of Intake I-1 during the baseline surveys.
Table 7.2 Overall Habitat
Loss due to the Drainage Improvement Works
|
Proposed Surface Structures |
Impacted Habitats |
Permanent loss (Land Take for the
Surface Structures) |
Potentially Temporary Loss (Works Areas)
during the Construction (1) (2) |
Ecological Value of the Affected
Habitat |
|
Intake
I-1 |
Stream/Channel |
15m
(<0.01 ha) |
140m
(0.15 ha) |
Low |
|
|
|
0.13
ha |
0.22
ha |
Low
to Moderate |
|
|
Urbanized/
Disturbed Area |
Nil |
0.12
ha |
Low |
|
Intake
I-2 |
Stream/Channel |
60
m (0.06 ha) |
Additional
0.03 ha at the same stream section |
Moderate |
|
|
Village-Orchard |
0.05
ha |
Nil |
Low
to Moderate |
|
|
Urbanized/
Disturbed Area |
0.03
ha |
Nil |
Low |
|
Intake
I-3 |
Stream/Channel |
75
m (0.02 ha) |
Additional
0.11 ha at the same stream section |
Moderate |
|
|
|
0.51
ha |
0.04
ha |
Low |
|
|
Village-Orchard |
0.10
ha |
Nil |
Low
to Moderate |
|
Outfall O-1 |
Intertidal
Habitat (Artificial/ Disturbed Seashore) |
55 m (0.15 ha) |
65 m (0.02 ha) |
Low |
|
|
|
0.48
ha |
1.16
ha |
Low
to Moderate |
|
|
Urbanized/
Disturbed Area |
0.11 ha |
0.21 ha |
Low |
Note: (1)
All of the areas within the boundary of
Works Area were assumed to be affected during the construction, and therefore
the sizes of the potentially affected areas are considered as the worst case
scenario.
(2)
Areas excluded the permanent resumed
land for the Project.
The construction activities in Intake I-2 will mainly
involve the channel modification works, construction of retaining wall on the
western side of the channel, vortex chamber and its associated on-line approach
channel, the dropshaft and underground deaeration chamber, the man access shaft
and connecting tunnel. The habitats to
be affected permanently due to the construction of Intake I-2 structures
include stream/channel of natural bottom, village-orchard and urbanized/ disturbed
area (Figure 7.2 and Table 7.2). The intake structures will be located mainly at the stream section
of partial modification (with concrete lining underneath the existing bridge
crossing) and disturbance (pollution due to residential sewage discharge)(Figure 7.9). The tentative construction sequences of the
proposed intake and channel flow diversion works will be divided into 4 phases
(details are presented in Section 2). The habitats to be affected during
each phase are summarised in Figure 7.3 and Table
7.3.
Table 7.3 Habitats
to be Affected during Construction of Intake I-2
|
Phase |
Habitats
to be Affected during Construction |
Construction Activities |
|
1 |
Stream/Channel – mainly stream bank (55m/ <0.01
ha) Village-Orchard (0.03 ha) Urbanized/ Disturbed Area (0.01 ha) |
Channel
modification to match the new Dry Weather Flow Channel (DWFC) Bridge
crossing concrete slabs modification to re-construct and re-locate the DWFC Channel
widening (modify the stream bank into stream/channel) and concrete wall
construction Provision
of natural bedding (granular bed) Construction
period: 01 Oct 07 to 29 Feb 08 |
|
2 |
Stream/Channel (30m/ 0.03 ha) Urbanized/ Disturbed Area (0.01 ha) |
Site formation works Drop
shaft, audit tunnel and deaeration chamber construction (the first 10m of the
structures will be constructed by hand digging only, drill and blast method
will be adopted for the deeper section) Construction period: 01
Mar 08 to 31 Aug 09 |
|
3 |
Stream/Channel (55m/ 0.05 ha) Urbanized/ Disturbed Area (0.01 ha) |
Construction of intake
chamber and guide wall Construction of
superstructure of drop shaft Construction period: 01
Nov 09 to 31 Mar 10 |
|
4 |
Nil (at the same location of the completed part of Phase
3) |
Construction
of guide wall on the completed slab constructed under Phase 3 Construction
period: 01 Feb |
|
Man access |
Village-Orchard (0.02 ha) |
Construction
of man access shaft and connecting tunnel by the drill and blast method Construction period: 01
Mar 10 to 31 Mar 11 |
The construction activities in Intake I-3 will mainly
involve the construction of the vortex chamber and its associated on-line approach
channel, dropshaft, aeration chamber and audit tunnel, access road and slope
works. The habitats to be affected
permanently due to the construction of Intake I-3 include stream/channel,
village-orchard and urbanized/ disturbed area (Figure 7.4 and Table
7.2). The intake structures will be located mainly at
the stream section of partial disturbance (pollution due to residential sewage
discharge). The tentative construction
sequences of the proposed intake and channel flow diversion works will be divided
into 4 phases (details are presented in Section 2). The habitats to be affected during each phase
are summarised in Figure 7.5 and Table
7.4. Since Intake I-3
is located within the boundary of the proposed location of Tso Kung Tam
Ecological Park (proposed by LCSD and still in planning stage), assessing the
impacts on the existing habitats due to the proposed drainage tunnel are
considered to be equivalent to and representative for the proposed Ecological
Park.
Table 7.4 Habitats to be Affected during Construction of Intake I-3
|
Phase |
Habitats
to be Affected during Construction |
Construction Activities |
|
Road access |
Village-Orchard (0.1 ha) |
Formation
of access road and associated slope works Slope
stabilisation works on the south western side of the drop shaft Construction
period: 01 Dec 07 to 31 May 08 |
|
1 |
Stream/Channel (14m/ <0.01 ha) |
Construction of vortex chamber
and drop shaft Construction period: 01
Jun 08 to 31 March 09 |
|
2 |
Stream/Channel (75m/ 0.08 ha) |
Modification of existing
stream bed and construction of approach channel with concrete lining Provision of natural
bedding (granular bed) Construction period: 01
Nov 09 to 31 Mar 10 |
|
3 |
Stream/Channel (75m/ 0.04 ha) |
Modification
of existing stream bed and construction of approach channel with concrete
lining Provision of natural
bedding (granular bed) Construction period: 01
Nov 10 to 15 Mar 11 |
The works at Outfall O-1 will include the construction of
tunnel portal, cascade, box culvert underneath the improved
The summarised potential impacts during construction phase
will be:
·
Permanent and temporary loss of the existing
habitats including stream/channel, plantation, village-orchard, intertidal
habitat (artificial/disturbed seashore) and disturbed/urbanized areas due to
the construction of the permanent access ramp, maintenance/ turning area,
intake/outfall structures and sand/boulder trap (details refer to Figures
7.1 - 7.6 and Table 7.2). In general, with the exception of moderate
ecological value of the middle course of Sam Dip Tam Stream (location of Intake
I-2) and Tso Kung Tam Stream (location of Intake I-3), all of the affected
habitats are of low ecological concern.
·
Direct
impact to the bottom of the stream channels reducing the number of riffles and
pools due to the land take for the surface structures, as well as secondary
impacts to the associated aquatic fauna. The upstream or downstream movement of
the aquatic fauna will also be restricted; and
·
Loss
of foraging and feeding ground of the associated wildlife, particularly species
of conservation interest (Common Rat Snake, Striated Heron and Plumbeous
Redstart) recorded in the vicinity of the proposed surface structures during
the August-November surveys (Table 7.5).
Table 7.5 Impacts
on the Species of Conservation Interest
|
Species of Conservation Interest |
Major Impacts |
Location Recorded |
|
Striated Heron (all birds are protected under WAPO
in |
Part of their foraging habitat (stream) will
be affected |
Downstream of Intake I-3 |
|
Plumbeous Redstart (all birds are protected under
WAPO in |
Part
of their foraging habitat (stream) will be affected |
Downstream
of Intake I-3 |
|
Common Rat Snake
(listed in Appendix 2 of CITES (Zhao 1998) and considered of potential
regional concern) |
Associated
habitats will be partially affected |
Urbanized/
disturbed area near proposed location of Intake I-2 |
·
Fragmentation and isolation of the continuous
patches of plantation (with low to moderate ecological value) restricting the wildlife
movement at Intakes I-1, I-3 and Outfall O-1 resulting from land take for the
construction activities for the proposed channels. Minimal effects of habitat fragmentation and
isolation due to the loss of other habitats will be expected.
·
Impacts
to Water Quality indirect impacts to aquatic ecological resources during the
construction phase include sediment release and chemical spillage associated
with the site formation, drill and blast works. Potential impacts to water quality
from sediment release are listed below:
-
increased
concentrations of suspended solids (SS); and
-
an
increase in nutrient concentrations in the water column.
The aquatic
organisms within the lower course of the stream may be susceptible to the effects
of increased sediment loads. Effects can
be lethal (ie suffocation) or sub lethal (eg reduction in reproductive
potential due to stress incurred by constantly having to flush out the
depositing material). The effects of
sedimentation on organisms will also depend on other factors, such as an
organism’s tolerance, growth orientation of sessile organisms and water
movement. Given that increases in SS
levels downstream are expected to be low and temporary, and within
environmentally acceptable limits (as defined by the WQOs and tolerance
criteria) (details refer to Section 5
Water Quality Impact Assessment), unacceptable impacts to the downstream
aquatic fauna arising from minor elevations in SS levels are not expected to
occur.
High levels of
nutrients (total inorganic nitrogen - TIN and ammonia) in water can cause rapid
increases in phytoplankton often to the point where an algal bloom occurs,
particularly in stream pools. An intense
bloom of algae can lead to sharp increases in DO levels in surface water. However, at night and when these algae die
there is usually a sharp decrease in the levels of dissolved oxygen in the
water, as dead algae fall through the water column and decompose on the bottom. Anoxic conditions may result if DO
concentrations are already low or are not replenished. This may result in mortality to aquatic
organisms due to oxygen deprivation. The
water quality assessment has indicated that the levels of Chlorophyll a, TIN
and ammonia do not change appreciably from background conditions during the
Project works (details refer to Section 5
Water Quality Impact Assessment). It is
thus expected that unacceptable impacts to the downstream habitats and the
associated aquatic fauna, will not occur.
No chemical
spillage affecting the downstream habitats and associated aquatic fauna will be
anticipated given that regular checks on good construction practice will be
conducted (details refer to Section 5
Water Quality Impact Assessment).
·
Secondary impacts to the surrounding habitats
(generally with low ecological value) and associated wildlife, particularly
species of conservation interest (Common Rat Snake, Striated Heron and
Plumbeous Redstart) recorded in the vicinity of the proposed surface
structures, may arise from the potential for increased noise impact, drilling
and blasting, human activities and disturbance such as import, storage or
dumping of construction material and construction site runoff. The impacts are expected to be low owing to
the temporary nature and small scale of the construction works, and given that
regular checks on good construction practice will be conducted.
The
Intake I-1 is designed to intercept up to 94% of the stream flow (59 m3/s)
in a 200-year rainfall event. Since the Intake I-1 is located on the existing
artificial concrete channel and the lower courses of the stream/channel are
underground man-made structures, no operational impacts will be expected.
The Intakes I-2 and I-3 are designed to capture 66%
(53 m3/s) and 38% (97 m3/s) of the upland flow under a
200-year storm respectively. The side
weir with a crest height of 1.3 m (Intake I-2) or 1.4 m (Intake I-3), used to
intercept the stormwater, would come into operation when rainfall exceeds
30mm/hr. Section 2.5 details the
interception at each intake. The major operational impact due to the Project is
the potential hydrological disruption, mainly influencing the water flow and
level, to the natural stream habitats downstream to the intake structures,
particularly Intakes I-2 and I-3. The
intake structures may alter the flow velocity of the stream water influencing
the downstream microhabitats and associated aquatic fauna. The downstream water level may be reduced and
this may reduce the stream habitats and therefore restrict the movement of
aquatic fauna. The reduction in the
water level may also reduce the number of riffles and pools of the lower course
of the streams. As a consequence, the
aquatic faunal communities and population may be influenced. The tunnel,
however, is not expected to affect groundwater levels (note it is a lined
tunnel) or the ecological resources above the tunnel. There will be no drawdown
effect on the water table, and a programme of monitoring is included to
demonstrate this.
The collected stormwater will be discharged to the
sea via the Outfall O-1. The significant
change of seawater salinity and flushing effects of the stormwater near the
Outfall O-1 may affect the associated intertidal floral and faunal communities
of the coastal habitats and nearshore benthic habitats. The distribution and abundance of marine
organisms are determined by the physical environment, including the substratum,
seawater salinity and water current. During the operational phase, the
reduction of seawater salinity and strong flushing of the stormwater may alter
the species diversity and abundance of the intertidal marine organisms
inhabited in the vicinity of the outfall although these are acknowledge to be
of low ecological value.
With the exception of Intake I-3, there are no planned
projects in the vicinity of the
intake and outfall structures of the drainage tunnel. Considering that the ecological impacts
arising from the construction and operation of Intake I-3 are low to moderate
only (see Section 7.6.4 below) and, as the best assumption in the
absence of detailed design information from LCSD, that the proposed Ecological
Park would adopt any necessary measures to minimise potential ecological
impacts arising from its implementation, the potential for cumulative
ecological impacts arising from these two projects would remain low.
Potential impacts to ecology have been evaluated according
to Table 1 of Annex 8 of the EIAO TM. Tables 7.6 to 7.8 present an evaluation of the habitat loss due to the
Project.
Table 7.6 Overall
Impact Evaluation for Stream/Channel
|
Evaluation Criteria |
Intake I-1 |
Intake I-2 |
Intake I-3 |
|
Habitat quality |
The habitat quality of the Intake I-1
Channel is low. The existing channel
has concrete bottom. |
Moderate. The Intake I-2 located on middle
course of Sam Dip Tam Stream has natural bottom and partially modified stream
bank (particularly at the bridge crossing).
Residential sewage input was recorded upstream of the Intake I-2. |
Moderate. The Intake I-3 located on middle
course of Tso Kung Tam Stream has natural bottom and stream bank. Residential
sewage input was recorded upstream of the Intake I-3. |
|
Species |
The
potential exists for direct and indirect impacts to the wildlife inhabiting
the stream. However, neither rare nor
protected species will be affected, and no aquatic fauna were recorded during
the surveys. |
The potential exists for direct and indirect
impacts to the wildlife inhabiting the stream. However, neither rare nor protected species
will be affected. Common Rat Snake
recorded in the urbanised/disturbed areas close to the Intake I-2 is
potentially be affected. The
downstream aquatic fauna may be affected due to the construction runoff
during construction. |
The potential exists for direct and indirect
impacts to the wildlife inhabiting the stream. Species of conservation concern potentially
affected included Striated Heron, Plumbeous Redstart. The downstream aquatic fauna may be
affected due to the construction runoff during construction. |
|
Size/Abundance |
Approximately
140 m (0.15 ha) of the stream will be temporarily affected. Only a small section of the existing
channel will be affected (15m (<0.01 ha)). |
Approximately
60 m (0.06 ha) of the stream will be lost and approximately 0.03 ha of stream
habitat will be temporarily affected. No additional areas will be affected
temporarily during the construction. |
Approximately
75 m (0.02 ha) of the stream will be lost and approximately 0.11 ha of stream
habitat will be temporarily affected. Approximately 0.06 ha of the stream
will be temporarily affected. |
|
Duration |
The
impact will persist during the construction phase. The temporary affected areas will be
reinstated after the completion of the works. |
The
impact will persist during the construction and operational phases. |
The
impact will persist during the construction and operational phases. |
|
Reversibility |
The
habitat loss could be recreated, if lands available, but this requires a
certain period of time to let the habitat mature. |
The
habitat loss could be recreated, if lands available, but this requires a
certain period of time to let the habitat mature. |
The
habitat loss could be recreated, if lands available, but this requires a
certain period of time to let the habitat mature. |
|
Magnitude |
The
scale of the habitat loss is small in the context of the surrounding similar
habitats. |
The
scale of the habitat loss is small in the context of the surrounding similar
habitats. |
The
scale of the habitat loss is small in the context of the surrounding similar
habitats. |
|
Overall
Impact Conclusion |
Low |
Low to Moderate |
Low to Moderate |
Table 7.7 Overall
Impact Evaluation for
|
Evaluation Criteria |
|
Village-Orchard |
|
Habitat quality |
Low to Moderate. |
Low to Moderate. |
|
Species |
The potential exists for
direct and indirect impacts to the wildlife inhabiting the areas. However, neither rare nor protected species
will be affected. |
The potential exists for
direct and indirect impacts to the wildlife inhabiting the areas. However, neither rare nor protected species
will be affected. |
|
Size/Abundance |
Area
loss are small in size: approximately 1.12 ha loss and 1.42 ha temporarily
affected. |
Area
loss are small in size: approximately 0.15 ha loss. |
|
Duration |
The impact will persist
during the construction and operational phases. But the temporary affected areas will be reinstated
after the completion of the works. |
The impact will persist
during the construction and operational phases. But the temporary affected areas will be
reinstated after the completion of the works. |
|
Reversibility |
|
Village-orchard is
man-made habitat. The habitat loss
could be recreated easily. |
|
Magnitude |
The scale of the habitat loss
is small in the context of the surrounding similar habitats. |
The scale of the habitat
loss is small in the context of the surrounding similar habitats. |
|
Overall
Impact Conclusion |
Low |
Low |
Table 7.8 Overall
Impact Evaluation for Intertidal Habitat (Artificial Disturbed Seashore) and
Urbanized/Disturbed Area
|
Evaluation Criteria |
Intertidal Habitat
(Artificial Disturbed Seashore) |
Urbanised/ Disturbed
Areas |
|
Habitat quality |
Low.
|
Low. |
|
Species |
The
potential exists for direct or indirect impacts to the wildlife inhabiting
the areas. However, neither rare nor
protected species will be affected. |
The potential exists for direct
or indirect impacts to the wildlife inhabiting the areas. Common Rat Snake recorded in the
urbanised/disturbed areas close to the Intake I-2 is potentially be
affected. |
|
Size/Abundance |
Approximately
55 m (0.15 ha) of the artificial/ disturbed seashore will be lost. Approximately 65 m (0.02 ha) of the
artificial/ disturbed seashore will be temporarily affected |
Area
loss are small in size: approximately 0.14 ha loss and 0.33 ha temporarily
affected. |
|
Duration |
The impact will persist during
the construction and operational phases. But the temporary affected areas
will be reinstated after the completion of the works. |
The impact will persist
during the construction and operational phases. But the temporary affected areas will be
reinstated after the completion of the works. |
|
Reversibility |
The habitat loss could be
recreated but required certain period of time to let the habitat to be
mature. |
Urbanised/
disturbed areas is man-made habitat.
The habitat loss could be recreated easily. |
|
Magnitude |
The scale of the habitat
loss is small in the context of the surrounding similar habitats. |
The scale of the habitat
loss is small in the context of the surrounding similar habitats. |
|
Overall
Impact Conclusion |
Low |
Low |
In conclusion, with the exception of low to moderate
impact to the middle course of Sam Dip Tam Stream (location of Intake I-2) and
Tso Kung Tam Stream (location of Intake I-3), the direct ecological impact due
to the construction and operation of the drainage channel is expected to be
low, and will not contribute to any potential cumulative impact.
The most sensitive potential impacts will be the loss of
stream sections of natural bottom and bank due to the land take for the
Project. Since the affected sections of
Sam Dip Tam Stream and Tso Kung Tam Stream (location of Intakes I-2 and I-3)
are partially disturbed (with relative less aquatic faunal diversity) due to
the residential sewage, relatively low diversity of aquatic fauna was recorded
in the affected sections, and small in size (the affected length are 60m (0.06
ha and additional 0.03 ha will be temporarily affected) and 75m (0.02 ha and
additional 0.11 ha will be temporarily affected) respectively). The impacts due to the land take for the
surface structures, as well as the secondary impacts to the associated aquatic
fauna, are therefore considered acceptable.
Habitat loss (permanent or temporary) due to the Project
during construction or operation will reduce the areas of foraging and feeding
grounds of the wildlife (particularly the species of conservation interest
recorded close to the Project areas, including Common Rat Snake, Striated Heron
and Plumbeous Redstart). The impacts are
expected to be low owing to the extensive habitats, including plantation and
stream/channel, available in the proximity, as well as the temporary nature and
small scale of the construction works, and given that regular checks on good
construction practice and appropriate works programme will be conducted.
The habitats within the proposed Ecological Park to be
affected included stream/channel (approximately 75m (0.07 ha), but 0.05 ha of
the stream habitat will be reinstated), plantation (approximately 0.51 ha) and
village-orchard (approximately 0.1 ha), the direct ecological impact (habitat
loss) due to the construction and operation of the drainage channel is expected
to be low to moderate due to the smaller size of the affected areas and the
extensive similar habitats in the vicinity. The impacts on Striated Heron and
Plumbeous Redstart (species of conservation interest) and the associated
wildlife, including herpetofauna, butterfly, dragonfly, aquatic fauna and bird,
recorded within the Study Area of Intake I-3 (refer to Appendix F) are
expected to be low owing to the large extent of similar habitats in the
vicinity that will remain unaffected by the drainage improvement works, as well
as the transient nature and small scale of the construction works, and given
that regular checks on good construction practice and appropriate works
programme will be conducted. The
associated wildlife and aquatic fauna inhabited in the vicinity of Intake I-3
and the proposed
Habitat Fragmentation and Isolation - In general,
the surface structures will be located in, or very close to, man-made habitats
(ie plantation and village-orchard) and disturbed areas (stream sections under
stress of pollution). The scale of the
habitat loss is small in the context of the surrounding similar habitats. Consequently, the impact of habitat
fragmentation and isolation are not considered unacceptable.
Water Quality – The construction works of intake structures
can only be conducted during dry season when the streams/channel of low water
flow. Increases in SS levels downstream
are expected to be low and temporary, and within environmentally acceptable
limits (as defined by the WQOs and tolerance criteria) (details refer to Section 5 Water Quality Impact
Assessment). No serious construction
runoff affecting the downstream habitats and associated aquatic fauna will be
anticipated given that regular checks on good construction practice will be conducted. There will be no drawdown effect on the water
table, and a programme of monitoring is included to demonstrate this.
Hydrological
Disruption – Under the normal
circumstances, the water flow and level of the lower course of Sam Dip
Tam Stream and Tso Kung Tam Stream (downstream of intake structures) would not
be affected during the operation of the drainage tunnel. No significant operational impacts will be
expected. The excessive stormwater, when
rainfall is greater than 30mm/hr, will be intercepted by a side weir of the
intake structures, with a crest height of 1.5 m (Intake I-2, make use of the
existing concrete slab underneath the bridge crossing) or 0.6 m (Intake I-3),
to prevent flooding of lowland areas
which may hazard or disturb the downstream structures and facilities as well as
the lower course of the streams and aquatic faunal communities. Additionally, the possibility of flushing
aquatic fauna downstream due to the excessive stormwater (flooding) will now be
reduced. Consequently, significant disruption of the hydrology of
the lower course of the streams
as well as consequent impacts on the aquatic fauna would not be
anticipated.
Other Impacts – Increased human activities and
disturbance due to the Project during construction may affect the surrounding
natural habitats and the associated wildlife (particularly the species of
conservation interest recorded close to the Project areas, including Common Rat
Snake, Striated Heron and Plumbeous Redstart). The blasting works (for shafts,
deaeration chamber and audit tunnel construction) will be restricted inside the
tunnel (with the provision of enclosure at the opening) and the works will be
specially planned and designed to avoid the impacts to the surrounding
environment. Impacts to the wildlife due
to the blasting works are therefore expected to be low. The overall impacts are
expected to be low owing to the temporary nature and small scale of the
construction works, and given that regular checks on good construction practice
will be conducted.
Annex 16 of the EIAO TM states that the general policy
for mitigation of significant ecological impacts, in order of priority, is:
Avoidance: Potential impacts should be avoided to the
maximum extent practicable by adopting suitable alternatives;
Minimisation: Unavoidable impacts should be minimised by
taking appropriate and practicable measures such as constraints on intensity of
works operations or timing of works operations; and
Compensation: The loss of important species and habitats
may be provided for elsewhere as compensation. Enhancement and other
conservation measures should always be considered whenever possible.
At each stage, residual impacts are to be re-assessed to
determine whether there is a need to proceed to the next stage of
mitigation. The following measures have
been developed in accordance with this approach to mitigate the impacts.
The mechanism of the intake structure is to divert
a portion of stream flow into the tunnel under high flow condition while the
stream flow will be maintained under normal condition to nourish the riparian
habitats downstream. An engineered
hydraulic structure is therefore required to be located on the existing
stream/channel to intercept the desire proportion of the stream flow under
different condition. This
interception arrangement must be an ‘on-line’ arrangement so as to have the
direct interaction with the stream flow.
Following the option selection as discussed in Section 2, the surface structures are
chosen to locate mainly on exiting disturbed areas and have generally avoided
the upstream natural and undisturbed stream habitats of higher species
diversity and abundance of aquatic organisms:
Intake I-1: Intake I-1 is located at low quality,
man-made and highly disturbed habitats including man-made channel with smooth
concrete bottom, plantation and urbanised/disturbed habitat.
Intake I-2: Intake I-2 is located mainly at the
stream section of partial modification (with concrete lining underneath bridge
crossing) and disturbance (pollution due to residential sewage discharge). The
major construction activities at the stream (Phases
1, 3 and 4), including shaft construction, modification of
existing channel and construction of guide wall
and approach channel, are scheduled to avoid wet season (only to be
undertaken during dry season (from October to March)) of high water flow
which may adversely affect the downstream natural habitats due to the
construction runoff. Although
the construction of the shaft and adit tunnel (Phase 2) will be extended
into wet season, the majority of the construction site runoff will be confined
inside the shaft and adit tunnel. The
chance of the construction runoff
over spilling into the existing
stream would be minimal. The runoff will be properly
discharged off-site through pumping under close supervision.
Intake I-3: Intake I-3 is located mainly at the
stream section of partial disturbance (pollution due to residential sewage
discharge) and located along the stream bank in order to avoid nearly half of
the natural stream section. The major
construction activities at the stream (Phases 2 and 3) are scheduled
to avoid wet season (only to be undertaken during dry season (from November to
March)) of high water flow which may adversely affect the downstream
natural habitats due to the construction runoff.
Outfall O-1: Outfall O-1 is located at low quality,
man-made and highly disturbed habitats including artificial/ disturbed
intertidal habitat, plantation and urbanised/disturbed habitat.
In order to minimize the extent of works as well as
the associated ecological impacts, the final layout plan has been
revised (deviated from the PPFS arrangement) through the replacement of the
twin vortex dropshafts by a single dropshaft. Further to such amendment, the
habitat loss (permanent and temporary) due to the Project are greatly reduced,
in particular the natural stream habitats at Sam Dip Tam Stream (location of
Intake I-2, temporary loss reduced to zero) and Tso
Kung Tam Stream (location of Intake I-3, both
permanent and temporary loss reduced by 0.18 ha and 0.17 ha respectively). The
permanent loss of the stream habitats for the revised option was totally
reduced 0.17 ha compare to the original option. The comparison of the original and
revised options is presented in Table 7.9.
Table 7.9 Overall
Habitat Loss due to the Drainage Improvement Works
|
Proposed |
Impacted Habitats |
Original
option (1) |
Revised
option (1) |
||
|
Surface Structures |
|
Permanent
loss |
Temporary
Loss (2) |
Permanent
loss |
Temporary
Loss (2) |
|
Intake
I-1 |
Stream/Channel |
15m (<0.01 ha) |
140m (0.15 ha) |
15m (<0.01 ha) |
140m (0.15 ha) |
|
|
|
0.13 ha |
0.22 ha |
0.13 ha |
0.22 ha |
|
|
Urbanized/
Disturbed Area |
Nil |
0.12 ha |
Nil |
0.12 ha |
|
Intake
I-2 |
Stream/Channel |
140m (0.07ha) |
110m (0.07ha) |
60 m (0.06ha) |
Additional 0.03 ha at the
same stream section |
|
|
Village-Orchard |
0.03 ha |
0.08 ha |
0.05 ha |
Nil |
|
|
Urbanized/
Disturbed Area |
0.01 ha |
0.11 ha |
0.03 ha |
Nil |
|
Intake
I-3 |
Stream/Channel |
180m (0.25ha) |
200m (0.23ha) |
75 m (0.02ha) |
Additional 0.11 ha at the
same stream section |
|
|
|
0.47 ha |
0.04 ha |
0.51 ha |
0.04 ha |
|
|
Village-Orchard |
0.09 ha |
0.33 ha |
0.10 ha |
Nil |
|
Outfall O-1 |
Intertidal
Habitat |
55 m (0.15 ha) |
65 m (0.02 ha) |
55 m (0.15 ha) |
65 m (0.02 ha) |
|
|
|
0.48 ha |
1.16 ha |
0.48 ha |
1.16 ha |
|
|
Urbanized/
Disturbed Area |
0.11 ha |
0.21 ha |
0.11 ha |
0.21 ha |
Note: (1)
The design of Intake I-1 and Outfall O-1 has no changes.
(2)
Areas excluded the permanent resumed land for the Project.
The previous discussion in Section 7.6.4 has indicated
that the impacts on ecological resources due to the construction and operation
of the proposed Project are generally expected not to be high. The following mitigation measures to further
minimise impacts and disturbance to the surrounding habitats, are recommended.
·
Install sheet piles or placing mass concrete beam/ block
and sealing the gap with cement (where applicable for the temporary stream diversion)
along the boundary of the works area within the stream habitats, in particular
Sam Dip Tam Stream and Tso Kung Tam Stream, before the commencement of works to
prevent construction runoff during construction. Provision of adequate designed sand/ silt
removal facilities such as sand traps, silt traps and sediment basin in the
areas which could potentially be affected may be required.
·
Construction
impacts to the water quality have largely been avoided during construction
through constraints on the works. Full
details of these constraints are presented in Section 5 - Water Quality Impact Assessment. The constraints were recommended in Section 5.7 to control water quality
impacts to within acceptable levels, are also expected to control impacts to
ecology.
·
Erect
fences along the boundary of the works area before the commencement of works to
prevent tipping, vehicle movements, and encroachment of personnel onto adjacent
areas, particularly the stream habitats.
·
Avoid any damage and disturbance, particularly
those caused by filling and illegal dumping, to the remaining and surrounding
natural stream habitats.
·
Regularly check the work site boundaries to
ensure that they are not breached and that no damage occurs to surrounding
areas.
·
Prohibit and prevent open fires within the site
boundary during construction and provide temporary fire fighting equipment in
the work areas.
·
Treat any damage that may have occurred to
individual major trees in the adjacent area with surgery.
·
Reinstate temporary work sites/disturbed areas,
particularly stream of natural bottom and bank, plantation, intertidal habitat,
and the areas located within the proposed Ecological Park, immediately after
completion of the construction works, ie through on-site tree/shrub planting
and reprovision of natural or semi-natural bottom (also refer to Section
7.7.3), in order to facilitate the recolonisation of the wildlife recorded
during the baseline surveys. Tree/shrub
species used should make reference from those in the surrounding area.
·
Provide
natural stream bed (approximately 0.03
ha) for the new Dry Weather Flow Channel (created from village-orchard)
by laying natural stones at Intake I-2 (Figure 7.7). The reinstated stream bed shall mimic the existing
natural conditions with certain portion of big boulders creating the lentic and
lotic zones for the aquatic fauna, and while it will be developed during
detailed design may draw on concepts shown in Figure 2.18.
·
Provide
natural stream bed (approximately 0.05
ha,) for the Approach Channel and Dry Weather Flow Channel by laying
natural stones at Intake I-3 (Figure 7.8). The reinstated stream bed shall mimic the
existing natural conditions (rocky
bottom with very limited aquatic plants) with certain portion of big
boulders creating the lentic and lotic zones for the aquatic fauna, and while
it will be developed during detailed design may draw on concepts shown in Figure 2.18.
·
Provide
natural bottom (ie retain the existing stream bed or reinstate the stream bed
by providing boulders/ rocks, riprap
or gabion) for the temporarily affected stream sections (Figure 7.8) wherever possible, in order
to allow natural colonisation of aquatic fauna.
·
Provide at least 2.2 ha of compensatory planting
on the permanent and temporary affected plantation areas, particularly the
slopes along access road and
adjacent to Intake I-3 and cascade at
Outfall O-1, after
construction to
stabilise the slope to present soil erosion and consequent stream
sedimentation. Among the 2.2 ha
compensatory planting, at least 0.5 ha of compensatory tree planting on the new
formed slope along the access road of the Intake I-3 and 0.5 ha of
compensatory tree planting over the cascade (by constructing
intermediate platform) at Outfall O-1 will be provided (location refer to Figures 7.4 – 7.6). Species used for
planting should take reference from the species identified in Appendix F and be native to
-
To compensate for the lost of
felled trees at Intake I-1, compensation trees are proposed along the toe of
new form slope and building structure for instant greenery effect and tree
seeding planting to restore the existing greenery within the works area (Figure 7.10). Trees to be compensated will be in 1:1.6
ratios with approximate planting area of 575 m2. Tree species
proposed for the compensation are mainly tree species found in this location
with this arrangement, all the compensatory trees will blend nicely with the
existing vegetation;
-
To compensate for the lost of
felled trees at Intake I-2, compensation trees are proposed along the toe of
new form slope and building structure for instant greenery effect and to
restore the existing greenery within the works area (Figure 7.11). Trees to be compensated will be in 1:5 ratios
with approximate planting area of 98 m2. Tree species
proposed for the compensation are mainly tree species found in this location
with this arrangement, all the compensatory trees will blend nicely with the
existing vegetation;
-
To compensate for the lost of
felled trees at Intake I-3, compensation trees are proposed along the toe of
new form slope and building structure for instant greenery effect and tree
seeding planting to restore the existing greenery within the works area (Figure 7.12). Trees to be compensated will be in 1:3.2
ratios with approximate planting area of 3,056 m2. Tree species
proposed for the compensation are mainly tree species found in this location
with this arrangement, all the compensatory trees will blend nicely with the
existing vegetation; and
-
To compensate for the lost of
felled trees at Outfall O-1, compensation trees are proposed along the toe of
new form slope and building structure for instant greenery effect and to
restore the existing greenery within the works area (Figure 7.13 Trees
to be compensated will be in 1:2.6 ratios with approximate planting area of 1,148 m2. Tree species proposed for the compensation
are mainly tree species found in this location with this arrangement, all the
compensatory trees will blend nicely with the existing vegetation.
·
Based on the preliminary design to date, the
estimated number of trees to be felled is 86, 16, 274 and 246 (including 89
trees in tree group) at Intakes I-1, I-2, I-3 and Outfall O-1 respectively. No
trees in the Register of Old and Valuable Trees will be affected. Depending on
the space allowed, one to three trees will be planted to compensate for one
felled tree. The proposed planting will be mainly native species such as Celtis sinensis, Cinnamomum camphora, Ficus
microcarpa, Schima superba etc.
but will also include a small number of non-native fast growing species such as
Acacia confusa and Acacia mangium to act as a nurse species
(as per CEDD (previously known as TDD) recommendations for best practice in
establishment of native woodlands).
·
Provide armour rocks for the affected intertidal
habitat in order to allow natural colonisation of intertidal organisms.
There will be the loss of approximately 150m (0.08 ha) of stream/channel,
1.12 ha of plantation, 0.15 ha of village-orchard, 55 m (0.15 ha) of intertidal
habitat (artificial/disturbed seashore) and 0.14 ha of disturbed/urbanized
areas. No adverse residual impact due to
the construction and operation of the channels is expected after the
implementation of the proposed mitigation measures including provision of 2.2
ha of compensatory planting (including 1 ha of tree planting), approximately 0.08 ha of natural
stream bottom (0.03 ha at Intake I-2 and 0.05 ha at Intake I-3) and
reinstatement of the intertidal habitat.
The implementation of the ecological mitigation measures
stated in Section 7.7 should be
checked as part of the environmental monitoring and audit procedures during the
construction period as presented in the separate Environmental Monitoring and Audit Manual. No other ecology-specific measures are
considered necessary.
In order to ensure the groundwater levels in the stream
courses and thus on the surrounding habitats will not be affected, the
groundwater levels along the tunnel will be measured throughout the
construction and maintenance period.
The ecological resources recorded within the Study Area
included woodland, plantation, grassland, village-orchard, stream channel,
intertidal habitat (artificial/disturbed seashore) and disturbed/urbanized, as
well as the associated wildlife. Of
these habitats, woodland and stream habitat (Sam Dip Tam Stream and Tso Kung
Tam Stream) have moderate ecological value. The remaining habitats are of low
to moderate ecological value. With the
exception of low to moderate impact to the middle course of Sam Dip Tam Stream
(location of Intake I-2) and Tso Kung Tam Stream (location of Intake I-3), the
direct ecological impact due to the construction and operation of the drainage
channel is expected to be low. No rare or protected species near the works
areas are affected by the proposed works.
The loss of stream sections of natural bottom and bank and hydrological
disruption to the natural stream habitats downstream to the intake structures,
particularly Intakes I-2 and I-3, have been minimised and properly mitigated.
No adverse residual impact is expected after the implementation of the
recommended mitigation measures. Since the
affected sections of Sam Dip Tam Stream and Tso Kung Tam Stream (location of
Intakes I-2 and I-3) are partially disturbed (with relatively less aquatic
faunal diversity) due to the residential sewage and the intake structures have
been appropriately designed to minimise habitat loss, the impacts due to the
land take for the surface structures and hydrological disruption are considered
acceptable. Adverse ecological impacts
on the proposed