CONTENTS
1.
Introduction.. 1
1.1
Project Background.. 1
2.
Project Description.. 2
2.1
Location and
Description of the Project 2
2.2
Need of the Project 3
2.3
Consideration of
Alternative Design Options. 3
2.4
Benefits of the
Project 3
2.5
Construction Methods
and Sequences of Works. 4
2.6
Construction Programme. 5
3.
Summary of
environmental Impact assessment.. 6
3.1
Introduction.. 6
3.2
Air Quality. 6
3.3
Noise. 6
3.4
Water Quality. 7
3.5
Waste Management 7
3.6
Ecology. 8
3.7
Landscape and Visual 9
3.8
Cultural Heritage. 10
4.
Environmental
Monitoring and Audit Requirement.. 12
5.
Conclusion.. 13
Figures
Figure 1.1 Location of Project Site and Its
Environs
Figure 2.1 General Layout of Design Option 1
1.
Introduction
1.1
Project Background
1.1.1
The Drainage Services Department
(DSD) completed the ¡§Stormwater Drainage Master Plan Study in Sai Kung, East
Kowloon and Southern Lantau¡¨ (DMP Study) in September 2000. The DMP Study
identified deficiencies and flooding problems in the existing drainage systems
in Sai Kung, East Kowloon and Southern Lantau. Drainage improvement works
(including improvement works at the three bends at Tai Tei Tong River,
construction of Luk Tei Tong Bypass Channel, bypass box culvert and floodwalls
for Pak Ngan Heung River and U-channel at Ling Tsui Tau) have been completed by
DSD Contract DC/2006/11 ¡V Drainage Improvement in South Lantau in 2010.
1.1.2
Despite the drainage
improvement in South Lantau completed in 2010, the Review of Drainage Master
Plan in Lantau and the Outlying Islands ¡V Feasibility Study (the DMP Review
Study) completed by DSD in 2018 revealed that the drainage provisions in some
areas in Mui Wo, including Tai Tei Tong, Luk Tei Tong, Nam Bin Wai, Ma Po
Tsuen, Ling Tsui Tau and Chung Hau (hereafter refer to ¡§the concerned area¡¨)
could not meet the current standard, taking cognisance of the topography,
existing drainage capacity and updated hydrological statistics. The inadequate
drainage are mainly caused by the under capacity of Tai Tei Tong River and the
adverse effect of tidal backwater affecting low topography areas adjacent to
the existing rivers. The flooding incident in Mui Wo recorded during the red
rainstorm warning in May 2015, typhoon Hato in August 2017 and typhoon Mangkhut
in September 2018 corroborated the above findings.
1.1.3
To relieve the flood
risk at Mui Wo, the DMP Review Study has proposed drainage improvement measures
in a combination of different approaches including diversion, pumping, drainage
upgrading and river reprofiling.
1.1.4
Binnies Hong Kong
Limited (Binnies) was commissioned by DSD to carry out an investigation of the
¡§Drainage Improvement Works in Mui Wo¡¨ (hereafter refer to ¡§the Project¡¨) in
July 2021 and propose design scheme for the above-mentioned drainage improvement
measures.
1.1.5
The proposed design
scheme should effectively mitigate the flood risk while land requirement for
project implementation has been kept minimal. Upon completion of the drainage
improvement measures, the flood protection standard in the areas concerned will
be upgraded to meet the requirements in the current DSD¡¦s Stormwater Drainage
Manual and the flood risks of the low-lying areas in Mui Wo thereon can be
significantly relieved.
1.1.6
An Environmental Impact
Assessment (EIA) Study Brief (ESB-334/2020) for the Project was issued by the
Environmental Protection Department (EPD) on 15 October 2020. The Project
is a designated project by virtue of Item C.12(a)(iii) of Schedule 2, Part I of
the EIAO, which specifies ¡§A dredging operation which is less than 500 m
boundary of an existing or planned bathing beach¡¨.
2.
Project Description
2.1
Location and Description of the Project
2.1.1
Location of the project
site and its environs of the preferred scheme are shown in Figure 1.1.
The Project comprises of drainage improvement works as well as enhancement
measures including river revitalization at Luk Tei Tong Bypass Channel and two
fish ladders at Tai Tei Tong River. The overall scope of the Project includes:
Tai Tei Tong
a)
Construction of flood walls (about 580m);
b)
Reconstruction of gabion walls (about 280m);
c)
River reprofiling
(about 1000m2);
d)
Modification of agricultural weir; and
e)
Construction of fish ladders and associated works (about 510m2).
Nam Bin Wai, Chung Hau, Ling Tsui Tau and Ma Po
Tsuen
a)
Construction of access across Pak Ngan Heung River (about 15m);
b)
Construction of stormwater pumping station and the associated drainage
works (about 1150m);
c)
Construction of diversion
box culvert from Tai Tei Tong River to Luk Tei Tong Bypass Channel (about
180m); and
d)
Construction of tidal gate at River Silver and other associated works.
Luk Tei Tong River (South) and Luk Tei Tong Bypass
Channel
a)
Reconstruction of gabion walls (about 290m);
b)
Construction of box culvert (about 10m);
c)
Construction of mechanical penstock; and
d)
River revitalisation and associated works.
2.2
Need of the Project
2.2.1
Although drainage
improvement works at Tai Tei Tong River was previously completed in 2010 under
DC/2006/11, the works was confined at three bottlenecks of the river and the
drainage capacity of Tai Tei Tong River remain inadequate.
2.2.3
Flooding incidents
recorded in Mui Wo during the red rainstorm warning in May 2015, typhoon Hato
in August 2017 and typhoon Mangkhut in September 2018 corroborated the
above findings in DMP Review Study.
2.2.4
Based on the above
consideration, this Project is necessary to be implemented so as to upgrade the
drainage provisions at Tai Tei Tong, Luk Tei Tong, Nam Bin Wai, Ma Po Tsuen,
Ling Tsui Tau and Chung Hau to meet the standards in the latest DSD¡¦s
Stormwater Drainage Manual and help safeguard the livelihood of existing and
future development along the river.
2.3
Consideration of
Alternative Design Options
2.3.1
Design options with
alternative locations of the proposed stormwater pumping station and tidal
gate, various alignments of the proposed stormwater drain and diversion box
culvert, as well as different extent of flood wall and gabion wall have been
critically considered and evaluated based on environmental factors, land
resumption practicability, and hydraulic performance. Whilst in general all the
design options could achieve similar hydraulic
performance, the preferred option (Design Option 1) has a shorter
diversion box culvert, a stormwater pumping station that is further away from
major residential area and the shortest construction time compare to other
design options, hence the duration and magnitude of the potential environmental
impact from Design Option 1 are anticipated to be the least compared to other
design options and is more preferable. The general layout of Design Option 1 is
shown in Figure 2.1.
2.4
Benefits of the Project
2.4.3
Enhancement measures such as river
revitalisation works will also be introduced along Luk Tei Tong Bypass Channel
which could improve and enhance the appearance of the rivers and surroundings.
Blue-green infrastructure concepts will be adopted in this Project, such as
planting and landscaping work along riverbanks to promote greening, enhance
biodiversity and beautify the surrounding environment. Leisure facilities will
also be provided appropriately along Luk Tei Tong Bypass Channel to improve the
amenity value.
2.4.4
Enhancement measures include provision of fish
ladders at mid-stream of Tai Tei Tong River and up-stream of Tai Tei Tong River
to relieve the level difference which hinders fish movement along the river.
Upon completion, fish movement along the river can be enhanced. The fish ladder will be designed
using natural bedding material with small ponds and waterfalls to mimic the
natural stream course and provide habitats for aquatic life.
2.4.6
In addition, the applicability of usage of
renewable energy (i.e. Solar Panel) for leisure facilities, street lighting,
flood control system and electrical and mechanical (E&M) system within the
stormwater pumping station will be adopted as far as practicable in order to
reduce the energy consumption and carbon emission during the operation phase of
the Project.
2.5
Construction Methods
and Sequences of Works
2.5.1
To minimise water
quality impact, river flow will be diverted to the far side of the works area.
Cofferdam and / or other means of temporary flow diversion will be undertaken
before any excavation / major works within the existing watercourses to ensure
the flow is not affected and to provide a dry working environment. In addition,
excavation of river sediment will be scheduled to carry out in dry seasons
(typically from November to March) as far as practicable. The same principal
will be adopted for construction of tidal gate and mechanical penstocks to
minimise the water quality impact during construction.
2.5.2
All excavated river
sediment will be reused on-site as backfill material. River sediment and / or
boulders excavated during river reprofiling works will be reused at Tai Tei
Tong River as natural bedding substrate and / or as backfilling material at
other works area. Such construction method could avoid the disposal of sediment
off-site.
2.5.3
Open-cut method will be
adopted for the construction of the diversion box culvert and stormwater
drainage while trenchless method will be adopted for the construction of the
section of stormwater drainage at the river crossing as appropriate.
2.5.4
Although precast flood
wall / pre-filled gabion wall could minimize the environmental impact as well
as shorten the construction period, as the works areas are closed to public
access which lifting and unloading of precast flood wall / gabion wall could
pose safety concern and nuisance to pedestrian nearby. As such, on-site
construction method for flood wall / gabion wall will be preferred.
2.5.5
On-site construction
will be preferred for the construction of the proposed stormwater pumping
station as it could allow more flexibility for on-site alteration of E&M
equipment and pumping system installation, hence reduce potential disturbance
to the environment and nearby sensitive receivers.
2.6
Construction Programme
2.6.1
The construction works
are expected to last for around 51 months. Subject to completion of statutory
procedures, the preliminary construction programme for the Project is
tentatively expected to commence in 3rd quarter of 2025 and complete
in 4th quarter of 2029.
3.
Summary of environmental Impact
assessment
3.1
Introduction
3.1.1
This Section summarises
the findings of the EIA associated with the construction and operation phases
of the Project.
3.2
Air Quality
3.2.1
Potential air quality
impact associated with the construction phases of the Project have been
assessed in accordance with the criteria and guidelines as stated in the
requirements given in Clause 3.4.4 of the EIA Study Brief, as well as Annexes 4
and 12 of EIAO-TM. The assessment area for air quality impact assessment is
within 500m from the Project boundary.
3.2.2
During construction
phase of the Project, potential air quality impact from fugitive dust may arise
from excavation works, stockpiling of excavated material and piling works.
Potential air quality impact may also arise from the gaseous emission due to
the use of Powered Mechanical Equipment (PME). However, adverse air
quality impact due to fugitive dust and gaseous emission from PME during the
construction phase is not expected with the implementation of recommended
mitigation measures.
3.2.3
During operation phase
of the Project, regular maintenance desilting and debris clearance will be
necessary. Adverse air quality impacts due to fugitive dust gaseous emission
from PMEs and odour impact arise from maintenance works are not anticipated
with the implementation of recommended mitigation measures.
3.2.4
Site inspections and
audits during construction phase of the Project to ensure proper implementation
of the mitigation measures are recommended. Air quality monitoring is considered
not necessary during the construction and operation phases of the Project.
3.3.1
Potential noise impact
associated with the construction and operation phases of the Project have been
assessed in accordance with the criteria and guidelines as stated in the
requirements given in Clause 3.4.5 of the EIA Study Brief, as well as Annexes 5
and 13 of EIAO-TM. The assessment area for noise impact assessment is within
300m from the Project boundary.
3.3.2
Owing to the close
proximity of some of the NSRs to the works area of the Project, mitigation
measures are required to be implemented to mitigate the construction noise
impact. Practicable mitigation measures, including good construction site
practices, use of quiet construction method / PME, temporary noise barriers /
noise enclosures, scheduling of PME / construction activities to avoid work
during sensitive time (e.g., school examination period) and reduce the
concurrent operation of PMEs are recommended. With the implementation of the
recommended mitigation measures, the mitigated construction noise levels at all
representative NSRs will comply with the daytime construction noise criteria
throughout the construction period. A Construction Noise Management Plan would
be prepared and submitted before commencement of construction works, so that
both the verification of the inventory of noise sources, and the assessment of
the effectiveness and practicality of all identified measures for mitigating
the construction noise impact of the Project would be performed during the
design, tendering and implementation stage of the construction works.
3.3.3
No adverse noise impact
is anticipated during operation phase after the implementation of the
recommended mitigation measures, and the proper design of the proposed
stormwater pumping station.
3.3.4
Noise monitoring is
recommended during the construction phase to ensure compliance with the noise
criterion at the NSRs. Regular site inspections and audits should be
conducted to ensure that the recommended mitigation measures are properly
implemented during the construction stage.
3.3.5
A commissioning test
should be conducted prior to the operation of the Project to ensure operation
noise levels would comply with the relevant noise standards.
3.4
Water Quality
3.4.1
Potential water quality
impact associated with the construction and operation phases of the Project has
been assessed in accordance with the criteria and guidelines as stated in the
requirements given in Clause 3.4.6 of the EIA Study Brief, as well as Annexes 6
and 14 of EIAO-TM. The assessment area for water quality impact assessment is
within 500m from the Project boundary.
3.4.2
Potential water quality
impact from construction surface runoff, wastewater and sediment release from
works into water bodies, sewage from workforce and construction works of
stormwater pumping station, outlet channel to River Silver and diversion box
culvert during the construction phase of the Project have been assessed. No
unacceptable water quality impact during the construction phase of the Project
is anticipated with the implementation of mitigation measures (in particular to
carry out excavation works for the Project in a confined and dry condition) and
good site management recommended.
3.4.3
Potential water quality
impact associated with maintenance works of the drainage channels and change in
flow regime during the operation phase of the Project has been assessed. No
unacceptable water quality impact from the operation phase of the Project is
anticipated.
3.4.4
Water quality
monitoring programme is recommended during construction phase to verify the
predictions of the assessment and ensure compliance with the assessment
criteria.
3.5
Waste Management
3.5.1
Potential waste
management implications arising from the construction and operational phases of
the Project have been assessed in accordance with the criteria and guidelines
as stated in the requirements given in Clause 3.4.7 of the EIA Study Brief, as
well as Annexes 7 and 15 of EIAO-TM.
3.5.2
Wastes generated by the
construction activities are likely to include construction and demolition
(C&D) materials from the construction works, general refuse from workforce
and chemical waste from any maintenance of construction plant and equipment
during construction phase. All excavated river sediment will be reused on-site
as backfilling material.
3.5.3
During the operation
phase of the Project, a small amount of desilted material and screened debris
will be generated from the routine maintenance works.
3.5.4
With the implementation
of good site practices, adverse environmental impact (potential air and odour
emissions, noise and wastewater discharge) arising from the management and
disposal of waste during the construction and operation phases of the Project
is not anticipated.
3.5.5
It is recommended that
regular site inspections of the waste management practices would be carried out
during the construction phase to assess whether wastes are being managed in
accordance with the recommended good site practices and Waste Management Plan
(WMP).
3.6
Ecology
3.6.1
Potential ecological
impact associated with the construction and operational phases of the Project
has been assessed in accordance with the criteria and guidelines as stated in
the requirements given in Clause 3.4.8 of the EIA Study Brief, as well as
Annexes 8 and 16 of EIAO-TM. The assessment area for ecological impact
assessment is within 500m from the Project boundary.
3.6.2
Ecological impact
assessment has been carried out based on literature reviews and the focused
field surveys of twelve months covering both wet and dry seasons completed in
2022. According to the Project alignment, the Project will cause potential
temporary and permanent habitat loss to marsh (~0.7ha; including ~0.5ha
temporary works area), semi-natural watercourse (~0.7km; including ~0.7km
temporary works area), channelised watercourses (~0.4km; including ~0.4km
temporary works area), agricultural land (~1.1ha; including ~0.8ha of temporary
works area) and village / developed area (~0.5ha; including ~0.5ha temporary
works area).
3.6.3
Majority of the
identified impact are considered to be low in the absence of mitigation
measures. However, the potential impact on direct loss (i.e.,
permanent, and temporary losses) of marsh, watercourses and agricultural
land, ecological impact on fauna species of conservation importance, and
ecological impact to watercourses due to river reprofiling, temporary stream
diversion and the associated change in water flow / level are considered as low
to moderate. Necessary mitigation measures and ecological monitoring programme
are proposed for the above potential impact.
3.6.4
It is predicted that
the impact will mainly arise during the construction phase, as no major
activities would be conducted during the operation phase. The routine
maintenance and the operation of the completed drainage channel and pumping
station would not cause any significant ecological impact. Good site practice
and mitigation measures are recommended to minimise potential impacts resulting
from operational phase activities.
3.6.5
With the implementation
of mitigation measures and precautionary measures, no adverse residual
ecological impacts from the Project within and in the vicinity of the works
area during construction and operation phases would be anticipated. Off-site
mitigation measures are therefore not considered necessary to mitigate the
residual impacts any further.
3.6.6
Updated ecological survey
shall be conducted by a qualified ecologist as part of the Environmental Team
(ET) with focus on the herpetofauna and freshwater community prior to
commencement of construction at the affected watercourse(s). Should species of
conservation importance be found within the surveyed watercourse sections, a
Translocation Plan should be prepared and the translocation work should be
conducted to move the individuals from the works area to suitable recipient
sites. As a precautionary measure, construction works for the proposed
stormwater drain near Mui Wo Municipal Services Building during night-time from
17:00 to 07:00 should be avoided to minimize potential disturbance to the
Ardeids. Clear signs should also be erected on site to alert all site staff and
workers about the precautionary measures.
3.7
Landscape and Visual
3.7.1
Potential landscape and
visual impact associated with the construction and operational phases of the
Project has been assessed in accordance with the criteria and guidelines as
stated in the requirements given in Clause 3.4.9 of the EIA Study Brief, as
well as Annexes 10 and 18 of EIAO-TM, and the EIAO Guidance Note No. 8/2010
¡§Preparation of Landscape and Visual Impact Assessment under the EIAO¡¨. The
assessment area for landscape and visual impact assessment is within 500m from
the Project boundary.
3.7.2
Landscape and visual
impact on Landscape Character Areas (LCAs), Landscape Resources (LRs) and
Visually Sensitive Receivers (VSRs) during the construction and operation
phases of the Project has been assessed.
3.7.3
Residual landscape
impact is slight on LCA3 (Rural Inland Plains of Mui Wo and Surrounding
Villages), LR5 (Agricultural Land) and LR9 (Semi Natural Water Course) during
construction and operation, and Insignificant on all other LRs and LCAs
with proper implementation of the recommended mitigation measures.
3.7.4
Residual visual impact
on VSRs is slight to insignificant during construction and
operation with proper implementation of the recommended mitigation measures.
3.7.5
Approximately 87 nos.
of trees will be affected and proposed to be felled by this Project. None
of them are Old and Valuable Trees. The main affected tree species
include Callistemon viminalis, Celtis sinensis, Melaleuca cajuputi subsp.
cumingiana and Terminalia
catappa. To
compensate for the trees loss, compensatory planting within the Project
boundary i.e. mainly along the Luk Tei Tong Bypass Channel is proposed.
3.7.6
During operation,
construction equipment will have been removed and earthworks have been
completed such that the landscape and visual impact during construction phase
will no longer exist. With sensitive architectural design of the structures,
tree planting and careful design of lighting, residual visual impact would
further reduce since operation commences. The new structures are expected to
blend into the surrounding environment, with denser vegetation after operation
at about 10 years. The residual impact on LCAs, LRs and VSRs will become slight
to insignificant after operation at about 10 years.
3.7.7
It is recommended that
regular site inspections and audits would be carried out during the
construction phase to ensure that the proposed mitigation measures and good
site practices proposed to manage and mitigate landscape and visual impact are
implemented. In addition, site audits should be undertaken bi-monthly for 12
months establishment period during the operation phase to check that the proposed
landscape and visual mitigation measures are properly implemented and
maintained as per their intended objectives.
3.7.8
In conclusion, the
Landscape and Visual Impacts of this Project, are considered acceptable with
mitigation measures adopted.
3.8
Cultural Heritage
3.8.1
Potential cultural
heritage impact associated with the construction and operation phases of the Project
has been assessed in accordance with the criteria and guidelines as stated in
the requirements given in Clause 3.4.10 of the EIA Study Brief, as well as
Annexes 10 and 19 of EIAO-TM. The assessment area for cultural heritage impact
assessment is within 300m from the Project boundary.
3.8.2
Chung Hau Sites of
Archaeological Interest (SAI) is found within the cultural heritage impact
assessment area (CHAA), at a distance of about 20m within the works area of the
Project. No excavation works of the project will exist in or adjacent to the
SAI, therefore no adverse archaeological impact due to the proposed development
is anticipated and thus, no mitigation measure is required.
3.8.3
No archaeological
potential area has been identified within the works area. No
archaeological impact is anticipated and thus no mitigation measures is
required.
3.8.4
As a precautionary
measure, the project proponent and contractors appointed by the project
proponent are required to inform Antiquities and Monuments Office (AMO)
immediately when any antiquities or supposed antiquities under the A&M
Ordinance (Cap. 53) are discovered during the course of works.
3.8.5
Desktop review
supplemented by built heritage survey identified no declared or proposed
monuments and Government historic sites identified by AMO in the CHAA. No
built heritage impact is anticipated and thus no mitigation measures is
required for these items.
3.8.6
Seven (7) graded
historic sites / buildings / structures identified in the CHAA are located over
70m from the Project boundary. Due to adequate separation distance between the
proposed works and graded historic sites / buildings / structures, no impact is
anticipated. However, special attention should be paid to avoid adverse
physical impact arising from the proposed works to them. Design proposal,
method of works and choice of machinery should be targeted to minimize adverse
impact to these graded historic sites / buildings / structures. Any vibration
and building movement induced from the proposed works should be strictly
monitored to ensure no disturbance and physical damages made to them during the
course of works. Monitoring proposal, including checkpoint locations,
installation details, response actions for each of the Alert / Alarm / Action
(3As) levels and frequency of monitoring should be submitted for AMO's
consideration.
3.8.7
Potential direct impact
to the built heritage items identified is not anticipated due to adequate
separation distance between the proposed works and the built heritage items
except for the two agricultural weirs (HB-22 and HB-76).
3.8.8
The two agricultural
weirs, HB- 22 and HB-76, are located within the works area of the river
reprofiling work at upstream of Tai Tei Tong River and the proposed fish ladder
at the midstream of Tai Tei Tong River. Modification of the agricultural weirs
and construction of fish ladder are proposed to achieve beneficial ecological
impact like improvement of the river hydraulic performance and fish movement.
The agricultural weirs (HB-22 and HB-76) are constructed with concrete and have
already undergone various modification and repair works. For instance, HB-22
was modified with wide steps at downstream in 1960s and a further modification
in 1970s; while HB-76 underwent significant modification in the early of 1990s,
only two concrete block and floor steps remained on site. Hence, their
cultural heritage significance is relatively low due to high level of modifications
underwent. Therefore, although the modification of the agricultural weir and
construction of fish ladder of this Project will bring direct impact to the
weirs, the impact would be acceptable with mitigation measures. It is
recommended that cartographic and photographic records be conducted to record
the weirs prior to commencement of modification works.
3.8.9
No adverse impact would
be anticipated on both built heritages and archaeology during the operation
phase of the Project.
4.
Environmental Monitoring and Audit
Requirement
4.1.1
Environmental
Monitoring and Audit (EM&A) requirements for air quality, noise, water
quality, waste management, ecological, landscape and visual impact as well as
cultural heritage have been recommended, with regular site inspection and
audits during construction phase to ensure that the recommended mitigation
measures are properly implemented. The EM&A requirements are
specified and detailed in the EM&A Manual.
5.
Conclusion
5.1.1
The environmental
impact assessment has concluded that with the implementation of the recommended
mitigation measures, the Project would comply with the requirements of the EIA
Study Brief and EIAO-TM, and would not give rise to unacceptable environmental
impacts during both the construction and operation phase.