11.1
Justification and
Benefits of the Project
11.1.1
The current flood protection standard
of Hang Hau Tsuen stream is very low. Upon completion of the Project, the
standard of flood protection will be increase to 1 in 50 years.
11.1.2
The Project is expected to contribute to the relief of the
present drainage problems that have repeatedly led to severe flooding in Hang
Hau Tsuen at Lau Fau Shan,
11.2
Population and
Environmental Sensitive Areas Protected
11.2.1
The Hang Hau Tsuen stream currently receives domestic and
industrial wastewater from Hang Hau Tsuen and upstream sources. The water
quality of the stream is very poor. Ecological survey reveals very little
aquatic fauna especially at the heavily modified upstream section. The stream
habitat is considered to have a low ecological value. However, site surveys
reveal that the downstream portion of the stream which is affected by the tidal
action of
11.2.2
Based on the ecological
assessment, the channelization of the downstream portion will cause moderate
ecological impacts due to the removal of the mangrove colony. However, to
maintain the required flood conveyance of the channel, total avoidance of the
mangroves would not be possible. Based on such findings, the channel design is
revised such that the downstream section will not be fully channelised in order
to preserve parts of the mangrove colony and natural stream bed. The upstream
portion which has been heavily modified will be constructed to a drainage
channel. With the minimization approach, only a small portion of the mangroves
(about 0.07 ha) will need to be removed for the proposed channel works.
11.2.3
The intertidal mudflats that can be found along the
11.2.4
A number of large trees in the Project area will be preserved
in-situ by adjusting the channel design.
11.2.5
By following the existing stream alignment, resumption of village
houses has been minimized hence reducing disturbance to the public due to land
resumption.
11.2.6
By retaining the existing stream bed as well as reusing some
of the excavated materials as channel bed material, the amount of sediment requiring
disposal to marine disposal sites can be minimized, thereby reducing the burden
on the disposal sites.
11.2.7
The current footbridges are in poor condition and will be
re-provided with properly designed crossings to ensure safety to the villagers.
11.2.8
Ultimately, the villagers of Hang Hau Tsuen at Lau Fau Shan in
11.3
Environmental Friendly
Designs Recommended
11.3.1
The principle of the channel design is to avoid environmental
impacts while at the same time to provide adequate flow capacity to achieve the
design flood protection standard, to consider public safety at low lying areas,
to take into account land constraints, to minimize public disturbance from land
resumption, cost effectiveness and ease of maintenance. Views and comments from
the Green Groups, Rural Committees, District Council members and oyster farmer
association obtained during public consultation have also been taken into
consideration in the design. Reference has also been made to the ETWB and DSD
technical circulars on protection of natural streams/rivers as far as
practicable.
11.3.2
When considering environmental impacts, minimization will be the
key design principle only when avoidance is not possible. The following
environmental friendly channel designs have been incorporated into the channel
design.
·
The downstream section of the stream will be preserved in-situ with natural stream bed and
substrates retained and re-provided as far as practicable.
·
Original stream bed materials will be reinstated in parts of
the upstream section of the channel instead of using concrete lining to allow
natural re-establishment of vegetation.
·
Grasscrete channel lining will be used instead of concrete
lining for the maintenance access section within the channel to allow some
vegetation to established thereby enhancing the landscape quality and visual
appearance as well as to provide some ecological value to the proposed channel.
·
Sediment will be allowed to accumulate in the channel to
permit re-colonisation of aquatic organisms.
·
Several large trees will be preserved in-situ by modification
of the channel layout and design.
·
The established mangrove stands near the downstream and
outfall of the stream have been avoided and preserved as far as practicable by
avoiding excavating the stream bed and mudflats at the locations where
mangroves are present, thus preserving the fragile stream habitat in the
Project area.
·
A viewing point and carpark will be provided near the outfall
of the channel for public to enjoy the scenery of
·
The viewing point will be designed to allow the public to
enjoy the scenery of
·
A small carpark will be provided to facilitate visitors’ use.
Traffic management measures will be used to restrict vehicles over 7 m long from
using the access road and carpark with the exception of essential maintenance
vehicles and emergency vehicles thereby minimizing traffic-related environmental
impacts to the nearby villagers.
·
Compensatory landscape tree planting and shrub planting have
been recommended to mitigate for the loss of trees and vegetation to improve
the landscape quality and visual appearance of the proposed channel.
·
About 0.08 ha of mangroves will be retained by avoiding
channelization work at the downstream section. Compensation planting of about
0.07 ha of mangroves will be provided for the unavoidable loss of mangroves due
to the works. Monitoring will be carried out during operational phase to ensure
the survival and growth of the compensatory mangrove planting.
11.4
Key Environmental
Problems Avoided
11.4.1
The key environmental problems involve noise, water quality,
ecological and landscape & visual impacts during the construction phase. Minor
impacts from dust and waste are expected. The provision of the access road,
viewing point and carpark is not expected to give rise to adverse environmental
impact during the operational phase as only a small numbers of vehicles and
visitors is expected.
11.4.2
The EIA study has critically
assessed the overall acceptability of environmental impacts which are likely to
arise as a result of the construction and operation of the Project. Where
necessary and practicable, the EIA study has specified the conditions and
requirements for the detailed design, construction and operation of the Project
in order to mitigate environmental impacts to an acceptable level.
11.4.3
In order to avoid or minimize
the environmental impacts of the Project, a number of mitigation measures have
been recommended in the EIA Report. The key environmental measures and problems
avoided are highlighted below.
·
The proposed maintenance access road will be open for public
use. Traffic management measure will be implemented to restrict vehicles longer
than 7 m from using the road, thereby minimizing traffic-related environmental
impacts to the nearby sensitive receivers.
·
The channel will be improved to a higher flood protection
standard thereby reducing flooding risks to the villagers.
·
With the implementation of dust
suppression measures during the construction phase, the dust emission from the
construction works will be reduced to acceptable level. No adverse construction
dust impact on the nearby air sensitive receivers is expected.
·
With the implementation of quiet plant, temporary noise
barriers and good site practices, construction noise from construction
activities will be reduced to acceptable level. No
adverse construction noise impact on the nearby noise sensitive receivers is
expected.
·
Properly designed site drainage
measures and good site working practices such as containment structures during
excavation of the channel will be implemented to ensure no adverse water
quality impact to
·
During construction, surplus excavated materials will be
reused on-site to minimize the amount of off-site disposal to public filling
facilities.
·
About 0.07 ha of mangroves will
be planted to compensate for the loss of mangroves during construction of the
channel.
·
Compensatory tree planting and
landscaping works will be provided to restore the loss of greenery and to
enhance the overall landscape quality.
·
A comprehensive EM&A
programme will be setup to ensure effective implementation of mitigation
measures recommended in the EIA Report, to assess the effectiveness of the mitigation
measures, and to identify any further need for additional measures or remedial
actions.
11.4.4
The EIA study has demonstrated
the acceptability of any residual impacts from the Project and the protection
of the existing Hang Hau Tsuen stream, adjacent residents, nearby fishponds,
Coastal Protection Area, mangrove colony, intertidal mudflats and other
environmentally sensitive resources. Environmental monitoring and audit works
have been recommended before and during construction to verify the expectations
of the EIA study and the effectiveness of the recommended mitigation measures.
11.5
Compensation
Areas Included
11.5.1
Compensatory planting of about 0.7 ha of mangroves will be
provided within the mangrove zone to mitigate for the loss of mangroves during
construction. Trees affected by the Project will be mitigated by planting heavy
standard native trees within the Project area. No compensation area outside of
the site boundary will be required for this Project.
11.6
Environmental
Benefits of Environmental Protection Measures Recommended
11.6.1
The environmental benefits of implementing the recommended
mitigation measures during construction and operation phases of the Project can
be summarized as follows:
·
The air, noise, water quality and visual impacts at the
sensitive receivers will all be minimized or mitigated to within the acceptable
criteria and standards.
·
The amount of construction and demolition materials requiring
off-site disposal will be minimized through reduction, reuse and/or recycling.
·
The landscape impact from the loss of tress and vegetation
will be mitigated through compensatory tree planting, amenity planting and
mangrove planting.
·
By retaining and recreating natural stream bed sections
within the channel as well as preserving and compensating the affected
mangroves at the downstream portion, impact on the stream habitat will be
minimized.
11.6.2
With the implementation of the recommended mitigation
measures, no unacceptable residual environmental impacts are expected. Details
of the implementation schedule of the recommended mitigation measures are
summarized in Appendix 11.