12.1.1
The “Drainage Improvement in
12.1.2
The proposed drainage
improvement works are regarded as a Designated Project (DP) under the Environmental
Impact Assessment Ordinance (EIAO) and are assessed in this EIA Report. The major
findings of the EIA are summarized below.
12.2
Location and
Description of the Project
12.2.1
The Project comprises the construction of drainage channels
and associated works to improve the secondary and local drainage systems in the
Man Uk Pin, Loi Tung (MUP03, MUP04A, MUP04B & MUP05) and Lin Ma Hang (LMH01)
areas. The scale of the Project is
shown below.
Scale of Proposed Drainage Works
|
Channel |
Proposed Works |
Extent of Works |
||
|
Approximate Length |
Approximate Width |
Approximate Depth |
||
|
MUP03 |
U-channel (Diameter = 0.6m) |
150m |
- |
- |
|
Drainage pipe (Diameter = 0.6m) |
12m |
- |
- |
|
|
Box culvert connecting MUP05 |
28m |
3m |
1m |
|
|
Trapezoidal channel with gabion walls and mattress
lining |
93m |
Top = 2.4m – 2.7m |
1.2m – 1.5m |
|
|
Re-provision of crossings |
One footbridge |
|||
|
MUP04A |
Trapezoidal channel with gabion walls and mattress
lining |
163m |
Top = 6.3m |
1.75m |
|
Drainage pipes (Diameter
= 1.95m) |
21m |
- |
- |
|
|
Re-provision of crossings |
Two vehicular bridges |
|||
|
MUP04B |
U-channel (Diameter = 0.9m) |
58m |
- |
- |
|
Drainage pipes (Diameter = 1.35m) |
138m |
- |
- |
|
|
MUP05 |
Trapezoidal channel with gabion walls and mattress
lining |
287m |
2m – 3m |
2m – 2.8m |
|
Trapezoidal channel with gabion walls and mattress
lining |
54m |
Top = 15.4m |
2.5m |
|
|
Two-stage channel with existing natural river bed
retained |
554m |
Top = 15.4m |
2.5m |
|
|
Trapezoidal channel with gabion walls and mattress
lining |
69m |
Top = 20.3m |
2.2m |
|
|
Box culvert |
50m |
3m |
2m |
|
|
Re-provision of crossings |
Five footbridges, four
vehicular bridges |
|||
|
LMH01 |
Gabion channel and localised bank improvement |
190m |
5m |
1.5m |
|
Re-provision of crossings |
Three vehicular bridges |
|||
Notes:
Other ancillary works include provision of inlet/outlet
pipes, maintenance ramps & accesses and final landscaping works.
12.3.1
The proposed alignment generally follows the alignment of
existing watercourses which is in line with the DMP Study to minimize resumption
of private land.
12.3.2 The concept of ‘avoidance’ has been incorporated into the design to protect ecologically important streams such as Lin Ma Hang and Loi Tung. Two-stage channel design with natural river banks and beds retained has been proposed for ecological significant sections of the watercourses. Other environmental friendly design includes the use of gabion banks and mattress lining which will encourage accumulation of sediments and eventually re-colonisation of the channel bed by benthic community.
12.4
Justifications
and Benefits of the Project
12.4.1
The DMP Study investigated the need to improve secondary and
local drainage systems to alleviate flooding in the study area. The proposed
Project is expected to contribute to the relief of the present drainage
problems that have repeatedly led to severe flooding in the study area
resulting in danger to life, economic loss and disruption to everyday life.
12.4.2
The current standard of protection of the watercourses is
very low, with the majority having a standard of protection of 1 year or less.
These watercourses were highlighted in the DMP Study as having insufficient
channel capacity leading to localized flooding. Upon completion of the Project,
the standard of protection will be increase to 1 in 10 years for village development.
12.4.3
The overall population directly benefited by the proposed
drainage improvement will be about 780 located in the Man Uk Pin and Lin Ma
Hang areas of
12.5.1
Construction
activities for the Project involve site clearance in the works areas;
excavation to formation levels of the channel; construction of channel
structures and linings; and restoration landscaping works. Small scale
routine maintenance would be necessary during the operation of the proposed
gabion channels to remove excessive silts, vegetation, debris and obstructions
in order to maintain its hydraulic performance and structural integrity. These activities have the potential to impact on the existing environment.
12.5.2
The key
environmental issues assessed in the EIA Report are:
·
Air
Quality;
·
Construction
Noise;
·
Water
Quality;
·
Waste
Management;
·
Ecology;
·
Landscape
and Visual; and
·
Cultural
Heritage.
12.5.3
Mitigation
measures have been recommended in the EIA Report to mitigate potential adverse
impacts from the construction and operation of the Project. Based on these
recommendations, Environmental Monitoring and Audit (EM&A) requirements
have been established.
12.6.1
The construction dust impact
assessment has identified Air Sensitive Receiver (
12.7
Construction
Noise Impact
12.7.1
The
use of powered mechanical equipment during the construction phase of this
drainage project is expected to create noise nuisance, due to the close
proximity between the works areas and noise sensitive receivers. Assessment
indicates that such noise impacts can be mitigated to acceptable levels by
appropriate measures, including the use of quiet plant, temporary noise
barriers, restricting concurrent usage of equipment and the implementation of
good site practices. The Contractor will be required to implement these
measures when powered mechanical equipment is used during the construction
phase. With these measures in place, residual
noise impact would not be expected from the construction works and will comply
with the EIAO-TM daytime construction noise standard of 75 dB(A).
12.7.2
Noise
monitoring is recommended at selected representative NSRs during the
construction period to check for compliance with permissible noise levels and
effectiveness of the proposed mitigation measures.
12.7.3
The
operation phase of the Project is not expected to pose any noise impact to the
surrounding area.
12.8.1 The current condition of the water bodies in the Study Area is relatively poor in the lower stretches with many of the streams receiving a variety of polluting inputs including livestock waste, and domestic wastewater from local villages.
12.8.2 The construction of the channels could adversely impact the water bodies through silt-laden site runoff, disturbance of stream sediment during excavation, concreting works, runoff from workshops & depot and increased sewage and wastewater resulting from the additional workforce on site. These impacts can be readily mitigated through the construction of a suitable drainage system with silt traps, good site management practices, careful working practices during excavation of the stream and proper sewage collection and disposal system. With the implementation of these measures, no adverse residual water quality impact from construction work is expected.
12.8.3
The major operational impacts
are a net increase in pollutant loadings to
12.8.4 Overall, the residual water quality impacts during construction and operation phases of the Project are considered acceptable with respect to the EIAO-TM and Water Pollution Control Ordinance.
12.9.1 Construction and demolition materials will inevitably be produced during the construction phase of the Project. Waste generated during construction works includes site clearance / demolition materials, excavated materials, chemical waste and general works waste. Waste types, quantities and timing have been estimated as far as possible and mitigation measures have been proposed in terms of avoidance-minimisation-reuse-recycling-disposal hierarchy.
12.9.2 Potential for reuse of inert construction & demolition material (public fill) within the Project will be rigorously explored in an effort to minimise off-site disposal.
12.9.3 Provided that there is strict control of construction and demolition materials generated from construction works and that all arisings are stored, handled, transported and disposed of in accordance with the recommended mitigation measures, potential impact is not expected.
12.9.4 The recommended waste management measures can be enforced by incorporating them into an environmental management plan as part of the contract document. Environmental audit would be necessary to ensure the implementation of proper waste management practices during construction.
12.9.5 Waste generated during operational maintenance is expected to be minimal. Proper waste management practices similar to those for construction impacts have been recommended.
12.9.6 Overall, the residual waste impacts of the Project are considered acceptable with respect to the EIAO-TM and Waste Disposal Ordinance.
12.10.1
The proposed works at MUP03 and MUP04B would have no
significant ecological impacts even in the absence of mitigation measures.
12.10.2
Proposed works at LMH01 were predicted to have minor
construction phase impacts on fauna of conservation importance in the absence
of mitigation. However, these can be fully mitigated by restricting works to
the dry season and implementation of site management measures. With these
measures in place potential impacts are considered to be very small and
acceptable.
12.10.3
Proposed works at MUP04A were predicted to have low to
moderate permanent adverse impacts on a stream and adjacent area of
long-inactive agricultural land. However, all impacts will now be avoided by
not channelising the upper section of this stream.
12.10.4
Proposed works at MUP05 were predicted to have moderate and
adverse impacts on a natural streamcourse with natural bed, banks and riparian
corridor. Substantial design changes in terms of ‘two-stage’ channel with
natural stream banks and bed retained which are in accordance with the advice
contained in ETWB & DSD Technical Circulars and DSD Practice Notes have
been adopted. These environmental
friendly channel designs along with site management measures and tree planting
will significantly reduce the predicted impacts to an acceptable level.
12.10.5
With these avoidance, minimization and mitigation measures in
place, all adverse ecological impacts of the project on MUP05 would be
eliminated or reduced to low and acceptable level. Low adverse impacts on
riparian vegetation are unavoidable but would be fully mitigated in time as a
result of planting and recolonisation by herbaceous vegetation, and are
considered acceptable in the overall context of the project.
12.10.6 Overall, the residual ecological impacts of the Project are considered acceptable with respect to the EIAO-TM.
12.11
Landscape and
Visual Impact
Landscape Impact
12.11.1 The landscape impacts on the landscape resources and character of MUP03, MUP04A, MUP04B and MUP05 are predicted to range from negligible to moderate to significant adverse, mainly due to the loss of the existing trees lining the road and channel sides. Trees have been preserved or transplanted as far as practicable. The retention of at least one natural riverbank side and the existing riverbed in MUP05 and minimizing the works at MUP04A have reduced the landscape impact largely. The incorporation of landscape mitigation measures through retention of natural riverbed and banks, tree planting alongside channels, the planting of embankment and toe zone plant mixes would lessen the landscape impacts to negligible to slight.
12.11.2
The landscape impacts on the landscape resources and
character of LMH01 are predicted to range from slight to negligible adverse.
The incorporation of landscape mitigation measures through planting of
embankment plant mixes would lessen the landscape impact to negligible overall.
Demolishing and reconstruction of vehicular crossing is expected to have a
slight positive impact on Residential Rural Fringe through the improved access.
Visual Impact
12.11.3 The unmitigated visual impact of the Project on VSRs at MUP05 is predicted to be significant adverse, due to the loss of the roadside and drainage channel trees and surrounding vegetation and the partial widening of the existing channel, in close proximity to the residential amenities such as a recreational park. However, in the other areas of MUP05, MUP04A, MUP04B and MUP03 the unmitigated visual impacts are negligible or slight.
12.11.4 The unmitigated visual impact of the Project on VSRs at LMH01 is predicted to be negligible and slight adverse. The improvement of riverbanks might result in slight adverse impacts when unmitigated. The demolishing and reconstruction of vehicular crossings may have beneficial visual impacts as the newly constructed crossings are expected to be more visually acceptable.
12.11.5 It is predicted that, through the incorporation of the proposed mitigation measures, adverse visual impacts can be further reduced to negligible to slight in most cases. For MUP05, sufficient screen tree planting alongside the channel and embankment planting are expected to reduce the visual impacts after mitigation to slight adverse impacts.
12.11.6 Overall, the residual landscape and visual impacts of the Project are considered acceptable with respect to the EIAO-TM.
12.12
Cultural Heritage
Impact
12.12.1
The
proposed drainage works will have no adverse impact on archaeological resources
in either the construction or operational phases. The majority of built heritage features
recorded in the survey will also not be adversely impacted. Potential impacts to
a stone terrace wall were identified only for the construction phase of the
project in the Lin Ma Hang Study Area and appropriate mitigation measures have
been proposed to negate the identified impacts. No operational phase impact on
the built heritage features is expected.
12.12.2
The
residual cultural heritage impact is considered acceptable with respect to the
EIAO-TM.
12.13
Environmental
Monitoring and Audit
12.13.1
Mitigation
measures have been recommended in the EIA Report to mitigate potential adverse
impacts from the construction and operation of the Project. Based on these
recommendations, EM&A requirements have been established.
12.13.2
An EM&A programme will be set up and implemented to
ensure compliance with the mitigation measures recommended in the EIA Report,
to assess the effectiveness of the recommended mitigation measures, and to
identify any further need for additional mitigation measures or remedial
measures.
12.13.3
To ensure that the environmental performance of the works
meet all relevant legal and contractual requirements, the Contractor will be
required to prepare and implement an Environmental Management Plan, which
details the approach the Contractor is to adopt in managing and controlling
potential environmental impact from construction activities for this Project.
12.14.1
Based on the findings of the EIA Study, the Project would not
cause any adverse environmental impacts to the concerned Conservation Area (for
MUP03, MUP04A, MUP04B and MUP05) and the planned SSSI i.e. Lin Ma Hang stream
(for LMH01). The residual construction phase and operational phase impacts are
considered acceptable with respect to EIAO-TM and relevant ordinance
requirements.
12.14.2
Overall this EIA concludes that
there are no unacceptable environmental impacts associated with the construction
and operation of the proposed secondary channels (MUP03, MUP04A, MUP04B, MUP05
and LMH01) provided that all the legislation, guidelines and recommended mitigation
measures are followed. The EIA has fully met the requirements of the Technical
Memorandum on EIA Process and the EIA Study Brief.
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