3.1.1.1
As
discussed in Section 2.3, the
primary objective of the pedestrian system is to resolve the prevailing
congestion issues that have been affecting the local communities and improve
the connectivity between the south of Yuen Long Town and West Rail Long Ping
Station. According to study findings, the existing junctions at Yuen Long On
Ning Road, Castle Peak Road – Yuen Long Section and Kau Yuk Road demand
immediate attention.
3.1.1.2
Several
approaches have been duly considered to address the prevailing congestion issues.
The first approach is using an at-grade arrangement by widening the footpath
along nullah. However, given the nature of the existing congestion issues
at street level, additional/improvement of pedestrian
crossings may result in further traffic delay and congestion. It cannot alter
the pedestrian characteristic and serve the purpose of abating the congestion issues and addressing the
connectivity issues. Furthermore the widening works would cause severe
hydraulic impacts, hence at-grade arrangement is therefore not further
considered.
3.1.1.3
The
second approach is a partially at-grade arrangement in which three individual
footbridge acting as pedestrian crossing facilities will be provided at the
junctions of Yuen Long On Ning Road, Castle Peak Road – Yuen Long Section and
Kau Yuk Road only. The advantage of this approach is that it can limit the need
for footbridge structure to those across the junctions at Yuen Long On Ning
Road, Castle Peak Road – Yuen Long Section and Kau Yuk Road and result in less
visual impact to the VSRs. However, this
approach cannot provide a convenient direct linkage for the pedestrians. The pedestrians would be required to
either use escalators or lifts to reach the footbridge from ground level, across
those critical junctions, and then take escalators or lifts to return to the
ground level. Obviously, this would cause lot of inconvenience to the
pedestrians, especially for those who want to use the pedestrian system to
reach or leave the West Rail Long Ping Station swiftly, and would definitely
compromise the attractiveness of the pedestrian system. Therefore, this
partially at-grade arrangement still would not be able to totally resolve the
prevailing congestion issues and connectivity issues in an effective manner.
3.1.1.4
Since
both at-grade and partially at-grade arrangements would not be able to resolve
the prevailing congestion issues and connectivity issues, footbridge
option would be the only feasible arrangement. Provision
of a continuous footbridge would provide a convenient and comfortable access to
the West Rail Long Ping Station and across busy roads within Yuen Long Town
with barrier-free facilities. It is conducive in altering the characteristic of
the pedestrians. The pedestrians can bypass the existing heavily utilised
pedestrian crossings and footpaths. As compared to the at-grade/partially at-grade arrangement, the footbridge
option can resolve the prevailing congestion issues at Yuen Long Town and at
the same time allow swift accessibility to West Rail Long Ping Station,
although the footbridge option may result in substantial visual impacts and
higher landscape impacts that require mitigation measures. Hence, the footbridge
option has been taken forward to develop alignment options for further
evaluation.
3.1.1.5
Referring to Section 2.1, the proposed elevated pedestrian corridor connects West
Rail Long Ping Station to the south of Kau Yuk Road along Yuen Long Town Nullah.
It will run across and above Yuen Long On Ning Road, Castle Peak Road – Yuen
Long Section and Kau Yuk Road and has a total length of approximately 540m (see
Figure 2.1). Given that there is a LRT line running along
the Castle Peak Road – Yuen Long Section, the soffit of the elevated pedestrian
corridor would be approximately 6.2m tall to comply with the relevant safety
requirements for both construction and operational phases.
3.2.1.1
The
proposed elevated pedestrian corridor is located in the vicinity of the Yuen
Long Town Nullah, which is a concrete paved modified water channel constructed
in the early 60s. Yuen Long Creek is located upstream of the Yuen Long Town
Nullah. The flow from the upstream area (i.e. Tai Tong) and the Yuen Long Town
Centre would pass along the nullah and then discharged to the downstream Shan
Rui River and subsequently to the Deep Bay.
3.2.1.2
The area
surrounding this section of the nullah is a highly urbanized town centre. There
are numbers of medium-rise and high-rise residential premises (e.g. Yen Tsui
Gardens, Healey Building, Ho Shun Fuk Building), schools (e.g. CCC Chun Kwong
Primary School), recreational facilities (e.g. football pitch, Chung Sing Path
Playground) and a village (i.e. Tai Kiu Tsuen) on both sides of the nullah.
3.2.1.3
According
to the latest information, there are about 80 trees scattered along the
footpaths along both sides of the nullah. All of these trees are common species
and none of them are Registered Old and Valuable Tree (OVT), “Important Tree”
or stonewall tree (see Chapter 10 for more information on trees). Besides, the
footpaths have accommodated many essential utilities, including drainage pipes,
water mains, telecom cables.
3.2.1.4
Other
than those existing buildings, there is a planned development in Tai Kiu Tsuen
near Long Ping Station. The planning permission of CDA development at Tai Kiu
Tsuen (A/YL/136) was approved in August 2010 and the extension of valid period
of the permission (A/YL/136-1) was subsequently approved in August 2014. The CDA
development will have a total floor area of 76874m2 and unit of 827
units. The development schedule however is not available at the time of
preparation of this report. The location of the CDA development at Tai Kiu
Tsuen is shown in
Figure 2.1.
3.3
Selection of Preferred Alignment Option
3.3.1
Potential Alignments Options
3.3.1.1
In order to enhance the pedestrian
connectivity of the Project, the northern end of the footbridge will be
connected to the West Rail Long Ping Station at the reserved corbel of Long
Ping Station’s Exit D, which is located at the eastern side of the nullah. Hence,
the first footbridge section of about 100 to 110m started from the West Rail
Long Ping Station will be maintained along the eastern side of the nullah to
enable future connection to the Tai Kiu CDA development.
3.3.1.2
From this end of this initial section, a
total of three Alignment Options of the footbridge have been developed and
evaluated by considering various environmental and engineering considerations. These
three alignment options are described in the subsequent sections.
Alignment Option 1 -
Footbridge along eastern side of the nullah
3.3.1.3
As mentioned in Section 3.3.1.1 and Section
3.3.1.2, the initial 100-110m of the footbridge connecting the West Rail
Long Ping Station would run along the eastern side of the nullah. For this
option, the remaining alignment will be kept along the eastern side of the nullah
running across Yuen Long On Ning Road, Castle Peak road – Yuen Long Section and
Kau Yuk Road.
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_V6_Clear_files/image006.jpg)
Alignment Option 1 - Footbridge along eastern side of the nullah
Alignment Option 2 - Footbridge along western side of the
nullah
3.3.1.4
Similar to the Alignment Option 1, the
initial 100-110m of the footbridge connecting the West Rail Long Ping Station
would run along the eastern side of the nullah. For this option, the remaining alignment
will be adjusted to align the western side of the nullah, also running across Yuen
Long On Ning Road, Castle Peak road – Yuen Long Section and Kau Yuk Road.
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Alignment Option 2 - Footbridge along western side of the nullah
Alignment Option 3 - Footbridge along middle of the
nullah
3.3.1.5
Similar to the Alignment Option 1, the
initial 100-110m of the footbridge connecting the West Rail Long Ping Station
would run along the eastern side of the nullah. For this option, the remaining alignment
will be adjusted along the middle of nullah, also running across Yuen Long On
Ning Road, Castle Peak road – Yuen Long Section and Kau Yuk Road.
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Alignment Option 3 - Footbridge along middle of the nullah
3.3.2
Environmental Considerations
for the Alignment Options
3.3.2.1
The environmental considerations for the Alignment
Options are presented in Table 3.1
below.
Table 3.1 Summary of the considerations for the Alignment Options
|
Options |
Environmental Benefits |
Environmental Disbenefits |
|
Alignment Option
1 |
Air
Quality & Noise · Majority
of the construction works will be conducted along the eastern side of the
nullah. The construction activities will therefore be located away (i.e.
about 35m) from the sensitive receivers along the western side (e.g. Shung
Tak Building, Yuen Tung Building and Fung Yue Building, etc.), hence less
impacts. Water · Six
pedestrian interchanges would be required. However, no intermediate footbridge
column will be located within the nullah. Therefore, less water quality and hydraulic
impact on the nullah is anticipated due to less structure and construction
activities within the nullah. Visual · The
alignment would pose lower visual obstruction to leisure space users and
travellers viewing north and south along Yuen Long Nullah which is a major
visual corridor and an important visual resource in Yuen Long Town. |
Air
Quality & Noise · Majority
of the construction works will be conducted along the eastern side of the
nullah. The construction activities will therefore be located close to (i.e. less
than 5m for the nearest receivers) the sensitive receivers along the eastern
side (e.g. Fook On Building, Siu Fung Building and CCC Chun Kwong Primary
School, etc.), and would have higher impacts on them. Landscape · As
the construction works and the footbridge alignment is located along the
eastern side of the nullah, more number of trees (i.e. about 63 trees) along
the eastern side of nullah will be affected by the Project and needed to be
felled. Visual · The
footbridge is closer to the residential sensitive receivers along the eastern
side of the nullah. Most of their side windows will have direct view towards
the proposed footbridge and it would pose higher visual impacts on them. (Refer
to Typical Cross Section Showing 3
Alignment Options at Pedestrian Interchange) |
|
Alignment Option
2 |
Air
Quality & Noise · Majority
of the construction works will be conducted along the western side of the
nullah. The construction activities will therefore be located away (i.e.
about 35m) from the sensitive receivers along the eastern side (e.g. Fook On
Building, Siu Fung Building and CCC Chun Kwong Primary School, etc.), hence
less impacts. Water · Six
pedestrian interchanges would be required. However, no intermediate footbridge
column will be located within the nullah. Therefore, less water quality and
hydraulic impact on the nullah is anticipated due to less structure and
construction activities within the nullah. Visual · The
alignment would pose lower visual obstruction to leisure space users and
travellers viewing north and south along Yuen Long Nullah which is a major
visual corridor and an important visual resource in Yuen Long Town. |
· Air
Quality & Noise · Majority
of the construction works will be conducted along the western side of the
nullah. The construction activities will therefore be located close to (i.e. less
than 5m for the nearest receivers) the sensitive receivers along the western side
(e.g. Shung Tak Building, Yuen Tung Building and Fung Yue Building, etc.), and
would have higher impacts on them. · Landscape · As
the construction works and the footbridge alignment is located along the both
side of the nullah, more number of trees (i.e. about 53 trees) along the both
side of nullah will be affected by the Project and needed to be felled. Visual · The
footbridge is closer to the residential sensitive receivers along the western
side of the nullah. Most of their side windows will have direct view towards
the proposed footbridge and it would pose higher visual impacts on them. (Refer
to Typical Cross Section Showing 3
Alignment Options at Pedestrian Interchange) |
|
Alignment Option
3 |
Air
Quality & Noise · Majority
of the construction works will be conducted at the middle of the nullah.
Hence, the separation distance between the alignment from the sensitive
receivers along both sides of the nullah will be increased to about 20m. This
would help to reduce the air quality and noise impact during the construction
phase. Landscape
and Visual · Least
trees to be affected comparing with other options due to construction works
and footbridge alignment is located at the middle of the nullah, except the 100-110m
long section near Tai Kiu Tsuen, fewer trees (about 38 trees) along the
nullah will be affected by the Project, in which 37 nos. needed to be felled and 1 no to be
transplanted. · Majority
of the footbridge is located along the middle of the nullah and hence would
pose lower visual impact on the sensitive receivers along both sides of the
nullah. |
Water · As
the majority of the footbridge is located in the middle of the nullah, intermediate
footbridge columns (e.g. two additional columns for short span options as
discussed in Section 3.5) are needed within the nullah. Higher water
quality and hydraulic impact on the nullah is therefore anticipated due to the
additional structures and construction activities within the nullah. Suitable
mitigation measures are required to minimize the impact to acceptable level.
(See Section 6.6) Landscape · About
38 trees along the nullah will be affected by the Project, in which 37
nos. needed to be felled and 1 no to
be transplanted. Visual · Although
the alignment would pose lower visual impact on the residential sensitive
receivers along both sides of the nullah, it will cause larger visual
obstruction to leisure space users and travellers viewing north and south along Yuen Long Nullah which
is a major visual corridor and an important visual resource in Yuen Long Town. (Refer to Typical Cross
Section Showing 3 Alignment Options at Pedestrian Interchange) |
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Typical Cross Section Showing 3 Alignment
Options at Pedestrian Interchange
3.3.2.2
For waste management and land
contamination, the quantity of excavated materials of different Alignment Options
would not have significant difference and there is no potential land
contamination issue identified in the vicinity (see Chapter 8). Therefore, it is anticipated that there are no
significant difference between the impacts caused by these three options.
3.3.2.3
For cultural heritage impact, the nearest
built heritage, No.21 Tai Kiu Tsuen (a Nil Graded Historic Building) is located
about 90m from the site boundary and there is no site of archaeological
interest in the vicinity of the Project. The impacts caused by these three Alignment
Options would not have significant difference due to the large separation
distance.
Selection of the Preferred Alignment
Option
3.3.2.4
All the key environmental considerations for the options, such as air
quality, noise, water, landscape and visual, etc., have been considered and
presented in Table 3.1. Alignment Option
3 is adopted for the following reasons:
·
For Alignment Options 1 and Option 2, the Project would pose lower water
quality and hydraulic impact on the nullah due to less structures (e.g.
columns) and construction activities within the nullah during both construction
and operational phases than Alignment Option 3. Also, with footbridge aligning
along either side of the nullah, it will pose lower visual obstruction to leisure
space users/travellers viewing north and south along the nullah and allow more sky
view for this important
visual resource in Yuen Long Town. However, the footbridge
aligning along east or west side of the nullah will be much
closer to either side of the sensitive receivers (e.g.
Fook On Building, Siu Fung Building and CCC Chun Kwong Primary School along
eastern side of the nullah for Option 1, and Shung Tak Building, Yuen Tung
Building and Fung Yue Building along western side of nullah for Option 2). As
compared to Alignment Option 3, it would definitely lead to higher air quality
and construction noise impact to these sensitive receivers due to shorter
separation distance between construction sites and the sensitive receivers. At
the same time, more trees (e.g. 63 trees for Alignment Option 1 and 53 trees
for Aliment Option 2 respectively) along the nullah will be needed to fell due
to the construction of footbridge along the edge of the nullah under Alignment Options
1 and 2. In addition, the footbridge will also cause higher visual impact to
the sensitive receivers next to the alignment due to the much shorter separation
distance. Therefore, Alignment Options 1 and 2 are not preferred due to the
higher air quality, noise and landscape impact during construction phase and higher
visual impact during the operation phase.
·
For Option 3, the Project would have more column structures within the
nullah (e.g. two more footbridge columns for short span option) and hence would
cause higher water quality and hydraulic impact and construction activities
within the nullah during both construction and operational phases. However, the
scope of the Project has included measures to mitigate the drainage impact and
there are well developed technology or mitigation measures (e.g. water tight
cofferdams and adoption of lens-shaped footbridge columns) to avoid or minimize
the potential water and hydraulic impacts. The water quality and hydraulic
impact can therefore readily be mitigated to acceptable levels. Besides, majority
of the footbridge (i.e. section between Yuen Long On Ning Road and south of the
Kau Yuk Road) is located at the middle of the nullah. The separation distance
from neighbouring receivers would be about 15m that it is much longer
than that for Alignment Options 1 and 2. In addition, fewer trees (i.e. 16 and 26 trees less than Options
2 and 1 respectively) will be required to fell during the construction phase. Although such an
alignment will cause relatively larger visual obstruction to leisure space
users and travellers viewing north and south along the nullah (i.e. the major
visual corridor of Yuen Long Town), the visual impact caused by the footbridge on the
residential sensitive receivers along both sides of nullah would be lower as compared to Alignment Option 1 and 2
due to larger separation distances between footbridge and the sensitive
receivers. With the consideration of all the above environmental
factors,
Option 3 is preferred due to lower air quality, noise and landscape impact
during the construction phase and lower visual impact to the residential
sensitive receivers during operational phase.
3.3.2.5 Besides the considerations of environmental impacts, the selection of Alignment Option has also considered engineering issues. For Alignment Options 1 and 2, more foundations will be located at the footpath along the nullah than Option 3. Due to the existing congested utilities along both sides of the nullah, including drainage pipe, fresh water main, telecom cables, etc., it would pose uncertainties on the construction programme and hence the duration of construction noise impacts would also increase.
3.3.2.6
Therefore, Alignment Option 3 is selected
as the Preferred Alignment Option taking into account of environmental and
engineering considerations. The selected Alignment Option 3 was presented to
and well received by the Yuen Long District Council on 21 May 2015.
3.4
Selection of Preferred Structural Scheme Option
3.4.1.1
A total of 7 Structural Scheme Options for
the footbridge have been developed and evaluated by considering the
environmental impacts, such as the hydraulic impact to Yuen Long Town Nullah,
the duration of foundation construction and etc.
3.4.1.2
The span of footbridge is one of the key
considerations for different structural schemes. It will affect the structural
form, size and also the number of substructures within Yuen Long Town Nullah, and
hence affect the hydraulic performance of the nullah. Both long span (i.e.
about 98m between supporting structures of the footbridge) and short span
(about 30m – 45m between supporting structures of the footbridge) options have
been investigated and compared in the following sections. Structural Scheme Options
1, 2A and 2B are long span options and Structural Scheme Options 3A, 3B, 3C and
4 are short span options. All the Structural Scheme Options have the same
alignment (i.e. Alignment Option 3) with different structural schemes.
3.4.2
Evaluation of Structural
Scheme Options
3.4.2.1
A total of 7 Structural Scheme Options
have been developed and described in Table
3.2.
Table 3.2 Descriptions of 7 Structural Scheme Options
|
Structural Scheme Option |
Description |
|
Scheme Option 1
Isometric View - Scheme Option 1 |
This option consists of long span extrados Vierendeel
truss deck spanning on Yuen Long Town Nullah supported by steel arch towers and
cables. 1. The extrados Verendeel truss is 98m long in maximum
and 3.5m deep. 2.
The steel arch
towers with stay cables are appropriately 18m tall. 3.
Hydraulic impact to the nullah is lower due to no intermediate support
or structure is required under the steel arch towers and within the nullah. 4.
Construction of foundations within the nullah is reduced to the minimum.
Shorter duration of foundations construction (i.e. 2 dry seasons). |
|
Scheme Option 2A
Isometric View - Scheme Option 2A |
This option is developed based on Option 1 and consists of long span Warren truss deck spanning on
Yuen Long Town Nullah supported by another steel
truss spanning across the nullah. 1.
The Warren truss
is 98m long in maximum and 5.2m deep. 2.
The steel
trusses spanning across the nullah supporting the footbridge deck are
appropriately 6m tall. 750mm(w)× 750mm(d) and 550mm(w)× 700mm(d) steel rectangular
hollow sections will be used for top and bottom chords of the supporting
truss respectively 3.
Hydraulic impact
to the nullah is lower due to no intermediate support or structure is required under the horizontal
steel Warren truss and within the nullah. 4.
Construction of
foundations within the nullah is reduced to the minimum. Shorter duration of foundations
construction (i.e. 2 dry seasons). |
|
Scheme Option 2B
Isometric
View - Scheme Option 2B |
This option is developed based on Option 1 and consists of long span Warren
truss deck spanning on Yuen Long Town Nullah supported by concrete box
culverts. 1.
The Warren truss
is 98m long in maximum and 5.2m deep. 2.
The concrete
portal frames supporting the footbridge deck are appropriately 6m tall and
within the footprint of the bridge deck. 3.
Hydraulic impact
to the nullah is medium due to
no intermediate support is required within the nullah but box culverts will
be provided at the pedestrian interchanges which will hinder the flow of
the nullah. 4.
Construction of
foundations within the nullah is reduced to the minimum. Shorter duration of foundation
construction (i.e. 2 dry seasons). |
|
Scheme Option 3A Isometric
View - Scheme Option 3A |
This option consists of short span Vierendeel truss
spanning on Yuen Long Town Nullah supported by intermediate columns in the
nullah. The lift shaft is located on the footpath at one side of the nullah. 1.
The Vierenceel truss is 30m – 45m long in maximum and
3.5m deep. 2.
2 concrete
columns will be provided in each of the pedestrian interchanges for
supporting the footbridge deck. 3.
The
3m×3m×12m(tall) lift shaft will be encroached onto the existing footpath and
connected to the proposed footbridge with a link bridge supported by the lift
shaft and pedestrian interchange. The link bridge is close to the adjacent
buildings. 4.
Hydraulic impact to the nullah is higher due to intermediate
columns and box culverts at pedestrian interchanges are required within the
nullah. 5.
Longer duration of foundations construction (i.e.
3 dry seasons). |
|
Scheme Option 3B
Isometric View - Scheme Option 3B |
This option is developed based on Option 2B. This option
consists of short span Vierendeel truss spanning on Yuen Long Town Nullah
supported by concrete box culverts and intermediate columns in YLTN. This option consists of short span Vierendeel truss
spanning on Yuen Long Town Nullah supported by concrete box culverts and
intermediate columns in YLTN. 1.
The Vierenceel
truss is 30m – 45m long in maximum and 3.5m deep. 2.
4 concrete
columns will be provided in each of the pedestrian interchanges for
supporting the footbridge deck. 3.
Hydraulic impact to the nullah is higher due to intermediate
columns and box culverts at pedestrian interchanges are required within the nullah.
Drainage impact assessment has been carried out and the hydraulic impact is
acceptable with appropriate mitigation measures. 4.
Longer duration of foundations construction (i.e.
3 dry seasons). |
|
Scheme Option 3C
Isometric
View - Scheme Option 3C |
This option is developed based on Option 3B. The pedestrian interchanges and
extended footpath are integrated and the arrangement of staircase, escalator
and lift at pedestrian interchange is modified to
be more user friendly. This option consists of short span Vierendeel
truss spanning on Yuen Long Town Nullah supported by concrete box culverts
and intermediate columns in the nullah. 1.
The Vierendeel
truss is 30m – 45m long and 3.5m deep. 2.
4 concrete
columns will be provided in each of the pedestrian interchanges supporting
the footbridge deck. Extra at-grade landscape area will be provided allowing
more planting and public area. 3.
Hydraulic impact
to the nullah is higher due to intermediate columns and box culverts at
pedestrian interchanges are required within the nullah. Drainage impact assessment
has been carried out and the hydraulic impact is acceptable with appropriate
mitigation measures. 4.
Longer duration of foundations construction (i.e.
3 dry seasons). |
|
Scheme Option 4
Isometric
View - Scheme Option 4 |
This option consists of short span concrete box girder
spanning on the nullah supported by concrete box culverts and intermediate
columns in the nullah. 1.
The concrete box
girder deck is 30m long in maximum and 1.5m deep. An additional 2.6m headroom
for pedestrian is required for this option. Therefore, the overall depth of
footbridge is 4.1m. 2.
1 concrete
column incorporating the lift shaft inside will be will be provided in each
of the pedestrian interchanges supporting the footbridge deck. 3.
Hydraulic
impact to the nullah is higher due to intermediate
columns and box culverts at pedestrian interchanges are required within the
nullah. 4.
Longer
duration of foundations construction: 3 dry seasons. |
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3.4.3
Environmental Considerations
for the Structural Scheme Options
3.4.3.1
The environmental considerations for the Structural Scheme Options are compared
and presented in Table 3.3 below.
Table 3.3 Summary of the considerations for the Scheme Options
|
Options |
Environmental Benefits |
Environmental Disbenefits |
|
Scheme Option 1 |
Air Quality
& Noise · No
intermediate support or structure
under pedestrian interchanges are required within the nullah. The
number of substructure and foundations
within the nullah is reduced to the minimum and hence
shorter construction duration (i.e. 2 dry seasons). This option would reduce
air quality and noise impact during construction stage, especially for the
residents along the nullah. Landscape and Visual · No
intermediate support is required. Less substructure within the nullah will
maximize the nullah view to pedestrian on ground level. Water · No box
culvert is constructed within the nullah and would have lowest water and
hydraulic impact in compared with other options. Waste · As no
intermediate support structure and hence less substructure within the nullah
is required, less C&D materials will be generated from construction of
foundations, and demolition of the existing nullah walls and slabs
respectively. |
Air Quality
& Noise · Some air
quality and noise impact to the sensitive receivers along the nullah during demolition
of the existing nullah wall near the pedestrian interchanges and construction
of foundations. Landscape and Visual · The 18m tall steel
arch towers with stay cables appear massive and would have visual impact on
the sensitive receivers next to the pedestrian interchanges and existing
carriageway of YLONR, CPR(YLS) and KYR. |
|
Scheme Option 2A |
Air Quality
& Noise · No
intermediate support or structure under pedestrian interchanges are required within
the nullah. The number of substructure and foundations
within the nullah is reduced to the minimum and hence
shorter construction duration (i.e. 2 dry seasons). This option would reduce
air quality and noise impact during construction stage, especially for the
residents along the nullah. Landscape and
Visual · No
intermediate support is required. Less substructure within the nullah will
maximize the nullah view to pedestrian on ground level. Water · No box
culvert is constructed within the nullah and would have lowest water and
hydraulic impact in compared with other options. Waste · As no
intermediate support structure and hence less substructure within the nullah
is required, less C&D materials will be generated from construction of
foundations, and demolition of the existing nullah walls and slabs
respectively. |
Air Quality
& Noise · Some air
quality and noise impact to the sensitive receivers along the nullah during
demolition of the existing nullah wall near the pedestrian interchanges and
construction of foundations. Landscape and
Visual · The 5.2m
deep steel truss supports appear massive and would have visual
impact on the sensitive receivers next to the pedestrian interchanges and
existing carriageway of YLONR, CPR(YLS) and KYR. · Some visual
impact from the diagonal members and deeper footbridge deck
(5.2m). |
|
Scheme Option 2B |
Air Quality
& Noise · No
intermediate support are required within the nullah. The number of
substructure and foundations within the
nullah is reduced to the minimum and hence shorter construction duration
(i.e. 2 dry seasons). This option would reduce air quality and noise impact
during construction stage, especially for the residents along the nullah. Landscape and
Visual · No
intermediate support is required. Less substructure within the nullah will
maximize the nullah view to pedestrian on ground level. Waste · As no
intermediate support structure and hence less substructure within the nullah
is required, less C&D materials will be generated from construction of
foundation and demolition of the existing nullah slabs due to the fewer
number of substructures to be built within the nullah. |
Air Quality & Noise · Some air
quality and noise impact to the sensitive receivers along the nullah during
demolition of the existing nullah wall and construction of foundations. Water · Construction
of box culverts under the six pedestrian interchanges are required within the
nullah. Hence, this option would have water quality and hydraulic impact on
the nullah. Landscape and Visual · Some visual
impact from the diagonal members and deeper
footbridge deck (5.2m). |
|
Scheme Option 3A |
Noise ·
Shorter and fewer piles are needed for short span
options in comparison with long span options. A shorter duration of piling
works is required, hence reduce duration of the noise impact arise from
piling works to the sensitive receivers close to the piling works. Landscape and
Visual · This
option would have less visual impact on the residential buildings along the
nullah due to smaller footbridge deck (i.e. 3.5m deep). |
Air Quality
& Noise · A longer
duration (i.e. 3 dry seasons) is required for construction of the
intermediate columns and box culverts at the pedestrian interchanges. It
would increase the air quality and noise impact on the sensitive receivers
during construction phase. Water · Construction
of box culverts under the six pedestrian interchanges and intermediate column
are required within the nullah. Hence, this option would have water quality
and hydraulic impact on the nullah. Landscape and Visual · Intermediate
supports within the nullah is required and reduce some nullah view to the
pedestrians. · The 3m×3m
lift shaft of 12m tall encroached onto the existing footpath with the 13m link
bridge to the footbridge deck and would cause significant visual impact from
encroachment of the lift shaft onto the existing footpath on pedestrians during
operational phase. · The link
bridge is very close to the adjacent residential buildings and cause issue of
privacy and visual impact to residents. Waste · As
intermediate columns and structures within the nullah are required, more
excavated materials and demolition materials will be generated from
construction of foundations, and demolition of the existing nullah walls and
slabs respectively. |
|
Scheme Option 3B |
Noise ·
Shorter and fewer piles are needed for short span
options in comparison with long span options. A shorter duration of piling
works is required, hence reduce duration of the noise impact arise from
piling works to the sensitive receivers close to the piling works. Landscape and
Visual · This
option would have less visual impact on the residential buildings along the
nullah due to smaller footbridge deck (i.e. 3.5m deep). · This option avoid
encroachment onto the existing footpath and would have less visual impact on
the pedestrians. |
Air Quality & Noise · A longer
duration (i.e. 3 dry seasons) is required for construction of the
intermediate columns and box culverts at the pedestrian interchanges. It
would increase the air quality and noise impact on the sensitive receivers
during construction phase. Water · Construction
of box culverts under the six pedestrian interchanges and intermediate column
are required within the nullah. Hence, this option would have water quality
and hydraulic impact on the nullah. Landscape and
Visual · Intermediate
supports within the nullah is required and reduce some nullah view to the
pedestrians. Waste · As
intermediate columns and structures within the nullah are required, more
excavated materials and demolition materials will be generated from
construction of foundations, and demolition of the existing nullah walls and
slabs respectively. |
|
Scheme Option 3C |
Noise ·
Shorter and fewer piles are needed for short span
options in comparison with long span options. A shorter duration of piling
works is required, hence reduce duration of the noise impact arise from
piling works to the sensitive receivers close to the piling works. Landscape and
Visual · This
option would have less visual impact on the residential buildings along the
nullah due to smaller footbridge deck (i.e. 3.5m deep). · This option
avoid encroachment onto the existing footpath and would have less visual
impact on the pedestrians. · The integrated
pedestrian intercahnge and footpath provide more at-grade landscape area
which allow more planting. |
Air Quality
& Noise · A longer
duration (i.e. 3 dry seasons) is required for construction of the
intermediate columns and box culverts at the pedestrian interchanges. It
would increase the air quality and noise impact on the sensitive receivers
during construction phase. Water · Construction
of box culverts under the six pedestrian interchanges and intermediate column
are required within the nullah. Hence, this option would have water quality
and hydraulic impact on the nullah. Landscape and
Visual · Intermediate
supports within the nullah is required and reduce some nullah view to the
pedestrians. Waste · As
intermediate columns and structures within the nullah are required, more
excavated materials and demolition materials will be generated from
construction of foundations, and demolition of the existing nullah walls and
slabs respectively. |
|
Scheme Option 4 |
Noise ·
Shorter and fewer piles are needed for short span
options in comparison with long span options. A shorter duration of piling
works is required, hence reduce duration of the noise impact arise from
piling works to the sensitive receivers close to the piling works. Landscape and
Visual · This
option would have less visual impact on the residential buildings along the
nullah due to smaller footbridge deck (i.e. 4.1m deep). |
Air Quality & Noise · A longer
duration is required for construction of the intermediate columns and box
culverts at the pedestrian interchanges. It would increase the air quality
and noise impact on the sensitive receivers during construction phase. Water · Construction
of box culverts under the six pedestrian interchanges and intermediate column
are required within the nullah. Hence, this option would have water quality
and hydraulic impact on the nullah. Landscape and Visual · A lager
platform on footbridge level around the lift shaft is required and cause some
visual impact. · Intermediate
supports within the nullah is required and reduce some nullah view to the
pedestrians. Waste · As
intermediate columns and structures within the nullah are required, more
excavated materials and demolition materials will be generated from construction
of foundations, and demolition of the existing nullah walls and slabs
respectively. |
Selection of Preferred Scheme Option
3.4.3.2
All the key environmental considerations, such as air quality, noise,
landscape and visual, and waste are considered for the Structural Scheme
Options. Option 3C is adopted for the following reasons:
·
As the scope of the Project has included measures to mitigate the
drainage impact and there are well developed technology or mitigation measures
(e.g. water tight cofferdams and adoption of lens-shaped footbridge columns) to
avoid or minimize the potential water and hydraulic impacts. In addition, the
size of permanent structures inside the nullah would be also minimized to
reduce the flood risk. Width of columns and walls within nullah will not exceed
1m in width and will be orientated in line with the nullah flow. Drainage
impact assessment was conducted to assess and mitigate the potential flood risk
and hydraulic impacts. As a result, the water quality and hydraulic impact can
therefore readily be mitigated to acceptable levels for all Structural Scheme Options.
Therefore, visual impact is considered as a more critical consideration than
water and hydraulic impact during selection of alternatives.
·
Long span options Scheme Option 1, 2A and 2B with minimum substructure
and foundation have been investigated in order to minimize the hydraulic impact
to the nullah. Although the number of substructure is reduced, the structural
height of footbridge / depth of the footbridge deck and the scale of supporting
system at pedestrian interchanges would eventually become larger. The massive
structure would cause higher visual impact to the to the existing carriageway
near YLONR, CPR(YLS) and KYR as well as the residential buildings next to the
pedestrian interchanges. As a result, long span options (i.e. Scheme Option 1,
2A and 2B) are not considered as reasonable alternatives due to the massiveness
of support and footbridge.
·
For Scheme Option 3A, the lift is located on one side of the nullah and
has encroached onto the existing footpath. The construction of lift shaft foundations
would cause higher air quality and noise impact to the sensitive receivers very
close to the shaft during construction phase in comparison with Scheme Options
3B, 3C and 4. In addition, the link
bridge between the footbridge and the lift is very close to residential
buildings and might pose issue on privacy for the residents as well as higher
visual impact to the pedestrians during operational phase. Therefore, Option 3A
is considered not a suitable alternative.
·
In order to enhance the connectivity of pedestrian interchanges,
different arrangements of lift shaft, staircase and escalator are studied and hence
Scheme Option 3B, 3C and 4 are developed. For Scheme Option 4, the concrete footbridge
deck has larger depth (i.e. 4.1m) in comparison with steel truss option (i.e.
3.5m) and the platform on footbridge level around the lift shaft would cause
higher visual impact to the sensitive receivers in comparison with Option 3B
and 3C.
·
Scheme Option 3B and 3C allow smaller scale of support and footbridge
deck would cause minimum visual impact among different Structural Scheme
Options during the operational phase. Due to the similar structural
arrangements, both options will give similar environmental impact. However,
given that Option 3C would provide additional 180m2 at-grade
landscaping area per pedestrian interchange (i.e. in total of 1080m2 for
six pedestrian interchanges) which allow more greening, Option 3C has more
landscape and visual advantages in comparison with Option 3B.
·
With the provision of mitigation measures, all the Scheme Options would
not cause significant difference in water quality impact. Although
the air quality and noise impacts during the construction phase of Scheme Option
3C will be longer than long span options (i.e. Scheme Option 1, 2A and 2B),
these environmental impacts are temporary during construction only. Taking into
account of all environmental considerations, Scheme Option 3C is selected as
the preferred Structural Scheme Option.
3.5.1.1 Yuen Long Town Nullah connects to and discharges into Shan Pui River, and eventually into the downstream Deep Bay where high ecological value has been recognised, such as important wetland system and important foraging and roosting ground for waterbirds. In order to address concern of the downstream ecology, the following best practices on construction methods have been adopted in order to avoid any possible impacts on the downstream ecology at the outset.
3.5.1.2
According to the current design intent, the footbridge will be supported
on piled foundations and box culverts as described below:
·
The footbridge section between West Rail Long Ping Station and Yuen Long
On Ning Road would be supported by 3 piled foundations and 1 piled box culvert
at the pedestrian interchange.
·
The footbridge section between Yuen Long On Ning Road and Castle Peak
Road (Yuen Long Section) would have same foundation layout with the footbridge
section between Castle Peak Road (Yuen Long Section) and Kau Yuk Road. i.e. 2
piled box culverts and 1 piled foundation within the nullah would be provided
for each section.
·
The footbridge section to the south of the Kau Yuk Road would be
supported by 1 piled box culvert at the pedestrian interchange.
3.5.1.3
The location of piled foundations and box culverts are shown in
Figure 3.2. The construction works (e.g.
excavation, piling works and etc.) that will be conducted on the nullah bed, are
4-5m lower than adjacent footpath. Foundation construction is targeted to be
carried out and completed in the dry seasons as much as practicable during
which the water flows would mostly in the dry weather flow channel except
during occasional rainfall events. Temporary earth lateral support will be
installed for demolition of the existing retaining wall of nullah and
constructions of the pile caps.
3.5.1.4
Installation of temporary platforms will be used to overcome the constraints
for construction works during wet seasons (e.g. foundations construction not
involving the nullah bed and superstructure). The temporary platform shall span
across the 30m wide nullah. Supports within and at both sides of the nullah are
required for the temporary platform. Either the permanent columns of the
footbridge or the temporary steel sheet piles can be adopted for the supports
of the temporary platform. Necessary assessment will be conducted in accordance
with DSD’s technical circular No. 14/2000 and submitted to DSD for approval so
as to ensure the capacity of existing nullah is not adversely affected by the
supports of temporary platform within the nullah.
_V6_Clear_files/image035.png)
General Arrangement of Temporary Platform
3.5.1.5
Notwithstanding
the abovementioned possible approaches for the footbridge construction, the following measures will be provided during construction phase in
order to prevent any discharges or construction waste from entering into Yuen
Long Town Nullah:
·
Cofferdams should be installed prior to demolition
of existing nullah structures or excavation in dry for pile cap construction.
One of the purposes of installing the cofferdams is to provide an isolated work
environment that can isolate the surrounding water during demolition and
excavation. Hence water pollution from site runoff would be adequately
controlled with the standard site drainage measures in place. The excavation
works within nullah for the foundation will be scheduled to be carried out in
the dry seasons as far as practicable to minimise impacts to water quality.
Similarly, this measure will also be adopted for the construction of the
supports for the temporary platform when necessary;
_V6_Clear_files/image037.png)
General Arrangement of Cofferdam
·
Closed grabs or sealed grabs should be used and the
mechanical grabs would need to be sealed;
·
The excavation operation should be carefully
controlled to avoid splashing excavated materials or wastes into the
surrounding water during the transportation. Dump trucks will be used to
transport the excavated materials or wastes so as to minimise the possibility
of splashing on nullah and the temporary stockpiles within the nullah will be
avoided. If stockpiling inside nullah or on the temporary platform is
inevitable, they will be covered with tarpaulin or similar fabric and provided
with water-tight containments structure (e.g. cofferdam), especially during the
wet season (April – September) or when heavy raining is predicted to avoid the
stockpiles from running into the nullah;
·
The works such as excavation for the foundation
construction within nullah will be
carried out in accordance with the approved method statement by the Engineer to
minimise the impact to water quality;
·
Toe boards along both edges of the footbridge deck
will be provided in order to avoid construction materials falling into the
nullah;
·
Temporary storage of materials should be located
away from the nullah during carrying out of the construction works;
·
Surface run-off and sewage from construction should
be treated via adequately designed silt removal facilities such as sand traps
and silt traps; and
·
All workers should be regularly briefed to avoid
water pollution from site runoff to the nullah and supervisory staff should be
assigned to station on site to closely supervise and monitor the works.
3.6.1.1 The construction of the elevated corridor and associated works is anticipated to commence in 2018 for completion in Year 2022. It is anticipated that the development will be commissioned in phases. In order to main sufficient capacity for the passage of flow over the entire nullah druing construction phase, the construction activities at the eastern side, central part and western side of the nullah would be conducted separately to minimize the potential hydraulic impact. The tentative implementation programme is summarised in Table 3.4 below.
Table 3.4 Summary of the tentative implementation programme
|
Construction Activities |
Tentative Implementation Programme |
|
Site Clearance (Eastern Side of the nullah) |
Q1 2018 |
|
Site Clearance (Western Side of the nullah) |
Q2 2019 |
|
Temporary Erection (Eastern Side of the nullah) |
Q2 2018 to Q4 2018 |
|
Temporary Erection (Western Side of the nullah) |
Q2 2019 to Q4 2019 |
|
Temporary Erection (Central part of the nullah) |
Q4 2020 |
|
Piling Works (Eastern Side of the nullah) |
Q4 2018 to Q1 2019 |
|
Piling Works (Western Side of the nullah) |
Q4 2019 to Q1 2020 |
|
Piling Works (Central part of the nullah) |
Q4 2020 to Q1 2021 |
|
Column and Table Top Construction |
Q2 2020 to Q4 2020 |
|
Pedestrian Interchanges Superstructure
Construction |
Q2 2020 to Q1 2021 |
|
Deck Structure and Steel Works |
Q2 2020 to Q4 2021 |
|
Parapet Wall Construction, and Associated Landscape and Streetscape
Works |
Q4 2021 to Q2 2022 |
3.7
Concurrent Projects and Evaluation of Potential
Cumulative Impacts
3.7.1
General
3.7.1.1
In order to assess the
cumulative impacts, a review of best available information at the time of
preparing this EIA report to identify a number of other projects that are
undergoing planning, design, construction and/or operation within the
construction and/or operation period for this Study has been conducted. A list
of the tentative concurrent projects identified at this stage is described
below and summarised in Table 3.5. The
locations of these concurrent projects are illustrated in
Figure 3.1.
3.7.2
Improvement of Yuen Long Town
Nullah (Town Centre Section) – Stage 1 Improvement Works
3.7.2.1
The project involves the construction of a dry weather flow interception
(DWFI) system to intercept the polluted dry weather flow being discharged to
YLTN from the town centre section and upstream main nullah. Approximately 60
existing storm water outfalls within the town centre section will be
intercepted by the proposed system.
3.7.2.2
According to the information provided from DSD, the construction of the
improvement works will be commenced in the 3rd quarter of Year 2022
and is targeted to be completed in Year 2026. As the construction period of the
development will not overlap with the Project, no cumulative environmental
impact is anticipated during the construction phase. During the operational
phase, cumulative water quality, ecological, and visual and landscape impact are
anticipated and would be considered during the assessment.
3.7.3
Improvement of Yuen Long Town
Nullah (Town Centre Section) – Stage 2 Beautification Works
3.7.3.1
The project involves beautification and landscaping works by modifying
and reconstructing the existing concrete nullah bed and wall along the 800m
town centre section of the Yuen Long Town Nullah.
3.7.3.2
According to the information provided from DSD, the construction of the
development will be commenced in Year 2027 and is targeted to be completed in
Year 2029. As the construction period of the development will not overlap with
the Project, no cumulative environmental impact is anticipated during the
construction phase. During the operational phase, cumulative water quality,
ecological, and visual and landscape impact are anticipated and would be
considered during this EIA study.
3.7.4
West Rail Long Ping Station
(North) Property Development
3.7.4.1 The development is located to the north of the WRLPS and to the southwest of the Tung Tau Industrial Area, covering the area bounded by Kwong Yip Street, Fo Yip Street and Wang Yip Street South. There are four residential buildings with a total gross floor area (GFA) of about 48,600m2 providing about 910 flats.
3.7.4.2 The construction of the development has commenced in Year 2013 and is targeted to be completed in Year 2018. As the construction period of the development will overlap with the Project, the cumulative construction dust, noise, water quality and ecological impact would be considered during this EIA study. During the operational phase, no cumulative environmental impacts from the development and the Project is anticipated. Nevertheless, the planned receivers in this property development will be considered in the environmental impact assessment.
3.7.5
West Rail Long Ping Station
(South) Property Development
3.7.5.1
The development is located to the west of the Yuen Long Town Nullah,
covering the area bounded by Yuen Long Town Nullah, Po Lok Square and Ping Shun
Street. There are four residential
buildings with a total gross floor area (GFA) of about 41,900m2 providing
about 720 flats.
3.7.5.2
The construction of the development has commenced in Year 2014 and is
targeted to be completed in Year 2019. As the construction period of the
development will overlap with the Project, the cumulative construction dust,
noise, water quality and ecological impact would be considered during this EIA
study. During the operational phase, no cumulative environmental impacts from
the development and the Project is anticipated. Nevertheless, the planned
receivers in this property development will be considered in the environmental
impact assessment. Nevertheless, the planned receivers in this property
development will be considered in the environmental impact assessment.
3.7.6
Housing Sites in Yuen Long
South
3.7.6.1
According to the information of the Stage 3 Community Engagement Digest
of Planning and Engineering Study for Housing Sites in Yuen Long South – Investigation
issued in January 2016 (hereafter called “Stage 3 Community Engagement Digest”).
The Potential Development Areas (PDAs) under the project is located to the
south of Yuen Long New Town, and largely bounded by Yuen Long Highway and Kung
Um Road. The PDAs include two main parts, one in Tong Yan San Tsuen area and
another one in the area along Kung Um Road. The project comprises housing sites
for both public and private housing development in Yuen Long South and the
associated infrastructure works. The associated infrastructure works would
include the necessary slope works, road works, drainage works, waterworks,
utility works, etc. within or outside the PDAs for serving the proposed public
and private housing developments.
3.7.6.2
There is no construction programme available at the time preparing this
report. Based on the information in the Stage 3 Community Engagement Digest,
the project would be developed in stages and the first population intake is
targeted in Year 2026. The cumulative water quality impact during both
construction phase and operational phase would be considered in this EIA study
for conservative purpose. As the development is located about 900m from the
Project, cumulative impact for other environmental aspects, such as air
quality, noise, etc., is not anticipated and would not be considered in this
EIA study.
3.7.7
Drainage Improvement Works
Near Four Village in Yuen Long – Sung Shan New Village, Tai Wo, Lin Fa Tei and
Ha Che
3.7.7.1
The project comprises drainage improvement works near four villages in
Yuen Long, namely Sung Shan New Village, Tai Wo, Lin Fa Tei and Ha Che. The
proposed drainage improvement works to be implemented at the four villages
include landscaping, waterscaping, utilities diversion, temporary traffic arrangements,
re-provisioning / improvement to existing dry weather flow intercepting system
and any other works incidental to the completion of the project.
3.7.7.2
According to the information provided from DSD, the project will be
commenced in Year 2017 and is targeted to be completed in Year 2022. As the
construction period of the drainage improvement works will overlap with the
Project between Year 2018 to Year 2022, cumulative water quality impact is
anticipated during the construction phase. During operational phase cumulative
water quality impact is also anticipated and would be considered during this
EIA study. As the drainage improvement works is located more than 1.5km from
the Project, cumulative impact for other environmental aspects, such as air
quality, noise, etc., is not anticipated and would not be considered in this
EIA study.