6.2.15
The evaluated ultimate total
ADWF within TKO catchment, with the further development proposed at TCS, TKL ,and
PSK and TKO
Stage 1 Landfill are shown in Table 6.7 below:
Table
6.7 Ultimate
ADWF in Year 2016 for TKO Sewerage Catchment, with Further Development at TCS,
TKL, PSK and TKO Stage 1 Landfill
|
Development
Type
|
ADWF
(m3/d)
|
|
Residential
|
103,615
|
|
Commercial (E2 to E5)
|
34,898
|
|
Industrial (E1)
|
10,716
|
|
School
|
1,697
|
|
Diversion from Port Shelter*
|
10,585
|
|
TOTAL
|
161,510
|
Notes: * Design ultimate
flows are based on Table B of the SENT Development Strategy Review Study
provided by EPD’s memo to TDD ref. (22) in EP 2/N8.Q/84 XII dated 16 June 2003.
Peaking Factors
6.2.16
Peak wet weather flows (PWWF)
are used in the assessment of hydraulic adequacy of the sewerage systems, TKO Preliminary Treatment
Works (PTW)
and the Harbour Area Treatment Scheme (HATS) Stage I Tunnel section from TKO to
Kwun Tong. Peaking factors including
stormwater allowance in accordance with the Sewerage Manual were applied to the
ADWF to establish the peak flows. A
flow rate of 240 l/h/d, which is in line with the recommendation of EEFS, was
adopted in the evaluation of equivalent population for determination of the
peaking factors. The recommended
peaking factors are presented in Table 6.8 below:
Table 6.8 Recommended Peaking Factors
for Sewers and PTWs
|
Population
|
Peaking
Factor for Sewers*
|
Population
|
Peaking
Factor for PTWs*
|
|
<
1,000
|
8
|
<
10,000
|
4
|
|
1,000
– 5,000
|
6
|
10,000
– 25,000
|
3.5
|
|
5,000
– 10,000
|
5
|
25,000
– 50,000
|
3
|
|
10,000
– 50,000
|
4
|
>
50,000
|
3.9/N0.075
|
|
>
50,000
|
7.3/N0.165
|
|
|
Notes:
* denotes peaking factors including
stormwater allowance based on Sewerage Manual Part 1 (DSD, 1995).
N denotes equivalent population /
1,000.
Equivalent population = ADWF (m3/d)
/ 0.24.
Reference has been made to Section
4.7.2 of Sewerage Manual Part 1 (DSD, 1995) for calculation of peaking factor
of PTW with population greater than 50,000.
Peak Wet Weather
Flow
6.2.17
Peaking factor including stormwater
allowance in accordance with Sewerage Manual have been adopted in the flow
estimation to provide a conservative basis for the performance assessment of
the sewerage system. It is also noted
that some sections of the existing sewerage system in TKO are suffering from
ground settlement and may therefore lead to ingress of stormwater or ground
water into the sewers.
Baseline Condition
6.2.18
The total projected ultimate
peak flows for the TKO sewerage catchment are evaluated and shown in Table 6.9 below:
Table 6.9 Ultimate PWWF in Year 2016 at TKO PTW
|
ADWF (m3/d)
|
Equivalent
Population
|
Peaking Factor *
|
PWWF (m3/s)
|
|
165,515
|
689,646
|
2.39
|
4.58
|
Notes:
* denotes peaking factors
including stormwater allowance based on Sewerage Manual Part 1 (DSD, 1995).
PWWF = ADWF x Peaking Factor
Reference has been made to
Section 4.7.2 of Sewerage Manual Part 1 (DSD, 1995) for calculation of Peaking
Factor of PTW with population greater than 50,000.
Sewerage Impact Assessment Condition
6.2.19
With the proposed further
development at TCS, TKL, PSK and TKO Stage 1 Landfill, the total projected
ultimate flows for the TKO sewerage catchment are evaluated and presented in Table 6.10 below:
Table 6.10 Ultimate PWWF in Year 2016, with Revised Flows due to
Further Development at TCS, TKL, PSK, and TKO at Stage
1 Landfill, at TKO PTW
|
ADWF (m3/d)
|
Equivalent
Population
|
Peaking Factor *
|
PWWF (m3/s)
|
|
161,510
|
672,958
|
2.39
|
4.47
|
Notes:
* denotes peaking factors
including stormwater allowance based on Sewerage Manual Part 1 (DSD, 1995).
PWWF = ADWF x Peaking Factor
Reference has been made to
Section 4.7.2 of Sewerage Manual Part 1 (DSD, 1995) for calculation of Peaking
Factor of PTW with population greater than 50,000.
Introduction
6.3.1
Sewage flows generated by
developments within the TKO sewerage catchment are collected by the existing
and committed sewerage systems en route to the TKO PTW for preliminary
treatment. There are proposed works
under the TKO Sewerage and Port Shelter Sewerage projects which are associated
with this catchment. The treated
effluent from TKO PTW is discharged into the existing Harbour Area Treatment
Scheme (HATS) Stage I Tunnel System for conveyance to the Stonecutters Island
Sewage Treatment Works (SCISTW) for chemical treatment and ultimate disposal
into the western approaches of the Victoria Harbour.
Sewerage System
Existing Sewerage Systems
6.3.2
The TKO sewerage catchment
comprises two major sewerage systems.
They are referred to as the Northwest and the South Systems in respect
of their locations relative to the TKO PTW.
Figure
6.1 shows the sewerage layout of the TKO catchment.
(i) Northwest System
6.3.3
The Northwest System collects
sewage generated from the majority of the residential developments in TKO,
including Po Lam, Tsui Lam, Hang Hau, Tiu Keng Leng, Pak Shing Kok, TKO Town
Centre and Siu Chik Sha.
6.3.4
There is a sewerage connection
from the Hong Kong University of Science and Technology (HK UST) to the
Northwest System via a 450mm diameter sewer.
The HK UST tunnel collects sewage from Tai Po Tsai, Pik Shui Sun Tsuen,
Ta Kwu Leng San Tsuen, HK UST and an additional development in Tai Po
Tsai. Another sewerage connection is
lately completed at Hang Hau Road via a 450mm diameter sewer. This newly built sewerage is catered for
planned developments in Silverstrand, Mang Kung Uk and Clear Water Bay
Peninsula.
6.3.5
The collected flows from the
Northwest System drain to an inflow chamber located near Tin Chau Road at Hang
Hau. At the inflow chamber, the flow
discharges to a 2,400mm internal diameter sewage tunnel which runs through
Planning Area 78, 103, 106 and 108. The
tunnel has a nominal depth range of 5m to 9m, except for the section which
passes through a hillside where the depth is up to 150m. The peak flow capacity of the sewage tunnel
varies from 3.15m3/s to 4.88 m3/s. The sewage tunnel is connected to a 2,500mm
diameter sewer at a roundabout on Shek Kok Road and eventually discharges into
the TKO PTW nearby.
(ii) South System
6.3.6
The South System covers mainly
the industrial area in Tai Chik Sha (including TKO Industrial Estate and Area
137) which has a total area of approximately 180 ha. Sewage generated from the industrial area is collected by the
sewers at Chun Yat Street, Chun Kwong Street, Chun Ying Street, Chun Wang
Street and Chun Choi Street, which are then connected to the trunk sewer
located along Wan Po Road. The system
will also serve the future Area 137 planned to accommodate a total employed
population of 11,500. 500mm DI rising mains have already been laid along
Wan Po Road (between Area 137 and junction at Chun Wang Road) to cater for the
development of Area 137. The
trunk sewer, of which the diameter is 1,650mm, is connected to the sewage
tunnel of the Northwest System at Shek Kok Road before discharging to TKO PTW.
Planned Sewerage Works
6.3.7
There are recommended sewerage
improvement works associated with the TKO sewerage catchment under the TKO SMP
and Port Shelter SMP. Though the
planned sewerage works under the Port Shelter and TKO Sewerage projects go beyond
2016, the impacts of these proposed works are therefore taken into
consideration in the performance assessment.
6.3.8
In general, the TKO SMP has
recommended the provision of sewerage connections to nine TKO villages. These include the Shui Bin Village, Ming Oi
New Village, TKO Upper Old Village, Boon Kin Village, Mau Wu Tsai Village, Hang
Hau Lower Old Village, Wo Tong Kong Village, Au Tau Village and Sun Tei Village of which the
locations are indicated on Figure 6.1.
There is no programme to implement the proposed works.
6.3.9
Under the Port Shelter SMP,
sewage flows are to be transferred into the TKO sewerage catchment from the
areas south of Ho Chung, including Silverstrand and Clearwater Bay areas. The existing HK UST sewage tunnel conveys
flows from the areas south of Ho Chung whilst flow from Silverstrand and
Clearwater Bay areas will be delivered by means of pumping and gravity
respectively. The proposed works are in
stages. Stage 1 works were fully
completed. Stage 2 and 3 works are
being designed and the implementation programmes are under detailed planning.
Sewage
Treatment Works
6.3.10
Sewage collected from the
catchment is conveyed by the existing and committed sewerage systems to the
existing TKO PTW for treatment. Sited
at the junction of Shek Kok Road and Wan Po Road in Area 85, the PTW was
upgraded under the Strategic Sewage Disposal Scheme, SSDS (now known as HATS)
Stage I in 1996. The upgrading works
included the coarse screen, raw sewage pumps, fine screens and vortex grit
tanks. The upgraded PTW now has a
capacity of 5.55m3/s, with a standby unit of 0.6m3/s. A layout of the PTW is shown in Figure 6.4. Capacities of the
individual treatment units are shown in Table 6.11 below:
Table
6.11 TKO PTW Treatment Unit Capacities
|
Treatment
Unit
|
No.
of Units
|
Capacity
of Each Unit (m3/s)
|
|
|
|
0.75
1.15
0.60
|
|
Coarse Screens
|
1 duty + 1 standby
|
4.50
|
|
Fine Screens
|
|
1.72
|
|
Grit Removal
|
2 duty
2 duty
|
1.90
1.50
|
6.3.11
Based on flow records
for 1999, 2000 and 2001, the average and daily peak flows to the TKO PTW are
about 75,000 m3/d
and 150,000 m3/d respectively (EEFS
Revised Draft Technical Note No. 2, June 2002)Based on EEFS Final
Report (Table 2-10), the average flow to the TKO PTW for 1999 to 2002 is 72,733m3/d..
6.3.12
Under normal conditions, the
treated effluent is discharged into the HATS Stage I Tunnel System en route to
SCI STW for further treatment and ultimate disposal to sea.
6.3.13
In the event of extreme
conditions, such as breakdown of major equipment that would affect normal
operation of the plant, the excess flows will be directly discharged into the
Tathong Channel via an existing 1,320mm diameter submarine outfall. The capacity of the submarine outfall is
approximately 3.0 m3/s (Feasibility Study for Intensification and
Extension of TKO New Town WP12 (Dec. 1998)).
EPD have raised concerns about the functionality of this submarine
outfall since it is being idled.
According to the advice from Sewage Treatment Division of DSD, the
condition of the submarine outfall would be checked as follow:-
(i)
There is a monthly flushing programme
to check if the outfall is working properly. The present outfall is in good
working condition despite its use has been terminated after the HATS deep
tunnel commissioning in December 2001.
(ii)
Presently, there is a hydrographic
survey conducted every two years to check the outfall condition. The last hydrographic survey conducted was
carried out in June 2002 and its condition is in order.
6.3.14
As the Eastern Channel and Inner
Junk Bay area would be utilised for water sport recreation, the potential
accidental discharge through the sewage overflow at the seawall on the south of
Area 86 development would need to be considered in the water quality study (see
Section 5).
HATS Stage I Tunnel Section
from Tseung Kwan O to Kwun Tong
6.3.15
A drop shaft and tunnel was
constructed as part of the HATS Stage I works to convey the treated effluent
from TKO PTW to SCI STW. The apparent
capacity of the HATS Stage I Tunnel from TKO to Kwun Tong of 4.89 m3/s
may impose a constraint when compared with the capacity of the TKO PTW (c.f.
5.55 m3/s). The apparent
design peak flow capacities of the Stage I Tunnels in accordance with the Final
Report of Further Development of SSDS Stage III/IV and PPFS (October 1999) are
listed in Table
6.12 below:
Table 6.12 HATS Stage I Tunnel System Capacity
|
Tunnel
Link
|
Apparent
Peak Flow Capacity (m3/s)*
|
|
|
4.89
|
|
|
14.81
|
|
To Kwa Wan à SCI STW
|
21.80
|
Notes: * based on Final Report of Further Development of SSDS Stage
III/IV and PPFS.
6.3.16
Based on HATS EEFS Final Report
(Section 2.7.6), there is no capacity constraint with respect to the HATS Stage
I system. Thus, it is confirmed that
the HATS Stage I Tunnel System has adequate hydraulic capacity to handle the
preliminary treated effluent from TKO PTW.
6.3.17
Although the EEFS
Study has confirmed that the HATS Stage I Tunnel Section from TKO to Kwun Tong
has no capacity constraint, it is understood that EPD has a long term plan to
upgrade the TKO PTW to cater for long term development needs and maintaining
sustainable developments in Kowloon and TKOThe existing TKO PTW
occupies part of Area 85. The land to
its south is reserved for the extension of the TKO PTW. The extension area is planned to be used for
upgrading of the TKO PTW so as to allow sewage from Tseung Kwan O to be treated
locally and TKO to be separated from the HATS, for the long term use. Such arrangement is to cater for the long term development needs and
maintaining sustainable developments in Kowloon and Tseung Kwan O..
Introduction
6.4.1
Section 6.2 revealed that the
projected ultimate population for TKO sewerage catchment are 484,318 and
453,318, whilst the ultimate sewage flows are 165,515m3/d and
161,510m3/d, for Baseline and SIA condition respectively. Intuitively, the decreased ADWF (4,005m3/d)
will not cause any adverse impacts on the sewerage infrastructures.
6.4.2
Although there is an overall
reduction in population and flows as a consequence of the proposed development
in TCS, TKL and PSK within TKO catchment, it is noted that there are local
increases of population and flows in Planning Area 66, 68 and 78 (see Table 6.2 and 6.6). These local effects on
the existing and committed sewerage system were assessed with the use of
hydraulic model. The constructed model
is depicted in Figures
6.5, 6.6 and 6.7.
6.4.3
According to the sewerage
records and the proposed works in TKO catchment, there were no existing or
planned sewerage systems to serve the developments at Planning Area 65B, 68 and
78. Sewerage systems connecting these
planning areas to the existing sewerage system are proposed. Well-developed sewerage systems have been
constructed in TKL and thus no proposed sewerage works are proposed under this
SIA except for the GIC cluster in Area 72 (along Road L721).
6.4.4
Improvement works are also
proposed to rectify the sewerage infrastructure identified with hydraulic
inadequacies in the performance assessment.
Proposed Sewerage Systems
for TCS and PSK
6.4.5
Sewerage records and the latest
drawings showing the planned sewerage works within the TKO catchment indicated
that there are no existing nor planned sewerage system to convey the flows
arising from Planning Area 65B, 68 and Pak Shing Kok (Planning Area 78) to the
existing trunk sewerage system along Po Yap Road and Wan Po Road
respectively. Therefore, new sewerage
systems are proposed to discharge the flows to the existing trunk sewers.
6.4.6
Planning Areas 67 and 68 are
located at the most southern part of TCS.
It is proposed to construct a new foul sewerage system comprising 600mm
diameter sewers to convey flows from Planning Areas 67 and 68 to the existing
1,050mm diameter sewers along three newly constructed roads, namely Road L661,
Road L671 and Road L672. The 1,050mm
diameter sewers will then discharge into the existing trunk sewers in Po Yap
Road as shown in Figure 6.8, which also illustrate the
alignments of the proposed sewers.
6.4.7
Planning Area 65B is located
near the Bauhinia Garden and there is no sewerage system to collect the flows
arising from this proposed residential area.
Therefore, it is proposed to construct a new sewerage system of 600mm
diameter along Road L651 and Road L652 and connect to the
existing 1,050mm diameter sewer along Road L661. (See Figure 6.8 for the proposed 600mm
diameter sewer alignment.)
6.4.8
There is an existing 750mm
diameter sewer at the junction of Road L781 and Wan Po Road. A sewerage system with 300mm diameter sewers
along Road L781 is proposed to drain the flows arising from Pak Shing Kok development
into this 750mm diameter sewer. The
proposed alignment is shown in Figure 6.9.
Performance Assessment for
Sewerage System
Introduction
6.4.9
The performance of the existing
and committed sewerage infrastructure was assessed for ultimate scenario incorporating
planning information reflective of the approved OZP condition and also flows
from Port Shelter. Hydraulic model of
the sewerage systems was constructed using the InfoWorks software on the basis
of sewerage record plans collected from DSD, as-built drawings for Contract No.
TK43/96 and Contract No. TK53/01, and details collected on the proposed works
under the Port Shelter SMP and TKO SMP.
The flows of 10,585m3/d from Port Shelter are discharged into
nodes no. V420-10 and V250-10 in the hydraulic model. Sewers of diameter 450mm and above are included in the hydraulic
model. Peak flows are used in the
assessment of hydraulic adequacy of the sewerage system, TKO PTW and HATS Stage
I Tunnel section from TKO to Kwun Tong.
6.4.10
Planning information at Planning
Area level was adopted for the evaluation of sewage flows. The flows were assigned to appropriate
manholes of the hydraulic model as inflows from the respective
developments. The cumulative peak flows
conveyed by the sewerage system were used in the assessment for hydraulic
adequacy.
6.4.11
Information on the existing
sewerage networks is sourced from the Drainage Record Plans obtained from DSD
on 21 August 2002 under this Study.
Baseline
Condition
6.4.12
The performance assessment
results showed that there were some existing sewers identified as hydraulic
inadequate in the model under the ultimate flows. Moreover, it is assessed that some sewers were surcharged due to
backwater effect.
6.4.13
In accordance with the Sewerage
Manual, the long-term goal is to implement sewerage improvement works to
eliminate all surcharged conditions.
The Sewerage Manual recognises the practical constraints for upgrading
all existing sewerage systems to ensure that there will be no surcharge of the sewerage
systems at any time. The Sewerage
Manual states that when some sewers are surcharged but with some freeboard,
improvement of these sewers should not need to be accorded as top priority if
the following is satisfied:
·
A minimum freeboard of 1 m; and
·
A minimum factor of safety
against overflow of 1.15, i.e. overflow will not occur at a flow rate of (1.15
times Peak Flow).
6.4.14
Surcharged sewers measuring a
total length of 655m ranging from 450mm to 1,050mm diameter were identified
under peak flow condition and the details are listed in Appendix 6.2. Under the 1.15 times peak
flow condition, the total length of surcharged sewers is 2,052m with a similar
range of pipe sizes. Table 6.13 and 6.14 summarize the pipe size and length of the identified surcharged
sewers.
Table 6.13 Summary of Surcharged
Sewers under Peak Flows at Baseline Condition
|
Pipe Dia. (mm)
|
Length (m)
|
|
450
|
308
|
|
525
|
96
|
|
600
|
55
|
|
675
|
164
|
|
1,050
|
32
|
|
Total
|
655
|
Table 6.14 Summary of
Surcharged Sewers under 1.15 x Peak Flows at Baseline Condition
|
Pipe Dia. (mm)
|
Length (m)
|
|
450
|
596
|
|
525
|
569
|
|
600
|
388
|
|
675
|
305
|
|
900
|
15
|
|
1,050
|
32
|
|
1,650
|
147
|
|
Total
|
2,052
|
6.4.15
There are no risks of overflow
at these surcharged sewers under the different flow conditions as the available
freeboards are greater than 1 m. The
surcharged sewers under peak flow and 1.15 times peak flow conditions are
illustrated in Figures
6.10, 6.11 and 6.12. See Appendix 6.3 for details
of the performance assessment results for the existing and committed sewerage
systems.
6.4.16
Some 302m of existing sewers
ranging from 450mm to 1,650mm diameter were identified with adverse
gradients. It is understood that some
areas of TKO are suffering from ground settlement. The table 6.15 below is a listing of the sewers with
backfall:
Table
6.15 Existing Sewers with Adverse
Gradient
|
Ref. No. in Fig. 6.4 to 6.6
|
Link
Ref.
|
D/S
Node
|
Location
|
Length
(m)
|
Pipe Dia. (mm)
|
U/S I.L. (mPD)
|
D/S I.L. (mPD)
|
|
1
|
18_39.1
|
18_42
|
Within TKO Industrial
Estate, along Chun Choi Street near Chun Ying Street
|
42
|
900
|
-0.530
|
-0.340
|
|
2
|
4_33.1*
|
2_81
|
Along Po Fung Road near Po
Lam Road North
|
60
|
675
|
1.800
|
1.810
|
|
3
|
10_72.1
|
10_73
|
Along Po Yap Road near Wan
Po Road
|
69
|
1,650
|
-1.840
|
-1.790
|
|
4
|
30_36.1
|
30_39
|
In Choi Ming Court Estate
Road to Road P2
|
15
|
900
|
2.790
|
3.000
|
|
5
|
30_42.1
|
30_45
|
In Road P2 near Tong Ming
Court
|
21
|
900
|
2.760
|
2.840
|
|
6
|
V20_20.1*
|
18_51
|
At the junction of Chun
Kwong Street and Chun Ying Street
|
40
|
450
|
-0.370
|
-0.090
|
|
7
|
V220_100.1*
|
V220_110
|
Near Nan Fung Plaza Tower 3
|
55
|
450
|
1.050
|
1.140
|
Remark: Sewer
sections marked with *are revealed to be surcharged in the hydraulic models in both “Peak Flow” and “1.15x
Peak Flow” scenarios of SIA condition (Appendix 6.3 refers). The remaining sections are not surcharged
and thus, not recommended to be upgraded in term of cost-effectiveness. Please refer to Para. 6.5.4 for justifications.
Sewerage Impact
Assessment
Condition
6.4.17
It is noted that similar
performance assessment results as under the Baseline Condition are identified
for the SIA Condition and the details are listed in Appendix 6.23. However, the surcharged
condition is improved due to the reduced population, especially in TKL. Therefore, it is assessed that less sewers
are surcharged as compared with the Baseline Condition under the 1.15 x Peak
Flow Scenario. Tables 6.16 and
6.17 present summaries of the surcharged sewers under
SIA.
Table 6.16 Summary of Surcharged Sewers at Peak Flow
under SIA Condition
|
Pipe Dia. (mm)
|
Length (m)
|
|
450
|
343
|
|
525
|
96
|
|
600
|
55
|
|
675
|
164
|
|
1,050
|
32
|
|
Total
|
690
|
Table 6.17 Summary of Surcharged Sewers at 1.15 x Peak
Flow under SIA Condition
|
Pipe Dia. (mm)
|
Length (m)
|
|
450
|
486
|
|
525
|
569
|
|
600
|
388
|
|
675
|
305
|
|
1,050
|
32
|
|
Total
|
1,780
|
6.4.18
Figures 6.13, 6.14 and 6.15 show the performance assessment of the existing and proposed
sewerage system under SIA Condition.
Checking of the
Hydraulic Model
6.4.19
In
order to verify the accuracy of the hydraulic performance
assessment, a comparison on the planning parameters and model results of the hydraulic
model between this study and a previous similar study, Feasibility Study for
Intensification and Extension of the TKO New Town has been carried out. A Technical Note on the comparison of which a
copy is attached in Appendix 6.6, has been prepared and submitted to EPD. The comparison reveals that there is a good
agreement in the hydraulic
model results from the two studies and demonstrated that the hydraulic model
under this Study has achieved an acceptable level of accuracy.
TKO Preliminary Treatment
Works
6.4.20
As mentioned earlier,
the hydraulic model constructed was based on DSD’s drainage record obtained in
2002. It was realized that there are differences in invert levels of node nos.
10_69, 2_48 and 2_63 between the hydraulic model input data and DSD’s drainage
records (2003 version): The capacity of the
TKO PTW is 5.55 m3/s
after completion of the upgrading works in 1996. The total ultimate catchment flow under the baseline condition
(based on current OZP) is estimated to be 4.58 m3/s. It is concluded that the TKO PTW has
adequate capacity to cater for the total flows generated by the TKO sewerage
catchment in ultimate scenario.
|
Nodes
|
2002
|
2003
|
|
2_48
|
5.10
|
5.11
|
|
2_63
|
2.75
|
2.76
|
|
10_69
|
-1.657
|
-1.71
|
It is noted that the difference in drainage record
is relatively minor and would not result in changes to the findings of
assessment and would not vary the extent of the surcharged sewers under both
Peak and 1.15x Peak conditions and hence variation to the extent of the
recommended sewerage upgrading works would not be resulted. Nevertheless, the
latest situation including the population figures and pipe asset data should be
taken into account in the detailed design stage of the recommended upgrading
works.
TKO
Preliminary Treatment Works
6.4.21
The capacity of the TKO PTW is
5.55 m3/s
after completion of the upgrading works in 1996. The total ultimate catchment flow under the
baseline condition (based on current OZP) is estimated to be 4.58
m3/s. It is concluded that the TKO PTW has adequate capacity to cater
for the total flows generated by the TKO sewerage catchment in
ultimate scenario.
6.4.22
The total flows arriving at the
TKO PTW, with the proposed further development at TCS, TKL and PSK, are
projected to be 4.47m3/s, which is less than that of Baseline
Condition. Therefore, TKO PTW is
capable of handling the projected ultimate flows (c.f. capacity = 5.5m3/s).
HATS Stage I Tunnel Section
from Tseung Kwan O to Kwun Tong
6.4.23
The current assessment of the
HATS Stage I Tunnel section from TKO to Kwun Tong is based on a design capacity
of 4.89 m3/s in accordance with the Final Report of the SSDS Stage
III/IV and PPFS. It is understood from
the Final Report of HATS EEFS that there is no capacity constraint of the HATS
Stage I Tunnel System.
6.4.24
The hydraulic adequacy of the
HATS Stage I Tunnel section from TKO to Kwun Tong was assessed on the basis of
the projected sewage flows arriving at the TKO PTW. It is understood that under normal conditions, the treated
effluent from the PTW will be discharged to the tunnels for transfer to Kwun
Tong en route to SCI STW for further treatment followed by final disposal to
sea.
6.4.25
The peak flow capacity of the
tunnel between TKO PTW and Kwun Tong Sewage Pumping Station (SPS) is 4.89 m3/s. The system capacity has already been
confirmed by the EEFS to be adequate.
This would also
be adequate to convey the projected treated effluent from TKO PTW in
ultimate scenario of 4.58 m3/s under Baseline Condition.
6.4.26
The estimated flows under SIA
Condition are less than that under the Baseline Condition, it is therefore
concluded that no further impacts to the overall performance of the HATS Stage
I Tunnel System would be anticipated under SIA Condition.
Scope of Works
6.5.1
There are new sewerage systems
proposed for the further development at TCS and PSK. The total length of the
proposed new 600mm and 300mm sewers are 1,203m and 1,081m at TCS and PSK
respectively. The proposed sewerage
works for TCS and PSK will be covered by the infrastructure provision by CEDD
under the TCS (between 10/2007 and 11/2009) and psk (between 9/2008 and 7/2010) construction packages.
6.5.2
The SIA of Section 6.4 has
identified sewers measuring a total length of 690m in the existing and
committed sewerage systems which would be subjected to surcharge or suffering
from adverse gradients under peak flow condition.
6.5.3
In accordance with the finding
from hydraulic model, two sections (links ref. 4_33.1, V20_20.1 and
V220_100.1) of the sewers with adverse gradient (as shown in Table 6.15.3)
are found to be surcharged. We would
recommend to rectifyupgrade these two three sections
of sewers, to rectify
the surcharge problems.
6.5.4
For the sewer sections with links ref. 18_39.1, 10_72.1,
30_36.1 and 30_42.1 presented in Table 6.15, the problem is relatively minor
without any surcharge revealed from the hydraulic model. It should also be noted that upgrading of
these sections of sewers will require lowering of the invert levels of the
downstream sewerage networks in order to cope with the upgrading works. Therefore, having , whereas it is considered it is not worthy to
upgrade the remaining ones at shown in Table 5.3 because the problem is very
minor. The conditions of sewers could be monitored by DSD during their
maintenance works. Should the conditions become worse, the sewers could be
rectified by DSD in future.taken the
cost-effectiveness of the works into consideration, it is not recommended to
upgrade these adverse gradient sewers
without surcharge problem. Instead,
conditions of these sewers should be monitored by DSD during their routine maintenance works. Should the conditions become worse, the sewers
could be rectified by DSD in future.
6.5.5
Based on the findings, there
should be no major hydraulic problem in the sewerage network and treatment
works. Urgent rectification work or interim measure is not required. However, it is recommended to upgrade
relevant sections of the sewers to relieve the projected hydraulic bottlenecks
and those pipes with adverse gradients in the sewerage systems in future. The recommended sewerage improvement works
has a total length of 1,563m and are shown in Figures 6.16, 6.17, 6.18
and listed in Appendix
6.4.
Table 6.18 Summary of
Recommended Sewerage Upgrading Works
|
Existing Pipe Size (mm)
|
Upgrading Pipe Size (mm)
|
Pipe Length
(m)
|
|
450
|
600
|
599
|
|
525
|
700
|
354
|
|
525
|
900
|
96
|
|
600
|
900
|
193
|
|
675
|
900
|
305
|
|
1,050
|
1,500
|
16
|
|
Total
|
1,563
|
Remark : By
Implementation of the above upgrading works, the bottlenecked sewers will be
removed and thus, there is no need to upgrade all the problematic sewers
presented in earlier tTables 6.17.
6.5.6
The hydraulic modelling results of the sewerage
network with the provision of recommended upgrading works are presented in
Appendix 6.3. It should be noted that
the predicted hydraulic performance of the upgraded network is satisfactory
without sign of surcharge.
6.5.7
However, it should be noted that
the available free boards in the surcharged manholes are all within the
tolerable condition as stated in Section 5.1.1 of Sewerage Manual Part 1. There
should be no urgency in the implementation of the above upgrading works. It is
suggested that such upgrading works could be carried out when opportunity arises, e.g.
in conjunction with road works and/or nearby sewerage projects. As new road
works and sewerage projects are not envisaged in these areas in the near
future, these upgrading works are recommended to be carried out when such
opportunity arises in the long term.
6.5.8
It should be noted that, during
implementation of the upgrading works in future, adequate interim measures,
such as temporary flow diversion, should be provided in order not to disrupt
the operation of the sewerage system.
Cost
Estimates
6.5.9
The total capital cost
associated with the construction of new sewers at TCS and PSK is $12M whilst
that for the recommended sewerage upgrading works is $9M. Appendix 6.5 shows the details of the
capital cost estimates for
the recommended works.
6.6.1
The performance of the existing
and committed sewerage infrastructure under full development condition for the
ultimate scenario was assessed and formed the Baseline Condition. The development projections for 2016 studied
is reflective of the approved OZP condition.
6.6.2
The SIA Condition takes into
account of the recommended development proposal for TKO sewerage catchment
which involves TCS, TKL and PSK.
6.6.3
The adopted unit flow factors
are generally based on the recommendations of the Sewerage Manual Part 1 (DSD,
1995) and are in line with the EEFS.
The total flows generated by the TKO sewerage catchment are estimated to
be 165,515m3/d and 161,510m3/d for Baseline and SIA
Conditions respectively.
6.6.4
The recommended peaking factors
are based on the Sewerage Manual. The
estimated peak flow is 4.58m3/s for Baseline Condition whilst peak
flow of 4.47m3/s is estimated under SIA Condition. These peak flows
are used in the hydraulic assessment of the existing and committed sewerage
systems, TKO PTW and the HATS Stage I Tunnel section from TKO to Kwun Tong.
6.6.5
The performance assessment
results have identified surcharged sewers measuring a total length of 690m with
diameters ranging from 450mm to 1,050mm under the SIA peak flow condition. Under 1.15 times of the SIA peak flow
condition, the total length of surcharged sewers is 1,780m with a similar range
of pipe sizes. The analyses indicated
that there are no risks of overflow under the various flow conditions as the
available freeboards exceed 1m. Works
to improve these surcharged sewers are not accorded as top priority in
accordance with the Sewerage Manual. In
addition, some 302m of sewers were identified with adverse gradients.
6.6.6
Whilst there is an overall
reduction in population and flows as a consequence of the reduction of development density in further
development in TCS, TKL and PSK within TKO catchment, it is noted that there
are local increases of population and flows in Planning Area 66, 68 and
78. The performance assessment results
showed that these local effects did not cause any additional adverse impacts on
the sewerage system.
6.6.7
The TKO PTW was assessed to be
adequate to convey the total ultimate catchment flows under both Baseline and
SIA Conditions under this Study. In accordance with the EEFS Final Report, the
HATS Stage I Tunnel section from TKO to Kwun Tong was assessed to be adequate
to handle the projected flows under both Baseline and SIA Conditions.
6.6.8
According to the sewerage
records and the proposed works in TKO catchment, there were no existing or
planned sewerage systems to serve the developments at Planning Area 65B, 68 and
Pak Shing Kok. New sewers of 300mm and
600mm diameter with total lengths of approximately 1,203m and 1,081m are
proposed to connect these areas to the existing sewerage system. The cost for the proposed new sewers is
about $12M.
6.6.9
Sewerage improvement works to
the existing and committed sewerage infrastructure were recommended when opportunity arises, e.g. in
conjunction with road works and/or nearby sewerage projects, in future. It is proposed to upgrade
the existing sewers with pipes of diameters ranging from 450mm to 1,050mm in
order to relieve the identified hydraulic inadequacies and surcharged
condition. The capital cost for the
upgrading works is about $9M. The
proposed upgrading works are tabulated in Table 6.19 below:
Table 6.19 Summary of Recommended Sewerage Upgrading
Works
|
Existing Pipe Size (mm)
|
Upgrading Pipe Size (mm)
|
Pipe Length
(m)
|
|
450
|
600
|
599
|
|
525
|
700
|
354
|
|
525
|
900
|
96
|
|
600
|
900
|
193
|
|
675
|
900
|
305
|
|
1,050
|
1,500
|
16
|
|
Total
|
1,563
|
6.6.10
The Sewerage Master Plan for TKO
is presented in Figure
6.19 for reference.