|
Contents |
Chapter Title Page
Figures
Figure 6.1 Layout
Plan of WKCD and the Surrounding Development
Figure 6.2 Existing
Sewerage System
Figure 6.3 Proposed
Sewerage Sub-catchment Plan
Figure 6.4 Proposed
Sewerage System
Figure 6.5 Access to Proposed Sewerage System
Figure 6.7 Proposed
Sewerage Layout Plan (Key Plan)
Figure 6.8 Proposed
Sewerage Layout Plan (Sheet 1 of 11)
Figure 6.9 Proposed
Sewerage Layout Plan (Sheet 2 of 11)
Figure 6.10 Proposed
Sewerage Layout Plan (Sheet 3 of 11)
Figure 6.11 Proposed
Sewerage Layout Plan (Sheet 4 of 11)
Figure 6.12 Proposed
Sewerage Layout Plan (Sheet 5 of 11)
Figure 6.13 Proposed
Sewerage Layout Plan (Sheet 6 of 11)
Figure 6.14 Proposed
Sewerage Layout Plan (Sheet 7 of 11)
Figure 6.15 Proposed
Sewerage Layout Plan (Sheet 8 of 11)
Figure 6.16 Proposed
Sewerage Layout Plan (Sheet 9 of 11)
Figure 6.17 Proposed
Sewerage Layout Plan (Sheet 10 of 11)
Figure 6.18 Proposed
Sewerage Layout Plan (Sheet 11 of 11)
Figure 6.19 Proposed
Sewerage System Manhole Schedule
Appendices
Appendix 6.1 Sewerage
Catchment Plan for the sewer at Canton Road
Appendix 6.2 Hydraulic
Assessment for Existing and Proposed Sewerage System
Appendix 6.3 Breakdown
of Sewage Flow Estimation at Upstream of Canton Road
This section presents assessment of the sewage discharge impact to the
existing sewerage system during the operation phase of the proposed WKCD
Development in accordance with section 3.4.7 of the Study Brief (ESB-237/2011).
The necessary mitigation measures and proposal for sewage discharge have been
recommended with a principle of having no adverse impact to the existing
drainage system.
6.2 Sewerage and Sewage Treatment Legislations, Standards and Guidelines
The sewage flow discharge from the proposed WKCD development is based on
the following standards, guidelines and reference for the sewerage and sewage
treatment design:
¡
Sewerage
Manual published by Drainage Services Department (DSD);
¡
Guidelines
for Estimating Sewage Flows for Sewerage Infrastructure Planning Version 1.0 by
EPD;
¡
North
and South Kowloon Sewerage Master Plan (SMP), April 1993;
¡
Review
of West Kowloon and Tsuen Wan Sewerage Master Plans –
Feasibility Study (WK&TW SMP Review) Technical Note No. 3 (TN3) –
Population and Land Uses, November 2007; and
¡
Review
of
6.3.1
Overall
Catchment
The proposed WKCD is located at West Kowloon Reclamation on the northern
shore of
¡
¡
West
Kowloon Terminus (WKT) and the associated development (Site A and B);
¡
Austin
Station and the associated developments at MTRC Kowloon Southern Link (Site C
and D);
¡
Government,
Institution and Community (GIC) Facilities at the north of Kowloon Station; and
¡
6.3.2
Existing
Sewerage Condition
With reference to the WK&TW SMP Review Report, the WKCD will be served
by DSD’s Sham Shui Po Sewage Screening Plant (SSP
SSP). The screened sewage is subsequently conveyed to Cheung Sha Wan Sewage Screening Plant and then discharged to the Stonecutter
Island Sewage Treatment Works (SCISTW) for further treatment and ultimate
disposal.
Originally there were two existing sewerage manholes located at the
southern side of
With reference to the sewerage design drawings for Contract 810B West
Kowloon Terminus Station South, the original sewerage system along Austin Road
West and Lin Cheung Road will be upgraded to a new sewer system with size
ranged from 450mm to 900mm in diameter and this sewer system is mainly serving
the WKCD, Kowloon Station (including the topside development) and the West
Kowloon Terminus development. The new
900mm diameter sewer is further connected to an existing 1350mm diameter trunk
sewer located at the eastern boundary of Site B of the West Kowloon Terminus
development and runs in north direction towards DSD’s SSP SSP
within the
Furthermore, there is also an existing sewer with size ranging from
200mm to 750mm in diameter running northward along
6.4.1
Background
According to the WK&TW SMP Review Final Report and the
relevant supplementary information from EPD, the average dry weather flow
(ADWF) and the peak flow allowed in the WK&TW SMP Review Study for the WKCD
are 68.17 L/s and 210 L/s respectively.
With reference to Clause 8.5.4 of the final WK&TW SMP report, no
sewerage improvement works are required based on the allowed sewage flows.
Under the development plan of the proposed WKCD, the estimated ADWF and peak
flow from WKCD are 52.50 L/s and 157.50 L/s respectively (refer to Section 6.5.2 for details of calculated sewage flow) which are lower than those allowed
in the WK&TW SMP Review.
Based on the above information, the trunk sewers in
The layout of the existing sewerage is shown on Figure 6.2.
6.4.2
Collected
Information
The following assessments and documents were collected and reviewed to
identify the current sewerage master planning in West Kowloon Area and the
sewerage provision to the infrastructure works in vicinity of the site area:
¡
North
and South Kowloon Sewerage Master Plan (SMP), April 1993;
¡
Review
of
¡
Review
of
¡
Express
Rail Link – Detailed Design for
¡
Express
Rail Link – Detailed Design for
¡
Drainage
Record Plans from Drainage Services Department (DSD); and
¡
Sewerage
design drawings for Contract 810B West Kowloon Terminus Station South.
6.4.3 Design Standard Guideline
This assessment has been prepared in according with the following
documents.
EPD’s “Guidelines for Estimating Sewage Flows for Sewage Infrastructure
Planning Version 1.0 (Report No.: EPD/TP1/05” (GESF) – The recommended unit
flow factors and peaking factors have been adopted to estimate the sewage
generated from the WKCD.
According to GESF, there is no recommendation on visitor’s unit flow
factor for art and cultural venues and government institutions. Therefore, the
unit flow factor for visitors of cultural venues and government institutions is
made reference to Table 3-4 of
"Wastewater Engineering Treatment and Reuse" published by Matcalf & Eddy.
For the roughness of sewers, the recommended value in DSD’s “Sewerage
Design Manuel Part 1” has been adopted.
6.4.4 Design Parameters
Based on the above reference documents, the unit flow factors for
different types of population as shown in Table 6.1 have been used in calculating the sewerage flow
from the WKCD.
Table 6.1: Recommended Unit Flow Factors
|
Development
Type |
Unit |
Unit Flow Factor (m3/day) |
|
Domestic1 |
|
|
|
Public Rental |
person |
0.19 |
|
Residential R1 |
person |
0.19 |
|
Residential R2 |
person |
0.27 |
|
Residential R3 |
person |
0.37 |
|
Residential R4 |
person |
0.37 |
|
Temporary and non-domestic |
person |
0.15 |
|
Commercial Employment1 |
|
|
|
Job Type J2 |
employee |
0.33 |
|
Job Type J3 |
employee |
0.18 |
|
Job Type J4 |
employee |
0.28 |
|
Job Type J5 |
employee |
0.08 |
|
Job Type J6 |
employee |
0.08 |
|
Job Type J7 |
employee |
0.08 |
|
Job Type J8 |
employee |
0.08 |
|
Job Type J9 |
employee |
0.23 |
|
Job Type J10 |
employee |
1.58 |
|
Job Type J11 |
employee |
0.28 |
|
Job Type J12 |
employee |
0.08 |
|
School1 |
|
|
|
Primary, Secondary & Tertiary |
student |
0.04 |
|
Others |
|
|
|
Visitor2 |
person |
0.015 |
Notes:
1. The unit
flow factors for domestic, commercial employment and school are according to
Table T-1 and Table T-2 of GESF of EPD.
2. The unit flow
factor for “Visitor” is according to Table 3-4 of "Wastewater Engineering
Treatment and Reuse" published by Matcalf &
Eddy
The peaking factors given in Table T-5 in EPD’s GESF will be adopted for
the peak flow calculation. The peaking factors are listed in Table 6.2.
|
Population Range for Sewers |
Peaking Factor (including storm water allowance) for
facility with existing upstream sewerage |
Peaking Factor (excluding storm water allowance) for
facility with new upstream sewerage |
|
<1000 |
8 |
6 |
|
1000 – 5000 |
6 |
5 |
|
5000 – 10000 |
5 |
4 |
|
10000 – 50000 |
4 |
3 |
|
>50000 |
Max (7.3 / N0.15, 2.4) |
Max (6 / N0.175, 1.6) |
|
Note: N is the contributing population in thousands. According to Clause 12.1 of EPD’s GESF, the contributing population is defined below: Contribution Population = Calculated total average flow (m3/day) / 0.27 (m3/person/day) |
||
The Colebrook White’s equation has been adopted for hydraulic analysis
of the pipe system. A roughness
coefficient, Ks, of 3.0mm for concrete pipe has been adopted in accordance with
DSD’s “Sewerage Design Manuel Part 1”.
6.4.5
Assumptions
The following assumptions have been made in the assessment of the
sewerage impact assessment arising from the development of the WKCD.
¡
The
sewage flows from the existing or proposed developments in the southern portion
of
¡
The
sewage generated for Kowloon Station is currently discharged into three
existing sewers at Austin Road West, Nga Cheung Road
and Jordan Road as shown on Figure 6.2. However, the actual sewage flow
discharging to each of the sewers is not available. Therefore, it is assumed
that all the sewage generated from Kowloon Station is discharged into the
upgraded sewer at
6.5 Evaluation and Assessment of Sewerage and Sewage Treatment Implications
The Development Plan for WKCD proposes a number of Core Art and Cultural
Facilities (CACF) combined with commercial, catering and retail facilities. A
park is also proposed to be located at the south western portion of the WKCD.
Under the development plan, the total population of WKCD is about 120,000.
According to the development plan of WKCD, the total estimated ADWF and
peak flow from WKCD are 52.50 L/s and 157.50 L/s respectively. The population of
WKCD and estimated ADWF are summarized in Table 6.3.
Table 6.3: Population and Sewage Flow Estimation for WKCD
|
Development Type |
Population2 |
Unit Flow Factor |
Sewage Flow ADWF (m3/day) |
||
|
Unit |
Type |
UFF (m3/day) |
|||
|
Domestic |
|
|
|
|
|
|
4,051 |
Person |
R1 |
0.19 |
769.69 |
|
|
Commercial |
|
|
|
|
|
|
Retail, Dining and Entertainment |
4,441 |
Employee |
J4 |
0.28 |
1243.48 |
|
Core Arts and Cultural Facilities |
1,761 |
Employee |
J6 |
0.08 |
140.88 |
|
Other Arts and Cultural Facilities |
758 |
Employee |
J6 |
0.08 |
60.64 |
|
Government, Institution and Community |
0 |
Employee |
J12 |
0.08 |
0.00 |
|
Office |
4,579 |
Employee |
J6 |
0.08 |
366.32 |
|
Residential |
42 |
Employee |
J6 |
0.08 |
3.36 |
|
Hotel |
267 |
Employee1 |
J10 |
1.58 |
421.86 |
|
1,204 |
Guest1 |
|
0 |
0 |
|
|
Visitor |
101,985 |
Person |
- |
0.015 |
1529.78 |
|
Others |
0 |
Employee |
J12 |
0.08 |
0.00 |
|
|
Total |
4536.01 |
|||
|
52.50 (l/s) |
|||||
|
Notes: 1. UFF of Hotel Guest has been counted in the UFF of Hotel Employee. 2. The population will be subject to review. 3. Based on the above estimated ADWF of WKCD, the contribution population of WKCD is 16,800(4,536.01/0.27=16,800). ). The peaking factor is 3.0 according to Table T-5 of EPD’s GESF. |
|||||
6.5.3
Proposed Sewerage System
The WKCD is proposed to be divided into 8 numbers of sewerage sub-catchments, S1 to S8. The proposed sewerage sub-catchment is presented on Figure 6.3 and the proposed sewer for the WKCD is also shown on Figure 6.4. The sewage flow generated from each sub-catchment is summarized in Table 6.4.
Table 6.4: Summary of Sewage Flow for Sub-catchment
|
Sewerage Sub-catchment |
ADWF (L/s) |
Peak Flow (L/s) |
|
S1 |
6.69 |
33.44 |
|
S2 |
6.89 |
34.43 |
|
S3 |
7.11 |
35.57 |
|
S4 |
5.86 |
29.32 |
|
S5 |
4.73 |
23.64 |
|
S6 |
6.53 |
32.65 |
|
S7 |
12.52 |
62.58 |
|
S8 |
1.93 |
9.63 |
The ground level of the road in the Park is ranging from +5.0 to +6.0 mPD which is lower than the road level of
The sewage generated from sub-catchments S2 and S3 are proposed to be
discharged to the new sewerage manholes F1.1 and F1.2 respectively, where the
flow will continue to the existing sewer on the southern side of
For the other 4 sub-catchments S4 to S7, the sewage from these
sub-catchments is proposed to be discharged to the new sewerage manholes (F1.5
to F1.8) at
Once the sewage from S1 to S7 is conveyed to the site boundary at
The sub-catchment S8 is for Parcel 1 (Xiqu) at
the east of WKCD. Sewage from this sub-catchment is proposed to be discharged
to the existing sewer at
For the buildings in sub-catchments S2 to S7, it is possible to
discharge the sewage from the buildings above podium level to the new sewerage
manholes through gravity pipes and only the sewage generated from buildings is
discharged to the new sewerage manholes through pumping facilities for
minimising the size of pump sumps within the basement. The design of the
sewerage system for the building and within the basement boundary will be
considered in the detailed design stage.
The principal invert levels of the proposed sewers are provided Figure
6.7 to 6.19.
As requested by DSD, the gravity sewers F2.1 to 2.14, pump sump P1 and
associated rising main to the existing manhole No.
FMH4028437 will be maintained by
6.5.4
Sewerage Impact Assessment
Impact to Existing 1350mm Truck Sewer
Based on the SIA reports of XRL SIA and XRL SIB, the sewage flow from
different catchments at the area under future condition are summarized in Table 6.5.
Table 6.5: Sewage Flow from Different Catchments discharged to the 1350mm Trunk Sewer
|
Catchment |
Sewage Flow (ADWF) (L/s) |
|
Site A (Topside Development) |
57.70 |
|
Site A (WKT) |
39.34 (Peak Flow) |
|
Site B |
29.60 (Peak Flow) |
|
Site C & D |
36.80 |
|
|
166.21 |
|
GIC |
0.34 |
|
HKGGA |
5.34 |
|
WKCD |
58.53 |
|
Total Sewage Flow (ADWF) (L/s) |
393.86 |
|
Peaking Factor |
3.64 |
|
|
1251.65 |
|
Note: The sewage flows are based on the SIA Report of XRL SIA and XRL SIB |
|
According to the SIA report of XRL SIB, the sewage from the above
catchments including the WKCD will be discharged to an existing trunk sewer
(1350mm diameter sewer) at the east of Site B.
The capacity of the existing 1350mm diameter sewer is 2118 L/s and the
utilization will be around 58%.
Based on the current development schedule of the WKCD and the proposed
sewerage system, the ADWF discharged to the existing 1350mm trunk sewer from
the WKCD is 4369.61 m3/day (50.57 l/s) (sewage from sub-catchment S1
to S7).
The updated ADWF (50.57 l/s) from WKCD is
smaller than that adopted in the SIA Reports of XRL SIA and XRL SIB. The peak
sewage flow discharged to the 1350mm diameter truck sewer is also reduced
accordingly. Therefore, it is
considered that the development of the WKCD will have no adverse impact to the
existing 1350mm trunk sewer.
Impact
to the sewer along
The sewage generated from sewerage sub-catchments S1 to S7 are proposed
to be discharged to the existing 1350mm diameter trunk sewer through the branch
sewer with sizes ranging from 750mm to 900mm along
A hydraulic assessment of the branch sewer has been conducted to assess
the sewerage impact on this branch sewer arising from the development of the
WKCD. Based on the hydraulic assessment, the flow capacity of the branch sewer
is more than 483 L/s and the peak sewage flow discharge to the branch sewer is
about 346.86l/s and the maximum utilization of this branch sewer is about 71.74%.
The branch sewer has sufficient flow capacity to cater for the sewage generated
from the WKCD. The details of the hydraulic assessment are presented in Appendix 6.2.
Impact to the sewer along
The sewage generated from the sewerage sub-catchment S8 is proposed to
be discharged to the existing sewer at
A hydraulic assessment has been conducted for assessing the sewerage
impact on the existing sewer at
The ADWF from sub-catchment S8 is 1.93 L/s (166.40m3/day). The
total peak sewage flow discharged to this existing sewer will become 301.70 L/s
which is smaller than the minimum flow capacity of the
existing sewer. The utilization of the existing sewer will become approximately
94.1% (only increase by approximately 1.8%). Therefore, it is considered that
the impact to the sewer is negligible.
Based on the above, the existing sewers have sufficient flow capacity to
cater for the sewage flow generated from the proposed development of WKCD and
no upgrading works to the existing sewer is required. Also, according to
WK&TW SMP Review Report and the information provided by EPD, the sewerage
facilities in West Kowloon has sufficient capacity to cater for the sewage from
WKCD.
6.5.5 Emergency Discharge
As discussed above, all the sewage generated from the proposed development would be discharged to the public sewer and treated by public treatment facilities before ultimate disposal. Also, the development of WKCD has been taken into account in the WK&TW SMP Review Study and the treatment facilities have adequate capacity to cater for the proposed WKCD development according to the WK&TW SMP Review Report.
For the proposed pump sumps, twin rising mains will be provided to ensure continuous operation of pumping when one of the mains is damaged or under maintenance. Standby pumps and electricity supplies will also be provided to ensure the operation can still be maintained during maintenance or mechanical failure. By adopting proper measures, emergency discharging of sewage to watercourse is considered as very unlikely.
InfoWorks CS version 8.0 was adopted for the purpose of hydraulic modelling. A hydraulic model network has been adopted to assess the capacity of the proposed sewer and existing sewer in the vicinity of WKCD.
The InfoWorks network for sewerage assessment is shown on Figure 6.6. The following boundary conditions shown in Table 6.6 have been obtained from EPD and adopted in the hydraulic model for assessment.
Table 6.6: Boundary Conditions for Hydraulic Model
|
Location |
ADWF (L/s) |
Max Water Level (mPD) |
|
Kowloon Station’s discharge point (Node FMH4028439) |
38.28 |
- |
|
Downstream of (Node Outfall 1) |
- |
0.194 |
|
Downstream of (Node Outfall 2) |
- |
3.138 |
Inflows for each sub-catchment were assigned to the proposed discharge points for the hydraulic analysis. The peaking factor of 3 for WKCD has been adopted as the global peaking for the whole network. The summary of the model result is shown in Table 6.7.
Table 6.7: Summary of Hydraulic Model Results
|
Node ID |
Ground Level (mPD) |
Maximum Water Level (mPD) |
Freeboard (m) |
|
F1.4 |
7.3 |
1.737 |
5.563 |
|
F1.10 |
7.3 |
1.239 |
6.061 |
|
F3.1 |
5 |
3.851 |
1.149 |
|
P1 |
7.67 |
1.149 |
6.521 |
|
P5 |
5.68 |
0.605 |
5.075 |
|
FMH4028439 |
8.19 |
1.185 |
7.005 |
|
FMH4002142 |
5 |
3.339 |
1.661 |
Based on the model results, all
the sewers have sufficient capacity to cater for the designed flow with free
broad more than 1m. Therefore, it is considered that there should be no adverse
sewerage impact to the existing sewerage system.
As discussed in Section 6.5, the proposed WKCD has been
taken into account in the WK&TW SMP Review. Based on the above assessment,
the sewage flow generated from the proposed WKCD is smaller than the flow
allowed in the WK&TW SMP Review Study and the sewerage facilities are adequate
for the proposed development. Therefore, no new proposed improvement work to
existing sewerage system and treatment facilities in
Furthermore, the assessment has identified that the proposed WKCD will not cause adverse impact to the local sewerage network, which should have sufficient capacity to cater for the sewage flow generated from the proposed WKCD. Therefore, no mitigation measures and upgrading works to the existing local sewer is required for the proposed development. Recommendations for the design, operation and maintenance of the sewerage system are provided in the following sections.
6.7.1 Design, Operation and Maintenance Requirements
6.7.1.1
General
Requirements
The design of the sewerage system should
follow the guidelines stipulated in:
¡
Stormwater
Drainage Manual by DSD;
¡
Sewerage
Manual Part 1 & Part 2 by DSD;
¡
Drainage
Services Department Standards Drawings; and
¡
Structures
Design Manual for Highways and Railways by Highways Department.
The detailed design of the proposed sewerage
system should be circulated to DSD, EPD and other relevant parties for comment
during planning and detailed design stage to ensure acceptance by relevant parties.
Access for plant, equipment and personnel for maintenance of the works should
be adequately provided. A plan showing the maintenance access to the proposed
sewers has been provided in Figure 6.5.
As discussed between DSD and WKCDA, the maintenance responsibilities for
the above proposed sewerage system, include gravity sewers, rising mains and
pumping facilities, will be discussed and agreed in the detailed design stage.
6.7.1.2
Gravity Sewers
The design of gravity sewers should be according
to the guidelines stipulated in Sewerage Manual Part 1. The general
requirements are summarized below:
¡
Pipe
size: The minimum pipe size of gravity sewer is 225mm in diameter.
¡
Capacity:
The gravity sewer should be designed to avoid under surcharge condition. 1m
freeboard should be provided if surcharge condition cannot be avoided.
¡
Flow
velocity: The flow velocity should be not less than 1m/s under full bore flow
for self-cleansing purpose. The maximum velocity should be limited to 3m/s.
¡
Alignment:
The alignment of the proposed sewer should be reviewed to avoid conflicting
with existing utilities and affecting traffic flow as far as possible.
¡
Hydraulic
Design: The detailed hydraulic design should follow the guidelines provided
under Section 5.2 of Sewerage Manual Part 1.
¡
Pipe
Material: Selection of pipe material shall be based on its suitability for the
proposed application. The selection process includes an evaluation of the
possible conditions to which the pipes may be exposed in order to specify the
appropriate material and installation requirements for the specific
application.
¡
Pipe
Joints: In order to accommodate differential settlement that may occur between
sewers and adjacent structures (including manholes), two flexible joints shall
be provided in accordance with the latest amendment of General Specification
for Civil Engineering Works 2006 Edition Volume 1 Clause 5.71 – Connections to
structures in providing the flexible joints to structures.
¡
Pipeline
Structural Design: The structural checking and bedding design should in
accordance with Section 6 of Sewerage Manual Part 1.
6.7.1.3
Manholes
Design
The design of manholes should be in accordance with Section 7 of
Sewerage Manual Part 1.
¡
Location:
Manholes should be provided at all changes in direction, at intersections and
to suit property connections. The maximum spacing between manholes should be as
follows:
|
Diameter of Pipe
(mm) |
Maximum Intervals
(m) |
|
Smaller than 600 |
40 |
|
Between 600 – 1050 |
80 |
|
Larger than 1050 |
120 |
¡
Access
Openings/Shafts: Desilting opening should not be smaller than 750mm by 900mm
and should be placed in the line of the sewer. The man access opening with
minimum size of 675mm x 750mm should be provided at manholes. Man access
openings should be placed off the line of the sewer for deep manhole and along
the line of the sewer for manholes shallower than 1.2m.
¡
Working
Chambers: Working Chambers should be provided to manholes deeper than 1.2m.
¡
Intermediate
Platforms: When the invert of a manhole is more than 4.25m from the cover level,
intermediate platforms should be provided at regular intervals. The headroom
between platforms should not be less than 2m nor greater than 4m. Hand railing
and safety chains should be provided at the edge of platform to protect persons
from falling down. The minimum size of platform should is 800mm by 1350mm.
¡
Covers:
The manhole cover should be designed strong enough to take the design loading
and should not rock when initially placed in position or develop a rock with
wear. The design of manhole covers should make reference to DSD standard
drawings.
¡
Backdrop
Manhole: When the level difference between the inlet pipe and the invert level
of manhole is greater than 600mm, backdrop manhole should be used. The design
of backdrop manhole should follow guidelines under Section 7.1.9 in Sewerage
Manual Part 1.
¡
Step-irons/Cat
Ladder: Step-irons should be securely fixed in position and should be equally
spaced and staggered about a vertical line at 300mm centres. Cat ladders should
be used in manholes deeper than 4.25m or where manholes are frequently entered.
Set-irons and ladders should be start at not more than 600mm below the cover
level and continue to the platform or benching. Corrosion resistance materials
should be used if step-irons and ladders are constantly in a damp atmosphere
and prone to corrosion.
6.7.1.4
Sump Pumps Design
The design of sewage sump pumps should follow
the requirements stipulated in the Sewerage Manual Part 2.
The number of pumps to be installed depends
on the sump capacity. Standby pumps should be provided to ensure the operation
can still be maintained during maintenance or mechanical failure.
The selected electrical equipment shall be
suitable to operate under high humidity, high temperature and presence of
corrosive gases.
Appropriate mitigation measures to control
noise and odour problems should be designed under
detailed design stage. The typical methods for noise and odour
control could refer to the Seweage Manual Part 2.
In order to control the septicity of sewage
due to operation of sewage pumping facilities, the retention time of sewage
should be minimized. Pumps with different small rate should be considered for
reducing the time of retention of sewage. Direct injection of oxygen could also
be used to control septicity. The mitigation methods should be considered under
detailed design stage.
Fresh water should be provided for the
operation and maintenance staff for hygienic reasons.
6.7.1.5
Rising Mains Design
The design of rising main should follow the
requirement stipulated in the Sewerage Manual Part 2.
Twin rising mains should be provided as far
as possible because of the following reasons:
¡
To
accommodate a wide range of flow conditions such that the velocity in the mains
can be kept within acceptable limits;
¡
To
provide continued operation when one of the mains is damaged; and
¡
To
facilities future inspection and maintenance while the normal sewage flow can be maintained.
The maximum velocity at peak flow should not
exceed 3m/s. The desirable range of velocity should be 1m/s to 2m/s with due
consideration given to the various combinations of number of duty pumps in
operation.
Air relief valves, check valves, isolating
valves and discharge sumps shall be provided in accordance to the Sewerage
Manual Part 2.
Septicity control methods for rising mains,
such as oxygen injection and reducing retention time of sewage, should be
designed under detailed design stage.
6.7.1.6
Thrust Blocks for Rising Mains
Thrust blocks should be provided to rising mains to prevent pipes from
being moved by forces exerted within the pipe by the flow of water hitting
bends, tapers, and closed or partially closed valves. The size of a thrust
block is dependent upon the deflection of the flow and the head of water inside
the pipe. Design of thrust block should
refer to DSD Sewerage Manual Part 2.
6.7.1.7
Inspection and General Maintenance Operations
All gravity sewers and rising mains shall be tested in accordance with
relevant GS sections as appropriate in the presence and to the satisfaction of
the staff of DSD upon completion of the installation.
Records of satisfactory testing on the completed works shall be
submitted to DSD after the testing. CCTV survey records, as-built drawings and
hydraulic and structural design calculations should be submitted to DSD for
records.
6.8 Environmental Monitoring and Audit
With the implementation of the proposed sewerage system according to the specifications stated in Section 6.7, no sewerage or sewage treatment implications are anticipated. No specific sewerage monitoring programme is thus required for the WKCD Development.
EPD has completed the WK&TW SMP Review study to identify the performance
of the existing sewerage systems. The SMP Review allows provision for sewage
flows from WKCD.
Comparing the latest estimated sewage flows from the WKCD development plan and
the sewage flows allowed in the SMP Review, the existing sewer system in
The sewage generated from the sub-catchments S1 to S7 will be discharged
to the branch sewer at
The sewage generated from sub-catchment S8 will be discharged to the
existing sewer at
A sewerage system is proposed to collect the sewage from WKCD and convey
the sewage to the upgraded branch sewer at
Based on the above, it is concluded that no adverse sewage impact would
be anticipated resulting from the development of WKCD.