10.1
This section comprises the following:
§
Introduction – Describes the background of the Assessment
and the structure of this report.
§
Sewerage Catchment Area – Introduces the study area in
Aberdeen Sewerage Catchment.
§
Design Assumption and Criteria – States the assumption made
in estimating the sewage flow.
§
Development and Flow Projections – Presents the planning
year studied and provides the corresponding projected population and sewage
flow figures for both the existing and redevelopment proposals.
§
Existing and Committed Sewerage Infrastructure – Describes
the sewerage infrastructure studied under this report.
§
Sewerage Impact Assessment – Identifies any adverse impacts
on the existing sewerage infrastructure due to the proposed redevelopments; and
presents the proposed sewerage improvement works for the study area.
§
Summary and Conclusions.
10.2
The purpose of this Sewerage Impact Assessment (SIA) is to
assess the impacts due to
10.3
The
10.4
Under the
10.5
The proposed hotel developments, at the new entry plaza and at
Tai Shue Wan area, are not considered as part of the current
10.6
The
Sewerage Catchment Area
10.7
The Aberdeen Sewerage Catchment embodies South Bay, Repulse
Bay, Deep Water Bay, Shouson Hill, the eastern part of the Peak area, Wong Chuk
Hang, Aberdeen, Tin Wan and Chi Fu Fa Yuen. Part of the sewage generated within
catchment is conveyed to the Aberdeen Preliminary Treatment Works (PTW) for the
treatment.
10.8
Sewage generated from the
Design
assumptions and criteria
10.9
This SIA has been carried out following the guidelines set
out in the Sewerage Manual Part 1 (DSD, 1995) (SM), based on the design peak
in-grounds attendance of 38,000 visitors per day by the year 2021/22.
10.10
As not all the population type (such as visitors) are
covered in Table 2 of the SM, assumptions are then made for the unit flow
factors of the populations type adopted in this SIA based on the global unit
flow factors in Table 2 of SM. Table 10.1 below provides a summary
of the flow factors used for different population types.
Table 10.1 Assumptions on Unit Flow Factors
|
Population Type |
Unit Flow Factor (m3/h/day) |
|
Restaurant Customers |
0.2125 |
|
Restaurant / General staff |
0.35* |
|
Visitors |
0.06 |
*Note: According to the SM Table 2,
combining sanitary and commercial activities
10.11
The global peaking factors, including stormwater allowance,
given in Table
10.12
A roughness coefficient, ks, of
Development and Flow Projections
Planning Year Considered
10.13
In accordance with the schedule of the proposed
redevelopment, it will be completed by mid 2011. Projections for population and
sewage flow estimates are therefore considered for the planning year of 2016
for conservatism to assess the sewerage impacts arising from the proposed
redevelopment.
10.14
In the estimation of population and sewage arising from
Aberdeen Sewerage Catchment in 2016, reference is made to the Review of Hong
Kong Island Sewerage Master Plans (HKISMP) Final Report (Dec. 2003). The
planning data of the population of each Planning Vision and Strategy (PVS) zone
in baseline estimation is based on the 2003
10.15
Average dry weather flows (ADWF) were estimated by applying
appropriate unit sewage flow factors to the population data. Reference was made to the unit flow factors
as recommended in the SM.
10.16
With the exception of industrial developments, the adopted
unit flow factors are consistent with the recommendations of the SM and shown in Table 10.2
below.
Table 10.2 Recommended Unit Flow
Factors
|
Development
Type |
Unit |
Unit Flow Factor (l/h/d) |
|
Residential |
|
|
|
Low Cost
Rental |
Person |
175 |
|
R1 |
Person |
240 |
|
R2 |
Person |
300 |
|
R3 |
Person |
370 |
|
Village |
Person |
240 |
|
Government/Institution/Community |
Person |
240 |
|
Commercial |
|
|
|
Job Types J2 to J5 |
Employee |
280* |
|
Industrial |
|
|
|
Job Type J1 |
Employee |
443* |
|
Schools |
|
|
|
School |
School
place |
25 |
Notes:
Based on Sewerage Manual
Part 1 (DSD, 1995).
* denotes in line with
Review of HKISMP Final Report (Dec. 2003).
10.17
The evaluated ultimate ADWF for the Aberdeen Sewerage
Catchment by development type are presented in Table 10.3 and the details of
planning and flow data are included in Appendix
10.1:
Table 10.3 ADWF in Year 2016 for the
|
Development Type |
ADWF (m3/d) |
|
Residential |
31,272 |
|
Commercial (J2 to J12) |
16,794 |
|
Industrial (J1) |
570 |
|
School |
630 |
|
TOTAL |
49,266 |
Peaking Factors
10.18
Peak wet weather flows (PWWF) are used in the assessment of
hydraulic adequacy of the sewerage systems. Peaking factors including
stormwater allowance in accordance with the SM were applied to the ADWF to
establish the peak flows. The recommended peaking factors are presented in Table 10.4 below:
Table 10.4 Recommended Peaking Factors
for Sewers
|
Population |
Peaking Factor for Sewers* |
|
< 1,000 |
8 |
|
1,000 – 5,000 |
6 |
|
5,000 – 10,000 |
5 |
|
10,000 – 50,000 |
4 |
|
> 50,000 |
7.3/N0.165 |
Notes:
1.
* denotes peaking factors including stormwater allowance
based on Sewerage Manual Part 1 (DSD, 1995).
2.
N denotes equivalent population / 1,000.
3.
Equivalent population = ADWF (m3/d) / 0.27.
Sewage Impact
Assessment Condition
10.19
With the proposed redevelopment of
The detailed breakdown is shown in Appendix 10.2.
Table 10.5 Estimated sewage flow from
|
Discharge
Location |
ADWF
(L/s) |
|
|
47.53 |
|
Shum Wan Road Sewer |
9.26 |
|
|
27.75 |
Existing & Committed Sewerage Infrastructure
10.20
Sewage flows generated by redevelopments within the study
area in Aberdeen Sewerage Catchment are collected by the existing sewerage
systems en route to the Aberdeen PTW for preliminary treatment. The treated
effluent from Aberdeen PTW is discharged into the sea.
10.21
The redevelopment site is located within the Aberdeen
Sewerage Catchment and is served by the Aberdeen PTW. A layout of the existing
sewerage system in Aberdeen Sewerage Catchment is shown on Figure 10.2. The sewerage system in the study area is shown in Figure 10.3.
10.22
Under the existing scenario, the existing sewerage of
Sewerage
Connection at Tai Shue Wan
10.23
For the sewage discharge from the Ocean Park at Tai Shue
Wan, sewage will be discharged to an existing
Sewerage
Connection at
10.24
The sewage from the existing Headland area is currently
discharged by gravity to an existing
Sewerage
Connection at
10.25
The sewage from the existing Lowland area is currently
discharged to the
10.26
Sewage collected from the
10.27
Aberdeen PTW is located at
Table 10.6 Existing Facilities of the
|
Treatment Unit |
No. of Units |
Capacity of Each Unit (m3/s) |
|
Coarse Screens |
1 Duty + 1 Standby |
2.45 |
|
Medium Screens |
1 Duty + 1 Standby |
2.45 |
|
Inlet Pumps |
3 Duty + 1 Standby |
2.45 |
|
Fine Screens |
2 Duty + 1 Standby |
2.08 |
|
Grit Trap |
2 Duty |
2.48 |
*Extracted from Review of
HKISMP Final Report (Dec. 2003)
10.28
Section 10.17 revealed that the contributing population for
Aberdeen Sewerage Catchment are 182,467 and 209,519, whilst the sewage flows
are 49,266m3/d (ADWF) and 56,570m3/d (ADWF), for the
Baseline and SIA conditions respectively.
10.29
It is noted that there are local increases of flows at 3
connections of sewers at Nam Long Shan Road,
10.30
Improvement works are also proposed to improve the sewerage
infrastructure identified with hydraulic inadequacies in the performance
assessment.
Performance
Assessment for Sewerage System
10.31
The performance of the existing sewerage infrastructure was
assessed for planning year (2016) incorporating TPEDM data. Hydraulic analysis has been carried out on
the basis of sewerage record plans collected from DSD. The flows of 190.12L/s,
37.05L/s and 110.98L/s from
10.32
Planning information at Street Block 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.
10.33
Information on the existing sewerage network is sourced from
the Drainage Record Plans obtained from DSD.
10.34
The performance assessment results showed that there were
some existing sewers identified as hydraulic inadequate in the model under the
flows in year 2016.
10.35
In accordance with the SM, the long-term goal is to
implement sewerage improvement works to eliminate all surcharged conditions.
Surcharged sewers are therefore identified for both the Baseline and Sewerage
Impact Assessment conditions. Upgrading works are recommended for the surcharged
sewers.
10.36
224m of 225mm diameter sewers were identified to be surcharged
under peak flow condition and the details are listed in Appendix 10.3.
10.37
The surcharged sewers under Baseline Condition are shown in Fig 10.5a, 10.5b and 10.5c.
Sewerage Impact Assessment Condition
10.38
Surcharged sewers measuring a total length of 1520m ranging
from
Table 10.7 Summary of Surcharged Sewers at Peak Flow under
SIA Condition
|
Pipe Dia. (mm) |
Length (m) |
|
225 |
1,211 |
|
300 |
37 |
|
375 |
272 |
|
Total |
1,520 |
10.39
The surcharged sewers under SIA Condition are shown in Fig 10.6a, 10.6b and 10.6c.
10.40
It shows that with the redevelopment of
10.41
The existing capacity of the Aberdeen PTW is
10.42
The detailed calculation of the sewage flow to Aberdeen PTW is
shown in Appendix 10.4.
10.43
There are upgrading sewerage systems proposed for the
redevelopment of
10.44
The SIA has identified sewers of a total length of 1520m in
the existing sewerage systems would be subjected to surcharge.
10.45
In accordance with the findings from the hydraulic analysis,
three sections (links ref. 322_3 to 322_55, 322_78 to 322_147 and 252_3 to 200_171)
of the sewers are surcharged and are recommended to be upgraded.
10.46
Based on the findings, there should be no major hydraulic
problem in the sewerage network. 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 surcharged conditions in the sewerage systems in
future. The recommended sewerage
improvement works has a total length of 1,543m which is summarised in Table 10.8 below. They are also shown in Fig 10.7a, 10.7b and 10.7c and
listed in Appendix 10.3.
Table 10.8 Summary of Recommended Sewerage Upgrading Works
|
Location |
Existing Pipe Size (mm) |
Upgrading Pipe Size (mm) |
Pipe Length (m) |
|
|
225 |
450 |
1,211 |
|
|
300 |
500 |
37 |
|
|
375 |
500 |
295 |
|
|
Total |
1,543 |
|
10.47
It is understood that CEDD is the proponent of the proposed
sewerage improvement works. The
construction works is therefore not part of the
Summary and Conclusion
10.48
The performance of the existing sewerage infrastructure
under TPEDM projected population condition was assessed and formed the Baseline
Condition
10.49
The SIA Condition takes into account of the redevelopment of
10.50
The adopted unit flow factors are generally based on the
recommendations of the SM.
10.51
The recommended peaking factors are based on the SM. The estimated peak flow is 1.88m3/s
for Baseline Condition whilst peak flow of 2.04m3/s is estimated
under SIA Condition. These peak flows are used in the hydraulic assessment of
the existing Aberdeen PTW.
10.52
The performance assessment results have identified
surcharged sewers measuring a total length of 1543m with diameters ranging from
10.53
The Aberdeen PTW was assessed to be adequate to convey the
total catchment flows under both Baseline and SIA Conditions under this Study.
10.54
Sewerage improvement works to the existing sewers were
recommended. It is proposed to upgrade the existing sewers with pipes of
diameters ranging from