5     HYDRODYNAMICS AND WATER QUALITY.. 5-1

5.1     Introduction. 5-1

5.2     Water Sensitive Receivers. 5-1

5.3     Environmental Legislation, Policies, Plans, Standards and Criteria. 5-2

5.4     Description of the Environment. 5-3

5.5     Identification of Environmental Impact. 5-3

5.6     Assessment Methodology. 5-3

5.7     Prediction and Evaluation of Environmental Impacts. 5-3

5.8     Mitigation of Adverse Environmental Impacts. 5-3

5.9     Evaluation of Residual Impacts. 5-3

5.10   Environmental Monitoring and Audit. 5-3

5.11   Conclusion. 5-3

 

List of Tables

 

Table 5.1        Summary Of Water Quality Objectives For Victoria Harbour WCZ. 5-3

Table 5.2        WSD’s Water Quality Criteria For Flushing Water At Sea Water Intakes. 5-3

Table 5.3        Summary Statistics Of 2005 Marine Water Quality In Victoria Harbour. 5-7

Table 5.4        Summary Statistics Of 2005 Marine Water Quality At The Causeway Bay Typhoon Shelter  5-9

Table 5.5        Summary Of Information of Water Cooling Systems. 5-19

Table 5.6        Flow Rates Of Water Cooling Systems For Thermal Plume Modelling. 5-20

Table 5.7        Summary Of Parameters For Thermal Plume Model (Delft3D-Flow) 5-21

Table 5.8        Summary Of Parameters For Modelling Of Residual Chorine (Delft3D-Part) 5-23

Table 5.9        Summary Of Parameters For Sediment Plume Model (Delft3D-Part) 5-33

Table 5.10      Maximum Dredging Rates Of WDII And CWB - Scenario 2a (Early 2009) 5-33

Table 5.11      Maximum Dredging Rates Of WDII And CWB - Scenario 2b (Late 2009 To 2010) 5-35

Table 5.12      Maximum Dredging Rates Of WDII And CWB - Scenario 2c (2011) 5-35

Table 5.13      Coastal Developments Incorporated In The Construction And Operational Phase Coastline Configurations. 5-41

Table 5.13a     Summary Of Modelling Scenarios. 5-43

Table 5.14      Pollution Loading From Stonecutters Sewage Treatment Works Under HATS. 5-44

Table 5.15      Locations And Pollution Loadings Survey Results (In 2000) Of Wan Chai Stormwater Outfalls  5-48

Table 5.16      Pollution Loading Inventory For Wan Chai, Causeway Bay And North Point - Year 2011 Dry Season  5-48

Table 5.17      Pollution Loading Inventory For Wan Chai, Causeway Bay And North Point - Year 2011 Wet Season  5-48

Table 5.18      Pollution Loading Inventory For Wan Chai, Causeway Bay And North Point - Year 2016 Dry Season  5-49

Table 5.19      Pollution Loading Inventory For Wan Chai, Causeway Bay And North Point - Year 2016 Wet Season  5-49

Table 5.20      Discharge Rates At Sections To The East And West Of Victoria Harbour. 5-53

Table 5.21      Operation Scenario – Temperature Elevations At Cooling Water Intakes. 5-57

Table 5.22      Construction Scenario 2a – Suspended Solids Concentrations At Sensitive Receivers (Base Case Scenario) 5-59

Table 5.22a     Construction Scenario 2a – Suspended Solids Concentrations At Sensitive Receivers (Sensitivity Test Using Higher Dredging Rate For Gas Main Construction) 5-60

Table 5.23      Construction Scenario 2b – Suspended Solids Concentrations At Sensitive Receivers  5-61

Table 5.24      Construction Scenario 2c – Suspended Solids Concentrations At Sensitive Receivers  5-62

Table 5.25      Predicted Water Quality At Temporary Embayment At Interim Construction Stage - Wet Season  5-64

Table 5.26      Predicted Water Quality At Temporary Embayment At Interim Construction Stage - Dry Season  5-65

Table 5.27      Comparison Of Phase I Marine Site Investigation Sediment Elutriate Test Results With The Water Quality Standards. 5-70

Table 5.28      Comparison Of Phase II Marine Site Investigation Sediment Elutriate Test Results With The Water Quality Standards. 5-71

Table 5.29      Comparison Of WDIICFS Marine Site Investigation Sediment Elutriate Test Results With The Water Quality Standards. 5-72

Table 5.30      Calculation Of The Effects Of Increased Suspended Sediment Concentrations On Dissolved Oxygen Concentrations Under Scenario 2a. 5-73

Table 5.30a     Calculation Of The Effects Of Increased Suspended Sediment Concentrations On Dissolved Oxygen Concentrations Under Scenario 2a (Sensitivity Test Using Higher Dredging Rate For Gas Main Construction) 5-73

Table 5.31      Calculation Of The Effects Of Increased Suspended Sediment Concentrations On Dissolved Oxygen Concentrations Under Scenario 2b. 5-75

Table 5.32      Calculation Of The Effects Of Increased Suspended Sediment Concentrations On Dissolved Oxygen Concentrations Under Scenario 2c. 5-76

Table 5.33      Maximum Elevations Of Nutrient Concentrations Under Scenario 2a. 5-78

Table 5.34      Maximum Elevations Of Nutrient Concentrations Under Scenario 2b. 5-79

Table 5.35      Maximum Elevations Of Nutrient Concentrations Under Scenario 2c. 5-80

Table 5.36      Maximum Elevations Of PCBS. 5-81

Table 5.39      Application Of Silt Screens At Interim Construction Stages. 5-87

Table 5.40      Construction Scenario 2a –Predicted SS Levels At The Seawater Intakes After The Implementation Of Mitigation Measures (Base Case Scenario) 5-89

Table 5.40a     Construction Scenario 2a –Predicted SS Levels At The Seawater Intakes After The Implementation Of Mitigation Measures (Sensitivity Test Using Higher Dredging Rate For Gas Main Construction) 5-90

Table 5.41      Construction Scenario 2b – Predicted SS Levels At The Seawater Intakes After The Implementation Of Mitigation Measures. 5-91

Table 5.42      Construction Scenario 2c – Predicted SS Levels At The Seawater Intakes After The Implementation Of Mitigation Measures. 5-91

Table 5.43      Predicted SS Elevations At Corals For Construction Scenario 2a - Mitigated. 5-93

Table 5.44      Predicted SS Elevations At Corals For Construction Scenario 2a - Mitigated (Sensitivity Test Using Higher Dredging Rate For Gas Main Construction) 5-93

Table 5.45      Predicted SS Elevations At Corals For Construction Scenario 2b – Mitigated. 5-93

Table 5.46      Predicted SS Elevations At Corals For Construction Scenario 2c – Mitigated. 5-93

Table 5.47      Recommended Maximum Dredging Rates. 5-94

Table 5.48      Cumulative Impact On Quarry Bay Intake. 5-95

 


5                    HYDRODYNAMICS AND WATER QUALITY

5.1              Introduction

5.1.1          This section presents the assessment results of the potential hydrodynamic and water quality impact associated with the construction and operation of the proposed Wan Chai Development Phase II (WDII) and Central-Wan Chai Bypass (CWB).  Mitigation measures are also recommended to minimise potential adverse impacts and to ensure the acceptability of any residual impact (that is, after mitigation).  It should be highlighted that no secondary contact recreation zones and water sports activities will be proposed for the coastal water within the Project site boundary.

5.1.2          Key environmental issues in respect of hydrodynamic and water quality impacts associated with the Project include:

·                     construction phase water quality impact due to dredging and filling, and construction site runoff and waste water from work force and general site activities

·                     change of flow regime after completion of the project and the associated water quality impact along the new coastline formed by the proposed reclamation.

5.1.3          Water Quality Impact Assessment: the assessment area should include the areas within and 300m extended beyond the boundary of the Project, plus the Victoria Harbour Water Control Zone (WCZ), the Eastern Buffer WCZ and the Western Buffer WCZ as declared under the Water Pollution Control Ordinance (WPCO).

5.2              Water Sensitive Receivers

5.2.1          In order to evaluate the potential water quality impacts from the Project, water sensitive receivers (WSR) in Victoria Harbour and its adjacent waters were considered.  Major water sensitive receivers identified include:

·                     WSD Flushing Water Intakes;

·                     Cooling Water Intakes; and

·                     Corals.

5.2.2          Water sensitive receivers identified outside the Project site boundary in farther field within Victoria Harbour and its adjacent waters are shown in Figure 5.1.  No sensitive coral sites were identified in the Victoria Harbour. The Green Island and Junk Bay coral communities are located more than 5.5 km west and 6.5 km east of the proposed reclamation site, respectively.  These ecological sensitive receivers are included for water quality assessment as they are potentially affected during the construction phase of the Project due to the sedimentation of suspended solids in the water column. Potential adverse impacts on the coral communities, in terms of sedimentation rate, are addressed in Section 5.7.  Further discussions are included in the marine ecological impact assessment (Section 9).

5.2.3          A number of cooling water pumping stations and intakes are located within the proposed permanent reclamation limit along the existing waterfront of Wan Chai. These intakes supply cooling water to the air conditioning systems of various commercial buildings in the Wan Chai area including:

·                     Hong Kong Convention and Exhibition Centre (HKCEC) Phase 1

·                     Shui On Centre

·                      Telecom House

·                      Government Buildings (Wan Chai Tower/Revenue Tower/Immigration Tower)

·                      China Resources Building

·                      Hong Kong Exhibition Centre

·                     Great Eagle Centre

·                     Sun Hung Kai Centre.

5.2.4          Cooling water intake for Sun Hung Kai Centre will be reprovisioned to the new waterfront of Wan Chai during operational phase of the Project. The rest of the above listed cooling water intakes will be reprovisioned to the intake chambers to the north of HKCEC Extension. 

5.2.5          An existing WSD flushing water intake is also located within the proposed reclamation limit at Wan Chai which will be uprated and reprovisioned to Wan Shing Street under this Project. 

5.2.6          Figure 5.2 shows the locations of the existing and reprovisioned seawater intakes within the Project site boundary.  Cooling water intakes for some potential future developments are also included in Figure 5.2 for reference.  Further description of these cooling water intakes are provided in Section 5.6.

5.2.7          It should be noted that the MTRC South Intake previously situated at the Wan Chai waterfront between Central Reclamation Phase III (CRIII) and HKCEC Extension has been relocated to the Central waterfront as shown in Figure 5.1. 

5.3              Environmental Legislation, Policies, Plans, Standards and Criteria

5.3.1          The criteria for evaluating water quality impacts in this EIA Study include:

Environmental Impact Assessment Ordinance (EIAO)

5.3.2          The Technical Memorandum on Environmental Impact Assessment Process (Environmental Impact Assessment Ordinance) (EIAO-TM) was issued by EPD under Section 16 of the EIAO.  It specifies the assessment method and criteria that were followed in this Study.  Reference sections in the EIAO-TM provide the details of assessment criteria and guidelines that are relevant to the water quality assessment, including:

·                     Annex 6 – Criteria for Evaluating Water Pollution

·                     Annex 14 – Guidelines for Assessment of Water Pollution.

Water Quality Objectives

5.3.3          The Water Pollution Control Ordinance (WPCO) provides the major statutory framework for the protection and control of water quality in Hong Kong.  According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZs).  Corresponding statements of Water Quality Objectives (WQO) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in the WCZ based on their beneficial uses.  The proposed Project is located within Victoria Harbour (Phase Three) WCZ and the corresponding WQO are listed in Table 5.1.


Table 5.1         Summary of Water Quality Objectives for Victoria Harbour WCZ

Parameters

Objectives

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

Dissolved oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg/l for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg/l for 90% of samples

Marine waters

pH

To be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2

Marine waters

Salinity

Change due to human activity not to exceed 10% of ambient

Whole zone

Temperature

Change due to human activity not to exceed 2 oC

Whole zone

Suspended solids (SS)

Not to raise the ambient level by 30% caused by human activity

Marine waters

Unionised ammonia (UIA)

Annual mean not to exceed 0.021 mg/l as unionised form

Whole zone

Nutrients

Shall not cause excessive algal growth

Marine waters

Total inorganic nitrogen (TIN)

Annual mean depth-averaged inorganic nitrogen not to exceed 0.4 mg/l

Marine waters

Toxic substances

Should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms.

Whole zone

Human activity should not cause a risk to any beneficial use of the aquatic environment.

Whole zone

Source:   Statement of Water Quality Objectives (Victoria Harbour (Phases One, Two and Three) Water Control Zone).

Water Supplies Department (WSD) Water Quality Criteria

5.3.4          Besides the WQO set under the WPCO, the WSD has specified a set of objectives for water quality at flushing water intakes as listed in Table 5.2 which shall not be exceeded at all stages of the Project.  The target limit for suspended solids (SS) at these intakes is 10 mg/l or less.

Table 5.2         WSD’s Water Quality Criteria for Flushing Water at Sea Water Intakes

Parameter (in mg/l unless otherwise stated)

Target Limit

Colour (HU)

< 20

Turbidity (NTU)

< 10

Threshold Odour Number (odour unit)

< 100

Ammoniacal Nitrogen

< 1

Suspended Solids

< 10

Dissolved Oxygen

> 2

Biochemical Oxygen Demand

< 10

Synthetic Detergents

< 5

E. coli (no. per 100 mL)

< 20,000

 


Cooling Water Intake Standards

5.3.5          Based on a questionnaire survey conducted under the approved Comprehensive Feasibility Study for Wan Chai Development Phase II (WDIICFS) EIA ([1]), a SS limit of 40 mg/L was adopted as the assessment criterion for Admiralty Centre intake and MTRC South intake.  No information on the SS limit is available for other cooling water intakes. These findings have been confirmed by a telephone survey conducted under the recent approved EIA for the Hong Kong Convention and Exhibition Centre (HKCEC) Atrium Link Extension (ALE).  The locations of the cooling water intakes are shown in Figure 5.1 and Figure 5.2.  The SS criterion for cooling water intakes is different from that for the WSD’s intakes as their beneficial uses are different (the former is used for cooling water system and the latter for flushing purpose).

Technical Memorandum

5.3.6          Discharges of effluents are subject to control under the WPCO. The Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS) gives guidance on the permissible effluent discharges based on the type of receiving waters (foul sewers, storm water drains, inland and coastal waters).  The limits control the physical, chemical and microbial quality of effluents. Any sewage from the proposed construction and operation activities must comply with the standards for effluents discharged into the foul sewers, inshore waters or marine waters of Victoria Harbour WCZ, as given in the TM-DSS.

Practice Note

5.3.7          A Practice Note for Professional Persons (ProPECC) was issued by the EPD to provide guidelines for handling and disposal of construction site discharges.  The ProPECC PN 1/94 “Construction Site Drainage” provides good practice guidelines for dealing with ten types of discharge from a construction site.  These include surface runoff, groundwater, boring and drilling water, bentonite slurry, water for testing and sterilisation of water retaining structures and water pipes, wastewater from building constructions, acid cleaning, etching and pickling wastewater, and wastewater from site facilities.  Practices given in the ProPECC PN 1/94 should be followed as far as possible during construction to minimise the water quality impact due to construction site drainage.

Assessment Criteria for Corals

5.3.8          Potential impacts on benthic organisms, including corals, may arise through excessive sediment deposition.  The magnitude of impacts on marine ecological sensitive receivers was assessed based on the predicted elevation of SS and sedimentation rate.

5.3.9          According to the WQO criteria, elevation of SS less than 30% of ambient level, which is set for among other reasons, to offer protection for marine ecological resources, is adopted in this assessment for coral protection. This criterion is more stringent than that previously adopted in other EIA study for assessing SS impact on hard corals in eastern Hong Kong waters (i.e. SS elevation less than 10 mg/L, ERM 2003 ([2])).

5.3.10      According to Pastorok and Bilyard ([3]) and Hawker and Connell ([4]), a sedimentation rate higher than 0.1 kg/m2/day would introduce moderate to severe impact upon corals.  This criterion has been adopted for protecting the corals in Hong Kong under other approved EIAs such as Tai Po Sewage Treatment Works Stage 5 EIA ([5]), Further Development of Tseung Kwan O Feasibility Study EIA, Wan Chai Reclamation Phase II EIA, Eastern Waters MBA Study ([6]), West Po Toi MBA Study ([7]) and Tai Po Gas Pipeline Study ([8]).  This sedimentation rate criterion is considered to offer sufficient protection to marine ecological sensitive receivers and is anticipated to guard against unacceptable impacts.  This protection has been confirmed by previous EM&A results which have indicated no adverse impacts to corals have occurred when this assessment criterion has been adopted.

5.3.11      The assessment criteria used in this Project for protection of corals identified at Green Island, Junk Bay and Cape Collinson is also based on the WQO for SS established under the WPCO, i.e. the SS elevations should be less than 30% of ambient baseline conditions.  The WQO for SS has also been adopted under the approved Tai Po Sewage Treatment Works Stage 5 EIA as one of the assessment criteria for evaluating the water quality impact from the sewage effluent on corals identified at Tolo Harbour, Green Island and Junk Bay.

5.3.12      The above assessment criteria would be used to assess water quality impact to coral habitats (i.e. the far field ecological sensitive receivers) as identified and indicated in Figure 5.1. 

Potential Water Quality Impacts Related to Cooling Water Discharges

5.3.13      Thermal plumes associated with the reprovisioned outfalls for cooling water discharges will lead to a temperature rise in the receiving water.  The WQO for Victoria Harbour WCZ stipulated that the temperature rise in the water column due to human activity should not exceed 2 oC (Table 5.1).

5.3.14      Chlorine, in the form of sodium hypochlorite solution or produced through electrolysis of sea water, is commonly used as an anti-fouling agent or biocide for the treatment of cooling water within the cooling systems.  Residual chlorine discharging to the receiving water is potentially harmful to marine organisms.  A previous study ([9]) indicated that a residual chlorine level of 0.02 mg/l would have an adverse impact on marine organisms.  EPD had commissioned an ecotoxicity study ([10]) on TRC using local species.  The lowest No Observable Effect Concentration (NOEC) value from that study was 0.02 mg/L. The United States Environmental Protection Agency (USEPA) has a more stringent limit of 7.5 mg L-1 for residual chlorine that has been adopted as the assessment criterion for this EIA.

5.3.15      C-Treat-6 is the trade name of a commercially available surfactant-based antifouling / anticorrosion chemical agent that is commonly used for the cooling water systems which contains the active ingredient ‘30% tallow 1,3-propylene diamine’ at a typical concentration of 33% (measured as amine content).  It is acutely toxic to aquatic life.  Ma et al ([11]) considered an interim maximum permissible concentration (based on an ecotoxicity study on marine brown shrimp) of 0.1 mg C-Treat-6 per litre in the ambient water acceptable from an ecotoxicological standpoint.

5.4              Description of the Environment

Marine Water Quality in Victoria Harbour

5.4.1          The marine water quality monitoring data routinely collected by EPD in Victoria Harbour were used to establish the baseline condition. A summary of water quality data for selected EPD monitoring stations extracted from the EPD’s publication “20 years of Marine Water Quality Monitoring in Hong Kong” (which is the latest version available at the time of preparing this report) is presented in Table 5.3 for Victoria Harbour WCZ (VM1 VM2, VM4-VM8, VM12 and VM15).  Locations of the monitoring stations are shown in Figure 5.1. 

5.4.2          In the past, wastewater from both sides of the Victoria Harbour was discharged into it after just simple screening, leading to marine water low in DO and high in organic nutrients and sewage bacteria. Commissioning of HATS Stage 1 in late 2001 has brought large and sustained improvements to the water quality of the eastern and central Victoria Harbour. However, improvements are less noticeable in the western harbour area which was still subject to the sewage discharges from local PTW (Central, Wan Chai West and Wan Chai East).As the HATS Stage 1 was commissioned in late 2001, the data for 2005 as shown in Table 5.3 represent the situation after the commissioning of HATS Stage 1.

5.4.3           In 2005, the marked improvements in eastern Victoria Harbour (VM1 and VM2) and moderate improvements in the mid harbour area (VM4 and VM5) and northern part of Rambler Channel (VM14) since HATS Stage 1 was commissioned were generally sustained.  Several monitoring stations in the WCZ are located close to sewage outfalls, including VM5 (Wan Chai East and Wan Chai West PTW outfall), VM6 (Central PTW outfall), VM4 (North Point PTW outfall) and VM8 (SCISTW – HATS Stage 1 outfall).  The water quality at these stations was inevitably subject to the direct impact of sewage discharge from these outfalls.  The WQO compliance in 2005 was 83%, slightly lower than that in 2004 (87%).  Full compliance with the WQO (for DO and UIA) was achieved in 2005 in the Victoria Harbour WCZ.  However, the WQO compliance for TIN was only 50% in 2005.


Table 5.3         Summary Statistics of 2005 Marine Water Quality in Victoria Harbour

 

Parameter

Victoria Harbour East

Victoria Harbour Central

Victoria Harbour West

Stonecutters Island

Rambler Channel

WPCO WQO (in marine waters)

VM1

VM2

VM4

VM5

VM6

VM7

VM8

VM15

VM12

VM14

Temperature (oC)

22.6

(15.7-27.9)

22.9

(15.8-28.0)

22.9

(15.8-27.8)

23

(15.9-27.9)

23

(15.9-27.8)

23.1

(15.8-27.9)

23.1

(15.6-27.7)

23

(16.0-27.8)

23.1

(15.8-27.7)

23.4

(15.9-27.9)

Not more than 2 oC in daily temperature range

Salinity

32.3

(30.4-33.4)

31.9

(28.5-33.3)

31.8(28.9-33.2)

31.4

(27.3-32.9)

31.3

(26.8-32.8)

30.9

(26.3-32.8)

31.1

(27.4-32.9)

31.3

(26.6-32.9)

31(27.7-33.0)

29.6

(23.0-33.0)

Not to cause more than 10% change

Dissolved Oxygen (DO) (% Saturation)

Depth average

79

(59-94)

78

(66-92)

75

(63-88)

76

(68-99)

77

(68-96)

78

(72-99)

80

(61-108)

77

(64-105)

75

(54-94)

80

(68-105)

Not available

Bottom

78

(46-93)

77

(54-90)

74

(51-88)

74

(46-99)

73

(45-94)

75

(54-94)

78

(35-108)

74

(43-101)

74

(42-92)

79

(52-103)

Not available

Dissolved Oxygen (DO)

(mg/l)

Depth average

5.7

(4.2-6.9)

5.6

(4.4-6.8)

5.4

(4.4-6.6)

5.5

(4.7-6.6)

5.5

(4.8-6.5)

5.6

(4.9-6.6)

5.8

(4.3-7.1)

5.5

(4.5-7.0)

5.4

(3.8-6.4)

5.7

(4.8-6.9)

Not less than 4 mg/l for 90% of the samples

Bottom

5.6

(3.3-6.9)

5.6

(3.8-6.8)

5.3

(3.6-6.5)

5.3

(3.3-6.6)

5.3

(3.2-6.5)

5.4

(3.8-6.5)

5.6

(2.5-7.1)

5.3

(3.1-6.7)

5.3

(2.9-6.2)

5.6

(3.7-6.9)

Not less than 2 mg/l for 90% of the samples

pH

8.1

(7.8-8.3)

8.1

(7.7-8.3)

8

(7.7-8.3)

8

(7.6-8.3)

8

(7.6-8.2)

8

(7.7-8.2)

8.1

(7.7-8.2)

8

(7.6-8.2)

8

(7.7-8.2)

8.1

(7.7-8.2)

6.5 - 8.5 (± 0.2 from natural range)

Secchi disc Depth (m)

2.3

(1.5-2.8)

2.2

(1.2-3.5)

2.1

(1.5-3.2)

2.1

(1.3-3.1)

2.1

(1.2-3.3)

1.8

(0.9-3.2)

1.9

(1.2-2.5)

1.9

(1.2-2.7)

1.7

(1.2-2.5)

1.8

(1.5-2.3)

Not available

Turbidity (NTU)

10

(5.1-16.2)

9.8

(4.8-15.8)

9.6

(4.5-15.3)

9.8

(4.9-14.5)

9.8

(5.0-14.8)

10.8(5.9-16.1)

11.9

(5.4-22.0)

10.7

(5.8-16.2)

14.4

(6.4-22.1)

11.3

(5.4-17.1)

Not available

Suspended Solids (SS) (mg/l)

4.5

(0.9-10.8)

3.6

(1.3-8.5)

3.6

(1.3-9.8)

3.4

(1.7-5.3)

3.7

(1.3-8.2)

4.1

(2.1-8.7)

5.2

(1.8-16.3)

5.1

(2.1-10.3)

7.2

(3.1-15.7)

4.7

(2.6-10.7)

Not more than 30% increase

5-day Biochemical Oxygen Demand (BOD5) (mg/l)

0.8

(0.5-1.2)

0.9

(0.4-1.5)

0.9

(0.5-1.1)

1.1

(0.6-1.4)

0.9

(0.4-1.4)

1

(0.6-1.4)

0.8

(0.5-1.4)

0.8

(0.5-1.2)

0.7

(0.4-1.2)

0.8

(0.4-1.6)

Not available

Nitrite Nitrogen (NO2-N)  (mg/l)

0.02

(0.01-0.05)

0.02

(0.01-0.05)

0.03

(0.01-0.05)

0.03

(0.01-0.05)

0.03

(0.01-0.05)

0.03

(0.01-0.06)

0.04

(0.01-0.07)

0.03

(0.02-0.06)

0.04

(0.02-0.07)

0.05

(0.01-0.09)

Not available

Nitrate Nitrogen (NO3-N) (mg/l)

0.1

(0.04-0.17)

0.12

(0.03-0.23)

0.13

(0.05-0.24)

0.15

(0.05-0.31)

0.16

(0.06-0.34)

0.19

(0.08-0.45)

0.18

(0.08-0.49)

0.16

(0.09-0.31)

0.2

(0.09-0.45)

0.27

(0.09-0.67)

Not available

Ammonia Nitrogen (NH3-N) (mg/l)

 

0.09

(0.05-0.16)

0.13

(0.04-0.21)

0.15

(0.06-0.27)

0.19

(0.06-0.29)

0.19

(0.07-0.26)

0.21

(0.12-0.32)

0.18

(0.09-0.30)

0.23

(0.08-0.32)

0.2

(0.14-0.25)

0.17

(0.10-0.25)

Not available

Unionised Ammonia (UIA) (mg/l)

0.004

(0.002-0.010)

0.006

(0.002-0.015)

0.006

(0.003-0.015)

0.007

(0.005-0.015)

0.008

(0.004-0.014)

0.009

(0.004-0.018)

0.009

(0.003-0.022)

0.009

(0.005-0.014)

0.008

(0.005-0.012)

0.008

(0.004-0.013)

Not more than 0.021 mg/l for annual mean

Total Inorganic Nitrogen (TIN) (mg/l)

0.22

(0.11-0.32)

0.28

(0.08-0.46)

0.31

(0.12-0.54)

0.37

(0.12-0.64)

0.38

(0.14-0.65)

0.43

(0.28-0.83)

0.4

(0.22-0.76)

0.42

(0.19-0.63)

0.44

(0.31-0.71)

0.49

(0.29-0.91)

Not more than 0.4 mg/l for annual mean

Total Nitrogen (TN) (mg/l)

 

0.34

(0.23-0.47)

0.43

(0.22-0.63)

0.47

(0.26-0.69)

0.55

(0.28-0.77)

0.55

(0.29-0.79)

0.58

(0.47-0.93)

0.59

(0.34-1.16)

0.58

(0.36-0.76)

0.63

(0.43-1.31)

0.66

(0.40-1.02)

Not available

Orthophosphate Phosphorus (PO4) (mg/l)

0.02

(0.01-0.03)

0.03

(<0.01-0.04)

0.03

(0.01-0.04)

0.04

(0.01-0.05)

0.03

(0.01-0.05)

0.04

(0.02-0.05)

0.03

(0.01-0.05)

0.04

(0.02-0.05)

0.03

(0.02-0.04)

0.03

(0.02-0.04)

Not available

Total Phosphorus (TP) (mg/l)

0.03

(0.02-0.05)

0.04

(0.02-0.06)

0.05

(0.03-0.06)

0.05

(0.03-0.07)

0.05

(0.03-0.07)

0.05

(0.04-0.06)

0.05

(0.03-0.17)

0.05

(0.03-0.07)

0.06

(0.04-0.17)

0.05

(0.03-0.11)

Not available

Chlorophyll-a

(µg/L)

2.5

(0.9-6.0)

2.4

(0.8-6.0)

2.4

(0.9-7.2)

2.8

(0.8-9.1)

2.6

(0.8-9.0)

2.2

(0.8-7.6)

2

(0.9-6.4)

3.2

(0.7-12.3)

1.8

(0.9-4.8)

2.8

(0.8-11.8)

Not available

E coli

(cfu/100 ml)

640

(88-4500)

1600

(120-31000)

2400

(310-11000)

7700

(2500-23000)

5700

(1200-33000)

9100

(1200-35000)

4900

(790-40000)

5400

(490-22000)

4000

(1200-17000)

2100

(520-8700)

Not available

Faecal Coliforms

(cfu/100 ml)

1300

(300-9100)

3600

(340-50000)

5200

(770-33000)

17000

(6800-40000)

12000

(2300-89000)

21000

(2700-130000)

12000

(1500-140000)

13000

(1800-97000)

9700

(2600-35000)

4700

(1500-31000)

Not available

Notes:                  1. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, mid-depth, bottom.

2. Data presented are annual arithmetic means of depth-averaged results except for E. coli and faecal coliforms that are annual geometric means.

3. Data in brackets indicate the ranges.


Marine Water Quality within Causeway Bay Typhoon Shelter

5.4.4          A summary of published EPD monitoring data (in 2005) collected from the monitoring station at the Causeway Bay Typhoon Shelter (VT2) is presented in Table 5.4. The data are extracted from the EPD’s publication “20 years of Marine Water Quality Monitoring in Hong Kong”.

Table 5.4         Summary Statistics of 2005 Marine Water Quality at the Causeway Bay Typhoon Shelter

Parameter

EPD Monitoring Station (Bi-Monthly)

WPCO WQOs (in marine waters)

VT2

Temperature (oC)

22.8

(15.9 – 27.3)

Not more than 2 oC in daily temperature range

Salinity (ppt)

30.2

(25.2 – 32.2)

Not to cause more than 10% change

Dissolved Oxygen (DO)

(% saturation)

Depth average

68

(53 – 103)

Not available

Bottom

68

(53 – 102)

Not available

DO (mg/l)

Depth average

4.9

(3.6 – 7.2)

Not less than 4 mg/L for 90% of the samples

 

Bottom

4.9

(3.6 – 7.1)

Not less than 2 mg/L for 90% of the samples

pH value

8.1

(7.9 – 8.3)

6.5 - 8.5 (± 0.2 from natural range)

Secchi disc (m)

1.9

(1.5 – 2.9)

Not available

Turbidity (NTU)

8.8

(5.0 – 9.9)

Not available

Suspended Solids (SS) (mg/l)

5.8

(3.0 – 13.8)

Not more than 30% increase

Silica (as SiO2)(mg/l)

1.0

(0.5 – 1.4)

Not available

5-day Biochemical Oxygen Demand (BOD5) (mg/l)

1.6

(1.2 – 2.9)

Not available

Nitrite Nitrogen  (NO2-N) (mg/l)

0.04

(0.02 – 0.05)

Not available

Nitrate Nitrogen  (NO3-N) (mg/l)

0.19

(0.11 – 0.32)

Not available

Ammoniacal Nitrogen (NH3-N)

(mg/l)

0.20

(0.18 – 0.30)

Not available

Unionised Ammonia  (UIA)

(mg/l)

0.011

(0.005 – 0.021)

Not more than 0.021 mg/L for annual mean

Total Inorganic Nitrogen (TIN) (mg/l)

0.43

(0.35 – 0.55)

Not more than 0.4 mg/L for annual mean

Total Nitrogen (TN)

(mg/l)

0.65

(0.56 – 0.80)

Not available

Ortho-Phosphate (OrthoP) (mg/l)

0.04

(0.02 – 0.05)

Not available

Total Phosphorus (TP)

(mg/l)

0.06

(0.05 – 0.08)

Not available

Chlorophyll-a

(µg L-1)

4.3

(0.5 – 16.5)

Not available

E. coli (cfu per 100 mL)

5,200

(2,300 – 12,000)

Not available

Faecal Coliform

(cfu per 100 mL)

17,000

(5,100 – 61,000)

Not available

Note:   1. Except as specified, data presented are depth-averaged data.

2.        Data presented are annual arithmetic means except for E. coli and faecal coliforms that are geometric means.

3.        Data enclosed in brackets indicate ranges.

5.4.5          Due to the embayment form and reduced flushing capacity of the typhoon shelter, marine water within the typhoon shelter is vulnerable to pollution.  In 2005, high levels of E.coli were recorded at the Causeway Bay Typhoon Shelter indicating faecal contamination.    The water quality level marginally exceeded the WQO for TIN but fully complied with the WQO for DO and UIA. Significant long-term improvements in terms of decreasing trends in TIN, TN, OrthoP and TP were observed in Causeway Bay Typhoon Shelter.

Sediment Quality

5.4.6          The results of marine sediment quality analysis from the marine ground investigation works at the Project site are presented in Section 6.  A review of the sediment quality data from the marine ground investigation indicated that the majority of marine sediments to be dredged at the WDII project area were classified as contaminated. Details of the sediment quality criteria and guidelines are given in Section 6.

5.5              Identification of Environmental Impact

Operational Phase

5.5.1          The WDII operation could have potential impact on the flow regime and the associated water quality impact in Victoria Harbour as a result of the change of coastline configurations. The formation of the WDII reclamation may affect the water levels, current velocity, and tidal flushing in the vicinity of the reclaimed land and, potentially, over a larger area.  In addition, the changes in the hydrodynamics in Victoria Harbour may affect the pattern of pollutant dispersion patterns from sewage outfalls and stormwater culverts into the surrounding waters.

5.5.2          The future potential for refuse accumulation near the coastal area of HKCEC and Wan Chai areas under the current WDII reclamation layout is expected to be improved as the existing embayment areas to the west and to the east of the HKCEC Extension and the HKCEC water channel will be reclaimed under the Project.  The future coastline in the HKCEC and Wan Chai areas will be more streamlined.  The existing storm outfalls, which are the key sources of floating refuse and debris, would be diverted to the more open water with larger pollutant dispersion capacity. 

5.5.3          On the other hand, the future potential for refuse accumulation in the PCWA area and the Causeway Bay typhoon shelter are expected to be similar to the existing situations, as no change of coastline or storm outfall diversion is currently proposed at these two embayment areas under the current reclamation layout.  It is not anticipated that there would be a need to increase the frequency of refuse collection currently adopted at the PCWA area and the Causeway Bay typhoon shelter.

5.5.4          It is considered that impacts resulting from the operation of CWB, in terms of water quality, will be minimal and similar for both the elevated and tunnel sections of the route.  Surface runoff from slip-roads and elevated structures may be contaminated by oils leaked from passing vehicles, and tunnel seepage would potentially be contaminated to the same extent.  It is considered that impacts upon water quality will be minimal provided that the tunnel and elevated sections of the CWB are designed with adequate drainage systems and appropriate oil interceptors, as required.


Construction Phase

5.5.5          Details of the reclamation and construction methods are given in Section 2.  Figure 2.7 shows the reclamation stages.  Key water quality concerns during the WDII and CWB reclamation are identified as follows:

·                     Dredging and filling works for temporary and permanent reclamations will disturb the marine bottom sediment, causing an increase in SS concentrations in the water column and forming sediment plume along the tidal flows.

·                     Temporary embayments will be formed between the partially reclaimed land as the WDII and CWB reclamation proceeds in stages.  Potential accumulation of pollutants from contaminated stormwater runoff (due to debris and oil / grease left on the ground, and organic matter from expedient connections) into the temporary embayments may increase the dissolved oxygen demand in the slack water, causing dissolved oxygen depletion and, in turn, potential odour impacts on the neighbouring sensitive receivers.

·                     Construction runoff and drainage, with effluents potentially contaminated with silt, oil and grease.

5.5.6          Dredging of contaminated mud within the CBTS is proposed to mitigate the operational phase odour impacts as detailed in Section 3.  The dredging operations within this embayed waters should be carefully planned and controlled and suitable mitigation measures are proposed (refer to Section 5.8) to minimize the potential impacts on the seawater intakes within the typhoon shelter.

5.5.7          Estimated volume of dredged and fill materials is provided in Section 2 and further discussed in Section 6. Potential impacts on water quality from dredging and filling will vary according to the quantities and level of contamination, as well as the nature and locations of the WSR at or near the dredging sites.  These impacts are summarised as follows:

·                     Increased suspension of sediment in the water column during dredging activities, with possible consequence of reducing DO levels and increasing nutrient levels.

·                     Release of previously bound organic and inorganic constituents such as heavy metals, polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and nutrients into the water column, either via suspension or by disturbance as a result of dredging activities, or depositing of fill materials.

·                    Release of the same contaminants due to leakage and spillage as a result of poor handling and overflow from barges during dredging and transport.

5.5.8          All of the above may result in deterioration of the receiving marine water quality and may have adverse effects on WSR.  They are elaborated in the following paragraphs.

Suspended Sediment

5.5.9          As a result of dredging and filling activities during the construction phase, fine sediment (less than 63 µm) will be lost to suspension.  The suspended sediment will be transported by currents to form sediment plumes, which will gradually resettle.  The impact from sediment plumes is to increase the suspended sediment concentrations, and cause non-compliance in WQO and other criteria.


5.5.10      Any sediment plume will cause the ambient suspended sediment concentrations to be elevated and the extent of elevation will determine whether or not the impact is adverse or not.  The determination of the acceptability of any elevation is based on the WQO.  The WQO of SS is defined as being an allowable elevation of 30% above the background.  EPD maintains a flexible approach to the definition of ambient levels, preferring to allow definition on a case-by-case basis rather than designating a specific statistical parameter as representing ambient.  As adopted in the approved WDIICFS EIA for assessing the environmental impacts of released SS, the ambient value is represented by the 90th percentile of baseline (pre-construction) concentrations.

Release of the Contaminants due to Leakage and Spillage

5.5.11      Release of the same contaminants due to leakage and spillage as a result of poor handling and overflow from barges during dredging and transport can be addressed by proper implementation of recommended mitigation measures in Section 5.8.

Stormwater Discharges

5.5.12      Stormwater and drainage discharges from the construction sites may contain considerable loads of SS and contaminants during construction activities.  Potential water quality impact includes run-off and erosion of exposed bare soil and earth, drainage channels, earth working area and stockpiles. Minimum distances of 100 m shall be maintained between the existing or planned stormwater discharges and the existing or planned WSD flushing water intakes during construction and operation phases.

5.5.13      Local and coastal water pollution impact may be substantial if the construction site run-off is allowed to discharge into the storm drains or natural drainage without mitigation.

Construction Runoff and Drainage

5.5.14      Surface runoff generated from the construction site may contain increased loads of SS and contaminants.  Potential water quality from site run-off may come from:

·                     contaminated ground water from any dewatering activities as a result of excavation and disturbance of contaminated sediments

·                     release of any bentonite slurries and other grouting materials with construction run-off, storm water or ground water dewatering process

·                     wash water from dust suppression sprays and wheel washing facilities

·                     fuel, oil and lubricants from maintenance of construction vehicles and equipment.

General Construction Activities

5.5.15      The general construction works that will be undertaken for the roads and infrastructure will be primarily land-based and may have the potential to cause water pollution.  These could result from the accumulation of solid waste such as packaging and construction materials, and liquid waste such as sewage effluent from the construction work force, discharge of bilge water and spillage of oil, diesel or solvents by vessels and vehicles involved with the construction.  If uncontrolled, any of these could lead to deterioration in water quality.  Increased nutrient levels result from contaminated discharges and sewage effluent could also lead to a number of secondary water quality impacts including decreases in DO concentrations and localised increase in NH3-N concentrations which could stimulate algal growth and reduction in oxygen levels.

5.5.16      Sewage will arise from sanitary facilities provided for the on-site construction work force.  It is characterised by high level of BOD, NH3-N and E.coli counts.  For some of the works areas, there will be no public sewers available for domestic sewage discharge on-site.

Potential Fill Source

5.5.17      While marine sand is proposed to be used generally for filling, detailed investigations have been conducted to explore the possibility of using public fill and surplus rock fill from appropriate sources that may be identified during the detailed implementation stages of the project, where engineering, programme and implementation constraints permit.  The investigations indicate that it is possible to use public fill from Penny’s Bay Reclamation Stage 2 (PBR2) in the upper formation layers, above +2.5 mPD.  For the temporary reclamation where settlement is not a major concern, public fill from PBR2 for the full depth of reclamation is proposed, to maximise the use of public fill materials.  Transportation of public fill from PBR2 to the works site will mainly by barges as both the supply and demand locations are at their respective shorelines.  Delivery of reused construction and demolition materials within the site and/or surplus materials to the public fill reception facilities will be by barges for large quantities and by truck for local and small quantities.  Release of the pollutants due to leakage and spillage as a result of poor handling and overflow from barges during dredging, filling and transport can be addressed by proper implementation of recommended mitigation measures in Section 5.8.

5.6              Assessment Methodology

5.6.1          To assess the potential water quality impacts due to the construction and operation of the Project, the sources and natures of water pollution to be generated during construction and operation phases have been identified and their impacts are quantified where practicable. 

Operational Phase Impact

Hydrodynamic and Water Quality

Modelling Scenarios

5.6.2          The presence of the proposed WDII reclamation may change the flushing capacity of Victoria Harbour and thus impact upon the water quality.     The proposed permanent reclamation may be divided into 3 main areas, namely:

·                     the Hong Kong Convention and Exhibition Centre Reclamation (HKCEC);

·                     the Wan Chai Reclamation (WCR); and

·                     the North Point Reclamation (NP)

 

5.6.3          Figure 1.1 shows the boundaries of the proposed permanent reclamations.  The extent of the reclamation has already been minimized to satisfy the Government’s requirement and the community’s aspiration. 

5.6.4          Construction of the Project is scheduled to commence in early 2009 for completion by 2016. Two time horizons (Year 2016 and Ultimate Year respectively) were considered for the operational phase impact.  Major factors that would affect the water quality simulated would be (i) the change in background pollution loading discharged from storm and sewage outfalls; and (ii) the change in coastline configurations between the two time horizons.

5.6.5          Sewage effluent discharged from the Harbour Area Treatment Scheme (HATS) would be the key background pollution source affecting the water quality in Victoria Harbour.  Stage 1 of HATS, comprising the Stonecutters Island Sewage Treatment Works (SCISTW) and the deep tunnels, was commissioned in late 2001, which collects sewage from Kwai Chung, Tsing Yi, Tseung Kwan O, parts of eastern Hong Kong Island and all of Kowloon and deliver it to SCISTW for chemically enhanced primary treatment (CEPT).  Stage 2 of HATS would be implemented in two phases, namely Stage 2A and Stage 2B.  Under Stage 2A, deep tunnels would be built to bring sewage from the northern and western areas of Hong Kong Island to SCISTW and the design capacity of the SCISTW would be expanded to meet the future demands.  Stage 2A is currently scheduled for implementation by 2014.  Stage 2B of HATS involves the provision of biological treatment at the SCISTW to improve the effluent quality. Stage 2B is tentatively scheduled for implementation by 2021.  It should however be highlighted that the way forward of the HATS is still being studied and the timing for implementation of Stage 2B is still subject to review.

5.6.6          In 2016 during early commissioning of WDII and CWB, the pollution loading discharged from HATS would be larger than that in the ultimate condition (even though the effluent flow in 2016 would be smaller than the ultimate flow).  This is based on an assumption that the treatment process of SCISTW would be upgraded from CEPT to biological treatment under Stage 2B by 2021 (before the ultimate condition). 

5.6.7          The pollution loading discharged from the storm water outfalls along the seafront of Victoria Harbour is mainly contributed by polluted stormwater runoff, expedient connections or cross connection between the drainage and sewerage systems in the catchment areas.  With the continuous efforts by the government to improve the sewerage system and implement water pollution control measures and enforcement in the catchments on both sides of Victoria Harbour, it is unlikely that the storm pollution problem under the ultimate condition would be worse than the 2016 scenario.

5.6.8          Based on the information on the planned developments from the EIA Reports registered under the EIAO, there would not be any change in the coastline configuration within Victoria Harbour between 2016 and the ultimate year.  The reclamations for Kai Tak Development (KTD) and Yau Tong Bay Reclamation (YTBR) are excluded as they are still subject to planning review.  It should be noted that the “no reclamation” scenario is being considered for the KTD but the feasibility of such scenario is still subject to detailed investigation.

5.6.9          Three proposed reclamation projects, namely Tuen Mun Siu Lang Shui Reclamation, Hei Ling Chau Reclamation and Tai O Reclamation, would unlikely to be in place before 2016 as no implementation schedule is currently available for these development proposals. These reclamations are thus excluded in the 2016 scenario.  All these 3 reclamations are located outside Victoria Harbour in farther field.  It is therefore anticipated that the possible change of coastline configuration for these 3 development projects would not affect the outcome of the water quality modelling.  Details of the coastline configurations assumed under various construction and operation scenarios are given in Table 5.13.

5.6.10      Based on the above considerations, the 2016 development scenario, with completion of WDII reclamation, represents a worst case in terms of both background pollution discharges and impact on tidal flushing within Victoria Harbour.  Year 2016 was therefore selected as the time horizon for operational phase hydrodynamic and water quality modelling.  Two scenarios were simulated to evaluate the change in the hydrodynamic regime due to the WDII reclamation:

Scenario 1A

l                     2016 Baseline Scenario without the proposed WDII reclamation

 

Scenario 1B

l                     2016 Development Scenario with the proposed WDII reclamation

 

5.6.11      Additional scenarios for addressing the hydrodynamic and water quality impact during different interim construction stages are considered in Sections 5.6.41 to 5.6.113. A summary of the modelling scenarios is given in Table 5.13a.

Hydrodynamic and Water Quality Modelling Tools

5.6.12      Computer modelling was used to assess the potential impacts on water quality in Victoria Harbour associated with the operation of the Project.  The hydrodynamic and water quality modelling platforms were developed by Delft Hydraulics, namely the Delft3D-FLOW and Delft3D-WAQ respectively. 

5.6.13      Delft3D-FLOW is a 3-dimensional hydrodynamic simulation programme with applications for coastal, river and estuarine areas.  This model calculates non-steady flow and transport phenomena that result from tidal and meteorological forcing on a curvilinear, boundary fitted grid. Delft3D-WAQ is a water quality model framework for numerical simulation of various physical, biological and chemical processes in 3 dimensions.  It solves the advection-diffusion-reaction equation for a predefined computational grid and for a wide range of model substances.

5.6.14      In the present study, the detailed Victoria Harbour (VH) model developed using Delft3D-FLOW and Delft3D-WAQ was employed for hydrodynamic and water quality impact assessment.  This detailed model was originally developed to assess the impacts of the proposed Shatin Sewage Treatment Works Stage III extension on the water quality in Victoria Harbour.  The model was extensively calibrated by comparing computational results with measurements of the 1988 Victoria Harbour measurement campaign, and accepted by the EPD. 

5.6.15      The model setup of the VH model was further modified under the previous approved Comprehensive Feasibility Study for Wan Chai Development Phase II (WDIICFS) EIA for assessing water quality impacts of the WDII.  For example, the grid layout of the original Victoria Harbour model was enhanced in the vicinity of the WDII reclamation resulting in a higher resolution of approximately 50 m by 100 m.  Details of the model setup and verification for the WDII Study were described in the “Technical Note on Hydrodynamic Model & Water Quality Model Set-up” prepared under the WDIICFS ([12]).

5.6.16      It was assumed under the approved WDIICFS EIA that all the existing storm and spent cooling water outfalls within the Causeway Bay typhoon shelter would be decommissioned and these outfalls would be diverted outside the typhoon shelter. This is deviated from the present Study that the existing storm and spent cooling water outfalls would remain within the Causeway Bay typhoon shelter.  The water quality impacts arising from such deviation from the approved WDIICFS EIA need to be examined.  In the present Study, the grid mesh of the detailed VH model was further modified with a higher resolution (approximately 50m x 50m) at Causeway Bay typhoon shelter to address the water quality concern.  Appendix 5.1 shows the grid layout of the refined VH model.

5.6.17      The performance of the detailed VH model refined under the present Study has been checked against that of the detailed VH model approved under the WDIICFS EIA. The results of water level, depth averaged flow speed and depth averaged flow directions predicted by the two models are compared at three indicator points (namely Stations 3, 6 and 8 respectively as shown in Figure 5.14a).  The results of momentary flows are compared at two selected cross sections.  The eastern cross section is located across the Lei Yue Mun Channel, while the western section is located between Yau Ma Tei and Sheung Wan (Figure 5.14a).    Momentary flow represents the instantaneous flow rate at a specific time in m3/s whereas accumulated flow represents the total flow accumulated at a specific time in m3. The comparison plots are given in Appendix A.5a and Appendix A.5b attached to Annex 15.3 of Appendix 15.1 (see Volume 6) of this EIA report. The results predicted by both models are in general consistent with each other which implied that the model setting of the refined VH model including the nesting procedure and the derivation of the boundary conditions were carried out correctly.

5.6.18      It is important to realize that the refined VH model has higher resolution than the original approved VH model in the Causeway Bay and nearby areas. The grid cells of the VH model have also been refined under the present Study to improve the orthogonality and smoothness of the grids. The differences in the grid resolution and grid layout between the two models have caused some minor deviations in the simulated flow directions and flow speeds between the two models.

5.6.19      In addition, the surface salinity results produced from the WAQ model of the refined VH model are compared with the surface salinity results produced by the FLOW model of the refined VH model as well as the FLOW model of the original VH model developed under the WDIICFS in Appendix A.6 (attached to Annex 15.3 of Appendix 15.1 of this EIA report) to check for the consistency.  It can be seen in Appendix A.6 that the three sets of salinity results are in general consistent with each other.  The differences between the data sets are considered acceptable.

5.6.20      The refined VH Model is linked to the regional Update Model, which was constructed, calibrated and verified under the project “CE42/97 Update on Cumulative Water Quality and Hydrological Effect of Coastal Development and Upgrading of Assessment Tool” (Update Study).  Computations were first carried out using the Update Model to provide open boundary conditions to the VH Model.  The Update model covers the whole Hong Kong and the adjacent Mainland waters including the discharges from Pearl River.  The influence on hydrodynamics and water quality in these outer regions would be fully incorporated into the VH Model.

5.6.21      It should be noted that after the water quality modelling for this EIA was completed, the permanent reclamation area in Wan Chai area (WCR) has been slightly reduced in response to public comments.  Thus, the final reclamation limit for WDII as shown in Figure 1.1 is slightly different from the configuration adopted in this modelling exercise.  The final WDII reclamation has a curved permanent coastline for the Wan Chai Reclamation Stage 4 (WCR4) as shown in Figure 2.7. Under this modelling exercise, a slightly larger reclamation area is adopted for WCR4 with a straight permanent coastline connecting the points between the northeast corner of Wan Chai Reclamation Stage 3 (WCR3) and the northwest corner of the PCWA. The model grid (with a straight permanent coastline at WCR4) adopted under this modelling exercise is compared against the final WDII reclamation limit (with a curved permanent coastline at WCR4) in Appendix 5.1.  The comparison showed that the deviation of the coastline configuration is small.  No significant effect on the water quality modelling results is expected from such deviation considering that there is no existing or planned water sensitive receivers located at the waterfront of WCR4.


Simulation Periods

5.6.22      For each operational phase modelling scenario, the simulation period of the hydrodynamic model covered two 15-day full spring-neap cycles (excluding the spin-up period) for dry and wet seasons respectively.  The hydrodynamic results were used repeatedly to drive the water quality simulations for one complete calendar year (excluding the spin-up period) as specified in the EIA Study Brief.  It was found that a spin-up period of 8 days and 45 days is required for hydrodynamic simulation and water quality simulation respectively to ensure that initial condition effects can be neglected.

5.6.23      The spin-up (8 days) of hydrodynamic simulation follows that adopted in the approved EPD Update Model and has been tested under the present EIA Study to be sufficient.  For water quality simulation, pollution load discharges are included within the embayment areas (e.g. Causeway Bay Typhoon Shelter) and a longer spin-up of 45 days is required for the model to reach an equilibrium status.  Spin-up of water quality simulation has also been tested under the present EIA study to be sufficient.

Model Setup for Discharges

5.6.24      The Pearl River estuary flows were incorporated in the hydrodynamic model. Flows from other storm and sewage outfalls within the whole Hong Kong waters are relatively small and would unlikely change the hydrodynamic regime in the area and were therefore excluded in the hydrodynamic model.     

5.6.25      Loading from the sewage outfalls was allocated in the bottom water layer. Pollution loads from storm outfalls and other point source discharges such as those from typhoon shelters, marine culture zones, landfills and beaches were specified in the middle layer of the water quality model. 

Potential Water Quality Impacts Associated with Cooling Water Discharges

Description of Cooling Water Discharges

5.6.26      The proposed WDII reclamation would require reprovisioning of the existing cooling water intakes and discharges along the Wan Chai waterfront. Computer modelling was employed to assess the potential impact due to the thermal plumes and discharge of residual chlorine associated with the reprovisioned outfalls for cooling water discharges upon full commissioning of the Project. Locations of intakes and discharges for the cooling systems within the study area have been identified in Figure 5.2 and Figure 5.3A respectively. Spent cooling water from these identified cooling water systems will be discharged through culverts / outfalls into the harbour causing a potential increase in water temperature.  Information on the cooling water discharges collected under the WDIICFS at the planning stage is given in Table 5.5. 


5.6.27      It should be noted that the WDIICFS adopted a conservative approach, based on the available information from the planning stage (Table 5.5).  For most of the spent cooling water discharges, the maximum discharge flow rates of the water cooling systems have been applied to the model continuously (that is, 24 hours daily). In reality, the maximum flow discharge would only occur during the office hours and depends on the outdoor air temperature in different seasons. Latest design flow rates of these cooling water systems provided in the Study “Implementation Study for Water-cooled Air Conditioning System at Wan Chai and Causeway Bay – Investigation (ISWACS-WCCB)” recently completed in 2005 have been reviewed and compared to those adopted under the WDIICFS.   The flow rates provided in the ISWACS-WCCB are based on the latest engineering information and a more detailed estimation. It was found that the cooling water discharge rates adopted under the WDIICFS are more conservative as compared to those used under the ISWACS-WCCB and are therefore used for this EIA for worst-case assessment.  The proposed discharge rates used under this EIA are provided in Table 5.6.

 


Table 5.5         Summary of Information of Water Cooling Systems

Name of Building

The Hong Kong Academy for Performing Arts

Hong Kong Convention and Exhibition Centre (Phase I)

Hong Kong Convention and Exhibition Centre (New Wing)

China Resources Building

Great Eagle Centre

Sun Hung Kai Centre

Windsor House

Seawater abstraction rate (m3 per hour)

 

3312

3033.0 with a range from 1213.2 to 4852.8

126

(maximum =6120)

2160, with a range from 414 to 3312

1400 (summer)

1085 (winter)

(maximum=1635)

1308

(maximum = 2616)

1362.4

Discharge frequency and duration

From 0800 to 2400 continuously

24 hours

24 hours with variable flow

24 hours

24 hours

24 hours

-

Cooling water intake temperature (oC)

30.0

Depends on sea water temperature

26

28 (summer)

24 – 27 (summer)

17 – 19 (winter)

28

26

Cooling water discharge temperature (oC)

35.4

34

32

35 (summer)

30 – 33 (summer)

21 – 23 (winter)

33 – 35

32

Method of treatment

Electrochlorinator

Chemical additives and electrochlorinator

Electro-chlorinate and Biocide dosing system

Electrochlorinator

Electrochlorinator

Chloropac

Electrochlorinator

Name and dosage of chemicals added

-

C-Treat-6, 6 ppm

Hypochlorite, 3 ppm

-

-

Sodium hypochlorite system

-

Main chemical constituents of the additives

Chlorine

Chlorine,

C-Treat-6

Chlorine

Chlorine

Chlorine

-

Chlorine

Effluent quality

-

Chlorine, 0.2 ppm;

C-Treat-6, 2 ppm

Residual chlorine level at discharge > 0.3 ppm

-

-

0.3 – 0.5 ppm at outlet

-

Remarks

-

-

The Centre was only 60% occupied during survey.

-

-

-

-

Note:      ppm = mg/l


Table 5.6         Flow Rates of Water Cooling Systems for Thermal Plume Modelling.

Outfall ID

(Figure 5.3A)

Buildings

Discharge Rate (m3/s)

Adopted in WDIICFS EIA

Adopted in this EIA

10

Proposed HKAPA Extension

1 

1 (1)

2a

The Hong Kong Academy for Performing Arts

0.92 

0.92 (1)

3

HKCEC (Phase I)

1.35 

1.35 (1)

2

Shui On Centre

0.94

0.94 (1)

2

Telecom House

0.84

0.84 (1)

4

Government Buildings

1.2 

1.2 (1)

5

China Resources Building and Hong Kong Exhibition Centre

0.92

0.92 (1)

5

Great Eagle Centre

0.45

0.45 (1)

6

Sun Hung Kai Centre

0.72

0.72 (1)

1

HKCEC (New Wing)

1.7

1.7 (1)

7

Proposed Exhibition Station

1.35

1.35 (1)

-

Proposed Hotel / Commercial Development WDII/28

1.4

Not included (2)

-

Proposed Leisure and Entertainment Complex Development WDII/30

1.4

Not included (2)

9

Windsor House

0.38

0.38 (1)

8a

No. 27-63 Paterson Street

0.38

0.38 (1)

8

Excelsior Hotel and World Trade Centre

1.4

1.4 (1)

11

City Garden

-

- (3)

12

Provident Centre

-

- (3)

Notes:

(1)     Based on values adopted under the WDIICFS EIA.

(2)     Under the WDIICFS EIA, WDII/28 and WDII/30 were proposed to be developed on the new reclamation land within the Causeway Bay Typhoon Shelter.  These developments are excluded in this EIA as no such developments / reclamation is currently proposed within the Causeway Bay Typhoon Shelter

(3)     No information on flow rate is available for this cooling water intake.  The potential short circuit problem of the re-circulation of heated water to the cooling water intake was qualitatively assessed in Section 5.7.


Thermal Plume Modelling Tools

5.6.28      In the present study, the basis for modelling of the harbour waters is the refined Victoria Harbour (VH) Model as discussed in Sections 5.6.12 to 5.6.16.

5.6.29      The Excess Temperature Model within Delft3D-FLOW model was employed to simulate the thermal plume dispersion in Victoria Harbour and to assess the impact on the neighbouring cooling water intakes.  The model allows for the excess temperature distribution and decay of the thermal plume, and addresses heat transferred from the water surface to the atmosphere.  While the total heat flux is proportional to the excess temperature at the surface, the heat transfer coefficient of the formulation depends mainly on water temperature and wind speed.  The parameters adopted for the thermal plume modelling are summarised in Table 5.7.  It should be noted that Delft3D-PART model was employed for the thermal plume modelling conducted under the WDIICFS EIA which did not take into account the surface heat loss as mentioned above.  Thus, the thermal plume impact for the WDIICFS EIA may be overestimated.  The thermal plume impact predicted by the Delft3D-FLOW model conducted under this Study is considered more realistic.

Table 5.7   Summary of Parameters for Thermal Plume Model (Delft3D-FLOW)

Delft3D-FLOW Excess Temperature Model Parameters

Background (Air) Temperature (oC)

18

28

Dry Season

Wet Season

Temperature of spent cooling water (oC)

24

32 (1)

Dry Season

Wet Season

Wind Speed (m s-1)

5

Dry Season and Wet Season

Ambient Water Temperature (oC)

18

To be computed by model (1)

Dry Season

Wet Season

(1)   The predicted temperature at various intake locations under the baseline scenario (without any cooling water discharges) have been checked and confirmed to be lower than 26°C for the entire simulation period, the discharge temperature of 32°C for wet season should provide a good approximation of the temperature of spent cooling water for thermal plume modelling and assessment.

 

5.6.30      The simulation periods for the hydrodynamic FLOW model cover a complete spring-neap tidal cycle, preceded by a spin-up period.  It was found that the long spin-up period (about 1.5 tidal cycles) is required to establish the quasi-steady thermal pattern within the Study Area. One-minute time step was used in the thermal plume modelling. In order to determine whether the time step of 1 minute is acceptable, a sensitivity hydrodynamic run was conducted using a smaller time step of 30 seconds.  Comparison of the flow results for the 1-minute time step and the 30-second time step showed that there is no significant deviation between the 2 sets of results.  The time step of 1 minute is therefore considered acceptable.

5.6.31      It is conservatively assumed that all cooling water discharges have an excess temperature of 6 oC with reference to the background seawater temperature. As adopted in the WDIICFS EIA, results of the predicted temperature elevation at the intakes were factored up by [1(1-E/k)] to take into account the potential short circuit problem of the re-circulation of heated water to the cooling water intake.

Where:

E = maximum of the mean temperature elevations predicted at the intakes

k = excess temperature of the cooling system = 6°C


5.6.32      The derivation of the heat re-circulation factor [1(1-E/k)] is given in Appendix 5.1a.

5.6.33      It should be noted that the thermal impact predicted by the temperature model is linearly proportional to the temperature loading of the cooling discharges.  A factor of 1.2 has been applied to all the flow rates for model input to allow a safety margin for the discharge rates.  Using the safety factor is a conservative approach as most of the concurrent discharges covered in this EIA are already the peak flow rates which were applied to the model constantly throughout the whole simulation period. It should be noted that the discharge rates as shown in Table 5.6 did not incorporate the safety factor of 1.2.

5.6.34      The purpose of applying the factor of 1.2 is to allow a safety margin for the assumed discharge rates. The factor of 1.2 mentioned in S5.6.33 is different from the factor [1(1-E/k)] mentioned in S5.6.31 for addressing the potential short circuit problem.

Residual Chlorine

5.6.35      The 3-dimensional particle tracking model (Delft3D-PART) developed by Delft Hydraulics was employed to model the residual chlorine discharged from the cooling water.  The discharge of residual chlorine was represented by discrete particles released into the surface layer of the model.  These discrete particles were transported with flow fields determined from the hydrodynamic simulation using the refined Delft3D-FLOW Victoria Harbour (VH) Model, and turbulent diffusion and dispersion, based on a random walk technique.  The residual chlorine elevation over the ambient level was then evaluated from the particle density in each cell of the curvilinear grid of Victoria Harbour model.  Due to the high decay rate of chlorine in marine waters, the ambient chlorine level was assumed to be negligible. 

5.6.36      The flow data adopted in Delft3D-PART model were obtained from the Delft3D-FLOW hydrodynamic model results.  Each Delft3D-FLOW simulation covered a complete spring-neap tidal cycle (about 15 days) for both dry and wet seasons.  The actual simulation period for Delft3D-FLOW was preceded by a spin-up period of 8 days. 

5.6.37      For Delft3D-PART, each simulation covered a complete spring-neap tidal cycle (about 15 days), preceded by a spin-up period of 15 days.  The 15-day Delft3D-FLOW simulation results were used repeated for the 30-day simulation period for Delft3D-PART with due consideration on the continuity of the tidal level between successive 15-day periods.  In order to determine whether the spin-up period for Delft3D-PART is adequate, the time series plot of predicted residual chlorine have been compared between the spin-up period and the actual simulation period at two locations (one at the Wan Chai waterfront and the other at the Causeway Bay typhoon shelter) as shown in Annex II attached to Annex 15.3 of Appendix 15.1 of this EIA report (see Volume 6).  It was found that there is no significant difference in the model results for the 2 successive periods.  Therefore, it is considered that the simulation period is acceptable.

5.6.38      Delft3D-PART makes use of the information on water flow derived from the Delft3D-FLOW model.  The time step applied in the Delft3D-FLOW model is one-minute (for numerical simulation) and six-minute (for saving model outputs). As the number of particles that can be used in the Delft3D-PART is limited, six-minute time step was used for numerical simulation in particle tracking.   The parameters adopted for the Delft3D-PART model for modelling residual chlorine are summarised in Table 5.8.  For cooling water discharge, the flow rate as shown in Table 5.6 was factored up by 1.2 and was input into the model as a constant rate throughout both dry and wet seasons simulations.  It is also conservatively assumed that all cooling water discharges have a residual chlorine concentration of 0.5 mg/l, which was assumed to be discharged continuously 24 hours a day at the corresponding factored discharge rates.


Table 5.8         Summary of Parameters for Modelling of Residual Chorine (Delft3D-PART)

 

Partical Track Model Parameters

Ambient Water Temperature (oC)

18

28

Dry Season

Wet Season

Ambient Salinity (ppt)

31

30

Dry Season

Wet Season

Ambient Water Density (kg m-3)

1024

1016

Dry Season

Wet Season

Horizontal Dispersion Coefficient DH

(m2 s-1)

A = 0.003

B = 0.4

DH = a t b,

where t is the age of particle from the instant discharge in seconds

Vertical Dispersion Coefficient DV

(ms-1)

5 x 10-3

1 x 10-5

Dry Season

Wet Season

Residual Chlorine (mg/l)

0.5

-

Decay Factor for Residual Chlorine, T90 (s)

8289 (2)

-

Excess Temperature at Intake

From model

-

Flow Rate (m3s–1)

Equivalent for Intake and Discharge

No loss of water in the cooling system.

Particle Settling Velocity (m s-1)

-0.005 (Constant)

Heated discharge is slightly less dense than ambient water

Critical Shear Stress(1)

N/A

No sedimentation or erosion

(1)       Sedimentation and erosion are irrelevant for thermal plume modelling

(2)       Reference: Approved EIA for Tai Po Sewage Treatment Works Stage V.

 

5.6.39      It should be noted that the residual chlorine concentration represents total residual chlorine as there is no mechanism in the Delft model to partition the chlorine into free chlorine or various compound species.  As compared to the decay factor for residual chlorine (T90 = 1800s) adopted under the WDIICFS EIA, a more conservative value (T90 = 8289s) was used under this EIA. The T90 factor adopted in this EIA is based on the assumption used under the approved EIA for Tai Po Sewage Treatment Works Stage V.  Upon our review of relevant past EIA studies, this T90 factor is the most conservative value and was therefore applied to the model for conservative assessment.

5.6.40      As chlorination is being considered as the disinfection method for the HATS, the discharge of residual chlorine from HATS was included in the model for cumulative assessment assuming that the HATS is reaching an extreme flow rate of 2,800,000 m3 per day with a residual chlorine content of 0.02 mg/l. The design capacity of HATS is only about 2,450,000 m3 per day based on the latest flow projections conducted under the on-going EIA Study for HATS Stage 2A.


Construction Phase Impact

General Description of Marine Construction Works

5.6.41      The proposed marine construction works will involve:

·                     Permanent reclamation at Hong Kong Convention and Exhibition Centre (HKCEC)

·                     Permanent reclamation at Wan Chai (WCR)

·                     Permanent reclamation at North Point (NPR)

·                     Temporary reclamation at Public Cargo Working Area (TPCWA) and Causeway Bay (TCBR) for construction of the CWB tunnel

·                     Construction of Temporary Typhoon Shelter (TBW)

·                     Construction of new cross-harbour water mains from Wan Chai to Tsim Sha Tsui

·                     Construction of Wan Chai East submarine sewage outfall.

·                     Temporary reclamation at Wan Chai (TWCR4) (Please see Section 5.6.53)

 

5.6.42      The proposed construction method adopts an approach where permanent and temporary seawalls will first be formed to enclose each phase of the reclamation. Bulk filling will be carried out behind the completed seawall. Demolition of temporary reclamation will involve excavation of bulk fills and dredging to the existing seabed level which will be carried out behind the temporary seawall. Temporary seawall will be removed after completion of all excavation and dredging works for demolition of the temporary reclamation. Therefore, the sediment plume can be effectively contained within the permanent and temporary reclamation area.  Demolition of temporary seawall will involve removal of rock fill and seawall blocks only, which would not create significant SS impact.  Fines content in the filling materials for seawall construction would be negligible and loss of fill material during seawall construction is therefore not expected. Thus, potential water quality impact of SS will only arise during the dredging for seawall foundation.

5.6.43      There will be a total of five main reclamation areas, namely HKCEC, WCR, NPR, TPCWA and TCBR respectively.  Each of these five reclamation areas is subdivided into different stages for different engineering and environmental constraints as shown in Figure 2.7.  Within the same reclamation area, seawall dredging will be performed in sequence instead of operating concurrently. Thus, dredging along the seawall will be undertaken for only one stage at a time to minimize the potential water quality impacts. The sequencing of the reclamation stages are presented in the construction programme in Appendix 2.1 (as discussed in Section 2).

5.6.44      Temporary reclamation of Causeway Bay will be divided into four stages (Figure 2.7). Construction of TCBR1W and TCBR1E will be undertaken at the first stage with seawall foundation to be constructed in sequence. Thus, dredging along the seawall of TCBR1W will not be carried out simultaneously with the dredging along the seawall of TCBR1E to minimize the dredging impact. At Stage 2, dredging at seawall of TCBR2 will take place when TCBR1W and TCBR1E are in place.  Demolition of TCBR1E will then proceed and the whole TCBR1E will be removed before the commencement of TCBR3.  Thus, during the third stage, dredging for seawall foundation and seawall trench filling at TCBR3 will take place when both TCBR1W and TCBR2 are in place at the same time.  Subsequently, TCBR1W will be removed before the TCBR4 commences. Therefore, water body behind temporary reclamation area will not be fully enclosed, which minimise water quality impacts (also refer to Figure 2.10 to Figure 2.14). 


5.6.45      After the construction of the western seawall of HKCEC Reclamation