5                    HYDRODYNAMICS, WATER AND SEDIMENT QUALITY IMPACTS

5.1              Introduction

5.1.1          This section presents the assessment results of the potential hydrodynamic, water and sediment quality impact associated with the construction and operation of the proposed Project.  Mitigation measures are also recommended to minimise potential adverse impacts and to ensure the acceptability of any residual impact (that is, after mitigation).

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

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

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

5.2              Environmental Legislation, Policies, Plans, Standards and Criteria

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

·         Technical Memorandum on Environmental Impact Assessment Process (Environmental Impact Assessment Ordinance) (EIAO-TM);

·         Water Pollution Control Ordinance (WPCO);

·         Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS);

·         Hong Kong Planning Standards and Guidelines (HKPSG);

·         Water Supplies Department (WSD) Water Quality Criteria; and

·         Practice Note for Professional Persons (ProPECC), Construction Site Drainage (PN 1/94).

5.2.2          Marine bottom sediment classification is described in Section 6 of this EIA Report.

Environmental Impact Assessment Ordinance (EIAO), Cap. 499, S.16

5.2.3          This Project is a Designated Project under Schedule 3 of the EIAO.  The EIAO-TM was issued by EPD under Section 16 of the EIAO.  It specified 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

5.2.4          The Water Pollution Control Ordinance (Cap. 358) 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 (WQOs) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in the WCZs based on their beneficial uses.  The proposed WDII reclamation is located within the Victoria Harbour (Phase Three) WCZ and the corresponding WQOs are listed in Table 5.1.

Table 5.1         Summary of Water Quality Objectives for the Victoria Harbour WCZ

Parameters

Objectives

Sub-Zone

Offensive Odour,  Tints

Not to be present

Whole zone

Colour

Not to exceed 50 Hazen units, due to human activity

Inland waters

Visible foam, oil scum, litter

Not to be present

Whole zone

E. coli

Not to exceed 1000 per 100 mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals between 7 and 21 days

Inland waters

Dissolved Oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg L-1 for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg L-1 for 90% of samples

Marine waters

Dissolved Oxygen

Not less than 4.0 mg L-1

Inland waters

pH

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

Marine waters

 

Not to exceed the range of 6.0 - 9.0 due to human activity

Inland 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

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

Marine waters

 

Annual median not to exceed 25 mg L-1 due to human activity

Inland waters

Ammonia

Annual mean not to exceed 0.021 mg L-1 as unionised form

Whole zone

Nutrients

Shall not cause excessive algal growth

Marine waters

 

Annual mean depth-averaged inorganic nitrogen not to exceed 0.4 mg L-1

Marine waters

BOD5

Not to exceed 5 mg L-1

Inland waters

Chemical Oxygen Demand

Not to exceed  30 mg L-1

Inland 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).

 

 

 

 

Hong Kong Planning Standards and Guidelines (HKPSG)

5.2.5          The HKPSG, Chapter 9 (Environment), provides additional information on regulatory guidelines against water pollution for sensitive uses such as aquaculture and fisheries zones, bathing waters and other contact recreational waters.

Water Supplies Department Water Quality Criteria

5.2.6          Besides the WQOs set under the WPCO, the WSD has also specified a set of water quality criteria for flushing water at the seawater intake.  The list is shown in Table 5.2.  The target limit for suspended solids (SS) at these intakes is 10 mg L-1 or less.

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

Parameter (in mg L-1 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

5.2.7          In order to assess the water quality impact on the existing cooling water intakes, questionnaires were sent to the individual cooling water intake owners or operators requesting their operation requirements in terms of water quality.  Based on the responses received, no specific requirement on seawater quality at the cooling water abstraction point was identified, except for the cooling water intake of Admiralty Centre to the west of the study area.

5.2.8          To assess the potential water quality impact on the cooling water systems, a limit for SS concentration of 40 mg L-1 at the Admiralty Centre intake and MTRC South Intake will be adopted as the assessment criterion.  This criterion had been confirmed with the MTRC Property Management Office.  An SS upper limit of 140 mg L-1 for the cooling water intake of Queen Mary Hospital was assembled by surveys under other studies([1]). 

Technical Memorandum

5.2.9          Besides setting the WQOs, the WPCO controls effluent discharging into the WCZ through a licensing system.  A Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS) was issued under Section 21 of the WPCO that 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. Sewage from the proposed construction activities should comply with the standards for effluents discharged into the foul sewers, inshore waters or marine waters of the Victoria Harbour WCZ, as shown in Table 1, Table 9a and Table 9b, respectively, of the TM-DSS.

Practice Note

5.2.10      A practice note for professional persons 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.

Sediment Quality

5.2.11      Dredged sediments destined for marine disposal are classified according to a set of regulatory guidelines for designation of sediments (Management of Dredged / Excavated Sediment, WBTC No. 3/2000) issued by the Works Bureau and Planning, Environment and Lands Bureau in April 2000.  These guidelines comprise a set of sediment quality criteria, which include organic pollutants and other toxic substances.  This set of guidelines are applicable to any reclamation work commencing after 31 December 2001 and, therefore, applicable to this Project.  More details are presented in Section 6.3.

5.2.12      The requirement for the marine disposal of sediment is specified in the Works Branch Technical Circular No. 3/2000 and No. 12/2000. 

5.2.13      Marine disposal of dredged materials is controlled under the Dumping at Sea Ordinance 1995.

Sedimentation at the Seabed

5.2.14      Benthic organisms, including corals, may be damaged by sediment deposition that blocks the respiratory and feeding organs of the corals.  An assessment of effects of backfilling in Mirs Bay([2]) has assumed that prolonged turbidity and a sustained sedimentation rate of 0.2 kg m-2 per day may damage the corals.  This is adopted as the assessment criterion for protecting the marine ecological sensitive receivers in the WDII study.  The same criterion was adopted in the Northshore Lantau Development Feasibility Study, Final EIA Report([3]).

5.3              Description of the Environment

Marine Water Quality Monitored by EPD

5.3.1          For the purpose of this EIA, the EPD marine water quality monitoring data routinely collected in the vicinity of the site, which documents the water quality in the Victoria Harbour WCZ, have been used.  The EPD monitoring stations of most relevance (that is, in the vicinity of WDII) include VM4, VM5 and VM6 (Figure 5.1).  A summary of the published EPD monitoring data (in 1998) collected at these stations is presented in Table 5.3 ([4]).

5.3.2          The monitoring results in 1998 for the Victoria Harbour WCZ showed that the dissolved oxygen (DO) content in the middle of the Victoria Harbour (that is, stations VM4 and VM5) was generally lower than other parts of the harbour.

5.3.3          Several monitoring stations in the WCZ are located close to sewage outfalls, including VM5 (Wan Chai East, Wan Chai West and Kolwoon South outfalls) and VM6 (Central outfall).  The water quality at these stations was inevitably subject to the direct impact of sewage discharge from these outfalls.

5.3.4          Full compliance with WQO for bottom DO was achieved at VM4, VM5 and VM6 in 1998.  However, none of these stations could achieve 100% compliance of the depth-averaged DO concentration of WQO.  Non-compliance with the total inorganic nitrogen (TIN) were found at all three stations while full compliance of the unionised ammoniacal nitrogen (NH3-N) criterion are observed.

Table 5.3         Summary Statistics of 1998 Marine Water Quality in the Victoria Harbour WCZ at the Vicinity of WDII Reclamation Site

Parameter

 

EPD Monitoring Station (Monthly)

WPCO WQOs (in marine waters)

 

 

VM4

VM5

VM6

Temperature (oC)

 

23.7

(17.2 – 32.4)

23.3

(17.1 – 27.8)

23.3

(17.1 - 27.6)

natural daily level ± 2 oC

Salinity (ppt)

 

30.9

(28.1 – 33.5)

30.8

(27.3 – 33.2)

30.6

(26.8 - 33.1)

natural ambient level ± 10 %

Dissolved Oxygen (DO)

(% saturation)

 

69

(49 – 93)

68

(45 – 97)

70

(46 - 99)

-

Bottom

64

(43 – 80)

59

(41 – 80)

59

(29 - 75)

-

DO (mg L-1)

 

4.8

(3.1 – 6.5)

4.8

(3.0 – 6.5)

4.9

(2.9 - 6.8)

³ 4 mg L-1

 

Bottom

4.4

(2.7 – 6.3)

4.2

(2.8 – 6.4)

4.2

(2.0 - 6.0)

³ 2 mg L-1

pH value

 

7.9

(7.4 – 8.2)

7.5

(6.6 – 8.1)

7.8

(7.2 - 8.2)

6.5 - 8.5 (± 0.2 from natural range)

Secchi disc (m)

 

2.5

(1.8 – 3.5)

2.2

(1.7 – 3.0)

2.2

(1.0 - 3.0)

-

Turbidity (NTU)

 

4.3

(2.9 – 6.7)

4.5

(3.1 – 5.9)

4.4

(2.8 - 6.1)

-

SS (mg L-1)

 

4.6

(2.6 – 10.5)

4.6

(2.2 – 8.0)

4.7

(1.9 - 7.6)

£ natural ambient level + 30%

Silica (as SiO2)

(mg L-1)

 

1.0

(0.4 – 1.5)

1.0

(0.5 – 1.6)

1.0

(0.6 - 1.7)

-

BOD5 (mg L-1)

 

1.0

(0.7 – 1.4)

1.2

(0.5 –2.3)

1.2

(0.5 - 1.8)

not applicable to marine waters

Nitrite Nitrogen (mg L-1)

 

0.02

(0.01 – 0.04)

0.02

(0.01 – 0.04)

0.02

(0.01 - 0.04)

-

Nitrate Nitrogen (mg L-1)

 

0.10

(0.04 – 0.20)

0.11

(0.04 – 0.25)

0.11

(0.04 - 0.25)

-

Ammoniacal Nitrogen (mg L-1)

 

0.31

(0.12 – 0.49)

0.31

(0.06 – 0.50)

0.31

(0.12 - 0.45)

-

Unionised Ammonia (mg L-1)

 

0.010

(0.003 – 0.022)

0.007

(0.003 – 0.020)

0.008

(0.004 - 0.019)

£ 0.021 mg L-1

Total Inorganic Nitrogen (mg L-1)

 

0.43

(0.23 – 0.72)

0.45

(0.21 – 0.72)

0.44

(0.24 - 0.67)

£  0.4 mg L-1

Total Nitrogen

(mg L-1)

 

1.23

(0.96 – 1.54)

1.22

(0.98 – 1.58)

1.21

(0.93 - 1.52)

-

Ortho-Phosphate (mg L-1)

 

0.05

(0.02 – 0.08)

0.05

(0.01 – 0.08)

0.05

(0.02 - 0.07)

-

Total Phosphorus (mg L-1)

 

0.09

(0.07 – 0.11)

0.09

(0.06 – 0.12)

0.09

(0.07 - 0.11)

-

Phaeo-pigment

(µg L-1)

 

1.6

(0.2 – 7.1)

1.5

(0.2 – 5.6)

1.8

(0.2 - 7.5)

-

Chlorophyll-a

(µg L-1)

 

4.8

(0.9 – 19.1)

4.7

(0.6 – 21.7)

4.9

(0.9 - 24.0)

-

E. coli

(cfu per 100 mL)

 

 

8,400

(910 – 82,000)

7,200

(570 – 33,000)

5,100

(1,400-12,000)

not applicable to marine waters

Faecal Coliform

(cfu per 100 mL)

 

29,000

(3,300 – 120,000)

29,000

(2,000 – 70,000)

12,000

(3,700-30,000)

-

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.

 

Water Quality within Causeway Bay Typhoon Shelter

5.3.5          A summary of published EPD monitoring data (in 1998) collected from the monitoring station at the Causeway Bay Typhoon Shelter (VT2) is presented in Table 5.4 ([5]).

Table 5.4         Summary Statistics of 1998 Marine Water Quality at the Causeway Bay Typhoon Shelter

Parameter

 

EPD Monitoring Station (Bi-Monthly)

WPCO WQOs (in marine waters)

 

 

VT2

 

Temperature (oC)

 

23.7

(17.3 – 28.1)

natural daily level ± 2 oC

Salinity (ppt)

 

30.1

(27.0 – 31.4)

natural ambient level ± 10 %

Dissolved Oxygen (DO)

(% saturation)

 

50

(23 – 89)

-

 

Bottom

48

(17 – 87)

-

DO (mg L-1)

 

3.5

(1.5 – 6.2)

³ 4 mg L-1

 

Bottom

3.3

(1.1 – 6.0)

³ 2 mg L-1

pH value

 

7.5

(7.3 – 7.9)

6.5 - 8.5 (± 0.2 from natural range)

Secchi disc (m)

 

1.7

(1.5 – 2.0)

-

Turbidity (NTU)

 

5.5

(3.7 – 7.2)

-

SS (mg L-1)

 

6.2

(3.4 – 7.8)

£ natural ambient level + 30%

Silica (as SiO2)

(mg L-1)

 

1.2

(1.0 – 1.4)

-

BOD5 (mg L-1)

 

1.3

(0.9 – 1.9)

not applicable to marine waters

Nitrite Nitrogen (mg L-1)

 

0.02

(0.01 – 0.03)

-

Nitrate Nitrogen (mg L-1)

 

0.11

(0.06 – 0.18)

-

Ammoniacal Nitrogen

(mg L-1)

 

0.45

(0.13 – 0.66)

-

Unionised Ammonia

(mg L-1)

 

0.007

(0.003 – 0.017)

£ 0.021 mg L-1

Total Inorganic Nitrogen (mg L-1)

 

 

0.58

(0.32 – 0.74)

£  0.4 mg L-1

Total Nitrogen

(mg L-1)

 

1.45

(1.17 – 1.71)

-

Ortho-Phosphate (mg L-1)

 

0.07

(0.03 – 0.09)

-

Total Phosphorus

(mg L-1)

 

0.12

(0.09 – 0.15)

-

Phaeo-pigment

(µg L-1)

 

1.5

(0.3 – 5.7)

-

Chlorophyll-a

(µg L-1)

 

3.8

(0.4 – 18.3)

-

E. coli (cfu per 100 mL)

 

17,000

(11,000 – 45,000)

< 610 cfu per 100 mL for keeping live seafood

Faecal Coliform

(cfu per 100 mL)

 

41,000

(18,000 – 100,000)

-

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.

 

5.3.6          Due to the embayment form and reduced flushing capacity of the typhoon shelter, marine water within the typhoon shelter is vulnerable to pollution.  In 1998, the Causeway Bay Typhoon Shelter was one of the monitored typhoon shelters that recorded the poorest water quality in Hong Kong.  The Causeway Bay Typhoon Shelter is subject to heavy faecal pollution and the seawater within is therefore not suitable for keeping live seafood. 

Environmental Trend of Water Quality in the Victoria Harbour

5.3.7          As reported in the “Marine Water Quality in Hong Kong in 1998” issued by EPD, an increasing trend of Escherichia coli (E. coli) at VM4 is observed together with other five monitoring stations (VM2, VM8, VM12, VM13 and VM14) within the WCZ.  An increasing trend of faecal coliforms at VM4 and VM5 as well as other stations in the WCZ is also observed.  These findings reflect a widespread and marked increase in faecal pollution in the Victoria Harbour.

5.3.8          A significant long-term increase in sea water temperature is also observed at VM4, VM5, VM6 and other stations within the WCZ.  It was estimated that the temperature (depth-averaged) at these stations experienced an average rise of 1.2 oC in the past ten years.

Sediment Quality

5.3.9          The results of marine sediment quality analysis from the marine ground investigation works at WDII are presented in Section 6.4 and Tables 6.2 and 6.3.  The results indicated that Category H sediment was found at 16 out of 18 vibrocoring locations due to the high contaminant levels of silver (Ag), copper (Cu), lead (Pb), zinc (Zn) and mercury (Hg) that exceed the Upper Chemical Exceedance Level (UPCL) under the new sediment classification system (WBTC No. 3/2000, Management of Dredged / Excavated Sediment).

5.4              Water Sensitive Receivers

5.4.1          In order to evaluate the water quality impacts during the construction and operational phases, the proximity of Water Sensitive Receivers (WSRs) to the reclamation site must be considered.  These have been identified in accordance with the HKPSG and EIAO-TM, which provide guidance for including environmental consideration in the planning of both public and private developments.

Salt Water Intakes

5.4.2          There are 11 WSD salt water pumping stations and intakes at the waterfront of Victoria Harbour that may be impacted by dredging and filling works of the Project:

·         Wan Chai Salt Water Pumping Station and Intake;

·         Central Water Front Salt Water Pumping Station and Intake;

·         Sheung Wan Salt Water Pumping Station and Intake ([6]);

·         Kennedy Town Salt Water Pumping Station and Intake;

·         Quarry Bay Salt Water Pumping Station and Intake;

·         Sai Wan Ho Salt Water Pumping Station and Intake;

·         Siu Sai Wan Salt Water Pumping Station and Intake;

·         Tai Wan Salt Water Pumping Station and Intake; and

·         Cha Kwo Ling Salt Water Pumping Station and Intake;

·         Yau Tong Salt Water Pumping Station and Intake; and

·         Kowloon South Salt Water Pumping Station and Intake.

5.4.3          It should be noted that the Wan Chai Salt Water Pumping Station intake will be temporarily reprovisioned to WCR1 during the reclamation (Figure 5.2) and will be permanently reprovisioned to the Kellett Island Marina promenade (Figure 5.2) during the operation phase of the WDII.  The invert level of the existing WSD Wan Chai salt water intake (-0.35 mPD) has been confirmed with WSD.  While the existing WSD Wan Chai salt water intake will be in place under Scenario 2A, it will be temporarily reprovisioned to WCR1 under Scenario 2B (with the intake within the top layer of the water column simulated by the model) and permanently reprovisioned to Kellett Island Marina breakwater during operational phase (with the intake within the second top layer of the water column simulated by the model).  The predicted concentrations of various water quality parameters presented in the report correspond to the existing and planned invert levels of the intakes under the baseline, construction and operation scenarios.

Cooling Water Intakes

5.4.4          A number of cooling water pumping stations and intakes are located along the waterfront of Wan Chai and Central, and will be impacted by dredging and filling works of WDII.  These intakes supply cooling water to the air conditioning systems of certain commercial buildings in Wan Chai and Causeway Bay:

·         Windsor House;

·         Excelsior Hotel and World Trade Centre;

·         Sun Hung Kai Centre;

·         Great Eagle Centre / China Resources Building;

·         Wan Chai Tower / Revenue Tower / Immigration Tower;

·         Hong Kong Convention and Exhibition Centre Phase I;

·         Hong Kong Convention and Exhibition Centre Extension;

·         Telecom House / Hong Kong Academy for Performing Arts (HKAPA) / Shun on Centre;

·         MTRC South Intake;

·         Prince’s Building Group at CRIII;

·         Queensway Government Offices at CRIII;

·         Admiralty Centre at CRIII; and

·         HSBC and Hotel Furama at CRIII.

5.4.5          The locations of these receivers are shown in Figure 5.2.

Marine Ecological Sensitive Receivers

5.4.6          The Green Island and Junk Bay coral communities are located more than 5.5 km west and 6.5 km east of the WDII reclamation site, respectively.  These ecological sensitive receivers are potentially impacted during the construction of the WDII due to the sedimentation of the suspended solids in the water column.  Potential adverse impacts on the coral communities, in terms of sedimentation rate, are addressed in Sections 5.7.5 and 5.7.9.  Further discussions are included in the marine ecological impact assessment (Section 9).

5.5              Assessment Methodology

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

Marine-based Impact

Model Setup

Hydrodynamic and Water Quality Models

5.5.2          Computer modelling is employed to assess the potential impacts on water quality in the Victoria Harbour associated with the construction and operation of WDII for different tidal conditions.  The hydrodynamic and water quality models were developed by Delft Hydraulics, namely the Delft3D-FLOW and Delft3D-WAQ respectively. 

5.5.3          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.

5.5.4          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.

5.5.5          In the present study, the basis for modelling of the harbour waters is the existing Victoria Harbour model.  This detailed model was originally developed to assess the impacts of the proposed Shatin Stage III extension on the water quality in the 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. 

5.5.6          In order to adapt the Victoria Harbour model for assessing water quality impacts of the WDII, minor modifications for the model setup are performed.  For example, the grid layout of the original Victoria Harbour model is 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”([7]).

5.5.7          The simulation periods for the hydrodynamic model cover a complete spring-neap tidal cycle, preceded by a spin-up period.  For the water quality simulations, the spring-neap tidal cycle hydrodynamic results are used repeatedly to simulate a time span covering several cycles, to ensure that initial condition effects can be neglected.  The hydrodynamic simulation periods are specified below:

·         spin-up dry season:  1 February 1996 15:00 – 8 February 1996 00:00

·         dry season:              8 February 1996 00:00 – 23 February 1996 00:00

·         spin-up wet season: 18 July 1996 14:00 – 26 July 1996 12:00

·         wet season:             26 July 1996 12:00 – 10 August 1996 12:00

5.5.8          In the operational hydrodynamic and water quality modelling, the hydrodynamic influence of the structural features of the CRIII promenade was not included in the model.  The promenade will include about 25 piles.  Each pile is about 1 m in diameter and there is more than 10 m separation between consecutive piles.  The piles will reduce the opening of the water basin formed by the HKCEC2E and HKCEC2W by about 10%, that is, from about 250 m to about 225 m wide.  The opening of the embayment is still wide enough to allow tidal flushing within the embayment and the piles are unlikely to introduce significant changes in the flushing capability or adverse impact on water quality within the water basin.

Pollution Loading Inventory

5.5.9          Marine works for the WDII Project are anticipated to start in March 2004 and will be completed in 2007.  A pollution loading inventory has been compiled for the Project, based on the WDII expedient connection survey in January 2000 and the pollution loading inventory compiled under the on-going study, titled “Update on Cumulative Water Quality Impacts and Hydrological Effects of Coastal Developments and Upgrading of Assessment Tool, Agreement No. CE 42/97” (hereinafter referred to as the Cumulative Impact Study), to provide information on the waste load discharging to the Victoria Harbour for the relevant design horizon years.  The pollution loading inventory that details the estimated sewage and stormwater flows and loads, both within and outside the WDII study area, has been revised in accordance with the comments from the EPD, the DSD and the planned population figures on the proposed WDII development, and submitted to various government departments.  The established pollution loading inventory for WDII has been input to the water quality model to simulate the baseline and operation phase conditions (Appendix 5.1).

5.5.10      There are two existing submarine sewage outfalls in the Victoria Harbour which are associated with the Wan Chai West Preliminary Treatment Works (WCW PTW) and the Wan Chai East Preliminary Treatment Works (WCE PTW).  The WCW PTW will be decommissioned by 2003, before the commencement of WDII construction works, and sewage will be diverted to the existing WCE PTW, which is being upgraded in capacity.  A new Wan Chai East Sewage Outfall will be constructed under the WDII Project.  The present water quality simulations assume that the new outfall will be located adjacent to the existing discharge point.

5.5.11      SSDS Stage III/IV is under review and is considered unlikely to be in place by the WDII operating year 2011.  Hence, as a conservative approach for the WDII study, it is assumed that only SSDS Stage I will be implemented.  The planned sewage diversions as presented in the Further Development of Strategic Sewage Disposal Scheme Stage III/IV and PPFS, Final Report (SSDS III/IV Study) have been taken into account in the pollution loading inventory.  It is also assumed that the disinfection facility will be implemented at the Stonecutters’ Island Sewage Treatment Works in the operation phase scenario resulting in a load reduction of E. coli at the SSDS interim outfall.

5.5.12      A stormwater flow and pollutant survey of outfalls entering the Victoria Harbour within the WDII reclamation area was also undertaken in 2000([8], [9]).  The outfall survey locations were chosen at manholes up stream of the outfalls where the tidal effects of harbour would be small.  Sampling for both water quality and flow were recorded during times when the tide was near its lowest.  These survey results are presented in Table 5.5.  They were used to derive Wan Chai storm loading for water quality simulations (Tables A5.7 and A5.8 in Appendix 5.1) of baseline scenario, interim construction stage and operational scenario in dry and wet seasons.

5.5.13      The pollution loading in Causeway Bay Typhoon Shelter from marine population is considered insignificant, and therefore not taken into account in the pollution load inventory for WDII.  The existing dwelling vessels will not be reprovided in the new typhoon shelter, nor will the vessels in the local craft anchorage, apart from some 20 working vessels (sampans, etc.) which provide ferry services to the typhoon shelter users.  The vessels that will be reprovisioned in the new typhoon shelter will therefore comprise private yachts and junks and some operational craft (pilots boats, sampans, etc), but no dwelling vessels.  Discharge from these vessels is not permitted but, notwithstanding, any pollution loading from these vessels will be insignificant.

 

Table 5.5         Locations and Pollution Loadings Survey Results (in 2000) of Wan Chai Stormwater Outfalls

Outfall

Location

Flow rate

(m3 per day)

Pollution Loadings

Easting

Northing

Suspended Solids

(kg per day)

BOD

(kg per day)

COD

(kg per day)

Ammoniacal Nitrogen

(kg per day)

Organic Nitrogen

(kg per day)

Total Kjeldhal Nitrogen

(kg per day)

E. coli

(cfu per day)

L

835467

815848

2743

2144.12

1337.73

3002.62

23.16

106.70

129.86

7.889E+14

M

836000

815889

13775

581.30

514.28

871.65

35.02

58.58

93.60

1.84E+14

N

836397

815977

1761

11.37

18.80

27.10

3.07

2.69

5.76

1.86E+12

O

836551

816059

3500

346.35

378.87

597.64

19.80

33.29

53.09

3.078+14

P

836921

815940

127

50.92

84.19

193.12

5.04

2.93

7.97

6.41E+12

Q

837139

816106

13302

464.28

372.54

607.47

35.17

126.39

161.56

4.08E+13

R

837551

816230

1197

362.21

105.25

158.58

6.01

9.81

15.82

9.71E+12

S

837595

816322

1030

3.10

5.86

11.64

0.68

0.64

1.32

1.93E+12

Sources:                 (1)  EGS (Asia) Limited  (2000).  Wan Chai Development Phase II, Comprehensive Feasibility Study, Section I, Stormwater Flow and Pollutant Survey of Outfalls Entering Victoria Harbour of Outfalls Entering Victoria Harbour, Final Report.

                              (2)  EGS (Asia) Limited (2000).  Wan Chai Development Phase II, Expedient Connection Survey, Supplementary Report for Section I of Works.


Coastline Configurations for Construction and Operation Phase Modelling Scenarios

5.5.14      For the hydrodynamic and water quality modelling of this EIA, a Regional Model has been setup to cover the whole of Hong Kong and the Pearl Estuary.  The Regional Model, based on the previous Upgraded Model for EPD, is used to provide the boundary inputs to a local Victoria Harbour Model for the present study.  The Victoria Harbour Model covers the neighbouring waters of Hong Kong Island, including the Victoria Harbour.  The construction and the operation phases were simulated using the Victoria Harbour Model. 

5.5.15      Two sets of boundary conditions for the detailed Victoria Harbour Model were generated for the baseline and operation phase modelling scenarios respectively using the Regional Model.  For the purpose of setting up the Regional Model properly, the coastline configurations was updated to mimic the envisaged conditions for the modelling scenarios.  For the construction phase scenarios, the boundary conditions for the baseline scenario have been used which have approximately the same coastline configuration.  Although the interim construction scenario would involve some reclaimed land as the reclamation proceeds, this partially reclaimed land is relatively small and is unlikely to have a major effect on the flow through the Victoria Harbour or on the boundary conditions of the detailed model.  Flow discharges through the eastern and western ends of the Victoria Harbour in different scenarios are summarised in Table 5.21.

5.5.16      The Delft3D Upgraded Model has been setup and calibrated for the entire Hong Kong and neighbouring waters.  The coastline configuration and the corresponding bathymetry for a number of planning horizons have been established and endorsed under the Cumulative Impact Study.  The cumulative effects of various coastal developments in Hong Kong were taken into account in the hydrodynamic and water quality modelling for the WDII study.  The following modelling scenarios have been set up for the WDII study:

·         Baseline Scenario – to simulate the pre-construction conditions of flow and water quality in Victoria Harbour in 2003;

·         Construction Phase – modified coastline based on the “2007” Scenario of the Cumulative Impact Study:

-          Scenario 2A to simulate the period between March 2004 and August 2005.

-          Scenario 2B to simulate the period between September 2005 and September 2007.

·         Operational Phase – modified coastline based on the 2012 Scenario of the Cumulative Impact Study to simulate the operation conditions of flow and water quality in Victoria Harbour in 2012.

5.5.17      The “2007 Scenario” of the Cumulative Impact Study is adopted as the basis of the construction phase coastline configuration because the time horizon is about midway through the WDII construction.  Neighbouring developments likely to be concurrent with the present Project will be excluded from the construction phase coastline configuration, to enable the simulation and assessment of the cumulative impacts from the concurrent mud dredging and sand filling activities in Victoria Harbour.  The “2012 Scenario” of the Cumulative Impact Study, with modification for the new conceptual layout of the South East Kowloon Development (SEKD) and revised layouts of other developments, will closely resemble the ultimate operation condition and will be adopted as the basis of the WDII operation scenario.

5.5.18      For the purpose of setting up the models for WDII, the pollution loading inventory for the years 2007 and 2012 finalised for the Cumulative Impact Study have been adopted to represent the pollution loading during the construction and operation phases of WDII.

5.5.19      The developments to be included in the construction and operation phase coastlines have been updated to incorporate the latest information received on the planned developments.  The details of the coastal developments to be incorporated in the WDII construction and operation phase coastline configurations, the source of information and the current status of the planned developments are summarised in Table 5.6.  The proposed construction phase coastline configurations, highlighting the incorporated coastal developments, are shown in Figure 5.3.

5.5.20      For those developments which the status remains unchanged, or for which no revised detailed layout is available at present, the coastline configurations of these developments were based on those adopted in the on-going Cumulative Impact Study.

5.5.21      Figure 5A-1 (Appendix 5.7), Figure 5F-1 (Appendix 5.6) and Figure 5B-1 (Appendix 5.8) show the coastline configuration and model grids for baseline scenario, interim construction stage and operation scenario, respectively.

 


Table 5.6         Coastal Developments to be Incorporated in the Construction and Operational Phase Coastline Configurations

Coastal Developments

Information Source

Description of Coastline Configuration for the WDII Comprehensive Feasibility Study

Included in Construction Phase Coastline Configuration

Included in Operation Phase Coastline Configuration

Proposed Container Terminals

CT10 and CT11

EPD

PlanD

The proposed development was adopted in the on-going Cumulative Impact Study(2).  However, the latest information indicated that these development sites are now reserved for the proposed theme park at Penny’s Bay and the proposed reclamation limit is shown in the North East Lantau Outline Zoning Plan No. S/I-NEL/5.

 

No

No

TKO Area 138 and the Cross Bay Link

TKO Area 131

PlanD

TDD/NTE

These developments are currently under review in the Feasibility Study for Intensification and Extension of Tseung Kwan O New Town (TKONT) and the Engineering Feasibility Study for the TKO Port Development at Area 131.

The latest information received from TDD/NTE (as at 3 November 1999) shows the concept plan for the full reclamation at TKONT at Area 138, including the corresponding layout for the Cargo Working Area (CWA) at Area 131, which represents the worst case scenario and will be adopted for the WDII study.

 

No

Yes

TKO Area 52

PlanD

TDD/NTE

This is currently under review in the Feasibility Study for Intensification and Extension of Tseung Kwan O New Town (TKONT).

According to the latest information from TDD/NTE (as at 3 November 1999), the concept plan for the full reclamation scenario in the TKONT study, which disconnects the water channel between Area 52 and Junk Bay, will be adopted in the present WDII study.  Hence, the water channel in Area 52 will be effectively removed from the coastline configuration for the WDII study.

 

No

No

Western Coast Road (WCR)

TDD/NTE

EPD

The WCR alignment and the associated reclamation area as adopted in the Cumulative Impact Study will be included in the WDII study.

 

No

Yes

Revised reclamation at Penny’s Bay to incorporate the proposed theme park layout

 

 

 

EPD

PlanD

CED

The proposed theme park (without container terminal no. 12 and 13) at Penny’s Bay and the proposed reclamation limit is shown in the North East Lantau Outline Zoning Plan No. S/I-NEL/5.  The same layout was adopted in the on-going Cumulative Impact Study.

 

 

No

Yes

Central Reclamation Phase III (CRIII)

TDD/HKI&Is

Latest reclamation limit for the CRIII Development has been obtained from the engineering consultants, Atkins China Ltd, who are undertaking the detailed design for the development.

 

Yes

(Intermediate layout)

Yes

Kowloon Point

Phases I, II and III

TDD/KD

PlanD

EPD

According to the communication with TDD/KD, no decision has been made since the completion of the feasibility study in 1997 on whether the project will proceed, the scale and time frame.  The layout as adopted in the on-going Cumulative Impact Study will be included in the WDII study.

 

No

Yes

Revised South East Kowloon Development (SEKD), including the Kai Tak Nullah Reclamation

TDD/KD

PlanD

EPD

Based on the latest information (as at 3 November 1999), there is only an Outline Concept Plan for the SEKD which will be subject to a comprehensive feasibility study at the end of year 1999.  This Outline Concept Plan will be adopted in the WDII study.

 

 

No

Yes

Green Island Reclamation

Stages I, II and III and

Hong Kong Lantau Link

 

TDD/HKI&Is

PlanD

EPD

All stages of the Green Island Reclamation are currently under review and no information on the development layout can be confirmed at present.

The full Green Island Reclamation as adopted in the on-going Cumulative Impact Study will be included in the WDII coastline configuration, representing the worst case scenario.

No

Yes

Tsuen Wan Bay Further Reclamation

Phases II, III, IV and V

 

TDD/NTW

EPD

The full reclamation layout of the development as adopted in the on-going Cumulative Impact Study will be included in the WDII study.

 

No

Yes

Route 9 – A link between Tsing Yi and Cheung Sha Wan

EPD

As adopted in the on-going Cumulative Impact Study.

 

 

 

Yes

Yes

North Lantau Development

Tung Chung Phase III and Tai Ho Phases III and IV

EPD

The phasing and reclamation program associated with this development are subject to the on-going Tung Chun and Tai Ho Comprehensive Feasibility Study.  The reclamation limits for the Tung Chung and Tai Ho Developments as adopted in the on-going Cumulative Impact Study will be included in the WDII coastline configuration.

 

Yes

Yes

Tuen Mun Port Development

Phases III and IV

CED

PlanD

EPD

As adopted in the on-going Cumulative Impact Study.

 

 

 

Yes

Yes

Peng Chau Typhoon Shelter

CED

PlanD

EPD

The Peng Chau Typhoon Shelter (TS) is subject to further study to ascertain the need, extent and timing of the TS.  The layout of the Peng Chau TS as adopted in the on-going Cumulative Impact Study will be included in the coastline configuration for the WDII.

 

Yes

Yes

Sham Tseng Further Reclamation (STFR)

CED

PlanD

EPD

The latest information (as at 3 November 1999) from the engineering consultant of the STFR, Scott Wilson (Hong Kong) Ltd. shows the reclamation limit of the CPLD endorsed STFR Option 1.  This layout will be included in the WDII study.

 

Yes

Yes

Siu Lam Typhoon Shelter

EPD

As adopted in the on-going Cumulative Impact Study.

 

 

Yes

Yes

Pak Shek Kok Reclamation

Stage II Phase 2

EPD

As adopted in the on-going Cumulative Impact Study.

 

 

 

Yes

Yes

North Tsing Yi Reclamation (NTYR)

TDD/NTW

EPD

The conceptual reclamation layout for the project “Reclamation Works for District Open Space, Government, Institution and Community Facilities in North Tsing Yi” (PWP Item No. 410CL) will be included in the coastline configuration for the WDII.  This layout is adopted in the on-going Cumulative Impact Study.

 

Yes

Yes

Lamma Power Station Extension

EPD

Proposed extension of the existing Lamma Power Station as adopted in the on-going Cumulative Impact Study will be included in the WDII coastline configuration.

 

Yes

Yes

Waste to Energy Incineration Facilities (WEIF)

EPD

This layout was not included in the on-going Cumulative Impact Study. However, the latest information reveals a proposed conceptual reclamation layout to the south of the Lamma Power Station to house two WEIF with a capacity of 3000 tonne per day and will be included in the WDII study.

 

Yes

Yes

Proposed Widening of  Tolo Highway / Fanling Highway

EPD

As adopted in the on-going Cumulative Impact Study.

 

 

 

Yes

Yes

Alteration Work for the Island Eastern Corridor – Section between North Point and Sai Wan Ho

EPD

As adopted in the on-going Cumulative Impact Study.

 

 

 

 

Yes

Yes

Route 10 – North Lantau to Yuen Long Highway

EPD

This is formally known as Sham Tseng Link that forms the second road link between the proposed port development in North Lantau to Yuen Long Highway.  This layout is included in the on-going Cumulative Impact Study.

 

Yes

Yes

Yau Tong Bay (YTB) Reclamation

Main Wealth Co. Ltd.

The layout is included in the on-going Cumulative Impact Study.  However, the proposed reclamation layout has been revised in the recent EIA study for the Reclamation of YTB.  The proposed layout adopted in the Draft EIA Report, which is now being reviewed by the various government departments, will be adopted for the WDII study.

 

No

Yes

Route 7 – A link between Kennedy Town and Aberdeen

EPD

As adopted in the on-going Cumulative Impact Study.

 

 

 

No

Yes

Wan Chai Development

Phase II (WDII)

TDD

The present project will be excluded at present to serve as a baseline scenario without the WDII reclamation.  A detailed reclamation layout will be incorporated in the Local / Victoria Harbour Model at a later stage when the preferred trunk road option and the corresponding extent of reclamation are agreed.

 

Yes

(Intermediate Layout)

Yes

Note:  (1)        The developments included in the coastline configuration of the construction phase scenario are also included in the operation phase scenario coastline configuration.

(2)           The Cumulative Impact Study refers to EPD’s on-going study titled “Update on Cumulative Water Quality Impacts and Hydrological Effects of Coastal Developments and Upgrading of Assessment Tool, Agreement No. CE 42/97”.  The coastline configuration and the corresponding bathymetry for a number of planning horizons have been established and endorsed by the project steering group of the Cumulative Impact Study.

 


Construction Phase Impact

(i)                 Suspended Solids

Sediment Plume Modelling

5.5.22      The proposed WDII works involves the reclamation of land along the existing coastline.  The suspended solids (SS) concentration in the water column may increase as a result of the sand filling and mud dredging activities during the reclamation works.  In the present study, a sediment plume model is employed to simulate the SS elevation in the Victoria Harbour associated with the dredging and filling activities and to assess the impact on the neighbouring water sensitive receivers.  Details of the sediment plume model are discussed as follows.

5.5.23      Sediment plumes arising from the sand filling and mud dredging activities during the reclamation works will be simulated using a 3-dimensional particle tracking model (Delft3D-PART) developed by Delft Hydraulics.  This model has been used in a number of previous reclamation studies in Hong Kong including the recent Northshore Lantau Development Feasibility Study([10]) and the Theme Park Development at Penny’s Bay Environmental Impact Assessment (EIA) Study([11]).

5.5.24      The loss of fines to the water column during dredging and filling operations are represented by discrete particles in the model.  These discrete particles are transported by advection, due to the tidal flows determined from hydrodynamic simulation, and turbulent diffusion and dispersion, based on a random walk technique.  The hydrodynamic data are provided by the detailed Victoria Harbour Model, which has been calibrated in the previous Shatin Sewage Treatment Works Stage III Extension EIA study([12]), and the model is updated and verified under the present study([13]).  The substance concentration distribution is then evaluated from the particle density in each cell of the curvilinear grid of the Victoria Harbour model.

5.5.25      The Delft3D-PART model takes into account the sedimentation process by means of a settling velocity, while erosion of bed sediment, causing resuspension of sediment, is governed by a function of the bed shear stress.  The parameters adopted in the present study are summarised in Table 5.7.

Table 5.7         Summary of Parameters for Sediment Plume Model (Delft3D-PART)

Sediment Plume Model Parameters

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 of discharge in seconds

Vertical Dispersion Coefficient DV

(m2 s-1 )

5x10-3

1x10-5

Dry Season

Wet Season

Particle Settling Velocity

0.0001 m s-1 (Constant)

Grain size diameter of 10 mm

Critical Shear Stress

0.05 Pa

0.15 Pa

Sedimentation

Erosion

 

5.5.26      As filling with marine sand and selected public fill will only be carried out behind completed seawalls (above high water mark), sediment plume generated during filling will be effectively contained within the reclamation area.  Thus, the potential impact of SS dispersion associated with dredging and sand filling along the seawall trench (for seawall foundations) are considered in the sediment plume modelling.

Modelling Scenarios

5.5.27      The proposed WDII reclamation may be divided into 3 main areas (Figure 5.4):

·         Causeway Bay Reclamation (CBR) in 2 stages;

·         Wan Chai Reclamation (WCR) in 3 stages, plus the Kellett Island Marine breakwater and the Wan Chai Public Cargo Working Area (PCWA); and

·         Hong Kong Convention and Exhibition Centre Reclamation (HKCEC) in 2 stages.

5.5.28      Each stage of the reclamation and marine works are further subdivided into different phases to account for different engineering and environmental constraints.

5.5.29      The present construction adopts an approach where permanent and temporary seawalls will first be formed to enclose each phase of the reclamation and bulk filling will be carried out behind the seawalls.  The sediment plume is effectively contained within the reclamation area, minimising the loss of fines to the adjacent water bodies.  Thus, the water quality impact of SS will arise during dredging for the seawall foundation and backfilling of the seawall trench using grab dredgers where SS may be transported to the neighbouring areas by advection and diffusion.

5.5.30      Existing storm outfalls will be temporarily diverted to the new waterfront (as shown in Figure 5.6) along the temporary seawall of the adjacent reclamation to avoid discharging into temporary embayments, in order to which minimise potential water quality impacts.  Flows from Culvert L, adjacent to the eastern end of the CRIII reclamation, will be channelled outside the embayment under the CRIII contract when the CRIII eastern seawall is constructed.

5.5.31      The construction of a new water mains from Wan Chai to Tsim Sha Tsui and a submarine sewage pipeline from the Wan Chai East Sewage Screening Plant will also be undertaken under the WDII Project, which will require dredging along the proposed alignments of the water mains and the submarine sewage pipeline.

5.5.1          The sequencing of the reclamation stages presented in the preliminary WDII construction programme (as discussed in Section 2) represents the currently anticipated construction approach, taking into account the constraints of the existing facilities and services and likely resource levels, under which the WDII land formation will be undertaken.  The programme is intended primarily to show the manner in which the works can be carried out to meet the critical completion dates, and within appropriate resource levels (these also being assessed in this EIA to ensure that the work rates and resource levels will not result in unacceptable environmental impacts).  However, ultimately it will be up to the contractor to propose his own works programme to suit his construction methods and resources.  Some flexibility must therefore be kept in hand when carrying out the assessments to provide confidence that any variation of the construction sequencing which may be proposed later by the contractor will still be environmentally acceptable.

5.5.2          Critical constraints that must be taken into account, whatever differences to the construction programme may be proposed at a later stage, are:

(i)                  the diversion of the existing cooling water intakes of Windsor House, Excelsior Hotel and World Trade Centre across new land formed under Causeway Bay Reclamation Stage 1 (CBR1), before Causeway Bay Reclamation Stage 2 (CBR2) can commence;

(ii)                the diversion of the existing cooling water intake of Sun Hung Kai Centre, WSD's  Wan Chai salt water intake and the Wan Chai East sewage outfall across new land formed under Wan Chai Reclamation Stage 1 (WCR1), before Wan Chai Reclamation Stages 2E and 3W (WCR2E and WCR3W) can commence;

(iii)               the diversion of the existing cooling water intakes along the HKCEC water channel to the intake chambers to the north of the HKCEC Extension before HKCEC Reclamation Stages 1 and 2  (HKCEC1, HKCEC2E and HKCEC2W) can commence and, additionally, the diversion of the WSD cross harbour water mains before Stage 2 (HKCEC2) can commence.

5.5.3          These constraints effectively divide the land formation works into two scenarios.  Dredging and filling operations for stages CBR1E, CBR1W, WCR1, WCR3E, the Kellett Island Marina breakwater, the PCWA basin and HKCEC1 will generally take place over the period from March 2004 to August 2005; the remaining stages will take place afterwards (after the diversions of the services and intakes), over the period September 2005 to September 2007.

5.5.4          The construction staging within each of these periods of construction could vary according to the contractor's detailed proposals.  For example, while the current programme indicates dredging during the first period of reclamation works in the sequence of WCR1, PCWA basin, WCR3E and then the Kellett Island Marina breakwater (with dredging of CBR1E and CBR1W concurrent with all of these areas), there is no particular reason why the contractor may not change some of these sequences (if, say, advance dredging were to be required alongside the PCWA breakwater to relieve operational constraints on the temporary helipad to be located there), or even undertake dredging at some of these areas concurrently (by spreading his resources over a wider area to relieve possible marine plant congestion).  Similar situations may prevail during the second period of reclamation works.

5.5.5          The water quality impacts have therefore been assessed for these two overall construction periods, with the modelling scenarios selected to ensure compatibility with possible later modifications to the programme.  Water quality impact assessments have also taken into account possible concurrent reclamation activities at other nearby projects that may have a cumulative influence on the water quality impacts.  The water quality impacts associated with the construction stages have been assessed for the following scenarios using the particle model (Delft3D-PART):

·         Scenario 2A – Potential construction impact between March 2004 and August 2005

5.5.6          To assess the worst case scenario during the above construction period, the marine works in the following areas are assumed to take place concurrently:

1.       Dredging and filling at CBR Stage 1 East (CBR1E) and CBR Stage 1 West (CBR1W);

2.       Dredging and filling at WCR Stage 1 (WCR1);

3.       Dredging at WCR Stage 3 East (WCR3E) and filling at the Kellett Island Marina breakwater.

4.       Dredging and filling at the CRIII Final Reclamation Area East (FRAE), with location shown in Figure 3.2b;

5.       Filling at Yau Tong Bay;

6.       Dredging along the proposed alignment of the WSD cross harbour water mains from Wan Chai to Tsim Sha Tsui; and

7.       Dredging along the proposed alignment of the submarine sewage pipeline of the Wan Chai East Sewage Treatment Works.

5.5.7          The Central – Wan Chai coastline configuration of Scenario 2A, including the intermediate layout of CRIII, is shown in Figure 5.5.

·         Scenario 2B – Potential construction impact between September 2005 and September 2007

5.5.8          To assess the worst case scenario during the above construction period, the dredging and filling activities in the following areas are assumed to take place concurrently:

1.       CBR Stage 2 East (CBR2E) and CBR Stage 2 West (CBR2W);

2.       WCR Stage 2 East (WCR2E);

3.       HKCEC Stage 2 West (HKCEC2W).

5.5.9          The Central – Wan Chai coastline configuration of Scenario 2B, including the intermediate layout of WDII and full layout of CRIII, is shown in Figure 5.6.

General Remarks

5.5.10      The coastline configuration for Scenario 2A is same as that adopted in the baseline scenario plus the intermediate coastline configuration of the CRIII that will be completed by early 2004, while Scenario 2B includes a few more pieces of reclamation as the construction proceeds.  The additional reclaimed land areas included in Scenario 2B are CBR1E, CBR1W, PCWA, WCR3E, the Kellett Island breakwater, WCR1, HKCEC1 and the completed CRIII.

5.5.11      The proposed construction phase scenarios above represents the realistic worst cases, including all the potentially concurrent activities, envisaged during the WDII construction.  Due to physical and engineering constraints, the reclamation adopts a staged construction approach so that dredging and filling for seawall foundation will be performed in sequence instead of operating concurrently.  Nevertheless, it is conservatively assumed that dredging and filling will be performed concurrently in the sediment plume modelling.

5.5.12      The existing cooling water intakes will have to be reprovisioned to the new water front in order to ensure continuous operation during the WDII construction.  The diversion of the existing cooling water intakes from the HKCEC to the HKCEC Extension will be completed before reclamation of HKCEC1 (water channel).  Dredging is not required for the construction of the temporary seawalls at either end of the water channel.  The seawall will be formed by rock fill foundations and precast concrete blocks.  According to the WDII construction programme (Appendix 2.1), reclamation at the HKCEC1 will be undertaken behind the temporary seawalls (above high water mark), and will not affect any intakes outside the water channel.  Thus, there will be no sediment plume dispersions away from the site during the construction of the HKCEC1.

5.5.13      The potential impacts from the works in WCR2W and WCR3W will be similar to that of WCR2E.  As the WDII reclamation programme indicates that the WCR2E and WCR2W will not be undertaken simultaneously, SS generating activities of WCR2E and WCR3W will also not be undertaken simultaneously.  The potential impact of the HKCEC2E reclamation will be similar to that of HKCEC2W.  Although the WDII construction programme shows that filling behind the constructed seawall at HKCEC2W will be undertaken simultaneously with dredging and seawall foundation works at HKCEC2E, sediment plume generated from filling at the HKCEC2W will be effectively confined within the reclamation area such that there will be no overlapping of sediment plumes from HKCEC2E and HKCEC2W.  Thus, Scenario 2B is considered conservative and representative of the potential worst case scenario.  The dredging and filling works in the PCWA will be performed within the existing breakwater and, thus, less impact is expected from this area than that at WCR3E and the Kellett Island Marina breakwater which are more exposed and therefore represent a conservative scenario modelled as Scenario 2A.

5.5.14      Considering the similarity of the potential construction phase impacts from the reclamation work areas mentioned above, the two worst case scenarios defined will be adequate for the present assessment.

5.5.15      The existing Causeway Bay Typhoon Shelter breakwater will be shortened by removal of rubble mound in the WDII project.  No dredging or filling work will be required and, thus, adverse water quality impact, in terms of SS elevation, is not anticipated.  Hence, the breakwater construction is not included in the sediment plume modelling.

Sediment Loss Rates

5.5.16      Assumptions made in the sediment plume modelling simulations are as follows:

·         The dry densities of sand fill and harbour mud are 1,680 kg m-3 and 1,370 kg m-3 respectively, based on the geotechnical site investigation for the WDII marine ground investigation works.

·         Sand filling of seawall trench will be carried out by closed grab dredger.  It has been assumed that a 16-hour working day will be undertaken 7 days per week for filling.

·         Spill loss during mud dredging by closed grab dredger will be continuous, 16 hours a day, 7 days per week.

·         With respect to rate of sediment loss during dredging, the Contaminated Spoil Management Study ([14]) (Mott MacDonald, 1991, Table 6.12) reviewed relevant literature and concluded that losses from closed grab dredgers were estimated at 11 – 20 kg m-3 of mud removed.  Taking the upper figure of 20 kg m-3 to be conservative, the loss rate in kg s-1 is calculated based on the daily volume rate of dredging. (Assuming a dry density for marine mud of 1,370 kg m-3, the sediment loss during dredging is equivalent to a spill amount of approximately 1.5%).

·         Spillings for mud dredging and sand filling by closed grab dredgers are assumed to take place uniformly over the water column.

·         Dredging of contaminated and uncontaminated mud will be carried out at the same rate.

5.5.17      The calculation of the loss rate from filling activities is based on an approach adopted in the recent EIA Study for the Theme Park and associated developments ([15]).  This method of calculation of loss rate is summarised below:

·         A series of trial uncontaminated marine mud disposal events were carried out at the East Tung Lung Chau Marine Borrow Area ([16]) and it was determined that the representative loss rate of fines to suspension from bottom dumping was 5%.

·         The material disposed of at the East Tung Lung Chau MBA consisted of approximately 60% fines.

·         By taking the fines content of the sand fill material for WDII and using a pro-rata basis, the percentage loss rate from sand filling for this Study is estimated as follows:

% loss rate from sand filling = % fines in filling material x 5%

                                                             60%

·         Fines content of the sand fill material is taken as 5% (a design requirement for reclamation is to specify a fines content for marine fill material not greater than 5%), and the percentage loss rate is estimated as 0.42% for bottom dumping.  As a conservative approach to estimate the potential water quality impact, it is assumed that the percentage loss rate of fines from open grab dredger during filling is equivalent to that of the bottom dumping, although the former is likely to be lower.  However, it is proposed that closed grab dredger will be used for seawall trench filling for the WDII reclamation.  Comparing the loss rates of 25 kg m-3 for open grab dredger and 20 kg m-3 for closed grab dredger in the Contaminated Spoil Management Study ([17]), the effective spill loss rate of a closed grab dredger will be at least 1.25 times lower than that by an open grab dredger.  Hence, the percentage loss rate of sand filling for seawall foundation works using closed grab dredger is estimated to be less than 0.33%.

·         A representative dry density of the sand fill is taken as 1,680 kg m-3.

·         The loss rate in kg s-1 is calculated by multiplying the percentage loss rate by the filling rate (in m3 s-1) multiplied by the dry density of the sand fill.

5.5.18      The calculated sediment loss rates for the Scenario 2A is shown in Table 5.8.  The maximum dredging and filling rates for the different construction phases were identified.  The corresponding source locations are given in Figure 5.5.

Table 5.8         Maximum Dredging and Filling Rates of WDII  - Scenario 2A

Source ID

Activity

Approx.

Duration (1) (days)

Maximum Production Rate

(m3 per day)

Sediment Loss Rate (kg s-1)

CBR1E and CBR1W

A1

Dredging  (1 closed grab dredger of 8 m3 capacity)

68

4500

1.56

A2

Seawall trench sand filling (1 closed grab dredger of 8 m3 capacity)

20

1875

0.18

WCR1

A3

Dredging  (1 closed grab dredger of 8 m3 capacity)

18

2250

0.78

A4

Seawall trench sand filling  (1 closed grab dredger of 8 m3 capacity)

 

28

1875

0.18

WCR3E and Kellett Island Marina Breakwater

A5

Dredging (1 closed grab dredger of 8 m3 capacity)

20

2250

0.78

A6

Seawall trench sand filling (1 closed grab dredger of 8 m3 capacity)

 

48

1875

0.18

Water Mains from Wan Chai to Tsim Sha Tsui

A7(2)

Dredging (1 closed grab dredger of 8 m3 capacity)

15

1000

0.35

A8(2)

Dredging (1 closed grab dredger of 8 m3 capacity)

15

1000

0.35

Wan Chai East STW Submarine Sewage Pipeline

A9

Dredging (1 closed grab dredger of 8 m3 capacity)

20

1000

0.35

Notes:     (1)   The duration of each operation is based on the construction programme presented in Appendix 2.1.

(2)     For the purpose of modelling, two dredging locations are considered with A7 close to Hong Kong Island and A8 close to Tsim Sha Tsui.  However, it should be noted that the dredging will be performed by 1 close grab dredger during the construction of the cross harbour water mains.  Thus, only one dredger will operate at one location at a time.

 

5.5.19      In addition, there will be other concurrent external dredging and filling projects that may impact the same areas.  An analysis of external projects, which could occur at the same time as the WDII reclamation, has found that there will be two projects that could contribute to cumulative impacts.  These projects are CRIII and reclamation for the Yau Tong Bay (YTB) Development (Figure 5.7).  The concurrent dredging and filling activities of these external projects were also simulated in Scenario 2A.  The Green Island Reclamation and the South East Kowloon Development Reclamation are not considered in both Scenarios 2A and 2B, as the construction programmes of these reclamations and their final reclamation layouts were not available at the time of modelling.  Table 5.9 shows the details of the dredging and filling activities of CRIII and YTB Development projects to be modelled in Scenario 2A.

Table 5.9         Sediment Loss Rates of CRIII and YTB Development Projects

Description

Production Rate (m3 per day)

Plant

Dump Interval (hours)

Fines Release Rate (kg s-1)

Maximum Fines Release Rate (kg s-1)

CRIII Dredge Final East (a)

100 m3 per hour

1 grab dredger of 8 m3 capacity

-

1.86

15.19

CRIII Fill Final East (a)

17,800 m3 per day

1 bottom dumping barge of 1,000 m3 capacity

0.9

13.33

 

Yau Tong (b) (Mitigated Scenario)

10,000 m3 per day

Bottom dumping with silt curtain

Spill loss during first 10 minutes for each 1 hour dumping cycle

45.26

45.26

Notes:     (a)    Reference source:  Scenario 2, Table 10.16 of CRIII Final EIA Report.  Scenario 2 selected as the sediment loss during dredging is continuous, giving a worst-case scenario.

(b)   Reference source:  Table 4.18 of the Final EIA Report, Reclamation of Yau Tong Bay.  A sandfilling rate of 10,000 m3 per day is the highest practicable rate envisaged in the YTB reclamation.  To provide conservative results, it was assumed that filling would take place before the construction of YTB seawalls.

5.5.20      The calculated sediment loss rates for the Scenario 2B is shown in Table 5.10.  The maximum dredging and filling rates for the different construction phases were also identified.  The corresponding source locations are given in Figure 5.6.

Table 5.10       Maximum Dredging and Filling Rates of WDII  - Scenario 2B

Source ID

Activity

Approx.

Duration (1) (days)

Maximum Production Rate

(m3 per day)

Sediment Loss Rate (kg s-1)

CBR2E & CBR2W

B1

Dredging  (1 closed grab dredger of 8 m3 capacity)

55

4500

1.56

B2

Seawall trench sand filling (1 closed grab dredger of 8 m3 capacity)

20

1875

0.18

WCR2E

B3

Dredging  (1 closed grab dredger of 8 m3 capacity)

48

4500

1.56

B4

Seawall trench sand filling (1 closed grab dredger of 8 m3 capacity)

74

1875

0.18

HKCEC2W

B5

Dredging (1 closed grab dredger of 8 m3 capacity)

18

4500

1.56

B6

Seawall trench sand filling (1 closed grab dredger of 8 m3 capacity)

52

1875

0.18

Notes:     (1)   The duration of each operation is based on the construction programme presented in Appendix 2.1.

 

5.5.21      The marine works of CRIII will be finished prior to the dredging and filling activities of WDII under Scenario 2B.  Although the filling activities at YTB Development will still be undertaken simultaneously with Scenario 2B of WDII, these filling activities will be undertaken behind the constructed seawalls at YTB.  Thus, overlapping of sediment plumes from WDII and YTB Development will not occur.

Uncertainties in Assessment Methodology

5.5.1          Quantitative uncertainties in the sediment dispersion modelling should be considered when making an evaluation of the modelling predictions.  Worst case conditions were adopted as model input to indicate the maximum extent of the potential environmental impacts.  The input data tends to be overestimated to provide a margin of tolerance.  Some examples of the conservative nature of the input parameters are given below:

·         The WDII reclamation program indicated that the construction works in the different areas can be conducted in sequence while the modelled construction scenarios assumes a conservative case where mutually independent construction works in different areas are modelled as concurrent activities.  This provides flexibility for the implementation of the works during the construction stage.

·         The dredging and filling rates adopted for the sediment plume modelling were increased by 50% over the average production rates, to represent the maximum production rates.

(ii)               Contaminant Release during Dredging

5.5.2          The loss of sediment to suspension during dredging may have chemical effects on the receiving waters.  This is because the sediment may contain organic and chemical pollutants.  As part of the marine site investigation works for this Project, laboratory testing of sediment samples was undertaken.  A full description of the sediment quality testing and the classification of the sediment according to levels of contaminants is contained in Section 6.

5.5.3          The spatial and depth-averaged 5-day sediment oxygen demand (SOD5) of the sediment samples collected from marine site investigation was used to determine the reductions in dissolved oxygen concentration, based on the predicted increases in suspended sediment concentrations for the construction phase scenarios.  The reductions were then compared with the ambient levels at EPD routine monitoring stations VM5 and VT2 to determine the relative effects of the increases in SS concentrations on DO.

5.5.4          The assessment of nutrient impacts from increased SS concentrations has been based on the water quality parameters of TIN and unionised NH3-N.  The increases in these parameters in the receiving waters have been calculated from the modelling predictions of SS elevations and the sediment quality data for TIN and NH3-N.  The release of TIN was first calculated that determined the corresponding increase in unionised NH3-N level.  The predicted increases were then compared with the ambient levels at stations VM5 and VT2 to assess the potential nutrient release impact associated with the marine operations.

5.5.5          An indication of the likelihood of release of heavy metals from the sediment during dredging is given by the results of the elutriation tests from the site investigation works.  If the contaminant levels are higher in the elutriates in comparison with the blanks (marine water from the same site), it can be concluded that the contaminants are likely to be released into the marine waters during dredging activities.  As there is no existing legislative standard or guideline for individual heavy metal contents in marine waters, the UK Water Quality Standards for Coastal Surface Water([18]) is adopted as the assessment criteria.

Operational Phase Impact

5.5.6          As stated in Section 5.5.16, operational phase modelling scenarios will be simulated using the modified coastline under the “2012 Scenario”, with 2012 pollution loading inventory as model inputs.  The SS, DO, biochemical oxygen demand (BOD), NH3-N and E. coli concentrations at various sensitive receivers during the operational phase of the Project will be predicted by the Delft3D-WAQ.

Cooling Water Discharge

5.5.7          The proposed WDII reclamation would require reprovisioning of the existing cooling water intakes and discharges along the Wan Chai waterfront.  Thermal plumes associated with the reprovisioned outfalls for cooling water discharges will lead to a temperature rise in the receiving water.  The WQO for the Victoria Harbour WCZ stipulated that the temperature rise in the water column due to human activity should not exceed 2 oC (Table 5.1).

5.5.8          Existing seawater intake and discharge locations for the cooling systems within the WDII study area have been identified (Figures 5.8A and 5.8B).  Spent cooling water from these identified cooling water system will be discharged through culverts / outfalls into the harbour causing a potential increase in water temperature.  Questionnaires were sent to the individual cooling water intake owners or operators to request for their operation or monitoring data in terms of the cooling water temperature rise via their systems and effluent quality.  A summary table is shown in Table 5.11.  Based on the responses received, the maximum flow discharges via the identified cooling systems range from 2,616 m3 per hour to 6,120 m3 per hour with a temperature difference of approximately 6 oC between the intake and the discharge points.  These heated discharges are generally located on the seawall near the water surface.  Due to the temperature difference of the heated discharge and the ambient water, it is expected that the heated discharge will form a surface plume in the vicinity of the outfall.  The maximum flow rates are adopted in the thermal plume modelling to provide a conservative prediction.  However, discharges from some of the water cooling systems within the study area are missing and the flow rates are estimated based on the maximum pump capacity installed for those systems or similar buildings as indicated in the Engineering Feasibility Study Report, WDII Comprehensive Development Study, November 2000.  The flow rate adopted for the different systems are summarised in Table 5.12.


Table 5.11         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)

 

 

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-1


Table 5.12       Flow Rates of Water Cooling Systems for Thermal Plume Modelling.

Cooling Water Systems

Flow Rate (m3 s-1)

Possible Commercial Development WDII/4

1 (1)

The Hong Kong Academy for Performing Arts

0.92 (2)

Hong Kong Convention and Exhibition Centre (Phase I)

1.35 (3)

Hong Kong Convention and Exhibition Centre (New Wing)

1.7 (3)

Shui On Centre

0.94 (2)

Telecom House

0.84 (2)

Government Buildings

1.2 (2)

China Resources Building and Hong Kong Exhibition Centre

0.92 (3)

Great Eagle Centre

0.45 (4)

Sun Hung Kai Centre

0.72 (3)

Proposed CDA Development WDII/11

1.35 (1)

Proposed Hotel / Commercial Development WDII/28

1.4 (1)

Windsor House

0.38 (4)

Excelsior Hotel and World Trade Centre

1.4 (2)

Note:

(1)     Assumed maximum flow rate based on similar building types.

(2)     Maximum flow rate adopted from Engineering Feasibility Study Report, WDII Comprehensive Development Study, November 2000.

(3)     Maximum flow rate based on responses from the water cooling system operations.

(4)    Averaged flow rate based on responses from the water cooling system operations.

 

5.5.9          In the present study, a 3-dimensional particle tracking model (Delft3D-PART) is employed to simulate the thermal plume dispersion in the Victoria Harbour and to assess the impact on the neighbouring water sensitive receivers.  This PART model is same as that used for sediment plume modelling but with slightly different model parameters to represent the heated discharge.  In particular, the thermal plume model excludes sedimentation and erosion effects and the settling velocity of the particles are set to zero.  The recirculation of heated water to the cooling water intake is taken into account in the temperature rise calculation at the discharge to account for any potential short circuiting problem.

5.5.10      The heated water are represented by discrete particles and discharged into the surface layer of the model.  These discrete particles are transported by advection, due to the tidal flows determined from the hydrodynamic simulation using the detailed Victoria Harbour Model, and turbulent diffusion and dispersion, based on a random walk technique.  The temperature rise and the residual chlorine elevation over the ambient level are then evaluated from the particle density in each cell of the curvilinear grid of the Victoria Harbour model.  Due to the high decay rate of chlorine in marine waters, the ambient chlorine level is assumed to be negligible.

5.5.11      The parameters adopted for the thermal plume modelling are summarised in Table 5.13.  It is conservatively assumed that all cooling water discharges have an excess temperature of 6 oC with reference to the intake temperature and a residual chlorine concentration of 0.5 mg L-1, which discharged continuously at the corresponding maximum discharge rate 24 hours daily.

Table 5.13       Summary of Parameters for Thermal Plume Model (Delft3D-PART)

Thermal Plume Model Parameters

Ambient Temperature (oC)

18

28

Dry Season

Wet Season

Ambient Salinity (ppt)

33

27

Dry Season

Wet Season

Ambient Water Density (kg m-3)

1024

1016

Dry Season

Wet Season

Horizontal Dispersion Coefficient DH (1) (m2 s-1)

a = 0.003

b = 0.4

DH = a t b,

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

Vertical Dispersion Coefficient DV (ms-1)

5x10-3

1x10-5

Dry Season

Wet Season

Excess Temperature (oC)

6

Net temperature increase from the intake to the discharge point

Residual Chlorine (mg L-1)

0.5

Maximum level from operators’ responses

Decay Factor for Residual Chlorine T90 (s)

1800 (2)

-

Excess Temperature at Intake

From model

-

Flow Rate (m3 s–1)

Equivalent for Intake and Discharge

No loss of water in the cooling system.

Particle Settling Velocity

0 (Constant)

Heated discharge is slightly less dense than ambient water

Critical Shear Stress (2)

N/A

No sedimentation or erosion

Note:

(1)   Heat loss to the atmosphere is not taken into account to provide a conservative assessment.  Hence, the horizontal dispersion coefficient remains the same as for the sediment plume model.

(2)                 Adopted from the EIA of a 1800 MW Gas-Fired Power Station at Lamma Extension, Final Report 1999.

(3)                Sedimentation and erosion are irrelevant for thermal plume modelling.

 

Land-based Impact

5.5.12      The extent of development above the WDII was reviewed to assess the impact of the land-based construction activities upon the nearby water bodies.  Construction activities likely to impact upon WSRs were identified.  Practical water pollution control measures / mitigation proposals (Section 5.8) have been subsequently recommended to prevent local flooding and to ensure that effluent discharged from the construction site will comply with the WPCO criteria.

5.6              Identification of Environmental Impact

Construction Phase

Dredging and Filling

5.6.1          A partially dredged reclamation is proposed, with the Wan Chai shoreline and most area of the Causeway Bay Typhoon Shelter being reclaimed by dredged method and the eastern and western portions of the Typhoon Shelter being reclaimed by drained method (that is, mud left in place) (Figure 2.3).  This approach is dictated by the minimum extent of dredging required for foundations and for engineering reasons which, due mainly to the narrow nature of the reclamation, effectively results in a dredged approach over most of the length of the site.

5.6.2          Marine sand fill is proposed to be used for filling up to + 2.5 mPD, except in the Causeway Bay Typhoon Shelter where selected public fill (completely decomposed granite) will be used in conjunction with rock fill culvert foundations.  Selected public fill will also be used in all areas for filling above +2.5 mPD.

5.6.3          The estimated volume of the dredged marine sediment from seawall foundation and marine basin works, and fill material, is listed in Table 5.14.

Table 5.14       Estimated Volume of Dredged and Fill Material

Type

Volume (Mm3)

Dredged Material

0.99

Selected Public Fill (CDG)

1.1

Rock Fill

1.4

Marine Sand Fill

1.2

 

5.6.4          Potential water quality impacts may occur from dredging and filling activities.  Figure 5.4 shows the reclamation phasing of WDII.  As presented in Section 5.5.27 to Section 5.5.40, two worst-case construction scenarios (2A and 2B) have been simulated.

5.6.5          Key water quality concerns during the WDII reclamation are identified as follows:

·         dredging and filling works that 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 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.

5.6.6          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 WSRs 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; and

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

5.6.7          All of the above may result in deterioration of the receiving marine water quality and may have adverse effects on WSRs.

Suspended Sediment

5.6.8          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 for particular sensitive receivers.

5.6.9          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 WQOs.  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 directed in a previous study of the environmental impacts of released SS([19]), the ambient value is represented by the 90th percentile of reported concentrations. 

5.6.10      The depth-averaged and surface SS reading and 90 percentiles during the dry and wet seasons are summarised in Table 5.15.  These values are derived from the marine water quality monitoring results of the three EPD’s routine monitoring stations VM4, VM5 and VM6, located near the reclamation site.  The SS records between 1997 and 1999 were used in this study.  As stipulated by the WQOs for the Victoria Harbour WCZ, the 30% allowable elevation of depth-averaged SS above the ambient will be 2.5 mg L-1 and 2.2 mg L-1 for dry and wet seasons, respectively.  For surface SS, however, the allowable elevations are 2.3 mg L-1 and 1.7 mg L-1 for dry and wet seasons, respectively.  Since sea water intakes are generally located near the water surface, the ambient surface SS concentration of 7.5 mg L-1 for dry season and 5.8 mg L-1 for wet season will be added to the predicted SS elevations at these sensitive receivers for comparison against the relevant water quality criteria.

Table 5.15       Depth-averaged and Surface SS concentrations near the Reclamation Site

Stations

Dry Season

Wet Season

VM4, VM5 and VM6

Depth-averaged

Surface

Depth-averaged

Surface

Average SS (mg L-1) between 1997 and 1999

5.4

4.7

4.4

3.6

90 percentile (ambient level)

8.2

7.5

7.2

5.8

30% increase above the ambient level

2.5

2.3

2.2

1.7

Data source:      EPD routine marine water quality monitoring programme.

 

Stormwater Discharges

5.6.11      Stormwater and drainage discharges from construction site 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 will be maintained between the existing or planned stormwater discharges and the existing or planned WSD salt water intakes during WDII construction and operation phases.

5.6.12      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

5.6.13      Sewage generated from construction activities 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;

·         pore water discharging through band drains installed in the reclamation during surcharging;

·         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; and

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

General Construction Activities

5.6.14      The general construction works that will be undertaken for the roads and infrastructures will be primarily land-based and may have the potential to cause water pollution.  These could result from the accumulation of solid and liquid waste such as packaging and construction materials, 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 level 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 would stimulate algal growth and reduction in oxygen levels.

5.6.15      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.  There will be no public sewers available for domestic sewage discharge on-site.

Operational Phase

5.6.16      Based on the review of the proposed land uses for the WDII operation, potential water quality impacts are identified in the following areas:

·         changes to tidal current patterns;

·         effluent discharge from marine outfalls and stormwater culverts;

·         floating refuse.

Hydrodynamics and Water Quality Impact

5.6.17      The formation of the WDII may affect the water levels, current velocity, and tidal flushing in the vicinity of the WDII reclaimed land and, potentially, over a larger area.  In addition, the changes in the hydrodynamics in the Victoria Harbour may affect the pollutant distribution patterns from sewage outfalls and stormwater culverts into the surrounding waters.

High Level Overflow Arrangement for the Proposed Culvert Extension in the Causeway Bay Typhoon Shelter

5.6.18      In view of the water quality concerns from the pollution load discharging via the existing stormwater culverts into the Causeway Bay Typhoon Shelter, a storm interceptor culvert is proposed to be built along the new promenade to collect the runoff from the stormwater catchments P, Q, R and S and discharge to the east of the Causeway Bay Typhoon Shelter.  The existing outfalls will need to be extended and connected to the proposed storm interceptor culvert.  With the implementation of the storm interceptor culverts diverting the discharge out of the Causeway Bay Typhoon Shelter, the water quality inside the typhoon shelter is expected to improve.

5.6.1          A “High Level Overflow” arrangement, which include emergency overflows into the Causeway Bay Typhoon Shelter, will be required to relieve the flood hazard during severe storm events (for example, 1 in 50 years).  The overflow level at the culvert is set at +2.5 mPD that is the Mean High Water Level (MHWL).  According to the “Territorial Land Drainage and Flood Control Strategy Study - Phase 1” (Volume 1), Section 6.2.6, the tide level of +2.5 mPD has a return period of 2 years.  The level of +2.5 mPD has also been adopted in the Civil Engineering Manual, Stormwater Drainage Manual and Portworks Manual with the same return period.  The potential overflow events may affect the water quality in the typhoon shelter for a short period of time.  To ensure that frequent bypass of flows into the Causeway Bay Typhoon Shelter will be avoided when the overflow is set at +2.5 mPD, a probability analysis has been carried out to substantiate the adoption of this overflow level.  Details of the drainage design and other considerations are included in the WDII Final Drainage Impact Assessment Report, January 2001.

5.6.2          The chance of overflow occurrence would fall under two categories: events when the hourly tide levels exceed +2.5 mPD irrespective of any co-incidental rainfall, and events when the hourly tide levels exceed +2.415 mPD with co-incidental rainfall.  Tide level and rainfall data for 5 years from 1995 to 1999 have been obtained from the Hong Kong Observatory.  The tide levels are measured at Quarry Bay and, thus, the WDII project can make reference to these data.  The tide levels are recorded every hour through the year (that is, 24 hours x 365 days).  The predicted sea levels exceeding +2.5 mPD during the period 1995 to 1999 are attached in Appendix 5.2.  The sea levels exceeding +2.5 mPD are summarised in Table 5.16.

Table 5.16       Probability of Sea Levels Exceeding +2.5 mPD between 1995 and 1999

Year

1995

1996

1997

1998

1999

No. of hours when the sea level is observed to exceed +2.5 mPD

29

26

18

29

18

Probability (%)

0.331

0.296

0.205

0.331

0.205

 

5.6.3          In general, the probability of tide levels exceeding +2.5 mPD in this five-year period (1995 - 1999) is 0.274% or approximately 24 hourly occurrences per year.

5.6.4          With the combination of tide levels exceeding +2.415 mPD and the occurrence of rainfall, the results are summarised in Table 5.17.

Table 5.17       Probability of Sea Levels Exceeding +2.415 mPD and the Occurrence of Rainfall between 1995 and 1999

Year

1995

1996

1997

1998

1999

No. of hours with +2.5 mPD tide level and coincident rainfall observed

1

2

11

3

7

Probability (%)

0.011

0.023

0.126

0.034

0.080

 

5.6.5          In general, the probability of tide levels exceeding +2.415 mPD in this five-year period (1995 - 1999), with associated recorded rainfall greater than 0.1 mm per hour, is only 0.055%.

5.6.6          The overall probability of occurrence of discharge into the typhoon shelter will be extremely low (0.329%, which can be translated as an annual average of 29 hourly events) and, in view of the considerable quantity of the runoff under severe storms, the concentration of the pollutants carrying by the stormwater will be diluted and should not cause adverse quality impacts in the typhoon shelter.  Engineering design plans for minimising direct discharge of dry weather flow into the typhoon shelter should be submitted in design stage for EPD agreement.

Floating Refuse

5.6.7          The formation of WDII reclaimed area may create areas susceptible to floating refuse accumulation, affecting the aesthetic quality of the marine water.  However, it is considered that the impact of floating refuse can be effectively controlled by regular refuse scavenging.

5.7              Prediction and Evaluation of Environmental Impacts

Construction Phase

Marine-based Impact

Suspended Solids

5.7.1          Two sediment dispersion scenarios were modelled, as defined in Tables 5.8, 5.9 and 5.10.  Absolute maximum and tidal-averaged surface SS concentrations for a spring-neap cycle at each WSR, taking into account the ambient SS concentration, are presented for each scenario.

·         Construction Scenario 2A

5.7.2          Construction Scenario 2A simulated the maximum possible dredging and filling rates during March 2004 and August 2005.  The scenario was simulated for two typical spring-neap tidal cycles during dry and wet seasons in Hong Kong (Section 5.5.7).  The predicted maximum SS concentrations at the WSRs are shown in Table 5.18 for dry seasons and wet seasons.

5.7.3          The results shown in Table 5.18 indicate exceedances (highlighted in bold) of WSD water quality (SS) criterion and target SS level of MTRC cooling water intake.  Mitigation measures are therefore required to minimise the impact.

5.7.4          The construction contours presented in Figures 5C-1 and 5C-2 of Appendix 5.3 show the extent of surface SS elevations over a spring-neap cycle, during wet and dry seasons.  As shown in these figures, the extent of SS impact during the dry season (Figure 5C-2 in Appendix 5.3) appears smaller than that of the wet season (Figure 5C-1 in Appendix 5.3).  Temporal variations of surface SS elevations at various WSRs during the wet and dry seasons are shown in Figures 5D-1A to 5D-1G and Figures 5D-2A to 5D-2G in Appendix 5.5, respectively.

5.7.5          Figures 5C-3 and 5C-4 of Appendix 5.3 show the tidal-averaged sedimentation rate of SS during wet and dry seasons, respectively.  Both figures indicate that the sedimentation rates at waters near the Green Island and within Junk Bay are much lower than 0.2 kg m-2 per day (Section 5.2.14).  Thus, it is considered that the WDII, CRIII and YTB Development will not adversely impact the coral communities at waters near the Green Island and within Junk Bay.

·         Construction Scenario 2B

5.7.6          Construction Scenario 2B simulated the maximum possible dredging and filling rates during September 2005 and September 2007.  The scenario was simulated for two typical spring-neap tidal cycles during wet and dry seasons (Section 5.5.7) in Hong Kong, which are equivalent to those for Scenario 2A.  The maximum SS concentrations at the WSRs are shown in Table 5.19 for wet season and dry seasons.

5.7.7          The results shown in Table 5.19 indicate few exceedances (highlighted in bold) of cooling water and WSD’s SS criterion during the construction of WDII alone.  The impact is also predicted to be substantial at intakes within the Causeway Bay Typhoon Shelter due to the construction works within the embayed water, and at the reprovisioned WSD Wan Chai Salt Water Intake due to the marine works in close vicinity (at WCR2E).  Thus, mitigation measures are required to minimise the impact.  The results indicated that the wet season tides generally produce higher impacts upon the seawater intakes than the dry season tides.  Tables A5.9 and A5.10 in Appendix 5.4 also show the breakdown of SS impacts from dredging and filling during wet and dry seasons.

5.7.8          The construction contours presented in Figures 5C-5 to 5C-6 of Appendix 5.3 show the surface SS concentrations during wet and dry seasons.  As shown in these figures, the extent of SS impact during the dry season (Figure 5C-6 in Appendix 5.3) also appears smaller than that of the wet season (Figure 5C-5 in Appendix 5.3).  Temporal variations of surface SS elevations at various WSRs during the wet and dry seasons are shown in Figures 5D-3A to 5D-3F and Figures 5D-4A to 5D-4F in Appendix 5.5, respectively.

5.7.9          Figures 5C-7 and 5C-8 of Appendix 5.3 show the tidal-averaged sedimentation rate of SS during wet and dry seasons, respectively.  Both figures indicate that the sedimentation rates at waters near the Green Island and within Junk Bay are much lower than 0.2 kg m-2 per day (Section 5.2.14).  Thus, it is considered that the WDII marine works will not adversely impact the coral communities at waters near the Green Island and within Junk Bay.


Table 5.18       Construction Scenario 2A – Suspended Solids Concentrations at Sensitive Receivers

Sensitive Receiver

SS concentration (absolute value) in surface layer (mg L-1)

 

Criterion

Dry season

Wet season

 

 

Mean (3)

Maximum (3)

% time in compliance

Mean (3)

Maximum (3)

% time in compliance

Cooling Water Intakes

 

 

 

 

 

 

 

Windsor House

-

10.1

30.4

-

23.8

236.3

-

Excelsior Hotel & World Trade Centre

-

8.1

20.6

-

14.0

55.8

-

Sun Hung Kai Centre

-

22.8

88.2

-

12.0

85.3

-

Great Eagle Centre / China Resources Building

-

11.3

59.7

-

7.3

62.2

-

Wan Chai Tower / Revenue Tower / Immigration Tower

-

11.3

59.7

-

7.3

62.2

-

Hong Kong Convention and Exhibition Centre Phase I

-

14.7

255.3

-

7.7

53.2

-

Hong Kong Convention and Exhibition Centre Extension

-

10.5

38.4

-

8.3

48.4

-

Telecom House / HKAPA / Shun On Centre

-

14.4

123.7

-

8.2

78.1

-

MTRC South Intake

< 40(1)

14.4

123.7

97.6

8.2

78.1

99.3

Prince's Building Group at CRIII

-

11.3

44.0

-

7.5

31.6

-

Queensway Government Offices at CRIII

-

15.9

178.4

-

9.3

262.8

-

Admiralty Centre at CRIII

< 40(1)

15.9

178.4

92.8

9.3

262.8

98.7

HSBC & Hotel Furama at CRIII

-

10.1

24.8

-

18.9

140.2

-

WSD Saltwater Intakes

 

 

 

 

 

 

 

Wan Chai (existing)

< 10(2)

12.2

38.1

50.1

9.3

31.1

68.0

Central Water Front

< 10(2)

8.7

20.8

75.7

6.6

31.9

92.2

Sheung Wan

< 10(2)

9.0

21.6

73.4

6.2

24.5

96.6

Quarry Bay (4)

< 10(2)

8.1

16.3

92.6

9.3

25.1

68.0

Kowloon South

< 10(2)

7.5

7.5

100.0

5.8

5.8

100.0

Tai Wan

< 10(2)

7.5

9.8

100.0

6.6

16.2

94.8

Kennedy Town

< 10(2)

7.7

11.3

98.8

5.8

6.6

100.0

Sai Wan Ho

< 10(2)

7.8

13.5

96.4

7.9

24.1

81.9

Siu Sai Wan

< 10(2)

7.5

8.8

100.0

7.3

13.8

89.0

Notes:     (1)           As advised by MTRC (letter dated 3 March 2000).

(2)                 WSD’s water quality criterion for flushing water.

(3)                 Absolute value of SS includes the ambient SS level (7.5 mg L-1 for dry season and 5.8 mg L-1 for wet season) in the surface layer of water column.

(4)                 The invert level of the existing WSD Quarry Bay salt water intake (-0.75 mPD) has been confirmed with WSD.  This level corresponds to the second top layer of the model.

-                      Bold number indicates exceedence of criterion.

-                      Other WSRs, including WSD Cheung Sha Wan intake, WSD Cha Kwo Ling intake, WSD Yau Tong intake, planned intakes at Green Island East, North and West, Kau Yi Chau Fishery, Queen Mary Hospital intake, Stage 1 Phase 1 intake and Wah Fu Estate intake were found not be impacted by marine works from CRIII and WDII under Scenario 2A.


Table 5.19     Construction Scenario 2B – Suspended Solids Concentrations at Sensitive Receivers

Sensitive Receiver

SS concentration (absolute value) in surface layer (mg L-1)

 

Criterion

Dry season

Wet season

 

 

Mean (3)

Maximum (3)

% time in compliance

Mean (3)

Maximum (3)

% time in compliance

Cooling Water Intakes

 

 

 

 

 

 

 

Prince's Building Group at CRIII

-

7.8

11.8

-

7.1

20.3

-

Queensway Government Offices at CRIII

-

8.6

19.1

-

9.1

112.8

-

Admiralty Centre at CRIII

< 40(1)

8.6

19.1

100.0

9.1

112.8

99.1

HSBC & Hotel Furama at CRIII

-

8.3

14.2

-

8.7

49.6

-

Reprovisioned Cooling Water Intakes

 

 

 

 

 

 

 

Windsor House

-

7.6

13.7

-

11.1

82.3

-

Excelsior Hotel & World Trade Centre

-

7.6

13.7

-

11.1

82.3

-

Sun Hung Kai Centre

-

9.7

25.5

-

14.0

180.4

-

Great Eagle Centre / China Resources Building

-

8.7

30.4

-

9.1

86.2

-

Wan Chai Tower / Revenue Tower / Immigration Tower

-

8.7

30.4

-

9.1

86.2

-

Hong Kong Convention and Exhibition Centre Phase I

-

8.7

42.9

-

8.5

61.7

-

Hong Kong Convention and Exhibition Centre Extension

-

8.7

42.9

-

8.5

61.7

-

Telecom House / HKAPA / Shun On Centre

-

8.7

42.9

-

8.5

61.7

-

MTRC South Intake

< 40(1)

8.7

42.9

99.95

8.5

61.7

99.5

WSD Saltwater Intakes

 

 

 

 

 

 

 

Wan Chai (temporary reprovisioned)

< 10(2)

9.7

25.5

71.0

14.0

180.4

75.5

Central Water Front

< 10(2)

7.6

10.2

99.9

6.2

18.6

96.1

Sheung Wan

< 10(2)

7.7

11.8

98.3

6.0

14.4

98.4

Quarry Bay (4)

< 10(2)

7.7

11.1

98.2

7.9

18.1

87.6

Kowloon South

< 10(2)

7.5

7.5

100.0

5.8

5.8

100.0

Tai Wan

< 10(2)

7.5

8.6

100.0

6.0

9.3

100.0

Kennedy Town

< 10(2)

7.5

8.3