Table of Contents
1.1Â Â Â Â Â Description of the Project
2.   WATER
QUALITY IMPACT ASSESSMENT
2.2Â Â Â Â Â Assessment Methodology
2.3Â Â Â Â Â Legislation and Standards
2.4Â Â Â Â Â Sensitive Receivers
2.5Â Â Â Â Â Baseline Conditions
2.6Â Â Â Â Â Water Quality Criteria
2.7Â Â Â Â Â Sediment Sampling, Elutriation Test and
Particle Size Analysis
2.8Â Â Â Â Â Assessment of Potential Impacts during
Dredging
2.9Â Â Â Â Â Concurrent Dredging/Disposal Activities
2.10Â Â Â Assessment of Potential Impacts after
Dredging
2.11Â Â Â Recommended Maximum Dredging Rates and
Proposed Dredging Schedule
2.12Â Â Â Mitigation Measures and Good Site Practice
2.13Â Â Â Summary and Conclusions
3.2Â Â Â Â Â Legislation and Assessment Criteria
3.3Â Â Â Â Â Overview of Habitats in the Study Area
3.6Â Â Â Â Â Intertidal Flora and Fauna
3.8Â Â Â Â Â Key Sensitive Receivers
3.9Â Â Â Â Â Impact Identification and Prediction
3.12Â Â Â Summary and Conclusions
4.   FISHERIES
IMPACT ASSESSMENT
4.2Â Â Â Â Â Legislation and Standards
4.3Â Â Â Â Â Baseline Conditions
4.4Â Â Â Â Â Culture Fisheries
4.5Â Â Â Â Â Impact Assessment
4.6Â Â Â Â Â Mitigation Measures
4.7Â Â Â Â Â Summary and Conclusions
5.2Â Â Â Â Â Legislation and Standards
5.3Â Â Â Â Â Noise Sensitive Receivers
5.4Â Â Â Â Â Con-Current Projects
5.5Â Â Â Â Â Assessment Methodology
5.6Â Â Â Â Â Assessment Results
5.7Â Â Â Â Â Mitigation Measures
5.8Â Â Â Â Â Monitoring and Audit Requirement
5.9Â Â Â Â Â Summary and Conclusions
6.2Â Â Â Â Â Legislation and Standards
6.3Â Â Â Â Â Potential Sources of Waste
6.5Â Â Â Â Â Sediment Disposal
6.6Â Â Â Â Â Potential Impact of Sediment Disposal
6.7Â Â Â Â Â Mitigation Measures
7.   Environmental
Monitoring and Audit
7.7Â Â Â Â Â Real-Time Reporting of Monitoring Data
8.   summary
and conclusions
8.1Â Â Â Â Â Maximum Dredging Rates
8.7Â Â Â Â Â Operational Impact
8.8Â Â Â Â Â Mitigation Measures
8.9Â Â Â Â Â Good Site Practice
List of APPENDICES
Appendix 1Â Â Â Â Â Elutriation Test
Appendix 2Â Â Â Â Â Review of Sediment Quality
Appendix 3Â Â Â Â Â Water Quality Modelling Output
Appendix 4 Â Â Â Â Implementation Schedule
Appendix 5Â Â Â Â Â Noise Calculations for Grab Dredger Option between 23:00 and 07:00
Appendix
6Â Â Â Â Â EM&A Manual (Construction
Phase) [under a separate cover]
List of Tables
Table 2.3Â Â Â Â Â Â Â Â Relevant Water Quality Objectives at the Relevant Water Control Zones
Table 2.4Â Â Â Â Â Â Â Â Background SS Concentrations and Tolerance Elevation at Sensitive
Receivers
Table 2.4a      Elutriation Test Results
Table 2.5Â Â Â Â Â Â Â Â Estimated Maximum Dredging Rates and Critical Sensitive Receivers
Table 2.11Â Â Â Â Â Â Standards for Heavy Metals and Micro-Pollutants Recommended for This
EIA
Table 2.14Â Â Â Â Â Â Estimated Maximum Dredging Rates for Worst-Case Scenarios
Table 2.15Â Â Â Â Â Â Recommended Maximum Dredging Rates for Worst-Case Scenarios
Table 2.16Â Â Â Â Â Â Recommended Maximum Dredging Rates for Working Zones
Table 2.17Â Â Â Â Â Â Proposed Working Schedule - Grab
Dredger Option
Table 2.18Â Â Â Â Â Â Proposed Working Schedule - TSHD Option
Table 3.1Â Â Â Â Â Â Â Â Biomass of Benthic Assemblages from the Lamma Island Area
Table 3.3Â Â Â Â Â Â Â Â Results of Dive Surveys Conducted along West Lamma Coast
Table 3.4 Â Â Â Â Â Â Â Dive Survey Conditions, 10 December 2001
Table 3.7Â Â Â Â Â Â Â Â Summary of Ecological Impact Assessment and Evaluation
Table 5.1Â Â Â Â Â Â Â Â Sound Power Level of Plant Likely to Be Deployed
Table 5.2Â Â Â Â Â Â Â Â Working Schedule and the Allocation of Dredgers for Grab Dredger
Option
Table 5.3Â Â Â Â Â Â Â Â Shortest Distances between the Dredging Area and the NSRs
Table 5.4Â Â Â Â Â Â Â Â Construction Noise Level during
Normal
Working Hours
Table 5.5Â Â Â Â Â Â Â Â Construction Noise Level during Day Time on Holidays
Table 5.6Â Â Â Â Â Â Â Â Construction Noise Level during Evenings
Table 5.7Â Â Â Â Â Â Â Â Construction Noise Level during Night Time
Table 7.1Â Â Â Â Â Â Â Â Action and Limit Levels for Water Quality
LIST OF FIGURES
Figure 1.1Â Â Â Â Â Â Â Project Area
Figure 1.2Â Â Â Â Â Â Â Provisional Dumping Sites and Vessel Movement Restricted Area
Figure 2.1Â Â Â Â Â Â Â Environmental Sensitive Receivers
Figure 2.2Â Â Â Â Â Â Â Working Zones for Lamma Channel Improvement
Figure 2.3Â Â Â Â Â Â Â Illustration of Cage Type Silt Curtain
Figure 3.1Â Â Â Â Â Â Â Major Habitat Types around South Lamma
Figure 3.2Â Â Â Â Â Â Â OPCF Study Area Showing Survey Sub-Areas and Transect Lines in Hong Kong
Figure 3.5Â Â Â Â Â Â Â Dive Survey Sites used by ERM 1998 and for this Study
Figure 3.6Â Â Â Â Â Â Â Location of Dive Surveys Conducted by HKIED along the West Lamma Coast
Figure 3.8Â Â Â Â Â Â Â Location of Key Porpoise Habitat around the Project Area
Figure 4.1Â Â Â Â Â Â Â Fishing Areas around Lamma Island
Figure 7.1Â Â Â Â Â Â Â Environmental Monitoring Stations
ABBREVIATIONS
AFCD |
- Agricultural, Food and Conservation
Department |
CCC |
- Criteria Continuous Concentration |
CITES |
- The Convention on the International
Trade in Endangered Species of Wild Fauna and Flora |
CMC |
- Criteria Maximum Concentration |
DO |
- Dissolved Oxygen |
EIA |
- Environmental Impact Assessment |
EIAO |
- Environmental Impact Assessment
Ordinance |
EIA-TM |
- Technical Memorandum on Environmental
Impact Assessment Process |
EM&A |
- Environmental Monitoring and Audit |
EPD |
- Environmental Protection Department |
HEC |
- Hongkong Electric Company Limited |
HKIEd |
- Hong Kong Institute of Education |
HKPSG |
- Hong Kong Planning Standards and
Guidelines |
IUCN |
- International Union for the Conservation of Nature |
LMX |
- Lamma Power Station Extension |
NSR |
- Noise Sensitive Receiver |
OPCF |
- Ocean Park Conservation Foundation |
PD |
- Principal Datum |
SOD |
- Sediment Oxygen Demand |
SR |
- Sensitive Receiver |
SS |
- Suspended Solids |
TIN |
- Total Inorganic Nitrogen |
TKN |
- Total Kjedahl Nitrogen |
TOC |
- Total Organic Carbon |
TLC EM&A Manual |
- Environmental Monitoring and Audit
Manual for Backfilling of Marine Borrow Areas at East Tung Lung Chau |
TSHD |
- Trailer Suction Hopper Dredger |
USACE |
- United States Army Corporate Engineers |
USEPA |
- United States Environmental Protection
Agency |
WCZ |
- Water Control Zone |
WPCO |
- Water Pollution Control Ordinance |
WQ |
- Water Quality |
WQO |
- Water Quality Objective |
WQSR |
- Water Quality Sensitive Receiver |
1.1
Description of the Project
1.1.1
The Hongkong
Electric Company Limited (HEC) is responsible for the generation and supply of
electricity to Hong Kong and Lamma Island.Â
At present, all electric power is generated from Lamma Power Station
(LPS) which is located on Lamma Island.Â
LPS, with a total installed capacity of 3,420MW, comprises 2,500MW
coal-fired units for base load operation and 920MW gas turbine units for peak
lopping  operation. The annual coal consumption in 2001 is about four million tons.
1.1.2
A coal jetty
designed for 100,000 DWT coal vessels and a dedicated Navigation Channel (the
Channel) have been in operation since the early 1980's to facilitate delivery
of coal from overseas to LPS by ocean going vessels. To ensure an adequate underkeel clearance for safe operation of
coal vessels involved, maintenance dredging was carried out at the Channel in
1989/90 to bring the seabed level to - 16.5mPD.  Again due to natural siltation, the water depth at the Channel has
now been reduced to about - 14mPD which is close to the limit for safe navigation of coal vessels of
Panamax size (about 65,000 DWT) which is the smallest class of ocean going coal
vessel in the market.
1.1.3
Even with the
first new 300MW gas-fired unit in service at Lamma Power Station Extension, the
coal-fired units of LPS still have to operate to meet the majority of
electricity demand. The annual coal consumption is around four
million tons.
1.1.4
As the siltation is building up and in view of the importance to have in
place a safe navigation channel with adequate water depth for ocean going coal
vessels, maintenance dredging must be carried out in 2003. Otherwise, coal supply to the LPS will
be seriously hampered and the
reliability of electricity supply will be jeopardized. The proposed maintenance dredging work involves deepening the existing Channel to - 16mPD
with an estimated total dredging
volume of 2.98 million m3.
1.1.5
The
Project Area is illustrated in Figure 1.1. The grey area shows the limit of the Channel
where dredging will be required under this Project. According to the latest
bathymetric survey of the Channel, there is already sufficient water depth and
no dredging will be required in the remaining section of the Channel in the
south (beyond the grey area in Figure 1.1).
1.1.6
The
dredging is scheduled to take place between May 2003 and December 2003. In order to minimise the dredging period thus
minimising the period of potential disturbance to environment and to suit the
normal operating mode of dredgers, it is planned that the dredgers will be operating on a 24-hour basis
during the dredging period. Marine
vessels will transport the dredged sediment to the Government approved disposal
sites at East Ninepin, East Tung Lung Chau and East Sha Chau as shown in Figure 1.2.Â
1.1.7
Coal
ships currently deliver about six shipments of coal per month to the Lamma
Power Station via the Channel. All
dredging works will be temporarily suspended when coal ships are navigating the
Channel.
1.1.8
As
the total dredging volume exceeds 500,000m3, the dredging operation
of the Channel improvement is a designated project according to the
Environmental Impact Assessment (EIA) Ordinance, Schedule 2, Part I, C.12. A Project Profile was submitted by HEC to
EPD on 11 June 2001 for application of an EIA Study Brief, which (Brief No.
ESB-078/2001) was issued by EPD on 23 July 2001. Hyder Consulting Ltd was commissioned by HEC to undertake the EIA
Study in accordance with the EIA Study Brief.
1.2.1
The
purpose of this EIA is to provide information on the nature and extent of
potential environmental impacts arising from the proposed Project and other
projects taking place concurrently, with specific objectives as follows:
(a)Â Â Â Â Â Â Â To
describe the proposed Project and associated works together with the
requirements for carrying out the proposed Project;
(b)Â Â Â Â Â Â Â To consider alternative method(s) for
the dredging work and design to ensure safe delivery of fuel to the Power
station; and to compare the environmental benefits and dis-benefits of each of
the method(s) and design in selecting a preferred one;
(c)Â Â Â Â Â Â Â To identify and describe elements of the
community and environment likely to be affected by the proposed Project and/or
likely to cause adverse impacts to the proposed Project, including natural and
man-made environment;
(d)Â Â Â Â Â Â Â To propose the provision of
infrastructure or mitigation measures so as to minimize pollution,
environmental disturbance and nuisance during construction and operation of the
proposed Project;
(e)Â Â Â Â Â Â Â To identify, predict and evaluate the
residual (i.e. after practicable mitigation) environmental impacts and the
cumulative effects expected to arise during the construction and operation
phases of the proposed Project in relation to the sensitive receivers (SRs) and
potential affected uses;
(f)Â Â Â Â Â Â Â Â To identify, assess and specify
methods, measures and standards, to be included in the detailed design,
construction and operation of the proposed Project which are necessary to
mitigate these environmental impacts and reducing them to acceptable levels;
(g)Â Â Â Â Â Â Â To investigate the extent of the
secondary environmental impacts that may arise from the proposed mitigation
measures, and to identify the constraints associated with the mitigation
measures recommended in the EIA study as well as the provision of any necessary
modification;
(h)Â Â Â Â Â Â Â To identify, within the study area, any
individual project(s) that fall under Schedule 2 of the EIA Ordinance (EIAO);
to ascertain whether the findings of this EIA study have adequately addressed
the environmental impacts of those projects; and where necessary to identify
the outstanding issues that need to be addressed in any further detailed EIA
study; and
(i)Â Â Â Â Â Â Â Â To design and specify environmental
monitoring and audit (EM&A) requirements, if required, to ensure the
implementation and the effectiveness of the environmental protection and
pollution control measures adopted.
1.3.1
Following
this introductory section, Section 2 presents an assessment of the
potential impacts on water quality (WQ).Â
Potential WQ sensitive receivers (WQSRs) are identified. The baseline WQ conditions at those SRs are
collated and the potential impacts of the Project on the SRs assessed.
1.3.2
Based
on the potential WQ impacts, an assessment of the potential impacts on the
marine ecology and fisheries has been carried out and the findings are
presented in Sections 3 and 4.
1.3.3
The
potential noise impact generated from the dredgers and barges to be deployed
for the works is assessed in Section 5, taking into account the other
ongoing noise generating activities around the area.
1.3.4
The
management and disposal of the dredged marine sediment is presented in Section
6. Section 7 outlines the
Environmental Monitoring and Audit (EM&A) requirements recommended from
this EIA and the main conclusions, recommendations and environmental outcomes
of the EIA Study are summarised in Section 8.
1.3.5
Detailed
technical information generated from this EIA Study is provided in the Appendices.
1.3.6
Appendix
1 presents the
methodology, sampling location and detailed testing results of the Elutriation
Test specifically conducted for this EIA Study, which aims to quantify the
potential release of various contaminants from the seabed sediment into the water
column in the vicinity of dredging.
1.3.7
The
sediment quality data collected in and around the Channel is presented in Appendix
2.
1.3.8
Detailed
graphical outputs from the water quality modelling are provided in Appendix
3. An Implementation Schedule for
the mitigation measures and good site practice recommended from this EIA Study
is presented in Appendix 4.Â
1.3.9
Detailed
Noise Calculations are presented in Appendix 5 and an EM&A Manual
(Construction Phase) is presented in Appendix 6 (under a separate
cover).
2.1.1 The Lamma Power Station Navigation Channel Improvement Work involves dredging of marine sediment within the existing Navigation Channel and disposal of the dredged sediment.
2.1.2 During the dredging operation, marine sediment leaking through the dredger will be released into the water column, thus leading to the elevation of the suspended solids (SS) level in the marine water. The coarse material, such as sand and gravel, of the released sediment will settle quickly back to the seabed close to the dredging site. However fine particles, such as silt and clay, together with any contaminants they may carry, will be transported away from the site by oceanic currents and tides, which may then affect WQSRs.
2.1.3 The potential WQSRs have been identified. The potential impact of the dredging operation on the SRs in terms of both pollution elevation and sediment deposition have been quantified, taking into account con-current dredging and disposal activities during the same period. Necessary mitigation measures have been recommended.
2.2.1 The WQSRs have been chosen based on the EIA study of the Lamma Power Station Extension completed in 1998 and the unique features of this dredging operation. Marine sediment sampling and elutriation test (following the USACE recommended methods) of the samples collected have been performed to determine the degree of mobilization of any likely contaminants. WQ modelling has then been carried out to ascertain the potential elevation of water pollution in terms of various WQ parameters at the WQSRs. As the WQ model developed from the earlier EIA study of the Lamma Power Station Extension is intended for the same Project Area, and has been fully calibrated and verified, it has also been adopted for this EIA study. Based on the results of the modelling, the elutriation tests and the baseline WQ conditions, the maximum dredging rates which would ensure no unacceptable environmental impacts are estimated.
2.3.1 The following legislation is applicable to the evaluation of WQ impacts associated with the dredging and disposal of marine sediment.
· Environmental Impact Assessment Ordinance and Technical Memorandum on Environmental Impact Assessment Process (EIA-TM)
· Water Pollution Control Ordinance (WPCO)
· Work Branch Technical Circular No. 3/2000, Management of Dredged/Excavated Sediment (WBTC No. 3/2000)
2.3.2 The WPCO is the primary legislation for the control of water pollution and WQ in Hong Kong. Under WPCO, Hong Kong waters are divided into 10 Water Control Zones (WCZs) each zone has a designated set of statutory Water Quality Objectives (WQOs). The Lamma Power Station Navigation Channel and most of the potential WQSRs lie within the Southern WCZ. The WQOs for these WCZs are the evaluation criteria for assessing the WQ impacts during dredging activities.
2.4.1 The dredging activities of the Navigation Channel will have the potential to directly affect WQ in the water along the western coast of Lamma Island. Beneficial uses have been defined in accordance with the requirements of the Hong Kong Planning Standards and Guidelines (HKPSG), which have been transposed into the EIA Technical Memorandum (TM). WQSRs have been identified in these potentially affected areas under the broad designations of gazetted and non-gazetted bathing beaches, water intakes, fish culture zones and sites of ecological value. The following list of WQSRs are identified in each of the categories:
Gazetted Bathing Beaches: Hung Shing Ye Beach and Lo So Shing Beach.
Water Intakes: Kennedy Town WSD Intake, Sha Wan Drive Intake, Queen Mary Hospital Intake, Wah Fu Estate Intake and HEC Lamma Power Station Intake. A new seawater intake at Cyberport is expected to start operating towards late 2002. Â The water intake is close to the seawater intake at Wah Fu Estate and is between the seawater intakes at Wah Fu Estate and at Queen Mary Hospital. The impact of this project on the seawater intake at Cyberport is considered to be acceptable as long as the impact on those at Wah Fu Estate and Queen Mary Hospital is acceptable.
Fish Culture Zones: Lo Tik Wan Fish Culture Zone and Sok Kwu Wan Fish Culture Zone.
Sites of Ecological Interest: Kau Yi Chau (fish fry nursery area), Pak Kok (corals present), Shek Kok Tsui (corals present), Luk Chau (corals present) and south Lamma water (finless porpoise habitat). Due to its ecological importance, the south Lamma water could be potentially designated as a marine park. Two points, South Lamma 1 and South Lamma 2, which are situated in the closest part of the south Lamma water to the works area, have been chosen to facilitate the quantification of the potential WQ impact of this Project on the south Lamma water. As long as the impact on this part of the water is acceptable, the impact on the other parts of the south Lamma water will be less and therefore also acceptable.
2.4.2
There are a number of EPD routine
water monitoring stations around the Study Area. The WQ data monitored from those stations has been used in this EIA
to derive the baseline WQ conditions at the identified WQSRs. The locations of
the above WQSRs and the EPD WQ monitoring stations are shown
in Figure 2.1.
Hydrodynamic Conditions
2.5.1 The Channel, located at the western side of the Lamma Power Station and extending along the outskirt of Ha Mei Wan, is within the West Lamma Channel. The residual flow through the West Lamma Channel is towards the south. The average residual flow through a cross-section from Cheung Chau Island in the west to Shek Kok Tsui (just to the north of Lamma Power Station) in the east is 700 m3/s and 2800 m3/s approximately during the dry and the wet season respectively [1]. The average tidal flow through the cross-section in the dry season is 26,000 m3/s at the flood tide and 33,800 m3/s at the ebb tide. In the wet season, the average flow is increased to 27,700 m3/s at the flood tide and 40,700 m3/s at the ebb tide.
2.5.2 The tidal currents in the Channel with a peak speed of just over 0.5 m/s, are predominantly from the southeast to the northwest at the flood tide and in the opposite direction during the ebb tide, i.e. from the northwest towards the southeast.
Water Quality Conditions
2.5.3 The Channel lies within the Southern WCZ. EPD carries out routine monitoring of marine WQ at the nearby stations, namely SM4, SM5, SM6, SM7, WM1 and WM2 as shown in Figure 2.1.
2.5.4 A number of EPD routine monitoring stations are in the vicinity of the dredging site, of which the closest is less than 1 km to the east of the Channel. Relevant WQ data for this site, SM5, and other nearby stations around Lamma Island and within the Southern and Western Buffer WCZs are summarised in Tables 2.1 and 2.2 for the dry (October to March) and wet (April to September) season respectively. This data was monitored in 2000. It is the most up to date information from EPD and is therefore used in this EIA to represent the baseline WQ conditions. All monitoring stations are within 8 km of the Project Area.
WQ Parameter |
SM3 |
SM4 |
SM5 |
SM6 |
SM7 |
WM1 |
WM2 |
DO (mg/L) |
6.99 (A) 6.69 (S) 7.17(B) (5.58-7.77) |
6.80 (A) 6.57 (S) 6.95 (B) (5.50-7.61) |
6.75 (A) 6.51 (S) 6.93 (B) (6.08-7.33) |
7.09 (A) 7.08 (S) 7.13 (B) (5.74-7.63) |
6.92 (A) 6.83 (S) 7.00 (B) (5.33-8.63) |
6.72 (A) 6.54 (S) 6.81 (B) (4.48-7.80) |
6.35 (A) 6.19 (S) 6.45 (B) (4.19-7.88) |
DO (% Sat.) |
92.08 (83.63-97.77) |
89.81 (82.46-94.51) |
89.53 (83.82-98.24) |
93.42 (86.31-98.33) |
91.08 (79.72-109.8) |
88.88 (66.65-100.2) |
83.93 (62.51-99.94) |
BOD5 (mg/L) |
0.49 (0.10-1.37) |
0.78 (0.35-1.47) |
0.93 (0.34-2.17) |
0.91 (0.31-2.13) |
1.08 (0.41-2.90) |
0.75 (0.15-2.00) |
0.85 (0.33-1.87) |
NH4 (mg/L) |
0.03 (0.01-0.07) |
0.05 (0.01-0.10) |
0.03 (0.01-0.05) |
0.03 (0.01-0.05) |
0.05 (0.02-0.11) |
0.05 (0.03-0.06) |
0.08 (0.02-0.13) |
NH3 (mg/L) |
0.001 (0.000-0.002) |
0.001 (0.000-0.002) |
0.001 (0.000-0.001) |
0.001 (0.000-0.002) |
0.002 (0.001-0.002) |
0.001 (0.000-0.002) |
0.002 (0.000-0.004) |
NO2 (mg/L) |
0.02 (0.01-0.08) |
0.02 (0.01-0.07) |
0.02 (0.01-0.04) |
0.03 (0.01-0.10) |
0.04 (0.01-0.16) |
0.04 (0.01-0.13) |
0.05 (0.01-0.19) |
NO3 (mg/L) |
0.10 (0.05-0.14) |
0.10 (0.05-0.16) |
0.09 (0.04-0.13) |
0.10 (0.03-0.15) |
0.12 (0.03-0.26) |
0.09 (0.04-0.15) |
0.12 (0.06-0.17) |
SS (mg/L) |
6.06 (1.13-10.70) |
7.11 (0.87-26.53) |
5.62 (1.30-10.87) |
8.46 (1.67-18.37) |
5.37 (2.13-12.83) |
6.29 (1.80-13.00) |
8.38 (1.47-22.33) |
TIN (mg/L) |
0.15 (0.10-0.20) |
0.17 (0.11-0.21) |
0.14 (0.09-0.16) |
0.15 (0.10-0.28) |
0.21 (0.08-0.45) |
0.18 (0.10-0.27) |
0.25 (0.17-0.36) |
TN (mg/L) |
0.27 (0.19-0.34) |
0.29 (0.21-0.35) |
0.23 (0.18-0.27) |
0.27 (0.20-0.42) |
0.33 (0.18-0.57) |
0.30 (0.26-0.39) |
0.40 (0.30-0.49) |
Note:      1.    Data presented are depth-averaged, except
as specified.
2.
Data presented are Dry Season arithmetic mean.
3.
Data enclosed in brackets indicate the ranges.
4.
Shaded cells indicate non-compliance with WQOs.
5.
(A), (S) and (B) represented the value of
depth-averaged, surface layer and bottom layer respectively.
2.5.5 The data in Tables 2.1~2.3 shows that the baseline WQ in the vicinity of the Channel was generally good, with compliance of WQOs for dissolved oxygen and unionised ammonia being achieved in both seasons at all monitoring stations. The total inorganic nitrogen (TIN) exceeded the WQO limits at all five stations in Southern WCZ. It is worth noting that the WQO for TIN is not exceeded at Stations WM1 and WM2, even though the average concentration was higher than those in Southern WCZ. This is because the TIN level in the WQOs for Western Buffer WCZ was higher than that for the Southern WCZ.Â
WQ Parameter |
SM3 |
SM4 |
SM5 |
SM6 |
SM7 |
WM1 |
WM2 |
DO (mg/L) |
5.95 (A) 6.75 (S) 5.40 (B) (4.91-7.14) |
6.24 (A) 6.41 (S) 5.82 (B) (4.62-8.18) |
7.28 (A) 7.59 (S) 6.56 (B) (4.82-9.24) |
6.47 (A) 7.61 (S) 5.31 (B) (5.04-8.24) |
7.03 (A) 7.11 (S) 6.59 (B) (4.77-10.31) |
5.54 (A) 6.22 (S) 4.93 (B) (3.89-6.81) |
5.74 (A) 6.06 (S) 5.43 (B) (4.15-8.06) |
DO (% Sat.) |
86.95 (72.35-107.92) |
91.94 (68.10-123.65) |
107.58 (71.50-139.19) |
95.30 (74.69-124.47) |
103.18 (69.95-154.10) |
80.31 (55.38-99.83) |
83.12 (59.50-120.78) |
BOD5 (mg/L) |
0.66 (0.37-0.81) |
0.77 (0.61-1.21) |
1.31 (0.78-2.63) |
1.11 (0.70-2.31) |
1.33 (0.58-3.07) |
0.82 (0.22-1.33) |
0.94 (0.35-1.90) |
NH4 (mg/L) |
0.04 (0.02-0.10) |
0.06 (0.03-0.10) |
0.03 (0.01-0.06) |
0.04 (0.02-0.08) |
0.07 (0.03-0.13) |
0.04 (0.02-0.06) |
0.07 (0.02-0.13) |
NH3 (mg/L) |
0.003 (0.001-0.008) |
0.003 (0.002-0.008) |
0.002 (0.000-0.006) |
0.003 (0.001-0.007) |
0.004 (0.002-0.011) |
0.002 (0.001-0.003) |
0.003 (0.001-0.006) |
NO2 (mg/L) |
0.02 (0.002-0.032) |
0.02 (0.01-0.04) |
0.02 (0.00-0.04) |
0.02 (0.00-0.04) |
0.03 (0.01-0.04) |
0.02 (0.00-0.05) |
0.04 (0.01-0.08) |
NO3 (mg/L) |
0.07 (0.01-0.15) |
0.09 (0.02-0.22) |
0.12 (0.00-0.31) |
0.01 (0.01-0.26) |
0.17 (0.04-0.30) |
0.12 (0.03-0.23) |
0.19 (0.11-0.26) |
SS (mg/L) |
5.48 (3.03-8.83) |
3.55 (1.47-6.17) |
3.71 (2.63-6.10) |
3.83 (2.80-5.37) |
4.89 (2.57-6.53) |
4.81 (1.83-7.00) |
3.49 (1.37-5.73) |
TIN (mg/L) |
0.13 (0.05-0.22) |
0.16 (0.10-0.30) |
0.17 (0.02-0.39) |
0.18 (0.03-0.34) |
0.26 (0.19-0.36) |
0.19 (0.07-0.32) |
0.30 (0.19-0.43) |
TN (mg/L) |
0.24 (0.13-0.34) |
0.29 (0.17-0.49) |
0.33 (0.10-0.63) |
0.32 (0.11-0.58) |
0.47 (0.27-0.86) |
0.29 (0.17-0.42) |
0.42 (0.29-0.55) |
Note:      1.    Data presented are depth-averaged, except
as specified.
               2.    Data presented are Wet Season arithmetic
mean.
               3.    Data enclosed in brackets indicate the
ranges.
               4.    Shaded cells indicate non-compliance with
WQOs.
5Â Â Â Â Â (A), (S)
and (B) represented the value of depth-averaged, surface layer and bottom layer
respectively.
Table 2.3Â Â Â Â Â Â Â Relevant Water Quality Objectives at the Relevant Water Control Zones
Locations
of WQSR |
Southern
WCZ |
Western
Buffer WCZ |
Victoria
Harbour (Phase 3) WCZ |
WQSR ID (see Fig 2.1) |
1, 7 - 15 |
3-6 |
2 |
PH |
6.5 – 8.5 |
||
Dissolved Oxygen (depth average, 90% of the sampling occasion during the year) |
4 mg/L |
||
Dissolved Oxygen (within 2 m from seabed, 90% of the sampling occasion during the year) |
2 mg/L |
||
Un-Ionised Ammonia Nitrogen (annual average) |
0.021 mg/L |
||
Total Inorganic Nitrogen (annual depth average) |
0.1 mg/L |
0.4 mg/L |
0.4 mg/L |
Suspended Solids |
< 30% increase over the ambient level |
2.6.1 Impacts from SS may be caused by sediment plumes being transported to SRs, such as water intakes, bathing beaches and areas of high ecological value, leading to the elevation of the SS levels at the SRs. The level of elevation will determine whether the impact is acceptable. The WQOs in terms of SS for the Southern and Western Buffer WCZs are defined as being an allowable maximum elevation of 30% above the background for bathing beaches and sites of ecological interest. Following recent research [29] by City University for AFCD, a maximum SS level of 50mg/l is recommended for the marine fish culture zones. The maximum SS levels allowed for the water intakes are 100mg/l for HEC’s Lamma Power Station cooling water intake, 20mg/l for the remaining water intakes. Based on the allowable maximum SS levels and the baseline SS levels, the SS tolerant elevation can be determined as in Table 2.4. As the seawater intakes are normally located in the mid-depth or above, the assessment criteria for the seawater intakes has been based on the pollution levels at the surface layer and the depth-averaged concentrations.
2.6.2 The WQOs in terms of other WQ parameters for the WQSRs have been taken as the same as those for the respective WCZs.
2.6.3 Silt and clay, also called cohesive sediment, will form large particles by the process of flocculation after being released into the water column, which will then settle back to the seabed, resulting in a smothering effect. This smothering effect can be detrimental to the corals found near the western coast of Lamma Island. Following the EIA for Sand Dredging at the West Po Toi Marine Borrow Area [30], a limit on the sedimentation rate of 0.1kg/m2/day was applied to this EIA in view of the ecological interests found in and around the area.
2.6.4 With reference to a previous EIA study for a 1,800MW Gas-Fired Power station at Lamma Extension [3], the background SS value for this EIA has been represented by the 90th percentile of the reported concentrations.
2.6.5 EPD routine WQ monitoring data has been used as the source of reported concentrations, with the monitoring station nearest to each SR being defined as representative of that SR. The predicted maximum SS elevation resulting from the dredging has been compared to the SS tolerance values in Table 2.4 and the predicted maximum concentration elevation of other pollutants plus the baseline level has been compared to Table 2.3, to determine the acceptability of the WQ impacts.
Table 2.4Â Â Â Â Â Â Â Background SS Concentrations and Tolerance Elevation at Sensitive Receivers
SRs (Relevant Monitoring Station) |
Dry Season |
Wet Season |
|||
90th Percentile |
Tolerance Elevation (mg/l) |
90th Percentile |
Tolerance Elevation (mg/l) |
||
Luk Cha (SM3) |
Aa |
9.18 |
2.75 |
8.07 |
2.42 |
Sb |
6.85 |
2.06 |
4.30 |
1.29 |
|
Bc |
14.50 |
4.35 |
21.00 |
6.30 |
|
Lo Tik Wan Fish Culture Zoned (SM3) |
A |
9.18 |
40.82 |
8.07 |
41.93 |
S |
6.85 |
43.15 |
4.30 |
45.7 |
|
B |
14.50 |
35.5 |
21.00 |
29.00 |
|
Sok Kwu Wan Fish Culture Zoned (SM4) |
A |
15.92 |
34.08 |
5.18 |
44.82 |
S |
5.30 |
44.7 |
4.80 |
45.20 |
|
B |
25.85 |
24.15 |
7.75 |
42.25 |
|
Hung Shing Ye Beach Lo So Shing Beach S. Lamma 1 S. Lamma 2 (SM5) |
A |
8.65 |
2.60 |
5.42 |
1.63 |
S |
6.00 |
1.80 |
4.35 |
1.31 |
|
B |
12.30 |
3.69 |
6.10 |
1.83 |
|
Sha Wan Drive Intakee Queen Mary Hospital Intakee Wah Fu Estate Intakee (WM1) |
A |
11.67 |
8.33 |
6.95 |
13.05 |
S |
7.00 |
13.00 |
3.60 |
16.40 |
|
Pak Kok Shek Kok Tsui (WM1) |
A |
11.67 |
3.50 |
6.95 |
2.09 |
S |
7.00 |
2.10 |
3.60 |
1.08 |
|
B |
16.50 |
4.95 |
14.00 |
4.20 |
|
Kennedy Town WSD Intakee (WM2) |
A |
19.00 |
1.00 |
5.10 |
14.90 |
S |
15.50 |
4.50 |
4.55 |
15.45 |
|
Kau Yi Chau (WM2) |
A |
19.00 |
5.70 |
5.10 |
1.53 |
S |
15.50 |
4.65 |
4.55 |
1.37 |
|
B |
25.50 |
7.65 |
5.85 |
1.76 |
|
HEC Power Station Intake f (SM5) |
A |
9.18 |
90.82 |
8.07 |
91.93 |
S |
6.85 |
93.15 |
4.30 |
95.70 |
Note:Â Â Â Â Â Â a. A represents depth-averaged
               b. S represents surface layer
               c. B represents bottom layer
               d. Fish Culture Zones can
tolerate a SS level of up to 50mg/l according to AFCD
               e. Flushing seawater intakes can
tolerate a SS level of up to 20mg/l
               f. HEC Power Station cooling water
intake can tolerate a SS level of up to 100mg/l according to HEC.
2.7
Sediment Sampling, Elutriation Test and Particle Size Analysis
2.7.1 An elutriation test has been carried out as part of this EIA study to assess the elutriation potential of various contaminants in the sediment during dredging.Â
2.7.2 Under normal conditions, the contaminants would bind firmly with the bottom sediment and remain in the seabed. However, it is possible that these contaminants might be released into marine water if mechanical actions such as dredging activities take place, thus affecting the ambient marine WQ.
2.7.3 The objective of carrying out elutriate testing was to investigate the potential for the sediment-bonded pollutants being released into the ambient marine water (in the immediate vicinity of dredging) during dredging activities for the Project. ALS Environmental, a laboratory accredited by HOKLAS, was appointed to conduct sample collection and elutriation analysis.
2.7.4 Sediment samples were collected in December 2001 from the Project Area at three locations (Sample A - 828240E, 808540N; Sample B - 828540E, 807270N and Sample C - 828780E, 806000N) as shown in Figure 2.1 using grab samplers. Representative blank marine water samples were also collected for the test. The three sediment samples were homogenized in the laboratory and extracted with the collected marine water in accordance with the elutriation method as recommended by USACE.
2.7.5 The sampling locations were chosen so that they are representative of the Channel and are close to the three dredging locations (representing the worst-case scenarios) to be modelled for WQ assessment.
The following WQ parameters were analyzed:
·
Nitrogen Nutrients
Ammonia nitrogen (NH3-N and NH4-N), Nitrite (NO2-N), Nitrate (NO3-N), Organic Nitrogen, Total Kjeldahl Nitrogen (TKN) and Total Inorganic Nitrogen (TIN).
·
Heavy Metals
Silver, Arsenic, Cadmium, Chromium, Copper, Nickel, Lead, Zinc and Mercury.
·
Micro-Pollutants
PCBs, PAHs, TBT and chlorinated pesticides.
·
Five-Day Sediment Oxygen Demand
(SOD5)
2.7.6 Unlike the above parameters for which the analysis was carried out on the mixture of sediment and water, sediment samples were analysed for SOD5.
2.7.7 The detection limits for the various WQ parameters were established based on the review of the international marine WQ standards which will be discussed later in this Report. A summary of the elutriation test results is given in Table 2.4a.
2.7.8 All heavy metals were found to be below the detection limits for all samples.
2.7.9 TBT, all PAHs, PCBs and chlorinated pesticides were also below the detection limit for all samples.
2.7.10 SOD5 were found to be 453, 706 and 380 mgO2/kg (dry weight sediment) for the samples collected at the locations A, B and C respectively.
Table 2.4a     Elutriation Test Results
Parameters |
Unit |
Sample
A |
Sample
B |
Sample
C |
Blank
Water |
pH Value @ 25'C |
|
7.6 |
7.6 |
7.8 |
8.1 |
Redox Potential |
mV |
266 |
263 |
262 |
260 |
Silver |
ug/L |
<1 |
<1 |
<1 |
<1 |
|
|
|
|
|
|
Heavey
Metals |
|
|
|
|
|
Arsenic |
ug/L |
<10 |
<10 |
<10 |
<10 |
Cadmium |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Chromium |
ug/L |
<5 |
<5 |
<5 |
<5 |
Copper |
ug/L |
<1 |
<1 |
<1 |
<1 |
Nickel |
ug/L |
<1 |
<1 |
<1 |
<1 |
Lead |
ug/L |
<1 |
<1 |
<1 |
<1 |
Zinc |
ug/L |
<10 |
<10 |
<10 |
<10 |
Mercury |
ug/L |
<0.05 |
<0.05 |
<0.05 |
<0.05 |
|
|
|
|
|
|
Nutrients |
|
|
|
|
|
Ammonia as N |
mg/L |
1.76 |
2.74 |
1.23 |
0.01 |
Nitrite + Nitrate as N |
mg/L |
0.02 |
0.02 |
0.02 |
0.11 |
Organic Nitrogen as N |
mg/L |
0.4 |
0.3 |
0.7 |
0.4 |
Total Kjeldahl Nitrogen as N |
mg/L |
2.2 |
3 |
1.9 |
0.4 |
Total Inorganic Nitrogen |
mg/L |
1.78 |
2.76 |
1.25 |
0.12 |
|
|
|
|
|
|
PCBs |
|
|
|
|
|
PCB8 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB18 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB28 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB44 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB52 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB66 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB77 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB101 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB105 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB118 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB126 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB128 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB138 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB153 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB169 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB170 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB180 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB187 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB195 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB206 |
ug/L |
<1 |
<1 |
<1 |
<1 |
PCB209 |
ug/L |
<1 |
<1 |
<1 |
<1 |
|
|
|
|
|
|
ORGANOCHLORINE PESTICIDES |
|
|
|
|
|
alpha-BHC |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
beta- & gamma-BHC |
ug/L |
<1 |
<1 |
<1 |
<1 |
delta-BHC |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Heptachlor |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Aldrin |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Heptachlor epoxide |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Endosulfan 1 |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Dieldrin |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
4,4'-DDE |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Endrin |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Endosulfan 2 |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
4,4'-DDD |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Endrin aldehyde |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Endosulfan sulfate |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
4,4'-DDT |
ug/L |
<2 |
<2 |
<2 |
<2 |
Endrin ketone |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
Methoxychlor |
ug/L |
<2 |
<2 |
<2 |
<2 |
Cypermethrins |
ug/L |
<0.5 |
<0.5 |
<0.5 |
<0.5 |
|
|
|
|
|
|
POLYNUCLEAR AROMATICS |
|
|
|
|
|
Naphthalene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Acenaphthylene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Acenaphthene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Fluorene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Phenanthrene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Anthracene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Fluoranthene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Pyrene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Benz(a)anthracene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Chrysene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Benzo(b) & (k)fluoranthene |
ug/L |
<4 |
<4 |
<4 |
<4 |
Benzo(a)pyrene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Indeno(1.2.3-cd)pyrene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Dibenz(a.h)anthracene |
ug/L |
<2 |
<2 |
<2 |
<2 |
Benzo(g.h.i)perylene |
ug/L |
<2 |
<2 |
<2 |
<2 |
|
|
|
|
|
|
ORGANOTIN COMPOUNDS |
|
|
|
|
|
Tributyltin - Soluble |
ng Sn/L |
<5 |
<5 |
<5 |
<5 |
2.7.11 The majority of the TIN (in excess of 98%) consists of ammoniacal nitrogen. There is significant elevation of all nitrogen components over the background levels except for NO2-N and NO3-N.
2.7.12 The level of NO2-N and NO3-N in the elutriation samples was found to be lower than the background levels, which is believed to be due to the sediment, on mixing with the seawater, acting as an oxygen absorption media in the mixing process which converts part of NO2-N and NO3-N into NH3-N.
2.7.13 In addition, the sediment samples were analysed for particle size distributions. All samples showed that 95% or more of the sediment was silt and clay.
2.7.14 The details of the sampling methodology and the elutriation testing results are provided in Appendix 1.Â
2.7.15 During the period from 1994 to 1998 three sets of sediment quality data were collected in and around the Channel. A summary of the sediment quality data is provided in Appendix 2. All measured contaminant levels of the samples are below the Lower Chemical Exceedance Level (LCEL) as defined in the Works Bureau Technical Circular (WBTC) No. 3/2000. Data from these three sediment quality studies indicated there have been no significant changes in sediment quality during the 4-year period and the sediment in and around the Channel belongs to Category L. An earlier study [3] also confirmed that the marine sediment at the site of the Lamma Power Station Extension, which is close to the northern section of the Channel, is uncontaminated.
2.8
Assessment of Potential Impacts during Dredging
The Water Quality Model
2.8.1 The WQ effect has been assessed using WQ modelling. The hydrodynamic and WQ model constructed using Delft3D for a previous EIA study, Environmental Impact Assessment of a 1,800MW Gas-Fired Power Station at Lamma Extension [3], has been adopted for the current study. The coverage and the computational grid system of the model are shown in Figure A3.1 in Appendix 3.
2.8.2 Due to lack of site specific data, a sediment settling velocity of 2m/d, derived from the calibration and verification of the Upgraded Model for Hong Kong waters, has been adopted for this EIA.
2.8.3 The dredging period is scheduled for between May 2003 and December 2003, covering both the dry and wet seasons. As the tidal circulation patterns in the vicinity of the Channel differs significantly between the two seasons, the model has been run for a typical 15-day spring to neap tidal cycle each for the dry and wet season for each dredging scenario. As in the previous EIA study for the Lamma Power Station Extension, the dry season simulation period has been from 6th to 20th January 1993 with a 5-day ‘spin-up’ period from 1st to 5th January 1993, and for the wet season the simulation period has been from 1st to 15th August 1992 with a ‘spin-up’ period from 28th to 31st July 1992. Those periods have been chosen since the existing model was already setup for those periods and they also represent a typical dry season period and wet season period in Hong Kong.
Dredging Scenarios
2.8.4 As different dredging contractors may be equipped with different dredgers, HEC would like to have the flexibility of appointing the most suitable contractors for carrying out the proposed dredging works. To this end, it would be most appropriate to estimate the maximum dredging rates which would ensure no unacceptable environmental impacts rather than fixing a detailed plant inventory at this early stage. In order to minimise the dredging period and therefore the associated costs, it is planned that the dredgers will be operating on a 24-hour basis during the dredging period.
2.8.5 The Channel to be dredged is divided equally in terms of the Northing Coordinates into four working zones: ABn, ABs, BCn and BCs as shown in Figure 2.2. While the location of dredging will be moving all the time within the Channel, the most adverse impact of the whole dredging operation can be represented by dredging at either Dredging Location A, B or C as shown in Figure 2.2. Without dividing the project area into smaller working zones, the only environmentally acceptable uniform dredging rate would have to be based on the worst case scenario, i.e. dredging at Location C. In view of the relatively large area to be dredged, this would significantly and unnecessarily lengthen the dredging programme.
2.8.6 The impact of dredging at Dredging Location A would represent the worst-case scenario for the WQSRs to the north of the Channel such as those in the Western Buffer WCZ.
2.8.7 Dredging at Dredging Location C would represent the worst-case scenario for the WQSRs to the south of the Channel such as those in the South Lamma water. Dredging Location C represents the most southern point where the dredging will take place. According to the latest bathymetric survey of the Channel, there is already sufficient water depth and no dredging will be required in the southern part of the Channel beyond Dredging Location C.
2.8.8 The other adverse scenarios which may not be covered by dredging at either Dredging Location A or C can be accounted for by dredging at Dredging Location B.
2.8.9 Based on the maximum dredging rates for dredging at Dredging Locations A, B or C, the maximum dredging rates for dredging at the individual working zones can be conservatively estimated as follows:
2.8.10 The maximum dredging rate at the mid point between A and B can be linearly interpolated from those at A and B. Likewise, the maximum dredging rate at the mid point between B and C can be linearly interpolated from those at B and C. When a working zone has two different estimated dredging rates at the northern and southern boundaries, the lesser is recommended for the working zone.Â
2.8.11 It should be noted that the maximum dredging rates thus estimated assume that all dredging activities take place at one single location (i.e. A or B or C) or at one single working zone (i.e. ABn or ABs or BCn or BCs). The maximum dredging rates for dredging activities taking place at more than one working zones concurrently will be addressed at the end of this section.
2.8.12 Two types of dredgers, i.e. grab dredgers and trailer suction hopper dredgers (TSHD), are likely to be deployed for the works based on HEC’s current and previous projects involving dredging in this area. In view of the relatively large quantity of the sediment to be dredged, medium to large size of grab with a grab capacity of no less than 8 m3 will be deployed for the grab dredger option. The maximum dredging rates have therefore been estimated using WQ modelling for those two types of dredgers.Â
2.8.13 For the TSHD option, it was assumed that there would be only one TSHD to be deployed at any one time for the dredging work, operating intermittently at a dredging cycle of 30 minute dredging and 2 hour travelling between the dredging site and the allocated dumping sites.
2.8.14 For grab dredgers, cage-type silt curtains as illustrated in Figure 2.3 will be deployed surrounding the grab and dredging will only take place within the water enclosed by the silt curtains which are mounted to the dredging barge. The silt curtains can move along with the dredging barge. According to HEC’s measurements for the dredging practice in the area, the reduction rate in SS concentration of the silt curtains is typically between 76% and 81%. For the purpose of this assessment, a reduction rate of 75% is adopted. It was assumed that the dredging would be carried out continuously with the dumping of the dredged material being handled by barges and tugboats. A maximum of five grab dredgers will be operating at any one time and the actual number of dredgers used will depend on the maximum dredging rates allowed.
2.8.15 The sediment loss rates, or the S-Factors, of 4.25 kg/m3 has been adopted in this EIA for the grab dredger option with cage-type silt curtain and grab capacity ³ 8 m3. This follows the EIA for International Theme Park and Associated Development [6] in which a S-Factor of 17kg/m3 was adopted for area of low debris. The Channel is low in debris and boulders as it is relatively remote from shore, has been dredged twice since 1981 and has been mainly used by the ships delivering coal fuel to Lamma Power Station.  Applying a 75% reduction rate to the S-Factor of 17kg/m3, due to use of cage-type silt curtain, a S-Factor of 4.25kg/m3 is obtained.   The S-factors for a TSHD (no overflow or Lean Mixture Overboard) typically ranges from 3 to 4 kg/m3 [5] and a S-factor of 4 kg/m3 has been adopted in this EIA, following a previous EIA study conducted for the same area [3].Â
2.8.16 The leakage from grab dredgers can be throughout the water column as the dredger is lifted from the seabed to the barge. However, any leakage from TSHD would be close to the seabed.
Suspended Sediment (SS)
2.8.17 For each dredging scenario, a unit sediment discharge rate was modelled. Based on the predicted SS elevation and the baseline SS level at each vertical layer and at each SRs, the most critical SRs (where the percentage SS elevation over the baseline level is the largest among all WQSRs) were identified as shown in Table 2.5. The maximum dredging rates were then estimated by scaling the unit sediment discharge rate by the ratio between the allowed elevation above the baseline SS level in Table 2.4 and the predicted SS elevation at the most critical SRs under the unit discharge rate. The maximum dredging rates estimated for various dredging scenarios are also provided in Table 2.5. Based on the resulting SS elevation and the baseline SS level, Shek Kok Tsui is the most critical WQSR when dredging at Dredging Location A. The south Lamma water generally represents the most critical WQSR when dredging at Dredging Locations B or C for both types of dredgers. However the WQSR at Hung Shing Ye becomes most critical when dredging at Dredging Location B using TSHD during the dry season. The contours of the SS elevations predicted under the estimated maximum dredging rates for various scenarios are provided in Figures A3.7 to A3.12 and A3.25 to A3.30 in Appendix 3.
2.8.18 It should be noted that the maximum dredging rates estimated in Table 2.5 are the total dredging rates allowed in the entire Project Area at any one time. Take the grab dredger with silt curtains option during the wet season for example. The total dredging rate should be no greater than 40,100 m3/day if all dredging activities take place at Dredging Location A, no greater than 34,916 m3/day if all dredging activities take place at Dredging Location B and no greater than 23,521 m3/day if all dredging activities take place at Dredging Location C.
2.8.19 It can be seen that the location of the critical SR differs between dredging locations, but remain largely unchanged for different seasons and for both grab dredgers and TSHD. As expected, the most critical SRs for dredging at Dredging Locations A and C are at Shek Kok Tsui and the South Lamma Water respectively. When dredging at Dredging Location B, the south Lamma water is also the most critical SR for both grab dredgers and TSHD except for the TSHD option during the dry season when Hung Shing Ye becomes the most critical SR.
2.8.20 According to the WQ modelling results, the WQ impact on South Lamma 1 and South Lamma 2 are among the highest in the south Lamma water due to its close vicinity to the southern section of the Project Area. The WQ impact on the other parts of the south Lamma water is considerably less and is negligible in the water around Sham Wan.Â
2.8.21 Table 2.6 summarises the maximum (over the 15-day spring to neap tidal cycle) SS elevation at the bottom layer (B), surface layer (S) and averaged over the water depth (A) at the SRs if grab dredgers with silt curtain are used at the maximum dredging rates. The similar information for TSHD at the maximum dredging rates is provided in Table 2.7. It is worth noting that the SS concentration elevation presented in Tables 2.6 and 2.7 and in Appendix 3 is the maximum concentration over the 15-day spring to neap tidal cycle. As such, the resulting SS concentration elevation will be lower most of the time.
Table 2.5Â Â Â Â Â Â Â Estimated Maximum Dredging Rates and Critical Sensitive Receivers
|
|
|
|
|
|
|
S-Factor (kg/m3, Grab with
silt curtain) |
4.25 |
|
4.00 |
|
|
|
S-Factor (kg/m3, TSHD, no
overflow) |
4 |
|
|
|
|
|
|
Wet Season (April to September) |
Dry Season (October to March) |
||||
Dredging Location |
A |
B |
C |
A |
B |
C |
Grab with Silt Curtain |
|
|
|
|
|
|
Critical Sensitive Receiver |
SKTd (Sb) |
SL1e (Bc) |
SL1e (S) |
SL1e (S) |
SL1e (S) |
SL2e (S) |
Max Loss Rate (kg/s) |
1.972 |
1.717 |
1.157 |
2.967 |
1.812 |
1.926 |
Predicted Max Dredging Rate
(m3/s) |
0.4641 |
0.4041 |
0.2722 |
0.6982 |
0.4264 |
0.4532 |
Predicted Max Dredging Rate
(m3/day) |
40,100 |
34,916 |
23,521 |
60,328 |
36,837 |
39,160 |
TSHD |
|
|
|
|
|
|
Critical Sensitive Receiver |
SKTd
(B) |
SL1e
(B) |
SL1e
(B) |
SKTd
(Aa) |
HSYf
(A) |
SL1e
(B) |
Max Loss Rate (kg/s) |
3.494 |
2.912 |
1.356 |
11.479 |
8.827 |
5.077 |
Predicted Max Dredging Rate (m3/s) |
0.8735 |
0.7280 |
0.3390 |
2.8698 |
2.2068 |
1.2693 |
Predicted Max Dredging Rate (m3/day) |
15,094 |
12,580 |
5,858 |
49,589 |
38,133 |
21,933 |
Note:Â Â Â Â Â a. A represents
depth-averaged                                      b.
S represents surface layer
               c. B represents bottom layer                                            d.
SKT - Shek Kok Tsui
               e. SL1 and SL2 - South Lamma 1
and 2 respectively f. HSY - Hung Shing Ye
Beach
Sediment Deposition
2.8.22
Under the maximum dredging rates
estimated, the predicted deposition rates are less than 0.01 kg/m2/day
along the west coast of Lamma Island and less than 0.001 kg/m2/day
in the south Lamma water for all dredging scenarios. The contours of the predicted sediment
deposition rates for the dredging scenarios are provided in Figures A3.13 to A3.18 and A3.31 to A3.36.
Sensitive
Receiver |
Depth |
Dredging
Location A (mg/l) |
Dredging
Location B (mg/l) |
Dredging
Location C (mg/l) |
|||
Dry |
Wet |
Dry |
Wet |
Dry |
Wet |
||
Kau Yi Chau (fish fry
nursery area) |
A |
0.168 |
0.161 |
0.089 |
0.106 |
0.051 |
0.054 |
S |
0.167 |
0.074 |
0.089 |
0.047 |
0.051 |
0.025 |
|
B |
0.168 |
0.252 |
0.088 |
0.169 |
0.051 |
0.088 |
|
Kennedy Town WSD Intake |
A |
0.287 |
0.123 |
0.130 |
0.100 |
0.087 |
0.053 |
S |
0.274 |
0.098 |
0.124 |
0.066 |
0.074 |
0.034 |
|
B |
0.294 |
0.138 |
0.133 |
0.120 |
0.093 |
0.065 |
|
Sha Wan Drive Intake |
A |
0.298 |
0.135 |
0.135 |
0.107 |
0.091 |
0.053 |
S |
0.271 |
0.151 |
0.118 |
0.108 |
0.078 |
0.036 |
|
B |
0.298 |
0.129 |
0.140 |
0.110 |
0.097 |
0.060 |
|
Queen Mary Hospital Intake |
A |
0.297 |
0.142 |
0.136 |
0.111 |
0.092 |
0.054 |
S |
0.272 |
0.168 |
0.119 |
0.123 |
0.080 |
0.040 |
|
B |
0.297 |
0.129 |
0.141 |
0.110 |
0.097 |
0.061 |
|
Wah Fu Estate Intake |
A |
0.297 |
0.172 |
0.138 |
0.124 |
0.097 |
0.056 |
S |
0.290 |
0.301 |
0.136 |
0.221 |
0.086 |
0.066 |
|
B |
0.284 |
0.107 |
0.135 |
0.081 |
0.100 |
0.047 |
|
Pak Kok (corals present) |
A |
2.131 |
1.313 |
1.212 |
0.906 |
0.669 |
0.360 |
S |
1.703 |
0.551 |
0.796 |
0.453 |
0.401 |
0.174 |
|
B |
2.501 |
1.720 |
1.456 |
1.345 |
0.840 |
0.531 |
|
Shek Kok Tsui (corals present) |
A |
2.588 |
1.966 |
1.497 |
1.081 |
0.884 |
0.421 |
S |
1.820 |
1.080 |
0.844 |
0.687 |
0.505 |
0.303 |
|
B |
3.202 |
3.052 |
1.860 |
1.599 |
1.118 |
0.607 |
|
Luk Chau (corals present) |
A |
1.187 |
0.433 |
0.612 |
0.334 |
0.373 |
0.146 |
S |
1.129 |
0.455 |
0.528 |
0.349 |
0.275 |
0.123 |
|
B |
1.197 |
0.263 |
0.665 |
0.239 |
0.417 |
0.118 |
|
Lo Tik Wan Fish Culture
Zone |
A |
0.614 |
0.272 |
0.305 |
0.193 |
0.195 |
0.083 |
S |
0.612 |
0.336 |
0.304 |
0.253 |
0.194 |
0.090 |
|
B |
0.610 |
0.191 |
0.304 |
0.161 |
0.195 |
0.081 |
|
HEC Power Station Intake |
A |
0.562 |
0.524 |
1.319 |
1.092 |
1.231 |
0.671 |
S |
0.347 |
0.297 |
0.671 |
0.580 |
0.631 |
0.341 |
|
B |
0.663 |
0.628 |
1.663 |
1.340 |
1.516 |
0.918 |
|
Hung Shing Ye Beach |
A |
0.561 |
0.343 |
1.438 |
0.614 |
1.383 |
0.364 |
S |
0.380 |
0.258 |
0.962 |
0.375 |
0.808 |
0.166 |
|
B |
0.680 |
0.482 |
1.764 |
0.873 |
1.680 |
0.501 |
|
Lo So Shing Beach |
A |
0.957 |
0.731 |
1.461 |
1.064 |
1.913 |
0.671 |
S |
0.905 |
0.925 |
1.271 |
0.974 |
1.276 |
0.467 |
|
B |
0.956 |
0.672 |
1.628 |
1.362 |
2.261 |
0.971 |
|
Sok Kwu Wan Fish Culture
Zone |
A |
0.316 |
0.120 |
0.150 |
0.083 |
0.097 |
0.048 |
S |
0.310 |
0.133 |
0.149 |
0.091 |
0.095 |
0.051 |
|
B |
0.323 |
0.094 |
0.153 |
0.069 |
0.100 |
0.045 |
|
South Lamma 1 (finless porpoise habitat) |
A |
1.683 |
0.996 |
1.860 |
1.497 |
2.059 |
1.176 |
S |
1.800 |
1.047 |
1.800 |
1.193 |
1.604 |
1.305 |
|
B |
1.460 |
0.821 |
1.865 |
1.830 |
2.488 |
1.563 |
|
South Lamma 2 (finless porpoise habitat) |
A |
1.216 |
0.542 |
1.135 |
0.957 |
1.857 |
0.914 |
S |
1.255 |
0.653 |
1.313 |
0.574 |
1.800 |
0.599 |
|
B |
1.187 |
0.295 |
1.040 |
0.918 |
1.844 |
0.781 |
Note: A – Depth-averaged, B – Bottom Layer, S – Surface Layer
Sensitive Receiver |
Depth |
Dredging Location A (mg/l) |
Dredging Location B (mg/l) |
Dredging Location C (mg/l) |
|||
Dry |
Wet |
Dry |
Wet |
Dry |
Wet |
||
Kau Yi Chau (fish fry nursery area) |
A |
0.144 |
0.080 |
0.087 |
0.051 |
0.028 |
0.016 |
S |
0.144 |
0.034 |
0.087 |
0.024 |
0.028 |
0.007 |
|
B |
0.144 |
0.149 |
0.087 |
0.084 |
0.277 |
0.030 |
|
Kennedy Town WSD Intake |
A |
0.251 |
0.046 |
0.135 |
0.040 |
0.050 |
0.013 |
S |
0.238 |
0.034 |
0.130 |
0.027 |
0.044 |
0.009 |
|
B |
0.257 |
0.055 |
0.135 |
0.048 |
0.053 |
0.016 |
|
Sha Wan Drive Intake |
A |
0.263 |
0.048 |
0.140 |
0.038 |
0.050 |
0.013 |
S |
0.238 |
0.038 |
0.125 |
0.029 |
0.044 |
0.010 |
|
B |
0.263 |
0.050 |
0.140 |
0.043 |
0.055 |
0.015 |
|
Queen Mary Hospital Intake |
A |
0.263 |
0.050 |
0.140 |
0.040 |
0.053 |
0.013 |
S |
0.238 |
0.040 |
0.125 |
0.029 |
0.044 |
0.010 |
|
B |
0.257 |
0.052 |
0.140 |
0.045 |
0.053 |
0.015 |
|
Wah Fu Estate Intake |
A |
0.257 |
0.044 |
0.140 |
0.037 |
0.053 |
0.012 |
S |
0.270 |
0.048 |
0.145 |
0.037 |
0.047 |
0.010 |
|
B |
0.238 |
0.038 |
0.130 |
0.032 |
0.055 |
0.011 |
|
Pak Kok (corals present) |
A |
2.126 |
0.853 |
1.322 |
0.473 |
0.388 |
0.102 |
S |
0.878 |
0.109 |
0.603 |
0.076 |
0.216 |
0.017 |
|
B |
2.954 |
1.787 |
1.770 |
0.883 |
0.494 |
0.174 |
|
Shek Kok Tsui (corals present) |
A |
3.500 |
1.476 |
1.978 |
0.595 |
0.533 |
0.137 |
S |
1.480 |
0.246 |
0.868 |
0.121 |
0.258 |
0.037 |
|
B |
4.805 |
4.200 |
2.566 |
1.149 |
0.682 |
0.237 |
|
Luk Chau (corals present) |
A |
0.922 |
0.151 |
0.584 |
0.129 |
0.200 |
0.036 |
S |
0.772 |
0.094 |
0.473 |
0.076 |
0.158 |
0.021 |
|
B |
0.960 |
0.116 |
0.632 |
0.110 |
0.219 |
0.032 |
|
Lo Tik Wan Fish Culture Zone |
A |
0.470 |
0.073 |
0.289 |
0.068 |
0.105 |
0.020 |
S |
0.496 |
0.078 |
0.294 |
0.078 |
0.105 |
0.021 |
|
B |
0.452 |
0.073 |
0.289 |
0.067 |
0.105 |
0.021 |
|
HEC Power Station Intake |
A |
0.408 |
0.168 |
2.301 |
0.732 |
0.860 |
0.342 |
S |
0.263 |
0.074 |
0.912 |
0.103 |
0.405 |
0.045 |
|
B |
0.477 |
0.216 |
3.237 |
1.362 |
1.124 |
0.627 |
|
Hung Shing Ye Beach |
A |
0.433 |
0.086 |
2.595 |
0.191 |
1.035 |
0.093 |
S |
0.276 |
0.044 |
1.669 |
0.041 |
0.580 |
0.019 |
|
B |
0.533 |
0.139 |
3.256 |
0.461 |
1.293 |
0.218 |
|
Lo So Shing Beach |
A |
0.734 |
0.191 |
1.843 |
0.399 |
1.545 |
0.348 |
S |
0.690 |
0.105 |
1.452 |
0.103 |
0.932 |
0.050 |
|
B |
0.734 |
0.252 |
2.209 |
0.821 |
1.900 |
0.785 |
|
Sok Kwu Wan Fish Culture Zone |
A |
0.245 |
0.032 |
0.145 |
0.027 |
0.055 |
0.010 |
S |
0.238 |
0.040 |
0.140 |
0.032 |
0.053 |
0.010 |
|
B |
0.251 |
0.027 |
0.145 |
0.022 |
0.055 |
0.009 |
|
South Lamma 1 (finless
porpoise habitat) |
A |
1.286 |
0.307 |
1.987 |
0.708 |
1.923 |
0.552 |
S |
1.349 |
0.149 |
1.626 |
0.143 |
0.838 |
0.089 |
|
B |
1.085 |
0.342 |
2.373 |
1.830 |
3.690 |
1.830 |
|
South Lamma 2 (finless
porpoise habitat) |
A |
0.859 |
0.115 |
0.989 |
0.403 |
1.079 |
0.385 |
S |
0.866 |
0.097 |
1.100 |
0.116 |
0.841 |
0.053 |
|
B |
0.853 |
0.076 |
0.936 |
0.516 |
1.359 |
1.023 |
Note: A – Depth-averaged, B – Bottom Layer, S – Surface Layer
Ammoniacal
Nitrogen
2.8.23 As mentioned in Section 2.7 above, the elutriation test revealed that more than 98% of the potential TIN elevation resulting from the proposed dredging works is contributed to by ammoniacal nitrogen. The test showed that the potential elevation of the ammoniacal nitrogen is 1.75, 2.73 and 1.22 mg/l for the samples collected at Sampling Locations A, B and C respectively. It should be noted that the test results only represent the potential pollution elevation in the very vicinity of the dredging locations.
2.8.24  In the marine environment, un-ionised ammonia exists in equilibrium with the ammonium ion. The tested ammonia nitrogen concentrations are the sum of both forms of ammoniacal nitrogen. Under a pH value of about 8 measured for the water samples collected from the site and at the likely temperature range of 10 to 280C in Hong Kong waters, more than 90% of the ammoniacal nitrogen would be in the ionised form. This would lead to an elevation of un-ionised ammoniacal nitrogen of less than 0.175, 0.273 and 0.122 mg/l at Sampling Locations A, B and C respectively. Compared to the threshold value of 0.021mg/l for un-ionised ammoniacal nitrogen as defined in the WQOs and taking into account the baseline ammoniacal nitrogen level, a dilution of just 9, 13 and 6 would be sufficient to enable the compliance with the WQOs for dredging at Locations A, B and C respectively.
2.8.25 Based on the Gaussian Dispersion Model [5] for a local velocity of 0.5m/s, a dispersion coefficient of 1m2/s and a local water depth of 15m, this dilution can be achieved within 50m of the dredging location in the direction normal to the main tidal stream (i.e. east-west direction).  However, in the direction along the main tidal stream of the Channel (i.e. north-south direction), the required distance will be 700m, 1700m and 400m approximately for dredging at Locations A, B and C respectively. As most of the WQSRs (except for South Lamma 2) are in the inshore area to the east of the Channel, at least 1000m from the dredging area and outside the path of the tidal stream passing the Channel, the potential impact of the proposed Channel Improvement on those WQSRs in terms of the ammoniacal nitrogen concentration is therefore negligible. South Lamma 2 is about 1200m to the nearest location of the Channel to be dredged (i.e. Location C) and the distance required along the main tidal stream to achieve the desired dilution is only 400m, the impact of the proposed dredging on South Lamma 2 is therefore also acceptable.
Dissolved Oxygen Depletion
2.8.26 The release of sediment contaminants into the water column consumes the dissolved oxygen in the ambient water. The oxygen depletion resulting from the dredging under the maximum dredging rates has been modelled and the results are presented in Appendix 3 (Figures A3.19 to A3.24 and A3.37 to A3.42). The sediment oxygen demand from the laboratory test (Appendix 1) and the estimated maximum dredging rates have been used to calculate the sediment depletion sources at Dredging Locations A, B and C.
2.8.27 Unlike the conventional definition of Sediment Oxygen Demand (SOD), the SOD tested from the laboratory for this EIA, having the unit of mgO2/kg sediment, is the total oxygen demand in 5 days due to the release of the sediment contaminants into the water. Due to lack of sufficient information on the composition of the sediment pollutants, the SOD was modelled as a source of BOD5 to the receiving water through sediment loss during dredging. The oxygen depletion in the WQSRs was calculated from the results of two water quality model runs. One model run simulated the DO level at the WQSRs without the dredging operation. The other simulated the DO level at the WQSRs during the dredging operation which releases SOD. The difference in the DO level at the WQSRs between the two sets of the model results is the oxygen depletion resulting from the proposed dredging operation. In both model runs, both the initial DO level and the DO level at the open boundaries were set at 7.6 mg/l.
2.8.28 As expected, the highest oxygen depletion is around the very vicinity of dredging. Â However, the maximum oxygen depletion at the WQSRs is only 0.0022mg/l for the grab dredger option and is less than 0.001mg/l for the TSHD option.
2.8.29 As for SS, the oxygen depletion presented in Appendix 3 is the maximum oxygen depletion over the 15-day spring to neap tidal cycle. The resulting oxygen depletion from the proposed dredging will be less than the maximum depletion most of the time.
2.8.30 From the baseline DO level (Table 2.2) and the predicted oxygen depletion resulting from the proposed dredging operation, the resulting DO levels at the WQSRs during the proposed dredging period are summarised in Tables 2.8 and 2.9.
2.8.31 It can be seen that for both options, the depth averaged DO levels at all the WQSRs are between 5.54 to 7.28mg/l and the bottom layer DO levels are between 4.93 to 7.16mg/l, well above the minimum requirement of 4 mg/l and 2 mg/l for the depth averaged and bottom layer DO respectively. It is concluded that the proposed dredging operation has little effect on the DO levels at the WQSRs and the resulting DO level at the WQSRs will continue to comply with the DO level defined in the water quality criteria (Section 2.6) throughout the dredging period.
Sensitive Receiver |
Depth |
Dredging Location A (mg/l) |
Dredging Location B (mg/l) |
Dredging Location C (mg/l) |
|||
Dry |
Wet |
Dry |
Wet |
Dry |
Wet |
||
Kau Yi Chau (fish fry nursery area) |
A |
6.347 |
5.738 |
6.347 |
5.738 |
6.347 |
5.738 |
S |
6.190 |
6.062 |
6.190 |
6.062 |
6.190 |
6.062 |
|
B |
6.451 |
5.432 |
6.451 |
5.432 |
6.451 |
5.432 |
|
Kennedy Town WSD Intake |
A |
6.347 |
5.738 |
6.347 |
5.738 |
6.347 |
5.738 |
S |
6.190 |
6.062 |
6.190 |
6.062 |
6.190 |
6.062 |
|
B |
6.451 |
5.432 |
6.451 |
5.432 |
6.451 |
5.432 |
|
Sha Wan Drive Intake |
A |
6.724 |
5.544 |
6.724 |
5.544 |
6.724 |
5.544 |
S |
6.539 |
6.221 |
6.539 |
6.221 |
6.539 |
6.221 |
|
B |
6.813 |
4.928 |
6.813 |
4.928 |
6.813 |
4.928 |
|
Queen Mary Hospital Intake |
A |
6.724 |
5.544 |
6.724 |
5.544 |
6.724 |
5.544 |
S |
6.539 |
6.221 |
6.539 |
6.221 |
6.539 |
6.221 |
|
B |
6.813 |
4.928 |
6.813 |
4.928 |
6.813 |
4.928 |
|
Wah Fu Estate Intake |
A |
6.724 |
5.544 |
6.724 |
5.544 |
6.724 |
5.544 |
S |
6.539 |
6.221 |
6.539 |
6.221 |
6.539 |
6.221 |
|
B |
6.813 |
4.928 |
6.813 |
4.928 |
6.813 |
4.928 |
|
Pak Kok (corals present) |
A |
6.723 |
5.544 |
6.723 |
5.544 |
6.724 |
5.544 |
S |
6.538 |
6.221 |
6.538 |
6.221 |
6.539 |
6.221 |
|
B |
6.812 |
4.928 |
6.812 |
4.928 |
6.813 |
4.928 |
|
Shek Kok Tsui (corals present) |
A |
6.723 |
5.544 |
6.723 |
5.544 |
6.724 |
5.544 |
S |
6.538 |
6.221 |
6.538 |
6.221 |
6.539 |
6.221 |
|
B |
6.813 |
4.928 |
6.812 |
4.928 |
6.813 |
4.928 |
|
Luk Chau (corals present)) |
A |
6.986 |
5.948 |