11.
MARINE ECOLOGY
11.1
INTRODUCTION
11.1.1
This chapter assesses the impacts of the Project upon marine
ecology.
11.1.2
The Project consists of the provision of a drainage tunnel
and collecting system for northern Hong Kong Island as well as a discharge
outlet at Cyber Port. The discharge outlet includes a stilling basin to release
the surface runoff arising from the Hong Kong Island catchment
to the Lamma Channel.
11.1.3
The objective of this assessment is to describe ecological
conditions in the marine environment of the Study Area, evaluate any impacts of
the Project at both construction and operational phases and, where required, to
propose mitigation measures to minimize adverse impacts. The assessment follows the criteria and
guidelines as stated in Annexes 8 and 16 of the EIAO TM and the EIA Study Brief
No. ESB-070/2001.
11.1.4
The assessment is mainly focused on the outlet structures at
the proposed Hong Kong West Drainage Tunnel and the receiving water body. The impacts from above-ground intake
structures along the tunnel are covered by the chapter for terrestrial
ecological assessment in this report.
11.1.5
The nature and scope of the Project are described in Section 2 of this Report. In accordance with the EIA Study Brief
No. ESB-070/2001, this section identifies and assesses the marine ecological
impact associated with the Designated Project described in Section 2.
11.1.6
Alternative alignments and design options were studied at an
earlier stage of this assignment.
Findings of those studies are summarized in Section 2.4 of this report.
The alignment and design option proposed in this report, as compared
with other alignments and design options, has minimum predicted impact.
11.1.7
There are no scheduled concurrent designated projects (DP) in
the vicinity of the proposed tunnel portals, intakes or tunnel alignment during
the construction and operation phase.
11.2
Environmental Legislation,
Standards and Guidelines
11.2.1
The following Hong Kong SAR Government legislation, standards
and guidelines are relevant to the assessment of impacts to marine ecology
associated with the construction and operation of the project:
l
Environmental
Impact Assessment Ordinance (Cap.499) and the Technical Memorandum on
Environmental Impact Assessment Process (EIAO TM);
l
Marine
Parks Ordinance (Cap. 476) and associated subsidiary legislation;
l
Wild
Animals Protection Ordinance (Cap. 170); and
l
Animals
and Plants (Protection of Endangered Species) Ordinance (Cap. 187).
11.2.2
This study also takes note of the following relevant
international agreements:
l
Convention
on International Trade in Endangered Species of Wild Fauna and Flora
("CITES"); and
l
Convention
on Biological Diversity (CBD).
11.3
Baseline Methodology
11.3.1
Based on the tunnel alignment and the TM guideline, the study
area boundary was set 500m outside the project boundary, and was located on
southwest Hong Kong Island including the shore line and the subtidal zone. The study area for marine ecology was
chosen to be the same as for marine water quality impact assessment (Figure 11.1). This includes 5 Water Control Zones (WCZs) within HKSAR (listed below), as well as any areas
likely to be impacted by the Project:
l
Eastern
Buffer WCZ;
l
Western
Buffer WCZ;
l
Victoria
Harbour WCZ;
l
Southern
WCZ; and
l
Second
Southern Supplementary WCZ.
11.3.2
A literature review was conducted to provide information on
existing conditions in the study area and to identify habitats and species of
potential importance that may be affected by the Project. Literature review included Government
and private sector reports, independent and Government published literature and
academic studies. Literature review
included the following:
l
Marine
Ecology of Hong Kong: Report on
Underwater Dive Surveys (October 1991 - November 1994) (Binnie
1995). Dive surveys at 86 sites in
central and eastern Hong Kong waters.
l
Ecological
Status and Revised Species Records of Hong Kong’s Scleractinian
Corals (
l
Marine
Benthic Communities in Hong Kong. Centre for Coastal Pollution and
Conservation, City University of Hong Kong prepared for Agriculture, Fisheries
and Conservation Department (CCPC 2002).
A territorial-wide benthic study in Hong Kong.
l
Monitoring
of Chinese White Dolphin (Sousa chinensis) in Hong Kong waters – Data collection Final
report (1 April 2003 to 31 March 2004) (AFCD 2004c). A
annual territorial-wide survey on local cetaceans.
11.3.3
Literature review was supplemented by field surveys. Field surveys were designed to fill data
gaps which would prevent an adequate assessment of the project's impacts upon intertidal and subtidal ecology,
and the development of appropriate mitigation measures. Intertidal
surveys and dive survey were conducted between September 2003 and March
2004. The detailed survey
methodology and results are provided in Appendix
A (Dive Survey) and Appendix B
(Ecological Baseline Survey) of this report.
11.4
Assessment Methodology
11.4.1
Impacts to habitats, species or groups were assessed based on
the guidelines in Annexes 8 and 16 of the TM, the consultants’ local
knowledge and international standards and practice in conservation biology.
11.4.2
The significance of ecological impacts is evaluated based
primarily on the criteria set forth in Table 1, Annex 8 of the TM:
l
habitat
quality;
l
species
affected;
l
size/abundance
of habitats/organisms affected;
l
duration
of impacts;
l
reversibility
of impacts; and
l
magnitude of environmental changes.
11.4.3
Impacts are generally ranked as "minor",
"moderate" or "severe", although in a few cases a ranking
of "minimal" (less than "minor") may be given. The ranking of a given impact varies
based on the criteria listed above.
For example, an impact might be ranked as "minor" if it
affected only common species and habitats, or if it affected only small numbers
of individuals or small areas, whereas it might be ranked as "severe"
if it affected rare species or habitats, large numbers of individuals or large
areas. The major factors giving
rise to a ranking are explained in the text. As noted in Annex 16 of the TM, a degree
of professional judgement is involved in the evaluation of impacts.
11.5
BASELINE CONDITIONS
11.5.1
The outfall location falls within the Western Buffer
WCZ. Although there are some
recognized/designated sites of marine conservation interest within the marine
ecological assessment area, none of them is located in the vicinity of the
outfall structure.
Recognized
Sites of Conservation Importance
11.5.2
The following recognized sites of conservation importance are
located at or near the study area and are shown in Figure 11.2:
l
SSSI
in Sham Wan: An area of 4 hectares including the sandy beach and the adjacent
shallow shore in Sham Wan was designated as an SSSI on 3 June 1999. This area has been identified as
important habitat for Green Turtle Chelonia mydas nesting (Morton 1998). This site is about 7.5 km from the
outfall of the drainage tunnel.
l
Restricted
Area for green turtles in Sham Wan:
The sandy beach of Sham Wan was also designated on 30 July 1999 as a
Restricted Area under the Wild Animals Protection Ordinance (Cap. 170). Entry is prohibited from 1 June to 31
October each year to protect breeding Green Turtles.
l
SSSI
in Tai Tam Bay: an inlet of about 600 m in length and 250m in width. It possesses a diversity of habitats and
associated plant and animal communities.
This site is about 10 km from the outfall of the drainage tunnel.
l
Cape D’Aguilar Marine Reserve: The Cape D' Aguilar Marine Reserve was
designated on 5 July 1996. It lies
in the southeastern tip of Hong Kong Island. The total sea area of the reserve is
about 20 hectares. The biodiversity
is rich, including numerous kinds of fishes, hard corals, soft corals,
gorgonian and marine invertebrates.
To protect these important habitats, water sports and coastal activities
are not allowed. This site is about
14.5 km from the outfall of the drainage tunnel.
l
The
horseshoe crab nursery site at Shui Hau: Shui Hau
is the third identified horseshoe crab nursery site in Hong Kong (Chiu &
Morton 1999). This site is about 22
km from the outfall of the drainage tunnel.
l
Proposed
Marine Parks south of Lantau: the Fan Lau Marine Park
and Soko Islands Marine Park were proposed to ExCo by
11.5.3
No other designated, proposed or recognised protected areas
or sites of conservation importance lie within the study area.
Intertidal habitats
11.5.4
The intertidal ecology of Hong Kong
is well studied (Morton and Morton 1983).
More recent publications on the intertidal
fauna and flora include Tam and Wong (2000), Williams (2003) and Chan and Caley (2003). Intertidal habitats in Hong Kong are of two major types,
hard shores such as rocky shore, and soft shores such as mudflats and
mangroves.
11.5.5
Intertidal mudflats, together with
the mangroves and seagrasses, are considered to be
the most ecologically important intertidal habitats
in Hong Kong. Ecological functions
provided by these communities include energy cycling, coastal stabilisation,
and habitat for wildlife such as coastal birds.
11.5.6
Mudflat is important not only because it provides a habitat
to infauna which are in turn
the prey items of many waterfowl, but also it is a suitable substrate for the
colonization of mangroves and seagrasses, both of
which are important habitat types in Hong Kong. Seagrass beds
are also an important nursery and feeding ground of horseshoe crabs. The physical complexity of the mudflat
habitat is diversified by colonizing vegetation. A large variety of microhabitat types
may contribute to a diverse intertidal fauna. The high species richness of crabs on
Mai Po mudflats, where 32 species of crabs have been recorded, is attributed to
the large variety of microhabitats there (Lee & Leung 1999). Mangrove communities are under threat
from urbanisation and reclamation, and because many stands have been destroyed
in Hong Kong they are considered to be a conservation priority (Tam and Wong
2000).
11.5.7
Although they are important, soft shore intertidal
habitats are not widely distributed in Hong Kong. Rather, they are concentrated in two
locations, northwest and northeast Hong Kong. Among the five WCZs
of the Study Area for the present project, there is no established soft shore
habitat in the Western Buffer, Victoria Harbour or Eastern Buffer WCZs. In the
two remaining WCZs, the only major softshores are sandy beaches and sandflats
(such as in Shui Hau and
Tai Tam), both are less productive than intertidal
mudflats. No significant/recognized
site of any of these habitats has been recorded within the Western Buffer WCZ,
where the Project is to be located.
11.5.8
The majority of hard shores in Hong Kong are rocky
shores. These are not rare in
HKSAR, nor are they characterized by high productivity, species richness or
diversity as are intertidal mudflats.
11.5.9
The intertidal communities on the
rocky shores in Sok Kwu Wan
were studied (Maunsell 2002) and were found similar
to those found on other semi-exposed coastlines in Hong Kong. Fauna records for wave-exposed shores in
that study included littorinid snails (Littorina scabra, Littorina brevicula and
Nodilittorina millegrana), Grapsus albolineatus
(Crustacea, Brachyura), Eriphia smithii (Crustacea, Brachyura) and Septifer bilocularis (Bivalvia, Lamellibranchia). Boulder shore species included Polycheir rufescens (Echinodermata, Holothuroidea), Petrolisthes japonicus (Crustacea, Anomura) and Gaetice depressus (Crustacea, Brachyura), were
recorded (ibid.). As with most shores of Hong Kong, zonation patterns were evident, but no rare fauna was
found. Overall the fauna appeared
to be lacking in diversity and abundance.
11.5.10
The existing coastline in Victoria Harbour is almost entirely
artificial and made of concrete or large granite rocks. Although fouling organisms were regarded
as common on artificial seawalls and wharf piles (Morton & Morton 1983),
due to the polluted nature of the water combined with the homogenous nature of
the concrete seawalls, the vertical concrete seawalls in the harbour are not a
favourable habitat for intertidal organisms. Few intertidal
species, such as Isopods, have colonised those vertical concrete seawalls.
11.5.11
Rubble-mount seawall usually provides more hiding cover for intertidal organisms and is thus regarded as of higher
ecological value than vertical concrete seawall.
11.5.12
The closest natural coast within the harbour is located at
Green Island. Natural coastline on
Green Island was surveyed in the Green Island Development Study (TDD
1998). The intertidal
community there was found to be typical of a semi-exposed shore. Abundant limpets and snail Monodonta labio were
found, while encrusting algae were common in the low intertidal
zone.
Intertidal habitat at
the Project Site
11.5.13
The entire coastline in Cyberport
had been converted to artificial seawalls.
The outfall location is located at the western end of the
coastline. This section of
coastline was also recently converted to artificial seawall to facilitate a haul
road for a road improvement project.
Though a small headland just to the west provides a very limited
sheltering effect, the outfall location is basically facing to the East Lamma Channel.
Immediately east of the outfall location is a section of large boulder
seawall for the sewage treatment plant which has been operated for a few
years. The intertidal
habitat in the vicinity (500m distance) of the tunnel outfall was comprised of
only a small section of natural rocky shore west of the outfall, and the
artificial seawalls along the rest of the Kong Sin Wan area. The location of the outfall was
previously part of the artificial seawall but is currently inside a
construction site where there is disturbance from ongoing construction
works. Building materials including
sand and rock have been deposited onto the shore within the construction site
including the outfall location.
During the field survey for the present project (see Appendix B), three intertidal
sampling transects were established and only 14 species were recorded. Snail Monodonta labio and Stalked barnacle Pollicipes mitella were found at all 3 transects and were the
commonest species. Numbers of
species varied from 9-12 and numbers of individuals from 100-304 among three
transects. Shannon’s species
diversity index (H’) ranged from 1.5 to 2.1. Recorded species are common and
characteristic of intertidal habitats throughout Hong
Kong. Abundant Monodonta labio were also found in an earlier
study at the nearby Green Island (TDD 1998). Pollicipes mitella is a typical barnacle of exposed Hong Kong
shores (Morton and Morton 1983).
Both species are considered very common rocky shore species (Williams
2003). The site supported low
species diversity and low abundance of intertidal
fauna.
Horseshoe
crab
11.5.14
Horseshoe crabs are an ancient and taxonomically isolated
group (class Merostomata, sub-class Xiphosura) related to spiders, ticks and mites. Though not presently protected under
local law, Horseshoe crabs have recently been identified as a species of
potential conservation importance in Hong Kong.
11.5.15
There are no general restrictions on taking of horseshoe
crabs in HKSAR, mainland China, or Vietnam. Taiwan and Guangdong Province, however,
have each designated at least one protected area within which taking is
prohibited. The Delaware Bay, USA
population of Limulus polyphemus required around a decade to recover
following a complete ban on taking.
This matches the duration of the horseshoe crab life cycle from egg to
breeding adult (Ecological Research & Development Group website, www.horseshoecrab.com).
11.5.16
Three species have been reported in HKSAR waters: Tachypleus tridentatus, T. gigas and Carcinoscorpius rotundicauda
(Chiu & Morton 1999). These
represent all species known from the South China Sea, and three of four species
known worldwide. All three species
appear to be in population decline and are thought to be under severe pressure
in the South China Sea, including Hong Kong waters, due to habitat loss,
pollution and over exploitation (Huang 1997). All three species are listed by IUCN Redlist of Threatened Species as data-deficient (DD). This means that the IUCN Species
Survival Commission concludes that there are not adequate data to determine the
status and/or trend of the global population of any of the three species.
11.5.17
The most critical habitat is the sandy shore and sandy
backshore where adult horseshoe crabs mate and lay eggs. These habitats are being degraded
regionally by construction of bulkheads, seawalls and groines. Bulkheads and seawalls prevent access of
breeding adults to preferred nesting areas. Groines
accelerate beach erosion.
11.5.18
It was reported that Tachypleus gigas and Tachypleus tridentatus were collected from trawl surveys at Tap Shek Kok just south of Lung Kwu Tan, and the beaches at Lung Kwu
Sheung Tan and Lung Kwu Tan
have been therefore identified as potential breeding sites for T. gigas (ERL
1993, ERM 1996).
11.5.19
In an extensive study of the distribution of horseshoe crabs
in Hong Kong conducted between March 1995 and June 1998, however, Tachypleus gigas was not
recorded and its local status is uncertain (Chiu and Morton 1999). It is likely that only two species of
horseshoe crab (T. tridentatus
and C. rotundicauda)
are extant in Hong Kong as no recent records of T. gigas have been reported (ibid.).
11.5.20
Horseshoe crabs are currently more often found in western
waters of Hong Kong, though they once thrived on many beaches in Hong Kong
including Tolo Harbour (Huang 1997; Huang et al. 1999). Horseshoe crabs, most commonly T. tridentatus,
have been recorded in HKSAR at Tap Shek Kok, Sha Chau,
Tai Po and Peng Chau,
though there are no recent records from any of these sites (Huang 1997). C.
rotundicauda was recorded in 1997 from Ma Wan
Chung, Lantau, at a site that was lost to development
of the Tung Chung New Town (ibid.). The other areas where horseshoe crabs
have been recorded in the HKSAR are on the shores of Outer Deep Bay and the
waters around Black Point-Tap Shek Kok.
11.5.21
During the Crosslinks 2 study,
horseshoe crabs were reported to have been captured in trawl surveys at Tap Shek Kok. Beaches at Lung Kwu
Sheung Tan and Lung Kwu Tan
were thought to be former breeding grounds for horseshoe crabs, based upon
information from the residents in Lung Kwu Tan (Mouchel 1999).
It was also reported that spawning of horseshoe crabs was seen in Lung Kwu Sheung Tan many years ago
(Huang et al. 1999).
11.5.22
In Hong Kong the preferred habitat of horseshoe crab was
identified as sandy to muddy shores, which provide habitats for mating and egg laying, and for juveniles.
11.5.23
Confirmed nursery sites for horseshoe crabs in recent years
include Pak Nai, San Tau
and Shui Hau (Huang et al. 1999), together with Tai Ho Wan
(Fong 1999) and Sok Kwu Wan
(Maunsell 2003).
Some other beaches on Lantau, including Tai O,
Yi O, Sham Wat Wan, Sha Lo
Wan and Tung Chung, are considered probable nursery sites because adult
horseshoe crabs are frequently captured offshore (Huang et al. 1999).
11.5.24
At a HKSAR-wide study, three locations, i.e. Pak Nai in Deep Bay, San Tau near
Tung Chung, and Shui Hau at
south Lantau, were identified as important horseshoe
crab nursery sites, all of which are located in western waters (Chiu &
Morton 1999). Of these three sites,
Shiu Hau is the only site
located within the marine study area for the present study and it is about 22 km
from the proposed outfall location.
As part of the historical records before the commencement of the Chiu
and Morton study, it was reported that an adult Tachypleus tridentatus was seen climbing up the
artificial rock shore at Kong Sin Wan (ibid.). However, no further sightings were
recorded at Kong Sin Wan during that study. The nearest location of a horseshoe crab
sighting reported by Chiu and Morton (1999) was within the East Lamma Channel approximately 4 km from the proposed outfall
location. While the location of juveniles reported in Sok
Kwu Wan was also about 6 km away from the outfall
location.
11.5.25
The coastline in Kong Sin Wan is currently all artificial
seawall and not suitable for use by juvenile horseshoe crabs. Aside from the single historical record,
there have been no sightings of juvenile or adult horseshoe crabs at or near
the outfall location from the territorial-wide study, or during the dive survey
(Appendix A) or the intertidal survey (Appendix
B) for the present EIA study.
We therefore conclude that the outfall location and its vicinity are not
important for horseshoe crab conservation.
Soft Bottom
Benthos
11.5.26
The first comprehensive study of Hong Kong subtidal benthos was conducted in 1976-1977 (Shin and
Thompson 1982). Shin & Thompson
(1982) studied benthic grab samples collected from 200 stations throughout Hong
Kong waters. Data from these
stations, however, was not treated separately, but was pooled with other
stations with similar species composition.
11.5.27
Thompson & Shin (1983) performed a further study which
concentrated on the Victoria Harbour area and also related the spatial
distribution of benthic infauna to sewage
pollution. Their report described
in detail the benthic conditions in Victoria Harbour. Its focus was on infauna
assemblages and substratum and organic nutrients. Another benthic sampling project was
conducted in 1995 (Cai et al. 1997) with the purpose of determining changes in infauna since the Thompson & Shin study. This report contains detailed background
information on benthic ecology. Its
focus is on temporal and spatial changes of benthic communities in Victoria
Harbour. Sediment samples were also
collected at three stations off the Central waterfront during November 1995
(ERM 1997) as part of the surveys for Central Reclamation Phase
11.5.28
In 2001, a second HKSAR-wide benthic survey commissioned by
Corals
11.5.29
Established coral communities of any size are regarded as
important habitat types in Hong Kong as defined in Annex 8 of EIAO-TM. Among the corals, however, hard corals
are more vulnerable than soft corals.
Soft corals and gorgonians do not contain symbiotic algae zooxanthellae and do not require light penetration for
photosynthesis. Many of the soft
corals can survive at greater depths (Morton and Morton 1983; Morton
1994). They are more widely
distributed in Hong Kong and are found in areas of higher turbidity such as
south Tsing Yi, where sea pens and gorgonians were
recorded during a trawl survey for epibenthic species
(ERM 1995).
11.5.30
Hard corals are protected in Hong Kong by the Animals and
Plants (Protection of Endangered Species) Ordinance (Cap. 187), which includes
the protection of all stony (hard) corals.
While the vertical distribution of hermatypic
corals is largely controlled by the requirements of their photosynthesising zooxanthellae which require strong light and hence
shallower water, the geographical distribution of hard corals in Hong Kong is
affected by the salinity of the water.
The Hong Kong waters can be broadly divided into estuarine, transitional
and oceanic zones based on the distance from the Pearl River estuary (Morton
and Morton 1983). The Study Area of
the Project covers a large area including the transitional zone and part of the
estuarine zone. Hard corals are
vulnerable and prefer clear oceanic water.
Hard corals in Hong Kong therefore exhibit distinct gradients in
distribution, species diversity and abundance, with the coral cover and
diversity increasing from west to east, with declining influence of the Pearl
River (Scott 1984).
11.5.31
Opposite to the abundance and diversity of corals in eastern
Hong Kong waters, the estuarine environment of the western waters was thought
unsuitable for the existence of scleractinians
(reef-building corals)(Scott 1984).
Water quality in the western waters, particularly elevated freshwater
and suspended sediment levels which are characteristic of estuarine
environments, prevent substantial coral growth (Hodgson and Yau
1997). Western waters are thus
characterized by the domination of soft and ahermatypic
corals. Soft corals, sea pens and
gorgonian corals (sea fans) are present throughout the northwestern
waters (Mouchel 2002). The hard coral species recorded in the northwestern waters are generally common throughout local
waters (Scott 1984) although they are more abundant in the eastern waters. The northwestern
waters may represent their westernmost distribution in Hong Kong.
11.5.32
It is notable that the ahermatypic
cup coral (Balanophyllia or Phyllangia sp.) and the pale-blue gorgonian (Euplexaura sp.)
have only rarely been recorded in the oceanic eastern and southern waters of
Hong Kong and it is likely that these species are adapted to the hyposaline waters of western Hong Kong (Mouchel
2001).
11.5.33
11.5.34
Inside Victoria Harbour WCZ, some soft corals and gorgonians
were found at Green Island and Little Green Island during the Green Island
Development Study (TDD 1998). Some
black corals (Anthipathes
sp.; protected by CITES and Cap. 187), were also found in Green Island.
11.5.35
Binnie (1995) carried out an extensive dive
survey in Hong Kong waters. Five
sites at the southeastern end of the Western Buffer
WCZ were surveyed but no sites were surveyed in the Victoria Harbour or Eastern
Buffer WCZs (see Figure
11.5). Rich soft corals and sea
fans were found at Pak Kok. Hard corals in Pak Kok
were also recorded as abundant.
However, Ap Lei Chau,
Magazine Island, south Telegraph Bay and north Telegraph Bay were all assigned
low conservation value in terms of the abundance and diversity of hard and soft
corals.
11.5.36
The survey point of North Telegraph Bay (Station 86 in the
Underwater Dive Survey, see Figure 11.5)
was very near the western portal at the headland immediately next to the
portal. The conservation value of
Station 86 was considered low due to the low diversity and abundance of marine
organisms. The seabed was muddy
beyond 6 m in depth. Only two
species of sea urchins, barnacles, gastropods and bryozoa
were recorded in the shallower waters.
Other than these organisms, only a few sea whips, Cardinalfish
and rabbitfish were found at the site. Dive surveys were also conducted in
various locations for Harbour Area Treatment Scheme (HATS) (
11.5.37
A dive survey was conducted for the present EIA study to (i) examine the subtidal communities
at the western portal location in Kong Sin Wan and its vicinity; and (ii) to
identify the locations and quantify the abundance of any marine species of
conservation concern (Appendix A). The topography of the subtidal zone at the outfall location is very steep,
reaching -10mCD within 35 m from the tideline, and
the underwater visibility was found to be very poor (about 0.5 –
0.7m). Both suggest unfavorable conditions for hard coral colonization. The portal area was disturbed by
previous and ongoing construction works and the shallow subtidal
area was covered by artificial boulders (Appendix
A).
11.5.38
No hard or soft coral colony was found during the
survey. The seabed consisted almost
entirely of muddy or sandy substrate with very little biota. Only some barnacles (on the surfaces of
boulders), several demersal fishes and two sea
urchins Diadema setosum were
recorded. Diadema setosum is widespread and common in
shallow marine waters of Hong Kong.
11.5.39
The findings of the present survey were basically similar to
those from the 1994 survey by Binnie, and therefore
the conservation value of the portal area should also be considered as low at
Station 86 due to the low diversity and abundance of marine organisms recorded.
Cetaceans
11.5.40
Of the fifteen cetacean species recorded in Hong Kong waters
only two, the Chinese White Dolphin (Sousa
chinensis) and Finless porpoise (Neophocaena phocaenoides)
are resident (Parsons et al.,
1995). Both are listed by the IUCN
World Conservation Union Species Survival Commission’s Cetacean
Specialist Group as “data deficient”, meaning that there is
inadequate information to assess their global population status or degree of
threat.
11.5.41
Chinese White Dolphin is present throughout shallow (< 20
m) coastal waters of the Indo-pacific, from Australia and China in the east to
South Africa in the west. Off the
coast of south China, at least seven separate populations were identified from
Guangxi northward to the Yangtze River, all found in estuaries.
11.5.42
In Hong Kong SAR, Chinese White Dolphin is also concentrated
in the more estuarine waters. They
are found in all the waters of western Hong Kong and throughout the Pearl River
estuary (Parsons et al. 1995;
Jefferson 2000, 2002, 2004; Hung 2002a & b, 2003, 2004; Jefferson &
Hung 2004). They are present and
common year-round in the waters north and west of Lantau,
and also occur seasonally or in small numbers south and east of Lantau Island, as well as in southern Deep Bay and west of Lamma Island (Jefferson 2000, Jefferson & Hung 2004). They are not present in the waters east
of Lamma Island, except on rare occasions, such as
the one which occurred in 2001/02 in Hebe Haven and Port Shelter (Jefferson personal
communication). That individual
dolphin has now left the area, and apparently returned to its normal range.
11.5.43
No dolphins have ever been recorded near the outfall
location. Two out of the five WCZs of the Study Area overlap with the distribution range
of Chinese White Dolphin in Hong Kong.
The southeast limit of the distribution range of Chinese White Dolphin
falls into the Southern WCZ and the western end of Western Buffer WCZ. In the Southern WCZ, the sightings
scatter between west Lamma and the south shore of Lantau, more concentrated in the southwest Lantau waters.
In the Western Buffer WCZ, where the tunnel outfall would be located,
there was only one dolphin sighting recorded during the 2003-2004 monitoring
programme of
11.5.44
Finless Porpoises occur in Hong Kong’s eastern and
southern waters, including Mirs Bay, Sai Kung, Po Toi, Ninepins, south
of Lamma Island, south of Hong Kong Island, in the
waters south and east of Lantau Island, and in
particular southwest of Lamma Island at Ha Mei Tsui. But they have
never been sighted north or west of Lantau (Figure 11.4)(Parsons
et al. 1995; Jefferson & Braulik 1999; Jefferson et
al. 2002a). There is no
sighting record of Finless Porpoise in the vicinity of the tunnel outfall
location, and even the entire Western Buffer WCZ in which the outfall is
located. The sighting records
nearest to the outfall location were made between Lamma
and Sunshine Island, over 4.5 km away.
11.5.45
The size of the local Finless Porpoise population is not
known. Based on line transect surveys,
there are estimated to be between 55 and 152 porpoises in Hong Kong waters in
different seasons. Up to 217
finless porpoises occur in Hong Kong waters plus Mainland waters immediately
southwest of Hong Kong where surveys have been completed (Jefferson et al. 2002a). The minimum estimate of the population
size is thus about 220 porpoises, although the true size of the population is
likely to be much larger. Breeding
is strongly seasonal, and although some may be born at other times of year,
most calves are born from October to January (Jefferson et al. 2002b).
11.5.46
Nothing is known of the range of individual finless porpoises
because individual specimens cannot be identified at sea, and no tagging or
marking studies have been done.
Feeding habits are known only from examination of stomachs of dead,
stranded specimens (Barros et al.
2002). Porpoise prey includes many
different species of fish, several types of cephalopods and at least one kind
of shrimp. Porpoises prey on
reef-associated organisms, but these are not primary constituents of the
Finless Porpoise diet. Although behavioral support is currently lacking, there is some
indication from stomach contents that porpoises may also feed in association
with fishing vessels (ibid).
11.5.47
Two marine parks are proposed for the protection of cetaceans
in southwest Lantau and Soko
Islands. They are .both far away from the outfall location (i.e. 22 km for the
nearer Soko Islands).
Green
Turtles
11.5.48
Five species of sea turtles have been recorded in Hong Kong
waters, these include: the leatherback turtle (Dermochelys coriacea), the olive ridley
turtle (Lepidochelys olivacea),
the green turtle (Chelonia mydas), the hawksbill
(Eretmochelys imbricata)
and loggerhead (Caretta caretta) (AFCD,
2004a). Among them, the green
turtle attributes to most local records and it is the only species that nests
in the territory at present.
11.5.49
The migratory green turtle, Chelonia mydas, is a highly endangered species
that is afforded international protection under Appendix I of CITES and the
Bonn Convention. It is also listed as a “Class II Protected Animal”
in the “List of State Key Protected Wildlife in China”. Locally all
sea turtles are protected by Cap 170 Wild Animals Protection Ordinance and Cap
187 Animals and Plants (Protection of Endangered Species) Ordinance.
11.5.50
Historically, sea turtles used to nest in many of the remote
beaches on Lamma Island, Lantau
Island, and Hong Kong Island.
However, increasing urban development and human disturbance have reduced
the number of sea turtle nesting sites in Hong Kong. Nowadays its only regular nesting
beach is at Sham Wan in South Lamma. Since the sandy beach at Sham Wan
remains the only regular green turtle nesting site in the territory, it has
been designated a SSSI since June 1999, and gazetted as a Restricted Area under
the Wild Animals Protection Ordinance since July 1999. Sham Wan in South Lamma is therefore an important ecological sensitive
receiver because of its significant conservation status. Sham Wan is about 7.5 km from the
proposed outfall location for the Project.
11.6
EVALUATION OF ECOLOGICAL
IMPORTANCE OF HABITATS
11.6.1
The “Important Habitats Types in the Territory”
listed in Note, Table (1), Annex 8 to the TM-EIAO existing in or near to the
study area are:
l
Undisturbed
natural coastal areas longer than 500 metres;
l
Established
coral communities of any size;
11.6.2
Habitats found within the study area were evaluated in terms
of ecological importance using the criteria set forth in Annex 8, Table 2 of
the TM-EIAO. Details are listed in
Tables 11.1 to 11.2 below.
11.6.3
The baseline study described above showed that Chinese White
Dolphin and Finless Porpoise are found west of and south of the project area,
respectively. Kong Sin Wan and its
vicinity are not a horseshoe crab nursery site, and
there has been no recent record of juveniles or adults near the area. In the vicinity of the outfall the
seabed was not colonized by coral and the marine benthic communities were not
of special conservation importance, and the intertidal
zone had been disturbed by ongoing construction works.
Table 11.1
Evaluation of ecological importance of intertidal habitat within 500m of the project
area
|
Criteria |
Remarks |
|
Naturalness |
Low. The majority
was artificial seawalls, while the outfall location
was disturbed
by land reclamation and construction
works nearby. |
|
Size |
0.3 ha in total
within 500m. |
|
Diversity |
Low.
Only 14 species of fauna recorded. |
|
Rarity |
Common habitat in Hong Kong. No
protected or rare fauna recorded |
|
Re-creatability |
Artificial coastline is readily re-creatable. but constrained by land availability |
|
Fragmentation |
Unfragmented. Continuous
within 500m. |
|
Ecological
linkage |
Generally, it is linked with open sea and upper shore shrubland. But not
functionally linked to any highly valued habitat in close proximity. |
|
Potential
value |
Low to moderate. Given sufficient time, it might be colonised by some intertidal and marine organisms |
|
Nursery/breeding
ground |
Limited
due to high human disturbance and the pollution level in the seawater. Only potentially for some
inter-tidal animals such
as snails, crustaceans and other invertebrates. |
|
Age |
Young for reclaimed section, old for natural shore section |
|
Abundance/Richness
of wildlife |
Low
|
|
Overall
Ecological value |
Low
|
Table 11.2
Evaluation of ecological importance of subtidal habitat
in the vicinity of the project area
|
Criteria |
Remarks |
|
Naturalness |
Low to moderate. Close to urbanised areas and artificial
coastline |
|
Size |
Over 39 ha
within 500m |
|
Diversity |
Low. |
|
Rarity |
Common habitat in Hong Kong. No
protected or rare fauna recorded.
|
|
Re-creatability |
Not re-creatable. |
|
Fragmentation |
Unfragmented. |
|
Ecological
linkage |
Generally, it is linked with open sea. But not
functionally linked to any highly-value habitat in close proximity. |
|
Potential
value |
Moderate. |
|
Nursery/breeding
ground |
Not known to be breeding/nursery ground |
|
Age |
N/A |
|
Abundance/Richness
of wildlife |
Low
|
|
Overall
Ecological value |
Low
to moderate |
11.6.4
In accordance with the criteria set forth in Table 3, Annex 8
of the EIAO-TM, the ecological importance of species within the study areas was
assessed in terms of:
l
Protection
status;
l
Species
distribution; and
l
Rarity.
11.6.5
Species recorded during the dive survey (sea urchin) are
typical of disturbed areas, while those recorded during the intertidal
field survey are very common in rocky shore habitats. They are not of conservation importance.
11.6.6
The list of recorded species of conservation importance is
evaluated according to the TM-EIAO in Table 11.3 below.
11.6.7
Chinese White Dolphin is a Class I protected species in the
Mainland. In HKSAR it is protected
from capture or direct harm under the Wild Animals Protection Ordinance. The degree of extinction threat to the
global population cannot be assessed by IUCN World Conservation Union due to a
deficiency of data. Finless
Porpoise is also protected by the Wild Animals Protection Ordinance in Hong
Kong and is also listed as “data deficient” by IUCN World
Conservation Union.
11.6.8
Though not presently protected under local law, horseshoe
crabs have recently been identified as a species of potential conservation importance
in Hong Kong.
11.6.9
Established coral communities of any size are regarded as
important habitat types in Hong Kong as defined in Annex 8 of EIAO-TM.
Table 11.3
Evaluation of fauna
species of ecological importance recorded within the Study Area
|
Species / Group |
Protection Status |
Distribution |
Rarity |
|
Chinese White Dolphin |
WAPO; Class 1
Protected Animal of China; expanding protected area system in Mainland;
intensifying habitat/prey enhancement in HKSAR |
Widely
distributed in the coastal and inshore waters of the Indian and western
Pacific oceans; Local population concentrated in the estuarine waters outside
the study area (close to Sha Chau
and Lung Kwu Chau) |
About 1,500
individuals in the Pearl River estuary and Hong Kong waters (Jefferson &
Hung 2004); locally common near Sha Chau and Lung Kwu Chau. Key
threats are vessel collisions, and enganglement in
fishing nets (IUCN Redlist). |
|
Finless Porpoise |
WAPO |
Local population
concentrated in the waters to the south of Lantau, Lamma, Hong Kong Island. |
up to 217 finless porpoises occur in the
area of Hong Kong plus Mainland waters immediately to the southwest. Key threats are entanglement in gill
nets, vessel collisions, and possibly bio-accumulation of pesticides (IUCN Redlist). |
|
Horseshoe crab |
No statutory
protection status in Hong Kong, Mainland China, or Vietnam. Both Taiwan and Mainland China have
established protected areas for horseshoe crab breeding. |
Three of four
species world-wide occur in the South China Sea; Two, Tachypleus tridentatus
and Carcinoscorpius rotundicauda,
have been recorded within the assessment area. |
Relatively rare
species of a taxonomically distinct and ancient class; rarity probably due to
unsustainable harvest |
|
Corals |
Cap. 187, and
CITES |
Exhibit strong
gradients in distribution, species diversity and abundance in Hong Kong, with
the cover and diversity decreasing from east to west, towards the influence
of the Pearl River. |
Not uncommon in
Hong Kong waters |
11.7
IMPACT ASSESSMENT
Identification of Environmental Impacts
11.7.1
The construction works at tunnel portals and intake shafts
will include site preparation and clearance, excavation, intake structures and
tunnel portal structure construction, utilization of ancillary equipment at
tunnel portals to support tunnel construction, material handling and blasting
at portals (or intakes if necessary).
11.7.2
Potential sources of impact during construction phase
include:
l
Habitat
loss caused by the portal itself and associated construction works; and
l
Water
quality degradation caused by dredging and earth works.
11.7.3
Potential sources of impact during operational phase include:
l
Water
quality degradation caused by the discharge.
Construction
phase
11.7.4
This section of the report assesses the potential impacts of
project construction on intertidal and subtidal ecology.
The construction activities at the western tunnel portal will include
site preparation and clearance, excavation, tunnel portal structure
construction, utilization of ancillary equipment at the tunnel portal to
support tunnel construction, material handling and blasting at the portal.
Habitat loss
11.7.5
To avoid increasing land-based traffic volume a temporary
barge berthing point will be constructed at the western portal at Kong Sin
Wan. The berth will be used for the
transportation of excavated spoil from the proposed drainage tunnel and
delivery of supporting materials or equipment for tunnel construction. The dimensions of this temporary pier
would be 11m x 40 m. An area of
440m2 of shallow subtidal zone and a
length of 11 m of intertidal seawall (of 22m2
in area assuming the tidal range to be 2m in height) would be occupied by this
berthing point. Construction works
for the proposed drainage tunnel would be finished within 4 years. The area occupied by the berthing point
would not be available for wildlife use during this period.
11.7.6
After the tunnel construction works are finished, the
temporary berthing point would be removed.
A stilling basin would be constructed at the same location but
on-shore. An armored
rock panel (25m x 25m, = 625m2) would be placed directly on the
existing seabed beneath the outlet of the stilling basin.Dredging
works would not be required for construction of the stilling basin or placement
of the rock panel. The purpose of
the rock panel is to protect the seabed from scouring. Each armor
rock is about 1 tonne in weight (about 1 m in size) and would rest on the
muddy/sandy bottom.
11.7.7
The dive survey showed that most of the area subject to
temporary and permanent seabed loss is muddy substrate with boulders. This type of habitat is not of special
conservation importance. No hard
and soft corals or any other marine species of conservation concern were
recorded. It was shown from
previous records that the waters near the seabed loss area (the outfall
location) were not used by Chinese White Dolphin or Finless Porpoise. In the last ten years there were no
sightings of horseshoe crabs in the vicinity of the seabed loss area. Given the low conservation importance of
the seabed habitat near the outfall portal and the small area (maximum 625 m2)
affected, the impact of seabed loss is ranked as minor.
11.7.8
An area of 22 m2 of intertidal
zone at the outfall location would be occupied by the berthing point during
most of the construction phase.
This site would be occupied by part of the outfall itself during the
operation phase. An area of 50 m2
(25m in width and assuming the tidal range to be 2m in height) of intertidal zone, which includes the original temporary
barging point and some other existing artificial seawall, would be permanently
replaced by the concrete structure of the outfall portal. However, as shown in Figure 1 of
Appendix A, the location is currently being disturbed by highway construction
works. The impact from the Project
would thus only affect some newly constructed artificial coastline. Indeed, even on the nearby natural intertidal zone, both the abundance and diversity of fauna
were low. Considering the low
ecological value of a recently constructed artificial coastline, the small area
involved, and the availability of similar habitat in the vicinity, the impact
of intertidal habitat loss is ranked as minimal.
Water
quality
11.7.9
At the western portal a pier would be built at Kong Sin Wan
as an alternative marine access for barges. This would involve approximately 4,500
m³ of imported fill material and may lead to re-suspension of sediment and
disturbance of the sandy seabed.
Suspended solids created during berthing point construction and
demolition would increase turbidityand thus reduce
the amount of light reaching the sea bed.
As they settle on the seabed the sediments could bury sessile benthic
organisms. Resuspension
of sediments would also reduce oxygen levels and potentially release pollutants
into the water column. These
factors could adversely affect the health and survival of marine
organisms. However, these impacts
are not predicted to be severe because they would be short-term and localised
in nature. Due to the small scale
of the works and the low ecological value of the site the impact is ranked as
minor. Mitigation measures for
these impacts would be required.
11.7.10
Siltation caused by construction
works could adversely affect water quality. Construction of the tunnel and the
ground surface structures for the western portal would result in site runoff
from a limited area of earth works.
11.7.11
Construction site runoff can contain sediments, organic
substances, oil, grease and solvents that can affect marine ecology. These substances can increase turbidity,
decrease oxygen levels and introduce contaminants, causing a short-term loss of
habitat or degradation of habitat quality.
This has potential to injure or kill benthic organisms, and drive mobile
organisms away from the affected area.
11.7.12
Impacts would be short-term and would be largely
self–correcting after project completion without active restoration
efforts. As the sea area in the
vicinity of the outfall is not used by dolphins or porpoises, and there are no
recent records of horseshoe crabs or corals, impacts from water quality
deteriorations on these species of conservation importance would not be
significant. Sensitive species near
the site that could be directly affected by runoff would only include juvenile
life stages of various marine organisms.
The impacts of such runoff to subtidal ecology
is therefore ranked as minor
11.7.13
No construction works would take place on areas with natural
coastline. Considering the scale of
the ground surface construction works and assuming that good site management
practices are followed, site runoff is not predicted to have an adverse impact
on the natural coastline.
Noise and disturbance
11.7.14
Noise and disturbance from underwater and coastal
construction could cause disturbance-sensitive marine fauna to migrate from the
area, or cause secondary effects such as reduced feeding efficiency. However, no dolphin or porpoise was
recorded near the outfall location and any other mobile species that are
sensitive to disturbance would most likely vacate the area at the onset of the
underwater works. Impacts are
therefore ranked as minimal.
11.7.15
There is no disturbance-sensitive receiver in the intertidal zone.
Due to the limited area of intertidal zone
that would be occupied, however, the impact would be expected to be minimal.
Marine Traffic
11.7.16
Some of the excavated material from the tunnel construction
works would be transported by barges from the outfall location. Marine traffic volume will thus
increase. Although there is little
information on the collision of Finless Porpoises with vessels, high speed
vessels are known to be potentially dangerous for Chinese White Dolphin. The speed of vessels (mainly barges)
would not be high, and this impact could be ranked as minor. Taking a pre-cautionary approach
however, measures for the marine traffic impact are still proposed.
Operation
phase
11.7.17
This section of the report considers the potential impacts of
project operation on intertidal and subtidal ecology.
Water quality change
11.7.18
The water quality assessment showed that the operation phase
effluent from the drainage tunnel would have only limited and localized impacts
on marine water quality. The water quality modelling simulated the 1 in 2 years
and the 1 in 50 year design storm event outfall hydrographs for the discharge
from the Western Portal. Three parameters, i.e. suspended solid, E. coli, and salinity, were simulated
and presented in figures. Four
coral sites in Lamma and Hong Kong Island (i.e. Pak Kok, Luk Chau
Wan, Sok Kwu Wan and Green
Island, see Table 11.4) were selected
as ecological sensitive receivers (SRs) for water
quality assessment due to their relatively closer distances to the outfall
location and the higher sensitivity of corals. All the recognised sites of marine
conservation importance are much farther away from the outfall than these SRs (Table 11.4).
Table 11.4
Distance from water
quality ecological sensitive receivers and the recognised sites of marine conservation
importance to the outfall location
|
Site |
Distance from the outfall (km) |
|
Water Quality Ecological
Sensitive Receivers |
|
|
Pak
Kok |
2.5
km |
|
Green
Island |
3
km |
|
Luk Chau Wan |
3.5
km |
|
Sok Kwu Wan |
5.5
km |
|
Recognised sites of
conservation importance |
|
|
SSSI
in Sham Wan & Restricted Area for green turtles in Sham Wan |
7.5km |
|
SSSI
in Tai Tam Bay |
10km |
|
Cape
D’Aguilar Marine Reserve |
14.5km |
|
The
horseshoe crab nursery site at Shui Hau |
22km |
|
Two
proposed Marine Parks south of Lantau |
22km
for the nearer one (Soko Islands) |
11.7.19
Predicted suspended solids concentrations were plotted to show
areas affected by suspended solids for the 1 in 2 year and
11.7.20
Tables 7.8a and 7.8b of Water Quality Assessment Chapter showed that for all the
Coral SRs, no net increase of the maximum and
cumulative SS concentrations are predicted for all flood and tide scenarios
from the model and therefore, all predicted results are well within the Marine WQOs. As these ecological SRs are
not affected by the SS, all other recognised sites of marine conservation importance
which are much farther away as shown in Table
11.4 are also not affected.
11.7.21
The predicted deposited sediment per m2 were also plotted (see Figure
6, 7, 14 and 15 in Appendix I - water quality modeling results).
Table 7.10 in Water Quality
Assessment Chapter summarized the results of the maximum deposition at the
coral SRs and showed that the maximum deposition are
very small (all < 3 g/m2) at all tide and discharge scenarios,
well below the coral sedimentation rate limit of 0.1kg/m2/day. Therefore, no adverse impacts to the
corals are expected to occur because of the proposed tunnel scheme. A
deposition rate of 0.1 kg/m2/day has been set as a threshold level
for coral protection. This
criterion has been applied in EIA studies in eastern Hong Kong waters (e.g. The
Proposed Submarine Gas Pipelines from Cheng Tou Jiao
Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production
Plant, Hong Kong) where corals are typically a key issue in marine ecological
conservation. For this reason the standard
for the deposition rate is very restrictive. To apply this high standard in the
transitional zone of Hong Kong such as the outfall location of the present
Project would be conservative. As these
ecological SRs are not affected by the sediment deposition,
all other recognised sites of marine conservation importance which are much
farther away as shown in Table 11.4 are
also not affected.
11.7.22
Maximum relative concentrations of E. coli higher than 100
cfu/100ml are limited to the immediate vicinity of the discharge point. E.
coli concentrations up to 95 cfu/100ml are limited to a narrow strip along
the west coast of Hong Kong Island. However, for all modelled flood and tide
scenarios no exceedance in terms of maximum
cumulative concentrations will occur at any of the Water Quality Sensitive Receivers
including sites of corals (see Tables 7.9a
and 7.9b). The impact is considered insignificant. As
these ecological SRs are not affected by E. coli, all other recognised sites of marine
conservation importance which are much farther away as shown in Table 11.4 are also not affected.
11.7.23
The minimum salinity plots (see Figure 10, 11, 18 and 19 in Appendix I - water
quality modelling results) again show the areas affected by the storm water
discharge. These areas are limited
to a narrow strip along the west coast of Hong Kong Island. The most affected waters are the surface
layer in areas located immediately adjacent to the Western Portal. Salinity will be higher in the middle
and bottom layers of the water column owing to the density gradient. In the
flood scenarios, the impact is stronger to the SE, while in the ebb scenarios
the NW direction is affected the most. It should be noted that the background
salinity shows a spatial gradient, due to the presence of the Pearl River
plume. In all cases, the impacted areas are smaller in the 1/2 years scenarios,
due to the smaller discharge water volume.
11.7.23
11.7.24
The change in salinity at the ecological SRs (coral sites) are assessed with the results
shown in Tables 11a and 11b for the 2-year and 50-year storm
events, respectively. The tables
show the maximum difference between the modelled baseline condition and the
modelled implementation scenario (which is the accumulation of the baseline and
the proposed tunnel’s discharge plume). The WQO requires that “human
activity should not cause the natural ambient salinity to change by more than
10%”. For both magnitude storm events and tide scenarios the change in
salinity is less than 1% and therefore meets the WQOs. Furthermore, the change in salinity
resulting from the freshwater plume discharged from the Western Portal is
significantly less than the natural daily fluctuations in salinity at the SRs. As these
ecological SRs are not affected by the salinity, all
other recognised sites of marine conservation importance which are much farther
away as shown in Table 11.4 are also
not affected.
11.7.25
The marine waters subject to change in water quality by the
operational discharge are limited to a narrow strip of the landward coastal
waters along the SW coast of Hong Kong Island, reaching to the western tip of
the island in the NW and to the waters around Ap Lei Chau in the SW, as discussed in the above paragraphs. The affected area is small and far away
from the recognised sites of conservation importance as well as ecological SRs for water quality assessment. Even Pak Kok
at the northeastern tip of Lamma,
the nearest (2.5 km) SR with hard coral communities, is outside the affected
area. None of the recognized sites
of marine conservation importance (including Sham Wan, Tai Tam, Cape d’Aguilar, Shui Hau, and two proposed Marine Parks, see Table 11.4) which are much farther away
would be affected. The distribution
of Chinese White Dolphin lies distant from the outfall and the affected area. Although the core area for Finless
Porpoise’s distribution (southwest of Lamma
Island at Ha Mei Tsui) is much closer to the project
area than that of the Chinese White Dolphin (Umston
Road), there is also no overlap between the affected area and the Finless
Porpoise sightings. No impact on
the two cetacean species is expected.
The impacts from the operation of the drainage tunnel
is thus ranked as minimal.
The construction and operation phase impacts were summarised in Table 11.5.
Table 11.5
Summary of construction
phase and operational phase impacts of the Project
Impacts
|
Due to
|
Duration
|
Receiver
|
Severity
|
Need for mitigation
|
Construction phase
|
|||||
Permanent
Intertidal Habitat Loss (only artificial seawall, about 22m2
when the baring point is build, and expand to about 50m2 when the
outfall is constructed)
|
Temporary berthing point
and
Outfall
|
Permanent
|
Intertidal communities
|
Minimal
|
No
|
Permanent Seabed
loss (muddy seabed, 440 m2 during the barging point is used,
and expand to 625m2 after the outfall is constructed)
|
Temporary berthing point and Armor rock panel outside outfall and stilling basin
|
Permanent
|
Marine organisms
|
Minimal
|
No
|
Marine water
quality
|
Resuspension during construction and
demolition of berthing point; construction of outfall and stilling basin Dumping, spilling, and leakage of
chemicals from vessels or equipment
|
Temporary
|
Marine organisms
|
Minor
|
Yes
|
Construction
Noise and Disturbance
|
Construction activities
|
Temporary
|
Intertidal and marine organisms
|
Minimal
|
No
|
Marine traffic
|
Vessel traffic
associated with construction
|
Temporary
|
Potentially Finless Porpoise
|
Minor to moderate
|
Yes
|
Operational Phase
|
|||||
Marine water
quality
|
Increase in suspended solid, nutrient, E.coli.
and freshwater during operation
|
Permanent
|
Marine organisms
|
Minimal
|
No
|
Cumulative
impacts
11.7.26
This section of the report assesses the potential cumulative impacts
from other concurrent projects in the study area.
11.7.27
There are no scheduled concurrent designated projects (DP) in
the vicinity of the proposed tunnel portals, intakes or tunnel alignment during
the construction or operation phase.
11.7.28
As stated in the results of the water quality assessment, no
cumulative impact on the marine water quality from other project is predicted. There is also no other concurrent marine
works project in the vicinity of the tunnel outfall. Therefore, no cumulative construction and
operational marine ecological impacts are likely to arise from this DP.
11.8
MITIGATION MEASURES
Construction
phase
11.8.1
As shown in Table 11.5,
above only construction phase mitigation measures for marine water quality
impacts and marine traffic impacts are needed for marine ecology.
11.8.2
Potential sources of marine water quality impacts during
construction phase include:
l
Site
runoff;
l
Suspended
solid during the construction and demolition of the berthing point; and
l
Construction
of the stilling basin.
11.8.3
Site runoff will be controlled by general site practices
during the construction works.
11.8.4
Silt curtains will be deployed during the construction and
demolition of the temporary berthing point. Deployment of silt curtains around the berthing
point area would effectively avoid adverse water quality impacts due to barge filling. No ecological impact is anticipated.
11.8.5
The invert of the stilling basin would be at -5.4 mPD. A
cofferdam in the form of a pipe-pile wall is to be constructed outside the
stilling basin prior to the construction of the basin. The cofferdam will be dewatered to
provide a working area for construction of the stilling basin. The boulders from the seawall will then
be removed by landbased grabs. Any increase in suspended solid concentrations
will thus be minimal. Upon
completion of the construction works the cofferdam would be removed and the
seawall reinstated.
11.8.6
High speed vessels are known to be potentially dangerous for
cetaceans. Although the speed of
the working vessels to be used in the present Project (mainly barges) would not
be high, a speed limit for marine traffic is proposed as a precautionary
measure. A speed limit of 10 knots
should be strictly enforced in the works areas, in particular in the waters
between the outfall location and the navigation channel in East Lamma Channel. This
particular speed limit has been applied in the Sha Chau and Lung Kwu Chau Marine Park since its establishment and appears to be
effective in protecting the dolphins from vessel collisions. The mitigation measures were summarised
in Table 11.6 below.
Impacts
|
Sources
|
Mitigation measures and effects
|
Marine water quality
|
Site Runoff
|
Good Site
practices
|
Construction and demolition of temporary berthing
point
|
Deployment of silt curtains
|
|
Construction of stilling basin
|
Cofferdams
Dewater the site prior to using land based grab.
|
|
Marine
traffic
|
Vessel
speed limit of10 knots
|
|
11.9
RESIDUAL IMPACT
11.9.1
The construction of the outfall and stilling basin will
result in some loss of subtidal muddy bottom habitat. However, the area is small (625 m2)
and the ecological value is low. This
habitat loss is not expected to have a significant negative impact on local marine
ecology. Residual impacts on habitat
loss are acceptable.
11.9.2
No residual impacts on the Chinese White Dolphin or Finless Porpoise
populations are predicted. This is
because there is no overlap of the geographic distributions of dolphins and
porpoises onto the waters affected during the operational phase of the proposed
project. There is also no residual
impact on all recognised sites of conservation importance as they are all far
away from the affected waters.
11.10
ENVIRONMENTAL AUDIT AND
MONITORING
11.10.1
Besides the EM&A for water quality, no specific EM&A
programme for marine ecology would be required for the Project.
11.11
CONCLUSION
11.11.1
The above discussion should make it apparent that the
construction and operation of the Project would have no significant impacts on Chinese
White Dolphin or Finless Porpoise, as their ranges lie west and south of the project
area, respectively. There is also
no significant impact on all recognised sites of conservation importance as
they are all far away from the affected waters. Similarly, there would be no significant
impacts on horseshoe crabs because there are no recent records of juveniles or
adults near the outfall portal. Although
there would be some permanent subtidal seabed loss (625m2) and
replacement of artificial intertidal habitat by newly constructed portal (50m2),
in the vicinity of the outfall the seabed was not colonized by coral and the
marine benthic communities were not of conservation concern. In addition the intertidal zone had been
disturbed by ongoing construction works. A well-planned program of site practices should
be able to maintain the impacts to acceptable level. Specific ecological monitoring during
both the construction and operational phases will not be needed.
11.12
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