5.        Ecology.. 5-1

5.1       Introduction. 5-1

5.2       EM&A Requirements during Construction Phase. 5-1

5.3       EM&A Requirements during Operational Phase. 5-5

5.4       Implementation Schedule. 5-6

 

 

List of Appendices

Appendix 1           Implementation Schedule of Recommended Mitigation Measures

 

 

5.           Ecology

5.1         Introduction

5.1.1     The potential ecological impact from the proposed drainage improvement project at Yuen Long has been evaluated in accordance with the applicable Technical Memorandum of the EIAO, and the works in Ha Che and Lin Fa Tei will unavoidably affect the watercourse habitat and potentially the local population of two endemic freshwater crab species Somanniathelphusa zanklon and Cryptopotamon anacoluthon in the Kam Tin area.

5.1.2     A range of mitigation measures including good site management, scheduling of the staged work program to avoid breeding season of the sensitive ecological resources, as well as translocation of two endemic freshwater crab species have been recommended to avoid or minimize the identified impact within or in the vicinity of the work areas.  The following section details the EM&A requirements for the ecological mitigation measures.

5.2         EM&A Requirements during Construction Phase

Project Management and Site Practice

5.2.1     The section of watercourse with construction activities should be hydrologically isolated from the rest of the watercourse as far as practicable (except discharge of treated runoff); and it should be commenced from downstream and progresses toward the upstream area and the reinstatement work especially the planting of riparian vegetation should also be undertaken in stages and commenced as soon as the hardscape work completed in the working section as such to fast track the reinstatement work, minimize the spatial disturbance and shorten the temporal ecological impact

5.2.2     The following good site practice should be implemented to avoid or minimize the potential disturbance to the habitats and wildlife inhabited within or adjacent to the work sites, and they should be audited regularly as part of the routine site inspection undertaken by the ET:

·      Effective implementation of an Environmental Management Systems in accordance with the ISO 14001 for all work sites;

·      Effective implementation of mitigation measures recommended for dust suppression, noise reduction, as well as water quality and waste management as detailed in other sections of this EIA report

·      Effective implementation of the Tree Preservation Measures as detailed in the guidelines published by the Tree Management Office

·      Staff awareness training on the ecological importance of the riverine habitats and inhabited wildlife, as well as briefing on the mitigation measures recommended in this report

·      Well defined and fenced Work Area to prevent intentional or accidental encroachment or trespassing into the adjacent habitats for access, parking and operation of plants/machineries, as well as stockpiling of construction material or waste;

·      Fence off any potentially ecologically sensitive resources within the work area with warning signpost;

·      Water diversion by means of submerged water pump should be avoided as far as practicable to prevent obstruction of wildlife movement along the channel

·      Waste and refuse should be stored or dumped in appropriate receptacles and on-site burning of waste should be strictly prohibited;

·      Excavated material should be properly covered or promptly disposed, and opportunities to stockpile and backfill the topsoil should be explored

·      No chemical should be stockpiled on-site until absolutely necessary

·      On-site maintenance of plant/machineries/vehicle should be avoided as far as practicable

·      Silt/ Sediment/ Oil traps should be installed to avoid direct discharge of effluent or site run-off

·      Regular ecological checks

·      Cut down of vegetation during site clearance should be in stages before groundwork takes place as such to disperse any wildlife that is sheltering in the immediate area; and

·      Minimise vehicle access

Mitigation Measures to Avoid Potential Impact to Cheung Po EIS

5.2.3     The construction work in Tai Wo should be scheduled in the dry season and sand bags or other similar facilities should be placed along the southern boundary of the work site to prevent any accidental discharge of untreated effluent into the buffered grassland and EIS under adverse weather condition. in addition, discharge of any treated or untreated effluent, either by means of soakaway or direct discharge to nearby waterways, should be directed away from the grassland buffer and the EIS.  The above measure should be audited regularly as part of the routine site inspection undertaken by the ET.

Preservation of Faunal Species of Conservation Interest

5.2.4     Two freshwater crab species of conservation concern were recorded within the work sites during the ecological baseline survey, including the Somanniathelphusa zankloni recorded at Lin Fa Tei and Ha Che; as well as the Cryptopotamon anacoluthon recorded in the upstream area at Ha Che.  Both species are endemic to Hong Kong and considered to be “Endangered” and “Vulnerable” by the IUCN respectively. The construction activities of the project will unavoidably disturb their natural habitats and potentially causing a direct loss of these two species because of their limited mobility.

5.2.5     Although measures such as undertaking the site clearance and ground work in stages to disperse the wildlife inhabited in the immediate area have been proposed, because of the ecological significance of these two species, it is recommended to conduct pre-construction survey to check any freshwater crab species of conservation concern within the site boundary and the cut-off section of the project’s watercourse at Lin Fa Tei and Ha Che. Should any be found, these species should be captured and translocated to suitable habitat free from any development pressure and in close proximity to the project sites wherever feasible, and the post-translocation monitoring of the translocated freshwater crabs should cover at least 12 months.

5.2.6     An Ecologist with relevant experience in freshwater habitats should prepare a “Freshwater Crab Translocation Plan” for the approval of AFCD.  The Plan should detail the methodology and logistics of the capture and translocation program, including the frequency and timing of field survey, details of the receptor site(s), logistics, equipment and measures to be deployed during the process, as well as the requirements for the post- translocation monitoring.  In addition, since the drainage work will be undertaken section-by-section, it is also recommended that, before the commencement of construction work in a new section, the site should be inspected by the ecologist to confirm no inhabitation of these two freshwater crab species, and if found they should be promptly captured and translocated in accordance with the approved translocation plan.

5.2.7     The selected receptor site(s) should match with the habitat requirements of these two freshwater crab species and free of any development pressure to ensure their long term survivorship after translocation.  Despite published information of the natural habitat of these two species is very limited (Ng and Dudgeon, 1992; Dudgeon, 1999; Stanton and Leven, 2016 and Stanton et al., 2017), according to the former two references, Somanniathelphusa zanklon inhabited in a variety of lotic and lentic lowland habitats and would prefers unpolluted riverine habitats with slow-flowing low-gradient streams, where it burrows in mud and clay banks, as well as the roots of floating plants or the trailing roots and stems of the riparian grasses and other vegetation.  In addition, this species is omnivorous with strongly carnivorous tendency, and prefer gastropod prey with light and fragile shells.  For Cryptopotamon anacoluthon, it is most numerous in upland area where the stream is shallow with clear, fast-flowing water, rocky substratum, as well as accumulations of leaf-litter, in which the latter is functioned as shelter and food source of this species.

Preservation of Plant Species of Conservation Interest

5.2.8     A protected tree species, Aquilaria sinensis, has been recorded in the riparian woodland within the site boundary of Sung Shan New Village.  As there is no direct conflict between Aquilaria sinensis (seedling) and the proposed works within the site boundary of the works, this plant will be protected in accordance with DEVB TCW No. 4/2020 Tree preservation and retained during construction. 

5.2.9     Before the commencement of construction work including site clearance within the site boundary of at Sung Shan New Village, Lin Fa Tei and Ha Che, a baseline vegetation survey with the aims to ascertain the location and/or the presence of any floral species of conservation concern - including but not limited to the recorded Aquilaria sinensis should be undertaken by an Ecologist with relevant experience in conducting vegetation survey in Hong Kong.   

Habitat Compensation for the affected Riverine Habitat

5.2.10   Minor to moderate or moderate impact from the temporary and long term loss of certain sections of the riverine habitats at Sung Shan New Village, Lin Fa Tei and Ha Che has been predicted and such impact should be mitigated by habitat restoration during the reinstatement and greening of the channel bed and embankment.  The EIA report recommended that the wildlife habitat lost to the Project should be restored during the reinstatement of the widened channel, in particularly the riverine habitats of the two endemic freshwater crabs lost to the project in Lin Fa Tei and Ha Che, and a Habitat Creation and Management Plan prepared by a collaboration of the Engineer, an Ecologist, as well as a Landscape Architect should be prepared to  detail the approach and design features that could facilitate and promote the establishment of riparian vegetation and colonization of the freshwater crab and other wildlife. 

5.2.11   In order to ensure the reinstated habitat could compensate the loss of the important riverine habitat, a Habitat Creation and Management Plan, detailed with the approach and design features that could facilitate and promote the colonization of the freshwater crab and other wildlife after the reinstatement work, should be prepared with a collaboration of a drainage engineer, an ecologist, as well as a landscape architect, and submitted to the AFCD for review and approval before the commencement of the construction works.  In addition, the Habitat Creation and Management Plan should also detail the monitoring program to monitor the physical environment of the restored habitat including the water quality, water current, as well as the establishment of riparian vegetation and the biota assemblage recolonize in the reinstated channel.

Instream

5.2.12   The channel bed should be laid with natural substrate composed of a mix of particles of different grain size, i.e., ranged from sand to boulder as far as the site condition and hydraulic capacity allowed, and the original natural substrates found within the watercourses should be retained and reintroduced to the reinstated channels after the construction works as far as practicable.  If those areas could only be created intermittently within the channel bed, they should be physically connected by corridor fringed with vegetation, such as low flow channel lined with natural substrate or area along the toe zone of embankment where riparian vegetation would be established as such to minimize the effect of habitat fragmentation and potential obstruction of wildlife movement along the channel.   

5.2.13   Elements that create roughness in the channel, such as a sinuous channel, channel deflector and constrictor (including gabion, boulder clusters or small vegetated island), weir, and rock vane should be strategically installed in the channel bed to create pools, riffles and water turbulence, trap suspended sediment as well as allow organic debris deposition, and hence increase the complexity of the flow pattern and availability of different types of micro-habitats and ecological niche available for aquatic wildlife.

5.2.14   In addition, in order to enhance fine materials holding capacity of any pools or riffles and facilitate the colonization of the aquatic fauna, round shapes rock would be more preferable, and the cervices formed should also be filled with a mixture of pebbles, gravel and sand to facilitate the establishment of aquatic plants and colonization of wildlife. Moreover, large rocks or boulders will be placed randomly on the top layer of natural bedding to prevent the natural substrate and riparian vegetation in the green channel from being washed away. The ground beams within the natural bedding will also help to hold the natural bedding material in position at the channel base, while the channel bed would not be lined with concrete in green channel. The minimum depth of filling natural gravels/pebbles/stone/sand is 500mm, with width equaling to full width of the channel.

Riparian Zone

5.2.15   Riparian vegetation along the toe zone of the embankment is an important habitat for aquatic fauna, especially the freshwater crabs recorded within the project areas where the animal is known to dwell among the submerged vegetative part of the riparian vegetation. Therefore, it is recommended to incorporate constantly-submerged vegetated ledge/aquatic planting bay along the toe zone of the channel for the establishment of riparian vegetation band, in which the emerged or submerged parts of the latter would provide shelter and refuge for the habitation of the Somanniathelphusa zanklon and other aquatic wildlife.  Those planting area should be filled either with geobag or a mix of fine particles, and should also be allowed trapping and settlement of silt particle to create a muddy habitat as favored by the freshwater crab Somanniathelphusa zanklon.  

5.2.16   The upper section of the embankment should also be vegetated with a mix of woody and herbaceous plants wherever suitable and adequate planting space available to promote the diversity of riparian vegetation and detritus input to the aquatic system for the aquatic fauna colonized in the channel.

5.2.17   In addition, in order to restore the habitat for the freshwater crab Cryptopotamon anacoluthon which prefer shallow water accumulated with dense leaf-litter, opportunity for tree planting within the embankment by planting bay should be explored, and inclusion of deciduous tree species in the greening design along the channel side, especially in the upstream section at Ha Che where the animal was recorded, should also be included to ensure adequate leaf litter input would be presented for the use of this species.

5.2.18   The plant species selected for the reinstatement and restoration of the riparian habitat should make reference to those existing species recorded in-situ and avoid any exotic or invasive species as far as possible, and comprised with a mix of different growth forms to increase the habitat heterogeneity and hence the ecological niche provided by the riparian vegetation.

 

5.3         EM&A Requirements during Operational Phase

5.3.1     In order to minimize the potential ecological impact associated with maintenance activities, the following mitigation measures should be implemented during the operational phase of the Project:

· Any maintenance activities within the channel bed should be scheduled in the dry season and beyond the breeding season of the freshwater crab, which normally spawning in the wet season;

· Staff awareness training on the ecological importance of the riverine habitats and inhabited wildlife and remind the team to minimize unnecessary disturbance to the channel;

· Vegetation maintenance of the embankment should avoid trespassing into the channel bed as far as practicable, and should focus on those plant species found to be too invasive or exotic in origin;

· The use of powered equipment should be with cautions to avoid accidental spillage of oil or fuel into the water body                                                                                                     

· If dredging or desilting is required, it should be undertaken in dry season and section-by-section to disperse any wildlife that may be sheltering in the immediate area, and vehicle access and the use of powered equipment should be minimized

5.3.2    On the other hand, operational phase monitoring focus on the habitat quality of the reinstated channel, such as the coverage and community structure of the established riparian and channel vegetation, the community structure and diversity of the fauna assemblage in the riverine habitats, the diversity of micro-habitats available for faunal use, the water quality, as well as abundance of detritus in the channel, etc.; and cover the area within 100m upstream and downstream of the project sites during the first and last session of the monitoring, should be undertaken for at least a 3 years period by an Ecologist of the ET with relevant experience, and follow those presented in the Habitat Creation and Management Plan approved by AFCD.

 

5.4         Implementation Schedule

5.4.1    The Contractor shall be responsible for the design and implementation of the mitigation measures as recommended in Appendix 1, Table A1-3.