11.                        ENVIRONMENTAL OUTCOMES

 

11.1                    Justification and Benefits of the Project

 

11.1.1              The current flood protection standard of Hang Hau Tsuen stream is very low. Upon completion of the Project, the standard of flood protection will be increase to 1 in 50 years.

 

11.1.2              The Project is expected to contribute to the relief of the present drainage problems that have repeatedly led to severe flooding in Hang Hau Tsuen at Lau Fau Shan, North West New Territories. It would minimise the danger to life, economic loss as well as disruption to everyday life as a result of flooding.

 

11.2                    Population and Environmental Sensitive Areas Protected

 

11.2.1              The Hang Hau Tsuen stream currently receives domestic and industrial wastewater from Hang Hau Tsuen and upstream sources. The water quality of the stream is very poor. Ecological survey reveals very little aquatic fauna especially at the heavily modified upstream section. The stream habitat is considered to have a low ecological value. However, site surveys reveal that the downstream portion of the stream which is affected by the tidal action of Deep Bay has been partly colonize by mangroves which support some intertidal fauna (e.g. mangrove crabs and mudskippers). The mangrove is considered to have a moderate to high ecological value. The Green Groups also expressed the importance of the mangroves to the ecology of Deep Bay.

 

11.2.2              Based on the ecological assessment, the channelization of the downstream portion will cause moderate ecological impacts due to the removal of the mangrove colony. However, to maintain the required flood conveyance of the channel, total avoidance of the mangroves would not be possible. Based on such findings, the channel design is revised such that the downstream section will not be fully channelised in order to preserve parts of the mangrove colony and natural stream bed. The upstream portion which has been heavily modified will be constructed to a drainage channel. With the minimization approach, only a small portion of the mangroves (about 0.07 ha) will need to be removed for the proposed channel works.

 

11.2.3              The intertidal mudflats that can be found along the Deep Bay coast will not be affected by the Project.

 

11.2.4              A number of large trees in the Project area will be preserved in-situ by adjusting the channel design.

 

11.2.5              By following the existing stream alignment, resumption of village houses has been minimized hence reducing disturbance to the public due to land resumption.

 

11.2.6              By retaining the existing stream bed as well as reusing some of the excavated materials as channel bed material, the amount of sediment requiring disposal to marine disposal sites can be minimized, thereby reducing the burden on the disposal sites.

 

11.2.7              The current footbridges are in poor condition and will be re-provided with properly designed crossings to ensure safety to the villagers.

 

11.2.8              Ultimately, the villagers of Hang Hau Tsuen at Lau Fau Shan in North West New Territories will be directly benefited as a result of the Project.

 

11.3                    Environmental Friendly Designs Recommended

 

11.3.1              The principle of the channel design is to avoid environmental impacts while at the same time to provide adequate flow capacity to achieve the design flood protection standard, to consider public safety at low lying areas, to take into account land constraints, to minimize public disturbance from land resumption, cost effectiveness and ease of maintenance. Views and comments from the Green Groups, Rural Committees, District Council members and oyster farmer association obtained during public consultation have also been taken into consideration in the design. Reference has also been made to the ETWB and DSD technical circulars on protection of natural streams/rivers as far as practicable.

 

11.3.2              When considering environmental impacts, minimization will be the key design principle only when avoidance is not possible. The following environmental friendly channel designs have been incorporated into the channel design.

 

·                  The downstream section of the stream will be preserved in-situ with natural stream bed and substrates retained and re-provided as far as practicable.

 

·                  Original stream bed materials will be reinstated in parts of the upstream section of the channel instead of using concrete lining to allow natural re-establishment of vegetation.

 

·                  Grasscrete channel lining will be used instead of concrete lining for the maintenance access section within the channel to allow some vegetation to established thereby enhancing the landscape quality and visual appearance as well as to provide some ecological value to the proposed channel.

 

·                  Sediment will be allowed to accumulate in the channel to permit re-colonisation of aquatic organisms.

 

·                  Several large trees will be preserved in-situ by modification of the channel layout and design.

 

·                  The established mangrove stands near the downstream and outfall of the stream have been avoided and preserved as far as practicable by avoiding excavating the stream bed and mudflats at the locations where mangroves are present, thus preserving the fragile stream habitat in the Project area.

 

·                  A viewing point and carpark will be provided near the outfall of the channel for public to enjoy the scenery of Deep Bay and to observe the mangrove and mudflat ecology of Deep Bay at a distance without disturbing the wildlife.

 

·                  The viewing point will be designed to allow the public to enjoy the scenery of Deep Bay while at the same time provide opportunity to observe the unique intertidal mudflat habitats. It will also provide an amenity area for the local villagers to enjoy.

 

·                  A small carpark will be provided to facilitate visitors’ use. Traffic management measures will be used to restrict vehicles over 7 m long from using the access road and carpark with the exception of essential maintenance vehicles and emergency vehicles thereby minimizing traffic-related environmental impacts to the nearby villagers.

 

·                  Compensatory landscape tree planting and shrub planting have been recommended to mitigate for the loss of trees and vegetation to improve the landscape quality and visual appearance of the proposed channel.

 

·                  About 0.08 ha of mangroves will be retained by avoiding channelization work at the downstream section. Compensation planting of about 0.07 ha of mangroves will be provided for the unavoidable loss of mangroves due to the works. Monitoring will be carried out during operational phase to ensure the survival and growth of the compensatory mangrove planting.

 


11.4                    Key Environmental Problems Avoided

 

11.4.1              The key environmental problems involve noise, water quality, ecological and landscape & visual impacts during the construction phase. Minor impacts from dust and waste are expected. The provision of the access road, viewing point and carpark is not expected to give rise to adverse environmental impact during the operational phase as only a small numbers of vehicles and visitors is expected.

 

11.4.2              The EIA study has critically assessed the overall acceptability of environmental impacts which are likely to arise as a result of the construction and operation of the Project. Where necessary and practicable, the EIA study has specified the conditions and requirements for the detailed design, construction and operation of the Project in order to mitigate environmental impacts to an acceptable level.

 

11.4.3              In order to avoid or minimize the environmental impacts of the Project, a number of mitigation measures have been recommended in the EIA Report. The key environmental measures and problems avoided are highlighted below.

 

·                  The proposed maintenance access road will be open for public use. Traffic management measure will be implemented to restrict vehicles longer than 7 m from using the road, thereby minimizing traffic-related environmental impacts to the nearby sensitive receivers.

 

·                  The channel will be improved to a higher flood protection standard thereby reducing flooding risks to the villagers.

 

·                  With the implementation of dust suppression measures during the construction phase, the dust emission from the construction works will be reduced to acceptable level. No adverse construction dust impact on the nearby air sensitive receivers is expected.

 

·                  With the implementation of quiet plant, temporary noise barriers and good site practices, construction noise from construction activities will be reduced to acceptable level. No adverse construction noise impact on the nearby noise sensitive receivers is expected.

 

·                  Properly designed site drainage measures and good site working practices such as containment structures during excavation of the channel will be implemented to ensure no adverse water quality impact to Deep Bay and the nearby oyster bed.

 

·                  During construction, surplus excavated materials will be reused on-site to minimize the amount of off-site disposal to public filling facilities.

 

·                  About 0.07 ha of mangroves will be planted to compensate for the loss of mangroves during construction of the channel.

 

·                  Compensatory tree planting and landscaping works will be provided to restore the loss of greenery and to enhance the overall landscape quality.

 

·                  A comprehensive EM&A programme will be setup to ensure effective implementation of mitigation measures recommended in the EIA Report, to assess the effectiveness of the mitigation measures, and to identify any further need for additional measures or remedial actions.

 

11.4.4              The EIA study has demonstrated the acceptability of any residual impacts from the Project and the protection of the existing Hang Hau Tsuen stream, adjacent residents, nearby fishponds, Coastal Protection Area, mangrove colony, intertidal mudflats and other environmentally sensitive resources. Environmental monitoring and audit works have been recommended before and during construction to verify the expectations of the EIA study and the effectiveness of the recommended mitigation measures.

 

11.5                    Compensation Areas Included

 

11.5.1              Compensatory planting of about 0.7 ha of mangroves will be provided within the mangrove zone to mitigate for the loss of mangroves during construction. Trees affected by the Project will be mitigated by planting heavy standard native trees within the Project area. No compensation area outside of the site boundary will be required for this Project.

 

11.6                    Environmental Benefits of Environmental Protection Measures Recommended

 

11.6.1              The environmental benefits of implementing the recommended mitigation measures during construction and operation phases of the Project can be summarized as follows:

 

·                     The air, noise, water quality and visual impacts at the sensitive receivers will all be minimized or mitigated to within the acceptable criteria and standards.

 

·                     The amount of construction and demolition materials requiring off-site disposal will be minimized through reduction, reuse and/or recycling.

 

·                     The landscape impact from the loss of tress and vegetation will be mitigated through compensatory tree planting, amenity planting and mangrove planting.

 

·                     By retaining and recreating natural stream bed sections within the channel as well as preserving and compensating the affected mangroves at the downstream portion, impact on the stream habitat will be minimized.

 

11.6.2              With the implementation of the recommended mitigation measures, no unacceptable residual environmental impacts are expected. Details of the implementation schedule of the recommended mitigation measures are summarized in Appendix 11.