Table 10.1 Summary of Key Environmental Outcomes/ Benefits

Issue	Environmental Outcomes/Benefits
The Project	After completion: · relieve the risk of flooding · minimise economic loss · minimise disruption to everyday life especially during the wet season in Mui Wo. · sustain the residential developments Benefited areas: · Tai Tei Tong, Luk Tei Tong, Mui Wo Town, Chung Hau, Ling Tsui Tau, Pak Ngan Heung. Potential consequences without the Project: · Persistent flooding along the Pak Ngan Heung River, Luk Tei Tong River, Luk Tei Tong (2) River, Ling Tsui Tau and Mui Wo Town; · Hinder future development in Mui Wo, Southern Lantau. · Damage to property and nuisance to the public.
Drainage Options, Alignment and Construction Methods	The factors such as social, ecological and other environmental aspects have been considered in light of different drainage options, alignment and construction method. The following outcomes are found: (a) The proposed alignments of the river channels follow the existing ones as far as possible. The affected area and hence land resumption and house clearance are minimum. (b) Diversion box culvert and channel are recommended in Pak Ngan Heung and Luk Tei Tong (2) River respectively to avoid affecting the existing rivers. (c) The proposed works provide a direct and effective way to discharge stormwater and prevent flooding. (d) The potential environmental impacts would be local and limited to the construction stage. The impacts could be mitigated by appropriate measures and choice of suitable construction methods. (e) The proposed drainage improvement works provide a longer-term solution for flooding. The following ecological-friendly design would be incorporated into the channel designs in order to mitigate the environmental impact. For Pak Ngan Heung, Tai Tei Tong and Luk Tei Tong Rivers: · The existing river will not be deepened and the existing riverbed will be untouched as far as practicable. · Channel beds would be constructed using natural materials such as small cobbles and boulders. Where possible, construction would utilise suitably sized cobbles/boulders found in the existing rivers. This recreated habitat would provide a suitable environment for many organisms dependent on the existing watercourses. · Channel banks would be largely trapezoidal, and lined with gabion blocks. · The depth of the channels would be varied to re-create the pool-riffle sequence found in natural streams. · Larger pools in the stream and river currently maintained for crop irrigation would be re-instated. For Luk Tei Tong (2) River: · A bypass drainage is proposed to convey floodwater to Luk Tei Tong River during heavy rainstorm. · The Luk Tei Tong By-pass Channel bed would be reinforced with geo-textile matting. The matting would be overlain with turf taken from adjacent areas of Luk Tei Tong Marsh that would be directly affected by the proposed works. This area would be maintained as compensatory marshland habitat. · The banks of the whole proposed Channel would be lined with rock-filled gabion.
Construction Programme	The preliminary construction programme was designed to minimize the potential environmental impact by taking account of the following factors: (a) High flooding risk for the outlets - the improvement works for the outlets should be carried out in the dry season only. (b) Impact to the existing marsh at Luk Tei Tong - as agreed with the green group, the construction works for the proposed Luk Tei Tong By-pass Channel should be carried out in the dry season in order to minimize the potential impact on the existing marsh area at Luk Tei Tong. (c) Cumulative impacts – in order to minimize the potential impacts to the existing sensitive receivers and public, the cumulative impacts for the concurrent projects, as well as those proposed works under this project have been duly considered. The Contractor should be encouraged to programme the construction activities under the project in such a manner that ongoing activities would be separated physically as far as possible from one another and other construction sites.
Construction Air Quality Impact	· Potential air quality impacts: dust nuisance and gaseous emissions from the construction plant and vehicles · Mitigation measures: implement the Air Pollution Control (Construction Dust) Regulation and good site practices. · No adverse air quality impact would be anticipated.
Construction Noise Impact	· Unmitigated cumulative construction noise levels: 62 dB(A) to 100 dB(A). · Recommended mitigation measures: adopting quiet construction plant; using movable/temporary noise barriers; and implementing good site practices. · Under mitigated scenario, all the NSRs would be protected to comply with the daytime construction noise standard as set out in the EIAO-TM, except the NSR in close proximity to the works sites of retaining wall at Pak Ngau Heung River outlet. However, it is expected that the residual impacts would be short-term and localized. · An EM&A programme would be implemented to monitor construction noise impact.
Water Quality Impact	· Key potential source of water quality impact: excavation works during construction phase. · Minimisation of potential impacts: working method controls recommended e.g. excavation works carried out in dry condition and containment measures used within the channel. · Other potential sources of impacts: construction site runoff and drainage; debris, refuse and liquid spillages from general construction activities; and sewage effluents from the construction workforce. · Minimisation of water quality deterioration: implementation of adequate mitigation measures, proper site management and good housekeeping practices; and appropriate treatment of sewage effluents. · Site inspections would be conducted during the construction phase. · No unacceptable impacts on water quality would be anticipated.
Waste Management Implications	· Main waste: excavated materials from the three rivers (approx. 45,200 m^3). · Excavated material with suitable characteristics should be reused on-site as far as practicable (approx. 6,400 m^3). Surplus material would require disposal to a public filling area. · Other wastes generated by construction activities: general refuse from the workforce, chemical wastes from plant and vehicle maintenance, and C&D material from the demolition of existing structures and site clearance. · With implementation of the recommended mitigation measures for the handling, transportation and disposal of the identified waste, no residual waste management impacts would be expected.
Ecology	· River channels designed to provide suitable habitats for existing aquatic communities, and to largely compensate for impacts to marsh habitats. A specific EM&A programme would be implemented to monitor the relative effectiveness of river and marsh habitat recreation. · Potential impacts to a breeding colony of the locally rare White-shouldered Starling would be largely avoided through scheduling of works close to the colony outside of the breeding season. A specific EM&A programme would be implemented to ensure impacts to the colony are avoided and minimised. · Impacts to woodland habitats and trees compensated through landscaping measures. · Fish and amphibian species of conservation interest potentially occurring within works areas would be temporarily translocated from works areas to suitable nearby habitats or holding aquariums to minimise impacts. · A fish ladder constructed in Pak Ngan Heung River would allow migration of fish species in this river, thus improving the value of the river to fish communities.
Impact of Cultural Heritage	· Further investigation and a watching brief are recommended for the excavation works associated with the proposed U-channel at Ling Tsui Tau Tsuen within the Chung Hau Archaeological Site. · Careful construction and vibration monitoring are recommended to minimize the potential vibration impact to the existing retaining wall and associated structures of the Yuen Compound during the construction of rubble seawall and retaining wall at the Luk Tei Tong River.