CONTENTS

2. PROJECT DESCRIPTION 2-2

2.1 Project Objectives 2-2

2.2 Site History and Project Location 2-2

2.3 Project Scope 2-3

2.4 Need for the Project 2-4

2.5 Benefits of the Project 2-5

2.6 Without Project Scenario 2-6

2.7 With Project Scenario 2-6

2.8 Design Considerations 2-7

2.9 Consideration of Alternatives Location, Design and Layout 2-7

2.10 Construction Aspects of the Project 2-14

2.11 Consideration of Alternative Construction Methods 2-16

2.12 Consideration of Alternative Construction Sequence 2-17

2.13 Implementation Programme 2-17

2.14 Concurrent Projects 2-18

2.15 Sustainability Considerations 2-20

2.16 Continuous Public Involvement 2-21

2.17 References 2-23

2. PROJECT DESCRIPTION

2.1 Project Objectives

2.1.1 The objectives of the Project are to enhance the flood protection level of the existing Yuen Long Nullah (YLN) and Kam Tin River (KTR) and minimise the flooding risk in accordance with DSD¡¦s Stormwater Drainage Manual (SDM), accounting for future development and climate change.

2.1.2 The proposed revitalisation works under the Project would enhance the social connectivity of YLN and its surroundings into an aesthetically-pleasing environment. The aim is to promote water-friendliness, ecological enhancements, biodiversity and beautification of YLN, taking into consideration of their effects on hydraulic performance.

2.2 Site History and Project Location

2.2.1 YLN is part of the oldest drainage system in the territory and is located in the middle of Yuen Long town centre. According to the DMP Review Study, YLN and KTR are within drainage basin ¡§Basin 9¡¨, covering approximately 89 km².

2.2.2 The surface runoff from the upstream rural & urban areas of ¡§Basin 9¡¨ is mainly collected by the existing natural watercourses / engineered open channels and urban drainage systems prior to discharging via Shan Pui River (SPR) and KTR to Deep Bay. Furthermore, two existing inflatable dams were constructed at the downstream of YLN near Wang Chau and Yuen Long Bypass Floodway (YLBF) to prevent backwater from Deep Bay to the town centre.

2.2.3 To meet the flood protection standards as stipulated in the SDM, the Yuen Long Barrage Scheme (YLBS) was developed under Agreement No. CE 24/2013(DS) ¡§Drainage Improvement Works in Yuen Long, Stage 2 ¡V Investigation¡¨. With the proposed location of YLBS situated at the most downstream part of YLN near the end of Shan Pui Ho East Road, the anticipated traffic, environmental and public impacts are minimised over the original stormwater storage scheme, situated near the town center and local villages. This arrangement also maximises the extent of flood protection area and enables shorter construction programmes with increased resilience to climate change. A location plan of the Project is shown in Drawing No. 400171/B&V/LAY/001 in Appendix 1.1.

2.2.4 The YLBS comprises tidal barrier, pumping station, E&M control room and a linkage bridge. While the tidal barrier serves to separate the high tide from the low-lying area of Yuen Long, the pumping station operates to convey upstream stormwater flows over the tidal barrier to Deep Bay during rainstorm events.

2.2.5 The proposed Project site falls within Government land, in which no land resumption is anticipated. The YLBS does not encroach into the nearby Conservation Area (CA) zone and Nam Sang Wai.

2.3 Project Scope

2.3.1 The scope of the Project includes the construction and operation of the flood protection facilities. In retaining the technical feasibility and resilience towards climate change, the flood protection scheme also comprises revitalisation of the nullah in tandem with blue-green infrastructures. The proposed works are summarised in Table 2.1. The proposed layout of the YLBS is provided in Drawing No. 400171/B&V/ LAY/002 in Appendix 1.1.

2.3.2 The scope and description of the proposed works are summarised in Table 2.1.

Table 2.1 - Summary of Project Scope

Proposed Works	Description and Scale of Works
Construction and operation of Pumping Stations	A pumping station, housing in two structures, are located at the western and eastern banks of the downstream YLN. With a total footprint of approx. 3,300 m^2, the pumping station is also equipped with low flow pumps to be operated during dry season.
Construction and operation of Tidal Barrier	The tidal barrier would be divided into bays, whereby each segment can be opened at various angles at the operator¡¦s discretion. Upon completion, the gates would span across YLN at a width of approx. 50 m.
Construction and operation of E&M Control Room	The E&M control room, with a footprint of approx. 1,300 m^2, houses all the E&M apparatus & facilities for public enjoyment among other ground level open areas.
Construction of Link Bridge	The link bridge provides an access for maintenance personnel between Wang Lok Street and Shan Pui Ho East Road and utility crossings. With intermediate piers, the bridge would be situated downstream of the pumping station, which spans approx. 110 m across the nullah.
Local Widening and Deepening of YLN	The proposed works at YLN would widen the nullah by 10 m on each side and deepen its bottom to facilitate flow intake to the pumping station. Inflow-guiding structures would be constructed to direct flow towards the pumping station.
Construction & Modification of Parapet Walls	An additional height of approx. 200 mm at the top of the existing parapet walls along KTR and additional parapet walls along YLN and Sham Chung River (SCR) would be constructed. The extent of works is approx. 3,000 m in total for both banks of KTR and approx. 800 m in total for both banks at YLN & SCR.
Refinements to the existing intersection of YLN & YLBF	The proposed works will involve minor excavation and concreting works at the existing concrete diversion structure, resulting in the diversion of additional flow to YLBF for the barrage¡¦s operation at the downstream.
Revitalisation works of YLN	Revitalisation works within YLN by applying the concept of revitalising water bodies to enhance the local environmental quality. Vegetation & landscape components would be introduced to enhance the nullah¡¦s biodiversity and social connectivity.
Decommissioning of the Existing Low Flow Pumping Station (LFPS) & Inflatable Dam	The function of the existing Kau Hui LFPS and the associated existing inflatable dam that spans approx. 75 m across YLN would be replaced by the tidal barrier of the barrage, thus would be decommissioned.

2.3.3 The modification of parapet wall at YLBF had been taken up by Mainland North Division of DSD, which would not be implemented under the YLBS.

2.4 Need for the Project

2.4.1 The topography of Yuen Long town is generally flat with ground levels ranging between +4.0 mPD to +4.7 mPD. With reference to the SDM, given the tide level under a 50-year return period (with consideration of the mid-21^st century climate change) is +4.32 mPD, there exists a risk of flooding in Yuen Long town even with the absence of rainfall event.

2.4.2 With reference to the tidal level of previous Super Typhoons Hato (+4.71mPD) and Mangkhut (+4.28mPD) in August 2017 and September 2018 respectively, Yuen Long is susceptible to flooding.

2.4.3 In view of the public safety, there is a need to provide a robust flood protection scheme that is both climate resilient and cost effective.

Existing Drainage Conditions

2.4.4 According to the DMP Review Study, low-lying areas in the Yuen Long District could not meet the required flood protection level upon catering for future developments, sedimentation at the downstream main channels, mangrove growth at river estuaries, updated extreme sea level statistics at Tsim Bei Tsui and climate change.

2.4.5 The existing drainage network is unable to cater for the design rainstorm and tidal scenarios. Flooding is anticipated covering a vast area of Yuen Long town centre. A number of flooding incidents from previous wet seasons corroborated with the findings of the Study.

Current and Predicted Flooding Susceptibility

2.4.6 On 23 August 2017, at the hoisting of Typhoon Signal No. 10 during the passage of Typhoon Hato, the sea level at Deep Bay hit a record high in Tsim Bei Tsui Tide Station and reached +4.71mPD, flooding had been recorded with significant impacts to traffic and local businesses across Yuen Long town.

2.4.7 The high magnitude of sea level had wide impacts on coastal areas as well as inland areas in Yuen Long (e.g. Wang Chau Tseung Tau Tsuen, Hong Lok Road near LRT station, Pau Cheung Square, Tai Fung Street, Tai Cheung Street, Tung Tai Street, Shui Che Kwun Street, Shan Pui Tsuen, Shui Pin Tsuen, Tung Shing Lei, Sha Po, Pak Wai Tsuen, Shui Tau, Shui Mei, Kam Hing Wai, Tai Tseng Wai, Lut Chau).

2.4.8 As a result, the YLBS emerges as the more pronounced solution among other options in mitigating the impacts of extreme tidal level.

2.5 Benefits of the Project

2.5.1 The implementation of YLBS embodies a comprehensive solution in providing adequate drainage performance & flood resilience to Yuen Long.

2.5.2 The tidal barrier will be operated in accordance with the real-time tidal level and the observed water quality in Deep Bay, while the details of a 300mm x 300mm ecological trench will be further explored in the detailed design stage to allow free passage of water and aquatic organisms, even when the tidal barriers are closed. This is to maintain ecological connectivity and prevent sea water back flow to Yuen Long Town Centre to resolve the long-standing odour issues. After the construction of barrage, the tidal barrier and pumps will operate cohesively to replace the existing inflatable dam, whereby the existing inflatable dam will be deflated and removed as part of the revitalisation works.

2.5.3 Upon implementation of the YLBS, the Kau Hui LFPS in YLN would no longer be necessary and its services would be suspended / decommissioned to achieve energy efficiency. No demolition works would be involved.

2.5.4 With reference to the 2019 Policy Address, the Chief Executive has proposed to develop and take forward the concept of ¡§Rivers in the City¡¨, emphasising the aim enhance public enjoyment of river facilities, experience the multiple values of water bodies, treasure water bodies and create a better living environment.

2.5.5 The increased flood protection provided by YLBS would facilitate the concept of ¡§Rivers in the City¡¨ via nullah revitalisation and aesthetic enhancement works. Subsequently retaining the ecological connectivity between Deep Bay and the YLN under non-critical operations.

2.5.6 Vegetation & landscape components would be introduced to enhance the nullah¡¦s biodiversity and social connectivity for the revitalisation works within YLN.

2.5.7 In addition to proposed green roofs and vertical greening, the use of solar panels will be adopted as far as possible. The applicability and extent of solar energy on the building façade or roof areas of the Pumping stations and E&M control room will be evaluated during the detailed design stage.

2.5.8 The current parapet wall along the existing KTR does not meet the standards for drainage & flood control performance under the latest climate change parameters, e.g. wave run-ups and safety margin requirements under DSD¡¦s Stormwater Drainage Manual. Hence, upgrading works at KTR is necessary to ensure adequate protection against extreme tides.

2.6 Without Project Scenario

2.6.1 Without the Project, the flood risk would persist and extent of flooding would continue to increase in Yuen Long town under extreme weather events and increasing sea-level due to climate change.

2.6.2 In accordance with the SDM, a vast area in Yuen Long town centre would be flooded with maximum flood depths in excess of 1 m. The flood extent maps of ¡§Without Project Scenario¡¨ are enclosed in Appendix 2.1. Moreover, the existing concrete-lined YLN would be maintained to preserve the drainage capacity, negating the opportunity of revitalising YLN.

2.7 With Project Scenario

2.7.1 With the Project, flooding extent from rainfall & tidal events under 50-year return periods would be significantly reduced in YL town with some remaining residual flooding (ranging between 150-300mm depth) in local low-lying areas. Rainfall & tidal events under 200-year return periods would also be capable of passing within the banks. The flood extent maps of ¡§With Project Scenario¡¨ are provided in Appendix 2.2, and an increase in flood risk downstream (i.e. the waterbody of Shan Pui River and Kam Tin River) of the YLBS is not anticipated as a result of its construction and operation.

2.7.2 The proposed revitalisation works along the existing concrete-lined YLN under the Project would provide an opportunity to implement scenic public spaces for leisure activities and enjoyment and reduces the heat island effect during hot climates. Thus, showcasing the concept of ¡§Rivers in the City¡¨. The nullah is currently not accessible by the public. However, the level of access into the nullah at certain periods throughout the year, such as during the dry season, would be explored during the detailed design stage, particularly for the section immediately downstream of the Long Ping Station, but this would be subject to the findings in the detailed design assessment, establishment of monitoring system and flood warning system, public safety, evacuation system, etc. Photomontages of the revitalised YLN are presented in Chapter 10 of this report.

2.7.3 The revitalisation schemes are subject to further development in the Design Stage. Nonetheless, investigation is being conducted to retain the existing habitat downstream of the existing inflatable dam, as much as possible. Meanwhile, the feasibility of new habitats along YLN would be explored to enhance the existing ecology. Further information can be found in Chapter 7 of this report.

2.7.4 Given the preliminary design and site investigation works are ongoing at the time of preparation of this report, the location and layout of the YLBS may subject to further slight adjustment upstream to surpass site constraints. Within the indicated boundary of the pumping station and tidal barrier (in yellow) as shown in Drawing No. 400171/B&V/LAY/001 in Appendix 1.1, all Chapters in this EIA report has taken into account the most conservative case for assessment.

2.8 Design Considerations

Design Performance and Climate Change

2.8.1 The Project is designed in accordance with DSD¡¦s SDM with a climate change projects of mid-21^st century (2041-2060). The barrage system necessitates a total pumping capacity of 300 m³/s and a tidal barrier that can withstand a maximum tide level of +5.0 mPD. The adopted climate change parameters in rainfall and sea level increments are summarised in Table 2.2.

Table 2.2 - Rainfall Increase and Sea Level Rise due to Climate Change

Scenario	Rainfall Increase	Sea Level Rise
Mid 21^st century (2041-2060)	10.4%	0.23m

2.8.2 The design has considered information from the Intergovernmental Panel on Climate Change (IPCC) regarding the Fifth Assessment Report (AR5) and other relevant data such as the historical and projected climate data from Hong Kong Observatory (HKO), study findings of other departments/projects, and research papers from the academia on global and local climate change. Appropriate AR5¡¦s climate change scenario has been adopted for hydraulic analysis of the Project.

2.8.3 Given the pioneering nature of this Project, reference has been made to overseas projects in Japan and USA such as the 17^th Street Canal Pumping Station of the Permanent Canal Closure & Pumps (PCCP) in New Orleans. These said pumping stations resemble a similar pump rate of 50 m³/s per pump and the ability to allow upstream flows to be discharged downstream. Other overseas examples include the Gulf Intracoastal Waterway West Closure Complex (GIWW) in New Orleans, the Seabrook Floodgate in New Orleans and the Able Pumping Station in Dallas.

2.8.4 To synergise with the planned beautification works in the area, a holistic approach to promote water-friendly cultures and ecological enhancements such as green roofs, solar panels and planting of vegetation within YLN would be adopted where applicable.

2.9 Consideration of Alternatives Location, Design and Layout

Development Option

2.9.1 To bring the flood protection level to the standards as stipulated in the SDM, the DMP Review Study has proposed drainage improvement works in a number of areas in Yuen Long District. For the Yuen Long town centre, the DMP Review Study recommended the construction of two underground storage tanks with pumping stations and associated interception drains and parapet wall (collectively known as the flood storage scheme [Option A]). The construction of diversion drains to convey the stormwater into the storage tanks in Yuen Long town centre would pose significant traffic impact and public nuisance to the nearby sensitive receivers.

2.9.2 DSD commissioned an Investigation Consultancy Agreement No. CE 24/2013 (DS) ¡§Drainage Improvement Works in Yuen Long, Stage 2 ¡V Investigation¡¨ (the YL Stage 2 Investigation) in March 2014 to develop a drainage improvement scheme that would be both hydraulically and technically feasible with public support for implementation. The YL Stage 2 Investigation recommended a flood resilient scheme (Barrage Scheme, Option B) comprising a barrage cum pumping station to be built at the downstream end of Yuen Long Nullah together with modification of the existing flow diversion structure at the intersection of Yuen Long Nullah and YLBF and installation of parapet walls.

2.9.3 A comparison on the environmental factors is shown in Table 2.3:

Table 2.3 ¡V Comparison Summary of Options A and B

	Option A ¡V Storage Tank Scheme	Option B ¡V Yuen Long Barrage Scheme (Selected)
Environmental Benefit	¡P Current habitat near inflatable dam remain unchanged	¡P Revitalises the existing concrete-lined nullah ¡P Creates new beneficial habitats ¡P Mitigates backflow of odorous seawater from Deep Bay
Environmental Disbenefit	¡P Generates large quantities of C&D materials ¡P Air quality deteriorates from substantial excavation ¡P Ingress of odorous seawater during high tides remain unchanged ¡P This option cannot sufficiently reduce the flooding risk and there is still risk of excess flooding damages to existing habitats ¡P Further expansion works is required to cater for future climate change	¡P Change in habitat downstream of the existing inflatable dam ¡P Potential visual impact from YLBS

Alternative Location of Barrage Scheme

2.9.4 An assessment on alternative location of the YLBS was carried out between the most downstream location of YLN as compared with the location near the existing inflatable dam under Agreement No. CE 24/2013 (DS).

2.9.5 Based on findings from the assessment, elements such as hydraulic performance, flood protection extent and impact on existing ecology were considered. The proposed YLBS at the downstream YLN was recommended with the following benefits:

¡P Effective mitigation of odour complaints from local villages;

¡P Fulfils latest SDM standards while optimising flood protection extent;

¡P Maximizes revitalisation extent;

¡P Less public nuisance; and

¡P Minimises land requirement with no land acquisition.

General Arrangement of Pumping Station

2.9.6 A total of 6 nos. of layouts were proposed, where after examination, Layouts 4A/4B were selected based on the following evaluations & environmental factors. Meanwhile, Layout 2 would serve as a fall-back option considering the complicated geological conditions in Yuen Long (i.e. Scheduled Area No. 2) and the potential geological constraints that may encounter.:

¡P Hydraulics & Flood Resilience:

The chosen layouts (Layout 4A/B) exhibit enhanced pump performance in response to various upstream water levels (WL) and ability for gravity flow without operation of pumps. This increases flood resilience for YLN and allows for optimisation at the forebay structures under the design scenarios of the latest SDM. Thus, benefiting the environment through increased flexibility in which the revitalisation schemes are designed with integral wetland compensation. While the backup option (Layout 2) is slightly inferior to Layout 4A/B in term of pump intake conditions, it retained a wider width in YLN which provides a good ability for gravity flow without operation of pumps. It also increases flood resilience for YLN and allows flexibility in the design of revitalisation schemes.

¡P Discharge Performance:

Layout 4A/B distribute the discharge evenly under extreme scenarios and has versatility to implement devices such as a submerged discharge to minimise surface turbulence that can be harmful to nearby aquatic ecology. The discharge of Layout 2 assembles in the western bank of YLN (Yuen Long Industrial Estate (YLIE) side), which is further away from the CA zone. With the implementation of devices such as submerged discharge, surface turbulence can be controlled to minimize the implications.

¡P Erosion & Sedimentation:

Layout 4A/B can effectively incorporate energy dissipators that work in conjunction with submerged discharges to further minimise the energy from the pumps, despite having a lower resultant peak flow under extreme weather. This enhances erosion control and better preserves the habitat downstream of the YLBS against scouring. The discharge of Layout 2 assembles in the western bank of YLN (Yuen Long Industrial Estate (YLIE) side), which is further away from the CA zone. With incorporation of energy dissipators in conjunction with submerged discharges, energy from the pumps can be minimised and preserves the habitat downstream of the YLBS in vicinity of the CA zone.

¡P Construction Aspects:

With Layout 4A/B, site accessibility for workers and plant is greatly enhanced as the pumping stations can be constructed independently from existing land. This increases safety and flexibility of construction staging and allows for phased commissioning of the YLBS. Subject to detailed design and the Contractor¡¦s proposal, a shorter construction duration may be achieved to minimise the potential environmental impacts incurred by the construction works. The modular nature of the layout also provides versatility for future pump upgrading over its lifecycle, thus an ease of expansion works. Regarding Layout 2, with the majority of the pumping station footprint is on land, site accessibility is enhanced which would ease the construction difficulties and facilitate future maintenance procedures. The backup option also allows flexibility for future expansion works. Besides, due to the minimized river occupancy, there will be less flow obstruction during construction which is beneficial in hydraulic and safety perspective.

¡P Ecological & Visual Aspects:

Layout 4A/B exhibit smaller sized pumping stations and an equidistant arrangement from the downstream. This enables more effective visual mitigation and minimises the impact to the flightpaths of low-flying species & avifauna whilst reserving a greater potential for ecological connectivity. Layout 2 retains a wider width in YLN, which allows a spacious and open view in downstream of YLN. With visual mitigation measures adopted, implications to the low-flying species & avifauna will be minimised and potential for ecological connectivity will be maintained.

Further benefits of Layout 4A/4B are elaborated in Appendix 2.3.

2.9.7 As an outcome of the options evaluation, the ¡§split pumping station on both banks of YLN¡¨, shown in Drawing No. 400171/B&V/LAY/002 in Appendix 1.1, is adopted in this EIA as it serves to be the most conservative assessment case for stormwater pumping from upstream to downstream of the tidal barrier. The other feasible layouts listed under Appendix 2.3 are also under investigation to delineate the most practicable design with consideration on optimal hydraulic performance, geotechnical constraints and the associated foundation design scheme.

Tidal Barrier

2.9.8 The proposed tidal barrier will be constructed with a total span of approx. 49 m and 6 m in height. To maximise operational flexibility, the proposed barrier will be divided into 3 bays to allow independent operation. The various types of tidal control structures investigated are as shown below:

¡P Inflatable Dam;

¡P Penstocks;

¡P Flap Gates;

¡P Segment Gates; and

¡P Sector Gates.

2.9.9 In view of the environmentally sensitive Nam Sang Wai, priority has been placed on height obstructions and ease of flow control when not in use. Hence, flap gates and sector gates were shortlisted for their low visual impact and height that would not obstruct the potential flight path of migratory birds. The application of these barrier is being investigated with potential suppliers to delineate the least environmentally and hydraulically obstructing arrangement.

2.9.10 As the total flow rate would be slightly reduced due to flow attenuation from the pumping operation and given the large waterbody of Deep Bay, increase in water level to Old Kam Tin River is not anticipated upon the implementation of the YLBS. Similarly, no significant impact on the existing habitat along Old Kam Tin River is anticipated. Changes to the hydrology of SPR is also not anticipated.

Pumping System

2.9.11 As the Project requires large design flows with relatively low head, the feasible pump types are shortlisted to kinetics pumps, namely Axial Flow Pumps and Mixed Flow Pumps with separately coupled end suction. Further liaison with potential suppliers would be kept obtaining the intake structure specifications.

2.9.12 Fish-friendly pumps would be adopted as much as practicable in case any fish enters through the intake screen into the pumping station.

Power Supply

2.9.13 Based on factors such as power ratings, reliability, capital & recurrent cost, required footprint and environmental impact, the following power supply arrangements were weighed:

¡P Dual Power Supply;

¡P Single Power Supply with supporting Generator Sets (Hybrid); and

¡P All-Generator Powered.

2.9.14 In light of its reliability from dual sources and minimal emissions on-site, a dual power supply is adopted in the design. Through continuous liaisons with CLP, it has been noted that a dual power supply can be supplied through a single source with dual feeds or from two standalone sources.

Discharge Outlet, Arrangement and Flow

2.9.15 Flow attenuation can be achieved through pumping operation. As the proposed 300 m³/s under YLBS is less than the existing peak discharge at YLN (~330 m³/s), scouring of the river bed and banks is not anticipated with the necessary design optimisations to the discharge orientation and implementation of adequate energy dissipators to prevent localized turbulent flow.

2.9.16 With reference to overseas examples in New Orleans (USA) such as the Bonnabel Pump Station and 17^th Street Pump Station under the Permanent Canal Closure & Pumps (PCCP), a submerged discharge is being considered to minimise surface disruptions and to be further developed in the Design Stage of the Project.

Operation Modes & Maintenance

2.9.17 The conceptual operational scenarios of the proposed tidal barrier and ancillary pumping station are simplified for easy understanding in Table 2.4.

Table 2.4 - Conceptual Operational Scenarios for the Barrage Scheme

Mode	Tidal Condition	Precipitation	Flow Condition	Barrier Status	Pump Status
1	Low	No	Dry Weather	Opened	Off
2	High			Closed	On
3	Low	Heavy	High	Closed	On
4	High			Closed	On

A visual illustration of the conceptual operation modes of the YLBS is enclosed in Appendix 2.4.

2.9.18 As the tidal barrier is intended to withstand the odourous tidal backflow from Deep Bay, operation of the gates would be optimised with a flexibility of opening and closing at designated times of the day through flow sensors and Supervisory Control and Data Acquisition (SCADA) systems.

2.9.19 The barrier would operate to combat both high tides and sub-standard water quality. Hence, subject to further developments in detailed design, the default is for the tidal barrier to remain closed during adverse weather conditions. The details of a 300mm x 300mm ecological trench will be further explored in the detailed design stage to allow free passage of water and aquatic organisms, even when the tidal barriers are closed. Indicative details of this scheme is provided in Appendix 2.4.

2.9.20 In accordance to a preliminary analysis of historical tidal data, approximately 2-12 hours of opening per day could be catered but subject to other parameters such as existing / predicted weather condition, water quality and water level upstream of the YLBS. In the case where water quality in Deep Bay has improved and there is no further odour concern for Yuen Long Town Centre and adjacent villages, opening of the gates can be considered to further maximise the amount of water upstream of the YLBS in the intertidal zone.

2.9.21 To balance the rate of water ingress at the tidal barrier and maintain the allowable water depth upstream, the YLBS would utilise low-flow pumps under normal conditions and be subjected to further studying for the opening/closing of the tidal barrier. Nonetheless, the ingress of water would require carefully designing to avoid posing flooding risk to Yuen Long Town. With further design optimisations required in detailed design, the dedicated high-capacity pumps of the YLBS would begin to operate accordingly when the upstream water level reaches +1.2mPD tentatively.

2.9.22 Given the proven reliability from CLP¡¦s dual power supply, no alternative power supply arrangements would be fitted to the large capacity pumps. Nonetheless, fail-safe provisions would be incorporated to ensure the tidal barrier can be disengaged without a primary power source. An access for maintenance personnel would be provided across the tidal barrier to facilitate regular inspections and maintenance works.

Revitalisation of YLN

2.9.23 After implementation of YLBS, the hydraulic performance of YLN is enhanced. The proposed revitalisation works along the existing concrete-lined YLN under the Project would provide an opportunity to implement scenic public spaces for leisure activities and enjoyment and reduces the heat island effect during hot climates. This promotes water-friendliness, ecological enhancements, biodiversity and beautification along the existing concrete-lined YLN. At nullah sections that are technically feasible (e.g. geotechnical, hydraulics, etc.), scope of revitalisation works may include: removal of sections of concrete nullah, provision of natural substrates and planting and provision of designated viewing points.

2.9.24 For the upstream sections in the town centre (i.e. upstream of Long Ping Station), structural integrity of the nullah will need to be carefully considered. Given the limited width of the upstream section and the need to maintain adequate flood protection standards, the revitalisation of the upstream sections would primarily aim at providing beautification with hard and soft landscaping works. This will be designed in synergy with the concurrent project, Improvement of Yuen Long Town Nullah (Town Centre Section) ¡V Stage 1 Improvement Works ¡V mentioned in Section 2.14 below, thus allowing their dry weather flow interceptors (DWFI) to become an integral part of our revitalisation design scheme. Potential synergy with other concurrent projects would be kept in view throughout detailed design.

2.9.25 The sparse numbers of public amenities downstream of the Long Ping West Rail Line Station can limit the ease of access and degree of public enjoyment. To enhance the social connectivity of the revitalisation scheme, the potential public attractions to be developed under YLBS would be explored in synergy with the architectural designs under Agreement No. CE 3/2015 (DS) Yuen Long Effluent Polishing Plant.

2.9.26 For the downstream section between the existing inflatable dam and YLBS which has adequate width, the revitalisation will aim for a more ¡¥nature¡¦ approach. This could include removing parts of the existing concrete beds, providing natural substrates, planting of suitable vegetation and provision of viewing platforms.

2.9.27 The preliminary architectural designs, feasible co-use schemes and revitalisation theme would be further developed throughout the progression of the Project and to be evaluated under the Landscape and Visual Impact Assessment (LVIA) of this report. The details of revitalisation would be subject to further stakeholder engagement, engineering studies, hydraulic assessments & optimisations.

2.9.28 As part of the nullah revitalisation, measures are being explored to retain the habitat between the existing inflatable dam and the proposed tidal barrier as far as practicable. Apart from periodic opening of the tidal gates and provision of ecological trench as mentioned above, the proposed nullah deepening works for the pump intakes can also be deepened at a gradient to further enhance ecological connectivity. In combination with the proposed 300mm x 300mm ecological trench, with details to be explored in the detailed design stage, this would facilitate an exchange of water and provide a similar environment to the existing tidal fluctuations.

2.9.29 With consideration of the gradual deepening, the water level to be maintained upstream of the YLBS is approximately +1.0mPD with a water depth range of between 0m to 2m. To cater for potential loss of watercourse habitat, the design could allow tidal water to flush 50m further upstream of the current inflatable dam. This would create a watercourse habitat area similar to existing conditions and be further enhanced by the revitalisation works. The details would be subject to further engineering studies, hydraulic assessments & optimisations.

2.9.30 The design and construction of the nullah revitalisation under the YLBS, would comply with the management of construction site drainage as provided in ProPECC PN 1/94. The Contractor would be instructed to be compliant with the Water Pollution Control Ordinance and its subsidiary regulations and obtain a discharge license under the Ordinance. The management of construction and demolition (C&D) materials, including the generation and reuse of surplus inert materials, and other mitigation measures including perimeter drainage channels, sand/silt removal facilities and suitable containment structures for nullah works would be adopted as far as possible. Please refer to Chapter 5 of this Report for further details.

2.10 Construction Aspects of the Project

Construction Method ¡V Barrage Scheme

2.10.1 To mitigate the potential adverse impacts incurred to the nullah¡¦s hydraulic performance, the environment and nearby stakeholders, the proposed works comprises a phased construction method with interim flow diversion schemes by cofferdams. Furthermore, piling works would be suspended during the dry seasons to minimise potential impact on migratory birds in Nam Sang Wai. The Contractor would be required to design and coordinate the corresponding temporary works and flow diversion schemes with DSD prior to Construction. An overview of the 3 primary phases are presented below in Table 2.5:

Table 2.5 - Key Construction Phases & Description

Phase 1 ¡V Local Widening and Deepening of YLN

¡P Cofferdam for Temporary Diversion

¡P Excavation Works by Open Cut

¡P Slope Stabilising (Concreting Works)

Phase 2 ¡V Construction of Pumping Stations, E&M Control Room & Link Bridge

¡P Cofferdam for Temporary Diversion

¡P Foundation Works (Piling / Concreting Works)

¡P Superstructure & E&M Installation Works

Phase 3 ¡V Construction of Tidal Barrier

¡P Cofferdam for Temporary Diversion

¡P Flow Optimising Walls in YLN

¡P Superstructure & E&M Installation Works

Upon Barrage Completion: Revitalisation of YLN

¡P Excavation Works by Open Cut

¡P Decommissioning of the Existing LFPS & Inflatable Dam

¡P Construction of Hard Landscapes (Concreting Works)

¡P Installation of Greenery (Planting)

Non-critical Path Works: Parapet Walls & Public Enjoyment Facilities

¡P Construction & Modification of Parapet Walls (Concreting Works)

¡P Refinements to the Existing Intersection of YLN & YLBF

¡P Installation of Pre-fabricated Opaque Panels & Public Space Amenities

Phase 1 ¡V Channel Deepening, Widening and Stabilisation Works

2.10.2 Channel deepening and widening works would be carried out one bank at a time to preserve the drainage performance of YLN as well as the impact on existing ecology. The cross sections of deepened forebay is shown in Drawing No. 400171/B&V/ LAY/003 & 004 in Appendix 1.1.

Phase 2 ¡V Construction of Pumping Stations, E&M Control Room & Link Bridge

2.10.3 To minimise the impact on over-wintering birds in Nam Sang Wai, no piling works would be conducted during the dry season. Sufficient time would be scheduled to allow for Testing and Commissioning (T&C) prior to the partial operation of the pumping station. The preliminary designs of Pumping Stations A & B, E&M Control Room and Link Bridge are shown in Drawing No. 400171/B&V/LAY/102, 202, 402 & 601 in Appendix 1.1 respectively.

Phase 3 ¡V Tidal Barrier Assembly & Installation

2.10.4 Upon completion of Phase 2, a cofferdam would be constructed between the pumping stations for subsequent construction of the tidal barrier and forebay optimisations. Through operating the pumps, it is anticipated to compensate for the loss of flow area during the tidal barrier¡¦s construction and its T&C. The preliminary design of tidal barrier is shown in Drawing Nos. 400171/B&V/LAY/ 003 in Appendix 1.1.

Revitalisation Works along Yuen Long Nullah and Decommissioning of Existing LFPS & Inflatable Dam

2.10.5 Subject to the selected design theme, it is anticipated for the revitalisation works to comprise hard landscape features and vegetation. The works would be carried out in sections along the length of YLN through temporary flow diversion with stacks of sand bags. The accumulated sediment downstream of the existing inflatable dam would be removed prior to works and the typical cross sections of the revitalisation extent is shown in Drawing No. 400171/B&V/LAY/501 & 502 in Appendix 1.1.

Construction & Modification of Parapet Walls

2.10.6 Additional concrete parapet walls would be constructed along YLN and SCR along sections that are vulnerable to flooding. The existing parapet walls along KTR would be heightened through metal-framed, opaque panels to minimise visual impact.

2.10.7 Ardeid night roost was recorded at a site along Kam Tin River. To avoid / minimise the disturbance to the ardeid night roost, no construction works should be undertaken within 100m from any night roost confirmed by the pre-construction survey after 17:00 from February to September and 16:30 from October to January.

Summary of Key Construction Activities

2.10.8 Construction of the barrage generally involves common civil engineering construction activities such as site clearance, excavation, formwork, substructure and superstructure construction, concreting, landscaping and E&M installation. Revitalisation of YLN involves smaller scale construction activities such as breaking of nullah bed, excavation and landscaping.

2.11 Consideration of Alternative Construction Methods

Barrage Scheme

2.11.1 Potential alternative construction method includes offsite precast structures or modular integrated construction (MiC) for the pumping stations and tidal barrier. The environmental benefit of offsite construction is that there will be less construction waste, shortened construction period, and less environmental disturbance and nuisance to nearby sensitive receivers. The applicability of adopting MiC would be explored.

2.11.2 To allow for flexibility in design and facilitate the installation of large sized pumps / gates, it is more practicable to construct the structures in-situ. The associated environmental impacts anticipated are generally temporary, localized and can be mitigated through appropriate pollution control measures.

Revitalisation of YLN

2.11.3 The revitalisation would generally be small scale and localized construction and landscaping works. Alternative construction methods will be limited. Nonetheless, the removal of the concrete bed of YLN should explore saw and lift method instead of traditional surface breaking using breakers. The concrete slab could be beneficially reused as flow deflector, stepping stones or sitting area in the revitalised channel enhancing the overall sustainability concept of the Project.

2.12 Consideration of Alternative Construction Sequence

2.12.1 Ardeid night roost was recorded at a site along Kam Tin River. To avoid / minimise the disturbance to the ardeid night roost, no construction works should be undertaken within 100m from any night roost confirmed by the pre-construction survey after 17:00 from February to September and 16:30 from October to January.

2.12.2 To reduce disturbance and nuisance to nearby sensitive receivers and to maintain adequate flood protection capacity in YLN, the pumping stations and tidal barrier will not be constructed simultaneously and the revitalisation works shall only commence upon completion and operation of the barrage. To further reduce the potential water quality impacts, excavation works in the YLN will only be undertaken in dry condition.

2.12.3 The design and construction of YLBS is anticipated to adopt an Early Contractor Involvement (ECI) under NEC4 Engineering and Construction Contract (ECC). The selected Contractor would be engaged early in the project lifecycle to collaborate with design groups and project owners on the constructability and cost control. The programme and methods of construction would be further developed subject to coordination with the ECI Contractor later in the Design Stage.

2.13 Implementation Programme

2.13.1 The construction works of the pumping stations and tidal barrier is anticipated to commence in Q4 of 2022 for completion by Q3 of 2027, with concurrent construction & modification of the parapet walls along Kung Um Road, Kiu Hing Road and KTR. Upon completion of the barrage, the LFPS would be decommissioned, and the existing inflatable dam would be removed from YLN. The revitalisation works along YLN would take place until Q3 of 2029. A tentative construction programme is shown in Chapter 4 for assessment purposes. Subject to detailed design and the Contractor¡¦s proposal, a shorter construction duration may be achieved such that general nuisance and potential environmental impacts are minimised.

2.14 Concurrent Projects

2.14.1 Based on best available information, the following projects to be undertaken concurrently in the vicinity of the Project Site are identified as potential concurrent projects. The potential cumulative construction / operation impacts due to these projects to be addressed in this EIA Study are presented in Table 2.6.

Improvement of Yuen Long Town Nullah (Town Centre Section) ¡V Stage 1 Improvement Works ⁽¹⁾

2.14.2 The project mainly comprises provision of a dry weather flow (DWF) interception system, including construction of DWF interceptors along the Town Centre Section of YLN and a new pumping station. The DWF interception system will convey the first 18,000 m³ of DWF being intercepted each day to the YLEPP for treatment.

2.14.3 The project will divert the polluted DWF and effectively eliminate the main source of odour nuisance at YLN. It will also provide favourable condition to allow the revitalisation of YLN to be implemented in this Project. Based on current information, the DWF interception system will need to be in operation before revitalisation works could begin. As such, concurrent construction work is not envisaged. Nonetheless, the locations of the DWF interceptors and associated nullah wall construction works is anticipated to interface with the proposed revitalisation design works under this Project.

Elevated Pedestrian Corridor in Yuen Long Town Connecting with Long Ping Station ⁽²⁾

2.14.4 In the project (EPC), an elevated pedestrian corridor, in form of a footbridge, along YLN from West Rail Long Ping Station to the south of the Kau Yuk Road will be constructed. The proposed elevated pedestrian corridor will be connected to at-grade footpath via pedestrian interchanges located along the nullah. According to the latest best information provided by HyD, the project was tentatively scheduled to commence in first quarter of 2020 for completion in first quarter of 2025 ¡Vsubject to the funding approval by LegCo.

2.14.5 Given the latest implementation challenges faced by this project in Yuen Long, further liaison and monitoring would be conducted to gauge the level of interface with YLBS. Therefore, the cumulative impact to YLN due to the footbridge would be further reviewed and incorporated in the hydraulic analysis of YLBS. To be conservative, the EPC project is assumed to be conducted concurrently with the Project.

Yuen Long Effluent Polishing Plant (YLEPP) ⁽³⁾

2.14.6 The existing Yuen Long Sewage Treatment Works (YLSTW) will be upgraded into YLEPP in order to cater for future needs in the catchment and improve the water quality of Deep Bay. The capacity of the YLEPP will be increased from 70,000 m³/day (for existing YLSTW) to 150,000 m³/day (Phase 1: 100,000 m³/day; Phase 2: 150,000 m³/day) with upgrading the treatment level from secondary to tertiary. The treatment capacity of YLEPP would be reduced to 35,000 m³/day during the upgrading period in Phase 1 (i.e. Year 2020 ¡V Year 2027). According to the EIA Report of the YLEPP, the construction works are tentatively scheduled to commence in third quarter of 2020 for completion in second quarter of 2027 for Phase 1 and 2030 for Phase 2 the earliest.

2.14.7 The project boundary of the YLEPP is outside the 500m study area of the Project. However, given that both projects are in close proximity to the contiguous wetland habitats of Shan Pui River and Nam Sang Wai, the likely cumulative impact on ecology will be addressed in this EIA Study.

Yuen Long South Development ¡V Stage 1 ⁽⁴⁾

2.14.8 The Revised Recommended Outline Development Plan (RODP) of the ¡§Planning and Engineering Study for Housing Sites in Yuen Long South (YLS) ¡V Investigation¡¨ was promulgated in May 2020. Under the Revised RODP, the YLS Development will provide about 32,850 new flats with a total population of about 101,200. The development covers approximately 223.5 ha and is located to the south of Yuen Long New Town. Other than housing development within the PDA, there are also some other supporting infrastructure works (such as public transport interchange, road construction / improvement works, main laying, partial nullah decking and reclaimed water service reservoir) outside the PDA. This study included proposed river revitalisation and partial decking at the upstream of Yuen Long Main Nullah and adjacent branches. The proposed river revitalisation works would collect and divert the drainage from the nearby existing village and low-rise residential area into Yuen Long West Nullah, Tin Tsuen Channel and upstream portions of YLN.

2.14.9 According to the construction programme in the EIA Report, the project is tentatively scheduled to commence in 2020 for completion in 2038. Regular liaisons would be maintained with CEDD and their consultants to gather the latest information to ascertain its impact to this Project.

2.14.10The Stage 1 project is to design and carry out site formation and infrastructure works to support the YLS Development. Part of the road improvement works include partial decking of YLN and providing nullah/river channel revitalisation works. The Stage 1 works also includes modification of drainage structure at junction of YLN and YLBF. Further liaisons with the responsible project team would be made to ascertain their extent of works and degree of interface with this Project. In particular, the proposed revitalisation of YLN shall be compatible with the revitalisation works to be carried out under the YLS Development.

River Revitalisation and Flood Resilience Planning in Yuen Long South

2.14.11This feasibility study is to investigate and develop a smart, green, resilient and sustainable drainage system for the YLS Development. Further liaisons with the responsible project team would be made to ascertain their extent of works and degree of interface with this Project.

2.14.12 A summary of the potential interfaces are shown below in Table 2.6:

Table 2.6 - Potential Concurrent Projects

Project	Project Proponent	Programme		Location of Potential Interface	Considered in this EIA
		Start	Complete		Construction Phase	Operation Phase
CE 37/2012 (DS) Improvement of Yuen Long Town Nullah (Town Centre Section) ¡V Stage 1 Improvement Works ¡V Design and Construction	DSD	Q2 2021	2026	Yuen Long Nullah	ü	ü
CE 32/2014 (HY) Elevated Pedestrian Corridor in Yuen Long Town Connecting with Long Ping Station ¡V Investigation, Design and Construction	HyD	2020*	2025	Yuen Long Town	ü	ü
CE 3/2015 (DS) Yuen Long Effluent Polishing Plant ¡V Investigation, Design and Construction	DSD	2020	2030	Shan Pui River	ü	ü
CE 32/2017 (CE) Yuen Long South Development ¡V Stage 1 ¡V Design and Construction	CEDD	2020	2038	Intersection of YLN and YLBF	ü	ü

*The commencement of construction of footbridge is subject to the funding approval by LegCo.

2.15 Sustainability Considerations

Blue Green Infrastructure

2.15.1 Blue-green drainage infrastructure is a form of development aiming to improve the sustainability and resilience of the drainage system. It facilitates the infiltration of rainfall and the process of natural filtering to reduce the quantity and improve the quality of stormwater runoff.

2.15.2 The concept of blue-green infrastructure is advocated to be incorporated in the future development, maximising amenity and biodiversity opportunities while minimising the impacts from climate change.

2.15.3 Various ecological features would be adopted in the proposed revitalisation works to provide habitats for aquatic life, thus promoting conservation of biodiversity and sustainable use of biological resources. Blue-green components, embracing Sustainable Drainage Systems (SuDS) such as green roofs, solar panels, porous pavements and rainwater harvesting facilities, would be subjected to further feasibility study in detailed design. While exterior elements such as vertical greening, porous pavements & green roofs are incorporated as far as practicable within the project site, internal elements such as the use of harvested rainwater for toilet flushing purposes would also be explored in detailed design. Hence, achieving a value-adding design to the proposed works and YLN.

Potential Water Sources

2.15.4 Based on a previous flow survey, a dry weather flow of 13,000 m³/day was observed to contribute from upstream Kung Um Road, which would serve as an environmental flow during dry season.

2.15.5 It is noted that the works under CE 6/2019 (DS) Project, for the construction and operation of Yuen Long South Effluent Polishing Plant (YLSEPP), aims to provide sewage treatment for YLS and other developments in North West New Territories for subsequent discharge into YLN. In accordance with the Project Profile issued in January 2019, the maximum Average Dry Weather Flow (ADWF) treatment is at 65,000 m³/day. In synergising with this, the feasibility of utilising the treated discharge for benefit of the revitalised YLN in the form of an ecological flow would be explored in the Design Stage of this Project. Further interfaces would be coordinated as necessary.

2.15.6 Apart from the water source from YLSEPP, another potential water source had been identified from the upstream Wong Nai Tun Irrigation Reservoir. Discharge of a portion of stored stormwater from the irrigation reservoir, which is currently used solely for irrigation purposes by AFCD, would provide ecological flow from the upstream to the downstream YLN for environment enhancement.

2.15.7 However, as a contingency, the two potential water sources (e.g. YLSEPP and Wong Nai Tung Irrigation Reservoir, etc.) are situated upstream of the Yuen Long catchment for supplying water to YLN by gravity without the need of pumping to achieve cost and energy efficiency.

Green Building Certification

2.15.8 The Project will aim to obtain BEAM Plus Gold or higher accreditation, as far as practicable for the existing and new buildings/structures. Where applicable, renewable energy sources such as photovoltaic panels would be incorporated.

2.16 Continuous Public Involvement

Public Comments during Project Profile

2.16.1 A public inspection of the project profile was conducted under Agreement No. CE 24/2013 (DS) and public comments were received. The main concerns and ways to address are outlined below and an overview of these comments concerning the proposed works location, existing ecology, drainage performance, sedimentation, construction methods and public aspiration is enclosed in Appendix 2.5.

Main Concerns / Ways to Address

¡P Ecologically Sensitive Area in the vicinity of the proposed Barrage

A full-scale Ecological Impact Assessment has been conducted and would contribute towards the corresponding Sections under the Environmental Impact Assessment (EIA).

¡P Cumulative Impact from Construction Activities

We acknowledge the project interfaces in the vicinity and would assess the cumulative effects to the environment as a result of the concurrent works in the EIA Report.

¡P Environmental Impacts to Nam Sang Wai

The anticipated works area and footprint for constructing YLBS does not include the use of Nam Sang Wai and would be confined to the south of Kam Tin River old channel to avoid corresponding environmental and ecological impacts.

2.16.2 With these preliminary comments and responses, further public engagements by means of ¡§Design Thinking Approach¡¨ commenced in mid-2020 to obtain in-depth aspirations from local stakeholders & advisory bodies.

Green Groups Liaison Meeting

2.16.3 The Project maintained a continuous communication with Green Groups and their views were obtained during meetings and site visit as listed below:

¡P 22 September 2016 ¡V Green Groups Liaison Meeting No. 13

¡P 1 February 2018 ¡V Green Groups Liaison Meeting No. 18

¡P 28 October 2019 ¡V Site meeting at the Proposed Location of YLBS

¡P 27 July 2020 ¡V Online Presentation of YLBS

¡P 5 & 6 November 2020 - Site meeting at the Proposed Location of YLBS

¡P 11 January 2021 ¡V Online Meeting with Green Groups

Main Concerns / Ways to Address

¡P Ecological Connectivity

In promoting ecological connectivity, the Project has proposed a 300mm x 300mm ecological trench and optmisation of the operation of tidal barriers to allow tidal flow coming-in for further investigation, as detailed in Chapter 7.

¡P Revitalisation Ideas

Different themes will be developed for the revitalisation works under different section of YLN, with details further developed in the detailed design, as detailed in Chapters 7 & 10.

Consultation with District Council, Rural Committee and Village Representative

2.16.4 The Project also engaged with corresponding community stakeholders to obtain their views during meetings and site visits as listed below:

¡P Working Group on Footbridge Planning and Improvement of Nullah of YLDC ¡V 29 October 2020

¡P Site visit with District Council (DC) members and Rural Committee (RC) members on 20, 22 & 28 October 2020

¡P Environment, Climate Change, Agriculture and Fisheries Committee of YLDC ¡V 9 November 2020 (followed by site visit with Rural Committees)

Main Concerns / Ways to Address

¡P Odour Nuisance

The existing inflatable dam at YLN, near Wang Chau (along with the existing low-flow pump station), as detailed in this Chapter 2, would be decommissioned upon completion of the Project. Thus, the build-up of debris & odours could be alleviated. Coupled with the dry weather flow intercepting system to be constructed under PWP No. 4161CD ¡V Improvement of Yuen Long Town Nullah (Town Centre Section), the quality of the local environment could be improved.

¡P Revitalisation Ideas

Different themes will be developed for the revitalisation works under different section of YLN, with details further developed in the detailed design, as detailed in Chapters 7 & 10

2.17 References

(1) DSD (2020) ¡V EIA Report for ¡§Improvement of Yuen Long Town Nullah (Town Centre Section)¡¨ (AEIAR-223/2020).

(2) HyD (2014) ¡V EIA Report for ¡§Elevated Pedestrian Corridor in Yuen Long Town Connecting with Long Ping Station¡¨ (AEIAR-200/2016).

(3) DSD (2019) ¡V EIA Report for ¡§Yuen Long Effluent Polishing Plant¡¨ (AEIAR-220/2019).

(4) CEDD (2017) ¡V EIA Report for ¡§Housing Sites in Yuen Long South¡¨ (AEIAR-215/201