March 2023

Dr. CHUI Ho Kwong, Samuel, JP
Acting Director of Environmental Protection
EIA Ordinance Register Office
Environmental Protection Department

Dear Dr. Chui,
Green Power’s comments on the EIA report of Revitalisation of Tai Wai Nullah (EIA-292/2022)

Green Power have the following comments on the captioned EIA report.

1. We welcome the project’s initiatives to enhance the ecological value and improve the water quality of the channelised Tai Wai Nullah (TWN) for the benefit of wildlife and public enjoyment. However, details of the designs and their implementation during the construction and operational phases require careful consideration.

<u>Water quality issues during the construction phase</u>

2. We agree “to collect dry weather flow and convey it to the Sha Tin Sewage Treatment Works” to eliminate polluted effluent discharging into TWN. However, the associated works should not impose adverse environmental and ecological impacts during both construction and operational phases.

3. Although the EIA report stated that any anticipated water pollution impacts could be avoided if the Best Management Practices (BMPs) are implemented, total elimination of sewage discharged from construction sites is rarely seen in practice. Pollutant-generating activities, including excavation and in-situ concrete casting proposed in the EIA report, require implementation and close monitoring with due diligence.

4. Any bare soil surfaces and temporarily stored loose materials should be covered and checked especially when rainstorms are anticipated, and kept away from rainfall or runoff. All sand/silt removal facilities should be adequately designed, checked and cleared to maintain sufficient removal capacity. Adequate barriers, such as silt curtains and perimeter channels should be provided to intercept all sewage or pollutants generated from the work sites.

<u>Channel modification</u>

5. Obstruction structures/features of migration of aquatic organisms should be removed to restore the ecological connectivity of Tai Wai Nullah to Shing Mun River and Tolo Harbour if it does not bring about any insurmountable environmental or hydraulic impacts. Any additional structures, such as the proposed in-stream weirs, should avoid hindering the within-stream movement of aquatic species. In fact, designs such as fixed weirs that mimic the morphology and ecological functions of natural boulders instead of bare concrete beams, would allow microhabitat creation and continuity for aquatic fauna while minimizing management cost and maintaining the channel’s flood discharge performance, and should be adopted to enhance the ecological value of TWN.

6. As many silt trap structures in existing man-made channels have been observed to support aquatic flora and fauna due to lower flow velocity, larger water surface area and accumulation of natural sediment. In fact, such setting is already formed in the current stilling basin of TWN and they should be considered at other points along the modified channel. Not only would this promote the native aquatic and riparian biodiversity of TWN, but also allow more effective maintenance of the channel (e.g. desilting only around a few locations rather than at different points along the channel to reduce disturbance).

7. All underground water pumps should be properly screened (with appropriate mesh sizes) and maintained so that no aquatic organisms will be killed or trapped. Renewable energy supply should also be considered to save energy, reduce carbon footprint, and promote sustainability.

<u>Ecological enhancement designs</u>

8. Although the adoption of ecological enhancement designs (e.g. treatment wetlands and nest boxes) is appreciated, their details are missing from the EIA report. Their designs and details of implementation largely dictate their efficiency (e.g. treatment efficiency of the wetlands depends on the types of plant chosen, their sizes, maintenance and pollution loading of the sewage). The project proponent is highly encouraged to involve green groups and academics during the early detailed design stage of these measures.

9. The selection of species and precise locations for greening should consider the hydraulic characteristics, substratum materials, shading effect, usability by local wildlife, aesthetic value and efficiency in alleviating the heat island effect. The planting list and plan should be reviewed by qualified ecologists.

<u>Construction-and-demolish (C&D) and other solid wastes</u>

10. Generation, transportation and disposal of C&D and other solid wastes should be under strict control. Apart from the trip-ticket and recording system mentioned in the EIA report, additional measures, including monitoring of associated vehicles with GPS trackers or equivalent systems to prevent illegal and environmentally vandalistic dumping of wastes, should also be implemented. Such measures should also be incorporated into the specifications of the works contracts.

<u>Maintenance during the operational phase</u>

11. The project proponent should also formulate an environmental-friendly management plan. Immediate check-ups and follow-up actions will be required after rainstorms or other extreme weather events. In addition, some widely-used routine green space management measures, such as the application of insecticide for mosquito control and intensive plant trimming, will not be suitable in the revitalised TWN. The use of environmentally-friendly materials, as well as managing plants within the channel in phases with consideration of wildlife seasonality, should be adopted and specified in the management plan and maintenance manual. A system for managing the treatment wetlands should also be established to ensure their treatment efficiency.

12. Strict management control should also be implemented to deter any ecologically destructive human activities, such as fishing, littering, and wildlife feeding. The design of areas available for public usage should deter littering and avoid refuse from being discarded into the water body (e.g. seating benches and rubbish bins, if provided, should not be located near the water as refuse could be easily thrown or blown into the water body). We strongly urge the proponent to work on this regard with relevant departments such as the Food and Environmental Hygiene Department.

13. Artificial lighting at night (ALAN) may trigger physiological or behavioural changes in nocturnal organisms. Although TWN is in an urbanised area, the project proponent should endeavour to protect the quality of habitats for nocturnal animals which are inhabiting/attracted to the revitalised area by minimising light pollution caused by ALAN. Mitigation measures such as minimization, appropriate shielding and filtering of light sources to the appropriate spectrum, should be considered during the detailed design stage.

Thank you very much for your kind attention. For any inquiries, please contact the undersigned (T: 3961 0200, F: 2384 4204, Email:

Yours sincerely,

YUEN Yan Ling, Elaine
Conservation & Research Manager
Green Power

Yours sincerely,

YUEN Yan Ling, Elaine
Conservation & Research Manager
Green Power