Advisory Council on the Environment

Report of the 66th and 67th Environmental Impact Assessment Subcommittee Meetings

(ACE Paper 5/2002)
For advice


At its meetings on 28 January and 7 February 2002, the Subcommittee considered the following EIA reports-

  1. EIA report on the widening of the Yuen Long Highway between Lam Tei and Shap Pat Heung Interchange; and
  2. EIA report on Sheung Shui to Lok Ma Chau Spur Line -Tunnel/Viaduct Option.


2. Members are requested to advise whether the two EIA reports should be endorsed.


EIA report on the widening of the Yuen Long Highway between Lam Tei and Shap Pat Heung Interchange
(ACE-EIA Paper 1/2002)

3. According to the EIA report, the section of Yuen Long Highway needs to be widened to cope with the anticipated increase in traffic after the opening of the Shenzhen Western Corridor and Deep Bay Link, as well as the rise in traffic due to the increasing population in North West New Territories. The project involves the widening of a 7-km long section of road from a dual-2 lane to a dual-3 lane carriageway together with associated works to interchanges, slip roads and structures. The works will be carried out within the reserve of the existing road and would not cause disturbance to adjacent area.

Views and Recommendations of EIA Subcommittee

4. Members agreed that there was no need to discuss the EIA report at meetings and the report should be endorsed without conditions in view of the findings of the assessments and the recommendations on mitigation measures to address air quality impact, noise impact as well as visual and landscape impacts arising from the project.

EIA report on Sheung Shui to Lok Ma Chau Spur Line - Tunnel/Viaduct Option
(ACE-EIA Paper 2/2002)

5. The project proponent explained at the meetings that the Spur Line was needed to relieve the congestion at Lo Wu and to serve the future Kwu Tung North New Development area. The tunnel/viaduct option was recommended after taking into account of the judgment handed down by the EIA Appeal Board in July 2001 on the appeal relating to the EIA report on the viaduct option of this project. According to the views of the Appeal Board, only three alternatives were considered reasonable and practicable, viz. the original viaduct alignment, the tunnel option and the Northern Link. The project proponent had therefore revised the construction method under which the Spur Line would involve a tunnel section to avoid the Long Valley. The tunnel would travel through Long Valley, Kwu Tung and Chau Tau and climb to a viaduct running from Chau Tau to Lok Ma Chau

Views and Recommendations of EIA Subcommittee

6. Members' concerns on the project were mainly on the soundness of the SEEP/W model that was used to study the impact of the tunnel on the groundwater system of Long Valley; the adequacy of data on which the hydrological models were based; whether the number of piezometers to be installed were sufficient to ensure reliable baseline hydrological information; the limitation of the monitoring parameters; whether trial tests had been done to validate the predictions of the hydrological models; the possible contamination of the groundwater by the construction materials used; the baseline survey on species of ecological importance; whether Town Planning Board (TPB) Guidelines for Application for Developments within Deep Bay Area were complied with; the issue of on-site versus off-site mitigation; the definition of ecological functions and carrying capacity of fishponds concerned; and the effectiveness of the proposed measures to double the carrying capacity of the fishponds at Lok Ma Chau. Details were summarized in the ensuing paragraphs.

The SEEP/W model

7. On the soundness of the SEEP/W model, the project proponent clarified that the model was a commonly used 2-Dimensional model to analyze groundwater movement and pore-water pressure distribution within porous materials. In the assessment, the movement of ground water at Long Valley was modeled and compared. It was found that the ground water movement was dominated by the main aquifer. As the tunnel would be located in the much less permeable "completely decomposed tuff" layer underneath the aquifer, the construction of the tunnel as well as the future operation of the railway would unlikely affect the movement of the groundwater. The results of the analysis showed that the water table remained unchanged with or without the tunnel except for a 10mm variation at a section north of the tunnel alignment which was considered negligible.

Data on which the hydrological models were based

8. Some Members noted that the data on which the hydrological models were based seemed to be incomplete and that "an additional definitive dry-season record has still to be run". The project proponent clarified that a set of 21 additional piezometers had been installed by November 2001 and that the Neap and Spring tide data from them was presented in the EIA report. Further, both the wet and dry season peizometric data showed a significant tidal influence in the Long Valley groundwater regime. The monitoring would continue during the project implementation stage.

Groundwater monitoring and surface settlement

9. On groundwater monitoring, the project proponent explained that the installation of five peizometers at each of the four sections within Long Valley would be sufficient to characterize the water table along the tunnel. When the piezometer readings reached 300mm above the lowest level for Neap tide dry season, groundwater augmentation actions would be taken. If those actions could not achieve the required minimum groundwater level, a fall back action would be to raise the downstream fabridam operated by the Water Services Department so as to impound River Beas and River Sutlej thereby flooding the alluvial aquifer across the Long Valley floor. The project proponent also assured Members that sufficient settlement markers would be installed to monitor the surface settlement.

Limitation of the monitoring parameters

10. A Member expressed concerns about the limitation of the monitoring parameters and considered that the designed acceptance criteria which defined the allowable fluctuation of the operating parameters and which facilitated the monitoring of the contractors' work should be provided. The project proponent agreed to consider the proposal when drawing up the monitoring programme.

Trial tests

11. On trial tests, the project proponent pointed out that the Tsing Tsuen Tunnel which was constructed by the same tunneling method and in soil conditions that were even more difficult than Long Valley and which was proved highly successful would serve as the best trial test Against a predicted settlement of below 25mm, only 16mm of surface settlement was recorded in the Tsing Tsuen Tunnel and there was no change in the water table.

Possible contamination of groundwater

12. On possible contamination of the groundwater, the project proponent clarified that the tunnel-boring machine would only use a biodegradable and non-toxic foam to facilitate the breakdown of materials during the tunneling operation. The foam, which had been tested and used in the construction of the Tsing Tsuen Tunnel, would not contaminate the groundwater.

Baseline surveys of species of ecological importance

13. A Member raised his concern that the butterflies reported in the ERM Report were not found in the baseline surveys for this project. The project proponent clarified that though the ERM Report was published in 1999, the list of rare butterflies was derived from a review of published and unpublished records. Those records were collected over 20 years ago and the woodland habitat concerned had degraded since that time, hence those butterfly species were considered to be no longer present. The present EIA was based on the results of the recent baseline surveys.

Compliance with relevant Town Planning Board (TPB) Guidelines

14. AFCD officer commented that in considering developing proposals in the Deep Bay Area, the TPB Guidelines adopted the principle of "no-net-loss in wetland". Specifically, paragraph 6.1 of the Guidelines mentioned that "New development within the Wetland Conservation Area would not be allowed unless…. the development is an essential infrastructural project with overriding public interest. Any such development should be supported by an ecological impact assessment to demonstrate that the development would not result in a net loss in wetland function and negative disturbance impact." The issue would hinge on whether Members considered the proposed project an essential infrastructural project with overriding public interest.

On-site compensations

15. On the issue of mitigation for the loss of 9.1 hectares of fishponds in Lok Ma Chau due to the construction of the station, the project proponent pointed out that they had explored the Lok Ma Chau area to provide on-site mitigation. Off-site compensation was not considered because according to the Technical Memorandum on EIA process, all practicable on-site ecological mitigation measures should first be exhausted. As land was not available on-site in Lok Ma Chau area for wetland restoration, the EIA report recommended compensating the loss of fishponds by enhancing the ecological functions of 27.1 hectares of existing fishponds in the same area. AFCD officers further pointed out that the compensation ratio so achieved was comparable to overseas practice.

Definitions of ecological function and carrying capacity

16. Some Members had different views from the project proponent over the definitions of "ecological value" and "carrying capacity" of wetland habitats. They considered that whilst the observed number of birds might give an indication of the carrying capacity of a habitat, the intrinsic "carrying capacity" of a habitat depended on its productivity (for food; or space for making nests, etc). If the total productivity remained constant, concentrating the resources in a small area would no doubt give an observed increase in bird number in that area but not real enhancement in the "carrying capacity".

17. The project proponent explained that the ecological value of the commercial fishponds laid in its being a source of food to certain species of water birds and hence an important foraging habitat for these birds. "Carrying capacity" was regarded as the maximum number of individuals that could be supported on a given area of habitat. The proposed mitigation measures therefore aimed to enhance the existing 27.1 hectares of fishponds by raising their carrying capacity for target species and hence their ecological value. The objective was to achieve an increase in bird usage by enhancing the fishponds concerned during construction and after the completion of the project on a long-term basis so as to compensate for the loss arising from the construction of the Lok Ma Chau station.

Effectiveness of the proposed measures

18. Some Members did not have full confidence that the proposed measures would, in balanced probability, double the ecological value and the carrying capacity of the fishponds in question. They were concerned about the availability of concrete plans to monitor the performance of the proposed works and actions that would be taken if the proposed measures failed to deliver the required results. One Member cautioned that draining down of fishponds too frequently might increase the acidity of the habitats. Having regard to the proponent's track record in the West Rail project, several Members were doubtful about the proponent's ability as far as environmental performance was concerned.

19. To facilitate the discussion, AFCD officers pointed out that the ecology of fishponds in Hong Kong, including their functions and value, was well studied. It was widely recognized that the drain-down of commercial fishponds for fish harvesting provided important feeding opportunities for water birds. However, the commercial practice of draining down a fishpond as quickly as possible would affect its ecological value for particular bird species. In addition, commercial fishponds were only drain down annually for a short period of time and provided a relatively uniform habitat.

20. AFCD officers explained that there were proven records of using habitat management measures to enhance the carrying capacity of wetland habitats. The most widely known case was the management plan of the Mai Po Nature Reserve. In addition to draining down the fishponds, other measures proposed by the project proponent included the clearance of bund vegetation, stocking of trash fish, adjustment of the water quality and water level, as well as re-profiling of the fishponds to better suit the water birds. The project proponent also emphasized that they had a detailed management plan for the enhanced fishponds to ensure that the birds affected would continue to use the area on a long-term basis. The standards to measure the performance of the management measures would be included in the Environmental Monitoring &Auditing Manual to be compiled in due course.

21. A Member raised the concern that fish farming was quickly phasing out in Hong Kong. A large number of commercial fishponds in Lok Ma Chau had in fact been left unattended. In his views, the fishponds would provide little value, if any, to bird species in the long run. On the other hand, the management measures proposed in the EIA report would better preserve the fishponds and enhance their values as habitats for the water birds. Instead he cautioned that too many birds might be attracted to the area because of the management measures and that a proper balance should be maintained. In assessing the effectiveness of the proposed management measures, the project proponent considered that the current commercial fishponds should be used as the baseline and that there would be long-term monitoring on the results of the proposed measures.

22 On monitoring the environmental work of the project, the project proponent pointed out that they would set up an Environmental Committee, chaired personally by the Senior Director of Capital Projects and comprising the contactors and all stakeholders, to ensure that there would be a high standard of performance.


23. The Subcommittee concluded that apart from the impacts of the tunneling work on the hydrology of Long Valley, the effectiveness of the proposed management measures to mitigate for the loss of 9.1 hectares of fishponds arising from the construction of the Lok Ma Chau station was the key concern of Members. After lengthy discussion, Members agreed that the whole issue boiled down to whether it was believed that the proposed management measures for the fishponds in Lok Ma Chau would have a high chance of success. If not, Members' concern was whether conditions could be imposed to require the proponent to compensate for the loss of the fishponds. After further discussion, the Subcommittee agreed that consideration should be given to impose the following conditions on the project proponent-

  1. the project proponent should consult the Council on the EM&A Manual to be compiled and report regularly to the Council on the progress of the monitoring work and the findings; and
  2. if the proposed management measures failed to deliver the specified results, the project proponent should be required to implement further compensation measures for the loss in fishponds. A possible way is to acquire additional land to compensate for such loss.

EIA Subcommittee Secretariat
February 2002




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