Environmental Impact Assessment Report on Shenzhen River Regulation Project Stage III

(ACE Paper 19A/2000)
For discussion

This paper supplements ACE-EIA Paper 6/2000 and ACE Paper 19/2000 regarding the Shenzhen River Regulation Project Stage III. The key findings and recommendations of the Environmental Impact Assessment (EIA) study for Shenzhen River Regulation Project Stage III (the Project) were presented to and discussed by the ACE EIA Subcommittee at its meeting on 8.5.2000. Whilst the Subcommittee endorsed most of the findings and recommendations on various environmental mitigation measures subject to certain conditions on post-project monitoring and preservation of the Lo Wu Railway Bridge, the project proponent was requested to re-examine the recommended disposal option with a view to reducing the amount of material to be filled in Nam Hang by exploring other suitable local disposal sites for the consideration of ACE. This paper describes the background of the disposal problem, the alternatives considered, the justifications for disposing the excavated material in Nam Hang and the scope for reducing the amount of soil filling in Nam Hang.

Need for Disposal

2.The Project involves improvement works to the stretch of Shenzhen River of about 4km between Lo Wu and its confluence with Ping Yuen River. Excavation is necessary for enlarging the river channel to achieve the design flood conveying capacity. Measures to reduce and reuse the excavated material have been considered in the EIA study and suitable excavated material will be used for forming the embankment on both sides of the river channel as far as possible. Apart from this, about 1.6Mm3 of excavated material will become surplus and has to be disposed of, out of which 0.2Mm3 is contaminated. The EIA report recommended that the 0.2Mm3 of contaminated material will be disposed of at East Sha Chau; about 0.5Mm3 of uncontaminated material will be disposed of on site in Nam Hang Middle Valley (see Annex 1 for location of the valley) adjacent to Shenzhen River; and the remaining 0.9Mm³ will be disposed of in NeiLingDing Marine Dumping Ground in the Mainland.

Alternatives Considered

3.Six disposal schemes have been identified and assessed varying from total marine disposal by barges to the Pearl River delta to total terrestrial disposal within or immediately adjacent to the site. Neither of the extremes is desirable from the environmental, economic and construction programme point of view and the preferred option must be able to satisfy the following conditions:

1. Environmentally acceptable;
2. Minimum construction time to achieve early protection against loss of human life and damage to property due to flooding; and
3. Minimum financial commitment (i.e. minimum construction cost)

4.The recommended option of disposing one third on land and two thirds to sea has proved to be environmentally acceptable, is a realistic compromise amongst all factors and offers much needed flexibility to the construction process.

Justifications for the Use of Nam Hang Middle Valley

Problems on Access

5.The site for Shenzhen River Regulation Project Stage III is located at the boundary area between the Shenzhen Special Economic Zone and the Hong Kong Special Administrative Region. It is surrounded by the urban city of Shenzhen in the north and by a series of hillside and the Sandy Ridge Cemetery of Hong Kong in the south. The only land access from Hong Kong is via the Man Kam To boundary control point and land access from Shenzhen is through the busy commercial area of the Lo Wu district. Transportation of the excavated material off site by land will cause an unacceptable impact on the already congested cross boundary traffic in Man Kam To and the busy traffic in Lo Wu. The relevant boundary control authorities of the Hong Kong side (i.e. the Police, Immigration and Customs) have strongly objected to the proposal of exporting the excavated material through Man Kam To as frequent passage of lorries through the boundary control area will cause unacceptable boundary control and security problems. Marine transportation is therefore the only feasible solution for off site disposal. Unfortunately, the existing river within the Stage III site does not offer suitable marine access and the improved river will only possess limited capacity for marine transportation because of the constraints imposed by the small headroom of the bridges at Lo Wu, which would only allow one way passage of small barges.

Effect of total export of material via marine access

6.Due to the constraints at Lo Wu, total export of the excavated material via marine access, if adopted to replace the EIA recommended option as mentioned in paragraph 2 above, would cause the construction time to increase by about 17 months. This is unacceptable from the flood control point of view as the much needed early flood relief to people of both sides cannot be achieved. Previous flooding incidents and the recent flooding on 14.4.2000 due to heavy rainstorm caused extensive damage to properties and interruption to the cross boundary traffic and living of people of both sides. Water discharge from the Shenzhen Reservoir would also aggravate the flooding in the river and its catchments upstream of Lo Wu. Delay in completion of the Stage III works would not be acceptable by the general public. Both the LegCo and District Board have urged the government to start the Project early to resolve the flooding problem. Besides, the cost of total export via marine access would be high due to long haulage.

Environmental Acceptability

7.In order to overcome the programme constraint, the feasibility of on-site disposal in the three valleys on the Hong Kong side lying between Lo Wu and Man Kam To was explored (see Annex 1 for location of the valleys). The EIA study showed that the in-filling of either of the two larger outer valleys would entail significant loss of good wetland including freshwater marsh and fishponds, together with significant woodland habitats and some derelict ephemerally wetted agricultural lands. The Nam Hang Middle Valley was considered to be an environmentally acceptable option but with less filling capacity.

8.The proposed Nam Hang Middle Valley in-filling will cause the lost of the river meander, a part fishpond remnant (after construction of the river embankment), an area of very low lying freshwater marsh (adjacent to the river) and a small area of ephemerally wetted derelict agricultural land surrounded by variously vegetated slopes. The woodland, vegetated slopes and grassland surrounding the derelict agricultural land in the valley floor are subjected to frequent fire as the area is surrounded by an active and expanding cemetery site. Most of the slopes have been benched and pre-excavated for burials. During the EIA study, a major fire over the Chung Yeung festival period razed all trees and vegetation on the slopes in question south of the security fence. The ecological value and potential of the middle valley is thus the least of the three valleys. This together with the increasing likelihood of further fires as the cemetery expands have led to its selection for disposal of surplus excavated material. The Nam Hang middle valley proposal does not entail any loss of significant wetland or woodland habitat.

9.The ecological value of the whole area has been carefully appraised. Significant fishponds, marsh and mature woodlands have been identified in the two outermost valleys. The eastern valley will be preserved. The commercial bloodworm ponds and their observed feeding value for avifauna have been upheld. The fishponds in the western valley will be taken over and reprofiled for ecological enhancement, producing a well-balanced valley area with all types of ecologically valuable habitats buffered on all sides. The enhancement will make it particularly suitable for roosting and foraging of avifauna.

10.Other environmental impacts caused by the soil filling in Nam Hang Middle Valley include water quality, air quality, visual and landscape, noise, and development constraints. These were assessed in the EIA study. With the necessary mitigation measures in place, there would not be any unacceptable environmental impact and there is no net ecological loss. Hence the proposed disposal scheme is environmentally acceptable. The in-filled valley would be planted with 4.8 ha of trees to enhance the ecological value and to improve landscape. The woodland will be carefully designed to prevent fire damage and to increase biodiversity by careful selection of species. The established woodland would also provide an effective ecological linkage between the preserved eastern valley and the enhanced western valley.

Considerations in spoil disposal

11.The use of Nam Hang Middle Valley for disposal of surplus excavated material is in line with the practice of spoil disposal in Hong Kong in which marine dumping should be undertaken if there are no other better and practical land based environmentally acceptable options. This is also in line with the approach adopted in the EIA Study for Stage II of the Shenzhen River Regulation Project, in which spoil was disposed of at Lok Ma Chau (land based disposal) prior to disposal in NeiLingDing (marine based disposal).

Scope for Reducing the Amount of Soil Filling in Nam Hang Middle Valley

12.The beneficial use of the excavated materials has been considered. Suitable excavated material will be used for forming the embankment on both sides of the channel as far as possible. Surplus material that is unsuitable for engineering purpose would need to be disposed of in marine dumping ground. Other surplus material contains a high proportion of silt/clay and can only be used as public fill for reclamation and the nearest public filling area is in Tuen Mun. However, land transportation of the excavated material to Tuen Mun will cause an unacceptable impact on the already congested Man Kam To boundary traffic as mentioned above. For marine transportation, the constraint at Lo Wu will cause a major problem on the construction programme similar to the total export option. In fact, any proposal for the beneficial use of the excavated material in both Hong Kong and Shenzhen will be seriously restrained by the access problems similar to the total export of material via marine access.

13.The scope for reducing the scale of soil filling in the Nam Hang Middle Valley is rather limited mainly due to the access problem and the associated environmental impacts caused. The habitat affected is situated mainly on the valley floor and the extent of habitat loss is not proportional to the scale of soil filling. Any reduction in soil filling would have an impact on the construction programme while a substantial reduction would cause an unacceptable delay to the completion of the Project. According to the programme, however, the tentative works completion date of September 2004 is quite near the end of the wet season of year 2004. The completion can possibly be extended to the onset of the following wet season. With this flexibility, it is possible to export part of the material and to reduce the filling quantity in the Nam Hang Middle Valley by about 100,000 m3. The material can be disposed of in the public filling area in Hong Kong such as Tuen Mun via marine transportation.

14.This modified disposal scheme is essentially the same as the recommended disposal option in the EIA report but with reduced amount of soil filling in the Nam Hang Middle Valley. It has similar environmental impact but with the completion of the channel work delayed to before the onset of the next wet season (see Annex 2 for comparison of completion time for various disposal options). It should however be stressed that there are many uncertainties in commencing the Project on time and the construction of a project of such scale and nature would be highly susceptible to delay. Any slippage would render the works completion to go beyond the onset of the wet season, which would be highly undesirable from the flood control point of view. The construction cost would also be higher due to longer haulage.

Conclusion

15.The Shenzhen River Regulation Project Stage III is a unique project located in the boundary area with very limited marine access for transportation of excavated materials. In order to resolve the construction difficulties and the programme constraints, the use of Nam Hang Middle Valley for the disposal of surplus excavated materials is essential. With the EIA study recommended mitigation measures and the restoration plan fully implemented, the impact of the disposal in the Nam Hang Middle Valley can be mitigated to within an acceptable level. Although it is feasible to reduce the amount of soil filling in the Nam Hang Middle Valley from 0.5Mm3 to 0.4Mm3, it will not result in any significant improvement to the environmental performance of the scheme nor any benefits to the cost and programme.

Endorsement Sought

16.Members are requested to endorse the option for the disposal of surplus excavated materials arising from the Project as recommended in the EIA report.

Attachment

Annex 1 - Location plan of Nam Hang Valley

Annex 2 - Comparison of completion time for various disposal options

Drainage Services Department
May 2000