2                   Project description

2.1                 Project Details and Design Consideration

2.1.1           Improvement works at the three rivers were recommended in the “Stormwater Drainage Master Plan Study in Sai Kung, East Kowloon and Southern Lantau” (DMP Study).  The total length of Sai Kung River is approximately 1.3km from upstream grassland flowing through Sai Kung town centre before entering into the Inner Port Shelter (Sai Kung Hoi). The concerned section is 150m long which is located at the mid section of the Sai Kung River. The proposed Sha Ha Diversion Box Culvert will connect the Sai Kung River at upstream and the box culvert constructed by Civil Engineering and Development Department (CEDD) at downstream.

2.1.2           The Pak Kong River runs alongside the Hiram’s Highway before entering a road crossing under the Hiram’s Highway to Pak Sha Wan. The total length is approximately 1.32km and the concerned section is 600m long located at the downstream end of the river as stated in the Project Brief.  During the public consultation, the local residents in Pak Kong objected the drainage improvement works in Pak Kong because of the need for resumption of village houses along both sides of the river bank. The local residents requested during the public consultation to minimise the extent of works as far as possible and they would accept a higher flooding risk instead of resumption of houses. As agreed with the local residents, this project will only re-construct two bottlenecks in Pak Kong River and stabilise an existing channel slope adjacent to Hiram’s Highway.

2.1.3           The Ho Chung Channel runs alongside Ho Chung Road before passing under the Hiram’s Highway to Pak Sha Wan in the south. The total length is approximately 1.6km and the concerned section is 650m long located at the downstream area.

2.1.4           The major items of the drainage improvement works are summarised in Table 2.1 below.



Table 2.1         Summary of Project Elements



Works Programme

Dec 2005 to April 2008

Major Elements in Sai Kung River and Sha Ha Diversion Culvert

(a) Open Trapezoidal Channel

Length = 150m

Depth = 3m – 3.5m


Bank width = 16m – 24m

Bed width = 5m


Gabion walls with rip-rap bases and natural substrates

(b) Diversion Box Culverts

Length = 280m

3 cells 3m(W) x 3m(H)

(c) Low Flow Pipes

Length = 12m

3 x 600mm diameter




Major Elements in Pak Kong River

(a) Channel Widening

Length = 100m

Depth = 3m (approx.)


Bank width = 13m  – 18m

Bed width = 7m – 18m


To be reinstated by gabion blocks and concrete retaining wall

(b) Reprovision of crossings

2 numbers (1 vehicular crossing and 1 pedestrian crossing)




Major Elements in Ho Chung Channel

(a) Open Trapezoidal Channel

Length = 300m

Depth = 3.8m – 5m


Bank width = 17m  – 42m

Bed Width = 17m – 34m


Gabion walls with rip-rap bases and natural substrates

(b) Rectangular Channel

Length = 350m

Depth = 5m

Width = 17m – 25m

(c) Reprovision of crossings

4 numbers (1 vehicular crossing and 3 pedestrian crossings)

(d) Floodwall

Length = 300m

Height = 1m



2.1.5           It is noted that natural lowland and estuarine river habitats are relatively rare habitats in Hong Kong, and are known to provide habitats for a diversity of aquatic organisms.  The detailed design of the drainage improvements should reflect the potential ecological value of the existing rivers, and natural features of the rivers should be retained wherever possible.  The following ecological-friendly design has been incorporated as basic principles:

(a)             Riverbeds should not be lined with concrete: the natural stream bed and substrate should be retained. 

(b)             Riverbanks should not be lined with concrete: soft engineering materials should be utilised as far as possible. 

(c)             Natural features of the rivers (such as pool/riffle sequences) should be retained and incorporated wherever possible. 

(d)             Compensatory planting should be provided to mitigate the loss of natural riparian vegetation.

2.1.6           Environmental benefits and dis-benefits, alternative drainage options, considerations and constraints for the proposed drainage improvement works at each river were evaluated. Public consultation was also undertaken with local residents, village representatives, the Rural Committee Members, the District Council and green groups. Comments from relevant parties have been addressed and incorporated into the design of the three layouts for the drainage improvement works.

2.2                 Do-nothing Scenario

2.2.1           With the existing drainage system at its current capacity level, there is a risk of flooding during heavy rainstorms in Sai Kung. The potential consequences of such flooding include:

(i)                  Flooding will persist in Sai Kung Town Centre, downstream area of Ho Chung and Pak Kong River.

(ii)                Development in Sai Kung, Pak Kong and Ho Chung will be hindered. The existing drainage system will not provide the flood protection standard required for future development.  Further development will increase the frequency, severity and extent of flooding.

(iii)               Damage to properties, blockage of roads and accesses, nuisance to the public and risk to lives will remain.

2.2.2           If the Project does not proceed, these risks to the community in Sai Kung and Ho Chung will continue and some future development may need to be compromised. There are no simple, small-scale works that can be implemented to reduce these risks. The only effective solution to provide adequate flood relief is to implement the drainage improvement works identified in this Project. For Pak Kong, due to the reduction in scope of the works, the flooding risk will remain.

2.3                 Project Programme

2.3.1           The construction programme of the Project will commence in December 2005 and is expected to complete by April 2008.

2.4                 Interaction with Other Projects       

2.4.1           Concurrent projects with likely interaction with this Project are identified. The potential cumulative impacts have been addressed in the relevant sections of the EIA Report. The construction programmes of the concurrent projects are based on the available information at the time of the submission of this Report.