A Green Focus
The Environment is Hong Kong's important asset. DSD is fully committed to integrating environmental protection and sustainable development principles into our plans and operations. Three of our new projects - the Yuen Long Bypass Floodway, Rehabilitation of Ping Yuen River and Ngong Ping Sewage Treatment Works, illustrate our endeavours in fulfilling these goals. These projects place particular emphasis on enhancing biodiversity and integration of the works into the surrounding environment.

Yuen Long Bypass Floodway
The Yuen Long Bypass floodway is a new channel constructed to divert storm water from south east of Yuen Long into Kam Tin River to reduce flood risk in Yuen Long town centre and other lower lying areas. In recognizing the value of biologically diverse community at the lower reach of Kam Tin River, this flood prevention project will incorporate two major ecological features - an artificial wetland and in-channel shallow ponds.

Artificial Wetland
Several fallow fish ponds in the north of the confluence of the Bypass Floodway and Kam Tin River will be enriched to become 7.9 ha of wetland, comprising 6.4 ha of marshes of varying depths, 1.2 ha of reedbed and 0.3 ha of crushed bricks.

Differential depths sustain a diversity of ecological niches. The deeper marsh provides habitat for large fishes and the associated bird community, while the shallower submerged marsh will be ideal as foraging grounds for wading birds. Planting of marsh vegetation will jump start the plant establishment process which will lead to colonisation of the wetland by insects, aquatic invertebrates, fishes, amphibians, reptiles and birds. The biodiversity of the created wetland will thus be a quantum leap from that of the original fishponds.

The reed bed will receive the flow from the channel through an area of crushed bricks that acts as a biofilter to break down organic matter. The reed bed further serves as an effective purifier which assimilates nutrients. Passage of flow over the boulder area and the reed bed therefore gives a steady supply of clean water to the marshes.

Two bat roosts will also be constructed in the wetland to encourage habitation of this type of flying mammal.

Ecologically important animal life attracted to the YLBF wetland will include damselflies, spotted narrow-mouth frog (Kalophrynus pleurostigma), bats such as Japanese Pipistrelle, birds both resident and visitors such as egrets, pond heron, Stints, and the endangered Black-faced Spoonbill.

Shallow pond feature
To promote and sustain stream life, 350 m length of channel bed or about 1.2 ha of the floodway will take the form of shallow ponds that are purposely engineered to provide habitat for freshwater fish, amphibians and water birds. It is the first of its kind in Hong Kong, of a man-made waterway that serves a flood prevention purpose while specially built to become a vibrant freshwater ecosystem.

Landscape quality of YLBF is enhanced with establishment of grass on the channel base and the inner embankment on grassing concrete, giving a total of 6.8ha of greenery. About 3,000 trees will be planted along the channel to compensate for the loss of 400 trees. Grass cover and trees have tremendous environmental benefits as they reduce heat retention, provide foliage, shades and landscape features to the water edge, trap dustfall and increase habitat diversity and amenity value.

Success of this project will go a long way in providing valuable reference for future channel engineering work to c o e x i s t w i t h n a t u r e conservation.

The Rehabilitation Works at Ping Yuen River
This project includes the construction of about 1.7km long trapezoidal drainage channel aiming at alleviating the flooding problem in the Northern NT, including Chow Tin Tsuen, Lei Uk, Fung Wong Wu, Lin Ma Hang Road and Ping Che Road in Ta Kwu Ling.

Realising the remoteness of this area which has nourished a number of native species of freshwater fishes and bats, DSD has incorporated nature conservation features in the design of this flood prevention works. These include:

(a) Enrichment of new channel banks with landscape planting preferably with native species of trees and shrubs
(b) Preservation of several meanders to allow some sections of riparian and stream habitats to remain totally undisturbed.
(c) Creation of a number of shallow pools as aquatic planting bays at channel base of the new river channels; and
(d) Use of fabric geotextile-reinforced grass lining at side slopes to provide a permeable substrate that would allow ecological succession of plant communities.

Harmonising new works with the surrounding
The Ngong Ping Sewage Treatment Works serves the Po Lin Monastery, Ngong Ping Village, and the future theme village associated with the Tung Chung Cable Car ride. Construction is already underway. The landscape and social setting had been studied in detail to path way for a meticulously designed architecture that blends seamlessly into the local area.

In particular, most of the major structures of the sewage treatment works will be underground or covered. Generous planting of native woodland trees and shrubs is specified in the landscape plan to compensate for loss of any existing vegetation, to screen sensitive views and to act as an environmental benefit for local residents, workers, and visitors.

Furthermore, the choice of architectural design and finishing of the superstructures will adopt traditional Chinese elements and colours interpreted in a contemporary manner to make the sewage treatment plant inconspicuous and fit smoothly into the landscape character of the area.

The Ngong Ping STW will also be Hong Kong's first tertiary treatment plant that includes ultra fine screening and effluent disinfection by ultraviolet light. Effluent will be reused as far as practicable. Surplus will be transported away by pipeline to Tai O Creek to avoid undermining the fragile ecology of the Ngong Ping highland area.