Yuen Long Bypass Floodway affected some fishponds and agricultural land. To compensate for the ecological loss, DSD engineered a piece of wetland with an area of 7 ha (i.e. 70,000m2 equivalent to 10 full size soccer pitches) from 3 abandoned fishponds, providing wetland habitat to wild birds, amphibians (frogs) and dragonflies.
View of Wetland
The engineered wetland mainly comprises 3 main ponds, 1 seasonal shallow pond and 1 permanent shallow pond. In addition, there are also crushed brick field, oyster shell field, reedbed and 1 deep pond as well. Outside the wetland, at the downstream of the Yuen Long Bypass Floodway, DSD has also created a shallow pond within the new river channel. Inside the engineered wetland and the channel shallow pond, various aquatic plants and different species of weeds and trees are planted extensively. Along the south of the engineered wetland, there is a bamboo cluster to attract herons.
The construction of the engineered wetland and channel shallow pond commenced in January 2003 and was completed in end 2005. After one year of establishment, a sustainable ecological habitat has been developed.
Wetland - Sedimentation Pond, Crushed Brick Field and Oyster Shell Field
- Sedimentation Pond
The water from the low flow channel of the Yuen Long Bypass Floodway first enters into the sedimentation pond so that solid particles in the water, e.g. sand, will settle.
- Crushed Brick Field and Oyster Shell Field
The water then flows into the crushed brick field and the oyster shell field for natural filtration and purification so as to reduce the nutrient in the water, and thus inhabiting the development of algae boom.
Sedimentation Pond, Crushed Brick Field and Oyster Shell Field
Wetland - Reedbed
- An area of 7,500m2
- After treatment by the crushed brick field and oyster shell field, the water is equally distributed into 4 reedbeds where the reeds further absorb the nutrient from the water.
- The reedbed is also one of the ecological habitats of the engineered wetland. It breeds different species of invertebrates such as worms and snails etc. and, as a result, it further attracts birds to forage and inhabit.
Wetland – Main Pond and Deep Pond
- 3 Main Ponds (depth about 1.4 – 1.8 m)
- The bevelled bank of the main ponds provide different water depth and there are marshes and land habitat. We have planted 20 species of a total of about 180,000 numbers of water plants to attract various wildlife such as coots, egrets, small birds, dragonflies and frogs etc to inhabit.
- Deep Pond (depth about 2 m)
The function of the deep pond is to store the surplus water discharged into the engineered wetland for subsequent water level adjustment in the various ponds. The outfall of the deep pond can discharge the surplus water into Kam Tin River. The exposed mud at the bottom of the pond in the dry season is another ecological habitat.
Wetland – Shallow Pond (depth about 0.5m)
- Seasonal shallow pond provides habitat for amphibians (frogs) to lay egg and tadpoles to grow.
- Permanent shallow pond provides habitat to dragonflies’ larvae to grow.
Channel Shallow Pond
- At the downstream of the Yuen Long Bypass Floodway, 350 m in length with an area of 1.8 ha (equivalent to 18 full size swimming pools).
- The bed of the shallow pond is designed to be lower by 0.3 m and allow ponding of water to become a shallow pond.
- Different aquatic plants at the riverbed and river bank also form a wetland ecological habitat.
Egrets in Channel Shallow Ponds
Achievements up to 2009-2010
- The engineered wetland had been handed over to Agriculture, Fisheries and Conservation Department (AFCD) in Dec 2006 after 1-year establishment by DSD, and was currently managed and maintained by AFCD.
- The water quality objectives and standards were generally achieved demonstrating that the reedbed filter was effective.
- Since the establishment of the wetland, a total of 118 species of birds have been recorded within the engineered wetland. In addition, a total of 21 species of dragonflies, 30 species of butterflies, 7 species of amphibians and 4 species of reptiles were also recorded including 7 uncommon species of butterflies in Hong Kong.
- A total of 130 plant species were recorded in Sep 2009, of which 68% were native species.