3. Engineered Wetland

A 7-hectare engineered wetland is provided near the downstream area of Yuen Long Bypass Floodway. The wetland was built from three abandoned fishponds, with an area equivalent to 10 football pitches, to compensate for the loss of fishponds and farmlands and to provide a habitat for birds, frogs, bats and dragonflies. A bamboo grove was also planted to the south of the wetland to attract egrets.

Human activities such as operating restaurants, car-repair workshops and farming leave food debris, chemicals, fertilizers and pesticides on roads or soil. During rainstorms or street cleaning, these pollutants will be washed into Yuen Long Bypass Floodway directly or through stormwater drains. Such pollutants, which are not from fixed locations, result in "non-point source pollution".

A natural ecological system automatically serves mankind through various "ecological services", such as provision of oxygen and degradation of pollutants. The engineered wetland purifies the flow of Yuen Long Bypass Floodway by natural process. The wetland consists of three Main Ponds, a Deep Pond, a Seasonal Shallow Pond, and a Permanent Shallow Pond. The water is pumped through ponds with crushed bricks and oyster shells to deposit and filter out suspended solids, while the nutrients are absorbed by reedbeds. The water then flows through some ponds for further purifications by the wetland ecosystem before discharging to Kam Tin River.

Overlook of the engineered wetland

Ponds with crushed bricks and oyster shells

Reedbeds

Water Lily pond in the engineered wetland

Non-point source pollution from stormwater drains