Yuen Long Bypass Floodway (YLBF)
|Low Flow Pumping Station & Inflatable Dam|
Beauty of Engineered Wetland
Shallow Ponds & Green Channel
Flooding of Yuen Long in the Past
Yuen Long is a low lying area. The rapid urbanization in the past decades has increased the surface runoff. At the same time, the flood storage from the flood plain and fish ponds has diminished. The existing Yuen Long Nullah built in the past cannot cope withthe increased flow. As a result, flooding occurredfrequently during heavy rainstorms causing disruption to social activities.
Yuen Long Bypass Floodway
Yuen Long Bypass Floodway is constructed to mitigate flooding in Yuen Long Town and its peripheral village areas. Yuen Long Bypass Floodway is a 3.8 km long large drainage channel built at the South of Yuen Long Town to intercept 40% of the runoff in the Yuen Long catchment. The intercepted flow is diverted to the downstream of Kam Tin River and then discharged to Deep Bay. This engineering solution is cost-effective and can avoid major construction activitiesin Yuen Long Town, and hence disruption to the traffic and living of Yuen Long residents.
The Bypass Floodway has incorporated a series of environmental designs. Its flow is not carried straightly to the sea but passing through different regimes including bends, shallow ponds and wetland. The channel bottom and slope are covered by different species of herbaceous plants to provide a natural riverbank with aesthetic and ecological value. A system of dry weather flow pumping station and inflatable dam is provided at the downstream end to control the water level of the Bypass Floodway and to prevent polluted water downstream from flowing back into the Bypass Floodway.
Engineered Wetland and Greening Work
The project includes the construction of a 7 hectares engineered wetland near the downstream and 3 shallow ponds within the downstream channel. Greening works carried out along the Bypass Floodway and in the engineered wetland include planting of 13,000 trees, 140,000 shrubs and 550,000 herbaceous plants.
The engineered wetland mainly consists of 3 main water ponds, a seasonal shallow pond and a permanent shallow pond. There are also crushed brick andoyster shell ponds, reed beds and a deep water pond within the wetland. The dry weather flow of the Bypass Floodway, after purified by passing through the oyster shells, crushed bricks and reed bed, flows into the engineered wetland toofferan ecologically enriched habitat for the wild birds, amphibians and dragonflies.
Managed by a professional team of the Agriculture, Fisheries and Conservation Department since December 2006, the engineered wetland has already developed into a sustainable ecological habitat. Continuous monitoring has shown great biodiversity with over 130 plant species and various species of birds, frogs, insects and bats.
Awards and Recognition
Through the application of innovative ideas for continuous improvements, and the continuous efforts and cooperation of the engineering team, Yuen Long Bypass Floodway was successfully completed in 2006. The Yuen Long Bypass Floodway was well supported and recognized by the other government departments, academic bodies, green groups and the general public, and was honored the Champion in Innovation Award and Cost Effectiveness Award of the Civil Service Outstanding Service Award Scheme 2007.
Yuen Long Bypass Floodway Project Information
|1. 3.8 km long main drainage channel from Sham Chung Tsuen to Kam Tin River;
2. An inflatable dam and a low flow pumping station at the downstream end of the bypass floodway;
3. 18 box-culverts;
4 Roads with associated drainage and water works along the bypass floodway;
5. 7 hectares engineered wetland; and
6. Landscaping work with about 700,000 no. of plants.
HK$470 million (civil andE&M works)
|Design Flow Capacity||317 m3/s|
|Width of Channel||Upstream end : 13 m (rectangular channel)
Downstream end : 50 m (trapezoidal channel)
Dry Weather Flow Pumping Station
|Screw Pump : 3 no. (1.5m dia.)
Dry Weather Flow : 0.9 m3/s