Estuary Processes and Managment - River Dynamics and Integrated River Management - page 537

million. The goal of this project is to restore the physical form of the historical rivers and reestablish the
natural functions. It is planned that once the hydrology is restored to approximate pre-channelized conditions,
the water quality will improve, with return of native vegetation such as pickeral weed and other broadleaf
marsh plant species. Once the habitat is restored, it will only be a matter of time before the wildlife
communities rebound (http://www.dep.state.fl.us). Beginning in 1999, a number of activities associated
with the project—including ecosystem restoration, restoration evaluation, aquatic plant management,
land management, water quality improvement, and water supply planning—have been carried out. These
restoration measures have produced good results—for example monitoring showed that the diversity of
birds in the restored areas has increased tremendously (https://my.sfwmd.gov).
8.6.3 Wetland Construction and Protection
In this section, we introduce two examples in Hong Kong that illustrate the importance attached to
wetland conservation in an urban environment. The engineered wetland constructed for the Yuen Long
Bypass Floodway (YLBF) project is first introduced as an example of environmental compensation and
enhancement for an engineering project. As a second example, the environmental litigation relating to the
environmental impact assessment of the proposed Sheung Shui-Lok Ma Chau Spur Line in 2001 is presented
to illustrate issues of ecological preservation against transport needs in urban development.
8.6.3.1 Engineered Wetland of Yuen Long Bypass Floodway, Hong Kong
Yuen Long town (population 341,000) is located in the northwestern part of the New Territories, Hong
Kong; it is a satellite town developed in the middle 1980s. The runoff from the steep upstream catchment
is drained into Deep Bay (Shenzhen Bay) through the Yuen Long town via three river channels: Yuen Long
Main Nullah, the Sham Chung Channel, and the San Hui Nullah (Fig. 8.82). The concrete channel system
built in the 1960s is not able to protect Yuen Long from serious flash floods at times of severe rainstorms.
For example, during Typhoon Brenda in 1989 road links to the rest of Hong Kong were flooded, thus
causing social and economic losses due to disruption of economic activities. The serious flooding in
1998 and 2000 had also caused major traffic disruptions to the Yuen Long Town, and in particular the
Light Rail Train service was suspended.
The Yuen Long Bypass Floodway (YLBF) was designed to protect Yuen Long town from flooding (e.g.,
Arega et al., 2008). The concept was for the YLBF to intercept flows from the Sham Chung Channel, the
San Hui Nullah, and part of the flow from the Yuen Long Main Nullah away from the town into the Kam
Tin River (Fig. 8.82). The drainage capacity of YLBF is 385 m 3 /s (200-year flood) (Wong et al., 2006);
the HK$470 million project was commissioned in 2006.
A number of river restoration features are built into this flood control project. Using an innovative
“green channel, ecological channel” concept, the YLBF was designed to simulate a natural lively river
system (Wong et al., 2006). First, the floodway meanders in the downstream, more rural sections of the
Floodway, with bends and different flow regimes, e.g., shallow ponds (area 18,000 m 2 ) and wetland.
Second, substantial greening work has been carried out to create a pleasant environment. The channel
bottom and slope is paved by cellular reinforced concrete paving (52,000 m 2 ) which contains many pockets
of soil on which vegetation of different species are planted. Third, as environmental compensation and to
enhance the ecological value of the project, an engineered wetland (Fig. 8.82, 8.83) has been constructed
from abandoned fields and fishponds near the downstream of YLBF and with an area of 7 hectares (i.e.
the size of 10 standard football fields). The engineered wetland consists of sedimentation ponds, crusted
brick fields, oyster shell fields, reed beds, 2 shallow ponds, 3 main ponds and 1 deep pond. The flow from
the YLBF is naturally filtered on passage through the crusted bricks and oyster shells, and purified through
the reed beds (nutrient uptake by plant growth), before it flows into the different ponds. The shallow