Building Flood Resilience For Hong Kong
By Patrick L.T. Chan 18 October, 2019
The Drainage Service Department is working hard to ensure HK doesn't go underwater. Their Chan explains
The Drainage Services Department (DSD) has been implementing a sustainable drainage system with an aim to build flood resilience and improve the livability of Hong Kong to face the challenge arising from climate change.
HK frequently experiences tropical cyclones with an avg. rainfall of 2,400mm p.a.
The city frequently experiences severe tropical cyclones with an average annual rainfall of about 2,400mm, making it one of the rainiest cities in the Pacific Rim. Under this climatic setting, Hong Kong often encountered substantial flooding in the 1990s.
Past efforts and an uncertain future
To prevent flooding in Hong Kong, DSD has adopted a 3-pronged approach:
- Constructing stormwater interception tunnels upstream;
- Providing stormwater storage tanks midstream, and
- Upgrading drainage pipework downstream.
DSD’s major achievements:
1. Completed a number of major flood prevention projects – manages approximately 2,400km stormwater drains, 360km river channels, 21km interception drainage tunnels, 4 stormwater storage tanks and runs 27 village flood protection schemes; and
2. Reduced the number of flooding blackspots from 90 to 6.
Nevertheless, the city drainage infrastructure requires further enhancement to adapt to the extreme weather conditions brought on by climate change. In 2008, the peak hourly rainfall intensity surged to a record high of 145.5mm and sea level was also recorded to be rising at a rate of 31mm per decade.
HK’s drainage infrastructure requires further enhancement to adapt to climate change
In addition, rural areas were being developed for the city’s long term economic and population growth. DSD has since then introduced more sustainable solutions for the drainage system and gradually evolved the existing drainage infrastructure into blue-green infrastructure.
A sustainable drainage system, or blue-green infrastructure, mimics the natural water cycle. In contrast to the traditional urban runoff system, a sustainable drainage system promotes high evaporation, high infiltration and low surface runoff. Examples of sustainable drainage systems include green roofs, rain gardens, bioswales, retention lakes, porous pavements, water harvesting, wetlands and river revitalisation. By designing the city like a sponge, flood resilience can be incorporated into the existing drainage infrastructure.
The Anderson Road Quarry Development is a signature project with the first retention lake in urbanised area in HK
The Anderson Road Quarry Development is one of the signature projects which DSD is pushing forward the first flood retention lake situated in urbanised area in Hong Kong. The remarkable design of the lake serves both open space with landscape feature for public enjoyment on dry days, and operates with the function of flood attenuation during the wet season.
Moreover, HK’s first river park is being envisaged at Tung Chung River
Moreover, Hong Kong’s first river park is being envisaged at Tung Chung River where the public will be able to get close to the river for enjoyment. In order to balance the impact to the habitat and enjoyment of the public, passive designs such as boardwalks, viewing decks and footpaths have been planned and native vegetation will be preserved as much as possible to maintain the existing habitat. To uphold a high water quality for the Tung Chung River, biofiltration was proposed to purify the stormwater collected from the adjacent developed areas. The river park will set an example for the public to treasure rivers as crucial social and ecological resources.
In an attempt to enhance the flood prevention capacity of West Kowloon to cope with the challenges posed by climate change, DSD commissioned the “Inter-Reservoirs Transfer Scheme” (IRTS) to construct a water tunnel with a total length of about 2.8 km connecting Kowloon Byewash Reservoir and Lower Shing Mun Reservoir, which will transfer the surface runoff collected from the Kowloon group of reservoirs to Lower Shing Mun Reservoir. The IRTS project serves a dual purpose: to substantially reduce stormwater discharge into the drainage system and generate an annual additional fresh water yield of about 3.4 million cubic metres.
Drainage facilities built in early years were mainly designed for flood prevention. As times change, the public is gradually concerned with the importance of protecting water ecology and effective use of urban space. DSD has been following the recommendations put forward in the 2015 Policy Address. In both large-scale drainage improvement works and the planning of drainage networks for New Development Areas, DSD has actively introduced innovative ideas for revitalising water bodies in nullahs and river channels.
When designing river channels, DSD promotes the concept of revitalisation of water bodies to make good use of water’s character. The recently completed river improvement projects that incorporated such concepts include Ho Chung River in Sai Kung and Upper Lam Tsuen River in Tai Po, as well as the Kai Tak River Improvement Works.
Recent river improvement projects aim to increase river biodiversity to cope with the huge threats brought by climate change
Going beyond the fundamental purpose of drainage, these projects aim to increase river biodiversity and integrate the river into the surrounding environment by introducing green elements and beautifying the scenery so as to foster a water-friendly culture and promote Hong Kong’s sustainability development to cope with the huge threats brought by climate change.
1. Kai Tak river
Known as Kai Tak Nullah in the past, the approximate 2.4km Kai Tak River is one of Kowloon East’s major drainage channels. Due to urban developments and extreme weather conditions, serious flooding occurred in Choi Hung Road during rainstorms, affecting nearby residents.
Before the project began, DSD rolled out “Building Our Kai Tak River”, a two-stage public engagement programme and finalised three key design principles of the project: prioritising flood prevention, avoiding decking the channel as far as possible, and transforming Kai Tak Nullah into the first urban green river corridor in Hong Kong – Kai Tak River
Kai Tak River is now able to withstand rainstorms of a 200-year return period
Upon completion of the works, Kai Tak River meets the latest flood prevention design standards and is able to withstand rainstorms of a 200-year return period, alleviating the flood risks in associated areas.
DSD also seized the opportunity to improve the scenery of the local urban setting and provide leisure places for the public to enhance the overall living environment of the area. To this end, greening and ecological elements were included in the Kai Tak River Improvement Works to revitalise this water body into an urban green river corridor that links the river closely with the local neighbourhood.
In addition to upgrading drainage capacity, DSD has also incorporated greening, ecological conservation and water landscape elements into the projects, such as preserving the natural river habitat.
DSD introduced ecological enhancement site trials to replace concrete channels with natural river bed substrates & riparian zone
DSD introduced ecological enhancement site trials at Lower Lam Tsuen River and Ma Wat River to replace concrete channels with natural river bed substrates and riparian zone. Diverse aquatic habitats such as pools, riffles, resting ground for birds and emergent vegetation were also established to improve microhabitats and biodiversity.
The preliminary findings of the site trials are promising and show that the complexity of instream habitat and the ecological value of the river channels have improved.
3. Identifying potential nullahs & rivers for revitalisation
DSD has also reviewed and assessed the revitalisation potential of major nullahs and river channels in Hong Kong. It will select nullahs and river channels that are suitable for revitalisation. In-depth investigation is now underway on Tai Wai Nullah, Fo Tan Nullah, and Jordan Valley Nullah to identify suitable revitalisation schemes with a view to enhancing quality of living by revitalising Hong Kong water bodies.
DSD will continue to turn Hong Kong into a climate-ready and flood-resilient city. The paradigmatic change in drainage system design – from a “resistance” approach to a more sustainable “resilience” approach, is crucial for Hong Kong to adapt and face the challenge arising from extreme weather events and climate change in the uncertain future.
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