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.

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.

River revitalisation

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.

2. Ecological enhancement in rivers

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.

Further Reading

• “Basin Winner”: A Sustainable Education Board Game – Managing rivers and balancing trade-offs can be difficult but ‘Basin Winner’ makes it a lot more fun. The game’s co-developer Zhiqiang Chen from Greencity shares more on pilots and next steps
• Blue Peace Index 2019 – Water is a geopolitical risk. What is the real state of transboundary river cooperation? What are the best practices? Economist Intelligence Unit’s Matus Samel & Beth Warne introduce the Blue Peace Index (BPI) which explores these issues in 5 basins across 24 countries
• Stormwater Recovery For A Healthy Sydney – Every drop counts. Star Water’s tech to clean and reuse stormwater keeps Sydney healthy plus saves water costs. Find out how from their CEO Christopher Rochfort in three case studies
• Rising Drought Risks In The Era Of Climate Crisis – With agriculture and power most at risk from drought, what should businesses do? Can individuals push them to action? We sat down with Juliane Vatter from WWF as she expands from their latest report
• 3 Takeaways From The Fortune Global Sustainability Forum – Green is growing up with innovations for food, renewables, plastics and more on show but as China Water Risk’s Woody Chan reviews in his takeaways, there are still gaps to be filled before “business unusual” really comes to life

• Hong Kong: A Climate Resilient Sponge City – Hong Kong is prone to tropical cyclones, which will be exacerbated by climate change. Can the city become climate & flood resilient? Hear from Richard Leung from the Drainage Services Department on actions taken so far
• Confronting Storms & Climate Risk In HK – Typhoons Hato and Mangkhut have wreaked havoc in the Greater Bay Area but Dr. Faith Chan from the University of Nottingham Ningbo believes these climate risks can be confronted, with Hong Kong leading the way
• Hot, Thirsty, Sweaty & Wet: HK’s Future Down The Drain? – China Water Risk’s Woody Chan & Debra Tan look beyond current tensions and see very real threats to Hong Kong’s future from climate change. Get ready for a hot, thirsty, sweaty & wet future
• Thirsty And Underwater: Rising Risks In Greater Bay Area – How will water & climate risks, including rising sea levels & droughts, threaten the already water-stressed Greater Bay Area (GBA)? CWR’s Tan & Mirando explain in their latest CLSA report and highlight companies’ failure in climate risk disclosures