Hong Kong: A Climate Resilient Sponge City

By Richard Leung 13 July, 2017

Leung from the Drainage Services Department shows how HK is building flood resilience under climate change

With an avg rainfall of 2400mm/yr, HK is prone to tropical cyclones & suffered substantial flooding in the 1990s
Since 1999, DSD has completed major flood prevention projects but need upgrading to adapt to climate change
From green roofs to retention lakes, DSD is changing infrastructure design from 'resistance' to 'resilience'

Under the threats of climate change, the Drainage Services Department (DSD) has been implementing a sustainable drainage system with an aim to building flood resilience and improving the living environment of Hong Kong.

Hong Kong is one of the most densely populated cities in the world. It is prone to tropical cyclones with an average annual rainfall of about 2400mm, making it one of the world’s wettest cities. Under this climatic setting, Hong Kong often experienced substantial flooding in the 1990s.

Past efforts and an uncertain future

To prevent flooding in Hong Kong, DSD has adopted a 3-pronged approach:

  1. constructing stormwater interception tunnels at the upstream;
  2. providing stormwater storage tanks at the midstream, and
  3. upgrading drainage pipework at the downstream.

DSD’s projects reduced the number of flooding blackspots in the city from 90 to 7…
…but such infrastructure requires further enhancement to adapt to climate change

Since its establishment in 1989, the DSD has completed a number of major flood prevention projects. DSD now owns approximately 2,400km of stormwater drains, 360km of river channels, 21km of interception drainage tunnels, 3 stormwater storage tanks and runs 27 village flood protection schemes. With these robust and reliable drainage infrastructure, DSD has successfully reduced the number of flooding blackspots in the city from 90 to 7.

However, such 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. Sea level has also been recorded to be rising at a rate of 31mm per decade. At the same time, rural areas are being developed to cope with the city’s long term economic and population growth. To tackle these challenges, DSD has started to explore more sustainable solutions for the drainage system and will gradually evolve the existing drainage infrastructure into blue-green infrastructure.

Building a sustainable drainage system

A sustainable drainage system, or blue-green infrastructure, mimics the natural water cycle. In contrast to the traditional urban runoff system, which results in low evaporation, low infiltration and high surface runoff, a sustainable drainage system promotes high evaporation, high infiltration and low surface runoff. Examples of sustainable drainage systems include green roofs, rain gardens, retention lakes, porous pavements, water harvesting, bioswales, wetlands and river revitalisations. By designing the city like a sponge, flood resilience can be built into the existing drainage infrastructure.

DSD is gradually evolving the existing drainage system into blue-green infrastructure…
… examples include green roofs, water harvesting, wetlands etc.

In the past years, DSD has gained a wide range of experience in the implementation of a sustainable drainage system. It has installed green roofs and vertical greening on 70 of its facilities including sewage treatment works and pumping stations with a total area of 30,000m2. The installation of green roofs is on-going at a rate of about 4,000m2 per year.

DSD has also implemented water harvesting at Lai Chi Kok Drainage Tunnel and the Happy Valley Underground Stormwater Storage Scheme which has resulted in annual water savings of 44,000m3 and 220,000m3 respectively. The harvested water can be used for toilet flushing, irrigation and street cleansing.

For some river training works such as the completed Ho Chung River and Lam Tsuen River, and the on-going projects like Shenzhen River and Kai Tak River, greening, ecological enhancement and water friendliness have been incorporated into the river channel design. A retention lake is being constructed on Shenzhen River to attenuate the peak runoff during heavy rainstorms and to provide a natural environment for wildlife, birds, etc, on calmer days.

In the Yuen Long Bypass Floodway project which partly diverts stormwater from the highly populated Yuen Long Town Centre to Kam Tin River, DSD has turned several abandoned fish ponds into an engineered wetland. The 7-hectare wetland provides a large freshwater habitat for birds and wildlife, and also serves as a purification and temporary storage area for stormwater.

The 7-hectare wetland in Yuen Long provides a large freshwater habitat for birds & wildlife…

… it also serves as a purification & temporary storage area for stormwater

Yuen Long wetland (2)
DSD’s project “Kowloon City Sewage Pumping Station” showcases the combined use of sustainable drainage systems in a built environment. It adopts several stormwater management measures including green roofs, porous pavements, rain gardens and water harvesting systems. The project became the first government facility to obtain the BEAM Plus Platinum rating, the highest rating for green buildings.

“Kowloon City Sewage Pumping Station” showcases the combined use of sustainable drainage systems in a built environment

kowloon city pumping station (2)

Future developments – from flood retention lakes to reservoir transfers

Notwithstanding the above experiences on sustainable drainage system, DSD is exploring more applications in new development areas. For example, in the Anderson Road Quarry Development, DSD is pushing forward the first flood retention lake in Hong Kong. It will become an open space with landscape feature for public enjoyment on dry days, and operate as the function of flood attenuation during the wet season.

The Anderson Road Quarry Development will become the first flood retention lake in Hong Kong that the public can enjoy on dry days

Anderson Road (1)
Moreover, Hong Kong’s first river park is being envisaged at Tung Chung River where the public can 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 far as possible to maintain the existing habitat. To uphold a high water quality on the Tung Chung River, biofiltration has been 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 resource.

DSD’s efforts show a paradigmatic change in drainage infrastructure design…

…from a “resistance” approach to a “resilient” sponge city approach

In addition, DSD is also planning the “Inter-Reservoirs Transfer Scheme”, which will see the construction of a water tunnel between the Kowloon Reservoir Group and the Lower Shing Mun Reservoir. The project serves a dual purpose: to substantially reduce stormwater discharge into the drainage system and to channel the overflow into the Lower Shing Mun Reservoir via the proposed tunnel to generate extra annual raw water yield at about 2.5 million m3.

DSD’s efforts in turning Hong Kong into a climate ready and flood resilient sponge city demonstrates a paradigmatic change in drainage infrastructure design – from a “resistance” approach to a more sustainable “resilient” approach. The change is crucial for Hong Kong to adapt and recover after the extreme weather events in the uncertain future.

Further Reading

  • Hong Kong’s Pricey Water Deal With China – Much is made of the DongShen Agreement’s price tag but discussions need to move onto more complex issues such as the city’s rampant overuse & leakage. Hear from Civic Exchange on HK’s ‘illusion of plenty’
  • Green Financing For Climate Resilience – We sat down with Dr Christine Chan from the Climate Bonds Initiative working group to get the latest on green finance globally & in China. How have China’s green bonds been received? What is next for investors?
  • ‘Science Unusual’ to Counter Fake News! – Science & policy have their own language but given significant climate risk overshadowed by fake news, can we afford to speak in tongues? Hu & Tan on why it’s time to step up efforts to bridge science and policy with finance
  • Rise of ZLD In China’s Power Sector – Treating air pollution in thermal power plants create hard-to-treat wastewater as a by-product: is zero liquid discharge the way forward? Bluetech Research’s Rhys Owen expands
  • Groundwater Shortage Calls For Urgent Action – China’s groundwater is overextracted and this needs immediate tackling. Prof Asit K Biswas & Kris Hartley from the Lee Kuan Yew School for Public Policy explore solutions, from desalination to sponge cities
  • Sponge Cities: An Answer To Floods – Floods have cost China close to RMB2 trillion between 2000-2014. Today, with 641 cities in China are prone to flood risk, the government has turned to sponge city pilots. Do they work? How much do they cost? China Water Risk’s Xu reviews
  • Securing Water For Hong Kong’s Future – The Jockey Club Water Initiative on Sustainability & Engagement (JC-WISE) aims to secure long-term water sustainability for Hong Kong. CWR sat down with Dr Frederick Lee of the University of Hong Kong
  • Hong Kong Water – Agenda & Goals – Hong Kong University’s Dr. Frederick Lee says it’s time for Hong Kong to adopt a users-pay-principle as the territory’s outdated water tariff regime will undermine the success of its water conservation goals
  • Hong Kong’s Thirst for Bottled Water – Hong Kong has a plastic waste issue & consuming less bottled water can help this. Why then is Hong Kong still thirsty for bottled water? Mandy Lao explores consumer attitudes towards these
  • Map to HK & Guangdong Water Governance – Amongst rising concerns over the supply of Hong Kong’s principal water source, the Dong River, Kris Hartley proposes a new collaboration framework for HK-Guangdong water governance
  • Hong Kong Water: 5 Challenges – Industry veteran, Daniel Cheng, MD of Dunwell Enviro-Tech and Deputy Chairman of the Federation of Hong Kong Industries talks about HK’s 5 challenges in securing reliable water supply
  • 8 Things You Should Know About Hong Kong Water – Is Hong Kong’s water supply guaranteed? Can you drink straight from the tap? How much bottled water does Hong Kong consume? China Water Risk sets out 8 interesting facts about Hong Kong water.
Richard Leung
Author: Richard Leung
Ir Richard WM LEUNG is a civil engineer by profession. After graduation from the University of Sheffield in the UK in 1988, he worked as an engineer in the Civil Engineering Development Department and Drainage Services Department since 1995 and 2006 respectively. Ir LEUNG is also an Accredited BEAM Professional of the Hong Kong Green Building Council since 2012. Ir LEUNG has been involved in various stages of planning, design and construction of numbers of new town development projects and drainage/sewerage works. Ir LEUNG is currently the senior engineer of the Research & Development Section in Land Drainage Division in the department. He is responsible for the overall coordination of the research & development projects and planning and promotion of the blue green infrastructure for the department.
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