Due to the effects of extreme weather events, torrential rainfall brought flooding to various districts in Hong Kong. This year’s Policy Address announced that taking forward expeditiously the $8 billion drainage improvement works projects, covering Wong Tai Sin, Hong Kong Island East and other areas hit by severe floods in the past. This time, I have invited colleagues from the Drainage Services Department (DSD) to talk about the response and recovery measures during the passage of previous rainstorms. Two engineering experts will also talk about Hong Kong’s and other international cities’ strategies in coping with extreme weather.

Acting Senior Engineer (Mainland South) of the DSD, Mr PUN Ho-yin, Joe, says that for the seven drainage improvement works projects, the DSD will adopt parallel tendering when seeking funding from the Legislative Council in 2024-25 to shorten the duration of engineering design, procurement and construction for commencing and completing the improvement works as soon as possible.

Besides, in order to further cope with the more frequent extreme weather events in recent years, the DSD has made advance arrangements by completing a “Strategic Planning Study on Flood Management Against Sea Level Rise and Extreme Rainfall" next year. The study’s purpose is to assess the impact of climate change on Hong Kong’s stormwater drainage systems till the end of the century and formulate new and comprehensive territory-wide flood management strategies.

Emergency Control Centre operating more than 200 hours

Whenever a Red or Black Rainstorm Warning signal, a Special Announcement on Flooding in the northern New Territories, or a Tropical Cyclone Warning Signal No. 8 or above is issued, the DSD will immediately activate the Emergency Control Centre (ECC). In September this year, in coping with the torrential rain brought by the low pressure associated with remnants of Typhoon Haikui, the ECC has been activated continuously for more than 200 hours. During the peak period, the number of emergency response teams for flooding incidents was doubled from ordinary 70 to 144, which composed of 550 workers, to coordinate the emergency clearance work for blocked drainage systems and address flooding incidents so as to restore normalcy to the city as quickly as possible.

Enhancing the city’s resilience

The President of the Hong Kong Institution of Engineers, Ir Dr LEE Chi-hong, Barry, says that the design of Hong Kong’s stormwater drainage system is comparable to advanced international cities such as New York, London, Tokyo and Singapore. The larger urban drainage trunks can withstand rainfall with a return period of 200 years, while drainage branches can withstand rainfall with a return period of 50 years.

He stresses that the purpose of designing and constructing stormwater drainage facilities is not to achieve “zero risk” of flooding, which would require a deployment of unlimited resources. Flood prevention works must strike a balance between cost and effectiveness. Apart from minimising flooding risk, the more important thing is quickly clearing blocked drains when flooding occurs in order to help resume normal daily lives for the community shortly. The Government has been adjusting policies and plans as necessary to deal with climate change and strengthen the infrastructure to enhance the city’s resilience in preparation for more frequent extreme weather.

Associate Professor of the Department of Civil Engineering of the University of Hong Kong, Dr CHUI Ting-fong, May, says that climate change is the defining global challenge of our time. In recent years, many countries and regions have been affected by super hurricanes and the torrential rain. Hong Kong was also hit by record-breaking downpours in September this year.

She explains that due to its unique geographical environment, the annual average rainfall in Hong Kong is one of the highest among the cities in the Pacific Rim. In formulating the flood prevention strategies, we need to consider the space and land constraints as well as the impacts on the environment. Currently, sustainable flood prevention infrastructures are being taken forward around the world, such as stormwater storage schemes. In Hong Kong, the Happy Valley Underground Stormwater Storage Scheme, which came into full operation in 2017, has adopted the concepts of “single site, multiple use” and rainwater reuse, providing flood protection and at the same time ground space for recreational facilities for the public.

Construction scheme of underground stormwater storage

Mr Joe PUN says that the four stormwater storage tanks under the DSD (located at Tai Hang Tung, Sheung Wan, Happy Valley and On Sau Road) have played prominent roles during the rainstorms. For example, during the flooding in various districts brought by Typhoon Haikui, the water storage of the Tai Hang Tung stormwater storage tank and Happy Valley underground stormwater storage tank reached their maximum design capacities during the peak period, while the water storage of the stormwater storage tanks at Sheung Wan and On Sau Road reached about 40 percent of their maximum design capacities.

The DSD is now carrying out the construction works of underground stormwater storage tanks beneath the Urban Council Centenary Garden in Tsim Sha Tsui and at Sau Nga Road Playground in Kwun Tong to further alleviate the flooding risk in Kowloon.

Adopting innovative technologies to enhance drainage work efficiency

Meanwhile, the DSD has proactively applied innovative technologies in its drainage works. For instance, before and after the recent rainstorms, the department has used desilting robots for urgent desilting works in different environment, including the latest robot in the “Innobros” series developed specially for desilting work in rivers, which can collect up to 18 tonnes of silt per day, and “Aquabot”, the smallest desilting robot used by the department so far and suitable for works at box culverts, which can collect about 10 tonnes of silt in a day.

"Smart Drainage Monitoring Sensors" system

Furthermore, the DSD has installed about 300 "Smart Drainage Monitoring Sensors”, such as gauging stations and water level sensors, at different locations across the territory, to collect real-time data on water levels and tidal levels round the clock. Operators can make use of their mobile phones and computers to monitor the conditions of main rivers and drainage channels, helping the department to swiftly take preventive and contingency measures.

Combating climate change is a challenge across the globe. Hong Kong will continue to address the issue with forward-thinking strategies proactively. By expediting the implementation of multiple flood control projects, Hong Kong's flood resilience will be further enhanced, more effectively reducing the flooding risk across the territory.