Trio storm water storage, Hong Kong

Year:2004, 2009 & 2017

Duration:3, 3 & 5 years


Country: Hong Kong

What did this project achieve?

Come up with a way of preventing serious flooding during the rainy season in Hong Kong

Hong Kong often sees very heavy storms during its April to June rainy season. Recent years have seen very fierce downpours resulting in floods of up to 1 metre deep in some areas.

The Hong Kong government’s Drainage Services Department’s (DSD’s) Trio storm water scheme was designed to combat rainy season flooding. The project was innovative as it included the storage of storm water.

Storing water temporarily means it doesn’t flow into – and overwhelm – drainage systems downstream. Existing storm drains were already struggling to deal with Hong Kong’s often high levels of rain.

The Trio scheme saw underwater storage tanks built under existing sports pitches or parks in 3 central locations of Hong Kong.

The Tai Hang Tung project covered the Mongkok area – years of urban development here had increased surface run-off. This meant rainfall was not absorbed into the ground and led to streets being flooded.

Sheung Wan was chosen as it’s a low lying area and prone to flooding in bad weather.

The third location was Happy Valley – home to Hong Kong’s famous race course.

Difference the scheme has made

The Trio scheme is regarded as a pioneer in reducing flooding at urban sites.

The project has reduced rainy season flooding in its target areas – all of them were previously city centre flood black spots.

Busy areas such as the Nathan Road shopping district have not flooded since the scheme was completed.

How the work was done

The Tai Hang Tung project saw engineers build a water storage tank 136m long x 130m wide and 7.5m deep under existing rugby and football pitches.

The storage tank has a capacity of 100,000m³ and was the first large-scale underground tank in the territory. It was designed to handle rainfall of 100mm an hour.

The Sheung Wan scheme saw engineers construct an underwater tank of 9,000m³ under a park overlooking the city’s Victoria Harbour.

The project team also built a single storey pump house as part of the system and improved local storm drains to collect 30% of the rainwater runoff from local streets.

The Happy Valley underground water storage project took 5 years to complete, opening in 2017.

A project team of engineers built a tank under the Happy Valley recreation ground with a capacity of 60,000m³ - about the same as 24 full-size swimming pools.

As well as coping with flooding, the scheme provides up to 220,000m³ of ‘grey water’ to the recreation ground every year. Grey water is water that can be used for flushing, washing and irrigation.


He has transformed a malodorous underground cavern into an artistic tribute to that most mundane of urban features, the Hong Kong drain.

The South China Morning Post

on artist Kingsley Ng Siu-king’s artwork ‘After the Deluge,’ staged in one of the Trio storm water storage tanks.

Fascinating facts

Heavy rain in Hong Kong – more than 70mm an hour - is called ‘black rain’ locally.

The Happy Valley scheme had its first test during the black rainstorm of October 2016. Neither the recreation ground or racecourse were flooded.

The Tai Hang Tung storm water storage tank was used for a ‘multi-sensory’ art experience called ‘After the Deluge’ in January 2018. A sound and light show mimicked the flow of water underground.

People who made it happen

  • Client: The Hong Kong government
  • Project team leader: Leung Cheuk-lun

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