Flooding has always been a big problem in Hong Kong. Its average annual rainfall is 2,400mm - the highest in the Pacific Rim, and the wet conditions have been exacerbated by the fact that the urban development is in an area surrounded by hilly terrain.
Exceptional levels of rainfall that can lead to severe flooding are not uncommon - in 2008 Hong Kong had more than half the annual average (1,346.1 mm) in one month alone. Unsurprisingly, it caused major flooding in the city, including the low lying area of Happy Valley.
While Hong Kong continues to be under threat of flooding, more recently, it has also been having more warmer and drier periods. This gives the authorities the dual problem of needing drainage infrastructure that will help deal with periods of heavy rainfall at the same time as being able to provide enough water for the city’s needs when the weather is a lot drier. And that’s when Hong Kong’s Drainage Services Department (DSD) turned its attention to sports.
After major flooding in 2000, 2006 and 2008 flooding incidents in the area, plans were put in place for the innovative Happy Valley Underground Stormwater Storage Scheme (HVUSSS). The sports grounds provided the ideal location for the work as it helped to significantly reduce the construction costs and time. A 650 metre long box culvert, a stormwater pump house with the capacity to pump 1.5 cubic metres of water per second, and a 60,000 cubic metre storage tank were installed underneath five sports pitches and part of the famous Happy Valley Racecourse.
At times of heavy rainfall, floodwater is captured and stored in the storage tank. An innovative Moveable Crest Weir uses real-time information about tidal levels and water levels collected by a Supervisory Control and Data Acquisition (SCADA) system in order to maximise the effectiveness of the tank by using the weir to release water from the tank into Hong Kong’s vast drainage tunnel system at the optimum time.
Underneath the sports ground there is a storage tank - that resembles an underground car park - from which HVUSSS harvests and stores rainwater and excess irrigation from the sports pitches and racecourse above it. The project also has an onsite treatment plant which ensures the water is clean enough for flushing toilets, watering plants and irrigating the sports pitches and racecourse.
HVUSSS is an example of innovative uses of urban locations when it comes to protecting city areas from flooding at the same time as finding ways of alleviating water shortages. Using the sports ground to build underground flood defences and water storage facilities shows solutions can be relatively quick and easy to implement, without too much disruption to the activities on top of the pitch.
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