Drainage Services Department

Aerial View of Happy Valley Underground Stormwater Storage Scheme

During the major rainstorms in August 2000, April 2006 and June 2008, severe flooding incidents occurred at Happy Valley and adjacent areas including Sing Woo Road, Wong Nai Chung Road, Morrison Hill Road, Lap Tak Lane, the Happy Valley Racecourse and the Happy Valley Recreation Ground. In these busy and densely populated areas, conventional drainage improvement schemes would require extensive upsizing of existing drains or laying of new drains, which would involve extensive road excavation works, leading to disruption to the public and commercial activities. Congested underground utilities will also jeopardise the viability of the conventional schemes.

In view of this, Drainage Services Department (DSD) commenced the construction works of Happy Valley Underground Stormwater Storage Scheme (HVUSSS) in 2012 comprising the construction of a 60,000 cubic metres (which is equivalent to the total volume of 24 standard swimming pools) underground stormwater storage tank underneath the Happy Valley Recreation Ground, a box culvert of about 650 metres long and a stormwater pump house with a peak flow rate of 1.5 cubic metres per second. The underground storage tank can temporarily store part of the stormwater collected from the recreation ground and upstream catchment for attenuating the peak flow through the downstream stormwater drainage systems during heavy rainstorms. The stormwater will be discharged by gravity and pumps to the sea via downstream stormwater drainage systems and thus greatly reduces the risk of flooding to low-lying area of Wan Chai and Happy Valley. The HVUSSS was divided into two phases which were commissioned in 2015 and 2017 respectively.

Happy Valley Underground Stormwater Storage Scheme 

Happy Valley Underground Stormwater Storage Tank

Happy Valley Underground Stormwater Storage Tank

Being the first flood prevention project in Hong Kong to combine the use of Movable Weir and Supervisory Control and Data Acquisition (SCADA) system, Happy Valley Underground Stormwater Storage Scheme (HVUSSS) monitors in real time tidal level, water levels inside the storage tank and in the box culvert immediate upstream and downstream of the tank. The positioning of the Movable Weir is based on the real-time monitoring data such that the overflowing of stormwater from the box culvert to the storage tank can be triggered at the optimal time.

Compared to the conventional fixed-weir design, the Movable Weir prevents pre-mature or belated filling of the storage tank, thereby maximising the effectiveness of the storage tank and reducing the required design tank volume. Furthermore, the storage tank is of a shallow-depth design. After heavy rain, as water level in the downstream box culvert subsides, the Movable Weir can be lowered further to allow about one-third of the stored stormwater to be discharged by gravity back to the box culvert, reducing the need for pumping.

The innovative design can effectively reduce the construction costs and time, thus saving operation energy consumption to achieve both flood prevention and environmental protection. The design was awarded 2012 International Water Association (IWA) Project Innovation Awards (East Asia Regional Awards) in the Planning Category and the Hong Kong Institution of Engineers “The Innovation Award for Engineering Industry 2012/2013” (Construction Category) - Merit Award.

Happy Valley Underground Stormwater Storage Tank (360° View)

Happy Valley Underground Stormwater Storage Tank (360° View)

Happy Valley Underground Stormwater Storage Tank

Movable Weir

Movable Weir 

Movable Weir

Operation Demonstration of Movable Weir

Operation Schematic Diagram of Movable Weir

Operation Schematic Diagram of Movable Weir

Operation Schematic Diagram of Movable Weir

Water Harvesting System

Use of Harvested Water for Irrigation at the Sport Pitches

Happy Valley Underground Stormwater Storage Scheme includes a new water harvesting system that allows groundwater, irrigation water at sport pitches and stormwater to be harvested from subsoil drainage systems that were built underneath the storage tank and sport pitches.

As the collected water is of better quality, it can attain the standard of reclaimed water for non-potable use after simple disinfection and be reused for irrigation at 11 football pitches, toilet flushing at two changing rooms within the Happy Valley Recreation Ground (HVRG) and two public toilets in the vicinity and supplying reclaimed water to the Food and Environmental Hygiene Department (FEHD) for street cleaning in Happy Valley and Wan Chai districts. The system is the largest water harvesting system of the same type in Hong Kong and can conserve precious potable water supply.

Pump House of Happy Valley Underground Stormwater Storage Scheme

Three stormwater pumps are installed inside the Pump House of Happy Valley Underground Stormwater Storage Scheme. The peak discharge capacity of the Pump House is 1.5 cubic metres per second, which can discharge the stormwater stored in Happy Valley Underground Stormwater Storage Tank to the downstream drainage system within 7.5 hours.

The Pump House is specially designed into a trapezoid shape and a turfed slop is built on the Pump House, which does not only help reducing indoor temperature, but also provides a serene public space as well as an open air vantage point of the Happy Valley Recreation Ground.

Pump House of Happy Valley Underground Stormwater Storage Scheme (360° View)

Green Roof of the Pump House (360° View)

Green Roof of the Pump House

Green Roof of the Pump House

Green Roof of the Pump House

Green Roof of the Pump House

Green Lawn next to the Pump House

Fan Room of the Happy Valley Underground Stormwater Storage Scheme and resting area

The Fan Room of the Happy Valley Underground Stormwater Storage Scheme has two exhaust fans which can ventilate the stormwater storage tank twice in an hour to ensure that there is ample supply of fresh air during regular maintenance.

To promote the sustainability development of Hong Kong, in addition to installing solar panels on top of the Fan Room for providing renewable energy, the traditional box-shaped structural form of the Fan Room is optimised by including a canopy design so that the public can rest comfortably outside the Fan Room in all weather conditions. Timber cladding mounts on the Fan Room adds to the building aesthetics. An outdoor sitting area is provided for public to relax. The Fan Room and Pump House have obtained Final Platinum Rating under the BEAM plus (New Buildings) from the Hong Kong Green Building Council.            

Fan Room also provides multimedia means to briefly describe the Drainage Services Department’s works in flood prevention and sustainability. Through model exhibitions, videos and interactive games in the Fan Room, visitors can learn more about Happy Valley Underground Stormwater Storage Tank.

Fan Room of Happy Valley Underground Stormwater Storage Scheme (360° View)

Fan Room of Happy Valley Underground Stormwater Storage Scheme (360° View)

Fan Room of Happy Valley Underground Stormwater Storage Scheme

Fan Room of Happy Valley Underground Stormwater Storage Scheme

Fan Room of Happy Valley Underground Stormwater Storage Scheme

Fan Room of Happy Valley Underground Stormwater Storage Scheme

Fan Room of Happy Valley Underground Stormwater Storage Scheme and Green Lawn next to the Pump House

Fan Room of Happy Valley Underground Stormwater Storage Scheme

Physical Model of Happy Valley Underground Stormwater Storage Scheme

Physical Model of Happy Valley Underground Stormwater Storage Scheme

Exhaust Fans of Happy Valley Underground Stormwater Storage Scheme