Innovative rainwater storage system goes down a storm

Binnies Hong Kong has used its technical expertise to solve the historical flooding problem in Happy Valley, Hong Kong. During the rainy season, heavy rainstorms and downpours had led to floods up to one metre deep in some areas, but an innovative stormwater storage scheme is now helping to combat the situation. 

The three-pronged flood prevention strategy has been introduced by the Hong Kong government’s Drainage Services Department (DSD) to help combat flooding during the rainy season. Intended to help relieve pressure on the overwhelmed drainage systems, the strategy involves stormwater interception by drainage tunnels, temporary storage of stormwater in underground stormwater storage tanks in the midstream and local pipe upgrading works. 

“Almost 20 years ago, Binnies Hong Kong completed the first large-scale underground storage tank in Hong Kong, at Tai Hang Tung, for temporary storage of stormwater during heavy rainstorms,” explains Binnies Hong Kong Managing Director, Andy Kwok. “With a storage capacity of 100,000 m3, the system effectively reduced flooding in Mong Kok, which is one of the busiest districts in the world. A major achievement was to cut back the length of drains to be upgraded from 94 km to around 48 km; these were laid under very busy roads with congestion of utilities and complex project interfaces. 

“More recently, we designed a 2.4 hectare, 60,000 m3 storage tank at Happy Valley. This storage system featured innovative designs, including a movable weir system, a foundation design with a peripheral sheet pile wall and subsoil drainage system and a water harvesting system. The robust nature of this scheme effectively reduced the required volume of the storage tank by 25% and shortened the construction time, thus minimising public and environmental impacts.” 

Speaking to the Institution of Civil Engineers (ICE) in a video about the Happy Valley underground stormwater storage scheme, Andy added, “The movable weir system enables excess stormwater to enter the tank at the optimal time and also enables the discharge of part of the stored stormwater back to the box culvert by gravity, instead of pumping, to achieve an energy saving.” 

The construction of the Happy Valley underground stormwater scheme was divided into two phases commissioned in 2015 and 2017, respectively. Over the years, the scheme has been performing as designed, to safeguard the general public from flood risk.

You can view the full video explaining the scheme on the ICE website.