Flood Alleviation Program Keeps Happy Valley, Hong Kong, Happy

Happy Valley, located in the Wan Chai District of Hong Kong, is a cultural, economic and entertainment centre for the city. Despite its metropolitan development, the area was prone to flooding as it is located on low-lying ground near the Victoria Harbor. The Happy Valley Racecourse, one of Hong Kong’s most popular attractions, was submerged under nearly three feet of stormwater during a severe rainfall event in 2008.

The traditional solution to resolve this type of flooding would be “throwing more drains at the problem areas" said Black & Veatch* Project Director Andy Kwok. However, enlarging and multiplying the number of drains would involve opening up busy roads in Wanchai and around the racetrack and disrupting popular racing and sporting events. Furthermore, even with all these disruptions, this strategy wouldn't effectively reduce flooding risk because part of the low-lying drains adjacent to the sea would still be occupied by tidal water, thus reducing the flood protection efficiency.

In view of the effectiveness and public interest, the Drainage Services Department (DSD) of the Government of the Hong Kong Special Administrative Region decided to implement an underground storage scheme, comprising a large tank to store stormwater runoff for reduction of downstream flooding risk during severe rainfall events.

Optimizing Design on Flood Alleviation

Black & Veatch was contracted by DSD for optimizing the scheme’s design through the adoption of the integrated 1D network, 2D overland flow and 3D computational fluid dynamics models, a first for flood alleviation in Hong Kong.

The resulting award-winning design uses Supervisory and Data Acquisition (SCADA) system monitoring to monitor water levels, which automatically triggers an adjustable weir system, another first for flood alleviation in Hong Kong. At the center of SCADA system is a network of sensors, which capture tidal levels in Victoria Harbor and water levels at several strategic locations, including the storage tank and upstream and downstream of the culvert. With the adjustable weirs and SCADA system, the tank remains dry most of the time as stormwater flows along the culvert adjacent to the storage tank straight to the downstream drainage network. During heavy rain, water level rises and SCADA triggers the adjustable weir system in which excess runoff enters the storage tank. After a rainfall event when the water level in the culvert drops, the movable weirs can be further lowered to drain the stored stormwater to the downstream drainage network by gravity.

Black & Veatch’s innovative design optimized the required volume of the tank by 25 to 30 percent, reduced excavation and material requirements and shortened the construction time by nearly one year, resulting in considerable cost savings, as well as minimizing public disruption and environmental impacts.

The storage tank holds 60,000 m3 of water, equivalent to 24 standard size swimming pools.

Community Benefit During and After Construction

The Wan Chai District and Happy Valley are very busy and densely populated areas. Previous flood events affected over 7,000 residents and 2,000 businesses, as well as the racing events. Black & Veatch's solution prevented serious disruption to the racing track and recreational grounds, as well as the traffic on the surrounding roads. While the financial savings of this plan were huge (more than HK$72 million), Kwok said “the benefits to the local communities can't be measured."

The design will save the DSD significant operational costs throughout the infrastructure lifecycle. The shallow design of the underwater storage tank allows more than two-thirds of the stored stormwater to drain by gravity, reducing energy costs of pumping after a rainstorm recedes.

Global Recognition

“Innovation was the key to the scheme’s success,” said Kwok. “The solution works with nature instead of against it while using the best technology on hand.”

The project earned numerous local, regional and international awards, including:

• The Merit Award for Innovation from the Hong Kong Institution of Engineers.

• The International Water Association Project Innovation Award in the East Asian Region.

• Highly commended as the New Engineering Contract's Large Project of the Year.

• A Gold Award in the Considerate Contractors Site Award Scheme.

• The highest rating, provisional platinum, in BEAM Plus Certification.

• Grand Award of 2017 Hong Kong Awards for Industries: Innovation and Creativity.

Utilities across the Asia Pacific region are steadily investing in advanced stormwater management strategies to improve water resource resilience and overall sustainability. The need for enhanced flood and stormwater management is driven by increased urban development and increased frequency of intense rainfall events.

“At Black & Veatch, we try to always think about being innovative and cost-effective while mitigating environmental impacts to local communities,” said Kwok. “The success of the Happy Valley project reinforces Black & Veatch’s global leadership and innovation in stormwater and flood mitigation solutions.”

*A project undertaken in Hong Kong SAR when Black & Veatch owned that business.