More people are affected by floods than by any other type of natural disaster – and the risk is rising. New analysis from the World Resources Institute (WRI) shows that approximately 21 million people worldwide are affected by river flooding every year – a figure that the report predicts could increase to 54 million in 2030 due to climate change and socio-economic development.

In Southeast Asia, which is one of the worst-affected regions, where monsoons claimed hundreds of lives last year – an estimated 15 million people will be affected, experts say. And along with the human cost comes a massive economic toll: flooding at the current level exposes US$96 billion in global GDP annually, rising to US$521 billion by 2030, according to the WRI report.

While the risks may be escalating, the report also notes that public and private sector decision-makers can do more to prevent catastrophic damage before it happens. Adept at dealing with the serious flooding it faces every summer, Hong Kong has devised solutions that are efficient, cost- effective, and replicable both in emerging and mature urban environments.


In busy urban hubs such as Hong Kong and Singapore, the solution is complex, notes Kelvin Lau, Associate Vice President and Senior Project Director, Black & Veatch, a global engineering company, which has delivered many iconic drainage works in Hong Kong. For below the streets, pipelines often many decades old criss-cross the service corridors with other modern utilities, all competing for the same space. “This makes expansion or repair of existing facilities challenging physically and technically,” he says.

“Given increasing density and climate uncertainties, we can no longer always simply throw wider and deeper drains at the problem. We need to be smarter and rethink how we manage torrential downpours in the urban setting.”

To alleviate problems in the heavily-trafficked, flood-prone hubs on both sides of the harbour, Hong Kong’s Drainage Services Department (DSD) devised a series of underground stormwater storage schemes, and tunnels to intercept surface runoff from uphill catchments. Together, these solutions allow the existing drainage systems to adequately cope with severe rainstorms, without the need for extensive upgrading works, explained Cheng Hung-leung, Assistant Director/Projects and Development, Drainage Services Department.


Mr Lau explained how, in one solution, an underground storage tank installed beneath Hong Kong’s famous Happy Valley racetrack intercepts and attenuates peak stormwater flows to take pressure off the existing infrastructure. “It also means the problem isn’t simply passed on to further down the drainage system.”

At its heart is Hong Kong’s first example of a movable crest weir system, together with Supervisory and Data Acquisition (SCADA) real-time monitoring of water and tidal levels. With intelligent data feedback, the volume of water within the storage tank can be monitored and adjusted to prevent either pre-mature or late overspill of stormwater, factoring in rising or lower sea levels.

Still under construction, the Happy Valley Underground Stormwater Storage Scheme has already been recognised by several prestigious awards, including Winner of the East Asia Region of the International Water Association Project Innovation Awards 2012 in the Planning Category.

AECOM Asia Company Ltd is engaged in formulating the Lai Chi Kok Drainage Tunnel (LCKDT), an integral part of the overall flood control strategy for West Kowloon.


The scheme involves a 3.7-kilometre long, 4.9-metre diameter drainage tunnel intercepting surface run-off from the West Kowloon hinterland for discharge directly into Victoria Harbour. “By diverting the upland flow to the drainage tunnel, extensive drainage upgrading works in the congested lower catchment urban areas can be substantially reduced,” said Tim Lee, Technical Director, AECOM Asia.

The LCKDT is another well-recognised project to win regional and global honours, including the Design category of International Water Association Project Innovation Awards 2014.

Mott MacDonald Hong Kong Ltd drew on its expertise to modernise outdated stormwater infrastructure in the densely-populated urban districts of Tsuen Wan and Kwai Chung.

“The districts’ decades-old drainage system was capable of dealing with routine storms, but didn’t have the spare capacity to handle the additional runoff arising from rapid urbanisation,” explained Chris Howley, Divisional Director, Mott MacDonald Hong Kong Ltd. History had shown the need: an exceptional deluge of 1997 overwhelmed the existing system, causing chest-high flooding in many areas, and leaving a trail of destruction in its wake.

Merely intercepting the entire flow would have an adverse environmental impact downstream, particularly within the ecological park at Tso Kung Tam.

“The tunnel project was thus conceived to extend the service life of the downstream drainage system,” Mr Howley said. “Run-off from three major local rivers is intercepted near mid-course and diverted to the 5.1 kilometre-long tunnel through vertical intake shafts, bypassing the town before being discharged directly to the sea.” The system effectively creates a defensive line that will protect the districts against flooding for up to 50 years.

Time and again, DSD and its consultancy partners have demonstrated innovative, cost-effective solutions at the cutting edge of flood control. In another example, a drainage master plan review for Yuen Long and North District, involving Mott MacDonald consultancy, was among the first to take into account the impact of climate change on inland drainage systems. “It was also the first master plan using one- and two-dimensional hydraulic models to simulate flood plain flow,” Mr Howley said.

In planning for the future, DSD has conducted pilot schemes to adopt the concept of blue-green infrastructure, which generates a multitude of environmental, ecological, socio-cultural and economic benefits, with a goal of building sustainable drainage facilities and providing a better environment.

Managing storm water events, mitigating flooding and optimising the way precious urban land is used remain issues faced by many urban centres throughout the world. As Kelvin Lau of Black & Veatch points out, the industry has moved beyond designing solutions for predictable events – “we now have to plan for the unthinkable.”

Innovative, multi-pronged solutions are needed to safeguard lives and minimise economic loss – solutions that Hong Kong has perfected over time.

Having implemented territory-wide drainage improvement projects costing some HK$24 billion, and eliminated some 120 flooding blackspots across the city, Hong Kong is well-placed to roll out its resilient, cost-effective and proven systems to mature and developing cities across the region.