Keeping the Sea at Bay

As Singapore faces down the existential challenge of sea-level rise, NTU’s Professor Tan Soon Keat, a leading expert in water resources and coastal engineering, discusses its options.

How will Singapore keep itself above water, with significant areas of the country at just four metres above the mean sea level or lower, and the sea level continuing to rise due to climate change? The answer may lie in tried and tested engineering feats: seawalls and polders.

Seawalls are coastal defences to keep the sea out, while polders are low-lying tracts of land, below the surrounding sea level, reclaimed by erecting a dyke and then draining the seawater behind the dyke via a network of drains, water pumping stations and water storage spaces.

The Netherlands has a long history of forming polders, and Singapore is currently building its first one, at the north-western tip of Pulau Tekong, with the help of Dutch experts. When the Singapore polder is completed in 2022, it will add 810 hectares of reclaimed land, equivalent to the area of two Toa Payoh towns.

Professor Tan Soon Keat, a leading expert in water resources and coastal engineering who led beach protection works, including rip-rap and breakwater projects that use rocks and other materials to shield shorelines from wave erosion, says that polders would benefit Singapore in several ways.

Prof Tan Soon Keat conducting an experiment on an underwater structure at his lab.

Prof Tan explains that, “In principle, polders would not require massive quantities of land-fill materials to top up the ground from the original sea bed to the desired platform level, except for the perimeter dykes. One could also implement multiple land uses, including on the dykes, such as roads, train tracks and green belts.”

“However, polders also need special drainage arrangements. With Singapore’s high rainfall, they would require more energy for mechanical water pumping devices, and dedicated and meticulous operation and maintenance.”

He adds that seawalls could offer Singapore long- term protection: “The land behind the walls could be elevated to a higher platform level well clear of projected sea-level rise. Drainage and other surface flow could be by gravity. Furthermore, although the walls are hard structures, they could be terraced and covered with green features.”

Whether Singapore goes for seawalls or polders, the works will require considerable expense. In 2019, Prime Minister Lee Hsien Loong estimated that Singapore will need to spend $100 billion or more in the next 50 to 100 years to prevent the country from going underwater.

As in the Pulau Tekong project, Singapore could learn from other nations’ successes. Prof Tan concludes: “For many of the defences, there are well-tested practices, and workable systems with appropriate designs and adaptations for various site conditions.”


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