Among the suggestions given by Prime Minister Lee Hsien Loong to tackle rising sea levels during his 2019 National Day Rally was one that involved reclaiming a series of islands offshore from Marina East to Changi, connecting them up with barrages and creating a reservoir, similar to Marina Reservoir.
Singapore has also already put in place some measures, including the use of polders, which are tracts of land that lie below sea level and are reclaimed through the building of dykes, drainage canals and pumping stations.
There is an ongoing polder project on Pulau Tekong, led by the Housing and Development Board, that is more than halfway complete and set to finish by the end of 2024.
Minister for National Development Desmond Lee said last month that the project, the first of its kind for Singapore, will help the nation to gain experience in developing polders, which “could be an option for coastal protection and resilience against sea-level rise”.
There are also plans to build infrastructure higher above the sea level. Professor Benjamin Horton, the director at the Earth Observatory of Singapore at the Nanyang Technological University, said that Changi Airport, for example, is building Terminal 5 at 5.5m above present sea level to protect against future rising sea levels.
“We can further think about engineering advances that will enable buildings to float,” he added.
PUB's coastal protection department is also looking at other possible solutions, with senior assistant director Sarah Hiong reiterating that it is “important to study all options, even long-term ones, comprehensively”.
Here are some other alternatives being studied by Singapore:
SEA WALLS AND ROCK REVETMENTS
Both are hard structures that protect against coastal erosion. At present, PUB says they line about 70 per cent of Singapore’s coastlines.
“Building sea walls around the entire Singapore is a simple and direct but not an entirely feasible solution, because we also have to consider the interactions between the land and sea,” said senior engineer Eugene Lim from PUB's coastal protection team.
For example, this could include natural coastal habitats, recreation and industries that require waterfront access.
“It will also not be aesthetically pleasing for the public too. Try imagining having a great wall built around the entire coastline of Singapore,” he added.
NATURE-BASED HYBRID SOLUTIONS
Mr Lim said PUB intends to explore hybrid solutions, which combine engineering solutions with nature-based elements, including the planting of mangroves, seagrasses or vegetation.
A benefit of this option, said Mr Lim, is that it provides an opportunity for Singapore to create habitats to enhance biodiversity.
However, it will not be possible to rely entirely on nature-based elements.
Taking mangroves as an example, Associate Professor Koh Tieh Yong, a weather and climate scientist from the School of Science and Technology at Singapore University of Social Sciences (SUSS), said that when sea level rises, the higher seawater will still infiltrate mangrove lands.
“During a storm, mangrove tree roots serve to break up the waves and hold down the earth, thus reducing coastal erosion. In this way, mangroves can protect areas further inland until the sea rises beyond a level where even mangroves cannot thrive.”
Thus, there will still be a need to pair it with man-made structures like sea walls as the main solution to sea level rise, he said.
Another downside is that most of Singapore’s coastal land is needed for residences, industries, maritime port, airport or recreational beaches and so cannot be replaced by mangroves.
MULTIFUNCTIONAL COASTAL DEFENCES
Due to Singapore’s land scarcity, multifunctional structures such as Marina Barrage, would be an ideal solution, said Mr Lim.
The barrage not only provides a source of water supply, it acts as flood control and even a venue for recreation — a “hot spot for families” to have picnics, fly kites and spend quality time together, he said.
One overseas example that protects against sea level rise which Ms Hiong highlighted is the Katwijk underground parking garage in the Netherlands, where much of the country is below sea level.
Designed by the Royal institute of Dutch Architects, it was the winner of the Best Dutch Building of the Year in 2016.
Situated beside a popular beach, the project is a car park that is not only able to house 650 cars, but also plays a critical role as a dyke to protect the small, eponymous town against future floods.
What is interesting about the project, said Ms Hiong, is that “you can't even tell that it's actually a coastal protection measure” because it is concealed within a sand dune so that it blends in with the beachfront.
“So this is an example that really inspired us… to build something that not only has such an important use for the nation, but also something that the public will actually come to enjoy,” she said.