Using nature, multi-use structures among solutions being studied to protect Singapore coastlines

Straits Times

3 days ago

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With a coastline that stretches over 300km, there is no one-size-fits-all solution for coastal protection in Singapore.
SINGAPORE – With a coastline that stretches over 300km, there is no one-size-fits-all solution for coastal protection in Singapore.
Currently, about 70 to 80 per cent of the country's coastline is covered by seawalls and stone embankments. But these just serve to prevent waves from eroding the shores.
Research is under way to develop the
most effective solutions against rising sea levels for the different parts of Singapore.
National water agency PUB said Singapore's coastal protection challenges require innovative solutions that go beyond conventional approaches.
'As a small island nation with limited land, we need to develop solutions that are not only cost-effective but also multifunctional to maximise land use,' said PUB, which was appointed as the country's coastal protection agency in 2020.
In 2023, the Coastal Protection and Flood Resilience Institute (CFI) Singapore was set up to bring together expertise from various universities, research institutes and industry players to advance knowledge and create innovative solutions for coastal protection and flood management.
There are now 17 research projects under the institute, which are funded by PUB's $125 million Coastal Protection and Flood Management Research Programme.
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The Straits Times looks at the different solutions Singapore is considering to protect its coastlines.
Using nature as an ally
Engineered solutions such as seawalls can offer predictability and control, but natural ecosystems like mangroves and coral reefs can also contribute to protection from sea-level rise.
Mangroves, for example, can serve as a living defence, as their roots trap sediment from the tides, allowing them to keep pace with rising seas.
They also act as a carbon sink, as their water-logged soils allow these habitats to soak up more planet-warming carbon dioxide from the atmosphere than land-based forests.
At CFI Singapore, some projects are dedicated to the research of solutions that combine nature and hard structures – so-called hybrid solutions.
For example, a three-year project by NUS Faculty of Science Associate Professor Peter Todd looks into identifying optimal combinations of 'green' solutions such as mangroves and corals and 'grey' solutions like seawalls and breakwaters, and the feasibility of their integration for Singapore.
'A concrete sea wall provides little in the way of ecosystem services and does not contribute very much to the natural marine environment,' said Prof Todd.
NUS marine biologist Huang Danwei said natural ecosystems such as mangroves and seagrass can help to dissipate wave energy and lower the impact of storm surges and coastal erosion, especially with the increase in frequency of extreme weather events.
Nature-based solutions are also more cost-effective and adaptive than hard engineering solutions, said Professor Huang.
This is because they are naturally regenerating and provide a slew of other ecosystem services, generally without the need for much man-made interference or enhancements, he added.
Ecosystem services include their ability to improve water quality and support populations of marine life, among others.
'These solutions are more cost-effective than hard coastal protection in the long run. It is very costly to try to out-engineer nature all the time,' Prof Huang said.
The National Environment Agency told ST it is looking into the possible use of mangroves as a nature-based solution to protect Semakau Landfill against coastal erosion and sea-level rise.
Predicting extreme weather
Developing the most optimal coastal protection solutions requires an understanding of how bad flooding could get.
Seven of CFI's projects are dedicated to coastal science and predicting extreme events.
In one of the projects, Singapore Institute of Technology (SIT) researchers are building a model that can predict storm surges within five days, so that residents and businesses can take emergency measures.
These measures could include staying indoors, moving vehicles to higher ground and installing barriers to prevent losses caused by coastal flooding.
Storm surges are higher-than-usual tides caused by offshore storms. Areas in Singapore that are most at risk from storm surges are likely to be the East Coast and Jurong Island, said Associate Professor Tay Zhi Yung from SIT's engineering cluster.
Current-wave and storm-surge models near Singapore's coasts are based on physics and mathematical equations.
SIT's model integrates machine learning with existing weather data, such as wind forecasts, to improve the accuracy of storm-surge predictions.
'A data-driven model can provide much faster predictions when compared with physics-based models,' said the project's lead, Associate Professor Victor Wang of SIT's engineering cluster.
The four-year project is currently 1½ years in, and the team is looking to incorporate other elements like sustained wind speed and rainfall to improve the model.
The other related projects are looking at predicting intense rain and other extreme coastal events more accurately.
'The eventual goal is to develop reliable early warning and operation response for coastal-related flooding occurrences,' said Prof Wang.
Separately, since 2021, PUB has been building a $13.4 million model that can simulate and evaluate inland and coastal floods in tandem, based on the latest climate projections.
When high tide happens to coincide with an intense deluge, coastal flooding worsens. This coastal-inland flood model is currently being validated and undergoing pilot testing, said Ms Hazel Khoo, director of the coastal protection department at national water agency PUB.
Flexible, multi-use options
Singapore is also looking at flexible structures that can help it tackle sea-level rise across a range of different scenarios.
This could include, for example, flexible seawalls with adjustable heights or modular units that can be added to seawalls.
Existing structures used for coastal protection typically do not allow provisions for subsequent add-ons or modifications to adapt to rising sea levels.
Researchers are now studying whether a flexible seawall with adjustable heights can also support a concrete structure that allows for multi-function uses, such as a road or a park.
PHOTO: PUB
But innovative engineering solutions can be deployed to better utilise land. They can also be adapted to future requirements and have multiple uses beyond protecting against sea-level rise.
Flood risk expert Matthijs Bos – who works at global engineering consultancy Haskoning – said Singapore could take reference from a sea-facing boulevard in The Hague, Netherlands, which doubles as a recreational spot on good weather days.
The popular Scheveningen Boulevard sits on top of a hidden sea wall – replacing a former sand dune ridge – and in front of it lies a widened beach that was topped up with sand.
The nourished beach acts as a buffer to weaken waves, and the sea wall prevents the boulevard from flooding during storm events.
Mr Bos envisions the future Long Island having a similar concept.
'For the outer edge facing the sea of Long Island, they will make sure it's not only a coastal protection but maybe a nice recreational area to go to. It could be a new waterfront,' he said.
Researchers are also studying whether a flexible seawall with adjustable heights can support a concrete structure that allows for multi-function uses, such as a road or a park.
The flexible seawall can also be used to separate water bodies to form a coastal reservoir that can be used as a water catchment area to reduce inland flooding and for freshwater storage.
Nanyang Technological University's (NTU) Professor Chu Jian, the project's principal investigator, said the flexible seawall will also be more cost-effective as less material is needed to build it.
'If you integrate it for other uses, the overall cost will be much cheaper as it also provides infrastructure,' he said.
The three-year project, which started in November 2023, mainly focuses on the design and modelling of the wall.
Another project under Prof Chu, who is also the chair of the NTU School of Civil and Environmental Engineering, involves lining the shoreline with tube-like barriers made of natural materials.
Each barrier resembles a number of sandbags, but its outer covering is made of plant fibre such as jute.
The barrier is filled with a mixture of sand, soya bean powder and calcium ions that will be cemented together to form an erosion-resistant 'rock' after the barrier has been placed.
Over a few years, as seawater seeps into the beams, the natural fibres will decompose. But ions from the water will react with the material inside the barrier to make it sturdier.
These bundles will not only shield the beach from strong waves but also allow sand and soil to slowly accumulate and raise the shores, turning the beachfront into a natural sea wall of sorts, to catch up with higher sea levels.
Such barriers made with environmentally friendly materials are suited for coastlines with fragile ecosystems such as mangroves and intertidal habitats.
'You cannot use concrete walls everywhere,' said Prof Chu, adding that they restrict nature from thriving.
Prof Chu hopes to conduct pilot tests for these tube-like barriers in Singapore soon.
Existing coastal protection structures can also be retrofitted with innovative solutions such as adding modular, watertight units on top of seawalls.
PUB is working with Delta Marine Consultants to explore the use of modular blocks known as XblocPlus – a single layer concrete armour unit placed in a regular pattern along the shoreline – on Singapore's coastlines.
It is a flexible and scalable design that minimises land take, as well as has the potential to be integrated with urban developments or natural habitats. The firm is looking forward to potentially test-bed and pilot these blocks here.
While the aim is to protect every corner of our coastline from flood waters, there might be a situation where some parts of the island – more remote and with lower footfall – may be left to flood once in a while, suggested Mr Bos and Mr James Lam, Surbana Jurong's executive director for coastal engineering.
These floodable areas could be coastal parks, nature spots and beach areas.
Mr Lam said: 'Certain places could tolerate flooding for a few hours before it subsides. If it's a parkland, you just have to close it for a few hours… It doesn't mean that you have to stop every centimetre of flooding. You cannot protect everything.'