A polder in the tropics

Singapore is regarded as a frontrunner in the development and application of new technology. However, when it came to reclaiming new land, the city-state turned to a distant country that excels in age-old polder expertise.Singapore, at the southern tip of the Malay Peninsula, consists of a main island and more than sixty smaller islands. Taken together, these are barely larger than the Noordoostpolder. With a population of over six million, space is at a premium.For two centuries, the city-state has therefore been expanding its land area. This has always been done in the traditional way: using stones, sand and cement to gradually make the sea off the coast shallower, until eventually there is no more water and new land has been created.‘An extremely effective method,’ says Mark van Zanten, Director of Water and Maritime at engineering firm Haskoning in Indonesia. ‘But one that requires enormous quantities of sand. From an ecological and geopolitical perspective, this is becoming an increasingly sensitive issue. Moreover, the sand was running out.’After all, reclaimed land also needs to be raised to prepare for the consequences of rising sea levels. ‘Just imagine how much sand that would take, especially when you’re starting five metres below sea level. That’s how deep the sea is in some places there.’eZBei7ckk5e3l0a590202ad2ccef1b97cd39f207f845aeZBei7ckk5e3lDescendantOf_%d0dbe915091d400bd8ee7f27f0791303%_188c2c12-e1c0-46dc-af55-5eb112a8cbd7,Node_%d0dbe915091d400bd8ee7f27f0791303%_188c2c12-e1c0-46dc-af55-5eb112a8cbd7eZBei7ckk5e3lPulau Tekong in 2016, voor de landaanwinning. Foto: HDBPulau Tekong in 2024, met de polder in aanbouw. Foto: HDBeZBei7ckk5e3lExpansion of Pulau TekongSometime during the previous decade, Singapore began exploring other methods of land reclamation. During the expansion of Pulau Tekong – a relatively large island just east of the main island of Singapore that serves as a military training ground – the Housing & Development Board (HDB), the body responsible for the project, decided to take a different approach. The reclaimed land was intended for use as a military training ground; this would free up land on the Singapore mainland for the construction of housing and facilities for civilians.The polder concept has been common practice in the Netherlands for centuries. Build a dyke in the water, then pump the water away, and the land that is left dry forms the polder. If the dykes are high and sturdy enough, there is no need to raise the level of the newly reclaimed land. The proposal that Van Zanten submitted to the Singaporean authorities on behalf of Haskoning in May 2013 essentially boiled down to this. ‘A few months later, we were invited to present the proposal. By November, we were able to get started.’Last autumn, seven years after work began in 2018, the polder was completed, covering an area of around eight hundred hectares. The new land lies 1.2 metres below sea level behind a ten-kilometre-long dyke with a crest width of up to fifteen metres and a height of up to six metres above sea level.De nieuwe polder op de noordoostpunt van het Singaporese eiland Pulau Tekong is behalve van een tot vijftien meter hoge dijk voorzien van een uitgebreid, geavanceerd drainagesysteem. Graphic: PUBBermuda grassThe dyke consists of sand with a cement-bentonite wall cast on site in the centre, designed to prevent seawater from seeping through the dyke. For any water that does manage to get through, a drainage channel has been constructed on the landward side of the dyke. On the seaward side, the dyke is lined with natural rock, which is strong enough to withstand the force of the waves.On the landward side, the dyke is covered with Bermuda grass (Cynodon dactylon), which is known for its strong, deep-reaching root system that helps to hold the soil firmly in place. As well as making the dyke body more stable, the vegetation also gives the dyke a natural appearance – particularly for those familiar with the Dutch polder landscape. In the Netherlands, the same grass species is found along the IJsselmeer and in the river clay area. Should rising sea levels make it necessary, the dyke can be raised in the future.Doorsnede van de aangelegde dijk met wand van cement-bentoniet. Graphic: HDBStormwater basin‘A polder works differently from traditionally reclaimed land,’ says Van Zanten. The investment in sand is certainly at least half as much, but more needs to be invested in infrastructure: in dykes, pumping stations, sensors and long-term management. ‘This shifts the costs from a one-off construction phase to a life-cycle approach.’ Singapore’s specific weather pattern, with enormous amounts of rain from time to time, presented a design challenge. The engineers from the consortium – which included Haskoning – resolved this by constructing an extensive water management system.At its heart is a 116-hectare excavated storm basin capable of storing five million cubic metres of water. In addition, 45 kilometres of drainage channels have been constructed, along with more than thirty water inlets and outlets. One pumping station circulates the water through the polder, whilst a second pumps water out to the sea.Het middelpunt van het waterbeheersysteem is een uitgegraven stormbekken dat vijf miljoen kuub water kan bevatten. Foto: HDBWater management system‘Precipitation is much heavier there than in the Netherlands,’ explains Van Zanten. ‘That means the water management system has to be extremely robust.’ To construct the storm basin, more than ten million cubic metres of clay-like soil had to be excavated – enough to fill four thousand Olympic-sized swimming pools to the brim. Some of that soil was used to raise the level of the polder land slightly.What also makes Pulau Tekong special is the high degree of technological integration. The polder area is equipped with advanced monitoring and control systems. Water levels, water quality and dyke stability are continuously measured by a network of more than 170 cameras and 260 sensors. ‘Data plays a crucial role,’ says Van Zanten. ‘You can only build safely below sea level if you know exactly what the system is doing, at any time of the day.’This data-driven approach is in line with Singapore’s broader ‘smart nation’ strategy. In the future, the insights gained from Pulau Tekong can be applied to other coastal areas, both within and outside the city-state. As such, the polder project serves as a living lab for climate-adaptive infrastructure. Learning processAlongside Haskoning and Deltares , Kees d’Angremond, a professor of coastal engineering who passed away in 2024, and dredging specialist Boskalis also contributed their specific expertise. In addition, local players such as the consultancy firm Surbana Jurong played a crucial role. ‘It wouldn’t be possible without local partners,’ says Van Zanten. ‘They have the specific knowledge of the site and the necessary certifications to be allowed to work there.’According to Van Zanten, the project was a learning process for all parties involved. ‘As this is Singapore’s first polder, there was no historical frame of reference. Everything had to be devised from scratch, from the initial design right through to the final maintenance strategy.’The parties involved are keeping the cost of the polder under wraps. ‘This is because operational and maintenance costs can only be accurately estimated after a period of use,’ says Van Zanten. However, the project does fit into the broader context of land reclamation in Singapore. Between 2013 and 2023, land reclamation cost between 270 and 850 Singapore dollars (180–570 euros) per square metre. In total, Singapore has set aside one hundred billion dollars to mitigate the effects of rising sea levels over the next hundred years.Het waterbeheersysteem is ontworpen op klimaat en neerslagpatroon van Singapore, met soms hevige neerslag. Foto: HDB Innovative hydraulic engineeringThe decision to opt for a polder is driven not only by technical considerations, but also by strategic ones. Sand is scarce, expensive and politically sensitive in South-East Asia. By developing alternative methods, Singapore is reducing its dependence on external raw materials: sand that would otherwise have to be sourced from elsewhere in the future. At the same time, the country is preparing for a future in which sea-level rise is no longer an abstract risk, but a daily reality. ‘Pulau Tekong demonstrates that land below sea level is not necessarily a weakness,’ says Van Zanten. ‘Provided it is well designed and managed, it can in fact be a controlled and sustainable solution.’Although Pulau Tekong has only just been completed, the project has already attracted international attention. Other coastal cities are watching Singapore’s approach with interest, particularly now that climate adaptation is higher on the global agenda.Furthermore, at the Hydraulic Engineering Day in autumn 2025, the project was awarded an honourable mention in the prestigious, quinquennial Jan Agema Prize for Dutch-engineered hydraulic engineering works worldwide. ‘This project proves that innovative hydraulic engineering is not confined to a single country or region,’ says Van Zanten. ‘It’s about cleverly combining proven knowledge with new technology and local conditions. Pulau Tekong is an important first step in this regard.’Photo above: Housing and Development Board, Singapore

A polder in the tropics

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A polder in the tropics

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