Fending off the floods – 5 things to know about polders and how they could work in Singapore

Fending off the floods – 5 things to know about polders and how they could work in Singapore

DELFT/NIJMEGEN, Netherlands: “If I show you around, you wont be aware that you are in a polder area,..

DELFT/NIJMEGEN, Netherlands: “If I show you around, you wont be aware that you are in a polder area,” said Tjitte Nauta from Dutch research institute Deltares.

Turning to me, he continued: “Where you sit is 3 metres below sea level.”

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While they be unfamiliar to many, polders are a crucial part of the Dutch landscape – a key defence in the European countrys centuries-long battle against water.

READ: Tides of change – Amid rising sea levels, the Dutch float new initiatives with farms and more homes on water

READ: Tides of change – From fighting against the seas to living with it – How the Netherlands kept itself dry

By building dykes alongside a network of drainage canals and water pumps, the Netherlands, which literally translates to “low lands”, has turned its flood-prone areas into usable land that is suitable for tens of millions of people to live, work and play.

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One example is where Deltares headquarters is located.

Deltares, an independent applied research institute, sits on a polder that is 3 metres below sea level. (Photo: Tang See Kit)

The polder, one of thousands across the country, was previously a vast swathe of swamps, according to Mr Nauta.

This Dutch model of polders is now a “serious option” for Singapores eastern coastline, Prime Minister Lee Hsien Loong said at his National Day Rally speech last month.

Already, a small polder is being built at Pulau Tekong to gain some experience. The new land will be used for military training, added Mr Lee.

So how do polders work and how different are they from the typical reclamation method?

READ: NDR 2019: It could cost S$100 billion or more to protect Singapore against rising sea levels, PM Lee says

READ: New reclamation method aims to reduce Singapore's reliance on sand

1. WHAT ARE POLDERS?

Polders are tracts of land that lie below sea level and are reclaimed from the ocean, lakes, rivers or wetlands through the building of dykes, drainage canals and pumping stations, according to Dutch experts that CNA spoke to.

“Polders are land reclamations, but not all land reclamations are polders. When the level of the land is higher than sea level and no pumping is required, there is no polder,” said Associate Professor Mick van der Wegen from the IHE Delft Institute for Water Education.

Hence a key feature of polders, according to Mr Nauta from Deltares, is that they are “hydrologically separated” from their surroundings.

“This means you can control the water within a polder through pumping stations usually.”

It works like this: The submerged area is first enclosed, or sometimes partially, by a dyke to keep water out. Water from within is then drained, creating a polder – dry land that is lower than sea level.

A polder is kept dry by an extensive grid of canals – from small drains to big canals with sluice gates to control water flow – and pumps. Retention areas may be created to store water in case of emergencies.

“Excess water will flow over land if you dont create space so you will always see canals in polders. From there, we will pump it out,” said Mr Mark van Zanten, a senior project manager at Dutch engineering consultancy firm Royal HaskoningDHV, who is involved in the polder development on Pulau Tekong.

While the most iconic images of the Dutch landscape usually show polders as rectangular plots of flat land, they can come in other shapes and have various heights – still below sea level.

These height variations can be naturally-occurring from sea or river beds. They can also be man-made, when sand is added to make the land suitable for residential and other purposes, said experts.

The 4,450-hectare Noordwaard polder is one of the thousands of polders that form a crucial part of the Dutch landscape. (Photo: Dutch Ministry of Infrastructure and Water Management)

2. HOW DID THEY COME ABOUT?

Having been around for a long time, some have said that the Netherlands would look very different without polders.

“If you look at the maps through the centuries, youd see the country growing,” said Mr van Zanten. “We wouldnt be who we are without polders.”

Bounded on one end by the North Sea and with three of Europes major rivers – the Rhine, Meuse and Scheldt – running through the heart of the country, the very first polders were built some 2,000 years ago by farmers who wanted to protect their land against flooding.

They built dykes, dug canals and began draining the waterlogged areas.

By the 15th century, the now-iconic windmills were built to help drive water pumps, making polder-draining much more efficient and reclaiming larger swamps and lakes possible.

Traditional windmills seen at tourist hotspot Zaanse Schans in the Netherlands. (Photo: Tang See Kit)

Steam-driven pumping stations arrived at the end of the 18th century, followed later by diesel and electricity-run ones.

These days, almost all pumping stations in the Netherlands are driven by electricity.

According to figures from the Union of Water Boards, there were 3,700 water pumping stations across the Netherlands in 2018.

3. WHAT ARE POLDERS USED FOR?

Agriculture remains a common use, as seen by vast fields dotted by farmhouses and grazing cows, as well as canals and the occasional windmill.

Polders are also used for other purposes in the Netherlands, including providing land for residential, commercial, industrial and military needs.

Amsterdams Schiphol Airport is built on polder land, which was created by the draining of the Haarlemmer Lake in 1852.

“Technically, the airport lies on the bottom of the lake, over four metres below sea level … making Schiphol one of the world's most low-lying airports,” according to its website.

Houses are built on this polder area in the city of Delft which lies more than 6 metres below the sea level. (Photo: Tang See Kit)

4. WHAT ARE THE PROS AND CONS?

Experts said the Dutch model of polders uses less sand compared with regular reclamation, which heightens th

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