Polders and Dykes in the Netherlands
Created | Updated Sep 2, 2012
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Nearly 50% of the Netherlands is protected from flooding by dykes and dams. Also quite a lot of the Netherlands used to be sea or lake bed.
A Brief History
It all started in the 19th Century. The Harlemmermeer (Harlem Lake) used to be an area with peat, used as fuel. By digging up the peat, lakes were formed. Due to the prevailing southwesterly wind, the lake grew bigger and bigger, threatening Amsterdam. The Dutch engineers decided to pump it dry and use it as farmland, which seems at first like a particularly stupid idea as it would keep flooding. They solved this by building a wall, or 'dyke', around the lake with a canal, or Ringvaart, just behind that. Windmills, and later on steam and electric pumps, were used to pump the water out of the lake into the Ringvaart which lead via other canals and rivers to the sea. The dry lake bed is called a polder.
This science of creating polders was perfected over the following decades. In the 1950s, the Dutch were tired of the constant floods in the Zuiderzee (South Sea), so they decided to close off the bay in the centre of the Netherlands by building a 70 kilometre long dyke through the sea1. This caused the whole Zuiderzee to become a lake: the Ijsselmeer. At first this was obviously a salt-water lake but through the years it has become a fresh-water lake.
Due to the need for agricultural ground, they carried on using this technique in the Ijsselmeer and made another lake within it. This was pumped dry and is now Flevoland, the largest polder in The Netherlands, and possibly the world!
After the Second World War, the Dutch started using the polders for cities. Flevoland is one of the biggest growing cities for people who want to live close to Amsterdam.
A polder is a piece of reclaimed land, either from the sea or a lake. The principle is very simple. You build a big wall, or dyke, around the piece of land you want. Then you put quite a few big pumps inside the wall and pump the water out. Now you have a piece of relatively dry land.
The problem is that the water seeps back under the dyke so you have to keep pumping. That is the reason why everywhere in The Netherlands there are canals. These collect the water which is then pumped into the sea.
The dykes are built to protect the polders, and keep the water from flowing into them. They have to be quite high, due to storms. Also every year more land is claimed from the sea. This means that more dykes have to be built, so in some parts of the Netherlands there are many dykes behind each other. The dyke closest to the sea is called the wakende dijk (guarding dyke), the one after that is the slapende dijk (sleeping dyke) and next ones are called the dromende dijken (dreaming dykes).
Dykes are also built next to the rivers. The rivers have to flow into the sea so they are always above sea level. Quite a lot of The Netherlands is below sea level. The dykes stop the rivers flowing into the polders, just like the dykes by the sea. Usually at rivers there are two dykes behind each other. The front one is a summer dyke and the other a winter dyke. In the summer there is land all the way to the summer dyke. In the winter the summer dyke is under water and the winter dyke stops the water. This way you have more ground in the summer for eg herding sheep. The extra ground in the summer is called Uiterwaarden.