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Introduction to watermanagement
25% of the Netherlands of today consists of land below sea level.
This land has been reclaimed from the sea.
Let's have a look of how the reclaiming takes place.
First a dike is built around a large piece of water.
Then the water is pumped out of a section of this large area.
These pieces of land which then are created are called polders and can now be
used for farming and industrial purposes. The actual definition of polder is
a piece of land below sea level surrounded by a dike.
The draining can take place by a windmill or by mechanical pumps.
Windmills drained the oldest areas and therefore Holland used to
have over 10.000 windmills in the past. Later large pieces of Holland were drained
by pumping stations that were first powered by steam machines and later
by electricity and diesel.
The main advantage of a windmill is that the wind is free form of energy where
fuel has to be paid. One of the disadvantages of a windmill is that the wind is
not a very reliable factor, when there is no wind there will be no pumping.
But the main disadvantage of a windmill is the amount of power a windmill can
produce is comparison with a mechanical pump. Not only can a mechanical pump move
more water, but it can also lift it higher than a windmill.
A windmill can lift the water to a maximum of about 1m30, to cope with a difference
of over 2m50 two windmills are placed in cascade and three water levels are created.
First there is the level of the polder, this is the level where the farming takes place.
Then a windmill pumps the water to the second level which is called the boezem level.
This water goes lake a vain through the Alblasserwaard and then brings the water to
Kinderdijk where the water is pumped up by a set of 8 windmills to another level
The water stays here until the reservoir level meets the average high tide of the
river and then the water is disposed into the river at low tide by means of sluices.