Polder

For other uses, see Polder (disambiguation).
Polder at Neßmersiel, Germany, aerial view in May 2012
Satellite image of Noordoostpolder, Netherlands (595.41 km²)

A polder is a low-lying tract of land enclosed by embankments (barriers) known as dikes that forms an artificial hydrological entity, meaning it has no connection with outside water other than through manually operated devices. There are three types of polder:

The ground level in drained marshes subsides over time and thus all polders will eventually be below the surrounding water level some or all of the time. Water enters the low-lying polder through water pressure of ground water, or rainfall, or transport of water by rivers and canals. This usually means that the polder has an excess of water, which is pumped out or drained by opening sluices at low tide. Care must be taken not to set the internal water level too low. Polder land made up of peat (former marshland) will sink in relation to its previous level, because of peat decomposing in dry conditions.

Polders are at risk from flooding at all times and care must be taken to protect the surrounding dikes. Dikes are typically built with locally available materials and each material has its own risks: sand is prone to collapse owing to saturation by water; dry peat is lighter than water and potentially unable to retain water in very dry seasons. Some animals dig tunnels in the barrier, allowing water to infiltrate the structure; the muskrat is well known for this activity and actively hunted in certain European countries because of it. Polders are most commonly, though not exclusively, found in river deltas, former fenlands and coastal areas.

Polders and the Netherlands

Pumping station in Zoetermeer, Netherlands. The polder lies lower than the surrounding water on the other side of the dike. The Archimedes' screws are clearly visible.

The Netherlands is frequently associated with polders. This is illustrated by the English saying: God created the world but the Dutch created Holland.

The Dutch have a long history of reclamation of marshes and fenland, resulting in some 3,000 polders[1] nationwide. About half the total surface area of polders in north-west Europe is in the Netherlands. The first embankments in Europe were constructed in Roman times. The first polders were constructed in the 11th century. As a result of flooding disasters, water boards called waterschap (when situated more inland) or hoogheemraadschap (near the sea, mainly used in the Holland region)[2] were set up to maintain the integrity of the water defences around polders, maintain the waterways inside a polder and control the various water levels inside and outside the polder. Water bodies hold separate elections, levy taxes and function independently from other government bodies. Their function is basically unchanged even today. As such they are the oldest democratic institution in the country. The necessary cooperation between all ranks in maintaining polder integrity also gave its name to the Dutch version of third way politics—the Polder Model.

The 1953 flood disaster prompted a new approach to the design of dikes and other water-retaining structures, based on an acceptable probability of overflowing. Risk is defined as the product of probability and consequences. The potential damage in lives, property and rebuilding costs is compared to the potential cost of water defences. From these calculations follows an acceptable flood risk from the sea at one in 4,000–10,000 years, while it is one in 100–2,500 years for a river flood. The particular established policy guides the Dutch government to improve flood defences as new data on threat levels becomes available.

Some famous Dutch polders and the year they were laid dry are:

As part of the Zuiderzee Works:

Examples of polders

Bangladesh

Bangladesh has 123 polders, of which 49 are sea-facing. These were constructed in the 1960s to protect the coast from tidal flooding and reduce salinity incursion.[3] They reduce long-term flooding and water-logging following storm surges from tropical cyclones. They are also cultivated.[4]

Belgium

Canada

France

Germany

Guyana

Black Bush Polder, Corentyne, Berbice

India

Italy

Japan

Lithuania

Netherlands

Poland

Slovenia

South Korea

United Kingdom

United States

See also

References

  1. ↑ "TKijk naar de geschiedenis". Rijkswaterstaat. Retrieved 2008-01-21.
  2. ↑ "waterschap". Archived from the original on 2012-11-02.
  3. ↑ Bangladesh polders under threat
  4. ↑ Bangladeshi project to enhance polders amidst climate woes
  5. ↑ "Rain continues to throw a challenge in Kuttanad". The Hindu (The Hindu Group). 2011. Retrieved 2011-06-10.
  6. ↑ Thampatti, Manorama (March 1999). "Rice Bowl in Turmoil: The Kuttanad Wetland Ecosystem". Resonance (Indian Academy of Sciences). Retrieved 2011-06-10.

External links

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