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© 2010 www.kustatlas.be | FAQ
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An initiative by the Co-ordination Centre for Integrated Coastal Zone Management
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| (after Prof. C. Baeteman) |
| Schematic representation of the coastal plain in the Roman period (after H. Thoen, ed., 1983) |
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» About 10,000 years ago: The North Sea reached our regions, which were influenced by the tides from that moment on. The history of the development of the coastal plain is characterized by constant shifts of different deposit environments such as tidal channels, mudflats and salt marshes.
» About 9,500 years ago: The sea level rose, causing the groundwater level to rise as well. A freshwater swamp was created in which peat accumulated. In the lowest lying part of the landscape a tidal area developed on top of the peat. For about 2,000 years the sea level continued to rise with an average speed of 7 metres/1,000 years, which resulted in the area being filled to a large extent with sand and clay.
At the same time the tidal area expanded inland at a fast rate.
» Holocene evolution of the western coastal landscape
(after Prof. C. Baeteman) (POP-UP)
» About 7,500-7,000 years ago: Because the rate at which the sea level rose slowed down considerably (to 2.5 metres/1,000 years) parts of the flats rose sufficiently high by accretion, as a result of which these flats were less frequently flooded. Freshwater swamps in which peat could develop were created. Tidal channels were constantly moving. About 5,500-5,000 years ago the speed at which the sea level rose slowed down a second time (to 0.7 metre/1,000 years), as a result of which the peat could continue to grow and to accumulate.
The reed vegetation that came into existence evolved into a vast coastal peat swamp, which covered the entire coastal plain about 4,200 years ago.
» In the period between 2,500-2,000 years ago:
The peat growth suddenly stopped about 2300 years ago when the tide re-entered the coastal plain through the tidal channels that were still open. These channels had been filled during the peat growth, but were now scoured again by means of increased transport of rainwater from the higher-located hinterland (caused by climate change and deforestation). Once the tidal channels were largely sediment-free again the tides could freely re-enter and the peat at the sides of the channels was swept away.
This erosion resulted in the dehydration of the peat area, as a result of which the surface subsided considerably in a relatively short time (1 to 1.5 m) and was filled with sediments again: new flats were created. About 1500 years ago the growth of peat finally also came to a stop in the areas of the coastal plain that were located most inland.
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It cannot be ruled out that human activities (such as drainage of the peat area for better accessibility or peat extraction for salt production) also contributed to the subsidence of the surface level in the Roman era.
» After the Roman period: The coastal plain dried up, the channels were filled until the surface was back on the same level as the sea level, and the major part of the area evolved into salt marshes. As the coastline started receding and large areas of land located in the sea eroded, large parts of the salt marshes were no longer flooded by the sea, not even at spring tide. Consequently, the area gradually freshened and the salt marsh vegetation was gradually replaced by freshwater vegetation. The elevated parts evolved into salt pastures.
» From the 10th century onwards: The first cultivations and embankments were realised. The salt pastures were used for sheep breeding and later on for habitation as well. As the area was still subject to flooding a couple of times a year during extremely high tides, people elevated their homes and constructed dykes.
These "old sea dykes" were not very high and most were situated perpendicular to the coast line as the water entered through the channels. Consequently, these dykes were not intended as coastal defence structures but were constructed to avoid that the land was still flooded during extremely high spring tides.
Because man continued to drain the embanked area by digging ditches the clay settled down and the land surface subsided as a consequence. However, sediments were still deposited in unembanked areas and the surface level in these areas continued to rise.
As tidal channels were filled and embanked to an increasing extent, the water level in them reached extreme heights during heavy storms, which resulted in catastrophic floods if a dyke broke. However, these floods had a local character and were limited to the areas surrounding the channels that were still open.
Since then the area has been embanked systematically and man has increasingly bent nature to his will. Reclamations, embankments, alignments, dredging operations and coastal defence structures have given the coastal plain its current appearance and shape.
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