The Netherlands could be characterised by three words: water and water and water. Water from the skies, water from the rivers and water from the sea.
75 years ago, this Pentecost-weekend, the last stretch of a thirty plus kilometres long seawall was closed between the North Sea and the Zuiderzee - the latter one now called the IJsselmeer (IJssel lake).
With old-fashioned steam engines and much hand labour, a large portion of the Dutch coastline was protected from wind and water coming from the North Sea.
Another advantage of the creation of the Ijsselmeer, which is fed by a branch of the river Rijn (Rhine), is a sweet water-area that can be used for human consumption and agriculture.
The water from the skies is hard to catch; by complicated channelling, it is fed into the IJsselmeer. Large rivers like the Rijn, Maas and Schelde bring water from Switzerland, France, Germany and Belgium, the greater part of Western Europe, to the area.
If heavy rains occur in those countries or lots of melt water is generated, rivers flood quite frequently, but the most serious threat is the North Sea. In 1953, due to heavy storms and very high sea water levels, several sea-walls broke on the islands in the South Western part of the country. The population suffered quite a few deaths and much property was destroyed. The storms were so heavy that it was impossible to close the holes in the sea-walls by conventional methods .
Luckily, some large caissons were left over from the allied activities at Arromanche, during the Second World War. These had been used to create an emergency harbour to land troops and materials during the invasion of Northern France, to roll the German troops back into their country. These caissons were huge concrete boxes that were cast in the South of England and brought over to France by tugboats where they were sunk to provide a pier for discharging troops and war materials.
Due to the expected rising sea levels, the North Sea coast of the Netherlands will need much better protection than at present. Approximately 140 kms. of coastline, from the Hook of Holland to Den Helder, should be better protected. Raising the level of individual sea walls, however, is not very practical. A better solution seems to be a new sea wall, several hundred meters into the sea, parallel to the present coastline. Concrete caissons - say one hundred meters long - could be strung together to provide the basis for this new sea wall.
The caissons could be sunk into a channel dredged into the sea bottom to keep them well in place. The ends of the caissons could be provided with concrete walls, sticking out like fingers, that would provide hollows between the caissons that would be filled with clay to provide sufficient water tightness. On the seaside, the caissons could be protected against the waves by concrete rocks or tetrapods.
The water from the rivers would have to be raised to sea level. This could be achieved by building alongside the rivers similar walls, as in the sea, over such a length of land inward, that the river water would be backed up efficiently to reach the sea level. That way there would be no need for all the river water to be got rid of by pumping.
ir. C. de Neeff
U.N. OBSERVER & International Report
75 years ago, this Pentecost-weekend, the last stretch of a thirty plus kilometres long seawall was closed between the North Sea and the Zuiderzee - the latter one now called the IJsselmeer (IJssel lake).
With old-fashioned steam engines and much hand labour, a large portion of the Dutch coastline was protected from wind and water coming from the North Sea.
Another advantage of the creation of the Ijsselmeer, which is fed by a branch of the river Rijn (Rhine), is a sweet water-area that can be used for human consumption and agriculture.
The water from the skies is hard to catch; by complicated channelling, it is fed into the IJsselmeer. Large rivers like the Rijn, Maas and Schelde bring water from Switzerland, France, Germany and Belgium, the greater part of Western Europe, to the area.
If heavy rains occur in those countries or lots of melt water is generated, rivers flood quite frequently, but the most serious threat is the North Sea. In 1953, due to heavy storms and very high sea water levels, several sea-walls broke on the islands in the South Western part of the country. The population suffered quite a few deaths and much property was destroyed. The storms were so heavy that it was impossible to close the holes in the sea-walls by conventional methods .
Luckily, some large caissons were left over from the allied activities at Arromanche, during the Second World War. These had been used to create an emergency harbour to land troops and materials during the invasion of Northern France, to roll the German troops back into their country. These caissons were huge concrete boxes that were cast in the South of England and brought over to France by tugboats where they were sunk to provide a pier for discharging troops and war materials.
Due to the expected rising sea levels, the North Sea coast of the Netherlands will need much better protection than at present. Approximately 140 kms. of coastline, from the Hook of Holland to Den Helder, should be better protected. Raising the level of individual sea walls, however, is not very practical. A better solution seems to be a new sea wall, several hundred meters into the sea, parallel to the present coastline. Concrete caissons - say one hundred meters long - could be strung together to provide the basis for this new sea wall.
The caissons could be sunk into a channel dredged into the sea bottom to keep them well in place. The ends of the caissons could be provided with concrete walls, sticking out like fingers, that would provide hollows between the caissons that would be filled with clay to provide sufficient water tightness. On the seaside, the caissons could be protected against the waves by concrete rocks or tetrapods.
The water from the rivers would have to be raised to sea level. This could be achieved by building alongside the rivers similar walls, as in the sea, over such a length of land inward, that the river water would be backed up efficiently to reach the sea level. That way there would be no need for all the river water to be got rid of by pumping.
ir. C. de Neeff
U.N. OBSERVER & International Report