Erosion of the Dutch Coast
Because the shoreline is continually crumbling due to coastal erosion, the ability of the dunes, sea dikes and other man-made flood defences for keeping out the water is slowly being undermined. Direct causes are the influences of the currents, tides, waves, wind and sea-level rise. The problems have a structural character and can be found along the whole coast.
 | This map from 1995 shows that the erosion of the sandy coast is strongest along the coast of North Holland north of the North Sea canal up to the Slufter on Texel. Along the South Holland coast and the Zeeland islands, there was some accretion directly along the beach, however the seaward coastal areas were also strongly eroding and therefore growing steeper. In the wadden region, the problems were the greatest near the northeastern part of Vlieland and its bordering sea arm, and to the north of Ameland and its bordering sea arm. The greatest sand-catchers in the Dutch coastal system are the Westerschelde and the Wadden Sea. |
Erosion of the fore banks
Although invisible for beach strollers, the most erosion by far takes place on the fore banks. The sand dunes and ridges under the sea surface are being continually moved about by the ocean currents. There is a net movement of sand in a northwesterly direction, towards the ebb deltas of the sea openings between the Wadden Islands. The sand washes into the Wadden Sea from these ebb deltas. The lack of sand on the fore banks is replenished from the beach.
Wandering islands
Coastal erosion leads to 'wandering' sandbanks and islands: sand is removed from the west coast and deposited on the east coast. On sandbanks where no management occurs, such as the Noorderhaaks near Texel, this process is following its most natural course. In the past, this wandering has resulted in the loss of villages on the western side of the islands of Vlieland and Schiermonnikoog.
Parched dunes
Fresh water floats on salt water. Under the dunes, a freshwater bell is floating on top of the salty groundwater. This freshwater bell is absolutely necessary for the survival of the plants, which retain the dunes. In addition, the high level of this freshwater table in the dune valleys provides a unique vegetation. However, coastal erosion can cause the freshwater bell to come in contact with the open sea and drain. If this happens, the dune valleys behind the first row of dunes dry up, resulting in a strong recession of the dune flora.
Wind erosion
If the vegetation on the beach ridge is damaged, the wind can get a hold of the sand. A hollow is created which usually expands in a northwesterly direction and continually grows deeper. In this way, a weak spot in the beach ridge can evolve. Up till recently, damages to the beach ridge used to be repaired as quickly as possible by planting marram grass. Presently, in the framework of 'dynamic dune management', such hollows are accepted in the dunes as long as they are not a danger with respect to coastal defence.
Wave erosion
Sand is only removed from the beach ridges during heavy storms, when there is a combination of high water levels and large waves. This sand settles on the momentarily flooded beach, which in turn slows down the action of the waves. After a heavy storm, the beach appears raised and flatter than before. The wind blows a good part of the eroded sand back towards the dunes and the process can begin all over. During calm weather, wave action does not damage the beach ridges.
Coastal erosion on Texel
Of all the coastal areas in the Netherlands, Texel endures the greatest structural erosion. Since 1985, Texel has been losing approximately two million cubic meters of sand yearly. Texel accounts for one third of the total erosion along the Dutch coast. Between 1979 and 2003, almost 32 million cubic meters of sand have been sprayed onto the beaches (sand nourishments). A nourishment is good for an average of five years. However at the north point of the island, the erosion was occurring so fast that the nourishments here had to take place more often.
A dam by Eierland, Texel
In 1995, a 550-meter long stone dam was built perpendicular to the north point of the island. This dam redirects the sea current away from the coast. The diminishing current allows the sea to deposit sand on both sides of the dam.
medio 1995
early 1997
Coastal erosion on Ameland
Another Wadden Island where erosion plays a major role is Ameland. After having decreased in the 1980s, it appears as if the erosion is again increasing. The Engelsman sandbank (between Ameland and Schiermonnikoog) is continually diminishing. If this sandbank ends up disappearing, the eastern tip of Ameland could expand in an easterly direction, however the necessary sand will come from the North Sea side of the island, particularly from the middle. Eventually, if no supplementary regulations are taken, Ameland could be so indented that it could split in half.
Coastal erosion in Holland and Zeeland
The coastline in the north of North Holland has known periods of increasing and decreasing erosion. How this coastal erosion will develop over a longer period is dependent upon the sand appetite of the Wadden Sea.
In the northern delta areas, the closure of the sea channels has had a positive effect on the coastal development by Voorne and Goeree (South Holland). Even the coastal area of Schouwen and Walcheren (Zeeland) are hardly experiencing any problems. However, Walcheren and the coast of North Beveland in the vicinity of the Oosterschelde floodgates are having many problems with erosion.
Weblinks
More about coastal erosion (Dutch):
http://www.natuurinformatie.nl/ndb.mcp/natuurdatabase.nl/i000338.html
Fore bank nourishments on Texel (Dutch):
http://projecten.nederlandleeftmetwater.nl/html/topic_22_281.htm
Source: de Vleet, Ecomare
