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Salt Intrusion - There are two major ways in which salt water can 

 intrude upon the Netherlands (the salt intruding the Netherlands via the 

 pollution of the river Rhine we shall leave aside) . The first way is 

 directly from the sea via the river branches coming out into the sea. The 

 Rotterdam Waterway is in this respect the one that causes the main 

 troubles . With the coming of larger and larger ships the Rotterdam 

 Waterway had to be made deeper and deeper. This caused the salt intrusion 

 not only to become more intense, but the salt also intruded further, 

 causing problems at water inlets for agricultural and drinking water 

 purposes. When Europoort, the new harbour area, was finished, further 

 deepening of the Rotterdam Waterway was no longer necessary. The depth 

 could even be decreased. 



A rising sea level will again cause an increase of the salt intrusion. 

 Figures A. 13 and A. 14 show the results of model calculations where sea 

 level was raised over 5 m and where bottom topography remained the same. 

 Big areas such as the Haringvliet, important for fresh water supply, will 

 under the circumstances be intruded with salt water. This salt water will 

 remain in the deeper parts of the Haringvliet and it will be extremely 

 difficult to remove it. If the bottom of the river system rises as fast as 

 the sea level the salt intrusion remains, of course, the same. 



The second major way in which salt water intrudes is via groundwater 

 flow through the subsoil (seepage). Large areas of the Netherlands are 

 below sea level, which causes a groundwater flow to these lower parts. 

 Because the deep groundwater layers in the western part of the Netherlands 

 are brackish, this upward seepage is brackish, too. In many polders the 

 seepage rate is more than 0.25 mm per day. If nothing is done grassland 

 and crops would be damaged. 



The solution is flushing and rinsing of polders and canals with fresh 

 water. In very dry summers not enough fresh water is available for this 

 purpose and crop damage is unavoidable. The amount of seepage is linearly 

 related to the difference in water level between the sea and the 

 groundwater in the polders. It is also linearly related to the distance 

 between polders and sea and the permeability of the subsoil. 



A higher sea level causes a greater gradient and an increase of the 

 seepage. Moreover in certain areas where today there is no seepage, a sea 



