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* Water resources. Increasing seepage of salt water into inland polders 

 and increasing salt intrusion via the rivers are of great concern. 

 The present natural drainage of the IJssel Lake during low tide may 

 have to be replaced by a pumping system. Storage of drinking water 

 below the dunes may be diminished. 



* Other structures. Harbours, bridges, locks, etc. may fact alteration. 



Preliminary impact studies by Rijkswaterstaat were first conducted with an 

 extreme scenario of a 5 m sea level rise in order to gain a better 

 understanding of the major mechanisms involved. The results obtained will 

 be discussed in the following sequence: impact on the tidal system in the 

 North Sea, on wage propagation, on coastal morphology, and on ecology. 

 Finally, the costs involved will be discussed. 



Impact on the Tidal System in the North Sea - A two-dimensional 

 hydraulic computer model (WAQUA) of the North Sea and part of the 

 Continental Shelf (Verboom et al . , 1989; see Fig. A. 9) was used to 

 calculate tidal system changes compared to the present situation for sea 

 level scenarios of 2.5 m and 5 m higher, and 2.5m lower, than today 

 (de Ronde and de Ruijter, 1986). 



The main effect was that at higher sea levels and greater water depths 

 the tidal wave propagated faster and tidal amplitudes (water levels and 

 currents) increased. A second effect was the changing of the positions of 

 the amphidromic points (=nearly zero amplitude) (Fig. A. 10). Thus, a 

 location from which the amphidromic point moves away will experience a 

 higher amplitude, and the location to which the amphidromic point moves 

 will experience a lower amplitude. These two effects combined resulted 

 along most North Sea coastlines in an increase of the tidal amplitude 

 (Fig. A. 11). Only locations near the line Cromer-Den Helder experienced a 

 decrease as the southern amphidromic point drew nearer. Here the decrease 

 of the tidal amplitude due to the moving away of the amphidromic is 

 stronger than the increase due to the greater water depth. 



With regard to storm surges, model results showed (de Ronde and de 

 Ruijter, 1986) that a rise of the sea level of 5 meters, while wind 



