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guilders (3 billion U.S. dollars). Interestingly, the possibility of a 

 storm surge barrier in the Rotterdam Waterway is currently under study as 

 an alternative to the very high cost of strengthening the dikes along the 

 lower river branches. The prospect of an increasing rate of sea level rise 

 makes this alternative all the more attractive. 



Although the structural adjustments required would be more complex 

 than for the coastal defense, the amount of money involved is less. An 

 investment of 3 billion guilders would be needed for pumps and changes in 

 the infrastructure. The annual input costs (fuel) will increase by about 

 10 million guilders per year. Furthermore, harbours, locks, bridges, etc. 

 would have to be adapted to the new situation; these costs would be roughly 

 1 billion guilders. 



The total costs of adaptation to a 1 -meter sea level rise over one 

 century can be estimated at about 10 billion guilders (5 billion U.S. 

 dollars). For comparison, the costs of the Delta Works (1958-1988) were 

 about 14 billion guilders. 



Conclusions 



Mean sea level rise in the Netherlands has been between 15 and 20 cm 

 per century. It is likely that sea level rise was not constant during the 

 last 300 years and even negligible before 1850. During the past 20 years 

 the Dutch coast has lost 5.3 million cubic meters of sand per year along 

 the eroding parts and gained 3.4 million cubic meters per year along the 

 accreting parts. As a whole, the Dutch coast is losing 1.9 million cubic 

 meters per year. 



A future acceleration of sea level rise will have great consequences 

 for a low- lying country like the Netherlands. Due to a 1 -meter sea level 

 rise: 



The tidal motion in the North Sea and along the Dutch coast will 

 hardly change. 



The storm surge heights will change insignificantly. The effect due 

 to changes in storm frequency or severity of storms will be much more 

 important, although at present it is unknown if frequency and severity 

 will increase or decrease. 



