253 



John G . de Ronde 



Ministry of Transport and Public Works 



Rijkswaterstaat , DGW 



Tidal Waters Division 



P. 0. Box 20904 



2500 EX Den Haag 



The Netherlands 



PAST AND FUTURE SEA LEVEL RISE IN THE NETHERLANDS 

 Introduction 



In the first part of this paper a view will be given of the changes 

 along the Dutch coast in mean sea level and coastal erosion during the last 

 century (centuries) . The second part will deal with the expected impacts 

 for the Netherlands of an accelerating sea level rise. 



Past Changes in Mean Sea Level and Coastal Erosion/Accretion 



The longest and oldest set of mean sea level in the world is recorded 

 in the Netherlands in Amsterdam (Van Veen, 1954). Fig. A. 2 shows the 

 filtered data sets of Amsterdam, Brest, and Den Helder together with the 

 global average data set made by Gornitz et al. (1982). The filter process 

 used cubic spline functions, where these splines were fitted to the data 

 with a least squares method. The curves of Amsterdam and Brest show a 

 remarkable "bend" between 1850 and 1900, which also seems to be present in 

 the curves of Den Helder and the global average. It is likely that sea 

 level rise was not constant during the last 300 years and even negligible 

 before 1850. 



The same filter procedure was used for eight stations along the Dutch 

 coast (Fig. A. 3). A map showing the positions of these stations is given 

 in Fig. A. 4. The curves of the eight stations agree rather well after 

 1900, but before 1900 only Flushing and IJmuiden show a large fluctuation, 

 which is not or only hardly present in the other curves . An explanation of 

 this behavior has not yet been found. For comparison, the trends have been 

 calculated over the period after 1900 to avoid the differences before 1900. 

 Table A. 5 shows the mean sea level rise together with the mean rise of 



