( 50) 

 Haarlemmermeer polder was present there already 50 years ago. 



Before that time conditions wei-e very different from what they 

 are now. Instead of tlie deep drainage there was bosom water. How 

 the fresh water then present, especially in tlie eastern part, had come 

 nnder tlie Haarlemmermeer, is difitlcnlt to tell for want of (hita. Was 

 the water of the Haarlem hike always so rich in cidorijie as some 

 old observations show? Certainly the difference in pressnre of the 

 deep gronndwater was smaller tliaii it is now and accordingly the 

 fpiantity of water moved was also smallei', while the direction of 

 the cnrrent in the deep groundwater e.g. near Sloten must have 

 been exactly the reverse. 



A thousand years ago when there were no dykes yet to kee[) out 

 the water of rivers and of the sea, and no mills yet to drain the 

 polders, when the dunes were so much l)i-oader at the seaside tlian 

 they are now, when there were no canals in the dunes yet for sand 

 transport and other jturposes, 1 imagine the stale of allairs in the 

 tract of land we aie considering, nnist have been such that fresh 

 water was also present in the diluvium and probably more than 

 ]iowadays, that in the dunes there existed a high level of ground- 

 water by which water was di-iveu to the diluxiuni, the pressure at 

 the west side under the "old sea-clay" l)eing greater than that of the 

 groundwater aboxe il. The level of the uronndwater in the alluvium 

 of the polderland was then i)robal)ly nuich more regular and slightly 

 higher than the average sea-level. How these conditions became pre- 

 valent 1 must leave to geologists to explain. 



By making dykes, by enclosing polders, by draining, the level of 

 t'he groundwater has gradually been lowered, now in one place, then 

 in another. The currents in the layers of fresh water in the diluvium 

 also had their directions changed by this; they certainly were very 

 small, however, before the great drainages were made. In the tract 

 we are dealing with, 3000 H.A. were drained before 1750, 10.000 

 H.A. between 1750 and 1850 and 2G.000 H.A. between 1850 

 and 1900. 



The dunes gradually decreased in breadth, while also the flow of 

 water towards the land increased by canals for sand-transport etc. 

 The height of the groundwater in the dunes will consequently also 

 have steadilv been decreasing. 



Bearing in mind the figure for the amoujit afflux to in the 

 Haarlemmermeer polder, we may safely assume the quantities of 

 water which befoie the drainages were made, pejietrated vertically 



