(751) 



such as tlie Haarlemmermeer polder and I ho adjacent deep ones, 

 upward. It is a wellknown fact that the water in deep wells rises 

 above tlie snrfaee of the nndergronnd water and above the grass- 

 land of the deep polders. In polders of smaller depth, tlie deep 

 welhvater remains below the surface. Likewise the ascending 

 power of tlie water, as a rule, gradually diminishes towards the 

 middle of the deep polders. In higher parts, such as in the dunes 

 and in the Hat sandy adjacent area, the surface of the undei-- 

 gronnd water is considerably higher than the level of the water 

 in the deep wells. So here we find increase of pression from 

 below upward, and descending movement of the water. In the 

 dunes near Castricum the level of the surface of the underground 

 water is about 1.30 M. higher than that reached in the deep 

 wells ; at Santpoort, at the inland side of ihe dunes, the difference 

 eveu being 1.80 M. 



In connection with the above indicated conditions, especially in 

 the colder seasons, when the underground ^vater is generally fed 

 with the water penetrating the soil from the rainfall, the dunes, 

 the shallow polders and the intermediate area will get a fresh 

 supply of water, wliereas there is always a loss by the pumping in 

 the deep polders, to which, certainly in no less degree than to the 

 sea, there is a constant affluence. The underground water not being 

 of distant origin, it can as a matter of coui-se be derived only from 

 rains on the spot itself, or at a small distance. 



.lust a passing reiuark in connection with the results arrived at, 

 to call the attention to the drying out of the dunes and especially 

 of the lower stretches of land west of the H. M. polder. This drying 

 out, i.e. considerable lowering of the surface-level of the underground 

 water, actually noticed for already half a century, has repeatedly been 

 attributed to the w^aterworks in the tlunes for the water-provision 

 of Amsterdam; to my opinion howevei- it is in the first jdace 

 due to the draining of the Haarlemmermeer, just iialf a century 

 ago, from which event dates the powerful subterranean cui-rent 

 from the dunes to the deep extensive Haarlemmermeer })older. 

 Especially in the lower tracts from Zuidschalkwijk to Benuebroek, 

 up to a few kilometers from that polder, the drying out process 

 has made itself felt, on account of clay above the coarse-grained 

 sand being almost entirely lacking. In those parts the water in the 

 ditches, when there is no fresh artificial in-flow, will soon sink down, 

 actually making its way under the encircling canal of I lie II. M. 

 polder, as is proved by the considerably lower level in part of 



