Mr. Downing on the Drainage of Haarlem Lake. 455 



of rain-fall ; nor can it be recommenced until the exterior waters have fallen 

 below the point d'arvM. We see now what a change in the Rynland has 

 been made by laying dry the Lake of Haarlem : 44,500 acres have been 

 deducted from the Basin, and added to the Polders. Instead, therefore, of 

 56,000 and 173,000 acres respectively, we have 11,500 and 217,500 acres for 

 the areas of basin and polders : — 



Before Draining Lake. After Draining Lake. 



Natural Lands, 7G,000 acres. 76,000 acres. 



Basin, 56,000 „ 11,500 „ 



Polder Lands, 173,000 „ 217,500 „ 



305,000 acres. 305,000 acres. 



Consequently, instead of the basin being able to bear nearly 3 inches of 

 rain-fall without stopping the discharge of water from the polders, as in the 

 example just given, it would not bear three-quarters of an inch without produc- 

 ing the same evil effect. The authorities of the Rynland were, therefore, 

 justified in demanding from the Commissioners of the Drainage of Lake Haar- 

 lem guarantees that it should not, when completed, entail any injury upon 

 the rest of the district under their charge. 



In another interesting point of view it was necessary to guard against any 

 injury to this Administration by the successful drainage of the Lake. 



It has been observed in navigable canals, that in very long and straight 

 reaches, the surface, which in calm weather is truly level, becomes, when the 

 wind blows with force and for some time in the direction of the length of the 

 canal, inclined, and sometimes so much so as to impede the navigation. The 

 Dutch have utilized this fact, so inconvenient to others, for, though it may seem 

 almost incredible, the surface of Lake Haarlem was observed, when the wind, 

 generally south-west, blew strongly for some time in the direction of its length, 

 to have a difference of level of up wards of 3 feet, the northern extremity being that 

 much higher than the southern: it is easy to perceive how powerfully this aids 

 the discharge through those sluices towards which the wind impels the waters. 

 A south-west wind not only raises the Lake against the northern sluices, but 

 lowers the surface of the Zuyder Zee, depressing its waters outside the same 

 points by the operation of the same cause, and thus doubling the beneficial 

 effect on the discharge of the waters of the basin of the Rynland. 



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