DRAINAGE. 



barrier to llie water. Such works 

 are generally undertaken by associa- 

 tions, few individuals being possess- 

 ed of sufficient capital, or having the 

 power to oblige all w-hose interests 

 are affected by the draining of the 

 land to give their consent and afford 

 assistance. 



" All these operations require the 

 science and experience of civil engi- 

 neers, and cannot be undertaken 

 without great means. The greater 

 part of the lowlands in the Nether- 

 lands, especially in the province of 

 Holland, have been reclaimed from 

 the sea, or the rivers which flowed 

 over them, by embanking and drain- 

 ing, and are only kept from floods by 

 a constant attention to the works 

 originally erected. 



" '\^"here the land is below the level 

 of the sea at high water, and without 

 the smallest eminence, it requires a 

 constant removal of the '-vater which 

 percolates through the banks or ac- 

 cumulates by rains ; and this can 

 only be effected by sluices and mills. 

 The water is collected in numerous 

 ditches and canals, and led to the 

 points where it can most convenient- 

 ly be discharged over the banks. The 

 mills commonly erected for this pur- 

 pose are small wind-mills, which turn 

 a kind of perpetual screw made of 

 wood several feet in diameter, on a 

 solid axle. This screw fits a semi- 

 circular trough, which lies inclined at 

 an angle of about 30" with the ho- 

 rizon. The lower part dips into the 

 water below, and by its revolution 

 discharges the water into a reservoir 

 above. All the friction of pumps, and 

 the consequent wearing out of the 

 machinery, is thus avoided. If the 

 mills are properly constructed they re- 

 quire little attendance, and work night 

 and day whenever the wind blows. 



" In hilly countries it sometimes 

 happens that water, which runs down 

 the slopes of the hills, collects in the 

 bottoms where there is no outlet, and 

 where the soil is impervious. In that 

 case it may sometimes be laid dry by 

 cutting a sufficient channel all round, 

 to intercept the waters as they flow 

 down, and to carry them over or 

 I' 2 



through tlie lowest part of the sur- 

 rounding barrier. If there are no 

 very abundant springs in the bottom, 

 a few ditches and ponds will sufli(;e 

 to dry the soil by evaporation from 

 their surface. We shall see that this 

 principle may be applied with great 

 advantage in many cases where the 

 water could not be drained out of 

 considerable hollows if it were allow- 

 ed to run into them. 



" When there are different levels at 

 which the water is pent up, the drain- 

 ing should always be begun at the 

 highest, because it may happen that 

 when this is laid dry tlie lower may 

 not have a great excess of water. 

 At all events, if the water is to be 

 raised by mechanical power, there is 

 a saving in raising it from the highest 

 level, instead of letting it run down 

 to the lower, from which it has to be 

 raised so much higher. 



" In draining a great extent of land, 

 it is often necessary to widen and 

 deepen rivers, and alter their course ; 

 and not unfrequently the water can- 

 not be let ofT without being carried, 

 by means of tunnels, under the bed 

 of some river, the level of which is 

 above that of the land. In more con- 

 fined operations, cast-iron pipes are 

 often a cheap and easy means of ef- 

 fecting this. They may be bent in a 

 curve, so as not to impede the course of 

 the river or the navigation of a canal. 

 " The draining of land ivhich is reii- 

 dcrcd u-et bi/ springs arising from under 

 the soil is a branch of more general 

 application. The principles on which 

 the operations are carried on apply 

 as well to a small field as to the great- 

 est extent of land. The object is to 

 find the readiest channels by which 

 the superfluous water may be car- 

 ried off; and for this purpose an accu- 

 rate knowledge of the strata through 

 which the springs rise is indispen- 

 sable. It would be useless labour 

 merely to let the water run into drains 

 after it had sprung through the soil 

 and appears at the surface, as igno- 

 rant men frequently attempt to do, 

 and thus carry it off after it has al- 

 ready soaked the soil. But the origin 

 of the springs must, if possible, ba 



233 



