DRAINAGE. 



605 



fall for drains is from 0*5 to 1 per cent., but sometimes the 

 lie of the ground may necessitate a certain length of drain of 

 greater gradient. 



The feeders should be obliquely inclined to the line of 

 greatest fall in order to collect the maximum amount of water 



o 



from the soil, and they should conduct the water into the 

 leaders, to which they may be either at right angles or oblique. 

 The former system, as shown in Fig. 270, has the advantage 

 of draining the largest area with the shortest length of drain. 

 Fig. 271 shows oblique drainage, and the more acute the angle 



Fig. 270. Fig. 271. 



Plans of drainage, h. Main-drain, s. Feeders. 



between the feeder and leader, the less will be the area drained 

 by a given length of ditches. 



Thus a, b, c, d > a, b, e, f > a, 6, g, h. 



The choice of the angle between the feeders and leaders 

 depends chiefly on the gradient of the ground, the less the 

 gradient the more acute the angle ; feeders the bed of which 

 gradually deepens as they approach the leader will be most 

 effective. 



Feeders can be laid out parallel to one another only when 

 the gradients are uniform. Figs. 272 to 274 show some 

 interesting ne'tworks of drains by G. Koch. 



