FLUSHING DKAINS. 



149 



outlet, and c, c, are the small collecting drains. The 

 small drains follow the direction of the greatest slope of 

 the ground. 



The system of drains to be adopted will, in all cases, 

 conform to that of the system of canals and furrows. When 

 in perfection the drainage system will be an exact counter- 

 part of that of the irrigation, and so devised as to carry 

 off the water after its service has been performed, and to 



Fig. 75. MANNER OF SUB-DRAINING AN IRRIGATED MEADOW. 



cause it to circulate completely through every portion of 

 the soil occupied by the roots of the grass, after it has 

 been spread completely over the surface. The construc- 

 tion of the drains is in no wise different from that of 

 ordinary tile drains, and therefore needs no description 

 here. 



It is sometimes found of great service, consequent 

 upon the frequency with which sand or earthy sediment 

 is carried into the drains, to provide a method of flooding 

 and flushing them. This is called intermittent drainage. 

 It is applied also very advantageously to fields that are 

 subjected to intermittent irrigation, or irrigation by sue- 



