444 



IRRIGATION FARMING. 



the soil on the upper side, from a distance of a rod or 

 more, by the porous texture of such soil, so the earth, 

 being equally porous on the lower side, will allow it 

 to leak out and pass a rod or more on the lower side 

 toward the next ditch below. 



If the trenches are cut dire<5lly down the slope by 

 the shortest course, no water can leak out, as there is 



•>1 



V. 4 





•V 



FIG. 112 — CORRECT DRAINAGE. 



no lower side, but it all takes the ready channel offered 

 it and rapidly escapes. This ready channel in effedl 

 draws the water from the soil on each side, the bottom 

 of the ditch being lower than the adjacent soil, while 

 the natural descent of the ground and the downward 

 currents are quickly carried off by the central ditches, 

 the arrows in both the figures showing the currents. 

 The difference should be always borne in mind between 

 the water currents as they soak slowly through the 

 earth by natural drainage, or as they rush rapidly 

 down-hill through tile or other smooth and straight 



