IRRIGATION TOOLS AND DEVICES 



431 



foot per second is often the maximum, while in clay, a 

 velocity of 3 feet per second may be adopted. Some soils 

 "wash" so easily that a very small velocity only may be 

 used. The farmer 

 must learn for himself 

 the nature of his soil 

 and the ditch grades 

 that may be safely 

 adopted. In ordinary 

 materials a velocity 

 of 2 to 2J/2 feet a 

 second are considered 

 safe. Naturally the 

 grade of the ditch can not exceed that of the land. 

 Fortier has figured the flow of water in each of five 

 types of farm ditches (Fig. 134) which cover ordinary 

 farm conditions. His results follow. 



FIG. 149. Lath check. 



tto'fots' it ^o'/9 **ljL_ idto J'-4 



FIG. 150. Conducting water down inclines in concrete pipes. 



