CANAL CONSTRUCTION. 



67 



grade must be allowed. The location of the well or 

 reservoir on or near the highest point fixes the point 

 of radiation of the ditches, their lines being located 

 according to the grades secured and the lay of the land 

 to be served. The aim will always be to keep the 



FIG 9 — DROP AND REDUCTION BOX. 



water up as high as possible, for it is useless to sacri- 

 fice grade or make a ditch run at a greater grade than 

 is necessary. It is an easy matter to let the water 

 down, but a difficult thing to raise it. 



A method for dropping the grade of a ditch when 

 the pitch becomes too great is shown in Fig. 9. This 



