IRRIGATION 



269 



necessity to protect the farmer who is the purchaser or consumer 

 and the company that furnishes the water. Many devices have been 

 used, hut the most common ami most satisfactory is the weir or 

 overfall (Fig. 120). The weir should be installed where the canal 

 is long, straight and level. A box is placed in the canal so that all 

 water must flow through it. A board with a notch is placed in the 

 box and across the stream. This notch may be several inches or even 



Flo. 121. Trapezoidal or Cippolctti weir, Hhowing method of dividing the stream. (Utah 

 Agricultural Experiment .Station.) 



several feet long and the depth of water flowing through this may 

 be easily measured and the total amount determined from a table. 

 These notches may be either rectangular, trapezoidal, or triangular. 

 The trapezoidal is coming into most general use. 



For purposes of distribution to different laterals the streams 

 are frequently divided at the overfall bv placing a hoard with a 

 sharp edge so as to separate the stream into two or more parts (Fig. 

 121). Each part is then conducted off in a separate lateral to the 

 region desired. 



