58 



BULLETIN 115, TJ. S. DEPARTMENT OF AGRICULTURE. 



the bottom of one bay and also serves to waste excess water by rais- 

 ing the radial gates above the upper cover to the sand ducts. 



The waste structure is designed to pass all the water the canal can 

 carry to it ; that is ; 870 second-feet. The check structure consists of 

 three 12-foot openings, regulated by radial gates attached to cables 

 wound around small drums through worm-and-wheel leverage. 



The distinctive feature of this structure, as explained under the 

 general description of the " Land " sand gate, page 55, is the double 

 floor with sand ducts between (fig. 18). On the assumption that 

 most of the sand is close to the bottom, two distinct currents are in- 



s'U boif- 

 Sliding plate B- 



\* Arrangement of floors 

 and ribs above check, t 



Fig. 18. — Portions of sand and waste gate on Amity Canal, Colorado. 



duced in the canal by covering the ducts for some distance above the 

 check gate. When the sand gate is open the steep grade of the ducts 

 causes a high velocity, uninfluenced by any slow water above the 

 floor. 



In order to facilitate the cleaning of clogged ducts, a portion of 

 the upper floor is made of reinforced cement mortar planks. The 

 various ribs forming the ducts serve a double purpose. They not 

 only support the upper floor, but divide the water under the upper 

 floor into several streams so that the sand is carried off in a more 

 general and even manner than would be the case if there were only 

 one large opening under the floor. If the latter condition existed, 

 there would be an excess of " draw " and velocity near the waste gate, 



