58 
BULLETIN 115, U. 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 2 870 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- 
'/4 sheet-iron ,_ 
•L'rods over 
expandec 
^ * Arrangement of! floors 
* and ribs above check. <- 
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, 
