GATE STEUCTUEES FOE IEEIGATION CANALS. 55 



crest of the gate shutters of this type of structure usually furnishes a 

 good opportunity to waste excess water in the canal by simply adjust- 

 ing the crest height of the closed gates to the water line deemed a 

 safe elevation. The radial gate offers a good opportunity in this class 

 of structures, the scouring action coming at the bottom where it is 

 desired. 



THE TRENCH GATE. 



The second type is used only on small ditches and is a modification 

 of the first. It consists of a channel or groove set in the floor of 

 the ditch across the line of the latter. A sliding gate is set in the 

 end of this channel, opening out through the lower bank. A check 

 board or strip of iron is fastened to the floor of the ditch immediately 

 below the channel. This serves to stop the sand and drop it into 

 the channel, from which it is flushed by a continuous stream, passing 

 out through the gate. In the opinion of the writer it is best to build 

 the channel across the bottom of the ditch at an angle, with the gate 

 at the lower end. This would cause the filaments of current in 

 the ditch to take the direction of the channel and help carry out the 

 sand. 



A sand gate in the South Boulder and Coal Creek Canal, a small 

 ditch diverting water from South Boulder Creek at the town of 

 El Dorado Springs, Colo., has a channel set in the bottom of a 

 section of wooden flume, opening over the side of the ditch into the 

 creek. This channel is about 5 inches wide and 6 inches deep, with 

 a check board made of simple 2 by 4 inch lumber set on edge imme- 

 diately below the lower edge of the channel. This channel is at 

 right angles to the flume. 



This type of gate is easily clogged with trash, the channel being 

 so small that a little stick could effectually commence the clogging 

 of the opening. This may be prevented by putting in a grating of 

 bars, slanting very gradually up from the floor above the channel 

 to the top of the check board. The gentle incline to the bars will 

 cause debris to be pushed on over the check board rather than " glue " 

 to the grate, while the sand is admitted readily between the bars. 



THE " LAND " GATE. 



The third type of sand gate, and the one commonly used in the 

 Arkansas Valley of Colorado, was first built by Mr. Gordon Land, 

 of Denver, Colo., and has been known as the Land gate. This 

 structure is essentially a check and waste gate with a double floor 

 above the check, the upper floor being on the normal grade of the 

 canal, while the space between the floors is separated by ribs into 

 ducts. These ribs carry the upper floor and are curved so that the 



