GATE STRUCTURES FOR IRRIGATION CANALS. ()0 
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 
