GATE STRUCTURES FOR IRRIGATION CANALS. 29 
so retarded along the edge of the ditch by grass, rocks, and other 
friction elements that in the case photographed the water flowing 
out of the small division at the left of the box had a velocity about 
one-fifth that at the middle of the box. Also in the case shown in 
the plate, the conditions of contraction are not such that the dis- 
charge over the check or weir board is proportional to the length. 
The division board should have been extended as far upstream from 
the check board as the side walls so that the contraction of the cur- 
rent would be completely suppressed by the time the water reached 
the board, and then the discharge would be proportional to the length, 
provided the velocity is uniform across the weir or check board. To 
secure this last condition it is better to pool the water above the box 
by widening and deepening the ditch or by installing baffle boards 
in some form. The nearer still the water is above the box the more 
nearly accurate is the division. 
As usually installed there is a very appreciable velocity toward the 
box, and the diverted water is less than the figured proportion for the 
reason that it is diverted at the side of the ditch while the greatest 
velocity is near the middle. The only thing that can be said in favor 
of this erroneous division is that the consumers at the head get less 
water than they are entitled to, and in this way involuntarily contrib- 
ute water to the ditch to help pay for the losses by seepage and evap- 
oration below their gates. If the division were brought about exactly 
as intended, then the stockholders at the lower end of the ditch would 
have to stand the brunt of the losses. The best way, from a theoreti- 
cal standpoint, is to determine what the losses in transmission actually 
are and take them into consideration in determining the position of 
any particular division wall. Figure 6 shows a wooden division box 
designed to apportion out water quite accurately provided the water 
has but a very low velocity toward the box. 
The box as designed by the writer and shown in figure 6 will deliver 
water to 11 shares of stock out of a total of 36 shares. That is, the 
net opening leading to the delivery box bears the same ratio to the 
total width of opening as 11 bears to 36. Assuming the division wall 
to be of 2-inch lumber, then the total width of opening is TO inches. 
On this basis the position of the division wall is found by the follow- 
ing proportion: 
70 36 
where x is the desired width of the opening leading to the delivery 
box, expressed in inches. Therefore 
70XU 770 
