Mar. 13,1916 
A New Irrigation Weir 
1131 
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-32.67- 
4 - 5 * 
Fig. 5.—Plan. of experimental weir box for No. 17, Table I. 
tion distances, lengths of weir box, contraction wings at entrance of weir 
box, and angle of sides of weir box. From these data a set of conditions 
was chosen to be the standard for the new type of weir, for it is obviously 
necessary that the weir box be definitely standardized in order that the 
specifications be duplicated in future installations if the formula and 
tables are to apply. The terms “standard tests” or “standard condi¬ 
tions” will be used to express those conditions which have been taken 
as the basis of the formula and discharge tables. 
The water passes through the weir box with a rather high velocity, 
but the velocity varies 
with the head, and the 
slope of the water sur¬ 
face changes accord¬ 
ingly. The extent of 
the draw-down curve 
also varies with the 
head and length of 
weir crest and it was 
therefore necessary to 
fix the point at which 
to take the head. 
Several measurements 
of draw-down curves 
resulted in choosing 
a point 6 feet back 
from the plane of the 
weir, which would be 
away from any con¬ 
siderable influence of 
draw-down for the 
weirs used in the ex¬ 
periments, and would 
surface. 
A total of 277 experiments were made on this new type of weir, which 
for want of a better name is called an “irrigation weir,” and of this num¬ 
ber 101 were preliminary tests and 176 were made under standard con¬ 
ditions. 
DEDUCTIONS FROM EXPERIMENTS 
Fig. 6. —Plan of experimental weir box for No. 19, Table I. 
o 
t 
*- 
_J 
----200-- 
Fig. 7.—Plan of experimental weir box for Nos. 21, 22, 24, and 25, 
Table I. 
not include much of the slope of the water 
The individual equations in simple form for each set of experiments 
and the conditions under which those experiments were made are given 
in Table I. The following deductions have been obtained from com¬ 
parisons of the equations stated in the table, the bottom contractions 
being entirely suppressed in all cases, but with various arrangements of 
sides of weir box. 
