Mar. X3,1916 
A New Irrigation Weir 
ii39 
Table II .—Computed discharges for the new irrigation weirs —Continued 
Head. 
Length of weir crest. 
jtieaa. 
I loot. 
1.5 feet. 
2 feet. 
3 feet. 
4 feet. 
Feet. 
I. 20 
Ft. 
I 
tft. 
2H 
4-97 
7- 39 
9- 77 
14. 41 
18. 87 
I. 21 
I 
2K 
5-03 
7-49 
9. 90 
14- 59 
19. 12 
I. 22 
I 
2 H 
5- 10 
7-58 
10. 02 
14. 78 
19.36 
I. 23 
I 
2 H 
5- 16 
7. 68 
10. 15 
14. 97 
19. 6l 
I. 24 
I 
2 y% 
5- 2 3 
7-77 
10. 28 
i$- 16 
19. 86 
i - 2 5 
I 
3 
5- 29 
7.87 
10. 41 
15-35 
20. 11 
Table III shows the differences between the discharges computed 
from the formula and those obtained by experiment, these differences 
being expressed in cubic feet per second and in percentages. The for¬ 
mula agrees with the experimental data within a maximum amount 
of 4.8 per cent for an individual point, but this discrepancy is no doubt 
due partly to experimental inaccuracy and partly to the assumption of 
a straight-line formula. Medium heads give values for discharges that 
agree within 1 per cent, but the high and low heads will have a some¬ 
what greater error. The formula agrees with the average straight lines 
drawn through the experimental data within a maximum error of 1 
per cent. The error is greatest with the small weirs, decreases as the 
length of the weir increases, and for a length of 4 feet the error is quite 
small. Although the formula is derived from experiments with weirs 
having a maximum length of 4 feet it seems probable that the formula 
will be even closer for weirs with greater crest lengths. 
Table III .—Difference between discharges computed from the formula 
_ o.o/L]LH( u52+0 - 0lL ) and those obtained by experiment , 
for the new type of weir 
I-FOOT WEIR 
Head. 
Observed Q 
corrected true 
for length. 
Computed Q. 
Difference in Q. 
Percentage of 
difference. 1 
Feet. 
0. 200. 
O. 314 
0. 320 
+0. 006 
+ 1. 94 
• 3 °o. 
• 595 
• 596 
-j-. 001 
+ • 17 
. 400. 
•935 
•925 
+ . 010 
+ l. 07 
.500. 
I. 299 
I. 302 
+ .003 
+ . 20 
‘599 . 
I. 727 
I. 716 
— . on 
— . 60 
• 699. 
2. 183 
2. 174 
— . 009 
- .40 
. 800. 
2. 66l 
2.673 
+ . 012 
+ * 50 
• 895. 
3 - ”3 
3-173 
+ . 060 
+ 1. 92 
1 Percentage of difference between discharge obtained by computations from the formula 
C=[3.83-o.o 7L1LW- 62+0 - ciI 0 
and by experiment, the bases of comparison being the experimental data. 
