io88 
Journal of Agricultural Research 
Vol. V, No. a 3 
Comparison op New Formula and Old Formula 
The discharges for the 90° notch computed by the new and the old 
formulas are compared in Table XI: 
TablP XI .—Comparison of new formula and old formula 
Discharge 
computed by 
new formula 
(cubic feet per 
second). 
Discharge computed by old 
formula, (2= a. S3H 5,2 . 
Head. 
Discharge in 
cubic feet per 
second. 
Percentage of 
discharge com¬ 
puted by new 
formula. 
Feet. 
0. 20 
O. 046 
O.O45 
97.8 
•33 
•159 
.158 
99.4 
• 50 
• 445 
• 447 - 
100. 4 
.67 
. 921 
•930 
101. 0 
• 85 
1. 66 
I. 69 
101. 8 
I. OO 
2. 49 
2. 53 
101. 6 
1-25 
4 - 33 
4. .42 
102. 1 
As no experiments have been made in the past to determine the coeffi¬ 
cients in general formulas for notches of 28° 4', 30°, or 6o°, no compari¬ 
son could be made with the discharges through such notches computed 
with the new formula. 
CIRCULAR NOTCHES 
Apparently no experiments have ever been made with circular or semi¬ 
circular notches placed in a vertical position with heads less than the 
height of the opening. In order to throw light upon the probable dis¬ 
charges through such notches and obtain data to use in determining the 
flow through circular head gates when acting as weirs rather than as 
orifices, 50 tests were made with thin-edged circular notches, 17 being 
with a notch 0.4995 foot in diameter and 33 with a notch 1.0025 feet i n 
diameter; and 34 tests were made with semicircular notches, 15 being 
with a notch 1.5011 feet in diameter and 19 with a notch 1.9990 feet in 
diameter. The discharge data obtained are shown graphically in 
figure 13. 
CONDITIONS OF NOTCH EDGES REQUIRED TO INSURE FREE FLOW 
The impression is common that the terms “thin edges” and “sharp 
crests,” as applied to weir notches, mean knife edges. Such edges are not 
necessary, and the edges are sufficiently sharp or thin if the upstream 
corner of the notch edges is a distinct angle of 90° or less and the thick¬ 
ness of the notch edges is not so great that the water will adhere to them. 
The allowable thickness of the edges depends upon the head that is being 
used. Experiments made in the laboratory with notches having edges 
