Mar. 6,1916 
Flow through Weir Notches 
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(10) The Cipolletti formula gives discharge values within per cent 
of the actual discharges so long as the head does not exceed one-third 
the length of the crest of the notch. 
(11) The formula 
Q=3.08 L 1 - 022 ^ 1 - 4 ™* 0031 ') + o.6tf 2 - 6 , 
which is based on the straight-line formula for rectangular notches, gives 
discharge values for the i-, 1.5-, 2-, 3-, and 4-foot Cipolletti notches that 
agree within a maximum of 1 per cent with the curves plotted from the 
experimental data, the divergences at all but a few points being 0.5 per 
cent or less. The formula for the 0.5-foot notch is < 2 = i. 566# 1,504 + 
0.5 6tf 255 . 
(12) The Cipolletti type of notch does not give discharges as nearly 
proportional to the length of crest as does the rectangular type, conse¬ 
quently, since rectangular notches are simpler to construct and the 
formula for such notch gives as accurate discharge values as does the 
formula for Cipolletti notches, the rectangular-notch weir is to be 
preferred. 
(13) The general formula for discharges through triangular notches 
of from 28° 4' to 90°, and probably up to 109°, is 
(„ Q-QI95 \ 
0 = (0.025 + 2.462 S)H V s™ ' 
where H is the head in feet and S the slope of the sides. Triangular 
notches having side slopes greater than about 1 to 4 (109°) are impracti¬ 
cal, as the nappe adheres. 
(14) The 90° triangular notch is the most practical triangular notch 
and should be used in preference to either rectangular or Cipolletti 
notches for discharges up to approximately 3 cubic feet per second. The 
approximate formula Q = 2.^gH 2A8 will give discharge values for 90° 
notches which agree very closely with the value obtained with the general 
formula for triangular notches. 
(15) The crest and sides of a weir notch need not be knife-edged. 
They are sufficiently sharp if the upstream comer of the edges is a dis¬ 
tinct angle of 90° or less and the thickness of the edges is not so great 
that the water will adhere to them. 
(16) The head should be measured upstream from the weir a distance 
of at least 4 H, or sidewise from the end of the crest in the plane of weir 
a distance of at least 2 H. 
(17) The distances required for full contractions with rectangular and 
Cipolletti notches are approximately 2H , but an additional cross- 
sectional area of the weir box is required to reduce the velocity of approach. 
(18) With end contractions equal to 2 H and a bottom contraction 
equal to 3//, or end contractions equal to 3 H and a bottom contrac¬ 
tion equal to 2 H } the mean velocities of approach are about % foot 
