Mar. 6,1916 
Flow through Weir Notches 
1063 
RECTANGULAR NOTCHES 
With rectangular notches 226 tests were made, the actual crest lengths 
used being 0.50721 foot, 1.0055 feet, 1.5026 feet, 2.0057 feet, 2.9970 feet, 
and 4.0065 feet. These actual lengths were used in all computations 
connected with the derivation of the formula. 
' Derivation op the Formula 
The discharge values for 0.05-foot increments of head, taken from the 
curves plotted from the experimental data, were used in the following 
deductions, thereby eliminating to a large extent the experimental 
Fig. 5.—Curve showing the relation between a in the equation Q=*aL—b and the heads on rectangular 
notches. 
irregularities. The discharge values for the different notches were 
plotted (fig. 4) with the lengths of crests (L) as abscissas, and the dis¬ 
charges (] Q ) as ordinates. A straight line was then drawn for each head 
by passing it through the points representing the discharges over the 3- 
and 4-foot crests with the given head. The equations of these straight 
lines were found to be of the form Q=aL—b. 
The slopes (a) of the lines were computed from the coordinates of the 
discharge values with the 3- and 4-foot crests. The relations between 
the heads ( H) and the slopes (a) in the above formula were plotted (fig. 
5) and gave a curve the equation for which was found to be a= 3.247# 1 - 48 . 
The relations between the heads (H) and the intercepts (b) in the 
equation Q=aL—b are shown in figure 6. The equation for the curve 
was found to be 6 = o.283H 1,9 . 
