6 DEPARTMENT BULLETIN 1110. 
The discharge values computed from Formula I agree very closely 
with the experimental data, except for heads of less than 0.2 foot. 
Formula II, however, which gives the submerged-flow discharges, 
does not give values that agree so closely with the experimental 
data. This is partly due to the variation in the observed discharges 
caused by the uncertainty of obtaining the true gauge heights. 
Formula IT, like Formula I, does not give accurate results for heads of 
less than 0.2 foot. The agreement of the discharges computed from 
Formulas I and II for the free flow and submerged conditions, 
respectively, with the experimental discharges for the same con- 
ditions, is shown graphically in Figure 3. The percentages given*‘in 
A 
i Potter tet 
O 
|. 
rie 
2 om Eb I Wr 
ae I 
Hl cdiosl liad. cdeilitdwel oobtddslael edaailoal 
peek UP i Ds 
=a | (= 
=a a 3 
oa Ge 
a i. 
ae 
LH 
0 
B53 10 
PER CENT DEVIATION 
Fig. 3.—Deviation of the computed data from the experimental data for free flow and submerged conditions. 
each case represent the deviation of the computed data from the 
experimental data. These diagrams indicate clearly that where 
accuracy is required the submerged condition must be avoided. 
FREE-FLOW DISCHARGE TABLE. 
Table 2 gives the free-flow discharges, in cubic feet per second, 
per foot in width of flume, for various heads and heights of weirs, 
computed from Formula I. The head at the upper gauge, which is 
used in the formula for computing the discharge, is given in both feet 
and inches at the left of the table. These values should be used to 
find the discharge in the table when the head is measured at the upper 
gauge point. If the head is measured on the crest, then the values 
in inches in the column to the left of the discharge column for the 
particular height of weir in question should be used. It will be noted 
