Apr. 23,1917 
Flow through Submerged Rectangular Orifices 
107 
The exponent decreases as the ratio of the area of the orifice to the 
wetted cross-sectional area of the channel of approach ~ increases. 
The coefficient increases with an increase in the depth of the orifice d. 
The coefficient increases with an increase in the area of the orifice a, 
but does not increase regularly when the area of the orifice a has been 
divided out of the aggregate coefficient value. 
Although the end-contraction distance has been taken as 1 foot for 
all sizes of orifices as a standard condition, a comparison of the deviation 
of discharges from the standard formula given in Table III indicates that 
little error would be introduced by making the contraction distance 0.5 
foot for the smaller sizes of orifices. Increasing the distance to 1.5 feet 
would cause a greater error. 
No. 13 to 23, inclusive, are for standard conditions. A comparison of 
these data with the data for other experiments, shows that lessening the 
depth of water in the channel of approach approximately 1 foot increases 
the discharge approximately 2 or 3 per cent. The increase is much 
greater for low heads than for high heads, especially with the smaller 
orifices. This action is difficult to explain, but it may be due to the 
existence of a critical velocity below which the velocity of approach has 
only a moderate effect upon the discharge and above which the effect may 
be somewhat overcome by increased friction and eddy currents. 
The addition of an angle-iron bottom contraction and iron gate guides 
(No. 51) increases the discharge about 8 per cent. 
No. 58 was an experiment to determine the effect upon the discharge 
caused by the iron gate guides projecting from the plane of the orifice as 
a comparatively narrow strip. A comparison of No. 58 and 57 shows that 
filling out the bulkhead until the face was flush with the edge of the gate 
guide (fig. 11) made practically no change in the discharge. 
An orifice made of wood about 1 % inches thick, with a bottom con¬ 
traction of the same material about ifyi inches high (No. 57), increased 
the discharge 3.3 per cent for the low head and 5.6 per cent for the high 
head. A comparison of this increase with that due to the angle-iron 
bottom contraction added to the standard condition of orifice indicates 
that the substitution of wood i s /i inches thick in place of the angle iron 
in the standard orifices will make the discharge about 2 per cent greater 
than that given in the standard discharge table. It will be observed 
that there would be no bottom contraction with this condition. 
A wood orifice 1 $/& inches thick, with wood gate guides (fig. 7), will give 
a discharge from 9.6 to 16 per cent greater than that of the standard 
table, and the increase is the greatest for the smaller orifices (see No. 53 
and 60). This increase probably is due to the guides being nearly the 
same distance apart as the length of the orifice, but set back from the 
plane of the orifice far enough to make the action similar to the flow 
through a short pipe. 
