Apr. *3,1917 
Flow through Submerged, Rectangular Orifices 
101 
4 - 
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Fig. 4.—Elevation and sections of orifice with 
bottom contraction. 
The head on the upstream side of the orifice was determined in the 
concrete still box by means of a standard type Boyden hook gage. 
The head was communicated to the still box through four lengths of 
^-inch hose connected to i-inch pipe nipples placed through the side 
of the channel of approach until just flush with the inner face. These 
pipes were placed close together, so as to give an average distance of 5 
feet from the plane of the orifice. The head on the upstream side of the 
orifice was kept constant by means 
of the by-passes and the main regu¬ 
lating gates at the storage reservoir. 
The head on the downstream side 
of the orifice was measured with a 
hook gage placed in a metal still 
box anchored to the concrete wall. 
The velocity of recession was so 
great in some cases as to cause a 
pulsation in the still box, which 
prevented a reasonably accurate measurement of the height of the water 
level. This was satisfactorily overcome by placing a metal tank, 12 by 12 
by 30 inches, between the hook gage still box and the channel of recession. 
This regulating tank was connected with the channel of recession by a 
i-inch pipe nipple placed through the side of the channel 1.5 feet from the 
plane of the orifice and 0.5 foot above the floor. The regulating tank was 
connected to the still box by a single piece of K-inch hose about 2 feet long. 
For each setting of orifice and 
arrangement of orifice box a num¬ 
ber of observations, sufficient to de¬ 
termine the discharge curve, were 
made with different elevations of the 
water levels upstream and down¬ 
stream from the orifice. The depth 
of water in the channel of approach 
remained constant for each set of ob¬ 
servations, while the depth down¬ 
stream was changed. However, no 
observation was started until the 
desired conditions of flow had been secured, and these conditions were 
not allowed to vary during the observation. The volume of water which 
flowed through the orifice during each test was determined accurately in 
the calibrated concrete tanks. 
The exact dimensions of the orifices were measured with a micrometer 
caliper before and after the experiment, and, where slight changes were 
caused by swelling of the wood, average dimensions were taken. Usually 
Fig. 5.—-Elevation and sections of orifice with iron 
gate guides. 
