Apr. 23. 1917 
Flow through Submerged Rectangular Orifices 
99 
accompanying text figures, and a corresponding correction applied to 
the discharge table. The corrections are given for several different 
arrangements of metal and of wood gate guides, metal and wood edges 
of the orifice, and with and without a bottom contraction strip such as 
often is used for a bottom gate stop. It is expected that with these data 
many engineers and canal managers can arrange structures to meet their 
local demands and still give a reasonably dependable measurement of the 
quantity of water passing through the orifices. If the orifice box is 
built of concrete, the cross wall in which the orifice is placed must be 
given a flaring enlargement downstream from the orifice, to allow lateral 
expansion of the issuing stream of water. 
Although the submerged orifice is a means to a satisfactory solution of 
some practical problems, it can not well be classed with precise measuring 
devices. Its discharge is influenced by comparatively trivial factors the 
identity of which often is unknown. Sand and silt troubles are elimi¬ 
nated by modifying the end and bottom contractions, but floating trash 
will accumulate in the orifice box. The new type of weir, 1 with sup¬ 
pressed bottom contraction, is entirely self-cleaning of trash, sand, and 
silt, and has practically the same accuracy as the modified orifice. It is 
therefore better to install the new weir where there is sufficient fall in 
the ditch to give free flow and where a separate headgate is provided. 
Since there is a close relation between the accuracy of the measurement 
of flow and the accuracy of the determination of the head acting on the 
orifice, it is essential that some form of close-reading gage be used with 
the submerged orifice. The stilling well is necessary because of the com¬ 
paratively high velocity of water in the orifice box: 
ARRANGEMENT OF EXPERIMENTAL APPARATUS 
The concrete weir box in the hydraulic laboratory is 6 feet deep, 10 feet 
wide, and 20 feet long, with a channel of approach about 60 feet long. 
By-passes in the side of the weir box permit a nice control of the water 
level. In an opening near the top and middle of the end wall of the weir 
box is placed a T-iron frame, 3 feet high by 6 feet long, in which the weir 
and orifice plates are placed for experimental purposes. In the series of 
experiments with orifices having modified contractions it was necessary 
to cover this opening with planks i $4 inches thick, made rigid and water¬ 
tight. A floor of matched lumber was built in the concrete weir box 
about 3 feet above the bottom, as shown in figure 2. This floor was made 
level, rigid, and tight against the orifice bulkhead. Another floor, having 
a length of 6 feet, was placed on the downstream side of the orifice bulk¬ 
head, and made level with the floor on the upstream side. 
The orifice was made by cutting a rectangular opening in the bulkhead, 
so the bottom of the opening was at the floor line. The smallest orifice 
1 Cone, V. M. A new irrigation weir. In Jour. Agr. Research, v. 5, no. 24, p. 1127-1143,16 fig. *916. 
