JOWL OF AGRiaHTLIRAL RESEARCH 
Voe. IX Washington, D. C., Aprie 23, 1917 No. 4 
FLOW THROUGH SUBMERGED RECTANGULAR ORI¬ 
FICES WITH MODIFIED CONTRACTIONS 1 
By V. M. Cone, 
Irrigation Engineer , Office of Public Roads and Rural Engineering, 
United States Department of Agriculture 
INTRODUCTION 
The measurement of water flowing in open channels is a matter of 
growing importance, especially throughout the irrigated West, where the 
adoption of more economical methods of water delivery and canal man¬ 
agement often is retarded by a lack of information concerning measuring 
devices adapted to specific field conditions. Where the use of free-flow 
weirs is prohibited by the low grade of canals and ditches, some type of 
submerged orifice has been substituted in many cases, though probably 
the majority of such ditches still are without any provision for measure¬ 
ment, except an occasional use of the current meter. The majority of 
the orifices installed have had complete end and bottom contractions, 
the choice being due, no doubt, to the more extensive and reliable in¬ 
formation available concerning orifices of this type. The principal 
objections to a submerged orifice with complete contractions are the cost 
of the structure and the fact that it is not adapted to the measurement 
of water that carries sand and silt. These factors have prevented the 
installation of many measuring devices, and many have been installed 
where accumulations of sand and silt have rendered the measurements 
either questionable or worthless. 
The complete suppression of the bottom contraction and the partial 
suppression of the end contractions will give a velocity of approach that 
will prevent sand and silt troubles in the orifice box, and will also lessen 
the cost of the structure. This is practically what has been done on 
many irrigation systems where lateral head gates and farmers' turnouts 
have been used directly as a means of measuring the flow. There are 
innumerable sizes, shapes, and conditions of setting such structures, 
1 The work upon which this paper is based was done in the hydraulic laboratory. Fort Collins. Colo., 
under cooperative agreements between the Office of Experiment Stations and the Office of Public Roads 
and Rural Engineering, United States Department of Agriculture, and the Colorado Experiment Station. 
Journal of Agricultural Research, 
Washington, D. C. 
ht 
(97) 
Vol. IX, No. 4 
Apr. 3311917 
Key No. D—9 
