THE VENTURI FLUME 
By 
Ralph L. Parshall, Senior Irrigation Engineer 
Carl Rohwer, Irrigation Engineer 
Irrigation Division, Bureau of Public Roads 
U. S. Department of Agriculture 
A preliminary report on the Venturi flume was prepared by 
V. M. Cone and published in the Journal of Agricultural Research, 
Vol. IX, No. 4, April 23, 1917. This report was not intended to 
cover the whole subject, but rather to present the possibilities of this 
device as a practical means of measuring flowing water for irriga- 
tion purposes. The original investigations were made at the hydrau- 
lic laboratory at Fort Collins, Colorado, but, due to the inadequate 
facilities, it was not possible to carry the experiments to the point 
most desirable from an irrigation standpoint. Under a co-operative 
agreement between this Bureau and Cornell University, experiments 
were conducted at the Cornell hydraulic laboratory under the super- 
vision of Dr. Schoder and the late Professor Turner on the larger 
sized flumes, where flows of 300 to 400 second feet were used. 
Additional experiments were performed at the field laboratory on 
the Cache la Poudre river at Bellvue, near Fort Collins, Colorado, 
in order to properly correlate all the tests previously made. All 
these data were not available at the time of the first published report, 
and in our subsequent study, various characteristics of the flume 
have become apparent which were not evident when the original 
experiments were made. 
This bulletin is intended to present a more complete statement 
as to the law of flow through the Venturi flume and also to define 
more clearly its limitations and advantages. 
Many devices have been developed for the measurement of 
water for irrigation, but, due to the great variation of the conditions 
as found in practice, no individual type has yet been found which 
exactly meets all of the requirements. The standard methods of 
measuring flowing water are all more or less affected by the ever- 
changing condition of the channel, either immdiately above or below 
the structure, or else the capacity of the device limits the discharge.* 
The overpour, sharp-crested weir is the most accurate method 
of determining the quantity of flow, but certain requirements as to 
contractions and velocity of approach must be maintained in order 
to keep the weir standard. The accuracy of measurement is only 
