A NEW IRRIGATION WEIR 1 
By V. M. Cone, 
Irrigation Engineer , Office of Public Roads and Rural Engineering 
INTRODUCTION 
The accurate measurement of water delivered to the irrigator has been 
retarded by lack of information concerning devices adapted to the various 
conditions of size and grade of canals, and to the sand and silt troubles 
encountered throughout the West. These conditions are so varied that 
it is very improbable that any one type of measuring device will be desir¬ 
able or practicable for all cases. Although the weir is the principal measur¬ 
ing device in use in the West, there are many places where the common 
types of weirs can not be used, and consequently water users are either 
making current-meter measurements occasionally or systematically or 
are doing without any measurement. 
Many attempts have been made to devise a weir that would be simple 
and inexpensive in construction, free from sand troubles, and accurate 
and simple in operation; but usually what has been gained in one direc¬ 
tion has been lost in another. 
Weirs with full contractions have been built in many places where 
sand and silt accumulations have resulted in inaccurate measurements, 
or constant attention has been required to keep the weir box clean. The 
first cost of such a weir is rather high and the nuisance and expense 
of keeping it clean often make it undesirable. In an attempt to overcome 
these objections many weirs have been built with incomplete contractions 
which have caused the water to pass through the weir box at a velocity 
sufficiently high to necessitate the addition of a correction factor to the 
discharge table, but not high enough to completely prevent the accumu¬ 
lation of sand. It usually occurs that full-contraction-weir tables without 
correction are used with the modified weirs, and therefore the measure¬ 
ment is not worth much more than the guess of an experienced ditch 
rider. Damage has resulted from the prevalent belief that the weirs 
in general carry the stamp of accuracy. Under proper conditions of con¬ 
struction and operation, full-contracted weirs are accurate within a 
small percentage, 2 but such conditions are not always to be found in the 
field. In the literature of hydraulics there are practically no records of 
1 The work on which this paper is based was done in the hydraulic laboratory, at Fort Collins, Colo., under 
a cooperative agreement between the Office of Experiment Stations, United States Department of Agricul¬ 
ture, and the Colorado Agricultural Experiment Station. 
3 Cone, V. M. Flow through weir notches with thin edges and full contractions. In Jour. Agr. Research, 
v. s, no. 23, p. 1051-1114, 1916. 
Vol. V, No. 24 
Mar. 13,1916 
D—7 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
cx 
(X127) 
