25 
If the water from the river alone be considered, the duty of a 
cubic foot per second liowing constantly will evidently be larger 
than when the water furnished by the rainfall is considered. 
The duty will also vary according to the length of the season 
assumed. Table III. gives the number of acres which would be 
served by the constant flow of one cubic foot per second, and cov¬ 
ered to the depths indicated in Table II‘. The first section of the 
table considers the water furnished by the river alone, the second 
portion the depths furnished by the river and the rain together.. 
The table is taken from Table II. bv the formula; 
•/ 
Duty=2 tiriies the number of days in the irrigation season. 
Depth of water required in feet. 
This gives a result which is 1-121 too great. 
The table, as well as the formula, shows that the duty thus^ 
found is greater as the number of days in the irrigation season, 
with a given depth of water needed, is greater. 
Table III. —Duty, Acres per Second Feet. 
Period. 
No. of 
Days. 
River Alone. 
Mver and Rain. 
1891. 
1892. 
1891. 
1892. 
April 1—Sept. 1. 
153 
170 
233 
116 
136 
May 1—Sept. 1... 
123 
141 
195 
101 
119 
May 1—Nov. 1. 
181 
195 
274 
137 
161 
This is equivalent to stating the number of acres which the 
constant flow of one cubic foot per second will cover to the required 
depth in the given period. This assumes a condition of things 
which is not attained as yet in Colorado. The diagrams of the 
water as used on the crops of wheat, and alfalfa, and hay, as well as 
the inflow into the canal, show that the period of need of water is 
much less than the legal period, which is from May 1 to November 
1, and unless the water which comes when not directly needed for 
the crops may be stored and saved until needed, the duties as thus 
found are misleading. 
The widely varying results obtained under the same condi¬ 
tions by different methods of estimating the duty of water, or dif¬ 
ferent lengths of the irrigation season, show that the duty as ex¬ 
pressed in acres per cubic feet per second may be very misleading 
unless the whole circumstances be understood. The better way 
would be to express the depth of water, or, still better, to determine 
\he depth required for a single irrigation, and the number of irriga- 
fons then would indicate the total depth of water needed, or would 
strve to measure the duty of water. 
From the tables given we may bring together the depths ap¬ 
plied to single crops: 
