5 
have required the use of the self-recording instruments at consider¬ 
able distances, and the visiting them in one single season has re¬ 
quired more than thirteen hundred miles travel with horse and 
buggy. The work of reduction has been far greater. 
WHAT IS THE DUTY OF WATEE. 
By duty of water is meant the irrigation performed by a given 
amount of water ; and this may be expressed in various ways. Ordin¬ 
arily by stating the number of acres which is irrigated by the con¬ 
stant flow of a given quantity of water, as a cubic foot per second. 
Sometimes the water is expressed in “ inches,” but as the ‘‘ inch ” 
varies between wide limits it has none of the characteristics of a 
unit, and should be avoided. 
The duty may also be expressed in terms of the depth of the 
w^ater which has been applied. 
The first method is that commonlv used where the water is taken 
%/ 
from streams, and as the basis of water rights and water contracts be¬ 
tween the canal company and the purchaser. It is in the unit most 
convenient for their purpose, for in this form the amount which 
should be delivered to the- irrigator when the supply to the ditch is 
sufficient, is at once found. But as this estimate varies with the as¬ 
sumed length of the irrigation season, it is not convenient as a basis 
for determining the actual depth of water which has been applied, 
or for estimating the number of acres which may be irrigated from a 
reservoir. The duty as expressed in one way may be expressed in 
'the other unit by remembering that there are 86,400 seconds in a 
day of 24 hours, and since there are 43,560 square feet in one acre, 
the flow of one cubic foot per second will cover very nearly two acres 
one foot deep in one day, and in 100 days will cover 200 acres one 
foot deep, or will furnish, as it is sometimes expressed, 200 acre-feet. 
The reverse reduction may be applied by remembering that two 
acre-feet is equivalent to the flow of one second-foot for 24 hours. 
Thus if the depth on a crop of 100 acres is one foot, it would require 
the constant flow of one cubic foot per second for 50 days, or one- 
half of a second-foot for an irrigation season of a hundred days. 
The expression of duty in the two ways may thus be equivalent 
ways of expressing the same amount of water. In terms of acres 
per second feet, the stream is supposed to be running constantly. The 
needs vary from one part of the season to another. No one wants his 
water for irrigation in as great quantities in May as in the latter 
part of June, or the same amount in August and September. When 
the flow of the cubic foot per second is assumed constant throughout 
this wdrole period, the duty found is much greater than if the month 
of June was taken as the basis. But under the conditions of dis¬ 
tribution from our streams, the quantity of water received by a ditch 
fluctuates according to the fluctuations of the streams, and the de¬ 
mands are such that there is rarely any surplus water. A farmer 
who is economical in one month cannot draw his saving in another 
