DUTY AND MEASUREMENT OF WATER. 109 



surfeit in application ; while on adjoining lands, through 

 jni i'ii forced economy, a higher duty, better condition of 

 the soil and greater productiveness have resulted. Un- 

 skilled labor has a penalty of twenty-five to fifty per cent 

 attached to it in the application of water, and unfortu- 

 nately this class is too prevalent in the irrigating fields, 

 in many cases no other being obtainable. An abundant 

 water supply tends to carelessness in its application, and 

 consequent waste. On the duty of water depends the 

 financial success of every irrigation enterprise, for as 

 water becomes scarce its value increases. In order to 

 estimate the cost of irrigation in projecting works, it is 

 essential to know how much water the land requires. In 

 order to ascertain the dimensions of canals and reservoirs 

 for the irrigation of given areas, the duty of water must 

 be determined. 



Numerical Expression. Before considering the 

 numerical expression of water duty the standard units 

 of measurement should be defined. For bodies of stand- 

 ing water, as in reservoirs, the standard unit is the cubic 

 foot. In the consideration of large bodies of water, 

 however, the cubic foot is too small a unit to handle 

 conveniently and the acre foot is the unit employed by 

 irrigation engineers. This is the amount of water which 

 will cover one acre of hind one foot in depth, and that is 

 43,560 cubic feet. In considering running streams, as 

 rivers or canals, the expression of volume must be cou- 

 pled with a factor representing the rate of movement. 

 The time unit usually employed by irrigation engineers 

 is the second, and the unit of measurement of flowing 

 water is the cubic foot a second, or the second foot as it 

 is called for brevity. Thus the number of second feet 

 flowing in a canal is the number of cubic feet which 

 passes a given point in a second of time. The cubic foot 

 a second is the unit of measurement usually adopted in 

 the distribution of water from or by the large canals of 



