142 



rainfall, which are given in inches of depth. In the humid regions 

 rainfall is usually from 3 to 4 inches per month during the crop 

 season. In the arid region, where the sunlight is more continuous and 

 the evaporation greater, there should be, for the ordinary crops at least 

 enough water during the growing season to cover the ground from 4 

 to 6 inches in depth each month. Carefully tilled orchards have been 

 maintained on far less. In Arizona, where the crop season is longest, 

 being practically continuous throughout the year, twice as much water 

 is needed as in Montana, where the crop season is short and the evapo- 

 ration is less. 



The second method of stating the quantities necessary for irrigation 

 is of convenience when considering a stream upon which there is no 

 storage. It is frequently estimated that one cubic foot per second, or 

 second-foot, flowing through an irrigating season of ninety days, will 

 irrigate 100 acres. One second-foot will cover an acre nearly 2 feet 

 deep during twenty-four hours, and in ninety days it will cover 180 acres 

 1 foot in depth, or 100 acres to a depth of 1*8 foot, or 21-6 inches. This 

 is equivalent to a depth of water of a little over 7 inches per month. 

 In several of the States, laws or regulations have been made to the effect 

 that in apportioning water not less than 66f acres shall be allowed to 

 the second-foot of continuous flow. This is extremely liberal, and 

 permits extravagant use of water. 



"When the ground is first irrigated, enormous quantities of water 

 must sometimes be used in order to saturate the subsoil. It has fre- 

 quently happened that, during the first year or two, a quantity of 

 water which would cover the ground to a depth of 20 to 10 feet has been 

 turned upon the surface. Frequently for several years an amount 

 equal to a depth of 5 feet or more per annum is thus employed. 

 Gradually, however, the dry soil is filled, and, as stated in another 

 place, the water table is raised nearer the surface, less and less water 

 being needed. 



The farmers, being accustomed to the use of large quantities of 

 water, often find it exceedingly difficult to get along with less, and 

 continue to use excessive amounts, often to their own disadvantage. 

 They are actuated in part by the consideration that, having paid for 

 the use of the water, they are entitled to a certain quantity, and fear 

 that if they do not take all of this, their claim to it may be disputed. 

 Some of them actually waste water to their own detriment from the 

 mistaken belief that in so doing they are establishing a perpetual right 

 to certain quantities. 



With the gradual development of the country, and the bringing of 

 more and more land under ditches, the need for water increases, and 

 equity demands that no irrigator shall take more than he can put to 

 beneficial use. Flowing water must be considered as a common fund, 

 subject to beneficial use by individuals according to orderly rules, each 

 man taking only the amount he can employ to advantage. Under any 

 other theory full development of arid regions is impossible. 



It is instructive in this connection to know what is the least amount 

 of water which has been used with success. To learn this, it is necces- 

 sary to go to south California, where the supply of water is least, 

 relative to the demand made upon it, and the economy is correspond- 

 ingly greatest. Successive years of deficient rainfall in California 



