58 



when all the losses of water by percolation, evaporation and waste which 

 can be controlled by ordinary careful methods of irrigation and cultivation, 

 have been eliminated. 



The duty of water can be stated in three ways: 



1st. In number of acres irrigated by a flow of water of one cubic foot 

 per second for a certain length of time during the irrigation period. 



2nd. In number of acres irrigated by one miners' inch for a certain 

 length of time during the irrigation period. 



3rd. In number of acre feet per acre which is equivalent to stating the 

 depth of water applied to the land. 



The first and second expressions must always include the time in order 

 to specify a given volume of water. For instance a duty of 1 cubic foot per 

 second for 100 acres during the entire irrigation season of 5 months or 

 150 days would mean 300 acre feet on 100 acres or a depth of 3 feet on 

 the land. If the length of time or period of delivery is only one-half of 

 the irrigation season, the water delivered will give a depth of 18 inches on 

 the land. In the same way a duty of 1 miners' inch to 2 acres during half 

 the time of an irrigation season of five months will give a depth of water 

 on the land of about 5 inches per month or a total depth of 25 inches 

 per season. 



The third method of expressing duty avoids any misunderstanding. For 

 instance 2 acre feet per acre means a depth of 2 feet of water on the land. 

 The duty when expressed by either of the first two methods can easily be 

 converted into acre feet or acre inches per acre by the relation previously 

 given which is: One cubic foot per second in 24 hours will give 2 acre feet, 

 or 1 acre inch per hour, and one British Columbia miners' inch in 36 hours 

 will give 1 acre inch. Based on this relation, the following equivalents 

 are obtained. 



Depth of Water Applied to the Land In One Month of Contlnuoux Flow. 



1. Principal Factors Affecting the Net Duty of Water in Irrigation. 



The factors which have more or less effect on the duty of water are: 

 1st. The kind of crops. It is known- tfet' some crops* require more 

 water than others; for instance, alfalfa requires more water than orchards, 

 and young orchards require less water than full bearing orchards. 



2nd. The preparation of land, method of application of water and skill 

 of the irrigator. Poor preparation of the land will cause water to accu- 

 mulate in the swales and uniform distribution of water is difficult. With 

 furrow irrigation unless great care is taken in the division of water be- 

 tween furrows, there will be a larger amount in some furrows than in 

 others. When the furrows are too long a large excess of water sinks into 

 the soil at the upper ends of the furrows and goes down beyond the plant 

 roots. At the lower ends of the furrows there is often a waste which may 

 cause injury to the neighbors' land or to the road below. If deep furrows 

 are used there is less water and wet soil exposed to the air and less evapo- 

 ration than with shallow furrows. 



