of pump, (3) the class of engine or driving power, ,(4*> the:flrs 

 fuel cost, (6) cost of fixed charges and attendance. "Th'e'se factors' are 1 " 

 interdependent and should be considered together. Their relative import- 

 ance will vary with local conditions and for that reason it is not possible 

 to state definite rules which will apply in all cases. A study of the con- 

 ditions affecting each factor is therefore necessary in each case. 



1. Capacity of Plant and Period of Operation. 



The required capacity of the plant will depend on the area irrigated, 

 the duty of water or depth of water required on the land and the period 

 of operation. For ordinary orchard soil in the arid part of British Colum- 

 bia a total depth of 12 inches of water during the irrigation season will be 

 sufficient for young orchards. For a full bearing orchard 18 inches should 

 be ample, while for alfalfa and other forage crops 24 to 36 inches is plenty. 

 Where the cost of pumping is high, such as for small plants and high 

 lifts, it will usually not be feasible to grow at a profit anything but 

 orchards. To reduce the cost of pumping, no excess water should be used, 

 all losses should be prevented by careful irrigation and thorough cultiva- 

 tion, in which case a young orchard on fairly deep retentive soil may not 

 require more than 6 to 9 inches of irrigation water and a full bearing 

 orchard not more than 12 or 15 inches during the irrigation season. To 

 put a depth of 2 feet of water on one acre, it takes a flow of very nearly 

 1 cubic foot per second for 24 hours; this is equivalent to 450 U. S. gal- 

 lons per minute for 24 hours. This relation can be applied to any case to 

 obtain the size of the pump. For example, if it is desired to irrigate a 

 40 acre orchard 1% feet deep, in an irrigation season of 120 days, this 

 requires 60 acre feet in 120 days, or % of an acre foot per day. This 

 will be obtained by a pump giving ^4 of a cubic foot per second, or 110 

 U. S. gallons per minute, when the pump is operated continuously 24 hours 

 a day every day during the irrigation season of four months. For a 10 

 acre orchard the required capacity based on the same conditions would be 

 1/4, the above or 28 gallons per minute or 1-16 of a cubic foot per second, 

 or about 2*4 British Columbia miners' inches. 



The above two examples are based on a pump operating continuously at 

 the rates given above. While continuous operation decreases the required 

 size of plant, it is usually preferable to select a plant of larger capacity 

 and operate it only a part of the time. This is especially desirable for very 

 small orchards in which case continuous operation gives a stream too 

 small to irrigate with. The other disadvantages of continuous opera- 

 tion are: 



1st. Continuous operation requires continuous irrigation and constant 

 attention to operate the pumping plant. For very small tracts a regulat- 

 ing reservoir may be used, but it must be of considerable capacity to be of 

 any service and it must be lined with concrete to prevent seepage losses of 

 the water which when pumped is too valuable to lose. Usually it is prefer- 

 able to purchase a larger plant and do without a reservoir. 



2nd. Continuous operation means that the water can not be applied to 

 the different parts of the orchard within a short time, so that only a small 

 part of the orchard or farm receives the water when most needed, and the 

 remainder must be irrigated either too early or too late. 



3rd. Continuous operation gives a small stream which can not be ap- 

 plied economically. 



