*:V 102 



, 4 :*th. A sri?.ll plant is less efficient and requires a proportionately larger 

 *'^u*i -consumption than a larger plant to pump the same quantity of water. 



On the other hand a very short period of operation requires a compara- 

 tively large pumping plant which will greatly increase the first cost of 

 installation, the interest on the capital invested, the depreciation and fund 

 necessary to provide for renewal. 



Usually it is desirable to operate the pump not over 1-2 or 1-3 of the 

 time during the irrigation season and often a shorter period is desirable. 

 This requires a pumping plant two or three times or more the size required 

 for continuous irrigation. The capacity of the pump must be sufficient in 

 all cases to give a large enough stream to irrigate economically; even for 

 the smallest orchards a stream of at least 5 miners' inches or about 63 

 U. S. gallons per minute, is desirable. 



For a full bearing orchard 18 inches of irrigation water applied in about 

 3 irrigations of 6 inches each at intervals of 30 to 40 days should be ample 

 in most cases. As stated above, where the water has to be pumped to a 

 high elevation the higher cost of the water demands great care in its use 

 and 12 to 15 inches total depth of irrigation water would be sufficient. 



The table below gives the required pump capacity for various sizes of 

 orchards or farms and for different periods of operation. It is based on a 

 depth of irrigation water of 6 inches each month, or 18 inches in 3 months, 

 which is taken as the irrigation season. The period of operation is given 

 in number of 24 hour days that the pumping plant is operated each month. 

 These days need not be consecutive; for instance if the operation period is 

 10 days, instead of applying 6 inches of water in one irrigation lasting 10 

 days, the soil may be so porous and gravelly that it will not retain moisture, 

 in which case it may be preferable to apply 3 inches at a time in two irri- 

 gations during the month, of 5 days each. The required pump capacity 

 is given in U. S. gallons per minute instead of Imperial gallons because the 

 pumps sold in British Columbia are mostly rated in U. S. gallons per 

 minute. 



\ r< - V.-M > Capacity of Pump* In V. S. Gallon* Per Minute to Give a Inch Depth 



of Water on the Land Each Month When Operated the Following 



Number of 24 Hour Day* Per Month. 



The capacity of pumps for smaller or greater depths of water applied 

 per month can be easily computed by proportion from the values given. 

 For different areas and different periods of operation the capacity may be 

 obtained by interpolation. 



2. Kind of Pump. 



The kinds of pump commonly used to raise water for irrigation are (1) 



