34 BULLETIN" 339, U. S. DEPARTMENT OF AGRICULTURE. 



0.01 foot in depth, or 0.5 per cent, will be required in the last half of 

 April"; 0.37 foot in depth, or 18.7 per cent, during May; 0.56 foot in 

 depth, or 28.3 per cent, during June; 0.65 foot in depth, or 32.8 per 

 cent, during July; 0.34 foot in depth, or 17.2 per cent, during August; 

 and 0.04 foot in depth, or 2 per cent, during the first half of September, 

 making a total of 1.98 acre-feet. 



The above estimates are based strictly upon the crop needs, as 

 shown by the irrigation-requirement investigation, and include noth- 

 ing for stock water or that which may be required for domestic pur- 

 poses, nor is there any included for waste from the fields or for late 

 fall or winter irrigation. If the data in this table are to be used in 

 allotting water to an irrigation project, and if the water is to be used 

 for the above-mentioned purposes, these factors must be taken into 

 consideration. 



Table XVIII shows that there is small need for water earlier than 

 May or later than August and that with all of the tracts considered 

 there has been no need for water during the four years of the investi- 

 gation by either alfalfa or grain during the last half of September. It 

 shows also that over 60 per cent of the total water required during 

 the season is required in the 61-day period covering June and July. 

 The table will be found useful to those called upon to design storage 

 projects, as a variety of curves can be worked up from it, which, 

 taken in connection with the hydrograph of the discharge of the 

 stream from which the supply is to be derived, will show how much 

 of the water it will be necessary to store. 



It also will be helpful in the designing of pumping plants, and par- 

 ticularly in determining the size of the various pumping units that 

 should be installed. The table shows that any large pumping plant 

 should consist of more than one unit, and possibly as many as three 

 or four, for a unit that could economically supply the maximum 

 demand during June and July could not possibly be operated economi- 

 cally with the decreased demands of May and August. This feature 

 must always be given consideration. 



The table seems to prove conclusively that the uniform continuous- 

 flow method of delivery is exceedingly wasteful, for if a right called 

 for a uniform continuous flow throughout the season with an allot- 

 ment per acre of sufficient size to deliver the required amount during 

 June and July, a large proportion of the quantity delivered could not 

 be used economically and would be wasted during April, May, August, 

 and September. While on the other hand, if the uniform continu- 

 ous flow were of the size required to deliver the 2 acre-feet required 

 during a six-months' or even a four-months' irrigation season, there 

 still would be more water than is actually required during the early 

 and late parts of the season and less than is actually required during 



