58 



rights to the use of Avatcr. Even after rights have been established, 

 the proper duty of water is still the cause of much dispute between 

 those who regulate, control, and administer the public waters of a 

 stream and the farmers who use the water. 



SOME CONDITIONS WHICH AFFECT THE DUTY OF WATER. 



The ordinary irrigation channel receives much more water from the 

 stream than it delivers to the irrigated fields. Porous soil and a high 

 sunnuer temperature cause losses in conveyance in the main canals, 

 seldom less than 10 per cent and rising occasionall}' to over 50 per cent 

 of the total volume diverted. The How, after it is turned out of the 

 main canal into laterals, is subjected to a still further reduction in vol- 

 ume from the same causes, so that in stating the quantity of water 

 used on a tract of land it is important to locate detinitel}^ the place of 

 measurement. When the irrigation stream is measured as it crosses 

 the highest l)Oundary of a field there is practically no loss in convey- 

 ance. When, however, the water is measured at the point of diver- 

 sion from the natural channel, all losses due to seepage, evaporation, 

 and leakage are included, and this shows a much larger quantity used. 



Rainfall, midsummer temperatures, and the length of the irrigation 

 period all modify the quantity of water required. In Montana all 

 three conditions are favorable from the standpoint of the economical 

 use of the water suppW. The average annual precipitation over the 

 cultivated portions of the State is over 1-i inches, and a large part of 

 this occurs in April, May, and June, when farmers need moisture most 

 to start their crops. In the Gallatin Valley in particular the rainfall 

 during these three spring montlis is fully equal to one irrigation, and 

 forms about 30 per cent of the average amount of water received by 

 fields under careful irrigation. The evaporation is likewise low during 

 the time when water is applied. The average weekly evaporation 

 from a water surface at Bozeman, Mont., for the past four years has 

 been 0.94 inch for the months of jNlav. June, July, and August — much 

 less than it is in the more southerly and warmer portions of the arid 

 region. For the same reason the period during which water can be 

 used is comparatively short. In some parts of the State irrigation 

 water is applied in April and Ma}-, l>ut, taken as a whole, the ordinary 

 crops receive the greater part of the season's supply from May 15 to 

 August 15. The average length of the irrigation period in Montana 

 does not exceed one hundred da3^s. 



Water can seldom ])e economicallv used on a one-crop farm. This is 

 particular!}' true of the cereals. If one's holding is all planted to 

 wheat, for exampl(», a large flow may be required for a short period, 

 but when the needs of this one crop are supplied the owner may have 

 no further use for the irrigation stream. In growing alfalfa, or an^^ 

 other leguminous crop, under irrigation it is possible to get a higher 



