91 



an old wooclon Hinue is to .substitute for it .soniethin*,*- more pormiinont. 

 This has l)een done by the ofKcers of the Hi«;- ditcii in Yellowstone 

 County. When this ciinal was lirst built man}' w^ooden flumes were 

 used to cross depressions. In time these structures decayed, but 

 instead of having*- them replaced the superintendent built earthen em- 

 bankments on each side. These carried water more efficiently and 

 were permanent structures, thus lessenin<»- the annual cost of mainte- 

 nance. 



Leaks arc sometimes caused by the shatterintif of rock or other ma- 

 terial by blastint^ during construction, or by failing to provide imi)er- 

 vious connections between canal embankments and the original surface. 

 Another source of loss is leaky gates. A slight leakage from the 

 closed head gate of a farmer's lateral is a trivial matter, but the com- 

 bined loss from a score or more of badly titting gates may amount to 

 a considerable volume of water. 



LOSS OF WATER BY EVAPORATION. 



The principal loss of water by evaporation occurs after the water is 

 spread over a tield and not while it is being conducted in canals. Dur- 

 ing the early part of the irrigation season in Montana the tempera- 

 tuie of water in canals is quite low, often between 50-^ and GO^ F., and 

 the evaporation in conseiiuence is low. 



The basis for computing the loss of water b}' evaporation from 

 ditches and canals has been the evaporation from a standard tank at 

 Bozeman. The records for the irrigation season extending from May 

 1-to September 30 of each year, from 1900 to 1903, are given in the 

 following table: 



Evaporation from water surface at Bozeman, Mont, {in inches). 



Mean temperature of water. . . 



Monthly evaporation 



Average weekly evaporation . 



Mean temperature of water. . . 



Monthly evaporation 



Average weekly evaporation , 



Mean temperature of water. . , 



Monthly evaporation 



Average weekly evaporation , 



1903. 



Mean temperature of water. . , 



Monthly evaporation 



Average weekly evaporation . 



May. 



5.52 

 1.24 



59° F. 

 5.27 

 1.19 



54° F. 

 3.40 

 0.77 



61° F. 



"1.12 



0.60 



June. 



73° F. 

 5.99 

 1.39 



60° F. 

 4.20 

 0.98 



67° F. 

 3.30 

 0.77 



62° F. 

 3.99 

 0.93 



July. 



3.59 

 0.80 



68° F. 

 4.34 

 0.98 



65° F. 

 4.07 

 0.92 



64° F. 

 3.90 

 0.88 



August. 



3.88 

 0.88 



69° F. 

 5.27 

 1.19 



65° F. 

 3.60 

 0.81 



67. 6° F. 

 3.38 

 0.76 



September. 



65° F. 

 2.74 

 0.63 



56° F. 

 3.43 

 0.80 



54° F. 

 3.01 

 0.70 



68° F. 

 3.36 

 0.78 



Mean. 



64° F. 

 4.34 

 0.99 



62° F. 

 4.30 

 1.03 



61° F. 

 3.49 

 0.79 



64. 5° F. 



0.79 



n May 19-31. 



