TEE IRRIGATION AGE. 11 



gated more profitable, to lessen the controversies over the distribu- 

 tion of water and secure its more systematic and economical use." 



During the year that Mr. Mead has had the work of irrigation 

 investigation in charge a great number of measurement have been 

 made of water used for irrigation at the heads of the large canals, at 

 the heads of the small canals or laterals and also at the margins of 

 the fields when used. These measurements show in many cases a sur- 

 prising discrepancy. The differences in the measurements at the 

 three places show the approximate loss of water in transit in canals. 

 The results which are given in full in Mr. Mead's report are expressed 

 in the depth to which the water measured would cover the land irri- 

 gated, provided it all reached the land. The table below gives the 

 averages of the three classes of measurements. 



Depth 



Measured at the heads of large canals. ... 2.63 feet 



Measured at the heads of large canals and laterals 2.40 feet 



Measured at the margins of fields when used 1.29 feet 



The causes assigned for these immense losses are improper con- 

 struction, the nature of the soil through which the canals pass, and 

 the practice of placing checks in canals to throw water on land too 

 high to be irrigated without their use. The report of the work on 

 the Gage Canal in California shows that practically all these losses 

 can be stopped when the value of the water will justify the necessary 

 expense. This saving would enable many existing canals to irrigate 

 double the area now reclaimed. 



Serious losses from evaporation do not occur in main canals, but 

 from the fields where water is distributed. During the midsummer 

 season the continuous sunshine heats the surface of the ground to a 

 very high temperature. A test made last summer by the govern- 

 ment irrigation man, showed the surface soil in southern California to 

 have a temperature of 120 degrees F. When a thin layer of water is 

 spread over land thus heated, as it is frequently done when flooding 

 is practiced, the loss from evaporation must be excessive. Mr. W. M. 

 Reed discusses this in his report on New Mexico, showing instances 

 where it has become so great as to entirely consume the volume sup- 

 plied. Irrigators know by practice how much faster an irrigation 

 head of water travels over fields at night and in the early morning 

 than during the afternoon. This is due to the difference in the rate of 

 evaporation. In order to lessen this loss it is important that fields be 

 irrigated as quickly as possible. To do this each irrigator should be 

 supplied with all the water he can distribute. Where only a small 

 stream is used, progress is slow, the soil next the laterals is satu- 

 rated; it is hard work to reach the high spots while the low ones are 

 over irrigated by the delay this causes. 



Contracts which provide for the delivery of a uniform constant 

 flow are, as a rule, wasteful of water. Contracts which charge for the 



