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one or more canals on each bench. In other instances the irrigated 

 lands occupy a plane which rises with a uniform grade from the bank 

 of the stream. In l)oth cases the canal, which is located next to the 

 highest in a series, receives a large part of the water which percolates 

 from the one above it and in turn transfers a part of its flow to the 

 next lower. 



The water supply of irrigated districts is still further influenced by 

 seepage water from irrigated areas. Only a part of the water which 

 is spread over the soil is utilized by the plants. The balance is either 

 evaporated from the surface or percolates slowl^^ through the subsoil. 

 When porous bench lands are heavily irrigated a portion of what 

 sinks beneath the surface returns to the river channels and augments 

 to a considerable extent the available flow. 



A knowledge of the quantities of water lost from canals and drain- 

 ing from irrigated lands and collected b}' other canals, or returning to 

 the stream to be rediverted, is of great importance to courts in the 

 adjudication of rights, and to administrative ofiicials in the distribu- 

 tion of water from streams. 



Seepage waters have likewise to be considered in providing for 

 drainage. It would be wrong to conclude that the seepage losses from 

 canals always return to the channel of the stream or were intercepted 

 by other canals. Waste water of this kind quite frequently gravitates 

 to the lower levels of an irrigated district and makes unproductive 

 marshes and alkali flats of what otherwise might have been fertile 

 flclds. It is important to determine the extent of this loss in order to 

 plan the size, number, and direction of the drains, and to endeavor 

 to intercept the waste water before it reaches the lower levels. 



Seepage from earthen canals represents the greatest loss of irriga- 

 tion water, and until the amount is approximately ascertained for each 

 canal it is not probable that any steps will be taken to lessen this loss. 



LOSSES IN CONVEYANCE OF WATER. 



The principal losses which occur in conve3dng water from a stream 

 or other source of supply to the place of use may be grouped under 

 one or the other of three heads. These are leakage, evaporation, 

 and percolation. 



LEAKAGE. 



The loss due to leakage is readily traceable to faulty construction 

 and can be remedied only by better structures and the exercise of 

 higher skill in the building of canals. The wooden flumes to be found 

 on nearly every canal are the chief source of leakage. Some leak so 

 badly as to endanger their safety. This can be remedied by using a 

 better grade of lumber and building the flumes in such a wa}' as to 

 insure water tightness. In many cases the best course to take with 



