CONCRETE LINING FOR IRRIGATION CANALS. 39 



The study of hydraulics has not yet reached that stage which will 

 justify the assignment of definite values to the various influences 

 which retard flow and thereby lower the efficiency of irrigation 

 canals. One can do little more than consider all such factors collec- 

 tively and designate them by the common term "frictional resist- 

 ance." This has been done in the empirical formula known as 

 Kutter's, where the letter n, called the coefficient of friction, repre- 

 sents not only the degree of roughness of the channel but all the 

 other retarding influences to which reference has been made. 



All the data pertaining to the carrying capacities of concrete- 

 lined canals procurable at this writing (March, 1914) have been assem- 

 bled and summarized in Table III. These results have been de- 

 rived from a number of sources and represent rather wide differences 

 in channel conditions. They likewise represent the work of a num- 

 ber of engineers who have employed somewhat different methods in 

 making the necessary measurements. They are therefore not strictly 

 comparable, but maybe used as a basis for general deductions. 



