106 WATER CONDUCTORS AND ACCESSORIES 



the closed construction generally becomes more economical, in 

 that tunnels may be built and the pipes follow more or less the 

 contour of the country. The selection of the particular type of 

 conduit construction is, therefore, an engineering problem of 

 considerable importance, and has to do with the economic oper- 

 ating features of the development. 



Canals. The velocity of water in a canal is affected by the 

 roughness of the bed, by the wetted surface of the form of the 

 cross-section, and finally by the grade. According to Chezy's 

 formula it is equal to: 



v = cVrs, 



where v = velocity in feet per second; 

 c = coefficient; 

 r = hydraulic radius in feet; 

 s = grade or hydraulic slope, 



the values of c may be obtained from the following two formulae, 

 both of which are in. common use. 

 Kutter's formula: 



where n is the coefficient of roughness, the values of which are 

 given in table XXVII. 1 



Bazin's Formula: 



87 



0.552+-^' 



Vr 



TABLE XXVIII 



VALUES OP m 



Smooth cement and planed boards . 06 



Planks and bricks .16 



Rubble masonry . 46 



Earth canals in excellent condition . 85 



Earth canals in fair condition 1 . 30 



Earth canals in bad condition 1 . 75 



1 R. E. Horton, " Engineering News," February 24, 1916. 



