356 HYDRAULICS 



FLOW OF WATER IN CHANNELS 



A channel is the bed of a long body of water flowing under the 

 action of gravity. An artificial channel whose bed is formed 

 by the natural soil is called a canal, and when the bed is artificial, 

 like a flume or a sewer pipe, it is called a conduit. A ditch is a 

 small canal. 



The slope s of a channel is the ratio of the fall h to the length 

 I in which the fall occurs; or 



The -welled perimeter of a cross-section of a channel is the 

 part of the boundary in contact with the water. The hydraulic 

 radius of a channel is the ratio of the area of the cross-section 

 of the water in the channel to the wetted perimeter. 



Chezy's Formula. The fundamental formula for the velocity 

 of flow in a channel is v = c \rs, 



in which 5 is the slope of the channel; r, the hydraulic radius; 

 and c, a variable coefficient whose value is given by Kutter's 



formula, which is, 1 .00155 



23 H --- 1 -- 

 n s 



s 



In this formula is the coefficient of roughness, whose values 

 are as follows: 



Character of Channel Value of n 



Clean well-planed timber 009 



Clean, smooth, glazed iron and stoneware pipes . . .010 

 Masonry smoothly plastered with cement, and 



for very clean smooth cast-iron pipe Oil 



Unplaned timber, ordinary cast-iron pipe, and 



selected pipe sewers, well laid and thoroughly 



flushed 012 



Rough iron pipes and ordinary sewer pipes laid 



under the usual conditions 013 



Dressed masonry and well-laid brickwork 015 



Good rubble masonry and ordinary rough or 



fouled brickwork. .. ... .017 



