CHAPTER XIII 



CAPACITY OF TILE DRAINS 



Cause of Flow in Tile Drains. If water be poured into an 

 inclined pipe or other conduit, it will flow toward the lower 

 end. This flow is produced by the action of gravity. The 

 effect of gravity may be observed in the phenomena of f ailing 

 bodies, and the law for the velocity of falling bodies is usual- 

 ly expressed by the formula: 



V - y 2 gh 



where V is equal to the velocity in feet per second, g the accelerating 

 force of gravity, and h the distance through which the body fa^s. 



Thus a freely falling body starting from rest will have 

 a velocity of 32.2 feet per second at the end of the first 

 second. At the end of the second second the velocity will 

 have increased to 64.4 feet per second, and there will be an 

 increase in velocity each second, or it will continue to accele- 

 rate thereafter. It is this same force which causes the flow 

 of water in tile drains, and there can be no other agent to 

 produce the flow. In the tile drains, however, there are 

 many influences to interfere with the acceleration of velocity, 

 which tend to make the velocity uniform. 



Velocity Formulas for Flow of Water. There have been 

 many attempts to incorporate into a formula the various 

 factors which produce and retard the flow in tile drains, and 

 many such formulas have been proposed. The extent to 

 which these forces retard the flow of water in pipes cannot be 

 determined accurately. Some of these forces are the resist- 



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