CHAPTER VI. 

 FIXING THE GRADE OF DRAINS. 



A grade line as determined by a survey is the line 

 along which the water of the drain, when constructed, 

 is to flow. 



Fall is the common term for slope of surface when 

 applied to land, and for total head when applied to 

 drains. 



The available fall is the fall that can be given to 

 a drain in a prescribed distance, as distinguished from 

 the fall of the land through which the drain extends. 



The grade of a drain is its rate of fall and is ex- 

 pressed in inches, or in decimals of a foot, per lOO feet* 

 When expressed in decimals of a foot per loo the 

 grade is said to be so much per cent. 



Determining the grades upon which the drains should 

 be laid requires much skill and knowledge of practical 

 details of construction, together with the understanding 

 of the requirements of the soil, capacity, cost, and 

 efficiency of various kinds and sizes of drains, some of 

 which subjects will be discussed in subsequent chapters 

 of this work. The minimum grade that may be suc- 

 cessfully used for the tile drains is a matter of great 

 moment where level lands are treated, and will de- 

 pend much upon the accuracy with which the drains 

 will be constructed. The topography of the surface 



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