74 



AGRICULTURAL ENGINEERING 



a grade of .02 foot per hundred feet is equal to .02 per cent, 

 etc. Again, the grade may be stated in inches per rod, as, 

 Yi inch per rod or 1 inch per rod. It is customary to refer 

 to the grade as the "fall." Then a grade of .1 foot per 100 

 feet is called a "fall" of .1 foot per hundred feet, and a grade 

 of 1 inch to the rod has a "fall" of 1 inch to the rod. The 

 line of the bottom of the finished ditch, or the line on which 

 the tile is laid, is called the grade line. 



Establishing Grade Lines. After the elevations of the 

 grade stakes have been obtained, it now falls to the lot of the 



+100 >fh 



I 345 6 7 S 



IO II 



Profile of Main. 



Fig. 51. A profile of a tile drain. 



drainage engineer to establish the grade for the tile lines. 

 There are two methods in common use for doing this, and 

 they will be explained in turn. 



Grade Profile. One simple and also very satisfactory 

 way of establishing the grade for the tile drain is to plot 

 the system on profile paper, using a vertical scale to show the 

 elevations of the various stations, and a horizontal scale, 

 the distance between stations. The vertical scale should 

 show differences of at least 1-10 of a foot in elevation. It 



