FIXING THE GRADE OF DRAINS. 8/ 



has been done. The cut measured from the top of the 

 grade pegs and connected by a line will give a true 

 and uniform grade from beginning to end. 



A change of grade is frequently necessary where the 

 land has any considerable slope, otherwise the drains 

 will be too deep or too shallow in places for economy 

 in digging or for efficiency of operation. This is 

 effected by dividing the lines into the necessary di- 

 visions, each division having a grade of its own. The 

 station where the change of grade is made should be 

 noted on the book. In the example of the notes given 

 the grade is .25 per 100 as far as station 4, and then 

 changes to .20 per 100. Where a cut is to be made 

 through a ridge to reach a flat which it is desired to 

 drain, determine the least depth of drain that should 

 be used at the upper end, take a safe grade, say .10 

 per 100, or .20 per 100, and run down by subtracting 

 the grade from the elevation of each station in order, 

 until the ridge is passed and the desired depth is 

 obtained, then change to a heavier grade. It is the 

 ordinary method of grading a drain reversed. 



A large number of examples might be given, but the 

 above are sufficient to show the beginner the general 

 plan of work. A few examples of his own worked out 

 will soon give him an insight into the practical details 

 of grades. 



When a sub-main or lateral enters another drain it 

 IS best to have an outfall from the branch line into the 

 main. This is commonly called a ** drop ' ' and should 

 be proportionate to the size of the tile used on both 

 lines. For example, branches into a 6-inch main 

 should drop .20, into an 8-inch .30, lo-inch .40, 12- 



