Gradient of Drains 447 



THE FALL OR GRADIENT FOR DRAINS 



In most cases where drainage is required, the sur- 

 face of the field is so flat that it is usually desirable 

 to secure as much fall for the drains as it is prac- 

 ticable to get, and so a careful study of the field 

 should be made with a view to learning where the 

 lowest land is and along what line the greatest rate 

 of fall may be secured. This is a matter of the 

 greatest importance, and the less the fall is the 

 greater should be the attention given to it. If a fall 

 of 2 inches or more in 100 feet can be secured, the 

 conditions are favorable for good results. It often 

 happens that less fall than this must be accepted, but 

 this should be done only after careful leveling has 

 proved a greater one impracticable. 



It will frequently happen that the line of lowest 

 ground is quite tortuous, making the distance from the 

 highest to the lowest point greater than to follow a 

 straight line. When this is the case, and the fall 

 very small, it may often be desirable to dig a little 

 deeper in places, cutting off bends, and thus increase 

 the fall. 



It will generally be true, however, that the main 

 drain should follow the lowest line in order to secure 

 as much fall for the laterals as possible, and this 

 point is made the more important because the axis 

 of each lateral should reach the main above its center, 

 in order that water in the main shall not set back 

 into it. 



Great pains should always be taken to get a per- 



