38 THE HANDBOOK FOR PRACTICAL FARMERS 



that soft quicksand quality, the more important it is to have 

 good close joints. It is a good plan in all cases to cover the 

 upper half to two-thirds the joint with a strip of tar paper or 

 burlap about three inches wide. Water should enter the tile 

 on the lower side of the joint. In tight clay or in other soil 

 inclined to hardpan properties, a fairly open joint with this 

 covering on the top will greatly facilitate drainage. 



Suitable grades for drains. — The low grade or slope at which 

 a tile drain will operate efficiently is one of the big advantages 

 it has over open ditches where the smaller volumes of water are 

 to be handled. If the slope is straiglit a tile will operate on as 

 small a grade as one or two inches per hundred feet. Naturally 

 this minimum depends on the size of the tile, the number of 

 turns, and the inclination to accumulate sediment, all of which 

 interfere with the use of low grade. Eight inches to one foot 

 of fall in one hundred feet of length is a more satisfactory 

 grade upon which to operate and simplifies the details of form- 

 ing the trench to receive the tile. AYhere very large grades are 

 used there is danger that the tile may be washed out by water 

 flowing along the outside of the tile in flood periods unless the 

 soil is worked down very closely around the tile. 



Arrangement of tile. — The arrangement and size of tile are 

 questions specially related to the particular land to be drained. 



First of all, if there is 

 any doubt about the direc- 

 tion and extent of grades 

 available, a survey ade- 

 quate to the situation 

 should be made. It may 

 involve the use of a very 

 accurate leveling instru- 

 ment with determination 

 of the form of the land 

 surface and position of 

 important points and 

 lines from which to con- 

 struct a map, or it may 

 involve only a few rough 

 levels such as may be se- 

 , „ , . cured from the flow or 



Fig. 15. — Sketch showing a "random drainage ,i i i ,? , ,1 



system and the location of tile used in the ICVel Ot Water, Or the 



draining forty acres of land in Scott -j^gg of the leSS aCCUrate 

 County, 111. Only part of this land needed r? i i i 



drainage.-t7. 8. Dept. of Agriculture. type of levels SUch as 



