282 



ENGINEERING ON THE FARM 



be shallow and close together, so that the water can readily 

 reach them. Some crops require a much higher degree of 

 drainage than others. In some close, tenacious soils, to get 

 good drainage for orchard or garden purposes, it has been 

 found necessary to lay the drains as close as 33 feet. In 

 light, open soils used for field crops drains 300 feet apart 

 have proved entirely satisfactory. The size of tile is 

 dependent on surface conditions, grade per 100 feet, area 

 drained, and the outlet. The following table shows the 

 number of acres drained by tile of a given size and laid to 

 a given grade : 



Table Showing the Number of Acres Drained by Tile of a 

 Given Size and Laid to a Given Grade* 



x This table is based on the removal of yi inch of rainfall from the 

 entire watershed in twenty-four hours. Local conditions of soil and 

 run-off will have some effect on the size of tile for the area drained, 

 but the area given is as near as can be determined in a general 

 statement.) 



Grade per 

 100 Feet 



.04 



.06 



08 . 10 



. 12 



14 . 16 



.18 



. 20 



• 25 



• 30 



.40 



• So 



.60 



.70 



.80 



Size of Tile 



4 

 5 

 6. 



7 

 8. 



9 



10. 

 12. 



14. 

 15 

 16 

 18. 



20. 



14 

 25 



42 



65 



94 

 130 



174 

 290 



444 

 536 

 639 

 885 

 1,180 



*After Stewart, University of Minnesota. 



Qualities of tile. Two classes of tile are in common use : 

 clay and concrete (Fig. 230). Tile should be straight 

 in length, circular in cross section, and well made. The 

 test for good tile requires that it give a sharp metallic 

 sound when struck with a piece of me + al. Average tile 

 overrun in length % to T / 2 inch. Tile may not be square 



