84 



AGRICULTURAL ENGINEERING 



Size of Laterals. The size of laterals may be fixed as 

 soon as the available fall is obtained by the taking of levels. 

 In general, it is not regarded good practice to use small tile in 

 laterals. The use of 3-inch tile has been quite generally dis- 

 continued in favor of 4-inch. The larger tile is less likely to 

 be influenced by imperfect construction, and the difference 

 in cost is small. There is a minimum grade for tile lines 

 less than which it is not practical to lay tile. If the soil is 

 free from sand or other sediment-forming elements, the grade 

 may be quite flat; however, if the soil is sandy a considerable 

 slope should be provided. 



On account of the resistance to flow in small tile, it is not 

 best to make lines of small tile longer than a certain length. 

 The following table gives the minimum grade and maximum 

 length of tile lines which are practical with various sizes of 

 tile. 



Table showing minimum grade and length for tiles of various sizes. * , 



"From Elliott's "Engineering for Land Drainage. 



PROBLEMS FOR PRACTICE IN THE USE OF THE FORMULA 



1. Find the number of acres that may be properly drained by a 

 6-inch tile line 20 rods long, if laid with a grade of 2-10 of a foot per 100 

 feet. 



