INLAND DRAINAGE 



129 



reason, the system shown in Fig. 91 is preferable to that shown in 

 Fig. 90, since the cost is less and the drainage more uniform. 

 In the East, for general farming purposes, the laterals are 

 placed from 32 to 70 feet apart. In the Middle West, on the 

 higher lands and closer soils, 132 feet frequently has proved 

 satisfactory. On level lands with porous subsoils, drains from, 

 160 to 192 feet apart have given good service. For truck land 



Do u 



/e 



d r^/incd / 



!Z 



U.5. Dcpar/wcnf- of Acjncu/fvre (Afcr5mith) 



Fig. 90. — Too much double-drain- 

 ing — a waste of money. 



Fig. 91. — Double-draining re- 

 duced to a minimum by proper 

 design. 



the laterals should be closer together than for land on which 

 general farming is carried on. 



No tile less than 3 inches in diameter should be used, and best 

 practice today in the Middle West seems to be to make 5 inches the 

 minimum size. However, no hard and fast rule can be given. 

 According to Smith, 1 in the dark silt-loam soils of Illinois and 

 Iowa,\where the rain-fall approximates 36 inches a year, an 8- 

 inch tile with a fall of 2 inches to 100 feet will furnish an outlet for 



l " Tile Drainage on the Farm," Farmer's Bulletin No. 524, U. S. Department 

 of Agriculture, 1917. 

 9 



