116 



LAND DRAINAGE AND IRRIGATION 



Good open ditches do not afford complete underdrainage 

 except for a few yards on either side of them. In order to secure 

 thorough underdrainage through the use of open ditches, they must 



Fig. 50. — A good outlet ditch. I'lns was dug with a floating dredge. It is 20 feet wide 

 at the top and 7 feet deep. (Wisconsin Station.) 



be dug about every four or eight rods; but many open ditches 

 take up considerable space, they cut farms and fields into incon- 

 venient and irregular shapes, they require the building of many 



Fig. 51. — Covered drains other than tile. A,B,C, cobblestone and rock drains ; D, pole drain. 



farm bridges, they are unsightly, they are difficult and expen- 

 sive to keep open and clean, they present a constant source of 

 danger to farm animals, they provide harborage for obnoxious 

 weeds, and are excellent breeding places for injurious and dis- 

 agreeable insects. 



