122 SUCCESSFUL FARMING 



the depth of the tile from the lower to the upper end of any branch. In 

 a drainage line 1200 feet in length a fall of one inch in each hundred feet 

 may be obtained by having the lower end of the line 3J feet below the 

 surface of the ground, and the upper end 2J feet below the surface, even 

 though the land along this line is absolutely level. 



The Outlet. The first essential for a satisfactory system of under- 

 ground drainage is a good outlet. The outlet must be the lowest point 

 in the whole drainage system, and water should seldom, if ever, stand 

 above the opening of the tile. 



The outlet of the main should be protected by a screen in such a way 

 that rabbits and other animals cannot enter. At the outlet the tiles are 



subject to freezing more than elsewhere in the 

 system, as a result of which they may be 

 broken. It is well to provide for this by 

 using a wooden box, or an iron pipe as a 

 substitute for the earthen tile. This should 

 extend back from the opening six or eight 

 feet to a position where it will not become 

 frozen. 



Size of Tile. The size of the main 



"^ rv^'F^Stotlir^^ ^' outlet or line is determined by the area to 

 be drained, together with the water-shed 

 contributary to it. Not only must we 

 WATER ISSUING FROM AN figure on removing all of the rainfall that 

 UNDERGROUND DRAIN.* descends directly on the land to be drained, 



but we must also calculate on the amount 



of water that reaches such land from adjacent higher land, whether 

 as surface wash or underground seepage. The maximum amount of 

 water necessary to remove from the land in order to effect satisfactory 

 drainage will depend chiefly on the rainfall likely to occur in short periods 

 of time during the growing season. It will seldom be necessary to provide 

 for the removal of more than one-half inch of water in twenty-four hours. 

 On this basis a system of tiles flowing at full capacity will remove rain- 

 fall at the rate of fifteen inches per month. This is much in excess of the 

 usual rainfall in any part of the country. The removal of one-quarter 

 inch of rainfall in twenty-four hours will generally provide adequate drain- 

 age. The size of tile required to accomplish removal of water at the 

 above mentioned rate will be determined largely by the grades that it is 

 possible to secure. The size of tile required is given in the chapter on 

 "Drainage and Irrigation." 



Courtesy of Orange Judd Company. From " Soils and Crops," by Hunt and Burkett. 



