AGRICULTURAL EXGIXEERIXG. 



165 



NUMBER OF ACRES DRAINED BY TILES REMOVING 

 1/4-INCH DEPTH OF WATER IN 24 HOURS. 



(ASHBAUGH.) 



The table is based on Poncelet's formula, and refers to drain - 

 age of ground water only. If surface water is also to be removed, 

 as in the case of ponds without other outlets, the tiles will drain 

 safely only one-half to one-third the number of acres given in 

 the table. When a part of the land in the watershed is rolling, 

 not requiring tiling, count only one-third of such rolling land 

 in addition to all of the low, flat land, in getting the size of tiles 

 to remove ground water only. 



If it is not practicable to use such a large tile as is required to 

 carry a large amount of surface drainage, a broad shallow depres- 

 sion, cultivated or kept in grass, may be maintained alongside 

 of the drain to carry the surface overflow from heavy rains. A 

 12-inch tile may thus often be used in place of the expensive 

 15-inch or 18-inch tile. 



