Silt Basin. 



299 



change from a steeper to a less steep grade, because if this 

 is done there is danger that sediment may lodge where the 

 fall is less and close up the drain. The case is different 

 where a change can be made from a small fall to one which 

 is greater, for then whatever sediment is carried by the 

 water along the flatter slope will be carried down the steeper 

 one. 



FIG. 119. Showing the construction of a silt basin. 



373. Silt Basin. In changing from a steeper gradient to 

 one which is less the danger of clogging- the tile can be re- 

 duced by introducing in the line, at the place where the 

 change is made, a silt well, Fig. 119, which provides still 

 water in which sediment falls and from which it may be re- 

 moved as often as necessary. Where these silt basins may 

 be small, glazed sewer tile of suitable size may be used for 

 the portion above the ground. 



374. Size of Tile The proper size of tile can only be de* 

 finitely stated when the detailed conditions under which the 

 drain is to work are known. They should be large enough 

 to remove in 24 to 48 hours the excess water of the heaviest 

 rflins likely to occur. 



