DRAINAGE 



99 



should be placed across the outlet to prevent the entrance of 

 small animals which might, by dying in the tile, become an 

 obstruction. 



Catch Basins, or Surface Inlets. Where there is sure to 

 be considerable surface flow, it is best that this be taken into 

 the tile as soon as possible. The catch basin is simply a 

 grated inlet leading directly to the tile. The basin is usually 

 built deeper than the tile to allow dirt, which might be 

 washed in, to settle and not be carried into the tile with the 

 water. This sediment should be cleaned out from time to 

 time. 



A concrete box, 33^2 feet across and with 4-inch walls, 

 makes a very satisfactory 



catch basin. The box 

 should extend 2 feet below 

 the line of tile and should 

 have a removable cover. 

 Large sewer pipes with 

 side connections can be 

 used conveniently for this 

 purpose. 



Silt Basins. Silt basins 

 have been recommended 

 for tile lines where the 

 grade is reduced, and are 



designed to provide a receptacle to catch the silt that is 

 likely to settle at that point. They are constructed with 

 removable covers through which the sediment may be re- 

 moved from time to time. There is little doubt that these 

 devices are very harmful in checking the flow of water in the 

 tile, and it has been the experience of the author that these 

 basins are never given attention when they require it. 



Fig. 64. A silt basin. 



