EXPERIMENT STATION BULLETINS. 



475 



and should be eighteen to twenty-four inches in diameter for large tile. 

 As the water enters the silt basin from the tile its velocity is suddenly 

 decreased and its capacity to carry silt is reduced. Most of the silt, 

 therefore, settles to the bottom of the silt basin as the water passes 

 through and into the outleading tile. When the silt has accumulated 

 siilticiently in the bottom of the silt basin, it may be removed with a 

 shovel or a hoe. 



Fig. 7. Silt basin built of cement and sewer tile. 



Fig. 8. Silt basin built of cement. 



With silt basins placed at reasonable distances, if any section of the 

 system fails to work properl}' the section can be located by an inspec- 

 tion of the silt basins of the system. 



THE CONSTRUCTION OF A SILT BASIN. 



A very common method of constructing a silt basin is to dig an open- 

 ing to a depth of at least twelve inches below the bottom of the tile and 

 from twenty to thirty inches in diameter, depending on the size of the tile 

 leading into and from the basin. This opening is then walled or curbed 

 with common brick to the top of the ground. See Fig. G. 



Sometimes the opening is walled with brick to just above the top of 

 the tile and then a large piece of sewer tile of sufficient diameter is placed 

 on end in upon the brick. Cement may be used in place of the brick. 

 See Fig. 7. 



In these days of cement a very simple method of constructing a wall 

 for tbe silt basin is to set in a form and then to build a wall of concrete, 

 using sandy gravel and cement in the proportions of seven to one. See 

 Fig. 8. 



In most cases it is desirable to carrv the basin wall to a few inches 



