GENERAL DRAINAGE INFORMATION 



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movement of the water below the point of change is likely 

 to be so slow as to find difficulty in moving the particles 

 of silt. They are also placed where a sub-main unites 

 with a main, and where a long lateral unites with a main 



FIG. 34. Silt-basin of concrete and sewer tile. 



or a sub-main, and at intervals along any considerable 

 line of tile, whether it is lateral, sub-main, or main. In 

 the last named case, the purpose is not only to gather 

 the silt moving down the line, but also as a provision for 

 examining the condition of the tile drain. By such a 

 distribution of silt-basins, the line or system is divided 

 into units, and if a mishap, resulting in the clogging of 

 any portion of the system, occurs, the unit in which it is 

 located can usually be established by examining the silt- 



