GENERAL DRAINAGE INFORMATION 93 



122. The construction of a silt-basin. A very com- 

 mon method of constructing a silt-basin is to dig an open- 

 ing to a depth of at least 12 inches below the bottom of the 

 outgoing tile, and from 20 to 30 inches in diameter, de- 

 pending on the size of the tile leading into and from the 

 basin. This opening is then walled or curbed with com- 

 mon brick to the top of the ground. (See Fig. 33.) Some- 

 times the opening is walled with brick to just above the 

 top of the tile and then a piece of sewer pipe of sufficient 

 diameter is placed on end upon the brick. Cement may 

 be used in place of the brick. (See Fig. 34.) In re- 

 gions where stone, and especially flat stone, is abundant, 

 this material is much used in building walls of silt-basins. 



In these days of cement, a very simple method of con- 

 structing a silt-basin is to dig an opening of proper size 

 and then build in a wooden form, and fill the space between 

 the form and the walls of the opening with a mixture of 

 one part of cement to five or six of sandy gravel. (See 

 Fig. 35.) 



123. Finishing the silt-basin. In most cases, it is 

 desirable to carry the basin wall to a few inches above 

 ground. Sometimes, however, where the field is culti- 

 vated, the top of the wall is stopped at 12 inches below 

 the surface of the ground. A heavy covering is then placed 

 on the top of the wall and the soil is filled in above it. In 

 this case it is necessary to use some special means for 

 locating the silt-basin. 



Where the wall is brought to or above the surface of 

 the ground, it should have placed upon it a substantial 

 cover of wood, concrete, or iron. Iron gratings are used 

 when it is desired to remove surface water by way of 

 the tile drains (see paragraph 208). 



