I 9 8 



FARM DEVELOPMENT 



Where deep subsoiling is practiced the top of the tiles 

 should be at least 15 inches deep, and, in no case, even 

 in rather open soil, which will not need subsoiling, 

 should the tiles be laid nearer the surface than 10 to 12 

 inches. In case of very dense subsoils, where fine, dense 

 clay is thrown back into the ditch over the deeply laid 

 tiles, the surface water may be prevented from reaching 

 the drain quickly, especially if it be laid too deeply, and 

 the drain be, therefore, of little service. If the ditch be 

 filled with gravel or other porous material, the water 



Figure 87. Cross section through two tile drains showing direction the water fol- 

 lows in reaching the openings in the tiles. After a heavy rainfall the surface of the 

 ground water rises to the line X. As this gradually seeps sidewise into the bottoms 

 of the tiles the surface of the water sinks, as to the line T. 



can get into the deep drain quite as readily as if it were 

 nearer the surface. This precaution is necessary only 

 in rare cases. 



Special survey notes. In surveying out the line of the 

 ditch, special notes should be made of all unusual fea- 

 tures, and of the exact points at which laterals branch 

 off, and, where practicable, the location of the drain at 

 different points, as where crossing a line of land survey, 

 or near a monument which has been recorded in previous 

 land surveys ; these should be carefully noted, showing 

 the exact distances and directions to given points, so 



