LAND DRAINAGE 661 



may be placed at the top of the well to insure its continu- 

 ous operation. Extensive systems of underdrains are 

 reported to have been discharged b\ this arrangement, 

 where it might otherwise have been necessary to go a 

 long distance in order to obtain an outlet. It should be 

 noted that in many cases a sufficiently porous stratum 

 is lacking in the structure of the surface portion of the 

 earth, so that the method could not often be employed. 



563. Drainage by means of explosives. — The use of 

 explosives for promoting drainage has been proposed 

 for three conditions : — 



1. To break up a hard subsoil and possibly make a 

 connection with a more porous stratum below^, so that the 

 soil could better handle the normal rainfall. This is 

 closely related to the operations of subsoiling. 



2. To break through a thin impervious layer in the 

 bottom of a wet basin-shaped area. This is identified 

 with vertical drainage described above. 



3. To open up channels for drainage purposes. This 

 use is the most extensive. By proper distribution of the 

 charges of explosives, coupled with favorable soil and 

 weather conditions, a very good channel can be opened 

 by this method. It is suited only to the excavation of 

 open ditches of medium size, three feet or more in width, 

 and it has the greatest advantages where the land is 

 much obstructed by stone or stumps. The force of the 

 explosive largely clears the ditch of earth and obstructions. 

 No very accurate grading of the bottom of the ditch can 

 be accomplished by this method. 



564. Resume. — The removal of the excess water 

 from the soil by any means constitutes drainage and is 

 one of the most fundamental operations in soil manage- 

 ment. The effects of adequate drainage are numerous 



