CHAPTER V 



DESTRUCTIVE PROCESSES — RUNNING WATER 



The source of all running water, whether surface or under- 

 ground, is atmospheric precipitation in the form of rain or snow. 

 All springs and streams are merely rain (or snow) water collected 

 together and fed from reservoirs. Of the rain-water which falls 

 upon the land, about one third is evaporated, a second third flows 

 over the surface to the nearest water-course, and the remainder 

 sinks into the soil to a greater or less depth, and though part of 

 it again comes to the surface in springs, yet a great portion must 

 reach the sea by subterranean channels. 



i. Underground Waters 



The flow of underground waters, as well as that of surface 

 waters, is determined by gravity, but surface topography has no 

 effect upon it, and often the superficial and subterranean flows are, 

 for considerable distances, in exactly opposite directions. Un- 

 derground drainage is determined by the inclination of the rocks, 

 the alternation of porous and impervious beds, the number and 

 character of their joints and fissures, for the flow is ordinarily 

 through these crevices, except in very porous materials, such as 

 loose sand, which allow of a flow through their substance. In 

 soluble rocks the water may dissolve out its own channels. 



These facts of the underground movement of water are of great 

 practical importance in all questions of drainage and water sup- 

 ply. Serious evils have followed from the careless assumption 

 that subterranean drainage would be in the same direction as that 

 on the surface of the ground. The accompanying diagram shows 

 an arrangement of cess-pool and well, which was planned on the 



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