CHAPTER IV 



THE WORK OF WATERS UNDERGROUND 

 FACTS ABOUT GROUND WATER 



WHEN a well, mine, or other opening of sufficient depth is 

 made in the ground, water seeps into it from the surround- 

 ing rocks. The existence of water beneath the surface (ground 

 water) is also proved in a simple way by the fact that it issues 

 from the ground to form great numbers of springs hi all 

 humid regions, and occasional ones even in very dry regions. 

 By digging deep enough it is possible almost anywhere to 

 reach a level where the rocks are saturated with water. The 

 level below which the rocks are full of water is the level of 

 ground water, or the water table. 



Source of ground water. The ground water is related 

 intimately to the rainfall, for water stands higher in wells 

 in rainy seasons than in periods of drought, and springs are 

 more numerous and of greater volume after plentiful rains 

 than during periods of dry weather. Indeed, no other 

 source exists from which important contributions to the 

 ground water can be made. Most of the water beneath 

 the ground therefore probably once fell as rain. 



Proportion of the rainfall which enters the ground. A 

 portion of the water which falls as rain runs directly off the 

 surface (the immediate run-off), another part is evaporated, 

 and a third sinks into the ground. The proportion of the 

 rainfall which enters the ground varies at different points 

 and at different times, with (1) the slope of the ground, 

 (2) the porosity of the soil and rocks, (3) the amount of 

 water already in the rocks, (4) the rate of precipitation, 



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