CHAPTER XVII 

 WATER OF SOILS 



III. GRAVITATIONAL WATER 



GRAVITATIONAL water is that which may be removed from the 

 soil by the force of gravity or drained from the soil under normal 

 conditions. The possible amount of the gravitational water is the 

 difference between the water held by a soil at its maximum capil- 

 lary capacity and at its maximum water capacity, when completely 

 saturated, or when the air space is completely filled. This amount 

 varies with the type of soil. 



The determination of the gravitational water capacity of soils 

 is very unsatisfactory. The amount depends upon the height above 

 the water table. The gravitational water is the difference between 

 the water content, when completely saturated, and when only satis- 

 fied with capillary water. This amount will vary, since the same soil 

 will be satisfied by a smaller amount of capillary water the greater 

 the distance above the water table. King shows the amount of 

 water at different heights above the water table with sands of dif- 

 ferent grades and two soils. 



Water at Different I frights Abort 



(he Water Table After Keing Saturated and 

 Drained l 



Percolation. ---The movement of gravitational water downward 

 through the soil bv the force of gravitv is called percolation. It 

 depends upon several factors. 



1. Physical Composition or Texture. The movement of 

 water through the soil bv the force of gravity varies directly as the 



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