Ground 'Water Surface. 



261 



It will be seen from the diagram that lip to 12 inches 

 above the ground water surface the space into which water 

 can settle in either sand is very small and hence that a 

 small amount of percolation will produce a relatively large 

 ol ovation of the ground water surface at first. 



80 



40 



1EEL 



Fia. 91. Showing the amouut of unoconpied space In completely drained 

 sands. Space between long rnles, one foot. 



In a tank filled with rather coarse sand and provided with 

 glass gauge tubes, as represented in Fig. 112, p. 293, to 

 show the level of the ground water surface, a single pound 

 of water added to the 14 square feet of surface raised the 

 level of the ground water .31 inch. In another trial 

 16.435 Ibs. of water or .226 inch raised the surface 6.7 

 inches. In still another trial the withdrawal of 33.575 Ibs. 

 of water from the tank, or .461 inch, lowered the ground 

 water 9.05 inches. 



In the table below are given the amounts of water re- 



Tdble showing amount of rain necessary to raise level of 

 ground water after thorough drainage. 



17 



