Capacity of Wells. 



Table showing the flow in a 6-inch well sunk different depths 

 into 200 feet of water-bearing sandstone where the pore space 

 is 82 per cent, and the diameter of the grains .25 m. m. 



346. Influence of Pressure on the Capacity of a Well. 

 Since the flow of water through sands and sandstone is some- 

 what nearly proportional to the effective pressure it is clear 

 that the depth of water in the well at low water stage should 

 be great enough to permit its surface to be lowered until the 

 needed pressure to force the water into the well is de- 

 veloped. 



If, in pumping, the water in a well is lowered 4 feet the 

 pressure developed will be about that of four f eert of water 

 and to lower it 8, 12, 16 or 20 feet will increase the pres- 

 sure 2, 3, 4 and 5-fold. This relation being true it is clear 

 that not only should there be an ample depth of water in the 

 well but the cylinder of the pump should be so placed as to 

 enable the full depth to be utilized. 



In the case of a 6-inch well sunk 100 feet into water- 

 bearing sandstone 200 feet thick having a pore space of 32 

 per cent, and diameter of grains of .25 mm. the capacity 

 of the well under different pressures is computed to be as 

 follows: 



Amount the water is lowered in the well in pumping. 



347. Influence of the Diameter of the Well on its Ca- 

 pacity. The capacity of wells when they extend any con- 

 siderable depth into the water-bearing beds does not in- 

 crease as rapidly with increase of diameter as might be ex- 



