2 CO Ground Water, Wells, and Farm Drainage 



no visible springs or streams anywhere along the line. 

 Fig. 92 shows the increase in 25,978 feet, determined by 

 gauging. 



326. Changes in the Level of the Ground Water. The 

 level of the ground water in a given section is usually sub- 

 ject to changes, the surface rising and falling with the sea- 

 son and with the rainfall of the place. The change may be 

 as much as 5 or 6 feet in a single season, as represented in 

 Fig. 93, and when a series of dry or of wet years follow in 



29 



30 



JZ. 



J4. 



35. 



Jf 



37 



/O. 



Levf-l /of I.nkf \\fendolh June j?/. 



FIG 93. Showing changes in the level of the ground water surface during 



the season. 



succession the changes may be larger than this. It is clear 

 from these facts that in digging wells whose water comes 

 from near the surface of the ground water the bottom 

 should be carried deep enough into the water bearing beds 

 to leave it below the lowest stages of the ground water. 



327. Elevation of the Ground Water through Precipitation 

 and Percolation. In Fig. 94 is represented the unoccupied 

 space in eight feet of five grades of sand, above .standing 

 water, after 2.5 years had been allowed for percolation 

 under conditions where no evaporation could take place 

 from the surface. The unshaded portions of this figure 

 represent the relative amounts of space into which rains 

 may percolate for each grade of sand, as compared with 

 the whole area of the diagram; that is to say, if an inch of 

 rain were to fall upon the whole surface of the diagram 

 and it were occupied with the No. 1-00 sand the space 

 into which the rain could descend is measured by the un- 

 shaded area under 100; so for each of the other sands. 



