37 



The curve of ground-water fluctuations has the general 

 characteristics of the curve of daily stream fluctuations; that 

 is, there are both a maxinmm and a minimum period in each 24 

 hours. These periods do not necessarily occur at the same time. 

 For the purpose of discussion, a representative ground-water 

 curve is shown in Figure 4. It v/ill be shown that this type of 

 curve establishes the daily relation of consumptive use of water 

 to ground-water discharge and recharge. 







6 A.M. 6 P.M. 

 NOON 



6 A.M. 6 P.M. 

 NOON 



FIGURE 4.-- Representative ground-water curve, 

 showing effect of the daily cycle of tran- 

 spiration by overlying vegetation (after 

 Troxell) . 



Assuming that the ground water rises during the night when 

 transpiration is at a minimum, there will approach a time during 

 the morning hours, with increasing transpiration, v;hen the demand 

 of vegetation just balances the inflow. This point is indicated 

 at the top of the daily ground-water curve "a" where the water 

 table starts to fall. On the other hand, at the bottom of the 

 curve "b" in the late afternoon, transpiration losses have 

 decreased to such an extent that they are balanced by the daily 

 recharge and the water table begins to rise. At some point 



