38 



between these two extremes vegetation is not only using all the 

 inflow into the basin, but is also making its maximum demand upon 

 the water held in storage in the soil. This point is indicated 

 by the steepest slope on the falling side at the point "c" be- 

 tween the top and bottom of the curve and represents the maximum 

 daily transpiration. Likewise, the rising side of the curve indi- 

 cates less transpiration than inflow and consequently an increase 

 in ground-water storage. The steepest slope on the rising side 

 "d" , then indicates the point of minimum or no transpiration, and 

 the time of this occurrence lies between the hours of midnight and 

 k a.m. At this point, the hourly rate of rise represents the 

 hourly rate of recharge. 



Evidence has been advanced by Troxell (34), however, to 

 show that the rate of recharge "r" is not constant throughout the 

 transpiration period, but changes as the rate increases, becoming 

 a maximum at the height of the transpiration season. There is 

 little evidence to show how seriously this will affect estimates 

 of consumptive use. It is not claimed that water-table fluctua- 

 tions provide a basis for precise measurements; rather, they are 

 considered a foundation for approximate estimates. 



