338 0. E. MEINZER ESTIMATING GROUND-WATER SUPPLIES 



widely distributed recharge will insure a large continuous 3deld, provided 

 the pumping plants are widely and regularly distributed. The rate at 

 which this body of water is creeping downstream — less than a mile in a 

 year — has really little to do with the total recharge or safe yield. 



Conclusion 



Estimates of ground-water recharge do not, and probably can not, 

 approach in accuracy the measurements of surface streams. The esti- 

 mates that have been made, though doubtless of much practical value, 

 express degrees of magnitude rather than definite quantities. 



There are, however, two very encouraging features of this work: The 

 first is that we have methods that are fairly dependable and applicable. 

 The work of the future is to refine these methods and to apply them in 

 sufficient detail, rather than to devise new ones. The two lines along 

 which additional research are most needed relate to the habits of phreato- 

 phytes and their rates of transpiration and to the specific yields of differ- 

 ent kinds of rocks. The second encouraging feature is that the three 

 main methods — intake, discharge, and water-table — are absolutely inde- 

 pendent of one another. In many areas two, or even all three, of these 

 methods can be applied, and in this way checks can be obtained on the 

 accuracy of the work. Thus, the discharge investigations in Owens A^al- 

 ley were checked by the intake method, and thus at the present time two 

 entirely independent sets of observations to determine recharge are being 

 made in Santa Clara Valley — one on water-table fluctuations and the 

 other on seepage losses of streams. 



