264 CONSERVATION OF GROUND WATER 



Estimates of safe yield have sometimes been made for small 

 portions of ground-water reservoirs, in some cases for indi- 

 vidual well fields, and these are of value in operation of those 

 wells. For effective regulation of ground-water development, 

 however, a comprehensive evaluation of the entire hydrologic 

 unit is essential, in order to embrace all the facilities for natu- 

 ral recharge, movement, and discharge of water within the 

 aquifer, as well as the extent to which development can change 

 those natural conditions. 



RESERVOIRS WITH NEGLIGIBLE REPLENISHMENT. Some ground- 

 Water reservoirs have a vast amount of water stored in them 

 but nevertheless have a very low safe yield, because of negligi- 

 ble replenishment (see pages 41-47). Regardless of the doctrine 

 under which rights are established in the water of those reser- 

 voirs, any rights on a perennial basis must be restricted to the 

 very low safe yield. 



The vast quantity in storage in the reservoir must be re- 

 garded as a nonrenewable resource. Its withdrawal is equiva- 

 lent to the development of such resources as petroleum, coal, 

 or metals, and rights cannot be on more than a temporary 

 basis, perhaps specifying a certain total quantity rather than 

 a certain quantity per year. The question for the state con- 

 cerned is whether the "mining" of the stored water in this 

 generation is socially and economically desirable or whether 

 it should be handed down untouched to future generations, 

 who must then make the same decision. 



Within a single ground-water reservoir there are commonly 

 some places where the yield is limited by the rate at which 

 water can flow from distant recharge areas, rather than by in- 

 sufficient recharge. A problem in regulation here involves the 

 question as to what extent the water user should be protected 

 in his selection of a site for wells to develop that water. 



EFFECT OF REGULATION UPON PRESENT DEVELOPMENT. The 



states of heaviest ground-water development have achieved 

 their eminence in the absence of any regulation. California, 

 Arizona, Texas, Louisiana, and Arkansas lead the nation in 

 quantity of water pumped from wells. California alone pumps 



