FUTURE NEEDS FOR DEVELOPMENT 263 



From the hydrologic viewpoint the safe yield should be pre- 

 sented as a "family of curves" rather than' as a single quantity, 

 to show the relation of safe yield to pumping lift, well con- 

 struction, well locations, and modifications that would result 

 from induced recharge from precipitation or streams or un- 

 usable water. This information can be obtained only in broad, 

 general terms prior to development. Revisions are necessary 

 to fit the circumstances as development proceeds toward com- 

 plete utilization of the perennial water supply. 



Economic considerations are a separate problem, of major 

 concern to the water user, since his purse is involved, and to 

 his water department or consulting engineer or attorney. The 

 hydrologist is likely to be out on a limb if he tries to include 

 them in his evaluation of "safe yield." 



The laudable efforts to develop ground-water reservoirs 

 without exceeding the "safe yield" will almost certainly be 

 more difficult than most people realize. The essence of develop- 

 ment is to divert ground water that under natural conditions 

 would be discharged into streams or into the atmosphere, 

 and a well does this by making a depression into which the 

 water will flow rather than continue on its natural way. It is 

 basic therefore that water levels must be lowered and some 

 water must be pumped from storage. When development is 

 complete, the average inflow to this depression formed by the 

 wells should be equivalent to the average draft. But in the 

 course of the development of this depression, a substantial 

 volume of water has been mined, and as a result the pump- 

 age may have been considerably greater than the sustained 

 yield. 



Many hydrologists after studying specific areas have rec- 

 ommended "slow, orderly development," which would lessen 

 the sharpness of the change from the mining economy of de- 

 velopment to the smaller quantity of perennial supply. But 

 when the basin is fully developed, there may be less water than 

 required for rights established during the development, unless 

 provision can be made for artificial replenishment to supple- 

 ment the natural "safe yield." 



