262 CONSERVATION OF GROUND WATER 



considered by the courts without the reservations of the tech- 

 nician when he uses the term, confusion is almost certain to 

 result, because the "safe yield" will vary widely depending 

 upon the stipulations that govern the determination. 



In a ground-water reservoir where the water is unconfined 

 in certain areas (the recharge areas) and under artesian pres- 

 sure in other places, the safe yield will be a certain quantity 

 if it is specified that all withdrawals must be by flow from ar- 

 tesian wells, a larger quantity if it is permissible to pump water 

 from depths as great as 50 feet, and still more if allowable 

 pumping lifts are as much as 500 feet. But the safe yield will 

 vary also depending upon the locations of wells and the type 

 of wells constructed. Assuming that the well construction and 

 spacing of individual wells are suitable for maximum recov- 

 ery of water, the safe yield will be a certain quantity if all wells 

 are 40 miles from the recharge area, considerably greater if 

 they are about 10 miles away, and still more if they are ad- 

 jacent to or within the recharge area. 



The development of ground water may alter the natural 

 conditions greatly enough to produce a significant modifica- 

 tion in the safe yield computed on the basis of those natural 

 conditions. In an area with water table so high that recharge 

 from precipitation is rejected periodically, the ground-water 

 replenishment may be increased materially after the water 

 table is lowered by pumping. Especially along watercourses, 

 when water levels in wells are lowered below river level by 

 pumping, infiltration may be induced from the river so that 

 the safe yield includes contributions from a source that may 

 have been no factor under natural conditions. 30 



Quality of water is an important consideration in several 

 ground-water reservoirs near the coasts or adjacent to brine- 

 bearing rocks, and the conclusions as to safe yield must vary 

 with the limitations as to chemical constituents in usable 

 water. 



so Charles, J. R., Discussion of "Utilization of Ground-water Storage in 

 Stream System Development," Trans. Am. Soc. Civil Eng., vol. Ill, pp. 319— 

 326, 1946. 



