136 CONSERVATION OF GROUND WATER 



tance: if the decline of recent years is only temporary, due 

 to deficient rainfall, there may be adequate replenishment 

 on a long-term basis to sustain present draft; but if the 

 water table in the recharge area is progressively lowered, it 

 will be proof that present pumping is in excess of natural 

 replenishment. 



Watercourse Problems 



The ground-water reservoirs in the alluvial valleys of peren- 

 nial streams are considered as a separate group because of their 

 intimate relationship to the water in the stream. The term 

 "watercourse" is applied here to the stream and its associated 

 ground-water reservoir. As defined by Hutchins, 63 a water- 

 course is "a definite stream in a definite channel with a definite 

 source or sources of supply, and includes the underflow. . . . 

 The underflow is as much a part of the watercourse and as 

 important from the standpoint of rights in the watercourse 

 as is the surface flow; for if the waters within this subterranean 

 area are withdrawn, the surface waters sink into the ground to 

 take their place. The legal implications of this are widely 

 recognized in court decisions. While the definitions of a sur- 

 face watercourse seldom refer to associated waters in the 

 ground, nevertheless the underflow is a physical part of the 

 whole and the courts have held it to be a component part." 



Various other definitions have been advanced for specific 

 "watercourses," some far more restrictive than the above, and 

 some that are hydrologically unsound. A watercourse, as dis- 

 cussed in the following pages, is considered to have the follow- 

 ing essential features: 



1. It is a geologic unit comprised of materials of varying 

 textures and permeabilities but all deposited by the 

 stream. 



2. It is a hydrologic unit, in which both surface water and 



63 Hutchins, Wells, Selected Problems in the Law of Water Rights in the 

 West, US. Dept. Agr. Misc. Publ. 418, pp. 7-8, 1942. 



