CONTROLLING FACTORS OF ARTESIAN FLOWS 631 



Modifying factors. 



Factors affecting pressure. 

 Barometric variations. 

 ~ Temperature variations. 

 Density of waters. 



Variations due to temperature. 

 Variations due to dissolved salts. 

 Height of adjacent water levels. 

 Water table. 



Neighboring water bodies and suppl5^ 

 Tides. 

 Winds. 

 Rock pressure. 

 Factors affecting movement. 

 Porosity. 



Size of grain openings. 

 Temperature. 



Requisites of Artesiaist Flows 



Having outlined the more important conditions bearing on the occnri-ence 

 and movements of underground waters, the controlling factors of artesian 

 flow may be considered. In doing this it is necessary to point out certain 

 objections to some of the commonly postulated requisites. 



Objections to Common Requisites 



CHAMBERLIX'S REQUISITE COXDITIOXS OF ARTESIAN" PLOWS 



Since the appearance in 1885 of the paper of T. C. Chamberlin on the 

 "Requisite and qualifying conditions of artesian wells," a single set of requi- 

 sites has, with few exceptions, been followed by writers of underground water 

 papers. These in brief are: (1) A pervious stratum, to permit the entrance 

 and the passage of water; (2) a water-tight bed below, to prevent the escape 

 of water downward; (3) a like impervious bed above, to prevent the escape 

 upward, for the water, being under pressure from the fountain head, would 

 otherwise find relief in that direction ; (4) an inclination of these beds, so 

 that the edge at which the waters enter will be higher than the surface at 

 the well; (5) a suitable exposure of the edge of the porous stratum, so that 

 it may take in a sufficient supply of water; (G) an adequate rainfall, to fur- 

 nish this supply; and (7) an absence of any escape for the water at a lower 

 level than the surface at the well. 



There is one very serious objection to the requisites outlined above, namely, 

 ^hey apply only to a single class of flows from stratified rocks, neglecting not 

 only flows from other varieties of rock, but even other tj-pes of flow from the 

 same rocks. There are, moreover, many exceptions to the postulated requisites, 

 which, taken in connection with the limitations mentioned, make new and more 

 comprehensive definitions desirable. Some of the objections to the requisites 

 are mentioned below. 



* Fiftlj Annual Report U. S. Geological Survey, pp. 125-173. 



