SOMK I'l OKIDA I.AKKs AND [.AKl-: I'.ASINS. 1^7 



The artesian water level, "b", in the vicinity of Gainesville on the plateau, 

 is 125 to 130 feet be'jovv the surface (50 to 55 ft. above sea level). In passing 

 to the coast, this line shows a gradient and at the St. Johns river is probably 

 about 50 feet above sea level. Tn the section represented by this sketch, 

 the artesian water line crosses the surface somewhat east of Orange Lake, 

 this beinti^ the border line between the flowing and the non-flowing artesian 

 areas. 



In the area of artesian flow, that is east of the point in this sketch, at 

 which the line representing the water level crosses the surface, sinks do not 

 occur and are not to be expected. Along the border line of the escarpment 

 sink formation is most active, in the pilateau where the limestones are 

 covered with a thickness of 100 feet or more of stratified materials, sinks 

 form less frequently. The escarpment shown in the sketch has been formed 

 and is being carried inland by surface erosion and underground solution, 

 the formation of sinks being one of tlie results of solution. 



VARIATION IN THE GROUND WATER LEVEL. 



The ground water level is first of all subject to change owing 

 to the annual wet and dry seasons. Almost one-half of the annual 

 rainfall in Florida occurs during the summer months, and following 

 this season the ground water level rises for a time, reaching its max- 

 imum some weeks after the rainy season ends. It then gradually 

 falls until the next following rainy season begins. This may be re- 

 garded as the normal variation on the ground water level, which 

 amounts in places where it has been measured to from eight to ten 

 feet or more. This variation in water level affects as a rule not ma- 

 terially the amount of water that a well will supply upon pumping, 

 but merely the level at which the water stands in the well. In the 

 case of flowing artesian wells, however, it is indicated by a change 

 in the pressure, and those wells located near the border line between 

 the flowing and the non-flowing area may cease to flow during the 

 dry season. 



A second and more marked variation in the ground water level 

 arises from those periods including often a succession of years, of 

 reduced rainfall, or a similar period of excessive rainfall. The varia- 

 tion of the ground water level during such time, although not ac- 

 curately determined, is evidently much greater than the normal an- 

 nual variation. 



Not only does tlie underground water level fluctuate according 

 to seasonal and periodic rainfall, but it is also being gradually low- 

 ered by the lowering of its outlet. The underground water finds its 

 natural outlet through springs which enter the streams or emerge 

 into the ocean. Since the streams are constantlv deepening their 

 channels it follows that the outlet for the underground water is be- 

 ing lowered and hence the water line itself is necessarilv beinsT o-rad- 



