TH£ ARTESIAN WATER SUPPLY OF EASTERN FLORIDA. 115 
the pipe are necessarily approximate measurements. Not only 
does the water lose in temperature in moving to the mouth of the 
pipe, but it mingles with the higher and colder waters entering the 
pipe which necessarily equalizes the temperature of the whole. 
They show, however, increase of temperature with increase of 
depth. 
LOSS OF HEAD AND REDUCTION IN FLOW. 
Exact measurements of loss of head and reduction in flow in 
artesian wells are usually difficult to obtain. In the case of the 
Jacksonville city water supply, fortunately measurements of flow 
have been taken at intervals from the time the first wells were 
put down in 1885 to the present time. These measurements kept 
through a period of 24 years afford records of especial interest and 
value. The following table of flow was supplied by Capt. R. N. 
Ellis, Superintendent of the Jacksonville city water supply, Two 
basins are used to receive the flow known as the north basin and 
the south basin. The wells are grouped in the table according to 
the basin into which they flow. The wells are numbered chrono¬ 
logically in the order of the date when completed. 
This table shows conclusively that although the rate of flow is 
variable for different wells and for the same wells at different 
periods, yet in this group of wells there is a continuous and progres¬ 
sive loss of flow. That the same is true of other wells throughout 
this area there can be no reasonable doubt. Those who give no 
special attention to their wells suppose as a rule that the flow re¬ 
mains unaffected indefinitely. Miany other well owners, however, 
have observed this loss in flow with succeeding years. The reduced 
flow is best observed near the margin of the flowing area in wells 
located on somewhat elevated ground. Many of the wells from 
which the water will flow only a few feet above the surface when 
first drilled may in time cease to flow. In these cases the pressure 
which originally caused the flow having been partly relieved, the 
water no longer rises above the surface of the ground. 
Exhaustion and ultimate failure of an artesian reservoir is 
not unknown. It is probably true that in nearly all artesian sec¬ 
tions the original pressure gradient in the water-bearing rock 
is appreciably lowered by the drafts made upon the subterranean 
supply,with a consequent actual decrease in the capacity of the 
wells. In this connection Professor C. S. Slichter states.* “It 
must be kept well in miind that there is a limit to the amount of 
water that can be withdrawn from an artesian basin. There is 
no such thing as an inexhaustible supply in this connection. The 
*U. S. Geol. Surv., Water Supply Paper, No. 67, p. 94, 95, 1902. 
