There will be another essential publication to be mentioned at a future date. Springs issuing from an unconfined aquifer tend to have a small, extremely variable flow and are directly and quickly affected by variations in precipitation. These springs may cease flowing during periods of less than normal precipitation. In contrast, springs issuing from a confined aquifer have a more constant flow because their flow is supplied by a much greater replenishment area. Accordingly, such springs tend to be unaffected by variations in precipitation unless there is prolonged drought.
Springs are common in areas of karst topography.
Spring flow is controlled by the size of the replenishment area, the difference in altitude between the spring opening or openings and the water level in the aquifer, and the size of the opening or openings through which the springs issue. Factors that have lesser effects on spring flow include atmospheric-pressure changes, earth and oceanic tides, and pumping of wells located near springs. The location of these springs is shown in figure 57. All of them issue from the Upper Floridan aquifer, and practically all of them are located in areas where the upper confining unit of the Floridan aquifer system either is less than 100 feet thick or is absent. The distribution of large springs discharging from the Floridan aquifer system, like the areas of greatest transmissivity within the aquifer system, is the direct result of dissolution of carbonate rocks, which results in the development of large conduits.