36
they are, progress can be made by studying selected areas wherein the other factors of the wafer budget are known. Ordinarily, if we subtract surface runoff from rainfall, we have a remainder consisting partly of ground-water recharge and partly of evapotranspiration, neither of which quantities can be measured. But if we select an area wherein ground-water recharge is known to be very small as compared with the other quantities, the difference between rainfall and runoff will provide an estimate of the evapotranspiration, which estimate can be applied to other areas having similar vegetation and topography to estimate ground-water recharge.
Although we know in general how and where the Floridan aquifer receives recharge, our knowledge is far from being adequate. The delineation of areas of recharge shown in figure 10 is based largely on inference, supported by observation and geologic mapping. An investigation, including extensive test drilling, of the geologic and hydrologic characteristics of the material overlying the aquifer in the areas of recharge must be made before we can have an adequate comprehension of the part that controlled recharge may play in optimum development of the artesian water.
We understand the recharge through sinkholes only in principle. We perceive that where sinkholes occur the piezometric surface stands high, and we infer that a substantial amount of recharge occurs through them. But beyond this we know very little. We wonder if appreciable recharge occurs through most of them or through only a small fraction of their number. Perhaps the gradual accumulation of muck has rendered a large percentage of them ineffective as recharge agents, and perhaps recharge could he increased materially by removing the muck. Studies of a representative number of the sinkholes would enable us to eliminate much of the guesswork from our present concepts.
Most of the wells currently being used for observations of water levels and artesian pressures in Florida are abandoned supply wells owned privately and by municipalities. They are used through the tolerance of the owners. Several valuable records have been interrupted when the owners rightfully elected to restore such wells to their own service. To the hydrologist, who recognizes long-term records as being indispensable to his studies, such interruptions are costly, especially when they terminate long records.
We have only a meager conception of how water moves about within the Floridan aquifer. For the sake of simplicity we have pictured the aquifer as though it were a hydrologic unit, a homogen-