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the water budget. We must first know how much water falls on the recharge area, how much runs off in streams, and how much returns to the atmosphere through transpiration and evaporation.
Much of Florida's rain comes in short, intense showers that drench a few square miles at a time while leaving surrounding areas undampened. Consequently, preciptation stations only a few miles apart commonly record substantially different quantities of rain in a given year. Existing stations are much too widely scattered to measure the volume of rainfall. Only when they have been greatly augmented can the gross supply of water in the recharge area be known as accurately as is needed.
We must know how much water runs off various parts of the recharge area. This means that we must gage the flow of many small tributaries. It means also that we must have topographic maps to enable us to define the drainage areas of these tributaries accurately.
Included in some of the larger drainage basins are sizable areas having no surface runoff at all-areas in which all the rainfall not evaporated or transpired filters into the ground. Lacking topographic maps that would enable us to delineate their boundaries, we cannot exclude these areas from the drainage basins of surface streams, although we know they do not contribute to the discharge of the streams. Accordingly, we are defeated in our effort to convert discharge records to meaningful figures representing runoff per unit area.
SAnother vexing complication is that many surface streams are fed by artesian springs whose water is derived from rain falling in the drainage basins of other streams. Obviously, we must evaluate and isolate the spring flow if we are to compute how much water is generated within a given drainage area. But the task of isolating spring flow will not be simple where the flow occurs in multitudinous vents along the bottoms of stream channels, as, for example, in the Suwannee River. The manner in which considerable quantities of water migrate underground without regard to surface basins has caused some hydrologists to ponder the wisdom of accepting surface basins as the logical hydrologic units in Florida.
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The problem that will be the most difficult to solve is that of determining, within permissible limits of error, the amount of evaporation and transpiration from land surfaces. Techniques for estimating these quantities directly where manifold types of vegetation grow in varying densities have not yet been perfected. Until