100 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
about the average rainfall, and 53 inches may, be safely assumed as a close approximation to the annual rainfall for this section. *
DISPOSITION OF RAINFALL.
O f the total rainfall of any area (I) a part is returned as vapor to the atmosphere without having entered the earth; (2) a part is carried off by streams and rivers to the ocean without penetrating the earth; (3) a part is absorbed into the earth.
(I) WATER EVAPORATED WITHOUT ENTERING THE EARTH.
Immediately following a rain the atmosphere is nearly or quite saturated. The evaporation at this time is slow, and the part r42 turned to the atmosphere directly from the land is an almost negligible amount. This is especially true of a soil into which the water enters quickly. Some of the 'water clinging to the leaves of plants is re-evaporated, as well as a part of that 'which falls into lakes., ponds and temporary pools. While an estimate of the amount evaporated must be regarded as only in the roughest way approximate, yet it is probably safe to assume that not more than two or three per cent. of the total rainfall is returned to the atmosphere by direct evaporation without having entered the earth.
(2) SURFACE RUN-OFF.
The relative proportion between the surface run-off and the surface in-take of water is dependent upon the character of the surface and the deeper formations and upon the t opography. The former affects rapidity of in-take of water into the earth; the latter the rapidity of surface run-off.
With regard- to topography eastern Florida is either flat or rolling. Rarely can a locality within this section be described as hilly. The elevation increases gradually from sea level at the coast to a maximum of scarcely more than 200 feet inland, while large sections are so flat as to present no perceptible slope. Topographically the conditions are, therefore, very unfavorable to surf ace run-off .
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