WATER RESOURCES OF ORANGE COUNTY 115
However, the relation between inflow, outflow, and recharge within the county are probably reasonably accurate. These relations indicate that about 93 percent of the water flowing through the county originates within the county.
A fourth method is to compute the surface runoff by sub-basins within the county. Rainfall, which is the only natural source of recharge, must move in one of three directions: (1) upward by evaporation or transpiration; (2) laterally through streams, canals, or pipes; or (3) downward by infiltration through a permeable soil. The water that moves downward must eventually move horizontally through the water-bearing material to points of discharge. An examination of the topography and stream-flow pattern of a region shows whether the water that enters the ground seeps into nearby streams from the nonartesian aquifer, or infiltrates to the artesian aquifer. Average rainfall is reasonably uniform throughout central Florida, therefore, a basin with a low rate of surface runoff must contribute more ground-water recharge per square mile than an area with a higher rate of surface runoffproviding evaporation and transpiration losses are uniform.
Figure 54 shows the average runoff from stream basins in Orange County for the period 1960 through 1963 and the deficiency of runoff in relation to runoff in the Econlockhatchee basin. The average runoff from the basins in the western part of the county is from 8.1 to 11.9 inches less than the runoff from the Econlockhatchee River basin in the eastern part where an examination of the geology and hydrology indicates that relatively little recharge to the artesian aquifer can occur.
A single stream basin may contain different types of terrain that vary widely in their ability to recharge the aquifer; therefore, the average rate of runoff from the basin may not give a true picture of the recharge in different parts of the basin. For example, the Wekiva River basin contains areas from which no surface runoff occurs and all water that is not evaporated or transpired recharges the aquifer. The basin also contains areas where no recharge can occur because the piezometric surface is above the land surface and all water that is not evapo-transpired runs off in streams.
To help define the areas within the basins that are most effective in providing recharge to the aquifer, use was made of the general soils maps of Orange and Lake counties. The soils in central Florida are classified into four general groups based on their surficial drainage characteristics. Group I comprises areas