WATER RESOURCES OF ORANGE COUNTY 145
Stable. The chemical quality of the water in these aquifers depends on the composition of the beds, the course taken by the water in reaching the aquifer, and the length of time of contact.
The source of all of the surface water in Orange County is rain. Water is stored on the surface in lakes, ponds, swamps, marshes, and stream channels. Evapotranspiration removes about 70 percent of the rainfall, runoff about 20 per cent, and underground outflow probably less than 10 percent. Lakes are the most reliable sources of surface water in Orange County. Swamps and marshes and most of the streams go dry after only short droughts. The Wekiva River flows at least 100 cfs at all times because of several large contributing springs. The flow of the St. Johns River is maintained in all but the most severe droughts but its flow declines to below 100 cfs in 40 percent of the years of record. The effluent of the Orlando sewerage plant contributes about 11 cfs to the Little Econlockhatchee River north of State Highway 50. All other streams in the county either go dry or recede to extremely low flow during dry periods.
On the average, rainfall exceeds evaporation and transpiration from June through September; so lake levels, ground-water levels, and streamflow tend to increase during these months. From October through May, the reverse is true.
The average rainfall during the period of record 1935 to 1963
used in this report compares very closely with those for lake periods since 1893 and therefore records are' probably representative of the long-term average condition and of future conditions.
- The amount of water that flows out of the county in streams is
estimated to average about 1,100 cfs (710 mgd), but it ranges from as little as one tenth of this amount during droughts to more than 40 times this amount during floods. In addition, an average of about 1,300 cfs (840 mgd) from sources outside the county flow along the eastern border in the St. Johns River. Use of water was about 22 billion gallons per year in 1963 and is expected to about double by 1975. Ground water is used for municipal, industrial, domestic and irrigational purposes. Surface water is used for
irrigation, cooling, and recreation.
CONCLUSIONS
The water resources of Orange County are very large and
generally are more than adequate for the needs of the immediate future. The most immediate water problems in Orange County are pollution of ground-water reservoirs by drainage wells, pollution