14 REPORT OF INVESTIGATIONS No. 50
DRAINAGE
The eastern and southern parts of Orange County arearained .prncipalybJy~urface streams. The St. Johns River and its tributaries drain the eastern and no r f the county ~hile Shinglere R ek, Boggy Creek and canals in hpuper Kissimmee Riverbasin drain most of the south-central and southwestern-part-sothe conty. Many swamps ad sloughsoccur in th eastern and-southernpartsf .the-county because.of the poorly
developeiddrainage.
Surface drainage in the western and northwestern parts- of
the county is mostl ihtocoied deprisi6is here 7iffier seeDs into the ground or evaporates. A few sinlihobl es- iThis area have open connections with solution channels in the underlying__limestone-Waef That collects in these sinkholes drains directly into t"ie- ilution channels. Most of the sinkholes, however, are floored with relatively impermeable sediments and the rate of seepage through these lake-filled sinkholes may be less than in areas
adp'cent to the lakes.
"More than 300 drainage wellswere-dilledhetween 1906an
1961 in the upland area of the _Countyespecially in Orlando and
icinity, to drafn surface water directly into the arteian aquife'
(fig. 5) The greatest activity was during 1960 when about 35 drainage wells were drilled. Considerable quantities of water-are drained underground in this manner, but the total amount is not Im6Wn- ater that enter-ls-i-aquifer through drainage sranges fro pur water used to us cow arns.
GEOLOGY
The occurrence, movement, availability,'.quality, and quantity
of the ground water in Orange County are 'losely related to the geology of the area. Therefore, knowledge of the structure, stratigraphy, and lithology of the geologic fo mations is essential
to an evaluation of the ground-water resources.
----Orange County is underlain mostly by marine limestone,
dolomite, shale, sand, and anhydrite to about 6,500 feet at which depth granite and other crystalline rock of the basement complex occur. Only the top 1,500 feet of sediments that have been penetrated by water wells will be discussed in this report. A summary of the properties of the formations is given in table 2.