Alafia River Minimum Flows and Levels - Southwest Florida Water ...

an adjacent area locally known as the Brandon Karst Terrain (BKT), an internally
drained basin (SWFWMD 1993). The western edge of the Polk Upland is defined by
the presence of the first of several paleo-shoreline scarps associated with the
Pleistocene Ice-Age sea level fluctuations. This physiographic feature is known as
the Pamlico Scarp or shoreline. Elevations in this part of the Gulf Coast lowlands
province range from sea level to 25 feet.
The rest of the Alafia River watershed is situated in the Polk Upland Province.
Elevations in the extensive Polk Upland range between 100 and 130 feet; however,
in this area of the province the elevations are mostly between 25 and 75 feet within
the watershed. Eastward of the Pamlico Scarp the river's banks attain a narrower,
steeper profile and some spots are very bluff-like with 20-25 feet of relief from the
river's water level. In the vicinity of Riverview and Bell Shoals, the physiography
adjacent and south of the river is composed of low sand hills, which in some cases
attain 75-80 feet elevation. The Talbot and Penholoway paleo-shorelines pass
through this area in a north-south orientation, with their surface features having
elevations of 42 and 75 feet, respectively. Moving eastward, further into the Polk
Upland province, in the vicinity of the town of Lithia, the river travels over the clayrich
Bone Valley Formation (Pliocene). This is the lithologic unit which is extensively
mined for phosphate minerals further into the eastern part of the Alafia River
watershed. The river's banks in this region become less steep with many low-relief
floodplain or wetland areas surrounding the river. The remainder of the Alafia River
watershed and its tributaries drain an area of the Polk Upland where the Pleistocene
marine sands (overburden), and the underlying materials of the ore-bearing Bone
Valley Formation and Hawthorn Group rocks have been disturbed for phosphate
strip-mining in many areas. Much of this area has had its physiography and
associated surface water drainage systems modified by this mining activity. This
process generally strips the overburden sediments out of the way, mines the ore
layer, and then redistributes the overburden sediments through land reclamation or
other processes. Outstanding physiographic features in this region include many
water-filled, former mine pits and large, bermed clay-settling areas of various
rectilinear configurations easily observable on maps and aerials photos. Most all the
areas identified as "Open Water" natural systems in the entire eastern half of the
basin south of State Road 60 are of phosphate mining origin.
Primary soil groups in the Alafia River watershed include the Myakka-Basinger-
Holopaw association, which predominates in the upland areas in the northern and
southern portions of the watershed. The Candler-Lake association occurs in the
vicinity of the Brandon-Bloomingdale area, while the Winder-Chobee-St. Johns
occurs along the main stem of the river including the main tributaries. A significant
area of Arents-Haplaquents-Quartzipsamments soils occupies an area surrounding
Durant, in the Turkey Creek drainage basin. Soil classification indicates these are
considered as manmade soil areas. This area extends from southern Dover through
the Medard Park/Reservoir and Lithia area, and to some minor areas on the east
side of State Road 39. This coincides with areas of former phosphate mining
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