BULLETIN NO. 68


Wales Ridge contains a very thick sequence of
permeable Pliocene-Pleistocene sediments (as
much as 350 ft [107 m]; see also Surficial
aquifer system, p. 53) overlying variably thick
clays of the Peace River Formation. In the
southern part of the Ridge, depth to carbonate
rocks exceeds 325 ft (99.1 m) BLS.

 Morphology of the eastern flank of the Lake
Wales Ridge was likely controlled by high-
energy shoreline currents throughout the
Pleistocene (and perhaps the late Pliocene) as
indicated by the sharp topographic relief on the
eastern side of the Ridge. The presence of
discoid quartz pebbles in these sediments
(Cypresshead Formation) also indicates a high
energy depositional environment (Tom Scott,
personal communication, 2004). In contrast, the
western side of the southern part of the Ridge is
flanked by less pronounced topographic relief on
the Polk Upland and DeSoto Plain.

 The general topographic relief of the
southern part of the Lake Wales Ridge mimics
that of the emergent part of the Florida Platform
with a steep shelf slope along the east and a
broad gentle slope to the west. Along the
southern margin of the Ridge (Figure 7), subtle
topographic ridges that trend toward the west
bear remarkable resemblance to the southern
Florida peninsula and the Florida Keys
suggesting that paleo-longshore and ocean
currents (e.g., loop current) that existed during
the Plio-Pleistocene are similar to those of
present day. Petuch (1994) referred to this area
as the Caloosahatchee Strait.

 Sinkholes

 In addition to paleo-sea levels and ocean
currents, karst processes have sculpted the
landscape of southwest Florida. Sinclair et al.
(1985) mapped four types of sinkholes in the
SWFWMD: 1) limestone dissolution: slow-
developing, funnel-shaped with a growth rate
similar to the rate at which the carbonate rocks
dissolve, overburden is thin; 2) limestone
collapse: forms abruptly and overburden is thin
3) cover- subsidence sinkholes: gradual
formation and generally small diameter, where
overlying sands infill limestone dissolution
cavities, overburden is greater than 30 ft (9.1 m)
thick; and 4) cover-collapse sinkholes: sudden
formation and relatively large in diameter,


forming upon a breach of clayey material
overlying a cavity, overburden is greater than 30
ft (9.1 m) thick. These sinkholes significantly
contribute to interaction between surface and
groundwater, intra-aquifer and inter-aquifer
communication (e.g., Tihansky, 1999) and the
vulnerability of aquifers to surface sources of
contamination (Arthur et al., 2007).

 Plate 3 reflects the distribution of closed
topographic depressions (CTD) throughout the
SWFWMD region. This map is based on a 15 m
(49.2 ft) resolution digital elevation model
(DEM) produced by the FDEP-FGS in
cooperation with other FDEP programs and
Florida's water management districts. While not
all CTDs reflect karst features (i.e., paleodunes,
etc. may also be included), this depression
coverage provides a good approximation of
sinkhole distribution patterns within the study
area. The coverage, however, does not reflect
the tens of thousands (if not more) of buried
sinkholes detectable by means of surface
geophysical surveys (e.g., Wilson and Beck,
1988; Moore and Stewart, 1983), nor does it
include small karst features detectable by
LIDAR or sinkholes that formed since the USGS
topographic maps were last updated.

 Springs

 Springs predominantly occur in the northern
two-thirds of the study area (Figure 6).
Submarine springs occur offshore of Lee County
and between Pinellas County and Citrus County
(Ryder, 1985; DeWitt, 2003). Five of Florida's
thirty-three first magnitude springs (>100 ft3/sec;
>2.83 m3/sec) occur within the study area: Kings
Bay Springs Group, Homosassa Springs Group,
Chassahowitzka Springs Group (all in Citrus
County), Weeki Wachee Springs Group
(Hernando County) and the Rainbow Springs
Group (Marion County) (Champion and Starks,
2001). The Coastal Springs Groundwater Basin
(Knochenmus and Yobbi, 2001) encompasses
parts of Citrus, Hernando and Pasco Counties
and includes three of the five first magnitude
springs. The Coastal Springs Groundwater
Basin is made up of four sub-basins: Aripeka,
Weeki Wachee, Chassahowitzka and Homosassa
Springs. These groundwater sub-basins
comprise part of the total recharge area for these
springs. Surface water basins comprise the other
component. As defined and described in DeHan