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Geographic Information Systems (GIS) analysis of sinkhole activity in north-central Florida

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Geographic Information Systems (GIS) analysis of sinkhole activity in north-central Florida
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Geographic Information Systems (GIS) analysis of sinkhole activity in north-central Florida
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Dodek, Brian D.
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Brian D. Dodek
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Aquifers ( jstor )
Databases ( jstor )
Geology ( jstor )
Limestones ( jstor )
Polygons ( jstor )
Population density ( jstor )
Ridges ( jstor )
Scarps ( jstor )
Sediments ( jstor )
Sinkholes ( jstor )
City of Ocala ( local )

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University of Florida
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A GEOGRAPHIC INFORMATION SYSTEMS (GIS) ANALYSIS OF SINKHOLE
ACTIVITY IN NORTH-CENTRAL FLORIDA:
CAUSES AND CORRELATIONS












By

BRIAN D. DODEK


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2003



























This thesis is dedicated to my parents. Without their love and support, my achievements
would not have been possible. I am proud of who I have become, and I have them to
thank for that.














ACKNOWLEDGMENTS

I would like to thank Dr. Anthony Randazzo for all his help and guidance through the

stages of this thesis as well as my tenure at the University of Florida. As a result, I

convey professionalism and a demeanor that ultimately helped start my career. For that I

am very grateful.

I would like to thank GeoHazards, Inc. for the use of its database and other proprietary

materials. I also would like to thank Dr. Douglas Smith and Dr. Jonathan Martin for their

help and guidance.















TABLE OF CONTENTS
page

A CKN OW LED GM EN TS ................................................................................................. iii

LIST OF TABLES .......................................................................................................... vi

LIST OF FIGURES ....................................................................................................... vii

ABSTRA CT....................................................................................................................... ix

CHAPTER

1 IN TRODU CTION ...........................................................................................................

2 STUDY AREA BACKGROUND INFORMATION ...................................................5...

Clim ate............................................................................................................................ 5
Physiographic Setting .................................................................................................. 6
Geologic Setting........................................................................................................ 9
Geologic Structure ........................................................................................................ 11
Hydrogeologic Setting ............................................................................................... 14

3 SINKH OLE A CTIV ITY ............................................................................................. 18

Lim estone-Solution Sinkholes................................................................................... 20
Lim estone-Collapse Sinkholes................................................................................... 20
Cover-Subsidence Sinkholes ..................................................................................... 20
Cover-Collapse Sinkholes.......................................................................................... 21
Hum an Induced Sinkholes .............................................. .................................... .......... 21
Sinkholes Caused by Groundwater Withdrawal .............................................. 21
Sinkholes Caused by Construction Activity .................................................... 22

4 M ETHODOLO GY .................................................................................................... 24

5 RESU LTS ........................... ..................................................................................... 28

Depth to the Top Surface of the Floridan Aquifer System............ ......................... 28
Recharge and Discharge Areas of the Floridan Aquifer System.................................. 31
Physiographic Provinces.................................................................................. ............. 35
Florida Surficial Geology ............................................................................................. 39
Florida Subsurface Geology ......................................................................................... 43


iv






v


Population Density by US Census Block Group ....................................................... 47

6 D ISCU SSION ................................................................................................................50

7 SUMMARY AND CONCLUSIONS .........................................................................59

APPENDIX

A ARCVIEW GEOPROCESSING COMMANDS.......................................................... 61

B POPULATION DENSITY FROM US CENSUS BLOCK GROUPS..........................62

REFERENCES CITED...................................................................................................67

BIOGRAPHICAL SKETCH ..........................................................................................70















LIST OF TABLES

Table page

4-1. Theme name and website location.......................................................................... 25

4-2. Theme parameters...................................................................................................26

5-1. Depth to Floridan aquifer system ........................................................................... 29

5-2. Recharge and discharge .......................................................................................... 32

5-3. Physiographic province ........................................................................................... 37

5-4. Florida surficial geology......................................................................................... 41

5-5. Florida subsurface geology..................................................................................... 45

A-1. Arcview geoprocessing commands ....................................................................... 61

B-1. U.S. block group population density data.............................................................. 62














LIST OF FIGURES


Figure page

1-1. Study area with county names ..................................................................................4...

2-1. Geomorphic configuration of the study area............................................................6...

2-2. Lithostratigraphy of the study area.........................................................................10

2-3. Structural features of Florida..................................................................................13

2-4. Relationship of regional hydrogeologic units to major stratigraphic units ...............15

3-1. Types of sinkhole activity....................................................................................... 19

3-2. Soil piping induced by modification of natural runoff and infiltration conditions ...23

3-3: Bar graph showing distribution of sinkhole collapses in Missouri based on records
kept since 1930 ...................................................................................................... 23

5-1. Depth to the surface of the Floridan aquifer system...............................................29

5-2. Sinkhole density chart for depth to the Floridan aquifer system............................30

5-3. Relative frequency of sinkhole occurrence for aquifer depth.................................30

5-4. Recharge and discharge in inches per year of the Floridan aquifer, with sinkhole
locations ............................................................................................................... 32

5-5. Sinkhole density for recharge and discharge zones................................................34

5-6. Relative frequency of sinkhole occurrence for recharge and discharge zones..........35

5-7. Physiographic provinces with sinkhole locations....................................................36

5-8. Sinkhole density chart for physiographic provinces................................................38

5-9. Relative frequency of sinkhole occurrence for physiographic province................39

5-10. Florida surficial geology with sinkhole locations.................................................40

5-11. Sinkhole density chart for surficial geology.........................................................41








5-12. Relative frequency for sinkhole occurrence with surficial geology.....................43

5-13. Florida subsurface geology with sinkhole locations.............................................44

5-14. Sinkhole density chart for Florida subsurface geology ........................................45

5-15. Relative frequency of sinkhole occurrence for subsurface geology.....................46

5-16. Population density in people per sqmi..................................................................47

5-17. Sinkhole density chart for population density ......................................................48

5-18. Relative sinkhole frequency for population density.............................................49

6-1. Population theme showing sinkhole correlation with S.R. 27................................51

6-2. Highest sinkhole density polygons with sinkhole locations...................................53

6-3. Highest relative frequency of sinkhole occurrence polygons with sinkhole locations.55

6-4. Distance to nearest sinkhole map. ........................................................................... 57














Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Master of Science

A GEOGRAPHIC INFORMATION SYSTEMS (GIS) ANALYSIS OF SINKHOLE
ACTIVITY IN NORTH-CENTRAL FLORIDA:
CAUSES AND CORRELATIONS

By

BRIAN D. DODEK

May 2003

Chair: Dr. Anthony Randazzo
Department: Geological Sciences

This study utilizes Geographic Information Systems to find patterns and to analyze

factors influential in sinkhole distribution in north-central Florida. The factors used were

depth to the top surface of the Floridan aquifer system, recharge and discharge areas of

the Floridan aquifer system, physiographic provinces, Florida surficial geology, Florida

subsurface geology, and population density by U.S. Census block group. Comparing

these factors with areas of high sinkhole density and high relative frequency of sinkhole

occurrence yielded strong correlations. Though a single factor influencing sinkhole

distribution could not be quantified, efforts were made to determine which factors appear

to have the largest control on sinkhole distribution. Amount of recharge to the Floridan

aquifer system and the depth to the Floridan aquifer system, combined with surficial and

subsurface geology, had the strongest correlations with sinkhole density and relative

frequency of sinkhole occurrence. When sinkhole localities overlie the Ocala Limestone









or thin sediments above the Ocala Limestone, sinkhole occurrence increases. Also, in an

area of high recharge where the Floridan aquifer system is shallow, sinkhole occurrence

increases. Analyses of the sinkhole locality data identified factors influential in sinkhole

distribution. Different combinations of factors can influence sinkhole distribution. This

explains their occurrence in regions of contrasting geology.

Predictions were made for future sinkhole occurrence from past sinkhole distributions

and by correlating the factors deemed influential in sinkhole distribution. These

predictions and the figures created in this study can be used for sinkhole risk assessment

on a regional scale.













CHAPTER 1
INTRODUCTION

Exponential population growth has coincided with a significant increase in sinkhole

activity reported in the State of Florida. Sudden collapse or gradual subsidence of the

ground surface can cause extensive damage to structures built on or near an area of

sinkhole activity. The process of limestone dissolution and ground surface subsidence is

not only dynamic, but also relentless, given the geologic conditions present. North-

central Florida is particularly plagued by sinkhole activity. The identification, rate,

distribution, and causes of sinkhole activity can increase awareness of risks, facilitate

management, and determine measures for avoiding economic loss and deleterious effects

to the environment.

By producing a regional Geographic Information Systems (GIS) database that can be

used to find areas of potential sinkhole activity, we can reduce or avoid some of the

economic and emotional loss that sinkhole activity can cause. Using the database for

urban and regional planning is advisable: its electronic format has advantages over paper

maps. One advantage is being able to quickly change the scale of the maps to meet the

need of a certain project. A versatile tool, GIS allows the access of data, overlaying the

thematic map of choice and zooming to the exact scale that suits a need. Whether it is a

city planner seeking a sinkhole location map of the city, or an insurance company that

desires a neighborhood layout and sinkhole distribution, both needs can quickly and

easily be met with the same database.








Sinkhole activity can be recognized by geotechnical investigation of the geologic

subsurface. Remote sensing techniques include geophysical tools such as electrical

resistivity (ER) and ground penetrating radar (GPR). Direct testing of the geophysical

anomalies detected is generally accomplished by drilling using recognized protocols

established by the American Society of Testing and Materials (ASTM).

Geophysical techniques inexpensively survey areas and detect suspected sinkhole

activity. Using that information, locations for boreholes can be identified. This

methodology eliminates the randomness of locating drilling positions (Smith and

Randazzo, 1986). If a drilling protocol is implemented over a large area with no prior

geophysical information, existing sinkhole activity may not be detected.

It is now widely accepted by the insurance industry and legal profession that

geophysics be used in fulfilling Florida Statues Section 627.707 requirements that

sinkhole investigations be of sufficient scope to verify or eliminate sinkhole activity as a

cause of distress. Additionally, geophysics is a commonly applied technique to evaluate

property prior to purchase or construction.

Isolated studies on a neighborhood scale provide important insight about the

occurrence and causes of sinkhole activity. Little attention, however, has been given to

integrating results from individual investigations to address sinkhole activity on a

regional or statewide scale. This study attempts to document the geologic conditions

responsible for sinkhole development, and to identify patterns in sinkhole occurrence.

Although there is a bias in the reported sinkhole localities, using confirmed sinkholes for

correlation with factors believed to be influential in sinkhole development is a valid

approach. This study is one of only a few using GIS to understand what potentially








controls sinkhole development on a regional scale. The database includes 739 confirmed

sinkhole localities, representing one of the largest databases used in published sinkhole

investigations. Previous published sinkhole investigations, located in world-renowned

karst areas, have been conducted using only a few hundred sinkholes (Denizman, 1998;

Ford and Williams, 1989). Thus, despite the biases of the database, using confirmed

sinkholes on a regional scale to develop correlations and predictions is of great

significance.

Hypotheses tested in this study are as follows:

Aqueous recharge environments are more acidic so the dissolution of the
limestone is more extensive, and sinkhole activity more prevalent.

GIS application of sinkhole locality data can identify patterns of occurrence.

A complex combination of factors control sinkhole occurrence and distribution.

Identifying patterns of occurrence allow the development of more accurate
sinkhole risk assessment on a regional scale.

The study area for this project is located in north-central Florida (Figure 1-1). It

covers Alachua, Bradford, Citrus, Columbia, Dixie, Gilchrist, Lafayette, Levy, Marion,

Suwannee, and Union Counties.





































Figure 1-1. Study area with county names (Florida Geographic Data Library, 1990).














CHAPTER 2
STUDY AREA BACKGROUND INFORMATION

Climate

Florida's climate is humid subtropical (Winsburg, 1990). Strong subtropical high-

pressure cells that develop over the ocean influence this climate. The subtropical cell that

affects Florida's climate is the Bermuda-Azores high (Winsburg, 1990). During the

summer this cell influences the weather, moving warm air across the ocean and into

Florida. During winter colder air masses from the continental interior influence Florida's

weather patterns (Winsburg, 1990).

The average annual maximum temperature for Gainesville, Florida, which is central to

the study area (Figure 2-1) is -27C. The average annual minimum temperature is ~-14C

(58F). Precipitation, the main source for aquifer recharge, is very high in a humid

subtropical climate. The annual precipitation average for the study area reported at

Gainesville, Florida, is 132 cm (52 inches). Florida's rainy season is May through

September. Just under 60% of the yearly precipitation total is received during this period

(Winsburg, 1990). During the summer, storms are convection driven, and precipitation

amounts differ from place to place. Winter storms are usually precursors to fronts

sweeping through the area, and produce uniformly distributed precipitation amounts

(Winsberg, 1990).








Physiographic Setting

The two largest physiographic provinces in the study area are the Northern Highlands

and the Gulf Coastal Lowlands (White, 1970). The Northern Highlands located in the

northeast comer of the study area (Figure 2-1) occupy more than 5000 km2.


Geomorphic Configuration
FHighlands
Lowlands, Gaps and Valleys
Plains
201 imdges
i Swamaps
eu plans



g d aGAINESVILLE



Fairfield Hills
Marion Upland




Coastal Swamps

\ Sumter Upland
DOcala Hill

Cotton Plant Ridge

Tsala Apopka Plain N

20 0 20 40 Kilometers



Figure 2-1. Geomorphic configuration of the study area (Florida Geographic Data
Library, 1997).

These highlands range in elevation from 30.5 76.2 meters (100 250 fi) asl. A relict

highland has been dissected by erosion and dissolution to yield the large Northern








Highlands mass and the ridges of the Central Highlands south of the study area (White,

1970). The scarp resulting from the erosion of the Northern Highlands platform is called

the Cody Scarp. It is referred to as ". .the most persistent topographic break in the

state." by Puri and Vernon (1964, p. 11). The scarp generally follows the 100 ft asl

contour line, except in a few places where it has been incised by rivers that flow over its

edge.

The Northern Highlands lithology consists of undifferentiated sediments (mainly sand

and clay), and the Hawthorn Group Sediments (sand, clay, limestone and dolostone)

(White, 1970). The Hawthorn Group Sediments are important because they influence the

topography of the Northern Highlands as well as the shape of the Cody Scarp. The clays

of the Hawthorn Group confine artesian flow to the point that the piezometric surface

remains above the ground surface in the stream valleys. This ensures that the rivers flow

above ground over the scarp edge. This is the case for the Cody Scarp east of

Gainesville. West of Gainesville the edge of the Hawthorn Group does not coincide with

the Cody Scarp. Instead the scarp consists of geologically older limestone. Because the

limestone does not confine artesian flow, the piezometric surface is much lower than the

stream valley floors as they cross the scarp. This causes streams between Gainesville

and the Suwannee River to go under ground before they reach the scarp's edge and flow

through cavernous limestone until they have reached the other side of the scarp (Gulf

Coastal Lowlands) where they re-emerge as springheads. The Suwannee River is the

only river west of Gainesville that crosses the Cody Scarp above ground (White, 1970).

The Gulf Coastal Lowlands make up the majority of the study area. This province

covers more than 7,000 km2. The Ocala Limestone underlies almost all of the Gulf








Coastal Lowlands. The Ocala Limestone is at or very near the surface throughout the

Gulf Coastal Lowlands. Because the Ocala Limestone is part of the Floridan aquifer

system (Miller, 1997), water enters the aquifer almost directly. The surficial aquifer can

be very thin in this province. Dissolution features are very common in the lowlands. The

Gulf Coastal Lowlands are a series of plateaus representing Pleistocene sea level terraces

(Schmidt, 1997). Remnants of the Northern Highlands are left in the form of depositional

fill in sinkholes and as small hills and ridges scattered around the Gulf Coastal Lowlands

province (Denizman, 1998). The largest of these is the Brooksville Ridge.

The Brooksville Ridge has a total length of nearly 177 km (110 miles). The

Withlacootchee River Valley divides the ridge into two parts. The northern section is

smaller, only 80.5 km long (50 miles). The larger southern section is 96.6 km long (60

miles). The elevation of the Brooksville Ridge is highly variable, ranging from 22.88 -

61 m (75 200 ft) asl in short distances. The highest elevations of 53.38 61 m (175 -

200 ft) asl are located in the southern half of the ridge. The ridge is topped with a few

meters of sand, which overly insoluble plastic sediments of the Bone Valley Formation

and the Hawthorn Group (White, 1970). Rolling plains dotted with sinkholes bound the

east side of the Brooksville Ridge. In the west a steeper scarp associated with a relic

terrace bounds the Brooksville Ridge (Fernald and Purdum, 1998). Dissolution is the

dominant factor shaping the ridge to the east.

There are other smaller physiographic provinces in the study area such as the Mount

Dora Ridge, Cotton Plant Ridge, Sumter Uplands, Marion Uplands, Fairfield Hills and

the Coastal Swamps. These ridges and uplands are capped with insoluble plastics, which

offer resistance to erosion and dissolution of the underlying limestone.








Geologic Setting

Deep beneath the study area is crystalline basement rock, a fragment of the African

tectonic plate (Smith and Lord, 1997). This piece of the African plate provided a surface

for initiation of carbonate deposition and development of the Florida Platform. Carbonate

deposition dominated the platform starting in the Mid-Mesozoic (approximately 100 ma)

in peninsular Florida and in the early Cenozoic (approximately 60 ma) in panhandle

Florida (Scott, 1992).

The carbonate-producing environment of the Florida Platform was isolated from the

rest of the North-American continent by the Gulf Trough and the Suwannee Straits

(Georgia Channel System) (Randazzo, 1997). This enabled any siliciclastics eroded from

the Appalachians, to be transported into the Gulf of Mexico and not deposited onto the

platform. This was the case until the late Oligocene when the Suwannee current ceased

to flow resulting from a sea level drop (Randazzo, 1997). This allowed siliciclastic

sediments to fill the trough and spread onto the Florida Platform, suppressing carbonate

sedimentation. By the mid-Pliocene most of the Florida Platform was covered by

siliciclastic sediment. Not until the late Pliocene would a small portion of southernmost

Florida again support carbonate production (Denizman, 1998).

The Tertiary stratigraphy for the Florida Platform is comprised mostly of limestone

and dolostone units. They are, from oldest to youngest, The Cedar Keys Formation,

Oldsmar Limestone, Avon Park Formation, Ocala Limestone and the Suwannee

Limestone (Randazzo, 1997). The Avon Park Formation is the oldest formation that is

exposed in the study area (Middle Eocene) (Figure 2-2). The Ocala Limestone is an

Upper Eocene limestone that is at or very near the surface throughout the Gulf Coastal










Lowlands. Surface water drainage is limited across the Gulf Coastal Lowlands. Instead

water mostly percolates directly into the Ocala Limestone, which


4.t


20 0 20 40 Kilometers


Figure 2-2. Lithostratigraphy of the study area (Florida Department of Environmental
Protection, 2000).

comprises the Floridan aquifer system. The Suwannee Limestone, which is difficult to

differentiate from the Ocala Limestone because of its similar lithology, is exposed in a

small zone at the southern end of the study area (Randazzo, 1997). After a late

Oligocene/early Miocene drop in sea level, Hawthorn Group siliciclastics began to spread


Flonda Subsurface Geology
i HOLOCENE SEDIMENTS
BEACH RIDGE AND DUNE
UNDIFFERENTIATED SEDS
TRAIL RIDGE SANDS
UNDI F FERENTIATED TQ SEDS
CYPRESSHEAD FM
f COOSAWHATCHIEFM
STATENVILLEFM
I UNDIFFERENTIATED HAWTHORN GP
S. SUWANNEE LS
I OCALA LS
AVON PARK








across the platform. These sediments became the confining unit for the Floridan aquifer

system (Scott, 2001). The Hawthorn Group contains a number of formations. The

Statenville Fm, Coosawhatchie Fm. and the undifferentiated Hawthorn sediment

sequence, which are all middle Miocene, are exposed within the study area (Scott, 1997;

Randazzo, 1997). The Statenville Fm and Coosawhatchie Fm. sediments are comprised

of clay and clayey sand with some dolostone and limestone occurring in them. These

sediments also contain abundances of phosphorite grains, as high as 20 % in some areas.

The undifferentiated Hawthorn Group sediments are deeply weathered and contain few

phosphatic grains.

Above the Miocene sediments are Plio-Pleistocene sands (Scott, 1997). The sands,

from oldest to youngest, consist of the Cypresshead Formation, undifferentiated

Quaternary sediments, Trail Ridge Sands, undifferentiated sediments, and beach ridge

and dune deposits (Figure 2-2). These sediments, transported from the north, were

reworked in a shallow marine environment during Pleistocene sea level changes. Sea

level in the Pleistocene is thought to have been 20 m higher than present sea level (Scott,

1997). This left just the highest of present-day topography exposed. The submerged

sediments were reworked into marine terrace-like deposits (Scott, 1997).



Geologic Structure

Situated on North America's passive margin, the Florida Platform is considered to be

in a relatively stable tectonic environment during the Mid-Mesozoic and Cenozoic.

However, there are features (Figure 2-3) that suggest the Florida Platform has undergone

faulting, uplift and subsidence over its history (Scott, 1997). There are three major

structural features that have affected deposition patterns in the study area.








The oldest features that have affected deposition in the study area are the Peninsular

Arch and Suwannee Strait (part of the Georgia Channel System) (Puri and Vernon,

1964). The Peninsular Arch forms the axis of Florida's Peninsula. It trends northwest to

southeast and runs from southeastern Georgia to central Florida (Puri and Vernon, 1964).

The crest of this feature is located in central Florida in Union and Bradford counties,

which are located in the northeast comer of the study area. The Peninsular Arch became

a topographic high in the early Cretaceous and affected deposition until the late

Oligocene (Denizman, 1998).

A younger structural component that affected deposition in the study area is the Ocala

Uplift (Puri and Vernon, 1964). The uplift is approximately 370.3 km (230 miles) long

and 112.7 km (70 miles) wide where it is exposed. The crest of the uplift runs northwest

to southeast, parallel with the Peninsular Arch. Murray (1961) thought that the Ocala

Uplift was a piece of the Peninsular Arch, though geophysical data presented by Antoine

and Harding (1963) has shown that is not true (Puri and Vernon, 1964). The uplift is

extensively faulted and fractured (Schmidt, 1997). High angle, strike faults help to

flatten the platform and increase its width. The uplift has affected the deposition of

sediments since the early Miocene (Puri and Vernon, 1964). The Hawthorn Group

sediments on the crest of the uplift have been eroded exposing the Eocene carbonates.

This has greatly influenced the karstification on the platform (Denizman, 1998).












































APPROXIMATE UPDIP LIMIT
AND AREA UNDERLAIN BY THE
FLORIDAN AQUIFER SYSTEM


SCALE


Figure 2-3. Structural features of Florida (from Scott, 1997).








Hydrogeologic Setting

Throughout the study area there are a total of three aquifer units (Scott, 1992).

Figure 2-4 shows the relationship among the three aquifer units and corresponding

stratigraphy. The uppermost is the Surficial aquifer. The Surficial aquifer, which

consists of permeable surficial, unconsolidated to poorly indurated siliciclastic deposits,

is present throughout the study area. These deposits range in age from Miocene to

Holocene. The Surficial aquifer exists in unconfined conditions throughout the study

area, except in a few places where cementation reaches a point where permeability of the

sediments is reduced and locally confined conditions occur. In the Northern Highlands

section of the study area the Surficial aquifer is the sediment that overlies the Hawthorn

Group. These deposits can range from 16.1 48.3 m in thickness (10 30 ft) (Scott,

1992). In the Gulf Coastal Lowlands where the Hawthorn Group has been eroded, the

base of the surficial aquifer is the Ocala Limestone or Suwannee Limestone. There, the

Surficial aquifer is in direct contact with the Floridan aquifer system. The Surficial

aquifer is much thinner and not present in all areas of the lowlands. The Surficial aquifer

may also be pierced by karst depressions that funnel surface water directly into the

Floridan aquifer system (Scott, 1992).

The Intermediate aquifer is defined by the Southeastern Geological Survey (SEGS)

(1986, p. 4) as "...all rocks that lie between and collectively retard the exchange of water

between the overlying Surficial aquifer system and the underlying Floridan aquifer

system." The Intermediate aquifer consists mostly of fine siliciclastic sediments and is














Panhandle Florida North Florida South Florida

System Series Stratigraphic Unit Hydrogeologic Stratigraphic Unit Hydrogeolgic Stratigraphic Unit Hydrogeologic
IUnit ,Unit LnI Unit


Undifferentiated
terrace marine and
fluvial deposits


Citronelle Formation

Undifferentiated
coarse sand and gravel

Alum Bluff Group
Pensacola Clay
Intracoastal Formation
Hawthorn Group
Chipola Formation
Bruce Creek Limestone
St. Marks Formation
Chattahoochee Formation


Oligocene ChlckauswhaV Limestone
Suwannee Limestone
Manrianna Limestone
Bucatunna Clay


Eocene Ocala Limestone
Lisbon Formation
Tallahatta Formation
Undifferentiated older Rocks


Paleooene


CreI8ceous
ana olaer


Surficlal
aquifer
system

(Sand and
Gravel
aquifer)






Intermediate
confining unit



Floridan
aquifer
system


Sub-Floridan
confining
unit


Undifferentiated
terrace marine and
fluvial deposits


Miccosukee Formation


Hawthorn Group


St. Marks Formation


Surfical
aquifer
system


Intermediate
aquifer system
or Intermediate
confining unit


Floridan
Suwannee Limestone aquifer
system


Ocala Limestone
Avon Park Formation
Oldsmar Formation


Cedar Keys Formation

Undifferentiated


Sub- Fordan
confining
unit
J


Terrace Deposits


Miami Limestone
Key Largo Umestone
Anastasia Formation
FortThompson Formalon
Caloosahatchee Marl



Tamnami Formation


Hawthorn Group


Suwannee Limestone


Ocala Umestone
Avon Park Formation
Oldsmar Formation


Cedar Keys Formation


Surfioial
aquifer
system


(Blacayne
aquifer)- -





Intermediate
aquifer system
or intermediate
confining unit


Floridan
aquifer
system











Sub-Floridan
confining ,
unit ,


Figure 2-4. Relationship of regional hydrogeologic units to major stratigraphic units (from Femald and Purdum, 1998).


Quatemary


Tertiary


Holocene

Pleistocene


Pliocene



Miocene


Undifferendated

Undifferentiated








interlayered with carbonate strata. Throughout the study area the aquifer is comprised of

the Hawthorn Group. The water contained in these siliciclastic beds is under confined to

semi-confined conditions. The Intermediate aquifer in the study area is mainly found in

the Northern Highlands. Here the Intermediate aquifer reaches a thickness of 376 m (234

feet) (Scott, 1992). In the rest of the study area the Intermediate aquifer is present where

outlier hills and sinkhole-fill of Hawthorn Group sediments occur.

The Floridan aquifer system (Miller, 1997) is the principal aquifer throughout the

study area. Many communities rely on the Floridan for their water supply. In 1985 total

withdrawals from the aquifer in one day were 2.5 billion gallons (U.S. Geological

Survey, 1990). Even though withdrawals are so high from the Floridan, the hydraulic

heads have decreased very little. This shows the productivity and transmissivity

capability of the Floridan aquifer system.

The top of the Floridan aquifer system is regarded to be where the siliciclastic

layers of the intermediate aquifer decrease and permeable carbonate layers begin. This is

generally the top of the Suwannee Limestone or the Ocala Limestone, though it is

common that the boundaries of the aquifer are within a certain stratigraphic unit (Miller,

1997). The bottom of the Floridan aquifer system in the study area is where the

carbonate rocks hit the regionally persistent anhydrite beds of the Cedar Keys Formation

(SEGS, 1986). In the Northern Highlands the Floridan aquifer system is deeply buried

beneath the siliciclastic sediments of the Hawthorn Group. It is here that the Floridan is

under confined conditions and is recharged by downward migration of water through the

surficial and intermediate aquifers. It is also recharged through point recharge, where

karst features have breached the overlying sediment, allowing water to flow directly into








the Floridan aquifer system. In the Gulf Coastal Lowlands province of the study area the

Floridan aquifer system exhibits unconfined conditions. Here the Floridan aquifer system

is most vulnerable to pollution because it is at or very near the surface allowing water to

enter directly into the aquifer. Surface runoff is limited, except for large rivers. The

recharge in the Floridan aquifer system that occurs in this environment has caused

extensive dissolution. In this area karst geomorphology has usually reached a mature

stage with numerous depressions some of which have coalesced over time (Scott, 1992).

Ground water flow in this area is complex. The majority of flow is through the 200

- 300 ft. of saturated Ocala, Suwannee, and Avon Park carbonate units (Denizman and

Randazzo, 2000). Flow occurs in two ways, diffuse flow or conduit flow. With diffuse

flow the water slowly moves through interconnected pore spaces. Conduit flow moves

water through enlarged fractures, joints or bedding planes. This process is can be much

faster and can accommodate a larger volume of water in the same amount of time

compared to flow through interconnected pore spaces. The cavernous systems created by

this process cover large areas throughout the aquifer and occur in an anastomotic pattern

(Denizman and Randazzo, 2000). Evidence for such dissolution and ground water flow

can be seen in the study area, especially near the Cody escarpment where surface water

sinks underground and into the Floridan aquifer system before it then re-emerges on the

other side of the scarp through spring heads.














CHAPTER 3
SINKHOLE ACTIVITY

Sinkholes are the most common feature in karst topography (Lane, 1986).

Sinkholes are usually classified as closed depressions, where the surface material has

subsided or collapsed into underlying solution cavities (Beck and Sinclair, 1986).

Sinkhole activity is the result of the dissolution of limestone. This is a chemical process

where acidic rain and surface water drains down into the limestone through primary and

secondary openings in the rock. Primary openings are generally pore spaces and

openings that were formed during deposition. Secondary openings are joints, faults,

bedding planes, and erosional surfaces. When water passes through the atmosphere and

comes in contact with CO2, carbonic acid is formed. White (1986) gives the overall

reaction for the dissolution of limestone as

CaCO3 + H20 + CO2 <> Ca2+ + 2 HCO3

When the chemically aggressive water drains through these openings it dissolves

the limestone. This further enhances drainage and secondary porosity (Sinclair et al.,

1985). The natural development of the dissolution process is the formation of cavities in

buried limestone and sinkholes.

Figure 3-1 displays five sinkhole types common to the study area. Four of the

sinkhole types shown are active, and one is a buried or inactive sinkhole. The active

types are limestone solution, limestone collapse, cover subsidence and cover collapse

sinkholes (Sinclair et al., 1985). The sinkholes are divided into the different categories






19


based on two characteristics. These characteristics are the thickness of overburden

material, and the time it takes for the sinkhole to form.


A) Limestone Solution Sinkhole


B) Limestone Collapse Sinkhole




_,...gI -



e


C) Buried Sinkhole


Figure 3-1. Types of sinkhole activity (Modified from Frank and Beck, 1991).


non-cohostve.....
coYFer


D) Left to right, stages in slow development of cover subsidence sinkhole.



E) Left to right, stages in development of cover collapse sinkhole.


cover -
- 5NmentIfi_ -- -


IP3


...........

...... .....
R-R/B' IN 91


--'~'


77


- -








Limestone-Solution Sinkholes

Limestone solution sinkholes (Figure 3-1) occur when overburden thickness is less

than 7.5 m (25 feet), and limestone dissolution is most aggressive at the limestone

surface. The subsidence of the ground surface occurs slowly, roughly at the same rate as

the limestone is dissolved (Sinclair et al., 1985). Cavities are not common with this type

of sinkhole activity as the ground subsides gradually with limestone dissolution.

Limestone solution sinkholes are usually funnel shaped, with the slope of the sinkholes

depending on how easily the overburden material is transported downward towards the

sinkhole bottom (Sinclair et al., 1985).

Limestone-Collapse Sinkholes

Limestone collapse sinkholes (Figure 3-1) form when a cavity is formed beneath the

limestone surface and begins to expand until the material above the cavity can no longer

be supported and collapse occurs. Collapse happens quickly and can be catastrophic

(Sinclair et al., 1985). This type of sinkhole generally occurs across bedding planes, or

porous zones when the water table is below the upper surface of the limestone. This

accelerates dissolution at a point below the limestone surface. The cavity continues to

enlarge until the overlying limestone fails and collapse occurs (Sinclair et al., 1985).

Cover-Subsidence Sinkholes

In cover subsidence sinkholes (Figure 3-1) the overburden thickness can be 15.2 m (50

feet) or more (Sinclair et al., 1985). Not only does the overburden thickness determine

sinkhole morphology but the lithology of the overburden thickness is very important as

well. If the overburden material is incohesive and permeable sand, then cover-subsidence

sinkholes can occur. The difference in head between the sandy surficial aquifer and the

limestone aquifer determine the rate at which the water moves downward into the








limestone (Sinclair et al., 1985). As the limestone slowly dissolves, sand and clay can

ravel downward into voids in the limestone. These sinkholes are usually small in size

because the cavity does not reach a great size before it is filled with sand (Sinclair et al.,

1985).

Cover-Collapse Sinkholes

Cover-collapse sinkholes (Figure 3-1) occur when the overburden material is cohesive.

The cohesiveness gives the overburden material the strength to resist collapse over a

cavity. If the overburden material was a thick (more than 15.2 m) clay or clayey sand it

is possible that it could bridge a large cavity, even after the limestone roof had collapsed

(Sinclair et al., 1985). Eventually small pieces of the clay will begin to ravel from the

ceiling, until finally the clay will collapse. This will cause a potentially catastrophic and

fairly large sinkhole to occur. If the material is not as cohesive or thick, a smaller

sinkhole will probably be the result of the collapse (Sinclair et al., 1985).

Human-Induced Sinkholes

Sinkholes can be triggered by human activity. There are two causes of human induced

sinkholes. The first is excessive ground-water withdrawal, and the second is construction

activity (Sinclair et al., 1985).

Sinkholes Caused by Groundwater Withdrawal

The Floridan aquifer system is recharged when the head difference between the

Surficial aquifer and the Floridan aquifer system is great enough to cause leakage through

the confining layer. When ground-water is pumped at a rate that causes the

potentiometric surface of the Floridan aquifer system to drop, this initiates recharge from

the surficial aquifer. This creates an environment that is prone to sinkhole collapse

(Sinclair, 1982). In Tampa, Florida in May, 1964, withdrawal from the Section 21 well








field was increased from 5 Mgal/d to 14 Mgal/d in the time span of two months. Over

the next month, 64 new sinkholes were reported within one mile of the well field

(Sinclair, 1982).

Sinkholes Caused by Construction Activity

Construction practices can trigger sinkhole collapse in a variety of ways. The most

common method is by altering the natural drainage pattern. This is done in many

different ways, from construction of parking lots, large buildings or houses, to streets and

driveways. Instead of water draining by uniform seepage into the soil, it is channeled

into the soil and can create a solution pipe in the limestone bedrock. With a structure

covering the soils, traveling of material into a cavity may first be noticed when cracking

of the structure occurs. Later collapse into a cavity may be forthcoming (White, 1988).

Figure 3-2 shows the modifications of natural drainage and infiltration that can affect

sinkhole formation. Besides altering the natural drainage, the structures can cause

sinkhole collapse because of their weight. Buildings with large footprints or multiple

floors can exert significant downward force on the subsurface below.

Retention ponds or man made lakes are other structures that change natural runoff.

Whether they are constructed so that water can percolate down through the bottom, or to

permanently hold water, both can cause sinkhole activity. With retention ponds that let

water percolate through the bottom, focused drainage can cause soil piping in the

limestone. The retention ponds that are designed to hold water cause increased stress on

the soil and bedrock from the weight of the water. Both cases can cause sinkhole

subsidence or collapse. Figure 3-3 shows the distribution of man-induced sinkholes in

Missouri recorded from 1930 1976.














































Figure 3-2. Soil piping induced by modification of natural runoff and infiltration
conditions (from White, 1988).


60 -


50 -

40 -

30 -

20 -

10 -

0-


25 -

20 -

15 -

10 -


5 -


51 46
Totals


24 10


Totals


Figure 3-3: Bar graph showing distribution of sinkhole collapses in Missouri based on
records kept since 1930 (from Williams and Vineyard, 1976).













CHAPTER 4
METHODOLOGY

The initial effort of this study involved going through the Geohazards, Inc.,

Database. Geohazards, Inc., is a geophysical consulting company located in Gainesville,

Florida. The insurance industry as well as private homeowners contract with this

company to determine if sinkhole activity is occurring. Their database consists of

numerous reports from 1985 until the present. Parameters gathered from these reports for

possible consideration in this study were geophysical methods used, geophysical

evidence, depth to limestone, proposed cause of failure, presence of nearby karst, and

location information. The information was then converted to database form using

Microsoft Excel. This allowed the information to be imported into a Geographical

Information Systems (GIS) database.

GIS is software that allows spatial analysis of information. GIS is capable of

retrieving parameters that make up individual themes. Individual and multiple themes

can be retrieved and viewed in various combinations. This software can locate patterns of

sinkhole occurrence, as well as geologic conditions present. The GIS software programs

that were used to manipulate the data are Arcview, and Arcview Spatial Analyst

(programs created by Environmental Systems Research Inc. ESRI, 1992-2000).

After the information was collected from the Geohazards Inc., database and

imported into Arcview, it had to be projected into a coordinate system. The information

was tied to street addresses. This is not a valid coordinate system for the GIS software.

Using a program called EZ Locate, the street addresses were converted into a latitude and


S24








longitude coordinate system. When the points were viewed in the GIS it was apparent

that more data points were needed for the study to be more comprehensive. A second

data set was obtained from the Florida Geologic Survey website

(http://dep.state.fl.us/geology/gisdatamaps), though the information was produced by the

now defunct Florida Sinkhole Research Institute. This data set was ready to import into

the GIS. Though it lacked the parameters that the Geohazards Inc. database had

provided, the database already contained locations for the sinkholes in a latitude

longitude coordinate system. These two themes were then joined into one single sinkhole

theme so that spatial analyses could be done on all sinkholes simultaneously.

Since the themes used came from different sources, they were in different projections.

Arcview Projection Utility was used to reproject the themes. Once the themes were

projected into a common coordinate system and ready to display in the GIS, other themes

or layers could be overlain to recognize any correlations. The following list shows the

themes used for possible correlation with the sinkhole theme and the source the data was

obtained from.

Table 4-1. Theme name and website location
Theme Name Source Website for Theme

Florida County Boundaries http://www.fgdl.org/
Depth to the Top Surface of the ftp.dep.state.fl.us/pub/gis/data
Floridan aquifer system
Physiographic Provinces http://www.swfwmd.state.fl.us/data/gis
Recharge and Discharge Areas of http://www.fgdl.org/
the Floridan aquifer system
Florida Surficial Geology http://www.fgdl.org/
Florida Subsurface Geology ftp.dep.state.fl.us/pub/gis/data

Population Density by U.S. Census http://www.census.gov/geo/www/cob/bgl990.html
Block Group









These themes came from different sources on the Internet, such as water management

districts, geologic surveys, and the Florida Geographic Data Library (FGDL). All the

themes were reprojected into the coordinate system used by FGDL. The parameters for

this coordinate system include the current coordinate system name, projection method

used to obtain that coordinate system, and the latitudinal and longitudinal origins used for

the coordinates.

Table 4-2. Theme parameters
Geographic Coordinate System GCS North American 1983

Base Projection Albers

Central Meridian -840

Central Parallel 240

Standard Parallel 1 240

Standard Parallel 2 31.50



With all of the themes now in a common coordinate system, they were displayed

with the sinkhole theme in Arcview. A visual comparison was done to establish which

themes had the best correlation, and where these correlations were most evident. This

was done so that a study area could be defined. After the study area was defined all the

themes were clipped (see Appendix A for definition) to that area or "polygon". This

means that all the points and polygons outside the study area and the data associated with

them would be clipped or deleted from the current themes.

Using the sinkhole theme, a spatial analysis of the sinkholes was performed to

search for correlations with the different parameters of the other themes. The sinkhole








theme was spatially joined with the other themes one at a time. Spatially joining two

themes tied the parameter (polygon) information of one theme to the location of the

sinkhole (point). The "Find Area" function of Areview's Spatial Analyst was used to

recalculate the area of the new polygons created after clipping all of the themes.

Information from the spatial joins was combined with the area values. This yielded

sinkholes per km2 for each parameter such as geologic formation, recharge area, or

physiographic region. Tables from the themes were exported into Microsoft Excel after

being spatially joined. Mathematic functions were performed to determine sinkhole

density per parameter value. The total number of sinkholes was divided by the total area

for each polygon. This yielded sinkhole density for each parameter. Also the number of

sinkholes for each parameter was divided by the total number of sinkholes for the study

area. This yielded relative frequency of sinkhole occurrence for each parameter. Charts

were used to display the results.














CHAPTER 5
RESULTS

Depth to the Top Surface of the Floridan Aquifer System

The depth to the surface of the aquifer theme was taken from data used for

DRASTIC calculation of the Floridan Aquifer (Figure 5-1). DRASTIC is a measure of

aquifer vulnerability. DRASTIC was developed by the Florida Department of

Environmental Protection. This process is used for pesticides so that the most vulnerable

areas of the aquifer can be protected from ground water contamination. The data for

depth to the aquifer are recorded by impact on the aquifer rather than depth relative to sea

level. An exact depth map was used to match relative depth vulnerability polygons to the

exact depth to the aquifer. Table 5-1 shows the sinkhole density values and relative

frequency of sinkhole occurrence values for each depth category. Figure 5-2 shows the

sinkhole densities for each category of depth to the Floridan Aquifer surface. There is a

strong correlation between depth to the aquifer and sinkhole distribution. Relative

frequency of sinkhole occurrence also shows a strong correlation (Figure 5-3). As the top

of the aquifer approaches the ground surface, sinkhole density and relative sinkhole

frequency increase steadily.









































20


0 20 40 Kilometers


Figure 5-1. Depth to the surface of the Floridan aquifer system (Florida Department of
Environmental Protection, 2000a).


Table 5-1. Depth to Floridan aquifer system


Aquifer Depth
> 100 ft (> 30.5 m)
75 100 ft (22.9 30.5 m)
50 75 ft (15.2 22.9 m)
30 50 ft (9.1 15.2 m)
15- 30 ft (4.5- 9.1 m)
0 15 ft 5m


Total Area km2 Number of
4629.59 26
1166.91 34
1849.89 54
3061.92 127
3460.03 152
6450.28 339


Sinkholes/ km2 Relative Frequency
5.62- 3.55%
2.91-2 4.64%
2.92-2 7.38%
4.152 17.35%
4.39-2 20.77%
5.262 46.31%


Sinkhole Locations
// Major Rivers
Depth to Floridan aquifer system
1> 100 ft (>30.5 m)
75 100 ft (22.9 30.5 m)
50 75 ft (15.2 22.9 m)
30- 50 ft (9.1 15.2 m)
15- 30 ft (4.5- 9.1 m)
0- 15 ft (0- 4.5 m)


I C I I I












0 15 ft (0- 4.5 m)

e 15- 30 ft (4.5- 9.1 m) 4.39

30 50 ft (9.1- 15.2 m) 4.15
U_
| 50 75 ft (15.2 22.9 m) .92

75 100 ft (22.9-30.5m) .91

S > 100 ft (> 30.5 m) 5.63

0.000 0.010 0.020 0.030 0.040 0.050
Sinkholes I km2


Figure 5-2. Sinkhole density chart for depth to the Floridan aquifer system


5.26-2


I 0.060


0 15 ft (0- 4.5 m) 41.

15 30 ft (4.5 9.1 m) 20.77%

a 30 50 ft (9.1-15.2m) 17.35%

r 50 75 ft (15.2 22.9 m) 7. 8%

75 -100 ft (22.9 30.5 m) 4.640

S > 100 ft (> 30.5 m) 3.55%

0% 10% 20% 30% 40% 50%
Percentage of sinkholes


Figure 5-3. Relative frequency of sinkhole occurrence for aquifer depth









Recharge and Discharge Areas of the Floridan Aquifer System

The recharge and discharge theme displays the location and amount of water that is

entering or exiting the aquifer in the time span of one year. Data for this theme were

obtained from the Southwest Florida Water Management District (SWFWMD). The

categories and units shown were created by the SWFWMD. The theme was clipped from

a statewide coverage to the study area (Figure 5-4), and then the sinkholes were spatially

joined to the theme.

The hypothesis to be tested was that recharge environments are more acidic so the

dissolution of the limestone is more extensive, and sinkhole activity more prevalent. In

discharge environments, as the water passed through primary and secondary openings in

the limestone, it chemically reacted with the limestone. Limestone interacts with the

water neutralizing the carbonic acid. This tends to increase the pH of the water so that

dissolution is not as extensive in discharge areas. Recharge was categorized as less than

one inch per year, between I 10 inches per year, and greater than 10 inches per year.

Discharge values were categorized as less than 1 inch per year, between 1 5 inches per

year, and greater than five inches per year. When comparing data between the discharge

and recharge categories, discharge values were lower for both the relative frequency of

sinkhole occurrence and for sinkhole density (Table 5-2). For the three recharge

categories, the average sinkhole density and average relative frequency of sinkhole

occurrence was 2.98-2 sinkholes/km2 and 29.48% respectively. The average sinkhole

density and relative frequency of sinkhole occurrence for the three discharge categories

was 2.03-2 sinkholes/km2 and 3.85% respectively, thus confirming the hypothesis.









Table 5-2. Recharge and discharge


Recharge/
Discharge Zone


Number of Total Area
Sinkholes (km2)


Sinkholes/ Relative Avg. Relative
(km2) Frequency ole Frequency
density uency


Discharge > 5 36
Discharge 1 5 47
Discharge < 1 2
Recharge > 10 388
Recharge 1 10 260
Recharge < 1__ 2


2101.16
1167.56
590.44
10093.43
5235.83
1475.65


1.71-2
4.03-2
3.39-3
3.84-2
4.9T2
1.36e


4.90%
6.39%
0.27%
52.79%
35.37%
0.27%


2.032


2.98-2


3.85%


29.48%


20 0 20 40 Kilometers




Figure 5-4. Recharge and discharge in inches per year of the Floridan aquifer, with
sinkhole locations (Southwest Florida Water Management District, 2002).








It was expected that the "Recharge > 10 inches/year" category would have the

greatest sinkhole density. However, it was the "Recharge 1 10 inches/year" category,

which possessed the greatest sinkhole density at 4.97-2 sinkholes/ km2 (Figure 5-5). This

is attributed to significant differences in area for these recharge categories. Table 5-2

shows the total area for each category.

Concentrations of sinkhole occurrence in the recharge zones occur along the

"Recharge > 10 inches/year" category that runs northwest to southeast through the study

area (Figure 5-4). This reflects the acidic environment mentioned earlier that occurs in

the high recharge zone. The concentration of sinkholes located in the southwest comer of

the study area is located in the "Recharge 1 10 inches/year" category. This is still an

acidic environment, though not as much as the "Recharge > 10 inches/year" category. A

possible reason for a concentration in this area may be the limited thickness of the

surficial sediments as water recharges the underlying carbonate unit (Floridan aquifer

system).

The "Discharge 1 5 inches/year" category yielded the highest sinkhole density

values of the three discharge zones (Figure 5-5); at 4.03-2 sinkholes/ km2, it was an order

of magnitude larger than the next closest category. This discharge category also had the

highest relative frequency of sinkhole occurrence value, at 6.39% (Figure 5-6).

The discharge zones in the study area coincide with rivers. The "Discharge > 5

inches/year" category, which is the zone of highest discharge in the study area, occurs

along the Suwannee and Santa Fe rivers (Figure 5-4). The directional trend of the

concentration of sinkholes located north of where the Suwannee River and the Santa Fe

River converge was thought to be the influenced by the discharge along the Suwannee









and Santa Fe rivers. Though the rivers may be responsible for the occurrence of

sinkholes in that area, the directional trend of this concentration is influenced by a bias

found in the sinkhole database. The Florida Department of Transportation (FDOT) was

the source of the sinkhole data recorded in this area, thus giving the directional trend

along a highway. However, these data are still useful for the general location of sinkhole

activity.





Discharge > 5 1. 12

Discharge 1 5 4.03-2

Discharge < 1 3.39-3

Recharge > 10

Recharge 1 10 4.97-T2

Recharge < 1 1.36-3

0.00 0.01 0.02 0.03 0.04 0.05 0.06
Number of Sinkholes I km2


Figure 5-5. Sinkhole density for recharge and discharge zones










Discharge > 5 4.90/o

Discharge 1 5 6.39%

Discharge < 1 0.27%

Recharge > 10

Recharge 1 10 35.37%

Recharge < 1 0.27%

0% 10% 20% 30% 40% 50% 60%
Percentage of Sinkholes


Figure 5-6. Relative frequency of sinkhole occurrence for recharge and discharge zones



Physiographic Provinces

The physiographic provinces theme displays the different morphological features

throughout the study area (Figure 5-7). The largest province was the Gulf Coastal

Lowlands. These lowlands consist of bare or thinly covered limestone and make up more

than 7000 km2 of the study area. The total number of sinkholes in the Gulf Coastal

Lowlands province was 360, almost 300 more than any other province in the study area

(Table 5-3). The large area skewed the sinkhole density value for the Gulf Coastal

Lowlands, which was 5.09-2 sinkholes/km2 (Figure 5-8), but relative frequency of

sinkhole occurrence yielded a strong correlation with the physiographic provinces (Figure

5-9). It shows that the Gulf Coastal Lowlands where the Ocala Limestone is near the

ground surface has the highest relative frequency of sinkhole occurrence and the

provinces that have the Ocala Limestone slightly deeper have the next highest relative

frequencies of sinkhole occurrence (Figure 5-9).


































Tsala Apopka Plain


0 20 40 Kilometers


Figure 5-7. Physiographic provinces with sinkhole locations (Florida Geographic Data
Library, 1997).


20


I a r r











Table 5-3. Physiographic province


Province Name
Alachua Lake Cross Valley
Bell Ridge
Brooksville Ridge
Central Valley
Coastal Swamps
Cotton Plant Ridge
Dunellon Gap
Fairfield Hills
Gulf Coastal Lowlands
High Springs Gap
Kenwood Gap
Marion Upland
Martel Hill
Mount Dora Ridge
Northern Highlands
Ocala Hill
St. Johns River Offset
Sumter Upland
Trail Ridge
Tsala Apopka Plain
WesternValley


Total Area Relative
Number of Sinkholes m2) Sinkholes/ (km2) Relative
0 76.28 0 0.00Frequency
0 76.28 0 0.00%
0 100.23 0 0.00%
61 1468.91 4.15-2 8.25%
62 1840.57 3.37-2 8.39%
25 876.38 2.85-2 3.38%
4 140.15 2.85-2 0.54%
1 110.88 9.02-3 0.14%
13 493.19 2.64"2 1.76%
360 7067.81 5.09-2 48.71%
13 149.91 8.67-2 1.76%
0 5.32 0 0.00%
0 360.13 0 0.00%
0 7.10 0 0.00%
0 488.75 0 0.00%
-2
57 5032.09 1.13.2 7.71%
34 89.59 3.80-1 4.60%
0 17.74 0 0.00%
36 684.78 5.26-2 4.87%
0 18.63 0 0.00%
-2
24 280.30 8.56-2 3.25%
49 826.09 5.93.-2 6.63%
49 826.09 5.93 6.63%










Alachua Lake Cross Valley
Bell Ridge
Brooksville Ridge
Central Valley
Coastal Swamps
Cotton Plant Ridge
Dunellon Gap
Fairfield Hills
Gulf Coastal Lowlands
High Springs Gap
Kenwood Gap
Marion Upland
Martel Hill
Mount Dora Ridge
Northern Highlands
Ocala Hill
St. Johns River Offset
Sumter Upland
Trail Ridge
Tsala Apopka Plain
Western Valley


0
0
4.15-2
3.3T2
l 2.85-2
2.85-2
I9.02-3
2.64-2
S 5.09-

0
0
0
0
I 1.13-2


.6T2


0
- 5.26
0
- .562
I5.93 02

[) 0.1


380-1


2 0.3 0.4


Sinkholeslkm2


Figure 5-8. Sinkhole density chart for physiographic provinces


777777,77 77-7-777-










Alachua Lake Cross Valley
Bell Ridge
Brooksville Ridge
Central Valley
Coastal Swamps
Cotton Plant Ridge
Dunellon Gap
Fairfield Hills
Gulf Coastal Lowlands
High Springs Gap
Kenwood Gap
Marion Upland
Martel Hill
Mount Dora Ridge
Northern Highlands
Ocala Hill
St. Johns River Offset
Sumter Upland
Trail Ridge
Tsala Apopka Plain
Western Valley


0%
0%



M 3.38'
10.54%
10.14%
[ 1.76%


S11.76%
0%
0%
0%
0%
-7
S4.6(
0%
g 4.8-
0%
*m 3.25,
6.


.25%
1.39%
0


.71%
%


10%


20% 30% 40%
Percentage of Sinkholes


18.71%


50% 60%


Figure 5-9. Relative frequency of sinkhole occurrence for physiographic province


Florida Surficial Geology

The surficial geology theme represents lithostratigraphy as it is exposed at the

surface. The Ocala Limestone had the largest total number of sinkholes with 448 (Figure

5-10, Table 5-4). The Ocala Limestone had the second highest sinkhole density at 5.414

sinkholes/km2. The unit with the highest sinkhole density was the Beach Ridge and Dune

sediment sequence at 1.1-2 sinkholes/km2 (Figure 5-11). Not only did the small extent of


~111111~









this unit cause its sinkhole density to be greater, but the Beach Ridge and Dune sediment

sequence in eastern Citrus County, where the large concentration of sinkholes is located,

is very thin from 25 feet thick to not present. Directly beneath the Beach Ridge and Dune


20 0 20 40 Kilometers


Figure 5-10. Florida surficial geology with sinkhole locations (Florida Geographic Data
Library, 1998)


* Sinkhole Locations
Cr county Boundaries
Florda Surfical Geology
- HOLOCENE SEDIMENTS
BEACH RIDGE AND DUNE
UNDIFF ERENTIATED
TRAIL RIDGE SANDS
UNDIFFERENTIATED TQ SEDS
CYPRESSHEAD FM
g COOSAWHATCHIE FM
g STATENV1LLE FM
- UNDIFFERENTIATED HAWTHORN GP
SUWANNEE LS
B OCALA LS
AVON PARK FM


I I I


&1









Table 5-4. Florida surficial geolog;
Formation Name

Avon Park Fm
Beach Ridge and Dune
Coosawhatchie Fm
Cypresshead Fm
Undifferentiated Hawthorn Group
Holocene Sediments
Ocala Limestone
Statenville Fm
Suwannee Limestone
Undifferentiated Sediments
Undifferentiated TQ Sediments


Number of Total Area Sinkholes/
Sinkholes (km2) (2kmn2
9 1845 4.883
50 4530 1.10 2
89 22,532.50 3.95-3
5 12722.5 3.93-4
22 9980 2.203
1 2542.5 3.934
448 82,740.00 5.41-3
2 3495 5.72-4
1 925 1.08-3
80 32617.5 2.45-3
25 16810 1.49-3


Relative Frequency
1.23%
6.83%
12.16%
0.68%
3.01%
0.14%
61.20%
0.27%
0.14%
10.93%
3.42%


Avon Park Fm 4.8 -

Beach Ridge and Dune 1.1 -2

Coosawhatchie Fm 3.95

Cypresshead Fm 3.934

Undifferentiated Hawthorn Group 2.20'

Holocene Sediments 3.93-4

Ocala Limestone 5 413

Statenville Fm 5.72"

Suwannee Limestone 1.08-3

Undifferentiated Sediments 2.45-3

Undifferentiated TQ Sediments 1 493

0.000 0.002 0.004 0.006 0.008 0.010 0.012

Number of Sinkholes I km2


Figure 5-11. Sinkhole density chart for surficial geology








sediment sequence in this area is the Ocala Limestone. The Coosawhatchie Formation,

which is part of the Hawthorn Group, is another thin formation that overlies the Ocala

Limestone. Near the edge of the Cody Scarp water drains through sinkholes in the thin

Hawthorn Group sediments down into the Ocala Limestone. This further demonstrates

that the Ocala Limestone has a strong correlation with sinkhole development. The unit

with the third highest sinkhole density was the Avon Park Formation at 4.88-3

sinkhole/km2 (Figure 5-11). The high density is a reflection of the small area where the

Avon Park Formation is exposed. When the relative frequency of sinkhole occurrence

was analyzed, the correlation was more apparent (Figure 5-12). The Ocala Limestone

had the greatest relative sinkhole frequency with the Coosawhatchie Formation and

Undifferentiated Sediments having the next highest values. This further illustrates the

point that the Ocala Limestone has the highest probability of sinkhole occurrence, and the

thin formations that overly them have the next highest probability for sinkhole

occurrence. Clearly there is a correlation between Surficial Geology and sinkhole

distribution.










Avon Park Fm

Beach Ridge and Dune

Coosawhatchie Fm
e-
3 Cypresshead Fm

Undifferentiated Hawthorn Group

In Holocene Sediments
Ocala Limestone
0
M Statenville Fm
Suwannee Limestone

Undifferentiated Sediments

Undifferentiated TQ Sediments

0


| 1.239A
6


10.68%

M3.01
0.14%


83%

B12.1


Yo


61.20

0.27%
0.14%
l 10.93%

3.4 %

% 10% 20% 30% 40% 50% 60% 70%
Percentage of Sinkholes


Figure 5-12. Relative frequency for sinkhole occurrence with surficial geology



Florida Subsurface Geology

The Florida Subsurface Geology theme is almost identical to the Florida Surficial

Geology theme. There is a slight change in the area of the units. Tables 5-4 and 5-5

show that the values are nearly the same. Because the values are so close, the

interpretation of the data is consistent with that for the Florida Surficial Geology theme.

Figure 5-13 displays the distribution of Florida subsurface geology with sinkhole

location. Sinkhole density and relative frequency of sinkhole occurrence are in Figures

5-14 and 5-15, respectively.







44








e Sinkhole Locations
[. A County Boundaries
Florida Subsurface Geology
HOLOCENE SEDIMENTS
S' BEACH RIDGE AND DUNE
UNDIFFERENTIATED SEDS
TRAIL RIDGE SANDS
UNDIFFERENTIATED TO SEDS
CYPRESSHEAD FM
I COOSAWHATCHIEFM
SSTATENVILLE FM
m UNDIFFERENTIATED HAWTHORN GP
SLVWANNEE LS
S mg OCALA LS
k, I AVON PARK









41











N



20 0 20 40 Kilometers





Figure 5-13. Florida subsurface geology with sinkhole locations (Florida Department of
Environmental Protection, 2000b).









Table 5-5. Florida subsurface geology
Number of
Formation Name Sinkholes
Avon Park Fm 9
Beach Ridge and Dune 50
Coosawhatchie Fm 91
Cypresshead Fm 5
Undifferentiated Hawthorn Group 22
Holocene Sediments 1
Ocala Limestone 446
Statenville Fm 2
Suwannee Limestone 1
Undifferentiated Sediments 81
Undifferentiated TQ Sediments 25


Total Area
_(kmT2.
1845
4587.5
23932.5
12722.5
9980
2542.5
79797.5
9702.5
925
39350
22347


Sinkholes/
.km 2
4.88-
1.09-2
3.80 3
-4
3.93 4
2.20-3
3.93-4
5.59-3
2.06 4
1.08-3
2.06-3
1.12-3


Relative Frequency

1.23%
6.82%
12.41%
0.68%
3.00%
0.14%
60.85%
0.27%
0.14%
11.05%
3.41%


Avon Park Fm

Beach Ridge and Dune

Coosawhatchie Fm


Cypresshead Fm 3.934


-I--I--I


Undifferentiated Hawthorn Group 2.20-3


Holocene Sediments ] 3.934


Ocala Limestone .59-3


Statenville Fm 2.064


Suwannee Limestone E 1.-8-3


Undifferentiated Sediments 2.06-3


Undifferentiated TQ Sediments


S1.12-3


0.000 0.002 0.004 0.006 0.008


0.010 0.012


Number of Sinkholes / km2


Figure 5-14. Sinkhole density chart for Florida subsurface geology


~


____


4.8-3


13.80-3











Avon Park Fm

Beach Ridge and Dune

Coosawhatchie Fm

*) Cypresshead Fm


0.
7} Undifferentiated Hawthorn Group
CO
Co Holocene Sediments

44 Ocala Limestone

Statenville Fm

Suwannee Limestone

Undifferentiated Sediments

Undifferentiated TQ Sediments

0


1.230






10.68%

S3.00'

0.14%


B2%

S12.4




V0


60.85%


0.27%

0.14%

11.05%

3.41%

% 10% 20% 30% 40% 50% 60% 70%
Percentage of Sinkholes


Figure 5-15. Relative frequency of sinkhole occurrence for subsurface geology


11111111~








Population Density by US Census Block Group

The theme shows population density (people per sqmi) divided into separate US

Census blocks. The US Census data is from the 1990 Census. Figures 5-16 and 5-17






Sinkhole Locations
Population Density
M 0 29.6
29.6 76.3
76.3 202.9
202.9 558.4
558.4 1943
1943 27029













N


20 0 20 40 Kilometers A ,


Figure 5-16. Population density in people per sqmi (U.S. Census Bureau, 1990)






48


show that the sinkhole distribution data correlates well with population density. One

factor that can possibly bias this result is that all the sinkhole locations contained in the

two databases are reported sinkholes. Sinkholes occurring in an area of low population

(farms, etc.) may not be reported. In a very large neighborhood, a confirmed sinkhole

under one home, may trigger other homeowners to have their properties investigated as

well, leading to possible detection and reported concentration of sinkholes in a small


8000-9000
6000-7000
3000-4000
2000-3000
1000-2000
900-1000
800-900
_= 700-800
E 600-700
.- 500-600
450-500 E
1 400-450
0 350-400
S 300-350
3 250-300
o 200-250
0I 150-200
100-150
50-100
0-50
0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070
Averaged Sinkholes I sq. mile

Figure 5-17. Sinkhole density chart for population density



area. When relative frequency of sinkhole occurrence (Figure 5-18) was analyzed, the

results were inverse to those of sinkhole density (Figure 5-17). The highest relative

sinkhole occurrence is in areas of low population density. Using U.S. census blocks to

gain population density is probably the cause for this inversion. As you near a city or a

place where population density begins to significantly increase, the U.S. Census blocks









decrease in area. This causes the sinkhole densities to increase even though the total

number or relative frequency of sinkhole occurrence is decreasing.


8000-9000
6000-7000
3000-4000
2000-3000
1000-2000
900-1000
_o 800-900
=" 700-800
E 600-700
0C 500-600
. 450-500
c 400-450
.2 350-400
% 300-350
"5 250-300
0. 200-250
0 150-200
100-150
50-100
0-50
0%


U


m


5% 10% 15%


20%


25%


Percentage of Sinkholes

Figure 5-18. Relative sinkhole frequency for population density


* The data table for sinkhole density correlated with population is located in Appendix B
because of its large size.


~C~














CHAPTER 6
DISCUSSION

Geographic Information Systems (GIS) were employed to analyze various factors or

themes to find correlations with sinkhole distribution in an efficient visual format. Not

only does the GIS significantly reduce analysis time, it performs the analyses in much

greater detail than human interpretation would yield. No single influential factor

controlling sinkhole distribution was evident from the use of the GIS. A complex

combination of factors (themes) determine sinkhole occurrence and distribution.

The hypothesis, "GIS application of sinkhole locality data will identify patterns of

occurrence", was supported as strong correlations were made between the locality data

and the combination of factors responsible for sinkhole occurrence. GIS displayed

different themes with sinkhole locations, as well as created charts that quantified how

many sinkholes occurred in each category. GIS displays can be employed in the

determination of the correlations between each theme and sinkhole distribution.

Although some correlations might be visually confirmed, assessment of other factors may

be needed to validate them. This was true for several of the themes used. The Florida

Surficial Geology and Florida Subsurface Geology themes showed a definite visual trend

with sinkholes occurring in the Ocala Limestone. The sinkhole density data on the other

hand shows the Beach Ridge and Dune sediment sequence to have the highest density,

with the Ocala Limestone much lower. The large area where the Ocala Limestone is









exposed affects the lower sinkhole density. For this reason relative frequency analysis

was employed for each theme to overcome the error caused by differences in area.

Another bias encountered while analyzing data was with the Florida Sinkhole

Research Institute's sinkhole database. Figure 6-1 shows sinkhole distribution that seems

to follow the census block divisions. Recognizing this is not a geologic control the

metadata for the FSRI database were consulted. It was discovered that half of FSRI's

sinkhole locations come from the Florida Department of Transportation. This creates a

bias in the data, especially if attempting to predict directional trends in sinkhole


* Sinkhole Locations
population Density
0 29.6
29.6 76.3
76.3 202.9
202.9 558.4
558.4- 1943
1943 -27029


20 0 20


40 Kilometers


Figure 6-1. Population theme showing sinkhole correlation with SR 27 (U.S. Census
Bureau, 1990)









distribution. Despite this bias the data are useful. The data may trend along roads, but

still displays the location of sinkhole activity, which is utilized in sinkhole distribution

analysis.

With those qualifications known, the themes were analyzed and charts created to show

what categories of each theme contained the highest sinkhole densities. To test the

hypothesis that "a complex combination of factors determine sinkhole distribution" GIS

polygons of the categories with the highest sinkhole densities from each theme were

extracted. This yields polygons that the data determined as factors for sinkhole

distribution. These polygons were combined to display together in the same view.

Figure 6-2 illustrates the complexities of making GIS correlations between where the

factors or separate themes overlap each other and where sinkhole densities occur.

Sinkhole density appears to be influenced by the interaction between the "Recharge 1 5

inches/year" zone and the "Depth to Floridan aquifer system less than 4.5 m" zone. The

circled areas of high sinkhole density are located where these two zones overlap (Figure

6-2). The concentration in east Dixie and northwest Levy County straddles the discharge

zone of the Suwannee River, although the majority of the sinkholes occur within the

"Recharge 1 5 inches/year" polygons (Figure 6-2). There are two concentrations of

sinkholes in Citrus County. They are divided by a zone that has aquifer depth increasing

from the surface to 30.5 m depth (0 100 ft.). The limited sinkhole occurrence in this

dividing zone is a result of the control that depth to the aquifer has on sinkhole

development. The western Citrus County concentration has the highest sinkhole density

in the study area (Figure 6-2). The other two high-density concentrations of sinkhole

occurrence are in central Alachua and Marion Counties.


















East Dixie &
Northwest Levy
County


Central Alachua
County


.Central Marion
E ".:", County





West Citrus (
County
N


20 0 20 40 Kilometers




Figure 6-2. Highest sinkhole density polygons with sinkhole locations


The high sinkhole density in these areas is attributed to the fact that they are the

locations of major cities. As a result sinkhole density is increased because of word of

mouth investigations as mentioned earlier.

Denizman and Randazzo (2000) performed analyses on sinkhole distribution and

morphometry in the Lower Suwannee River Basin. Sinkhole locations were obtained

from topographic maps and digitized into a GIS environment. These non-reported


* Sinkhole Locations
County Boundaries
Recharge 1 to 5 in/yr
Population greater than 600 people/sqmi
--] Beach Ridge and Dune
] Depth to Floridan aquifer system less than 4.5 m
Ocala Hill








sinkholes were then added to a database of reported sinkholes. For an area much smaller

than this project there were over 25,000 sinkholes used in the study. The large number of

sinkholes would decrease the amount of error in sinkhole distribution analysis.

Figure 6-3 shows the polygons with the highest relative frequency of sinkhole

occurrence. It is difficult to see where the different polygons overlap in Figure 6-3

because they cover the same areas, but in computer manipulated GIS operations it can be

clearly recognized. For example, where the surface of the Floridan aquifer system is less

than 4.5 meters deep (yellow area of Figure 6-3), Ocala Limestone is the surficial

lithostratigraphic unit that is present. When population density is set to less than 50

people per sqmi, the polygon covers the entire study area except for the main cities in

each county. Even though the relative frequency polygons cover a large part of the study

area, they still show that sinkhole distribution lies in areas where polygons overlap.

Figure 6-3 displays three major concentrations of sinkhole occurrence (circled). They

are central Alachua County, central Marion County and western Citrus County. The

Alachua and Marion County concentrations overly the 'recharge greater than 10 inches

per year' and 'Ocala Limestone' polygons. In these two locations it appears the greatest

potential influence on sinkhole occurrence is a combination of recharge, and surficial and

subsurface geology. The Citrus County concentration is slightly different from the other

two because it has more factors to influence sinkhole distribution. Here the sinkhole

concentration overlies the Ocala Limestone, Gulf Coastal Lowlands, Depth to Floridan

aquifer system less than 4.5 meters, and Surficial and Subsurface Geology polygons.

Although, it is not possible to determine a single factor controlling sinkhole distribution,

generalizations can be made.























Central Marion
' County


20 0 20 40 Kilometers




Figure 6-3. Highest relative frequency of sinkhole occurrence polygons with sinkhole
locations.

The factors that potentially have the greatest influence on sinkhole distribution in the

study area are surficial geology, subsurface geology, recharge to the Floridan aquifer

system, and depth to Floridan aquifer system. When recharge to the aquifer is high and

limestone units (aquifer) are near the ground surface, sinkhole development increases.

If there are no near surface carbonate units (aquifer) present or recharge or discharge

is very low, sinkhole development is less. Also areas that already have these factors for


Sinkhole Locations
I Depth to Floridan Aquifer less than 4.5 m
Ocala Limestone
Gulf Coastal Lowlands
Recharge Greater Than 10 in/yr
Population less than 50 people/sqmi
County Boundanes








sinkhole development may see a further increase if population density continues to

increase.

The correlations obtained by GIS manipulation of the sinkhole databases can be used

for sinkhole risk assessment. Sinkhole risk assessment identifies what areas have the

highest potential for future sinkhole development. To help identify the zones for future

sinkhole development in the study area, a "distance to the nearest sinkhole" map was

created (Figure 6-4). The map shows sinkhole locations with buffer zones surrounding

them, in one-kilometer increments. The red zones, which indicate a sinkhole within one

kilometer, may have the highest potential for sinkhole development. The orange zones,

which indicate a sinkhole within two kilometers, may have the next highest potential, and

the yellow zones at three kilometers may have the third highest potential for future

sinkhole development.

Of the four concentrations of sinkhole occurrence (circled in Figure 6-4), western

Citrus County has the highest potential for future sinkhole development. The red zone

covers nearly the whole west side of Citrus County. This can be attributed to the

proximity of the Floridan aquifer system to the ground surface. Because it is near the

surface, it is exposed to more chemically aggressive water, as opposed to the central

Alachua and Marion County concentrations, where aquifer depth is greater. With an

elevated level of dissolution the extent of sinkhole development should continue to

increase and coalesce into the orange and yellow zones.

The concentration of sinkholes in central Marion County will also continue to spread.

Sinkhole development in this area will migrate north, south and to the west because of the

Ocala Limestone exposure and the depth to Floridan aquifer system



















Central Alachua
County


Central Marion
County


20 0 20 40 Kilometers


Figure 6-4. Distance to nearest sinkhole map


in the area. The discharge zone of Ocklawaha River bounds eastward migration of

sinkhole development in central Marion County (Figure 5-4). In this discharge zone the

depth to the Floridan aquifer system increases to over 30.5 m (100+ ft.) (Figure 5-1).

When the surface of the Floridan aquifer system is this deep sinkhole development is


Distance to nearest sinkhole
0 1 km
1 -2 km
[] 2-3km
| County Boundaries









drastically reduced. Only 3.55% of all the reported sinkholes in the study area occur

when the Floridan aquifer system is at this depth (Figure 5-3).

The Cody Scarp (Figure 2-1) controls sinkhole development in central Alachua and in

east Dixie and northwest Levy County. Here a complex environment exists in which

water sinks through the Hawthorn Group sediments into the Ocala Limestone and travels

through the aquifer until it rises at the Gulf Coastal Lowlands through springheads. The

anastomotic fracture systems and conduits, through which the water passes, make

detailed prediction of sinkhole development difficult, and it can occur anywhere along

these flow paths. The areas with the highest potential for future sinkhole development

are the Hawthorn Group sediments located near the edge of the Cody Scarp, and the

Ocala Limestone in front of the scarp. Sinkhole development may spread along both sides

of the Cody Scarp.

The combination of the previous figures and predictions of future sinkhole

development, make it possible to perform sinkhole risk assessment on a regional scale.








CHAPTER 7
SUMMARY AND CONCLUSIONS

Analyses of sinkhole activity and factors such as: surficial and subsurface geology,

Floridan aquifer system depth, recharge and discharge to the aquifer, physiographic

province, and population density yielded many strong GIS correlations. The dominating

influence of any single factor to control sinkhole distribution could not be quantified.

Sinkhole distribution is controlled by a complex interaction among these factors.

The two factors that appear to have the greatest influence on sinkhole distribution are

depth to the Floridan aquifer system, and amount of recharge into the aquifer. When the

Floridan aquifer system, a carbonate unit, is near the ground surface and conditions of

high recharge occur, the potential for sinkhole activity is greater. Also, in areas of greater

population density, reported sinkhole density increases. However, this may be biased

since the database sinkholes are reported, and not derived from topographic contour maps

and aerial photographs. Even with the bias in the reported sinkhole localities, using

confirmed sinkholes for correlation with factors believed to be influential in sinkhole

development provides a capability for characterizing sinkhole activity. The database

includes 739 confirmed sinkhole localities, representing one of the largest databases used

in published sinkhole investigations. Thus, despite the biases of the database, this

investigation has identified actual sinkholes on a regional scale that allow for causal

correlations. Such correlations represent the basis for predictions of future sinkhole

activity.

Predictions of future sinkhole development were made on the basis of the largest

concentrations of sinkhole occurrence in the study area and the GIS factors recognized as

the most influential. Central Alachua and Marion Counties, western Citrus County and








east Dixie and northwest Levy Counties are among those representing high potential for

sinkhole occurrence. The predictions made from the "distance to nearest sinkhole" map

(Figure 6-4), incorporated with information from the "highest density" (Figure 6-2) and

"highest relative frequency of occurrence" maps (Figure 6-3), will make it possible to

conduct sinkhole risk assessment on a regional scale.

When comparing the sinkhole locality data from Denizman and Randazzo (2000) with

the GIS factors (themes) from this study, the areas of high sinkhole occurrence coincide

with areas of high recharge and overlie a shallow Floridan aquifer system. They also

coincide with the Ocala Limestone or thin sediments that overlie the Ocala Limestone.

Factors determined to influence sinkhole distribution in this study are also impacting

sinkhole distribution in the study area of Denizman and Randazzo (2000).

Future efforts in this project would be the incorporation of non-reported sinkholes into

the sinkhole database. Obtaining digital topographic maps could do this. Computer

software could extract circular depressions from the maps and point locations could be

established. The increased sinkhole inventory would yield more precise correlation data

with the factors considered in this project.














APPENDIX A
ARCVIEW GEOPROCESSING COMMANDS

These are the geoprocessing commands used in ARCVIEW version 3.2a (ESRI. INC)

along with a description of what each command does.



Table A-1. Arcview geoprocessing commands
Command Description

Dissolve This process combines polygons that posses the same value for a

specific attribute that the user determines.

Merge This process combines polygons from two or more themes. All

attributes with the same name are retained.

Clip This process involves using a clip theme to cut an input theme.

Everything outside of the clip theme is deleted (polygons and

attributes). Clipped attributes are not combined with the resultant input

theme.

Intersect This process involves using one theme to cut the input theme. Only

with the intersect command both themes attributes are combined.

Union This process combines the polygons and attributes of both themes.

Spatial Join This process joins only the data from one theme to the features of the

second theme that share the same polygons.














APPENDIX B
POPULATION DENSITY FROM US CENSUS BLOCK GROUPS


Table B-1. U.S. block group population density data
Population Average Relative 1990 N
Bracket Sinkholes/ Frequency Population
sq.mkesqu. mie /sqmi
0-50 0.00254 23.42% 0.0
0-50 1.7
0-50 5.0
0-50 6.1
0-50 8.5
0-50 10.8
0-50 11.1
0-50 13.4
0-50 13.6
0-50 15.7
0-50 15.8
0-50 16.8
0-50 16.8
0-50 18.4
0-50 18.7
0-50 19.6
0-50 20.7
0-50 20.7
0-50 21.7
0-50 22.1
0-50 22.8
0-50 23.7
0-50 26.0
0-50 26.1
0-50 26.3
0-50 26.7
0-50 26.9
0-50 26.9
0-50 27.6
0-50 28.6
0-50 29.0
0-50 29.0
0-50 29.3
0-50 29.6
0-50 31.6
0-50 34.3


umber of
inkholes
3
3
3
2
4
7
3
5
1
5
2
3
1
3
2
2
2
1
1
1
5
6
3
13
1
1
3
1
1
1
11
5
3
5
1
1


Total area sqmi

3068.43
2983.38
1053.34
883.24
667.34
4952.67
2558.12
5508.79
3238.54
1805.73
2564.66
4514.33
3519.87
1799.19
634.62
2427.27
732.76
2571.20
4507.78
837.44
2433.81
314.04
3140.40
3493.70
523.40
1223.45
1007.55
3323.59
660.79
3460.98
1478.61
2911.41
889.78
647.71
2525.41
215.90


Sinkholes/
sqmi
0.00098
0.00101
0.00285
0.00226
0.00599
0.00141
0.00117
0.00091
0.00031
0.00277
0.00078
0.00066
0.00028
0.00167
0.00315
0.00082
0.00273
0.00039
0.00022
0.00119
0.00205
0.01911
0.00096
0.00372
0.00191
0.00082
0.00298
0.00030
0.00151
0.00029
0.00744
0.00172
0.00337
0.00772
0.00040
0.00463








0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
100-150
100-150
100-150
100-150
100-150


34.6
35.2
36.7
37.4
37.6
39.2
39.9
41.2
41.2
41.3
42.5
44.1
45.7
46.8
49.4
50.1
0.00407 12.40% 53.8
55.1
58.8
59.1
60.2
60.3
60.9
61.9
62.3
62.9
67.0
69.8
72.2
72.2
74.2
74.9
81.2
81.3
83.6
84.1
86.0
86.3
87.4
89.3
93.3
94.0
94.8
99.4
99.5
0.00896 9.50% 107.4
107.5
108.1
114.7
116.9


3696.51
2754.39
2316.05
215.90
2296.42
3958.21
3860.08
1544.03
9048.28
902.87
660.79
1792.65
2721.68
1079.51
1969.29
4730.23
2093.60
1930.04
85.05
1125.31
104.68
1890.78
1118.77
2937.58
680.42
2996.47
693.51
1014.09
5606.92
477.60
1354.30
1530.95
1406.64
418.72
143.94
477.60
2420.73
523.40
7733.24
601.91
549.57
1282.33
3781.57
2250.62
484.15
3506.78
1426.27
405.64
1805.73
372.92


0.00027
0.00399
0.00086
0.01390
0.00044
0.00025
0.00026
0.00583
0.00011
0.00443
0.00151
0.00614
0.00184
0.00093
0.00051
0.00042
0.00096
0.00052
0.01176
0.00178
0.01911
0.00106
0.00179
0.00306
0.00147
0.00100
0.00577
0.00296
0.00071
0.00209
0.00960
0.00131
0.00427
0.00716
0.01390
0.00838
0.00041
0.00191
0.00013
0.00498
0.00364
0.00156
0.00106
0.00355
0.00207
0.00171
0.00070
0.00740
0.00055
0.00804








100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
200-250
200-250
200-250
200-250
200-250
200-250
200-250
200-250
200-250
250-300
250-300
250-300
250-300
250-300
250-300
300-350
300-350
300-350
300-350
300-350


117.0
118.9
124.2
128.9
132.6
136.0
136.9
137.2
140.7
142.7
144.6
145.5
147.6
7.85% 151.8
152.8
154.4
155.7
159.2
159.6
162.0
163.0
165.1
171.9
173.9
179.8
180.3
180.7
181.2
194.3
198.6
3.99% 202.9
210.9
213.4
213.4
214.5
219.6
223.5
225.5
236.8
5.65% 251.0
256.4
278.0
285.3
288.2
293.4
1.52% 316.9
319.3
338.9
340.7
342.2


1
1
4
5
2
17
1
1
4
5
1
2
11
6
1
2
2
14
2
4
1
9
2
4
1
1
1
1
3
3
5
3
1
2
2
5
1
8
2
6
2
6
20
2
5
1
1
5
3
1


3323.59
2296.42
1210.36
510.32
1138.40
281.33
621.54
1851.53
686.96
104.68
157.02
5031.18
2525.41
3003.01
2388.01
896.32
693.51
471.06
1275.79
202.82
7752.86
1282.33
8138.87
719.68
1223.45
641.17
1086.06
451.43
1203.82
804.73
490.69
425.26
340.21
65.43
543.03
1118.77
189.73
516.86
412.18
386.01
1406.64
536.49
1086.06
562.66
268.24
209.36
65.43
130.85
222.45
228.99


0.00490


















0.00939









0.01146





0.01523


0.00030
0.00044
0.00330
0.00980
0.00176
0.06043
0.00161
0.00054
0.00582
0.04776
0.00637
0.00040
0.00436
0.00200
0.00042
0.00223
0.00288
0.02972
0.00157
0.01972
0.00013
0.00702
0.00025
0.00556
0.00082
0.00156
0.00092
0.00222
0.00249
0.00373
0.01019
0.00705
0.00294
0.03057
0.00368
0.00447
0.00527
0.01548
0.00485
0.01554
0.00142
0.01118
0.01842
0.00355
0.01864
0.00478
0.01528
0.03821
0.01349
0.00437








350-400
350-400
350-400
400-450
400-450
400-450
400-450
400-450
400-450
400-450
400-450
450-500
450-500
450-500
450-500
450-500
450-500
500-600
500-600
500-600
500-600
600-700
600-700
600-700
600-700
700-800
700-800
700-800
700-800
800-900
800-900
800-900
800-900
800-900
900-1000
900-1000
900-1000
900-1000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000


0.01910


0.01782








0.03244





0.02644



0.03101



0.01919



0.02822




0.04845



0.05958


2.20% 350.3
370.3
376.1
4.68% 400.2
403.1
411.4
412.4
422.4
430.5
430.6
435.6
6.75% 451.9
453.2
454.0
455.0
462.5
480.5
1.10% 511.9
514.9
518.2
548.9
4.41% 615.7
633.4
666.7
680.5
1.52% 701.6
716.4
724.8
795.2
2.07% 851.0
851.3
861.6
870.4
885.8
2.07% 910.8
938.2
944.9
987.5
5.92% 1095.2
1243.1
1394.5
1415.3
1436.5
1454.2
1469.0
1469.8
1535.3
1606.3
1651.1
1673.5


2
2
12
15
3
4
1
5
1
2
3
2
4
1
31
2
9
2
3
1
2
25
5
1
1
5
1
1
4
4
4
3
1
3
2
1
9
3
3
2
2
2
3
1
1
1
3
4
1
3


2859.07
353.30
235.53
372.92
143.94
85.05
143.94
588.83
366.38
274.79
333.67
124.31
883.24
327.13
431.81
2139.40
91.60
26.17
137.39
255.16
556.11
274.79
228.99
163.56
196.28
196.28
78.51
157.02
124.31
71.97
196.28
98.14
45.80
235.53
274.79
242.07
52.34
287.87
111.22
26.17
39.26
176.65
85.05
52.34
111.22
58.88
58.88
202.82
71.97
52.34


0.00070
0.00566
0.05095
0.04022
0.02084
0.04703
0.00695
0.00849
0.00273
0.00728
0.00899
0.01609
0.00453
0.00306
0.07179
0.00093
0.09826
0.07642
0.02184
0.00392
0.00360
0.09098
0.02184
0.00611
0.00509
0.02547
0.01274
0.00637
0.03218
0.05558
0.02038
0.03057
0.02184
0.01274
0.00728
0.00413
0.17195
0.01042
0.02697
0.07642
0.05095
0.01132
0.03527
0.01911
0.00899
0.01698
0.05095
0.01972
0.01390
0.05732








1000-2000 1759.1 1 26.17 0.03821
1000-2000 1761.0 1 104.68 0.00955
1000-2000 1811.5 8 19.63 0.40759
1000-2000 1815.3 5 26.17 0.19106
1000-2000 1836.3 1 78.51 0.01274
1000-2000 1868.0 1 39.26 0.02547
2000-3000 0.05541 2.48% 2064.7 1 39.26 0.02547
2000-3000 2287.3 1 32.71 0.03057
2000-3000 2304.0 1 65.43 0.01528
2000-3000 2326.2 2 39.26 0.05095
2000-3000 2366.0 3 32.71 0.09171
2000-3000 2480.9 3 157.02 0.01911
2000-3000 2567.8 3 32.71 0.09171
2000-3000 2671.5 1 39.26 0.02547
2000-3000 2827.7 1 19.63 0.05095
2000-3000 2940.3 2 13.09 0.15285
3000-4000 0.04792 2.07% 3064.0 3 2813.28 0.00107
3000-4000 3110.2 1 13.09 0.07642
3000-4000 3380.1 4 39.26 0.10190
3000-4000 3723.2 7 569.20 0.01230
6000-7000 0.05095 0.28% 6453.1 2 39.26 0.05095
8000-9000 0.01528 0.14% 8451.8 1 65.43 0.01528













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Gulf of Mexico (preliminary report): The Agricultural and Mechanical College of
Texas, Dept. of Oceanography and Meteorology, A & M project 286-1, 18 p.

Beck, B.F. and Sinclair, W.C., 1986, Sinkholes in Florida-an introduction: Orlando,
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Casper, J., and Degner, J., 1981, A remote sensing evaluation of the potential for sinkhole
occurrence: Remote Sensing Applications Laboratory, 103 p.

Denizman, C., 1998, Evolution of karst in the lower Suwannee River Basin, Florida
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Denizman, C., and Randazzo A.F., 2000, Post-Miocene subtropical karst evolution, lower
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Environmental Systems Research Inc., 1992-2000, Arcview 3.2a. http://www.esri.com.

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171 p.













BIOGRAPHICAL SKETCH

Brian Dodek was born in Oakland, California on June 22, 1978. After traveling

the world in a military family, 18 years later he was accepted to the University of Florida

in 1996. Four years later, not ready to leave Gainesville, he began graduate school at the

University of Florida in pursuit of a Masters of Science degree in Geological Sciences.









I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a thesis for the degree of Master of Science.



Anthony F. Randazzo, Chairman
Professor of Geological Sciences


I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a thesis for the degree of Master of Science.



Douglas L. Smith
Professor of Geological Sciences


I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a thesis for the degree of Master of Science.



lTopathan B. Martin
Associate Professor of Geological Sciences

This thesis was submitted to the Graduate Faculty of the Department of Geology
in the College of Liberal Arts and Sciences and to the Graduate School and was accepted
as partial fulfillment of the requirements for the degree of Master of Science.



May, 2003
Dean, Graduate School










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Full Text

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xml record header identifier oai:www.uflib.ufl.edu.ufdc:UF0008953600001datestamp 2009-02-09setSpec [UFDC_OAI_SET]metadata oai_dc:dc xmlns:oai_dc http:www.openarchives.orgOAI2.0oai_dc xmlns:dc http:purl.orgdcelements1.1 xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.openarchives.orgOAI2.0oai_dc.xsd dc:title Geographic Information Systems (GIS) analysis of sinkhole activity in north-central Floridadc:creator Dodek, Brian D.dc:publisher Brian D. Dodekdc:date 2003dc:type Bookdc:identifier http://www.uflib.ufl.edu/ufdc/?b=UF00089536&v=0000152731475 (oclc)002935910 (alephbibnum)dc:source University of Floridadc:language English


A GEOGRAPHIC INFORMATION SYSTEMS (GIS) ANALYSIS OF SINKHOLE
ACTIVITY IN NORTH-CENTRAL FLORIDA:
CAUSES AND CORRELATIONS
By
BRIAN D. DODEK
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2003

This thesis is dedicated to my parents. Without their love and support, my achievements
would not have been possible. I am proud of who I have become, and 1 have them to
thank for that.

ACKNOWLEDGMENTS
I would like to thank Dr. Anthony Randazzo for all his help and guidance through the
stages of this thesis as well as my tenure at the University of Florida. As a result, I
convey professionalism and a demeanor that ultimately helped start my career. For that I
am very grateful.
I would like to thank GeoHazards, Inc. for the use of its database and other proprietary
materials. I also would like to thank Dr. Douglas Smith and Dr. Jonathan Martin for their
help and guidance.
in

TABLE OF CONTENTS
page
ACKNOWLEDGMENTS iii
LIST OF TABLES vi
LIST OF FIGURES vii
ABSTRACT ix
CHAPTER
1 INTRODUCTION 1
2 STUDY AREA BACKGROUND INFORMATION 5
Climate 5
Physiographic Setting 6
Geologic Setting 9
Geologic Structure 11
Hydrogeologic Setting 14
3 SINKHOLE ACTIVITY 18
Limestone-Solution Sinkholes 20
Limestone-Collapse Sinkholes 20
Cover-Subsidence Sinkholes 20
Cover-Collapse Sinkholes 21
Human Induced Sinkholes 21
Sinkholes Caused by Groundwater Withdrawal 21
Sinkholes Caused by Construction Activity 22
4 METHODOLOGY 24
5 RESULTS 28
Depth to the Top Surface of the Floridan Aquifer System 28
Recharge and Discharge Areas of the Floridan Aquifer System 31
Physiographic Provinces 35
Florida Surficial Geology 39
Florida Subsurface Geology 43
IV

V
Population Density by US Census Block Group 47
6 DISCUSSION 50
7 SUMMARY AND CONCLUSIONS 59
APPENDIX
A ARCVIEW GEOPROCESSING COMMANDS 61
B POPULATION DENSITY FROM US CENSUS BLOCK GROUPS 62
REFERENCES CITED 67
BIOGRAPHICAL SKETCH 70

LIST OF TABLES
Table page
4-1. Theme name and website location 25
4-2. Theme parameters 26
5-1. Depth to Floridan aquifer system 29
5-2. Recharge and discharge 32
5-3. Physiographic province 37
5-4. Florida surficial geology 41
5-5. Florida subsurface geology 45
A-1. Arcview geoprocessing commands 61
B-l. U.S. block group population density data 62

LIST OF FIGURES
Figure page
1 -1. Study area with county names 4
2-1. Geomorphic configuration of the study area 6
2-2. Lithostratigraphy of the study area 10
2-3. Structural features of Florida 13
2-4. Relationship of regional hydrogeologic units to major stratigraphic units 15
3 -1. Types of sinkhole activity 19
3-2. Soil piping induced by modification of natural runoff and infiltration conditions ...23
3-3: Bar graph showing distribution of sinkhole collapses in Missouri based on records
kept since 1930 23
5-1. Depth to the surface of the Floridan aquifer system 29
5-2. Sinkhole density chart for depth to the Floridan aquifer system 30
5-3. Relative frequency of sinkhole occurrence for aquifer depth 30
5-4. Recharge and discharge in inches per year of the Floridan aquifer, with sinkhole
locations 32
5-5. Sinkhole density for recharge and discharge zones 34
5-6. Relative frequency of sinkhole occurrence for recharge and discharge zones 35
5-7. Physiographic provinces with sinkhole locations 36
5-8. Sinkhole density chart for physiographic provinces 38
5-9. Relative frequency of sinkhole occurrence for physiographic province 39
5-10. Florida surficial geology with sinkhole locations 40
5-11. Sinkhole density chart for surficial geology 41
vii
r

viii
5-12. Relative frequency for sinkhole occurrence with surficial geology 43
5-13. Florida subsurface geology with sinkhole locations 44
5-14. Sinkhole density chart for Florida subsurface geology 45
5-15. Relative frequency of sinkhole occurrence for subsurface geology 46
5-16. Population density in people per sqmi 47
5-17. Sinkhole density chart for population density 48
5-18. Relative sinkhole frequency for population density 49
6-1. Population theme showing sinkhole correlation with S.R. 27 51
6-2. Highest sinkhole density polygons with sinkhole locations 53
6-3. Highest relative frequency of sinkhole occurrence polygons with sinkhole locations. 5 5
6-4. Distance to nearest sinkhole map 57

Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Master of Science
A GEOGRAPHIC INFORMATION SYSTEMS (GIS) ANALYSIS OF SINKHOLE
ACTIVITY IN NORTH-CENTRAL FLORIDA:
CAUSES AND CORRELATIONS
By
BRIAN D. DODEK
May 2003
Chair: Dr. Anthony Randazzo
Department: Geological Sciences
This study utilizes Geographic Information Systems to find patterns and to analyze
factors influential in sinkhole distribution in north-central Florida. The factors used were
depth to the top surface of the Floridan aquifer system, recharge and discharge areas of
the Floridan aquifer system, physiographic provinces, Florida surficial geology, Florida
subsurface geology, and population density by U.S. Census block group. Comparing
these factors with areas of high sinkhole density and high relative frequency of sinkhole
occurrence yielded strong correlations. Though a single factor influencing sinkhole
distribution could not be quantified, efforts were made to determine which factors appear
to have the largest control on sinkhole distribution. Amount of recharge to the Floridan
aquifer system and the depth to the Floridan aquifer system, combined with surficial and
subsurface geology, had the strongest correlations with sinkhole density and relative
frequency of sinkhole occurrence. When sinkhole localities overlie the Ocala Limestone
IX

X
or thin sediments above the Ocala Limestone, sinkhole occurrence increases. Also, in an
area of high recharge where the Floridan aquifer system is shallow, sinkhole occurrence
increases. Analyses of the sinkhole locality data identified factors influential in sinkhole
distribution. Different combinations of factors can influence sinkhole distribution. This
explains their occurrence in regions of contrasting geology.
Predictions were made for future sinkhole occurrence from past sinkhole distributions
and by correlating the factors deemed influential in sinkhole distribution. These
predictions and the figures created in this study can be used for sinkhole risk assessment
on a regional scale.

CHAPTER 1
INTRODUCTION
Exponential population growth has coincided with a significant increase in sinkhole
activity reported in the State of Florida. Sudden collapse or gradual subsidence of the
ground surface can cause extensive damage to structures built on or near an area of
sinkhole activity. The process of limestone dissolution and ground surface subsidence is
not only dynamic, but also relentless, given the geologic conditions present. North-
central Florida is particularly plagued by sinkhole activity. The identification, rate,
distribution, and causes of sinkhole activity can increase awareness of risks, facilitate
management, and determine measures for avoiding economic loss and deleterious effects
to the environment.
By producing a regional Geographic Information Systems (GIS) database that can be
used to find areas of potential sinkhole activity, we can reduce or avoid some of the
economic and emotional loss that sinkhole activity can cause. Using the database for
urban and regional planning is advisable: its electronic format has advantages over paper
maps. One advantage is being able to quickly change the scale of the maps to meet the
need of a certain project. A versatile tool, GIS allows the access of data, overlaying the
thematic map of choice and zooming to the exact scale that suits a need. Whether it is a
city planner seeking a sinkhole location map of the city, or an insurance company that
desires a neighborhood layout and sinkhole distribution, both needs can quickly and
easily be met with the same database.
1

2
Sinkhole activity can be recognized by geotechnical investigation of the geologic
subsurface. Remote sensing techniques include geophysical tools such as electrical
resistivity (ER) and ground penetrating radar (GPR). Direct testing of the geophysical
anomalies detected is generally accomplished by drilling using recognized protocols
established by the American Society of Testing and Materials (ASTM).
Geophysical techniques inexpensively survey areas and detect suspected sinkhole
activity. Using that information, locations for boreholes can be identified. This
methodology eliminates the randomness of locating drilling positions (Smith and
Randazzo, 1986). If a drilling protocol is implemented over a large area with no prior
geophysical information, existing sinkhole activity may not be detected.
It is now widely accepted by the insurance industry and legal profession that
geophysics be used in fulfilling Florida Statues Section 627.707 requirements that
sinkhole investigations be of sufficient scope to verily or eliminate sinkhole activity as a
cause of distress. Additionally, geophysics is a commonly applied technique to evaluate
property prior to purchase or construction.
Isolated studies on a neighborhood scale provide important insight about the
occurrence and causes of sinkhole activity. Little attention, however, has been given to
integrating results from individual investigations to address sinkhole activity on a
regional or statewide scale. This study attempts to document the geologic conditions
responsible for sinkhole development, and to identify patterns in sinkhole occurrence.
Although there is a bias in the reported sinkhole localities, using confirmed sinkholes for
correlation with factors believed to be influential in sinkhole development is a valid
approach. This study is one of only a few using GIS to understand what potentially

3
controls sinkhole development on a regional scale. The database includes 739 confirmed
sinkhole localities, representing one of the largest databases used in published sinkhole
investigations. Previous published sinkhole investigations, located in world-renowned
karst areas, have been conducted using only a few hundred sinkholes (Denizman, 1998;
Ford and Williams, 1989). Thus, despite the biases of the database, using confirmed
sinkholes on a regional scale to develop correlations and predictions is of great
significance.
Hypotheses tested in this study are as follows:
• Aqueous recharge environments are more acidic so the dissolution of the
limestone is more extensive, and sinkhole activity more prevalent.
• GIS application of sinkhole locality data can identify patterns of occurrence.
• A complex combination of factors control sinkhole occurrence and distribution.
• Identifying patterns of occurrence allow the development of more accurate
sinkhole risk assessment on a regional scale.
The study area for this project is located in north-central Florida (Figure 1-1). It
covers Alachua, Bradford, Citrus, Columbia, Dixie, Gilchrist, Lafayette, Levy, Marion,
Suwannee, and Union Counties.

4
Figure 1-1. Study area with county names (Florida Geographic Data Library, 1990).

CHAPTER 2
STUDY AREA BACKGROUND INFORMATION
Climate
Florida’s climate is humid subtropical (Winsburg, 1990). Strong subtropical high-
pressure cells that develop over the ocean influence this climate. The subtropical cell that
affects Florida’s climate is the Bermuda-Azores high (Winsburg, 1990). During the
summer this cell influences the weather, moving warm air across the ocean and into
Florida. During winter colder air masses from the continental interior influence Florida’s
weather patterns (Winsburg, 1990).
The average annual maximum temperature for Gainesville, Florida, which is central to
the study area (Figure 2-1) is ~27°C. The average annual minimum temperature is ~14°C
(58°F). Precipitation, the main source for aquifer recharge, is very high in a humid
subtropical climate. The annual precipitation average for the study area reported at
Gainesville, Florida, is 132 cm (52 inches). Florida’s rainy season is May through
September. Just under 60% of the yearly precipitation total is received during this period
(Winsburg, 1990). During the summer, storms are convection driven, and precipitation
amounts differ from place to place. Winter storms are usually precursors to fronts
sweeping through the area, and produce uniformly distributed precipitation amounts
(Winsberg, 1990).
5

6
Physiographic Setting
The two largest physiographic provinces in the study area are the Northern Highlands
and the Gulf Coastal Lowlands (White, 1970). The Northern Highlands located in the
northeast comer of the study area (Figure 2-1) occupy more than 5000 km .
Cody Scarp
Fairfield Hills
Marion Upland
Coastal Swamps
Sumter Upland
Ocala Hill
Cotton Plant Ridge
Tsala Apopka Plain
N
20 0 20 40 Kilometers
Figure 2-1. Geomorphic configuration of the study area (Florida Geographic Data
Library, 1997).
These highlands range in elevation from 30.5 - 76.2 meters (100 - 250 ñ) asl. A relict
highland has been dissected by erosion and dissolution to yield the large Northern

7
Highlands mass and the ridges of the Central Highlands south of the study area (White,
1970). The scarp resulting from the erosion of the Northern Highlands platform is called
the Cody Scarp. It is referred to as “.. .the most persistent topographic break in the
state.” by Puri and Vernon (1964, p. 11). The scarp generally follows the 100 ft asl
contour line, except in a few places where it has been incised by rivers that flow over its
edge.
The Northern Highlands lithology consists of undifferentiated sediments (mainly sand
and clay), and the Hawthorn Group Sediments (sand, clay, limestone and dolostone)
(White, 1970). The Hawthorn Group Sediments are important because they influence the
topography of the Northern Highlands as well as the shape of the Cody Scarp. The clays
of the Hawthorn Group confine artesian flow to the point that the piezometric surface
remains above the ground surface in the stream valleys. This ensures that the rivers flow
above ground over the scarp edge. This is the case for the Cody Scarp east of
Gainesville. West of Gainesville the edge of the Hawthorn Group does not coincide with
the Cody Scarp. Instead the scarp consists of geologically older limestone. Because the
limestone does not confine artesian flow, the piezometric surface is much lower than the
stream valley floors as they cross the scarp. This causes streams between Gainesville
and the Suwannee River to go under ground before they reach the scarp’s edge and flow
through cavernous limestone until they have reached the other side of the scarp (Gulf
Coastal Lowlands) where they re-emerge as springheads. The Suwannee River is the
only river west of Gainesville that crosses the Cody Scarp above ground (White, 1970).
The Gulf Coastal Lowlands make up the majority of the study area. This province
covers more than 7,000 km2. The Ocala Limestone underlies almost all of the Gulf

8
Coastal Lowlands. The Ocala Limestone is at or very near the surface throughout the
Gulf Coastal Lowlands. Because the Ocala Limestone is part of the Floridan aquifer
system (Miller, 1997), water enters the aquifer almost directly. The surficial aquifer can
be very thin in this province. Dissolution features are very common in the lowlands. The
Gulf Coastal Lowlands are a series of plateaus representing Pleistocene sea level terraces
(Schmidt, 1997). Remnants of the Northern Highlands are left in the form of depositional
fill in sinkholes and as small hills and ridges scattered around the Gulf Coastal Lowlands
province (Denizman, 1998). The largest of these is the Brooksville Ridge.
The Brooksville Ridge has a total length of nearly 177 km (110 miles). The
Withlacootchee River Valley divides the ridge into two parts. The northern section is
smaller, only 80.5 km long (50 miles). The larger southern section is 96.6 km long (60
miles). The elevation of the Brooksville Ridge is highly variable, ranging from 22.88 -
61 m (75 - 200 ft) asl in short distances. The highest elevations of 53.38 -61 m (175 -
200 ft) asl are located in the southern half of the ridge. The ridge is topped with a few
meters of sand, which overly insoluble clastic sediments of the Bone Valley Formation
and the Hawthorn Group (White, 1970). Rolling plains dotted with sinkholes bound the
east side of the Brooksville Ridge. In the west a steeper scarp associated with a relic
terrace bounds the Brooksville Ridge (Femald and Purdum, 1998). Dissolution is the
dominant factor shaping the ridge to the east.
There are other smaller physiographic provinces in the study area such as the Mount
Dora Ridge, Cotton Plant Ridge, Sumter Uplands, Marion Uplands, Fairfield Hills and
the Coastal Swamps. These ridges and uplands are capped with insoluble elastics, which
offer resistance to erosion and dissolution of the underlying limestone.

9
Geologic Setting
Deep beneath the study area is crystalline basement rock, a fragment of the African
tectonic plate (Smith and Lord, 1997). This piece of the African plate provided a surface
for initiation of carbonate deposition and development of the Florida Platform. Carbonate
deposition dominated the platform starting in the Mid-Mesozoic (approximately 100 ma)
in peninsular Florida and in the early Cenozoic (approximately 60 ma) in panhandle
Florida (Scott, 1992).
The carbonate-producing environment of the Florida Platform was isolated from the
rest of the North-American continent by the Gulf Trough and the Suwannee Straits
(Georgia Channel System) (Randazzo, 1997). This enabled any siliciclastics eroded from
the Appalachians, to be transported into the Gulf of Mexico and not deposited onto the
platform. This was the case until the late Oligocene when the Suwannee current ceased
to flow resulting from a sea level drop (Randazzo, 1997). This allowed siliciclastic
sediments to fill the trough and spread onto the Florida Platform, suppressing carbonate
sedimentation. By the mid-Pliocene most of the Florida Platform was covered by
siliciclastic sediment. Not until the late Pliocene would a small portion of southernmost
Florida again support carbonate production (Denizman, 1998).
The Tertiary stratigraphy for the Florida Platform is comprised mostly of limestone
and dolostone units. They are, from oldest to youngest, The Cedar Keys Formation,
Oldsmar Limestone, Avon Park Formation, Ocala Limestone and the Suwannee
Limestone (Randazzo, 1997). The Avon Park Formation is the oldest formation that is
exposed in the study area (Middle Eocene) (Figure 2-2). The Ocala Limestone is an
Upper Eocene limestone that is at or very near the surface throughout the Gulf Coastal

10
Lowlands. Surface water drainage is limited across the Gulf Coastal Lowlands. Instead
water mostly percolates directly into the Ocala Limestone, which
Florida Subsurface Geology
Hi HOLOCENE SEDIMENTS
BEACH RIDGE AND DUNE
UNDIFFERENTIATED SEDS
TRAIL RIDGE SANDS
UNDIFFERENTIATED TQ SEDS
CYPRESSHEAD FM
COOSAWHATCHIE FM
STATENVILLE FM
UNDIFFERENTIATED HAWTHORN GP
SUWANNEE LS
OCALA LS
AVON PARK
N
20 0 20 40 Kilometers
Figure 2-2. Lithostratigraphy of the study area (Florida Department of Environmental
Protection, 2000).
comprises the Floridan aquifer system. The Suwannee Limestone, which is difficult to
differentiate from the Ocala Limestone because of its similar lithology, is exposed in a
small zone at the southern end of the study area (Randazzo, 1997). After a late
Oligocene/early Miocene drop in sea level, Hawthorn Group siliciclastics began to spread

11
across the platform. These sediments became the confining unit for the Floridan aquifer
system (Scott, 2001). The Hawthorn Group contains a number of formations. The
Statenville Fm, Coosawhatchie Fm. and the undifferentiated Hawthorn sediment
sequence, which are all middle Miocene, are exposed within the study area (Scott, 1997;
Randazzo, 1997). The Statenville Fm and Coosawhatchie Fm. sediments are comprised
of clay and clayey sand with some dolostone and limestone occurring in them. These
sediments also contain abundances of phosphorite grains, as high as 20 % in some areas.
The undifferentiated Hawthorn Group sediments are deeply weathered and contain few
phosphatic grains.
Above the Miocene sediments are Plio-Pleistocene sands (Scott, 1997). The sands,
from oldest to youngest, consist of the Cypresshead Formation, undifferentiated
Quaternary sediments, Trail Ridge Sands, undifferentiated sediments, and beach ridge
and dune deposits (Figure 2-2). These sediments, transported from the north, were
reworked in a shallow marine environment during Pleistocene sea level changes. Sea
level in the Pleistocene is thought to have been 20 m higher than present sea level (Scott,
1997). This left just the highest of present-day topography exposed. The submerged
sediments were reworked into marine terrace-like deposits (Scott, 1997).
Geologic Structure
Situated on North America’s passive margin, the Florida Platform is considered to be
in a relatively stable tectonic environment during the Mid-Mesozoic and Cenozoic.
However, there are features (Figure 2-3) that suggest the Florida Platform has undergone
faulting, uplift and subsidence over its history (Scott, 1997). There are three major
structural features that have affected deposition patterns in the study area.

12
The oldest features that have affected deposition in the study area are the Peninsular
Arch and Suwannee Strait (part of the Georgia Channel System) (Puri and Vernon,
1964). The Peninsular Arch forms the axis of Florida’s Peninsula. It trends northwest to
southeast and runs from southeastern Georgia to central Florida (Puri and Vernon, 1964).
The crest of this feature is located in central Florida in Union and Bradford counties,
which are located in the northeast comer of the study area. The Peninsular Arch became
a topographic high in the early Cretaceous and affected deposition until the late
Oligocene (Denizman, 1998).
A younger structural component that affected deposition in the study area is the Ocala
Uplift (Puri and Vernon, 1964). The uplift is approximately 370.3 km (230 miles) long
and 112.7 km (70 miles) wide where it is exposed. The crest of the uplift runs northwest
to southeast, parallel with the Peninsular Arch. Murray (1961) thought that the Ocala
Uplift was a piece of the Peninsular Arch, though geophysical data presented by Antoine
and Harding (1963) has shown that is not true (Puri and Vernon, 1964). The uplift is
extensively faulted and fractured (Schmidt, 1997). High angle, strike faults help to
flatten the platform and increase its width. The uplift has affected the deposition of
sediments since the early Miocene (Puri and Vernon, 1964). The Hawthorn Group
sediments on the crest of the uplift have been eroded exposing the Eocene carbonates.
This has greatly influenced the karstification on the platform (Denizman, 1998).

13
Figure 2-3. Structural features of Florida (from Scott, 1997).

14
Hydrogeologic Setting
Throughout the study area there are a total of three aquifer units (Scott, 1992).
Figure 2-4 shows the relationship among the three aquifer units and corresponding
stratigraphy. The uppermost is the Surficial aquifer. The Surficial aquifer, which
consists of permeable surficial, unconsolidated to poorly indurated siliciclastic deposits,
is present throughout the study area. These deposits range in age from Miocene to
Holocene. The Surficial aquifer exists in unconfmed conditions throughout the study
area, except in a few places where cementation reaches a point where permeability of the
sediments is reduced and locally confined conditions occur. In the Northern Highlands
section of the study area the Surficial aquifer is the sediment that overlies the Hawthorn
Group. These deposits can range from 16.1 - 48.3 m in thickness (10-30 ft) (Scott,
1992). In the Gulf Coastal Lowlands where the Hawthorn Group has been eroded, the
base of the surficial aquifer is the Ocala Limestone or Suwannee Limestone. There, the
Surficial aquifer is in direct contact with the Floridan aquifer system. The Surficial
aquifer is much thinner and not present in all areas of the lowlands. The Surficial aquifer
may also be pierced by karst depressions that funnel surface water directly into the
Floridan aquifer system (Scott, 1992).
The Intermediate aquifer is defined by the Southeastern Geological Survey (SEGS)
(1986, p. 4) as “...all rocks that lie between and collectively retard the exchange of water
between the overlying Surficial aquifer system and the underlying Floridan aquifer
system.” The Intermediate aquifer consists mostly of fine siliciclastic sediments and is

Panhandle Florida
North Florida
South Florida
System
Series
Stratigraphic Unit
Hydrogeologic
Unit
; Stratigraphic Unit
•
Hydrogeologic
Unit
| Stratigraphic Unit
Hydrogeologic
Unit
Quaternary
Holocene
Pleistocene
Undifferentiated
terrace marine and
fluvial deposits
Surtí cl al
aquifer
system
(Sand and
Undifferentiated
terrace marine and
fluvial deposits
Surfidal
aquifer
system
Terrace Deposits
Miami Limestone
Key Largo Limestone
Anastasia Formation
Fort Thompson Formation
Catoosahatchee Marl
Surfidal
aquifer
system
(Blscayne
aquifer) ^ '
Tertiary
Pliocene
Citronelle Formation
aquifer)
Miccosukee Formation
y
s
Undifferentiated
coarse sand and gravel
y
s
*
Intermediate
aquifer system
or intermediate
confining unit
^ -1
Tamlami Formation
y
y
Miocene
Alum Bluff Group
Pensacola Clay
Intracoastal Formation
Hawthorn Group
Chipóla Formation
Bruce Creek Limestone
St. Marks Formation
Chattahoochee Formation
Intermediate
confining unit
Floridan
aquifer
system
Hawthorn Group
St. Marks Formation
Hawthorn Group
Intermediate
aquifer system
or intermediate
confining unit
/
/
s
/
s
/
s
/
<
Oligocene
Chlckasawhay Limestone
Suwannee Limestone
Marianna Limestone
Bucatunna Clay
Suwannee Limestone
Floridan
aquifer
system
Suwannee Limestone
Floridan
aquifer
system
Eocene
Ocala Limestone
Lisbon Formation
Tallahatta Formation
Undifferentiated older Rocks
Sub-Floridan
confining
unit
Ocala Limestone
Avon Park Formation
Oldsmar Formation
Ocala Limestone
Avon Park Formation
Oldsmar Formation
y
y
y
Paleocene
Undifferentiated
Cedar Keys Formation
Sub-Floridan
Cedar Keys Formation
Sub-Floridan
Cretaceous
and older
Undifferentiated
y
y
y
Undifferentiated
confining
unit x'
y
y
confining ,,
unit ^
y
y
Figure 2-4. Relationship of regional hydrogeologic units to major stratigraphic units (from Femald and Purdum, 1998).

16
interlayered with carbonate strata. Throughout the study area the aquifer is comprised of
the Hawthorn Group. The water contained in these siliciclastic beds is under confined to
semi-confined conditions. The Intermediate aquifer in the study area is mainly found in
the Northern Highlands. Here the Intermediate aquifer reaches a thickness of 376 m (234
feet) (Scott, 1992). In the rest of the study area the Intermediate aquifer is present where
outlier hills and sinkhole-fill of Hawthorn Group sediments occur.
The Floridan aquifer system (Miller, 1997) is the principal aquifer throughout the
study area. Many communities rely on the Floridan for their water supply. In 1985 total
withdrawals from the aquifer in one day were 2.5 billion gallons (U.S. Geological
Survey, 1990). Even though withdrawals are so high from the Floridan, the hydraulic
heads have decreased very little. This shows the productivity and transmissivity
capability of the Floridan aquifer system.
The top of the Floridan aquifer system is regarded to be where the siliciclastic
layers of the intermediate aquifer decrease and permeable carbonate layers begin. This is
generally the top of the Suwannee Limestone or the Ocala Limestone, though it is
common that the boundaries of the aquifer are within a certain stratigraphic unit (Miller,
1997). The bottom of the Floridan aquifer system in the study area is where the
carbonate rocks hit the regionally persistent anhydrite beds of the Cedar Keys Formation
(SEGS, 1986). In the Northern Highlands the Floridan aquifer system is deeply buried
beneath the siliciclastic sediments of the Hawthorn Group. It is here that the Floridan is
under confined conditions and is recharged by downward migration of water through the
surficial and intermediate aquifers. It is also recharged through point recharge, where
karst features have breached the overlying sediment, allowing water to flow directly into

17
the Floridan aquifer system. In the Gulf Coastal Lowlands province of the study area the
Floridan aquifer system exhibits unconfined conditions. Here the Floridan aquifer system
is most vulnerable to pollution because it is at or very near the surface allowing water to
enter directly into the aquifer. Surface runoff is limited, except for large rivers. The
recharge in the Floridan aquifer system that occurs in this environment has caused
extensive dissolution. In this area karst geomorphology has usually reached a mature
stage with numerous depressions some of which have coalesced over time (Scott, 1992).
Ground water flow in this area is complex. The majority of flow is through the 200
- 300 ft. of saturated Ocala, Suwannee, and Avon Park carbonate units (Denizman and
Randazzo, 2000). Flow occurs in two ways, diffuse flow or conduit flow. With diffuse
flow the water slowly moves through interconnected pore spaces. Conduit flow moves
water through enlarged fractures, joints or bedding planes. This process is can be much
faster and can accommodate a larger volume of water in the same amount of time
compared to flow through interconnected pore spaces. The cavernous systems created by
this process cover large areas throughout the aquifer and occur in an anastomotic pattern
(Denizman and Randazzo, 2000). Evidence for such dissolution and ground water flow
can be seen in the study area, especially near the Cody escarpment where surface water
sinks underground and into the Floridan aquifer system before it then re-emerges on the
other side of the scarp through spring heads.

CHAPTER 3
SINKHOLE ACTIVITY
Sinkholes are the most common feature in karst topography (Lane, 1986).
Sinkholes are usually classified as closed depressions, where the surface material has
subsided or collapsed into underlying solution cavities (Beck and Sinclair, 1986).
Sinkhole activity is the result of the dissolution of limestone. This is a chemical process
where acidic rain and surface water drains down into the limestone through primary and
secondary openings in the rock. Primary openings are generally pore spaces and
openings that were formed during deposition. Secondary openings are joints, faults,
bedding planes, and erosional surfaces. When water passes through the atmosphere and
comes in contact with CO2, carbonic acid is formed. White (1986) gives the overall
reaction for the dissolution of limestone as
CaC03 + H20 + C02 <» Ca2+ + 2 HC03'
When the chemically aggressive water drains through these openings it dissolves
the limestone. This further enhances drainage and secondary porosity (Sinclair et al.,
1985). The natural development of the dissolution process is the formation of cavities in
buried limestone and sinkholes.
Figure 3-1 displays five sinkhole types common to the study area. Four of the
sinkhole types shown are active, and one is a buried or inactive sinkhole. The active
types are limestone solution, limestone collapse, cover subsidence and cover collapse
sinkholes (Sinclair et ah, 1985). The sinkholes are divided into the different categories
18

19
based on two characteristics. These characteristics are the thickness of overburden
material, and the time it takes for the sinkhole to form.
Figure 3-1. Types of sinkhole activity (Modified from Frank and Beck, 1991).

20
Limestone-Solution Sinkholes
Limestone solution sinkholes (Figure 3-1) occur when overburden thickness is less
than 7.5 m (25 feet), and limestone dissolution is most aggressive at the limestone
surface. The subsidence of the ground surface occurs slowly, roughly at the same rate as
the limestone is dissolved (Sinclair et al., 1985). Cavities are not common with this type
of sinkhole activity as the ground subsides gradually with limestone dissolution.
Limestone solution sinkholes are usually funnel shaped, with the slope of the sinkholes
depending on how easily the overburden material is transported downward towards the
sinkhole bottom (Sinclair et al., 1985).
Limestone-Collapse Sinkholes
Limestone collapse sinkholes (Figure 3-1) form when a cavity is formed beneath the
limestone surface and begins to expand until the material above the cavity can no longer
be supported and collapse occurs. Collapse happens quickly and can be catastrophic
(Sinclair et al., 1985). This type of sinkhole generally occurs across bedding planes, or
porous zones when the water table is below the upper surface of the limestone. This
accelerates dissolution at a point below the limestone surface. The cavity continues to
enlarge until the overlying limestone fails and collapse occurs (Sinclair et al., 1985).
Cover-Subsidence Sinkholes
In cover subsidence sinkholes (Figure 3-1) the overburden thickness can be 15.2 m (50
feet) or more (Sinclair et al., 1985). Not only does the overburden thickness determine
sinkhole morphology but the lithology of the overburden thickness is very important as
well. If the overburden material is incohesive and permeable sand, then cover-subsidence
sinkholes can occur. The difference in head between the sandy surficial aquifer and the
limestone aquifer determine the rate at which the water moves downward into the

21
limestone (Sinclair et al., 1985). As the limestone slowly dissolves, sand and clay can
ravel downward into voids in the limestone. These sinkholes are usually small in size
because the cavity does not reach a great size before it is filled with sand (Sinclair et al.,
1985).
Cover-Collapse Sinkholes
Cover-collapse sinkholes (Figure 3-1) occur when the overburden material is cohesive.
The cohesiveness gives the overburden material the strength to resist collapse over a
cavity. If the overburden material was a thick (more than 15.2 m) clay or clayey sand it
is possible that it could bridge a large cavity, even after the limestone roof had collapsed
(Sinclair et al., 1985). Eventually small pieces of the clay will begin to ravel from the
ceiling, until finally the clay will collapse. This will cause a potentially catastrophic and
fairly large sinkhole to occur. If the material is not as cohesive or thick, a smaller
sinkhole will probably be the result of the collapse (Sinclair et al., 1985).
Human-Induced Sinkholes
Sinkholes can be triggered by human activity. There are two causes of human induced
sinkholes. The first is excessive ground-water withdrawal, and the second is construction
activity (Sinclair et al., 1985).
Sinkholes Caused by Groundwater Withdrawal
The Floridan aquifer system is recharged when the head difference between the
Surficial aquifer and the Floridan aquifer system is great enough to cause leakage through
the confining layer. When ground-water is pumped at a rate that causes the
potentiometric surface of the Floridan aquifer system to drop, this initiates recharge from
the surficial aquifer. This creates an environment that is prone to sinkhole collapse
(Sinclair, 1982). In Tampa, Florida in May, 1964, withdrawal from the Section 21 well

22
field was increased from 5 Mgal/d to 14 Mgal/d in the time span of two months. Over
the next month, 64 new sinkholes were reported within one mile of the well field
(Sinclair, 1982).
Sinkholes Caused by Construction Activity
Construction practices can trigger sinkhole collapse in a variety of ways. The most
common method is by altering the natural drainage pattern. This is done in many
different ways, from construction of parking lots, large buildings or houses, to streets and
driveways. Instead of water draining by uniform seepage into the soil, it is channeled
into the soil and can create a solution pipe in the limestone bedrock. With a structure
covering the soils, raveling of material into a cavity may first be noticed when cracking
of the structure occurs. Later collapse into a cavity may be forthcoming (White, 1988).
Figure 3-2 shows the modifications of natural drainage and infiltration that can affect
sinkhole formation. Besides altering the natural drainage, the structures can cause
sinkhole collapse because of their weight. Buildings with large footprints or multiple
floors can exert significant downward force on the subsurface below.
Retention ponds or man made lakes are other structures that change natural runoff.
Whether they are constructed so that water can percolate down through the bottom, or to
permanently hold water, both can cause sinkhole activity. With retention ponds that let
water percolate through the bottom, focused drainage can cause soil piping in the
limestone. The retention ponds that are designed to hold water cause increased stress on
the soil and bedrock from the weight of the water. Both cases can cause sinkhole
subsidence or collapse. Figure 3-3 shows the distribution of man-induced sinkholes in
Missouri recorded from 1930 - 1976.

23
Figure 3-2. Soil piping induced by modification of natural runoff and infiltration
conditions (from White, 1988).
60 —
Natural c ol la p se s
To ta Is
Figure 3-3: Bar graph showing distribution of sinkhole collapses in Missouri based on
records kept since 1930 (from Williams and Vineyard, 1976).
Roof runoff

CHAPTER 4
METHODOLOGY
The initial effort of this study involved going through the Geohazards, Inc.,
Database. Geohazards, Inc., is a geophysical consulting company located in Gainesville,
Florida. The insurance industry as well as private homeowners contract with this
company to determine if sinkhole activity is occurring. Their database consists of
numerous reports from 1985 until the present. Parameters gathered from these reports for
possible consideration in this study were geophysical methods used, geophysical
evidence, depth to limestone, proposed cause of failure, presence of nearby karst, and
location information. The information was then converted to database form using
Microsoft Excel. This allowed the information to be imported into a Geographical
Information Systems (GIS) database.
GIS is software that allows spatial analysis of information. GIS is capable of
retrieving parameters that make up individual themes. Individual and multiple themes
can be retrieved and viewed in various combinations. This software can locate patterns of
sinkhole occurrence, as well as geologic conditions present. The GIS software programs
that were used to manipulate the data are Arcview, and Arcview Spatial Analyst
(programs created by Environmental Systems Research Inc. - ESRI, 1992-2000).
After the information was collected from the Geohazards Inc., database and
imported into Arcview, it had to be projected into a coordinate system. The information
was tied to street addresses. This is not a valid coordinate system for the GIS software.
Using a program called EZ Locate, the street addresses were converted into a latitude and
24

25
longitude coordinate system. When the points were viewed in the GIS it was apparent
that more data points were needed for the study to be more comprehensive. A second
data set was obtained from the Florida Geologic Survey website
(http://dep.state.fl.us/geology/gisdatamaps), though the information was produced by the
now defunct Florida Sinkhole Research Institute. This data set was ready to import into
the GIS. Though it lacked the parameters that the Geohazards Inc. database had
provided, the database already contained locations for the sinkholes in a latitude
longitude coordinate system. These two themes were then joined into one single sinkhole
theme so that spatial analyses could be done on all sinkholes simultaneously.
Since the themes used came from different sources, they were in different projections.
Arcview Projection Utility was used to reproject the themes. Once the themes were
projected into a common coordinate system and ready to display in the GIS, other themes
or layers could be overlain to recognize any correlations. The following list shows the
themes used for possible correlation with the sinkhole theme and the source the data was
obtained from.
Table 4-1. Theme name and website location
Theme Name
Source Website for Theme
Florida County Boundaries
http://www.fgdl.org/
Depth to the Top Surface of the
Floridan aquifer system
ftp.dep.state.fl.us/pub/gis/data
Physiographic Provinces
http ://www. swfwmd. state. fl .us/data/ gis
Recharge and Discharge Areas of
the Floridan aquifer system
http://www.fgdl.org/
Florida Surficial Geology
http://www.fgdl.org/
Florida Subsurface Geology
ftp.dep.state.fl.us/pub/gis/data
Population Density by U.S. Census
Block Group
http ://www.census .go v/geo/www/cob/bg1990.html

26
These themes came from different sources on the Internet, such as water management
districts, geologic surveys, and the Florida Geographic Data Library (FGDL). All the
themes were reprojected into the coordinate system used by FGDL. The parameters for
this coordinate system include the current coordinate system name, projection method
used to obtain that coordinate system, and the latitudinal and longitudinal origins used for
the coordinates.
Table 4-2. Theme parameters
Geographic Coordinate System
GCS North American 1983
Base Projection
Albers
Central Meridian
O
00
Central Parallel
24°
Standard Parallel 1
24°
Standard Parallel 2
31.5°
With all of the themes now in a common coordinate system, they were displayed
with the sinkhole theme in Arcview. A visual comparison was done to establish which
themes had the best correlation, and where these correlations were most evident. This
was done so that a study area could be defined. After the study area was defined all the
themes were clipped (see Appendix A for definition) to that area or “polygon”. This
means that all the points and polygons outside the study area and the data associated with
them would be clipped or deleted from the current themes.
Using the sinkhole theme, a spatial analysis of the sinkholes was performed to
search for correlations with the different parameters of the other themes. The sinkhole

27
theme was spatially joined with the other themes one at a time. Spatially joining two
themes tied the parameter (polygon) information of one theme to the location of the
sinkhole (point). The “Find Area” function of Arcview’s Spatial Analyst was used to
recalculate the area of the new polygons created after clipping all of the themes.
Information from the spatial joins was combined with the area values. This yielded
sinkholes per km2 for each parameter such as geologic formation, recharge area, or
physiographic region. Tables from the themes were exported into Microsoft Excel after
being spatially joined. Mathematic functions were performed to determine sinkhole
density per parameter value. The total number of sinkholes was divided by the total area
for each polygon. This yielded sinkhole density for each parameter. Also the number of
sinkholes for each parameter was divided by the total number of sinkholes for the study
area. This yielded relative frequency of sinkhole occurrence for each parameter. Charts
were used to display the results.

CHAPTER 5
RESULTS
Depth to the Top Surface of the Floridan Aquifer System
The depth to the surface of the aquifer theme was taken from data used for
DRASTIC calculation of the Floridan Aquifer (Figure 5-1). DRASTIC is a measure of
aquifer vulnerability. DRASTIC was developed by the Florida Department of
Environmental Protection. This process is used for pesticides so that the most vulnerable
areas of the aquifer can be protected from ground water contamination. The data for
depth to the aquifer are recorded by impact on the aquifer rather than depth relative to sea
level. An exact depth map was used to match relative depth vulnerability polygons to the
exact depth to the aquifer. Table 5-1 shows the sinkhole density values and relative
frequency of sinkhole occurrence values for each depth category. Figure 5-2 shows the
sinkhole densities for each category of depth to the Floridan Aquifer surface. There is a
strong correlation between depth to the aquifer and sinkhole distribution. Relative
frequency of sinkhole occurrence also shows a strong correlation (Figure 5-3). As the top
of the aquifer approaches the ground surface, sinkhole density and relative sinkhole
frequency increase steadily.
28

20 0 20 40 Kilometers
o
Sinkhole Locations
A/ Major Rivers
Depth to Floridan aquifer system
> 100 ft (>30.5 m)
75-100 ft (22.9 - 30.5 m)
50 - 75 ft (15.2-22.9 m)
30 - 50 ft (9.1 -15.2 m)
15-30 ft (4.5-9.1 m)
0-15 ft (0-4.5 m)
Figure 5-1. Depth to the surface of the Floridan aquifer system (Florida Department of
Environmental Protection, 2000a).
Table 5-1. Depth to Floridan aquifer system
.2 Number of
Sinkholes
Aquifer Depth
Total Area km
Sinkholes/ km2 Relative Frequency
> 100ft(> 30.5 m)
75- 100 ft (22.9-30.5 m)
50 -75 ft (15.2 -22.9 m)
30-50 ft (9.1 -15.2 m)
15-30 ft (4.5-9.1 m)
0-15 ft (0-4.5 m)
4629.59
26
5.62’3
3.55%
1166.91
34
2.9T2
4.64%
1849.89
54
2.92’2
7.38%
3061.92
127
4.15’2
17.35%
3460.03
152
4.39"2
20.77%
6450.28
339
5.26'2
46.31%

J L
30
0 -15 ft (0- 4.5 m) [
5.26'
0)
o
•fc
3
CO
Í-.
©
15-30 ft (4.5-9.1 m) [
14.39"2
30-50 ft (9.1 -15.2 m) [
¡I 50-75 ft (15.2-22.9 m) [
3
O’
<
O 75- 100 ft (22.9-30.5 m) [
> 100 ft (> 30.5 m)
Q.
a
|:
I I:
â–¡ 5.6:
r
i 4.15"-
2.92-
2.91
-2
0.000 0.010 0.020 0.030 0.040 0.050 0.060
Sinkholes / km2
Figure 5-2. Sinkhole density chart for depth to the Floridan aquifer system
a>
o
t
3
0)
L-
3
O’
<
o
a
a>
a
0-15 ft (0-4.5 m) [
146.31%
15-30 ft (4.5-9.1 m) [
I 20.77%
30-50 ft (9.1 -15.2 m) [
17.35%
50-75 ft (15.2-22.9 m) [
I 7.38%
75 - 100 ft (22.9 - 30.5 m) l 14.64%
> 100 ft (> 30.5 m) â–¡ 3.55%
0% 10%
20% 30% 40%
Percentage of sinkholes
50%
Figure 5-3. Relative frequency of sinkhole occurrence for aquifer depth

31
Recharge and Discharge Areas of the Floridan Aquifer System
The recharge and discharge theme displays the location and amount of water that is
entering or exiting the aquifer in the time span of one year. Data for this theme were
obtained from the Southwest Florida Water Management District (SWFWMD). The
categories and units shown were created by the SWFWMD. The theme was clipped from
a statewide coverage to the study area (Figure 5-4), and then the sinkholes were spatially
joined to the theme.
The hypothesis to be tested was that recharge environments are more acidic so the
dissolution of the limestone is more extensive, and sinkhole activity more prevalent. In
discharge environments, as the water passed through primary and secondary openings in
the limestone, it chemically reacted with the limestone. Limestone interacts with the
water neutralizing the carbonic acid. This tends to increase the pH of the water so that
dissolution is not as extensive in discharge areas. Recharge was categorized as less than
one inch per year, between 1-10 inches per year, and greater than 10 inches per year.
Discharge values were categorized as less than 1 inch per year, between 1 - 5 inches per
year, and greater than five inches per year. When comparing data between the discharge
and recharge categories, discharge values were lower for both the relative frequency of
sinkhole occurrence and for sinkhole density (Table 5-2). For the three recharge
categories, the average sinkhole density and average relative frequency of sinkhole
occurrence was 2.98'2 sinkholes/km2 and 29.48% respectively. The average sinkhole
density and relative frequency of sinkhole occurrence for the three discharge categories
was 2.03'2 sinkholes/km2 and 3.85% respectively, thus confirming the hypothesis.

32
Table 5-2. Recharge and discharge
Recharge/
Discharge Zone
Number of
Sinkholes
Total Area
(km2)
Sinkholes/
(km2)
Relative
Frequency
Avg.
Sinkhole
density
Avg. Relative
Frequency
Discharge > 5
36
2101.16
1.7T2
4.90%
Discharge 1 - 5
47
1167.56
4.03'2
6.39%
2.03'2
3.85%
Discharge < 1
2
590.44
3.39‘3
0.27%
Recharge >10
388
10093.43
3.84'2
52.79%
Recharge 1-10
260
5235.83
4.97‘2
35.37%
2.98"2
29.48%
Recharge < 1
2
1475.65
1.36"3
0.27%
Figure 5-4. Recharge and discharge in inches per year of the Floridan aquifer, with
sinkhole locations (Southwest Florida Water Management District, 2002).

33
It was expected that the “Recharge > 10 inches/year” category would have the
greatest sinkhole density. However, it was the “Recharge 1-10 inches/year” category,
which possessed the greatest sinkhole density at 4.97’ sinkholes/ km (Figure 5-5). This
is attributed to significant differences in area for these recharge categories. Table 5-2
shows the total area for each category.
Concentrations of sinkhole occurrence in the recharge zones occur along the
“Recharge > 10 inches/year” category that runs northwest to southeast through the study
area (Figure 5-4). This reflects the acidic environment mentioned earlier that occurs in
the high recharge zone. The concentration of sinkholes located in the southwest comer of
the study area is located in the “Recharge 1-10 inches/year” category. This is still an
acidic environment, though not as much as the “Recharge > 10 inches/year” category. A
possible reason for a concentration in this area may be the limited thickness of the
surficial sediments as water recharges the underlying carbonate unit (Floridan aquifer
system).
The “Discharge 1 - 5 inches/year” category yielded the highest sinkhole density
values of the three discharge zones (Figure 5-5); at 4.03'2 sinkholes/ km2, it was an order
of magnitude larger than the next closest category. This discharge category also had the
highest relative frequency of sinkhole occurrence value, at 6.39% (Figure 5-6).
The discharge zones in the study area coincide with rivers. The “Discharge > 5
inches/year” category, which is the zone of highest discharge in the study area, occurs
along the Suwannee and Santa Fe rivers (Figure 5-4). The directional trend of the
concentration of sinkholes located north of where the Suwannee River and the Santa Fe
River converge was thought to be the influenced by the discharge along the Suwannee

34
and Santa Fe rivers. Though the rivers may be responsible for the occurrence of
sinkholes in that area, the directional trend of this concentration is influenced by a bias
found in the sinkhole database. The Florida Department of Transportation (FDOT) was
the source of the sinkhole data recorded in this area, thus giving the directional trend
along a highway. However, these data are still useful for the general location of sinkhole
activity.
Discharge > 5
Discharge 1 - 5
Discharge < 1
Recharge > 10
Recharge 1-10
Recharge < 1
0.00 0.01 0.02 0.03 0.04 0.05 0.06
Number of Sinkholes / km2
i.|r2
I
14.03"2
| 13.39~3
I3
,84'2
. ;
l
[] 1.36'3
Figure 5-5. Sinkhole density for recharge and discharge zones

35
Discharge > 5
Discharge 1 - 5
Discharge < 1
Recharge >10
Recharge 1-10
Recharge < 1
0% 10% 20% 30% 40% 50% 60%
Percentage of Sinkholes
Figure 5-6. Relative frequency of sinkhole occurrence for recharge and discharge zones
I 14.90%
6.39%
| 0.27%
j 0.27%
1 52.79°/
35.37%
Physiographic Provinces
The physiographic provinces theme displays the different morphological features
throughout the study area (Figure 5-7). The largest province was the Gulf Coastal
Lowlands. These lowlands consist of bare or thinly covered limestone and make up more
than 7000 km2 of the study area. The total number of sinkholes in the Gulf Coastal
Lowlands province was 360, almost 300 more than any other province in the study area
(Table 5-3). The large area skewed the sinkhole density value for the Gulf Coastal
Lowlands, which was 5.09'2 sinkholes/km2 (Figure 5-8), but relative frequency of
sinkhole occurrence yielded a strong correlation with the physiographic provinces (Figure
5-9). It shows that the Gulf Coastal Lowlands where the Ocala Limestone is near the
ground surface has the highest relative frequency of sinkhole occurrence and the
provinces that have the Ocala Limestone slightly deeper have the next highest relative
frequencies of sinkhole occurrence (Figure 5-9).

36
o
Sinkhole Locations
Geomorphic Configuration
Highlands
Hills
Lowlands, Gaps and Valleys
Plains
Ridges
Swamps
Uplands
Cody Scarp
Fairfield Hills
Marion Upland
Coastal Swamps
Sumter Upland
Ocala Hill
Cotton Plant Ridge
Tsala Apopka Plain
N
20 0 20 40 Kilometers
Figure 5-7. Physiographic provinces with sinkhole locations (Florida Geographic Data
Library, 1997).

37
Table 5-3. Physiographic province
Province Name
Number of Sinkholes
Total Area
(km2)
o- i u i / /i 2v Relative
Sinkholes/(km ) Frequency
Alachua Lake Cross Valley
0
76.28
0
0.00%
Bell Ridge
0
100.23
0
0.00%
Brooksville Ridge
61
1468.91
4.15
8.25%
Central Valley
62
1840.57
3.37"2
8.39%
Coastal Swamps
25
876.38
2.85"2
3.38%
Cotton Plant Ridge
4
140.15
2.85
0.54%
Dunellon Gap
1
110.88
9.02"J
0.14%
Fairfield Hills
13
493.19
2.64'z
1.76%
Gulf Coastal Lowlands
360
7067.81
5.09"2
48.71%
High Springs Gap
13
149.91
8.67'2
1.76%
Kenwood Gap
0
5.32
0
0.00%
Marion Upland
0
360.13
0
0.00%
Martel Hill
0
7.10
0
0.00%
Mount Dora Ridge
0
488.75
0
0.00%
Northern Highlands
57
5032.09
1.13"2
7.71%
Ocala Hill
34
89.59
3.80"
4.60%
St. Johns River Offset
0
17.74
0
0.00%
Sumter Upland
36
684.78
5.26"2
4.87%
Trail Ridge
0
18.63
0
0.00%
Tsala Apopka Plain
24
280.30
8.56"2
3.25%
Western Valley
49
826.09
5.93"2
6.63%

38
(A
CD
O
c
â– >
o
Q.
re
i_
D)
O
"5
Alachua Lake Cross Valley
Bell Ridge
Brooksvllle Ridge
Central Valley
Coastal Swamps
Cotton Plant Ridge
Dunellon Gap
Fairfield Hills
Gulf Coastal Lowlands
High Springs Gap
Kenwood Gap
Marion Upland
Martel Hill
Mount Dora Ridge
Northern Highlands
Ocala Hill
St. Johns River Offset
Sumter Upland
Trail Ridge
Tsala Apopka Plain
Western Valley
Sinkholes/km2
Figure 5-8. Sinkhole density chart for physiographic provinces

39

o
c
>
o
1_
0.
o
E
o.
re
i_
O)
o
'55
>»
Alachua Lake Cross Valley
Bell Ridge
Brooksville Ridge
Central Valley
Coastal Swamps
Cotton Plant Ridge
Dunellon Gap
Fairfield Hills
Gulf Coastal Lowlands
High Springs Gap
Kenwood Gap
Marion Upland
Martel Hill
Mount Dora Ridge
Northern Highlands
Ocala Hill
St. Johns River Offset
Sumter Upland
Trail Ridge
Tsala Apopka Plain
Western Valley
0% 10% 20% 30% 40% 50% 60%
Percentage of Sinkholes
Figure 5-9. Relative frequency of sinkhole occurrence for physiographic province
Florida Surficial Geology
The surficial geology theme represents lithostratigraphy as it is exposed at the
surface. The Ocala Limestone had the largest total number of sinkholes with 448 (Figure
5-10, Table 5-4). The Ocala Limestone had the second highest sinkhole density at 5.4L4
sinkholes/km2. The unit with the highest sinkhole density was the Beach Ridge and Dune
sediment sequence at 1 ,T2 sinkholes/km2 (Figure 5-11). Not only did the small extent of

40
this unit cause its sinkhole density to be greater, but the Beach Ridge and Dune sediment
sequence in eastern Citrus County, where the large concentration of sinkholes is located,
is very thin from 25 feet thick to not present. Directly beneath the Beach Ridge and Dune
o Sinkhole Locations
| County Boundaries
Florida Surficial Geology
HI HOLOCENE SEDIMENTS
BEACH RIDGE AND DUNE
UNDIFFERENTIATED
TRAIL RIDGE SANDS
UNDIFFERENTIATED TQ SEDS
CYPRESSHEAD FM
COOSAWHATCHIE FM
STATENVILLE FM
UNDIFFERENTIATED HAWTHORN GP
SUWANNEE LS
OCALA LS
AVON PARK FM
Figure 5-10. Florida surficial geology with sinkhole locations (Florida Geographic Data
Library, 1998)

41
Table 5-4. Florida surficial geology
Formation Name
Number of Total Area
Sinkholes (km2)
Sinkholes/
(km2)
Relative Frequency
Avon Park Fm
9
1845
4.88'3
1.23%
Beach Ridge and Dune
50
4530
1.10'2
6.83%
Coosawhatchie Fm
89
22,532.50
3.95'J
12.16%
Cypresshead Fm
5
12722.5
3.9S"4
0.68%
Undifferentiated Hawthorn Group
22
9980
2.20 J
3.01%
Holocene Sediments
1
2542.5
3.93"4
0.14%
Ocala Limestone
448
82,740.00
5.41'3
61.20%
Statenville Fm
2
3495
5J2"4
0.27%
Suwannee Limestone
1
925
1.08'3
0.14%
Undifferentiated Sediments
80
32617.5
2.45'3
10.93%
Undifferentiated TQ Sediments
25
16810
1 49"3
3.42%
Avon Park Fm
Beach Ridge and Dune
Coosawhatchie Fm
Cypresshead Fm
Undifferentiated Hawthorn Group
Holocene Sediments
Ocala Limestone
Statenville Fm
Suwannee Limestone
Undifferentiated Sediments
Undifferentiated TQ Sediments
I"3
I 14.88
I 13 95-3
â–¡ 3.93"4
J 2.20"3
J
â–¡ 3.9S"4
Zl 5.41
â–¡ 5.72-
I 110
8"3
J 2.45 3
â–¡ 1
.49 3
-
0.000 0.002 0.004 0.006 0.008 0.010 0.012
Number of Sinkholes / km2
Figure 5-11. Sinkhole density chart for surficial geology

42
sediment sequence in this area is the Ocala Limestone. The Coosawhatchie Formation,
which is part of the Hawthorn Group, is another thin formation that overlies the Ocala
Limestone. Near the edge of the Cody Scarp water drains through sinkholes in the thin
Hawthorn Group sediments down into the Ocala Limestone. This further demonstrates
that the Ocala Limestone has a strong correlation with sinkhole development. The unit
with the third highest sinkhole density was the Avon Park Formation at 4.88'3
sinkhole/km2 (Figure 5-11). The high density is a reflection of the small area where the
Avon Park Formation is exposed. When the relative frequency of sinkhole occurrence
was analyzed, the correlation was more apparent (Figure 5-12). The Ocala Limestone
had the greatest relative sinkhole frequency with the Coosawhatchie Formation and
Undifferentiated Sediments having the next highest values. This further illustrates the
point that the Ocala Limestone has the highest probability of sinkhole occurrence, and the
thin formations that overly them have the next highest probability for sinkhole
occurrence. Clearly there is a correlation between Surficial Geology and sinkhole
distribution.

43
Avon Park Fm Q 1.23%
Beach Ridge and Dune I 16.83%
â–¡ 12.16%
Coosawhatchie Fm
Z>
o
!E
Q.
re
L_
O)
‘■5
re
*-*
U)
o
Cypresshead Fm 0 0.68%
Undifferentiated Hawthorn Group â–¡ 3.01 %
Holocene Sediments | 0.14%
J
Ocala Limestone I
Statenville Fm | 0.27%
Suwannee Limestone |0.14%
Undifferentiated Sediments
Undifferentiated TQ Sediments
] 10.93%
] 61.20%
3.42%
0% 10% 20% 30% 40% 50% 60% 70%
Percentage of Sinkholes
Figure 5-12. Relative frequency for sinkhole occurrence with surficial geology
Florida Subsurface Geology
The Florida Subsurface Geology theme is almost identical to the Florida Surficial
Geology theme. There is a slight change in the area of the units. Tables 5-4 and 5-5
show that the values are nearly the same. Because the values are so close, the
interpretation of the data is consistent with that for the Florida Surficial Geology theme.
Figure 5-13 displays the distribution of Florida subsurface geology with sinkhole
location. Sinkhole density and relative frequency of sinkhole occurrence are in Figures
5-14 and 5-15, respectively.

44
o Sinkhole Locations
| County Boundaries
Florida Subsurface Geology
HI HOLOCENE SEDIMENTS
BEACH RIDGE AND DUNE
UNDIFFERENTIATED SEDS
TRAIL RIDGE SANDS
UNDIFFERENTIATED TQ SEDS
CYPRESSHEAD FM
HI COOSAWHATCHIE FM
STATENVILLE FM
UNDIFFERENTIATED HAWTHORN GP
SUWANNEE LS
OCALA LS
AVON PARK
Kilometers
Figure 5-13. Florida subsurface geology with sinkhole locations (Florida Department of
Environmental Protection, 2000b).

45
Table 5-5. Florida subsurface geology
Formation Name
Number of
Sinkholes
Total Area
(km2)
Sinkholes/
(km2)
Relative Frequency
Avon Park Fm
9
1845
4.88'3
1.23%
Beach Ridge and Dune
50
4587.5
1.09"2
6.82%
Coosawhatchie Fm
91
23932.5
3.80"J
12.41%
Cypresshead Fm
5
12722.5
3.93’4
0.68%
Undifferentiated Hawthorn Group
22
9980
2.20’J
3.00%
Holocene Sediments
1
2542.5
3.93'4
0.14%
Ocala Limestone
446
79797.5
5.59 3
60.85%
Statenville Fm
2
9702.5
2.06-4
0.27%
Suwannee Limestone
1
925
1.08'3
0.14%
Undifferentiated Sediments
81
39350
2.06’J
11.05%
Undifferentiated TQ Sediments
25
22347
1.12 3
3.41%
Avon Park Fm [
Coosawhatchie Fm
I"3
I 14.88
] 3.80"'
c
D
o
!E
a
re
L.
O)
03
L.
4->
O
Cypresshead Fm [] 3.93"'
Undifferentiated Hawthorn Group
2.20"
Holocene Sediments [] 3.93"‘
Ocala Limestone
] 5.59"'
1.09"'
Statenville Fm 0 2.06"4
r
Suwannee Limestone â–¡ i.d8"3
Undifferentiated Sediments | 12.06'3
Undifferentiated TQ Sediments | 11.12"3
0.000 0.002 0.004 0.006 0.008 0.010 0.012
Number of Sinkholes / km2
Figure 5-14. Sinkhole density chart for Florida subsurface geology

Lithostratigraphic Unit
46
Percentage of Sinkholes
Figure 5-15. Relative frequency of sinkhole occurrence for subsurface geology

47
Population Density by US Census Block Group
The theme shows population density (people per sqmi) divided into separate US
Census blocks. The US Census data is from the 1990 Census. Figures 5-16 and 5-17
20 0 20 40 Kilometers
° Sinkhole Locations
Population Density
rn o - 29.6
29.6 - 76.3
76.3-202.9
202.9-558.4
558.4- 1943
1943-27029
Figure 5-16. Population density in people per sqmi (U.S. Census Bureau, 1990)

48
show that the sinkhole distribution data correlates well with population density. One
factor that can possibly bias this result is that all the sinkhole locations contained in the
two databases are reported sinkholes. Sinkholes occurring in an area of low population
(farms, etc.) may not be reported. In a very large neighborhood, a confirmed sinkhole
under one home, may trigger other homeowners to have their properties investigated as
well, leading to possible detection and reported concentration of sinkholes in a small
¡T
»
c
o
'5
TO
3
Q.
O
0.
8000-9000
6000-7000
3000-4000
2000-3000
1000-2000
900-1000
800-900
700-800
600-700
500-600
450-500
400-450
350-400
300-350
250-300
200-250
150-200
100-150
50-100
0-50
0.000
0.010 0.020 0.030 0.040 0.050
Averaged Sinkholes / sq. mile
0.060 0.070
Figure 5-17. Sinkhole density chart for population density
area. When relative frequency of sinkhole occurrence (Figure 5-18) was analyzed, the
results were inverse to those of sinkhole density (Figure 5-17). The highest relative
sinkhole occurrence is in areas of low population density. Using U.S. census blocks to
gain population density is probably the cause for this inversion. As you near a city or a
place where population density begins to significantly increase, the U.S. Census blocks

49
decrease in area. This causes the sinkhole densities to increase even though the total
number or relative frequency of sinkhole occurrence is decreasing.
8000-9000
6000-7000
3000-4000
2000-3000
1000-2000
900-1000
« 800-900
e 700-800
. 600-700
O' 500-600
* 450-500
c 400-450
.2 350-400
TS 300-350
3 250-300
Q. 200-250
P 150-200
100-150
50-100
0-50
0% 5% 10% 15% 20% 25%
Percentage of Sinkholes
Figure 5-18. Relative sinkhole frequency for population density
* The data table for sinkhole density correlated with population is located in Appendix B
because of its large size.

-L
CHAPTER 6
DISCUSSION
Geographic Information Systems (GIS) were employed to analyze various factors or
themes to find correlations with sinkhole distribution in an efficient visual format. Not
only does the GIS significantly reduce analysis time, it performs the analyses in much
greater detail than human interpretation would yield. No single influential factor
controlling sinkhole distribution was evident from the use of the GIS. A complex
combination of factors (themes) determine sinkhole occurrence and distribution.
The hypothesis, “GIS application of sinkhole locality data will identify patterns of
occurrence”, was supported as strong correlations were made between the locality data
and the combination of factors responsible for sinkhole occurrence. GIS displayed
different themes with sinkhole locations, as well as created charts that quantified how
many sinkholes occurred in each category. GIS displays can be employed in the
determination of the correlations between each theme and sinkhole distribution.
Although some correlations might be visually confirmed, assessment of other factors may
be needed to validate them. This was true for several of the themes used. The Florida
Surficial Geology and Florida Subsurface Geology themes showed a definite visual trend
with sinkholes occurring in the Ocala Limestone. The sinkhole density data on the other
hand shows the Beach Ridge and Dune sediment sequence to have the highest density,
with the Ocala Limestone much lower. The large area where the Ocala Limestone is
50

51
exposed affects the lower sinkhole density. For this reason relative frequency analysis
was employed for each theme to overcome the error caused by differences in area.
Another bias encountered while analyzing data was with the Florida Sinkhole
Research Institute’s sinkhole database. Figure 6-1 shows sinkhole distribution that seems
to follow the census block divisions. Recognizing this is not a geologic control the
metadata for the FSRI database were consulted. It was discovered that half of FSRI’s
sinkhole locations come from the Florida Department of Transportation. This creates a
bias in the data, especially if attempting to predict directional trends in sinkhole
High
J 1943 - 27029
• Sinkhole Locations
Population Density
0 - 29.6
29.6 - 76.3
76.3-202.9
202.9- 558.4
558.4- 1943
Figure 6-1. Population theme showing sinkhole correlation with SR - 27 (U.S. Census
Bureau, 1990)

52
distribution. Despite this bias the data are useful. The data may trend along roads, but
still displays the location of sinkhole activity, which is utilized in sinkhole distribution
analysis.
With those qualifications known, the themes were analyzed and charts created to show
what categories of each theme contained the highest sinkhole densities. To test the
hypothesis that “a complex combination of factors determine sinkhole distribution” GIS
polygons of the categories with the highest sinkhole densities from each theme were
extracted. This yields polygons that the data determined as factors for sinkhole
distribution. These polygons were combined to display together in the same view.
Figure 6-2 illustrates the complexities of making GIS correlations between where the
factors or separate themes overlap each other and where sinkhole densities occur.
Sinkhole density appears to be influenced by the interaction between the “Recharge 1 - 5
inches/year” zone and the “Depth to Floridan aquifer system less than 4.5 m” zone. The
circled areas of high sinkhole density are located where these two zones overlap (Figure
6-2). The concentration in east Dixie and northwest Levy County straddles the discharge
zone of the Suwannee River, although the majority of the sinkholes occur within the
“Recharge 1-5 inches/year” polygons (Figure 6-2). There are two concentrations of
sinkholes in Citrus County. They are divided by a zone that has aquifer depth increasing
from the surface to 30.5 m depth (0-100 ft.). The limited sinkhole occurrence in this
dividing zone is a result of the control that depth to the aquifer has on sinkhole
development. The western Citrus County concentration has the highest sinkhole density
in the study area (Figure 6-2). The other two high-density concentrations of sinkhole
occurrence are in central Alachua and Marion Counties.

53
» Sinkhole Locations
H County Boundaries
Recharge 1 to 5 in/yr
| | Population greater than 600 people/sqmi
| | Beach Ridge and Dune
| | Depth to Floridan aquifer system less than 4.5 m
| 1 Ocala Hill
East Dixie &
Northwest Levy
County
West Citrus
County
20 0 20 40 Kilometers
Central Alachua
County
Central Marion
County
N
Figure 6-2. Highest sinkhole density polygons with sinkhole locations
The high sinkhole density in these areas is attributed to the fact that they are the
locations of major cities. As a result sinkhole density is increased because of word of
mouth investigations as mentioned earlier.
Denizman and Randazzo (2000) performed analyses on sinkhole distribution and
morphometry in the Lower Suwannee River Basin. Sinkhole locations were obtained
from topographic maps and digitized into a GIS environment. These non-reported

54
sinkholes were then added to a database of reported sinkholes. For an area much smaller
than this project there were over 25,000 sinkholes used in the study. The large number of
sinkholes would decrease the amount of error in sinkhole distribution analysis.
Figure 6-3 shows the polygons with the highest relative frequency of sinkhole
occurrence. It is difficult to see where the different polygons overlap in Figure 6-3
because they cover the same areas, but in computer manipulated GIS operations it can be
clearly recognized. For example, where the surface of the Floridan aquifer system is less
than 4.5 meters deep (yellow area of Figure 6-3), Ocala Limestone is the surficial
lithostratigraphic unit that is present. When population density is set to less than 50
people per sqmi, the polygon covers the entire study area except for the main cities in
each county. Even though the relative frequency polygons cover a large part of the study
area, they still show that sinkhole distribution lies in areas where polygons overlap.
Figure 6-3 displays three major concentrations of sinkhole occurrence (circled). They
are central Alachua County, central Marion County and western Citrus County. The
Alachua and Marion County concentrations overly the ‘recharge greater than 10 inches
per year’ and ‘Ocala Limestone' polygons. In these two locations it appears the greatest
potential influence on sinkhole occurrence is a combination of recharge, and surficial and
subsurface geology. The Citrus County concentration is slightly different from the other
two because it has more factors to influence sinkhole distribution. Here the sinkhole
concentration overlies the Ocala Limestone, Gulf Coastal Lowlands, Depth to Floridan
aquifer system less than 4.5 meters, and Surficial and Subsurface Geology polygons.
Although, it is not possible to determine a single factor controlling sinkhole distribution,
generalizations can be made.

55
Sinkhole Locations
Depth to Floridan Aquifer less than 4.5 m
Ocala Limestone
Gulf Coastal Lowlands
Recharge Greater Than 10 in/yr
Population less than 50 people/sqmi
County Boundaries
Central Alachua
County
Central Marion
County
West Citrus
County
20 0 20 40 Kilometers
N
Figure 6-3. Highest relative frequency of sinkhole occurrence polygons with sinkhole
locations.
The factors that potentially have the greatest influence on sinkhole distribution in the
study area are surflcial geology, subsurface geology, recharge to the Floridan aquifer
system, and depth to Floridan aquifer system. When recharge to the aquifer is high and
limestone units (aquifer) are near the ground surface, sinkhole development increases.
If there are no near surface carbonate units (aquifer) present or recharge or discharge
is very low, sinkhole development is less. Also areas that already have these factors for

56
sinkhole development may see a further increase if population density continues to
increase.
The correlations obtained by GIS manipulation of the sinkhole databases can be used
for sinkhole risk assessment. Sinkhole risk assessment identifies what areas have the
highest potential for future sinkhole development. To help identify the zones for future
sinkhole development in the study area, a “distance to the nearest sinkhole” map was
created (Figure 6-4). The map shows sinkhole locations with buffer zones surrounding
them, in one-kilometer increments. The red zones, which indicate a sinkhole within one
kilometer, may have the highest potential for sinkhole development. The orange zones,
which indicate a sinkhole within two kilometers, may have the next highest potential, and
the yellow zones at three kilometers may have the third highest potential for future
sinkhole development.
Of the four concentrations of sinkhole occurrence (circled in Figure 6-4), western
Citrus County has the highest potential for future sinkhole development. The red zone
covers nearly the whole west side of Citrus County. This can be attributed to the
proximity of the Floridan aquifer system to the ground surface. Because it is near the
surface, it is exposed to more chemically aggressive water, as opposed to the central
Alachua and Marion County concentrations, where aquifer depth is greater. With an
elevated level of dissolution the extent of sinkhole development should continue to
increase and coalesce into the orange and yellow zones.
The concentration of sinkholes in central Marion County will also continue to spread.
Sinkhole development in this area will migrate north, south and to the west because of the
Ocala Limestone exposure and the depth to Floridan aquifer system

57
Distance to nearest sinkhole
0 -1 km
1 - 2 km
2-3 km
County Boundaries
East Dixie &
Northwest Levy
County
Central Alachua
County
Cody Scarp
Central Marion
County
West Citrus
County
20 0 20 40 Kilometers
N
Figure 6-4. Distance to nearest sinkhole map
in the area. The discharge zone of Ocklawaha River bounds eastward migration of
sinkhole development in central Marion County (Figure 5-4). In this discharge zone the
depth to the Floridan aquifer system increases to over 30.5 m (100+ ft.) (Figure 5-1).
When the surface of the Floridan aquifer system is this deep sinkhole development is

58
drastically reduced. Only 3.55% of all the reported sinkholes in the study area occur
when the Floridan aquifer system is at this depth (Figure 5-3).
The Cody Scarp (Figure 2-1) controls sinkhole development in central Alachua and in
east Dixie and northwest Levy County. Here a complex environment exists in which
water sinks through the Hawthorn Group sediments into the Ocala Limestone and travels
through the aquifer until it rises at the Gulf Coastal Lowlands through springheads. The
anastomotic fracture systems and conduits, through which the water passes, make
detailed prediction of sinkhole development difficult, and it can occur anywhere along
these flow paths. The areas with the highest potential for future sinkhole development
are the Hawthorn Group sediments located near the edge of the Cody Scarp, and the
Ocala Limestone in front of the scarp. Sinkhole development may spread along both sides
of the Cody Scarp.
The combination of the previous figures and predictions of future sinkhole
development, make it possible to perform sinkhole risk assessment on a regional scale.

CHAPTER 7
SUMMARY AND CONCLUSIONS
Analyses of sinkhole activity and factors such as: surficial and subsurface geology,
Floridan aquifer system depth, recharge and discharge to the aquifer, physiographic
province, and population density yielded many strong GIS correlations. The dominating
influence of any single factor to control sinkhole distribution could not be quantified.
Sinkhole distribution is controlled by a complex interaction among these factors.
The two factors that appear to have the greatest influence on sinkhole distribution are
depth to the Floridan aquifer system, and amount of recharge into the aquifer. When the
Floridan aquifer system, a carbonate unit, is near the ground surface and conditions of
high recharge occur, the potential for sinkhole activity is greater. Also, in areas of greater
population density, reported sinkhole density increases. However, this may be biased
since the database sinkholes are reported, and not derived from topographic contour maps
and aerial photographs. Even with the bias in the reported sinkhole localities, using
confirmed sinkholes for correlation with factors believed to be influential in sinkhole
development provides a capability for characterizing sinkhole activity. The database
includes 739 confirmed sinkhole localities, representing one of the largest databases used
in published sinkhole investigations. Thus, despite the biases of the database, this
investigation has identified actual sinkholes on a regional scale that allow for causal
correlations. Such correlations represent the basis for predictions of future sinkhole
activity.
Predictions of future sinkhole development were made on the basis of the largest
concentrations of sinkhole occurrence in the study area and the GIS factors recognized as
the most influential. Central Alachua and Marion Counties, western Citrus County and
59

60
east Dixie and northwest Levy Counties are among those representing high potential for
sinkhole occurrence. The predictions made from the “distance to nearest sinkhole” map
(Figure 6-4), incorporated with information from the “highest density” (Figure 6-2) and
“highest relative frequency of occurrence” maps (Figure 6-3), will make it possible to
conduct sinkhole risk assessment on a regional scale.
When comparing the sinkhole locality data from Denizman and Randazzo (2000) with
the GIS factors (themes) from this study, the areas of high sinkhole occurrence coincide
with areas of high recharge and overlie a shallow Floridan aquifer system. They also
coincide with the Ocala Limestone or thin sediments that overlie the Ocala Limestone.
Factors determined to influence sinkhole distribution in this study are also impacting
sinkhole distribution in the study area of Denizman and Randazzo (2000).
Future efforts in this project would be the incorporation of non-reported sinkholes into
the sinkhole database. Obtaining digital topographic maps could do this. Computer
software could extract circular depressions from the maps and point locations could be
established. The increased sinkhole inventory would yield more precise correlation data
with the factors considered in this project.

APPENDIX A
ARCVIEW GEOPROCESSING COMMANDS
These are the geoprocessing commands used in ARCVIEW version 3.2a (ESRI. INC)
along with a description of what each command does.
Table A-l. Arc view geoprocessing commands
Command
Description
Dissolve
This process combines polygons that posses the same value for a
specific attribute that the user determines.
Merge
This process combines polygons from two or more themes. All
attributes with the same name are retained.
Clip
This process involves using a clip theme to cut an input theme.
Everything outside of the clip theme is deleted (polygons and
attributes). Clipped attributes are not combined with the resultant input
theme.
Intersect
This process involves using one theme to cut the input theme. Only
with the intersect command both themes attributes are combined.
Union
This process combines the polygons and attributes of both themes.
Spatial Join
This process joins only the data from one theme to the features of the
second theme that share the same polygons.
61

APPENDIX B
POPULATION DENSITY FROM US CENSUS BLOCK GROUPS
Table B-l. U.S. block group population density data
Population
Bracket
Average
Sinkholes/
sq. mi
Relative
Frequency
1990
Population
/sqmi
Number of
sinkholes
Total area sqmi
Sinkholes/
sqmi
0-50
0.00254
23.42%
0.0
3
3068.43
0.00098
0-50
1.7
3
2983.38
0.00101
0-50
5.0
3
1053.34
0.00285
0-50
6.1
2
883.24
0.00226
0-50
8.5
4
667.34
0.00599
0-50
10.8
7
4952.67
0.00141
0-50
11.1
3
2558.12
0.00117
0-50
13.4
5
5508.79
0.00091
0-50
13.6
1
3238.54
0.00031
0-50
15.7
5
1805.73
0.00277
0-50
15.8
2
2564.66
0.00078
0-50
16.8
3
4514.33
0.00066
0-50
16.8
1
3519.87
0.00028
0-50
18.4
3
1799.19
0.00167
0-50
18.7
2
634.62
0.00315
0-50
19.6
2
2427.27
0.00082
0-50
20.7
2
732.76
0.00273
0-50
20.7
1
2571.20
0.00039
0-50
21.7
1
4507.78
0.00022
0-50
22.1
1
837.44
0.00119
0-50
22.8
5
2433.81
0.00205
0-50
23.7
6
314.04
0.01911
0-50
26.0
3
3140.40
0.00096
0-50
26.1
13
3493.70
0.00372
0-50
26.3
1
523.40
0.00191
0-50
26.7
1
1223.45
0.00082
0-50
26.9
3
1007.55
0.00298
0-50
26.9
1
3323.59
0.00030
0-50
27.6
1
660.79
0.00151
0-50
28.6
1
3460.98
0.00029
0-50
29.0
11
1478.61
0.00744
0-50
29.0
5
2911.41
0.00172
0-50
29.3
3
889.78
0.00337
0-50
29.6
5
647.71
0.00772
0-50
31.6
1
2525.41
0.00040
0-50
34.3
1
215.90
0.00463
62

63
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
0-50
50-100 0.00407 12.40%
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
50-100
100-150 0.00896 9.50%
100-150
100-150
100-150
100-150
34.6
1
3696.51
0.00027
35.2
11
2754.39
0.00399
36.7
2
2316.05
0.00086
37.4
3
215.90
0.01390
37.6
1
2296.42
0.00044
39.2
1
3958.21
0.00025
39.9
1
3860.08
0.00026
41.2
9
1544.03
0.00583
41.2
1
9048.28
0.00011
41.3
4
902.87
0.00443
42.5
1
660.79
0.00151
44.1
11
1792.65
0.00614
45.7
5
2721.68
0.00184
46.8
1
1079.51
0.00093
49.4
1
1969.29
0.00051
50.1
2
4730.23
0.00042
53.8
2
2093.60
0.00096
55.1
1
1930.04
0.00052
58.8
1
85.05
0.01176
59.1
2
1125.31
0.00178
60.2
2
104.68
0.01911
60.3
2
1890.78
0.00106
60.9
2
1118.77
0.00179
61.9
9
2937.58
0.00306
62.3
1
680.42
0.00147
62.9
3
2996.47
0.00100
67.0
4
693.51
0.00577
69.8
3
1014.09
0.00296
72.2
4
5606.92
0.00071
72.2
1
477.60
0.00209
74.2
13
1354.30
0.00960
74.9
2
1530.95
0.00131
81.2
6
1406.64
0.00427
81.3
3
418.72
0.00716
83.6
2
143.94
0.01390
84.1
4
477.60
0.00838
86.0
1
2420.73
0.00041
86.3
1
523.40
0.00191
87.4
1
7733.24
0.00013
89.3
3
601.91
0.00498
93.3
2
549.57
0.00364
94.0
2
1282.33
0.00156
94.8
4
3781.57
0.00106
99.4
8
2250.62
0.00355
99.5
1
484.15
0.00207
107.4
6
3506.78
0.00171
107.5
1
1426.27
0.00070
108.1
3
405.64
0.00740
114.7
1
1805.73
0.00055
116.9
3
372.92
0.00804

64
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
100-150
150-200 0.00490 7.85%
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
150-200
200-250 0.00939 3.99%
200-250
200-250
200-250
200-250
200-250
200-250
200-250
200-250
250-300 0.01146 5.65%
250-300
250-300
250-300
250-300
250-300
300-350 0.01523 1.52%
300-350
300-350
300-350
300-350
117.0
1
3323.59
0.00030
118.9
1
2296.42
0.00044
124.2
4
1210.36
0.00330
128.9
5
510.32
0.00980
132.6
2
1138.40
0.00176
136.0
17
281.33
0.06043
136.9
1
621.54
0.00161
137.2
1
1851.53
0.00054
140.7
4
686.96
0.00582
142.7
5
104.68
0.04776
144.6
1
157.02
0.00637
145.5
2
5031.18
0.00040
147.6
11
2525.41
0.00436
151.8
6
3003.01
0.00200
152.8
1
2388.01
0.00042
154.4
2
896.32
0.00223
155.7
2
693.51
0.00288
159.2
14
471.06
0.02972
159.6
2
1275.79
0.00157
162.0
4
202.82
0.01972
163.0
1
7752.86
0.00013
165.1
9
1282.33
0.00702
171.9
2
8138.87
0.00025
173.9
4
719.68
0.00556
179.8
1
1223.45
0.00082
180.3
1
641.17
0.00156
180.7
1
1086.06
0.00092
181.2
1
451.43
0.00222
194.3
3
1203.82
0.00249
198.6
3
804.73
0.00373
202.9
5
490.69
0.01019
210.9
3
425.26
0.00705
213.4
1
340.21
0.00294
213.4
2
65.43
0.03057
214.5
2
543.03
0.00368
219.6
5
1118.77
0.00447
223.5
1
189.73
0.00527
225.5
8
516.86
0.01548
236.8
2
412.18
0.00485
251.0
6
386.01
0.01554
256.4
2
1406.64
0.00142
278.0
6
536.49
0.01118
285.3
20
1086.06
0.01842
288.2
2
562.66
0.00355
293.4
5
268.24
0.01864
316.9
1
209.36
0.00478
319.3
1
65.43
0.01528
338.9
5
130.85
0.03821
340.7
3
222.45
0.01349
342.2
1
228.99
0.00437

65
350-400
350-400
350-400
400-450
400-450
400-450
400-450
400-450
400-450
400-450
400-450
450-500
450-500
450-500
450-500
450-500
450-500
500-600
500-600
500-600
500-600
600-700
600-700
600-700
600-700
700-800
700-800
700-800
700-800
800-900
800-900
800-900
800-900
800-900
900-1000
900-1000
900-1000
900-1000
1000-2000 0.05958 5.92%
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
1000-2000
350.3
2
2859.07
0.00070
370.3
2
353.30
0.00566
376.1
12
235.53
0.05095
400.2
15
372.92
0.04022
403.1
3
143.94
0.02084
411.4
4
85.05
0.04703
412.4
1
143.94
0.00695
422.4
5
588.83
0.00849
430.5
1
366.38
0.00273
430.6
2
274.79
0.00728
435.6
3
333.67
0.00899
451.9
2
124.31
0.01609
453.2
4
883.24
0.00453
454.0
1
327.13
0.00306
455.0
31
431.81
0.07179
462.5
2
2139.40
0.00093
480.5
9
91.60
0.09826
511.9
2
26.17
0.07642
514.9
3
137.39
0.02184
518.2
1
255.16
0.00392
548.9
2
556.11
0.00360
615.7
25
274.79
0.09098
633.4
5
228.99
0.02184
666.7
1
163.56
0.00611
680.5
1
196.28
0.00509
701.6
5
196.28
0.02547
716.4
1
78.51
0.01274
724.8
1
157.02
0.00637
795.2
4
124.31
0.03218
851.0
4
71.97
0.05558
851.3
4
196.28
0.02038
861.6
3
98.14
0.03057
870.4
1
45.80
0.02184
885.8
3
235.53
0.01274
910.8
2
274.79
0.00728
938.2
1
242.07
0.00413
944.9
9
52.34
0.17195
987.5
3
287.87
0.01042
1095.2
3
111.22
0.02697
1243.1
2
26.17
0.07642
1394.5
2
39.26
0.05095
1415.3
2
176.65
0.01132
1436.5
3
85.05
0.03527
1454.2
1
52.34
0.01911
1469.0
1
111.22
0.00899
1469.8
1
58.88
0.01698
1535.3
3
58.88
0.05095
1606.3
4
202.82
0.01972
1651.1
1
71.97
0.01390
1673.5
3
52.34
0.05732
0.01910 2.20%
0.01782 4.68%
0.03244 6.75%
0.02644 1.10%
0.03101 4.41%
0.01919 1.52%
0.02822 2.07%
0.04845 2.07%

66
1000-2000
1759.1
1
26.17
0.03821
1000-2000
1761.0
1
104.68
0.00955
1000-2000
1811.5
8
19.63
0.40759
1000-2000
1815.3
5
26.17
0.19106
1000-2000
1836.3
1
78.51
0.01274
1000-2000
1868.0
1
39.26
0.02547
2000-3000
0.05541
2.48%
2064.7
1
39.26
0.02547
2000-3000
2287.3
1
32.71
0.03057
2000-3000
2304.0
1
65.43
0.01528
2000-3000
2326.2
2
39.26
0.05095
2000-3000
2366.0
3
32.71
0.09171
2000-3000
2480.9
3
157.02
0.01911
2000-3000
2567.8
3
32.71
0.09171
2000-3000
2671.5
1
39.26
0.02547
2000-3000
2827.7
1
19.63
0.05095
2000-3000
2940.3
2
13.09
0.15285
3000-4000
0.04792
2.07%
3064.0
3
2813.28
0.00107
3000-4000
3110.2
1
13.09
0.07642
3000-4000
3380.1
4
39.26
0.10190
3000-4000
3723.2
7
569.20
0.01230
6000-7000
0.05095
0.28%
6453.1
2
39.26
0.05095
8000-9000
0.01528
0.14%
8451.8
1
65.43
0.01528

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BIOGRAPHICAL SKETCH
Brian Dodek was bom in Oakland, California on June 22, 1978. After traveling
the world in a military family, 18 years later he was accepted to the University of Florida
in 1996. Four years later, not ready to leave Gainesville, he began graduate school at the
University of Florida in pursuit of a Masters of Science degree in Geological Sciences.
70

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a thesis for the degree of Master of Science.
Anthony F. Randazzo, Chairman
Professor of Geological Sciences
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a thesis for the degree of Master of Science.
u
Z
Douglas L. Smith
Professor of Geological Sciences
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a thesis for the degree of Master of Science.
Johathan B. Martin
Associate Professor of Geological Sciences
This thesis was submitted to the Graduate Faculty of the Department of Geology
in the College of Liberal Arts and Sciences and to the Graduate School and was accepted
as partial fulfillment of the requirements for the degree of Master of Science.
May, 2003
Dean, Graduate School

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