U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

Southwest Florida Water Management District and

Tampa Bay Water

Factors that Influence the Hydrologic Recovery 

of Wetlands in the Northern Tampa Bay 

Area, Florida

 Scientific Investigations Report 2011–5127
On the Cover: W–33 Cypress wetland, Cypress Creek well field.

Opposite page: S– 68 Cypress wetland, Starkey well field.

Photographs taken by the author, P.A. Metz.
Factors that Influence the 

Hydrologic Recovery of Wetlands

in the Northern Tampa Bay Area, 

Florida

By P.A. Metz

Scientific Investigations Report 2011–5127

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the 

Southwest Florida Water Management District 

and Tampa Bay Water
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Metz, P.A., 2011, Factors that influence the hydrologic recovery of wetlands in the Northern Tampa Bay area, Florida: 

U.S. Geological Survey Scientific Investigations Report 2011–5127, 58 p.

978 1 4113 3231 7
iii

Acknowledgments

The author acknowledges Southwest Florida Water Management District (SWFWMD) 

employees Michael Hancock for his help with the study wetland selection and for his 

constructive technical discussions and review comments, Robert Peterson for his help in 

compiling groundwater withdrawal data for the Northern Tampa Bay well fields, and Vince 

Pelham and Robert Parker for performing geophysical logging tests for several study wells. 

Special recognition is given to former SWFWMD employee Ted Rochow for his long-term effort 

in documenting the history of wetlands in the Northern Tampa Bay area. 

The author also acknowledges Tampa Bay Water employees Warren Hogg and Jeff Geurink 

for their constructive technical review comments, and Patricia Fesmire and Chris Shea for their 

help with the study wetland selection. The author would like to thank Reynolds, Smith, and 

Hills employee Cynthia Wheeler for her assistance with initial logistics in the monitoring of the 

study area wetlands.

Special recognition is given to U.S. Geological Survey (USGS) employees Terrie M. Lee and 

Amy Swancar for their valuable technical insight during this project, and Leel Knowles, James 

LaBaugh, and Arturo Torres for their constructive technical review comments. The author 

acknowledges the assistance of Nancy DeWitt and Billy J. Reynolds of the USGS St Petersburg 

Coastal and Marine Science Center for the collection of vibracores at six of the study 

wetlands. The author also expresses gratitude for field support and data analysis provided 

by the USGS interns from the University of South Florida; Geoffrey Fouad, Robert Schroeder, 

William Pfeiffer, Scott Orr, Suzana Hernandez, and Gene Morell.
iv
v

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................4

Description of Study Area ............................................................................................................................4

Wetland Setting.....................................................................................................................................6

Anthropogenic Impacts on Regional Wetlands...............................................................................7

Description of Well Fields..................................................................................................................10

Study Design.................................................................................................................................................14

Study Wetlands ...................................................................................................................................14

Methods of Investigation...................................................................................................................16

Factors that Influence the Hydrologic Recovery of Wetlands .............................................................20

Topographic Setting ...........................................................................................................................20

Hydrogeologic Setting .......................................................................................................................22

Permeability of Sediments Underlying the Wetlands ..........................................................22

Influence of Karst Features on Wetland Hydrology.............................................................26

Potentiometric Surface of the Upper Floridan Aquifer.................................................................33

Historical Trends in Groundwater Levels...............................................................................33

Potentiometric Surface Elevations before and after Reductions in 

Groundwater Withdrawals .........................................................................................36

Effects of Groundwater Withdrawals on Wetland Hydroperiods......................................42

Ranking of Factors Influencing the Hydrologic Recovery of Wetlands.....................................46

Summary........................................................................................................................................................49

References Cited..........................................................................................................................................51

Appendix 1. Potentiometric surface map of the Upper Floridan aquifer prior to 

 development at the Starkey and Cypress Creek well fields..................................56

Appendix 2. Potentiometric surface map of the Upper Floridan aquifer at the 

 Starkey well field for September 2008 and May 2009 ............................................57

Appendix 3. Potentiometric surface map of the Upper Floridan aquifer at the 

 Cypress Creek well field for September 2008 and May 2009 ................................58

Figures

1. Map showing wetland study area and the 11 consolidated well fields located 

in the Northern Tampa Bay area................................................................................................3

2. Graphs showing rainfall departures and 3-year moving average of this 

departure at the Tarpon Springs and Saint Leo rainfall stations 

for 1970–2009 .................................................................................................................................5

3. Diagrams showing generalized interactions of groundwater with the study 

wetlands, including groundwater recharge, groundwater flow-through, and 

groundwater discharge ...............................................................................................................6
vi

4. Aerial photographs showing isolated wetlands connecting through low-gradient 

surface-water drainage channels and outflow ditches from wetlands..............................8

5. Graphs showing combined groundwater withdrawals from the 11 consolidated 

well fields, allocation for water supply in the Northern Tampa Bay area, and 

annual groundwater withdrawal rates for the Starkey, Cypress Creek, and 

Cypress Bridge well fields...........................................................................................................9

6–8. Photographs and aerial site maps showing location of the study wetlands 

and productions wells at the: 

6. Starkey well field and individual study wetlands...........................................................11

7. Cypress Creek well field and individual study wetlands ..............................................12

8. Cypress Bridge well field, monitoring sites and land-use development 

 surrounding the wetland, encroachment of upland species and tree fall, 

 and small and large sinkholes at the Cypress Bridge 01 wetland..............................13

9. Light Detection and Ranging (LIDAR) digital elevation maps showing topography 

surrounding the study wetlands at the Starkey and Cypress Creek well fields...............21

10. Generalized hydrogeologic sections showing an unimpacted to minimally 

impacted wetland, a moderately impacted wetland, and two severely impacted 

wetlands.......................................................................................................................................23

11. Photographs showing vibracore samples and graphs showing percentage of 

sand, silt, and clay in the upper 2 feet of wetland sediments, and clay content 

at and below land surface for six of the study wetlands .....................................................24

12. Photographs showing vibracore sample collection and core samples highlighting 

the variability of the clay layers in cores beneath the study wetlands .............................25

13. Map showing generalized thickness of the intermediate confining unit overlying 

the Upper Floridan aquifer ........................................................................................................26

14. Geologic and natural-gamma logs showing the variability in the clay units near 

the study wetlands at the Cypress Creek and Starkey well fields .....................................27

15. Maps showing bathymetry of severely impacted wetlands, an unimpacted 

wetland, and a minimally impacted wetland..........................................................................29

16. Maps showing bathymetry of the Cypress Bridge 01 wetland ...........................................30

17–19. Aerial photographs showing:

17. Location of sinkholes that formed in and around the Section 21 well field 

 due to groundwater withdrawals...................................................................................... 30

18. Location of ground-penetrating radar transect lines, and geophysical 

 profile A–A’ with interpreted geologic features below Cypress Bridge 01 

 at the Cypress Bridge well field......................................................................................... 31

19. Location of ground-penetrating radar transect lines, and geophysical 

 profile D–D’ with interpreted geologic features below W–16 Marsh at 

 the Cypress Creek well field............................................................................................... 32

20. Box plots showing water-level differences between the wetland/surficial 

aquifer and Upper Floridan aquifer for the study wetlands, 2007–08 ................................33

21. Hydrographs showing long-term water levels for the Upper Floridan aquifer 

and surficial aquifer at the Cypress Creek well field and surrounding areas ..................34

22. Hydrographs showing long-term water levels for the Upper Floridan aquifer 

and surficial aquifer at the Starkey well field and surrounding areas ..............................35
vii

23–25. Maps showing elevation difference between land surface and the potentiometric 

surface of the Upper Floridan aquifer:

23. Prior to well-field production at the Starkey and Cypress Creek well fields.......... 38

24. During September 2008 and May 2009 at the Starkey well field............................... 39

25. During September 2008 and May 2009 at the Cypress Creek well field.................. 40

26. Box plots showing elevation of the potentiometric surface of the Upper Floridan 

aquifer above or below the study-wetland bottom elevations prior to and after 

the reductions in groundwater withdrawals at the Starkey and Cypress Creek 

well fields .....................................................................................................................................41

27. Graphs showing groundwater withdrawals within a 1-mile radius of the center 

of the study wetlands prior to and after reductions in groundwater withdrawals..........42

28. Hydrographs of historical water levels at an unimpacted, a minimally impacted, 

and two severely impacted wetlands .....................................................................................43

29. Maps showing the shape of flooded areas at different levels of inundation and 

graphs showing duration of flooding prior to and after reductions in groundwater 

withdrawals at S–68 and S–44 Cypress at the Starkey well field.......................................44

30. Maps showing the shape of flooded areas at different levels of inundation 

and graphs showing duration of flooding prior to and after reductions in 

groundwater withdrawals at W–33 Cypress and W–16 Marsh at the Cypress 

Creek well field............................................................................................................................45

31. Graph showing total ranking of factors that influence the hydrologic recovery 

of wetlands in the Northern Tampa Bay area........................................................................48

Tables

1. Name, location, and other characteristics of the study wetlands .............................................15

2. Methods used to describe the factors affecting the hydrologic condition and 

 recovery of each study wetland......................................................................................................17

3. Well characteristics and other data collected at the study wetlands ............................... 18–19

4. Relation between surficial and Upper Floridan aquifer levels at the study wetlands ............33

5. Ranking of the study wetlands based on the factors that influence the hydrologic 

 recovery of wetlands in the Northern Tampa Bay area..............................................................48
viii

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

million gallons (Mgal) 3,785 cubic meter (m3)

acre-foot (acre-ft) 1,233 cubic meter (m3)

Flow rate

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Leakage

inch per day (in/d) 2.54 centimeter per day (cm/d)

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 1929).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum. 

Acronyms and Additional Abbreviations

GIS geographic information system

GPR ground-penetrating radar

LIDAR Light Detection and Ranging

NOAA National Oceanic and Atmospheric Administration

NWI National Wetland Inventory

SWFWMD Southwest Florida Water Management District

USGS U.S. Geological Survey

WAP Wetland Assessment Procedure

< less than

> greater than
The increase in the potentiometric surface of the Upper 

Floridan aquifer below the wetland was the primary factor 

influencing the hydrologic recovery of the study wetlands, 

even in areas affected by karst subsidence. For one of the 

study wetlands influenced by karst subsidence (S–44 Cypress 

at Starkey well field), the potentiometric surface of the Upper 

Floridan aquifer increased to the level of the wetland-bottom 

elevation following the reductions in groundwater withdrawals. Despite the karst subsidence in the wetland, having 

the level of the potentiometric surface just below the wetland 

bottom limited the downward leakage potential and resulted 

in an increase in the flooded area and duration of the wetland 

hydroperiod.

 In contrast, two study wetlands affected by karst 

subsidence (W–12 Cypress and W–16 Marsh at Cypress 

Creek) remained mostly dry during the period of groundwater 

withdrawal reductions, even though the median elevation of 

the potentiometric surface of the Upper Floridan aquifer rose 

about 5 feet in this area of the well field. These wetlands are 

located in an area of the well field where large groundwater 

withdrawals are concentrated, and during the last 20 years 

(1989–2009) the wetlands were inundated only during periods 

of extreme rainfall. During these brief inundation periods, the 

wetland water levels receded after 1 to 2 months, much more 

rapidly than wetlands located in areas without karst subsidence 

or concentrated pumping, indicating the increased leakage 

between the wetlands and underlying aquifers. Because of 

this interconnection, water levels in these wetlands and others 

impacted by karst subsidence in this region will not recover 

if the potentiometric surface of the Upper Floridan aquifer 

remains at its current (2009) elevation (median distance of 

about 10 feet below the wetland-bottom elevation). 

Factors that Influence the 

Hydrologic Recovery of Wetlands 

in the Northern Tampa Bay Area, 

Florida

By P.A. Metz

Abstract

Reductions in groundwater withdrawals from Northern 

Tampa Bay well fields were initiated in mid-2002 to improve 

the hydrologic condition of wetlands in these areas by 

allowing surface and groundwater levels to recover to previously higher levels. Following these reductions, water levels 

at some long-term wetland monitoring sites have recovered, 

while others have not recovered as expected. To understand 

why water levels for some wetlands have not increased, nine 

wetlands with varying impacts from well field pumping 

were examined based on four factors known to influence the 

hydrologic condition of wetlands in west-central Florida. 

These factors are the level of the potentiometric surface of 

the Upper Floridan aquifer underlying the wetland, recent 

karst activity near and beneath the wetland, permeability of 

the underlying sediments, and the topographic position of the 

wetland in the landscape. 

The combination of two factors, the presence of recent 

karst activity below or near the wetlands and the depth to the 

potentiometric surface of the Upper Floridan aquifer below the 

wetlands, had the most influence on the hydrologic recovery 

of the study wetlands. The study wetlands are located in an 

area where numerous localized surface or buried depressions (karst features or sinkholes) are common throughout 

the mantled karst landscape, which increases the hydrologic 

connection between the wetlands and the underlying aquifers. 

Breaches or breaks in the underlying sediments or in the 

intermediate confining unit due to recent karst subsidence 

activity act as pathways for downward leakage. For the study 

wetlands, the leakage potential increased when the vertical 

separation between the potentiometric surface of the Upper 

Floridan aquifer and the wetland-bottom elevation (a surrogate 

for the wetland water level) increased.
2 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Low permeability sediments and the absence of karst 

features underlying the wetlands had a positive influence on 

the wetland recovery following the reductions in groundwater 

withdrawals. In these settings, intact low permeability 

subsurface layers help maintain water within and beneath the 

wetland, and limit the downward leakage potential to the Upper 

Floridan aquifer. For wetlands in these settings, the increase in 

potentiometric surface of the Upper Floridan aquifer below the 

study wetland-bottom elevations resulted in an increase in the 

flooded area and the duration of the wetland hydroperiod. 

Although of less importance than the other three factors, 

a low-lying topographical position benefited the hydrologic 

condition of several of the study wetlands (S–68 Cypress 

and W–12 Cypress) both before and after the reductions in 

groundwater withdrawals. Compared to wetlands in a higher 

topographical position, those in a lower position had longer 

hydroperiods because of their greater ability to receive more 

runoff from higher elevation wetlands and to establish surfacewater connections to other isolated wetlands and surface-water 

bodies through low-lying surface-water channels during wet 

conditions. In addition, wetlands in low-lying areas benefited 

from groundwater inflow when groundwater levels were 

higher than wetland water levels. 

Introduction

Groundwater use in the Northern Tampa Bay area has 

increased steadily since the 1930s, and by the early 2000s, 

groundwater was withdrawn for public supply from the 

Upper Floridan aquifer at an average annual rate of 165 

million gallons per day (Mgal/d) (Robert Peterson, Southwest 

Florida Water Management District, written commun., 2009). 

Groundwater is the major component of the water supply for 

the Northern Tampa Bay area, and most of this groundwater 

is withdrawn from 11 consolidated well fields managed by 

the regional utility, Tampa Bay Water (fig. 1). Due to the 

long-term groundwater withdrawals from the well fields, the 

potentiometric surface of the Upper Floridan aquifer has been 

lowered within and around the well fields in the Northern 

Tampa Bay area (Hutchinson, 1984; Southwest Florida Water 

Management District, 1996). Surface-water bodies generally 

are well-connected to the groundwater system in the Northern 

Tampa Bay area, and water-level declines have also been 

observed in many lakes and wetlands in the areas around the 

well fields (Metz and Sacks, 2002; Lee and others, 2009). For 

some of the wetlands in these areas, water-level declines have 

reduced the length of time these wetlands contain standing 

water (wetland hydroperiod), and in some cases have caused 

extensive damage to wetland ecosystems (Dooris and others, 

1990; Rochow, 1998; Lee and others, 2009). 

 Most of the well fields in the Northern Tampa Bay 

area are located on undeveloped tracts of land that contain 

many acres of isolated cypress domes, freshwater marshes, 

and wet prairies (Rochow, 1998). The Southwest Florida 

Water Management District (SWFWMD) has established 

minimum surface-water levels in areas where groundwater 

withdrawals have contributed to or have the potential to create 

substantial harm to wetland ecosystems (Southwest Florida 

Water Management District, 1999a,b). Currently (2009), a 

number of wetlands in and around the well fields are below 

their established minimum levels and a decline in the health of 

many wetlands has been observed (Mike Hancock, Southwest 

Florida Water Management District, unpub. data, 2009). 

In response to lowered groundwater, lake, and wetland 

water levels, efforts have been made to reduce the reliance 

on groundwater for public-water supply. With the reduction 

in groundwater use, river and desalinated water have served 

as supplementary resources (Tampa Bay Water, 2010b). 

In addition, water conservation and reuse measures have been 

implemented to further reduce overall water use and reliance 

on groundwater (Southwest Florida Water Management 

District, 2009). Reductions in groundwater withdrawals began 

in mid-2002, and the average annual groundwater withdrawn 

from the 11 well fields decreased from about 130 Mgal/d in 

2002 to about 96 Mgal/d during 2003–09 (Robert Peterson, 

Southwest Florida Water Management District, written 

commun., 2009). 

 Because of the reductions in groundwater withdrawals, 

groundwater levels surrounding some of the previously 

impacted wetlands have increased and some of the wetlands 

may return to naturally functioning ecosystems. Based on 

historical benchmark levels, however, water levels in a 

number of wetlands have not rebounded as expected (Mike 

Hancock, Southwest Florida Water Management District, 

unpub. data, 2009). To address this issue, the U.S. Geological 

Survey initiated a 2-year study in 2007 to characterize the 

factors that influence the general hydrologic condition of 

wetlands and the recovery of water levels for wetlands 

impacted by well-field pumping in the Northern Tampa 

Bay area. The study was conducted in cooperation with the 

Southwest Florida Water Management District and Tampa 

Bay Water. Four factors known to influence the hydrologic 

condition of the wetlands in west-central Florida were examined at selected wetlands during the study: the topographic 

setting, the permeability of the underlying sediments, recent 

karst activity, and the depth to the potentiometric surface of 

the Upper Floridan aquifer underlying the wetlands. This 

analysis provided an indication of the hydrologic condition of 

each wetland and identified which factors limit the increase 

in wetland water levels. Reducing pumping is expected to 

raise wetland water levels by raising groundwater levels and 

decreasing the distance of the potentiometric surface below 

wetlands, but it will have little direct effect on the other three 

factors. For this reason, all four factors need to be examined 

to understand why the water levels in some wetlands have not 

increased as expected. 

 The data collected and knowledge gained during 

this investigation provide an understanding of the factors 

affecting wetland water levels in relation to the elevation of 

the potentiometric surface of the Upper Floridan aquifer in a 
Introduction 3

Starkey

Cross Bar Ranch

Cypress Creek

Morris Bridge

Eldridge- Wilde

CosmeOdessa

Section 21

South Pasco

North

Pasco

Regional

Cypress Bridge

NW Hillsborough Regional

EXPLANATION

Well-field boundary

Cone Ranch boundary

Palustrine wetlands

Estuarine wetlands

Lakes

Dispersed well-field boundary

National Weather Service station

City

Study wetland

– And other water bodies

– Location and number

Tampa

Dade City

Clearwater

Zephyrhills

Weeki Wachee

Land O' Lakes

Tarpon Springs

Temple Terrace

St. Petersburg

New Port Richey

HERNANDO COUNTY

PASCO COUNTY

HILLSBOROUGH

COUNTY

POLK COUNTY

PINELLAS

COUNTY

1 2

3

4

5

7 6

8

9

1

6 W-16 Marsh

7 W-56 Cypress

8 W-33 Cypress

9 Cypress Bridge 01

OLD

TAMPA

BAY

GULF

OF MEXICO

River

Anclote

River

Hillsborough

Blackwater Creek

River

Pith

o

lachasc tee

Cone

Ranch

10 Other wetlands referred to in study – Location and number

10 W-05 Cypress

11 Cone Ranch

10

11

Big Cypress Swamp

Saint Leo

TAMPA

BAY 1 S-68 Cypress

2 Starkey Central

3 S-44 Cypress

4 Grass Prairie

5 W-12 Cypress

FLORIDA

Northern Tampa

Bay area

82°30’ 82°00’

28°30’

28°00’

0 10 MILES

0 10 KILOMETERS

Figure 1. Wetland study area and the 11 consolidated well fields located in the Northern Tampa Bay area.
4 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

karst hydrogeologic setting. A broader understanding of the 

interaction between surface water, groundwater, and wetland 

ecosystems is an important component of the USGS Strategic 

Plan. Understanding the issues of surface-water response 

to groundwater withdrawals, and groundwater recharge 

responses to surface-water management changes is vital to 

the protection and management of wetland ecosystems in the 

Northern Tampa Bay area. 

Purpose and Scope

The purpose of this report is to document the effects of 

four factors known to influence the hydrologic condition of 

the wetlands in west-central Florida, namely, the topographic 

setting, the permeability of underlying sediments, recent karst 

activity, and the depth to the potentiometric surface of the 

Upper Floridan aquifer underlying the wetland. The study 

wetlands included a relatively unimpacted wetland and eight 

wetlands with documented impacts from well-field pumping 

located at Starkey, Cypress Creek, and Cypress Bridge well 

fields (fig. 1). This report also evaluates how each of these 

factors has affected the hydrology of the nine wetlands 

following the reduction of groundwater pumping.

 Comparisons and analyses of the nine study wetlands 

were made using hydrologic, vegetation, bathymetric, 

geophysical, geologic, and land-surface elevation data. 

Historical data from 1975 to 2009 were compiled for this 

investigation, and consisted of surface-water and groundwater 

levels, groundwater withdrawal rates, rainfall amounts, and 

geologic, vegetation, and soil data. These data were collected 

by the USGS, SWFWMD, Tampa Bay Water, National 

Oceanic and Atmospheric Administration (NOAA), and 

private consultants. Additional data used for analysis were 

collected by the USGS from November 2007 to May 2009 as 

part of this study, and consisted of surface-water and groundwater-level data, precipitation data, and geologic, geophysical, 

and bathymetric data. 

Description of Study Area 

 The Northern Tampa Bay study area covers about 1,800 

square miles (mi2) and includes all of Pinellas County, and 

parts of Pasco, Hernando, Hillsborough, and Polk Counties 

(fig. 1). The population in the area has increased from 

1.1 million in 1980 to an estimated 2.4 million in 2009 (U.S. 

Census Bureau, 2002; Tampa Bay Water, 2010a). Despite the 

increased use of surface water, the area continues to rely on 

groundwater withdrawn from regional well fields for almost 

half of the public supply.

 The topography of the Northern Tampa Bay area is 

characterized by flat, marshy lowlands along the coast, low 

rolling hills in the central region, and sand ridges and terraces 

of up to 200 feet (ft) in elevation in the northern and eastern 

regions. Much of the recharge to the study area occurs along 

these sand ridges and terraces (Southwest Florida Water 

Management District, 1993). Hundreds of lakes, wetlands, and 

marshes are interspersed throughout the study area, and range 

from less than 1 acre to more than 2,500 acres in extent (Haag 

and Lee, 2010). The majority of residential and commercial 

land use is concentrated along the coast and in the southern 

part of the study area near Tampa Bay, whereas the majority 

of the freshwater wetlands are scattered throughout the central 

and eastern regions of the study area (Metz and others, 2007). 

Groundwater withdrawals are concentrated in areas that 

contain numerous wetlands and small tributary streams that 

have wetlands as headwaters.

 The regional hydrogeologic setting of the Northern 

Tampa Bay area is one of a mantled karst landscape. Such 

areas are characterized by a thick sequence of weathered limestone, overlain by a clay layer 0- to 200-ft thick, overlain by a 

sequence of sand 10- to 100-ft thick (Southwest Florida Water 

Management District, 1996). The landscape contains sinkhole 

depressions ranging in their period of development from older 

stable depressions to recent collapsed features (Sinclair, 1982). 

The older shallow surface depressions commonly contain 

swamps, marshes, or cypress domes, the latter of which are one 

of the most characteristic vegetative and geomorphic features 

in the study area (Sinclair, 1982). The deeper depressions form 

sinkhole lakes (Metz and Sacks, 2002). 

The broad range of karst development in the study area is 

reflected by varying degrees of hydraulic connection between 

the wetlands and underlying aquifers. The shallow hydrogeologic system in the study area consists of, in descending order: 

the unconfined surficial aquifer system, the intermediate 

confining unit, and the Upper Floridan aquifer. The surficial 

aquifer system in this area consists of unconsolidated to 

poorly indurated clastic deposits of sand and clayey sand 

(Southeastern Geological Society, 1986). Commonly, this unit 

is called the surficial aquifer system where more than one 

permeable zone is present or where the deposits are interbedded. In this report, these deposits are considered to form a 

single homogeneous aquifer and are referred to as the surficial 

aquifer. Sediments that compose this unit consist of silt, sand, 

and clay that range in thickness from less than 10 ft in coastal 

areas to over 100 ft along sandy ridges (Southwest Florida 

Water Management District, 1996). Recharge to the water 

table within the surficial aquifer is relatively rapid because the 

surficial sands are generally permeable and the water table is 

close to land surface. Although water recharged to the surficial 

aquifer can move laterally along short flow paths to points 

of discharge, most of the water leaks downward through the 

underlying intermediate confining unit (where present) to the 

Upper Floridan aquifer. 

 The intermediate confining unit is a non-water-yielding 

stratum that consists of a dense, marine green-gray plastic 

clay that contains varying amounts of sand and carbonate 

mud. The clay unit is variable in extent, permeability, and 

thickness throughout the study area (Sinclair, 1974). Although 

the intermediate confining unit impedes downward flow 

between the surficial aquifer and Upper Floridan aquifer, the 
Description of Study Area 5

hydraulic connection between the aquifers is compromised in 

areas where the intermediate confining unit is thin, permeable, 

contains sand filled conduits (piping features), or is breached 

by sinkhole development (Stewart and Parker, 1992). 

 The Upper Floridan aquifer consists of a series of 

carbonate units and is the primary source of water supply 

in the study area. The limestone and dolomite of the Upper 

Floridan aquifer contain many solution-enlarged fractures 

and typically yield large quantities of groundwater to public 

and private wells (Metz and Sacks, 2002). Groundwater 

within this aquifer is pressurized or under artesian conditions, except in the extreme northern part of the Northern 

Tampa Bay area (Southwest Florida Water Management 

District, 1996). The general direction of regional groundwater 

flow is west to southwest towards the Gulf of Mexico, but 

is locally modified by major centers of groundwater withdrawals, including municipal well fields and industrial and 

agricultural withdrawals. 

 Warm, wet summers and relatively mild, dry springs 

typically characterize the subtropical climate of the study 

area. Long-term average annual rainfall recorded at the 

National Weather Service Tarpon Springs (1892–2009) 

and Saint Leo (1895–2009) stations in Florida was about 

52 and 55 inches (in.), respectively (National Oceanic and 

Atmospheric Administration, 2010; station locations shown in 

fig. 1). Typically, rainfall totals at both stations are lowest in 

November, followed by December, April, and January; totals 

are highest in July, followed by June, August, and September. 

Rainfall during the wet season (June through September) 

accounts for more than half of the total annual rainfall. 

Cumulative rainfall departures at the two rainfall sites 

(Tarpon Springs and Saint Leo, Florida; fig. 2) during a 

40-year period (1970–2009) were used to help determine 

when relative wet and dry periods occurred in the study area 

prior to and during well-field production at the study well 

fields. Departures from the long-term average annual rainfall 

for 1970 to 2009 indicate that rainfall was below average 

for 21 and 27 years out of the 40-year period for Tarpon 

Springs and Saint Leo rainfall sites, respectively (fig. 2). 

The minimum annual average rainfall for Tarpon Springs 

occurred in 2007 and was about 17 in. below average; the 

minimum for Saint Leo occurred in 2000 and was about 16 in. 

below average. The maximum average annual rainfall for 

both stations occurred in 1983, and totaled about 23 and 20 in. 

above the annual averages for Tarpon Springs and Saint Leo, 

respectively. 

 A 3-year moving average of the cumulative rainfall 

departure was used to help determine the duration and magnitude of wet or dry periods for the two rainfall stations (fig. 2). 

Based on the 3-year moving average at Tarpon Springs rainfall 

station, the wettest period occurred during 1984, and the driest 

period occurred during 2007. Based on the 3-year moving 

average at the Saint Leo rainfall station, the wettest period 

occurred during 2004, which was the culmination of 3 years 

of above average rainfall that included several hurricanes 

and tropical storms in 2004. Two similar low rainfall periods 

occurred at Saint Leo station during 2001 and 2008 due 

to 3 and 4 years of below average rainfall, respectively. 

For a number of wells with long-term record (1949–2009) 

throughout the study area, the lowest groundwater levels 

occurred after extended dry periods in 2000–2002, and 2007 

(http://wdr.water.usgs.gov/wy2009/search.jsp).

 In addition to rainfall, evaporation and evapotranspiration 

partly determine the hydrology of wetlands in the study area. 

Evaporation rates are relatively high in Florida and are higher 

than most areas of the country (Farnsworth and others, 1982). 

The high evaporation rates in this subtropical climate are 

primarily due to high solar radiation and water temperatures. 

Long-term annual estimates of shallow lake evaporation range 

from 48 to 59 in. in central Florida and can vary depending on 

climatic conditions (Amy Swancar, U.S. Geological Survey, 

Figure 2. Rainfall departures and 3-year moving average of 

this departure at the A, Tarpon Springs and B, Saint Leo rainfall 

stations for 1970–2009. Locations of the rainfall stations are shown 

in figure 1.

Departure in inches, from the average annual

rainfall of 55.49 inches, at the rainfall

station from 1895 through 2009.

Saint Leo

Departure in inches, from the average annual

rainfall of 51.73 inches, at the

rainfall station from 1892 through 2009.

Tarpon Springs

1975

1980

1985

1990

1995

2000

2005

2009

-20

-15

0

15

20

25

Departure from average rainfall, in inches

10

5

-5

-10

B

-20

-15

0

15

25

10

5

-5

-10

1970

1975

1980

1985

1990

1995

2000

2005

2009

A

Departure from average rainfall, in inches

3-year moving average — Of the annual rainfall departure.

EXPLANATION

20

1970

Years

Years
6 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

written commun., 2010). The annual evapotranspiration 

rate for cypress wetlands is about 38 inches per year (in/yr) 

(Bidlake and others 1996; Sumner, 2001). 

 Although rainfall and evaporation can vary among 

wetlands and rainfall dominates wetland water-budgets over 

short time periods (Sumner, 2006; Lee and others, 2009), 

atmospheric factors are assumed to affect all wetlands in this 

region equally over long time periods. All Northern Tampa 

Bay area wetlands are more likely to be dry during droughts 

and to flood during wet years, but how individual wetlands 

respond to reductions in groundwater withdrawals is more a 

function of differences in their physical and hydrogeologic 

settings than differences in climate. 

Wetland Setting 

 More than 33,000 wetlands are located throughout the 

Northern Tampa Bay area with the majority (81 percent) 

consisting of freshwater wetlands (Southwest Florida Water 

Management District, 2004; fig. 1). The numerous wetlands in 

the study area are widely distributed, relatively small, and are 

typically isolated. In many places, wetlands are surrounded by 

uplands, forming a mosaic of contrasting environments. These 

wetlands typically contain unique wildlife habitat that is often 

adjacent to dense human development (Haag and Lee, 2010). 

The relatively small size and vast numbers of wetlands challenge efforts to characterize them collectively as a statewide 

water resource (Lee and Haag, 2006).

 The Northern Tampa Bay area contains a variety of 

freshwater wetland types; the most common in the study area are 

floodplain wetlands, cypress domes, marshes, and wet prairies 

(Rochow, 1998; Southwest Florida Water Management District, 

2004). The floodplain wetlands consist of more than one wetland 

type, and may include both mixed-hardwood and cypress swamp 

forests. The cypress domes in the study area are dominated 

by pond cypress trees (Taxodium ascendens), which form the 

characteristic dome-shaped profile. Marshes and wet prairies are 

mostly treeless wetlands that support a diverse assemblage of 

grasses, sedges, and forbs (Rochow, 1998). These wetland types 

are typically surrounded by upland pine flatwoods. 

Three general groundwater flow conditions were 

observed at the study wetlands based on the seasonal 

configuration of water levels in the surficial aquifer and 

Upper Floridan aquifer relative to the wetland levels. 

The most commonly observed condition was groundwater 

recharge, indicated by downward leakage from the wetland 

into the underlying aquifers (fig. 3A). This condition exists 

when water levels in a wetland are generally higher than the 

levels in the surficial aquifer, allowing water to leak into and 

recharge the underlying aquifers. The next most common 

condition, groundwater flow-through, was observed at several 

study wetlands. This condition is indicated by simultaneous 

groundwater inflow and outflow along different parts of 

a wetland perimeter (fig. 3B). The third flow condition, 

groundwater discharge, occurred during wet conditions when 

B

EXPLANATION

Water table

Groundwater flow path

A

C

Figure 3. Generalized interactions of groundwater with 

the study wetlands, including A, groundwater recharge; 

B, groundwater flow-through, and C, groundwater 

discharge. Modified from Winter and others (1998) and Lee 

and others (2009).
Description of Study Area 7

the potentiometric surface of the Upper Floridan aquifer was 

generally at or slightly above land surface, which limited the 

downward leakage potential from the surficial aquifer and 

wetland (fig. 3C). 

 The typical annual water-level pattern for isolated 

wetlands in the study area includes two wet periods (summer 

and winter) and two dry periods (spring and fall) (Carr and 

others, 2006). Wetlands in the study area commonly follow 

a hydrologic pattern in which water levels decline during 

the spring dry period and reach a minimum in May and June 

(Lee and others, 2009). During the dry season, the water table 

remains below land surface, forming a shallow groundwater 

mound beneath the wetland bottom. Wetland water levels 

typically begin rising during the summer rainy season and 

reach a maximum in September (Berryman and Hennigar, 

Inc., 2000; Lee and others, 2009). 

 During years with average rainfall, unimpacted marshes 

and cypress wetlands typically contain standing water (and 

thus have a hydroperiod of) more than 6 months per year 

(Ewel and Wickenheiser, 1988). For a shallow, unimpacted 

cypress wetland located in the study area (S–68 Cypress), 

the 19-year average hydroperiod was 235 days, or the 

wetland contained standing water during 63 percent of the 

year and was dry during 37 percent of the year (Lee and 

others, 2009). The hydroperiod of wetlands in the study area 

is largely determined by the difference between precipitation and evapotranspiration, but also is influenced by the 

elevation of the potentiometric surface of the Upper Floridan 

aquifer. When aquifer levels decline in the Upper Floridan 

aquifer because of groundwater withdrawals or sustained 

drought, the decline induces downward leakage from the 

overlying surficial aquifer, which in turn decreases wetland 

water levels (Metz and Sacks, 2002; Lee and others, 2009). 

A small (<0.5 ft) change in wetland water levels resulting 

from groundwater withdrawals or climatic conditions can 

cause large changes in wetland surface area, because these 

wetlands are situated in relatively shallow topographic 

depressions (Lee and others, 2009). 

Anthropogenic Impacts on Regional Wetlands

 The numerous wetlands in the Northern Tampa Bay 

area provide important environmental functions in regards 

to the contribution and maintenance of baseflow to streams, 

recharge to the groundwater system, flood control, waterquality enhancements, and wildlife habitat and breeding 

grounds (Haag and Lee, 2010). In the rapidly developing 

area of Northern Tampa Bay, the hydrology and ecology of 

these wetlands have been affected by anthropogenic activities 

such as urban and agricultural development, construction of 

roadways and ditches, and large groundwater withdrawals in 

surrounding areas. Understanding the impacts of wetland loss 

and wetland responses to anthropogenic activities is necessary 

for effectively managing this important resource.

 The first wetland inventory in Florida, completed 

in 1845, indicated that wetlands composed 59 percent of 

the State; by 1996, wetlands composed only 29 percent 

of the State (Dahl, 1990, 2000, 2005, and 2006). The loss 

of wetlands in Florida has primarily been attributed to the 

conversion of wetlands to agricultural and urban lands (Tiner, 

1984; Pittman and Waite, 2009). Other reasons for the loss of 

wetlands include flood control, forestry, road development, 

and mosquito control (Carter, 1986; Dahl, 1990; Frayer and 

Hefner, 1991). Although wetland mitigation banks have been 

used in the past decade to offset wetland loss, the methods 

and accounting systems for these losses have not been fully 

understood and further research is needed (Reiss and others, 

2009). The examples that follow briefly explain how changes 

in surface-water flow patterns, land-use changes, ditching, 

and groundwater withdrawals have affected the hydrology of 

wetlands in the study area. 

 Runoff or surface-water inflow to wetlands has played 

a major role in the hydrology of some of the wetlands in the 

Northern Tampa Bay area. Water-budget analyses conducted 

by Lee and others (2009) provided insight into the importance 

of runoff on the hydrology of isolated wetlands. Lee and 

others (2009) found that overland flow from surrounding 

areas contributed half to almost twice as much water to some 

Northern Tampa Bay wetlands as direct rainfall during high 

rainfall events. Ewel and Odum (1984) indicated that the 

transition from isolated wetlands to wetland chains connected 

by streams usually occurs at the end of a wet season for 

cypress-pine flatwoods wetlands (fig. 4A). Lee and others 

(2009) found that all five cypress wetlands studied during 

the 2003–05 wet period generated an outflow stream during 

part of the period, and four received inflow from neighboring 

wetlands. Runoff estimates in the study by Lee and others 

(2009) emphasize the importance of preserving the linkage 

between wetlands and surrounding uplands to sustain the 

natural wetland hydrology.

 The study wetlands in Lee and others (2009) were 

located in relatively undisturbed areas where intermittent linkages formed between isolated wetlands as well as streams and 

rivers. In many areas of Northern Tampa Bay area, however, 

land-use changes have severed these linkages. During high 

rainfall events, many isolated wetlands become interconnected 

through surface-water flow channels. Although these channels are often barely discernable on the ground because of 

their extremely low gradients, the “trails” between wetlands 

shown in figure 4B provides visual evidence of these channels. 

Land-use changes can interfere with overland flow patterns 

and consequently reduce or increase surface-water inflow to 

wetlands, altering their predevelopment hydroperiod (Mike 

Hancock, Southwest Florida Water Management District, 

unpub. data, 2009). In one example, the natural connection 

between two adjacent wetlands has been restricted by a land 

berm that surrounds the northern half of one wetland, limiting 

surface-water inflow (fig. 4C).
8 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

A B

C D

Land berm

Outflow

ditches

Wetlands

connecting

through

low-gradient

surface-water

flow channels

Wetlands

connecting through

low-gradient surface-water

flow channels

Aerial photos courtesy of the Southwest Florida Water Management District, 2009

Figure 4. A–C, isolated wetlands connecting through low-gradient surface-water drainage channels and D, outflow ditches 

from wetlands.

 Changes in land use, such as road construction, also 

have affected wetland hydrology for hundreds of years 

(Biebighauser, 2007). Many roads in Florida were originally 

built through wetlands and their construction required 

wetland drainage, reducing the predevelopment flooded 

area (fig. 4C). Haag and others (2005) reported that a small 

roadway through the eastern part of the 8.8-acre W–05 

Cypress wetland in the Cypress Creek well field (fig. 1) 

reduced the potential flooded area by 18 percent. A ditch 

created along the western side of the roadway reduced the 

outflow elevation below that of the wetland perimeter, 

artificially reducing the flooded area of the wetland at high 

levels. This was confirmed by stage-volume relation curves 

of W–05 Cypress wetland, which indicated that the maximum 

inundated area of the wetland was only 7.2 acres. Therefore, 

the inundated area of W–05 Cypress never covered the entire 

8.8-acre extent of the wetland. Although W–05 Cypress has 

been affected by the roadway and ditch construction, lowered 

groundwater levels from localized groundwater withdrawals 

and karst subsidence also impacted the wetland. As of 2009, 

this wetland was augmented with groundwater to maintain 

surface-water levels. 

Although ditching has been beneficial to agricultural 

needs, associated declines in the hydrology of wetlands 

have been documented. Ditches are often constructed in 

agricultural areas to reduce the amount of standing water and 
Description of Study Area 9

enhance productivity (fig. 4D). A study by Bailey (1994) in 

the Cone Ranch (fig. 1) showed that wetland ditching eliminated some wet prairie wetlands and reduced the hydroperiod 

of other isolated cypress wetlands. The study determined that 

49 percent of the wetlands originally present at Cone Ranch 

had been converted to uplands. The elevations of nearby 

creeks were lowered by artificial excavation, and wetlands 

connected to these creeks by ditches had undergone induced 

surface-water drainage. The percentage of individual wetland 

loss at the ranch was directly related to ditch size and distance 

from the ditch (Bailey, 1994). 

 Increased groundwater withdrawals have contributed 

substantially to the hydrologic decline of some impacted 

wetlands in the study area. In 2005, Florida ranked sixth in 

the Nation in groundwater use (Marella, 2009), and in the 

Northern Tampa Bay area, the majority of the groundwater 

is obtained from the Upper Floridan aquifer. Groundwater is 

obtained for a variety of uses, including agriculture, industry, 

and recreation, with public supply accounting for the largest 

use (Metz and others, 2007). The largest groundwater withdrawals are from the 11 interconnected well fields located 

throughout the study area (fig. 1). Average annual groundwater 

withdrawals from the consolidated well fields have increased 

steadily since the 1930s to an average of 165 Mgal/d by the 

early 2000s (fig. 5A; Robert Peterson, Southwest Florida 

Water Management District, unpub. data, 2009). 

 Prior to 1999, Tampa Bay Water (previously known 

as West Coast Regional Water Supply Authority), obtained 

the public water supply exclusively from groundwater in 

the Northern Tampa Bay area (fig. 5B; Tampa Bay Water, 

2010b). As efforts have been made to reduce the reliance on 

groundwater, alternative sources such as surface water and 

desalinated water have been used to supplement this use 

(fig. 5B; Tampa Bay Water, 2010b). Reductions in groundwater withdrawals were initiated in late 2002 at various well 

fields, and withdrawals decreased from an average annual rate 

of about 150 Mgal/d in 2001 to 96 Mgal/d during 2003–09 

(Robert Peterson, Southwest Florida Water Management 

District, unpub. data, 2009). In 2008, Tampa Bay Water’s 

potable water supply consisted of 61 percent groundwater, 

28 percent surface water, and 11 percent desalinated water 

(fig. 5B; Tampa Bay Water, 2010b). Future (2012) water plans 

for the study area include increasing the use of surface water 

to 45.5 percent to augment water supplies, thereby reducing 

the dependency on groundwater by about 16 percent and 

desalinated water by 2 percent (fig. 5B; Tampa Bay Water, 

2010b). The remainder of this report will examine current 

and long-term monitoring data at three well fields (Starkey, 

Cypress Creek, and Cypress Bridge) to determine the factors 

that influence the recovery of wetlands impacted by historical 

groundwater withdrawals.

Figure 5. A, Combined groundwater withdrawals from 

the 11 consolidated well fields; B, allocation for water 

supply in the Northern Tampa Bay area; and C, annual 

groundwater withdrawal rates for the Starkey, Cypress 

Creek, and Cypress Bridge well fields.

1998 2012

100 percent

2008

61

percent

28

percent

45.5

percent 45.5

percent

11 percent 9 percent

0

50

100

150

Combined groundwater withdrawals,

in million gallons per day

0

5

10

15

20

25

Annual groundwater withdrawal rates,

in million gallons per day

12-month moving average

A

EXPLANATION

B

Source: Tampa Bay Water, 2010

200

250

30

35

C

Cypress Creek

Cypress Bridge

Starkey

EXPLANATION

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

2006

2008

Source: Southwest Florida Water Management District, 2009

Year

EXPLANATION

Groundwater

Surface water

Desalination water

1930 35 40 45 50 55 60 65 70 75 80 85 90 95 2000 05 2010

Year

Source: Southwest Florida Water Management District, 2009
10 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Description of Well Fields 

 Wetlands selected for this study are located at three well 

fields (Starkey, Cypress Creek, and Cypress Bridge) in the 

Northern Tampa Bay area (fig. 1). The annual groundwater 

withdrawal rates for these well fields are shown in figure 5C. 

Starkey well field is located about 7 miles (mi) east of the Gulf 

of Mexico on a flat coastal flood plain situated in a hummocky 

karst environment (Hutchinson, 1984). Starkey well field 

covers about 12 mi2 of undeveloped land that mostly consists 

of pine flatwoods and sand hills; about a third of the area 

consists of cypress domes, marshes, and wet prairies (Rochow, 

1998). Large strands of riverine swamps (associated with the 

Pithlachascotee and Anclote Rivers) are located to the north, 

south, and east of the well field. Lands adjacent to the well 

field are mostly rural, although moderate-density residential 

development borders the western side of the property and a 

four-lane highway borders the eastern side. 

 In the Starkey well field, 14 production wells pump 

groundwater from the Upper Floridan aquifer, and these wells 

are located along an approximate 5-mi east-west orientation 

(fig. 6A). Between 1975 and 1983, annual pumpage ranged from 

about 1 to 6 Mgal/d, and from 1984 to 2007, annual pumpage 

ranged from 8 to 13 Mgal/d. Groundwater withdrawals were 

then reduced to less than 4 Mgal/d during 2008 (fig. 5C).

 Groundwater withdrawals began in the mid-1970s 

from four production wells on the western part of Starkey 

well field, and by the late 1970s, hydrologic and vegetation 

changes were noted in these areas (Rochow and others, 

1976; Rochow and Bartos, 1978). The first observations of 

environmental declines affecting Starkey well-field wetlands 

included reduced hydroperiods followed by stresses to the 

aquatic vegetation (Rochow 1982, 1983a, 1985a, 1998). 

Later impacts to the wetlands included replacement of 

aquatic plants by upland plants or trees, introduction of 

invasive species, wetland-bottom subsidence, soil loss and 

compaction, leaning and fallen trees, intense fires, and a 

reduction in wetland-dependent wildlife (Dooris and others, 

1990; Rochow, 1998). By 1983, groundwater withdrawals 

were concentrated at the center of the well field, and in 

following years, similar adverse effects were noted in this 

area (Rochow, 1998). In 1989, groundwater production 

began at two wells in the eastern part of the well field, but at 

a smaller rate (2.7 Mgal/d). Consequently, wetlands in this 

area were not as impacted as those in the central and western 

parts of the well field (Rochow, 1998). 

 Because of the adverse effects of groundwater withdrawals on the hydrology of wetlands at Starkey well field, 

various water-management measures were implemented to 

minimize the impacts to wetlands and reduce the reliance on 

groundwater. Since 1990, one impaired wetland at Starkey 

well field has been augmented with groundwater to raise 

water levels and protect native flora and fauna (Tampa Bay 

Water, 2000). In 1998, Tampa Bay Water implemented the 

Optimized Regional Operations Plan to rotate and optimize 

production between the 11 well fields (Tampa Bay Water, 

2004, 2010b). In 2008, groundwater withdrawals at Starkey 

well field were reduced to an average annual rate of about 

4 Mgal/d, a reduction of more than half the 2007 rate of 

11 Mgal/d (Robert Peterson, Southwest Florida Water 

Management District, unpub. data, 2009).

 Cypress Creek well field is about 7 mi2, and is located 

about 8 mi east of Starkey well field (fig. 1). Most of the 

well field lies within a natural, relatively undisturbed setting 

surrounded by agricultural and residential areas. About 62 

percent of the well field is composed of palustrine wetlands 

that are bisected by Cypress Creek, which flows southward 

through the center of the well field (fig. 7A). The creek is 

poorly defined where it meanders through the Big Cypress 

Swamp (figs. 1 and 7A). In the low-lying areas, the water 

table is at or above land surface part of the year, and in the 

upland areas the water table gently slopes toward Cypress 

Creek (Yobbi, 2002). 

 A total of 12 Upper Floridan aquifer production wells 

are located at Cypress Creek well field trending along an 

approximate 2.5-mi northeast to southwest orientation 

(fig. 7A). Groundwater withdrawals expanded from three 

wells in mid-1976 to 13 wells by 1980. The average annual 

production rate from 1978 to 2002 was approximately 

28 Mgal/d (fig. 5C). Groundwater withdrawals were reduced 

to an average of 15 Mgal/d after 2002 to lessen the impacts 

to wetlands at this well field (fig. 5C).

 As with Starkey well field, large declines in surficial 

and Upper Floridan aquifer water levels negatively affected 

wetlands at Cypress Creek well field after the production rate 

increased (Rochow, 1998). These impacts included reduced 

hydroperiods, stresses to aquatic vegetation, replacement of 

aquatic plants by upland plants, wetland-bottom subsidence, 

development of sinkholes, leaning and fallen trees, intense 

fires, soil loss and compaction, and the reduction in wetlanddependant wildlife (Rochow and Bradbury, 1978; Rochow 

1981, 1983b, 1983c; Mike Hancock, Southwest Florida 

Water Management District, unpub. data, 2009). Because 

of declines in aquifer water levels and the resulting reduced 

hydroperiods, five wetlands in the Cypress Creek well field 

have been augmented with groundwater to protect native 

flora and fauna (Tampa Bay Water, 2004). 

 Cypress Bridge is a dispersed well field located several 

miles south of Cypress Creek well field, and encompasses 

about 73 acres of proximate but unconnected publicly 

and privately owned land parcels in Pasco and northern 

Hillsborough Counties (fig. 1). The 10 production wells 

are interspersed among marshes, cypress domes, wet prairies, and residential and commercial areas; in recent years 

residential and commercial development have increased 

(fig. 8A). About 32 percent of Cypress Bridge well field 

is composed of palustrine wetlands that include mixedhardwood and cypress swamp forests associated with several 

small creeks in the area. 
Description of Study Area 11

Figure 6. A, location of the study wetlands and production wells at the Starkey well field and B-E, individual 

study wetlands. 

STK9 STK3 STK7

STK8 STK6 STK2

STK1 STK4

STK14

STK11

STK12

STK13

STK15

STK10

S-68 Cypress

Starkey Central

S-44 Cypress

Grass Prairie

B. S-68 Cypress, December, 2009 C. Starkey Central, November, 2007

D. S-44 Cypress, November, 2007 E. Grass Prairie, January, 2009

A.

36-39

40-42

43-45

25

26-27

28-30

31-35

1 KILOMETER

0 1 MILE

0

0.5

0.5

Photo credit: P.A. Metz Photo credit: P.A. Metz

Photo credit: P.A. Metz Aerial photo courtesy of the Southwest Florida

Water Management District, 2009

Study wetland – Name

and boundary.

EXPLANATION

S-68

Cypress

24

STK3

46

47

Aerial photo courtesy of the Southwest Florida Water Management District, 2009

N

Starkey well-field

boundary

Well and rain gage –

Location and index

number in table 3.

Production well –

Name and location.
12 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Figure 7. A, location of the study wetlands and production wells at the Cypress Creek well field and B-E, individual 

study wetlands. 

CC9

CC8

CC7

CC6 CC5

CC4 CC3

CC2

CC 1

CC10

CC13

CC12

CC11

W-33 Cypress

W-56 Cypress

W-16 Marsh

B. W-33 Cypress, April 7, 2008 C. W-56 Cypress, April 7, 2008

D. W-12 Cypress, April 7, 2008 E. W-16 Marsh, April 7, 2008

A.

Big Cypress Swamp

Cypress

Creek

19-20

24AB

15-18

12-14

7-8

9-11

21

22-24

24CD

W-12 Cypress

Aerial photo courtesy of the Southwest Florida Water Management District, 2009

0 1 MILE

0 1 KILOMETER

0.5

0.5

Photo credit: P.A. Metz Photo credit: P.A. Metz

Photo credit: P.A. Metz Photo credit: P.A. Metz

Study wetland – Name and boundary.

Cypress Creek well-field boundary

Production well

Well and rain gage

– Name and location.

– Location and

index number in table 3.

EXPLANATION

W-12

Cypress

17

CC9

N
Description of Study Area 13

Figure 8. A, location of the study wetland and production wells at the Cypress Bridge well field; B, monitoring sites and 

land-use development surrounding the wetland; C, encroachment of upland species and tree fall; and D-E, small and large 

sinkholes at the Cypress Bridge 01 wetland. 

EXPLANATION

6

Cypress

Bridge 01

CY8

Study wetland – Name and boundary.

0 1 MILE

0 1 KILOMETER

0.5

0.5

CY8 CY9

CY7

CY6

CY4

CY5

CY2

CY1

CY11

CY10

Cypress

Bridge 01 Cypress

Bridge 01

A B

C

D E

Interstate 75

1-2

3-5 6

6A

Aerial photo courtesy of the Southwest Florida Water Management District, 2009

Aerial photo courtesy of the Southwest Florida Water Management District, 2009

Photo credit: P.A. Metz

Photo credit: P.A. Metz Photo credit: P.A. Metz

N

Production well – Name and location.

Well and rain gage – Location and index

number in table 3.
14 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Unlike groundwater withdrawals at the Starkey and 

Cypress Creek well fields, withdrawals have increased at 

Cypress Bridge well field. The annual average withdrawal 

rate at Cypress Bridge well field was less than 0.5 Mgal/d 

from 1982 to 1995. Production increased to an annual 

average withdrawal rate of approximately 8 Mgal/d from 

1996 to 2009 (fig. 5C). 

Study Design 

 To determine the factors that influence the hydrologic 

recovery of wetlands in the Northern Tampa Bay area, nine 

wetlands in various stages of hydrologic impairment were 

examined. Established minimum surface-water levels for 

wetlands set by the Southwest Florida Water Management 

District (1999a,b) were used to help determine the degree of 

wetland impairment (Southwest Florida Water Management 

District, 1999c). For wetlands that did not have an established minimum surface-water level, the classification was 

based on comparisons with control wetlands from a study 

by Lee and others (2009), and with nearby wetlands that had 

achieved minimum surface-water levels. In addition, historical 

(1975–98) and recent (2005–07) ecological monitoring data 

collected by the Wetland Assessment Procedure (WAP) 

were used to help determine the hydrologic impairment 

resulting from groundwater withdrawals (Southwest Florida 

Water Management District, 2005; Southwest Florida Water 

Management District 2008; Mike Hancock, Southwest Florida 

Water Management District, unpub. data, 2009). The study 

wetlands were then classified as unimpacted, minimally 

impacted, moderately impacted, or severely impacted. 

In the present study, the wetland classified as unimpacted generally had similar historical flooded-area duration 

characteristics to natural wetlands in west-central Florida 

(Lee and others, 2009). Vegetation surveys of the unimpacted 

wetland reported native indicator species adapted for growing 

in standing water or saturated soils (Hancock and others, 

2005; Mike Hancock, Southwest Florida Water Management 

District, unpub. data, 2009).

Minimally impacted wetlands had hydroperiods influenced by groundwater withdrawals or above-average rainfall 

conditions. These wetlands had a slightly above average 

decline in wetland water levels during average rainfall years 

and had some vegetation changes. Vegetation surveys indicated stresses to the tree canopy and a reduction in vegetative 

groundcover (Hancock and others, 2005; Mike Hancock, 

Southwest Florida Water Management District, unpub. 

data, 2009).

Moderately impacted wetlands had a more reduced 

wetland hydroperiod than minimally impacted wetlands 

under the same climatic conditions. Historical flooded-area 

duration characteristics for moderately impacted wetlands 

were similar to those of impacted wetlands in west-central 

Florida as described by Lee and others (2009). Documented 

impacts include soil loss by desiccation and compaction, 

vegetation changes, or changes in surface-water inflow and 

outflow patterns (Mike Hancock, Southwest Florida Water 

Management District, unpub. data, 2009). Field observations revealed that the moderately impacted wetlands were 

influenced by karst subsidence or sinkhole development. 

Vegetation surveys indicated leaning trees, introduction of 

non-native species, and encroachment of upland species within 

the deepest areas of the wetlands. 

Severely impacted wetlands generally had little to no 

standing water during the study period or in prior years. 

Impacts to the wetlands included loss of wetland soil sediments by desiccation and compaction, loss of sediment due to 

intense fires, or both. Karst subsidence features were observed 

at these wetlands. Vegetation surveys indicated extensive tree 

loss, leaning and fallen trees, and encroachment of upland 

species within the deepest areas of the wetlands (Hancock 

and others, 2005; Mike Hancock, Southwest Florida Water 

Management District, unpub. data, 2009).

Study Wetlands

 The study wetlands located in the Starkey well field 

consist of three isolated cypress domes (S–68 Cypress, 

Starkey Central, and S–44 Cypress) and one isolated marsh 

(Grass Prairie) (fig. 6A and table 1). S–68 Cypress wetland is 

a 5.8-acre cypress dome in the southeastern part of the well 

field, and is classified as unimpacted (fig. 6B and table 1). 

Long-term hydrologic monitoring data (1989–2009) at S–68 

Cypress indicate the wetland has not experienced a reduced 

hydroperiod and has similar hydroperiods to wetlands located 

in a natural setting (Lee and others, 2009). Data collected 

through the WAP indicate that this wetland is in good health, 

with all trees, shrubs, and groundcover located in appropriate 

zones within the wetland boundary (Hancock and others, 

2005; Mike Hancock, Southwest Florida Water Management 

District, unpub. data, 2009). 

 Starkey Central is a 2.8-acre cypress dome located in the 

center of Starkey well field, and is classified as moderately 

impacted (fig. 6C and table 1). Hydrologic and biological 

monitoring began in 1985, 2 years after pumping was shifted 

to the center of the well field. Wetland data collected at this 

time indicated the cypress dome was still in good health. 

Within 4 to 5 years after monitoring began, however, observations indicated a reduced hydroperiod, influx of transitional 

and upland species, moderate soil subsidence around tree 

roots, land surface subsidence, and increased mortality and 

leaning of cypress trees (Rochow, 1998; Mike Hancock, 

Southwest Florida Water Management District, unpub. data, 

2009). In addition, an intense fire in the 1990s compounded 

the deterioration of ecological conditions in the cypress dome. 

S–44 Cypress is a 2.5-acre cypress dome in the center 

of Starkey well field, and is classified as severely impacted 

(fig. 6D and table 1). Hydrologic and biological monitoring, 

which began at this site in 1988, documented a reduced 
Study Design 15

hydroperiod, fire scars on most of the cypress trees, soil 

subsidence due partly to burning of the wetland-bottom 

sediments, and many leaning and fallen trees (Rochow, 1998). 

In 1990, the central part of the wetland subsided several feet 

due to a subsurface limestone collapse (Stewart and Stedje, 

1990; Watson and others, 1990), and the number of fallen trees 

increased during subsequent years. Aerial photographic surveys 

of the wetland conducted from 1952 to 1989 indicate that the 

wetland canopy was healthy through 1981, but had deteriorated 

by 1989 (Rochow and Rhinesmith, 1991). Currently (2009), 

most of the cypress trees in S–44 Cypress have fallen (fig. 6D). 

 Grass Prairie is a 68-acre marsh in the western part of 

Starkey well field, and is classified as a moderately impacted 

(fig. 6E and table 1). Long-term monitoring indicates the 

wetland has a reduced hydroperiod, a reduction in native 

aquatic vegetation, and has undergone extensive soil subsidence (Rochow, 1998; Hancock and others, 2005; Mike 

Hancock, Southwest Florida Water Management District, 

unpub. data, 2009). The reduced hydroperiod has created 

cracks and fissures in the wetland-bottom sediments, and soil 

subsidence has caused large clumps of soil to detach from the 

wetland bottom. Sediment loss was estimated to be 1 to 2 ft in 

thickness and to cover an area of 30 × 200 ft (Rochow, 1998). 

 The study wetlands located in the Cypress Creek well 

field consist of three isolated cypress domes (W–33 Cypress, 

W–56 Cypress, and W–12 Cypress) and one isolated marsh 

(W–16 Marsh) (fig. 7A and table 1). W–33 Cypress is a 

1.2-acre cypress dome in the southern part of Cypress Creek 

well field, and is classified as minimally impacted (fig. 7B). 

In 1980, initial observations of this wetland indicated no 

noticeable adverse impacts to wetland health. By 1984, 

however, vegetative stresses to the wetland canopy were 

evident, and in 1999, a fire damaged the wetland and adjacent 

forested area (Rochow, 1998). Long-term water-level records 

(1989–2009) do not indicate a reduced wetland hydroperiod, 

although some encroachment of upland species has occurred 

(Hancock and others, 2005; Mike Hancock, Southwest Florida 

Water Management District, unpub. data, 2009). 

 W–56 Cypress is an 0.9-acre cypress dome in the 

southern part of Cypress Creek well field, and is classified 

as minimally impacted (fig. 7C and table 1). W–56 Cypress 

is located about 1 mi from the high-production area of the 

well field, and although observations since 1980 indicate a 

below average hydroperiod during drought periods, they also 

indicate that wetland water levels recover during average 

rainfall periods (Rochow, 1985b; 1998; Mike Hancock, 

Southwest Florida Water Management District, unpub. data, 

2009). Long-term vegetation monitoring indicates that the 

wetland has remained healthy, although some encroachment 

of transitional tree and groundcover species has occurred 

(Hancock and others, 2005; Mike Hancock, Southwest Florida 

Water Management District, unpub. data, 2009).

W–12 Cypress is an 8.4-acre cypress wetland in the 

center of Cypress Creek well field, and is classified as 

severely impacted (fig. 7D and table 1); groundwater withdrawals are more concentrated in this part of the well field 

than at W–33 Cypress and W–56 Cypress. Based on longterm monitoring, W–12 Cypress has experienced a reduction 

in hydroperiod, encroachment of upland species, soil subsidence, tree root exposure, wetland-bottom subsidence, and 

canopy thinning due to abnormally high tree fall (Hancock 

and others, 2005; Mike Hancock, Southwest Florida Water 

Table 1. Name, location, and other characteristics of the study wetlands.

[IC, isolated cypress; M, marsh; latitude and longitude in degrees (°), minutes (′), and seconds (′′)]

Wetland name Alternate wetland name Latitude Longitude Type Classification Approximate 

size (acres)

Starkey well field

S–68 Cypress Starkey DD 28°14′21.00′′N 82°34′31.00′′W IC Unimpacted 5.8

Starkey Central1 Central #1 28°14′40.62′′N 82°35′46.65′′W IC Moderately impacted 2.8

S–44 Cypress Starkey Western; Widow Maker 28°14′48.41′′N 82°36′23.21′′W IC Severely impacted 2.5

Grass Prairie Starkey G; S-24 28°14′55.26′′N 82°38′23.18′′W M Moderately impacted 68

Cypress Creek well field

W-33 Cypress East Cypress Head 28°16′34.53′′N 82°23′34.98′′W IC Minimally impacted 1.2

W–56 Cypress1 Cypress Creek G 28°16′21.57′′N 82°24′18.56′′W IC Minimally impacted 0.9

W–12 Cypress1 T2 Cypress Head 28°17′34.00′′N 82°23′41.23′′W IC Severely impacted 8.4

W–16 Marsh Marsh D; Ted’s Marsh 28°17′21.34′′N 82°23′33.10′′W M Severely impacted 4.2

Cypress Bridge well field

Cypress Bridge 01 CYB–01 28°13′20.10′′N 82°22′06.58′′W IC Moderately impacted 1.7

1

Surface-water minimum levels established by Southwest Florida Water Management District, 1999.
16 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Management District, unpub. data, 2009). During 16 of the 

past 30 years, the wetland has been completely dry. Water 

was present in this wetland during above-average rainfall 

periods during 1981–83, 1997–98, and 2002–05 (Mike 

Hancock, Southwest Florida Water Management District, 

unpub. data, 2009). 

 W–16 Marsh is a 4.2-acre wetland, and is the most 

severely impacted of the study wetlands (fig. 7E and table 1). 

Similar to W–12 Cypress, this marsh is located in the center 

of Cypress Creek well field where groundwater withdrawals 

are concentrated (fig. 7A). Prior to the first groundwater 

withdrawals in 1975, W–16 Marsh contained standing water 

in the center of the wetland for 8 to 10 months of the year and 

contained native aquatic species (Rochow, 1998). Within the 

first several years of well field production, however, the marsh 

drained completely, and standing water was present at this site 

for only brief periods during large rainfall events (Rochow and 

Bradbury, 1978; Rochow, 1998; Mike Hancock, Southwest 

Florida Water Management District, unpub. data, 2009). 

In 1983, five sinkholes were reported near the perimeter of 

the wetland (Rochow, 1983c). Other observed effects at W–16 

Marsh include oxidation of wetland soil, several intense fires, 

a decrease in native aquatic vegetation, and encroachment of 

upland species (Pinus elliotti; slash pine). 

 Cypress Bridge 01 is a 1.7-acre cypress dome in the 

northern part of Cypress Bridge well field (figs. 1 and 8A) and 

is classified as moderately impacted (table 1). The wetland is 

located directly south of a high-density housing development 

(fig. 8B) and wetland mitigation ponds are present to the 

south and east. A small ditch that borders the western side of 

Cypress Bridge 01 channels water into the wetland during 

high rainfall events. Production well CY2 is 0.43-mi northeast of the wetland, and several sinkholes formed along the 

wetland bottom during well development in 1996 (Mike 

Hancock, Southwest Florida Water Management District, 

unpub. data, 2009; fig. 8D–E). In addition to the sinkholes, 

interruptions in surface-water flow patterns from connecting 

wetlands have resulted from residential and highway development. Because of these changes, the wetland has experienced 

a reduced hydroperiod, excessive tree fall, introduction of 

upland species, and a decrease in tree canopy (Hancock 

and others, 2005; Mike Hancock, Southwest Florida Water 

Management District, unpub. data, 2009; fig. 8C). 

Methods of Investigation

 The study wetlands were examined based on four factors 

known to influence the hydrologic condition and recovery of 

wetlands in west-central Florida including the topographic 

setting, permeability of the underlying sediments, recent 

karst activity, and depth to the potentiometric surface of the 

Upper Floridan aquifer beneath the wetland. Multiple lines 

of evidence were used to establish how each of these four 

factors has affected the ability of water levels in the study 

wetlands to recover. Depending on the availability of data, 

comparisons were made between all or subsets of the nine 

study wetlands. Table 2 lists each factor, supporting evidence 

for that factor, and which of the study wetlands had data that 

could be used to describe the effect.

The topographic settings of the study wetlands were 

analyzed using surface-elevation data collected by LIDAR 

(Light Detection and Ranging)―a remote sensing system 

used to collect topographic data (Fugro Earthdata, Inc., 2010). 

The surface-elevation data were used to determine the physical 

setting of the study wetlands and its relation to other topographical features such as upland areas, rivers, or low-lying 

discharge areas. The LIDAR data, satellite imagery, and aerial 

photography also were used to determine depressional inflow 

and outflow connections between isolated wetlands.

 The underlying geology at or near the study wetlands 

was interpreted from existing geologic and borehole 

geophysical logs, geologic contour maps, grain-size analysis, 

and descriptions of cuttings from USGS wells drilled during 

the study. To compare and contrast the underlying geology 

and wetland-bottom sediments between study wetlands, 

continuous cores were collected at six study wetlands using 

a vibracore (table 2). These cores were collected using a 

Bradford pneumatic vibrator, which drove a 3-in.-diameter 

aluminum core barrel into the underlying substrate material 

until an impenetrable substrate was encountered (Lanesky 

and others, 1979). This method produced a complete intact 

profile of the wetland-bottom sediments and a shallow profile 

of the underlying geology. The vibracores were split in half 

for visual inspection, measured, described, and photographed 

for archiving. At selected intervals within the vibracores, 

samples were collected to determine the relative mass percentages of sand, silt (organics), and clay. These samples were 

analyzed using grain-size analysis techniques as described by 

Wentworth (1929) and Shepard (1954). 

 To define the geometry and to detect any subtle 

depressional features in the wetland bottom, bathymetric data 

were collected at six of the study wetlands by USGS personnel 

(table 2). The elevation of the wetland bottom was surveyed 

at numerous locations across its extent using a Topcon Total 

Station (Topcon GTS 303D). Bathymetric maps were then 

created using a GIS (geographical information system) in 

which digital interpolation and contouring routines were used 

to delineate the wetland-bottom configuration. Bathymetric 

maps also were used to determine the size of the inundated 

area and the water volume stored in the wetlands over a range 

of historical stage values. These methods are discussed further 

in Haag and others (2005) and Lee and others (2009).

 To provide evidence of karst subsidence in wetland 

basins, ground-penetrating radar (GPR) surveys were 

conducted at a severely impacted wetland (W–16 Marsh) and 

a moderately impacted wetland (Cypress Bridge 01). This 

surface-geophysical technique can profile subsurface layers 

and identify areas where deposits are slumped downward 

or breached by subsidence from sinkhole development 

(Wilson and Garmen, 2002). In both GPR surveys, data were 

collected only within the wetland perimeter. The surveys were 
Study Design 17

performed using a Professional Explorer (ProEx) system in the 

manner described by Barr (1993) and Kruse and others (2006). 

The depth of reflected signals was correlated with geologic 

data at known reference points. 

 Wetland water levels were compared to water levels in 

the underlying aquifers. The analysis incorporated long-term 

historical monthly to bimonthly groundwater and surfacewater level data collected by the USGS, SWFWMD, and 

Tampa Bay Water from 1989 to 2009. In addition, groundwater levels at or near all study sites were continuously 

monitored by the USGS (December 2007 to March 2009) to 

obtain detailed data on water-level differences for each study 

wetland (table 3). Water levels were recorded at each wetland 

using a fully-screened well that monitored surface-water 

levels during flooded periods and groundwater levels during 

dry periods. Consequently, several analyses in this report are 

based on data that represent alternating surface-water and 

groundwater levels, and the term “wetland/surficial aquifer” 

is used to describe these measurements. Water levels in the 

Upper Floridan aquifer also were monitored in the vicinity 

of each wetland. Pressure transducers and data loggers were 

used to continuously measure and record water levels in the 

wetland/surficial aquifer and the Upper Floridan aquifer in 

accordance with standard methods described in Freeman and 

others (2004). In addition, rainfall data were collected at seven 

of the study wetlands from December 2007 to March 2009 

to determine if rainfall accumulations at wetland sites were 

similar. Rainfall was measured by the USGS using storage 

rain gages, and tipping-bucket rain gages that recorded at 

15-minute intervals. 

Well characteristics and a data summary for the study 

wetlands are listed in table 3, and locations of the monitoring 

sites are shown in figures 6–8. Groundwater and surface-water 

level data collected during this study are available online from 

the USGS National Water Information System database using 

the USGS identification number at http://waterdata.usgs.gov/

fl/nwis/gw/dv/.

 Daily average wetland and aquifer levels were compared 

directly to help determine the relations between the wetland/

surficial aquifer and Upper Floridan aquifer, and to understand 

the connection between aquifer units. Linear regression 

analyses were used to help determine the strength of these 

water-level relations. The coefficient of determination, r2, 

indicates how much water-level variability in the wetland/

surficial aquifer is associated with water-level variability 

in the Upper Floridan aquifer. For example, an r2 value of 

0.50 means that 50 percent of the variability in wetland 

water levels is explained by variability in Upper Floridan 

aquifer levels. A significant statistical relation indicates a 

high degree of interconnection between the two aquifers 

Table 2. Methods used to describe the factors affecting the hydrologic condition and recovery of each study wetland.

Factors and methods 

Wetlands

S–68 

Cypress

Starkey 

Central

S–44 

Cypress

Grass 

Prairie 

W–33 

Cypress

W–56 

Cypress

W–12 

Cypress

W–16 

Marsh

Cypress 

Bridge 01

Topographical setting 

Light detection and ranging (LIDAR) data, satellite 

imagery, aerial photography, topographic maps

x x x x x x x x x

Permeability of underlying sediments

Existing historical geologic data near wetland x x x x x x x x x

Visual inspection of wetland-bottom sediments x x x x x x x x x

Collection and description of vibracores x x x x x x

Grain-size analysis of vibracore x x x x x x

Evidence of recent karst subsidence

Historical sinkhole data x x x x x x x x x

LIDAR data, satellite imagery, aerial photography x x x x x x x x x

Field inspection of suspected karst features x x x x x x

Ground-penetrating radar survey x x

Bathymetric survey x x x x x x

Potentiometric surface of the Upper Floridan aquifer

Historical trends in wetland/surficial aquifer 

water-level data in relation to water levels in the 

Upper Floridan aquifer

x x x x x x x x x

Historical groundwater withdrawal data within a 

1-mile radius from center of wetland

x x x x x x x x x

Depth to the potentiometric surface of the Upper 

Floridan aquifer below the wetland

x x x x x x x x x
18 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Table 3. Well characteristics and other data collected at the study wetlands.

[USGS, U.S. Geological Survey; SW, surface water; SA, surficial aquifer, UFA, Upper Floridan aquifer; CWR, continuous water-level recorder; 

WL, periodic water level; —, unknown casing depth; na, not applicable]

Index 

number Identification number Name

Total well 

depth 

(feet)

Total well cased 

interval 

(feet)

Hydrologic 

unit

Data

 summary

Cypress Bridge well field 

1 281325082215301 FL-2-1000 704 186 UFA CWR

2 281327082215401 CYB WT 2-1000 14 — SA WL

3 281320082220701 CYB-01 Sink 2 5 5 SA CWR

4 281320082220700 CYB-01 Crest Stage Indicator na na SW WL

5 281319082220701 CYB-01 13 ft 13 — SA CWR

6 281318082220701 CYB-01 Sink 1 16 11 UFA CWR

6A 281318082220700 CYB-01 rain gage na na na Rain

Cypress Creek well field 

7 281637082233201 CCWF-829D 52 49 UFA CWR

8 281637082233202 CCWF-829S 14 — SA WL

9 281635082233501 CCWF-W33A 6 — W/SA CWR

10 281635082233502 CCWF-W33 9 — SA WL

11 281637082233700 CCWF-W33 Rain na na na Rain

12 281723082233602 CCWF BIO-4 15 — W/SA WL

13 281722082233401 CCWF W-16 USGS Center 19 9 W/SA CWR

14 281723082233601 CCWF W-16 Upland 21 11 SA CWR

15 281729082234100 CCWF W-12 rain gage na na na Rain

16 281731082233901 CCWF W-12 Upland 14 — SA CWR

17 281733082234001 CCWF W-12 INT 18 — SA CWR

18 281733082234002 CCWF-W12A 8 — SA WL

19 281726082234601 CCWF 826 Deep 37 32 UFA CWR

20 281726082234602 CCWF 826 Shallow 11 — SA WL

21 281622082241301 Cypress Creek Deep 3 352 136 UFA CWR, Rain

22 281622082241801 CCWF G WTL 6 — SA CWR

23 281622082242001 CCWF G UPL 7 — SA CWR

24 281622082242002 CCWF BIO-6 11 — SA WL

24A 281746082233701 CCWF-TMR-3 Deep 625 160 UFA CWR

24B 281746082233702 CCWF-TMR-3 Shallow 11 7 SA CWR

24C 281650082244501 CCWF-TMR-4 Deep 592 99 UFA CWR

24D 281650082244501 CCWF-TMR-4 Shallow 24 20 SA CWR

 Starkey well field

25 281418082343001 Starkey S-68 CTR 3 3 W/SA CWR

26 281421082343101 Starkey S-68 UNW NRSD 14 10 SA CWR

27 281421082343102 Starkey S-68 FLRD 130 80 UFA CWR, Rain

28 281442082354901 STWF 1A Central 100 98 UFA CWR, Rain

29 281442082354902 STWF 1B Central 13 5 SA WL

30 281442082354903 STWF 1C Central 7 6 SA WL

31 281442082351601 STWF Central 30 5 SA WL

32 281441082354601 STWF 2B Central 30 8 SA CWR

33 281441082354401 STWF 3A Central 21 20 SA WL
Study Design 19

(r2 = 1.00). The linear regressions presented are all significant 

to an alpha level of 0.05, which corresponds to a 95-percent 

confidence interval.

 To understand the effects of groundwater withdrawals 

on the hydrology of each wetland, pumpage records were 

examined for the total period-of-record for individual 

well fields (Robert Peterson, Southwest Florida Water 

Management District, unpub. data, 2009). In addition, the 

combined withdrawal rate within a 1-mi radius from the 

center of each study wetland was examined to determine 

how the withdrawals affected the hydrology of the individual 

wetlands. The 1-mi-radius combined withdrawal rates were 

then compared among study wetlands.

 Long-term hydrographs and water-level trends for the 

surficial and Upper Floridan aquifers at both Starkey and 

Cypress Creek well fields were examined to help determine 

when impacts to wetlands may have occurred and if there was 

a substantial recovery in water levels. Statistical analyses were 

performed on the water-level data to determine trends for each 

aquifer. Linear regression analysis and the distance-weighted 

least-squares fitting method (McLain, 1974) were used to help 

determine trends in aquifer water levels.

 Generalized elevation-difference maps were created for 

Starkey and Cypress Creek well fields to define the groundwater conditions prior to and after groundwater development 

at these well fields. Land-surface elevation data obtained in 

2005 using LIDAR (Furgo Earthdata, Inc, 2010) were used to 

map the distance of the potentiometric surface of the Upper 

Floridan aquifer below the study wetlands. LIDAR data were 

provided by the SWFWMD for this analysis. Elevationdifference maps prior to groundwater development were 

created by subtracting the estimated potentiometric surface 

of the Upper Floridan aquifer prior to groundwater development (Johnston and others, 1980; app. 1) at the Starkey 

and Cypress Creek well fields from the recent land-surface 

elevation LIDAR data. Elevation-difference maps also were 

created for current (2008–09) pumping conditions at both well 

fields by subtracting the potentiometric surface of the Upper 

Floridan aquifer in September 2008 and May 2009 (apps. 2 

and 3, respectively) from the LIDAR data. Box plots were 

used to compare the historical and current levels of the Upper 

Floridan aquifer to the study wetland-bottom elevation prior 

to and after groundwater withdrawals were reduced at both 

well fields. 

Index 

number Identification number Name

Total well 

depth 

(feet)

Total well cased 

interval 

(feet)

Hydrologic 

unit

Data

 summary

34 281441082354402 STWF 3B Central 11 1 SA WL

35 281441082354403 STWF 3C Central 6 1 SA WL

36 281449082362501 STWF 1A West 95 85 UFA CWR, Rain

37 281449082362502 STWF 1B West 16 5 SA WL

38 281449082362503 STWF 1C West 23 15 SA WL

39 281449082362504 STWF 1D West 10 5 SA WL

40 281449082362301 STWF 2A West 56 46 SA WL

41 281449082362302 STWF 2B West 31 26 W/SA CWR

42 281449082362303 STWF 2C West 18 13 SA CWR

43 281448082362101 STWF 3A West 23 22 SA WL

44 281448082362102 STWF 3B West 30 25 SA WL

45 281448082362103 STWF 3C West 10 5 SA WL

46 281500082350402 Starkey 10 deep 392 153 UFA CWR

47 281427082382802 Starkey 728 Shallow 18 17 SA CWR

47A 281447082354302 SM-2 Shallow 18 17 SA WL

Other study wells

48 281558082264601 Pasco 13 49 43 UFA CWR

49 281636082372001 Moon Lake Deep 115 65 UFA CWR

50 281715082164401 State Hwy 577 150 57 UFA CWR

51 281949082332001 State Hwy 52 73 60 UFA CWR

Table 3. Well characteristics and other data collected at the study wetlands.—Continued

[USGS, U.S. Geological Survey; SW, surface water; SA, surficial aquifer, UFA, Upper Floridan aquifer; CWR, continuous water-level recorder; 

WL, periodic water level; —, unknown casing depth; na, not applicable]
20 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

 To compare and contrast the hydrologic condition of 

the wetlands prior to and after the reduction in groundwater 

withdrawals at the Starkey and Cypress Creek well fields, 

flooded-area maps and frequency-distribution graphs were 

developed for four study wetlands: an unimpacted wetland, 

a minimally impacted wetland, and two severely impacted 

wetlands. Bathymetric data and historical wetland/surficial 

aquifer levels were used to create the flooded-area maps and 

frequency-distribution graphs. 

A ranking system was used to determine the cumulative 

effect of the factors that influence the hydrologic recovery of 

wetlands. Ranking for three of the four factors (topographic 

setting, permeability of sediments underlying wetlands, and 

depth to the potentiometric surface of the Upper Floridan 

aquifer below the wetlands) was based on whether each factor 

had a positive influence, a neutral influence, or a negative 

influence. Ranking for the remaining factor (karst feature near 

or underlying wetland) was based on whether karst features 

were absent, near, or underlying the study wetland.

Factors that Influence the Hydrologic 

Recovery of Wetlands

 The following sections examine the four factors that 

influence the hydrologic recovery of wetlands in the study 

area, including: (1) the topographic setting, (2) the permeability of the sediments underlying the wetlands, (3) recent 

karst activity, and (4) the depth to the potentiometric surface 

of the Upper Floridan aquifer underlying the wetland. 

Examples from all or subsets of the study wetlands are used 

to demonstrate how each factor influences the hydrology of 

the wetlands. The effects of these factors on each of the study 

wetlands are then ranked to show the relative magnitude of 

each factor in relation to the wetland’s potential to recover 

when groundwater withdrawals are reduced. 

Topographic Setting

In the low-lying topographic setting of the study area, 

subtle elevation differences can influence the flow patterns of 

surface water and groundwater around wetlands. For example, 

if a wetland is topographically lower in the landscape than the 

surrounding areas, surface-water connections are made more 

easily to other wetlands and to other surface-water bodies 

through low-lying surface-water channels (fig. 4A–B). In addition, wetlands that are farther downgradient in a watershed 

drainage system are more likely to receive runoff from a larger 

contributing area than wetlands at higher elevations in the 

watershed (Lee and others, 2010). 

Several of the study wetlands have benefited from their 

position in a low-lying topographical setting. For example, 

S–68 Cypress is located near low-gradient surface-water 

channels and receives overland flow from surrounding areas 

and upgradient wetlands during high rainfall periods (fig. 9A). 

Daily water-budget results from Lee and others (2009) 

provide insights into the importance of this surface runoff to 

the hydrology of the isolated wetland. During periods when 

S–68 Cypress was gaining water in excess of direct rainfall, 

the daily increase in wetland volume was 1.74 times the daily 

rainfall volume. 

Wetlands that are topographically lower in the drainage 

basin and have surface-water connections had longer wetland 

hydroperiods than wetlands with no surface-water connections. Comparisons of water levels were made for two 

severely impacted wetlands (W–12 Cypress and W–16 Marsh; 

fig. 9B) that are located in the same area of the well field 

and have similar geology and elevation of the potentiometric 

surface underlying the wetland. During the high rainfall 

period of 2003–2005, W–12 Cypress was connected to other 

wetlands and had a longer hydroperiod in comparison to the 

nearby W–16 Marsh. The area surrounding W–12 Cypress 

is about 5 ft lower in elevation than W–16 Marsh, and the 

wetland is lower relative to the nearest surface-water bodies. 

Surface-water connections to nearby isolated wetlands and 

surface-water bodies are made more easily through localized 

low-gradient surface-water channels for W–12 Cypress than 

W–16 Marsh; thus extending the duration and volume of 

surface-water inflow that the wetland receives.

The topographic setting also influences the groundwater 

flow patterns surrounding and underlying the study wetlands. 

Relatively low-lying wetlands surrounded by uplands have 

a greater potential to be in either a groundwater discharge or 

flow-through setting (fig. 3B or C), and benefit from greater 

groundwater inflow or reduced leakage than wetlands in 

higher topographic settings. In a study by Lee and others 

(2009), the eastern side of W–19 Impaired Cypress was 

topographically higher than the western side, and the wetland 

received groundwater inflow from the higher side because 

the water table was close to land surface and higher than the 

wetland water level. As a result of this topographic setting, 

W–19 Impaired Cypress received greater groundwater inflow 

than other wetlands in that study, which were typically in 

recharge settings. W–19 also had the highest volume ratio of 

runoff to rainfall of the 10 wetlands analyzed in that study.

Separating the effects of differences in topographic 

setting on the potential for wetland recovery from other factors 

is difficult, because information on how subtle differences 

in topography can affect surface and groundwater flow to 

and from wetlands, and data on flows between wetlands, 

are not available. Studying wetlands on well fields is further 

complicated by the effects of pumping. Integrated modeling 

combined with LIDAR data is a promising methodology for 

quantifying these effects over broad wetland landscapes (Lee 

and others, 2010). When all other factors that influence the 

hydrologic condition of wetlands are the same, wetlands in 

a low-lying topographic setting have a greater potential to 

recover when groundwater withdrawals are reduced. 
Factors that Influence the Hydrologic Recovery of Wetlands 21

Figure 9. Light detection and ranging (LIDAR) digital elevation maps showing topography surrounding the 

study wetlands at the A, Starkey, and B, Cypress Creek well fields.

Starkey Central

S-44 Cypress Grass Prairie

S-68 Cypress

High: 64.18

Low 9.00

Elevation, in feet above NGVD 1929

Elevation, in feet above NGVD 1929

High: 82.79

Low 52.13

S-68 Cypress

43 Feet

43 Feet

A

B

37 Feet 46 Feet

35 Feet

Pithlachascotee

Anclote

River

Cross Cypress

Branch

River

Big

Cypress Swamp

Creek

Cypress

W-12 Cypress

W-16 Marsh

72 Feet W-33 Cypress

68 Feet

63 Feet

W-56 Cypress

65 Feet

0 1 MILE

0 1 KILOMETER

0.5

0.5

0 1 MILE

0 1 KILOMETER

0.5

0.5

EXPLANTION

Well-field boundary

Study wetlands – Name

and approximate elevation

of surrounding area.

N
22 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Hydrogeologic Setting

 The hydrogeologic setting beneath a wetland can 

substantially affect its potential for water-level recovery. 

Two aspects of the hydrogeology that affect wetland waterlevel recovery are the permeability of the sediments underlying wetlands, and the presence of karst features underlying 

or near the wetland. 

Permeability of Sediments Underlying the 

Wetlands

 Wetlands in the study area form in shallow saucer-shaped 

depressions in the mantled karst landscape (Sinclair, 1982). 

The low permeability layers that typically underlie these 

wetlands help retard the downward movement of water from 

the wetlands to the underlying Upper Floridan aquifer (Lee 

and others, 2009). The restriction of flow can create a lens or 

shallow groundwater recharge mound beneath a wetland that 

expands and contracts depending on hydrologic conditions 

(Lee and others, 2009). 

 Several components of the hydrogeologic framework 

help maintain the hydrology of shallow depressional wetlands 

in the study area, including (1) a thin clay layer in the nearsurface wetland-bottom sediments that slows the downward 

movement of water from the wetland (fig. 10A; Lee and 

others, 2009); (2) a clay or hard-pan layer that lies about 5 to 

10 ft below the wetland and retards the downward movement 

of groundwater (fig. 10A; Lee and others, 2009); and (3) an 

intact or thick clay layer of low permeability, referred to as the 

intermediate confining unit, that slows the movement of water 

between the wetland/surficial aquifer and the Upper Floridan 

aquifer (fig. 10A; Metz and Sacks, 2002; Lee and others, 

2009). For wetlands that reside in a groundwater recharge 

setting in the study area, these low permeability layers help 

sustain the wetland water levels by slowing the vertical 

leakage between the wetland and the underlying aquifers. 

Clay and organic matter in the wetland-bottom sediments 

are an important component of the wetland geology, and 

the thickness, structure, and consistency of these sediments 

varied widely among study wetlands (fig. 11). The top 2 ft 

of organic material collected from six of the study wetlands 

was (1) fibrous and matted (S–68, W–33, and W–56 Cypress 

wetlands), (2) peat and mud-like in consistency (S–44 Cypress 

and Grass Prairie wetlands), and (3) a sandy organic layer 

devoid of any fibrous and matted material (W–16 Marsh). 

Underlying the top organic sediments are mottled soils 

that contain dark stains or streaks. These mottled soils may 

indicate water-table fluctuations, poor surface drainage, or 

biological mixing (Tiner, 1999). 

Grain-size analysis of the top 2 ft of the wetland-bottom 

sediments indicates a generally decreasing trend in the organic 

matter (silt) with depth (fig. 11B). For some wetlands, a relatively thin clay-rich layer is present at the upper surface of the 

wetland-bottom sediments. In low-energy environments such 

as wetlands, fragments of organic matter act as a substrate 

for the adherence of settling clay particles, allowing them to 

accumulate (Mitsch and Gosselink, 2000). These near-surface 

clays in the wetland-bottom sediments helped slow the movement of water from the wetland, and the relative percentage of 

clays ranged from about 2 to 5 percent. The lowest percentage 

of near-surface clays was at the minimally impacted W–56 

Cypress (2 percent), whereas the highest percentage of 

near-surface clays was at the relatively unimpacted S–68 

Cypress and the severely impacted S–44 Cypress (about 4 and 

5 percent, respectively; fig. 11C). 

 The vibracores collected at six of the study wetlands 

provided insight into the variability of the low permeability 

layers underlying the wetland-bottom sediments (fig. 12A). 

These cores were collected until the impenetrable clay or 

hardpan layer below the wetland bottom was encountered, 

which ranged in depth from about 6 to 10 ft. At W–33 Cypress 

and Grass Prairie wetlands, a dense green-gray clay unit 

(fig. 12B) was encountered about 6 and 8 ft below the wetland 

bottom, respectively. At W–56 Cypress and S–68 Cypress, 

a tan colored, sandy-clay layer (fig. 12C) was encountered 

at about 6 and 8 ft below the wetland bottom, respectively. 

At S–44 Cypress, the core consisted of over 8 ft of peat-like 

material, followed by 1 ft of white sand, and by an impenetrable sandy-clay layer at about 10 ft. At W–16 Marsh, an 

impenetrable, clayey iron-stained layer was encountered about 

4.5 ft below the wetland bottom (fig. 12D). 

 Grain-size analysis of the sediments indicated that clay 

content increased with depth below five of the six study 

wetlands that were cored. As described earlier, these lowpermeability layers provide a mechanism to slow vertical 

groundwater flow so that water tends to accumulate or moundup underneath the wetlands. For Grass Prairie, W–16 Marsh, 

S–68 Cypress, and S–44 Cypress wetlands, clay percentages 

were greatest from about 3 to 10 ft below land surface, 

and ranged from about 6 to 10 percent (fig. 11C). At W–56 

Cypress, clay content ranged from about 2 to 3 percent and did 

not increase substantially with depth. 

 Another low permeability layer present beneath the 

wetlands is the intermediate confining unit, which separates 

the wetland/surficial aquifer from the Upper Floridan aquifer. 

This unit is about 20 to 30 ft below the study wetlands and 

its thickness varies throughout the study area (fig. 13). In the 

Cypress Creek well field, the confining unit thickness ranges 

from less than 25 ft along the southeastern boundary to 

about 50 ft near the northeastern boundary. The intermediate 

confining unit is less than 25-ft thick beneath the Starkey and 

Cypress Bridge well fields.

 Natural-gamma logs combined with lithologic data for 

wells near four of the study wetlands were used to delineate 

the sand to clayey sand layers and the position of the intermediate confining unit, which is composed mainly of sandy 

clay at these sites (fig. 14A–D). The underlying lithology at 

Starkey and Cypress Creek well fields shown in figure 14A–D
Factors that Influence the Hydrologic Recovery of Wetlands 23

Intermediate confining unit is thick,

intact, and has low permeability

Leaning trees

due to loss of

ground support

Movement of

upland tree species

to the center of

the wetland

Encroachment of

Loss of wetland sediments caused upland species

by drying and compaction or by

intense fires

Subsidence due to natural

karst development or

from sinkholes that have

been induced from

groundwater withdrawals

Wetland sediment – Includes a thin clay layer

in the top of the soft organic sediments.

Sand and organics

Sand with increasing clay content with depth.

Sand, clay, and carbonate mud

Limestone

Surficial

aquifer

Intermediate

confining unit

Upper Floridan

aquifer

EXPLANATION

A B

C D

Subsidence due to natural

karst development or

from sinkholes that have

been induced from

groundwater withdrawals

Breaches in hard-pan or

clayey sand layer below

wetland due to

subsidence

Intermediate confining unit is thin,

contains breaches, or is highly permeable

(more sand than clay)

Intermediate confining unit is thin or absent,

contains breaches, or is highly permeable

(more sand than clay)

Intermediate confining unit is

thin or absent, contains breaches,

or is highly permeable

(more sand than clay)

Collapse in the underlying limestone

NOT TO SCALE NOT TO SCALE

NOT TO SCALE NOT TO SCALE

Hard-pan or clayey sand

Potentiometric surface – Of the Upper

Floridan aquifer.

Shallow depth to the potentiometric surface of the

Upper Floridan aquifer below the wetland-bottom elevation

Deep depth to the potentiometric

surface of the Upper Floridan aquifer

below the wetland-bottom elevation

Subsidence or

sinkhole near

perimeter of

wetland

Figure 10. Generalized hydrogeologic sections showing 

A, an unimpacted to minimally impacted wetland, B, a 

moderately impacted wetland, and C–D, two severely 

impacted wetlands.
24 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

EXPLANATION

Sand Silt – Organics Clay

A

Depth of grain-size analysis test for clay

Photo credit: P.A. Metz

S-68 Cypress S-44 Cypress Grass Prairie W-33 Cypress W-56 Cypress W-16 Marsh

S-44

Cypress

S-68

Cypress

Grass

Prairie

0

1

2

W-56

Cypress

W-16

Marsh

Sand, silt, and clay, in percent

W-33

Cypress

0

1

2

0

1

2

0

1

2

0

1

2

0

1

2

B

Depth below land surface, in feet

0 10 20 30 40 50 60 70 80 90 100

C

2

4

6

8

10

12

2 4 6 8 10

Clay content, in percent

0

0

Grass Prairie

S-68 Cypress S-44 Cypress

W-16 Marsh

W-33 Cypress W-56

Cypress

Depth below land surface, in feet

Figure 11. Photographs showing A, vibracore samples, and graphs showing B, percentage of sand, silt, and clay in 

the upper 2 feet of wetland sediments, and C, clay content at and below land surface for six of the study wetlands.
Factors that Influence the Hydrologic Recovery of Wetlands 25

A. Grass Prairie B. W-33 Cypress

C. S-68 Cypress D. W-16 Marsh

Photo credit: P.A. Metz Photo credit: P.A. Metz

Photo credit: P.A. Metz Photo credit: P.A. Metz

Figure 12. Photographs showing A, vibracore sample collection, and B–D, core samples highlighting the variability of the clay 

layers in cores beneath the study wetlands. 
26 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

indicates the variability in the clay content with depth within 

and between sites, as shown by the fluctuations in the naturalgamma log signatures, vertical hydraulic conductivity values, 

and by the grain-size analysis.

 The variability of the underlying sediments is reflected 

by the differences in vertical hydraulic conductivity values 

between wetland sites and well fields. Vertical hydraulic 

conductivity, as used herein, is a measure of the ease by which 

water moves downward through pore spaces of the sediments 

underlying wetlands, quantified in feet per day. The vertical 

hydraulic conductivity controls the movement of water 

between the wetland/surficial aquifer and the Upper 

Floridan aquifer. 

 Where the vertical hydraulic conductivity is relatively 

high, ranging from about 1 to 10 feet per day (ft/d), water 

moves easily through the sand layers (fig. 14B–C). As water 

moves downward into the clayey sand to sandy clay layers, 

however, the vertical movement slows as hydraulic conductivity decreases. The vertical hydraulic conductivity in the 

upper clayey sand layers ranges from 10–1 to 10–4 ft/d, and 

in the sandy clay layers of the intermediate confining unit, 

it ranges from 10–2 to 10–6 ft/d (fig. 14A–C). The vertical 

hydraulic conductivity of the sandy clay layers in the 

intermediate confining unit was lowest (10–6 ft/d) near the 

minimally impacted W–33 Cypress at the Cypress Creek 

well field (fig. 14A), and was highest (10–2 to10–3 ft/d) near 

the severely impacted S–44 Cypress at Starkey well field 

(fig. 14C). 

 The hydrogeologic analysis of the study wetlands shows 

the large variability in the permeability of the sediment layers 

underlying the wetlands. The recovery of water levels for a 

particular wetland will be different, depending on the permeability of the underlying sediments.

Influence of Karst Features on Wetland 

Hydrology

 Numerous localized surface or buried depressions 

(collapsed features or sinkholes) are common throughout the 

mantled karst landscape and contribute to the highly variable 

geologic framework of the study area. Sinkholes develop 

when acidic waters percolate downward, dissolving the 

underlying limestone, and eventually forming cavities in the 

limestone substrate. As the cavities expand, the overlying sand 

and clay subside into solution openings forming depressions 

of varying sizes and depths in the land surface. 

N

Dade City

Zephyrhills

Land O' Lakes

New

Port

Richey

GULF

OF MEXICO

Anclote

Saint Leo

50

25

25

25 25

HERNANDO COUNTY

PASCO COUNTY

Cypress Bridge

well field

EXPLANATION

River

25

50

25

Cypress Creek

well field

Starkey

well field

0 10 MILES

0 10 KILOMETERS

5

5

50

5

6

7 8

3 2 1 4

9

1

Boundary of

study area

48

50

51

49

24AB

24CD

36

47A

46

47

Well-field boundary

Palustrine wetlands

Estuarine wetlands

Open water

Boundary of dispersed well field

National Weather Service station

City

Line of equal thickness of

the intermediate confining

unit – Interval is 25 and 50 feet.

Study wetland

Well

– Location and

number in table 3.

– Location and number in

table 3.

Figure 13. Generalized thickness of the intermediate confining unit overlying the Upper Floridan aquifer. 

Modified from Buono and others (1979).
Factors that Influence the Hydrologic Recovery of Wetlands 27

C. S-44 Cypress and

Starkey Central D. S-68 Cypress

Clay content, in percent

Sand, fine 0

10

20

30

40

50

60

70

Intermediate

confining

unit

Surficial

aquifer

Limestone

Upper

Floridan

aquifer

0 50 100

Sand

Clayey sand

Sandy clay

B. W-12 Cypress

and W-16 Marsh

0

10

20

30

40

50

Intermediate

confining unit

Surficial

aquifer

Limestone

Upper

Floridan

aquifer

0 1 10 20

60

70

0 50 100

Sand

Clayey sand

Sandy clay

0

10

20

30

40

50

Surficial

aquifer

Limestone

Upper

Floridan

aquifer

1.0-6 1.0-4 1.0-2 0 2 1 10 0

60

70

0 50 100

Sand

Clayey sand

Sandy clay

0

10

20

30

40

50

Depth below land surface, in feet

Intermediate

confining

unit

Surficial

aquifer

Limestone

Upper

Floridan

aquifer

1.0-6 1.0-4 1.0-2 0 2 1 10 0

A. W-33 Cypress

60

70

0 50 100

Sand

Clayey sand

Sandy clay

Vertical hydraulic conductivity,

in feet per day

Natural-gamma log – In counts per

second. Increased signature

corresponds to clay

Clay content

Vertical hydraulic conductivity

– Additional values

obtained from grain-size analysis

from Hutchinson (2003) and

Lee and others (2009).

–

Values obtained from falling-head

permeameter tests by Hutchinson (2003).

content.

EXPLANATION

Intermediate

confining

unit

Vertical hydraulic conductivity,

in feet per day

Clay content, in percent

Vertical hydraulic conductivity,

in feet per day

Clay content, in percent Clay content, in percent Depth below land surface, in feet

Depth below land surface, in feet

Depth below land surface, in feet

Vertical hydraulic conductivity

values are not available 1.0-6 1.0-4 1.0-2

Figure 14. Geologic and natural-gamma logs showing the variability in the clay units near the study wetlands at the 

A–B, Cypress Creek, and C–D, Starkey well fields. 
28 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

 Many wetlands in the area are thought to be remnants 

of sinkholes and sites of active karst development (Sinclair, 

1982). Watson and others (1990) identified three types of 

geologic settings beneath cypress wetlands at several well 

fields located throughout the study area based on GPR data. 

These wetland types included shallow depressions, shallow 

depressions with solution features, and relict sinkholetype systems. Their study results indicated that wetlands 

that formed in relict sinkhole-type systems are the most 

hydrologically impacted (reduced hydroperiods).

 Several aspects of the karst geologic framework enhance 

the connection between the wetland/surficial aquifer and the 

underlying Upper Floridan aquifer, including (1) sinkholes or 

depressional piping features that have formed in the wetland 

bottom and extend into the clay or hardpan layer underlying 

the wetlands (fig. 10C); (2) similar sinkholes or depressional 

piping features that have formed near the perimeter of the 

wetland (fig. 10C) and; (3) evidence of an intermediate 

confining unit that contains breaches or is thin, absent, or is 

highly permeable (fig. 10B-D). Breaches or breaks in the sediments underlying wetlands or in the intermediate confining 

unit due to karst subsidence activity provide pathways for 

downward leakage to the underlying Upper Floridan aquifer, 

especially when wetlands are in areas of recharge.

 Relatively deep depressions in the wetland bottom, 

evident in the bathymetric data for the study wetlands, were 

interpreted to be karst subsidence features. For example, the 

bathymetry of two impacted study wetlands (S–44 Cypress 

and W–16 Marsh) indicated depressions about 7 ft below 

the wetland perimeter elevation (fig. 15A–B). These two 

wetlands had substantially shorter hydroperiods than other 

wetlands without these depressions. In comparison, the 

bathymetry of an unimpacted and minimally impacted wetland 

(S–68 Cypress and W–33 Cypress, respectively), revealed a 

shallow wetland-bottom configuration less than 2 ft in depth 

(fig. 15C–D). These shallow depressional wetlands did not 

have a reduced hydroperiod. 

 One of the moderately impacted wetlands (Cypress 

Bridge 01) contained a number of small visible sinkholes 

along the wetland bottom (fig. 8D–E) that extended almost 

10 ft below the wetland perimeter elevation (fig. 16). Several 

small channels, which have been eroded into the wetland 

bottom, direct surface-water flows toward the sinkholes. These 

small-to-large circular depressions or subsidence features that 

form in wetland bottoms probably channel most of the localized recharge from the wetlands into the underlying aquifers 

(Metz and Sacks, 2002; Lee and others, 2009). The rate of 

recharge into the underlying aquifers depends upon the size, 

frequency of occurrence, and hydraulic conductivity of the 

subsidence features (Stewart and Parker, 1992).

Sinclair (1982) and Rochow (1983c) suggest that the 

formation of some of the recently formed subsidence features 

(sinkholes) in the study wetlands were influenced by groundwater withdrawals. Although sinkholes develop naturally, their 

high density near well fields and major agricultural areas can 

be explained, in part, by the large increase in groundwater 

withdrawals for a particular area (Sinclair, 1982; Shock and 

Wilson, 1996; Tihansky, 1999). For example, in May 1964, 

46 sinkholes formed near the Section 21 well field, in northwestern Hillsborough County, due to an increase in well-field 

pumping (Sinclair, 1982) (fig. 17; location of Section 21 

well field shown in fig. 1). Groundwater production at the 

Section 21 well field began in 1963, and withdrawal rates 

nearly tripled 1 year later, lowering groundwater levels more 

than 10 ft and causing these sinkholes to form (Sinclair, 1982; 

Tihansky, 1999). Similarly, 110 sinkholes developed in an area 

20 mi east of Tampa due to groundwater levels that declined 

about 60 ft for several days. This large, rapid decline in 

groundwater levels was the result of groundwater withdrawn 

for frost-freeze protection during January 2010 (Southwest 

Florida Water Management District, 2010). A large decline 

in groundwater levels near well fields and agricultural lands 

can remove the hydraulic support of overburden sediments 

lying above limestone cavities, resulting in sinkhole formation 

(Newton, 1986).

To provide evidence of karst activity in the shallow 

subsurface (less than 30 ft deep) beneath the study wetlands, 

GPR surveys were conducted within the perimeter of two 

study wetlands, Cypress Bridge 01 and W–16 Marsh. Analysis 

of the GPR record revealed well-defined reflectors beneath 

areas of the wetlands where the lateral bedding within the 

surficial deposits was found to be intact. In other areas of the 

GPR record, discontinuous and dipping reflectors indicated 

that the surficial deposits had been disrupted by karst subsidence. At the Cypress Bridge 01 wetland, numerous shallow 

swales or depressional features were found along the wetland 

bottom. The GPR record also shows the dipping reflectors 

where the surficial deposits have been disrupted. This depression in the land surface may be a piping feature that forms 

where surficial deposits ravel into the underlying karst limestone (fig. 18A–B). Other GPR surveys in west-central Florida 

have shown similar reflectors that were identified as vertical 

sand columns or piping features (Wilson and Garmen, 2002). 

In areas where these features occur, water in the surficial 

aquifer has the potential to leak faster to the underlying Upper 

Floridan aquifer than in areas where the sediments are intact.

 Small filled or buried sinkholes, not evident as depressions on the land surface, were found in the GPR record for 

W–16 Marsh (fig. 19A–B). GPR transect D–D′ at W–16 Marsh 

shows the surficial deposits and the intermediate confining 

unit overlies the irregular limestone surface of the Upper 

Floridan aquifer (fig. 19B). Several breaches in the clay 

confining unit also are evident in the record, and create the 

potential for increased downward leakage (fig. 19B). Other 

transects across W–16 Marsh are similar to transect D–D′, and 

show breaches in the clay confining unit beneath this wetland. 
Factors that Influence the Hydrologic Recovery of Wetlands 29

28°16'35”

82°23'36” 82°23'34”

28°16'36”

28°16'34”

0 200 FEET

0 60 METERS

70.3 69.8 69.3 68.8

1

2

W-33 Cypress

C 82°34'32” 82°34'28” 82°34'24” D

28°14'18”

28°14'14”

EXPLANATION

0 300 FEET

0 90 METERS

43.7 43.2 42.7 42.2

26

25

Bathymetry survey point

Observation well – Location and index number in table 3.

S-68 Cypress

24

69.5 69.0 68.5 68.0 67.5 67.0 66.5 66.0 65.5 65.0 64.5 64.0 63.5 63.0

82°36'25” 82°36'23” 82°36'21”

28°14'49”

28°14'47”

A

34.2 33.7 33.2 32.7 32.2 31.7 31.2 30.7 30.2 29.7 29.2 28.7 28.2 27.7 27.2

44 43

42

41 40 39

38

37

35 36

S-44 Cypress

Bottom elevation, in feet above NGVD 1929

82°23'36” 82°23'34” 82°23'32”

28°17'24”

28°17'22”

28°17'20”

12

13

W-16 Marsh

B

0 150 FEET

0 45 METERS

0 200 FEET

0 60 METERS

2

28°14'16”

Bottom elevation, in feet above NGVD 1929

Bottom elevation, in feet above NGVD 1929 Bottom elevation, in feet above NGVD 1929

EXPLANATION EXPLANATION

EXPLANATION EXPLANATION

Figure 15. Bathymetry of A–B, severely impacted wetlands, C, an unimpacted wetland, and D, a minimally impacted wetland.
30 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

82°22'8 82°22'6

28°13'21

28°13'19

66.0 65.5 65.0 64.5 64.0 63.5 63.0 62.5 62.0 61.5 61.0 60.5 60.0 59.5 59.0 58.5

EXPLANATION

!

6a

3

5 6

4

0 100 FEET

0 30 METERS

3 Data site – Location and index number in table 3.

Bottom elevation, in feet above NGVD 1929

Bathymetry survey point

Figure 16. Bathymetry of the Cypress Bridge 01 wetland.

Section 21 well field

Aerial photo courtesy of the

Southwest Florida Water Management District, 2009

0 1 MILE

0 1 KILOMETER

0.5

0.5

N

EXPLANATION

Well-field boundary

Public-supply well

Sinkhole location

Figure 17. Aerial photograph showing the location of sinkholes that 

formed in and around the Section 21 well field due to groundwater 

withdrawals. Modified from Sinclair (1974) and Tihansky (1999).
Factors that Influence the Hydrologic Recovery of Wetlands 31

Results of water-level analyses performed on the study 

wetlands yield insight into the degree of confinement or 

hydraulic connection between the wetland/surficial aquifer 

and the Upper Floridan aquifer. Water-level differences 

between the aquifers may indicate the localized nature of the 

confining-unit sediments or the influence of karst subsidence. For example, where the confining unit is thin, relatively 

permeable, breached by sinkholes, or contains sand-filled 

piping features, these characteristics will enhance the downward movement of water from the wetland/surficial aquifer 

to the Upper Floridan aquifer, resulting in a small water-level 

difference between the two aquifers. Conversely, a relatively 

large water-level difference between the aquifers indicates 

potentially greater confinement of the Upper Floridan aquifer 

beneath the wetland (fig. 20). Large water-level differences 

can be used as evidence of confinement in areas where there 

are pumping stresses. The strengths of linear relations (r2

values; with 1.0 being the most significant) were used to help 

evaluate the vertical head relations between the wetland/

surficial aquifer and the Upper Floridan aquifer at the study 

wetlands (table 4). An r2 value closer to 1 generally indicates 

a higher degree of hydraulic connection between the wetland/

surficial aquifer and the Upper Floridan aquifer.

 Box plots of water-level data collected during this study 

(January 2007 to March 2008) indicate that the median daily 

average water-level difference between the wetland/surficial 

aquifer and the Upper Floridan aquifer varied from about 1 to 

16 ft among eight of the study wetlands (fig. 20). Water-level 

differences indicate that the permeability of the underlying 

sediments and the presence of karst features are a dominant 

control on potential for vertical flow. For example, the median 

water-level difference between the wetland/surficial aquifer 

and the Upper Floridan aquifer for the study period at the 

minimally impacted W–33 Cypress wetland was about 16 ft, 

reflecting the integrity of the intermediate confining unit 

between these two aquifers at this site. Geologic data for this 

wetland (fig. 14A) indicate high clay content within the upper 

sediment layers and the intermediate confining unit that retard 

downward leakage to the Upper Floridan aquifer. Likewise, 

the linear relation between the wetland/surficial aquifer and 

Upper Floridan aquifer levels at the W–33 Cypress wetland 

was relatively poor (r2 = 0.49, table 4), confirming the weak 

hydraulic connection between the hydrogeologic units. W–33 

Cypress is classified as minimally impacted, and the integrity 

of the underlying clay confining unit is an important factor in 

controlling the hydrologic response of this wetland. 

 Two severely impacted wetlands, (S–44 Cypress and 

W–16 Marsh) and a moderately impacted wetland (Cypress 

Bridge 01) all had a relatively small median water-level 

difference between the wetland/surficial aquifer and the Upper 

Floridan aquifer (0.90, 2, and 1 ft, respectively; fig. 20). 

All three of these wetlands have either karst subsidence or 

sinkholes in the wetland bottom that were exacerbated by 

large groundwater withdrawals. Linear relations between the 

wetland/surficial aquifer and Upper Floridan aquifer water 

0

7

14

21

28

0 7 14 21 28

Distance, in feet

Depth below land surface, in feet

Grid A

Grid

B

GRID A GRID A′

EXPLANATION

Ground penetrating radar transect

Ground penetrating radar

three-dimensional grid

Water

table

level

A

B

0 100 FEET

0 30 METERS

Possible piping

feature

Aerial photo courtesy of the Southwest Florida Water Management District, 2009

E

A ′

B

C

F

D

F ′

A

B ′ D ′

C ′

E ′

0

7

14

21

Grid

A′

N

Figure 18. A, Aerial photograph showing the location 

of ground-penetrating radar (GPR) transect lines, and 

B, geophysical profile A–A’ with interpreted geologic 

features below Cypress Bridge 01 at the Cypress Bridge 

well field.
32 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

82°23'35” 82°23'30”

28°17'25”

28°17'20”

A ′

B ′

C ′

D ′

N ′ OO O ′ ′

P ′

Q ′

F ′

G ′

H ′

I ′

J ′

K ′

0 120 230

32

16

0

24

8

60 180

0 100 200 FEET

0 25 50 METERS

D

D D ′

Distance, in feet

EXPLANATION

Ground-penetrating radar transect

Ground-penetrating radar transect D-D’

Depth below land surface, in feet

Top of intermediate confining unit Breach

in the

intermediate

confining

unit

A

B

A

B

C

F

G

H

I

J

K

Q

P

OO

O

N

Aerial photo courtesy of the Southwest Florida Water Management District, 2009

Water table level

Surficial deposits

Figure 19. A, Aerial photograph showing the location of ground-penetrating radar (GPR) transect lines, and 

B, geophysical profile D–D’ with interpreted geologic features below W–16 Marsh at the Cypress Creek well field.
Factors that Influence the Hydrologic Recovery of Wetlands 33

levels for S–44 Cypress, W–16 Marsh, and Cypress Bridge 01 

wetlands indicate that much of the variability in water levels 

between the aquifers is statistically related (r2 = 0.83, 0.80, and 

0.75, respectively; table 4). This analysis indicates that when 

karst subsidence activity disrupts the confining layers beneath 

a wetland, a connection is created between the wetland and the 

underlying aquifers, which reduces the water-level differences 

between them. 

Potentiometric Surface of the Upper Floridan 

Aquifer

 A number of groundwater modeling studies have 

documented that groundwater withdrawals from the Upper 

Floridan aquifer at the Northern Tampa Bay well fields have 

lowered the potentiometric surface within and surrounding 

the well fields (Hutchinson, 1984; Southwest Florida Water 

Management District, 1996). Groundwater modeling results in 

Hutchinson (1984) indicate that a large part of the water that 

replaces this groundwater withdrawal comes from downward 

leakage from the surficial aquifer and wetlands in these well 

field areas. Consequently, this downward leakage has resulted 

in reduced hydroperiods for some wetlands in these areas, and 

in some cases, has adversely affected wetland health (Sinclair, 

1982; Rochow, 1998; Lee and others, 2009). 

Historical Trends in Groundwater Levels

 Examining historical groundwater levels beneath the 

study wetlands provides an understanding of how changing 

water-level conditions can impact wetlands. A number of 

Northern Tampa Bay area well fields came online during 

the 1970s, including Starkey and Cypress Creek well fields, 

where production began during 1974 and 1976, respectively. 

The long-term hydrographs (ranging from 1949 to 2010) from 

wells tapping the Upper Floridan aquifer and surficial aquifer 

within and surrounding the study well fields show the variability of water levels influenced by groundwater withdrawals 

and climatic conditions (figs. 21 and 22A–F; well locations 

shown in fig. 13). 

 The distance-weighted least squares method (McClain, 

1974) was used as a smoothing and interpolation approximation technique to reveal the overall pattern or trend in the 

long-term surficial and Upper Floridan aquifer levels within 

and surrounding Cypress Creek and Starkey well fields. For 

some of the wells examined, the highest aquifer water levels 

occurred prior to well-field production, but aquifer levels 

were also high in 1998 and 2004 (figs. 21 and 22A–F), when 

several large rain events occurred (fig. 2). Some of the lowest 

groundwater levels occurred during a severe drought in 2000 

(Verdi and others, 2006), when groundwater withdrawals were 

highest in the Northern Tampa Bay area (fig. 5A). 

W-56

Cypress

W-16

Marsh

W-12

Cypress

Cypress

Bridge 01

Starkey

Central

S-68

Cypress

S-44

Cypress

25

20

15

10

5

0

W-33

Cypress

Cypress Creek

well field

Starkey

well field

Cypress

Bridge

well field

Water-level difference, in feet

EXPLANATION

Unimpacted wetland

Minimally impacted wetland

Moderately impacted wetland

Severely impacted wetland

Maximum value

75th percentile

50th percentile

25th percentile

Minimum value

Interquartile

range

Table 4. Relation between surficial and Upper Floridan aquifer 

levels at the study wetlands.

[r2, coefficient of determination between daily surficial and Upper Floridan 

aquifer levels for December 2007- March 2008; all regressions significant to 

alpha level of 0.05; S, Starkey; CC, Cypress Creek; CB, Cypress Bridge]

Well 

field Wetland name

Wells 

used for 

comparison1

r

2 Classification

S S-68 Cypress 26, 27 0.51 Unimpacted

S Starkey Central 28, 32 0.73 Moderately impacted

S S-44 Cypress 36, 41 0.83 Severely impacted

CC W-33 Cypress 7, 9 0.49 Minimally impacted

CC W-56 Cypress 21, 23 0.75 Minimally impacted

CC W-12 Cypress 16, 19 0.60 Severely impacted

CC W-16 Marsh 14, 19 0.80 Severely impacted

CB Cypress Bridge 01 1, 5 0.75 Moderately impacted

1

Well index numbers are shown in table 3.

Figure 20. Box plots showing water-level differences between 

the wetland/surficial aquifer and Upper Floridan aquifer for the 

study wetlands, 2007–08.
34 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Figure 21. Hydrographs showing long-term water levels for the Upper Floridan aquifer and surficial aquifer at the Cypress 

Creek well field and surrounding areas. Well construction data and index number are shown in table 3 and location of wells are 

shown in figure 13.

1948 52 56 60 64 68 72 76 80 84 88 92 96 2000 04 2008

70

75

80

85

90

95

100

105

110

35

40

45

50

55

60

65

70

50

55

60

65

70

75

80

85

90

Pasco well 13,

Upper Floridan aquifer

index number 48

30

45

50

55

60

65

70

35

40

30

30

35

40

45

50

55

60

65

70

30

35

40

45

50

55

60

65

70

30

35

40

45

50

55

60

65

70

dotted when

well is dry

Cypress Creek well field,

TMR-4 Deep well,

Upper Floridan aquifer,

index number 24C

Cypress Creek well field,

TMR4 Shallow well,

surficial aquifer,

index number 24D

Cypress Creek well field,

TMR-3 Deep well,

Upper Floridan aquifer,

index number 24A

Cypress Creek well field,

TMR-3 Shallow well,

surficial aquifer,

Index number 24B

E

A B

C

F

D

dotted when

well is dry

State Highway 577 well,

Upper Floridan aquifer,

index number 50

Water level, in feet above NGVD 1929

Beginning of well-field production

Distance-weighted least squares fitting (McLain, 1974)

Upper Floridan aquifer

Surficial aquifer

EXPLANATION

1948 52 56 60 64 68 72 76 80 84 88 92 96 2000 04 2008

1948 52 56 60 64 68 72 76 80 84 88 92 96 2000 04 2008 1948 52 56 60 64 68 72 76 80 84 88 92 96 2000 04 2008

1948 52 56 60 64 68 72 76 80 84 88 92 96 2000 04 2008

Year Year

1948 52 56 60 64 68 72 76 80 84 88 92 96 2000 04 2008

Water level, in feet above NGVD 1929

Year Year

Year Year
Factors that Influence the Hydrologic Recovery of Wetlands 35

Figure 22. Hydrographs showing long-term water levels for the Upper Floridan aquifer and surficial aquifer at the Starkey well 

field and surrounding areas. Well construction data and index number are shown in table 3 and location of wells are shown in 

figure 13.

E

A B

C

F

D

Year Year

Year Year

Year Year

1965 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008 1965 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008

1965 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008 1965 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008

1965 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008 1965 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008

Water level, in feet above NGVD 1929

15

20

25

30

35

40

45

50

30

35

40

45

50

10

10

15

20

25

30

35

40

45

50

35

40

45

50

55

60

65

70

30

10

15

20

25

30

35

40

45

50

20

25

30

35

40

45

50

55

60

Water level, in feet above NGVD 1929

Moon Lake Deep,

Upper Floridan aquifer,

index number 49

State Highway 52 Deep near Fivay Junction,

Upper Floridan aquifer,

index number 51

Starkey well field,

Starkey Shallow 728,

surficial aquifer,

index number 47

Starkey well field,

Starkey SM-2 Shallow,

surficial aquifer,

index number 47A

Starkey well field,

Starkey 10 Deep well,

Upper Floridan aquifer,

index number 46

Starkey well field,

Starkey 1A Central well,

Upper Floridan aquifer,

index number 36

15

20

25

10

Beginning of well-field production

Distance-weighted least squares fitting (McLain, 1974)

Upper Floridan aquifer

Surficial aquifer

EXPLANATION
36 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Long-term water-level data for the Upper Floridan aquifer 

wells to the east (State Highway 577 well; fig. 21A; well location shown in fig. 13) and southwest (Pasco well 13; fig. 21B; 

well location shown in fig. 13) of Cypress Creek well field 

show varying degrees of fluctuation, which are attributed to 

the level of confinement overlying the Upper Floridan aquifer 

and localized groundwater withdrawals in that area (fig. 14). 

The intermediate confining unit overlying the Upper Floridan 

aquifer is thicker to the east of the well field (Buono and 

others, 1979), resulting in a greater amplitude of water-level 

fluctuations at State Highway 577 well than at Pasco well 13. 

Water-level trends for State Highway 577 well indicate about a 

10-ft decline from 1965 to 2009, whereas water-level trends for 

Pasco well 13 indicate about a 2-ft decline from 1949 to 2009 

(fig. 21A–B). 

 Groundwater level fluctuations resulting from Upper 

Floridan aquifer withdrawals in the Cypress Creek well field 

are greatest near the TMR-3 Deep well (fig. 21C). In addition, 

the confining layer overlying the Upper Floridan aquifer is 

thicker at this location than in areas southwest of the well 

field, which also contributes to the attenuation of these levels 

(Buono and others, 1979). Long-term water-level trends for 

TMR-3 Deep shows a descending trend from 1975 to the 

early-1990s and an ascending trend during the high rainfall 

periods of 1998 and 2003–05 (fig. 21C). The ascending trend 

during 2003–05 also coincided with the reductions in groundwater withdrawals at Cypress Creek well field, which began in 

2003 (fig. 5C). The water-level trend was relatively flat during 

2005–06, and declined slightly during 2007–09. This most 

recent decline was caused by a return to a rainfall deficit and 

increased groundwater withdrawals in the well field (figs. 2A

and 5C). Water-level trends for the TMR-4 Deep well, which 

also taps the Upper Floridan aquifer, are flatter than those at 

TMR-3 Deep, probably because TMR-4 Deep is farther from 

the pumping center (fig. 21D and fig 7). 

Surficial aquifer levels are influenced by rainfall, 

seasonal evapotranspiration, and by leakage to the Upper 

Floridan aquifer. Long-term water-level trends for the surficial 

aquifer (TMR-3 Shallow and TMR-4 Shallow wells) at the 

Cypress Creek well field include a general decline from 1976 

to the late-1980s, an increase during late 1990s and 2003–04, 

and a decline after 2005 (fig. 21E–F). The largest declines in 

water levels for TMR-3 Shallow usually occurred during dry 

periods when recharge to the surficial aquifer was minimal 

or absent (fig. 2), and when the need for groundwater supply 

from the Upper Floridan aquifer increased. TMR-3 Shallow 

frequently was dry during 1979–2009, with the longest dry 

period being 1989–95. The increased stresses on the Upper 

Floridan aquifer, which induced downward leakage from the 

surficial aquifer during these extended dry periods, likely 

caused adverse effects to many wetlands in this large drawdown area (app. 3A). The TMR-4 Shallow well also went dry 

several times, but not as frequently as TMR-3 Shallow most 

likely because TMR-4 Shallow is deeper than TMR-3 Shallow 

and farther from the large drawdown area in the Upper 

Floridan aquifer (app. 3A). 

 Long-term water-level data for two Upper Floridan 

aquifer wells to the northeast and the north (fig. 22 A-B) of 

Starkey well field show similar water-level fluctuations and 

long-term trends, including a small (2 ft) overall decline from 

1965 to 2009 for both wells. Water-level fluctuations were 

smaller in Upper Floridan aquifer wells within Starkey well 

field (fig. 22 C-D) compared to those at the Cypress Creek 

well field (fig. 21 C-D). There are several reasons for the 

attenuation of water-level fluctuations at Starkey well field, 

including (1) the smaller volume of water pumped from 

Starkey well field; (2) the greater spacing of production wells 

over a larger area, which influences the size and shape of the 

cone of depression; and (3) less confinement between the 

wetland/surficial aquifer and the Upper Floridan aquifer at 

Starkey well field.

Long-term water-level trends for Starkey 10 Deep well 

(Upper Floridan aquifer), located west of the pumping center 

at Starkey well field, indicates a small (2 ft) descending trend 

from 1974 to 2009 (fig. 22C). Long-term water-level trends 

for Starkey 1A Central well, located in the center of Starkey 

well field, are based on a shorter period of record (1988–2009) 

and generally shows an ascending trend during this period 

(fig. 22D). This ascending trend in Upper Floridan aquifer 

levels at this well is the result of above average rainfall conditions that existed in the Starkey well field area during 2002, 

2004, and 2009 (fig. 2A) and the reductions in groundwater 

withdrawals (from 12 to 4 Mgal/d), that were initiated in 

December 2007 (fig. 5C). As a result, the maximum water 

levels for the 1988–2009 period of record for this well 

occurred in 2009 (fig. 22D).

Water-level trends for two surficial aquifer wells at 

Starkey well field remained relatively flat for most of the 

analysis period (fig. 22E–F), although a slight descending 

trend was observed after 2005 due to below-average rainfall during 2005–08 (fig. 2A). A reduction in groundwater 

withdrawals from the Upper Floridan aquifer was initiated in 

December 2007 at Starkey well field, but this reduction is not 

yet discernable in the trends for the surficial aquifer because 

of drought conditions during 2005–08. 

Potentiometric Surface Elevations before 

and after Reductions in Groundwater 

Withdrawals

To determine the hydrologic condition of a wetland, 

it is important to know the vertical position of the potentiometric surface of the Upper Floridan aquifer relative to 

the wetland bottom. When the potentiometric surface of the 

Upper Floridan aquifer is at or near land surface, it limits 

the downward leakage potential and helps sustain the water 

needed for wetland functions. The leakage potential increases 

as the potentiometric surface of the Upper Floridan aquifer 

recedes below the wetland bottom, and, if sufficiently large, 

this decline can substantially reduce the wetland hydro-
Factors that Influence the Hydrologic Recovery of Wetlands 37

period. The hydrologic condition of the wetland is further 

compromised (1) when the geology surrounding or underlying 

the wetland is influenced by sinkhole development, such 

as breaches in the intermediate confining unit, or (2) where 

permeable surficial sediments underlie the wetland. 

 Elevation-difference maps based on potentiometric 

surface maps and LIDAR data were created to spatially 

define the potentiometric surface of the Upper Floridan 

aquifer relative to the wetland-bottom elevation prior to any 

groundwater development at Starkey and Cypress Creek 

well fields (fig. 23A–B). Areas where the potentiometric 

surface was above or at land surface were considered 

discharge areas having upward flow, and areas where the 

potentiometric surface of the Upper Floridan aquifer was 

below land surface were considered recharge areas having 

downward flow. 

 Elevation-difference maps using data collected prior to 

groundwater development at the Cypress Creek and Starkey 

well fields show large areas of groundwater discharge within 

and surrounding the well fields. Most of the study wetlands 

(except Starkey Central and W–33 Cypress wetlands) were 

located in discharge areas. Most of the discharge areas in 

the Starkey well field were associated with low lying areas, 

including the Pithlachascotee River and its tributaries north of 

the well field, Cross Cypress Branch near the center, Anclote 

River to the south, and the large headwater area of the Anclote 

River east of the well field (fig. 23A). At Cypress Creek well 

field, the discharge areas were associated with low-lying areas 

of the Big Cypress Swamp and the floodplain of Cypress 

Creek, both of which constitute a large part of the well field 

(fig. 23B). Maps of areal discharge and recharge by Aucott 

(1988) and Vecchioli and others (1990), also show parts of 

Starkey and Cypress Creek well fields identified as discharge 

areas. In these areas, the potentiometric surface of the Upper 

Floridan aquifer ranges from about 0 to 5 ft above land 

surface, which helps limit the downward leakage potential 

from the wetlands. 

 Elevation-difference maps also were created to show 

the current and seasonal changes in the potentiometric surface 

of the Upper Floridan aquifer relative to land-surface elevations (figs. 24 and 25). A comparison of these maps to the 

predevelopment maps in figure 23 indicates a large shift from 

mostly discharge conditions prior to groundwater development, to mostly recharge conditions during 2008–09. During 

September 2008, however, several discharge areas were present 

at both well fields. At Starkey well field, the discharge areas 

were associated with a narrow band around the channels of 

the Pithlachascotee River, Cross Cypress Branch, and Anclote 

River (fig. 24A). At Cypress Creek well field, a small discharge 

area associated with Cypress Creek was present along the 

southwestern boundary of the well field (fig. 25A). During 

May 2009, areas of discharge were reduced further at both well 

fields compared to September 2008 (figs. 24B and 25B). 

 To help alleviate the decline in wetland water levels, 

reduced groundwater withdrawals from the Upper Floridan 

aquifer were implemented at Starkey and Cypress Creek well 

fields at the end of 2007 and 2002, respectively. The reduction 

in groundwater withdrawals varied over time at each well 

field. At Cypress Creek well field, for example, groundwater 

withdrawals averaged about 30 Mgal/d during 1978–2000, 

declined to 9 Mgal/d during 2003, then increased to an average 

of about 16 Mgal/d during 2004–09 (fig. 5C). At Starkey well 

field, the reduction in groundwater withdrawals was more 

immediate; after an interconnector pipeline was completed 

between well fields in late 2007, the pumpage was reduced 

from an average of about 12 Mgal/d during 1988–2007 to 

4 Mgal/d after November 2007 (fig. 5C).

 Box plots were used to assess the historical and current 

levels of the Upper Floridan aquifer relative to the study 

wetland-bottom elevations prior to and after the reductions in 

groundwater withdrawals at the Starkey and Cypress Creek 

well fields. The box plots for the study wetlands (fig. 26) were 

constructed to show the daily average elevation difference 

between the lowest point along the wetland bottom and the 

potentiometric surface of the Upper Floridan aquifer prior to 

and after the reductions in groundwater withdrawals at the two 

well fields. The wetland bottom elevation is used as a surrogate 

for the wetland water level to allow comparisons between 

surface and groundwater levels even when wetlands were dry. 

Because wetlands are typically shallow, the elevation difference computed using the wetland bottom is generally only 

several feet less than the water level derived from the wetland 

stage when the wetland is flooded (Lee and others, 2009). 

The elevation-difference analysis period for the 

wetlands prior to the reduction in groundwater withdrawals 

included January 1989 to December 2007 and January 1989 

to December 2002 for Starkey and Cypress Creek well fields, 

respectively. The elevation-difference analysis period for 

the wetlands after the reduction in groundwater withdrawals 

included January 2008 to March 2010 and January 2003 

to May 2009 for Starkey and Cypress Creek well fields, 

respectively. 

A general comparison between the two well fields prior 

to and after the reduction in groundwater withdrawals indicates that the median potentiometric surface elevation of the 

Upper Floridan aquifer was generally closer to the wetlandbottom elevation for wetlands at Starkey well field compared 

to wetlands at Cypress Creek well field (fig. 26). In addition, 

the elevation range of the potentiometric surface of the Upper 

Floridan aquifer was generally far less below wetlands at 

Starkey well field than at Cypress Creek well field.

 Prior to the reduction in groundwater withdrawals at 

Starkey well field, the median potentiometric surface elevation ranged from near land surface (S–44 Cypress and Grass 

Prairie) to about 15 ft below the wetland-bottom elevation 

(Starkey Central). The potentiometric surface was occasionally above land surface at Grass Prairie and S–44 Cypress, 

indicating discharge conditions (fig. 26). 

 The S–44 Cypress wetland bottom contained a number 

of karst subsidence features that had lowered the natural depth 

of the cypress wetland in several areas. Undisturbed cypress 

wetlands usually have an average maximum depth of about 
38 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Figure 23. Elevation difference between land surface and the potentiometric surface of the Upper Floridan 

aquifer at the A, Starkey well field and the B, Cypress Creek well field. Elevation difference map, in feet, based on 

subtracting the potentiometric surface of the Upper Floridan aquifer prior to development (Johnston and others, 

1980) from land-surface elevation data (2005 LIDAR data) provided by the Southwest Florida Water Management 

District.

82°39' 82°36' 82°33'

28°18'

28°15'

28°12'

A

82°27' 82°24' 82°21'

28°18'

28°15'

B

Big

Cypress

Swamp

Cypress

Creek

Pithlachascotee

River

Anclote

River

Cross Cypress 

Branch

W-12 Cypress

W-16 Marsh

W-33

Cypress

S-44

Cypress

S-68 Starkey Cypress Central

Grass Prairie "

" "

"

"

"

"

"

W-56

Cypress

EXPLANATION

Open water

Well-field boundary

Study wetland and name

0.01 to 7

21.01 to 28

Greater than or equal to 0

Elevation difference, in feet

at or above land surface

Elevation difference, in feet

below land surface

"

W-16 Marsh

7.01 to 14

14.01 to 21

0 1 MILE

0 1 KILOMETER

0.5

0.5
Factors that Influence the Hydrologic Recovery of Wetlands 39

S-44 Cypress

S-68 Cypress

Starkey Central

A. September 2008

B. May 2009

S-44 Cypress

S-68 Cypress

Starkey Central

Pithlachascotee

Anclote

River

Cross Cypress Branch

River

Grass

Prairie

Pithlachascotee

Anclote

River

Cross Cypress Branch

River

EXPLANATION

Open water

Well-field boundary

Monitor well

Unimpacted

Severely impacted

Moderately impacted

Study wetland classification

0.01 to 7 7.01 to 14

14.01 to 21 21.01 to 28

Greater than or equal to 0

Elevation difference, in feet

at or above land surface

Elevation difference, in feet

below land surface

Grass

Prairie

N

1 KILOMETER

0 1 MILE

0

0.5

0.5

Figure 24. Elevation difference between land surface and the potentiometric surface of the Upper Floridan 

aquifer during A, September 2008, and B, May 2009 at the Starkey well field. Elevation difference map, in 

feet, based on subtracting the potentiometric surface of the Upper Floridan aquifer during September 2008 

and May 2009 from land-surface elevation data (2005 LIDAR data) provided by the Southwest Florida Water 

Management District.
40 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Figure 25. Elevation difference between land surface and the potentiometric surface of the Upper 

Floridan aquifer during A, September 2008, and B, May 2009 at the Cypress Creek well field. Elevation 

difference map, in feet, based on subtracting the potentiometric surface of the Upper Floridan aquifer 

during September 2008 and May 2009 from land-surface elevation data (2005 LIDAR data) provided by 

the Southwest Florida Water Management District.

W-56 Cypress

W-12 Cypress

W-16 Marsh

W-33 Cypress

Big Cypress Swamp

Creek

Big Cypress Swamp

Cypress

Creek

Cypress

W-56 Cypress

W-12 Cypress

W-16 Marsh

W-33 Cypress

A. September 2008

B. May 2009

N

1 KILOMETER

0 1 MILE

0

0.5

0.5

EXPLANATION

Open water

Well-field boundary

Monitor well

Minimally impacted

Severely impacted

Study wetland classification

0.01 to 7

21.01 to 28

Greater than or equal to 0

Elevation difference, in feet

at or above land surface

Elevation difference, in feet

below land surface

7.01 to 14

14.01 to 21
Factors that Influence the Hydrologic Recovery of Wetlands 41

1.5 ft below the wetland perimeter (Brown and others, 1983 

and 1991), whereas S–44 Cypress contained several deep 

depressions as much as 7 ft below the wetland perimeter 

(fig. 15A). To understand the impacts of these karst features and 

the level of the potentiometric surface of the Upper Floridan 

aquifer at S–44 Cypress, two wetland-bottom elevations were 

used in the elevation-difference analysis. These elevations 

included the lowest elevation point along the wetland bottom, 

where the karst features are located (27.2 ft; fig. 15A), and a 

higher elevation (32.7 ft; fig. 15A) that was more representative 

of the “natural” wetland depth. Results for the lower elevation (27.2 ft) indicated that the potentiometric surface of the 

Upper Floridan aquifer was at or near land surface, at about 

the same elevation as the top of the karst features. Results for 

the higher wetland-bottom elevation indicated that the potentiometric surface of the Upper Floridan aquifer was about 5 ft 

below the wetland-bottom elevation, which was similar to the 

potentiometric-surface elevations measured at S–68 Cypress 

and Grass Prairie wetlands (fig. 26). 

 At Cypress Creek well field, the elevation difference 

between the wetland bottom and the potentiometric surface 

of the Upper Floridan aquifer was smallest at the minimally 

impacted W–56 Cypress and largest at the minimally impacted 

W–33 Cypress both before and after reductions (fig. 26). 

W–33 Cypress had the largest elevation difference among 

the study wetlands at Cypress Creek well field because it is 

higher topographically than the other wetlands on this well 

field (fig. 9). The land-surface elevation of W–33 Cypress 

is 7 ft higher than W–56 Cypress, and the aforementioned 

differences shown in figure 26 for these two sites highlight 

the importance of understanding the topographic setting when 

making comparisons between wetlands. 

-40

-30

-20

-10

0

10

EXPLANATION

Unimpacted wetland

Minimally impacted wetland

Moderately impacted wetland

Severly impacted wetland

After reductions in groundwater withdrawals

Wetland-bottom elevation

W-56

Cypress

W-16

Marsh

W-12

Cypress

Starkey

Central

S-68

Cypress

S-44

Cypress

W-33

Cypress

Grass

Prairie

Starkey well field Cypress Creek well field

(1) (2)

Elevation, in feet above or below wetland bottom

S-44

Cypress

Using the bottom

of the karst depression

for the wetland-bottom

elevation

Using 1.5 feet below

wetland perimeter

for the wetland-bottom

elevation

(3) (4)

(1) (2)

(1) (1) (2) (1)

(2)

(3) (4) (3) (4)

(3) (4)

(2)

Recharge

conditions

Discharge

conditions

Interquartile

range

Elevation difference analysis period

(1) January 1989 to December 2007-

Prior to the reduction in

groundwater withdrawals at

Starkey well field

(2) January 2008 to March 2010-

After the reduction in

groundwater withdrawals at

Starkey well field

(3) January 1989 to December 2002-

Prior to the reduction in

groundwater withdrawals at

Cypress Creek well field

(4) January 2003 to May 2009-

After the reduction in

groundwater withdrawals

at Cypress Creek well field

Outlier value

Maximum value

75th percentile

50th percentile

25th percentile

Minimum value

Outlier value

Figure 26. Elevation of the potentiometric surface of the Upper Floridan aquifer above or below the study-wetland bottom elevations 

prior to and after the reductions in groundwater withdrawals at the Starkey and Cypress Creek well fields.
42 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

 The severely impacted W–12 Cypress and W–16 Marsh 

experienced the widest range in elevation differences before 

reductions, due in part to the large groundwater withdrawals 

from this area of the well field (fig. 26). Prior to groundwater 

development, both of these wetlands were located in discharge 

areas (fig. 23) where the potentiometric surface of the Upper 

Floridan aquifer was either at or slightly above land surface. 

After groundwater development, the median level of the 

potentiometric surface of the Upper Floridan aquifer declined 

to about 14 (W–12 Cypress) and 16 ft (W–16 Marsh) below 

the wetland-bottom elevation, impacting the hydrology of the 

wetlands (fig. 26). 

The potentiometric surface of the Upper Floridan aquifer 

rose beneath most study wetlands at both well fields after 

groundwater withdrawals were reduced. At Starkey well field, 

the median potentiometric surface elevation increased by 

about 3 and 5 ft beneath Starkey Central and S–68 Cypress 

wetlands, respectively (fig. 26). At Grass Prairie and S–44 

Cypress wetlands, the median elevation remained about the 

same after groundwater withdrawals were reduced because 

these reductions were not concentrated in the western part of 

Starkey well field. At Cypress Creek well field, the median 

elevation increased by about 5 ft beneath W–16 Marsh, W–12 

Cypress, and W–56 Cypress wetlands, and by about 2 ft 

beneath W–33 Cypress wetland (fig. 26).

Effects of Groundwater Withdrawals on Wetland 

Hydroperiods

 Groundwater withdrawals from wells surrounding the 

study wetlands were analyzed to determine the effects of these 

withdrawals on study wetland hydroperiods. The combined 

average annual withdrawal rate from wells within a 1-mi 

radius from the center of the study wetlands was determined 

prior to and after the reduction in groundwater withdrawals 

at the study well fields (fig. 27). Groundwater withdrawals 

were lowest near Grass Prairie, where four production wells 

were pumped at a combined average annual rate of 1 Mgal/d 

during 1983–2007, with no reduction in withdrawal rates 

during 2008–09 (fig. 27). Groundwater withdrawals were 

highest near W–16 Marsh, where seven production wells were 

pumped at a combined annual average withdrawal rate of 

about 16 Mgal/d during 1976–2002, after which, withdrawals 

were reduced to about 9 Mgal/d during 2003–08 (fig. 27). 

 The effects of these groundwater withdrawals are evident 

at the severely impacted W–16 Marsh, where the median 

level of the potentiometric surface of the Upper Floridan 

aquifer below the wetland bottom was about 16 ft prior to 

groundwater withdrawal reductions (fig. 26). W–16 Marsh is 

located in an area of the well field that has the lowest Upper 

Floridan aquifer levels, as indicated by the cone of depression 

in appendix 3A–B. Two of the production wells are in close 

proximity to W–16 Marsh, with distances ranging from 0.06 

to 0.20 mi (fig. 7A), locally influencing aquifer levels beneath 

the wetland. 

 Hydrographs, flooded-area maps, and flooded-area duration graphs were used to compare and contrast the hydrologic 

conditions of four study wetlands before and after the reductions in groundwater withdrawals at Starkey and Cypress 

Creek well fields (figs. 28, 29, and 30). The 1989–2009

hydrographs of the unimpacted wetland (S–68 Cypress), 

a minimally impacted wetland (W–33 Cypress), and two 

severely impacted wetlands (S–44 Cypress and W–16 Marsh) 

show the period of time during which the wetland water levels 

were above or below the wetland-bottom elevation (fig. 28). 

The wetland water levels for the unimpacted and minimally 

impacted wetlands (S–68 Cypress and W–33 Cypress, 

respectively) show a relatively narrow range in wetland 

water-level fluctuations (fig. 28A-B). In contrast, water-level 

fluctuations at the severely impacted S–44 Cypress are larger 

because the wetland has been affected by karst subsidence that 

has lowered the wetland-bottom elevation below the natural 

depth range for cypress wetlands (fig. 28C). At the severely 

impacted W–16 Marsh, the hydrograph shows the limited 

periods when the wetland contained surface water, along with 

the lower surficial aquifer water levels that existed below the 

wetland-bottom elevation (fig. 28D). 

The flooded area of a wetland, when expressed as a 

percentage of the total wetland area, is an informative measure 

that can be used to characterize and compare the hydrologic 

2

4

6

8

10

12

14

16

0

Groundwater withdrawals, in million gallons per day

EXPLANATION

Groundwater withdrawals

Unimpacted

Moderately impacted

Severely impacted

3

7

2

6

6

7

Starkey well field Cypress Creek well field

S-68

Cypress

S-44

Cypress

Starkey

Central

W-56

Cypress

W-33

Cypress

W-12

Cypress

W-16

Marsh

Grass

Prairie

4

*

Minimally impacted

4

2

4

6

*

Numbers indicate

total production wells

within a 1-mile radius

from the center of

study wetland

4

Study wetland classification

*

*

*

*

*

*

*

Prior to reductions

After reductions

18

Study wetland

Figure 27. Groundwater withdrawals within a 1-mile radius of 

the center of the study wetlands prior to and after reductions in 

groundwater withdrawals.
Factors that Influence the Hydrologic Recovery of Wetlands 43

D. W-16 Marsh, Cypress Creek well field

Well dry

when flatlined

Elevation of wetland levels

Elevation of groundwater levels

EXPLANATION

A. S-68 Cypress, Starkey well field B. W-33 Cypress, Cypress Creek well field

C. S-44 Cypress, Starkey well field

Surface and groundwater levels – At Starkey S-68 CTR well,

index no. 25 in table 3.

Surface and groundwater levels – At CCWF-W33A well,

index no. 9 in table 3.

Elevation of wetland perimeter – B

uter edge of wetland. Water levels above wetland

perimeter line indicate the wetland is flooded.

athymetry data were used to

determine o

Elevation when wetland is dry – Bathymetry data were used

to determine lowest point of wetland.

Surface and groundwater levels – At STWF 2B West well,

index no. 41 in table 3.

Surface and groundwater levels – At CCWF BIO-4 well,

index no. 12 in table 3.

Groundwater levels – At W-16 USGS Center well,

index no. 13 in table 3.

52

54

56

58

60

62

64

66

68

70

72

60

62

64

66

68

70

72

74

76

78

80

Year Year

Year Year

33

35

37

39

41

43

45

47

49

51

53

17

19

21

23

25

27

29

31

33

35

37

Water level, in feet above NGVD 1929 Water level, in feet above NGVD 1929

1989 90 91 92 93 94 95 96 97 98 99 2000 01 02 03 04 05 06 07 08 2009 1989 90 91 92 93 94 95 96 97 98 99 2000 01 02 03 04 05 06 07 08 2009

1989 90 91 92 93 94 95 96 97 98 99 2000 01 02 03 04 05 06 07 08 2009 1989 90 91 92 93 94 95 96 97 98 99 2000 01 02 03 04 05 06 07 08 2009

Figure 28. Hydrographs of historical water levels at A, an unimpacted, B, a minimally impacted, and C–D, two severely 

impacted wetlands.
44 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

B. S-44 Cypress wetland, Starkey well field

A. S-68 Cypress wetland, Starkey well field

Dry during 1989–2007 (before groundwater reductions)

Flooded area, in percent of total wetland area

EXPLANATION

>0-20

21-40

41-60

61-80

81-100

Dry during 2008–2009 (after groundwater reductions)

Flooded area duration

0

20

40

60

80

100

Dry >0-20 21-40 41-60 61-80 81-100

Percentage of total wetland area inundated

Percentage of time

>0-20 21-40 41-60 61-80 81-100

0

20

40

60

80

100

Dry

Percentage of time

Percentage of total wetland area inundated

50 METERS

0 150 FEET

0

50 METERS

0 150 FEET

0

N

N

Flooded at a percent area interval during 1989–2007

(before groundwater reductions)

Flooded at a percent area interval during 2008–2009

(after groundwater reductions)

Figure 29. The shape of flooded areas at different levels of inundation, and graphs showing duration of flooding prior to and 

after reductions in groundwater withdrawals at A, S–68 Cypress, and B, S–44 Cypress at the Starkey well field.
Factors that Influence the Hydrologic Recovery of Wetlands 45

Figure 30. The shape of flooded areas at different levels of inundation, and duration graphs showing duration of flooding prior to 

and after reductions in groundwater withdrawals at A, W–33 Cypress, and B, W–16 Marsh at the Cypress Creek well field.

>0-20 21-40 41-60 61-80 81-100

0

20

40

60

80

100

DRY

0

20

40

60

80

100

DRY >0-20 21-40 41-60 61-80 81-100

Percentage of total wetland area inundated

Percentage of time

A. W-33 Cypress, Cypress Creek well field

B. W-16 Marsh, Cypress Creek well field

Percentage of time

Percentage of total wetland area inundated

50 METERS

0 150 FEET

0

50 METERS

0 150 FEET

0

Dry during 1989–2002 (before groundwater reductions)

Flooded area, in percent of total wetland area

EXPLANATION

>0-20

21-40

41-60

61-80

81-100

Dry during 2003–2009 (after groundwater reductions)

Flooded at a percent area interval during 1989–2002

(before groundwater reductions)

Flooded at a percent area interval during 2003–2009

(after groundwater reductions)

Flooded area duration

N

N
46 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

condition of an isolated wetland in a region regardless of size 

(Lee and others, 2009). Maps for four of the study wetlands 

show the distribution of the flooded area in 20 percent intervals, and the associated flooded-area duration graphs show 

the percentage of time that the wetland is contained within a 

particular flooded-area interval (figs. 29 and 30). The floodedarea duration graphs also show the percentage of time that 

each wetland was dry during a particular analysis period. 

These contrasting hydrologic conditions reflect the wetland’s 

response to the seasonal wet and dry periods and the influence 

of groundwater withdrawals.

During the 19-year period (1989–2007) at Starkey well 

field, S–68 Cypress and S–44 Cypress wetlands were dry 37 

percent and 45 percent, respectively, and in various stages of 

inundation during the remaining time (fig. 29A–B). During 

the inundated period, S–68 Cypress was most frequently 

inundated in the 41–60 and 61–80 percentile ranges (fig. 29A), 

whereas S–44 Cypress was most frequently inundated in the 

0–20 percentile range (fig. 29B). 

During a 2-year period (2008–09), the groundwater withdrawals from wells surrounding S–68 Cypress were reduced 

from 4.4 to about 1 Mgal/d (fig. 27) and the wetland was inundated 53 percent of the time, with almost equal intervals in the 

21–40, 41–60, and the 81–100 percentile ranges (fig. 29A). 

Although S–68 Cypress was dry a greater percentage of time 

in 2008–09 than in the preceding 19 years (47 and 37 percent, 

respectively), the increase was probably due to the rainfall 

deficit during 2007–08 (fig. 2B).

The flooded area of S–44 Cypress increased during 

2008–09, and the wetland was dry only 22 percent of the 

time. The wetland was most frequently inundated in the 

>0–20 and 21–40 percentile ranges (fig. 29B). The increase 

in flooded area at S–44 Cypress was the result of the reduction in groundwater withdrawals near the wetland (from 6 

to 2 Mgal/d; fig. 27), and a resulting increase of about 1 ft 

in the potentiometric surface for the Upper Floridan aquifer 

below the wetland bottom. The flooded area of S–44 Cypress 

during 2008–09 remained mostly within the deepest part of 

the wetland (>0–20 percent range), where karst depressions 

are located, but also extended outward to the 21–40 percent 

range, indicating an increase in the overall area of inundation. 

In addition, there was a slight increase in the 81–100 percent 

range for S–44 Cypress (fig. 29B).

During a 14-year period (1989–2002) when groundwater 

withdrawals averaged about 26 Mgal/d at the Cypress Creek 

well field (fig. 5C), the minimally impacted W–33 Cypress 

was dry 43 percent of the time and was most frequently 

inundated in the 81–100 percent range (fig. 30A). In contrast, 

the severely impacted W–16 Marsh was dry 99 percent of the 

time and was only inundated in the >0–20 percentile range 

(fig. 30B). W–16 Marsh was inundated only in February and 

March 1998 (fig. 28D) during the 1997–98 El Niño event 

(National Oceanic and Atmospheric Administration, 2010). 

The groundwater withdrawals surrounding W–16 Marsh 

were much greater than at W–33 Cypress, averaging about 

16 and 6 Mgal/d, respectively (fig. 27). In addition to the 

large withdrawals that occur near W16 Marsh, four sinkholes 

located along the wetland bottom in 1982 likely influenced the 

downward leakage potential for this wetland (Rochow, 1983c). 

During a 7-year period (2003–09) when groundwater 

withdrawals were reduced from an annual rate of 26 

(1998–2002) to about 15 Mgal/d (2003–09) at Cypress Creek 

well field (fig. 5C), the inundation period for W–33 Cypress 

increased from 57 to 66 percent, and the wetland was again 

most frequently inundated in the 81–100 percent range 

(fig. 30A). Withdrawal rates from wells near W–33 Cypress 

were reduced by about 2 Mgal/d during this period (fig. 27). 

Due to this reduction, the potentiometric surface of the Upper 

Floridan aquifer rose by about 2 ft beneath the wetland bottom 

(fig. 26). The increase in the potentiometric surface of the 

Upper Floridan aquifer beneath the wetland bottom (fig. 26) 

helped reduce the potential for downward leakage from 

this wetland. 

 Even though the groundwater withdrawals from individual wells surrounding W–16 Marsh were reduced by almost 

half (from 16 to 9 Mgal/d) during 2003–09 (fig. 27), the 

wetland remained dry 77 percent of the time and was inundated only 23 percent of the time (fig. 30B). The wetland was 

inundated only twice during the post groundwater-reduction 

period (2003–09), and only during extreme rainfall events 

(fig. 28D). The first flooding event occurred during August 

2003, following a year when rainfall was over 20 in. above 

average. Because of the cumulative rainfall, the wetland 

remained about 64 percent inundated for several weeks. 

The second flooding event occurred during September 2004 

after several tropical storms and hurricanes passed through the 

area, and following a year when rainfall was over 23 in. above 

average (fig. 28D). Consequently, over 63 percent of W–16 

Marsh was inundated for several months in late 2004. After 

both of these flooding events, the water level in the wetland 

quickly receded, indicating the interconnection between the 

wetland and underlying aquifer. Following the reductions 

in groundwater withdrawals, the median 5-ft increase in the 

potentiometric surface of the Upper Floridan aquifer below 

the wetland bottom (fig. 26) has not reduced the downward 

leakage potential at this wetland, indicating the influence of 

karst subsidence. 

Ranking of Factors Influencing the Hydrologic 

Recovery of Wetlands

 Ranking of factors that influence the hydrologic recovery 

of wetlands was used to determine the relative recovery 

potential of water levels in study wetlands following reductions in groundwater withdrawals. The total ranking was 

determined by summing the rank assigned to each factor. 

Ranking for three of the four factors (topographic setting, 

permeability of sediments underlying wetlands, and depth to 

the potentiometric surface of the Upper Floridan aquifer below 

the wetlands) was based on whether each factor had a positive 

influence, a neutral influence, or a negative influence (ranking 
Factors that Influence the Hydrologic Recovery of Wetlands 47

numbers 1, 2, and 3, respectively). Ranking for the remaining 

factor (karst feature near or underlying wetland) was based 

on whether karst features were absent, near, or underlying the 

study wetland (ranking numbers as 1, 2, and 3, respectively). 

A wetland with a minimum total rank of 4 indicated that the 

wetland is positively influenced by all the factors and is in 

good hydrologic condition. In contrast, a maximum total rank 

of 12 indicated that water levels in the wetland were not likely 

to recover under current conditions. This ranking system can 

be used as a preliminary tool to help make more informed 

decisions about wetland water-level recovery at other wetlands 

in the study area using available information. Although 

qualitative, rankings are an informative and practical tool 

for comparing the influence of multiple factors on wetland 

hydrology.

 Based on this ranking system, S–68 Cypress at Starkey 

well field has the lowest possible total rank of 4, indicating 

the good hydrologic condition of this wetland. The wetland 

is positively influenced by its low-lying topographic setting 

where surface-water connections can be made easily to nearby 

Cross Creek Branch, intact low-permeability layers below the 

wetland, a lack of karst features, and a relatively shallow depth 

of the potentiometric surface of the Upper Floridan aquifer 

below the wetland bottom (about 7 ft) (table 5 and fig. 31). 

 W–33 Cypress at Cypress Creek well field, with a total 

rank of 6, has good potential for hydrologic recovery because 

of the thick, low-permeability sediment layers underlying 

the wetland that are not influenced by karst subsidence. This 

wetland is neutrally influenced by other factors; the relatively 

high topographic setting compared to surrounding wetlands 

(fig. 9), and a large median depth (about 16 ft after the 

reduction in groundwater withdrawals) to the potentiometric 

surface of Upper Floridan aquifer—the greatest depth below 

any of the study wetlands (fig. 26). During the groundwater 

withdrawal reductions of 2003–09, there was a median 2-ft 

increase in the potentiometric surface of the Upper Floridan 

aquifer below W–33 Cypress, resulting in an increase in 

duration of the hydroperiod and flooded area of the wetland 

(fig. 30A). Even with the relatively large depth to the potentiometric surface of the Upper Floridan aquifer below this 

wetland after the reductions in groundwater withdrawals 

(fig. 26), this analysis indicates that the downward leakage 

potential is substantially reduced for wetlands in areas where 

the underlying sediments are thick, impermeable, and are not 

influenced by karst subsidence.

 W–56 Cypress, located in the Cypress Creek well field, 

was assigned a total rank of 7 (table 5). Sediments at this 

wetland are more permeable than those at W–33 Cypress, and 

there are no apparent karst features underlying or near this 

wetland. Neutral factors were the topographic setting (fig. 9) 

and median depth (about 11 ft) to the potentiometric surface of 

Upper Floridan aquifer below the wetland (fig. 26). During the 

groundwater withdrawal reductions of 2003–09, there was a 

median 5-ft increase in the potentiometric surface of the Upper 

Floridan aquifer below this wetland. As a result, the flooded 

duration at W–56 Cypress increased from 28 to 34 percent, 

and the flooded area of the wetland increased mostly in the 

81–100 percent inundation range.

 The six remaining study wetlands (Grass Prairie, 

Starkey Central, S–44 Cypress, Cypress Bridge 01, W–12 

Cypress, and W–16 Marsh) are affected by adjacent or underlying karst features, and were assigned total ranks ranging 

from 7 to 12 (table 5). The karst features provide pathways 

for downward leakage, and the extent of wetland recovery 

when withdrawals were reduced was dependent on how deep 

the potentiometric surface of the Upper Floridan aquifer was 

below the study wetland.

 For example, because of karst subsidence at S–44 

Cypress, the wetland bottom is about 5 ft deeper than a typical 

cypress wetland in several areas. The controlling factor in the 

recovery of this wetland is the shallow depth to the potentiometric surface of the Upper Floridan aquifer below the wetland 

(fig. 26). As the potentiometric surface approached land surface 

below this wetland, as a result of reductions in groundwater 

withdrawals during 2008–09, the duration of flooding increased, 

and the flooded area expanded from mostly in the >0–20 

percent area (where karst features are located) into the 21–40 

percent inundated area. For S–44 Cypress, the presence of 

the karst features did not affect the hydrologic recovery of the 

wetland because the elevation of the potentiometric surface 

of the Upper Floridan aquifer was about equal to the wetlandbottom elevation, limiting the downward leakage potential.

 W–12 Cypress and W–16 Marsh, assigned total ranks 

of 10 and 12, respectively, are both located in the region of 

Cypress Creek well field where large groundwater withdrawals 

are concentrated, and both have reported sinkholes or subsidence beneath or near the wetlands. Prior to groundwater development, both wetlands were located in groundwater discharge 

areas where the potentiometric surface of the Upper Floridan 

aquifer was either at or slightly above land surface (fig. 23). 

Prior to reductions in groundwater withdrawals, the median 

depth of the potentiometric surface of the Upper Floridan 

aquifer was about 14 to 16 ft below the wetland bottoms 

(fig. 26). Despite a median 5-ft increase in the potentiometric 

surface of the Upper Floridan aquifer after groundwater reductions (2003–09), these two wetlands have remained mostly dry, 

except during the high-rainfall events in 2003–05.

 During these inundation periods at W–16 Marsh during 

2003–05, the wetland water levels receded after 1 to 2 months, 

indicating a good interconnection with the underlying aquifers 

(fig. 28D). W–12 Cypress retained surface water for longer 

periods during 2003–05 compared to W–16 Marsh. W–12 

Cypress may benefit from its relatively low topographic 

setting, which facilitates inflow from other surface-water 

features during high-water periods (fig. 9). In addition, 

karst subsidence is not as severe at W–12 Cypress wetland 

compared to W–16 Marsh, where several karst features are 

present in the wetland bottom. W–16 Marsh also is about 

0.06 mi from a production well that affects water levels 

beneath this wetland. 
48 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

Table 5. Ranking of the study wetlands based on the factors that influence the hydrologic recovery of 

wetlands in the Northern Tampa Bay area.

Study wetland

Factors that influence the hydrologic recovery of wetlands

Topographical 

setting of 

wetland1

Permeability of 

sediments 

underlying 

wetland1

Karst feature 

near or underlying 

wetland2

Depth to the 

potentiometric surface 

of the Upper Floridan 

aquifer below 

wetland1

Total

Starkey well field 

S-68 Cypress 1 1 1 1 4

Grass Prairie 1 2 3 1 7

Starkey Central 2 2 2 1 7

S-44 Cypress 2 2 3 1 8

Cypress Creek well field

W-33 Cypress 2 1 1 2 6

W-56 Cypress 2 2 1 2 7

W-12 Cypress 1 3 3 3 10

W-16 Marsh 3 3 3 3 12

Cypress Bridge well field

Cypress Bridge 01 3 2 3 1 9

1

Ranking of hydrologic factor: 1, positive influence; 2, neutral influence; 3, negative influence.

2

Ranking for karst features: 1, no evidence of karst features; 2, karst features near wetland; 3, karst features underlying wetland. 

0

2

4

6

8

10

12

Starkey well field Cypress Creek well field Cypress

Bridge

well

field

Total rank

Wetlands

S-68

Cypress

Grass

Prairie

Starkey

Central

S-44

Cypress

W-33

Cypress

W-56

Cypress

W-12

Cypress

W-16

Marsh

Cypress

Bridge 01

Depth to the potentiometric surface – Of the

Upper Floridan aquifer underlying wetland.

Karst features

Permeability of sediments

Physical setting of wetland

– Located near or underlying wetland.

– Underlying wetland.

EXPLANATION

Figure 31. Total ranking of factors that influence the hydrologic recovery 

of wetlands in the Northern Tampa Bay area.
Summary 49

 Because of karst subsidence at both W–12 Cypress and 

W–16 Marsh, wetland water levels will not recover if the 

potentiometric surface of the Upper Floridan aquifer remains 

at its current depth of about 9 and 11 ft below the wetland 

bottom, respectively. Both wetlands retain water for only 

several months during high rainfall periods when groundwater 

withdrawals are reduced and the potentiometric surface of the 

Upper Floridan aquifer increases. 

Based on these rankings and the response of study 

wetlands to reductions in groundwater withdrawals, two 

factors primarily limited the hydrologic recovery of wetlands: 

the presence of recent karst activity below or near the 

wetlands, and the depth to the potentiometric surface of the 

Upper Floridan aquifer below the wetlands. Breaches and 

breaks in the near-surface sediment layers or the intermediate 

confining unit due to sinkhole activity beneath the wetlands 

provide pathways for downward leakage, and the leakage 

potential increases when the depth to the potentiometric 

surface of the Upper Floridan aquifer is substantially below 

the wetland most of the time. 

 Low-permeability layers and the absence of adjacent or 

underlying karst features improve a wetland’s ability to recover 

if groundwater withdrawals are reduced. In this setting, intact 

subsurface layers help retain water within and beneath the 

wetland and limit the downward leakage potential, even when 

water levels in the Upper Floridan aquifer are lower. 

 A relatively low topographic setting was found to 

influence wetlands during high-water periods because it 

facilitates surface-water connections to other wetlands and 

other surface-water bodies through low-lying surface-water 

channels. Wetland hydroperiods were longer during wet 

conditions for wetlands in low topographic settings compared 

to wetlands in higher topographic settings.

Summary

 More than 33,000 wetlands are located throughout 

the Northern Tampa Bay area in Florida, with the majority 

(81 percent) consisting of freshwater wetlands. The numerous 

wetlands in the study area are widely distributed, relatively 

small, and are typically isolated. In the rapidly developing 

area of Northern Tampa Bay, anthropogenic impacts such as 

wetland losses, agricultural and urban development, construction of roadways and ditches, and the influence of groundwater withdrawals have provided challenges to maintaining 

the hydrologic and ecologic functions of this resource. 

Long-term groundwater withdrawals from well fields, along 

with a series of extended droughts in the Northern Tampa 

Bay area, have lowered the potentiometric surface of the 

Upper Floridan aquifer, which has induced downward leakage 

from the surficial aquifer and wetlands in areas within and 

around the well-field boundaries. Water-level declines in these 

wetlands have reduced the wetland hydroperiod, and in some 

cases, caused a series of side effects including replacement of 

wetland-dependent plant species with upland species, introduction of invasive plant species, drying and compaction of 

wetland-bottom sediments, tree fall, intense fires, and loss of 

habitat for aquatic or water-dependent wildlife.

 A reduction in groundwater withdrawals from the 

Northern Tampa Bay well fields was initiated in mid-2002 

to improve the hydrologic condition of local wetlands by 

allowing groundwater and wetland water levels to recover to 

previously higher levels. The groundwater reductions began in 

late 2002 and 2007 for Cypress Creek and Starkey well fields, 

respectively. As a result of this reduction, the potentiometric 

surface of the Upper Floridan aquifer in 2009 has risen at two 

study well fields, with the median rise ranging from about 2 

to 5 ft at Cypress Creek well field and 0 to 5 ft at Starkey well 

field. In response to the reduction in groundwater withdrawals, 

water levels in some long-term monitored wetlands have 

recovered, while others have not recovered as expected. 

 To understand why some wetland water levels have not 

recovered, an unimpacted wetland and eight wetlands affected 

to varying degrees by well field pumping were examined 

at Starkey, Cypress Creek, and Cypress Bridge well fields. 

The study wetlands were examined based on four factors 

known to influence the hydrologic condition of the wetlands 

in west-central Florida, including the topographic setting, the 

permeability of underlying sediments, recent karst activity, and 

the depth to the potentiometric surface of the Upper Floridan 

aquifer beneath the wetland bottom. This analysis provided 

an indication of the hydrologic condition of each wetland, and 

which of the four factors could be limiting the recovery of 

wetland water levels. 

When all other factors that influence the hydrologic 

condition of wetlands are the same, wetlands in a low-lying 

topographic setting have a greater potential to recover when 

groundwater withdrawals are reduced. Comparison of the 

physical setting of wetlands in the study area indicated that 

a low-lying topographic setting relative to the surrounding 

area benefited the hydrologic condition of isolated wetlands. 

Compared to wetlands in higher areas, those in lower areas 

had longer hydroperiods partly because of their greater ability, 

during wet conditions, to establish surface-water connections 

to other isolated wetlands and surface-water bodies through 

low-lying surface-water channels. Relatively low-lying 

wetlands surrounded by uplands have a greater potential to be 

in either a groundwater discharge or flow-through setting and 

benefit from greater groundwater inflow or reduced leakage 

than wetlands in higher topographic settings. 

The continuity and the permeability of the sediments 

underlying the study wetlands substantially affected the 

hydrologic condition of the wetlands. The absence of karst 

features below or near the wetland and low permeability 

sediments underlying the wetland both improved the ability 

of wetlands to recover when groundwater withdrawals were 

reduced. Several aspects of the geologic framework helped 

maintain the hydrology of shallow depressional wetlands in 

the study area, including: (1) a thin clay layer in the nearsurface wetland-bottom sediments that slows the downward 
50 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

movement of water from the wetland; (2) a clay or hard-pan 

layer that lies about 5 to 10 ft below the wetland bottom that 

retards the downward movement of groundwater underlying 

the wetland; and (3) an intact or thick clay layer of low 

permeability, referred to as the intermediate confining unit, 

that slows the movement of water between the wetland/surficial aquifer and the Upper Floridan aquifer. 

 Recent karst subsidence activity underlying or near the 

wetlands facilitated the hydrologic decline of several of the 

study wetlands. Several aspects of the karst geologic framework 

enhance the connection between the wetland/surficial aquifer 

and the underlying Upper Floridan aquifer, including (1) sinkholes or depressional piping features that have formed in the 

wetland bottom and extend through the clay or hardpan layer 

underlying the wetlands; (2) sinkholes or depressional piping 

features that have formed near the perimeter of the wetland; and 

(3) an intermediate confining unit that contains breaches or is 

thin, absent, or is highly permeable. Breaches or breaks in the 

underlying surficial layers or in the intermediate confining unit 

due to karst subsidence activity provide pathways for downward 

leakage to the underlying Upper Floridan aquifer, especially 

when wetlands are located in recharge areas.

 Six of the nine wetlands examined in this study had 

varying degrees of localized karst subsidence underlying or 

near them based on bathymetric and ground-penetrating radar 

surveys, water-level data, and topographic analysis. The most 

severely impacted wetland (W–16 Marsh) was found to 

have karst subsidence features along the wetland bottom, in 

addition to a large vertical separation (median 15 ft) between 

the potentiometric surface of the Upper Floridan aquifer and 

the wetland-bottom elevation. However, wetlands that had 

both karst subsidence in the wetland bottom and a shallow 

depth to the potentiometric surface, such as S–44 Cypress, had 

longer periods of inundation during the groundwater reduction period. At this wetland, the presence of karst features did 

not affect the hydrologic recovery of the wetland because the 

elevation of the potentiometric surface of the Upper Floridan 

aquifer was about the same as the wetland-bottom elevation, 

limiting the downward leakage potential.

 The increase in the potentiometric surface of the Upper 

Floridan aquifer below the wetland-bottom elevation was the 

primary factor affecting the hydrologic recovery of the study 

wetlands, especially those affected by karst subsidence. Two 

study wetlands affected by karst subsidence (W–12 Cypress 

and W–16 Marsh), remained mostly dry during the period 

of groundwater withdrawal reductions (2003–09), despite a 

median 5-ft increase in the potentiometric surface of the Upper 

Floridan aquifer below the wetlands. Both wetlands are located 

in an area of the well field where large groundwater withdrawals 

are concentrated, and during the last 20 years of water-level 

data collection (1989–2009), both were inundated only during 

periods of extreme rainfall. During these inundation periods, 

the wetland water levels receded after 1 to 2 months, indicating 

good interconnection with the underlying aquifers. Because of 

this interconnection, water levels for these wetlands and other 

wetlands impacted by karst subsidence in this region will not 

recover if the potentiometric surface of the Upper Floridan 

aquifer remains at the current (2009) median depth of about 

10 ft below the wetland-bottom elevation. 
References Cited 51

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Appendixes 1–3

 
56 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

82°42’ 82°39’ 82°36' 82°33' 82°30’

28°18'

28°15'

28°12'

82°27' 82°24' 82°21’

28°18'

28°15'

A

B

Starkey

Central

S-44 Cypress

Grass

Prairie S-68 Cypress

W-12 Cypress

W-16 Marsh

W-33

Cypress

W-56

Cypress

80

70

60

70

10

20

30

40

50

60

Source: U.S. Fish and Wildlife Service, National Wetlands Inventory polygon data,

March, 2004; Universal Transverse Mercator projection, zone 17

0 1 2 MILES

0 1 2 KILOMETERS

Source: U.S. Fish and Wildlife Service, National Wetlands Inventory polygon data,

March, 2004; Universal Transverse Mercator projection, zone 17

EXPLANATION

Wetland

Estimated potentiometric surface

Study wetland name and location

– Of the Upper Floridan aquifer.

Contour interval 10 feet. Datum is NGVD 1929.

W-33 Cypress

20

Appendix 1. Potentiometric surface map of the Upper Floridan aquifer prior to development at the 

A, Starkey, and B, Cypress Creek well fields. Modified from Johnston and others (1980).
Appendixes 57

30

34

22

26

38

42

18

14

50

82°39' 82°36' 82°33'

28°18'

28°15'

28°12'

EXPLANATION

Well field

Well-field boundary

Potentiometric contour

Observation well and value

Study wetland name and location

– Shows altitude at which water would have

stood in tightly cased wells. Contour interval 2 feet. Datum is NGVD 1929.

28°18'

28°15'

28°12'

A

B

46

S-44

Cypress

S-44

Cypress

S-68 Cypress

35

32 15.1

34.2

28.63

25.53

38.72

41.48

31.81

47.41

38.15

27.47

23.64

42.58

15.44

14.27

10.98

39.71

30.32

32.66

26.83

37.66

38.84

15.44

42

34.9

33.82

27.06

44.72

50.59

42.84

43.34

39.04

30.17

18.03

36.76

43.91

16.36

13.86

29.77

51.14

39.72

42.38

43.27

Grass

Prairie Starkey

Central

S-68 Cypress

38.36

33.13

23.08 18.53

Grass

19.13Prairie Starkey

Central

S-68 Cypress

12

16

20

24

28

32

36

40

44

48

12

20

24

28

32

36

40

44

48

16

14

50

18

22

26

30

34

38

42

46

82°39' 82°36' 82°33'

20

0 1 2 MILES

012 KILOMETERS

Source: U.S. Fish and Wildlife Service, National Wetlands Inventory polygon data,

March, 2004; Universal Transverse Mercator projection, zone 17

Appendix 2. Potentiometric surface map of the Upper Floridan aquifer at the 

Starkey well field for A, September 2008 and B, May 2009. 
58 Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida 

74

60

62

64

66

68

70

72

60

68

66

64

62

52

W-56 Cypress

"

"

"

" W-56 Cypress

W-12 Cypress

62.16

51.9

74.95

69.72

67.27

71.68

70.95

67.47

58.67

51.73

65.15

52.58

54.73

61.09

52.35

55.99

77.06 62.38

64.45

55.99

76

54

56.53

68

66

70

66

70

54.62

50.77

51.77

74

72

68

70

76

78

80

48.3

67.63

64.71

69.65

68.31

68.68

51.73

48.65

50.11

46.33

57.38

46.75

48.36

55.81

48.79

53.35

45.37

61.27

44.6

W-33 Cypress

45.56

55.38

W-16 Marsh

58.59

61.91

61.93

47.94 52.63

65.11

67.61

46.23

54

56

58

52

57.61

TMR-3

wells

W-12 Cypress

W-33 Cypress

W-16 Marsh

TMR-4 wells

54

50.45

60

62

64

66

58

66

64

62

60

58

66

60

68

68

68

64

62

66

68

56

58

60

54

52

50

48

46

48

50

52

54

64

62

56

70

0 1 2 MILES

0 1 2 KILOMETERS

28°18'

28°16'

28°18’

28°16’

82°28' 82°26' 82°24' 82°22' 82°20'

82°28’ 82°26’ 82°24’ 82°22’ 82°20’

A

B

Source: U.S. Fish and Wildlife Service, National Wetlands Inventory polygon data,

March, 2004; Universal Transverse Mercator projection, zone 17

EXPLANATION

Potentiometric contour – Shows altitude at

which water would have stood in tightly

cased wells. Hachures indicate depressions.

Contour interval 2 feet. Datum is NGVD 1929.

20

W-33 Cypress

70.95

Well field

Well-field boundary

Observation well and value

Study wetland name and location

Appendix 3. Potentiometric surface map of the Upper Floridan aquifer at the Cypress Creek well field for 

A, September 2008 and B, May 2009. 
Prepared by:

USGS Science Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

USGS publishing staff:

Mike Deacon, Editor

Ronald S. Spencer, Illustration assistance

For information regarding this publication, contact:

Director

USGS Florida Water Science Center

10500 University Center Dr., Suite 215

Tampa, FL 33612

http://fl.water.usgs.gov/
Metz, P.A.—Factors that Influence the Hydrologic Recovery of Wetlands in the Northern Tampa Bay Area, Florida—SIR 2011–5127

Printed on recycled paper