U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010-5189

Prepared in cooperation with the Southwest Florida Water Management District

Effect of Groundwater Levels and Headwater 

Wetlands on Streamflow in the Charlie Creek Basin, 

Peace River Watershed, West-Central Florida

Effect of Groundwater Levels and 

Headwater Wetlands on Streamflow in 

the Charlie Creek Basin, Peace River 

Watershed, West-Central Florida

By T.M. Lee, L.A. Sacks, and J.D. Hughes

Prepared in cooperation with the Southwest Florida Water Management District

Scientific Investigations Report 2010-5189

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Lee, T.M., Sacks, L. A., and Hughes, J.D., 2010, Effects of Groundwater Levels and Headwater Wetlands 

on Streamflow in the Charlie Creek Basin, Peace River Watershed, West-Central Florida: U.S. Geological 

Survey Scientific Investigations Report 2010-5189, 77 p.

978411330221
iii

Contents

Acknowledgments........................................................................................................................................ix

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

Introduction.....................................................................................................................................................3

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

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

Methods of Investigation............................................................................................................................11

Hydrogeologic Characterization ......................................................................................................11

Basin Stratigraphy.....................................................................................................................11

Basin Topography and Hydrography ......................................................................................11

Groundwater Monitoring Network .........................................................................................12

Mapping and Spatial Analysis of Potentiometric Levels in Confined Aquifers...............12

Seepage Runs ............................................................................................................................15

Hydrologic Analysis............................................................................................................................15

Integrated Modeling of Surface Water and Groundwater .................................................15

Modeling Approach..........................................................................................................16

Spatial Discretization and Assignment of Model Parameters ..................................16

Temporal Discretization and Boundary Conditions.....................................................18

Hydrologic Input Variables in the Model ......................................................................18

Model Calibration and Error............................................................................................18

Observed and Simulated Water Budgets for the Basin ......................................................19

Hydrogeologic Framework of the Charlie Creek Basin .........................................................................20

Hydrogeologic Units...........................................................................................................................20

Surficial Aquifer.........................................................................................................................20

Intermediate Aquifer System...................................................................................................20

Upper Floridan Aquifer..............................................................................................................24

Groundwater Use................................................................................................................................24

Aquifer Potentiometric Levels ..........................................................................................................26

Upper Floridan Aquifer..............................................................................................................26

Intermediate Aquifer System...................................................................................................27

Head Differences between the Intermediate Aquifer System and 

Upper Floridan Aquifer................................................................................................29

Surficial Aquifer.........................................................................................................................31

Temporal Changes in Vertical Head Differences between Aquifers ................................32

Groundwater and Stream Interactions ...........................................................................................33

Artesian Flow Conditions in the Basin ...................................................................................33

Vertical Flow Potential between Streams and the Intermediate Aquifer System ..........36

Stream Interactions with the Surficial Aquifer.....................................................................38

Charlie Creek .....................................................................................................................38

Tributaries ..........................................................................................................................39

Seepage Inflow to Charlie Creek ............................................................................................43

Stream Specific Conductance.................................................................................................45

Hydrologic Analysis of the Charlie Creek Basin.....................................................................................46

Simulated Streamflow in Charlie Creek and its Tributaries .........................................................47
iv

Basin and Subbasin Water Budgets................................................................................................51

Rainfall and Evapotranspiration Differences between Subbasins....................................51

Wetland Water-Storage Differences between Subbasins .................................................53

Groundwater Flow Differences between Subbasins...........................................................57

Runoff and Streamflow Differences between Subbasins...................................................61

Hydrologic Differences between the Upper and Lower Parts of the Charlie Creek Basin ....62

Summary and Conclusions.........................................................................................................................65

Selected References...................................................................................................................................67

Appendix 1.....................................................................................................................................................72

Appendix 2.....................................................................................................................................................74

Appendix 3.....................................................................................................................................................75

Figures

1-5. Maps showing—

1. The Peace River watershed and its principal basins in west-central Florida...........2

2. Land surface elevations in the Charlie Creek basin ......................................................5

3. NEXRAD basin-wide average monthly rainfall totals during 2004-2005, and the 

long-term rainfall average at the NOAA Climate Station in Avon Park, Florida, 

and paths of hurricanes Charley, Frances, and Jeanne during 2004..........................7

4. Charlie Creek basin, its five principal subbasins, and the location of streamflow 

monitoring stations used for this study............................................................................8

5. Generalized land use and land cover in the Charlie Creek basin..............................10

6. Streamflow hydrographs for the three tributaries to Charlie Creek, and 

duration curves for streamflows measured at Oak Creek, Little Charley 

Bowlegs Creek, Buckhorn Creek, and Charlie Creek near Crewsville, Florida 

from approximately April 2004 through December 2005, and for Charlie Creek 

near Gardner, Florida from October 2002 through December 2005....................................11

7. Map showing the location of geologic cross sections, carbonate rock outcrops in 

the Charlie Creek stream channel, and seepage-run measurement sites in the 

Charlie Creek basin ....................................................................................................................13

8. Map showing the location of the groundwater monitoring sites, streamflow 

monitoring stations, and well transect sites in the Charlie Creek basin...........................14

9. Chart showing relation between stratigraphic and hydrogeologic units in the 

Charlie Creek basin ....................................................................................................................21

10. Generalized hydrogeologic section A–A’ in and near the Charlie Creek basin ...............22

11. Generalized hydrogeologic section B–B’ in and near the Charlie Creek basin...............22

12. Photograph showing fractured carbonate rock exposed in the bed of Charlie 

Creek at the southernmost of the two outcrops shown in figure 7 ....................................23

13. Map showing decrease in the potentiometric surface of the Upper Floridan 

aquifer from predevelopment levels to May 2007 for the Southern West-Central 

Florida Groundwater Basin .......................................................................................................25

14. Graphs showing estimated groundwater pumping in the Charlie Creek basin by 

use category for 2004 and 2005, and as annual averages from 1992 to 2005 ...................25

15. Maps showing potentiometric surface of the Upper Floridan aquifer for low 

(May 2004) and high (September 2004) conditions for the 2004-2005 study period.........27 
v

16. Graphs showing wet and dry season water levels in two Upper Floridan 

aquifer wells in the Charlie Creek basin from 1975 to 2008 .................................................28

17. Maps showing potentiometric surfaces of the intermediate aquifer system for 

dry (May 2004) and wet (Sept. 2004) conditions during the study, also 

showing areas where the intermediate aquifer system heads are greater 

and less than heads in the Upper Floridan aquifer...............................................................29

18-20. Graphs showing—

18. Wet and dry season water levels in three intermediate aquifer system 

wells in the Charlie Creek basin from 1986 to 2008 ......................................................30

19. Daily average water levels in the surficial aquifer at upland wells in the 

three tributary subbasins .................................................................................................31

20. Water levels in wells in the surficial aquifer, Zones 2 and 3 of the 

intermediate aquifer system, and the Upper Floridan aquifer at 

ROMP 30, ROMP 26, and ROMP 43 .................................................................................32

21. Maps showing artesian flow conditions in the intermediate aquifer system 

and the Upper Floridan aquifer in the Charlie Creek basin for low (May 2004) 

and high (Sept. 2004) head conditions during the 2004-2005 study period .......................34

22. Maps showing difference between head in the intermediate aquifer system 

and streambed elevation for Charlie Creek and major tributaries, for low 

(May 2004) and high (Sept. 2004) head conditions during the 2004-2005 study 

period, and for very low head conditions (May 2000)...........................................................36

23-33. Graphs showing—

23. General groundwater flow direction around Charlie Creek at the upstream 

transect site for July 1, 2004, and October 28, 2004 .....................................................39

24. General groundwater flow direction around Charlie Creek at the 

downstream transect site for July 1, 2004, and October 28, 2004..............................40 

25. Water levels in representative wells and Charlie Creek at the upstream and 

downstream well-transect sites .....................................................................................41

26. Water levels in the stream and adjacent surficial aquifer system at 

Buckhorn Creek, Little Charley Bowlegs Creek, and Oak Creek ...............................42

27. Groundwater inflow to Charlie Creek for different stream reaches 

during May 2005, all four seepage runs for sections upstream and 

downstream of the confluence with Oak Creek, and all seepage runs 

for the entire stream reach ..............................................................................................44

28. The range of daily values of specific conductance at the five streamflow 

stations in the Charlie Creek basin, and the relationship between the 

median specific conductance in the streams and the percent of the gaged 

basin in citrus agriculture in 2005 ...................................................................................46 

29. Observed and simulated streamflow at Little Charlie Bowlegs Creek near 

Sebring, Florida, and weekly total NEXRAD rainfall at the pixel closest to the 

streamflow monitoring station, 2003 to 2005 .................................................................48

30. Observed and simulated streamflow at Buckhorn Creek near Griffins Corner, 

Florida, and weekly total NEXRAD rainfall at the pixel closest to the streamflow 

monitoring station, 2003 to 2005 ......................................................................................48

31. Observed and simulated streamflow at Charlie Creek near Crewsville, Florida, and 

weekly total NEXRAD rainfall at the pixel closest to the streamflow monitoring 

station, 2003 to 2005...........................................................................................................49

32. Observed and simulated streamflow at Oak Creek near Gardner, Florida, and 

weekly total NEXRAD rainfall at the pixel closest to the streamflow monitoring 

station, 2003 to 2005...........................................................................................................49
vi

33. Observed and simulated streamflow at Charlie Creek near Gardner, Florida, 

and weekly total NEXRAD rainfall at the pixel closest to the streamflow 

monitoring station, 2003 to 2005 ......................................................................................50

34. Maps showing NEXRAD rainfall totals in the Charlie Creek basin for the week with the 

greatest rainfall in 2004 (Sept. 1-7), and the 2004 calendar year........................................52 

35. Maps showing annual potential evapotranspiration and simulated 

evapotranspiration in the Charlie Creek basin for 2004 .......................................................54

36. Graph showing simulated range of weekly evapotranspiration rates for the 

five subbasins and for the upper and lower halves of the Charlie Creek basin 

from October 2002 through December 2005...........................................................................55

37. Maps showing simulated depths for water stored above the land surface in the 

Charlie Creek basin for May 4, 2004, and September 8, 2004..............................................56

38. Chart showing simulated range in the spatially-averaged, daily water depth 

stored above land surface for the five subbasins, and for the upper and lower 

halves of the Charlie Creek basin, from October 2002 through December 2005..............57

39. Map showing microtopographic features in the upper part of the Charlie Creek 

basin, including wetlands and shallow topographic depressions and the surface 

channels connecting them to streams....................................................................................58

40. Maps showing simulated cumulative groundwater flux from the Upper Floridan 

aquifer to the surficial aquifer for January through June 2004, July through 

December 2004, January through June 2005, and July through December 2005............59

41-44. Graphs showing—

41. Selected water-budget components for the entire Charlie Creek basin for the 

2004 calendar year, and for the wet season of July through December 2004..................63 

42. Differences between water-budget terms spatially-averaged for the entire Charlie 

Creek basin during the wet season in 2004 and their spatially-averaged value in the 

upper half and lower half of the Charlie Creek basin for the same period.......................64

43. Relationship between the cumulative daily values of available water and 

streamflow for the upper half and the lower half of the Charlie Creek basin ..................65

44. Percentage of the daily streamflow at Charlie Creek near Gardner generated by 

the upper half of the basin from January 2004 to December 2008 .....................................65
vii

Tables

1. Physical characteristics of the principal tributary basins of the Peace River 

watershed in west-central Florida.............................................................................................4

2. Physical characteristics of subdivided areas within the Charlie Creek basin...................9

3. Groundwater use in subdivided areas of the Charlie Creek basin.....................................26

4. Differences between head in the intermediate aquifer system and the overlying 

streambed elevation for subbasins in the Charlie Creek basin ..........................................36 

5. Seepage run results with error estimates for 2005-2006 measurement dates.................43

6. Summary calibration statistics for the simulated streamflows at five streamflow 

stations in the Charlie Creek basin ..........................................................................................50

7. Observed percentile-flow values and the error in the simulated percentile-flow 

values for the five streamflow stations in the Charlie Creek basin....................................51

8. Simulated water-budget components for the Charlie Creek subbasins for 2003-2005...52

9. Simulated annual evapotranspiration rates for the land uses and land covers 

represented in the model ..........................................................................................................54

10. Simulated percentage of the Charlie Creek basin where the surficial aquifer is 

recharging downward or receiving upward groundwater discharge, and the groundwater volumes for 6-month periods in 2004 and 2005...................................................... 60

11. Baseflow contributions to streamflow in the Charlie Creek basin in 2005 based on 

measured and simulated streamflow......................................................................................61

12. Runoff from subdivided areas of the Charlie Creek basin ...................................................62

13. Average annual streamflow and the number of days with no flow at streamflow 

stations in the upper and lower reach of Charlie Creek ......................................................62

Appendix Tables

1-1. Characteristics of wells used in the study .....................................................................................72

2-1. Discharge and specific conductance measurements for the four seepage runs...................74

3-1. Unsaturated and saturated hydraulic properties applied to various hydrologic 

soil groups represented in the model......................................................................................76

3-2. Manning’s roughness coefficient and vegetation parameters applied to the various 

types of land uses and land covers represented in the model ...................................................76

3-3. Monthly vegetation crop coefficients applied to various types of land uses and land 

covers represented in the model .....................................................................................................77
viii

Conversion Factors

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)

acre 0.4047 square hectometer (hm2) 

acre 0.004047 square kilometer (km2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

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

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3) 

Flow rate

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

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

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

Specific capacity

gallon per minute per foot 

[(gal/min)/ft)]

 0.2070 liter per second per meter 

[(L/s)/m]

Hydraulic conductivity

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

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d) 

Seepage

cubic foot per second per mile 

[(ft3/s)/mi]

0.0176 cubic meter per second per 

kilometer [(m3/s)/km]

Leakance

foot per day per foot [(ft/d)/ft] 1 meter per day per meter

Storage

cubic foot per square mile 

(ft3/mi2)

0.01095 Cubic meter per square kilometer 

(m3/ km2)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

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

(NGVD 1929). 

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

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

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Acronyms and Additional Abbreviations

DEM Digital elevation model

in/wk inches per week

LIDAR Light detection and ranging

NED National Elevation Dataset

ROMP Regional Observation and Monitor-well Program

SWFWMD Southwest Florida Water Management District

USGS U.S. Geological Survey

NEXRAD Next-Generation Radar (WSR-88D Weather Radar)

NOAA National Oceanographic and Atmospheric Administration

Acknowledgments

The authors gratefully acknowledge the property owners and property caretakers who 

provided access to their wells and to Charlie Creek and its tributaries, including: James A. 

Messana, James H. Webb, Wilbur Robertson, Ouida Roberts, Norman Paulsen, D & H Ranch, 

Ben Hill Griffin, Jr., and Sunny South Packing Company. We also recognize the contributions 

of two former USGS hydrologists, Billy Lewelling and Donald Herndon, who initially worked 

on the study, Geoffrey Fouad, who provided invaluable technical support, and Amy Swancar, 

whose reviews improved a succession of report drafts.
x
Abstract    1

Abstract

The Charlie Creek basin was studied from April 2004 to 

December 2005 to better understand how groundwater levels 

in the underlying aquifers and storage and overflow of water 

from headwater wetlands preserve the streamflows exiting this 

least-developed tributary basin of the Peace River watershed. 

The hydrogeologic framework, physical characteristics, and 

streamflow were described and quantified for five subbasins 

of the 330-square mile Charlie Creek basin, allowing the 

contribution of its headwaters area and tributary subbasins to 

be separately quantified. A MIKE SHE model simulation of 

the integrated surface-water and groundwater flow processes 

in the basin was used to simulate daily streamflow observed 

over 21 months in 2004 and 2005 at five streamflow stations, 

and to quantify the monthly and annual water budgets for the 

five subbasins including the changing amount of water stored 

in wetlands. Groundwater heads were mapped in Zone 2 of the 

intermediate aquifer system and in the Upper Floridan aquifer, 

and were used to interpret the location of artesian head conditions in the Charlie Creek basin and its relation to streamflow. 

Artesian conditions in the intermediate aquifer system induce 

upward groundwater flow into the surficial aquifer and help 

sustain base flow which supplies about two-thirds of the 

streamflow from the Charlie Creek basin. Seepage measurements confirmed seepage inflow to Charlie Creek during the 

study period.

The upper half of the basin, comprised largely of the 

Upper Charlie Creek subbasin, has lower runoff potential than 

the lower basin, more storage of runoff in wetlands, and periodically generates no streamflow. Artesian head conditions in 

the intermediate aquifer system were widespread in the upper 

half of the Charlie Creek basin, preventing downward leakage 

from expansive areas of wetlands and enabling them to act as 

headwaters to Charlie Creek once their storage requirements 

were met. Currently, the dynamic balance between wetland 

storage, rainfall-runoff processes, and groundwater-level 

differences in the upper basin allow it to generate approximately half of the streamflow from the Charlie Creek basin. 

Therefore, future development in the upper basin that would 

alter the hydraulic connectivity of wetlands during high flow 

conditions or expand recharging groundwater conditions could 

substantially affect streamflow in Charlie Creek. LIDAR 

(Light detection and ranging) based topographic maps and 

integrated modeling results were used to quantify the water 

stored in wetlands and other topographic depressions, and to 

describe the network of shallow stream channels connecting 

wetlands to Charlie Creek and its tributaries over distances 

of several thousand feet. Peak flows at all but one streamflow 

station were underpredicted in MIKE SHE simulations, possibly because the hydraulics of surface channels connecting 

wetlands to stream channels were not explicitly simulated in 

the model. Explicitly simulating the smaller channels connecting wetlands and stream channels should improve the ability 

of future watershed models to simulate peak flows in streams 

with headwater wetlands. 

The runoff potential was greater in the lower half of the 

Charlie Creek basin than in the upper half, and the streambed 

of Charlie Creek had greater potential to both directly gain 

streamflow from groundwater and lose streamflow to groundwater. Charlie Creek is more incised into the surficial aquifer 

in the lower basin than in the upper basin, and the streambed 

intersects the top of the intermediate aquifer system at two 

known locations. Groundwater levels in the intermediate aquifer system varied widely in the lower half of the basin from 

artesian conditions inducing upward flow toward the surficial 

aquifer and streams, to recharging conditions allowing downward flow and stream leakage. Recharge areas were greatest in 

May 2004 when rainfall was at a seasonal low and irrigation 

pumping was at a seasonal high. Recharge conditions in May 

2004 extended to beneath the streambed and included areas 

where fractured carbonate rocks at the top of the intermediate aquifer system crop out in the streambed, increasing the 

possibility for flow between the stream and aquifer. Groundwater withdrawals from wells open to the intermediate aquifer 

system exclusively, or to both the Upper Floridan aquifer 

and intermediate aquifer system, increased the occurrence of 

recharging conditions in Lower Charlie Creek subbasin as well 

as in Buckhorn Creek subbasin. 

Agricultural irrigation water returning to the stream as 

runoff or base flow sustained flow in the Oak Creek tributary 

during a dry season when flow ceased in the two other main 

tributaries to Charlie Creek. With the exception of Little Charley Bowlegs Creek, dissolved minerals in agricultural return 

water increased the specific conductance of water in streams 

monitored in the Charlie Creek basin, particularly Oak and 

Buckhorn Creeks.

Effect of Groundwater Levels and Headwater

Wetlands on Streamflow in the Charlie Creek Basin,

Peace River Watershed, West-Central Florida

By T.M. Lee, L.A. Sacks, and J.D. Hughes
2    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Figure 1. The Peace River watershed and its principal basins in west-central Florida. Map shows areas of artesian 

groundwater flow for estimated predevelopment groundwater levels in the Upper Floridan aquifer, and for recorded 

periods with very low (May 2000) and very high (Sept. 2004) groundwater levels in the Upper Floridan aquifer.

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Gulf of Mexico

0 25 MILES

0 25 KILOMETERS

82°30’ 82°30’ 81°30’

28°00’

27°30’

27°00’

Tampa Bay

Location of the

Peace River watershed

Gulf

of

Mexico

Location of

Green Swamp

Nocatee

Arcadia

Gardner

Fort Ogden

Bartow

Bowling Green

EXPLANATION

Peace River watershed

Estimated predevelopment Upper Floridan

aquifer head above land surface

May 2000 Upper Floridan aquifer head above land surface

Surface-water feature

Drainage basin divide

September 2004 Upper Floridan aquifer head above land surface

POLK

MANATEE

HILLSBOROUGH

PASCO

OSCEOLA

Shell-Prairie

Creek basin

Charlie

Creek

basin

Horse Creek

basin

Payne

Creek basin

Joshua

Creek

basin

SARASOTA

HIGHLANDS

DE SOT0

HARDEE

CHARLOTTE

Upper

Peace

River

basin

GLADES

Peace

River

basin
Introduction    3

Introduction

Understanding the hydrology of tributary streams in 

central Florida is challenging because it requires quantifying 

the effects of two complex watershed processes on streamflow: the storage and overflow of water from headwater 

wetlands, and the interaction between groundwater and 

streams. Consequently, it remains difficult to predict streamflow losses that will occur when (1) an undeveloped landscape 

is altered by surface mining or other land-use changes that 

eliminate wetlands or alter their previous drainage patterns, or 

(2) groundwater levels are lowered substantially by pumping. 

It also remains difficult to determine how those losses will 

affect dry-season base flows and wet-season peak flows. In 

the mantled karst terrain of central Florida, peak streamflows 

generated by the runoff from tropical storms and hurricanes 

often include runoff routed through wetlands. These wetseason peak flows can be followed during drier months by 

base flows sustained solely by groundwater inflow (seepage). The first-order streams present in the headwaters of 

basins, where incipient streamflow begins, are particularly 

susceptible to dry climatic conditions and may intermittently 

dry out. In contrast, the successively higher-order streams 

(second, third, and so forth), created by the confluence of 

lower-order streams, rarely go dry. Seasonally-flooded depressional wetlands are a characteristic landscape feature in central 

Florida, and the overflow from wetlands generates streamflow 

in first-order streams. Depressional wetlands in the expansive, wetland-rich “Green Swamp” region of central Florida 

form the headwaters of four major rivers, including the Peace 

River―the largest river in west-central Florida in both magnitude of discharge and basin area (Fernald and Purdum, 1998). 

Like a fractal pattern that remains evident when viewing a 

whole image at a variety of scales, smaller networks of 

depressional wetlands form the headwaters of smaller 

tributaries in the Peace River watershed, including those in 

the Charlie Creek basin (fig. 1).

Tributary flows typically receive increased attention 

by water managers and the public when flows decline in the 

major rivers they drain into. For this reason, the hydrologic 

character of tributary streams is of particular interest in the 

Peace River watershed (Florida Department of Environmental Protection, 2007). Streamflow along upper reaches of 

the Peace River has declined over the past several decades, 

concurrent with declining outflow from its headwaters in the 

Upper Peace River basin― the largest in area of the Peace 

River’s six main tributary basins (fig. 1) (Florida Department 

of Environmental Protection, 2007; Metz and Lewelling, 

2009). 

Factors affecting tributary streamflow in the Peace River 

basin need to be characterized in order for Federal, State, and 

local agencies to effectively manage and preserve the hydrologic conditions and landscape features necessary to maintain 

streamflow. Surface strip-mining for phosphate has altered the 

topography and eliminated numerous wetlands and first-order 

streams in the Payne Creek basin and in the Upper Peace 

River basin (fig. 1) (Florida Department of Environmental 

Protection, 2007). Groundwater levels in underlying aquifers 

have been lowered by pumping, which has led to substantial 

streamflow losses, particularly in the Upper Peace River basin 

where karst features (sinkholes) are present along the stream 

channel (Metz and Lewelling, 2009). Farther downstream in 

the Peace River watershed, the groundwater used to irrigate 

extensive areas of citrus and agricultural crops has increased 

flows in the tributaries of Joshua Creek, Horse Creek, and 

Shell-Prairie Creeks (fig. 1 and table 1). By comparison, the 

landscape and streamflows in the Charlie Creek basin have 

remained relatively unaltered. Assuming that hydrologic processes were comparable in all basins prior to development, the 

hydrologic processes still occurring in the Charlie Creek basin 

provide a useful tool for understanding those processes altered 

or lost in other basins of the Peace River watershed. 

Of the six main tributary basins in the Peace River 

watershed, the Charlie Creek basin has the greatest streamflow, and its historical basin and streamflow characteristics 

are the least altered. The Charlie Creek and Horse Creek 

basins have the lowest percentages of native land converted 

to phosphate mining, urbanization, or intensive agriculture 

since the 1940s (Florida Department of Environmental Protection, 2007). The Charlie Creek basin has the smallest loss of 

natural stream channels due to these conversions (table 1). The 

Charlie Creek basin is predominantly a landscape of pasture, 

open lands, forested wetlands, and citrus groves, although the 

relative proportion of these land uses and other physical features vary in different areas of the basin. Although streamflow 

leaving the Charlie Creek basin has been measured since 1951, 

little is known about which areas of the basin generate most 

of this flow, as well as the relation between wetlands, karst 

hydrogeology, and streamflow generation in Charlie Creek. 

For example, it is unclear what percentage of total streamflow originates in the headwater wetlands, what percentage is 

generated as runoff from areas bordering the main channel of 

the stream, and how the efficiency of streamflow generation 

differs between these regions. Artesian groundwater flow 

conditions existed in all basins of the Peace River watershed 

prior to development (Bush and Johnston, 1988) and may be 

better preserved in the contemporary Charlie Creek basin than 

in other basins in the Peace River watershed (fig. 1). 

However, the importance of hydrogeologic conditions, and 

particularly the prevalence of artesian head conditions, in 

maintaining streamflows in different areas of the Charlie 

Creek basin also is unclear. 

To gain a better understanding of the natural hydrologic 

conditions affecting streamflow generation from a tributary basin in southwest Florida, the U.S. Geological Survey 

(USGS), in cooperation with the Southwest Florida Water 

Management District (SWFWMD), began a study in 2003 

to characterize the hydrology of the Charlie Creek basin. 

Knowledge gained from the study will aid the establishment 

of State-mandated minimum surface-water flows and groundwater levels for Charlie Creek and neighboring basins, and 

contribute to our understanding of how surface mining and 

other land-use alterations can affect streamflow in similar 

watersheds. 
4    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Purpose and Scope

The purpose of this report is to characterize how 

streamflow in the Charlie Creek basin is affected by hydrologic processes, primarily (1) seasonal-flooding of headwater wetlands, and (2) groundwater interactions with Charlie 

Creek, its tributaries, and headwater wetlands. Field data were 

collected in the Charlie Creek basin from April 2004 through 

January 2006 and include streamflow, groundwater elevation, 

and rainfall. Daily streamflow was monitored during 2004-

2005 at five streamflow gaging stations in the basin―two 

along the main stem of Charlie Creek and three along its main 

tributaries. The flows within these subdivided areas of the 

basin were related to the physical characteristics such as vegetation and topography, as well as the hydrogeologic framework and stream/groundwater interactions in the subbasin. 

This report consists of two parts; the first describes the 

hydrogeologic framework of the overall basin and the various 

subbasins in detail, including hydrostratigraphy, groundwater 

flow patterns, and groundwater/stream interactions. The second part presents results of the numerical model used to simulate the coupled surface and groundwater flows in the subbasins using the hydrogeologic framework, climate data, and 

physical data (soils, topography, land use and cover, groundwater use) as input. Daily streamflow was simulated at the five 

stream gaging locations and calibrated to the observed flows. 

Modeling results also generated water budgets for the entire 

basin and individual subbasins. Differences in water-budget 

components between subbasins were related to the hydrogeological and physical differences between the subbasins. 

Description of Study Area

The 330-mi2 Charlie Creek basin occupies the eastern 

third of Hardee County, overlapping into southern Polk, 

western Highlands, and northern DeSoto Counties (fig. 1). It 

drains the east-central portion of the Peace River watershed. 

The Charlie Creek basin is in the mid-peninsular physiographic zone of White (1970), and it includes parts of three 

subdivisions: the Polk Upland, the De Soto Plain, and the 

Lake Wales Ridge. The majority of the basin lies within the 

De Soto Plain―a relict submarine shoal or plateau that is flat 

except in areas eroded by stream channels (White, 1970). The 

northern drainage divide is in the adjacent Polk Upland and 

the eastern drainage divide is along the Lake Wales Ridge 

where the elevation of land surface can exceed 180 ft above 

NGVD 1929. The lowest areas are along the stream channels 

and in wetland depressions, with elevations as low as 20 to 30 

ft above NGVD 1929 in the stream channel at the most downstream end of the Charlie Creek basin (fig. 2). Away from the 

ridges and stream channels, much of the Charlie Creek basin 

ranges in land-surface elevation from 85 to 95 ft above 

NGVD 1929. 

Three principal hydrogeologic units are present in the 

Charlie Creek basin. From shallowest to deepest they are 

the surficial aquifer, the intermediate aquifer system, and the 

Tributary

basinname

USGS

streamflow

monitoring

station name

USGS

station

identifier

USGS

Gaged

basin

area,

mi2

USGS

Average

daily

streamflow

(1980-2005),

ft3/s

USGS

Annual

average

runoff

(1980- 2005),

in.

Trend in

base flow

Kendall Tau

(at Q10, Q50, Q90)

Mined

land

use,

%

Citrus and

intense

agriculture,

%

Improved

pasture

open land,

%

Wetlands

and

forested

uplands,

%

Estimated

loss of

stream

channel

(1940-1999),

%

Estimated

groundwater

pumping

(1997-1999),

Mgal/d

(in/yr)

Peace River 

Headwaters

Peace River at Bartow, FL 02294650 390 195.4 6.8 Declining 9 14 15 23 60 151 

(8.1)

Payne Creek Payne Creek near Bowling 

Green, FL

02295420 121 124.1 13.9 Increasing1 63 10 8 16 52 24 

(4.1)

Charlie Creek Charlie Creek near Gardner, 

FL

02296500 330 254.8 10.5 No trend <1 19 45 36 5 62 

(3.9)

Joshua Creek Joshua Creek at Nocatee, FL 02297100 132 117.6 12.1 Increasing Q50

and Q90

<1 31 41 24 24 36 

(5.7)

Horse Creek Horse Creek near Arcadia, FL 02297310 218 203.5 12.7 Increasing 6 10 37 46 18 37 

(3.6)

Shell-Prairie 

Creek

Prairie Creek near Fort 

Ogden, FL

02298123 233 227.1 13.2 Increasing <1 31 25 42 20 55 

(4.9) 

1 No trend statistics. Graphical evidence only due to gap in record.

Table 1. Physical characteristics of the principal tributary basins of the Peace River watershed in west-central Florida.[All data from Florida Department of Environmental Protection (2007). %, percent; ft3/s, cubic foot per second; in., inch; in/yr, inch per year; Mgal/d, million gallons per day; mi, mile; <, less than; Q10, flowrate exceeded by 10 percent of the daily flow values; Q50, flowrate exceeded by 50 percent of the daily flow values; Q90, flowrate exceeded by 90 percent of the daily flow values]
Introduction    5

Figure 2. Land surface elevations in the Charlie Creek basin.

Lake

Wales

Ridge

Polk

Upland

De Soto

Plain

De Soto Plain

D

e

S

oto

Plain

HARDEE COUNTY

POLK COUNTY

HIGHLANDS

COUNTY

DE SOTO COUNTY

HIGHLANDS

COUNTY

Bereah

Gardner

Avon

Park

Zolfo

Springs

EXPLANATION

Stream gage

Surface-water feature

Subbasin boundary

Physiographic subdivision,

by White, 1970.

Lake

Chilton

100 foot digital elevation map,

in feet above NGVD 1929

High 183.67

Low 19.23

0

0 5 KILOMETERS

5 MILES

81°50' 45' 40' 35' 81°30'

27°40'

35'

30'

25'

20'

27°15'

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983
6    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Upper Floridan aquifer. The stream channel of Charlie Creek 

predominantly lies in the sandy deposits of the surficial aquifer, but in some areas may erode into the clay- and carbonaterich layers at the top of the intermediate aquifer system. Only 

groundwater in the surficial aquifer and intermediate aquifer 

system has the potential to interact with Charlie Creek and its 

tributaries. The deeper Upper Floridan aquifer is the principal source of irrigation water and potable water in the basin. 

Although groundwater in the Upper Floridan aquifer does not 

interact directly with Charlie Creek, hydraulic heads in this 

aquifer affect Charlie Creek indirectly by governing the direction and magnitude of vertical flow occurring in the surficial 

aquifer and intermediate aquifer system. 

The climate in the study area has distinct wet and dry 

seasons, with heavy rains from local convective and tropical 

storms during summer through early autumn, and a drier season from late fall through late spring with rainfall from frontal 

systems associated with continental air masses (Chen and 

Gerber, 1990). The average annual rainfall in the study area is 

49.09 in., based on long-term (1949-2005) data from the 

Avon Park, Florida climate station (National Oceanographic 

and Atmospheric Administration, 2005). Monthly rainfall in 

the Charlie Creek basin was below average between January 

and June of 2004 (fig. 3A). Three named hurricanes raised 

the monthly total rainfall in August and September of 2004, 

and the 2004 annual total, above long-term averages. Hurricane Charley made landfall on August 13, 2004, followed 

by Hurricanes Frances and Jeanne on September 5 and 26, 

2004, respectively (National Oceanographic and Atmospheric 

Administration, 2008) (fig. 3B). Monthly rainfall in the basin 

during 2005 was mostly at or above average. June was the 

wettest month in 2005 due to unnamed tropical storms that 

deposited 15.98 in. of rainfall, 7.73 in. greater than average. 

Hurricane Wilma made landfall in southern Florida on 

October 24, 2005 and outer bands of rain affected the Charlie 

Creek basin. 

The Charlie Creek basin was subdivided into five smaller 

subbasins for this study, and streamflows exiting these subbasins were monitored for approximately 21 months (U.S. 

Geological Survey, 2007). The five subbasins include the 

subbasins of three tributary streams: Buckhorn Creek, Little 

Charley Bowlegs Creek, and Oak Creek (fig. 4). In addition, two more subbasins encompass the main Charlie Creek 

channel: Upper Charlie Creek subbasin and the Lower Charlie 

Creek subbasin. The northern half of the Charlie Creek basin 

is comprised of the three northernmost subbasins: Upper 

Charlie Creek, Buckhorn Creek, and Little Charley Bowlegs 

Creek. The collective outflow from these basins is measured at 

the USGS streamflow station Charlie Creek near Crewsville 

(fig. 4). The collective surface-water outflow of all five subbasins is measured at the Charlie Creek near Gardner streamflow station, in the Lower Charlie Creek subbasin (fig. 4). 

Streamflow generated by the two subbasins constituting the 

lower half of the Charlie Creek basin, Lower Charlie Creek 

and Oak Creek, was determined by subtracting flow at the 

Charlie Creek near Crewsville station from flow at the Charlie 

Creek near Gardner station. The northern or upper half of the 

basin makes up 57 percent of the gaged area of the Charlie 

Creek basin. The area below the Charlie Creek near 

Crewsville station composes the remaining 43 percent. About 

2 percent of the Charlie Creek basin is located downstream 

from the Charlie Creek near Gardner station and is ungaged 

(fig. 4). The physical characteristics of the five component 

subbasins, and the upper and lower halves of the basin, are 

summarized in table 2. 

Historically, the landscape in Charlie Creek basin was 

extensive pine flatwoods. This terrain was lowered by erosion 

and karst subsidence into areas occupied by stream channels 

and depressional wetlands. Forests adapted to withstand inundation occupy lower, flood-prone areas of the Charlie Creek 

basin (Abrahamson and Hartnett, 1990; Ewel, 1990). Much of 

the pine flatwoods have been cleared and maintained as rangeland, pasture, and open land used for grazing cattle (fig. 5). 

Pine flatwoods have been cleared and maintained as rangeland, pasture, and open land used for grazing cattle. 

(Photograph by T.M. Lee, USGS.)
Introduction    7

four times larger than the Buckhorn Creek subbasin (table 2). 

Streamflow measured in Oak Creek was the greatest of the 

three tributary stations, perhaps because its gaged area was 

larger than that of Little Charley Bowlegs Creek subbasin. 

Buckhorn Creek had less flow than the other two tributaries, but peak flows were pronounced at Buckhorn Creek, 

approaching or exceeding the maximum flows observed for 

Little Charley Bowlegs Creek and Oak Creek (fig. 6A). 

Occasionally, minimal or no streamflow exited the 

subbasins of the three tributary streams or the Upper Charlie 

Creek subbasin. Streamflow duration curves based on flows 

between April 2004 and December 2005 show that Buckhorn 

Creek and Charlie Creek near Crewsville flowed during about 

90 percent of the study period (fig. 6B). Buckhorn Creek had 

the most days with no flow during the study (58), followed by 

54 no-flow days at Charlie Creek near Crewsville. All 

no-flow periods occurred during the spring and early summer 

of 2004. Little Charley Bowlegs Creek had more flow during 

this period with only 24 no-flow days, indicating that for 

30 days streamflow either went into storage or was otherwise 

lost before reaching the Charlie Creek near Crewsville station. 

In contrast, Oak Creek had continual flow during the study, 

but the flattened slope at the declining end of the duration 

curve and specific conductance results presented later in the 

report suggest that water from crop irrigation during the dry 

season augmented the smallest streamflows in this subbasin 

(fig. 6B). The streamflow duration curve for Charlie Creek 

near Gardner shows continual flow exiting the basin from 

October 2002 through December 2005, including the model 

simulation period. 

Figure 3. A, NEXRAD basin-wide average monthly rainfall totals during 2004-2005, and the long-term rainfall average at the NOAA 

Climate Station in Avon Park, Florida, and B, paths of hurricanes Charley, Frances, and Jeanne during 2004. NEXRAD is (Next 

Generation Radar); NOAA is National Oceanic and Atmospheric Administration.

Avon Park – NOAA rainfall

Charlie Creek – NEXRAD basin average

Avon Park – NOAA 1949-2005 average

Avon Park – NOAA climate station

Hurricane Charley – Landfall August 13, 2004

– Landfall September 5, 2004

– Landfall September 26, 2004

Hurricane Frances

Hurricane Jeanne

EXPLANATION

A

0

2

4

6

8

10

12

14

16

18

J F M A M J J A S O N D J F M A M J J A S O N D

MONTHLY RAINFALL, IN INCHES

2004 2005

An exception is the preserved upland forests within Highlands 

Hammock State Park in the Little Charley Bowlegs subbasin. 

Based on 2005 land use data, 46 percent of the Charlie Creek 

basin is pasture, open lands, and rangeland, and probably is 

not irrigated (table 2). Together with citrus production and 

wetland areas, these three land use categories represent the 

largest percentage of the land use in the basin. Irrigated citrus 

crops account for about 16 percent of the land area of the 

basin on average, but range from less than 6 percent of the 

land area of the Little Charley Bowlegs subbasin to 27 percent 

of the Buckhorn Creek subbasin. Forested and non-forested 

(marsh) wetlands occupy the largest percentage of area in the 

Little Charley Bowlegs subbasin (27 percent), and the smallest 

percentage of the Buckhorn Creek subbasin (11 percent). 

Streamflow generated by the Charlie Creek basin has 

remained relatively unchanged during the past half century 

with no statistically significant trend (α = 0.05) from 1951 to 

2008 in the annual median, minimum, maximum, and percentile flows at P90, P75, P25, and P10 (where P90 indicates a 

flow rate exceeded 90 percent of the time). This is consistent 

with results reported by Florida Department of Environmental 

Protection (2007). Streamflow has been monitored in Charlie 

Creek near its confluence with the Peace River since May 

1950 at the USGS streamflow station at Charlie Creek near 

Gardner, Florida (U.S. Geological Survey, 2007). 

Streamflow measured at the five streamflow stations in 

the basin varied with the size of the gaged subbasin area and 

other factors discussed herein (U.S. Geological Survey, 2007). 

The tributary subbasins of Oak Creek and Little Charley Bowlegs Creek are the most similar in size and are each almost 

Charlie

Creek

basin

0 50 MILES

0 50 KILOMETERS

25°

26°

27°

84° 83° 82° 81° 80°

Base from U.S. Geological Survey digital data, 1:24,000, datum nad83

Albers Equal-Area Conic Projection,

Standard parallels 29° ° 30’ and 45 30’, central meridian -83°00’

Atlantic Ocean

Gulf of Mexico

28°

B
8    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Figure 4. Charlie Creek basin, its five principal subbasins, and the location of streamflow monitoring stations 

used for this study.

0 5 MILES

0 5 KILOMETERS

81°50' 45' 40' 35' 81°30'

27°40'

35'

30'

25'

20'

27°15'

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Buckhorn Creek

Oak Creek

Little Charley

Bowlegs Creek

Ch l ar ie Creek

EXPLANATION

Line dividing subbasin upstream

and downstream of surfacewater monitoring site

Stream gage

HARDEE COUNTY

POLK COUNTY

HIGHLANDS

COUNTY

DE SOTO

COUNTY

UPPER

CHARLIE CREEK

SUBBASIN

LITTLE CHARLEY

BOWLEGS CREEK

SUBBASIN

OAK CREEK

SUBBASIN

LOWER

CHARLIE CREEK

SUBBASIN

BUCKHORN

CREEK

SUBBASIN

Charlie Creek near Gardner

Charlie Creek near Crewsville

Peace River

Bereah

Gardner

Avon Park

Zolfo Springs

Crewsville

27

17

66

634
Introduction    9

Basin or

subbasin

name

USGS

streamflow

monitoring

station name

Station

identifier

Subbasin

area

(mi2)1

Gaged

subbasin

area

Pasture,

open

lands,

and

rangeland

area

(%)2

Wetland

area

(%)2

Citrus

area

(%)2

Upland

forest

area

(%)2

Depression

storage,

million

ft3/mi2

Area

with

B/D soil

type

(%)3

Stream

length/

basin

area

(mi/mi2)4

Artesian flow area (%)

(mi2) (%)

IAS,

May

2004

UFA,

May

2004

IAS,

Sept.

2004

UFA,

Sept.

2004

Buckhorn Creek 

Subbasin 

Buckhorn 

Creek near Griffins Corner, FL

02296057 18.4 17.4 95 48 11 27 5.3 2.61 81 0.45 1 2 6 22

Little Charley 

Bowlegs Subbasin

Little Charley 

Bowlegs C AB CT5near Sebring, FL

02296222 65.2 42.8 66 37 27 6.7 19 3.18 69 0.43 23 2 39 18

Upper Charlie 

Creek Subbasin

NA NA 108.7 132.0 121 42 20 17 11 3.32 62 0.52 41 13 52 39

Oak Creek 

Subbasin

Oak Creek near 

Gardner, FL

02296389 67.7 65.0 96 53 18 20 5.9 2.99 76 0.31 2 0 6 1

Lower Charlie 

Creek Subbasin

NA NA 74.1 68.9 93 54 17 16 8.8 2.05 72 0.50 3 7 25 30

Upper half of 

Charlie Creek Basin

Charlie Creek 

near Crewsville, FL

02296260 192.3 192.3 100 41 22 15 13 3.20 66 0.48 31 8 44 30

Lower half of 

Charlie Creek Basin

NA NA 141.9 133.8 96 53 18 18 7.4 2.50 74 0.41 3 4 16 17

Charlie Creek 

Basin

Charlie Creek 

near Gardner, FL

02296500 334.1 326.1 98 46 20 16 11 2.90 69 0.43 19 7 32 25

1Charlie Creek subbasins derived from Southwest Florida Water Management District (SWFWMD) (accessed June 2006, at http://www.swfwmd.state.fl.us/data/gis/layer_library/category/physical_

sparse). 

2Land use and land cover data from SWFWMD for 2005.3Soils shapefile provided by SWFWMD accessed June 2006, at http://www.swfwmd.state.fl.us/data/gis/layer_library/category/physical_dense).4Hydrography stream lengths and depression storage estimates derived using hydrology modeling tools in ArcMap from a 5-ft LIDAR digital elevation model resampled to 100 ft. 5C AB CT abbreviation for “Creek above control.”

Table 2. Physical characteristics of subdivided areas within the Charlie Creek basin.[NA, not applicable; IAS, intermediate aquifer system; UFA, Upper Floridan aquifer; ft3/mi2, cubic foot per square mile; mi2, square mile; mi/mi2; mile per square mile; %, percent]
10    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Figure 5. Generalized land use and land cover in the Charlie Creek basin.

Buckhorn Creek

Oak Creek

Little Charley

Bowlegs Creek

C i harl e Creek

Char

e

lie Cre k

Bereah

Avon

Park

Zolfo Springs

Gardner

Highlands

Hammock

State Park

81°50' 45' 40' 35' 81°30'

27°40'

35'

30'

25'

20'

HARDEE COUNTY

POLK COUNTY

HIGHLANDS

COUNTY

DE SOTO

COUNTY

0 5 MILES

0 5 KILOMETERS

Subbasin boundary

Surface-water features

Streamflow monitoring station

EXPLANATION

Citrus

Disturbed lands

Forested and non-forested wetlands

Rangeland, pasture, and open lands

Row crops

Open water

Upland forest

Urban

27°15'

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983
Methods of Investigation 11

Figure 6. A, Streamflow hydrographs for the three tributaries to Charlie Creek, and B, duration curves for streamflows measured at

Oak Creek, Little Charley Bowlegs Creek, Buckhorn Creek, and Charlie Creek near Crewsville, Florida from approximately April 2004

through December 2005, and for Charlie Creek near Gardner, Florida from October 2002 through December 2005.

Methods of Investigation

The hydrogeologic characterization of the Charlie Creek 

basin focused on understanding the stratigraphy of the intermediate aquifer system in the basin, and relied on published 

lithologic logs and measured surface-water and groundwater 

levels. Water-budget components used for the hydrologic 

characterization of the basin were measured, derived from 

remote-sensing data, or derived from MIKE SHE simulated 

flows. 

Hydrogeologic Characterization

Specific approaches used to define the hydrogeologic 

setting in the Charlie Creek basin include describing the 

stratigraphic and hydrogeologic units, quantifying groundwater pumpage, examining lateral and vertical flow within and 

between aquifers, and defining the interaction between 

the groundwater and streams. 

Basin Stratigraphy

Information on the depth and thickness of hydrogeologic units was compiled from 43 well logs obtained from the 

Florida Geological Survey (2008) and the Southwest Florida 

Water Management District (LaRoche, 2007), and from maps 

by Arthur and others (2008). Hydrogeologic cross sections 

through the Charlie Creek basin were constructed from these 

data to illustrate the spatial variability in thickness and depth 

of the units. 

Basin Topography and Hydrography

Land-surface elevation within the Charlie Creek basin 

was interpreted from LIDAR data provided by the SWFWMD 

(A. Karlin, Southwest Florida Water Management District, 

written commun., 2008; Petrie and Toth, 2009). The LIDAR 

data are collected with aircraft-mounted lasers and the method 

provides land-surface elevations with a vertical precision of 

approximately 6 in. (Habib, 2009). Raw data acquired from 

this airborne technique consist of densely clustered elevation points that are typically averaged over different-sized 

areas. LIDAR data used in this study were spatially averaged 

to provide elevation values for raster grid cells with x- and 

y- horizontal dimensions equal to 5 ft. The resulting digital 

elevation model (DEM) of the basin topography was used for 

most analyses in the study except the integrated modeling. The 

MIKE SHE integrated model used a DEM based on LIDAR 

data averaged over a raster grid with a 300-ft cell size. The 

land-surface elevations of the entire Peace River watershed, 

shown in figure 1, are from the National Elevation Dataset 

(NED) from the USGS National Map Seamless Server (http://

seamless.usgs.gov/index.php, accessed April 15, 2009). The 

horizontal resolution for 1/3 arc second elevation grids downloaded from this site is approximately 10 m (32.8 ft). The 

vertical accuracy of the NED is 8.00 ft (Maune, 2007). 

Historical land-surface elevations have been altered 

by phosphate mining in limited areas of Horse Creek, and 

extensive areas of Payne Creek and Upper Peace River basins. 

These changes limit the ability to represent the predevelopment artesian head conditions in these basins in figure 1.

0.1 0.5 2 10 30 50 70 90 98 99.5 99.9

0.01

0.1

1

10

100

1,000

10,000

M

A B

J J A S O N D J F M A M J J A S O N D J

2004 2005 2006 PERCENTAGE OF TIME STREAMFLOW

EXCEEDED AT A GIVEN DISCHARGE RATE

0.01

0.1

1

10

100

1,000

10,000

DISCHARGE, IN

CUBIC FEET PER SECOND

DISCHARGE, IN

CUBIC FEET PER SECOND

EXPLANATION

Oak Creek near Gardner

Buckhorn Creek near Griffin’s Corner

Little Charley Bowlegs Creek

Charlie Creek near Crewsville

Charlie Creek near Gardner
12    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

The hydrography, or locations of stream channels, within 

the Charlie Creek basin was derived from an analysis of the 

LIDAR data averaged over 100-ft grid cells. First, the flow 

direction within each grid cell was determined by comparing 

its elevation to that of adjacent cells. A flow accumulation grid 

was then derived using the flow direction in adjacent cells to 

resolve the down-slope direction. The complete analysis generated an interconnected network of stream channels based on 

the elevation dataset (Olivera and Maidment, 1999). 

Groundwater Monitoring Network

Hydrogeologic data were collected from 29 shallow 

monitoring wells drilled for the study, as well as from existing 

wells and stratigraphic logs (figs. 7 and 8, and app. 1). At two 

locations along the main channel of Charlie Creek, shallow 

wells were drilled along transects crossing the stream 

(fig. 8). Wells on either side of the stream were used to measure the elevation of the adjacent water table. The northern, 

or upstream, transect of wells was near the Charlie Creek near 

Crewsville streamflow gage and the downstream transect was 

near the Charlie Creek near Gardner gage (figs. 4 and 8). The 

two transects were about 14 river miles apart. 

At each of the three main tributaries, Buckhorn, Little 

Charley Bowlegs, and Oak Creeks, a single well, or (in some 

places) two wells completed at different depths in the surficial 

aquifer, were drilled near the gaging station and used to monitor the water-table elevation near the stream. Water levels in 

all of these wells were measured monthly from June or July 

2004 until early February 2006. The water-table elevation also 

was monitored continuously in wells 17, 25, and 50, which are 

located in the three tributary subbasins, to assess changes in 

groundwater storage in the Charlie Creek basin (fig. 8 and 

app. 1). 

Groundwater levels were obtained at three locations from 

existing wells tapping the surficial aquifer, the intermediate 

aquifer system, and the Upper Floridan aquifer to examine 

vertical head differences. These wells are maintained and 

monitored by the SWFWMD as part of the Regional Observation and Monitor-well Program (ROMP), and have a “ROMP” 

prefix as part of the site name (for example, LaRoche, 2007). 

At the three closest sites to the Charlie Creek basin, ROMP 

26, 30, and 43, multiple wells were drilled to different depths 

using strict protocols, allowing water levels to be measured in 

the surficial aquifer and in discreet permeable units within the 

intermediate aquifer system and Upper Floridan aquifer. Only 

one of these well sites, ROMP 43, is inside the Charlie Creek 

basin, and it was under construction during the study (fig. 8). 

At this site, water levels were periodically measured for wells 

completed in the surficial aquifer, Zone 2 and Zone 3 of the 

intermediate aquifer system, and the Upper Floridan aquifer. 

Water levels also were monitored continuously for these same 

aquifers and zones during the study at two other sites (ROMP 

26 and ROMP 30), just outside the Charlie Creek basin to the 

south and west (fig. 8). All three of these sites were considered upland sites, as they were not immediately adjacent to a 

stream. 

Mapping and Spatial Analysis of 

Potentiometric Levels in Confined Aquifers 

Potentiometric surface maps of the Upper Floridan 

aquifer within the Charlie Creek basin were constructed for 

May and September of 2004 and 2005 using data collected 

from Upper Floridan aquifer wells. Groundwater-level data 

were collected as part of the semi-annual, synoptic mapping 

by the USGS of the regional potentiometric surface of the 

Upper Floridan aquifer in west-central Florida (for example, 

Ortiz, 2006). The May measurement date typically captures 

the lowest annual water levels near the end of the dry season when groundwater pumping is highest; conversely, the 

September measurements typically capture the highest annual 

groundwater levels near the end of the wet season. The May 

and September 2005 maps were supplemented by water-level 

data from four wells in the Charlie Creek basin. 

Potentiometric surface maps of the intermediate aquifer 

in the Charlie Creek basin also were constructed for May and 

September of 2004 and 2005. The potentiometric surface was 

mapped locally within the basin using well-construction information and lithologic data to identify which permeable zone(s) 

the intermediate aquifer system wells were open to. Several of 

the monitor wells used for mapping the intermediate aquifer 

system in the Charlie Creek basin were part of the regional 

monitor-well network operated by the USGS (Ortiz, 2006). 

Measurements collected from seven existing intermediate 

aquifer system wells were added to the map in 2005. Information provided by these additional wells guided the placement 

of equipotential contour lines interpreted from the 2004 data 

(which involved fewer wells), especially in the north and east 

part of the basin.

Potentiometric surface maps for both aquifers were 

converted to raster data, permitting a spatial analysis of aquifer 

heads in the basin. Potentiometric surfaces were subtracted 

from one another to quantify the vertical head differences 

between the intermediate aquifer system and Upper Floridan 

aquifer throughout the basin. In addition, the 5-ft LIDARbased elevation model of the land surface was subtracted from 

the potentiometric surfaces to determine where aquifer heads 

exceeded the elevation of land surface. Areas of a confined 

aquifer where the elevation of the potentiometric surface is 

above land surface elevation have artesian head conditions, 

and groundwater here would flow freely out of uncapped wells 

tapping these aquifers (Bear 1979; deMarsily 1986). Potentiometric surface maps and the LIDAR DEM also were used 

to calculate the head difference of the intermediate aquifer 

system above or below the streambed elevation of Charlie 

Creek and its tributaries, and to infer the relative potential for 

interaction between groundwater and streams. 
Methods of Investigation    13

Figure 7. Location of geologic cross sections, carbonate rock outcrops in the Charlie Creek stream channel, and 

seepage-run measurement sites in the Charlie Creek basin.

81°50' 45' 40' 35' 81°30'

27°40'

35'

30'

25'

20'

27°15'

0 5 MILES

0 5 KILOMETERS

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Charlie

Creek

Basin

Buckhorn Creek

Oak Creek

Little Charley

Bowlegs Creek

C i harl e Creek

Charlie

Creek

A

B C

D

E

F

A

B

A’

B’

Peace River

ROMP 26

ROMP 30

W-9172

W-9289

W-9092

ROMP 43

W-11946

W-9074

A

EXPLANATION

Line of hydrogeologic section

Cross section control well and number

Seepage run stream measurement location

Reach where seepage was calculated

Carbonate rock outcrop in Charlie Creek

A A’ W-9074

HARDEE COUNTY

POLK COUNTY

HIGHLANDS

COUNTY

DE SOTO

COUNTY
14    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Figure 8. Location of the groundwater monitoring sites, streamflow monitoring stations, and well transect sites in 

the Charlie Creek basin.

81°50' 45' 40' 35' 81°30'

27°40'

35'

30'

25'

20'

27°15'

0 5 MILES

0 5 KILOMETERS

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Charlie

Creek

Basin

Buckhorn Creek

Oak Creek

Little Charley

Bowlegs Creek

Ch l ar ie Creek

UPSTREAM

TRANSECT

DOWNSTREAM

TRANSECT

22 27 26

23

45

7-14

43,44

24

25

17,18

19-21

49-50

46-47

30

5

6

15 16

56

51

48

35-42

28,29

ROMP 26

1-4

ROMP 30

31-34

ROMP 43

52-55

24

5

23

ROMP 26

1-4

EXPLANATION

HARDEE COUNTY

POLK COUNTY

HIGHLANDS

COUNTY

DE SOTO

COUNTY

Subbasin boundary

Surficial aquifer well location and number from Appendix 1

Intermediate aquifer system well location and number from Appendix 1

Upper Floridan aquifer well location and number from Appendix 1

ROMP site location, name, and number from Appendix 1

Surface-water monitoring site

Peace River
Methods of Investigation    15

Seepage Runs

A direct method for determining areas where groundwater is entering or leaving a stream is called a “seepage run.” 

Seepage runs are typically done during dry periods when 

surface inflows are minimal and stream stage is stable. Over a 

short period of time when stream stage is constant, streamflow 

is measured at various cross sections along the channel, as 

well as at any tributaries entering the stream between the 

measured sections. Gains in streamflow that are not explained 

by tributary inflows are attributed to groundwater seeping into 

the channel. Streamflow losses not accounted for are attributed 

to water seeping out of the channel into the aquifer. Seepage 

was estimated as:

Qs = Qd - Qu - Qt (1) 

where 

Qs	 is seepage, or the gain (positive) or loss 

(negative) in streamflow for 

the reach between two measured sections; 

Qd is streamflow at the downstream section; 

Qu	 is streamflow at the upstream section; and 

Qt is total streamflow from all tributaries 

between the upstream and downstream 

sections. All of the streamflow values are 

in units of cubic feet per second.

An estimate of the error in the calculated seepage was 

directly computed for each stream reach. As seepage is a 

residual term (streamflow difference minus inflows), small 

uncertainties (or errors) in streamflow measurements can 

greatly affect the uncertainty in the calculated seepage. The 

uncertainty or error in seepage was computed as the square 

root of the sum of the squared individual errors:

eQs = [(eQd)2 + (eQu)2 + (eQt)2]1/2 (2)

where e is the estimated error in the terms in equation (1), in 

cubic feet per second. Streamflow measurement errors were 

assumed to be 5 to 10 percent, depending on flow and conditions. The uncertainty for Qs

 calculated from equation 2 should 

be considered a maximum possible error because it assumes 

that all of the errors are in the same direction and do not 

cancel each other. Most seepage run analyses do not consider 

individual estimates of error and do not discuss the error relative to the calculated seepage (Lewelling and others, 1998; 

Trommer and others, 2007; Metz and Lewelling, 2009). The 

analysis described herein attempts a more thorough approach 

to interpreting seepage run results. Further discussion of error 

analysis in hydrologic studies is provided in Winter (1981). 

Whenever calculated seepage in a reach was less than 

10 percent of the average streamflow in that reach, the seepage 

value was less than the estimated error and was not considered significant. This approach is more conservative than 

that of Trommer and others (2007), who considered seepage 

results statistically significant when differences in streamflow 

between upstream and downstream sections were greater 

than 5 percent of the average streamflow in the reach (after 

Hortness and Vidmar, 2005), or greater than 0.5 ft3/s. Other 

studies (Lewelling and others, 1998) used an even less conservative approach that considered errors in seepage results to 

be comparable to errors in the discharge measurement 

(5-8 percent) regardless of the magnitude of the seepage. But 

the error in seepage can be the same magnitude or greater than 

the calculated seepage, especially when seepage values are 

small. In this study, errors in seepage estimates are presented 

along with the seepage values to allow a more rigorous 

interpretation of seepage results. Addressing the larger errors 

in residual terms such as seepage helps ensure the interpreted 

values are valid (Winter, 1981). 

All seepage runs were made along the main channel of 

Charlie Creek within the Lower Charlie Creek subbasin. Measurements were made on February 18, 2005; May 26, 2005; 

December 29, 2005; and January 23, 2006 (app. 2). Seepage 

was estimated along six reaches, located between the gage at 

S.R. 66 (Charlie Creek near Crewsville; close to the upstream 

transect site) and the gage at U.S. 17 (Charlie Creek near 

Gardner; close to the downstream transect site) (figs. 4 and 7). 

Surface inflows were measured at up to 11 tributaries between 

these sites. Seepage was normalized to the length of the stream 

reach to allow seepage rates to be compared. Seepage also was 

estimated for combined reaches, and for the entire run using 

equation 1. 

Hydrologic Analysis

Measured and model-simulated values were used to 

quantify the hydrologic characteristics and water-budget components of the five subbasins of Charlie Creek. Model-derived 

characteristics included the volume of surface water stored in 

land surface depressions over time and the rate of groundwater 

exchange between the surficial aquifer and deeper aquifers. 

Directly measured characteristics included stream discharge 

and specific conductance, and basin groundwater levels. 

Rainfall and evapotranspiration rates were quantified using 

remotely-sensed data and were used in both the numerical 

model and the arithmetic water-budget calculations.

Integrated Modeling of Surface Water 

and Groundwater 

The rainfall-runoff response and streamflow in Charlie 

Creek and its tributaries were simulated using MIKE SHE, 

a numerical model that simulates coupled groundwater and 

surface-water flow processes. Remotely-sensed imaging of 

the physical features of the land surface, as well as energy and 

water fluxes above the land surface, provide the model 

with input variables for rainfall, evapotranspiration, basin 

topography, hydrography, soils, and land cover that are 

spatially distributed across the Charlie Creek basin. 
16    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

from simplified lumped-parameter process representations to 

spatially-distributed, physically-based process representations. 

Spatial Discretization and Assignment 

of Model Parameters

The modeled area corresponds to the surface-water basins 

contributing flow to the Charlie Creek near Gardner gage and 

delineated by the Florida Department of Environmental Protection (FDEP, http://ca.dep.state.fl.us/www.dep.state.fl.us/

metadata.jsp?layer=dep.drainage_basins_areas, accessed 

December 10, 2008). The numerical approaches used in MIKE 

SHE require that the basin area be represented as layered, 

square grids of model cells. Specifically, the model domain 

was represented spatially as a grid with 490 rows and 390 

columns of square cells, each with dimensions of 300 × 300 ft. 

Line segments representing the location of stream channels are 

linked to the x-y coordinates of the grid. The surficial aquifer was represented as an unconfined aquifer using a single 

model grid layer. The bottom elevation of the surficial aquifer 

was calculated using an interpolated surface of the top of the 

Hawthorn Group that was developed from well log data collected by the Florida Geological Survey (Scott, 1988; Arthur 

and others, 2008). The exchange of groundwater between the 

surficial and Upper Floridan aquifers was represented in the 

model using a linear head-dependent flux boundary with a 

constant leakance value of 8.64 × 10-6 (ft/d)/ft, representing 

the vertical hydraulic properties of the Hawthorn Group based 

on data in Knochenmus (2006). This leakance value results in 

a net vertical flux of approximately 1 in/yr from the surficial 

aquifer to the Upper Floridan aquifer.

Surficial aquifer properties were distributed based on 

hydrologic soil groups (app. 3). A thickness-weighted 

arithmetic mean was used to calculate representative horizontal hydraulic conductivities and specific yield for each hydrologic soil group. The saturated vertical hydraulic conductivity 

is identical in the surficial aquifer and the overlying 

unsaturated zone. A thickness-weighted harmonic mean was 

used to calculate representative saturated vertical hydraulic 

conductivities for hydrologic soil groups. 

The LIDAR data provided in 5-ft grid cells by the 

SWFWMD were resampled, or averaged spatially, to the 

300 × 300-ft grid-cell size used in the model. Resampling was 

accomplished by calculating the mean topographic elevation 

within each grid cell. The topographic data represent the 

elevation of the overland flow plane and the top elevation 

of the surficial aquifer in the model. The elevation gradient 

between adjacent grid cells was used in combination with 

simulated overland water-surface depth to calculate the 

overland flow between adjacent cells.

The main channels of Little Charlie Bowlegs Creek, 

Buckhorn Creek, Oak Creek, and Charlie Creek were explicitly represented in the one-dimensional, streamflow routing 

component of the model. Creek segments were conceptualized as triangular channels with maximum top-widths and 

depths based on a GIS analysis of the Charlie Creek watershed 

The uniform spatial distribution of data permits the basin to be 

subdivided into smaller areas that can be compared and 

contrasted to one another in an equivalent manner. 

Model discretization, assignment of hydraulic 

properties, and model boundary conditions are described 

herein and provide the spatial and temporal framework 

necessary for solving finite-difference approximations to 

surface-water and groundwater flow equations. MIKE SHE 

is a well-established numerical code that has been applied in 

hundreds of studies worldwide (Graham and Butts, 2006). 

The theory and governing equations in the MIKE SHE model 

are fully described in DHI Water and Environment (2008a, b). 

The numerical model developed is used to evaluate subbasin 

water budgets and factors contributing to differences in major 

water-budget terms between subbasins.

Modeling Approach

Integrated surface-water/groundwater models are useful 

for analyzing water-resources problems in complex watersheds because they allow the dynamic coupling of evapotranspiration, surface runoff, streamflow, unsaturated zone 

flow, and groundwater flow processes. A fully integrated 

surface-water/groundwater approach was used because it was 

important to simulate the surface-water/groundwater interactions and quantify differences in surface-water characteristics 

between the Charlie Creek subbasins. 

Representing the physical processes of infiltration, 

depression storage, unsaturated flow, and the exchange of 

water between the surficial aquifer, surface water, and underlying aquifers, was considered critical to understanding 

streamflow in the Charlie Creek basin. The topographic relief 

is low and water-table elevations are high and variable in 

much of the Charlie Creek basin. As a result, soil saturation 

and runoff are important processes, and parts of the watershed 

can rapidly change from infiltration to runoff conditions as 

the water table changes and/or rainfall intensity increases. 

Because the Charlie Creek basin has low topographic relief, 

water may accumulate at land surface to sufficient depth to 

allow runoff to be driven by water-surface gradients rather 

than topographic gradients. Consequently, spatial differences 

in rainfall may result in topographic gradients driving runoff in 

one portion of a surface-water subbasin and water-surface gradients driving runoff in another portion of the same subbasin. 

MIKE SHE was developed specifically to simulate fully 

coupled surface-water and groundwater flow and transport 

processes using a spatially-distributed, physically-based 

approach or a hybrid, lumped conceptual and distributed 

physically-based approach (Graham and Butts, 2006). MIKE 

SHE includes a number of self-contained modules to represent rainfall, snow-melt, canopy interception, overland flow, 

saturated-unsaturated flow, evapotranspiration, irrigation, and 

channel flow processes. A variety of numerical approaches are 

available in MIKE SHE for simulating individual hydrologic/

hydraulic processes; these allow models to vary in complexity 
Methods of Investigation    17

(B. Dixon, University of South Florida, written commun., 

2008). The bed elevations for creek cross sections at junctions 

between segments were developed from the 5-ft LIDAR data. 

Bed elevations between junctions were linearly interpolated 

between bed elevations defined at the start and end of creek 

segments. A uniform Manning’s n roughness coefficient of 

0.03, representative of a weedy earth channel, was assigned to 

all creek segments (www.engineeringtoolbox.com/manningsroughness-d_799.html, accessed Nov. 19, 2009). The weir at 

the Little Charlie Bowlegs Creek gage was explicitly defined 

in the model, based on leveling data collected during installation of the gage. The weir crest is 90 ft wide and at an elevation of 76.8 ft NGVD 1929. There are two, 2-ft diameter culverts adjacent to the weir that allow discharge when the stage 

in Little Charlie Bowlegs Creek is above 75.3 ft NGVD 1929. 

Surface-water/groundwater exchange between the creek 

segments and the surficial aquifer are controlled in the model 

by the simulated creek-wetted perimeter and the specified 

creek-bed leakance coefficient in each grid cell. A constant 

leakance coefficient of 0.432 (ft/d)/ft was specified for all 

creek segments. Leakance values are based on an estimated 

creek sediment thickness ranging from 1 to 2 ft and typical 

vertical hydraulic conductivity values for sandy clay surficial 

aquifer sediments (0.01 to 2.0 ft/d) in west-central Florida 

(Sinclair, 1974).

The land-use and land-cover characteristics of the modeled area were obtained from the 2006 SWFWMD shapefile 

library (http://www.swfwmd.state.fl.us/data/gis/layer_library/

category/physical_dense, accessed May 13, 2008) (fig. 5). The 

spatial distribution of different types of land cover and land 

use were used as a template to define the spatial characteristics 

of other model parameters, namely those related to vegetation, 

overland flow processes, or irrigation rates. Vegetation parameters that have been related to land use/land cover include the 

leaf area index, root depth, and crop coefficients used to scale 

reference evapotranspiration rates to vegetation-specific rates. 

The methods for distributing the overland flow parameters and 

irrigation rates over the model domain are described in further 

detail in appendix 3.

Unsaturated flow in the Charlie Creek basin was 

simulated using a simplified water-balance approach. In the 

model, the unsaturated zone extends from the land surface 

Charlie Creek in the Lower Charlie Creek subbasin. (Photograph by T.M. Lee, USGS.)
18    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

to the water table with the maximum thickness defined by 

the root depth. Unsaturated zone parameters were distributed according to hydrologic soil groups and developed from 

laboratory analyses of representative soil profiles (Carlisle and 

others, 1988). Unsaturated parameters that have been related 

to hydrologic soil groups include saturated hydraulic conductivity and the water content at the wilting point, field capacity, 

and saturation. Thickness-weighted parameters were used 

to calculate representative properties used by the simplified 

water-balance approach.

Temporal Discretization and Boundary Conditions

Daily values of boundary input variables were used by 

the model to simulate sub-daily water fluxes and streamflow 

values. Model time-step lengths were adjusted based on 

changes in streamflow or rainfall intensity, with maximum 

time-step lengths of 30 minutes for the stream-flow and overland routing component, 12 hours for the unsaturated component, and 24 hours for the groundwater component. Hydraulic 

head or flux boundary conditions were provided at the daily 

time step for the complete simulation period from October 

2002 through December 2005. The specified flux conditions 

applied to the upper model boundary were derived from daily 

values of rainfall and potential evapotranspiration. Overland 

water depths at the edge of the model domain were specified 

to be zero and time-invariant for all external overland cells. 

Specifying a zero depth still allows overland flow out of the 

model boundary when the water-surface elevation gradient 

between the active model domain and model boundary would 

allow discharge to occur. The daily average observed stage at 

the Charlie Creek near Gardner streamflow gage was applied 

as a water-level boundary at the downstream end of Charlie 

Creek. No other boundary conditions were specified for the 

creek segments. Dynamic lateral inflows (runoff and base 

flow) to stream segments were calculated by the model.

Groundwater flux was set to zero along the lateral boundaries of the surficial aquifer, which correspond to surfacewater subbasin divides. Along these divides, the water table 

is expected to have the highest elevations in the subbasin and 

therefore these areas correspond to groundwater flow divides. 

Heads in the Upper Floridan aquifer were specified as the 

lower boundary condition for the model and these heads were 

varied to reflect the effect of groundwater withdrawals on the 

potentiometric surface. 

Hydrologic Input Variables in the Model

Rainfall and potential evapotranspiration rates derived 

from satellite-based remote-sensing techniques were used 

in the model because of the increased spatial resolution of 

these datasets compared to data collected at widely-spaced 

weather stations. Daily rainfall data used as input to the model 

were based on WSR-88D (NEXRAD) radar reflectance data 

calibrated to data from raingages (Hoblit and others, 2003). 

NEXRAD rainfall data were obtained from the SWFWMD 

(2005) and are spatially distributed to a 2 × 2-km (1.24 × 

1.24-mi) grid.

Daily potential evapotranspiration rates were calculated 

from satellite-based solar radiation data using the PriestleyTaylor method—a technique that uses the concept of the theoretical lower limit of evaporation from a wet surface (Holmes 

and others, 2008; Jacobs and others, 2008; U.S. Geological 

Survey, 2009). Potential evapotranspiration estimates were 

spatially distributed to the 2 × 2-km cell dimensions of the 

NEXRAD grid. 

Groundwater used to irrigate agricultural land use/

land cover types in the basin was represented in the model 

as coming from external sources, as the effect of pumping in 

the basin already was reflected in the potentiometric levels 

specified as the Upper Floridan aquifer model boundary. There 

are substantial groundwater withdrawals in the Charlie Creek 

basin from the Upper Floridan aquifer to meet local irrigation demands. Irrigation water demands were calculated for 

each model time step and irrigation water was applied to those 

areas defined as agricultural land-use/land cover types until 

the simulated evapotranspiration was equal to the potential 

evapotranspiration rate.

Spatially-distributed Upper Floridan aquifer water levels 

were developed for each grid cell using May and September 

potentiometric surface maps for 2002 through 2006 (Knochenmus and others 2003; Blanchard and others 2003, 2004; 

Blanchard and Seidenfeld 2005; Ortiz and Blanchard 2006; 

Ortiz 2006, 2007). Daily Upper Floridan aquifer water levels 

were linearly interpolated from May and September potentiometric surface elevations developed for each grid cell. 

Model Calibration and Error

The model was calibrated using daily streamflow values 

published by the USGS for the five Charlie Creek subbasins. 

Initially, model calibration focused on getting the basin and 

subbasin water budgets within expected ranges for watersheds 

in central Florida (Swancar and others, 2000; Knochenmus 

and Yobbi, 2001; Spechler and Halford, 2001; Sumner, 2001; 

Knowles and others, 2002). Vegetation-specific crop coefficients were the primary parameters adjusted to achieve evapotranspiration and runoff rates within expected ranges.

Overland roughness coefficients, surficial aquifer 

hydraulic conductivity, simplified water balance approach 

parameters, and leakance coefficients representing the vertical 

hydraulic properties of the Hawthorn Group were adjusted to 

improve the match between simulated and observed streamflow while maintaining an average surficial aquifer to Upper 

Floridan aquifer exchange of 1 in/yr. During model calibration, it was assumed that land use/land cover based parameters 

could be developed that were applicable to the entire Charlie 

Creek basin. No attempt was made to develop land use/land 

cover based parameters for individual subbasins to improve 

model performance.

Qualitative and quantitative measures were used to 

assess model performance. Quantitative measures of model 
Methods of Investigation    19

performance included the mean error and the Nash-Sutcliffe 

coefficient (Nash and Sutcliffe, 1970). The mean error, ME, is 

calculated as: 

 (3)

where nobs is the number of observations at the respective streamflow gage during the simulation period, on

 is the 

observed daily streamflow (in cubic feet per second), and sn is 

the simulated daily streamflow (in cubic feet per second) for 

the same day. The mean error is a measure of model bias, and 

a value close to zero indicates little model bias at the evaluated 

location.

The Nash-Sutcliffe coefficient, NS, is calculated as:

 (4)

where ō is mean observed streamflow (in cubic feet per 

second) for the simulation period and all other terms are as 

previously defined. The Nash-Sutcliffe coefficient is a measure of the percentage of the data variance explained by the 

hydrologic model. Model accuracy increases as the coefficient 

approaches 1, with NS = 1 indicating perfect model predictions. A zero or negative Nash-Sutcliffe coefficient indicates 

model predictions that are as accurate as, or less accurate than, 

the mean of the observed data, respectively.

Model performance also was assessed by comparing the 

distribution of simulated values to the distribution of observed 

flow values using the percentile flow method. Daily streamflow values, either simulated or observed, are ranked from 

largest to smallest and five values, or “breaks,” are identified 

that divide the entire range of flow values into 10th, 25th, 

50th, 75th, and 90th percentile categories. The 10th percentile 

category, or the uppermost 10 percent of either observed or 

simulated flows, contains the largest flow values, including 

peak flows. The value representing the break for the 10th 

percentile flows is denoted P10, and all values equal to or 

greater than this value are in the 10th percentile range. By 

comparison, P50 is a lesser flow rate equaled or exceeded by 

half of the values in the distribution and, by definition, is the 

median value. P90 is the smallest value used to characterize 

the distribution of flow values, those equaled or exceeded by 

90 percent of the record. Simulated and observed P90 values 

were compared to assess the ability of the model to simulate 

the smallest stream discharges, typically base flow.

Observed and Simulated Water Budgets 

for the Basin

Water budgets were calculated for individual subbasins, 

and for the collective upper and lower halves of the Charlie 

Creek basin, using the observed and simulated streamflows. 

As noted earlier, the upper half of the basin contains the headwaters area of Charlie Creek (Upper Charlie Creek subbasin), 

and two tributary basins (Little Charley Bowlegs and Buckhorn Creek subbasins). The lower half of the basin includes 

the Lower Charlie Creek subbasin and the largest tributary 

subbasin, Oak Creek. Water-budget results are presented for 

June 2004 through December 2005, the only period with 

concurrent streamflow measurements for all five subbasins, 

as well as for 2003, the model year for which streamflow was 

known only at the outlet of the basin. The observed waterbudget period from June 2004 through December 2005 was 

wetter than average. The model was used to simulate 2003, 

a relatively dry year, to infer the effect of dry conditions on 

basin and subbasin water budgets. 

Assuming each subbasin defines a control volume, the 

comprehensive water budget was calculated from simulated 

results using:

Rai – ET ± OLL – Ro + I ± GWL ± GWV ± 

AC ± ΔSS ± ΔSGW – Err = 0 (5) 

where 

Rai is rainfall, 

ET is evapotranspiration, 

OLL is overland flow across subbasin boundaries, 

Ro is runoff to the stream, 

I is irrigation, 

GWL is lateral groundwater flow across subbasin 

boundaries, 

GWV is the vertical groundwater exchange between 

the surficial aquifer and the Upper Floridan 

aquifer, 

AC is aquifer-creek exchanges, 

∆SS is the change in overland (depressional and 

canopy) storage in the surface water 

system, 

∆SGW is the change in groundwater storage in the 

surficial aquifer, and 

Err is the simulated model error. 

All terms in the equation are in volumetric units of cubic 

feet, and water budgets were calculated for monthly time 

periods.

The observed water budgets include only rainfall, net 

precipitation, and runoff (observed streamflow) in each 

subbasin. Rainfall was defined as the cumulative rainfall in 

a basin computed from the spatially-distributed NEXRAD 

rainfall data. Net precipitation for a subbasin was calculated 

as the difference between cumulative rainfall and cumulative 

evapotranspiration losses from the subbasin. The cumulative evapotranspiration losses were computed using methods 

described in the modeling methods section herein. Stream 

discharge measurements were made according to USGS 

protocols (Rantz and others, 1982; Oberg and others, 2005), 

and specific conductance of the stream was monitored at each 

of these sites using USGS field methods (Wagner and others, 

2006). Daily stream discharge values and specific conductance 

ME

o s

nobs

n n

n

nobs

=

( ) − =

∑1

NS

o s

o o

n n

n

nobs

n

n

= − nobs

( ) −

( ) −

=

=

∑

∑

1

2

1

2

1
20    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

spatial variability can cause localized differences in its interaction with the overlying surficial aquifer, or with stream channels that have eroded into the top of the intermediate aquifer 

system. The Upper Floridan aquifer does not interact directly 

with Charlie Creek, but hydraulic heads in this aquifer can 

affect Charlie Creek indirectly by affecting vertical groundwater exchange with the intermediate aquifer system. 

Surficial Aquifer

The surficial aquifer comprises undifferentiated beds of 

sand, clay, and fossil fragments of Holocene to Pliocene age, 

and it is unconfined, with the water table at the top of the saturated sediments (fig. 9). Surficial deposits range in thickness 

from 0 to 150 ft in the Charlie Creek basin (figs. 10 and 11). 

The surficial aquifer is thickest in ridge areas along the eastern 

basin divide and thin or absent in the stream channel of lower 

Charlie Creek. Localized phosphate-rich beds also are present, 

because surficial aquifer deposits include reworked sediments 

from the underlying Peace River Formation. Clay content 

generally increases with depth, and the phosphate-rich beds, 

along with the upper part of the Peace River Formation, form 

a confining unit between the surficial aquifer and intermediate 

aquifer system. 

Although the surficial aquifer is not a major water-supply 

source for the area, it is important for storing water that 

recharges deeper aquifers or discharges into streams, 

wetlands, and lakes. Reported hydraulic conductivity of the 

surficial aquifer in the study area ranges from 1 to 34 ft/d. 

Transmissivity values increase with aquifer thickness, and 

probably range from around 10 to 1,000 ft2/d (Wilson, 1977; 

LaRoche, 2007).

Intermediate Aquifer System

The intermediate aquifer system is a heterogeneous unit, 

consisting of interbedded phosphate-rich sands, clays, and 

carbonates of the Hawthorn Group and, to a lesser extent, 

overlying undifferentiated surficial deposits (fig. 9). The Hawthorn Group sediments are mostly of Miocene age, but range 

from late Oligocene to early Pliocene age. The heterogeneity 

of the unit is the result of changing depositional environments 

as sea level and ocean circulation patterns fluctuated when the 

Hawthorn Group was deposited (Scott, 1988; Knochenmus, 

2006; Arthur and others, 2008). This heterogeneity means the 

beds have varying permeability. As a result, the intermediate 

aquifer system contains several permeable zones separated by 

zones of lower permeability. The unit also acts as a confining 

unit, limiting water exchange between the overlying surficial 

aquifer and the underlying Upper Floridan aquifer. In the study 

area, the Hawthorn Group is composed of the Peace River and 

Arcadia Formations. 

The shallower Peace River Formation is thinner and overlies the Arcadia Formation (fig. 9). The Peace River Formation 

is predominantly siliciclastic, consisting of sands, phosphaterich sediments, and clays, although localized carbonate beds 

values are available from the USGS online at http://waterdata.

usgs.gov/fl/nwis/. 

Gaged streamflows were analyzed further to estimate 

the base flow contribution to the total streamflow in Charlie 

Creek. Base flow is streamflow not associated with overland 

runoff from rainfall events but, rather, water that enters the 

stream channel more gradually and continually between rainfall events. Base flow magnitude was estimated using graphical and digital filter techniques applied to daily streamflow 

values (Rutledge, 1998; Eckhardt, 2005). In both techniques, 

filtering is used to estimate base flow by removing the streamflow component associated with overland runoff from rainfall 

events. The origin of the base flow is then deduced from what 

is known about the physical setting of the stream channel. 

For streams that fully penetrate the thickness of a non-leaky 

surficial aquifer, base flow generally is groundwater discharge 

to the stream channel. In the Charlie Creek basin, some stream 

channels do not fully penetrate the surficial aquifer, and the 

terrain is relatively flat with many depressional wetlands 

that store runoff. For these reasons, base flow estimates may 

include the effects of delayed runoff from wetlands, or agricultural runoff, in addition to groundwater discharge. 

The numerous years of streamflow data needed to characterize long-term average base flow for the entire Charlie 

Creek basin were available at the Charlie Creek near Gardner 

gage, but not for individual subbasins. To allow comparisons 

between subbasins, base flow estimates were made using 

the observed streamflow record from 2005. These base flow 

estimates were compared to ones derived from streamflows 

simulated in the MIKE SHE model for the 3-year period from 

2003 through 2005.

Hydrogeologic Framework of the

Charlie Creek Basin

This section details the hydrogeologic framework within 

the Charlie Creek basin and relates the groundwater levels 

and flow direction in the underlying aquifers to streamflow in 

Charlie Creek and its tributaries. The general hydrogeologic 

framework of Hardee and DeSoto Counties including the 

Charlie Creek basin has been described by Wilson (1977), 

Duerr and Enos (1991), Metz (1995), and Knochenmus 

(2006). The relation between stratigraphic and hydrogeologic 

units in the Charlie Creek basin is summarized in figure 9. 

Hydrogeologic Units

Three principal hydrogeologic units are present in the 

Charlie Creek basin: the surficial aquifer, the intermediate 

aquifer system, and the Upper Floridan aquifer. The intermediate aquifer system received detailed analysis in this study 

because the impermeable and permeable layers that compose 

this hydrogeologic unit are more limited in their spatial extent 

than the units that compose the Upper Floridan aquifer. This 
Hydrogeologic Framework of the Charlie Creek Basin    21

are present (Scott, 1988; Arthur and others, 2008). In the 

Charlie Creek basin, the Peace River Formation ranges from 

20 to 70 ft thick and averages 45 ft in thickness (based on 17 

lithologic logs). The top of the unit ranges from land surface in 

the western part of the basin to 150 ft below land surface in the 

southern part of the basin (77 ft above to 58 ft below NGVD 

1929 for 22 logs). Beds dip steeply to the east just beyond 

the eastern edge of the basin boundary, toward a trough in the 

surface of the Peace River Formation beneath the Lake Wales 

Ridge (Arthur and others, 2008) (fig. 10). Fractured carbonate 

rock in the Peace River Formation crops out in the streambed 

of Charlie Creek above and below its confluence with Oak 

Creek, at elevations of 32.5 and 42.6 ft above NGVD 1929 

(figs.11 and 12), and creates a small cataract at low streamflow 

(fig. 12a). The elevation of these outcrops is consistent with 

the elevation of carbonate beds from the Peace River Formation at two nearby wells (38 and 39 ft above NGVD 1929). 

The Bone Valley Member of the Peace River Formation is 

present in the extreme northwest corner of the Charlie Creek 

basin. This unit has economically valuable phosphate deposits, 

and has been mined extensively to the northwest of the study 

area.

The Arcadia Formation underlies the Peace River 

Formation, and its lowermost sediments form the Nocatee 

Member in the study area (fig. 9). The undifferentiated Arcadia 

Formation is primarily a carbonate unit, with varying amounts 

of sand, clay, and phosphate grains (Scott, 1988; Arthur and 

others, 2008). It contains the most permeable beds in the 

intermediate aquifer system in the study area. The unit is 140 

to 340 ft thick in the Charlie Creek basin (based on 

14 well logs). The top of the Arcadia Formation ranges from 

66 to 175 ft below land surface (36 ft above to 88 ft below 

NGVD 1929, based on 17 logs), with the depth increasing 

from west to east across the basin (fig. 10). 

The Nocatee Member of the Arcadia Formation is 

predominantly a siliciclastic unit, with interbedded sands, 

clays, and carbonates (Scott, 1988; Arthur and others, 2008). 

This lower-permeability unit forms the lowermost confining 

bed between the intermediate aquifer system and the Upper 

Floridan aquifer. The Nocatee Member ranges from 20 to 

100 ft thick in the Charlie Creek basin (based on 14 logs), 

and is 215 to 400 ft below land surface (104 to 315 ft below 

NGVD 1929). 

SERIES STRATIGRAPHIC UNIT GENERAL

LITHOLOGY

HYDROGEOLOGIC UNIT

Holocene and

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Undifferentiated

surficial deposits

Sand and

fossil fragments Surficial aquifer

Sand, clay,

and phosphate

Hawthorn

Group

Peace River

Formation

Arcadia

Formation

Intermediate aquifer system

Nocatee

Member

Suwannee Limestone

Ocala Limestone

Avon Park Formation

Limestone

and

dolostone

Upper Floridan aquifer

Middle

confining unit

Floridan aquifer system

Limestone and

dolostone with

gypsum and

anhydrite

Bone Valley

Member Confining or

semi-confining unit

Confining or

semi-confining unit

Confining or

semi-confining unit

Zone 2

Zone 3

Suwannee

permeable

zone

Semi-confining

unit

Avon Park

permeable

zone

Phosphate,

clay, sand,

and

dolostone

Figure 9. Relation between 

stratigraphic and hydrogeologic units 

in the Charlie Creek basin modified 

from Metz and Lewelling (2009).
22    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Figure 10. Generalized hydrogeologic section A–A’ in and near the Charlie Creek basin (section 

location shown in fig. 7).

Figure 11. Generalized hydrogeologic section B–B’ in and near the Charlie Creek basin (section location shown in fig. 7). 

UPPER FLORIDAN

AQUIFER

SURFICIAL

AQUIFER

INTERMEDIATE

AQUIFER

SYSTEM (IAS)

Open-hole

interval

B B’

-600

-500

-400

-300

-200

-100

NGVD

1929

100

200

Surficial sands and clays

Peace River Formation

Arcadia Formation

Nocatee Member of

Suwannee Limestone

Ocala Limestone

zone 2

of IAS

zone 3

of IAS

well

depth

-1245

feet

zone 2 of IAS

zone 3 of IAS

De Soto County

Hardee County

Basin divide

W-9092

W-9172

ROMP 26

W

ROMP 43

-11946

W-9289

Carbonate rock

outcrops in

Charlie Creek

channel

Section A-A'

FEET

0 5 MILES

0 5 KILOMETERS

Vertical scale greatly exaggerated

Arcadia Formation

Open-hole interval

Open-hole interval

-600

-500

-400

-300

-200

-100

NGVD

1929

100

200

Basin divide

Basin divide

W

Hardee County

Highlands County

-9074

W-11946

ROMP 30

Surficial sands and clays Peace River Formation

Arcadia Formation

Nocatee Member of Arcadia Formation

Suwannee Limestone

Ocala Limestone

UPPER FLORIDAN

AQUIFER

Zone 2 of IAS

Zone 3 of IAS

SURFICIAL AQUIFER

Charlie Creek

Little Charley

Bowlegs Creek

A A’ Section B-B'

FEET

0 5 MILES

0 5 KILOMETERS

Vertical scale greatly exaggerated

SYSTEM (IAS)

AQUIFER

INTERMEDIATE

Open-hole

interval

Well depth = -1196 feet

Open-hole

interval

Lithologic contacts at the basin divide are extrapolated from

geologic maps in Arthur and others (2008).

A’
Hydrogeologic Framework of the Charlie Creek Basin    23

Figure 12. Fractured carbonate rock exposed in the bed of Charlie Creek at the southernmost of the 

two outcrops shown in figure 7. The photo in B was taken looking down at the rocks through the water.

(Photograph by T.M. Lee, USGS.)

A

B
24    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Permeability in the intermediate aquifer system varies 

greatly because of its heterogeneity. In the study area, two 

regionally extensive permeable zones are present: Zones 2 

and 3 (fig. 9). Nomenclature for these permeable zones varies 

in previous reports, and nomenclature used in this report follows Knochenmus (2006). Zone 2 is in the lower Peace River 

Formation and upper Arcadia Formation, and also is referred 

to as the upper Arcadia aquifer (LaRoche, 2007; Gates, 2009, 

Metz and Lewelling, 2009). Zone 3 is in the lower part of the 

undifferentiated Arcadia Formation, and also is referred to as 

the lower Arcadia aquifer (LaRoche, 2007). Lateral continuity 

and flow within these permeable zones is not well understood. 

Zone 2 appears to be present throughout the Charlie Creek 

basin, and is the most regional and hydraulically isolated of 

the permeable zones (Basso, 2003; Knochenmus, 2006). Zone 

3 thins out considerably or is not present in the eastern and 

northern part of the Charlie Creek basin (Knochenmus, 2006), 

but appears to be present in the rest of the basin.

Limited data are available concerning the thickness and 

hydraulic properties of the permeable zones in the intermediate aquifer system in the Charlie Creek basin. At ROMP 43, 

in the northern part of the Charlie Creek basin, wells were 

recently installed and aquifer performance tests were conducted in both zones (LaRoche, 2007). Zone 2 is about twice 

as thick as Zone 3 at that site (64 and 37 ft, respectively) and 

between 52 and 116 ft below land surface (46 ft above to 18 ft 

below NGVD 1929); Zone 3 is between 196 and 233 ft below 

land surface (98 to 135 ft below NGVD 1929). Hydraulic 

conductivity in Zones 2 and 3 were similar (average of 8 and 

11 ft/d, respectively). Because Zone 2 was thicker than Zone 

3, however, its transmissivity values were twice that of Zone 3 

(800 and 400 ft2/d, respectively). Permeable zone information 

also is available for two monitoring well sites just outside the 

Charlie Creek basin. At those sites (ROMP 30 and ROMP 26; 

fig. 8), Zone 2 was 125 and 40 ft thick, respectively, and Zone 

3 was 36 and 175 ft thick, respectively. No data on hydraulic 

properties were available for permeable zones at these sites. 

Upper Floridan Aquifer

The Upper Floridan aquifer is a vertically continuous 

sequence of carbonate rocks of generally high permeability 

underlying the intermediate aquifer system (Southeastern 

Geological Society, 1986). In the study area, the Upper 

Floridan aquifer consists of carbonate rocks of the Suwannee 

Limestone of Oligocene age, and the Ocala Limestone and 

Avon Park Formation, both of Eocene age (fig. 9). The top of 

the Upper Floridan aquifer deepens from north to south in the 

Charlie Creek basin. The top of the Upper Floridan aquifer 

ranges from less than 150 ft below NGVD 1929 at the northern part of the basin, to more than 375 ft below NGVD 1929 at 

the southern part of the basin (Arthur and others, 2008; Florida 

Geological Survey, 2008). The base of the Upper Floridan 

aquifer consists of vertically persistent evaporites (anhydrite 

and gypsum), which infill porosity in carbonate rocks in the 

lower Avon Park Formation. This low permeability zone 

forms the middle confining unit, separating the Upper Floridan 

aquifer from the Lower Floridan aquifer. The middle confining 

unit was found at 1,580 ft below land surface (1,480 ft below 

NGVD 1929) at ROMP 43 in the northern part of the Charlie 

Creek basin (LaRoche, 2007).

The Upper Floridan aquifer is the most productive aquifer 

in the study area and consists of two water-bearing zones: the 

shallower Suwannee permeable zone and the deeper, more 

transmissive, Avon Park permeable zone (fig. 9). At ROMP 43, 

the hydraulic conductivity of the Suwannee permeable zone is 

about 90 ft/d, whereas the hydraulic conductivity of the Avon 

Park permeable zone is about 4 times greater, or approximately 400 ft/d (LaRoche, 2007). This translates into an even 

greater transmissivity because of the greater thickness of the 

Avon Park permeable zone (13,000 ft2/d and 300,000 ft2/d for 

the Suwannee and Avon Park permeable zones, respectively). 

The higher permeability of the Avon Park permeable zone is 

due to fractures and well-developed secondary porosity. 

These two zones are separated by the Ocala Limestone, 

which has lower permeability due to its fine-grained texture 

(LaRoche, 2007). 

Groundwater Use

Charlie Creek basin is a region of moderate groundwater withdrawals and use, flanked by regions with greater 

groundwater withdrawals. Pumping in the surrounding regions 

has the potential to lower Upper Floridan aquifer heads in 

the Charlie Creek basin. Most notably, a large region-wide 

depression in the potentiometric surface of the Upper Floridan 

aquifer forms during the dry season in southern Hillsborough 

and central Manatee Counties, about 25 mi west of the Charlie 

Creek basin, where heads are regularly below NGVD 1929 

(Southwest Florida Water Management District, 1993: Duerr, 

2001; Ortiz, 2006). These potentiometric lows are caused by 

high rates of groundwater pumping, primarily for agricultural 

use. The pumping magnitude depends upon climatic conditions and seasonal pumping rates, and is typically greatest 

during the spring (Southwest Florida Water Management 

District, 1993) (fig. 13). The estimated groundwater pumpage 

in the Charlie Creek basin in 1997-1999, when normalized 

to inches per year over the basin area, was the lowest of all 

basins in the Peace River watershed except for Horse Creek 

basin (table 1). Smaller subbasins immediately surrounding 

Charlie Creek to the north, west, and east have roughly twice 

the annual groundwater withdrawal rate, per area, of the Charlie Creek basin (Southwest Florida Water Management 

District, Data & Maps, 2008, http://www.swfwmd.state.fl.us./

data/gis/layer_library/category/physical_sparse, accessed 

March 8, 2008; Mike Kelley, Southwest Florida Water 

Management District, written commun., 2007).

Virtually all water used in the Charlie Creek basin 

during the study period was groundwater, based on pumping 

estimates from wells and surface-water bodies with water-use 

permits (Mike Kelley, Southwest Florida Water Management 
Hydrogeologic Framework of the Charlie Creek Basin    25

District, written commun., 2007). For example, 99.5 percent 

of water used in 2004 and 2005 was groundwater, when over 

2,200 wells in the Charlie Creek basin had groundwater use 

permits. The intermediate aquifer system and Upper Floridan 

aquifer are both used as a water-supply source. The majority 

(57 percent) of wells with groundwater use permits are open to 

both aquifers. Pumping from these wells accounted for 

56 percent of the groundwater use for 2004 and 2005. Of the 

remaining 44 percent of water pumped, 39 percent was solely 

from the Upper Floridan aquifer, and 4 percent was from wells 

completed in the intermediate aquifer system. Less than 

1 percent of groundwater pumped was from wells completed 

in the surficial aquifer.

More than 90 percent of the groundwater was used for 

agriculture (including livestock), with the majority used 

for citrus irrigation (59 and 63 percent for 2004 and 2005, 

respectively) (fig. 14A). Most of this water (58 percent in 

2004-2005) was pumped from the Upper Charlie Creek and 

Lower Charlie Creek subbasins. However, the Buckhorn 

Creek subbasin had the greatest volume of groundwater 

pumped relative to its size, and had more water pumped 

exclusively from the intermediate aquifer system than did 

other basins (table 3). Expressed as pumpage per surface area, 

total groundwater withdrawals from Buckhorn Creek subbasin 

were about 1.6 times greater than the average of the other four 

subbasins in 2004-2005. The Buckhorn Creek subbasin also 

had a greater percentage of its basin used for citrus agriculture 

than the other four subbasins (table 2). Little Charley Bowlegs 

Creek subbasin, which had the lowest percentage of its basin 

used for citrus agriculture, also had the least groundwater 

pumping relative to its size in 2004 and 2005 (table 3).

EXPLANATION

Decrease in the potentiometric surface level of the Upper Floridan aquifer

based on predevelopment level, in feet (Johnston and others, 1980)

Greater than 50

40 to 50

30 to 40

20 to 30

10 to 20

0 to 10

83° 82° 81°

28°

27°

POLK

SARASOTA

MANATEE

HILLSBOROUGH

HIGHLANDS

DE SOT0

HARDEE

CHARLOTTE

0 25 50 MILES

Southern West-Central

Florida Groundwater

Basin

Peace River

Gulf of Mexico

0 25 50 KILOMETERS

PASCO

OSCEOLA

GLADES

HENDRY

LEE

COLLIER

LAKE

PINELLAS

ORANGE

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Charlie

Creek

basin

Figure 13. Decrease in the potentiometric surface of the Upper 

Floridan aquifer from predevelopment levels to May 2007 for the 

Southern West-Central Florida Groundwater Basin (modified 

from Metz and Lewelling, 2009).

Citrus

agriculture

3.0

2.5

2.0

1.5

1.0

0.5

0 Other agriculture

and livestock

use

Recreation

(primarily golf

course irrigation)

Public

supply

2004

2005

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

YEAR

A

B

AVERAGE ANNUAL GROUNDWATER PUMPING, IN MILLIONS OF CUBIC FEET PER DAY 7.0

6.0

5.0

4.0

3.0

2.0

1.0

0

Figure 14. Estimated ground-water pumping in the Charlie Creek 

basin A, by use category for 2004 and 2005, and B, as annual 

averages from 1992 to 2005.
26    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Water use in the Charlie Creek basin during 2005 was 

almost half that of 2004 (fig. 14A and table 3). Agricultural 

pumping was lower in 2005 because the 12.2 in. of precipitation received during the spring growing season from March 

through May was several inches above the long-term average 

for those months, compared to the drier spring of 2004 when 

the basin received only 4.8 in., half of the long-term average. 

Rainfall data for Hardee County and the long-term average 

are based on records from 1915 to 2008 (http://www.swfwmd.

state.fl.us/data/wmdbweb/rainfall_data_summaries.php, accessed May 15, 2009). 

 Although annual rainfall for both years was above average, most of the rainfall in 2004 was due to tropical storms 

and hurricanes in August and September. For the 14 years 

(1992-2005) with available groundwater-use data, groundwater pumpage was greatest in 2000 (table 3) and the largest 

groundwater withdrawals occurred in the 4 years from 1999 to 

2002 (fig. 14B), followed by 2004; withdrawals were lowest 

in 2005. 

Aquifer Potentiometric Levels

The groundwater conditions in the Charlie Creek basin 

vary due to elevation changes in the potentiometric surfaces of 

the intermediate aquifer system and the Upper Floridan aquifer. A concurrent response in the overlying surficial aquifer 

brings the water table closer to or farther from the land surface 

Basin or

subbasin

Groundwater pumping (in/yr)1 Groundwater pumping, in inches over subbasin, in

2004, from wells open to:2,3

2000 2004 2005 IAS only

(in)

IAS and

UFA (in)

All wells

open to IAS

(in)

UFA only

(in)

Buckhorn Creek subbasin 4.09 3.13 1.65 0.22 2.06 2.28 0.63

Little Charley Bowlegs subbasin 1.75 1.36 0.78 0.01 0.88 0.89 0.46

Upper Charlie Creek subbasin 2.86 2.11 1.32 0.03 0.92 0.95 1.15

Oak Creek subbasin 3.37 1.94 1.13 0.10 0.99 1.09 0.85

Lower Charlie Creek subbasin 3.47 1.93 1.15 0.14 1.14 1.28 0.58

Upper half of Charlie Creek basin 2.60 1.95 1.17 0.04 1.01 1.05 0.87

Lower half of Charlie Creek basin 3.42 1.94 1.14 0.12 1.06 1.19 0.71

Charlie Creek Basin 2.95 1.94 1.16 0.08 1.03 1.11 0.80

1

Groundwater pumping data from M. Kelley (Southwest Florida Water Management District, written commun. 2007).

2

The sum of ‘UFA only’ and ‘All wells open to IAS’ can be less than ‘Groundwater pumping (in/yr) in 2004’ due to pumping from the surficial aquifer system or from wells without depth information.

3

Depth to aquifers generalized for each subbasin from Arthur and others (2008).

Table 3. Groundwater use in subdivided areas of the Charlie Creek basin.

[UFA, Upper Floridan aquifer; IAS, intermediate aquifer system; in, inch; mi2, square mile]

and changes the potential for both runoff from rainfall and 

groundwater inflow to streams. Collectively, these changes 

affect the potential for groundwater inflow to Charlie Creek. 

Upper Floridan Aquifer

During the 2004-2005 study period, heads in the Upper 

Floridan aquifer in the Charlie Creek basin were lowest in 

May 2004 and highest in September 2004. The potentiometric surface consistently sloped downward from the northeast 

toward the southwest, with heads in May 2004 decreasing 

from more than 70 ft above NGVD 1929 in the northeastern 

part of the basin to less than 40 ft above NGVD 1929 in the 

southwestern part (fig. 15). In September 2004, heads were 

about 15 ft higher overall and ranged from about 90 ft above 

NGVD 1929 in the northeastern part of the basin to about 

50 ft above NGVD 1929 in the southwestern part. Water levels 

in two wells in the central part of the Charlie Creek basin 

were 17.6 and 20.4 ft higher in September 2004 than in May 

2004. Groundwater flow paths had a slightly more westerly 

component in May 2004 than in September 2004 because of 

a regional low in the potentiometric surface west of Charlie Creek. The Upper Floridan aquifer levels changed more 

between September 2004 and May 2004 in the western part of 

the basin than in the northern and eastern parts.

Heads in the Upper Floridan aquifer were considerably 

higher during the study period than during the preceding 
Hydrogeologic Framework of the Charlie Creek Basin    27

several years, when a regional drought resulted in greater 

groundwater withdrawals and less recharge. During May 2000, 

heads in the Charlie Creek basin were as much as 40 ft below 

those observed in September 2004 (Duerr, 2001). May 2000 

potentiometric contours focus flow lines toward the depressed 

potentiometric surface west of the Charlie Creek basin, where 

minimum heads were more than 20 ft below NGVD 1929. 

In May 2000, heads in the southwestern part of the Charlie 

Creek basin were lowered comparatively more than heads in 

the northern part of the basin. May 2000 heads in the 

Charlie Creek basin ranged from greater than 60 ft above 

NGVD 1929 in the northern part of the basin to less than 

20 ft above NGVD 1929 in the southwestern part.

Two Upper Floridan aquifer wells in the Charlie Creek 

basin (wells 26 and 45; app. 1) with more than 20 years of data 

were evaluated for long-term trends (fig. 16). Potential trends 

were evaluated for the entire period of record for both wells, 

with wet and dry seasons analyzed separately. No statistically 

significant trends were observed for the dry season data or for 

all data grouped together (t-statistic on slope of the regression 

line, α = 0.05). A statistically significant declining trend was 

noted for well 26 for the wet season (p = 0.01; R2 = 0.27), 

although data are missing for 9 of the 34 years of record.

Intermediate Aquifer System

There are enough data available to construct potentiometric surface maps for permeable Zone 2 of the intermediate 

aquifer system in the Charlie Creek basin for the study period. 

Potentiometric surface maps constructed for Zone 2 relied on 

data from wells either open only to Zone 2, or open to both 

Zones 2 and 3. Wells open to both zones were included for two 

reasons. First, it was assumed that the composite intermediate 

Bereah

Gardner

Avon

Park

Zolfo

Springs

Bereah

Gardner

Avon

Park

Zolfo

Springs

0 5 MILES

0 5 KILOMETERS

40

50

70

60

70

60

50

80

80

90

A May 2004 B September 2004

27°40'

35'

30'

25'

20'

27°15'

27°40'

35'

30'

25'

20'

27°15'

81°50' 45' 40' 35' 81°30' 81°50' 45' 40' 35' 81°30'

EXPLANATION

Charlie Creek basin

Subbasin boundary

Surface-water feature

Potentiometric surface contour – Shows the

potentiometric surface of the Upper Floridan

aquifer, in feet above NGVD 1929

Upper Floridan aquifer regional well

50

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Figure 15. Potentiometric surface of the Upper Floridan aquifer for A, low (May 2004) and B, high (September 2004) conditions 

for the 2004-2005 study period.
28    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida WATER LEVEL, IN FEET ABOVE NGVD 1929

70

60

50

40

30

20

10

80

70

60

50

40

30

20

R =0.17 2

R =0.27 2

R =0.02 2

R =0.04 2

1975

1980

1985

1990

1995

2000

2005

2009

1975

1980

1985

1990

1995

2000

2005

2009

Upper Floridan aquifer (well 26) Oak Creek subbasin

Upper Floridan aquifer (well 45) Upper Charlie Creek subbasin

Wet season (September)

Dry season (May)

EXPLANATION

Figure 16. Wet and dry season water levels in two Upper Floridan aquifer wells in the Charlie Creek basin from 1975 to 2008. 

Well locations shown in figure 8.

aquifer system head would be more similar to Zone 2 in areas 

where that zone is thick (north and east part of the basin). 

Second, heads in both zones are similar at two ROMP sites 

just south and west of the Charlie Creek basin (median 

difference less than 1 ft, based on daily data from 2004-2005). 

Therefore, composite heads in the southern and western parts 

of the basin were assumed to be similar to those in the uppermost permeable zone (Zone 2) in the intermediate aquifer 

system. The 10-ft contour interval used for the maps should 

allow for minor errors inherent in both assumptions. Permeable Zone 2 is referred to simply as the intermediate aquifer 

system hereafter.

During the study period, heads were lowest in the 

intermediate aquifer system in May 2004 and highest in 

September 2004, as was the case in the Upper Floridan aquifer 

(fig. 17A-B). For both conditions, heads were highest in the 

northern part of the basin and lowest in the southwestern 

part of the basin, near the mouth of Charlie Creek. Heads in 

May 2004 ranged from less than 40 ft above NGVD 1929 

in the southwestern part of the basin to greater than 110 ft 

above NGVD 1929 in the northern part. Similar to the Upper 

Floridan aquifer, heads in the intermediate aquifer system in 

September 2004 were about 10 to 15 ft higher than in May 

2004, and ranged from about 50 ft above NGVD 1929 in 

the southwestern part of the basin to more than 120 ft above 

NGVD 1929 in the northern part.

During the regional drought in May 2000, heads in the 

intermediate aquifer system were much lower than during the 

study period. The water level in well 30 in the central part of 

the Charlie Creek basin (fig. 8) was 39 ft lower in May 2000 

than in September 2004. Heads during May 2000 ranged 

from about 20 ft above NGVD 1929 in the southwest part of 

the basin to more than 80 ft above NGVD 1929 in the 

northern part. 

Of the three wells in the intermediate aquifer system in 

the Charlie Creek basin with long-term record (wells 56, 30, 

and 5 shown on fig. 17), two have about 20 years of waterlevel data (wells 5 and 30). No long-term trends in water 

levels were observed for well 30 in the central Charlie Creek 

basin (α = 0.05) (fig. 18). The water-level responses in well 
Hydrogeologic Framework of the Charlie Creek Basin    29

Charlie Creek

basin

Charlie Creek

basin

Bereah

Gardner

Avon

Park

Zolfo

Springs

Bereah

Gardner

Avon

Park

Zolfo

Springs

30

5

29

56

2

32

54

30

5

29

56

2

32

54

0 5 MILES

0 5 KILOMETERS

30

50

70

60

70

60

50

80

90

90

40

70

80

100

110

100

110

120

B September 2004

27°40'

35'

30'

25'

20'

27°15'

27°40'

35'

30'

25'

20'

27°15'

81°50' 45' 40' 35' 81°30' 81°50' 45' 40' 35' 81°30'

IAS is 5

IAS and UFA are within 5 feet

IAS is 5 or more feet less than UFA

or more feet greater than UFA

Difference between the potentiometric

surfaces of the

intermediate aquifer system (IAS)

Upper Floridan aquifer (UFA)

and the

EXPLANATION

2

Potentiometric surface contour – Showing the

potentiometric surface of the intermediate

aquifer system, in feet above NGVD 1929

Subbasin boundary

Surface-water feature

Intermediate aquifer system regional well

Intermediate aquifer system well and number from Appendix 1

50

A May 2004

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Figure 17. Potentiometric surfaces of the intermediate aquifer system for A, dry (May 2004) and B, wet (Sept. 2004) conditions 

during the study, also showing areas where the intermediate aquifer system heads are greater and less than heads in the Upper 

Floridan aquifer.

56 in the northern basin were similar to well 30, but the short 

record prevented the interpretation of trends. However, a 

statistically significant declining trend was noted for dryseason water levels (p = 0.02) for well 5 in the southern part 

of the basin. For that well, no significant trends were observed 

for the wet season, or for all of the data considered together.

Head Differences between the Intermediate 

Aquifer System and Upper Floridan Aquifer 

A potential for downward flow from the intermediate 

aquifer system (Zone 2) to the Upper Floridan aquifer existed 

over about 80 percent of the Charlie Creek basin during both 

May and September of 2004. In the remaining 20 percent of 

the basin, the heads in the Upper Floridan aquifer were above 

those in the intermediate aquifer system. Because the contour 

lines cannot be positioned precisely due to limited data, figure 

17 illustrates areas where the vertical head difference between 

aquifers was greater than 5 ft. The majority of the basin, 67 

and 50 percent for May and September 2004, respectively, 

still displayed heads in the intermediate aquifer system that 

were 5 ft or more higher than heads in the underlying Upper 

Floridan aquifer. The downward flow potential between the 

two aquifers existed in the eastern and central parts of the 
30    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

basin, which corresponds to much of the upper Charlie Creek 

and Little Charley Bowlegs subbasins, and parts of Oak Creek 

subbasin. Only about 10 percent of the basin had an upward 

head difference of more than 5 ft. These conditions existed 

in the west-central part of the basin, centered over much of 

Buckhorn Creek basin, in May and September 2004. In May 

2004, the southwest part of the Charlie Creek basin showed 

a similar potential for upward flow from the Upper Floridan 

aquifer toward the intermediate aquifer.

The spatial extent of the downward flow potential 

between the intermediate and Upper Floridan aquifers was 

considerably larger during May 2000, when groundwater 

levels were extremely low because of an extended drought 

and increased pumping. During this period, 93 percent of the 

basin had a downward head difference between the aquifers, 

compared to 80 percent during 2004. However, the percentage 

of the basin with a downward head difference of more than 

5 ft in May 2000 was comparable to that in May 2004, at 65 

1986 88 90 92 94 96 98 2000 02 04 06 2008

YEAR

WATER LEVEL, IN FEET ABOVE NGVD 1929

70

65

60

55

50

45

40

35

30

25

70

65

60

55

50

45

40

35

30

25

105

100

95

90

85

80

75

70

65

60

Wet season (September)

Dry season (May)

R = 0.0007 2

R = 0.11 2

R = 0.005 2

R = 0.27 2

R = 0.20 2

R = 0.0004 2

Intermediate aquifer system (well 30) Lower Charlie Creek subbasin

Intermediate aquifer system (well 5) Oak Creek subbasin

Intermediate aquifer system (well 56) Upper Charlie Creek subbasin

Figure 18. Wet and dry season water levels in three intermediate aquifer system wells in the 

Charlie Creek basin from 1986 to 2008. Well locations are shown in figure 8. 
Hydrogeologic Framework of the Charlie Creek Basin    31

and 67 percent, respectively. Only 7 percent of the basin had 

an upward head difference in May 2000, and less than 1 percent of the basin had an upward head difference greater than 

5 ft. This suggests that the Upper Floridan aquifer was drawn 

down to lower levels during the drought than the intermediate 

aquifer system. 

Surficial Aquifer

The water table in the surficial aquifer of Charlie Creek 

was not mapped due to sparse data; however, the water table 

is assumed to generally reflect land surface topography, with 

higher elevations in upland areas and lower elevations near 

streams. For the network of surficial aquifer wells monitored 

for this study, water-table elevations ranged from a low of 

25 ft above NGVD 1929 near Charlie Creek at the downstream well transect to a high of 97 ft above NGVD 1929 at 

ROMP 43. The highest water-table elevations in the basin 

were inferred from lake stages to be along ridge areas near the 

eastern and northern basin divide. For example, the average 

stage of Lake Chilton, at the northeastern basin divide (fig. 2), 

was 112 ft above NGVD 1929 during 2004-2005, indicating a 

slightly higher water table in that area than at ROMP 43 

(fig. 8). The greatest water-table depths also were inferred 

to be in these areas where ridge elevations can exceed 150 ft 

above NGVD 1929. The lowest measured water-table elevations were in the southwestern part of the basin near Charlie 

Creek, where flow is toward stream channels. At upland sites, 

the water table fluctuated between 3 and 7 ft during the study. 

In monitoring wells near streams, the range was greater 

(7-12 ft), reflecting, in part, the bank storage caused by peak 

streamflows. The relation between the water table and the 

streams is described later in the discussion of groundwater 

interactions with Charlie Creek. The water table in monitoring 

wells ranged from at land surface during wet periods to greater 

than 10 ft below land surface during drier periods.

Water-table elevations were continuously monitored near 

the centers of the three tributary subbasins and showed similar 

temporal patterns (fig. 19). As with the potentiometric surface, 

the water-table elevations at the three sites decreased from the 

north and east toward the southwest and were highest in the 

Little Charley Bowlegs subbasin (typically above 90 ft NGVD 

1929) and lowest in the Oak Creek subbasin, as indicated by 

water levels in wells 25 and 17, respectively (fig. 8 and 

app. 1). The lowest water-table elevations were recorded at the 

beginning of the data collection period, in mid-June to early 

July 2004 (fig. 19). The highest water-table elevations were 

generally in September 2004, following a wet rainy 

season and heavy rainfall from Hurricanes Charley, Frances, 

and Jeanne. The water table remained relatively high during 

2005 compared to the low levels recorded at the beginning 

of the study. Rainfall was above average during the spring of 

2005 (fig. 3), resulting in higher water-table elevations than 

during the drier spring of 2004. When the water table was 

highest, the water levels in wells 25 and 17 approached land 

surface (fig. 19).

76

78

80

82

84

86

88

90

92

94

96

WATER LEVEL, IN FEET ABOVE NGVD 1929

M J J A S O N D J F M A M J J A S O N D J F

2004 2005 2006

Little Charley Bowlegs Creek

subbasin, well number 25

Land surface elevation

Buckhorn Creek subbasin,

well number 50

Land surface elevation

Oak Creek subbasin,

well number 17

Land surface elevation

EXPLANATION

Figure 19. Daily average water levels in the surficial aquifer at upland wells in the three tributary subbasins. Well locations are shown 

in figure 8.
32    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Temporal Changes in Vertical Head 

Differences between Aquifers

Vertical head differences between aquifers indicated 

the surficial aquifer continually recharged the underlying 

intermediate aquifer system at the three ROMP sites (fig. 20). 

However, the flow direction varied over time between zones 

within the intermediate aquifer system, and between the intermediate and Upper Floridan aquifers. Heads in the surficial 

aquifer were higher than in Zone 2 of the intermediate aquifer 

system at all three sites, although the difference ranged from 

a median value of 2.2 ft at ROMP 43 to 24.9 ft at ROMP 26, 

possibly indicating greater confinement between these aquifers 

at ROMP 26 (fig. 20).

2004 2005 2006

J F M A M J J A S O N D J F M A M J J A S O N D J F

WATER LEVEL, IN FEET ABOVE NGVD 1929

20

30

40

50

60

70

30

40

50

60

80

70

60

70

80

90

100

ROMP 30

ROMP 26

ROMP 43

Surficial aquifer well

Intermediate aquifer system well – Zone 2

Intermediate aquifer system well – Zone 3

Upper Floridan aquifer well

Figure 20. Water levels in wells in the surficial aquifer, Zones 2 and 3 of the intermediate aquifer system, and 

the Upper Floridan aquifer at ROMP 30, ROMP 26, and ROMP 43.
Hydrogeologic Framework of the Charlie Creek Basin    33

At all three ROMP sites, groundwater in Zone 2 of the 

intermediate aquifer system predominantly flowed downward toward Zone 3. Heads in Zone 2 of the intermediate 

aquifer system were higher than in Zone 3 for the majority of 

the study period, but the magnitude of this difference varied 

considerably between sites (median 0.1 to 11.5 ft; fig. 20). At 

ROMP 26 and ROMP 30, the median downward head difference between the zones was less than 1 ft, and the direction 

occasionally reversed to an upward head difference. In contrast, heads in Zone 2 were always substantially higher than 

in Zone 3 at ROMP 43. Leakance estimates at ROMP 43 were 

two orders of magnitude lower for Zone 2 than for Zone 3, 

indicating that Zone 3 has a stronger hydraulic connection to 

the Upper Floridan aquifer than to Zone 2 of the intermediate 

aquifer system (LaRoche, 2007). Leakance estimates were not 

available for the other sites. 

At two of the three ROMP sites, ROMP 26 and ROMP 

43, heads in Zone 3 were similar to those in the Upper Floridan aquifer and typically slightly lower (median 0.3 and 0.6 ft 

lower, respectively, fig. 20), suggesting substantial hydraulic 

connection between Zone 3 of the intermediate aquifer system 

and the Upper Floridan aquifer and indicating the potential for 

upward discharge. This may be the result of local groundwater 

pumping from wells open to both aquifers. Because the Upper 

Floridan aquifer has a considerably higher transmissivity than 

the intermediate aquifer system, the Upper Floridan aquifer 

is expected to have less drawdown than the intermediate 

aquifer system for a given withdrawal rate. At ROMP 30, the 

head in Zone 3 was typically greater than the Upper Floridan 

aquifer (median difference 1.8 ft), indicating predominantly 

downward recharge into the Upper Floridan aquifer; however, 

reversals did occasionally occur at this site.

Groundwater and Stream Interactions

The changing groundwater levels in the basin determine 

the interaction of Charlie Creek with groundwater. This section examines in greater detail the groundwater heads controlling lateral and vertical flow patterns in the aquifers adjacent 

to and beneath Charlie Creek and its tributaries, and then 

describes the measured contribution of seepage to Charlie 

Creek. The specific conductance of streamflow in different 

areas of the basin is described and provides further evidence of 

the interaction between the stream network and the watershed. 

Artesian Flow Conditions in the Basin

Groundwater in both the Upper Floridan aquifer and 

the intermediate aquifer system (Zone 2) exhibited artesian 

head conditions in areas of the Charlie Creek basin. 

Artesian head conditions exist where the potentiometric surface of groundwater in the aquifers is higher than land surface 

elevation, allowing groundwater to flow upward and out of 

any uncapped wells at land surface (http://ga.water.usgs.gov/

edu/gwartesian.html). Artesian flow conditions in the intermediate aquifer system are of greater interest than those in 

the Upper Floridan aquifer in the Charlie Creek basin because 

groundwater leaks between the intermediate aquifer system 

and the overlying surficial aquifer. Prior to this study, only 

data for the potentiometric surface of the Upper Floridan aquifer were available and, therefore, could be used to infer areas 

of artesian flow conditions in the intermediate aquifer system. 

Heads mapped in the intermediate aquifer system during this 

study were higher than those in the Upper Floridan aquifer 

over the majority of the Charlie Creek basin. As a result, areas 

of artesian flow conditions in the intermediate aquifer system 

covered a larger area than those in the Upper Floridan aquifer 

basin-wide, but exceptions occurred in two subbasins (fig. 21).

Artesian head conditions in an aquifer cause the water level in a well to rise above land surface. 

(Photograph on left by A.M. Cressler, USGS; photograph on right by USGS.)
34    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Charlie Creek basin Charlie Creek basin

ROMP 43

ROMP 30

ROMP 26

ROMP 43

ROMP 30

ROMP 26

A Intermediate aquifer system B Upper Floridan aquifer

27°40'

35'

30'

25'

20'

27°15'

27°40'

35'

30'

25'

20'

27°15'

81°50' 45' 40' 35' 81°30' 81°50' 45' 40' 35' 81°30'

0 5 MILES

0 5 KILOMETERS

Subbasin boundary

Surface-water feature

ROMP site location and number

Location of flowing well as shown

on USGS topographic map

EXPLANATION

Area of artesian head

condition in the intermediate

aquifer system

May 2004

September 2004

0 5 MILES

0 5 KILOMETERS

Subbasin boundary

Surface-water feature

ROMP site location and number

Location of flowing well as shown

on USGS topographic map

EXPLANATION

Area of artesian head

condition in the Upper

Floridan aquifer

May 2004

September 2004

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Figure 21. Artesian flow conditions in A, the intermediate aquifer system and B, the Upper Floridan aquifer in the Charlie Creek 

basin for low (May 2004) and high (Sept. 2004) head conditions during the 2004-2005 study period.

In the Buckhorn Creek and Lower Charlie Creek 

subbasins, the area of artesian flow conditions in the Upper 

Floridan aquifer was larger than that of the intermediate 

aquifer system at both low and high water-level conditions 

(fig. 21A and B). This result is consistent with the fact that the 

potentiometric surface of the intermediate aquifer system was 

more than 5 ft below the potentiometric surface of the Upper 

Floridan aquifer near Buckhorn Creek subbasin during May 

and September 2004 (fig. 17), as well as in the southern end 

of the Lower Charlie Creek subbasin for May 2004. These 

relative head positions indicate that groundwater could flow 

upward from the Upper Floridan aquifer toward the intermediate aquifer system; however, flow in the intermediate aquifer 

may not move upward into the surficial aquifer. 

Groundwater pumping from the intermediate aquifer 

system in these two areas probably explains the lower heads 

in this aquifer relative to the Upper Floridan aquifer. In 2004, 

comparatively more groundwater was pumped in the Buckhorn Creek and Lower Charlie Creek subbasins than any other 

subbasins of Charlie Creek, from wells open exclusively to the 

intermediate aquifer system (0.22 in/yr and 0.14 in/yr, respectively), or to both the intermediate aquifer system and Upper 

Floridan aquifer (2.28 in/yr and 1.28 in/yr, respectively) 

(table 3). In contrast, groundwater withdrawals from the 

intermediate aquifer system were lowest in the northern subbasins (Little Charley Bowlegs and Upper Charlie Creek), 

where artesian flow conditions were extensive; withdrawals 

in the Oak Creek subbasin were only slightly greater (table 3). 

This comparatively greater pumping stress on the intermediate 
Hydrogeologic Framework of the Charlie Creek Basin    35

aquifer system in the southern and western regions of the 

Charlie Creek basin during the study could explain the lower 

heads in the intermediate aquifer system compared to the 

Upper Floridan aquifer in these parts of the basin (fig. 17).

Currently, no ROMP sites are within any of the areas of 

artesian flow mapped for this study. Therefore, vertical head 

differences between aquifers were not available to confirm 

whether (1) upward flow occurred between all three aquifers, 

or (2) water flowed from both the surficial aquifer and Upper 

Floridan aquifer into the intermediate aquifer system. During 

the highest water-level conditions of this study, the expanding areas of artesian flow approached the ROMP 43 site, but 

never reached it (fig. 21). Six flowing wells, originally shown 

on USGS 1:24,000-scale quadrangle maps from the 1950s, 

are located in the lower parts of Charlie Creek or Oak Creek 

subbasins within, or very near, mapped areas of artesian conditions for both aquifers in September 2004 (fig. 21). However, 

these wells were outside the areas of artesian conditions for 

both aquifers for May 2000 and May 2004. The six flowing 

wells are all clearly within the areas of artesian head conditions associated with the predevelopment potentiometric 

surface of the Upper Floridan aquifer (Ryder, 1985). 

Delineating the areas of the Charlie Creek basin that have 

artesian conditions, and the duration of these conditions, helps 

define where the surficial aquifer and its embedded streams 

and wetlands have the potential to gain water from or lose 

water to the underlying intermediate aquifer system. The 

quantity of water exchanged between these aquifers can 

be small because the rate of water movement is typically 

slowed by clay layers within the intermediate aquifer system. 

However, artesian conditions contribute flow to the surficial 

aquifer, and moreover, prevent water from leaking downward 

out of wetlands, streams, and the surficial aquifer, especially 

through preferential flow paths. 

The Upper Peace River basin provides an extreme 

example of a setting where artesian flow conditions below the 

stream have been largely lost (fig. 1). In areas of the Upper 

Peace River basin, heads in the intermediate aquifer system 

can be tens of feet below the elevation of the Peace River 

streambed, and water leaking through karst features in the 

streambed periodically leaves sections of the river dry (Metz 

and Lewelling, 2009). If the confining clays between the 

surficial and intermediate aquifer system become breached 

by subsidence, erosion, or mining, more permeable carbonate rocks can become exposed, creating preferential paths for 

groundwater flow. The creation of preferential flowpaths could 

also be accelerated if overlying clayey sand sediments become 

dry, shrink, and ravel down into karst solution openings 

(Metz and Lewelling, 2009). 

In the Charlie Creek basin, the distribution of recharge 

and artesian flow conditions varied seasonally and annually. 

In the upper half of the basin, artesian flow conditions in the 

intermediate aquifer system were relatively consistent during the study, ranging from 31 to 44 percent of the total area 

in May and September of 2004, respectively (table 2). Most 

of the expansion in September 2004 resulted from artesian 

conditions advancing upstream along Little Charley Bowlegs Creek tributary and downstream along Charlie Creek in 

the Upper Charlie Creek subbasin, as well as spreading into 

headwater wetlands and areas bordering the stream channel 

(fig. 21A). 

In contrast, artesian conditions in the lower half of 

the basin underwent a more extreme change. In May 2004, 

artesian conditions in the intermediate aquifer system were 

present in only 3 percent of the Lower Charlie Creek subbasin, 

subjecting most of the lower channel of the creek to potential 

recharge conditions, with only a small area at the downstream 

end of Charlie Creek exhibiting artesian flow conditions 

(fig. 21A). By September 2004, artesian flow conditions in 

the intermediate aquifer system expanded to encompass 

25 percent of the Lower Charlie Creek subbasin (table 2), 

including all of the area below the main channel of Charlie 

Creek and the adjacent riverine floodplain, and extending 

upstream along small tributaries and Oak Creek―the principal 

tributary in the lower basin (fig. 21A). In May 2004, artesian 

head conditions in the intermediate aquifer system were 

present in only 2 percent of the Oak Creek subbasin, 

and were absent beneath the stream channel of Oak Creek―

as was the case along the lower channel of Charlie Creek. 

Instead, artesian conditions encompassed a roughly circular 

area of isolated wetlands in the Oak Creek subbasin and an 

associated tributary flowing into Oak Creek about halfway 

up its reach (fig. 21A and fig. 5). The wetter conditions of 

September 2004 expanded the size of the artesian flow conditions around this wetland area. During the drought in May 

2000, artesian conditions in the intermediate aquifer system 

existed in only 2 percent of the entire Charlie Creek basin, in 

the headwaters of the Upper Charlie Creek subbasin. 

In the upper half of the Charlie Creek basin, areas with 

artesian flow conditions in the Upper Floridan aquifer differed 

substantially from those in the intermediate aquifer system, 

and the size of artesian flow areas in the Upper Floridan aquifer were not a consistent predictor of its size in the intermediate aquifer system (fig. 21B). In May 2004, artesian conditions 

in the Upper Floridan aquifer encompassed about 8 percent of 

the upper half of the Charlie Creek basin while artesian conditions in the intermediate aquifer system encompassed nearly 

4 times that amount, or 31 percent of the upper basin (table 2). 

In September 2004, the two areas were more similar in relative 

size; artesian conditions in the Upper Floridan aquifer encompassed 30 percent of the upper half of the basin, and artesian 

conditions in the intermediate aquifer system encompassed 

about 1.5 times that amount, or 44 percent of the upper basin. 

 In the lower half of the Charlie Creek basin, areas of 

artesian flow predicted from the two aquifers were more 

comparable, but the Upper Floridan aquifer heads typically 

implied larger areas of artesian flow than the intermediate 

aquifer system heads. Individual subbasins had greater 

disparities, but in most cases the areas were closer in relative size during the wet season than during the dry season. In 

contrast with the study period, during the drought in May 2000 

artesian conditions in the Upper Floridan aquifer were nearly 
36    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Elevation

difference

statistic

Stream

Charlie Creek,

Upper Channel1

Charlie Creek,

Lower Channel2 Oak Creek Buckhorn Creek Little CharleyBowlegs Creek

All stream

channels in

Charlie Creek

basin

May 2004

Average 6 3 -14 -14 -1 -2

Minimum -52 -8 -37 -33 -25 -52

Maximum 25 16 2 6 11 25

% positive 81% 69% 1% 12% 46% 48%

% negative 19% 31% 99% 88% 54% 52%

September 2004

Average 18 19 -5 -1 10 10

Minimum -33 6 -28 -17 -16 -33

Maximum 38 33 18 16 20 38

% positive 94% 100% 39% 44% 89% 78%

% negative 6% 0% 61% 56% 11% 22%

May 2000

Average -7 -16 -30 -31 -24 -19

Minimum -44 -29 -41 -57 -50 -57

Maximum 14 0 -18 -6 -5 14

% positive 25% 0% 0% 0% 0% 9%

% negative 75% 100% 100% 100% 100% 91%

1

 Upstream from streamflow monitoring station near Crewsville, including Bee Branch.

2

 Downstream from streamflow monitoring station near Crewsville, main channel only.

Table 4. Differences between head in the intermediate aquifer system and the overlying streambed elevation for subbasins in the 

Charlie Creek basin.

[All values shown except percentages are in feet. Positive elevation differences indicate upward flow conditions; negative differences indicate downward 

flow conditions. %, percent]

absent from the entire Charlie Creek basin. For predevelopment groundwater levels, the artesian flow area estimated in 

the Upper Floridan aquifer covered about 35 percent of the 

entire basin (Ryder, 1985), compared to 25 percent of the 

basin in September 2004 (figs. 1A and 21B). 

Vertical Flow Potential between Streams 

and the Intermediate Aquifer System

The potential for upward and downward groundwater 

flow along the stream network changed substantially between 

the low and high head conditions during the study (May and 

September 2004, respectively), and relative to the historically 

low head conditions of May 2000 (fig. 22). 

For the histroically low head condition in May 2004, 

about half (52 percent) of the total length of Charlie Creek 

and its tributaries had a downward head difference, and the 

intermediate aquifer system heads were an average of 2 ft 

below the corresponding elevations of Charlie Creek and its 

tributaries (fig. 22A; table 4). Of the streams with an upward 

head difference, the upward head difference was greater and 

covered more of the stream network in the Upper Charlie 

Creek subbasin than the Lower Charlie Creek subbasin 

(81 percent, compared to 69 percent). For Little Charley 

Bowlegs Creek subbasin, about half the stream length was 

subject to an upward head difference and the average intermediate aquifer head was 1 ft below the channel. Tributary 

streams in the Buckhorn Creek and Oak Creek subbasins 

were dominated by downward head differences. Heads in the 

intermediate aquifer system were an average of 14 ft below the 

streambed elevations in both subbasins, and only a small 

percentage of the length of either Buckhorn Creek or Oak 

Creek experienced an upward head difference (12 and 

1 percent, respectively). 

For the high head condition observed in September 2004, 

the vast majority of the streams in the Charlie Creek basin 
Hydrogeologic Framework of the Charlie Creek Basin    37

Charlie Creek basin Charlie Creek basin

Charlie Creek basin

Little Charley

Bowlegs

Creek

Cha

Oak Creek rlie Creek

Charlie

Creek

Buckhorn

Creek

Little Charley

Bowlegs

Creek

Cha

Oak Creek rlie Creek

Charlie

Creek

Buckhorn

Creek

Little Charley

Bowlegs

Creek

Cha

Oak Creek rlie Creek

Charlie

Creek

Buckhorn

Creek

Subbasin boundary

Surface-water feature

0 5 MILES

0 5 KILOMETERS

EXPLANATION

20 feet or greater above

0 to 20 feet above

0 to 20 feet below

20 to 40 feet below

40 feet or greater below

Distance of the potentiometric surface

of the intermediate aquifer system above or

below the streambed elevation, in feet

A May 2004, low head conditions B September 2004, high head conditions

27°40'

35'

30'

25'

20'

27°15'

27°40'

35'

30'

25'

20'

27°15'

81°50' 45' 40' 35' 81°30' 81°50' 45' 40' 35' 81°30'

C May 2000, extreme low head conditions

27°40'

35'

30'

25'

20'

27°15'

81°50' 45' 40' 35' 81°30'

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Figure 22. Difference between head in the 

intermediate aquifer system and streambed elevation 

for Charlie Creek and major tributaries, for A, low (May 

2004) and B, high (Sept. 2004) head conditions during 

the 2004-2005 study period, and for C, very low head 

conditions (May 2000).
38    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

experienced upward head conditions (78 percent of all stream 

channels) and heads in the intermediate aquifer system averaged 10 ft above the average streambed elevation in the basin 

(fig. 22B; table 4). Upward head conditions were concentrated 

along the main channel of Charlie Creek: 100 percent of the 

main channel of Charlie Creek in the Lower Charlie Creek 

subbasin experienced upward head conditions averaging 

19 ft above the streambed. In the headwaters-dominated Upper 

Charlie Creek subbasin, 94 percent of all stream channels 

experienced upward head conditions that averaged 18 ft above 

the streambed. Of the three tributary streams, the majority 

of Little Charley Bowlegs Creek was affected by upward 

head differences, whereas the percentage of stream channels 

experiencing upward head differences in the Oak Creek and 

Buckhorn Creek subbasins increased to 39 and 44 percent, 

respectively.

The historically low head conditions of May 2000 

provided the greatest potential for water in Charlie Creek 

and its tributaries to leak downward (fig. 22C). Intermediate 

aquifer system heads averaged 19 ft below the bed elevation of 

the stream network over the entire basin (table 4). Intermediate aquifer system heads averaged 16 ft below the streambed 

elevations in the Lower Charlie Creek subbasin compared to 

7 ft below in the Upper Charlie Creek subbasin. The largest 

downward head differences were in Buckhorn Creek and Oak 

Creek subbasins, which averaged about 30 ft below the stream 

channel. The only place in the entire basin with an upward 

head difference was at the headwaters wetland area of the 

Upper Charlie Creek subbasin (fig. 22C). 

For all three conditions depicted in figure 22, Oak Creek 

was the subbasin with vertical head differences that most consistently allowed for downward recharge between the stream 

and intermediate aquifer system. Alternatively, the Lower 

Charlie Creek and Little Charlie Bowlegs Creek subbasins 

exhibited the largest swings in vertical head differences, from 

large upward head differences to large downward ones. These 

changes altered conditions in the Lower Charlie Creek subbasin the most, with 100 percent of the main channel experiencing an upward potential for groundwater flow in September 2004, and 100 percent experiencing downward leakage 

potential in May 2000 (table 4). The complete head reversal 

and loss of artesian head conditions in the Lower Charlie 

Creek subbasin did not occur in the other subbasins for these 

two periods. The larger than expected change in the Lower 

Charlie Creek subbasin is probably attributable to groundwater 

pumping effects on the intermediate aquifer system within and 

outside the subbasin, lowering heads comparatively more in 

this subbasin than others during the May 2000 drought. 

Stream Interactions with the Surficial Aquifer 

The surficial aquifer contributed groundwater directly to 

Charlie Creek and its tributaries whenever the water table in 

the adjacent surficial aquifer was higher than the stream stage. 

Vertical groundwater flow patterns were described at two cross 

sections through Charlie Creek and used to examine seasonal 

changes in these patterns at different locations in the basin. 

Groundwater levels in the surficial aquifer were taken from 

transect wells at each cross section. Heads in the deeper intermediate aquifer system and Upper Floridan aquifer were interpolated at each location from potentiometric surface maps.

Charlie Creek 

Charlie Creek almost continually received groundwater 

inflow from the surficial aquifer during the study period, but 

the magnitude of the inflow gradients differed at the downstream transect location compared to the upstream location. 

Groundwater levels measured approximately monthly in 

transect wells were plotted on a cross section through the 

stream channel. The conditions shown in figures 23 and 24 are 

close to the lowest and highest head conditions observed in 

the intermediate aquifer system and Upper Floridan aquifer for 

the study period. The dates representing the lowest and highest 

measurable head conditions are July 1, 2004, and October 28, 

2004, respectively, and bracket the hurricanes of August and 

September 2004. Although intermediate aquifer system heads 

in the basin were actually highest in September 2004 (fig. 25), 

many of the wells were flooded that month as a result of high 

stream stage.

The stream profile near the upstream transect is broad and 

shallow, and the stream probably receives less groundwater 

inflow here than at the more deeply incised downstream site. 

Compared to the downstream transect, the slope of the water 

table toward the stream was lower at the upstream transect, 

and was sometimes away from the stream (fig. 23). The 

median lateral gradient of the water table at the upstream site 

was 0.0023 (for wells 1, 2, 5, 6, and 8), an order of magnitude 

lower than at the downstream site. The upstream site also 

experienced upward head gradients within the surficial aquifer 

near the stream less frequently compared to the downstream 

site. The median vertical gradient was 0.042 (for wells 3 and 

4), which also is an order of magnitude lower than at the 

downstream site. In July and October 2004, heads in the intermediate aquifer system exceeded the stream stage elevation by 

6 and 17 ft, respectively. 

Recharging conditions probably occurred at the upstream 

site when the stream stage rose above the adjacent water 

table. At lower stream stages, however, the water table sloped 

toward the stream, and very small upward head gradients were 

present in the surficial aquifer. Groundwater inflow was probably minimal during the low water-level conditions of July 1, 

2004, when the stream had stopped flowing, and the stream 

stage and adjacent water-table were low (fig. 23A). However, peak streamflows occurring while the water table was 

low probably resulted in recharge to the surficial aquifer. For 

example, around August 10, 2004, stream stage rose higher 

than the adjacent water table and flooded wells near the stream 

channel. The stage peaked at even higher elevations during the 

next 2 months, flooding monitoring wells and recharging the 

surficial aquifer (fig. 25A). 
Hydrogeologic Framework of the Charlie Creek Basin    39

At the downstream transect, groundwater flow was 

characterized by upward flow in the surficial aquifer near the 

stream and fairly steep lateral gradients toward the stream 

(fig. 24). The water table consistently sloped toward the stream 

during all observations, with steeper slopes on the south bank 

of the river. Both lateral and vertical head gradients were lowest at high stream stage, but were still toward the stream. The 

highest lateral and vertical gradients were on September 22, 

2005, following the end of the rainy season, when the stream 

stage receded much faster than the adjacent water table. 

The upward flow potential from the intermediate aquifer 

system also tended to be greater at the downstream transect 

compared with the upstream transect. When the potentiometric 

head of the intermediate aquifer system was near the seasonal 

low on July 1, 2004, the head at the downstream transect was 

about 19 ft higher than the stream stage (fig. 24A). When the 

potentiometric head was near its highest level on October 28, 

45.07

45.17 45.39 45.40

45.20 45.41

45.60

45.62

Deeper intermediate aquifer system head approximately 51 feet

and Upper Floridan aquifer head approximately 49 feet.

Well 42

Surficial aquifer system

Approximate top of intermediate aquifer system (Peace River Formation)

Well 41

Well 40

Well 38 (deep)

Well 39 (shallow)

Well 37 (shallow)

Well 36 (deep)

Well 35

50.71

50.82 n/d

51.43

50.87

50.73

50.22

50.22

Water table

Surficial aquifer system

Approximate top of intermediate aquifer system (Peace River Formation)

Well 42

Well 41

Well 40

Well 38 (deep)

Well 39 (shallow)

Well 37 (shallow)

Well 36 (deep)

Well 35

Deeper intermediate aquifer system head and

Upper Floridan aquifer head approximately 67 feet.

Water table

West East

ELEVATION, IN FEET ABOVE NGVD 1929

A

West East

B

20

30

40

50

60

70

80

10

0 100 200 300 400 500

HORIZONTAL DISTANCE, IN FEET

20

30

40

50

60

70

80

10

45.36

50.11

EXPLANATION

General direction of

groundwater flow

50.11 Surface-water level

51.43

Well 35

Water level in well

Monitoring well

and number

Figure 23. General groundwater flow direction around Charlie Creek at the upstream transect site for A, July 1, 2004, and 

B, October 28, 2004.
40    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

30.17

25.64

28.68

24.34

29.02

34.72

26.23

26.35

Well 14

Well 8

Well 11

W

W

ell 12

ell 13

34.73

30.82

32.91 33.15

36.62

30.09

36.49

28.10

Well 14

Well 8

Well 10 (deep)

Well 9 (shallow)

Well 11

Well 12

Well 13

Approximate top of intermediate aquifer system

(Peace River Formation)

Approximate top of intermediate aquifer system

(Peace River Formation)

Surficial aquifer system

Surficial aquifer system

Deeper intermediate aquifer system head and

Upper Floridan aquifer head approximately 52 feet.

Deeper intermediate aquifer system head approximately 43 feet

and Upper Floridan aquifer head approximately 41 feet.

Well 10 (deep)

Well 9 (shallow)

0

10

20

30

40

50

A

North South

0

10

20

30

40

50

B

North South

ELEVATION, IN FEET ABOVE OR BELOW NGVD 1929

60

60

70

70

-10

-10

0 100 200 300 400 500

HORIZONTAL DISTANCE, IN FEET

EXPLANATION

General direction of

groundwater flow

28.10 Surface-water level

36.62

Well 8

Water level in well

Monitoring well

and number

Figure 24. General ground-water flow direction around Charlie Creek at the downstream transect site for 

A, July 1, 2004, and B, October 28, 2004.

2004, the head in the intermediate aquifer system was about 

24 ft higher than the stream stage (fig. 24B). These were larger 

upward head differences than at the upstream transect for the 

same dates. Greater lateral and vertical head gradients at the 

more incised, downstream transect site existed throughout the 

study (fig. 25B).

Tributaries 

The three Charlie Creek tributaries also showed the 

potential to receive groundwater inflow from the surficial 

aquifer. Buckhorn Creek showed a potential to gain from, and 

lose to, the surficial aquifer. Groundwater levels measured in 

a deeper well in the surficial aquifer near the Buckhorn Creek 
Hydrogeologic Framework of the Charlie Creek Basin    41

gage consistently had a higher head than the shallow well, 

indicating upward flow in the surficial aquifer (figs. 8 and 

26A). A fairly steep upward gradient was present between 

the two surficial aquifer wells (median 0.61), with a slightly 

lower upward gradient between the deeper well and the stream 

(median 0.17). During this time, the head in the intermediate 

aquifer system near this site was higher than stream stage and 

the head in surficial wells (fig. 26A), indicating the potential 

for upward flow. Although flow potential between the wells 

was upward, the water level in the shallow surficial aquifer 

well was usually lower than the stream stage, possibly due to 

evapotranspiration from shoreline vegetation depressing the 

water table near the stream. Water levels in the shallow well 

were higher than stream stage for several months following 

the recession of peak flood flows in September 2004, probably 

due to the effects of bank storage. Water levels in the deep 

surficial aquifer well were higher than the stream stage for all 

observations except in early August of 2004 and possibly May 

2004. Measurements were not available in May 2004 to establish whether downward head conditions existed in the surficial 

aquifer, but the intermediate aquifer system head was below 

the stream stage in Buckhorn Creek, indicating the potential 

for downward flow. 

Upward flow also occurred consistently in the surficial 

aquifer near Little Charley Bowlegs Creek (fig. 26B). Like 

Buckhorn Creek, the deeper surficial aquifer well at Little 

Charley Bowlegs Creek had a greater head than the shallow 

surficial aquifer well, indicating a potential for upward flow. 

The median vertical gradient between surficial aquifer wells 

(0.052) was an order of magnitude less at this creek than at 

Buckhorn Creek, but the vertical gradient between the deep 

surficial aquifer well and the stream was similar to that for 

Surficial aquifer wells

Well 1

Well 4

Well 8

Intermediate aquifer system head

(interpolated from potentiometric maps)

Stream

Stream—daily

EXPLANATION

Surficial aquifer wells

Well 1

Well 4

Intermediate aquifer system head

(interpolated from potentiometric maps)

Stream

Stream—daily

EXPLANATION

B Downstream transect

A Upstream transect

M J J A S O N D J F M A M J J A S O N D J F

2004 2005 2006

M J J A S O N D J F M A M J J A S O N D J F

2004 2005 2006

GROUNDWATER ELEVATION OR STREAM STAGE, IN FEET ABOVE NGVD 1929

70

65

60

55

50

45

40

55

50

45

40

35

30

25

20

Figure 25. Water levels in representative wells and Charlie Creek at the A, upstream and B, downstream well-transect sites.
42    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

A Buckhorn Creek

B Little Charley Bowlegs Creek

M J J A S O N D J F M A M J J A S O N D J F

2004 2005 2006

M J J A S O N D J F M A M J J A S O N D J F

2004 2005 2006

GROUNDWATER ELEVATION OR STREAM STAGE, IN FEET ABOVE NGVD 1929

70

C Oak Creek

M J J A S O N D J F M A M J J A S O N D J F

2004 2005 2006

EXPLANATION

65

60

55

50

90

85

80

75

70

65

60

55

50

45

Surficial aquifer well water level

Deep

Shallow

Intermediate aquifer system

well water level – head in

intermediate aquifer system

interpolated from May and

September potentiometric

surface maps

Stream stage

Stream stage—daily

Land-surface elevation of wells

Figure 26. Water levels in the stream and adjacent surficial aquifer system at A, Buckhorn Creek, B, Little Charley Bowlegs Creek, and 

C, Oak Creek.
Hydrogeologic Framework of the Charlie Creek Basin    43

Buckhorn Creek (median 0.12). The water level in the shallow 

surficial aquifer well was most frequently greater than the 

stream stage, except in late June and early August 2004, when 

the water level was lower (fig. 26B). The median lateral head 

gradient between the shallow well and the stream was 0.0095, 

which is greater than at the upstream transect on Charlie 

Creek, and indicates inflow. Heads in the intermediate aquifer 

system near Little Charlie Bowlegs Creek were consistently 

higher than the stream stage and water levels in the surficial 

wells, indicating upward flow toward the surficial aquifer. 

There was only one well at Oak Creek, and, consequently, the vertical flow direction within the surficial aquifer 

could not be determined (fig. 26C). The single surficial aquifer 

well was at a depth similar to the deep wells at the other tributary sites. The vertical head gradient between the stream and 

well was about an order of magnitude lower than at the other 

sites (median 0.0095). The groundwater level was similar to 

stream stage (median difference 0.07 ft) and slightly above it 

about 80 percent of the time. Reversals in flow occurred during high stage, when stream water was probably recharging 

the surficial aquifer. The head in the intermediate aquifer system near the Oak Creek gage was below stream stage in May 

2004, and on the other three measurement dates the upward 

head difference between the intermediate aquifer system and 

stream stage was less than at the two other tributaries 

(fig. 26C). 

Reach

Reach

length

(miles)

February 18, 2005 May 26, 2005 December 29, 2005 January 23, 2006

Seepage

(ft3/s)/mi

Error

(ft3/s)/mi

Seepage

(ft3/s)/mi

Error

(ft3/s)/mi

Seepage

(ft3/s)/mi

Error

(ft3/s)/mi

Seepage

(ft3/s)/mi

Error

(ft3/s)/mi

A 1.3 0.57 0.60 -0.18 0.40 0.09 1.70 -0.37 0.70

B 3.4 0.61 0.35 0.70 0.20 -0.10 0.70 -0.13 0.30

C 1.4 0.58 0.95 1.19 0.60 1.00 1.80 0.06 0.70

D 2.3 0.40 0.74 1.16 0.60 -0.93 1.30 0.47 0.50

E 1.7 0.79 1.18 -- -- 1.34 1.90 0.51 0.80

F 4.1 0.24 0.54 11.0 0.35 0.81 0.90 0.78 0.40

A-C 6.1 0.59 0.16 0.62 0.13 0.19 0.40 -0.14 0.15

D-F 8.1 0.40 0.23 1.04 0.22 0.43 0.40 0.63 0.18

A-F 14.2 0.49 0.11 0.86 0.12 0.33 0.22 0.30 0.10

1

 No measurement made at upstream section, so combined reaches E and F.

Table 5. Seepage run results with error estimates for 2005-2006 measurement dates.

[Locations of seepage run reaches are provided in figure 7 and appendix 2. Negative values indicate seepage loss from stream. 

(ft3/s)/mi, cubic foot per second per river mile; --, data not available]

Seepage Inflow to Charlie Creek

Seepage runs quantified the groundwater inflow to 

Charlie Creek implicit in the groundwater flow patterns. 

Groundwater inflow was greater than outflow during the seepage runs, as indicated by seepage gains for all significant seepage values. May 26, 2005, was the only date when the seepage 

gains measured within five of the six river reaches were large 

enough to be interpreted discretely and without being summed 

over multiple reaches (table 5). For that date, reaches with 

the greatest seepage corresponded to areas where the intermediate aquifer system head was highest above the streambed 

(fig. 27A). Seepage inflow had to be interpreted over combined stream reaches for the other three seepage-run dates 

because otherwise seepage inflow was not significantly 

greater than the potential seepage error. 

Seepage errors for stream reaches with significant 

seepage, where the seepage rate was greater than 10 percent 

of the average streamflow in the reach, ranged from 30 to 

58 percent, with a median of 53 percent. In contrast, stream 

reaches where seepage magnitudes were less than 10 percent 

of the average streamflow had errors ranging from 100 to 

over 5,000 percent because the quantity of seepage between 

sections was small compared to streamflow. Results from 

this study indicate that the uncertainty in seepage estimates is 

potentially much higher than percentage errors associated with 

the discharge measurements alone. 
44    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Seepage quantities were consistently significant when 

the individual reaches of Charlie Creek were combined and 

considered as two larger reaches located upstream and downstream of the confluence with Oak Creek (A-C and D-F on 

fig. 7, fig. 27B and table 5). Average seepage for all four runs 

for the downstream reach (0.63 (ft3/s)/mi) was about twice that 

of the upstream reach (0.31 (ft3/s)/mi), confirming the greater 

importance of groundwater inflow along the downstream 

reach of the stream. Seepage values for the upstream reach 

(A-C) were greater than the estimated error for February and 

May 2005, but were less than the error for December 2005 

and January 2006 seepage runs, and there was a possibility of 

negative seepage (leakage) in January. The downstream reach 

(D-F) had seepage values greater than the estimated error for 

all four seepage runs, with the greatest amount of seepage in 

May 2005 [8.4 ft3/s or 1.04 (ft3/s)/mi] (fig. 27B). 

Seepage inflow was greatest when vertical and lateral 

gradients were largest in the shallow groundwater near the 

stream. These larger gradients probably resulted in more 

groundwater inflow from the surficial aquifer. Total 

seepage over the entire reach (A-F) ranged from 4.3 to 

12.2 ft3/s (table 5), with an average seepage of 7.1 ft3/s (or 

[0.50 (ft3/s)/mi]) for the four runs. Errors estimated for the 

entire reach were all less than calculated seepage, and ranged 

from 14 to 68 percent. The largest seepage inflow was on 

May 26, 2005, and the smallest was on January 23, 2006 

(fig. 27C). 

 Although seepage inflow was related to vertical and 

lateral head gradients in the surficial aquifer, the seepage rates 

measured during this study did not appear to be correlated to 

the upward head differences between the intermediate aquifer 

system and the stream channel. In fact, the smallest upward 

head difference of the four seepage runs occurred in May 

2005, coinciding with the largest measured seepage. Larger 

upward head differences would be expected to result in more 

upward flow potential from the deeper aquifer. However, the 

inability to discern any relation may be a consequence of the 

relatively high intermediate aquifer system heads during all 

four seepage runs. For example, heads at the ROMP 30 Zone 2 

well, if used as an overall index of conditions, ranged between 

49.4 and 56.4 ft for the seepage runs. Yet heads in the intermediate aquifer system at this site can be considerably lower. 

The lowest heads measured at the ROMP 30 site during the 

study were more than 13 ft lower than those measured during the seepage runs (36 ft NGVD 1929 in early June 2004), 

whereas the lowest heads on record were about 30 ft lower 

(21 ft NGVD 1929 in May 2000). Seepage runs conducted 

along Charlie Creek during periods when heads are lowest 

in the intermediate aquifer system could yield lower seepage 

inflow values, and possibly outflow values. 

Seepage inflow is an important contributor to flow in 

Charlie Creek, particularly along its lower reach. On average, 

seepage determined from the four seepage runs accounted 

for 20 percent of the total outflow from the basin (measured 

at the Charlie Creek near Gardner gage on the same date), 

and 30 percent of the average flow along the combined A-F 

Figure 27. Groundwater inflow to Charlie Creek for A, different 

stream reaches during May 2005, B, all four seepage runs for 

sections upstream and downstream of the confluence with Oak 

Creek, and C, all seepage runs for the entire stream reach.

2.0

1.5

1.0

0.5

0

-0.5

-1.0

A B C D E-F

SEEPAGE, IN CUBIC FEET PER SECOND PER RIVER MILE

11

10

9

8

7

6

5

DIFFERENCE BETWEEN HEAD IN

INTERMEDIATE AQUIFER SYSTEM AND

STREAMBED ELEVATION, IN FEET

SECTION OF SEEPAGE RUN

SEEPAGE, IN CUBIC FEET PER SECOND

1.6

1.2

0.8

0.4

0

-0.4

14

12

10

8

6

4

2

0

0.058

0.056

0.054

0.052

0.050

0.048

0.046

0.044

DATE OF SEEPAGE RUN

LATERAL GRADIENT IN SURFICIAL AQUIFER,

IN FEET

Upstream of Oak

Creek confluence

Downstream of Oak

Creek confluence

Seepage

Lateral gradient

Seepage

May 2005 head difference

A

B

C

February 18 May 26 December 29

2005

Range in error

EXPLANATION

January 23

2006

Plus

uncertainty

Minus

uncertainty
Hydrogeologic Framework of the Charlie Creek Basin    45

reach. Seepage into Charlie Creek (per river mile) measured 

during this study was greater than seepage measured during 

December 1993 for a 43-mi reach of Horse Creek, another 

tributary to the Peace River with a basin about two-thirds the 

size of Charlie Creek (table 1) (Lewelling, 1997). Total seepage into Horse Creek during the high base-flow conditions 

in December 1993 was about one quarter of the seepage into 

Charlie Creek measured in this study during periods of greatest seepage, although seepage accounted for a similar fraction 

of downstream flow for both streams. During a low base flow 

seepage run in May 1994, Horse Creek had a net loss of river 

water to groundwater (Lewelling, 1997). 

 Seepage data from previous studies in the Peace River 

basin are only roughly comparable to Charlie Creek because 

of different climate and groundwater pumping conditions 

than those during this study. Seepage inflow estimated for 

some reaches of the lower Peace River in Hardee County in 

April 1988 was 1.5 (ft3/s)/mi (Duerr and Enos, 1991), slightly 

greater than that estimated for the entire reach of Charlie 

Creek in May 2005 [(12.2 ft3/s or 0.86 (ft3/s)/mi] 

(table 5). Seepage along other reaches of the lower Peace 

River in 1988, however, was up to four times greater than 

the greatest observed seepage at Charlie Creek during this 

study. Although seepage to other streams in the Peace River 

basin varied widely in magnitude, it generally represented a 

similar fraction of downstream flow (18 to 39 percent). 

Stream Specific Conductance

Surface-water specific conductance provided an 

additional line of evidence for interpreting the flow paths 

and sources of water in Charlie Creek and its tributaries. 

Continuous specific conductance, measured at all five streamflow gages (fig. 4), varied considerably over time at each site 

and was negatively correlated with streamflow (α = 0.05). 

Specific conductance also varied considerably between stream 

sites (fig. 28A), being lowest at Little Charley Bowlegs Creek 

(median 95 μS/cm) and highest at Buckhorn and Oak Creeks 

(median 396 and 311 μS/cm, respectively). The highest value 

observed was 863 μS/cm at Oak Creek, and the lowest value 

was 60 μS/cm at Little Charley Bowlegs Creek. The specific 

conductance of Charlie Creek was between those of its tributaries, with median values increasing from 169 μS/cm at the 

upstream gage to 211 μS/cm at the downstream gage.

Differences in agricultural land use in the basin appear to 

be an important factor controlling the specific conductance of 

stream water. Little Charley Bowlegs Creek had the smallest 

percentage of citrus agriculture in its basin 

(5 percent upstream of the gage), and the lowest median 

specific conductance (fig. 28B). In contrast, Buckhorn Creek 

had the greatest percentage of citrus agriculture in its basin 

(26 percent upstream of the gage) and the highest median 

specific conductance. The percentage of citrus agriculture in 

the Charlie Creek basin overall was between these extremes at 

16 percent. 

Maximum

75 percent

Median

25 percent

Minimim

Number of observations

Charlie Creek

near Gardner

500

400

300

200

100

0

MEDIAN SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER CENTIMETER

(493) (371)

(366) (410)

(507)

0

CITRUS AGRICULTURE IN BASIN UPSTREAM OF GAGE,

IN PERCENT

Charlie Creek near Gardner

Charlie Creek near Crewsville

Little Charley Bowlegs Creek

Oak Creek

Buckhorn Creek

Charlie Creek

near Crewsville

Buckhorn

Creek

Oak Creek

Little Charley

Bowlegs Creek

5 10 15 20 25 30

900

800

700

600

500

400

300

200

100

0

AVERAGE DAILY SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER CENTIMETER

(493)

Interquartile

range

A

B

SURFACE-WATER MONITORING STATION

EXPLANATION

Figure 28. A, The range of daily values of specific conductance 

at the five streamflow stations in the Charlie Creek basin, and 

B, the relationship between the median specific conductance 

in the steams and the percent of the gaged basin in citrus 

agriculture in 2005. 
46    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Drainage from this citrus grove will eventually flow to a tributary in the Lower Charlie creek subbasin.

(Photograph by T.M. Lee, USGS.)

Specific conductance is a general estimate of dissolved 

constituents in the water. Citrus agriculture has been associated with higher concentrations of many dissolved constituents in the surficial aquifer due to applications of fertilizers, 

salts, and pesticides (Stauffer, 1991; Sacks and others, 1998). 

Whether agricultural chemicals enter streams in the Charlie Creek basin mostly through the shallow groundwater or 

through drainage ditches fed by shallow groundwater and 

runoff is not known. Shallow groundwater quality was not 

sampled for this study. During seepage runs, however, the 

specific conductance in several small streams and ditches that 

drained agricultural areas was elevated (greater than 

300 μS/cm), which is typical for agricultural runoff (app. 2).

Hydrologic Analysis of the

Charlie Creek Basin

The prominent hydrologic processes in the Charlie Creek 

basin are examined herein by comparing the magnitude of the 

water-budget components within and among the subbasins. 

Simulated streamflows are addressed first, as the ability of the 

model to accurately simulate observed streamflows can greatly 

affect the accuracy of the other model-derived water-budget 

components. The water-budget results, whether derived from 

the model or calculated, are used individually and collectively to address (1) whether hydrologic characteristics are 

distinctively different in the subbasins; (2) which physical 
Hydrologic Analysis of the Charlie Creek Basin     47

characteristics (land cover, physiography, hydrogeologic 

framework) contribute to the observed differences in streamflows; and (3) which factors in the landscape of the basin are 

most responsible for maintaining the magnitude and timing of 

the streamflow of Charlie Creek. 

Simulated Streamflow in Charlie Creek

and its Tributaries

Global mass-balance errors in the numerical simulation 

of the Charlie Creek basin were small, indicating that the 

model was numerically stable. The model-generated discrepancies between total inflows and total outflows for all subbasins evaluated were always less than 0.4 percent of the sum 

of inflows (rainfall, irrigation, and lateral flow terms). 

For the five subbasins, the model typically was able 

to accurately simulate the observed timing of streamflow 

responses to daily rainfall as well as the receding limb of 

the hydrograph between streamflow peaks (figs. 29-33). As 

expected in a watershed without significant anthropogenic 

surface-water discharges, streamflow peaks were associated 

with rainfall events. The magnitude of the simulated peak 

streamflow, however, was typically substantially less than 

observed streamflow during extreme rainfall events, most 

markedly for the three streamflow peaks following the rainfall 

from Hurricanes Charley, Frances, and Jeanne in August and 

September 2004. Underpredicting extreme events is a common shortcoming of regional scale integrated surface-water/

groundwater flow models (Refsgaard, 1997; Vázquez and others, 2002; Interflow Engineering, 2008).

Overall, the simulated streamflow was closest to the 

observed streamflow at Little Charley Bowlegs Creek, the 

only tributary with a flow-control structure (weir), followed by 

Charlie Creek at the two streamflow stations: Charlie Creek 

near Crewsville and Charlie Creek near Gardner (figs. 29, 

31, and 33). The mean error for the overall simulation period 

ranged from 7.47 ft3/s to 57.43 ft3/s, and was 15 percent or less 

of the daily average streamflow measured at the Charlie Creek 

near Crewsville, Charlie Creek near Gardner, and Little Charley Bowlegs Creek stations (table 6). The mean errors were 

a larger percentage of the daily average flow simulated at the 

two tributary gages, Buckhorn Creek near Griffins Corner and 

Oak Creek near Gardner. The mean errors for these two tributaries were small, however, relative to the peak streamflows at 

these stations. Nash-Sutcliffe statistics for the five simulated 

streamflows ranged from 0.35 to 0.80 and indicated the model 

was a better predictor of daily streamflow than mean streamflow (table 6). Streamflows predicted in Charlie Creek at the 

Crewsville and Gardner streamflow stations, and at Little 

Charley Bowlegs Creek gage, had the highest Nash-Sutcliffe 

correlation values of the five subbasins: 0.78, 0.69, and 0.80, 

respectively.

Peak flows simulated for the second and third hurricanes 

in August and September 2004 were well below observed 

values at Buckhorn Creek, which is the smallest of the three 

tributary subbasins and the tributary with the lowest daily 

average flow (fig. 30). The large peak flows followed by 

extremely low base flows typical of this basin were difficult to 

simulate. As a result, predicted flows for Buckhorn Creek had 

the lowest Nash-Sutcliffe value and the second largest mean 

error of the five subbasins (table 6). 

Overall cumulative percent errors in streamflow for the 

2003-2005 period ranged from 3.7 to 60 percent at the five 

stations, with Oak Creek having the greatest error (table 6). 

Annual cumulative percent errors varied at the five streamflow 

gages in the Charlie Creek basin, but were lowest in 2004 at 

the two streamflow gages along Charlie Creek. Large negative cumulative percent differences for the Buckhorn Creek 

near Griffins Corner gage were a result of underpredicted peak 

streamflows during the 2004 wet season. Large positive cumulative percent differences for the Oak Creek near Gardner gage 

resulted from overpredicting streamflows that were less than 

about 200 ft3/s (fig. 32). 

Comparing the simulated and observed streamflow 

distributions generally indicated that peak flow values were 

underpredicted by the model, and lesser flows were overpredicted. The simulated P10 flow value was 16 to 33 percent 

lower than the P10 value for the observed streamflows for 

all gages except Oak Creek near Gardner; for that gage, the 

model overpredicted peak flows, and the simulated P10 was 

larger than the observed P10 by 38 percent (table 7). In contrast, the model typically overpredicted the P25, P50, P75, and 

P90 for all subbasins, and the percentage differences generally 

increased as the observed percentile flow values decreased. 

The underprediction of peak events (P10 ) and overprediction 

of moderate and low flows (P25, P50, P75, and P90 ) indicates 

there was a temporal displacement in simulated runoff in the 

model. That is, water not simulated to arrive fast enough to 

contribute to the peak flow was distributed into the lower 

flow events. This result suggests the connectivity between 

surface-water features in the model may not be sufficient to 

adequately represent runoff processes for the full range of 

rainfall conditions observed in the Charlie Creek basin. In 

contrast, the model does not adequately account for processes 

in the Oak Creek basin that diminish the observed streamflow 

peak. Although model simulations generally underpredicted 

peak streamflows, the Nash-Sutcliffe statistic and cumulative streamflow comparisons indicated the model was a good 

overall predictor of hydrologic responses in the Charlie Creek 

basin. 

In this study, overland and channel roughness 

coefficients generally have the greatest direct effect on simulated streamflow because rainfall is prescribed and infiltration 

and evapotranspiration are solved for implicitly. The weighted 

roughness coefficients used in the model are effective parameters that attempt to characterize the flow resistance across 

the model cell. Decreasing the effective roughness speeds the 

arrival of runoff from the basin to the stream, increasing peak 

streamflow and shortening the duration of high flow events. 

Conversely, increasing the effective roughness of model cells 

slows the arrival of runoff from the basin, decreasing total 
48    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Observed streamflow

Simulated streamflow

1,500

1,000

500

0

0

5

10

RAINFALL, IN INCHES

STREAMFLOW,

IN CUBIC FEET PER SECOND

2003 2004 2005

J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

Figure 29. Observed and simulated streamflow at Little Charlie Bowlegs Creek near Sebring, Florida, and weekly total NEXRAD 

(Next Generation Radar) rainfall at the pixel closest to the streamflow monitoring station, 2003 to 2005.

Observed streamflow

Simulated streamflow

1,500

1,000

500

0

0

5

10

RAINFALL, IN INCHES

STREAMFLOW,

IN CUBIC FEET PER SECOND

2003 2004 2005

J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

Figure 30. Observed and simulated streamflow at Buckhorn Creek near Griffins Corner, Florida, and weekly total NEXRAD 

(Next Generation Radar) rainfall at the pixel closest to the streamflow monitoring station, 2003 to 2005.
Hydrologic Analysis of the Charlie Creek Basin     49

6,000

5,000

4,000

3,000

2,000

1,000

0

0

5

10

RAINFALL, IN INCHES

STREAMFLOW,

IN CUBIC FEET PER SECOND

Observed streamflow

Simulated streamflow

2003 2004 2005

J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

Figure 31. Observed and simulated streamflow at Charlie Creek near Crewsville, Florida, and weekly total NEXRAD (Next 

Generation Radar) rainfall at the pixel closest to the streamflow monitoring station, 2003 to 2005.

Observed streamflow

Simulated streamflow

1,500

1,000

500

0

0

5

10

RAINFALL, IN INCHES

STREAMFLOW,

IN CUBIC FEET PER SECOND

2003 2004 2005

J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

Figure 32. Observed and simulated streamflow at Oak Creek near Gardner, Florida, and weekly total NEXRAD (Next 

Generation Radar) rainfall at the pixel closest to the streamflow monitoring station, 2003 to 2005.
50    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Observed streamflow

Simulated streamflow

2003 2005

6,000

5,000

4,000

3,000

2,000

1,000

0

0

5

10

RAINFALL, IN INCHES

STREAMFLOW,

IN CUBIC FEET PER SECOND

2004

J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

Figure 33. Observed and simulated streamflow at Charlie Creek near Gardner, Florida, and weekly total NEXRAD (Next 

Generation Radar) rainfall at the pixel closest to the streamflow monitoring station, 2003 to 2005.

USGS streamflow station

Number of

observations

Mean

error,

(ft3/s)

Mean gaged

streamflow,

(ft3/s)

NashSutcliffe,

(-)

Cumulative percent errors

Overall 2003 2004 2005

Little Charlie Bowlegs Creek near 

Sebring

638 7.78 50.70 0.80 -15 -- -20 11

Buckhorn Creek near Griffins Corner 608 7.47 28.64 0.35 -26 -- -47 4.3

Charlie Creek near Crewsville 638 -10.39 277.71 0.78 3.7 -- -4.6 11

Oak Creek near Gardner 638 -51.98 85.83 0.65 60 -- 44 75

Charlie Creek near Gardner 1186 57.43 492.47 0.69 -9.8 -43 -1.5 15

Table 6. Summary calibration statistics for the simulated streamflows at five streamflow stations in the Charlie Creek basin. 

[--, no value; ft3/s, cubic foot per second; (-), dimensionless] 

and peak streamflow but prolonging the duration of high flow 

events. Roughness coefficients used in the model are representative of land-use/land cover types in the basin and the stream 

characteristics.

Measurements of runoff from smaller areas of the Charlie 

Creek basin that have a uniform land use/land cover also 

would improve the ability to develop effective overland and 

stream roughness coefficients and to simulate streamflow 

in the model. For example, Variano and others (2009) used 

the tracer sulfur hexafluoride to evaluate surface-water flow 

dynamics and develop site-specific roughness coefficients at 

two sites in the Everglades. Results of this study indicated 

roughness coefficients in the study area exceeded typical 

overland values (for example, Chow (1959)).

Simulated streamflows probably also were affected by 

not modeling the flow in selected small channels carrying the 

spillover from wetlands and other depressional features across 

the landscape to the larger stream channels. These smaller 

stream features are not explicitly represented in the model 

using a 300 ft grid resolution, but are hypothesized to be 
Hydrologic Analysis of the Charlie Creek Basin     51

Streamflow

station name

P10

observed

flow

(ft3/s)

Simulated

P10 error

(%)

P25

observed

flow

(ft3/s)

Simulated

P25 error

(%)

P50

observed

flow

(ft3/s)

Simulated

P50 error

(%)

P75

observed

flow

(ft3/s)

Simulated

P75 error

(%)

P90

observed

flow

(ft3/s)

Simulated

P90 error

(%)

Little Charlie Bowlegs 

Creek near Sebring

147 -16 59 15 19 -8.4 7.6 -55 0.62 -73

Buckhorn Creek near 

Griffins Corner

79 -20 17 60 2.7 120 0.51 -41 0.06 -52

Charlie Creek near 

Crewsville

847 -18 294 42 76 120 17 310 0.39 7,900

Oak Creek near Gardner 248 38 68 150 22 210 7 420 3.2 550

Charlie Creek near 

Gardner

1,660 -33 524 -2.5 137 63 48 160 22 300

Table 7. Observed percentile-flow values and the error in the simulated percentile-flow values for the five streamflow stations in 

the Charlie Creek basin. 

[Error computed as ((simulated-observed)/observed); negative errors indicate simulated flow values were less than observed flow values; ft3/s, cubic foot per 

second; %, percent]

important factors affecting the total and peak downstream flow 

during high-intensity events. In the current model, the effect 

of flow in small stream channels on the runoff from a model 

cell has been represented in the effective overland roughness 

coefficients. Measuring the magnitude of streamflow in these 

small channels during high-intensity events would improve the 

ability to calibrate effective overland roughness coefficients 

and simulate streamflow in the model.

Basin and Subbasin Water Budgets

Basin and subbasin water budget components were evaluated using both model-derived fluxes from the MIKE SHE 

simulation of streamflow in the basin and calculated waterbudget components. The modeling results quantified components of the water budget that could not be directly measured, 

focusing on groundwater exchange between the surficial 

aquifer and deeper aquifers, exchange between groundwater 

and streams, and the volume of surface water stored in topographic depressions in the terrain (table 8). Four categories 

of water-budget components were then compared between 

subbasins: the climate-driven fluxes of rainfall and evapotranspiration, surface water stored overland in topographic depressions in the landscape, groundwater exchanges, and observed 

streamflow. 

Rainfall and Evapotranspiration 

Differences between Subbasins

Rainfall and evapotranspiration were the two largest 

water-budget components in the Charlie Creek basin, and 

differences between subbasins in the amount of rainfall 

received were generally greatest over shorter time periods. 

Weekly rainfall totals differed by as much as 40 percent 

between subbasins, whereas the largest annual difference in 

rainfall between subbasins (6.47 in. in 2003) (table 8), was 

only 15 percent of the basin-wide annual rainfall. 

Subbasin differences in annual rainfall were considerably less 

in the following years, equaling 3 percent and 6 percent of 

the basin-wide total in 2004 and 2005, respectively. For the 

week with the greatest amount of rainfall (Sept. 1-7, 2004), the 

cumulative rainfall at individual 2 × 2-km (1.24 × 1.24-mi.) 

pixels ranged from about 3.3 to 9.5 in. (fig. 34A), whereas the 

spatially-averaged rainfall for the 5 subbasins ranged from 

5.10 to 7.23 in. A difference in the subbasin rainfall of 2 in. 

or more in a week should affect the magnitude of streamflow 

generated by subbasins. This temporal variability in rainfall 

may average out over the year and exert a comparable effect 

on the capacity of subbasins to generate annual streamflow. 

Annual rainfall totals for the five subbasins ranged from 

55.23 to 57.43 in. for 2004, and from 58.53 to 62.09 in. for 

2005 (table 8). Over the annual time period, however, the total 

rainfall at individual pixels varied from about 48 to 65 in. 

(fig. 34B).

Differences in the spatially-averaged rainfall rates 

decreased for larger subbasin areas. For the upper half of the 

Charlie Creek basin, for example, the spatially-averaged rainfall was 56.68 in. for 2004, of which 42.36 in. occurred during 

the wet season between July and December 2004. Average 

rainfall for the lower half of the Charlie Creek basin was about 

2 percent less during 2004 and totaled 55.33 in., with 38.77 in. 

occurring in the wet season. 

Differences in evapotranspiration between subbasins 

were much less than rainfall. Potential evapotranspiration rates 

increased southward across the Charlie Creek basin by a little 
52    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida Basin or subbasin Rain- fall ET Overland boundary flow Runoff Irriga- tion Lateral ground- water flow Surficial aquifer exchange with UFA Surficial aquifer exchange with creeks Canopy/ overland storage change Sub- surface storage change Error Stream- flow Runoff and base flow Stream storage change 2003 Little Charlie Bowlegs Creek near Sebring 41.88 -38.16 -0.59 -3.60 1.54 -0.12 -1.20 -3.42 1.48 1.99 -0.19 -4.18 -7.02 2.84 Buckhorn Creek near Griffins Corner 41.62 -35.16 -2.69 -1.32 5.68 -0.05 -0.78 -10.43 0.95 1.97 -0.22 -5.69 -11.74 6.06 Charlie Creek near Crewsville 40.87 -37.01 0.20 -4.99 2.83 0.01 -0.63 -5.64 1.94 2.23 -0.19 -9.90 -10.63 0.73 Oak Creek near Gardner 44.86 -36.46 0.14 -4.49 3.48 0.03 -1.22 -7.99 0.86 0.61 -0.18 -15.52 -12.48 -3.04 Charlie Creek near Gardner 47.34 -36.44 -0.06 -6.15 3.14 0.03 -0.73 -8.92 0.85 0.72 -0.23 -17.91 -15.07 -2.85 Total 43.20 -36.83 -0.12 -4.76 3.01 0.00 -0.85 -6.76 1.38 1.54 -0.20 -11.73 -11.52 -0.21 2004 Little Charlie Bowlegs Creek near Sebring 55.62 -38.24 -1.88 -9.45 1.60 -0.12 -1.21 -3.89 -0.90 -1.39 0.15 -10.52 -13.34 2.82 Buckhorn Creek near Griffins Corner 57.43 -35.78 -5.46 -4.32 5.86 -0.05 -0.79 -13.74 -1.29 -1.73 0.13 -11.99 -18.06 6.07 Charlie Creek near Crewsville 56.93 -37.04 0.14 -12.08 2.92 0.01 -0.59 -6.99 -1.22 -1.92 0.18 -17.91 -19.07 1.15 Oak Creek near Gardner 55.23 -37.24 0.10 -10.30 3.59 0.03 -1.27 -9.14 -0.29 -0.65 0.06 -23.07 -19.44 -3.63 Charlie Creek near Gardner 55.40 -37.40 -0.01 -9.86 3.25 0.03 -0.74 -9.41 -0.53 -0.62 0.10 -22.61 -19.28 -3.33 Total 56.12 -37.25 -0.46 -10.50 3.11 0.00 -0.85 -7.88 -0.85 -1.31 0.13 -18.64 -18.38 -0.26 2005 Little Charlie Bowlegs Creek near Sebring 59.07 -39.84 -2.73 -12.45 1.56 -0.14 -1.27 -4.99 0.48 0.23 -0.08 -13.87 -17.45 3.58 Buckhorn Creek near Griffins Corner 58.53 -36.89 -7.96 -3.88 5.58 -0.07 -0.73 -15.91 0.47 0.75 -0.11 -16.16 -19.79 3.63 Charlie Creek near Crewsville 61.03 -38.57 0.49 -17.03 2.84 0.01 -0.59 -9.02 0.41 0.34 -0.10 -23.90 -26.05 2.15 Oak Creek near Gardner 60.54 -38.11 -0.04 -13.09 3.54 0.05 -1.32 -12.05 0.08 0.34 -0.05 -29.58 -25.14 -4.44 Charlie Creek near Gardner 62.09 -38.25 0.09 -14.13 3.22 0.03 -0.76 -12.62 0.00 0.24 -0.09 -30.66 -26.75 -3.91 Total 60.76 -38.49 -0.57 -14.33 3.04 0.00 -0.87 -10.22 0.27 0.33 -0.09 -24.73 -24.55 -0.18 2003 - 2005 Little Charlie Bowlegs Creek near Sebring 52.19 -38.75 -1.73 -8.50 1.57 -0.12 -1.23 -4.10 0.36 0.28 -0.04 -9.52 -12.60 3.08 Buckhorn Creek near Griffins Corner 52.52 -35.95 -5.37 -3.17 5.71 -0.06 -0.77 -13.36 0.04 0.33 -0.06 -11.28 -16.53 5.25 Charlie Creek near Crewsville 52.94 -37.54 0.28 -11.37 2.86 0.01 -0.60 -7.21 0.38 0.22 -0.04 -17.24 -18.58 1.34 Oak Creek near Gardner 53.54 -37.27 0.07 -9.30 3.54 0.03 -1.27 -9.72 0.22 0.10 -0.06 -22.72 -19.02 -3.70 Charlie Creek near Gardner 54.94 -37.36 0.01 -10.05 3.20 0.03 -0.74 -10.32 0.10 0.11 -0.07 -23.73 -20.36 -3.36 Total 53.36 -37.52 -0.39 -9.86 3.05 0.00 -0.86 -8.29 0.27 0.19 -0.05 -18.37 -18.15 -0.22 Table 8. Simulated water-budget components for the Charlie Creek subbasins for 2003-2005. [All values are shown in inches per year. ET, evapotranspiration; UFA, Upper Floridan aquifer]
Hydrologic Analysis of the Charlie Creek Basin     53

Charlie Creek basin Charlie Creek basin

Bereah

Gardner

Avon

Park

Zolfo

Springs

Bereah

Gardner

Avon

Park

Zolfo

Springs

A September 1-7, 2004

27°40'

35'

30'

25'

20'

27°15'

27°40'

35'

30'

25'

20'

27°15'

81°50' 45' 40' 35' 81°30' 81°50' 45' 40' 35' 81°30'

0 5 MILES

0 5 KILOMETERS

0 5 MILES

0 5 KILOMETERS

NEXRAD rainfall, in inches

Subbasin boundary

Surface-water feature

Streamflow monitoring

station

3.26 - 4

>4 - 5

>5 - 6

>6 - 7

>7 - 8

>8 - 9

>9 - 9.46

EXPLANATION

NEXRAD rainfall, in inches

Subbasin boundary

Surface-water feature

Streamflow monitoring

station

48.04 - 51

>51 - 54

>54 - 57

>57 - 60

>60 - 63

>63 - 65.31

EXPLANATION

B Calendar year 2004

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Figure 34. NEXRAD (Next Generation Radar) rainfall totals in the Charlie Creek basin for A, the week with the greatest rainfall in 

2004 (Sept. 1-7), and B, the 2004 calendar year.

over an inch due to the increase in available solar energy 

with decreasing latitude (fig. 35A). Simulated evapotranspiration had far greater spatial variability than potential 

evapotranspiration, however, because its rates were determined by land use/land cover across the basin and vegetationspecific parameters (fig. 35B; app. 3).

The upper basin had slightly greater simulated evapotranspiration rates than the lower basin because it contained a 

greater proportion of wetlands and open water land 

use/land cover types (22 percent) than the lower basin 

(18 percent) (table 2). For example, the median, spatiallyaveraged, simulated evapotranspiration rate was slightly 

higher (0.71 in/wk) in the upper half of the basin than in the 

lower half (0.69 in/wk). Simulated evapotranspiration rates 

in the subbasins composing the lower basin were slightly less 

variable overall than the upper half (fig. 36). Average simulated evapotranspiration rates were highest for the land use/

land cover classifications that define wetlands and open water 

(53.1 in/yr), and row crops (46.8 in/yr). The remaining 

land use/land cover classifications in the basin result in 

simulated evapotranspiration rates that ranged from 29.7 to 

35.7 in/yr during 2003-2005 (table 9). Year-to-year differences 

in evapotranspiration rates were higher for the wetlands and 

open water (3.55 in/yr) and row crops (7.25 in/yr) landuse/

land cover classifications (table 9). 

Wetland Water-Storage Differences 

between Subbasins

Although the overall topography in the basin directed 

runoff toward Charlie Creek and its tributaries, isolated 

wetlands and other naturally occurring topographic depressions intercepted and stored runoff overland in the landscape, 

removing it from the cumulative streamflow. Each of the subbasins to Charlie Creek stored overland water, and the area of 

the basin covered with water varied substantially from the dry 

season to the wet season (fig. 37). The amount of water stored 

above land surface at any given time was simulated in the 

MIKE SHE model by routing the inflows and outflows across 

each model cell and storing accumulated water as standing 

water above the model cell when inflows exceeded outflows. 
54    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Charlie Creek basin Charlie Creek basin

Bereah

Gardner

Avon

Park

Zolfo

Springs

Bereah

Gardner

Avon

Park

Zolfo

Springs

A B

27°40'

35'

30'

25'

20'

27°15'

27°40'

35'

30'

25'

20'

27°15'

81°50' 45' 40' 35' 81°30' 81°50' 45' 40' 35' 81°30'

0 5 MILES

0 5 KILOMETERS

0 5 MILES

0 5 KILOMETERS

Subbasin boundary

Surface-water feature

Streamflow monitoring

station

Potential evapotranspiration

for 2004, in inches

High 52.12

Low 50.83

EXPLANATION

Subbasin boundary

Surface-water feature

Streamflow monitoring

station

Simulated evapotranspiration

for 2004, in inches

High 57.38

Low 16.33

EXPLANATION

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Figure 35. Annual A, potential evapotranspiration and B, simulated evapotranspiration in the Charlie Creek basin for 2004.

General land use/

land cover

classification

2003 2004 2005 Average

Wetlands and 

open water

52.0 51.8 55.4 53.1

Upland forest 34.7 35.6 35.6 35.3

Pasture and 

rangeland

34.6 35.1 35.7 35.1

Citrus 29.9 30.9 31.0 30.6

Row crops 43.8 45.5 51.1 46.8

Urban 30.9 29.7 33.2 31.3

Average 36.8 37.3 38.5 37.5

Table 9. Simulated annual evapotranspiration rates for the land 

uses and land covers represented in the model.

[All values in inches per year]
Hydrologic Analysis of the Charlie Creek Basin     55

A tropical storm floods the pasture near the Buckhorn Creek streamflow station.

(Photograph by T.M. Lee, USGS.)

1.5

1

0.5

0

Upper half of

Charlie Creek Basin

Lower half of

Charlie Creek Basin

Little Charley Bowlegs

Creek Subbasin

Buckhorn

Creek Subbasin

Upper Charlie

Creek Subbasin

Oak Creek Subbasin

Lower Charlie

Creek Subbasin

EXPLANATION

Outlier

90th percentile

75th percentile

50th percentile

25th percentile

10th percentile

Interquartile

range

SIMULATED WEEKLY

EVAPOTRANSPIRATION, IN INCHES

Figure 36. Simulated range of weekly evapotranspiration rates 

for the five subbasins and for the upper and lower halves of the 

Charlie Creek basin from October 2002 through December 2005.

Surface-water flow into model cells representing local landsurface depressions is one process that results in surface-water 

storage. The standing water depth can increase until it rises 

higher than an adjacent model cell.

 Areas of the basin having the greatest standing water 

depths generally corresponded to areas with a land use/land 

cover classification of forested and non-forested wetlands or 

open water (figs. 5 and 37). For September 8, 2004, a day 

following Hurricane Frances and during the week with the 

greatest rainfall during the 2004 wet season, the maximum 

water depth simulated in the model was about 14 ft, with about 

21.9 percent of the upper half of the basin and 16.2 percent of 

the lower half of the basin predicted to have standing water 

depths of more than 1.0 ft (fig. 37B). Nearly two-thirds of 

this area was classified as wetlands. In contrast, for the week 

that had the most rainfall during the dry season of 2004, 

6.1 percent of the upper basin and 3.9 percent of the lower 

basin had water stored above land surface. The majority of this 

water (75 percent) was stored in wetlands (fig. 37A).

The volume of water stored daily within each subbasin 

was expressed as an equivalent water depth over the subbasin area (fig. 38). The Upper Charlie Creek subbasin stored 

a greater volume of water per unit area of basin than any other 

subbasin. The Upper Charlie Creek and Little Charlie Bowlegs 

subbasins both consistently stored more water per unit area 

than the other three subbasins, and Buckhorn Creek and Oak 

Creek stored the least. Overall, substantially more water was 

stored in the upper half of the Charlie Creek basin per unit 

area than in the lower half. 
56    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Oak Creek

Little

Creek

Bowlegs

Charley

Buckhorn

Creek

Oak Creek

Little

Creek

Bowlegs

Charley

Buckhorn

Creek

Bereah

Gardner

Avon

Park

Zolfo

Springs

Bereah

Gardner

Avon

Park

Zolfo

Springs

B September 8, 2004 Wet Season

81°50' 45' 40' 35' 81°30'

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Charlie Creek basin

EXPLANATION

Subbasin boundary

Surface-water feature

Streamflow monitoring

station

0 - 1

>1 - 3

>3 - 5

>5 - 7

>7 - 9

>9 - 11

>11 - 13

Overland water depth, in feet

A May 4, 2004 Dry Season

27°40'

35'

30'

25'

20'

27°15'

81°50' 45' 40' 35' 81°30'

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

Charlie Creek basin

0 5 MILES

0 5 KILOMETERS

27°40'

35'

30'

25'

20'

27°15'

Figure 37. Simulated depths for water stored above the land surface in the Charlie Creek basin for A, May 4, 2004, and 

B, September 8, 2004.

The wetlands and landscape depressions that store water 

in the Charlie Creek basin are shown more clearly on a 5-ft 

LIDAR DEM than on the digital elevation model used in 

MIKE SHE, which resampled the original LIDAR data to 

a 300-ft horizontal resolution (fig. 39). The higher resolution reveals the shallow swales and channels that convey the 

outflow from the filled wetland depressions to the streams. 

Some of these channels have been ditched to accelerate the 

drying out of wetlands, while other channels have remained 

undeveloped. Whereas the larger horizontal dimension used 

in the model preserves the physical function of many of the 

wetland depressions, it may not account for small-scale drainage features that convey water from the wetlands to Charlie 

Creek and its tributaries. In this study, using the 5-ft resolution 

data in MIKE SHE made model simulation times unacceptably long, although the approach should be suitable to much 

smaller basins.

During extremely wet conditions, the water flowing 

from the surface depressions to the stream channels may

originate 0.5 mi or more from the stream (fig. 39). This 

connectivity would accelerate the delivery of runoff from the 

basin to the stream, increasing the peak streamflow 

generated by the basin. These channels represent the firstorder streams in the Charlie Creek watershed that, by definition, have no other streams feeding into them, thus representing the headwaters where flow originates. In MIKE SHE, and 

most regional-scale watershed models, lower order conveyance features are not explicitly represented. Instead, the part 

of the cell typically contributing runoff to adjacent cells, and 

ultimately to downstream creek segments, is assigned effective parameters that represent weighted roughness coefficients 

characteristic of the flow resistance. Because extremely highintensity events are relatively infrequent, effective parameters 

developed for long-term simulations generally undersimulate 

peak flow events. 
Hydrologic Analysis of the Charlie Creek Basin     57

Small channels carry flow from wetlands into Charlie Creek.

(Photographs by T.M. Lee, USGS.)

Groundwater Flow Differences 

between Subbasins

The simulated groundwater exchange between the 

surficial and Upper Floridan aquifers varied by subbasin 

and season (fig. 40). Areas of the basin with upward groundwater discharge resembled the areas where artesian head 

conditions were mapped in the Upper Floridan aquifer 

(fig. 21B). Downward recharge from the surficial aquifer to 

the Upper Floridan aquifer was the predominant groundwater 

flow process simulated within the Charlie Creek watershed 

during this study, occurring over 80 to 91 percent of the total 

basin (table 10). The area of recharge and the total recharge 

volume (8,907 ac-ft) were greatest during the first half of 2004 

(January-June), when the downward head differences between 

the surficial aquifer and the Upper Floridan aquifer were greatest. The potentiometric level of the Upper Floridan aquifer 

rose following the hurricanes in August and September 2004, 

and recharge during the second half of 2004 (July-December) 

decreased to its lowest level during the study (6,659 ac-ft). 

The recharge volume increased moderately to 7,796 ac-ft 

during the first half of 2005 and did not change substantially 

during the second half of 2005 (table 10). 

EXPLANATION

Outlier

90th percentile

75th percentile

50th percentile

25th percentile

10th percentile

Interquartile

range

10

9

8

7

6

5

4

3

2

1

0

Upper half of

Charlie Creek basin

Lower half of

Charlie Creek basin

Little Charley Bowlegs

Creek Subbasin

Buckhorn

Creek Subbasin

Upper Charlie

Creek Subbasin

Oak Creek Subbasin

Lower Charlie

Creek Subbasin

SIMULATED AVERAGE OVERLAND

WATER DEPTH, IN INCHES

Figure 38. Simulated range in the spatially-averaged, daily 

water depth stored above land surface for the five subbasins, 

and for the upper and lower halves of the Charlie Creek basin, 

from October 2002 through December 2005.
58    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

In the second half of 2004, as areas of the basin with 

downward recharge became areas with upward discharge, the 

magnitude of discharge changed by a greater percentage than 

the amount of land area converted. The area of groundwater 

discharge more than doubled in the second half of 2004, from 

9 percent to nearly 20 percent of the basin, however the 

magnitude of groundwater discharge more than tripled, from 

169 to 532 ac-ft (figs. 40A and B; table 10). During the 

first half of 2005, when the area of discharge decreased by 

about 30 percent, the discharge volume declined by about 

40 percent. 

0 1 KILOMETER

0 1 MILE

EXPLANATION

Elevation, in feet

above NGVD 1929

High : 91.68

Low : 55.71

 ̄

MANMADE CHANNELS

TOPOGRAPHIC

DEPRESSIONS

AND WETLANDS

NATURAL

CHANNELS

Figure 39. Microtopographic features in the upper part of the Charlie Creek basin, including wetlands and 

shallow topographic depressions and the surface channels connecting them to streams.

The largest areas of simulated upward flow from the 

Upper Floridan aquifer to the surficial aquifer were in the 

Upper Charlie Creek subbasin where water flows upward 

below the creek, and below the network of topographic 

depressions, wetlands, and first-order streams described in the 

previous section (fig. 40). Upward discharge also occurred 

over smaller areas in the three tributary subbasins, occurring 

near the confluence of Buckhorn Creek with Charlie Creek 

during the wet season of 2004 and in 2005 (fig. 40B and D). 
Hydrologic Analysis of the Charlie Creek Basin     59

Charlie Creek

basin

Charlie Creek

basin

Charlie Creek

basin

Charlie Creek

basin

Bereah

Gardner

Avon

Park

Zolfo

Springs

Bereah

Gardner

Avon

Park

Zolfo

Springs

Bereah

Gardner

Avon

Park

Zolfo

Springs

Bereah

Gardner

Avon

Park

Zolfo

Springs

A January - June 2004 B July - December 2004

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985

Albers NAD projection 1983

0 5 MILES

0 5 KILOMETERS

EXPLANATION

# Stream gage

Surface-water feature

Subbasin boundary

C January - June 2005 D July - December 2005

N N

N N

-0.40 to >-0.45

-0.35 to >-0.40

-0.30 to >-0.35

Groundwater flux, in inches

-0.25 to >-0.30

-0.20 to >-0.25

-0.15 to >-0.20

-0.10 to >-0.15

-0.05 to >-0.10

0 to >-0.05

Buckhorn

Creek

Cha

Oak Creek rlie Creek

Little

Charley

Bowlegs

Creek

Charlie Creek

Buckhorn

Creek

Oak Creek

Little

Charley

Buckhorn

Creek

Oak Creek

Little

Charley

Charlie Creek

Buckhorn

Creek

Oak Creek

Little

Charley

Bowlegs

Creek

Bowlegs

Creek

Bowlegs

Creek

Charlie Creek

Charlie Creek

Charlie Creek

Charlie Creek

Charlie Creek

Figure 40. Simulated cumulative groundwater flux from the Upper Floridan aquifer to the surficial aquifer for A,

January through June 2004, B, July through December 2004, C, January through June 2005, and D, July through 

December 2005.
60    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Table 10. Simulated percentage of the Charlie Creek basin 

where the surficial aquifer is recharging downward or receiving 

upward groundwater discharge, and the groundwater volumes 

for 6-month periods in 2004 and 2005. 

[ac-ft, acre-feet; %, percent] 

Period

Percentage of Charlie

Creek Basin Volume , ac-ft

Downward

(Recharge)

(%)

Upward

(Discharge)

(%)

Recharge Discharge

Jan-Jun 2004 91 9 8,907 169

Jul-Dec 2004 80 20 6,659 532

Jan-Jun 2005 86 14 7,796 322

Jul-Dec 2005 86 14 8,048 351

This same transition to wetter conditions expanded the area 

of upward discharge in the Little Charley Bowlegs 

subbasin. Upward discharge was negligible beneath the Oak 

Creek subbasin, even during the wet season of 2004. 

Groundwater discharge conditions changed the most in the 

Lower Charlie Creek subbasin. 

Overall, upward groundwater discharge into the surficial 

aquifer was more extensive in the upper half of the basin than 

in the lower half (fig. 40; table 10). During the high groundwater conditions between July and December 2004, discharge 

from the Upper Floridan aquifer was simulated in 25 percent 

of the upper basin and only 10 percent of the lower basin. 

Similarly, during low water conditions from January to June 

of 2004 and 2005, upward discharge from the Upper Floridan 

aquifer was simulated in 12.5 and 18 percent of the upper half 

of the basin, but only 2 and 6 percent of the lower half of the 

basin, respectively. 

Using the higher potentiometric surface of the 

intermediate aquifer system as the boundary condition to 

the model should both expand the area of upward flow and 

increase the upward discharge rates in the basin compared 

to areas delineated by the Upper Floridan aquifer heads. 

The surficial aquifer that interacts with streams in the Charlie Creek basin also receives water from the intermediate 

aquifer system, which had a potentiometric surface more 

than 5 ft higher than the Upper Floridan aquifer in much of 

the northern and eastern basin during the study (fig. 17). At 

present, only the potentiometric surface of the Upper Floridan aquifer is routinely mapped to compare past and present 

hydrologic conditions in the Charlie Creek basin. For this 

reason, head conditions in the Upper Floridan aquifer were 

used in the MIKE SHE model. As a result, the model probably 

simulates comparatively less upward flow into the surficial 

aquifer than it would if intermediate aquifer system heads 

were used. Upward potential for flow from the intermediate 

aquifer system covered approximately 50 percent more area 

in the upper half of the Charlie Creek basin in September of 

2004, and over three times more area in May 2004, than areas 

inferred from Upper Floridan aquifer heads (table 2). 

In the headwater regions of Charlie Creek and its 

tributaries, artesian head conditions in the intermediate aquifer 

system may be more important in preventing downward flow 

than generating upward flow. By preventing downward leakage, artesian head conditions maintain water in the surficial 

aquifer, elevating the water table. This, in turn, maintains 

water in wetlands, increasing the frequency of spillover 

from wetlands into first-order streams. Elevated water-table 

conditions also increase the potential for groundwater in the 

surficial aquifer to return to stream channels as base flow. 

Base flow contributed the majority of the total annual 

streamflow in the Charlie Creek basin whether estimated 

from observed or simulated daily streamflows (table 11). 

Base flow analysis of observed streamflow records from 1952 

to 2003 using the PART model (Rutledge, 1998) indicated that 

73 percent of the annual average daily flow at Charlie Creek 

near Gardner was base flow. On average, the mean annual 

streamflow of 10.86 in/yr (264 ft3/s) over that period included 

7.94 in/yr of base flow (table 11). Yearly base flow during 

this 52-year period ranged from 1.99 in/yr in 1981 to 

19.85 in/yr in 1998. Groundwater discharge from the 

surficial aquifer is probably the primary contributor of base 

flow to Charlie Creek. Base flow also could include gradual 

surface-water inflows from wetlands and groundwater 

discharge from the intermediate aquifer system. 

During 2005, the year with concurrent streamflow observations at all stations, base flow contributed the majority of the 

observed annual flow at all stations except Buckhorn Creek 

near Griffiths Corner (table 11). The Buckhorn Creek subbasin 

was notable for its comparatively low proportion of base flow. 

Base flow estimated from the observed streamflows using two 

techniques ranged from 37 to 44 percent of the annual total 

streamflow, making Buckhorn Creek the only tributary in the 

Charlie Creek basin dominated by runoff. Little Charley 

Bowlegs Creek had the largest base flow contribution to 

streamflow (66-81 percent of the total flow), and only 

slightly less of the total flow at Oak Creek was base flow 

(61-74 percent) (table 11). Base flow accounted for 63 to 

79 percent of the total annual flow leaving the upper half of 

the Charlie Creek basin, and a similar fraction (65-75 percent) 

of the flow exiting the basin at Charlie Creek near Gardner 

station (table 11). 

Base flows also were derived from the model-simulated 

daily flows for 2005, and contributed a comparable percentage 

of the total streamflow at the five stream gages as base flows 

computed from observed daily streamflows (table 11). However, the absolute magnitude of simulated base flow differed 

from observed amounts, particularly at the Oak Creek near 

Gardner station, due to discrepancies between simulated and 

observed streamflows. 
Hydrologic Analysis of the Charlie Creek Basin     61

Runoff and Streamflow Differences 

between Subbasins

The five subbasins yielded substantially different 

amounts of runoff, or streamflow per square mile of gaged 

area, based upon the observed streamflows during the study. 

For the 19-month period from June 2004 through December 

2005, Little Charley Bowlegs Creek subbasin generated the 

least runoff of the five subbasins (29.5 in., table 12). The result 

is consistent with more rainfall stored in depressions in this 

subbasin, which has the largest percentage area of wetlands 

and a weir controlling streamflows. Oak Creek, the tribu-

tary subbasin in the lower half of the Charlie Creek basin, 

generated the next lowest runoff value, greater than that of 

the Little Charlie Bowlegs subbasin, and less than that of the 

Upper Charlie Creek subbasin. The lower runoff from these 

three subbasins may reflect their similar depression stor-

age: 2.99 million ft

3

/mi

2

 in Oak Creek compared to 3.18 and 

3.32 million ft

3

/mi

2

, respectively, for Little Charlie Bowlegs 

subbasin and Upper Charlie Creek subbasin (table 2). Oak 

Creek subbasin also has a wetland area comparable to that of 

the Upper Charlie Creek subbasin (20 percent). Lower runoff 

from the Oak Creek subbasin compared to the Upper Charlie 

Creek subbasin may reflect more water being lost as recharge 

to deeper aquifers, as Oak Creek subbasin consistently had the 

smallest percentage area of artesian head conditions.

With the exception of the Lower Charlie Creek subbasin, 

the magnitude of measured runoff was broadly comparable 

in the other four subbasins between June 2004 and December 

2005 (29.5-39.2 in.). Runoff from the three tributary subbasins 

and Upper Charlie Creek subbasin represented roughly 

one third (28-37 percent) of the total rainfall (table 12). 

Buckhorn Creek, which had the lowest percentage of wetland 

area and the next-to-lowest depression storage of the five sub-

basins, yielded both the most runoff (39.2 in.) and the most 

efficient runoff (37 percent of the rainfall). 

The distinctively greater runoff from the Lower Charlie 

Creek subbasin compared to the other four subbasins indicates 

that there are hydrologic characteristics unique to this subbasin. Lower Charlie Creek subbasin produced approximately 

twice the runoff of the other four subbasins, and runoff was 

equivalent to 60 percent of the total rainfall (table 12). Runoff 

may have been magnified by the smaller depression storage 

in this basin, which is roughly two-thirds that of the other 

subbasins (table 2). Runoff may have been highly efficient in 

this subbasin whenever rainfall was falling on saturated land 

surfaces, or flooded areas. The Lower Charlie Creek subbasin 

has the lowest land-surface elevations, and lowest relief of the 

five subbasins (fig. 2). 

Greater streamflow generation in the Lower Charlie 

Creek subbasin also could reveal the contribution of compara-

tively greater groundwater discharge from the surficial aquifer 

and intermediate aquifer system along this more incised sec-

tion of Charlie Creek. Artesian head conditions in the inter-

mediate aquifer system increased by a greater percentage in 

this subbasin (from 3 to 25 percent) than in any other between 

USGS

streamflow monitoring

station name

Gaged

drainage

area (mi2)

Average

streamflow

(ft3/s)

Average

streamflow

(in/yr)

PART

base flow

(in/yr)

PART

base flow

index (%)

RDF

base

flow

(in/yr)

RDF base

flow

index

(%)

MIKE SHE

simulated

streamflow for

2005

(in/yr)

MIKE SHE

simulated

base flow

for 2005

(in/yr)

MIKE SHE

simulated

base flow

index

(%)

Buckhorn Creek near Griffins Corner, FL 17.4 19.8 15.5 5.7 37 6.8 44 16.2 9.0 56Little Charley Bowlegs C AB CT near Sebring, FL 42.8 49.4 15.7 12.7 81 10.3 66 13.9 10.0 72Charlie Creek near Crewsville, FL 192.3 268 19.0 14.9 79 11.9 63 21.0 15.9 76Oak Creek near Gardner, FL 65.0 80.9 16.9 12.5 74 10.3 61 29.6 20.1 68Charlie Creek near Gardner, FL 326.1 515 

(264)

21.4 

(10.9)

16.2 

(7.9)

75 

(73)

13.9 65 24.8 18.3 74

Table 11. Baseflow contributions to streamflow in the Charlie Creek basin in 2005 based on measured and simulated streamflow.[Values in parentheses are for 52 years of record (1952-2003). Baseflow estimated from measured streamflow using RDF, Recursive Digital Filter (Eckhardt, 2005) and PART computer program (Rutledge, 1998). Baseflow estimated from model simulated streamflow using RDF. mi2, square mile; in/yr, inch per year; ft3/s, cubic foot per second; %, percent]
62    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Basin or subbasin Streamflow station name

Gaged

subbasin

area

(mi2)

Average

daily discharge for

June 2004–

Dec. 2005

(ft3/s)

Total runoff

for

June 2004–

Dec. 2005

(in.)

Total rainfall for

June 2004–

Dec. 2005

(in.)

Runoff,

in

percentage of

rainfall

Buckhorn Creek subbasin Buckhorn Creek near Griffins 

Corner, FL

17.4 30.2 39.2 105.9 37

Little Charlie Bowlegs Creek 

subbasin

Little Charley Bowlegs C AB CT 

near Sebring, FL

42.8 55.6 29.5 106.6 28

Upper Charlie Creek subbasin1 132.0 221 38.0 109.4 35

Upper half of Charlie Creek basin Charlie Creek near Crewsville, FL 192.3 307 36.2 NA NA

Oak Creek subbasin Oak Creek near Gardner, FL 65.0 94.5 33.0 105.8 31

Lower Charlie Creek subbasin1 68.9 191 62.9 105.7 60

Lower half of Charlie Creek basin1 133.8 286 48.4 NA NA

Charlie Creek basin Charlie Creek near Gardner, FL 326.1 592 41.2 107.3 38

1

 Runoff from the subbasin computed by difference

Table 12. Runoff from subdivided areas of the Charlie Creek basin. 

[mi2, square mile; ft3/s, cubic foot per second; in., inch; NA, not applicable]

May and September 2004 (table 2). In addition, the increased 

area was largely below and bordering the stream (figs. 21 and 

22). Carbonate rocks also were exposed in the streambed only 

in this subbasin, potentially allowing direct inflow from the 

intermediate aquifer system. However, unless upward flows 

included undocumented spring flow, or flow from uncapped 

artesian wells, it is unlikely that groundwater discharge from 

the intermediate aquifer system alone could explain the greater 

streamflow generated by this subbasin.

The greater runoff potential of the Lower Charlie Creek 

subbasin probably helps maintain the continual streamflow 

observed downstream at the Charlie Creek near Gardner station. In contrast, the entire upper half of the Charlie Creek 

basin, upstream of the Charlie Creek near Crewsville station, 

can generate no streamflow. In 3 of the 5 years between 2004 

and 2008 (including a break in the record in 2006), streamflow 

measured at the Charlie Creek near Crewsville station was 

zero from 1 to 54 days (table 13).

Hydrologic Differences between the Upper and

Lower Parts of the Charlie Creek Basin

The traits of the individual subbasins create hydrologic 

differences between the upper and lower halves of the Charlie 

Creek basin. Analysis of the simulated water budgets for all of 

2004 and for just the wet season from July to December 2004 

indicate substantial differences between the upper and lower 

halves of the Charlie Creek basin for selected water-budget 

components. Water-budget components computed for the 

entire Charlie Creek basin show that the majority of changes 

in annual rainfall, runoff, base flow, and storage took place 

during the wet season between July and December 2004 

(fig. 41). To contrast their differences, water-budget terms 

for the upper and lower halves of the basin also are shown as 

inches of departure from the basin-wide values (fig. 42).

During the wet season of 2004, the change in total water 

storage, which is dominated by the change in surface water 

storage, was greater in the upper half of the basin (1.38 in.) 

(fig. 42A) than in the overall basin, and less in the lower half 

of the basin (-1.99 in.) (fig. 42B). Evapotranspiration rates 

in the upper and lower basins were only slightly above and 

below the basin-wide average, respectively. Rainfall departures show that the upper basin received more rainfall than the 

lower basin, yet generated less base flow than the lower half, 

Year

Upper Reach

Charlie Creek near

Crewsville

Lower Reach

Charlie Creek near

Gardner

Flow,

ft3/s

Observations

(days)

Noflow

days

Flow,

ft3/s

Observations

(days)

Noflow

days

2004 290 275 54 568 366 0

2005 268 365 0 515 365 0

2006 49.3 155 0 107 365 0

2007 12.7 365 1 337 365 0

2008 73.4 363 44 146 366 0

Table 13. Average annual streamflow and the number of days 

with no flow at streamflow stations in the upper and lower reach 

of Charlie Creek.

[ft3/s, cubic foot per second] 
Hydrologic Analysis of the Charlie Creek Basin     63

59.23

37.25

10.50

7.88

2.16

60

50

40

30

20

10

0

Rainfall / Irrigation

Evapotranspirtion

Runoff

Baseflow

Storage

DEPTH, IN INCHES

41.85

17.05

10.09

5.91 7.73

60

50

40

30

20

10

0

Rainfall / Irrigation

Evapotranspirtion

Runoff

Baseflow

Storage

DEPTH, IN INCHES

A 2004 calendar year B July through December 2004

SELECTED WATER-BUDGET COMPONENTS, FOR ENTIRE CHARLIE CREEK BASIN

Figure 41. Selected water-budget components for the entire Charlie Creek basin for A, the 2004 calendar year, and B, for the wet 

season of July through December 2004.

1.66

0.17 0.26

-0.49

1.38

-2.38

-0.25 -0.37

0.70

-1.99

A Upper half of the basin 3

2

1

0

-1

-2

-3

3

2

1

0

-1

-2

-3

Rainfall / Irrigation

Evapotranspirtion

Runoff

Baseflow

Storage

Rainfall / Irrigation

Evapotranspirtion

Runoff

Baseflow

Storage

B Lower half of the basin

DIFFERENCE FROM BASIN 

AVERAGE,

IN INCHES

DIFFERENCE FROM BASIN 

AVERAGE,

IN INCHES

SELECTED WATER-BUDGET COMPONENTS, FOR CHARLIE CREEK BASIN

Figure 42. Differences between water-budget terms spatially-averaged for the entire Charlie Creek basin during the wet season in 

2004 and their spatially-averaged value in the A, upper half and B, lower half of the Charlie Creek basin for the same period.
64    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

October, 2005

1:1 slope June, 2005

Upper half of

Charlie Creek basin

Lower half of

Charlie Creek basin

October, 2005

October, 2004

October, 2004

October, 2003

June, 2003

June, 2004 June, 2005

STREAMFLOW, IN INCHES

0 10 20 30 40 50 60 70 80

0

10

20

30

40

50

60

70

80

AVAILABLE WATER, IN INCHES

Figure 43. Relationship between the cumulative daily values of 

available water and streamflow for the upper half and the lower 

half of the Charlie Creek basin.

probably due to greater surface storage of water in wetlands 

in the upper basin. Taken together, simulated overland water 

depths, vertical groundwater flow, base flow, and water budget 

results indicate differences in hydrologic response between the 

upper and lower basin. 

Graphing the cumulative simulated daily streamflow 

against the available water (the sum of rainfall and irrigation 

minus evapotranspiration) for the upper and lower basins 

highlights differences in the temporal response of runoff from 

these basins (fig. 43). Streamflow for the upper basin is the 

simulated streamflow at the Charlie Creek near Crewsville 

gage, and streamflow for the lower basin is the difference 

between streamflows simulated at the Charlie Creek near 

Gardner gage and the Charlie Creek near Crewsville gage. 

Over the simulation period from January 2003 to December 

2005, the slope of net available water to net streamflow is less 

than 1 for the upper half of the basin and approximately 1 for 

the lower half of the basin. The period from October to June is 

typically a period when stored water contributes to streamflow 

in both the upper and lower halves of the basin, making the 

slope greater than 1. The period from June to October is characterized by an initial period with a slope less than 1 (water 

going into storage or recharging the surficial aquifer) followed 

by a period with an approximate slope of 1, where available 

water generally goes directly to streamflow. The upper basin 

was generally characterized by a longer period of time with a 

slope less than 1 from June to October, especially from June to 

October 2004.

Temporal variations in overland water depths (figs. 

37 and 38), water budget results (figs. 41 and 42), and the 

comparison of available water and net streamflow (fig. 43) 

suggest that wetland storage and hydraulic connectivity 

between wetlands and tributary streams are controlling factors 

for rainfall-runoff processes for the upper half of the Charlie 

Creek basin. During the dry season, water is depleted from 

storage by evapotranspiration processes and vertical groundwater flux to the intermediate and Upper Floridan aquifers. 

During the wet season, available water initially replenishes 

depleted storage and some streamflow from areas near major 

conveyance features. As the wet season continues, wetland 

storage can reach capacity and allow runoff to be delivered 

from a large percentage of the upper basin. The lower basin 

behaves similarly during the dry season, but during the wet 

season available water is converted to net streamflow more 

quickly here than in the upper basin. During dry seasonal 

conditions, the upper half of the basin can generate little or no 

flow for days or weeks. Development that lowers groundwater 

levels in the upper half of the basin below current levels could 

increase the number of no-flow days at the Charlie Creek near 

Crewsville gage.

Although wetland storage is a controlling factor in the 

hydrology of the upper basin, streamflow from the upper half 

of the basin still accounts for approximately 40 to 50 percent 

of the annual flow discharging from the Charlie Creek basin. 

The upper basin contributed from 0 to 100 percent of the daily 

flow exiting the basin between 2004 and 2008 (fig. 44). This 

means that the overflow of water from wetlands is an important component of the Charlie Creek basin water budget, and 

an important source of streamflow to the Peace River and 

ultimately, Charlotte Harbor.
Summary and Conclusions    65

Summary and Conclusions

The Charlie Creek basin was studied to better understand 

how groundwater levels in the underlying aquifers and storage 

and overflow of water from headwater wetlands preserve the 

streamflows exiting this least-developed tributary basin of the 

Peace River watershed. The hydrogeologic framework, physical characteristics, and daily streamflow were described and 

quantified for five subbasins of the 330-square mile Charlie 

Creek basin, allowing the contribution of its headwaters area 

and tributary subbasins to be separately quantified. Streamwater specific conductance was monitored to interpret the 

concentration of dissolved minerals in streams in the basin. 

A MIKE SHE model simulation of the integrated surface- and 

groundwater flow processes in the basin was used to simulate 

daily streamflow observed over 21 months in 2004 and 2005 

at five streamflow stations, and to quantify the monthly and 

annual water budgets for the five subbasins including the 

changing amount of water stored in wetlands. 

Study results suggest that agricultural land-use practices 

have increased the specific conductance of stream water in the 

Charlie Creek basin. The specific conductance of stream water 

monitored at five stream gages was positively correlated to the 

percent of citrus land use in the area upstream of the gage. 

 Study results further indicate that mapping the potentiometric surface of groundwater in Zone 2 of the intermediate 

aquifer system is necessary to understand the hydrogeologic 

setting of Charlie Creek and the association between groundwater levels and streamflow in different parts of the basin. 

Groundwater levels in the intermediate aquifer system affect 

the groundwater exchanges that occur in the overlying surficial 

aquifer, streams, and wetlands, and therefore, are an important 

indicator of hydrologic conditions in the Charlie Creek basin. 

The potentiometric surface of the intermediate aquifer system 

was mapped over time for this study and used in geospatial 

analyses, along with refined LIDAR-based land surface elevations and the potentiometric surface of the Upper Floridan 

aquifer, to derive three new mapping products for the Charlie 

Creek basin. The maps depict (1) the vertical flow direction 

and head differences between the intermediate aquifer system 

and the Upper Floridan aquifer in the basin, (2) the changing location of artesian head conditions and recharging head 

conditions in the basin over time, and (3) the vertical distance 

of the potentiometric surface in the intermediate aquifer 

system above and below the streambed of Charlie Creek and 

its tributaries over time. 

2004 2005 2006 2007 2008

10,000

1,000

100

10

1

0.1

0.01

100

75

50

25

0

Streamflow exiting

upper half of Charlie Creek basin

Total streamflow exiting

Charlie Creek basin

DAILY STREAMFLOW,

IN CUBIC FEET PER SECOND

Percentage of total daily streamflow

from upper half of basin

YEAR

STREAMFLOW GENERATED

BY UPPER HALF OF BASIN,

IN PERCENTAGE OF

TOTAL STREAMFLOW

Figure 44. Percentage of the daily streamflow at Charlie Creek near Gardner generated by the upper half of the basin from 

January 2004 to December 2008.
66    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Downward recharge between the surficial aquifer, intermediate aquifer system, and Upper Floridan aquifer prevailed 

over most of the Charlie Creek basin. Upward groundwater 

flow from the Upper Floridan aquifer to the intermediate 

aquifer system was attributed to a higher concentration of 

wells pumping from the intermediate aquifer system in two 

areas of the basin. 

Artesian head conditions in the intermediate aquifer 

system were an important source of upward flow to the surficial aquifer in the vicinity of headwater wetlands and stream 

channels. Artesian head conditions in the intermediate aquifer 

system generally covered a larger area of the Charlie Creek 

basin than artesian conditions defined by heads in the Upper 

Floridan aquifer. The discrepancy in the size of the two areas 

was greatest when groundwater levels reached a seasonal low. 

Mapping areas of artesian head conditions helped to describe 

their location relative to streams, wetlands, stratigraphic units, 

ROMP wells, flowing wells, sinkholes, and geologic outcrops. 

Activities that lower or eliminate artesian head conditions 

in the intermediate aquifer system in the Charlie Creek basin 

have the potential to decrease the magnitude of streamflow. 

In the upper part of the basin, artesian head conditions in 

the intermediate aquifer system were consistently associated 

with wetland-dominated headwater regions of Charlie Creek 

where they generated upward flow into the surficial aquifer 

and prevented water in the surficial aquifer and wetlands from 

recharging downward. Both processes should prolong wetland 

flooding, and increase peak streamflows and total runoff by 

increasing the frequency with which water overflows wetlands 

into streams, compared to an analogous setting where the 

surficial aquifer leaks downward. The loss of artesian head 

conditions in the intermediate aquifer system in the upper part 

of the basin would be expected to reduce streamflow by lowering wetland water levels, increasing depression storage, and 

reducing the frequency with which water stored in wetlands 

spills over to streams.

In the lower half of the Charlie Creek basin, artesian head 

conditions in the intermediate aquifer system were smaller 

in area and tended to closely border the main channel of the 

creek. Charlie Creek is more deeply incised into the surficial aquifer in the lower basin than in the upper basin, and 

the streambed intercepts the top of the Peace River Formation at two locations. At these locations, fractured carbonate 

rocks crop out in the streambed and may provide preferential 

groundwater flow paths. Heads in the intermediate aquifer 

system have the potential to directly affect streamflow in these 

areas, although no conclusive evidence was found of a direct 

exchange in this study. Both outcrops are in the stream reach 

that had the largest measured seepage inflows during the May 

2005 seepage run, and base flow and seepage inflows measured during low-flow periods were greater in the lower part of 

the Charlie Creek basin than in the upper part. Artesian head 

conditions in the intermediate aquifer in the Lower Charlie 

Creek subbasin also cause slow upward movement of water 

into the surficial aquifer below the stream, raising or maintaining the water-table near the stream compared to recharging 

conditions. The Lower Charlie Creek subbasin generated 

nearly twice as much runoff as the other four subbasins of the 

Charlie Creek basin. One cause of this higher runoff efficiency 

is speculated to be rain falling on flooded or saturated land 

areas adjacent to the creek channel during peak streamflows. 

Artesian head conditions in the intermediate aquifer 

system appeared to be more vulnerable to pumping effects in 

the Lower Charlie Creek subbasin than any other subbasin 

during the study. Pumping from wells open to the intermediate aquifer system in the Lower Charlie Creek subbasin has 

the potential to reduce the magnitude and duration of artesian 

head conditions and to increase periods of recharging conditions below the stream, especially during drought years such 

as 2000. In addition, groundwater levels in the Upper Floridan 

aquifer in the Lower Charlie Creek subbasin appear to be 

subject to lowering by pumping that occurs outside and mostly 

west of the Charlie Creek basin. 

 Depression storage associated with headwater wetlands affected the hydrology of the upper half of the Charlie 

Creek basin, causing it to generate less streamflow per unit 

area and less base flow per unit area on an annual basis than 

the lower half of the basin. Periodically, during drier months 

when streamflow in the downstream reach was being sustained by base flow, the upper part of the basin generated no 

streamflow at all. Yet the upper half (57 percent) of the basin 

generated about 52 percent of the total streamflow exiting the 

Charlie Creek basin during this study. The shallow channels 

connecting wetlands to Charlie Creek are expected to deliver 

runoff faster and with greater efficiency than sheetflow across 

the land surface. The absence of features in the MIKE SHE 

model to simulate the flow in these smaller channels probably explains why the model consistently underpredicted peak 

flows during extreme events at four of the five streamflow 

stations. 

Measuring the intermittent streamflow in small 

channels draining wetland-dominated landscapes would 

improve model calibration of runoff quantities from the 

headwaters area of Charlie Creek and similar basins. The 

LIDAR-based topographic map of the Charlie Creek basin 

indicates that shallow channels can hydraulically connect 

the overflow from depressional wetlands back to the stream 

channels over distances of half a mile or more. Small channels delivering overflow from wetlands back to streams extend 

farther distances than are routinely considered when buffering 

stream channels and wetlands from upland alterations. The 

loss of wetlands and the channels connecting them to streams 

due to phosphate mining or other landscape alterations could 

decrease peak streamflows generated by the basin. 

Currently, there is a dynamic balance between wetland 

storage, rainfall-runoff processes, and groundwater-level differences in the upper basin that allow it to account for approximately half of the streamflow from the Charlie Creek basin. 

Therefore, any future development in the upper basin that 

would alter the hydraulic connectivity of wetlands during high 

flow conditions or reduce groundwater levels could substantially affect streamflow in Charlie Creek. Numerous wetlands 
Selected References    67

and stream channels have been lost due to phosphate mining 

in other areas of the Peace River watershed (Florida Department of Environmental Protection, 2007). If wetland hydraulic 

connectivity is completely lost in the upper basin of Charlie 

Creek, it is possible that streamflow from Charlie Creek to the 

Peace River would decline substantially, affecting the ability 

of the lower Peace River to meet minimum flows and levels. 

Additional groundwater withdrawals from the Upper Floridan 

aquifer to meet future water demands in this area would likely 

(1) increase water-level differences between the surficial aquifer and the Upper Floridan aquifer, (2) increase the potential 

for downward groundwater flow, (3) reduce the percentage of 

the basin where the intermediate aquifer system discharges 

upward into the surficial aquifer, and (4) decrease surficial 

aquifer groundwater levels. The model used to simulate 

surface and groundwater interactions in the Charlie Creek 

basin demonstrated the linkage between Upper Floridan 

aquifer water levels, upward groundwater discharge, base 

flow, and streamflow. 

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Appendixes    71

Appendixes
72    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida Well number Abbreviated well name Latitude (DDMMSS) Longitude (DDMMSS) Land eleva- tion, ft above NGVD of 1929 Well depth (feet) Casing depth (feet) Aquifer Measure- ment frequency

1 ROMP 26 SA well 271757 814930 75 15 10 SA continuous2 ROMP 26 Hawthorn well (Zone 2 and Zone 3 of IAS) 271757 814930 75 180 140 IAS continuous3 ROMP 26 Tampa well (Zone 3 of IAS) 271757 814930 75 430 255 IAS continuous4 ROMP 26 Avon Park well 271757 814930 75 1320 580 UFA continuous5 Amoco 2 Oil Test Well 272015 813927 94 312 -- IAS semiannual6 Brookside Bluff Trailer Park, #1 well IAS1 272211 814750 120 -- -- IAS semiannual7 Brookside Bluff Trailer Park, #2 well IAS1 272226 814737 46 12.6 8.1 SA ~monthly8 Downstream Transect well 8 272228 814737 46 18.4 13.9 SA ~monthly9 Downstream Transect well 6 272231 814738 44 20.7 16.2 SA ~monthly

10 Downstream Transect well 7 272231 814738 44 27.3 22.8 SA ~monthly

11 Downstream Transect well 4 272232 814738 30 23.65 19.15 SA ~monthly

12 Downstream Transect well 3 272234 814738 33 26.2 21.7 SA ~monthly13 Downstream Transect well 2 272236 814738 34 14.1 9.6 SA ~monthly14 Downstream Transect well 1 272242 814738 38 10.4 5.9 SA ~monthly15 Bryan Hodge IAS well1 272318 814734 50 -- -- IAS semiannual16 Paulson Residential IAS well1 272341 814521 55 -- -- IAS semiannual17 Bentley Shallow SA well 272402 813624 82 10.7 3.5 SA ~monthly18 Bentley Deep SA well 272402 813624 82 19.1 4.5 SA continuous19 Westby well 1 272423 814444 41 19 14.3 SA ~monthly20 Westby well 2 272426 814443 43 18.7 15.2 SA ~monthly21 Westby well 3 272428 814443 44 19.7 14.95 SA ~monthly22 Sunny South UFA well1 272436 814504 66 1400 -- UFA semiannual23 Hwy 634 roadside well1 272437 814642 65 241 -- IAS semiannual24 Oak Creek SA well 272442 814143 62 23 18.5 SA ~monthly25 Sebring SA well 272452 813141 94 -- -- SA continuous26 Marrls Floridan well nr Gardner 272509 814104 82 1100 -- UFA semiannual27 Messana UFA well1 272521 814406 56 1100 -- UFA semiannual28 Crewsville SA well 272538 813508 90 26 6 SA ~monthly29 Crewsville Upper Intermediate well1 272538 813508 90 115 96 IAS ~monthly

Appendix 1Table 1–1. Characteristics of wells used in the study. [DDMMSS, latitude or longitude presented with degrees as first two digits, minutes as second two digits, and seconds as last two digits; SA, surficial aquifer; IAS, intermediate aquifer system; UFA, Upper Floridan aquifer; --, data not available; ~, approximately]
Appendix 1    73

Well

number Abbreviated well name Latitude (DDMMSS) Longitude (DDMMSS)

Land elevation, ft above

NGVD of

1929

Well depth

(feet)

Casing depth

(feet) Aquifer

Measurement

frequency

30 Wilbur Robertson Hawthorn well 272715 814016 75 343 103 IAS semiannual31 ROMP 30 SA well 272728 814747 70 15 10 SA continuous32 ROMP 30 Arcadia well (Zone 2 of IAS) 272728 814747 70 180 55 IAS continuous33 ROMP 30 Tampa well (Zone 3 of IAS) 272728 814747 70 316 280 IAS continuous34 ROMP 30 Avon Park well 272728 814747 70 1266 380 UFA continuous35 Upstream Transect well 8 272729 814036 56 15.3 10.8 SA ~monthly36 Upstream Transect well 7 272730 814039 55 21.5 17 SA ~monthly37 Upstream Transect well 6 272730 814040 55 11 6.5 SA ~monthly38 Upstream Transect well 4 272730 814042 50 11.1 6.6 SA ~monthly39 Upstream Transect well 5 272730 814042 50 7 2.5 SA ~monthly40 Upstream Transect well 3 272730 814043 48 10.7 6.2 SA ~monthly41 Upstream Transect well 2 272730 814046 49 12.7 8.2 SA ~monthly42 Upstream Transect well 1 272730 814050 53 12.8 8.38 SA ~monthly43 Little Charley Bowlegs Creek Shallow SA well 272840 813329 82 10 5.5 SA ~monthly44 Little Charley Bowlegs Creek Deep SA well 272840 813329 82 25.9 21.4 SA ~monthly45 Peace River Ranch Floridan well nr Crewsville 272855 814007 76 1163 141 UFA semiannual46 Buckhorn Creek Shallow SA well 273104 813958 59 9 4.5 SA ~monthly47 Buckhorn Creek Deep SA well 273104 813958 59 18 13.5 SA ~monthly48 Stevens / Crazy Cow IAS well1 273135 813958 68 120 -- IAS semiannual49 Prescott Shallow SA well 273143 814210 90 9.7 3.5 SA ~monthly50 Prescott Deep SA well 273143 814210 90 23.4 4.5 SA continuous51 Rest Haven IAS well1 273310 814047 123 -- -- IAS semiannual52 ROMP 43 MW-1 SA well 273501 813519 98 12 2 SA ~monthly53 ROMP 43 MW-2 Upper Arcadia well (zone 2 of IAS)1 273501 813519 98 116 52 IAS ~monthly54 ROMP 43 MW-3 Lower Arcadia well (zone 3 of IAS) 273501 813519 98 233 196 IAS ~monthly55 ROMP 43 43 MW-4 Suwannee well1 273501 813519 98 464 306 UFA ~monthly56 John White Hawthorn well nr Wauchula 273555 814030 117 270 63 IAS semiannual

1 Water level only measured for 2005 potentiometric surface maps.

Table 1-1. Characteristics of wells used in the study. —Continued[DDMMSS, latitude or longitude presented with degrees as first two digits, minutes as second two digits, and seconds as last two digits; SA, surficial aquifer; IAS, intermediate aquifer system; UFA, Upper Floridan aquifer; --, data not available; ~, approximately]
74    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida Site description1 February 18, 2005 May 26, 2005 December 29, 2005 January 23, 3006 Discharge (ft3/s) Specific conductance

(mS/cm)

Discharge

(ft3/s)

Specific

conductance

(mS/cm)

Discharge

(ft3/s)

Specific

conductance

(mS/cm)

Discharge

(ft3/s)

Specific

conductance

(mS/cm)

Charlie Creek at Highway 66 Bridge 14.30 201 8.34 222 32.30 170 12.50 202Inflow downstream of Highway 66 Bridge (LEW) 0.14 -- 0.00 -- 0.47 184 0.17 --Charlie Creek on Robertson property downstream of 

HWY 66 (A)

15.20 196 8.09 222 32.89 -- 12.19 211

Inflow on D&H Ranch from Citrus Grove (LEW) 0.75 347 0.82 348 0.71 337 0.59 326Charlie Creek on Faulkner Property (D&H Ranch) (B) 18.00 -- 11.27 261 33.25 197 12.35 224Inflow across from D&H Ranch (REW) -- -- 1.89 -- 1.25 486Charlie Creek above Oak Creek (C ) 18.80 -- 12.90 287 36.52 206 13.68 252Inflow Oak Creek above Charlie Creek confluence 

(LEW)

7.57 -- 8.83 315 10.37 271 4.59 280

REW Tributary #1 downstream of Oak Creek -- -- -- -- -- -- 0.02 405REW Tributary #2 downstream of Oak Creek -- -- -- -- -- -- 0.05 430Charlie Creek at Highway 634 (D) 27.30 -- 24.40 298 44.75 220 19.42 274Inflow along Highway 634 (REW) 0.01 442 -- -- 0.26 -- 0.06 --Inflow Unnamed tributary creek north of limestone 

rapids (REW) Westby

0.12 -- 0.03 -- -- -- -- --

Inflow through Taylor Property (LEW) "Badlands Northernmost" 0.54 -- -- -- -- -- 0.50 --Inflow through Westby property (LEW) "Badlands 

Middle"

-- -- -- -- 0.78 -- 1.26 276

Fish Branch Tributary across from Paulson Property 

(LEW)

1.10 284 1.00 302 1.70 252 -- --

Charlie Creek at Paulsen Property (E) 30.43 276 -- -- 49.82 233 22.13 --Inflow on Bryan Hodge Property (REW) -- -- -- -- 0.03 -- 0.02 --Inflow just North of DOT transect wells (LEW) -- -- 0.03 -- 0.03 -- 0.02 --Charlie Creek at Hwy 17 near Gardner (F) 31.40 297 31.20 295 53.19 -- 25.32 --

1 (A), (B), (C), (D), (E), and (F) refers to the downstream measurement section for this reach.

Appendix 2 Table 2-1. Discharge and specific conductance measurements for the four seepage runs.[ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; --, no data; REW, right edge of water looking downstream; LEW, left edge of water looking downstream]
Appendixes    75

Appendix 3 

Detailed Hydrologic Modeling Methods

Hydrologic soil groups were used to assign soil properties as part of the simplified water-balance approach used to 

represent flow and evapotranspiration in the unsaturated zone 

(app. 3, table 1). Soil horizon thickness, soil moisture, and 

hydraulic conductivity data from Robbins and others (1984) 

and Carlisle and others (1988) were used to develop representative soil properties for hydrologic soil groups A, B, C, D, 

W, and B/D present in the study area. A thickness-weighted 

arithmetic mean was used to calculate representative water 

contents at the wilting point, field capacity, and saturation for 

hydrologic soil groups. A thickness-weighted harmonic mean 

was used to calculate representative saturated vertical hydraulic conductivities for hydrologic soil groups. 

The soil classes contributing to the hydrologic soil groups 

A, B, C, D, W, and B/D in the study area are described below.

• Archbold sand is the predominant soil classification 

in hydrologic soil group A, composing 34 percent of 

this hydrologic soil group, and data from Carlisle and 

others (1988) were used to develop representative soil 

parameters. 

• Hydrologic soil group B is composed solely of Jonathan sand, and data from Robbins and others (1984) 

were used to develop representative soil parameters. 

• Zolfo fine sand is the predominant soil classification 

in hydrologic soil group C, composing 41 percent of 

this hydrologic soil group, and data from Robbins and 

others (1984) were used to develop representative soil 

parameters. 

• The Bradenton-Felda-Chobee soil association is the 

predominant soil classification in hydrologic soil group 

D, composing 48 percent of this hydrologic soil group, 

and data from Carlisle and others (1988) were used to 

develop representative soil parameters. 

• Soil parameters from hydrologic soil group D were 

used for hydrologic soil group W. 

• Myakka fine sand is the predominant soil classification in hydrologic soil group B/D, composing 18 

percent of this hydrologic soil group, and data from 

Carlisle and others (1988) were used to develop 

representative soil parameters.

A sinusoidal pattern was used to assign leaf area indices and root depths for non-agricultural land use/land cover 

types throughout the year. A constant leaf area index and 

root depth was used for citrus. Spring and winter row crops 

were simulated by assigning two periods with large leaf 

area indices and root depths. Maximum crop coefficients 

for agricultural crops were assigned based on data from 

Allen and others (1998). Crop coefficients for non-forested 

wetlands, forested wetlands, and open water were adjusted 

to constrain annual evapotranspiration rates to be no greater 

than long-term evaporation rates observed at Lake Starr 

(57.29 in/yr, A. Swancar, U.S. Geological Survey, written commun., 2009). Crop coefficients for upland forests, 

pasture/open lands, rangeland, and utilities/communications 

facilities were adjusted to reflect the observed seasonal 

ratio of actual evapotranspiration to reference evapotranspiration at a pasture evapotranspiration station located 

in Pasco County, Florida (A. Swancar, U.S. Geological 

Survey, written commun., 2008) (app. 3, table 3). Irrigation was enabled for agricultural areas, with crop demand 

calculated using the crop stress factor approach that applies 

irrigation to meet daily crop-specific evapotranspiration 

rates.

Overland flow parameters that have been related to 

land use/land cover include overland roughness coefficients 

(app. 3, table 2) and separated overland flow areas. Separated overland flow areas were defined for agricultural land 

uses (citrus and row crops) to represent perimeter berms 

around farm fields used to manage surface-water discharge. 

Land use/land cover data distributed model parameters are 

comparable to parameters used in an integrated surfacewater/groundwater model developed for the upper Myakka 

River watershed (Interflow Engineering, 2008). 
76    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Hydrologic

soil group

Saturated

horizontal

hydraulic

conductivity

(ft/d)

Saturated

vertical

hydraulic

conductivity

(ft/d)

Specific

yield

( - )

Water

content

at

saturation

( - )

Water

content

at field

capacity

( - )

Water

content at

wilting

point

( - )

A 19.53 19.44 0.39 0.40 0.033 0.0082

B 20.52 3.00 0.37 0.40 0.083 0.032

C 7.43 6.55 0.38 0.40 0.065 0.017

B/D 6.58 1.50 0.35 0.39 0.13 0.040

D–W 2.13 0.17 0.25 0.38 0.23 0.13

Table 3-1. Unsaturated and saturated hydraulic properties applied to various hydrologic soil grou

represented in the model.

[ft/d, feet per day]

General land use/

land cover

classification

Overland

Mannings M1

coefficient

( - )

Minimum

leaf-area

index

(unitless)

Maximum

leaf-area

index

(unitless)

Minimum

root

depth,

(inches)

Maximum

root

depth,

(inches)

Non-forested wetlands 1.43 2 4.8 6 24

Open water 20 0 0 0 0

Upland forests 1.67 3.4 5.5 60 60

Pasture/

open lands 4.17 2 4 36 60

Rangeland 2.5 3 4.8 36 60

Citrus 5.88 4.5 4.5 60 60

Urban 6.67 1 2 24 24

Row crops 5.88 0 2.7 0 8.1

Forested wetlands 1.25 3 7 24 60

Disturbed land 10 1 1 12 12

Utilities/communications 4.17 2 4 36 60

1

 Mannings M is the reciprocal of Mannings n

Table 3-2. Manning’s roughness coefficient and vegetation parameters applied to the various types of land use

and land covers represented in the model.
Appendixes    77

General land use/

land cover

classification

Month of the year

1 2 3 4 5 6 7 8 9 10 11 12

Non-forested 

wetlands

1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1

Open water 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1

Upland forests 0.8 0.8 0.8 0.8 0.8 0.8 0.5 0.5 0.5 0.8 0.8 0.8

Pasture/open lands 0.8 0.8 0.8 0.8 0.8 0.8 0.5 0.5 0.5 0.8 0.8 0.8

Rangeland 0.8 0.8 0.8 0.8 0.8 0.8 0.5 0.5 0.5 0.8 0.8 0.8

Citrus 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

Urban 0.8 0.8 0.8 0.8 0.8 0.8 0.5 0.5 0.5 0.8 0.8 0.8

Row crops 1 1.15 1.15 1.15 1.15 1 1 1 1.15 1.15 1.15 1.15

Forested wetlands 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1

Disturbed land 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

Utilities/

communications

0.8 0.8 0.8 0.8 0.8 0.8 0.5 0.5 0.5 0.8 0.8 0.8

Table 3-3. Monthly vegetation crop coefficients applied to various types of land uses and land covers represented in the mode
78    Effect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin, West-Central Florida

Manuscript approved on August 30, 2010 by:

Sandra C. Cooper, USGS Bureau Approving Official

This project on which this publication is based was funded in part by: 

Southwest Florida Water Management District 

For more information concerning this publication contact:

Terrie M. Lee, Hydrologist, U.S. Geological Survey

The University Center for Business

10500 University Center Drive, Suite 215

Tampa, FL 33612-6427

(813) 975-8620, ext. 135

Technical reviews of this publication were provided by 

USGS scientists:

Eve L. Kuniansky, Regional Groundwater Specialist

Gary L. Mahon, Supervisory Hydrologist

Robert A. Renken, Supervisory Hydrologist

Rick M. Spechler, Hydrologist

Eric D. Swain, Hydrologist

Amy Swancar, Hydrologist

 Arturo Torres, Supervisory Hydrologist

Publishing support for this publication was provided by the 

USGS Office of Communications and Publishing,

Fort Lauderdale Publishing Service Center

Lee, T.M., Sacks, L.A., and Hughes, J.D.— —USGS/SIR 2010-5189

Printed on recycled paper

Peace River Watershed, West-Central FloridaEffect of Groundwater Levels and Headwater Wetlands on Streamflow in the Charlie Creek Basin,