U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2004-5073

Ground-Water and Surface-Water Flow and 

Estimated Water Budget for Lake Seminole, 

Southwestern Georgia and Northwestern Florida

By Melinda S. Dalton, Brent T. Aulenbach, and Lynn J. Torak

Prepared in cooperation with the

 Georgia Department of Natural Resources 

 Environmental Protection Division 

 Georgia Geologic Survey
Cover photograph: Polk Lake, Chattahoochee, Florida, 1950

 View looking east along the fixed-crest spillway during construction of Jim Woodruff Lock 

and Dam. During 2002, the U.S. Army Corps of Engineers and the U.S. Geological Survey 

participated in a dye-tracing study that found lake water moving through the ground-water 

system to the Apalachicola River via Polk Lake Spring.

Photograph by: U.S. Army Corps of Engineers, archives, Mobile District, Mobile, Alabama
Ground-Water and Surface-Water Flow and 

Estimated Water Budget for Lake Seminole, 

Southwestern Georgia and Northwestern Florida

By Melinda S. Dalton, Brent T. Aulenbach, and Lynn J. Torak

Prepared in cooperation with the

Georgia Department of Natural Resources

 Environmental Protection Division

 Georgia Geologic Survey

Scientific Investigations Report 2004-5073

U.S. Department of the Interior

U.S. Geological Survey

Atlanta, Georgia
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

This report is available on the World Wide Web at http://infotrek.er.usgs.gov/pubs/

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Dalton, Melinda S., Aulenbach, Brent T., and Torak, Lynn J., 2004, Ground-water and surface-water flow and 

estimated water budget of Lake Seminole, southwestern Georgia, and northwestern Florida, U.S. Geological Survey, 

Scientific Investigations Report 2004-5073, p. 54.
 iii

Contents

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

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

Purpose and Scope ................................................................................. 2

Study Area .......................................................................................... 4

Physiography ....................................................................................... 4

Climate ................................................................................................ 5

Previous Studies .................................................................................... 5

Well and Surface-Water-Station Numbering System .......................................... 6

Acknowledgments ................................................................................. 6

Ground Water ............................................................................................. 7

Hydrogeologic Setting .............................................................................. 8

Hydraulic Characteristics ........................................................................ 8

Overlying Semiconfining Units ............................................................... 8

Upper Floridan Aquifer ..................................................................... 9

Lisbon Formation .............................................................................. 9

Ground-Water Levels .............................................................................. 9

Seasonal Fluctuations ........................................................................ 9

Effects of Drought and Pumping ............................................................ 10

Surface-Water Influence ..................................................................... 10

Surface Water ............................................................................................. 12

Drainage ............................................................................................. 12

Streamflow .......................................................................................... 12

Dams and Navigational Improvements ......................................................... 13

Water-Budget Calculations for Lake Seminole ...................................................... 14

Precipitation ....................................................................................... 14

Surface Water ....................................................................................... 15

Ungaged Inflow to Lake Seminole ......................................................... 16

Error Analysis ................................................................................. 17

Lake Storage ....................................................................................... 17

Ground-Water Inflow and Lake Leakage ......................................................... 18

Estimation of Flow Rates ..................................................................... 18

Error Analysis ................................................................................. 20

Lake Evaporation .................................................................................... 22

Energy-Budget Method ..................................................................... 22

Empirical Equations ........................................................................... 25

Priestley-Taylor Equation ..................................................................... 25

Penman Equation .............................................................................. 25

DeBruin-Keijman Equation .................................................................. 25

Papadakis Equation ........................................................................... 25

Georgia Automated Environmental Monitoring Network ................................. 26

Evaluation of Evaporation Estimates and Methods ............................................. 26

Water-Budget Summary ................................................................................. 27

Water-Budget Error ................................................................................. 31

Sensitivity Analysis ................................................................................. 31
iv 

Summary ................................................................................................... 33

References Cited .......................................................................................... 33

Appendix —Methods and Instrumentation ............................................................ 37

Figures

 1–2. Maps Showing:

1. Location of study area, boundaries of the lower Apalachicola –Chattahoochee – 

Flint River Basin, and physiographic divisions of the Coastal Plain Province in 

southeastern Alabama, northwestern Florida, and southwestern Georgia ...... 3

 2. Study area, wells, surface-water , and climate stations near Lake Seminole ... 5

 3. Schematic diagram of the ground-water flow system in the lower Apalachicola–

Chattahoochee–Flint River Basin ......................................................... 7

 4. Correlation chart of geologic and hydrologic units in the lower Apalachicola–

Chattahoochee–Flint River Basin ......................................................... 8

 5. Hydrograph showing seasonal water-level fluctuations in the semiconfining unit 

(well 09G003) and the Upper Floridan aquifer (well 09F520), 1980–2001 ............... 10

 6. Generalized map of the water-level surface of the Upper Floridan aquifer, 

(A) August 2000 and (B ) July 1962 ......................................................... 11

 7. The hydrologic cycle for Lake Seminole ................................................... 14

 8–17. Graphs Showing:

 8. Difference in discharge between the Apalachicola River at Chattahoochee, 

Florida, and Jim Woodruff Lock and Dam ............................................. 15

 9. Regression defining the stage-volume relation for Lake Seminole ............... 18

 10. Lake Seminole ground-water inflow and lake leakage derived from simulated

results for the period April 2000 – September 2001 .................................... 18

 11. Regression showing relation between total solar radiation and observed net 

radiation at (A ) Cummings Access, Georgia, and (B ) Sneads Landing, Florida ... 22

 12. Relation between average air temperature and surface-water temperature at 

Lake Seminole, July 2000 ............................................................... 24

 13. Monthly estimates of evaporation computed using the energy budget and 

empirical equations: (A) Priestley-Taylor, (B) Penman, (C ) DeBruin-Keijman, 

(D ) Papadakis, and (E ) Georgia Automated Environmental Monitoring 

Network, April 2000 – September 2001 ................................................ 28

 14. Percent contribution of Lake Seminole water-budget components ............... 30

 15. Monthly average precipitation during the study period compared with 

long-term average precipitation at climate station in Arlington, Georgia, 

1960 – 2002 ................................................................................. 31

 16. Relative sensitivity of the Lake Seminole water budget to component inflow ... 32

 17. Relative sensitivity of the Lake Seminole water budget to component outflow ... 33

 A1. Diagram showing (A) Location of climate stations installed over water on 

Lake Seminole; (B ) climate-station installation at Sneads Landing, Florida, 

on Lake Seminole; and (C ) schematic of instruments used in overwater 

installation of climate stations ......................................................... 37

 A2. Map showing temperature probe arrays in Lake Seminole, Georgia ............... 41
 v

A3–A4. Graphs Showing:

 A3. Time-series plot for temperature probe array 1 ....................................... 45

 A4. Plots of seasonal-temperature profiles illustrating spatial temperature 

differences seasonally on (A ) July 1, 2000, (B ) October 1, 2000, and 

(C ) January 1, 2001 ........................................................................ 46

Tables

1. Climate data for Arlington, Early County, Georgia, 1959–2000 ........................... 6

 2. Surface-water inflows to Lake Seminole ................................................... 13

 3. Ungaged inflows to Lake Seminole ......................................................... 13

 4. Comparison of long-term average (based on 42 years of record, 1959 –2000, 

Georgia Automated Environmental Monitoring Network, 2002) precipitation to 

monthly precipitation during the study period ............................................. 15

 5. Summary of streamflow measurements for substantial ungaged inflows to 

Lake Seminole ................................................................................. 16

 6. Summary of Cauchy-type boundaries used to estimate flow between the 

Upper Floridan aquifer and stream channels ............................................. 19

 7. Summary of surface-water inflows and outflows used in the water and energy 

budgets and the temperature arrays used to calculate daily average 

temperatures of surface-water inflows and outflows for energy budget ............ 23

 8. Summary of daily temperature arrays used to calculate daily average temperature 

of surface-water inflow and outflow for the main body of the Lake Seminole and 

impoundment arms ........................................................................... 23

 9. Evaporation rates calculated using the energy budget, those derived from 

empirical equations, and those values posted to the Georgia Automated 

Environmental Monitoring Network at http://www.griffin.peachnet.edu/bae/ ...... 27

 10. Monthly water-budget variables and cumulative error for Lake Seminole ............ 29

 11. Average study period percent difference in water budget of Lake Seminole 

comparing empirical equations, long-term average annual pan evaporation, 

and the energy budget ........................................................................ 32

 A1. Instrumentation of the climate stations installed on Lake Seminole .................. 38

 A2. Monthly statistics for average climate conditions on Lake Seminole .................. 39

 A3. Temperature probe arrays, probe depth, installation data and probe elevation ...... 42

 A4. Mean, median, minimum, and maximum temperatures for each area of 

Lake Seminole during the study period, April 2000–September 2001 .................. 48

Abstract

Lake Seminole is a 37,600-acre impoundment formed at 

the confluence of the Flint and Chattahoochee Rivers along 

the Georgia–Florida State line. Outflow from Lake Seminole 

through Jim Woodruff Lock and Dam provides headwater to 

the Apalachicola River, which is a major supply of freshwater, 

nutrients, and detritus to ecosystems downstream. These rivers, together with their tributaries, are hydraulically connected 

to karst limestone units that constitute most of the Upper 

Floridan aquifer and to a chemically weathered residuum of 

undifferentiated overburden. 

The ground-water flow system near Lake Seminole consists 

of the Upper Floridan aquifer and undifferentiated overburden. 

The aquifer is confined below by low-permeability sediments 

of the Lisbon Formation and, generally, is semiconfined above 

by undifferentiated overburden. Ground-water flow within 

the Upper Floridan aquifer is unconfined or semiconfined and 

discharges at discrete points by springflow or diffuse leakage 

into streams and other surface-water bodies. The high degree of 

connectivity between the Upper Floridan aquifer and surfacewater bodies is limited to the upper Eocene Ocala Limestone 

and younger units that are in contact with streams in the Lake 

Seminole area. The impoundment of Lake Seminole inundated 

natural stream channels and other low-lying areas near streams 

and raised the water-level altitude of the Upper Floridan aquifer 

near the lake to nearly that of the lake, about 77 feet.

Surface-water inflow from the Chattahoochee and Flint 

Rivers and Spring Creek and outflow to the Apalachicola 

River through Jim Woodruff Lock and Dam dominate the 

water budget for Lake Seminole. About 81 percent of the 

total water-budget inflow consists of surface water; about 18 

percent is ground water, and the remaining 1 percent is lake 

precipitation. Similarly, lake outflow consists of about 89 percent surface water, as flow to the Apalachicola River through 

Jim Woodruff Lock and Dam, about 4 percent ground water, 

and about 2 percent lake evaporation. Measurement error 

and uncertainty in flux calculations cause a flow imbalance 

of about 4 percent between inflow and outflow water-budget 

components. Most of this error can be attributed to errors in 

estimating ground-water discharge from the lake, which was 

calculated using a ground-water model calibrated to October 

1986 conditions for the entire Apalachicola–Chattahoochee–

Flint River Basin and not just the area around Lake Seminole. 

Evaporation rates were determined using the preferred, but 

mathematically complex, energy budget and five empirical 

equations: Priestley-Taylor, Penman, DeBruin-Keijman, 

Papadakis, and the Priestley-Taylor used by the Georgia 

Automated Environmental Monitoring Network. Empirical 

equations require a significant amount of data but are relatively easy to calculate and compare well to long-term average 

annual (April 2000 –March 2001) pan evaporation, which is 

65 inches. Calculated annual lake evaporation, for the study 

period, using the energy-budget method was 67.2 inches, 

which overestimated long-term average annual pan evaporation by 2.2 inches. The empirical equations did not compare 

well with the energy-budget method during the 18-month 

study period, with average differences in computed evaporation using each equation ranging from 8 to 26 percent. The 

empirical equations also compared poorly with long-term 

average annual pan evaporation, with average differences in 

evaporation ranging from 3 to 23 percent. Energy budget and 

long-term average annual pan evaporation estimates did compare well, with only a 3-percent difference between estimates. 

Monthly evaporation estimates using all methods ranged from 

0.7 to 9.5 inches and were lowest during December 2000 and 

highest during May 2000. Although the energy budget is generally the preferred method, the dominance of surface water in 

the Lake Seminole water budget makes the method inaccurate 

and difficult to use, because surface water makes up more than 

two-thirds of the energy budget and errors in measured streamflow can be substantial.

Ground-Water and Surface-Water Flow and 

Estimated Water Budget for Lake Seminole, 

Southwestern Georgia and Northwestern Florida

By Melinda S. Dalton, Brent T. Aulenbach, and Lynn J. Torak
Introduction

Lake Seminole is a 37,600-acre lake located in the lower 

Apalachicola–Chattahoochee–Flint (ACF) River Basin at the 

border between southwestern Georgia and northwestern Florida (fig. 1). The lake was created from the late 1940s to mid1950s with the construction of Jim Woodruff Lock and Dam 

on the Apalachicola River, about 1,000 feet (ft) downstream of 

the confluence of the Flint and Chattahoochee Rivers 

(U.S. Army Corps of Engineers and others, 1948; James H. 

Sanders, Jr., U.S. Army Corps of Engineers, Mobile, Alabama, written commun., 2002). The lake was intended to aid 

navigation on the Chattahoochee and Flint Rivers, provide lift 

for hydroelectric-power generation, and serve recreational purposes. Lake Seminole is the source of headwater to the Apalachicola River and is the major supply of freshwater, nutrients, 

and detritus to ecosystems downstream, including Apalachicola Bay and its estuaries. Despite its size, Lake Seminole 

is a run-of-the-river impoundment, having less than 67,000 

acre-feet (acre-ft) of useful storage. About 240 miles(mi) of 

shoreline encompass four impoundment arms: two major arms 

extend the lake from the dam to about 47 mi upstream along 

the natural courses of the Chattahoochee and Flint Rivers; two 

minor impoundment arms are present along Fishpond Drain 

and Spring Creek, both of which are tributaries to the Flint 

River arm of the lake (U.S. Army Corps of Engineers, 1980).

Recently, Lake Seminole and the water released from it 

have become focal points in water-allocation negotiations—

resulting from the ACF River Basin Compact1—between 

Georgia, Florida, and Alabama. Increases in population, 

agriculture, and industry and the recent drought of 1998–2002 

have made water supply and use in the lower ACF River Basin 

a major concern for water-resource managers in the region, 

as the three States place conflicting demands on the basin’s 

limited water resources. These concerns led the three States 

to sign an interstate water compact in 1997, which intended to 

ensure the equitable use and availability of water resources in 

the region while protecting river ecology. 

Essential to the State of Georgia’s water-allocation plans 

was the necessity to undertake a technical study to develop 

a comprehensive water budget of the Lake Seminole area, to 

reasonably estimate the volume of water flowing into Florida 

before and after construction of the dam, and to monitor the 

effects of any sinkhole collapse within the lake (Harold F. 

Reheis, Director, Georgia Department of Natural Resources, 

Environmental Protection Division, written commun., 1997). 

The State of Georgia requested that the U.S. Geological Survey (USGS) conduct a technical study to address these issues; 

and the following four objectives were developed for a 3-year 

study, which began during 1999.

• Develop a water budget for Lake Seminole that will 

promote a reasonable understanding of the effect of 

the lake on the overall flow system in the lower ACF 

River Basin, and that can be used to guide water allocations between Alabama, Florida, and Georgia.

• Compare current and pre-Lake Seminole groundwater and surface-water flow regimes to determine 

whether the volume of water flowing out of Georgia 

has changed substantially after construction of Jim 

Woodruff Lock and Dam and the filling of the lake.

• Evaluate the possibility of a substantial amount of 

water entering the ground-water regime from Lake 

Seminole, flowing beneath Jim Woodruff Lock and 

Dam, and entering Florida downstream of the dam.

• Assess the likelihood of failure of dissolution features 

in the karst limestone of the lake bottom, such as sinkhole collapse, and the likelihood of sudden partial or 

complete draining of the lake. If such an occurrence is 

likely, then propose a data-collection system to monitor 

pertinent hydrologic features that could lead to a sudden draining of Lake Seminole, and could provide 

a warning of its occurrence.

The 3-year study investigated features of the hydrologic 

system near Lake Seminole that contribute directly to the 

surface- and ground-water flow regime of the lake. The study 

focused on only those elements of the hydrologic cycle, 

surface-water features, and hydrogeologic units that are in 

hydraulic connection with the lake. A multidiscipline investigative approach was used that involved acquisition of chemical, limnologic, hydrogeologic, and meteorologic information, 

followed by analysis, interpretation, and reporting of the 

resulting data and corresponding uncertainty.

Purpose and Scope

This report is one of a series of reports documenting a 

study to evaluate the effects of impoundment of Lake Seminole on water resources in the lower ACF River Basin. The 

first of the four study objectives listed previously is addressed 

herein, namely, to develop a water budget for Lake Seminole 

that will promote a reasonable understanding of the effects of 

the lake on the overall flow system in the lower ACF River 

Basin, and that can be used to guide water allocations between 

Alabama, Florida, and Georgia. The following technical tasks 

were performed to achieve this objective and are discussed in 

this report: 

1

As adopted by: the Alabama Legislature on February 18, 1997, and signed by the Governor of Alabama on February 25, 1997, as Alabama Acts 97-67, 

Alabama Code, Title 33-19-1 et seq.; the Florida Legislature on April 14, 1997, and signed by the Governor of Florida on April 24, 1997, as Chapter 97-25, 

Laws of Florida, Section 373.71, Florida Statutes (1997); the Georgia Legislature on February 11, 1997, as Georgia Acts No. 7, and signed by the Governor 

of Georgia on February 25, 1997, as Georgia Code Annual Section 12-10-100 et seq., and passed by the United States Congress on November 7, 1997, and 

signed by the President of the United States on November 20, 1997, as Public Law Number 105-104, 111 Statute 2219

2 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Figure 1. Location of study area, boundaries of the lower Apalachicola – 

Chattahoochee – Flint River Basin, and physiographic divisions of the Coastal Plain Province in southeastern Alabama, northwestern Florida, and

southwestern Georgia (modified from Torak and others, 1996).

30°

31°

32°

85° 84°

Map

area

0

0

10

10

20 MILES

20 KILOMETERS

SEMINOLE

MILLER

COLQUITT

WORTH

TURNER

CRISP

DOUGHERTY CALHOUN

RANDOLPH

STEWART

CLAY

TERRELL

LEE

MITCHELL

BAKER

DOOLY

SUMTER WEBSTER

GADSDEN

GULF

JACKSON

CALHOUN

HOUSTON

HENRY

BARBOUR

DECATUR

LIBERTY

FRANKLIN

GRADY

EARLY

Blountstown

Dothan

Chattahoochee

Bristol

Woods

Orange

Bainbridge

Cordele

Albany

Apalachicola

Eufaula

UPDIP

LIMIT

OF UPPER

FLORIDAN

AQUIFER

SOLUTION

ESCARPMENT

AL

FL

FL

GA

FALL

LINE

HILLS

GULF COASTAL LOWLANDS

DOUGHERTY

PLAIN

TIFTON

UPLAND

Base modified from U.S. Geological Survey

1:100,000-scale digital data

AL GA

Gulf of Mexico

Apalachicola Bay

Lake

Seminole

ALABAMA

Apalachicola–

Chattahoochee–

Flint River Basin

GEORGIA

FLORIDA

EXPLANATION

Lower Apalachicola–

 Chattahoochee–

 Flint River Basin

Physiographic division 

 boundary

Flint River

Chattahoochee R Apalachicola River

Walter F

George

Lake

Study area

Introduction 3
• Describe the ground-water and surface-water flow 

systems of Lake Seminole and vicinity as a framework for identifying water-budget components;

• Develop a water budget for Lake Seminole that 

accounts for inflows to and outflows from the lake 

on a month-to-month basis;

• Evaluate techniques used for estimating evaporation; 

and

• Assess the importance of each water-budget component 

through sensitivity analyses.

Ground-water and surface-water flow systems described 

in this report are based on results of numerous hydrogeologic 

investigations that have been performed in the study area 

since 1965. From an initial investigation on the geology and 

water resources of the Lake Seminole area by Sever (1965) 

to an evaluation of stream-aquifer relations and the potentiometric surface of the Upper Floridan aquifer in the lower ACF 

River Basin by Mosner (2002), this report combines results 

of previous hydrogeologic investigations with recent and 

historical data to provide pertinent information for developing 

concepts of ground- and surface-water flow in the reservoirstream-aquifer flow system. The ground-water conceptualization contains descriptions of the hydrogeologic setting of 

Lake Seminole and the Upper Floridan aquifer, a discussion 

of hydraulic characteristics of the Upper Floridan aquifer 

system, and a discussion of seasonal and long-term variations 

in ground-water levels.

The surface-water conceptualization contains descriptions 

of the drainage network, streamflow, dams, and navigational 

improvements for the main streams of the lower ACF River 

Basin. These descriptions are intended to provide necessary 

hydrologic information from which reservoir-stream-aquifer 

interaction can be evaluated for development of the Lake 

Seminole water budget.

The calculation of fluxes for water-budget components 

utilized limnologic and climatologic information obtained 

from instrumentation installed in and over Lake Seminole 

for this study and results of digital modeling of ground-water 

flow having surface-water interaction. Two overwater climate 

stations supplied values for climatic variables pertinent to 

the empirical formulas used to calculate lake evaporation. A 

network of lake-temperature monitoring and surface-water stations supplied data necessary to calculate lake evaporation by 

the energy-budget method. Previous digital modeling in 

the lower ACF River Basin provided estimates of leakage rates 

to and from the Upper Floridan aquifer that occur along the 

lake boundary.

Study Area

Lake Seminole is located in the lower ACF River Basin in

parts of southwestern Georgia and northwestern Florida (fig. 1). 

The 6,800-square mile (mi2) lower ACF River Basin includes 

Lake Seminole and the land area that exchanges ground- and 

surface-water flow with the lake. In Georgia, the study area 

includes Baker, Decatur, Early, Grady, Miller, Mitchell, and 

Seminole Counties; in Florida, the study area includes Gadsden and Jackson Counties (fig. 2).

Physiography

The lower ACF River Basin lies within the Coastal Plain 

physiographic province in southwestern Georgia, northwestern Florida, and southeastern Alabama, and is drained by the 

Apalachicola, Chattahoochee, and Flint Rivers and their tributaries (Torak and others, 1996) (fig. 1). The northern extent of 

the study area is located in the Fall Line Hills district near the 

updip limit of the Ocala Limestone (Clark and Zisa, 1976). 

The Fall Line Hills district is highly dissected with steep-hill 

slopes and streams that lie from about 50 to 250 ft below adjacent ridges. Relief diminishes gradually to the south and east 

where the Fall Line Hills district grades into the Dougherty 

Plain (Torak and others, 1996). 

The Dougherty Plain is a nearly level lowland that pinches 

out where the Fall Line Hills district and Tifton Upland meet 

(Clark and Zisa, 1976). Formed by erosion, land-surface altitude

ranges from about 300 ft at the northern extent of the plain to 

about 77 ft at Lake Seminole, and about 40 ft directly downstream of Jim Woodruff Lock and Dam. Land-surface slopes 

average about 5 feet per mile (ft/mi) (Hicks and others, 1987). 

Karst topography defines the landscape of the Dougherty Plain.

A major feature near Lake Seminole and upstream along the 

Flint River is internal drainage, where streams connect the surface- and ground-water flow systems through karst conduits in 

the streambed. Sinkhole formation is responsible for the development of numerous ponds and wetlands that characterize the 

region; the bottoms of these ponds are filled with low-permeability sediment and hold water year-round. Underground 

channels created from dissolution of the Ocala Limestone 

capture surface water, and account for a substantial percentage 

of drainage in the Dougherty Plain (Hicks and others, 1987).

To the east, the basin is bordered by a well-defined northwest-facing feature called the Solution Escarpment (MacNeil, 

1947), which forms a prominent boundary between the Tifton 

Upland and the Dougherty Plain. The crest of the Solution 

Escarpment creates a topographic and a surface-water divide 

between the Flint River to the west and the Ochlockonee and 

Withlacoochee Rivers to the east (Torak and others, 1996). 

The southern limit of the study area terminates in northwestern Florida in the Tallahassee Hills, the equivalent of the 

Tifton Upland. Here, altitudes range from about 330 ft near the 

Georgia–Florida State line to about 100 ft south of the study 

area. Sediments in this area are composed of clayey sand, silt, 

and clay that end abruptly at the Apalachicola River (Torak 

and others, 1996). 

4 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Figure 2. Study area, wells, surface-water, and climate stations near Lake Seminole.

Climate

The climate of the study area is humid subtropical. The 

mean annual temperature for the 42-year period 1959–2000 

at Arlington in Early County, Georgia, is 66.7 degrees 

Fahrenheit (°F) (table 1; see fig. 2 for location). The coldest months, December and January, average about 51.3°F; 

occasional freezing temperatures occur during this time. The 

warmest months, July and August, have an average temperature of about 81.1°F; and temperatures near 100°F are not 

uncommon. Average annual rainfall is about 53.9 inches; 

highest monthly rainfall occurs during March; lowest rainfall 

occurs during October.

Previous Studies

Several hydrogeologic investigations have been conducted 

in the study area in Georgia. Sever (1965) described the 

hydrogeology in Seminole, Decatur, and Grady Counties, 

Georgia, and the water resources of the area surrounding Lake 

Seminole. Hayes and others (1983) described the hydrology 

of the Upper Floridan aquifer in the Dougherty Plain. Miller 

(1986) described the hydrogeologic framework of the Floridan 

aquifer system; Johnston and Bush (1988) summarized the 

hydrology of the Floridan aquifer system; Bush and Johnston 

(1988) evaluated the ground-water hydraulics, regional flow, 

and ground-water development of the Floridan aquifer system 

Spring Creek

Fishpond Drain

Flint

Rive r

Chattahoochee River Apalachicola River

Cooleewahee

Creek

Ichawaynochaway Creek

JACKSON

GADSDEN

BAKER

SEMINOLE

DECATUR

MILLER

EARLY MITCHELL

GRADY

Blakely

Milford

Elmodel

Newton

Camilla

Pelham

Bainbridge Cairo

Iron

City

Donalsonville

Marianna

Chattahoochee

Quincy

Colquitt

Brinson

Arlington

31°

02355350

02357000

02358000

02357050

02343801

02343940

02356000 02357150

02353000

09G003

09F520

06F001

0 5

0 5 10 15 20 KILOMETERS

10 20 MILES

N

15

GA

FL

Base from U.S. Geological Survey 

1:1,000,000-scale digital data

Jim Woodruff

Lock and Dam

Sneads Landing

Cummings Access

Lake Seminole

Well and site name

Surface-water station 

 and identification number

Climate station

EXPLANATION

02358000

06F001

Study

area

ALABAMA GEORGIA

FLORIDA

Introduction 5
that included the study area. Torak and McDowell (1995) 

and Torak and others (1996) evaluated the hydrogeology and 

ground-water resources in the lower ACF River Basin. Albertson (2001), Torak (2001), and Mosner (2001), respectively, 

described the hydrogeology, water chemistry, and streamaquifer relations in the lower ACF River Basin near Lake 

Seminole. Mosner (2002) evaluated stream-aquifer relations, 

ground-water seepage, and the potentiometric surface of the 

Upper Floridan aquifer in the lower ACF River Basin.

Selected investigations in the study area in Florida include a 

report by Vernon and others (1958), describing the geology of 

the area near Lake Seminole, and a report by Pratt and others 

(1996), describing the hydrogeology of the Northwest Florida 

Water Management District. 

Several studies have been conducted that examine the 

instrumentation and methodologies associated with determining lake evaporation and developing lake water budgets. 

DeBruin (1978) developed a model for determining evaporation from a lake by combining two well-known models, the 

Priestley-Taylor and Penman equations. DeBruin and Keijman (1979) discussed the application of the Priestley-Taylor 

model for determining evaporation. Lee and others (1991) 

discussed the instrumentation required to estimate evaporation 

and developed a preliminary water budget of a seepage lake 

in central Florida. Rosenberry and others (1993) evaluated 

the instrumentation required to produce the energy budget for 

a lake in Minnesota. The energy-budget model is considered 

by most investigators to be one of the most accurate methods 

available for determining evaporation (Thomas C. Winter, 

U.S. Geological Survey, Denver, Colorado, oral commun., 

May 2000), because calculations of latent heat represent 

“true” values of latent-heat flux (Keijman, 1974; Stewart and 

Rouse, 1976). Lee and Swancar (1996) described the water 

budget and energy budget of a seepage lake in central Florida 

and compared methods for determining evaporation from the 

lake surface. Winter and others (1995) compared 11 analytical equations, including the 4 listed above, that are used to 

estimate evaporation with similar estimates computed from the 

energy-budget method. Their results showed that the PriestleyTaylor, Penman, and DeBruin-Keijman models agreed most 

closely with the energy-budget method when climate data 

were available near the lake. 

Well and Surface-Water-Station 

Numbering System

In this report, wells are identified with either a numbering system based on USGS topographic maps (Georgia) or a 

numbering system developed by the Northwest Florida Water 

Management District (Florida). In Georgia, each 71⁄2–minute 

topographic quadrangle map has been given a number and 

letter designation beginning at the southwestern corner of 

the State. Numbers increase eastward through 39, and letters 

increase alphabetically northward through “Z,” then become 

double-letter designations “AA” through “PP.” The letters “I,” 

“O,” “II,” and “OO” are not used. Wells inventoried in each 

quadrangle are numbered sequentially beginning with “1.” 

Thus, the third well inventoried in the Chattahoochee quadrangle is designated 06D003. In Florida, wells are inventoried 

using a triple-A numbering identification system; each well 

is assigned a 4-digit identifier following “AAA,” for example 

AAA1640. Springs are considered ground-water sites and, 

therefore, are identified in the same manner as wells.

Surface-water stations are identified by a numbering system 

used for all USGS reports and publications since October 1, 

1950. The order of listing stations is in a downstream direction 

along the main channel. All stations on a tributary entering 

upstream from each mainstream are listed before that station. 

Each surface-water station is assigned a unique 8-digit number. The station number such as 02351890 includes the 2-digit 

number “02,” which designates the site as a surface-water station, and the 6-digit downstream order number “351890.”

Acknowledgments

The authors extend appreciation to the many agencies that 

contributed to the collection of data used in this report, including the Northwest Florida Water Management District and the 

U.S. Army Corps of Engineers. Gratitude is extended to all the 

landowners and land managers who allowed access to wells 

and springs to collect water-resource data. 

Table 1. Climate data for Arlington, Early County, Georgia, 

1959–2000 (see figure 2 for location).

[°F, degree Fahrenheit. Data from Georgia Automated Environmental 

Monitoring Network (2002)]

Month

Average maximum 

temperature 

 (°F)

Average minimum 

temperature 

 (°F)

Total

precipitation

(inches)

January 61.9 38.1 5.37

February 65.5 40.8 4.92

March 72.5 46.9 6.09

April 80.4 53.8 3.79

May 86.2 60.6 3.65

June 90.7 67.6 5.1

July 92.3 70.3 4.96

August 91.8 69.8 4.8

September 88.5 65.8 3.84

October 80.6 54.7 2.65

November 72.1 46 3.15

December 64.9 40.1 5.61

Average 78.9 54.5 53.9

Average annual temperature 66.7 °F

6 Ground-water and surface-water flow and estimated water budget for Lake Seminole
? ?

80

80

80

Upper Floridan aquifer

Semiconfining unit

Terrace and undifferentiated,

Hawthorn Group, residuum

Tampa Limestone

Suwannee Limestone

Ocala Limestone

Lisbon Formation

Sub-Floridan confining unit

NOT TO SCALE

 80 Water-level contour—In feet.

 Datum is NAVD 88

EXPLANATION

Ground-water flow direction

 Section view

Surface-water flow direction Plan view

GADSDEN CO

SEMINOLE CO DECATUR CO

JACKSON CO

G A

F L

Brinson

Bainbridge

Fowltown

Recovery

Dellwood

Sneads

Reynoldsville

N

JIM

WOODRUFF DAM

Ground Water

The description of the ground-water flow system (fig. 3) is 

based on previous works by Sever (1965), Hayes and others 

(1983), Miller (1986), Hicks and others (1987), Johnston and 

Bush (1988), Torak and McDowell (1996), Torak and others 

(1996), and Stewart and others (1999). These studies indicate that recharge to the Upper Floridan aquifer is mainly by 

infiltrated precipitation, either directly through the limestone 

units of the aquifer or through the undifferentiated overburden. The undifferentiated overburden consists of chemically 

weathered limestone residuum and alluvium—composed of 

sand, silt, and clay—that partially confine the Upper Floridan 

aquifer. Although most layers of similar lithology in the undifferentiated overburden are discontinuous and can be traced 

for only short distances, a layer of clay is present that might 

be continuous throughout the lower half of the overburden 

(Torak and others, 1996). Low vertical hydraulic conductivity 

and the relative thickness of this clay layer within the overburden create a hydrologic barrier to vertical flow of water to 

and from the aquifer (Torak and others, 1996). The clay layer 

affects ground-water flow in the aquifer system by causing 

ground water to perch in overlying deposits following periods 

of heavy rainfall, thus decreasing the amount of ground-water 

recharge to the aquifer from infiltration and controlling the 

infiltration rate (Torak and others, 1996). Regional groundwater flow is from northwest to southeast; near streams, 

discharge is toward the stream channel.

Because the river channels cut into the overburden and are 

in contact with the Upper Floridan aquifer, there is potential 

for direct hydraulic connection between the aquifer and surface-water features. Sudden changes in river stage, however, 

do not necessarily correspond to a rise in ground-water level 

(Torak and others, 1996), indicating little hydraulic interaction between the stream and the Upper Floridan aquifer. When 

the ground-water level is higher than the stream stage, water 

in the Upper Floridan aquifer discharges to the stream, and 

the stream becomes a gaining stream. Conversely, when the 

ground-water level is lower than the stream stage, the stream 

may discharge water to the aquifer, and the stream becomes a 

losing stream. The rate of discharge depends on the hydraulic 

gradient between the aquifer water level and stream stage, and 

the permeability of the streambed (Hicks and others, 1987). 

Figure 3. Schematic diagram of the ground-water flow system in the lower Apalachicola–Chattahoochee–Flint 

River Basin (modified from Torak and others, 1996).

Ground water 7
Hydrogeologic Setting

The Coastal Plain Province is underlain by pre-Cretaceous 

to Quaternary sediments. In the study area, these sediments 

consist of alternating sand, clay, dolostone, and limestone, 

which dip gently and thicken to the southeast (Hicks and others, 1987). The Dougherty Plain is characterized by a highly 

transmissive flow system developed through dissolution and 

karst processes in the Ocala Limestone, which is the main 

water-bearing unit of the Upper Floridan aquifer. This flow 

system is defined by high rates of direct recharge through 

sinkholes, indirect recharge by vertical leakage through the 

overburden, and discharge to surface-water bodies such as the 

Flint and Chattahoochee Rivers, when ground-water levels 

exceed stream levels (Torak and others, 1996). 

The Upper Floridan aquifer is a complex hydrogeologic 

system with a vertical and areal distribution that adds complexity to the dynamics of stream-aquifer interactions. Dissolution of the limestone by fluctuating ground-water levels 

and infiltrating rainfall have produced secondary permeability 

in the Ocala Limestone, making the aquifer highly productive. 

Solution conduits between the Solution Escarpment and the 

Flint River transmit large amounts of water from the Upper 

Floridan aquifer to springs that discharge along streams. The 

hydraulic gradient and the amount of dissolution and connectivity of conduits determine the relative speed with which 

water moves through the aquifer.

Throughout much of the study area, ground-water flow 

within the Upper Floridan aquifer is unconfined or semiconfined and discharges at discrete points by springflow or diffuse 

leakage into streams and other surface-water bodies (Johnston 

and Bush, 1988). The high degree of connectivity between the 

Upper Floridan aquifer and surface-water bodies is limited to 

the Ocala Limestone and younger units that are in contact with 

streams in the Lake Seminole area. Geologic units comprising 

the Upper Floridan aquifer systems are late-Eocene age and 

younger, forming, in ascending order, the Lisbon Formation, 

Clinchfield Sand, Ocala Limestone, Suwannee Limestone, 

Tampa Limestone, Hawthorn Formation, Miccosukee Formation, and surficial deposits of terraced and undifferentiated 

overburden (fig. 4). Hayes and others (1983), Miller (1986), 

Hicks and others (1987), Bush and Johnston (1988), Torak and 

McDowell (1995), and Torak and others (1996) provide details 

about these geologic units.

Hydraulic Characteristics

Variations in thickness and hydraulic conductivity determine the ability of geologic units to function as aquifers and 

to transmit usable amounts of ground water for consumption. These aquifer characteristics also provide a mechanism 

for vertical leakage between aquifers and surface water, or 

between subunits within aquifers that are separated by semiconfining units (Torak and others, 1996). Variations in lithology and patterns of secondary porosity result in a complex 

ground-water flow system characteristic of many karst areas.

Overlying Semiconfining Units

In the lower ACF River Basin in Alabama, Georgia, and the 

northern panhandle of Florida (Jackson County), the Upper 

Floridan aquifer is semiconfined above by undifferentiated overburden, consisting of alternating layers of sand, silt, and clay 

and chemically weathered residuum of the Ocala Limestone. In 

Gadsden County, Florida, however, the Upper Floridan aquifer is 

semiconfined by a clay bed at the base of the Tampa Limestone. 

The relatively low vertical hydraulic conductivity and the 

substantial thickness of the laterally continuous clay layer 

present in some places in the overlying semiconfining units 

create a hydrologic barrier to vertical flow of ground water 

to and from the aquifer. This clay layer can have an effect on 

ground-water flow in the aquifer system, causing ground water 

to perch following periods of heavy rainfall, thus decreasing 

recharge of water to the aquifer by infiltration of precipitation 

(Torak and others, 1996). Where the clay in the lower-half 

SERIES

GEORGIA

Geologic unit Hydrologic

unit

 HOLOCENE

AND 

PLEISTOCENE

Terraced and 

undifferentiated 

deposits

MIOCENE

Miccosukee

Formation

Hawthorn

Formation

Tampa

Limestone

Suwannee 

Limestone

Undifferentiated overburden

(residuum)

Semiconfining unit

EOCENE

Ocala Limestone

Clinchfield

Sand

Lisbon Formation

Upper

Floridan

aquifer

Lower

confining

unit

Figure 4. Correlation chart of geologic and hydrologic units 

in the lower Apalachicola–Chattahoochee–Flint River Basin 

(from Torak and others, 1996).

8 Ground-water and surface-water flow and estimated water budget for Lake Seminole
thickness of the overburden is absent, however, flow of water 

from the surface through the overburden and into the aquifer is 

relatively unimpeded and rapid.

Upper Floridan Aquifer

The Upper Floridan aquifer generally ranges in thickness 

from a few feet at the updip limit to more than 700 ft in Florida; near Lake Seminole, the Upper Floridan aquifer ranges 

from about 150 to 400 ft thick (Torak and others, 1996). The 

aquifer is confined below by low-permeability sediments of 

the Lisbon Formation and, generally, is semiconfined above 

by undifferentiated overburden. The aquifer is exposed along 

sections of major streams — such as the Apalachicola, Chattahoochee, and Flint Rivers, and Spring Creek — where erosion 

has removed the overburden (Maslia and Hayes, 1988).

The capacity of the Upper Floridan aquifer to store and 

transmit large quantities of water is attributed to the fractured 

nature of the Ocala Limestone (Hayes and others, 1983) and 

associated dissolution of limestone by ground water circulating along bedding planes and fractures, and to interconnected 

conduits or solution openings (Hicks and others, 1987). Solution conduits transmit a major portion of the ground-water 

flow and contribute greatly to shaping the potentiometric 

surface of the aquifer (Hayes and others, 1983). 

Computed values of transmissivity for the study area, from 

field tests of the Upper Floridan aquifer, generally range from 

about 2,000 to 1,300,000 feet squared per day (ft2/d) (Hayes 

and others, 1983; Wagner and Allen, 1984). Although locally 

accurate, values of transmissivity derived from field tests 

might not be representative of regional transmissivity because 

of variability in hydraulic conductivity caused by fracture 

and solution openings (Torak and others, 1996); the large 

range of variation in hydraulic conductivity is the result 

of variations in size and distribution of solution openings. 

Regional values of transmissivity commonly range from 

2,000 to 300,000 ft2/d (Hayes and others, 1983). Transmissivity is lowest near the updip limit of the Ocala Limestone, 

where the aquifer is relatively thin. Transmissivity generally 

increases to the south, where the aquifer thickens, and adjacent 

to major streams, where flowing water has accelerated the 

development of solution openings (Maslia and Hayes, 1988).

Lisbon Formation

The lower confining unit in the lower ACF River Basin is 

the Lisbon Formation. The hard, well-cemented, and argillaceous nature of the limestone of the Lisbon Formation 

makes it a nearly impermeable base to the Upper Floridan 

aquifer (Hayes and others, 1983). Because of the relatively low 

hydraulic conductivity compared with the Upper Floridan aquifer, wells yield only a few gallons per minute from the Lisbon 

Formation; although southeast of the Dougherty Plain, domestic supplies of water can be obtained (Hayes and others, 1983).

Recharge by upward leakage to the Upper Floridan aquifer 

across the Lisbon Formation occurs in the northernmost part 

of the lower ACF River Basin at a flow rate of about 10 cubic 

feet per second (ft3/s). Discharge from the Upper Floridan 

aquifer through the Lisbon Formation occurs in the southern 

part of the basin at a rate of about 5 ft3/s, with no leakage in 

the Dougherty Plain. In contrast, the total lateral-flow component through the Upper Floridan aquifer in the study area is 

about 4,000 ft3/s. Thus, in this area, the Lisbon Formation acts 

as a nearly impermeable lower boundary to the Upper Floridan 

aquifer (Faye and Mayer, 1996).

Ground-Water Levels

Ground-water levels in the Upper Floridan aquifer and 

overlying units in the study area fluctuate in response to seasonal and longer cycle variations in recharge from infiltrating 

precipitation, discharge by pumping and evapotranspiration, 

and interaction with surface-water features. The natural pattern 

of higher water-level altitude (or shallow depth to water with 

regard to land surface) in recharge areas and lower waterlevel altitude in discharge areas, such as near streams, can be 

affected by heavy ground-water pumping for agricultural and 

residential water use. Altitude of water levels in the Upper 

Floridan aquifer generally ranges from about 190 ft northwest 

of Lake Seminole to about 65 ft south of the lake. Near the 

lake, ground-water levels are influenced by lake stage, varying from about 80 ft near the northern impoundment arms 

of the lake to about 70 ft near the southern part of the Flint 

River impoundment arm and dam (Mosner, 2002). Magnitude 

and timing of water-level response to recharge and pumping 

stresses vary areally within each hydrologic unit and can be 

large or barely perceptible, and nearly instantaneous or very 

slow (Torak and others, 1996).

Seasonal Fluctuations

The water level in the semiconfining unit overlying the 

Upper Floridan aquifer in the lower ACF River Basin usually is highest from January or February through April, 

declines during summer and fall, and is at a minimum during 

November through December or January (fig. 5). Beginning 

in December and continuing through January, water levels 

in wells generally rise quickly in response to recharge by 

infiltrating precipitation (Torak and others, 1996). During late 

spring and summer, however, water-level response to precipitation is subdued because the precipitation either replaces the 

soil-moisture deficit in the unsaturated zone or is lost to evapotranspiration or runoff (Hayes and others, 1983). Summer 

precipitation generally is from convective storms, which produce rainfall that is more intense and of shorter duration than 

rainfall associated with frontal passages during other seasons; 

most summer precipitation is lost to runoff. 

Ground water 9
Ground-water levels in the Upper Floridan aquifer also fluctuate seasonally in response to precipitation, evapotranspiration, 

and pumping (fig. 5). Late winter and early spring recharge by 

infiltrating precipitation, coupled with low evapotranspiration 

and pumping rates, cause the water level in the Upper Floridan 

aquifer to reach a maximum during February through April. 

During the growing season, combined effects of increased 

ground-water pumping for irrigation, higher evapotranspiration, 

and decreased recharge, when compared with winter and spring 

conditions, cause the ground-water level to reach a minimum 

by late summer through fall. Seasonal water-level fluctuations in the Upper Floridan aquifer range from about 2 ft in the 

eastern parts of the lower ACF River Basin in Georgia to about 

30 ft near Albany, Georgia. Near Lake Seminole, however, 

ground-water-level fluctuations are subdued because of the 

strong aquifer-lake hydraulic connection. Near major centers of 

agricultural and industrial pumping, seasonal water-level fluctuations can exceed 30 ft and are amplified by drought conditions (Torak and others, 1996). Ground-water pumping does not 

result in formation of distinct cones of depression (Hicks and 

others, 1987); rather, because of the relatively uniform spacing 

of wells and pumpage throughout the lower ACF River Basin 

and the relatively high hydraulic conductivity, the potentiometric surface of the Upper Floridan aquifer is raised and lowered 

uniformly (Torak and others, 1996).

Effects of Drought and Pumping

Long-term declines in water level from drought conditions 

or pumping are not observed in the major water-bearing units 

in the lower ACF River Basin. During droughts of 1980–81, 

1986 – 88, and 1998 –2001, water levels in wells located in the 

Dougherty Plain declined to record or near-record lows, but 

recovered to predrought levels with the return of normal precipitation. Typical water-level response of the Upper Floridan 

aquifer in Georgia to recent drought conditions is shown in 

the water-level hydrograph of well 09F520 (fig. 5). During the 

drought of 1998–2001 record low water levels were recorded 

in the Lake Seminole area, where ground-water levels also 

fluctuate seasonally in response to climatic changes and 

ground-water pumping. Near the lake, however, these fluctuations are subdued as lake stage influences water levels in the 

Upper Floridan aquifer and undifferentiated overburden.

Predevelopment and recent potentiometric surfaces of the 

Upper Floridan aquifer (fig. 6) show that pumping rates, 

ranging from 54 to 119 million gallons per day (Mgal/d) from 

1980 to 1999 in Seminole and Decatur Counties, failed to produce long-term water-level declines near Lake Seminole. Lake 

leakage into the Upper Floridan aquifer minimizes water-level 

declines caused by drought and pumping.

Surface-Water Influence

Surface-water features have a variable effect on groundwater levels in the area surrounding Lake Seminole. The 

impoundment of Lake Seminole inundated natural stream 

channels and other low-lying areas near streams and raised 

the water level of the Upper Floridan aquifer near the lake to 

about the same level as the lake. This process decreased the 

rate of ground-water discharge to streams and to Lake Seminole by reducing the hydraulic gradient between ground water 

and surface water. Because the pool elevation at Lake Seminole is maintained at an altitude of about 77 ft year-round, 

water levels in the adjacent aquifer and overlying semiconfining unit also are about 77 ft and remain nearly constant. Prior 

to impoundment, the hydraulic gradient from the aquifer to the 

streams was relatively steep, and flow was directed toward the 

Flint and Chattahoochee Rivers, Fishpond Drain, and Spring 

Creek. After impoundment, backwater conditions upstream of 

Jim Woodruff Lock and Dam reduced the hydraulic gradient 

from the aquifer toward the stream along the Chattahoochee 

and Flint Rivers for 47 mi, and to a lesser extent for the other 

two newly formed impoundment arms. The reduced gradient under impoundment conditions produced a corresponding 

reduced ground-water flow toward each impoundment arm 

(Jones and Torak, 2003). 

0

10

20

30

40

50

60

70

1980 1985 1990 1995 2000

Blank where 

data missing

Well 09F520

Drought

Recovery

WATER LEVEL, IN FEET BELOW LAND SURFACE

Well 09G003

Figure 5. Seasonal water-level fluctuations in the semiconfining unit (well 09G003) and 

the Upper Floridan aquifer (well 09F520), 1980–2001 (see figure 2 for well locations).

10 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Spring Creek

Fishpond Drain

Flint

River

Chattahoochee River Apalachicola River

Spring Creek

Fishpond Dra ni

31°

0 5

0 5 10 15 20 KILOMETERS

10 20 MILES

N

15

GA

FL

Base from U.S. Geological Survey 

1:1,000,000-scale digital data

Jim Woodruff 

Lock and Dam Lake Seminole

Jim Woodruff 

Lock and Dam

Lake Seminole

Study

area

ALABAMA GEORGIA

FLORIDA

90

90

100

100

110

130

120

140

190

170

150

160

180

80

70

80

80

90

80

70

100

90

80

100

110

90

80

JACKSON

GADSDEN

BAKER

SEMINOLE

DECATUR

MILLER

EARLY MITCHELL

GRADY

DECATUR

SEMINOLE

EXPLANATION

80 Water-level surface contour—Shows 

 approximate altitude at which water level 

 would have stood in tightly cased wells 

 completed in the Upper Floridan aquifer.

 Contour interval 10 feet. Datum is NAVD 88

A. August 2000

B. July 1962

Arlington

Blakely Milford

ElmodelNewton

Camilla

Pelham

Cairo Bainbridge

Iron

City Donalsonville

Marianna

Chattahoochee

Quincy

Colquitt

Brinson

Bainbridge

Iron City

Donalsonville

Brinson

Figure 6. Generalized map of the water-level surface of the Upper Floridan aquifer, 

(A) August 2000 (Mosner, 2002) and (B ) July 1962 (Sever, 1965).

Ground water 11
Downstream of Lake Seminole, ground-water levels in the 

floodplain are influenced by the stage of the Apalachicola 

River and upgradient aquifer conditions. These water-level 

fluctuations are damped, however, by movement of water 

through the floodplain soils (Leitman and others, 1984). 

Observations indicate that ground-water-level fluctuations 

decrease with distance from the river; water levels in wells 

located more than 1.5 mi from the river are influenced mostly 

by local rainfall (U.S. Army Corps of Engineers, 1948). 

Surface Water

Hydrologic factors that affect surface-water resources play 

an important role in the evaluation of reservoir-stream-aquifer 

relations because they influence surface-water interaction with 

ground water. The drainage network established by streams 

provides evidence of water-resource availability and streamaquifer connection; changes in magnitude and duration of 

streamflow in the absence of direct channel precipitation and 

runoff indicate active communication between surface water 

and the underlying ground-water system; and, control structures show human attempts to harness the resource for many 

purposes (Torak and others, 1996). 

Drainage

Lake Seminole is located at the confluence of the Chattahoochee and Flint Rivers, which provide headwater to the 

Apalachicola River that flows south to Apalachicola Bay and 

the Gulf of Mexico. The Chattahoochee River Basin drains an 

area of 8,770 mi2, beginning in the Blue Ridge Mountains in 

northeastern Georgia and flowing southwest across the Piedmont and Coastal Plain physiographic provinces before entering 

Lake Seminole. Near Lake Seminole, the river is deeply incised 

within in its floodplain and cuts into the underlying limestone 

aquifer. There are no large tributaries to the Chattahoochee 

River within the study area, only small streams and creeks—

such as Sawhatchee Creek—that mostly drain the undifferentiated overburden to the limestone (Torak and others, 1996). 

The Flint River Basin drains an area of 8,460 mi2, beginning in the Piedmont physiographic province south of Atlanta 

and flowing south across the Coastal Plain physiographic 

province before entering Lake Seminole. Major tributaries 

originate west of the river in the Coastal Plain and include 

Cooleewahee, Ichawaynochaway, and Spring Creeks. Spring 

Creek originates north of Colquitt, Georgia, and flows south 

into Lake Seminole, about 3 mi northeast of the confluence 

of the Flint and Chattahoochee Rivers. Only minor tributaries exist east of the Flint River draining from the Solution 

Escarpment, which creates a ground- and surface-water divide 

and forms the eastern basin boundary (Torak and others, 

1996). The area between the Flint and Chattahoochee Rivers is 

drained internally, defined by streams that emerge and disappear underground. This area seems to be disconnected from 

the surface-water flow system (fig. 2); but because the Upper 

Floridan aquifer crops out in the river channels, the distinction 

between surface and ground water is not straightforward.

The Apalachicola River drains about 2,400 mi2 of Coastal 

Plain sediments as it flows approximately 106 mi from Lake 

Seminole to Apalachicola Bay and the Gulf of Mexico (fig. 1) 

(Torak and others, 1996). Surface water from Lake Seminole 

flows through reverse springs into the ground-water system 

and eventually discharges into the Apalachicola River just 

downstream of the dam as springflow and diffuse channel 

leakage (Crilley, 2003). 

Streamflow

The Chattahoochee and Flint Rivers provide most of the 

surface-water flow into Lake Seminole. Because the lake 

inundated much of the river channel, many tributaries to the 

Chattahoochee and Flint Rivers now enter the lake directly. 

Inflow to Lake Seminole was determined from daily streamflow measured at four USGS surface-water stations during 

the period of study (fig. 2 and table 2). The inflow to Lake 

Seminole from the Chattahoochee River was measured at the 

surface-water station near Columbia, Alabama (station number 

02343801). The inflow to Lake Seminole from the Flint River 

was estimated by combining flows from the surface-water 

stations on the Flint River at Newton, Georgia (station number 02353000), and on the Ichawaynochaway Creek below 

Newton (station number 02355350). Ichawaynochaway Creek 

enters the Flint River below the gage at Newton but upstream 

of Lake Seminole. The inflow to Lake Seminole from Spring 

Creek, a tributary of the Flint River that now flows directly 

into the lake, is measured at the gage near Reynoldsville, Georgia

(station number 02357150). These four inflows represent 90.5 

percent of the entire drainage area of Lake Seminole (table 2).

All possible inflows to Lake Seminole from tributaries that 

are downstream of active surface-water stations were identified by examining the lake shoreline on 71⁄2-minute USGS 

topographic maps. Eight tributaries were identified, which 

may contribute a small amount of ungaged inflow to Lake 

Seminole (table 3). Five of these tributaries are located along 

the Chattahoochee River impoundment arm: Cedar Creek 

(river mile 41.6) (river miles are defined as miles upstream 

from Jim Woodruff Lock and Dam); Sawhatchee Creek (river 

mile 35.5); Kirkland Creek (river mile 31.9); Bryans Creek 

(river mile 29.2); and Irwin Mill Creek (river mile 24). Two of 

the eight tributaries are located along the Flint River impoundment arm: Big Slough (river mile 33) and Fourmile Creek 

(river mile 24). One tributary, Fishpond Drain, enters Lake 

Seminole along its north shore between the Chattahoochee 

River and Spring Creek. These eight larger tributaries account 

for about 4 percent of the drainage area of Lake Seminole.

An additional 43 possible sources of surface-water inflows 

to Lake Seminole were identified by examining the lake shoreline on 71⁄2-minute USGS topographic maps, but corresponding inflows were considered insignificant. Generally, these are 

12 Ground-water and surface-water flow and estimated water budget for Lake Seminole
intermittent streams, streams that drain small areas, and small 

wetlands along the shoreline. Most of these are along the Chattahoochee River impoundment arm and the south shore of the 

lake. Because of the proximity of drainage divides to the southeast and southwest of the lake, there is little contributing drainage area to the lake in these areas. There are no other inflows to 

Lake Seminole along the northeastern part of the lake because 

internal drainage and karst topography of the Dougherty Plain 

(fig. 1) provide ample solution conduits for surface water to 

drain to the underlying Upper Floridan aquifer.

Dams and Navigational Improvements

Inflow to Lake Seminole from the Chattahoochee and Flint 

Rivers is partially controlled by upstream dams and reservoirs, 

which are used for multiple purposes—including navigation, 

water supply, power generation, recreation, flood control, and 

fish and wildlife enhancement. Beginning in the late 1800s, 

two dams—City Mills and Eagle Phenix—were built on the 

Chattahoochee River at the Fall Line near Columbus, Georgia, 

and Phenix City, Alabama. Initially built for hydromechanical 

power in the textile mills, the dams have since been converted 

to hydroelectric projects. The Georgia Power Company also 

has six relatively small hydropower projects along the 30-mi 

reach of the Chattahoochee River in the Columbus, Georgia, 

area. These projects, however, do not contain appreciable 

storage capacity; therefore, they do not have a notable effect 

on the flow of the Chattahoochee River (U.S. Army Corps of 

Engineers, 1988). 

The U.S. Army Corps of Engineers constructed and operates five large impoundments in the basin. They are, in order 

from the Chattahoochee River headwaters: Lake Sidney 

Lanier (Buford Dam), near Gainesville, Georgia; West Point 

Lake (West Buford Dam), near West Point, Georgia; Walter F. 

George Lake (Walter F. George Lock and Dam), near Eufaula, 

Alabama; Lake George W. Andrews (George W. Andrews 

Lock and Dam), near Columbia, Alabama; and Lake Seminole (Jim Woodruff Lock and Dam), at the Georgia–Florida 

State line and headwater of the Apalachicola River. The major 

stream regulation on the Chattahoochee River is provided 

by the 38,000-acre Lake Sidney Lanier, located about 50 mi 

northeast of Atlanta, Georgia. Minor, but important, amounts 

of storage and flow regulation are provided by West Point 

Lake and Walter F. George Lake. Lakes Andrews and Seminole are run-of-the-river projects, which largely depend on 

inflow controlled by upstream impoundments. Lake Seminole’s limited storage is capable of short-duration-flow augmentation of the Apalachicola River for navigation purposes 

(U.S. Army Corps on Engineers, 1988).

Another impoundment, the Morgan Falls Dam, on the 

Chattahoochee River near Atlanta, Georgia, regulates releases 

from Buford Dam and assists in maintaining adequate flow 

for waste assimilation downstream. Georgia Power Company 

operates this impoundment.

Flint River flows are relatively unimpeded with only 

two reservoirs along its length before entering Lake Seminole: Lake Blackshear (Warwick Dam), operated by the Crisp 

County Power Commission; and Lake Chehaw (Flint River 

Dam), operated by the Georgia Power Company. These 

projects are primarily run-of-the-river and do not affect 

downstream flows appreciably (U.S. Army Corps of 

Engineers, 1988). 

Table 3. Ungaged inflows to Lake Seminole.

[mi2, square mile; DA, drainage area; do., ditto]

Tributary name River 

basin

Drainage 

area

(mi2)

Percent of Lake 

Seminole DA 

Cedar Creek Chattahoochee 30.9 0.18

Sawhatchee Creek do. 75.6 .44

Kirkland Creek do. 39.6 .23

Bryans Creek do. 38.3 .22

Irwin Mill Creeka do. 21.6 .13

Big Slough Flint River 334.2 1.94

Fourmile Creek do. 24.4 .14

Fishpond Drain do. 127.3 .74

Total substantial ungaged inflows 691.9 4.02

a

Drainage area of Irwin Mill Creek is approximate.

Table 2. Surface-water inflows to Lake Seminole.

[mi2, square mile; DA, drainage area]

Surface-water station name Station 

number

Drainage area 

(mi2)

Percent of Lake 

Seminole DA 

Chattahoochee River near Columbia, Ala. 02343801 8,210 47.6

Flint River at Newton, Ga. 02353000 5,740 33.3

Ichawaynochaway Creek below Newton, Ga. 02355350 1,040 6

Spring Creek near Reynoldsville, Ga. 02357150 623 3.6

 Total gaged inflows 15,613 90.5

Surface water 13
Jim Woodruff Lock and Dam controls outflow from Lake 

Seminole. Lake stage varies around a normal pool altitude of 

77 ft. At normal pool, the lake has an area of 37,500 acres, 

impounding the lower 47 mi of the Flint River (to approximately 10 mi downstream of Newton, Georgia) and the lower 

47 mi of the Chattahoochee River (to George W. Andrews 

Lock and Dam near Columbia, Alabama).

Water-Budget Calculations for 

Lake Seminole

Water-budget calculations provide a means to quantify 

contributions of hydrologic components to the total inflow 

and outflow of water for Lake Seminole, to evaluate the 

relative importance of each hydrologic component to the 

water budget, and to estimate errors associated with the measurement and calculation of each component. Error estimates 

for each hydrologic component indicate the accuracy and 

reliability by which a component is known or can be measured, and can be used to guide future data collection and 

measurement techniques.

Lake Seminole receives water from direct precipitation, 

surface-water inflow, and ground-water inflow, and loses water 

by evaporation, surface-water outflow, and leakage to the subsurface (fig. 7). These hydrologic components operate continuously to provide a change in lake storage volume, ∆S, which is 

expressed by the water-budget equation:

∆S = P + SWin – SWout + GWin – GWout – E, (1)

where

∆S = change in lake storage;

P = precipitation;

SWin = surface-water inflow;

SWout = surface-water outflow;

GWin = ground-water inflow;

GWout = lake leakage to the undifferentiated over-burden 

and Upper Floridan aquifer; and

E = evaporation.

Volume for each term is expressed in units of length by dividing by average lake surface area. 

Volume calculations for each hydrologic component were 

computed daily and averaged monthly, and water-budget terms 

were expressed as monthly rates, in inches. Implicit to the 

volume calculation for each hydrologic component in equation (1) is an error term, e, which is evaluated separately from 

component calculations; error is discussed later in this report.

When calculating the water budget, each hydrologic component was measured or estimated independently; that is, no 

component was computed as the residual of other component 

contributions to the water budget. Inputs to the lake include 

direct precipitation, inflowing streams, and ground water. Outputs from the lake include lake evaporation, outflow through 

Jim Woodruff Lock and Dam to the Apalachicola River, and 

lake leakage. Lake storage was estimated from lake stage and 

the relation between lake stage and volume. Monthly estimates 

for these hydrologic components were computed for the study 

period from April 2000 to September 2001, yielding monthly 

estimates of change in lake storage. All components were used 

to calculate error in the lake water budget.

Precipitation

Precipitation was measured at two overwater climate 

stations (fig. 2) using tipping-bucket rain gages. Daily precipitation values from the two stations were then averaged to 

account for variability in precipitation over the lake surface. 

Weather patterns, especially during summer months, include 

a large number of convective thunderstorms that typically 

produce local variations in precipitation; several occurrences 

of significant precipitation variation between stations were 

noted during the study period. Average monthly precipitation 

during water year 2001 (October 2000–September 2001) was 

0.45 inch higher at the climate station at Cummings Access, 

Georgia (4.16 inches), than at the climate station at Sneads 

Landing, Florida (3.71 inches). The variation in the differences 

in monthly precipitation was large between the two stations 

during the study period with a mean difference of 0.45 inch 

and a standard deviation of 0.83 inch. Seasonal variation of 

precipitation in the study area was similar to patterns in the 

long-term record, ranging from a low of 0.20 inch during May 

2000 to a high of 10.61 inches during March 2001 (table 4).

P + SWin – SWout + GWin – GWout – E = ∆S

P = precipitation

SWin = surface-water inflows

SWout = surface-water outflows

GWin = ground-water inflows

GWout = ground-water outflows

E = evaporation

∆S = change in lake storage

P

E

Lake Seminole

Solution feature 

in Upper Floridan 

aquifer

NOT TO SCALE

SWin SWin

GWin

GWout

GWout

SWout

GWin

SWin

Figure 7. The hydrologic cycle for Lake Seminole.

14 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Surface Water

Surface-water inflow to Lake Seminole was measured at four 

surface-water stations (fig. 2; table 2) on the Chattahoochee and 

Flint Rivers, Ichawaynochaway Creek, and Spring Creek. These 

inflows have a combined drainage area of 15,613 mi2, 90.5 percent of the total drainage area of Lake Seminole (17,230 mi2

). 

Daily inflow to the Chattahoochee River impoundment 

arm was measured near Columbia, Alabama (station number 

02343801). This surface-water station is located at the 

George W. Andrews Lock and Dam at river mile 47 (river 

miles are defined as miles upstream from Jim Woodruff Lock 

and Dam), which is the most upstream point of Lake Seminole, on the Chattahoochee River impoundment arm, when 

the lake is at a normal pool altitude of 77 ft. 

Daily inflow to Lake Seminole from the Flint River is 

the sum of flows of the Flint River at Newton, Georgia, and 

Ichawaynochaway Creek, which enters the Flint River below 

Newton. The Newton surface-water station (station number 

02353000) on the Flint River is located about 72 mi upstream 

from Jim Woodruff Lock and Dam. The surface-water station 

on Ichawaynochaway Creek below Newton, Georgia (station 

number 02355350), is located just upstream of its confluence 

with the Flint River at approximately river mile 55. 

Daily inflow was measured on the Spring Creek impoundment arm near Reynoldsville, Georgia (station number 

02357150), using acoustic velocity metering (AVM). AVM 

was used at this surface-water station to measure velocities in 

the stream section due to the existence of backwater conditions. Traditional streamgaging methods estimate discharge 

using stream stage, which is inaccurate under backwater conditions; the AVM measures the velocity of water in the stream 

channel independent of stage, and, with the stream-channel 

cross section, can be used to develop a volumetric flow rate.

The U.S. Army Corps of Engineers measured daily outflow 

from Lake Seminole at Jim Woodruff Lock and Dam and on 

the Apalachicola River at Chattahoochee, Florida (station 

number 02358000), about 0.6 mi downstream of the dam. 

Measured outflow generally is higher on the Apalachicola 

River than at the dam (fig. 8), which can be attributed to 

ground-water inflow to the river channel along the reach 

between the dam and the surface-water station. Outflow 

generally was lower at the Apalachicola River gage from April 

through July 2000 than from the dam (fig. 8). Large (greater 

than 5,000 ft3/s) differences in daily outflow existed during 

March and April 2001. Measurement error, if any, cannot be 

discerned from discharge measured at either the dam or the 

surface-water station. Therefore, discharge measurements 

at the Apalachicola River gage were used in water-budget 

calculations, but were modified to account for the gain in 

streamflow from ground water and used as outflow from Lake 

Seminole. Measured outflow was decreased by 550 ft3/s to 

account for the streamflow gain due to ground-water discharge 

(see “Lake Leakage” section).

Table 4. Comparison of long-term average (based on 

42 years of record, 1959 –2000, Georgia Automated 

Environmental Monitoring Network, 2002) precipitation 

to monthly precipitation during the study period.

[All values in inches]

Month and 

year

Monthly longterm averageTotal monthly 

precipitation Difference

Apr. 2000 3.79 3.20 0.59

May 2000 3.65 .20 3.46

June 2000 5.10 2.70 2.40

July 2000 4.96 3.16 1.80

Aug. 2000 4.80 1.93 2.87

Sept. 2000 3.84 6.62 2.78

Oct. 2000 2.65 .45 2.20

Nov. 2000 3.15 3.77 .62

Dec. 2000 5.61 2.47 3.14

Jan. 2001 5.37 1.84 3.53

Feb. 2001 4.92 .73 4.19

Mar. 2001 6.09 10.61 4.52

Apr. 2001 3.79 1.32 2.47

May 2001 3.65 1.04 2.61

June 2001 5.10 8.44 3.34

July 2001 4.96 8.67 3.71

Aug. 2001 4.80 4.86 .06

Sept. 2001 3.84 3.06 .78

 Oct. 2001 2.65 2.41 .24

Total 82.72 67.48 15.24

–10,000

–5,000

0

5,000

10,000

15,000

20,000

DIFFERENCE, IN CUBIC FEET PER SECOND

2000 2001

APR AUG DEC APR AUG

Figure 8. Difference in discharge between the Apalachicola 

River at Chattahoochee, Florida, and Jim Woodruff Lock and 

Dam (see figure 2 for locations).

Water-budget calculations for Lake Seminole 15
Ungaged Inflow to Lake Seminole

A small amount of inflow to Lake Seminole is not accounted 

for by the four gaged inflows. The drainage area represented 

by the four gaged inflows represents about 91 percent of the 

total drainage area to Lake Seminole (table 2), leaving about 

9 percent ungaged. Fifty-one minor inflows to Lake Seminole 

were identified on 71⁄2-minute USGS topographic maps, downstream of the four gaged inflows. Of these, the eight largest 

ungaged inflows represent about 4 percent of the total drainage 

area of Lake Seminole (table 3). The remaining 5 percent of 

unaccounted drainage area is made up of small areas along the 

lake that include the 43 minor inflows and karst areas north of 

the lake, which have little surface-water drainage.

Six of the eight largest inflows were measured during 

drought conditions, the results of which are summarized in 

table 5. Discharge measurements for three of the inflows on 

October 23–28, 1986, were made as part of a ground-water 

modeling study (Torak and others, 1996); discharge measurements were made for six inflows during three synoptic runs 

performed between October 1999 and August 2000, as part 

of a ground-water seepage study (Mosner, 2002). The USGS 

recently installed a gage on Sawhatchee Creek at Cedar 

Springs (station number 02343940). Daily flows measured 

from January 19 to September 30, 2002, range from a minimum of 5.8 ft3

/s to a maximum of 206 ft3/s, with an average 

flow for this period of 34 ft3/s.

Table 5. Summary of streamflow measurements for substantial ungaged inflows to Lake Seminole.

[mi2,square mile; DA, drainage area; ft3/s; cubic foot per second; %, percent. Kirkland Creek drainage area is 

approximated as 90 percent of entire Kirkland Creek drainage area]

Streamflow 

station name

Station 

number

Drainage 

area 

(mi2)

Percentage of basin DA 

accounted for 

in analysis

Percentage of 

Lake Seminole 

DA

Streamflow 

(ft3/s)

Date(s)

Cedar Creek at State High-way 

95 near Calumet, Ala. 02343850 30.3 98.1 0.18

19.4 Apr. 25, 2000

6.14 July 27, 2000

Sawhatchee Creek at Cedar 

Springs, Ga. 02343940 64.2 84.9 .37

9.7 Oct. 23–28, 1996

10.6 Oct. 18, 1999

36.2 Apr. 25, 2000

5.21 July 27, 2000

Kirkland Creek at Williams 

Road, near Jakin, Ga. 02344009 35.6 90 .21 9.86 Apr. 25, 2000

Bryans Creek at State Highway 95 near Crosby, Ala. 02344025 34.7 90.5 .2 0 Apr. 25, 2000

Big Slough at Georgia 

Highway 97 near 

Bainbridge, Ga.

02355950 315 94.3 1.83

0 Oct. 23–28, 1996

0 Oct. 18, 1999

0 Apr. 24, 2000

0 July 31, 2000

Fishpond Drain at State Route 

285 near Donalsonville, Ga. 02357310 38.8 30.5 .23

0 Oct. 23–28, 1996

0 Oct. 19, 1999

0 Apr. 24, 2000

The inflow to Lake Seminole from the eight largest 

ungaged inflows was approximated based on limited streamflow information available along with drainage-area size 

and knowledge of flow characteristics of the tributaries. It is 

assumed that the 43 minor inflows do not contribute substantial inflow to the lake. The tributary inflows were analyzed in 

groups, depending on the basin into which they flowed. Five 

of the eight largest ungaged inflows are located in the Chattahoochee River Basin; of these, Sawhatchee Creek has the 

largest drainage area (75.6 mi2, table 3). Average flows 

measured on Sawhatchee Creek from January 19 to September 30, 2002, were 0.47 percent of the average flows of the 

Chattahoochee River near Columbia, Alabama, for the same 

period. The sum of the flows at Cedar Creek, Kirkland Creek, 

and Bryans Creek (29.3 ft3/s) measured on April 25, 2000, was 

similar to the flow of Sawhatchee Creek that same day 

(36.2 ft3/s). No flow measurements were available for Irwin 

Mill Creek, but this basin has the smallest drainage area of 

the five inflows (21.6 mi2) and, hence, likely contributes only 

a small amount of flow. Based on this limited information, it 

is reasonable to assume that these ungaged inflows constitute 

approximately 1 percent of the flow in the Chattahoochee 

River at Columbia, Alabama. Therefore, in order to account 

for these five inflows, daily inflow was approximated as 

1 percent of the daily Chattahoochee River flow.

16 Ground-water and surface-water flow and estimated water budget for Lake Seminole
The Flint River Basin contains three of the eight largest 

ungaged inflows (table 3). Fourmile Creek has the second 

smallest drainage area of the eight largest ungaged inflows 

(24.4 mi2) and probably provides only a minimal amount of 

flow, although no flow measurements were available for verification. Big Slough and Fishpond Drain have the two largest 

drainage areas of the eight largest ungaged inflows, 334.2 mi2

and 127.3 mi2, respectively (table 3). All low-flow synoptic measurements indicated that there was no flow on these 

tributaries (table 5). Big Slough normally flows during wet 

conditions, but was dry at the time flow measurements were 

made; however, the flow occasionally reverses due to internal 

drainage of the karst topography and backwater conditions of 

Lake Seminole. Flows in Big Slough tend to be smaller than 

expected for the drainage-area size because the karst topography in the basin reduces surface-water drainage.

The synoptic-flow measurements indicating no flow for 

Fishpond Drain were taken far upstream of where it flows into 

the lake, thus representing only about 30 percent of the drainage area of Fishpond Drain (table 5). The karst flow system 

in the lower part of the Fishpond Drain Basin minimizes the 

potential for surface-water drainage. There is a low potential for ground-water inflow to Fishpond Drain due to small 

hydraulic gradients between surface water and the aquifer in 

this part of the basin. In contrast, high ground-water inflow 

occurs along Spring Creek, where hydraulic gradients are 

higher than those in adjacent Fishpond Drain, as indicated by 

numerous springs that are present along Spring Creek. Despite 

the larger drainage areas of the ungaged inflows in the Flint 

River Basin, ungaged inflows in the Flint River Basin are 

lower than ungaged inflows in the Chattahoochee River Basin. 

Therefore, as an approximation, daily inflow from the three 

ungaged inflows in the Flint River Basin were calculated as 

0.5 percent of the average flows measured on the Flint River 

near Newton, Georgia.

Error Analysis

The accuracy of streamflow records depends on the stability of the stage-discharge relation, accuracy of stage measurements, accuracy and frequency of discharge measurements, 

and interpretation of records (Novak, 1985). A determination 

of accuracy of USGS daily average streamflow records is 

reported on a water year (October–September) basis for each 

surface-water station. Daily streamflow records are rated as 

excellent, good, fair, or poor. An excellent rating indicates that 

95 percent of the daily discharges are within 5 percent of the 

true discharge. A good rating indicates that 95 percent of the 

daily discharges are within 10 percent of the true discharge. A 

fair ration indicates that 95 percent of the daily discharges are 

within 15 percent of the true discharge. A poor rating indicates 

that the daily streamflow records do not meet the fair rating 

(McCallum and Hickey, 2000; Franklin and others, 2000; 

McCallum and others, 2001).

Discharge measurements for the Chattahoochee River (station number 02343801) were reported as good in water year 

2000 and fair in water year 2001. During this study (April 

2000–September 2001), 66 days (12 percent) of daily streamflow record were estimated. Estimated values are considered 

poor (McCallum and Hickey, 2000).

Streamflow records for the Flint River (station number 

02353000) and Ichawaynochaway Creek (station number 

02355350) were reported as good in both water years 2000 

and 2001. The Flint River data had only 1 day of estimated 

flow; Ichawaynochaway Creek had 11 days of estimated flows 

(2 percent) during the period of study. Flow measurements 

for Spring Creek (station number 02357150) were reported as 

good in both water years 2000 and 2001, except when flows 

were greater than 2,000 ft3/s, which were considered fair. 

Flows were greater than 2,000 ft3/s on 9 days during the study 

period (1.6 percent) (McCallum and Hickey, 2000, McCallum 

and others, 2001).

Measured streamflow for the Apalachicola River (station 

number 02358000) was reported as good in both water years 

2000 and 2001. There were only 2 days with estimated flows. 

Accuracy of flow measurements was not reported for gages 

operated by the U.S. Army Corps of Engineers at Jim Woodruff Lock and Dam.

Although estimated ungaged inflow in the study area is 

small (less than 1 percent of total lake inflow), the error in 

estimating ungaged inflow can be quite large and add to the 

errors in total surface-water inflow. There are few measurements of streamflow for the eight largest ungaged inflows; 

these were made on specific dates during low-flow conditions, 

which are not indicative of all flow conditions. The method 

of approximating ungaged inflows as a percentage of the 

gaged inflows assumes that ungaged drainage areas exhibit 

similar hydrologic response as gaged drainage areas. This is 

unlikely because the Chattahoochee River flows are regulated, 

so flow variations on the Chattahoochee River will not be 

representative of flow variations on unregulated streams in 

smaller basins.

Lake Storage

A relation between lake stage and storage enabled daily 

estimates of lake storage to be obtained as a continuous function of lake stage. A regression equation developed from stage 

and storage data predicted lake storage to within 0.1 percent 

of the published stage-volume relation for the range of lake 

stage measured during the study period (fig. 9). The U.S. 

Army Corps of Engineers takes daily measurements of lake 

stage at midnight. These measurements are available at 

http://water.sam.usace.army.mil/acfframe.htm. Stage-area 

relations also were used to calculate evaporation by the 

energy-budget method and empirical equations. 

Water-budget calculations for Lake Seminole 17
Ground-Water Inflow and Lake Leakage

Ground-water inflow to Lake Seminole consists of flow 

across the lake-aquifer boundary from the aquifer into the lake 

and stream channels located below the surface-water stations. 

Lake leakage consists of ground water that flows across the 

lake-aquifer boundary from the lake into the aquifer. Rates 

of ground-water inflows and lake leakage were obtained 

from results of a previous digital simulation of October 1986 

conditions (Torak and others, 1996). The model developed 

for that simulation was based on an application of the USGS 

modular finite-element model, MODFE (Cooley, 1992; and 

Torak, 1993a,b). The simulation results were used to approximate ground-water conditions in the Upper Floridan aquifer 

around and beneath the lake during the current study period. 

Simulated rates of ground-water inflow along stream channels and impoundment arms were adjusted monthly based on 

calculated stream baseflow to account for seasonal variations 

in ground-water flow rates. Lake leakage was determined by 

streamflow gain of the Apalachicola River just downstream of 

Jim Woodruff Lock and Dam. Streamflow gain is attributed to 

lake leakage that enters the aquifer and then discharges into 

the river.

Estimation of Flow Rates

Rates of ground-water inflow to Lake Seminole and lake 

leakage (fig. 10) were estimated from simulated discharge 

across finite elements, representing the main body of the lake 

and across linear and nonlinear head-dependent (Cauchy-type) 

ground-water flow boundaries. The Cauchy-type boundaries 

represent streams and impoundment arms of the lake; the lake 

was represented by finite elements (Torak, 1993a). Cauchytype boundaries, which are coincident with element sides, 

represented the channels of the main gaged inflows to Lake 

Seminole—that is, the Chattahoochee and Flint Rivers, and 

Spring and Sawhatchee Creeks. On the Chattahoochee River, 

the surface-water station was located outside of the model 

area, so Cauchy-type boundaries represented the stream channel from the model boundary into the upper reaches of the 

corresponding impoundment arm of the lake and Sawhatchee 

Creek. The Flint River and Spring Creek were represented 

with Cauchy-type boundaries that extend downstream of the 

gages and into the corresponding impoundment arms, but not 

along the pre-impoundment channels in the main body of the 

lake. Simulated ground-water flow rates represent hydrologic 

conditions that existed in October 1986, which is the steadystate calibration period for the model. There was a drought in 

October 1986 similar in intensity to the drought that occurred 

during the study period; therefore, simulated ground-water 

flow around Lake Seminole and lake leakage for October 1986 

conditions were assumed to closely approximate the flow 

conditions that existed during the study period.

The model simulated small-magnitude, areally distributed 

flow (ground-water inflow and lake leakage) across finite 

elements that represent the main body of the lake. Simulated 

ground-water inflow to the main body of Lake Seminole was 

about 34 ft3/s, and lake leakage was about 14.7 ft3/s. This 

ground-water inflow was included in the total ground-water 

inflow to the lake but was not varied seasonally like the other 

simulated ground-water inflows (see below). Because the 

areally distributed inflow rates are relatively small, seasonal 

variation would have little effect on the overall lake water budget. Lake leakage was approximated using another approach 

(see below) because the rate of lake leakage appears to be 

underestimated according to ground-water model results.

33,000

35,000

29,000

31,000

37,000

39,000

41,000

75 75.5 76 76.5 77 77.5 78

STAGE, IN FEET ABOVE NAVD 88

VOLUME, IN ACRE-FEET

Minimum

stage

Maximum

stage

y = 5.8333x3 – 7.5x2 – 65103x + 2761600

R2 = 1

Figure 9. Regression defining the stagevolume relation for Lake Seminole.

VOLUMETRIC FLOW RATE,

IN CUBIC FEET PER SECOND

2000 2001

A M J J A S O N D J H M A M J J A S

Ground-water inflow

Lake leakage

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

Figure 10. Lake Seminole ground-water inflow and lake 

leakage derived from simulated results for the period 

April 2000 – September 2001.

18 Ground-water and surface-water flow and estimated water budget for Lake Seminole
All Cauchy-type boundaries representing streams simulated 

ground-water inflow to stream channels and impoundment

arms from the Upper Floridan aquifer (table 6). Unit discharge 

across the Cauchy-type boundary, or ground-water inflow per 

unit of channel length, generally is larger for upstream reaches 

along the Chattahoochee River and Flint River impoundment 

arms than for the downstream reaches, even though boundary 

coefficients generally are higher for downstream reaches than 

upstream reaches. Boundary coefficients are a function of hydraulic conductivity, streambed width, and streambed thickness, 

and describe how easily water flows across the boundaries for a 

given hydraulic gradient. Thus, for inflow rates to be higher in 

the upstream reaches than in the downstream reaches, hydraulic gradients toward the stream in the upstream reaches need 

to be much higher than those in the downstream reaches to 

overcome the low boundary coefficient values in the upstream 

reaches. This indicates that ground-water inflow along these 

impoundment arms is more sensitive to hydraulic gradients in 

the aquifer close to the streams than to boundary coefficients. 

Seasonal variations in ground-water inflow across Cauchytype boundaries along each impoundment arm were simulated 

on a monthly basis during the study period. The inflows were 

varied according to changes in monthly baseflow estimates 

of streamflows measured at gages along the impoundment 

arms using HYSEP, a hydrograph separation program (Sloto 

and Crouse, 1996). A scaling factor was developed for each 

impoundment arm, defined as the ground-water inflow 

downstream of the gage derived from the October 1986 

ground-water simulation (Torak and others, 1996) divided by 

the estimated October 1986 baseflow from HYSEP. (Since 

streamflow data were unavailable in October 1986 for Spring 

Creek near Reynoldsville, Georgia, station number 02357150, 

the average of the estimated baseflows for October 2000 and 

2001 was substituted for the October 1986 value, because 

2000 and 2001 both were drought years similar to 1986.) 

Monthly ground-water inflow was calculated as the product 

of the monthly estimated average baseflow from HYSEP and 

the scaling factor, to proportionally adjust ground-water inflow 

to the amount of upstream baseflow. Scaling factors for the 

Chattahoochee and Flint Rivers and Spring Creek were 0.448, 

0.426, and 0.173, respectively. Thus, baseflow contributes a 

larger percentage of total streamflow during low-flow conditions than during high-flow conditions, a result that is consistent with that found by Mosner (2002).

Table 6. Summary of Cauchy-type boundaries used to estimate flow between the Upper Floridan aquifer 

and stream channels.

[ft/d, foot per day; ft3/s, cubic foot per second, mi, mile; ft3/s/mi, cubic foot per second per mile; do., ditto]

Zonea Boundary

type

Stream

name

Boundary 

coefficient 

(ft/d)

Ground-water 

inflow

(ft3/s)

Length of 

channel 

(mi)

Ground-water inflow 

per channel length 

(ft3/s/mi)

37 Linear Chattahoochee River 2.0 10.5 3.1 3.3

38 do. do. 60 185.6 10 18.5

39 do. do. 100 142.7 9 15.8

40 do. do. 150 45.7 5 9.2

12 do. Flint River 120 15.8 .8 20.2

13 do. do. 100 156.7 16.8 9.3

14 do. do. 100 81.5 4.3 18.9

15 do. do. 120 275.3 13.8 20

16 do. do. 170 64.9 7.4 8.8

17 do. do. 200 36.7 10.1 3.6

36 Nonlinear Spring Creek 32 24.8 6.7 3.7

41 do. Sawhatchee Creekb 1.3 8.1 6.3 1.3

42 do. do. 1.8 1 1.4 .8

43 do. do. 2 3.8 3 1.3

aZones refer to numbered stream reaches used in the report by Torak and others (1996) and are numbered separately for each boundary 

type. Ground-water inflow and channel length are adjusted to reflect the percentage of Zone 36 located downstream of the gage.

b

Sawhatchee Creek is a tributary to the Chattahoochee River that enters downstream of gage.

Water-budget calculations for Lake Seminole 19
Although results of digital modeling by Torak and others 

(1996) indicated that leakage from the main body of the lake 

occurred at a rate of 14.7 ft3/s during October 1986, there is 

evidence that such leakage occurs at a much greater rate. Dye 

tracing performed by the U.S. Army Corps of Engineers near 

sinkholes and other solution structures in the bottom of the 

lake along the western shore near the dam indicated that lake 

water discharges from the lake through some of these features, 

which act as conduits. Some of this lake water enters these 

features at a distance from 0.5 to 0.7 mi upstream of the dam 

and flows through the Upper Floridan aquifer around the dam, 

emerging at a spring just downstream of the dam. Dye-tracing results indicate a travel time from about 5 to 7 hours for lake 

water to enter the spring downstream of the dam (James H. Sanders, Jr., U.S. Army Corps of Engineers, Mobile District, written 

commun., August 2001). This spring flow joins ground-water 

discharge from a diffuse area to the south, and discharges to 

a sinkhole, only to reemerge in a conduit in the bottom of the 

Apalachicola River, about 280 yards downstream of the dam. 

Flow rates measured using acoustic Doppler current profiling 

(ADCP; Lipscomb, 1995) at this conduit on October 21, 1999, 

and April 17, 2000, were about 140 and 210 ft3/s, respectively. 

The USGS surface-water station on the Apalachicola River at 

Chattahoochee, Florida (station number 02358000), is located 

about 0.6 mi downstream of the dam and measures streamflow 

that consists of dam outflow and channel leakage, such as the 

leakage observed from this conduit, as well as diffuse channel inflow from the aquifer. Water chemistry of flow from the 

conduit indicated that the discharging water was a mixture 

of about 93 percent lake water and 7 percent ground water 

(Crilley, 2003), illustrating that most of the water discharging 

to the river at this boil originated as lake water. The groundwater component could be the result of mixing with ground 

water already present in the aquifer and/or hydrochemical 

interaction of the lake water with the limestone aquifer, altering the water chemistry toward a ground-water signature.

A comparison of lake-outflow measurements during 

periods of good record, beginning during August 2000 and 

excluding the outliers during March and April 2001, indicates 

that flows at the Apalachicola River gage are consistently 

about 550 ft3/s higher than outflows from the dam (fig. 8). 

This streamflow gain most likely is due to lake leakage that 

flows around the dam through the ground-water flow system 

and enters the channel farther downstream, before the surfacewater station. Hence, lake leakage was estimated as 550 ft3

/s. 

Likewise, lake outflow, as measured from the Apalachicola 

River gage, was decreased by the same 550 ft3/s, which represents streamflow gain below the dam due to ground-water 

discharge that originated as lake leakage. The value for lake 

leakage and ground-water discharge to the river are reasonable because they are larger than the flow from the River Boil; 

additional inflows to the river from other boils or diffuse flow 

are possible along this stretch of the river. In general, it is 

expected that ground-water discharge and lake leakage would 

not change appreciably because the hydraulic gradient from 

the aquifer to the stream along this reach is relatively constant, 

although variation in lake leakage was observed in the two 

measured flows from the boil (140 and 210 ft3/s).

Error Analysis

Limitations to the ground-water model could produce 

misleading results for this water-budget component. When the 

model was developed in the late 1980s, limited field data were 

available to properly assign aquifer properties and boundary 

conditions as model inputs near Lake Seminole. The paucity 

of field measurements in the Lake Seminole area limited the 

ability of the model to simulate local stream-lake-aquifer 

interaction; therefore, calibration was affected in this area on 

a regional scale. The model simulated drought and pumping 

conditions during October 1986, which may not be completely 

representative of the conditions that occurred during the current study. In addition, seasonal variations in ground-water 

conditions were not simulated by the steady-state model for 

October 1986 conditions.

The hydrologic framework of the model is based on a conceptualization of flow through a heterogeneous porous media 

rather than more complex flow through discrete conduits, 

which are characteristic of the karst limestone comprising the 

Upper Floridian aquifer in the Lake Seminole area. Hence, 

values of hydraulic conductivity that were assigned to the 

model represent the combined effects of discrete conduits 

and the limestone matrix. The distribution and connectivity 

of discrete conduits could have a large effect on the hydraulic 

conductivity and flowpaths in the Lake Seminole area. A careful examination of aerial photographs of the lake area before 

the dam was constructed identified sinkholes that, if interconnected, could provide preferred paths for ground-water flow. 

Sever (1965) identified numerous springs in the bottom of the 

lake, indicating the potential for such conduits for groundwater flow. A previous study involving the Upper Floridian 

aquifer in the Albany, Georgia, area used sinkhole and rockcavity distributions to delineate hydraulic-property zones for 

simulation (Torak and others, 1993). Applying this approach 

to the Lake Seminole study area by delineating discrete flow 

conduits and evaluating hydraulic properties into a zoned 

arrangement for model input would improve the model. The 

only limitation to applying this approach to the Lake Seminole 

study area would be the availability of hydrogeologic information for characterization.

Despite the limitations of the digital model prepared by 

Torak and others (1996), it is the best method to quantify 

ground-water inflow to Lake Seminole and lake leakage. 

Several assessments can be made to test whether the flows 

computed by the model are reasonable. Ground-water flow 

estimates from the Cauchy-type boundaries that were simulated along the Spring Creek impoundment arm were verified 

by performing a streamflow survey between the Reynoldsville, 

Georgia (station number 02357150), and the measurement 

site at Brinson, Georgia (station number 02357050) (fig. 2), 

on September 15, 2000. Measurements of stream discharge 

20 Ground-water and surface-water flow and estimated water budget for Lake Seminole
were made at seven sites, and discharge was measured at 

four springs along this reach. All tributary flow entering 

Spring Creek occurred along spring runs that resembled 

creeks. Discharge from these runs was measured and traced to 

spring origins upstream of the main channel. Other discharge 

measurements that were performed in Spring Creek between 

the spring runs indicated diffuse channel leakage, which was 

attributed to ground-water inflow. Flow increased from about 

31 ft3/s near Brinson, Georgia, to about 131 ft3/s near Reynoldsville, Georgia, a net gain of about 100 ft3

/s. Of this, about 

52 ft3/s was measured from four springs. The remaining flow 

was derived either from unmeasured, in-channel springs or 

from diffuse ground-water inflow along the wetted perimeter 

of the channel.

Although ground-water conditions on the day of the survey 

were not the same as the simulated conditions of October 

1986, both conditions represent drought periods. The model 

simulated 26 ft3/s of ground-water discharge along this stream 

reach (Cauchy-type boundary). This is almost one-quarter of 

the 100 ft3/s obtained from the streamflow survey, indicating that the model could underrepresent ground-water inflow 

along this reach of the Spring Creek impoundment arm. 

Despite this apparent incongruity between model results and 

flow measurements, the model simulated 37 ft3/s of streamflow gain between Iron City, Georgia, and Brinson, Georgia; 

on September 15, 2000, a gain of 31 ft3/s was measured 

between Iron City and Brinson.

Simulated ground-water flows along the Flint River impoundment arm can be verified by examining increases in flow along 

the Flint River between Newton and Bainbridge, Georgia. 

Unfortunately, the USGS surface-water stations at Ichawaynochaway Creek near Newton, Georgia, and at the Flint River 

at Bainbridge, Georgia, were not in use at the time data were 

collected for model calibration during October 1986. The 

synoptic data collection, however, that was performed during 

October 23–28, 1986, to obtain measurements for calibration 

of the model (Torak and others, 1996) adequately documented 

the flow conditions of the time. The gain of the Flint River 

between Newton and the auxiliary surface-water station upstream 

of Bainbridge, Georgia (station number 02355700), excluding 

tributary flow from Ichawaynochaway Creek, was 290 ft3/s. 

Simulated ground-water inflows along this reach of the Flint 

River were about 80 percent greater, 530 ft3/s, indicating that 

although simulated ground-water inflows are the same order of 

magnitude as the measured inflows, the model may have overestimated the inflow of ground water along this reach during 

October 1986. Ground-water inflows could not be assessed in 

this manner along the Chattahoochee River impoundment arm 

because upstream and downstream surface-water stations did 

not exist to define a reach that was simulated with the model.

Measurements of streamflow gains from ground-water 

inflow along a gaged segment of the Flint River were compared with baseflow estimates derived from HYSEP to determine if it is reasonable to scale simulated ground-water inflow 

to the stream by monthly HYSEP-derived baseflows to mimic 

seasonal variations in ground-water inflows. Near the end of 

the study period during August 2001, the USGS reinstated the 

surface-water station on the Flint River at Bainbridge, Georgia (station number 02356000). This station, along with the 

gages on the Flint River at Newton, Georgia (station number 

02353000), and on Ichawaynochaway Creek below Newton, 

Georgia (station number 02355350), allows the calculation 

of ground-water inflow along the reach of the Flint River 

between Newton and Bainbridge. This reach contains only 

one ungaged tributary, Big Slough, which flows only during 

extreme rainfall events and sometimes reverses flow. There 

was a linear relation between measured streamflow gains from 

ground-water inflow between Newton and Bainbridge and 

monthly HYSEP baseflow calculated at Newton for the period 

August 2001 through May 2003 (r2 = 0.50). This suggests that 

proportional scaling of simulated ground-water inflow is a 

reasonable approximation for obtaining monthly ground-water 

inflow along the Cauchy-type boundaries to the lake. The 

slope of the relation (0.19) was about half as much as the scaling factor used to scale simulated ground-water flow (0.43). 

The simulated ground-water flow across Cauchy-type 

boundaries not only contains the flow between Newton and 

Bainbridge but also the flow downstream from Bainbridge. 

This additional flow cannot fully account for the differences between the scaling factor and the slope of the relation between baseflow and ground-water inflow because the 

simulated ground-water inflow downstream from Bainbridge 

accounts for only 11 percent of the total simulated flow to the 

reach. Hence, it is likely that the scaling factor approximated 

by October 1986 conditions overestimates the ground-water 

inflows along the Flint River during the study period. 

Because lake leakage was estimated as the average difference in streamflows between Jim Woodruff Lock and Dam and 

the stream gage on the Apalachicola River at Chattahoochee, 

Florida (station number 02358000), when streamflow measurements appeared reasonable, the estimates are subject to the 

same measurement errors as streamflows. Apalachicola River 

flows were reported as good in both water years 2000 and 

2001, indicating that measurement errors were within 10 percent of the true discharge 95 percent of the time. Accuracy 

of flows was not reported for the gages operated by the U.S. 

Army Corps of Engineers at the dam. Lake leakage, set to a 

constant 550 ft3/s, represents 4.1 percent of the average flow at 

the Apalachicola River gage. Hence, the estimate of lake leakage is within the error of the streamflow measurements used 

to determine it. Furthermore, there is no reason to suspect that 

all lake leakage discharges into the small section of river reach 

between the dam and the surface-water station on the Apalachicola River. Ground-water flowpaths delineated by Jones 

and Torak (2003) indicate that additional, unquantified lake 

leakage could discharge to the river downstream of the gage, 

or enter the aquifer, becoming part of the regional groundwater flow and not entering the river. Lake leakage is likely 

the least accurate component in the water budget.

Water-budget calculations for Lake Seminole 21
Lake Evaporation

Six methods were used to determine lake evaporation: these 

are the energy-budget method and five empirical equations. 

The energy budget is one of the most accurate methods for 

determining evaporation, but the complexity in data collection 

makes it difficult to use (Harbeck and others, 1958). Although 

energy-budget estimates for lake evaporation are used in the 

development of the water budget for this study, those estimates 

are compared with long-term average annual pan evaporation 

measurements and estimates calculated using five empirical equations to determine which equations, if any, would be 

appropriate for use at Lake Seminole. The following empirical 

equations were used to compute lake evaporation: PriestleyTaylor, Penman, DeBruin-Keijman, and Papadakis, along with 

estimates calculated by the Georgia Automated Environmental 

Monitoring Network (GAEMN) using climate-station data and 

the Priestley-Taylor equation. 

The energy-budget method requires large amounts of 

climatic and hydrologic data to implement; these data are 

labor intensive and expensive to collect. On the other hand, 

the better empirical equations require the calculation of stored 

heat to determine evaporation, and some empirical equations

require only basic climate data. These data are readily available from two overwater climate stations that were installed 

on Lake Seminole during this study and are currently being 

managed by The University of Georgia as part of the GAEMN 

(Hoogenboom, 1996). In addition to providing near real-time 

climate data from the climate stations, GAEMN calculates 

lake evaporation at each climate station using the PriestleyTaylor equation and posts these estimates at http://www.griffin.

peachnet.edu/bae/ (accessed on June 12, 2004). 

Evaporation estimates calculated using the energy-budget 

method were compared with those calculated using the five 

empirical equations listed above to determine whether there 

is a future need for the cost- and labor-intensive-data collection required to support calculation of lake evaporation by the 

energy-budget method. 

Energy-Budget Method

The energy budget requires measurements of heat added 

to the lake by inflowing surface water and ground water, and 

direct precipitation, measurements of heat lost from the lake 

by surface-water outflow and lake leakage, the influence of 

net radiation, and measurements of the change in heat stored 

in the lake. The net addition of heat to the lake that does not 

result in an increase heat stored in the lake is then attributed to 

evaporation using the equation (Anderson, 1954):

Qx = Qs – Qr + Qa – Qar – Qbs + Qv – Qh – Qe, (2)

where

Qx = change in stored energy; 

Qs = incident solar radiation;

Qr = reflected solar radiation;

Qa = incoming atmospheric longwave radiation;

Qar = reflected longwave radiation;

Qbs = longwave radiation emitted by the lake;

Qv = net energy advected by streamflow, ground water, 

and precipitation;

Qh = energy removed from the lake as sensible heat; and

 Qe = energy used in evaporation.

All terms in equation 2 are expressed in calories per square 

centimeter per day (cal/cm2/day).

The variables Qs, Qr, Qa, Qar, and Qbs were not measured 

directly; instead, net radiation (Qn = Qs – Qr + Qa – Qar – Qbs) 

was measured with a net radiometer located at each of the two 

overwater climate stations (Cummings Access in Georgia and 

Sneads Landing in Florida) (fig. 2), and the resulting data were 

averaged to obtain an estimate of net radiation for the entire 

lake. Because of the fragility of the net radiometer’s polyethylene domes, which became brittle in the hot climate, there were 

periods when the instrument was not functioning. Therefore, 

a relation was developed between net radiation and total-solar 

radiation measured at each station (R2 = 0.8949 for the Cummings Access site, and 0.8958 for the Sneads Landing site; 

fig. 11) to determine daily net radiation from measurements of 

total-solar radiation during those periods when net radiation 

could not be measured.

y = 0.7195x – 2.0944

R2 = 0.8949

–5

0

5

10

15

20

25

y = 0.7371x – 1.748

R2 = 0.8958

0

5

10

15

20

25

0 5 10 15 20 25 30 35

TOTAL SOLAR RADIATION, IN MEGAJOULES PER SQUARE METER

NET SOLAR RADIATION, IN MEGAJOULES PER SQUARE METER

B. Sneads Landing, Florida

A. Cummings Access, Georgia

Figure 11. Regression showing relation between total solar 

radiation and observed net radiation at (A ) Cummings 

Access, Georgia, and (B ) Sneads Landing, Florida (see

figure 2 for climate-station locations).

22 Ground-water and surface-water flow and estimated water budget for Lake Seminole
The net advected heat, Qv

, to Lake Seminole consists of 

heat added to the lake by surface- and ground-water inflow 

and precipitation, and heat exported from the lake by surface-water outflow and leakage. Heat added to the lake by 

surface-water inflow was calculated from measurements of 

daily average streamflow at surface-water stations and stream 

temperature, which was measured using a network of temperature probes that were installed in 26 vertical arrays to obtain 

temperature profiles at the most upstream locations of the 

impoundment arms (table 7). When temperature data from the 

most upstream vertical arrays in the impoundment arms were 

not available, data from alternate arrays positioned closest to 

the most upstream arrays were used. A complete description 

of thermal profiles, temperature-probe installation, and laketemperature monitoring is given in the appendix.

Heat added to the lake by precipitation was estimated from 

the volume and temperature of precipitation, which was collected

and recorded at the two overwater climate stations on the lake. 

It was assumed that the temperature of the precipitation was 

similar to the air temperature. Heat from precipitation at each 

climate station was averaged on 15-minute intervals as the product of the volume of precipitation, average air temperature, and 

specific heat and density of water. These values of heat were 

summed on a daily basis, and the results were averaged for the 

two climate stations to obtain the average daily heat advected 

by precipitation. Heat exported from the lake by surface-water 

outflow was calculated as the product of the discharge and 

temperature of the Apalachicola River at Jim Woodruff Lock 

and Dam, and the specific heat and density of water. 

Heat advected to the lake from ground-water inflow and 

lost through lake leakage was calculated as the product of simulated rates of ground-water flow and lake-leakage, groundwater and lake temperature, and specific heat and density of 

water. Ground-water inflow was assumed to have a constant 

temperature of 20 degrees Celsius ( ̊C), which was the temperature of ground water measured in springs located beneath 

the lake (in-lake springs; see fig. 4A in appendix) and was 

about the mean annual air temperature of the region (Sever, 

1965; fig. 12; http://www.griffin.peachnet.edu/bae/—accessed 

on June 12, 2004). 

Daily change in heat stored in the lake, Qx, was calculated 

using daily lake volume, changes in lake temperature, volume 

of the lake, and the specific heat and density of water. Daily 

changes in heat stored in the lake were calculated separately 

for each impoundment arm and for the main body of the lake 

as follows. Initially, the average daily temperature change in 

each part of the lake was determined by averaging the changes 

in daily temperature from all working probes located in that 

part of the lake (table 8). These values were then multiplied by 

the estimated percentage of lake volume in each corresponding part of the lake. The resulting values were then summed 

and multiplied by the average daily lake volume (determined 

as the average of lake volumes estimated at the beginning and 

end of each day) and summed to obtain the daily change in 

stored heat for the lake. Probes 1-0 and 25-0, placed specifically in spring runs along the lake bottom, were excluded from 

calculations of lake temperature because these probes measure 

the temperature of local ground-water inflow, which is not 

representative of lake-water temperature in the impoundment 

arm. Problems estimating Qx arise from missing data, resulting 

from temperature-probe failure and degree of representation of 

measured temperature and estimated volume for different parts 

of the lake (discussed in the appendix).

Daily volumes of each part of the lake were derived from 

lake stage by using a polynomial relation and lake bathymetry (fig. 9). Proportions of lake volume were calculated by 

using the length, width, and depth of channels in each part of 

the lake (table 8). Although volume estimates are not precise, weighting the temperature by the approximate volume 

proportions is an improvement over assigning equal weight 

Table 7. Summary of surface-water inflows and outflows used in 

the water and energy budgets and the temperature arrays used 

to calculate daily average temperatures of surface-water inflows 

and outflows for energy budget.

Surface-water inflows 

and outflows

Primary 

temperaturea

Backup 

temperatureb

Flint River at Newton, Ga., 

and Ichawaynochaway 

Creek downstream of 

Newton, Ga.

Array 2 Probe 3-0

Spring Creek near 

Reynoldsville, Ga. Array 24 Probe 23-0

Chattahoochee River near 

Columbia, Ala. Array 6 Array 7

Apalachicola River at 

Woodruff Dam, Fla. Probe 13-0 Probe 14-4

a

See figure A2 for location of temperature probe arrays.

b

Probe n – m, where n is array number and m is height above lake bottom.

Water-budget calculations for Lake Seminole 23

Table 8. Summary of daily temperature arrays used to calculate 

daily average temperature of surface-water inflow and outflow for 

the main body of the Lake Seminole and impoundment arms.

Area of lake Temperature 

arraysa,b

Percent of lake 

volume

Flint River 

impoundment arm 1–5; excluding probe 1-0 16.6

Spring Creek 

impoundment arm 20–24 3.2

Fishpond Drain 17, 18 1.7

Chattahoochee River 

impoundment arm 6–8 9.7

Main body of lake 9–16; 19; 25, 26; 

excluding probe 25-0

68.8

a

See figure A2 for location of temperature probe arrays.

b

Probe n – m, where n is array number and m is height above lake bottom.
ally expressed as a rate, for example, volume per unit area per 

day, and the energy is converted to volume units using 

the equation:

 E = Qe / ρL, (5)

where E is the evaporation rate expressed in centimeters per 

day, and

Qe = energy used for evaporation, in calories per square 

centimeter per day; 

ρ = density of water, in grams per cubic centimeter; and,

L = latent heat of evaporation, in calories per gram.

The latent heat of evaporation, L, varies with water-surface 

temperature according to the following relation (Maidment, 1992):

 L = 2.501 – 0.002361Ts, (6)

where

 Ts = water-surface temperature, in degrees Celsius.

Water-surface temperature was obtained from temperature sensors located at the water surface at the climate stations rather 

than from the shallowest temperature probes in each array, 

which occasionally were out of the water because of low lake 

stage during drought conditions during the study period.

The volume of water evaporated from the lake then becomes:

 E = (Qn + Qv – Qx) / ρL (1 + BR). (7)

Evaporation was calculated on a daily basis using daily average climate data for each climate station. The evaporation 

20

22

24

26

28

30

32

34

36

38

40

1 5 10 15 20 25 31

JULY 2000

Air temperature

TEMPERATURE, IN DEGREES CELSIUS

Lake Seminole

probe number 

one at depth 

of 12 feet

Figure 12. Relation between average air temperature and surface-water temperature 

at Lake Seminole, July 2000.

to each temperature-probe value. There was no weighting 

of lake temperature by water depth, even though there is 

a larger percentage of shallow areas in the lake than deep, 

because the water column was well mixed and there was little 

thermal stratification. 

Sensible heat, Qh, and the energy used for evaporation, Qe, 

were not measured directly, but were obtained from estimates 

of the Bowen Ratio, BR, defined as the ratio of sensible heat to 

the energy used for evaporation. The Bowen Ratio is calculated using the equation (Bowen, 1926):

BR = Qh / Qe

= 0.00061 P (T0 – Ta)/(e0 – ea), (3)

where 

P = barometric pressure in millibars;

T0 = water-surface temperature in degrees Celsius;

Ta = air temperature at height of 2 meters above water 

surface in degrees Celsius;

e0 = saturated vapor pressure at water surface in 

millibars; and,

ea = vapor pressure at height of 2 meters above the water 

surface in millibars.

Using net radiation, Qn, and the Bowen Ratio, BR, the energybudget equation becomes:

Qe (1 + BR) = Qn + (Qv – Qx). (4)

The energy required for evaporation was measured in calories 

per square centimeter per day. Evaporation, however, is gener24 Ground-water and surface-water flow and estimated water budget for Lake Seminole
estimates from each climate station were then averaged to 

represent evaporation for the entire lake.

A balanced water budget was a necessary first step to achieving a balanced energy budget. A net loss or gain of water in the 

lake that is not defined by the storage term, ∆S, corresponds 

to a deficiency, or excess, of heat that would correspond to the 

energy available for evaporation calculated by the energy-budget method. Ground-water inflow and lake leakage were the 

most uncertain of all water-budget components because they 

were not measured directly; hence, flows and volumes derived 

from these sources were adjusted to balance the water budget. 

Volumes of water derived from these sources correspond to 

heat fluxes that were used in the energy-budget equations. 

It was not possible initially to balance the water budget, 

which, in turn would be used to estimate lake evaporation with 

the energy-budget method, because the water budget requires 

that lake evaporation be known. Therefore, an iterative process 

was used to determine the amount of ground-water inflow and 

lake leakage required to balance the water budget and compute lake evaporation by the energy-budget method. An initial 

estimate of lake evaporation was used in the water budget to 

obtain initial values for lake leakage and ground-water inflow, 

which were used to balance the water budget. These values 

were then used in the energy budget to estimate evaporation 

for each day. The new evaporation estimates were then used to 

update estimates of lake leakage and ground-water inflow in 

the water budget. Lake leakage was adjusted before adjusting 

ground-water inflow, because there was more uncertainty in 

estimates of lake leakage than ground-water inflow. The new 

rates of lake leakage and ground-water inflow were used to 

obtain an updated evaporation rate; this process was repeated 

until the solutions from both energy and water budgets converged. No further changes in the estimates of lake leakage 

and evaporation were needed after three iterations. 

Empirical Equations

Five empirical equations were used to estimate evaporation: 

Priestley-Taylor, Penman, DeBruin-Keijman, and Papadakis, 

and the Priestley-Taylor equation method used by GAEMN. 

GAEMN also uses the Priestley-Taylor equation to calculate 

evaporation; differences between the two Priestley-Taylor estimates arise in the manner in which lake-temperature measurements are used to determine heat stored in the lake. GAEMN 

uses lake temperature measured at the climate stations only; 

whereas the Priestley-Taylor calculation employs a more 

detailed heat budget, using temperature measurements collected from the temperature-probe network located throughout 

the lake (described in the appendix). Calculations of lake evaporation using each empirical method were compared with lake 

evaporation derived from the energy-budget method to determine the most accurate method, and to determine if GAEMN 

estimates of evaporation provide an accurate, cost-efficient 

method of determining evaporation from Lake Seminole. 

Priestley-Taylor Equation

The Priestley-Taylor equation determines evaporation as a 

function of latent heat of evaporation and heat flux in a water 

body and is defined by the equation (Winter and others, 1995):

E = α[s/(s + γ)][(Qn – Qx)/L], (8)

where all terms have been defined previously except,

α = 1.26, Priestley-Taylor empirically derived 

constant, dimensionless, and

s/(s + γ) = derived from slope of saturated vapor 

pressure at the mean air temperature; γ is the 

psychrometric constant, dimensionless.

Penman Equation

The Penman equation calculates evaporation based on the 

energy that is removed from the water-body surface as water 

vapor and is defined by the equation (Winter and others, 1995):

E = [s/(s + γ)](Qn – Qx) + [γ (s + γ)]{

[15.36(0.5 + 0.01U2)] (e0 – ea)}, (9)

where all terms have been defined previously except,

γ (s + γ) = derived from slope of saturated vapor pressuretemperature curve at the mean air temperature; 

γ is the psychrometric constant, dimensionless, 

and

U2 = wind speed at 2 meters height above the lake 

surface, in meters per second.

DeBruin-Keijman Equation

The DeBruin-Keijman equation computes evaporation rates 

by using the moisture content of the air above a water body, 

heat stored in the water body, and the psychrometric constant, 

which is a function of atmospheric pressure and latent heat of 

evaporation, as (Winter and others, 1995):

E = [SVP / 0.95 SVP + 0.63γ)] (Qn – Qx), (10)

where SVP = saturated vapor pressure at mean air temperature, 

in millibars per degree Kelvin, and other terms are as 

defined previously.

Papadakis Equation

The Papadakis equation does not account for the heat 

flux at the water surface of the lake to calculate evaporation. 

Instead, it depends on the difference between the minimum 

and maximum saturated vapor pressure above the water body 

and is defined by the equation (Winter and others, 1995):

E = 0.5625[e0 max – (e0 min – 2)], (11)

where 

e0 = saturated vapor pressure at maximum (e0 max) and 

minimum (e0 min) air temperatures.

Water-budget calculations for Lake Seminole 25
Georgia Automated Environmental 

Monitoring Network

GAEMN estimates of lake evaporation are calculated using 

the Priestley-Taylor equation; estimates and are reported online

at http://www.griffin.peachnet.edu/bae. Unlike the calculation of the Priestley-Taylor equation, however, where water 

temperature was determined by a series of temperature probes 

located throughout the lake, the GAEMN calculation uses 

temperature data from temperature sensors that are located at 

the two overwater climate stations. Temperature data from the 

climate stations represent the two types of lake habitat that are 

present, that is, open water (Sneads Landing, Florida) and submerged vegetation (Cummings Access, Georgia), which occur 

in nearly equal proportions. Therefore, evaporation calculations from the two climate stations were averaged to produce 

monthly evaporation rates for the lake, which were then compared with evaporation estimates obtained from energy-budget 

and empirical-equation computations.

Evaluation of Evaporation 

Estimates and Methods

Annual evaporation calculated by the energy budget for 

the period April 2000 through March 2001 was 67.2 inches. 

Monthly estimates range from a minimum of 3 inches during 

February 2001 to a maximum of 6.9 inches during June 2000, 

and averaged 5.6 inches per month during the study period 

(table 9). The long-term average annual pan evaporation estimate for the region is 65 inches (April 2000 – March 2001) and 

is based on measurements from January 1959 to December 

1978 (Farnsworth and Thompson, 1982). Annual evaporation 

calculated during the study using the energy budget is about 

2.3 inches greater than long-term average pan evaporation. 

Average monthly estimates of evaporation that were 

computed using the Priestley-Taylor equation ranged from 

1.7 inches to 8 inches for the study period with an average 

monthly rate of 4.8 inches for the period April 2000 through 

March 2001 (table 9). Monthly differences in evaporation 

estimates computed using the Priestley-Taylor equation and 

the energy budget averaged 0.8 inch. The Priestley-Taylor 

equation underestimated evaporation by 9.7 inches during the 

study period, an average difference of 14 percent (table 9).

Average monthly estimates of evaporation that were 

computed using the Penman equation ranged from 1.6 to 

6.9 inches for the study period, with an average monthly rate 

of 4.2 inches during the period April 2000 through March 

2001 (table 9). Monthly differences in evaporation estimates 

computed using the Penman equation and the energy budget 

averaged 1.4 inches. The Penman equation underestimated 

evaporation by 17.2 inches during the study period, an average 

difference of 26 percent (table 9).

Average monthly estimates of evaporation that were 

computed using the DeBruin-Keijman equation ranged from 

2.9 to 9.5 inches with an average monthly rate of 6 inches for 

the period April 2000 through March 2001 (table 9). Monthly 

differences in evaporation estimates computed using the 

DeBruin-Keijman equation and the energy budget averaged 

0.4 inches. The DeBruin-Keijman equation overestimated 

evaporation by 5.1 inches during the study period, an average 

difference of 8 percent (table 9).

Average monthly estimates of evaporation using the Papadakis equation ranged from 2.7 to 6.7 inches with an average 

monthly rate of 4.6 inches for the period April 2000 through 

March 2001 (table 9). Monthly differences in evaporation 

estimates between the Papadakis equation and the energy 

budget average 1 inch. The Papadakis equation underestimated 

evaporation by 11.7 inches during the study period, an average 

difference of 17 percent (table 9).

Average monthly estimates of evaporation using the 

GAEMN climate stations ranged from 0.7 to 7.5 inches with 

an average monthly rate of 4.2 inches during for the period 

April 2000 through March 2001 (table 9). Monthly differences 

in evaporation estimates between the GAEMN climate stations 

and the energy budget average 1.4 inches. GAEMN underestimated evaporation by 17.1 inches during the study period, an 

average difference of 25 percent (table 9).

Energy-budget estimates of evaporation were largest in the 

early summer (June) and smallest in the winter (February) 

(fig. 13). In comparison, the Priestley-Taylor equation estimated evaporation to be largest during the spring (May) and 

smallest during the winter (December), as did the Penman 

equation, the DeBruin-Keijman equation, and the GAEMN 

method. The Papadakis equation estimated evaporation to be 

largest during the summer (July and August) and smallest 

during the winter (December). While evaporation estimates 

computed by the empirical methods, excluding the Papadakis 

equation, followed the same general seasonal pattern as values 

derived from the energy-budget method, evaporation computed by the Priestley-Taylor and DeBruin-Keijman equations 

tended to be larger than the values computed by the energybudget method during the warm months and smaller than the 

energy-budget method during the cool months. The Penmanequation estimates were nearly equal to or less than estimates 

derived from the energy-budget method. Evaporation results 

from the Papadakis equation had a less discernable pattern; 

however, evaporation estimates from the Papadakis equation 

were always less than those obtained from the energy budget; 

except for February, when the computed evaporation from the 

energy-budget method was smaller.

Lake-water temperature is a common variable to the 

energy-budget method and the empirical equations and is used 

in computing Qx, the change in heat stored in the lake. This 

variable influences the seasonality of evaporation estimates 

because changes in lake-water temperature affect the ease with 

which water is vaporized from the lake surface. The energy 

budget further refines evaporation estimates by taking into 

account the temperature of water entering and leaving the 

lake by ground- and surface-water inflow and lake leakage, 

respectively, thus, defining the differences between the empirical equations (Priestley-Taylor, DeBruin-Keijman, Penman, 

and GAEMN) and the energy-budget method. Each of these 

26 Ground-water and surface-water flow and estimated water budget for Lake Seminole
equations takes into account the meteorological components of 

evaporation. The volume and temperature of water that enters 

and leaves the lake, however, have a substantial affect on the 

amount of lake water that is evaporated; the energy budget 

accounts for this with the term Qv, net heat advected to the 

lake by streamflow, ground water, and precipitation.

Variation in evaporation estimates between the empirical 

equations is expected because each equation uses different climatic variables to calculate evaporation. For example, all the 

equations require some information on heat flux in the lake, 

except for the Papadakis equation. The Priestley-Taylor equation relies on an estimate of latent heat, the Penman on wind 

speed, and the DeBruin-Keijman on saturated vapor pressure. 

Although there is some variation in evaporation estimates 

between the methods, seasonality of the estimates is common 

to all methods (fig. 13).

Water-Budget Summary

Inflow to Lake Seminole is dominated by surface-water 

flows (table 10, fig. 14). Streamflow accounted for 81 percent of the inflow to Lake Seminole. The Chattahoochee and 

Flint Rivers contributed most of the total inflow, 47 and 28 

percent, respectively; tributary flow to the Flint River from 

Ichawaynochaway Creek contributed 4 percent; Spring Creek 

contributed the remaining 2 percent. Ground water accounted 

for 18 percent of lake inflow. The contribution of ground water 

to the lake actually was slightly higher than this value because 

streamflow measurements at gages located in the impoundment arms of the Flint River and Spring Creek includes a component of ground-water inflow to the stream channels. This 

affects only that part of ground- and surface-water inflow 

Table 9. Evaporation rates calculated using the energy budget, those derived from empirical equations, and those values posted to the 

Georgia Automated Environmental Monitoring Network (GAEMN) at http://www.griffin.peachnet.edu/bae/

[DBK, DeBruin-Keijman; NA, not applicable; pan, pan evaporation. Evaporation rates in inches per month] 

Month and year DBK 

equation

Penman 

equation

Priestly-Taylor 

equation

Papadakis 

equation GAEMN Energy budget Pan

Apr. 2000 8.0 5.3 6.1 4.5 5.3 6.8 6.5

May. 2000 9.5 6.9 8.0 5.9 7.5 6.0 7.3

June 2000 8.4 6.2 7.2 5.6 6.9 6.9 7.8

July 2000 8.4 6.4 7.4 6.7 7.1 6.9 7.3

Aug. 2000 7.7 5.8 6.8 6.6 6.3 6.1 7.0

Sept. 2000 5.7 4.1 4.8 4.7 4.4 6.3 6.5

Oct. 2000 6.2 4.3 4.9 5.8 3.8 5.7 5.4

Nov. 2000 3.3 2.1 2.3 3.7 1.6 5.0 3.4

Dec. 2000 2.9 1.6 1.7 2.7 0.7 4.4 2.6

Jan. 2001 3.6 2.0 2.1 3.0 1.4 3.6 2.6

Feb. 2001 3.6 2.3 2.6 3.2 2.1 3.0 3.3

Mar. 2001 5.0 3.1 3.5 3.1 3.0 6.7 5.2

Apr. 2001 7.6 5.1 5.9 4.4 5.3 5.8 6.5

May 2001 8.7 6.2 7.2 5.3 6.7 6.0 7.3

June 2001 7.1 5.1 6.1 4.4 5.9 5.9 7.8

July 2001 7.8 5.7 6.8 4.8 6.5 5.7 7.3

Aug. 2001 6.9 5.0 6.0 4.9 5.6 5.3 7.0

Sept. 2001 6.2 4.5 5.2 4.5 4.5 6.7 6.5

Minimum monthly evaporation (inches) 2.9 1.6 1.7 2.7 0.7 3.0 2.6

Maximum monthly evaporation (inches) 9.5 6.9 8.0 6.7 7.5 6.9 7.8

Study period evaporation (April 2000 – September 2001) 116.5 81.6 94.6 83.8 84.7 102.6 107.4

Annual evaporation (April 2000 – March 2001) 72.3 50.0 57.5 55.5 50.1 67.2 65.0

Average monthly evaporation (April 2000 – March 2001) 6.0 4.2 4.8 4.6 4.2 5.6 5.4

Difference from energy budget (April 2000 – March 2001) 5.1 17.2 9.7 11.7 17.1 NA 2.2

Monthly average difference from energy budget 0.4 1.4 0.8 1.0 1.4 NA 0.2

Monthly average percent

difference from the energy budget 8 26 14 17 25 NA 3

Monthly average percent difference from

long-term average annual pan evaporation 11 23 11 15 23 3 NA

Water-budget calculations for Lake Seminole 27
0

1

2

3

4

5

6

7

8

9

10

0

1

2

3

4

5

6

7

8

9

10

EVAPORATION, IN INCHES

0

1

2

3

4

5

6

7

8

9

10

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

A. Priestly-Taylor

B. Penman

C. DeBruin-Keijman

D. Papadakis

E. Georgia Automated Environmental 

 Monitoring Network

2000 2001

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

Energy budget

Empirical

equation

2000 2001

Figure 13. Monthly estimates of evaporation computed using the energy budget and empirical equations: 

(A) Priestley-Taylor, (B) Penman, (C ) DeBruin-Keijman, (D ) Papadakis, and (E ) Georgia Automated 

Environmental Monitoring Network, April 2000 – September 2001.

28 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Table 10. Monthly water-budget variables and cumulative error for Lake Seminole.

[GW, ground water; -, outflows greater than inflows. All values in cubic feet per second]

Inflows to Lake Seminole Outflows from Lake Seminole

Month and 

year

Spring 

Creek

Chattahoochee 

River Flint River Ichawaynochaway Creek Precipi- tation Total inflows Apalachicola River Lake leakage Evapo- ration Total outflows 

Apr. 2000 361 9,628 5,618 609 166 19,539 16,780 550 345 17,676 May 2000 202 5,148 1,944 200 9 9,443 7,863 550 307 8,720 June 2000 121 3,986 1,217 86 130 7,314 4,276 550 351 5,177 July 2000 121 3,113 1,305 131 149 6,137 4,567 550 343 5,460 Aug. 2000 97 3,608 1,283 105 89 6,470 5,256 550 312 6,118 Sept. 2000 114 3,020 2,105 221 318 7,095 5,339 550 321 6,210 Oct. 2000 136 2,778 1,426 176 22 5,866 5,109 550 292 5,951 Nov. 2000 146 3,342 2,549 305 193 8,033 5,811 550 256 6,617 Dec. 2000 175 5,929 2,685 449 121 11,051 9,751 550 227 10,528 Jan. 2001 328 7,517 4,575 706 93 16,362 14,140 550 183 14,873 Feb. 2001 304 6,126 4,086 538 41 14,317 11,439 550 151 1,2140 Mar. 2001 1,274 28,881 16,977 2,424 555 58,457 56,640 550 341 57,532 Apr. 2001 1,287 13,017 10,074 1,802 72 31,903 30,313 550 294 31,158 May 2001 406 5,535 2,990 518 52 11,952 11,012 550 308 11,869 June 2001 392 9,776 5,573 739 457 20,709 18,049 550 302 18,901 July 2001 320 4,672 3,291 274 439 10,976 10,602 550 293 11,445 Aug. 2001 237 4,556 2,058 199 245 9,167 9,035 550 268 9,853 Sept. 2001 183 3,026 2,010 266 156 7,072 6,623 550 340 7,513 

Study period 

average

 345 6,870 3,987 542 184 14,548 12,937 550 291 13,763 

Percent of 

Lake Seminole 

water budget

 2 47 28 4 1 89 4 2 
arms and not total lake inflow. Direct precipitation on the 

lake made up only a minor portion of inflow, about 1 percent, 

except during storm events when lake inflow from precipitation made up 10 to 20 percent of total lake inflow (fig. 14).

Chattahoochee and Flint River flows varied seasonally 

(highest in winter and spring) with the highest flows during 

March 2001, the month with the highest local precipitation, 

and lowest in the fall and summer (table 10). The Chattahoochee and Flint Rivers had similar patterns of monthly flows 

during the period of study even though Chattahoochee River 

flows are controlled by several large reservoirs, and the Flint 

River has only two small reservoirs upstream of Lake Seminole. In comparison, seasonal flow variation on Spring and 

Ichawaynochaway Creeks is more subdued than on the Flint 

and Chattahoochee Rivers (table 10). Streamflow from Spring 

Creek exhibited less monthly variation in flows than the Chattahoochee and Flint Rivers, and higher flows in the winter and 

spring than in the summer and fall (table 10, fig 14).

Monthly patterns in ground-water flows (fig. 10) were 

somewhat similar to the variation in streamflow for the Chattahoochee and Flint Rivers, which was expected because 

monthly patterns of ground-water inflow were derived from 

100 90 80 70 60 50 40 30 20 10

Ground

water

Precipitation

Surface water

2000 2001

RELATIVE PERCENT OF FLOW OF THE LAKE SEMINOLE WATER BUDGET

INFLOW OUTFLOW

Surface-water inflow

Ichawaynochaway Creek Flint River Chattahoochee River Spring Creek

JAN

FEB

MAR

APR

MAY

JUNE

JULY

AUG

SEPT

APR

MAY

JUNE

JULY

AUG

SEPT

OCT

NOV

DEC

EXPLANATION

Apalachicola River

0 10 20 30 40 50 60 70 80 90 100

Ground

water

Evaporation

the calculated baseflows of these rivers. Monthly ground-water 

flows, however, were lower than monthly streamflow. During 

periods of high inflow to the lake and high streamflow, ground 

water comprised a smaller percentage of total inflow to the 

budget than the other inflows (table 10, fig. 14).

Monthly average inputs from direct precipitation constituted a small part of the total inflow (fig. 14). The normal 

pattern of seasonal precipitation was not observed during the 

study; instead, the largest amounts occurred during September 

2000 and March, June, and July 2001 (table 10, fig. 15). 

Outflow from Lake Seminole was dominated by flow 

from Jim Woodruff Lock and Dam, which accounted for about 

89 percent of lake outflow (table 10, fig. 14). Lake leakage 

constituted about 4 percent of the budget. Evaporation, determined by the energy budget, made up about 2 percent of total 

lake outflow. The small change in lake storage that occurred 

during the study period could not accommodate the 4-percent 

deficiency in outflow, compared with total inflow. This difference between inflow and outflow represents measurement 

error, as described previously, as it relates to stream-discharge 

measurements, ground-water inflow, precipitation, and lake 

evaporation and leakage. 

Figure 14. Percent contribution of Lake Seminole water-budget components.

30 Ground-water and surface-water flow and estimated water budget for Lake Seminole
There were fewer monthly variations in lake outflow 

than inflow, which was nearly constant from June through 

November 2000 (table 10). Differences in the pattern between 

surface-water outflow and inflow from the Chattahoochee and 

Flint Rivers are due largely to fluctuations in reservoir storage 

and release during the study period. Monthly lake leakage did 

not show a seasonal pattern and was estimated to be 550 ft3/s 

(table 10). 

Evaporation estimates calculated by the energy budget 

exhibited a seasonal pattern in response to energy inputs, highest during the summer and lowest during the winter, with the 

highest rate occurring during June 2000 (6.9 inches) and the 

lowest occurring during February 2001 (3 inches) (fig. 13 and 

table 9). The methods used to calculate evaporation included, 

the energy budget, which was used in calculating the water budget of Lake Seminole, and five empirical equations: PriestleyTaylor, Penman, DeBruin-Keijman, Papadakis, and GAEMN. 

There was considerable variation among evaporation estimates 

computed with the empirical equations, with differences in the 

estimates between the equations and the energy-budget method 

ranging from an underestimation of 5.1 inches and overestimation of 17.2 inches during the period April 2000 through March 

2001 (table 9). Because evaporation accounts for only 1 percent 

of the lake outflow, its effect on the total water in the budget 

ranges from 0.3 to 0.71 percent (table 11), depending on the 

method used to estimate evaporation. This percentage of total 

water is insignificant compared with the measurement error 

for surface water, which usually ranges from 5 to 15 percent, 

depending on streamflow-measurement accuracy. 

Water-Budget Error

Differences between monthly inflow and outflow, taking 

into account changes in storage of the lake, ranged from a 

deficit of 393 ft3/s, or 1.4 percent of the budget, during 

September 2001 to a surplus of 2,477 ft3/s, or 8.7 percent of 

the budget, during April 2000 (table 10). Most of the error 

in the water budget is attributed to surface-water flow, which 

accounts for 81 percent of the inflow and 89 percent of the 

outflow in the budget, with measurement errors that range 

from 5 to 15 percent, depending on flow conditions. 

Unlike other studies that developed lake water budgets 

(Lee and Swancar, 1996; Swancar and others, 2000), the proportion of surface-water flow to the other components of the 

Lake Seminole water budget (ground water, precipitation, and 

evaporation) is so large that these other components contribute only minor amounts of water to lake inflow and outflow. 

Because surface water encompasses such a large percentage 

of inflow and outflow for Lake Seminole, other hydrologic 

components seemingly are insignificant to the development of 

a water budget. While quantifying these hydrologic components is essential for developing a better understanding 

of reservoir-stream-aquifer interaction and for improving 

hydrologic monitoring in the region, error in their measurement is inconsequential to the Lake Seminole water budget. 

A sensitivity analysis of the water budget to changes in each 

component was used to illustrate the importance of individual 

measurement accuracy. 

Sensitivity Analysis

The sensitivity analysis demonstrates the relative importance of individual components to the overall accuracy of the 

water budget. Accurate measurement of precipitation and 

simulation of ground-water inflow becomes less important 

when the volume of water derived from these water-budget 

components is compared with the volume of surface water that 

flows into Lake Seminole. If each component is varied by the 

same percentage, then their effect on the water budget fluctuates according to their relative contribution, or importance to 

lake inflow or outflow. For example, if ground-water flow and 

precipitation are increased by 50 percent each, then the total 

inflows to the water budget increase by 5.3 and 0.4 percent, 

respectively; but if surface-water flow is increased by 

50 percent, then the total inflows to the water budget increases 

by about 20 percent (fig. 16). Because the water budget is 

dominated by surface water, better accuracy in estimating 

inputs to the water budget would be attained by improving 

the accuracy by which surface-water inflows are measured. 

Improvements to estimating ground-water inflow or measuring 

lake precipitation would result in minimal, if not insignificant, 

improvements to quantifying lake inflow.

0

2

4

6

8

10

12

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

PRECIPITATION, IN INCHES

2000 2001

Long-term average,

Arlington, Georgia

Monthly precipitation

during study period,

Lake Seminole

Figure 15. Monthly average precipitation during the study 

period compared with long-term average precipitation at 

climate station in Arlington, Georgia, 1960 – 2002 (see

figure 2 for climate-station location).

Water-budget summary 31
A similar sensitivity analysis of lake outflow components 

indicates that surface-water flow dominates the water budget 

to such an extent that a rationale for quantifying lake evaporation and leakage more accurately than by the methods used 

in this study simply cannot be substantiated. That is, very 

little improvement in the accuracy of lake outflow would be 

gained by improving the current methods used to compute 

lake evaporation and leakage. This is not to say, however, that 

lake evaporation and leakage are not important to understanding reservoir-stream-aquifer interaction. If evaporation and 

lake leakage decrease by 50 percent, then the water budget 

decreases by 0.8 and 1.5 percent, respectively; however, if surface-water outflow decreases by 50 percent, the water budget 

decreases by more than 21 percent (fig. 17). Thus, accuracy in 

measuring surface-water outflow is critical for improving the 

accuracy of the water budget for Lake Seminole.

Table 11. Average study period percent difference in water budget of Lake Seminole comparing 

empirical equations, long-term average annual pan evaporation, and the energy budget.

[DBK, DeBruin-Keijman; GAEMN, Georgia Automated Environmental Monitoring Network; pan, pan evaporation]

Month and year DBK 

equation

Penman 

equation

Priestley-Taylor 

equation

Papadakis 

equation GAEMN Pana

Apr. 2000 0.45 0.37 0.11 0.61 0.35 0.08

May 2000 1.60 .19 .81 .31 .53 .73

June 2000 .85 1.13 .17 1.65 .53 .94

July 2000 .99 .79 .13 .54 .14 .56

Aug. 2000 .77 .69 .05 .07 .30 .70

Sept. 2000 .82 2.02 1.51 1.59 1.80 .19

Oct. 2000 .20 1.41 .92 .16 1.77 .26

Nov. 2000 1.39 2.27 2.12 1.13 2.66 1.22

Dec. 2000 .78 1.41 1.36 .88 1.82 .90

Jan. 2001 .03 .57 .51 .20 .77 .33

Feb. 2001 .42 .18 .05 .24 .29 .13

Mar. 2001 .14 .31 .28 .31 .32 .13

Apr. 2001 .35 .08 .07 .19 .03 .12

May 2001 1.12 .05 .48 .34 .27 .53

June 2001 .40 .15 .11 .35 .08 .52

July 2001 .94 .01 .48 .39 .36 .71

Aug. 2001 .79 .15 .31 .21 .13 .88

Sept. 2001 .28 1.47 .99 1.45 1.46 .10

Average study period difference in water 

budget using empirical equation in lieu of 

energy budget, in percent

0.30 0.71 0.31 0.56 0.60 0.17

a

Long-term average annual pan evaporation estimates for the region are based on measurements from January 1959–December 1978 

(Farnsworth and Thompson, 1982)

Ground water

Precipitation

Surface water

PERCENT DIFFERENCE IN INFLOW

PERCENT DIFFERENCE OF LAKE WATER BUDGET

–25

–20

–15

–10

–5

5

0

10

15

20

25

–60 –40 –20 0 20 40 60

Figure 16. Relative sensitivity of the Lake Seminole 

water budget to component inflow.

32 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Summary

The stream-aquifer-lake flow system consists of inflow to 

Lake Seminole by precipitation, the Chattahoochee and Flint 

Rivers, Spring and Ichawaynochaway Creeks, Fishpond Drain, 

and other ungaged streams and ground-water flow from the 

Upper Floridan aquifer. Outflow from the lake consists of lake 

evaporation and leakage to the aquifer and flow through Jim 

Woodruff Lock and Dam. 

Water-budget calculations for the period from April 2000 

to September 2001 indicate that surface-water inflow and 

outflow dominate the water budget, comprising 81 percent of 

inflows and 89 percent of outflows. Ground water makes up 

18 percent of total inflow, based on estimates of October 1986 

flow rates that were modified by hydrograph-separation techniques. Lake leakage comprises 4 percent of total outflow and 

was derived from streamflow measurements at Jim Woodruff 

Lock and Dam and on the Apalachicola River, at the surfacewater station at Chattahoochee, Florida. Precipitation was 

estimated as 1 percent of total inflow, and evaporation made 

up about 2 percent of total outflow. Errors in streamflow measurements represented a component of flow that is larger than 

the other (minor) components of the water budget, namely, 

ground-water inflow, lake leakage, evaporation, and precipitation. Because surface water dominates the water budget, 

alternative, economical, and efficient methods were used to 

determine ground-water inflow, lake leakage, and evaporation 

rates for Lake Seminole.

Comparisons of monthly evaporation rates calculated by 

the energy-budget method with estimates obtained from five 

empirical equations — Priestley-Taylor, Penman, DeBruinKeijman, Papadakis, and the estimate provided by the Georgia Automated Environmental Monitoring Network — and 

reported long-term pan evaporation rates indicate that the 

energy-budget method provided the closest match between 

evaporation rates and pan evaporation. Evaporation estimates 

derived from the empirical equations were less accurate, in 

comparison with the energy-budget method, ranging from 8 to 

26 percent of the rates obtained from the energy budget. The 

dominance of surface water in the Lake Seminole water budget, however, made the choice of technique used to calculate 

lake evaporation superfluous; the effect of the evaporation estimate on the total water volume in the budget ranged from 0.3 

to 0.71 percent, depending on the evaporation method used. 

This percentage variation in total water in the water budget is 

within the measurement error for streamflow. Twenty-percent 

variation in streamflow caused about an 8-percent change in 

total water in the water budget.

The evaporation method used by GAEMN is the most 

time- and cost-efficient means of determining lake evaporation 

on a monthly basis for the water budget of Lake Seminole. 

GAEMN uses the Priestley-Taylor empirical equation, which 

provides evaporation estimates with sufficient accuracy to be 

used in water-budget computations. Additionally, GAEMN 

provides the climate data needed for the evaporation computations, performs the computations, and makes these results 

available online (http://www.griffin.peachnet.ed/bae/).

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Figure 17. Relative sensitivity of the Lake Seminole 

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Summary 33

Evaporation

Ground water

Surface water

PERCENT DIFFERENCE IN OUTFLOW

PERCENT DIFFERENCE OF LAKE WATER BUDGET –25

–20

–15

–10

–5

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Athens, Georgia, CD. 

Keijman, J.Q., 1974, The estimation of the energy balance of a 

lake from simple weather data. Bound-Layer Meteorology, 

7:399–407.

Lee, T.M., Adams, D.B., Tihansky, A.B., and Swancar, A., 

1991, Methods, instrumentation, and preliminary evaluation of data for the hydrologic budget assessment of Lake 

Lucerne, Polk County, Florida: U.S. Geological Survey 

Water-Resources Investigations Report 90-4111, 42 p.

Lee, T.M., and Swancar, A., 1996, Influence of evaporation, 

ground water, and uncertainty in the hydrologic budget of 

Lake Lucerne, a seepage lake in Polk County, Florida: U.S. 

Geological Survey Water-Supply Paper 2439, 61 p. 

Leitman, H.M., Sohm, J.E., and Franklin, M.A., 1984, Wetland hydrology and tree distribution of the Apalachicola 

River flood plain, Florida: U.S. Geological Survey WaterSupply Paper 2196-A, 52 p.

Lipscomb, S.W., 1995, Quality assurance plan for discharge 

measurements using broadband acoustic Doppler current 

profilers: U.S. Geological Survey Open-File Report 

95-701, 7 p.

MacNeil, F.S., 1947, Geologic map of the Tertiary and Quaternary Formations of Georgia: U.S. Geological Survey 

Professional Paper 708, 70 p.

Maidment, D.R., 1992, Handbook of hydrology: McGrawHill, Inc., New York (variously paged).

Maslia, M.L., and Hayes, L.R., 1988, Hydrogeology and simulated effects of ground-water development of the Floridan 

aquifer system, southwest Georgia, northwest Florida, and 

southwest Alabama: U.S. Geological Survey Professional 

Paper 1403-H, 71 p.

34 Ground-water and surface-water flow and estimated water budget for Lake Seminole
McCallum, B.E., and Hickey, A.C., 2000, Water Resources 

Data, Georgia, Water Year 2000: Water Data Report 

GA-00-1, v. 1.

McCallum, B.E., Kerestes, J.F., and Hicket, A.C., 2001, Water 

Resources Data, Georgia, Water Year 2001: Water Data 

Report GA-01-1, v. 1.

Miller, J.A., 1986, Hydrogeologic framework of the Floridan 

aquifer system in Florida and in parts of Georgia, Alabama, 

and South Carolina: U.S. Geological Survey Professional 

Paper 1403-B, 91 p.

Mosner, M.S., 2001, Effects of drought on stream discharge 

and ground-water levels near Lake Seminole, southwestern 

Georgia and northwestern Florida, October 1999–August 

2000: in Proceedings of the 2001 Georgia Water Resources 

Conference, held March 26–27, 2001, at the University of 

Georgia, Kathryn J. Hatcher, editor, Institute of Ecology, 

The University of Georgia, Athens, Georgia, p. 118–121.

Mosner, M.S., 2002, Stream-aquifer relations and the potentiometric surface of the Upper Floridan aquifer in the lower 

Apalachicola–Chattahoochee–Flint River basin in parts of 

Georgia, Florida, and Alabama, 1999–2000: U.S. Geological Survey Water-Resources Investigations Report 02-4244, 

45 p., 1 plate.

Novak, C.E., 1985, WRD data reports preparation guide: U.S. 

Geological Survey publication, 199 p.

Pratt, T.R., Richards, C.J., Milla, K.A., Wagner, J.R., Johnson, 

J.L., and Curry, R.J., 1996, Hydrogeology of the Northwest 

Florida Water Management District: Northwest Florida 

Water Management District Water Resources Special 

Report 96-4, 99 p.

Rosenberry, D.O., Sturrock, A.M., and Winter, T.C., 1993, 

Evaluation of the energy budget method of determining 

evaporation at Williams Lake, Minnesota, using alternative 

instrumentation and study approaches: Water Resources 

Research, v. 29, no., 8, p. 2473–2483.

Sever, C.W., 1965, Ground-water resources and geology of 

Seminole, Decatur and Grady counties, Georgia: U. S. 

Geological Survey Water-Supply Paper 1809-Q, 30 p.

Sloto, R.A., and Crouse, M.Y., 1996, HYSEP: A computer 

program for streamflow hydrograph separation and analysis: 

U.S. Geological Survey Water-Resources Investigations 

Report 96-4040, 46 p.

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Hydrogeology and water quality of the Upper Floridan aquifer, western Albany area, Georgia: U.S. Geological Survey 

Water-Resources Investigations Report 99-4140, 42 p.

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determining lake evaporation in high latitudes: Journal of 

Applied Meteorology 16:649–650.

Swancar, Amy, Lee, T.M., and O’Hare, T.M., 2000, Hydrogeologic setting, water budget, and preliminary analysis of 

ground-water exchange at Lake Starr, a seepage lake in Polk 

County, Florida: Water-Resources Investigations Report 

00-4030, 65 p.

Torak, L.J., 1993a, A MODular Finite-Element model 

(MODFE) for areal and axisymmetric ground-water-flow 

problems part 1: model description and user’s manual: U.S. 

Geological Survey Techniques of Water Resources Investigations, book 6, chap. A3, 136 p.

Torak, L.J., 1993b, A MODular Finite-Element model 

(MODFE) for areal and axisymmetric ground-water-flow 

problems part 1: model description and user’s manual: U.S. 

Geological Survey Techniques of Water Resources Investigations, book 6, chap. A5, 243 p.

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southwestern Georgia and northwestern Florida: in Proceedings of the 2001 Georgia Water Resources Conference, held 

March 26–27, 2001, at The University of Georgia, Kathryn 

J. Hatcher, editor, Institute of Ecology, The University of 

Georgia, Athens, Georgia, p. 118–121.

Torak, L.J., Davis, G.S., Strain, G.A., and Herndon, J.G., 

1993, Geohydrology and evaluation of water-resource 

potential of the Upper Floridan aquifer in the Albany area, 

southwestern Georgia: U.S. Geological Survey Water-Supply Paper 2391, 59 p.

Torak, L.J., and McDowell, R.J., 1995, Ground-water 

resources of the lower Apalachicola–Chattahoochee–Flint 

River Basin in parts of Alabama, Florida, and Georgia—

Subarea 4 of the Apalachicola–Chattahoochee–Flint and 

Alabama–Coosa–Tallapoosa River Basins: U.S. Geological 

Survey Open-File Report 95-321, 145 p.

Torak, L.J., Davis, G.S., Strain, G.A., and Herndon, J.G., 

1996, Geohydrology and evaluation of stream-aquifer relations in the Apalachicola–Chattahoochee–Flint River Basin, 

southwestern Alabama, northwestern Florida, and southwestern Georgia: U.S. Geological Survey Water-Supply 

Paper 2460, 94 p.

U.S. Army Corps of Engineers, Mobile district, 1948, Definite project report on Jim Woodruff dam (formerly junction 

project) Apalachicola River, Florida: prepared in the Mobile 

District, U.S. Army Corps of Engineers, Mobile, Alabama, 

v. II, appendix II, p. 2-1—2-19.

References cited 35
U.S. Army Corps of Engineers, Mobile district, 1980, Waterquality management studies, Lake Seminole, April–November 1978, phase 1: Technical Report ACF 80-10 (Final 

Report), 510 p.

U.S. Army Corps of Engineers, Mobile district, 1988, Final 

Apalachicola–Chattahoochee–Flint Comprehensive “308” 

Basin Study Plan of Study: U.S. Army Corps of Engineers, 

Mobile, Alabama, 52 p.

Vernon, R.O., Hendry, C.W., Jr., and Yon, J.W., Jr., 1958, 

Geology of the area in and around the Jim Woodruff 

Reservoir: Florida Geological Survey Report of Investigations 16, 52 p.

Wagner, J.R., and Allen, T.W., 1984, Ground water section: 

in 1984 water assessment for the Apalachicola–Chattahoochee–Flint River basin water management study: U.S. 

Army Corps of Engineers, and States of Alabama, Florida, 

and Georgia, v. 3, appendix III, sec. 3, 129 p.

Winter, T.C., Rosenberry, D.O., and Sturrock, A.M., 1995, 

Evaluation of eleven equations for determining evaporation 

for a small lake in the north central United States: Water 

Resources Research, v. 31, no. 4, p. 983–993.

36 Ground-water and surface-water flow and estimated water budget for Lake Seminole
The water budget of Lake Seminole can be described as a 

means of accounting for hydrologic components that contribute to the change in lake storage, which can be expressed 

as the difference between the volume of water flowing into 

the lake and the volume of water flowing out of the lake. 

Individual components used to construct the water budget 

(fig. 7, eq. A1) can be obtained using various methods. The 

most complicated of the components to measure accurately is 

evaporation because of data-collection needs. The energy-budget method, the most accurate method for estimating evaporation, requires large amounts of climatic and hydrologic data 

to implement; these data are labor intensive and expensive to 

collect. On the other hand, some empirical equations, which 

are less accurate than the energy budget, require only basic 

climate data, which are readily available from two overwater 

climate stations that were installed on Lake Seminole during 

this study. The accuracy of several methods were compared 

and weighed against cost and effort to determine the method 

of estimating evaporation that would be used in the construction of the water budget of Lake Seminole. Excluding ground 

water, which was determined using a ground-water flow model 

developed for the Lake Seminole study area (Torak, 1993a,b), 

each of the components was measured directly.

∆S = P + SWin - SWout + GWin - GWout - E (A1)

∆S = change in lake storage

 P = precipitation

 SWin = surface-water inflows

 SWout = surface-water outflows

 GWin = ground-water inflows

 GWout = lake leakage

 E = evaporation

Overland flow was virtually nonexistent and was ignored 

as part of the water budget because the Dougherty Plain was 

internally drained due to karst solution features. The size 

and irregular geometry of Lake Seminole adds complexity to 

evaporation estimates, which are the main focus of the water 

budget, because evaporation ultimately could be an important 

component of the overall budget. 

Climate Stations and Variables

Two overwater climate stations were installed on Lake 

Seminole (figs. 2; A1) to record climatic variables used to estimate evaporation (table A1). The University of Georgia as part 

of the Georgia Automated Environmental Monitoring Network 

(GAEMN) (http://www.griffin.peachnet.edu/bae/) operates 

and maintains these stations. Measurements of net radiation, 

Appendix — Methods and Instrumentation

Figure A1. (A) Location of climate stations installed over water 

on Lake Seminole; (B ) climate-station installation at Sneads 

Landing, Florida, on Lake Seminole; and (C ) schematic of instruments used in overwater installation of climate stations (from 

www.campbellsci.com, accessed on November 17, 1999).

A.

B.

C.

Lightning rod*

Solar panel

034A wind 

speed and 

direction sensor

41002 gill radiation shield

HMP45C relative humidity

 and temperature probe

CM6 or CM10 tripod

and guying kit

Environmental

enclosure

Ground stakes*

(not shown)

019ALU crossarm

sensor mount

LI200X pyranometer

025 pyranometer

crossarm stand

5-foot

grounding rod*

TE525WS

tipping bucket

rain gage

*Included with CM6/10 purchase.

Other items purchased separately;

alternate sensors available.

Lake Seminole

Sneads Landing

Cummings

Access

Appendix 37
wind speed and direction, barometric pressure, water surface 

and air temperature, precipitation, and humidity were made 

each second and summarized at 15-minute intervals and at 

midnight daily; monthly averages are shown in table A2. Data 

were recorded by a datalogger and transmitted by cell phone 

to a microcomputer at the College of Agriculture and Biological Sciences, Georgia Experiment Station (Georgia Automated 

Environmental Monitoring Network, 2002).

Two ecological conditions exist in the lake that require 

separate instrumentation of corresponding climatic conditions. Submerged vegetation covers nearly half of the lake 

area and affects not only surface-water temperature but also 

the humidity and net radiation in areas densely vegetated. To 

account for differences related to these conditions, the climate 

stations were installed to record data over both openwater and 

highly vegetated areas. The climate station at Sneads Landing (Florida) was installed over open water, and the climate 

station at Cummings Access (Georgia) was installed over 

submerged vegetation. The data from these two climate stations were averaged to determine the climatic conditions for 

the entire lake. 

Thermal Profiles and Temperature 

Probe Installation

Temperature probes were installed in Lake Seminole to 

monitor continuously the temperature of the lake in order to 

calculate the stored heat in the lake. Vertical arrays of temperature probes were distributed at 26 sites to measure the temperature of surface-water inflow and outflow and springflow 

Table A1. Instrumentation of the climate stations installed on Lake Seminole.

[oC, degree Celsius; %, percent; NA, not applicable; m/s, meter per second; mbar, millibar; W/m2, watts per square meter; 

Wm-2mV-1; watts per square meter per millivolt]

Instrument

type Model Purpose Unit

Datalogger CR10X Data collection and storage NA

Tripod and grounding kit CM10 Instrument support NA

Temperature and humidity probes HMP45C Collection of temperature and humidity measurements °C and %

Radiation shield 41002 Shields temperature and humidity probes from direct sunlight NA

Pyranometer LI200X Measurement of solar radiation W/m2

Pyranometer base and leveling fixture LI2003S Support and leveling of pyranometer NA

Wind sensor 034A Measurement of wind speed and direction m/s 

Rain gage TE525 Precipitation measurement inch

Barometric pressure sensor CS105 Measures barometric pressure mbar

Net radiometer Q-7.1 Generates a millivolt signal proportional to net radiation Wm-2mV-1

(ground-water inflow), and to determine the vertical temperature distribution (fig. A2; table A3). Locations for monitoring 

lake temperature (fig. A2) were selected to provide a somewhat uniform areal distribution; the specific location of each 

vertical array was dependent on the availability of permanent 

attachment points for the cable containing the array probes, 

such as docks, piers, large trees, and channel markers. Some 

arrays were intentionally located at spring openings or in 

spring runs — that is, in channels along the lake bottom where 

spring discharge flows — in order to measure the temperature 

of ground-water inflow to the lake. 

Vertical-temperature profiles were obtained at each array 

site using from three to five probes, depending on depth, 

distributed uniformly throughout the water column (fig. A3). 

About 100 probes were installed during March 3 – 9, 2000. 

Onset Optic StowAway® Temp temperature probes were 

installed, which have a range of -5 to 37°C and an accuracy of 

0.2°C. Water temperature was recorded at 24-minute intervals. 

The probes were affixed to a steel cable that was attached to a 

stationary structure above or near the water surface such that 

the position of each probe in the water column did not vary 

with time. An exception occurred for array 6, which was relocated on April 23, 2001, and for array 8, which was relocated 

on September 14, 2000. Probe height in the water column was 

referenced by vertical distance above the lake bottom, and the 

probes were distributed over somewhat equal vertical intervals 

such that the top probe was just below the water surface. Individual temperature probes are identified by the array location 

number (1 to 26), followed by a dash (-), and then the height 

above the lake bottom in feet. For example, probe 1-12 identifies the probe at location 1, which is 12 feet above the lake 

bottom (table A3). 

38 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Table A2. Monthly statistics for average climate conditions on Lake Seminole.

[mbar, millibar; °C, degree Celsius; m/s, meter per second; cal/cm2/day, calories per square centimeter per day]

Date

Vapor 

press

(mbar)

Average surface 

temperature

(°C)

Average 

wind

(m/s)

Regression net 

radiation

(cal/cm2/day)

Average air 

temperature

(°C)

Apr. 2000 Average 14.34 22.49 2.53 356.92 18.82

Median 14.41 22.38 2.27 390 19

Minimum 6.94 20.65 1.38 88.32 11.16

Maximum 22.4 24.47 5.19 466.56 22.95

Standard deviation 3.87 .9 .92 107.39 2.93

May 2000 Average 20.57 28.46 2.17 413.32 25.28

Median 20.02 28.99 2.21 423.94 25.19

Minimum 12.8 23.62 1.47 269.79 21.6

Maximum 27.27 30.3 3.42 482.37 28.2

Standard deviation 3.79 1.55 .48 45.88 1.78

June 2000 Average 23.83 30.2 2.09 367.69 26.74

Median 25.53 30.22 2.07 389.83 26.74

Minimum 14.42 28.81 1.51 187.48 24.09

Maximum 27.7 31.96 2.98 483.92 29.28

Standard deviation 3.65 .8 .4 93.69 1.29

July 2000 Average 26.1 31.69 1.89 359.74 28.22

Median 26.22 31.54 1.9 387.86 27.91

Minimum 21.94 30.24 1.29 107.22 24.65

Maximum 29.18 33.74 2.94 452.47 31.32

Standard deviation 1.87 .92 .36 88.29 1.86

Aug. 2000 Average 26.16 31.16 1.71 325.89 27.65

Median 26.87 31.11 1.67 336.99 27.76

Minimum 20.59 29.93 1.21 183.69 24.8

Maximum 29.6 32.45 2.44 418.45 30.07

Standard deviation 2.38 .7 .28 70.26 1.28

Sept. 2000 Average 23.64 27.8 2.08 252.49 24.61

Median 25.28 27.7 1.91 297.72 25.6

Minimum 14.22 24.62 1.03 20.95 19.03

Maximum 29.64 30.11 3.94 381.67 27.88

Standard deviation 4.96 1.62 .67 102.15 2.65

Oct. 2000 Average 15.67 22.88 1.6 267.2 19.85

Median 16.53 22.98 1.35 262.75 20.68

Minimum 6.36 20.27 .64 139.01 11.65

Maximum 25.87 26.91 5.88 337.33 26.6

Standard deviation 4.62 1.81 1.07 49.88 3.35

Nov. 2000 Average 13.48 18.83 2.1 145.85 15.09

Median 11.59 18.82 1.57 182.41 14.02

Minimum 5.06 13.69 .94 -6.55 5.73

Maximum 23.35 24 4.53 252.44 23.97

Standard deviation 5.54 3.82 1.12 87.95 5.66

Dec. 2000 Average 8.81 12.48 2.28 126.2 8.93

Median 7.18 12.81 2.09 154.65 7.7

Minimum 3.34 8.61 .99 -12.56 -.7

Maximum 20.78 16.61 4.41 218.92 20.36

Standard deviation 4.9 2.17 .96 77.36 5.32

Appendix 39
Table A2—continued. Monthly statistics for average climate conditions on Lake Seminole.

[mbar, millibar; °C, degree Celsius; m/s, meter per second; cal/cm2/day, calories per square centimeter per day]

Date 

Vapor 

press

(mbars)

Average surface 

temperature

(°C)

Average 

wind

(m/s)

Regression net 

radiation

(cal/cm2/day)

Average air 

temperature

(°C)

Jan. 2001 Average 8.37 10.25 2.12 152.63 8.92

Median 7.94 10.84 1.78 167.88 7.88

Minimum 0 7.19 1.03 .67 .63

Maximum 18.91 13.8 4.52 243.16 18.67

Standard deviation 4.2 2.05 .95 67.42 4.96

Feb. 2001 Average 13.03 16.33 2.09 173.39 15.29

Median 13.25 16.61 1.75 173.81 14.82

Minimum 5.41 12.63 .88 9.26 8.25

Maximum 20.16 20.61 5.04 292.31 21.38

Standard deviation 4.51 2.34 .98 89.19 3.89

Mar. 2001 Average 11.61 17.73 2.33 211.76 14.57

Median 11.15 17.17 2.28 255.53 14.38

Minimum 4.62 15.19 1.24 7.2 8.23

Maximum 22.66 21.38 4.07 369.81 22.1

Standard deviation 4.51 1.67 .71 130.53 3.87

Apr. 2001 Average 16.28 23.49 2.13 344.03 20.37

Median 16.24 24.16 1.96 354.6 20.84

Minimum 6.59 17.76 1.15 107.56 11.98

Maximum 25.31 26.92 4.07 431.33 24.86

Standard deviation 4.85 2.67 .69 76.84 3.07

May 2001 Average 18.57 27.09 1.96 376.11 23.66

Median 17.61 27.31 1.82 394.04 23.9

Minimum 11.74 24.92 1.25 210.85 20.84

Maximum 26.29 28.73 3.37 474.13 27.04

Standard deviation 3.77 .96 .5 69.17 1.44

June 2001 Average 25.07 29.6 1.84 319.89 25.71

Median 25.4 29.6 1.84 386.14 25.65

Minimum 18.17 28.09 1.09 36.76 23.51

Maximum 27.96 31.11 3.02 459.17 27.46

Standard deviation 2.26 .76 .45 124.4 1.1

July 2001 Average 27.15 30.91 1.8 330.99 27.22

Median 27.96 31.18 1.76 341.28 27.34

Minimum 19.97 29.13 1.14 64.77 25.17

Maximum 29.6 32.31 3.6 435.12 29.46

Standard deviation 2.23 .8 .42 82.07 1.04

Aug. 2001 Average 27.01 30.22 1.76 290.68 26.58

Median 27.32 30.46 1.61 307.43 26.43

Minimum 20.81 28.36 .98 41.74 24.37

Maximum 30.99 31.75 5.01 422.4 28.6

Standard deviation 2.14 .94 .77 90.26 1.06

Sept. 2001 Average 21.98 28.17 1.93 266.75 23.81

Median 24.21 28.34 1.64 278.47 25.08

Minimum 11.54 23.7 1.04 30.57 16.83

Maximum 28.03 30.6 3.82 345.58 27.43

Standard deviation 5.64 1.99 .69 69.15 3.08

40 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Because of drought, lake stage during the study period 

often was lower than the stage that existed when the probes 

were installed. As a result, the top probe on many of the arrays 

was out of the water, measuring air temperature during periods 

of low lake stage. In order to prevent the use of air temperature-affected probes, those probes near (0.2 feet or less below) 

or above the water surface were excluded from analyses. Data 

also were excluded from malfunctioning probes and temperature spikes that occurred while servicing the probes.

Lake-Temperature Monitoring

Temporal and spatial patterns in lake-water temperature 

were evaluated to ensure accurate volumetric representation of 

lake temperature with point-temperature data. These patterns 

in lake-water temperature determined the appropriate scheme 

for categorizing and spatially averaging point-temperature data 

to ensure that estimates for changes in heat stored by the lake 

can be calculated accurately. Each of the impoundment arms 

and the main lake body have differing hydrologic conditions 

that determine their temperature regimes. Therefore, instead of 

treating lake-water temperature as being areally uniform, the 

relative temperature and volume in each part of the lake were 

represented in heat-exchange calculations. 

Temporal and spatial patterns in lake-water temperature 

were assessed using time-series and seasonal-temperatureprofile plots. Time-series plots generated for each temperature 

array illustrate diurnal and seasonal patterns in temperature 

profiles (fig. A3). Plots of seasonal-temperature profiles are 

useful for illustrating changes in spatial distribution of temperature in the lake through time (fig. A4; table A4).

Patterns of lake-water temperature profiles in the five distinct lake areas—Flint River impoundment arm (arrays 1–5), 

Chattahoochee River impoundment arm (arrays 6–8), Fishpond Drain (arrays 17–18), Spring Creek impoundment arm 

(arrays 20–24), and the main body of the lake (arrays 9–16, 

19, and 25–26)—make it necessary to weight temperature 

data by their representative water volume. For example, the 

Spring Creek impoundment arm generally is colder than the 

other regions (fig. A4); and, therefore, the heat budget should 

account for heat exchange in the corresponding volume of 

water. Similarly, if the lake is well stratified, then temperature 

data may be weighted by its representative water volume at 

different depths. 

Figure A2. Temperature probe arrays in Lake Seminole, Georgia.

Appendix 41

9

8

7

6

5

4

N 3

2

1

26

25

25

24

23

22

21

20

19

18

17

16

15

14

13

12

11

10

Lake Seminole

Flint River

Spring

Creek

Fishpond Drain

Chattahoochee River

EXPLANATION

Temperature probe array 

 and number

Lake Seminole

GEORGIA
Table A3. Temperature probe arrays, probe depth, installation data and probe elevation.

[ft, feet; do., ditto]

Probe Array

Probe height 

above bottom 

(ft)

Bottom depth 

at installation 

(ft)

Installation 

date

Probe 

elevation 

(ft)

1-0 1 0 16.0 Mar. 3, 2000 60.87

1-7 do. 7 do. do. 67.87

1-12 do. 12 do. do. 72.87

2-0 2 0 19.3 do. 57.57

2-5 do. 5 do. do. 62.57

2-10 do. 10 do. do. 67.57

2-16 do. 16 do. do. 73.57

3-0 3 0 10.5 do. 66.37

3-4 do. 4 do. do. 70.37

3-8 do. 8 do. do. 74.37

4-0 4 0 13.7 do. 63.17

4-7 do. 7 do. do. 70.17

4-11 do. 11 do. do. 74.17

5-0 5 0 9.3 do. 67.57

5-4 do. 4 do. do. 71.57

5-7 do. 7 do. do. 74.57

6-0 6 0 20 Mar. 8, 2000 57.05

6-4 do. 4 do. do. 61.05

6-10 do. 10 do. do. 67.05

6-14 do. 14 do. do. 71.05

6-18 do. 18 do. do. 75.05

6-0 6 0 19.5 Apr. 23, 2001 57.86

6-4 do. 4 do. do. 61.86

6-8 do. 8 do. do. 65.86

6-12 do. 12 do. do. 69.86

6-17 do. 17 do. do. 74.86

7-0 7 0 12 do. 65.05

7-6 do. 6 do. do. 71.05

7-10 do. 10 do. do. 75.05

8-0 8 0 20 do. 57.05

8-4 do. 4 do. do. 61.05

8-10 do. 10 do. do. 67.05

8-14 do. 14 do. do. 71.05

8-18 do. 18 do. do. 75.05

8-0 8 0 14 Sept. 14, 2000 61.97

8-4 do. 4 do. do. 65.97

8-8 do. 8 do. do. 69.97

8-11 do. 11 do. do. 72.97

8-14 do. 14 do. do. 75.97

42 Ground-water and surface-water flow and estimated water budget for Lake Seminole
Table A3—continued. Temperature probe arrays, probe depth, installation data and probe elevation.

[ft, feet; do., ditto]

Probe Array

Probe height 

above bottom 

(ft)

Bottom depth 

at installation 

(ft)

Installation 

date

Probe 

elevation 

(ft)

9-0 9 0 7 Mar. 8, 2000 70.05

9-3 do. 3 do. do. 73.05

9-5 do. 5 do. do. 75.05

10-0 10 0 7 do. 70.05

10-3 do. 3 do. do. 73.05

10-5 do. 5 do. do. 75.05

11-0 11 0 10 do. 67.05

11-5 do. 5 do. do. 72.05

11-8 do. 8 do. do. 75.05

12-0 12 0 13 do. 64.05

12-4 do. 4 do. do. 68.05

12-8 do. 8 do. do. 72.05

12-11 do. 11 do. do. 75.05

13-0 13 0 12 do. 65.05

13-4 do. 4 do. do. 69.05

13-7 do. 7 do. do. 72.05

13-10 do. 10 do. do. 75.05

14-0 14 0 15 Mar. 9, 2000 62.14

14-4 do. 4 do. do. 66.14

14-8 do. 8 do. do. 70.14

14-11 do. 11 do. do. 73.14

14-14 do. 14 do. do. 76.14

15-0 15 0 16.5 do. 60.64

15-4 do. 4 do. do. 64.64

15-8 do. 8 do. do. 68.64

15-12 do. 12 do. do. 72.64

15-15 do. 15 do. do. 75.64

16-0 16 0 8.75 do. 68.39

16-4 do. 4 do. do. 72.39

16-7 do. 7 do. do. 75.39

17-0 17 0 8 do. 69.14

17-3 do. 3 do. do. 72.14

17-6 do. 6 do. do. 75.14

Appendix 43
Table A3—continued. Temperature probe arrays, probe depth, installation data and probe elevation.

[ft, feet; do., ditto]

Probes Array

Probe height 

above bottom 

(ft)

Bottom depth 

at installation 

(ft)

Installation 

date

Probe 

elevation 

(ft)

18-0 18 0 6.2 Mar. 9, 2000 70.94

18-3 do. 3 do. do. 73.94

18-5 do. 5 do. do. 75.94

19-0 19 0 11 do. 66.14

19-3 do. 3 do. do. 69.14

19-6 do. 6 do. do. 72.14

19-9 do. 9 do. do. 75.14

20-0 20 0 15.8 do. 61.34

20-3 do. 3 do. do. 64.34

20-7 do. 7 do. do. 68.34

20-11 do. 11 do. do. 72.34

20-14 do. 14 do. do. 75.34

21-0 21 0 17.8 do. 59.34

21-3 do. 3 do. do. 62.34

21-8 do. 8 do. do. 67.34

21-13 do. 13 do. do. 72.34

21-16 do. 16 do. do. 75.34

22-0 22 0 11.5 do. 65.64

22-4 do. 4 do. do. 69.64

22-8 do. 8 do. do. 73.64

22-10 do. 10 do. do. 75.64

23-0 23 0 8 do. 69.14

23-4 do. 4 do. do. 73.14

23-6 do. 6 do. do. 75.14

24-0 24 0 9.5 do. 67.64

24-3 do. 3 do. do. 70.64

24-6 do. 6 do. do. 73.64

24-8 do. 8 do. do. 75.64

25-0 25 0 21.5 do. 55.64

25-6 do. 6 do. do. 61.64

25-12 do. 12 do. do. 67.64

25-17 do. 17 do. do. 72.64

25-20 do. 20 do. do. 75.64

26-0 26 0 18.85 do. 58.29

26-7 do. 7 do. do. 65.29

26-14 do. 14 do. do. 72.29

26-17 do. 17 do. do. 75.29

44 Ground-water and surface-water flow and estimated water budget for Lake Seminole
A high density of probes was installed in areas of the lake 

where temperatures were expected to be more variable, such 

as areas where there were multiple sources of water at different temperatures. For example, the Spring Creek impoundment arm has a large ground-water component to mean annual 

baseflow, almost 62 percent (Mosner, 2002), which affects 

lake-water temperature (fig. A4). The Spring Creek impoundment arm represents less than 5 percent of the total lake 

volume but contains almost one-fifth of the temperature arrays 

(arrays 20–24; fig. A2). 

Temperature arrays also were categorized by water depth, 

either as shallow (less than 10 feet deep, 11 arrays) or deep 

(deeper than 10 feet, 15 arrays), to identify temperature patterns associated with water depth. Patterns may be attributed 

to factors such as light reflection or absorption by the lake 

bottom and differences in absorption and reflectivity due to the 

presence of submerged vegetation. Note that because temperature arrays commonly were located based on the convenience 

of preexisting attachment points, the water-depth categories do 

not necessarily represent the depth characteristics of the different areas of the lake.

Temporal Variation in LakeWater Temperature

Time-series plots identify seasonal and diurnal patterns 

in the variation and stratification of lake-water temperature 

(fig. A3). In general, patterns of water temperature are similar 

to fluctuations of average air temperature (fig. 12), high during 

summer and low during winter. The highest water temperature recorded during the study was about 30°C during July 

and August of 2000 and 2001; the lowest water temperature 

0

5

10

15

20

25

30

35

LAKE TEMPERATURE, IN DEGREES CELSIUS

Surface

7 feet below surface

12 feet below surface

JUNE JULY AUG SEPT OCT NOV DEC JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV

2000 2001

Probe depth

Data download/initialization 

 spike—to be ignored

Figure A3. Time-series plot for temperature probe array 1 (see figure A2 for location of array 1).

recorded was about 5°C during early January 2001. Because 

there was evidence of stratification in each part of the lake in 

the summer and winter, temperature was evaluated temporally 

during these periods.

Winter Lake-Temperature Patterns

During the winter period, November through March, lake 

water generally was well mixed; however, in deep parts of the 

lake, where there is less influence by large inflows, there was 

evidence of stratification. During the winter, two temperature 

arrays (23 and 25) did not have enough probes functioning to 

assess patterns in temperature responses. Of the remaining 

24 temperature arrays, 13 arrays indicated that waters were 

well mixed. The arrays representing well-mixed lake water 

included all five arrays in the Flint River and Chattahoochee 

River impoundment arms, upstream arrays in the Spring Creek 

impoundment arm (22 and 24), and arrays in the main body 

of the lake near the Chattahoochee River impoundment arm 

(arrays 9–11) (fig. A2). The areal extent of mixing suggests 

that surface-water inflow into the lake keeps these areas well 

mixed during the winter period.

Eleven temperature arrays exhibited some degree of thermal stratification during the winter period, with colder, denser 

water located at the bottom of the water column and warmer, 

less-dense water at the top (fig. A2). These arrays are located 

in the main body of the lake (arrays 12–16 and 26) and in the 

Spring Creek impoundment arm (arrays 20 and 21) (fig. A2). 

These arrays were not influenced greatly by large inflows and 

showed a diurnal pattern in temperature associated with air 

temperature. The magnitude of diurnal variations was highest 

for probes located close to the surface of the lake as opposed 

to probes located deeper (fig. A2).

Appendix 45
54

58

62

66

70

74

78

54

58

62

66

70

74

78

54

58

62

66

70

74

78

ELEVATION, IN FEET ABOVE NORTH AMERICAN VERTICAL DATUM OF 1988

5 10 15 20 25 30 32

TEMPERATURE, IN DEGREES CELSIUS

A. July 1, 2000

B. October 1, 2000

C. January 1, 2001

Main body of Lake Seminole

Lake Seminole water level

EXPLANATION

Impoundment arm

Flint River

Chattahoochee River

Fishpond Drain

Spring Creek

Figure A4. Plots of seasonal-temperature profiles illustrating spatial temperature differences 

seasonally on (A ) July 1, 2000, (B ) October 1, 2000, and (C ) January 1, 2001.

46 Ground-water and surface-water flow and estimated water budget for Lake Seminole
54

58

62

66

70

74

78

54

58

62

66

70

74

78

54

58

62

66

70

74

78

TEMPERATURE, IN DEGREES CELSIUS

5 10 15 20 25 30 32

D. April 1, 2001

E. July 1, 2001

F. October 1, 2001

Lake Seminole water level

EXPLANATION

Impoundment arm

Flint River

Chattahoochee River

Fishpond Drain

Spring Creek

Main body of Lake Seminole

ELEVATION, IN FEET ABOVE NORTH AMERICAN VERTICAL DATUM OF 1988

Figure A4—continued. Plots of seasonal-temperature profiles illustrating spatial temperature 

differences seasonally on (D ) April 1, 2001, (E ) July 1, 2001, and (F ) October 1, 2001.

Appendix 47
Summer Lake-Temperature Patterns

From late spring and summer into early fall, April through 

October, a variety of patterns were identified in the watertemperature time-series data. Most of the shallow probes and 

many of the deep probes showed a diurnal variation with air 

temperature. The magnitude of the diurnal fluctuation was 

high for the shallow probes and low for relatively deep probes.

In the Flint River impoundment arm, the most upstream 

arrays that were not affected by springflow into the lake bottom (arrays 2 and 3) indicate that waters were well mixed. 

Diurnal variations were more pronounced in the shallow 

probes than in relatively deep probes. The influence of inflowing cold ground water along the lake bottom was evident in the 

thermal profiles for the remaining three arrays (1, 4–5) in the 

Flint River impoundment arm.

Water temperature along the Chattahoochee River 

impoundment arm (arrays 6–8) and in the main body of the 

lake close to the Chattahoochee River impoundment arm 

(arrays 9–11) remained unstratified during the summer period, 

which was similar to the winter; the exception being for the 

uppermost upstream array, which showed some stratification 

during the summer.

Summer thermal profiles of lake water located in Fishpond 

Drain (arrays 17–18) and in the main body of the lake near 

Fishpond Drain (array 16) indicated water temperatures were 

stratified, as during the winter. Water temperatures at the lake 

bottom for these arrays showed little or no diurnal patterns. 

During warming periods (April through August), this water 

gains heat slowly, lagging behind the temperature response of 

the water above, suggesting that during the summer, some of 

the water at depth is from ground-water discharge. Another 

possible explanation for thermal stratification in Fishpond 

Drain is the very small, almost negligible, streamflow that 

enters the lake from this impoundment arm. The small 

streamflow, coupled with shallow water depth and incidence 

of submerged vegetation, causes water in Fishpond Drain to 

move slowly, allowing thermal stratification to occur due to 

radiational heating.

Along the Spring Creek impoundment arm, lake-water 

temperature profiles indicate increased stratification with 

distance downstream toward the main body of the lake. The 

lower-depth probes in arrays located near the main body of 

the lake indicate little or no diurnal-temperature variation. 

These observations suggest that the water was well mixed in 

the upstream reaches of the impoundment arm. Ground-water 

inflow to Spring Creek along the length of the impoundment 

arm adds relatively cooler water (about 20°C) to the bottom of 

the water column, resulting in increased downstream stratification during the summer period. 

Probe 1-0, located along the Flint River impoundment 

arm, and 25-0, located in the main body of the lake near the 

Flint River impoundment arm, were installed where springflow enters the lake bottom; summer temperature patterns 

at these probes are dominated by ground water. When lake 

temperatures are warmer than ground water, usually from May 

through mid-November, these probes record nearly constant 

water temperature, varying between 20 and 21°C, indicating 

ground-water inflow (fig. A3). These temperatures are slightly 

warmer than the average ground-water temperature in the 

region (about 68°F, or 20°C). Occasionally, after a heavy rainfall event, lake water becomes well mixed temporarily with 

ground water from these springs, resulting in an unstratified 

thermal profile. At other times, when the temperature of the 

lake water is slightly warmer than the incoming springflow, 

some mixing of water not associated with heavy rainfall events 

occurs. Near the end of the summer period, usually from late 

October to early November, lake water cools to temperatures 

Table A4. Mean, median, minimum, and maximum temperatures 

for each area of Lake Seminole during the study period, April 

2000–September 2001 (see figure A2).

[CRIA, Chattahoochee River impoundment arm; FPD, Fishpond Drain; FRIA, 

Flint River impoundment arm; MBL, main body of the lake; SCIA, Spring 

Creek impoundment arm, all temperatures in degrees Celsius]

Probes Date Count Mean Median Minimum Maximum

All July 1, 2000 84 28.99 29.09 20.48 31.51

CRIA do. 8 29.37 29.33 29.09 29.71

FPD do. 6 30.42 30.85 29.01 31.51

FRIA do. 14 28.16 28.61 20.48 30.13

MBL do. 40 29.21 29.32 20.67 30.89

SCIA do. 16 28.45 28.4 25.56 31.32

All Oct. 1, 2000 92 24.11 24.28 20.42 25.42

CRIA do. 9 24.95 24.94 24.18 25.25

FPD do. 6 24.46 24.43 23.99 24.98

FRIA do. 16 23.66 23.76 20.42 24.67

MBL do. 41 24.35 24.34 20.67 25.42

SCIA do. 20 23.47 23.73 21.54 24.56

All Jan. 1, 2001 88 8.33 8.27 6.63 10.69

CRIA do. 8 8.17 8.24 7.61 8.39

FPD do. 6 7.81 7.85 7.35 8.16

FRIA do. 16 7.21 6.96 6.63 8.46

MBL do. 37 8.42 8.55 7.52 9.25

SCIA do. 21 9.21 9.72 7.78 10.69

All Apr. 1, 2001 88 15.96 15.72 14.26 18.71

CRIA do. 8 14.82 14.9 14.26 15.07

FPD do. 6 17.93 18.21 16.9 18.71

FRIA do. 16 14.95 14.93 14.59 15.35

MBL do. 37 15.86 15.67 14.27 18.17

SCIA do. 21 16.76 16.96 15.5 17.74

All July 1, 2001 84 27.33 27.59 20.38 29.59

CRIA do. 9 26.54 26.4 25.96 27.42

FPD do. 6 28.68 28.73 27.72 29.59

FRIA do. 16 26.92 27.36 20.38 27.68

MBL do. 40 27.85 28.14 20.67 28.91

SCIA do. 13 26.18 25.8 23.87 28.17

All Oct. 1, 2001 85 22.65 22.9 19.77 24.37

CRIA do. 12 24.11 24.15 23.63 24.37

FPD do. 6 22.05 22.11 21.16 22.78

FRIA do. 13 22.08 22.2 20.52 22.6

MBL do. 38 23.08 23.1 20.77 23.98

SCIA do. 16 21.25 20.98 19.77 23.12

48 Ground-water and surface-water flow and estimated water budget for Lake Seminole
that are below that of the inflowing ground water, and the 

thermal profiles indicate no stratification until the following 

spring, although temperature data collected at the spring orifices indicate that the springs are still flowing. Temperatures 

at the remaining arrays located in the main body of the lake 

(arrays 12–15, 19, 25–26) are stratified during the summer.

Spatial Variation in Lake-Water 

Temperature

Seasonal differences in water temperature for the five lake 

areas are illustrated in quarterly plots of temperature and 

temperature-probe altitude for January and April 2001, and for 

July and October 2000 and 2001 (fig. A4). Water temperatures 

recorded at midnight were plotted to reduce the effects associated with diurnal temperature variations. 

There were no distinguishing patterns in temperature profiles between shallow- and deep-water temperature arrays 

(not shown), indicating that water depth is not an important 

factor to establishing vertical patterns of lake-temperature 

variation. The lack of any distinguishable pattern in lake 

temperature in relation to depth also suggests that the presence 

of submerged vegetation, which is widespread in the shallow 

waters covering about half of the lake area, does not affect 

water-temperature profiles appreciably. There were, however, 

distinct seasonal patterns in temperature profiles among the 

different lake areas (fig. A4). 

On July 1, 2000, most lake-water temperature measurements were similar, ranging between 28 and 31°C (fig. A4A). 

The deep water in the Spring Creek impoundment arm and 

in the shallow Fishpond Drain was colder than the lake-water 

temperature in most of the other lake areas. The low temperature along the Spring Creek impoundment arm indicates 

the influence of ground-water inflow to the lake. Two probes 

(1-0 and 25-0), identified earlier as being located at or near 

springs that discharge ground water into the lake along the 

bottom, recorded the coldest temperatures of all the probes 

(20.5 and 20.7°C, respectively).

On October 1, 2000, there were small differences in lake 

temperature among the different areas of the lake; temperatures along the Flint River impoundment arm were slightly 

colder, and temperatures along the Chattahoochee River 

impoundment arm were slightly warmer than other areas of 

the lake (fig. A4B). Colder temperatures were apparent along 

the Spring Creek impoundment arm for the two uppermost 

upstream arrays (23 and 24) at all depths, due to ground-water 

inflow. The coldest lake temperatures again were recorded at 

probes 1-0 and 25-0, which monitor springflow temperature 

along the lake bottom, with values similar to those measured 

on July 1, 2000. 

On January 1, 2001, lake temperatures were the lowest of 

any time period evaluated, with temperatures ranging from 6.5 

to 10.5°C (fig. A4C). Lake temperatures at the four uppermost 

upstream arrays in the Flint River impoundment arm were 

colder than temperatures recorded at nearly all of the other 

probes. The three uppermost upstream arrays in the Spring 

Creek impoundment arm recorded the warmest lake temperatures of all the other arrays due to ground-water inflow.

On April 1, 2001, most lake temperatures ranged from 14.5 

to 17.5°C (fig. A4D). Lake temperatures along the Flint River 

and Chattahoochee River impoundment arms were colder than 

the main body of the lake; whereas, lake temperatures along 

the Spring Creek impoundment arm and Fishpond Drain were 

warmer than the main body of the lake. 

On July 1, 2001, there was a more distinct separation in 

temperature of the different areas compared with July 1, 2000 

(compare figs. A5A, E). With the exception of two probes 

that monitor springflow along the lake bottom, temperatures 

ranged from about 24 to 29°C. The coldest lake area was 

the Spring Creek impoundment arm, followed by the Chattahoochee River and Flint River impoundment arms, and the 

main body of the lake; the warmest area was Fishpond Drain. 

The most distinct separation in temperatures among the 

impoundment arms occurred on October 1, 2001 (fig. A4F); 

temperatures ranged from 19.5 to 24.5°C. The areas of the 

lake from coldest to warmest were the Spring Creek impoundment arm, Flint River impoundment arm, main body of the 

lake, and Chattahoochee River impoundment arm. Temperatures in Fishpond Drain were somewhat similar to those in the 

Flint River impoundment arm, except with a larger range. 

Plots of temperature profiles for the six dates categorized 

by depth of array (shallow or deep) indicated that there was no 

pattern in water temperatures associated with depth of water. 

However, because of the pronounced differences in temperature patterns and representative volumes of each area of the 

lake (fig. A4), it was necessary to weight the temperatures 

Appendix 49