Evaluation of Ground-Water Contribution to 

Streamflow in Coastal Georgia and Adjacent 

Parts of Florida and South Carolina 

 By Sherlyn Priest 

 Prepared in cooperation with the 

Georgia Department of Natural Resources 

 Environmental Protection Division 

 Scientific Investigations Report 2004-5265 

 U.S. Department of the Interior 

 U.S. Geological Survey 
 This report is available online at http://pubs.usgs.gov/ 

 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. 

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

 Atlanta, Georgia 

 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: 

 Priest, Sherlyn, 2004, Evaluation of ground-water contribution to streamflow in coastal Georgia and parts of Florida 

and South Carolina: U.S. Geological Survey Scientific Investigations Report 2004-5265, p. 46. 

 U.S. Department of the Interior 

 Gale A. Norton, Secretary 

 U.S. Geological Survey 

 Charles G. Groat, Director 
iii

 Contents 

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

Introduction ................................................................................................ 1

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

Description of Study Area ........................................................................ 2

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

Method of Study .................................................................................... 6

Baseflow Estimation ........................................................................ 6

Precipitation Trends ........................................................................ 8

Well and Streamflow Gaging Station Identification Systems ................................. 9

Stream-Aquifer Relations .............................................................................. 9

Stream-Aquifer Flow Systems ..................................................................... 9

Climate .......................................................................................... 1 0

Surface Water ................................................................................. 1 0

Ground Water ................................................................................. 1 5

Hydrogeologic Units .................................................................. 1 5

Upper Coastal Plain ............................................................... 1 5

Lower Coastal Plain ............................................................... 1 6

Ground-Water Levels .................................................................. 1 6

Long-Term Fluctuations and Trends ............................................................ 1 7

Salkehatchie–Savannah–Ogeechee River Basin ....................................... 1 7

Altamaha–Satilla–St Marys River Basin ................................................... 1 8

Suwannee River Basin ..................................................................... 2 1

Ground-Water Contribution to Streamflow ...................................................... 2 1

Hydrograph Separation ..................................................................... 2 4

Drought Streamflow ........................................................................ 2 5

Linear-Regression Analysis of Streamflow Duration .................................... 28 

Comparison of Results ........................................................................ 3 4

Summary ................................................................................................... 3 6

Selected References .................................................................................... 3 8
iv

 Figures 

 1. Map showing location of study area, streamflow gaging stations, wells, and 

National Weather Service stations ......................................................... 3 

 2. Chart showing geologic and hydrogeologic units of the upper and lower Coastal 

Plain, Georgia ................................................................................. 7

 3. Graphs of differences in separating baseflow using fixed-interval, sliding-interval, 

and local-minimum methods of HYSEP at Beaverdam Creek (station 02198100) 

near Sardis, Georgia, 1999 .................................................................. 8

 4. Schematic diagram of the conceptual hydrologic flow system in the upper and 

lower Coastal Plain of Georgia ............................................................... 9

 5. Map showing mean annual precipitation for selected National Weather Service stations 

in the Coastal Plain of Georgia and South Carolina, 1971–2000 ........................ 1 1

 6. Graphs showing mean monthly precipitation at selected National Weather 

Service stations in the Coastal Plain area of Georgia and South Carolina, 

1971–2001 ....................................................................................... 1 2

 7. Map showing mean annual runoff for the Coastal Plain of Georgia, 1941–70 ......... 1 3

 8. Boxplots showing distribution of daily streamflow for Brier Creek (station 

02198000) near Millhaven, Georgia; Canoochee River (station 02203000) near 

Claxton, Georgia; and Little Satilla River (station 02227500) near Offerman, 

Georgia, for the period of record ............................................................ 1 4

9–14. Graphs Showing— 

 9. Mean monthly streamflow at a selected streamflow gaging station within the 

Salkehatchie–Savannah–Ogeechee, Altamaha–Satilla–St Marys, and Suwannee 

River Basins for the periods of record ...................................................... 1 5

 10. Daily water-level measurements in wells 35P094 and 36Q008, Chatham County; 

and daily rainfall at National Weather Service station, Savannah Municipal 

Airport, Chatham County, Georgia, 2001 ................................................... 1 7

 11. Daily mean water levels in the surficial, upper Brunswick, and Upper Floridan 

aquifers at the Gardi site, Wayne County, Georgia, 1983–2001 ........................... 1 8

 12. Mean annual stream discharge, daily mean ground-water level, and cumulative 

departure from normal precipitation for the upper and lower parts of 

Salkehatchie–Savannah–Ogeechee River Basin, Georgia and South Carolina, 

1971–2001 ....................................................................................... 1 9

 13. Mean annual stream discharge, daily mean ground-water level, and cumulative 

departure from normal precipitation for the upper and lower parts of the 

Altamaha–Satilla–St Marys River Basin, Georgia, 1971–2001 ........................... 2 0

 14. Mean annual stream discharge, daily mean ground-water level, and cumulative 

departure from normal precipitation for the upper and lower parts of the 

Suwannee River Basin, Georgia, 1971–2001 ................................................ 22 

 15. Potentiometric surface of the Upper Floridan aquifer, May 1998 ........................ 2 3

 1 6. Baseflow separation using the local-minimum method for the wet, average, 

and dry years at Canoochee River (station 02203000) near Claxton, Georgia, 

1971–2001 ....................................................................................... 2 5

 17. Comparison of drought streamflow between two adjacent streamflow gaging 

stations in the Salkehatchie–Savannah–Ogeechee River Basin ........................ 2 6
v

18–20. Maps Showing— 

 18. Selected streamflow gaging stations monitored during the 1954 drought and 

corresponding intermediate unit-area discharge ....................................... 30 

 19. Selected streamflow gaging stations monitored during the 1981 drought and 

corresponding intermediate unit-area discharge ....................................... 3 1

 20. Selected streamflow gaging stations monitored during the 2000 drought and 

corresponding intermediate unit-area discharge ....................................... 3 2

21–26. Graphs Showing—

 21. Comparison of two flow-duration curve types: gentle curve along Brier Creek 

(station 02198000) and a steep curve along the Alapaha River (station 02317500) ... 3 3

 22. Duration of mean daily streamflow for Brushy Creek (station 02197600) near 

Wrens, Georgia, and Brier Creek (station 02198000) at Millhaven, Georgia, 

1971–2001 ....................................................................................... 3 3

 23. Duration of mean daily streamflow for Canoochee River (station 02203000) near 

Claxton, Georgia, in the upper Salkehatchie–Savannah–Ogeechee River Basin, 

1971–2001 ....................................................................................... 3 4

 24. Duration of mean daily streamflow for Little Satilla River (02227500) near 

Offerman, Georgia, and Ocmulgee River (02215500) at Lumber City, Georgia, in 

the Altamaha–Satilla–St Marys River Basin, 1971–2001 ................................. 3 4

 25. Duration of mean daily streamflow for Alapaha River (station 02317500) at 

Statenville, Georgia, in the Suwannee River Basin, 1971–2001 ........................ 3 5

 26. Regression of Q 35 versus mean annual baseflow for the 8 and 14 streamflow 

gaging stations selected for hydrograph-separation technique, Georgia and 

South Carolina, 1971–2001 .................................................................. 3 5

 Tables 

 1. Selected streamflow gaging and partial-record stations in Salkehatchie–

Savannah–Ogeechee, Altamaha–Satilla–St Marys, and Suwannee River Basins ... 4

 2. Well construction data for selected wells used in Georgia .............................. 6

 3. Summary of mean annual baseflow estimated using HYSEP at selected 

streamflow gaging stations in the upper and lower parts of the basins in coastal 

Georgia and South Carolina, 1971–2001 ................................................... 2 4

 4. Measured stream discharge at selected streamflow gaging stations in the upper 

and lower Coastal Plain during the 1954, 1981, and 2000 droughts in Georgia 

and Florida .................................................................................... 2 7

 5. Estimated ground-water discharge to selected streams in the Salkehatchie–

Savannah–Ogeechee, Altamaha–Satilla–St Marys, and Suwannee River 

Basins during the 1954, 1981, and 2000 droughts.......................................... 29 

 6. Flow-duration curve index [(Q 25 /Q 75 ) 1⁄2 ] and curve shape for selected streams in the 

Salkehatchie–Savannah–Ogeechee, Altamaha–Satilla–St Marys, and Suwannee 

River Basins, 1971–2001 ..................................................................... 3 3

 7. Coefficient of determination (r 2 ) and residual standard of error for flow durations 

evaluated as indicators of baseflow for 8 and 14 streamflow gaging stations 

selected in the Salkehatchie–Savannah–Ogeechee, Altamaha–Satilla–St Marys, 

and Suwannee River Basins, 1971–2001 ................................................... 3 5

 8. Comparison of three methods used to calculate baseflow for selected streamflow 

gaging stations in the Salkehatchie–Savannah–Ogeechee, Altamaha–Satilla–

St Marys and Suwannee River Basins, 1971–2001 ....................................... 36 
vi

 Conversion Factors and Datum 

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

 °F = (1.8×°C)+32 

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

 °C = (°F-32)/1.8 

 Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88). Historical data collected and stored as National Geodetic Vertical Datum of 1929 

have been converted to NAVD 88 for this publication. 

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

Historical data collected and stored as North American Datum of 1927 (NAD 27) have been 

converted to NAD 83 for use in this report. 
Abstract 

 Stream-aquifer relations in the coastal area of Georgia 

and adjacent parts of Florida and South Carolina were evaluated as part of the Coastal Georgia Sound Science Initiative, 

the Georgia Environmental Protection Division’s strategy to 

protect the Upper Floridan aquifer from saltwater intrusion. 

Ground-water discharge to streams was estimated using three 

methods: hydrograph separation, drought-streamflow measurements, and linear-regression analysis of streamflow duration. 

Ground-water discharge during the drought years of 1954, 

1981, and 2000 was analyzed for minimum ground-water 

contribution to streamflow. Hydrograph separation was used to 

estimate baseflow at eight streamflow gaging stations during 

the 31-year period 1971–2001. Six additional streamflow gaging stations were evaluated using linear-regression analysis of 

flow duration to determine mean annual baseflow. The study 

area centers on three major river systems — the Salkehatchie–

Savannah–Ogeechee, Altamaha–Satilla–St Marys, and Suwannee — that interact with the underlying ground-water system to 

varying degrees, largely based on the degree of incision of the 

river into the aquifer and on the topography. Results presented 

in this report are being used to calibrate a regional groundwater flow model to evaluate ground-water flow and streamaquifer relations of the Upper Floridan aquifer. 

 Hydrograph separation indicated decreased baseflow to 

streams during drought periods as water levels declined in the 

aquifer. Average mean annual baseflow ranged from 39 to 

74 percent of mean annual streamflow, with a mean contribution of 58 percent for the period 1971–2001. In a wet year 

(1997), baseflow composed from 33 to 70 percent of mean 

annual streamflow. Drought-streamflow analysis estimated 

baseflow contribution to streamflow ranged from 0 to 24 percent of mean annual streamflow. Linear-regression analysis 

of streamflow duration estimated the Q 35 (flow that is equaled 

or exceeded 35 percent of the time) as the most reasonable 

estimate of baseflow. The Q 35 , when compared to mean annual 

streamflow, estimated a baseflow contribution ranging from 

65 to 102 percent of streamflow. The Q 35 estimate tends to 

overestimate baseflow as evidenced by the baseflow contribution greater than 100 percent. Ground-water contributions to 

streamflow are greatest during winter when evapotranspiration is low, and least during summer when evapotranspiration is high. Baseflow accounted for a larger percentage of 

streamflow at gaging stations in the Salkehatchie–Savannah–

Ogeechee River Basin than in the other two basins. This difference is due largely to the availability of data, proximity to 

the Piedmont physiographic province where the major rivers 

originate and are by supplied ground water, and proximity 

to the upper Coastal Plain where there is greater topographic 

relief and interconnection between streams and aquifers. 

Introduction 

 Population growth, increased tourism, and sustained 

industrial activities in the coastal area of Georgia have affected 

the area’s water resources and limited the availability of 

ground water. The principal source of water in the 24-county 

coastal Georgia area is the Upper Floridan aquifer, which 

underlies most of the Coastal Plain of Georgia, southwest 

South Carolina, southeast Alabama, and all of Florida (Miller, 

1986). The Upper Floridan aquifer is an extremely permeable, 

high-yielding aquifer that was first developed in the 1880s and 

has been used extensively since. Saltwater contamination of 

the Upper Floridan aquifer at Brunswick, Ga., Jacksonville, 

Fla., and Hilton Head Island, S.C., also limit the availability of 

ground water in coastal Georgia (Krause and Clarke, 2001). 

 The Coastal Georgia Sound Science Initiative is a 

program of scientific and feasibility studies to support 

develop ment of Georgia Environmental Protection Division’s 

(GaEPD) final strategy to protect the Upper Floridan aquifer 

 Evaluation of Ground-Water Contribution to 

Streamflow in Coastal Georgia and Adjacent 

Parts of Florida and South Carolina 

 By Sherlyn Priest 
2 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

from salt water contamination. In support of the Coastal Georgia Sound Science Initiative, the U.S. Geological Survey 

(USGS) — in cooperation with GaEPD — is conducting studies 

to characterize and monitor ground-water flow and saltwater 

contamination; evaluate possible alternative sources of water 

to the Upper Floridan aquifer; simulate ground-water flow and 

movement of saltwater in response to various water-management approaches; and monitor changes in the hydrologic system. The study area includes southeast Georgia and adjacent 

parts of northeast Florida and southwest South Carolina (fig. 1). 

 As part of the Coastal Georgia Sound Science Initiative, ground-water discharge to streams was estimated for 

selected streams and rivers in a 67-county area of southeast 

Georgia, northeast Florida, and southwest South Carolina 

(55 counties in Georgia, 5 counties in Florida, and 7 counties 

in South Carolina). Results presented herein are being used 

to calibrate a regional ground-water flow model to evaluate 

ground-water flow and stream-aquifer relations of the Upper 

Floridan aquifer. 

Purpose and Scope 

 This report describes stream-aquifer relations in the 

coastal area of Georgia and adjacent parts of Florida and South 

Carolina by estimating ground-water discharge to streams 

under a variety of climatic conditions. These estimates were 

made using hydrograph-separation techniques, droughtstreamflow measurements, and linear-regression analysis of 

streamflow duration. The estimated ground-water discharge is 

being used to calibrate a regional ground-water flow model to 

evaluate ground-water flow and stream-aquifer relations of the 

Upper Floridan aquifer. 

 Continuous-discharge records from eight streamflow 

gaging stations (stations) were used to estimate baseflow 

using hydrograph-separation techniques for the 31-year period 

from 1971 to 2001; and continuous-discharge records from an 

additional six stations were used to estimate baseflow using 

linear-regression analysis of streamflow duration for the same 

period. Historical streamflow data collected from 22 stations 

during the 1954 drought, 7 stations during the 1981 drought, 

and 19 stations during the 2000 drought were used to evaluate 

intermediate basin ground-water discharge during dry periods 

(table 1). Precipitation data from 11 National Weather Service 

(NWS) stations (National Oceanic and Atmospheric Administration, 2002) and ground-water levels from 9 USGS wells 

(table 2) were evaluated for long-term trends (1971–2001). 

 Several tributaries to major rivers — Altamaha, Ogeechee, 

Salkehatchie, Satilla, Savannah, St Marys, and Suwannee —

drain the study area. Streamflow records for continuous-record 

stations and several partial-record stations along the major rivers and tributaries were used in the investigation. Stream-discharge measurements were taken at 18 continuous-record and 

partial-record stations from July 31 through August 2, 2000, 

and stream-discharge measurements from 24 continuousrecord stations were used to evaluate surface-water conditions 

(fig. 1 and table 1). Measurements from 24 partial-record 

stations and continuous-record stations were collected for 

1954 and from 12 partial-record stations and continuousrecord stations for 1981. Data were collected from 62 continuous-record and partial-record stations on tributaries including 

synoptic measurements. Unless otherwise indicated, the primary source of data used in this report is the USGS National 

Water Information System (NWIS) (at http://waterdata.usgs.

gov/ga/nwis/nwi s). All data presented are by calendar year. 

Description of Study Area 

 The GaEPD defines the coastal area of Georgia to include 

the 6 coastal counties and adjacent 18 counties, an area of 

about 12,240 square miles (mi2) (fig. 1). To account for 

natural hydrologic boundaries used for model simulation, the 

study area has been expanded to 32,661 mi2 and includes the 

24 coastal counties and outlying 43 counties extending into 

northeast Florida and southwest South Carolina. 

 The study area is located in the northern part of the southeastern Coastal Plain of Georgia, South Carolina, and Florida 

(fig. 1). Coastal Plain geology consists of layers of sand, clay, 

limestone, and dolomite that range in age from Late Cretaceous through Holocene. The northern limit of these strata and 

the contact between Coastal Plain sediments and Piedmont 

crystalline rocks correspond approximately to the Fall Line 

(Clarke and Zisa, 1976), a physiographic boundary between 

the Piedmont and Coastal Plain. The various strata dip and 

progressively thicken from the Fall Line to the southeast. 

The sedimentary sequence unconformably overlies Paleozoic 

to Mesozoic igneous, metamorphic, and sedimentary rocks 

(Chowns and Williams, 1983). 

 Coastal Plain sediments consist of fluvial, deltaic, and 

marine coastal and shelf deposits (Prowell and others, 1985). 

Numerous marine transgressions and regressions have 

deposited, removed, and redistributed sediments in the study 

area and the vicinity (Colquhoun, 1981). Carter and Putnam 

(1977) divided the Coastal Plain physiographic province into 

upper and lower Coastal Plain. In the upper Coastal Plain in 

Richmond County, Ga., sediments predominantly consist of 

non marine siliciclastic sediments. Marine sediments are more 

abundant in the lower Coastal Plain and include carbonateshelf deposits in some Tertiary strata (Atkins and others, 1996). 

 The principal source of ground water for all uses in the 

coastal area is the Floridan aquifer system, consisting of the 

Upper and Lower Floridan aquifers (Miller, 1986; Krause 

and Randolph, 1989). Secondary sources of water include 

the surficial and Brunswick aquifer systems (Clarke, 2003), 

consisting of sand of Miocene to Holocene age. A generalized 

correlation chart of geologic and hydrologic units is shown in 

figure 2. 

 Land use primarily is urban in industrial areas and cities. 

Outside of these areas, land use is a mix of forest, wetlands, 

row crops, and pasture. Altitude ranges from sea level along 

the coast to about 400 feet (ft) near the Fall Line. 
Figure 1. Location of study area, streamflow gaging stations, wells, and National Weather Service (NWS) stations. 

Introduction 3

Boundary between 

upper and lower

Coastal Plain

Boundary

of model

02231280

02317500

02314500

02226500

02227000

02225000

02202240

02198500

02176500

02175500

02197415

02198100

02202210

02198120

02197500

02197980

02225315

02225360

02223500

02215100

02223248 02201270

02201300

02225405

02225500

02203000

02202600

02215500

02216180

02228000

02226000

02225850

02227500

02197200

02197600

02201365

02201350

02200410 02197590

02200440

02201000

021973444

02224000

02198170

02198280

WARE

COLUM

SOUTH

GEORGIA OLINA

Atlantic Ocean

pper

Plain

Study

area

24-county area

Fall line

Satilla R

River Basin Site and name or number

Salkehatchie–Savannah–Ogeechee

Altamaha–Satilla–St Marys

Suwannee

Streamflow gaging station

Well 

NWS station

0 30 60 MILES

0 30 60 KILOMETERS

N

EXPLANATION

Base from U.S. Geological Survey

1:100,000-scale digital data

EORGIA

FLORIDA

Suwannee R

Ocmulgee R

Ohoopee R

Altamaha R

Little Satilla

Canochee R

Alapaha R

Atlantic

Ocean

Jacksonville

Hilton Head Island

Salkehatchie R

St Marys R
4 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

 Table 1. Selected streamflow gaging and partial-record stations in Salkehatchie–Savannah–Ogeechee, Altamaha–Satilla–St Marys, 

and Suwannee River Basins. 

 [*, partial-record station; —, data not available; mi 2 , square miles; do., ditto] 

Station 

number Station name Drainage area (mi2) County Basin

Salkehatchie–Savannah–Ogeechee River Basin 

02175500 Salkehatchie River near Miley, S.C. 341.00 Hampton Salkehatchie 

1

02176500 Coosawhatchie River near Hampton, S.C. 203 do. do.

02197200* McBean Creek (Ga. Hwy 56) at McBean, Ga 71.4 Burke Savannah

021973444* Beaverdam Creek at River Rd near Girard, Ga. 23.3 do. do.

02197415 Lower Three Runs at Martin, S.C. 109 Allendale do.

02197500 Savannah River at Burtons Ferry Bridge, Millhaven, Ga. 8,650 Allendale/Screven do.

02197590* Brushy Creek at Wrens, Ga. 9.4 Jefferson do.

02197600 Brushy Creek near Wrens, Ga. 28 do. do.

02197830* Brier Creek near Waynesboro, Ga. 473 Burke do.

02197980* Brier Creek (Ga. Hwy 23) near Sardis, Ga. 579 do. do.

02198000 Brier Creek at Millhaven, Ga. 646 Screven do.

02198060* Brier Creek at US 301 near Sylvania, Ga. 669 do. do.

02198100 Beaverdam Creek near Sardis, Ga. 30.8 Burke/Jenkins do.

02198120* Beaverdam Creek at Hilltonia, Ga. 85.3 Screven do.

02198170* Beaverdam Creek near Sylvania, Ga. 116 do. do.

02198280* Beaverdam Creek near Sylvania, Ga. 143 do. do.

02198500 Savannah River near Clyo, Ga. 9,850 Effingham do.

02200410* Duhart Creek (SR 80) at Stapleton, Ga. 3.17 Jefferson Ogeechee

02200440* Rocky Comfort Creek (US 221) at Louisville, Ga. 286 do. do.

02200720* Big Creek (Penns Bridge Rd) near Wrens, Ga. 8.07 do. do.

02200810* Big Creek above Louisville, Ga. 56.9 do. do.

02200900* Big Creek near Louisville, Ga. 95.8 do. do.

02201000 Williamson Swamp Creek at Davisboro, Ga. 109 Washington do.

02201070* Williamson Swamp Creek at Bartow, Ga. 185 Jefferson do.

02201150* Williamson Swamp Creek at Wadley, Ga. 233 do. do.

02201270* Barkcamp Creek (SR 17) near Midville, Ga. 31.7 Burke do.

02201300* Chow Mill Creek near Herndon, Ga. 23 Jenkins do.

02201350* Buckhead Creek near Waynesboro, Ga. 64 Burke do.

02201360* Rocky Creek at SR 24 near Waynesboro, Ga. 31.7 do. do.

02201365* Rocky Creek near Waynesboro, Ga. 34.8 Burke Ogeechee

02201430* Buckhead Creek at Millen, Ga. 272 Jenkins do.

02202210* Ogeechee Creek near Sylvania, Ga. 14 Screven do.

02202240* Ogeechee Creek near Oliver, Ga. 141 do. do.

02202500 Ogeechee River near Eden, Ga. 2,650 Effingham/Bryan do.

02202600 Black Creek near Blitchton, Ga. 232 Bryan do.

02202969* Cedar Creek (SR 129) at Claxton, Ga. — Evans do.

02203000 Canoochee River near Claxton, Ga. 555 do. do.
 Previous Studies 

 Hydrogeologic investigations of ground water in coastal 

Georgia include Miller (1986), who described the hydrogeologic framework of the Floridan aquifer system in Georgia, 

Florida, South Carolina, and Alabama; Krause and Randolph 

(1989), who simulated ground-water flow in the Floridan 

aquifer system in southeast Georgia and adjacent parts of 

South Carolina and Florida; and Clarke and others (1990), 

who described the geology and ground-water resources of 

13 counties in the present study area. 

 Reports on stream-aquifer relations in the study area 

include Faye and Mayer (1990), who described streamaquifer relations and ground-water flow in the northern 

Coastal Plain of Georgia and adjacent South Carolina and 

Alabama. Atkins and others (1996) estimated ground-water 

contribution to streams in the central Savannah River Basin 

using hydrograph-separation techniques and a droughtstreamflow analysis. Clarke and West (1997, 1998) simulated 

ground-water flow and stream-aquifer relations near the 

Savannah River Site in Georgia and South Carolina. Peck 

and others (2001) evaluated hydrogeologic conditions and 

pond-aquifer relations at two test sites in coastal Georgia. 

Abu-Ruman and Clarke (2001) described preliminary simulations of pond-aquifer interaction at a test site near Brunswick, 

Georgia. Mosner (2002) described stream-aquifer relations 

and the potentiometric surface of the Upper Floridan aquifer in 

southwest Georgia. 

Introduction 5

 Table 1. Selected streamflow gaging and partial-record stations in Salkehatchie–Savannah–Ogeechee, Altamaha–Satilla–St 

Marys, and Suwannee River Basins.—Continued 

 [*, partial-record station; —, data not available; mi 2 , square mile; do., ditto] 

Station 

number Station name Drainage area (mi2) County Basin

Altamaha–Satilla–St Marys River Basin

02215100 Tucsawhatchee Creek near Hawkinsville, Ga. 163.00 Pulaski Altamaha

02215500 Ocmulgee River at Lumber City, Ga. 5,180 Telfair/Jeff Davis do.

02216180 Turnpike Creek near McRae, Ga. 49.2 do. do.

02223248 Oconee River near Oconee, Ga. 3,770 Wilkins/Washington do.

02223500 Oconee River at Dublin, Ga. 4,390 Laurens do.

02224000 Rocky Creek near Dudley, Ga. 62.9 do. do.

02225000 Altamaha River near Baxley, Ga. 11,600 Toombs/Appling do.

02225315* Jacks Creek near Wesley, Ga. 8.63 Emanual do.

02225360* Pendleton Creek near Normantown, Ga. 101 Toombs/Emanual do.

02225395* Swift Creek (SR 130) near Vidalia, Ga. 36 Toombs do.

02225405* Swift Creek (US 1) near Lyons, Ga. 46.3 do. do.

02225420* Swift Creek (SR 152) near Lyons, Ga. 55.6 do. do.

02225480* Ohoopee River (US 280) near Reidsville, Ga. 1,070 Tattnall/Toombs do.

02225500 Ohoopee River near Reidsville, Ga. 1,110 Tattnall do.

02225850* Beards Creek near Glennville, Ga. 74.4 Long/Tattnall do.

02226000 Altamaha River at Doctortown, Ga. 13,600 Long/Wayne do.

02226100 Penholoway Creek near Jesup, Ga. 209 Wayne do.

02226500 Satilla River near Waycross, Ga. 1,190 Ware Satilla

02227000 Hurricane Creek near Alma, Ga. 139 Bacon do.

02227500 Little Satilla River near Offerman, Ga. 646 Wayne/Pierce Satilla

02228000 Satilla River at Atkinson, Ga. 2,790 Brantley do.

02229000 Middle Prong St Marys River at Taylor, Fla. 125 Baker St Marys

02231280 Thomas Creek near Crawford, Fla. 29.9 Duval/Nassau do.

Suwannee River Basin

02314500 Suwannee River at Fargo, Ga. 1,260 Clinch Suwannee

02317500 Alapaha River at Statenville, Ga. 1,390 Echols do.

 1 For the purpose of this study, data from station 02716500 in the Broad–St Helen River Basin were included in the Salkehatchie–Savannah–Ogeechee 

River Basin. 
6 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

and 2000, to estimate minimum values of ground-water discharge. Comparison of data was made between the upper and 

lower Coastal Plain when data were available. When no or few 

data were available, comparison was made between the upper 

and lower parts of the basins within the study area. This is an 

informal division done solely for comparison in this report. 

 Literature review provided information necessary to 

describe a conceptual model of stream-aquifer relations. 

Much of the conceptual model is based on results of previous 

investigations by Toth (1962; 1963), Freeze and Witherspoon 

(1966; 1967; 1968), Faye and Mayer (1990), Atkins and others 

(1996), and Clarke and West (1998). These studies show that 

large rivers and their tributaries function as hydraulic drains for 

ground-water flow; and that during severe droughts, most of 

the discharge in these streams is contributed by ground water. 

Baseflow Estimation 

 During periods of little or no rainfall, streamflow is 

assumed to be composed almost entirely of ground water 

(baseflow). As a result, the amount of streamflow contributed 

by ground water can be estimated. Three methods were used 

to estimate ground-water contribution to streamflow: hydrograph separation, field measurements during droughts, and linear-regression analysis of streamflow duration. Baseflow was 

estimated at eight stations using HYSEP (Sloto and Crouse, 

1996), a computer program that separates the streamflow 

hydrographs into baseflow and surface-runoff components. 

The method for streamflow hydrograph separation used by this 

program was adapted from Pettyjohn and Henning (1979) and 

uses streamflow data in standard USGS daily values format. 

 Since 1977, the USGS has described ground-water levels 

annually in reports for selected wells in Georgia. The most 

recent of these reports described ground-water conditions 

in Georgia for 2002, including annual and period-of-record 

water-level fluctuations and trends for wells in the 67-county 

study area (Leeth and others, 2003). Peck and others (1999) 

described the potentiometric surface of the Upper Floridan 

aquifer in Georgia and adjacent parts of Alabama, Florida, 

and South Carolina, and water-level trends in Georgia during 

1990–98. Fanning (1999; 2003) described water use in coastal 

Georgia during 1980–97 and 1980–2000, respectively. 

 Streamflow conditions are described annually in Georgia 

in the report series, “Water resources data for Georgia.” The 

most recent of these reports described streamflow conditions 

in Georgia during 2002, including records for 62 stations in 

the study area (Hickey and others, 2002; Coffin and others, 

2002). Thomson and Carter (1955) reported effects of 

drought on streamflow for the 1954 drought; Carter (1983) 

for the 1980–81 drought; and Hale and others (1989) for the 

1986 drought. 

Method of Study 

 This study includes several work elements to estimate the 

ground-water discharge to streams under a variety of climatic 

conditions. The work includes compiling discharge, precipitation, and water-level data; separation of streamflow hydrographs to estimate mean annual ground-water contribution to 

streams; and evaluation of streamflow records and periodic 

discharge measurements during drought periods 1954, 1981, 

Table 2. Well construction data for selected wells used in Georgia. 

 [ft, foot; altitude in feet below North American Vertical Datum 1988; screened or opened interval in feet below land surface; ° , degree; ', minute; ", second] 

Well 

identification 

number

(fig. 1)

Well name County Latitude Longitude

Altitude of 

land surface 

datum 

(ft)

Top of 

screened or 

open interval 

(ft)

Bottom of 

screened or 

open interval

(ft) 

Aquifer

18K049 U.S. Geological Survey, 

test well 1

Tift 31°27'12" 82°59'33" 330.00 270 620 Upper Floridan 

19E009 City of Valdosta Lowndes 30°49'51" 83°16'58" 217 200 342 Upper Floridan 

21T001 Danny Hogan Laurens 32°27'06" 83°03'28" 259 89 123 Upper Floridan 

32L015 Georgia Geologic Survey, Gardi, 

test well 1

Wayne 31°32'52" 81°43'36" 74 545 750 Upper Floridan 

32L016 Georgia Geologic Survey, Gardi, 

test well 2

Wayne 31°32'52" 81°43'36" 74 320 340 Upper Brunswick

32L017 Georgia Geologic Survey, Gardi, 

test well 3

Wayne 31°32'52" 81°43'36" 74 200 215 Surficial

32R003 Bulloch South, test well 2 Bulloch 32°12'40" 81°41'15" 120 134 155 Miocene

35P094 University of Georgia, Bamboo Farm Chatham 31°59'50" 81°16'12" 18.7 15 15 Surficial

36Q008 Layne-Atlantic Company Chatham 32°05'30" 81°08'50" 9.91 250 406 Upper Floridan 
Figure 2. Geologic and hydrogeologic units of the upper and lower Coastal Plain, Georgia. 

HYSEP uses three methods to separate baseflow: fixed interval, sliding interval, and local minimum (fig. 3). Each method 

uses a different algorithm to separate baseflow systematically from runoff by connecting low points on the streamflow 

hydrograph (Sloto and Crouse, 1996). The duration of surface 

runoff is calculated from the empirical relation: 

 N=A0.2, 

 where N is the number of days for the cessation of runoff, and 

A is the drainage area of the basin (Linsley and others, 1982). 

All three methods use an algorithm based on the interval 2N*, 

which is the odd integer between 3 and 11 that is nearest to 

2N (Pettyjohn and Henning, 1979). The three methods as 

described by Sloto and Crouse (1996) are: 

 • The fixed-interval method fixed-interval method ixed-interval method assigns the lowest discharge assigns the lowest discharge 

in each 2N* interval to all days in that interval starting 

with the first day of the period of record. 

 • The sliding-interval method finds the lowest discharge finds the lowest discharge 

in one-half the interval minus 1 day [0.5(2N*–1) days] 

prior to and after the day being considered and assigns 

the discharge value to that day; overlapping of intervals 

is allowed. 

Introduction 7

Lower Middle Upper

Post-Miocene

Miocene

Eocene

Oligocene

Paleocene

Upper Cretaceous

Undifferentiated

Tiger Leap Formation

Suwannee Limestone

Ocala Limestone

Avon Park Formation

 Oldsmar Formation

Cedar Keys Formation

Undifferentiated

Surficial aquifer

Confining unit

Upper Floridan aquifer

Confining

unit

Lower Floridan

aquifer

Fernandina

permeable 

zone

Confining

unit

Confining

unit

Lazaretto Creek Formation

Parachucla Formation

Marks Head Formation

Confining unit

Lower Brunswick 

 aquifer

Confining unit

Coosawhatchie Formation

Upper Brunswick 

 aquifer

Ebenezer Formation

Lower Coastal Plain1

Geologic unit

2 Hydrogeologic unit

Barnwell Group

Undifferentiated

Santee Limestone

Upper Coastal Plain3

Congaree 

Formation

Geologic unit

Snapp Formation

Ellenton Formation

(undifferentiated)

Upper Three 

Runs aquifer

Confining unit

Gordon aquifer

Hydrogeologic 

unit

Steel Creek 

Formation

Black Creek Group

(undifferentiated)

Confining unit4

Upper Dublin 

aquifer

1/Modified from Randolph and others, 1991; Clarke and Krause, 2000.

2/Modified from Randolph and others 1991; Weems and Edwards, 2001.

3/Modified from Falls and others, 1997.

4/In local areas includes Millers Pond aquifer. System Lower Middle Upper

Series

Savannah Brunswick
8 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

 • The local-minimum method checks each day to determine whether the discharge is the lowest discharge in 

one-half the interval minus 1 day [0.5(2N*–1) days]; 

overlapping of intervals is not allowed. 

 Mosner (2002) compared the results of the three methods 

using four basins in southwest Georgia and found that the 

fixed-interval and sliding-interval methods are biased toward 

baseflow; and thus, overpredict ground-water contribution to 

streamflow. A plot of the three methods of hydrograph separation for Beaverdam Creek (station 02198100) near Sardis, Ga., 

is shown in figure 3. The plot shows the overestimation of the 

fixed-interval and sliding-interval methods; for this reason, the 

local-minimum method was used to estimate baseflow in the 

study area. 

 Surface-water discharge measurements collected during the three drought periods — 1954, 1981, and 2000 — were 

used to estimate baseflow for selected tributaries of the 

Salkehatchie–Savannah–Ogeechee (SSO) River, Altamaha–

Satilla–St Marys (SAS) River and Suwannee River Basins. 

The minimum ground-water discharge to tributaries between 

two adjacent reaches during the 1954 (22 stations), 1981 

(7 stations), and 2000 (19 stations) drought years were collected from continuous-record stations and periodic discharge 

measurements. Unit-area ground-water discharge was measured for 24 stations during 1954, 12 stations during 1981, and 

24 stations during 2000 within the three major basins. Drought 

year 1986 was not used in this evaluation because the drought 

effect on streamflow in this region was minor compared to 

other droughts. 

 Linear-regression analysis was used to determine the 

flow duration that most closely estimates baseflow in the study 

area. Flow duration is a cumulative frequency curve that shows 

the percentage of time a specific discharge was equaled or 

exceeded during a given period of time. Flow-duration curves 

integrate the effects of topography, geology, and climate of the 

basin. For example, baseflow of streams in the glacial till/

outwash of Long Island was estimated from 55-percent flow 

duration (Reynolds, 1982); whereas in the southeastern sand 

aquifer, baseflow was estimated to range between 60–65 percent of mean annual streamflow (Stricker, 1983). Mean annual 

baseflow for 14 stations in the study area was compared to 

flow durations ranging from Q1 to Q99 (streamflow equaled or 

exceeded 1 percent to 99 percent of the time) to derive flow 

duration that is representative of baseflow. This flow duration 

can be applied to streams in the study area to estimate baseflow for a given period. 

Precipitation Trends 

 National Weather Service stations within the upper and 

lower parts of the SSO, SAS, and Suwannee River Basins 

were selected to estimate how long-term variations in precipitation affect fluctuations in streamflow and ground-water 

levels. The cumulative departure from normal precipitation for 

Figure 3. Differences in separating baseflow using 

fixed-interval, sliding-interval, and local-minimum 

methods of HYSEP at Beaverdam Creek (station 

02198100) near Sardis, Georgia, 1999. 

the period 1971–2001 was used to evaluate any trends in the 

precipitation. Cumulative departure describes the long-term 

surplus or deficit of precipitation during a designated period, 

and is derived by adding successive monthly values of 

departures from normal precipitation. Normal precipitation 

for a given month is defined as the average of total monthly 

precipitation during a specified 30-year period (National 

Oceanic and Atmospheric Administration, 2002); for this 

report, the period 1971–2000 was used to determine normal precipitation for computation of cumulative departure. 

Average precipitation is the arithmetic mean of total monthly 

precipitation for the period of study 1971–2001. DISCHARGE, IN CUBIC FEET PER SECOND

Fixed-interval

Sliding-interval

Local-minimum

1

1

1

10

10

10

100

100

100

1,000

1,000

1,000

1999

JAN

FEB

MAR

APR

MAY

JUNE

JULY

AUG

SEPT

OCT

NOV

DEC

Measured

 flow

Estimated

 baseflow
Well and Streamflow Gaging Station 

Identification Systems 

 Wells in Georgia are identified by a system based on 

USGS topographic maps. Each 71⁄2-minute topographic quadrangle map in Georgia has been assigned a number and letter 

designation beginning at the southwest corner of the State. 

Numbers increase sequentially eastward through 39; letters 

advance northward through “Z,” then double-letter designations “AA” through “PP” are used. The letters “I,” “O,” “II,” 

and “OO” are not used. Wells inventoried in each quadrangle 

are numbered sequentially beginning with “1.” Thus, the 

second well inventoried in the Folkston quadrangle (29E) is 

designated 29E002. 

 Stations are assigned an 8- to 14-digit station identification number according to downstream order along the main 

stream. The first two digits of the station identification number 

represent the “Part” number with the remaining digits representing the downstream order number. All stations on a tributary entering upstream from a mainstream station are listed 

before that station. A station on a tributary that enters between 

two mainstream stations is listed between them. A similar 

order is followed in listing stations on first rank, second rank, 

and other ranks of tributaries. Gaps are left in the series of 

numbers to allow for new stations that may be established; 

hence, the numbers are not consecutive. 

Stream-Aquifer Relations 

 Water in streams and aquifers interact within a dynamic 

hydrologic system that includes aquifers, streams, reservoirs, 

and floodplains. These systems are interconnected and form a 

single hydrologic entity that is stressed by natural hydrologic, 

climatic, and anthropogenic factors. 

Stream-Aquifer Flow Systems 

 Under steady-state conditions, most ground-water systems can be divided into three subsystems: local, intermediate, 

and regional (Toth, 1962; 1963). Relatively shallow and short 

flowpaths that extend from a topographic high (recharge area) 

to an adjacent topographic low (discharge area) characterize a 

local flow system. Intermediate flowpaths include at least one 

local flow system between their respective points of recharge 

and discharge, and are longer and deeper than local flowpaths. 

Regional flowpaths begin at or near a major ground-water 

divide and terminate at a regional drain (fig. 4). 

 The number, distribution, and depth of influence of local 

flow regimes are largely a function of water-table configuration and aquifer thickness relative to watershed relief (Faye 

and Mayer, 1990). Where aquifer sediments are thin, local 

flow systems may dominate. Local flow systems are affected 

Figure 4. Schematic diagram of the conceptual hydrologic flow system in the upper and lower Coastal Plain of Georgia 

(modified from Toth, 1962; 1963). 

Stream-Aquifer Relations 9

Wetlands

Upper Coastal Plain— High relief and thinner confining

unit results in deep penetration of recharge into confined

aquifer systems (intermediate

and regional flow systems)

Lower Coastal Plain—Low relief results in more local flow system, with shallow 

penetration of aquifer recharge

Confined aquifers

(Confined surficial aquifer, 

Upper and Lower Brunswick aquifers 

and Upper and Lower Floridan aquifers)

Water table

Unsaturated zone

Unconfined

surficial aquifer

NOT TO SCALE

Ground-w

flow direction

ater

Intermedia

 flo

te

w system

Local

flow system

Regional flow system

Ocmulgee

River

Little

Ocmulgee

River

Altamaha

River
10 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

mostly by climatic variations. The net recharge and amount 

of ground-water flow are distributed according to the flow 

system, with flow and net recharge being greatest in local 

flow systems and least in regional flow systems (Toth, 1963). 

Local flow systems are most dynamic in areas of high relief 

such as the upper Coastal Plain (fig. 4). 

 In the study area, recharge to the hydrologic system is 

provided by rainfall that ranges spatially from an average of 

about 47 to 53 inches per year (in/yr), based on mean annual 

precipitation for the 30-year period 1971–2000 (fig. 5). Most 

of the recharge is discharged from the shallow, local flow 

systems into small streams or is lost as evapotranspiration. In 

the intermediate flow system, some of the water is discharged 

to major tributaries. A smaller percentage of recharge infiltrates through clayey confining units and enters the deeper 

regional flow system (Clarke and West, 1997). In the regional 

flow system, some of the water discharges to the Savannah and 

Altamaha River valleys and some flows southward discharging into the Atlantic Ocean. Faye and Mayer (1990) estimated 

mean annual ground-water discharge to the Savannah River 

by computing the gain in stream discharge between Augusta 

(station 02197000) and Millhaven (station 02197500). This 

estimate includes contribution from surface runoff and should 

be considered to represent the maximum aquifer discharge 

for that reach. Faye and Mayer (1990) estimated a gain of 

660 cubic feet per second (ft3/s) from combined intermediate and regional flow systems and a gain of 560 ft3

/s from 

the local flow system. Baseflow was estimated by a modified 

hydrograph-separation technique to be 1,220 ft3/s. Thus, in 

the Savannah River Basin about 54 percent of ground-water 

recharge entered the intermediate and regional flow systems, 

and the remaining 46 percent entered the local flow system 

(Faye and Mayer, 1990). The local and intermediate flow 

systems affect much of the stream discharge in the northern 

part of the study area, and the intermediate and regional flow 

systems affect stream discharge in the southern part of the 

study area. 

 In the upper Coastal Plain, where relief is relatively high, 

local flow systems dominate. In upland areas, the altitude of 

the water table in the vicinity of a stream generally is higher 

than the altitude of the stream-water surface making possible 

the discharge of ground water into the stream. Small streams 

may have very little runoff because pervious sandy soil 

drains water rapidly and the channels of streams do not cut 

deep enough to intercept ground water (Thomson and Carter, 

1955). Large streams in the upper Coastal Plain generally have 

uniform flow because of small runoff and high yields due to 

ground-water discharge (Thomson and Carter, 1955). 

 In the lower Coastal Plain, the relatively flat topography 

is dominated by estuaries and marshes. Local flow systems 

have less affect on stream conditions because of low relief 

and shallow ground-water hydraulic gradients from aquifers 

toward streams. Thomson and Carter (1955) described the 

lower Coastal Plain as having the least streamflow within Georgia because of high air temperatures and low flow-producing 

land characteristics, and because of high consumptive demands 

for water by the dense growth in the swamps. The terrain consists of wide and flat ridges separated by wide, swampy, and 

heavily wooded valleys (Thomson and Carter, 1955). Tidal 

effects and differences in runoff, due to soil type and vegetative

cover, account for the variation in baseflow between upper and 

lower Coastal Plain (Carter and Putnam, 1977). 

Climate 

 The study area has a mild climate with warm, humid 

summers and mild winters. Mean annual temperature ranges 

from about 63 degrees Fahrenheit (oF) in Burke County, Ga., 

to about 70°F in Glynn County, Ga., for the period 1971–2000 

(National Oceanic and Atmospheric Administration, 2002). 

 Precipitation data were evaluated from 10 NWS stations in Georgia and 1 in South Carolina. Of these stations, six 

were selected to determine long-term trends that could affect 

ground-water recharge and associated water-level fluctuations. 

The Georgia stations are located at Alma, Brooklet, Brunswick, Dublin, Folkston, Homerville, Jesup, Savannah, Tifton, 

and Waynesboro; the South Carolina station is located at 

Bamberg (figs. 1 and 5). Mean annual precipitation, based on 

the period 1971–2000 ranges from about 47 in/yr in Waynesboro, Ga., to about 53 in/yr in Folkston, Ga. (fig. 5). Rainfall 

is not evenly distributed throughout the year. The maximum 

rainfall generally occurs during the summer months of June, 

July, and August (fig. 6). Estimated evapotranspiration ranges 

from 31 in/yr in the northern part of the study area to more 

than 40 in/yr in Charlton and Ware Counties, Ga., near the 

Okefenokee Swamp (Krause and Randolph, 1989). Rainfall as 

a source of recharge to aquifers is most important during the 

nongrowing season, generally October through March, when 

evapotranspiration is lowest. 

Surface Water 

 The study area is drained by several major river systems: 

SSO River Basin, SAS River Basin, and Suwannee River 

Basin (fig. 1; table 1). The largest river basins are the SAS, 

with a drainage area of about 14,142 mi2; and the SSO, with 

a drainage area of about 10,734 mi2. The Suwannee River has 

a drainage area of about 6,400 mi2. With the exception of the 

Suwannee River, which drains to the Gulf of Mexico, each of 

the rivers discharges into the Atlantic Ocean. 

 Surface-water discharge in the study area primarily is affected 

by precipitation, baseflow, evapotranspiration, and pumpage. 

Four power plants use surface water within the SSO River 

Basin, and one power plant within the SAS River Basin. Surface water accounts for about 75 percent of total water usage 

in the Georgia Coastal Plain (Fanning, 1999). In the Coastal 

Plain, mean annual runoff ranges between 24 and 31 percent 

of total rainfall (Carter and Stiles, 1983). In the study area, 

runoff during the period 1941–70 was about 

14 in/yr in the upper Coastal Plain, and about 12 in/yr in the 

lower Coastal Plain (Carter and Stiles, 1983) (fig. 7). 
Figure 5. Mean annual precipitation for selected National Weather Service (NWS) stations in the 

Coastal Plain of Georgia and South Carolina, 1971–2000. 

Stream-Aquifer Felations 11

N

SOUTH

GEORGIA CAROLINA

FLOR

Atlantic Ocean

Atlantic

Ocean

Study

area

GA

FL

GA

SC

33°

32°

31°

30°

82°

81°

83°

Waynesboro

47

Tifton

47

Jesup

49

Homerville

53

Brooklet

47

Savannah

50

Folkston

53

Dublin

47

Brunswick

49

Alma

49

Bamberg

 49

47

48

49

50

50

51

52

53

Base from U.S. Geological Survey 

1:100,000-scale digital data 

EXPLANATION

Line of equal mean annual precipitation (1971–2000)—

 Dashed where approximate. Interval 1 inch

10

NWS station, name, and precipitation amount in inches

0

0 2 10 0 30 KILOMETERS

10 20 30 MILES

Tifton

47
12 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

Figure 6. Mean monthly precipitation at selected National Weather Service stations in the 

Coastal Plain area of Georgia and South Carolina, 1971–2001. 

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

MEAN MONTHLY PRECIPITATION, IN INCHES

Alma, Georgia

Bamberg, South Carolina

Brooklet, Georgia

Brunswick, Georgia

Dublin, Georgia

Folkston, Georgia

Homerville, Georgia

Jesup, Georgia

Savannah, Georgia

Tifton, Georgia

Waynesboro, Georgia

J

J

F

F

M

M

A

A

M

M

J

J

J

J

A

A

S

S O

O N

N

D

D
Figure 7. Mean annual runoff for the Coastal Plain of Georgia, 1941–70. 

Stream-Aquifer Relations 13

l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l

l l l l l l l l l l l l l l l l l l l

l l l l l l l l l l l l l l l l l l

l

l

l l

l

l

l

l l l

l l l

l

l l l

GEORGIA OLINA

FLO

A

Atlantic Ocea

Study n

area

Inner margin

of Coastal Plain

sediments

14

14

14

14

12

10

10

12

12

10

16

Line of equal mean annual runoff, 1941–70—Interval 2 inches

EXPLANATION

10

Base from U.S. Geological Survey 

1:100,000-scale digital data 

0

0 2 10 0 30 KILOMETERS

10 20 30 MILES

Atlantic

Ocean

33°

32°

31°

30°

82°

81°

83°

GA

FL

GA

SC

N
14 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

Figure 8. Distribution of daily streamflow for (A) Brier Creek (station 02198000) near Millhaven, Georgia; 

(B) Canoochee River (station 02203000) near Claxton, Georgia; and (C) Little Satilla River (station 02227500) 

near Offerman, Georgia, for the period of record. 262 365 365 366 365 365 365 366 365 365 365 366 365 365 365 366 365 365 365 366 365 365 365 366 365 365 365 366 365 365

365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365

220365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365

339366365329365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365365366365365351366365365365366365365365366365

xx

x

xxx

o

o xx

xx

x x

xx

x

x

xxx x

x

x

oo

o

x x x xx

x

x xx

x

x

x

x

x

xx

xx

x

x

x

xx x

xx

x x

x

x xx xx

xx

xx

xx

o

xx

x

x x

xxx

x

x

x xxx

x

x

x

x xxx

xx

x

x

x x x x

339 x

x

o

o

100

10

1

0.1

0.01

1,000

10,000

100,000

x

x x

xxxxxx

x

xx

x

x

xxx

xx

x

x

x

xx

xxxx

x

1

0.1

0.01

10

100

1,000

10,000

100,000

x

xx

xxxxxx

xx

xxxxxxxxx

xx

xx

x

x

x

x

x

x

xxx

x

x

x

x

x

xxxxxxxxx

x

xxxx

xxx xx

x

xx

xx

x

xxxx

x

x

xx

x

xx xxxxx

xx

xxxxx

xx

xxx

xxxxxx

x

xx

xx

x

xxxxxx

x

x

x

xx

x

xxxx xxxxxxxxxxxxx

x

xxx

xxx

x

xxxxxx

xx x

x

x

xxxxxxxxxxxxxxxxxx

x

x

xx

x

x

xx

x

oo

1

0.1

0.01

10

100

1,000

10,000

100,000

DISCHARGE, IN CUBIC FEET PER SECOND

A. Brier Creek

B. Canoochee River

C. Little Satilla River

19541964198119982000

Mean annual discharge

EXPLANATION

Period of record

1954

1981

2000 

Number of values

Upper detached

Lower detached

Upper outside

Lower outside

75th percentile

Median

25th percentile

1937

1940

1945

1950

1955

1960

1965

1970

1975

1980

19851990

19952000
 Streamflow characteristics are summarized in boxplots showing streamflow duration for each year during the period of 

record for selected stations in the study area (fig. 8). For three 

comparably sized basins, boxplots of daily streamflows were 

prepared for each year of the period of record. The boxplots 

depict the minimum, maximum, mean, and median daily 

discharge; and the 25 and 75 percentiles for each calendar 

year. The mean annual discharge was computed for the period 

of record and used as a reference for the drought-year streamflow. Brier Creek (station 02198000) in the SSO River Basin 

shows climatically driven rise and fall (cyclical) in streamflow 

throughout the period of record (fig. 8). The mean annual 

discharges indicate that the 2000 drought was the most severe 

followed by the 1954 and 1981 droughts, respectively. The 

Canoochee River (station 02203000) in the SSO River Basin 

also shows a climatically driven cyclical trend in discharge 

throughout the period of record. At this station, the 1981 

drought was the most severe followed by the 1954 and 2000 

droughts, respectively (fig. 8). The Little Satilla River (station 02227500) is less cyclical than the previous two stations, 

with the 1981 drought the most severe followed by the 2000 

and 1954 droughts, respectively (fig. 8). Pronounced dry years 

are evident at each site during 1954, 2000, and 2001, and wet 

periods are evident during 1964 and 1998. In any given year, 

streamflow generally is highest during the winter-spring and 

lowest during the summer-fall when evapotranspiration is 

highest (fig. 9). 

Ground Water 

 Sediments and rock form a series of aquifers and confining units that have variable geologic and hydrologic properties 

in the upper and lower Coastal Plain (fig. 2). The following 

sections describe the various hydrogeologic units and waterlevel fluctuations and trends — long-term incline or decline in 

overall water levels — in major aquifer units in the upper and 

lower Coastal Plain. 

Hydrogeologic Units 

 Principal water-bearing units in the upper Coastal Plain 

are, in order of increasing depth, the Upper Three Runs 

aquifer, Gordon aquifer, and Upper Dublin aquifer (fig. 2). 

In the lower Coastal Plain, the principal water-bearing units 

are in descending order, the surficial aquifer system, Brunswick aquifer system, and Floridan aquifer system (fig. 2). 

Low-permeability clayey confining units separate these waterbearing units. 

Upper Coastal Plain 

 The Upper Three Runs aquifer, formerly referred to as 

the Jacksonian aquifer (Vincent, 1982), consists of quartz, 

calcareous sand, and limestone of the Barnwell Group and 

undifferentiated post-Miocene deposits (fig. 2) (Falls and 

others, 1997; Huddlestun and Hetrick, 1986). The sands are 

highly permeable; however, low-permeability clay beds and 

lenses are present at the top of the aquifer (Huddlestun and 

Summerour, 1996). The Upper Three Runs aquifer is hydrogeologically equivalent to the Upper Floridan aquifer in the 

lower Coastal Plain. 

 The Gordon aquifer, underlying the Upper Three Runs 

aquifer, consists of sand and calcareous sand of the Congaree Formation (fig. 2) (Falls and others, 1997). The Gordon 

aquifer is the updip equivalent of the Lower Floridan aquifer 

in the lower Coastal Plain. The Gordon aquifer is underlain 

by a confining unit that consists of black laminated clay of the 

Ellenton Formation and moderately to poorly sorted, fine to 

very coarse sand of the Snapp Formation. 

 The Upper Dublin aquifer underlies the Gordon aquifer. 

The Upper Dublin aquifer consists of poorly to moderately 

sorted fine quartz sand with thin beds of clay of the Steel 

Figure 9. Mean monthly streamflow at a selected 

streamflow gaging station within the Salkehatchie–

Savannah–Ogeechee, Altamaha–Satilla–St Marys, 

and Suwannee River Basins for the periods of record. 

Stream-Aquifer Relations 15

0

10

20

30

40

50

0

100

200

300

400

500

0

1,000

2,000

3,000

Salkehatchie–Savannah–Ogeechee River Basin

02197600, Brushy Creek, Georgia (1958–2001)

Altamaha–Satilla–St Marys River Basin

02227500, Little Satilla River, Georgia (1950–2001)

Suwannee River Basin

02317500, Alapaha River, Georgia (1921, 1932–2001)

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

DISCHARGE, IN 

CUBIC FEET PER SECOND
16 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

Creek Formation and Black Creek Group, undifferentiated 

(fig. 2). The Upper Dublin aquifer is hydrogeologically 

equivalent to the Fernandina permeable zone of the Lower 

Floridan aquifer in the lower Coastal Plain. 

Lower Coastal Plain 

 In the lower Coastal Plain, the surficial aquifer system 

consists of interlayered sand, clay, and thin limestone beds 

of post-Miocene age (Clarke and others, 1990; Leeth, 1999). 

Generally, the surficial aquifer is under water-table conditions 

throughout the study area. Locally, however, the aquifer may 

be confined or semiconfined by dense phosphatic limestone 

or dolomite, and phosphatic silty clay of undifferentiated 

Miocene sediments (Leeth, 1999; Clarke, 2003). A confining 

unit that consists of clay, silt, phosphatic limestone or dolomite, and sand of Miocene age underlies the surficial aquifer 

(fig. 2). Sand and limestone within this unit have been identified as a source of water in parts of the coastal area. Clarke 

and others (1990) designated this unit as the upper and lower 

Brunswick aquifers. 

 The upper Brunswick aquifer consists of poorly sorted, 

fine to coarse, slightly phosphatic and dolomitic quartz sand 

of the Coosawhatchie and Marks Head Formations (fig. 2) 

(Randolph and others, 1991; Weems and Edwards, 2001). This 

aquifer is confined by upper and lower confining units of the 

Miocene Parachucla Formation. The upper Brunswick aquifer 

is present in the Brunswick area and generally is absent in the 

Savannah area. 

 The lower Brunswick aquifer consists of quartzose calcarenite to calcareous quartz sand of the Tiger Leap Formation 

(fig. 2) (Weems and Edwards, 2001). The Parachucla Formation in most of coastal Georgia overlies the Tiger Leap Formation. In the lower Coastal Plain, the lower Brunswick aquifer 

mostly is absent in the Savannah area and in Bulloch County 

because the permeable upper sand in Miocene sediments either 

has been eroded away or was never deposited (Clarke and 

others, 1990). At the base of the lower Brunswick aquifer is a 

confining unit consisting of Oligocene fossilerous limestone 

of the Lazaretto Creek Formation (Huddlestun, 1993). The 

surficial and Brunswick aquifer systems and Upper Floridan 

aquifer are hydrogeologically equivalent to the Upper Three 

Runs aquifer in the upper Coastal Plain. 

 The Upper Floridan aquifer supplies most of the drinking 

water obtained from ground water for coastal Georgia. In the 

lower Coastal Plain, this aquifer is largely carbonate, consisting of Eocene to Oligocene limestone and dolomite. The 

Oligocene Lazaretto Creek Formation overlies the Upper 

Floridan aquifer (Huddlestun, 1993). Units composing the 

Upper Floridan aquifer crop out at or near land surface in the 

upper Coastal Plain, where the aquifer is under confined to 

semiconfined conditions. The Upper Floridan aquifer is separated from the underlying Lower Floridan aquifer by a confining unit of dense, low-permeability, recrystallized Eocene 

limestone and dolomite. The confining unit has very low 

primary hydraulic conductivity; however, in the Brunswick 

area, joints and fractures produce zones of high secondary 

hydraulic conductivity (Krause and Randolph, 1989). 

 The Lower Floridan aquifer mostly consists of Eocene 

dolomitic limestone but locally may include Paleocene to 

Upper Cretaceous dolomitized limestone. This aquifer is 

confined throughout the coastal area and is subdivided into at 

least three permeable units in the Brunswick area — the brackish-water zone, deep freshwater zone (Gregg and Zimmerman, 

1974), and Fernandina permeable zone (Krause and Randolph, 

1989). The Fernandina permeable zone is highly permeable 

and cavernous, and contains high salinity water that may be 

the source of saltwater contamination in the Brunswick area. 

The Fernandina permeable zone consists of Paleocene to 

Upper Cretaceous pelletal, recrystallized limestone and finely 

crystallized dolomite. 

Ground-Water Levels 

 Ground-water level fluctuations reflect changes in 

recharge to and discharge from an aquifer. Recharge varies 

in response to precipitation, and discharge varies in response 

to leakage to adjacent aquifers, withdrawal from wells, and 

evapotranspiration from shallow unconfined aquifers. 

 In the surficial aquifer, water levels show a pronounced 

response to climatic effects throughout the study area. Where 

climatic effects dominate, water levels generally are highest 

in the winter and early spring when precipitation is greatest 

and evapotranspiration is least; water levels are lowest during 

the summer and fall when precipitation is least and evapotranspiration is highest. These fluctuations are illustrated on the 

hydrograph for well 35P094 near Savannah (fig. 10). The 

15-ft-deep well is completed in the surficial aquifer and shows 

pro nounced water-level rise in response to precipitation, followed by a gradual decline that corresponds to discharge from 

the aquifer. 

 In the lower Coastal Plain, with the exception of the 

unconfined part of the surficial aquifer system, aquifers are 

deeply buried and confined. In these areas, climatic effects 

are greatly diminished, and fluctuations largely are because 

of changes in ground-water pumping. These fluctuations are 

illustrated for well 36Q008 near Savannah (fig. 10). The 

406-ft-deep well is completed in the Upper Floridan aquifer 

and shows a pronounced response to changes in local and 

regional pumping, but little response to changes in precipitation. Water-level response to pumping in adjacent aquifers 

may be similar due to interaquifer leakage. This response in 

adjacent aquifers is most pronounced in the upper Coastal 

Plain and results from greater aquifer interconnection because 

of the thin, sandy, and discontinuous nature of the confining 

units in this area. In addition, ground-water pumping in the 

lower Coastal Plain may have produced hydraulic gradients 

that resulted in increased aquifer leakage and similar waterlevel responses. Such similarities are indicated on the hydrographs for wells completed in the surficial, upper Brunswick, 

and Upper Floridan aquifers (32L017, 32L016, and 32L015, 

respectively) at Gardi, Wayne County, Georgia (fig. 11). 
Long-Term Fluctuations and Trends 

 Long-term fluctuations in precipitation, ground-water 

levels, and streamflow show the effects of natural and anthropogenic stresses on the stream-aquifer flow system. Precipitation changes are reflected in streamflow and in ground-water 

levels of aquifers that are unconfined or semiconfined. When 

ground-water levels are high from natural recharge (precipitation), ground-water contribution to streamflow is correspondingly high. Conversely, when ground-water levels are low 

because of lack of recharge or increased pumping, groundwater contribution to streamflow is correspondingly low. 

Fluctuations and trends are shown on selected graphs of 

cumulative departure from normal precipitation, groundwater levels, and streamflow in the SSO, SAS, and Suwannee 

River Basins (figs. 12–14, respectively). Normal precipitation 

for a given month is defined as the average of total monthly 

precipitation during a specified 30-year period; for this report, 

the period 1971–2000 was used to determine normal precipitation for computation of cumulative departure. 

 Upward or positive slopes on the graph indicate periods 

of above-normal precipitation; downward or negative slopes 

on the graph indicate periods of below-normal precipitation; 

no slope indicates periods of normal precipitation. Trend is the 

overall slope over a period of time. A short-term trend covers 

a period of 5 years or less; a long-term trend covers a period 

greater than 5 years. An above-normal trend means that the 

slopes over a period of time are positive or upward; whereas 

a below-normal trend means that the slopes over a period 

of time are negative or downward. Fluctuations and trends 

in the major river basin groupings are plotted for the period 

1971–2001. 

Salkehatchie–Savannah–Ogeechee River Basin 

 In the upper part of the SSO River Basin, precipitation trends are illustrated on the cumulative departure graph 

for the Waynesboro, Ga., station (fig. 12). In general, there 

were several short-term trends of above- and below-normal 

precipitation during 1971–84 followed by a long-term trend 

of below-normal precipitation during 1984–91. A longterm trend of above-normal precipitation is observed during 

1992–98 with intermittent short-term trends of below-normal 

precipitation. During 1999–2001, there was a short-term trend 

of below-normal precipitation in Waynesboro, Ga., reflecting 

the 2000 drought. By the end of the study period, the overall 

cumulative departure was +19.47 inches at Waynesboro. 

 Streamflow in the upper part of the SSO River Basin 

is shown on bar graphs of mean annual discharge for Brier 

Creek (station 02198000) (fig. 12). Generally, about half of the 

streamflow was at or above the 31-year mean for this station. 

Changes in streamflow correspond to above- and belownormal periods of precipitation for the area. Two of the three 

severe drought periods — 1981 and 2000 — are more than 

200 ft3/s below the 31-year mean of about 598 ft3/s. 

 Ground-water levels in the upper part of the SSO River 

basin are shown for well 32R003, Bulloch County (fig. 12), 

completed in the surficial aquifer to a depth of 155 ft. Data 

are insufficient to recognize a trend in the water level; however, well 32R003 taps a deeper part of the surficial aquifer 

where semiconfined conditions occur as a result of a clay 

confining unit. 

 In the lower part of the SSO River Basin, precipitation 

trends are illustrated on the cumulative departure from normal 

precipitation graph for the Savannah, Ga., station (fig. 12). 

In general, there was a long-term trend of below-normal 

precipitation during 1973–90 with intermittent short-term 

trends of above-normal precipitation. There was a long-term 

trend of generally above-normal precipitation during 1990–95, 

followed by a long-term trend of generally below-normal precipitation during 1996–2001. Effects of drought are evidenced 

by a short-term trend of below-normal precipitation during 

1999–2001. By the end of the study period, the overall cumulative departure was –13.26 inches at Savannah. 

Figure 10. Daily water-level measurements in wells 35P094 

and 36Q008, Chatham County; and daily rainfall at National 

Weather Service station, Savannah Municipal Airport, 

Chatham County, Georgia, 2001. 

Stream-Aquifer Relations 17

2001

0

0.5

1.0

1.5

2.0

2.5

PRECIPITATION, IN INCHES

96

94

92

90

88

86

84

WATER LEVEL, IN FEET

BELO

W NAVD 88

WATER LEVEL, IN FEET

BELO

W NAVD 88

Savannah Municipal Airport

Well 36Q008

MAY

JUNE

JULY

AUG

SEPT

OCT

NOV

JA

DEC

N

FEB

MAR

APR

10

8

6

4

2

0

Well 35P094
18 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

 Streamflow in the lower part of the SSO River basin is 

shown on bar graphs for Canoochee River (station 02203000) 

(fig. 12). Generally, about half of the streamflow was at or 

above the 31-year mean for this station. Changes in streamflow correspond to above- and below-normal periods of 

precipitation for the area. Two of the three severe drought 

periods — 1981 and 2000 — are more than 350 ft 3 /s below the /s below the 

31-year mean of about 484 ft 3 /s. Drought conditions had a 

greater effect on streamflow in the lower part of the basin than 

in the upper part of the basin, probably because of interconnectivity with the aquifer. 

 Ground-water levels in the lower part of the SSO 

River Basin are shown for well 35P094, Chatham County, 

completed in the surficial aquifer to a depth of 15 ft (fig. 12). 

No long-term trend is evident, and water levels show a pronounced response to climatic effects. Recharge by precipitation is reflected by a sharp rise in the water level followed 

by a gradual decline that represents evapotranspiration and 

recharge of water into the aquifer. 

Altamaha–Satilla–St Marys River Basin 

 In the upper part of the SAS River Basin, precipitation 

trends are illustrated on the cumulative departure graph for 

the Dublin station (fig. 13). There was a long-term trend of 

at- or below-normal precipitation during 1975–91, followed 

by a long-term trend of above-normal precipitation during 

1992–98, followed by another short-term trend of belownormal precipitation during 1999–2001, reflecting effects of 

drought. By the end of the study period, the overall cumulative 

departure was –17.14 inches at Dublin. 

 Streamflow in the upper part of the SAS River Basin is 

shown on bar graphs for the Oconee River (station 02223500) 

(fig. 13). Streamflow appears to fluctuate in a similar manner 

as precipitation, with low streamflow occurring during 

below-normal precipitation years and high streamflow 

occurring during above-normal precipitation years. During 

two-thirds of the study period, streamflow was at or above 

the 31-year mean. During the drought years of 1981 and 2000, 

streamflow was about 2,000 ft3/s below the 31-year mean of 

about 4,393 ft3/s. 

 Ground-water levels in the upper part of the SAS River 

Basin are shown for well 21T001 (fig. 13) Laurens County, 

completed in the Upper Floridan aquifer to a depth of 123 ft. 

The hydrograph shows seasonal fluctuations of the water 

level in response to precipitation. Starting in 1999, the 

hydrograph slopes downward slightly, indicating the effects 

of the 2000 drought. 

 In the lower part of the SAS River Basin, precipitation 

trends are illustrated on the cumulative departure graph for 

the Jesup site (fig. 13). Generally, there were two long-term 

trends of at- or above-normal precipitation during 1976–87, 

and 1989–95. Following these trends was a short-term trend 

of generally below-normal precipitation during 1998–2001. 

By the end of the study period, the overall cumulative departure was –12.39 inches. 

 Streamflow in the lower part of the SAS River Basin 

is shown on bar graphs for the Little Satilla River (station 

02227500) (fig. 13). Streamflow appears to fluctuate in a 

similar manner as precipitation, with low streamflow occurring during below-normal precipitation years and high streamflow occurring during above-normal precipitation years. More 

than half of the mean annual streamflow was at or above the 

31-year mean for the station. During the drought years of 1981 

and 2000, streamflow was about 500 ft 3 /s below the 31-year /s below the 31-year 

mean of about 542 ft 3 /s. 

Figure 11. Daily mean water levels in the surficial, upper Brunswick, and Upper Floridan aquifers at the Gardi site, 

Wayne County, Georgia, 1983–2001. 

70

65

60

55

50

45

40

35

WATER LEVEL, IN FEET BELOW NAVD 88

30

Well 32L017 Surficial aquifer (200–215 ft)

Well 32L016 Upper Brunswick aquifer (320–340 ft)

Well 32L015 Upper Floridan aquifer (545–750 ft)

Blank where 

data missing

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
Figure 12. Mean annual stream discharge, daily mean ground-water level, and cumulative 

departure from normal precipitation for the upper and lower parts of Salkehatchie–

Savannah–Ogeechee River Basin, Georgia and South Carolina, 1971–2001. 

Stream-Aquifer Relations 19

Blank where

data missing

Blank where

data missing

Data collection

began in 1983

31-year

mean

31-year mean

Well 32R003 (Upper Floridan aquifer, Bulloch County, Georgia, 155 feet deep)

Waynesboro, Georgia, station

Station 02198000 (Brier Creek) Millhaven, Georgia

Station 02203000 (Canoochee River) Claxton, Georgia

16

12

8

4

0

–40

–20

0

20

40

60

0

Lower Salkehatchie–Savannah–Ogeechee River Basin

Well 35P094 (Surficial aquifer, Chatham County, Georgia, 15 feet deep)

Savannah, Georgia, station

CUMULATIVE 

DEPARTURE

FROM NORMAL 

PRECIPITATION,

IN INCHES

WATER LEVEL,

IN FEET BELO

W

NAVD 88

MEAN ANNUAL

DISCHARGE, IN CUBIC

FEET PER SECOND

19711973197519771979198119831985

1987

1989199119931995

199719992001

Upper Salkehatchie–Savannah–Ogeechee River Basin

CUMULATIVE 

DEPARTURE

FROM NORMAL 

PRECIPITATION,

IN INCHES

WATER LEVEL,

IN FEET BELO

W

NAVD 88

MEAN ANNUAL

DISCHARGE, IN CUBIC

FEET PER SECOND

16

12

8

4

0

–40

–20

0

20

40

60

0

200

400

600

800

1,000

200

400

600

800

1,000
20 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

Figure 13. Mean annual stream discharge, daily mean ground-water level, and cumulative 

departure from normal precipitation for the upper and lower parts of the Altamaha–Satilla–

St Marys River Basin, Georgia, 1971–2001. 

Blank where

data missing

1971

Well 21T001 (Upper Floridan aquifer, Laurens County, Georgia, 123 feet deep)

Lower Altamaha–Satilla–St Marys River Basin

Jesup, Georgia, station

Well 32L017 (Surficial aquifer, Wayne County, Georgia, 215 feet deep)

Data collection

began in 1983

197319751977197919811983198519871989

1991

1993

1995

1997

1999

2001

Upper Altamaha–Satilla–St Marys River Basin

Dublin, Georgia, station

–40

–20

0

20

40

–20

–40

0

20

40

CUMULATIVE 

DEPARTURE

FROM NORMAL 

PRECIPITATION,

IN INCHES

CUMULATIVE 

DEPARTURE

FROM NORMAL 

PRECIPITATION,

IN INCHES

WATER LEVEL,

IN FEET BELO

W

NAVD 88

WATER LEVEL,

IN FEET BELO

W

NAVD 88

40

50

30

20

50

40

30

20

MEAN ANNUAL

DISCHARGE, IN CUBIC

FEET PER SECOND

MEAN ANNUAL

DISCHARGE, IN CUBIC

FEET PER SECOND

0

200

400

600

800

1,000

1,200 Station 02227500 (Little Satilla River) Offerman, Georgia

Station 02223500 (Oconee River) Dublin, Georgia

0

2,000

4,000

6,000

8,000

10,000

31-year mean

31-year

mean
 Ground-water levels in the lower part of the SAS River 

Basin are shown for well 32L017, Wayne County, completed 

in the surficial aquifer to a depth of 215 ft. In this area, the 

water level of the surficial aquifer is influenced largely by 

ground-water pumping and, to a lesser extent, changes in 

recharge because of the depth of the aquifer. Water levels in the well declined about 6 ft during 1983–2001, with 

the most rapid decline beginning in 1999 as a result of the 

2000 drought. 

Suwannee River Basin 

 In the upper part of the Suwannee River Basin, precipitation trends are illustrated on the cumulative departure graph 

for the Tifton station (fig. 14). In general, there was a longterm trend of above-normal precipitation during 1971–88, 

followed by a long-term trend of below-normal precipitation 

during 1989–2001. By the end of the study period, the overall 

cumulative departure was –1.9 inches at Tifton. 

 Streamflow in the upper part of the Suwannee River 

Basin is shown on bar graphs for Alapaha River (station 

02317500) (fig. 14). Streamflow generally responds to 

changes in precipitation, with low flow occurring during 

below-normal periods, such as 1999–2001, and high flow 

occurring during above-normal periods, such as 1983–84. 

Less than half of the mean annual streamflows are at or above 

the 31-year mean for the period. During the drought years of 

1981 and 2000, streamflow was more than 700 ft3/s below the 

31-year mean. 

 Ground-water levels in the upper part of the Suwannee River Basin are shown for well 18K049, Tift County, 

completed in the Upper Floridan aquifer to a depth of 620 ft 

(fig. 14). Water levels in this well are influenced mostly by 

changes in pumping. The general water-level trend in this 

well is an approximate decline of 35 ft from 1978, when 

data collection began, to 2001. 

 In the lower part of the Suwannee River Basin, precipitation trends are illustrated on the cumulative departure 

graphs for the Homerville station (fig. 14). Generally, there 

were long-term trends of above-normal precipitation during 

1971–77 and 1991–98, with a long-term trend of below-normal precipitation during 1978–83, and a short-term trend of 

below-normal precipitation during 1999–2001. By the end 

of the study period, the overall cumulative departure was 

–9.44 inches at Homerville. 

 Streamflow in the lower part of the Suwannee River 

Basin is shown on bar graphs for Suwannee River (station 

02314500) (fig. 14). Streamflow generally follows precipitation patterns, with pronounced declines in streamflow during 

below-normal precipitation periods. About half of the mean 

annual streamflow was at or above the 31-year mean for the 

period 1971–2001. During the drought years of 1981 and 

2000, streamflow was more than 800 ft3/s below the 31-year 

mean of about 941 ft3/s. 

 Ground-water levels in the lower part of the Suwannee 

River Basin are shown for well 19E009, Lowndes County 

(fig. 4), completed in the Upper Floridan aquifer to a depth 

of 342 ft. Both pumping and recharge influence water levels in this well. Although the well is deep, it is located in 

an area of karst topography where there is interconnection 

between streams and the Upper Floridan aquifer. Water levels 

in the well generally followed precipitation trends during 

1971–2001. 

Ground-Water Contribution to Streamflow 

 The degree of aquifer interconnection with streams varies in the upper and lower Coastal Plain. In general, relief is 

greater and local flow occurs more in the upper Coastal Plain. 

In this area, the Upper Floridan and equivalent aquifers are 

unconfined or semiconfined and are incised by streams flowing through the area. In the lower Coastal Plain, the Upper 

Floridan aquifer is deeply buried and confined. 

 The interconnection between ground water and streams 

is illustrated on a map showing the potentiometric surface 

of the Upper Floridan aquifer for May 1998 (fig. 15). In the 

upper Coastal Plain, aquifer interconnection with streams is 

indicated by steep hydraulic gradients toward streams and 

potentiometric contours that cross in a “V” pattern upstream, 

indicating ground-water flow toward the stream. In the lower 

Coastal Plain, the aquifer is more deeply buried and is not 

incised. Here, potentiometric contours indicate little connection between the aquifer and overlying streams. An exception 

is in the karstic Valdosta area, where the aquifer is interconnected with streams. 

 Streamflow composes two major components — surface 

runoff and baseflow. On a typical hydrograph, peaks indicate 

rapid response to precipitation and represent the runoff component of a hydrograph. The slope of the streamflow recession 

indicates ground-water discharge to streams and represents the 

baseflow component of a hydrograph. 

 In relation to the conceptual model (fig. 4), baseflow in 

streams comprises contributions from the local, intermediate, and regional ground-water flow systems. Because local 

flow systems are most affected by rainfall during periods 

of extended drought, streamflow is assumed to be sustained 

entirely by baseflow. 

 Ground-water contribution to streamflow (baseflow) 

was estimated by using three methods. Hydrograph-separation analysis was used to estimate baseflow based on data 

from eight continuous-record stations. Field measurements of 

drought discharge from headwater to an adjacent streamflow 

gaging station and between two adjacent stations were used to 

estimate the minimum ground-water contribution to streamflow. Linear-regression analysis of streamflow duration and 

mean annual baseflow was performed to estimate the percentile of streamflow that most closely represents baseflow. 

Stream-Aquifer Relations 21
22 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

Figure 14. Mean annual stream discharge, daily mean ground-water level, and cumulative 

departure from normal precipitation for the upper and lower parts of the Suwannee River Basin, 

Georgia, 1971–2001. 

–20

0

20

40

60

–20

0

20

40

60

Upper Suwannee River Basin

Homerville, Georgia, station

Blank where

data missing

Well 18K049 (Upper Floridan aquifer, Tift County, Georgia, 620 feet deep)

Well 19E009 (Upper Floridan aquifer, Lowndes County, Georgia, 342 feet deep)

Data collection

began in 1978

160

140

120

100

160

140

120

100

Lower Suwannee River Basin

Tifton, Georgia, station

CUMULATIVE 

DEPARTURE

FROM NORMAL 

PRECIPITATION,

IN INCHES

CUMULATIVE 

DEPARTURE

FROM NORMAL 

PRECIPITATION,

IN INCHES

WATER LEVEL,

IN FEET BELO

W

NAVD 88

WATER LEVEL,

IN FEET BELO

W

NAVD 88

MEAN ANNUAL

DISCHARGE, IN CUBIC

FEET PER SECOND

MEAN ANNUAL

DISCHARGE, IN CUBIC

FEET PER SECOND

19711973197519771979

1981

19831985

1987

19891991

1993

1995

1997

1999

2001

0

500

1,000

1,500

2,000

2,500

0

500

1,000

1,500

2,000

2,500 Station 02317500 (Alapaha River) Statenville, Georgia

Station 02314500 (Suwannee River) Fargo, Georgia

31-year mean

31-year mean
Figure 15. Potentiometric surface of the Upper Floridan aquifer, May 1998. 

Stream-Aquifer Relations 23

100

0

50

50

50

100

100

250

300

350

300

300

350

200

200

250

200

Oc

Oconee River

A ive

avannah

Rive

O

r

geechee River

O

Potentiometric contour—Shows altitude at which water level would 

have stood in tightly cased wells during May 1–26, 1998. Hachures 

indicate depression. Contour interval 10 ft. Datum is NAVD 88

Axis of Gulf Trough—Approximately located (Kellam and Gorday, 1990)

10

Base from U.S. Geological Survey 

1:100,000-scale digital data 

EXPLANATION

0

0 2 10 0 30 KILOMETERS

10 20 30 MILES

GEORGIA

FLORIDA

GEORGIA

33°

32°

31°

30°

82° 81°

83°

Atlantic Ocean

SOUTH

CAROLINA

GEORGIA

area

SC

Atlantic Ocean
24 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

Hydrograph Separation 

 Hydrograph separation was completed on streamflow 

data using HYSEP, a computer program that uses mathematical techniques to separate streamflow into baseflow and runoff 

components (Sloto and Crouse, 1996). The mathematical 

formulation of HYSEP does not consider the geology of the 

basin; therefore, it can be used on a site-by-site basis in any 

hydrologic setting. There are limitations on its use, however, 

because HYSEP bases hydrograph separation only on basin 

area and streamflow hydrograph characteristics. 

 Estimates of baseflow from HYSEP were used to 

determine changes in baseflow contribution during a variety 

of climatic conditions. Baseflow estimates are affected by 

regulation of flows and physical properties of the basin such 

as vegetation cover, slope, area, shape, land use, soil thickness, and infiltration capacity (Horton, 1933; Riggs, 1963; 

Bevans, 1986; Sloto and Crouse, 1996), as well as antecedent 

soil moisture and depth to ground water. The river or tributary 

at each station selected for HYSEP analysis had negligible 

diversion or regulation upstream, a drainage area less than 

1,400 mi2, and at least 31 years of continuous record (table 3). 

The accuracy of the estimates depends on the period of record 

used (Sloto and Crouse, 1996) and the size of the drainage 

basin (Pettyjohn and Henning, 1979). A long-term record with 

representative long-term climatological conditions provides a 

more reliable baseflow estimate because periods of extreme 

dry or extreme wet climates would have less influence (Sloto 

and Crouse, 1996). In addition, the river or tributary at each 

station was not dominated by losing reaches, interaction with 

deeper aquifers, evapotranspiration effects, or prolonged 

periods of surface runoff. 

 During 1971–2001, baseflow represented a greater portion of streamflow during years of lower rainfall, and a lower 

portion during years of higher rainfall. At the eight stations 

selected for HYSEP, mean annual baseflow was from 39 to 

74 percent of streamflow, with a mean contribution of 58 percent (table 3). Figure 16 shows the amount of streamflow at 

the Canoochee River (station 02203000) in the lower Coastal 

Plain near Claxton, Ga., originating from baseflow for average, wet, and dry years (based on the Brooklet NWS station). 

During a high-precipitation year, baseflow accounted for 

48 percent of total streamflow; during an average-precipitation 

year, about 63 percent; and during a low-precipitation year, 

about 60 percent. During dry periods, there is a reduction in 

runoff, and baseflow becomes the major contributor to streamflow. During drought conditions, there is less water available 

to recharge the aquifer, as indicated by ground-water level 

declines. As ground-water levels drop, the hydraulic gradient 

between the stream and aquifer decreases, reducing groundwater discharge to streams. In some instances, the gradient 

between the stream and aquifer reverses and stream-water 

discharges into the aquifer, but this usually is of short duration 

because the streambed eventually dries up. 

 Baseflow estimates vary within the upper and lower parts 

of a basin. Mean annual baseflow for the period 1971–2001 in 

the upper SSO River Basin ranges from 66 to 74 percent and 

in the lower basin is 54 percent (table 3). In the upper SAS 

River Basin, baseflow is about 57 percent of total streamflow 

at station 02225500 (Ohoopee River). In the lower SAS River 

Basin, baseflow ranges from about 39 to 43 percent of total 

streamflow. In the lower part of the Suwannee River Basin, 

baseflow is about 56 percent of total streamflow. Mean annual 

baseflow was estimated for 1981 and 2000 (drought condiTable 3. Summary of mean annual baseflow estimated using HYSEP at selected streamflow gaging stations in the upper and lower 

parts of the basins in coastal Georgia and South Carolina, 1971–2001. 

 [in/yr, inch per year; ft 3 /s, cubic foot per second; mi 2 , square mile; part of basin: U, upper; L, lower; do, ditto] 

Station 

identification

Drainage 

area (mi2)

Part of 

basin

Period of record 

(calendar year)

Station 

identification

Outcropping hydrogeologic unit

Mean annual baseflow

in/yr ft3/s (in percent of total streamflow)

1971–2001 1981 2000 1997

Salkehatchie–Savannah–Ogeechee River Basin

02175500 341 U 1951-01 02175500 Upper Three Runs 9.79 246.0 69 77 65 64

02197600 28 U 1958-01 02197600 do. 8.02 16.5 66 74 81 68

02198000 646 U 1936-01 02198000 do. 9.29 442 74 72 80 70

02203000 555 L 1937-01 02203000 Surficial 6.29 257 54 51 51 48

Altamaha–Satilla–St Marys River Basin 

02225500 1,110 U 1903-07, 37-01 02225500 Surficial 7.16 585 57 53 62 56

02226500 1,190 L 1937-01 02226500 do. 5.41 478 43 47 34 47

02227500 646 L 1951-01 02227500 do. 4.46 212 39 27 34 33

Suwannee River Basin

02317500 1,390 L 1931-01 02317500 Surficial 6.36 656 56 56 50 56

Mean of stations for each period 58 57 57 55
Drought Streamflow 

 Drought streamflow represents a quantitative estimate of 

minimum ground-water discharge to streams because during 

drought periods, streamflow is composed mostly of baseflow. 

Drought baseflow is a minimum estimate because groundwater levels are lowered during droughts; and as a result, less 

water is available to the streams than would be available during average precipitation conditions. During droughts, streams 

receive baseflow mostly from the intermediate and regional 

flow systems because the water level in the local flow system 

is substantially decreased (Faye and Mayer, 1990). Streamflow 

at selected stations was compiled for the 1954 (Thomson and 

Carter, 1955), 1981 (Carter, 1983; Faye and Mayer, 1990), and 

2000 drought years (table 4). Streamflow was normalized to 

unit-area discharge to separate out effects of basin size on discharge rates. The computed unit-area discharge was estimated 

for selected stations in the SSO, SAS and Suwannee River 

Basins. The minimum streamflow during each calendar year 

was used in the calculations. 

 A comparison of the unit-area discharge in the upper 

and lower Coastal Plain was made in the SSO River Basin, 

using data from the 1954, 1981, and 2000 drought years. 

Streamflow data were collected on the same date from two 

adjacent stations (02197830 and 02198000) along Brier 

Creek near Waynesboro, Ga., and Millhaven, Ga. (fig. 17). 

During the 1954 and 2000 droughts, streamflow along that 

reach decreased in response to the droughts. During 1954, 

unit-area discharge decreased from 0.23 to 0.16 (ft3/s)/mi2

from Waynesboro, Ga., to Millhaven, Ga., a distance of about 

20 mi. During 2000, unit-area discharge decreased from 

0.32 to 0.25 (ft3/s)/mi2 from Waynesboro to Millhaven. There 

was no significant change in unit-area discharge between the 

two stations during 1981. For this comparison, these discharge measurements were made on the same date at each 

site (fig. 17). A comparison of the lowest discharge measured 

between the two stations for the calendar years 1954, 1981, 

and 2000 shows a decrease in unit-area discharge from 0.23 to 

0.10 (ft3/s)/mi2 from Waynesboro to Millhaven for 1954; no 

change for 1981; and a decrease from 0.32 to 0.18 (ft3/s)/mi2

for 2000. Similar comparisons were not made in the SAS or 

Suwannee River Basins because of insufficient data (table 4). 

 Drought unit-area discharge shows little variation among

 the three basins, with a few exceptions. In the SSO River 

Basin, the median unit-area discharge was 0.11 cubic feet per

second per square mile (ft3/s)/mi2 for the 1954 drought, 

0.11–0.14 (ft3/s)/mi2 for the 1981 drought, and 0.18 (ft3/s)/mi2 

for the 2000 drought. During each drought period, unitarea discharge generally was higher for the stations in the 

upper Coastal Plain than for stations in the lower Coastal 

Plain. During the 1954 drought, seven stations in the upper 

Coastal Plain had unit-area discharges ranging from 0.08 to 

0.63 (ft3/s)/mi2 (table 4). The unit-area discharge ranged from 

0 to 0.56 (ft3/s)/mi2 at 15 stations in the lower Coastal Plain 

during 1954. During 1981, two stations in the upper Coastal 

Plain had unit-area discharge of 0.14 and 0.18 (ft3/s)/mi2; 

Figure 16. Baseflow separation using the local-minimum 

method for the wet, average, and dry years at Canoochee River 

(station 02203000) near Claxton, Georgia, 1971–2001. 

tions) and 1997 (year most representative of mean annual 

precipitation for the period 1971–2001). Mean annual baseflow was greater in the upper part of the SSO and SAS River 

Basins than in the lower parts (table 3). The average mean 

annual baseflow for the 31-year period was 58 percent; for 

1981 and 2000, 57 percent each; and for 1997, 55 percent. The 

difference in baseflow is attributed to variations in topography, 

geology, and vegetation in the upper and lower Coastal Plain. 

The upper Coastal Plain is characterized by steep slopes and 

porous sand and gravel soils that have high infiltration rates 

and support little vegetation. In this area, aquifers are shallower than in the lower Coastal Plain because the topographic 

relief is greater in the upper Coastal Plain. The steeper topography results in deeper incision of streams into the aquifers, 

thereby increasing baseflow to streams. Gentle slopes that 

facilitate low runoff and more abundant vegetation, which 

derive water from soil moisture, characterize the lower Coastal 

Plain. In these areas, the streams do not incise into the more 

deeply buried aquifers, resulting in lower baseflow. Hydraulic 

conductivity of an aquifer, which also can have an effect on 

ground-water discharge, was not studied for this report. 

Stream-Aquifer Relations 25

1

10

100

1,000

10,000

1

.01

.01

10

100

1,000

10,000

JAN

FEB

MAR

APR

MAY

JUNE

JULY

AUG

SEPT

OCT

NOV

DEC

Wet year (1991)—Baseflow is about 

48 percent of total streamflow

Average year (1972)—Baseflow is 

about 63 percent of total streamflow

Dry year (2001)—Baseflow is about 

60 percent of total streamflow

100

1,000

10,000

10

1

.01

DISCHARGE, IN CUBIC FEET PER SECOND

Measured

 flow

Estimated

 baseflow
26 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina Table 4. Measured stream discharge at selected streamflow gaging stations in the upper and lower Coastal Plain during the 1954, 1981, and 2000 droughts in Georgia and Florida. [DA, drainage area; mi 2 , square mile; ft 3 /s, cubic foot per second; (ft 3 /s)/mi 2 , cubic foot per second per square mile; U, upper; L, lower; —, data not available] Station identification Station name DA (mi2

)

Part of 

Coastal 

Plain

Date

(1954)

Stream

discharge

(ft3/s)

Unit-area

discharge

[(ft3/s)/mi2

]

Date(s)

(1981)

Stream

discharge

(ft3/s)

Unit-area

discharge 

[(ft3/s)/mi2

]

Date

(2000)

Stream

discharge

(ft3/s)

Unit-area

discharge 

[(ft3/s)/mi2

]

Salkehatchie–Savannah–Ogeechee River Basin 

02197200 McBean Creek (Ga Hwy 56) at McBean, Ga. 71.4

U 4 Oct 141.4 0.58

—

—

—

—

—

—

021973444 Beaverdam Creek at River Rd nr Girard, Ga. 23.3

L 20 July 13.1 .56

—

—

—

—

—

—

02197590 Brushy Creek at Wrens, Ga. 9.4

L 5 Oct 11.6 .17

—

—

—

—

—

—

02197600 Brushy Creek near Wrens, Ga. 28

U

—

—

— 1 July 24.00 .14 30 May 2.7 0.10

02197830 Brier Creek near Waynesboro, Ga. 473

U 4 Oct 1107 .23 30 Sept 84 .18 31 July 153 .32

02197980 Brier Creek (GA Hwy 23) near Sardis, Ga. 579

L

—

—

—

—

—

— 31 July 119 17.5

02198000 Brier Creek at Millhaven, Ga. 646

L 5 Sept 164 .10 30 Sept 114 .18 22 July 76 .18

02198060 Brier Creek at US 301 near Sylvania, Ga. 669

L 30 July 1182 .27

—

—

—

—

—

—

02198100 Beaverdam Creek near Sardis, Ga. 30.8

L

—

—

—

—

—

— 21 July 2.3 .07

02198120 Beaverdam Creek at Hilltonia, Ga. 85.3

L 29 July 11.3 .02

—

—

—

—

—

—

02198170 Beaverdam Creek near Sylvania, Ga. 116

L 20 July 113.1 .11 22 Oct 30.58 0 —

—

—

02198280 Beaverdam Creek near Sylvania, Ga. 143

L 29 July 126.7 .19

—

—

—

—

—

—

02200410 Duhart Creek (SR80) at Stapleton, Ga. 3.17

U 6 Oct 11.5 .48

—

—

—

—

—

—

02200440 Rocky Comfort Creek (US 221) at Louisville, Ga. 286

U 13 Oct 446.7 .63

—

—

—

—

—

—

02200720 Big Creek (Penns Bridge Rd) near Wrens, Ga. 8.07

U 6 Oct 12.4 .30

—

—

—

—

—

—

02200810 Big Creek above Louisville, Ga. 56.9

U 6 Oct 14.74 .08

—

—

—

—

—

—

02200900 Big Creek near Louisville, Ga. 95.8

U 13 Oct 423.6 .25

—

—

—

—

—

—

02201000 Williamson Swamp Creek at Davisboro, Ga. 109

L

—

—

— 4 Oct 12 .11

—

—

—

02201070 Williamson Swamp Creek at Bartow, Ga. 185

L 15 Oct 17.1 .09

—

—

—

—

—

—

02201150 Williamson Swamp Creek at Wadley, Ga. 233

L 15 Oct 421.7 .09

—

—

—

—

—

—

02201270 Barkcamp Creek (SR 17) near Midville, Ga. 31.7

L 10 Sept 4

0 0 —

—

—

—

—

—

02201300 Chow Mill Creek near Herndon, Ga. 23

L 10 Sept 0.23 .01

—

—

—

—

—

—

02201350 Buckhead Creek near Waynesboro, Ga. 64

L 5 Oct 0 0 —

—

— 1 Aug 36.6 .57

02201360 Rocky Creek at SR 24 near Waynesboro, Ga. 31.7

L 5 Oct 10.12 0 —

—

—

—

—

—

02201365 Rocky Creek near Waynesboro, Ga. 34.8

L 5 Oct 0 0 —

—

—

—

—

—

02202210 Ogeechee Creek near Sylvania, Ga. 14

L 9 Sept 1

0 0 —

—

—

—

—

—

02202240 Ogeechee Creek at Oliver, Ga. 141

L

—

—

— 22 Oct .07 0 —

—

—

02203000 Canoochee River near Claxton, Ga. 555

L

—

—

—

—

—

— 16 June 3.3 .04
Stream-Aquifer Relations 27

 Table 4. Measured stream discharge at selected streamflow gaging stations in the upper and lower Coastal Plain during the 1954, 1981, and 2000 droughts in Georgia and Florida.—Continued  [DA, drainage area; mi 2 , square mile; ft 3 /s, cubic foot per second; (ft 3 /s)/mi 2 , cubic foot per second per square mile; U, upper; L, lower; —, data not available] 

Station

identification Station name DA (mi2) Part of Coastal Plain Date (1954) Stream discharge (ft3/s) Unit-area discharge [(ft3/s)/mi2] Date (1981) Stream discharge (ft3/s) Unit-area discharge [(ft3/s)/mi2] Date(s) (2000) Stream discharge (ft3/s) Unit-area discharge [(ft3/s)/mi2]

Altamaha-Satilla-St Marys River Basin 

02215500 Ocmulgee River at Lumber City, Ga. 5,180.0 L — — — — — — 30 Aug 905.0 .1702216180 Turnpike Creek near McRae, Ga. 49.2 L — — — — — — 28 May 0 002224000 Rocky Creek near Dudley, Ga. 62.9 L 6 Oct .23 0 — — — — — —02225000 Altamaha River near Baxley, Ga. 11,600 L — — — 25 Oct 1,680 .14 29 Aug 1450 .1302225315 Jacks Creek near Wesley, Ga. 8.63 L — — — — — — 31 July 0 002225360 Pendleton Creek near Normantown, Ga. 101 L — — — — — — 1 Aug 0 002225395 Swift Creek SR 130 near Vidalia, Ga. 36 L — — — — — — 31 July 0 002225405 Swift Creek US 1 near Lyons, Ga. 46.3 L — — — — — — 31 July 0 002225420 Swift Creek (SR 152) near Lyons, Ga. 55.6 L — — — — — — 31 July 0.7 .0102225480 Ohoopee River at US 280 near Reidsville, Ga. 1,070 L — — — — — — 1 Aug 45.1 .0402225500 Ohoopee River near Reidsville, Ga. 1,110 L — — — — — — 1 Aug 49.2 .0402225850 Beards Creek near Glennville, Ga. 74.4 L — — — — — — 31 July 002226000 Altamaha River at Doctortown, Ga. 13,600 L — — — 9 Oct 1,790 .13 31 Aug 1,410 .102226100 Penholoway Creek near Jesup, Ga. 209 L — — — 27 July 0 0 1 July 0 002227000 Hurricane Creek near Alma, Ga. 139 L 1 June 10 — — — — — — —02229000 Middle Prong St Marys River at Talylor, Fla. 125 L — — — 17 July .32 0 1 June 0 002231280 Thomas Creek near Crawford, Fla. 29.9 L — — — — — — 11 June 0.09 0

Suwannee River Basin

02314500 Suwannee River at Fargo, Ga. 1,260 L — — — 3 Nov 7.80 0 16 June 5.4 002317500 Alapaha River at Statenville, Ga. 1,390 L — — — 19, 20 Oct 25 .02 20 July 37 0

 1 Thomson and Carter, 1955  2 Faye and Mayer, 1990  3 Hale and others, 1989  4 Carter, 1983 
28 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

Figure 17. Comparison of drought streamflow between two 

adjacent streamflow gaging stations in the Salkehatchie–

Savannah–Ogeechee River Basin. 

whereas, four stations in the lower Coastal Plain had unit-area 

discharge ranging from 0 to 0.18 (ft3/s)/mi2 (table 4). During 

2000, two stations in the upper Coastal Plain had unit-area 

discharge of 0.10 and 0.32 (ft3/s)/mi2, and five stations in the 

lower Coastal Plain had unit-area discharge ranging from 0.04 to 

17.5 (ft3/s)/mi2 (table 4). The relatively higher contribution of 

baseflow in the upper Coastal Plain compared to the lower 

Coastal Plain reflects the greater relief, higher interconnection 

between aquifers and streams, greater soil permeability, and 

different vegetation. 

 In the SAS and Suwannee River Basins, all stations are 

located in the lower Coastal Plain. In the SAS River Basin, 

the unit-area discharge was 0 (ft3/s)/mi2 for two stations during 

1954; ranged from 0 to 0.14 (ft3/s)/mi2 for four stations during 

1981; and ranged from 0 to 0.17 (ft3/s)/mi2 for 15 stations 

during 2000 (table 4). In the Suwannee River Basin, the unitarea discharge for two stations was 0 and 0.02 (ft3

/s)/mi2

during 1981; 0 (ft3/s)/mi2 during 2000; no data were available 

for 1954 (table 4). 

 Observed differences in streamflow between upstream 

and downstream stations give an indication of the gain or loss 

of water from or to the ground-water flow system. In the SSO 

and SAS River Basins, near-concurrent discharge measurements taken at partial-record stations and daily mean flow at 

continuous-record stations during the three drought periods 

were used to estimate ground-water discharge to selected 

reaches. Observed gains or losses along selected stream 

reaches were determined in the SSO and SAS River Basins 

during the 1954, 1981, and 2000 droughts (table 5). Gain or 

loss determinations were not made in the Suwannee River 

Basin because of insufficient data. 

 In the SSO River Basin, ground water provided baseflow to most stream reaches evaluated during the 1954, 1981, 

and 2000 droughts. In some reaches, streams were either 

dry or lost water to the ground-water system. For example, 

in the Brier Creek Basin, during the 1954 drought, a loss of 

0.25 (ft3/s)/mi2 was measured between stations 02197830 

and 02198000 (fig. 18; table 5). In this same reach during the 

1981 drought, a gain of 0.17 (ft3/s)/mi2 was measured (fig. 19; 

table 5). During the 2000 drought, a loss of 0.45 (ft3/s)/mi2

was measured (fig. 20; table 5) in the same reach. Losses 

were observed in the SSO River Basin at Rocky Creek 

between stations 02201360 and 02201365 in 1954 (fig. 18; 

table 5) and in the SAS River Basin along the Altamaha 

River between stations 02225000 and 02226000 during 2000 

(fig. 20; table 5). Losses most likely are due to stream-water 

seepage into the surficial aquifer along the reach. Gains most 

likely are due to baseflow. 

Linear-Regression Analysis of 

Streamflow Duration 

 A linear-regression analysis was used to develop a relation 

between mean annual baseflow and flow duration for streams 

in the study area. A flow-duration curve is a cumulative frequency curve that shows the percentage of time that specified 

discharges are equaled or exceeded during a given period at 

stations where continuous records of daily flow are collected. 

Flow-duration curves integrate the effects of climate, topography, and geology. Visual inspection of the slopes of curves 

gives some indication of flow from ground water. Ground 

water dominates streamflow at the inflection point on a curve, 

where the curve begins to flatten. Generally, steep slopes are 

indicative of limited basin storage and dominant contribution 

from runoff, whereas flat slopes are indicative of equal contribution of ground water and runoff (Stricker, 1983) (fig. 21). 

 Many studies have compared ground-water discharge to 

streams using the flow-duration characteristics of a stream. 

Stricker (1983) estimated baseflow using streamflow-duration curves for 35 stations in the southeastern Coastal Plain of 

South Carolina, Georgia, Alabama, and Mississippi. Stricker 

(1983) found that the 60- and 65-percent flow-duration points 

on the flow-duration curves were representative of mean 

annual baseflow for streams having mean discharges greater 

than 10 ft3/s. Stricker (1983) found that the shape of streamflow-duration curves is affected by the lithology of the Coastal 

Plain sediments. Steep curves are associated with basins 

underlain by low-permeability clay or chalk with high runoff 

and low baseflow, whereas flatter curves are associated with 

basins underlain by high-permeability sand and gravel where a 

high percentage of the discharge is baseflow (Stricker, 1983). 

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

UNIT-AREA DISCHARGE, IN CUBIC FEET

PER SECOND PER SQUARE MILE

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Upper Coastal Plain

Brier Creek (station 02197830) near Waynesboro, Georgia

Lower Coastal Plain

Brier Creek (station 02198000) at Millhaven, Georgia

October 4

1954

September 30

1981

July 31

2000
Stream-Aquifer Relations 29

Table 5. Estimated ground-water discharrge to selected streams in the Salkehatchie–Savannah–Ogeechee, Altamaha–Satilla–St Marys, and Suwannee River Basins during the 1954, 1981, and 2000 droughts.  [—, not applicable; mi 2, square mile; ft 3 /s, cubic foot per second; Do., ditto; bold and negative sign “–”, loss] /s, cubic foot per second; Do., ditto; bold and negative sign “–”, loss] 3 

Stream name

and state

Intermediate area of 

stream reach

Intermediate drainage area 

(mi2)

1954 drought (fig. 18) 1981 drought (fig. 19) 2000 drought (fig. 20)

Date(s) Net gain/loss in

stream discharge

Date(s) Net gain/loss in

stream discharge

Date(s) Net gain/loss in

stream discharge 

(ft3/s) [(ft3/s)/mi2] (ft3/s) [(ft3/s)/mi2] (ft3/s) [(ft3/s)/mi2]

Salkehatchie–Savannah –Ogeechee River Basin 

Barkcamp Creek, Ga. between headwater and station 02201270 31.70 10 Sept 0.00 0.00 — — — — — —

Beaverdam Creek, Ga. between stations 02198120 and 02198170 30.7 20 & 29 July 11.8 .38 — — — — — —

Do. between headwater and station 021973444 23.3 20 July 13.1 .56 — — — — — —Do. between headwater and station 02198100 30.8 — — — — — — 21 July 2.3 .07Do. between headwater and station 02198120 85.3 29 July 1.3 .02 — — — — — —Do. between headwater and station 02198170 116 — — — 27 Oct .58 0 — — —Do. between stations 02198170 and 02198280 27 29 July 13.6 .5 — — — — — —

Big Creek, Ga. between headwater and station 02200720 8.07 6 Oct 2.4 .3 — — — — — —

Do.. between stations 02200720 and 02200810 48.9 6 Oct 2.3 .05 — — — — — —Do. between stations 02200810 and 02200900 38.9 6 & 13 Oct 18.9 .49 — — — — — —

Brier Creek, Ga. between stations 02197830 and 02198000 173 4 Oct & 5 Sept – 43 – .25 30 Sept 30 .17 22 & 31 July – 77 – 0.45

Do. between stations 02198000 and 02198060 24 30 July & 5 Sept 118 4.9 — — — — — —

Brushy Creek, Ga. between headwater and station 02197600 28 — — — — — — 30 May 2.7 .1

Do. between headwater and station 02197590 9.4 5 Oct 1.56 .17 — — — — — —

Buckhead Creek, Ga. between headwater and station 02201350 64 5 Oct 0 0 — — — 1 Aug 36.6 .57Chow Mill Creek, Ga. between headwater and station 02201300 23 10 Sept .23 .01 — — — — — —Duhart Creek, Ga. between headwater and station 02200410 3.17 6 Oct 1.9 .6 — — — — — —

Do. between stations 02200410 and 02200440 283 6 & 13 Oct 44.8 .16 — — — — — —

McBean Creek, Ga. between headwater and station 02197200 71.4 4 Oct 41.4 .58 — — — — — —Ogeechee Creek, Ga. between headwater and station 02202210 14 9 Sept 0 0 — — — — — —

Do. between headwater and station 02202240 141 — — — 22 Oct .07 0 — — —

Rocky Creek, Ga. between stations 02201360 and 02201365 3.1 5 Oct –.12 – .04 — — — — — —Williamsonswamp Creek, Ga. between headwater and station 02201000 109 — — — 4 Oct 12 .11 21 July 11.0 .10

Do. between stations 02201070 and 02201150 48 15 Oct 4.6 .1 — — — — — —

Altamaha–Satilla–St Marys River Basin 

Altamaha River, Ga. between stations 02225000 and 02226000 1,990 — — — 30 Sept 110 0.05 20 & 31 Aug – 40.0 – 0.02Beards Creek, Ga. between headwater and station 02225850 74.4 — — — — — — 31 July 0 0Jacks Creek, Ga. between headwater and station 02225315 8.63 — — — — — — 31 July 0 0Middle Prong St Marys, Fla. between headwater and station 02229000 125 — — — 17 July 0.32 0 1 June 0 0Ohoopee River, Ga. between stations 02225480 and 02225500 40 — — — — — — 1 Aug – 4.1 0Pendleton Creek, Ga. between headwater and station 02225360 101 — — — — — — 1 Aug 0 0Penholoway Creek, Ga. between headwater and station 02226100 209 — — — 27 July 0 0 1 July 0 0Swift Creek, Ga between headwater and station 02225395 36 — — — — — — 31 July 0 0

Do. between stations 02225395 and 02225405 10.3 — — — — — — 31 July 0 0Do. between stations 02225405 and 02225420 9.3 — — — — — — 31 July 0.7 0.08

Turnpike Creek, Ga. between headwater and station 02216180 49.2 — — — — — — 28 May 0 0
30 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

 where Q25 (75th percentile) is the streamflow equaled or 

ex ceeded 25 percent of the time and less than or equal to 

75 percent of the time; and Q75 (25th percentile) is the streamflow equaled or exceeded 75 percent of the time and less than 

or equal to 25 percent of the time. Stricker (1983) found that 

the lower the ratio, the greater the portion of baseflow from 

ground water. 

 Discharge data from 14 stations for the period 1971–2001 

were analyzed to determine the streamflow index (table 6). 

Streamflow indices ranged from a low of 1.48 at the Brushy 

Creek (station 02197600) in the SSO River Basin to a high 

to 7.31 at Little Satilla River (station 02227500) in the SAS 

River Basin. 

 The lowest index in the SSO River Basin is for the 

station on Brushy Creek near Wrens, Ga. (station 02197600) 

(fig. 22; table 6), where the lithology is mostly sand interlayered with clay, aquifers are more deeply incised by streams, 

and ground water contributes a large percentage of baseflow. 

The flow-duration curve has a gentle slope. Brushy Creek 

is the only station in the upper Coastal Plain area of the 

SSO River Basin. The highest index in the SSO River Basin 

is Canoochee River near Claxton, Ga. (station 02203000) 

(fig. 23), where the lithology is mostly sand. The curve is 

steep, indicating high runoff. In this area, aquifers are deeply 

buried and ground water contributes only a small percentage 

to baseflow. There appears to be little difference between the 

flow duration of mean daily streamflows in the upper and 

lower Coastal Plain in the SSO River Basin. Brushy Creek 

in the upper Coastal Plain has an index of 1.48, and Brier 

Creek in the lower Coastal Plain has an index of 1.74 

(fig. 22; table 6). 

 The shape of a flow-duration curve can be described 

by a streamflow index, modified by Pettyjohn and Henning 

(1979) as: 

Figure 18. Selected streamflow gaging stations monitored during the 1954 drought and corresponding 

intermediate unit-area discharge. 

02197590

02197200

(+0.58)

(0)

(0)

(+0.56)

(+0.01) (+0.10)

(+0.17)

(+0.60)

(+0.30) (+0.05)

(+0.49)

(+0.16)

(–0.25)

(+4.9)

(+0.50) (0)

(+0.38)

(+0.02)

(–0.04)

021973444

02198000

02198060

02198280

02198170

02198120

02201365

02201360

02197830 02200720

02200410

02200440

02201150 02201270 02201300

02202210

02201070

02200810

02200900

02201350

JEFFERSON

JENKINS

SCREVEN

BURKE

GLASCOCK

Area of 

enlarged 

map

0

0 10 20 KILOMETERS

10 20 MILES

Base from U.S. Geological Survey 

1:100,000-scale digital data

N

02201270

(–0.04)

EXPLANATION

Streamflow gaging station 

 and identification number 

Unit-area discharge, in 

 cubic feet per second 

 per square mile—gray 

 indicates zero or positive;

 hachures indicate negative

(0)

SOUTH

GEORGIA CAROLINA

A

Rocky Cr

Brushy Cr

Beaverdam Cr

Brier Cr

Atlantic Ocean

Q25

Q75 , 
Figure 19. Selected streamflow gaging stations monitored during the 1981 drought and corresponding 

intermediate unit-area discharge. 

Stream-Aquifer Relations 31

WASHINGTON

BACON

GLYNN

WARE

CHARLTON

CAMDEN

NASSAU

BAKER

TATTNALL

EVANS BRYAN

LONG

WAYNE

LIBERTY

EMANUEL

JENKINS

EFFINGHAM

CANDLER BULLOCH

GLASCOCK

02229000 02229000

02198000

02198170

02202240

(0)

02197830

02201000

02226100

(+0.11) (+0.17)

(0)

(0)

(+0.05)

(0)

(+0.11)

Area of 

enlarged 

map

aha River

W on Swamp

SOUTH

GEORGIA CAROLINA

FLORIDA

Atlantic Ocean

Base from U.S. Geological Survey 

1:100,000-scale digital data

N

GA

FL

0

0 10 20 30 KILOMETERS

10 20 30 MILES

EXPLANATION

Streamflow gaging station 

 and identification number 

Unit-area discharge,

 in cubic feet per second

 per square mile

Atlantic

Ocean
32 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

Figure 20. Selected streamflow gaging stations monitored during the 2000 drought and 

corresponding intermediate unit-area discharge. 

SOUTH

GEORGIA CAR

FL

Atlantic Ocean

Area of 

enlarged 

map

DODGE

BACON

GLYNN

WARE

BAKER

CHARLTON

CAMDEN

NASSAU

EVANS

LONG

WAYNE

APPLING

LIBERTY

MCINTOSH

BULLOCH CANDLER

BURKE

GLASCOCK

0

0 10 20 30 KILOMETERS

10 20 30 MILES

Base from U.S. Geological Survey 

1:100,000-scale digital data

N

GA

FL

Alta

(–0.02)

02229000

EXPLANATION

Streamflow gaging station 

 and identification number 

(0)

Unit-area discharge, in 

 cubic feet per second 

 per square mile—gray 

 indicates zero or positive;

 hachures indicate negative

Atlantic

Ocean

02226000

02225850

02225500

02225000

02229000

02216180

02225315

02198100

02198000

02197830

02201000 02201350

02197600

02225360

02225395

02225405

02225420

02225480

02226100

(0)

(–0.45)

(+0.07)

(+0.10)

(+0.10)

(0)

(0)

(0)

(0)

(0)

(0)

(0)

(+0.08)

(–0.02)

(0)

(+0.57)
10,000

1,000

100

10

0 10 20

DISCHARGE, IN CUBIC FEET

PER SECOND

30 40 50 60 70 80 90 100

PERCENT OF TIME FLOW WAS

EQUALED OR EXCEEDED

Brier Creek

(02198000)

Alapaha River

(02317500) Upper Coastal Plain

Brushy Creek

Lower Coastal Plain

Brier Creek

10,000

1,000

100

10

1

0 10 20

DISCHARGE, IN CUBIC FEET

PER SECOND

30 40 50 60 70 80 90 100

PERCENT OF TIME FLOW WAS

EQUALED OR EXCEEDED

Table 6. Flow-duration curve index [(Q 25 /Q 75 ) 1⁄2 ] and curve shape for selected streams in the Salkehatchie–Savannah–Ogeechee, 

Altamaha–Satilla–St Marys, and Suwannee River Basins, 1971–2001. 

 [mi 2 , square mile; ft 3 /s, cubic foot per second; part of basin: U, upper; L, lower] /s, cubic foot per second; part of basin: U, upper; L, lower] 

Station 

identification Station name Part of basin

Drainage area 

(mi2)

Q25 

(ft3/s)

Q75

(ft3/s) Index Curve shape

Salkehatchie–Savannah–Ogeechee River Basin 

02175500 Salkehatchie River near Miley, S.C. U 341 444 157 1.68 Gentle

02197600 Brushy Creek near Wrens, Ga. U 28 24 11 1.48 do.

02198000 Brier Creek at Millhaven, Ga. U 646 755 250 1.74 do.

02202500 Ogeechee River near Eden, Ga. L 2,650 2,940 557 2.3 Steep

02203000 Canoochee River near Claxton, Ga. L 555 674 23 5.41 do.

Altamaha–Satilla–St Marys River Basin

02215500 Ocumulgee River at Lumber City, Ga. U 5,180 6,920 2,060 1.83 Gentle

02223500 Oconee River at Dublin, Ga. U 4,390 5,480 1,120 2.21 Steep

02225000 Altamaha River near Baxley, Ga. U 11,600 15,300 3,680 2.04 do.

02225500 Ohoopee River near Reidsville, Ga. U 1,110 1,410 105 3.66 do.

02226000 Altamaha River at Doctortown, Ga. L 13,600 18,700 4,140 2.13 do.

02226500 Satilla River near Waycross, Ga. L 1,190 1,260 66 4.37 do.

02227500 Little Satilla River near Offerman, Ga. L 646 642 12 7.31 do.

02228000 Satilla River at Atkinson, Ga. L 2,790 2,995 218 3.71 do.

Suwannee River Basin

02317500 Alapaha River at Statenville, Ga. L 1,390 1,450 96 3.89 Steep

Stream-Aquifer Relations 33

Figure 21. Comparison of two flow-duration curve types: 

gentle curve along Brier Creek (station 02198000) and a steep 

curve along the Alapaha River (station 02317500). 

Figure 22. Duration of mean daily streamflow for Brushy Creek 

(station 02197600) near Wrens, Georgia, and Brier Creek (station 

02198000) at Millhaven, Georgia, 1971–2001. 
34 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

 In the SAS River Basin, all measured discharges have indices 

greater than 2, except the Ocmulgee River, which has an index 

of 1.83. An index greater than 2 corresponds to a steep slope. 

The lowest ratio in the SAS River Basin is Ocmulgee River 

at Lumber City, Ga. (station 02215500) (fig. 24), where the 

lithology is a heterogeneous mix of sand, silt, and clay. This 

station is located in the upper part of the basin where baseflow 

dominates streamflow. The highest index (7.31) in the SAS 

River Basin is the station on the Little Satilla River at Offerman, Ga. (station 02227500) (fig. 24), where the lithology is 

mostly clay, sand, and silt beds containing phosphate. This 

station is located in the lower part of the basin, where runoff 

dominates streamflow and the aquifer is deeply buried. 

 In the Suwannee River Basin, the only discharge that 

was analyzed was at the Alapaha River at Statenville, Ga. 

(station 02317500) (fig. 25), where the lithology is mostly 

sand, silt, clay, limestone, and dolomite. The shape of the 

curve indicates there is a large contribution of runoff to 

streamflow, which corresponds to a higher index (3.89) than 

observed in the upper Coastal Plain. 

 Linear-regression analysis was used to determine the 

flow duration that best estimates baseflow for streams in 

the area. Mean annual baseflow calculated by HYSEP for 

the 14 stations for the period 1971–2001 were compared to 

flow durations at the stations ranging from Q1 to Q99; the best 

fit between HYSEP estimates and flow duration was at the 

Q35 flow duration (flow is equaled or exceeded 35 percent 

of the time). The best regression model had an r-squared (r2) 

value of 0.9970 and a p-value of less than 0.0001 (table 7). 

Linear-regression analysis was used on the eight stations 

selected for HYSEP to compare results. Both sets of data show 

the Q35 as the best estimate of baseflow. The linear regression 

of flow duration is probably more representative of average 

climatic conditions rather than drought conditions because 

the analysis compares mean annual baseflow and flow duration for several stations with differing drainage areas for the 

31-year period. Linear-regression analysis of flow duration 

shows drought conditions most likely occur above the Q80 flow 

duration. Figure 26 illustrates the regression of Q35 with mean 

annual baseflow from HYSEP. 

Comparison of Results 

 Major variation exists between baseflow estimation using 

drought-streamflow analysis and both HYSEP and linearregression analysis of flow duration. Slight variation exists 

between HYSEP and flow-duration methods. The same 

14 stations were selected to make a comparison of the three 

methods. Using the drought-streamflow analysis, the minimum contribution to streamflow from baseflow was observed. 

During drought conditions, the following observations were 

made: (1) total streamflow was equivalent to baseflow; 

(2) surface-water runoff to streamflow and ground-water contribution was reduced; (3) ground-water levels decreased; and 

(4) some streams reaches went dry. Under average precipitation conditions during 1971–2001, baseflow ranged from 

33 to 70 percent of total streamflow during 1997 (average 

conditions are best represented by 1997 data) and increased to 

27 to 81 percent in drought years 1981 and 2000, respectively 

(table 3). For the study area, mean annual baseflow during 

drought conditions (1981 and 2000) ranged from 0 to 

24 percent of mean annual streamflow for 1971–2001 

(table 8). These values are far below the 39–74 percent 

estimated using HYSEP and 65–102 percent estimated using 

linear-regression analysis of flow duration (fig. 8). 

Figure 23. Duration of mean daily streamflow for Canoochee 

River (station 02203000) near Claxton, Georgia, in the upper 

Salkehatchie–Savannah–Ogeechee River Basin, 1971–2001. 

Figure 24. Duration of mean daily streamflow for Little Satilla 

River (station 02227500) near Offerman, Georgia, and Ocmulgee River (station 02215500) at Lumber City, Georgia, in the 

Altamaha–Satilla–St Marys River Basin, 1971–2001. 

10,000

1,000

100

10

1

0 10 20

DISCHARGE, IN CUBIC FEET

PER SECOND

30 40 50 60 70 80 90 100

PERCENT OF TIME FLOW WAS

EQUALED OR EXCEEDED

100,000

10,000

1,000

100

10

1

0.1

0 10 20

DISCHARGE, IN CUBIC FEET

PER SECOND

30 40 50 60 70 80 90 100

PERCENT OF TIME FLOW WAS

EQUALED OR EXCEEDED

Upper Basin

Ocmulgee River

Lower Basin

Little Satilla River
 Table 7. Coefficient of determination (r 2 ) and residual standard 

of error for flow durations evaluated as indicators of baseflow 

for 8 and 14 streamflow gaging stations selected in the 

Salkehatchie–Savannah–Ogeechee, Altamaha–Satilla–St Marys, 

and Suwannee River Basins, 1971–2001. 

 [P-value = less than 0.5 for the 8 stations; less than 0.0001 for the 14 stations] 

Flow

duration

r-squared Residual standard error

8 stations 14 stations 8 stations 14 stations

Q01 0.69 0.98 128.40 463.7

Q05 0.75 0.98 116.40 346.3

Q10 0.77 0.98 110.10 345

Q15 0.82 0.98 97.04 311.4

Q20 0.88 0.99 80.82 238.7

Q25 0.92 0.99 66.41 202.8

Q30 0.95 0.99 52.09 179.8

Q35 0.98 1.00 29.71 168.8

Q40 0.98 0.99 36.56 169.4

Q45 0.92 0.99 63.81 205.7

Q50 0.81 0.99 100.60 224.7

Q55 0.65 0.99 136.60 257.1

Q60 0.46 0.99 170.20 266.1

Q65 0.33 0.99 189.60 275.4

Q70 0.24 0.98 202.50 307.4

Q75 0.18 0.98 209.30 347.5

Q80 0.15 0.98 213.90 377.8

Q85 0.12 0.98 217.80 412.6

Q90 0.11 0.97 219.30 456.4

Q95 0.10 0.97 219.50 481.6

Q99 0.13 0.97 216.70 518.2

The flow-duration method of estimating baseflow gives 

an overestimation of baseflow for a particular stream. Regression analyses of streamflow data indicate that the flow-duration point that most closely estimates baseflow is the 35-percent flow-duration point (Q 35 ) (flow is greater than or equaled 

to 35 percent of the time and less than or equaled to 65 percent 

of the time). Stricker (1983) estimated baseflow as the 

65-percent flow-duration point (Q 65 ). The difference could 

merely be a matter of interpretation. Q 35 is the flow that is 

equaled or exceeded 35 percent of the time or less than or 

equal 65 percent of the time, corresponding to a Q 65 . Nevertheless, the linear regression of streamflow duration is not a 

reliable estimator of baseflow, particularly in the upper part of 

the basin area where streams intersect the aquifer as indicated 

by the 102-percent baseflow estimation of the Salkehatchie 

River, nor in the lower part of the study area where the aquifer 

is deeply buried. The variability in basin size, the lithology, 

and ground-water levels affect the reliability of using the flowduration method as a good estimator of baseflow. 

 The HYSEP method of estimating baseflow most likely 

relates to actual baseflow of the three methods used. HYSEP 

systematically separates baseflow from runoff by connecting low points of the streamflow hydrograph. HYSEP is most 

Figure 25. Duration of mean daily streamflow for Alapaha 

River (station 02317500) at Statenville, Georgia, in the 

Suwannee River Basin, 1971–2001. 

Figure 26. Regression of Q35 versus mean annual baseflow 

for the (A) 8 and (B) 14 streamflow gaging stations selected for 

hydrograph-separation technique, Georgia and South Carolina, 

1971–2001. 

Stream-Aquifer Relations 35

DISCHARGE AT 35-PERCENT DURATION

(Q35) IN CUBIC FEET PER SECOND

r2 = 0.9836

0 100 200 300 400 500 600

0

100

200

300

400

500

600

MEAN-ANNUAL BASEFLOW, IN CUBIC FEET PER SECOND

0 2,000 4,000 6,000 8,000

0

2,000

4,000

6,000

8,000

r2 = 0.9970

A.

B.

0 10 20

10,000

1,000

100

10

1

0.1

DISCHARGE, IN CUBIC FEET

PER SECOND

30 40 50 60 70 80 90 100

PERCENT OF TIME FLOW WAS

EQUALED OR EXCEEDED
36 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

reliable for estimating drainage areas of less than 100 mi2 with 

at least 20 years of continuous streamflow data. Because of 

the limited availability of data, the drainage-area size criterion 

was increased and the period-of-record criterion was increased 

to include extremes in precipitation conditions. Table 8 

compares mean annual baseflow of selected streams using 

the hydrograph-separation and linear-regression analysis of 

flow duration, and drought-streamflow analysis methods. An 

example of the variability in baseflow estimation is observed 

at station 02175500 (Salkehatchie River) (fig. 1). Part of the 

river is in the upper Coastal Plain where there is a high degree 

of interconnection between the stream and the aquifer resulting in a substantial contribution of ground water to streamflow. 

According to the methods used, linear-regression analysis 

estimates that baseflow is equivalent to the flow at Q35, which 

in this case is 102 percent of the mean annual streamflow. 

The drought-streamflow analysis estimates that baseflow is 

11 percent of total streamflow. Again, this is an unreasonable 

estimation because the stream is in the upper Coastal Plain 

where there is a greater interconnectivity with the aquifer. 

The HYSEP method estimates baseflow as 69 percent of total 

streamflow, which seems most reasonable of the three methods, considering the size and location of the basin. 

Summary 

 Stream-aquifer relations were evaluated in the 

67-county area of southeast Georgia, southwest South Carolina, and northeast Florida (55 counties in Georgia, 5 counties in Florida, and 7 counties in South Carolina) during a 

variety of climatic conditions for the period from 1971–2001. 

Ground-water discharge to streams was estimated using three 

methods: (1) HYSEP, an automated hydrograph-separation 

program; (2) drought measurement of baseflow; and (3) a 

comparison of mean annual baseflow and flow-duration data 

using a simple linear-regression analysis. The hydrographseparation method provides the best estimate of mean annual 

ground-water discharge to streams in the study area. The 

analysis of drought streamflow provides an estimate of the 

minimum ground-water discharge to streamflow, whereas 

linear-regression analysis overestimates an average value 

for a given basin. Analyses were conducted using 8 continuous-record streamflow gaging stations for hydrograph separation, 14 continuous-record streamflow gaging stations for 

streamflow duration, and 62 continuous-record and partialrecord streamflow gaging stations for drought streamflow; 

9 U.S. Geological Survey wells; and 11 National Weather 

Table 8. Comparison of three methods used to calculate baseflow for selected streamflow gaging stations in the Salkehatchie–

Savannah–Ogeechee, Altamaha–Satilla–St Marys and Suwannee River Basins, 1971–2001. 

 [bold, stations selected for HYSEP; mi 2 , square mile; ft 3 /s, cubic foot per second; in/yr, inch per year; %, percent of total streamflow] /s, cubic foot per second; in/yr, inch per year; %, percent of total streamflow] 

Station 

identification

Drainage 

area

31-year mean 

annual streamflow

Estimated baseflow

Flow duration (Q35) HYSEP

1981 and 2000 average 

of lowest flow

Mean annual 

streamflow

1981 2000

 (mi2) (ft3/s) (in/yr) (ft3/s) (in/yr) (%) (ft3/s) (in/yr) (%) (ft3/s) (in/yr) (%) (ft3/s) (ft3/s)

Salkehatchie–Savannah–Ogeechee River Basin

02175500 341.0 357.0 14.23 365.0 14.50 102 246 9.80 69 28.0 1.11 11 189.0 174.0

02197600 28 24.5 11.87 19 9.21 78 17 8.24 69 3.35 1.62 20 13.8 12.1

02198000 646 598 12.58 588 12.4 98 442 9.29 74 95 2 21 383 297

02202500 2,650 2,330 11.94 2,160 11.1 93 1,529 7.83 66 136 .69 9 823 803

02203000 555 484 11.84 401 9.82 83 257 6.29 54 2.5 .06 1 116 169

Altamaha–Satilla–St Marys River Basin

02215500 5,180 5,510 14.44 5,210 13.7 95 3,811 10 69 928 2.43 24 2,570 2,460

02223500 4,390 4,390 13.54 3,950 12.2 90 2,238 6.9 51 399 1.23 18 2,230 1,780

02225000 11,600 11,700 13.69 10,800 12.6 92 7,704 9.02 66 1,570 1.84 20 5,330 4,850

02225500 1,110 1,040 12.72 863 10.6 83 585 7.15 57 28 .34 5 309 476

02226000 13,600 13,900 13.87 12,900 13 93 9,330 9.31 67 1,590 1.6 17 6,050 5,640

02226500 1,190 1,110 12.56 725 8.2 65 478 5.41 43 8.75 .1 2 118 252

02227500 646 542 11.38 353 7.42 65 212 4.45 39 0 0 0 75.4 85.2

02228000 2,790 2,390 11.63 1,860 9.05 78 1,171 5.7 49 33 .16 3 326 438

Suwannee River Basin

02317500 1,390 1,170 11.34 876 8.49 75 656 6.36 56 31.0 0.30 5 138 437
Service stations. Streams and tributaries were grouped into the 

Salkehatchie–Savannah–Ogeechee River, Altamaha–Satilla–

St Marys River, and Suwannee River Basins for this study. 

 Water in streams and aquifers interact through a dynamic 

hydrologic system including aquifers, streams, reservoirs, 

and floodplains. These systems are interconnected and form a 

hydrologic environment that is stressed by natural hydrologic, 

climatic, and anthropogenic factors. Under steady-state 

conditions, most ground-water systems can be divided into 

three subsystems: local flow, characterized by relatively shallow and short flowpaths that extend from a topographic high 

to an adjacent topographic low; intermediate flow, which 

includes at least one local flow system between respective 

points of recharge and discharge; and regional flow, which 

begins at or near a major ground-water divide and terminates 

at a regional drain. 

 Recharge to the hydrologic system is provided by rainfall 

that ranges from an average of about 47 to 53 inches per year 

based on the 30-year period 1971–2000. Most of the recharge 

is either discharged from the shallow, local flow systems 

into small streams, or is lost as evapotranspiration. In the 

intermediate flow system, some water is discharged to major 

tributaries. Climatic effects dominate in the surficial aquifer. 

Water levels generally are highest in the winter and early 

spring when precipitation is greatest and evapotranspiration 

is least; water levels are lowest during the summer and fall 

when precipitation is least and evapotranspiration is highest. 

In the lower Coastal Plain, with the exception of the unconfined section of the surficial aquifer system, the aquifers are 

deeply buried and confined. In this area, climatic effects are 

greatly diminished, and fluctuations are due to changes in 

ground-water pumping. 

 Three methods to estimate baseflow were compared 

because a number of variables can affect baseflow including 

regulation of flows; physical properties of the basin such as 

vegetative cover, slope, area, shape, land use, soil thickness; 

and infiltration capacity as well as antecedent soil moisture 

and depth to ground water. The river or tributary at each 

streamflow gaging station selected for HYSEP analysis had 

negligible diversion or regulation, drainage area less than 

1,400 square miles, and at least 31 years of continuous record. 

For the 8 streamflow gaging stations selected for HYSEP, 

baseflow contributed from 39 to 74 percent of streamflow 

with a mean contribution of 58 percent. 

 During a high-precipitation year, baseflow accounted 

for 48 percent of total streamflow, 63 percent during an average-precipitation year, and 60 percent during a low-precipitation year. During dry periods, there is a reduction in runoff, 

and baseflow is the major contributor to streamflow. During 

drought conditions, there is less water available to recharge 

the aquifer and ground-water levels decline. 

 Baseflow estimates vary from the upper and lower parts 

of a basin. Mean annual baseflow in the upper Salkehatchie–

Savannah–Ogeechee River Basin during 1971–2001 ranges 

from 66 to 74 percent and is 54 percent in the lower basin. 

In the upper Altamaha–Satilla–St Marys River Basin, baseflow 

is about 57 percent of total streamflow; in the lower part of 

the basin, baseflow ranges from about 39 to 43 percent of total 

streamflow. In the lower part of the Suwannee River Basin, 

baseflow is about 56 percent of total streamflow. 

 Drought streamflow represents a quantitative estimate of 

minimum ground-water discharge to streams because during 

drought periods, streamflow is composed mostly of baseflow 

as estimated by HYSEP. During droughts, ground-water 

contribution to streamflow mostly is from the intermediate and 

regional flow systems. During the 1981 and 2000 droughts, 

baseflow contribution ranged from 0 to 24 percent of streamflow. This low contribution most likely is due to a lower 

ground-water levels during drought. 

 Linear-regression analysis was used to determine the 

flow duration that best estimates baseflow for streams in the 

area. Mean annual baseflow at 14 streamflow gaging stations 

in the study area for 1971–2001 were compared to the Q 1 to 

Q 99 flow durations at those stations using a statistical computer 

program; the best fit between HYSEP estimates and flow 

duration was at the Q 35 flow duration. Discharge data during 

1971–2001 for 14 streamflow gaging stations were analyzed 

to determine the streamflow index. Indices ranged from a low 

of 1.48 at the Brushy Creek station in the Salkehatchie–Savannah–Ogeechee River Basin to a high of 7.31 at Little Satilla 

River in the Altamaha–Satilla–St Marys River Basin. Generally, high indices are associated with steep slopes that are 

indicative of limited basin storage and dominant contribution

from runoff. Low indices are associated with flat slopes that 

are indicative of equal contribution of ground water and runoff. 

 Comparison of the three methods used to estimate 

baseflow shows that drought-streamflow conditions are a 

minimum estimate of mean-annual baseflow contributions. 

Because ground-water levels may decline during droughts, 

the amount of baseflow to streamflow correspondingly 

declines. The linear-regression analysis of streamflow duration overestimates baseflow when generalizing across a large 

basin because of variability in size and geology of basins. The 

HYSEP method of baseflow estimation most likely provides 

a reasonable estimate because of the stringent requirements 

placed on basin selection, which helps to reduce the number 

of errors in estimation. This comparison is illustrated in the 

baseflow estimation at Salkehatchie River (station 02175500). 

Part of the Salkehatchie River is in the upper Coastal Plain 

where there is a high degree of interconnection between the 

stream and the aquifer, resulting in a substantial contribution 

of ground water to streamflow. According to the methods 

used, linear-regression analysis estimates that baseflow is 

equivalent to the flow at Q35, which in this case is 102 percent of the mean annual streamflow. The drought-streamflow 

analysis estimates baseflow as 11 percent of total streamflow. 

This is an unreasonable estimation because part of the stream 

is in the upper Coastal Plain where there is a high degree of 

interconnectivity with the aquifer. The HYSEP method estimates baseflow as 69 percent of total streamflow. The same 

14 stations were used to make a comparison among the three 

methods used to estimate baseflow. 

Summary 37
38 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

 Overall, for the study area, mean annual baseflow during 

the 1981 and 2000 droughts ranged from 0 to 24 percent of 

mean annual total streamflow for the period 1971–2001 using 

drought-streamflow analysis. During 1971–2001, baseflow 

was estimated as ranging from 39–74 percent of streamflow 

using HYSEP and 65–102 percent using linear-regression 

analysis of flow duration. 

Selected References 

 Abu-Ruman, Malek, and Clarke, J.S., 2001, Preliminary 

simulation of pond-aquifer flow and water availability at a 

seepage pond near Brunswick, Georgia, in Proceedings of 

the 2001 Georgia Water Resources Conference held March 

26–27, 2001, at The University of Georgia, Kathryn J. 

Hatcher, ed ., Institute of Ecology, The University of Georgia, Athens, Georgia, p. 669–672. 

 Atkins, J.B., Journey, C.A., and Clarke, J.S., 1996, Estimation of ground-water discharge to streams in the central 

Savannah River basin of Georgia and South Carolina: U.S. 

Geological Survey Water-Resources Investigations Report 

96-4179, 36 p. 

 Bevans, H.E., 1986, Estimating stream-aquifer interactions in 

coal areas of eastern Kansas by using streamflow records, 

in Subitzky, Seymour, ed., Selected papers in the Hydrologic Sciences: U.S. Geological Survey Water-Supply Paper 

2290, p. 51–64. 

 Brooks, R., Clarke, J.S., and Faye, R.E., 1985, Hydrogeology 

of the Gordon aquifer system of east-central Georgia: 

Georgia Geologic Survey Information Circular 75, 41 p. 

 Carter, R.F., 1983, Effects of the drought of 1980–81 on 

streamflow and ground-water levels in Georgia: U.S. 

Geological Survey Water-Resources Investigations Report 

83-4158, 46 p. 

 Carter, R.F., and Putnam, S.A., 1977, Low-flow frequency of 

Georgia streams: U.S. Geological Survey Water-Resources 

Investigations Report 77-127, 104 p. 

 Carter, R.F., and Stiles, H.R., 1983, Average annual rainfall 

and runoff in Georgia, 1941–1970: Georgia Geologic Survey Hydrologic Atlas 9, 1 sheet. 

 Chowns, T.M., and Williams, C.T., 1983, Pre-Cretaceous 

rocks beneath the Georgia Coastal Plain — Regional 

implications, in Gohn, G.S., ed., Studies related to the 

Charleston, South Carolina earthquake of 1886 — Tectonics 

and seismisity: U.S. Geological Survey Professional Paper 

1313-L, p. L1–L42. 

 Clark, W.Z., Jr., and Zisa, A.C., 1976, Physiographic map of 

Georgia: Georgia Geologic Survey State map 4, 1 sheet. 

 Clarke, J.S., 2003, The Surficial and Brunswick aquifer systems-alternative ground-water resources for Coastal Georgia 

in Proceedings of the 2003 Georgia Water Resources 

Conference held April 23–24, 2003, at The University of 

Georgia, Kathryn J. Hatcher, ed., Institute of Ecology, The 

University of Georgia, Athens, Georgia, CD–ROM. 

 Clarke, J.S., Hacke, C.M., and Peck, M.F., 1990, Geology 

and ground-water resources of the coastal area of Georgia: 

Georgia Geologic Survey Bulletin 113, 106 p. 

 Clarke, J.S., and Krause R.E., 2000, Design, revision, and 

application of ground-water flow models for simulation of 

selected water-management scenarios in the coastal area of 

Georgia and adjacent parts of South Carolina and Florida: 

U.S. Geological Survey Water-Resources Investigations 

Report 00-4084, 93 p. 

 Clarke, J.S., and West, T.C., 1997, Ground-water levels, 

predevelopment ground-water flow, and stream-aquifer 

relations in the vicinity of the Savannah River Site, 

Georgia and South Carolina: U.S. Geological Survey 

Water-Resources Investigations Report 97-4197, 120 p. 

 Clarke, J.S., and West, T.C., 1998, Simulation of groundwater flow and stream-aquifer relations in the vicinity of the 

Savannah River Site, Georgia and South Carolina, Predevelopment through 1992: U.S. Geological Survey WaterResources Investigations Report 98-4062, 134 p. 

 Coffin, Robert, Grams, S.C., Leeth, D.C., and Peck, M.F., 

2002, Continuous ground-water-level data and periodic 

surface-water- and ground-water-quality data, Calendar 

Year 2002, in Water Resources Data-Georgia, 2002, U.S. 

Geological Survey Water-Data Report GA-02-2, CD–ROM. 

 Colquhoun, D.J., 1981, Variation in sea level on the South 

Carolina Coastal Plain, in Variation in sea level on the South 

Carolina Coastal Plain, Colquhoun, D.J., ed., International 

Geological Correlation Program, no. 61, p. 1–44. 

 Cressler, A.M., Blackburn, D.K., and McSwain, K.B., 2001, 

Ground-water conditions in Georgia, 2001: U.S. Geological 

Survey Open-File Report 01-220, 184 p. 

 Falls, W.F., Baum, J.S., Harrelson, L.G., Brown, L.H., and 

Jerden, James, L., Jr., 1997, Geology and hydrogeology of 

Cretaceous and Tertiary strata, and confinement in the vicinity of the U.S. Department of Energy Savannah River Site, 

South Carolina and Georgia: U.S. Geological Survey WaterResources Investigations Report 97-4245, 125 p. 

 Fanning, J.L., 1999, Water use in coastal Georgia by county 

and source, 1997; and water-use trends, 1980–97: Georgia 

Geologic Survey Information Circular 104, 37 p. 

 Fanning, J.L., 2003, Water use in Georgia by county for 2000 

and water-use trends for 1980–2000: Georgia Geologic 

Survey Information Circular 106, 176 p. 
 Faye, R.E., and Mayer, G.C., 1990, Ground-water flow and 

stream-aquifer relations in the northern Coastal Plain of 

Georgia and adjacent parts of Alabama and South Carolina: 

U.S. Geological Survey Water-Resources Investigations 

Report 88-4143, 83 p. 

 Faye, R.E., and Mayer, G.C., 1996, Simulation of groundwater flow in Southeastern Coastal Plain clastic aquifers in 

Georgia and adjacent parts of Alabama and South Carolina: 

U.S. Geological Survey Professional Paper 1410-F, 77 p. 

 Freeze, R.A., and Witherspoon, P.A., 1966, Theoretical analysis of regional groundwater flow –1. Analytical and numerical solutions to the mathematical model: Water Resources 

Research, v. 2, no., 4, p. 641–656. 

 Freeze, R.A., and Witherspoon, P.A., 1967, Theoretical analysis of regional groundwater flow – 2. Effect of water-table 

configuration and subsurface permeability variation: Water 

Resources Research, v. 3, no., 2, p. 623–634. 

 Freeze, R.A., and Witherspoon, P.A., 1968, Theoretical analysis of regional groundwater flow – 3. Quantitative interpretations: Water Resources Research, v. 4, no. 3, p. 581–590. 

 Gregg, D.O., and Zimmerman, E.A., 1974, Geologic and 

hydrologic control of chloride contamination in aquifers at 

Brunswick, Glynn County, Georgia: U.S. Geological Survey 

Water-Supply Paper 2029-D, 44 p. 

 Hale, T.W., Hopkins, E.H., and Carter, R.F., 1989, Effects 

of the 1986 drought on streamflow in Alabama, Georgia, 

North Carolina, South Carolina, Tennessee, and Virginia: 

U.S. Geological Survey Water-Resources Investigations 

Report 89-4212, 102 p. 

 Hickey, A.C., Kerestes, J.F., and McCallum, B.E., 2002, 

Continuous water-level, streamflow, water-quality data, 

and periodic water-quality data, Water Year 2002 in Water 

Resources Data — Georgia, 2002: U.S. Geological Survey 

Water-Data Report GA-02-1, CD–ROM. 

 Horton, R.E., 1933, The role of infiltration in the hydrologic 

cycle: Transactions of American Geophysical Union, v. 14, 

p. 446–460. 

 Huddlestun, P.F., 1988, A revision of the lithostratigraphic 

units of the Coastal Plain of Georgia, Miocene through 

Holocene: Georgia Geologic Survey Bulletin 104, 162 p. 

 Huddlestun, P.F., 1993, The Oligocene stratigraphic framework on the Coastal Plain of the Southeastern United States: 

Abstracts with Programs, Geological Society of America, 

v. 25, no. 4, p. 24. 

 Huddlestun, P.F., and Hetrick, J.H., 1986, Upper Eocene 

stratigraphy of central and eastern Georgia: Georgia 

Geologic Survey Bulletin 95, 78 p. 

 Huddlestun, P.F., and Summerour, J.H., 1996, The lithostratigraphic framework of the uppermost Cretaceous and lower 

Tertiary of eastern Burke County, Georgia: Georgia Geologic Survey Bulletin 127, 94 p. 

 Kellam, M.F., and Gorday, G.L., 1990, Hydrogeology of the 

Gulf Trough-Apalachicola Embayment area, Georgia: 

Georgia Geologic Survey Bulletin 94, 74 p. 

 Krause, R.E., and Clarke, J.S., 2001, Saltwater contamination 

of ground water at Brunswick, Georgia and Hilton Head 

Island, South Carolina, in Proceedings of the 2001 Georgia 

Water Resources Conference held March 26–27, 2001, at 

The University of Georgia, Kathryn J. Hatcher, ed., Institute 

of Ecology, The University of Georgia, Athens, Georgia, 

p. 756–759. 

 Krause, R.E., and Randolph, R.B, 1989, Hydrology of the 

Floridan aquifer system in southeast Georgia and adjacent 

Florida and South Carolina: U.S. Geological Survey 

Professional Paper 1403-D, 65 p. 

 Leeth, D.C., 1999, Hydrogeology of the Upper Floridan 

Aquifer in the vicinity of the Marine Corps Logistics Base 

near Albany, Georgia: U.S. Geological Survey WaterResources Investigations Report 98-4202, 49 p. 

 Leeth, D.C., Clarke, J.S., Craigg, S.D., and Wipperfurth, C.J., 

2003, Ground-water conditions and studies in Georgia, 

2001: U.S. Geological Survey Water-Resources Investigations Report 03-4032, 96 p. 

 Linsley, R.K., Kohler, M.A., and Paulhus, J.L.H., 1982, 

Hydrology for Engineers (3rd ed.): New York, McGrawHill, 508 p. 

 McCallum, B.E., Cressler, A.M., Blackburn, D.K., and 

McSwain, K.B., 2000, Water resources data, Georgia, 

2000 — Continuous ground-water level data, and periodic 

surface-water- and ground-water-quality data, Calendar 

Year 2000: U.S. Geological Survey Water-Data Report 

GA-00-2, CD–ROM. 

 McCallum, B.E., and Hickey, A.C., 2000, Water resources 

data, Georgia, 2000 — Continuous water-level, streamflow, 

water-quality data, and periodic water-quality data, Water 

Year 2000: U.S. Geological Survey Water-Data Report 

GA-00-1, CD–ROM. 

 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., 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. 

Selected References 39
40 Evaluation of Ground-Water Contribution to Streamflow in Coastal Georgia and Adjacent Parts of Florida and South Carolina

 National Oceanic and Atmospheric Administration, 2002, 

Monthly station normals of temperature, precipitation, and 

heating and cooling degree days 1971–2000: Asheville, 

N.C., no. 81, 28 p. 

 Peck, M.F., Clarke, J.S., Abu-Ruman, Malek, and Laitta, M.T., 

2001, Hydrogeologic conditions at two seepage ponds in the 

coastal area of Georgia, August 1999 to February 2001, in 

Proceedings of the 2001 Georgia Water Resources Conference held March 26–27, 2001, at The University of Georgia, 

Kathryn J. Hatcher, ed., Institute of Ecology, The University 

of Georgia, Athens, Georgia, p. 768–771. 

 Peck, M.F., Clarke, J.S., Ransom, Camille, III, and 

Richards, C.J., 1999, Potentiometric surface of the Upper 

Floridan aquifer in Georgia and adjacent parts of Alabama, 

Florida, and South Carolina, May 1998; and water-level 

trends in Georgia, 1990–1998: Georgia Geologic Survey 

Hydrologic Atlas 22, 1 sheet. 

 Pettyjohn, W.A., and Henning, Roger, 1979, Preliminary 

estimate of ground-water recharge rates, related streamflow, 

and water quality in Ohio: Ohio State University, Water 

Resources Center, 321 p. 

 Price, Van, Jr., Fallaw, W.C., and McKinney, J.B., 1991, 

Geologic setting of the new production reactor reference 

site within the Savannah River Site (U): Aiken, S.C., 

Westinghouse Savannah River Company, report no. 

WSRC-RP-91-96, ESH-EMS-90171, 80 p. 

 Prowell, D.C., and O’Conner, B.J., 1978, Belair fault 

zone — Evidence of Tertiary fault displacement in eastern 

Georgia: Geology, v. 6, no. 11, p. 681–684. 

 Prowell, D.C., Christopher, R.A., Edwards, L.E., Bybell, L.M., 

and Gill, H.E., 1985, Geologic section of the updip Coastal 

Plain from central Georgia to western South Carolina: U.S. 

Geological Survey Miscellaneous Field Studies Map, 

MF-1737, 10 p. 

 Randolph, R.B., Pernik, L.M., and Garza, Regina, 1991, 

Water-supply potential of the Floridan aquifer system in 

the Coastal area of Georgia — A digital model approach: 

Georgia Geologic Survey Bulletin 116, 30 p. 

 Reynolds, R.J., 1982, Ground-water contributions of streams 

on Long Island, New York: U.S. Geological Survey WaterResources Investigations Report 81-48, 33 p. 

 Reynolds, R.J., 1969, Mean streamflows from discharge 

measurements: International Association of Scientific 

Hydrology Bulletin, v. XIV, no. 4, p. 95–110. 

 Riggs, H.C., 1963, The base-flow recession curve as an 

indicator of ground water: International Association of 

Scientific Hydrology Publication 63, p. 353–363. 

 Rutledge, A.T., 1993, Computer programs for describing the 

recession of ground-water discharge and for estimating 

mean ground-water recharge and discharge from streamflow 

records: U.S. Geological Survey Water-Resources Investigations Report 93-4121, 45 p. 

 Searcy, J.K., 1959, Flow-duration curves: U.S. Geological 

Survey Water-Supply Paper 1542-A, 33 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, 67 p. 

 Southeast Regional Climate Center, accessed October 10, 

2002, at http://cirrus.dnr.state.sc.us/cgi-bin/sercc/cliMAIN.

pl?sc044 8. 

 Stricker, V.A., 1983, Baseflow of streams in the outcrop areas 

of southeastern sand aquifer: South Carolina, Georgia, 

Alabama, and Mississippi: U.S. Geological Survey WaterResources Investigations Report 83-4106, 17 p. 

 Thomson, M.T., and Carter, R.F., 1955, Surface water 

resources of Georgia during the drought of 1954: Georgia 

Department of Mines, Mining, and Geology Information 

Circular 17, 79 p. 

 Toth, J.A., 1962, A theory of groundwater motion in small 

drainage basins in central Alberta, Canada: Journal of 

Geophysical Research, v. 67, no. 11, p. 4375–4387. 

 Toth, J.A., 1963, A theoretical analysis of groundwater flow 

in small drainage basins: Journal of Geophysical Research, 

v. 68, no. 16, p. 4795–4812. 

 Vincent, H.R., 1982, Geohydrology of the Jacksonian aquifer 

in central and east-central Georgia: Georgia Geologic 

Survey Hydrologic Atlas 8, 3 sheets. 

 Weems, R.E., and Edwards, L.E., 2001, Geology of Oligocene, Miocene, and younger deposits in the coastal area of 

Georgia: Georgia Geologic Survey Bulletin 131, 124 p. 
Prepared by U.S. Geological Survey, Water Resources 

Discipline, Georgia District, Atlanta, Georgia.

Figure design and production by Bonnie J. Turcott and 

Caryl J. Wipperfurth .

Editing and page layout by Patricia L. Nobles.