Stream-aquifer relations in the coastal area of Georgia and adjacent parts of Florida and South Carolina [2004]

~
~ ----

Stream-Aquifer Relations in the

~

Coastal Area of Georgia and Adjacent

Parts of Florida and South Carolina

by
Sherlyn Priest U.S. Geological Survey

Upper Coastal Pla1n I rll lt

Lower Coastal Pla.n

-
Confined aquifers

-

Ro.Qionott~o

w s ystv"tn_...,.

Wetlands

GEORGIA DEPARTMENT OF NATURAL RESOURCES E NVIRONMENTAL PROTECTION DIVISION GEORGIA GEOLOGIC SURVEY
Prepared in cooperation ll'ith tlw
U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY
INFORMATION CIRCULAR 108

Stream-Aquifer Relations in the Coastal Area of Georgia and Adjacent Parts of
Florida and South Carolina
B y Sherlyn Priest U.S. Geological Survey
GEORGI A DEPARTMENT OF NAT URAL RESOU RCES Lonice C. Barrett. Commissioner
ENV IRONMENTAL PROTECTION DIVIS ION Carol Couch, Director
G EORGIA GEOLOGIC SURV EY William H. McLemore, State Geologist
Prepared as part of the Coastal Georg ia Sound Science lnitiative
In cooperatio n with the U.S . Department of the Interior
U.S. Geological Survey
Atlama. Georgia 2004
lNFORMATJON CIRCULAR 108

iii
Contents
Abstract ... . ....... . ..... ................ ..... .. ... ..... ...... ........... .... .... ..... ........ ...... ...... . 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 ..... ..... ... .. . ..... .. .. ........ ...... .... ....... ..... ...... ... .... ... ... .... ....... ..... 10 Surface Water ... ...... .. .. ...... .. . ... ............ ... ......... .......... ... ... ............ ... . 10 Ground Water . .......... ........ ... .... .. .. .. .. .... ............ .. .. .. .. ... ...... .. .... ........ 15
Hydrogeologic Units ...... ......... ......... ... ...... ................... .. ............ 15 Upper Coastal Plain . .. ... .. ..... .. ... .... ......... ........ ......... .. .. ........... 15 Lower Coastal Plain .... ........... ............... ..... .... ......... ... ..... .. .. ... 16
Ground-Water Levels . ....... .. .. .......... ........ .... ........ .... ..... ..... .. .. ...... 16 long -Term Fluctuations and Trends ... . .. ............. .............. ...... .... ...... .. ... ...... 17
Salkehatchie- Savannah- Ogeechee River Basin .... ... .. .... ............... .. ... ...... 17 Altamaha- Satilla- St Marys River Basin .... .... .... . ..... ........ ... ...... ........ .. .. ... . 18 Suwan nee River Ba sin ....... ... ..... ... .. ... .. .. .... ........... ............... ..... ...... . 21 Ground-Water Contribution to Streamflow ... .... ..... ........... .......... . ........ .... .... .... 21 Hydrograph Separation .......... ... .... ... ............. ................ ... .. .... ...... ..... 24 Drought Streamflow ... .... ... .. .... ..... .. ... .. ... ...... ...... ..... .................. .... .. 25 linea r-Regression Analysis of Streamflow Duration .... .... ..... .. .... .......... ... .... 26 Compa rison of Results........ .. ... .............. .... .... .. ... ... ........... ..... .......... ... 34 Summary . ..... .... .. .... ... .... . ... ........ ... . ... .. .... .. .. ...... ... ... ... ... ..... ... .... ... ......... ..... 36 Selected References . ... ...... ............ .................... .................. ... .... .. ........... .. .. 38

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 ....... ........ 11
6. Graphs showing mean monthly precipitation at selected National Weather Service stations in the Coastal Plain area of Georgia and South Carolina. 1971- 2001 ........ .. .. ... ...... ... ...... ... ... .............................. ...... ............ .. . 12
7. Map showing mean annual runoff for the Coastal Plain of Georgia. 1941- 70 ......... 13 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 ................................................. ... ...... .. 14
9-14. Graphs Showing9. 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 ................. ........ ............. ..... ... ........ 15 10. Daily water-level measurements in wells 35P094 and 360008, Chatham County; and daily rainfall at National Weather Service station, Savannah Municipal Airport, Chatham County, Georgia, 2001 ... .. ... ... .. .. ... ............. .. .... .. .... ..... ... 17 11 . Daily mean water levels in the surficial, upper Brunswick, and Upper Floridan aquifers at the Gardi site, Wayne County, Georgia, 1983-2001 ........................... 18 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 ......................... ................ ............ .................................. 19 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 ........................... 20 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 ........................ 23 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 ............ .. ....... ..... ........................ . .................................... 25 17. Comparison of drought streamflow between two adjacent streamflow gaging stations in the Salkehatchie-Savannah-Ogeechee River Basin ........................ 26

v

18-20. 18.
19.
20.

Maps ShowingSelected streamflow gaging stations monitored during the 1954 drought and corresponding intermediate unit-area discharge ......................... ....... ... .... 30
Selected streamflow gaging stations monitored during the 1981 drought and corresponding intermediate unit-area discharge ... .... ........... ... ..... . ... .. ....... 31
Selected streamflow gaging stations monitored during the 2000 drought and corresponding intermediate unit-area discharge ........... .. ........ .................. 32

21- 26. 21. 22.
23.
24.
25. 26.

Graphs Showing-
Comparison of two flow-duration curve types: gentle curve along Brier Creek (station 02198000) and a steep curve along the Alapaha River (station 02317500) ... 33
Duration of mean daily streamflow for Brushy Creek (station 02197600) near Wrens, Georgia, and Brier Creek (station 02198000) at Millhaven, Georgia,
1971- 2001 ................. ... 33 Duration of mean daily streamflow for Canoochee River (station 02203000) near Claxton, Georgia, in the upper Salkehatchie-Savannah- Ogeechee River Basin, 1971- 2001 .... ... ........... ........ ... ......................... ........... .... ....... ..... ..... . 34
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 ................................. 34
Duration of mean daily streamflow for Alapaha River (station 02317500) at Statenville, Georgia. in the Suwannee River Basin, 1971-2001 ........................ 35 Regression of~ versus mean annual baseflow for the 8 and 14 streamflow gaging stations selected for hydrograph-separation technique. Georgia and South Carolina, 1971- 2001 .................................................................. 35

Tables

1. Selected streamflow gaging and partial-record stations in SalkehatchieSavannah- 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 ................................................... 24

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 ... ... . ......... .. ... .. .. .. . .. ... ............ .. .... ..... .. .. ...... ... ... ...... .... .. 27

5. Estimated ground-water discharge to selected streams in the SalkehatchieSavannah- Ogeechee. Altamaha-Satilla-St Marys, and Suwannee River Basins during the 1954, 1981, and 2000 droughts .......................................... 29

6. Flow-duration curve index ll~/~)11) and curve shape for selected streams in the Salkehatchie- Savannah- Ogeechee, Altamaha- Satilla-St Marys, and Suwannee River Basins, 1971 - 2001 ..................................................................... 33

7. Coefficient of determination (r2) and residual standard of error for flow durations

~

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

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selected in the Salkehatchie-Savannah-Ogeechee, Altamaha-Satilla-St Marys, and Suwannee River Basins. 1971- 2001 ................................................... 35



8. Comparison of three methods used to calculate baseflow for selected streamflow gaging stations in the Salkehatchie- Savannah- Ogeechee, Altamaha- SatillaSt 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 (1.8xC)+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). Historica l data collected and stored as North American Datum of 1927 (NAD 27) have been converted to NAD 83 for use in this report.

STREAM-AQUIFER RELATIONS IN THE COASTAL AREA OF GEORGIA AND ADJACENT PARTS OF FLORIDA AND SOUTH CAROLINA
By Sherlyn Priest

Abstract
Str~am-aquifcr relations in the coastal area of Georgia and adjacent parL~ of Florida and South Caroli na were evaluated as part of the Coastal Georgia Sound Science lnitjative. 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 J954, 1981. and 2000 was analy1.ed for minimum ground-water contribution to str~amflow. Hydrograph separation was used to estimate basefl ow at eight streamflow gaging stations during the 31 -year period 197 I- 200 I. Six additional streamllow gaging stations were evaluated using linear-reg r~ss ion analysis of flow duration to determin~ mean annual baseflow. The study area centers on three major river systems- the SalkehatchieSavannah- Ogeechee. Altamaha- S:uilla-St Marys. and Suwann~e-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 arc 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 10 74 perccnL of mean annual streamflow, with a mean contribution of 58 percent for the period 1971 - 200 I. In a wet year ( 1997). baseflow composed from 33 to 70 percent of mean annual streamflow. Drought-streamflow analysis estimated bascflow contribution to streamflow ranged from 0 to 24 percent of mean annual streamflow. Linear-regression analysis
of strcnmflow duration estimated the Q3~ (flow that is equaled
or exceeded 35 percem of the time) as the most reasonable

estimate of bascflow. The Q35, when compared to mean annual
streamflow. estimated a bascflow contribution ranging from 65 to 102 percent of streamflow. The Q,5 estimate tends to overestimate basetlow as evidenced by the bascflow contribution greater than I00 percent. Ground-water contributions to streamflow arc greatest during winter when evapotranspiration is low, and least during summer when evapotranspiration is high. Bascflow accounted for a larger percentage of streamflow at gaging stations in the Salkchatchie- SavannahOgeechec River Basin than in the other two basi ns. This difference is due largely to the availability of d~tta. 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, incrcused 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 sourc~.: of water in the 24-county coastal Georgia area is the Upper Floridan aquifer, which underlies most of the Coastal Plain o f 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, 200 I).
The Coastal Georgia Sound Science Initiative is a program of scientific and feasibility studies to support development of Georgia Environmental Protection Division's (GaEPD) final strategy to protect the Upper Floridan aquifer

2 Stream-aquifer relations in the coastal area of Georgia and adjacent parts of Florida and South Carolina

fro m salt wntcr contamination. In support of the Coastal Gcorgia Sound Science lnttiativc. the U.S . Geological Survey (USGS )- in cooperation with GaEPD- i:. conducting ~tutlies to charactertt.c.: :lllcl monitor ground-watcr no"'' and saltwatcr contarnin:Hio n: evaluate possible altcrnativc sources of water to the Upper Florida n aqu ifer ; simu late ground-water fl ow and movement of salt water in response to vario us water-manageme nt approaches; and monitor changes in the hydrologit: syste m. The study area incl udes southca<;t Georgia and adjacent parts of nort heast Florida and <.,outhv.cst South Carolina (fig.. I ).
/\ <:. pan of the Coastal Georgta Sound Science Initiati ve, ground-wntcr discharge to stream!> was estimated for selected streams and rivers in a 67-c:ounty area of south ea~> t Georgia, nonhcast Florid a. and south west Sout h Carolina (55 count ies in Gcorgia, 5 cou nti e~ in f-lorida, and 7 counties in South Carolina). Results prcsentc:d hcn :in arc being used to calibrate a rcg ionnl ground-water flow m odel to evaluate ground -water fl ow and stream-aquifer relations of the Upper Floridan aq ui fer.
Purpose and Scope
This re pon describes stream-aquifer re lations in the coastal area o f Georgia and adjacent parts o f f-lorida and South Caro lina by estimating ground-water discharge to stre;uns under a variety of c limatic condit ions. These estimates were made using hydrograph-sepuration techniques. droughtstreamn ow measurements, and linear-regressio n analysis o f stream n ow duration. The esti mated ground-water discharge is being used to calibrate a regio nal ground-wate r now model to evaluate ground-water n ow and stream-aquifer relations o f the Upper Floridan aqui fer.
Co nti nu ou s-d isch~trgc records from e ight streamfl ow gaging sttllions (stations) were used to estim ate basefl ow using hydrograph-separaLio n techniques for the 3 1-ycar period from 197 1 to 200 I: and continuous-discharge records from an add itional six stations were used to estimalC baseflow using linear-regression analysis o f streamn ow duration for the same period. H istorical streamflow data collected from 22 stations d uring the 1954 drought. 7 stations du ring the 198 1 dro ught, and 19 stations d uring the 2000 drought were used to evaluate intermediate basin ground-water discharge d uring dry periods (ta ble 1). Precipitat ion data from I I National Weather Service ( NWS) stations ( National Oceanic and Atmospheric Administration, 2002) and g round-water levels from 9 USG S wells (table 2) were evaluated for long-term tre nds ( 197 1- 200 I).
Several tributaries to major rivers -Altamaha, O geechee, Salkehatchic , Satilla. Sava nnah, St Marys, and Suwannee drain the stud y 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 measure ments were taken at 18 continuo us-record and partial-record stations from Jul y 3 1 through August 2, 2000. and stream-d ischarge measurements from 24 contin uousrecord stations were used to evaluate surface-water cond itions

( fig.. l and tabk l ). M easu reme nt ~ from :!4 JKHlial record st:.ttionl-o and contHluous-rec.:ord -;tauons wen.: colle<:ll.:d for 195..J and from 12 partial -record .;tat ions and conttnu ou~ record station ~ for 198 1. Data were collected from 62 cominuou~- reconl and part ial-record l>tations on t rihutaric~ tncluding synoptic mc::~surernents. Unless ()thc rwise ind icated. the primary source.: o f data used in thi!'> report is the USGS National Water Information Syste m (NW ISl (<tt http://wml'l'dma.usgs. gmlgn!nll'isln wis). All da ta prcscnted are hy calendar year.
Description of Study Area
or T hc G aE PD dclines the coastal area Georg ia to include
the 6 coastal counties a nd adj acent 18 couotie!-. a n a rea of about 12.240 square m iles (mi2) (fig. I). To account for natural hydrologic boundaries used for model s unulation. the study area hac; hecn expanded to 32.661 mi=and tnc:ludes the 24 coastal counties and outlying 4 3 counties ex tending into northeast Florida and south west South Caro lina.
The study area is located in the nort hern part o f the southeastern CoasUtl Plain o f Georgia, South Carolina, and f-lorida (fi g. I). Coastal Plain geology consists o f layers o f sand. clay. limestone. and dolomite that range in age from Late Cretaceous through Holocene. T he nort hern limit of these strata and the contact between Coastal Plain sediments and Piedmont c rystalline rocks correspond approximately to the Fall Line (C larke and Z isa, 1976). a physiogmphic boundary between the Piedmont and Coastal Plain. T he various stra ta dip and progressively thicken from the Fall Line to the southeast. The sed imentary sequence unconformably overlies Paleozoic to Mesozoic igneous. metamorphic, and sedimentary rocks (Chowns and Williams, 1983).
Coastal Plain sediments consist of fluvi al, deltaic, and rmtrinc coastal and sheIf deposits (Prowell and others, 1985). Numerous marine transgressions and regressions have deposited. re moved , and redistributed sediments in the study area and the vicinity (Co lquhoun. 198 1). Can er and Putnam ( 1977) d ivided the Coastal Plain physiographic province into upper and lower Coastal Plain. In the upper Coastal Plain in Richmond County, G a., sediments predominantly consist of nonmarine siliciclastic sediments. Marine sediments arc more abundant in the lower Coastal Plain and inc lude carbonateshe! f deposits in some Tertiary strata (Atkins and others. 1996).
The principal source o f gro und wate r for all uses in the coastal area is the A oridan ~quifer sys tem, consisting o f the Upper and Lower Floridan aquifers (Miller, 1986: Krause and Ra ndolph. 1989). Seco ndary source of water inc lude the surlic ial and Brunswic k aquifer systems (Clarke , 2003), consisting o f sand of Miocene to Holocene age . A general ized correlation chan of geologic and hydrologic uni ts is show n in figure 2.
Lantluse primarily is urban in industrial areas and c ities.
Outside o f these areas, land usc is a mix of forest. wetlands,
row crops, and pasture. Altitude ranges from sea level along the coast to about 400 feet (ft) ncar tl1e Fall Line.

Boundary between upper and lower Coastal Plain
~

Introduction 3

30

60 MILES

30

60 KILOMETERS

Base from U.S. Geoklgteal Survey 1: IOO,OOOscale dgtal data

EXPLANATION

River Basin

Site and name or number

Salkehatchie- Savannah-Ogeechee Streamflow gaging station

Allamaha-Satilla-St Marys Suwann ee

Well
0 NWS station

Figure 1. location of study area, streamflow gaging stations, wells, and National Weather Service (NWS) stations.

4 Stream-a quifer re lations in the coastal area of Georgia a nd adjacent parts of Florida a nd South Carolina

Table 1. Selected streamflow gaging and partial-record stations in Salkehatchie- Savannah- Ogeechee. Altamaha- SatillaSt Marys, and Suwannee River Basins.
1. pan tal rccortl ''lion. . dala nol a\ ail;tblc: mi . 'qu;Jrc mil~: do. diuoJ

Station number

Station name

Drainage area (mi1}

County

Basin

Salkehatche- Savannah-Ogeechee River Basin

02175500 Salkchatchic River ncar Miley. S.C. 102176500 Coo~aw h:u ch ic River n~.:ar !Iampton. S.C. 02197200~ McBean Creek (Ga. IJwy 56) al McBean. Ga. 02 1973444"' Beaverdam Creek a1 River Rtl ncar Girard, Ga. 02 1974 15 LowcrTitrcc Run~ a1 Manin, S.C. 02197500 Savannah River at Bunons Ferry Bridge.:. Millhaven. Ga. 02197590* Brw.hy Creek at Wrens, Ga. 02197600 Bnshy Creek ncar Wrens, Ga. 02197830* Brier Creek ncar Waynesboro. Ga. 02197980* Brier Creek (Ga. IJwy 23) ncar Sardis, Ga. 02198000 Brier Crock at Millhaven. Ga. 02198060* Brier Creek at US 301 ncar Sylvania. Ga. 02198100 Beaverdam Creek ncar Sardis, Ga. 02198120* Beaverdam Creek a1 llilllonia. Ga. 02198170* Beaverdam Creek ncar Sylvania. Ga. 02198280* Beaverdam Creek ncar Sylvania. Ga. 02 198500 S:wannah River ncar Clyo. Ga. 02200410... Duhart Creek (SR 80) at Stapleton. Ga. 02200440* Rocky Comfon Creek (US 221) at Louisville. Ga. 02200720* Big Creek (Penns Bridge Rd) ncar Wrens, Ga. 02200810"' Big Creek above Louisville. Ga. 02200900... Big Creek ncar Loui:;vil lc. Ga. 02201000 Williamson Swnmp Creek at Davisboro. Ga. 02201070* Williamson Swamp Creek at Banow, Ga. 02201150* Williamson Swamp Creek a1 Wadley. Ga. 02201270* Barkcamp Creek (SR 17) near Midville, Ga. 02201300"' Chow Mill Creek ncar Herndon. Ga. 02201350* Buckhead Creek ncar Waynesboro. Ga. 02201360* Rocky Creek at SR 24 ncar Waynesboro. Ga. 02201365* Rocky Creek ncar Waynesboro. Ga. 02201430* Buckhead Creek at Millen. Ga. 02202210* Ogecchec Creek ncar Sylvania, Ga. 02202240"' Ogceehee Creek ncar Oliver, Ga. 02202500 Ogccchcc River ncar Eden. Ga. 02202600 Black Creek neur Blitchton. Ga. 02202969* Cedar Creek (SR 129) at Claxton. Ga. 02203000 Canoochcc River ncar Claxton. Ga.

34 1.00 203 71.4 23.3 109 R.650
9.4 28 473 579 646 669 30.8 85.3 116 143 9.850 3.17 286 8.07 56.9 95.8 109 185 233 31.7 23 64 31.7 34.8 272 14 141 2.650 232
555

Hampton do.
Burke do.
All end alt.: Allcndalc/Scrcvcn
Jdferson do.
Burke do.
Screven do.
Burke/Jenkins Screven do. do. Effingham Jefferson do. do. do. do.
Washington Jeffers on
do. Burke Jenkins Burke
do. Burke Jenkins Screven
do. Effinghum!Bryan
Bryan Evans
do.

SalkchaLchic do.
Savannah do.
do.
do.
cit).
do. do. do. do. do. do. do. do. do. do. Ogccchcc do. do. do.
do.
do. do. do. do. do. do. do. Ogccchcc do. do. do. do. do. do. do.

==~
~ ~ ~
; =~
;
.!~.1.
.-."--..-"..
......~~-~ .......



Introduction 5

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

j . parria l-rcwrd st:tion; - . d:11:1 not avai lable: mi ' . squ:m: mik: do.. tlino ]

Station number

Station name

Drainage area (mi1)

County

Basin

----
02215100 022 15500 02216180 0222324R 02223500 02224000 02225000 02225315* 02225360* 02225395* 02225405* 02225420* 02225480* 02225500 02225850"' 02226000 02226100 02226500 02227000 02227500 02228000 02229000 0223 1280

Altamaha- Satilla- St Marys River Basin

Tucsa;vhatchcc Creek ncar Hawkinsville, Ga.

163.00

Oemulgee River at Lumber City, Ga.

5.180

Turnpike Creek ncar McRae. Ga. Oconee River near Oconee. Ga.

49.2 3,770

Oconee River at Dublin. Ga.

4.WO

Rocky Creek ncar Dudley. Ga. Altamaha River ncar Baxky, Ga.

62.9 11 ,600

Jacks Creek ncar Wesley. Ga.

8.63

Pendleton Creek ncar Normantown. Ga.

101

Swift Creek (SR 130) ncar Vidalia, Ga.

36

Swift Creek (US 1) ncar Lyons, G<t

46.3

Swift Creek (SR 152) ncar Lyons, Ga. Ohoopcc River (US 280) ncar Reidsville. Ga.

55.6 l,Q70

Ohoopce River ncar Reidsville. Gt1. Bear-ds Creek ncar Glennville, Ga. Altamaha River at Doctortown, Ga. Pcnholoway Creek ncar Jesup. Ga. Satilla River near Waycross. Ga. Hurricane Creek near Alma, Ga.

1.110 74.4
13.600 209
1.190 139

Little Satilia River near Offerman. Ga. Satilia River at Atkinson. Ga. Middle Prong St Marys River at Taylor. Fla. Thomas Creek ncar Crawford. Fla.

646 2.790
125 29.9

Suwannee River Basin

Pulaski Tel fair/Jeff Davis
do. Wilkins/Washington
l.:wrcn s do.
Toombs/Appling Emanual
ToombsiEmanual Toombs do. do.
Tattnall{foornbs Tmtnall
Long!Tattnall Long/Wayne
Wayne Ware Bacon Wayne/Pierce Brantley Baker Duvai/Nassau

Altarnaha do . do. do.
do.
dt1.
do.
do. do. do. do. do. do. do. do. do. do. Satilla do. Satilla do. St Marys do.

023 14500 Suwannee River at Fargo. Ga.

1.260

Clinch

Suwannee

023 17500 Alapaha River at Statenville. Ga.

1.390

Echols

do.

'For the purpose of this ~tudy. data from station 02716500 in the Broad- St Helen River Basin were included in the Salkchatchic-Savann~h-Ogccchec
River Basin.

Previous Studies

Coastal Plain of Georgia and adjacent South Carolina and

Alabama. Atkins and others (I 996) estimated ground-water

Hydrogeologic investigations of ground water in coastal contribution to streams in the central Savannah River Basin

Georgia include Miller ( 1986). who described the hydrogeo- using hydrograph-separation techniques and a drought-

logic framework of the Floridan aquifer system in Georgia,

streamflow analysis. Clarke and West ( 1997. 1998) simulated

Florida, South Carolina, and Alabama; Krause and Randolph ground-water flow and stream-aquifer relations near the

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

Savannah River Site in Georgia and South Carolina. Peck

aquifer system in southeast Georgia and adjacent parts of

and others (200 I) evaluated hydrogeologic conditions and



South Caroli na and Florida; and Clarke and others ( 1990). who described the geology and ground-water resources of 13 counties in the present study area.

pond-aquifer relations at two test sites in coastal Georgia. Abu-Ruman and Clarke (200 1) described preliminary s imulations of pond-aquifer interaction at a test site near Brunswick,



Repons on stream-aquifer re lations in the study area include Faye and Mayer ( 1990), who described streamaquifer relations and ground-water flow in the northern

Georgia. Mosner (2002) described stream-aquifer relations and the potentiometric surface of the Upper Floridan aquifer in southwest Georgia.

6 Stream-aquifer relations in the coastal area of Georgia and adjacent parts of Florida and South Carolina

Table 2. Well construction data for selected wells used in Georgia.
- (h. font . .tltituclc in fnot hclnw No11h Amcncan Vcntc:tl Datum 1988: ,crccncd or \lpcncd mtcn.tlmlcct hclo\\ land \Urtacc. .d.:grct:;. minute. . wcclntll

Well identification
number (fig. 1)

Well name

ISK0-19 US Cicnlogtc:tl Sun'c). tC\t \\ell 1

191:()()1) C'tt) t>l V.tldthta

:? ITOO l D:umy llo!!:ut

32Ul 15 (~cm( i :t (icnlo!!i..: Sut vey, Gardi, tc't well I

121.01(> (icmri:tGeologic Sttrvcy. Garda. test well :!

:12UJI 7 CicMrin (icologie Survey. Ganli. te't well 3

32R003 Bullo.:h Sou th. test well 2

35 P094 Umvcr~ity t)( Gcorgi:t. Bamboo Fann

36Q008 L:aync-Atl:tntic Company

County
Tift
l.owndc,; Lauren'
W:~ yne
Wayne
Wayne
Bulloch Chatham Chatham

Latitude Longitude

31"27'12" 8:!'59'.13"

30"-19'5 1" l!:l 16'58" 3227'06" K:I '0'\'28" 31 32'52" !! I "1:1'.16"

3132'52" !11"..13'3(,"

3132'52" !n"-13'36"

3212'4()" 3159'50" 3:!005'30"

81 -1 I'15" 811Cl'12" 11 1osso

Altitude of land surface
datum
(It)
:no oo
217 251) 7-1
74
7-1
120 18.7 9.9 1

Top of

Bottom of

screened or screened or open interval open interval

Aquifer

(It)

- -(-It)

270

620 \,;ppcr Aond.tn

200

'\.:2 Upper Fluriuan

89

123 Upper f'lolidan

5..15

750 Up(X'r Huriclan

320

340 Uppa IIrun\\\ld.

200

215 Surficial

134

155 :\lloccnc

15

15 Surficaal

250

406 Upper Aoridan

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 Georgiu and adjacent pans of Alabama. Florida. and South Carolina, and wmer-level trends in Georgia during 1990-98. Fanning ( 1999; 2003) described water usc in coastal Georgia during 1980- 97 and 1980- 2000. respectively.
Streamflow conditions arc 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) reponed effects of drought on streamflow for the 1954 drought: Carter ( 1983) for the 1980-8 1drought; 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 ,

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 swdy area. This i an informal division done solely fnr comparison in this report.
Litermure review provided infom1ation necessary to describe a co nceptual model of stream-aquifer relations. Much of the conceptual model is based on results of previow. 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 func1ion as hydraulic drains for ground-water flow ; and that during severe droughts. most of the dischnrge 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 (basenow). 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 lincar-regression analysis of streamflow duration. Baseflow was estimated at eight stations using HYSEP (SiotO 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.

Introduction 7

~

E

Lower c oastal p la.m1

Cll

iii

- - >
(/)
'---

Geologic unit='

Hydrogeologic unit

Savannah

Brunsw1ck

PostM1occno

I

T
(i;
aa.. :::>

Undi fferentiated

I

I Ebenezer Formation

Surficial aqu1fer

-

~-

Confining unit

Q)

r Miocene

'0

"0

~

~ '
J

~

Oligocene

I
Coosawhatch1e Formation
-
Marks Head Formation Parachucla Formation
Tiger Leap Formation
-Lazaretto Creek Formation
Suwannee Limestone

Iupper Brunswick
aqUIIer

Confining unit

Lower Brunswick

aquifer Conhnmg un11

-

Upper Floridan aquifer

(i;
aa.. :::>

Q)

Eocene

'0
"0

~

-

Ocala Limestone Avon Park Formation

Confining un1t
Lower Floridan aqu1fer

g(i;

Oldsmar Formation

...J

Conhn1ng unit

c Upper oastal Plain3

Geologic unit

Hydrogeologic unit

Und1ffcrcnhated
Upper Three Runs aqu1fer

Barnwell Group

Santee L1mestone Confining umt

Congaree Format1on

Gordon aquifer

Paleocene

Cedar Keys Formation

Confining unit

Fernandina permeable
zone

Upper Cretaceous

Undifferentiated

IIModlfied from RMdolph and others. 1991: Clarke and Krause. 2000. 21Modl tiecllrom Randolph and others 1991: Weems and Edwards. 2001 . 31Modifled from Falls and otMrs. 1997. 4'1n local areas includes Millers Pond aQuifer.

Snapp Formation Ellenton Formation Confining unir (undifferentiated)

Steel Creek Formation
Black Creek Group (undi lferenllated)

Upper Dublin aqUifer

Figure 2. Geologic and hydrogeologic units of the upper and lower Coastal Plain, Georgia.

HYSEP uses rhree methods to separate ba<>eflow: fixed inrerval, sliding imerval, and l ocal minimum (fig. 3). Each merhod uses a different algorithm 10 separate baseflow systemati cally from runoff by connccring low points on the streamflow
h ydrograph (Sioto and Crouse. 1996). The duration of surface
runoff is calculated from rhc empirical relation:
N=Ao.2,
where N is the number of days for the cessation of runoff. and
A is the tlrainage area o f the basin (Linsley and others. 1982). All three mcrhods usc un algorithm based on the interval 2N*, which is the odd integer between 3 and I I that is nearest to

2N ( Pettyjohn and H enning. I 979). The three m ethods as described by Sl oto and Crouse ( I 996) are:
Thefixed-imervalmethod assigns lhe lowes! discharge in each 2N* interval to all days in that interval starting
with rhc first day of the period of record.
The sliding-inlen,al method finds the lowcsr discharge in one-half the interval minus I day f0.5(2N*- 1) days]
prior to and after the day being considered and assigns the discharge value to that day: overlapping of intervals is allowed.

8 Stream-aquifer relat ions in the coastal area of Georgia and adjacent parts of Florida and South Carolina

Th~.: local-minimum m ethod c hecks each day to determine whether the d~charge is the lowest di scharg~.: in one-half the uHcrvalminus I day !0.5(2 * - I) d~lys): overlapping of intervals i:-. not allowed.
Mosner (2002) compared the results of the three metlux:l:. using four ba-;ins in -;nuthwcM Georgia and found that the fixed -interval and -;lading-interval methods arc biased toward basellow; and thus. overprcdict ground-water contribution to streamflow. 1\ plot of' the thr~.:e methods of hydrograph separation for l3caverd:un Creek (station 02 1981 00) ncar Sardi ~ . Ga.. is ~h own in fi gun: 3. The plot shows the overestimation of the fixeJ-intcrval and :;liding- interval methods; for this reason, the local-minimum method was used to cstimatt: basdl ow in thl.! study an:a .
Surface-w:lter discharge measuremcnrs collectoo during the three drought peri od~ - 1 954. 1981. and 2000- wcre used to estimate hasellow for se lected tributaries of the Salkehntchie- Savannah- Ogecehec (SSO) River. AltamahaSatilla- St Marys (SJ\S) River and Suwannee River Basins. The minimum ground-wmer discharge to tributaries between two adjacent r0aches during the 1954 (22 stations), 1981 (7 stations), and 2000 ( IC) stations) drought years were collected from continuous-record stat1ons 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 lhe 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 drou ght~.
Linenr-rcgrcssion analysis was used to determine the flow duration that most closely estimates basctlow in the study area. Flow duration is a cumulative frequency curve that shows the percentage Of time H Specific discharge WaS equaled Or exceeded during a given period of time. f-l ow-duration curves integrate the effects of topography, geology. and climate of the basi n. ror example, baseflow of streams inlhe glacial till/ outwash of Long lslnnd was estimated from 55-percent now duration (Reynolds, 1982); whereas in the southeastern sand aquifer. bascflow was estimated to range between 6().-Q5 percent of mean annual streamfl ow (Stricker, 1983). Mean annual bascllow for 14 stations in the study area was compared to flow durations nmging from Q, to Qw (streamflow equaled or exceeded I percent to 99 percent of lhe time) to derive flow duration that is representative of bascflow. This flow duration can be applied to streams in the study area to estimate basenow 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 fluctuati ons in streamflow and ground-water levels. The cumulative departure from normal precipitation for

t . ~~~--~~-----,--~--c-------~----~

Fixed-i nterval

- Measured .;

I.ow

Estm:u!!d

;()()

ba~How

0 z

8 r w 1 000

r --r-1 T - , -

(/)
a:

Siiding intOrval

aw..

tu tOO
w
IL

(.)

1Xi
;:)

(.)
z

w

(a!:)

<(

J:

(.)

(/)

0

l ocal-minimum

----r-:- !
:.l
,j
-i
-jI
1

~~~--~~--~~--~~----~~~--~~
":>~ </<,'?J 'to~ ~~ ~:- i>4<- i>~ ~0 C:>l' ovA.. -<:-o~ ()~o
1999
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 -200 I 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 lhc 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 detennine normal precipitation for computation of cumulative departure. Average precipitation is the arithmetic mean of total monthly precipitation for the period of study 1971- 200 I.

Stream-aquifer relations 9

Well and Streamflow Gaging Station Identification Systems
Wdb in Glorgia arc idcmilied hy a system based on USGS topographic maps. Each ?'12-minutc topographic quadrangle map in Georgia has been as!oigncd a number and letter designation beginning at the southwest corner of the State. Number!> incrca!>e ~oequentially eastward through 39; letters advance northward through "Z." then double-letter design:ltions ''AA" through "PP" arc used. The letters "1.'' "0," "II." and "00" arc not used. Wells inventoried in each quadrangle an: nurnbt.:rcd sequentially beginning with ''I ." Thus. the second well inventoried in the Fo lkston quadrang le (29E) is designated 291\002.
Stations arc ussigned an 8- to 14-digi t station identi~i ca tion number according 10 downstream order along the main streum. TIK~ first two digits of the station identi fi cation number represent the ran" 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 tributuries. Gaps arc 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 lotreams and aquifers interact within a dynamtc hydrologic ~ystemthat include<> aquifers. streams. reservoirs. and noodplams. These systems arc interconnected and form a single hydrologic entity that i!> stressed by natural hydrologic. climatic, and anthropogenic factors.
Stream-Aquifer Flow Systems
Under steady-state conditions, most ground-water systems l!an be divided into three subsystems: local. intcrmedi ~llc. and regional (Toth. 1962: 1963). Relatively shallow ancl short nowpuths that extend from a topographic high (recharg~ area) to an adjacent topographic low (discharge area) characterize a local now system. Intermediate llowpaths includt: at least one local flow system between their respecuvt: points of recharge and discharge. and arc longer and deeper than local nowpaths. Regional llowpaths begin at or ncar a major ground-water divide and terminate at a regional drain (fig. 4).
The number, distribution, and depth of influence of local now regimes arc largely a function of water-table configuration and aquifer thickness relative to watershed relief (Faye and Mayer, 1990). Where aquifer sediments arc thin, local flow systems may dominate. Local flow systems arc affected mostly by climatic variations. The net recharge and amount

Upper Coastal Plain-
High reliel and thin conlining unit result in deep penetration of recharge Into confined aquifer systems (Intermediate and regionalllow systems)
/.It 1/e Ocnwlgee
l?lvcr

Lower Coastal Pla in -Low relief results in more local !low system. with shallow penetration of aquifer recharge

Unsaturated zone
Unconfined surf1cial aquifer

lfnloterm""v-u'JiiJte

G

wsystem

flo~J.dwater

ulrect;on

--

Confined aquifers

(Confined surficial aquifer,

NOT TO SCALE

Upper and Lower Brunswick aquifers ___. Regional flow

and Upper and Lower Aoridan aquifers)

6Ystem ---.,...

Wetlands
--

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

10 Stream-aquifer relation s in the coastal area of Georgia and adjacent parts of Florida and South Carolina

of ground-water flow arc di-;tributcd accord ing to the flow sy~tem. w1th flow and m.:t recharge be1ng greatest in local flow ~ystem:-. and Jcw;t in regional flow systems (Toth. 1963 ). Local flow !>)'Stem!\ arc most dynamic in areas of high relief such as the upper Coas tal PI:\in (fig. 4).
In the study area. recharge to the hydrologic system is provided by rainl"allthat ranges spatially from an average of about -17 to 53 inchcl> per year (in/yr). based on mean annual precipitation for the 30-year period 1971 - 2000 (fi g. 5). Mo~t of the rcdwrgc is dischargcd rromthc shallow. local llow systems into sma ll streams or i:-; lost as evapotranspiration. In the intcrmcdiHte flow systcm. some of thc water is discharged to major tributaries. A small<.:r pcrccntage of recharge infiltrates through clayey eonfinin g 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. Fuye and Mayer ( 1990) estimated mean annual ground-water discharge to the Savannah River by computing the gain in stream discharge between Augusta (station 02 197000) and Millhavcn (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 (fl3/s) from combined intermediate and regional now sys tems and a gai n of 560 ft3/s from the local flow system. Baseflow was estimated by a modified hydrograph-separation technique to be 1.220 ftlfs. Thus. in the Savannah Ri ver Basin about 54 percent of ground-water recharge entered the intermediate and regional tlow systems. and the remaining 46 percent entered the local 11ow system (Faye and Mayer. 1990). The local and intermediate flow systems affect much of the stream discharge in the northern part of the study Mea. and the intermediate and regional flow systems affect stream discharge in the southern part of the study area.
ln the upper Coastal Plain. where relief is relatively high. local fl ow systems dominate. In upland areas, the altitude of Lhe 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 Lhe 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 fl ow 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 tcnain con-;ists of wide and f1:11 ridges separated by wide. swampy. and hc.:a\'ily wocxkd \'allcys (Thomson and Carter. 1955). Tidal e ffec t~ and dillc rences 111 runoff. due to ~oil type and 'egetative co\'er. account for 1he variation in haseflow between upper and lower Coastal Plain (Carter and Putnam. 1977).
Climate
Thc study area ha!'. a mild climate with \.va.rm. humid summers and mild winters. Mean annual tcmpcrature ranges from about 63 degree:. f-ahrenheit (0 1') in Burke County. Ga.. to about 70F in Glynn County. Ga.. (()r the period 1971 - 2000 (National Oceanic and Atmospheric Administration. 2002).
Precipitntion data were cvnluated from I0 N\VS stations in Georgia and I in South Carolina. Of these stations. six wcre selected to detcnninc long-term trends that could affect ground-water recharge and associated water-level fluctuations. The Georgia station!> arc located at Alma, Brooklet. Brunswick. Dubl in, Folkston. Homerville. Jesup. Savannah. Tifton. and Waynesboro: the South Carolina station is located at Bamberg (figs. I and 5). Mean annual precipitation. based on the period 1971 - 2000 range. from about 47 in/yr in Waynesboro. Ga.. to about 53 in/yr in Folkston. Ga. (fig. 5). Rainfall is not even ly distributed throughout the year. The maximum rainfall generally occurs during the summer months of June. July. and August (fig. 6). Estimated c'apotranspirmion ranges from 3 1 in/yr in the northcm part of the study area to more than 40 in/yr in Charlton and Ware Counties. Ga.. ncar 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. I: table I). The largest river bas ins are the SAS. with a drainage area of about 14.142 mi2: and the SSO, with a drainage area of about I0.734 rni' . The Suwannee River has a drainage area of about 6.400 mi2 Wilh 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 pumpagc. Four power plants use surface water within the SSO River Bas in, and one power plant within the SAS River Bas in. Surface water accounts for about 75 percent of total water usage in t11e Georgia Coastal Plain (Fanning. 1999). In the Coastal Plain, mean annual runoff ranges between 24 and 3 1 percent of total rainfall (Carter and Sti les, 1983). In the study area, runoff during the period 194 1- 70 was about 14 in/yr in the upper Coastal Plain, and about J2 in/yr in the lower Coastal Plain (Carter and Stiles. 1983) (fig. 7).

,-,

r

83

'

~ ~

~ '
'\

~

\

\\

..I.

~

\

\-

\

\

.~

..

\ \

Dubl111 H

\

~

\

I

\

I

~

/

, '\

\ I

f.

~

(

'

\

~

\

~

(:J2

~

~

...

~

~
~ ~

~
"
~
~ ~

Stream-aquifer relations 11

/

81

/

' '

.,.

J

30 t...,,

t
~

\
"

-

J

)

0

10

20

I I I I

I I

30 MILES I

0 10 20 30 KILOMETERS

Base Irom u.s.GeOlogical Survey

1: 100.000scale dtg11al data

- 10-
T1f1on 47

EXPLANATION
Line of equal mean annual precipitation (1971-2000)Dashed where approx1mate. Interval 1 1nch
NWS station, name, and precipitation amount in inches

Figure 5. Mean annual precipitation for selected National Weather Service (NWSJ stations in the Coasta l Plain of Georgia and South Carolina, 1971- 2000.

12 Stream-aquifer relations in the coastal area of Georgia and adjacent parts of Florida and South Carolina

10
Alma. Georgia 8 6
2 0

Home rvill e. Georgia

I

[Oihfllh-rui

I()
Bamberg. South Carolina
8

0

4

?

0 l '---'--'---''-.l--'-----1--'---'----'---.J'---'--'-'

(/)

UJ

I 0 ~

10 ~----------------~
Brooklet. Georgia
8

: z
z
0
~
1-'

6 ~[JJ]jf[[hru~

u0:

Uaa.:J.

10 . - - - - - - - - - - - - - - - - - - - - - .
Brunswick. Georgia

~ 8

I.z... 6

0

::E z

2

<( UJ

0 l-L--l-.l---L-....1..-l- l . . --L--l---L--l

::E

10 ~---------------~

a Dublin. Georgia

6

Jesup. Georgia Savannah. Georgia Tilton. Georgia Waynesboro. Georgia

2 0 ~-~-'-~--'---.J~J_~__L__J_J_.J__w

10
a

r------------------------~ Folkston. Georgia

6

J F MA MJ J A S 0 N 0

2
0 ~__J-L--L-....1..-l-L--L-....1..--L~~~_w J F MA MJ J A S 0 N 0

Figure 6. Mean monthly precipitation at selected National Weather Service stations in the Coastal Plain area of Georgia and South Carolina. 1971- 2001.

\/ ,'4)
.- 1
32

Stream-aquifer relations 13

/

81

33

I

\

\ \

r'

\
- , .. \ y l ...

\

r-
\~ "
( '-..:.. \

....

/. .,
/

31
Inner IT!argln
or Coastal Ptoln
sodfrnonl~

- , L.!J)

-

\

I
!

I

IJi

I

J

0

10

20

I I I I 11

30 MILES
I

0 10 20 30 KILOMETERS

Base from u.s Geologacal Survoy
1 100,()()()-scalo dog11a1 data

EXPLANATION - 10- Line of equal mean annual runoff, 1941- 70-lnterval 21nches

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

14 Stream-aquifer relations in the coastal area of Georgia and ad jacent parts of Florida and South Carolina
A. Brier Creek 10,000

100

10
r 1

01 f

co

"' 0.01 ~------------------------------------------------------------------_J

0 z

B. Canoochce River

::.u 0
(..)

100.000

~ iUU ~iU Ulil:~ ~

~ ~ ~~ iU;}lU~UlU~~ :il ~;;-~ill :9U:..U~ ~U~ ).1:.;;;11!;~~:~ UU ~ ~:;t~~

w

(/)
a:

10,000

w

Q.

1000

1-

I

~I

'II

1h

I

.,. POH

UJ

UuJ.

100 :=:l

(..)

jJ

Ci5 ::>

10

u

I JL ll
Jl ~~ ll

II
) ~

"" 00
i '!).1 81

(..)

~



~

u.i

(a!:)

0.1

<(

:r:

(..) (/)

0.0 1

I

L

i

0

C. Little Satil/a River

100,000

a~~ ~ ~~~~~~!ll~~ ~~ ~~~~~~~~~~~~~~ ~ ~!ll~~~~~~~~~~~~~~ ~ U i

10.000

I

I

1.000
100 --------------------------- lf
10
I
01

J!

)I

Jl

;f."

I

I

1

1 I

I

-

)I
I I

/ POR . / 54
"-::-00 81

0.01

,o."," ,o.,~ ,o.,r.<:> ,Ojr.'J ,o_,'J<:) ,o_,'J? ,o.,~ ,o.,ro? ,o.,"l<:)

,'?1><:) ,o.,9:>? ,o_,o.,<:> ,~" 'l-#

EXPLANATION
Mean annual discharge Period of record (POR) 1954 (54) 1981 (81 ) 2000 (00)

~ Number of values 0 Upper detached
Upper outside
75th percentile
Median
~ 25th percentile
Lower out.side
() Lower detached

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.

Stream-aquifer relations 15

Streamflow characteristics an; summarized in boxplots showing stn.:amflow duration for each year during the period of record for sdccted ~tations in the study area (fig. 8). For three comparabl y sized basins, boxpiOLs nf dail y streamfl ows were prepared for each year of the period of record. The boxplot.s depict the minimum, maximulll. mean. and median daily discharge; and the 25 and 75 percentiles for each calendar year. The mean annual di:,charge was computed for the period of record and used as u refere nce for the droughtyear streamnow. Brier Creek (station 02 198000) in the SSO River Basin show~ clirnatically driven rise and fall (cyclical ) in stream !low 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 droug hts, respectively. The Canom:hce River (stat ion 02203000) in the SSO River Basin also shows a cl imatically driven cyclical trt;;nd in discharge throughout the period of record. At this station, the 198 1 drought was the most severe followed by the 1954 and 2000 droughts, respectively (fig. 8). The Liule Satilla River (station 02227500) is less cyclical than the previous two stations. with the 198 1 drought the most severe followed by the 2000 and 1954 clroughts. respecti vely (fig. 8). Pronounced dry years are ev ident at each site during 1954, 2000. and 200 1, and wet pcri<lds arc evident during 1964 and 1998. In any given year, stream11ow 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 <lf aquifers and confining units that have variable geologic and hydrologic properties in the upper and lower Coastal Plain (fig. 2). The follow ing 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.

Salkehatchie -Savannah-Ogeechee River Basin 02197600. Brushy Creek, Georga { 1958- 2001 )

0 z
0
(.)
UJ
(/)

aaw : .

twwu-.

(.)

iii ::>
(.)

~

ui

0

(.?
a:

<!

I

(.) Cl)

3.000

0

2.000

Attama ha-Satilla-St M arys River Basin 02227500. Lillie Satlla R1ver. Georga ( 1950- 2001 )
Suwannee River Basin 02317500. Alapaha River. Goorga {192 1. 1932-2001)
I

1.000

JAN FEB MAR APR MAY JUNI: JULY AUG SEPT OCT NOV DEC
Figure 9. Mean monthly streamflow at a selected streamflow gaging station within the Sa lkehatchie- SavannahOgeechee, Altamaha- Satilla- St Marys, and Suwannee River Basins for the periods of record.

Hydrogeologic Units
Principal water-bearing units in the upper Coastal Plain nrc, 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 (tig. 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 Bamwell Group and undifferentiated post-Miocene deposits (fig. 2) (Falls and others, 1997; Huddlcstun and Hetrick, 1986). The sands arc

highly permeable: however, low-permeability clay beds and lenses arc present at the top of the aquifer (Huddlcstun 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 aq uifer, consists of sand and calcareous sand of the Congaree Formation (fi g. 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, tine 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 ~orted fine quartz sand with thin beds of clay of the Steel

16 Stream-aquifer relatio ns in the coastal area of Georgia and adjacent parts of Florida and South Carolina

Creek Formation and Olack Creek Group. undifferentiated (fi g. 2). The Upper Dublin aqui fer is hydrogcologically cqui valctll to the Fcrnandina pcrmcablc zonc of the Lower Floridan aquifer in thc lower Coastal Plain.
lower Coastal Plain
In the; lower Coastal Plain. the surficial aquifer sy:.tem con~ists of interlayercd sand. clay. and thin limestone beds of post-Miocene age (Clarke and others. 1990: Leeth. 1999}. Generally. the surficial nquifer is undcr wmer-tablc condition' throughout the study area. l.ocally. howcver, the aquifer may he confinccl or semiconlinccl by dense phosphatic li mcstom.: or dolomite, and phosphat ic silt y clay of undifferentiated Miocene scdiments (Leeth, 1999: Clarke, 2003). A confi ning unit that consists of clay. si lt. phosphatic limestone or dolomllc. and snnd of Miocene age underlies the surficial nquifcr (fi g. 2). Sand and limestone within this unit have been identified as a source of wntcr in part!> 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. sligluly phosphatic and dolomitic quanz sand of the Coosawhatchie and Marks Head Formations ( lig. 2) (Randolph und others. 1991 ; Weems and Edwards. 200 I). This uquifer is contined by upper and lower confining units of the Miocene Parachucla Formation. The upper Brunswick aqui fer is present in the Brunswick area and generally is absent in the Savannah area.
The lower Brunswick aquifer consists of quanzosc calcnrenite to calcareous quan z sand of the Tiger Leap Formation (fig. 2) (Weems and Edwards, 200 I). The Parachucla Fonnation 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 nrca and in Bulloch County because the pcnncablc upper sand in Miocene sediments either has heen 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 (Huddlcstun. 1993). The surficial and Brunswick aquifer systems and Upper Floridan aquifer arc 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 La7-aretto 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-pcrmenbility. recrystallized Eocene limestone and dolomite. The confining unit has very low primary hydraulic conductivity; however. in the Brunswick

area. joints and fractures produce tonc.;s of high sc.;condary hydraulic conductivity (Krausc and Randolph. 1989).
Thc Lower Floridan aquifer mostly consists of Eocene dolomit ic limestone but locally may include.; Palcocenc to Upper Cretaceous dolomitizcd limestone. This aquifer is confined throughout the coastal area and is subdivided into at least three permeable units in the Brunswick are::t- thc brackish-water zone. deep freshwater zone (Grc.;gg and Zimmerman. 1974 ). and Fernandina permeable zone (Krause Md Randolph. 1989). The Fernandina penncahle zone io., highly perrneablc and cavernous. and contains high salinity water that may be th e source of saltwater co ntn mina tion in the Brunswick area. The r:c rnandina pcrmcablc zone cons ists of Paleocene to Upper Cretaceous pdlctal. recrystallized limestone <1nd finely crystall ized clolomite.
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 rcspon!.e to leakage to adjacent aqui fers. withdrawal from wells, and evapotranspiration from shallow unconfined aquifers.
In the surficial aqui fer, water levels show a pronounced response to cl imatic effects throughout the study area. Where climatic effects dominate. wmcr levels generally arc highllst in the winter and early spring when precipitation is greatest and evapotranspiration is least: water levels arc lowest during the summer and fall when precipitation is least and evapotran spiration is highest. These fluctuations are illustrated on the hydrograph for well 35P094 ncar Savannah (fig. I0). The 15-ft-deep well is completed in the surficial aquifer and shows pronounced water-level rise in response to precipitation. fol lowed by a gradual decline that corresponds to discharge from the aquifer.
ln the lower Coastal Plain, with the exception of the unconfined part of the surfi cial aquifer system, aquifers arc deeply buried and confined. In these areas. climatic effects arc greatly diminished, and fluctuations largely arc because of changes in ground-water pumping. These fluctuations arc illustrated for well 36Q008 near Savannah (lig. 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 ~tclj acent 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 nat ure 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 arc indicated on the hydrographs for wells completed in the surficial. upper Brunswick, and Upper Floridan aquifers (32LO 17, 32LO 16, and 32LO 15, respectively) at Gardi, Wayne County, Georgia (fig. II ).

:r f-
lU
li: ~

Zo

. : C '"':::>
-w'<z

t. r-

>w3::

-'
a:

a0 ;

:w~:; r o

84

>UJ 136
W en U..<J:)
~ ? 88

..J <(

U:l:l>lJ"-"~"

-'0
.Ow.,Ccwo-'

92

<~ 94

96

2.!'i
<ll UJ :X:
0 2.0
~ ~
;i L5 0
!;i
ta:. 1.0
@
ca.:.: 0.5

Well360008

~

Savannah Municipal Airport

ouu~~~~~~~-~~~~~~-r~~~
~.f <v<o ...~~ ~Q:- ~- l<v ~~ ~0 eo<l' o(;- ~o~ Q<vCJ

2001
Figure 10. Daily water-level measurements in wells 35P094 and 360008, Chatham County; and daily rainfall at National Weather Service station, Savannah Municipal Airport, Chatham County, Georgia, 2001.

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 syswm. Precipitation changes arc reflected in streamflow and in ground-water levels of aquifers that a.re unconfined or semiconfined. When ground-water levels are high from natural rccha.rge (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 (ligs. 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,

Stream-aquifer relations 17
the period 197 1- 2000 was used to determine normal precipitation for computation of cumulative depart ure.
Upward or positi ve slopes on the graph indicate periods of above-normal precipitation: downward or ncgati v~.: slopes on the graph indicate periods of below-normal precipitation: no s lope indit:<Hcs periods of no rmal prec ipitation. Trt.:nd is the overall slope over a period of time. A short-term trend covers
a period or 5 years or less; a long-term trend covers a period
g reater than 5 years. An above -normal trend means that the slopes over a period of time arc positive nr up\vard: whereas a bclow-no nnal trend means that the slopes over a period of tim~.: arc negative or downward. Fluctuations and tre nds in the major river basin grouping arc plolted for the period 197 1-200 1.
Salkehatchie-Savannah-Ogeechee River Basin
In the upper part of the SSO River Bas in, precipitation uends arc illustrated on the cumulative d~.:panure graph for the Waynesboro, Ga., station (fig. 12). In general, there were several short-term tre nds of above- and below-normal precipitation during 1971 - 84 followed by a long-term trend of below-normal precipitation during 1984-9 I. A longterm trend of above-normal precipitation is observed durin g I992- 98 with intermittent short-term trends of below-normal precipitation. During 1999-200 I, there was a short-term trend of below-normal precipitation in Waynesboro. Ga.. reflecting the 2000 drought. By the end of the stud y period, the overall cumulative departure was+ 19.47 inches at Waynes boro.
Streamflow in the upper part of rhc SSO River Bas in 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 3 1-year mean for this station. C hanges in streamflow correspond to above- and belownormal periods of precipitarion for the area. Two of the three severe drought pcriods - 1981 and 2000- are more than 200 ftJ/s below the 3 I-year mean of about 598 ft3/s.
Ground-water levels in the upper part of the SSO River basin arc shown for well 32R003, Bulloch County (fig. 12), completed in the surficial aquifer to a depth of 155 ft. Data are insuffic ient to recognize a trend in the water level: however, well 32R003 taps a deeper part of the surfic ial aquifer where semiconfined conditions occur as a result o f a clay confining unit.
In the lower part of the SSO River Basin. precipitation trends are illustrated on the cumulative depa.rture from normal precipitation graph for the Savannah, Ga., station (fig. 12). In general, there was a long-term trend of below-normal precipitation during I973-90 with intermittent shon-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 generall y below-normal precipitation during 1996-200 I. Effects of drought are evidenced by a shon-term uend of below-normal precipitation during 1999-2001. By the end of the study period, the overall cumulative departure was - 13.26 inches at Savannah.

18 Stream-aquifer relations in the coastal area of Georgia and ad jacent parts of Fl orida and South Carolina

30

CX)

CX)

0 35

z ~
>

40

L 0
w...J

<~ s

m

1w w

50~

LL

~
_j

55 1-

r w

> w
...J

60

:tw0:
~
~

Wcl132l017 Surficial aquifer (200 215 It)

Well 32L016 Upper Brunswick aquifer (320- 340 ttl

. . . .., ,VV'fJCC\ O.\..J,\a..n{f,,fJ.",\.t.,-\~j-~ "-..,N'-

/',~t, ""'---.

.

~-- . -v I '-v-

Well 32L015 Upper Floridnn aquifer (545- 750 It) '\..

1982

1984

1986

1988

1990

'-' '0t. ,./"~~~1vI_V;,,'...\I -.r~1-.v

J --'-J A~-' "'--~

~~ ./\..o.J, 1

1992

199.1

1996

1998

2000

Figure 11. Daily mean water levels in the surficial, upper Brunswick, and Upper Floridan aquifers at the Gardi site, Wayne County, Georgia. 1983-2001.

Streamflow in the lower part of the SSO River basin is shown on btu graphs for Cnnoochcc River (station 02203000) (fig. 12). Generally. about half of the streamflow was at or above the 3 1-year mean for this stntion. 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 ft3/s below the 3 1-year mean of about 484 !Ws. Drought conditions had a greater effect on streamflow in the lower part of the basin than in the upper p:ut of the basin, probably because of interconnectivity with the aquifer.
Ground-water levels in the lower part of the SSO River Basin arc 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 rcspon e 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 tre nds are illustrated on the cumulat ive de parture graph for the Dublin station (fig. 13). There was a long-term trend of at- or below-nonnal 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- 200 I, 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 Bas in 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 bdow-normal precipitation years and high streamflow occurring during above-normal precipitation years. During two-thirds of the study period, streamfl ow was at or above the 3 1-year mean. During the drought years of 1981 and 2000. streamfl ow was about 2,000 tWs below the 3 1-ycar mean of about 4.393 ft' /s.
Ground-water levels in the upper part of the SAS River Basin arc shown for well 21 TOO I (fig. 13) Laurens County. completed in the Upper Floridan aquifer to a depth of 123ft. 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 c umulative 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 1998-200 I. By the end of the study period, the overall cumulative departure was - 12.39 inches.
Streamflow in the lower part of the SAS River Bas in is shown on bar graphs for the Little Sat ilia River (station 02227500) (fi g. 13). Streamflow appears to fluctuate in a similar manner as precipitation , with low streamflow occurring during below-normal precipitation years and high streamfl ow occurring during above-nonnal precipitation years. More than half of the mean annual streamflow was at or above the 3 1-year mean for the station . During the drought years of I981 and 2000, streamflow was about 500 ftlfs below the 31-year mean of about 542 ft3/s.


Stream-aquifer relations 19

Upper Salkehatchie - Savannah- Ogeechee River Basin (.) 1,000 Station 02198000 (Brier Creek) Millhaven..;G_e_o_rg:.:i..a__ _ _ __

I ffiO

..J:::>Z

:zz<::(>:(.:,..w)((0./))

800 600 ~

<CWO:

ze>w
ctctCL

400

W<(I-

.- . : ::Xu:wW !Qu..

200

0

- ~~-
[ I

- - [1 31year m>an

I

r-

~

-.

~ ~1 - ~

0

1 Woii32R003 (Upper Floridan aquiler. Bulloch County, Georgia, 1551cot deep)

--.--..--,-r--r--r--.

: r-r-1 l , 1 1 1

I I

I 1 I I I r-r-r-r

n nnk ,t.nro 8
Oatn co foctor' bognn n 198:.1

1
~
'--'--'--'--'--

Waynesboro, Georgia. station
so r-r-r-~.-~~-r-r-r-r-r~~-,-,r-r-r-,-.-,-,--r~-r-r~-,-,-,r-~

40







lower Salkehatchie- Savannah- Ogeechee River Basin

Station 02203000 (Canoochee River) Claxton. Georgia
(.) 1,000

ffiO

<..J(:(::>.)z0 800

'r'

:zz::>_z.wl(>/) 600

3 t yoar

<(WO:

UzJe~>

w
CL

400

- --

-- -m-e-an--- ---- ----

-- --- ------

:::E~:x:ltuf 200
0
0

0

n

n nnn

Savannah, Georgia, station 60
40
20 0 - 20
Figure 12. Mean annual stream discharge, daily mean ground-water level, and cumulative departure from normal precipitation for the upper and lower parts of SalkehatchieSavannah- Ogeechee River Basin, Georgia and South Carolina, 1971 - 2001 .

20 Stream-aquifer relations in the coastal area of Georgia and adjacent parts of Florida and South Carolina Upper Altamaha - Satilla - St Marys River Basin

Woii21T001 (Upper Floridan aquifer. laurens County. Georgia. 1231cet deep) .,-,--.,--.,-----,--.---.--.-.

20

-

--r -, 1 1 1 r ": T I r - r - 1 , -

3{1

~0

...J;i L2U!_LtiU:~<io=;(L/U)
s=~>ag:~sZ~-~:Uzr ::!Ea:::Eu:u:>owau:o.aaw:. ?;

50

Dublin. Georgia. station

40

1

20

0

-20

40

Lower Altamaha - Satilla- St Marys Rive r Basin Station 02227500 (little Satilia River) OHorrnan Georgia t .200

t.OOO

800
GOO - -- --

31-year
-- ---- --. --m-oa-n-- -- - ---- ------

400

200

n n nnn

n n_rrD

0

20

Weii32L017 (Surficial aquifer. Wayne County, Goorgia_:.:.:2:;1:5;..f._o,e.;.t;..d:ro-.e:.Jprl--r--r--,r-~..-,--.-r-r-:--,....,
-r

30

40

Onla COi.ccloon

bcgnn '" 1933

50

r

20

./

0

- 20

Fi gure 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- SatillaSt Marys River Basin, Georgia, 1971- 2001.

Stream-aquifer relations 21

Ground-water levels in the lower part of the SAS River Bas in are shown for well 32LO 17, Wayne County. completed in the surticial aquifer to a depth of 215 ft. fn this area. the water level of the surlicial aquifer is innuenced largely hy ground-water pumping and. to a lesser extent. changes in rcchargt: because of the depth of the aquifer. Water levels in the well dedi ned about 6 f1 during 1983- 200 I, with the OIOSl rapid dcdinc beginning in I999 as a result of the 2000 droug hl.

Ground- water levels in the lower part of the S uwannee River Basin arc shown l'or well 19E009. Lowndes County (fig. 4), completed in the Upper Floridan aq uifer to a depth o f 342 ft. Both pumping and recharge inOucncc water levels in this well. Although the well is deep. it is located in
an area or karst topography where there is intcrconneclio n
between streams and the Upper Floridan aquifer. Water levels in the well generall y followed precipitation trends during 1971 - 200 1.

.

Suwannee River Basin

Ground-Water Contribution to Streamflow

.

In the uppa part of the Suwannee Rivt:r Basin, precipita-

The dcgrcc of aq uifer interconnection with streams var-

tion tre nds an; illustrated on tht.: cumulative departure g raph

ies in the upper and lower Coastal Plain. In general. rdid is



for the Tifton station (fig. 14). In general. there was a long-

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

.

term tre nd or above-normal precipitation during 197 1-88. followed by a long-term trend of below-normal precipitation

In this area, the Upper Florida n and equivalent aquifers are unconlined or semiconfined and arc inc ised by streams flow-

during 1989- 200 I. By the end of the stud y period, the overall ing through the area. In the lower Coastal Plain, the Upper

..

cumulative departure was - 1.9 inches at Tifton. Streamflow in the upper part of the Suwannee River

Floridan aquifer is deeply buried and confined. The imerconnection between ground water and streams

Basin is shown on bar graph~ for Alapaha River (station

is illustrated on a map showing the potentiometric surface

023 17500) (fig. 14). Streamflow generally responds to

o f the Upper Floridan aquifer for May 1998 (fig. 15). Ln the

r

changes in precipitation, with low llow occurring duri ng

upper Coastal Plain. aquifer interconnection with streams is

r

below-nonnal periods, such as 1999-200 I. and high flow

indicated by steep hydraulic gradients toward streams and

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

potentiometric contours that cross in a "V'' pattern upstream,

Less than half of the mean annual stream l'1ows are at or above indicating ground-water flow toward the stream. in the lower

the 3 I-year mean for the period. During the drought years of Coastal Plai n, the aquifer is more dee ply buried and is nol

198 1 and 2000, stre.am llow was more than 700 ft3/s below the incised. Here. potentiometric contours indicate little connec-

3 1-year mean.

tion between the aquifer and overlying streams. An exception

"

Ground-wMer level~ in the upper part of the Suwannee River Basin are shown for well 18K049, Tift County,

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

completed in the Upper F loridan aquifer to a depth of 620ft

Streamflow composes two major components- surface

"
,

(fig. 14). Water levels in this well are influenced mostly by changes in pumping. The general water-level trend in this

runoff and baseflow. On a typical hydrograph. peaks indicate rapid response lO precipitation and represent the runoff com-

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

ponent of a hydrograph. The slope of the streamflow recession

data collection began, to 200 I.

indicates ground-water discharge to streams and represents the

In rhc lower part of the Suwannee River Basin. pre-

baset1ow component of a hydrograph.

cipitation trends arc illustrated on the cumulative departure

In re lation to the conceptual model (fi g. 4), baseflow in

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

streams comprises contributions from the local, intermedi-

were long-term trends of above-normal precipitation du ring

ate, and regional ground-water flow systems. Because local

1971 - 77 and 199 1- 98. with a long-term trend of below-nor- tlow systems are most affected by rainfall during periods

mal precipitation during 1978- 83. and a short-term trend of

of extended drought. streamflow is assumed to be sustained

below-normal precipitation during 1999-200 I. By the end

entirely by baseflow.

of the study period, the overall cumulative departure was

Ground-water contribution to streamflow (baseOow)

- 9.44 inches at Homerville.

was estimated by using three methods. Hydrograph-separa-

Streaml1ow in the lower parr of the Suwannee River

tion analysis was used to estimate basetlow based on data

Basin is shown on bar graphs for Suwannee River (station

from eight continuous-record stations. Field measurements of

02314500) (lig. 14). Streamflow generally follows precipita- drought discharge from headwater to an adjacent streaml'low

tion patterns, with pronounced declines in streamtlow during gaging station and between two adjacent stations were used to

below-normal precipitation periods. About half of the mean

estimate the minimum ground-water contribution to stream-

annual streamtlow was at or above the 3 1-year mean for the

n ow. Linear-regression analysis of streamflow duration and

period 1971 -200 I. During the drought years of 1981 and

mean annual baseflow was performed to estimate the percen-

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

tile of streamflow that most closely represents baseflow.

mean of about 941 ft3/s.

22 Stream-aquifer relations in the coastal area of Georgia and adjacent parts of Florida and South Carolina

Upper Suwannee River Basin

Station 02317500 (Al apaha River} Statenville, Georgia

(iX.)i 0 2.500

-

_t:::>Z
8 c~(~(.U) J :>.000
-~wa.e:n l.500
nu~ z<w:<(!ec!~(>ra1Ww.- 1.000

' ,.,.. ,.~

mo"
------ , -n_____

on~uD~

~ tf 500

0

n l
oo[

0

~- ~I Woii18K049 (Upper Floridan aquifer, Tih County. Georgia, 620 f_c,et_d_crc.:p...;)---,-,--,.--,---.--,-,--,.--:--,

100 -

lll~nk wnor; '"\.--- '\.. l t- o l I I

(1\ vI \

1:>.0

daia mossonp

1~0
O.un CoiiCCb011 ~>egan .n 1978
1 60 1 --~~~-L-L-L~--'--~~~~~-L-L~~~~~~-L-L-L~~-~~~---L~

40

Lower Suwannee River Basin

Station 02314500 (Suwannee River) Fargo, Georgia

?. .500

(.)

-'

ii)
:::>

O z

2.000

c((.)O

:zz::> ~-e(w.n) 1.500

. cz(W~a~;: 1,000

U)~lii

:::: (.) UJ 500 ~u.

0

0

-

- - --- __3_1-year ~':a~ ___

n ~ nn n

------
n~n

---- ------
n n ..... n

We11 19E009(Uppor Floridan aquifer, Lowndes County, Georgia. 342 foot deep)
1 00.-~,.-.-~~------~--~,.--,--r-r~--y~r-~,.-.--r-r-r-.-.r-r-~,.-.--r~

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.

33 -, ; \

,-- ----

I I

'

,,

- - - .,,I \'

Stream-aquifer relations 23

82

81

..

- 10 -

EXPLANATION Ax is of GulfTrough- Approxlmately located (Kellam and Gorday, 1990)
Potentiometric contour-Shows alt1tude at which water level would have stood in tightly cased wells during May 1-26, 1998. Hachuros indicate depression. Contour 1nterval 50 feet. Datum IS NAVDil8

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

24 Stream-aquifer re lations in the coastal area of Georgia and adjacent parts of Florida and South Carolina

Hydrograph Separation
Hydrograph :.cparation was completed on streamflow data using HYSEP. a computer program that usr.::s mathern:uical technique!> to sep~uate streamflow into bast::flow :md runoff components (Sioto and Crouse. 1996). The mathematical fnn uulation of IIYSEP docs not consider the geology of the basin: therefore. it can he used on a site-by-site basis in any hydrologic setting. There ~ue limitations o n its usc. however. because HYSEP ba:-cs hydrograph separation only on ba-;in area and strcam11ow hydrograph characteristic!>.
Estimates of ba~cllow from HYSCP were used to determine changc~ in base11ow contribution during a variety of climatic conditions. 13ascflow estimates arc affected by regu lation of flows and physical properties of the basi n such as vegetation cover. slope. area, shape. land usc, 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 th::tn 1.400 mi2 and at least 3 1 years of continuous record (table 3). The accuracy of the est imates depends on the period of record used (Sioto and Crouse. 1996) and the siz.e of the drainage basin (Peuyjohn and Henning. 1979). A long-term record with representative long-term climatological conditions provide:-. a more re liable bascllow estimate bcc::tuse periods of extreme dry or extreme wet climates would havc less influence (Sioto 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 yean; of higher rainfall. At the eight ~tation~ selected for IIYSEP. mean annual b:a...cllow was from 39 to 74 pcrcent o r streamflow. with a mean comribution of 58 percent (table 3). Ftgure 16 shows the amount of streamflow at the Canoochec River (station 02203000) in the lowcr Coastal Plain ncar Claxton, Ga., originating from basellow for average. wet. and dry years (ba!"ed o n the Brooklet WS station). During a high-prccipitation ycar. basetlow accounted for 48 percem of total streamflow: dunng an a\cragt:-prectprtation year, about 63 percent: and during a low-pn:cipllation year. about 60 percent. During dry pcnod!>. there is a reduction tn runoff, and basellow becomes the major contributor to strr.;amflow. During drought condit ion!>, then~ is less water <Wai lablc to recharge the aquifer. as indicated by ground-water level declines. As ground-water levcl drop. the hydraulic gradient between the stream and aquifer decreases. reducing groundwater discharge to streams. In some instances, the gradie nt between the stream and aquifer reverses and stream-water discharges into the aquifer. bur this usu<tlly is of short duration because the streambed eventually dries up.
Bascflow estimates vary within the upper and lower parts of a basin. Mean annual b<~seflow for the period 1971-200 I in the upper SSO River Basin ranges from 66 to 74 perccll! and in the lower basin is 54 percent (table 3). ln the upper SAS River Basin, baseflow is about 57 percent of total streamflow at station 02225500 (Ohoopce River). In the lower SAS River Basin, baseflow ranges from about 39 LO 43 percent of total streamflow. In the lower part of the Suwannee River Basin. bascflow is about 56 percent of total streamflow. Mean annual baseflow was estimated for 1981 and 2000 (drought eondi-

Table 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 'J,, cubi c foot per second: mil. ~q uare mile: part ofbnsin: U. upper: L. lower: do. dnto)

Station Drainage Part of identification area (mi1) basin

Period of record (calendar year)

Station Outcropping hydroidentification geologic unit

in/yr

02175500 341

u

02197600

28

u

02198000 646

u

02203000 555

L

02225500 1.110

u

02226500 1.1 90

L

02227500 646

L

023 17500 1,390

L

Mean of station~ for each period

Salkehatchie- Savannah- Ogeechee River Basin

1951-01

02175500 Upper Three Runs 9.79

1958-01

02 197600

do.

8.02

1936-0 1

02198000

do.

9.29

1937-01

02203000

Surficial

6.29

Altamaha- Satilla- St Marys River Basin

1903-07. 37-01 02225500

Surficial

7.16

1937-01

02226500

do.

5.41

1951-01

02227500

do.

4.46

Suwannee River Basin

1931-01

02317500

Surficial

6.36

Mean annual baseflow ffl/s (in percent of total streamflow)
1971- 2001 1981 2000 1997

246.0 69

16.5 66

442

74

257

54

77 65 64 74 81 68 72 80 70 51 51 48

585

57

53 62 56

478

43

47 34 47

212

39

27 34 33

656

56

56 50 56

58

57 57 55

Stream-aqui fer relations 25

tions) and 1997 (year most rcprl.!scntative of mean annual precipitation for the pcnod 1971 - 2001). Mean annual ba~e llow was greater 111 the upper part of the SSO and SAS River Basins than in th~: lower part.; (table 3). The aYerage mean ;mnual baseflow for the 31-ycar period was 58 percent: for 198 1 and 2000. 57 pcrcelll each; and for 1997. 55 pcrccnt. The difference in ba:-t.:flow is attributed to variations in topography. geology, and vcgcl:ltion in the upper and lower Co;~stal Pl:lin. The upper Coastal Plain is characterized by ~teep slopes and porous sand and g ravel soils that have high infiltration rates and support little vegetatio n. In this area. aquifers ~uc shallower th<lll in the l<1wcr Coastal Plain because the to pographic rel ie f is greater in the upper Coastal Plain. The steeper topography resu lts in deeper incision of strc;uns into the aquifers. thereby increas ing bast:fl ow to s treams. Gt.:ntlc slopes that f:.~cilitat e low runoff a nd more abundant vegetation. which derive wmcr from soil mo isture, characteri%e the lower Coastal
Plain. In these urcas. the streams do not incise into the more
deeply buried aquifer!>. resulting in lower baseflow. Hydraulic conductivit y of an aquifer, which also can have an effect on ground-water discharge. w;ls not studied for this report.

10.000

1,000

100

10

0 z

0
(.)

UJ
(/)

.01

a: 10,000
cU.J.

1- 1,000

UJ

UuJ.
(.)

100

Ci5

:::>

10

(.)

;

u.i

(!)

a: 01
<(

I
(e.n)

10.000

B 1,000

Wet year (1991)-Baseflow is about 48 percent of total streamflow
Average year (19721-Baseflow Is about 63 percent of total streamflow
..----r--

100

10

Dry year 120011- Baseflow is about

60 percent of total streamflow
.01 ~~--~~--~~~-L--L-~--~--L-~--J

~ ~

/r<;~
X

~-rr-~

~~~

~~-

~~, ~.~

,\0 Y

~~t-

r...-<--
0

~o~

~v 0

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 .

Drought Streamflow
Drought :.trcamnow represents a quantitative estimate of mmimum ground-water discharge to stre:uns bc.:cau e dunn:":> drought pcnods. :-.trcamnow is composed mostly of basenow. Drought ba-.cflow 1~ a minimum estimate bc.:causc groundwater levels arc lowered dunng droughll;: and as a result. lcs~ water is available to the stream s than would be available during average.: precipitation conditions. During droughts. streams receive basetlow n1o!>tl y from the intermediate and regional
now system~ because thc water level in the local flo\\~system
is substantially decreased (Faye.: a nd M:1ycr. 1990). Streamllow at select!;d station:-. was compiled for the 1954 ( fhomson and Carter, 1955). 19X I (Cart!;r, 1983: Faye and Mayer, 1990). and 2000 dro ught years (table 4 ). S tream flo\\' was normalized to unit -an~a discharge to separate o ut effects of basin size on discharge rates. The compu ted unit -area discharge was estimated for selected statio ns in the SSO. SAS and Suwannee Ri ver Basins. Tht.: minimum streamfl ow during eac h calendar year was used in the calc ulations.
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, 198 1. and 2000 drought years. Streamflow data were collected o n the same date from two adjacent stations (02 197830 and 02198000) along Brier Creek ncar Way nesboro. Ga.. and Millhaven , Ga. ( fi g. 17). During the 1954 and 2000 droughts, streamflow along that reach decreased in response to the dro ughtS. During 1954, unit-area discharge decreased fro m 0.23 to 0 .1 6 (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 (ft '/s)/mil from Waynesboro to Millhaven. There was no significant change in unit-area discharge between the two stations during 198 1. For this comparison. these discharge mcasure menrs were made on the same date at each site (tig. 17). A comparison o f the lowest discharge me:.1sumd between the two stations for the calendar years 1954, 198 1, and 2000 shows a decrease in unit-area discharge from 0.23 to 0.10 (ft1/s)/mi2 from Waynesboro to Millhaven for 1954; no change for 198 1: and a decrease from 0.32 to 0.18 (l"tlls)/mi2 for 2000. S imilar comparisons were not made in the SAS or Suwannee Ri ver Basins because of insufficient data (table 4).
Drought unit-area discharge shows little variation among the three bas ins. with a few exceptions. In the SSO River Basin. the median unit-area discharge was 0. 11 cubic feet per second per square mile (ft>ts)/mil for the 1954 drought, 0.1 1-0. 14 (ft)/s)/mi 2 for the 198 1 drought. and 0.18 (ftlfs)/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 rangi ng from 0.08 to 0.63 (ft3/s)/mi2 (table 4). The unit-area discharge ranged from 0 to 0.56 (ft 3/s)/mi2 at 15 stations in the lower Coastal Plain during 1954. During 198 1, two Statio ns in the upper Coastal Plain had unit-area discharge of 0.14 and 0.18 (ft3/s)/mi2;

Table 4. Measured s tream discharge a t selected streamflow gaging stations in the upper and lowe r Coastal Plain during the 1954, 1981, and 2000 droughts in

eN n

Georgia and Rorida.

IDA. drainage area: mF, squnre mile; 0'/s, cubic foot per second : (f1'/s)lmi'. cubic foot per second per square mile; U. upper: L. lower: - . data not ava ilnhlcl

Station identificatio n

Station name

02 197200 McBean Creek (Ga Hwy 56) at McBean, Ga.

DA (mi'}
71.4

Part of Coastal Plain

Date (1954)

Stream disc harge
(ftl/s)

Unit-a re a discharge ((ft'/ s)lm i']

Salkehatchie- Savannah-Ogeechee River Basin

u 40ct

141.4

0.58

Date(sl (1981 )
-

Stream discharg e
(h'/s )

Unit-area disch arge
-((f-t'/sl/mi'] -

-

-

Date (2000}
-

St ream di sc ha rge
{ft'/s)

----
Unit-area disc harge ((h'/sl/mi']

-

-- --

-.e..n.
"'Cll
3
='.Ccll
~...
"~'

021973-144 Bea\'erdam Creek at Ri,-er Rd nr Girard, Ga.

23.3

L 20 July

13. 1

.56

-

-

-

-

-

-

0 ::l

02197590 02 197600 02 197830

Brushy Creek at Wrens. Ga. Brushy Creek near Wrens. Ga. Brier Creel: ncar Waynesboro. Ga.

---~

9.4 28 473

L 50ct
u -
u 40ct

' 1.6
-
1!07

.17

-

-

I July

.23 30 Sept

-
l-t.OO 8-1

-

-

-

-

.14

301\lay

2.7

0. 10

. IS 31 July 153

:12

V>
-;
:::r
"n '
s0

02 197980

Brier Creek (GA H" y 23) near S:mli~. Ga.

579

L

-

-

-

-

-

31 Jul>

11 9

17.5

V>
I

02 198000 Brier Creek at Millhan:n. Ga.

646

L 5 Sept

'64

. 10 30 Sept 11 4

18

22 Jul y

76

18

s....

02 198060 02198100

- - Brier Creek at US 301 near Syhanil, Ga.

669

Beaverdam Creek near Sardis, Ga.

30.8

L 30 July
L -

1182 -
-

.27

-

-

- ~~- - -

-----

-

-

-

-

2 1July

2.3

-

"s'

!a.

.07

C")

02198120 02198170 02 198280 02200410 02200440 02200720 02200810 02200900

Beaverdam Creek at Hilltonia. Ga.

85.3

Beaverdam Creel: near Sylvania. Ga.

11 6

Beaverdam Creek near Sylvani3. G:1.

----- 1-B

Duhart Creek (SR80) at Stapleton. Gn .

3.17

Rocky Comfort Creek CUS 221) at Louiwillc. Ga. 286

Big Creek (Penns Bridge Rd) ncar Wren~. Ga.

8.07

Big Creek above Louis,~ lle. Ga. Big Creek ncar Louisville. Ga.

..-- - ...---.---~

---

56.9 95.8

L 29 July
L :!O July
L 29 July
u 60c1 u 13 Oct
u 60ct u 60tl
u 130ct

' 1.3 '13.1 126.7
' 1.5 '46.7 12.4 14.74 '23.6

.02

-

-

-

. I I 22 Oct

~o . s8

0

.19 -

-

-

.48 -

-

-

.63 -

-

-

.30 -

-

-

.08 -

-

-

.25

- - ---~---

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

".0..'

-
-

<se .
=s
0.

--

s E:

-
--
-

sn
'"=s0'-
::1

V>

-

!a.

02201000

William.~on Swamp Creek at D:lvisboro. Ga.

109

L

-

-

-

-tOct

12

.I I

-

-

-

0.::.:.!!

02201070 Williamson Swamp Creek 3t Bartow. G3.

185

L IS Oct

17.1

.09 -

-

-

-

-

-

a:
Q)

02201 150 02201270 02201300

Williamson Swamp Creek 31Wadley, G3. Barkcamp Creek CSR 17) ncar Mid' illc. Ga. Chow Mill Creel: near Herndon. Ga.

233

L ISOct

'21.7

31.7

L IOScpt

o

- .09

---
"

-

-

0

-

:n

L IOSepl

0.23

.01 -

-

- ----

-
-

-

-

=Cll
c.

-

-

-

-

-

-

-

-en
= 0
::r

02201350 Buckhead Creek near W3ynesboro. Ga..

6-t

L 50ct

0

0

-

-

0220 1360

Rocky Creek :u SR 24 near W:t) nc~boro. Ga.

31.7

L

5 Oct

10.12

0

-

-

-

I Aug

36.6

57

(")
.s...

-

--

-

0
;

-- --~- - --- - -

s

02201365

Rocky Creek near Waynesboro. Ga.

3-1 .8

L 50ct

0

0

022022 10 02202240 02203000

Ogccchee Creek near Sylvania. Ga. Ogeechee Creek at Olher, Ga. Canoochcc River ncar Claxton. Ga.

I-I

L 9Scpl

'0

14 1

L

-

-

555

L

-

-

0

-

220ct

.o7

0

-

-

-

16 June

3.3

.()..!

I _l_.t_l~l

1--"l~_)_\_l_l_}_l_}_).}_l_}_l \ \ \ \ ., \ '\_1J

~

~

' 1111'-' '"Y , .... , .... \ -. ' -. ' . , ._..-, y ' .. , .., . , ._.,- , ..,-, . -, "' ' . . .. . .. ' . ~--- -~ - '!1' .

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

IDA. drainage=: mP. square mile; ft'/s. cubic foot per serond: (ft1/()lmF. cubic foot per second per square mile: U. upper: L. lo"cr: - .data not a1ailable)

-

Station identificat io n

Station name

Part of

Stroam Un it-area

DA (mi')

Coasta l

Date 11954)

di s charge

dis c ha rge

Pla in

(ftl/s) {(ft'/s)/mil)

Date (1981)

Stream discharge
(ttJ/s)

Unit-area discha rge
- [(ft'/sl/mi1)

Altamaha-Satilla-St Marys River Basin

Date(sl [2000)

Stream discharg e
(ft1/s)

Uni t-a rea disc harge [(ft'/s)/mi'l

02215500 022 16180 02224000 02225000 02225315 02225360 02225395 02225405 02225420 02...?25480 02225500 02225850 02226000 02"226100

Ocmulgec Ril'er at Lumber City. Ga.

5.1 80.0

Turnpike Creek near McRae. Ga.

49.2

Rocky Creek near Dudley, Ga.

62.9

Altamaha River near Baxley. Ga.

11.600

~--

Jacks Creek n.:ar Wesley. Ga.

8.63

Pendleton Creek ncar Nonnantown. Ga.

10 1

Swift Creek SR 130 near Vidalia. Ga.

36

Swift Creek US I near Lyons. Ga.

-16.3

~- ~

Swift Creek (SR 152) ncar Lyons. Ga.

55.6

Ohoopee Ril'er at US 280 ncar Reidsville. Ga. I.Q70

Ohoopee Ri\-cr near Reidsville. Ga.

1, 110

Beards Creek near Glennville, Ga.

74.4

-~

Altamaha River at Doctonown. Ga.

13.600

Penholoway Creek near Jesup, Ga.

209

L

-

-

-

-

-

L -

-

-

-

-

L

60ct

.23

0

L

- . --- ----"" - - - - - - -- - - 25 Oct

1.680

L

-

-

-

-

-

L

-

-

-

-

-

L -

-

-

-

-

L L

- - - -- - - - ~-- -....-.-----.,;- --~--------

-

-

-

-

-

-
-

L -

-

-

-

-

L

-

-

-

-

-

L L

-
-

- - -- -------- ~--~~~~-

-

-

90ct

-
1.790

L -

-

-

27 July

0

-

30 Aug 905.0

. 17

-

28 May

0

0

. I-I

29Aug 1-150

.13

Jl July

0

0

-

I Aug

0

0

-

'I J ul~

0

0

-

.< I Jul)

0

0

-

31 July

0.7

.01

-

I Aug

45. 1

.04

-

I Aug

-19.2

.0-l

-

31 July

0

"

31 Aug I.JIO

.I

I Jul y

0

02227000 02">">9000 02231280

Hurricane Creek near Alma, Ga. Middle Prong St M3r)'S Ri l'er at Talylor. Aa. Thomas Creek ncar Crn" ford. Aa.

139

L

125

L

29.9

L

I June '0

-

-

--

-

17 July

.32

0

I Jun.:

0

-

-

-

-

II June

0.09

0

02314500 Suwannee River at Fargo. Ga. 02317500 Alapaha Ri1er at Statenville, Ga.
'Thomson and Qlner. 1955 ' Faye and Mayer. 1990 3llnlc and others. 1989 'Carter. 1983

1.260

L -

1.390

L

-

Suwannee River Basin

-

-

-

-

3 Nov 19. 200ct

-.. ------

7.80

0

16 June

5.!

0

....(..I..)

~

25

02

20 July

J7

()

Ql

3

Q' l

.c=

:::;;

.(...l..)..

(l)

i::.

0

:::1

VI

N
...,j

28 Stream-aq uifer r elations i n the coastal area of Georgia and adjacent parts of Florida and South Carol ina

tu
Ww
cuu=-.o>..wa-~.J:
(.)<(
(-Zw!:)ca:o:n>:
O<:aw. :r:a
U !a!?uzo
<(W
UJ(/)
a: a:
<w
z,_!.a_
::>

Upper Coastal Plain

Bncr Creek (statiOn 02197830) ncar Waynesooro. Gco~g1a

03!>

,....--

030

025
r--o:>o
0 15

,...--

0 10

005 0

lower Coastal Pl<tin Bnor Cro ck tstnl10n 0~ 198000) at Millhaven. Gcor~J I!I 0.35

0.30

0 25

,...--

0.20

015

-

,...--

010

005

reac.:hc.:!> wc.:re determined in the SSO and SAS Rna Ba ~ins dunng the 1954. 198 I. and :WOO droughts (tablt.: 5). Gain or los. determination:; were not made in tht: Suwannee Riva Ba~tn because.: of msuf!icicnt data.
In the SSO River Basin. ground water provided bao,efl ow to most stream reaches evaluated during the 195-1. 1981. and 2000 droug hts. In some.: reaches . stream wc.:n; either dry or lost watc.:r to the ground-\v:tter system. For example, in the Brier Creek Basin . during the 1954 drought . a loss of 0.25 ( fl 1/~)/mi ~ w::~s mca:.ured between stations 02 197830 and 02 198000 (fi g. 18: table 5). I n this same rt:ach du ring th~o: 1981 drought. a gain of 0. 17 (ft 1/s)/mi2 was measured (fig. 19: table 5). During the 2000 drought , a loss of 0.45 ( ft 3/s)/rni ~ was mcasun;d ( fig . 20: table 5) in the.: same reach. Lossc-; were observed in the SSO Ri ver Basin at Roc ky Creek betwec.:n stations 0220 1360 and 0220 1365 in 1954 ( fi g. 18: table 5) and in the SAS Ri ver Basin a long the Altamaha Ri v~.:r between stations 02225000 and 02226000 during 2000 (fi g. 20: table 5). Losses most likely are due to stream-water seepage into the surficial aq ui fer along the reach. Gains most like ly arc due to basc now.

0

Octobor4 September 30

Juty31

1954

1981

2000

Figure 17. Comparison of drought streamflow between two adjacent streamflow gaging stations in the SalkehatchieSavannah- Ogeechee River Basin.

whereas. four stations in the lower Coastal Plain had unit-area discharge ranging from 0 to 0.18 (ft 1/s)/mi2 (table 4). During 2000. two stations in the upper Coastal Plain had unit-area discharge of 0.10 unci 0.32 (l"tl/s)/mi2 and five stations in the lower Coastal Plain had unit-area discharge ranging from 0.04 to 17.5 (l'tl/s)/mi2 (table 4). The relat ively high~.:r contribution of bnscflow in the upper Coastal Plain compared to the lower Coastal Plain re fl ects the greater relief, higher interconnection between aquifers and streams. greater soil permeability, and
different vegetat ion. In the SAS and Suwannee River Bas ins. all stations are
located in the lower Coastal Plain. In the SAS Rjver Basin. the unit-arc.:a discharge was 0 (ft1/s)/mi: for two statio ns during 1954; ranged from 0 to 0. 14 (ft '/s)/mi: fo r four stations during 1981: nnd ranged from 0 to 0. 17 (ft3/s)/mi2 for 15 stations during 2000 (table 4 ). In the Suwannee River Basin, the unit-area 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 di fferences in streamflow between upstream and downstream stations give an indication of the gain or loss of water fro m or to the ground-water flow system. In the SSO and SAS River Basins, ncar-concurrent discharge measurements taken at pnnial-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 gai ns or losses along selected stream

Linear- Regression Analysis of Streamflow Duration
A line:tr-regression analysis was used to develop a relation bc.:twcen mean annual baseflow and flow duration for stream:. in the study area. A flow-duration c urve is a cumulative frequency curve that shows the percentage of time that specified discharges arc equaled or exceeded during a given period at stations where continuous records of dail y flow arc collected. n ow-duration curves integrate the effects of climate, topog ruphy. and geology. Visual inspection of the slopes of curves gives some indication of flow from gro und water. Ground water dominates streamflow at the inflection point on a curve. where the curve begins to fl atten. Generally. steep slopes arc indicative of limited basin storage and domjnant contribution from runoff. whereas nat slopes arc indicative of equal contribution of g round water and runoff (Stricker. 1983) (fig. 21 ).
Many studies have compared ground-water discharge to streams using the n ow-duration characteristics of a stream. Stricker ( 1983) estimated basetlow using s treamflow-duratio n curves for 35 statio ns in the southeastern Coastal Plain of South Carolina. Georgia. Alabama. and Mississippi. Stricker ( 1983) fou nd that the 60- and 65-percent flow-duration point:. on the now-duration curves were representative of mean annual baseflow for streams having mean discharges greater than I0 ft3/s. Stricker ( 1983) found that the shape of streamfl ow-duratio n curves is affec ted by the lithology of the Coastal Plain sediments. Steep curves arc associated with basins underlain by low-permeability clay or chal k with high runoff and low bascnow. whereas flatter curves arc associated with basins unde rlain by high-permeability sand and gravel where a high percentage o f the discharge is baseflow (Suicker, 1983).

---- --

-- "

,,.. ,__.. ,,.. '

~ ~ - , -y~ " :"J' --. ';"'~ .. --.. , , : - ~ ~ .. - , - y , " ,..., ., - - - - -:-)'

Table 5. Estimated groundwater discharge 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; mF square mtle: fi'ls. cubic foot per second: Do., diuo: bold and negathc sign . loss)

Stream name and state

Intermediate area of stream reach

Intermediate drainage area (mi1)

1954 drought (fig. 18)

Date(s)

Net gain/loss in stream discharge

(ftl/s) [(lt1/s)/mi1)

Salkehatchie-Savannah - Ogeechee River Basin

1981 drought (fig. 19)

2000 drought (fig. 20)

Oate(s)

Net gainnoss in stream discharge

Date(s)

Net gain/loss in stream discharge

------------------------ (lt1/sl [(1"/s)/milj

lltllsl ltlt1/sl/mi'l

Barkcamp Creek. Ga. Bca\-erdam Cn:ek, Ga
Do. Do. Do. Do. Do. Big Creek. Ga. Do.. Do. Brier Creek. Ga Do. Brushy Creek. Ga Do. Buckhead Creek. Ga Chow Mill Creek, Ga. Duhart Creek, Ga Do. McBean Cn:ek. Ga. Ogeechee Creek, Ga. Do. Rod.'Y Crcek. Ga. Williamsons.,..'3Jllp Crcek, Ga. Do.

between headwater :1nd suuion 02201 270 bel"'een statioM 02198120 and 02198170 bet"'een hcadwat.er and station 021973M4 between headwater and station 02198100 between headwater and station 02 198120 bet\\ecn headwater and station 02198 I 70 beiWeen stations 02198170 and 02198280 between headwater and station 02200720 between stations 02200720 and 022008 10 between stations 022008 10 :1nd 02200900 between Stations 02197830 and 02198000 between station~ 02198000 nnd 02198060 between headwnter and station 02197600 bet\\een head\\;ller nnd station 02197590 beiWeen head~~ter and station 02201350 between headwater and stnti on 02201 300 beiWeen headwater and suuion 0220Q.I IO bet,..-een stations 022()().110 and 02200140 betw-een head,.. ater and station 02 197200 between headwater and station 02202210 between headwater and station 02202240 bet,.. een station( 02201360 and 02201365 between headwater :1nd station 0220I000 between stations 0220I070 and 02201150

31.70 30.7 23.3 30.8 85.3 116 27 8.07 48.9 38.9 173 24 28 9.4 64 23 3.17 283 71.-1 14 141 3. 1 109 48

IOSept 20& 29 July
20 July

0.00 11.8 13.1

29 July

1.3

29 July 6 Oct 6 Oct 6 & 13 0ct 4 Oct & 5 Sept 30 July & 5 Sept

13.6 2..1 2.3 18.9 -43 118

50ct 50ct IOSe pt 60ct 6&130ct 4 0ct 9 Sept

1..56 0
.23 1.9 44.8 41.4 0

5 0ct

-.12

150ct

4.6

0.00 .38 .56

.02

27 Oct

.58

.5

.3

.05

.49

-.15 30Sept 30

4.9

. 17

0

.01

.6

. 16

.58

0

220ct

.07

-.~

40ct 12

.I

21 July 2.3 0
. 17 22 & 31July - 77 30 1>13)' 2 7 I Aug 36.6

0

.II

2 1Jul} 11.0

.07
-0.45 .I .57
.1 0

Ah:lmah:l Ri\'e r. G:1 . Beard~ Creek. Ga. Jacks Creek, Ga. Middle Prong St Marys. Fb. Ohoopcc Rher. Ga. Pendleton Creek. Ga. Penholoway Creek, Ga. Swift Creek. Ga
Do. Do. Turnpike Creek. Ga.

between stations 02225000 and 02226000 bet.,..een he:~dwnter and suuion 02225850 between headwater and station 022253 15 bet"'een headwater and ~tation 02229000 between stations 02225-tSO :1nd 02225500 between hendwatcr and station 02225360 bct.,., een headwater and station 02226100 between headwater :1nd station 01225395 between stntions 02225395 :1nd 02225405 between stations 02225-105 and 02225420 bet\\ten hc;~d....ater and st:llion 022 16 180

Altamaha- Satill a- St Marys River Basin
1.990 74.4 8.63 125 -10 101 209 36 10.3 9.3 492

JO Sept 110

0.05 20 & 31 Aug - -10.0

- 0.02

.s.a.

31 July

0

0

(1) Q)

31 July

0

0

3

I

17 July 0.32

0

I June

0

0

I Aug --1.1

0

Q)
D c :;:

I Aug

0

0

...(.1..).

27 Jul)

0

0

I July

0

0

31 July

0

0

-or(1)
c;

31 July

0

0

:::1

31 July 0.7

0.08

Ill

28 :-fa~

n

()

~

30 Stream-aquifer relations in the coastal area of Georgia and adjacent parts of Florida and South Carolina

or The shape a Oow-durution curve can be described
by a streamnow index. modified by Pettyjohn and Henning
( 1979) as:
where Q , (75'h pcrcemile) is the slreamnow equaled or 2
excceded 25 percent of the time and less than or equal to
or 75 percent of the time; and Q7~ (25'11 perccnLilc) is the stream-
now equaled or excecdcd 75 pcrccnt the time and less than or equal to 25 perccnt of the t imc. Stricker ( 1983) found that th e lower th c ratio. thc greater thc portion of ba!;c fl ow from
ground water. Discharge data from 14 stati ons for the period 1971 - 200 I
were analyzed to detenninc the stre<lml1ow index (tabl e 6).
Streamflow indices ranged from n low of 1.48 at rhe Brushy Creek (slnti on 02 197600) in thc SSO Ri ver Basin to a high to 7.31 at Little Smilla Ri ver (station 02227500) in the SAS River Basin.

The lowest index in thc SSO Ri ver Basm is for the stati on on l3n1shy Creek ncar 'Wrens. Ga. (station 02 197600)
( fig. 22: table 6). whcrc the lithology is mostly sand lnlerl::tyercd with cia), ::tquifer~ arc more deeply incised hy stream. . and ground walcr contributcs a large percentage of baseflow.
The now-duration curve has a gemle sloJX:. Brushy Creek i!> thc only s1:11ion in the uppa Coastal Plain area of the
SSO Ri vcr Bas111. The highest index in the SSO Rj ver Basin i~ Canoochec River near Claxton. Ga. (station 02203000) (fig. 23). where the lithology is mostly sand. The c urve i~
steep, indicati ng hig h runoff. In thi s area. aquifers arc dceply
buried and ground water contribu tes only a small percentage to bascllow. Thcrc appears to be liule di tTcrcnce between the
flow duration of mean daily strcamflows in the upper and lower Coastal Plain in the SSO Rivcr Basin. Brushy C reek in the upper Coastal Pl:lin has an index of 1.48. and Brier C reek in the lower Coaswl Plai n has an index of I .74 ( fi g. 22: wble 6).

~ r~ ( : : \ ' '-..._/

..,.. " " ' \

02197200 --

,,.., ~'-'"

/

.I' ( t0.60); .6. "

\ ' ) 02200410
r ~,

(+0. 17)

\ ~~

'

A02197I5J91.0-\~. 1~ I

A 02200120 ,

.._

'-- A {+0.58)

'\._
{ ,

>/ -

~ !..._"''~;,, ~ o~.02200440 1 ~ I

(+0.30)

\-
'-\
(+0. t6) )

l ~'I

\

{.__'

(+0.05
I
.~.0. 2(2+00.0l~89)t0 02200900

"rl o,.,\
(0)

"
'

r

7,40~1/0B2222(0l-0l1\013[.360060425)1~ -9-7%~ 830~ (+...0-;.:.5;~ 0;6-/2:);1; ( 9f/7,,31A~4...4..4'....(..-.._.0....2_5..)....~"/:' "\~

'

\
.....

'-'

,

)

'

'r

I 02201350

-!

" .llllfi1SON
~'' I 02201070 '

~
I I) \

'\
\ / I~,-

, ''r;. -1(02198000 \

v . ' /
(+0 .02)

'2- (+4 -9> '

r .1.. , \
'

~ 0220

(+0.10)
I
11~A --

/\

~ { 1 ~, -

(0) , ~20~ 1270.-1.\I (

\-

)

(+O.o 1>
':._02201300
, \_.~

.$ jI

0219812..0.. (+0.38)

,~.02198060 , 02198280 '- ~

0219817i>\

I (0) A 202

(+0.50)

1

~~{' '-: ~~~ ~ _)

\

JEKI"J\

' VEN

\, u ) ~

\~

< EXPLANATION '-., '- ...........-- -

N" '\'\

I I"'

'""\.

t ""\./'J~ l _/ Unit-area discharge, in

(0)

cubic feet per second

. . . . .__ v per square mile-gray

(-0.04) ::~ ;::.:.:.:-:::::

indicates zero or positive: hachures indicate negat1ve

I

0

10

20MILES

/

02201270 Streamflow gaging station A and identification number

0

10

20 KILOMETERS

Baso from U.S. Geological Survey 1: IOO,OOOscale oogilal dala

Figure 18. Selected streamflow gaging stations monitored during the 1954 drought and corresponding intermediate unit-area discharge.

Stream-aquifer relations 31

(+0.11 )

EXPLANATION
Unit-area disch arge, in cubic feet per second per square mile

02229000 Streamflow gaging station
.t.. an d identification number

Figure 19. Selected streamflow gaging stations monitored during the 1981drought and corresponding intermediate unit-area discharge.

32 Stream-aquifer relations in the coastal area of Georgia and adjacent parts of Florida and South Carolina

_.,. (+0 tO)'

A 02 19 7 6 0 0

02197830 \
A;-, (-0' 45) .... ...

\

.'..

(+0.57) ... (+0.07) / . ;;~

\ J

02201000 '

02201350

.... ........ 02198000

02198100

..

\

\

/

EXPLANATION

(0)
(-0.02) %~
....-

Unit-area discharge. in cubic feet per second per square mile- gray ind1cates zero or positive; hachures indicate negative

... 02229000 Streamflow gaging station and Identification number

N
t

/

0

10 20

I I I I II

30 MILES I

0 10 20 30 KILOMETERS

Base from U.S. Geological Survey I:IOO.OOOscale diQIIal data

Figure 20. Selected streamflow gaging stations monitored during th e 2000 drought and corresponding intermediate unit-area discharge.

Stream-aquifer relations 33

"~T-,'-,r-, ,-,..,'.-,--r-r--,--1--.--,..--r-~

I 000

f-

~

w w

lL

(-c.)ooz

. 1,000

'

~

=>o
(.)(,)

~w

~

.(f)
Wa:

<~a!.lw. 100

I 0
(f)
0

Alapaha River

(02317500)

' '

fww-
lL
-(c,)ooz =>o
0(,)
~w
.(f)
Wa: <~a!J.w.
I
(,) (f)
0

r .ooo
100 ~
10

--- -----
Upper Coastal Plain Brushy Creek

--- ---

10
0 10 20 30 <10 50 60 70 80 90 100
PERCENT OF T IME FLOW WAS EQUALED OR EXCEEDED

1 L-~--~--~--L-~--~--L-~L-~--~
0 10 20 30 40 50 60 70 80 90 100
PERCENT OF TIME FLOW WAS EQUALED OR EXCEEDED

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.

JO,l Table 6. Flow-duration curve index [(02 1l and curve shape for selected streams in the Salkehatchie- Savannah- Ogeechee,
Altamaha- Satilla- St Marys, and Suwannee River Basins, 1971- 2001 .
[mil. sq uare mile: ft'!s. cubic foot per second: part of basin: U. upper: L. lower!

Station identification
02 175500 02 197600 02 198000 02202500 02203000
022 15500 02223500 02225000 02225500 02226000 02226500 02227500 02228000
023 17500

Station Name

Part of Drainage area

basin

(mil)

Salkehatchie- Savannah- Ogeechee River Basin

Salkchatchic Ri ver ncar Miley. S.C. Brushy Creek ncar Wrens. Ga. Brier Creek at Millhaven, Ga.

u

341

u

28

u

646

Ogccchec River ncar Eden, Ga.

L

2,650

Canoochcc River ncar Claxton, Ga.

L

555

Altamaha- Satilla- St Marys River Basin

Ocurnulgcc River at Lumber City. Ga. Oconee River at Dublin, Ga. Altamaha River ncar Baxley. Ga. Ohoopec River near Reidsville, Ga. Altamaha River at Doctortown. Ga. Satilla River ncar Waycross, Ga. LilLie Sa1illa River ncar Offerman, Ga. Satilla River at Atkinson, Ga.

u

5.180

u

4.390

u

11.600

u

1,1 10

L

13,600

L

1.190

L

646

L

2,790

Suwannee River Basin

Alapaha Ri ver at Statenville. Ga.

L

1,390

~s (ftl/s)
444
24 755 2.940 674
6,920 5.480 15.300 1.41 0 18,700 1.260
642 2.995
1.450

~
(ft1/s)
157
II
250 557 23
2.060 1.120 3.680
105 4.1 40
66 12 218
96

Index

Curve shape

1.68 Gentle

1.48

do.

1.74

do.

2.3

Steep

5.41

do.

1.83 Gentle

2.21

Steep

2.04

do.

3.66

do.

2.13

do.

4.37

do.

7.31

do.

3.7 1

do.

3.89

Sleep

34 Stream-aquifer relations in the coasta l area of Georgia and adjacent parts of Florida and South Carolina

10 ,0 00

l:i:i
uw. 1,000

(c-.)noz =>o
(.)(.)
~. elln.l 100
LU 0:
<~.Q!>.w

:I:
(.)

10

en

0

I,00000

1ww- 10.000 u.

-m (.)oz =>o
(.)(.)
~.wen ~a:
a:W
<:::Q.
:I:
(.)
en 0

1.000 100 10

, , ,

Upper Ba s1n

--- - --- ' -- ---,__ _

Ocnulgcc Rver
-- -- ---- ..

Lmle Sa1illa R1ver

0 10 20 30 40 50 60 70 80 90 100
PERCENT OF TIME FLOW WAS EQUALED OR EXCEEDED
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.

01 ~~~~---L--~--~~--~--~--~~ 0 10 20 30 40 50 60 70 80 00 100
PERCENT OF TIME FLOW WAS EQUALED OR EXCEEDED
f igure 24. Duration of mean daily streamflow for linlc Satilla River (02227500) near Offerman. Georgia. and Ocmulgee River (02215500) at Lumber City, Georgia. in the Altamaha- SatillaSt Marys River Basin. 1971 - 2001 .

In the SAS Ri ver Basin. all measured discharges have indices greater than 2. except the O crnulgec River. which has an index o f 1.83. An index greater than 2 corresponds to a steep slopl:. The lowest ratio in the SAS River Basin is Ocmulgce Rivl:r at Lumber City. Ga. (station 02215500) (fi g. 24), where the lithology is a heterogeneous mix of sand, si lt. and clay. Thi:; station is located in thl: upper part o f the basin where basenow dominates streamnow. The highest mdcx (7.31 ) in the SAS River Basin is the station on the Liule Satilla River at Offerman. Ga. (station 02227500) (fi g. 24), whl:re the lithology is mostly c lay. sand, and silt beds containing phosphate. This station is located in the lower part of the basin. where runo ff dominates slrc::unl1ow and the aquifer is deeply buried.
In the Suwannee Ri ver Basin, the only discharge that was analyzed was at the Alapaha River at Statenville. Ga. (station 023 17500) (lig. 25). where the lithology is mostl y sand. silt, clay. limestone, and dolomite. The shape o f the curve indicates thcr~ is a large contribution of runoff to stn:amllow, 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 bascflow for streams in the area. Mean annual baseflow calculated by HYSEP for the 14 stations for the period 1971 -200 I were compared to now dura tions at the !\tations ranging from Q1 to Q9'J; the best fit between HYSEP estimates and n ow duration was at the
Q,5 flow duration (n ow is equaled or exceeded 35 percent
o f the time). The best regression model had an r-squared (r) value of 0.9970 and a p-value of less than 0.000 I (table 7). Linear-regression a nalysis was used on the eight stations selected for HYSEP to compare results. Bmh sets of data show the Q35 as the best estimate of basef1ow. The linear regression

of n ow duration is probably more representative of average climatic condition" rather than drought conditions because the analysi. compares mean annual baseflow and n ow 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 Qll(, flow duration. Figure 26 illustrates the reg ression of QHwith mean
annual basenow from HYSEP.
Compa rison of Results
Major variation exists between bascflow cstimntion using drought-strearnnow analysis and both HYSEP and linearregression analysis of flow duration. Slight variation exists between HYSEP and now-duration methods. The same 14 stations were selected to make n comparison of the three methods. Using the drought-streamflow analysis. the mmimum contribution to streamflow from baseflow was observed. During dro ught conditions. the following observations were made: ( I) total streamflow was equivalent to basen ow; (2) surface-wate r runoff to streamn ow 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. basenow ranged from 33 to 70 percent of total streamflow during 1997 (average conditions arc best represented by 1997 data) and increased to 27 to 81 percent in drought years 198 I and 2000, respectively (table 3). r or the study area. mean annual bascflow during drought conditions ( 1981 and 2000) ranged fro m 0 to 24 percent of mean annual streamnow for 1971 -200 I (table 8). These values arc far below the 39-74 percent estimated using HYSEP and 65- 102 percent estimated using linear-regression analysis of flow duratio n (fig. 8).

Stream-aquifer rel ations 35

Table 7. Coefficient of determination (r2) and residual standard

of error for flow durations evaluated as indicators of baseflow

f-UJ UJ lL
0
3Ciio~
~hl .(/)
w a:
(!)u;
~0..
I 0
(/)
iS

100
10 -
-~!_j
0.1 '--'----'-- ' - ..L-- .. 0 10 20 30 ~0 50 60 70 60 90 100

PERCENT OF TIME FLOW WAS EQUALED OR EXCEEDED

Figure 25. Duration of mean daily streamflow for Alapaha River (station 02317500) at Statenville, Georgia, in the Suwannee River Basin, 1971 - 2001.

for 8 and 14 streamflow gaging stations selected in the Salkehatchie- Savannah- Ogeechee. Altamaha- Satilla- St Marys, and Suwannee River Basins. 1971 - 2001.
1P-vah11.: = lc.<s than 0.5 for the 8 stalion,: less 1h:m 0.000 I for the 1-l stations !

Flow r-squared duration 8 stations

0 ,,

0.69

0",

0.75

Ow

0.77

Q,,

0 .82

Q ,,,

0.88

0,,

0.92

Q ,.,

0.95

Q ,,

0.98

Q.,,

0.98

Q.,

0.92

Q!<l

0.8 1

Q,

0.65

Q...,

0.46

Residual standa rd error

14 stations 8 stations 14 stations

0.98

12!\.-10

-163.7

0.98

116.-10

3-16.3

0 .98

110.10

345

0.91!

97.114

311.-1

0.99

80.82

238.7

0.99

66.41

202.8

0.99

52.09

179.8

1.00

29.7 1

168.8

0.99

36.56

169.4

0.99

63.81 205.7

0.99

100.60

224.7

0.99

136.60

257.1

0.99

170.20

266.1

Q.,

0.33

0.99

189.60

275.4

Q.,.,

0.24

0.98

202.50

307.4

Q,

0.18

0.98

209.30

347.5

600 A.

o.u

0. 15

0.98

213.90

377.8

Czl 500
8UJ 400
(/)

r2 =0.9836

/
/0 0 /
/

Q.,

0. 12

0...,

0. 11

Q.,

0. 10

0.98

217.80

412 .6

0.97

219.30

456.4

0.97

219.50

481 .6

a:
UJ

300

0..

Q.

0. 13

0.97

216.70

518.2

ljj 200

wu. 0

100

:a:>i

0 9/

0

0

100 200 300 400 500 600

~

The fl ow-duration method of estimating basellow gives an overestimation of base flow for a particular stream. Regression analyses of streamflow data indicate that the flow-duration point that most closely estimates basefl ow is the 35-per-

~tt a.ooo B.

(/)

r 2 =0.9970

<t:

CD

/

..1 6.000

/

:3zz
<t:

4,000

/
<>



~
:::E 2.000

/
-"o
/

cent fl ow-duration point (Q35) (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-perccm flow-durati on point C<4s). The difference could
merely be a matter of interpl'etation. Q35 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 Q65 Never-
theless, the linear regression of streamflow duration is not a
re liable estimato r of baseflow, panicularly in the upper pan of

the basin area where streams intersect the aquifer as indicated

0

2 ,000

4,000

6.000

8.000

DISCHARGE AT 35-PEACENT DURATION (0 35) IN CUBIC FEET PEA SECOND

by the I02-percent baseflow estimatio n of the Salkehatchie River, nor in the lower pan 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 fl ow-

0. Figure 26. Reg ression of 5 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.

duration method as a good estimator of basefl ow. The HYSEP method of estimating baseflow mos1 likely
relates to actual bascfl ow of the three methods used. HYSEP systematically separates basctlow from runoff by connecting low points of the streamflow hydrograph. HYSEP is most

36 Stream-a quifer relations in the coastal a rea of Georgia and adjacent parts of Florida and South Carolina

Table 8. Comparison of three methods used to calculate baseflow for selected streamfl ow gaging stations in the Salke hatchie Savannah- Ogeechee, Altamaha- Satilla- St Marys and Suwannee River Basins, 1971 - 2001.

Ihold. ~1 3t ions ~<.:l<.:l'l<.:tl fnr II YSI:P: tni . M)l13T<.: mik: n'!~. c ubic fool Jl<.:Ts.:..:ond: utlyr. inch per )'C:t r: t;<. Jl<.:r'CCIII of tOI:tl Strc:unllO\\ 1
--Estimated bascllow

Station Drainage 31-year mean identification area annual streamflow

Flow duration (!1,1

HYSEP

1981 and 2000 average of lowest flow

Mea n annua l streamflow

1981

2000

(mi') (ft'/s ) (in/yr) (ftl/s) (inJyr) (%) (ftl/s) (i n/yr) (%) Salkehatchie Savannah- Ogeechcc River Basin

(h' /s) (in/yr) (%)

(ft'/s) (ft'/s) ----

02 175500 02 t97600 02t9!i000 02202500 02203000

'\.) 1.0 :;57.0 I.J.23

28

24.5 1Ul7

646 598 12.58

2.650 2.330 11.9.J

555

.J !W

11.84

365 () 14.50 102 246

19 9.2 1 7!!

17

51!8 12.4

')!\

442

2. 160 11.1 93 1.529

.)(})

9.82 83

257

9.!!0 61) S.2.J 69 IJ.29 74 7.11:1 66 6.29 5.J

21\.0 1.11 II

1.35 1.62 .!0

95 2 21

136

69 C)

2.5 .06

189 I) 13.!!
3!D
82.' 116

174.0 12. 1 297
803
169

Altamaha- Satilla- St Marys Rtver Basin

022 15500 02223500 02225000 022255(10 0:!226000 02226500 02227500 02228000

5.1 80 4.390 11.600 1. 1I0 13.600 1.190
(>46
2.790

5.510 4.390 11.700 1.040 13.9CXl t, JJ()
542 2.390

1-t..J.J 5.210 13.7

13.54 3.950 t2.2

13.69 t0.800 t2.6

12.72 t!63 10.6

t3.87 12,<)()() 13

12.56 n5 8.2

11.38

35~

7.42

11.63 1.860 9.05

95 3.811 90 2.238 9:! 7.704 t!J 585 93 9.330 65 478 65 2t2 78 1.171

)()

69

6.9 51

9.02 66

7. 15 57

9.3 1 67

5.4 t 43

4.45 39

5.7 49

928 2.43 2.J

399 1.23 18

1.570 1.84 20

28

.34 5

1,590 1.6 17

8.75 . I 2

0 0

0

33

.16 3

2.570 2.230 5.330
309 6.050
11 8 75.4 326

2.460 1.780 -1.850
476 5.640
25:! 85.2 438

Suwannee River Basin

02.\17500

1.390 l,t70 tl.34

876 8.49 75 656 6.36 56

31.0 0.30 5

1311

437

re liable for c.:stim:.u ing drainage areas of less than 100 mi2 with at least 20 years of contin uous streamflow data. Because of the limited avai lability of data. the dra inage-area size criterion was increased and the period-of-record criterion was increased to include extremes in precipitation conditions. Table 8 compares mea n annual basef1ow of selected streams using the hydrograph-separation and linear-regression analysis of fl ow duration, and d rought-streamflow analysis methods. An example of the variability in baseflow estimation is observed at station 02175500 (Salkehatchie River) (fig. I ). Part of the river is in the upper Coastal Plai n where there is a high degree of interconnection between the stream and the aquifer resulting in a substantial contributi on o f ground water to streamll ow. According to the methods used. linear-regression analysis estimates that baseflow is equivalent to the flow at Q35, which in this case is I 02 percent of the mean annu:.l strea mflow. The dro ught-streamflow a nalysis estimates that base flow is I I percent of total streamflow. Again, this is an unreasonable estimation because the stream is in the upper Coasta l Plain where there is a greater intcrconnectivity with the aquifer. The HYSEP method estimates basefl ow as 69 percent of total streamflow, which seems most reasonable of the three meth ods, considering the size and location of the basin.

Summary
Stream-aquifer relations were evaluated in the 67-coumy area of southeas t Georgia. southwest South Carolina. and northeast Florida (55 counties in Georgia, 5 counties in Florida, and 7 counties in South Carolina) dun ng a variety of climatic conditio ns for the period from 1971 - 200 I. Gro und-water discharge to streams was estimated using three methods: ( I) HYSEP, an auto mated hydrograph-separatio n program; (2) d rought measurement of baseflow: and (3) a comparison of mean annual baseflow and fl ow-dur::nion data using a simple linear-regression analysis. The hydrographseparation method provides the best es timate of mean annual ground-water discharge to streams in the study area. The analysis of drought streamflow provides an estimate of the minimum gro und-water discharge to streamflow, whereas linear-regression analysis overestimates an ave rage value for a given basin. Analyses were conducted using 8 continuo us-record streamflow gaging stations fo r hydrograph separatio n, 14 continuo us-record streamfl ow gaging stat ions for streamflow duration, and 62 continuous-record and partialrecord streamflow gaging stations for dro ught streamflow; 9 U.S. Geological Survey we lls: and I I Natio nal Weather

Summary 37

Service stations. Str<.::ams and tributaries were grouped into the Salkchatchic- Savannah- Ogccchec River. Altamaha- SatillaSt Marys Ri ver, a nd Suwannee River Basi ns for this study.
Water in streams and aquifers inwract through a dynamic hydrologic system includ ing aquifers. streams. I'Cscrvoirs. and floodplains. These systems arc interconnected and form a hydrologic environment that is stressed by natural hydrologic. climatic, and anthropogenic factors. Under steady-state Cl)nditions. most ground-water systems can be divided into three subsyste ms: local now, characterized by relatively shallow and short flow paths that extend from a topographic high to an adjat:ent topographic low; intermediate now. which inc ludes at least one local flow system bctw0cn respective point!~ of recharge and discharge: and regional flow. which begins at or near a m<vor ground-water divide and terminates at a regional drain.
Recharge to the hydro logic system is provided by rainfall that ranges from an average of about 47 to 53 inches per year based on the 30 -year period 197 1-2000. Most of the recharge is either discharged from the shallow, local flow systems into small streams, or is lost as evapotranspiration. ln the intermediate t1ow system, some water is discharged to major tributaries. Climatic effects dominate in the surficial aquifer. Water levels generally arc highest in the winter and early spring when precipitation is greatest and evapotranspiration is least; water levels arc lowest during the summer and fall when precipitation is least and evapotranspiration is highest. In the lower Coastal Plain, with the exception o f the unconfined section of the surficial aquifer system, the aquifers are deeply buried and confined. In this area, c limatic effects arc greatly diminished, and fluctuation s are due to changes in ground-water pumping.
Three methods to estimate basetlow were compared because a number of variables can affect basellow including regulation of flows; physical properties of the basin such as vegetative cover, slope. area. shape, land usc, soil thickness; and infillrati on 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 neglig ible diversion or regulation, drainage area less than I,400 square miles, and at least 3 1 years o f continuous record. For the 8 streamflow gaging stations selected for HYSEP, basellow contributed from 39 to 74 percent of streamflow with a mean contribution of 58 percent.
During a high-precipita tion year, basetlow accounted for 48 percent of total streamflow, 63 percent during an average-precipitation year. and 60 percent during a low-precipitatio n 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.
Basetlow estjmates vary f'rom U1e upper and lower parts of a basin. Mean annua l baseflow in the upper SalkehatchieSavannah- Ogeechee River Basin during 1971 - 200 I ranges from 66 to 74 perce nt and is 54 percent in the lower basin. In the upper Altamaha- Satilla- Sr Marys River Basin , baseflow

is about 57 percent of total strcamt1ow : in the lower part of

the basin, baseflow ranges from about 39 to 43 percent of total

streamflow. In the lower part of the Su wannee River Basin,

basefl ow is about 56 percent of total stream!low.

Drought streamflow represents a quantitative estimate of

minimum ground-water discharge to streams because during

drought periods, streamflow is composed mostly of basefl ow

as estimated by HYSEP. During droughts. ground-water

contribution to streamflow mostly is from the intermediate and

regional flow syste ms. During the I98 I and 2000 droughts,

basdlow contribution ranged from 0 to 24 percent of stream-

flow. This lo\v contribution most likely is due to a lower

ground-water levels during drought.

Linear-regression analysis was used to determine the

now duration that b0St estimates bascflow for streams in the

an:a. Mean annual baseflow at 14 streamflow gaging stations

in the study area for 197 1- 200 I were compared to the Q to

1

Q 99

flow

durations

at

those

stations

us in g

a

stati s tic al

c o m p ut e r

program; the best fit between HYSEP estimates and flow

duration was at the Q3S now duration. Discharge data during

197 1-2001 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- Savan-

nah-Ogecchce River Basin to a high of 7.31 at Little Satilia

River in the Altamaha- Satilla-St Marys River Basin . Gener-

ally, high indices are associated with steep slopes that are

indicative of limited basin storage and dominant contribution

from runoff. Low indices arc associated with nat slopes that

arc indicative of equal contribution of ground water and mnoff.

Comparison of the three methods used to estimate

baseflow shows that drought-streamflow conditions arc a

minimum estimate o f mean-annual bascf1ow contributions.

Because ground-water levels may decline during droughts,

the amount of basefl ow to streamflow correspondingly

declines. The linear-regression analysis of streamflow dura-

tion overestimates baseflow when generalizing across a large

basin because of variability in size and geology o f 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

basetlow estimation at Salkehatchic River (station 02175500).

Part of the Salke hatchie 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 contr ibution

o f ground water to streamflow. According to the methods

used, linear-regression analysis estimates that baseflow is

equivalent to the n ow at Ql.~' which in this case is 102 per-

cent of the mean annual streamflow. The drought-streamflow

analysis estimates basef1ow as I I percent of total streamfl ow.

This is an unreasonable estimation because part of the stream

is in the upper Coastal Plain where there is a high degree o f

imerconnectivity with the aquifer. The HYSEP method esti-

mates basefl ow as 69 percent of total streamflow. The same

14 stations were used to make a comparison among the three

methods used to est imate bascflow.

38 Stream-aquifer rel ations in the coastal area of Georgia and adjacent parts of Florida and South Carolina

Overall. for the study area. mean annual bascflow during the 1981 and 2000 droughts ranged from 0 to 24 pcrcelll of
mean annual towI strcarnllow for the pcnod 1971 - 200 I using
drought-streamflow analysis. During 1971 - 200 I . baseflow was e~timmcd a~ ranging from 39- 74 pcrcem of streamflow using HYSEP and 65- 102 percelll u~ing ljnear-rcgression analysis of flow dur;Hion .
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