GROUND-WATER RESOURCES OF THE

UPPER CHATTAHOOCHEE RIVER BASIN IN 

GEORGIA—SUBAREA 1 OF THE

APALACHICOLA-CHATTAHOOCHEE-FLINT AND

ALABAMA-COOSA-TALLAPOOSA RIVER BASINS

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

ALABAMA DEPARTMENT OF ECONOMIC AND COMMUNITY AFFAIRS

OFFICE OF WATER RESOURCES

GEORGIA DEPARTMENT OF NATURAL RESOURCES

ENVIRONMENTAL PROTECTION DIVISION

NORTHWEST FLORIDA WATER MANAGEMENT DISTRICT

U.S. ARMY CORPS OF ENGINEERS, MOBILE DISTRICT

Open-File Report 96-363

GROUND-WATER RESOURCES OF THE UPPER 

CHATTAHOOCHEE RIVER BASIN IN GEORGIA—SUBAREA 1

OF THE APALACHICOLA-CHATTAHOOCHEE-FLINT AND 

ALABAMA-COOSA-TALLAPOOSA RIVER BASINS

By Melinda J. Chapman and Michael F. Peck

U.S. GEOLOGICAL SURVEY

Open-File Report 96-363

Prepared in cooperation with the

ALABAMA DEPARTMENT OF ECONOMIC AND COMMUNITY AFFAIRS

OFFICE OF WATER RESOURCES

GEORGIA DEPARTMENT OF NATURAL RESOURCES

ENVIRONMENTAL PROTECTION DIVISION

NORTHWEST FLORIDA WATER MANAGEMENT DISTRICT

U.S. ARMY CORPS OF ENGINEERS, MOBILE DISTRICT

Atlanta, Georgia

1997
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

For further information, please write to

District Chief

U.S. Geological Survey

Peachtree Business Center

3039 Amwiler Road, Suite 130

Atlanta, GA 30360-2824

Copies of this report may be purchased from

U.S. Geological Survey

Branch of Information Services

Denver Federal Center

Box 25286

Denver, CO 80225-0286

_____________________________________________________________________________________________
iii

CONTENTS

Abstract 1

Introduction 2

Purpose and scope 2

Physical setting of study area 4

Physiography 4

Climate 4

Ground-water use 4

Previous investigations 6

Well and surface-water station numbering systems 8

Approach and methods of study 8

Mean-annual baseflow analysis 9

Drought-flow analysis 11

Acknowledgments 12

Conceptual model of ground-water flow and stream-aquifer relations 12

Hydrologic setting 14

Ground-water system 14

Geology 14

Aquifers 15

Ground-water levels 18

Surface-water system 19

Ground-water discharge to streams 22

Mean-annual baseflow 22

Drought flow for 1941, 1954, and 1986 24

Ground-water utilization and general development potential 31

Ground-water exploration-program examples 32

Summary 33

Suggestions for further study 34

Selected references 35
iv

ILLUSTRATIONS

Figures 1-2. Maps showing:

 1. Subareas and major streams in the Apalachicola-Chattahoochee-Flint and Alabama-CoosaTallapoosa River basins 3

 2. Physiographic provinces and subareas in the Apalachicola-Chattahoochee-Flint and AlabamaCoosa-Tallapoosa River basins 5

Figure 3. Graph showing a streamflow hydrograph, separated by program SWGW 10

4. Schematic diagrams showing (A) distribution of ground-water flow in an areally extensive, isotropic, 

homogeneous aquifer system and (B) example of local, intermediate, and regional groundwater flow 13

5. Map showing major aquifers in and subareas of the Apalachicola-Chattahoochee-Flint and AlabamaCoosa-Tallapoosa River basins 16

Figures 6. Schematic diagram showing the conceptual ground-water and surface-water systems in Subarea 1: 

fracture-conduit aquifer in the igneous and metamorphic rocks of the Blue Ridge and 

Piedmont Provinces 17

Figure 7. Graph showing water-level fluctuations in regolith well 11FF04, DeKalb County, Georgia, during

(A) 1980-95 and the (B) drought of 1986 19

8. Map showing selected stream-gaging stations, well fields, and observation well 11FF04, 

Subarea 1 20

9. Graph showing relations among mean-annual stream discharge, mean-annual baseflow, and drought 

flow, Chattahoochee River, Subarea 1 30

TABLES

Table 1. Estimated ground-water use, by category, Subarea 1, 1990 4

2. Generalized geologic units in Subarea 1, and water-bearing properties, chemical characteristics, and 

well yields 15

3. Selected active and discontinued continuous-record stream-gaging stations in the upper 

Chattahoochee River basin, Subarea 1 21

4. Major impoundment in the upper Chattahoochee River basin, Subarea 1 21

5. Mean-annual stream discharge, estimated annual and mean-annual baseflow, and unit-area 

mean-annual baseflow at selected gaged streams in the upper Chattahoochee River basin, 

Subarea 1 23

6. Stream discharge during the month of October of the drought of 1941, Subarea 1 24

7. Stream discharge during the months of September and October of the drought of 1954, Subarea 1 25

8. Stream discharge during the month of July of the drought of 1986, Subarea 1 27

9. Relations among mean-annual stream discharge, and estimated mean-annual baseflow and drought 

flow in the Chattahoochee River, Subarea 1 29

10. Estimated drought flows and mean-annual baseflow in the upper Chattahoochee River basin; and ratio 

of average drought flow to mean-annual baseflow, Subarea 1 29

11. Relation between 1990 ground-water use and ground-water discharge during mean-annual baseflow, 

average drought flow, and minimum drought flow, Subarea 1 31
v

CONVERSION FACTORS, ABBREVIATIONS AND ACRONYMS,

AND VERTICAL DATUM

CONVERSION FACTORS

Multiply by to obtain

Length

inch (in.) 25.4 millimeter

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

foot (ft) 0.3048 meter 

square foot (ft2) 0.0929 square meter

mile (mi) 1.609 kilometer

feet per mile (ft/mi) 0.1894 meter per kilometer

Area

acre 4,047 square meter

square mile (mi2) 2.59 square kilometer

Volumetric rate and volume

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

448.831 gallon per minute 

0.6463 million gallons per day

cubic foot per second per square mile (ft3/s/mi2) 0.01093 cubic meter per second per square 

kilometer

gallon per minute (gal/min) 6.309 x 10-5 cubic meter per second

2.228 x 10-3 cubic foot per second

0.06308 liter per second

1,440 gallon per day

gallon per day (gal/d) 3.785 x 10-3 cubic meters per day

million gallons per day (Mgal/d) 1.547 cubic foot per second

63.09 cubic meter per second

694.44 gallons per minute

gallon per minute per foot 

of drawdown (gal/min/ft)

1.24 x 10-2 cubic meters per minute per minute 

per meter of drawdown

acre-foot 325,900 gallon

Transmissivity

foot squared per day (ft2/d) 0.0929 meter squared per day

Temperature

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

° C = 5/9 x (° F - 32)
vi

ABBREVIATIONS AND ACRONYMS

ACF Apalachicola-Chattahoochee-Flint River basin

ACT Alabama-Coosa-Tallapoosa River basin

ADAPS Automated Data Processing System

CMWA Cobb-Marietta Water Authority

Corps U.S. Army Corps of Engineers

MOA Memorandum of Agreement

GWSI Ground Water Site Inventory database

PGC Peachtree Golf Club

RORA Computer program (Rutledge, 1993)

SWGW Surface Water-Ground Water; computer program (Mayer and Jones, 1996)

USGS U.S. Geological Survey

VERTICAL DATUM

Sea Level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NVGD of 1929)—a 

geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, 

formerly called Sea Level Datum of 1929.
vii

GLOSSARY

Alluvium—Sediment transported and deposited by flowing water.

Altitude—As used in this report, refers to the distance above sea level.

Anisotropic—Condition having varying hydraulic properties of an aquifer according to flow direction.

Annual—As used in this report, refers to a water year.

Aquifer—A formation, group of formations, or part of a formation that contains sufficient saturated permeable material to 

yield significant quantities of water to wells and springs.

Artesian—Synonymous with confined.

Baseflow—That part of the stream discharge that is not attributable to direct runoff from precipitation or melting snow; it 

is usually sustained by ground-water discharge.

Bedrock—A general term for the consolidated rock that underlies soils or other unconsolidated surficial material.

Clastics—Rocks composed of fragments of older rocks, for example, sandstone.

Colluvium—Heterogeneous aggregates of rock detritus resulting from the transporting action of gravity.

Cone of depression—A depression of the potentiometric surface, often in the shape of an inverted cone, that develops 

around a well which is being pumped.

Confined aquifer—An aquifer bounded above and below by impermeable beds or by beds of distinctly lower permeability 

than that of the aquifer itself; ground water in the aquifer is under pressure significantly greater than that of the 

atmosphere.

Continuous-record gaging station—Complete records of discharge obtained using a continuous stage-recording device 

through which either instantaneous or mean-daily discharge may be computed for any time, or any period of time, 

during the period of record.

Crystalline rock—A general term for igneous and metamorphic rocks.

Darcian flow—Flow that is laminar and in which inertia can be neglected.

Dendritic drainage—A branching stream pattern that resembles the branching of trees.

Drought—There is no accepted definition of drought. As used in this report, a period of deficient rainfall extending long 

enough to cause streamflow to fall to unusually low levels for the period of record.

Evapotranspiration—The combined evaporation of water from the soil surface and transpiration from plants.

Faults—Fractures in the Earth along which there has been displacement parallel to the fault plane.

Foliation—A planar or layered structure in metamorphic rocks that is caused by parallel orientation of minerals or bands 

of minerals.

Fluvial—Pertaining to the actions of rivers.

Fracture—Breaks in rocks due to intense folding or faulting.

Geologic contact—The boundary surface between one body of rock or sediment and another.

Ground-water recharge—The process of water addition to the saturated zone or the volume of water added by this 

process.

Head, static—The height above a standard datum of the surface of a column of water (or other liquid) that can be 

supported by the static pressure at a given point. The static head is the sum of the elevation head and the pressure head.

Head, total—The total head of a liquid at a given point is the sum of three components:

(a) the elevation head, which is equal to the elevation of the point above a datum, (b) the pressure head, which is the 

height of a column of static water that can be supported by the static pressure at the point, and (c) the velocity head, 

which is the height to which the kinetic energy of the liquid is capable of lifting the liquid.

Heterogeneous—Pertaining to a substance having different characteristics in differing locations.
viii

GLOSSARY—Continued

Hydraulic conductivity—The capacity of a rock to transmit water. It is expressed as the volume of water that will 

move through a medium in a unit of time under a unit hydraulic gradient through a unit area measured 

perpendicular to the direction of flow.

Hydraulic gradient—A change in the static pressure of ground water, expressed in terms of the height of water above 

a datum, per unit of distance in a given direction.

Hydrograph separation—Division of the stream hydrograph into components of aquifer discharge and surface 

runoff.

Igneous rock—Rocks which have solidified or crystallized from a hot fluid mass called magma. 

Intergranular porosity—Porosity resulting from space between grains.

Intrusive igneous rocks—Masses of igneous rock formed by magma cooling beneath the surface.

Isotropic—Condition in which hydraulic properties of an aquifer are equal in all directions.

Joints—Fractures in rocks, often across bedding planes, along which little or no movement has taken place.

Mafic—Applied to the ferromagnesian minerals or to igneous rocks relatively rich in such minerals.

Mean annual—As used in this report, refers to the average of the annual values for a specified period of record.

Metamorphic rock—Rocks derived from pre-existing rocks by mineralogical, chemical, and structural alterations due 

to endogenetic processes.

Partial-record gaging station—Is a particular site where limited streamflow and/or water-quality data are collected 

systematically over a period of years.

Permeability—The property of a porous medium to transmit fluids under an hydraulic gradient.

Porosity—The amount of pore space and fracture openings, expressed as the ratio of the volume of pores and 

openings to the volume of rock.

Potentiometric surface—An imaginary surface representing the static head of ground water and defined by the level 

to which water will rise in a tightly cased well.

Primary porosity—Porosity due to the soil or rock matrix; the original interstices created when a rock was formed.

Recession index—The number of days required for discharge to decline one complete log cycle.

Regolith—Loose, unconsolidated and weathered rock and soil covering bedrock.

Residuum—The material resulting from the decomposition of rocks in place and consisting of the nearly insoluble 

material left after all the more readily soluble constituents of the rocks have been removed.

Rock—Any naturally formed consolidated material consisting of two or more minerals.

Run-off—Precipitation that flows from the surface of the land and into streams and rivers.

Saprolite—Surficial deposits produced by the decay of rocks and remaining as residuals.

Secondary openings—Voids produced in rocks subsequent to their formation through processes such as solution, 

weathering, or movement.

Secondary porosity—Porosity due to such phenomena as dissolution or structurally controlled fracturing.

Soil—The layer of unconsolidated material at the land surface that supports plant growth.

Specific capacity—The rate of discharge of water from the well divided by the related drawdown of the water level 

within the well.

Specific yield—The ratio of the volume of water which the porous medium after being saturated, will yield by gravity 

to the volume of the porous medium.

Storage coefficient—The volume of water an aquifer releases from or takes into storage per unit surface area of the 

aquifer per unit change in head (virtually equal to the specific yield in an unconfined aquifer).
ix

GLOSSARY

Stream discharge—The volume of water flowing past a given point in a stream channel in a given period of time.

Transmissivity—The rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of an 

aquifer under a unit hydraulic gradient. It equals the hydraulic conductivity multiplied by the aquifer thickness.

Trellis drainage—A river system resembling a trellis or rectangular pattern and characteristic of areas of folded 

sedimentary rocks where tributaries cut channels through less resistant beds.

Unconfined aquifer—An aquifer in which the water table is a free surface at atmospheric pressure.

Unit-area discharge—Stream or ground-water discharge divided by the drainage area.

Water table—Upper surface of a zone of saturation under atmospheric pressure.

Water year—The standard water-year used by the U.S. Geological Survey is from October 1 to September 30 of the 

second calendar year.
1

GROUND-WATER RESOURCES OF THE UPPER CHATTAHOOCHEE 

RIVER BASIN IN GEORGIA—SUBAREA 1 OF THE

APALACHICOLA-CHATTAHOOCHEE-FLINT AND

ALABAMA-COOSA-TALLAPOOSA RIVER BASINS

By Melinda J. Chapman and Michael F. Peck

ABSTRACT

Drought conditions in the 1980’s focused attention on the multiple uses of the surface- and ground-water 

resources in the Apalachicola-Chattahoochee-Flint (ACF) and Alabama-Coosa-Tallapoosa (ACT) River basins in 

Georgia, Alabama, and Florida. State and Federal agencies also have proposed projects that would require additional 

water resources and revise operating practices within the river basins. The existing and proposed water projects create 

conflicting demands for water by the States and emphasize the problem of water-resource allocation. This study was 

initiated to describe ground-water availability in the upper Chattahoochee River basin of Georgia, Subarea 1 of the 

ACF and ACT River basins, and to estimate the possible effects of increased ground-water use within the basin.

Subarea 1 encompasses about 2,430 square miles in the Piedmont and Blue Ridge physiographic provinces of 

north-central Georgia. Subarea 1 includes about 28 percent of the total 8,740 square-mile area of the Chattahoochee 

River basin. The study area is underlain by a two-component aquifer system composed of a fractured, crystalline-rock 

aquifer characterized by little or no primary porosity or permeability; and the overlying weathered regolith 

(saprolite), which generally behaves as a porous-media aquifer. In some areas, a transition zone lies between the 

regolith and unweathered crystalline bedrock.

The conceptual model described for this study qualitatively subdivides the ground-water flow system into 

local (shallow), intermediate, and regional (deep) flow regimes. Ground-water discharge to tributaries mainly is from 

local and intermediate flow regimes and varies seasonally. The regional flow regime probably approximates steadystate conditions and discharges chiefly to major drains such as the Chattahoochee River. Ground-water discharge to 

major drains originates from all flow regimes. Mean-annual ground-water discharge to streams (baseflow) is 

considered to approximate the long-term, average recharge to ground water. The mean-annual baseflow was 

estimated using an automated hydrograph-separation method, and represents discharge from the local, intermediate, 

and regional flow regimes of the ground-water flow system. Mean-annual baseflow exiting Subarea 1 was estimated 

to be 2,570 cubic feet per second. Mean-annual baseflow represented about 69 percent of total mean-annual stream 

discharge for the period of record. 

Stream discharge for selected sites on the Chattahoochee River and its tributaries were compiled for the years 

1941, 1954, and 1986, during which sustained severe droughts occurred throughout most of the ACF-ACT area. 

Stream discharge was assumed to be sustained entirely by baseflow during the latter periods of these droughts. 

Estimated baseflow (unregulated) near the end of the individual droughts (1941 and 1954) averaged about 19.3 

percent of the estimated mean-annual baseflow in Subarea 1.

The potential exists for the development of ground-water resources on a regional scale throughout Subarea 1. 

Estimated ground-water use in 1990 was about 1.1 percent of the estimated mean-annual baseflow; and 5.8 percent of 

the average drought flow. Because ground-water use in Subarea 1 represents a relatively minor percentage of groundwater recharge, even a large increase in ground-water use in Subarea 1 in one State is likely to have little effect on 

ground-water and surface-water occurrence in the other. Indications of long-term ground-water level declines were 

not observed; however, the number and distribution of observation wells for which long-term water-level 

measurements are available in Subarea 1 are insufficient to draw conclusions. 
2

INTRODUCTION

Increased and competing demands for water and the droughts of 1980-81, 1986, and 1988 in the ApalachicolaChattahoochee-Flint (ACF) and Alabama-Coosa-Tallapoosa (ACT) River basins have focused the attention of water 

managers and users in Alabama, Florida, and Georgia, on the water resources in the two basins. The ACF-ACT River 

basins encompass about 42,400 square miles (mi2

) and extend from near the Georgia-Tennessee State line, through 

most of central and southern Alabama and Georgia and part of the Florida panhandle to the Gulf of Mexico (fig. 1). 

Ground- and surface-water systems of the ACF-ACT River basins behave as an integrated, dynamic flow system 

comprised of an interconnected network of aquifers, streams, reservoirs, control structures, floodplains, and estuaries. 

The degree of hydrologic interaction between ground water and surface water suggests that the water resources be 

investigated and managed as a single hydrologic entity, to account for the climatic and anthropogenic factors that 

influence the flow systems.

Recent water projects and resource allocations, and other actions proposed by Federal, State, and local 

agencies, have resulted in conflicts among the States of Alabama, Florida, and Georgia, and the U.S. Army Corps of 

Engineers (Corps). The Corps has been given the authority to regulate the Nation’s surface waters through the Rivers 

and Harbors Act of 1927, in accordance with the U.S. House of Representatives Document Number 308, 69th U.S. 

Congress. Proposed projects designed to increase development and to re-allocate surface-water supplies in Georgia, 

based on revised operating practices of control structures for flood control, navigation, and hydropower generation, 

and a proposal to construct a dam and reservoir have met with opposition from Alabama and Florida. As a result, in 

1991, the U.S. Congress authorized the Corps to initiate a Comprehensive Study of the ACF-ACT River basins that 

would “develop the needed basin and water-resources data and recommend an interstate mechanism for resolving 

issues” (Draft Plan of Study, Comprehensive Study, Alabama-Coosa-Tallapoosa and Apalachicola-ChattahoocheeFlint River basins, prepared by: The Comprehensive Study Technical Coordination Group, July 1991, U.S. Army 

Corps of Engineers, Mobile District).

In 1992, the Governors of Alabama, Florida, and Georgia; and the U.S. Army, Assistant Secretary for Civil 

Works, signed a Memorandum of Agreement (MOA) establishing a partnership to address interstate water-resource 

issues and promote coordinated systemwide management of water resources. An important part of this process is the 

Comprehensive Study of the ACF and ACT River basins. Since this signing, the Study Partners defined scopes of 

work to develop relevant technical information, strategies, and plans, and to recommend a formal coordination 

mechanism for the long-term, basinwide management and use of water resources needed to meet environmental, 

public health, and economic needs (U.S. Army Corps of Engineers, written commun., 1993). The U.S. Geological 

Survey (USGS) was requested to assist in the development of a scope of work for the ground-water-supply element of 

the Comprehensive Study, and in June 1993, was asked to conduct that study element.

Eight subareas of the ACF-ACT River basins were identified by the Study Partners and the USGS on the basis 

of hydrologic and physiographic boundaries. Addressing the study at the smaller, subarea scale within the ACF-ACT 

River basins facilitated evaluation of the ground-water resources on a more detailed scale. This report is one of a 

series of eight reports that present results of ground-water studies of the ACF-ACT subareas. 

Purpose and Scope

This report describes the ground-water resources of the upper Chattahoochee River basin of Georgia—

Subarea 1 of the ACF-ACT River basins. The report provides an analysis of ground-water resources that can be used 

to address resource-allocation alternatives created by existing and proposed uses of the water resources in the river 

basin. Specific objectives of this study were to:

• describe a conceptual model of ground-water flow and stream-aquifer relations;

• describe the hydrologic setting of Subarea 1;

• quantify mean-annual and drought period ground-water contributions to the Chattahoochee 

River from the headwaters to Whitesburg, Ga., and the ground water exiting Subarea 1; and

• describe and evaluate ground-water utilization and general development potential.
3
4

Findings contained herein are but one component of a multidiscipline assessment of issues related to the 

basinwide utilization and management of water. This report is not intended to provide definitive answers regarding 

the acceptability of ground-water-resource utilization or the potential for additional resource development. Such 

answers are dependent on the synthesis of results from all components of the Comprehensive Study and on 

subsequent consideration by the State and Federal water managers responsible for decision making within the basin.

The report scope includes literature and data searches and an assessment of existing geologic data. A 

conceptual model that describes the hydrologic processes governing the ground- and surface-water flow was 

developed, and an evaluation of ground-water utilization was made by compiling and evaluating existing hydrologic, 

geologic, climatologic, and water-use data. Field data were not collected during this study.

Physical Setting of Study Area

The Subarea 1 study area encompasses about 2,430 mi2 in northern Georgia (fig. 1). The study area is 

bounded to the northwest by the Tennessee River basin, to the east-northeast by the Savannah River basin, and to the 

east by the Altamaha River basin. To the west, the study area is bounded by the Coosa River basin (Subarea 6) and 

Tallapoosa River basin (Subarea 5), and to the south by the middle Chattahoochee and upper Flint River basins 

(Subarea 2) (fig. 1).

Physiography

Eighty-eight percent of Subarea 1 lies within the Piedmont Province and 12 percent lies with the Blue Ridge 

Province (fig. 2). Land-surface altitudes in the study area range from about 4,430 feet (ft) above sea level in the 

northeastern Blue Ridge Province to about 700 ft near the Chattahoochee River at Whitesburg, Ga.; altitude of 

intermountain plateaus within the province ranges from about 1,600 to 1,700 ft (Brackett and others, 1991). Most 

streams are characterized by rectangular or trellis drainage patterns. Piedmont topography is characterized by low, 

rolling hills in the north and a broad rolling upland or plateau in the south (Cressler and others, 1983). The Blue 

Ridge is distinguished from the Piedmont chiefly by its greater topographic relief (Clark and Zisa, 1976). These two 

provinces are comprised of metamorphic and igneous rocks and are covered by regolith of varying thickness. The 

regolith in the study area is composed of semi-consolidated to unconsolidated saprolite (weathered bedrock), soil, and 

other surficial deposits (Clarke and Peck, 1991).

Climate

The climate in Subarea 1 is moist and temperate. The area receives an average of 58 inches (in.) of 

precipitation annually, which occurs primarily during the winter and early spring (Cressler and others, 1983; Carter 

and Stiles, 1983). The Blue Ridge receives substantially more rainfall—about 65 in. because of the orographic effect 

on the mountains—compared to about 50 in. in the Metropolitan Atlanta area (Miller, 1990). The percentage of 

rainfall resulting in runoff also is higher in the mountainous areas of northeastern Georgia. The average monthly 

temperature in the Metropolitan Atlanta area ranges from about 44 to 78 degrees Fahrenheit; and in Cleveland 

(northeastern Georgia mountains), from 39 to 78 degrees Fahrenheit (U.S. Department of Commerce, 1992).

Ground-Water Use

The estimated ground-water use in Subarea 1 during 1990 was about 18.6 million gallons per day (Mgal/d) or 

about 28.8 cubic feet per second (ft3

/s) (Marella and others, 1993). Of this total, about 16 percent was for public 

water supply, about 53 percent for domestic water supply, 9 percent for self-supplied industrial and commercial 

activities, and 22 percent for agricultural use. The largest ground-water use in Subarea 1 in Georgia is for domestic 

water supply (table 1).

Table 1. Estimated ground-water use, by category, Subarea 1, 1990

[Mgal/d, million gallons per day; ft3/s, cubic feet per second]

Public water supply Self-supplied industrial 

and commercial Agricultural Domestic Total

(Mgal/d) (ft3/s) (Mgal/d) (ft3/s) (Mgal/d) (ft3/s) (Mgal/d) (ft3/s) (Mgal/d) (ft3/s)

Subarea 1 total 3.0 4.6 1.6 2.5 4.2 6.5 9.8 15.2 18.6 28.8
5
6

Ground-water use reported by Marella and others (1993) is by county; ground-water use in those counties that 

are partially in Subarea 1 are reported herein for Subarea 1 only. Ground-water use for public water supply, and selfsupplied industrial and commercial uses were determined by using site-specific data. Ground-water pumpage for 

domestic purposes was determined by subtracting the population served by public supply facilities from the total 

population of the county or hydrologic unit, then multiplying that number by a water-use coefficient of 75 gallons per 

day (gal/d) per person. Agricultural ground-water use was estimated by multiplying the reported county use by the 

percentage of the land area of the county in Subarea 1.

Many small communities outside the Metropolitan Atlanta area use ground water as their primary water 

supply. Rapid increases in population in the Metropolitan Atlanta area, along with the variability of surface-water 

supplies during drought conditions, have caused some municipalities to investigate the possibility of supplementing 

surface-water supplies with ground water. The Cobb–Marietta Water Authority, Cobb County, Ga., is presently 

(1996) installing clusters of wells to supplement the water supply during peak demand; and the city of Lawrenceville, 

Gwinnett County, Ga., also is actively exploring ground water as a supplemental water-supply resource.

Previous Investigations

The results of several regional studies have described ground-water resources in crystalline-rock 

hydrogeologic settings in the Piedmont Province of the southeastern United States. The major objectives of regional 

studies were to formulate concepts regarding the availability of ground water and to determine possible controlling 

factors that affect or control well yield and ground-water quality. Conceptual models of hydrogeologic frameworks of 

the crystalline-rock aquifers in this region evolve as information increases (Chapman and others, 1993). 

Some of the earliest reports describing ground-water resources in the crystalline rocks of the Piedmont were 

by McCallie (1898, 1908), who concluded that the yield of wells completed in bedrock would be sufficient only for 

rural use, and would not be a viable source for large cities such as Atlanta and Macon. In urban areas, wells would be 

susceptible to contamination from “local drainage”; an Atlanta public supply well (2,175 ft deep), apparently was 

contaminated after only a few years of use (McCallie, 1898).

Herrick and LeGrand (1949) inventoried a large number of wells in the Atlanta region and conducted regional 

geologic mapping to determine possible factors influencing ground-water availability and quality. They concluded 

that the occurrence of ground water in the Metropolitan Atlanta area depended largely on factors, such as rock type, 

structural features, degree of weathering, and topography. Geologic settings considered to be favorable for 

developing high-yielding wells were discussed for a variety of rock types, geologic structural conditions, and 

topographic settings. Although the study represented a reconnaissance rather than a detailed evaluation, Herrick and 

LeGrand (1949) recognized that variations in the rock character and attitude strongly influence the availability of 

ground water, and distinct differences could be observed within intervals of feet in the Piedmont region. Herrick and 

LeGrand (1949) also related the quality of ground water to rock type. Ground water from granitic rocks was 

substantially less mineralized compared to water from amphibolites and hornblende gneisses, which contained 

elevated concentrations of calcium and magnesium. 

Carter and Herrick (1951) evaluated water use and sources of water supply (including surface water) in the 

Metropolitan Atlanta area and estimated future water-supply needs. Historically, dug wells were the primary sources 

of water supply in the Atlanta area until the late 1800’s, when surface-water sources were developed to meet 

increasing water-supply demands. The study examined the relation between ground-water availability and certain 

geologic factors, such as joints, faults, and other fractures. The investigators evaluated well yield, total depth of wells, 

and the importance of aquifer tests in assessing sustained yield and potential well interference. The report concluded 

that the potential for ground-water development in the Atlanta area was considerable, and that wells could serve as 

sole sources of water supply for rural communities and some industries throughout the Piedmont region. Carter and 

Herrick (1951) related hardness of ground water to mafic rocks, such as amphibolites and hornblende gneisses, and 

determined that granitic rocks contained softer water. 

Thomson and Carter (1955) presented streamflow data for the 1954 drought throughout Georgia, including the 

Chattahoochee River in Subarea 1. The authors included a discussion of the lack of rainfall—the rainfall deficit in 

most areas was at least 15 in. Streamflow was below normal in the Piedmont region by July 1954. Record low flows 

were recorded during September and early October.
7

A later report by Thomson and Carter (1963) continued a discussion of the 1954 drought streamflow data for 

Georgia. The authors state that the 1954 data may be the last available extreme drought streamflow data representing 

natural flow conditions. For the Chattahoochee River in subarea 1 in the northern part above the Norcross, Ga., 

gaging station, the 1954 drought was the fourth to sixth most severe in 60 years. The most severe drought for the 

Norcross station occurred in 1925. The remainder of the Chattahoochee River downstream of the Norcross station, 

the 1954 drought was the most severe in 61 years.

Stewart and others (1964) and Stewart (1964) conducted an investigation to determine the effects of wastedisposal migration in weathered crystalline rocks at the Georgia Nuclear Laboratory, Dawson, Ga. Infiltration tests 

were conducted in a saprolite disposal pit to determine the rate and areal extent of possible waste leakage into the 

shallow ground-water system. The purpose of the study was to determine the feasibility of using infiltration pits 

constructed in weathered crystalline rocks for the disposal of liquid wastes. The three water-bearing units evaluated 

were near-surface alluvium, regolith, and unweathered crystalline bedrock. The investigation of regolith material 

included estimates of saprolite porosity and permeability and ion-exchange capacity from core samples, the 

measurement of infiltration rates, and shallow aquifer testing. Bedrock wells also were drilled and estimates of 

transmissivity were made from aquifer-test data. A noticeable increase in ground-water mounding was observed 

along the strike of schistosity in the regolith. Other fieldwork included surficial geologic mapping and the collection 

of ground-water quality samples, streamflow data, and continuous ground-water levels in wells. During aquifer 

testing, the largest drawdowns in the saprolite wells were along the strike of schistosity. Rates of ground-water 

movement were calculated from hydraulic gradient data and estimates of porosity and permeability in the saprolite.

LeGrand (1967) proposed a rating system, based on topographic setting and soil (regolith) thickness, to assess 

ground-water conditions in the Piedmont and Blue Ridge Provinces of the southeastern United States. LeGrand 

(1967) developed the concept of a statistical percentage chance of obtaining a certain yield under various conditions. 

Actual quantifiable yields were said to be difficult to estimate because well yields were shown to vary substantially 

within 100 ft of lateral distance. LeGrand (1967) also stated that fractures seemed to diminish with increasing depth, 

and that the relation between well yield and depth was complex.

Cressler and others (1983) conducted a study of ground-water in the Atlanta area to assess the availability, 

quality, and quantity of ground water in crystalline rocks and to devise methods for locating sites for high-yielding 

wells that could serve as alternative or supplemental sources of water supply. Results from that study indicated that 

the highest well yields in the Atlanta area seemed to be associated with wells tapping contact zones between rocks of 

contrasting lithology, fault zones, stress-relief (horizontal) fractures, drainage features controlled by local structural 

characteristics, concentrated jointing within folded rocks, and shear zones. Results of this study indicated that 

topographic drainage features may or may not be related to underlying water-bearing features in the rocks. From data 

gathered using borehole geophysical logs of wells, Cressler and others (1983) determined that the size, spacing, and 

interconnection of water-bearing openings differed greatly from one rock type to another. The range in well yield 

within an identified water-bearing unit was highly variable, and high-yielding wells were present in each unit. Local 

features in the rocks were recognized as generally controlling well yield. The authors also noted that water from wells 

open to mafic rock types contained higher concentrations of iron, magnesium, manganese, dissolved solids, and 

possibly chloride, than water from wells open to granitic rocks in the Metropolitan Atlanta area. The pH of water 

samples collected from wells completed in mafic rocks also was relatively high compared to samples collected from 

wells completed in granitic rocks.

Hale and others (1989) presented streamflow data for the 1986 drought in Alabama, Georgia, North Carolina, 

South Carolina, Tennessee, and Virginia. Minimum flows occurred in midsummer during 1986, which was several 

months earlier than the regional droughts of 1954 and 1981. The source of this drought was a rainfall deficit that 

began in 1985 and persisted until late summer 1986. The range of 7-month precipitation totals was about 30 to 85 

percent of normal. The authors reported minimum low flows for 1, 7, 30, 60, and 90 days from April 1, 1986 through 

March 31, 1987.

Clarke and Peck (1991) conducted a study of a nine-county area south of the Metropolitan Atlanta area. The 

study consisted of a general evaluation of the existing and possible future development of ground-water resources. 

Data collection consisted of the compilation of geologic, hydrologic, and water-quality data. An extensive inventory 

of wells and springs was assembled. The study followed the same method as that used by Cressler and others (1983). 

Many high-yielding wells were inventoried; reported yields for two of which were 600 and 700 gallons per minute 
8

(gal/min). Clarke and Peck (1991) concluded that ground water is a viable resource that had been underutilized in the 

variety of hydrogeologic settings in the area. Ground-water quality problems included elevated concentrations of 

iron, manganese, fluoride, and radon.

The most recent investigation of ground-water resources near the study area was by Chapman and others 

(1993). A study of the relation of geologic controls, well yields, and ground-water quality was conducted in the area 

of Zebulon, Pike County, Ga. Well yields and potential ground-water quality problems were similar to those indicated 

by Cressler and others (1983) and Clarke and Peck (1991).

Reports describing methods of estimating streamflow and ground-water discharge to streamflow include 

Bingham (1982), Hirsch (1982), Hoos (1990), Rorabaugh (1960, 1964), Rutledge (1991, 1992, 1993), and Mayer and 

Jones (1996). Data collected as part of the ongoing surface-water monitoring program of the USGS are published 

annually in the reports “Water-Resources Data, Georgia.” Other reports containing information about the surface- and 

ground-water resources of the ACF-ACT River basin area are listed in the “Selected References” section of this 

report.

Well and Surface-Water Station Numbering Systems

Wells in Georgia are numbered by a system based on U.S. Geological Survey topographic maps. Each 7 1/2-

minute topographic quadrangle map in Georgia has been assigned a number and letter designation beginning at the 

southwest corner of the State. Numbers increase sequentially eastward through 39; letters advance northward through 

“Z,” then double-letter designations “AA” through “PP” are used. The letters “I,” “O,” “II,” and “OO” are not used. 

Wells and springs inventoried in each quadrangle are numbered sequentially beginning with “1.” Thus, the second 

well inventoried in the Leaf quadrangle (designated 16LL) is designated 16LL02.

Wells in the USGS Ground-Water Site Inventory (GWSI) data base are assigned a 15-digit identification 

number based on the latitude and longitude grid system. The first six digits denote the degrees, minutes, and seconds 

of latitude. The next seven digits the degrees, minutes, and seconds of longitude. The last two digits (assigned 

sequentially) identify wells within a one-second grid.

The USGS established a standard identification numbering system for all surface-water stations in 1950. 

Stations are numbered according to downstream order. Stations on a tributary entering upstream of a main-stream 

station are numbered before and listed before the main-stream station. No distinction is made between continuousrecord and partial-record stations. Each station has a unique eight-digit number that includes a two-digit part number 

(02 refers to natural drainage into the Eastern Gulf of Mexico) and a six digit downstream order number. Gaps are left 

in the series of numbers to allow for new stations that may be established; hence, the numbers are not consecutive. 

The complete number for each station includes a two-digit part number “02” plus the downstream-order number, 

which can be from 6 to 12 digits. All records for a drainage basin, encompassing more than one State, can easily be 

correlated by part number and arranged in downstream order. 

 Approach and Methods of Study

This study included several work elements used to appraise the ground-water resources of Subarea 1, 

including the description of a conceptual model of ground-water flow and stream-aquifer relations, and an assessment 

of ground-water availability. The approach and methods used to accomplish these tasks included:

• compilation of information and data from pertinent literature, including geologic, groundwater, streamflow, and ground-water use data;

• separation of streamflow hydrographs to estimate mean-annual ground-water contribution to 

the Chattahoochee River and its tributaries;

• evaluation of streamflow records and periodic discharge measurements during drought 

periods to estimate “worst-case” streamflow conditions; and

• comparison of 1990 ground-water use with mean-annual and drought-flow conditions to 

evaluate ground-water availability.
9

Literature and data reviews provided information necessary to describe a conceptual model of groundwater/surface-water relations. Much of the conceptual model is based on results of previous investigations by Toth 

(1962, 1963), Freeze (1966), Freeze and Witherspoon (1966, 1967, 1968), Winter (1976), Heath (1984, 1989), Faye 

and Mayer (1990), and Miller (1990). These studies suggest that large rivers, such as the Chattahoochee, and their 

tributaries function as hydraulic drains for ground-water flow, and that during significant droughts, most of the 

discharge in these streams is contributed by ground water.

Streamflow data were compiled from the USGS Automated Data Processing System (ADAPS) database. 

Streamflow records from continuous-record and miscellaneous discharge-measurement stations were used for 

hydrograph-separation analyses and drought streamflow evaluation.

Stream-aquifer relations were quantified using two approaches: (1) the hydrograph-separation method of 

Rorabaugh (1960, 1964) and Daniel (1976), called the recession-curve-displacement method; and (2) a drought-flow 

mass-balance analysis of streamflow. The hydrograph-separation method was used to estimate the mean-annual 

discharge of ground water (baseflow) to the basin. The mean-annual baseflow was used as a base or reference with 

which to compare and evaluate droughts under “worst-case” conditions. An estimate also was made of the meanannual volume of ground water discharged from Subarea 1 to Subarea 2 as baseflow in the Chattahoochee River. 

The mass-balance analysis was used to estimate the baseflow contributions to the surface-water system during 

historically significant droughts and the ground water delivered as baseflow from Subarea 1 to Subarea 2 near the end 

of these droughts.

Mean-Annual Baseflow Analysis 

Discharge data from continuous-record gaging stations along the Chattahoochee River and its tributaries 

were selected for baseflow analysis based on the period of record of unregulated flow. Streamflow representative of 

low, average, and high years of stream discharge were evaluated by hydrograph-separation methods to estimate 

annual baseflow. The mean-annual baseflow was then computed as the average baseflow of the three representative 

flow years.

The selection process for the most representative year of low, average, and high stream discharge involved 

objective statistical examination of the discharge data, followed by some subjectivity in the final choice of the water 

year selected. Hydrographs acceptable for separation were characterized by relatively normal distributions of daily 

stream discharge, small ranges of discharge, and the absence of extremely high, isolated peak stream discharge. For 

each station, the mean annual stream discharge was computed for the period of record of unregulated flow and used 

as a reference mean for low-, average-, and high-flow conditions for that station. The mean- and median-annual 

stream discharge for those water years identified as acceptable were compared to the reference mean. Because 

extremely high discharge during a water year could greatly influence the mean but not the median (which is similar to 

the geometric mean for positively skewed data sets, such as discharge), the process of selecting representative water 

years for low-, average-, and high-flow conditions considered the position of the mean discharge for the selected year 

relative to the median and the reference mean. The hydrographs for these representative water years were examined 

and separated. True subjectivity in the selection process entered only at this point, such that, if acceptable 

hydrographs were available for several years, one year arbitrarily was chosen over the others. 

The separation analyses were conducted using the computer program SWGW (Mayer and Jones, 1996); which 

is an automated version of the recession-curve-displacement method, often referred to as the Rorabaugh or 

Rorabaugh-Daniel method. The SWGW program was applied to a water-year period of streamflow data. SWGW 

utilizes daily mean discharge data collected at unregulated stream-gaging sites and requires at least 10 years of record 

to accurately estimate a recession index necessary for hydrograph-separation analysis.

The hydrograph-separation method estimates the ground-water component of total streamflow. In general, the 

streamflow hydrograph can be separated into two components—surface runoff and baseflow (ground-water discharge 

to streams). Figure 3 shows the graphical output from the SWGW program. Surface runoff is the quick response 

(peaks) of stream stage to precipitation and nearby overland flow.

Application of the recession-curve-displacement method requires the use of the streamflow recession index. 

The streamflow recession index is defined as the number of days required for baseflow to decline one order of 

magnitude (one log cycle), assuming no other additional recharge to the ground-water system. The streamflow 

recession index is a complex number that reflects the loss of ground water to evapotranspiration (Daniel, 1976) or 
10
11

leakage, and the influence of geologic heterogeneities in the basin (Horton, 1933; Riggs, 1963). The slope of the 

streamflow recession is affected by evapotranspiration, such that the streamflow recession index varies from a 

maximum during the major rise period to a minimum during the major recession period (fig. 3). The major rise period 

of streamflow generally occurs from November through March or April, when precipitation is greatest and 

evapotranspiration is least. The major recession period occurs during late spring through fall and coincides with a 

period of lesser precipitation, higher temperatures, and greater evapotranspiration (fig. 3). Two recession indices were 

estimated for streamflow observed at each continuous-record gaging station used in the mean-annual baseflow 

analysis; one index for the major rise period and one for the major recession period.

Available ground-water-level data indicate that long-term changes in ground-water storage are minimal in 

Subarea 1. Because long-term storage changes are minimal, mean-annual ground-water discharge, estimated using 

the hydrograph-separation method, is considered an estimate of minimum mean-annual recharge. Also, aquifers at a 

regional scale in Subarea 1 are considered, for purposes of analysis, to respond as homogeneous and isotropic media.

Results of the mean-annual baseflow analysis are based on measured and estimated data, and the analytical 

methods to which they are applied. Drainage areas were measured using the most accurate maps available at the time 

of delineation (Novak, 1985), and are reported in units of square miles. Drainage areas are reported to the nearest 

square mile for areas greater than 100 mi2; to the nearest tenth of a square mile for areas between 10 and 100 mi2; and 

to the nearest hundredth of a square mile for areas less than 10 mi2

, if the maps and methods used justify this degree 

of accuracy (Novak, 1985). Annual stream discharge, the sum of the daily mean stream discharges for a given water 

year, is reported in units of cubic foot per second (ft3/s), to the nearest cubic foot per second. Daily mean discharge is 

reported to the nearest tenth of a cubic foot per second for discharge between 1.0 and 9.9 ft3

/s; to the nearest unit for 

discharge between 10 and 100 ft3/s; and is reported using three significant figures for discharge equal to or greater 

than 100 ft3/s (Novak, 1985).

The accuracy of stream-discharge records depends primarily on: (1) the stability of the stage-discharge 

relation or, if the control is unstable, the frequency of discharge measurements; and (2) the accuracy of measurements 

of stage and discharge, and the interpretation of records. Accuracy of records of streamflow data used in this report 

can be found in annually published USGS data reports, for example, Stokes and McFarlane (1994). The accuracy 

attributed to the records is indicated under “REMARKS” in the annual data reports for each station. “Excellent” 

means that about 95 percent of the daily discharges are within 5 percent of the true discharge; “good,” within 10 

percent; and “fair,” within 15 percent. Records that do not meet these criteria are rated “poor.” Different accuracies 

may be attributed to different parts of a given record (Novak, 1985). 

Results of the mean-annual baseflow analyses are inherently uncertain. The hydrograph-separation method of 

analysis is partly subjective, relying on the input of several user-selected variables. As such, the results of the 

analyses derived and reported herein, are difficult to independently confirm and are presented as estimates of 

unknown quality and confidence. However, because the values in this report are used in several water budgets, not 

only within Subarea 1 but also from subarea to subarea, hydrograph-separation results may be reported to a greater 

significance than the data and analyses warrant to maintain the numerical balance of the water budget; implication of 

accuracy to the extent shown is not intended.

Drought-Flow Analysis

Daily mean streamflow data collected at gaging stations during periods of low flow and corresponding 

periodic measurements of stream discharge collected at partial-record stations were compiled for the drought years 

1941, 1954, and 1986. These data included nearly concurrent daily measurements of streamflow in the 

Chattahoochee River and periodic measurements of tributary discharge. 

Standard periods of analyses for drought studies were selected for all ACF-ACT subareas. The period of 

analysis selected for compiling 1954 drought data was September 15 through November 1, 1954. The selected period 

for the 1986 drought was July 1 through August 14, 1986. Streamflow during these periods was considered to 

represent the “worst-case” of ground-water storage and availability throughout the ACF-ACT study area. Discharge 

data were sparse during the 1941 drought; therefore, a standard period of analysis was not selected for the entire 

ACF-ACT study area. 
12

The period of “worst-case” conditions may not include the minimum streamflow that occurred during a 

drought at a streamflow measurement site. Minimum drought flows typically occur at different times at different 

stations within large watersheds, such as the Chattahoochee River basin. Rather, the “worst-case” evaluation was 

designed to describe streamflow during the advanced stages of each drought; thus, providing a near-contemporaneous 

summary of streamflow conditions during periods of low flow throughout the ACF–ACT study area.

The estimated “worst-case” distribution of Chattahoochee River streamflow near the end of the 1941, 1954, 

and 1986 drought periods was determined by balancing mass in the stream network in a general downstream direction 

during a relatively short interval of time. The tributary discharge to the Chattahoochee River during drought periods 

was calculated using a unit-area discharge extrapolated to the entire drainage area of the tributary. Unit-area 

discharges are based on streamflow measurements that generally are inclusive of only part of the tributary drainage, 

and may not be representative of an average unit-area discharge for the entire tributary drainage. Therefore, most 

unit-area discharges used to estimate discharge at ungaged and unmeasured tributaries were based on streamflow data 

measured near the mouths of tributaries to better represent the entire tributary contributing area.

Acknowledgments

The authors acknowledge the following for contributing information on the ground-water exploration program 

in Cobb County: Dr. Philip Karr (deceased), General Manager, Cobb–Marietta Water Authority, Marietta, Ga.; Emery 

and Garrett Groundwater, Inc., Lavonia, N.H.; and John Quinn, Law Environmental, Inc., Kennesaw, Ga. The authors 

also wish to thank Doug Shellnut, Peachtree Golf Club, Chamblee, Ga., and Thomas J. Crawford, private consultant. 

CONCEPTUAL MODEL OF GROUND-WATER FLOW

AND STREAM-AQUIFER RELATIONS

The conceptual model of the ground-water flow and stream-aquifer relations in Subarea 1 is based on previous 

work done in other areas by Toth (1962, 1963), Freeze (1966), Freeze and Witherspoon (1966, 1967, 1968), 

Winter (1976), and Faye and Mayer (1990). These studies suggest that recharge originates from precipitation that 

infiltrates the land surface, chiefly in upland areas, and percolates directly, or leaks downward to the water table. 

Ground water subsequently flows through the aquifer down the hydraulic gradient and either discharges to a surfacewater body or continues downgradient into confined parts of an aquifer. Major elements of this conceptual model 

include descriptions of flow regimes, stream-aquifer relations, recharge to ground water, and ground-water discharge 

to streams.

Toth (1963) observed that most ground-water flow systems could be qualitatively subdivided into paths of 

local (shallow), intermediate, and regional (deep) flow. Local flow regimes are characterized by relatively shallow 

and short flow paths that extend from a topographic high to an adjacent topographic low. Intermediate flow paths are 

longer and somewhat deeper than local flow paths and contain at least one local flow path. Regional flow paths 

(fig. 4) begin at or near the major topographic (drainage) divide and terminate at regional drains, which is the 

Chattahoochee River in Subarea 1. Depending on local hydrogeologic conditions, all three flow regimes may not be 

present everywhere within the subarea.

The water table in Subarea 1 probably is a subdued replica of the land-surface topography but generally has 

less relief. The presence of ground-water flow regimes depends largely on the configuration of the water table, such 

that recharge occurs in highland areas and discharge occurs in lowland areas. Quantities of recharge to the water table 

and ground-water discharge to streams are variably distributed throughout the local, intermediate, and regional flow 

regimes. Local regimes receive the greatest ground-water recharge from the water table and provide the most groundwater discharge to streams. Ground-water discharge to tributary drainages primarily is from local and intermediate 

flow regimes; ground-water discharge to regional drains, such as the Chattahoochee River, includes contributions 

from the regional as well as local and intermediate regimes.

Seasonal variation in rainfall affects the local ground-water flow regime most significantly, and affects the 

regional flow regime least significantly. Generally, regional flow probably approximates steady-state conditions, and 

long-term recharge to and discharge from this regime will not vary significantly.
13

Continuum methods of analysis of ground-water flow, such as hydrograph separation, are based on 

assumptions of laminar flow through a medium characterized by systematic changes in primary porosity and 

permeability. Such media generally are classified as porous media. Ground-water flow through porous media is 

commonly termed Darcian flow. Fractured rock media in the Blue Ridge and Piedmont Provinces contain virtually no 

primary porosity or permeability and virtually all ground-water flow occurs through secondary openings. For 

purposes of analysis, continuum methods based on assumptions of Darcian flow are applied to ground-water flow 

through fractured rock media. Such approaches commonly are justified on a regional scale because fracture systems 

typically are ubiquitous and intersecting. 

Results of smaller-scale studies also demonstrate the continuity of ground-water flow through fractured 

media. For example, long-term ground-water pumping operations near Ridgeway, S.C., began in the fall of 1988 to 

dewater fractured Piedmont rocks to accommodate open-pit mining of gold-bearing ore (Glenn and others, 1989). 

Detailed ground-water monitoring around and within the mined areas indicated that after less than one year of 

pumping, drawdown extended in an oblong distribution for more than 1 mi beyond the center of pumping. 

Drawdown decreased uniformly with distance from pumped wells. Nelson (1989) used water-level data from 

numerous monitoring wells at a 120-acre study site constructed in fractured Piedmont rocks to describe streamaquifer relations (non-pumping conditions) near the Rocky River in North Carolina. Nelson (1989) concluded that the 

Rocky River was a drain for ground water discharged from Piedmont rocks, and that observed hydraulic relations 
14

between the fractured-rock aquifer and the river and within the aquifer at various depths, were consistent with porous 

media concepts of ground-water flow, as described by Toth (1962, 1963). Under pumping conditions, drawdown can 

extend across surface-water drainage divides in a fractured-rock aquifer, similar to drawdown conditions observed in 

porous media. As part of an ongoing ground-water-resources investigation in the Lawrenceville, Ga., area (in the 

Piedmont Province), drawdown across drainage divides was observed at a distance of about 0.9 mi during a 96-hour 

constant-discharge aquifer test (U.S. Geological Survey, unpublished data from 1995). A study of 18 bedrock wells in 

the Piedmont Province in Virginia showed the influence of a pumping well across drainage-basin divides, where 

significant drawdown was observed in a nonpumping well located 1,900 ft from a pumping well in an adjacent 

drainage basin (Tinkham and others, 1989).

HYDROLOGIC SETTING

The hydrologic framework of Subarea 1 contains dynamic hydrologic systems consisting of aquifers, streams, 

reservoirs, and floodplains. These systems are interconnected and form a single hydrologic entity that is stressed by 

natural hydrologic and climatic factors and by anthropogenic factors. For this discussion, the hydrologic framework 

is separated into two systems: the ground-water system and surface-water system. 

Ground-Water System

The ground-water system forms as geology and climate interact. Geology primarily determines the aquifer 

types present, as well as the natural quality and quantity of ground water. Climate primarily influences the quantity of 

ground water. 

Geology

A detailed description of the diverse and complex geology of Subarea 1 is beyond the scope of this study; 

however, a brief description of the geology of the subarea is presented, based on selected published descriptions 

of various geologic investigations. The “Selected References” section of this report lists selected geologic 

investigations.

The Blue Ridge and Piedmont Provinces are characterized by complex sequences of igneous rocks of 

Precambrian to Paleozoic age, and metamorphic rocks of late Precambrian to Permian age (Miller, 1990); in the 

Piedmont, isolated igneous rocks of Mesozoic age also are present (D.C. Prowell, U.S. Geological Survey, oral 

commun., 1996). Collectively, these rocks are called crystalline rocks. The metamorphic rocks originally were 

sedimentary, volcanic, and volcaniclastic rocks that have been altered by several stages of regional metamorphism to 

slate, phyllite, schist, gneiss, quartzite, and marble; a variety of cataclastic rocks also are present. The metamorphic 

rocks are extensively folded and faulted. The intrusive igneous rocks, dominantly granites and lesser amounts of 

diorite and gabbro, occur as widespread plutons. The rocks are characterized by a complex outcrop and subsurface 

distribution pattern, as shown on geologic maps of various scales (Szabo and others, 1988). Because rock characteristics can vary significantly on the scale of a few tens of feet within the same lithologic unit, detailed geologic-unit 

differentiation can be accomplished only on the scale of a topographic quadrangle, or larger. The Piedmont contains 

major fault zones that generally trend northeast-southwest and form the boundaries between major rock groups 

(Georgia Geologic Survey, 1976). One such fault is the Brevard Zone of Cataclasis, which extends from Cornelia in 

northwestern Georgia, through the Metropolitan Atlanta area; and to Whitesburg, near the boundary with Subarea 2 

(Georgia Geologic Survey, 1976). The Chattahoochee River generally is within or parallel to the Brevard Zone of 

Cataclasis in Subarea 1. The trellised and rectangular drainage patterns of the river reflect geologic control.

The crystalline igneous and metamorphic rocks largely are covered by a layer of weathered rock and soil 

known as regolith. The regolith ranges in thickness from a few to more than 150 ft, depending upon the type of parent 

rock, topography, and hydrogeologic history. From the land surface, the regolith consists of a porous and permeable 

soil zone that grades downward into a clay-rich, relatively impermeable zone that overlies and grades into porous and 

permeable saprolite, generally referred to as a transition zone (Heath, 1989). The transition zone grades downward 

into unweathered bedrock. Regolith thickness generally is less in the Blue Ridge Province than in the Piedmont 

because of the steeper slopes (Schmitt and others, 1989; Brackett and others, 1991). In general, the massive granite 

and gabbro rocks are poorly fractured and are characterized by a thin soil cover; in contrast, the schists and gneisses 

are moderately to highly fractured. The weathering of the rocks is erratic and usually deep; remnants of the original 

texture and foliation are retained in the saprolite in many places (Clarke, 1963). 
15

The ground-water system in the crystalline rocks of the Piedmont and Blue Ridge Provinces of Georgia is 

controlled largely by geology. Various textural and structural properties in the rocks control permeability characteristics; however, hydraulic head gradients and recharge may be influenced by topography and climatic factors. 

Aquifers

The principal aquifers in Subarea 1 are fracture-conduit aquifers in igneous and metamorphic rocks of the 

Blue Ridge and Piedmont Provinces (fig. 5); the general physical characteristics of these aquifers are given in table 2. 

As a result of intense heat and pressure during metamorphism and structural deformation, bedrock aquifers of the 

Piedmont Province contain little or no primary porosity (less than two percent), and are poorly permeable. In the 

bedrock, water-bearing zones occur in areas where differential weathering along geologic features produces openings 

that enhance permeability and enable the storage and flow of ground water (Chapman and others, 1993). Geologic 

features favorable for the development of secondary openings include lithologic contacts, foliation, joints, fractures, 

faults, folds, quartz veins, and pegmatites. 

Table 2. Generalized geologic units in Subarea 1, and water-bearing properties, chemical characteristics, and well 

yields

[—, no available data]

Physiographic province Geologic age and lithology Aquifer type Water-bearing properties 

and chemical characteristics Well yield

Piedmont and Blue Ridge regolith: soil, alluvium, colluvium, 

and saprolite derived from 

various-aged rocks

porous-media; and 

preferential flow

generally suitable for 

domestic use only

—

Precambrian to Paleozoic bedrock: 

quartzite, slate, gneiss, schist, 

marble, phyllite, granite, 

amphibolite

fracture-conduit local, discontinuous 

properties, well yields 

variable, water quality 

generally good

1 to 25 gallons per minute 

typical; may exceed 700 

gallons per minute 

(Kidd, 1989; Clarke and 

Peck, 1991)

Fracture-conduit aquifers in the Piedmont and Blue Ridge Provinces consist of two water-bearing zones—a 

shallow, regolith zone and a deeper, bedrock zone (fig. 6). The regolith may consist of soil, alluvium, colluvium, and 

saprolite (weathered bedrock retaining geologic structural characteristics). In general, the regolith consists of a 

porous, permeable soil at land surface, grading downward into a highly weathered, clay-rich relatively impermeable 

zone that overlies a less-weathered and more permeable transition zone (Heath, 1989). In some instances, ground 

water in the regolith is similar to that in porous media, where intergranular porosity is present in the soil or alluvium, 

or where rocks have been deeply weathered, and retain little structural characteristics. Porosity of the regolith can 

range from 20 to 30 percent (Heath, 1984). The transition zone between the saprolite and bedrock contains weathered 

material and boulders, and along structural features, such as foliation and jointing, generally is more permeable than 

the saprolite. Ground-water flow can be preferential in saprolite, where weathered rock retains relict structural 

features (Stewart, 1964; Stewart and others, 1964). 

The fracture-conduit aquifers are anisotropic and heterogeneous because of the highly complex and locally 

variable geologic characteristics controlling the presence of the water-bearing units in the bedrock and regolith. Rock 

type, structural features, and regolith thickness vary locally and affect the storage capacity and hydraulic conductivity 

of an aquifer (LeGrand, 1967, 1089; Daniel, 1987; Guthrie and DeJarnette, 1989; Schmitt and others, 1989; Chapman 

and others, 1993; Guthrie and others, 1994). 

Recent studies have shown that a thorough evaluation of hydrogeologic settings in areas characterized by 

fracture-conduit aquifers can lead to an increased likelihood of successful development of ground-water resources. 

Most municipal, industrial, and commercial ground-water exploration plans now include consultation with hydrogeologists, who evaluate surficial geology, including structural features, topographic relation to geologic features, 

existing well information, and land use. Surface and borehole geophysical surveys also may be conducted to 

delineate subsurface features that indicate the sources of water to wells and the water-bearing properties of the rocks.
16
17
18

Ground water in the study area is obtained from either shallow, bored wells that are completed in the regolith, 

or deeper, drilled wells that are completed in the bedrock. Public supply wells are completed in the bedrock and 

casing is grouted about 5 ft into the bedrock to avoid possible contamination from surface runoff and direct 

infiltration through the weathered regolith. Wells drilled for industrial or commercial use generally also are 

completed in the bedrock primarily due to the potential for higher yields. Domestic wells are completed in both the 

regolith (bored wells) and bedrock (drilled wells) (fig. 6). Shallow bored wells that are completed in the regolith can 

be susceptible to contamination and to water-level decline during droughts. 

Well depth in Subarea 1 generally ranges from 100 to 700 ft. Wells may yield water from several fractures 

throughout a borehole, or from a single productive fracture. Conversely, a borehole may not intersect a fracture, or 

the fracture may not be water bearing, and thus, may yield little or no water. Because of the complex nature of the 

secondary permeability in fracture-conduit aquifers, production zones generally are of limited extent. Quantitative 

estimates of aquifer properties such as transmissivity, hydraulic conductivity, and storage coefficient are difficult to 

assess because of the highly localized geologic controls on secondary permeability.

Fracture-conduit aquifers formed in crystalline rocks may yield quantities of water suitable for public or 

industrial supply. Yields from wells completed in the fractured crystalline-rock aquifers of Subarea 1 are highly 

variable. A high-yielding wells produces 100 gal/min or greater and yields of as much as 550 gal/min have been 

reported in Subarea 1; typical well yields, however, are 1 to 25 gal/min (table 2). Bedrock wells often are more able 

to sustain yields during droughts.

Ground-water movement in fracture-conduit aquifers mainly is through secondary openings, such as fractures 

and joints, or other enhanced openings along lithologic contacts. Secondary porosity is created by faulting and 

fracturing and is enhanced by weathering along these openings. The bedrock below the weathered zone and laterally 

beyond fractures typically has little or no matrix porosity or primary permeability. Ground-water storage primarily is 

in the overlying weathered rock (regolith or saprolite, which behaves like a porous-media aquifer). The volume of 

water in storage in the regolith is controlled by the porosity and thickness. To a lesser degree, the volume of water in 

storage in the bedrock is controlled by the degree of fracturing. Because of the limited storage in fractures, water 

levels in fracture-conduit aquifers typically respond rapidly to pumping.

Ground water pumped from fracture-conduit aquifers in Subarea 1 generally is suitable for drinking. However, 

elevated concentrations of iron, manganese, sulfate, dissolved solids, and nitrates are known to occur in some areas. 

Other potential problems include acidic water that can corrode copper water lines, and the presence of radon gas in 

the water from the natural radioactive decay of uranium in the rocks.

Ground-Water Levels

Ground-water levels fluctuate in response to natural and anthropogenic processes, such as seasonal changes in 

rainfall, interaction with the surface-water system, and ground-water withdrawal. These fluctuations indicate changes 

in the amount of water in storage in an aquifer. In the Piedmont and Blue Ridge Provinces, ground-water levels in 

wells may represent differing degrees of confinement. Because of their shallow depth, wells completed in the regolith 

are highly influenced by climatic changes, such as variations in evapotranspiration and precipitation. During 

droughts, shallow bored wells temporarily may go dry when the water table falls. Water-level changes in bedrock 

wells may exhibit both semiconfined and confined behavior; the former responding most directly to recharge. 

Flowing bedrock wells, however, exhibit more confined conditions and related yields probably are less influenced by 

climatic variability.

As part of the evaluation of ground-water levels, observation well data were analyzed for wells completed in 

the fractured bedrock water-bearing zones. Long-term ground-water-level data are available for only a few bedrock 

wells in Subarea 1. Figure 7 shows water levels in well 11FF04, located in the Piedmont Province in DeKalb County, 

Ga. Continuous ground-water level data are not available for wells completed in the regolith in Subarea 1.

Well 11FF04 is located along an unnamed tributary of Nancy Creek which flows into the Chattahoochee River 

(fig. 8). This well was drilled as part of an investigation by Cressler and others (1983) and water-level data are 

available from 1980 to 1995 (fig. 7). The well was completed in a schist and granitic gneiss and the casing was set at 

36 ft (C.J. Thurmond, U.S. Geological Survey, written commun., 1980). Before the casing was set, the regolith zone 

produced about 25 gal/min, but after completion of the well, the yield was estimated to be 7.5 gal/min. Most of the 

water was obtained at depths of 525 to 528 ft in a biotite schist. 
19

Water levels in well 11FF04 ranged from about 5.7 to 7.7 ft below land surface for the period of record. 

During the 1986 and 1988 droughts, the water level decreased about 1 ft from the average water level for the period of 

record (fig. 7). The annual hydrograph shows sharp peaks, probably related to precipitation and stage variations in 

the stream, which is located about 5 ft from the well. The effects of evapotranspiration are observed from the 

hydrograph of 1986, when ground-water levels exhibited a steady decline from mid-March through mid-August. The 

water level in bedrock well 11FF04 only declined about 1.2 ft during the drought of 1986.

Surface-Water System

The surface-water system in Subarea 1 includes the upper Chattahoochee River and its tributaries. The 

drainage area of the Chattahoochee River basin also encompasses about 2,600 mi2 in Alabama (not in Subarea 1) 

(U.S. Army Corps of Engineers, 1985a,b) and about 5,940 mi2 in Georgia, of which 2,430 mi2 is in Subarea 1. The 

river serves as water supply for much of the Metropolitan Atlanta area. The Chattahoochee originates near Helen, Ga. 

(fig. 8), in the Blue Ridge Province (fig. 2). The boundary with Subarea 2 along the river is located near Whitesburg, 

Ga. Major tributaries to the upper Chattahoochee River include the Soque River, Chestatee River, Suwanee Creek, 

Big Creek, Sope Creek, Nancy Creek, Peachtree Creek, Sweetwater Creek, and Snake Creek (fig. 8).
20
21

For this report, the mean-annual stream discharge of a surface-water drainage measured at a gaging station is 

defined as the arithmetic average of all reported annual discharges for the period of record. Note that, by definition, 

the stream discharge includes both surface runoff and baseflow. The estimated mean-annual stream discharge of the 

Chattahoochee River from Subarea 1 to Subarea 2 is about 3,740 ft3

/s (table 3), using values based on data from the 

continuous-record stream-gaging station—Chattahoochee River near Whitesburg, Ga. (02338000) (table 3; fig. 8).

Table 3. Selected active and discontinued continuous-record stream-gaging stations in the upper Chattahoochee 

River basin, Subarea 1

[I, fracture-conduit aquifer in igneous or metamorphic rock; —, not applicable]

Station 

number Station name

Drainage 

area

(square 

miles)

Type

of

stream

Major 

aquifer 

drained

Period of record 

of unregulated 

flow

(water years)

Mean-annual stream 

discharge

1/Stokes and McFarlane (1994).

1/

(cubic feet per 

second)

02330450 Chattahoochee River at Helen, Ga. 44.7 regional I 1982-present 134

02331000 Chattahoochee River near Leaf, Ga. 150 do. do. 1940-71

2/U.S. Geological Survey (1971).

2/402

02331600 Chattahoochee River near Cornelia, Ga. 315 regional do. 1958-present 828

02333000 Chattahoochee River near Gainesville, Ga. 559 do. do. 1902-03

1938-55

3/1,240

3/U.S. Geological Survey (1963).

02333500 Chestatee River near Dahlonega, Ga. 153 tributary do. 1929-32

1940-present

367

02334430 Chattahoochee River at Buford Dam, near Buford, Ga. 1,040 regional do. — —

02334885 Suwanee Creek near Suwanee, Ga. 46.8 tributary do. 1985-present 61.7

02334500 Chattahoochee River near Buford, Ga. 1,060 regional do. 1943-55 2,173

02335000 Chattahoochee River near Norcross, Ga. 1,170 do. do. 1902-46 2,265

02335500 Chattahoochee River near Roswell, Ga. 1,230 do. do. 1942-55 2,329

02335700 Big Creek near Alpharetta 72.0 tributary do. 1961-present 114

02335870 Sope Creek near Marietta 29.2 do. do. 1985-present 48.8

02336000 Chattahoochee River at Atlanta, Ga. 1,450 regional do. 1929-31

1937-55

2,567

02336300 Peachtree Creek at Atlanta, Ga. 85.4 tributary do. 1959-present 137

02337000 Sweetwater Creek near Austell, Ga. 246 tributary do. 1905

1938-present

337

02337170 Chattahoochee River near Fairburn, Ga. 2,060 regional do. — —

02337500 Snake Creek near Whitesburg, Ga. 35.5 tributary do. 1955-present 56.3

02338000 Chattahoochee River near Whitesburg, Ga. 2,430 regional do. 1939-53 3,740

The most upstream major storage impoundment on the Chattahoochee River system is Lake Sidney Lanier 

(table 4, fig. 8), which provides 65 percent of total usable storage capacity for flow regulation in federally operated 

reservoirs—Lake Sidney Lanier, West Point, Walter F. George, and Lake Seminole—in the Chattahoochee-Flint 

River basin (Comprehensive Study Newsletter, written commun., Fall 1993; Apalachicola Basin Reservoir 

Regulation Manual, U.S. Army Corps of Engineers, 1991). Lake Sidney Lanier provides hydroelectric power, 

recreation, water supply for much of the Metropolitan Atlanta area, and support for downstream navigation. 

Withdrawal and return flow also affects streamflow at various locations along the river’s corridor.

Table 4. Major impoundment in the upper Chattahoochee River basin, Subarea 1

Impoundment structure Station 

number Location Installation date Major uses

Total storage 

capacity 

(acre-feet)

Lake Sidney Lanier

(Buford Dam)

02334400 Gwinnett–Forsyth Counties 1959 power generation, water supply, flood 

control, recreation

1/Stokes and McFarlane (1994).

1/2,554,000
22

GROUND-WATER DISCHARGE TO STREAMS

Streamflow is comprised of two major components—a typical hydrograph integrates these components as: 

• overland or surface runoff, represented by peaks, indicating rapid response to 

precipitation; and 

• baseflow, represented by the slope of the streamflow recession, indicating 

ground-water discharge to the stream. 

In relation to the conceptual model, baseflow in streams is comprised of contributions from the local, 

intermediate, or regional ground-water flow regimes. Estimates of recharge to the ground-water system are minimum 

estimates because the budgets were developed as ground-water discharge to streams, and do not include ground water 

discharged as evapotranspiration, to wells, or ground water that flows downgradient into other aquifers beyond the 

topographic boundary defining Subarea 1. Local flow regimes likely are the most affected by droughts. Discharge 

measured in unregulated streams and rivers near the end of a drought should be relatively steady and composed 

largely of baseflow. 

Mean-Annual Baseflow

Mean-annual baseflow was determined by estimating mean-annual ground-water discharge to the 

Chattahoochee River and selected major tributaries. Streamflow data used to determine mean-annual ground-water 

discharge at continuous-record gaging stations were selected according to periods of record when flow was 

unregulated. The hydrograph-separation program SWGW (Mayer and Jones, 1996) was applied to estimate meanannual baseflow at six continuous-record gaging stations in the upper Chattahoochee River basin (table 5). For each 

gaging station, two recession indices are listed in table 5; one represents the rate of streamflow recession during the 

major rise period, generally in winter; and the other, the major recession period, generally in summer. Some variables 

that are supplied by the user to SWGW for each hydrograph separation are not listed in table 5, but can be obtained 

from the U.S. Geological Survey, Georgia District Office, Atlanta, Ga. These variables include the time-base (in 

days) from the peak to the cessation of surface runoff, the time period (the beginning and ending months) for 

application of the summer recession index, and the adjustment factor for the displacement of the recession curve. 

See Rutledge (1993) for a discussion of time-base, and Mayer and Jones (1996) for a discussion of the other usersupplied variables.

The mean-annual baseflow, in cubic feet per second; and the related unit-area baseflow, in cubic feet per 

second per square mile (ft3/s/mi2), were computed for each station. Mean unit-area baseflow estimated for six 

stations representing discharge from igneous and metamorphic rocks along the Chattahoochee River in Subarea 1 

ranged from 1.06 to 2.19 ft3

/s/mi2 (table 5).

Data for gaging stations located downstream of Lake Sidney Lanier on the Chattahoochee River in Subarea 1 

(fig. 8) were evaluated for the period prior to its impoundment by Buford Dam in 1956. Where possible, data for the 

same years were used for the hydrograph-separation analyses for each station throughout the study area. In general, 

in the upper Chattahoochee River basin, the lowest streamflow occurred during the drought of 1941; the highest 

streamflow occurred in 1949. The average flow year selected for analysis varied for each station with regard to the 

available period of record for unregulated flow.

In general, estimated mean unit-area baseflow decreases downstream; those near the Blue Ridge Province are 

higher. Mean unit-area baseflow generally is greater than 1 ft3/s/mi2. Estimated mean-annual baseflow in the 

Chattahoochee River ranges from about 69 to 82 percent of mean-annual stream discharge in Subarea 1. The 

contribution of mean-annual baseflow to streamflow from Subarea 1 to Subarea 2 was estimated using data from the 

Whitesburg, Ga., gaging station (fig. 8; table 3). This discharge to the Chattahoochee River at the Subarea 1–2 

boundary near Whitesburg was estimated to be about 2,570 ft3

/s. The mean-annual baseflow represents about 

69 percent of the mean-annual stream discharge at the Subarea 1–Subarea 2 boundary.
23

Table 5. Mean-annual stream discharge, estimated annual and mean-annual baseflow, and unit-area mean-annual baseflow at selected ga

Chattahoochee River basin, Subarea 1

[I, fracture-conduit aquifer in igneous and metamorphic rocks]

Station 

number Station name Type of stream

Drainage 

area

(square 

miles)

Major 

aquifer 

type

Recession index

Water 

year

Flow 

conditions

Mean-annual 

stream 

discharge1/

(cubic feet 

per second)

Annual

baseflow2/,,3/ 

(cubic feet per 

second)

Me

bas

(cub

s

Winter

(days)

Summer

(days)

02330450 Chattahoochee River at Helen, Ga. regional 44.7 I 150 100 1986

19871983

LowAverageHigh

68.2

110180

59.378.0

138

02331000 Chattahoochee River near Leaf, Ga. do. 150 do. 120 100 1941

19591949

LowAverageHigh

210340649

159271554

02333000 Chattahoochee River near Gainesville, Ga. do. 559 do. 150 120 1941

19521949

LowAverageHigh

697

1,3972,015

564857

1,524

02334500 Chattahoochee River near Buford, Ga. do. 1,060 do. 150 130 1951

19441949

LowAverageHigh

1,5682,2003,432

1,2701,6602,440

1

02336000 Chattahoochee River at Atlanta, Ga. do. 1,450 do. 150 120 1941

19531949

LowAverageHigh

1,4542,3684,406

1,1901,5503,180

1

02338000 Chattahoochee River near Whitesburg, Ga. do. 2,420 do. 130 100 1941

19521949

LowAverageHigh

2,1664,1706,221

1,3702,4603,890

2

Drainage area and mean-annual baseflow exiting 

Subarea 1

2,420 2

1/From annually published U.S. Geological Survey data reports, for example: Stokes and McFarlane (1994).2/Estimated using SWGW (Mayer and Jones, 1996).3/Values are reported to three significant digits to maintain the numerical balance of the water budget; implication of accuracy to the degree show4/Estimated by averaging discharges for low, average, and high flow years for the period of unregulated flow.5/Discharge divided by drainage area.
24

Drought Flow for 1941, 1954, and 1986

Regional drought periods of 1938-45, 1950-63, and 1984-88 were marked by severe droughts in the years of 

1941, 1954, and 1986 in the ACF and ACT River basins. Typically, the lowest mean-annual streamflow for the period 

of record occurred during one of these years. Streamflow was assumed to be sustained entirely by baseflow near the 

end of these droughts. Near-synchronous discharge measurements at partial-record gaging stations or daily mean 

streamflow at continuous-record gaging stations during these periods were assumed to provide a quantitative estimate 

of near minimum baseflow from Subarea 1 into Subarea 2. Where available, streamflow data for an interval of a few 

days were compiled; and where not available, streamflow was estimated using various techniques—discussed below.

Estimated and measured streamflow near the end of the 1941, 1954, and 1986 drought years at selected sites 

on the upper Chattahoochee River and its tributaries are shown in tables 6, 7, and 8, respectively, and summarized in 

table 9. Most of the data presented represent minimum daily mean streamflow from continuous-record gaging 

stations. Some miscellaneous streamflow measurements were used for the analyses.

Historical streamflow data are available throughout the upper Chattahoochee River basin during the 1941 and 

1954 drought years, except for 1954 drought data for the Chattahoochee River near Whitesburg; the Whitesburg gage 

was discontinued in June 1954 and reinstalled in 1965. An attempt was made to estimate the flow for the period 

analyzed in Subarea 1 by balancing mass in the stream network downstream from the Chattahoochee River at 

Atlanta. The tributary discharges to the Chattahoochee River were estimated using the unit-area discharge computed 

at a measurement site extrapolated to the entire tributary drainage. These unit-area discharges also were applied to the 

intermediate areas on the Chattahoochee River not accounted for by the measured tributaries. Streamflow data for the 

1954 drought are presented in detail by Thomson and Carter (1955; 1963). Minimum daily streamflow data were 

similar for most gaging stations during the historical droughts of 1941 and 1954 (tables 6 and 7). For example, 

streamflow at the Leaf station was 72 and 82 ft3

/s for 1941 and 1954, respectively; Gainesville was 242 and 282 ft3/s, 

respectively; and at Roswell was 389 and 350 ft3/s, respectively. 

Data from 1986 drought year measured at stations on the Chattahoochee River downstream from Buford Dam 

(02334430) indicate higher streamflow due to releases upstream at Lake Sidney Lanier (Hale and others, 1989); and 

therefore, could not be used in the drought flow analysis. An estimate of the unregulated flow was computed using 

the procedure described above downstream from the Chattahoochee River near Cornelia, the last unregulated gaged 

site.

Table 6. Stream discharge during the month of October of the drought of 1941, Subarea 1

[—, not applicable]

Station 

number Station name

Type

of

stream

Drainage

area

(square 

miles)

Date

Stream 

discharge1/

(cubic feet 

per second)

Unit-area 

discharge2/ 

(cubic feet per 

second per 

square mile)

02331000 Chattahoochee River near Leaf, Ga. regional 150 10-26-41 72 0.480

02333000 Chattahoochee River near Gainesville, Ga. do. 559 10-26-41 242 .433

02335000 Chattahoochee River near Norcross, Ga. do. 1,170 10-26-41 382 .326

02335500 Chattahoochee River near Roswell, Ga. do. 1,230 10-26-41 389 .316

02336000 Chattahoochee River at Atlanta, Ga. do. 1,450 10-26-41 422 .291

02338000 Chattahoochee River near Whitesburg, Ga. do. 3/2,420 10-26-41 468 .193

Drainage area and stream discharge exiting Subarea 14/ 2,420 468

1/Daily mean discharge.

2/Discharge divided by the drainage area.

3/Carter and others (1989).

4/Represents entire Chattahoochee River basin in Subarea 1.
25

Table 7. Stream discharge during the months of September and October of the drought of 1954, Subarea 1

[—, not applicable]

Station 

number Station name

Type

of

stream

Drainage

area1/

(square 

miles)

Date

Stream 

discharge2/

(cubic feet 

per second)

Unit-area 

discharge3/ 

(cubic feet 

per second 

per square 

mile)

02330350 Chattahoochee River at Helen regional 44.7 10/15/54 4/24.4 .546

02331000 Chattahoochee River near Leaf do. 150 09/28/54 82 .547

02333000 Chattahoochee River near Gainesville do. 559 09/28/54 282 .504

02334500 Chattahoochee River near Buford do. 1,060 09/28/54 381 .359

02335000 Chattahoochee River near Norcross do. 1,170 09/14/54

10/12/54

4/471 .403

02335500 Chattahoochee River near Roswell do. 1,230 09/28/54 350 .285

02336000 Chattahoochee River at Atlanta do. 1,450 09/28/54 346 .239

— intermediate-area contribution between 02336000 and 

Chattahoochee River above mouth of Peachtree Creek

— 6 — 5/0.2 —

02336300 Peachtree Creek at Atlanta tributary 85.4 09/30/54 4/2.31 .027

— Peachtree Creek at mouth do. 131 — 6/3.5 —

— intermediate-area contribution between mouths of Peachtree 

Creek and Proctor Creek

— 6 — 5/.4 —

02336530 Proctor Creek at Bolton Road at Atlanta do. 15.9 09/30/54 4/.95 .060

— Proctor Creek at mouth do. 16.4 — 6/1.0 —

— intermediate-area contribution between Proctor Creek and 

Utoy Creek

— 55 — 5/2.5 —

02336680 North Utoy Creek at Freeborn near Ben Hill tributary 8.9 09/30/54 4/.31 .035

02336710 South Utoy Creek at Freeborn Road near Ben Hill do. 13.2 09/30/54 4/.70 .053

— confluence of South Utoy Creek and North Utoy Creek do. 22.1 — 7/1.0 .045

— Utoy Creek at mouth do. 34.2 — 8/1.5 —

— intermediate-area contribution between Utoy Creek and 

Sweetwater Creek

— 8 — 5/.1 —

02337000 Sweetwater Creek near Austell tributary 246 09/27/54 3.3 .013

— Sweetwater Creek at mouth do. 264 — 6/3.4 —

— intermediate-area contribution between Sweetwater Creek 

and Deep Creek

— 55 — 5/3.0 —

02337160 Deep Creek at State Route 154 near Tell tributary 29.5 09/27/54 4/1.62 .055

— Deep Creek at mouth do. 29.9 — 6/1.6 —

— intermediate-area contribution between Deep Creek and Pea 

Creek

— 44 — 5/1.9 —

02337233 Pea Creek at State Route 154 near Palmetto tributary 13.5 09/27/54 4/.60 .044

— Pea Creek at mouth do. 14.5 — 6/.6 —

— intermediate-area contribution between Pea Creek and Bear 

Creek

— 2 — 5/.4 —

02337250 Bear Creek from right at State Route 166 near Douglasville tributary 16.8 09/29/54 4/3.18 .189

— Bear Creek at mouth do. 17.3 — 6/3.3 —

— intermediate-area contribution between right side of Bear 

Creek and left side of Bear Creek

— 1 — 5/0 —

02337310 Bear Creek from left at Woodruff Road near Palmetto tributary 26.8 09/27/54 4/.04 .001
26

1/Carter and others (1989).

2/Daily mean discharge.

3/Discharge divided by the drainage area.

4/Miscellaneous discharge measurement. 5/Estimated by multiplying drainage area of the intermediate area by unit-area discharge that was computed using 

the discharge at the next downstream miscellaneous measurement site or daily mean-discharge site. 6/Estimated by multiplying the drainage area at the tributary mouth by the unit-area discharge that was computed 

using the discharge at that tributary’s miscellaneous measurement site or daily mean-discharge site. 7/Sum of the flows in North and South Utoy Creeks and corresponding unit-area discharge. 8/Estimated by multiplying the drainage area at the mouth of Utoy Creek by the unit-area discharge at the 

confluence of North and South Utoy Creeks. 9/Computed by multiplying drainage area by estimated unit-area discharge at the mouth of Dog River. 10/Estimated by summing the estimated discharges of Dog River above Mobley Creek and of Mobley Creek at 

mouth. 11/Estimated by multiplying the drainage area by the estimated unit-area discharge of Dog River below Mobley 

Creek. 12/Estimated by multiplying intermediate drainage area by Snake Creek unit-area discharge. 13/Computed by adding the discharge at station 02326000 to the sum of all estimates of intermediate-area 

discharges and discharges at tributary mouths downstream from station 02338000, except for Mobley Creek, 

which is a tributary to Dog River.

02337330 Bear Creek at mouth near Rico tributary 29.0 — 6/0 —

— intermediate-area contribution between Bear Creek from left 

and Dog River

intermediate 4 — 9/0.1 —

02337400 Dog River at Post Road near Douglasville tributary 46.9 09/29/54 4/.72 .015

— Dog River above Mobley Creek do. 49.7 — 6/.7 —

02337420 Mobley Creek at Pool Road near Douglasville do. 10.2 09/29/54 4/.38 .037

— Mobley Creek at mouth do. 16.0 — 6/.6 —

— Dog River below Mobley Creek do. 65.7 — 10/1.3 .020

02337440 Dog River at mouth do. 78.5 — 11/1.6 —

— intermediate-area contribution between Dog River and Snake 

Creek

intermediate 66 — 5/5.0 —

02337500 Snake Creek near Whitesburg tributary 35.5 09/28/54 2.7 .076

— Snake Creek at mouth do. 49.2 — 6/3.7 —

— intermediate-area contribution between Snake Creek and 

02338000

intermediate 56 — 12/4.3 —

02338000 Chattahoochee River near Whitesburg regional 2,420 — 13/384 .159

Drainage area and stream discharge exiting Subarea 1 2,420 384

Table 7. Stream discharge during the months of September and October of the drought of 1954, Subarea 1—

Continued

Station 

number Station name

Type

of

stream

Drainage

area1/

(square 

miles)

Date

Stream 

discharge2/

(cubic feet 

per second)

Unit-area 

discharge3/ 

(cubic feet 

per second 

per square 

mile)
27

Table 8. Stream discharge during the month of July of the drought of 1986, Subarea 1

[—, not applicable]

Station 

number Station name

Type

of

stream

Drainage 

area1/ 

(square 

miles)

Date

Stream 

discharge 

(cubic feet 

per 

second)2/

Unit-area 

discharge 

(cubic feet 

per second 

per square 

mile)3/

02330450 Chattahoochee River at Helen regional 44.7 07/07/86 29 0.649

02331600 Chattahoochee River near Cornelia do. 315 07/08/86 162 .514

— Chattahoochee River above mouth of Chestatee River do. 576 — 4/296 —

02333500 Chestatee River near Dahlonega tributary 153 07/08/86 54 .353

— Chestatee River above Yahoo Creek do. 155 — 5/55 —

02333600 Yahoola Creek at Dahlonega do. 31.3 07/08/86 6/8.2 .262

— Yahoola Creek at mouth do. 34.4 — 7/9.0 —

— Chestatee River below Yahoola Creek do. 189 — 8/64 .339

— Chestatee River at mouth do. 318 — 9/108 —

— Chattahoochee River below Chestatee River regional 894 — 10/404 .452

02334430 Chattahoochee River at Buford Dam near Buford — 1,040 — 11/470 —

— intermediate-area contribution between station 02334430 

and Chattahoochee River above mouth of 

Suwanee Creek

— 65 — 12/4.0 —

02334885 Suwanee Creek near Suwanee tributary 46.8 07/09/86 2.9 .062

— Suwanee Creek at mouth do. 51.2 — 7/32 —

— intermediate-area contribution between Suwanee Creek and 

Big Creek

— 77 — 12/6.6 —

02335700 Big Creek near Alpharetta tributary 72 07/09/86 6.2 .086

— Big Creek at mouth do. 103 — 7/8.9 —

— intermediate-area contribution between Big Creek and Sope 

Creek

— 42 — 12/5.5 —

02335870 Sope Creek near Marietta tributary 29.2 07/09/86 3.8 .130

— Sope Creek at mouth do. 35.4 — 7/4.6 —

— intermediate-area contribution between Sope Creek and 

station 02336000

— 39 — 13/5.1 —

02336000 Chattahoochee River at Atlanta regional 1,450 — 14/508 .350

— intermediate-area contribution between station 02336000 and 

Peachtree Creek

— 6 — 12/.8 —

02336300 Peachtree Creek at Atlanta tributary 86.8 07/09/86 12 .138

— Peachtree Creek at mouth do. 131 — 7/18.1 —

— intermediate-area contribution between Peachtree Creek and 

Sweetwater Creek

— 119 — 12/6.8 —

02337000 Sweetwater Creek near Austell tributary 246 07/09/86 14 .057

— Sweetwater Creek at mouth do. 264 — 7/15 —

— intermediate-area contribution between Sweetwater and 

Annewakee

— 87 — 12/18.8 —

02337200 Annewakee Creek near Douglasville tributary 29 07/07/86 6.3 .217

— Annewakee Creek at mouth do. 29.9 — 7/6.5 —

— intermediate-area contribution between Annewakee and 

Dog River

— 79 — 12/11.4 —
28

1/Carter and others (1989).

2/Daily mean discharge.

3/Discharge divided by the drainage area.

4/Estimated by multiplying unit-area discharge for station 02331600 by drainage area of listed site. 5/Estimated by multiplying unit-area discharge for station 02333500 by drainage area of listed site. 6/Miscellaneous discharge measurement. 7/Estimated by multiplying the drainage area at the tributary mouth by the unit-area discharge that was computed 

using the discharge at that tributary’s miscellaneous measurement site or daily mean-discharge site. 8/Sum of estimated discharges for the Chestatee River above Yahoola Creek and Yahoola Creek at mouth. 9/Estimated by multiplying drainage area by unit-area discharge for Chestatee River below Yahoola Creek. 10/Sum of estimated discharges for the Chattahoochee River above mouth of Chestatee River and Chestatee River 

at mouth. 11/Estimated unregulated discharge computed by multiplying drainage area by unit-area discharge of 

Chattahoochee River below Chestatee River. 12/Estimated by multiplying drainage area of the intermediate area by unit-area discharge that was computed 

using the discharge at the next downstream miscellaneous measurement site or daily mean-discharge site. 13/Estimated by multiplying drainage area by the unit-area discharge that was computed using the discharge at the 

nearest upstream tributary daily mean-discharge site. 14/Estimated unregulated discharge at station 02334430, added to the tributary mouth discharges, and 

intermediate area discharges downstream to station 02336000. 15/Estimated unregulated discharge at station 02336000, added to the tributary mouth discharges, and 

intermediate area discharges downstream to station 02338000.

02337438 Dog River near Fairplay tributary 76.4 07/07/86 6/11 .144

— Dog River at mouth do. 78.5 — 7/11.3 —

— intermediate-area contribution between Dog River and 

Snake Creek

— 66 — 12/15.6 —

02337500 Snake Creek near Whitesburg tributary 35.5 07/09/86 8.4 0.237

— Snake Creek at mouth do. 49.2 — 7/11.7 —

— intermediate-area contribution between Snake Creek and 

station 02338000

— 56 — 13/13.3 —

02338000 Chattahoochee River near Whitesburg regional 2,420 — 15/637 .263

Table 8. Stream discharge during the month of July of the drought of 1986, Subarea 1—Continued

[—, not applicable]

Station 

number Station name

Type

of

stream

Drainage 

area1/ 

(square 

miles)

Date

Stream 

discharge 

(cubic feet 

per 

second)2/

Unit-area 

discharge 

(cubic feet 

per second 

per square 

mile)3/
29

 

Table 9. Relations among mean-annual stream discharge, and estimated mean-annual baseflow and drought flow in 

the Chattahoochee River, Subarea 1

[Mean-annual stream discharge is mean for the period of record; —, not applicable or no available data]

Station 

number 

or 

estimation 

site

Station name

Drainage 

area 

(square 

miles)

Stream discharge, in cubic feet per second

Mean-annual 

stream 

discharge1/

Estimated 

mean-annual 

baseflow2/

Drought 

of 

19413/

Drought 

of 

19544/

Drought 

of 

19865/

02330450 Chattahoochee River at Helen, Ga. 44.7 134 91.8 — 24.4 29

02331000 Chattahoochee near Leaf, Ga. 150 402 328 72 82 —

02331600 Chattahoochee River near Cornelia, Ga. 315 828 — — — 162

02333000 Chattahoochee River near Gainesville, Ga. 559 1,240 982 242 282 —

02334430 Chattahoochee River at Buford Dam, near Buford, Ga. 1,040 — — — — 470

02334500 Chattahoochee River near Buford, Ga. 1,060 2,173 1,790 — 381 —

02335000 Chattahoochee River near Norcross, Ga. 1,170 2,265 — 382 471 —

02335450 Chattahoochee River above Roswell, Ga. 1,220 — — — — —

02335500 Chattahoochee River near Roswell, Ga. 1,230 2,329 — 389 350 —

02336000 Chattahoochee River at Atlanta, Ga. 1,450 2,567 1,970 422 346 7/508

02336490 Chattahoochee River at State Highway 280, near 

Atlanta, Ga.

1,590 — — — — —

02337170 Chattahoochee River near Fairburn, Ga. 2,060 — — — — —

02338000 Chattahoochee River near Whitesburg, Ga.6/ 2,420 3,740 2,570 468 384 637

Drainage area, mean-annual stream discharge, mean-annual 

baseflow, and drought flows exiting Subarea 1

3,740 2,570 468 384 7/637

1/From table 3.

2/From table 5; values are reported to three significant digits to maintain the numerical balance of the water budget; implication 

of accuracy to the degree shown is not intended. 3/From table 6.

4/From table 7.

5/From table 8.

6/Represents entire Chattahoochee River basin in Subarea 1.

Baseflow during the later parts of the droughts of 1941, 1954, and 1986 averaged about 19.3 percent of the 

estimated mean-annual baseflow to the surface-water system (table 10). Ground-water contribution to streamflow 

during the drought periods at the Subarea 1-2 boundary was estimated using data from the Whitesburg, Ga., gage 

along the Chattahoochee River. Historical drought flows (prior to upstream storage in Lake Sidney Lanier) for 1941 

and 1954 were 468 and 384 ft3

/s, respectively (table 10). Streamflow for the 1986 drought was estimated to be 

637 ft3/s. In relation to the conceptual model of ground-water flow and stream-aquifer relations, baseflow during 

droughts represents greatly reduced contributions from the local and intermediate flow regimes. Downstream 

baseflow in the upper Chattahoochee River basin near the end of the 1941, 1954, and 1986 droughts is related to 

drainage area in figure 9 and summarized in tables 9 and 10.

 

Table 10. Estimated drought flows and mean-annual baseflow in the upper Chattahoochee River basin; and ratio of 

average drought flow to mean-annual baseflow, Subarea 1

Drought flow, in cubic feet per second Mean-annual baseflow1/,2/

(in cubic feet per second)

Ratio of average drought flow to 

mean-annual baseflow5/

1941 (in percent) 3/ 19544/ 19865/ Average drought flow

Flow exiting Subarea 1 468 384 637 496 2,570 19.3

1/From table 5.

2/Values are reported to three significant digits to maintain the numerical balance of the water budget; implication 

of accuracy to the degree shown is not intended. 3/From table 6.

4/From table 7.

5/From table 8.
30
31

GROUND-WATER UTILIZATION AND

GENERAL DEVELOPMENT POTENTIAL

Ground-water utilization is defined as the ratio of ground-water use in 1990 to mean-annual ground-water 

recharge. The degree of ground-water utilization is scale dependent. For example, local ground-water pumping may 

result in substantial storage change and water-level declines near a center of pumping; whereas, such pumping 

relative to the entire Subarea would be small compared to mean-annual recharge. Because ground-water use in 

Subarea 1 represents a relatively minor percentage of ground-water recharge, even a large increase in ground-water 

use in Subarea 1 in one State is likely to have little effect on ground-water and surface-water occurrence in the other.

Ground-water use of about 28.8 ft3/s in 1990 in Subarea 1 represented 1.1 percent of the mean-annual 

baseflow in the surface-water system and 5.8 percent of the average drought flow. Local problems of ground-water 

overuse were not identified. However, the number and distribution of wells having long-term water-level data in 

Subarea 1 are insufficient to draw conclusions regarding regional water-level declines or storage change.

Table 11. Relation between 1990 ground-water use and ground-water discharge during mean-annual baseflow, 

average drought flow, and minimum drought flow, Subarea 1

Ground-water use, 1990

(cubic feet per second)

Baseflow to the Chattahoochee River and tributaries

(cubic feet per second0

Ratio of ground-water use to baseflow

(percent)

Mean-annual 

baseflow

Average drought 

flow

Minimum 

drought flow

Mean-annual 

baseflow

Average drought 

flow

Minimum 

drought flow

1/28.8 2,570 496 384 1.1 5.8 7.5

1/From Marella and others (1993).

In general, ground-water resources are underutilized throughout the study area. The rural population relies on 

ground water as their principal source of water supply; whereas, more densely populated areas rely on surface-water 

resources. However, wells supplied water to many communities prior to the development of large surface-water 

reservoirs. In recent years, suburban communities have developed ground-water supplies in response to curtailed 

surface-water resources.

Ground-water exploration in the Blue Ridge and Piedmont Provinces of Georgia historically has been 

“difficult” and its success “unpredictable.” The crystalline-rock aquifers of this region are characterized by little or 

no primary porosity and complex development of secondary permeability. The yield of bedrock wells depends on the 

presence and characteristics of the water-bearing zones penetrated by the open borehole in the bedrock. The aquifers 

in the Piedmont are extremely anisotropic and heterogeneous due to complex geologic controls in the crystalline 

bedrock (fig. 6). Depth to water-bearing zones is highly variable. Wells may yield water from several fractures 

throughout a borehole, or from a single productive fracture. Conversely, a borehole may not intersect an opening; 

and thus, may yield little or no water. 

A general assessment of ground-water development potential in Subarea 1 would reflect, in part, the cumulative effects of current and anticipated future hydrologic stresses imposed on the ground-water resources, and to a 

lesser extent, current availability of surface-water resources. The nature of such an assessment is necessarily limited 

in its scope and range of application by knowledge of current hydrologic conditions and the acceptance of these 

conditions by Federal, State, or local water-resource managers as standards upon which the effects of additional stress 

and future development are evaluated. Current stresses and hydrologic conditions might be unknown in some areas, 

making the results of an evaluation of development potential highly uncertain. Future stresses also might be linked to 

water-management practices that have yet to be formulated, or to water-management decisions that have yet to be 

made. Therefore, an assessment of ground-water development potential provides insight only into one aspect of the 

broader question of how water-management decisions affect ground-water availability; specifically, whether existing 

hydrologic data document flow-system behavior adequately to allow quantification of the potential effects of future 

development on the flow system. Further, an assessment of development potential does not account for the suitability 

of existing ground-water-resource management approaches or the effects of future approaches on further resource 

development. Such answers are dependent on the synthesis of results from the various Comprehensive Study 
32

components and subsequent consideration by the Federal, State, or local water managers responsible for decisionmaking within the basin.

The identification of areas that could be developed for ground-water supply rather than surface-water sources 

could not be determined from available data for Subarea 1. Because geologic controls affecting ground-water 

availability are highly variable, even on a local scale, regional evaluations are inherently difficult. Ground-water 

availability may be a constraint in areas underlain by Piedmont and Blue Ridge crystalline-rock terranes more 

because of the difficulty in locating water-bearing voids in the rocks, rather than because of a lack of water. Groundwater resources probably could provide supplemental supply during peak demand periods throughout most suburban 

areas of the Subarea 1. In more rural areas, ground-water supplies could serve as a primary resource depending upon 

demands. Generally, wells need only supply about 5 gal/min for domestic users, and may not be drilled to a depth that 

taps the available ground-water supply at a site. Most municipal or industrial users generally require well yields of at 

least 50 to 100 gal/min or more, and wells for such supplies likely are drilled to a depth sufficient to intersect as many 

water-bearing zones as feasible. Municipal and industrial users also tend to drill multiple wells to obtain the required 

ground-water supply.

Ground-Water Exploration-Program Examples

An example of a successful ground water exploration program in Subarea 1 is in Cobb County, Ga. The CobbMarietta Water Authority (CMWA) began an evaluation of the ground water resources of the county in 1988 to 

develop supplemental sources of drinking water. The CMWA supplied about 75 Mgal/d for public supply in 1990 

(Fanning and others, 1992). Population projections for the area to the year 2040 indicate that the demand for water 

will be about 330 Mgal/d (Brown and Caldwell, Consulting Engineers, Inc., written commun., 1988). Presently 

(1996), all the drinking water is obtained from two surface-water sources—the Chattahoochee River and Lake 

Allatoona on the Etowah River (fig. 8). The CMWA plans to develop well fields throughout Cobb County to 

supplement the drinking water supply during periods of peak demand.

Two CMWA studies were conducted in 1993 and 1994 using different methodologies to locate areas favorable 

for drilling high-yielding wells. The first study used only existing data; no field work was conducted other than the 

drilling and monitoring of one well. The drilling area was selected using a geographic information systems and 

computer-aided design to map and analyze geologic, hydrologic, water use, land use, potential threats to ground 

water, and water distribution network data. Once the drilling site was selected, a local-scale geologic map was 

constructed to further refine the site selection. The test well was drilled in a biotite gneiss/amphibolite to a depth of 

603 ft. Aquifer tests indicated that the well could be pumped at about 100 to 150 gal/min. Borehole geophysical logs 

also were used to evaluate water-bearing characteristics. Approximately 75 percent of the water was obtained at 

depths of less than 400 ft from several fractures. The quality of the water, however, was not suitable for drinking 

because of the high concentration of sulfate, and would require treatment before use for public supply 

(Law Environmental Inc., written commun., 1993). 

The second CMWA study involved detailed geologic mapping throughout the county (Emery and Garrett 

Groundwater, Inc., written commun., 1994). The mapping was combined with photolineament analyses, collection of 

background well information, topography, soils data, watershed geomorphology, and assessment of contamination 

potential. Two clusters of three wells each were drilled and preliminary aquifer tests were performed. One of the 

sites was selected for future development. All the wells at this site were drilled in a north-south line about 0.1 mi 

apart. Estimated yields of the wells range from 180 to 300 gal/min. The northern-most well had the lowest yield and 

an elevated sulfate concentration of 1,800 milligrams per liter (mg/L). The two southern-most wells flowed naturally 

at about 7 to 12 gal/min. The southern-most well was airlift tested at 550 gal/min. Chemical analysis of the water 

indicated no sulfate present, and the water was suitable for public supply (J.J. Brady, Emery and Garrett 

Groundwater, Inc., oral commun., 1993).

In December 1988, a hydrogeologic investigation was conducted at the Peachtree Golf Club (PGC) in 

DeKalb County, Ga., to evaluate the potential for the use of ground water as a source for irrigation. Surficial geologic 

mapping was conducted and correlated with topographic lineaments in the selection of drilling sites. The dominant 

rock type at the PGC site is a fine-grained granitic gneiss. Discontinuous layers of hornblende gneiss are present 

within the granitic gneiss. Scattered pegmatites and quartz veins also were mapped. The fine-grained texture is a 

result of shearing granulation under high, confining pressure; thus, the rock has very low primary permeability. Depth 

of weathering is shallow, and outcrops are present along creek bottoms.
33

Four drilling sites were selected. Initial test-well production estimates were highly variable, and ranged from 

1 to 200 gal/min. Three of the four test sites are located in stream-valley bottoms, and the other site is located at a 

higher hillside location along a stream drainage. As with yield, depths to water-bearing zones and types of waterbearing zones were highly variable. One well which produced more than 200 gal/min, yielded most of the water from 

a “bottom-hole” zone (terminology and definition from Cressler and others, 1983) at a depth of 455 to 465 ft. The 

zone apparently was a deeply weathered feldspathic zone having numerous fractured quartz veins. Two other wells 

derive water from various zones throughout the open-hole interval, penetrating rocks having abundant chlorite, which 

creates greater differential weathering along foliation planes. The fourth well tapped quartz-rich rocks and yielded 

only a very small amount of water.

SUMMARY

Drought conditions in the 1980’s have focused attention on the multiple uses of the surface- and ground-water 

resources in the Apalachicola-Chattahoochee-Flint (ACF) and Alabama-Coosa-Tallapoosa (ACT) River basins in 

Alabama, Florida, and Georgia. Federal, State, and local agencies also have proposed projects that are likely to result 

in additional water use and revisions of reservoir operating practices within the river basins. The existing and 

proposed water projects have created conflicting demands for water and emphasized the problem of allocation of the 

resource. This study was initiated to describe ground-water availability in the upper Chattahoochee River basin in 

Georgia, Subarea 1 of the ACF-ACT River basins, and to estimate the possible effects of increased ground-water use 

in the basin.

Subarea 1 encompasses about 2,430 square miles in the Piedmont and Blue Ridge physiographic provinces of 

north-central Georgia, which covers about 28 percent of the total 8,740 square-mile area of the Chattahoochee River 

basin. The basin also includes about 2,600 square miles in Alabama; however, that part of the basin is not in the study 

area. Subarea 1 is bounded to the northwest by the Tennessee River basin, to the east by the Savannah River basin and 

the Altamaha River basin. To the west, the study area is bounded by the Coosa River basin (Subarea 6) and 

Tallapoosa River basin (Subarea 5) and to the south by the middle Chattahoochee and upper Flint River basins 

(Subarea 2). 

The Piedmont and Blue Ridge Provinces are characterized by a two-component aquifer system composed of a 

fractured crystalline-rock aquifer characterized by little or no primary porosity or permeability. The overlying 

weathered regolith (saprolite) behaves as a porous-media aquifer. In some areas, a transition zone lies between the 

regolith and unweathered crystalline bedrock.

The conceptual model of ground-water flow and stream-aquifer relations subdivides the ground-water flow 

system into local (shallow), intermediate, and regional (deep) flow regimes. The regional flow regime probably 

approximates steady-state conditions and water discharges chiefly to the Chattahoochee River. Ground-water 

discharge to tributaries primarily is from the local and intermediate flow regimes. Ground water that discharges to 

regional drains is composed of local, intermediate, and regional flow regimes. Mean-annual ground-water discharge 

to streams (baseflow) is considered to approximate the long-term, average recharge to ground water.

Mean-annual baseflow in Subarea 1 was estimated using an automated hydrograph-separation method. Total 

mean-annual baseflow to the upper Chattahoochee River and tributaries was estimated to be about 2,570 cubic feet 

per second in Georgia (from the headwaters to Subarea 1–Subarea 2 boundary). Mean-annual baseflow represents 

about 69 percent of the mean-annual stream discharge at the Subarea 1–Subarea 2 boundary. 

Stream discharges for selected sites on the Chattahoochee River and tributaries were compiled for the years 

1941, 1954, and 1986, during which historically significant droughts occurred throughout most of the ACF-ACT 

River basins. Stream discharge was assumed to be sustained entirely by baseflow during the latter periods of these 

droughts. Estimated baseflow (unregulated) near the end of the individual droughts averaged about 19.3 percent of 

the estimated mean-annual baseflow in Subarea 1.

The limited scope, lack of field-data collection and short duration of the ACF-ACT River basin study has 

resulted in incomplete descriptions of ground- and surface-water-flow systems, which may affect the future 

management of water resources in the basins. For example, the extent and continuity of local and regional flow 

systems and their relation to geology largely is unknown. Similarly, quantitative descriptions of stream-aquifer 

relations, ground-water flow across State lines, water quality, drought flows, and ground-water withdrawal and 

subsequent effects on the flow systems (the availability and utilization issue) are highly interpretive; therefore, the 

descriptions should be used accordingly.
34

Estimates of water-use and ground-water discharge to streams are dependent on methodologies employed 

during data collection, computation, and analyses. Results reported herein are limited by a lack of recent data and the 

non-contemporaneity of all data. Analyses using limited data may not adequately describe stream-aquifer relations. 

Most importantly, analyses in this report describe only two hydrologic conditions—(1) mean-annual baseflow and (2) 

drought-flow conditions during 1941, 1954, and 1986. Analyses derived from extrapolation to other hydrologic 

conditions, such as much longer drought periods or increased ground-water withdrawal, should be used with caution. 

Special concern also should be directed to the effects of increased post-1990 withdrawal on ground-water discharge 

to streams in Subarea 1. 

The potential exists for the development of ground-water resources on a regional scale throughout Subarea 1. 

Ground-water use in 1990 represented about 1.1 percent of the estimated mean-annual baseflow and 5.8 percent of 

the average drought flow. Because ground-water use in Subarea 1 represents a relatively minor percentage of groundwater recharge, even a large increase in ground-water use in Subarea 1 in one State probably would have little effect 

on the quantity of ground-water and surface-water occurrence in the other. Long-term ground-water level declines 

were not observed; however, long-term water-level data at wells in Subarea 1 are few in number and poorly distributed areally, and conclusions regarding regional water-level declines or storage changes cannot be reasonably drawn.

SUGGESTIONS FOR FURTHER STUDY

This report presents a discussion of ground-water resources and interaction of ground- and surface-water 

systems in the upper Chattahoochee River basin, Subarea 1, of the ACF-ACT River basins. In Subarea 1, groundwater availability is addressed only from a regional perspective using historical data. Data collection was not a part of 

this study; therefore, lack of streamflow and ground-water data necessitated that estimation methods be used 

extensively to describe stream-aquifer relations. Additional data, particularly data describing surface- and groundwater conditions on a local scale, are needed to further refine and quantify the interaction of ground- and surfacewater systems in the Subarea. Analyses of these data could better describe stream-aquifer relations, as well as groundwater availability and development potential in Subarea 1. 

Although the overall objectives of this study were to evaluate the ground-water resources and supply, the data 

used to accomplish these objectives were stream-discharge data. Stream-discharge data were sufficient to meet study 

objectives; however, such data either were not totally adequate or were not available at critical sites. Future streamdischarge data collection to support resource management should emphasize (1) continuous-record data at critical 

hydrologic and political boundaries for a period of years; and (2) concurrent stream-discharge measurements at 

critical sites during drought periods.

Continuous stream-stage data collected over a period of years at critical locations provide the basic 

information essential to basinwide water-resource planning and management. Current data coverage is incomplete. 

For example, stream-gaging stations located on major tributary streams would have eliminated or reduced the need to 

extrapolate and interpolate data from stations distant to these boundaries, and consequently, would have improved the 

accuracy of estimates of ground-water contributions from subarea to subarea.

The collection of drought-flow data obviously is contingent on the occurrence of a drought; thus, collection of 

drought data is not routine and is not easily planned. A contingency plan to collect drought data should be in place. 

The plan could consider, but not be limited to, logistics, manpower needs, and the preselected of stream datacollection locations. For more rigorous planning, field reconnaissance of preselected stream sites could be conducted.

Data-base development also is critical to resource management. Data elements, such as well construction and 

yield; hydraulic characteristics of aquifers; water quality; and ground-water withdrawals—both areally and by 

aquifer—are particularly important. Seepage runs (detailed streamflow measurements of drainage systems made 

concurrently during baseflow conditions) can be used to identify individual ground-water flow systems and improve 

the understanding of stream-aquifer relations, especially in crystalline and mixed-rock terranes. Once identified, a 

flow system can be studied in detail to define its extent, recharge and discharge areas, movement of water, chemical 

quality, and the amount of water that can be withdrawn with inconsequential or minimal effects. These detailed 

studies might include test drilling, borehole geophysical logging, applications of surface geophysics, aquifer testing, a 

thorough water-withdrawal inventory, and chemical analyses of ground water to delineate the extent of the groundwater-flow system and evaluate its potential as a water supply. Evaluation of several such flow systems would greatly 
35

improve the understanding of ground-water resources throughout the subarea. Because aquifer properties vary 

substantially on a local scale and data are sparse, field studies are needed to obtain quantitative definitions of the 

hydraulic interactions of aquifers and streams in Subarea 1. 

SELECTED REFERENCES

Adams, G.I., 1926, The crystalline rocks, in Adams, G.I., Butts, Charles, Stephenson, L.W., and Cooke, C.W., eds., 

Geology of Alabama: Geological Survey of Alabama Special Report 14, p. 40-223. 

____1933, General geology of the crystalline of Alabama: Journal of Geology 41, p. 159-173. 

Adams, G.I., Butts, Charles, Stephenson, L.W., and Cooke, C.W., 1926, Geology of Alabama: Geological Survey of 

Alabama Special Report 14, 312 p. 

Arora, Rom, and Gorday, L.L., eds., 1984, in proceedings, A conference on the water resources of Georgia and 

adjacent areas: Georgia Geologic Survey Bulletin 99, 194 p.

Bailey, Z.C., and Lee, R.W., 1991, Hydrogeology and geochemistry in Bear Creek and Union Valleys, near Oak Ridge, 

Tennessee: U.S. Geological Survey Water-Resources Investigations Report 90-4008, 72 p.

Baker, Jack, 1957, Geology and ground water in the Piedmont area of Alabama: Geological Survey of Alabama 

Special Report 23, 99 p.

Barksdale, H.C., and Moore, J.D., eds., 1976, Water content and potential yield of significant aquifers in Alabama: 

Geological Survey of Alabama Open-File Report, 449 p.

Bentley, R.D., and Neathery, T.L., 1970, Geology of the Brevard fault zone and related rocks of the Inner Piedmont 

of Alabama, in Bentley, R.D., and Neathery, T.L., eds., Geology of the Brevard fault zone and related rocks of the 

Inner Piedmont of Alabama: Alabama Geological Society, 8th Annual Field Trip Guidebook, p. 1-79.

Bevans, H.E., 1986, Estimating stream-aquifer interactions in coal areas of eastern Kansas by using streamflow 

records, in Subitzky, Seymour, ed., Selected papers in the Hydrologic Sciences: U.S. Geological Survey WaterSupply Paper 2290, p. 51-64.

Bingham, R.H., 1982, Low-flow characteristics of Alabama streams: U.S. Geological Survey Water-Supply Paper 

2083, 27 p.

Bossong, C.R., 1989, Geohydrology and susceptibility of major aquifers to surface contamination in Alabama; area 2: 

U.S. Geological Survey Water-Resources Investigations Report 88-4177, 22 p.

Brackett, D.A., Steele, W.M., Schmitt, T.J., Atkins, R.L., Kellam, M.F., and Lineback, J.L., 1991, Hydrogeologic data 

from selected sites in the Piedmont and Blue Ridge provinces, Georgia: Georgia Geologic Survey Information 

Circular 86, 160 p.

Carr, J.E., Chase, E.B., Paulson, R.W., and Moody, D.W., 1990, Hydrologic events and water supply and use, in 

National Water Summary, 1987: U.S. Geological Survey Water-Supply Paper 2350, p. 141-148.

Carter, R.F., 1959, Drainage area data for Georgia streams: U.S. Geological Survey Open-File Report, 252 p.

Carter, R.F., and Herrick, S.M., 1951, Water resources of the Atlanta Metropolitan area: U.S. Geological Survey 

Circular 148, 19 p.

Carter, R.F., Hopkins, E.H., and Perlman, H.A., 1989, Low-flow profiles of the upper Chattahoochee River and 

tributaries in Georgia: U.S. Geological Survey Water-Resources Investigations Report 89-4056, 194 p.

Carter, R.F., and Putnam, S.A., 1978, Low-flow frequency of Georgia streams: U.S. Geological Survey Open-File 

Report 77-127, 104 p.

Carter, R.R. and Stiles, H.R., 1983, Average annual rainfall and runoff in Georgia, 1941-1970: Georgia Geologic 

Survey Hydrologic Atlas 9, 1 sheet.

Cederstrom, D.J., Boswell, E.H., and Tarver, G.R., 1979, Summary appraisals of the nation’s ground-water resourcesSouth Atlantic-Gulf Region: U.S. Geological Survey Professional Paper 813-0, 35 p.
36

SELECTED REFERENCES—Continued

Chandler, R.V., 1976, Aquifers of the Piedmont region, in Barksdale, M.C., Jelks, and Moore, J.D., eds., 1976, Water 

content and potential yield of significant aquifers in Alabama: Geological Survey of Alabama Open-File Report, 

p. 15-1—15-22.

Chapman, M.J., Milby, B.J., and Peck, M.F., 1993, Geology and ground-water resources in the Zebulon area, Georgia: 

U.S. Geological Survey Water-Resources Investigations Report 93-4161, 27 p.

Chapman, M.J., and Peck, J.F., 1997, Ground-water resources of the middle Chattahoochee River basin in Georgia and 

Alabama; and upper Flint River basin in Georgia—Subarea 2 of the Apalachicola–Chattahoochee–Flint and 

Alabama–Coosa–Tallapoosa River basins: U.S. Geological Survey Open-File Report 96-492, 48 p.

Clarke, J.S., and Peck, M.F., 1991, Ground-water resources of the south Metropolitan Atlanta region, Georgia: 

Georgia Geologic Information Circular 88, 56 p.

Clarke, O.M. Jr., 1963, Residual clays of the Piedmont Province in Alabama: Geological Survey of Alabama Circular 

20-A, 60 p.

Clark, W.Z., Jr., and Zisa, A.C., 1976, Physiographic map of Georgia: Georgia Geologic Survey State Map 4, 1 sheet.

Cressler, C.W., Blanchard, H.E., and Hester, W.G., 1979, Geohydrology of Bartow, Cherokee and Forsyth Counties: 

Georgia Geologic Survey Information Circular 50, 45 p.

Cressler, C.W., Thurmond, C.J., and Hester, W.G., 1983, Ground water in the greater Atlanta Region, Georgia: 

Georgia Geologic Survey Information Circular 63, 144 p.

Crickmay, G.W., 1952, Geology of the crystalline rocks of Georgia: Georgia Geologic Survey Bulletin 58, 54 p.

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37

SELECTED REFERENCES—Continued

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38

SELECTED REFERENCES—Continued

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____1994, Pumping test results from a flowing artesian well system, Cherokee County, Georgia: Georgia Geologic 

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Kidd, R.E., 1989, Geohydrology and susceptibility of major aquifers to surface contamination in Alabama; area 5: U.S. 

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39

SELECTED REFERENCES—Continued

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40

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41

SELECTED REFERENCES—Continued

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42

SELECTED REFERENCES—Continued

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43

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