U.S. Department of the Interior

U.S. Geological Survey

Figure 1. Generalized cross section in the Suwannee River 

basin showing karst features that facilitate the exchange of water 

between the surface and subsurface.

SINKHOLE

SINKHOLE GROUND-WATER

DISCHARGE TO

A SPRING/RIVER

DIRECTION OF

GROUND-WATER

FLOW

UPPER FLORIDAN AQUIFER

CONDUIT SYSTEM

SURFICIAL SANDS

AND CLAYS

ment measures to protect the functions of

the State’s ecosystems. Watershed management is one of the main components of

a program designed to protect and manage

Florida’s ecosystems. The FDEP has

identified several key objectives to effectively address watershed management

issues: (1) more coordinated management

of ground- and surface-water resources,

(2) more effective partnerships with local,

regional, State, and Federal government

agencies, (3) coordination of ground- and

surface-water monitoring efforts to assess

the quality and quantity of the water

resources and delineate the boundaries of

three-dimensional watersheds, and (4) the

development and maintenance of comprehensive statewide data bases for water

resource information and monitoring networks oriented toward targeted watersheds.

The Suwannee River basin in Florida

is one of several watersheds in the U.S.

that was chosen for a pilot study by the

Intergovernmental Task Force on Monitoring Water Quality (ITFM) to evaluate the

effectiveness of current monitoring proIn most watersheds (river basins) in

Florida the interactions between ground

water and surface water typically result in

a single dynamic flow system. This direct

hydraulic linkage results from numerous

karst features (such as sinkholes, conduit

systems in the underlying limestone, and

springs) that facilitate the exchange of

water between the surface and subsurface

(fig. 1). Unique problems can

arise in protecting water quality

in karst areas because of the

direct and rapid transport of

recharge through conduits to the

subsurface and through resurgence by springs. In some areas,

recharge from unknown drainage

pathways to areas of discharge

may contribute to chemical and

biological contamination of water

supplies. Such contamination in

karst areas has been documented

by many studies.

Legislation enacted in 1993

mandated the Florida Department of Environmental Protection

(FDEP) to develop and implegrams that are coordinated among Federal,

State, and local agencies in addressing the

key issues related to monitoring water

resources. The ITFM previously found

that information gaps existed in State and

Federal monitoring programs and recommended that these gaps be addressed by

developing an integrated, voluntary,

nationwide strategy for water-quality

monitoring. The ITFM recommended the

watershed approach as a highly effective

way to manage water resources because

this approach integrates ground-water and

surface-water systems.

The Suwannee River basin pilot

study is attempting to provide answers to

critical watershed-management questions

such as: (1) Can boundaries be delineated

for ground-water and surface-water

basins and do these boundaries change

depending upon hydrologic conditions?

(2) What does existing information tell

about the hydrochemical interaction

between ground water and surface water

in the basin? (3) Can natural processes

provide a remediation of elevated concentrations of nitrate in the Upper Floridan

aquifer (UFA) during high or low flow

conditions and or mixing of surface and

ground water? and (4) Can a framework

be developed in this study for evaluating

the interactions between ground water and

surface water and for delineating watershed boundaries that can be extrapolated

to other watersheds within Florida and

nationwide that have similar hydrogeologic conditions? 

 The Suwannee River basin in Florida

comprises an area of 4,230 mi2

 (fig. 2).

The basin is characterized by karstic wetland and lowland topography, a small number of tributary streams, and an abundance

of discharge as springs from the UFA. Historically, ground-water and surface-water

systems in the Suwannee River basin have

been monitored as separate media

under specific programs, with the

exception of a small number of

local studies. During the past 30

years, a considerable amount of

hydrologic data (such as river

stage and ground-water level) was

collected as part of extensive surface-water and ground-water networks.

The Suwannee River Water

Management District (SRWMD)

in cooperation with the FDEP and

U.S. Geological Survey (USGS),

maintains extensive monitoring

networks for surface water and

ground water in the Suwannee

River basin. As part of a surfacewater network, water levels are being measured regularly at 17 lakes, river stage and

discharge are monitored at 18 sites, and

daily rainfall is recorded at 34 stations.

Surface-water quality samples are collected

monthly or bimonthly at 52 sites by the

SRWMD as part of the Surface Water

Improvement and Management Program.

Currently, ground-water levels are being

measured at 328 sites in the basin, which

includes monthly measurements at 43 wells

and continuous measurements (using

water-level recorders) at 32 wells. Since

1987, extensive information on groundwater quality is being collected as part of

the Florida Ground Water Quality Monitoring Program (FGWQMNP), which contains 107 wells designed to monitor

background water quality of the principal

aquifers. Water from these wells is sampled every three years for major ions, nutrients, trace elements, and selected organic

compounds (Maddox and others, 1992).

Also as part of the FGWQMNP, the effects

of various land-use practices on groundwater quality are being investigated at a

mixed urban-industrial site and at an agriIntroduction

The Suwannee River Basin Pilot Study: 

Issues for Watershed Management in Florida

Monitoring Programs

in the Basin
cultural area in the Suwannee River

basin. As part of the National Water Quality Assessment Program (NAWQA), the

USGS has sampled water from six wells

in its regional background network for the

surficial aquifer system. Seven sites on

the Suwannee River in Florida and one

site on the Santa Fe River are being sampled by NAWQA for bed material, water

quality, and biological species.

Comparison of groundwater and surface-water

basin boundaries

The accurate delineation of karst

drainage basins represents a considerable

challenge because of complex patterns of

surface-water and ground-water flow. In

studies of karst areas in other parts of the

world it was determined that surface water

basins typically do not coincide with corresponding ground-water basins. For

example, streams that sink within one surface drainage basin can reappear in a different basin. Ground-water divides are

controlled by aquifer properties as well as

by topographic conditions.

Two-dimensional boundaries for surface-water and ground-water subbasins in

the Suwannee River basin were compared

for two different hydrologic conditions:

low-flow conditions during December

1990 to January 1991 and high-flow

conditions during April to May 1984. Patterns of ground-water flow were derived

from potentiometric-surface maps of the

UFA constructed for low flow and high

flow conditions. These patterns were

superimposed on surface water drainage

areas for the major subbasins in the

Suwannee River basin. Generally, the

regional flow patterns indicate that boundaries for ground-water basins do not coincide with surface-water drainage

subbasins except in some parts of the

lower Suwannee River basin and the Santa

Fe River subbasin. There are several areas

in the basin where ground water that originates outside of the Suwannee River basin

crosses surface-water basin boundaries

during both low flow and high flow conditions. However, the measured groundwater levels were part of a network whose

objective is to delineate the regional

potentiometric surface of the UFA. The

wells in this network are open to different

depths in the aquifer and probably intercept more localized ground-water flow

systems. Therefore, the wells in the

present network (approximately 250 wells

in the basin) are not adequately distributed

to accurately define two-dimensional

ground-water basin boundaries in most

areas of the Suwannee River basin. 

To more accurately define drainage

areas, the connection between discharge

areas (such as springs) for the UFA and

surface water must be determined for different flow conditions using tracer techniques involving dyes and naturally

occuring isotopes and, in some cases,

human exploration (cave diving). In one

such study in the Santa Fe River basin, the

degree of interconnection among springs

that discharge from Ginnie Springs Park to

the Santa Fe River was investigated using

rhodamine dye tracing experiments.

Based on the dispersion of dye to more

than one spring, Wilson and Skiles (1988)

concluded that there is an extensive network of three-dimensional braided conduits in the aquifer system and unique

ground-water drainage divides do not exist

within a few hundred meters of the spring

discharge points. 

In some cases, the linkage between

ground water and surface water can be

obvious, as when water levels in the UFA

respond directly to changes in stage of a

nearby river. One such example is a monitoring well located near the Alapaha River

(fig. 3). There is a high correlation

between stage of the river and water levels

in the aquifer. As the stage increases in

the Alapaha River, ground water sampled

at the Alapaha Tower well sometimes represents a mixture of river water and

ground water. However, additional

geochemical evidence is needed to determine the extent of mixing of river water

with water from the UFA. 

In other cases, the interaction

between ground water and surface water

can be subtle and tracers have been used to

establish the relation. For example, several local studies have effectively used naturally occurring radionuclides, such as

uranium (238U and 234U), radium (226Ra),

and radon (222Rn), to trace the amount of

ground water influx to rivers and amount

of streamflow losses to ground water.

These studies rely on the fact that the

mobility of U, Ra, and Rn is controlled by

different geochemical and physical processes that lead to their separation or fractionation in ground-water and surfacewater systems. For example, 222Rn is a

gas and, hence, its concentration in ground

water is about 1,000 times that in surface

water. Based on measurements of 222Rn

in ground water and in a 2-kilometer reach

of the Santa Fe River, a tributary to the

Suwannee River, Kincaid (1994) reported

that as the river discharge increased, corresponding increases were observed for

ground-water discharge to springs, streamflow losses to ground water, and input to

springs from resurgent streamflow. One

particularly noteworthy finding was that

even though the regional potentiometricInteractions Between

Ground Water and Surface

Water in the Basin

Figure 2. Location of monitoring sites and subbasins in Suwannee River watershed, Florida.

GEORGIA

FLORIDA

G u l f

o f

M e x i c

o

Suwannee River

Santa Fe River

Withlacoochee

River

Alapaha River HAMILTON

SUWANNEE

LAFAYETTE

DIXIE

LEVY

ALACHUA GILCHRIST

MARION

UNION

BRADFORD

BAKER

COLUMBIA

DUVAL

CLAY

PUTNAM

NASSAU

TAYLOR

MADISON JEFFERSON

EXPLANATION

WITHLACOOCHEE ALAPAHA

UPPER SUWANNEE SANTA FE

LOWER SUWANNEE

GROUND-WATER LEVELS

BACKGROUND GROUND-WATER

QUALITY

MONITORING SITES FOR

SUBBASINS OF THE SUWANNEE

RIVER WATERSHED IN FLORIDA

0 20 40 MILES

0 20 40 KILOMETERS

30°

84° 83° 82°

29°

STUDY

AREA

GA

FLA
surface map of the UFA indicates

that the Santa Fe River is a gaining

stream, streamflow is actually being

lost to the UFA in many places

along the river. Siphons that are visible at the surface also provide direct

evidence of stream water being

diverted to the subsurface. As much

as 55 percent of spring discharge at

the Devil’s Ear basin was supplied

by resurgent surface water that originated in the the overlying Santa Fe

River and not water from the UFA. 

Crane (1986) used differences

in the 234U/238U activity ratio (UAR)

and uranium (U) concentrations in

ground water and surface water to determine the source and amount of recharge

for different parts of the aquifer and

ground-water contributions to the Suwannee River. Most sampled sites produced

waters with low activity ratios and high U

concentrations, which are typically associated with areas of the UFA that are unconfined and where recent and intense

dissolution of aquifer minerals is occurring, such as in places where material overlying the UFA has been breached by

sinkholes. For example, three water samples (the Little River springs and wells

upgradient) from the Little River basin (in

which material overlying the UFA has

undergone recent and fairly intense dissolution) had very low activity ratios (0.57)

and high U concentrations (1.76 micrograms per liter). Many springs had activity

ratios greater than 0.75, which Crane

attributed to a mixture of waters from areas

of high recharge with those from areas of

little or no recharge. The Suwannee River

has UAR values and U concentrations that

are anomalous when compared to those of

other river systems of the world (Crane,

1986). The anomalous values result from

mixing of some surface runoff (high UAR,

low U concentration) with large amounts

of ground-water flow from springs and

seeps (generally low UAR and high U concentrations). 

The input of water to the Suwannee

River from large springs south of Branford, Fla., was traced using 226Ra (Burnett and others, 1990). They found that

stream stations north of Branford, Fla.,

tended to have a lower mean concentration

of 226Ra (0.189 disintegrations per minute

per liter) compared to the mean concentration for stations south of Branford (0.270

disintegrations per minute per liter). Even

though 226Ra has a strong affinity for

adsorption on aquifer minerals, the concentration of 226Ra in ground water is generally several times to several orders of

magnitude higher than in surface waters.

Several of the first-order magnitude

springs have relatively high 226Ra concentrations (0.155 to 0.917 disintegrations per

minute per liter) and the concentration of

226Ra in these springs progressively

increased in a downstream direction. This

trend was attributed to the increasing contribution of water from deeper parts of the

UFA that supply spring water to the lower

reaches of the river. 

An ongoing study that began in 1994

is investigating the connection between

the Suwannee River and the unconfined

UFA along a 75-kilometer reach from

Ellaville to Branford, as part of the

NAWQA study, in collaboration with the

SRWMD and the University of Florida.

Based on existing data from ten wells,

sampled as part of the FGWQMNP during

1991 to 1994 for water levels and waterquality constituents, Hirten (1995) found

that water-level data indicate that the

direction of the hydraulic gradient is away

from the river during high-flow conditions, in contrast to low flow conditions

when the direction of the hydraulic gradient is toward the river. The effect of elevated river stage on the potentiometric

surface may extend as much as 8 kilometers away from the river.

High nitrogen loading from wastes

generated by poultry and dairy farms, and

fertilizers applied to cropland along the

Suwannee River in Lafayette and Suwannee Counties has resulted in elevated nitrate

levels in the river and in parts of the UFA.

Changes in water quality and flow patterns

in the UFA are being evaluated in a 73-

square kilometer study area in Lafayette

County, which is located near the Suwannee River and consists mainly of agricultural land use, such as dairy and poultry

Natural Remediation of

Contaminants in

Ground Water

farms, cropland, and silvaculture. In

1990, 1991, and 1994, 18 wells tapping the UFA and 7 springs that discharge into the Suwannee River were

sampled for major dissolved inorganic constituents, trace elements,

nutrients, and volatile and nonvolatile

organic compounds as part of the

FGWQMNP. In the study area,

ground-water flow patterns remained

relatively unchanged during 1990,

1991, and 1994, even though large

fluctuations in ground-water levels

were observed. For example, measured ground-water levels in 1991

increased by as much as 20 feet at

some wells following three months of

above normal rainfall, compared to water

levels in 1990. 

Nitrate concentrations in ground

water had large fluctuations from one sampling period to the next and were associated with fluctuations in water levels in the

UFA. For instance, the median and range

(in parentheses) of nitrate concentrations in

water samples from the UFA, in milligrams per liter as nitrogen, were: AprilMay 1990, 1.52 (<0.02-17); March 1991,

0.20 (<0.05-9.5); and June 1994, 2.0

(<0.02-22.). Substantially lower concentrations of nitrate were measured in water

from 76 percent of wells sampled in 1991

compared to 1990, and probably resulted

from denitrification reactions. The process

of denitrification involves the transformation of nitrate by bacteria (present in the

soil and aquifer) to nitrogen gases, resulting in lower amounts of nitrogen. Based

on extensive analysis of chemical and

hydrologic data, evidence for denitrification in water from the UFA was indicated

by increased concentrations of dissolved

organic carbon, a decrease in measured

redox potential, and an increase in pH and

dissolved iron concentrations. Dilution of

nitrate concentrations in ground water was

unlikely because concentrations of chloride and other major ions did not show a

corresponding decrease from 1990 to

1991. In fact, chloride concentrations

increased in water samples from 75 percent of the wells in which nitrate concentrations decreased from 1990 to 1991.

Thus, the combination of higher groundwater levels in 1991 with increased

amounts of organic carbon and decreased

amounts of dissolved oxygen in ground

water created conditions favorable for the

natural reduction of nitrate in ground

water. As a result, less nitrate was discharged by ground water to the Suwannee

River. 

Figure 3. Comparison of Alapaha River stage and water 

level in Alapaha Fire Tower well.

120

20

40

60

80

100

ALTITUDE, IN FEET ABOVE SEA LEVEL

III IV I II III IV I II III IV I II III IV I II III IV I II

1989 1994 1990 1991 1992 1993

ALAPAHA RIVER STAGE

WATER LEVEL IN ALAPAHA FIRE TOWER WELL
Lessons Learned

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet FS-080-96

AUTHORS:

Brian G. Katz

U.S. Geological Survey

and

Rodney S. DeHan

Florida Department of 

Environmental Protection

available, in the foreseeable

future, to conduct statewide delineation and mapping of zones of

interaction between ground water

and surface water. One solution to

this problem would involve the

establishment of watershed coalitions, involving the private sector

stakeholders, that could be responsible for generating the necessary

resources for proper watershed

assessments. The watershed coalitions will benefit their communities

by participitating in, not only identifying, the threats to watersheds

health and function, but also by

being a part of the solution to

existing problems. 

The vast amount of

information that has been

gathered on ground-water and

surface-water systems in the

Suwannee River basin provides an extensive data base

from which water-resource

managers can begin to understand the importance of the

hydraulic and hydrochemical

linkage between ground water

and surface water in the basin.

However, to address specific

management issues, several

gaps have been identified

where more information is

critically needed:

 • It is difficult to use existing data

to evaluate basin boundaries and

the extent of interaction between

ground water and surface water

because these data were collected

by different agencies for programs

with different monitoring objectives. Existing information indicates that ground-water basin

divides, as delineated from potentiometric-surface maps, do not

Burnett, W.C., Cowart, J.B., and Deetae, S., 1990,

Radium in the Suwannee River and estuary: Biogeochemistry, v. 10, p. 237-255.

Crane, J.J., 1986, An investigation of the geology,

hydrogeology, and hydrochemistry of the lower

Suwannee River Basin: Florida Geological Survey Report of Investigations No. 96, 205 p.

Hirten, J.J., 1995, Influence of the Suwannee River on

ground water height in the Upper Floridan aquifer,

Geological Society of America, Annual Meeting,

Abstracts with Programs, v. 27, no. 6, p. A-181.

Kincaid, T.R., 1994, Groundwater and surface water

interaction in the western Santa Fe River basin

near High Springs, Florida: Masters Thesis, University of Florida, Gainesville, Florida, 186 p.

Maddox, G.L., Lloyd, J.M., Scott, T.M., Upchurch,

S.B., and Copeland, R., eds., 1992, Florida’s

ground-water quality monitoring program: background hydrogeochemistry. Florida Geological

Survey Special Publication no. 34, 364 pp.

Wilson, W.L., and Skiles, W.C., 1988, Aquifer characterization by quantitative dye tracing at Ginnie

Spring, northern Florida: The Proceedings of the

Second Conference on Environmental Problems

in Karst Terranes and Their Solutions, Nashville,

Tennessee, Association of Ground Water Scientists and Engineers, p. 121-141

REFERENCES

Two studies are currently gathering detailed information on the hydrochemical interaction between ground water and surface water in the Little River

basin, a tributary basin to the Suwannee River. One study, which is part of the

NAWQA Program, is investigating the extent of the mixing zone between the Suwannee River and ground water during various flow conditions. Another study, which is a

cooperative effort among the FDEP, the SRWMD, and the USGS, is investigating the

hydrochemical linkage between the UFA and the Little River where the river disappears underground through a series of sinkholes. Results from these studies are

expected to provide important information on ground-water basin boundaries, the

hydrochemical effect of surface water migration into the aquifer during various

hydrologic conditions, and natural processes that could remediate contaminants in the

aquifer and surface water.

Ongoing Studies in the Little River Basin

always coincide with boundaries

for surface water basins; that is,

there is flow of ground water

across surface-water basin

divides. However, to more precisely define ground-water basin

boundaries, additional wells are

needed to refine the map of the

potentiometric surface for the UFA

and obtain data to determine more

detailed flow patterns. 

 • Complex ground-water flow

patterns can be revealed only

through consistent monitoring

over time and during varying

hydrologic conditions. Sampling

of ground water and surfacewater should be coordinated and

performed during changing

hydrologic conditions, such as

periods of high and low flow. 

 • Reduction in nitrate concentrations in ground water by denitrification processes is likely to

occur naturally during periods of

high flow conditions (high water

levels in the UFA and high stages

in the river and its tributaries).

More detailed investigations,

however, are needed to confirm

and document this preliminary

finding.

 • Insufficient information exists

at present to determine the lateral

extent of mixing of river water

with water in the UFA during

periods of high flow conditons. 

 • The Suwannee River is both a

gaining and losing stream

depending on the stage of the

river. However, the existing spatial distribution of wells in the

UFA is not sufficient to delineate

areas of ground water flow to the

river and areas where the river

recharges the aquifer.

 • A combination of naturally

occurring tracers (isotopes,

chemical constituents), artificially

introduced tracers (dyes), and

detailed water-level data could

provide much needed information

on hydaulic interactions between

ground water and surface water,

such as the amount of recharge to

the aquifer from surface-water

inflow, the amount of resurgent

surface water in spring flow to the

river, and the amount of groundwater flow to the river during low

and high stages. 

 • It is unlikely that adequate

State and Federal funding will be

For more information on this and related studies, contact:

John Vecchioli, District Chief Mimi Drew, Director

U.S. Geological Survey Division of Water Facilities

227 N. Bronough St. Florida Department of Environmental Protection

Suite 3015 2600 Blair Stone Road

Tallahassee, FL 32301 Tallahassee, FL 32399-2400

(904) 942-9500 (904) 488-3601