U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005-3008

April 2005

Ground-Water Models of the Alluvial and Sparta Aquifers: 

Management Tools for a Sustainable Resource

Printed on recycled paper

Introduction

Arkansas is the fourth largest user of ground water in the 

United States. The Mississippi River Valley alluvial aquifer 

(alluvial aquifer) is a water-bearing assemblage of gravels 

and sands that underlies most of eastern Arkansas and several 

adjacent States. Ground-water withdrawals have caused cones 

of depression to develop in the alluvial aquifer water-level 

surface, some as much as 100 feet deep. Long-term water-level 

measurements show an average annual decline of 1 foot per 

year in some areas. The Sparta aquifer is largely a confined 

aquifer of regional importance that comprises a sequence of 

unconsolidated sand, silt, and clay units. Several large cones 

of depression have developed in the Sparta aquifer, causing 

hydraulic heads to drop below the top of the formation in parts 

of central and southern Arkansas and several areas in north-central Louisiana.

Several counties in the Grand Prairie area and south Arkansas have been designated Critical Ground-Water Areas (areas 

where alluvial aquifer water levels dropped below 50 percent of 

the original saturated thickness or below the top of the Sparta 

Sand formation) by the Arkansas Soil and Water Conservation Commission (ASWCC). The expansion of the cones of 

depression and the consistent water-level declines indicate that 

ground-water withdrawals are occurring at a rate that is greater 

than the sustainable yield of the aquifer.

Ground-Water Models

For many years, the ASWCC has worked with the U.S. 

Geological Survey (USGS) and other agencies in the development of ground-water flow models to be used as management 

tools to determine the sustainability of the water resource. 

Ground-water flow models of two areas of the alluvial aquifer 

(north alluvial and south alluvial—divided by the Arkansas 

River) and the Sparta aquifer were developed for eastern Arkansas and parts of northern Louisiana and adjacent States (Reed, 

2003; Stanton and Clark, 2003; McKee and Clark, 2003). 

The flow models showed that continued ground-water withdrawals at 1997 rates for the alluvial aquifer and 1990-97 rates 

for the Sparta aquifer could not be sustained indefinitely without 

causing water levels to decline below 50 percent of the original 

saturated thickness of the alluvial aquifer or below the top of 

the Sparta Sand formation. To develop estimates of withdrawal 

rates that could be sustained relative to the constraints of critical 

ground-water area designation, conjunctive-use optimization 

modeling was applied to the flow models (Czarnecki and others, 2003a,b; McKee and others, 2004). An optimization model 

calculates the maximum sustainable yield from wells and rivers, 

while maintaining simulated water levels and streamflows at or 

above minimum specified limits or constraints. 

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Mississippi

Arkansas

Louisiana

Missouri

Arkansas

Texas

Mississippi

River

Arkansas River

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North Alluvial Model

The alluvial flow model in northeastern Arkansas was 

used to predict ground-water flow for a 50-year period from 

1998-2049 with different hypothetical pumping scenarios. 

If pumping remains at 1997 rates (635.7 million cubic feet 

per day (Mft3/d), large simulated water-level declines occur 

in two areas of the aquifer, one in the Grand Prairie area 

between the Arkansas and White Rivers and the other west 

of Crowleys Ridge along the Cache River. Simulations show 

that by 2009 over 100 square miles (mi2) of the alluvial 

aquifer could be dry (demand exceeding sustainable yield) 

with about 400 mi2 of the aquifer going dry by 2049. Given 

imposed constraints, ground-water sustainable yield is 360.3 

Mft3/d—57 percent of the 635.7 Mft3/d demand in 1997. This 

unmet demand of 275.5 Mft3/d of ground water could be 

obtained from large sustainable surface-water withdrawals. 

Total sustainable yield from all rivers combined was 12,806 

Mft3/d, which represents a substantial source for supplementing ground water to meet the total water demand.

Sustainable

 yield from

 ground water

 (Mft3/d)

Groundwater

 demand 

 (Mft3/d)

Unmet

demand for

ground water

(Mft3/d)

Sustainable

 yield from

 rivers

(Mft3/d)

360.3 635.7 275.5 12,806

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Cache River

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Sustainable yield is the rate at which water can be withdrawn indefi nitely from ground- and surface-water sources without violating 

specifi ed constraints. This rate is calculated through the use of a conjunctive-use optimization model. Sustainable yield is dependent on 

upper limits of specifi ed withdrawal rates for wells and rivers and can vary given various imposed constraints. Demand is the amount of 

ground water used or withdrawn during the period. Unmet demand is the difference between a desired withdrawal rate (demand) and the 

sustainable yield. Sustainable yield from rivers represents a potential source of water that could supplement ground water.

North Alluvial Model - What happens if pumping continues at 1997 rates?

LEE

WHITE

CLAY

DESHA

LONOKE

ARKANSAS

RIPLEY

BUTLER

CROSS

PRAIRIE

PHILLIPS

MISSISSIPPI

JEFFERSON

POINSETT

MONROE

GREENE

JACKSON

PULASKI

DUNKLIN

CRAIGHEAD

RANDOLPH

ST FRANCIS

LAWRENCE

NEW MADRID

WOODRUFF

CRITTENDEN

PEMISCOT

INDEPENDENCE

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Percentage of 1997 withdrawal from alluvial aquifer that is 

sustainable by county (north alluvial model)
South Alluvial Model - What happens if pumping continues at 1997 rates?

South Alluvial Model

The flow model for the alluvial aquifer in southeastern Arkansas was used to predict ground-water flow for a 50-year period 

from 1998-2049 with different hypothetical pumping scenarios. 

If pumping remains at 1997 rates (73.5 Mft3/d), an area centered 

in Desha County and two areas in Ashley County show simulated water levels dropping below 50 percent of the saturated 

thickness of the alluvial aquifer by 2009. Simulated water levels 

for 2029 and 2049 indicate enlargement and deepening of these 

areas and up to 81 mi2 where the aquifer drops below 50 percent 

of the saturated thickness, although no areas of the aquifer go 

dry. Given imposed constraints, ground-water sustainable yield 

is 70.3 Mft3/d—96 percent of the demand of 73.5 Mft3/d. Unmet 

demand for the model area is 3.3 Mft3/d. Total sustainable yield 

from the rivers is about 4,918 Mft3/d, or about 6,700 percent of 

the amount of ground water withdrawn in 1997, which represents 

a substantial source for supplementing ground water to meet the 

total water demand.

Sustainable

 yield from

 ground water

 (Mft3/d)

Groundwater 

demand

 (Mft3/d)

Unmet

demand for

ground water

(Mft3/d)

Sustainable

 yield from

rivers

(Mft3/d)

70.3 73.5 3.3 4,918

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DREW

ASHLEY

DESHA

CHICOT

LINCOLN

JEFFERSON

MOREHOUSE WEST

CARROLL EAST CARROLL

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Percentage of 1997 withdrawal from alluvial aquifer that is 

sustainable by county (south alluvial model)
Sparta Model

The Sparta flow model was used to predict the effects of 

three hypothetical withdrawal scenarios on water levels over a 

30-year period from 1998-2027. In one scenario, withdrawal 

rates (30.6 Mft3/d) from 1990-97 were held constant for 30 

years from 1998-2027 and simulated water levels decreased 

by 10 feet in El Dorado and 17 feet in Pine Bluff, Arkansas. 

Through 2027, simulated water levels continue to decline in 

the center of cones of depression in areas of El Dorado, Pine 

Bluff, Magnolia in Arkansas, and in Monroe, Louisiana. Cones 

of depression continue to deepen and expand, and areas where 

water levels have dropped below the top of the Sparta Sand 

formation grow to 1,787 mi2 in size in Arkansas and 2,821 mi2

in Louisiana by 2027. Given imposed constraints, ground-water 

sustainable yield in Arkansas and Louisiana is 11.9 Mft3/d—39 

percent of the total ground-water demand of 30.6 Mft3/d. The 

remainder, 18.8 Mft3/d, is defined as unmet demand that could 

be obtained from the 5,396 Mft3/d sustainable yields from rivers.

Sustainable

yield from

ground water

(Mft3/d)

Groundwater

demand

(Mft3/d)

Unmet

demand for 

ground water

(Mft3/d)

Sustainable

yield from

river

(Mft3/d)

11.9 30.6 18.8 5,396

— David A. Freiwald

Any use of trade, product, or firm names is for descriptive 

purposes only and does not imply endorsement by the U.S. 

Government.

Information on technical reports and hydrologic data 

related to this study can be obtained from:

Director

U.S. Geological Survey

Arkansas Water Science Center

401 Hardin Road 

Little Rock, AR 72211

Email: dc_ar@usgs.gov

Phone: (501) 228–3600

FAX: (501) 228-3601

World Wide Web: http://ar.water.usgs.gov/ 

References

Czarnecki, J.B., Clark, B.R., and Stanton, G.P., 2003a, Conjunctive-use optimization model of the Mississippi River Valley 

alluvial aquifer of southeastern Arkansas: U.S. Geological 

Survey Water-Resources Investigations Report 03-4233, 26 p.

Czarnecki, J.B., Clark, B.R., and Reed, T.B., 2003b, Conjunctive-use optimization model of the Mississippi River Valley 

alluvial aquifer of northeastern Arkansas: U.S. Geological 

Survey Water-Resources Investigations Report 03-4230, 29 p.

McKee, P.W., and Clark, B.R., 2003, Development and calibration of a ground-water flow model for the Sparta aquifer of 

southeastern Arkansas and north-central Louisiana and simulated response to withdrawals, 1998-2027: U.S. Geological 

Survey Water-Resources Investigations Report 03-4132, 71 p.

McKee, P.W., Clark, B.R., and Czarnecki, J.B., 2004, Conjunctive-use optimization and sustainable-yield estimation for the 

Sparta aquifer of southeastern Arkansas and north-central 

Louisiana: U.S. Geological Survey Water-Resources Investigations Report 03-4231, 30 p.

Reed, T.B., 2003, Recalibration of a ground-water flow model 

of the Mississippi River Valley alluvial aquifer of northeastern Arkansas, 1918-1998, with simulations of water levels 

caused by projected ground-water withdrawals through 2049: 

U.S. Geological Survey Water-Resources Investigations 

Report 03-4109, 58 p.

Stanton, G.P. and Clark, B.R., 2003, Recalibration of a 

ground-water flow model of the Mississippi River Valley 

alluvial aquifer in southeastern Arkansas, 1918-1998, with 

simulations of hydraulic heads caused by projected groundwater withdrawals through 2049: U.S. Geological Survey 

Water-Resources Investigations Report 03-4232, 48 p.

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Mississippi

Arkansas

Louisiana

Texas

Mississippi

Louisiana

Magnolia

El Dorado

Monroe

River

Mississippi

Pine Bluff

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Percentage of 1990-97 withdrawal from Sparta aquifer that is 

sustainable by county (Sparta model).