1/1953

1/19561/19591/19621/19651/19681/19711/19741/19771/19801/19831/19861/19891/19921/19951/19981/20011/20041/20071/19531/19561/19591/19621/19651/19681/19711/19741/19771/19801/19831/19861/19891/19921/19951/19981/20011/20041/2007

Altitude, in feet above or below NGVD 29

135

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G0029 TUNICA

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J0005 COAHOMA

90

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115

120

125

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135

F0020 BOLIVAR

65

70

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80

85

90

95

100

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110

L0027 SUNFLOWER

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M0038 SUNFLOWER

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O0037 LEFLORE

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F0059 HUMPHREYS

65

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90

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S0004 WASHINGTON

y = 0.0008x + 188.33

R2

 = 0.4621

y = 0.0009x + 145.16

R2

 = 0.8796

y = 0.0021x + 152.08

R2 = 0.8796

y = 0.0006x + 120.35

R2

 = 0.5118

y = 0.0005x + 106.72

R2

 = 0.2033

y = 0.0004x + 121.39

R2

 = 0.0646

y = –9E–05x + 100.94

R2

 = 0.0135

y = 0.0003x + 154.12

R2

 = 0.275

Figure 3. Hydrographs for selected wells screened in the alluvial aquifer in northwestern Mississippi. See figure 1

for well locations.

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2011–5019

Prepared in cooperation with the Yazoo Mississippi Delta Joint Water Management District

Simulation of Water-Use Conservation Scenarios 

for the Mississippi Delta Using an Existing Regional 

Groundwater Flow Model
Cover photographs: Dry stream beds during the summer months due to lack of base flow for Big Sunflower River at 

Sunflower, Mississippi (left), and Bogue Phalia River near Leland, Mississippi (right) (photographs by Claire E. Rose, USGS). 

Background image: Charts taken from figure 3 (p. 4).
Simulation of Water-Use Conservation Scenarios 

for the Mississippi Delta Using an Existing Regional 

Groundwater Flow Model

By Jeannie R.B. Barlow and Brian R. Clark

Prepared in cooperation with the Yazoo Mississippi Delta Joint Water Management District

Scientific Investigations Report 2011–5019

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

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Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Barlow, J.R.B., and Clark, B.R., 2011, Simulation of water-use conservation scenarios for the Mississippi

Delta using an existing regional groundwater flow model: U.S. Geological Survey Scientific Investigations

Report 2011–5019, 14 p.

ISBN 978 1 4113 3098 6
iii

Contents

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

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

Regional Groundwater Flow Model............................................................................................................5

Conservation Scenario Development.........................................................................................................6

Conservation Scenario Results ...................................................................................................................8

Model Limitations.........................................................................................................................................10

Summary........................................................................................................................................................13

References....................................................................................................................................................13

Figures

1. Map showing location of study area, extent of Mississippi Embayment Regional

Aquifer Study (MERAS) groundwater flow model, approximate extent of cone

 of depression, and locations of wells for which hydrographs are

 shown in figure 3...........................................................................................................................2

2. Map showing principal aquifers of the United States with the five highest

withdrawal rates in 2000..............................................................................................................3

3. Hydrographs for selected wells screened in the alluvial aquifer in northwestern

 Mississippi. See figure 1 for well locations..............................................................................4

4. Chart showing annual minimum daily discharge of the Big Sunflower River

at Sunflower, Mississippi, and cumulative estimated storage loss in the area

of the cone of depression in the alluvial aquifer as determined by the Yazoo

 Mississippi Delta Joint Water Management District in northwestern

 Mississippi. Discharge graph is blank where data are missing...........................................5

5. Photos showing dry streambeds during the summer months due to lack of base

flow for (A) Big Sunflower River at Sunflower, MS, and (B) Bogue Phalia

 River near Leland, Mississippi....................................................................................................6

6. Maps showing (A) Mississippi Embayment Regional Aquifer Study model domain

and surficial geology; and (B) generalized section of hydrogeologic and

geologic units ................................................................................................................................7

7. Maps showing percentage of change in 2038 water level for each conservation

scenario relative to the base scenario .....................................................................................9

8. Map showing subregional zones designated for ZONEBUDGET waterbudget computations .................................................................................................................11

9. Hydrogeologic section and charts showing water-budget inflows and outflows

for base scenario simulation period (2007–2038)..................................................................12

10. Chart showing percentage of increase in storage within the alluvial aquifer

relative to the base scenario for each conservation scenario for the entire

alluvial aquifer (Delta-wide) and the area of the cone of depression...............................13

Table

1. Average percentage of increase relative to the base scenario in alluvial aquifer

water levels for each conservation scenario ........................................................................10
iv

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2)

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square inch (in2) 6.452 square centimeter (cm2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

million gallons (Mgal) 3,785 cubic meter (m3)

cubic foot (ft3) 28.32 cubic decimeter (dm3) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

acre-foot (acre-ft) 1,233 cubic meter (m3)

Flow rate

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3/yr)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

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

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

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Conversion Factors

Inch/Pound to SI
Abstract

The Mississippi River alluvial plain in northwestern 

Mississippi (referred to as the Delta), once a floodplain to the 

Mississippi River covered with hardwoods and marshland, is 

now a highly productive agricultural region of large economic 

importance to Mississippi. Water for irrigation is supplied 

primarily by the Mississippi River Valley alluvial aquifer, and 

although the alluvial aquifer has a large reserve, there is evidence that the current rate of water use from the alluvial aquifer is not sustainable. Using an existing regional groundwater 

flow model, conservation scenarios were developed for the 

alluvial aquifer underlying the Delta region in northwestern 

Mississippi to assess where the implementation of water-use 

conservation efforts would have the greatest effect on future 

water availability—either uniformly throughout the Delta, 

or focused on a cone of depression in the alluvial aquifer 

underlying the central part of the Delta. Five scenarios were 

simulated with the Mississippi Embayment Regional Aquifer 

Study groundwater flow model: (1) a base scenario in which 

water use remained constant at 2007 rates throughout the 

entire simulation; (2) a 5-percent “Delta-wide” conservation 

scenario in which water use across the Delta was decreased by 

5 percent; (3) a 5-percent “cone-equivalent” conservation scenario in which water use within the area of the cone of depression was decreased by 11 percent (a volume equivalent to the 

5-percent Delta-wide conservation scenario); (4) a 25-percent 

Delta-wide conservation scenario in which water use across 

the Delta was decreased by 25 percent; and (5) a 25-percent 

cone-equivalent conservation scenario in which water use 

within the area of the cone of depression was decreased by 

55 percent (a volume equivalent to the 25-percent Delta-wide 

conservation scenario).

The Delta-wide scenarios result in greater average 

water-level improvements (relative to the base scenario) 

for the entire Delta area than the cone-equivalent scenarios; 

however, the cone-equivalent scenarios result in greater average water-level improvements within the area of the cone of 

depression because of focused conservation efforts within that 

area. Regardless of where conservation is located, the greatest 

average improvements in water level occur within the area of 

the cone of depression because of the corresponding large area 

of unsaturated aquifer material within the area of the cone of 

depression and the hydraulic gradient, which slopes from the 

periphery of the Delta towards the area of the cone of depression. Of the four conservation scenarios, the 25-percent coneequivalent scenario resulted in the greatest increase in storage 

relative to the base scenario with a 32-percent improvement 

over the base scenario across the entire Delta and a 60-percent 

improvement within the area of the cone of depression. 

Overall, the results indicate that focusing conservation efforts 

within the area of the cone of depression, rather than distributing conservation efforts uniformly across the Delta, results in 

greater improvements in the amount of storage within the alluvial aquifer. Additionally, as the total amount of conservation 

increases (that is, from 5 to 25 percent), the difference in storage improvement between the Delta-wide and cone-equivalent 

scenarios also increases, resulting in greater gains in storage in 

the cone-equivalent scenario than in the Delta-wide scenario 

for the same amount of conservation. 

Introduction

The Mississippi River alluvial plain in northwestern 

Mississippi (locally referred to as the Delta), once a floodplain to the Mississippi River covered with hardwoods and 

marshland, is now a highly productive agricultural region of 

large economic importance to Mississippi (fig. 1) (Economic 

Research Service, U.S. Department of Agriculture, 2010). 

Fertile soils, a long growing season, average annual rainfall of greater than 54 inches (in.), and a productive alluvial 

aquifer make the Delta a prime area for agriculture. Primary 

crops grown in this region include soybean, corn, cotton, and 

rice. Water for irrigation is supplied primarily by the Mississippi River Valley alluvial aquifer (hereafter referred to as the 

alluvial aquifer), which is the third most used aquifer in the 

United States (Maupin and Barber, 2005; fig. 2). The extent 

of the alluvial aquifer covers parts of Arkansas, Mississippi, 

Missouri, Louisiana, and Tennessee, Kentucky, and Illinois. 

Mississippi is the second largest user of the alluvial aquifer, 

and Arkansas is the largest user. Both States rely largely on the 

Simulation of Water-Use Conservation Scenarios for the 

Mississippi Delta Using an Existing Regional Groundwater 

Flow Model 

By Jeannie R.B. Barlow and Brian R. Clark
2 Simulation of Water-Use Conservation Scenarios for the Mississippi Delta

P

P

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P P

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P P

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!.

!.

!.

!.

TENNESSEE

MISSISSIPPI

G0029 TUNICA

J0005 COAHOMA

F0020 BOLIVAR

O0037 LEFLORE

L0027 SUNFLOWER

M0038 SUNFLOWER

F0059 HUMPHREYS

S0004 WASHINGTON

B ogue Phalia Rive r

Coldwate r River

Tallahatchie Rive r

Big Black Rive r

Y alobus ha Rive r

Yockanookany Rive r

Yaz oo R ive r

S unflower Rive r

Yocona Riv e r

Skuna River

Pearl River

Little Tallhatchie River

S trong River

Yo cona Riv er

YAZOO

BOLIVAR

HOLMES

PANOLA

TATE

CARROLL LEFLORE

TUNICA

COAHOMA

WASHINGTON

DE SOTO

SUNFLOWER

WARREN

SHARKEY

GRENADA

TALLAHATCHIE

QUITMAN

ISSAQUENA

HUMPHREYS

Eden

Boyle

Isola

Walls

Renova

Crowder

Cleveland Ruleville

Hollandale

Doddsville

Friars Point

-91° -90°

35°

34°

33°

LA

AR

MS AL

TX

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TN

KY

OK

IL KS

0 10 20 Miles

BLUFF

HILLS

0 10 20 Kilometers

EXPLANATION

Mississippi River Valley alluvial aquifer

Mississippi Delta

MERAS model domain, extent of Mississippi

 Embayment aquifer system

Approximate extent of cone of depression

Well screened in alluvial aquifer with

 hydrograph shown in figure 3

Webb

Greenville

Benoit

Beulah

Duncan

Leland

Rosedale

Gunnison

Metcalfe

Alligator

Drew

Lyon

Lula

Shelby

Sumner

Tunica

Coahoma

Merigold

Tutwiler

Glendora

Jonestown

Clarksdale

Mound Bayou

Winstonville

Marks

Falcon

Sledge

Lambert

Crenshaw

Sidon

Cruger

Belzoni Tchula

Schlater

Greenwood Itta Bena

Silver City

Morgan City

Cary

Satartia

Anguilla

Yazoo City

Mayersville

Rolling Fork

Shaw

Moorhead

Inverness

Indianola

Louise

Vicksburg

Sunflower

Figure 1. Location of study area, extend of Mississippi Embayment Regional Aquifer Study (MERAS) groundwater flow model,

approximate extent of cone of depression, and locations of wells for which hydrographs are shown in figure 3.

ARKANSAS

LOUISIANA

.!

Figure 1. Location of study area, extent of Mississippi Embayment Regional Aquifer Study (MERAS) groundwater flow 

model, approximate extent of cone of depression, and locations of wells for which hydrographs are shown in figure 3.
Introduction 3

alluvial aquifer to supply water for irrigation. Approximately 

9,290 million gallons per day (Mgal/d) of water are withdrawn 

from the alluvial aquifer in Mississippi, which makes it the 

most used aquifer in the State (Maupin and Barber, 2005). 

The Mississippi River, which forms the axis of the Mississippi Embayment aquifer system, generally incises the entire 

thickness of the alluvial aquifer, thereby creating two independent flow systems on the west and east side of the Mississippi 

River (Arthur, 2001).

The alluvial aquifer consists of Quaternary-age sand and 

gravel deposits overlying an erosional Tertiary-age surface 

(Fisk, 1944; Arthur, 2001). Recharge from infiltration typically is low because of the overlying clay and fine-grained 

material in the upper part of the aquifer. Previous studies have 

reported recharge rates of 2.5 inches per year (in/yr), which is 

5 percent of the average annual rainfall that falls on this region 

(Arthur, 2001; H.L. Welch, U.S. Geological Survey, written 

commun., 2010). Other sources of recharge to the aquifer 

include leakage from the Mississippi River and interior Delta 

streams and lakes, interflow from sediments and aquifers 

within the Bluff Hills escarpment (fig. 1) on the eastern edge 

of the alluvial aquifer, and flow from underlying aquifers 

in direct connection with the alluvial aquifer. Discharge 

components from the alluvial aquifer include pumpage from 

wells screened within the alluvial aquifer, leakage to the Mississippi River and interior Delta streams and lakes, leakage to 

the Bluff Hills escarpment on the eastern edge of the alluvial 

aquifer, and leakage to underlying aquifers. Prior to extensive 

development, the regional groundwater flow path was composed of two flow components—flow from the north to the 

south and from the east and west peripheries toward the center 

of the Delta. These flow paths generally followed the topography of the alluvial plain, which slopes from north to south and 

is bounded by the Mississippi River levees on the west and 

Bluff Hills on the east, both of which are topographic highs 

relative to the interior of the Delta. During these predevelopment conditions, water from the alluvial aquifer likely is discharged to the Sunflower and Yazoo Rivers, which are regional 

drains for the alluvial aquifer (Arthur, 2001). Presently (2010), 

the regional groundwater flow path is intercepted by a large 

cone of depression in the central Delta centered on Sunflower 

County (fig. 1), formed as a result of groundwater pumping for 

irrigation (Arthur, 2001). 

Although the alluvial aquifer has a large reserve 

(Arthur, 2001), there is evidence that the current rate of water 

use from the alluvial aquifer is not sustainable. Water-level 

Principal aquifers of the

United States

EXPLANATION

High Plains aquifer

Central Valley aquifer system

Mississippi River Valley alluvial aquifer

Basin and Range basin-fill aquifers

Floridan aquifer system

3,640 Mgal/d

9,290 Mgal/d

17,500 Mgal/d

9,810 Mgal/d

5,620 Mgal/d

Figure 2. Principal aquifers of the United States with the five highest withdrawal rates in 2000.

Figure 2. Principal aquifers of the United States with the five highest withdrawal rates in 2000.
4 Simulation of Water-Use Conservation Scenarios for the Mississippi Delta

1/19531/19561/19591/19621/19651/19681/19711/19741/19771/19801/19831/19861/19891/19921/19951/19981/20011/20041/20071/19531/19561/19591/19621/19651/19681/19711/19741/19771/19801/19831/19861/19891/19921/19951/19981/20011/20041/2007

Altitude, in feet above or below NGVD 29

135

130

140

145

150

155

160

165

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G0029 TUNICA

105

110

115

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J0005 COAHOMA

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F0020 BOLIVAR

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L0027 SUNFLOWER

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M0038 SUNFLOWER

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O0037 LEFLORE

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F0059 HUMPHREYS

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105

110

S0004 WASHINGTON

y = 0.0008x + 188.33

R2

 = 0.4621

y = 0.0009x + 145.16

R2

 = 0.8796

y = 0.0021x + 152.08

R2 = 0.8796

y = 0.0006x + 120.35

R2

 = 0.5118

y = 0.0005x + 106.72

R2

 = 0.2033

y = 0.0004x + 121.39

R2

 = 0.0646

y = –9E–05x + 100.94

R2

 = 0.0135

y = 0.0003x + 154.12

R2

 = 0.275

Figure 3. Hydrographs for selected wells screened in the alluvial aquifer in northwestern Mississippi. See figure 1

for well locations.

Figure 3. Hydrographs for selected wells screened in the alluvial aquifer in northwestern Mississippi. See figure 1 

for well locations.
Regional Groundwater Flow Model 5

declines are variable across the Delta, and the largest declines 

are observed in the central part of the Delta within the area 

of the cone of depression (figs. 1 and 3). The Yazoo Mississippi Delta Joint Water Management District (YMD), an 

agency formed in 1989 to assist with the development of nonregulatory strategies for the management of water resources in 

the Delta region, delineated the approximate extent of the area 

of the cone of depression (fig. 1) to examine changes in water 

levels and the effects on aquifer storage within the cone of 

depression (Yazoo Mississippi Delta Joint Water Management 

District, 2007; fig. 4). Using annual water-level data within 

this area and a specific yield value of 0.32, YMD determined 

that the average fall-to-fall change in storage since 1987 is 

150,750 acre-feet per year (acre-ft/yr), which has resulted 

in a cumulative loss of approximately 3,316,500 acre-feet 

(acre-ft) within the area of the cone of depression from 1987 

to 2009 (Yazoo Mississippi Delta Joint Water Management 

District, 2010; fig. 4). Water-level declines also have resulted 

in decreases in baseflow in many Delta streams (fig. 4) to 

the extent that in the absence of rainfall or irrigation return 

flow, some stream reaches are dry during the summer 

months (fig. 5). 

The YMD is currently (2010) considering several options 

for reducing the annual groundwater deficit including the 

implementation of conservation programs to use water more 

efficiently, which would reduce the demand for water in crop 

production. However, it is unclear whether conservation 

efforts should be applied uniformly to the Delta, as a whole, 

or if efforts should be focused on areas experiencing large 

groundwater declines within the cone of depression. Using an 

existing calibrated U.S. Geological Survey (USGS) regional 

groundwater flow model, the USGS, in cooperation with the 

YMD, evaluated conservation scenarios for the alluvial aquifer 

underlying the Delta in northwestern Mississippi. Simulations 

of conservation scenarios, varying in both total amount and 

location, were run for each year from 2008 to 2038 in order to 

determine the most effective implementation of conservation 

efforts. The purpose of this report is to document the results of 

the model simulations to aid the YMD in the development of 

water-use conservation programs for the study area.

Regional Groundwater Flow Model

Recently, the USGS, completed a large-scale regional 

model covering the entire Mississippi embayment and extending through the primary drinking-water aquifers as part of the 

Mississippi Embayment Regional Aquifer Study (MERAS) 

(fig. 6). This model was constructed using MODFLOW-2005, 

a software package developed by the USGS (Harbaugh, 2005). 

The construction and calibration of the MERAS model used 

for this study is documented in Clark and Hart (2009). The 

MERAS model consists of a set of discrete blocks in space 

–3,500,000

–3,000,000

–2,500,000

–2,000,000

–1,500,000

–1,000,000

–500,000

0

0

20

40

60

80

100

120

140

160

1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006 2009

Cumulative storage loss within cone of

depression area, in acre-feet

Discharge, in cubic feet per second

Cumulative estimated storage loss within

cone of depression area, in acre-feet

Annual minimum daily discharge of the Big

Sunflower River at Sunflower gage 

Storage data from Yazoo Mississippi Delta Joint Water Management District, 2010

1955

EXPLANATION

No data

Figure 4. Annual minimum daily discharge of the Big Sunflower River at

Sunflower, Mississippi, and cumulative estimated storage loss in the

area of the cone of depression in the alluvial aquifer as determined by

the Yazoo Mississippi Delta Joint Water Management District in

northwestern Mississippi.

Figure 4. Annual minimum daily discharge of the Big Sunflower River at Sunflower, 

Mississippi, and cumulative estimated storage loss in the area of the cone of 

depression in the alluvial aquifer as determined by the Yazoo Mississippi Delta Joint 

Water Management District in northwestern Mississippi. Discharge graph is blank 

where data are missing.
6 Simulation of Water-Use Conservation Scenarios for the Mississippi Delta

and time. The blocks represent cells of porous material within 

which the hydraulic properties are the same. In plan view, the 

cells have a uniform horizontal spacing of 1 mile on a side, 

but have variable thicknesses in the vertical direction. A set of 

finite-difference equations describes groundwater flow through 

each cell. These equations can be solved to simulate either 

equilibrium (steady-state) conditions or transient conditions, 

which simulate changes in stresses (such as water withdrawal 

from wells) over fixed periods of time. The finite-difference 

grid is oriented north-south and consists of 414 rows, 397 

columns, and 13 layers. 

The MERAS model simulates 137 years (1870–2007) of 

system response to stress divided into 69 stress periods. The 

first stress period is simulated as steady state to represent predevelopment conditions. Stress periods 2 through 27 are variable in length to reflect embayment-wide changes in groundwater withdrawals. Stress periods 28 (beginning in 1986) 

through 69 are each 6 months in length to reflect spring–

summer (April–September) and fall–winter (October–March) 

conditions related to irrigation (Clark and Hart, 2009). 

Areal recharge is applied throughout the MERAS 

model area using the MODFLOW-2005 Recharge Package 

(Harbaugh, 2005) and represents net recharge. Net recharge 

is defined as “the entry into the saturated zone of water made 

available at the water-table surface, together with the associated flow away from the water table within the saturated zone” 

(Freeze and Cherry, 1979) because evapotranspiration (ET) 

is not explicitly simulated. A total of 19 recharge zones were 

classified for the MERAS model; 3 of these zones cover the 

alluvial aquifer within Mississippi. Each recharge zone was 

assigned a recharge fraction, which was used to estimate daily 

recharge rates by multiplying the recharge fraction by precipitation. Recharge rates across the three zones for the alluvial 

aquifer in Mississippi range from 0.1 to 3.25 in/yr. 

Pumpage from irrigation, municipal, and industrial wells 

were simulated using the Multi-Node Well (MNW) Package 

(Halford and Hanson, 2002). The MNW Package allows for 

simulation of flow in wells that are completed in multiple 

aquifers or model layers. There are 43 streams included within 

the MERAS model. Each stream in the MERAS model area 

was represented using the Streamflow-Routing (SFR) Package 

of MODFLOW (Prudic and others, 2004). The initial criterion 

for the inclusion of streams in the MERAS model was a mean 

annual flow of 1,000 cubic feet per second (ft3/s) or more. 

Other streams were added based on inclusion by previous 

model studies that demonstrated the interaction of the streams 

with surficial aquifers. 

The perimeter of the MERAS model area and the base 

of the flow system are represented as no-flow boundaries. 

The MERAS model simulation assumed that the density of 

water remained constant in time throughout the flow system. 

The downdip limit of each model layer is a no-flow boundary, which approximates the extent of water with less than 

10,000 milligrams per liter (mg/L) of dissolved solids.

Conservation Scenario Development

Conservation scenarios were developed to simulate 

where the implementation of water-use conservation efforts 

might have the greatest effect on storage in the alluvial 

aquifer—either uniformly throughout the Delta, or focused 

in the area of the cone of depression. The scenarios were 

simulated with the MERAS model by extending the simulation period by 30 years, to 2038. Sixteen stress periods were 

used to represent the projected 30-year period. The first stress 

period is 275 days in length, to extend the MERAS model to 

the end of 2007. Each stress period following 2007 is 2 years 

in length. For each scenario, recharge to the alluvial aquifer 

underlying the Delta is held constant by multiplying the 

recharge fraction assigned to each of the three recharge zones 

within the Delta by the long-term average precipitation value 

for the Delta (54 in/yr). Calibrated recharge fractions from the 

three recharge zones within the Delta were 0.00342, 0.038, 

and 0.0446, resulting in recharge rates (for 54 in/yr of rainfall) 

Figure 5. Dry streambeds during the summer months due to lack 

of base flow for (A) Big Sunflower River at Sunflower, Mississippi, 

and (B) Bogue Phalia River near Leland, Mississippi.
Conservation Scenario Development 7

Monroe Uplift

Jackson

Dome

Arkansas fault

zone

Sabine

Uplift

Pickens-Gilbertown fault zone

EXPLANATION

Hydrogeologic and geologic units

Loess, silt, sand, gravel deposits

Undifferentiated alluvial deposits

Vicksburg-Jackson confining unit

Upper Claiborne aquifer

Middle Claiborne confining unit

Claiborne Group undifferentiated

Middle Claiborne aquifer (Memphis Sand)

Middle Claiborne aquifer (Sparta Sand)

Lower Claiborne confining unit

Lower Claiborne aquifer

Upper and middle Wilcox aquifers

Midway confining unit

Undifferentiated

MERAS model domain

94° 93° 92° 91° 90° 89° 88° 87°

37°

36°

35°

34°

33°

32°

31°

KENTUCKY

ILLINOIS

MISSOURI

ARKANSAS

LOUISIANA

MISSISSIPPI

ALABAMA

TENNESSEE

TEXAS 0 25 50 100 KILOMETERS

0 25 50 100 MILES

Mississippi River

Crowley’s Ridge

Mississippi River Valley alluvial aquifer

Gravel deposits

Lower Claiborne aquifer

unit

Figure 6. (A) Mississippi Embayment Regional Aquifer Study model domain and surficial geology;

and (B) generalized section of hydrogeologic and geologic units.

B.

A.

WEST EAST

Mississippi River Valley

alluvial aquifer Outcrop

area

Outcrop

area

Upper Claiborne aquifer

Midway 

confining unit

Midway 

confining unit Middle Claiborne aquifer

Middle and lower Wilcox aquifers

Middle

confining

unit

Not to scale Geology modified from Arthur and Taylor, 1990

EXPLANATION

Claiborne

Vicksburg-Jackson confining

Loess

unit

, silt, sand

Lower Claiborne confining unit

Ground-water 

 flow direction

Figure 6. (A) Mississippi Embayment Regional Aquifer Study model domain and surficial 

geology; and (B) generalized section of hydrogeologic and geologic units.
8 Simulation of Water-Use Conservation Scenarios for the Mississippi Delta

of 0.18, 2.05, and 2.41 in/yr, respectively. Water use from the 

alluvial aquifer underlying the Delta was modified to represent 

varying amounts and distributions of conservation to produce 

the following simulation scenarios:

• Base scenario—Water use from existing regional 

model remains constant at 2007 rates throughout the 

simulation period. 

• 5-percent Delta-wide conservation scenario—Water 

use is reduced by 5 percent from the base scenario across 

the Delta, beginning in 2010, and then held constant 

throughout the simulation period. 

• 5-percent cone-equivalent conservation scenario—

Water use is reduced by 11 percent from the base 

scenario (volume amount is equivalent to 5-percent 

Delta-wide conservation scenario) within the area of 

the cone of depression, beginning in 2010, and then 

held constant throughout the simulation period. Water 

use in the remaining part of the Delta is held at the base 

scenario rates.

• 25-percent Delta-wide conservation scenario—Water 

use is reduced by 25 percent from the base scenario 

across the Delta, beginning in 2010, and then held constant throughout the simulation period. 

• 25-percent cone-equivalent conservation scenario—

Water use is reduced by 55 percent from the base 

scenario (volume amount is equivalent to 25-percent 

Delta-wide conservation scenario) within the area of 

the cone of depression, beginning in 2010, and then 

held constant throughout the simulation period. Water 

use in the remaining part of the Delta is held at the base 

scenario rates.

Conservation Scenario Results

Results from each conservation scenario were compared 

to the results from the base scenario to determine the effectiveness of each conservation scenario. The effectiveness of 

each conservation scenario was measured by the changes in 

the depth to water and the volume of water in storage within 

the alluvial aquifer relative to the base scenario. Depth to 

water represents the thickness of the unsaturated zone, and 

as this value increases, the thickness of the saturated zone 

decreases. Storage represents the amount of water available 

for use within the pore spaces, fractures, and cracks beneath 

land surface. Water taken from storage is no longer available 

for future use unless recharged from another source. Groundwater overdraft, defined as annual withdrawal in excess of the 

amount that can safely be withdrawn without an undesirable 

effect (Freeze and Cherry, 1979), occurs when more water is 

removed from storage than is replaced each year by recharge. 

The base scenario, in which no conservation was employed, 

represents the largest overall water-level declines and loss of 

storage within the aquifer over the simulation period; therefore, each conservation scenario results in improvement of 

water level and storage within the aquifer. 

Using the model output, depth to water after the 2038 

stress period was determined for the base scenario and for 

each of the four conservation scenarios. For each conservation 

scenario, the percentage of change in water level relative to 

the percentage of change in water level for the base scenario 

was then determined for each model cell (fig. 7). Percentage 

values greater than 0 indicate that the conservation scenario 

water level increased. A percentage value equal to 0 indicates 

either that the depth to water for the conservation scenario 

is equal to that of the base scenario (no change), or water 

levels decreased between the base scenario and the conservation scenario. Typically, a decrease in water levels between 

the base scenario and conservation scenario occurs within a 

model cell when pumping from a well is reduced or shut off 

during the base simulation due to constraints within the model 

that do not let a well pump until the cell is completely dry. 

During the conservation scenario, the well is allowed to pump 

throughout the simulation (due to the conservation measures 

resulting in greater saturated thickness); therefore, the conservation scenario water level is lower than in the base scenario. 

For the entire Delta area, the Delta-wide scenarios result in 

greater average water-level improvements (relative to the base 

scenario) than the cone-equivalent scenarios. For the area of 

the cone of depression, the cone-equivalent scenarios result in 

greater water-level improvements (relative to the base scenario) than the Delta-wide scenarios because all conservation 

efforts are concentrated within the area of the cone of depression (table 1). In comparing average water-level improvements 

across the entire Delta to those within the area of the cone of 

depression, the greatest average improvements in water level 

occur within the area of the cone of depression for all conservation scenarios. This is caused by the relatively larger volume 

of unsaturated aquifer material within the area of the cone of 

depression and the hydraulic gradient, which slopes from the 

periphery of the Delta towards the cone of depression. 

Net withdrawal from storage throughout each scenario 

simulation was determined using the USGS program 

ZONEBUDGET (Harbaugh, 1990), which uses MODFLOW 

cell-by-cell flow data and user-defined subregional zones 

to compute water budgets for each subregional zone. Five 

subregional zones were designated within the MERAS 

model (fig. 8). Water budget inflows to the alluvial aquifer 

include storage, recharge from precipitation, stream leakage, 

discharge from underlying units, leakage from the Mississippi River on the western periphery, and interflow from the 

Bluff Hills escarpment on the eastern periphery. Water budget 

outflows from the alluvial aquifer include storage, pumpage, leakage to the underlying units, leakage to the Mississippi River on the western periphery, leakage to streams, 

and leakage to the Bluff Hills escarpment on the eastern 

periphery (fig. 9). The dominant transient stress (outflow) on 
Conservation Scenario Results 9

TATE TUNICA

DE SOTO

-91° -90°

35°

EXPLANATION

5-percent Delta-wide scenario 

Relative improvement in 2038

 water-level, in percent

0

1–2

3–5

6–10

11-25

26–50

51–100

BOLIVAR

PANOLA

COAHOMA

GRENADA

TALLAHATCHIE

QUITMAN

34°

EXPLANATION

25-percent Delta-wide scenario 

Relative improvement in 2038

 water-level, in percent

0

1–2

3–5

6–10

11-25

26–50

51–100

EXPLANATION

5-percent cone-equivalent scenario 

Relative improvement in 2038

 water-level, in percent

0

1–2

3–5

6–10

11-25

26–50

51–100

EXPLANATION

25-percent cone-equivalent scenario 

Relative improvement in 2038

 water-level, in percent

0

1–2

3–5

6–10

11-25

26–50

51–100

HOLMES

CARROLL

LEFLORE

WASHINGTON

SUNFLOWER

SHARKEY

HUMPHREYS

33°

YAZOO

WARREN

ISSAQUENA

0 10 20 Miles

0 20 Kilometers

0 10 20 Miles

0 20 Kilometers

0 10 20 Miles

0 20 Kilometers

0 10 20 Miles

0 20 Kilometers

PANOLA

TATE TUNICA

DE SOTO

PANOLA

TATE TUNICA

DE SOTO

BOLIVAR

CARROLL

LEFLORE

COAHOMA

SUNFLOWER

GRENADA

TALLAHATCHIE

QUITMAN

BOLIVAR

LEFLORE

COAHOMA

SUNFLOWER

GRENADA

CARROLL

TALLAHATCHIE

QUITMAN

YAZOO

WASHINGTON HOLMES

SHARKEY

ISSAQUENA

HUMPHREYS

YAZOO

WASHINGTON HOLMES

SHARKEY

ISSAQUENA

HUMPHREYS

WARREN

ISSAQUENA

WARREN

ISSAQUENA

TATE TUNICA

DE SOTO

-91° -90°

-91° -90° -91° -90°

35°

BOLIVAR

PANOLA

COAHOMA

GRENADA

TALLAHATCHIE

QUITMAN

34°

HOLMES

CARROLL

LEFLORE

WASHINGTON

SUNFLOWER

HUMPHREYS

SHARKEY 33°

35°

34°

33°

35°

34°

33°

YAZOO

WARREN

ISSAQUENA

Figure 7. Percentage change in 2038 water level for each conservation scenario relative to the base scenario. Figure 7. Percentage of change in 2038 water level for each conservation scenario relative to the base scenario.
10 Simulation of Water-Use Conservation Scenarios for the Mississippi Delta

storage between the cone-equivalent and Delta-wide scenarios 

also increases, resulting in greater gains in storage in the coneequivalent scenario than in the Delta-wide scenario, for the 

same amount of conservation.

Model Limitations

Limitations of analysis using the MERAS model are 

documented in Clark and Hart (2009). The basic limitations 

that should be considered when interpreting model results 

are restated here. An understanding of model limitations is 

essential to effective use of simulated water-level and storage 

results. The accuracy of a groundwater model is limited by 

simplification of complexities within the flow system (conceptual model), space and time discretization effects, and assumptions made in the formulation of the governing flow equations. 

Model accuracy also is affected by cell size, number of layers, 

accuracy of boundary conditions, accuracy and availability 

of hydraulic property data, accuracy of withdrawal and areal 

recharge estimates, historical data for calibration, parameter 

sensitivity, and the interpolations and extrapolations that are 

inherent in using data in a model. Although a model might be 

calibrated, the calibration parameter values are not unique in 

yielding acceptable distributions of hydraulic head. 

Information on the amount of groundwater withdrawn 

from the various aquifers (water use) and the amount of 

recharge entering the groundwater system is crucial to the 

MERAS model. While some site-specific information on 

water use exists for some areas, particularly irrigation water 

use in Arkansas, the period of record for this information is 

only about 10 to 15 years, which is a relatively small amount 

of time compared to the simulation calibration period of 

137 years. Recharge in the MERAS model is calibrated based 

on water-level and streamflow observations. The range of 

recharge values in the MERAS model is within the range of 

values used by past models constructed in the study area and 

based on streamflow separation methods; however, field values to validate these ranges are sparse or difficult to compare. 

For much of the study area and simulation period, each of 

these datasets pertaining to water use and recharge currently 

has little or no information on actual values.

Another critical component of the alluvial aquifer water 

balance is the interaction of the many miles of rivers and 

streams with the alluvial aquifer in the Delta. To simulate 

stream leakage in the MERAS model, basic factors such as the 

thickness and hydraulic conductivity of the streambed were 

estimated because there have been very few studies to quantify 

these factors. The factors used in the model could change if 

new information becomes available.

the alluvial aquifer is pumping, and the majority of water supplied from pumping is from storage within the alluvial aquifer. 

To compare storage loss from each conservation scenario 

relative to the base scenario, the percentage of increase in storage within the alluvial aquifer relative to the base scenario was 

determined for both Delta-wide (zones 1 and 2 in fig. 8) and 

the area of the cone of depression only (zone 2 in fig. 8) using 

storage data throughout the conservation period of the simulation (2010–2038). Of the four conservation scenarios, the 

25-percent cone-equivalent scenario resulted in the greatest 

Delta-wide increase in storage relative to results for the base 

scenario, with a 32-percent improvement (fig. 10). For the 

area of the cone of depression, the 25-percent cone-equivalent 

scenario also had the greatest increase in storage relative to the 

base scenario, with a 60-percent improvement. The 25-percent 

Delta-wide scenario resulted in a 29-percent improvement 

relative to the results for the base scenario for both the Deltawide and cone of depression areas. Relative improvements in 

storage from the 5-percent Delta-wide and cone-equivalent 

scenarios were less than that from the 25-percent scenarios; 

however, they were similar to the 25-percent scenarios in that 

the 5-percent cone-equivalent scenario resulted in a small 

improvement Delta-wide relative to the 5-percent Delta-wide 

scenario because all conservation was focused on the area 

of the cone of depression. Delta-wide, the relative amount 

of storage increased by 1 percent between the 5-percent 

cone-equivalent and Delta-wide scenarios, and by 3 percent 

between the 25-percent cone-equivalent and Delta-wide scenarios. These results imply that focusing conservation efforts 

within the area of the cone of depression, rather than distributing conservation efforts uniformly across the Delta, results in 

greater improvements in the amount of storage within the alluvial aquifer. In addition, as the total amount of conservation 

increases (that is from 5 to 25 percent), the relative increase in 

Table 1. Average percentage of increase relative to the base 

scenario in alluvial aquifer water levels for each 

conservation scenario.

Average increase in water level relative to base scenario, in percent

Conservation scenario Delta-wide Within cone of 

depression

5-percent Delta-wide 2.5 3.1

5-percent cone-equivalent 2.0 6.3

25-percent Delta-wide 12.1 15.8

25-percent cone-equivalent 9.8 31.7
Model Limitations 11

YAZOO

BOLIVAR

HOLMES

PANOLA

TATE

CARROLL

LEFLORE

TUNICA

COAHOMA

WASHINGTON

DE SOTO

SUNFLOWER

WARREN

SHARKEY

GRENADA

TALLAHATCHIE

QUITMAN

ISSAQUENA

HUMPHREYS

BigBlackRiver Bogue PhaliaRiver

Yockanookany River

SkunaRiver

Yocona River

PearlRiver

YalobushaRiver

Yazoo R iver

SunflowerRiver

Little TallhatchieRiver

LeafR vi er Strong River

YalobushaRiver

Yocona River

-91° -90°

35°

34°

33°

EXPLANATION

ZONEBUDGET zones

Alluvial aquifer

Cone of depression area

Bluff Hills

Underlying units

Mississippi River

0 10 20 Miles

0 10 20 Kilometers

Underlying units

Figure 8. Subregional zones designated for ZONEBUDGET water-budget computations.

TENNESSEE

MISSISSIPPI

ARKANSAS

LOUISIANA

Figure 8. Subregional zones designated for ZONEBUDGET water-budget computations.
12 Simulation of Water-Use Conservation Scenarios for the Mississippi Delta

Water Budget

Inflows Outflows

Storage

67 percent

Recharge

14 percent

Stream

leakage

9 percent 

Bluff Hills

2 percent

Underlying

units

5 percent Mississippi

River

3 percent

Storage

0.2 percent

Stream

leakage

 1.7 percent

Pumpage

87.7 percent

Bluff Hills

0.2 percent

Underlying

units

 8.0 percent 

Mississippi

River

 2.3 percent 

Clay confining unit

Bluff Hills

Mississippi River

Recharge from precipitation

Storage

Saturated

zone of 

alluvial

aquifer

Unsaturated

zone of 

alluvial

aquifer

Water table

Land surface

Underlying units

Figure 9. Figure 9. Water-budget inflows and outflows for base scenario simulation period (2007--2038). Water-budget inflows and outflows for base scenario simulation period (2007–2038). 
Summary 13

Summary

The Mississippi Delta, once a floodplain to the Mississippi River covered with hardwoods and marshland, is now a 

highly productive agricultural region of large economic importance to Mississippi. Water for irrigation is supplied primarily 

by the Mississippi River Valley alluvial aquifer, and although 

the alluvial aquifer has a large reserve, there is evidence that 

the current rate of water use from the alluvial aquifer is not 

sustainable. To sustain water resources in the Delta, the Yazoo 

Mississippi Delta Joint Water Management District (YMD) 

is currently (2010) considering several options for reducing 

the annual groundwater deficit including the implementation of conservation programs to use water more efficiently 

and stop or slow declining water levels. Recently, the U.S. 

Geological Survey (USGS) completed a large-scale regional 

model of the Mississippi embayment, extending through the 

primary drinking-water aquifers as part of the Mississippi 

Embayment Regional Aquifer Study (MERAS). Using this 

regional groundwater flow model, conservation scenarios 

were evaluated by the USGS, in cooperation with the YMD, 

for the alluvial aquifer underlying the Delta region in northwestern Mississippi. Conservation scenarios were developed 

to assess where the implementation of water-use conservation 

efforts would have the greatest effect on future water availability—either uniformly throughout the Delta, or focused in 

the area of the cone of depression in the central Delta. Five 

scenarios were simulated with the MERAS model: (1) a base

scenario in which water use remained constant at 2007 rates 

throughout the entire simulation; (2) a 5-percent “Delta-wide” 

conservation scenario in which water use across the Delta 

was decreased by 5 percent; (3) a 5-percent “cone-equivalent” 

conservation scenario in which water use within the area of 

the cone of depression was decreased by 11 percent, a volume 

equivalent to the 5-percent Delta-wide conservation scenario; 

(4) a 25-percent Delta-wide conservation scenario in which 

water use across the Delta was decreased by 25 percent; and 

(5) a 25-percent cone-equivalent conservation scenario in 

which water use within the area of the cone of depression 

was decreased by 55 percent, a volume equivalent to the 

25-percent Delta-wide conservation scenario.

The simulated Delta-wide scenarios resulted in greater 

average water-level improvements (relative to the base 

scenario) for the entire Delta area than the cone-equivalent 

scenarios. The cone-equivalent scenarios resulted in greater 

average water-level improvements within the cone of depression because of focused conservation efforts. Regardless of 

the location of conservation (Delta-wide or within the cone of 

depression), the greatest average improvements in water level 

occur within the area of the cone of depression because of the 

large area of unsaturated aquifer material within the area of the 

cone of depression and the hydraulic gradient, which slopes 

from the periphery of the Delta towards the area of the cone 

of depression. 

Of the four conservation scenarios, the 25-percent coneequivalent scenario resulted in the greatest increase in storage 

relative to the base scenario with a 32-percent improvement 

over the base scenario across the entire Delta and a 60-percent 

improvement within the area of the cone of depression. 

Although the improvements in storage for the 5-percent Deltawide and cone-equivalent scenarios were less than for the 

25-percent scenarios, they were similar to the improvements 

for the 25-percent scenarios in that the 5-percent cone-equivalent scenario resulted in a small improvement Delta-wide 

relative to the 5-percent Delta-wide scenario because all 

conservation was focused on the area of the cone of depression. Therefore, these results imply that focusing conservation efforts within the area of the cone of depression, rather 

than distributing conservation efforts uniformly across the 

Delta, results in greater improvements in the amount of storage within the alluvial aquifer. In addition, as the total amount 

of conservation increases (that is from 5 to 25 percent), the 

difference in storage improvement between the Delta-wide 

and cone-equivalent scenarios also increases, resulting in 

greater gains in storage in the cone-equivalent scenario over 

the Delta-wide scenario for the same amount of conservation.

5 6

29 32

5

11

29

60

0

10

20

30

40

50

60

70

5% Deltawide5% Cone

equivalent

25% Delta

wide

25% Cone

equivalent

Percentage increase in storage

relative to base scenario 

-

EXPLANATION

Delta-wide

Cone of depression

 area

Figure 10. Percentage of increase in storage within the 

alluvial aquifer relative to the base scenario for each 

conservation scenario for the entire alluvial aquifer 

(Delta-wide) and the area of the cone of depression.

Figure 10. Percentage of increase in storage within 

the alluvial aquifer relative to the base scenario for each 

conservation scenario for the entire alluvial aquifer (Deltawide) and the area of the cone of depression. 
14 Simulation of Water-Use Conservation Scenarios for the Mississippi Delta

Harbaugh, A.W., 1990, A computer program for calculating 

subregional water budgets using results from the U.S. Geological Survey modular three-dimensional finite-difference 

ground-water flow model: U.S. Geological Survey OpenFile Report 90–392, 24 p. 

Harbaugh, A.W., 2005, MODFLOW-2005, the U.S. Geological Survey modular ground-water model—The 

ground-water flow process: U.S. Geological Survey Techniques and Methods 6–A16, variously paged.

Hosman, R.L., 1988, Geohydrologic framework of the Gulf 

Coastal Plain: U.S. Geological Survey Hydrologic Investigations Atlas 695, 2 sheets.

Maupin, M.A., and Barber, N.L., 2005, Estimated withdrawals 

from principal aquifers in the United States, 2000: 

U.S. Geological Survey Circular 1279, 46 p.

Prudic, D.E., Konikow, L.F., and Banta, E.R., 2004, A new 

streamflow-routing (SFR1) package to simulate streamaquifer interaction with MODFLOW-2000: U.S. Geological 

Survey Open-File Report 2004–1042, 95 p.

Yazoo Mississippi Delta Joint Water Management District, 

2007, 2006 Annual report, accessed Febuary 1, 2009, at 

http://www.ymd.org/pdfs/2006annualreport.pdf.

Yazoo Mississippi Delta Joint Water Management District, 

2010, 2009 Annual work summary, accessed September 10, 

2010, at http://www.ymd.org/pdfs/2009annualsummary.pdf.

References

Arthur, J.K., 2001, Hydrogeology, model description, and 

flow analysis of the Mississippi River Alluvial Aquifer in 

Northwestern Mississippi: U.S. Geological Survey WaterResources Investigations Report 01–4035, 47 p. 

Clark, B.R., and Hart, R.M., 2009, The Mississippi Embayment Regional Aquifer Study (MERAS)—Documentation 

of a groundwater flow model constructed to assess water 

availability in the Mississippi embayment: U.S. Geological 

Survey Scientific Investigations Report 2009–5172, 62 p.

Economic Research Service, U.S. Department of Agriculture, 

2010, The economics of food, farming, natural resources, 

and rural America—State fact sheets—Mississippi, accessed 

January 20, 2011, at http://www.ers.usda.gov/State Facts/

MS.htm.

Fisk, H.N., 1944, Geological investigation of the alluvial 

valley of the lower Mississippi River: U.S. Department of 

Army, Mississippi River Commission, 78 p. 

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Englewood Cliffs, New Jersey, Prentice-Hall, 604 p. 

Halford, K.J., and Hanson, R.T., 2002, User guide for the 

drawdown-limited, Multi-Node Well (MNW) Package for 

the U.S. Geological Survey’s modular three-dimensional 

finite-difference ground-water flow model, versions

MODFLOW-96 and MODFLOW-2000: U.S. Geological 

Survey Open-File Report 02–293, 33 p.

Prepared by:

USGS Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

For additional information regarding this 

publication, contact:

 USGS Mississippi Water Science Center

 308 South Airport Road

 Jackson, MS 39208

 (601) 933-2900

Or visit the USGS Mississippi Water Science 

Center Web site at:

 http://ms.water.usgs.gov/ 
Barlow and Clark—Simulation of Water-Use Conservation Scenarios for the Mississippi Delta—Scientific Iinvestigations Report 2011–5019

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