U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3426

Sheet 1 of 2

laf19-0909_fig.01

ARKANSAS

MISSOURI

ARKANSAS

LOUISIANA

KENTUCKY

TENNESSEE

ILLINOIS

TENNESSEE

MISSISSIPPI

LOUISIANA

MISSISSIPPI

KENTUCKY

ILL

NI OIS

MISSOURI

Little Rock

Pine Bluff

Alexandria

Monroe

Houma

New Orleans

HelenaWest Helena

Jonesboro

Clarksdale

Cleveland

Greenville

Greenwood

Jackson

Natchez

Vicksburg

Yazoo City

Cape Girardeau

Poplar Bluff

Memphis

Baton Rouge

Lafayette

0 15 30 45 60 MILES

0 15 30 45 60 KILOMETERS

Base modified from U.S. Geological Survey,

digital data 1:100,000 scale

Albers Equal Area projection;

World Geodetic System of 1984 

EXPLANATION

Mississippi Alluvial Plain extent

Bottom altitude, in feet. Datum is North American

 Vertical Datum of 1988

−429.06 to −400

−399.99 to −300

−299.99 to −200

−199.99 to −100

−99.99 to −50

−49.99 to 0

0.01 to 50

50.01 to 100

100.01 to 200

200.01 to 300

300.01 to 367

91°30' 90°0' 88°30'

37°30'

36°0'

34°30'

33°0'

31°30'

30°0'

Figure 1. The Mississippi Alluvial Plain extent (Painter and 

Westerman, 2018) and geostatistical estimation of the bottom 

altitude of the Mississippi River Valley alluvial aquifer.

laf19-0909_fig 02

0 15 30 45 60 MILES

0 15 30 45 60 KILOMETERS

Base modified from U.S. Geological Survey,

digital data 1:100,000 scale

Albers Equal Area projection;

World Geodetic System of 1984

Mississippi Alluvial Plain extent

Data source

Saucier (1994)

Wilson and Hosman (1987)

Hoffman (2017)

Missouri Department of Natural

 Resources (2007)

Csontos (2007)

EXPLANATION

91°30' 90°0' 88°30'

37°30'

36°0'

34°30'

33°0'

31°30'

30°0'

Figure 2. Locations of boreholes located in the 

Mississippi Alluvial Plain that contain lithologic and 

geophysical data used to define the bottom altitude and 

thickness of the Mississippi River Valley alluvial aquifer.

laf19-0909_fig03

0 15 30 45 60 MILES

0 15 30 45 60 KILOMETERS

Base modified from U.S. Geological Survey,

digital data 1:100,000 scale

Albers Equal Area projection;

World Geodetic System of 1984

EXPLANATION

Mississippi Alluvial Plain extent

Thickness, in feet

28.6 to 80

80.1 to 120

120.1 to 160

160.1 to 200

200.1 to 240

240.1 to 280

280.1 to 320

320.1 to 360

360.1 to 400

400.1 to 434.3

91°30' 90°0' 88°30'

37°30'

36°0'

34°30'

33°0'

31°30'

30°0'

Figure 3. The Mississippi Alluvial Plain extent (Painter 

and Westerman, 2018) and geostatistical estimation of the 

thickness of the Mississippi River Valley alluvial aquifer.

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Suggested citation:

Torak, L.J., and Painter, J.A., 2019, Geostatistical estimation of the bottom altitude and thickness 

of the Mississippi River Valley alluvial aquifer: U.S. Geological Survey Scientific Investigations 

Map 3426, 2 sheets, https://doi.org/10.3133/sim3426.

ISSN 2329-132X (online)

https://doi.org/10.3133/sim3426

Geostatistical Estimation of the Bottom Altitude and Thickness of the 

Mississippi River Valley Alluvial Aquifer

By

L.J. Torak and J.A. Painter

2019

The Mississippi River Valley alluvial 

aquifer (MRVA) caps a shallow system 

of aquifers and confining units in the 

Mississippi Alluvial Plain (MAP) that 

extends across 45,000 square miles of the 

midwestern and southern United States 

from Illinois to Louisiana (fig. 1). Irrigation 

water from the MRVA is required to 

sustain extensive crop production, which 

has resulted in groundwater-level declines 

since the late 1920s equal to nearly half of 

its thickness and in reduced baseflow of 

streams. Increased groundwater withdrawal 

for irrigation is expected to continue 

and threatens complete and irreversible 

aquifer dewatering (depletion) (Clark and 

others, 2013; Reba and others, 2017). 

The exact amount of dewatering in the 

MRVA is uncertain because its vertical 

extent is poorly defined and the effects of 

groundwater withdrawal on the aquifer 

are not well understood. To provide 

stakeholders and managers with information 

and tools that promote understanding of 

the hydrogeologic framework of the MAP 

extent (Painter and Westerman, 2018) and 

its role in water-resource management, 

the U.S. Geological Survey (USGS) 

Water Availability and Use Science 

Program (WAUSP) has funded a 5-year 

effort to assess groundwater availability 

and project future sustainability of water 

resources. Part of this study involves 

mapping the bottom altitude and thickness 

of the aquifer by using compilations of 

hydrogeologic data and applications of 

geostatistical analytics. Results of this 

mapping effort, presented here, are intended 

to enhance characterization of the shallow 

hydrogeologic framework and direct future 

airborne, ground-based, and waterborne 

geophysical surveys. Data used in support 

of the findings presented in this report are 

available as a USGS data release (Torak and 

Painter, 2019).

Bottom altitudes of the MRVA 

were compiled from interpretations of 

subsurface lithologic and geophysical 

logs (log picks) at about 10,000 boreholes 

located throughout the MAP extent 

that were available from previous 

investigations (fig. 2). Log picks were 

corrected to the National Elevation 

Dataset (NED) 10-meter digital elevation 

model (DEM; https://nationalmap.gov/

elevation.html). Log picks that required a 

DEM correction of less than 20 feet were 

used for the geostatistical estimation of 

the MRVA bottom altitude, after additional 

filtering removed duplicate log picks, 

yielding a bottom-altitude dataset of 

9,392 data points.

Introduction Data Compilation, Processing, and Filtering Prior to Estimation