Potentiometric Surface

The potentiometric surface of the Carrizo-Wilcox aquifer 

(fig. 1) was constructed by using the altitude of water levels 

from 77 wells measured March–May 2013 (table 2). Water 

levels were measured by using a steel or electric tape marked 

with 0.01-ft graduations and were reported to one-hundredths 

of a foot, following procedure in Cunningham and Schalk 

(2011). Water levels were measured in wells that were not 

being pumped at the time of measurement. The altitude of 

water levels ranged from 43.35 ft above the National Geodetic 

Vertical Datum of 1929 (NGVD 29) in De Soto Parish to 

296.22 ft above NGVD 29 in Caddo Parish.

Groundwater movement in the Carrizo-Wilcox aquifer 

generally is toward the Red River Valley and areas of heavy 

withdrawals (fig. 1). Localized cones of depressions in the 

potentiometric surface caused by heavy withdrawals (more 

than 0.5 Mgal/d; Sargent, 2011) are located near or at the 

towns of Mansfield (De Soto Parish), Keithville (southern 

Caddo Parish), and Castor (Bienville Parish) and have altered 

the regional flow patterns in these areas.

Water-Level Differences

Differences in water levels in the Carrizo-Wilcox aquifer 

measured at 30 wells in 1991 and 2013 are listed in table 2 

and shown on figure 3. Water-level differences were calculated 

by subtracting the 2013 water-level measurement from the 

1991 water-level measurement. These differences do not 

necessarily indicate a trend but show whether water levels 

have increased or decreased from 1991 to 2013. 

Of these 30 wells, 15 showed an increase in water level, 

and the other 15 showed a decrease in water level. In general, 

wells with decreasing water levels are located in Bienville and 

Red River Parishes and the southwestern part of Caddo Parish, 

and wells with increasing water levels are located in Bossier, 

Natchitoches, and Webster Parishes (fig. 3).

Hydrographs for most wells screened in the CarrizoWilcox aquifer show seasonal fluctuations with little net 

change in water levels (figs. 4A, B, and C). The hydrograph 

for well Bo-265 (fig. 4A), located in Bossier Parish, shows 

an upward trend of about 1.5 ft per year since 2002, and 

hydrographs for wells DS-517 (fig. 4B) and RR-278 (fig. 4C) 

show slight downward trends (less than 1 ft per year) in water 

levels since the mid-1990s. These slight downward trends are 

probably the result of increased withdrawals in the parishes 

rather than changes in precipitation. Figure 4D shows annual 

precipitation data for the period 1981–2013 for the Red River 

Research Station (Station ID: COOP 167738), located in 

Shreveport, La. (National Climactic Data Center, 2014).

50

60

70

80

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

10

15

20

25

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014

Water level, in feet below land surface Water level, in feet below land surface

A. Well: Bo-265

B. Well: DS-517

15

20

25

1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2014

C. Well: RR-278

10

20

30

40

50

60

70

80

90

D. Red River Research Station (COOP167738), Shreveport, Louisiana

Annual precipitation, in inches Water level, in feet below land surface

Year

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 

Year

Figure 4. Hydrographs for selected wells in northwestern Louisiana.

Table 2. Water-level data used to construct maps of the potentiometric surface, March–May 2013, and water-level differences, 1991–2013, in the Carrizo-Wilcox aquifer in

northwest Louisiana.

[NGVD 29, National Geodetic Vertical Datum of 1929; –, no data]

Well

number

Altitude of 

land

surface

(feet above

NGVD 29)

Well depth

(in feet)

Date

measured

1991 water 

level 

(in feet 

below land 

surface)

Date

measured

 2013 water 

level 

(in feet 

below 

land surface)1

2013 water 

level

(in feet 

above 

NGVD 29)

Difference 

between 

water level 

(in feet)2

Bienville Parish

Bi-12 230 350 – – 04-18-13 61.28 168.72 –

Bi-131 275 311 11-21-90 86.65 03-21-13 106.78 168.22 -20.13

Bi-194 200 477 – – 05-20-13 81.22 118.78 –

Bi-214 177 159 11-22-91 17.95 04-03-13 22.18 154.82 -4.23

Bi-215 270 215 11-22-91 47.49 03-21-13 55.67 214.33 -8.18

Bi-236 200 410 12-04-91 64.15 05-20-13 85.85 114.15 -21.70

Bi-276 270 336 12-04-91 99.40 04-29-13 98.40 171.60 1.00

Bi-9267Z 225 400 – – 05-20-13 71.62 153.38 –

Bossier Parish

Bo-136 155 180 11-12-91 14.45 04-09-13 11.58 143.42 2.87

Bo-265 220 258 11-12-91 74.22 04-26-13 53.93 166.07 20.29

Bo-454 170 220 11-14-91 8.99 03-19-13 8.00 162.00 0.99

Bo-495 200 250 – – 04-05-13 33.06 166.94 –

Bo-496 165 220 – – 04-05-13 19.52 145.48 –

Bo-510 167 200 – – 04-08-13 19.81 147.19 –

Caddo Parish

Cd-52 225 660 11-14-91 61.00 04-22-13 50.31 174.69 10.69

Cd-322 290 295 – – 04-09-13 59.69 230.31 –

Cd-375 250 275 – – 03-18-13 70.58 179.42 –

Cd-492 190 180 – – 03-25-13 49.19 140.81 –

Cd-546 202 215 – – 04-29-13 120.24 81.76 –

Cd-551 202 270 11-19-91 68.41 04-29-13 83.54 118.46 -15.13

Cd-582 260 212 – – 04-03-13 45.66 214.34 –

Cd-615 240 240 – – 04-29-13 102.53 137.47 –

Cd-696 210 170 11-19-91 14.70 04-08-13 15.27 194.73 -0.57

Cd-698 230 260 – – 04-02-13 122.17 107.83 –

Cd-712 270 200 12-03-91 22.98 04-03-13 23.78 246.22 -0.80

Cd-771 300 211 12-03-91 0.30 04-02-13 23.13 276.87 -22.83

Cd-789 268 190 – – 04-08-13 14.37 253.63 –

Cd-794 217 240 – – 04-08-13 29.33 187.67 –

Cd-812 190 200 12-02-91 83.15 03-19-13 71.52 118.48 11.63

Cd-823 150 160 – – 04-23-13 14.97 135.03 –

Cd-5221Z 160 250 – – 04-03-13 37.80 122.20 –

Cd-5925Z 221 57 – – 04-09-13 13.01 207.99 –

Cd-6189Z 260 180 – – 04-04-13 78.38 181.62 –

Cd-6742Z 182 150 – – 04-04-13 12.04 169.96 –

Cd-8080Z 340 220 – – 04-04-13 43.78 296.22 –

Cd-8226Z 225 71 – – 04-09-13 16.61 208.39 –

Cd-8687Z 180 140 – – 04-04-13 23.74 156.26 –

De Soto

DS-18 300 245 12-07-91 157.12 03-20-13 144.78 155.22 12.34

DS-329 265 258 – – 04-04-13 114.57 150.43 –

DS-351 310 400 12-17-91 78.82 03-19-13 63.80 246.20 15.02

DS-363 160 80 – – 04-10-13 114.88 45.12 –

DS-384 160 293 – – 04-10-13 116.65 43.35 –

Well

number

Altitude of 

land

surface

(feet above

NGVD 29)

Well depth

(in feet)

Date

measured

1991 water 

level 

(in feet 

below land 

surface)

Date

measured

 2013 water 

level 

(in feet 

below 

land surface)1

2013 water 

level

(in feet 

above 

NGVD 29)

Difference 

between 

water level 

(in feet)2

De Soto—Continued

DS-385 180 275 – – 04-10-13 120.55 59.45 –

DS-387 200 312 – – 04-11-13 13.08 186.92 –

DS-430 325 427 – – 04-11-13 126.44 198.56 –

DS-442 160 267 – – 04-10-13 106.60 53.40 –

DS-443 280 304 11-07-91 43.56 04-04-13 65.19 214.81 -21.63

DS-450 290 262 12-03-91 127.94 04-10-13 81.66 208.34 46.28

DS-473 300 340 – – 04-11-13 13.63 286.37 –

DS-504 280 260 12-05-91 68.52 03-19-13 47.74 232.26 20.78

DS-512 315 400 – – 04-23-13 21.87 293.13 –

DS-517 225 131 10-03-91 14.76 04-04-13 17.90 207.10 -3.14

DS-624 270 290 – – 04-23-13 32.40 237.60 –

DS-5442Z 345 260 – – 04-29-13 57.45 287.55 –

DS-6000Z 265 240 – – 04-11-13 60.24 204.76 –

DS-6134Z 181 260 – – 04-22-13 30.54 150.46 –

Natchitoches Parish

Na-339 130 140 12-11-91 43.08 03-21-13 -3.6 133.60 46.68

Na-357 248 469 – – 04-08-13 98.12 149.88 –

Na-479 210 106 – – 05-13-13 46.11 163.89 –

Na-491 250 493 11-06-91 97.50 03-21-13 117.05 132.95 -19.55

Na-529 120 540 12-12-91 flowing 04-03-13 -4.35 124.35 –

Na-537 170 115 11-06-91 79.65 05-14-13 58.02 111.98 21.63

Red River Parish

RR-263 140 181 12-11-91 33.29 03-21-13 26.00 114.00 7.29

RR-274 235 206 12-03-91 59.10 04-03-13 63.76 171.24 -4.66

RR-278 160 348 12-03-91 18.02 04-03-13 20.60 139.40 -2.58

Sabine Parish

Sa-103 220 170 – – 03-18-13 18.50 201.50 –

Sa-394 265 278 11-07-91 109.23 04-08-13 112.00 153.00 -2.77

Sa-395 210 293 12-12-91 8.53 04-29-13 16.95 193.05 -8.42

Sa-462 280 178 – – 03-18-13 103.14 176.86 –

Sa-465 265 80 – – 04-08-13 43.33 221.67 –

Webster Parish

Wb-257 180 116 – – 03-25-13 48.03 131.97 –

Wb-384 226 451 – – 03-26-13 108.93 117.07 –

Wb-385 224 398 11-14-91 144.55 03-26-13 95.58 128.42 48.97

Wb-434 215 356 – – 03-25-13 100.03 114.97 –

Wb-436 215 250 – – 03-19-13 112.73 102.27 -–

Wb-443 190 280 11-21-91 56.02 04-19-13 49.13 140.87 6.89

Wb-453 210 138 – – 03-20-13 56.38 153.62 –

1

A negative depth to water level indicates water level above land surface.

2

Negative (-) numbers indicate a decline in water level from the 1991 measurement to the 2013 measurement.

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3311

Potentiometric Surface, 2013, and Water-Level Differences, 1991–2013,

of the Carrizo-Wilcox Aquifer in Northwest Louisiana

By

Robert B. Fendick, Jr., and Kayla Carter

2015

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, 

Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://dx.doi.org/10.3133/sim3311

Suggested citation: Fendick, R.B., Jr, and Carter, Kayla, 2015, Potentiometric surface, 2013, and 

water-level differences, 1991–2013, of the Carrizo-Wilcox aquifer in northwest Louisiana: U.S. 

Geological Survey Scientific Investigations Map 3311, 1 sheet, http://dx.doi.org/10.3133/sim3311.

Printed on recycled paper

Prepared in cooperation with the

Louisiana Department of Natural Resources

The Carrizo Sand of Eocene age (fig. 2), the oldest formation of the Claiborne Group, is 

a discontinuous, massive sand that lies unconformably over the eroded surface of the Wilcox 

Group (Page and May, 1964). In northwestern Louisiana, the Wilcox Group is composed of an 

undifferentiated series of interbedded sands and clays mixed with sandy lignite layers. Because 

the Carrizo Sand and Wilcox Group are hydraulically connected, the units act as a single aquifer 

(Ryals, 1982) which is referred to as the “Carrizo-Wilcox aquifer.”

The Carrizo-Wilcox aquifer ranges in total thickness from zero feet (ft) in Caddo Parish 

to about 3,700 ft in southeastern Natchitoches Parish. In the study area, the thickness of the 

Carrizo Sand ranges from a few feet in Caddo Parish to about 130 ft in Natchitoches and 

Sabine Parishes. Individual sands in the Wilcox Group range in thickness from a few feet to 

115 ft. The Carrizo Sand contains medium to coarse sand, whereas the Wilcox Group contains 

very fine to medium sand (Ryals, 1982). The average hydraulic conductivity is about 27 feet 

per day (ft/d) for the Carrizo Sand and about 12 ft/d for the Wilcox Group (Page and May, 

1964). The lower hydraulic conductivities in the Wilcox Group are due to the limited areal 

extent of individual sands and variations in sand thickness, depth, grain size, and sorting.

The Carrizo-Wilcox aquifer crops out within most of the study area (fig. 3). Water in 

the Carrizo-Wilcox aquifer is under confined conditions except in the outcrop areas where 

water-table conditions occur. The aquifer is mostly horizontal within the recharge area but 

dips near the edge of the Sabine Uplift (fig. 1), a broad structural dome located in northwest 

Louisiana. Formations affected by the Sabine Uplift dip radially from the top of the dome in 

all directions (Page and May, 1964). Secondary structural features affecting the hydrogeologic 

system in the study area include a complex and extensive system of faults, probably the result 

of stresses induced by the Sabine Uplift (Rapp, 1996). Recharge occurs from infiltration of 

precipitation in areas where the aquifer crops out and from overlying aquifers including the Red 

River alluvial aquifer, Upland terrace aquifer, and the Sparta aquifer (fig. 2). Discharge from the 

Carrizo-Wilcox aquifer primarily is to pumping wells and to deposits of Quaternary age (Page 

and May, 1964). 

Introduction Hydrogeology

The Carrizo-Wilcox aquifer is the primary source of fresh groundwater for public 

supply as well as industrial, agricultural, and domestic uses in several parishes in 

northwestern Louisiana, including Bienville, Bossier, Caddo, De Soto, Natchitoches, 

Red River, Sabine, and Webster (fig. 1). In 2010, about 19 million gallons per day 

(Mgal/d) (table 1) were withdrawn from the Carrizo-Wilcox aquifer in Louisiana 

(Sargent, 2011). This is an increase of over 6 Mgal/d (table 1) from 1990 withdrawal 

amounts. The largest increase in withdrawals occurred in Caddo (3.79 Mgal/d) and De 

Soto Parishes (2.32 Mgal/d), whereas the largest decrease in withdrawals occurred in 

Natchitoches Parish (1.17 Mgal/d). Groundwater withdrawals from the Carrizo-Wilcox 

aquifer have caused water-level declines throughout much of the aquifer in the study 

area (fig. 1). Additional knowledge about the effects of withdrawals on water levels and 

flow directions in the Carrizo-Wilcox aquifer are needed to assess current conditions 

in the aquifer. In 2012, the U.S. Geological Survey (USGS) in cooperation with the 

Louisiana Department of Natural Resources began a study to document current water 

levels and water-level changes in selected aquifers.

This report presents data and maps that illustrate the potentiometric surface of the 

Carrizo-Wilcox aquifer during March–May 2013 and water-level differences from 

1991 to 2013. The potentiometric surface map (fig. 1) can be used for determining the 

direction of groundwater flow, hydraulic gradients, and effects of withdrawals on the 

groundwater resource. The rate of groundwater movement also can be estimated from 

the gradient when the hydraulic conductivity is applied. Water-level data collected for 

this study are stored in the USGS National Water Information System (NWIS) (http://

waterdata.usgs.gov/nwis) and are on file at the USGS office in Baton Rouge, La.

References

Cunningham, W.L., and Schalk, C.W., comps., 2011, 

Groundwater technical procedures of the U.S. Geological 

Survey: U.S. Geological Survey Techniques and Methods 

1–A1, 151 p. [Available online at http://pubs.usgs.gov/

tm/1a1/.]

Lovelace, J.K., 1991, Water use in Louisiana, 1990: 

Louisiana Department of Transportation and Development 

Water Resources Special Report no. 6, 131 p.

Lovelace, J.K., and Lovelace, W.M., 1995, Hydrogeologic 

unit nomenclature and computer codes for aquifers and 

confining units in Louisiana: Louisiana Department of 

Transportation and Development Water Resources Special 

Report no. 9, 12 p. 

National Climactic Data Center, 2014, Annual precipitation 

data—Red River Research Station (COOP 167738): 

National Oceanic and Atmospheric Administration, 

accessed September 30, 2014, at http://www.ncdc.noaa.

gov/cdo-web/.

Page, L.V., and May, H.G., 1964, Water resources of 

Bossier and Caddo Parishes, Louisiana: Department of 

Conservation, Louisiana Geological Survey, and Louisiana 

Department of Public Works Water Resources Bulletin no. 

5, 105 p.

Rapp, T.R., 1996, Ground-water resources of Caddo Parish, 

Louisiana, 1992: Louisiana Department of Transportation 

and Development Water Resources Technical Report no. 

58, 89 p.

Ryals, G.N., 1982, Regional geohydrology of the northern 

Louisiana salt-dome basin, part I, conceptual model and 

data needs: U.S. Geological Survey Open-File Report 

82–343, 23 p.

Sargent, B.P., 2011, Water use in Louisiana, 2010: State of 

Louisiana Department of Transportation and Development 

Public Works and Water Resources Division, Water 

Resources Section, U.S. Geological Survey Water 

Resources Special Report no. 17, 134 p.

Seanor, R.C., and Smoot, C.W., 1995, Louisiana groundwater map no. 8—Potentiometric surface, 1991, of the 

Carrizo-Wilcox aquifer in northwestern Louisiana: U.S. 

Geological Survey Water-Resources Investigations Report 

95-4176, 1 sheet.

Cook Mountain aquifer or

confining unit 

Sparta Sand Sparta aquifer or surficial

confining unit 

Claiborne Group

Cook Mountain

Formation 

(modified from Lovelace and others, 1995)

Cane River Formation Cane River aquifer or 

confining unit

Carrizo Sand

Carrizo-Wilcox aquifer or

surficial confining unit

Paleocene

Wilcox Group, undifferentiated

Midway Group, undifferentiated Midway confining unit

Tertiary

 Pliocene

Pliocene and Miocene aquifers are absent in this area

Vicksburg-Jackson

confining unit

Eocene

Jackson Group, undifferentiated

System Series Stratigraphic unit Hydrogeologic unit

Aquifer or confining unit

Quaternary

Holocene

and

Pleistocene

Red River alluvial deposits

Northern Louisiana terrace

deposits

Unnamed Pleistocene deposits

Red River alluvial aquifer or

surficial confining unit

Upland terrace aquifer or

surficial confining unit

Cockfield Formation Cockfield aquifer or surficial

confining unit 

Miocene

Oligocene Vicksburg Group, undifferentiated

?

Figure 2. Hydrogeologic column of aquifers in north Louisiana.

laf14-0658_fig03

Red River

Red River

CADDO

PARISH

BOSSIER

PARISH

DE SOTO

PARISH

WEBSTER

PARISH

SABINE

PARISH

NATCHITOCHES

PARISH

BIENVILLE

PARISH

Mansfield

Minden

Many

Natchitoches

Shreveport

RED RIVER

PARISH

94° 93°

33°

32°

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Difference between 1991 water 

level and 2013 water level, 

in feet

Outcrop area of the CarrizoWilcox aquifer

-25 to -15.1

-15 to -3.1

-3.0 to 3.0

3.1 to 15

15.1 to 50

Area of 

Enlargement

Study 

Area

LOUISIANA

MISSISSIPPI

TEXAS

GULF OF MEXICO

ARKANSAS

Figure 3. Water-level differences, 1991–2013, in the Carrizo-Wilcox aquifer in northwest Louisiana.

Table 1. Groundwater withdrawals from the Carrizo-Wilcox 

aquifer, in the study area, 1990 and 2010.

Parish

Withdrawals by parish

(million gallons per day)

1990 2010

Bienville 0.54 0.99

Bossier 2.07 2.39

Caddo 2.99 6.78

De Soto 1.79 4.11

Natchitoches 2.20 1.03

Red River 0.76 1.19

Sabine 1.57 1.81

Webster 1.38 1.03

Total 13.30 19.33

SABINE

PARISH

CADDO

PARISH

BOSSIER

PARISH

DE SOTO

PARISH

NATCHITOCHES

PARISH

BIENVILLE

PARISH

WEBSTER

PARISH

RED RIVER

PARISH

Many

Minden

Mansfield

Shreveport

Natchitoches

Mooringsport

Castor

Keithville

Toledo 

Bend 

Reservoir

Lake 

Bistineau

Caddo 

Lake

Cross 

Lake

Clear 

Lake

Black 

Lake

Ivan Lake

Kepler 

Creek

 Lake

Cypress 

Bayou

 Reservoir

Black 

Bayou

 Lake Paper 

Mill 

Pond

Red River

Black Lake Bayou

Bayou Dorcheat

Twelvemile Bayou

160

140

120

220

200

160

180

140

100

120

60

80

160 180

200

280260 240

280 260

240

220

200

160

140

180

120

100

180

160

140

120

180

160

DS-18

Cd-52

Wb-453

Wb-443

 Wb-434

Wb-384

Wb-257

Sa-465

Sa-462

Sa-395

Sa-394 Sa-103

RR-278

RR-274

RR-263

Na-529

Na-491

Na-357

Na-339

DS-517

DS-512

DS-504

DS-473

DS-450

DS-443

DS-442 DS-430

DS-387

DS-385

DS-384

DS-363

DS-351

DS-329

Cd-823 Cd-812

Cd-794

Cd-771

Cd-712

Cd-698

Cd-696

Cd-615

Cd-582

Cd-546

Cd-492

Cd-375

Cd-322

Bo-510 Bo-496

Bo-454 Bo-265

Bo-136

Bi-236

Bi-215

Bi-214

Bi-194

Bi-131 Bi- 12

DS-6134Z

DS-6000Z

DS-5442Z

Cd-8687Z

Cd-8080Z

Cd-6742Z

Cd-6189Z

Cd-5221Z

Bi-9267Z

Cd-551

Cd-8226Z

Bi- 276

Na-479

Bo-495

Wb-385

 Wb-436

DS-624

Cd-5925Z

Na-537

94° 93°

33°

32°

0 10 20 MILES

0 10 20 KILOMETERS

Area of 

enlargement

Study 

area

LOUISIANA

MISSISSIPPI

T

E

X

A

S

GULF OF MEXICO

ARKANSAS

EXPLANATION

Eastern edge of the Sabine Uplift

General direction of groundwater flow

Potentiometric contour—Shows altitude at which

 water level would have stood in tightly cased

 wells. Dashed where approximately located.

 Contour interval 20 feet. Datum is National

 Geodetic Vertical Datum of 1929 

Control point

Observation well for which hydrograph is shown

Approximate downdip limit of freshwater

 in the Carrizo-Wilcox aquifer system—Freshwater is

 defined as water containing less than 250 milligrams

 per liter of chloride. (Modified from Seanor and Smoot, 1995) 

Sa-465

RR-278

220

Recharge area for the Carrizo-Wilcox aquifer

Figure 1. Potentiometric surface of the Carrizo-Wilcox aquifer in north-central Louisiana, March–May 2013.

ISSN 2329-1311

ISSN 2329-132X

http://dx.doi.org/10.3133/sim3311