U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the Arkansas Natural Resources Commission

Effects of Recent Climate Variability on Groundwater Levels 

in Eastern Arkansas

Scientific Investigations Report 2012–5258
Cover: Approaching storm wall cloud, Prairie County, Arkansas, May 25, 2011 (photograph by John B. 

Czarnecki, U.S. Geological Survey).
Effects of Recent Climate Variability on 

Groundwater Levels in Eastern Arkansas

By John B. Czarnecki and T.P. Schrader

Prepared in cooperation with the Arkansas Natural Resources Commission

Scientific Investigations Report 2012–5258

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: 2013

This and other USGS information products are available at http://store.usgs.gov/

U.S. Geological Survey

Box 25286, Denver Federal Center

Denver, CO 80225

To learn about the USGS and its information products visit http://www.usgs.gov/

1-888-ASK-USGS

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:

Czarnecki, J.B., and Schrader, T.P., 2013, Effects of recent climate variability on groundwater levels in eastern 

Arkansas: U.S. Geological Survey Scientific Investigations Report 2012–5258, 17 p.
iii

Contents

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

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

Methods ..........................................................................................................................................................1

Water-Level Monitoring Network ..............................................................................................................3

Effects of Recent Climate Variability on Groundwater Levels ...............................................................3

Water Use and Conservation ......................................................................................................................7

Groundwater Depletion ..............................................................................................................................10

Long- and Short-Term Water-Level Changes: A Case for Continuous Monitoring ..........................14

Future Water-Level Monitoring ................................................................................................................16

Summary .......................................................................................................................................................17

References Cited .........................................................................................................................................17

Figures

1. Graph showing annual precipitation for Adams Field in Little Rock, Arkansas, 

for the period 1878 to 2010 ..........................................................................................................2

2. Maps showing four-year water-level difference in the Mississippi River Valley 

alluvial aquifer in eastern Arkansas (A) 2004–8, and (B) 2006–10 .......................................4

3. Map showing active water-level monitoring network in Arkansas County, 

Arkansas, and vicinity .................................................................................................................6

4. Histogram of differences in water-level altitudes for the alluvial aquifer in 

eastern Arkansas .........................................................................................................................7

5. Map showing percentage of water use in 2008 from the alluvial aquifer in 

eastern Arkansas .........................................................................................................................8

6. Graph showing groundwater use in Arkansas County, 1965 to 2009 ..................................9

7. Photograph showing tailwater recovery reservoir in Prairie County .................................9

8. Photograph showing polypipe used for irrigation of a soybean field ...............................10

9. Map showing simulated altitude of the bottom of the northern part of the 

alluvial aquifer from the model of Czarnecki .........................................................................11

10. Map showing simulated water-level altitude in 2010 ..........................................................12

11. Map showing simulated thickness for the Mississippi River Valley alluvial 

aquifer, 2010 ................................................................................................................................13

12. Graph showing periodic depth-to-water measurements made in Arkansas 

County well 04S03W32BCB1 completed in the alluvial aquifer, 1937 to 2010 ..................14

13. Graph showing continuous depth-to-water measurements made in Arkansas 

County well 03S04W03DCA16, completed in the alluvial aquifer, 2000 to 2011 ...............15

14. Hydrograph of Arkansas County well 04S05W05ACC1 completed in the 

Sparta aquifer showing substantial decline in water levels from 1948 to 2010 ..............16
iv

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

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

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3) 

Flow rate

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

foot per year (ft/yr) 0.3048 meter per year (m/yr)

million gallons per day (Mgal/d) 3.7853 million liters per day (ML/d)

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

(NAVD 29).

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

Altitude, as used in this report, refers to distance above the vertical datum.
Effects of Recent Climate Variability on Groundwater 

Levels in Eastern Arkansas

By John B. Czarnecki and T.P. Schrader

Abstract

Water-level fluctuations in wells completed in the 

Mississippi River Valley alluvial aquifer in eastern Arkansas 

were compared to variability in annual precipitation, an 

indicator of climate variability. The wettest year on record in 

Little Rock, Arkansas, occurred in 2009 with 81.79 inches of 

precipitation compared to an average of 47.1 inches per year. 

In contrast, 2005 and 2010 were the 7th and 14th driest years 

on record with 34.55 and 36.52 inches per year, respectively. 

This variability in precipitation was reflected in water-level 

altitude changes between 2004 and 2008 and 2006 and 2010. 

Generally, drier conditions between 2004 and 2008 led to an 

average decline in water levels of 1.62 feet, whereas wetter 

conditions between 2006 and 2010 led to an average rise in 

water levels of 1.36 feet. Drier periods likely resulted in less 

recharge compared to wetter periods. Groundwater use from 

the alluvial aquifer peaked in 2000 and has since declined, 

in part, because of conservation measures and substantial 

reduction in aquifer saturated thickness. Groundwater-flow 

model results showed some areas of the alluvial aquifer 

simulated as dry in 2010, indicating a reduced capacity of 

the alluvial aquifer to produce water in those areas. Additional 

factors affecting groundwater use include the types of crops 

grown in an area and the availabitiliy of crop subsidies. 

Real-time continuous water-level measurements in wells 

allow for a more accurate assessment of the effect of 

variability in precipitation and water use than periodic waterlevel measurements.

Introduction

Arkansas experienced wide extremes in climate 

variability during the period of 2005 to 2010, recording 

the largest annual precipitation ever recorded in the State 

(100.05 inches [in.]) in 2009 (National Weather Service, 

2012). Many weather stations across the State reported 

between 80 to 90 in. of rainfall in 2009. For comparison, the 

average annual precipitation in Little Rock, Arkansas for the 

period 1878 to 2010 was 47.1 in. (fig. 1). In contrast, 2005 

and 2010 were the 7th and 14th driest years on record in Little 

Rock with 34.55 and 36.52 in., respectively; both tied as the 

hottest years ever recorded in Arkansas (National Oceanic 

and Atmospheric Administration, 2011). The wettest year on 

record in Little Rock (2009) occurred between these dry years, 

with a total of 81.79 in. Fifteen out of a total of 60 National 

Oceanic and Atmospheric Administration weather stations 

within the State ranked 2009 as the wettest year on record 

(National Weather Service, 2012).

Extremes in annual precipitation rates may lead to greater 

variability in groundwater-recharge rates and water use, 

particularly in the agricultural areas in eastern Arkansas that 

rely heavily on groundwater produced from the Mississippi 

River Valley alluvial aquifer (hereafter referred to as the 

alluvial aquifer). Are the effects of climate variability 

discernable in measured water levels in wells? 

The purpose of this report, which was prepared 

in cooperation with the Arkansas Natural Resources 

Commission, is to attempt to answer this question by 

reviewing water-level and water-use data in eastern Arkansas 

in the context of climate variability reflected by changes in 

annual precipitation. The report also reviews the benefits of 

continuous water-level monitoring as well as factors affecting 

water use. The period for precipitation data extends back 

to 1878, and water-level altitude data extend back to 1937. 

Emphasis was placed on water-level changes and annual 

precipitation from spring 2004 through spring 2010 in the 

alluvial aquifer. Because conservation measures and reduction 

in aquifer saturated thickness can have effects on water 

use (and therefore water levels), the report discusses these 

confounding factors related to the analysis of the effects of 

climate variability on groundwater levels.

Methods

Precipitation data were compiled from the National 

Weather Service (2011) for Adams Field at Little Rock 

National Airport in Little Rock, Arkansas, and presented 

as annual totals for the period 1878 to 2010. Adams Field 

precipitation data were used because that station has the 

longest continuous dataset and is located on the west-central 

edge of the alluvial aquifer. Average annual precipitation was 
2 Effects of Recent Climate Variability on Groundwater Levels in Eastern Arkansas

0

1880 1900 1920 1940 1960 1980 2000 2020

10

20

30

40

50

60

70

80

90

Annual precipitation, in inches

Year

2010 – 36.52 inches (14th driest year)

2005 – 34.55 inches (7th driest year)

2009 – 81.79 inches (wettest year)

Average precipitation: 47.1 inches/year

1860

Figure 1. Annual precipitation for Adams Field in Little Rock, Arkansas, for the period 1878 to 2010 (National Weather Service, 2011). 
Effects of Recent Climate Variability on Groundwater Levels 3

calculated for that dataset to compare against extreme amounts 

for the period 2004 through 2010. Annual precipitation 

amounts were sorted and ranked relative to the wettest and 

driest years. 

Water-level data from the U.S. Geological Survey 

National Water Information System (NWIS) from 659 wells in 

eastern Arkansas were used to compute spatial and temporal 

changes in water-level altitude within the alluvial aquifer in 

eastern Arkansas from 2004 to 2008 and from 2006 to 2010 

(fig. 2). The alluvial aquifer in Arkansas defines the extent 

of the study area. Hydrographs showing water-level altitude 

plotted against time were compiled for three wells to illustrate 

changes in water levels and to compare the temporal resolution 

provided by continuous water-level daily averages compared 

to periodic measurements made every other year in the spring. 

As an example of the information obtained in the study area, 

a screen capture of the active water-level-data collection 

network in Arkansas County was downloaded from the 

internet to show the locations of wells for which hydrographs 

were obtained. Included in the download were: (1) realtime wells from which hourly water-level measurements are 

downloaded to the internet every 6 hours; (2) continuous 

wells from which hourly water-level measurements are made 

automatically but require site visits to retrieve the data; and 

(3) periodic-measurement wells are measured manually using 

an electric tape at intervals that typically recur every other 

year in the spring prior to the irrigation season. Well locations 

are depicted (fig. 2) by colored points that represent the most 

recent water level at the time of the download as it occurs 

within the percentile class for all the measurements at a well.

Water-use data were compiled by county for the alluvial 

aquifer. Total water use from the alluvial aquifer in 2008 

was provided through the Aggregate Water-Use Data System 

(AWUDS) (U.S. Geological Survey, 2012). 

Water-Level Monitoring Network

The U.S. Geological Survey (USGS) monitors 

water levels in about 1,100 water wells throughout 

Arkansas in conjunction with the Arkansas Natural Resources 

Commission, Arkansas Geological Survey, Union County 

Conservation District, and U.S. Department of Agriculture 

Natural Resources Conservation Service. Water levels from 

659 wells completed in the alluvial aquifer were measured 

during the spring prior to the irrigation season to allow the 

water level in a well to stabilize and to better reflect conditions 

within the aquifer. Arkansas County (fig. 3) is one of several 

areas in the State that has experienced substantial declines in 

water levels because of groundwater pumping for irrigation 

(Schrader, 2010). Periodic and continuous water levels 

are monitored as part of the USGS water-level monitoring 

network.

Effects of Recent Climate Variability on 

Groundwater Levels

Between 2004 and 2010, water levels generally 

declined and then rose similar to annual precipitation 

(fig. 1). Water-level change maps generated using waterlevel data collected 4 years apart (Schrader, 2010) are shown 

in figure 2. Such maps are useful in observing regional 

trends in water levels that might correlate with changes in 

recharge and water-use rates. Water levels decreased an 

average of 1.62 ft (ft) in eastern Arkansas with a median 

value of 2.00 ft between 2004 and 2008, in part, as a result 

of the small amount of precipitation in 2005. Water levels 

rose an average of 1.36 ft with a median value of 0.82 ft 

between 2006 and 2010, resulting from the record amount 

of precipitation in 2009. From 2004 to 2008, water levels 

in most wells decreased 0 to 6 ft, whereas from 2006 to 

2010, water levels in most wells increased 0 to 4 ft (fig. 4). 

The average increase in water levels of about 3 ft between 

dry (2004 to 2008) and wet (2006 to 2010) periods represents 

an approximate increase in groundwater storage of about 

10 million acre-ft, assuming a specific yield of 0.3 and an 

area covered by the alluvial aquifer of 17,000 square miles 

(mi2). Available water-level data were sufficient to show 

that water-level change on a regional scale was affected by 

climate variability.
4 Effects of Recent Climate Variability on Groundwater Levels in Eastern Arkansas

A

Western extent of 

alluvial aquifer 

and study area

EXPLANATION

Water-level difference, in feet

Less than -2

-1.9 to -0.5

-0.49 to +0.49

0.5 to 2

Greater than 2

92o

36o

35o

34o

33o

Base from U.S. Geological Survey digital data, 1:100,000

0 15 30 60 MILES

0 15 30 60 KILOMETERS

91o 90o

Figure 2. Four-year water-level difference in the Mississippi River Valley alluvial aquifer in eastern Arkansas (A) 2004–8, and (B) 2006–

10. 
Effects of Recent Climate Variability on Groundwater Levels 5

B

Western extent of 

alluvial aquifer 

and study area

EXPLANATION

Water-level difference, in feet

Less than -2

-1.9 to -0.5

-0.49 to +0.49

0.5 to 2

Greater than 2

92o

36o

35o

34o

33o

Base from U.S. Geological Survey digital data, 1:100,000

0 15 30 60 MILES

0 15 30 60 KILOMETERS

91o 90o

Figure 2. Four-year water-level difference in the Mississippi River Valley alluvial aquifer in eastern Arkansas (A) 2004–8, and (B) 2006–

10.—Continued
6 Effects of Recent Climate Variability on Groundwater Levels in Eastern Arkansas

Figure 3. Active water-level monitoring network in Arkansas County, Arkansas, and vicinity (U.S. Geological Survey, 2011).

92o

34o30’

34o

91o

Base from Google Earth, 2011 0 15 30 60 MILES

0 15 30 60 KILOMETERS

34o

Well 04S05W05ACC1 (fig. 14)

Well 03S04W03DCA16 (fig. 13)

Well 04S03W32BCB1 (fig. 12)

Low Decreasesing

Increasing

Normal

Less than 10

10-24

25-75

76-90

Greater than 90

High

Not rated

EXPLANATION

Percentile classes

(symbol color based on 

most recent measurement)

Real time

Arkansas County 

boundary

Well type

Continuous

Periodic measurements
Water Use and Conservation 7

Water Use and Conservation

Observed water-level rises between 2006 and 2010 

resulted, in part, from reduced water use. Record precipitation 

rates in 2009 likely resulted in decreased water use. A total 

of 7.87 million acre-ft (3.43 billion gallons) of groundwater 

was pumped from the alluvial aquifer in 2008 compared to 

a total of 0.17 million acre-ft (7.4 billion gallons) from the 

Sparta aquifer (Terrance E. Holland, U.S. Geological Survey, 

written commun., 2011). In 2009, total groundwater pumpage 

from the alluvial aquifer decreased by 22.9 percent to 6.07 

million acre-ft (2.64 billion gallons), and from the Sparta 

aquifer by 17.6 percent to 0.144 million acre-ft (6.27 billion 

gallons) (Terrance E. Holland, U.S. Geological Survey, written 

commun., 2012). The five largest water users, by county, 

of all the water pumped from the alluvial aquifer in 2008 

were Clay (9.2 percent), Poinsett (9.0 percent), Cross (7.8 

percent), Jackson (5.6 percent), and Arkansas (5.4 percent) 

Counties (fig. 5). A closer inspection of water use in Arkansas 

County (fig. 6) shows that water use peaked in 2000, and 

had the second largest water use by county (8.6 percent) 

from the alluvial aquifer with Poinsett County ranking first 

with 9.0 percent of the total water use (Terrance E. Holland, 

U.S. Geological Survey, written commun., 2011). Reasons 

for the subsequent decline in water use in Arkansas County 

from 2000 to 2009 may include use of water-conservation 

methods such as tailwater recovery reservoirs (fig. 7) and 

plastic polypipe (fig. 8) (Terrance E. Holland, U.S. Geological 

Survey, oral commun., 2011). Tailwater recovery reservoirs 

store runoff water from irrigation and precipitation from 

nearby farm fields, and water is recycled into the irrigation 

system. Polypipe is an efficient method of water application 

allowing for more accurate and even application of irrigation 

water. In addition to conservation practices, less waterintensive crops may have been planted or less water used 

because of higher energy costs, but data for these explanations 

were not analyzed for this study.

EXPLANATION

2006 to 2010

2004 to 2008

0

20

40

60

80

100

120

140

160

180

Number of occurrences

Difference in groundwater-level altitude, in feet

-28 -18 -16 -14 -12 -10 -8 -6 -4 -2 0246 8 10 12 14 16 18 20

Figure 4. Differences in water-level altitudes for the alluvial aquifer in eastern Arkansas.
8 Effects of Recent Climate Variability on Groundwater Levels in Eastern Arkansas

Figure 5. Percentage of water use in 2008 from the alluvial aquifer in eastern Arkansas.
Water Use and Conservation 9

Sparta aquifer

EXPLANATION

Alluvial aquifer

0

100

200

300

400

500

600

Ground

water use, in million gallons per day 

Year

1965 1970 1975 1980 1985 1990 1995 2000 2005 2008 2009

Figure 6. Groundwater use in Arkansas County, 1965 to 2009.

Figure 7. Tailwater recovery reservoir in Prairie County.
10 Effects of Recent Climate Variability on Groundwater Levels in Eastern Arkansas

Figure 8. Polypipe used for irrigation of a soybean field.

Groundwater Depletion

Although conservation measures have resulted in declines 

in pumping in Arkansas County since 2000, a large component 

of the decline in pumping is the result of farmers being unable 

to pump sufficient water from the alluvial aquifer. Waterlevel declines have caused reduced saturated thickness in the 

alluvial aquifer, which translates into reduced transmissivity 

and ultimately less flow to wells, making groundwater 

pumping uneconomical and impractical in some areas (Dennis 

Carman, White River Irrigation District, oral commun., 2011). 

Using a groundwater-flow model of the northern part of the 

alluvial aquifer (Czarnecki, 2010), saturated thickness in 2010 

was calculated by subtracting the altitude of the bottom of the 

aquifer (fig. 9) from the simulated water-level altitude in 2010 

(fig. 10). The 2010 simulated saturated thickness in Arkansas 

County contained many areas that are 20 ft or less; some parts 

of the alluvial aquifer in Arkansas County were simulated as 

dry in 2010 (fig. 11).
Groundwater Depletion 11

260

220

180

140

100

60

20

-20

EXPLANATION

Simulated altitude of the 

bottom of the alluvial

aquifer, in feet above 

Geodetic Vertical Datum

of 1929

92o

36o

35o

34o

Base from U.S. Geological Survey digital data, 1:100,000

Datum is National Geodetic Vertical Datum of 1929.

0 15 30 60 MILES

0 15 30 60 KILOMETERS

91o 90o

Figure 9. Simulated altitude of the bottom of the northern part of the alluvial aquifer from the model of Czarnecki (2010).
12 Effects of Recent Climate Variability on Groundwater Levels in Eastern Arkansas

310

270

190

150

110

70

30

230

EXPLANATION

Simulated water-level 

altitude, in feet above 

Geodetic Vertical Datum

of 1929

Dry model cells

92o

36o

35o

34o

Base from U.S. Geological Survey digital data, 1:100,000

Datum is National Geodetic Vertical Datum of 1929.

0 15 30 60 MILES

0 15 30 60 KILOMETERS

91o 90o

Figure 10. Simulated water-level altitude in 2010.
Groundwater Depletion 13

Figure 11. Simulated thickness for the Mississippi River Valley alluvial aquifer, 2010. 

92o

36o

35o

34o

91o 90o

Base from U.S. Geological Survey digital data, 1:100,000

160

180

140

120

100

80

60

40

20

EXPLANATION

Saturated 

thickness, in feet

Dry model cells
14 Effects of Recent Climate Variability on Groundwater Levels in Eastern Arkansas

Long- and Short-Term Water-Level 

Changes: A Case for Continuous 

Monitoring

Water-level monitoring is essential for evaluating trends 

in water levels with time. Water-level declines have been 

observed in the alluvial aquifer in Arkansas County since 

at least 1937 (fig. 12). Water-level declines vary with time 

and location. Continuous water-level data, as exemplified by 

hydrographs (figs. 13 and 14) from the 25 wells continuously 

monitored in Arkansas, provide a better understanding of 

the seasonal and long-term trends in water levels. To assess 

the trends in these data, linear regression analysis was used 

to generate regression lines (Helsel and Hirsch, 1992). This 

analysis assumes that water-level altitude is dependent only on 

one variable (time). The general equation for each regression 

line can be written as 

y = mx + b (1)

where

y is the dependent variable (water-level altitude, 

in feet), 

m is the slope (rate of water-level change with 

time, in feet per year), 

x is the independent variable (time, in years), 

and 

b is the y-axis intercept (water-level altitude, in 

feet). 

The slope and y-axis intercept are estimated for each 

regression line so as to minimize the difference between the 

observed and predicted water-level altitudes. Despite the 

seasonal effects, regression lines through the continuous 

water-level data for periods 2000–6, 2006–9, and 2009–11 

show declines (fig. 13). In 2010, water levels appear to have 

rebounded somewhat, possibly as a result of wetter conditions 

in 2009 coupled with less groundwater use. Furthermore, the 

average rate of water decline following the wettest year (2009) 

was only 0.02 ft/yr from 2009 to 2011, compared to a decline 

of 0.22 ft/yr from 2000 to 2006 and a decline of 0.34 ft/yr 

from 2006 to 2009. 

60

70

80

90

100

110

120

130

140

Year

Depth to 

water, in feet

04S03W32BCB1, Arkansas Co.

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Figure 12. Periodic depth-to-water measurements made in Arkansas County well 04S03W32BCB1 completed in the alluvial aquifer, 

1937 to 2010 (see figure 3 for location). 
Long- and Short-Term Water-Level Changes: A Case for Continuous Monitoring 15

As wells in some areas produce less water from the 

alluvial aquifer, reliance on the deeper Sparta aquifer occurs 

to make up for some, but not all, of the unmet demand (fig. 6). 

Although pumping decreased in the alluvial and Sparta 

aquifers between 2000 and 2005, the decrease in the alluvial 

aquifer pumping was larger. From 2000 to 2005, pumping 

in Arkansas County from the alluvial aquifer decreased by 

86.64 million gallons per day (Mgal/d), or 15.5 percent 

reduction from that aquifer compared to a reduction of 

60.72 Mgal/d from the Sparta aquifer (a 62.8 percent 

reduction from 2000 rates for that aquifer). However, from 

2005 to 2008, pumping from the alluvial aquifer decreased 

93.08 Mgal/d (28.6 percent) compared to an increase in 

pumping from the Sparta aquifer of 5.02 Mgal/d (5.2 percent). 

Drawdown in the Sparta aquifer has been considerable 

as indicated by the hydrograph for well 04S05W05ACC1 in 

Arkansas County (fig. 14). Periodic measurements were made 

in this well between 1948 and 2005, and during this time water 

levels dropped about 116 ft. Because the measurements were 

not sufficiently frequent, seasonal water-level fluctuations 

could not be observed. Beginning in August 2007, frequent, 

hourly water-level measurements were recorded in the well 

and showed that annual changes in water levels generally 

exceeded 50 ft. Water levels in 2009 (the wettest year on 

record) fluctuated only 40 ft, compared to 73 ft in 2010 

(14th driest year on record). Without continuous water-level 

measurements, a comparison of the effect of wet and dry 

years on water-level changes would have been less accurate. 

Although the well is not pumped, it does respond to waterlevel changes in the Sparta aquifer caused largely by seasonal 

pumping from irrigation wells located about 1 to 2 miles 

away. Periodic measurements made in well 04S05W05ACC1 

confirm the accuracy of the continuous measurements 

(fig. 14); however, without the hourly continuous 

measurements there would have been little incentive to 

perform the confirmatory, periodic measurements because the 

cyclic water-level changes caused by seasonal pumping would 

have gone unobserved. Real-time continuous water-level 

measurements provide a better representation of the waterlevel changes occurring within the aquifer, which then can be 

evaluated in the context of potential causes such as seasonal 

changes in pumping rates or wetter/drier climatic conditions. 

97

98

99

100

101

102

103

104

Depth to

water, in feet

Year

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

2000 to 2006 

rate of water-level 

decline: 0.22 feet/year

2006 to 2009

rate of water-level

decline: 0.34 feet/year 2009 to 2011 

rate of water-level 

decline: 0.02 feet/year

Figure 13. Continuous depth-to-water measurements made in Arkansas County well 03S04W03DCA16, completed in the alluvial 

aquifer, 2000 to 2011 (see figure 3 for location).
16 Effects of Recent Climate Variability on Groundwater Levels in Eastern Arkansas

In addition, real-time continuous water-level measurements 

generally are obtained at a reduced cost per measurement 

compared to periodic measurements made manually and allow 

for offsite evaluation of measurement equipment and well 

conditions without having to visit the well site.

Future Water-Level Monitoring

The water-level monitoring network is a vital component 

for understanding and managing the groundwater resources 

in Arkansas. Although the program has been effective 

in providing reliable water-level data, improvements are 

possible. One such improvement would be to increase the 

distribution of continuous monitoring wells, particularly in 

counties with Critical Groundwater Areas (Arkansas Natural 

Resources Commission, 2011) that pump groundwater from 

the alluvial or Sparta aquifers. By increasing the distribution 

of continuous monitoring wells, a better understanding of 

how quickly water levels in the alluvial and Sparta aquifers 

respond to climate variability and changes in water use 

will be possible—particularly the anticipated reductions 

in groundwater use associated with the Grand Prairie Area 

Demonstration Project (U.S. Army Corps of Engineers, 

2012), which will divert water from the White River to supply 

irrigation water to Arkansas, Prairie, and Lonoke Counties. 

As demands on groundwater resources continue, it will be 

more important to continuously monitor changes in water 

levels, which will provide water managers with accurate and 

timely information to help protect these vital resources for 

future generations.

0

50

100

150

200

250

Year

Depth to

water, in feet

Continuous hourly measurements

EXPLANATION

Periodic measurements

1945 1955 1965 1975 1985 1995 2005

Figure 14. Hydrograph of Arkansas County well 04S05W05ACC1 completed in the Sparta aquifer showing substantial decline in water 

levels from 1948 to 2010 (see figure 3 for location).
References Cited 17

Summary

Water levels in wells completed in the Mississippi 

River Valley alluvial aquifer and the Sparta aquifer in eastern 

Arkansas respond to variability associated with annual 

precipitation. The wettest year on record in Little Rock, 

Arkansas, occurred in 2009 with 81.79 inches of precipitation 

compared to an average of 47.1 inches per year (in/yr). In 

contrast, 2005 and 2010 were the 7th and 14th driest years 

on record with 34.55 and 36.52 in/yr, respectively. This 

variability in precipitation was reflected in water-level 

altitude changes between 2004 and 2008 and 2006 and 2010. 

Generally, drier conditions between 2004 and 2008 led to an 

average decline in water levels in eastern Arkansas of 1.62 feet 

(ft), whereas, wetter conditions between 2006 and 2010 led 

to an average rise in water levels of 1.36 ft. Drier periods 

likely result in less recharge compared to wetter periods. 

Groundwater use from the alluvial aquifer peaked in 2000 

and has been on the decline, in part, because of conservation 

measures and substantial reduction in aquifer saturated 

thickness. Groundwater-flow model results show some areas 

of the alluvial aquifer simulated as dry in 2010, resulting in 

reduced capacity of the alluvial aquifer to produce water in 

those areas. Periodic and real-time continuous water-level data 

show substantial changes in the alluvial and Sparta aquifers. 

However, real-time continuous water-level measurements 

allow for a more complete and accurate assessment of 

water-level changes resulting from the effect of variability 

in precipitation and water use than do periodic water-level 

measurements.

References Cited

Arkansas Natural Resources Commission, 2011, The facts 

about critical ground water designation: Arkansas Natural 

Resources Commission, accessed February 15, 2012, 

at http://www.arkansas.gov/awwcc/gw_designation_

graphic.pdf.

Czarnecki, J.B., 2010, Groundwater-flow assessment of the 

Mississippi River Valley alluvial aquifer of northeastern 

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