U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3135

February 2013

Drought and Deluge: Effects of Recent Climate Variability on 

Groundwater Levels in Eastern Arkansas

Printed on recycled paper

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) was interspersed within these dry years, with 

a total of 81.79 in. Fifteen 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). How does this variability affect the groundwater 

system and water use therein? Are the effects of this variability 

discernable in measured water levels in wells? Czarnecki and 

Schrader (2012) examined these questions and provided some 

insights, the results of which are presented here.

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 in about 600 wells completed in the 

alluvial aquifer are 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. 2) is one of several areas in the State that has 

experienced substantial declines in water levels because of 

groundwater pumping for irrigation. 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 water-level data collected 4 years 

apart (Schrader, 2010) are shown in figure 3. 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 feet (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 waterlevel data were sufficient to show that water-level change on a 

regional scale was affected by climate variability. 

Figure 1. Precipitation for Adams Field in Little Rock, Arkansas, 

for the period 1878 to 2010 (National Weather Service, 2011). 

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 2. Active water-level monitoring network in Arkansas County, Arkansas and vicinity.

Figure 3. Four-year water-level difference in the Mississippi River Valley alluvial aquifer in eastern Arkansas (A) 2004–8, and (B) 2006–10. 

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

o19 o09

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

o19 o09

0 0351 SELIM 06

0 15 30 60 KILOMETERS

92o

34o30’

34o

91o

Base from Google Earth, 2011

34o

Well 04S05W05ACC1 (fig. 14)

Well 03S04W03DCA16 (fig. 13)

Well 04S03W32BCB1 (fig. 12)

EXPLANATION

Low Decreasesing

Increasing

Normal

Less than 10

10-24

25-75

76-90

Greater than 90

High

Not rated

Percentile classes

(symbol color based on 

most recent measurement)

Real time

Arkansas County 

boundary

Well type

Continuous

Periodic 

 measurements
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 of groundwater was pumped from the 

alluvial aquifer in 2008 compared to a total of 0.17 million 

acre-ft from the Sparta aquifer. In 2009, total groundwater 

pumpage from the alluvial aquifer decreased by 22.9 percent to 

6.07 million acre-ft, and from the Sparta aquifer by 17.6 percent 

to 0.144 million acre-ft (Czarnecki and Schrader, 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). 

The occurrence of record precipitation in 2009 is insufficient 

to explain the decline in water use in Arkansas County since 

2000. Reasons for the subsequent decline in water use in 

Arkansas County from 2000 to 2009 may include use of 

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 water-intensive 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.

Effect of Groundwater Depletion on Water Use

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 alluvial aquifer, saturated 

thickness in 2010 was calculated by subtracting the altitude of 

the bottom of the aquifer from the simulated water-level altitude 

in 2010 (Czarnecki, 2010; Czarnecki and Schrader, 2012). 

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. 9). 

Figure 4. Differences in water-level altitudes for the alluvial 

aquifer in eastern Arkansas.

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 5. Percentage of water use in 2008 from the alluvial aquifer 

in eastern Arkansas.

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

92o

36o

35o

34o

33o

9 o1 9 o0
Figure 9. Simulated saturated thickness for the Mississippi River 

Valley alluvial aquifer, 2010. 

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. 10). Water-level declines vary with time 

and location. Continuous water-level data, as exemplified 

by hydrographs (figs. 11 and 12) from the 25 continuously 

monitored wells, 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 (Czarnecki and Schrader, 2012). This analysis 

assumes that water-level altitude is dependent only on one 

variable (time). 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, 2006–8, and 2009–11 

show declines (fig. 11). 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 

Sparta aquifer

EXPLANATION

Alluvial aquifer

0

100

200

300

400

500

600

Groundwater use, in million gallons per day 

Year

5691 198019751970 199519901985 9002800250020002

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

Figure 7. Tailwater recovery reservoir in Prairie County. 

Photograph by John B. Czarnecki, U.S. Geological Survey.

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

Photograph by Ralf Montanus, U.S. Geological Survey.

92o

36o

35o

34o

o19 o09

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
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. 

As wells produce less water in some areas 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 86.64 million 

gallons per day (Mgal/d) compared to a reduction of 60.72 

Mgal/d from the Sparta aquifer. However, from 2005 to 2008, 

pumping from the alluvial aquifer decreased 93.08 Mgal/d 

compared to an increase in pumping from the Sparta aquifer of 

5.02 Mgal/d. 

Drawdown in the Sparta aquifer has been considerable 

as indicated by the hydrograph for well 04S05W05ACC1 

in Arkansas County (fig. 12). 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 (the 

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. 12); 

however, without the 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. Realtime continuous water-level measurements provide a better 

representation of the water-level 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. 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 

Figure 10. Periodic depth-to-water measurements made in well 

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

60

70

80

90

100

110

120

130

140

Year

Depth to water, in feet

04S03W32BCB1, Arkansas Co.

1935194019451950195519601965197019751980198519901995

200020052010

Figure 11. Continuous depth-to-water measurements made in well 

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

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 12. Arkansas county hydrograph from a well completed in 

the Sparta aquifer showing substantial decline in water levels from 

1948 to 2010 (from Schrader, 2010).

0

50

100

150

200

250

Year

Depth to water, in feet

Continuous hourly measurements

EXPLANATION

Periodic measurements

58915791569155915491 1995 5002
Publishing support provided by

Lafayette Publishing Service Center

For additional information, contact 

Director, USGS Arkansas Water Science Center 

401 Hardin Road 

Little Rock, Arkansas 72211 

501–228–3600 

Email: dc_ar@usgs.gov 

Or visit the Arkansas Water Science Center Web site at: 

http://ar.water.usgs.gov 

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.

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 1.38 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 that 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 

Arkansas: U.S. Geological Survey Scientific Investigations 

Report 2010–5210, 33 p.

Czarnecki, J.B., and Schrader, T.P., 2012, Effects of recent 

climate variability on groundwater levels in eastern Arkansas: 

U.S. Geological Survey Scientific Investigations Report 

2012–5258, 17 p.

National Oceanic and Atmospheric Administration, 2011, 

NOAA: 2010 Tied For Warmest Year on Record, accessed 

February 15, 2012, at http://www.noaanews.noaa.gov/

stories2011/20110112_globalstats.html.

National Weather Service, 2011, Climate statistics for the Little 

Rock area: National Weather Service, accessed January 11, 

2011, at http://www.srh.noaa.gov/images/lzk/pdf/clilit.pdf.

National Weather Service, 2012, Little Rock yearly climate 

summary (2009): National Weather Service, accessed 

January 19, 2012, at http://www.srh.noaa.gov/lzk/?n=2009.

htm.

Schrader, T.P., 2010, Water levels and selected water-quality 

conditions in the Mississippi River Valley alluvial aquifer in 

eastern Arkansas, 2008: U.S. Geological Survey Scientific 

Investigations Report 2010–5140, 71 p., 2 plates.

U.S. Army Corps of Engineers, 2012, Grand Prairie area 

demonstration project: U.S. Army Corps of Engineers, 

Memphis District, accessed January 25, 2012, at http://www.

mvm.usace.army.mil/grandprairie/overview/default.asp.

U.S. Geological Survey, 2011, Groundwater watch: Arkansas 

County, Arkansas: U.S. Geological Survey, accessed April 

28, 2011, at http://groundwaterwatch.usgs.gov/countymaps/

AR_117.html.

U.S. Geological Survey, 2012, Aggregate Water-Use Data 

System (AWUDS) of USGS, accessed February 15, 2012, at 

http://water.usgs.gov/watuse/wuawuds.html.

—John B. Czarnecki and T.P. Schrader