science for a changing world

Prepared in cooperation with the 

COLORADO WATER CONSERVATION BOARD

Analysis of Hydrologic Factors That Affect 

Ground-Water Levels in the Arkansas River 

Alluvial Aquifer Near La Junta, 

Colorado, 1959-99

Water-Resources Investigations Report 00-4047

U.S. Department of the Interior 

U.S. Geological Survey

Analysis of Hydrologic Factors That 

Affect Ground-Water Levels in the 

Arkansas River Alluvial Aquifer Near 

La Junta, Colorado, 1959-99

By Clifford R. Bossong

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 00-4047

Prepared in cooperation with the

COLORADO WATER CONSERVATION BOARD

Denver, Colorado 

2000
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does 

not constitute endorsement by the U.S. Geological Survey.

For additional information write to:

District Chief 

U.S. Geological Survey 

Box25046, Mail Stop 415 

Denver Federal Center 

Denver, CO 80225-0046

Copies of this report can be purchased 

from:

U.S. Geological Survey 

Information Services 

Box 25286 

Federal Center 

Denver, CO 80225
CONTENTS

Abstract ...................................................................................................................................................................^ 1

Introduction...........................................................................................................................................^ 1

Previous Investigations................................................................................................................................................ 3

Acknowledgments....................................................................................................................................................... 3

Water-Table Conditions in March 1999................................................................................................................................. 3

Water-Table Map...........................................................................................^^ 7

Estimate of Ground-Water Storage.............................................................................................................................. 7

Depth to Water.......................................................................................................................................................^ 7

Historical Water Levels ......................................................................................................................................................... 7

General Changes in Water Levels................................................................................................................................ 9

Regression Characterization........................................................................................................................................ 14

Fluctuations in Water Levels........................................................................................................................................ 15

Short-Term Variation in Water Levels ......................................................................................................................... 15

Hydrologic Factors That Affect Ground-Water Levels ......................................................................................................... 15

Surface-Water Conveyances........................................................................................................................................ 16

Surface-Water Applications......................................................................................................................................... 19

Ground-Water Withdrawals......................................................................................................................................... 21

Channel Processes ...................................................................................................................................................... 21

Interrelations of Ground-Water Levels and Affecting Factors .................................................................................... 22

Summary..............................................................................................................................................^ 24

References Cited......................................................................^ 25

FIGURES

1-3. Maps showing:

1. Location of study area and selected wells......................................................................................................... 2

2. Generalized water-table contours derived from measurements made March 9 through March 19, 1999......... 6

3. Generalized depth-to-water calculated from measured water table and digital representation

of land-surface elevations.................................................................................................................................. 8

4-6. Hydrographs showing:

4. General trends in ground-water levels............................................................................................................... 14

5. Mean daily and annual total flow in the Fort Lyon Canal................................................................................. 17

6. Mean daily and annual total flow in the Arkansas River at La Junta................................................................ 20

7. Comparison of annual-total, daily mean, and instantaneous time-series data for hydrologic

factors in the study area..................................................................................................................................... 23

TABLES

1. Description of wells used to measure water table, March 9 through March 19, 1999............................................ 4

2. Frequency analysis for calculated depths to water.................................................................................................. 9

3. Summary for Ground Water Site Inventory wells with multiple measurements in and near the study area........... 10

4. Annual values for hydrologic records in the study area.......................................................................................... 18

5. Flow-duration statistics for the Fort Lyon Canal and the Arkansas River at La Junta............................................ 19

CONTENTS III
CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

Length

foot (ft) 

foot per mile (ft/mi) 

mile (mi)

0.3048 

0.1894 

1.609

meter (m) 

meter per kilometer (m/km) 

kilometer (km)

Area

acre, 

acre-foot (acre/ft) 

square mile (mi2)

0.4047 

0.001233 

259

hectare (ha) 

cubic hectometer (hm3) 

hectare (ha)

Volume

million gallons (Mgal) 

cubic foot (ft3 ) 

acre-foot (acre-ft)

3,785 

0.028317 

0.001233

cubic meter (m3 ) 

cubic meter (m43 ) 

cubic hectometer (hm3 )

Flow

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

Hydraulic gradient

foot per mile (ft/mi) 0.1786 meter per kilometer (m/km)

Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 

a geodetic datum derived from a general adjustment of the first-order level nets of the United States

and Canada, formerly called Sea Level Datum of 1929.

IV CONTENTS
Analysis of Hydrologic Factors That Affect 

Ground-Water Levels in the Arkansas River 

Alluvial Aquifer Near La Junta, Colorado, 1959-99

By Clifford R. Bossong

Abstract

The water table is sometimes near the land 

surface in the vicinity of La Junta, Colorado, and 

may impair the use of agricultural and personal 

property. A water-table map prepared for the 

alluvial aquifer in the vicinity of La Junta, indicated that, in March 1999, the Fort Lyon Canal 

and the Arkansas River provided recharge to the 

aquifer. A depth-to-water map prepared for the 

same area and period indicated that the water 

table was relatively shallow (less than 10 feet) in 

about 50 percent of the area studied. Available 

historical water-level records visually indicated 

that water levels tended to increase throughout the 

study area during the past nearly 4 decades, and 

regression analysis quantifies this relation. The 

available records do not address short-term 

changes.

Several hydrologic factors that affect water 

levels in the study area were identified, and some 

simple relations between these factors and 

changes in water levels also were identified on the 

basis of coincidence of changes in the time series 

for the various records. Indications are that flow in 

the Fort Lyon Canal, surface-water applications 

for irrigation, and ground-water withdrawals have 

acted in concert to affect both increases and 

decreases in ground-water levels. Relatively low 

levels of ground-water withdrawals in the 1990's 

may be associated with increases in ground-water 

levels as well. The elevation for the base of the 

Arkansas River at the gaging station in La Junta 

has steadily increased from about 1960 to 1997

and has probably influenced water levels in 

lowland wells.

INTRODUCTION

La Junta is located in southeastern Colorado on 

the Arkansas River (fig. 1). Much of the land near the 

Arkansas River in the vicinity of La Junta is irrigated 

for agricultural purposes. Water used for irrigation 

either is taken from the Fort Lyon Canal, which diverts 

water from the Arkansas River a few miles west of 

La Junta, or is withdrawn from the local alluvial 

aquifer in the flood plain of the Arkansas River, which 

is highly transmissive and capable of yielding relatively large amounts of water to wells. The Fort Lyon 

Canal provides irrigation water for about 90,000 acres 

of agricultural land between La Junta and Lamar, 

about 60 miles downstream. The Fort Lyon Canal is 

the principal source of water used for irrigation in the 

study area; however, withdrawals from the local alluvial aquifer can represent as much as 40 to 60 percent 

of total irrigation when surface-water availability is 

low (Goff and others, 1998).

Tracts of agricultural land and many residences 

in the vicinity of La Junta may be affected by the 

water table which, in places, is near the land surface. 

Effects include flooded basements and soggy, or 

water-logged, conditions in agricultural fields that 

impair their suitability for agriculture. Conveyance 

losses from the Fort Lyon Canal, recharge from the 

Arkansas River, and ground-water withdrawals are 

potential sources of recharge and discharge to the local 

aquifer that affecting water-table conditions.

In order to better understand hydrologic 

factors that affect the water table near La Junta, the 

U.S. Geological Survey (USGS), in cooperation with

Abstract
103-34' 103'26'

38'04' 

38°00' -

Base modified by Denver Water Board, 1998

From U.S. Geological Survey Digital Line Graphs, 100 000, 1981-82

Roads and cities from Colorado Department of Transportation, 50,000, 1998

Albers Equal-Area Conic projection

standard parallels 38° 30'N and 40° 30'N

Central meridan 10? 30'W

3 KILOMETERS

COLORADO

0 Denver

STUDY AREA

Pueblo.Reservoir \

^ V-,, \

Pueblo

EXPLANATION

Lamar

3800551032828(4)

WELL-16-digit number indicates well identifier 

in table 3. Number in parenthesis sometimes 

used in text.

Figure 1. Location of study area and selected wells.

Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
the Colorado Water Conservation Board, conducted a 

study in 1999 to analyze hydrologic factors that affect 

ground-water levels in the Arkansas River alluvial 

aquifer. This report presents the results of that study. 

More specifically, the report describes water-table 

conditions in March 1999, historical water levels, and 

hydrologic factors that affect water levels.

The study was limited to the area between the 

Fort Lyon Canal and the Arkansas River from the Fort 

Lyon Canal headgate east to the Otero County line 

(fig. 1). The description of March 1999 conditions is 

based on water level measurements made in 49 wells. 

The description of earlier conditions (generally 1959 

through 1998) is based on time-series records for 

ground-water levels, ground-water withdrawals, applications of ground water and surface water for irrigation, discharge in the Arkansas River, diversions to the 

Fort Lyon Canal, and channel conditions in the 

Arkansas River. The study was limited to data that are 

maintained in a computer system, or archived as 

digital records.

Previous Investigations

Several hydrologic investigations have been 

completed in the study area. The results of these investigations are valuable sources of background information to interested readers. Konikow and Bredehoeft 

(1974) characterized the study area as part of a 

ground-water modeling investigation of ground-water 

flow and chemistry. Watts and Lunsford (1992) 

modeled several different water-management alternatives designed to affect changes in water-table conditions in the study area. Using a digital model that 

characterized ground-water levels in the area as sensitive to leakage from the Arkansas River, leakage from 

the Fort Lyon Canal, and ground-water withdrawals, 

they found that most alternatives would have relatively 

local effects although modifications to the Arkansas 

River channel could change ground-water levels 

throughout the area. Goff and others (1998), provided 

a modeling analysis of the effects of irrigation in the 

study area and found that salinity of ground water and 

surface water was related to irrigation activities. The 

report by Goff and others (1998) is the source of many 

data used in this study. Dash (1995) reported on the 

irrigation water use for the Fort Lyon Canal and documented losses from the canal.

Acknowledgments

The assistance of certain agencies and individuals were critical to the completion of this study. In 

particular, Lloyd Wadleigh and Don Taylor, from Division II office of the Colorado Division of Water 

Resources located in La Junta, were extremely helpful 

with records available from their office that were used 

for identifying and locating wells for the March 1999 

water-level measurements. In addition, many landowners provided access to wells that were measured; 

without this access, it would not have been possible to 

characterize water-table conditions in March 1999.

WATER-TABLE CONDITIONS IN 

MARCH 1999

To document current water-table conditions, the 

water table was mapped in the spring of 1999 on the 

basis of measurements from 49 wells. Wells were 

identified and depths to water from a point where the 

land surface elevation could be estimated were 

measured between March 9 and March 19, 1999; the 

results of those measurements are listed in table 1. 

During the measurement period, flow in the Fort Lyon 

Canal was steady but relatively low, about 100 to 

200 cubic feet per second, and flow in the Arkansas 

River at La Junta varied from about 50 to 150 cubic 

feet per second.

The depth-to-water measurements were 

converted to elevations of the water-table surface, and 

the resultant elevations were contoured by hand to 

produce a generalized water-table map for the study 

area that is shown in figure 2. Estimates of landsurface elevations were made using l:24,000-scale 

topographic maps, and map accuracy and estimation 

techniques dictated the estimates may depart from 

actual elevations by as much as 2.5 feet.

In places where water-table surfaces are near the 

land surface, there is often interest in knowing how 

close the water-table surface is to the land surface. To 

show this information, digital elevation models of the 

generalized water-table map (fig. 2) and the land 

surface were used to create a depth-to-water map. The 

digital elevation models provide estimates of either 

ground-water elevation or land surface elevation for 

individual grid cells in a gridded network of the study 

area. Ground-water elevations for individual grid cells 

were estimated using measurements of ground-water

WATER-TABLE CONDITIONS IN MARCH 1999
Table 1. Description of wells used to measure water table, March 9 through March 19, 1999

[State permit number, identifier used by Colorado Division of Water Resources; depth to water, measured depth to water adjusted to land-surface datum; 

land-surface datum, land-surface elevation estimated from 1:24,000 U.S. Geological Survey topographic map; mmddyyyy, date of measurement in month 

day year format; hhmm, time of measurement in military hours and minutes format; ft, feet; GWSI ID, refers to 15 digit latitude and longitude based identifier used in U.S. Geological Survey Ground-Water Site Inventory data base; , not available]

State 

permit 

number

 309

312

316

482

483

653

1023

1791R

1792

1793

1794

2540

2978

4467

4523

6778

6780

6902

10016

10118

10122

11878

12062

12216

15093

13215

13318

13709

14180

14375

14381

14776

14778

14809

15103

15344

15501

15934

Depth 

to 

water 

(ft)

13.10

6.43

22.40

11.28

6.15

16.49

19.09

1.72

18.40

19.15

13.39

13.75

10.56

9.45

9.25

20.52

18.94

14.19

8.30

9.53

16.01

7.80

8.15

32.52

20.27

6.42

12.42

15.98

11.35

3.88

15.02

15.96

16.48

16.88

4.72

13.33

7.90

5.17

Landsurface 

datum 

(ft)

4,055.00

4,035.00

4,048.00

4,075.00

4,078.00

4,041.00

4,011.00

4,019.00

4,039.00

4,041.00

4,059.00

4,080.00

3,991.00

4,038.00

4,085.00

4,030.00

4,048.00

4,068.00

4,062.00

4,065.00

4,033.00

3,994.00

3,998.00

4,058.00

4,085.00

4,038.00

4,095.00

4,055.00

4,045.00

4,042.00

4,046.00

4,018.00

4,031.00

4,024.00

4,031.00

4,093.00

4,065.00

4,030.00

Date of 

measurement 

(mmddyyyy)

03151999

03191999

03151999

03091999

03091999

03191999

03151999

03151999

03151999

03191999

03161999

03091999

03161999

03191999

03091999

03151999

03101999

03161999

03161999

03011999

03101999

03161999

03101999

03151999

03161999

03161999

03161999

03151999

03191999

03151999

03151999

03101999

03101999

03101999

03151999

03091999

03091999

03101999

Time of 

measurement 

(hhmm)

1555

1415

1220

1109

1645

1500

1120

1740

1021

1530

1635

1122

1030

1430

1805

1041

1605

1301

1440

1710

1710

1110

1215

1430

1346

1605

1225

1530

1400

1651

0941

1526

1010

1040

1716

1310

1620

1751

Distance 

from 

measuring 

point to land 

surface 

(ft)

0.50

1.00

0.90

2.00

3.00

0.50

0.70

0.60

2.00

1.00

0.40

1.30

2.00

1.75

1.00

1.00

1.50

1.50

0.00

0.20

0.60

1.80

0.40

1.40

0.00

1.60

1.80

0.30

0.00

2.00

2.00

1.20

0.80

0.60

1.60

1.50

1.50

1.20

Description of 

measuring Remarks 

point

Base of pump

Top of casing

Pipe

Top of casing

Top of shelter

Hole in casing

Hole in casing

Top of casing

Plug in casing

Hole in casing

Hole in casing

--

Top of casing

Top of casing

Top of casing

Base of pump

Top of casing

Top of casing

Land surface

Base of well

Top of casing

Top of casing

Top of casing

Base of pump

Land surface

Top of casing

Top of casing

Top of casing

Land surface

Top of casing

Top of casing

Top of casing

Top of casing

Hole in base of

pump

Top of casing

Top of casing

Floor of shelter

Top of casing

Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
Table 1. Description of wells used to measure water table, March 9 through March 19, 1999 Continued

[State permit number, identifier used by Colorado Division of Water Resources; depth to water, measured depth to water adjusted to land-surface datum; 

land-surface datum, land-surface elevation estimated from 1:24,000 U.S. Geological Survey topographic map; mmddyyyy, date of measurement in month 

day year format; hhmm, time of measurement in military hours and minutes format; ft, feet; GWSI ID, refers to 15 digit latitude and longitude based identifier used in U.S. Geological Survey Ground-Water Site Inventory data base; --, not available]

State 

permit 

number

21377

21780

175747

195453

201493

--

--

--

--

--

--

Mean

Minimum

Median

Maximum

Skewness

Depth 

to 

water 

(ft)

11.05

19.63

34.87

8.77

15.65

2.35

1.40

6.57

4.17

-.44

6.76

12.30

-0.44

11.35

35.31

0.79

Landsurface 

datum 

(ft)

4,050.00

4,025.00

4,058.00

4,052.00

4,010.00

4,052.00

4,057.00

4,023.00

4,033.00

4,013.00

3,980.00

Date of 

measurement 

(mmddyyyy)

03161999

03151999

03151999

03091999

03101999

03091999

03181999

03171999

03221999

03181999

03181999

Time of 

measurement 

(hhmm)

1511

1055

1555

1440

1441

-

--

~

~

--

--

Distance 

from 

measuring 

point to land 

surface 

(ft)

1.40

0.90

1.50

0.00

1.00

0.60

--

--

-

-

-

Description of 

measuring 

point

Top of casing

Top of casing

Top of casing

Land surface

Hole in pump

Top of casing

--

-

--

~

--

Remarks

GWSI ID 375940103330500

GWSI ID 380036103282100

GWSI ID 380041 103294900

GWSI ID 380055 10328 1800

GWSI ID 380229103263300

WATER-TABLE CONDITIONS IN MARCH 1999
103-34' 103'26'

38°04'

38°00' 

Base modified by Denver Water, 1

From U.S. Geological Survey Digital Line Graphs, 100 000, 1981-82

Roads and cities from Col. Department of Transportation, 24 000, 1998

Albers Equal-Area Conic projection

standard parallels 38°30'N and 40 °30'N

Central meridan 105°30'W

3 KILOMETERS

EXPLANATION

STUDY AREA

 4050 WATER-TABLE CONTOUR-shows generalized altitude of water table. Contour interval 10 feet. 

National Geodedic Vertical Datum 1929

* WELL- shows location of well with measured water level

Figure 2. Generalized water-table contours derived from measurements made March 9 through 

March 19, 1999.

Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
from March 1999 and an algorithm based on iterative 

finite-difference methods (Hutchinson, 1989) that is 

implemented in the Environmental Sciences Resource 

Institute geographic information system software 

known as Arclnfo. Land-surface elevations were available in digital elevation models prepared by USGS 

(REF). The depth-to-water map shown in figure 3 was 

prepared by subtracting the ground-water elevation 

model from the land-surface elevation model.

Water-Table Map

The generalized water-table map (fig. 2) indicates the direction of ground-water movement, which 

is perpendicular to the water-table contours. The map 

indicates that the general direction of ground-water 

movement in the study area was from west to east. The 

gradient of the water table, indicated by the spacing of 

the contours was comparable to that of the river 

about 6 feet per mile.

The map also indicates that in much of the study 

area, ground water was moving from the area of the 

Fort Lyon Canal and the Arkansas River toward the 

center of the study area; a condition indicating that the 

aquifer was receiving recharge from both the canal and 

the river. The gradient from the area of the Fort Lyon 

Canal to the center of the study area is sometimes 

steeper than the gradient from the river to the center of 

the study area, especially in the eastern part of the 

study area.

Estimate of Ground-Water Storage

The generalized water-table map (fig. 2) was 

used with information describing the elevation for the 

base of the local alluvial aquifer (Nelson and others, 

1989), and with an estimate of the specific-yield of the 

aquifer (Watts and Lunsford, 1992), to estimate the 

amount of water stored in the aquifer. The difference 

between the water-table surface and the base of the 

aquifer represents the volume of the aquifer. The 

specific yield, estimated as 0.20 in the study area, is 

the ratio of the content of water that will drain, due to 

gravitational forces, to the water content of the aquifer 

from which it is drained. To obtain the estimate of 

water contained in the aquifer, the aquifer volume was 

multiplied by the estimated specific yield. These 

methods indicated an estimated water content of about

40,000 acre-feet; however, the entire estimated water 

content of the aquifer would be available to wells only 

under ideal conditions. Further, under similar ideal 

conditions, only the water contained in the aquifer that 

is above the elevation of the Arkansas River would be 

able to provide ground-water contributions to the river.

Depth to Water

The generalized depth-to-water map (fig. 3) 

indicates that water levels ranged from less than 5 feet 

below the land surface to about 50 feet below the land 

surface. In general, the range of depths to water was 

greatest in the eastern one-half of the study area.

The digital elevation model for depth to water 

indicates that water levels were within 5 feet of the 

land surface in about 31 percent of the study area 

(table 2), mostly in a zone that parallels the river 

(fig. 3). Water levels were relatively shallow, from 5 to 

10 feet below the land surface, in about 20 percent of 

the study area. The area of relatively shallow water 

levels is prominent in the western one-half of the study 

area where the area is relatively wide compared to the 

eastern one-half of the study area where it generally is 

a thin strip; however, there is an area in the eastern part 

of the study area, mostly in section 21 of township 

23 south, range 54 west, where relatively shallow 

depths to water are more extensive.

Maps made at different times have different 

locations for the Arkansas River. These differing locations indicate the shifting nature of the river and also 

indicate that the river channel location, on a decadal 

scale, is variable.

HISTORICAL WATER LEVELS

The USGS has monitored ground-water levels 

in the study area for several decades. Water-level 

records are maintained in a system known as the 

Ground-Water Site Inventory (GWSI) data base. As 

part of the study, the GWSI data base was accessed to 

obtain water-level records from wells in and around 

the study area; information from 224 wells was 

obtained. A subset of these wells consisting of 

141 wells that wells that have been measured more 

than one time, is listed in table 3. A brief summary of 

the information available for each well also is included 

in table 3.

HISTORICAL WATER LEVELS
103'34I 10326*

3ff04' -

38°00' -

Base modified by Denver Water, 1998

From U.S. Geological Survey Digital Line Graphs. 100 000, 1981-82

Roads and cities from Col. Department of Transportation, 24 000, 1998

Albers Equal-Area Conic projection

standard parallels 38°30'N and 40 °30'N

Central meridan 105°30'W

EXPLANATION

3 KILOMETERS

Depth to water, in feet below land-surface 

[ | 0-2.5 

j j 2.5-5 

[""] 5-10

10-15

^| 15-20 

^J 20-30 

[J 30 - 40 

^H 40 - 50

Figure 3. Generalized depth-to-water calculated from measured water table and digital representation of 

land-surface elevations.

8 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
Table 2. Frequency analysis for calculated depths 

to water

[Depth to water was calculated for a grid of 98 X 98-foot cells; 

values for individual cells were assigned using an distribution 

method similar to inverse distance squared weighting]

Interval 

(feet)

0-5

5-10

10-15

15-20

20-25

25-30

30-35

35-40

40^5

45-50

Total

Absolute

11,432

7,432

4,730

5,149

3,103

2,387

1,009

683

511

287

36,723

Frequency

Relative 

(percent)

31.13

20.24

12.88

14.02

8.45

6.50

2.75

1.86

1.39

0.78

100.00

Cumulative 

(percent)

31.13

51.37

64.25

78.27

86.72

93.22

95.97

97.83

99.22

100.00

General Changes in Water Levels

Some of the most useful information available 

from the historical records concerns how water levels 

have generally changed through time. For instance, 

have water levels remained about the same or have 

they changed substantially, and if they have changed, 

have the changes been steady or abrupt? A visual 

inspection of the records indicated that, in most representative cases, ground-water levels have generally 

had a net increase during the study period. Examples 

of these increases for the five wells in figure 1 are 

shown in hydrographs (fig. 4)

For the purposes of this discussion, the wells 

shown in figure 4 are referred to as "well 1" 

(SC02405503AAC), "well 2" (SC02305415DCC), 

"well 3" (SC02305421BCC), "well 4" 

(SC02305428CCB1), and "well 5" 

(SC02305430DBD). Information concerning the 

period of record and the number of measurements for 

each of these five wells is listed in table 3. Water levels 

in all five wells have been measured for much of the 

study period, and water levels in all wells except well 

5 have been measured more than 100 times; well 5 has 

only been measured 36 times.

Wells 1 and 4 are located near the Arkansas 

River and the other three wells are either close to the

Fort Lyon Canal or nearly centrally located between 

the canal and river (fig. 1); wells 1 and 4 are referred to 

as "lowland," and wells 2, 3, and 5, are referred to as 

"upland" wells in this report. This simple geographic 

classification also fits the differences between the 

hydrographs for the lowland wells and the upland 

wells. The lowland wells have water levels that are 

relatively close to the land surface. Also, although 

both lowland wells have water-level records that are 

relatively flat, their water levels still indicate a general 

tendency to increase through time. In this report, water 

levels are referred to as "high" or "low", and high 

water levels correspond to shallow depths to water. In 

general, the difference between the shallowest and the 

deepest depth to water, or the difference between the 

highest and lowest water levels, measured at a given 

well and referred to as range in this report, is relatively 

small (table 3) for the lowland wells. However, 

each lowland well does have at least a few 

measurements that seem to represent short-term 

changes in water levels, for instance 1965 for well 4 

(SC02305428CCB1) and 1987 for well 1 

(SC02405503AAC).

The three upland wells, wells 2, 3, and 5, have 

hydrographs with shapes that are very different from 

the hydrographs for the wells near the river (fig. 4). All 

three wells have much greater ranges than the ranges 

from the wells near the river. In addition, the hydrographs for these upland wells each have much higher 

water levels at the end of the period of record than at 

the early part of the period, indicating a general 

tendency for increases in water levels that is much 

more apparent than in the hydrographs for the lowland 

wells.

Although water levels the in upland wells 

exhibit long-term general increases in water levels, all 

three also have a period, from about 1967 through 

about 1979, during which they had a fairly steady 

decrease. The decrease is most apparent in wells 2 and 

3 and least apparent in well 5. During the 1980s water 

levels were generally high, increasing in the early part 

of the decade and decreasing in the later part. Two of 

the three upland wells experienced the highest water 

levels measured in the mid-1980's. From about 1990, 

water levels in the wells began to increase slowly in a 

trend that continued for the remainder of the period of 

record.

HISTORICAL WATER LEVELS
Table 3. Summary for Ground Water Site Inventory wells with multiple measurements in and near the study area

[GWSI ID, 15-digit latitude- and longitude-based identifier used in GWSI; GWSI local, local township range and section identifier stored in GWSI; state 

permit number, identifier used by Colorado Division of Water Resources; Rolodex number, local identifier used by La Junta Colorado Division of Water 

Resources office; n, number of measurements; begin date, beginning date of records; end date, ending date of measurements; regression slope, negative value 

indicates an increasing slope - wells with 10 or fewer measurements were excepted from regressions; range, the difference between the maximum and 

minimum water levels measured; , not available; Text indentifier indicates simple indentifier for well used in text]

GWSI ID GWSI local permit number n Begin date End 

number

Date

Regression slope, 

in feet per 

year

Text

Range identifier

380055103281800

380041103294900

380007103311200

380036103282100

375940103330500

375940103323000

380019103335400

380229103263300

380203103281500

380253103253400

380117103271600

380111103285100

380025103311500

375933103313000

380101103294400

380004103303200

380029103312101

380052103281700

380037103350501

380017103285300

380015103331900

380107103281800

380001103313801

375956103353600

380103103290500

375927103312000

380008103312701

380053103300000

375954103305400

380112103293300

Wells with significant increases in water levels

SC02305428CCB1

SC02305431ABB1

SC02305536CAD

SC02305432AAD

SC02405503AAC

SC02405502BBD

SC02305533ADD

SC02305415DCC

SC02305421BCC

SC02305414CAA

SC02305428ADA

SC02305429ACC

SC02305536BDA

SC02405501BCB

SC02305430DBD

SC02305431CBC

SC02305536BAC

SC02305428CCB2

SC02305532AAB

SC02305432BDD

SC02305534BDD

SC02305428CBB

SC02305535DDAA

SC02305532CDA

SC02305429CAB

SC02405501BDB

SC02305536CBDD

SC02305430CDA

SC02305536DCD

SC02305430ADC

1791

27156

10119

21780

317

14831

13919

3409

2943

2784

2314

2396

11451

10120

1791

10122

14382

13215

2943

3409

147

2943

2188

151

415

223

40

164

41

178

222

107

24

26

40

34

59

36

19

51

53

35

24

25

77

49

36

12

17

92

11

11

14

04-01-1965 

02-01-1971 

08-01-1961 

02-01-1971 

05-01-1966

03-01-1966

04-01-1960 

08-01-1961 

04-01-1960 

02-01-1971 

07-01-1959 

04-01-1960 

07-01-1959 

11-14-1964 

03-24-1965 

07-01-1959 

04-06-1984 

02-01-1971 

04-01-1960

03-01-1965

04-01-1960 

10-09-1961 

04-06-1984 

03-27-1965

10-01-1959

11-01-1965 

04-06-1984 

08-01-1959 

10-01-1963 

07-01-1959

11-19- 

10-22- 

03-07- 

10-20- 

10-22- 

01-17-

10-26-

11-19- 

03-09- 

03-09- 

03-10- 

03-09- 

03-09- 

03-08- 

03-09- 

03-10- 

11-14- 

05-23- 

03-09- 

03-09- 

03-15- 

03-12- 

05-16- 

03-10- 

03-25- 

03-01- 

01-11- 

03-26- 

10-04-

03-25- 

Total wells with significant increases in water levels = 30

Wells with insignificant increases in water levels

26 04-01-1960 01-16- 

14210 3552 34 07-01-1959 03-15 

15934 2275 13 04-01-1960 03-25- 

15103 2244 21 10-01-1963 03-29- 

13 02-01-1971 02-22 

14777 2770 12 07-01-1959 03-24 

1792 2382 13 04-01-1960 03-25

380143103284900

380148103274000

380052103293000

380032103294500

375959103301300

380247103262200

380152103275900

SC02305420DCB

SC02305421DBD3

SC02305430DDA

SC02305431ABD

SC02305431CDB

SC02305415DAB

SC02305421CAC

1998

1998

1996

1998

1998

1987

1995

1998

1993

1993

1993

1993

1993

1988

1993

1981

1986

1983

1993

1981

1977

1976

1985

1993

1969

1973

1987

1969

1967

1969

1975

1977

1969

1976

1972

1969

1969

-0.1689011

-0.4368751

-0.1945448

-0.2367512

-0.1114008

-0.1376830

-0.2824091

-0.3186632

-0.3893873

-0.1768588

-0.1492389

-0.3125154

-0.1828608

-0.1612941

-0.2226240

-0.2051883

-0.5668344

-0.1241117

-0.0824205

-0.1135396

-0.2034496

-0.1696023

-0.5666288

-0.0532789

-0.5160856

-0.1140037

-0.6429105

-0.4483872

-0.9872103

-0.5345963

-0.2874012

-0.1785594

-0.2641783

-0.0662243

-0.2870563

-0.3368387

-0.4615746

6.42

11.24

10.26

7.21

5.19

4.07

15.31

26.04

22.04

5.86

6.43

14.13

10.65

6.93

9.15

5.82

5.55

3.75

7.61

3.09

7.02

8.36

2.10

4.79

6.18

1.68

12.03

5.87

6.73

8.79

11.13

31.60

4.57

3.02

0.79

5.52

8.41

well 4

well 1

well 2 

well 3

well 5

10 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
Table 3. Summary for Ground Water Site Inventory wells with multiple measurements in and near the study area Continued

[GWSI ID, 15-digit latitude- and longitude-based identifier used in GWSI; GWSI local, local township range and section identifier stored in GWSI; state 

permit number, identifier used by Colorado Division of Water Resources; Rolodex number, local identifier used by La Junta Colorado Division of Water 

Resources office; n, number of measurements; begin date, beginning date of records; end date, ending date of measurements; regression slope, negative value 

indicates an increasing slope - wells with 10 or fewer measurements were excepted from regressions; range, the difference between the maximum and 

minimum water levels measured; , not available; Text indentifier indicates simple indentifier for well used in text]

GWSI ID GWSI local

State 

permit 

number

Rolodex 

number Begin date End Date

Regression slope, 

in feet per 

year

Range

Text 

identifier

Wells with insignificant increases in water levels Continued

380128103290600

380222103260500

380011103310701

380211103271100

380218103265300

380243103263800

375927103335600

380319103235400

380017103314400

380212103243300

380001103315900

380226103273700

380032103281600

380018103310501

380001103311001

380249103260500

375944103343900

380010103310000

380223103274400

375929103314301

380148103271300

380024103315001

SC02305429BAB

SC02305423BBB

SC02305536CADA

SC02305422BCB

SC02305422BAC

SC02305415DBC

SC02405504ADA

SC02305413AAA3

SC02305535ADC1

SC02305424BDA

SC02305535DCA

SC02305421ABA

SC02305433BBB

SC02305536ACCC

SC02305536CDAA

SC02305414CBB

SC02305533CDC

SC02305536DBC

SC02305421ABB

SC02405502ADD

SC02305422CCB

SC02305535ADCD

12216

--

--

14778

-

--

4792

--

--

11876

10938

--

--

-

14776

--

--

--

--

«

--

2395 12

32

68

3514 15

13

14

3138 19

128

11

4129 22

2988 31

12

24

92

69

2381 11

21

13

25

94

40

94

07-01-1959

08-08-1959

04-06-1984

07-01-1959

07-01-1959

04-01-1960

03-01-1965

02-01-1971

04-01-1960

07-01-1959

03-26-1965

07-01-1959

08-03-1964

04-06-1984

04-06-1984

04-01-1960

03-27-1965

02-01-1971

07-01-1959

04-06-1984

05-01-1966

04-06-1984

03-25-1969

03-24-1969

04-14-1986

12-21-1971

03-25-1969

03-24-1969

03-15-1977

11-19-1998

03-26-1969

03-07-1979

03-10-1981

01-17-1975

03-16-1977

01-11-1987

04-14-1986

03-24-1969

03-15-1977

02-22-1972

03-11-1980

01-17-1987

03-16-1977

01-11-1987

-0.4647539

-0.1186065

-0.2186752

-0.2684900

-0.3066510

-0.2748295

-0.0629570

-0.0139926

-0.2874747

-0.0296657

-0.0289099

-0.0838574

-0.0266024

-0.0453751

-0.0442102

-0.0693489

-0.0112203

-0.1266400

-0.0116218

-0.0026296

-0.0007356

-0.0045215

9.08

6.59

4.50

9.20

6.86

9.96

4.90

7.80

10.30

4.20

4.66

6.12

4.25

4.00

2.70

8.07

3.75

2.06

11.75

4.05

1.98

12.05

~

-

-

-

-

-

-

-

-

~

-

-

-

~

~

~

-

-

-

-

Wells with significant decreases in water levels

380209103235400

380008103320101

380158103271300

375934103315701

380228103254600

380002103314601

380318103235500

380228103243800

380013103320800

375932103310401

380304103252100

380224103245700

375937103312101

375952103320001

380029103342700

375945103314201

SC02305413DDA

SC02305535DBDD

SC02305421DAA

SC02405502ACAA

SC02305414CDC

SC02305535DDAB

SC02305413AAA2

SC02305413CDC2

SC02305535DBB

SC02405501ACBC

SC02305414ACA

SC02305424BBB

SC02405501BACC

SC02305535DCDA

SC02305533BAD

SC02405502AAA

--

--

--

--

--

--

--

--

--

--

1023

--

--

--

21458

93

58

43

102

28

92

55

14

52

63

4004 22

13

106

76

11

77

10-01-1961

04-06-1984

05-27-1966

04-06-1984

03-25-1965

04-06-1984

04-01-1965

04-24-1964

04-25-1964

04-13-1984

07-01-1960

04-24-1964

04-06-1984

04-06-1984

07-01-1959

04-06-1984

11-03-1970

09-13-1986

03-10-1981

01-11-1987

03-11-1980

01-11-1987

05-26-1971

03-09-1978

03-01-1973

08-15-1986

03-29-1976

10-04-1968

01-17-1987

09-21-1986

03-28-1969

09-21-1986

0.2890213

0.5922046

0.3119051

0.3717283

0.1949933

0.2621876

0.2675896

0.3300888

0.7555794

0.2854597

0.1269777

0.4894681

0.1475387

0.2332515

0.3247730

0.2021285

5.33

2.60

8.93

3.51

4.46

2.86

5.02

10.67

10.92

3.20

4.53

4.98

3.60

2.91

4.59

3.63

-

~

-

~

--

-

-

-

-

-

~

-

-

-

Total cases with significant decreases in water levels = 16

HISTORICAL WATER LEVELS 11
Table 3. Summary for Ground Water Site Inventory wells with multiple measurements in and near the study area Continued

[GWSI ID, 15-digit latitude- and longitude-based identifier used in GWSI; GWSI local, local township range and section identifier stored in GWSI; state 

permit number, identifier used by Colorado Division of Water Resources; Rolodex number, local identifier used by La Junta Colorado Division of Water 

Resources office; n, number of measurements; begin date, beginning date of records; end date, ending date of measurements; regression slope, negative value 

indicates an increasing slope - wells with 10 or fewer measurements were excepted from regressions; range, the difference between the maximum and 

minimum water levels measured; , not available; Text indentifier indicates simple indentifier for well used in text]

GWSI ID GWSI local

State 

permit 

number

Rolodex 

number n Begin date End Date

Regression slope, 

in feet per 

year

Range

Text 

identifier

Wells with insignificant decreases in water levels

375950103313901

380027103343400

380122103264400

375957103351600

375953103332400

375944103315801

375949103325700

380014103313501

380218103262200

375929103311701

380311103244300

380026103344300

380009103334900

380029103313501

380023103333300

380154103281600

375951103310401

380034103355800

375929103313101

380013103310101

375937103313001

380157103264300

380322103250300

380033103305900

380053103274400

380010103292000

380004103291900

375941103313400

380237103270500

SC02305535DDD

SC02305533BDB

SC02305427BDA

SC02305532DCA

SC02305534CDD

SC02405502ABAD

SC02305534DDC

SC02305536CBB

SC02305422AAC

SC02405501BDCA

SC02305413BAC

SC02305533BCA

SC02305534CBB

SC02305536BCBD

SC02305533ADA

SC02305421CBC

SC02305536DCCC

SC02305532BBB

SC02405501BCCA

SC02305536CACC

SC02405501BCAB

SC02305422CAA

SC02305411DDD

SC02305536ABC

SC02305428DCB

SC02305432CBB1

SC02305432CBC

SC02405501BBC

SC02305415CCB

~

482

--

--

--

-

-

~

--

--

2362

--

14818

-

2540

315

--

--

--

--

--

~

1794

-

-

--

--

--

--

2873

--

--

--

--

--

-

--

--

3660

--

3853

-

2873

2314

--

--

--

--

--

-

-

2961

--

--

--

--

--

43

11

13

15

13

99

11

90

22

91

48

11

12

94

12

13

75

18

91

92

108

13

19

11

15

14

13

12

25

04-06-1984

07-01-1959

02-01-1971

04-01-1960

04-01-1964

04-06-1984

03-26-1965

04-06-1984

04-01-1960

04-06-1984

08-01-1960

03-26-1965

04-01-1960

04-06-1984

07-01-1960

09-01-1959

04-06-1984

05-01-1964

04-13-1984

04-06-1984

04-06-1984

02-01-1971

04-01-1965

03-01-1965

02-01-1971

04-01-1960

02-01-1971

02-01-1971

04-01-1960

09-21-1986

03-28-1969

02-22-1972

03-28-1969

03-27-1969

01-17-1987

03-27-1969

01-11-1987

03-16-1977

01-17-1987

03-06-1979

03-27-1969

03-27-1969

01-11-1987

10-29-1969

03-15-1977

09-21-1986

03-10-1981

01-17-1987

01-11-1987

01-17-1987

02-22-1972

03-16-1977

03-26-1969

03-16-1977

03-28-1969

02-22-1972

02-22-1972

03-10-1981

0.1240969

0.2297103

0.4381429

0.1379271

0.1998883

0.1091177

0.3564490

0.2126850

0.1577617

0.0967708

0.1124897

0.3185980

0.1440952

0.3193643

0.1934459

0.1901084

0.1340026

0.0416717

0.0553622

0.0497712

0.0401740

0.3436175

0.0152895

0.1731950

0.0231947

0.0190229

0.0212911

0.0083816

0.0026804

1.60

4.28

1.04

15.99

2.61

3.30

3.20

4.40

7.39

2.60

9.12

3.79

3.58

8.66

4.81

7.62

4.00

3.67

2.70

4.57

4.26

3.13

2.13

5.69

1.36

5.08

1.17

1.03

10.52

-

-

-

-

-

-

-

-

-

-

-

-

-

--

~

--

-

~

-

-

-

-

-

~

--

-

-

-

-

Wells with too few measurements to analyze

375924103314400

375928103335300

375928103342400

375937103313100

375937103354200

375943103332100

375943103351400

375946103352700

375947103333200

SC02405502ADA

SC02405504ADD

SC02405504ACC

SC02405501BBD1

SC02405505BAC

SC02405503BAA

SC02405505ABA

SC02305532DCC

SC02405503BAB

15438

--

--

--

15344

--

~

13318

2800

--

-

-

2591

--

--

2809

10

2

10

8

10

4

5

10

7

03-26-1965

09-01-1963

10-14-1964

06-01-1960

09-01-1959

03-26-1965

03-27-1965

03-27-1965

03-26-1965

10-03-1968

03-10-1981

03-28-1969

03-31-1976

03-28-1969

03-27-1969

03-28-1969

03-28-1969

03-25-1967

-

-

-

-

~

~

-

~

-

~

~

~

-

~

-

-

~

-

-

~

-

-

-

-

12 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
Table 3. Summary for Ground Water Site Inventory wells with multiple measurements in and near the study area Continued

[GWSI ID, 15-digit latitude- and longitude-based identifier used in GWSI; GWSI local, local township range and section identifier stored in GWSI; state 

permit number, identifier used by Colorado Division of Water Resources; Rolodex number, local identifier used by La Junta Colorado Division of Water 

Resources office; n, number of measurements; begin date, beginning date of records; end date, ending date of measurements; regression slope, negative value 

indicates an increasing slope - wells with 10 or fewer measurements were excepted from regressions; range, the difference between the maximum and 

minimum water levels measured; --, not available; Text indentifier indicates simple indentifier for well used in text]

GWSI ID GWSI local

State 

permit 

number

Rolodex 

number Begin date End Date

Regression slope, _ Ranae in feet per y

year

Text 

identifier

Wells with too few measurements to analyze Continued

380012103305400

380013103303200

380028103305200

380032103322300

380032103345100

380038103355200

380044103300000

380059103282800

380113103271400

380118103283200

380119103272300

380122103282300

380202103251600

380209103271300

380214103245100

380214103280000

380238103260200

380246103262900

Mean

Minimum

Median

Maximum

Skewness

SC02305536DBA1

SC02305431BCC

SC02305536ABD

SC02305535CAB

SC02305533BBC2

SC02305529CCC

SC02305430CDD2

SC02305429DAC

SC02305428ADD

SC02305429ADB

SC02305428ADB

SC02305429AAD

SC02305423ADC

SC02305421ADA

SC02305424BBD

SC02305421BAC

SC02305414CCB

SC02305415DBD

15024

310

--

483

--

15327

--

--

--

--

--

--

11877

--

--

--

9

2262 9

7

10

2543 10

6

2738 6

5

7

10

8

5

8

4

4129 10

10

6

3

41.8

2

19

415

3.4

04-01-1960

03-01-1965

07-01-1959

03-24-1965

03-01-1965

03-27-1965

03-24-1965

07-01-1959

04-01-1960

07-01-1959

02-01-1971

07-01-1959

10-01-1963

06-01-1960

07-01-1959

04-01-1964

04-01-1965

07-01-1959

03-26-1969

10-01-1968

03-26-1969

03-27-1969

10-04-1968

10-04-1967

10-07-1966

10-01-1968

03-28-1969

03-25-1969

12-21-1971

03-25-1969

03-26-1968

07-30-1965

10-04-1968

03-25-1969

03-24-1969

07-30-1965

-

..

..

..

..

..

..

..

..

..

--

._

~

6.24

0.79

4.98

30.81

2.46

~

-

-

--

-

-

-

-

~

-

-

-

--

-

~

-

HISTORICAL WATER LEVELS 13
-10

Note: Woter levels for well SC02305428CCB 1 adjusted by -2.0 feet for plotting purposes: : :

< 10

20

30

S «> 

oI 

X 50 hCL 

UJ 

0

60

- (1)SC02405503AAC (J)SC02305421BCC (5)SC023054JODBD ___ __

(2)SC023054150CC ______ (4)SC02J05428CCB1,

1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997

Figure 4. General trends in ground-water levels.

Regression Characterization

General change in water levels through time 

also can be characterized with simple linear regression. The results of regression analyses can be tabulated and are more convenient to work with than a 

large number of hydrographs. Linear regression techniques relate a dependent variable (for this study, 

measured depths to water) to an independent variable 

(for this study, time). The results of regression analyses can be characterized with an equation, which 

includes a term describing the slope for a straight line. 

For regressions of depths to water with time, a negative slope indicates a general decrease in depths to 

water with time. A decrease in depth to water represents a net increase in water-level elevation.

When using results from linear regression to 

characterize monotonic changes such as an increasing 

or decreasing slope, the significance of the slope term 

in the regression equation can be used to screen slopes 

that are not considered significant. For the purposes of 

this report slopes that were not at least 95 percent 

significant were considered insignificant. Regression 

slopes for the 141 wells evaluated are listed in table 3 

and are characterized as increasing or decreasing and 

significant or insignificant. The regression slopes indicate that, for wells that have significant slopes, twothirds of the slopes indicate increasing ground-water 

levels through time.

Most wells that have increases in water levels 

also have records that are representative of the period 

being studied; that is, they span most of the study 

period. When the regression results are plotted on a 

map, wells with increasing water levels are distributed 

uniformly throughout the study area. Although most 

of the wells have increases in water levels, some have 

decreases in water levels. Wells that have significant 

decreases in water levels generally have records that 

end before the 1980's or have records for only a few 

years. The hydrographs in figure 4 indicate a prominent period of water-level increase that began about 

1980 that is common to wells that have record for this 

period. Because wells that have decreases in water 

levels are missing periods of prominent increases or 

represent only a small part of the period studied, 

excluding them from a characterization of general 

trends for water levels in the study area is reasonable. 

However, they do indicate that the phenomenon of 

water-level increases in the study area has a temporal 

element to it and that there can be short-term deviations from the general long-term trend of water-level 

increases.

14 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
Fluctuations in Water Levels

The hydrographs in figure 4 are developed from 

relatively long records in which the wells were 

measured systematically, usually in the spring and fall 

of each year, as a minimum. In general, the deepest 

depths to water are measured in the fall and the shallowest in the spring. For a period of time such as used 

in this study, about 40 years, measurements of groundwater levels in the spring and fall probably do a 

reasonable job of characterizing the extremes of 

ground-water level fluctuations.

The range in water-level measurements at individual wells is included in table 3. The mean of the 

ranges is 6.24 feet. The mean range reported here is 

nearly twice the mean range reported by Konikow and 

Bredehoeft in 1974. The difference between these two 

reported ranges reflects the relatively robust nature of 

the data used for the study described in this report, 

which covers a period of decades, compared to the 

Konikow and Bredehoeft (1974) study for which only 

1 year of data was available.

To determine if the measured ranges have a 

distinctive spatial pattern, they were plotted on a map. 

The mapped ranges seemed to visually indicate a 

tendency for ranges to be small near the Arkansas 

River and to increase away from the river. However, 

closer examination indicated that although fluctuations 

greater than 10 feet and sometimes as much as 30 feet 

commonly occur in areas near the Fort Lyon Canal, 

relatively large fluctuations of about 10 feet also occur 

near the Arkansas River and there were no statistically 

significant relations between geographic setting and 

the range of water level fluctuation. The magnitude of 

fluctuations near the river are probably due to occasional high flows related to flooding or local effects of 

ground-water withdrawals, or both.

Short-Term Variation in Water Levels

One question that may arise, especially when a 

temporal aspect to patterns in water levels has been 

identified, is "How quickly do water levels change?" 

Many of the historical water-level records based on 

spring and fall measurements do not describe potential 

short-term changes in water levels. The historical 

records do include some wells that have been 

measured as frequently as weekly; however, these 

wells are not located in areas where relatively large 

fluctuations in water levels have been measured.

Some of the remaining records are in areas 

where water levels have had relatively large fluctuations and have been measured monthly or bimonthly 

for at least some part of the record. These records indicate that water levels, in some areas, can change at 

least as much as 1 foot per month a rate that would 

produce the mean fluctuation in 6 months (table 3). 

However, water levels could change at rates greater 

than the rates reported for this study.

The historical records also were evaluated for 

adequacy in their ability to represent changes in crosssectional gradients between the Fort Lyon Canal and 

the Arkansas River. Five roughly north-south cross 

sections of three to seven wells were identified, and 

the GWSI data base was accessed to obtain historical 

water levels along the cross sections that were 

measured within a reasonably narrow window of time 

(2 weeks). The results of this evaluation principally 

indicated that the historical records are not ideal for 

preparation of cross sections. In almost all cases, water 

levels were not available for all points in a given cross 

section. In the few cases when data were sufficient, 

indications are that gradients along some parts of some 

cross sections became reversed. That is, for a given set 

of wells, sometimes the gradient might be towards the 

river and sometimes the gradient might be away from 

the river; however, it was not possible to determine if 

such changes occurred routinely or even if they 

occurred in the short term.

HYDROLOGIC FACTORS THAT AFFECT 

GROUND-WATER LEVELS

Ground-water levels are controlled by recharge 

to and discharge from the aquifer. In relatively simple 

systems, recharge may consist only of precipitation, 

and discharge may consist only of evapotranspiration 

and ground-water withdrawals made from wells 

completed in the aquifer. However, there are additional 

sources of recharge and discharge in the study area 

that complicate the system. Some of these additional 

sources, particularly those related to irrigation, represent major changes from a natural setting. The additional sources of recharge and discharge that can be 

related to hydrologic processes in the study area are 

referred to as "hydrologic factors" and are discussed in 

this section. Precipitation and evapotranspiration are 

not discussed.

HYDROLOGIC FACTORS THAT AFFECT GROUND-WATER LEVELS 15
The alluvial aquifer in the study area is hydraulically connected to the Arkansas River. Accordingly, 

the aquifer and the river can exchange water; if the 

water-surface elevation in the river is higher than the 

water-table surface in the surrounding aquifer, then the 

river provides recharge to the aquifer and vice versa. 

In addition, the aquifer also can be recharged as a 

result of modifications to the system made to accommodate irrigation procedures such as application of 

water derived from surface-water diversions or from 

ground water, or both. The aquifer also may discharge 

water to local irrigation and water-supply wells.

Surface-Water Conveyances

There are two principal surface-water conveyances in the study area (fig, 1): the Fort Lyon Canal 

and the Arkansas River. Records of discharge for the 

Fort Lyon Canal, that are from the gaging station 

located downstream from the canal headgate were 

obtained from the Colorado Division of Water 

Resources. Records of discharge for the Arkansas 

River at La Junta, a streamflow-gaging station that is 

located at La Junta and is downstream from the diversion at the headgate for the Fort Lyon Canal, are stored 

in a USGS data base known as the Automated Data 

Processing System (ADAPS).

There are two facts about the Fort Lyon Canal 

that need to be considered. First, the canal is unlined; 

that is, the bottom and banks consist of native materials, and, as a consequence there are conveyance 

losses (in this sense the Fort Lyon Canal provides 

recharge to the local aquifer). In a 1989 to 1990 study, 

Dash (1995) estimated that losses could be as high as 

about 15 acre-feet per day per canal mile.

Second, the Fort Lyon Canal gaging station is 

located downstream from two structures that are sometimes used to divert water from the canal for maintenance activities related to suspended sediment loads in 

the canal. As a result, the gaging station does not 

record water diverted through these structures.

Also, beginning 1975, about the middle of the 

period being studied, Pueblo Reservoir began to 

operate (Abbott, 1985). Reservoir operations most 

pertinent to the study described in this report are the 

distribution of water stored in the reservoir for use at a 

later time (winter water) and the distribution of water 

available from transmountain diversion projects 

(project water).

The discharge record for the Fort Lyon Canal is 

shown in figure 5 and table 4. Figure 5 includes the 

annual total hydrograph, a smoothed curve of the 

annual total hydrograph, and a line indicating the 

long-term mean. A smoothed curve indicates general 

patterns and is prepared using a technique called 

locally weighted scatterplot smoothing (Cleveland and 

others, 1979), a computationally intensive technique 

that is comparable to a moving average. Figure 5 indicates that, generally, flow in the canal was greater than 

the long-term mean from 1980 through 1989 during 

the 1980's. This period includes one year of relatively 

low flow, 1981, and also includes the highest annual 

total flow for the period of record, 1985 (fig. 5). After 

1989, figure 5 indicates that, generally, diversions to 

the canal were less than the long-term mean, although 

flow was greater than the long-term mean in 1996 and 

1997 and the 1997 flow was almost as high as the 1985 

diversion. The mean-daily hydrograph (fig. 5) shows 

typical seasonal variation of flow for the period 

studied and indicates that flow is highest in June.

The record for flow in the Fort Lyon Canal, as 

well as flow in the Arkansas River, indicates a change 

during the late 1970's. Accordingly, flow-duration 

analyses were prepared to describe differences in flow 

characteristics for two periods, 1960 to 1980 and 1981 

to 1997. The results for this study (table 5) list a 

percentage of time, from the period of record being 

analyzed, that the corresponding rate of flow was 

exceeded.

The flow-duration statistics in table 5 indicate 

that there was flow in the Fort Lyon Canal more often 

during the first period than the second. For instance, 

there were very low flows (less than 1 cubic foot per 

second) in the canal for only 1 to 3 percent of the first 

period, whereas there were very low flows in the canal 

for 10 to 15 percent of the second period. Perhaps 

more importantly, the flow-duration statistics indicate 

that, due to large flows during the 1980's, flow in the 

canal was greater, usually by a factor of 1.5 to 2, than 

in the first period. For example, diversions in the canal 

were greater than about 345 cubic feet per second for 

50 percent of the second period; in the first period the 

50 percent exceedance flow was about 213 cubic feet 

per second.

The discharge record for the Arkansas River at 

La Junta is shown in figure 6. The annual total and 

particularly the mean-daily hydrographs are generally 

similar to the hydrographs for the Fort Lyon Canal 

(fig. 5). The smoothed curve for the annual total flow

16 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
1200.0

1000.0

800.0

600.0

< 400.0 

O

200.0

0.0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

0.3 ! T ! ! T I

LU 

LJ 

U. 

I 

LJ

or 

o

O

</> 0.2

z 

o

Fort Lyon Conol - totol

Fort Lyon Conol - totol (smooth)

Fort Lyon Conol - long-term meon

Project woter

Winter woter

o.i

0.0 N ; ; /Ll-Li-i-!

1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

Figure 5. Mean daily and annual total flow in the Fort Lyon Canal.

HYDROLOGIC FACTORS THAT AFFECT GROUND-WATER LEVELS 17
Table 4. Annual values for hydrologic records in the study area

[Year, calendar year; ground-water withdrawals, based on records of withdrawals for city of La Junta municipal supply wells and 

electric power consumption records for irrigation wells (Goff and others, 1998); surface water used for irrigation estimated based on 

Fort Lyon Canal diversions as reported in Goff and others, 1998; , not available]

Flow volume 

(millions of acre-feet)

Year

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

Mean

Arkansas 

River

0.08 

0.13 

0.12 

0.06 

0.06 

0.45 

0.09 

0.05 

0.10 

0.10 

0.15

0.10

0.08

0.10

0.07

0.12

0.11

0.06

0.09

0.14

0.31

0.07

0.20

0.25

0.43

0.30

0.17

0.43

0.10

0.11

0.17

0.15

0.16

0.19

0.23

0.58

0.14

0.37

0.17

Fort Lyon 

Canal

0.10 

0.13 

0.15 

0.08 

0.07 

0.15 

0.12 

0.11 

0.12 

0.15 

0.18

0.11

0.10

0.16

0.07

0.11

0.07

0.06

0.08

0.09

0.13

0.05

0.14

0.18

0.21

0.22

0.13

0.17

0.11

0.07

0.08

0.08

0.08

0.10

0.10

--

0.13

0.21

0.12

Project 

water

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.01

0.01

0.02

0.01

-

0.01

0.00

0.002

.... . Ground-water 

Wmtter withdrawal 

water (feet)

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.01

0.00

0.02

0.00

0.02

0.00

0.00

0.00

0.00

0.04

0.04

0.06

0.03

0.07

0.04

--

0.10

0.00

0.01

--

--

2.05

1.24

2.10

2.37

3.10

3.01

2.71

1.67

1.37

2.48

1.56

1.19

1.18

1.31

0.95

0.53

0.99

1.29

1.27

1.42

1.33

1.12

1.40

-

--

--

1.64

Irrigation 

(feet)

Surface 

water

--

--

2.17

2.17

1.37

2.17

1.58

1.02

1.68

2.79

2.46

1.26

2.92

3.62

4.46

3.92

2.42

3.61

2.09

1.78

1.86

1.64

1.81

2.38

2.06

-

--

2.31

Groundand 

surfacewater 

combined

--

--

4.22

3.41

3.47

4.54

4.68

4.03

4.39

4.46

3.83

3.74

4.48

4.81

5.64

5.23

3.37

4.14

3.08

3.07

3.13

3.06

3.14

3.50

3.46

-

--

--

3.95

Gage height in 

Arkansas River 

at discharge of 

60 cubic feet 

per second

3.22 

3.86 

3.76 

3.99 

4.03 

3.77 

3.58 

3.64 

3.64 

3.90 

4.26

4.37

4.16

4.43

4.61

4.76

4.68

4.58

4.51

4.70

4.75

4.73

4.99

5.28

5.19

5.46

4.70

5.01

5.29

5.29

-

5.49

5.32

5.45

5.50

4.98

-

6.08

4.60

18 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
Table 5. Flow-duration statistics for the Fort Lyon Canal and the Arkansas River at La Junta

[ft3/s, cubic feet per second]

Flow value, Fort Lyon Canal 

(in ft3/s)

Percentage of 

record flow 

was exceeded

99

98

95

90

85

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

2

1

1960-1980

0.50

2.59

55.95

97.60

130.74

152.38

160.85

169.31

177.77

186.23

194.69

212.62

246.48

281.42

318.84

359.42

415.64

481.53

583.61

701.39

847.30

1035.61

1098.38

1981-1997

0.09

0.18

0.44

0.88

142.00

160.52

172.39

184.26

196.12

235.07

288.65

345.23

408.79

476.45

557.77

635.17

705.55

775.93

866.86

977.09

1087.31

1387.67

1642.28

Flow value, Arkansas River at La Junta 

(in ft3/s)

1960-1980

4.63

5.80

8.61

12.90

16.34

19.74

23.21

26.84

30.86

35.05

40.08

47.08

55.94

66.21

81.55

103.07

140.85

203.22

310.97

451.43

605.25

930.43

1714.47

1981-1997

20.38

24.99

33.52

44.12

53.60

63.30

73.54

83.97

94.51

105.10

118.09

133.17

148.26

178.33

215.44

263.11

324.50

404.29

512.36

683.10

1283.85

2807.05

3992.77

indicates that flow in the river experienced a high 

period in the 1980's similar to the canal. However, the 

high in the river is not as pronounced as the high in the 

canal, indicating that most of the relatively large 

amounts of water in the river were diverted to the 

canal. After 1989, flow in the river, unlike diversions 

to the canal, remained above the long-term mean and, 

generally, continued to increase.

The flow-duration statistics for the Arkansas 

River listed in table 5 also are similar to those for the 

Fort Lyon Canal. The tendency for flows to be greater 

in the second period is more pronounced for the 

Arkansas River; second period flows often exceed first 

period flows by a factor of 2 and sometimes by a 

factor of 3. For example, flow in the Arkansas River 

was greater than about 133 cubic feet per second for 

50 percent of the second period; in the first period the

50 percent exceedance flow was about 47 cubic feet 

per second.

Surface-Water Applications

As indicated in the Introduction, there is a large 

diversion of water from the Arkansas River into the 

Fort Lyon Canal a few miles west of La Junta. The 

Fort Lyon Canal often carries more water than the 

Arkansas River and is a contributor to the fact that 

the median flow for the Arkansas River at La Junta, 

which has a contributing drainage area of about 

12,000 square miles, is only about 60 cubic feet per 

second.

The Fort Lyon Canal conveys water to many 

areas east of the study area, and only part of the water 

diverted to the canal is used in the study area. Local

HYDROLOGIC FACTORS THAT AFFECT GROUND-WATER LEVELS 19
3.000.0

2.000.0

O

< 1.000.0 

O

0.0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

0.6

IUJ

ui

t 0.5

LJ 

O

o °- 4

Zi 

_J

i

? 0.3

0.2

0.0

Arkonsos Riverl - totol 

Arkansas River - total (smooth) 

Arkansas River - long-term mean

1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

Figure 6. Mean daily and annual total flow in the Arkansas River at La Junta.

20 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
surface-water applications for irrigation are made 

through diversions out of the Fort Lyon Canal into 

local laterals that deliver water to fields. Usually, the 

water is used to flood the fields. In this respect, the 

Fort Lyon Canal represents a source of recharge to the 

local aquifer.

Goff and others (1998) computed annual 

surface-water applications using an algorithm that was 

based on the amount of water in the canal and the ratio 

of irrigation-program participants in the study area to 

the total number of participants who are supplied by 

the canal. The results of their estimates are listed in 

table 4. Surface-water applications were greater than 

the long-term mean during most of the 1980's, similar 

to flow in the Fort Lyon Canal, which generally was 

high during that decade. After the 1980's, surfacewater applications decreased and returned to levels 

slightly higher than those preceding the 1980's.

Ground-Water Withdrawals

When necessary, generally when water is not 

available from the Fort Lyon Canal, ground water is 

routinely withdrawn from the local aquifer for irrigation purposes to supplement irrigation made with 

surface-water diversions. Ground water also is withdrawn for public water supply. These withdrawals 

represent discharge from the aquifer. Irrigation wells 

are distributed throughout the study area in a relatively 

uniform fashion; however water-supply wells, operated by the city of La Junta are clustered in an area of 

La Junta on the north side of the Arkansas River. 

Ground water is withdrawn for irrigation throughout 

the study area and is usually used to flood fields, 

although some alternative methods, such as spray and 

drip irrigation, are used. The records available for 

analysis in this study are from a previous study (Goff 

and others, 1998) and are summarized in table 4.. They 

are annual records and are based on reported withdrawals from the city of La Junta and on a power 

conversion method (Boyle Engineering Corp., 1990) 

for irrigation wells that estimates the amount of water 

withdrawn at individual wells based on electric power 

meter readings.

The Colorado Division of Water Resources has 

recently begun to maintain records of withdrawals 

made by irrigation wells. The records are for individual wells and have more detail than is available 

from the historical records. These contemporary

records should be very useful, in the future, for characterizing the amount of ground water withdrawn for 

irrigation.

The records from Goff and others (1998) indicate that ground-water withdrawals generally have 

decreased in the study area (table 4). In 1972 and from 

1974 through 1978, withdrawals were greater than the 

long-term mean and increased steadily to a high for 

the period of record. After a peak in mid 1976, 

decreases began and continued through about 1987, 

after which ground-water withdrawals became relatively steady at a level less than the long-term mean. 

The records indicate that ground-water withdrawals at 

the end of the period of record were much less than the 

withdrawals made in the late 1970's and early 1980's. 

The records also indicate that although ground-water 

withdrawals in the study area sometimes have a nearly 

one-to-one inverse relation to surface-water applications, such as in the late 1970's and early 1980's, the 

relation is not necessarily constant, such as in the 

period after the mid-1980's when surface-water applications are nearly constant and ground-water withdrawals tend to increase.

Channel Processes

As stated previously, the Arkansas River and the 

surrounding alluvial aquifer can exchange water. 

When the river is recharging the aquifer, the amount of 

recharge increases as the level of the river increases. In 

the short term, increases in river level, or stage, are 

related to changes in rates of flow. For instance, flow 

typically increases when there are widespread rains. In 

the long term, however, the level of the river may 

change due to increases in the elevation of the river 

bed. Long-term changes in the river-bed elevation 

affect ground-water discharge, or drainage, to the 

river. In general, ground water at elevations lower than 

the river bed will not drain from the system and the 

river bed forms a base level for ground water.

Watts and Lunsford (1992) documented a 

general increase in the elevation of the river bed for 

the Arkansas River at La Junta by evaluating the elevation of the point of zero flow, which is determined 

routinely as a part of maintaining streamflow records. 

In this study, a similar method was used to evaluate 

changes in river-bed elevation.

The method used in this study, sometimes 

referred to as the "specific-stage method"

HYDROLOGIC FACTORS THAT AFFECT GROUND-WATER LEVELS 21
(Simon, 1994), tracks the river surface elevation, 

which is a function of the river bed elevation, for a 

specified discharge. Use of this method can return 

more frequent values and also provides an analysis 

based on a cross section of the river rather than a 

single point in the cross section. Even though the 

method may be based on a cross section rather than a 

point, it still describes the river bed only at that cross 

section and cannot be applied to a river reach without 

additional supporting information.

The results of this analysis are listed in table 4. 

The results indicate that the elevation of the river bed 

has generally increased throughout the study period. 

The changes in river-bed elevations, unlike the 

changes in most of the factors previously discussed in 

this section, are relatively steady. The total increase, 

from 1960 to 1995, is about 1.76 feet. Between 1996 

and 1997 the records indicated an increase of about 

1.1 feet, which is a much greater increase than has 

occurred historically and may be a short-term 

phenomenon.

The information used as part of this study does 

not provide definitive findings about why the elevation 

of the river bed has increased. The changes could be 

the result of relatively large-scale processes that may 

affect several miles of the river or they could be the 

result of local processes related to the maintenance of 

sediment in the Fort Lyon Canal.

Interrelations of Ground-Water Levels 

and Affecting Factors

Ground-water levels and factors that affect them 

can be compared graphically. For this comparison, 

records were transformed and expressed as a fraction 

of their range (fig. 7). This transformation facilitates 

comparisons between factors that are sometimes 

expressed in different units and generally experience 

different ranges than ground-water levels that are 

expressed as depths to water in feet.

A comparison of ground-water levels for two 

wells (one lowland well and one upland well) with the 

elevation of the Arkansas River bed, diversions to the 

Fort Lyon Canal flow from the winter- and projectwater programs related to Pueblo Reservoir operation, 

diversions to the Fort Lyon Canal (annual total flow), 

flow in the Arkansas River (annual total and daily 

mean flow), ground-water withdrawals, and surfacewater applications is shown in figure 7. There are

some qualifications that need to be made concerning 

such a comparison. First, all factors, except groundwater levels, daily mean discharges, and the river-bed 

elevations are annual values and are represented as the 

given annual value for the entire year in figure 7. 

Second, most factors represent data measured at a 

specific geographic point. The hydrographs for 

ground-water withdrawals and surface-water applications are exceptions; they represent the overall study 

area. The areal nature of the withdrawal and application data means that they may be insensitive to local 

phenomena.

Even though the curves in figure 7 require some 

qualifications, the figure still allows for observations 

of the interrelations being discussed. Some simple 

relations are readily apparent. One of the most prominent features of the smoothed curves for depths to 

ground water in figure 7 is that ground-water levels are 

high in the 1980's. Three of the hydrologic factors, 

surface-water applications, ground-water withdrawals, 

and flow in the Fort Lyon Canal, all show clear, either 

direct or inverse, relations to the high water levels 

observed in the 1980's. The levels of flow in the Fort 

Lyon Canal and surface-water applications are both 

greater than long-term means during this period and 

represent recharge to the local aquifer. The levels of 

ground-water withdrawals are less than long-term 

means and represent a decrease in aquifer discharge. 

The combination of increased recharge and decreased 

aquifer discharge result in the high ground-water 

levels observed in the 1980's.

A prominent feature of the smoothed curve for 

ground-water levels in well 2 in figure 7 is the relatively steady decrease during the 1970's. Even though 

the records for ground-water withdrawals and surfacewater applications do not include all of the 1970's, 

their records, along with those for flow in the Fort 

Lyon Canal, portray the opposite of conditions 

observed in the 1980's when ground-water levels were 

high. Recharge to the aquifer from diversions to the 

canal and surface-water applications is low, and 

discharge from the aquifer from ground-water withdrawals is high; these conditions combine to affect a 

decrease in water levels.

The smoothed curves for both wells in figure 7 

indicate a tendency for modest increase from about 

1990 on. During this time, surface-water applications 

are relatively constant but are at levels less than, but 

comparable, to the long-term mean. Ground-water 

withdrawals are also constant during this period,

22 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
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HYDROLOGIC FACTOR VALUE. IN FRACTION OF FACTOR RANGE

magnitude informotion for all foctors except doily mean flow for Arkansas River, in tables 3 and 5

moximum doily mean flow for Arkansas River is 18.400 cubic feet per second
however, they are less than the long-term mean and 

indicate that there are relatively low levels of 

discharge due to ground-water withdrawals from the 

aquifer, a condition that contributes to increases in 

water levels.

Water levels in well 1, a lowland well, are below 

the long-term mean before about 1980 and above the 

long-term mean after 1980. The smoothed curve for 

the daily-mean flow in the Arkansas River has a 

similar, nearly step-like pattern indicating the general 

flow conditions in the river may affect water levels in 

lowland wells. The step-like increase described here 

coincides with the appearance of project water in the 

system.

The elevation for the Arkansas River bed has 

one of the most consistent patterns of all the hydrologic factors, one of steady increase through the period 

of record. The pattern is similar to the smoothed curve 

for water levels in the lowland well indicating that as 

the river-bed elevation increases local ground-water 

levels increase too. In addition, the relatively high 

river-bed elevations of the 1990's combined with relatively low amounts of ground-water withdrawals are 

likely related to increases in ground-water levels in 

well 1 observed in the 1990's.

The water level in the lowland well also clearly 

indicates that it can be affected by short-term condition in the river. The water level in well 1 measured 

June 1,1987, is the highest water level measured at the 

well. The daily mean flow in the Arkansas River 

peaked at 6,840 cubic feet per second 10 days earlier; 

on June 1 the flow was 1,680 cubic feet per second. 

According to the flow-duration statistics in table 5, 

these are relatively high daily mean flows for the 

Arkansas River that are exceeded less than 1 and 

5 percent of the time during 1981 to 1997. The relation 

between high flow in the river coinciding with high 

water levels in well 1 is clear in figure 7 when 

comparing the daily mean flow in the Arkansas River 

and the water levels in well 1 during June 1987.

The affects of hydrologic factors, some of which 

appear to have good visual correlation with changes in 

ground-water levels, can be quantified with regression 

techniques. For instance, simple linear regression techniques can be used to explain about 61 percent of the 

variability measured in upland wells based on groundwater withdrawals and about 70 percent of the variability measured in lowland wells based on river-bed 

elevation. Other, more advanced regression techniques 

such as stepwise regression, which automates the

procedure of selecting the most effective algorithm for 

several independent variables (in this case, the independent variables would consist of all hydrologic 

factors) can be implemented. When stepwise regression was implemented as part of this study, it was not 

possible to explain more than about 90 percent of the 

variability observed in either the upland or lowland 

wells. That is, the results of stepwise regression using 

all the hydrologic factors to explain changes in waterlevels, provided relatively modest improvements over 

regression models using only ground-water withdrawals for upland wells and river-bed elevation for 

lowland wells.

One way to improve the current (1999) level of 

knowledge might be to introduce a data collection 

effort specifically designed to document losses from 

the Fort Lyon Canal and the effects of surface-water 

application in the short term. Such efforts could most 

likely make use of existing wells to define cross 

sections of the water table between the canal and the 

Arkansas River.

SUMMARY

High ground-water levels in the alluvial aquifer 

between the Fort Lyon Canal and the Arkansas River 

in the vicinity of La Junta, Colorado, from the Fort 

Lyon Canal headgate east to the Otero County line, 

can impair the use of agricultural land and personal 

property. Water-table and depth-to-water maps made 

on the basis of water levels measured during March 

1999 indicate that the local alluvial aquifer received 

recharge from the Fort Lyon Canal and the Arkansas 

River and that the water table was within 5 feet of the 

land surface in about 31 percent of the study area. In 

general, water levels are shallowest near the river and 

become deeper closer to the canal; areas of relatively 

shallow water levels are fairly widespread in the 

western part of the study area.

A visual analysis of hydrographs for five wells 

with water-level measurements from about 1965 to 

1995 indicates a general tendency for water levels to 

have increased. A more detailed examination of the 

hydrographs indicates:

 Water levels in the two lowland wells near the 

Arkansas River are relatively close to the land 

surface.

24 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99
 Lowland wells near the Arkansas River have relatively flat hydrographs compared to the three 

upland wells.

 In general, the three upland wells have hydrographs 

that are similar to each other.

 Water levels in upland wells may be as little as about 

10 feet to as much as about 40 feet from the land 

surface.

 Periods of water-level declines exist in the

records for upland wells but are absent or less 

pronounced in records for wells near the Arkansas River.

Historical water levels for 141 wells also indicated that the average range in ground-water levels at 

individual wells was about 6 feet and that the largest 

fluctuations occurred in upland wells. Although there 

are some wells in which water levels have been 

measured as frequently as once a 1 week, the historical 

water-level data, in general, do not describe short-term 

changes. Also, even though a few places where shortterm reversals in water-level gradients between the 

river and the aquifer can be identified, the historical 

water-level data generally are not sufficient to determine short-term gradient changes.

Several hydrologic factors that affect water 

levels are flow in the Fort Lyon Canal, flow in the 

Arkansas River, surface-water applications for irrigation, ground-water withdrawals, and changes in the 

river-bed elevation. All of these factors had temporal 

changes in the study area. The Fort Lyon Canal and the 

Arkansas River generally conveyed larger amounts of 

water after about 1980 and during most of the 1980's 

than before that time. Ground-water withdrawals and 

surface-water applications have generally decreased 

although surface-water applications, much like 

surface-water conveyances, did increase noticeably in 

the 1980's.

Some simple interrelations, mostly on the basis 

of coincidence of change, between hydrologic factors 

can be described:

 The combined effects of flow in the Fort Lyon 

Canal, surface-water applications, and groundwater withdrawals can be associated with both 

increases in the 1980's and decreases in the 

1970's in ground-water levels.

Steady, long-term increases in ground-water levels 

in a well near the Arkansas River are similar to 

changes in the river-bed elevation.

Short-term increases for water levels in the 

Arkansas River are associated with short-term 

high ground-water levels observed in a well near 

the river.

The high river-bed elevation combined with relatively low amounts of ground-water withdrawals 

are likely related to increases in ground-water 

levels observed in a well near the river during the 

1990's.

Sustained levels of relatively high flows in the 

Arkansas River also can be associated with a 

step-like increase in ground-water levels 

observed in a well near the river in about 1980.

REFERENCES CITED

Abbott, P.O., 1985, Descriptions of water-systems 

operations in the Arkansas River Basin, Colorado: 

U.S. Geological Survey Water-Resources Investigations Report 85^092, 67 p.

Boyle Engineering Corp. 1990, Arkansas River Basin 

Study: Estimates of groundwater pumping in the 

Arkansas River Basin, Pueblo Dam to Stateline: 

Prepared for the Office of the State Engineer, Division 

of Water Resources, Lakewood Colorado: Boyle 

Engineering.

Cleveland, W.S. and others 1979, Robust locally weighted 

regression and smoothing scatterplots: Journal of 

American Statistical Association, v. 74, p. 829-836.

Dash, R.G., 1995, Irrigation water use for the Fort Lyon 

Canal, southeastern Colorado, 1989-90: U.S. 

Geological Survey Water-Resources Investigations 

Report 94-4051,47 p.

Goff, Karin, Lewis, M.E., Person, M.A., and Konikow, L.F., 

1998, Simulated effects of irrigation in the Arkansas 

River Valley in Colorado: Ground Water, v. 36, no. 1, 

p. 76-86.

Hutchinson, M.F., 1989, A new procedure for gridding 

elevation and stream line data with automatic 

removal of spurious pits: Journal of Hydrology, v. 106, 

p. 211-232.

Konikow, L.F., and Bredehoeft, J.D, 1974, Modeling flow 

and chemical quality changes in an irrigated streamaquifer system: Water Resources Research, v. 10, 

no. 3, p. 546-562.

REFERENCES CITED 25
Nelson, G.A., Hurr, R.T., and Moore, J.E, 1989, Hydrogeo- Watts, K.R., and Lunsford, J.L., 1992, Evaluation of

logic characteristics of the valley-fill aquifer in the proposed water-management alternatives to lower the 

Arkansas River Valley, Crowley and Otero Counties, high water table in the Arkansas River Valley near 

Colorado: U.S. Geological Survey Open-File Report La Junta, Colorado: U.S. Geological Survey Water95-255, 3 sheets, 1:62 500. Resources Investigations Report 91-4046, 59 p.

Simon, Andrew, 1994, Gradation processes and channel 

evolution in modified west Tennessee streamsProcess, response, and form: U.S. Geological Survey 

Professional Paper 1470, 84p.

26 Analysis of Hydrologic Factors That Affect Ground-Water Levels in the Arkansas River Alluvial Aquifer Near La Junta, Colorado, 

1959-99

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