U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5252

Prepared in cooperation with the City of Aurora, Colorado Springs Utilities, Colorado Water Conservation Board, 

Lower Arkansas Valley Water Conservancy District, Pueblo Board of Water Works, Southeastern Colorado 

Water Conservancy District, and Upper Arkansas Water Conservancy District

Estimates of Gains and Losses from Unmeasured Sources and 

Sinks for Streamflow and Dissolved-Solids Load in Selected 

Reaches of the Arkansas River, Southeastern Colorado, 2009–2010
Cover: Photo taken August 2009 at sluice gates on Fort Lyon Storage Canal near Rocky Ford, Colo., by Roderick Ortiz.
Estimates of Gains and Losses from 

Unmeasured Sources and Sinks for 

Streamflow and Dissolved-Solids Load in 

Selected Reaches of the Arkansas River, 

Southeastern Colorado, 2009–2010

By Roderick F. Ortiz

Prepared in cooperation with the City of Aurora, Colorado Springs Utilities, 

Colorado Water Conservation Board, Lower Arkansas Valley Water Conservancy 

District, Pueblo Board of Water Works, Southeastern Colorado Water 

Conservancy District, and Upper Arkansas Water Conservancy District

Scientific Investigation Report 2012–5252

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2013

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Ortiz, R.F., 2013, Estimates of gains and losses from unmeasured sources and sinks for streamflow and dissolvedsolids load in selected reaches of the Arkansas River, southeastern Colorado, 2009–2010: U.S. Geological Survey 

Scientific Investigations Report 2012–5252, 53 p.
iii

Contents

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

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Description of the Study Reaches .....................................................................................................4

Methods of Investigation..............................................................................................................................4

Streamflow Data ...................................................................................................................................8

Streamflow Data in the Upper Arkansas River Basin Study Reach....................................8

Streamflow Data in the Lower Arkansas River Basin Study Reach..................................11

Water-Quality Data.............................................................................................................................11

Continuous Specific-Conductance Data ...............................................................................12

Periodic Water-Quality Data....................................................................................................12

Statistical Analyses............................................................................................................................12

Quality Assurance and Quality Control ...........................................................................................12

Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks...................15

Gains and Losses in Streamflow in the Upper Arkansas River Basin Study Reach................16

Canon City to Portland ..............................................................................................................16

Portland to Pueblo Reservoir...................................................................................................16

Gains and Losses in Streamflow in the Lower Arkansas River Basin Study Reach ...............21

Avondale to Catlin Dam.............................................................................................................27

Catlin Dam to Las Animas.........................................................................................................27

Potential Unmeasured Sources and Sinks for Streamflow.........................................................34

Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources 

and Sinks..........................................................................................................................................34

Gains and Losses in Dissolved-Solids Load in the Upper Arkansas River Basin 

Study Reach ...........................................................................................................................37

Canon City to Portland ..............................................................................................................37

Portland to Pueblo Reservoir...................................................................................................40

Gains and Losses in Dissolved-Solids Load in the Lower Arkansas River Basin 

Study Reach ...........................................................................................................................40

Avondale to Catlin Dam.............................................................................................................40

Catlin Dam to Las Animas.........................................................................................................44

Potential Unmeasured Sources and Sinks for Dissolved-Solids Load ......................................50

Summary........................................................................................................................................................50

Acknowledgments.......................................................................................................................................52

References Cited..........................................................................................................................................52
iv

Figures

1. Location of the Arkansas River Basin in Colorado..................................................................3

2. Delineation of the Upper Arkansas River study reach showing the location of 

streamflow and water-quality monitoring sites from Canon City to Pueblo Reservoir, 

Colorado .........................................................................................................................................5

3. Delineation of the Lower Arkansas River study reach showing the location of 

streamflow and water-quality monitoring sites from Avondale to Las Animas, 

Colorado .........................................................................................................................................6

4. Annual hydrographs for Arkansas River at Portland (U.S. Geological Survey 

(USGS) station number 07097000), Arkansas River near Avondale (USGS station 

number 07109500), and Arkansas River at Las Animas (USGS station number 

07124000), Colorado, 2009–2010..................................................................................................8

5. (A) Total monthly streamflow and (B) percentage change in total monthly 

streamflow between Arkansas River at Canon City to Arkansas River at Portland, 

Colorado, 2009–2010...................................................................................................................17

6. Estimated daily gains and losses from unmeasured streamflow along a subreach 

of the Upper Arkansas River Basin from Arkansas River at Canon City downstream 

to Arkansas River near Canon City, Colorado, (A) 2009 and (B) 2010.................................18

7. Estimated daily gains and losses from unmeasured streamflow along a 

subreach of the Upper Arkansas River Basin from Arkansas River near Canon 

City downstream to Arkansas River at Portland, Colorado, (A) 2009 and (B) 2010 ..........19

8. Estimated daily gains and losses from unmeasured streamflow along a 

subreach of the Upper Arkansas River Basin from Arkansas River at Portland 

downstream to Arkansas River near Portland, Colorado, (A) 2009 and (B) 2010 .............20

9. (A) Total monthly streamflow and (B) percentage change in total monthly 

streamflow from Arkansas River near Avondale to Arkansas River at Catlin 

Dam, Colorado, 2009–2010.........................................................................................................22

10. (A) Total monthly streamflow and (B) percentage change in total monthly 

streamflow from Arkansas River at Catlin Dam to Arkansas River at Las 

Animas, Colorado, 2009–2010 ...................................................................................................23

11. (A) Total monthly streamflow and (B) percentage change in total monthly 

streamflow from Arkansas River at Catlin Dam to Arkansas River near Rocky 

Ford, Colorado, 2009–2010.........................................................................................................24

12. (A) Total monthly streamflow and (B) percentage change in total monthly 

streamflow from Arkansas River near Rocky Ford to Arkansas River at La Junta, 

Colorado, 2009–2010...................................................................................................................25

13. (A) Total monthly streamflow and (B) percentage change in total monthly 

streamflow from Arkansas River at La Junta to Arkansas River at Las Animas, 

Colorado, 2009–2010...................................................................................................................26

14. Estimated daily gains and losses from unmeasured streamflow along a 

subreach of the Lower Arkansas River Basin from Arkansas River near 

Avondale downstream to Arkansas River at Nepesta, Colorado, (A) 2009 

and (B) 2010 .................................................................................................................................28

15. Estimated daily gains and losses from unmeasured streamflow along a 

subreach of the Lower Arkansas River Basin from Arkansas River at Nepesta 

downstream to Arkansas River at Catlin Dam, Colorado, (A) 2009 and (B) 2010..............29

16. Estimated daily gains and losses from unmeasured streamflow along a subreach 

of the Lower Arkansas River Basin from Arkansas River at Catlin Dam downstream 

to Arkansas River near Rocky Ford, Colorado, (A) 2009 and (B) 2010................................30
v

17. Estimated daily gains and losses from unmeasured streamflow along a subreach 

of the Lower Arkansas River Basin from Arkansas River near Rocky Ford 

downstream to Arkansas River at La Junta, Colorado, (A) 2009 and (B) 2010..................31

18. Estimated daily gains and losses from unmeasured streamflow along a subreach 

of the Lower Arkansas River Basin from Arkansas River near Rocky Ford 

downstream to Arkansas River at Swink, Colorado, (A) 2009 and (B) 2010 ......................32

19. Estimated daily gains and losses from unmeasured streamflow along a subreach 

of the Lower Arkansas River Basin from Arkansas River at Swink downstream to 

Arkansas River at La Junta, Colorado, (A) 2009 and (B) 2010..............................................33

20. Estimated daily gains and losses from unmeasured streamflow along a subreach 

of the Lower Arkansas River Basin from Arkansas River at La Junta downstream to 

Arkansas River at Las Animas, Colorado, (A) 2009 and (B) 2010 ........................................35

21. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Upper Arkansas River Basin from Arkansas River at Canon City downstream to 

Arkansas River at Portland, Colorado, (A) 2009 and (B) 2010..............................................38

22. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Upper Arkansas River Basin from Arkansas River at Canon City downstream to 

Arkansas River near Canon City, Colorado, (A) 2009 and (B) 2010 .....................................39

23. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Upper Arkansas River Basin from Arkansas River near Canon City downstream to 

Arkansas River at Portland, Colorado, (A) 2009 and (B) 2010..............................................41

24. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Upper Arkansas River Basin from Arkansas River at Portland downstream to 

Arkansas River near Portland, Colorado, (A) 2009 and (B) 2010 .........................................42

25. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Lower Arkansas River Basin from Arkansas River near Avondale downstream to 

Arkansas River at Nepesta, Colorado, (A) 2009 and (B) 2010..............................................43

26. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Lower Arkansas River Basin from Arkansas River at Nepesta downstream to 

Arkansas River at Catlin Dam, Colorado, (A) 2009 and (B) 2010..........................................45

27. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Lower Arkansas River Basin study area from Arkansas River at Catlin Dam downstream to Arkansas River near Rocky Ford, Colorado, (A) 2009 and (B) 2010 ..................46

28. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Lower Arkansas River Basin from Arkansas River near Rocky Ford downstream to 

Arkansas River at Swink, Colorado, (A) 2009 and (B) 2010 ..................................................47

29. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Lower Arkansas River Basin from Arkansas River at Swink downstream to 

Arkansas River at La Junta, Colorado, (A) 2009 and (B) 2010..............................................48

30. Estimated daily gains and losses in dissolved-solids load along a subreach of the 

Lower Arkansas River Basin from Arkansas River at La Junta downstream to 

Arkansas River at Las Animas, Colorado, (A) 2009 and (B) 2010 ........................................49
vi

Tables

1. Site names and station names for the Upper Arkansas River Basin and Lower 

Arkansas River Basin study reaches in Colorado with available monitoring 

equipment, 2009–2010 ..................................................................................................................9

2. Number of specific-conductance measurements and dissolved-solids samples 

collected at sites in the Upper Arkansas River Basin and Lower Arkansas River 

Basin study reaches in Colorado, 2009–2010.........................................................................13

3. Estimation of daily specific conductance at selected diversion structures using 

linear regression equations relating specific conductance at main-stem sites in 

the Arkansas River Basin in Colorado with data for long-term continuous specificconductance monitors, 2009–2010...........................................................................................36

Conversion Factors

Multiply By To obtain

mile (mi) 1.609 kilometer (km)

cubic foot per second (ft3

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

ton (2,000 lb) 0.9072 megagram (Mg)

milligram (mg) 0.00003527 ounce (oz)

liter (L) 61.02 cubic inch (in3

)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the insert datum name (and abbreviation) here, 

for instance, “North American Vertical Datum of 1988 (NAVD 88)”

Horizontal coordinate information is referenced to the insert datum name (and abbreviation) 

here, for instance, “North American Datum of 1983 (NAD 83)”

Altitude, as used in this report, refers to distance above the vertical datum.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3

/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C). Concentrations of chemical constituents in water are given either in milligrams per liter 

(mg/L) or micrograms per liter (μg/L).

NOTE TO USGS USERS: Use of hectare (ha) as an alternative name for square hectometer 

(hm2) is restricted to the measurement of small land or water areas. Use of liter (L) as a special 

name for cubic decimeter (dm3) is restricted to the measurement of liquids and gases. No prefix 

other than milli should be used with liter. Metric ton (t) as a name for megagram (Mg) should be 

restricted to commercial usage, and no prefixes should be used with it.
vii

Acronyms Used in this Report

ADAPS Automated Data Processing System

DS Dissolved solids

DWR Division of Water Resources

LARB Lower Arkansas River Basin

LOWESS Locally weighted scatterplot smoothing

NWIS National Water Information System

RRPG Regional Resource Planning Group

SC Specific conductance

UARB Upper Arkansas River Basin

USGS U.S. Geological Survey

Abstract

The Arkansas River is an important municipal water 

supply and is the primary supply for about 400,000 acres 

of irrigated land in southeastern Colorado. The suitability 

of this water for domestic, agricultural, and industrial use is 

affected by high salinity in parts of the Arkansas River. There 

is a need to quantify mass loading of dissolved solids (DS) in 

the Arkansas River. In 2009, the U.S. Geological Survey, in 

cooperation with the Arkansas River Basin Regional Resource 

Planning Group and the Colorado Water Conservation Board, 

began a study to estimate gains and losses from unmeasured 

sources and sinks for streamflow and DS load in selected 

reaches of the Arkansas River in southeastern Colorado. Two 

study reaches were selected for investigation—Canon City to 

just upstream from Pueblo Reservoir (UARB) and Avondale to 

Las Animas (LARB). 

The results from the water-budget analyses indicated that 

potential areas of unmeasured sources and sinks of streamflow 

were identifiable in the two study reaches. In the UARB, a 

substantial volume of water in the subreach from Ark at Canon 

City to the seasonal gaging station 5 miles downstream (Ark nr 

Canon City) was unaccounted for by the methodology used in 

this analysis. The daily gain from unmeasured sources in this 

subreach was estimated to be about 100 cubic feet per second 

(ft3

/s) or about 20 ft3/s per river mile. Water-budget estimates 

for the remaining 18 miles of the UARB study reach indicated 

that gains or losses from unmeasured sources or sinks were 

within the measurement error as defined for this report.

In the LARB, gains and losses from unmeasured sources 

and sinks were identified in some of the subreaches but the 

magnitude of the flux generally was small. Unmeasured 

sources ranging from less than 2 to 3 ft3

/s per mile were 

identified in the river subreaches from Ark at Catlin Dam 

downstream to Ark at Swink. A streamflow loss was indicated 

along the subreach from Ark at Nepesta to Ark at Catlin Dam, 

particularly in 2010. The mechanism and spatial extent of this 

sink was not identified, and further investigation would be 

required to better quantify the loss.

The results from the analyses of unmeasured sources of 

DS load indicated that potential source areas were identifiable 

in the study areas. It might be expected that unmeasured DS 

load flux would be identified along the same reaches where 

unmeasured streamflow flux was identified. To that extent, 

some of the observed results from the analysis of daily DS 

loading did mirror the streamflow results. In some subreaches 

of the Arkansas River, however, unmeasured sources and 

sinks of DS load did not appear to be directly associated with 

unmeasured sources and sinks of streamflow.

In the UARB from Ark at Canon City to Ark nr Canon 

City, unmeasured gains in DS load were estimated to range 

from 11 to 22 tons per day per mile in 2009 and from about 

8 to 13 tons per day per mile in 2010; streamflow from 

unmeasured sources was estimated to be about 20 ft3

/s per 

mile along this same reach. Downstream from this short 

reach, DS load to the river from unmeasured sources was 

estimated to range from 5.4 to 7.6 tons per day per mile in 

2010 for Ark nr Canon City to Ark at Portland and from 

11 to 16 tons per day per mile in 2009 for Ark at Portland 

to Ark nr Portland. Unmeasured gains in streamflow were 

not identified in either of these subreaches. Several small 

tributaries with DS concentrations ranging from 3,000 mg/L 

to as high as 6,000 mg/L enter the river along these 

subreaches. These inputs may indicate a potential source of 

groundwater that could affect DS loading in the river. Further 

investigation would be needed to identify the unmeasured 

source or sources of DS load to determine the nature and 

extent of unmeasured inputs.

In the LARB, gains in DS load from unmeasured sources 

were identified for the subreach from Ark nr Avondale to Ark 

at Nepesta, although no substantial amounts of streamflow 

from unmeasured sources were identified for this subreach. In 

2009, the estimated gain in DS load from unmeasured sources 

for this subreach was 4.7 tons per day per mile. An increase in 

DS load from unmeasured sources also was identified along 

the subreach of the river from Ark at Catlin to Swink; the DS 

load from unmeasured sources was estimated to range from 

10 to 28 tons per day per mile. The only loss of DS load was 

Estimates of Gains and Losses from Unmeasured Sources 

and Sinks for Streamflow and Dissolved-Solids Load 

in Selected Reaches of the Arkansas River, 

Southeastern Colorado, 2009–2010

By Roderick F. Ortiz
2 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

identified for the subreach from Nepesta to Catlin Dam in 

2010. The mechanism and spatial extent of the losses were not 

identified, and further investigation would be required to better 

understand the results.

Introduction

The Arkansas River is an important municipal water 

supply and is the primary supply for about 400,000 acres 

of irrigated land in southeastern Colorado. The suitability 

of this water for domestic, agricultural, and industrial use 

is affected by high salinity in parts of the Arkansas River. 

Specific conductance (a surrogate for salinity) in the river 

increases substantially along the 370 miles downstream 

from the headwaters to the Colorado-Kansas border (fig. 1). 

Miller and others (2010) reported that median specificconductance values increased more than 6,000 percent along 

this reach; much of the increase occurred along the heavily 

irrigated areas from Canon City to Las Animas. Miles (1977) 

attributed the increase in salinity to consumptive use of 

surface water and groundwater by agricultural irrigation. 

Numerous entities have expressed concerns about a wide 

range of water-quality issues in the Arkansas River Basin 

including salinity. Although numerous investigations have 

documented salinity in the Arkansas River Basin (Cain, 

1985; Cain, 1987; Ortiz and others, 1998; Lewis and 

Brendle, 1998; Miller and others, 2010), few have attempted 

to quantify and identify potential source loading areas along 

any reach in the river. 

The Arkansas River Basin Regional Resource Planning 

Group (RRPG) adopted a strategy to address multiple 

water-quality concerns in the basin (including salinity). To 

date (2012), the RRPG entities include the City of Aurora, 

Colorado Springs Utilities, Lower Arkansas Valley Water 

Conservancy District, Pueblo Board of Water Works, 

Southeastern Colorado Water Conservancy District, and the 

Upper Arkansas Water Conservancy District. The overall goals 

of the strategy include (1) synthesizing electronically available 

data and studies that could be integrated to help provide a 

basin-wide understanding of water-quality conditions, (2) 

identifying and prioritizing water-quality issues within the 

Arkansas River Basin based on concerns of stakeholders, and 

(3) identifying gaps in existing data. The U.S. Geological 

Survey (USGS) is working in cooperation with the RRPG to 

help address the goals of the strategy. As part of the first goal 

of the strategy, the USGS has developed, and is maintaining, 

a water-quality database for selected study areas in Colorado 

including the Arkansas River Basin. The database combines 

water-quality data from the USGS National Water Information 

System (NWIS) and the U.S. Environmental Protection 

Agency STORET databases; STORET databases include data 

from many other entities. The interactive repository for the 

Arkansas River Basin can be accessed online at http://rmgsc.

cr.usgs.gov/cwqdr/Arkansas/index.shtml. To help address 

the second goal of the strategy, Miller and others (2010) 

described the occurrence and distribution of dissolved solids, 

selenium, and uranium in groundwater and surface water in 

the Arkansas River Basin from 1970 through 2009; dissolved 

solids, selenium, and uranium were identified as constituents 

of concern by the RRPG. As part of the third goal of the 

strategy, data-collection activities were conducted in 2009–

2010 to quantify data gaps that were identified in the existing 

water-quality dataset for the Arkansas River Basin. Ivahnenko 

and others (2012) used these data to provide an updated 

characterization of the water quality in selected reaches of the 

Arkansas River. 

Additional information, however, is needed to meet 

the goals of the strategy. One of the needs is to quantify 

mass loading of dissolved solids in the Arkansas River. This 

information would help identify stream reaches where streamaquifer interactions could have a pronounced effect on the 

water quality in the river, thus providing the RRPG with 

specific focus areas for further investigation and potential 

remediation. In 2009, the USGS, in cooperation with the 

RRPG and the Colorado Water Conservation Board, began a 

study to estimate gains and losses from unmeasured sources 

and sinks for streamflow and dissolved-solids load in selected 

reaches of the Arkansas River in southeastern Colorado. 

Data were collected during 2009–2010 to provide a basis for 

estimating the gains or losses for selected reaches from Canon 

City to Las Animas. 

Purpose and Scope

The purpose of this report is to describe estimates of 

gains and losses from unmeasured sources and sinks for 

streamflow and dissolved-solids load in the Arkansas River 

along two main study reaches in order to help identify 

subreaches where gains or losses from unmeasured sources 

and sinks could have a pronounced effect on the water 

quality in the Arkansas River. Streamflow data collected 

from established or seasonal (2009–2010) streamflowgaging sites were analyzed to determine a reasonable water 

budget in selected reaches of the Arkansas River and to 

identify subreaches where gains or losses in streamflow from 

unmeasured sources and sinks may be occurring. Specificconductance (SC) and dissolved-solids (DS) data were 

analyzed to derive estimates of daily DS concentrations at 

main-stem, tributary, and diversion sites. The results of these 

two analysis components were combined to derive a massload analysis that was applied at a subreach scale to help 

identify potential source and sink areas of unmeasured DS 

loading in the river.

The types of water-quality data needed to assess the 

dominant physical and chemical processes that result in the 

existing water-quality conditions were generally unavailable 

for the study reaches. Data-collection activities by the USGS 

in 2009–2010 for this study were designed to address these 

data gaps, thus providing data for an analysis of water 

budgets and, subsequently, the analysis of mass loading in the 

Arkansas River.
106°

39°

38°

37°

105° 104° 103° 

40

20

20

0 50 KILOMETERS0 50 MILES

30

30

10

10

40

Base from U.S. Geological Survey digital data, 2011Universal Transverse Mercator projectionZone 13North American Datum of 1983 (NAD 83)

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_01.ai

CONEJOS

Chicosa Creek

EAGLE SUMMIT

PARK

FREMONT

CUSTER

HUERFANO

TELLER

PITKIN

LAKE

Leadville

Buena Vista

Salida

Cañon City

Pueblo Avondale

NepestaFlowler

Rocky Ford

Westcliffe

Walsenburg

Trinidad

JEFFERSON DOUGLAS ELBERT

LINCOLN

CROWLEY

OTERO

KIT CARSON

CHEYENNE

NEW MEXICO OK

KIOWA

BENT

PRO

BACA

EL PASO

Colorado Springs

CHAFFEE

GUNNISON

SAGUACHE

RIO GRANDE ALAMOSA

Lake

Creek

Currant Creek Tallahassee Creek

Grap

e

Creek

Puebleo Reservoir

John Martin Reservoir

PUEBLO

Saint Charles River Sixmile Creek

Huerfano River

Arkansas River

Wild Horse Creek

Fountain Creek

Monument

Cre

ek

Big Sandy Creek

Chico

Creek Horse Creek

A

dobe

Creek

Rush Creek

EXPLANATION

Upper Arkansas River Basin study areaLower Arkansas River Basin study area COSTILLA

LAS ANIMAS

Apishapa

River

Chicosa Arroya

Purgatoire River

Timpas

Creek

Crooked Arroyo La Junta

Las Animas Lamar 

Watershed boundary

Figure 1. Location of the Arkansas River Basin in Colorado.
4 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Currently (2012), the existing streamflow network in the 

Arkansas River Basin provides a framework for the analysis 

of water budgets and mass loading. The USGS and the State 

of Colorado operate and maintain numerous streamflow gages 

on the Arkansas River, at the diversion points of major canals, 

and near the mouth of major tributaries. However, unmeasured 

tributary and return flows frequently result in poorly defined 

water budgets that are the basis for determining source 

contributions. As such, seasonally operated streamflow gages 

were installed at selected sites in the Arkansas River and at 

numerous tributary sites to augment the existing streamflowgaging network in the study reaches. 

Periodic measurements of SC and sampling for DS 

concentrations occurred from May through December of 

2009–2010 at numerous main-stem, tributary, and irrigation 

diversion sites. Existing data collected by other USGS 

programs also were used as part of this investigation to 

increase the sample size for regression analysis. Several 

continuous specific-conductance monitors were installed and 

operated seasonally at selected locations along the Arkansas 

River to support existing water-quality monitor sites. 

For the purposes of this report, two main study 

reaches were selected for investigation. The first study 

reach includes the Arkansas River Basin from Canon City 

to just upstream from Pueblo Reservoir (fig. 2). This reach 

is identified as the Upper Arkansas River Basin (UARB) 

study reach. The second study reach is located downstream 

from Pueblo Reservoir and includes the Arkansas River 

Basin from Avondale to Las Animas (fig. 3). This reach 

is identified as the Lower Arkansas River Basin (LARB) 

study reach. The use of this naming convention is 

consistent with the water-quality characterization report by 

Ivahnenko and others (2012).

Description of the Study Reaches

The Arkansas River originates among some of the 

highest peaks in the continental United States and flows from 

the high-mountain basins onto the plains of southeastern 

Colorado. The river flows through the UARB and LARB 

study areas (fig. 1), which contain the UARB and LARB 

study reaches (figs. 2 and 3). Upstream from Canon City, 

the Arkansas River is characterized by steep-gradient, highvelocity flows that are confined to a relatively narrow rock 

and cobble stream channel. The river gradient decreases 

downstream from Canon City as the river flows generally 

eastward out of the mountains onto the plains. Pueblo 

Reservoir is the first main-stem reservoir on the Arkansas 

River (fig. 1) and controls the release of stored water to 

the predominantly agricultural river valley from Pueblo 

downstream to the Colorado-Kansas State line. Water is 

stored in Pueblo Reservoir as a part of several Federal, 

State, and municipal programs for a variety of reasons 

including flood control, irrigation, and public water supply. 

One program, the Winter-Water Storage Program, allows 

downstream irrigation-canal companies to store their directflow water in the reservoir for release in the spring or late 

summer when natural streamflow in the river may not be 

sufficient for irrigation needs. Under the guidelines of the 

Winter-Water Storage Program, water is stored in Pueblo 

Reservoir from November 15 of each year to March 15 of 

the next year (Southeastern Colorado Water Conservancy 

District, 2011). 

Fountain Creek is a major tributary in the basin and 

flows into the Arkansas River within the city limits of Pueblo. 

Fountain Creek is used to convey transmountain return flows 

from Colorado Springs to the Arkansas River. Expected 

growth by the City of Colorado Springs could result in larger 

volumes of wastewater effluent entering Fountain Creek and, 

ultimately, the Arkansas River (Ortiz, 2004).

Downstream from Fountain Creek, the river channel 

is a shifting sand channel that meanders along the alluvial 

flood plain (Miller and others, 2010). For nearly 120 miles 

downstream from Pueblo Reservoir, water from the river is 

diverted through a network of irrigation canals and is applied 

and reapplied to grow crops in the valley. Ultimately, the 

river flows into John Martin Reservoir near Las Animas 

(fig. 1); John Martin Reservoir regulates the streamflow for 

more downstream uses. Storage decreases substantially in 

both reservoirs by the end of the growing season because 

of decreased inflow and large downstream demands for 

irrigation water. 

Streamflow in the Arkansas River exhibits considerable 

seasonal variability (fig. 4). The majority of the total annual 

streamflow results from snowmelt runoff in the mountains in 

the western region of the basin. Streamflow is at an annual 

minimum from October through March and is maintained by 

natural base flow and main-stem and off-channel reservoir 

releases. Starting in April, streamflow begins to increase 

as snow at the lower elevations begins to melt. Maximum 

streamflow runoff occurs during May and June when the 

deep snowpack melts at the highest elevations. During July 

through September, streamflow in the Arkansas River includes 

decreasing amounts of snowmelt and increased augmentation 

of stored water from reservoirs. During this period, runoff 

from intense thunderstorms can substantially increase 

streamflow in the river for short periods. 

Methods of Investigation

In general, the data collected for this study can be 

categorized as either streamflow or water quality. Various 

types of data-collection methods were associated with 

each of these two categories. The following sections of 

this report characterize the different types of available 

streamflow data and water-quality data used as part of the 

data analysis for this report. Additionally, data-analysis 

techniques used to characterize and describe the data are 

provided here.
105°15'

38°25'

38°20'

105°10' 105°05' 105°00' 

Canon City

Florence

Arkansnear P

Arkansas River

at Portland

Arkansas Rivernear Canon City

Arkansas Riverat Canon City

Arkansas River return

at Highway 112

Fremont wastewatertreatment plant

Beaver Creek

Bear Creek

Hardscrabble Creek

Brush Hollow Creek

Oil Creek Ditch return

Fourmile Creek

Arkansas River

tributary 1 at

Highway 120

Arkansas River

tributary 2 at County Road 112

Arkansas River

tributary 2 at County Road 119

Arkansas River

tributary 1 at County Road 119

Arkansas River

tributary 1 at County Road 112

Oak Creek tributary

Oak Creek

Chandler Creek

Sand Creek

RangerCreek

Minn

Beaver Creek Bear

Creek

Hardscrabble

Cre

ek

Brush

Ho

llo

w

Cre

e

k

Arkansas River

67

50

67

120

115

115

Chandler Creek

San

d

Creek

Fremont Ditch

Canon City Ditch

Fourmile

Creek

Oak

Creek

FREMONT

COUNTY

4

2

2

0 5 KILOMETERS0 5 MILES

3

3

1

1

4

Base from U.S. Geological Survey digital data, 2011Universal Transverse Mercator projectionZone 13North American Datum of 1983 (NAD 83)

EXPLANATION

Upper Arkansas River Basin study areaDiversion ditchPeriodic discharge and periodic water-quality site and site name

Chandler Creek

Seasonal continuous discharge and periodic water-quality site and site name

Beaver Creek

Long-term continuous discharge and periodic water-quality site with long-term water-quality monitor and site name

Arkansas River

at Portland

Seasonal continuous discharge and periodic water-quality site with seasonal water-quality monitor and site name

Arkansas River

near Canon City

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_02.ai

Figure 2. Delineation of the Upper Arkansas River study reach showing the location of streamflow and water-quality monitoring sites from Canon CitColorado.
Figure 3 (Inset on following page). Delineation of the Lower Arkansas River study reach showing the location of streamflow and water-quality monito Las Animas, Colorado.

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_03.ai

104°30'

38°15'

38°00'

104°15' 104°00' 103°45' 103°30' 

Arkansas 

Fort Lyon Canal

Avondale

Nepesta

La Junta

Arkansas River

near Avondale

Arkansas River belowHighline Canal

Arkansas Riverat Nepesta

Arkansas Rivernear Rocky Ford

Arkansas Riverat Swink

Arkansas Riverat La Junta

Anderson Arroya

Crooked

Timpas Creek Arroyo

Fort Lyon Canal

Sixmile Creek Huerfano River

Highline Canal

Oxford Canal

Chicosa Creek

Collier Ditch

Colorado Canal

IR-43

Sixmile Creek

Chico

Creek

Huerfano River 50

10

96

Chicosa Creek

Colorado Canal Horse Creek

Fort Lyon Storage Ca

Timpas

Creek

Apishapa

River

350

La Junta wtreatment p

Crooked Arroyo Ande

rs

o

n

A

rroyo

Inset

PUEBLO

COUNTY

HUERFANO

COUNTY

CROWLEY

COUNTY

OTERO

COUNTY

LakeMeredith

16

8

8

0 20 KILOMETERS0 20 MILES

12

12

4

4

16

Base from U.S. Geological Survey digital data, 2011Universal Transverse Mercator projectionZone 13North American Datum of 1983 (NAD 83)
Inset

CROWLEY

COUNTY

OTERO

COUNTY

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_03_inset.ai

EXPLANAT

Lower Arkansas Diversion ditchPeriodic dischar site and site na

IR-43

Long-term contin water-quality s

Holbrook Ditch

Holbrook Ditch

Rocky Ford Ditch

Fort LyonStorage Canal

Otero Canal

Catlin Canal

HungerfordHollow

PattersonHollow

Arkansas River

at Catlin Dam

Lake Meredith

outlet Lake Meredith

Apishapa Rivernear Fowler

Apishapa Riverat Highway 50 Seasonal contin

 water-quality s

Paterson Hollow

Long-term contin water-quality s monitor and sit

Arkansas River

at Las Animas

Long-term contin water-quality s monitor and sit

Arkansas River

near Nepesta

Seasonal contin water-quality s monitor and sit

Arkansas River

at Swink

Base from U.S. Geological Survey digital data, 2011Universal Transverse Mercator projectionZone 13North American Datum of 1983 (NAD 83)

38°08'

104°00' 103°56' 103°52' 103°48' 103°44'

38°04'

4

2

2

0 5 KILOMETERS0 5 MILES

3

3

1

1

4

Rocky Ford

Fowler

Oxford Farmers Ditch

Apishapa

River

Rocky Ford Highline Canal

Otero CanalCatlin CanalRocky Ford Ditch

50

96
8 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 4. Annual hydrographs for Arkansas River at Portland (U.S. Geological Survey (USGS) station number 07097000), Arkansas 

River near Avondale (USGS station number 07109500), and Arkansas River at Las Animas (USGS station number 07124000), Colorado, 

2009–2010.

1,000

January 1, 2009

March 2, 2009

May 2, 2009

July 1, 2009

August 31, 2009

October 30, 2009

December 30, 2009

February 28, 2010

April 30, 2010

June 29, 2010

August 29, 2010

October 28, 2010

December 28, 2010

0

2,000

3,000

4,000

5,000

6,000

Daily mean streamflow, in cubic feet per second

EXPLANATION

Arkansas River at Portland—U.S. Geological Survey

 station 07097000

Arkansas River near Avondale—U.S. Geological Survey

 station 07109500

Arkansas River near Las Animas—U.S. Geological Survey

 station 07124000

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_04.ai

Streamflow Data

Streamflow data analyzed for this report consisted 

primarily of daily streamflow records retrieved from 

established long-term streamflow gages or from seasonal 

gages installed and operated as part of this study. In some 

instances, where relatively small streamflows were observed, 

daily values were estimated from available periodic 

streamflow measurements. Streamflow data from selected 

wastewater-treatment facilities were provided to the USGS 

by the plant operators. Typically, daily streamflow data 

from established gages are published by either the USGS or 

the State of Colorado Division of Water Resources (DWR) 

at their individual web sites. The USGS Colorado Water 

Science Center Web site interface for annual water data 

reports can be accessed at http://wdr.water.usgs.gov/index.

html. The Colorado DWR Web site interface for surfacewater conditions can be accessed at http://www.dwr.state.

co.us/SurfaceWater/default.aspx.

Streamflow Data in the Upper Arkansas River 

Basin Study Reach

The Colorado DWR operates and maintains two 

streamflow gages along the UARB study reach of the Arkansas 

River (table 1 and fig. 2). Monitoring site names herein are 

those used in table 1. At least 20 years of streamflow data are 

available for the two gaging sites—Ark at Canon City and Ark 

at Portland. Generally, daily-mean streamflow (herein referred 

to as daily streamflow) values were available for all dates during 

the study period. No established long-term USGS streamflow 

gages were operational in the UARB study reach; however, 

seasonal streamflow gages were installed at the monitoring 

sites Ark nr Canon City and Ark nr Portland (table 1 and fig. 2). 

Pressure-transducer equipment was installed at each of these 

sites, and daily streamflow values generally were computed 

from July–December 2009 and from May–November 2010. 

Suggested procedures for maintaining records for these seasonal 

sites are described in Rantz and others (1982a,b).
Methods of Investigation 9

Table 1. Site names and station names for the Upper Arkansas River Basin and Lower Arkansas River Basin study reaches in 

Colorado with available monitoring equipment, 2009–2010.—Continued

[USGS, U.S. Geological Survey; MS, main stem; TR, tributary; DV, diversion canal or ditch; WW, wastewater treatment facility; eQgs, existing USGS 

streamflow station; eQco, existing CODWR streamflow station; sQgs, seasonal USGS streamflow station; user; user supplied streamflow data; eQWgs, existing 

USGS water-quality station; sQWgs, seasonal USGS water-quality station; WWTP, wastewater treatment plant; --, none available; R, River; Cr, Creek; nr, near; 

trib, tributary; CR, County Road; BR, Business Road; blw, below; Rd, Road; Hwy, Highway; abv, above]

Site name USGS 

station number USGS station name Site type

Available

monitoring

equipment

on site

Upper Arkansas River Basin study reach: Canon City to Pueblo Reservoir 

(bold type denotes subreach boundaries)

Ark at Canon City 07096000 Arkansas R at Canon City MS eQco, eQWgs

Canon City ditch -- Canon City and Oil Creek Ditch DV(1) eQco

Fremont ditch -- Fremont Ditch DV(1) eQco

Sand Cr 382536105113901 Sand Creek near mouth at Canon City TR --

Fourmile Cr 07096500 Fourmile Creek near Canon City TR sQgs

Ark nr Canon City 07096515 Arkansas R at Fourmile Rd near Canon City MS sQgs, sQWgs

Oil Cr Ditch return 382520105104101 Oil Creek Ditch return flow at Fourmile Road near Canon City TR eQco

Minnequa Canal 07096530 Minnequa Canal at head gate near Florence DV(1) eQco

Chandler Cr 382409105081701 Chandler Creek at Hwy 115 near Florence TR --

Oak Cr 382348105073901 Oak Creek at Hwy 115 near Florence TR --

Oak Cr trib 382334105071701 Oak Creek tributary at Hwy 115 at Florence TR --

Ark trib 2 at CR 119 382330105052301 Arkansas R trib 2 at CR 119 near Florence TR --

Ark trib 1 at CR 119 382323105045001 Arkansas R trib 1 at CR 119 near Florence TR --

Ark rtn at Hwy 115 382324105040601 Arkansas R return at Hwy 115 near Florence TR --

Fremont WWTP 382322105040501 Fremont County WWTP effluent outfall near Florence WW user

Brush Hollow 382410105032301 Brush Hollow at Hwy 115 near Florence TR sQgs(2)

Hardscrabble Cr 382337105014600 Hardscrabble Creek at Hwy 120 at Portland TR sQgs

Ark at Portland 07097000 Arkansas R at Portland MS eQco, eQWgs

Bear Cr 382320105002901 Bear Creek at Hwy 120 at Portland TR sQgs

Ark trib 1 at CR 112 382240105010301 Arkansas R trib at CR 112 near Portland TR --

Ark trib 2 at CR 112 382226105001501 Arkansas R trib 2 at CR 112 near Portland TR --

Ark trib 1 at Hwy 120 382308104583201 Arkansas R trib 1 at Hwy 120 near Portland TR --

Ranger Cr 382236104580101 Ranger Creek at Old Portland Hwy near Portland TR --

Beaver Cr 07099100 Beaver Creek near Portland TR sQgs(3)

Ark nr Portland 07099200 Arkansas R near Portland MS sQgs, sQWgs

Lower Arkansas River Basin study reach: Avondale to Las Animas 

(bold type denotes subreach boundaries)

Ark nr Avondale 07109500 Arkansas R near Avondale MS eQgs, eQWgs

Sixmile Cr 381440104234401 Sixmile Creek trib abv Hwy 50 near Avondale TR sQgs

Collier Ditch 381632104202001 Collier Ditch at Hwy 50 near Avondale DV eQco(3)

IR-43 381412104202101 IR-43Avondale D at BR 50 near Avondale TR --

Colorado Canal 381443104153301 Colorado Canal at Hwy 209 near Boone DV eQco

Huerfano R 07116500 Huerfano R near Boone TR eQgs

Highline Canal 381334104142301 Rocky Ford Highline Canal head gate near Boone DV eQco

Ark blw Highline Canal 381317104135400 Arkansas R below Rocky Ford Highline head gate MS sQgs(3)
10 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Table 1. Site names and station names for the Upper Arkansas River Basin and Lower Arkansas River Basin study reaches in 

Colorado with available monitoring equipment, 2009–2010.—Continued

[USGS, U.S. Geological Survey; MS, main stem; TR, tributary; DV, diversion canal or ditch; WW, wastewater treatment facility; eQgs, existing USGS 

streamflow station; eQco, existing CODWR streamflow station; sQgs, seasonal USGS streamflow station; user; user supplied streamflow data; eQWgs, existing 

USGS water-quality station; sQWgs, seasonal USGS water-quality station; WWTP, wastewater treatment plant; --, none available; R, River; Cr, Creek; nr, near; 

trib, tributary; CR, County Road; BR, Business Road; blw, below; Rd, Road; Hwy, Highway; abv, above]

Site name USGS 

station number USGS station name Site type

Available

monitoring

equipment

on site

Oxford Canal 381046104091501 Oxford Canal at Huckleberry Rd near Nepesta DV eQco

Ark at Nepesta 07117500 Arkansas R at Nepesta MS eQco, sQWgs

Chicosa Cr 07117600 Chicosa Creek near Fowler TR sQgs

Otero Canal 380819104020601 Otero Canal at sluice near Fowler DV eQco(4)

Hungerford Hollow 380739103593701 Hungerford Hollow at Hwy 50 near Fowler TR sQgs

Apishapa R at Hwy 50 380715103564701 Apishapa R at Hwy 50 near Fowler TR sQgs

Apishapa R nr Fowler 07119500 Apishapa R near Fowler TR eQgs

Catlin Canal 380727103544201 Catlin Canal at CR 9 near Manzanola DV eQco

Ark at Catlin Dam 07119700 Arkansas R at Catlin Dam near Fowler MS eQco, eQWgs

Holbrook Ditch 380636103444801 Holbrook Ditch at Hwy 71 near Rocky Ford DV eQco

Ft. Lyon Storage Canal 380633103444901 Fort Lyon Storage Canal at Hwy 71 near Rocky Ford DV eQco

Rocky Ford Ditch 380610103483501 Rocky Ford Ditch at Road 14.5 near Vroman DV eQco

Lake Meredith outlet 07120480 Lake Meredith outlet at Hwy 71 near Ordway TR eQco, eQWgs, 

Patterson Hollow 380456103473701 Patterson Hollow at Hwy 50 near Vroman TR sQgs

Ark nr Rocky Ford 07120500 Arkansas R near Rocky Ford MS eQco, sQWgs

Timpas Cr 07121500 Timpas Creek at mouth near Swink TR eQgs

Ark at Swink 07121700 Arkansas R at Swink MS eQco, sQWgs

Ft. Lyon Canal 07122005 Fort Lyon Canal near La Junta DV eQco

Crooked Arroyo 375955103351201 Crooked Arroyo at Hwy 50 near La Junta TR sQco

Anderson Arroyo 07122800 Anderson Arroyo at La Junta TR sQgs(2)

Ark at La Junta 07123000 Arkansas R at La Junta MS eQco, sQWgs

La Junta WWTP 07123080 La Junta sewage effluent at La Junta WW user

Ark at Las Animas 07124000 Arkansas R at Las Animas MS eQgs, eQWgs

1

No periodic sampling occurred at this diversion canal or ditch. Water-quality data were estimated from a main-stem site on the Arkansas River given the close 

proximity of the diversion head gate to a sampled location on the river.

2

Seasonalstreamflow only in 2010.

3

Seasonal streamflow only in 2009.

4

Daily streamflow data provided by Colorado Division of Water Resources Division 2 Water Commissioner, written commun., Aug. 23, 2011).
Methods of Investigation 11

No established streamflow gages were operational 

on any tributary in the UARB during the study period. 

Historical data, however, were available for Fourmile Cr 

and Beaver Cr. Additionally, pressure transducers were 

installed and operated seasonally at five tributary sites in 

the UARB to aid in the quantification of inflows to the 

river during the study period (table 1). Seasonal streamflow data were available at Fourmile Cr, Brush Hollow, 

Hardscrabble Cr, Bear Cr, and Beaver Cr (fig. 2). Generally, daily streamflow for these seasonal sites was computed for a period of record similar to that of the two 

main-stem sites with two exceptions: Beaver Cr was only 

operational in 2009 and Brush Hollow was only operational in 2010. Several other tributaries to the Arkansas 

River were only measured periodically (table 1). Generally, streamflow from these tributaries was small compared 

to other tributaries in the study reach and (or) anticipated 

DS loading to the river was expected to be minimal.

Diversion data from three ditches were analyzed to 

quantify streamflow diverted from the river during the study 

period. The Canon City and Fremont ditches divert water near 

Canon City for irrigation purposes. The Minnequa Canal is 

a large diversion structure that diverts approximately 53,000 

acre-feet of water annually from the Arkansas River for 

industrial use (fig. 2).

Streamflow Data in the Lower Arkansas River 

Basin Study Reach

Two established streamflow gages are operated by the 

USGS in the LARB study reach from Avondale to Las Animas 

(table 1 and fig. 3). At least 20 years of streamflow data were 

available for Ark nr Avondale and Ark at Las Animas. Unitvalue (15-minute record) and daily streamflow data were 

available for each of these two sites for the study period 

(2009–2010). One streamflow-gaging site (Ark at Swink) 

was operated seasonally on the main stem of the river during 

parts of the study period. A pressure transducer was installed 

and operated seasonally at Ark at Swink and, generally, daily 

streamflow at this site was computed for July–December 

2009 and May–November 2010. Suggested procedures for 

maintaining records at the seasonal streamflow-gaging sites 

are described in Rantz and others (1982a,b).

The Colorado DWR maintains and operates three 

streamflow gages on the Arkansas River in the LARB (table 1 

and fig. 3). The three sites are Ark at Nepesta, Ark nr Rocky 

Ford, and Ark at La Junta; at least 20 years of daily streamflow 

data were available for each site. Generally, daily streamflow 

values were available for all dates during the study period.

Three established streamflow gages on tributaries 

to the Arkansas River are operated by the USGS. Data 

from two of the sites, Huerfano R and Timpas Cr, were 

used directly in the computation of tributary flow to the 

Arkansas River. Data from the third site, Apishapa R nr 

Fowler, were used to supplement data at a downstream 

streamflow gage that was operated seasonally, Apishapa 

River at Hwy 50. Seasonal streamflow data were obtained 

at seven tributary sites in the LARB by installing and 

operating pressure transducers at each site (table 1 and 

fig. 3). Seasonal streamflow data were available for 

Sixmile Cr, Chicosa Cr, Hungerford Hollow, Apishapa R at 

Hwy 50, Patterson Hollow, Crooked Arroyo, and Anderson 

Arroyo (fig. 3). Generally, daily streamflow was computed 

for a period of record similar to that of the main-stem site 

at Swink with the exception of Anderson Arroyo, which 

only was operational in 2009. A pressure transducer was 

not installed at site IR-43 because streamflow was small 

and anticipated DS loading to the river was minimal. 

Streamflow measurements were performed periodically 

at all these sites, as needed, to help determine seasonal 

streamflow characteristics.

In the LARB, streamflow data were collected by the 

State of Colorado at 10 diversion sites. Daily diversion 

streamflow data were available for Collier Ditch, Colorado 

Canal, Highline Canal, Oxford Canal, Otero Canal, Catlin 

Canal, Holbrook Ditch, Ft. Lyon Storage Canal, Rocky Ford 

Ditch, and Ft. Lyon Canal. With the exception of Collier Ditch 

and Otero Canal, data for all these sites were available from 

the “Current Streamflow Conditions” Web site maintained 

by the Colorado DWR at http://www.dwr.state.co.us/

SurfaceWater/default.aspx. Data for these sites were used to 

quantify diversion flows from the river during the study period 

(table 1). One reservoir outlet site (Lake Meredith outlet) is 

operated by the State. Generally, daily streamflow data were 

available for a period of record when water was being diverted 

at the head gates.

Water-Quality Data

The water-quality data used in this report consisted 

of (1) SC values from continuous-monitoring sites, (2) 

periodic SC measurements at selected sites, and (3) DS 

concentrations from water samples collected at numerous 

sites in the two study reaches. Daily-mean SC data (herein 

referred to as daily SC) were retrieved from the USGS 

NWIS database for continuous water-quality monitoring 

sites (established or seasonal) on the main stem of the 

Arkansas River. Periodic measurements of SC were 

available for all sites in both study reaches and were 

typically paired with DS concentrations. As such, linear 

regression analyses to estimate DS concentrations from 

SC could be performed. All these data were collected as 

part of a larger sampling effort to assess the water quality 

in the Arkansas River Basin as described in Ivahnenko 

and others (2012). Estimated DS concentrations combined 

with streamflow could then be used to determine DS 

mass-loading characteristics for the study reaches. The 

following sections of this report describe the continuous 

SC network on the main stem of the Arkansas River and 

the periodic collection of SC and DS data at main-stem, 

tributary, and diversion sites including the estimation of 

DS concentrations through regression techniques.
12 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Continuous Specific-Conductance Data

Two established water-quality monitoring sites on the 

Arkansas River are operated by the USGS in the UARB 

study reach (table 1 and fig. 2). At least 20 years of daily SC 

data were available for the sites Ark at Canon City and Ark 

at Portland. Additionally, two water-quality monitors were 

installed and operated seasonally on the main stem of the river. 

Monitors at Ark nr Canon City and Ark nr Portland (table 1 

and fig. 2) were operational from July through December 2009 

and May through November 2010. Generally, daily SC data 

for these two sites were available for these dates. 

In the LARB, three established water-quality monitoring 

sites are operated by the USGS on the Arkansas River (fig. 3). 

At least 20 years of SC data are available for the sites Ark 

nr Avondale, Ark at Catlin Dam, and Ark at Las Animas. 

Additionally, one water-quality monitor was installed and 

operated seasonally on the main stem of the river at Ark at 

Swink (table 1 and fig. 3). This monitor was operational from 

July through December 2009 and May through November 

2010; daily SC data generally were available for these 

dates. Continuous SC data also were collected by the USGS 

downstream from Lake Meredith (fig. 3).

Periodic Water-Quality Data

Data-collection activities were conducted for 2 years in 

the two study reaches. In general, water-quality samples were 

collected from July through December 2009 and May through 

October 2010. In each study reach, samples were collected 

periodically to characterize the water quality throughout 

the various hydrologic conditions observed in the Arkansas 

River Basin (Ivahnenko and others, 2012). Periodic sampling 

techniques used established protocols as described in USGS 

National Field Manual (U.S. Geological Survey, variously 

dated). Analysis of water samples for the quantification of DS 

concentrations was performed at the USGS National Water 

Quality Laboratory in Lakewood, Colo., using approved 

methods for the determination of DS using residue-onevaporation techniques (Fishman and Friedman, 1989). Data 

collected in the study area by other USGS water-quality 

monitoring programs during this time were obtained from the 

USGS NWIS database and used to supplement spatial and 

temporal gaps in the data-collection network. Additionally, 

historical data for selected sites (where available) were used 

to increase the number of paired SC and DS values used in the 

regression analyses.

Thirteen water-quality sampling events were 

conducted from July 2009–October 2010 in the UARB 

along a reach from Ark at Canon City downstream to 

Ark nr Portland and in the LARB along a reach from 

Ark nr Avondale to Ark at Las Animas (Ivahnenko and 

others, 2012). Sampling events included routine periodic 

sampling and synoptic sampling using time-of-travel 

(parcel tracking) techniques. Numerous miscellaneous SC 

measurements also were recorded at all tributary sites. 

Table 2 summarizes the SC and DS data collected for 25 

sites in the UARB and for 28 sites in the LARB during the 

study period. 

Statistical Analyses

Specific conductance has been shown to be highly 

correlated with DS concentrations in the Arkansas River 

(Miller and others, 2010; Ortiz and others, 1998). Simple 

linear regression provides a best straight-line fit between 

two variables (one independent and one dependent variable) 

to obtain a predictive equation. Ivahnenko and others 

(2012) provided simple linear-regression relations between 

instantaneous SC (the independent variable) and DS (the 

dependent variable) values using paired data measured at 

selected surface-water sites in the two study reaches from 

July 2009 through November 2010. For this report, the 

regressions described by Ivahnenko and others (2012) were 

used to estimate daily DS concentrations from measured 

daily or instantaneous SC values at most main-stem and 

tributary sites; additional historical paired data were used in 

selected instances to increase the number of comparisons for 

regression (table 2). 

Locally weighted scatterplot smoothing (LOWESS) 

techniques were used to evaluate gains or losses from 

unmeasured sources and sinks in daily streamflow and 

estimated daily DS load for selected sites in the Arkansas 

River. Originally developed by Cleveland (1979) and 

further developed by Cleveland and Devlin (1988), 

LOWESS specifically denotes a method that is more 

descriptively known as locally weighted polynomial 

regression. The smoothing technique describes the relation, 

in this instance, between streamflow and time or between 

DS and time without assuming linearity or normality of 

the residuals (Helsel and Hirsch, 1992). At each point in 

the dataset, a low-degree polynomial is fit to a subset of 

the data with explanatory variable values near the point 

whose response is being estimated. The polynomial is 

fit using weighted least-squares regression, giving more 

weight to points near the point whose response is being 

estimated and less weight to points further away. The value 

of the regression function for the point is then obtained 

by evaluating the local polynomial using the explanatory 

variable values for that data point. The LOWESS fit is 

complete after regression-function values have been 

computed for each of the data points in question.

Quality Assurance and Quality Control

Streamflow and water-quality data collected as part of 

this report were varied with respect to their quantity and 

quality. All of the data were reviewed using appropriate 

methodologies and (or) procedures as required by the 

USGS or the State of Colorado. In general, these data can 

be accessed through the World Wide Web as described 

previously in this report.
Methods of Investigation 13

Table 2. Number of specific-conductance measurements and dissolved-solids samples collected at sites in the Upper Arkansas River 

Basin and Lower Arkansas River Basin study reaches in Colorado, 2009–2010.—Continued

[SC, specific conductance; DS, dissolved solids; MS, main stem; DV, diversion canal or ditch; TR, tributary; WW, wastewater treatment plant; --, no data available]

Site name Site type

Number of

periodic SC

values available

2009–2010

Number of 

periodic DS

values available

2009–2010

Number of 

paired 

SC and DS 

values used

in analysis

Were historical 

(1990–2008) 

SC and DS data

used as part of

data analysis?

Upper Arkansas River Basin study reach: Canon City to Pueblo Reservoir 

(in downstream order)

Ark at Canon City(1) MS 13 13 39 yes

Canon City and Oil Creek ditch(2) DV -- -- -- --

Fremont ditch(2) DV -- -- -- --

Sand Cr TR 13 7 7 --

Fourmile Cr TR 18 7 20 yes

Ark nr Canon City(1) MS 14 13 13 --

Oil Cr Ditch return TR 14 7 7 --

Minnequa Canal(2) DV -- -- -- --

Chandler Cr TR 11 5 5 --

Oak Cr TR 14 7 7 --

Oak Cr trib TR 13 7 7 --

Ark trib 2 at CR 119 TR 15 7 7 --

Ark trib 1 at CR 119 TR 17 7 7 --

Ark rtn at Hwy 115 TR 14 10 10 --

Fremont WWTP WW 9 8 8 --

Brush Hollow TR 16 7 7 --

Hardscrabble Cr TR 18 6 19 yes

Ark at Portland(1)(3) MS 49 21 21 no

Bear Cr TR 19 7 7 --

Ark trib 1 at CR 112 TR 16 7 7 --

Ark trib 2 at CR 112 TR 11 6 6 --

Ark trib 1 at Hwy 120 TR 17 7 7 --

Ranger Cr TR 17 7 7 --

Beaver Cr TR 18 7 7 no

Ark nr Portland(1) MS 23 13 13 no

Lower Arkansas River Basin study reach: Avondale to Las Animas 

(in downstream order)

Ark nr Avondale(1)(3) MS 42 14 14 no

Sixmile Cr TR 23 7 7 --

Collier Ditch(4) DV 5 1 1 --

IR-43 TR 21 7 7 --

Colorado Canal(4) DV 16 3 3 --

Huerfano R TR 26 4 16 yes

Highline Canal(4) DV 35 4 4 --

Oxford Canal(4) DV 34 4 4 --

Ark at Nepesta(1) MS 26 15 15 no
14 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Table 2. Number of specific-conductance measurements and dissolved-solids samples collected at sites in the Upper Arkansas River 

Basin and Lower Arkansas River Basin study reaches in Colorado, 2009–2010.—Continued

[SC, specific conductance; DS, dissolved solids; MS, main stem; DV, diversion canal or ditch; TR, tributary; WW, wastewater treatment plant; --, no data available]

Site name Site type

Number of

periodic SC

values available

2009–2010

Number of 

periodic DS

values available

2009–2010

Number of 

paired 

SC and DS 

values used

in analysis

Were historical 

(1990–2008) 

SC and DS data

used as part of

data analysis?

Chicosa Cr TR 22 7 7 --

Otero Canal(4) DV 18 4 4 --

Hungerford Hollow TR 26 7 7 --

Apishapa R at Hwy 50 TR 26 7 7 no

Catlin Canal(4) DV 25 3 3 --

Ark at Catlin Dam(1)(3) MS 37 14 14 no

Holbrook Ditch(4) DV 20 1 1 --

Ft. Lyon Storage Canal(4) DV 11 1 1 --

Rocky Ford Ditch(4) DV 34 4 4 --

Patterson Hollow TR 26 7 7 --

Ark nr Rocky Ford(1)(3) MS 37 28 28 no

Timpas Cr TR 30 7 7 --

Ark at Swink(1) MS 25 16 16 --

Ft. Lyon Canal(4) DV 33 3 3 --

Crooked Arroyo TR 31 7 7 no

Anderson Arroyo TR 27 7 7 --

Ark at La Junta(1) MS 26 16 16 no

La Junta WWTP(5) WW 6 6 6 --

Ark at Las Animas(1) MS 36 4 44 yes

1

Continuous water-quality monitor at this site.

2

No dissolved-solids data collected; characteristics of nearest upstream main-stem site used in data analyses.

3

Additional dissolved-solids data collected as part of other USGS water-quality sampling efforts included.

4

Limited dissolved-solids data collected; characteristics of nearest upstream main-stem site used in data analyses.

5

Samples only collected in 2009 at the La Junta wastewater treatment plant.
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 15

Typically, daily streamflow data for established 

USGS gages are published in Annual Water Data Reports; 

streamflow data are published by water year (October 1 

through September 30). Recent data (post-2005) can be 

accessed online at http://wdr.water.usgs.gov/index.html. 

Documentation describing the accuracy of the data and 

methodology used to collect and report these data also 

can be accessed at this web site. Seasonal streamflow data 

collected at numerous sites in the study reaches can be 

accessed through the USGS Automated Data Processing 

System (ADAPS) developed for the processing, storage, 

and retrieval of water data (U.S. Geological Survey, 2003). 

ADAPS is part of the NWIS developed by the USGS 

and is a distributed water database in which data can be 

processed over a network of computers at USGS offices 

throughout the United States.

The Colorado Division of Water Resources also 

publishes streamflow data for the Arkansas River 

Basin (Colorado Division of Water Resources, 2010). 

Hydrographic Program staff for the State of Colorado visit 

streamflow-gaging stations on a frequent basis to maintain 

equipment and ensure correct operation. They also perform 

discharge measurements for purposes of calibrating the 

stage-discharge relation for a gaging station, as well as 

take note of physical factors present at the station that may 

be affecting the stage-discharge relation. 

Water-quality data collected as part of this report 

included continuous specific-conductance data collected 

at long-term or seasonally monitored sites and periodic 

water-quality data collected onsite. Daily SC data from 

established sites in the study area can be accessed through 

the NWIS web interface at http://waterdata.usgs.gov/nwis/

qw. Procedures for operation, computation, and reporting of 

continuous water-quality monitors are described in Wagner 

and others (2006). Continuous SC data collected at three 

seasonal sites in the study area can be accessed through 

ADAPS. Water-quality samples were collected on site and 

submitted to the USGS National Water Quality Laboratory in 

Lakewood, Colo., for chemical analysis. Quality-control and 

quality-assurance measures associated with these data are 

described by Ivahnenko and others (2012). 

Estimation of Gains and Losses in 

Streamflow from Unmeasured Sources 

and Sinks

A common approach to investigating the flow of 

water from unmeasured sources or sinks is to measure 

streamflow at numerous points along a study reach to 

determine a water budget. These measurement points 

(sites) subdivide the stream into subreaches and account 

for inputs (such as tributaries and return flows) and outputs 

(such as diversions). The difference between inflows and 

outflows may be attributed to unmeasured sources or 

sinks, such as the interaction between the stream and the 

underlying aquifer. When applied to a defined reach, the 

quantity of flow attributable to unmeasured sources or 

sinks (the flux) can be estimated as 

Qflux = Qds – Qus + ∑Qout – ∑Qin (1)

where

Qds is the streamflow at the downstream end of 

the subreach,

Qus is the streamflow at the upstream end of the 

subreach,

Qout are outputs from the subreach such as 

diversions, and

Qin are inputs to the reach such as tributaries or 

sewage outfalls. 

As such, a positive Qflux indicates a net gain of water 

to the subreach in the form of groundwater or unmeasured 

surface-water inflow. A negative Qflux indicates a net loss of 

surface water to the groundwater system, evapotranspiration, unmeasured diversions, or other sinks. This loss is 

commonly termed a transmission loss.

The quantification of all fluxes to or from the river is 

a simple concept, but can be difficult to apply. The method 

requires an accurate measurement of streamflow as well as a 

complete accounting of all other gains and losses evident for 

the reach. The uncertainties associated with the streamflow 

measurements and estimates for water-balance components 

such as unmetered extraction, evapotranspiration, ungaged 

tributary flows, overbank flooding losses, and flood return 

flows can exceed the magnitude of the seepage flux being 

estimated (Commonwealth of Australia, 2006). Streamflow 

measurement errors can be +25 percent during high-flow 

conditions, and from –50 to +100 percent for flash floods in 

semiarid catchments (Lerner and others, 1990). 

A water budget provides a reasonable accounting 

of the water in the system if all identified inflow and 

outflows have been quantified. However, inherent 

uncertainties are associated with the collection of the data 

needed to calculate a water budget for the Arkansas River. 

Typically, streamflow measurements performed by the 

USGS and the State of Colorado can be assumed to have 

an error of less than 10 percent (Rantz and others, 1982a). 

Given the other unmeasured components of error in this 

analysis, error bars of ±15 percent of the averaged daily 

streamflow of the upstream and downstream main-stem 

sites within a subreach were calculated to help evaluate 

the results. A value of ±15 percent was determined to be 

sufficiently conservative to allow for the identification 

of stream reaches where streamflow gains or losses 

exceeded the measurement error. Consistent exceedences 

of the error bars could potentially indicate stream reaches 

where surface-water inflows or groundwater inputs from 

unmeasured sources and sinks are a substantial part of the 

water budget.
16 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Gains and Losses in Streamflow in the Upper 

Arkansas River Basin Study Reach

The UARB study reach contains two long-term 

streamflow gages (fig. 2); both sites are managed by the State 

of Colorado. Comparisons of total annual streamflow for the 

upstream site, Ark at Canon City, and the downstream site, Ark 

at Portland, indicated that this generally was a gaining reach. In 

2009 and 2010, total annual streamflow increased 3.7 percent 

and 4.0 percent, respectively, in the downstream direction.

Comparisons of monthly streamflow totals, however, 

indicated substantial variations in the percentage change in 

streamflow on a seasonal basis (fig. 5). Overall, changes in total 

monthly streamflow in 2009 and 2010 for the reach ranged 

from –4.7 percent (indicating a losing reach) to 36.2 percent 

(indicating a gaining reach). Typically, a loss of water occurred 

during the winter months (December–March) when base-flow 

conditions were prevalent. During this period, as much as 

60 percent of the streamflow observed at the upstream gaged 

site (Ark at Canon City) was diverted into the Minnequa 

Canal. During the snowmelt runoff period (April–August), 

streamflow increased in the downstream direction as tributary 

and groundwater inputs exceeded the amount of water diverted 

from the river. Generally, diversion totals accounted for less 

than 10 percent of the streamflow in the river at these higher 

streamflow conditions. Overall, the increase in total monthly 

streamflow from Ark at Canon City to Ark at Portland during 

the snowmelt runoff period was between 1.5 and 12.2 percent. 

From September through November, groundwater return flows 

became more pronounced as streamflow in the river decreased. 

The increase in streamflow along the reach during this period 

ranged from 10.6 to 36.2 percent even as diversions continued 

to remove water from the river. 

Data collected as part of this study were intended to fill 

data gaps associated with an analysis of water budgets along 

subreaches of the Arkansas River. In the UARB, the collection 

of additional streamflow data at previously ungaged tributary 

sites and two main-stem sites provided additional data needed 

to improve the estimates of streamflow from unmeasured 

sources during the study period. The results of these analyses 

for the subreaches are described in the following sections of 

this report. Statistical smoothing of the gains and losses from 

unmeasured streamflow using LOWESS techniques were 

used to help interpret the results of the overall water budget. 

Error bars of ±15 percent were used to indicate the potential 

error associated with the streamflow estimations. As such, 

it was assumed that inputs to the river from unmeasured 

sources of surface water or groundwater were evident when 

the LOWESS line consistently exceeded the upper 15-percent 

error bar. Conversely, a loss of water within a subreach 

(a sink) was evident when the LOWESS line consistently 

exceeded the lower 15-percent error bar. Subreaches of the 

UARB between main-stem gages are discussed to examine 

if gains or losses from unmeasured sources or sinks, such 

as ungaged surface flows or surface-water groundwater 

interactions, occurred along any particular subreach. 

Canon City to Portland

Estimates of gains or losses from unmeasured streamflow 

along the 5-mile river subreach from Ark at Canon City 

downstream to Ark nr Canon City during 2009 and 2010 are 

shown in figure 6. Estimates were only made for periods when all 

the seasonal streamflow gages in this subreach were operational. 

Daily streamflow data from two tributary inputs and two 

diversion structures were used to estimate the daily water budget 

along this reach (table 1). In 2009, estimates of unmeasured 

streamflow exceeded the 15-percent error bar (an unmeasured 

gain) during August through October (fig. 6A). Similar results 

were observed the following year from August into November, 

when data collection was discontinued (fig. 6B). These results 

generally were consistent with the description of total monthly 

streamflow described previously in this report. The magnitude of 

the unmeasured streamflow flux to the Arkansas River along this 

subreach was relatively consistent between the 2 years and was 

estimated to be about 100 cubic feet per second (ft3

/s) or 20 ft3/s 

per river mile. The river mileage of this subreach of the Arkansas 

River is approximately one-third of the total river mileage 

between the Ark at Canon City and Ark at Portland gages. 

Estimates of gains and losses from unmeasured streamflow 

along the 11-mile river subreach from Ark nr Canon City 

downstream to Ark at Portland during 2009–2010 are shown 

in figure 7. Estimates were only made for periods when all the 

seasonal streamflow gages in this subreach were operational. 

Daily streamflow data from nine tributary or ditch-return inputs, 

one wastewater input, and one diversion structure were used 

to estimate the daily water budget along this reach (table 1). 

Estimates of the daily water budget during the late summer and 

fall of 2009 indicated that the unmeasured streamflow flux to the 

river was within the potential error of measurement (± 15 percent), 

as defined earlier in this report (fig. 7A). Similar results were 

observed for daily estimates in 2010 including the high-flow 

period from late May through July (fig. 7B). As such, there is no 

indication that gains or losses from unmeasured streamflow could 

be quantified in this subreach of the Arkansas River. 

Portland to Pueblo Reservoir

Estimates of gains and losses from unmeasured 

streamflow along the 7-mile subreach from Ark at Portland 

downstream to Ark nr Portland during 2009–2010 are shown 

in figure 8. Estimates were only made for periods when all 

the seasonal streamflow gages in this reach were operational. 

Daily streamflow data from six tributary inputs were used to 

estimate the daily water budget along this subreach (table 1). 

During 2009, estimates of the daily water budget along this 

subreach of the river indicated that the unmeasured streamflow 

flux to the river was within the potential error of measurement, 

as defined for this analysis (fig. 8A). Similar results were 

observed for daily estimates in 2010 (fig. 8B) including the 

high-flow period from late May through July. As such, there is 

no indication that gains or losses from unmeasured streamflow 

could be quantified in this subreach of the Arkansas River. 
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 17

Figure 5. (A) Total monthly streamflow and (B) percentage change in total monthly streamflow between Arkansas River at Canon City 

to Arkansas River at Portland, Colorado, 2009–2010.

20,000

0

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

Total monthly streamflow, in acre-feet Change in total monthly streamflow between Arkansas River at

Canon City and Arkansas River at Portland, in percent

LOSS

GAIN

B

A

–10

Jan. Feb. Mar. Apr. May June July

2009 2010

Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

–5

0

5

10

15

20

25

30

35

40

Year and month

EXPLANATION

Arkansas River at

Canon City

Arkansas River at

Portland

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_05.ai
18 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

May June July August

2009

September October November December

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

A

–100

–200

–300

–400

–500

–100

–200

–300

–400

–500

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_06.ai

Figure 6. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Upper Arkansas River Basin from 

Arkansas River at Canon City downstream to Arkansas River near Canon City, Colorado, (A) 2009 and (B) 2010. 
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 19

Figure 7. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Upper Arkansas River Basin from 

Arkansas River near Canon City downstream to Arkansas River at Portland, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

A

–100

–200

–300

–400

–500

0

–100

–200

–300

–400

–500

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_07.ai

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach
20 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 8. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Upper Arkansas River Basin from 

Arkansas River at Portland downstream to Arkansas River near Portland, Colorado, (A) 2009 and (B) 2010.

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

May June

June

July August

2009

September October November December

A

500

400

300

200

100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May July August

2010

September October November December

B

500

400

300

200

–

–

–

–

–

–

–

–

–

–

100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_08.ai
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 21

Gains and Losses in Streamflow in the Lower 

Arkansas River Basin Study Reach

The LARB study reach contains several long-term 

streamflow gaging sites (table 1); the sites are operated 

and maintained either by the USGS or by the State of 

Colorado. Historical analyses of the total annual streamflow 

at streamflow gages in the LARB typically have focused on 

three main-stem sites (Ark nr Avondale, Ark at Catlin Dam, 

and Ark at Las Animas) where long-term streamflow data are 

coupled with continuous SC data collection (fig. 3). Miller 

and others (2010) compared average annual streamflow at 

these three sites and reported that a substantial decrease 

in streamflow was observed in the downstream direction 

for their analysis period of 2000–2006. The Arkansas 

River in the LARB study reach has been shown to exhibit 

decreased streamflow in the downstream direction by other 

investigators including Ortiz and others (1998), Lewis and 

Brendle (1998), and Cain (1985).

Comparisons of total annual streamflow (2009–2010) 

for the two upstream gages, Ark nr Avondale and Ark at 

Catlin Dam, indicated that substantial amounts of water 

were removed along this subreach of the river. Total annual 

streamflow decreased by 44 percent (2009) and 41 percent 

(2010) between the two gaging sites. Several large diversion 

ditches including the Rocky Ford Highline and the Colorado 

Canal are located between these two main-stem gages. 

Similarly, comparisons of total annual streamflow between 

Ark at Catlin Dam and Ark at Las Animas exhibited decreased 

flow in the downstream direction. In 2009 and 2010, 

streamflow decreased 54 percent and 58 percent, respectively, 

between the two gaging sites. Several large diversion ditches 

including the Catlin Canal and the Fort Lyon Canal remove 

water along this subreach. 

Comparisons of total monthly streamflow from Ark nr 

Avondale to Ark at Catlin Dam indicated that streamflow 

generally decreased in this subreach (fig. 9). Decreases in 

total monthly streamflow from Avondale to Catlin Dam 

ranged from 15 percent to nearly 80 percent for most of 

the year. Some gains in streamflow occurred in the late 

fall just after the cessation of the irrigation season in the 

LARB. One intermediate main-stem site, Ark at Nepesta, 

is located along this subreach and is operated by the State 

of Colorado. Comparisons of total monthly streamflow 

along the subreaches from Avondale to Nepesta and 

from Nepesta to Catlin Dam generally were similar to 

the overall profile shown in figure 9 for the reach from 

Avondale to Catlin Dam.

Overall, comparisons of total monthly streamflow 

from Ark at Catlin Dam to Ark at Las Animas indicated 

decreased streamflow in this subreach (fig. 10). Decreases 

in total monthly streamflow during 2009–2010 ranged 

from about 8 percent to about 80 percent. A gain in 

streamflow was observed during a low-flow period 

in February 2009 when the total monthly streamflow 

increased downstream by 2,224 acre-ft, resulting in a 

49-percent increase in streamflow. 

Although streamflow generally decreased in 2009 

and 2010 in the subreach from Ark at Catlin Dam to Ark at 

Las Animas, monthly streamflow comparisons at a smaller 

subreach level showed different seasonal patterns. The State 

of Colorado operates two intermediate long-term main-stem 

sites (Ark nr Rocky Ford and Ark at La Junta) within this 

reach (fig. 3). A third site, Ark at Swink, was located between 

Rocky Ford and La Junta. This site was operated seasonally 

by the USGS but limited data were available for monthly 

streamflow analysis. 

Decreases in streamflow were prevalent during most 

months between Ark at Catlin Dam and Ark nr Rocky 

Ford, but there was a marked difference in the magnitude 

of the losses seasonally (fig. 11). In contrast to the losses 

in streamflow in the subreach upstream from Catlin Dam, 

streamflow losses along this subreach occurred during the 

late fall and winter after most irrigation companies had 

stopped diverting water. Water is diverted during this time, 

however, into the Fort Lyon Storage Canal for storage in two 

off-channel reservoirs. The Fort Lyon Storage Canal diverted 

nearly 60,000 acre-ft of water in 2009 with the vast majority 

of the diversions occurring from mid-November to April 

(Colorado Decision Support System, 2011).

Between Ark nr Rocky Ford and Ark at La Junta, 

losses were prevalent during most months when irrigation 

diversions were operating in the LARB (fig. 12). Of particular 

importance in this subreach is the Fort Lyon Canal. In 2010, 

nearly 190,000 acre-ft of water were diverted through the 

Fort Lyon Canal (Colorado Decision Support System, 2011). 

Located just west of La Junta, the Fort Lyon Canal is the 

largest diversion in the study area. Similar to other reaches of 

the river, streamflow increased downstream during the winter 

after the irrigation season had ended. It is important to note 

the magnitude of the streamflow gains during the nonirrigation 

season (low flows) and losses during the irrigation season 

(high flows) when evaluating the percentage changes on a 

seasonal basis (fig. 12A). A 56-percent gain in February 2009 

resulted in an additional 1,500 acre-ft of water in the river, 

while a 56-percent loss in May 2010 resulted in the removal 

about 28,000 acre-ft of water from the river. 

From Ark at La Junta downstream to Ark at Las 

Animas, losses were prevalent during the irrigation season 

but the decrease in total monthly streamflow generally 

was less than 20 percent (fig. 13). Similar to most other 

subreaches in the LARB, increased monthly streamflow in 

the river was observed during the winter after the irrigation 

season had ended. Increases of only a few percent to near 

100 percent were observed in this subreach. It is important 

to note that streamflow in the Arkansas River is at its lowest 

at La Junta during the winter (fig. 13A), and relatively small 

increases in downstream flows can result in a relatively 

large increase in the overall percentage increase calculated 

for this analysis.
22 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

20,000

0

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

Total monthly streamflow, in acre-feet Change in total monthly streamflow between Arkansas River near

Avondale and Arkansas River at Catlin Dam, in percent

LOSS

GAIN

B

A

Jan. Feb. Mar. Apr. May June July

2009 2010

Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. −80

−70

−60

−50

−40

−30

−20

−10

0

10

20

Year and month

EXPLANATION

Arkansas River 

near Avondale

Arkansas River at

Catlin Dam

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_09.ai

Figure 9. (A) Total monthly streamflow and (B) percentage change in total monthly streamflow from Arkansas River near Avondale to 

Arkansas River at Catlin Dam, Colorado, 2009–2010.
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 23

0

20,000

40,000

60,000

80,000

100,000

Total monthly streamflow, in acre-feet Change in total monthly streamflow between Arkansas River at

Catlin Dam and Arkansas River at Las Animas, in percent

LOSS

GAIN

B

A

−100

Jan. Feb. Mar. Apr. May June July

2009 2010

Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

−80

−60

−40

−20

0

20

40

60

Year and month

EXPLANATION

Arkansas River at

Catlin Dam

Arkansas River at

Las Animas

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_10.ai

Figure 10. (A) Total monthly streamflow and (B) percentage change in total monthly streamflow from Arkansas River at Catlin Dam to 

Arkansas River at Las Animas, Colorado, 2009–2010.
24 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 11. (A) Total monthly streamflow and (B) percentage change in total monthly streamflow from Arkansas River at Catlin Dam to 

Arkansas River near Rocky Ford, Colorado, 2009–2010.

0

20,000

40,000

60,000

90,000

100,000

Total monthly streamflow, in acre-feet

10,000

30,000

50,000

80,000

70,000

Change in total monthly streamflow between Arkansas River at

Catlin Dam and Arkansas River near Rocky Ford, in percent

LOSS

GAIN

B

A

−100

Jan. Feb. Mar. Apr. May June July

2009 2010

Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

−80

− 60

− 40

− 20

0

20

40

Year and month

EXPLANATION

Arkansas River at

Catlin Dam

Arkansas River near

Rocky Ford

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_11.ai
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 25

0

20,000

40,000

60,000

90,000

100,000

Total monthly streamflow, in acre-feet

10,000

30,000

50,000

80,000

70,000

Change in total monthly streamflow between Arkansas River near

Rocky Ford and Arkansas River at La Junta, in percent

LOSS

GAIN

B

A

−100

Jan. Feb. Mar. Apr. May June July

2009 2010

Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

−50

50

0

100

150

Year and month

EXPLANATION

Arkansas River near

Rocky Ford

Arkansas River at

La Junta

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_12.ai

Figure 12. (A) Total monthly streamflow and (B) percentage change in total monthly streamflow from Arkansas River near Rocky Ford 

to Arkansas River at La Junta, Colorado, 2009–2010.
26 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 13. (A) Total monthly streamflow and (B) percentage change in total monthly streamflow from Arkansas River at La Junta to 

Arkansas River at Las Animas, Colorado, 2009–2010.

0

10,000

20,000

30,000

45,000

50,000

Total monthly streamflow, in acre-feet

5,000

15,000

25,000

40,000

35,000

Change in total monthly streamflow between Arkansas River at

La Junta and Arkansas River at Las Animas, in percent

LOSS

GAIN

B

A

−60

Jan. Feb. Mar. Apr. May June July

2009 2010

Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

−20

−40

40

20

0

100

60

80

120

Year and month

EXPLANATION

Arkansas River at

La Junta

Arkansas River at

Las Animas

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_13.ai
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 27

Avondale to Catlin Dam

Estimates of gains and losses from unmeasured streamflow 

along the 21-mile subreach from Ark nr Avondale downstream 

to Ark at Nepesta during 2009–2010 are shown in figure 14. 

Estimates were only made for periods when all the seasonal 

streamflow gages in this subreach were operational; long-term 

annual data were available for the main-stem sites, but data for 

many of the tributaries were seasonal. Daily streamflow data 

from three tributary inputs and four diversion structures were 

used to estimate the daily water budget along this subreach 

(table 1). In 2009, estimates of gains or losses from unmeasured 

streamflow did not exceed the ±15-percent error bars, as 

illustrated by the LOWESS line in figure 14A. Recall that 

LOWESS estimates greater than the error bars were considered 

an indicator of unmeasured sources or sinks to the Arkansas 

River that were not accounted for in the water budget. Similar 

results were observed the following year in 2010 (fig. 14B). 

Estimates of gains and losses from unmeasured 

streamflow for the 15-mile subreach from Ark at Nepesta 

downstream to Ark at Catlin Dam during 2009–2010 are shown 

in figure 15. Estimates were only made for periods when all the 

seasonal streamflow gages in this subreach were operational; 

long-term annual data were available for the main-stem sites, 

but data for many of the tributaries were seasonal. Daily 

streamflow data from three tributary inputs and two diversion 

structures were used to estimate the daily water budget along 

this subreach (table 1). In 2009, estimates of unmeasured 

streamflow exceeded the lower 15-percent error bar 

(unmeasured losses) for a brief time in September; otherwise, 

the estimates remained within the stated error bars until 

data collection ended in late December (fig. 15A). In 2010, 

estimated losses from unmeasured streamflow occurred for an 

extended period from September through November (fig. 15B). 

Estimated losses from unmeasured streamflow occurred at a 

rate of about 6 ft3

/s per river mile. The mechanism and spatial 

extent of the losses in this subreach of the Arkansas River were 

not identified, and further investigation would be required to 

better quantify the estimated losses. 

Catlin Dam to Las Animas

Estimates of daily gains and losses from unmeasured 

streamflow for the 20-mile subreach from Ark at Catlin Dam 

downstream to Ark nr Rocky Ford during 2009–2010 are 

shown in figure 16. Estimates were only made for periods when 

seasonal streamflow gages in this subreach were operational. 

Long-term annual data were available for the main-stem 

sites, but data for the one tributary site were seasonal. Daily 

streamflow data from one tributary, one reservoir outlet site 

(Lake Meredith), and three diversion structures were used to 

estimate the daily water budget along this subreach (table 1). 

In 2009, estimates of unmeasured streamflow exceeded the 

15-percent error bar (unmeasured gain) from early September 

through mid-October and from mid-November through 

December, when data collection ceased (fig. 16A). In 2009, there 

appeared to be a consistent positive shift to the LOWESS line, 

which suggested that gains from unmeasured flow sources were 

evident along the subreach. The estimated gain occurred at a rate 

of less than 2 ft3

/s per river mile. In 2010, there appeared to be no 

consistent exceedence of the 15-percent error bar (fig. 16B).

Estimates of daily gains and losses from unmeasured 

streamflow for the 13-mile subreach from Ark nr Rocky 

Ford downstream to Ark at La Junta during 2009–2010 are 

shown in figure 17. Estimates were only made for periods 

when all the seasonal streamflow gages in this subreach were 

operational; long-term annual data were available for the 

main-stem sites, but data for the tributary sites were seasonal. 

Daily streamflow data from three tributary inputs and one 

diversion structure were used to estimate the daily water 

budget along this subreach (table 1). In 2009, estimates of 

unmeasured streamflow exceeded the 15-percent error bar 

(unmeasured gains) from September through mid-October 

and from mid-November to mid-December (fig. 17A). Similar 

results were observed the following year in 2010 (fig. 17B). 

Overall, there appeared to be a consistent positive shift to the 

LOWESS line from September through December for both 

years, which suggested that gains from unmeasured flow 

sources were evident along the subreach. The estimated gains 

from unmeasured sources were about 26 ft3

/s, which equated 

to a rate of about 2 ft3

/s per river mile.

Estimated daily gains and losses from unmeasured 

streamflow along the subreach from Rocky Ford to La Junta 

utilized two long-term streamflow gages operated by the State 

of Colorado (fig. 17). However, an intermediate streamflow 

gage at Swink was operated seasonally by the USGS during 

the study period. As such, data were available to calculate daily 

water budgets for two subreaches between Rocky Ford and La 

Junta. Estimations of daily gains and losses from unmeasured 

streamflow along the short subreach from Rocky Ford to Swink 

(fig. 18) and from Swink to La Junta (fig. 19) are discussed here.

Daily streamflow data from one tributary input was used to 

estimate the daily water budget along the 6.3-mile subreach from 

Ark nr Rocky Ford to Ark at Swink (table 1). In 2009, estimates 

of gains and losses from unmeasured streamflow exceeded 

the 15-percent error bar (unmeasured gains) in September and 

October; the LOWESS line mostly exceeded the 15-percent error 

bar during this period (fig. 18A). In 2010, the LOWESS line only 

exceeded the error bars in October and November (fig. 18B). The 

estimated gains from unmeasured sources were about 20 ft3

/s, 

which equated to a rate of about 3 ft3

/s per river mile.

Daily streamflow data from two tributary inputs and 

one diversion structure were used to estimate the daily water 

budget along the 6.8-mile subreach from Ark at Swink to Ark 

at La Junta (table 1). In 2009, estimates of gains or losses 

from unmeasured streamflow did not exceed the ±15-percent 

error bar, and there appeared to be little if any shift to the 

LOWESS line from the zero line during this time (fig. 19A). In 

2010, estimates of unmeasured streamflow only exceeded the 

15-percent error bar (unmeasured gain) in late August through 

September and for a short time in October. Overall, there 

appeared to be no consistent positive shift to the LOWESS line 

in the later months of the analysis (fig. 19B).
28 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 14. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Lower Arkansas River Basin from 

Arkansas River near Avondale downstream to Arkansas River at Nepesta, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

A

−

−

−

−

−

500

400

300

200

100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_14.ai
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 29

Figure 15. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Lower Arkansas River Basin from 

Arkansas River at Nepesta downstream to Arkansas River at Catlin Dam, Colorado, (A) 2009 and (B) 2010.

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

May June July August

2009

September October November December

A

500

400

300

200

−

−

−

−

−

100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_15.ai
30 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 16. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Lower Arkansas River Basin from 

Arkansas River at Catlin Dam downstream to Arkansas River near Rocky Ford, Colorado, (A) 2009 and (B) 2010.

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_16.ai
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 31

Figure 17. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Lower Arkansas River Basin from 

Arkansas River near Rocky Ford downstream to Arkansas River at La Junta, Colorado, (A) 2009 and (B) 2010.

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_17.ai
32 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 18. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Lower Arkansas River Basin from 

Arkansas River near Rocky Ford downstream to Arkansas River at Swink, Colorado, (A) 2009 and (B) 2010.

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

May June July August September

2009

October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_18.ai
Estimation of Gains and Losses in Streamflow from Unmeasured Sources and Sinks 33

Figure 19. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Lower Arkansas River Basin from 

Arkansas River at Swink downstream to Arkansas River at La Junta, Colorado, (A) 2009 and (B) 2010.

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_19.ai
34 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

The results of the water-budget analysis along the reach 

from Ark nr Rocky Ford to Ark at La Junta indicated that there 

likely was unmeasured surface water and (or) groundwater 

entering the Arkansas River along this reach. When coupled 

with the estimated water budgets for the two subreaches 

of this reach, it appeared that the subreach contributing the 

unmeasured streamflow flux was most likely the upstream 

subreach from Ark nr Rocky Ford to Ark at Swink. Additional 

investigation of this reach would be needed to verify and 

better quantify the gains from unmeasured sources.

Daily gains and losses from unmeasured streamflow for 

the 25-mile subreach from Ark at La Junta downstream to 

Ark at Las Animas during 2009–2010 are shown in figure 20. 

Estimates were only made for periods when all the seasonal 

streamflow gages in this subreach were operational. Longterm annual data were available for the main-stem sites, but 

data for the input sites were seasonal. Streamflow data from 

one wastewater treatment plant were used to estimate the daily 

water budget along this subreach (table 1). Other tributaries 

and diversions are located in this subreach; however, flows 

were not quantified as part of the study objectives. In 2009 

and 2010, estimates of unmeasured streamflow exceeded the 

15-percent error bar (unmeasured gains) from mid-November 

to late December (figs. 20A and 20B). The estimated surfacewater and (or) groundwater gain occurred at a rate of about 

1 ft3

/s per river mile. 

Potential Unmeasured Sources and Sinks for 

Streamflow

In general, the methodology used to quantify streamflow 

water budgets along the UARB and LARB study reaches 

accounted for a large percentage of the streamflow. However, 

the results from the water-budget analyses, as described in the 

two previous sections of this report, indicated that potential 

areas of unmeasured sources and sinks of streamflow were 

identifiable in the two study reaches. Further investigations 

would be needed to better quantify the gains or losses and 

to determine the extent of unmeasured surface-water or 

groundwater inputs, or both, to the river. 

In the UARB, a substantial volume of water in the river 

subreach from Ark at Canon City to the seasonal USGS 

gaging station 5 miles downstream at Ark nr Canon City was 

unaccounted for by the methodology used in this analysis 

(fig. 6). The daily gain from unmeasured sources in this 

subreach was estimated at about 100 ft3

/s or about 20 ft3/s per 

river mile. Water-budget estimates for the remaining 18 miles 

of the UARB study reach indicated that gains or losses from 

unmeasured sources and sinks were within the measurement 

error (±15 percent) as defined for this report. 

In the LARB, the mechanisms and timing for diverting 

water from the river and for return flows to the river are 

inherently tied to the irrigation practices of the region. As 

such, a highly variable water budget was observed in this 

study reach as daily and even hourly changes in streamflow 

resulted from reservoir releases and demand for irrigation 

water. Gains and losses from unmeasured sources and sinks 

were identified in some of the subreaches but the magnitude of 

the streamflow flux generally was small. Unmeasured sources 

ranging from less than 2 to 3 ft3

/s per river mile were identified 

in the river subreaches from Ark at Catlin Dam downstream 

to Ark at Swink (figs. 16 and 18). Unmeasured sources of 

streamflow from La Junta to Las Animas also was evident 

(fig. 20), but the results could be misleading because known 

diversions and inputs along this subreach were not quantified; 

the main focus of the project did not include extensive data 

collection downstream from Ark at La Junta. 

A streamflow loss was indicated along the subreach 

from Ark at Nepesta to Ark at Catlin Dam, particularly in 

2010 (fig. 15). The mechanism and spatial extent of this 

transmission loss was not identified, and further investigation 

would be required to better quantify the loss.

Estimation of Gains and Losses 

in Dissolved-Solids Load from 

Unmeasured Sources and Sinks

Dissolved-solids (DS) loads are difficult to measure 

directly; instead they are computed as the product of DS 

concentration and streamflow. Direct determination of DS 

concentration requires an extensive program of sample 

collection and chemical analysis. DS data for a given 

streamflow site commonly have been collected at infrequent 

intervals or do not represent the entire flow regime; however, 

specific conductance (SC) and streamflow may be measured 

by automatic monitoring equipment, and their daily-mean 

values (herein referred to as daily values) routinely are 

reported for a large number of streamflow sites. If a significant 

relation is established between SC, DS, and streamflow, then 

daily DS concentration and loads can be estimated from daily 

SC and streamflow values, resulting in reasonably accurate 

and complete estimates of salinity at the stream location 

(Liebermann and others, 1986). 

DS loads for this report were estimated using several 

different approaches depending on the type, quantity, and 

quality of SC, DS, and streamflow data available for each 

site. Daily DS concentrations were estimated using linear 

regression relations developed between SC and DS at 

sites having continuous daily SC and streamflow data as 

described in Ivahnenko and others (2012). Estimated daily 

DS concentrations (in mg/L) then were multiplied by daily 

streamflow (ft3

/sec) and a unit conversion factor (0.0027) 

to obtain daily DS loads in tons per day. This approach was 

restricted to main-stem sites on the Arkansas River and the 

Lake Meredith outlet site (table 1).

Estimates of daily SC at diversion sites were made using 

linear regression relations developed between discrete SC 

measurements at or near the diversion head gates and daily 

SC measured at nearby continuous water-quality sites on the 

Arkansas River. Estimates of daily SC were subsequently 
Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources and Sinks 35

Figure 20. Estimated daily gains and losses from unmeasured streamflow along a subreach of the Lower Arkansas River Basin from 

Arkansas River at La Junta downstream to Arkansas River at Las Animas, Colorado, (A) 2009 and (B) 2010.

EXPLANATION

Unmeasured streamflow flux

LOWESS smoothing curve

15-percent error bar—The averaged estimated

 daily streamflow of the upstream and downstream

 main-stem sites in the subreach

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_20.ai
36 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

converted to daily DS concentrations using published regression 

relations from Ivahnenko and others (2012). Estimated daily 

DS concentrations and published daily streamflow for the 

diversions were used to estimate daily loads. As an example, 

periodic SC measured near the Colorado Canal diversion 

head gate were linearly related to daily SC values measured 

at the nearest upstream main-stem site with continuous SC 

data (in this instance, Ark nr Avondale). A significant relation 

between the two indicated that the SC values were 8 percent 

higher, for the period of record, at the downstream Colorado 

Canal site. Adjusted estimates of daily SC for Colorado Canal 

then were converted to estimated daily DS values using 

published relations for the Ark nr Avondale site. Estimated 

daily DS concentrations were multiplied by the daily diversion 

streamflow published for the canal by the State of Colorado 

to obtain the daily DS loads. The list of regression equations 

used to estimate SC at the headgates of selected diversions 

sampled as part of this study are shown in table 3. In some 

instances, comparisons made as part of this report utilized 

relations developed between diversions and seasonal gages, 

which typically had higher r-squared (r2

) values but were only 

applicable on a seasonal basis. The coefficient of determination, 

r

2

, is a statistical measure of how well the predictive equation 

(regression line) fits the data points (Helsel and Hirsch, 1992).

Table 3. Estimation of daily specific conductance at selected diversion structures using linear regression equations 

relating specific conductance at main-stem sites in the Arkansas River Basin in Colorado with data for long-term 

continuous specific-conductance monitors, 2009–2010.

[SC, specific conductance in microsiemens per centimeter; na, not available]

Site Regression equation Number of

comparisons

Coefficient of

determination (r2

)

Upper Arkansas River Basin study reach

Canon City and Oil Creek Ditch1 SC= (1.00 × SC Ark at Canon City) na na

Fremont Ditch1 SC= (1.00 × SC Ark at Canon City) na na

Minnequa Canal2 SC= (1.53 × SC Ark at Canon City) – 59 na 0.94

Lower Arkansas River Basin study reach

Collier Ditch1 SC= (1.00 × SC Ark nr Avondale) na na

Colorado Canal SC= (1.08 × SC Ark nr Avondale) – .4 16 0.97

Highline Canal SC= (1.12 × SC Ark nr Avondale) + 20 35 0.90

Oxford Canal SC= (1.07 × SC Ark nr Avondale) + 38 34 0.95

Otero Canal SC= (1.11 × SC Ark at Catlin Dam) – 60 32 0.73

Catlin Canal1 SC= (1.00 × SC Ark at Catlin Dam) na na

Holbrook Ditch SC= (0.85 × SC Ark at Catlin Dam) + 108 20 0.84

Rocky Ford Ditch SC= (1.09 × SC Ark at Catlin Dam) + 119 34 0.77

Ft. Lyon Storage Canal SC= (0.82 × SC Ark at Catlin Dam) + 225 11 0.81

Ft. Lyon Canal SC= (1.36 × SC Ark at Catlin Dam) + 51 33 0.62

1

 Due to proximity, specific-conductance values were assumed to be the same as the upstream main-stem site with a long-term data-collection 

record.

2

 Estimation of specific conductance at this site was assumed to be the same as Arkansas River near Canon City, which was linearly related to 

the upstream main-stem site with a long-term data-collection record.

Periodic streamflow and SC data were available, at 

least on a seasonal basis, for most tributary sites sampled 

as part of this study; however, no continuous SC data 

were available for any of these tributary sites. As such, 

daily SC values were estimated for selected sites in both 

the UARB and LARB reaches using streamflow as the 

independent variable. Periodic and synoptic sampling 

for DS concentrations paired with instantaneous SC 

measurements provided sufficient data to develop 

regression equations to estimate daily DS concentrations 

from SC measurements. Finally, DS loads were estimated 

using daily DS concentrations and daily streamflow data. 

In selected instances where no continuous streamflow or 

SC data were available, estimates of daily SC were made 

using the median value of all periodic measurements made 

at a site. Linear regressions were developed to estimate 

DS concentrations from paired SC measurements collected 

during the study period. As such, median DS concentrations 

were defined for each of the sites. A median streamflow 

value was calculated from all instantaneous measurements 

made at a site, and this value was used to calculate a daily 

DS load. Typically, this methodology to determine DS loads 

only was used on small tributaries where mass loading was 

expected to be relatively small. 
Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources and Sinks 37

When applied to a defined reach, the quantity of DS load 

attributable to unmeasured sources or sinks (the flux in load) 

can be estimated as 

Loadflux = Loadds – Loadus + ∑Loadout – ∑Loadin (2)

where 

 Loadds is the DS load at the downstream 

end of the subreach, 

 Loadus is the DS load at the upstream end 

of the subreach, 

 LOADout are DS load outputs from the 

subreach such as diversions, and 

 Loadin are DS load inputs to the reach such 

as tributaries or sewage outfalls. 

As such, a positive Loadflux indicates a net gain to the 

reach in the form of unmeasured DS load from groundwater or 

unmeasured surface-water inputs. A negative Loadflux indicates 

a net loss of DS load to the groundwater system, unmeasured 

diversions, or other potential sinks. 

Given the inherent uncertainties associated with the 

data needed to calculate DS mass loading on the Arkansas River, error bars were applied to evaluate the level of 

reasonableness of the load estimations. In order to have 

confidence in the identification of river subreaches where 

stream-aquifer interactions could have a pronounced effect 

on water quality, the magnitude of the flux had to exceed 

the magnitude of the inherent uncertainties of the measurement errors. For the purposes of this report, error bars 

of ±20 percent of the averaged estimated daily DS loads 

of the upstream and downstream main-stem sites within 

a subreach were calculated to help evaluate the results. 

Given that the streamflow error in this analysis was set at 

±15 percent, a value of ±20 percent was considered to be 

sufficiently conservative given potential analytical error 

associated with DS analysis and estimation techniques for 

DS concentrations at some sites. 

Gains and Losses in Dissolved-Solids Load in 

the Upper Arkansas River Basin Study Reach

Miller and others (2010) reported that DS concentrations 

increased substantially downstream from Canon City (based 

on data from 1976 through 2007); median DS concentrations 

increased by 138 percent from Canon City to the outlet of 

Pueblo Reservoir. Median DS concentrations increased by 

as much as 78 percent along a shorter 16-mile subreach 

from Ark at Canon City to Ark at Portland. The increase in 

DS concentrations was attributed to changes in geology and 

chemical composition of rocks and increased irrigation return 

flows (Miles, 1977; Cain, 1987). 

Similarly, average annual DS loads increased 

substantially between Canon City and the outlet of Pueblo 

Reservoir with the largest increase occurring between 

Canon City and Portland. Based on data from January 1995 

through December 2006, average annual DS loads increased 

72 percent from Ark at Canon City (82,700 tons per year) 

to Ark at Portland (142,000 tons per year). During the same 

period, the Minnequa Canal diverted an average of about 

18,700 tons per year of DS loads from the river between 

these two sites (Miller and others, 2010). As such, more 

than half of the average annual DS loads observed at Ark 

at Portland entered the Arkansas River between Canon City 

and Portland. 

Canon City to Portland

Estimated daily gains and losses in dissolved-solids 

load for the 16-mile river subreach from Ark at Canon City 

downstream to Ark at Portland during 2009–2010 are shown 

in figure 21. Estimates only were calculated for those periods 

when all the seasonal water-quality monitors in this subreach 

were operational. Estimates of daily DS loads in 2009 and 

2010 indicated that unaccounted gains in DS load exceeded 

the 20-percent error bar during nearly all of the periods of data 

collection (figs. 21A and 21B). In 2009, the magnitude of the 

gains in DS load in the Arkansas River sloped downward with 

respect to time and varied from 138 tons per day in August to 

64 tons per day in December. Given that the study reach was 

approximately 16 miles in length, the daily unaccounted DS 

load flux was estimated to range from 4 to 8.6 tons per day 

per river mile. In 2010, the gain in load was more consistent 

varying from 123 to 112 tons per day during the same time 

frame; the daily unaccounted DS load flux was estimated to 

range from 7 to 7.7 tons per day per river mile. These results 

indicate that unmeasured gains in DS load entered the river 

along this subreach. 

Additional spatial definition was available along this 

reach because an intermediate site between Canon City and 

Portland was operational during the study period. The site, 

Ark nr Canon City, was selected as an intermediate site to 

help identify potential source areas along the longer river 

reach. The following discussion describes the characteristics 

of gains and losses in DS load for the subreaches Ark at 

Canon City to Ark nr Canon City and from Ark nr Canon City 

to Ark at Portland. 

The estimates of unaccounted gains and losses in DS load 

in the 5-mile subreach from Ark at Canon City downstream 

to Ark nr Canon City (fig. 22) appeared to be similar to those 

observed along the longer study reach from Ark at Canon 

City downstream to Ark at Portland (fig. 21). Estimates of 

DS load flux in 2009 and 2010 indicated that unaccounted 

gains exceeded the 20-percent error bar during most of the 

data-collection period (figs. 22A and 22B). In 2009, the 

magnitude of the gains (represented by the LOWESS line) 

sloped downward and varied from 110 tons per day in August 

to 55 tons per day in December; the daily unaccounted gain 

in DS load was estimated to range from 11 to 22 tons per day 

per river mile. In 2010, the gain was mostly consistent varying 

from 65 to 40 tons per day. The daily unaccounted DS load 

flux was estimated to range from about 8 to 13 tons per day 
38 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 21. Estimated daily gains and losses in dissolved-solids load along a subreach of the Upper Arkansas River Basin from 

Arkansas River at Canon City downstream to Arkansas River at Portland, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

A

−300

−200

−100

0

100

200

300

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−300

−200

−100

0

100

200

300

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_21.ai
Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources and Sinks 39

Figure 22. Estimated daily gains and losses in dissolved-solids load along a subreach of the Upper Arkansas River Basin from 

Arkansas River at Canon City downstream to Arkansas River near Canon City, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

A

300

−

−

200

−100

0

100

200

300

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−300

−200

−100

0

100

200

300

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_22.ai
40 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

per river mile along the 5-mile subreach. These results indicate 

that unaccounted sources of DS load exist along this subreach. 

Overall, these results might be expected given that 20 ft3

/s per 

mile of unmeasured streamflow flux was estimated to have 

entered the river along this subreach. If the gains in DS load 

were spatially consistent, inputs of about 400 mg/L would be 

needed to account for the 22 tons per day per mile of increased 

DS load. Miller and others (2010) reported that the median DS 

concentration in the river at Ark at Canon City between 1970 

and 2009 was 143 mg/L.

Estimated daily gains and losses in DS load for the 

11-mile river subreach from Ark nr Canon City downstream 

to Ark at Portland during 2009–2010 are shown in figure 23. 

In 2009, estimated gains and losses in DS load did not 

exceed the 20-percent error bar (fig. 23A). In 2010, the 

estimates of unaccounted gains exceeded the error bar 

in May, briefly in July, and from September through 

November (fig. 23B). The magnitude of the unaccounted 

gains in DS load in 2010 was similar to the gains observed 

in the upstream subreach from Ark at Canon City to Ark nr 

Canon City; the flux ranged from 84 tons per day in May to 

59 tons per day in November along the subreach. The daily 

unaccounted gain in DS load was estimated to range from 5.4 

to 7.6 tons per day per river mile. 

Analysis of the water budget indicated little evidence to 

suggest that unmeasured streamflow flux along this subreach 

could be quantified (fig. 7), yet there appeared to be a source 

of DS load to the river. Ivahnenko and others (2012) reported 

numerous small tributaries with high DS concentrations 

downstream from Florence, Colo. In some of these tributaries, 

DS concentrations were in excess of 3,000 mg/L. Although DS 

loading was relatively small, the tributaries may be indicators 

of substantial groundwater inputs along this reach of the 

river with high DS concentrations. Additional information 

pertaining to groundwater interactions with the river is needed 

to address these results.

Portland to Pueblo Reservoir

Estimated daily gains and losses in dissolved-solids 

load for the 7-mile river subreach from Ark at Portland 

downstream to Ark nr Portland, which is near the upper 

end of Pueblo Reservoir, are shown in figure 24. Estimates 

only were calculated for those periods when all the seasonal 

water-quality monitors in this subreach were operational. In 

2009, the estimated unaccounted gain in DS load increased 

through the estimation period and ultimately exceeded 

the 20-percent threshold from early November through 

December (fig. 24A). The magnitude of the unaccounted load 

flux in 2009 ranged from 77 tons per day in early November 

to 110 tons per day in late December along the subreach; 

the daily unaccounted gain in DS load was estimated to 

range from 11 to 16 tons per day per river mile. In 2010, 

the LOWESS line was relatively unchanged from near the 

zero line and estimates of DS load flux did not exceed the 

20-percent error bar at any time (fig. 24B). 

Previous analysis of the water budget provided little 

evidence to suggest that unmeasured gains or losses in 

streamflow could be quantified along this subreach in 2009; 

however, there appeared to be an increase in unaccounted 

DS load to the river in November and December of 2009. 

A similar occurrence was not observed in 2010. The 

contradicting results for the 2 years are difficult to interpret 

and further investigation of groundwater inputs along this 

reach may be warranted given the potential for high DS 

concentrations in the groundwater; Ivahnenko and others 

(2012) reported numerous small tributaries along this reach 

of the river with DS concentrations that ranged from about 

2,000 mg/L to as high as 6,000 mg/L. DS concentrations in 

this reach of the river in November and December typically 

were about 400 mg/L.

Gains and Losses in Dissolved-Solids Load in 

the Lower Arkansas River Basin Study Reach

Miller and others (2010) reported that DS concentrations 

in the Arkansas River increased downstream by more than 

634 percent from Avondale to the Colorado-Kansas Stateline. 

The largest increase in median DS concentration (46 percent) 

in the LARB study reach occurred between Rocky Ford and 

La Junta. Typically, DS concentrations were lower during 

the irrigation season (March–October) than during the 

nonirrigation season (November through February). DS loads, 

however, were higher during the irrigation season because 

streamflows were much higher during this time. Miller and 

others (2010) reported that DS loads can be as much as 23 

times higher during the irrigation season. Average annual 

DS loads (2000–2006) in the Arkansas River increased by 

about 30 percent between Ark nr Avondale and a streamflow 

gage downstream from John Martin Reservoir (USGS station 

07130500 ) (fig. 1). Within the LARB study reach, however, 

average annual DS loads decreased substantially from Ark 

nr Avondale to Ark at Catlin Dam (21 percent) and from Ark 

at Catlin Dam to Ark at Las Animas (31 percent). The only 

increase in average annual load occurred between Las Animas 

and the outlet of John Martin Reservoir.

Avondale to Catlin Dam

Estimated daily gains and losses in DS load for the 

21-mile river subreach from Ark nr Avondale downstream 

to Ark at Nepesta during 2009–2010 are shown in figure 25. 

Estimates only were calculated for those periods when all 

the seasonal water-quality monitors in this subreach were 

operational. In 2009, estimates of daily DS loads indicated 

that unaccounted gains or losses in DS load only exceeded 

the 20-percent error bar during short periods in August, 

September, and October (fig. 25A). Although the error 

bars were not exceeded during most other times in 2009, 

the LOWESS line was relatively level and averaged about 

100 tons per day. The estimated daily gain in DS load was 
Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources and Sinks 41

Figure 23. Estimated daily gains and losses in dissolved-solids load along a subreach of the Upper Arkansas River Basin from 

Arkansas River near Canon City downstream to Arkansas River at Portland, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

A

−300

−200

−100

0

100

200

300

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−300

−200

−100

0

100

200

300

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_23.ai
42 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 24. Estimated daily gains and losses in dissolved-solids load along a subreach of the Upper Arkansas River Basin from 

Arkansas River at Portland downstream to Arkansas River near Portland, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

A

−300

−200

−100

0

100

200

300

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−300

−200

−100

0

100

200

300

Daily streamflow flux, in cubic feet per second

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_24.ai
Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources and Sinks 43

Figure 25. Estimated daily gains and losses in dissolved-solids load along a subreach of the Lower Arkansas River Basin from 

Arkansas River near Avondale downstream to Arkansas River at Nepesta, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

0

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_25.ai
44 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

4.7 tons per day per river mile. Estimates of DS loads in 

2010 indicated that unmeasured DS loads did not exceed the 

20-percent error bar at any time (fig 25B). It is important to 

note that estimates of DS load flux in 2010 included a highflow period from May through July that were not represented 

in any of the 2009 estimates.

Estimated daily gains and losses in DS load for the 

15-mile river subreach from Ark at Nepesta downstream to 

Ark at Catlin Dam during 2009–2010 are shown in figure 

26. Estimates only were calculated for those periods when 

all the seasonal water-quality monitors in this subreach were 

operational. Estimates of daily DS loads in 2009 indicated 

that unmeasured gains in DS load only exceeded the upper 

20-percent error bar during short periods in December 

(fig. 26A). In 2010, a contrasting flux profile was observed as 

a net loss of DS load along the subreach was observed from 

mid-September until late November (fig. 26B). The magnitude 

of the losses ranged from about 90 tons per day in September 

to more than 300 tons per day by late November. The 

mechanism and spatial extent of the losses in DS load were 

not specifically identified, and further investigation would be 

required to better quantify the losses.

Catlin Dam to Las Animas

Miller and others (2010) computed average annual 

streamflow, DS concentration, and DS loads for numerous 

main-stem sites for a 6-year period from 2000 to 2006. 

Estimates for the sites Ark at Catlin Dam and Ark at Las 

Animas were included in their analysis. Overall, there was a 

substantial increase in DS concentrations from Catlin Dam to 

Las Animas as irrigation return flows entered the river (Miller 

and others, 2010). Correspondingly, a decrease in streamflow 

occurred along this reach of the river as large quantities of 

water were continually diverted from the river. The overall 

result was a 31-percent decrease in the average annual DS 

load between these two sites (from 238,540 to 164,685 tons 

per year). 

Estimated daily gains and losses on DS load for the 

20-mile river subreach from Ark at Catlin Dam downstream 

to the next main-stem site, Ark nr Rocky Ford, are shown 

in figure 27. Estimates only were calculated for those 

periods when all the seasonal water-quality monitors in this 

subreach were operational. In 2009, daily estimates of DS 

load indicated that unmeasured gains in DS load exceeded 

the upper 20-percent error bar during most of the estimation 

period with the exception of a short period in late October 

through mid-November (fig. 27A). Although the error bars 

were not exceeded all the time in 2009, the LOWESS line was 

relatively level and averaged about 200 tons per day; the daily 

unmeasured DS load flux along this subreach was estimated 

at 10 tons per day per river mile. In 2010, the LOWESS line 

was much more variable with a decreasing slope throughout 

the estimation period particularly during the high-flow period 

in the summer months (fig. 27B). Overall, the LOWESS line 

exceeded the 20-percent error bar for much of this time. These 

results indicate that unmeasured gains in DS load entered the 

river along this subreach, particularly in 2009.

Estimated daily gains and losses in DS load for the 

6.3-mile river subreach from Ark nr Rocky Ford downstream 

to Ark at Swink during 2009–2010 are shown in figure 28. 

Estimates only were calculated for those periods when all 

the seasonal water-quality monitors in this subreach were 

operational; the site at Swink was the only main-stem site in 

the LARB where continuous streamflow and SC monitoring 

were operated on a seasonal basis. Estimates of daily DS 

loads in 2009 indicated that unmeasured gains in DS load 

only exceeded the upper 20-percent error bar from September 

through mid-October (fig. 28A). However, the LOWESS line 

was relatively level and averaged about 175 tons per day or 

about 28 tons per day per river mile. In 2010, the LOWESS 

line exceeded the upper error bar from mid-October through 

November (fig. 28B). Unmeasured gains during this period 

were about 30 percent lower than those observed in 2009. 

Estimated daily gains and losses in dissolved-solids 

load for the 6.8-mile river subreach from Ark at Swink 

downstream to Ark at La Junta during 2009–2010 are shown 

in figure 29. Estimates only were calculated for those periods 

when all the seasonal water-quality monitors in this subreach 

were operational. Estimates of daily DS loads indicated that 

unmeasured gains and losses in DS load did not exceed the 

20-percent error bar for any extended period in 2009 or 2010 

(figs. 29A and 29B). This subreach of the Arkansas River is 

a relatively short distance with only one tributary input. The 

site at Swink was originally selected as a monitoring site to 

subdivide the subreach from Rocky Ford to La Junta because 

Miller and others (2010) had indicated that the largest 

percentage increase in median DS concentrations between 

Pueblo Reservoir and John Martin Reservoir occurred 

between these two sites. However, no substantial unmeasured 

gains or losses in DS load were observed in this subreach by 

this analysis.

Estimated daily gains and losses in DS load for the 

25-mile river subreach from Ark at La Junta downstream to 

Ark at Las Animas during 2009–2010 are shown in figure 30. 

Estimates only were calculated for those periods when all 

the seasonal water-quality monitors in this subreach were 

operational. Estimates of DS loads in 2009 indicated that 

unmeasured gains in DS load exceeded the upper 20-percent 

error bar for most of November through December (fig. 30A). 

In 2009, the LOWESS line was variable with an upward slope 

throughout the estimation period. In 2010, the LOWESS line 

exceeded the 20-percent error bar for much of the time after 

the high-flow period ended in August (fig. 30B). Although 

the error bars were not exceeded all the time in 2010, the 

LOWESS line was relatively level and averaged about 

100 tons per day during most of the analysis period; the daily 

unmeasured load flux along the reach was estimated at 4 tons 

per day per river mile. It should be noted that estimates along 

this 25-mile reach did not include any estimates of inflow 

loads other than the La Junta wastewater effluent, because the 

focus of much of the data-collection activities in the LARB 
Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources and Sinks 45

Figure 26. Estimated daily gains and losses in dissolved-solids load along a subreach of the Lower Arkansas River Basin from 

Arkansas River at Nepesta downstream to Arkansas River at Catlin Dam, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

0

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_26.ai
46 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 27. Estimated daily gains and losses in dissolved-solids load along a subreach of the Lower Arkansas River Basin study area 

from Arkansas River at Catlin Dam downstream to Arkansas River near Rocky Ford, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

0

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_27.ai
Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources and Sinks 47

Figure 28. Estimated daily gains and losses in dissolved-solids load along a subreach of the Lower Arkansas River Basin from 

Arkansas River near Rocky Ford downstream to Arkansas River at Swink, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

0

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_28.ai
48 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

Figure 29. Estimated daily gains and losses in dissolved-solids load along a subreach of the Lower Arkansas River Basin from 

Arkansas River at Swink downstream to Arkansas River at La Junta, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

0

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_29.ai
Estimation of Gains and Losses in Dissolved-Solids Load from Unmeasured Sources and Sinks 49

Figure 30. Estimated daily gains and losses in dissolved-solids load along a subreach of the Lower Arkansas River Basin from 

Arkansas River at La Junta downstream to Arkansas River at Las Animas, Colorado, (A) 2009 and (B) 2010.

May June July August

2009

September October November December

A

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

May June July August

2010

September October November December

B

−500

−400

−300

−200

−100

0

100

200

300

400

500

Daily streamflow flux, in cubic feet per second

EXPLANATION

Dissolved-solids load flux

LOWESS smoothing curve

20-percent error bar—The averaged estimated

 daily dissolved-solids load of the upstream and

 downstream main-stem sites in the subreach

0

N:\Jeff\den12_cmre00_0036_sir_ortiz\report_figures\figure_30.ai
50 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

reach ended at La Junta. Identified tributaries along this reach 

include Horse Creek and Adobe Creek, which historically 

have high SC values and, potentially, could add substantial DS 

loads to the river. Miller and others (2010) reported that the 

median SC value for Horse Creek was 3,390 microsiemens 

per centimeter. The median SC value for 15 samples collected 

from Adobe Creek was 2,120 microsiemens per centimeter 

(U.S. Geological Survey, 2003). One large diversion ditch, the 

Las Animas Consolidated ditch, removes water from the river 

along this subreach and was not included in this analysis.

Potential Unmeasured Sources and Sinks for 

Dissolved-Solids Load

The results from the analyses of unmeasured sources 

and sinks of DS load, as described in the two previous 

sections of this report, indicated that potential source areas 

were identifiable in the study reaches. It might be expected 

that unmeasured DS load flux would be identified along 

the same reaches where unmeasured streamflow flux was 

identified. To that extent, some of the observed results from 

the analysis of daily DS loading did mirror the streamflow 

results. In some subreaches of the Arkansas River, however, 

unmeasured sources and sinks of DS load did not appear to 

be directly associated with unmeasured sources and sinks 

of streamflow. 

In the UARB from Ark at Canon City to Ark nr Canon 

City, unmeasured gains in DS load were estimated to range 

from 11 to 22 tons per day per mile in 2009 and from 8 to 

13 tons per day per mile in 2010 (fig. 22); streamflow from 

unmeasured sources was estimated to be about 20 ft3/s per 

mile along this same reach. Downstream from this short reach, 

DS load to the river from unmeasured sources was estimated 

to range from 5.4 to 7.6 tons per day per mile in 2010 for 

Ark nr Canon City to Ark at Portland (fig. 23) and from 11 

to 16 tons per day per mile in 2009 for Ark at Portland to 

Ark nr Portland (fig. 24). Gains from unmeasured sources of 

streamflow were not identified in either of these subreaches. 

Several small tributaries with DS concentrations ranging 

from 3,000 mg/L to as high as 6,000 mg/L enter the river 

along these subreaches. These inputs may indicate a potential 

source of groundwater that could affect DS loading in the 

river. Further investigation would be needed to identify the 

unmeasured source or sources of DS load to determine the 

nature and extent of unmeasured inputs. 

In the LARB, gains in DS load from unmeasured 

sources were identified for the subreach from Ark nr 

Avondale to Ark at Nepesta although no substantial amounts 

of streamflow from unmeasured sources were identified for 

this subreach. In 2009, the estimated gain in DS load from 

unmeasured sources for this subreach was 4.7 tons per day 

per mile. An increase in DS load from unmeasured sources 

also was identified along the subreach of the river from 

Ark at Catlin to Swink (figs. 27 and 28); the DS load from 

unmeasured sources was estimated to range from 10 to 28 

tons per day per mile. The only other river subreach where 

a gain in DS load from unmeasured sources was identified 

was from La Junta to Las Animas. Caution should be used 

interpreting these results because the focus of the data 

collection did not extend downstream from La Junta and 

some known inputs and diversions were not quantified. 

The only loss of DS load was identified for the 

subreach from Nepesta to Catlin Dam in 2010 (fig. 26). 

The mechanism and spatial extent of the losses were not 

identified, and further investigation would be required to 

better understand the results.

Summary

The Arkansas River is an important municipal water 

supply and is the primary supply for about 400,000 acres 

of irrigated land in southeastern Colorado. The suitability 

of this water for domestic, agricultural, and industrial use 

is affected by high salinity in parts of the Arkansas River. 

Previous studies report that median specific-conductance 

(SC) values increased more than 6,000 percent from the 

headwaters to the Colorado-Kansas border; much of the 

increase occurred along the heavily irrigated areas from 

Canon City to Las Animas. 

The Arkansas River Basin Regional Resource Planning 

Group (RRPG) adopted a strategy to address multiple waterquality concerns in the basin. The strategy included the 

need to quantify mass loading of dissolved solids (DS) in 

the Arkansas River to help identify stream reaches where 

stream-aquifer interactions have a pronounced effect on water 

quality in the river. In 2009, the U.S. Geological Survey 

(USGS), in cooperation with the RRPG and the Colorado 

Water Conservation Board, began a study to estimate gains 

and losses from unmeasured sources and sinks for streamflow 

and dissolved-solids load in selected reaches of the Arkansas 

River in southeastern Colorado. Data were collected during 

2009–2010 to provide a basis for estimating the gains or losses 

for selected reaches from Canon City to Las Animas.

The purpose of this report is to describe estimates of 

gains and losses from unmeasured sources and sinks for 

streamflow and dissolved-solids load in the Arkansas River 

along two main study reaches. The estimates will help identify 

subreaches where gains or losses from unmeasured sources 

and sinks could have a pronounced effect on the water quality 

in the Arkansas River.

Streamflow data collected from established or seasonal 

(2009–2010) streamflow-gaging sites were analyzed to 

determine a reasonable water budget in selected reaches of 

the Arkansas River and to identify subreaches where gains 

or losses in streamflow from unmeasured sources may be 

occurring. SC and DS data were analyzed to derive estimates 

of daily DS concentrations at main-stem, tributary, and 

diversion sites. The results of these two analysis components 

were combined to derive a mass-load analysis that was applied 

at a subreach scale to help identify potential source areas of 

unmeasured DS loading in the river. 
Summary 51

For the purposes of this report, two main study reaches 

were selected for investigation. The first study reach includes 

the Arkansas River Basin from Canon City to just upstream 

from Pueblo Reservoir. This reach is identified as the Upper 

Arkansas River Basin (UARB) study reach. The second 

study reach is located downstream from Pueblo Reservoir 

and includes the Arkansas River Basin from Avondale to Las 

Animas. This reach is identified as the Lower Arkansas River 

Basin (LARB) study reach. In general, the data collected 

for this study can be categorized as either streamflow or 

water quality. Various types of data-collection methods were 

associated with each of these two categories. Streamflow data 

analyzed for this report consist primarily of daily streamflow 

records retrieved from established long-term streamflow 

sites or from seasonal gages installed and operated as part 

of this study. In some instances, estimated daily values were 

used in the analysis. Typically, daily streamflow data from 

established sites are published by either the USGS or the State 

of Colorado Division of Water Resources. 

The water-quality data used in this report consisted 

of SC values from continuous-monitoring sites, periodic 

SC measurements at selected sites, and DS concentrations 

from water samples collected at numerous sites in the study 

reaches. Daily SC data were retrieved from USGS databases 

for continuous water-quality monitoring sites (established or 

seasonal) on the main stem of the Arkansas River. Periodic 

measurements of SC were available for all sites in both 

study reaches. Additionally, paired SC measurements and 

DS concentrations were available. As such, linear regression 

analyses to estimate DS concentrations from SC could be 

performed. Estimated DS concentrations combined with 

streamflow data could then be used to determine mass-loading 

characteristics in the study reaches.

Locally weighted scatterplot smoothing (LOWESS) 

techniques were used to evaluate gains or losses from 

unmeasured sources and sinks in daily streamflow and 

estimated daily DS load for selected sites in the Arkansas 

River. The smoothing technique describes the relation, in this 

instance, between streamflow and time or between DS and 

time without assuming linearity or normality of the residuals. 

A common approach to investigating the flow of water 

from unmeasured sources or sinks is to measure streamflow 

at numerous points along a study reach to determine a 

water budget. These measurement points (sites) subdivide 

the stream into subreaches and accounts for inputs and 

outputs. The difference between inflows and outflows may 

be attributed to unmeasured sources or sinks, such as the 

interaction between the stream and the underlying aquifer. 

Given the other unmeasured components of error in this 

analysis, error bars of ±15 percent of the averaged daily 

streamflow of the upstream and downstream main-stem 

sites within a subreach were calculated to help evaluate 

the results. A value of ±15 percent was determined to be 

sufficiently conservative to allow for the identification of 

stream reaches where streamflow gains or losses exceeded the 

measurement error. Consistent exceedences of the error bars 

could potentially indicate stream reaches where surface-water 

inflows or groundwater inputs from unmeasured sources are a 

substantial part of the water budget.

In general, the methodology used to quantify streamflow 

water budgets along the UARB and LARB study reaches 

accounted for a large percentage of the streamflow. However, 

the results from the water-budget analyses indicated 

that potential areas of unmeasured sources and sinks of 

streamflow were identifiable in the two study reaches. Further 

investigations would be needed to better quantify the gains 

or losses and to determine the extent of unmeasured surfacewater or groundwater inputs, or both, to the river. In the 

UARB, a substantial volume of water in the subreach from 

Ark at Canon City to the seasonal USGS gaging station 5 

miles downstream at Ark nr Canon City was unaccounted 

for by the methodology used in this analysis. The daily gain 

from unmeasured sources in this subreach was estimated to 

be about 100 cubic feet per second (ft3

/s) or about 20 ft3/s per 

river mile. Water-budget estimates for the remaining 18 miles 

of the UARB study reach indicated that gains or losses from 

unmeasured sources and sinks were within the measurement 

error as defined for this report. 

In the LARB, the mechanisms and timing for diverting 

water from the river and for return flows to the river are 

inherently tied to the irrigation practices of the region. As 

such, a highly variable water budget was observed in this 

study reach as daily and even hourly changes in streamflow 

resulted from reservoir releases and demand for irrigation 

water. Gains and losses from unmeasured sources and sinks 

were identified in some of the subreaches but the magnitude of 

the streamflow flux generally was small. Unmeasured sources 

ranging from less than 2 to 3 ft3

/s per mile were identified in 

the river subreaches from Ark at Catlin Dam downstream to 

Ark at Swink. A streamflow loss (sink) was indicated along 

the subreach from Ark at Nepesta to Ark at Catlin Dam, 

particularly in 2010. The mechanism and spatial extent of this 

sink was not identified, and further investigation would be 

required to better quantify the losses.

The results from the analyses of unmeasured sources 

and sinks of DS load indicated that potential source areas 

were identifiable in the study areas. It might be expected that 

unmeasured DS load flux would be identified along the same 

reaches where unmeasured streamflow flux was identified. To 

that extent, some of the observed results from the analysis of 

daily DS loading did mirror the streamflow results. In some 

subreaches of the Arkansas River, however, unmeasured 

sources and sinks of DS load did not appear to be directly 

associated with unmeasured sources and sinks of streamflow.

In the UARB from Ark at Canon City to Ark nr Canon 

City, unmeasured gains in DS load were estimated to range 

from 11 to 22 tons per day per mile in 2009 and from about 

8 to 13 tons per day per mile in 2010; streamflow from 

unmeasured sources was estimated to be about 20 ft3

/s per 

mile along this same reach. Downstream from this short 

reach, DS load to the river from unmeasured sources was 

estimated to range from 5.4 to 7.6 tons per day per mile in 
52 Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010

2010 for Ark nr Canon City to Ark at Portland and from 

11 to 16 tons per day per mile in 2009 for Ark at Portland 

to Ark nr Portland. Unmeasured gains in streamflow 

were not identified in either of these subreaches. Several 

small tributaries with DS concentrations from 3,000 

mg/L to as high as 6,000 mg/L enter the river along these 

subreaches. These inputs may indicate a potential source of 

groundwater that could affect DS loading in the river. Further 

investigation would be needed to identify the unmeasured 

source or sources of DS load to determine the nature and 

extent of unmeasured inputs. 

In the LARB, gains in DS load from unmeasured sources 

were identified for the subreach from Ark nr Avondale to Ark 

at Nepesta although no substantial amounts of streamflow 

from unmeasured sources were identified for this subreach. In 

2009, the estimated gain in DS load from unmeasured sources 

for this subreach was 4.7 tons per day per mile. An increase in 

DS load from unmeasured sources also was identified along 

the subreach of the river from Ark at Catlin to Swink; the DS 

load from unmeasured sources was estimated to range from 

10 to 28 tons per day per mile. The only loss of DS load was 

identified for the subreach from Nepesta to Catlin Dam in 

2010. The mechanism and spatial extent of the losses were not 

identified, and further investigation would be required to better 

understand the results.

Acknowledgments

The authors would like to thank the many individuals who 

assisted in the collection and interpretation of data collected in 

support of this report. Thanks to Colorado Division of Water 

Resources Water Commissioners (Division 2) John Van Oort, 

Brian Sutton, Lonnie Spady, Charlie Judge (retired), and Don 

Taylor (retired) for providing timely responses to data requests. 

Thanks also to USGS personnel Robert Stogner, Sheryl 

Ferguson, Shaylynn Mincic, Pamela Tello, Crystal Brown, 

Ryan Kopp, Russ Lewins, and Brenden Ortiz (volunteer) for 

their tireless efforts collecting data.

References Cited

Cain, Doug, 1985, Quality of the Arkansas River and irrigation 

return flows in the lower Arkansas River valley, Colorado: 

U.S. Geological Survey Water-Resources Investigations 

Report 84–4273, 85 p.

Cain, Doug, 1987, Relations of specific conductance to 

streamflow and selected water-quality characteristics of the 

Arkansas River Basin, Colorado: U.S. Geological Survey 

Water-Resources Investigations Report 87–4041, 93 p.

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

smoothing scatterplots: Journal of the American Statistical 

Association, v. 74, p. 829–836.

Cleveland, W.S., and Devlin, S.J., 1988, Locally weighted 

regression: An approach to regression analysis by local 

fitting: Journal of the American Statistical Association, 

v. 83, p. 596–610. 

Colorado Decision Support System, 2011, Published monthly 

streamflow: Colorado Decision Support System Web 

site, accessed August 8, 2011, at http://cdss.state.co.us/ 

onlineTools/Pages/StreamflowStations.aspx.

Colorado Division of Water Resources, 2010, Cumulative 

yearly statistics of the Colorado Division of Water 

Resources–2009: Colorado Department of Natural 

Resources Web site, accessed February 23, 2011, at http://

water.state.co.us/DWRIPub/DWR%20Annual%20Reports/

CYS_rpt_2009.pdf.

Commonwealth of Australia, 2006, Connected water—

Managing the linkages between surface water and ground 

water: Commonwealth of Australia Web site, accessed June 

4, 2011, at http://www.connectedwater.gov.au/copyright.

html.

Fishman, M.J., and Friedman, L.C., eds., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigation, Book 5, Chapter Al, 545 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, Chapter A3, 510 p.

Ivahnenko, Tamara, Ortiz, Roderick, and Stogner, Robert, 

Sr., 2012, Characterization of streamflow, water quality, 

and instantaneous dissolved solids, selenium, and uranium 

loads in selected reaches of the Arkansas River Basin, 

southeastern Colorado, 2009–2010: U.S. Geological Survey 

Scientific Investigations Report 2012–5234, 60 p.

Lerner, D.N., Issar, A.S., and Simmers, Ian, 1990, 

Groundwater recharge—A guide to understanding and 

estimating natural recharge: Hannover, Germany, Heinz 

Heise, International Contributions of Hydrogeologists, v.8, 

345 p.

Lewis, M.E., and Brendle, D.L., 1998, Relations of streamflow 

and specific-conductance trends to reservoir operations 

in the lower Arkansas River, southeastern Colorado: U.S. 

Geological Survey Water-Resources Investigations Report 

97–4239, 48 p.

Lieberman, T.D., Middelburg, R.F., and Irvine, S.A., 

1986, User’s manual for estimation of dissolved-solids 

concentrations and load in surface water: U.S. Geological 

Survey Water-Resources Investigations Report 86–4124, 51 p.

Miles, D.L., 1977, Salinity in the Arkansas valley of 

Colorado: U.S. Environmental Protection Agency and 

Colorado State University, Interagency Agreement, EPA–

IAG– D4–0544, 80 p.
References Cited 53

Miller, L.D., Watts, K.R., Ortiz, R.F., and Ivahnenko, Tamara, 

2010, Occurrence and distribution of dissolved solids, 

selenium, and uranium in groundwater and surface water in 

the Arkansas River Basin from the headwaters to Coolidge, 

Kansas, 1970–2009: U.S. Geological Survey Scientific 

Investigations Report 2010–5069, 59 p. (Also available at 

http://pubs.usgs.gov/sir/2010/5069/.)

Ortiz, R.F., 2004, Methods to identify changes in background 

water-quality conditions using dissolved-solids 

concentrations and loads as indicators, Arkansas River 

and Fountain Creek, in the vicinity of Pueblo, Colorado: 

U.S. Geological Survey Scientific Investigations Report 

2004–5024, 20 p. (Also available at http://pubs.usgs.gov/

sir/2004/5024.)

Ortiz, R.F., Lewis, M.E., and Radell, M.J., 1998, Water-quality 

assessment of the Arkansas River Basin, southeastern 

Colorado, 1990–93: U.S. Geological Survey WaterResources Investigations Report 97–4111, 69 p.

Rantz, S.E., and others, 1982a, Measurement and computation 

of streamflow—v. 1, Measurement of stage and discharge: 

U.S. Geological Survey Water-Supply Paper 2175, 283 p. 

(Also available online at http://water.usgs.gov/pubs/wsp/

wsp2175; accessed July 21, 2011.)

Rantz, S.E., and others, 1982b, Measurement and computation 

of streamflow—v. 2, Computation of discharge: U.S. 

Geological Survey Water-Supply Paper 2175, 347 p. (Also 

available online at http://water.usgs.gov/pubs/wsp/wsp2175;

accessed July 21, 2011.)

Southeastern Colorado Water Conservancy District, 2011, 

Winter water storage program: Southeastern Colorado 

Water Conservancy District Web site, accessed August 28, 

2011, at http://www.secwcd.org/WinterWtr.htm.

U.S. Geological Survey, 2003, User’s manual for the 

National Water Information System of the U.S. Geological 

Survey—Automated Data Processing System (ADAPS): 

U.S. Geological Survey Open-File Report 03–123 ver. 4.3, 

407 p. (Also available at http://pubs.usgs.gov/of/2003/

ofr03123/; accessed October 10, 2011.)

U.S. Geological Survey, variously dated, National field manual 

for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chaps. A1–A9. (Also available online at http://pubs.water.

usgs.gov/twri9a.)

Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, 

B.A., 2006, Guidelines and standard procedures for 

continuous water-quality monitors—Station operation, 

record computation, and data reporting: U.S. Geological 

Survey Techniques and Methods 1–D3, 51 p. (Also 

available online at http://pubs.water.usgs.gov/tm1d3; 

accessed October 10, 2011.)

Publishing support provided by: 

Denver Publishing Service Center

For more information concerning this publication, contact:

Director, USGS Colorado Water Science Center

Box 25046, Mail Stop 415

Denver, CO 80225

(303) 236-4882

Or visit the Colorado Water Science Center Web site at:

http://co.water.usgs.gov/

(303) 236-2000
Ortiz—Streamflow and Dissolved-Solids Load, Arkansas River, Colorado, 2009–2010–—Scientific Investigations Report 2012–5252