Using Tracers to Evaluate Streamflow 

Gain-Loss Characteristics of Terror Creek, 

in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

By Cory A. Williams and Kenneth J. Leib

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with

DELTA COUNTY

Scientific Investigations Report 2005–5018
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.
Contents iii

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

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

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Description of Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Hydrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Previous Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Streamflow Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Discharge by Constant-Rate-Injection Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Measurement Location and Site Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Accounting for Streamflow Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Water-Sample Collection and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Water-Sampling Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Analytical Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Error Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Sensitivity Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Error Propagation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Streamflow Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Graphical Comparison. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Statistical Comparison. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Evaluation of Streamflow Gain-Loss Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Measurement Set 1, Streamflow Gain-Loss Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Measurement Set 2, Streamflow Gain-Loss Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Interpretation of Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Factors Affecting Streamflow Gain-Loss Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Hyporheic Flow System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Deep Flow System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Supplemental Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figures

1. Map showing location of Terror Creek study area, measurement locations, and 

mine-permit area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2. Graphs showing daily-mean streamflow at USGS streamflow-gaging stations 

(A) East Fork Terror Creek Below Cottonwood Stomp near Bowie, Colo., and 

(B) Terror Creek at Mouth near Bowie, Colo., for water year 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

3. Tracer design schematic diagram modeled after (I) Zellweger (1994) and (II) tributary 

variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

4–12. Graphs showing:

4. Streamflow unit values bracketing measurement set 1 at USGS 

 streamflow-gaging stations (A) East Fork Terror Creek Below Cottonwood Stomp near 

 Bowie, Colo., and (B) Terror Creek at Mouth near Bowie, Colo., 

 for water year 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

5. Specific-conductance log for traveltime determination following the 

 single-point injection method for measurement set 1, Terror Creek, Colo. . . . . . . . . . . . . . . . . . . . . . .9
iv 

6. Streamflow unit values bracketing measurement set 2 at USGS 

 streamflow-gaging stations (A) East Fork Terror Creek Below Cottonwood Stomp near

 Bowie, Colo., and (B) Terror Creek at Mouth near Bowie, Colo., for water year 2003. . . . . . . . . . . . 10

7. Comparison of streamflow between measurement-location pairs during measurement 

 set 1, June 17–18, 2003, Terror Creek, Colo., water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

8. Comparison of relative streamflow among measurement locations during measurement 

 set 1, June 17–18, 2003, Terror Creek, Colo., water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

9. Comparison of streamflow among measurement locations during measurement 

 set 2, September 16–17, 2003, Terror Creek, Colo., water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

10. Comparison of relative streamflow among measurement locations during measurement 

 set 2, September 16–17, 2003, Terror Creek, Colo., water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

11. Comparison of relative streamflow among measurement locations during measurement 

 set 1 (June 17–18, 2003) and measurement set 2 (September 16–17, 2003), 

 Terror Creek, Colo., water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

12. Comparison of streamflow among measurement locations from Brooks (1983), 

 October 5, 1982, Terror Creek, Colo., water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Tables

1. Relative traveltimes for use in the modified multiple-tracer method, measurement set 1, 

Terror Creek, Colo., water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

2. Measurement set 1–Results for modified multiple-tracer method, Terror Creek, Colo., 

water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3. Measurement set 2–Results for multiple-tracer method, Terror Creek, Colo., 

water year 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4. Summary of results from statistical tests of measured streamflow loss within the

mine-permit area, Terror Creek, Colo., water year 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

5. Supplemental information for the modified multiple-tracer method, measurement set 1, 

and multiple-tracer method, measurement set 2, Terror Creek, Colo., water year 2003 . . . . . . . . . . . . 27
 v

CONVERSION FACTORS, DATUMS, ABBREVIATIONS, AND ACRONYMS

Horizontal coordinate information is referenced to the North American Datum of 

1983 (NAD 83).

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

1929 (NGVD 29).

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

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 in milligrams per liter (mg/L).

L/min liters per minute

mL milliliters

BLM Bureau of Land Management

NaBr sodium bromide

USDA U.S. Department of Agriculture

USGS U.S. Geological Survey

NWQL U.S. Geological Survey National Water-Quality Laboratory

WY Water year—A continuous 12-month period representing an annual hydrologic cycle 

selected to present data relative to hydrologic or meteorological phenomena. The 

water year used by the U.S. Geological Survey runs from October 1 through 

September 30 and is designated by the year in which it ends.

Multiply By To obtain

Length

inch (in.) 2.54 centimeter

feet (ft) 0.3048 meter

yard (yd) 0.9144 meter

mile (mi) 1.609 kilometer

Volume

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter

Flow rate

cubic feet per second (ft3/s) 0.02832 cubic meter per second

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

Mass

pound, avoirdupois (lb) 0.4536 kilogram

ton, short (2,000 lb) 0.9072 megagram
Using Tracers to Evaluate Streamflow Gain-Loss 

Characteristics of Terror Creek, in the Vicinity of a 

Mine-Permit Area, Delta County, Colorado, 

Water Year 2003

By Cory A. Williams and Kenneth J. Leib

Abstract

In 2003, the U.S. Geological Survey, in cooperation with 

Delta County, initiated a study to characterize streamflow gainloss in a reach of Terror Creek, in the vicinity of a mine-permit 

area planned for future coal mining. This report describes the 

methods of the study and includes results from a comparison of 

two sets of streamflow measurements using tracer techniques 

following the constant-rate injection method. Two measurement sets were used to characterize the streamflow gain-loss 

associated with reservoir-supplemented streamflow conditions 

and with natural base-flow conditions.

A comparison of the measurement sets indicates that the 

streamflow gain-loss characteristics of the Terror Creek study 

reach are consistent between the two hydrologic conditions 

evaluated. A substantial streamflow gain occurs between measurement locations 4 and 5 in both measurement sets, and 

streamflow is lost between measurement locations 5 and 7 

(measurement set 1, measurement location 6 not visited) and 5 

and 6 (measurement set 2). A comparison of the measurement 

sets above and below the mine-permit area (measurement locations 3 and 7) shows a consistent loss of 0.37 and 0.31 cubic foot 

per second (representing 5- and 12-percent streamflow losses 

normalized to measurement location 3) for measurement sets 1 

and 2, respectively. This indicates that similar streamflow 

losses occur both during reservoir-supplemented and natural 

base-flow conditions, with a mean streamflow loss of 

0.34 cubic foot per second for measurement sets 1 and 2. 

Findings from a previous investigation support the 

observed streamflow loss between measurement locations 3 and 

7 in this study. The findings from the previous investigation 

indicate a streamflow loss of 0.59 cubic foot per second occurs 

between these measurement locations. 

Statistical testing of the differences in streamflow between 

measurement locations 3 and 7 indicates that there is a discernible streamflow loss. The p-value of 0.0236 for the parametric 

paired t-test indicates that there is a 2.36-percent probability of 

observing a sample mean difference of 0.34 cubic foot per 

second if the population mean is zero. The p-value of 0.125 for 

the nonparametric exact Wilcoxon signed rank test indicates 

that there is a 12.5-percent probability of observing a sample 

mean difference this large if the population mean is zero. 

The similarity in streamflow gain-loss between measurement sets indicates that the process controlling streamflow may 

be the same between the two hydrologic conditions evaluated. 

Gains between measurement locations 4 and 5 may be related to 

hyporheic flow from tributaries that were dry during the study. 

No other obvious sources of surface water were identified 

during the investigation. The cause for the observed streamflow 

loss between measurement locations 5 and 6 is unknown but 

may be related to mapped local faulting, 100 years of coal 

mining in the area, and aquifer recharge.

Introduction

Terror Creek, in western Colorado along the North Fork 

Gunnison River (fig. 1), is situated among sedimentary rock 

formations of Cretaceous age that are rich in economical 

deposits of coal. Underground coal mining has been active in 

the North Fork Gunnison River area since about 1900. The 

Bowie mine has been active in the area between Hubbard and 

Terror Creeks since about 1952 (Chaney and others, 1987). 

Mine operators anticipate increasing mining activity to the 

western part of the mine-permit area, including the area directly 

beneath the surface of Terror Creek (J.E. Stover, J. E. Stover 

and Associates, written commun., 2001) (fig. 1).

Coal mining at the mine-permit area employs a continuous 

mining technique to extract the coal. This technique begins with 

the extraction of coal in a crosshatch pattern, referred to as first 

mining, which leaves regularly spaced pillars of coal to support 

the roof of the mine. Later these support columns are removed 

to increase the amount of coal available for extraction. Removal 

of the support columns can cause fractures and subsidence in 

the formations overlying the coal seam (Dunrud, 1976). The 

exact extent of the potential fracturing is not known and will be 

minimized by performing first mining only (no pillar extraction) for areas immediately near Terror Creek (J.E. Stover, 

J. E. Stover and Associates, oral commun., 2004). If fracturing 

extends to near ground surface, streamflow in Terror Creek 
2 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

RIO

GRANDE

Pueblo

Colorado Springs

DENVER

Grand 

Junction

ARKANSAS RIVER

SOUTH

PLATTE RIVER

Yampa River

Dolores River

Gunnison

River

North Fork

COLORADO

 RIVER Grand

Mesa

Grand Mesa

Stevens Gulch

Minnesota Creek

N. Fork Gunnison River

133

Terror Creek

Study Area

107°37'30" 107°35' 107°32'30"

38°52'30"

38°55'

38°57'30"

EXPLANATION

Measurement locations

 and number

U.S. Geological Survey

 streamflow-gaging station

 locations and number

Streams

Lakes

Bureau of Land Management

 land

Highway

Roadways

Railroads

Mine-permit boundary

National Forest boundary Paonia

Bowie

Mine-permit area

1

2

3

4

5

Terror Creek

Reservoir

6

7

7

09132985

09132995

Garvin Mesa

Diversion

Garvin Mesa

0 1 MILE

0 0.5 1 KILOMETER

West Fork

East Fork

Hubbard Creek

Gunnison National Forest

Roatcap Creek

Terror Creek

Terror Creek

Canals

09132995

1/2

Figure 1. Location of Terror Creek study area, measurement locations, and mine-permit area.
Introduction 3

could be affected by ground-water losses from the alluvium 

along and under Terror Creek into the fractures. Streamflow 

loss through recharge to the Mesa Verde Formation of Cretaceous age within the mine-permit area near Terror Creek also 

may occur. Information is needed by interested parties to assess 

future changes in streamflow characteristics in Terror Creek. 

Irrigation companies, the Bureau of Land Management (BLM), 

and mine operators will use the information in this report, which 

was done by the U.S. Geological Survey (USGS) in cooperation 

with Delta County, as a baseline characterization of streamflow 

gain-loss in Terror Creek in the vicinity of the mine-permit area.

Purpose and Scope

The purpose of this report is to describe the methods and 

results for the study of streamflow gain-loss characteristics of 

Terror Creek in the vicinity of a mine-permit area scheduled for 

future coal mining, during reservoir-supplemented and baseflow hydrologic conditions. Reservoir-supplemented streamflow conditions were evaluated June 17–18, 2003, and baseflow conditions were evaluated September 16–17, 2003. 

Streamflow gain-loss characteristics were determined using 

tracer techniques following the constant-rate injection method. 

Streamflow was determined at seven measurement locations 

along Terror Creek over the course of the study. The study reach 

was about 1 mi in length and less than one-fourth of the total 

length of Terror Creek.

Description of Study Area

Terror Creek is a high mountain stream located on the 

southeast flank of the Grand Mesa in western Colorado and 

about 5 mi north of the town of Paonia. The headwaters of 

Terror Creek originate in the Gunnison National Forest (fig. 1). 

Terror Creek flows south from its headwaters (elevation about 

10,200 ft) to its confluence with the North Fork Gunnison River 

(elevation about 5,700 ft). The upper boundary of the study 

reach is located at the confluence of the East and West Forks 

Terror Creek; the lower boundary is located just below the 

mine-permit area, approximately 0.5 mi upstream from a small 

irrigation diversion referred to locally as the Garvin Mesa 

Diversion (fig. 1). 

The stream channel of Terror Creek is typical of a high 

mountain stream, characterized by a narrow channel with a 

steep gradient. The stream channel consists mostly of cobbles 

and boulders surrounded by gravels and sands. The stream 

channel is commonly braided by cobbles and boulders in areas 

of relatively flat gradient, and consists of one or more small riffles and cascades in areas of steeper gradient. The streambed 

material typically is alluvium, but an exposed bedrock channel 

exists intermittently in the study reach.

The study area is characterized by steep and rugged terrain 

primarily covered by oak brush and evergreen and deciduous 

forest. Precipitation ranges from 17 to 43 inches annually, most 

of which occurs as snow at higher elevations during late winter 

and early spring (Daly and Taylor, 1998). Primary land use in 

the area is cattle grazing and coal mining, with the majority of 

the basin managed by the U.S. Department of Agriculture 

(USDA) Forest Service and BLM (Colorado Department of 

Transportation, 2003). Underground coal-mining production 

near Terror Creek ranked within the top 50 for the United States 

in 2002 (based on quantity), with nearly 5.4 million short tons 

produced annually by one local mining company (Energy 

Information Administration, 2002).

Geology

The variations in the stream-channel gradient reflect the 

geology of the area with the combination of erosion-resistant 

sandstones and siltstones interbedded with more erosive shales 

producing the stairstep stream profile. The predominant geologic outcrop within the study reach is the Upper Cretaceous 

Mesa Verde Formation, which consists of interbedded sandstones, siltstones, and shales. The Cretaceous Mancos Shale is 

present along the lower part of the study area. Geologic formations in the area generally dip 5 degrees north into the Grand 

Mesa (Brooks, 1983; Ellis and others, 1987). Previous geologic 

investigations located a subsurface fault 3 mi north of Paonia, 

mapped along the profile of Terror Creek in the study reach 

(Brooks, 1983; Ellis and others, 1987; and Dunrud, 1976). The 

mapped subsurface fault along Terror Creek is related to 

regional tectonics occurring well before Terror Creek existed. 

Faulting and fracturing may have been exacerbated 

by mining and other anthropogenic activities over the last 

100 years. 

The study reach contains economic deposits of bituminous 

coal bound by layers of shale and sandstone within the Mesa 

Verde Formation. The deposits are present intermittently as 

much as 600 ft above the Rollins Sandstone Member, a 

150-ft-thick basal sandstone unit of the Mesa Verde Formation 

(Brooks, 1983). The most likely coal bed to be mined in the 

study area (D-seam) is located more than 200 ft above the 

Rollins Sandstone (Brooks, 1983; Dunrud, 1976). The D-seam 

occurs locally within the mine-permit area along the Terror 

Creek study reach. 

Hydrology

Terror Creek is a perennial stream comprised of the East 

and West Forks Terror Creek. Two USGS streamflow-gaging 

stations are currently active (2001–present) along Terror Creek 

and bracket the study reach (fig. 1). The upstream station is on 

East Fork Terror Creek (USGS 09132985, East Fork Terror 

Creek below Cottonwood Stomp near Bowie, Colo.). The 

downstream station is near the mouth of Terror Creek (USGS 

09132995, Terror Creek at Mouth near Bowie, Colo.). No 

streamflow-gaging stations are located on West Fork Terror 

Creek. Streamflow conditions on East Fork Terror Creek are 

supplemented by Terror Creek Reservoir. Streamflow conditions on West Fork Terror Creek are more natural (not reservoir 
4 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

supplemented). The Garvin Mesa Diversion is downstream 

from the study reach and was actively diverting water during 

both measurement sets (fig. 1). This diversion structure provides water locally along the Garvin Mesa for irrigation needs. 

Approximately 6 ft3

/s of streamflow is diverted from Terror 

Creek from early spring to late fall. No actively flowing tributaries or diversions were present in the study reach during either 

measurement set.

Most of Terror Creek streamflow is derived from snowmelt runoff. The highest streamflows at the mouth occur during 

early spring, with peak streamflow generally occurring in late 

April or early May (fig. 2). Reservoir operations decrease peak 

streamflows in East Fork Terror Creek and attenuate the 

hydrograph (fig. 2A). Snowmelt runoff stored in Terror Creek 

Reservoir is released from early summer to late fall to augment 

streamflow available for diversion to Garvin Mesa. In 2003, 

releases from Terror Creek Reservoir augmented the stream

DAILY-MEAN STREAMFLOW FOR WATER YEAR 2003, IN CUBIC FEET PER SECOND

50

0

100

150

200

250

0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

DATE

DATE

B

Measurement set 1

Measurement set 2

Measurement set 1

Measurement set 2

 Terror Creek at Mouth near Bowie, Colo.

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

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

A

East Fork Terror Creek Below Cottonwood Stomp near Bowie, Colo.

8.0

 Seasonal gage, no winter record

Figure 2. Daily-mean streamflow at USGS streamflow-gaging stations (A) East Fork Terror Creek 

Below Cottonwood Stomp near Bowie, Colo., and (B) Terror Creek at Mouth near Bowie, Colo., for 

water year 2003.
Methods 5

flow in East Fork Terror Creek with streamflows greater than 

2.0 ft3/s from early June to mid-September, whereas streamflow 

along Terror Creek at Mouth receded below 2.0 ft3

/s after May 

(fig. 2B). Numerous ephemeral tributaries also contribute to 

Terror Creek during spring runoff and the monsoon season of 

late summer.

Previous Studies

Previous published reports of interest regarding the Terror 

Creek area include a report by Brooks (1983) that describes the 

hydrology and subsidence potential of coal-lease tracts in Delta 

County and a report by Dunrud (1976) that describes geologic 

factors controlling coal-mine subsidence in Utah and Colorado. 

Maps of interest include a digital geologic map of Colorado by 

Green (1992) and a geologic coal map by Ellis and others 

(1987).

Acknowledgments

The authors acknowledge with appreciation the following 

individuals involved in this study. Thanks to Brent Troutman 

(USGS) for his assistance in error propagation and sensitivity 

analysis; Alisa Mast (USGS) for analytical assistance; and Eric 

Adams, Dan Bartling (USGS), and Winfield Wright (USGS) 

for assisting with fieldwork. Thanks to J.E. Stover (J.E. Stover 

and Associates) for information pertaining to mine operations 

and for assistance with site access.

Methods

A preliminary reconnaissance of the study area in October 

2001 showed that the stream channel consists mostly of large 

cobbles and boulders. The stream channel is commonly braided 

in areas of relatively flat gradient and consists of one or more 

small riffles and cascades in areas of steeper gradient. These 

conditions preclude the use of traditional current-meter 

measurements that use the standard discharge techniques 

described by Rantz and others (1982) because of discrepancies 

in the theoretical and observed vertical velocity profile of the 

stream (Marchand and others, 1984). Larger sized bed material 

such as boulders, in combination with steep gradients (greater 

than 0.01 slopes), produce nonlogarithmic vertical velocity 

profiles. Under these conditions, traditional current-meter 

measurements tend to underestimate the true velocity and 

streamflow (Marchand and others, 1984). Therefore, the 

decision was made to measure streamflow in Terror Creek 

using tracers with the discharge by dilution method. This 

method uses the principle of conservation of mass to calculate 

streamflow (Rantz and others, 1982).

Two sets of measurements were made to determine the 

streamflow gain-loss characteristics of Terror Creek. Measurement set 1 was done June 17–18, 2003, during reservoirsupplemented streamflow conditions. Measurement set 2 was 

done September 16–17, 2003, during low base-flow conditions. 

These two time periods were selected to determine seasonal 

gain-loss (hydrologic condition) differences in the gain-loss 

characteristics of Terror Creek. 

Streamflow Determination

A variety of methods are available to determine streamflow using the discharge by dilution method (Rantz and others, 

1982). Two commonly used methods are the sudden-injection 

method (slug injection) and the constant-rate-injection method. 

The differences between these methods are based on the manner 

in which the tracer, or injectate, is introduced into the stream 

(see Rantz and others [1982] for a detailed comparison). The 

constant-rate-injection method was used for this investigation.

Discharge by Constant-Rate-Injection Method

Streamflow was determined in the Terror Creek study 

reach by using the constant-rate-injection method described in 

Rantz and others (1982) and Zellweger (1994). Preliminary 

assessment and previous investigations suggested that Terror 

Creek contains stream segments that are losing streamflow 

volume within the study reach; traditional discharge measurements by tracer-injection methods cannot indicate loss of 

streamflow volume (Zellweger, 1994). Therefore, a modified 

method of discharge determination was used to account for 

streamflow losses through the use of multiple-injection locations as suggested by Zellweger (1994) and hereinafter referred 

to as “the multiple-tracer method.” Separate injections at seven 

measurement locations were coordinated throughout the length 

of the study reach along Terror Creek (fig. 1). A schematic diagram of the study reach is provided in figure 3. The streamflow 

determined at each measurement location will be construed as a 

point measurement for that location and time, which are comparable to streamflow measurements at other locations. It was 

assumed for this investigation that no decreases in streamflow 

volumes occurred in the mixing zones of each tracer-injection 

measurement.

A solution of sodium bromide was selected for the tracer 

injectate; changes in bromide concentrations were used to 

determine streamflow following the principle of conservation 

of mass. Bromide was selected as the tracer constituent because 

it is conservative and unique to the water chemistry of Terror 

Creek. The streamflow was computed, as shown in equation 1 

(Rantz and others, 1982), which follows:

or

QBCB Q1C1 QB Q1 C2 + = ( + )

C C K

C C Q Q

B

B ( )

( )

−

− =

2

1 2 1

(1)
6 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

where

QB is the discharge of the stream, in cubic feet per 

second;

CB is the background bromide concentration of the 

stream, in milligrams per liter;

Q1 is the rate of flow of the injected tracer solution, in 

liters per minute;

C1 is the bromide concentration of the tracer solution

injectate, in milligrams per liter;

C2 is the downstream bromide concentration, 

completely mixed with the stream, in milligrams 

per liter; and 

K is a metric to standard units conversion factor 

(1.6992 × 103).

A solution of sodium bromide was prepared for use as the 

injectate for the tracers and was prepared for each tracer individually by combining about 4.34 lb of sodium bromide to 

about 1.3 gal of streamwater from each injection site. The applicable measurement procedures, such as tracer volume, injection 

rate, injection duration, and tracer-sampling location and timing, followed the methods prescribed in Kilpatrick and Cobb 

(1985) and in Kilpatrick and Wilson (1989). A log of 

specific conductance was collected at each measurement location to demonstrate that the bromide concentration had reached 

a plateau, indicating that complete mixing of the injectate solution had occurred before sampling.

{

{

{

{

{

{

Streamflow measurement locations

Tracer setup method

Zellweger (1994)

Tributary variation

Injection sites (injectate concentration, C1)

Background sites (background concentration, CB)

Downstream sites (downstream concentration, C2)

West Fork

Terror Creek East Fork

Terror Creek

EXPLANATION

Upper mine-permit boundary

Lower mine-permit boundary

II

I

I

I

I

1 2

5

4

3

6

7

I

II

Figure 3. Tracer design schematic diagram modeled after (I) Zellweger (1994) and (II) tributary 

variation.
Methods 7

Measurement Location and Site Selection

Streamflow was determined at seven measurement locations in the study area: (1 and 2) immediately upstream from the 

confluence of East and West Forks Terror Creek; (3) immediately downstream from the confluence of East and West Forks 

Terror Creek, above the upstream boundary of the mine-permit 

area; (4, 5, and 6) at intermediate points within the mine-permit 

area; and (7) downstream from the downstream boundary of the 

mine-permit area, which is about 0.5 mi upstream from Garvin 

Mesa Diversion (figs. 1 and 3). The general positions of these 

measurement locations were selected at roughly equal spacing 

to best determine the gain-loss characteristics of the stream and 

to bracket gain-loss features controlled by tributaries and 

geology. 

The specific position of each measurement location was 

selected in the field on the basis of discharge-measurement 

criteria and was mapped using a global positioning system. 

Streamflow values for each measurement location required 

three sampling sites and one injection site. The sampling sites 

were marked with flagging in the field, and the same sample and 

injection-site locations were used for both measurement sets. 

The arrangement of these sites follows the design of Zellweger 

(1994) and consists of a background site upstream from the 

injection site (background concentration), the injection site 

(injectate concentration), and a site downstream from the injection site (downstream concentration) (fig. 3I). The measurement-location position is coincident with the downstream 

sampling site. A variation of this design (tributary variation) 

was made at the uppermost tracer (measurement locations 1, 2, 

and 3), which allowed for the determination of streamflow at 

both East and West Forks Terror Creek through a single-tracer 

injection. To facilitate the determination of streamflow for each 

fork of Terror Creek, two background samples were collected 

(one upstream from the injection site on West Fork Terror 

Creek and one on East Fork Terror Creek), two downstream 

samples were collected (one downstream from the injection site 

and upstream from the confluence on West Fork Terror Creek, 

and one downstream from the confluence), and one injection 

sample is needed (fig. 3II). Streamflow in East Fork Terror 

Creek (measurement location 2) is assumed to be the difference 

between the streamflow downstream from the confluence 

(measurement location 3) and West Fork Terror Creek at the 

mouth (measurement location 1). 

Accounting for Streamflow Variation

In order to understand the timing of streamflow, a preliminary assessment of the hydrologic conditions (before each 

measurement set) was done on discharge records for the two 

USGS streamflow-gaging stations located along Terror Creek: 

the upstream station (09132985) East Fork Terror Creek and the 

downstream station (09132995) Terror Creek at Mouth (fig. 1). 

The streamflow-gaging-station discharge record for East Fork 

Terror Creek was used to examine the hydrology upstream from 

the East and West Forks Terror Creek confluence. Interpretation is limited because the discharge record represents a reservoir-supplemented streamflow system controlled in part by 

Terror Creek Reservoir releases and does not match the more 

natural streamflow conditions in West Fork Terror Creek. The 

streamflow-gaging station discharge record for Terror Creek at 

Mouth was used to examine the hydrology of Terror Creek 

downstream from the confluence of East and West Forks Terror 

Creek; however, the Garvin Mesa Diversion structure downstream from the study area (but upstream from the Terror Creek 

at Mouth streamflow-gaging station) typically diverts a considerable portion of the streamflow during high-flow conditions 

and almost all of the streamflow during low-flow conditions. 

This diversion does not directly affect the gain-loss characteristics of the study reach on Terror Creek, but it does limit the usefulness of the streamflow record for purposes of examining 

hydrologic conditions during each measurement set.

Hydrologic conditions for measurement set 1 were evaluated for the period leading up to the measurement set. This 

information was needed so adjustments to pump rates and injection concentrations could be made just prior to the beginning of 

the injection to account for streamflow variations. A 10-day 

excerpt from the hydrograph bracketing the time period for 

measurement set 1 is shown in figure 4A for the East Fork 

Terror Creek streamflow-gaging station. Interpretation of the 

record for measurement set 1 shows substantial step increases 

in streamflow for the days immediately preceding measurement 

set 1, caused by increased releases from Terror Creek 

Reservoir. A 10-day excerpt from the hydrograph bracketing 

the time period for measurement set 1 is included in figure 4B

for Terror Creek at Mouth streamflow-gaging station. Interpretation of the record for measurement set 1 shows substantial 

fluctuations of streamflow, probably resulting from a combination of increased releases from Terror Creek Reservoir and variable adjustments to the Garvin Mesa Diversion structure downstream from the study area.

Stairstep increases in streamflow observed in the 10-day 

period of gage record during measurement set 1 (caused by 

reservoir releases) precluded the direct comparison of the 

streamflow measurements at the seven measurement locations. 

This is because the variations in streamflow observed in the 

gage record due to the reservoir releases could indicate false 

increases or decreases in streamflow simply because of 

unresolved timing issues. To provide a better comparison of 

streamflow measurements among measurement locations for 

streamflow gain-loss analysis for measurement set 1, the 

multiple-tracer method was modified to include an estimate of 

traveltimes between measurement locations. This method was 

necessary to compensate for the reservoir release variations 

from East Fork Terror Creek and hereinafter will be referred to 

as the “modified multiple-tracer method.” 

The modified multiple-tracer method relies on the pairing 

of measurement locations to a reference measurement location 

(measurement location 3 was selected for this purpose), so 

adjustments to start times for tracer injections and sampling can 

coincide with the traveltime between reference measurement 
8 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

location 3 and the downstream measurement locations. This 

modification to the multiple-tracer method facilitates the measurement of the same package of water at two different measurement locations (measurement-location pairs A–C) and 

determination of relative changes in streamflow volume 

between measurement locations associated with real streamflow gain-loss rather than reservoir-release variations.

A sodium chloride single-point slug injection was 

performed to determine streamflow traveltimes between 

measurement locations in the study reach on June 16, 2003. A 

single injection of concentrated sodium chloride was traced 

downstream from measurement location 3 to each measurement 

location included in measurement set 1using specificconductance values. The traveltimes were defined by the difference in times between the arrivals of the sodium chloride 

between measurement locations (Hubbard and others, 1982; 

Kimball, 1996) (fig. 5) as indicated by specific conductance 

logs. Specific conductance was measured at measurement 

locations 4, 5, and 7 (table 1); traveltimes originated from 

measurement location 3. Measurement location 6 was not 

visited during measurement set 1.

Hydrologic conditions for measurement set 2 were evaluated for the days before the measurement set. This information 

was needed so adjustments to pump rates and injection concentrations could be made just prior to the beginning of the injection to account for streamflow variations. A 10-day excerpt 

from the hydrograph bracketing the time period for measurement set 2 is included in figure 6A for East Fork Terror Creek 

streamflow-gaging station. Interpretation of the record for measurement set 2 shows no substantial fluctuation of streamflow, 

and the stream appears to be at a steady-state hydrologic condition for the days immediately preceding measurement set 2. A 

10-day excerpt from the hydrograph bracketing the time period 

for measurement set 2 is included in figure 6B for the Terror 

Traveltime study 

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

STREAMFLOW UNIT VALUES, IN CUBIC FEET PER SECOND

JUNE

0

0.5

1.0

1.5

2.0

2.5

Measurement-location pair A

Measurement-location pair B

Traveltime study 

Measurement-location pair C 

Measurement-location pair B

Measurement-location pair A 

Measurement-location pair C

East Fork Terror Creek Below Cottonwood Stomp near Bowie, Colo.

 Terror Creek at Mouth near Bowie, Colo.

13 14 15 16 17 18 19 20 21 22 23

JUNE

13 14 15 16 17 18 19 20 21 22 23

A

B

Figure 4. Streamflow unit values bracketing measurement set 1 at USGS streamflow-gaging 

stations (A) East Fork Terror Creek Below Cottonwood Stomp near Bowie, Colo., and (B) Terror 

Creek at Mouth near Bowie, Colo., for water year 2003.
Methods 9

Table 1. Relative traveltimes for use in the modified multiple-tracer method, measuremen

t set 1, Terror Creek, Colo., water year 2003.

[--, not measured]

Streamflow measurement location or 

streamflow gaging station

Relative traveltimes, in minutes

209132985 13 209132995

09132985 0 -- 571

1 -- -- 419

2 153 -- 418

3 160 0 411

4 183 23 388

5 217 57 354

6 -- -- --

7 288 128 283

09132995 571 -- 0

1

Traveltimes measured using the single-point slug-injection method. 2

Estimation of traveltimes using a combination of the average velocity from the single-point 

slug-injection method and the calculation of traveltimes measured using the single-point 

slug-injection method.

SPECIFIC CONDUCTANCE, IN 

MICROSEIMENS PER CENTIMETER

CLOCK TIME, IN MILITARY TIME

EXPLANATION

Measurement location 4

110

120

130

140

150

160

170

180

1445 1500 1515 1530 1545 1600 1615 1630 1645 1700 1715 1730

Start time for single-point injection at 1448 hours

Measurement location 5

Measurement location 7

t7 = 128 minutes

t

5

 = 57 minutes

t

4 = 23 minutes

Traveltime from measurement 

 location 3 to measurement location n

t

n

Figure 5. Specific-conductance log for traveltime determination following the single-point injection 

method for measurement set 1, Terror Creek, Colo.
10 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

Creek at Mouth streamflow-gaging station. Interpretation of the 

record for measurement set 2 shows no substantial fluctuation 

of streamflow; however, the Garvin Mesa diversion structure 

downstream from the study area was diverting most of the water 

in Terror Creek, preventing a more precise characterization of 

streamflow conditions present in West Fork Terror Creek. 

Based on available data, Terror Creek was assumed to be in a 

steady-state hydrologic condition, and no adjustments or modifications to the multiple-tracer method were necessary for 

measurement set 2.

Water-Sample Collection and Analysis

Water samples from each tracer measurement location 

were collected and analyzed for use in equation 1 of the constant-rate-injection method. The field methods used for the 

collection, processing, filtration, and preservation of inorganic 

constituents follow the guidelines listed in the USGS National 

Field Manual for the Collection of Water-Quality Data (Wilde 

and others, 2003).

0

0.10

0.20

0.30

0.40

0.50

0

0.10

0.20

0.30

0.40

0.50

0.60

STREAMFLOW UNIT VALUES, IN CUBIC FEET PER SECOND

SEPTEMBER

SEPTEMBER

Measurement set 2

Measurement set 2

East Fork Terror Creek Below Cottonwood Stomp near Bowie, Colo.

 Terror Creek at Mouth near Bowie, Colo.

 No data

A

B

12 13 14 15 16 17 18 19 20 21 22

12 13 14 15 16 17 18 19 20 21 22

Figure 6. Streamflow unit values bracketing measurement set 2 at USGS streamflow-gaging 

stations (A) East Fork Terror Creek Below Cottonwood Stomp near Bowie, Colo., and (B) Terror 

Creek at Mouth near Bowie, Colo., for water year 2003.
Methods 11

Water-Sampling Techniques

Water samples were collected at each measurement location in areas where the stream was confined to a single-channel 

cascade or bedrock ledge to ensure maximum stream mixing. 

Samples were collected in 1-L high-density polyethylene 

bottles after being field rinsed with native streamwater at each 

measurement location. Owing to shallow depths, narrow 

widths, and turbulent conditions, collection of the samples was 

done by using the single-point grab method (Wilde and others, 

2003). The samples were transported to a central processing 

location near measurement location 3 as soon after collection as 

possible. Samples were filtered through a 0.45-micron capsule 

filter into 250-mL high-density polyethylene bottles. Forty-one 

environmental samples were collected during the investigation: 

24 samples were collected during measurement set 1 (table 2), 

and 17 samples were collected during measurement set 2 

(table 3). In addition, five quality-assurance samples were collected during the investigation. Two quality-assurance field 

blanks were collected during the investigation, one during each 

measurement set. Three concurrent replicate pairs (two samples 

collected at the same time) were collected: two during measurement set 1, and one during measurement set 2. One sample was 

destroyed during shipping (measurement location 1, 06/17/03, 

1211, C2), which prevented the determination of one streamflow value each for measurement locations 1 and 2 during 

measurement set 1. 

Quality assurance of field-method techniques was done for 

each measurement set. Field-blank samples of deionized water 

certified to be free of detectable amounts of trace elements were 

analyzed to determine if field methods contaminated the water 

sample with bromide. The blank samples were collected, pro

Table 2. Measurement set 1-Results for modified multiple-tracer method, Terror Creek, Colo., water year 2003.

[C1, injectate bromide concentration; C2, downstream bromide concentration; CB, background bromide concentration; Q1, rate of flow of the injectate; 

QB, measured streamflow; QB / QB 3, measured streamflow expressed as percentage of streamflow at measurement location 3 within each measurement-location 

pair; SQB, streamflow measurement error; mg/L, milligrams per liter; L/min, liters per minute; ft3/s, cubic feet per second; --, no data or not applicable]

Streamflow

measurement 

location

 Tracer injections Variables from equation 1 Error propagation

Date Time

CB

(mg/L)

C1

(mg/L)

Q1

(L/min)

C2

(mg/L)

QB

(ft3/s)

QB / QB 3

(percent)

SQB

(ft3/s)

SQB

(percent)

East and West Fork Terror Creek coincident with measurement-location pair A

1 06/17/03 1107 0.00 268,300 0.0600 --1 -- -- -- --

2 06/17/03 1107 -- -- -- -- -- -- -- --

Measurement-location pair A

3 06/17/03 1107 0.00 268,300 0.0600 1.61 5.90 100 0.186 3.2

4 06/17/03 1130 1.44 256,700 0.0910 3.72 6.04 102 0.136 2.3

East and West Fork Terror Creek coincident with measurement-location pair B

1 06/17/03 1403 0.00 267,100 0.0838 4.15 3.17 48 0.046 1.5

2 06/17/03 1403 -- -- -- -- 3.50 52 0.177 5.0

Measurement-location pair B

3 06/17/03 1403 0.00 267,100 0.0838 1.97 6.67 100 0.170 2.6

5 06/17/03 1500 2.39 264,800 0.0825 3.62 10.47 157 0.413 3.9

East and West Fork Terror Creek coincident with measurement-location pair C

1 06/18/03 1100 0.00 267,600 0.0860 4.80 2.82 40 0.038 1.3

2 06/18/03 1100 -- -- -- -- 4.20 60 0.186 4.4

Measurement-location pair C

3 06/18/03 1100 0.00 267,600 0.0860 1.93 7.02 100 0.183 2.6

7 06/18/03 1308 1.48 253,900 0.0840 3.36 6.65 95 0.177 2.7

1

Sample destroyed during shipping.
12 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

cessed, preserved, and transported using the same techniques 

and locations as the environmental samples. Analysis of the two 

blank samples determined that bromide concentrations of the 

blank samples were at or near the detection limit of the analysis 

method and considered to be insignificant as a bias to the 

results. The three concurrent replicate pairs were collected to 

determine the repeatability (precision) of the water-sampling 

methods. Analytical results for the concurrent replicates incorporate the variations inherent in sampling, processing, and preservation methods and allow an estimate of the precision of the 

streamflow measurements through error analysis. The use of the 

replicate results for error analysis is discussed in the Error 

Analysis section.

Analytical Techniques

Water samples were analyzed for bromide using two methods: (1) low-ionic-strength bromide detection was performed 

on stream samples (background and downstream concentrations) by the USGS National Water-Quality Laboratory 

(NWQL) in Denver, Colo., and (2) high-ionic-strength bromide 

detection was performed on the tracer-injectate solution by the 

USGS Colorado District Laboratory in Lakewood, Colo. Two 

separate methods are required to measure the bromide concentrations in this investigation based on the extreme differences of 

ionic strengths between the stream samples and the injectate 

solutions. The low-ionic-strength detection techniques for bromide are determined using colorimetric procedures (Fishman 

and Friedman, 1989). The high-ionic-strength detection techniques for bromide are determined using a gravimetric method 

to determine the residue on evaporation (Fishman and Friedman, 1989). 

Quality assurance of analytical techniques was conducted 

for each measurement set. Replicate samples and standardized 

samples were analyzed for the low-ionic and high-ionic 

bromide detection methods. The low-ionic method is internally 

monitored at the USGS NWQL through in-house testing programs according to their quality-assurance plan (Michael 

Lewis, U.S. Geological Survey, written commun., 2004). The 

high-ionic bromide detection methods also were checked for 

precision by using replicate samples from the investigation. A 

comparison of the values reflects the repeatability (precision) of 

the procedures. Precision is used in the following section to 

estimate error associated with measuring streamflow by using 

the constant-rate-injection method.

Error Analysis

In order to determine the compounded effects of measurement error on the streamflow calculations from equation 1, error 

analysis was performed on each measurement set by using 

error-propagation techniques. Error introduced through field 

methods (sampling, processing, preservation, and shipping) as 

well as analytical methods (storage, processing, and analysis) 

are estimated on the basis of the standard deviation of the differences between replicate measurements for each variable in 

equation 1. 

A correction factor was applied to the resulting standard 

deviations to compensate for the loss of degrees of freedom 

resulting from the calculations of the differences between replicate measurements and each mean for the sample. This correction factor is consistent with techniques used in analysis of variance techniques described by Helsel and Hirsch (2002) and Ott 

and Longnecker (2001) and is included in the calculation of the 

standard deviation. The equation used for the calculation of the 

Table 3. Measurement set 2-Results for multiple-tracer method, Terror Creek, Colo., water year 2003.

[C1, injectate bromide concentration; C2, downstream bromide concentration; CB, background bromide concentration; Q1, rate of flow of the injectate; QB, 

measured streamflow; QB / QB 3, measured streamflow expressed as percentage of streamflow at measurement location 3; SQB, streamflow measurement error; 

mg/L, milligrams per liter; L/min, liters per minute; ft3/s, cubic feet per second; --, no data or not applicable]

Streamflow 

measurement 

location

Tracer injections Variables from equation 1 Error propagation

Date Time

CB

(mg/L)

C1

(mg/L)

Q1

(L/min)

C2

(mg/L)

QB

(ft3/s)

QB / QB 3

(percent)

SQB

(ft3/s)

SQB

(percent)

1 09/16/03 1718 0.00 261,800 0.0713 4.96 2.21 81 0.031 1.4

2 09/16/03 1718 -- -- -- -- 0.51 19 0.053 10.4

3 09/16/03 1718 0.00 261,800 0.0713 4.04 2.72 100 0.043 1.6

4 09/16/03 1406 0.00 267,800 0.0731 4.20 2.74 101 0.041 1.5

5 09/16/03 1138 0.00 265,600 0.0808 4.06 3.11 114 0.047 1.5

6 09/17/03 1340 0.00 271,800 0.0625 4.22 2.37 87 0.038 1.6

7 09/17/03 1137 0.00 270,100 0.0738 4.87 2.41 88 0.034 1.4
Methods 13

standard deviation is shown in equation 2 (Helsel and Hirsch, 

2002), which follows:

where

S is the standard deviation of the differences between 

replicate samples and their means,

S2 is the variance of the differences between replicate 

samples and their means,

is the jth replicate for sample i,

is the mean of the replicates for sample i,

is the number of replicates for sample i,

M is the number of samples, and

N is the total number of replicates for all samples.

Sensitivity Analysis

Evaluation of the sensitivity of each parameter in 

equation 1 allows for the determination of the extent to which 

uncertainty in the variables results in uncertainty of the streamflow measurements. A comparison of these absolute sensitivities provides the error in streamflow for one unit of measure for 

the variable. The partial derivative of equation 1 is calculated 

with respect to each variable. The calculation of these values 

follows the forms:

where

is the change in QB (cubic feet per second) relative 

to change in CB (milligrams per liter),

is the change in QB (cubic feet per second) relative 

to change in C1 (milligrams per liter),

is the change in QB (cubic feet per second) relative 

to change in C2 (milligrams per liter),

is the change in QB (cubic feet per second) relative 

to change in Q1 (liters per minute),

QB is the discharge of the stream (cubic feet per 

second),

CB is the background bromide concentration of the 

stream (milligrams per liter), 

C1 is the bromide concentration of the tracer solution 

injectate (milligrams per liter),

C2 is the downstream bromide concentration, 

completely mixed with the stream (milligrams per 

liter),

Q1 is the rate of flow of the injected tracer solution 

(liters per minute), and

K is a metric to standard units conversion factor 

(1.6992 × 103).

Because the units of each variable are different, a relative 

sensitivity can be compared between variables in units of percent change in streamflow per percent change in each variable. 

The values now indicate a unitless percentage, which allows all 

of the variables to be directly compared. When these values are 

compared to the standard deviation of each variable, the level of 

error introduced from the measurement of each variable can be 

determined. Comparisons between variables can indicate field 

and analytical method improvements necessary to reduce the 

error of the calculations.

N M

X X

S S

M

i

N

j

ij i

i

−

−

= =

∑∑= = 1 1

2

2

( )

C C K

C C Q

C

Q

B

B

2

2 B

1 2 1

( )

( )

−

− = ∂

∂

C C K

Q

C

QB

( ) 2 B

1

1 − = ∂

∂

C C K

C C Q

C

Q

B

B B

2

2

1 1

2 ( )

( )

−

− = ∂

∂

C C K

C C

Q

Q

B

B

( )

( )

−

− = ∂

∂

2

1 2

1

B

B

C

Q

∂

∂

C1

QB

∂

∂

C2

QB

∂

∂

1

∂

∂

Q

Q

B

Ni

Xi

(3)

(4)

(5)

(2)

(6)

Xij
14 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

Error Propagation

The error inherent to the constant-rate-injection streamflow measurement method was quantified using error analysis. 

Following the rules of error propagation described in Bevington 

and Robinson (2003) and Taylor (1997), a Taylor Series was 

used to determine the error-propagation equation, which calculates the error in streamflow resulting from the error of the field 

and analytical methods. The calculation of the standard deviation of the streamflow error is based on the following equation:

where

is the standard deviation of error in QB (cubic feet per 

second),

is the variance of the error in QB (cubic feet per 

second) squared,

is the variance of the error in CB (milligrams per liter) 

squared,

is the variance of the error C1 (milligrams per liter) 

squared,

is the variance of the error C2 (milligrams per liter) 

squared,

is the variance of the error Q1 (liter per minute) 

squared,

is the change in QB (cubic feet per second) relative to 

change in CB (milligrams per liter),

is the change in QB (cubic feet per second) relative to 

change in C1 (milligrams per liter),

is the change in QB (cubic feet per second) relative to 

change in C2 (milligrams per liter),

is the change in QB (cubic feet per second) relative to 

change in Q1 (liters per minute),

is the discharge of the stream (cubic feet per second),

is the background bromide concentration of the stream 

(milligrams per liter), 

is the bromide concentration of the tracer solution 

injectate (milligrams per liter),

is the downstream bromide concentration, completely 

mixed with the stream (milligrams per liter), and

is the rate of flow of the injected tracer solution (liters 

per minute).

Error analysis is used as an indicator of the accuracy of the measured streamflow value. The error-analysis calculations provide 

a range of streamflow values and are depicted as error bars. 

These error bars provide context to the certainty of the streamflow values.

Streamflow Comparisons

Streamflow measurements were compared to determine 

the gain-loss characteristics of the Terror Creek study reach by 

using two methods: a graphical comparison and statistical 

testing. The graphical comparison was used to determine 

streamflow gain-loss characteristics among the seven measurement locations (upstream to downstream). The difference in the 

streamflow values among measurement locations indicates 

streamflow gains or losses during each measurement set and 

corresponding streamflow condition. A comparison of the two 

measurement sets and previous investigations was included in 

the interpretation of the overall streamflow gain-loss characteristics of the Terror Creek study reach. Statistical testing was 

used to evaluate the significance level associated with the 

overall streamflow gain or loss along the study reach within the 

mine-permit area; confidence intervals also were calculated for 

the gains or losses observed within the mine-permit area during 

measurement sets 1 and 2. Use of a combination of these methods allows the comparison of streamflow measurements within 

and between the two measurement sets. 

Graphical Comparison

A graphical comparison of streamflow among measurement locations was used to determine the streamflow gain-loss 

characteristics of the Terror Creek study reach within the 

same hydrologic conditions. A graphical comparison of streamflow values and the corresponding error bars allows for an 

assessment of the likelihood that two streamflow values are 

discernibly different. For this investigation, a comparison of 

two streamflow values with overlapping error bars indicates 

that the two measurements are not discernibly different; a comparison of two measurements with error bars that are not over2 1 

1 

2 

1 

2 

2 

2 +

1 

2 2

Q 

B

C 

B

C 

B

C 

B

B

Q Q 

S 

Q 

Q S 

C 

Q

S 

C 

Q S 

C

Q S S B B B 

⎟

⎟ 

⎠ 

⎞ 

⎜

⎜

⎝

⎛

∂ 

∂

+ ⎟ ⎟ 

⎠ 

⎞

⎜

⎜

⎝

⎛

∂

∂ 

⎟

⎟

⎠ 

⎞

⎜

⎜

⎝

⎛

∂

∂

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

= =

2

2

2

2

QB S

S QB

2

B S C

2

1

2 S C

2

2 S C

1

2 S Q

B

B

C

Q

∂

∂

C1

QB

∂

∂

C2

QB

∂

∂

Q1

QB

∂

∂

QB

CB

C1

C2

Q1

(7)
Evaluation of Streamflow Gain-Loss Characteristics 15

lapping indicates that the measurement values are discernibly 

different.

A direct comparison of streamflow values (comparison of 

streamflow between measurement locations, in cubic feet per 

second) was used to aid in the interpretation of streamflow gainloss characteristics between measurement locations under the 

same hydrologic condition (measurement locations within the 

same measurement-location pairs A–C during measurement 

set 1, and all measurement locations within measurement set 2). 

This method does not allow for the quantification of gain-loss 

characterization between measurement locations under different hydrologic conditions. 

An indirect comparison of streamflow values (comparison 

of streamflow between measurement locations, as a percentage 

of streamflow at measurement location 3) was used to aid in the 

interpretation of streamflow gain-loss characteristics among all 

measurement locations within the entire study reach, even 

under different hydrologic conditions and measurement sets. 

The streamflow values are normalized to a reference measurement location (measurement location 3), which removes the 

variations observed in the direct comparison of streamflow 

values. The indirect comparison between measurement locations is possible because each pairing of a new measurement 

location includes the same reference measurement location 

(measurement location 3). Therefore, any changes in streamflow between a specific measurement location and the reference 

measurement location can indicate a relative change among all 

the measurement locations. The units are expressed as percentages of the streamflow at measurement location 3 and can be 

compared across all measurement locations and measurement 

sets. This removes any erroneously perceived streamflow gains 

or losses, which actually are the result of variations in reservoir 

releases from Terror Creek Reservoir. 

Statistical Comparison

Statistical tests are a second means by which a comparison 

of streamflow values is possible. Statistical testing was not done 

for each comparison of streamflow values, because the number 

of comparable streamflow values is insufficient for testing 

statistical significance (p-values <0.05) to be determined 

regardless of the magnitude of difference between streamflows. 

Statistical testing of streamflow values for the overall streamflow gain-loss (streamflow gain-loss indicated by the difference 

of streamflow values downstream and upstream from the

mine-permit area) was performed, in addition to the graphical 

assessment previously described, because three sets of measurements are available for measurement locations 3 and 7 

(including results of a previous study done by Brooks [1983]). 

Because of the small sample size available for statistical testing, 

a comparison of parametric (required assumptions: normality of 

distribution, independent sample pairs, and equal variance 

between data sets) and nonparametric (required assumptions: 

symmetric distribution about the median) methods was considered necessary. Under parametric assumptions, the paired t-test 

is appropriate for the comparison of streamflow for measurement locations 3 and 7 for measurement sets 1 and 2; under 

nonparametric assumptions, the exact Wilcoxon signed-rank 

test is appropriate for measurement sets 1 and 2, as well as the 

previous investigation by Brooks (1983), following guidelines 

described by Helsel and Hirsch (2002) and Ott and Longnecker 

(2001). Confidence intervals were calculated to quantify the 

certainty of the overall streamflow gain-loss observed for measurement sets 1 and 2. In this context, the comparison of streamflow measurements will be presented to determine the streamflow gain-loss characteristics of the Terror Creek study reach.

Evaluation of Streamflow Gain-Loss 

Characteristics

The determination of streamflow gain-loss characteristics 

for the study reach of Terror Creek included seven measurement locations and two measurement sets. A comparison of 

streamflow at measurement locations (from upstream to downstream) was used to quantify and locate gain-loss characteristics 

in the Terror Creek study reach. Quantification of the gain-loss 

characteristics was based on the direct (quantity) and indirect 

(percentage normalized to measurement location 3) comparison 

of streamflow measurements at the seven measurement locations visited during the study, as well as a statistical assessment 

of the difference in streamflow within the mine-permit area for 

available measurements.

Measurement Set 1, Streamflow Gain-Loss 

Characteristics 

Measurement set 1 began June 17, 2003, and included 

three measurement-location pairs (A–C) following the modified multiple-tracer method (to account for variations in the 

reservoir releases to East Fork Terror Creek) (table 1). Measurements were made at measurement locations 1, 2, 3, 4, 5, and 7 

over a 2-day period. Details concerning tracer operation and 

other tracer-injection information are included in the supplemental table at the back of this report (see table 5). Bromide 

concentrations, calculated values for streamflow, and error 

analysis are presented in table 1.

The streamflow gain-loss characteristics of the Terror 

Creek study reach for measurement set 1 was based on the 

direct comparison of the streamflows within each measurement-location pair (fig. 7). The first measurement-location pair 

(A), measurement locations 3 and 4, shows no discernible 

streamflow gain or loss; the error bars for both values overlap. 

The second measurement-location pair (B), measurement locations 3 and 5, shows a streamflow gain of 3.80 ft3

/s. The third 

measurement-location pair (C), measurement locations 3 and 7, 

shows a moderate streamflow loss of 0.37 ft3

/s. The indicated 
16 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

0

1

2

3

4

5

6

7

8

9

10

11

12

34 35 37

A

A

B

C

Error bar

Measurement and location pairs

(tables 2 and 5)

MEASUREMENT-LOCATION PAIRS, IN DOWNSTREAM ORDER

STREAMFLOW, IN CUBIC FEET PER SECOND

Figure 7. Comparison of streamflow between measurement-location pairs during measurement set 1, 

June 17–18, 2003, Terror Creek, Colo., water year 2003.

loss between measurement locations 3 and 7 is interpreted 

as the overall streamflow loss within the mine-permit area for 

measurement set 1.

In order to determine any discernible gains or losses 

among all measurement locations, an indirect comparison of the 

streamflow gain-loss (comparison of streamflow between measurement locations, normalized as a percentage of streamflow at 

measurement location 3) is necessary because of the stairstep 

increase in streamflow derived from Terror Creek Reservoir 

releases during measurement set 1. An indirect comparison of 

measurement locations 3 and 4 shows no discernible streamflow gain or loss within the precision of the measurements 

(fig. 8). A streamflow gain was shown between measurement 

locations 4 and 5, with an increase in streamflow of 55 percent 

normalized to measurement location 3. A streamflow loss was 

shown between measurement locations 5 and 7, with a decrease 

in streamflow of 62 percent normalized to measurement 

location 3.

Measurement Set 2, Streamflow Gain-Loss 

Characteristics 

Measurement set 2 began September 16, 2003, and 

included five tracer injections following the multiple-tracer 

method. Measurements were made at measurement locations 1, 

2, 3, 4, 5, 6, and 7 over a 2-day period. Details concerning tracer 

operation and other tracer-injection information are included in 

a supplemental table at the back of this report (see table 5). Bromide concentrations, calculated values for streamflow, and 

error analysis are presented in table 3. 

The streamflow gain-loss characteristics for measurement 

set 2 were based on the direct comparison of each measurement 

location due to the steady-state hydrologic condition (fig. 9). 

The streamflow gain-loss characteristics of the Terror Creek 

study reach for measurement set 2 also was based on the indirect comparison of the streamflows for each measurement location (fig. 10). Measurement locations 3 and 4 had no discernible 

streamflow gain or loss. A streamflow gain was shown between 

measurement locations 4 and 5, with an increase in streamflow 

of 0.37 ft3/s. A streamflow loss was shown between measurement locations 5 and 6, with a decrease in streamflow of 

0.74 ft3/s. No discernible streamflow gain or loss was shown 

between measurement locations 6 and 7. Normalized to measurement location 3, a streamflow gain of 13 percent was shown 

between measurement locations 4 and 5, and a streamflow loss 

of 27 percent was shown between measurement locations 5 and 

6.

For consistency between measurement sets, each measurement location for measurement set 2 also was compared to

measurement location 3. Measurement locations 3 and 5 show 

a streamflow gain of 0.39 ft3

/s. A streamflow loss was shown 

between measurement locations 3 and 6, with a decrease in 

streamflow of 0.35 ft3

/s. A similar streamflow loss was shown 
Evaluation of Streamflow Gain-Loss Characteristics 17

No data

0

100

200

12345 7

MEASUREMENT LOCATIONS, IN DOWNSTREAM ORDER

50

150

6

STREAMFLOW, IN PERCENTAGE OF 

STREAMFLOW AT MEASUREMENT 

LOCATION 3

Error bar

Figure 8. Comparison of relative streamflow among measurement locations during measurement set 1,

June 17–18, 2003, Terror Creek, Colo., water year 2003.

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

STREAMFLOW, IN CUBIC FEET PER SECOND

MEASUREMENT LOCATIONS, IN DOWNSTREAM ORDER

1234567

Error bar

Figure 9. Comparison of streamflow among measurement locations during measurement set 2, 

September 16–17, 2003, Terror Creek, Colo., water year 2003.
18 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

0

100

150

200

1234567

MEASUREMENT LOCATIONS, IN DOWNSTREAM ORDER

50

STREAMFLOW, IN PERCENTAGE OF 

STREAMFLOW AT MEASUREMENT 

LOCATION 3

Error bar

Figure 10. Comparison of relative streamflow among measurement locations during measurement set 2, 

September 16–17, 2003, Terror Creek, Colo., water year 2003.

between measurement locations 3 and 7, with a decrease in 

streamflow of 0.31 ft3/s. The indicated loss between measurement locations 3 and 7 is interpreted as the overall streamflow 

loss within the mine-permit area for measurement set 2.

Interpretation of Findings

A comparison of the measurement sets indicates that the 

streamflow gain-loss characteristics of the Terror Creek study 

reach are consistent between time periods between the two 

hydrologic conditions evaluated: (1) reservoir-supplemented 

streamflow conditions of the summer during measurement set 

1, and (2) the more natural base-flow conditions of early fall 

during measurement set 2 (fig. 11). A substantial streamflow 

gain is shown between measurement locations 4 and 5 in both 

measurement sets, but streamflow decreases between measurement locations 5 and 7 (measurement set 1, measurement 

location 6 not visited) and 5 and 6 (measurement set 2). During 

measurement set 1, the 55-percent streamflow gain between 

measurement locations 4 and 5, normalized to measurement 

location 3, is less than the 62-percent streamflow loss between 

measurement locations 5 and 7. During measurement set 2, the 

13-percent streamflow gain between measurement locations 4 

and 5, normalized to measurement location 3, is less than onehalf the 27-percent streamflow loss observed between measurement locations 5 and 6. A comparison of the measurement sets 

for the measurement locations upstream and downstream from 

the mine-permit area (measurement locations 3 and 7) shows a 

consistent streamflow loss of 0.37 and 0.31 ft3

/s (representing 

5- and 12-percent streamflow losses, normalized to measurement location 3) for measurement sets 1 and 2, respectively 

(tables 1 and 3). This result indicates that similar streamflow 

losses occur during both reservoir-supplemented and natural 

base-flow conditions, with a mean streamflow loss of 0.34 ft3

/s 

for measurement sets 1 and 2. The similarity in streamflow 

losses also indicates that the process controlling streamflow 

losses are the same between reservoir-supplemented and natural 

base-flow conditions.

Findings from a previous investigation (Brooks, 1983) to 

determine ground-water recharge in Terror Creek support the 

observed streamflow losses between measurement locations 3 

and 7 for this investigation. The investigation in October 1982 

compared current-meter style measurements at measurement 

locations 1 and 2 (the sum of which is equivalent to measurement location 3) with a measurement location 0.5 mi downstream from measurement location 7 (located directly upstream 

from the Garvin Mesa Diversion). Findings by Brooks indicate 

a 0.59-ft3

/s streamflow loss occurs between these measurement 

locations (fig. 12). The precision of the current-meter style 

discharge measurements made by Brooks was estimated for use 
Evaluation of Streamflow Gain-Loss Characteristics 19

0

100

50

200

1234567

MEASUREMENT LOCATIONS, IN DOWNSTREAM ORDER

STREAMFLOW, IN PERCENTAGE OF 

STREAMFLOW AT MEASUREMENT 

LOCATION 3

150

Measurement set 1

Measurement set 2

Error bar

Figure 11. Comparison of relative streamflow among measurement locations during measurement set 1 

(June 17–18, 2003) and measurement set 2 (September 16–17, 2003), Terror Creek, Colo., water year 2003.

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

MEASUREMENT LOCATIONS, IN DOWNSTREAM ORDER

STREAMFLOW, IN CUBIC FEET PER SECOND

No data No data No data

1234567

Error bar

Figure 12. Comparison of streamflow among measurement locations from Brooks (1983), October 5, 1982, 

Terror Creek, Colo., water year 2003.
20 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

in this investigation at the USGS designation of fair (8-percent 

error), which is used to calculate the error bars in figure 12. 

Statistical testing of the streamflow difference between 

measurement locations 3 and 7 was evaluated to determine the 

likelihood that the observed loss between the measurement 

locations truly represents the gain-loss characteristics of the 

study reach and to determine what level of certainty can be 

assigned to the findings. Calculations of the statistical tests were 

performed using S-Plus 2000 Professional software (Insightful 

Corporation, 2000), and the findings are presented in table 4. 

The statistical testing of the differences in streamflow 

between measurement locations 3 and 7 indicates that the there 

is a discernible streamflow loss. The difference between measurement locations 3 and 7 for measurement set 1 is 0.37 ft3/s 

with a standard deviation of the difference of 0.25 ft3

/s. The 

standard deviation of the difference for measurement set 1 indicates a confidence interval of about 92 percent (1.43 standard 

deviations from zero), indicating that there is about an 8-percent 

probability of observing a sample mean difference greater than 

or equal to 0.37 ft3/s if the population mean is zero (that is, if 

there is no true difference in streamflow between these two 

locations). The difference between measurement locations 3 

and 7 for measurement set 2 is 0.31 ft3/s with a standard 

deviation of the difference of 0.05 ft3/s. The standard deviation 

of the difference for measurement set 1 shows a confidence 

interval of approximately 100 percent (5.77 standard deviations 

from zero), indicating that there is almost no possibility of 

observing a sample mean difference greater than or equal to 

0.31 ft3/s if the population mean is zero. The standard deviation 

of the difference between measurement locations 3 and 7 for 

both measurement sets 1 and 2 is 0.34 ft3/s for samples meeting 

parametric assumptions (measurement sets 1 and 2). The 

p-value of 0.0236 for the parametric paired t-test indicates that 

there is a 2.36-percent probability of observing a sample mean 

difference of 0.34 ft3/s if the population mean is zero. This 

result is statistically significant at the standard 5 percent (pvalue 0.05) generally accepted as the designation of a statistically significant result. The sample mean difference between 

measurement locations 3 and 7 is 0.42 ft3

/s for the samples 

meeting nonparametric assumptions (measurement sets 1 and 2, 

and Brooks (1983)). The p-value of 0.125 for the nonparametric 

exact Wilcoxon signed rank test indicates that there is a 

12.5-percent probability of observing a sample mean difference 

this large if the population mean is zero. This level of significance is above the 5 percent (p-value 0.05) generally accepted 

designation of a statistically significant result. The lack of statistical significance in the nonparametric test is caused by the 

number of observations available for comparison being too few 

for a definitive assessment. The exact level of statistical significance is undetermined, but the incorporation of each of the 

available methods to detect a streamflow loss, including graphical interpretation, error analysis, repeatability of results, and 

two methods of testing of statistical significance, provides good 

evidence that there is a loss of about 0.34 ft3

/s within the minepermit area (between measurement locations 3 and 7) for the 

hydrologic conditions investigated during measurement set 1 

and 2. 

Factors Affecting Streamflow Gain-Loss 

Characteristics

The observed streamflow gain-loss characteristics of the 

Terror Creek study reach are the result of two types of groundwater systems interacting with Terror Creek surface water. The 

first ground-water system is the shallow ground water that travels as hyporheic flow parallel to the stream channel or is stored 

seasonally in the adjacent alluvium of the stream channel. 

Water in the hyporheic system contributes to streamflow gains 

and losses in Terror Creek and has relatively short residence 

times. The second ground-water system is the deep groundTable 4. Summary of results from statistical tests of measured streamflow loss within the mine-permit area, Terror Creek, 

Colo., water year 2003.

[ft3/s, cubic feet per second; n, number of sample pairs; df, degrees of freedom; p, probability that the true difference between streamflow values at 

measurement locations 3 and 7 is equal to or greater than zero]

Data source

Streamflow at measurement

location

(ft3

/s)

Test type

Statistical diagnostics

3 7 n df p

Paired t-test (one-sided) 

Measurement set 1 7.02 6.65 Parametric 2 1 0.0236

Measurement set 2 2.72 2.41

Exact Wilcoxon signed-rank test (one-sided)

Measurement set 1 7.02 6.65 Nonparametric 3 2 0.1250

Measurement set 2 2.72 2.41

Brooks (1983) 4.32 3.73
Evaluation of Streamflow Gain-Loss Characteristics 21

water system that receives recharge from the stream channel 

and transmits it out of the basin through fractures and bedrock 

aquifers, in turn causing a loss to the total surface water of the 

stream. This deeper ground water has substantially longer residence times and is not believed to return to Terror Creek.

Hyporheic Flow System

Investigation of the geology of the stream channel within 

the Terror Creek study reach indicates that alluvium is present 

throughout much of the study reach (Ellis and others, 1987). 

Hyporheic flow can occur throughout an alluvial setting and 

may contribute 20–25 percent of the total streamflow (Cleasby 

and Nimick, 2002; Nimick and Cleasby, 2000; and Zellweger 

and others, 1989). Variations in the proportions of streamflow 

that is transmitted as hyporheic flow or surface water along the 

Terror Creek study reach must be evaluated in order to fully 

interpret streamflow gain-loss characteristics. 

Determination of the volume of hyporheic flow within the 

study reach with any certainty was beyond the scope of the 

investigation because the multiple-tracer method used to 

account for the losing subreaches of Terror Creek cannot 

include estimates of hyporheic flow volumes (Zellweger and 

others, 1989); however, some understanding of the proportion 

of streamflow transmitted as hyporheic flow at each measurement location is needed for interpretation of the relative streamflow values. 

For this analysis, observed geologic and hydrologic characteristics identified onsite during this study and in previous 

investigations and analyses were used to indicate whether 

hyporheic flow is present. The thickness of alluvium adjacent to 

and below the stream channel at a given measurement location 

is related directly to the volume of hyporheic flow and available 

shallow ground-water storage. Variations in the thickness of 

these sediments can cause fluctuations in the amount of measurable surface water relative to the total surface water of the 

stream. In areas where these sediment deposits are thin or nonexistent, most of the total streamflow is present as surface water 

in the stream. 

Measurement locations 3, 6, and 7, as well as the measurement location used by Brooks (1983) upstream from the Garvin 

Mesa Diversion, were located in areas where outcrops of 

sandstone decrease the amount of alluvium in the streambed. 

Ten yards downstream from measurement location 3, a sandstone outcrop was observed along the right bank. Five yards 

downstream from measurement location 6, the streambed of 

Terror Creek consisted of exposed sandstone bedrock. The bedrock channel continued on for 35 yards, before reverting to an 

alluvial channel. Extensive outcrops of sandstone were 

observed along the right bank of Terror Creek, approximately 

100 yards downstream from measurement location 7, with 

small cascades caused by exposed bedrock ledges located just 

upstream. Similar cascades were observed just downstream 

from measurement location 7, but no observable outcrops of 

sandstone were located. The Rollins Sandstone was observed at 

the Garvin Mesa Diversion with exposed bedrock adjacent to 

the right bank of Terror Creek, as well as intermittently 

upstream. Field observations of channel characteristics and 

geologic outcrops support the statement that measurement 

locations 3, 6, and 7, as well as the measurement section used 

by Brooks (1983) upstream from the Garvin Mesa Diversion, 

have minimal to no hyporheic flow. This characterization is 

based on the thickness of observed alluvium within the stream 

channel at these locations, and the presence of sandstone outcrops adjacent to the stream channel. Subsequently, the streamflow measurements made at these measurement locations 

should represent the total streamflow of Terror Creek at these 

locations. 

Measurement locations 4 and 5 have characteristics that 

indicate that the measurements made at these locations also may 

represent the total surface water of Terror Creek. Dense vegetation and various Quaternary deposits along the flanks of Terror 

Creek Basin obstructed field observation of sandstone outcrops 

along measurement locations 4 and 5. Comparisons of the 

stream-channel characteristics of measurement locations 4 and 

5 with areas known to have sandstone outcrops indicate that 

sandstone outcrops and near bedrock-channel conditions could 

be present at these locations. Field observations indicate that 

variations in the stream profile were related to the presence of 

sandstone outcrops. In areas where sandstone dominated the 

stream channel, step-pool sequences and exaggerated rockledge cascades were common. Large, flat tracts of slower water 

also were common upstream from these sandstone outcrops due 

to the inability of the stream channel to downcut through these 

more resistant layers (as observed at measurement location 6). 

These stream characteristics also were observed at measurement locations 4 and 5. 

Longitudinal consistency of streamflow-measurement 

values indicates similar channel and alluvial characteristics. 

The nearly identical streamflow values between measurement 

locations 3 and 4 within each measurement set indicate that the 

channel conditions are similar between the two measurement 

locations (nearly bedrock channels). Therefore, the assumption 

that total streamflow was measured at measurement location 4 

is further supported. A more complex relation exits between 

measurement location 5 and measurement locations 4 and 6 and 

is not as readily apparent.

The streamflow gain observed between measurement 

locations 4 and 5 is followed by a proportional streamflow loss 

between measurement locations 5 and 6. If hyporheic flow 

occurs at measurement location 5 at the 20–25 percent typical 

of some mountain streams (Cleasby and Nimick, 2002; Nimick 

and Cleasby, 2000; and Zellweger and others, 1989), then the 

indicated gain between measurement locations 4 and 5 the and 

loss between measurement locations 5 and 6 would be even 

greater than previously estimated. Quantification of the amount 

of hyporheic flow at measurement location 5 is not possible 

without further investigation; however, based on channel characteristics, the assumption will be made for this analysis that the 

streamflow values from measurement location 5 include the 

total streamflow of Terror Creek at this location.
22 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

Based on field observations and measurement analysis, the 

volume of hyporheic flow within the Terror Creek study reach 

is considered to be negligible at all measurement locations. 

However, indicated gains between measurement locations 4 

and 5 may be related to hyporheic flow from tributaries that 

were dry during the study between measurement locations 4 and 

5. No other obvious surface-water sources were identified 

during the investigation.

Deep Flow System

Other factors that could affect the streamflow gain-loss 

characteristics of the Terror Creek study reach are fractures and 

bedrock aquifers that are part of the deep flow system. Investigation of the geology of the stream channel within the Terror 

Creek study reach indicates that such losses may occur through 

fractures associated with a mapped subsurface fault along the 

profile of Terror Creek (Brooks, 1983; Ellis and others, 1987). 

Secondary streamflow losses also may occur as recharge to 

bedrock aquifers and coal seams of the Mesa Verde Formation 

(Brooks, 1983). Most of the total streamflow loss within 

the Terror Creek study reach appears to occur between 

measurement locations 5 and 7. The loss in streamflow between 

measurement locations 5 and 7 exceeds the gain in streamflow 

between measurement locations 4 and 5 for both measurement 

sets. With the addition of measurement location 6 in measurement set 2, streamflow comparisons indicate that the losses are 

likely limited to the stream reach between measurement locations 5 and 6. The comparability in overall streamflow loss 

between measurement locations 3 and 7 (overall loss within the 

mine-permit area) for both measurement sets demonstrates that 

the mean overall-streamflow loss is approximately 0.34 ft3/s.

The exact cause for the loss between measurement locations 5 and 6 is unknown but may be related to a combination of 

factors. The location of the loss is coincident with the D-seam 

coal bed, based on interpretation of a local Mesa Verde Formation geologic cross section located a few miles to the east in the 

Bear Creek drainage (Dunrud, 1976). The D-seam coal bed may 

act as an aquifer, enhanced by local faults and fractures transmitting ground water to the north, following the structural dip 

of the area. The mapped subsurface fault present along Terror 

Creek could act as a conduit for ground water to move between 

strata in the Mesa Verde Formation, as well as to the north, 

following the structural dip of the area. Further complication 

of the structural geology of the area may be the result of 

collapse structures and dewatering processes related to the past 

100 years of coal mining in the area (Dunrud, 1976; Brooks, 

1983). A combination of factors is most likely the reason for the 

observed streamflow losses along the Terror Creek study reach.

Summary

In 2003, the U.S. Geological Survey, in cooperation with 

Delta County, initiated a study to characterize streamflow gainloss in a reach of Terror Creek, in the vicinity of a mine-permit 

area planned for future coal mining. This report describes the 

methods of the study and includes results from a comparison of 

two sets of streamflow measurements determined using tracer 

techniques following the constant-rate injection method. Characterization of streamflow gain-loss for the Terror Creek study 

reach included seven measurement locations and two measurement sets (measurement location 6 not visited during measurement set 1): measurement set 1, June 17–18, and measurement 

set 2, September 16–17, 2003. 

Streamflow at measurement locations in each measurement set was compared graphically by using direct and indirect 

methods. A graphical comparison of streamflow values among 

measurement locations allows for an assessment of the likelihood that two streamflow values are discernibly different. The 

difference in the streamflow values between measurement locations indicates streamflow gains or losses. A direct comparison 

of streamflow values (in cubic feet per second) was used for 

steady-state hydrologic conditions (measurement-location pairs 

(A–C) for measurement set 1, and all measurement locations for 

measurement set 2). An indirect comparison of streamflow 

values (the comparison of streamflow values as a percentage of 

streamflow at measurement location 3) was used to account for 

variations in streamflow resulting from Terror Creek Reservoir 

during measurement set 1 and to normalize streamflow between 

measurement sets. In addition to the graphical comparison, a 

comparison of the two measurement sets and previous investigations of the study area was included in the interpretation of 

the streamflow gain-loss characteristics of the Terror Creek 

study reach and includes statistical testing of the overall streamflow losses within the mine-permit area.

The streamflow gain-loss characteristics of the Terror 

Creek study reach for measurement set 1, using the direct comparison of the streamflows in each measurement-location pair, 

indicate that there is no discernible streamflow gain or loss 

between measurement locations 3 and 4. There is a 3.80-ft3

/s 

streamflow gain between measurement locations 3 and 5. 

There is a 0.37-ft3/s streamflow loss between measurement 

locations 3 and 7. The indicated loss between measurement 

locations 3 and 7 is interpreted as the overall streamflow loss 

within the mine-permit area for measurement set 1.

An indirect comparison of the streamflows for each 

measurement location during measurement set 1 also was done 

because of the stairstep increase in streamflow from Terror 

Creek Reservoir. Measurement locations 3 and 4 had no discernible streamflow gain or loss within the precision of the measurements. There was a 55-percent streamflow gain, normalized 

to measurement location 3, between measurement locations 4 
References Cited 23

and 5 and a 62-percent streamflow loss between measurement 

locations 5 and 7.

The streamflow gain-loss characteristics for measurement 

set 2 allowed for direct (cubic feet per second) and indirect 

(percentage difference normalized to measurement location 3) 

methods of comparison of the streamflows for each measurement location due to the steady-state hydrologic condition. 

Measurement locations 3 and 4 show no discernible streamflow 

gain or loss. There was a 0.37-ft3/s (13 percent) streamflow gain 

between measurement locations 4 and 5. There was a 0.74-ft3/s 

(27 percent) streamflow loss between measurement locations 5 

and 6. No discernible streamflow gain or loss was shown 

between measurement locations 6 and 7.

In order to determine the overall streamflow gain or loss 

within the mine-permit area for measurement set 2, the streamflow value from measurement location 3 was paired with the 

streamflow value from measurement location 7, using the direct 

method. A 0.31-ft3

/s streamflow loss was shown between 

measurement locations 3 and 7. The streamflow loss between 

measurement locations 3 and 7 is interpreted as the overall 

streamflow loss within the mine-permit area for measurement 

set 2.

A comparison of the measurement sets indicates that the 

streamflow gain-loss characteristics of the Terror Creek study 

reach are consistent between time periods for the overall minepermit area but differ in magnitude between individual 

measurement locations for the two hydrologic conditions evaluated. A substantial streamflow gain is shown between measurement locations 4 and 5 in both measurement sets, and 

streamflow decreases between measurement locations 5 and 7 

(measurement set 1, measurement location 6 not visited) and 5 

and 6 (measurement set 2). A comparison of the measurement 

sets above and below the mine-permit area (measurement locations 3 and 7) shows a consistent streamflow loss of 0.37 and 

0.31 ft3

/s, representing 5- and 12-percent streamflow losses for 

measurement sets 1 and 2, respectively, normalized to streamflow at measurement location 3. This result indicates that similar streamflow losses occur during reservoir-supplemented and 

during natural base-flow conditions. 

Findings from a previous investigation support a streamflow loss between measurement locations 3 and 7 observed in 

this study. The findings indicate that a 0.59-ft3

/s streamflow 

loss occurs between these measurement locations. 

Statistical testing of the differences in streamflow between 

measurement locations 3 and 7 indicates that there is a discernible streamflow loss. The p-value of 0.0236 for the parametric 

paired t-test indicates that there is a 2.36-percent probability of 

observing a sample mean difference of 0.34 ft3/s if the population mean is zero (that is, if there is no true difference in streamflow between these two locations). This level of significance is 

below the standard 5 percent (p-value 0.05) generally accepted 

as the designation of a statistically significant result. The pvalue of 0.125 for the nonparametric exact Wilcoxon signed 

rank test indicates that there is a 12.5-percent probability of 

observing a sample mean difference this large if the population 

mean is zero. The lack of statistical significance in the nonparametric test is caused by the number of observations available for 

comparison being too few for a definitive assessment. The exact 

level of statistical significance is undetermined, but the incorporation of all the available methods to detect a streamflow loss, 

including graphical interpretation, error analysis, repeatability 

of results, and two methods of testing of statistical significance, 

provides good evidence that there is a loss of about 0.34 ft3

/s 

between measurement locations 3 and 7 for the hydrologic conditions investigated. 

The similarity in streamflow gain-loss between measurement sets indicates that the process controlling streamflow may 

be the same between the two hydrologic conditions evaluated. 

Indicated gains between measurement locations 4 and 5 may be 

related to hyporheic flow from tributaries that were dry during 

the investigation. No other obvious sources of surface water 

were identified during the investigation. The cause for the 

observed streamflow loss between measurement locations 5 and 

6 is unknown but may be related to mapped local faulting, 

100 years of coal mining in the area, and aquifer recharge.

References Cited

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proposed coal-lease tracts in Delta County, Colorado: 

U.S. Geological Survey Water-Resources Investigations 

Report 83–4069, 27 p.

Chaney, T.H., Kuhn, Gerhard, Brooks, Tom, and others, 1987, 

Hydrology of Area 58, Northern Great Plains and Rocky 

Mountain coal provinces, Colorado and Utah: U.S. Geological Survey Water-Resources Investigations/Open-File 

Report 85–479, 103 p.

Colorado Department of Transportation, 2003, Delta County 

public lands digital dataset, data available at Colorado 

Department of Transportation, accessed March 30, 2004, 

http://www.dot.state.co.us/App_DTD_DataAccess/GeoData/index.cfm?fuseaction=GeoDataMain&MenuType=

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and sources in the Miller Creek watershed, Park County, 

Montana, August 2000: U.S. Geological Survey WaterResources Investigations Report 02–4148, 32 p.

Daly, Chris, and Taylor, George, 1998, Colorado average 

monthly or annual precipitation, 1961–1990: Water and 

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24 Using Tracers to Evaluate Streamflow Gain-Loss Characteristics of Terror Creek, in the Vicinity of a Mine-Permit Area, 

Delta County, Colorado, Water Year 2003

Dunrud, R.C., 1976, Some engineering geologic factors 

controlling coal mine subsidence in Utah and Colorado: 

U.S. Geological Survey Professional Paper 969, 39 p.

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map of the Paonia and Gunnison Area, Delta and Gunnison 

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Supplemental Information
26 Distribution and Mass of Nitrate in the Unconfined Aquifer Beneath the Intensively Cultivated Area North of the Rio Grande,

San Luis Valley, Colorado, 1997 through 2001
SUPPLEMENTAL INFORMATION 27

Table 5. Supplemental information for the modified multiple-tracer method, measurement set 1, and multiple-tracer method, 

measurement set 2, Terror Creek, Colo., water year 2003.

[M.S.T., Mountain Standard Time; TC1, time of sample for injectate bromide concentration; TC2, time of sample for downstream bromide concentration; 

TCB, time of sample for background bromide concentration; Q1, rate of flow of the injectate; L/min, liters per minute; min, minutes; --, no data or not applicable]

Streamflow

measurement 

location

Date

Tracer injection and sample times (M.S.T.) Q1

(L/min)

Duration of injection

Pump start Pump stop TC (min) 1 TC2 TCB

Measurement set 1

East and West Fork Terror Creek coincident with measurement-location pair A

1 06/17/03 1107 1213 1212 12111 1206 0.0600 66

2 06/17/03 1107 1213 1212 -- 1203 -- 66

Measurement-location pair A

3 06/17/03 1107 1213 1212 1157 -- 0.0600 66

4 06/17/03 1130 1225 1224 1220 1215 0.0910 55

East and West Fork Terror Creek coincident with measurement-location pair B

1 06/17/03 1403 1507 1506 1455 1450 0.0838 64

2 06/17/03 1403 1507 1506 -- 1515 -- 64

Measurement-location pair B

3 06/17/03 1403 1507 1506 1503 -- 0.0838 64

5 06/17/03 1500 1601 1600 1600 1552 0.0825 61

East and West Fork Terror Creek coincident with measurement-location pair C

1 06/18/03 1100 1158 1157 1152 1147 0.0860 58

2 06/18/03 1100 1158 1157 -- --2 -- 58

Measurement-location pair C

3 06/18/03 1100 1158 1157 1200 -- 0.0860 58

7 06/18/03 1308 1408 1407 1408 1406 0.0840 60

Measurement set 2

1 09/16/03 1718 1818 1817 1812 1806 0.0713 60

2 09/16/03 1718 1818 1817 -- 1830 -- 60

3 09/16/03 1718 1818 1817 1822 -- 0.0713 60

4 09/16/03 1406 1449 1448 1448 1442 0.0731 43

5 09/16/03 1138 1227 1226 1223 1220 0.0808 49

6 09/17/03 1340 1429 1428 1425 1418 0.0625 49

7 09/17/03 1137 1222 1221 1218 1211 0.0738 45

1

Sample destroyed during shipping. 2

CB for this site measured during previous tracer injection.