A Thermal Profile Method to Identify Potential 

Ground-Water Discharge Areas and Preferred 

Salmonid Habitats for Long River Reaches

Scientific Investigations Report 2006–5136

Prepared in cooperation with the 

Bureau of Reclamation, 

Washington State Department of Ecology, and the 

Yakama Nation

U.S. Department of the Interior

U.S. Geological Survey
Cover: Photograph of Clark Well No. 1, located on the north side of the Moxee Valley in North Yakima, 

Washington. The well is located in township 12 north, range 20 east, section 6. The well was drilled 

to a depth of 940 feet into an artesian zone of the Ellensburg Formation, and completed in 1897 at a 

cost of $2,000. The original flow from the well was estimated at about 600 gallons per minute, and 

was used to irrigate 250 acres in 1900 and supplied water to 8 small ranches with an additional 47 

acres of irrigation. (Photograph was taken by E.E. James in 1897, and was printed in 1901 in the U.S. 

Geological Survey Water-Supply and Irrigation Paper 55.)
A Thermal Profile Method to Identify 

Potential Ground-Water Discharge Areas 

and Preferred Salmonid Habitats for 

Long River Reaches

By J.J. Vaccaro, U.S. Geological Survey; and K.J. Maloy, Oregon State University

Prepared in cooperation with the

Bureau of Reclamation,

Washington State Department of Ecology, and the

Yakama Nation

Scientific Investigations Report 2006-5136

U.S. Department of the Interior

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

Dirk A. Kempthorne, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

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Box 25286, Denver Federal Center

Denver, CO 80225

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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.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Vaccaro, J.J., and Maloy, K.J., 2006, A thermal profile method to identify potential ground-water discharge areas and 

preferred salmonid habitats for long river reaches: U.S. Geological Survey Scientific Investigations Report 2006-5136, 

16 p. 
iii

Contents

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

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

Purpose and Scope ................................................................................. 1

Background ....................................................................................... 3

Temperature ....................................................................................... 3

Role in River Ecology ........................................................................ 3

Measuring .................................................................................... 4

Measuring Ground-Water Discharge .................................................................. 4

Basis for Thermal Profiling .............................................................................. 5

Thermal Profile Method ................................................................................. 5

Equipment .......................................................................................... 5

Protocol ............................................................................................. 6

Limiting Factors .................................................................................... 7

Example of Method Application ........................................................................ 8

Background.......................................................................................... 8

Thermal Profile .................................................................................... 9

Summary and Conclusions .............................................................................. 13

References Cited.......................................................................................... 13

Figures

Figure 1. Map showing location of Yakima River Basin, Washington ........................... 2

Figure 2. Photograph of temperature probe, container, and partially 

disassembled container .................................................................. 6

Figure 3. Graph showing example of time-plotted thermal profiles, August 8 and

September 13, 2001, Yakima River Basin, Washington ................................. 9

Figure 4. Graph showing example of distance-plotted thermal profiles, August 8 and

September 13, 2001, Yakima River Basin, Washington ................................. 9

Figure 5. Graph showing thermal profile and depth for the cooling part of the example

reach, August 8, 2001, Yakima River Basin, Washington .............................. 11

Figure 6. Map showing example of thermal profiled reach and salmon redd locations

overlaid on an infrared image, Yakima River Basin, Washington ..................... 12
iv

Conversion Factors, Datums, and Abbreviations and 

Acronyms

Conversion Factors

Multiply By To obtain

centimeter (cm) 0.3937 inch

cubic meter per second (m3/s) 35.31 cubic foot per second

kilometer (km) 0.6214 mile

kilometer (km) 0.5400 mile, nautical

meter (m) 3.281 foot

meter per second (m/s) 3.281 foot per second

square kilometer (km2) 0.3861 square mile

Temperature in degrees Celsius (oC) may be converted to degrees Fahrenheit (oF) as follows:

°F=(1.8×°C)+32.

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

25oC).

Datums 

Vertical coordinate information in referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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

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

Abbreviations and Acronyms

Abbreviations and Acronyms Definition

FLIR Forward-looking infrared radiometer

GPS Global Positioning System

LTC Laptop computer

WAAS Wide Area Augmentation System
Abstract

The thermal regime of riverine systems is a major 

control on aquatic ecosystems. Ground water discharge is an 

important abiotic driver of the aquatic ecosystem because it 

provides preferred thermal structure and habitat for different 

types of fish at different times in their life history. In large 

diverse river basins with an extensive riverine system, 

documenting the thermal regime and ground-water discharge 

is difficult and problematic. A method was developed to 

thermally profile long (5-25 kilometers) river reaches by 

towing in a Lagrangian framework one or two probes that 

measure temperature, depth, and conductivity. One probe 

is towed near the streambed and, if used, a second probe is 

towed near the surface. The probes continuously record data 

at 1-3-second intervals while a Global Positioning System 

logs spatial coordinates. The thermal profile provides valuable 

information about spatial and temporal variations in habitat, 

and, notably, indicates ground-water discharge areas.

This method was developed and tested in the Yakima 

River Basin, Washington, in summer 2001 during low 

flows in an extreme drought year. The temperature profile 

comprehensively documents the longitudinal distribution of 

a river’s temperature regime that cannot be captured by fixed 

station data. The example profile presented exhibits intrareach diversity that reflects the many factors controlling the 

temperature of a parcel of water as it moves downstream. 

Thermal profiles provide a new perspective on riverine system 

temperature regimes that represent part of the aquatic habitat 

template for lotic community patterns.

1U.S. Geological Survey.

2Oregon State University.

Introduction

In many basins in the western United States, ongoing activities include enhancing fisheries, meeting rules 

implemented under the Endangered Species Act for resident 

and anadromous salmonid fish, and obtaining additional 

water for agriculture, population growth, and instream flows. 

The thermal regime of a riverine system and ground-water 

discharge to rivers is an issue for all these activities. The 

Yakima River Basin in eastern Washington, is typical of these 

basins (fig. 1), where the U.S. Geological Survey (USGS) 

is investigating ground-water/surface-water interactions 

and aquatic habitat for salmonids using the thermal regime. 

This report was prepared in cooperation with the Bureau 

of Reclamation, Yakama Nation, and Washington State 

Department of Ecology.

Purpose and Scope

The purposes of this report are to document a method 

to thermally profile long (5-25 km), river reaches and to 

describe the importance of streamflow temperature and 

ground-water discharge, both of which are functionally related 

to a thermal profile in controlling aquatic ecosystems, and in 

particular fish. A thermal profile is a record of longitudinal 

measurements of stream temperature near the reach streambed. 

Measurements were made from a watercraft by towing in a 

Lagrangian framework one or two probes that measure and 

log temperature, depth, and conductivity at 1- to 3-second 

intervals. One probe is always used for measurements at the 

streambed and if a second probe is used, it measures near 

the surface. Spatial coordinates are logged with a Global 

Positioning System (GPS). Measurements can be referenced to 

a time, a position in space, or a distance from beginning of the 

profile.

A Thermal Profile Method to Identify Potential 

Ground-Water Discharge Areas and Preferred 

Salmonid Habitats for Long River Reaches

By J.J. Vaccaro1 and K.J. Maloy2
82 

22

22

97 

97

97

12

12

82

82

240

24

410

240

90 

90 

90 

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241

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82 12 

KITTITAS COUNTY 

YAKIMA COUNTY 

COUNTY

BENTON COUNTY

KLICKITAT

COUNTY

YAKIMA

EXPLANATION

BOUNDARY OF YAKIMA

 RIVER BASIN

Canal

Roza

Sunnyside Canal

Main Canal

Extension

Kennewick

Main Canal

Marion Drain

North

Branch

Canal

Kittitas Main Canal

Bumping

Lake N Fk 

S Fk

S Fk 

N Fk 

S Fk 

N Fk 

N Fk 

Cle Elum River

Swauk Creek

Caribou Cr

Coleman Cr

Naneum

Cr

Cooke Cr

Crow Creek

Bumping River

American River

Rattlesnake Cr

Little Rattlesnake Cr

Nile Creek

Manastash

Badger Creek

Lmuma Cr

Ahtanum Creek

Oak Creek

Tieton River

Wide Hollow Cr

Wenas Creek

Selah Creek

North Fork

Dry Creek

Simcoe Creek

Agency Creek

Creek

Toppenish

Corral Cr

RIVE

Sp

R

ring Cr

Logy Creek

Satus

Creek

Mule Dry

Creek

Cle

Elum

Lake

Rimrock

Lake

Kachess Lake

Keechelus Lake

Lake

Wallula

Priest

Rapids

Lake

Teanaway River Reecer Cr

Wilson Creek

Park Cr

Taneum Creek

Umtanum Creek

Little Naches River

Cr

Cowiche Creek

Cowiche Creek

River

Naches

Snipes Cr

Sulphur Cr Wasteway

Cherry

Cr

S Fk

N Fk

YAKIMA

YAKIMA

RIVER

Cle Elum

Parker

Wapato

Ellensburg

Umtanum

Kittitas

Thrall

Toppenish

Moxee City Union Gap

Yakima

Selah

Naches

Sunnyside Richland

Kiona

Kennewick Prosser

Grandview

Mabton

Satus

Zillah

Granger

Roza

Easton

Teanaway

Tieton Rimrock COLUMBIA

RIVER

Snoqualmie

Pass

Van Epps 

Pass

Esmeralda

Peaks

K I T T I T A S

V A L L E Y

M A N A S T A S H

KACHESS RIDGE

R I D G E

UNION GAP

CLEMAN 

MOUNTAIN 

TEANAWAY

NORTH RIDGE

U M T A N U M

R I D G E

Deception

Pass

Y A K I M A 

 V A L L E Y 

AHTANUM RIDGE

COWICHE MTN

AMERICAN RIDGE

CLE ELUM

RIDGE

RIDGE

TOPPENISH RIDGE

R A T T L E S N A K E H I L L S

Y A K I M A R I D G E

H O R S E

H E A V E N

H I L L S

C

A

S C A

D E R

A

N

G

E

W E N AT C H E E

M O U N TA I N S

Gilbert

Peak

121°

47°

47°

30'

46°

121°30' 120°30' 120° 119°30'

46°

30'

0 5 10 20 30 40 MILES 

0 5 10 20 30 40 50 60 KILOMETERS 

Yakima

River

Basin

WASHINGTON

waA4WT1_03_fig01

Figure 1. Location of Yakima River Basin, Washington.

 Thermal Profile Method to Identify Potential Ground-Water Discharge Areas
The report first presents a background on the ecological 

importance of temperature and ground-water discharge in 

riverine systems and the methods typically used to measure 

these two environmental variables. The newly developed 

method to thermally profile reaches is then described. Last, 

an example of a thermal profile is presented and discussed to 

provide readers with an overview of a profile, including its 

information content, how a profile may be interpreted, and 

the reproducibility of the results using this method. To the 

extent possible, references and discussions are related back 

to the importance of temperature as a resource for fish, and in 

particular salmonids.

Background 

Processes that control the heat content of a parcel of 

surface water as it travels from headwaters to a river mouth are 

well documented. The processes include radiation, advection, 

conduction, evaporation, and convection (Anderson, 1954; 

Harbeck and others, 1959; Raphael, 1962; Messinger, 1963; 

Koberg, 1964; Edinger and Geyer, 1968; Edinger and others, 

1968; Stevens and others, 1975; Jobson, 1977; Sinokrot 

and Stefan, 1993). Ground-water discharge represents a 

significant form of thermal advection in many river systems. 

Ground-water discharge (including water discharged 

from the hyporheic zone) (1) provides preferred thermal 

structure and habitat for different types of fishes at different 

life-history stages (Power and others, 1999), and (2) is an 

important abiotic variable of the aquatic ecosystem basic to 

the ecological function of riverine systems (Hynes, 1983; 

Stanford and Ward, 1993; Stanford and Simons, 1992; Brunke 

and Gonser, 1997). The ground- and surface-water interface 

is a unique ecotone and is similar to other ecotones known as 

some of the most productive habitats (Wetzel, 1990). Much 

of the year, streamflow is mostly baseflow—a product of 

ground-water discharge; therefore, water quality also is largely 

influenced by ground water. An overview of the current 

understanding of the interaction between ground water and 

surface water is presented in Winter and others (1998).

Temperature

Role in River Ecology

Temperature is one of the most important abiotic 

variables of the riverine system because it influences dissolved 

oxygen concentrations, photosynthesis, the metabolic 

rates of aquatic organisms, timing of life-history stages 

of many species, and the decomposition rates of organic 

material, which in turn, affect the spatial arrangement in 

the riverine system of many ecosystem components such 

as algal, invertebrate, and fish communities. Therefore, the 

bioenergetics of riverine ecosystems ultimately is determined 

by the thermal regime. The presence of diversity and structure 

in the temperature regime leads to increased biodiversity 

(Magnuson and others, 1979), including biodiversity of fish 

(Brett, 1956; Beschta and others, 1987), insects (Vannote and 

Sweeney, 1980), and macrophytes (Haslam, 1978; White and 

others, 1987). Diversity represents long temporal variations 

from expected heating trends (overall thermal profile shape—

longitudinal gradient) and structure represents the short 

spatial-temporal variations (the spikes in the thermal profile). 

Diversity and structure display unique spatial patterns that are 

functionally related to ground-water discharge. In turn, the 

variations in the thermal diversity and structure increase with 

basin size and attendant variations in climatic regimes and 

landscape characteristics—an upland 5 km2 headwater basin 

has much less variation than a large 12,000 km2 basin.

Diversity in a basin’s thermal regime represents the 

riverine system’s temperature template or longitudinal 

gradient, which is consistent with an environmental gradient. 

Temperature essentially defines a physical habitat template 

(Southwood, 1977; Poff and Ward, 1990) that explicitly 

includes temporal variability and provides for the overall 

biological community template—including the different life 

stages and life history patterns of salmonids. The template 

leads to a logical progression of the longitudinal gradient 

of fish assemblages. Small scale temperature variations 

(structure) represent cooling patches (possible refugia) or 

heating (avoidance areas) overlaid on the basin-wide template, 

and reflect the localized lateral and vertical connections 

measured in both natural and modified river systems (Hynes, 

1983; Stanford and Ward, 1993) that salmonids use or avoid 

(Power and others, 1999; Rieman and Dunham, 2000). These 

ground-water discharge zones provide refugia, the preferred 

salmonid habitat during summer when river temperatures are 

warm and during winter in colder regions when rivers may 

freeze. Salmonids seek out and take advantage of this habitat. 

The longitudinal gradient, overlaid with the distribution of 

patches, composes a continuum from the headwaters to the 

mouth, along which habitat and species are arranged (Vannote 

and others, 1980).

The thermal regime at salmon redds (gravel spawning 

nests) also is important for incubation (Combs and Burrows, 

1957; Combs, 1965; Alderdice and Velsen, 1978). The thermal 

regime and ground-water discharge effects egg survival for 

salmonid species (Sowden and Power, 1985; Woessner and 

Brick, 1992: Curry and others, 1995) including wild bull, 

rainbow, steelhead, and kokanne trout in the Yakima River 

Basin. Ground-water discharge areas also appear to be the 

preferred winter habitat for trout (Brown and Mackay, 1995), 

and temperature habitat limitations may affect behavior 

(Gregory and Griffith, 1996). Power and others (1999) 

identified winter as critical time (1) when overwintering fish 

mortalities may be high and (2) in the establishment of basic 

stock densities based on temperature habitat availability. 

Introduction 
Measuring

In large diverse basins with an extensive riverine system, 

documenting the thermal regime is difficult. Methods typically 

used to document the regime are continuous measurements 

at fixed stations, synoptic manual measurements, and multispectral imaging. Fixed station and synoptic data measure 

only heat content of a particular water parcel, so information 

on the spatial structure of the thermal regime, which describes 

a habitat template, must be interpolated. However, accurate 

interpolation requires additional measurements (longitudinal, 

transverse, and advectional) to quantify thermal variation in 

a stream. Using multi-spectral techniques such as forwardlooking infrared radiometer (FLIR) can yield the thermal 

regime of a riverine system, but only for one period, and 

these methods are costly and synoptic. How the regime 

varies temporally is unknown. Moreover, FLIR measures 

surface radiance and does not document vertical structure. 

As a result, excluding features such as springbrooks, groundwater discharge cannot be precisely located with FLIR until 

manifested at the water surface.

Measuring Ground-Water Discharge

Several methods are used for quantifying groundwater discharge in riverine systems. The most common 

method is to make a series of discharge measurements. Such 

measurements provide useful information on net gain or loss 

in a reach defined by the bounding measuring sites for some 

particular time. When used in conjunction with dye-dilution 

gaging measurements (Kilpatrick and Cobb, 1985), discharge 

measurements also can provide information on ground-water 

discharge and recharge (sum equals net gain or loss) over a 

reach (Harvey and Wagner, 2000). In large systems, many 

discharge measurements, which can be costly, are needed 

to identify ground-water discharge locations, especially 

in extensively modified systems or when investigating the 

temporal variability in the discharge.

Seepage meters were used in lake studies to measure 

ground-water discharge (Lee, 1977; Lee and Cherry, 1978). 

Seepage meters are best suited for sandy lakeshores, and 

installation in rivers is problematic (Lee and Hynes, 1978; 

Harvey and Wagner, 2000). Using mini-piezometers was 

described early in the literature and has been oriented to 

studies of salmonid habitat (Terhune, 1958; Gangmark and 

Bakkala, 1958; Coble, 1961; Vaux, 1962). This method 

was modified for the reach survey using manometer-style 

measurements (Fokkens and Weijenberg, 1968; Lee and 

Cherry, 1978; Winters and others, 1988), which use minipiezometers to measure the pressure head in shallow ground 

water with a concurrent measurement of the river head; these 

are done conjunctively using a portable manometer. Detailed 

information is provided by such surveys. For example, 

Simonds and others (2004) determined that, for some gaining 

reaches in the Dungeness River, Washington, identified from 

discharge measurements at bounding sites, the river was losing 

water over most of the reach and the ground-water discharge 

was local. Jackman and others (1997) measured large 

variations in discharge across the width of a small stream. 

Data presented in White and others (1987) also suggested 

variations in discharge across a 7-m wide river.

Monitoring of streamflow and vertical distribution of 

temperature below the streambed (Lapham, 1989; Silliman 

and Booth, 1993; Constanz, 1998; Constanz and others, 

2001) yielded data for estimating ground-water discharge. 

Such monitoring with concurrent modeling provided detailed 

ground- and surface-water interactions at the diurnal to 

seasonal scale. The method is most easily applied to the 

ephemeral and lower order parts of the stream network and is 

difficult to use in larger stream reaches with high streamflow, 

especially with limited boat access. As with fixed station data, 

the usefulness of results are highly dependent on locations 

selected for monitoring.

Introduced stream tracers can be used to estimate 

discharge areas (Bencala and Walters, 1983; Jackman and 

others, 1984; Kilpatrick and Cobb, 1985; Triska and others, 

1989). Tracers can include environmental tracers such as 

temperature (White and others, 1987), and tracer studies 

may or may not include modeling. Tracers are best applied 

to short reaches (less than the length scale of the longitudinal 

dispersion coefficient) and mainly for hyporheic flow analysis 

(Harvey and Wagner, 2000). 

Continuous measurements of water levels and 

temperature in ground water in shallow piezometers near and 

in the river also are used to estimate ground-water discharge 

(or river losses) (Harvey and Wagner, 2000). The latter two 

methods become intractable over long reaches or for an entire 

riverine system.

Electrical conductivity profiling also can be used to locate 

ground-water discharge areas. Lee and others (1997) used two 

electrodes encased in a tubular shell with a brass nose cone 

towed from the back of a motorized watercraft. Electrodes 

were connected to a laptop computer (LTC) by a cable. The 

electrodes’ output, which was converted to a value of electrical 

conductivity, was used as a measure of the difference between 

river water and ground water. Location of the shell was 

determined by a continously logging GPS. For many riverine 

systems, using a towed measurement device connected to an 

LTC would not be applicable due to channel configuration, 

water depths, rapids, various bottom materials, log-jams, 

diversion dams, riprap, and partially submerged or buried 

tree limbs. However, the basic concept of profiling provides a 

technique that can be modified for most riverine systems.

 Thermal Profile Method to Identify Potential Ground-Water Discharge Areas
Basis for Thermal Profiling

Applying these measuring methods to most large riverine 

systems, such as the Yakima River Basin, is challenging 

because many systems were extensively modified with 

diversions and return canals, and there are usually thousands 

of kilometers of stream network. In turn, many parts of such a 

network may provide habitat for several life-history stages of 

anadromous and resident salmonids and other fish. To partially 

address this issue, a method was developed to thermally 

profile long (about 5-25 km) river reaches. The profile is based 

on measuring water temperature at 1- to 3-second intervals 

at or near the streambed, and in some cases, concurrently 

measuring (profiling) the water temperature near the surface. 

Measurements are taken in a Lagrangian framework, which 

entails drifting at the ambient streamflow velocity. This 

method produces a longitudinal, Lagrangian profile of stream 

temperature near the streambed.

Electrical conductivity profiling of the cobble-bottom 

streambed of the Hanford Reach on the Columbia River, 

Washington, by Lee and others (1997) identified ground-water 

discharge areas. This method was similar to that of Lee and 

Dal Bianco (1994), who applied it to a small, gravelly bottom 

river. The profiling method was based on techniques to locate 

ground-water discharge areas in lakes (Lee, 1985; improved 

on by Harvey and others, 1997). Together, these studies 

demonstrated that profiling is an effective method for locating 

ground-water discharge areas, especially when combined with 

piezometer measurements.

The conceptual basis for development of the method was 

to determine if a robust, thermal-profiling method could be 

developed, and if so, to document the thermal profile, with its 

attendant diversity and structure, of selected reaches. Profiles 

should yield information related to salmonid habitat because 

the complexity in salmonid life histories is functionally related 

to diversity in thermal habitat (Rieman and Dunham, 2000). 

If a thermal profile could be documented, it then needed to 

be determined if areas of ground-water discharge could be 

identified from the thermal profile.

Profiling in a Lagrangian framework (moving 

downstream at the same velocity as the river) allows for 

tracking temperature of a parcel of water as it moves 

downstream in a reach. Deviations from the diurnal heating of 

a parcel should principally be due to ground-water discharge, 

surface-water inflows, and depending on setting, streamflow 

losses or riparian-vegetation shading. In particular, deviations 

(anomalies) from an overall heating response may represent 

ground-water discharge areas. Using temperature anomalies 

to identify ground-water discharge areas is not a new concept 

(e.g., Cartwright, 1970); discharge areas will have a larger 

vertical thermal gradient than recharge areas. Areas with sharp 

thermal gradients are candidates for more intensive studies.

Thermal Profile Method

Equipment

A self-contained temperature measuring and recording 

probe, encased in stainless steel and designed for groundwater monitoring, was selected as the best option for thermal 

profiling because no cables are needed to be towed, therefore, 

preventing damage to or loss of sensor/cable. The probe 

(CTD-DiverTM, Van Essen Instruments; now manufactured by 

Solinst® and called a Levelogger®) has the added benefits of 

also measuring conductivity and depth with a variable sample 

rate. The probe (fig. 2) is 2.2-cm diameter, 26.0-cm long, and 

weighs 160 grams; an optical read-out unit connected to an 

LTC is used to program and read out the datalogger. 

Probe accuracy was rated as 0.1°C for temperature, 

0.1 percent of the full range of depth (in cm), and 0.05 μS/cm 

for conductivity. The reported accuracy of the probe’s internal 

clock is better than 1 second per day at 20°C. Temperature 

measurement reliability was checked using a controlled 

temperature bath (accuracy of 0.05°C) over a range 6 to 30°C. 

Results confirmed an accuracy of 0.1°C over the full range 

and temperature change over 1-second intervals was captured 

by the probe. A probe that only measures temperature or 

temperature and depth also can be used in this method. 

A light, rugged container consisting of white 5.1 cm 

plastic pipe with a rounded cap on one end, and a total length 

of about 38 cm was designed for the probe (fig. 2). Water 

flowed through 1.5-cm holes drilled throughout the container 

body. A stainless steel eye bolt on the end of the cap with two 

bolts provides a connection for a 15-m tow rope. A 15.25-cm 

piece of 2.5-cm diameter flexible wire conduit is centered 

in the cap, and a bolt hole is drilled through (perpendicular 

to) the cap and conduit; a bolt allows for probe attachment. 

A greased bolt is then inserted and the surrounding area is 

filled with silicon caulk; greasing the bolt allows for easy bolt 

removal after the caulk hardens. Caulk helps prevent the bolts 

on the eyebolt from loosening, holds the conduit in place, and 

adds weight to the front of the container for towing. About 

9 cm of the probe extends into the conduit and the probe 

extends about 2 cm inside the container end. A neoprene 

bicycle handle is inserted over the probe extending beyond the 

conduit (but not covering the sensor) and is held in place with 

2.5-cm wide, 10-mil, all weather pipe-wrap tape. The conduit 

and neoprene prevent the probe from contacting the sides of 

the container, but allow some movement to absorb shocks 

when contacting various bottom structures such as boulders. 

Neoprene also provides some buoyancy needed to allow the 

container to move around or over a stream’s bottom structure 

such as large boulders. After many profiles, the container 

withstood constant contact with the streambed, boulders, 

woody debris, and other objects.

Thermal Profile Method 
Protocol

One or two probes can be used in this method. Two 

probes initially were used during method development; 

currently (2006) one probe is deployed for a profile. If using 

two probes, one is for streambed measurements and the 

other is for shallow measurements. If more than one reach 

is profiled using two probes, for consistency in inter-reach 

comparison, identify one probe for shallow measurements and 

the other probe for streambed measurements.

While developing and testing this method, the 

probe’s sample rate was set at 3 seconds. For conductivity 

measurements, Harvey and others (1997) used a sample 

rate of 0.1 sec and Lee and others (1997) used a sample 

rate of 0.05 sec. The 3-second rate was used based on 

expected streamflow velocity and initial reach length 

because measuring temperature every 0.2-6 m would capture 

differences representative of large discharge quantities without 

compromising probe storage capacity and allow for sensor 

equilibration. However, based on datalogger capacity and 

profiled reach length with its attendant average velocity, the 

sample rate (ranging from 1 to 3 seconds) was adjusted for 

each reach. Expected average velocity for a reach should be 

analyzed in conjunction with the reach length to estimate a 

sample rate based on storage capacity of the particular probe 

and the GPS used. Additionally, if possible, the probe and 

GPS should use the same sample rate to simplify merging the 

resulting two data series. A slower sampling rate can be used 

depending on the specific purpose for measuring a profile. For 

example, other investigators used this method along a reach 

with measured large quantities of ground-water discharge and 

set the sample rate at 6 seconds to identify the area where 

ground-water discharge begins (G. Gregory, written. commun., 

Washington State Department of Ecology, 2006).

Probe

Top

Bolt

Container

bottom

Assembled

container

Attached tow line

Wrapped

neoprene

handle

Flexable

conduit

Probe top to

show hole

Attached for bolt

bolt

waA4WT1_03_fig02

Figure 2. Temperature probe, container, and partially disassembled container.

 Thermal Profile Method to Identify Potential Ground-Water Discharge Areas
Two methods were used to determine the location of 

the watercraft towing the CTD-DiverTM. First, a Garmin 76 

GPS was connected to a LTC using Garmin’s MapSourceTM 

software. MapSourceTM enables streaming of GPS data to a 

stored route at a 1-second sample rate. Each GPS data point 

on the route is time stamped, and latitude, longitude, altitude, 

and for each leg between readings, the length, speed, and 

course are recorded. For this method, the LTC was placed in 

a waterproof container and the GPS was placed in a smaller 

container bolted to the top of the LTC container and sealed 

with caulk. An opening between the two containers allowed 

for cable connection between the GPS and LTC. The LTC 

operated from a small gel-cell battery through an inverter that 

makes a warning sound when the battery is low. Two back-up 

batteries should be carried in waterproof bags.

Second, a Trimble® GeoXMTM, operating with 

TerraSyncTMand Geoexplorer CETM software, was used. This 

method does not require an LTC in the watercraft, and the 

GeoXMTM collects GPS coordinates at a user-defined time 

interval and accuracy. Both GPS units are WAAS (Wide Area 

Augmentation System) enabled and when receiving the WAAS 

signal, the horizontal accuracy generally is less than 3 m (15 m 

without WAAS). The Garmin® set-up from the first method 

also was used to synchronize the clock in the probe to GPS 

time.

To start a profile, the LTC’s time is set to GPS time using 

the Garmin® and its software. The probe’s internal clock is 

then set to the LTC’s time, closely synchronizing it to GPS 

time. Start times and sample rate of the probe or probes are 

then set.

The probe or probes are then placed in the water 

for at least 5 minutes to equilibrate to the ambient water 

temperature. Equilibration is needed because the combined 

mass of the probe and container affects the measured 

temperature when a large temperature differential exists 

between the probe/container and streamflow. For example, 

on a warm day, the probe and the container may obtain an 

ambient temperature of 35°C during transport to a site and 

streamflow temperature may be 15°C. Starting a profile with 

such a differential would result in a sensor slowly equilibrating 

to streamflow temperature. After equilibrating to near 

ambient streamflow temperature, the semiconductor sensor is 

unaffected by the probe and container temperature.

Next, either the Garmin® GPS was connected to the LTC 

and a route was started with data logging or the GeoXMTM 

was started for data logging a line feature. A profile was then 

started with the shallow probe (if one is used) just under the 

water surface and the deep probe hand held with a towline. 

The deep probe is hand held for safety reasons. For example, if 

an attached tow line was snagged in fast current, the watercraft 

could become submerged or capsize. Although not done for 

this study, a small buoy can be attached to the towline. The 

buoy would allow towline recovery if it is lost. Profiling is as 

continuous as possible to avoid temporal discontinuities due to 

the water-temperature increases during the time the profiling is 

suspended. Profiles are best completed at lower flows, staying 

near the thalweg.

Last, temperature dataloggers were deployed at the 

head and tail of the profiled reach. Temperature data from 

these loggers provided additional information on the diurnal 

temperature change in water entering and leaving the reach. 

The difference between upstream temperature and thermal 

profile also provided information on variations from the 

expected warming of a water parcel. These differences relate 

to the change in the heating rate.

The type of watercraft used usually depends on physical 

characteristics of a particular reach and streamflow volume. 

Profiling was completed over a wide range of flows, about 

1 to 110 m3/s. During the method’s initial development, a 

two-man inflatable raft with a rowing platform was used. To 

obtain greater mobility and control, a two-person, self-bailing 

inflatable kayak was used instead of the raft and was a good 

work platform. A motorized watercraft was used for one reach, 

but because it did not provide as much control as a kayak for 

measuring in a Lagrangian framework, it was determined 

that motorized watercraft is best suited for non-braided 

reaches with streamflow velocities less than about 0.2 m/s. 

Other investigators using this method have used a single-seat, 

inflatable pontoon watercraft (G. Gregory, Washington State 

Department of Ecology, written. commun., 2006), which also 

should be a good working platform.

Time required to profile a reach depends on reach length, 

average velocity, and potential impediments such as diversion 

dams or log jams. Profiling a reach of about a 5 km starts 

at about 10:00-11:00 a.m., and for longer reaches profiling 

generally starts as early as 8:30 a.m. to ensure that diurnal 

heating is strongly initiated. Ideally, reaches are profiled 

on cloudless days. Shorter reaches with lower streamflow 

volumes can be profiled by wading. A handheld GPS with data 

logging capabilities is the best instrument to use for waded 

reaches.

Limiting Factors

Profiling in a Lagrangian framework at velocities as 

much as 2.0 m/s results in the sensor moving rapidly over the 

streambed. In turn, low volumes of ground-water discharge 

results in a high volume of stream water contacting the sensor 

compared to ground water. Therefore, a high-resolution survey 

of temperature variations due to ground-water discharge at 

the streambed is not documented using this method. Testing 

the potential to conduct high-resolution surveys indicated the 

method would work, but the maximum drift velocity should 

be less than about 0.20-0.25 m/s. This conclusion however, 

is based on conditions during the profiling while developing 

and testing the thermal-profiling method. For neutral or losing 

parts of reaches, the thermal profile resolution generally is 

good and is a function of combined effects of the sampling 

interval and streamflow velocity. 

Thermal Profile Method 
Another limiting factor is that a particular volume of 

water measured may not be representative of streambed water 

in ground-water discharge areas due to mixing. Mixing can 

mask the ground-water signature and is affected by channel 

morphology and streamflow volume and velocity. Probe 

location relative to the streambed also varies. Problems with 

the actual location of measurements arise because the tow-line 

length can change (0.5-3 m) to keep the probe as close to the 

raft as possible for accurate GPS locations while attempting 

to stay at the streambed. Length also is changed when moving 

through rapids, areas of woody debris, and riprap or to 

avoid submerged objects that can snag the streambed probe. 

These tasks are difficult in fast-moving current and rapidly 

changing bottom conditions. Therefore, the accuracy of the 

measurement location is reduced, but the position is accurate 

when referenced to the nearby logged positions. Of the tens 

of thousands of measurements made during the method 

testing and use, relatively few were upstream of the previous 

recorded position and few were on the stream bank. More 

challenging is the loss of GPS reception, in which case, the 

latitude and longitude are linearly interpolated between GPS 

values that bracket that period and are then assigned to the 

CTD data. This method produces a straight line track, which 

may not represent that part of a reach. However, Geographic 

Information System (GIS) can be used to fit the track to the 

channel center to improve accuracy of the profile location.

The nature of ground-water discharge also can confound 

profiling results because discharge can occur as low-volume 

diffuse to high-volume spring, and older, and perhaps colder 

ground water near the thalweg compared to younger, perhaps 

warmer, ground water near channel edges (Modica and others, 

1997). 

A thermal profile documents a linear track of temperature 

and does not capture any three-dimensional aspects of the 

thermal regime in a reach. However, areas of interest are 

readily identified. These areas can be investigated in more 

detail using discharge measurements in conjunction with minipiezometer measurements.

Example of Method Application

Background

Initial profiling in the Yakima River Basin was done 

July through September 2001, an extreme drought year, when 

heat flux was large and the difference between temperature of 

ground water and stream water should be greatest, especially 

for downstream, low-gradient reaches of this large riverine 

system. Drought led to lower than average streamflows 

and greatly decreased (in some cases eliminated due to 

demand) surface-water agricultural return flows; nonetheless, 

measured low flows were relatively large (between about 8.6 

to 9.2 m3/s in the example reach) compared to low flows in 

many river systems. Methods were checked and a protocol, 

described above, was developed during the initial profiling. 

Other profiles have been completed for reaches based on the 

methods and protocols described in this report. For the other 

profiles, streamflow temperatures ranged from 2 to 24°C and 

velocities ranged from nearly 0 to as much as 1.8 m/s.

Profiling a reach was timed to coincide with the lowest 

summer flows for a reach based on operation of reservoirs in 

the basin, and, when possible to coincide with the building 

of redds by anadromous spring Chinook salmon. Summer 

also is important for other life-history stages of salmonids, 

and temperature is identified as a limiting factor in some 

reaches (Systems Operations Advisory Committee, 1999). 

Physiological functions of salmonids are impaired when 

temperatures are greater than their preferred range (Beschta 

and others, 1987).

Two contiguous reaches profiled in August were 

re-profiled in September to (1) verify that results from 

the method are reproducible; (2) determine the types of 

differences that may occur under two different heat fluxes; 

and (3) re-examine a long stretch of the reach with potential 

ground-water discharge noted during the August profiling. 

Results for one reach profiled on August 8 and September 13, 

2001, are presented as an example of the profiling method 

to highlight information contained in the profile data related 

to diversity, structure, and reproducibility of measurements, 

and to show how profiles may be analyzed, interpreted, and 

presented. 

For August and September, maximum and minimum 

air temperatures were similar near the upstream part of the 

reach and maximum and minimum air temperatures were 

lower during September at the downstream part of the reach. 

Maximum air temperatures were about 34°C at 16:45 in 

August and 14:15 in September. Cooler reservoir water 

released in September, combined with cooler nighttime 

temperatures, resulted in slightly cooler water entering 

the reach compared to August. In August and September, 

the streamflow temperatures entering the reach varied by 

only 0.36 and 0.32°C, respectively, during profiling; these 

small variations are due to the large volume of reservoir 

releases to meet diversions just upstream of the example 

reach. The profiled reach is just below two large diversions, 

with streamflows about 66 m3/s for August and 51 m3/s for 

September.

The example reach was nearly 23 km with an average 

depth of about 90 cm; the reach has a gradient lower than 

headwater reaches, a highly braided channel, and a reasonably 

intact floodplain. Bed sediment in this reach is used by or 

otherwise suitable for anadromous salmonid (autumn chinook 

stock and coho) spawning and by several salmonid for prespawning holding, rearing, and emigration. 

 Thermal Profile Method to Identify Potential Ground-Water Discharge Areas
Thermal Profile

Reproducing measurments and identifying ground-water 

discharge areas are illustrated using distinctive cooling at 

about 14:40 on August 8 followed by an overall cooling to the 

end of the profiled reach (6.4 km section) (figs. 3 and 4). A 

12-min portage between about 14:52 and 15:04 masks the true 

extent of cooling due to streamflow heating during that period. 

These smooth line segments in the time-plotted data (note the 

large segment at about hour 12, fig. 3) clearly identify the time 

when profiling was stopped for downloading data from the 

probe. Similar line segments would be seen if profiling was 

stopped for other reasons such as a portage around a log jam 

or areas with dangerous river conditions. 

Figure 3. Example of time-plotted thermal profiles, August 8 and September 13, 2001, Yakima River Basin, Washington.

Figure 4. Example of distance-plotted thermal profiles, August 8 and September 13, 2001, Yakima River Basin, Washington.

17

18

19

20

21

22

23

24

1000 1100 1200 1300 1400 1500 1600 1700 1800

TIME, IN HOUR AND MINUTE

TEMPERATURE, IN DEGREES CELSIUS

August 8

September 13

17

18

19

20

21

22

23

24

0 5 10 15 20 25

DISTANCE, IN KILOMETERS

TEMPERATURE, IN DEGREES CELSIUS

August 8

September 13

Example of Method Application 
A trend through the smoother, earlier part of the August 

data indicates an expected ending temperature of 2°C higher 

than the measured value of 22.7°C. For the September profile, 

ending temperature was about 21.4°C, and a trend line also 

indicated an expected ending value of about 2°C higher. 

Most co-temporal differences in water temperature between 

the two profiles were about 2°C (figs. 3-4). The cooling start 

times for the two profiles (fig. 3) indicated that cooling is 

opposite of the diurnal cycle because cooling started at about 

the same location at different times for the two profiles. Data 

from a fixed-station temperature site downstream of the reach 

indicated maximum water temperatures at about hour 17:45 

in August and 16:45 in September—lagging air temperature 

by about 2 hours and the start of the cooling by about 2-3 

hours. For distance-plotted thermal profile data (fig. 4) cooling 

starts at about the same location, and GPS data puts the initial 

cooling of the two profiles within about 30 m of each other. 

Note that distance-plotted data (in contrast to the GPS data) do 

not exactly represent location due to differences in the route 

and drift velocity. Under two different heat fluxes, repeated 

profiles indicate a consistent cooling over this 6.4 km section, 

showing the reproducibility of measurements and the ability to 

locate ground-water discharge areas.

The overall, large-scale changes in temperature along 

the reach depicted in the profile, such as cooling, are referred 

to as diversity. Prior to measuring a thermal profile, the 

simple conceptual model of a profile would be an analog 

for a temperature trace during the diurnal heating measured 

at a fixed site on a clear and hot summer day. That is, the 

diurnal heating of the streamflow would be nearly linear with 

some variations if ground-water discharge occurred or other 

inflows (warmer or colder) existed. Therefore, diversity in a 

sample profile is dramatically different from measurements at 

bounding fixed sites.

To estimate minimum ground-water load (temperature 

and discharge), it can be assumed that streamflow reached 

equilibrium temperature (Edinger and Geyer, 1968; Edinger 

and others, 1968; Sinokrot and Stefan, 1993) at the start of 

cooling. Therefore, the start and end temperatures for this 

part of the reach and discharge that entered the reach at the 

beginning of the August and September profiles can be used 

for a mass-balance calculation using the following equation

Q T in × × in + = Q T gw gw Q T out o × ut , (1)

where

Qin is inflow to the reach at start of the profile,

Tin is temperature of inflow to the cooling part of the 

reach,

Qgw is ground-water discharge over the cooling system,

Tgw is temperature of ground-water discharge,

 Qout is outflow from the reach at end of the profile, and is 

equal to Q Q in + gw, and

Tout is temperature of streamflow at end of profile.

Measured temperatures of a ground-water spring in a 

nearby reach and of ground water in shallow piezometers at 

the end of the reach, indicate that ground-water temperatures 

are about 15-17°C. Using these ground-water temperatures 

and estimating ground-water discharge based on equation 1 

(only unknown is Qgw ) gives ground-water discharge values 

ranging from about 0.55-0.82 m3/s (about 6-9 percent of 

the streamflow) for the two profiles. These ground-water 

discharge estimates would be conservative (the minimum) 

because the underlying assumption is based on the net heat 

loss equal to net heat gain; that is, after a parcel of water enters 

the cooling stretch, temperature is considered a conservative 

quantity with no energy gains or losses due to radiation, 

conduction, evaporation, or convection. Improved groundwater discharge estimates would be necessary to account for 

potential heating of streamflow. 

A more detailed view of the 6.4-km cooling reach 

(fig. 5) for the August 8 data indicates not only diversity but 

also structure with complex interactions of different waters. 

Streambed morphology (pool-riffle complexity) displayed 

by depth data is poorly correlated to this cooling (correlation 

coefficient of 0.2 to detrended temperature data), but indicates 

that potential habitat for different salmonid life-stages may 

be available, although at temperatures that are not preferred 

(Brett, 1956, Burrows, 1963; Jobling, 1981; Beschta and 

others 1987; Berman and Quinn, 1991; Eaton and others, 

1995). Measured water volume is mostly river water, and 

therefore, water temperature measurements using a fixed 

probe at the streambed would show lower temperatures than 

the profile for much of this part of the reach due to groundwater discharge. The structure contained in a profile represents 

patches of cooling (possible refugia) or heating (avoidance 

areas). The cool structures may represent refugia, and this part 

of the reach may represent an area of preferred thermal habitat 

for rearing salmonids, especially because most preferred 

side-channel habitat was dewatered during the 2001 drought. 

10 Thermal Profile Method to Identify Potential Ground-Water Discharge Areas
During low-flows, these small cool structures (environments) 

may provide important habitat for summer thermal refugia 

holding or rearing and winter refugia for rearing (Reeves 

and others, 1991; Keller and others, 1996; Power and others, 

1999); the importance of ground-water refugia for salmonids 

has long been recognized (Benson, 1953).

Much of the structure contained in the two profiles for the 

example reach is spatially coherent based on GPS data, further 

indicating the reproducibility of this method. The structure in 

the profiles also provides additional information about effects 

and mixing of warm and cold inflows under two different 

temperature regimes. For example, the spiky temperature 

increases in the September data are displayed by the August 

data, but because of the higher temperatures in August, 

they are attenuated (fig. 4). Conversely, the major cooling 

in August at about kilometer 12.4 is also represented in the 

September data, but the cooler streamflow attenuates this cool 

structure in September (fig. 4).

Depth and conductivity profiles also provide valuable 

information. Depth profiles (fig. 5) document the longitudinal 

arrangement of the pool-riffle-run mosaic over long distances 

at the streamflow volume during a profile. Obtaining such 

information is difficult and expensive when combining 

several long reaches (about 100 km). Typical methods such 

as a bathymetric survey using scientific depth sounders and 

real-time kinematic GPS systems are expensive and time 

consuming, and do not provide the temperature or conductivity 

information. Conductivity profiles provide valuable 

information for instances where large differences exist 

between the ground water and surface water conductivity.

Several other methods are available to display and 

analyze profile information. Information input to a GIS can 

be plotted spatially using the USGS Digital Raster Graphs to 

display all or part of the profile. Spatially displayed profile 

data using Digital Ortho-Quadrangles and color infra-red 

images for the base map also were used for this study. An 

example of color infra-red images of a map for a short section 

of a profiled reach is shown in figure 6; this map also shows 

locations of salmon redds in this spawning reach. Images can 

show small features (for example, reconnecting side channels), 

which may help explain temperature variations in the profile. 

Another method to display the data is to graph temperature 

changes between readings. Diversity in such a plot is generally 

represented by similar changes for reasonable distances and 

structure by large changes over small distances. The spatial 

plot of such changes also provides valuable insight into the 

relative spatial variations of temperature changes. Temperature 

changes also can be accumulated and plotted against either 

distance or time. Such a plot has the same shape as the actual 

data, but is in terms of cumulative change in temperature for 

the profile. 

Figure 5. Thermal profile and depth for the cooling part of the example reach, August 8, 2001, Yakima River Basin, Washington.

Temperature

Depth

DEPTH, IN CENTIMETERS

22.0

22.5

23.0

23.5

16 17 18 19 20 21 22 23

0

100

200

300

400

TEMPERATURE, IN DEGREES CELSIUS 

DISTANCE, IN KILOMETERS

Example of Method Application 11
waA4WT1_03_fig06

121°01'40" 121°01'30"

47°12'20"

47°12'30"

0

0

200 300

50 100 150 200 METERS

100 400 500 600 700 FEET

Salmon redd locations

Temperature, in degrees Celsius

EXPLANATION

14.72 - 14.76

14.77 - 14.80

14.81 - 14.83

14.84 - 14.86

14.87 - 14.93

Base from Bureau of Reclamation, Upper Columbia Office

Map images Nov. 1, 2000, at a scale of 1:4,800 

State Plane Projection, Washington South Zone, NAD83

WASHINGTON

Yakima

River

Basin

Seattle Spokane

Map

area

Columbia

River

Snake River

Columbia

River

Yakima

Figure 6. Example of thermal profiled reach and salmon redd locations overlaid on an infrared image, Yakima River Basin, 

Washington.

12  Thermal Profile Method to Identify Potential Ground-Water Discharge Areas
Summary and Conclusions

The thermal profile method developed for long river 

reaches proved to be robust, reliable, and reproducible and can 

be applied while drifting in a Lagrangian framework, wading, 

and by using motorized watercraft. Motorized watercraft 

are best used in quiescent waters such as lakes or boat 

accessible, non-braided stream reaches. The CTD-DiverTM 

probe and its container functioned excellently under adverse 

conditions—typified by large temperature variations (reach 

temperatures varied from about 2 to 24°C), and continual 

contact and impact with the streambed. Under both 1- and 

3-second sample rates, the CTD-DiverTM probe’s storage was 

not exceeded and the response of multiple sensors was good. 

Streaming of spatial coordinates using a Global Positioning 

System (GPS) connected to a laptop computer also functioned 

well, as did the self-contained GPS. Considering that the 

terrain varied greatly over the study reaches and included 

canyon type areas and heavily forested stream banks in more 

headwater areas, the loss of GPS reception did not occur as 

often as may be expected. Reception loss occurred less than 

5 percent of the time; however, it can be problematic. The 

method’s advantages and cost-effectiveness outweighs its 

limitations.

Profiles for the example reach (1) display much intraprofile diversity and structure; (2) indicate that the diversity 

and structure measurements are reproducible; and (3) identify 

ground-water discharge areas. Minimum ground-water 

discharge values were estimated for a broad area. These 

values were conservatively estimated to range from about 6 

to 9 percent of measured upstream discharge, and under the 

assumption of equilibrium temperature, they are within the 

range of error in the discharge value from the streamflow 

measuring station at the upstream end of the reach. The 

method is able to locate ground-water discharge areas that 

may not be identifiable from discharge measurements. 

These ground-water discharge areas were located using 

deviations from the diurnal heating. In the thermal profile, 

broad discharge areas are typified by stabilization, cooling, 

or declining rate of change in temperature increases. Local 

discharge is exhibited as structure (short temporal variations) 

contained in the thermal profile. Some local discharge areas 

were not only small, but were identified based on minor water 

temperature changes while drifting at high velocities (1.2–

1.8 meters per second).

Thermal processes leading to end-member temperatures 

of a reach could not have been identified using available 

techniques. Realistic thermal modeling of these reaches would 

be time-consuming and would not provide details of the 

thermal habitat information contained in the profiles.

For habitat assessment, thermal profiles delineate the 

thermal habitat at a small scale. When combined with detailed 

pool-riffle-run structure documented in the depth data, a 

clearer picture of habitat for salmonids can be obtained. 

Profiling of many reaches and inclusion of fish survey data can 

potentially lead to an improved understanding of the relation 

between the different life-history stages of salmonids and the 

thermal-depth habitat in a basin.

Although this method does not supplant other methods, 

it is a cost-effective way to enhance analysis and use of data 

gathered using other techniques. Thermal-depth profiling of 

headwater and first to second order streams was not tested. In 

many areas in the western United States, these parts of streams 

represent the only remaining patches of suitable habitat for 

some salmonids (Rieman and Dunham, 2000). Determining 

whether this method can be applied in these areas would be 

beneficial, because terrain may disallow GPS reception. This 

leads to the question of the value of a thermal-depth profile for 

a reach that is not tied in with spatial coordinates, especially 

because temperature is thought to be a limiting factor for most 

life-history stages of salmonids in many river basins. Without 

spatial coordinates, a thermal profile completed between two 

fixed stations may well provide valuable information on the 

response of a water parcel as it moves downstream in these 

environments. Thus, providing a better estimate of the value 

of the fixed station data relative to processes occurring along 

a reach.

A thermal profile provides valuable information on 

spatial and temporal variations in the thermal regime and 

habitat, indicates ground-water discharge areas, and identifies 

areas for more detailed study. Thermal profiles display 

diversity and structure that can not be captured by fixed station 

data.

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16  Thermal Profile Method to Identify Potential Ground-Water Discharge Areas
Manuscript approved for publication, June 13, 2006

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A Thermal Profile Method to Identify Potential Ground-Water Discharge Areas 

and Preferred Salmonid Habitats for Long River Reaches