U.S. Department of the Interior

U.S. Geological Survey

Quality-Assurance Data, Comparison to Water-Quality 

Standards, and Site Considerations for Total Dissolved 

Gas and Water Temperature, Lower Columbia River, 

Oregon and Washington, 2001

By DWIGHT Q. TANNER and HEATHER M. BRAGG

Water-Resources Investigations Report 01–4273

Prepared in cooperation with the 

U.S. ARMY CORPS OF ENGINEERS

Portland, Oregon: 2001
U. S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

The 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.

For additional information: Copies of this report may be purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

10615 S.E. Cherry Blossom Dr. Box 25286

Portland, OR 97216-3159 Denver, CO 80225-0286

Internet URLs:

Oregon Water Resources: http://or.water.usgs.gov

Suggested citation: Tanner, D.Q., and Bragg, H.M., 2001, Quality-assurance data, comparison to water-quality 

standards, and site considerations for total dissolved gas and water temperature, lower Columbia River, Oregon 

and Washington, 2001: U.S. Geological Survey Water-Resources Investigations Report 01–4273, 14 p. 
III

CONTENTS

Significant Findings ....................................................................................................................................................................1

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

Background .......................................................................................................................................................................2

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

Acknowledgments.............................................................................................................................................................2

Methods of Data Collection ........................................................................................................................................................2

Summary of Data Completeness and Quality .............................................................................................................................4

Quality-Assurance Data ..............................................................................................................................................................5

Effects of Spill on Total Dissolved Gas......................................................................................................................................7

Comparison of Total Dissolved Gas and Temperature to Water-Quality Standards..................................................................9

Site-Specific Considerations .....................................................................................................................................................10

Variability of Total Dissolved Gas and Water Temperature at John Day Forebay ........................................................11

Variability of Total Dissolved Gas and Water Temperature at Camas...........................................................................11

Lateral Distribution of Total Dissolved Gas at the Skamania–Warrendale Cross Section.............................................12

Compensation Depth at Warrendale ...............................................................................................................................12

References Cited .......................................................................................................................................................................14

FIGURES

1. Map showing the location of total-dissolved-gas fixed stations, lower Columbia River, 

Oregon and Washington, water year 2001....................................................................................................................3

2.–15. Graphs showing:

2. Accuracy of total-dissolved-gas sensors when compared to a certified pressure gauge 

after 2 to 3 weeks of field deployment....................................................................................................................5

3. Difference between the secondary standard and the field barometers....................................................................6

4. Difference between the secondary standard and the field temperature instrument ................................................6

5. Difference between the secondary standard and the field total-dissolved-gas instrument .....................................6

6. Total dissolved gas above and below John Day Dam and spill over John Day Dam.............................................8

7. Total dissolved gas above and below The Dalles Dam and spill over The Dalles Dam ........................................8

8. Total dissolved gas above and below Bonneville Dam and spill over Bonneville Dam ........................................9

9. Total-dissolved-gas distributions and Oregon standards at the eight monitoring sites.........................................10

10. Water-temperature distributions at the eight monitoring sites from April 1 to September 15, 2001 ...................10

11. Water-temperature distributions at the eight monitoring sites on August 29, 2001 .............................................10

12. Total dissolved gas at John Day forebay and water temperature at John Day forebay 

and John Day tailwater..........................................................................................................................................11

13. Diurnal variations of total dissolved gas and water temperature at Camas ..........................................................12

14. Comparison of total dissolved gas at Warrendale and Skamania .........................................................................13

15. Compensation depth and actual probe depth at Warrendale.................................................................................14

TABLES

1. Total-dissolved-gas fixed stations, lower Columbia River, Oregon and Washington, water year 2001 ......................3

2. Total-dissolved-gas data completeness and quality, water year 2001 ..........................................................................4
IV

CONVERSION FACTORS

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

°F = (1.8 × °C) + 32

Multiply By To obtain

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2)

cubic foot per second (cfs) 0.02832 cubic meter per second
1

Quality-Assurance Data, Comparison to Water-Quality 

Standards, and Site Considerations for Total Dissolved 

Gas and Water Temperature, Lower Columbia River, 

Oregon and Washington, 2001

By Dwight Q. Tanner and Heather M. Bragg

SIGNIFICANT FINDINGS

• For eight monitoring sites, in water year 2001, 

an average of 99.3% of the total-dissolved-gas 

data were received in real time and passed qualityassurance checks.

• After 2 to 3 weeks of deployment in the river, 

most comparisons of field total-dissolved-gas 

sensors with a secondary standard (another calibrated total-dissolved-gas sensor) were within 1%. 

• The only exceedances of Oregon water-quality standards for total dissolved gas occurred on 

May 23 and 24, 2001, at the Camas, Washington, 

station.

• At the forebay of the John Day Dam, temporary increases in water temperature and total 

dissolved gas occurred on hot afternoons during 

periods of low wind. These increases were not 

observed at the John Day tailwater station.

• At Camas, Washington, daily variations 

of total dissolved gas were probably due to the 

production of oxygen by aquatic plants and to 

water-temperature variations on warm, sunny 

days. 

• During spill over Bonneville Dam in water 

year 2001, the site on the Oregon side of the 

Columbia River, Warrendale, measured larger 

total-dissolved-gas levels than the site directly 

across on the Washington side at Skamania. 

Apparently, streamflow through generating facilities on the north side of the dam forced supersaturated water from the spill bays over to the 

Oregon side of the river.

• At times in July and August 2001, the totaldissolved-gas probe at Warrendale could not 

be positioned below the minimum compensation 

depth because the river was too shallow at that 

location. Consequently, degassing at probe depth 

may have occurred, and total dissolved gas may 

have been larger in locations with greater depths.

INTRODUCTION

The U.S. Army Corps of Engineers (USACE) 

operates dams in the Columbia River Basin, which 

encompasses 259,000 square miles of the Pacific 

Northwest. These dams are multipurpose facilities 

that fill regional needs for flood control, navigation, 

irrigation, recreation, hydropower production, fish 

and wildlife habitat, water-quality maintenance, and 

municipal and industrial water supply. When water 

is released over the spillways of these dams, air is 

entrained in the water, increasing the concentration of 

total dissolved gas (TDG) downstream from the spillways. Consequently, TDG may exceed Oregon and 

Washington water-quality standards for the protection 

of freshwater aquatic life. Concentrations above 110% 

saturation have been shown to cause gas-bubble trauma 

in fish and adversely affect other aquatic organisms 

(U.S. Environmental Protection Agency, 1986). The 

USACE minimizes spill and regulates streamflow in 

the region to minimize the production of excess TDG 

downstream from its dams. The USACE also oversees 

the collection of real-time TDG and water-temperature 

data (data available within about 4 hours of current 

time) upstream and downstream from the dams in a 

network of fixed-station monitors.
2

Background

Real-time TDG and water-temperature data are 

vital to the USACE for dam operation and for monitoring compliance with environmental regulations. 

The data are used by water managers to maintain waterquality conditions that facilitate fish passage and survival in the lower Columbia River. The U.S. Geological 

Survey (USGS), in cooperation with the Portland 

District of USACE, has collected TDG and related data 

in the lower Columbia River every year since 1996. 

Current TDG and water temperature data can be found 

on the USGS website at http://oregon. usgs.gov/ projs_ 

dir/pn307.tdg/. Reports that were published in 1996 and 

2001 contained descriptions of the methods of data 

collection and quality-assurance data for water years 

(WY) 1996 and 2000, respectively (Tanner and others, 

1996; Tanner and Johnston, 2001). 

To provide a suitable data set for managing and 

modeling TDG in the lower Columbia River, real-time 

hourly data for WY 2001 were reviewed in relation 

to measurements made during instrument calibration. 

Some TDG data were deleted because they were not of 

suitable quality. The reviewed hourly data are stored in 

a USGS data base (Automated Data Processing System

—ADAPS), and in the USACE data base (Columbia 

River Operation Hydromet Management System—

CROHMS), which also provides discharge and spill 

data at http://www.nwd-wc.usace.army.mil/TMT/tdg 

_data. 

Purpose and Scope

The purpose of TDG monitoring in the lower 

Columbia River is to provide the USACE with (1) realtime data for managing streamflows and TDG levels 

upstream and downstream from its project dams and 

(2) reviewed TDG data to evaluate conditions in relation to water-quality standards and to develop a TDG 

data base for modeling the effect of various management scenarios of streamflow and spill on TDG levels.

This report describes the TDG data and related 

quality-assurance data for the monitoring program on 

the lower Columbia River, from the forebay of the John 

Day Dam (river mile [RM] 215.6) to Camas, Washington (RM 121.7). Data for WY 2001 (October 1, 2000 

through September 30, 2001) included TDG pressure, 

barometric pressure, water temperature, and probe 

depth at eight fixed stations on the lower Columbia 

River (fig. 1, table 1).

Acknowledgments

We wish to acknowledge the aid and funding support of the U.S. Army Corps of Engineers. Our special 

thanks to James L. Britton (USACE) for technical and 

logistical support of the project. The authors also 

acknowledge Matt Johnston and Amy Brooks (USGS) 

for assistance in data collection and for preparing summaries and analyses of data. Rebecca Treat, a USGS 

volunteer, also assisted with data collection in the field.

METHODS OF DATA COLLECTION

Methods of data collection for TDG, barometric 

pressure, and water temperature are described in detail 

in Tanner and Johnston (2001). A summary of these 

methods follows. Instrumentation at each fixed station 

consisted of a Hydrolab water-quality probe; a Common Sensing, Inc., electronic barometer; a power supply; and a Sutron Model 8200 data-collection platform 

(DCP). The barometer, probe, and DCP were powered 

by a 12-volt battery that was charged by a solar panel 

and/or a 120-volt alternating-current line. Every 

4 hours, the DCP transmitted the most recent logged 

data to the Geostationary Operational Environmental 

Satellite (GOES) system (Jones and others, 1991). 

The data were automatically decoded and transferred 

to the USACE CROHMS data base, and to the USGS 

ADAPS data base. At the John Day tailwater station, 

two TDG sensors were installed on the same Hydrolab. 

This was done to ensure that data were reliably collected at this important site and to provide an assessment of the variability of the TDG measurement at a 

single point in the river cross section.

The fixed-station monitors were calibrated every 

2 weeks from March 10 to September 15, 2001, and 

every 3 weeks for the remainder of the year, at which 

time Warrendale and Bonneville forebay were the only 

sites in operation. The field calibration procedure was 

as follows: A recently calibrated Hydrolab (which was 

used as a secondary standard) was deployed alongside 

of the field Hydrolab to obtain check measurements of 

TDG and water temperature prior to removing the field 

Hydrolab for calibration. Then the field Hydrolab was 

replaced with one that had been recently calibrated at 

the Oregon District laboratory. Again, the secondary 

standard instrument was used to check TDG and temperature in the river. The electronic barometer at the 

fixed station was calibrated using a portable barometer 

that had been recently calibrated. 
3

3

5 8 2 1 4 7

6

Deschutes 

Willamette

River

River 

River 

River 

Lewis

Cowlitz

River John Day

Portland

123 ̊ 121 ̊

45 ̊

46 ̊

John Day

Dam

The Dalles

Dam

Bonneville

Dam

Study

area

Washington

Oregon

PACIFIC OCEAN

COLUMBIA

RIVER

8

EXPLANATION

Monitoring site

Map reference number

(see table 1)

0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

Figure 1. Total-dissolved-gas fixed stations, lower Columbia River, Oregon and Washington, water year 2001. 

Table 1. Total-dissolved-gas fixed stations, lower Columbia River, Oregon and Washington, water year 2001

[Map reference number refers to figure 1; USACE, U.S. Army Corps of Engineers; Columbia River mile locations were determined from U.S. Geological 

Survey (USGS) 7.5-minute topographic maps; stations are referenced by their abbreviated name or USACE site identifier in this report; °, degree; ’, minute; 

”, second]

Map

reference

number

USACE

site

identifier

Columbia

River 

mile

USGS 

station number

USGS station name

(abbreviated station name) Latitude Longitude

Period 

of 

 record

1 JDA 215.6 454257120413000 Columbia River at John Day Dam forebay, 

Washington (John Day forebay)

45°42’57” 120°41’30” 03/27/01–

09/20/01

2 JHAW 214.7 454249120423500 Columbia River, right bank, near Cliffs, 

Washington (John Day tailwater)

45°42’49” 120°42’35” 03/27/01– 

09/20/01

3 TDA 192.6 453712121071200 Columbia River at The Dalles Dam forebay, 

Washington (The Dalles forebay)

45°37’12” 121°07’12” 03/28/01– 

09/21/01

4 TDDO 188.9 14105700 Columbia River at The Dalles, 

Oregon (The Dalles tailwater)

45°36’27” 121°10’20” 03/28/01– 

09/21/01

5 BON 146.1 453845121562000 Columbia River at Bonneville Dam forebay, 

Washington (Bonneville forebay)

45°38’45” 121°56’20” Year-round

6 SKAW 140.5 453651122022200 Columbia River, right bank, near Skamania, 

Washington (Skamania)

45°36’51” 122°02’22” 02/27/01– 

09/20/01

7 WRNO 140.4 453630122021400 Columbia River, left bank, near Dodson, 

Oregon (Warrendale)

45°36’30” 122°02’14” Year-round

8 CWMW 121.7 453439122223900 Columbia River, right bank, at Washougal, 

Washington (Camas)

45°34’39” 122°22’39” 02/27/01– 

09/19/01
4

The Hydrolab that had been deployed for 2 to 

3 weeks was then calibrated in the Oregon District 

laboratory. The integrity of the TDG membrane was 

checked, and the TDG sensor was calibrated at 100, 

200, and 300 mm Hg (millimeters of mercury) above 

atmospheric pressure to cover the expected range of 

TDG pressure in the river.

During each field calibration, the minimum 

compensation depth was calculated to determine 

whether the Hydrolab was positioned at an appropriate 

depth to measure TDG. This depth, which was calculated according to Colt (1984, p. 104), is the depth 

above which degassing will occur due to decreased 

hydrostatic pressure. To measure TDG accurately, 

the Hydrolabs were positioned during each calibration 

visit at a depth below the minimum calculated compensation depth, whenever possible. 

SUMMARY OF DATA COMPLETENESS 

AND QUALITY

Year-end summaries of water year 2001 TDG 

data completeness and quality are shown in table 2. 

Data in this table are based on the total amount of 

hourly TDG data and barometric-pressure data that 

could have been collected during the scheduled monitoring season. At all part-year stations, more data were 

collected than was scheduled because the monitors 

were set up early to ensure correct operation. Any hour 

without TDG-pressure data or barometric-pressure 

data was counted as an hour of missing data for TDG 

in percent saturation, which is calculated as TDG 

pressure, in millimeters of mercury, divided by the 

barometric pressure, in millimeters of mercury, multiplied by 100. The percentage of real-time data received 

shown in table 2 represents the data that were received 

via satellite telemetry at the USGS downlink. The 

USACE downlink operated independently, but the 

amount and quality of the data were similar. 

At each station, at least 98.8% of the data was 

received real-time by the USGS downlink, with an 

overall average of 99.7% (table 2). Problems with 

the amount of real-time data received were usually 

due to malfunction or mistakes in programming of the 

data-collection platform. At Bonneville forebay, realtime data were lost on several occasions in October 

because a large maintenance crane was blocking the 

DCP antenna. 

The fourth column in table 2 shows the percentage of data that was received real-time and passed 

quality-assurance checks. TDG data were considered 

to meet quality-assurance standards if they were within 

1% TDG of the expected value, based on calibration 

data and ambient river conditions at adjacent sites. 

The lowest percentage for a station was 97.8% at The 

Dalles forebay (site 3). Most of this data loss occurred 

in June, when the logged TDG values were constant for 

hours at a time, indicating that the data were not being 

updated. Several field visits were made before the 

problem was resolved by sequentially replacing equipment, but the missing data could not be recovered. 

Most other problems with meeting quality-assurance 

standards were related to the TDG membrane leaking 

or tearing. At Warrendale on July 14, 7 hours of TDG 

data were deleted because the TDG membrane became 

buried in the mud as the river stage fell. The overall 

average of real-time data passing quality-assurance 

standards was 99.3%. 

The collection of barometric-pressure and 

water-temperature data had fewer complications 

than did TDG data collection. Except for instances 

where all data parameters were missing due to problems with the DCP, there were only a few hours of 

missing or incorrect barometric-pressure or watertemperature data. 

Table 2. Total-dissolved-gas data completeness and quality, 

water year 2001

[TDG, total dissolved gas]

Abbreviated 

station name

Planned 

monitoring, 

in hours

Percentage of 

real-time TDG 

data received

Percentage of 

real-time TDG 

data passing 

quality assurance

John Day forebay 4,032 99.3 98.3

John Day tailwater 4,032 100.0 100.0

The Dalles forebay 4,032 99.8 97.8

The Dalles tailwater 4,032 100.0 100.0 

Bonneville forebay 8,760 98.8 98.8 

Skamania 4,560 99.8 99.8

Warrendale 8,760 100.0 99.9

Camas 4,560 100.0 100.0

Average 99.7 99.3
5

QUALITY-ASSURANCE DATA

Data collection for TDG, barometric pressure, 

and water temperature included several qualityassurance procedures, such as the calibration of 

instruments in the field and in the laboratory, daily 

checks of the data, and data review and archive. These 

methods are explained in detail in Tanner and Johnston 

(2001), and the results of the quality-assurance data for 

WY 2001 are presented in this section.

After field deployment for 2 or 3 weeks, the TDG 

sensors were calibrated in the laboratory. First, the unit 

was tested, with the membrane in place, for response to 

increased pressure and to super-saturation conditions. 

The membrane was then removed from the sensor and 

allowed to dry for at least 24 hours. Before replacing 

the membrane, the TDG sensor was examined independently. The calibration test procedure involved reading 

the TDG sensor at the barometric pressure (100% 

saturation) and, using a certified digital pressure gauge 

(primary standard), at added pressures of 100, 200, and 

300 mm Hg (approximately 113%, 126% and 139% 

saturation, respectively). The accuracy of the TDG 

sensors was calculated by computing the difference 

between the expected reading and the Hydrolab TDG 

sensor reading (expected minus actual) for each of the 

four test conditions. As shown in figure 2, most of 

the differences were within 0.4% saturation. There are 

two groups of outlying data. The data points above 

1% saturation for the 100%, 113%, and 126% test 

conditions were the result of a faulty TDG sensor that 

had been deployed at The Dalles forebay for 2 weeks. 

During the subsequent laboratory testing, the sensor 

would not accept calibration. The group of data points 

below -1% saturation for the 113%, 126%, and 139% 

test conditions was also the result of a malfunctioning 

TDG sensor. This sensor was calibrated at 100% and 

126% saturation in the laboratory but continued to read 

inaccurately when retested. This malfunctioning sensor 

affected 6 days of data at Warrendale. Both units were 

removed from field use and sent to the manufacturer 

for repair.

The differences in barometric pressure, water temperature, and TDG between a secondary standard instrument and the fixed-station monitors after 2 to 3 weeks 

of field deployment were measured and recorded as 

part of the field inspection and calibration procedure. 

10th percentile

25th percentile

Median

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

EXPLANATION

CALIBRATION TEST CONDITION, IN PERCENT SATURATION

100% 113% 126% 139%

-3

2

-2

-1

0

1

CERTIFIED PRESSURE GAGE READING MINUS

VALUE FROM FIELD-TOTAL-DISSOLVED-GAS PROBE,

IN PERCENT SATURATION

Figure 2. Accuracy of total-dissolved-gas sensors when compared to a certified pressure gauge after 2 to 3 weeks of field 

deployment. (There were 131 tests at each pressure.) 

These differences, defined as the secondary standard 

value minus the field instrument value, were used to 

compare and quantify the precision between two independent instruments. For water temperature and TDG, 

the measurements were made in-situ with the secondary standard (a recently calibrated Hydrolab) positioned alongside of the field Hydrolab in the river. 

Figures 3, 4, and 5 illustrate the distribution of qualityassurance data for each of the three parameters from 

all eight field sites.

The comparisons of the aneroid barometer used 

as a secondary standard and the electronic field barometer are shown in figure 3. Most of the field 

values are within 2 mm Hg of the standard values. 

Several of the outlying points reflect calibrations of 

the field barometers (adjustment of the DCP offset values) shortly after the site installations in the spring. 
6

JDA JHAW TDA TDDO BON SKAW CWMW

-4

4

-2

0

2

SECONDARY STANDARD VALUE MINUS 

FIELD INSTRUMENT VALUE,

IN MILLIMETERS OF MERCURY

EXPLANATION

10th percentile

Number of samples

25th percentile

Median

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

N = 15 N = 15

WRNO

N = 14 N = 13 N = 15 N = 13 N = 22 N = 23

N = 22

SITE IDENTIFIER

Figure 3. Difference between the secondary standard and the field barometers. (Refer to table 1 for site identifier.) 

JDA JHAW TDA TDDO BON SKAW CWMW

-0. 4

0. 4

-0. 2

0

0. 2

SECONDARY STANDARD VALUE MINUS 

FIELD INSTRUMENT VALUE,

IN DEGREES CELSIUS

EXPLANATION

10th percentile

25th percentile

Median

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

N = 14 N = 12 N = 13 N = 12 N = 22 N = 14 N = 14

WRNO

N = 22

0.47

N = 22 Number of samples

SITE IDENTIFIER

Figure 4. Difference between the secondary standard and the field temperature instrument. (Refer to table 1 for site identifier.) 

JDA JHAW TDA TDDO BON SKAW CWMW

-3

3

-2

-1

0

1

2

SECONDARY STANDARD VALUE MINUS 

FIELD INSTRUMENT VALUE,

IN PERCENT SATURATION

EXPLANATION

10th percentile

25th percentile

Median

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

N = 14 N = 14

WRNO

N = 13 N = 24 N = 14 N = 11 N = 22 N = 21

N = 22 Number of samples

SITE IDENTIFIER

Figure 5. Difference between the secondary standard and the field total-dissolved-gas instrument. (Refer to table 1 for site identifier.) 
7

The temperature-sensor secondary standard and the 

field temperature sensor results are presented in figure 

4. Most of the differences are within 0.1°C (degrees 

Celsius). The slightly wider distribution of values for 

the Bonneville forebay and Warrendale sites may be 

the result of a larger data set. These two sites were in 

operation year-round, nearly twice as long as the other 

six sites. The one significant outlier (+ 0.47°C) 

occurred at Warrendale. Shortly after its field deployment at this site, the temperature sensor demonstrated 

obvious malfunction and was removed from field use 

for the remainder of the year.

The differences between the TDG sensor used as 

a secondary standard and the field TDG sensors were 

calculated following equilibration of the secondary 

standard unit to the site conditions with both Hydrolabs 

side by side in the river. This equilibration was considered complete after a minimum of 20 minutes when the 

TDG values for each sensor remained constant for 4 to 

5 minutes. As shown in figure 5, most of the data demonstrates less than 1% saturation difference between 

the two sensors; however, the site at John Day forebay 

often exceeded this value. Three different TDG probes 

were sequentially deployed for field operation at the 

site. Each probe gave similar results, suggesting instrument malfunction was not the cause of the larger TDG 

differences. Although the secondary standard and the 

field TDG sensors were positioned at approximately 

the same depth during these field checks, the field 

sensor was always positioned in the pipe housing and 

the secondary standard was positioned in the open 

water. During the low flows in WY 2001, partially 

stagnant water in the pipe housing may have caused 

these differences. 

Duplicate TDG data were collected at John Day 

tailwater. Data from the two sensors on the same instrument showed smaller differences in WY 2001 than in 

WY 2000 (Tanner and Johnston, 2001) when two 

Hydrolabs were positioned at different depths in the 

pipe housing (one above the other). For WY 2001, 

there were 4,140 hourly values from March 27 to 

September 20, and 95% of the differences between 

the primary and the duplicate sensor were between 

-0.7 and +0.1% saturation. There was little bias, with 

the median of the differences being -0.1% saturation. 

EFFECTS OF SPILL ON TOTAL DISSOLVED GAS

Spill over each dam increased the level of TDG, 

causing the monitoring site below the dam to have 

larger TDG levels than the site above the dam. Spill 

over John Day Dam occurred from May 25 to June 16 

(fig. 6). The spill (between about 20,000 and 65,000 cfs 

[cubic feet per second]) was released during 

the evening hours. Figure 6 shows that TDG below 

John Day Dam increased in close response to spill over 

the dam, with a level of 113–115% saturation being 

common. TDG levels above John Day Dam generally 

formed the baseline to which the tailwater site returned 

to when there was no spill. Exceptions to this return 

to baseline occurred on May 26, May 31, and June 1st. 

It is likely that during these periods, heating of a 

stagnant (nonmoving) pool of water near the fixed 

station caused a transient increase in TDG, as has 

been observed in the past.

Continuous spill over The Dalles Dam from 

May 16 to June 15 and July 24 to August 31 caused 

increased TDG at the site below The Dalles Dam 

(fig. 7). Spill of about 15,000 to about 65,000 cfs 

caused TDG levels below the dam to increase to 

about 108–113% saturation. During periods of no 

spill, the TDG level above and below The Dalles Dam 

were essentially identical (fig. 7).

At Bonneville Dam, there were three periods of 

spill in WY 2001 (fig. 8). From March 10 to March 13, 

there were periods of nighttime spill of about 47,000 

cfs to flush released hatchery fish to the ocean. The 

TDG at Warrendale during these spills increased to 

about 113–114%. Nearly continuous spill of about 

50,000 cfs from May 16 to June 15 resulted in TDG 

levels of about 113–116% at Warrendale. Finally, 

periods of nighttime and continuous spill of about 

50,000 cfs from July 24 to August 31 caused TDG 

levels at Warrendale to rise to about 110–113%. As 

expected, during times of no spill, the TDG level at 

Bonneville forebay was very similar to the level below 

Bonneville Dam at Warrendale (fig. 8). 
8

95

100

105

110

115

120

TOTAL-DISSOLVED-GAS SATURATION,

IN PERCENT

John Day forebay

John Day tailwater

25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

2001

0

10

20

30

40

50

60

70

80

SPILL,

IN THOUSANDS OF CUBIC FEET PER SECOND

Spill from John Day Dam

MAY JUNE

Figure 6. Total dissolved gas above and below John Day Dam and spill over John Day Dam. 

95

100

105

110

115

120

The Dalles forebay

The Dalles tailwater

15 25 4 14 24 4 14 24 3 13 23 2

0

10

20

30

40

50

60

70

80

90

100

110

Spill from The Dalles Dam

2001

MAY JUNE JULY SEPT AUG

TOTAL-DISSOLVED-GAS SATURATION,

IN PERCENT

SPILL,

IN THOUSANDS OF CUBIC FEET PER SECOND

Figure 7. Total dissolved gas above and below The Dalles Dam and spill over The Dalles Dam.
9

8 18 28 7 17 27 7 17 27 6 16 26 6 16 26 5 15 25 4

0

10

20

30

40

50

60

Spill from Bonneville Dam

90

95

100

105

110

115

120

Bonneville forebay

Warrendale

2001

APR MAY MAY JULY SEPT JUNE AUG

TOTAL-DISSOLVED-GAS SATURATION,

IN PERCENT

SPILL, IN THOUSANDS OF

CUBIC FEET PER SECOND

Figure 8. Total dissolved gas above and below Bonneville Dam and spill over Bonneville Dam. 

COMPARISON OF TOTAL DISSOLVED GAS 

AND TEMPERATURE TO WATER-QUALITY 

STANDARDS

Oregon water-quality standards for TDG and 

water temperature for the lower Columbia River are 

similar to Washington standards. In this report, Oregon 

standards specifically are addressed. The USACE may 

obtain a variance from the Oregon TDG water-quality 

standard of 110% saturation relative to atmospheric 

pressure for a specified period of time to facilitate fish 

passage. From April 10 to August 31, 2001, the variance was 115% for forebay sites (John Day forebay, 

The Dalles forebay, Bonneville forebay, and Camas) 

and the variance was 120% for tailwater sites directly 

downstream from dams (John Day tailwater, The 

Dalles tailwater, Warrendale, and Skamania). 

Although the Camas site is not located in the forebay 

of a dam, it is located more than 24 miles downstream 

of Bonneville Dam and is regulated as a forebay site. 

The variance was exceeded if the average of the highest 

12 hourly values in 1 day (1:00 a.m. to midnight) was 

larger than the numerical standard (Stephanie Hallock, 

Oregon Department of Environmental Quality, written 

commun., March 23, 2001). In addition, TDG should 

not exceed 125% saturation, based on the highest 

2 hours during the 12 highest hourly measurements 

per day. 

The distribution of all the hourly TDG measurements in WY 2001 is shown on figure 9, in relation to 

the Oregon numerical standards. The hourly values 

for all of the sites did not exceed 118% saturation. 

Analysis of the hourly values showed that the Camas 

site was the only site for which the 12-hour average 

was in exceedance of 115%; this occurred on May 23 

and 24, 2001. 

Water-temperature standards that apply to the 

lower Columbia River are complex and depend on the 

effects of anthropogenic activities and the locations 

of salmonid rearing, spawning, and egg incubation 

areas (Oregon Department of Environmental Quality 

website at http://www.deq.state.or.us/wq/wqrules.htm, 

2001). When the temperature of the Columbia River 

exceeds 20°C from RM 309 to the mouth, no measurable surface water temperature increase resulting from 

anthropogenic activities is allowed by the Oregon 

water-quality standard. Water-temperature data for 

spring and summer 2001 are shown in figure 10. The 

highest water temperature, 24.7°C, was recorded at the 

John Day forebay site on August 12, 2001, at 7:00 p.m. 
10

JDA JHAW TDA TDDO BON SKAW CWMW

SITE IDENTIFIER

90

95

100

105

110

115

120

125

TOTAL-DISSOLVED-GAS SATURATION, IN PERCENT

N=4195 N=4248 N=4246 N=4248 N=8700

WRNO

N=4894 N=8753 N=4896

Oregon standard for

forebay water

Oregon standard for tailwater

EXPLANATION

10th percentile

25th percentile

Median

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

N = 22 Number of samples

Figure 9. Total-dissolved-gas distributions and Oregon standards 

at the eight monitoring sites. (Refer to table 1 for site identifier; 

N = sample size.)

JDA JHAW TDA TDDO BON SKAW WRNO CWMW

5

10

15

20

25

WATER TEMPERATURE, IN DEGREES CELSIUS

SITE IDENTIFIER

EXPLANATION

10th percentile

25th percentile

Median

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

Figure 10. Water-temperature distributions at the eight monitoring sites from April 1 to September 15, 2001. (Refer to table 1 for 

site identifier. There were 4,032 measurements at each site.)

For each site, the 75th percentile of hourly values was 

higher than 20°C. During August, all sites exhibited 

water temperatures higher than 20°C. 

The distributions of hourly water temperatures for 

1 day, August 29, 2001, are shown in figure 11. On that 

day, water temperatures were higher than 20°C at all 

hours at all sites. Camas was the only site for which the 

median (22.1°C) fell outside of the narrow range of 

21.6–21.9°C. The elevated temperature at Camas may 

be due to the physical characteristics of the shallower 

free-flowing section of the Columbia River near Camas. 

Water temperatures at John Day forebay were notably 

higher than at other stations, possibly due to localized 

heating near the fixed station. The water-temperature 

variations at Camas and John Day forebay are discussed 

next in the section on site-specific considerations. 

JDA JHAW TDA TDDO BON WRNO SKAW CWMW 21.0

21.5

22.0

22.5

23.0

23.5

24.0

Median = 21.6 Median = 21.6

Median = 21.9

WATER TEMPERATURE, IN DEGREES CELSIUS

SITE IDENTIFIER

EXPLANATION

10th percentile

25th percentile

Median

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

Figure 11. Water-temperature distributions at the eight monitoring sites on August 29, 2001. (Refer to table 1 for site identifier. 

There were 24 measurements at each site.)

SITE-SPECIFIC CONSIDERATIONS

Even though the same types of electronic equipment and instruments were used at each site, there 

were differences among the sites in the stream environment where the equipment was installed along the 

river banks. Some sites were at river locations that were 

poorly mixed, had limited probe depth at certain 

times of the year, or had greater circulation of water 

around the probe. The important effects of site-specific 

considerations are summarized next.
11

Variability of Total Dissolved Gas 

and Water Temperature at 

John Day Forebay

At the John Day forebay, TDG values rose on 

several occasions by 3 to 5% saturation for several 

hours, concurrent with a 2 to 3°C increase in water 

temperature. Data for several days in August, when 

there was no spill from John Day Dam, are shown in 

figure 12. The fact that the temperature below John 

Day Dam did not vary greatly during this period 

indicates that the water-temperature excursions at the 

John Day forebay were anomalous. These excursions 

of TDG and water temperature were observed on hot, 

sunny days, and it is believed that a localized parcel of 

heated water on the river surface caused the increase in 

water temperature observed at the fixed station. 

It was documented by Mike Schneider (USACE, 

written commun., 2001) that these events happened 

when winds were nearly calm, a favorable condition 

for surface heating. TDG and temperature anomalies 

also were observed in WY 2000 during periods of 

similar weather conditions (Tanner and Johnston, 

2001, p. 19).

8 9 10 11 12 13 14

AUGUST 2001

20

21

22

23

24

25

John Day forebay

John Day tailwater

95

100

105

110

John Day forebay

WATER TEMPERATURE, IN DEGREES CELSIUS

TOTAL-DISSOLVED-GAS SATURATION,

IN PERCENT

Figure 12. Total dissolved gas at John Day forebay and water temperature at John Day forebay and John Day tailwater.

Variability of Total Dissolved Gas 

and Water Temperature at Camas

During much of the monitoring season at the 

Camas site, water temperature and TDG were 

observed to fluctuate in a smooth, diurnal pattern. 

For example, from May 23 to 25, at about 8:00 a.m., 

minima were observed for water temperature (about 

15 to 15.5°C) and for TDG (about 111 to 112% saturation) (fig. 13). Maxima were observed at about 

5:00 p.m. for water temperature (about 16.5 to 17°C) 

and for TDG (about 116 to 117% saturation). There 

was sufficient flow at the Camas site to preclude any 

afternoon heating of localized parcels of water as was 

observed at the John Day forebay site. 

One probable cause for the TDG variations is 

primary productivity in the Columbia River. During 

the same time period (May 23–26), the USGS measured dissolved oxygen at the Camas site and found 

variations of the same pattern, with morning minima 

of 11 mg/L (milligrams per liter) and afternoon maxima of 12 mg/L (USGS data files). Water-temperature 

variations at the Camas site could be due to the 

shallow, free-flowing river characteristics at Camas 

that would be very different from the other Columbia 

River TDG sites, which are affected by the reservoirs. 
12

15.0

15.5

16.0

16.5

17.0

17.5

18.0

110

112

114

116

118

WATER TEMPERATURE, IN DEGREES CELSIUS

TOTAL-DISSOLVED-GAS SATURATION,

IN PERCENT

Total dissolved gas

Water temperature

12

midnight

12

noon

12

midnight

12

noon

12

midnight

MAY 23 MAY 24

2001

Figure 13. Diurnal variations of total dissolved gas and water 

temperature at Camas.

Calculations by Joe Carroll, (USACE, written commun., 2001) showed that on May 24, theoretical pressure changes due to the measured temperature and 

dissolved oxygen variations accounted for a TDG pressure increase of 38 mm Hg, when an actual increase of 

36 mm Hg was measured by the TDG sensor at Camas. 

These independent measures of the components of 

TDG match TDG measurements well, indicating that 

the diurnal variations in TDG were probably due to the 

production of oxygen by aquatic plants and to diurnal 

temperature variations, and not due to the spill operations of the upstream dams. Depending on the barometric pressure at the time of measurement, the 36–38 mm 

of TDG pressure increase would be equivalent to about 

5% saturation, which is significant because this is the 

same time period (May 23 and 24) that the variance of 

115% saturation was exceeded at Camas.

Lateral Distribution of Total Dissolved Gas 

at the Skamania–Warrendale Cross Section

The TDG stations at Skamania, Washington, and 

Warrendale, Oregon, are almost directly across the 

Columbia River from one another—their locations 

differ laterally by only 0.1 river mile (table 1). Data 

from these stations show the river is not well mixed 

with respect to TDG at this cross section. TDG 

levels at Skamania and Warrendale for the spring 

and summer of 2001 are shown on figure 14. If TDG 

levels for each hourly value had been the same at both 

sites, the data points would have fallen directly on the 

line labeled “Slope = 1.” Instead, when the TDG was 

larger than about 105% saturation at Skamania, the 

measured TDG at Warrendale was 3–5% larger than at 

Skamania (fig. 14). Water temperatures at these two 

stations did not differ appreciably from each other during the monitoring season, so it was not a case of heating causing a change in TDG. 

The cause of this uneven distribution of TDG in 

the river cross section was probably related to the 

configuration of power generation equipment at 

Bonneville Dam. Powerhouse 2, north of the spill bays 

at Bonneville, was used to generate power in WY 2001, 

and flow from the powerhouse forced supersaturated 

water from the spill bays south to the Oregon side of the 

Columbia River, where the Warrendale site is located. 

During spill events, TDG exceeded 105% 

saturation at Warrendale (fig. 8), and TDG levels at 

Warrendale exceeded levels at Skamania by about 

3–5% (fig. 14). Consequently, it is likely that the 

spill during the use of powerhouse 2 is responsible 

for the poor mixing in the river at this cross section. 

This finding illustrates the need for operating both the 

Skamania and Warrendale monitoring sites to describe 

TDG levels in the river cross section under varying 

conditions of spill and power generation.

Compensation Depth at Warrendale

Compensation depth for TDG measurement is the 

depth above which degassing is possible. In order to 

measure TDG accurately, the probe must be deeper 

than the compensation depth, which is calculated as 

(TDG pressure, in millimeters of mercury, minus barometric pressure, in millimeters of mercury) divided by 

23. This equation was based on a formula derived from 

Colt (1984, p. 104). If the probe is above the minimum 

compensation depth, the measured TDG may be less 

than it would be if measured at a greater depth. In other 

words, degassing may have occurred.

To ensure that the TDG probe was below the 

compensation depth when the TDG in the river was 

120% saturation, the following formula could be used 

to calculate the compensation depth:

CD = [(TDGe/100) X Bp) - Bp] / 23

where 

CD = Compensation depth, in feet;

TDGe = Highest expected TDG, in percent saturation;

Bp = Barometric pressure in millimeters of mercury. 
13

90 95 100 105 110 115 120

90

95

100

105

110

115

120

Slope = 1 

TOTAL-DISSOLVED-GAS SATURATION AT WARRENDALE, IN PERCENT

TOTAL-DISSOLVED-GAS SATURATION AT SKAMANIA, IN PERCENT

Figure 14. Comparison of total dissolved gas at Warrendale and Skamania. (There were 4,886 measurements at each site.)

For example, if the Bp is 760 mm Hg, and the 

highest expected TDG level is 120% saturation, the CD

is 6.6 feet. Therefore, the TDG probe must be located 

at a depth greater than 6.6 feet to avoid potential 

degassing and the formation of bubbles on the TDG 

membrane. If the highest expected TDG level in the 

river is 145% saturation, then the compensation depth 

would be 14.9 feet. For the fixed stations on the lower 

Columbia River, TDG probes were kept at a depth of 

15 feet or greater, where possible.

Warrendale was the only site where the TDG 

probe was above the compensation depth at any time in 

WY 2001. During the spill from Bonneville Dam from 

July 24 to August 31, the water depth at the Warrendale 

fixed station was only a few feet so the probe depth was 

only about 1.5 to 3 feet. Consequently, the probe was 

above the compensation depth and degassing may have 

occurred (fig. 15). Measured TDG at Warrendale then 

was 110–115% (fig. 8), and in this range, the TDG is 

higher at Warrendale than across the river at Skamania 

(fig. 14). The conclusion to be drawn from these 

data is that although the Warrendale site was a better 

place than Skamania to measure elevated TDG at this 

time, an even higher TDG could possibly have been 

measured at a deeper location on the Oregon side 

(or, alternatively, at a location closer to Bonneville 

Dam).

The problem with attaining sufficient probe depth 

at Warrendale is related to the physical characteristics 

of the site. The instruments were housed on 

a floating wooden dock, and the TDG probe was 

suspended from the dock. When the river was shallow 

at the Warrendale site, as it was from mid-July to 

the end of the water year, the probe was maintained 

about a foot above the river bottom. In order to measure 

TDG at a greater depth, the probe would need to be 

moved to a deeper part of the river at another fixedstation location. 
14

8 18 28 7 17 27 7 17 27 6 16 26 6 16 26 5 15 25 4

MAR APR MAY JUNE JULY AUG SEPT

0

1

2

3

4

5

6

7

8

9

10

DEPTH, IN FEET

Probe depth at Warrendale

Compensation depth

2001

Figure 15. Compensation depth and actual probe depth at Warrendale.

REFERENCES CITED

Colt, J., 1984, Computation of dissolved gas concentrations 

in water as functions of temperature, salinity, and pressure: American Fisheries Society Special Publication 

14, 154 p.

Jones, J.C., Tracey, D.C., and Sorensen, F.W., eds., 1991, 

Operating manual for the U.S. Geological Survey’s 

data-collection system with the Geostationary Operational Environmental Satellite: U.S. Geological Survey 

Open-File Report 91–99, 237 p. 

Tanner, D.Q., Harrison, H.E., and McKenzie, S.W., 1996, 

Total dissolved gas, barometric pressure, and water 

temperature data, lower Columbia River, Oregon and 

Washington, 1996: U.S. Geological Survey Open-File 

Report 96–662A, 85 p.

Tanner, D.Q., and Johnston, M.W., 2001, Data-collection 

methods, quality-assurance data, and site considerations for total dissolved gas monitoring, lower 

Columbia River, Oregon and Washington, 2000: 

U.S. Geological Survey Water-Resources Investigations Report 01–4005, 19 p.

U.S. Environmental Protection Agency, 1986, Quality criteria for water: Washington, D.C., EPA-440-5-86-001.
U.S. Department of the Interior

U.S. Geological Survey

Quality-Assurance Data, Comparison to Water-Quality 

Standards, and Site Considerations for Total Dissolved 

Gas and Water Temperature, Lower Columbia River, 

Oregon and Washington, 2001

Water-Resources Investigations Report 01–4273

Prepared in cooperation with the 

U.S. ARMY CORPS OF ENGINEERS
Cover photograph:

Calibration of monitoring equipment on the Columbia River downstream of John Day Dam, September 2001. 

(Photograph by Rebecca Treat, U.S. Geological Survey volunteer)