-I

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with

Unified Sewerage Agency of Washington County, Oregon

Effects of Hypothetical Management Scenarios

on Simulated Water Temperatures in the

Tualatin River, Oregon

Water-Resources Investigations Report 00–4071

Supplement to Water-Resources Investigations Report 97–4071
Cover photograph. Stafford Bridge on the Tualatin River, Oregon. (Photograph courtesey of Tirian Mink,

Portland, Oregon.)
U.S. Department of the Interior

U.S. Geological Survey

Effects of Hypothetical Management Scenarios

on Simulated Water Temperatures in the

Tualatin River, Oregon

By JOHN C. RISLEY

Water-Resources Investigations Report 00–4071

Supplement to Water-Resources Investigations Report 97–4071

Prepared in cooperation with the

Unified Sewerage Agency of Washington County, Oregon

Portland, Oregon

2000
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBIT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

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.

__________________________________________________________________

For additional information contact: Copies of this report can be

purchased from:

District Chief

U.S. Geological Survey U.S. Geological Survey

10615 S.E. Cherry Blossom Drive Branch of Information Services

Portland, OR 97216-3159 Box 25286, Federal Center

E-mail: info-or@usgs.gov Denver, CO 80225-0046

Internet: http://oregon.usgs.gov
III

CONTENTS

Significant Findings ..........................................................................................................................................................

Introduction .......................................................................................................................................................................

Background..............................................................................................................................................................

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

Description of the Study Area .................................................................................................................................

Data Collection..................................................................................................................................................................

Water Temperature ..................................................................................................................................................

Streamflow...............................................................................................................................................................

Riparian Shading .....................................................................................................................................................

Computer Models..............................................................................................................................................................

Shading Coefficients................................................................................................................................................

Upper River Section ................................................................................................................................................

Lower River Section ...............................................................................................................................................

Management Scenario Simulations...................................................................................................................................

1995 Model Simulation ...........................................................................................................................................

Previous Scenarios...................................................................................................................................................

Additional Scenarios................................................................................................................................................

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

References Cited ...............................................................................................................................................................

FIGURES

1. Map showing the Tualatin River Basin, Oregon....................................................................................................

2.–4. Schematic diagrams showing the:

2. Relative positions of selected tributaries, fixed-station continuous-monitoring sites, and wastewater-treatment

plants, Tualatin River Basin, Oregon, 1994–95.....................................................................................................

3. Diffusion Analogy Flow/Branched Lagrangian Transport Model configuration for the Tualatin River from

river mile 63.9 to river mile 38.4 ...........................................................................................................................

4. CE-QUAL-W2 model configuration for the Tualatin River from river mile 38.4 to river mile 3.4 ......................

5.– 74. Graphs showing:

5. Observed and simulated discharge from May through October 1995 in the Tualatin River, Oregon ...................

6. Observed and simulated water temperatures from May through October 1995 in the Tualatin River, Oregon ....

7. Monthly mean of the 7-day moving average of daily maximum simulated and observed 1994 water temperatur

for scenario 1, existing conditions .........................................................................................................................

8. Monthly mean of the 7-day moving average of daily maximum simulated and observed 1995 water temperatur

for scenario 1, existing conditions .........................................................................................................................

9. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 11, existing conditions with 1.33 cubic feet per second decrease in Rock Creek Wastewater-Treatmen

Plant effluent ..........................................................................................................................................................

10. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 11, existing conditions with 1.33 cubic feet per

second decrease in Rock Creek Wastewater-Treatment Plant effluent ..................................................................

11. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 11, existing conditions with 1.33 cubic feet per second decrease in Rock Creek Wastewater-Treatmen

Plant effluent ..........................................................................................................................................................

12. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 11, existing conditions with 1.33 cubic feet

per second decrease in Rock Creek Wastewater-Treatment Plant effluent............................................................
IV

13. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 12, existing conditions with 1.33 cubic feet per second river withdrawal and 2.0 cubic feet per

second Henry Hagg Lake release...........................................................................................................................

14. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 12, existing conditions with 1.33 cubic feet per

second river withdrawal and 2.0 cubic feet per second Henry Hagg Lake release................................................

15. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 12, existing conditions with 1.33 cubic feet per second river withdrawal and 2.0 cubic feet per

second Henry Hagg Lake release...........................................................................................................................

16. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 12, existing conditions with 1.33 cubic feet per

second river withdrawal and 2.0 cubic feet per second Henry Hagg Lake release................................................

17. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 13, existing conditions with effluent releases of 5 million gallons per day at river mile 55.2 and

river mile 43.8 and 10 million gallons per day at river mile 38.1..........................................................................

18. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 13, existing conditions with effluent releases of

5 million gallons per day at river mile 55.2 and river mile 43.8 and 10 million gallons per day at river mile 38.

19. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 13, existing conditions with effluent releases of 5 million gallons per day at river mile 55.2 and

river mile 43.8 and 10 million gallons per day at river mile 38.1..........................................................................

20. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 13, existing conditions with effluent releases of

5 million gallons per day at river mile 55.2 and river mile 43.8 and 10 million gallons per day at river mile 38.

21. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 14, existing conditions with effluent releases of 5 million gallons per day at river mile 55.2 and

river mile 43.8 and 20 million gallons per day at river mile 38.1..........................................................................

22. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 14, existing conditions with effluent releases of

5 million gallons per day at river mile 55.2 and river mile 43.8 and 20 million gallons per day at river mile 38.

23. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 14, existing conditions with effluent releases of 5 million gallons per day at river mile 55.2 and

river mile 43.8 and 20 million gallons per day at river mile 38.1..........................................................................

24. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 14, existing conditions with effluent releases of

5 million gallons per day at river mile 55.2 and river mile 43.8 and 20 million gallons per day at river mile 38.

25. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 15, existing conditions with effluent releases of 5 million gallons per day at river mile 55.2 and

river mile 43.8 and 30 million gallons per day at river mile 38.1..........................................................................

26. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 15, existing conditions with effluent releases of

5 million gallons per day at river mile 55.2 and river mile 43.8 and 30 million gallons per day at river mile 38.

27. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 15, existing conditions with effluent releases of 5 million gallons per day at river mile 55.2 and

river mile 43.8 and 30 million gallons per day at river mile 38.1..........................................................................

28. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 15, existing conditions with effluent releases of

5 million gallons per day at river mile 55.2 and river mile 43.8 and 30 million gallons per day at river mile 38.

29. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 16, existing conditions with 25 million gallons per day of effluent released at river mile 38.1 and

river mile 9.3..........................................................................................................................................................

30. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 16, existing conditions with 25 million gallons

per day of effluent released at river mile 38.1 and river mile 9.3 ..........................................................................
V

31. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 16, existing conditions with 25 million gallons per day of effluent released at river mile 38.1 and

river mile 9.3..........................................................................................................................................................

32. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 16, existing conditions with 25 million gallons p

day of effluent released at river mile 38.1 and river mile 9.3 ................................................................................

33. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 17, existing conditions with 45 million gallons per day of effluent released at river mile 38.1 and

river mile 9.3..........................................................................................................................................................

34. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 17, existing conditions with 45 million gallons p

day of effluent released at river mile 38.1 and river mile 9.3 ................................................................................

35. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 17, existing conditions with 45 million gallons per day of effluent released at river mile 38.1 and

river mile 9.3..........................................................................................................................................................

36. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 17, existing conditions with 45 million gallons p

day of effluent released at river mile 38.1 and river mile 9.3 ................................................................................

37. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 18, existing conditions with 65 million gallons per day of effluent released at river mile 38.1 and

river mile 9.3..........................................................................................................................................................

38. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 18, existing conditions with 65 million gallons

per day of effluent released at river mile 38.1 and river mile 9.3 ..........................................................................

39. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 18, existing conditions with 65 million gallons per day of effluent released at river mile 38.1 and

river mile 9.3..........................................................................................................................................................

40. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 18, existing conditions with 65 million gallons p

day of effluent released at river mile 38.1 and river mile 9.3 ................................................................................

41. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 19, existing conditions with Gaston temperature data replaced with Lee Falls data...............................

42. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 19, existing conditions with Gaston temperature

data replaced with Lee Falls data...........................................................................................................................

43. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 19, existing conditions with Gaston temperature data replaced with Lee Falls data...............................

44. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 19, existing conditions with Gaston temperature

data replaced with Lee Falls data...........................................................................................................................

45. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 20, “natural” conditions with Gaston temperature data replaced with Lee Falls data ............................

46. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 20, “natural” conditions with Gaston temperatur

data replaced with Lee Falls data...........................................................................................................................

47. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 20, “natural” conditions with Gaston temperature data replaced with Lee Falls data ............................

48. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 20, “natural” conditions with Gaston temperatur

data replaced with Lee Falls data...........................................................................................................................

49. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 21, existing conditions with wastewater-treatment plant effluent temperature equal to receiving river

temperature ............................................................................................................................................................
VI

50. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 21, existing conditions with wastewater-treatmen

plant effluent temperature equal to receiving river temperature ............................................................................

51. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 21, existing conditions with wastewater-treatment plant effluent temperature equal to receiving river

temperature ............................................................................................................................................................

52. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 21, existing conditions with wastewater-treatmen

plant effluent temperature equal to receiving river temperature ............................................................................

53. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 7, existing conditions without wastewater-treatment plants, and scenario 21, existing

conditions with wastewater-treatment plant effluent temperature equal to receiving river temperature ...............

54. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 7, existing conditions without wastewater-treatment plants, and scenario 21, existing

conditions with wastewater-treatment plant effluent temperature equal to receiving river temperature ...............

55. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 22, existing conditions with up to 10 million gallons per day of Unified Sewerage Agency flow

augmentation released near Rock Creek Wastewater-Treatment Plant outfall ......................................................

56. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 22, existing conditions with up to 10 million

gallons per day of Unified Sewerage Agency flow augmentation released near Rock Creek Wastewater-Treatm

Plant outfall............................................................................................................................................................

57. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 22, existing conditions with up to 10 million gallons per day of Unified Sewerage Agency flow

augmentation released near Rock Creek Wastewater-Treatment Plant outfall ......................................................

58. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 22, existing conditions with up to 10 million gal

per day of Unified Sewerage Agency flow augmentation released near Rock Creek Wastewater-Treatment Plan

outfall.....................................................................................................................................................................

59. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 23, existing conditions with 20 million gallons per day of 17.8 degree Celsius effluent released at

river mile 38.1 and river mile 9.3...........................................................................................................................

60. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 23, existing conditions with 20 million gallons p

day of 17.8 degree Celsius effluent released at river mile 38.1 and river mile 9.3................................................

61. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 23, existing conditions with 20 million gallons per day of 17.8 degree Celsius effluent released at

river mile 38.1 and river mile 9.3...........................................................................................................................

62. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 23, existing conditions with 20 million gallons p

day of 17.8 degree Celsius effluent released at river mile 38.1 and river mile 9.3................................................

63. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 24, existing conditions with 25 million gallons per day of 17.8 degree Celsius effluent released at

river mile 38.1 and river mile 9.3...........................................................................................................................

64. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 24, existing conditions with 25 million gallons p

day of 17.8 degree Celsius effluent released at river mile 38.1 and river mile 9.3................................................

65. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 24, existing conditions with 25 million gallons per day of 17.8 degree Celsius effluent released

at river mile 38.1 and river mile 9.3.......................................................................................................................
VII

66. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 24, existing conditions with 25 million gallons

per day of 17.8 degree Celsius effluent released at river mile 38.1 and river mile 9.3..........................................

67. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 25, existing conditions with 45 million gallons per day of 17.8 degree Celsius effluent released at

river mile 38.1 and river mile 9.3...........................................................................................................................

68. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994

water temperatures for scenario 1, existing conditions, and scenario 25, existing conditions with 45 million

gallons per day of 17.8 degree Celsius effluent released at river mile 38.1 and river mile 9.3 .............................

69. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 25, existing conditions with 45 million gallons per day of 17.8 degree Celsius effluent released

at river mile 38.1 and river mile 9.3.......................................................................................................................

70. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 25, existing conditions with 45 million gallons

per day of 17.8 degree Celsius effluent released at river mile 38.1 and river mile 9.3..........................................

71. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for

scenario 26, existing conditions with 65 million gallons per day of 17.8 degree Celsius effluent released

at river mile 38.1 and river mile 9.3.......................................................................................................................

72. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water

temperatures for scenario 1, existing conditions, and scenario 26, existing conditions with 65 million gallons

per day of 17.8 degree Celsius effluent released at river mile 38.1 and river mile 9.3..........................................

73. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for

scenario 26, existing conditions with 65 million gallons per day of 17.8 degree Celsius effluent released

at river mile 38.1 and river mile 9.3.......................................................................................................................

74. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water

temperatures for scenario 1, existing conditions, and scenario 26, existing conditions with 65 million gallons

per day of 17.8 degree Celsius effluent released at river mile 38.1 and river mile 9.3..........................................

TABLES

1. U.S. Geological Survey fixed-station continuous-monitoring sites in the Tualatin River Basin, Oregon, 1994–95...

2. Root mean square error between observed and simulated daily mean water temperatures at sites on the Tualatin R

from May through October 1994 and 1995 ...............................................................................................................

3. Water temperature data from the Oswego diversion dam at river mile 3.4 near West Linn, Oregon, 1991–98 ..........

4. Air temperature data from the Hillsboro Airport near Hillsboro, Oregon, 1991–98...................................................

5. Precipitation data from the Hillsboro Airport near Hillsboro, Oregon, 1991–98........................................................

6. Hypothetical water-management scenarios from the initial modeling study...............................................................

7. Additional hypothetical water-management scenarios ................................................................................................

8. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature

in degrees Celsius for each management scenario at Golf Course Road...................................................................

9. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and

1995 water temperature in degrees Celsius for each management scenario and Scenario 1 at Golf Course Road ...

10. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature at

Golf Course Road exceeds 17.8 degrees Celsius for each management scenario during each month ......................

11. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature

in degrees Celsius for each management scenario at Rood Bridge ...........................................................................

12. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and

1995 water temperature in degrees Celsius for each management scenario averaged over each month and

Scenario 1 at Rood Bridge .........................................................................................................................................

13. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature

at Rood Bridge exceeds 17.8 degrees Celsius for each management scenario during each

month .........................................................................................................................................................................
VIII

14. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature

in degrees Celsius for each management scenario at Scholls Bridge ........................................................................

15. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and

1995 water temperature in degrees Celsius for each management scenario and Scenario 1 at Scholls Bridge.........

16. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature

at Scholls Ferry Road exceeds 17.8 degrees Celsius for each management scenario during

each month .................................................................................................................................................................

17. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature in

degrees Celsius for each management scenario at Elsner Road ................................................................................

18. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and

1995 water temperature in degrees Celsius for each management scenario averaged over each month and

Scenario 1 at Elsner Road ..........................................................................................................................................

19. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature at

Elsner Road exceeds 17.8 degrees Celsius for each management scenario during each month................................

20. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature in

degrees Celsius for each management scenario at Stafford Road..............................................................................

21. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and

1995 water temperature in degrees Celsius for each management scenario averaged over each month and

Scenario 1 at Stafford Road .......................................................................................................................................

22. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature at

Stafford Road exceeds 17.8 degrees Celsius for each management scenario during each month.............................

CONVERSION FACTORS

______________________________________________________________________________

Multiply By To obtain

______________________________________________________________________________

acre 0.001562 square mile (mi2)

square mile (mi2) 2.590 square kilometer (km2)

cubic foot per second (ft3

/s) 0.646317 millions of gallons per day (Mgal/d)

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

inch 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Temperature in degrees Celsius (oC) as follows: oC = (oF - 32)/1.8.

______________________________________________________________________________

Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodeti

derived from a general adjustment of the first-order level nets of both the United States and Canada, called Mean Sea Le

1929.
IX

ACKNOWLEDGMENTS

The author gratefully acknowledges several agencies and individuals for providing assistance and dat

in the analyses for this report. The Unified Sewerage Agency of Washington County, Oregon, provided effl

flow and temperature data in addition to financial assistance. Jerry Rodgers, Oregon Water Resources Depa

provided stage and discharge data, which were used to define boundary conditions for model simulations. T

Lake Oswego Corporation provided operation data for the Oswego diversion dam at river mile 3.4. The Or

State Climate Service provided meteorological data collected at Hillsboro Airport. Finally, the U.S. Geolog

Survey extends its appreciation to landowners who provided river access for data collection.
1

Effects of Hypothetical Management Scenarios on Simula

Water Temperatures in the Tualatin River, Oregon

By John C. Risley

SIGNIFICANT FINDINGS

Water temperature is one of the most important factors determining the health of fish and

other aquatic organisms. If water temperatures

warm beyond a critical threshold, particularly

during the sensitive life stages of fish, survival can

markedly decrease. In 1996, the State of Oregon

adopted a revised maximum water temperature

standard of 17.8οC (degrees Celsius) (64οF

[degrees Fahrenheit]) for most waterways, including the Tualatin River in northwestern Oregon. To

assess water temperature conditions in the Tualatin River, a recent cooperative study between the

U.S. Geological Survey and the Unified Sewerage

Agency of Washington County, Oregon, used two

dynamic-flow heat-transport models, DAFLOWBLTM (river mile [RM] 63.9-RM 38.4) and CEQUAL-W2 (RM 3 8.4-RM 3.4). After the models

were calibrated with data collected during the

1994 low-flow season, they were used to simulate

various hypothetical water-management scenarios. Results from the first 10 scenarios were published in an earlier report. This report presents the

results of an additional 16 scenarios for both 1994

and 1995 conditions. In all 16 scenarios, the

State’s temperature standard (17.8οC) was

exceeded in much of the lower reaches of the

Tualatin River during the warmer months in both

years.

* The effect of diverting 1.33 ft3

/s (cubic feet per

second) of Rock Creek Wastewater-Treatment

plant (WWTP) effluent for irrigation was evaluated. Temperatures downstream of that f

(RM 38.1) for most months decreased ab

0.05οC or less. Farther downstream, near 

10, the effect was almost negligible. The 

of the diversion is slightly more apparent 

1994 simulation than in the 1995 simulati

a similar follow-up scenario, a constant fl

1.33 ft3

/s was withdrawn from the river a

37.3 and an additional constant flow of 2.

was released from Henry Hagg Lake to c

pensate. The effect of this diversion/augm

tion on the river system was also fairly mi

for both 1994 and 1995. Temperatures ge

ally decreased from RM 60.0 to RM 3.4 b

about 0.05 to 0.1οC. For most months, th

all cooling resulting from this scenario w

slightly greater than the cooling resulting 

the former scenario.

* In another set of scenarios, the effect of p

and then releasing Rock Creek WWTP ef

at two upstream locations (RM 43.8 and R

55.2) was evaluated. A constant flow of 5

Mgal/d (million gallons per day) was rele

at each upstream location, in addition to a 

stant release of either 10, 20, or 30 Mgal/

effluent at RM 38.1. Temperatures increa

between RM 55.2 and RM 38.1 by about 

or less, but were still within compliance w

the water-quality standard. Downstream o

38.1 the river temperature decreased (gen

0.6οC or less) if the release from Rock Cr

WWTP was only 10 Mgal/d. If the release 

Rock Creek WWTP was 20 or 30 Mgal/d
2

peratures downstream of RM 38.1 generally

increased. However, the magnitude of the

increase was generally less than 1.0οC.

* The temperature effect resulting from constant

25, 45, or 65 Mgal/d effluent releases from the

Rock Creek (RM 38.1) and Durham (RM 9.3)

WWTPs was evaluated. Temperatures throughout the reach downstream of Rock Creek

WWTP and, to a lesser extent downstream of

Durham WWTP, increased proportionately.

The magnitude of the increases was as much as

0.6, 1.5, and 2.2οC for the three scenarios,

respectively.

* In another scenario, a cooler water-temperature

data set, representing more shaded “natural”

background conditions, was used as input to the

model upper boundary at Gaston (RM 63.9).

Water temperatures decreased substantially

between RM 63.9 and the confluence with

Scoggins Creek (RM 60.0) by as much as

4.0οC. However, the effect of the temperature

decrease was dampened by the large volume of

colder water flowing from Scoggins Creek as a

result of releases from Henry Hagg Lake. For

most of the reach downstream of RM 60.0, the

overall cooling effect of this scenario was less

than 0.5οC. In a follow-up scenario, the same

model upper boundary condition was used in

conjunction with the “natural” background conditions scenario from an earlier study. Water

temperatures again decreased substantially

between RM 63.9 and the confluence with

Scoggins Creek (RM 60.0). However, between

Scoggins Creek and the Dairy Creek confluence (RM 44.8), water temperatures gradually

increased because the unnaturally cool water

released from Henry Hagg Lake was not

present. However, almost all of the reach above

Rood Bridge (RM 38.4) was still in compliance

with the water-quality standard. Below RM

38.4 temperatures increased (1.0οC or less) for

July and August and decreased for other

months.

* The effect of setting the temperature of effluent

released at RM 38.1 and RM 9.3 equal to the

temperature of the river was evaluated. Temperatures downstream of RM 38.1 decrea

as much as 2.4οC. The reduction then tap

off to 0.5οC upstream of RM 9.3. Downs

of RM 9.3, temperatures decreased by as 

as 1.2οC.

* Another scenario was used to evaluate the 

of releasing a purchased allotment of Sco

Dam flow (up to, but not exceeding 10 M

at RM 38.1 instead of into Scoggins Cree

Observed Scoggins Dam temperature dat

used for the allotted flow. Temperatures

increased for all months except October 

RM 60.0 to RM 38.1 by as much as 0.6οC

However, downstream of RM 38.1, temp

tures decreased from as much as 0.7οC fo

months except October. However, the eff

the supplemental release became less pro

nounced farther downstream.

* The effect of constant effluent releases of 

25, 45, and 65 Mgal/d at two WWTPs (R

38.1 and RM 9.3) was evaluated. The 199

1995 measured effluent temperature data 

the WWTPs were used, except that the te

atures were not permitted to be greater th

17.8οC. For most months, the temperatur

the reach downstream of both WWTPs

decreased in all four scenarios. From RM 

to RM 9.3, the temperature decrease was 

than 1.0οC. Downstream of the Durham

WWTP (RM 9.3), temperatures decrease

almost by 2.0οC.

INTRODUCTION

In 1994, the U.S. Geological Survey (USG

and the Unified Sewerage Agency of Washingt

County, Oregon (USA) began a cooperative stu

better understand water-temperature variations 

Tualatin River and to assess mitigative water-m

ment solutions. Continuous water-temperature 

were collected at locations along the main stem 

river and along the major tributaries during the 

flow periods of 1994 and 1995. The 1994 data 

used to develop and calibrate flow and water-te

ture models characterizing conditions in the ma

stem. The models were used to simulate 10 hyp
3

cal water-management scenarios, which would enable

water managers to understand the effects of various

human activities on water temperatures. Modeling

results from the study are presented in Risley (1997);

the data collected are presented in Risley and Doyle

(1997). This report presents the water-temperature

model simulation results of 16 additional hypothetical

water-management scenarios using the 1994 and 1995

data. The additional modeling was funded by the

USGS and the USA under a cooperative agreement.

For a comprehensive description of the water-temperature models and their underlying assumptions, refer to

Risley (1997).

Background

Water temperature is one of the most important

factors determining the overall health of fish and other

aquatic organisms. If water temperatures warm

beyond a critical threshold, particularly during sensitive life stages of fish, survival can markedly decrease

(Mullane and others, 1995). In the Tualatin River and

many other Oregon streams, the critical water-temperature threshold for many cold-water species is reached

and surpassed during the low-flow periods from May

to October. Under State of Oregon regulations revised

in 1996, for waterways like the main-stem of the Tualatin River, where salmonoid rearing and migration has

been declared a beneficial use, an activity is not permitted to raise the temperature of the receiving water

body if the receiving water body already has exceeded

17.8οC (degrees Celsius) (64οF [degrees Fahrenheit])

(Oregon Administrative Rules [OAR] 340-041-0445

(2) (b) (A) (i)) on the basis of a 7-day moving average

of daily maximum temperatures (OAR 340-41-006

(54), January 11, 1996). In waters and periods of the

year designated by the State to support “native salmonid spawning, egg incubation, and fry emergence from

the egg and from the gravels” a more stringent criterion of 12.8οC (55.0οF) can apply (OAR 340-041-

0445 (2) (b) (A) (iv)).

Oregon Department of Fish and Wildlife

(ODFW) surveys have identified streams in the Tualatin Basin as spawning, rearing, and migration habitat

for winter steelhead, coho salmon, and cutthroat trout

(Oregon Department of Environmental Quality,

unpub. data, 1999). (Although the coho salmon are not

native in the Tualatin Basin, they are now resident

there as a result of the fish ladder at Willamette Falls).

Some streams in the basin also could be rearing and

migration (but not spawning) habitat for spring 

nook. The spawning periods (which includes in

tion and fry emergence) for the winter steelhead

salmon, and cutthroat trout are from mid-Decem

the end of May, mid-October to the end of Febr

and April to the end of June, respectively. Most

not all, of the stream reaches included in this mo

study are along the main stem and have been ide

as rearing and migration habitat. Exceedance o

State temperature standards could occur in mos

this reach if temperatures exceed 17.8οC (64.0ο

However, Scoggins Creek from the Henry Hag

to the Tualatin River, also within the study area

spawning habitat for the three fish species men

Exceedance of the State standards could occur 

reach if temperatures exceed 12.8οC (55.0οF) f

mid-October to the end of June. A reach on the 

atin River from Gaston (RM 63.9) to Wapato C

(RM 61.9) is spawning habitat for the coho salm

and the winter steelhead. Exceedance of the Sta

standards could occur in this reach if temperatu

exceed 12.8οC (55.0οF) from mid-October to th

of May.

The Oregon Department of Environmenta

ity (ODEQ) and the ODFW are in the process o

mining for which streams in the basin spawnin

rearing/migration will be designated as benefic

uses. The ODEQ is using this information to de

total maximum daily loads (TMDLs) for tempe

In compliance with the Federal Clean Water Ac

ODEQ listed the Tualatin River as “water-quali

ited” for temperature in 1998. Once a waterway 

been designated as water-quality limited, TMD

must be developed for that water body to meet 

established water-quality standard. Aside from 

regulations, agencies like the ODEQ, ODFW, a

USA also are concerned about the relationship

between water temperature and fish survival be

winter steelhead and spring chinook were listed 

“threatened” under the Endangered Species Ac

1999 by the U.S. National Marine Fisheries Se

Cutthroat trout also may be listed as “threatene

the near future.

From May through October, the mean tem

ture of wastewater-treatment-plants effluent on 

Tualatin River is approximately 20οC. During J

through September, water temperatures in the l

part of the Tualatin River downstream of Rood 

(river mile [RM] 38.4 to RM 0.0) typically exc

17.8οC criterion. Most point-source discharges 
4

Tualatin River are effluent and urban runoff. Other

human-caused water-temperature modifications

include removal of riparian vegetation (resulting in a

decrease in shading) and reduction of natural baseflows caused by timber harvesting, agriculture, and

urban development. During some months of the year,

flow releases from Scoggins Dam can decrease the

temperature in the main river body. However, only

after the separate impacts of these human-caused

factors have been more clearly quantified and characterized will it be possible to develop cost-effective

remedial measures to the problem.

Purpose and Scope

The objectives of the USGS-USA cooperative

water-temperature study were to (1) quantify the temporal and spatial patterns of water temperature in the

main stem of the Tualatin River and the mouths of its

major tributaries, (2) determine the relation of water

temperature in the Tualatin River and its major tributaries to climatic conditions, seasonal and daily variations, and human-caused factors, and (3) assess the

effects of various flow-management practices on water

temperature during the low-flow season (May through

October).

This report provides a brief description of the

data-collection network and the simulation models

used in the study, a description of the 1995 model simulation (not included in the initial study report [Risley,

1997]), and the results of additional simulations of

hypothetical water-management scenarios (also not

included in the initial study report). The current USGS

Tualatin water-temperature-modeling activities are a

component of a broader, ongoing USGS-USA cooperative water-quality study of the Tualatin River. Additional information about these studies and their

publications can be found at http://oregon.usgs.gov/

projs_dir/pn356/.

Description of the Study Area

The Tualatin River, a major tributary to the Willamette River, is located in northwestern Oregon west

of Portland (fig. 1). The 712-square-mile (mi2

) basin is

bounded by the Coast Range on the west and northwest, the Tualatin Mountains on the east and northeast, and the Chehalem Mountains on the south. The

study reach extended from Gaston (RM 63.9) to the

Oswego diversion dam (RM 3.4) and had an ap

mate 80-foot change in elevation. The study rea

regulated system. Completion of Scoggins Dam

Scoggins Creek, in the early 1970s created Hen

Hagg Lake. With the exception of the reach 2 t

miles below RM 63.9, most of the study reach 

and meandering. Major tributaries to the Tualat

River include Scoggins, Gales, Dairy, Rock, an

Fanno Creeks. The study area has a modified-m

climate, with annual precipitation averaging ab

inches per year; minimum and maximum air te

tures average between 0 and 17οC (32 and 62οF

ing the winter and between 5 and 28οC (42 and 

during the summer. Approximately 50 percent 

drainage basin is forestland, 35 percent is used 

agriculture, and 15 percent is urbanized. Urban 

opment is expanding in the eastern and central r

of the basin. Vegetation along the study reach i

nated by white oak, ash, and cottonwood, with 

understory of grass and shrubs. Some coniferou

mostly Douglas firs, border the river in the low

tion of the study reach. Most soils in the study 

can be characterized as silt loams and loams th

moderately well-drained and generally contain 

rally high concentrations of phosphorus.

As agriculture and urban development gre

ing the 20th century, the Tualatin River came u

increasing flow regulation. In addition to the flo

mentation provided by Henry Hagg Lake, flow

headwaters of the Tualatin River are augmented 

diversion from the Trask River Basin, which is l

on the western side of the Coast Range Mounta

the Springhill Pumping Plant (RM 56.1), withd

are made for both irrigation by the Tualatin Val

gation District and municipal and industrial wa

by the Joint Water Supply Commission. Additi

irrigation withdrawals are taken directly from th

by users at numerous locations along the main 

Flows from Gales Creek and Dairy Creek are u

lated and predominately from farmland and for

drainage. Rock Creek flow is from a mixture of 

cultural and urban drainage. Most of Fanno Cre

flow is from urban drainage. During the summe

1994 and 1995, the two principal USA-operate

WWTPs, at Rock Creek (RM 38.1) and Durham 

9.3), each discharged an average of approximat

ft3

/s (18 million gallons per day [Mgal/d]) of tr

effluent into the river. At RM 6.7, a gravity flow 

(Oswego Canal) diverts approximately 60 ft3

/s 

water from the Tualatin River to Lake Oswego

flow through the canal is enabled by the Osweg
5

RIVER

WILLAMETTE

Tigard

Durham

King

City

W

L

Beaverton

Tualatin

Lake

Oswego

Sherwood

Scholls

Farmington

Hillsboro

Cornelius

Dilley

Forest

Grove

Cherry

Grove

Gaston

26 5

5

205

Scoggins Creek

Creek

Wapato

Henry

Hagg

Lake

Gales

Creek

Dairy Creek McKay

Tanner

Creek

Sain

Creek

Creek

Creek

Fanno

Creek

Beaverton Creek

Creek

Rock

Bronson

Butternut Cr

Christensen Creek

Burris Creek

McFee

Creek

Heaton Cr

Cr

Baker

Rock

Creek

Chicken Creek

Cr

Cedar Mill

Nyberg

LakeOswego

Cr

Oswego

Canal

TUALATIN

RIVER

TUALATIN RIVER

Base modified from U.S. Geological Survey

1:100,000, topographic quadrangles, 1978-84 0

0 5 10 KILOMETERS

5 10 MILES

Portland

O R E G O N

Study

area

RM

60

RM

30

RM

40

RM

50

RM

10

RM

20

RM0

45o 30'

45o 22' 30''

123o 15' 123o 00' 122o 45' 1

1

2

4

3

5

6

7

8

9

11

12

10

13

14

15

16

17

18

19

12 Sampling site and map number —See table 1

1 Tualatin River near Gaston

2 Scoggins Creek below Henry Hagg Lake, near 

Gaston

3 Tualatin River near Dilley

4 Gales Creek at Route 47 at Forest Grove

5 Tualatin River at Golf Course Road

near Cornelius

6 Dairy Creek at Route 8 near Hillsboro

7 Tualatin River at Rood Bridge at Hillsboro

8 Rock Creek near Hillsboro

9 Rock Creek Wastewater-Treatment Plant near 

Hillsboro

10 Tualatin River at irrigation pumphouse at 

Meriwether Golf Course

11 Tualatin River at Farmington

12 Tualatin River near Scholls

13 Tualatin River near Tualatin

14 Durham Wastewater-Treatment Plant near Durham

15 Fanno Creek at Durham

16 Tualatin River at Oswego Canal at Tualatin

17 Oswego Canal near Lake Oswego

18 Tualatin River at Oswego diversion dam near 

West Linn

19 Tualatin River at West Linn

EXPLANATION

Figure 1. The Tualatin River Basin, Oregon. (RM, river mile)

diversion dam on the Tualatin River near West Linn at

RM 3.4.

DATA COLLECTION

Continuous water-temperature and streamflow

data were collected in 1994 and 1995 from May 1 to

November 30 at 19 fixed-station continuous-monitoring sites established by the USGS, Oregon Water

Resources Department (OWRD), and other agencies

(fig. 2 and table 1). Meteorological data used as 

to the models included air temperature, wind sp

and solar radiation collected at three locations in 

study reach. Additional input data included dew

temperature, wind direction, and precipitation c

lected at the Hillsboro Airport. Data used for co

ing the model parameters included bathymetric,

channel cross-section, and riparian shading mea

ments. Risley and Doyle (1997) described the d

collection equipment, data-collection protocols, 

quality-assurance protocols used in the study.
6

Water Temperature

Continuous water-temperature measurem

were recorded half hourly by the USGS at 13 lo

on the main stem of the Tualatin River (RM 63

RM 3.4) and on major tributaries near their mo

USA also measured and recorded half hourly e

temperature data at the Rock Creek and Durham

WWTPs. Temperature probes used by the USA 

WWTPs were checked by the USGS with certi

temperature probes during both seasons. Correc

shifts were applied to the USA data before they 

used in the modeling.

Streamflow

Streamflow data were collected by the US

and OWRD at locations in the Tualatin River Ba

this and other studies. Flow data collected at ni

stream-gaging stations were used as upstream b

aries to the models. Data from six other station

the main stem within the study reach, were use

calibrate the flow models. The data were collec

USGS and OWRD according to standardized te

niques of the USGS (Rantz and others, 1982). T

USGS-operated streamflow-gaging stations inc

Scoggins Creek below Henry Hagg Lake near G

(14202980), Tualatin River near Dilley (14203

Fanno Creek at Durham (14206950), and Tuala

River at West Linn (14207500). The remaining 

tions used in the simulations were operated by

OWRD. In addition to the streamflow-gaging st

stage data were recorded by OWRD on the Tua

River at the Oswego Canal (14206990). Althoug

computations were not made for this station, th

data were used in determining the approximate 

level of the river during the calibration simulati

Hourly effluent flow measurements from both t

Rock Creek and Durham WWTPs were made a

recorded by the USA. These data also were use

boundary conditions for the simulations.

Riparian Shading

Riparian shading data were compiled from 

cross-section surveys, aerial photography, and t

graphic maps. Because of the high level of vari

in riparian shading along stream reaches, estab

field techniques (Bartholow, 1989) were used to 

Figure 2. Relative positions of selected tributaries, fixedstation continuous-monitoring sites, and wastewatertreatment plants, Tualatin River Basin, Oregon, 1994–95.

EXPLANATION

Wastewater-treatment plant (WWTP) discharge

Tributary inflow or withdrawal

Fixed-station continuous-monitoring sites

60.0 River mile—measured from mouth of Tualatin River

Henry Hagg

Lake

(Scoggins Dam)

14202500

14203500

14204800

14204530

14206200

14206440

14206450

452938122565500

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

14202980

Rock Creek WWTP

Fanno Creek

14206500

14206700

14206800

452359122454500

63.9

60.0

58.8

56.7

51.5

44.8

38.4

38.1

33.3

23.2

10.0

9.3

Willamette River

0.0

14206950

14207000

14206990

6.7 Oswego Canal

Oswego diversion dam 3.4

1.8 14207500

Durham WWTP

14207200

56.1

14204650

Springhill

36.8 14206460

Joint Water Commission

Pumping Tualatin Valley Irrigation District

Plant
7

Table 1. U.S. Geological Survey fixed-station continuous-monitoring sites in the Tualatin River Basin, Oregon,

1994–95

[D, Discharge; WT, water temperature; AT, air temperature; WS, wind speed; SR, solar radiation; ---, data not collected]

Site Station Station location River Data collected

number Station name number Latitude Longitude mile D WT AT WS 

1 Tualatin River 14202500 45o26’15" 123o10’05" 63.9 X X --- --- 

near Gaston

2 Scoggins Creek 14202980 45o28’10" 123o11’56" 4.3 X X --- X 

below Henry Hagg

Lake, near Gaston

3 Tualatin River 14203500 45o28’30" 123o07’23" 58.8 X X --- --- 

near Dilley

4 Gales Creek 14204530 45o

30’39" 123o06’52" 1.5 X X --- --- 

at Route 47

at Forest Grove

5 Tualatin River 14204800 45o30’08" 123o03’18" 51.5 X X X --- 

at Golf Course Road

near Cornelius

6 Dairy Creek 14206200 45o31’12" 123o00’34" 2.1 X X --- --- 

at Route 8

near Hillsboro

7 Tualatin River 14206440 45o

29’25" 122o57’01" 38.4 X X --- --- 

at Rood Bridge

at Hillsboro

8 Rock Creek 14206450 45o30’09" 122o56’48" 1.2 X X X --- 

near Hillsboro

9 Rock Creek 45293812- 45o

29’38" 122o56’55" 38.1 X X --- X 

Wastewater-Treatment 2565500

Plant near Hillsboro

10 Tualatin River at 14206460 45o28’42" 122o56’24" 36.8 --- X1 X1 --- 

irrigation pumphouse at

Meriwether Golf Course

near Hillsboro

11 Tualatin River 14206500 45o27’00" 122o57’00" 33.3 X X2 --- --- 

at Farmington

12 Tualatin River 14206700 45o

23’39" 122o53’51" 23.2 --- X X1 --- 

near Scholls

13 Tualatin River 14206800 45o23’28" 122o46’22" 10.0 --- X --- --- 

near Tualatin

14 Durham 45235912- 45o

23’59" 122o45’45" 9.3 X X X2 X 

Wastewater-Treatment 2454500

Plant near Durham

15 Fanno Creek 14206950 45o24’13" 122o45’13 " 1.1 X X --- --- 

at Durham

16 Tualatin River 14206990 45o22’57” 122o43’12" 6.7 X3 --- --- --- 

at Oswego Canal

at Tualatin

17 Oswego Canal 14207000 45o23’20 " 122o43’10" .4 X --- --- --- 

near Lake Oswego

18 Tualatin River at 14207200 45o21’24" 122o41’02" 3.4 --- X X --- 

Oswego diversion dam

near West Linn

19 Tualatin River 14207500 45o21’03" 122o40’30" 1.8 X -- --- --- 

at West Linn

1Data collected in 1995 only. 2Data collected in 1994 only. 3Stage-recording station only.
8

mize data collection, assuring that sufficient data were

collected within project resources. Field equipment

included a hand held clinometer, a distance range

finder, a light meter, and measuring tapes. Collected

shading parameters included average vegetation

height, crown measurement (average tree width), average vegetation offset, vegetation density, stream

width, and bank height. The most significant obstruction of solar radiation on the water surface of the Tualatin River is vegetation. Because of the flatness of the

Tualatin Valley, topographic blockage of radiation in

the study area was generally limited to the height of

the stream bank.

Aerial photography was used to determine the

approximate canopy thickness and vegetation density

of both banks of each stream segment. The canopy

thickness of each segment was categorized as (1) no

vegetation, (2) single row vegetation with approximately 50 percent crown closure, (3) single row vegetation with approximately 100 percent crown closure,

(4) thick double row vegetation, and (5) completely

wooded areas. Additional details regarding the riparian shading field surveying are documented in Risley

(1997).

COMPUTER MODELS

The Stream Network Temperature (SNTEMP)

model estimated riparian shading coefficients for the

full study reach (RM 63.9 to RM 3.4) (Theurer and

others, 1984); the Diffusion Analogy Flow

(DAFLOW) model and the Branched Lagrangian

Transport Model (BLTM) simulated flow and heat

transport in the upper river section (RM 63.9 to RM

38.4) Jobson and Keefer, 1979; Jobson, 1981; Jobson

and Schoellhamer, 1987; Jobson, 1989 and Jobson,

1997; and the CE-QUAL-W2 model simulated flow

and heat transport in the lower river section (RM 38.4

to RM 3.4) (Cole and Buchak, 1995). Riparian shading coefficients estimated by the SNTEMP model

were used as input data for the flow and heat-transport

models used in both the upper and lower river sections. The full study reach (RM 63.9 to RM 3.4) was

divided into an upper and a lower river section,

because flow conditions in each section warranted

using different models. Streamflow in the upper river

section above Rood Bridge (RM 38.4) is vertically

well mixed throughout the year. However, the river at

pool locations below Scholls Bridge (RM 26.9) can

become thermally stratified during low-flow periods.

A one-dimensional flow and heat-transport mod

selected for the upper river section, and a two-d

sional laterally averaged flow and heat-transpor

model was selected for the lower river section. 

more information on the computer models used 

study, refer to Risley (1997).

Shading Coefficients

The shading algorithms in the SNTEMP m

(Theurer and others, 1984) were used in this stu

estimate solar-radiation-weighted riparian shad

resulting from both topography and vegetation.

Monthly mean shading coefficients (from May

through October) were estimated for approxim

270 stream segments within the full study reach 

63.9 to RM 3.4).

Variations in topography and vegetation o

side of the stream are taken into account in the m

computations. Although the algorithms took in

account variations in solar radiation for each ca

day, the model output was lumped into monthly 

values. Required input data, which were collec

the field, for the shading model include (1) Juli

endar date, (2) site latitude, (3) stream segment 

muth (general orientation of the stream segmen

respect to due south), (4) topographic altitude a

sides), (5) vegetation height (both sides), (6) cr

measurement (both sides), (7) vegetation offset 

sides), (8) vegetation density (both sides), and 

stream width.

Upper River Section

DAFLOW and BLTM, used for the Gasto

63.9) to Rood Bridge (RM 38.4) river reach, ar

and heat-transport models, respectively, develop

maintained by the USGS (fig. 3). The models h

been used in various surface-water and water-q

studies (Jobson and Keefer, 1979; Jobson, 1981

son, 1989). The two models are typically used 

junctively. The output file from DAFLOW cont

half-hourly flow (for this study), cross-sectiona

width, and tributary flows and was used as inpu

BLTM.

DAFLOW is an unsteady-state (dynamic)

dimensional (longitudinal), streamflow-routing 

based on a simplified version of the momentum 

tion. DAFLOW uses a Lagrangian solution sch
9

such a scheme uses a computational x-coordina

erence frame that moves with the flow rather th

remaining at a fixed grid location. Further detai

the numerical methods have been described by 

(1989).

BLTM is a one-dimensional transport (wa

quality) model capable of simulating the transp

solutes and/or heat in branched river systems. B

solves the convective-dispersion equation using 

Lagrangian reference frame in which the comp

tional nodes move with the flow. One-dimensio

transport theory is explained in more detail in t

BLTM’s user’s manual (Jobson and Schoellham

1987; Jobson, 1997).

In this study the river main stem between 

(RM 63.9) to Rood Bridge (RM 38.4) was divid

89 stream segments. Additional stream segmen

used to define the adjoining reaches of Scoggin

Gales, and Dairy Creeks. The net heat-transfer 

through the water surface was simulated for ev

stream segment on a half-hourly basis. This is d

in BLTM as:

Hn = -K (T - Te), 

where

Hn is the net heat-transfer rate,

K is the heat-exchange coefficient,

T is the water temperature, and

Te is the equilibrium temperature.

Half-hourly incoming shortwave solar rad

wind speed, air temperature, and dewpoint-tem

ture data were used to compute the heat-exchan

coefficient and equilibrium temperatures at eac

stream segment for every half-hour time step. T

account for variations in riparian shading along 

stream, the incoming shortwave solar radiation 

given stream segment was reduced by the mont

riparian shading coefficient estimated by the

SNTEMP model for that stream segment by us

following equation:

S = Sm(1 - RS), 

where

S is incoming shortwave solar radiation reduc

riparian shading,

Sm is measured incoming shortwave solar radi

and

RS is the monthly riparian shading coefficient.

Figure 3. Diffusion Analogy Flow/Branched Lagrangian

Transport Model configuration for the Tualatin River from

river mile 63.9 to river mile 38.4.

6

2

1

4

8

3

6

4

7

8

5

9

10

1

7

5

3

2

9

61.9

 63.9

60.5

2.0

4.8

2.4

60.0

59.6

59.1

57.5

56.7

56.1

53.4

52.9

49.4

47.7

44.8

41.5

38.4

Scoggins Creek

Gales Creek

Dairy Creek

EXPLANATION

1

7

Model branch number

Model junction number

Withdrawal

Inflow

2.1

53.4 River mile—measured from mouth

of tributary or Tualatin River

Gaston

Irrigation

Irrigation

 Irrigation

Irrigation

 Irrigation

 Irrigation

Irrigation

Irrigation

Scoggins

Old Hwy 47 near

Route 8

near

Hillsboro

Rood Bridge

Dam

Forest Grove

TVID and JWC

withdrawal1

1 Tualatin Valley Irrigation District and Joint Water

Commission (both located at the Springhill

pumping plant).
10

Output from DAFLOW and BLTM includes

simulated half-hourly Rood Bridge flow and watertemperature data files, respectively. These files are

used as upper boundary input data to the lower river

section model.

Lower River Section

CE-QUAL-W2 is a two-dimensional, laterally

averaged, hydrodynamic water-quality model used for

the Rood Bridge (RM 38.4) to Oswego diversion dam

(RM 3.4) reach, developed and maintained by the

Waterways Experiment Station of the U.S. Army

Corps of Engineers in Vicksburg, Mississippi (fig. 4;

Cole and Buchak, 1995). The version of CE-QUALW2 used in this study contains modifications made for

another USGS Tualatin River water-quality modeling

study (Rounds and others, 1998). Some additional

modifications specific to the water-temperature study

have been documented in Risley (1997).

CE-QUAL-W2 is a dynamic model capable of

simulating water flow, heat flow, and water quality.

Both hydrodynamics and water quality are simulated

within the same model. CE-QUAL-W2 uses the laterally averaged equations of fluid motion derived from

three-dimensional governing equations. Because of

the complexity of the governing equations, it is necessary to use advanced numerical-solution techniques.

The model uses a variable time-step algorithm that is

designed to ensure the mathematical stability of the

numerical methods. The time steps were generally less

than 30 minutes.

The two dimensions simulated are longitudinal

(along the length of the water body) and vertical. The

model is well suited for narrow lakes and reservoirs

that have minimal variation from side to side but tend

to stratify. During low-flow periods the main stem

reach from Rood Bridge (RM 38.4) to the Oswego

diversion dam (RM 3.4) can be characterized as a reservoir. Using CE-QUAL-W2, the main stem was configured as a single model branch and subdivided into

153 stream segments. The number of layers varied

with each segment. Although the user can select simulated temperature output from any layer, all simulated

temperatures presented in this report were based on

a volume-weighted 10-foot vertical average. The

10-foot water column, rather than the entire water

column, was used to avoid possible distortions caused

by occasional deep pools (containing cooler waters) in

the river.

Figure 4. CE-QUAL-W2 model configuration for t

Tualatin River from river mile 38.4 to river mile 3.4

38.1 Rock Creek and RC WWTP

35.7 Butternut Creek

33.5 Irrigation withdrawal

31.9 Christensen Creek

Burris Creek 31.6

Baker and McFee Creeks 28.2

15.2 Rock (S) and Chicken Creeks

9.3 Fanno Creek and Durham WWT

Nyberg Creek 7.5

6.7 Oswego Canal

Irrigation withdrawal 28.5

Irrigation withdrawal 23.4

Irrigation withdrawal 18.4

13.4 Irrigation withdrawal

8.6 Irrigation withdrawal

Irrigation withdrawal 3.6

33.3 Farmington Road

38.4 Rood Bridge

26.9 Scholls Bridge

16.2 Elsner Road

11.6 Hwy 99W

10.0 Cook Park

8.7 Boones Ferry Road

5.5 Stafford Road

3.4 Oswego diversion dam

EXPLANATION

Withdrawal

Inflow

26.9 River mile—measured from

mouth of Tualatin River

Scholls, Oregon 23.2
11

For the temperature study, the CE-QUAL-W2 heat

budget subroutine was modified to compute the net

heat-transfer rate through the water surface for every

stream segment and every time step using the term-byterm energy equation. The equation is defined in the following:

Hn = Hs + Ha + He+ Hc - (Hsr + Har + Hbr), (3)

where

Hn is the net heat-transfer rate through the water

surface,

Hs is incoming shortwave solar radiation,

Ha is incoming long-wave (atmospheric) solar

radiation,

He is evaporative heat loss,

Hc is air/water surface heat conduction

Hsr is reflected shortwave solar radiation,

Har is reflected long-wave solar radiation, and

Hbr is long-wave back radiation of the water surface.

Time-varying input data required for the model

included flow, water temperature, shortwave solar radiation, wind speed, wind direction, air temperature, and

dewpoint temperature. The time-varying flow and

water-temperature data were assigned as boundary conditions for the main branch and each of the tributaries.

To account for variations in riparian shading along the

stream, the incoming shortwave solar radiation for a

given stream segment was reduced by the riparian

shading coefficient estimated by the SNTEMP model

(equation 2).

MANAGEMENT SCENARIO SIMULATIONS

The focus of the water-temperature study was a

better understanding of spatial and temporal water-temperature variations in the Tualatin River. The development and calibration of water-temperature models, and

the simulation of 10 initial hypothetical water-management scenarios using flow and water-temperature data

collected from May to November 1994 were reported in

Risley (1997). The scenarios enable water managers to

understand the effects of various human activities on

water temperatures. After completion of the study, the

calibrated models were used to simulate 16 additional

management scenarios using both 1994 and 1995 data.

1995 Model Simulation

In the 1995 simulation, all model paramete

channel hydraulic coefficients, and riparian shad

coefficients were set to the same values as those 

for the 1994 calibration. Comparisons of observe

simulated hydrographs from May through Octobe

at Dilley (RM 58.8), Golf Course Road (RM 51.

Rood Bridge (RM 38.4) are shown in figure 5. C

isons of observed and simulated water temperatu

the same time period at Dilley (RM 58.8), Golf C

Road (RM 51.5), Rood Bridge (RM 38.4), Meriw

Golf Course (RM 36.8), Scholls (RM 23.2), Coo

(RM 10.0), and the Oswego diversion dam (RM 3

shown in figure 6. Because 1995 was climatically 

ent from 1994, its simulated water temperatures 

not expected to match its 1995 observed water-te

ture data as well as the 1994 calibration. The gre

differences between simulated and observed tem

tures were during transition months of May and 

ber. However, the timing of simulated daily maxi

and daily minimum temperatures appears to mat

timing of the observed data at all seven sites. The 

mean square errors (an indication of model accur

between the observed and simulated daily mean 

temperatures at selected sites for 1994 and 1995

monthly and 6-month periods are shown in table 

1995 simulation errors were larger than the 1994 

lation errors. However, many of the errors were u

0.5οC. This margin of error was considered acce

(the USGS does not publish temperature data wi

accuracy greater than 0.5οC).

Monthly mean water-temperature data colle

the Oswego diversion dam from May to Novemb

the years 1991 to 1998 are shown in table 3. Mon

mean air temperature and monthly precipitation 

collected at the Hillsboro Airport for the years 19

1998 are shown in table 4 and 5, respectively. Fo

water and air temperature, the differences betwee

1994 and 1995 monthly mean data are approxim

1οC or less (with the exception of November). Th

and 1995 monthly mean values were also close t

year mean of monthly mean values for both wate

air temperature. Although the 1994 and 1995 tem

tures were close to each other, 1995 was wetter (

thus cloudier) for 5 out of the 7 months (May to N

ber) and had less shortwave solar radiation.
12

May June July August September Oct

1995

0

250

50

100

150

200

OBSERVED

SIMULATED

A. Dilley, Or

(1420350

May June July August September Oct

1995

0

500

100

200

300

400

DISCHARGE, IN CUBIC FEET PER SECOND

May June July August September Oct

1995

0

1,000

200

400

600

800

B. Golf Course R

near Cornelius, O

(14204800)

C. Rood Brid

at Hillsboro, Ore

(14206440)

Figure 5. Observed and simulated discharge from May through October 1995 in the Tualatin River, Oregon.
13

May June July August September Octob

1995

4

28

6

8

10

12

14

16

18

20

22

24

26

TEMPERATURE, IN DEGREES CELSIUS

OBSERVED

SIMULATED

May June July August September Octob

1995

4

28

6

8

10

12

14

16

18

20

22

24

26

TEMPERATURE, IN DEGREES CELSIUS

A. Dilley, Oregon

(14203500)

B. Golf Course Road

near Cornelius, Oregon

(14204800)

Figure 6. Observed and simulated water temperatures from May through October 1995 in the Tualatin River, Oregon.
14

May June July August September Octob

1995

4

28

6

8

10

12

14

16

18

20

22

24

26

TEMPERATURE, IN DEGREES CELSIUS

OBSERVED

SIMULATED

May June July August September Octob

1995

4

28

6

8

10

12

14

16

18

20

22

24

26

TEMPERATURE, IN DEGREES CELSIUS

C. Rood Bridge

at HIllsboro, Oregon

(14206440)

D. Meriwether Golf Course

near Hillsboro, Oregon

(14206460)

Figure 6. Observed and simulated water temperatures from May through October 1995 in the Tualatin River, Oregon—C
15

May June July August September Octob

1995

4

28

6

8

10

12

14

16

18

20

22

24

26

TEMPERATURE, IN DEGREES CELSIUS

OBSERVED

SIMULATED

May June July August September Octob

1995

4

28

6

8

10

12

14

16

18

20

22

24

26

TEMPERATURE, IN DEGREES CELSIUS

E. Scholls, Oregon

(14206700)

F. Cook Park

 (14206800)

Figure 6. Observed and simulated water temperatures from May through October 1995 in the Tualatin River, Oregon—C

near Tualatin, Oregon
16

May June July August September Oct

1995

4

28

6

8

10

12

14

16

18

20

22

24

26

TEMPERATURE, IN DEGREES CELSIUS

OBSERVED

SIMULATED

G. Oswego diversion dam

near West Linn

(14207200)

Figure 6. Observed and simulated water temperatures from May through October 1995 in the Tualatin River, Oregon—C

Previous Scenarios

The hypothetical water-management scenarios

documented in Risley (1997) are listed in table 6. In

addition to existing conditions, the other scenarios

included various changes in Henry Hagg Lake operation, riparian shading along the main stem, WWTP

operation, and Oswego diversion dam operation. For

each scenario, plots showing the monthly mean (May

through October) of the 7-day moving average of daily

maximum simulated water temperatures along the

main-stem of the river were created. The 7-day moving

average of daily maximum water temperatures is plotted because it is the statistic used by the 1996 State of

Oregon water-temperature standard. Plots showing the

monthly mean of the 7-day moving average of daily

maximum simulated and observed 1994 and 1995

water temperatures for existing conditions (scenario 1)

are shown in figures 7 and 8, respectively.

Both figures 7 and 8 show the usual sudden cooling effect on the river caused by releases from Henry

Hagg Lake. (An exception to this was in October 1994

when the lake was drawn down and the temperature of

Scoggins Creek was higher than that of the river.) As

water moves downstream, there is a general war

trend in most months. The plots also show the p

nounced effect of warmer discharge from the m

tributaries and the Rock Creek and Durham WW

For most of the months in the plots, there is a no

able drop in temperature at Rood Bridge (RM 3

This apparent temperature decrease is an artifact 

minor instabilities in the numerical solution of th

erning equations of CE-QUAL-W2 caused by th

inflow of significantly warmer water from Rock 

WWTP just downstream of RM 38.1. The plots 

show erratic temperature fluctuations in the lowe

section below RM 27.0. From this location down 

Oswego diversion dam (RM 3.4), the river is mo

ervoir-like and can become thermally stratified i

some locations. Being a two-dimensional model

QUAL-W2 accounts for thermal stratification an

channel depth variations in the simulation. Dips 

graphs correlate to known shallow locations in t

river. The model simulates the upwelling of coo

waters from the lower layers in the pools just up

of the shallow sills. Thus, the water flowing ove

sills is simulated as cooler than water in the poo

Because flows are better mixed above RM 27.0, 
17

1

 Root mean square error =

Table 2. Root mean square error between observed and simulated daily mean water temperatures at sites on the Tua

from May through October 1994 and 19951.

[RM = river mile; ---, no data collected; Tobs, observed daily mean water temperature; Tsim, simulated daily mean water temperature; and Sept., 

Oct. October. A smaller root mean square error is an indication of more accurate model performance]

1994 1995

Site May June July August Sep-. Oct.

6-

month

period May June July August Sept. O

Dilley

(RM 8.8)

0.729 0.568 0.300 0.316 0.273 0.416 0.464 2.540 2.159 0.771 0.722 1.509 20

Golf Course

Road

(RM 51.5)

.482 .465 .220 .234 .425 .626 .436 2.316 1.613 .616 .517 .920 1.9

Rood Bridge

(RM 38.4)

.365 .377 .475 .364 .438 .690 .466 .515 .560 .486 .614 .583 1.

Meriwether

Golf Course

(RM 36.8)

--- --- --- --- --- --- --- .690 .462 .335 .452 .430 1.0

Farmington

(RM 33.3)

.299 .231 .328 .149 .203 .306 .261 --- --- --- --- --- -

Scholls

(RM 23.2)

.554 .673 .887 .848 .494 .666 .703 1.188 1.395 .657 .752 .806 1.2

Cook Park

(RM 10)

.421 .682 .277 .339 .860 .405 .535 .694 .742 .809 .642 1.010 .3

Oswego

diversion

dam

(RM 3.4)

.334 .612 .425 .612 .477 .449 .476 .713 .651 .574 .353 .664 .4

1

N

---- 〈 〉 Tobs Tsim – 2

n = 1

N

∑

Table 3. Water temperature data from the Oswego diversion dam (at river mile 3.4) near West Linn, Oregon, for 1991–

[All values are in degrees Celsius. Values in first eight rows are monthly mean temperatures. Values in the ninth row are means of the first

eight rows.; --- = missing data. Shaded cells indicate model simulation periods]

Year May June July August September October November

1991 --- 16.2 21.2 21.4 18.3 14.2 9.8

1992 17.0 20.9 21.5 21.4 17.9 14.5 10.0

1993 15.3 17.3 18.8 20.8 --- 14.4 8.5

1994 15.9 18.3 22.0 --- 18.7 14.3 ---

1995 --- 18.4 22.1 20.1 18.6 14.2 10.8

1996 --- 17.8 21.2 20.7 16.7 13.9 8.8

1997 16.4 18.0 20.9 21.8 17.8 13.0 10.3

1998 14.5 18.0 21.4 21.7 19.1 14.1 10.7

8-year

mean

--- 18.1 21.1 --- --- 14.1 ---
18

Table 4. Air temperature data from the Hillsboro Airport near Hillsboro, Oregon, 1991–98

[All values are in degrees Celsius. Values in first eight rows are monthly-mean temperatures. Values in the ninth row are means of the first eight

rows. Values in the last row are mean-monthly temperatures from 1948 to 1998. Source: Oregon Climate Service. Shaded cells indicate model

simulation periods]

Year May June July August September October November

1991 11.8 14.8 19.3 20.0 18.0 12.0 7.9

1992 15.8 18.7 20.2 19.8 15.7 12.7 7.3

1993 15.6 15.9 16.6 19.2 17.4 13.2 3.7

1994 14.6 15.9 20.2 19.2 18.3 10.5 4.5

1995 15.3 16.7 20.6 18.2 18.4 11.4 10.0

1996 12.4 16.6 21.8 20.1 15.5 11.4 6.7

1997 16.6 16.9 20.2 21.2 17.9 11.7 11.6

1998 14.4 18.7 22.3 21.6 19.6 12.9 10.1

8-year

mean

14.6 16.8 20.2 19.9 17.6 12.0 7.7

Long-term

mean

13.3 16.5 19.2 19.1 16.5 11.6 7.3

Table 5. Precipitation data from the Hillsboro Airport near Hillsboro, Oregon, 1991–98

[All values are in inches. Values in first eight rows are monthly precipitation. Values in the ninth row are means of the first eight rows. Values in t

are mean-monthly precipitation from 1930 to 1998. Source: Oregon Climate Service. Shaded cells indicate model simulation periods]

Year May June July August September October November

1991 2.34 1.70 0.25 0.65 0.39 1.66 5.66

1992 .13 .36 .77 .31 1.21 2.47 4.54

1993 3.52 2.68 1.49 .16 .00 1.08 1.26

1994 1.15 .94 .00 .42 .60 4.52 7.02

1995 1.43 1.80 .98 .39 1.57 2.91 7.74

1996 4.34 .97 .58 .13 2.96 4.22 8.70

1997 1.81 2.30 .29 1.47 3.01 5.52 5.98

1998 4.77 1.49 .07 .00 .90 2.84 11.01

8-year

mean

2.44 1.53 .554 .441 1.33 3.15 6.49

Long-term

mean

1.82 1.43 .465 .732 1.46 3.05 5.69
19

Table 6. Hypothetical water-management scenarios from the initial modeling study (Risley, 1997)

[USA, Unified Sewerage Agency; Mgal/d, million gallons per day; WWTP, wastewater-treatment plant]

_____________________________________________________________________________________________

Scenario Title Description

number

_____________________________________________________________________________________________

 1 Existing conditions Observed and simulated 1994 and 1995 meteorologic, flow, shade, and

hydraulic data were used as input to the models to determine spatial

and temporal temperature variations along the main stem of the river.

Mean effluent released from each WWTP from May to October for both

years was approximately 18 Mgal/d.

 2 Existing conditions Existing conditions used in scenario 1 were simulated except allotted

without USA allotted flows flows for the USA were not released from Henry Hagg Lake reservoir.

 3 “Natural” conditions No flow augmentation from Trask River was provided. Both Henry

Hagg Lake reservoir and the low-head diversion dam at RM 3.4 were

assumed to not exist. No withdrawals for irrigation, urban water supply,

or the Oswego Canal were made. No effluent was released from

wastewater-treatment plants. Maximum possible shading along the

main stem and tributaries was assumed.

 4a No shading Existing conditions used in scenario 1 were simulated except no

vegetative shading along the main stem and the tributaries was used.

 4b Maximum shading Existing conditions used in scenario 1 were simulated except maximum

possible vegetative shading along the main stem and the tributaries

was used.

 5 Existing conditions Existing conditions used in scenario 1 were simulated except the

without low-head low-head diversion dam at RM 3.4 was assumed to not exist.

diversion dam at RM 3.4

 6 Existing conditions with Existing conditions used in scenario 1 were simulated except the

tributary temperature temperatures of all upstream tributary boundaries, except Scoggins

reduction Creek, were reduced by 2 degrees Celsius.

 7 Existing conditions Existing conditions used in scenario 1 were simulated except no effluent

without WWTPs was released from either the Rock Creek or Durham WWTPs.

 8 Existing conditions Existing conditions used in scenario 1 were simulated except allotted

without USA allotted flows, flows for the USA were not released from Henry Hagg Lake reservoir,

lower section withdrawals, withdrawals for irrigation and the Oswego Canal were not made in

and WWTPs the lower stream section, and no effluent was released from either the

Rock Creek or Durham WWTPs.

 9 Existing conditions Existing conditions used in scenario 1 were simulated except the lowwithout low-head head diversion dam at RM 3.4 was assumed to not exist and no effluent

diversion dam at RM 3.4 releases were made from either the Rock Creek or Durham WWTPs.

and WWTPs

10 Existing conditions with Existing conditions used in scenario 1 were simulated except the

tributary temperature temperatures of all upstream tributary boundaries, except Scoggins

reduction and without Creek, were reduced by 2 degrees Celsius and no effluent was released

WWTPs from either the Rock Creek or Durham WWTPs.

_____________________________________________________________________________________________

plotted lines for each month are smoother for the upper

and middle sections of the river’s main stem.

Additional Scenarios

In the current study, the flow and water-temperature models have been used to simulate an additional

16 hypothetical water-management scenarios (S

ios 11 through 26). Unlike the scenarios publish

viously (Risley, 1997), the additional scenarios 

simulated for the May through October periods o

1994 and 1995. A brief description of each of th

narios is provided in table 7. Additional discuss

pertaining to the purpose of the scenarios and th

simulation results are shown in this section.
20

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

261012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAY SIMULATEDJUNE SIMULATEDJULY SIMULATEDAUGUST SIMULATEDSEPTEMBER SIMULATEDOCTOBER SIMULATEDMAY OBSERVEDJUNE OBSERVEDJULY OBSERVEDAUGUST OBSERVEDSEPTEMBER OBSERVEDOCTOBER OBSERVED

17.8 degree State water temperature criterion

Scenario 1: 1994

existing

conditions

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins Creek

Figure 7. Monthly mean of the 7-day moving average of daily maximum simulated and observed 1994 water temperatures for scenaexisting conditions. (WWTP, wastewater-treatment plant.)
21

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAY SIMULATEDJUNE SIMULATEDJULY SIMULATEDAUGUST SIMULATEDSEPTEMBER SIMULATEDOCTOBER SIMULATEDMAY OBSERVEDJUNE OBSERVEDJULY OBSERVEDAUGUST OBSERVEDSEPTEMBER OBSERVEDOCTOBER OBSERVED

17.8 degree State water temperature criterion

Scenario 1: 1995

existing

conditions

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins Creek

Figure 8. Monthly mean of the 7-day moving average of daily maximum simulated and observed 1995 water temperatures for scena

(WWTP, wastewater-treatment plant.)
22

Table 7. Additional hypothetical water-management scenarios

[USA, Unified Sewerage Agency; RM, river mile; WWTP, wastewater-treatment plant; ft3/s, cubic feet per second;

Mgal/d, million gallons per day]

________________________________________________________________________________________________

Scenario Title Description

number

________________________________________________________________________________________________

11 Existing conditions All existing conditions described in scenario 1 were simulated except

with 1.33 ft3/s decrease effluent from the Rock Creek WWTP was reduced by a constant 1.33

in Rock Creek WWTP ft3/s for the entire simulation period.

effluent

12 Existing conditions All existing conditions described in scenario 1 were simulated except

with 1.33 ft3

/s river withdrawal a constant 1.33 ft3/s was withdrawn from the river at RM 37.3 and an

and 2.0 ft3/s Henry Hagg additional 2.0 ft3/s was released from Henry Hagg Lake for the

Lake release entire simulation period.

13 Existing conditions All existing conditions described in scenario 1 were simulated except

with effluent releases of constant 5 Mgal/d flows of effluent were released at RM 55.2 and RM

5 Mgal/d at RM 55.2 and RM 43.8, respectively; and a constant 10 Mgal/d flow of effluent was released

43.8 and 10 Mgal/d at RM 38.1 at RM 38.1. Rock Creek WWTP 1994 (or 1995) observed effluenttemperature data were used for all three effluent releases.

14 Existing conditions All existing conditions described in scenario 1 were simulated except

with effluent releases of constant 5 Mgal/d flows of effluent were released at RM 55.2 and RM

5 Mgal/d at RM 55.2 and RM 43.8, respectively; and a constant 20 Mgal/d flow of effluent was released

43.8 and 20 Mgal/d at RM 38.1 at RM 38.1. Rock Creek WWTP 1994 (or 1995) observed effluenttemperature data were used for all three effluent releases.

15 Existing conditions All existing conditions described in scenario 1 were simulated except

with effluent releases of constant 5 Mgal/d flows of effluent were released at RM 55.2 and RM

5 Mgal/d at RM 55.2 and RM 43.8, respectively; and a constant 30 Mgal/d flow of effluent was released

43.8 and 30 Mgal/d at RM 38.1 at RM 38.1. 1994 and 1995 Rock Creek WWTP observed effluenttemperature data were used for all three effluent releases.

16 Existing conditions All existing conditions described in scenario 1 were simulated except

with 25 Mgal/d of effluent constant 25 Mgal/d flows of effluent were released from both the Rock

released at RM 38.1 and Creek (RM 38.1) and the Durham (RM 9.3) WWTPs for the entire

RM 9.3 simulation period. However, 1994 and 1995 measured effluenttemperature data from the two WWTPs were used.

17 Existing conditions All existing conditions described in scenario 1 were simulated except

with 45 Mgal/d of effluent constant 45 Mgal/d flows of effluent were released from both the Rock

released at RM 38.1 and Creek (RM 38.1) and the Durham (RM 9.3) WWTPs for the entire

RM 9.3 simulation period. However, 1994 and 1995 measured effluenttemperature data from the two WWTPs were used.

18 Existing conditions All existing conditions described in scenario 1 were simulated except

with 65 Mgal/d of effluent constant 65 Mgal/d flows of effluent were released from both the Rock

released at RM 38.1 and Creek (RM 38.1) and the Durham (RM 9.3) WWTPs for the entire

RM 9.3 simulation period. However, 1994 and 1995 measured effluenttemperature data from the two WWTPs were used.

19 Existing conditions with All existing conditions described in scenario 1 were simulated except

Gaston temperature data 1997 stream-temperature data collected at Lee Falls were used as

replaced with Lee Falls data stream-temperature input at Gaston for both the 1994 and 1995

simulation periods.

20 “Natural” conditions with “Natural” conditions described in scenario 3 were simulated except

Gaston temperature data 1997 stream-temperature data collected at Lee Falls were used as

replaced with Lee Falls data stream-temperature input at Gaston for both the 1994 and 1995

simulation periods.
23

Table 7. Additional hypothetical water-management scenarios—Continued

[USA, Unified Sewerage Agency; RM, river mile; WWTP, wastewater-treatment plant; ft3/s, cubic feet per second; Mgal/d, million gallons per da

________________________________________________________________________________________________

Scenario Title Description

number

_____________________________________________________________________________________________

21 Existing conditions All existing conditions described in scenario 1 were simulated except

with WWTP effluent the temperature of the effluent from the Rock Creek and Durham

temperature equal to WWTPs were approximately equal to the receiving river temperature.

receiving river temperature

22 Existing conditions All existing conditions described in scenario 1 were simulated except all

with up to 10 Mgal/d of flow, up to 10 Mgal/d, allotted for USA was released into the Tualatin at

USA allotted flows were River at the Rock Creek WWTP (RM 38.1) instead of from Scoggins

released at RM 38.1 Dam. Any remaining USA allotted flow in excess of 10 Mgal/d was still

released from Scoggins Dam. The temperature of the allotted flow,

regardless of the release point, was not changed from scenario 1.

23 Existing conditions with All existing conditions described in scenario 1 were simulated except

20 Mgal/d of 17.8 degrees constant 20 Mgal/d flows of effluent were released from both the Rock

Celsius effluent released Creek (RM 38.1) and the Durham (RM 9.3) WWTPs for the entire

at RM 38.1 and RM 9.3 simulation period. The temperature of the effluent was also constant at

17.8 degrees Celsius.

24 Existing conditions with All existing conditions described in scenario 1 were simulated except

25 Mgal/d of 17.8 degrees constant 25 Mgal/d flows of effluent were released from both the Rock

Celsius effluent released Creek (RM 38.1) and the Durham (RM 9.3) WWTPs for the entire

at RM 38.1 and RM 9.3 simulation period. The temperature of the effluent was also constant at

17.8 degrees Celsius.

25 Existing conditions with All existing conditions described in scenario 1 were simulated except

45 Mgal/d of 17.8 degrees constant 45 Mgal/d flows of effluent were released from both the Rock

Celsius effluent released Creek (RM 38.1) and the Durham (RM 9.3) WWTPs for the entire

at RM 38.1 and RM 9.3 simulation period. The temperature of the effluent was also constant at

17.8 degrees Celsius.

26 Existing conditions with All existing conditions described in scenario 1 were simulated except

65 Mgal/d of 17.8 degrees constant 65 Mgal/d flows of effluent were released from both the Rock

Celsius effluent released Creek (RM 38.1) and the Durham (RM 9.3) WWTPs for the entire

at RM 38.1 and RM 9.3 simulation period. The temperature of the effluent was also constant at

17.8 degrees Celsius.

________________________________________________________________________________________________

Scenario 11: Existing conditions with 1.33 ft3/s

decrease in Rock Creek WWTP effluent to the main

stem

The purpose of scenario 11 was to determine the

effect of diverting 1.33 ft3

/s of effluent from the Rock

Creek WWTP (RM 38.1) for nearby irrigation. No

increase in return flow to the river was assumed. The

diversion of 1.33 ft3

/s was held constant throughout

the entire simulation period. All other conditions in the

models remained unchanged from 1994 and 1995

existing conditions (scenario 1).

The monthly means of the 7-day moving average

of daily maximum simulated 1994 temperatures plotted for the main stem of the river are shown in figure 9.

Figure 10 shows the difference between the mon

mean of the 7-day moving average of daily max

simulated 1994 water temperatures for scenario 

scenario 1. Positive values show the warming ef

scenario 11 over existing conditions. Likewise, 

tive values show the cooling effect of the scenar

pair of similar plots for 1995 are shown in figur

and 12, respectively. (Sets containing these 4 typ

plots are presented for each of the other scenario

The effect of scenario 11 on the river syste

minimal for both 1994 and 1995. Temperatures 

stream of the Rock Creek WWTP (RM 38.1) fo

months decreased about 0.05o

C or less. The imp

gradually tapers off downstream and is negligib
24

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 11: 1994 existing

conditions with 1.33 ft3/s

decrease in Rock Creek

WWTP effluent

Gaston

Scoggins

Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 9. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 11, existin

feet per second decrease in Rock Creek WWTP effluent. (ft3/s, cubic feet per second; WWTP, wastewater-treatment plant.)
25

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

0.10

-0.10

0.080.060.040.02

0

-0.02-0.04-0.06-0.08

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 11: 1994 existing

conditions with 1.33 ft3/s

decrease in Rock Creek

WWTP effluent

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show warming t

values show the cooling effec

Figure 10. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures tions, and scenario 11, existing conditions with 1.33 cubic feet per second, decrease in Rock Creek WWTP effluent. (ft3/s, cubic feet 

water-treatment plant.)
26

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 11: 1995 existing

conditions with 1.33 ft3/s

decrease in Rock Creek

WWTP effluent

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

17.8 degree State water temperature criterion

Creek

WWTP

Figure 11. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 11, existin

feet per second decrease in Rock Creek WWTP effluent. (ft3/s, cubic feet per second; WWTP, wastewater-treatment plant.)
27

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

0.12

-0.12

0.100.080.060.040.02

0

-0.02-0.04-0.06-0.08-0.10

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 11: 1995 existing

conditions with 1.33 ft3/s

decrease in Rock Creek

WWTP effluent

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warming effect, while negative

values show the cooling effect, of scenario 11.

Figure 12. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures tions, and scenario 11, existing conditions with 1.33 cubic feet per second decrease in Rock Creek WWTP effluent. (ft3/s, cubic feet p

water-treatment plant.)
28

around RM 10.0. The effect of the scenario is slightly

more apparent in the 1994 simulation than the 1995

simulation.

Scenario 12: Existing conditions with 1.33 ft3/s river

withdrawal and 2.0 ft3/s Henry Hagg Lake release

In scenario 12, 1.33 ft3

/s was withdrawn from

the river at RM 37.3 for nearby irrigation at a constant

rate for the entire simulation period. No increase in

return flow to the river was assumed. To compensate

for the withdrawal, an additional constant flow of

2.0 ft3

/s was released from Henry Hagg Lake for the

entire simulation period. All other conditions in the

models were held constant to existing conditions

(scenario 1).

The effect of scenario 12 on the river system

was also fairly minimal for both 1994 and 1995

(figs. 13–16). Relative to the scenario 1 simulation,

temperatures generally decreased over the entire reach

between RM 60.0 and RM 3.4 by about 0.05 to 0.1οC.

However, the overall cooling effect of this scenario,

particularly during the month of July, was slightly

greater than the cooling effect of scenario 11 since

an additional 2.0 ft3/s was released from Henry Hagg

Lake. However, October 1995 was an exception

because flows released from the lake were warmer

than the main stem of the river.

Scenarios 13, 14, and 15: Existing conditions with

effluent releases of 5 Mgal/d at RM 55.2 and RM

43.8 and 10, 20, and 30 Mgal/d at RM 38.1

In scenarios 13, 14, and 15, the effect on river

temperatures of piping some of the effluent produced

at the Rock Creek WWTP (RM 38.1) to upstream

locations (Hillsboro West WWTP at RM 43.8 and the

Forest Grove WWTP at RM 55.2) and releasing it

there was examined. In the existing-conditions scenario, the mean flow of effluent from the Rock Creek

WWTP was approximately 18 Mgal/d for the 1994

and 1995 May through October periods. For all three

of the new scenarios, a constant flow of 5 Mgal/d of

effluent was released at both RM 43.8 and RM 55.2

for the entire simulation period. Constant flows of 10,

20, and 30 Mgal/d of effluent at the Rock Creek

WWTP (RM 38.1) were simulated for scenarios 13,

14, and 15, respectively. The temperature of the

diverted effluent (to RM 43.8 and RM 55.2) was

not adjusted for possible cooling that could occur during travel in an underground pipe. 1994 and 1995

measured effluent-temperature data from the R

Creek WWTP were used in all three scenarios. 

other conditions in the simulations were held co

to existing conditions (scenario 1).

For scenario 13, temperature increased be

RM 55.2 and the Rock Creek WWTP (RM 38.

to the release of effluent at RM 55.2 and RM 4

(figs. 17–20). The increase in temperature was 

ally less than 1.0οC and did not cause a violatio

the State water-quality standard. For the reach 

stream of RM 38.1, the river temperature decre

(generally less than 0.6οC) due to a reduction o

ent released at Rock Creek WWTP. This coolin

downstream of RM 38.1 was eliminated in scen

14, in which Rock Creek WWTP effluent produ

increased to 20 Mgal/d (figs. 21–24). Water tem

ture generally increased throughout the river sy

downstream of RM 38.1. In scenario 15, Rock 

WWTP effluent increased to 30 Mgal/d (figs. 2

Water temperatures increased downstream of R

38.1; however, the magnitude of the increase w

erally less than 1.0οC. Interestingly, some mino

ing of the river is observed in scenario 15 for Ju

probably due to the decreased travel time result

from the increase in river discharge.

Scenarios 16, 17, and 18: Existing conditions 

25, 45, and 65 Mgal/d of effluent at RM 38.1 a

RM 9.3

In light of the forecast expansion in efflue

duction at both the Rock Creek and Durham W

due to regional population growth, the purpose 

narios 16, 17, and 18 was to determine the temp

effect resulting from substantial increases in ef

loading. Constant 25, 45, and 65 Mgal/d flows 

effluent were released from both WWTPs for th

entire simulation periods for scenarios 16, 17, a

respectively; however, 1994 and 1995 measure

ent temperature data from the two WWTPs wer

used. All other conditions in the models were h

constant to existing conditions (scenario 1).

Because the effluent released from the tw

WWTPs was substantially above the actual am

effluent released from these plants in 1994 and 

simulated water temperatures throughout the re

downstream of Rock Creek WWTP, and to less

extent downstream of Durham WWTP, proport

ately increased (figs. 29–40). The magnitude of 

temperature rise was generally under 0.6, 1.5, a

2.2οC for effluent releases of 25, 45, and 65 Mg

respectively.
29

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 12: 1994 existing

conditions with 1.33 ft3/s

river withdrawal and 2.0 ft3/s

Hagg Lake release

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins

Creek

Figure 13. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 12, existinper second river withdrawal and 2.0 cubic feet per second Henry Hagg Lake release. (ft3/s, cubic feet per second; WWTP, wastewat
30

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

0.25

-0.25

0.200.150.100.05

0

-0.05-0.10-0.15-0.20

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 12: 1994 existing

conditions with 1.33 ft3/s

river withdrawal and 2.0 ft3/s

Hagg Lake release

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

 Creek

Figure 14. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures 

conditions, and scenario 12, existing conditions with 1.33 cubic feet per second river withdrawal and 2.0 cubic feet per second Henry H

feet per second; WWTP, wastewater-treatment plant.)
31

Figure 15. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 12, existin

feet per second river withdrawal and 2.0 cubic feet per second Henry Hagg Lake release. (ft3/s, cubic feet per second; WWTP, waste

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

261012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 12: 1995 existing

conditions with 1.33 ft3/s

river withdrawal and 2.0 ft3/s

Hagg Lake release

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

 Creek

WWTP
32

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

0.20

-0.20

0.150.100.05

0

-0.05-0.10-0.15

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 12: 1995 existing

conditions with 1.33 ft3/s

river withdrawal and 2.0 ft3/s

Hagg Lake release

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 16. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures conditions, and scenario 12, existing conditions with 1.33 cubic feet per second river withdrawal and 2.0 cubic feet per second Henry H

feet per second; WWTP, wastewater-treatment plant.)
33

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 13: 1994 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

10 Mgal/d at RM 38.1

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins

Creek

Figure 17. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 13, existin

releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 10 Mgal/d at RM 38.1. (Mgal/d, million gallons per day; RM, river mile; and WWT
34

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.2

-1.2

1.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 13: 1994 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

10 Mgal/d at RM 38.1

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effect, 

Figure 18. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatureconditions, and scenario 13, existing conditions with effluent releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 10 Mgal/d at RM 38.day; RM, river mile; and WWTP, wastewater-treatment plant.)
35

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

26

8

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 13: 1995 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

10 Mgal/d at RM 38.1

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins

 State water temperature criterion

Creek

Figure 19. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 13, existi

releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 10 Mgal/d at RM 38.1. (Mgal/d, million gallons per day; RM, river mile; and WWT
36

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.2

-1.2

1.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 13: 1995 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

10 Mgal/d at RM 38.1

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effec

Figure 20. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatureconditions, and scenario 13, existing conditions with effluent releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 10 Mgal/d at RM 38.1day; RM, river mile; and WWTP, wastewater-treatment plant.)
37

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

261012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 14: 1994 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

20 Mgal/d at RM 38.1

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins

 Creek

Figure 21. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 14, existin

releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 20 Mgal/d at RM 38.1. (Mgal/d, million gallons per day; RM, river mile; and WWTP
38

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.2

-1.2

1.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 14: 1994 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

20 Mgal/d at RM 38.1

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effect

Figure 22. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures 

conditions, and scenario 14, existing conditions with effluent releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 20 Mgal/d at RM 38.1day; RM, river mile; and WWTP, wastewater-treatment plant.)
39

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 14: 1995 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

20 Mgal/d at RM 38.1

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins

State water temperature criterion

 Creek

Figure 23. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 14, existing 

releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 20 Mgal/d at RM 38.1. (Mgal/d, million gallons per day; RM, river mile; and WWTP
40

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.2

-1.2

1.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 14: 1995 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

20 Mgal/d at RM 38.1

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effec

Figure 24. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures conditions, and scenario 14, existing conditions with effluent releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 20 Mgal/d at RM 38.day; RM, river mile; and WWTP, wastewater-treatment plant.)
41

Figure 25. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 15, existin

releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 30 Mgal/d at RM 38.1. (Mgal/d, million gallons per day; RM, river mile; and WWTP

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

261012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 15: 1994 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

30 Mgal/d at RM 38.1

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins

Creek
42

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.2

-1.2

1.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 15: 1994 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

30 Mgal/d at RM 38.1

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effect

Figure 26. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures 

conditions, and scenario 15, existing conditions with effluent releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 30 Mgal/d at RM 38.1day; RM, river mile; and WWTP, wastewater-treatment plant.)
43

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 15: 1995 existing

conditions with effluent

releases of 5 Mgal/d at

RM 55.2 and RM 43.8 and

30 Mgal/d at RM 38.1

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

State water temperature criterion

Creek

Figure 27. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 15, existin

releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 30 Mgal/d at RM 38.1. (Mgal/d, million gallons per day; RM, river mile; and WWTP
44

Figure 28. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures conditions, and scenario 15, existing conditions with effluent releases of 5 Mgal/d at RM 55.2 and RM 43.8 and 30 Mgal/d at RM 38.1day; RM, river mile; and WWTP, wastewater-treatment plant.)

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.2

-1.2

1.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 15: 1995 existing

conditions with effluent releases

of 5 Mgal/d at RM 55.2 and

RM 43.8 and 30 Mgal/d at RM 38.1

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec
45

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 16: 1994 existing

conditions with 25 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins

Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

WWTP

Figure 29. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 16, existineffluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewater-treatment plant.)
46

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

0.8

-0.8

0.60.40.2

0

-0.2-0.4-0.6

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 16: 1994 existing

conditions with 25 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effect

Figure 30. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures conditions, and scenario 16, existing conditions with 25 Mgal/d of effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons peWWTP, wastewater-treatment plant.)
47

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

261012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 16: 1995 existing

conditions with 25 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

State water temperature criterion

WWTP

Creek

Figure 31. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 16, existin

effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewater-treatment plant.)
48

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

0.6

-0.6

0.50.40.30.20.1

0

-0.1-0.2-0.3-0.4-0.5

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBOCTOBER

Scenario 16: 1995 existing

conditions with 25 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 32. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperature

ditions, and scenario 16, existing conditions with 25 Mgal/d of effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per da

wastewater-treatment plant.)
49

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 17: 1994 existing

conditions with 45 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 33. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 17, existiof effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewater-treatment plan
50

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.6

-1.6

1.41.21.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0-1.2-1.4

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 17: 1994 existing

conditions with 45 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Scoggins Creek

Note: Positive values show the warmin

values show the cooling effect

Figure 34. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures conditions, and scenario 17, existing conditions with 45 Mgal/d of effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons pWWTP, wastewater-treatment plant.)
51

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

26

8

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 17: 1995 existing

conditions with 45 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

State water temperature criterion

Creek

Figure 35. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 17, existineffluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewater-treatment plant.)
52

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.0

-1.0

0.90.80.70.60.50.40.30.20.1

0

-0.1-0.2-0.3-0.4-0.5-0.6-0.7-0.8-0.9

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 17: 1995 existing

conditions with 45 Mgal/dMgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effec

Figure 36. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures 

tions, and scenario 17, existing conditions with 45 Mgal/d of effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per daywastewater-treatment plant.)
53

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 18: 1994 existing

conditions with 65 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 37. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 18, existineffluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewater-treatment plant.)
54

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

3.0

-3.0

2.82.62.42.22.01.81.61.41.21.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0-1.2-1.4-1.6-1.8-2.0-2.2-2.4-2.6-2.8

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 18: 1994 existing

conditions with 65 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effec

Figure 38. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures 

conditions, and scenario 18, existing conditions with 65 Mgal/d of effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons pWWTP, wastewater-treatment plant.)
55

Figure 39. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 18, existin

effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewater-treatment plant.)

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 18: 1995 existing

conditions with 65 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Gaston

Scoggins

 Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

 WWTP

 State water temperature criterion
56

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.6

-1.6

1.41.21.00.80.60.40.2

0

-0.2-0.4-0.6-0.8-1.0-1.2-1.4

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 18: 1995 existing

conditions with 65 Mgal/d of

effluent released at

RM 38.1 and RM 9.3

Note: Positive values show the warm

values show the cooling effec

Figure 40. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures conditions, and scenario 18, existing conditions with 65 Mgal/d of effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons pWWTP, wastewater-treatment plant.)

Gaston

Gales Creek

Dairy Creek

Scoggins Creek

Rock Creek

Rock Creek WWTP
57

Scenarios 19 and 20: Existing and “natural” conditions with Gaston temperature data replaced with

Lee Falls data

Because of sparse riparian shading in the reach

between Lee Falls near Cherry Grove (RM 70.0) and

the model upper boundary at Gaston (RM 63.9), water

entering the model’s upstream boundary does not represent “natural” or “background” conditions. The

intent of scenarios 19 and 20 was to determine the

effect of cooler water entering the river system at Gaston relative to existing and “natural” conditions. For

the existing conditions, 1994 and 1995 observed flow

at Gaston were still used as input to the model simulations; however, to compensate for warming that may

occur between Lee Falls and Gaston, observed watertemperature data at Gaston were replaced with

observed water-temperature data collected at Lee Falls

from May to October 1997. All other conditions in the

models were held constant to existing conditions (scenario 1).

In the existing conditions simulation, water temperatures decreased substantially between Gaston

(RM 63.9) and the confluence with Scoggins Creek

(RM 60.0) by as much as 4.0οC in July (figs. 41–44);

however, the effect of the temperature decrease was

overwhelmed by the large volume of colder water

flowing from Scoggins Creek as a result of releases

from Henry Hagg Lake. For most of the reach downstream of RM 60.0, the overall cooling effect of this

scenario was less than 0.5οC (figs. 42 and 44).

For the “natural” conditions scenario, Gaston

water-temperature data were again substituted with

1997 Lee Falls water-temperature data for the 1994

and 1995 simulations. All other conditions in the

model were held to the “natural” conditions defined in

scenario 3 instead of the existing conditions (scenario

1). A full description of scenario 3 is provided on page

27 in Risley (1997). The simulation of “natural” conditions was based on the following assumptions:

(1) No flow augmentation from the Trask River

(Barney Reservoir) to the main stem of the

Tualatin River was provided.

(2) Both Henry Hagg Lake and the Oswego

diversion dam at RM 3.4 were assumed not to

exist.

(3) No withdrawals for irrigation or urban water

supply were made.

(4) No flow diversions for the Oswego Canal

were made.

(5) No effluent was released from WWTP

(6) Maximum possible riparian shading alo

main stem was assumed.

In scenario 20, as in scenario 19, water te

tures decreased substantially between Gaston (

63.9) and the confluence with Scoggins Creek 

60.0) (figs. 45–48). Between Scoggins Creek an

the Dairy Creek confluence (RM 44.8), water t

atures gradually increased because the unnatura

cool water released from Henry Hagg Lake wa

present; however, nearly all of the upper river r

above Rood Bridge (RM 38.4) for every month 

not in violation of the water-quality standard. Th

an improvement over the 1994 “natural” condit

scenario simulation shown in Risley (1997). In 

simulation, which used observed Gaston water-

perature data, approximately 5 miles of the reac

downstream of Gaston (RM 63.9) had temperat

greater than 17.8οC for July and August. For the 

river section below Rood Bridge, the water tem

tures generally increased (1.0οC or less) for Jul

August, and decreased for other months.

Scenario 21: Existing conditions with WWTP 

ent temperature equal to receiving river tempe

In this scenario, existing conditions (scen

were simulated for 1994 and 1995, except the t

ature of the effluent from the two WWTPs was 

ferent than the receiving river temperature at th

WWTPs (RM 38.1 and RM 9.3). The intent of 

scenario was to examine the hydrologic effects 

volume of WWTP effluent flow on river tempe

as opposed to the direct effects of warmer efflu

temperature. This scenario was similar to scena

(Risley, 1997); however, in scenario 7 effluent fl

from both WWTPs were completely eliminated

The effect of scenario 21 on the river syste

similar to the effect of scenario 7 (figs. 49–54). 

peratures downstream of RM 38.1 decreased by 

much as 2.4οC. The reduction then tapers off to 

upstream of RM 9.3. Downstream of RM 9.3, t

atures decreased by as much as 1.2οC; however

because the flow in the river downstream of the

WWTPs was greater in scenario 21 than in scen

scenario 21 had the effect of decreasing river te

tures slightly more than scenario 7. The magnit

this difference generally ranged from 0.3 to 0.1
58

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 19: 1994 existing

conditions with Gaston

temperature data replaced

with Lee Falls data

Gaston

Scoggins

Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 41. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 19, existin

temperature data replaced with Lee Falls data. (WWTP, wastewater-treatment plant.)
59

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

5.0

-5.0

4.54.03.53.02.52.01.51.00.5

0

-0.5-1.0-1.5-2.0-2.5-3.0-3.5-4.0-4.5

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 19: 1994 existing

conditions with Gaston

temperature data replaced

with Lee Falls data

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effect

Figure 42. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures conditions, and scenario 19, existing conditions with Gaston temperature data replaced with Lee Falls data. (WWTP, wastewater-trea
60

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 19: 1995 existing

conditions with Gaston

temperature data replaced

with Lee Falls data

Gaston

Scoggins

Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

 State water temperature criterion

WWTP

Figure 43. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 19, existin

temperature data replaced with Lee Falls data. (WWTP, wastewater-treatment plant.)
61

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

5.0

-5.0

4.54.03.53.02.52.01.51.00.5

0

-0.5-1.0-1.5-2.0-2.5-3.0-3.5-4.0-4.5

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 19: 1995 existing

conditions with Gaston

temperature data replaced

with Lee Falls data

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effect

Figure 44. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures 

conditions, and scenario 19, existing conditions with Gaston temperature data replaced with Lee Falls data. (WWTP, wastewater-trea
62

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 20: 1994 "natural"

conditions with Gaston

temperature data replaced

with Lee Falls data

Gaston

Gales

Dairy

Rock

Rock Creek

Scoggins

Creek

Creek

Creek

WWTP

Creek

Figure 45. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 20, “naturtemperature data replaced with Lee Falls data. (WWTP, wastewater-treatment plant.)
63

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

10

-10

9876543210

-1-2-3-4-5-6-7-8-9

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 20: 1994 "natural"

conditions with Gaston

temperature data replaced

with Lee Falls data

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 46. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatureconditions, and scenario 20, “natural“ conditions with Gaston temperature data replaced with Lee Falls data. (WWTP, wastewater-tre
64

Figure 47. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 20, “naturtemperature data replaced with Lee Falls data. (WWTP, wastewater-treatment plant.)

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 20: 1995 "natural"

conditions with Gaston

temperature data replaced

with Lee Falls data

Gaston

Scoggins

 Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

WWTP

TEMPERATURE, IN DEGREES CELSIUS
65

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

10

-10

9876543210

-1-2-3-4-5-6-7-8-9

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 20: 1995 "natural"

conditions with Gaston

temperature data replaced

with Lee Falls data

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effec

Figure 48. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperature

conditions, and scenario 20, “natural“ conditions with Gaston temperature data replaced with Lee Falls data. (WWTP, wastewater-tre
66

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

261012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 21: 1994 existing

conditions with WWTP

effluent temperature equal

to receiving river

temperature

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 49. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 21, existin

effluent temperature equal to receiving river temperature. (WWTP, wastewater-treatment plant.)
67

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

2.5

-2.5

2.01.51.00.5

0

-0.5-1.0-1.5-2.0

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 21: 1994 existing

conditions with WWTP

effluent temperature equal

to receiving river

temperature

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 50. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperature

conditions, and scenario 21, existing conditions with WWTP effluent temperature equal to receiving river temperature. (WWTP, wast
68

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 21: 1995 existing

conditions with WWTP

effluent temperature equal

to receiving river

temperature

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

 State water temperature criterion

Creek

TEMPERATURE, IN DEGREES CELSIUS

Figure 51. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 21, existing 

effluent temperature equal to receiving river temperature. (WWTP, wastewater-treatment plant.)
69

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

2.00

-2.00

1.751.501.251.000.750.500.25

0

-0.25-0.50-0.75-1.00-1.25-1.50-1.75

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 21: 1995 existing

conditions with WWTP

effluent temperature equal

to receiving river

temperature

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 52. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures conditions, and scenario 21, existing conditions with WWTP effluent temperature equal to receiving river temperature. (WWTP, waste
70

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

0.5

-0.5

0.40.30.20.1

0

-0.1-0.2-0.3-0.4

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 21: 1994 existing

conditions with WWTP

effluent temperature equal

to receiving river

temperature

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warming 

values show the cooling effect, o

Figure 53. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures 

conditions without WWTPs, and scenario 21, existing conditions with WWTP effluent temperature equal to receiving river temperaturtreatment plant.)
71

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

0.5

-0.5

0.40.30.20.1

0

-0.1-0.2-0.3-0.4

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 21: 1995 existing

conditions with WWTP

effluent temperature equal

to receiving river

temperature

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 54. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures 

conditions without WWTPs, and scenario 21, existing conditions with WWTP effluent temperature equal to receiving river temperaturment plant.)
72

Scenario 22: Existing conditions with up to 10 Mgal/

d of USA flow augmentation released near Rock

Creek WWTP outfall

To mitigate water-quality problems and maintain

a minimum flow in the river during the summer, the

USA purchases an annual allotment of flow from

Henry Hagg Lake. These flows are released from

Scoggins Dam and enter the river from Scoggins

Creek. The purpose of scenario 22 was to determine if

the temperature impact of effluent released from the

WWTPs could be lessened if the 1994 and 1995 USA

allotted flow (when less than but not exceeding 10

Mgal/d) were released into the river near the Rock

Creek WWTP (RM 38.1). On days when the USA

allotted flow was greater than 10 Mgal/d, the excess of

10 Mgal/d was released into the system at Scoggins

Dam. Measured 1994 and 1995 Scoggins Dam temperature data were used as the temperature of the allotted flow released at RM 38.1 (Measured 1994 and

1995 Rock Creek WWTP effluent flow and temperature data were still used for the released effluent).

With a decrease in the cooler Scoggins Creek

flows entering the river at RM 60.0, the simulations

showed temperature increases for all the months

except October (figs. 55–58). The magnitude of the

increase was generally under 0.6οC for 1994 and

0.3οC for 1995; however, downstream of the Rock

Creek WWTP (RM 38.1), temperatures decreased

from as much as 0.7οC in 1994 and 0.3οC in 1995 for

all months except October; however, the effect of the

10 Mgal/d release becomes gradually less pronounced

downstream.

Scenarios 23, 24, 25, and 26: Existing conditions

with 20, 25, 45, and 65 Mgal/d of 17.8 degrees Celsius effluent released at RM 38.1 and RM 9.3

In scenarios 23, 24, 25, and 26, the 1994 and

1995 measured effluent temperature data from the

WWTPs were used, except that the temperatures were

not permitted to be greater than 17.8οC. The flow of

effluent from each WWTP was constant during 

simulation periods: 20, 25, 45, and 65 Mgal/d, 

tively, for the four scenarios. All other existing 

tions were used.

For most of the months, the temperature i

reaches downstream of both WWTPs decreased 

four simulations (figs. 59–74). The magnitude 

decrease in temperature was usually less than 1

but reached 2.0οC in some locations. For scena

the rate of effluent flow was 20 Mgal/d, which w

much more than the mean rate of effluent relea

from the WWTPs in 1994 and 1995. In this sce

most of the decrease in temperature was in prox

of the WWTPs; however, in scenario 26, the im

the 65 Mgal/d of effluent released from Rock C

WWTP can be seen all the way downstream to 

Durham WWTP (RM 9.3). Downstream of the

Durham WWTP, temperatures decreased by an 

greater magnitude. The temperature of the river 

reach was already well above 17.8οC. But, the 

stantial volume of effluent released from Durha

WWTP (65 Mgal/d) had a temperature of 17.8ο

less and produced a greater reduction.

Simulation results for the 16 scenarios

specific to 5 locations on the river, Golf Course 

(RM 51.5), Rood Bridge (RM 38.4), Scholls B

(RM 26.9), Elsner Road (RM 16.2), and Staffor

(RM 5.5) are shown in tables 8 through 22. The

set of three tables for each location. The first ta

shows comparisons of the monthly mean of the 

moving average of daily maximum simulated 1

and 1995 water temperatures averaged over eac

month (May through October) for the 16 scena

The second table shows the difference in the m

water temperature resulting from each scenario 

narios 11–26) relative to existing conditions (sc

1) for each month. The third table shows the pe

age of time that the 7-day moving average of d

maximum simulated 1994 and 1995 water temp

exceeds 17.8οC for each scenario during each m

(May through October).
73

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 22: 1994 existing

conditions with up to

10 Mgal/d of USA flow

augmentation released near

Rock Creek WWTP outfall

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 55. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 22, existi

Mgal/d of USA flow augmentation released near Rock Creek WWTP outfall. (Mgal/d, million gallons per day; USA, Unified Seweragwastewater-treatment plant.)
74

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.25

-1.25

1.000.750.500.25

0

-0.25-0.50-0.75-1.00

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 22: 1994 existing

conditions with up to 10 Mgal/d of

USA flow augmentation released

near Rock Creek WWTP outfall

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 56. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures 

conditions, and scenario 22, existing conditions with up to 10 Mgal/d of USA flow augmentation released near Rock Creek WWTP outfa

day; USA, Unified Sewerage Agency; and WWTP, wastewater-treatment plant.)
75

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 22: 1995 existing

conditions with up to 10 Mgal/d of

USA flow augmentation released

near Rock Creek WWTP outfall

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

 State water temperature criterion

Creek

WWTP

Figure 57. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 22, existin

Mgal/d of USA flow augmentation released near Rock Creek WWTP outfall. (Mgal/d, million gallons per day; USA, Unified Sewerage water-treatment plant.)
76

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.25

-1.25

1.000.750.500.25

0

-0.25-0.50-0.75-1.00

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

Scenario 22: 1995 existing

conditions with up to 10 Mgal/d of

USA flow augmentation released

near Rock Creek WWTP outfall

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 58. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures 

conditions, and scenario 22, existing conditions with up to 10 Mgal/d of USA flow augmentation released near Rock Creek WWTP outper day; USA, Unified Sewerage Agency; and WWTP, wastewater-treatment plant.)
77

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 23: 1994 existing

conditions with 20 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 59. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 23, existinof 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, waste
78

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.25

-1.25

1.000.750.500.25

0

-0.25-0.50-0.75-1.00

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 23: 1994 existing

conditions with 20 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warmi

values show the cooling effec

Figure 60. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures conditions, and scenario 23, existing conditions with 20 Mgal/d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (MgaRM, river mile; and WWTP, wastewater-treatment plant.)
79

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 23: 1995 existing

conditions with 20 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek

 State water temperature criterion

Creek

WWTP

Figure 61. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 23, existin

d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, was
80

Figure 62. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures conditions, and scenario 23, existing conditions with 20 Mgal/d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (MgaRM, river mile; and WWTP, wastewater-treatment plant.)

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.25

-1.25

1.000.750.500.25

0

-0.25-0.50-0.75-1.00

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 23: 1995 existing

conditions with 20 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec
81

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 24: 1994 existing

conditions with 25 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 63. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 24, existin

17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewa
82

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.25

-1.25

1.000.750.500.25

0

-0.25-0.50-0.75-1.00

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 24: 1994 existing

conditions with 25 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 64. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures conditions, and scenario 24, existing conditions with 25 Mgal/d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (MgaRM, river mile; and WWTP, wastewater-treatment plant.)
83

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 24: 1995 existing

conditions with 25 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

 State water temperature criterion

Creek

Figure 65. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 24, existing of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastew
84

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.25

-1.25

1.000.750.500.25

0

-0.25-0.50-0.75-1.00

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 24: 1995 existing

conditions with 25 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 66. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures 

conditions, and scenario 24, existing conditions with 25 Mgal/d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (MgRM, river mile; and WWTP, wastewater-treatment plant.)
85

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree State water temperature criterion

Scenario 25: 1994 existing

conditions with 45 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins

Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 67. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 25, existinof 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastew
86

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.50

-1.50

1.251.000.750.500.25

0

-0.25-0.50-0.75-1.00-1.25

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 25: 1994 existing

conditions with 45 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Fanno Creek

Note: Positive values show the warm

values show the cooling effec

Figure 68. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures 

conditions, and scenario 25, existing conditions with 45 Mgal/d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (MgaRM, river mile; and WWTP, wastewater-treatment plant.)
87

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

261012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree

Scenario 25: 1995 existing

conditions with 45 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

 State water temperature criterion

Creek

Figure 69. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 25, existinof 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, waste
88

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

1.50

-1.50

1.251.000.750.500.25

0

-0.25-0.50-0.75-1.00-1.25

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 25: 1995 existing

conditions with 45 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Fanno Creek

Note: Positive values show the warm

values show the cooling effec

Figure 70. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures 

conditions, and scenario 25, existing conditions with 45 Mgal/d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/

river mile; and WWTP, wastewater-treatment plant.)
89

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

8

26

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree, State water temperature criterion

Scenario 26: 1994 existing

conditions with 65 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Figure 71. Monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures for scenario 26, existin17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewa
90

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

2.00

-2.00

1.751.501.251.000.750.500.25

0

-0.25-0.50-0.75-1.00-1.25-1.50-1.75

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 26: 1994 existing

conditions with 65 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 72. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1994 water temperatures 

conditions, and scenario 26, existing conditions with 65 Mgal/d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/

river mile; and WWTP, wastewater-treatment plant.)
91

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

26

8

1012141618202224

TEMPERATURE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

17.8 degree, State water temperature criterion

Scenario 26: 1995 existing

conditions with 65 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins

Gales Creek

Dairy Creek

Rock Creek

Figure 73. Monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures for scenario 26, existin17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mgal/d, million gallons per day; RM, river mile; and WWTP, wastewa

Creek

WWTP
92

70 60 50 40 30 20 

RIVER MILE UPSTREAM FROM MOUTH

2.00

-2.00

1.751.501.251.000.750.500.25

0

-0.25-0.50-0.75-1.00-1.25-1.50-1.75

TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

MAYJUNEJULYAUGUSTSEPTEMBEROCTOBER

Scenario 26: 1995 existing

conditions with 65 Mgal/d of

17.8 degree Celsius effluent released

at RM 38.1 and RM 9.3

Gaston

Scoggins Creek

Gales Creek

Dairy Creek

Rock Creek

Rock Creek WWTP

Note: Positive values show the warm

values show the cooling effec

Figure 74. Difference between the monthly mean of the 7-day moving average of daily maximum simulated 1995 water temperatures 

conditions, and scenario 26, existing conditions with 65 Mgal/d of 17.8 degree Celsius effluent released at RM 38.1 and RM 9.3. (Mga

RM, river mile; and WWTP, wastewater-treatment plant.)
93

Table 8. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature in degrees Celsiu

scenario at Golf Course Road (river mile 51.5)

1994 1995

Scenario May June July August September October May June July Augu

1 14.1 14.8 13.1 13.2 15.8 13.6 12.4 14.1 14.1 12.8 

11 14.1 14.8 13.1 13.2 15.9 13.6 12.4 14.1 14.1 12.8 12 14 14.6 13 13.2 15.9 13.5 12.3 14 14.1 12.8 13 14.4 15.3 13.6 13.8 16.4 14.2 12.6 14.5 14.8 13.4 14 14.4 15.3 13.6 13.8 16.4 14.2 12.6 14.5 14.8 13.4 15 14.4 15.3 13.6 13.8 16.4 14.2 12.6 14.5 14.8 13.4 16 14.1 14.8 13.1 13.2 15.9 13.6 12.4 14.1 14.1 12.8 17 14.1 14.8 13.1 13.2 15.9 13.6 12.4 14.1 14.1 12.8 18 14.1 14.8 13.1 13.2 15.9 13.6 12.4 14.1 14.1 12.8 19 13.6 14.8 12.8 13.1 15.6 13.5 12 13.7 13.9 12.8 20 12.4 13.6 16.5 15.6 13.7 8.8 12.2 13.4 16.6 15.6 21 14.1 14.8 13.1 13.2 15.9 13.6 12.4 14.1 14.1 12.8 22 14.2 14.9 13.4 13.4 15.9 13.2 12.4 14.2 14.2 13 23 14.2 14.8 13.1 13.2 15.8 13.6 12.4 14.1 14.1 12.8 24 14.2 14.8 13.1 13.2 15.8 13.6 12.4 14.1 14.1 12.8 25 14.2 14.8 13.1 13.2 15.8 13.6 12.4 14.1 14.1 12.8 26 14.2 14.8 13.1 13.2 15.8 13.6 12.4 14.1 14.1 12.8 
94

Table 9. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temp

each management scenario and Scenario 1 at Golf Course Road (river mile 51.5)

[Positive values show the warming effect, while negative values show the cooling effect, of the management scenario.]

1994 1995

Scenario May June July August September October May June July Augu

11 0 0 0 0 0 0 0 0 0 0 12 -.1 -.1 0 0 0 -.1 0 -.1 -.1 0 13 +.3 +.6 +.5 +.6 +.5 +.6 +.2 +.4 +.6 +.6 14 +.3 +.6 +.5 +.6 +.5 +.6 +.2 +.4 +.6 +.6 15 +.3 +.6 +.5 +.6 +.5 +.6 +.2 +.4 +.6 +.6 16 0 0 0 0 0 0 0 0 0 0 17 0 0 0 0 0 0 0 0 0 0 18 0 0 0 0 0 0 0 0 0 0 19 -.5 0 -.2 -.1 -.2 -.1 -.4 -.4 -.2 0 20 -1.7 -1.2 +3.4 +2.4 -2.1 -4.8 -.2 -.7 +2.4 +2.8 21 0 0 0 0 0 0 0 0 0 0 22 0 +.2 +.3 +.2 +.1 -.4 0 +.1 +.1 +.2 23 0 0 0 0 0 0 0 0 0 0 24 0 0 0 0 0 0 0 0 0 0 25 0 0 0 0 0 0 0 0 0 0 26 0 0 0 0 0 0 0 0 0 0 
95

Table 10. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature at Golf Cours

exceeds 17.8 degrees Celsius for each management scenario during each month

1994 1995

Scenario May June July August September October May June July Augu

1 0 0 00 0 0 0 0 00 

11 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 0 13 0 0 0 0 0 0 0 0 0 0 14 0 0 0 0 0 0 0 0 0 0 15 0 0 0 0 0 0 0 0 0 0 16 0 0 0 0 0 0 0 0 0 0 17 0 0 0 0 0 0 0 0 0 0 18 0 0 0 0 0 0 0 0 0 0 19 0 0 0 0 0 0 0 0 0 0 20 0 0 29 0 0 0 0 0 19.4 0 21 0 0 0 0 0 0 0 0 0 0 22 0 0 0 0 0 0 0 0 0 0 23 0 0 0 0 0 0 0 0 0 0 24 0 0 0 0 0 0 0 0 0 0 25 0 0 0 0 0 0 0 0 0 0 26 0 0 0 0 0 0 0 0 0 0 
96

Table 11. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature in degrees Ce

scenario at Rood Bridge (river mile 38.4)

[Shaded cells indicate potential violations of the 17.8 degrees Celsius State temperature standard]

1994 1995

Scenario May June July August September October May June July Augu

1 14.9 16 16.7 15.7 16 11.5 13.8 16 18.2 15.7 

11 14.9 16 16.8 15.7 16 11.5 13.8 16 18.2 15.7 12 14.8 16 16.7 15.7 16 11.5 13.6 16 18.1 15.7 13 15.2 16.5 17.2 16.5 16.8 12.6 13.8 16.3 18.4 16.3 14 15.2 16.4 17.1 16.4 16.7 12.4 13.8 16.2 18.4 16.2 15 15.2 16.4 17 16.3 16.6 12.2 13.8 16.2 18.4 16.1 16 14.8 16 16.7 15.6 16 11.4 13.6 16 18.1 15.7 17 14.7 15.9 16.6 15.4 15.8 11.1 13.6 15.9 18.1 15.5 18 14.7 15.8 16.5 15.3 15.6 10.9 13.6 15.9 18 15.4 19 14.7 16 16.6 15.7 15.9 11.5 13.5 15.9 18 15.7 20 12.6 13.4 16.3 16.3 13.8 10.1 12.6 14.1 17.3 15.7 21 15 16.2 17 16.1 16.4 12 13.7 16.1 18.3 16 22 14.9 16.2 17.6 16.4 16.2 11.2 13.6 16.1 18.3 16.1 23 14.9 16.1 16.9 16 16.3 11.7 13.6 16.1 18.3 15.9 24 14.9 16.1 16.9 16 16.3 11.6 13.6 16.1 18.3 15.9 25 14.8 16.1 16.9 15.9 16.2 11.4 13.6 16 18.3 15.8 26 14.7 16 16.9 15.9 16.2 11.3 13.6 16 18.4 15.8 
97

Table 12. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temeach management scenario averaged over each month and Scenario 1 at Rood Bridge (river mile 38.4)[Positive values show the warming effect, while negative values show the cooling effect, of the management scenario.]

1994 1995

Scenario May June July August September October May June July Augu

11 0 0 0 0 0 0 0 0 0 0 12 0 0 -.1 0 0 0 -.1 0 -.1 0 13 +.4 +.5 +.5 +.8 +.8 +1.1 0 +.3 +.3 +.6 14 +.3 +.4 +.4 +.6 +.6 +.9 0 +.2 +.2 +.5 15 +.3 +.3 +.3 +.5 +.5 +.7 0 +.2 +.2 +.4 16 0 0 -.1 -.1 -.1 -.1 -.1 0 0 -.1 17 -.1 -.2 -.2 -.3 -.3 -.4 -.2 -.1 -.1 -.2 18 -.2 -.2 -.3 -.4 -.4 -.6 -.2 -.1 -.1 -.3 19 -.2 0 -.1 0 -.1 0 -.2 -.2 -.1 0 20 -2.2 -2.7 -.5 +.5 -2.2 -1.4 -1.1 -2 -.8 0 21 +.1 +.2 +.2 +.4 +.3 +.5 -.1 +.1 +.1 +.2 22 0 +.2 +.8 +.7 +.2 -.3 0 +.1 +.1 +.4 23 0 +.1 +.2 +.3 +.3 +.2 0 +.1 +.2 +.2 24 0 +.1 +.2 +.3 +.3 +.1 0 +.1 +.2 +.2 25 -.1 0 +.2 +.2 +.2 -.1 -.1 0 +.2 +.1 26 -.1 0 +.2 +.2 +.2 -.2 -.1 0 +.2 +.1 
98

Table 13. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature at Rood Brid17.8 degrees Celsius for each management scenario during each month

1994 1995

Scenario May June July August September October May June July Augu

1 0 0 6.5 0 0 0 9.7 23.3 58.1 19.4 

11 0 0 6.5 0 0 0 9.7 23.3 58.1 19.4 12 0 0 3.2 0 0 0 9.7 23.3 54.8 19.4 13 0 13.3 19.4 0 20 0 9.7 26.7 74.2 22.6 14 0 3.3 16.1 0 20 0 9.7 26.7 71 19.4 15 0 0 12.9 0 13.3 0 9.7 26.7 71 19.4 16 0 0 6.5 0 0 0 9.7 23.3 58.1 19.4 17 0 0 3.2 0 0 0 9.7 23.3 48.4 16.1 18 0 0 0 0 0 0 6.5 23.3 48.4 16.1 19 0 0 3.2 0 0 0 3.2 20 54.8 19.4 20 0 0 22.6 3.2 0000 25.8 0 

21 0 0 9.7 0 3.3 0 9.7 26.7 67.7 19.4 22 0 26.7 38.7 0 0 0 9.7 26.7 64.5 19.4 23 0 0 12.9 0 3.3 0 9.7 26.7 71 19.4 24 0 0 12.9 0 3.3 0 9.7 26.7 71 19.4 25 0 0 12.9 0 3.3 0 9.7 26.7 71 19.4 26 0 0 12.9 0 3.3 0 9.7 26.7 71 19.4 
99

Table 14. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature in degrees Ce

scenario at Scholls Bridge (river mile 26.9)

[Shaded cells indicate potential violations of the 17.8 degrees Celsius State temperature standard]

1994 1995

Scenario May June July August September October May June July Augu

1 15.6 17.5 20.3 19.2 18.2 13.5 14.9 17.4 20.6 18.6 

11 15.6 17.5 20.3 19.2 18.2 13.5 14.9 17.4 20.6 18.6 12 15.6 17.5 20.2 19.2 18.2 13.5 14.9 17.4 20.6 18.6 13 15.7 17.5 20.1 19 18.1 13.4 14.9 17.4 20.5 18.5 14 15.8 17.6 20.2 19.2 18.3 13.8 14.9 17.4 20.5 18.6 15 15.9 17.7 20.2 19.3 18.5 14.2 15 17.5 20.5 18.7 16 15.7 17.6 20.3 19.3 18.4 13.8 14.9 17.5 20.6 18.7 17 15.9 17.9 20.3 19.6 18.7 14.6 15 17.6 20.6 18.9 18 16.1 18.1 20.5 19.8 19 15.2 15.1 17.7 20.6 19.1 19 15.6 17.5 20.2 19.2 18.2 13.5 14.8 17.4 20.5 18.6 20 14.1 15.8 20.1 19.4 16.6 12 14.3 16.3 20.2 18.7 

21 15.4 17.2 19.8 18.5 17.6 12.5 14.8 17.2 20.3 18.1 22 15.6 17.4 19.9 19 18.1 13.7 14.9 17.4 20.6 18.4 

23 15.6 17.3 19.9 19 17.7 13.2 14.9 17.3 20.3 18.3 

24 15.6 17.4 19.8 18.7 17.7 13.3 14.9 17.3 20.2 18.2 25 15.8 17.4 19.6 18.5 17.7 13.7 15 17.4 20 18.2 26 15.9 17.5 19.5 18.5 17.7 14.1 15.1 17.4 19.9 18.2 
100

Table 15. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temeach management scenario averaged over each month and Scenario 1 at Scholls Bridge (river mile 26.9)[Positive values show the warming effect, while negative values show the cooling effect, of the management scenario]

1994 1995

Scenario May June July August September October May June July Augu

11 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 0 13 0 -.1 -.1 -.2 -.1 -.1 0 -.1 -.1 -.1 14 +.1 +.1 -.1 +0 +.1 +.3 0 0 -.1 0 15 +.3 +.2 0 +.1 +.3 +.7 +.1 +.1 -.1 +.1 16 +.1 +.1 +.1 +.1 +.1 +.3 0 0 0 +.1 17 +.3 +.3 +.1 +.4 +.5 +1.1 +.1 +.2 0 +.3 18 +.4 +.5 +.2 +.6 +.8 +1.7 +.2 +.3 0 +.5 19 -.1 0 0 0 0 0 -.1 -.1 -.1 0 20 -1.5 -1.7 -.1 +.2 -1.7 -1.5 -.6 -1.1 -.4 +.1 21 -.3 -.4 -.4 -.7 -.7 -1 -.2 -.3 -.2 -.5 22 0 -.1 -.3 -.2 -.1 +.2 0 -.1 0 -.1 23 -.1 -.2 -.4 -.5 -.5 -.3 0 -.1 -.3 -.3 24 0 -.2 -.4 -.6 -.5 -.2 0 -.1 -.3 -.3 25 +.1 -.1 -.6 -.7 -.5 +.2 +.1 -.1 -.6 -.4 26 +.3 0 -.7 -.7 -.5 +.6 +.2 0 -.7 -.4 
101

Table 16. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature at Scholls Br17.8 degrees Celsius for each management scenario during each month

1994 1995

Scenario May June July August September October May June July Augu

1 0 36.7 100 100 66.7 0 19.4 36.7 100 64

11 0 36.7 100 100 66.7 0 19.4 36.7 100 6412 0 36.7 100 100 70 0 19.4 36.7 100 6413 0 36.7 100 100 63.3 0 19.4 36.7 100 6414 0 36.7 100 100 70 0 22.6 36.7 100 71 15 0 40 100 100 73.3 3.2 22.6 36.7 100 7416 0 36.7 100 100 73.3 3.2 19.4 36.7 100 71 17 0 40 100 100 83.3 6.5 22.6 40 100 8018 0 53.3 100 100 93.3 9.7 22.6 40 100 8319 0 36.7 100 100 70 0 19.4 36.7 100 6420 0 3.3 80.6 100 0 0 3.2 20 100 7421 0 33.3 87.1 83.9 40 0 19.4 36.7 100 4122 0 36.7 93.5 100 63.3 0 19.4 36.7 100 5423 0 36.7 93.5 90.3 50 0 19.4 36.7 100 5124 0 36.7 93.5 87.1 50 0 19.4 36.7 100 5425 0 36.7 93.5 87.1 50 0 19.4 36.7 100 5426 0 36.7 96.8 87.1 46.7 0 22.6 36.7 100 54
102

Table 17. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature in degrees Ce

scenario at Elsner Road (river mile 16.2)

[Shaded cells indicate potential violations of the 17.8 degrees Celsius State temperature standard]

1994 1995

Scenario May June July August September October May June July Augu

1 16 18 21.7 20.3 18.9 13.5 15.4 18.3 21.9 19.8 

11 16 18 21.7 20.3 18.9 13.5 15.4 18.3 21.9 19.8 12 16.1 18 21.7 20.3 18.9 13.5 15.4 18.3 21.9 19.8 13 16.1 18 21.6 20.2 18.8 13.5 15.4 18.3 21.9 19.8 14 16.1 18 21.6 20.2 18.9 13.7 15.4 18.3 21.8 19.8 15 16.2 18.1 21.5 20.2 19 13.9 15.4 18.4 21.8 19.8 16 16.1 18.1 21.7 20.3 18.9 13.7 15.4 18.3 21.9 19.8 17 16.2 18.1 21.6 20.3 19.1 14.1 15.5 18.4 21.8 19.9 18 16.3 18.2 21.5 20.4 19.2 14.6 15.5 18.4 21.7 19.9 19 16 18 21.7 20.3 18.9 13.5 15.3 18.3 21.9 19.8 20 15.1 16.9 21.6 20.7 18.3 13.1 15 17.6 21.8 20.1 21 15.9 17.8 21.5 20 18.6 13.1 15.3 18.2 21.8 19.6 22 16 18 21.6 20.2 18.8 13.6 15.4 18.3 21.9 19.7 23 16 17.9 21.5 20.1 18.6 13.4 15.4 18.3 21.8 19.6 24 16 17.9 21.5 20 18.6 13.4 15.4 18.3 21.7 19.6 25 16.1 17.9 21.2 19.8 18.6 13.7 15.4 18.3 21.5 19.5 26 16.2 17.9 21 19.6 18.5 13.9 15.5 18.2 21.3 19.4 
103

Table 18. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temeach management scenario averaged over each month and Scenario 1 at Elsner Road (river mile 16.2)[Positive values show the warming effect, while negative values show the cooling effect, of the management scenario.]

1994 1995

Scenario May June July August September October May June July Augu

11 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 -.1 0 0 0 13 0 0 0 -.1 0 0 -.1 0 0 -.1 14 +.1 0 -.1 -.1 0 +.2 -.1 0 -.1 0 15 +.2 0 -.2 -.1 +.1 +.4 0 0 -.2 0 16 0 0 0 0 +.1 +.2 -.1 0 0 0 17 +.1 +.1 -.1 0 +.2 +.6 0 0 -.1 0 18 +.3 +.2 -.2 +.1 +.4 +1.1 +.1 +.1 -.3 +.1 19 0 0 0 0 0 0 -.1 0 0 0 20 -1 -1.1 -.1 +.4 -.6 -.4 -.4 -.7 -.1 +.3 21 -.2 -.2 -.2 -.3 -.3 -.4 -.2 -.2 -.1 -.2 22 0 0 -.1 -.1 0 +.1 0 0 0 -.1 23 0 -.1 -.1 -.2 -.2 -.1 0 -.1 -.1 -.2 24 0 -.1 -.2 -.3 -.2 -.1 0 -.1 -.2 -.2 25 +.1 -.1 -.5 -.5 -.3 +.1 0.1 -.1 -.4 -.3 26 +.2 -.1 -.7 -.6 -.4 +.4 +.1 -.1 -.7 -.5 
104

Table 19. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature at Elsner Road 

degrees Celsius for each management scenario during each month

1994 1995

Scenario May June July August September October May June July Augu

1 0 43.3 100 100 83.3 6.5 25.8 53.3 100 100 

11 0 43.3 100 100 83.3 6.5 25.8 53.3 100 100 12 0 43.3 100 100 83.3 6.5 25.8 53.3 100 100 13 0 43.3 100 100 83.3 6.5 25.8 50 100 100 14 0 43.3 100 100 83.3 6.5 25.8 50 100 100 15 0 50 100 100 83.3 6.5 25.8 53.3 100 100 16 0 43.3 100 100 83.3 6.5 25.8 53.3 100 100 17 0 50 100 100 90 9.7 25.8 53.3 100 100 18 0 56.7 100 100 96.7 9.7 25.8 53.3 100 100 19 0 43.3 100 100 83.3 6.5 25.8 50 100 100 20 0 30 100 100 73.3 3.2 19.4 40 100 100 21 0 36.7 100 100 76.7 3.2 25.8 46.7 100 9022 0 43.3 100 100 83.3 6.5 25.8 53.3 100 100 23 0 40 100 100 76.7 3.2 25.8 50 100 9324 0 40 100 100 76.7 3.2 25.8 50 100 9025 0 36.7 100 100 76.7 3.2 25.8 50 100 9026 0 36.7 100 100 76.7 3.2 25.8 50 100 90
105

Table 20. Monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature in degrees Ce

scenario at Stafford Road (river mile 5.5)

[Shaded cells indicate potential violations of the 17.8 degrees Celsius State temperature standard]

1994 1995

Scenario May June July August September October May June July Augu

1 16.5 18.5 22.3 21.3 19.3 14.2 16.1 19 22.6 20.9 

11 16.5 18.5 22.3 21.3 19.3 14.2 16.1 19 22.6 20.9 12 16.5 18.5 22.3 21.3 19.3 14.2 16.1 19 22.6 20.9 13 16.6 18.5 22.3 21.2 19.3 14.2 16.1 19 22.6 20.9 14 16.6 18.5 22.3 21.2 19.3 14.2 16.1 19 22.6 20.8 15 16.6 18.5 22.2 21.1 19.3 14.3 16.1 19 22.6 20.8 16 16.6 18.6 22.3 21.3 19.5 14.5 16.1 19.1 22.6 20.9 17 16.8 18.6 22.2 21.3 19.7 15.1 16.3 19.2 22.6 21 18 17 18.8 22.1 21.3 19.9 15.6 16.4 19.3 22.5 21.1 19 16.5 18.5 22.3 21.3 19.3 14.2 16 19 22.6 20.9 20 16.3 17.9 22.4 21.4 18.9 13.3 16 18.8 22.4 20.7 21 16.3 18.3 22.3 21 18.9 13.5 15.8 18.7 22.5 20.5 22 16.5 18.5 22.3 21.2 19.3 14.2 16.1 19 22.6 20.9 23 16.5 18.4 21.9 20.7 18.8 14 16 18.8 22.1 20.3 24 16.5 18.3 21.8 20.6 18.8 14.1 16 18.7 21.9 20.2 25 16.7 18.3 21.4 20.2 18.7 14.3 16.1 18.7 21.5 19.9 26 16.9 18.2 21.1 20 18.6 14.6 16.3 18.8 21.2 19.7 
106

Table 21. Difference between the monthly means of the 7-day moving average of daily maximum simulated 1994 and 1995 water temeach management scenario averaged over each month and Scenario 1 at Stafford Road (river mile 5.5)[Positive values show the warming effect, while negative values show the cooling effect, of the management scenario.]

1994 1995

Scenario May June July August September October May June July Augu

11 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 -.1 0 0 0 13 +.1 0 0 0 0 0 -.1 0 0 0 14 +.1 0 0 -.1 0 0 -.1 0 0 -.1 15 +.1 0 0 -.1 0 +.1 -.1 0 -.1 -.1 16 +.1 0 0 0 +.2 +.3 -.1 +.1 0 0 17 +.3 +.1 -.1 0 +.4 +.9 +.1 +.2 -.1 +.2 18 +.5 +.2 -.2 +.1 +.6 +1.3 +.3 +.3 -.1 +.2 19 0 0 0 0 0 0 -.1 0 0 0 20 -.3 -.6 +.1 +.1 -.4 -.9 -.1 -.1 -.2 -.2 21 -.2 -.2 0 -.2 -.4 -.7 -.3 -.2 -.1 -.4 22 0 0 0 0 0 0 0 0 0 0 23 0 -.2 -.4 -.5 -.4 -.3 -.1 -.2 -.5 -.6 24 0 -.2 -.5 -.6 -.5 -.2 0 -.2 -.7 -.7 25 +.2 -.3 -.9 -1 -.6 +.1 +.1 -.3 -1.1 -1 26 +.4 -.3 -1.2 -1.3 -.7 +.4 +.2 -.2 -1.4 -1.2 
107

Table 22. Percentage of time the 7-day moving average of daily maximum simulated 1994 and 1995 water temperature at Stafford R

17.8 degrees Celsius for each management scenario during each month

1994 1995

Scenario May June July August September October May June July Augu

1 0 70 100 100 83.3 9.7 29 66.7 100 100 

11 0 70 100 100 100 9.7 29 66.7 100 100 12 0 70 100 100 100 9.7 29 66.7 100 100 13 0 70 100 100 100 9.7 29 66.7 100 100 14 0 70 100 100 100 9.7 29 66.7 100 100 15 0 70 100 100 100 9.7 29 66.7 100 100 16 0 70 100 100 100 12.9 29 66.7 100 100 17 6.5 73.3 100 100 100 16.1 29 73.3 100 100 18 25.8 73.3 100 100 100 19.4 32.3 73.3 100 100 19 0 70 100 100 100 9.7 29 66.7 100 100 20 0 40 100 100 86.7 3.2 29 63.3 100 100 21 0 53.3 100 100 90 6.5 25.8 60 100 100 22 0 70 100 100 100 9.7 29 66.7 100 100 23 0 63.3 100 100 90 6.5 29 63.3 100 100 24 0 60 100 100 90 6.5 29 63.3 100 100 25 0 63.3 100 100 90 6.5 29 66.7 100 100 26 6.5 56.7 100 100 90 6.5 32.3 66.7 100 100 
108

SUMMARY AND CONCLUSIONS

In 1994, the USGS and the Unified Sewerage

Agency of Washington County, Oregon, began a cooperative study whose objectives were:

(1) To quantify the temporal and spatial patterns of

water temperature in the main stem of the Tualatin

River and the lower reaches of its major tributaries.

(2) To determine the relation of water temperature in

the Tualatin River and its major tributaries to climatic conditions, seasonal and diel variations, and

human-caused factors.

(3) To assess the effects of various flow-management

practices on water temperature during the lowflow season (May through October).

Streamflow, water-temperature and meteorological data were collected at various locations on the

main stem of the Tualatin River from RM 63.9 to RM

3.4 from May through November during 1994 and

1995.

The data were used to calibrate two dynamicflow heat-transport models, DAFLOW-BLTM and

CE-QUAL-W2. The DAFLOW-BLTM models are

one-dimensional; they were applied to the section of

the river upstream of Rood Bridge (RM 63.9 to RM

38.4). The CE-QUAL-W2 model is a laterally averaged two-dimensional model; it was applied to the

lower river section (RM 38.4 to RM 3.4). A variety of

hypothetical water-management scenarios were

assessed through model simulations, which included

changes in Henry Hagg Lake operation, riparian shading along the main stem, wastewater-treatment plant

operation, and the Oswego diversion dam operation.

The results of modeling simulations for 10 different

scenarios, using data from the 1994 low-flow season,

were documented by Risley (1997).

This report presents model simulation results of

16 additional hypothetical water-management scenarios that were made after completion of the original

study. Simulations for these scenarios used data collected in 1995 in addition to that from 1994. Although

the 16 additional scenarios showed varying effects on

the water temperature of the river system, the State of

Oregon temperature standard was still exceeded in

most of the lower river reaches during the warmer

months in both years. Also, the most extreme cooling

(or warming) effect of any of the scenarios was never

greater than 2.0οC (degrees Celsius) at any location

along the whole reach. The results of these scen

included:

Scenario 11: Existing conditions with 1.33 ft3

decrease in Rock Creek WWTP effluent

The effect of diverting 1.33 ft3

/s of Rock 

wastewater-treatment plant (WWTP) effluent f

gation was evaluated. Temperatures downstrea

that WWTP (RM 38.1) for most months decrea

about 0.05οC or less. Farther downstream, the e

was almost negligible near RM 10.0. The effec

thisscenario is slightly more apparent in the 19

ulation than the 1995 simulation.

Scenario 12: Existing conditions with 1.33 ft3/

withdrawal and 2.0 ft3

/s Henry Hagg Lake rel

In a follow-up scenario, a constant flow o

ft3

/s was withdrawn from the river at RM 37.3 

additional constant flow of 2.0 ft3

/s was release

Henry Hagg Lake to compensate. Again the eff

this scenario on the river system was fairly min

for in 1994 and 1995. Temperatures generally

decreased from RM 60.0 to RM 3.4 by about 0

0.1οC. For most months the overall cooling eff

scenario 12 was slightly greater than the cooling 

of scenario 11.

Scenarios 13–15: Existing conditions with effl

releases of 5 Mgal/d at RM 55.2 and RM 43.8 

10, 20, and 30 Mgal/d at RM 38.1

In another set of scenarios, the effect of p

and then releasing Rock Creek WWTP effluent 

upstream locations (RM 43.8 and RM 55.2) wa

uated. A constant flow of 5 million gallons per 

(Mgal/d) was released at each upstream locatio

addition to a constant release of either 10, 20, o

Mgal/d of effluent at RM 38.1. Temperatures

increased between RM 55.2 and RM 38.1 by ab

1.0οC or less, but were still in compliance with 

water-quality standard. Downstream of RM 38

river temperature decreased (generally 0.6οC o

if the release from Rock Creek WWTP was onl

Mgal/d. If the releases from Rock Creek WWT

20 and 30 Mgal/d, temperatures downstream of 

38.1 generally increased; however, the magnitu

the increase was almost entirely less than 1.0οC
109

Scenarios 16–18: Existing conditions with 25, 45,

and 65 Mgal/d of effluent at RM 38.1 and RM 9.3

The temperature effect resulting from constant

25, 45, or 65 Mgal/d effluent releases from the Rock

Creek (RM 38.1) and Durham (RM 9.3) WWTPs was

evaluated. Temperatures throughout the reach downstream of Rock Creek WWTP, and to a lesser extent

downstream of Durham WWTP, increased proportionately. The magnitude of the increases were by as much

as 0.6, 1.5, and 2.2οC for the three scenarios, respectively.

Scenarios 19–20: Existing and “natural” conditions

with Gaston temperature data replaced with Lee

Falls data

In another scenario, a cooler water-temperature

data set, representing more shaded, “natural” background conditions, was used as input to the model

upper boundary at Gaston (RM 63.9). Water temperatures decreased substantially between RM 63.9 and

the confluence with Scoggins Creek (RM 60.0) by as

much as 4.0οC. However, the effect of the temperature

decrease was overwhelmed by the large volume of

colder water flowing from Scoggins Creek as a result

of releases from Henry Hagg Lake. For most of the

reach downstream of RM 60.0, the overall cooling

effect of this scenario was less than 0.5οC. In a followup scenario, the same model upper boundary condition was used in conjunction with the “natural” background conditions scenario from Risley (1997). Water

temperatures again decreased substantially between

RM 63.9 and the confluence with Scoggins Creek

(RM 60.0); however, between Scoggins Creek and the

Dairy Creek confluence (RM 44.8), water temperatures gradually increased because the unnaturally cool

water released from Henry Hagg Lake was not

present. Nonetheless, almost all of the reach above

Rood Bridge (RM 38.4) was within compliance of the

water-quality standard. Below RM 38.4, temperatures

increased (1.0οC or less) for July and August, and

decreased for other months.

Scenario 21: Existing conditions with WWTP effluent temperature equal to receiving river temperature

The effect of setting the temperature of effluent

released at RM 38.1 and RM 9.3 equal to the temperature of the river was evaluated. Temperatures downstream of RM 38.1 decreased by as much as 2.4οC.

The reduction then tapers off to 0.5οC upstream 

RM 9.3. Downstream of RM 9.3, temperatures

decreased by as much as 1.2οC.

Scenario 22: Existing conditions with up to 10 

d of USA flow augmentation released near Ro

Creek WWTP outfall

Another scenario was used to evaluate the 

of releasing a purchased allotment of Scoggins 

flow (up to, but not exceeding 10 Mgal/d) at RM 

instead of into Scoggins Creek. Observed Scog

Dam temperature data were used for the allotte

Temperatures increased for all months except O

from RM 60.0 to RM 38.1 by as much as 0.6οC

ever, downstream of RM 38.1, temperatures dec

from as much as 0.7οC for all months except O

However, the effect of the supplemental release

became less pronounced moving downstream.

Scenarios 23–26: Existing conditions with 20, 

and 65 Mgal/d of 17.8 degrees Celsius effluen

released at RM 38.1 and RM 9.3

The effect of constant effluent releases of 

45, and 65 Mgal/d at two WWTPs (RM 38.1 an

9.3) was evaluated. The 1994 and 1995 measur

effluent-temperature data from the WWTPs we

used, except that the temperatures were not per

to be greater than 17.8οC. For most months, the 

perature in the reach downstream of both WWT

decreased in all four scenarios. From RM 38.1 

9.3, the temperature decrease was less than 1.0

Downstream of the Durham WWTP (RM 9.3), 

peratures decreased by almost 2.0οC.

REFERENCES CITED

Bartholow, J.M., 1989, Stream temperature investig

Field and analytic methods: U.S. Fish and Wi

Service, Instream Flow and Information Pape

13, 139 p.

Cole, T.M., and Buchak, E.M., 1995, CE-QUAL-W

two-dimensional, laterally averaged, hydrody

and water quality model—Version 2.0-users m

U.S. Army Corps of Engineers, Waterways Ex

ment Station, Instruction Report EL-95-1, 352 
110

Jobson, H.E., 1981, Temperature and solute-transport simulation in streamflow using a Lagrangian reference

frame: U.S. Geological Survey Water-Resources

Investigations Report 81–2, 165 p. [available from the

National Technical information Service, U.S. Department of Commerce, Springfield, VA 22161 as PB-81

225 757]

–——— 1989, Users manual for an open-channel streamflow model based on the Diffusion Analogy: U.S.

Geological Survey Water-Resources Investigations

Report 89–4133, 73 p.

–——— 1997, Enhancements to the Branched Lagrangian

Transport Modeling system: U.S. Geological Survey

Water-Resources Investigations Report 97–4050,

57 p.

Jobson, H.E., and Keefer, T.N., 1979, Modeling highly transient flow, mass, and heat transport in the Chattahoochee River near Atlanta, Georgia: U.S. Geological

Survey Professional Paper 1136, 41 p.

Jobson, H.E., and Schoellhamer, D.H., 1987, Users manual

for a Branched Lagrangian Transport model: U.S.

Geological Survey Water-Resources Investigations

Report 87–4163, 73 p.

Mullane, N., Sturdevant, D., and Baumgartner, R., 1995,

1992–1994 Water quality standards review—Temperature final issue paper: Portland, Oregon, Oregon

Department of Environmental Quality, Standa

Assessment Section, 114 p.

Rantz, S.E., and others, 1982, Measurement and com

tion of streamflow—Volume 1, Measurement 

and discharge; Volume 2—Computation of dis

U.S. Geological Survey Water-Supply Paper 2

631 p.

Rounds, S.A., Wood, T.M., and Lynch, D.D., 1998, 

ing discharge, temperature, and water-quality 

Tualatin River, Oregon: U.S. Geological Surv

Open-File Report 98–186, 122 p.

Risley, J.C., 1997, Relations of Tualatin River water

temperatures to natural and human-caused fac

U.S. Geological Survey Water-Resources Inve

tions Report 97–4071, 143 p.

Risley, J.C., and Doyle, M.C., 1997, Water-tempera

specific-conductance, and meteorological data 

Tualatin River Basin, Oregon, 1994–95: U.S. 

ical Survey Open-File Report 96–315, 124 p.

Theurer, F.D., Voos, K.A., and Miller, W.J., 1984, In

water temperature model—Instream flow info

paper 16: U.S. Fish and Wildlife Service, FW

84/15 [variously paged].