Prepared in cooperation with the U.S. Army Corps of Engineers

Development of CE-QUAL-W2 Models for the Middle Fork 

Willamette and South Santiam Rivers, Oregon

Open-File Report 2013–1186

U.S. Department of the Interior

U.S. Geological Survey
Cover: U.S. Army Corps of Engineers operated dams in the Middle Fork Willamette and South Santiam River Basins. 

From top: (1) Green Peter, (2) Foster, (3) Hills Creek, (4) Lookout Point, (5) Dexter. Photos courtesy of the U.S. Army 

Corps of Engineers.
 

Development of CE-QUAL-W2 Models for the Middle Fork 

Willamette and South Santiam Rivers, Oregon

By Norman L. Buccola, Adam J. Stonewall, Annett B. Sullivan, Yoonhee Kim, and Stewart A. Rounds

Prepared in cooperation with the U.S. Army Corps of Engineers Portland District

Open File Report 2013–1186

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014 

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copyright owners to reproduce any copyrighted material contained within this report.

Suggested citation:

Buccola, N.L., Stonewall, A.J., Sullivan, A.B., Kim, Yoonhee, and Rounds, S.A., 2013, Development of CE-QUAL-W2 

models for the Middle Fork Willamette and South Santiam Rivers, Oregon: U.S. Geological Survey Open-File Report 

2013-1186, 55 p. http://dx.doi.org/10.3133/ofr20131186

ISSN 2331-1258 (online)
iii

Contents

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

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

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

Middle Fork Willamette River Models ............................................................................................................................ 4

Study Area ................................................................................................................................................................. 4

Methods and Data...................................................................................................................................................... 5

Model Description................................................................................................................................................... 5

Model Grids............................................................................................................................................................ 6

Middle Fork Willamette River Model from River Mile 232.5 to 217.7 ...................................................................... 6

Boundary Conditions .............................................................................................................................................. 7

Selection of Time Periods................................................................................................................................... 7

Meteorological Data...........................................................................................................................................10

Hydrologic Data.....................................................................................................................................................11

Inflow Water Temperature .................................................................................................................................13

Lake Profile Data and Outflow Water Temperature...............................................................................................14

HCL Model Development and Calibration.................................................................................................................14

Water Balance.......................................................................................................................................................14

Water Temperature ...............................................................................................................................................16

MFWR Model Development and Calibration .............................................................................................................22

Water Balance.......................................................................................................................................................22

Water Temperature ...............................................................................................................................................24

LOP-DEX Model Development-Calibration ...............................................................................................................26

Water Balance.......................................................................................................................................................26

Water Temperature ...............................................................................................................................................30

Combined MFWR Model Development and Calibration............................................................................................34

Green Peter and Foster Lake Models...........................................................................................................................35

Study Area ................................................................................................................................................................35

Methods and Data.....................................................................................................................................................37

Green Peter and Foster Lake Model Grids............................................................................................................37

Boundary Conditions.................................................................................................................................................37

Meteorological Data ..............................................................................................................................................37

Hydrologic Data.....................................................................................................................................................38

Inflow Water Temperature.....................................................................................................................................38

Lake Profile Data and Outflow Water Temperature...............................................................................................39

GPR-FOS Model Development/Calibration...............................................................................................................39

Water Balance.......................................................................................................................................................39

Water Temperature ...............................................................................................................................................41

Implications for Future Research and Monitoring .........................................................................................................49

Acknowledgments ........................................................................................................................................................49

Supplemental Materials ................................................................................................................................................49

References Cited..........................................................................................................................................................50

Appendix A.Updated Model Parameter Sets ................................................................................................................53
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Figures

Figure 1. Map showing Willamette River Basin study area, Oregon. Circled areas indicate (A) the Middle Fork 

Willamette River and (B) the South Santiam River. ....................................................................................................... 3

Figure 2. Map showing Middle Fork Willamette River study area, Oregon. .................................................................. 5

Figure 3. Diagram showing model grid for the Middle Fork Willamette River (RM 232.5–218.7), Oregon. ................... 7

Figure 4. Graph showing total streamflow into Hills Creek Lake, Oregon, 2002, 2006, 2008, and 2011, along with 

historical percentiles of streamflow data into Hills Creek Lake for 1936–2011. ............................................................. 9

Figure 5. Graph showing estimated and measured temperature at U.S. Geological Survey stream-gaging station 

14144800, North Fork of Middle Fork Willamette River, Oregon. ................................................................................ 14

Figure 6. Graphs showing final water balance for Hills Creek Lake, Oregon, 2002, 2006, 2008, 2011, showing 

measured and modeled water-surface elevations along with the operational rule curve for the lake. ......................... 15

Figure 7. Diagrams showing elevations of operational goals and structures for Hills Creek, Lookout Point, Dexter, 

Green Peter, and Foster Dams, Oregon. Elevations refer to distance above mean sea level (USACE, 2009)............ 16

Figure 8. Graphs showing measured and modeled vertical temperature profiles in Hills Creek Lake, Oregon, 2002. 

(A) near the dam, and (B) near a mid-lake location. .................................................................................................... 18

Figure 9. Graphs showing measured and modeled water temperatures at specific depths in Hills Creek Lake near the 

dam, Oregon, 2011...................................................................................................................................................... 19

Figure 10. Graphs showing measured and modeled outflow temperatures and release rates from Hills Creek Lake 

(HCL), Oregon, 2002 and 2011. Releases were through the power penstocks and the regulating outlet (RO)........... 20

Figure 11. Graphs showing model outflow and temperature for Middle Fork Willamette River and measured flows and 

temperatures at U.S. Geological Survey station 14148000, Oregon, 2002, 2006, 2008, and 2011............................. 23

Figure 12. Graphs showing measured and modeled water-surface elevations at Lookout Point Lake, Oregon, 2002, 

2006 , 2008, and 2011, along with the target rule curve for the lake. .......................................................................... 27

Figure 13. Graphs showing measured and modeled water-surface elevations at Dexter Lake, Oregon, 2002, 2006 , 

2008, and 2011, along with the target rule for the lake................................................................................................ 28

Figure 14. Graphs showing modeled release rates and water temperatures from Dexter Dam and measured 

streamflow and water temperatures at USGS station 14150000, located 2.6 miles downstream of Dexter Dam, 

Oregon, 2002, 2006, 2008, and 2011.......................................................................................................................... 29

Figure 15. Graphs showing continuous measured and modeled water temperatures at specific depths in Lookout 

Point Lake near the dam, Oregon, 2011...................................................................................................................... 31

Figure 16. Graphs showing measured and modeled vertical temperature profiles in Lookout Point Lake near the dam, 

Oregon, 2002............................................................................................................................................................... 32

Figure 17. Graphs showing continuous measured and modeled water temperatures in Dexter Lake near the dam, 

Oregon, 2011............................................................................................................................................................... 33

Figure 18. Graphs showing measured and modeled vertical temperature profiles in Dexter Lake, Oregon, 2002. (A) 

near the dam, and (B) at a mid-lake location. .............................................................................................................. 34

Figure 19. Map showing the Santiam River Basin, Oregon, including the South Santiam River Basin study area and 

key streamflow-gaging sites ........................................................................................................................................ 36

Figure 20. Graphs showing measured and modeled forebay water-surface elevations in Green Peter Lake, Oregon, 

2002, 2006, 2008, and 2011........................................................................................................................................ 40

Figure 21. Graphs showing measured and modeled forebay water-surface elevations in Foster Lake, Oregon, 2002, 

2006, 2008, and 2011.................................................................................................................................................. 41
v

Figure 22. Graphs showing forebay thermistor string data for Green Peter Lake, Oregon, 2011, and model output at 

the same depths and times.......................................................................................................................................... 43

Figure 23. Graphs showing vertical profile temperature data for Green Peter Lake, Oregon, 2002, and model output 

at the same location and dates.................................................................................................................................... 44

Figure 24. Graphs showing modeled outflow temperatures and measured water temperatures for Green Peter Lake, 

Oregon, just downstream of Green Peter Dam, and daily average total and regulating outlet (RO) release rates, 2002, 

2006, 2008, and 2011.................................................................................................................................................. 45

Figure 25. Graphs showing forebay thermistor string data for Foster Lake, Oregon, 2011, and model output at the 

same depths and times................................................................................................................................................ 46

Figure 26. Graphs showing modeled outflow temperatures and measured water temperatures for Foster Lake, 

Oregon, downstream of Foster Dam, and daily average flow through the power and spill outlets, 2002, 2006, 2008, 

and 2011...................................................................................................................................................................... 47

Tables

Table 1. Percentiles of Hills Creek inflow, calendar years 1970–2011.......................................................................... 9

Table 2. Meteorological data sources for the Hills Creek Lake (HCL), Middle Fork Willamette River (MFWR), and 

Lookout Point-Dexter Lake models (LOP-DEX), Oregon............................................................................................. 10

Table 3. Streamflow and water-temperature data sources for the flow and temperature models, Oregon.................. 12

Table 4. Inflow-temperature estimation regression information and fit statistics.......................................................... 13

Table 5. Differences between outlet structure characteristics in original and updated model for Hills Creek Lake, 

Oregon......................................................................................................................................................................... 17

Table 6. Goodness-of-fit statistics comparing measured and modeled water temperatures for the Hills Creek Lake, 

Middle Fork Willamette River, and Lookout Point-Dexter Lakes models, Oregon........................................................ 21

Table 7. Selected model parameters used in the Hills Creek Lake, Middle Fork Willamette River, and Lookout PointDexter Lakes models, Oregon. .................................................................................................................................... 25

Table 8. Differences between outlet structure characteristics in original and updated Lookout Point-Dexter Lakes

models, Oregon. .......................................................................................................................................................... 26

Table 9. Selected model parameter values used in the models for Green Peter and Foster Lakes,Oregon. .............. 42

Table 10. Model goodness-of-fit statistics for water temperature for Green Peter and Foster Lakes, Oregon. .......... 42

Table A1. Differences in model parameter values between the original West Consultants models and the updated 

U.S. Geological Survey Hills Creek Lake and Lookout Point and Dexter Lakes models, Oregon................................ 53

Table A2. Differences between meteorological data sources in the original West Consultants models and the updated 

U.S. Geological Survey Hills Creek Lake and Lookout Point and Dexter Lakes models, Oregon................................ 54

Table A3. Differences in model parameter values between the original West Consultants models and the updated 

U.S. Geological Survey Green Peter Lake and Foster Lake models, Oregon ............................................................. 55
vi

Conversion Factors, Datums, and Abbreviations and Acronyms

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2) 

acre 4,047 square meter (m2)

acre-foot (acre-ft) 1,233 cubic meter (m3)

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

square foot per second (ft2/s) 0.0929 square meter per second (m2/s)

SI to Inch/Pound

Multiply By To obtain

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

square kilometer (km2) 0.3861 square mile (mi2)

square meter (m2) 0.0002471 acre

cubic meter (m3) 0.0008107 acre-foot (acre-ft) 

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

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

square meter per second (m2/s) 10.764 square foot per second (ft2/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: C=(°F-32)/1.8

Datums

Unless otherwise noted, vertical coordinate information is referenced to the North American Vertical Datum of 1988

(NAVD 88).

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

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

Abbreviations and Acronyms

Abbreviation or 

acronym Definition

CE-QUAL-W2 Two-dimensional hydrodynamic and water-quality model

CY Calendar Year

DEX Dexter Lake

FOS Foster Lake

FWSO Foster Dam Weather Station

GPR Green Peter Lake

HCL Hills Creek Lake

HCWO Hills Creek Dam Weather Station

LOP Lookout Point Lake

LOP-DEX Lookout Point-Dexter Lakes

LPWO Lookout Point Dam Weather Station

MAE mean absolute error

ME mean error

NFMFWR North Fork of Middle Fork Willamette River

MFWR Middle Fork Willamette River

NCDC National Climatic Data Center (National Oceanic and Atmospheric Administration)

ODEQ Oregon Department of Environmental Quality

QDT distributed tributary inflow 

RM river mile

RMSE root mean square error

RO Regulating Outlet

RPA Reasonable and Prudent Alternative

SRML Solar Radiation Monitoring Laboratory (University of Oregon)

TDT distributed tributary temperature 

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey
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1

Development of CE-QUAL-W2 Models for the Middle Fork 

Willamette and South Santiam Rivers, Oregon

By Norman L. Buccola, Adam J. Stonewall, Yoonhee Kim, Annett B. Sullivan, and Stewart A. Rounds

Abstract

Hydrodynamic (CE-QUAL-W2) models of 

Hills Creek Lake (HCL), Lookout Point Lake

(LOP), and Dexter Lake (DEX) on the Middle 

Fork Willamette River (MFWR), and models of 

Green Peter Lake and Foster Lake on the South 

Santiam River systems in western Oregon were 

updated and recalibrated for a wide range of flow 

and meteorological conditions. These CE-QUALW2 models originally were developed by West 

Consultants, Inc., for the U.S. Army Corps of 

Engineers. This study by the U.S. Geological 

Survey included a reassessment of the models’ 

calibration in more recent years—2002, 2006, 

2008, and 2011—categorized respectively as low, 

normal, high, and extremely high flow calendar 

years. These years incorporated current damoperation practices and more available data than 

the time period used in the original calibration. 

Modeled water temperatures downstream of both 

HCL and LOP-DEX on the MFWR were within 

an average of 0.68 degree Celsius (°C) of 

measured values; modeled temperatures 

downstream of Foster Dam on the South Santiam 

River were within an average of 0.65°C of 

measured values. A new CE-QUAL-W2 model 

was developed and calibrated for the riverine 

MFWR reach between Hills Creek Dam and the 

head of LOP, allowing an evaluation of the flow 

and temperature conditions in the entire MFWR 

system from HCL to Dexter Dam.

The complex bathymetry and long residence 

time of HCL, combined with the relatively deep 

location of the power and regulating outlet 

structures at Hills Creek Dam, led to a HCL 

model that was highly sensitive to several outlet 

and geometric parameters related to dam 

structures (STR TOP, STR BOT, STR WIDTH). 

Release temperatures from HCL were important 

and often persisted downstream as they were 

incorporated in the MFWR model and the LOPDEX model (downstream of MFWR). The

models tended to underpredict the measured 

temperature of water releases from Dexter Dam 

during the late-September-through-December 

drawdown period in 2002, and again (to a lesser

extent) in 2011, but simulations were much more 

accurate in 2006 and 2008. This episodic model 

bias may have been a result of hot, dry 

conditions; lower lake elevations; and earlier 

drawdown at both HCL and LOP in 2002. These

dry conditions in 2002 may have contradicted 

assumptions inherent in the estimation of certain 

model inputs, such as unmeasured inflows and 

water temperatures, which may respond 

differently during dry years than during normal 

and wet years.

This report documents the development and 

calibration of new and revised flow and watertemperature models for riverine and reservoir 

reaches in the Middle Fork Willamette River and 

South Santiam River systems. Methods and 

model parameter values were established for the 

accurate simulation of flows and temperatures in 

these systems under current conditions. By 

extension, these models should be able to 

accurately simulate flows and temperatures under 

potential future conditions in which dam 

operations and dam outlet structures may be

changed as part of a strategy to improve habitat, 

fish passage, and temperature conditions for 

endangered fish.
2

Introduction

The existence and operation of 13 dams in 

the Willamette River Basin, Oregon (fig. 1), 

owned and operated by the U.S. Army Corps of 

Engineers (USACE), have altered the natural 

hydrological and thermal regime throughout the 

basin (Gregory and others, 2007). Discharge from 

many of these dams is unusually warm in 

autumn, which contributes to high mortality rates 

of incubating eggs of spring Chinook Salmon

(Oregon Department of Fish and Wildlife and 

National Marine Fisheries Service Northwest 

Region, 2011). Reasonable and Prudent 

Alternatives (RPAs) specified in the 2008 

Biological Opinion from the National Marine 

Fisheries Service require the evaluation and 

implementation of feasible operational and (or) 

structural modifications of the dams to address 

flow and water-quality effects of USACE

projects on Upper Willamette River Chinook 

Salmon and winter Steelhead (National Marine 

Fisheries Service, 2008). The objective of these 

RPAs is to improve habitat conditions for 

anadromous fish species listed under the 

Endangered Species Act that will result in 

increased egg survival and increased survival of 

adult and juvenile life stages, causing increases in 

abundance and productivity. 

Mortality rates for spring Chinook Salmon at 

water temperatures greater than 16.0 and 17.0  ̊C 

can exceed 50 and 98 percent, respectively.

Temperatures downstream of dams on the Middle 

Fork Willamette River can exceed these water 

temperatures from the middle of the spawning 

season (September) through mid-October. 

CE-QUAL-W2 models of Hills Creek, 

Lookout Point, and Dexter Lakes on the Middle 

Fork Willamette River (fig. 1, area designated by 

“A”), and Green Peter and Foster Lakes on the 

South Santiam River (fig. 1, area designated by 

“B”), were developed to help manage dam 

releases, understand the effects of the dams on 

stream temperatures, and plan strategies that will 

result in water temperatures less detrimental to 

Chinook Salmon and winter Steelhead 

populations (West Consultants, Inc., 2004a, 

2004b, 2005). CE-QUAL-W2 is a twodimensional, longitudinal-vertical, hydrodynamic

and water-quality model constructed and 

maintained by USACE and Portland State 

University. The model assumes lateral 

homogeneity within each cell of the grid, and, 

therefore, is best suited for relatively narrow 

water bodies that tend to stratify, resulting in 

predominantly longitudinal and vertical waterquality gradients. CE-QUAL-W2 has been 

applied to rivers (Annear and others, 2005), 

reservoirs (Hanna and others, 1999; Bartholow 

and others, 2000; Buccola and others, 2012), 

estuaries (Bowen and Hieronymus, 2003), and 

combinations thereof (Rounds, 2010; Sullivan 

and others, 2011).

Purpose and Scope

This report documents the updated 

calibration and further development of CEQUAL-W2 reservoir models on the Middle Fork 

Willamette and South Santiam Rivers, as well as 

the construction of a CE-QUAL-W2 riverine 

model between Hills Creek Dam and Lookout 

Point Lake on the Middle Fork Willamette River. 

The reservoir models originally were developed 

and calibrated by West Consultants to include 

dam operations as recent as 2002, but those 

models required further testing and updates. The 

main objectives of this study were to: 

• Update the calibration of reservoir models on 

the Middle Fork Willamette River (Hills 

Creek Lake and Lookout Point-Dexter Lakes) 

and the South Santiam River (Green Peter and 

Foster Lakes) for calendar years 2002, 2006, 

2008, and 2011 to include current (2013) dam 

operations and expanded temperature 

monitoring that has occurred since the 

original development of these models. 

• Develop a CE-QUAL-W2 temperature model 

for the riverine reach of the Middle Fork 

Willamette River between Hills Creek Dam 

(river mile [RM] 232.5) and the boat ramp at 

the head of Lookout Point Lake (RM 218.7). 
3

Figure 1. Map showing Willamette River Basin study area, Oregon. Circled areas indicate (A) the Middle Fork 

Willamette River and (B) the South Santiam River.
4

• Link and calibrate the combined models of 

Hills Creek Lake, the Middle Fork Willamette 

River, Lookout Point Lake, and Dexter Lake. 

• Describe and document the new and updated 

CE-QUAL-W2 models, including 

construction, calibration, sensitivity analysis, 

departures from the original West Consultants 

models, and results. 

Two study areas were investigated: (1) the 

Middle Fork Willamette models, which include 

Hills Creek Lake and all Middle Fork Willamette 

River reaches downstream to the outflow at 

Dexter Dam; and (2) the South Santiam model, 

which covers Green Peter Lake on the Middle 

Fork Santiam River downstream to the outflow at 

Foster Dam on the South Santiam River. 

Documentation of the previously existing 

CE-QUAL-W2 reservoir hydrological and 

temperature models is limited in this report to 

significant changes or updates from the original 

model development previously documented by 

West Consultants (2004a, 2004b, 2005). 

Middle Fork Willamette River Models

Study Area

The Middle Fork Willamette River is located 

in the southern, most upstream reaches of the 

Willamette River Basin in western Oregon (figs. 

1 and 2). The river generally runs northwesterly 

and flows through or near the communities of 

Oakridge, Westfir, Dexter, and Lowell before 

joining with the Coast Fork Willamette River to 

form the Willamette River near Eugene and

Springfield, Oregon. Major tributaries of 

consideration include Hills Creek, Salt Creek, 

Salmon Creek, the North Fork of the Middle Fork 

Willamette River, and Fall Creek. The river is 

impounded by three dams (in downstream 

order)—Hills Creek Dam, Lookout Point Dam, 

and Dexter Dam. 

Hills Creek Dam is an earthen dam that is

304 ft (92.7 m) in height; it was completed in 

1961. Hills Creek Lake impounds 355,500 acre-ft 

(4.39×108

 m3) of water at a full pool elevation of 

1,543 ft (470 m). Lookout Point Dam is an earth

and gravel-fill dam with a concrete gated 

spillway; the dam is 276 ft (84 m) in height and 

was completed in 1954. Lookout Point Lake is 

the largest reservoir in the Willamette River 

Basin, impounding 455,800 acre-ft (5.89×108 m3) 

of water at a full pool elevation of 929 ft (283 m). 

Dexter Dam, also an earth and gravel-fill dam 

with a concrete gated spillway, is 93 ft (28.3 m) 

in height and was completed in 1954. Dexter 

Lake impounds 27,500 acre-ft (3.39×107 m3) of 

water at a full pool elevation of 695 ft (212 m). 

Dexter Dam is a re-regulating dam that buffers 

the sometimes irregular flows released from 

Lookout Point Dam. These dams were 

constructed for flood-damage minimization, 

hydropower, and recreation, as well as 

downstream flow augmentation during the lowflow summer season. 

The Middle Fork Willamette River Basin has 

a drainage area of 1,001 mi2

 (2,593 km2). 

Elevation ranges from 618 ft (188 m) at the U.S. 

Geological Survey (USGS) streamflow gage 

(14150000) near Dexter to 8,744 ft (2,665 m) at 

Diamond Peak in the Cascade Range. The reach 

of interest begins at the head of Hills Creek Lake 

and extends downstream through Lookout Point 

and Dexter Lakes to Dexter Dam, a total of 36.2 

river miles (58.3 river kilometers). 

The Middle Fork Willamette River Basin has 

a temperate marine climate typified by dry 

summers and wet winters. Most precipitation falls 

between November and April, and summers and 

early autumn are usually dry. Precipitation in the 

study area averages 62.4 in/yr (158 cm/yr) (U.S. 

Geological Survey, 2012a). At elevations greater 

than 4,000 ft (1,219 m), about 35 percent of 

annual precipitation falls as snow (Lee and 

Risely, 2002). Diurnal and annual air temperature 

ranges are relatively small for this latitude, owing 

largely to the dominance of eastward-moving 

marine airflow patterns. The average maximum 

daily air temperature for the study area is 13.9°C, 

and the average minimum daily air temperature is 

2.1°C (U.S. Geological Survey, 2012a).
5

Figure 2. Map showing the Middle Fork Willamette River Basin, Oregon, including the Middle Fork Willamette River 

Basin study area and key streamflow-gaging sites.

For the entire Middle Fork Willamette River 

Basin (both the study area and downstream to its 

confluence with the Coast Fork Willamette 

River), 94.7 percent of land use is forest (72

percent public, and 28 percent private) (Middle 

Fork Willamette Watershed Council, 2012). 

Other land uses include water (1.9 percent), nonrange agricultural (1.3 percent), urban and 

residential (1.3 percent) and wetlands (0.5 

percent).The study area is mostly rural. The entire 

Middle Fork Willamette River Basin has a 

population of only 24,000 residents (Middle Fork 

Willamette Watershed Council, 2012). 

Methods and Data

Model Description

The Middle Fork Willamette and South 

Santiam River models were developed using the 

CE-QUAL-W2 model, version 3.7, revision 12 

(Cole and Wells, 2011). Initial development of 

the CE-QUAL-W2 reservoir models used in this 

study was completed by West Consultants as 

follows: Hills Creek Lake (HCL) (West 

Consultants, Inc., 2004a), and Lookout Point and 

Dexter Lakes (LOP-DEX) (West Consultants, 

Inc., 2004b); further details can be found in those 

references. 

Development and calibration of these models 

generally occur in a three-step procedure: 

(1) creating the model grids, (2) compiling or 
6

estimating boundary conditions, and (3) 

calibrating lake elevations, streamflow and 

circulation, and temperature. Model bathymetric

grids for the HCL and LOP-DEX models 

remained unchanged from the original West 

Consultants models, but many new parameter 

values and datasets were used to update and 

improve the calibration (appendix A). 

Model Grids 

The longitudinal dimension (upstream and 

downstream) of the CE-QUAL-W2 model grid is 

constructed from model segments. Each segment 

contains layers of defined width that either 

increase or remain constant from the bottom of 

the channel to the top of the grid. Collections of 

segments can be grouped together into 

“branches.” Branches typically are used to define 

specific reaches of river, potentially including 

tributaries. Similarly, one or more branches can 

be grouped together to form “waterbodies,” the 

largest building blocks of the model grid. Each 

waterbody can have unique sets of 

meteorological conditions, hydrologic 

coefficients, and structures. In effect, a model 

with more than one waterbody is composed of 

separate models where the output of the mostupstream waterbody model is the input for the 

next waterbody model downstream. 

The HCL model is composed of a single 

waterbody with four branches. The HCL model 

grid contains 43 segments (ranging from 259.7 to 

497.4 m in length) and 178 layers (0.5 m in 

height). The LOP-DEX model incorporated 2 

waterbodies (a single branch for each waterbody) 

in a single model. The LOP grid (waterbody 1 of 

LOP-DEX) is composed of 35 segments (503.5 m 

in length) and 74 layers (1 m in height), although 

the DEX grid (waterbody 2 of LOP-DEX) is 

composed of 19 segments (249.1 m in length) and 

74 layers (1 m in height). Between Hills Creek 

Dam and the head of Lookout Point Lake, 

however, is an almost 15-mi reach of the Middle 

Fork Willamette River that was not covered by a 

model, making it difficult to use the HCL and 

LOP-DEX models together. In this study, a 

separate and new CE-QUAL-W2 model was 

developed to simulate the streamflow and 

temperature conditions in the Middle Fork 

Willamette River between Hills Creek Dam and 

Lookout Point Lake. 

Middle Fork Willamette River Model from River 

Mile 232.5 to 217.7 

The Middle Fork Willamette River (MFWR) 

model grid (fig. 3) was developed in several 

steps. First, data from the two long-term USGS 

stream-gaging stations (14145500 and 14148000) 

located along the stretch of river included in the 

model were evaluated. Cross sections for the 

model were developed using historical, highstreamflow measurements of the channel shape 

taken from cableways placed across the river.

Second, aerial photography of the reach was 

evaluated to allow the inclusion of variations in 

the river’s surface width and other characteristics. 

Measured gage height at the two streamgages on 

the date the aerial photographs were taken was 

used to calculate water depths for 28 equidistant 

reaches along the river. River width and 

orientation were estimated using the aerial 

photographs. Channel shape and segment 

elevation were estimated using Geographic 

Information System (GIS) techniques, 

extrapolating the channel shapes from the gage 

locations. Initial channel cross-sectional shapes, 

however, were determined to be too narrow near 

the base, and a more gradual decrease in width 

was integrated into the channel shape by 

establishing minimum channel widths based on a 

combination of aerial photography and the cross 

sections developed from the two streamgaging 

stations.

The 28 river reaches originally were each 0.5 

mi (804.7 m) in length. Subsequent analysis 

revealed that specific segments were too steep for 

the CE-QUAL-W2 model to run without failing. 

The steepest segments were divided into smaller 

segments until the model became sufficiently 

stable. The resulting MFWR model grid (fig. 3) 

contained 84 active segments in one waterbody. 
7

Figure 3. Diagram showing model grid for the Middle Fork Willamette River (RM 232.5–218.7), Oregon.

Segments ranged in length from 134.11 to 804.67 

m, with an average length of 265 m. Total model 

length was 22.3 km (13.8 mi) and covered the 

length of the Middle Fork Willamette from the 

outlet at Hills Creek Dam to about 1 mi upstream 

of the Hampton Boating dock, near the 

confluence of Rock Creek (RM 232.5 to 218.7). 

Layer heights were fixed at 0.2 m. Tributaries of 

Salt Creek, Salmon Creek, and the North Fork of 

the Middle Fork Willamette River (NFMFWR) 

flow into the MFWR model in segments 14, 27 

and 70, respectively. The MFWR model reach 

has a mean slope of 0.0049 m/m. 

Boundary Conditions

Selection of Time Periods

In order to consider a wide range of 

hydrologic and meteorological conditions within 

the Middle Fork Willamette River Basin,

calendar years were selected that represented 

relatively wet, normal, and dry conditions. The 

calendar year was selected instead of the water 

year to compare water temperatures that were 

linked with dam operations, which are based on 

the calendar year. calendar years were evaluated 

for the amount of streamflow and temperature 

data available within the basin. Data-rich years 

are easier to calibrate, as fewer inputs need to be 

estimated and model results can be calibrated to 

measured conditions. The years 1970 through 

2011 were adopted for consideration, 

representing the 33 years of data simulated with 

the West Consultants models (through 2002) and

more recent years. calendar years were evaluated 

using the following criteria: 

• Comparability of streamflow to the historical

percentiles designated for wet (75th

percentile), normal (median), and dry (25th

percentile) years; 
8

• Availability and frequency of streamflow data 

upstream and downstream of all model 

reaches; 

• Availability and frequency of stream

temperature data upstream and downstream of 

all model reaches; 

• Availability of vertical temperature profile 

data in all three reservoirs; and

• Availability of streamflow and stream 

temperature data for major tributaries entering 

the system.

Availability of streamflow data was the least 

restrictive of the criteria. Between the USGS 

streamgages 14144800 (MFWR near Oakridge), 

14145500 (MFWR upstream of Salt Creek, near 

Oakridge), 14148000 (downstream of NFMFWR 

near Oakridge), and 14150000 (MFWR near 

Dexter) (fig. 2), all but the first station had 

streamflow data available for the entire study 

period. Additionally, estimates of streamflow 

inputs and outputs for each reservoir system were 

available from USACE for the entire study 

period. 

Temperature data were less abundant than 

streamflow data. Periods with the most 

temperature data available included 1978–1982, 

when the most USGS temperature gages in the 

study area were active; 2002, when temperature 

data from the Oregon Department of 

Environmental Quality (ODEQ) were most 

actively collected; and 2011. Discrete vertical

profile measurements of water temperature in the 

reservoirs were available for 1971, 1975–76, and 

2002, while continuous time-series profile 

measurements were made in 2010–11. USGS 

streamflow and temperature data were available 

at a daily frequency prior to about 1987, and at 

frequencies between hourly and every 15 minutes

after 1987. 

The year 2002 was selected to represent dry 

conditions. In addition to having ample 

temperature and streamflow data, 2002 was one 

of only six of the potential years evaluated with 

temperature profile data available. Finally, 2002 

was modeled by West Consultants in their 

original model development work, allowing for a 

comparison of model results to the updated 

models from this study. The year 2002 was 

characterized by a mild spring and a relatively 

warm and dry summer (fig. 4, table 1). 
9

Figure 4. Graph showing total streamflow into Hills Creek Lake, Oregon, 2002, 2006, 2008, and 2011, along with 

historical percentiles of streamflow data into Hills Creek Lake for 1936–2011.

Table 1. Percentiles of Hills Creek inflow, calendar years 1970–2011.

Year

Full calendar 

year

January–

September

Spring flow: 

March–May

Summer flow: 

June–September

Fall flow:

October–

December

2002 0.18 0.32 0.39 0.21 0.19

2006 0.78 0.71 0.29 0.53 0.78

2008 0.71 0.81 0.90 0.90 0.40

2011 0.90 0.88 0.91 0.99 0.08

Spring and summer of 2006 were selected to 

represent average (normal) streamflow 

conditions. Although 2006 was not rich in data, 

late spring and summer streamflow conditions 

during 2006 were usually near the median 

historical flow (fig. 4), making most of 2006 

representative of average conditions. 

Spring and summer of 2008 were 

representative of historical wet conditions. 

Similar to 2006, 2008 had incomplete data, but 

more temperature data were available in 2008 

than in other calendar years that were considered 

representative of wet conditions. Late spring and 

early summer streamflows in 2008 were typically 
10

near or above the 75th percentile (fig. 4). 

Towards the end of both 2006 and 2008, 

streamflow levels began to deviate from summer 

and early autumn conditions. Beginning in early 

November 2008, drier conditions resulted in lessthan-average streamflows for most of December. 

Conditions from 2011 did not fit well with 

any of the three categories used for data 

selection—dry, normal, or wet. An especially wet 

spring in 2011 resulted in high summer flows, 

which were followed by a dry autumn. The year 

2011 was the most data-rich of all calendar years

considered for selection; therefore, 2011 was 

added to the study so that at least one data-rich 

calendar year was available to aid in the 

calibration of the models. 

Meteorological Data

CE-QUAL-W2 requires time series inputs of 

six meteorological parameters: air temperature, 

dew-point temperature, wind speed, wind 

direction, cloud cover, and solar radiation. 

Meteorological data for the models were obtained 

from four sources (table 2): 

1. USACE Hills Creek Dam Weather Station 

(HCWO), 

2. USACE Lookout Point Dam Weather Station 

(LPWO), 

3. National Oceanic and Atmospheric 

Administration site at the Eugene airport 

(National Climatic Data Center [NCDC]), and 

4. University of Oregon Solar Radiation 

Monitoring Laboratory (SRML) in Eugene. 

All datasets were screened for outliers, and when 

possible, compared with similar datasets from 

nearby locations.

Table 2. Meteorological data sources for the Hills 

Creek Lake (HCL), Middle Fork Willamette River 

(MFWR), and Lookout Point-Dexter Lake models 

(LOP-DEX), Oregon. 

[Abbreviations: NCDC, National Climatic Data 

Center; EUG, Eugene; USACE, U.S. Army Corps of 

Engineers; HCWO, Hills Creek weather station; LPWO, 

Lookout Point weather station]

Parameters HCL

MFWR, 

LOP-DEX

Air temperature, dew 

point temperature

NCDC EUG 

regression 

(20021

), 

USACE HCWO

NCDC EUG 

regression 

(20021

), 

USACE 

LPWO

Wind speed, wind 

direction, cloud 

cover, solar radiation

NCDC EUG NCDC EUG

1 In 2002, NCDC EUG data from 2006, 2008, 2009, and 

2011 were used to estimate USACE LPWO and 

HCWO.

Air temperature data were retrieved from the 

USACE Dataquery website (U.S. Army Corps of 

Engineers, 2012a) for the weather stations at 

Hills Creek Dam (HCWO) and Lookout Point 

Dam (LPWO), and converted to degrees Celsius. 

For the MFWR model, comparisons of model 

results were made using data from HCWO and 

LPWO, and it was determined that the data from 

LPWO provided better results. 

Dew-point temperature can be estimated 

from air temperature and relative humidity with 

the following equation (Lawrence, 2005): 

Tdp = Ta − 100−RH

5 (1)

where 

Tdp = Dew point temperature in degrees Celsius; 

Ta = Air temperature in degrees Celsius; and

RH = Relative humidity in percent. 

Dew-point temperatures were calculated using 

this equation and air temperature and relative 

humidity data from HCWO and LPWO. 

Four sources were considered for wind speed 

data—LPWO, HCWO, the Primet station 
11

operated by the U.S. Forest Service in the H.J. 

Andrews Experimental Forest, and the weather 

station at the Eugene airport. Despite their 

relative proximity, the wind speeds recorded at 

the four sites were dissimilar. West Consultants, 

Inc. (2004a, 2004b) noted that the wind speeds at 

both Hills Creek and Lookout Point Dams are 

subject to updrafts at the dam faces and, 

therefore, those sites do not provide reliable 

measurements of wind speed or direction for their 

respective areas. Similarly, the Primet station is 

located in a forest clearing (West Consultants, 

Inc., 2004a). Therefore, wind speeds at the Primet 

station may be under-representative of that area 

because of sheltering of the sensor by the nearby 

forest. Finally, it was surmised that of the three 

remaining wind stations, the data from the 

Eugene airport were believed to be most 

rigorously controlled for quality. As a result, 

wind speed and direction data from the Eugene 

airport station were used in the models. Wind 

speed was converted to metric units and wind 

direction was converted to radians for the model, 

where 0 radians means wind from the north. The 

wind speed measurement height (CE-QUAL-W2 

parameter WINDH) was set to 10 m.

Cloud-cover data were obtained from the 

weather station at the Eugene airport. The coding 

used for cloud cover data by NCDC (National 

Oceanic and Atmospheric Administration, 1998) 

was converted from text to the numeric (1-10) 

format required for CE-QUAL-W2 input similar 

to U.S. Environmental Protection Agency (1997) 

methods as follows: “CLR”=0, “FEW”=1.5, 

“SCT”=3.8, “BKN”=6.9, “POB”=8, “OBS”=9, 

“OVC”=10.0, “***”=NA (where NA is missing 

data).

Solar radiation data were retrieved from the 

SRML (University of Oregon, 2012). Global 

radiation values were used (the sum of direct, 

diffuse, and ground-reflected values), and 

converted from Langleys per hour to watts per 

square meter.

Precipitation data were available from 

USACE at HCWO and LPWO for 2006, 2008, 

and 2011. Precipitation data were available from 

Agrimet Station CRVO in Corvallis, Oregon, for 

2002 (fig. 1). Precipitation temperature was 

estimated to be equal to air temperature. 

Hydrologic Data

Measured streamflow and temperature data 

were used when available, but many input 

datasets had to be estimated (table 3). The three 

primary sources of data were the USGS National 

Water Information System (U.S. Geological 

Survey, 2012b), the USACE Dataquery Web site 

(U.S. Army Corps of Engineers, 2012a), and the 

ODEQ Laboratory Analytical Storage and 

Retrieval (LASAR) database (Oregon 

Department of Environmental Quality, 2011a).
12

Table 3. Streamflow and water-temperature data sources for the flow and temperature models, Oregon. 

[Shaded rows indicate model connection nodes. Abbreviations: USGS, U.S. Geological Survey; E: estimated, M: 

measured;]

Model 

Inflow/Outflow 

Location Station name USGS ID

2002 2006 2008 2011

Q T Q T Q T Q T

HCL, Branch 1 MF Willamette R above 

Hills Creek

14144800 E E E E E E E M

HCL, Branch 2 Packard Creek - E E E E E E E E

HCL, Branch 3 Larison Creek - E E E E E E E E

HCL, Branch 4 Hills Creek 14144900 E E E E E E E M

MFWR, Segment 

11

MF Willamette R above 

Salt Creek near Oakridge

14145500 M M1 M M M M

MFWR, Segment 

14

Salt Creek 14146000 E E E E E E E E

MFWR, Segment 

27

Salmon Creek 14146500 E E E E E E E E

MFWR, Segment 

70

North Fork of Middle 

Fork Willamette River

14147500 E E E E E E E M

LOP, Branch 1 MF Willamette R blw 

NFMFW

14148000 M M M M M

2.4 Miles 

downstream of 

DEX

MF Willamette R blw 

Dexter

14150000 M M M M M M M M

1 Partial year of data existed from the Oregon Department of Environmental Quality.

For the Hills Creek Lake model, measured 

streamflow data were not available for the Middle 

Fork Willamette River near Oakridge (USGS 

station 14144800) and Hills Creek upstream of 

Hills Creek Lake (USGS station 14144900) after 

1997 and 1981, respectively. However, 

streamflow data were collected at the two stations 

for 40 and 24 years, respectively, providing 

adequate data to perform a regression analysis 

with nearby USGS stations and the USACEcomputed inflow into Hills Creek Lake. A 

forward stepwise regression was created to 

estimate streamflows for the study period at 

stations 14144800 and 14144900. 

Streamflow was estimated for Larrison 

Creek using a logarithmic regression analysis 

with data from Hills Creek. Because no 

streamflow data were available for Larrison

Creek, the 95th percentile of streamflow 

exceedance, median streamflow, and 2-year flood 

were estimated using Streamstats (U.S. 

Geological Survey, 2012a) for both creeks. The 

logarithmic regression model then was run using 

those three points. Packard Creek streamflow was

estimated in the same manner, also using Hills 

Creek as an index.

The reach of the Middle Fork Willamette 

River between Hills Creek Dam and Lookout 

Point Lake is about 13.8 mi in length. Three

significant tributaries join the MFWR along this 

stretch—Salt Creek (USGS station 14146000), 

Salmon Creek (USGS station 14146500) and the 
13

North Fork of the Middle Fork of the Willamette 

River (USGS station 14147500) (fig. 2). All three 

tributaries have been gaged by USGS in the past. 

Tributary inflows for modeled calendar years 

without gage data were estimated using multiple 

linear regressions with regional gaged streams. 

When possible, regional gaged streams that 

represented similar climatological and 

topographical conditions were selected. 

Additionally, streamgages were selected that had 

the most overlap of record, and that surrounded

the Middle Fork Willamette River in all 

directions so as to minimize any bias from the 

movement of weather patterns. Streamflow data 

for the upper end of this reach of the MFWR was 

taken from USGS station 14145500 (fig. 2). At 

the end of the reach upstream of Lookout Point 

Lake, streamflow calculations were compared 

with data from USGS station 14148000. Both 

stations were in operation throughout the 4 

calendar years modeled for this study. 

For the Lookout Point and Dexter Lakes 

model, USGS streamflow data were available as 

both inputs (station 14148000) and outputs 

(14150000) for all 4 calendar years modeled (fig.

2). Hourly release rates from the various outlets 

of HCL, LOP, and DEX were obtained from 

USACE and were used as outflow boundary 

conditions to the models. Forebay water-surface 

elevations were measured by USACE at HCL, 

LOP, and DEX, and those data were compared to 

modeled elevations during the water-balance 

calibration.

Inflow Water Temperature

Measured upstream boundary condition 

temperature data were available in 2011 for the 

HCL model (USGS stations 14144800 and 

14144900), the MFWR model (1USGS station 

4145500), and the LOP-DEX model (USGS 

station 14148000) (table 3). Additionally, 

measured temperature data were available in 

2011 for the largest tributary in the MFWR 

model (NFMFWR, 14147500). 

All other inflowing temperature boundary 

conditions to the models were approximated 

using a nonlinear multiple loess regression (R 

Development Core Team, 2009). Stream 

temperatures measured by ODEQ during the 

summer of 2002 (June 1–September 9) were used 

to develop these regression models for Salt 

Creek, Hills Creek (USGS 14144900; ODEQ 

27982), and MFWR (USGS 14144800; ODEQ 

27986) based on measured temperatures at other 

USGS sites in the Willamette River Basin (table 

4). The regression model for the NFMFW (USGS 

14147500) was based on calendar year (CY) 

2011 measured data and resulted in an accurate 

stream temperature estimate (fig. 5, table 4). Salt 

Creek temperature estimates were used as inflow 

temperatures for Larrison and Packard Creeks 

(branches 2 and 3 of the Hills Creek Lake 

model). Similarly, the data from the NFMFWR 

were used as the inflow temperatures for Salmon 

Creek (tributary 2 in the MFWR model). 

Table 4. Inflow-temperature estimation regression information and fit statistics.

[Abbreviations: sfmck, South Fork McKenzie River (14159200); nsbld, North Santiam River at Boulder (14178000); 

blwcr, Blowout Creek (14180300) ; USGS, U.S. Geological Survey; ODEQ, Oregon Department of Environmental 

Resources-, no USGS site ID].

Model inflow 

location

Model inflow 

temperature estimate

Site ID

Year

Dependent 

variables

Goodness of fit statistics

USGS ODEQ MAE ME RMSE

HCL, Branch 1 MF Willamette R above 

Hills Creek 14144800 27986 2002 sfmck, nsbld, blwcr 0.35 0 0.45

HCL, Branch 2 Hills Creek 14144900 27982 2002 sfmck, nsbld, 

blwcr 0.57 0.01 0.79

MFWR, Segment 70 North Fork of Middle 

Fork Willamette River 14147500 28003 2011 sfmck, nsbld, blwcr 0.44 -0.02 0.55

MFWR, Segment 14 Salt Creek - 28007 2002 sfmck, blwcr 0.38 0 0.48
14

Figure 5. Graph showing estimated and measured temperature at U.S. Geological Survey stream-gaging station

14144800, North Fork of Middle Fork Willamette River, Oregon.

Lake Profile Data and Outflow Water Temperature

Vertical lake profile data for two locations at 

HCL, one location at LOP, and two locations at 

DEX were provided by USACE for 2002 and 

2011. Profile data were collected near the dam in

all three reservoirs for both years. In 2002, 

instantaneous temperature profile measurements 

were made once or twice a month from late 

spring to late summer. Additional profiles at HCL 

(2002 only) and DEX (2002 and 2011) were 

collected farther upstream of the dam, and were 

labeled as “Mid-Lake”. This location was 

estimated to coincide with segments 20 and 48 in 

the HCL and DEX models, respectively. In 2011, 

profile data were collected in 15-minute intervals

by USACE from DEX from late April to late 

October, and from HCL and LOP from the start 

of 2011 through late November. 

Hourly temperature data were available 

downstream of HCL at USGS station 14145500 

during the summer 2002 and all of 2011. 

Downstream of DEX at USGS station 14150000, 

hourly temperature data were available in 2002, 

2006, 2008, and 2011. 

HCL Model Development and Calibration

Water Balance

Prior to the calibration of temperature, the 

Hills Creek Lake (HCL) model was calibrated to 

simulate the lake water-surface elevation for each 

of the 4 years: 2002, 2006, 2008, and 2011. Lake 

elevation can have a substantial effect on the 

accuracy of the simulated temperatures. The 

process of closing the water balance for the lake 

minimizes the error owing to differences between 

measured and modeled lake elevation. To match 

modeled water-surface elevations with measured 

lake elevations (fig. 6), a distributed tributary 

inflow time series (QDT) was iteratively 

developed for each year by converting the daily 

average difference between measured and 

modeled lake elevation into a daily inflow (or 

loss) to the model. Distributed tributary 

streamflows are created to account for small, 

unmodeled tributaries and gains and losses from 

groundwater interaction or dam leakage. The 

percentage of QDT inflow compared to total 

inflow to the model varied for each calendar year, 

but median values ranged from 1.0 (2002) to 9.2 

percent (2011). Similarly, 90th-percentile values 

ranged from 12.7 (2006) to 19.5 percent (2011). 
15

Figure 6. Graphs showing final water balance for Hills Creek Lake, Oregon, 2002, 2006, 2008, 2011, showing 

measured and modeled water-surface elevations along with the operational rule curve for the lake.
16

Water Temperature

Hills Creek Dam has two radial tainter 

spillway gates that are only used in emergencies, 

two regulating outlets (ROs), and two power 

outlets (U.S. Army Corps of Engineers, 2009). 

The Hills Creek Lake model originally was 

configured with two structures at elevations of 

455.5 and 442 m (West Consultants, Inc., 2004a). 

In this study, the structure elevations were reset 

to the centerline structure elevations (433.0 and 

425.0 m) gathered from USACE documentation 

for Hills Creek Dam (U.S. Army Corps of 

Engineers, 2009; Kathryn Tackley, U.S. Army 

Corps of Engineers, oral commun., 2012) (fig. 7).

Figure 7. Diagrams showing elevations of operational goals and structures for Hills Creek, Lookout Point, Dexter, 

Green Peter, and Foster Dams, Oregon. Elevations are relative to the National Geodetic Vertical Datum of 1929 

(NGVD 29) (U.S. Army Corps of Engineers, 2009). 

Because Hills Creek Dam does not have 

outlets near the bottom of the reservoir, there is 

little opportunity to release deeper water during 

the winter when lake elevations are lower. This 

leads to a long theoretical retention time (0.5–2.0 

years) and a greater tendency for turbid water to 

remain at depth through the summer compared to 

the downstream Lookout Point Lake (Larson, 

2001). Additionally, the ROs and the power 

penstocks at HCL are at similar depths and are 

the only outlets used, causing the thermocline to 

be situated near these outlet structures in late

summer and early autumn. The strong influence 

of Hills Creek Dam outlet structures and releases 

on the circulation and vertical thermal structure in 

the lake led to a model that was highly sensitive 
17

to outlet structure parameters. In this study, the 

model parameters STR TOP and STR BOT 

(representing the upper and lower layer [depth] 

limits from which water is allowed to flow 

through model outflow structures) were varied to 

calibrate the HCL model with respect to outflow 

temperatures and profile temperatures near the 

dam. Changes that were made to the original 

West Consultants HCL model relating to outlet 

structure parameters are summarized in table 5. 

Table 5. Differences between outlet structure characteristics in original and updated model for Hills Creek Lake, 

Oregon. 

[Abbreviations: STR, structure; RO, regulating outlet; Power, power penstock outlet; m, meter; USGS, U.S. Geological 

Survey]

Parameter

West Consultants model USGS model

Description

STR 1 

(Power)

STR 2 

(RO)

STR 1

(RO)

STR 2 

(Power)

STR TOP 2 2 10 10 Structure top selective withdrawal limit

STR BOT 69 69 89 99 Structure bottom selective withdrawal limit

STR SINK POINT LINE LINE LINE Sink type used in the selective withdrawal 

algorithm

STR ELEV 442.0 455.5 431.3 423.3 Centerline elevation of structure, m

STR WIDTH - 38.4 6.0 5.8 Width of structure (line sink), m

The Hills Creek Lake model distributed 

tributary flow estimates (QDT) were

accompanied by distributed tributary temperature 

estimates (TDT). The TDT was estimated as 

follows: 

TDT = 0.9Ta + 0.1Ts (2)

where

Ta = average annual air temperature measured at 

Hills Creek Lake, and

Ts = estimated Salt Creek temperature, both in 

degrees Celsius. 

Groundwater temperatures tend to be well 

represented in many areas by an annual average 

air temperature (Ta). Modeled temperatures near 

the bottom of Hills Creek Lake were sensitive to 

the TDT values, and tended to fit measured 

temperatures better when the TDT was assumed 

to be relatively constant and near an assumed 

groundwater temperature for the area.

Instantaneous temperature profiles measured

by USACE in 2002 near Hills Creek Dam and at 

the “mid-lake” locations were well matched by 

the HCL model, except for some errors near the 

lake surface (fig. 8). Continuous profiles in 2011, 

also measured by USACE, were matched well by 

the model, especially in the epilimnion (depths 

less than 39.4 ft [12.0 m] in fig. 9). During July–

November, 2011, the HCL model tended to 

overpredict temperatures between depths of 12 m 

(39.4 ft) and 43 m (141 ft). The bathymetry of the 

lake near the dam is complex, and circulation 

near the Hills Creek arm of the lake may be 

affecting the ability of the model to capture some 

of these seasonal temperature patterns near the 

depth of the outlets. Accurately capturing the 

thermal structure in the lake was somewhat of a 

compromise against accurately simulating the 

release temperatures; improvements in one often 

led to degradation of the other. Model 

performance, however, was deemed acceptable, 

as the downstream release temperatures were 

matched with good accuracy. 
18

Figure 8. Graphs showing measured and modeled vertical temperature profiles in Hills Creek Lake, Oregon, 2002. 

(A) near the dam, and (B) near a mid-lake location.
19

Figure 9. Graphs showing measured and modeled water temperatures at specific depths in Hills Creek Lake near 

the dam, Oregon, 2011. 

Measured temperatures in the Middle Fork 

Willamette River downstream of Hills Creek 

Dam at USGS site 14145500 were available from 

Oregon Department of Environmental Quality 

(2011a) for the summer of 2002 (June 1–

September 9) and for all of 2011 from U.S. 

Geological Survey (2012b) for model outflow 

temperature calibration. Modeled outflow 

temperatures from HCL were slightly low (mean 

error [ME] of -0.52°C) compared to measured 

values in 2002 (table 6 and fig. 10). In 2011, 

HCL model outflow temperatures matched 

closely for the majority of the year (ME = 

0.03°C, mean absolute error [MAE] = 0.50°C) 

despite some over-predictions during the 

November and December drawdown period 

(fig. 10). 
20

Figure 10. Graphs showing measured and modeled outflow temperatures and release rates from Hills Creek Lake 

(HCL), Oregon, 2002 and 2011. Releases were through the power penstocks and the regulating outlet (RO).
21

Table 6. Goodness-of-fit statistics comparing measured and modeled water temperatures for the Hills Creek 

Lake, Middle Fork Willamette River, and Lookout Point-Dexter Lakes models, Oregon. 

[Goodness-of-fit statistics are in degrees Celsius. Abbreviations: DEX, Dexter Lake; HCL, Hills Creek Lake; LOP, 

Lookout Point Lake; ME, mean error, MAE, mean absolute error; MFWR, Middle Fork Willamette River; RMSE, root 

mean square error; Q, flow; T, water temperature; USGS, U.S., Geological Survey]

Model

Upstream 

Boundary

Type of 

Measurement 

Data Year

Number of 

Observations ME MAE RMSE

HCL Measured Q, T

Outflow

2002 2,401 -0.52 0.68 0.82

2011 8,735 0.03 0.50 0.61

Near-dam 

depth profiles 2002 215 -0.54 0.86 1.09

Thermistor 

string 2011 96,020 0.30 0.65 1.04

MFWR at USGS 

14148000

HCL 

Modeled Q, T Outflow

2002 2,688 -0.49 0.75 0.96

2008 2,242 0.40 0.61 0.76

2011 34,934 -0.01 0.49 0.62

Measured Q, T Outflow 2011 34,934 -0.06 0.53 0.66

LOP Measured Q, T

Near-dam 

depth profiles 2002 216 -0.58 0.74 0.99

Thermistor 

string 2011 91,848 0.17 0.54 0.77

DEX

Measured Q; 

MFWR 

Modeled T

Near-dam 

depth profiles 2002 65 0.00 0.72 0.93

Measured Q, T

Thermistor 

string

2011 34,952 0.34 0.83 1.08

Outflow 2011 8,731 -0.15 0.44 0.55

MFWR 

Modeled Q, T Outflow

2002 8,724 -0.43 0.63 0.82

2006 8,731 -0.17 0.55 0.69

2008 8,717 0.26 0.50 0.66

2011 8,731 -0.16 0.49 0.60

USGS temperature cross-sectional 

measurements taken at station 14145500 (1.1 mi 

downstream of Hills Creek Dam) show that the 

river at that site is well-mixed, with crosssectional variation typically less than or equal to 

0.2°C. The USGS temperature probe is located 

near the right bank (looking downstream), where 

most of the streamflow occurs.
22

MFWR Model Development and Calibration

The Middle Fork Willamette River is 

relatively wide and shallow, with a mean width 

and depth of 50.4 and 1.5 m, respectively. This 

river has a relatively steep bottom slope, resulting 

in high water velocities (average of 1 m/s in 

2011) and short travel times (average of 6 hours 

in 2011) through this 13.8-mi reach (fig. 4). With 

these topographic characteristics and resulting 

effects, water temperature generally was affected 

more by the inflows and outflows from the river 

model as boundary conditions rather than model 

parameters related to the hydrodynamics and heat 

budget. Shading coefficients for each segment of 

the MFWR model were set to 0.6. 

Water Balance

Upstream inflows for the MFWR were 

tabulated from USGS station 14145500. Three 

significant tributaries were included in the 

model—Salt Creek, Salmon Creek, and the 

Middle Fork of the North Fork Willamette River

(MFNFWR) (USGS stations 14146000, 

14146500, and 14147500, respectively). 

Streamflow records for these three tributaries do 

not exist after 1994. Streamflow inputs were

estimated for each tributary using a regression 

analysis from neighboring USGS stations on 

rivers of similar size.

Surface-water elevations simulated by the 

MFWR model were compared with measured 

gage height data at USGS station 14148000 (the 

station near the downstream end of the MFWR 

model; see fig. 2). The MFWR model was 

sensitive to adjustments in slope and bottom 

friction parameters (SLOPE, SLOPEC, and 

FRICT), owing partly to the relative steepness of 

the channel. The parameters of SLOPE and 

SLOPEC were set at 0.0042 (m/m) and 0.0010 

(m/m) respectively. The Manning’s bottom 

friction type (FRICC) was selected and the 

bottom friction values (FRICT) were set to 0.06 

along the length of the river, which is typical for 

a free-flowing river in the region (Barnes, 1967). 

The spillway option was selected in this river 

model as the outlet structure at the downstream 

end of the river system. 

Without accounting for ungaged inflows, the 

resulting downstream streamflow from the 

MFWR model was consistently biased low 

compared to measured streamflow. To maintain a 

correct energy and water balance within the 

model, deficit streamflow was added to the river 

model using the distributed tributary flow input, 

resulting in a more accurate match to the 

measured streamflow at the downstream end of 

the model (fig. 11).
23

Figure 11. Graphs showing model outflow and temperature for Middle Fork Willamette River and measured flows 

and temperatures at U.S. Geological Survey station 14148000, Oregon, 2002, 2006, 2008, and 2011.
24

Although it would be possible to correct the 

model to match measured streamflow for each 

unit of time, such a procedure would not be 

reproducible for simulations with altered flow 

requirements, such as outflow from 2002 that 

incorporates more recent dam operation 

protocols. Additionally, although the simulated

streamflow without added ungaged flows shows a 

clear negative bias, correcting the water balance

for each individual time step would introduce a 

large degree of noise (variation). An alternate 

approach was developed to overcome these 

issues, in which the flow in the distributed 

tributary was set as follows:

QDTi = 

Qi

∑i Qi

�

∑i QME− ∑i QMO

Ti

� (3)

where 

QDTi = Distributed tributary input for time 

step i, in cubic meters per second; 

Qi = Inflows for time step i, in cubic 

meters per second; 

∑ QME i = Annual streamflow volume 

measured, in cubic meters; 

∑ QMO i = Annual streamflow volume modeled, 

in cubic meters; and

Ti = Length of time step i, in seconds. 

For each calendar year, the total amount of 

streamflow modeled was subtracted from the 

total amount of streamflow measured at the 

model downstream boundary, in cubic meters. 

For each time step, the total amount of 

streamflow input (without ungaged inflows) was 

calculated, and divided by the total streamflow 

input for the calendar year. This resulted in a time 

series of percentages. Each percentage was then 

multiplied by the initial calculation of the total 

annual streamflow measured minus the total 

annual streamflow modeled, and then divided by 

the interval time. The end result was a time series 

of streamflows that represented the total amount 

of deficit streamflow from the model, but was

weighed based on the amount of streamflow 

entering the system. 

Water Temperature

Temperature calibration of the MFWR 

model was particularly sensitive to the windsheltering coefficient and inflow temperature.

Temperature inputs for Salmon Creek, which 

enters the MFWR between the entry locations of 

Salt Creek and NFMFWR, was initially estimated 

identically to the temperatures of Salt Creek, 

which is closer in size to Salmon Creek than 

NFMFWR. Better model results, however, were 

achieved by using estimated NFMFWR 

temperatures as the temperatures assigned to 

Salmon Creek. For the MFWR model, a windsheltering coefficient of 0.3 (identical to that used 

on the upstream Hills Creek Lake model) was 

applied for the entire calendar year. This implies 

that using only 30 percent of the wind speed 

measured at the Eugene airport NCDC weather 

station (used as wind-speed boundary conditions 

for the HCL, MFWR, and LOP-DEX models 

[table 2]) led to a better calibration of the MFWR 

model. The MFWR has riparian vegetation along 

its banks, which is consistent with a significant 

amount of wind sheltering. 

Other model parameters that also affected

temperature calibration included the maximum 

vertical eddy viscosity (AZMAX) and bottom 

friction coefficient (FRICC). Selected parameter 

values used for the temperature calibration of the 

MFWR model are given in table 7. Other 

parameters were obtained from CE-QUAL-W2 

default values as described in the W2 User’s 

Manual (Cole and Wells, 2011). 
25

Table 7. Selected model parameters used in the Hills Creek Lake, Middle Fork Willamette River, and Lookout

Point-Dexter Lakes models, Oregon.

[Abbreviations: HCL, Hills Creek Lake, MFWR, Middle Fork Willamette River; LOP-DEX, Lookout Point-Dexter 

Lakes; °C, degrees Celsius; m2

/s, square meters per second]

Parameter HCL MFWR LOP-DEX Description

WSC 0.3 0.3 1.0 Wind sheltering coefficient, 

dimensionless

DYNSHD 1.0 0.6 1.0 Allows all incoming solar to reach 

the water surface

TSED 10.3 10.5 10.7 Sediment temperature, °C

AZC W2N W2N W2N Vertical turbulence closure 

algorithm

FRICC CHEZY (70.0) MANN (0.06) CHEZY (70.0) Bottom-friction calculation method

AZMAX 0.005 1.0 0.1 Maximum vertical eddy viscosity, 

m2/s

EXH2O 0.20 0.20 0.20 Light extinction coefficient for 

water, m-1

The simulated temperature time series from 

the calibrated model compare well with the 

measured time series data at USGS station 

14148000 for each calendar year (fig. 11). 

However, the model underpredicted slightly at 

some high temperatures and overpredicted at 

some low temperatures. The seasonal variations 

from the model during June–July 2002 and 

October 2011 were slightly cooler than the 

measured temperatures. Conversely, measured 

temperatures during the winter of 2008 and the 

summer of 2011 were slightly cooler than model 

predictions. 

An error analysis was conducted to 

determine the acceptability of model results. The

goodness-of-fit statistics included the mean error 

(ME), the mean absolute error (MAE), and the 

root mean square error (RMSE). The results from 

each of these analyses are shown in table 6. 

Overall, the results from the MFWR model 

temperature calibration matched the measured 

data well, with the ME between -0.49 and 

0.40°C, the MAE within 0.75°C, and the RMSE 

within 1.0°C. Negative ME values indicate that

the model results were slightly cooler than the 

measured data. Although no definitive guide 

exists for evaluating these goodness-of-fit 

statistics, previous modeling work in many 

systems has indicated that a well-calibrated W2 

temperature model should produce MAE values 

of less than 1.0°C (Rounds, 2010; Sullivan and 

others, 2011); these model results are consistent 

with that level of performance. 

For 2011, two models were compared with 

different upstream streamflow and temperature 

boundary conditions—one that used HCL model 

output and another that used measured data from 

USGS station 14145500. Results from both of 

these 2011 MFWR models were nearly identical 

(fig. 11, table 6).

A partial accounting for the error between 

the model and measurement could be attributed to 

the measurement location. USGS temperature 

cross sections taken at station 14148000 show a 

significant amount of cross-sectional variation (as 

much as 0.6°C), especially in summer. However, 

the temperature probe is located near the left 

bank, whereas most of the temperature variation 

occurs on the right bank, which has slower, 

shallower water and, therefore, more solar 

heating throughout a summer day. 
26

LOP-DEX Model Development-Calibration

Lookout Point Dam has five radial tainter 

spillway gates, four ROs, and three power outlets, 

while Dexter Dam has seven radial tainter 

spillway gates, one power outlet, and no ROs

(U.S. Army Corps of Engineers, 2009) (fig. 7).

Centerline elevations for all outflow structures 

were re-ordered in descending order (to follow 

rules for blending between outlets in CE-QUALW2, v. 3.7) and reset to the actual elevations in 

the updated LOP-DEX combined model (U.S. 

Army Corps of Engineers, 2009; Kathryn 

Tackley, U.S. Army Corps of Engineers, oral 

commun., 2012) (table 8). A RO structure was 

added to the LOP model at centerline of 222.9 m 

(731.3 ft) with a line width of 4.0. Top and 

bottom model outlet structure layers (CE-QUALW2 parameters STR TOP and STR BOT) were 

adjusted during the temperature calibration.

 

Table 8. Differences between outlet structure characteristics in original and updated Lookout Point-Dexter Lakes

models, Oregon.

[Abbreviations: DEX, Dexter Lake; LOP, Lookout Point Lake; m, meter; n/a, not applicable; Power, power penstock outlet;

RO, regulating outlet; STR, structure]

Parameter

West Consultants model USGS model

STR 1 (Power) Description

STR 2 

(Spillway)

STR 1 

(Spillway) STR 2 (Power) STR 3 (RO)

STR TOP (LOP) 2 2 2 2 2 Structure top selective 

withdrawal limit

STR BOT (LOP) 68 68 49 73 73 Structure bottom selective 

withdrawal limit

STR SINK

LOP: POINT

DEX: POINT

LOP: LINE

DEX: LINE

LOP: LINE

DEX: LINE

LOP: LINE

DEX: POINT

LOP: LINE

DEX: n/a

Sink type used in the 

selective withdrawal 

algorithm

STR ELEV

LOP: 237.7

DEX: 197.0

LOP: 270.5

DEX: 206.2

LOP: 270.5

DEX: 201.2

LOP: 240.5

DEX: 196.0

LOP: 222.9 Centerline elevation of 

structure, m

STR WIDTH

LOP: n/a

DEX: n/a

LOP: 75.71

DEX: 109.4

LOP: 75.71

DEX: 109.4

LOP: 19.0

DEX: n/a

LOP: 4.0 Width of structure (line 

sink), m

Water Balance

The water balance for Lookout Point Lake 

was calibrated by comparing measured and 

modeled water-surface elevations and placing the 

flow required to close the water budget into a 

distributed tributary to represent ungaged flows. 

The resulting comparison between measured and 

modeled water-surface elevations showed good 

agreement (fig. 12). For any given time 

increment, the total amount of flow derived from 

the distributed tributary inflow can be calculated 

by dividing the distributed tributary inflow by the 

total inflow, and the percentage of flow from the 

distributed tributary varied depending on the 

calendar year of interest. Median values ranged 

from 3.9 (2011) to 20.3 percent (2006). Similarly, 

90th percentile values ranged from 15.3 (2011) to 

119.7 percent (during an extreme high-flow event 

during January 2006).
27

Figure 12. Graphs showing measured and modeled water-surface elevations at Lookout Point Lake, Oregon, 2002, 

2006 , 2008, and 2011, along with the target rule curve for the lake.

The water balance for Dexter Lake was more 

difficult than for Lookout Point Lake (fig. 13). 

The storage capacity at Dexter Lake (29,990 

acre-ft) is about 15 times smaller than the storage 

capacity at Lookout Point Lake (455,800 acre-ft).

Therefore, small changes to reservoir inflow

resulted in relatively large changes in watersurface elevation. Several algorithms were 

developed outside of the W2 model to balance 

inflows with water-surface elevations. Initial 

attempts were ineffective, as small changes in 

inflow often resulted in a flooded or completely 

dry reservoir. Subsequent, iterative attempts 

provided better results, but required hours or even 

days of computing time.
28

Figure 13. Graphs showing measured and modeled water-surface elevations at Dexter Lake, Oregon, 2002, 2006, 

2008, and 2011, along with the target rule for the lake.

The operating range for the water-surface 

elevation at Dexter Dam is relatively narrow. 

During the 4 years used in this study, the lowest 

reservoir water-surface elevation was 210.27 m 

(689.86 ft), and the maximum elevation was 

211.78 m (694.81 ft), allowing for an effective 

operating range of only 1.51 m (4.95 ft). 

Subsequent analysis showed that attempting to 

model Dexter Lake at a relatively constant watersurface elevation was much less computationally 

difficult and time-consuming than attempting to 

match exact water-surface elevations. A new, 

iterative algorithm was developed for the Dexter 

Lake water-balance calculations that attempts to 

keep water-surface elevations between 210 and 

212 m, with a mean elevation of about 211 m. 

Model release rates from Lookout Point Dam 

were from USACE records. Release rates from

Dexter Dam were derived by calculating a 3-day 

moving average of the hourly outflow from 

Lookout Point Dam. This 3-day averaging 

window was based on the average residence time 

calculated by the CE-QUAL-W2 pre-processor 

for the operating elevation limits at Dexter Lake. 

Model outflows from Dexter Dam were

compared to measured streamflow at USGS 

station 14150000 (about 2.6 mi downstream of 

Dexter Dam), and were determined to be 

satisfactory (fig. 14). 
29

Figure 14. Graphs showing modeled release rates and water temperatures from Dexter Dam and measured 

streamflow and water temperatures at USGS station 14150000, located 2.6 miles downstream of Dexter Dam,

Oregon, 2002, 2006, 2008, and 2011.
30

Water Temperature

After completion of the water balance, initial 

runs of the CE-QUAL-W2 model for Lookout 

Point and Dexter Lakes resulted in modeled water 

temperatures released from Dexter Dam that were 

cooler than those recorded downstream at USGS 

station 14150000. Several changes were made to 

the original West Consultants model (tables 5 and

8) in an attempt to eliminate these discrepancies.

All changes were made based on one or more of 

the following criteria, in order of importance: (1) 

Documentation (USACE dam schematics, 

recorded data, etc.), (2) computed or estimated 

data (temperature of sediment, etc.), and (3) 

calibration of the model (light extinction 

coefficient, etc.). All estimated or calibrated 

model parameters were evaluated for 

reasonableness.

The model was initially calibrated to 2011 

conditions, which is the most data-rich of the 4 

years included in the study and, therefore,

providing the greatest amount and highest quality 

of feedback during the calibration process. 

Temperature profiles for 2011 at Lookout Point 

Lake match well with modeled temperatures from 

the surface to at least 9 m in depth (fig. 15). From 

depths of 12–24 m (39–79 ft), the model matches 

recorded data well for most of the year, but tends 

to slightly overpredict during the months of 

warmest water temperatures (August and 

September). Comparisons of LOP model output 

with measured temperatures at various depths on 

eight days in 2002 match well, showing only a 

small underprediction near the surface (fig. 16).

Temperature profiles in Dexter Lake were given 

less weight during the calibration process. 
31

Figure 15. Graphs showing continuous measured and modeled water temperatures at specific depths in Lookout 

Point Lake near the dam, Oregon, 2011.
32

Figure 16. Graphs showing measured and modeled vertical temperature profiles in Lookout Point Lake near the 

dam, Oregon, 2002.
33

As discussed in the section “Water Balance,” 

modeled water-surface elevations in Dexter Lake

were held at relatively constant levels compared 

to measured data for ease of computation. The 

constant water-surface elevations resulted in a 

small amount of additional variability to the 

discrepancy between measured and modeled 

temperature profiles in Dexter Lake during 2011 

(fig. 17). Despite this increase in variability, 

modeled depth-specific temperatures matched 

recorded temperatures well, especially near the 

water surface and near the dam (fig. 18A). 

Similar to the LOP temperature profiles, the DEX 

modeled temperatures were sometimes 

underpredicted near the surface in the summer 

months and overpredicted at deeper depths in late 

summer and autumn of 2011. Similar results were 

obtained for 2002 conditions at two locations 

where vertical temperature profiles were 

measured in Dexter Lake (fig. 18). Near-dam 

comparisons of modeled temperatures matched 

well, but “mid-lake” comparisons differed 

greatly, possibly because of the uncertainty 

regarding the location of the “mid-lake” 

measurement in 2002. 

Figure 17. Graphs showing continuous measured and modeled water temperatures in Dexter Lake near the dam, 

Oregon, 2011.
34

Figure 18. Graphs showing measured and modeled vertical temperature profiles in Dexter Lake, Oregon, 2002, 

(A) near the dam, and (B) at a mid-lake location.

Modeled temperature outflows for 2011 

compared well with data measured at USGS station 14150000 downstream of Dexter Dam (fig.

15). ME and MAE fit statistics for that comparison were well within acceptable limits at -0.15 

and 0.44°C, respectively (table 6). Because 

USGS station 14150000 is 2.6 mi downstream of 

Dexter Dam, temperatures may warm during 

travel between the dam outlets and the gage, especially during the summer months of June, July, 

and August. Based on Rounds (2010), water temperatures could increase by as much as 0.29 °C in 

mid-summer over the course of 2.6 mi, explaining some of the slight negative bias in the results. 

Combined MFWR Model Development and 

Calibration

The HCL, MFWR, and LOP-DEX models 

were used in series to constitute what is termed 

the “Combined Model.” In the combined model, 

the streamflow and temperature output from the 

HCL model was used as input for the MFWR

model, and the output of the MFWR model was

used as input for the LOP-DEX model. Results 

discussed previously were for the individual 

models run independently with measured 

upstream inputs. 

Boundary conditions between the calibrated

and combined models are not geographically 

identical. The upstream boundary condition used 

to calibrate the MFWR model is USGS station 

14145500 (RM 231.4). Hills Creek Dam is at RM 

232.5, which represents the upstream boundary 

condition for the combined MFWR model. 

Similarly, the upstream boundary to the LOPDEX model is USGS station 14148000 (RM 

220.2), which is about 1.5 mi upstream of the

Middle Fork Willamette River model output at 

segment 85 (RM 218.7). Outflow boundary 

conditions at LOP and DEX were identical 

between the combined MFWR model and the 

independently calibrated LOP-DEX model. These 

outflows were estimated based on what was 

necessary to keep the pool elevation constant in 

Dexter Lake. 
35

The designated warm and dry year, 2002, 

was the most difficult to simulate with the 

combined model, and resulted in the highest 

RMSE, ME, and MAE of the 4 calendar years 

evaluated. Outflow temperatures for the 

combined model were biased 0.43°C low in 2002, 

with the most pronounced bias occurring in 

September–December (fig. 14, table 6). 

Simulated temperatures during the rest of the year

matched well with measured temperature data

downstream of Dexter Dam, with a mean 

absolute error of 0.63°C. The year 2002 also was 

the year that showed the most spatial variability 

in temperature cross sections measured at USGS 

station 14150000 (as high as 0.7°C). Temperature 

variability was lower in other calendar years, and 

average cross-sectional temperature variation 

typically was within 0.3°C of the recorded probe 

values. High variability of temperature cross 

sections and poorer goodness-of-fit statistics in 

2002 could be related. Instream temperature 

variability typically results in colder water in the 

middle of the cross section, and warmer water 

near the banks. As the summer of 2002 was 

especially warm and dry, the width of the stream 

could have diminished, resulting in the exposure 

of the temperature probe to more shallow, slower 

water than in normal summer conditions. This 

would produce warmer recorded temperatures 

than the stream average. This potential 

discrepancy, combined with the 2.6 mi of 

exposure to additional solar heating between the 

dam and the gaging station, could account for 

some or all of the bias observed in 2002. 

Annual bias of the combined model was 

small for 2006, 2008, and 2011 (within 0.26°C; 

table 6). In 2002, a negative bias was most 

pronounced in the spring, and a positive bias 

extended through much of the autumn and early 

winter. The most pronounced bias in 2008 

occurred in January and September, with the rest 

of the year matching well with the measured data.

The overall accuracy of the combined model was 

good, with MAE values of 0.63°C or less for the 

most downstream temperature comparison for 

each of the 4 years simulated.

For 2011, the temperature releases from 

Dexter Dam from the combined model and the 

calibrated model were nearly identical, resulting

in RMSE, ME, and MAE fit statistics that were 

within 0.05°C of each other (table 6). In the 

combined model, some perceptible negative bias

was present in March and October–December, 

and some perceptible positive bias may be 

evident in September (fig. 14), but the overall 

match to the measured data was excellent. Both 

the independently calibrated and combined 

models capture the use of the spillway in July 

2011 (see the anomalous increase in release 

temperature in fig. 14) with only a minor 

underprediction. 

Green Peter and Foster Lake Models

Study Area

The South Santiam River is part of the larger 

Santiam River Basin (fig. 19), which is located 

north of the Middle Fork Willamette River Basin

(fig. 1). The entire watershed lies in the Western 

Cascades High Montane ecoregion, with climate 

characterized by warm, dry summers and cool, 

wet winters (E&S Environmental Chemistry, 

Inc., and South Santiam Watershed Council, 

2000). The South and Middle Santiam Rivers are

impounded by two USACE dams that form 

Foster and Green Peter Lakes, respectively. The 

reservoirs are used for flood-damage protection, 

power generation, irrigation, recreation, and 

improvement of downstream navigation. 
36

Figure 19. Map showing the Santiam River Basin, Oregon, including the South Santiam River Basin study area 

and key streamflow-gaging sites. 

Green Peter Dam is a 327-ft-high (100-mhigh) concrete dam completed in 1968. The 

watershed upstream of Green Peter Dam includes 

275.3 mi2 of mostly evergreen forest and scrubshrub that is managed primarily by the U.S. 

Forest Service, Bureau of Land Management, and 

private interests (Johnson and others, 1985). The 

reservoir formed by Green Peter Dam is about 11 

mi long and stores 428,100 acre-ft (5.28×108

 m3) 

of water at a full pool elevation of 1,015 ft (309 

m). The two largest inflows to Green Peter Lake

are the Middle Santiam River and Quartzville 

Creek. Power generation at Green Peter Dam 

during peak use hours can lead to large 

fluctuations in release flows to the Middle 

Santiam River downstream of the dam. 

Foster Dam is about 8 mi downstream of 

Green Peter Dam. Foster Dam is a re-regulating 

dam that is operated to smooth the irregular flows 

released from Green Peter Dam. Construction of 

this rock-fill dam was completed in 1968. The 

Foster Lake drainage basin includes 216.3 mi2 of 

evergreen forest and scrub-shrub that is managed 

largely by the U.S. Forest Service and private 

entities (Johnson and others, 1985). Foster Lake 

stores 60,700 acre-ft (7.49×107

 m3) of water at a 

full pool elevation of 641 ft. Major inflows to 

Foster Lake include the Middle and South 

Santiam Rivers. 

Winter Steelhead and spring Chinook 

Salmon are anadromous fish native to the South 

Santiam River Basin, and both are listed as 

threatened under the Endangered Species Act 
37

(E&S Environmental Chemistry, Inc., and South 

Santiam Watershed Council, 2000). Upper 

Willamette River Chinook Salmon in the South 

Santiam River are considered to be at high risk of 

extinction (McElhany and others, 2007), and 

water temperature affected by dam operations is 

thought to be a limiting factor (National Marine 

Fisheries Service, 2008). Alteration of water 

temperatures downstream of high-head dams can 

affect fish factors such as cues for migration and 

spawning, the emergence timing of juvenile fish, 

and egg mortality (U.S. Army Corps of 

Engineers, 2012b). South Santiam River 

temperature effects on aquatic life vary from year 

to year. For example, although autumn water 

temperatures downstream of Foster Dam were 

warmer than ideal for spring Chinook spawning 

in 2010, conditions in 2011 were close to ideal, 

despite no active temperature management (U.S. 

Army Corps of Engineers, 2012b).

Methods and Data

The USGS Green Peter Lake (GPR) and 

Foster Lake (FOS) models for 2002, 2006, 2008, 

and 2011 developed in this study were based on 

CE-QUAL-W2 models of the reservoirs 

developed by West Consultants, Inc. (2005) for 

1970–2002. For the current study, the model grid 

and some model parameters were the same as 

those used in the West Consultants model. 

However, different input datasets were developed 

for the years modeled in this study, and some 

model parameters were changed during the 

process of calibration (table A3). The USGS GPR

and FOS CE-QUAL-W2 models were developed 

to simulate water-surface elevations, flow, 

velocities, and water temperatures.

Green Peter and Foster Lake Model Grids

The model grid developed by West 

Consultants, Inc. (2005) was used in this study. 

They developed the grid using digitized maps of 

the study area before the reservoirs were filled.

The resulting grid was found to agree within 5 

percent of the USACE volume-elevation curves 

(West Consultants, Inc., 2005). The part of the 

model grid representing Green Peter Lake was 

composed of six branches representing the main 

channel of the Middle Santiam River, Quartzville 

Creek, and four minor tributaries to the reservoir.

Segment lengths ranged from 377.2 to 2,921.1 m, 

with 0.50-m-high vertical layers. The part of the 

model grid representing Foster Lake included the 

riverine reach immediately downstream of Green 

Peter Lake as well as Foster Lake. One branch 

represented the Foster Lake main channel and a 

second branch represented the South Santiam 

reach of Foster Lake reservoir. Segment lengths 

ranged from 505.8 to 510.4 m, with vertical 

layers 1 m high. The GPR and FOS model grids 

are set up as two “waterbodies” within one CEQUAL-W2 model. 

Boundary Conditions

Meteorological Data

CE-QUAL-W2 requires air temperature, 

dew-point temperature, cloud cover, solar 

radiation, wind speed, and wind direction as 

meteorological inputs; the same meteorological 

inputs were used for the Green Peter Lake and 

Foster Lake waterbodies in the model. Air 

temperature from Foster Dam weather stations 

(FWSO) was available and used for all 4 years.

Measured air temperature and relative humidity 

at FWSO in 2006, 2008, and 2011 were used to 

calculate dew-point temperature (Linsley and 

others, 1982): 

Td = Ta − [(14.55 + 0.114Ta)X

+ [(2.5 + 0.007Ta)X]3

+ (15.9 + 0.117Ta)X14] (4)

where 

Td = dew-point temperature, in degrees Celsius;

Ta = the air temperature, in degrees Celsius; and

X = 1.00 − � f

100�, where f = relative humidity, in 

percent. 

Relative humidity was not measured at 

Foster Dam in 2002, so air temperature and 

humidity from the University of Oregon Solar 

Radiation Monitoring Laboratory (SRML) were 
38

used to estimate dew-point temperature in that 

year. Measured air temperature at FWSO was 

similar to air temperature at SRML that year.

Solar radiation data for the models were

obtained from SRML. Some solar data were 

available at Foster Dam for part of the period 

modeled. A comparison between the Foster and 

SRML solar data in 2011 showed similar 

seasonal and daily patterns of solar radiation at 

those two locations. 

Various sources of wind data were compared 

for possible use as model input. Wind speeds 

varied widely between sites. After some initial 

testing with the models, wind speed and wind 

direction from the Eugene airport were used for 

all years, and when necessary the effective wind 

speed was adjusted with the wind sheltering 

coefficient during model calibration. 

The CE-QUAL-W2 cloud-cover input was 

derived from Eugene airport observations and 

converted to CE-QUAL-W2 model units using 

the same method as discussed for the Middle 

Fork Willamette River models. 

Precipitation data were available from Foster 

Dam site FWSO for 2006, 2008, and 2011. 

Precipitation data from the Detroit Dam for 2002 

were used as an estimate of precipitation rates in 

the study area in 2002. Precipitation temperature 

was estimated as air temperature, with any 

negative air temperature values set to zero.

Hydrologic Data

Streamflow was measured at one of the main 

inflows to Green Peter Lake, Quartzville Creek 

(USGS station 14185900, fig. 19), in all 4 years 

modeled. The Middle Santiam River flow into 

Green Peter Lake was based on Quartzville Creek 

flows, as estimated from a regression equation 

documented by West Consultants, Inc. (2005). 

The flows for Whitcomb, Thistle, Tally, and 

Rumbaugh Creeks were estimated from 

Quartzville Creek flows and the ratio of their 

drainage basin area to the Quartzville Creek 

drainage basin area.

Releases from Green Peter Dam in the years 

modeled were withdrawn for power generation 

from a penstock at elevation 810 ft (246.9 m) or 

spilled through a RO with a centerline elevation 

of 750 ft (228.6 m). The Green Peter Dam 

spillway was not used in the 4 years modeled; all 

“spill” was released through the RO. Hourly 

release rates for these outlets were obtained from 

USACE. The model was set up to release flows 

from these two outlets at their specified 

elevations and to discharge them into the model 

segment downstream of Green Peter Dam.

The main inflow into the FOS model was the 

outflow release from Green Peter Lake. Flow 

from the other major inflow into Foster Lake, the 

South Santiam River, was measured at USGS 

station 14185000 in all years modeled. 

Releases from Foster Dam were either 

discharged from a spillway with a crest elevation 

of 596.8 ft (181.9 m) or were withdrawn for 

power generation through a penstock at an 

elevation of 583.3 ft (177.8 m). Hourly release 

data were obtained from USACE, and the model 

was set to release those flows at the specified 

outlet elevations.

Forebay water-surface elevations were 

measured in both Green Peter Lake and Foster 

Lake. Measured elevations were compared to 

modeled elevations during the water-balance 

calibration.

Inflow Water Temperature

Measured water temperature data at 

Quartzville Creek were available from USGS for 

part of 2008 and all of 2011, and from ODEQ for 

part of 2002. For periods without measured data, 

a regression equation (Rounds, 2010) between 

water temperatures in Quartzville Creek and 

Blowout Creek (USGS station 14180300) in the 

North Santiam River Basin, along with Blowout 

Creek water temperatures, was used to estimate 

hourly Quartzville Creek water temperatures 

flowing into Green Peter Lake. Measured water 

temperatures for the Middle Santiam River were 

available for 2011 at USGS station 14185800, but 
39

not for the other years. A comparison of 

Quartzville Creek and Middle Santiam River 

water temperatures in 2011 showed similar 

seasonal and daily water temperature patterns; 

therefore, Quartzville Creek water temperatures 

were used to estimate Middle Santiam River 

water temperatures for the years when measured 

water temperatures were not available. No water 

temperature data were available for the smaller 

tributary inflows to Green Peter Lake, including 

Whitcomb, Thistle, Tally, and Rumbaugh Creeks, 

so their water temperatures were estimated as

equal to Quartzville Creek water temperatures. 

The major Foster Lake inflow was the 

release from Green Peter Lake, and the 

temperature of that water was determined within 

the model. That water entered the Foster Lake

part of the grid immediately downstream of 

Green Peter Dam. The water temperature for the 

South Santiam River inflow was measured from 

late October 2008 through all of 2011 at USGS 

station 14185000. To estimate South Santiam 

River water temperature for 2002, 2006, and part

of 2008, a regression was completed between 

water temperatures for Blowout Creek in the 

North Santiam River Basin and for the South 

Santiam River using October 2008–December 

2011 half-hourly data (John Risley, U.S. 

Geological Survey, written commun., 2012). The 

resulting equation took the form: 

TSS = 0.973 + 1.1174TmBC + (TBC −

TmBC)(−0.0258TrBC

2 + 0.7303TrBC +

0.2096)/TrBC (5)

where 

TSS = the estimated water temperature for the 

South Santiam River inflow to Foster 

Lake, in degrees Celsius; 

TmBC = the measured daily mean water 

temperature at the Blowout Creek site, 

in degrees Celsius; 

TBC = the half-hourly temperature from 

Blowout Creek, in degrees Celsius; and

TrBC = the daily temperature range from the 

Blowout Creek site, in degrees Celsius. 

Lake Profile Data and Outflow Water Temperature

Measured water temperature profiles, 

thermistor string data, and water temperatures 

downstream of the dams were used for 

comparison to modeled temperatures during 

model calibration. In 2002, vertical profiles of 

water temperature in Green Peter Lake were 

measured at two sites, GPTR1 and GPTR4, on 

nine dates from April to October. Geographic 

coordinates were not provided for these sites, so 

their location in the reservoir was estimated from 

a map provided by West Consultants, Inc. (2005). 

Site GPTR1 was in the Green Peter Lake forebay

(near the dam) and site GPTR4 was upstream of 

the Rumbaugh Creek confluence with Green 

Peter Lake. In 2011, water temperatures were 

measured hourly from a string of 13 thermistors 

suspended in the Green Peter forebay at depths of 

0.5–200 ft (0.2–61 m). Green Peter Lake modeled 

release temperatures were compared to measured 

water temperatures about 330 ft (100 m) 

downstream of Green Peter Dam at USGS station 

14186200, which has measured water 

temperatures for part of 2008 and all of 2011. 

For Foster Lake, water temperatures were 

measured hourly near the dam in 2011 from 11 

suspended thermistors at depths of 0.5–80 ft (0.2–

24.4 m). Foster Dam release temperatures were 

compared to hourly temperatures measured at 

USGS station 14187200 on the South Santiam 

River about 0.6 mi (1 km) downstream of Foster 

Dam in all years of the study. Wiley Creek flows 

into the South Santiam River between Foster 

Dam and station 14187200, so these temperatures 

are not expected to match exactly, but mixing 

calculations for 2011 showed that the effect of 

Wiley Creek on downstream temperatures was 

minor. 

GPR-FOS Model Development/Calibration

Water Balance

Preliminary model runs showed that 

additional flows were needed to complete the 

water balance. Distributed tributary flow was 
40

added to the model to account for flow from 

ungaged tributaries, overland flow during storms, 

gage errors, and groundwater interactions. In CEQUAL-W2, a distributed tributary apportions that 

flow to all segments along a branch. Distributed 

tributary flow varied through the years, and 

generally was higher in winter and during storms. 

Because the distributed tributary was likely 

mostly representative of surface water, the 

temperature of the distributed tributary was 

estimated as a mix of 20 percent groundwater 

with a temperature of 11.1°C, and 80 percent

surface water, represented by Quartzville Creek 

water temperature for the GPR distributed 

tributary, and the South Santiam River water 

temperature for the FOS distributed tributary. 

At times, distributed tributary flow was 

negative, which could indicate seepage loss from 

the reservoir. On an annual average basis, the 

GPR distributed tributary was about 9, 14, -3, and

3 percent of total inflows for 2002, 2006, 2008, 

and 2011, respectively. The FOS distributed 

tributary was about 2, 7, 13, and 16 percent of 

total inflows for 2002, 2006, 2008, and 2011, 

respectively. After addition of the distributed 

tributary, the final modeled forebay water-surface 

elevations matched the measured water-surface 

elevations closely for Green Peter Lake and 

Foster Lake (figs. 20 and 21). The operation of a 

fish weir in the spillway of Foster Dam from 

April 15 through May 15 in each year of this 

study caused lake elevations to be lower than the 

rule curve at Foster Lake. 

Figure 20. Graphs showing measured and modeled forebay water-surface elevations in Green Peter Lake, 

Oregon, 2002, 2006, 2008, and 2011.
41

Figure 21. Graphs showing measured and modeled forebay water-surface elevations in Foster Lake, Oregon,

2002, 2006, 2008, and 2011.

Water Temperature

During model water-temperature calibration, 

a set of model parameters were adjusted within 

reasonable bounds to optimize the comparison of 

measured and modeled water temperatures. Final 

values for this set of model parameters are shown 

in table 9. Comparison of modeled water 

temperatures at specific depths within Green 

Peter Lake are shown in figures 22 and 23 for 

comparison to measured temperatures in 2011 

and 2002, respectively. Modeled and measured 

water temperatures just downstream of Green 

Peter Dam are compared in figure 24 for all 4 

years of the study. Depth-specific modeled and 

measured water temperatures in 2011 within

Foster Lake are shown in figure 25. Modeled and 

measured water temperatures just downstream of 

Foster Dam for all 4 years are shown in figure 26. 

Error statistics summarizing this comparison of 

model output and measured data are shown in 

table 10. 
42

Table 9. Selected model parameter values used in the models for Green Peter and Foster Lakes,Oregon.

 [Abbreviations: °C, degrees Celsius; m2/s, square meters per second]

Parameter Green Peter Lake Foster Lake Description

WSC 1.0 0.5 Wind sheltering coefficient, dimensionless

TSED 11.1 11.1 Sediment temperature, °C

AZC W2N W2N Vertical turbulence closure algorithm

AZMAX 0.001 0.001 Maximum vertical eddy viscosity, m2/s

EXH2O 0.45 0.60 Light extinction coefficient for water, m-1

STR SINK spill: POINT

power: POINT

spill: POINT

power: LINE (3.8)

Withdrawal structure type. Withdrawal width (meters) 

given for LINE structures.

STR TOP 2 2 Structure Top Selective Withdrawal Limit

STR BOTTOM 185 185 Structure Bottom Selective Withdrawal Limit

Table 10. Model goodness-of-fit statistics for water temperature for Green Peter and 

Foster Lakes, Oregon. 

Year and Type of 

Measured Data

Mean Error 

(ME)

Mean Absolute Error 

(MAE)

Root Mean Square Error 

(RMSE)

Green Peter Lake

2008 Outflow 0.10 0.48 0.54

2011 Outflow -0.28 0.45 0.58

2002 Depth Profiles 0.35 0.77 0.98

2011 Thermistor string 0.00 0.60 0.82

Foster Lake

2002 Outflow -0.12 0.43 0.55

2006 Outflow -0.08 0.50 0.63

2008 Outflow -0.24 0.62 0.79

2011 Outflow -0.19 0.65 0.79

2011 Thermistor string -0.01 0.72 1.06
43

Figure 22. Graphs showing forebay thermistor string data for Green Peter Lake, Oregon, 2011, and model output 

at the same depths and times.
44

Figure 23. Graphs showing vertical profile temperature data for Green Peter Lake, Oregon, 2002, and model 

output at the same location and dates. 
45

Figure 24. Graphs showing modeled outflow temperatures and measured water temperatures for Green 

Peter Lake, Oregon, just downstream of Green Peter Dam, and daily average total and regulating outlet 

(RO) release rates, 2002, 2006, 2008, and 2011.
46

Figure 25. Graphs showing forebay thermistor string data for Foster Lake, Oregon, 2011, and model output at the 

same depths and times.
47

Figure 26. Graphs showing modeled outflow temperatures and measured water temperatures for Foster 

Lake, Oregon, downstream of Foster Dam, and daily average flow through the power and spill outlets, 

2002, 2006, 2008, and 2011.
48

In the years modeled, Green Peter Lake was 

thermally stratified from spring through autumn 

with cold deep water and warmer water near

surface. The power penstock and RO are 

relatively deep in the lake. In the years modeled, 

and because of the fluctuating water-surface 

elevation, the Green Peter Dam power penstock 

centerline was at depths of 112–200 ft (34–61 m), 

although the RO centerline was at depths of 171–

259 ft (52–79 m). Owing to these depths, Green 

Peter Dam discharged stored cold water until late 

in the season when the reservoir surface was 

drawn down (fig. 20) and the outlets could access 

warmer water closer to the surface. These factors 

caused the maximum Green Peter Lake outflow 

water temperatures to occur in October or 

November (fig. 24), rather than during midsummer as is typical of the unimpounded streams 

flowing into Green Peter Lake. 

Measured and modeled Green Peter Lake

water temperatures showed more daily and shortterm variability near surface and less variability 

in the deeper areas of the reservoir (fig. 23).

Measured data indicated that the largest 

variability occurred from 20 to 40 ft (6 to 12 m). 

The model showed most variability from 0.5 to

40 ft (0.2 to 12 m). Overall, the GPR model was 

able to simulate water temperatures within the 

reservoir and its outflow well, with mean 

absolute errors ranging from 0.45 to 0.77°C (table 

10). 

Green Peter Lake and Foster Lake were 

thermally stratified from spring through autumn 

in the study period. Foster Lake is shallower and 

has withdrawal outlets closer to the water surface

than Green Peter Lake. In the years modeled, the 

Foster Dam power penstock centerline was at 

water depths of 16–56 ft (5–17 m), and the 

spillway crest was at depths of 3–43 ft (1–13 m). 

Owing partly to these shallower outlet depths, the 

water temperatures released from Foster Dam 

were closer to a natural seasonal temperature 

pattern, with the warmest release temperatures in 

mid-summer (fig. 26). Other contributors to a 

more natural seasonal temperature pattern could 

include warming in the riverine reach between 

Green Peter Dam and Foster Lake, and the 

unregulated inflow from the South Santiam 

River. Although the maximum water temperature 

of Foster Dam releases tended to occur in midsummer, temperatures throughout summer were 

colder than might have occurred without the 

upstream dams because releases from Green 

Peter Dam were so cool during summer (Rounds, 

2010). 

Calibration of the FOS model included 

adjustment of the wind sheltering coefficient 

(WSC) to 0.5 and an increase in the light 

extinction coefficient (EXH2O) to 0.60. Remote 

sensing data has suggested that Foster Lake may 

have occasional algae blooms (Oregon 

Department of Environmental Quality, 2011b) 

that could explain the need for greater light 

extinction compared to Green Peter Lake, where 

algal blooms have not been an issue (Oregon 

Department of Environmental Quality, 2011b).

The Foster Dam power penstock withdrawal 

structure also was adjusted during calibration. It 

was set as a CE-QUAL-W2 “LINE” type 

structure with a width of 3.8 m. In CE-QUALW2, the width of LINE structures affects which 

depths are able to be accessed by the outflow 

structure. As the model outlet line width 

increases, the model withdraws more water from 

model layers (depths) nearer the outlet. As the 

outlet line width decreases, it withdraws water 

from a greater portion of the reservoir depths. 

Because the model’s selective withdrawal 

algorithm does not have a perfect representation 

of the three-dimensional dynamics near the 

outlet, the outlet width can be considered a model 

calibration factor (for example, Buccola and 

others, 2012, p. 51). The FOS model simulated 

water temperature well, with MAE from 0.43 to 

0.72° (table 10). 
49

Implications for Future Research and 

Monitoring

River and reservoir models on the Middle 

Fork Willamette and South Santiam River 

systems were constructed or evaluated, set up to 

simulate recent conditions with current dam 

operations, and calibrated so that they accurately 

simulated water-surface elevations, streamflow, 

and water temperatures in those waterbodies. 

Water temperatures generally were simulated 

with typical errors of 0.4–0.8 °C and little to no 

bias when compared to measured data. These 

models are now ready to be used to evaluate 

different types of dam operations, to determine 

the effects of wet or dry future conditions or the 

effects of climate change, and to provide insights 

into the potential effects of using different types 

of outlets at these dams.

These models, while accurate and useful, 

demand a large quantity of certain types of data. 

If these models are to be updated to reflect future 

conditions, it will be important to continue to 

collect the most critical types of data needed to 

drive and calibrate the models, or be prepared to 

estimate those data. Streamflow, water 

temperature, and meteorological conditions are 

the most obvious critical inputs to the models, but 

verification and refinement of the model grids 

might be aided through periodic bathymetric 

surveys of the river and reservoir reaches of 

interest. An underwater survey of the outlets at 

Hills Creek Dam might improve the model 

calibration near the dam, as the outlets in the 

model were particularly hard to define in the 

calibration process. A field survey of tree canopy 

cover and topographic features or Geographic 

Information System processing of LiDAR along 

the Middle Fork Willamette River between Hills 

Creek Dam and Lookout Point Lake could 

provide additional information leading to further 

calibration of shading parameters in the model. 

Additionally, discrete or continuous vertical 

profiles of water temperature in each lake are 

invaluable for checking the calibration of these 

models. 

Finally, the accuracy of these models is only 

as good as the most-critical model algorithms in 

those models. The flow and heat-exchange 

algorithms in CE-QUAL-W2 use good 

mathematical interpretations of the physical 

processes acting in those waterbodies. Potentially 

valuable model refinements might include a more 

detailed physical representation of the selective 

withdrawal process, in which flow from different 

layers of the model is directed to the structural 

outlets of the dams, and perhaps a quasi-threedimensional representation of circulation in areas 

of reservoirs where the currents are complex, 

such as the area where the Hills Creek arm of 

Hills Creek Lake joins the main branch very 

close to the dam. 

Acknowledgments

The authors thank John Risley of the USGS 

Oregon Water Science Center for his assistance 

in completing water-temperature regressions for 

the South Santiam River Basin, and Steven 

Sobieszczyk of the USGS Oregon Water Science 

Center for assistance with the analysis of aerial 

photographs of the Middle Fork Willamette River 

reach between Hills Creek Dam and Lookout 

Point Lake. 

Supplemental Materials

The models developed and refined during 

this study, along with the model source code and 

model inputs, are available for download at 

http://or.water.usgs.gov/proj/mfw_ssr_temp/. 
50

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53

Appendix A. Updated Model Parameter Sets

This appendix details the specific changes made to the original West Consultants models of (1) 

Hills Creek Lake, (2) Lookout Point and Dexter Lakes, and (3) Green Peter and Foster Lakes. The 

differences in model parameter values between the West Consultants models and the updated Hills 

Creek Lake and Lookout Point and Dexter Lake models are listed in table A1. The differences in data 

sources for those models are listed in table A2. The differences in model parameter values between the 

West Consultants models and the updated USGS Green Peter and Foster Lakes models are listed in 

table A3. 

Table A1. Differences in model parameter values between the original West Consultants models and the 

updated U.S. Geological Survey Hills Creek Lake and Lookout Point and Dexter Lakes models, Oregon. 

[Abbreviations: °C, degrees Celsius; HCL, Hills Creek Lake; LOP-DEX, Lookout Point and Dexter Lakes ] 

Parameter West Consultants USGS Description

WSC 0.75 for HCL

0.80 for LOP-DEX

0.30 for HCL

1.00 for LOP-DEX Wind sheltering coefficient, dimensionless

DYNSHD 0.63 for HCL

0.60 for LOP-DEX

1.0 for HCL

1.0 for LOP-DEX Allows all incoming solar to reach the water surface

VISC OFF ON Vertical eddy viscosity limitation on timestep

CELC OFF ON Internal gravity wave limitation on timestep

PQC OFF ON Density placed inflows

PRC OFF ON Precipitation included

QINIC OFF ON for HCL Interpolate inflows

DTRIC OFF ON for HCL Interpolate distributed tributary inflows

HDIC OFF ON for HCL Interpolate boundary conditions

METIC OFF ON for HCL Meteorological data interpolation

FRICC MANN (0.025) CHEZY (70.0) Bottom-friction calculation method

AX 2.0 for HCL 1.0 Longitudinal eddy viscosity, m2/s

DX 2.0 for HCL 1.0 Longitudinal eddy diffusivity, m2/s

TSED 10.0 10.3 for HCL

10.7 for LOP-DEX Sediment temperature, °C

TSEDF 0.00 for HCL 1.00 for HCL Heat lost to sediments that is added back to water column

AZC W2 for HCL W2N for HCL Form of vertical turbulence closure algorithm

AZMAX 0.5 for HCL 0.005 for HCL Maximum value for vertical eddy viscosity, m2/s

QOT Daily for HCL Hourly Branch Outflows

QDT Not Used Estimated to close 

water balance Distributed tributaries

TDT Not Used

10 percent surface 

water, 90 percent 

groundwater

Distributed tributary temperature

EXH20 0.45 for LOP-DEX 0.20 for LOP-DEX Extinction coefficient for pure water
54

Table A2. Differences between meteorological data sources in the original West Consultants models and the 

updated U.S. Geological Survey Hills Creek Lake and Lookout Point and Dexter Lakes models, Oregon.

[Abbreviations: HCL, Hills Creek Lake; HCWO, Hills Creek Dam Weather Station; LOP, Lookout Point Lake; DEX, 

Dexter Lake; LPWO, Lookout Point Dam Weather Station; NCDC, National Climatic Data Center; EUG, Eugene airport 

weather station; USACE, U.S. Army Corps of Engineers; SRML, Solar Radiation Monitoring Laboratory]. 

Parameter Model West Consultants USGS Description

TAIR

HCL NCDC EUG regression, 

Agrimet HCKO

NCDC EUG regression 

(2002), USACE HCWO1

Air temperature

LOP-DEX NCDC EUG regression, 

Agrimet LKPO

NCDC EUG regression 

(2002), USACE LPWO1

TDEW

HCL NCDC EUG regression, 

Agrimet HCKO

NCDC EUG regression 

(2002), USACE HCWO1 

Dew point temperature

LOP-DEX NCDC EUG regression, 

Agrimet LKPO

NCDC EUG regression 

(2002), USACE LPWO1

WIND, 

PHI

HCL

NCDC EUG NCDC EUG Wind speed, wind direction

LOP-DEX

CLOUD

HCL

unknown NCDC EUG Cloud cover

LOP-DEX

SRO

HCL PRIMET2

, Agrimet HCKO

SRML EUG Solar radiation

LOP-DEX PRIMET2, Agrimet LKPO

1

 In 2002, NCDC EUG data from 2006, 2008, 2009, and 2011 were used to estimate USACE LPWO and HCWO.

2

 Solar radiation data was multiplied by 2. 
55

Table A3. Differences in model parameter values between the original West Consultants models and the updated 

U.S. Geological Survey Green Peter Lake and Foster Lake models, Oregon

[Abbreviations: Airp, Airport; °C, degrees Celsius; (W/m2)/s ,watt per square meter per second; GPR, Green Peter Lake; 

FOS, Foster Lake; spill, spillway; power, power penstock outlet; EUG, Eugene airport weather station; SRML, Solar 

Radiation Monitoring Laboratory]

Parameter West Consultants USGS Description

WSC 1.00 for GPR

0.70 for FOS

1.00 for GPR

0.50 for FOS Wind sheltering coefficient, dimensionless

DYNSHD 0.90 1.00 Allows all incoming solar to reach the water surface

VISC OFF ON Vertical eddy viscosity limitation on timestep

CELC OFF ON Internal gravity wave limitation on timestep

PQC OFF ON Density placed inflows

EVC OFF ON Evaporation included in water budget

PRC OFF ON Precipitation included

QINIC OFF ON Interpolate inflows

DTRIC OFF ON Interpolate distributed tributary inflows

HDIC OFF ON Interpolate boundary conditions

METIC OFF ON Meteorological data interpolation

CBHE 7E-08 0.3 Coefficient of bottom heat exchange, (W/m2

)/s

TSED

7.00 for GPR

9.0 for FOS

11.1 Sediment temperature, °C

TSEDF 0.00 1.00 Heat lost to sediments that is added back to water column

STR SINK FOS spill: LINE

FOS power: POINT

FOS spill: POINT

FOS power: LINE Outlet structure types

STR WIDT FOS power=5.8 FOS power=3.8 Outlet structure width

EXH2O FOS: 0.45 FOS: 0.60 Light extinction coefficient for water, m-1

TDT 100 percent surface 

water

80 percent surface 

water, 20 percent 

groundwater

Distributed tributary temperature

Met source

TAIR: EUG, FOS

DEWT: EUG

WIND: EUG

PHI: FOS

SRO: Primet

CLOUD: zero

TAIR, DEWT: FOS

WIND, CLOUD: EUG 

SRO: SRML

Source of meteorological data
Buccola and others— Development of CE-QUAL-W2 Models for the Middle Fork Willamette and South Santiam Rivers, Oregon—Open-File Report 2013-1186

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20131186