U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2015–1012

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

Simulations of a Hypothetical Temperature 

Control Structure at Detroit Dam on the 

North Santiam River, Northwestern Oregon

Simulations of a Hypothetical Temperature Control 

Structure at Detroit Dam on the North Santiam River, 

Northwestern Oregon 

By Norman L. Buccola, Adam J. Stonewall, and Stewart A. Rounds

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

Open-File Report 2015–1012

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director 

U.S. Geological Survey, Reston, Virginia: 2015 

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Suggested citation:

Buccola, N.L., Stonewall, A.J., and Rounds, S.A., 2015, Simulations of a hypothetical temperature control 

structure at Detroit Dam on the North Santiam River, northwestern Oregon: U.S. Geological Survey OpenFile Report 2015–1012, 30 p., http://dx.doi.org/10.3133/ofr20151012. 

ISSN 2331-1258 (online)
iii

Contents

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

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

Purpose and Scope ............................................................................................................................................4

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

Flow and Temperature Models........................................................................................................................5

Environmental Scenarios ................................................................................................................................5

Without-Dams Water Temperature Estimation................................................................................................6

Temperature Targets ......................................................................................................................................6

Dam Outflow Estimation..................................................................................................................................8

Detroit Dam.................................................................................................................................................8

Big Cliff Dam................................................................................................................................................9

CE-QUAL-W2 Model Structure Parameters....................................................................................................9

North Santiam River Model Setup.................................................................................................................11

Results..............................................................................................................................................................11

Detroit Dam Release Rates and Simulated Lake Elevations.........................................................................11

Detroit Dam Release Temperatures..............................................................................................................13

Big Cliff Lake Water Balance and Heat Exchange ........................................................................................17

Effects Downstream of Detroit-Big Cliff Dams...............................................................................................19

Downstream Temperatures .......................................................................................................................19

Potential Biological Effects ........................................................................................................................23

Estimated Emergence Dates .................................................................................................................23

Summary ..........................................................................................................................................................27

Acknowledgments.............................................................................................................................................28

References Cited..............................................................................................................................................29

Figures

Figure 1. Map showing North Santiam and Santiam Rivers and the North Santiam River Basin,

northwestern Oregon ......................................................................................................................................... 2

Figure 2. Graph showing temperature targets for the North Santiam River downstream of Detroit Dam, 

northwestern Oregon. ........................................................................................................................................ 7

Figure 3. Graph showing simulated total inflows under all environmental scenarios, North Santiam River, 

northwestern Oregon ....................................................................................................................................... 12

Figure 4. Graphs showing simulated Base operational scenario (imposed conditions for scenarios c1, n1, h1, 

c2, n2, h2) for (A) total outflows and (B) water-surface elevation and rule curve, North Santiam River, 

northwestern Oregon ....................................................................................................................................... 12

Figure 5. Graphs showing simulated HighPeak operational scenario (imposed conditions for

scenarios c3, n3, h3) for (A) total outflows and (B) water-surface elevation and rule curve............................. 13

Figure 6. Graphs showing simulated release temperatures at Detroit Dam, Oregon, under three structural 

scenarios: (A) NoBlend (scenarios c1, n1, h1), (B) Existing (scenarios c2, n2, h2), and (C) SlidingWeir 

(scenarios c3, n3, h3). ..................................................................................................................................... 14

Figure 7. Graph showing simulated percent spill at Detroit Dam, northwestern Oregon, for 

Existing structural scenarios and Base operational conditions (scenarios c2, n2, h2). .................................... 15
iv

Figure 8. Graphs showing simulated release rates from (A) hypothetical upper weir, (B) hypothetical 

lower weir, and (C) spill under SlidingWeir structural scenarios and HighPeak operational conditions 

(scenarios c3, n3, h3) at Detroit Dam, northwestern Oregon........................................................................... 16

Figure 9. Graphs showing simulated lake elevations and rule curve from (A) Base and (B) HighPeak 

operational scenarios under three environmental scenarios (cool/wet, normal, and hot/dry) at Big Cliff 

Dam, northwestern Oregon.............................................................................................................................. 17

Figure 10. Graphs showing simulated temperature difference between releases from Big Cliff and 

Detroit Dams, northwestern Oregon, under three structural scenarios: (A) NoBlend (scenarios c1, n1, h1), 

(B) Existing (scenarios c2, n2, h2), and (C) SlidingWeir (scenarios c3, n3, h3)............................................... 18

Figure 11. Graphs showing simulated temperatures at Mehama (RM 38.7) on the North Santiam River, 

northwestern Oregon, under three environmental scenarios (cool/wet, normal, and hot/dry) and three 

structural scenarios: (A) NoBlend, (B) Existing, and (C) SlidingWeir ............................................................... 20

Figure 12. Graphs showing simulated temperatures at Greens Bridge (RM 14.6) on the North Santiam 

River, northwestern Oregon, under three environmental scenarios (cool/wet, normal, and hot/dry) and

three structural scenarios: (A) NoBlend, (B) Existing, and (C) SlidingWeir...................................................... 21

Figure 13. Graphs showing simulated heating or cooling effect of the (A) Existing and (B) SlidingWeir

structural scenario results relative to the temperatures simulated in the NoBlend structural scenarios at 

Greens Bridge (RM 14.6) on the North Santiam River, northwestern Oregon, under three environmental 

scenarios (cool/wet, normal, and hot/dry) ........................................................................................................ 22

Figure 14. Mean accumulated thermal units (ATUs) starting May 1 from Existing, NoBlend, and 

SlidingWeir structural scenarios at (A) Big Cliff Dam, (B), Mehama, and (C), Greens Bridge sites on the 

North Santiam River, northwestern Oregon ..................................................................................................... 24

Figure 15. Graphs showing mean accumulated thermal units (ATUs) starting September 20 from 

Existing, NoBlend, and SlidingWeir structural scenarios at (A) Big Cliff Dam, (B) Mehama, and 

(C) Greens Bridge sites on the North Santiam River, northwestern Oregon.................................................... 26

Tables

Table 1. Description of environmental scenarios, North Santiam River, northwestern Oregon ......................... 5

Table 2. Minimum and maximum outflow requirements for operational scenarios at Detroit Dam, North 

Santiam River, northwestern Oregon................................................................................................................. 8

Table 3. Operational scenario group descriptions, Detroit Dam, North Santiam River, 

northwestern Oregon ......................................................................................................................................... 9

Table 4. Structural scenario group descriptions and model parameter settings, Detroit Dam, North Santiam 

River, northwestern Oregon............................................................................................................................. 10

Table 5. Specification and naming convention of model scenarios, Detroit Dam, North Santiam River, 

northwestern Oregon ....................................................................................................................................... 11

Table 6. Calculated average emergence day for the cool/wet, normal, and hot/dry environmental 

forcings at four locations from the Detroit Lake, Big Cliff Lake, and North Santiam River models, 

northwestern Oregon. ...................................................................................................................................... 25
v 

Conversion Factors, Datums, and Abbreviations and Acronyms

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

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

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

SI to Inch/Pound

Multiply By To obtain

meter (m) 3.281 foot (ft) 

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

Datums

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 1927 (NAD 27).

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

Abbreviations and Acronyms

Name Description

7dADM

ATU

BiOp 

CE-QUAL-W2

RM 

RO 

TMDL

USACE

USGS

7-day moving average of the daily maximum

accumulated thermal unit 

biological opinion

2- dimensional hydrodynamic and water-quality model

river mile

regulating outlet 

total maximum daily load

U.S. Army Corps of Engineers

U.S. Geological Survey
1 

Simulations of a Hypothetical Temperature Control 

Structure at Detroit Dam on the North Santiam River, 

Northwestern Oregon

By Norman L. Buccola, Adam J. Stonewall, and Stewart A. Rounds

Abstract

Water temperature models of Detroit Lake, Big Cliff Lake, and the North Santiam River in 

northwestern Oregon were used to assess the potential for a hypothetical structure with variable 

intake elevations and an internal connection to power turbines at Detroit Dam (scenario 

SlidingWeir) to release more natural, pre-dam temperatures year round. This hypothetical structure 

improved outflow temperature control from Detroit Dam while meeting minimum dry-season 

release rates and lake levels specified by the rule curve specified for Detroit Lake. 

A water temperature target based on long-term, without-dams temperature estimates was 

developed and used to guide the Detroit Lake model to blend releases from the user-defined outlets 

at Detroit Dam. Simulations that included warm surface water releases during the spring and 

summer, and cool, deep hypolimnetic water releases later during autumn typically met the 

temperature target. Immediately downstream of Detroit Dam, these simulations resulted in 

temperatures within the range of the without-dams temperature estimates for most of the year until 

about November. The minimum release rates of flow imposed at Detroit Dam during late summer 

and early autumn exceeded unregulated, without-dams flow estimates. This higher flow led to 

temperatures near the low end of the without-dams temperature range 46.3 river miles downstream 

at Greens Bridge from July to September; the high flows released from Detroit Dam were less 

susceptible to downstream warming than the low unregulated flows. Simulations that blended

warm and cool water from different outlets at Detroit Dam resulted in less daily temperature 

variation compared to the without-dams scenarios as far downstream as Greens Bridge. 

Estimated egg-emergence days for endangered Upper Willamette River Chinook salmon 

(Oncorhynchus tshawytscha) and Upper Willamette River winter steelhead (Oncorhynchus mykiss) 

were assessed for all scenarios. Estimated spring Chinook fry emergence under SlidingWeir

scenarios was 9 days later immediately downstream of Big Cliff Dam, and 4 days later at Greens 

Bridge compared with existing structural scenarios at Detroit Dam. Despite the inclusion of a 

hypothetical sliding weir at Detroit Dam, temperatures exceeded without-dams temperatures during 

November and December. These late-autumn exceedances likely represent the residual thermal 

effect of Detroit Lake operated to meet minimum dry-season release rates (supporting instream 

habitat and irrigation requirements) and lake levels specified by the current (2014) operating rules 

(supporting recreation and flood mitigation). 
2 

Introduction

Detroit Dam was constructed in 1953 by the U.S. Army Corps of Engineers (USACE) on 

the North Santiam River in northwestern Oregon and resulted in the formation of Detroit Lake (fig. 

1). The North Santiam River drains an area on the western slopes of the Cascade Range and is one 

of several major tributaries to the Willamette River. Detroit Dam is the tallest dam (463 ft) in the 

Willamette River Basin and impounds 455,100 acre-ft of water at full pool, making it one of the 

largest reservoirs in the basin. The small re-regulating dam downstream of the Detroit and Big Cliff 

Dams ensures steady streamflows in the North Santiam River and allows Detroit Dam’s power 

generating facility (and releases) to be turned on and off during the course of a day to meet peak 

electrical demands. Big Cliff Lake is much smaller than Detroit Lake, with a reservoir volume of 

6,450 acre-ft at full pool. The Big Cliff–Detroit Dam complex typically generates among the most 

hydroelectric power of Willamette River basin USACE facilities, and Detroit Lake ranks as one of 

the most important recreational resources among the 13 reservoirs managed by USACE in the 

Willamette Project. 

Figure 1. Map showing North Santiam and Santiam Rivers and the North Santiam River Basin, 

northwestern Oregon. (Modified from Sullivan and Rounds, 2004.) 
3 

Prior to 2007, power generation was a high priority for the Big Cliff–Detroit Dam complex, 

and releases from Detroit Dam generally were routed through the power penstocks (centerline 

elevation 427.6 m or 1,403 ft) except for times when excess flows were released through the upper 

regulating outlets (ROs) (center-line elevation 408.4 m or 1,340 ft) or over the spillway (crest 

elevation 469.7 m or 1,541 ft). During those years, midsummer releases were unseasonably cold 

because the power penstocks are located 166 ft below Detroit Lake’s full-pool level, well below the 

thermocline at that time of year. Releases from that depth allowed summer solar energy inputs to 

accumulate in a growing layer of warm water at the lake surface. Drawdown of the lake in 

September to make room for winter flood storage typically resulted in warmer waters at the level of 

the power penstocks and unseasonably warm releases in late summer and autumn. The thermal 

effects of Willamette River Basin dams have been quantified in recent modeling studies, and the 

effects can extend for many miles and many days of travel time downstream of the dams (Rounds, 

2010). 

The North Santiam River and its tributaries (fig. 1) provide habitat for endangered Upper 

Willamette River Chinook salmon (Oncorhynchus tshawytscha) and Upper Willamette River

winter steelhead (Oncorhynchus mykiss). The Oregon Department of Environmental Quality has set 

maximum water-temperature standards for stream reaches in Oregon, including the North Santiam 

and Santiam Rivers, to protect certain life stages of these sensitive fish (Oregon Department of 

Environmental Quality, 2009). These criteria are based on the 7-day moving average of the daily 

maximum (7dADM) water temperature. For example, the North Santiam River is designated as 

core cold-water habitat for June 16–August 31 annually, with the 7dADM water temperature not to 

exceed 16.0 °C. A stricter 13.0 °C criterion is in place for salmon and steelhead spawning habitat 

during September 1–June 15. Farther downstream, the Santiam River is designated as salmon and 

trout rearing and migration habitat, with a maximum 7dADM water temperature of 18.0 °C for 

May 16–October 14, and salmon and steelhead spawning habitat for October 15–May 15, with the 

13 °C maximum criterion (Oregon Department of Environmental Quality, 2009). Unusually warm 

temperatures have been associated with negative impacts to various life stages of spring Chinook 

salmon, including high prespawn mortality (Keefer and others, 2010), delayed migration (Goniea 

and others, 2006; Angilletta and others, 2008), and premature fry emergence (U.S. Army Corps of 

Engineers, 2009). To protect and enhance these beneficial uses and habitats, the National Marine 

Fisheries Service wrote a 2008 Willamette Basin Biological Opinion (BiOp) that, among other 

things, urges the USACE to assess the feasibility of developing project-specific alternatives for 

achieving long-term temperature control at the Big Cliff–Detroit Dam complex (National Marine 

Fisheries Service, 2008). The USACE is in the process of evaluating alternatives for both current 

and long-term downstream temperature management and fish passage at many of the dams in the 

Willamette Project.

Detroit Dam is an excellent facility for the USACE to test strategies for downstream 

temperature management because the dam has outlets at several fixed elevations, allowing water to 

be released from multiple depths and blended to meet a downstream temperature target. In 

particular, the release of warm water over the spillway in midsummer and cool water from deep in 

the lake in late summer and early autumn can help mitigate problems associated with water 

temperatures that otherwise would be too cold or too warm for fish. Since 2007, USACE has 

released water through the spillway, the upper ROs, and the power penstocks to improve 

downstream fish habitat during the various life stages of endangered salmonid fish species, while at 

the same time balancing the need to generate hydropower. 
4 

To help evaluate potential dam operation strategies and future structural options, the 

USACE can use predictions from several models that simulate water temperature in Detroit Lake, 

Big Cliff Lake, and the North Santiam River. The U.S. Geological Survey (USGS) previously 

constructed and calibrated a model of Detroit Lake to examine water temperature and suspendedsediment conditions in the lake and downstream (Sullivan and others, 2007). The model was built 

using CE-QUAL-W2, a two-dimensional, laterally averaged hydrodynamic and water-quality 

model from USACE (Cole and Wells, 2002) that has been widely applied to river and reservoir 

systems around the world. The USGS Detroit Lake model was calibrated to conditions that 

occurred during calendar years 2002 and 2003 and also was tested for high-flow conditions during 

winter 2005–06. The model and many results are available at 

http://or.water.usgs.gov/santiam/detroit_lake/ (U.S. Geological Survey, 2013). 

The USGS Detroit Lake model was originally built with a modification of CE-QUAL-W2 

version 3.12 (Sullivan and others, 2007) but has since been upgraded to version 3.7 (Cole and 

Wells, 2011) and modified to enhance the algorithm that allows a model user to easily estimate the 

release rates that are required from different dam outlets to achieve a time series of downstream 

temperature targets (Rounds and Sullivan, 2006; Buccola and others, 2012; Rounds and Buccola, 

2015). In this way, dam operations can be forecast to meet certain downstream fish habitat criteria 

at different times of the year. A CE-QUAL-W2 model of Big Cliff Lake (Buccola and others, 2012) 

and a HEC-RAS model of the North Santiam and Santiam Rivers (Stonewall and Buccola, 2015) 

also have been constructed and calibrated. Using those models, predicted flows and water 

temperatures from the Detroit Lake model can be translated downstream to evaluate how 

temperatures change in the 60.9 mi of river downstream of Detroit Dam before the Santiam River 

joins the Willamette River. 

Purpose and Scope

The purpose of this report is to provide water temperature estimates throughout the North 

Santiam River system from Detroit Dam to Greens Bridge (46.4 mi downstream of Detroit Dam, 

near the junction of the North Santiam and South Santiam Rivers) under a range of environmental 

conditions and potential structural changes at Detroit Dam. Model results presented in this report 

are intended to provide insight into what potential temperatures may result from a hypothetical 

temperature control structure at Detroit Dam for the purpose of improving current downstream 

temperature conditions for fish in the North Santiam River. Biological impacts related to water 

temperature are addressed during spring and autumn, which are critical seasons for 

threatened/endangered salmon and steelhead habitat. The results published in this report augment 

results in Buccola and others (2012). 

A range of environmental conditions that represent “cool/wet,” “normal,” and “hot/dry”

hydrological and meteorological conditions based on historical data and defined by Buccola and 

others (2012) were used for all model scenarios in this study. Results of simulations with the 

temperature control structure at Detroit Dam were compared at various points along the North 

Santiam River downstream of the dams with results from other simulations that included the 

existing structures at Detroit Dam and results from scenarios that were based on without-dams 

estimated temperatures as documented by Buccola and others (2012). 
5 

This study used previously developed CE-QUAL-W2 models of Detroit Lake (Sullivan and 

others, 2007) and Big Cliff Lake (Buccola and others, 2012) for all simulations of water discharge 

and temperature in the reservoirs. An enhanced blending routine was added to CE-QUAL-W2 

version 3.7 (Rounds and Buccola, 2015) and used for all model simulations of Detroit Lake. A onedimensional HEC-RAS flow and temperature model of the North Santiam River (Stonewall and 

Buccola, 2015) was used for all simulations of water discharge and temperature downstream of Big 

Cliff Dam. 

Methods

Flow and Temperature Models

Two separate CE-QUAL-W2 models were used in this study to simulate Detroit and Big 

Cliff Lakes. The North Santiam River downstream of Big Cliff Dam was simulated using the HECRAS model with its water-quality module (Stonewall and Buccola, 2015). For this study, a 

customized version 3.7 CE-QUAL-W2 model (Rounds and Buccola, 2015) was used for 

temperature models at Detroit and Big Cliff Lakes. Big Cliff Lake is a small re-regulating reservoir 

just downstream of Detroit Dam, and its operation has a small effect on water temperature at some 

times of the year. HEC-RAS model version 4.10 (Brunner, 2010) was used to develop a onedimensional flow and temperature model for the North Santiam River and calibrated to conditions 

in 2011 and 2002 with emphasis on the low-flow period during summer and autumn (Stonewall and 

Buccola, 2015).

Environmental Scenarios

Three distinctly different environmental forcing scenarios named cool/wet, normal, and 

hot/dry were originally documented by Buccola and others (2012) to capture a wide range of 

possible streamflow, water temperature, and meteorological conditions. These environmental 

scenarios consisted of the measured conditions from various timeframes spliced together (table 1).

All inflows used in this study (including precipitation and distributed tributaries) and 

meteorological inputs remained identical to those original environmental scenarios documented by 

Buccola and others (2012). In brief, inflow discharge and temperature were mostly measured at 

USGS sites near Detroit Lake. Air temperature, dew-point temperature, wind speed, and wind 

direction were measured near Stayton, Oregon, while solar radiation and precipitation were 

measured at Eugene and Detroit, Oregon, respectively.

Table 1. Description of environmental scenarios, North Santiam River, northwestern Oregon. 

[From Buccola and others (2012), table 2] 

Environmental forcings

Measured time-frame Concatenate date 

(month/day) Spring/Summer Autumn/Winter

cool/wet 2009 2006 10/12

normal 2006 2009 9/27

hot/dry 2005 2002 9/27
6 

Without-Dams Water Temperature Estimation

Hourly water temperatures for the North Santiam River were estimated at two locations: (1) 

Big Cliff Dam (river mile [RM] 58)- for a “without-dams” scenario, and (2) Detroit Dam [RM 

60.9] to develop a temperature target for the CE-QUAL-W2 model scenarios and described further 

in section, “Temperature Targets.” Without-dams estimates at Big Cliff Dam (where Detroit and 

Big Cliff Dams do not exist in this simulation) for cool/wet, normal, and hot/dry environmental 

scenarios followed methods documented in Buccola and others (2012). The estimates were 

computed using a simple mass and energy balance approach combined with a nominal downstream 

warming rate applied during summer, following methods documented by Rounds (2010).

Temperature Targets

Recent developments of the blending algorithm within CE-QUAL-W2 allow a user to 

impose a time-series of temperature targets that the model will try to meet, mixing outflow from the 

available outlets at the dam (Rounds and Buccola, 2015). Previous studies have used temperature 

targets developed by USACE for the McKenzie River system downstream of another dam (Cougar 

Dam on the South Fork McKenzie River) as representative of the conditions needed to support a 

restoration of uses by endangered fish (Buccola and others, 2012; U.S. Army Corps of Engineers, 

2012). To compare this previously applied set of targets with temperatures that may better represent 

the North Santiam subbasin, a new set of targets were developed based on the long-term maximum 

of measured daily average temperatures from USGS stations on the North Santiam River below 

Boulder Creek (station 14178000) and the Breitenbush River above French Creek (station

14179000), and Blowout Creek near Detroit (station 14180300). A flow-weighted average of 

temperatures from these three stations was computed using the following equation:

Test = (QNS TNS + QBB TBB + QBL TBL)/ (QNS + QBB + QBL), (1)

where

Test is mixed water temperature estimate, in degrees Celsius, 

QNS is measured streamflow in the North Santiam River at station 14178000, in cubic 

feet per second, 

TNS is measured water temperature in the North Santiam River at station 14178000, 

in degrees Celsius, 

QBB is measured streamflow in the Breitenbush River at station 14179000, in cubic 

feet per second, 

TBB is measured water temperature in the Breitenbush River at station 14179000, in 

degrees Celsius, 

QBL is measured streamflow in Blowout Creek at station 14180300, in cubic feet per 

second, and

TBL is measured water temperature in Blowout Creek at station 14180300, in degrees 

Celsius. 

The long-term (water years 1998–2013) maximum of these daily mean water temperatures

for each day (that is, the maximum of the daily mean values for each January 1 day from 1998 to 

2013, and so on) then were computed and adjusted to account for the instream warming that most 

likely occurred as water traverses the 9-mi reach between the upstream end of Detroit Lake (where 

these tributaries were assumed to join and mix) and Detroit Dam. From November 1 to April 13, or 
7 

any time of the year when water temperatures were less than 6 °C, no instream warming 

adjustments were made to water temperature estimates. From April 14 to October 31, a downstream 

warming rate was applied as a function of the mixed temperature estimate. All water temperature 

estimates greater than 14 °C were increased by 0.99 °C to account for a nominal maximum 

downstream warming rate of 0.11 °C/mi over 9 mi of distance. This maximum downstream 

warming rate was based on historical data (Moore, 1964, 1967) as well as previous watertemperature modeling in the North Santiam River in the 4 mi just downstream of Big Cliff Dam 

(Rounds, 2010). Water-temperature estimates less than 14 °C but greater than 6 °C were increased 

to account for some downstream warming, but less than the maximum rate of 0.11 °C/mi, using the 

following linear interpolation:

Tfinal = Test + 0.99 (Test – 6.0) / (14.0 - 6.0), 6.0 ≤ Test ≤ 14.0. (2)

To create a continuous time-series temperature target for the model, this time-series was 

smoothed using a centered 30-day moving average (fig. 2). When applied with the CE-QUAL-W2 

temperature model to scenarios in this study, the final version of this temperature target specified

the peak value from this smoothed time series (15.9 °C) from Julian day 1 to 216 (January 1 to 

August 4). This change essentially directed the model to release as much warm water as possible 

from the lake during the spring and early summer, while saving cool, deeper water for release later 

in autumn. 

Figure 2. Graph showing temperature targets for the North Santiam River downstream of Detroit Dam, 

northwestern Oregon. Existing, target used for the McKenzie River, Oregon; 30DMADMin, 30-day moving 

average of long-term daily minimum; 30DMADA, 30-day moving average of long-term average daily; 

30DMADMax, 30-day moving average of long-term daily maximum; 30DMMaxDA, 30-day moving maximum 

of average daily. All targets except for Existing are based on flow-weighted measured temperatures of the 

Detroit Lake inflows and were warmed by 0.11 °C/mi for 9 mi during summer months. 
8 

Dam Outflow Estimation

Detroit Dam

The total release rates (outflows) from Detroit Dam were set to adhere to the following 

conditions: 

1. Releases from Detroit Dam should meet minimum and maximum flow requirements as 

specified by the BiOp (National Marine Fisheries Service, 2008), with some exceptions 

during March and April in the hot/dry scenario (table 2).

2. Computed water levels in Detroit Lake should not exceed the reservoir rule curve (the 

operational target for the lake water-surface elevation throughout the year) for more than 5 

days when the lake is at full-pool elevation. 

3. Total outflow should be based on the use of one (Base) or two (HighPeak) turbines at Detroit 

Dam and concentrated for specific hours of the day (table 3) to simulate “power peaking” 

operations. The Base operational scenario group as described in Buccola and others (2012) 

was used as a reference condition. 

Table 2. Minimum and maximum outflow requirements for operational scenarios at Detroit Dam, North 

Santiam River, northwestern Oregon. 

[Flows are daily mean streamflow, in cubic feet per second (ft3

/s). Altered flows 

for the hot/dry scenario are indicated by the numbers in italics] 

Month/Day Operational scenario group minimum flows (ft3/s)

cool/wet normal hot/dry

Minimum flow 

Jan. 1 1,200 1,200 1,200

Feb. 1 1,000 1,000 1,000

Mar. 1 1,000 1,000 1,000

Mar. 16 1,500 1,500 1,000

Apr. 1 1,500 1,500 1,000

Apr. 16 1,500 1,500 1,500

May 1 1,580 1,580 1,580

May 16 1,580 1,580 1,580

June 1 1,280 1,280 1,280

July 1 1,280 1,280 1,280

July 16 1,080 1,080 1,080

Sept 1 1,500 1,500 1,500

Oct. 16 1,200 1,200 1,200

Dec. 1 1,200 1,200 1,200

Dec. 31 1,200 1,200 1,200

Maximum flow

Jan. 1 15,000 15,000 15,000

Sept. 1 3,000 3,000 3,000

Sept. 30 3,000 3,000 3,000

Dec. 31 15,000 15,000 15,000
9 

Table 3. Operational scenario group descriptions, Detroit Dam, North Santiam River, northwestern Oregon.

[(ft3

/s, cubic feet per second]

Operational scenario groups Power peaking operation 

maximum flow (ft3/s)

Order of peaking hours in 

each day

Maximum total 

outflow (ft3/s)

Base 2,472 0600–2200 5,000

HighPeak 4,900 (1) 1700–2400 5,600

(2) 0500–1200

(3) 1300–1600

(4) 0100–0400 

Big Cliff Dam

A method of estimating outflows at Big Cliff Dam was developed to simulate outflows that 

closely approximated typical dam operations while balancing inflows and outflows and recreating 

relatively stable lake levels in Big Cliff Lake. The outflow at Big Cliff Dam initially was assumed 

to be a moving daily average of the total inflow to Big Cliff Lake. Efforts were made to limit the 

pool elevation in Big Cliff Lake between its minimum conservation pool (360.3 m or 1,182.0 ft) 

and full pool (367.5 m or 1,205.8 ft) (further discussed in section, “Big Cliff Lake Water Balance 

and Heat Exchange”). The addition of a distributed tributary inflow (median discharge of 

approximately 35 ft3

/s) to the Big Cliff model helped to achieve relatively constant lake levels 

while accounting for unmeasured tributary inflows. An iterative process then was used to adjust 

this distributed tributary based on the difference between subsequent modeled water-level 

elevations and a mean pool elevation of 362.1 m or 1,188 ft. This resulted in simulations of Big 

Cliff Lake that both resembled current operating elevation rules and led to simulations with a 

relatively constant pool elevation, which is acceptable for the purposes of this study. 

CE-QUAL-W2 Model Structure Parameters 

Within the model, the “w2_con.npt” and “w2_selective.npt” files define the outlet 

parameters used by the blending algorithm. For this study, parameters related to structure centerline 

elevation and width (STR ELEV and STR WIDTH in the w2_con.npt file) were adjusted from 

original values in Sullivan and others (2007). All structures were assigned STR SINK values of 

“LINE”, while STR WIDTH values were varied (table 4). Other parameters in the w2_selective.npt 

file of the modified version of CE-QUAL-W2 (Rounds and Buccola, 2015) related to the 

preference of outlets (PRIORITY), minimum flow fraction (MINFRAC), floating outlet depth 

below the water surface (DEPTH), maximum flow limitation (MAXFLOW), and maximum head 

limit (MAXHEAD) for a given outlet also were adjusted for this study (table 4). 

Of primary importance to this report was the simulation of a hypothetical temperature 

control structure at Detroit Dam in which a weir gate floats 2.3 m below the lake surface (named 

“upper weir” with DEPTH=2.3 m in structural scenario SlidingWeir; table 4). This hypothetical 

upper weir gate was assumed to resemble some characteristics of the existing upper RO (STR 

WIDTH=6.8 m), with a minimum outflow of 11.3 m3

/s (MINFRAC = -11.3 in table 4) that is 

routed through the dam to the hydropower turbines in such a way that releases from this surface 

outlet (typically warmer than that of the water near the power penstocks) would not be limited by 
10 

hydropower demands. A lower weir gate with centerline outlet elevation close to the elevation of 

the existing upper RO (STR ELEV = 408.4 m) was blended with this upper weir gate (upper weir 

and lower weir both have PRIORITY = 1 in table 4). The SlidingWeir scenario also included the 

existing spillway and upper RO outlets at Detroit Dam, used only as overflow, when total outflow 

at the dam exceeded the powerhouse maximum (MAXFLOW = 158.5 m3

/s in table 4). To ensure 

that the upper and lower weir outlets did not release more than a combined 158.5 m3/s (5,600 ft3/s), 

the time series of overflow values (total Detroit Dam outflow in exceedance of 158.5 m3/s ) for the 

spillway/upper RO were specified in the outflow boundary condition file and both outlets were 

given PRIORITY= -1 (table 4). A priority of -1 tells the model to include those outflows in its 

attempt to meet the user-specified target temperature for the releases, but that these flows are set by 

the user and cannot be changed by the model’s blending algorithm. 

For the Detroit Lake model, two reference scenarios were included—one in which no 

blending of releases occurred (all outflow was directed to the power penstocks – named NoBlend) 

and another in which only the existing outlets at Detroit Dam were used (spillway, power 

penstocks, and upper RO – named Existing). Under Base operational scenarios, a minimum fraction 

(40 percent) of the outflow in the Existing scenario was routed to the power penstocks for power 

generation (MINFRAC=0.4, PRIORITY=1 in table 4) while the remaining outflow was blended 

between the power penstocks, the spillway (PRIORITY = 2) when lake levels were above the 

spillway crest (STR ELEV=469.7 m in table 4), and the upper RO (PRIORITY=2) when lake levels 

were below 471 m (STR ELEV=408.4 m, MAXHEAD=61 m in table 4). The TSSHARE input to 

was set to OFF in this Base scenario, causing the model to choose either the spillway or the upper 

RO, but never both at the same time, as a preferred outlet to blend releases with the power 

penstocks. 

Table 4. Structural scenario group descriptions and model parameter settings, Detroit Dam, North Santiam 

River, northwestern Oregon.

[STR ELEV and STR WIDTH are parameters specified in the w2_con.npt file, while PRIORITY, MINFRAC, DEPTH, 

MAXFLOW, and MAXHEAD are parameters specified in the w2_selective.npt file. Negative PRIORITY values indicate that 

outflow boundary conditions for the structure are used. Negative MINFRAC values indicate a specific minimum flow in cubic 

meters per second [m3

/s]] 

Structural 

scenario

groups

Stucture name Model parameter

STR ELEV

(meters)

STR WIDTH

(meters)

PRIORITY MINFRAC DEPTH 

(meters)

MAXFLOW

(m3/s)

MAXHEAD

(meters)

SlidingWeir upper weir 481.3 6.8 1 -11.3 2.3 158.5 0 

spillway 469.7 25 -1 0 0 0 0 

lower weir 408.4 6.8 1 0 0 158.5 0

upper RO 410 6.8 -1 0 0 158.5 0

Existing spillway 469.7 25 2 0 0 0 0

power penstocks 427.6 6.8 1 0.4 0 0 0

upper RO 408.4 6.8 2 0 0 158.5 61

NoBlend power penstocks 427.6 6.8 not 

applicable
11 

The two operational scenarios described in table 3 were combined with three structural 

scenarios (table 4), projected onto the three environmental forcing conditions of cool/wet, normal, 

and hot/dry, and combined with a set of temperature target requirements to produce the model 

scenarios of interest (table 5). The combination of these three conditions—operational scenario, 

structural scenario, and environmental scenario—fully describes the major differences between the 

model scenarios and provides a consistent naming convention. 

Table 5. Specification and naming convention of model scenarios, Detroit Dam, North Santiam River, 

northwestern Oregon. 

[Scenario identifier: c, cool/wet; n, normal; h, hot/dry]

Structural scenarios Operational scenarios

Scenario identifier

Environmental forcings

cool/wet normal hot/dry

NoBlend Base c1 n1 h1

Existing Base c2 n2 h2

SlidingWeir HighPeak c3 n3 h3

North Santiam River Model Setup

Release flows and temperatures from the CE-QUAL-W2 Big Cliff Lake model were used as 

hourly time-series inflow boundary conditions to the North Santiam River model (Stonewall and 

Buccola, 2015). Tributary inflow and temperature inputs, and meteorological input data sources 

were similar to those described by Stonewall and Buccola (2015).

Results

Detroit Dam Release Rates and Simulated Lake Elevations 

Before comparing modeled outflow temperatures from the various scenarios, it is helpful to 

compare the imposed release rates (outflows) and simulated lake water-surface elevations in each 

of the operational scenarios, because the timing of the rule curve can contribute greatly to the 

resulting temperature regime in the lake. Both Base and HighPeak operational scenarios generally 

led to simulated lake levels that closely matched the USACE rule curve for most of the year. Some 

deviations from the rule curve existed in January–March as lake levels were rising and in mid-July–

mid-October as minimum release requirements exceeded inflows (figs. 3, 4, and 5). The HighPeak 

operational scenario release rates led to minor lake elevation differences compared to Base

operations, primarily January–March under normal and cool/wet environmental scenarios (fig. 5). 

Lake elevations in hot/dry scenarios were lower than normal and cool/wet scenarios year round. 
12 

Figure 3. Graph showing simulated total inflows under all environmental scenarios, North Santiam River, 

northwestern Oregon. 

Figure 4. Graphs showing simulated Base operational scenario (imposed conditions for scenarios c1, n1, h1, 

c2, n2, h2) for (A) total outflows and (B) water-surface elevation and rule curve, North Santiam River, 

northwestern Oregon. 
13 

Figure 5. Graphs showing simulated HighPeak operational scenario (imposed conditions for scenarios c3, n3, 

h3) for (A) total outflows and (B) water-surface elevation and rule curve. 

Detroit Dam Release Temperatures

Simulated temperatures from the NoBlend structural scenario with the Base operational 

scenario reflect the result of typical dam operations at Detroit Dam prior to 2007 and serve as a 

basis to compare other structural and operational scenario outcomes (fig. 6A). As NoBlend 

scenarios were limited to only one outlet (power penstocks), the resulting release temperatures from 

Detroit Dam during summer months were as much as 7 °C below the temperature target (“Rule 

Curve” in fig. 6) while autumn temperatures were as much as 6 °C above the target. The power 

penstocks (centerline 427.6 m elevation) can be about 50 m below the surface of Detroit Lake 

during the summer, which leads to the release of deeper, cool water at this time. As the lake is 

drawn down in September–November, warm surface water not yet released during the summer is 

drawn closer to the power penstocks, resulting in unseasonably warm autumn release temperatures

under the NoBlend scenario. 
14 

Figure 6. Graphs showing simulated release temperatures at Detroit Dam, Oregon, under three structural 

scenarios: (A) NoBlend (scenarios c1, n1, h1), (B) Existing (scenarios c2, n2, h2), and (C) SlidingWeir 

(scenarios c3, n3, h3). 30DMMaxDM-WODams, temperature target used in this study; McKenzie R. Max/Min 

Target, maximum and minimum temperature target established for the McKenzie River. 
15 

By allowing blending between the power penstock releases and either the spillway or upper 

ROs at Detroit Dam, release temperatures from the Existing structural scenarios under Base

operating conditions were warmer in summer months and cooler in the autumn compared with the 

NoBlend scenarios (figs. 6A and 6B). In this scenario, at least 40 percent of the total release was 

reserved for power production at all times (MINFRAC = 0.4 for the penstocks, table 4), and other 

releases (called “spill” in this report regardless of whether it was over the spillway or through the 

upper RO) ranged from 0 to 60 percent, as needed to try to meet the release temperature target (fig. 

7). As the lake elevation declined below the spillway crest under Existing structural scenarios (late 

July in h2; early September in c2, n2), the spillway could no longer be used, resulting in an 

immediate decrease in release temperature from Detroit Dam (fig. 6B). During autumn, all Existing 

scenarios resulted in release temperatures warmer than the temperature target. Because of lower 

lake elevations in scenario h2, spillway usage was limited during the summer and led to the 

warmest release temperatures during the autumn for Existing scenarios. 

With the addition of a hypothetical withdrawal near the surface of the lake and a lower weir 

withdrawal (hypothetically routed through the Detroit Dam power house), release temperatures 

from SlidingWeir structural scenarios under HighPeak operational scenarios were warmer from 

May to mid-September and cooler from mid-October to December compared with NoBlend and 

Existing structural scenarios (fig. 6C). Simulated releases primarily were from the hypothetical 

upper weir during January to mid-July, at which point the temperature target begins decreasing and 

deeper, cooler water (from the lower weir) was needed to mix with warmer surface water to meet 

the temperature target (figs. 8A and 8B). Some instances of spill (flow through the spillway or the 

upper RO, as scheduled) occurred during high inflow events (scenarios c3, n3) but seemed to affect 

the outflow temperatures only minimally (figs. 8C and 6C).

Figure 7. Graph showing simulated percent spill at Detroit Dam, northwestern Oregon, for Existing structural 

scenarios and Base operational conditions (scenarios c2, n2, h2). Percent spill is the percentage of total flow 

directed to outlets other than the power penstocks. 
16 

Figure 8. Graphs showing simulated release rates from (A) hypothetical upper weir, (B) hypothetical lower 

weir, and (C) spill under SlidingWeir structural scenarios and HighPeak operational conditions (scenarios c3, 

n3, h3) at Detroit Dam, northwestern Oregon. Spill, spillway outflow when lake levels are above spillway crest 

and flow through upper RO when lake levels are below spillway crest. 
17 

Big Cliff Lake Water Balance and Heat Exchange

Short residence times in Big Cliff Lake (about 1 day) led to some difficulty in achieving a 

water balance that resulted in relatively constant simulated lake elevations (fig. 9). Simulated Big 

Cliff Lake elevations under the Base operational scenarios generally were between 1,180 and 1,200 

ft except for a few days under the normal and cool/wet environmental scenarios (fig. 9A). Under 

HighPeak operational scenarios, the simulated lake levels were within the normal operating range 

(1,182.0– 1,205.8 ft) (fig. 9B). 

Figure 9. Graphs showing simulated lake elevations and rule curve from (A) Base and (B) HighPeak 

operational scenarios under three environmental scenarios (cool/wet, normal, and hot/dry) at Big Cliff Dam, 

northwestern Oregon. 

Heat exchange within Big Cliff Lake depended largely on the difference between Detroit 

Dam release temperatures and the seasonal ambient air temperature. The largest changes occurred

during the summer months in the NoBlend scenarios, in which unseasonably cool water released 

from Detroit Dam led to as much as 1 °C in warming from Detroit Dam to Big Cliff Dam in late 

July (fig. 10A). Likewise, during the autumn (September–December), unseasonably warm water 

was released from Detroit Dam in the NoBlend scenarios and that water cooled as much as about 

0.6 °C in Big Cliff Lake (fig. 10A). The greatest warming in Big Cliff Lake during the Existing

structural scenarios occurred in late July or early September as a result of Detroit Lake levels 

declining below the spillway crest elevation, which resulted in the only available outlets at Detroit 

Dam (power penstocks and upper RO) releasing unseasonably cool water (fig. 10B). Relatively less 

heat exchange was seen in Big Cliff Lake under the SlidingWeir scenarios because the release 

temperatures from Detroit Dam already had a more natural seasonal profile, closer to equilibrium 

with expected temperatures (fig. 10C).
18 

Figure 10. Graphs showing simulated temperature difference between releases from Big Cliff and Detroit 

Dams, northwestern Oregon, under three structural scenarios: (A) NoBlend (scenarios c1, n1, h1), (B) Existing 

(scenarios c2, n2, h2), and (C) SlidingWeir (scenarios c3, n3, h3). 
19 

Effects Downstream of Detroit-Big Cliff Dams

Temperatures in the North Santiam River downstream of the Detroit-Big Cliff Dam 

complex were simulated using the North Santiam River HEC-RAS model and assessed at Mehama

(USGS station 14183000) and Greens Bridge (USGS station 14184100) (RM 38.7 and 14.6, 

respectively). Along with results from the structural scenarios, a set of WithoutDams scenarios 

using the without-dams temperatures estimated at the Big Cliff Dam site also were run through the 

North Santiam River model to provide a comparison for a more natural seasonal temperature 

pattern.

Downstream Temperatures

About 19.39 river miles downstream of Big Cliff Dam at the USGS streamflow-gaging 

station at Mehama, the temperature effects occurring immediately downstream of the dams are still 

apparent, but somewhat affected by river dynamics and heat gains and losses during the travel time 

to that location (fig. 11). Similar to results downstream of Detroit Dam, NoBlend scenario results 

are cooler during June–August and warmer during October–December compared to results from 

without-dams scenarios run with the three environmental scenario conditions (fig. 11A). Existing

scenario temperatures at Mehama are similar to the simulated without-dams temperatures (fig. 11B) 

until the spillway at Detroit Dam becomes unavailable and additional cool, deep lake water from 

the power outlets must be released instead (late July in hot/dry and early September in cool/wet, 

normal). SlidingWeir scenario results are largely within the range of the simulated WithoutDams

temperatures (under cool/wet, normal, and hot/dry environmental conditions) for most of the year, 

aside from exceedances (primarily h2 scenario) in late September through December and some 

short periods during the spring. 

Farther downstream at Greens Bridge, more day-to-day variation in stream temperature was 

evident as the river had more time to exchange heat with its surroundings and come closer to a 

dynamic temperature equilibrium as the water traveled about 43.5 river miles downstream of Big 

Cliff Dam (fig. 12). Relative to WithoutDams temperatures, many of the same patterns that 

occurred at Mehama also were apparent at Greens Bridge. While all temperatures were simulated to 

increase as the water moved farther downstream in mid-summer, the WithoutDams temperatures 

increased to a greater extent than those in the NoBlend, Existing, and SlidingWeir scenarios from 

July through mid-October (comparing figs. 11 and 12). The difference is due to the higher 

streamflows in mid- to late-summer for the scenarios that included the dams, in order to fulfill 

minimum instream flow and irrigation requirements. The greater mass associated with higher 

discharge rates was less affected by instream heating, and the higher velocities associated with the 

higher flows allowed less time for heat exchange, compared to WithoutDams flows, leading to 

cooler temperatures relative to those produced in the WithoutDams scenarios. Later in November, 

temperatures from the NoBlend and Existing scenarios were similar at both Mehama and Greens 

Bridge, while December temperatures showed similarities among all three structural scenarios 

(NoBlend, Existing, and SlidingWeir) at these two stations.
20 

Figure 11. Graphs showing simulated temperatures at Mehama (RM 38.7) on the North Santiam River, 

northwestern Oregon, under three environmental scenarios (cool/wet, normal, and hot/dry) and three 

structural scenarios: (A) NoBlend, (B) Existing, and (C) SlidingWeir. The range of the simulated WithoutDams

scenario temperatures is shaded.
21 

Figure 12. Graphs showing simulated temperatures at Greens Bridge (RM 14.6) on the North Santiam River, 

northwestern Oregon, under three environmental scenarios (cool/wet, normal, and hot/dry) and three 

structural scenarios: (A) NoBlend, (B) Existing, and (C) SlidingWeir. The range of the simulated WithoutDams 

scenario temperatures is shaded.
22 

These temperature simulations can be used to estimate how much warmer or cooler the river 

might be under various structural and operational scenarios, relative to what might have occurred if 

the dams continued to be operated without any blending, maximizing the power production at 

Detroit Dam in the manner of operation prior to 2007. Computing those temperature differences 

reveals that the changes are large, even as far downstream as Greens Bridge (fig. 13), and range as 

high as 6 °C or more of warming in July and August and a similar amount of cooling in October. 

This is a significant downstream effect, and likely would trigger a meaningful biological response 

with regard to the timing of anadromous fish migration and spawning. 

Figure 13. Graphs showing simulated heating or cooling effect of the (A) Existing and (B) SlidingWeir

structural scenario results relative to the temperatures simulated in the NoBlend structural scenarios at 

Greens Bridge (RM 14.6) on the North Santiam River, northwestern Oregon, under three environmental 

scenarios (cool/wet, normal, and hot/dry). The range of the simulated WithoutDams scenario relative to the 

NoBlend structural scenario temperatures is shaded.
23 

Potential Biological Effects

Salmon have adapted the timing of their upstream migration and spawning relative to their 

home stream (Knudsen and McDonald, 1999). The date at which spawning occurs has been 

evolutionarily linked to the temperature in which egg incubation has occurred (Brannan, 1987). 

Because salmon have adapted to temperature regimes that were in existence prior to the 

construction of dams, the without-dam temperature estimates are a useful baseline from which to 

measure the relative success of scenarios in this report to restore a more-natural seasonal 

temperature pattern. 

Estimated Emergence Dates

An accumulated thermal unit (ATU) is a calculated quantity used to estimate the date on 

which spring Chinook salmon first emerge from their eggs (U.S. Army Corps of Engineers, 2012). 

This type of calculation was used to compare the potential emergence dates among the scenarios 

during spring and autumn spawning periods. The ATU calculation in this report is the cumulative 

sum of the daily average temperature (°F) exceeding 32 °F beginning on September 20 and May 1 

to estimate the timing of spring Chinook and winter Steelhead egg emergence, respectively. For 

winter Steelhead, the estimated emergence day is derived as the date when ATU values reach

1,000–1,100 °F/day in early summer (U.S. Army Corps of Engineers, 2009). In contrast, spring 

Chinook are known to emerge at an ATU between 1,650 and 1,850 °F/day in autumn (based on 

observed egg emergences at the Oregon Department of Fish and Wildlife Willamette Hatchery in 

Oakridge, Oregon [U.S. Army Corps of Engineers, 2012]). 

Near Big Cliff Dam, estimated winter steelhead emergence timing during the spring for 

SlidingWeir, Existing, and NoBlend scenarios was before, within, and after the range of emergence 

timing computed for the WithoutDams scenarios, respectively (fig. 14). While earlier emergence of 

winter steelhead during spring can allow more time for fry to feed during summer (should enough 

food exist) and develop before over-wintering, emergence timing within the bounds of the 

WithoutDams scenarios could indicate that the effect of the dams is minimal for Existing scenarios. 

Relatively early emergence times from the SlidingWeir scenarios during the spring reflects the 

ability of these hypothetical structures to release surface water from Detroit Lake that is warmer 

than that produced in the WithoutDams scenarios. This is likely a result of using a maximum value 

(15.9 °C) for the temperature target from January through July; the results might have been closer 

to the range of the results from the WithoutDams scenarios if the temperature target were to reflect 

historical without-dams conditions year round. Moving downstream of Big Cliff Dam to Mehama 

and Greens Bridge, the diminished effects of the dams with increasing downstream distance led to

earlier winter Steelhead emergence estimates and a smaller difference between emergence timing 

under all four scenarios (fig. 14). For example, at Big Cliff Dam the range of emergence timing 

from SlidingWeir and NoBlend scenarios was greater than the difference at Greens Bridge (figs. 

14A and 14C). 
24 

Figure 14. Mean accumulated thermal units (ATUs) starting May 1 from Existing, NoBlend, and SlidingWeir

structural scenarios at (A) Big Cliff Dam, (B), Mehama, and (C), Greens Bridge sites on the North Santiam 

River, northwestern Oregon. ATU range is shown in gray for scenarios. Colored “C”, “N”, and ”H” next to lines 

indicate cool/wet, normal, and hot/dry environmental scenarios.
25 

During autumn, mean estimated spring Chinook emergence times were more variable 

among scenarios than winter steelhead emergence times. Estimated emergence under Existing and 

SlidingWeir scenarios for normal and cool/wet environmental conditions were similar and closest to 

the WithoutDams range (fig. 15). A larger divergence among structural scenarios was evident and 

persistent from Big Cliff Dam to Greens Bridge under the hot/dry environmental scenarios 

compared with the normal and cool/wet (labeled “H”, “N”, and “C” respectively, fig. 14). The 

average emergence days beginning September 20 for each scenario at four locations (Detroit Dam, 

Big Cliff Dam, Mehama, and Greens Bridge) are shown in table 6. All scenarios except for 

NoBlend resulted in earlier emergence days moving downstream of Big Cliff Dam to Mehama and 

Greens Bridge (table 6). This is a result of North Santiam River temperatures generally warming 

from Big Cliff Dam to Greens Bridge during the autumn under all scenarios except NoBlend. 

Table 6. Calculated average emergence day for the cool/wet, normal, and hot/dry environmental forcings at 

four locations from the Detroit Lake, Big Cliff Lake, and North Santiam River models, northwestern Oregon. 

[Emergence days are based on the day at which the accumulated thermal units (ATUs) for simulated temperatures reached 1,750 °Fday. ATU values were calculated as the cumulative sum of the average daily water temperature above 32 °F from September 20 

through December 31. Dates in January and February were estimated based on model results from earlier in the year of each 

environmental scenario] 

Scenario 

identifier

Scenario description Scenario 

type

Average spring Chinook emergence day

Detroit Dam 

(RM 60.9)

Big Cliff Dam 

(RM 58)

Mehama 

(RM 38.7)

Greens Bridge 

(RM 14.6)

c1, n1, h1 NoBlend operational Dec. 2 Dec. 5 Dec. 7 Dec. 1

c2, n2, h2 Existing operational Jan. 6 Jan. 8 Jan. 3 Dec. 23

c3, n3, h3 SlidingWeir structural Jan. 13 Jan. 17 Jan. 9 Dec. 27

-- WithoutDams1 -- Mar. 30 Mar. 30 Feb. 18 Jan. 11

1

Without-dams scenario estimated at Big Cliff Dam, then simulated in North Santiam River model.
26 

Figure 15. Graphs showing mean accumulated thermal units (ATUs) starting September 20 from Existing, 

NoBlend, and SlidingWeir structural scenarios at (A) Big Cliff Dam, (B) Mehama, and (C) Greens Bridge sites 

on the North Santiam River, northwestern Oregon. ATU range is shown in gray for WithoutDams scenarios. 

Colored “C”, “N”, and ”H” next to lines indicate cool/wet, normal, and hot/dry environmental scenarios.
27 

Summary 

The circulation and water temperature in Detroit Lake were simulated with a CE-QUALW2 model to assess the potential for a hypothetical sliding weir at Detroit Dam (SlidingWeir

scenario) to release more natural, without-dam temperatures year round. A temperature target based 

on long-term without-dam temperature estimates was developed and used to guide the CE-QUALW2 temperature model in mixing releases among the user-defined outlets at Detroit Dam. The 

hypothetical sliding weir (named “upper weir”) was assumed to be internally connected to the 

power penstocks within Detroit Dam so that blending among warmer and cooler outlets to meet the 

temperature target did not infringe on power production. SlidingWeir scenarios typically released 

warm surface water during spring and summer, while saving cooler, deeper hypolimnetic water for

release later during autumn. Near Detroit Dam, SlidingWeir scenarios resulted in temperatures 

within the range of without-dams scenario results for most months of the year until about 

November. At that time of year, the heat captured by the lake during the warmer summer months 

still has a residual effect at all depths of the lake, leading to dam releases that are warmer than 

inflowing tributaries to Detroit Lake.

Between Detroit and Big Cliff Dams, a comparison of scenarios revealed that heat exchange

within Big Cliff Lake generally increased as Detroit Dam release temperatures departed from

seasonal ambient air temperature or without-dam temperature estimates. Scenarios in which 

blending between warmer and cooler outlets occurred (Existing, SlidingWeir scenarios) resulted in 

less heating within Big Cliff Lake in summer than scenarios in which Detroit Dam releases were 

cooler in summer and solely from the power penstocks (NoBlend scenarios). 

Downstream of the dams, the minimum release rates imposed at Detroit Dam during late 

summer and early autumn exceeded the unregulated without-dams flow estimates. This larger mass 

of water exchanged less heat with its surroundings as it moved downstream of the dams, as

compared to results from the WithoutDams scenarios. For SlidingWeir simulations, this pattern led 

to temperatures near the lower minimum of the WithoutDams temperature range downstream (46.3 

river miles) at Greens Bridge during July– September. Later in November and December, 

SlidingWeir scenario results were closer to the maximum WithoutDams temperatures at Greens 

Bridge than upstream at Mehama. Among all Detroit Dam scenarios, the effects during November 

and December of Detroit Dam were persistent, but less pronounced at Greens Bridge than at 

Mehama when compared to WithoutDams scenarios. Simulations that included the blending of 

warm and cool water from different outlets at Detroit Dam (Existing, SlidingWeir scenarios) led to 

less day-to-day temperature variation than WithoutDams scenarios as far downstream as Greens 

Bridge.
28

The calculation of estimated egg-emergence dates helped to evaluate the cumulative effect 

of temperature during winter steelhead and spring Chinook incubation periods and served to 

compare scenario results during these critical life history stages. As with water temperatures, 

emergence dates were more divergent among scenarios near Big Cliff Dam than downstream at

Mehama and Greens Bridge. For example, the average spring Chinook emergence day for 

SlidingWeir scenarios was 9 days later than it was for Existing scenarios at Big Cliff Dam, but only 

4 days later than it was for Existing scenarios downstream at Greens Bridge. The difference 

between spring Chinook emergence estimates for SlidingWeir and Existing scenario was greater 

under hot/dry scenarios, most likely because of lower Detroit lake levels (lower lake volume). This 

result shows that the benefit of blending operations can be more extreme. Similarly, the difference 

between Detroit Dam scenarios and the WithoutDams scenarios estimated emergence days 

decreased from Big Cliff Dam to Greens Bridge. 

Simulations of a hypothetical sliding weir (connected internally within the dam to the power 

penstocks) at Detroit Dam resulted in near-dam temperatures that closely matched without-dam 

temperature estimates during January through October, from Big Cliff Dam to Greens Bridge on 

the North Santiam River. This hypothetical structure improved outflow temperature control from 

Detroit Dam while meeting minimum dry-season release rates and lake levels specified by the 

current rule curve specified for Detroit Lake. Despite this inclusion of a hypothetical sliding weir at 

Detroit Dam, temperatures exceeded without-dams temperatures during November and December.

These exceedances likely represent the residual thermal effect of the mere existence of Detroit 

Lake. Further optimization of temperature management at Detroit Lake/Dam might focus towards 

the balance of release rates (streamflow), lake elevation, and downstream water temperature at 

specific spawning grounds or habitat zones downstream of Big Cliff Dam throughout the year, 

especially during late summer and autumn.

Acknowledgments

This study was a collaboration between U.S. Geological Survey and the U.S. Army Corps 

of Engineers, Portland District. Daniel Turner and Kathryn Tackley (USACE) provided data, 

helpful discussions, and strategic details and direction on potential options for dam operations and 

structural possibilities. Jenny Borth (USGS) provided support in setting-up and running the HECRAS simulations.
29

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Publishing support provided by the U.S. Geological Survey

 Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

Director, Oregon Water Science Center

U.S. Geological Survey

2130 SW 5th Avenue

Portland, Oregon 97201

http://or.water.usgs.gov
Buccola and others—Simulations of a Hypothetical Temperature Control Structure at Detroit Dam on the North Santiam River, Northwestern Oregon—Open-File Report 2015–1012

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20151012