An Environmental Streamflow Assessment for the Santiam 

River Basin, Oregon

By John C. Risley, J. Rose Wallick, Joseph F. Mangano, and Krista L. Jones

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

Open-File Report 2012–1133

U.S. Department of the Interior

U.S. Geological Survey
Cover: North Santiam River downstream from Detroit Lake near Niagara at about river mile 57. (Photograph by 

Casey Lovato, U.S. Geological Survey, June 2011.) 
An Environmental Streamflow Assessment for the Santiam 

River Basin, Oregon

By John C. Risley, J. Rose Wallick, Joseph F. Mangano, and Krista L. Jones

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

Open-File Report 2012–1133

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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Suggested citation:

Risley, J.C., Wallick, J.R., Mangano, J.F., and Jones, K.F., 2012, An environmental streamflow assessment for the 

Santiam River basin, Oregon: U.S. Geological Survey Open-File Report 2012-1133, 66 p. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

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

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

Contents

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

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

Scope of the Study..................................................................................................................................................... 2

Purpose of the Report................................................................................................................................................ 2

Description of the Study Area .................................................................................................................................... 4

Study Framework....................................................................................................................................................... 6

Streamflow Regulation............................................................................................................................................... 8

Previous Santiam River basin Studies ......................................................................................................................10

Environmental Regulatory Issues .............................................................................................................................11

Methods........................................................................................................................................................................12

Streamflow Data .......................................................................................................................................................12

Measured and Estimated Streamflow....................................................................................................................12

Computed Unregulated Streamflow ......................................................................................................................14

Computed Regulated Streamflow..........................................................................................................................14

Bankfull Discharge Estimation Methods....................................................................................................................14

Indicators of Hydrologic Alteration ............................................................................................................................17

Water-Use Compilation.............................................................................................................................................18

North Santiam River..............................................................................................................................................18

South Santiam River .............................................................................................................................................18

Main-Stem Santiam River......................................................................................................................................19

Pre- and Post-Dam Comparisons .............................................................................................................................19

Streamflow Assessment ...............................................................................................................................................20

North Santiam River..................................................................................................................................................21

South Santiam River.................................................................................................................................................32

Main-Stem Santiam River .........................................................................................................................................39

Geomorphic and Ecological Synopsis ..........................................................................................................................43

Geomorphic Characteristics of Study Reaches.........................................................................................................44

North Santiam River Channel Morphology ............................................................................................................44

South Santiam River Channel Morphology............................................................................................................47

Main-Stem Santiam River Channel Morphology....................................................................................................49

Terrestrial and Aquatic Habitats and Key Species ....................................................................................................50

Potential Geomorphic and Ecological Response to Environmental Flow Releases ..................................................51

Future Studies ..............................................................................................................................................................52

Streamflow Data and Analysis ..................................................................................................................................53

Bed-Material Transport Rates and Sediment Budget................................................................................................53

Detailed Channel and Flood-Plain Morphology Assessment ....................................................................................54

Terrestrial and Aquatic Responses ...........................................................................................................................54

Summary ......................................................................................................................................................................55

Acknowledgements.......................................................................................................................................................57

References Cited..........................................................................................................................................................57

Appendix A. Streamflow Data Time-Series Extension..................................................................................................61

Appendix B. U.S. Army Corps of Engineers Computed Unregulated Streamflow Data Time Series ............................61

Appendix C. Indicators of Hydrologic Alteration Results...............................................................................................66

Appendix D. Description of Study Reaches ..................................................................................................................66
iv

Figures

Figure 1. Map showing major streams and dams in the Santiam River basin, Oregon................................................. 3

Figure 2. Diagram showing profile of the Santiam River basin, Oregon........................................................................ 4

Figure 3. Map showing geology of the Santiam River basin, Oregon. .......................................................................... 5

Figure 4. Map showing location of study reaches, Santiam River basin, Oregon. ........................................................ 7

Figure 5. Diagram showing dams and selected streamflow gaging stations in the Santiam River basin, Oregon. ....... 9

Figure 6. Graph showing daily mean streamflow in Reach 2 at North Santiam River at Mehama, Oregon (14183000), 

water years 1922–2011. .............................................................................................................................................. 21

Figure 7. Graph showing mean daily streamflow in Reach 1 at North Santiam River at Niagara, Oregon (14181500), 

water years 1953–2009. .............................................................................................................................................. 22

Figure 8. Graph showing mean daily streamflow in Reach 2 at North Santiam River at Mehama, Oregon (14183000), 

water years 1953–2009. .............................................................................................................................................. 22

Figure 9. Graph showing mean daily streamflow in Reach 3 at North Santiam River at Green’s Bridge near Jefferson, 

Oregon (14184100), water years 1953–2009. ............................................................................................................. 23

Figure 10. Graph showing daily mean streamflow in Reach 1 at North Santiam River at Niagara, Oregon (14181500), 

water year 1975........................................................................................................................................................... 24

Figure 11. Graph showing daily mean streamflow in Reach 2 at North Santiam River at Mehama, Oregon 

(14183000), water year 1975....................................................................................................................................... 24

Figure 12. Graph showing daily mean streamflow in Reach 3 at North Santiam River at Green’s Bridge near 

Jefferson, Oregon (14184100), water year 1975. ........................................................................................................ 25

Figure 13. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 1 at North Santiam 

River at Niagara, Oregon (14181500), water years 1953–2009. ................................................................................. 31

Figure 14. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 2 at North Santiam 

River at Mehama, Oregon (14183000), water years 1953–2009................................................................................. 31

Figure 15. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 3 at North Santiam 

River at Green’s Bridge near Jefferson, Oregon (14184100), water years 1953–2009. .............................................. 32

Figure 16. Graph showing daily mean streamflow in Reach 6 at South Santiam River at Waterloo, Oregon 

(14187500), water years 1924–2011........................................................................................................................... 33

Figure 17. Graph showing mean daily streamflow in Reach 4 at Middle Santiam River at mouth near Foster, Oregon 

(14186500), water years 1967–2009........................................................................................................................... 34

Figure 18. Graph showing mean daily streamflow in Reach 5 at South Santiam River at Foster, Oregon (14186700), 

water years 1967–2009. .............................................................................................................................................. 34

Figure 19. Graph showing mean daily streamflow in Reach 6 at South Santiam River at Waterloo, Oregon 

(14187500), water years 1967–2009........................................................................................................................... 35

Figure 20. Graph showing daily mean streamflow in Reach 4 at Middle Santiam River at mouth near Foster, Oregon 

(14186500), water year 1975....................................................................................................................................... 36

Figure 21. Graph showing daily mean streamflow in Reach 5 at South Santiam River at Foster, Oregon (14186700), 

water year 1975........................................................................................................................................................... 36

Figure 22. Graph showing daily mean streamflow in Reach 6 at South Santiam River at Waterloo, Oregon 

(14187500), water year 1975....................................................................................................................................... 37

Figure 23. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 4 at Middle Santiam 

River at mouth near Foster, Oregon (14186500), water years 1967–2009.................................................................. 38

Figure 24. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 5 at South Santiam 

River at Foster, Oregon (14186700), water years 1967–2009..................................................................................... 38
v

Figure 25. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 6 at South Santiam 

River at Waterloo, Oregon (14187500), water years 1967–2009................................................................................. 39

Figure 26. Graph showing daily mean streamflow in Reach 7 at Santiam River at Jefferson, Oregon (14189000), 

water years 1940–2011. .............................................................................................................................................. 40

Figure 27. Graph showing mean daily streamflow in Reach 7 at Santiam River at Jefferson, Oregon (14189000), 

water years 1953–2009. .............................................................................................................................................. 41

Figure 28. Graph showing daily mean streamflow in Reach 7 at Santiam River at Jefferson, Oregon (14189000), 

water year 1975........................................................................................................................................................... 42

Figure 29. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 7 at Santiam River at 

Jefferson, Oregon (14189000), water years 1953–2009. ............................................................................................ 43

Figure 30. Aerial photograph showing channel and flood-plain morphology in study Reach 1 of the Santiam River 

basin, Oregon, on the North Santiam River. ................................................................................................................ 44

Figure 31. Map showing surficial geology and revetments in alluvial segments of the Santiam River, Oregon, study 

area. ............................................................................................................................................................................ 46

Figure 32. Aerial photograph showing channel and flood-plain morphology in study Reach 3 of the Santiam River 

basin, Oregon, on the North Santiam River. ................................................................................................................ 47

Figure 33. Aerial photograph showing channel and flood-plain morphology in study Reach 5 of the Santiam River 

basin, Oregon, on the South Santiam River. ............................................................................................................... 48

Figure 34. Aerial photograph showing channel and flood-plain morphology in study Reach 6 of the Santiam River 

basin, Oregon, on the South Santiam River. ............................................................................................................... 49

Figure 35. Aerial photograph showing channel and flood-plain morphology in study Reach 7 of the Santiam River 

basin, Oregon, Santiam River main stem. ................................................................................................................... 50

Tables

Table 1. Study reach locations in the Santiam River basin, Oregon.............................................................................. 8

Table 2. Dams in the Santiam River Basin, Oregon.................................................................................................... 10

Table 3. Minimum and maximum streamflow objectives below Big Cliff and Foster Dams ......................................... 11

Table 4. U.S. Geological Survey streamflow gaging stations in the Santiam River basin, Oregon.............................. 13

Table 5. Study-reach streamflow gaging stations and bankfull discharge and flood estimates, Santiam River basin, 

Oregon......................................................................................................................................................................... 15

Table 6. Indicators of Hydrologic Alteration streamflow statistics at study reach streamflow gaging stations based on 

unregulated streamflow conditions in the Santiam River basin, Oregon, for water years 1953–2009. ........................ 17

Table 7. Salem, Oregon, and Waterloo, Oregon, median monthly precipitation totals. ............................................... 20

Table 8. Pre- and post-dam flood statistics for selected Santiam River basin, Oregon, streamflow gaging stations, 

computed from annual peak streamflow data based on the Bulletin 17B Log Pearson III method. ............................. 26

Table 9. One-day maximum annual streamflow statistics from regulated and unregulated daily mean streamflows for 

the Santiam River, Oregon. ......................................................................................................................................... 27

Table 10. Seven-day minimum annual streamflow statistics from regulated and unregulated daily mean streamflows 

for the Santiam River, Oregon. .................................................................................................................................... 28

Table 11. Median monthly streamflow statistics from regulated and unregulated daily mean streamflows for the 

Santiam River, Oregon ................................................................................................................................................ 29

Table 12. Streamflow exceedance statistics from regulated and unregulated daily mean streamflows for the Santiam 

River, Oregon. ............................................................................................................................................................. 30
vi

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square yard (yd2) 0.08361 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

cubic foot (ft3) 0.02832 cubic meter (m3) 

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

Flow rate

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

cubic foot per second per square mile 

[(ft3/s)/mi2]

0.01093 cubic meter per second per 

square kilometer [(m3/s)/km2]

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.

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.
1

An Environmental Streamflow Assessment for the 

Santiam River Basin, Oregon

By John C. Risley, J. Rose Wallick, Joseph F. Mangano, and Krista L. Jones

Abstract

The Santiam River is a tributary of the Willamette River in northwestern Oregon and drains 

an area of 1,810 square miles. The U.S. Army 

Corps of Engineers (USACE) operates four dams 

in the basin, which are used primarily for flood 

control, hydropower production, recreation, and 

water-quality improvement. The Detroit and Big 

Cliff Dams were constructed in 1953 on the 

North Santiam River. The Green Peter and Foster 

Dams were completed in 1967 on the South Santiam River. The impacts of the structures have 

included a decrease in the frequency and magnitude of floods and an increase in low flows. For 

three North Santiam River reaches, the median of 

annual 1-day maximum streamflows decreased 

42–50 percent because of regulated streamflow 

conditions. Likewise, for three reaches in the 

South Santiam River basin, the median of annual 

1-day maximum streamflows decreased 39–52 

percent because of regulation. 

In contrast to their effect on high flows, the 

dams increased low flows. The median of annual 

7-day minimum flows in six of the seven study 

reaches increased under regulated streamflow 

conditions between 60 and 334 percent. On a seasonal basis, median monthly streamflows decreased from February to May and increased 

from September to January in all the reaches. 

However, the magnitude of these impacts usually 

decreased farther downstream from dams because 

of cumulative inflow from unregulated tributaries 

and groundwater entering the North, South, and 

main-stem Santiam Rivers below the dams. A 

Wilcox rank-sum test of monthly precipitation 

data from Salem, Oregon, and Waterloo, Oregon, 

found no significant difference between the preand post-dam periods, which suggests that the 

construction and operation of the dams since the 

1950s and 1960s are a primary cause of alterations to the Santiam River basin streamflow regime. 

In addition to the streamflow analysis, this 

report provides a geomorphic characterization of 

the Santiam River basin and the associated conceptual framework for assessing possible geomorphic and ecological changes in response to 

river-flow modifications. Suggestions for future 

biomonitoring and investigations are also provided. This study was one in a series of similar 

tributary streamflow and geomorphic studies 

conducted for the Willamette Sustainable Rivers 

Project. The Sustainable Rivers Project is a national effort by the USACE and The Nature Conservancy to develop environmental flow requirements in regulated river systems.
2

Introduction

In 2002, The Nature Conservancy (The Nature Conservancy) and the U.S. Army Corps of 

Engineers (USACE) formed the Sustainable Rivers Project (The Nature Conservancy, 2009), a 

partnership aimed at developing, implementing, 

and refining environmental flow requirements 

downstream from dams. Environmental flows can 

be defined as the streamflow needed to sustain 

ecosystems while continuing to meet human 

needs. Developing environmental flow requirements typically involves a collective process of 

stakeholders to identify and prioritize streamflow 

objectives. The process is a series of steps and 

feedback loops that include defining the streamflow requirements, implementing them into the 

dam operations, monitoring and modeling the 

streamflow changes and their effect on the river 

ecosystem, and then adjusting and refining the 

streamflow requirements if necessary. In addition 

to dams, other anthropogenic factors in a watershed can contribute to freshwater ecosystem degradation, such as water diversions, channel revetment, timber harvest, wetland draining, invasive species, gravel mining, and other factors, 

which also are commonly considered during the 

development process (Tharme, 2003; Acreman 

and Dunbar, 2004; Richter and others, 2006; The 

Nature Conservancy, 2009).

The Santiam River environmental flow study 

is a collaborative effort of the USACE, The Nature Conservancy, and the U.S. Geological Survey (USGS) to develop environmental flow requirements for the Santiam River, which is a tributary of the Willamette River in northwestern Oregon (fig. 1).

Scope of the Study

As a continuation of the Willamette Sustainable Rivers Project, the streamflow and geomorphic analyses from this study will assist the 

USACE and The Nature Conservancy in developing an environmental flow framework for the 

Santiam River basin. The framework will supplement a broader assemblage of ecological, hydrologic, and geomorphologic baseline data. The 

analyses include an assessment of changes to the 

ecosystem resulting from anthropogenic activities, such as dam operations and water withdrawals that have taken place in the basin. 

The goals of this study are to analyze streamflow trends in the main reaches of the Santiam 

River basin and describe geomorphic and biological conditions to facilitate the development of 

environmental flow guidelines. Tasks to achieve 

these goals include:

1. Characterize streamflows in reaches under 

regulated and unregulated conditions.

2. Qualitatively describe dominant geomorphic 

and ecologic issues in reaches that could be 

affected by environmental flow modifications.

3. Communicate study results in a report and at 

future environmental flow workshops. 

Purpose of the Report

This report will provide Santiam River basin

stakeholders with a compilation of streamflow

conditions under regulated and unregulated conditions in various reaches in the basin that are defined by their geomorphic and ecological characteristics. Using streamflow data and the results

from the analysis of the data, it will be possible to 

identify the rate, frequency, duration, and timing 

of flow releases from Santiam River basin dams

needed at downstream locations to achieve specific ecological and geomorphic objectives. 
3

Figure 1. Map showing major streams and dams in the Santiam River basin, Oregon.
4

Description of the Study Area

The Santiam River basin is a subbasin of 

1,810 mi2 within the Willamette River basin in 

northwestern Oregon (fig. 1). Major tributaries in 

the Santiam River basin include the North Santiam River, Little North Santiam River, Middle 

Santiam River, South Santiam River, Thomas 

Creek, and Crabtree Creek. The North Santiam 

River begins high in the Cascade Range near 

Three Fingered Jack mountain and flows more 

than 100 mi before it joins the South Santiam 

River about 2 mi upstream from Jefferson. The 

South Santiam River begins at a lower elevation 

in the Western Cascades, west of the McKenzie 

River basin, and flows about 70 mi before joining 

the North Santiam River. From Jefferson, the 

main-stem Santiam River flows about 9 mi before 

it joins the Willamette River south of Salem and 

north of Albany. Elevations in the basin range 

from 162 ft at the Willamette confluence to 

10,497 ft at the summit of Mt. Jefferson. The river channel slope, within the study area downstream from the dams, ranges from less than 0.1

percent for the lower reach between the North 

and South Santiam River confluences to almost 1

percent for the North Santiam River below Big 

Cliff Dam (fig. 2). The basin has long, cool, wet 

winters and warm, dry summers. Average daily 

maximum and minimum temperatures at Stayton 

from 1951 to 2011 were 63 and 42°F, respectively. Average annual precipitation at Stayton for 

this period was 52.4 in. Because of greater precipitation at higher elevations, the mean annual 

precipitation for the entire Santiam River basin is 

78.2 in. (1971–2000) (U.S. Geological Survey,

2012). 

Figure 2. Diagram showing profile of the Santiam River basin, Oregon.
5

Higher elevation areas are underlain by 

young, relatively permeable material consisting 

of High Cascade volcanic rocks and glacial deposits. Middle and lower elevations of the basin 

contain the older, less permeable, weathered volcanic material of the Western Cascades. The lower reach of the river, near the Willamette River 

confluence, mainly comprises a wide, unconstrained flood plain underlain by Quaternary alluvium (fig. 3). The economy of the Santiam 

River basin is supported by agriculture, timber 

harvesting, recreation, and manufacturing. Approximately 70 percent of the basin is forested. 

Timber is harvested on both private and Federal 

lands. Higher elevation areas in the basin are 

managed by the Willamette National Forest.

Figure 3. Map showing geology of the Santiam River basin, Oregon.
6

Study Framework

The Santiam River system in the study area 

was divided into seven reaches, each having distinct streamflow, geomorphic, and ecological 

conditions (fig. 4, table 1). The North Santiam 

River portion of the study area was divided into

three reaches. Reach 1 extends from Detroit Dam 

to the confluence of the Little North Santiam 

River. Reach 2 continues downstream to river 

mile (RM) 26 near Stayton. Reach 3 continues

downstream to the South Santiam River confluence. The South Santiam River basin was also 

divided into three reaches. Reach 4 is along the 

Middle Santiam River, a tributary of the South 

Santiam River, between Green Peter Dam and 

Foster Lake reservoir. Reaches 5 and 6 extend 

from Foster Dam to RM 23.4 (upstream from

USGS streamflow gaging station (hereinafter 

“gage”) at Waterloo [14187500]) and from RM 

23.4 to the North Santiam River confluence, respectively. The final reach, Reach 7, extends 

from confluence of the North and South Santiam 

Rivers through Jefferson to the Willamette River 

confluence. For all reaches where the downstream boundary is near a major stream confluence, the downstream boundary was set just upstream from the confluence. Streamflow from the 

confluent stream is included in the streamflow of 

the next downstream reach. This was done to 

minimize the difference in streamflow between 

both ends of the reach and to use a single representative reach discharge in the analyses. 
7

Figure 4. Map showing location of study reaches, Santiam River basin, Oregon. 
8

Table 1. Study reach locations in the Santiam River basin, Oregon.

Reach

number River name Upstream end description

Upstream

end river 

mile Downstream end description

Reach

length

(miles)

Northern basin

1 North Santiam Detroit Dam 60.9 Little North Santiam River confluence21.7

2 North Santiam Little North Santiam River 

confluence

39.2 Below Stayton, Oregon 13.2

3 North Santiam Below Stayton, Oregon 26.0 South Santiam confluence 14.2

Southern basin

4 Middle Santiam Green Peter Dam 5.5 Foster Dam 5.5

5 South Santiam Foster Dam 38.1 Above Waterloo, Oregon 14.7

6 South Santiam Above Waterloo, Oregon 23.4 N. Santiam River confluence 23.4

Lower basin

7 Lower Santiam North and South Santiam River confluence11.8 Willamette confluence 11.8

Streamflow Regulation

The USACE operates four dams in the Santiam River basin (fig. 5, table 2). The Detroit and 

the Big Cliff Dams, on the North Santiam River, 

were completed in 1953. In addition to flood control and recreation uses, the Detroit Dam also 

produces up to 100 megawatts of power. The 

smaller Big Cliff Dam, 3 mi downstream from 

the Detroit Dam, is also used for hydropower 

production and for regulating power-generating 

water releases from Detroit Dam. The Green Peter and Foster Dams, in the South Santiam River

basin, were completed in 1968. The two dams 

work in conjunction to provide flood control, hydropower production, irrigation supply, recreation, water-quality improvement, and aquatic 

habitat. Foster Dam, about 7 mi downstream from 

Green Peter Dam, is used to produce hydropower 

and regulate power-generating water releases 

from Green Peter Dam. The Green Peter and Foster Dams have generators capable of producing a 

combined total of 100 megawatts. Surface-water 

withdrawals for urban water supply and irrigation 

are made at locations downstream from the dams. 

The city of Salem withdraws approximately 67 

ft3/s from the North Santiam River at RM 31.0 on 

Geren Island (Oregon Water Resources Department, 2012). On the South Santiam River, an average of 90 ft3

/s of streamflow (water years 

1993–2011) was diverted mostly for municipal 

water supply to the Lebanon-Santiam Canal at 

RM 20.8 as measured at the USGS gage on the 

canal (14187600).
9

Figure 5. Diagram showing dams and selected streamflow gaging stations in the Santiam River basin, Oregon.
10

Table 2. Dams in the Santiam River Basin, Oregon.

[Data from the U.S. Army Corps of Engineers, http://www.nwd-wc.usace.army.mil/report/, accessed October 27, 2011. Abbreviations: fad, feet above North 

American Vertical Datum of 1988; na, not applicable; mi2, square miles; KW, kilowatt; HP, hydropower; FC, flood control; N, navigation; I, irrigation; F, fisheries; WQ, water-quality; RR, Reregulation; R, recreation.]

Dam name River

Year 

completed

Lake pool 

elevation Upstream

drainage 

area

(mi2)

River

mile

Reservoir

useable 

storage

(acre-feet)

Reservoir

surface area

(acres) Reservoir use

Maximum

power output

(KW)

Min.

(fad)

Max.

(fad)

Detroit North Santiam 1953 1,450 1,574 435 60.9 321,000 3,500 FC, HP, N, F, I, 

WQ, R

100,000

Big Cliff North Santiam 1953 1,180 1,210 449 58.1 na na RR, HP, R 18,000

Green Peter Middle Santiam 1968 922 1,015 276 5.5 312,500 3,720 FC, HP, N, I, F, 

WQ, R

80,000

Foster South Santiam 1968 613 641 492 38.1 28,300 1,220 RR, FC, HP, N, I, 

F, WQ, R

20,000

Previous Santiam River basin Studies

Speers and Versteeg (1982) presented procedures for longterm forecasts of spring-season water supply for Detroit reservoir operations. Laenen and Risley (1997) and Lee and Risley 

(2002) created a set of precipitation-runoff watershed models for 

the entire Willamette River basin for water-quality and groundwater analyses, respectively. In these studies, the Santiam River 

basin was divided into 22 subbasins, from which 22 watershed 

models were created. Thayer (1936a, 1936b) presented early research on geology in the Santiam River basin. Helm and Leonard (1977) described groundwater resources in the lower basin. 

Conlon and others (2005) described groundwater hydrologic 

conditions in the entire Willamette River basin, including the 

Santiam River basin. Fletcher and Davidson (1988) analyzed the 

geomorphic response to regulation and bank protection in the 

lower section of the South Santiam River. Hill and Priest (1992) 

described the geologic setting of the Santiam Pass area. Sherrod 

and others (1996) presented an overview of geology, hydrology, 

and geothermal resources in the North Santiam River basin.

The USGS conducted studies pertaining to the effect of reservoir operations in the Santiam River basin on water temperatures in and downstream from reservoirs. Laenen and Hanson 

(1985) and Hanson and Crumrine (1991) simulated water temperatures downstream from reservoirs on the North and South 

Santiam Rivers using a daily mean, one-dimensional Lagrangian 

computer model. More recent studies by Sullivan and Rounds 

(2004), Sullivan and others (2007), and Buccola and Rounds 

(2011) also simulated water temperatures on the North Santiam 

River in and downstream from reservoirs using temporally and 

spatially detailed two-dimensional models. In addition to water 

temperatures, heavy flooding and landslides in the late 1990s 

resulted in a major water-quality concern over suspended sediment in North Santiam River. Uhrich and Bragg (2003) presented a method for estimating suspended-sediment loads and yields 

using turbidity data. Bragg and Uhrich (2010) presented a suspended-sediment budget for the entire North Santiam River basin. Suspended sediment and turbidity in the basin are also described in Bragg and others (2007), Piatt and others (2011), and 

Sobieszcyk and others (2007).
11

Environmental Regulatory Issues

In early 1999, the National Marine Fisheries 

Service (NMFS) listed Upper Willamette River 

Chinook salmon (Oncorhynchus tshawytscha) 

and the Upper Willamette River steelhead (Oncorhynchus mykiss) in the Santiam River basin

and other upper Willamette River basins as

threatened under the Federal Endangered Species 

Act (ESA). In 1993, the U.S. Fish and Wildlife 

Service (USFWS) listed the Oregon chub (Oregonichthys crameri) as endangered in Marion and 

Linn Counties, which includes the Santiam River 

basin. In 2010, the Oregon chub was reclassified 

from endangered to threatened. As a result of these listings, the USACE submitted its first Biological Assessment in 2000 and a supplemental Biological Assessment in 2007 for the Willamette 

River basin that included specific recovery plans 

for the Santiam River basin (U.S. Army Corps of 

Engineers, 2000, 2007). 

In July 2008, NMFS released their decision 

on the Biological Assessment plans through a 

Willamette Project Biological Opinion (National 

Marine Fisheries Service, 2008a; 2008b). The 

USFWS also released a Biological Opinion for 

the Willamette River basin because they have jurisdiction over the Oregon chub (U.S. Fish and 

Wildlife Service, 2008). NMFS and the USFWS 

decided that the USACE Biological Assessment 

plans were insufficient for mitigating the effect of 

the water projects on critical habitat. The Biological Opinion ordered additional measures, which 

included improved fish passage, temperature control, and changes in downstream streamflows. 

The Biological Opinion includes flow-release 

targets for Big Cliff and Foster Dams for different seasonal life histories for the ESA-listed fish 

(table 3). The Biological Opinion also includes a 

measure for implementing environmental flow 

releases from the dams. 

Table 3. Minimum and maximum streamflow objectives below Big Cliff and Foster Dams.

[Source: National Marine Fisheries Service, 2008]

Period Primary Use

Minimum

flow (ft3/s)

Maximum

flow (ft3/s)

Big Cliff Dam

September 1–October 15 Chinook spawning 1,500 3,000

October 16–January 31 Chinook incubation 1,200

February 1–March 15 Chinook rearing/adult migration 1,000

March 16–May 31 steelhead spawning 1,500 3,000

June 1–July 15 steelhead incubation 1,200

July 16–August 31 steelhead rearing 1,000

Foster Dam

September 1–October 15 Chinook spawning 1,500 3,000

October 16–January 31 Chinook incubation 1,100

February 1–March 15 Chinook rearing 800

March 16–May 15 steelhead spawning 1,500 3,000

May 16–June 30 steelhead incubation 1,100

July 1–August 31 steelhead rearing 800
12

The Oregon Department of Environmental 

Quality (ODEQ), as required under the Federal 

Clean Water Act, released a stream-temperature 

Total Maximum Daily Load (TMDL) plan in 

2006 for the Willamette River basin (Oregon Department of Environmental Quality, 2006). 

Stream reaches in the North and South Santiam 

River basins found to be thermally impaired and 

not meeting state temperature standards for salmonid rearing, spawning, and cold-water refuges, 

as a result of reservoir releases, channel geomorphology alterations, streamflow diversions, and 

limited riparian shade, were placed on the Federal 

Clean Water Act section 303(d) list as having exceeded their temperature TMDL.

Methods

For this study, various methods were employed to assess the effects of dams and withdrawals on streamflows. These included a compilation of measured and estimated daily mean gage

statistics under regulated and unregulated conditions, bankfull streamflow estimation, pre- and 

post-dam peak-flow analysis, and a pre- and postdam period climate comparison.

Streamflow Data

Measured and Estimated Streamflow

The USGS began continuous streamflow 

monitoring within the Santiam River basin (table 

4) in the 1920s. Eighteen of these stations were 

active during water year 2011. The stations with 

the longest streamflow time series are the North 

Santiam River at Mehama (14183000: 1921–

2011) and the South Santiam River at Waterloo

(14187500: 1923–2011). From 2005 to 2010, the 

USGS also operated eight temporary streamflow 

measurement sites (14183430, 14183450, 

14183500, 14183550, 14183570, 14183580, 

14183585, and 14183590) in the vicinity of Geren Island on the North Santiam River. (Map at 

http://or.water.usgs.gov/northsantiam/sites/). 

Streamflow and stage were measured intermittently at these sites during six summers to create

rating curves. One station was upstream from

Geren Island, five stations were in the north and 

south channels around the island, and two stations were in side diversion cannels. The purpose 

of the data monitoring was to gain a better understanding of the spatial and temporal distribution 

of surface waters during low-flow conditions upstream and downstream from the island, in the 

alcoves and secondary channels, and near the Salem municipal water-supply intakes.

Seven of the gages from table 4 were representative of flow conditions in the seven defined 

study reaches and could be used in the statistical 

analyses (table 5). Streamflow data for Reaches 

1, 2, 6, and 7 represented unregulated and regulated flow conditions because they extended from 

the 1920s and 1930s to water year 2011. However, for the other three reaches (Reaches 3, 4, and 

5), it was necessary to augment the measured 

streamflow period with computed regulated and 

computed unregulated daily mean streamflow 

time series provided by the USACE. Microsoft®

Excel® files containing measured and estimated 

daily mean streamflows for the seven reaches can 

be downloaded from the link in Appendix A.
13

Table 4. U.S. Geological Survey streamflow gaging stations in the Santiam River basin, Oregon.—continued

[A water year is from October 1 of the previous year to September 30. Abbreviations: mi2, square miles; *, stage or elevation data only; na, not applicable.]

Station

number Streamflow station name

Drainage

area 

(mi2)

Period of record 

(water years)

14178000 North Santiam River below Boulder Creek near Detroit, Oregon 216 1928–2011

14178700 East Humbug Creek near Detroit, Oregon 7.32 1978–1994

14179000 Breitenbush River above French Creek near Detroit, Oregon 108 1932–1987; 

1998–2011

14179100 French Creek near Detroit, Oregon 9.9 2002–2005

14180300 Blowout Creek near Detroit, Oregon 26.0 1998–2011

14180500 Detroit Lake near Detroit, Oregon 437 1953–2004*

14181500 North Santiam River at Niagara, Oregon 453 1938–2011

14181750 Rock Creek near Mill City, Oregon 14.8 2005–2008

14182400 Little North Santiam River below Canyon Creek near Mehama, Oregon 93.0 2007–2008

14182500 Little North Santiam River near Mehama, Oregon 112 1931–2011

14183000 North Santiam River at Mehama, Oregon 654 1921–2011

14184100 North Santiam River at Greens Bridge near Jefferson, Oregon 736 1964–1967; 

2011

14185000 South Santiam River below Cascadia, Oregon 174 1935–2011

14185700 Middle Santiam River near Upper Soda, Oregon 74.6 1981–1994

14185800 Middle Santiam River near Cascadia, Oregon 104 1964–1981; 

1988

14185880 Packers Gulch near Cascadia, Oregon 7.45 1983–1986

14185900 Quartzville Creek near Cascadia, Oregon 99.2 1963–2011

14186000 Middle Santiam River near Foster, Oregon 271 1931–1947

14186100 Green Peter Lake near Foster, Oregon 273 1974–2003*

14186200 Middle Santiam River below Green Peter Lake near Foster, Oregon 273 2010–2011*

14186500 Middle Santiam River at mouth near Foster, Oregon 287 1950–1966

14186600 Foster Lake at Foster, Oregon 492 1974–2003*

14186700 South Santiam River at Foster, Oregon 493 1966–1973

14187000 Wiley Creek near Foster, Oregon 51.8 1947–1973; 

1988–2011

14187100 Wiley Creek at Foster, Oregon 62.3 1973–1988

14187200 South Santiam River near Foster, Oregon 557 1973–2011

14187500 South Santiam River at Waterloo, Oregon 640 1923–2011
14

Table 4. U.S. Geological Survey streamflow gaging stations in the Santiam River basin, Oregon.—continued

[A water year is from October 1 of the previous year to September 30. Abbreviations: mi2, square miles; *, stage or elevation data only; na, not applicable.]

Station

number Streamflow station name

Drainage

area 

(mi2)

Period of record 

(water years)

14187600 Lebanon Santiam Canal near Lebanon, Oregon na 1993–2011

14188000 Albany Santiam Canal near Lebanon, Oregon na 1926–1957

14188610 Schafer Creek near Lacomb, Oregon 1.03 1993–2011

14188700 Crabtree Creek near Crabtree, Oregon 111 1963–1970

14188800 Thomas Creek near Scio, Oregon 110 1962–1987;

2002–2011

14188850 Thomas Creek near Crabtree, Oregon 143 2002–2008*

14189000 Santiam River at Jefferson, Oregon 1,790 1940–2011

Computed Unregulated Streamflow

The USACE compiled and computed unregulated daily mean streamflow time series for water years 1936–2009 at North Santiam River at 

Detroit Dam (upstream from 14181500), North 

Santiam River at Mehama (14183000), Middle 

Santiam River at Green Peter Dam (upstream 

from 14186500), South Santiam River at Foster 

Dam (14186700), South Santiam River at Waterloo (14187500), and Santiam River at Jefferson 

(14189000) (Alan Donner, U.S. Army Corps of 

Engineers, written commun., 2011). These time 

series are an estimate of streamflow (1936–2009) 

at these locations if the four USACE dams had 

not been constructed. For this study, these time 

series were used to evaluate the hydrologic effect 

of the dams by comparing pre- and post-dam 

streamflow conditions.

The daily mean streamflow time series for 

the North Santiam River at Detroit Dam and the 

Middle Santiam River at Green Peter Dam were 

computed using USACE reservoir models. However, the time series for the other locations were 

computed by adding these simulated time series 

with estimated downstream local inflows. The 

inflow time series were computed using correlations with nearby unregulated USGS streamflow 

records in the region. Details on how the unregu

lated time series were computed are provided in 

Appendix B.

For Reaches 1, 3, and 4, it was necessary to 

adjust the USACE unregulated daily mean 

streamflows using a drainage-area ratio to create 

unregulated streamflow conditions at the USGS 

gages in those reaches. Details of the adjustments

are included in the Excel files for each reach 

(Appendix A).

Computed Regulated Streamflow

USACE also provided this study with computed regulated daily mean streamflow time series for Big Cliff Dam (1960–2011), Green Peter 

Dam (1967–2011), and Foster Dam (1968–2011). 

The time series for Green Peter and Foster Dams 

were used to create the Reach 4 and 5 regulated 

streamflow time series, respectively, because

measured USGS streamflow data were unavailable at these locations for these time periods. 

Bankfull Discharge Estimation Methods

In geomorphology, bankfull discharge is 

generally assumed to represent the geomorphically significant flow that fills the banks without 

spilling onto the flood plain. It is commonly used 

as a streamflow metric in environmental flow 

studies when creating flow prescriptions that will 
15

meet the habitat needs of an aquatic or terrestrial species at various life stages. The estimation of bankfull discharge has substantial uncertainty because it has to be estimated at a specific location and is not necessarily representative of a reach. Wolman and 

Miller (1960) defined bankfull discharge as having a recurrence 

interval of 1.5 years in a variety of rivers. However, that approach could not be used consistently in all seven study reaches,

because not all the reaches have an adequate number of years of 

pre-dam peak-flow data to complete a flood-frequency analysis.

For this study, several methods of estimating bankfull discharge were compared and evaluated. These included bankfulldischarge estimates provided by the USACE, unit-discharge estimates based on USACE estimates, field observations at gages, 

calculation of the 1.5-year peak-flow frequency, and channel 

cross-section plots derived from high-flow measurement data 

(table 5). Estimates based on the latter method are not included 

in the table because of insufficient channel detail in the data or 

because flow events had insufficient magnitude.

Bankfull flood stage and discharge estimates for gages in 

Reaches 2, 6, and 7 were previously determined by the USACE

using field-site-level surveys, aerial photography, and flood 

analyses (Keith Duffy, U.S. Army Corps of Engineers, written 

commun., 2011). The corresponding gages, which include North 

Santiam River at Mehama, Oregon (14183000) (Reach 2), South 

Santiam River at Waterloo, Oregon (14187500) (Reach 6), and 

Santiam River at Jefferson, Oregon (14189000) (Reach 7), have 

the longest streamflow records in the Santiam River basin and 

also are used as flood-forecast sites by the U.S. National Weather Service River Forecasting Center.

Table 5. Study-reach streamflow gaging stations and bankfull discharge and flood estimates, Santiam River basin, Oregon.

[Abbreviation: USACE, U.S. Army Corps of Engineers; LPIII, Bulletin 17B Log Pearson III flood frequency analysis; mi2, square mile; ft3/s, cubic feet per second; na, not available. River mile is distance from the nearest downstream confluence.]

Reach

number

Station

number Streamflow gaging-station name

Drainage

area

(mi2)

River

mile

Bank full discharge estimates

USACE 

flood 

estimate 

(ft3/s)

USACE

(ft3/s)

Unit

discharge 

estimate 

(ft3/s)

USGS field

estimate

(ft3/s)

LPIII flood frequency 

Pre-dam period of 

record

1.5-year 

peak 

(ft3/s)

1 14181500 North Santiam River at Niagara, Oregon 453 57.3 na 11,100 3,000 1909–52 16,700 na

2 14183000 North Santiam River at Mehama, Oregon 654 38.7 17,000 na na 1906–52 28,500 30,500

3 14184100 North Santiam River at Greens Bridge 

near Jefferson, Oregon

732 14.6 na 18,000 na na na na

4 14186500 Middle Santiam River at mouth near Foster, Oregon287 1.0 na 7,050 na 1950–66 23,100 na

5 14186700 South Santiam River at Foster, Oregon 493 38.0 na 12,100 5,550 na na na

6 14187500 South Santiam River at Waterloo, Oregon 640 23.3 18,000 na na 1906–52 31,500 25,700

7 14189000 Santiam River at Jefferson, Oregon 1,790 9.6 35,000 na na 1908–52 62,400 55,900
16

For gages in the other study reaches, Reach 1 

(14181500), Reach 3 (14184100), Reach 4 

(14186500), and Reach 5 (14186700), bankfull 

discharge was estimated using an average of the 

unit discharges of the three USACE estimates for 

Reaches 2, 6, and 7. The unit discharges were 

computed by dividing the USACE estimates by 

the upstream drainage areas of the gages. The average of the three unit discharges was 24.6 

(ft3/s)/mi2. This value was multiplied by the upstream drainage areas of the Reach 1, Reach 3, 

Reach 4, and Reach 5 gages to get bankfull discharge estimates for those reaches.

Field estimates of bankfull stage were made 

by the USGS for this study in January 2011 at the 

gages for Reach 1, North Santiam River at Niagara, Oregon (14181500), and for Reach 5, South 

Santiam River at Foster, Oregon (14186700). 

Stage height was estimated using a hand-held 

leveler because time and funding restrictions precluded measuring stage heights using a transit 

and rod. At both gages, readings from outside 

staff gages were taken while standing just below 

flood-plain level. The height of the observer was 

then subtracted from the staff reading. With a 

bankfull stage estimate, the bankfull discharge 

could be determined using the rating curve. In 

comparison to the other two methods of bankfull 

discharge estimation, these field observation estimates were considerably smaller.

A major limitation with bankfull discharge 

estimates made from field observation is that 

their representation of the reach is limited to 

proximity of the gage. It was not possible to 

make a bankfull discharge field estimate at the 

Reach 3 gage, South Santiam River at Green’s 

Bridge near Jefferson (14184100), because of 

visual obstructions in the line of sight. It was also 

not possible to make a bankfull discharge field 

estimate at the Reach 4 gage, Middle Santiam 

River at mouth near Foster (14186500) because it 

was active only during the pre-dam period (1950–

66) and is now submerged beneath Foster Reservoir. Field estimates were not made at gages for 

Reach 2, North Santiam River at Mehama

(14183000), Reach 6, South Santiam River at 

Waterloo (14187500), or Reach 7, Santiam River 

at Jefferson (14189000) because the USACE had 

previously estimated bankfull discharge at those 

sites. 

Using measured pre-dam annual peak-flow 

data, the 1.5-year flood frequency, based on the 

Bulletin 17B Log Pearson III method (Interagency Committee on Water Data, 1982), was computed for the gages in Reaches 1, 2, 6, and 7. It 

was not possible to compute a flood frequency 

for the Reach 3 and Reach 5 gages, 14184100 

and 14186700, respectively, because their records 

did not contain peak-flow data during the predam period. As shown in table 5, the 1.5-year 

flood frequencies were higher than the other 

USACE bankfull discharge estimates for the 

Reach 2 (14183000), Reach 6 (14187500), and 

Reach 7 (14189000) gages. 

To estimate bankfull discharge from channel 

cross-section plots, it is sometimes possible to 

create the plots using stage and discharge data 

from USGS discharge measurement notes from 

gages. With a detailed channel cross section during a measured high-flow event, bank and floodplain features can sometimes be defined to estimate the bankfull stage. With a bankfull stage 

estimate, the bankfull discharge can be determined from the rating curve. The bankfull stage 

estimate could not be estimated at the Reach 1

gage on the North Santiam River at Niagara 

(14181500) and the Reach 4 gage at the Middle 

Santiam River at the mouth near Foster 

(1418650) because the channel cross-section 

plots from these high-flow events contained insufficient detail to delineate the streambank and 

flood-plain features. Bankfull stage estimates for 

Reach 3 gage on the North Santiam River at 

Green’s Bridge near Jefferson (14184200) and 

the Reach 5 gage on the South Santiam River at 

Foster (14186700) were not made because the 

magnitude of high-flow measurements was insufficient.
17

Indicators of Hydrologic Alteration

Developed by The Nature Conservancy for 

the Sustainable Rivers Project, the Indicators of 

Hydrologic Alteration (IHA) software program

allows users to compute streamflow statistics that

can be used to quantify hydrologic changes resulting from the construction of dams and diversion canals in a river basin (The Nature Conservancy, 2007). For a given daily mean streamflow 

record, the program computes an extreme lowflow threshold, high-flow threshold, small floods 

(2-year events), and large floods (10-year events)

(table 6). The high-flow threshold, which is also 

the 25 percent streamflow exceedance, is analogous to a high-flow pulse. The extreme low-flow 

category includes the lowest 10 percent of daily 

mean streamflows that are less than the high-flow 

threshold. The IHA program estimates flood 

magnitudes for the 2- and 10-year recurrence intervals using a Weibull distribution. 

Streamflow statistics in table 6 were computed using data provided by the USACE representing unregulated streamflow conditions for each 

reach. A common period (water years 1953–

2009) was used for all seven reaches. Like bankfull flow estimates, estimates of low flows, pulse 

flows, small floods, and large floods are used in 

environmental flow studies to define flow prescriptions that will meet the habitat needs of an 

aquatic or terrestrial species at various life stages.

Output from the IHA program can be downloaded at the link in Appendix C.

Table 6. Indicators of Hydrologic Alteration streamflow statistics at study reach streamflow gaging stations based 

on unregulated streamflow conditions in the Santiam River basin, Oregon, for water years 1953–2009.

[Abbreviation: ft3/s, cubic feet per second.]

Reach 

number

Station 

number Streamflow gaging station name

Extreme 

low-flow 

threshold

(ft3/s)

High-flow 

threshold 

(ft3/s)

2-year flood 

(ft3/s)

10-year flood 

(ft3/s)

1 14181500 North Santiam River at Niagara, Oregon 635 2,810 21,300 32,200

2 14183000 North Santiam River at Mehama, Oregon 685 4,270 35,400 53,900

3 14184100 North Santiam River at Greens Bridge near Jefferson, 

Oregon

767 4,780 39,600 60,400

4 14186500 Middle Santiam River at mouth near Foster, Oregon 130 2,190 20,700 33,200

5 14186700 South Santiam River at Foster, Oregon 210 3,420 32,600 49,900

6 14187500 South Santiam River at Waterloo, Oregon 223 3,980 35,800 59,100

7 14189000 Santiam River at Jefferson, Oregon 551 10,100 85,000 144,000
18

Water-Use Compilation

Major surface-water withdrawals along the 

lower reaches of the North Santiam, South Santiam, and Santiam Rivers were compiled in order 

to quantify natural streamflow conditions. Much 

of the water-use data and information was from 

the Oregon Water Resources Department website 

(http://www.wrd.state.or.us) and Sullivan and 

Rounds (2004).

North Santiam River

For Reach 1, from Detroit Dam to the Little 

North Santiam River confluence, direct surfacewater withdrawals are minimal. The towns of 

Gates (RM 51.2) and Mill City (RM 47.5) withdraw 0.13 and 0.35 ft3

/s on a mean annual basis, 

respectively, for municipal water supply. However, downstream from the Little North Santiam 

River confluence to RM 26 (Reach 2), surfacewater withdrawals are more significant. The city 

of Salem withdraws approximately 67 ft3/s on a 

mean annual basis from intakes near Geren Island 

at RM 31. The city of Stayton and the Santiam 

Water Control District withdraw approximately 

260 ft3/s on a mean annual basis at RM 29.5. At 

RM 27.0, NORPAC Foods withdraws 0.40 ft

3

/s

from June to October. In Reach 3, from RM 26 to 

the South Santiam River confluence, approximately 40 ft3

/s is withdrawn from May to September by the Sidney Irrigation Cooperative at 

RM 19.6.

Water-use data for the North Santiam River 

was used for extending the measured daily mean

streamflow time series for the Reach 3 gage, 

North Santiam River at Green’s Bridge near Jefferson (14184100). The period of operation for 

this station was from water years 1964 to 1967 

and 2006 to 2011. To create a longer time series 

(water years 1951–2011) for this site, daily mean 

streamflow data from the upstream gage, North 

Santiam River at Mehama (14183000), were proportionally adjusted to the increased drainage area of the Reach 3 Green’s Bridge near Jefferson

gage (14184100). These adjusted streamflows 

were used to fill in missing periods in the measured (14184100) streamflow time series. Next, all 

major surface-water withdrawals between the two 

gages (14183000 and 14184100) were subtracted 

from the estimated 14184100 streamflow time 

series. Monthly surface-water withdrawals 

(2001–2011) for Salem, Stayton Water Control 

District, NORPAC Foods, and Sidney Irrigation 

Cooperative were compiled and summed. This 

amount was offset by effluent from Stayton (3.33

ft3/s on a mean annual basis) at RM 27.5. Monthly net water withdrawals were converted to daily 

values and then smoothed using a 30-day running 

average. Estimated mean annual net water withdrawal between the two gages (14183000 and 

14184100) was 335 ft3/s (water years 2001–

2010).

Prior to its subtraction from the estimated 

streamflow time series for Green’s Bridge near 

Jefferson (14184100), Salem municipal-use withdrawals and Stayton effluent return flows were 

adjusted for population growth between 1950 and 

2011. Using Marion County population for 1950, 

1960, 1970, 1980, 1990, 2000, and 2010 from the 

U.S. Census, a regression was created to estimate 

the county population for each year from 1950 

and 2011. Monthly-mean Salem municipal-use 

withdrawals and Stayton effluent return flows for 

the 2001 to 2010 were adjusted to 1950 using a 

ratio of the population in the earlier year to the 

population in 2010. However, estimated withdrawals for irrigation use were not adjusted for 

population growth on the assumption that irrigation use has not increased as rapidly as municipal 

use has from 1951 to 2011.

South Santiam River

For Reach 4, from Green Peter Dam to Foster Dam, withdrawals from the Middle Santiam 

River (which flows into the South Santiam River)

are minimal or nearly nonexistent. However, in 

Reach 5, downstream from Foster Dam to RM 

23.4, above the Waterloo gage (14187500), mean 

annual water use reported by the City of Sweet 

Home was 1.76 ft3/s for water years 2001–2010. 

In Reach 6, which extends from the Waterloo 
19

gage (14187500) to the North Santiam River confluence, water is diverted from the South Santiam 

River through the Lebanon-Santiam Canal at RM 

20.9, upstream of Lebanon. For water years 

1992–2011, mean annual streamflow was 89 ft3/s

as measured at the USGS gage (14187600) on the 

canal and near the canal diversion point on the 

river. Since 2007, withdrawals from the river to 

the canal have been as high as 200 ft3/s during the 

summer. The canal water is used for irrigation, 

small project hydropower generation, and municipal water supply for Lebanon and Albany. Lebanon withdrew 3.01 ft3

/s (average for water years 

2001–2010) from the canal (Oregon Water Resources Department, 2012). Previously, the canal 

diverted water from the South Santiam River at a 

location slightly downstream from Lebanon at 

RM 17.0 and was known as the “Albany-Santiam 

Canal.” Mean annual streamflow in the canal during this earlier period was 209 ft3

/s (water years 

1926–1957) as measured at the inactive USGS 

gage (14188000) on the canal.

In addition to the Sweet Home municipal 

water supply and the Lebanon-Santiam Canal, 

other substantial diversions in the South Santiam 

River are for irrigation. From RM 21.1 to the 

North Santiam River confluence, mean direct surface-water withdrawals for irrigation are 16.9 

ft3/s annually, on the basis of Oregon Water Resources Department water-availability data 

(Cooper, 2002; Oregon Water Resources Department, 2012). 

Main-Stem Santiam River

Surface-water withdrawals in Reach 7, from 

the confluence of the North and South Santiam 

Rivers to the Willamette River confluence, include the Jefferson municipal water supply and 

irrigation for agricultural. Mean annual water use 

reported by the City of Jefferson was 0.51 ft3/s

for water years 2001–2010. Surface-water withdrawals for irrigation from the Santiam River in 

Reach 7 are 5.02 ft3/s on a mean annual basis 

based on Oregon Water Resources Department 

water-availability data (Cooper, 2002). 

Pre- and Post-Dam Comparisons

Statistical and graphical comparisons were 

used to assess the effects of dams on streamflows. 

These included comparisons of annual peak and 

daily mean streamflow data measured before and 

after the dams were constructed. Comparisons 

were also made of post-dam period measured daily mean streamflows with the post-dam period 

computed unregulated daily mean streamflows 

provided by the USACE.

Comparisons of pre- and post-dam period 

measured streamflow data were possible in four 

of the reaches, which had lengthy continuous 

streamflow records that began in the 1920s or 

1930s. These included North Santiam River at 

Niagara (14181500), North Santiam River at Mehama (14183000), South Santiam River at Waterloo (14187500), and Santiam River at Jefferson 

(14189000). In using this method of comparison,

it was necessary to determine whether climate 

was a contributing factor to changes in streamflow by evaluating monthly precipitation data at 

Salem and Waterloo from the pre- and post-dam 

periods. On the basis of a Wilcox rank-sum test, 

there was no significant difference in monthly 

precipitation between the two periods. The pvalues for all the months, with the exception of 

February in Salem, were greater than 0.5 

(table 7). 
20

Table 7. Salem, Oregon, and Waterloo, Oregon, median monthly precipitation totals.

[Source: Western Regional Climate Center (2012). Abbreviation: WY, water year. p-values less than 0.05 resulting 

from a Wilcox rank-sum test indicate there is a significant difference in the monthly precipitation totals between 

the pre-dam and post-dam periods. Salem and Waterloo precipitation data from stations 357500 and 359083, respectively.]

Salem, Oregon (North Santiam River basin) Waterloo, Oregon (South Santiam River basin)

Pre-dam 

1935–1952 

(inches)

Post-dam 

1953–2010 

(inches) p-value

Pre-dam 

1935–1966 

(inches)

Post-dam 

1967–2010 

(inches) p-value

WY total 41.1 39.6 0.56 41.6 45.0 0.34

January 5.34 6.43 0.51 5.29 6.98 0.58

February 5.57 4.28 0.03 4.74 4.41 0.47

March 4.02 3.82 0.92 4.80 4.55 0.78

April 1.88 2.44 0.12 2.62 3.25 0.08

May 1.60 1.90 0.68 1.86 2.20 0.47

June 0.98 1.17 0.47 1.11 1.57 0.06

July 0.36 0.23 0.30 0.03 0.26 0.14

August 0.35 0.38 0.66 0.20 0.57 0.28

September 1.38 1.20 0.83 1.26 1.37 0.19

October 2.87 2.89 0.65 3.30 3.18 0.79

November 5.36 6.05 0.72 6.63 6.47 0.78

December 6.25 6.95 1.00 5.59 7.13 0.59

Statistical metrics representing different environmental flow components, such as low flows 

(7-day annual minimum, 95-percent exceedance), 

high flows (1-day maximum annual, 5-percent 

exceedence), floods (annual peak), and median 

monthly flows, were computed to compare preand post-dam conditions.

Graphical comparisons of pre- and poststreamflow regulation include mean daily streamflow plots. Mean daily streamflow for any one 

day, October 10, for example, is the arithmetic 

mean of the discharge on all October 10s of the 

record, or a specified period of a record. This is 

different from daily mean streamflow, which is 

defined as the mean streamflow for that one day.

Because a mean daily streamflow plot dampens 

the magnitude of floods, comparisons of measured daily mean streamflows and USACE computed unregulated daily streamflows for a single 

water year (1975) also were included. Water year 

1975 data were used in the daily mean streamflow comparison plots because it approximates an

average year in the historic streamflow record 

(water years 1939–2011) for the Santiam River at 

Jefferson (14189000).

Streamflow Assessment

Results from an assessment of the effects of 

dams and surface-water withdrawals on the full 

streamflow regime for the seven study reaches in 

the Santiam River basin are described below. 
21

North Santiam River

The hydrologic effect of the Detroit and Big 

Cliff Dams, completed in 1953, is evident in the 

streamflow record at the USGS gage on the North 

Santiam River at Mehama (14183000) (fig. 6). 

Prior to dam regulation, daily mean streamflow 

exceeded the USACE defined bankfull (17,000 

ft3/s) and flood (30,500 ft3/s) threshold discharges

on average 3.39 and 0.68 times per year, respectively, from 1922 to 1952. However, from 1953 

to 2011, bankfull and flood threshold discharges 

were exceeded on average only 0.97 and 0.03 

times per year, respectively. The two times the

flood threshold was exceeded in the post-dam 

period were December 22, 1964, at 36,200 ft3/s

and February 7, 1996, at 46,700 ft3/s, respectively. The USACE estimated that these two events 

would have been 91,600 and 96,400 ft3/s, respectively, had the dams not been constructed (fig. 6)

(Alan Donner, U.S. Army Corps of Engineers, 

written commun., 2011).

Figure 6. Graph showing daily mean streamflow in Reach 2 at North Santiam River at Mehama, Oregon 

(14183000), water years 1922–2011.

A comparison of measured and computed 

unregulated mean daily streamflows (water years 

1953–2009) at North Santiam River gages in 

Reaches 1–3 at Niagara (14181500), Mehama 

(14183000), and Green’s Bridge (14184100) 

showed that February–April streamflows decreased and August–November streamflows increased under regulated streamflow conditions 

(figs. 7–9), respectively. These streamflow alterations are typical of locations downstream from

reservoirs used for hydropower production and 

flood control. Flows are decreased in the spring 

when the reservoirs are filling up. The increased 

fall flows are the result of reservoir drawdown 

each year prior to the annual flood season. 
22

Figure 7. Graph showing mean daily streamflow in Reach 1 at North Santiam River at Niagara, Oregon

(14181500), water years 1953–2009.

Figure 8. Graph showing mean daily streamflow in Reach 2 at North Santiam River at Mehama, Oregon

(14183000), water years 1953–2009.
23

Figure 9. Graph showing mean daily streamflow in Reach 3 at North Santiam River at Green’s Bridge near 

Jefferson, Oregon (14184100), water years 1953–2009.

Changes in seasonal streamflow patterns 

caused by the dams is also evident in a comparison of measured regulated and computed unregulated daily mean streamflows at these three gages 

during a single average hydrologic year (1975). 

Although the timing of high-flow events remained constant, the magnitude of these events 

decreased. The dam operation and its effect on 

streamflow can be seen at Niagara (14181500) 

(fig. 10), particularly in March and April and 

again in August and September. The effect of 

dam operation on streamflow becomes dampened 

at the two downstream gages (figs. 11–12). 

Using annual peak-flow data, flood frequencies based on the Bulletin 17B Log Pearson III 

method were computed for the pre-dam and postdam periods for Niagara (14181500) and Mehama (14183000). The period of record for peakflow measurements is longer, extending to 1909 

for Niagara (14181500) and to 1906 for Mehama 

(14183000), than the period of record for collection of continuous discharge at these stations. For 

both gages, the 1.5-, 10-, 50-, 100-, and 500-year

peak flows decreased in the post-dam period 

(1953–2010) (table 8). The range of decrease in 

peak flows was greater for the Niagara 

(14181500) gage (-43 – -81 percent) than the 

Mehama (14183000) gage (-38 – -44 percent).
24

Figure 10. Graph showing daily mean streamflow in Reach 1 at North Santiam River at Niagara, Oregon

(14181500), water year 1975.

Figure 11. Graph showing daily mean streamflow in Reach 2 at North Santiam River at Mehama, Oregon

(14183000), water year 1975.
25

Figure 12. Graph showing daily mean streamflow in Reach 3 at North Santiam River at Green’s Bridge near 

Jefferson, Oregon (14184100), water year 1975.
26

Table 8. Pre- and post-dam flood statistics for selected Santiam River basin, Oregon, streamflow gaging stations,

computed from annual peak streamflow data based on the Bulletin 17B Log Pearson III method.

[Abbreviations: POR, period of record in water years; ft3/s, cubic feet per second.]

Station

number

Streamflow gaging-station 

name and study reach number

Recurrence

interval

(years)

Pre-dam period Post-dam period

Percent

POR change

Streamflow 

(ft3/s) POR

Streamflow 

(ft3/s)

14181500 North Santiam River at 

Niagara, Oregon, Reach 1

1.5 1909–

1952

16,700 1953–

2010

9,540 -43

10 44,700 15,200 -66

50 69,600 18,000 -74

100 81,300 19,000 -77

500 111,000 21,100 -81

14183000 North Santiam River at 

Mehama, Oregon, Reach 2

1.5 1906–

1952

28,500 1953–

2010

17,800 -38

10 58,300 32,700 -44

50 79,800 45,500 -43

100 89,000 51,500 -42

500 111,000 67,200 -39

14187500 South Santiam River at 

Waterloo, Oregon, Reach 6

1.5 1906–

1966

31,500 1967–

2010

14,200 -55

10 65,600 20,900 -68

50 91,300 24,800 -73

100 103,000 26,300 -74

500 130,000 29,700 -77

14189000 Santiam River at Jefferson, 

Oregon, Reach 7

1.5 1908–

1952

62,400 1953–

2010

44,200 -29

10 152,000 102,000 -33

50 231,000 157,000 -32

100 268,000 184,000 -31

500 364,000 259,000 -29
27

Under regulated streamflow conditions, the 

median of annual 1-day maximum streamflows at 

the three North Santiam River gages at Niagara 

(14181500), Mehama (14183000), and Green’s 

Bridge (14184100) decreased by 42 to 50 percent 

for 1953–2009 compared to computed unregulated streamflow conditions (table 9). In contrast, 

the median of annual 7-day minimum streamflows increased by 25 to 93 percent at these three 

stations (table 10). The median monthly streamflows at all three gages decreased in the late winter and spring (February–June) and all increased 

in the late summer to winter (September–

January) (table 11). For the Reach 1 and 2 gages,

Niagara (14181500) and Mehama (14183000), 

respectively, median monthly streamflows increased in July and August as a result of dam 

regulation. However, for Reach 3, median monthly streamflows decreased in July and August, because the regulated streamflow time series, based 

on measured data, includes surface-water withdrawals for municipal water use and irrigation in 

Reach 3. The unregulated time series, computed 

by the USACE, does not take into account these 

withdrawals because it was created for the purpose of quantifying the effects of the dams on 

streamflow.

Table 9. One-day maximum annual streamflow statistics from regulated and unregulated daily mean streamflows for the Santiam River, Oregon.

[Regulated and unregulated streamflows based on observed and computed data as described in the text. Medians computed from the 1-day maximum annual flows for the period of record.]

Reach

number

Station

number Streamflow gaging station name

Period of 

record (water years)

Unregulated

streamflow

median

(ft3/s)

Regulated

streamflow

median

(ft3/s)

Percent

change

1 14181500 North Santiam River at Niagara, 

Oregon

1953–2009 17,900 10,300 -42

2 14183000 North Santiam River at Mehama, 

Oregon

1953–2009 28,700 14,500 -49

3 14184100 North Santiam River at Greens 

Bridge near Jefferson, Oregon

1953–2009 32,200 16,000 -50

4 14186500 Middle Santiam River at mouth 

near Foster, Oregon

1967–2009 16,400 9,950 -39

5 14186700 South Santiam River at Foster, 

Oregon

1967–2009 24,900 11,900 -52

6 14187500 South Santiam River at Waterloo, 

Oregon

1967–2009 27,700 13,600 -51

7 14189000 Santiam River at Jefferson, 

Oregon

1953–2009 71,800 43,900 -39
28

Table 10. Seven-day minimum annual streamflow statistics from regulated and unregulated daily mean streamflows for the Santiam River, Oregon.

[Regulated and unregulated streamflows based on observed and computed data as described in the text. Medians were 

computed from the 7-day minimum annual flows for the period of records.]

Reach

number

Station

number Streamflow gaging station name

Period of 

record 

(water years)

Unregulated

streamflow

median

(ft3/s)

Regulated

streamflow

median

(ft3/s)

Percent

change

1 14181500 North Santiam River at Niagara, 

Oregon

1953–2009 579 928 60

2 14183000 North Santiam River at Mehama, 

Oregon

1953–2009 554 1,070 93

3 14184100 North Santiam River at Greens 

Bridge near Jefferson, Oregon

1953–2009 620 773 25

4 14186500 Middle Santiam River at mouth 

near Foster, Oregon

1967–2009 85.6 52.6 -39

5 14186700 South Santiam River at Foster, 

Oregon

1967–2009 155 636 310

6 14187500 South Santiam River at Waterloo, 

Oregon

1967–2009 145 631 335

7 14189000 Santiam River at Jefferson, Oregon 1953–2009 359 1,210 237
29

Table 11. Median monthly streamflow statistics from regulated and unregulated daily mean streamflows for the Santiam River, Oregon.

[POR, Period of record; WY, water year from October 1 to September 30. ft3/s, cubic feet per second. Regulated and unregulated streamflows based on observed

and computed data as described in the text. Medians computed from monthly flows for the period of records.]

Reach 

number

Station 

number

POR in 

WY

Streamflow 

condition

January 

(ft3/s)

February 

(ft3/s)

March 

(ft3/s)

April 

(ft3/s)

May 

(ft3/s)

June 

(ft3/s)

July 

(ft3/s)

August 

(ft3/s)

September 

(ft3/s)

October 

(ft3/s)

November

(ft3/s)

December 

(ft3/s)

1 14181500 1953–

2009

Unregulated 2,610 2,400 2,420 2,710 2,660 1,700 937 687 665 760 1,720 2,470

Regulated 2,900 1,090 1,050 1,420 2,220 1,530 1,090 1,020 1,780 2,360 3,060 3,020

Percent change 11 -55 -57 -48 -17 -10 16 48 168 211 78 22

2 14183000 1953–

2009

Unregulated 4,180 3,680 3,740 3,980 3,610 2,160 1,090 755 721 891 2,670 3,930

Regulated 5,050 2,690 2,530 2,780 3,270 2,070 1,270 1,120 1,880 2,490 4,140 5,350

Percent change 21 -27 -32 -30 -9 -4 17 48 161 179 55 36

3 14184100 1953–

2009

Unregulated 4,680 4,120 4,190 4,450 4,040 2,420 1,220 845 807 998 2,990 4,400

Regulated 5,460 2,820 2,630 2,850 3,250 1,880 983 830 1,710 2,480 4,400 5,780

Percent change 17 -32 -37 -36 -20 -22 -19 -2 112 148 47 31

4 14186500 1967–

2009

Unregulated 2,340 1,880 1,960 1,880 1,410 641 228 126 147 273 1,560 2,350

Regulated 2,660 526 568 993 1,290 673 599 631 1,060 1,340 2,310 3,570

Percent change 14 -72 -71 -47 -9 5 163 401 621 391 48 52

5 14186700 1967–

2009

Unregulated 3,660 2,970 3,020 3,010 2,250 1,030 377 210 228 426 2,340 3,680

Regulated 4,390 1,680 1,700 2,220 1,770 1,040 743 708 1,110 1,560 3,300 5,350

Percent change 20 -43 -44 -26 -21 1 97 237 387 266 41 45

6 14187500 1967–

2009

Unregulated 4,220 3,570 3,710 3,540 2,500 1,120 388 206 251 489 2,650 4,270

Regulated 5,180 2,390 2,360 2,760 2,050 1,120 771 691 1,150 1,660 3,570 6,000

Percent change 23 -33 -36 -22 -18 0 99 235 358 239 35 41

7 14189000 1953–

2009

Unregulated 10,800 9,370 9,270 9,020 6,940 3,470 1,160 551 639 1,280 6,060 10,300

Regulated 12,700 7,960 7,330 7,270 6,280 3,520 1,690 1,370 2,480 3,920 8,550 13,000

Percent change 18 -15 -21 -19 -10 1 46 149 288 206 41 26
30

For the Reach 1 gage, North Santiam River 

at Niagara (14181500), the 5-percent streamflow 

exceedance under regulation decreased by about 

6 percent (table 12). Changes in the 5-percent 

streamflow exceedance as a consequence of regulation at the Reach 2 and 3 gages, Mehama 

(14183000) and Green’s Bridge (14184100), 

were less than 2 percent (table 12 and figs. 13–

15). For low-flow periods, the 95-percent streamflow exceedance increased for all three of the 

North Santiam River gages by 13 to 75 percent. 

This is typical for low flows with reservoir regulation. It is also noteworthy that the increase in 

low flows is less noticeable at the Reach 3 gage

because of major water withdrawals between the 

Reach 2 and 3 gages (fig. 15).

Table 12. Streamflow exceedance statistics from regulated and unregulated daily mean streamflows for the 

Santiam River, Oregon.

[POR, Period of record; WY, water year from Oct. 1 to Sept. 30. cfs, cubic feet per second. Regulated and unregulated

streamflows based on observed and computed data as described in the text.]

Reach

number

Station

number POR in WY

Streamflow

condition

Percent of daily mean streamflow, in cubic feet per second, equaled or 

exceeded

5 10 25 50 75 90 95

1 14181500 1953–2009 Unregulated 5,910 4,380 2,810 1,680 864 635 583

Regulated 5,560 4,640 2,880 1,680 1,050 958 900

Percent change -5.9 5.8 2.4 0.2 21 51 54

2 14183000 1953–2009 Unregulated 9,660 6,870 4,270 2,420 1,040 685 593

Regulated 9,680 6,970 4,130 2,450 1,590 1,150 1,040

Percent change 0.2 1.4 -3.3 1.3 53 68 75

3 14184100 1953–2009 Unregulated 10,800 7,680 4,780 2,710 1,170 767 663

Regulated 10,600 7,520 4,420 2,430 1,440 882 752

Percent change -1.8 -2.1 -7.5 -10 23 15 13

4 14186500 1967–2009 Unregulated 5,770 3,890 2,190 1,050 263 126 97

Regulated 4,940 4,310 2,130 1,040 557 294 53

Percent change -14 11 -2.7 -1.0 112 133 -46

5 14186700 1967–2009 Unregulated 8,730 5,950 3,410 1,640 421 208 167

Regulated 8,930 6,130 3,230 1,530 830 686 612

Percent change 2.3 3.0 -5.3 -6.7 97 230 266

6 14187500 1967–2009 Unregulated 9,880 6,880 4,000 1,950 470 222 164

Regulated 10,300 7,050 3,810 1,840 957 709 629

Percent change 4.2 2.5 -4.7 -5.6 104 220 283

7 14189000 1953–2009 Unregulated 24,600 17,000 10,100 5,120 1,280 551 386

Regulated 25,100 17,500 9,750 5,120 2,570 1,480 1,200

Percent change 2.0 3.1 -3.2 0.1 100 169 211
31

Figure 13. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 1 at North Santiam River at Niagara, Oregon (14181500), water years 1953–2009.

Figure 14. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 2 at North Santiam River at Mehama, Oregon (14183000), water years 1953–2009.
32

Figure 15. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 3 at North Santiam River at Green’s Bridge near Jefferson, Oregon (14184100), water years 1953–2009.

South Santiam River

The longest streamflow time series in the 

South Santiam River basin was recorded at South 

Santiam River at Waterloo (14187500), which 

has been in continuous operation since 1923 (fig. 

16). The highest daily mean streamflow in the 

record was on December 22, 1964, at 77,000 ft3/s

prior to the construction of the Green Peter and 

Foster Dams in 1967. Prior to dam regulation,

daily mean streamflow exceeded the USACE defined bankfull and flood threshold discharges on 

average 4.12 and 1.72 times per year, respectively, for the period from the start of water year 

1924 to the end of water year 1966. For water 

years 1967–2011, bankfull and flood threshold 

discharges were exceeded on average only 0.18 

and 0.02 times per year, respectively. The one 

time the flood threshold was exceeded in the 

post-dam period was February 7, 1996, at 24,200 

ft3/s. If the dams had not been constructed, the 

USACE estimated that this event would have 

been 83,800 ft3/s at Waterloo (14187500).

Using annual peak flows, which have been 

measured at the Waterloo (14187500) gage since

1906, flood frequencies were separately computed for the pre-dam (1906–1966) and post-dam 

(1967–2010) periods. As a result of dam regulation, the 1.5-, 10-, 50-, 100-, and 500-year peak 

flows decreased by 55 to 77 percent (table 8).
33

Figure 16. Graph showing daily mean streamflow in Reach 6 at South Santiam River at Waterloo, Oregon 

(14187500), water years 1924–2011.

Following a similar pattern as the North Santiam gages, a comparison of measured and computed unregulated mean daily streamflows (water 

years 1967–2009) at the three South Santiam 

River basin gages (Reaches 4–6) showed that 

February–May streamflows decreased and July–

November streamflows increased under regulated 

streamflow conditions (figs. 17–19). The Middle 

Santiam River at mouth near Foster (14186500) 

gage (Reach 4) shows the effects of regulation 

from Green Peter Dam. The Reach 5 gage is on 

the South Santiam River at Foster (14186700) 

just below Foster Dam. Farther downstream, in 

Reach 6, the streamflow record for Waterloo 

(14187500) at RM 23.3 shows the effects of Foster Dam streamflow regulation combined with 

unregulated inflow from Wiley, Ames, and 

McDowell Creeks. 
34

Figure 17. Graph showing mean daily streamflow in Reach 4 at Middle Santiam River at mouth near Foster, Oregon (14186500), water years 1967–2009.

Figure 18. Graph showing mean daily streamflow in Reach 5 at South Santiam River at Foster, Oregon

(14186700), water years 1967–2009.
35

Figure 19. Graph showing mean daily streamflow in Reach 6 at South Santiam River at Waterloo, Oregon

(14187500), water years 1967–2009.

A comparison of measured regulated and 

computed unregulated daily mean streamflows at 

these three gages (Reaches 4–6) during a single 

average hydrologic year (1975) showed the effects of dam regulation in the annual hydrograph

(figs. 20–22). Green Peter Dam operation and its 

effect on streamflow at the Reach 4 gage

(14186500) (fig. 20) is evident in comparison to 

the measured streamflow at the Reach 5 gage

(14186700) (fig. 21), which is below Foster Dam. 

Because one of the objectives of Foster Dam is 

re-regulating Green Peter Dam discharge, measured streamflow below Foster Dam appears more 

natural and less regulated than streamflow from 

Green Peter Dam. 
36

Figure 20. Graph showing daily mean streamflow in Reach 4 at Middle Santiam River at mouth near Foster, Oregon (14186500), water year 1975.

Figure 21. Graph showing daily mean streamflow in Reach 5 at South Santiam River at Foster, Oregon

(14186700), water year 1975.
37

Figure 22. Graph showing daily mean streamflow in Reach 6 at South Santiam River at Waterloo, Oregon

(14187500), water year 1975.

Under regulated streamflow conditions for 

1967–2009, the median annual 1-day maximum 

streamflow at the three gages (Middle Santiam 

River at mouth near Foster [14186500], South 

Santiam River at Foster [14186700], and South 

Santiam River at Waterloo [14187500]) decreased by 39 to 52 percent in comparison to 

computed unregulated streamflow conditions (table 9). In contrast, the median of annual 7-day 

minimum streamflows increased by 310 to 335

percent at Foster (14186700) and Waterloo 

(14187500) gages, respectively (table 10). Both 

those gages are downstream from Foster Dam. 

However, for the gage below Green Peter Dam 

(Middle Santiam River at mouth near Foster 

[14186500]), the median annual 7-day minimum 

streamflow decreased by 39 percent. Summer low 

flows commonly increased as a result of dam 

regulation. The decrease in low flows for the 

Reach 4 gage below Green Peter Dam may have 

been because of an error in the regulated streamflow time series. The 1967–2009 regulated 

streamflow time series for this station was entirely computed because the gage was discontinued 

in 1966. The time series, provided by USACE, 

was compiled from reservoir modeling output 

and contained many consecutive days of exactly 

50 ft3/s of discharge.

The median monthly streamflows at the three 

Reach 4–6 gages (Middle Santiam River at mouth 

near Foster [14186500], South Santiam River at 

Foster [14186700], and South Santiam River at 

Waterloo [14187500]) decreased in the late winter and spring (February–May) and increased 

from summer to winter (July–January) as a result 

of dam regulation (table 11).

For the two gages below Foster Dam, South 

Santiam at Foster (14186700) and at Waterloo 

(14187500), the 5-percent streamflow exceedance 

increased slightly (less than 5 percent) under regulation (figs. 23–25; table 12). The 95-percent 

streamflow exceedance increased 266 and 283 

percent for gages 14186700 and 14187500, respectively. However, the 95-percent streamflow 

exceedance for the gage below Green Peter Dam 

(14186500) decreased by 46 percent, possibly 

because of an error in the computed streamflow 

time series as previously mentioned.
38

Figure 23. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 4 at Middle Santiam 

River at mouth near Foster, Oregon (14186500), water years 1967–2009.

Figure 24. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 5 at South Santiam 

River at Foster, Oregon (14186700), water years 1967–2009.
39

Figure 25. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 6 at South Santiam 

River at Waterloo, Oregon (14187500), water years 1967–2009.

Main-Stem Santiam River

The Santiam River at Jefferson (14189000) 

gage began continuous operation in water year 

1940 and is downstream from all four USACE 

dams (Detroit, Big Cliff, Green Peter, and Foster) 

(fig. 26). Although the effect of the four dams is 

evident in this streamflow record, the effect is 

less than the effect seen in the streamflow data in 

the North and South Santiam River basins because those gages are closer to the dams. In addition to the greater travel time, the effect of the 

dams is also decreased at the Jefferson 

(14189000) gage because of substantial natural

inflow between the dams and the station.
40

Figure 26. Graph showing daily mean streamflow in Reach 7 at Santiam River at Jefferson, Oregon (14189000), 

water years 1940–2011.

Prior to construction of the North Santiam 

River dams in 1953, daily mean streamflow exceeded the USACE defined bankfull and flood 

threshold discharges on average 7.46 and 1.92

times per year, respectively. During water years 

1953–2011, daily mean streamflow exceeded 

bankfull and flood threshold discharges on average 4.12 and 0.66 times per year, respectively. 

The largest flood events in the post-dam regulation period were 143,000 ft3

/s (December 23, 

1964) and 115,000 ft3/s (February 7, 1996). If the 

dams had not been constructed, the USACE estimated that these two events would have been 

219,000 ft3/s (December 22, 1964) and 240,000

ft3/s (February 7, 1996) (fig. 26). The full effect 

of flood control does not appear until water year 

1967 when the South Santiam dams were completed. Although it may appear that the North 

Santiam River dams provide less flood control 

than the South Santiam River dams, it should be 

noted that the late 1950s and early 1960s (before 

construction of the South Santiam River dams) 

was a wet period. The effect of flood control in 

the North and South Santiam Rivers likely is

comparable because the drainage area above Foster Dam (492 mi2

) is comparable to the drainage 

area above Big Cliff Dam (449 mi2). Also, at 

their confluence, the drainage areas of the North 

and South Santiam Rivers are 1,770 and 1,810 

mi2, respectively.

Using annual peak flows, which have been 

measured at the Jefferson (14189000) gage starting in 1908, flood frequencies were separately 

computed for the pre-dam (1908–1952) and postdam (1953–2010) periods. As a result of dam 

regulation, the 1.5-, 10-, 50-, 100-, and 500-year 

peak flows decreased by 29 to 33 percent (table 

8). This is substantially less than the peak-flow 

decreases computed for the gages in the North 

and South Santiam River basins because those 

gages are upstream closer to the dams.

Similar to the North and South Santiam River gages, a comparison of measured and computed unregulated mean daily streamflows (water 
41

years 1953–2009) at the Jefferson (14189000) 

gage showed that February–May streamflows decreased and July–November streamflows increased under regulated streamflow conditions 

(fig. 27). Because the Jefferson (14189000) gage

is farther downstream from the dams, the effect 

of streamflow regulation caused by the dams is 

less pronounced than at the upstream gages.

Figure 27. Graph showing mean daily streamflow in Reach 7 at Santiam River at Jefferson, Oregon (14189000), 

water years 1953–2009.
42

A comparison of measured regulated and 

computed unregulated daily mean streamflows at 

the Jefferson (14189000) gage during a single 

average hydrologic year (1975) showed the effects of dam regulation (fig. 28). Flood peaks 

were reduced in magnitude and streamflows were 

higher in September and October. The day-to-day 

dam operation that is noticeable in the hydrographs for North Santiam River at Niagara 

(14181500) and Middle Santiam River near Foster (14186500), which are both immediately 

downstream from Big Cliff and Green Peter 

Dams, respectively, does not appear in the Jefferson (14189000) hydrograph. 

Figure 28. Graph showing daily mean streamflow in Reach 7 at Santiam River at Jefferson, Oregon (14189000), 

water year 1975.
43

Under regulated streamflow conditions from

1953 to 2009, the median of annual 1-day maximum streamflows at the Jefferson (14189000) 

gage decreased by 39 percent (table 9). However, 

the median of annual 7-day minimum streamflows increased by 237 percent (table 10). The 

median monthly streamflows were consistent 

with the median monthly streamflows at the six 

upstream gages (Reaches 1–6). Monthly streamflows at the Jefferson (14189000) gage decreased 

in the late winter and spring (February–May) and 

increased in the summer to early winter (June–

January) as a result of dam regulation (table 11).

The 5-percent streamflow exceedance increased 

slightly (less than 5 percent), whereas the 95-

percent streamflow exceedance increased by 211 

percent (fig. 29, table 12).

Figure 29. Graph showing percent of daily mean streamflows equaled or exceeded in Reach 7 at Santiam River at 

Jefferson, Oregon (14189000), water years 1953–2009.

Geomorphic and Ecological Synopsis

This section provides a brief assessment of 

geomorphic and ecological characteristics within 

the Santiam River basin and their responses to

streamflow. The findings from this assessment 

are based primarily on qualitative observations

and simple measurements drawn from existing 

datasets and a review of prior relevant studies.

Because a comprehensive spatially explicit study 

of terrestrial and aquatic habitats and species of 

concern is lacking for the Santiam River basin,

this study used information from Gregory and 

others (2007a, 2007b) that provided a broad 

summary of species and habitats for the 

Willamette River basin. Other datasets used in 

this Santiam assessment include U.S. Department 

of Agriculture National Agriculture Imagery Program (NAIP) 2009 digital orthophotographs (1-m 

resolution); a Quaternary geology map 

(O’Connor and others, 2001); locations of 

USACE revetments (Jerry Otto, U.S. Army Corps 

of Engineers, written commun., Jan 13, 2012); 

and a land-cover map from 1850 (Gregory and 

others, 2002a). General summary reports including the Willamette Project Biological Opinions
44

(National Marine Fisheries Service, 2008; U.S. 

Fish and Wildlife Service, 2008), Biological Assessment (U.S. Army Corps of Engineers, 2007), 

and watershed assessments (E and S Environmental Chemistry Inc., 2002; E and S Environmental Chemistry Inc. and South Santiam Watershed Council, 2000) also were used. Previous 

studies of historical channel change in the Santiam River basin (Fletcher and Davidson, 1988; 

Klingeman, 1973), as well as other nearby basins,

including the Willamette (Wallick and others, 

2006, 2007), Middle and Coast Fork (Gregory 

and others, 2002a, 2002b) and McKenzie River 

basins (Risley and others, 2010a, 2010b) also 

were incorporated in this study. 

Geomorphic Characteristics of Study Reaches

In the following section, geomorphic characteristics of the North, South, and main-stem Santiam Rivers are briefly summarized and displayed. More complete descriptions for each 

reach are provided in Appendix D. Although the 

Middle Santiam River (Reach 4) is listed in Appendix C, it is not described in this section because it has limited habitat potential owing to releases from the upstream Green Peter Dam that 

likely scour the channel in the upper portion of 

the reach and because the lower portion of the 

reach is under constant inundation by the downstream Foster Lake reservoir. 

North Santiam River Channel Morphology

The upper 2.8 mi of Reach 1 is bounded by 

Detroit and Big Cliff Dams. Downstream from

the dams, the North Santiam River transitions 

from a narrow channel confined by steep bedrock 

valley walls to a broad, alluvial river with numerous side channels and gravel bars before joining 

the South Santiam River near Jefferson. Between 

Big Cliff Dam (RM 58.1) and the USGS gage at 

Niagara (14181500) (RM 57.3), the North Santiam River flows predominantly over bedrock and 

coarse bed material through a narrow canyon

with few gravel bars. Downstream from the bedrock rapids near the town of Niagara (RM 55.0), 

the flood plain widens to about 0.6 mi, and active 

gravel bars begin to appear, though they are small 

(2,000–3,000 yds2) and typically more than a 

mile apart (fig. 30). There are several large (up to 

16,000 yd2) densely vegetated mid-channel bars 

near the downstream end of Reach 1 near the Little North Santiam River confluence. Channel and 

flood-plain confinement owing primarily to basin 

topography throughout Reach 1 limit channel 

complexity and flood-plain processes; however, 

small, relict secondary channel features such as 

those between RM 40 and RM 44 may provide

off-channel habitat at high flows.

Figure 30. Aerial photograph showing channel and flood-plain morphology in study Reach 1 of the Santiam River

basin, Oregon, on the North Santiam River.
45

Downstream from the Little North Santiam 

River, the flood plain of the North Santiam River

along Reach 2 widens from 0.2 mi to nearly 1.5 

mi as the channel adopts an increasingly complex, multi-threaded morphology (fig. 31). Just 

below the upstream boundary of Reach 2, the river flows through a short, confined segment where 

the flood plain is about 0.2 mi wide and is closely 

flanked by Pleistocene terraces (fig. 31). Within 

this segment, historical channel change has likely 

been minimal, and a specific gage analysis by 

Klingeman (1973) found little indication of aggradation or incision between 1935 and 1965 at 

the USGS streamflow gage at Mehama 

(14183000) (RM 38.7). Farther downstream, the 

North Santiam River below RM 35 flows through 

a broad flood plain and historically probably displayed an anastomosing planform, meaning the 

river had multiple converging and diverging

channels separated by large, semi-stable islands 

much like the upper Willamette River above Harrisburg as described in Gregory and others 

(2002b). Presently, many of the secondary channel features along Reach 2 are densely vegetated,

and flow is mainly confined to a single channel, 

except for RM 26–33, where the active channel is 

over 0.25 mi wide and accommodates a diverse 

array of side channels, alcoves, islands, and gravel bars (fig. 31).
46

Figure 31. Map showing surficial geology and revetments for alluvial segments of the Santiam River, Oregon, 

study area. Late Pleistocene alluvium is a combination of units Qff2, Qg1, and Qg2; Holocene alluvium is a combination of units Qalc, Qalf, Qau, and Qbf; all other units shown from O’Connor and others (2001).
47

Channel complexity increases downstream 

along North Santiam River through Reach 3. This 

historically dynamic, multi-channeled reach is 

flanked by a broad flood plain 0.7–1.5 mi wide

(fig. 31). Active gravel bars up to 25,000 yd2in 

area are present throughout the reach and are 

nearly continuous along the multi-channeled 

segment near RM 17–21 (fig. 32). While nearly

half of Reach 3 presently displays complex, multi-channeled planform, densely vegetated, relict 

secondary channel and flood-plain features are 

found throughout the entire reach. An example of 

a segment in Reach 3 containing modern channel 

complexity and relict channel features is shown 

in figure 32. Because there is little revetment 

along the North Santiam River in Reaches 2 and 

3 (fig. 31), channel processes including meander 

migration, bar growth and creation, and maintenance of secondary channel features are mainly 

determined by the flow and coarse-sediment regimes. These processes have been altered by upstream dams.

Figure 32. Aerial photograph showing channel and flood-plain morphology in study Reach 3 of the Santiam River

basin, Oregon, on the North Santiam River.

South Santiam River Channel Morphology

Historically, the lower South Santiam River 

between RM 0 and RM 18 along Reach 6 likely 

displayed a complex, anastomosing planform. 

Presently, this segment, as well as Reach 5 (14.7 

mi of channel below Foster Dam), primarily occupies a low-sinuosity, single-thread channel (fig.

31). Although the flood plain in Reach 5 varies 

from 0.1 mi wide near Sweet Home to nearly 1 

mi wide elsewhere, much of the channel flows 

against naturally occurring hard surfaces including the flood-plain margin and basalt underlying 

the valley walls that limits channel complexity 

and provides stability (fig. 3). A specific gage 

analysis at the USGS gage at Waterloo 

(14187500) (RM 23.3) near the boundary between Reach 5 and Reach 6 indicates minimal

change in bed elevation between 1935 and 1965 

(Klingeman, 1973) underscoring the overall stability of this segment of the South Santiam River. 

There is only one area with moderate channel 

complexity along Reach 5 (between RM 28 and 

RM 29) where the river is flanked on both sides 

by Holocene alluvium and has multiple channels. 

Active gravel bars are sparse throughout Reach 5 

and are relatively small (less than 1,500 yd2). The

reach has a number of densely vegetated bar surfaces such as the island at RM 36 (fig. 33). 
48

Figure 33. Aerial photograph showing channel and flood-plain morphology in study Reach 5 of the Santiam River

basin, Oregon, on the South Santiam River. 

The South Santiam River along Reach 6 can 

be divided into two distinct segments. From RM 

18 (Lebanon) to its confluence with the North 

Santiam River, the river flows through a broad 

Holocene flood plain 1.75–3 mi wide that historically had a dynamic, multi-thread channel. Upstream between RM 18 and RM 23, the river 

flowed through a relatively narrow flood plain

(0.2–0.8 mi wide) that historically supported a 

more stable, single-thread channel (fig. 31). Although the channel in the lower segment (RM 0–

18) is flanked on both sides by easily erodible 

Holocene alluvium and was historically prone to 

rapid meander migration, much of the reach is 

presently stabilized by revetments constructed in 

the mid-to-late 20th century (fig. 31). Bank stabilization in combination with construction of the 

Foster and Big Cliff Dams resulted in substantial 

reductions in channel complexity and gravel-bar 

area. For example, Fletcher and Davidson (1988) 

reported a 56-percent reduction in the area of 

gravel bars between 1936 and 1981. The 2009 

orthophotographs show numerous bare, active 

gravel bars up to 25,000 yd2, downstream from

RM 18 in areas lacking bank revetment (for example, RM 4.5 in fig. 34). Gravel bars and channel complexity is much less where one or both 

banks are stabilized with revetment (Fletcher and 

Davidson, 1988; as depicted between RM 5 and

RM 6 in fig. 34). Downstream from RM 18, extensive formerly active bar surfaces and relic secondary channel features are presently stabilized 

with dense vegetation (for example, RM 5–7 in 

fig. 34). 
49

Figure 34. Aerial photograph showing channel and flood-plain morphology in study Reach 6 of the Santiam River

basin, Oregon, on the South Santiam River.

Main-Stem Santiam River Channel Morphology

The main-stem Santiam River below the confluence of the North and South Santiam Rivers 

historically formed dynamic multi-thread channels that were prone to rapid meander migration 

and avulsion prior to flood control and bank protection. Presently, the Santiam River along Reach 

7 is mainly confined to a single channel (fig. 31)

with several sections where flow is split by midchannel bars (for example, RM 5.3 in fig. 35).

Although Reach 7 flows through a broad flood 

plain that ranges up to 3 mi wide, revetment currently flanks much of the channel, restricting 

bank erosion, channel complexity, and bar 

growth (fig. 31). Between the confluence of the 

South and North Santiam Rivers and RM 10, the 

channel is confined by sedimentary rocks (fig. 

31). Large, bare, active gravel bars are intermittent but can exceed 100,000 yd2

, especially in 

the lower 5 mi of Reach 7 near its confluence 

with the Willamette River (fig. 35). Throughout 

the reach, there are many relict bar surfaces and 

secondary channel features that presently have 

dense vegetative cover. However, these features 

may be activated during exceptionally high flows 

(fig. 35). 
50

Figure 35. Aerial photograph showing channel and flood-plain morphology in study Reach 7 of the Santiam River

basin, Oregon, Santiam River main stem.

Specific gage analyses at the USGS gage at 

Jefferson (14189000) (RM 9.6) for the period 

1941–1986 shows substantial (greater than 1 ft) 

erosion from 1941 to 1964 (Klingeman, 1973)

and then relatively stable channel conditions from

1964 to 1986 (Fletcher and Davidson, 1988). 

Fletcher and Davidson (1988) attribute these 

overall changes to initial scouring of alluvial deposits and later cross-section control by an exposed bedrock outcrop slightly downstream. This 

bedrock outcrop is probably a remnant from the 

adjacent Pleistocene terraces composed of partially cemented gravels (unit Qg1) (fig. 31), which

can form resistant shoals and riffles (Wallick and 

others, 2006). Therefore, the specific gage analysis for the Jefferson gage may not be representative of other locations in this reach because the 

bank materials here are not the easily erodible 

Holocene alluvium found elsewhere along this 

reach.

Terrestrial and Aquatic Habitats and Key Species 

Geomorphic processes in response to streamflow are critical for creating and maintaining 

aquatic and terrestrial habitat. A few examples of 

ecological responses to geomorphic and hydrologic processes can include (1) fish spawning in 

gravel substrates created from flooding; (2) fish

migration and spawning in response to minimum 

streamflows and cooler stream temperatures; or

(3) cottonwood seed dispersal in response to fresh 

bare ground exposure caused by flood scouring.

The Santiam River basin historically provided 

diverse habitats that supported many aquatic and 

terrestrial ecosystems. Many of these habitats 

have been substantially altered by modifications 

in the river’s flow and sediment transport or are 

inaccessible because of passage issues at dams 

and culverts. Gregory and others (2007a, 2007b)

and Risley and others (2010a) provide detailed 

synopses of aquatic and terrestrial species likely 

to be affected by flow modifications in the Middle and Coast Fork Willamette and McKenzie 

River drainages. A brief summary of key ecological species and habitat needs are outlined below 

and are provided by reach in Appendix D.

The multi-channel segments with off-channel 

and secondary features along the North Santiam 

River below RM 33 and the main-stem Santiam 

River below RM 7 provide off-channel and 

backwater habitats critical for species such as Or-
51

egon chub, red legged frog, and western pond 

turtle (Gregory and others, 2007a, 2007b). These 

segments also have secondary channel features 

and sloughs that provide high-flow refugia and 

rearing habitat for native fish, including spring 

Chinook and winter steelhead. Although these 

features are present on the South Santiam River 

below RM 18, they are much less extensive because of revetments and channel simplification

than on the North Santiam River. Other native 

fish species that use the North, South, and mainstem Santiam Rivers include rainbow trout, cutthroat trout, northern pike minnow, sand rollers, 

shiners, sculpins, and dace (Gregory and others, 

2007a, 2007b). 

The broad, low-gradient flood plains of the 

Santiam River historically contained a complex 

mosaic of riparian forests and wetlands, which 

has been simplified throughout the study area

since the 1850s. Presently, the riparian forest corridor is nearly contiguous along lower North Santiam River below RM 33, the South Santiam River below RM 18, and the main-stem Santiam 

River below RM 7. Within these sections, the 

forest corridor ranges in width from a narrow 

band of trees to more than 0.7 mi (as shown in 

figs. 32, 34, and 35) and likely includes tree species such as black cottonwood, riparian willows, 

and white alder (Gregory and others, 2007a, 

2007b). These species are associated with the 

more dynamic multi-channel stretches because 

they depend on high flows in winter and spring 

for seed dispersal, active sediment transport and 

deposition to create exposed fine sediment patches for germination, and erosion to remove canopy 

cover that otherwise may preclude establishment. 

Potential Geomorphic and Ecological Response to Environmental Flow Releases

No comprehensive study relating streamflow 

with specific geomorphic or ecological responses

exists for the Santiam River basin. Hence, the 

following section discusses possible effects of 

environmental flow releases on physical habitat 

and riparian ecosystems based on known relations between channel processes and flow and 

sediment regimes and previous environmental

flow studies in the Willamette River basin.

With a wide active channel, abundance of 

gravel bars and secondary channel features, and 

limited revetments, the lower North Santiam River below RM 33 would likely respond dynamically to environmental flow releases. Channel and 

flood-plain response to high-flow releases (including high-flow pulses and small and large 

floods) may include meander migration and possibly avulsions at very high discharges. Bank erosion from meander migration and avulsions 

would likely supply coarse bed-material sediment

for deposition downstream, forming gravel bars, 

riffles, pools, and spawning habitats. Bank erosion along forested portions of the flood plain

could introduce large wood into the active channel, providing cover and habitat complexity for 

fish, amphibians, and mammals and possible

blockages that support further bar growth and 

pool formation. High flows may also support the 

maintenance and creation of secondary channel 

features; scour stabilizing vegetation from relict 

gravel bars depending on flow magnitude; and 

assist with seed dispersal, organic matter exchange between the river and riparian areas, and 

deposition of sediment suitable for seedling germinations. 

Reaches lined by revetment or naturally occurring material resistive to erosion may have 

more limited responses to flow modifications. For 

instance, Reach 6 of the South Santiam below 

RM 18 has extensive revetment that limits bank 

erosion, recruitment of gravel and large wood 

from the flood plain, and creation of new habitats 

suitable to riparian vegetation establishment. Because revetments have also restricted lateral migration and limited bar growth along the South 

Santiam River (Fletcher and Davidson, 1988), 

environmental flow releases on the South Santiam may not be as effective at increasing bar area and spawning habitat as they might be on the 

lower North Santiam River, which has fewer revetments. Other areas unlikely to display dynamic channel response to environmental flow releases include the stable semiconsolidated gravel and 
52

bedrock dominated segments of the study area 

including the North Santiam River (Reaches 1 

and 2) above RM 33 and the South Santiam River 

above RM 18 (Reaches 4, 5, and 6).

Another important consideration of environmental flow releases is the possibility of channel 

incision and bed coarsening in response to high 

flows caused by sediment trapping behind the 

dams. The dams on the North and South Santiam 

Rivers trap sediment from 59 and 47 percent of 

these basins, respectively. The beds of downstream reaches have likely coarsened in response 

to excess transport capacity because dams limit 

sediment supply (National Marine Fisheries Service, 2008; Fletcher and Davidson, 1988). Therefore, it is possible that high-flow releases may 

further coarsen the bed or trigger bed-level lowering, especially along alluvial segments where 

there are limited upstream sources of bed material 

from tributaries or bank erosion. Further assessment of the influence of environmental flow releases on bed coarsening and channel lowering 

would entail development of a bed-material

budget along with a comprehensive analysis of 

historical changes in grain size and bed elevations. 

In addition to modifying physical habitat, 

streamflow also affects the spawning, rearing,

and migration behavior of fish species. Discharge 

during autumn increased throughout the study 

area, which coincides with late summer and early 

autumn spawning by spring Chinook and is followed by lower than historical flows during the 

late winter (table 11). Such flood-control operations in late winter may lead to dewatering of 

salmon redds and could potentially kill incubating eggs and alevins (Reiser and White, 1983).

Additionally, stream-temperature regimes have 

been modified by flow regulations, causing temperatures to be cooler in summer and warmer in 

autumn (Rounds, 2010). Changes to the thermal 

regime can have a direct impact on salmonid 

outmigrations in winter and spawning and incubation in fall (Gregory and others, 2007a, 2007b). 

Reach 5 of the South Santiam River between RM 

30 and RM 35 may be especially sensitive to such 

flow and, probably, stream-temperature fluctuations because spawning of spring Chinook salmon is especially heavy in this area (National Marine Fisheries Service, 2008, section 4.5). Relations between life history and monthly streamflow and stream temperature similar to those developed for the Middle and Coast Fork 

Willamette and McKenzie Rivers (Gregory and 

others, 2007a, 2007b; Risley and others, 2010a) 

could assist in developing basin-specific environmental flow releases for the Santiam River 

basin.

Streamflow patterns also influence other 

aquatic and riparian species. For example, extreme low-flow periods, which can be exacerbated by withdrawals, can lower groundwater levels 

and threaten the survival of riparian seedlings 

such as black cottonwood and white alder (Gregory and others, 2007a, 2007b). In contrast, large 

floods may erode young trees on low-lying floodplain surfaces, but they can also disperse seeds 

and stems and deposit fresh sediment patches at 

lower elevations within the active channel, where 

new seedlings can germinate, ultimately increasing the diversity and age classes of riparian vegetation (Gregory and others, 2007a, 2007b). To 

assist in the development of environmental flow 

releases that aim to increase the diversity and age 

classes of native riparian forests, relations between streamflow and riparian vegetation could 

be created for the Santiam River basin similar to 

those developed for the Middle and Coast Fork 

Willamette and McKenzie River basins (Gregory 

and others, 2007a, 2007b; Risley and others, 

2010a).

Future Studies

This study provides a framework and baseline information for developing environmental 

flow guidelines in the Santiam River basin. Central to a sound environmental flow program is 

establishing robust, quantitative relations between 

streamflow, channel and flood-plain processes, 

and ecosystem response. These relations can be 

quantified by (1) understanding existing channel 
53

and flood-plain processes (post-dam, postrevetment) along lower, alluvial reaches, (2) understanding relations between environmental 

flows and terrestrial and aquatic habitats and species, and (3) documenting existing conditions and 

those following environmental flow releases of 

different magnitudes. Such information would 

provide a solid basis for evaluating future hydrologic, geomorphic, and ecological changes and 

comprehensive adaptive management in the Santiam River basin. To address the three objectives 

above, it will be necessary to evaluate streamflow

data and analyses, bed-load material transport 

rates and sediment budget, channel and floodplain morphology, and terrestrial and aquatic responses to environmental flows. 

Streamflow Data and Analysis 

Modeling and predicting channel and habitat 

response to environmental flow releases requires 

streamflow information, particularly for peak 

flows, when bed-material transport, bank erosion,

and off-channel habitat creation occurs. Although 

there is currently a good network of gages

throughout the Santiam River basin, additional 

streamflow and stage monitoring (both continuous and partial-record) are needed in highpriority, multi-thread reaches to relate geomorphic processes (such as flood-plain inundation and scouring of secondary channels) with 

streamflow. Streamflow data can be tied with 

ecological information, such as hydrologic connectivity between main-stem and off-channel 

habitats during high flows and flow recession, to 

better assess the specific impacts of environmental flow releases on habitat availability to target 

species.

In addition to new data collection, one- or 

two-dimensional hydraulic modeling can be used 

to estimate water-surface elevations during lowflow conditions in reaches that are affected by 

surface-water withdrawals and possible dam operations. This type of modeling can predict habitat loss caused by the dewatering of side channels 

and alcoves in alluvial flood plains.

Bed-Material Transport Rates and Sediment 

Budget 

A sediment budget for the Santiam River basin would help assess the effects of environmental flow releases on channel erosion and aggradation, which affect the quality of terrestrial and 

aquatic habitats. The budget would focus on estimates and (or) measurements of bed-load 

transport, which carries gravel and other material 

that build and maintain spawning habitats, gravel 

bars, and other low-elevation features within the 

active channel. By comparing the volumes of 

gravel exiting the Santiam River basin to the volume of gravel delivered to the study area and the 

volume released through bank erosion, future 

channel change under different flow and sediment-release scenarios can be evaluated.

Because sediment budgets rely on sediment 

transport rates, which are difficult to measure, an 

approach for developing a sediment budget might 

include several of the following methods to estimate sediment transport:

1. Sediment flux estimates based on bedload transport equations (Wallick and others, 2010, 2011). Bed-load transport equations calculate transport capacity, and because bed-material supply has been substantially reduced by the Santiam River 

basin dams, most downstream reaches are 

likely supply limited (meaning the 

transport capacity of the river exceeds the 

available supply of sediment). Sediment 

flux estimates from bed-load transport 

equations applied to alluvial reaches will 

likely provide an estimate of maximum 

plausible transport. 

2. Direct measurements of bed-load 

transport to verify bed-load transport 

equations and to estimate bed-load fluxes. 

Ideally, such measurements would be collected near active USGS gages and downstream from potentially gravel-rich tributaries to provide accurate estimates of total bed-material flux into the lower, alluvial reaches. 
54

3. Empirical GIS-based sediment-yield analyses, factoring in sediment production, 

delivery to the channels, in-channel attrition, and trapping by dams (Wallick and 

others, 2011). 

4. Sediment flux estimates based on mapped 

changes in bank erosion and bar area over 

specific temporal intervals (Wallick and 

others, 2010). Volumetric change in bank 

erosion and bar area can be calculated by 

comparing high-resolution topographic 

data such as LiDAR from two time periods in alluvial reaches. This component 

can also serve as a basis for monitoring 

long-term changes in channel and floodplain conditions.

Detailed Channel and Flood-Plain Morphology 

Assessment 

A detailed assessment of channel morphology in the Santiam River study area is needed to 

better understand current channel and habitat 

conditions and predict changes under different 

environmental flow scenarios. Mapping channel 

and flood-plain conditions for different time periods using high-resolution aerial photographs 

could serve as the starting point for more comprehensive temporal analyses of morphological 

trends. For example, detailed analyses of changes 

in channel features (for example, bar area and 

secondary channel features) could be related to 

patterns of erosion, deposition, and establishment 

of vegetation. These analyses will require accounting for the uncertainties associated with the 

mapping protocols and differences in discharge 

between the aerial photographs.

Terrestrial and Aquatic Responses

To predict ecological response to flow management, knowledge of the relations between 

streamflow, water temperature, sediment fluxes, 

and species of concern and available habitats specific to the Santiam River basin is essential. 

However, at present, only generalized relations

developed for the Middle and Coast Fork 

Willamette River basins (Gregory and others, 

2007a, 2007b) and the McKenzie River basin

(Risley and others, 2010a) are available for use in 

neighboring basins. Additionally, developing 

flow-management strategies to benefit terrestrial 

and aquatic species and habitats would be further 

supported by (1) documentation of terrestrial and 

aquatic conditions representing post-dam streamflow and sediment-transport conditions and the 

baseline for determining the success of future 

flow restorations and (2) supplemental assessments before and after environmental flow releases of different magnitudes to assess terrestrial 

and aquatic responses and to adapt flow releases 

to meet restoration targets.
55

Summary

This report provides a baseline assessment of 

the hydrology, geomorphology, and effect of 

streamflow on the ecology of the Santiam River,

a tributary of the Willamette River in northwestern Oregon. The assessment was made for the 

Santiam River environmental flow study, which 

is a collaborative effort of the U.S. Army Corps 

of Engineers, The Nature Conservancy, and the 

U.S. Geological Survey (USGS) under auspices 

of the Sustainable Rivers Project. In 2002, The 

Nature Conservancy and the U.S. Army Corps of 

Engineers began the Sustainable Rivers Project 

for the purpose of modifying dam operations and 

implementing environmental flow requirements 

for various river systems around the country. Information from this report can assist water managers and stakeholders in the development of future environmental flow requirements for the 

Santiam River basin.

The Santiam River basin has an area of 1,810 

mi2; elevations range from 162 ft at the 

Willamette River confluence to almost 10,500 ft 

in the Cascade Range. The two main tributaries in 

the basin are the North and South Santiam Rivers,

which join approximately 9 mi upstream from the

Willamette River. Higher elevations in the basin 

are underlain by young, relatively permeable material consisting of High Cascade volcanic rocks 

and glacial deposits. Middle and lower elevations 

of the basin contain older, weathered, less permeable volcanic material characteristic of the Western Cascades. The lower reach in the wide unconstrained flood plain near the Willamette confluence is composed of Quaternary alluvium. Downstream reaches of the basin are mostly privately 

owned and used for agriculture. Approximately 

70 percent of the basin is forested. The basin has

long, cool, wet winters and warm, dry summers. 

Average daily maximum and minimum temperatures at Stayton from 1951 to 2011 were 63 and 

42°F, respectively. 

The U.S. Army Corps of Engineers owns and 

operates four dams in the Santiam River basin. 

The Detroit and the Big Cliff Dams, on the North 

Santiam River, were put into service in 1953. In 

1968 the Green Peter and Foster Dams were 

completed in the South Santiam River basin. The 

dams are operated to provide flood control, hydropower production, irrigation, water supply, 

recreation, water-quality improvement, and 

aquatic habitat. Surface-water withdrawals within 

the Santiam River basin for municipal water supply and irrigation are made at various locations 

downstream from the dams. The LebanonSantiam Canal diverts approximately 90 ft3

/s

from the South Santiam River upstream from

Lebanon. The USGS has operated a network of 

continuous streamflow monitoring throughout the 

Santiam River basin since the 1920s. The stations 

with the longest streamflow records are the North 

Santiam River at Mehama (14183000: 1921–

2011) and the South Santiam River at Waterloo 

(14187500: 1923–2011). 

Seven river reaches, each having distinct 

streamflow, geomorphic, and ecological conditions, were defined for the study area. The North 

Santiam River was divided into three reaches between Detroit Dam and the confluence with the 

South Santiam River. The South Santiam River 

was also divided into three reaches between 

Green Peter Dam and the North Santiam River 

confluence. The final reach along the main-stem 

Santiam River is between the confluence of the 

North and South Santiam Rivers and the 

Willamette River confluence. 

To assess the effects of dams and withdrawals on the streamflow regime, measured daily

mean streamflow and annual peak-flow data were 

compiled and used to compute statistics that describe regulated and unregulated conditions. In all 

seven study reaches, the dams had the effect of 

decreasing annual high flows. For the North Santiam River Reaches 1, 2, and 3, the median of annual 1-day maximum streamflows decreased 42, 

50, and 50 percent, respectively, under regulated 

streamflow conditions. Likewise in the South 

Santiam River basin, the median of annual 1-day 

maximum streamflows for Reaches 4, 5, and 6 

decreased 39, 52, and 51 percent, respectively. In 
56

contrast to their effect on high flows, the dams 

had the effect of increasing low flows. The median of annual 7-day minimum flows in six of the 

seven study reaches increased under regulated 

streamflow conditions from 25 to 334 percent

depending on the reach. On a seasonal basis, median monthly streamflows decreased from February to May and increased from September to January in all the reaches. However, the magnitude

of these changes usually decreased in the reaches 

farther downstream from dams because of natural

tributary and groundwater inflow entering the 

river below the dams. At the North Santiam River 

at Mehama gage, bankfull discharge was exceeded on average 3.39 times per year prior to construction of the dams in 1953. After the dams 

were built, bankfull discharge has been exceeded 

on average only 0.97 times per year. Farther 

downstream from the dams at the Santiam River 

at Jefferson gage, bankfull discharge was exceeded on average 7.46 times per year prior to the 

construction of the dams in 1953. After the dams 

were built, bankfull discharge has been exceeded,

on average, 4.12 times per year. Climatic differences between the pre- and post-dam periods also 

were assessed in the study. A Wilcox rank-sum 

test of monthly precipitation data from Salem and

Waterloo found no significant difference between 

the two periods. That would suggest that the operation of the dams since the 1950s and 1960s is

the primary cause of alterations to the Santiam 

River basin streamflow regime.

The geomorphology and the possible geomorphic and ecological changes in response to 

river-flow modifications were characterized. The 

characterization was based primarily on qualitative observations and information from previous 

studies. Channel processes, including meander 

migration, bar growth, and creation and maintenance of secondary channel features, are mainly 

determined by the flow and coarse-sediment regimes; however, these processes have been altered by flow releases from the upstream dams.

The North Santiam River below Big Cliff 

Dam transitions from a narrow channel confined 

by steep bedrock valley walls to a broad, alluvial 

river with many side channels and gravel bars 

before joining the South Santiam River near Jefferson. Overall, there is little revetment along the 

North Santiam study reaches. 

The South Santiam River below Foster Dam 

occupies mostly a low-sinuosity, single-thread 

channel with a flood plain. Active gravel bars are 

sparse and small (less than 1,500 yd2). Instead,

the reach has a number of densely vegetated bar 

surfaces relict of gravel bars that were active before dam and revetment construction. Much of 

the reach presently is stabilized by revetments 

constructed in the mid- to late 20th century. Bank 

stabilization, in combination with construction of 

the Foster and Big Cliff Dams, resulted in substantial reductions in channel complexity.

The main-stem Santiam River below the confluence of the North and South Santiam Rivers 

historically had dynamic, multi-thread channels 

that were prone to rapid meander migration and 

avulsion prior to flood control and bank protection. The reach flows through a broad flood plain

that ranges up to 3 mi wide. However, bank revetment currently flanks much of the channel, 

restricting bank erosion, channel complexity, and 

bar growth. Many relict bar surfaces and secondary channel features presently have dense vegetative cover.

Historically, the Santiam River basin supported diverse aquatic and terrestrial ecosystems 

ranging from steep, pool-riffle channel systems, 

abundant large wood, and riparian forests dominated by upland species in the upper reaches to 

dynamic multi-thread channels containing offchannel and secondary features, with alder and 

cottonwood forests flanking and interacting with 

the channel in the lower reaches and main stem. 

Similar to the Middle and Coast Fork Willamette 

and McKenzie River basins, many of these habitats have been substantially altered by modifications in the river flow and sediment regimes or 

are inaccessible because of passage issues at 

dams. The streamflow analysis and geomorphic 

characterization provide a framework to develop 
57

environmental flows to restore the historic diverse aquatic and terrestrial ecosystems. 

Suggestions for future ecological monitoring 

and investigations in the Santiam River basin include additional streamflow data collection and 

analysis, computing bed-material transport rates 

and a sediment budget, a detailed channel and 

flood-plain morphology assessment, and determining terrestrial and aquatic responses to 

streamflow management.

Acknowledgements

The authors thank Christine Budai, Keith 

Duffy, Jerry Otto, and Greg Taylor, Portland District, U.S. Army Corps of Engineers; Leslie Bach, 

The Nature Conservancy, Portland, Oregon; Mike 

McCord and Michael Mattick, Oregon Water Resources Department; and Jay Spillum, U.S. Geological Survey Oregon Water Science Center for 

their assistance in this study.

References Cited

Acreman, M., and Dunbar, M.J., 2004, Defining 

environmental flow requirements–A review: 

Hydrology and Earth System Sciences, v. 8, no. 

5, p. 861–876.

Bragg, H.M., Sobieszczyk, Steven, Uhrich, M.A., 

and Piatt, D.R., 2007, Suspended-sediment 

loads and yields in the North Santiam River basin, Oregon, water years 1999-2004: U.S. Geological Survey Scientific Investigations Report 

2007–5187, 27 p.

Bragg, H.M., and Uhrich, M.A., 2010, Suspended-sediment budget for the North Santiam River basin, Oregon, water years 2005–08: U.S. 

Geological Survey Scientific Investigations 

Report 2010–5038, 26 p.

Buccola, N.L., and Rounds, S.A., 2011, Simulating potential structural and operational changes 

for Detroit Dam on the North Santiam River, 

Oregon—Interim Results: U.S. Geological 

Survey Open-File Report 2011–1268, 25 p.

Conlon, T.D., Wozniak, K.C., Woodcock, Douglas, Herrera, N.B., Fisher, B.J., Morgan, D.S., 

Lee, K.K., and Hinkle, S.R., 2005, Groundwater hydrology of the Willamette basin, Oregon: U.S. Geological Survey Scientific Investigations Report 2005–5168, 83 p.

Cooper, R.M., 2002, Determining surface water 

availability in Oregon: State of Oregon Water 

Resources Department Open-File Report SW 

02–002, 157 p.

E and S Environmental Chemistry, Inc., 2002, 

North Santiam River watershed assessment: 

Corvallis, Oregon, 290 p., accessed July 2, 

2012, at

http://www.nsantiamwatershed.org/wp-content

/uploads/2009/09/NSW_Assessment.pdf.

E and S Environmental Chemistry, Inc., and 

South Santiam Watershed Council, 2000, South 

Santiam watershed assessment: Corvallis, Oregon, 224 p., accessed July 2, 2012, at

http://www.sswc.org/wpcontent/uploads/2008/12/South-SantiamWatershed-Assessment-January-2000.pdf.

Fletcher, W.B., and Davidson, L.D., 1988, South 

Santiam River Bank Protection Study, Pilot 

Project for Willamette River Bank Protection 

Study: Portland, Oregon, U.S. Army Corps of 

Engineers, 36 p. 

Gregory, S., Ashkenas, L., Haggerty, P., Oetter, 

D., Wildman, K., Hulse, D., Branscomb, A. and 

Van Sickle, J., 2002a, Riparian vegetation, in

Hulse, D., Gregory, S., and Baker, J., eds., 

Willamette River basin atlas: Corvallis, Oregon, Oregon State University Press, p. 40., accessed July 2, 2012, at

http://www.fsl.orst.edu/pnwerc/wrb/Atlas_web_

compressed/4.Biotic_Systems/4c.riparian_

veg_web.pdf.

Gregory, S., Ashkenas, L., Oetter, D., Minear, P. 

and Wildman, K., 2002b, Historical Willamette 

River channel change, in Hulse, D., Gregory, 

S., and Baker, J., eds., Willamette River basin 

atlas: Corvallis, Oregon, Oregon State University Press, p. 18–24., accessed July 2, 2012, at

http://www.fsl.orst.edu/pnwerc/wrb/

Atlas_web_compressed/

3.Water_Resources/3c.historic_chl_web.pdf.
58

Gregory, S., Ashkenas, L., and Nygaard, C., 

2007a, Summary report to assist development 

of ecosystem flow recommendations for the 

Middle Fork and Coast Fork of the Willamette 

River, Oregon: Corvallis, Oregon, Institute for 

Water and Watersheds, Oregon State University, 237 p. 

Gregory, S., Ashkenas, L., and Nygaard, C., 

2007b, Summary report—Environmental flows 

workshop for the Middle Fork and Coast Fork 

of the Willamette River, Oregon: Corvallis, Oregon,Institute for Water and Watersheds, Oregon State University, 34 p.

Hansen, R.P., and Crumrine, M.D., 1991, The 

effects of multipurpose reservoirs on the water 

temperature of the North and South Santiam 

Rivers, Oregon: U.S. Geological Survey Water 

Resources Investigation Report 91–4007, 51 p.

Helm, D.C., and Leonard, A.R., 1977, Groundwater resources of the lower Santiam River basin, middle Willamette Valley, Oregon: Oregon 

Water Resources Department--Groundwater 

Reports, vii, 75 p.

Hill, B.E., and Priest, G.R., 1992, Geologic setting of the Santiam Pass area, central Cascade 

Range, Oregon: State of Oregon, Department 

of Geology and Mineral Industries Open-File 

Report, O-92-3, pp. 5–18

Interagency Committee on Water Data, 1982, 

Guidelines for determining flood flow frequency—Bulletin #17B of the Hydrology Subcommittee: Reston, Virginia, U.S. Geological Survey, accessed April 27, 2012, at 

http://water.usgs.gov/osw/bulletin17b/

dl_flow.pdf.

Klingeman, P.C., 1973, Indications of streambed 

degradation in the Willamette Valley: Corvallis, Oregon, Oregon State University, Water 

Resources Research Institute Report WRRI–21, 

99 p.

Laenen, Antonius, and Risley, J.C., 1997, Precipitation-runoff and streamflow-routing models for the Willamette River basin, Oregon: 

U.S. Geological Survey Water-Resources Investigations Report 95–4284, 197 p.

Laenen, Antonius, and Hansen, R.P., 1985, Preliminary study of the water-temperature regime 

of the North Santiam River downstream from 

Detroit and Big Cliff Dams, Oregon: U.S. Geological Survey Water Resources Investigation 

Report 84–4105, 45 p.

Lee, K.K., and Risley, J.C., 2002, Estimates of 

ground-water recharge, base flow, and stream

reach gains and losses in the Willamette River 

basin, Oregon: U.S. Geological Survey WaterResources Investigations Report 01–4215, 52 p.

National Marine Fisheries Service, 2008a, Endangered Species Act Status of West Coast 

Salmon and Steelhead: , Seattle, Washington, 

NOAA National Marine Fisheries Service, 

Northwest Region, accessed May 22, 2012, at 

http://www.nwr.noaa.gov/ESA-SalmonListings/upload/1-pgr-8-11.pdf.90

National Marine Fisheries Service, 2008b, Endangered Species Act Section 7(a)(2) Consultation biological opinion and Magnuson-Stevens 

fishery conservation and management act essential fish habitat consultation: Seattle, Washington,NOAA National Marine Fisheries Service, Northwest Region, NOAA Fisheries Log 

Number FINWRl2000/02117, [various pagination], accessed January 16, 2012, at 

http://www.nwr.noaa.gov/SalmonHydropower/Willamette-basin/WillametteBO.cfm.

O’Connor, J.E., Sarna-Wojcicki, Andrei, Wozniak, K.C., Polette, D.J., and Fleck, R.J., 2001, 

Origin, extent, and thickness of Quaternary geologic units in Willamette Valley, Oregon: U.S. 

Geological Survey Professional Paper 1620, 52 

p. Dataset available online at 

http://or.water.usgs.gov/pubs_dir/Online/Cd/

WRIR99-4036/GIS_FILES/will_geol.html, accessed January 11, 2012.

Oregon Department of Environmental Quality, 

2006, Willamette basin total maximum daily 

load order memorandum: accessed November 

30, 2011, at 

http://www.deq.state.or.us/wq/tmdls/docs/willa

mettebasin/willamette/ordermemo.pdf.
59

Oregon Water Resources Department, 2012, Water use reporting database: accessed March 7, 

2012, at 

http://apps.wrd.state.or.us/apps/wr/wateruse_

report/.

Piatt, D.R., Johnston, M.W., Bragg, H.M., 

Brooks, A.M., Sobieszczyk, Steven, and 

Uhrich, M.A., 2011, Water-quality in the North 

Santiam River basin, Oregon—Comparison of 

water-quality data for water year 2007 with the 

preceding period of record: U.S. Geological 

Survey Open-File Report 2011–1008, 75 p.

Reiser, D.W., and White, R.G., 1983, Effects of 

complete redd dewatering on salmonid egghatching success and development of juveniles:

Transactions of American Fisheries Society, v.

112, p. 532–540.

Richter, B.D., Warner, A.T., Meyer, J.L., and 

Lutz, K., 2006, A collaborative and adaptive 

process for developing environmental flow recommendations: River Research and Applications, v. 22, p. 297–318, DOI: 10.1002/rra.892.

Risley, John, Wallick, J.R., Waite, Ian, and 

Stonewall, Adam, 2010a, Development of an 

environmental flow framework for the McKenzie River basin, Oregon: U.S. Geological Survey Scientific Investigations Report 2010–

5016, 94 p.

Risley, J.C., Bach, L., and Wallick, J.R., 2010b, 

Summary report—Environmental flows workshop for the McKenzie River, Oregon: The Nature Conservancy, Portland, Oregon, 40 p.

Rounds, S.A., 2010, Thermal effects of dams in 

the Willamette River basin, Oregon: U.S. Geological Survey Scientific Investigations Report 

2010–5153, 64 p.

Sherrod, D., Ingebritsen, S.E., Curless, J.M., 

Keith, T.E., Diaz, N.M., and DeRoo, T.G., and 

Hurlocker, S.L., 1996, Water, rocks, and 

woods; a field excursion to examine the geology, hydrology, and geothermal resources in the 

Clackamas, North Santiam, and McKenzie 

River drainages, Cascade Range, Oregon: Oregon Geology, v. 58, no. 5, 103 p.

Sobieszczyk, Steven, Uhrich, M.A., and Bragg, 

H.M., 2007, Major turbidity events in the North 

Santiam River basin, Oregon, water years 

1999–2004: U.S. Geological Survey Scientific 

Investigations Report 2007–5178, 51 p.

Speers, D.D., and Versteeg, J.D., 1982, Runoff 

forecasting for reservoir operations—The past 

and the future (Santiam River basin, Detroit 

reservoir), Proceedings of the Eastern Snow 

Conference, 39th annual meeting, April 19–23, 

Reno, Nevada: p. 149–156.

Sullivan, A.B., and Rounds, S.A., 2004, Modeling streamflow and water temperature in the 

North Santiam and Santiam Rivers, Oregon, 

2001–02: U.S. Geological Survey Scientific Investigations Report 2004–5001, 36 p.

Sullivan, A.B., Rounds, S.A., Sobieszczyk, Steven, and Bragg, H.M., 2007, Modeling hydrodynamics, water temperature, and suspended 

sediment in Detroit Lake, Oregon: U.S. Geological Survey Scientific Investigations Report 

2007–5008, 40 p.

Tharme, R.E., 2003, A global perspective on environmental flow assessment: emerging trends 

in the development and application of environmental flow methodologies for rivers: River 

Research and Applications, v. 19, p. 397–441, 

DOI: 10.1002/rra.736.

Thayer, T.P., 1936, Geology of the Salem Hills 

and the North Santiam River basin, Oregon: 

Oregon Department of Geology and Mineral 

Industries, Bulletin no. 15, 40 p.

Thayer, T.P., 1936, Structure of the North Santiam River section of the Cascade Mountains in 

Oregon: The Journal of Geology, v. 44, no. 6, 

p. 701–716.

The Nature Conservancy, 2007, Indicators of hydrologic alteration—Version 7 User’s manual: 

The Nature Conservancy, 75 p., accessed December 19, 2011, at

http://conserveonline.org/workspaces/iha/docu

ments/download/view.html.

The Nature Conservancy, 2009, The Sustainable 

Rivers Project: accessed November 18, 2011, at 
60

http://www.nature.org/ourinitiatives/habitats/ri

verslakes/sustainable-rivers-project.xml

Uhrich, M.A., and Bragg, H.M., 2003, Monitoring instream turbidity to estimate continuous 

suspended-sediment loads and yields and claywater volumes in the Upper North Santiam 

River basin, Oregon, 1998–2000: U.S. Geological Survey Water Resources Investigation Report 03–4098, 44 p.

U.S. Army Corps of Engineers (USACE), 2007, 

Supplemental biological assessment of the effects of the Willamette River basin flood control project on species listed under the Endangered Species Act—Submitted to National Marine Fisheries Service and U.S. Fish and Wildlife Service, [variously paged]: accessed May 

22, 2012, at

http://www.nwp.usace.army.mil/Portals/24/doc

s/environment/biop/Final_Will_Suppl_BA.pdf

U.S. Fish and Wildlife Service (USFWS), 2008, 

Final Biological Opinion on the continued operation and maintenance of the Willamette River basin Project and effects to Oregon Chub, 

Bull Trout, and Bull Trout Critical Habitat designated under the Endangered Species Act—

Submitted to U.S. Army Corps of Engineers, 

Bonneville Power Administration, and Bureau 

of Reclamation, [variously paged]: accessed 

January 16, 2012, at 

http://www.nwr.noaa.gov/SalmonHydropower/Willamette-basin/WillametteBO.cfm.

U.S. Geological Survey, 2012, StreamStats: accessed March 7, 2012, at 

http://water.usgs.gov/osw/streamstats

/index.html.

Wallick, J.R., Lancaster, S.T., and Bolte, J.P., 

2006, Determination of bank erodibility for 

natural and anthropogenic bank materials using 

a model of lateral migration and observed erosion along the Willamette River, Oregon—

USA: River Research and Applications, v. 22, 

p. 631–649.

Wallick, J.R., Grant, G.E., Lancaster, S.T., Bolte, 

J.P., and Denlinger, R.P., 2007, Patterns and 

controls on historical channel change in the 

Willamette River, Oregon, in Gupta, A.V., ed., 

Large rivers—Geomorphology and management: John Wiley and Sons, p. 491–516. 

Wallick, J.R., Anderson, S.W., Cannon, Charles, 

and O’Connor, J.E., 2010, Channel change and 

bed-material transport in the lower Chetco River, Oregon: U.S. Geological Survey Scientific 

Investigations Report 2010–5065, 68 p.

Wallick, J.R., O'Connor, J.E., Anderson, Scott, 

Keith, Mackenzie, Cannon, Charles, and Risley, J.C., 2011, Channel change and bedmaterial transport in the Umpqua River basin, 

Oregon: U.S. Geological Survey Scientific Investigations Report 2011–5041, 112 p., accessed November 10, 2011, at 

http://pubs.usgs.gov/sir/2011/5041/.

Western Regional Climate Center, 2012, Website—Cooperative climatological data summaries: accessed June 14, 2012, at 

http://www.wrcc.dri.edu/climatedata/climsum/.

Wolman, M.G., and Miller, J.P., 1960, Magnitude 

and frequency of forces in geomorphic processes: Journal of Geology, v. 68, no. 1, p. 54–

74.
61

Appendix A. Streamflow Data Time-Series Extension

Microsoft® Excel® files containing the daily mean streamflow data time-series extensions for each

of the seven study reaches can be downloaded from http://pubs.usgs.gov/of/2012/1133/.

In each file, there is a “Read me” worksheet that explains how the streamflow time series for the 

reach was extended to cover missing periods. Each file also includes computed unregulated daily-mean 

streamflow data time series, provided by the U.S. Army Corps of Engineers, which were used in the 

study. The equations used to compute the unregulated daily-mean streamflow time series are provided 

in Appendix B.

Appendix B. U.S. Army Corps of Engineers Computed Unregulated Streamflow 

Data Time Series

This appendix contains methods and equations from U.S. Army Corps of Engineers used to compute six daily mean unregulated streamflow time series for the Santiam River basin (Keith Duffy, U.S. 

Army Corps of Engineers, written commun., 2011). One or more of these six time series were used in 

each of the seven Excel files described in Appendix A. However, all six time series are shown together 

in the worksheet labeled “2. Unregulated flow” in the Flow_extension_reach7.xls Excel file.

1. North Santiam River at Detroit Dam

10/01/1935–09/30/1938

Combined observed flows of:

USGS 14178000 (North Santiam River above Boulder Creek near Detroit, Oregon) and

USGS 14179000 (Breitenbush River above French Creek near Detroit, Oregon)

Plus local inflows computed as:

USGS 14183000 (North Santiam River at Mehama, Oregon)

Minus the sum of:

USGS 14182500 (Little North Santiam River near Mehama, Oregon),

USGS 14178000 (lagged by 6 hours), and

USGS 14179000 (lagged by 6 hours)

Adjusted by a drainage area ratio (DAR) of 0.509

10/01/1938–10/30/1952

Observed flow of:

USGS 14181500 (North Santiam River at Niagara, Oregon)

Adjusted by DAR (0.960)
62

10/01/1952–09/30/1960

Calculated inflow (Modified Flows)

Adjusted by DAR (0.960)

10/01/1960–09/30/2009

Quality controlled Dataquery project inflows

2. Local inflows to North Santiam River at Mehama, Oregon (14183000)

10/01/1935–09/30/1938

Observed flow of:

USGS 14172500 (Little North Santiam River near Mehama, Oregon)

Plus local inflows computed as:

USGS 14183000 (North Santiam River at Mehama, Oregon)

Minus the sum of:

USGS 14182500 (Little North Santiam River near Mehama, Oregon), 

USGS 14178000 (lagged by 6 hours), and

USGS 14179000 (lagged by 6 hours)

Adjusted by DAR (0.491)

10/01/1938–09/30/2009

Observed flow of:

USGS 14183000 (North Santiam River at Mehama, Oregon)

Minus routed flow of:

USGS 14181500 (North Santiam River at Niagara, Oregon)

Adjusted by DAR (1.091)

3. Middle Santiam River at Green Peter Dam

10/01/1935–09/30/1947

Observed flow of:

USGS 14186000 (Middle Santiam River near Foster, Oregon)
63

10/01/1947–09/30/1950

Observed flow of:

USGS 14185000 (South Santiam River below Cascadia, Oregon) 

Adjusted by regression coefficient (2.022)

10/01/1950–09/30/1966

Observed flow of:

USGS 14186500 (Middle Santiam River at mouth near Foster, Oregon)

Adjusted by DAR (0.959)

10/01/1966–06/21/1967

Combined observed flow of:

USGS 14185800 (Middle Santiam River near Cascadia, Oregon) and

USGS 14185900 (Quartzville Creek near Cascadia, Oregon)

Sum adjusted by regression coefficient (1.245)

06/22/1967–09/30/2009

Calculated inflow (Dataquery)

4. Local inflows to South Santiam River at Foster Dam

10/1/1935–8/22/1968

Observed flow of:

USGS 14185000 (South Santiam River below Cascadia, Oregon)

Adjusted by regression coefficient (1.194)

8/23/1968–9/30/2009

Calculated inflow (Dataquery) minus Green Peter outflow (Dataquery)

5. Local inflows to South Santiam River at Waterloo, Oregon (14187500)

10/01/1935–09/30/1947

Observed flow of:

USGS 14187500 (South Santiam River at Waterloo, Oregon)
64

Minus combined routed flow of:

USGS 14185000 (South Santiam River below Cascadia, Oregon) and

USGS 14186000 (Middle Santiam River near Foster, Oregon)

Adjusted by DAR (0.761)

10/01/1947–09/30/1950

Observed flow of:

USGS 14187500 (South Santiam River at Waterloo, Oregon)

Minus routed flow of:

USGS 14185000 (South Santiam River below Cascadia, Oregon)

Adjusted by DAR (0.318)

10/01/1950–09/30/1966

Observed flow of:

USGS 14187500 (South Santiam River at Waterloo, Oregon)

Minus combined routed flow of:

USGS 14185000 (South Santiam River below Cascadia, Oregon) and

USGS 14186500 (Middle Santiam River at mouth near Foster, Oregon)

Adjusted by DAR (0.829)

10/01/1966–07/31/1973

Observed flow of:

USGS 14187500 (South Santiam River at Waterloo, Oregon)

Minus routed flow of:

USGS 14186700 (South Santiam River at Foster, Oregon)

08/01/1973–09/29/1988

Observed flow of:

USGS 14187500 (South Santiam River at Waterloo, Oregon)

Minus routed flow of:

USGS 14187200 (South Santiam River near Foster, Oregon)

Adjusted by DAR (1.037)

Plus routed flow of:

USGS 14187100 (Wiley Creek at Foster, Oregon)
65

09/30/1988 -09/30/2009

Observed flow of:

USGS 14187500 (South Santiam River at Waterloo, Oregon)

Minus routed flow of:

USGS 14187200 (South Santiam River near Foster, Oregon)

Adjusted by DAR (1.164)

Plus routed flow of:

USGS 14187000 (Wiley Creek near Foster, Oregon)

6. Local inflows to Santiam River at Jefferson, Oregon (14189000)

10/01/1935–09/30/1939

Observed flow of:

USGS 14191000 (Willamette River at Salem, Oregon)

Minus combined routed flows of:

USGS 14187500 (South Santiam River at Waterloo, Oregon), 

USGS 14183000 (North Santiam River at Mehama, Oregon), and

USGS 14174000 (Willamette River at Albany, Oregon)

Adjusted by DAR (0.433)

10/01/1939–09/30/2009

Observed flow of:

USGS 14189000 (Santiam River at Jefferson, Oregon)

Minus combined routed flows of:

USGS 14187500 (South Santiam River at Waterloo, Oregon)

USGS 14183000 (North Santiam River at Mehama, Oregon)
66

Appendix C. Indicators of Hydrologic Alteration Results

Microsoft Excel files containing the results of the Indicator of Hydrologic Alteration analysis for 

each of the seven study reaches may be downloaded from http://pubs.usgs.gov/of/2012/1133/.

Appendix D. Description of Study Reaches

A Microsoft Excel spreadsheet containing descriptions of the seven study reaches may be accessed 

at http://pubs.usgs.gov/of/2012/1133/.
Risley and others— An Environmental Streamflow Assessment for the Santiam River Basin, Oregon—Open-File Report 2012–1133