U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2018–5161

Prepared in cooperation with the U.S. Army Corps of Engineers and Levee Ready Columbia

Assessment of Columbia and Willamette River Flood 

Stage on the Columbia Corridor Levee System at 

Portland, Oregon, in a Future Climate
Cover: Photograph showing Willamette Falls on Willamette River looking downstream. 

Photograph by U.S. Army Corps of Engineers, February 1996.
Assessment of Columbia and Willamette 

River Flood Stage on the Columbia Corridor 

Levee System at Portland, Oregon, in a 

Future Climate

By Susan A. Wherry, Tamara M. Wood, Hans R. Moritz, and Keith B. Duffy

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

and Levee Ready Columbia

Scientific Investigations Report 2018–5161

U.S. Department of the Interior

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

DAVID BERNHARDT, Acting Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Wherry, S.A., Wood, T.M., Moritz, H.R., and Duffy, K.B., 2019, Assessment of Columbia and Willamette River flood 

stage on the Columbia Corridor Levee System at Portland, Oregon, in a future climate: U.S. Geological Survey 

Scientific Investigations Report 2018-5161, 44 p., https://doi.org/10.3133/sir20185161.

ISSN 2328-0328 (online)
iii

Contents

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

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

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

Hydrology and Morphology of the Lower Columbia River.............................................................2

Effects of Climate Change on Streamflow in the Pacific Northwest ...........................................7

Previous Climate Change Studies......................................................................................................7

Selection of Prototype Flood ..............................................................................................................9

Methods.........................................................................................................................................................10

Datasets Used for Hydraulic Models ..............................................................................................10

Model Terrain Data....................................................................................................................11

Aerial Images ....................................................................................................................11

Historical Flood Boundary Conditions....................................................................................11

Hourly Flow Hydrographs at the Upstream Boundaries ............................................11

Water-Surface Elevations Offshore of the Mouth of the Columbia River ...............13

Historical Events Calibration Data ..........................................................................................13

Future Climate Boundary Conditions......................................................................................13

Hydrology and Streamflows............................................................................................13

Water-Surface Elevations Offshore of the Mouth of the Columbia River ...............15

Two-Dimensional River Stage Modeling.........................................................................................17

Hydraulic Model Comparison ..................................................................................................18

Delft3D-Flexible Mesh...............................................................................................................22

Lower Columbia River Model Development.................................................................22

Lower Columbia River Model for Climate Change Study ...........................................22

Adaptive Hydraulics (AdH) Model ..........................................................................................24

Lower Columbia River Model Development.................................................................24

Lower Columbia River Model for Climate Change Study ...........................................24

Historical Simulations .................................................................................................................................26

Simulations for 1996............................................................................................................................26

Simulations for 1997............................................................................................................................34

Future Climate Scenarios ...........................................................................................................................34

Summary and Conclusions.........................................................................................................................40

Acknowledgments.......................................................................................................................................42

References Cited..........................................................................................................................................42
iv

Figures

1. Map showing locations of model domains and measurement sites along the

Columbia and Willamette Rivers near Portland, Oregon .......................................................3

2. Map showing Columbia corridor levee system including locations of drainage

district areas and drainage improvement company area near Portland, Oregon ............4

3. Map showing land-surface elevations, levees, and pile dikes in the Columbia River

for river miles 28 to 48, near Astoria, Oregon...........................................................................5

4. Map showing land-surface elevations, levees, and pile dikes near the confluence

of the Columbia and Willamette Rivers and near Multnomah County Drainage

District levees, Portland, Oregon ...............................................................................................6

5. Graphs showing scenarios for global greenhouse gas emissions and surface

warming projections from 2000 to 2100.....................................................................................8

6. Boxplots showing change in mean annual precipitation and temperature in all

future climate scenarios considered by the River Management Joint Operating

Committee, and the changes in the warmer and wetter scenario considered in this

study ...............................................................................................................................................9

7. Graphs showing future inflow flood hydrographs for the Columbia River at

Bonneville Dam and the Willamette River below Willamette Falls, Oregon.....................15

8. Graph showing estimated sea-level change scenarios at Astoria, Oregon.....................16

9. Graph showing storm surge peak water levels at Toke Point, Washington, March

1999, February 2006, and December 2007...............................................................................17

10. Graph showing simulated astronomical tide, storm surge, and future tidal

conditions at the mouth of the Columbia River, Oregon and Washington.........................18

11. Maps showing comparison of Delft3D-Flexible Mesh (Delft3D-FM) (A) and Adaptive

Hydraulics (AdH) (B) model meshes with assignments of elevation along the

Columbia and Willamette Rivers, Oregon...............................................................................19

12. Mesh diagrams showing comparison of Delft3D-Flexible Mesh (Delft3D-FM) mesh

with assignments of bathymetry (A) and roughness coefficients (B), to Adaptive

Hydraulics (AdH) mesh with assignments of bathymetry (C) and mesh material

types (D) along the Columbia and Willamette Rivers, Oregon............................................20

13. Graphs showing measured and simulated time series on the Columbia River at

Astoria, Oregon, 1996 and 1997 ................................................................................................28

14. Graphs showing measured and simulated water-surface elevations at the

Willamette River at Morrison Bridge, Oregon, 1996 and 1997.............................................29

15. Graphs showing measured and simulated water-surface elevations at the

Columbia River at Vancouver, Washington, 1996 and 1997 .................................................30

16. Stream profile showing simulated water-surface elevation, river miles 0–150,

Columbia River, Oregon and Washington...............................................................................32

17. Stream profile showing future simulated maximum river stage from AdH and

Delft3D-FM models along the Columbia River, Oregon and Washington..........................35

18. Time series graphs showing simulated future water-surface elevations from AdH

and Delft3D-FM models, Columbia River at Astoria, Oregon ..............................................36

19. Time series graphs showing measured historical and simulated future

water-surface elevations from AdH and Delft3D-FM models, Willamette River at

Morrison Bridge, Oregon...........................................................................................................38

20. Time series graphs showing measured historical and simulated future

water-surface elevations from AdH and Delft3D-FM models, Columbia River at

Vancouver, Washington.............................................................................................................39
v

Tables

1. Definitions of greenhouse gas emissions scenarios..............................................................9

2. Sources and types of data from measurement sites in the Columbia and Willamette

River Basins, Oregon and Washington. .................................................................................12

3. Peak-flow rankings for historical winter unregulated flow and future winter

unregulated flow, Columbia and Willamette Rivers, Oregon, winter 1996........................14

4. Timeline of peak stage and discharge in future climate prototype flood along the

Columbia and Willamette Rivers, Oregon and Washington ................................................17

6. Elevation data compiled from light detection and radar surveys along the Columbia

corridor levee system, Oregon and Washington...................................................................21

5. Model roughness values for Delft3D-Flexible Mesh (Delft3D-FM) and Adaptive

Hydraulics (AdH) along the Columbia and Willamette Rivers, Oregon..............................21

7. Hydraulic model performance statistics, Willamette and Columbia Rivers, Oregon

and Washington, 1996 and 1997 ...............................................................................................30

8. Comparison of peak stage for historical simulations, Willamette and Columbia

Rivers, Oregon and Washington, 1996 and 1997....................................................................31

9. High-water marks measured by CH2MHILL for the U.S. Army Corps of Engineers

along the Columbia River, Oregon and Washington, February 1996 ..................................33

10. Measured historical and simulated future peak stage and projected sea-level

change for selected areas in the Willamette and Columbia Rivers, Oregon and

Washington..................................................................................................................................37
vi

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

International System of Units to U.S. customary units

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 247.1 acre

square kilometer (km2) 0.3861 square mile (mi2)

Volume

cubic kilometer (km3) 0.2399 cubic mile (mi3) 

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

Flow rate

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

cubic meter per second per 

square kilometer ([m3/s]/km2)

91.49 cubic foot per second per square 

mile ([ft3/s]/mi2)

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

°F = (1.8 × °C) + 32.

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88) unless indicated otherwise in the text. 

Mean lower low water (MLLW) is calculated at Astoria, Oregon, during the 1983–2001 epoch.

Mean sea level is calculated at Astoria, Oregon, during the 1983–2001 epoch and is 1.37 m 

(4.51 ft) above MLLW.

The Columbia River Datum (CRD) plane for areas downstream of Harrington Point, Washington, 

is based on MLLW. Upstream of Harrington Point to Bonneville Dam, zero CRD roughly 

corresponds to the river level at minimum operating discharge from Bonneville Dam (2000 m3/s 

[70,000 ft3/s]). Zero CRD at Vancouver, Washington (RM 105), is equal to -1.6 m (-5.3 ft) NAVD 88 

and zero CRD at Skamokawa, Washington, is equal to -0.4 m (-1.4 ft) NAVD 88.

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

Abbreviations

AdH Adaptive Hydraulics

AEP annual exceedance probability hydraulics model

CIG Climate Impacts Group

CMIP Coupled Model Intercomparison Project

Delft3D-FM Delft3D-Flexible Mesh model

FEM finite element method

FEMA Federal Emergency Management Agency

GCM general circulation model

GEBCO General Bathymetric Chart of the Oceans

LCR lower Columbia River

LRC Levee Ready Columbia

MCDD Multnomah County Drainage District No. 1

MCR mouth of the Columbia River

MOVE.1 Maintenance Of Variance-Extension, type 1

MSL mean sea level 

NOAA National Oceanic and Atmospheric Administration

PEN 1 Peninsula Drainage District No. 1

PEN 2 Peninsula Drainage District No. 2

RM river mile

RMJOC River Management Joint Operating Committee

RMSE root mean squared error

SDIC Sandy Drainage Improvement Company

SLC sea-level change

SREF Streamflow Record Extension Facilitator

SRES Special Report on Emissions Scenarios

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey

Assessment of Columbia and Willamette River Flood 

Stage on the Columbia Corridor Levee System at Portland, 

Oregon, in a Future Climate

By Susan A. Wherry1, Tamara M. Wood1, Hans R. Moritz2, and Keith B. Duffy2

Abstract

To support Levee Ready Columbia’s (LRC’s) effort to 

re-certify levees along the Columbia and Willamette Rivers 

and remain accredited, two 2-dimensional hydraulic models, 

Adaptive Hydraulics and Delft3D-Flexible Mesh, were used 

to simulate the effects of plausible extreme high water during 

the 2030 to 2059 period. The Columbia River was simulated 

from Bonneville Dam, situated at river mile (RM) 145, to 

the mouth of Columbia River, and the Willamette River was 

simulated from Willamette Falls, RM 26.2, to the Columbia 

River confluence. Inputs to the models included light detection 

and ranging (lidar) and bathymetric mapping data to determine 

bed level, and boundary conditions in the form of daily inflow 

hydrographs and water levels in the ocean offshore of the 

mouth of the Columbia River.

Future conditions were based on climate science data 

developed by the U.S. Army Corps of Engineers and others. 

These conditions included future streamflow and coastal 

ocean water levels. The hypothetical, extreme but plausible, 

upstream boundary was based on scaling up the hydrographs 

from the 1996 flood. Scaling factors were determined by 

comparing the peak flow rankings determined from flood 

frequency analyses of historical unregulated periods and 2040s 

simulated unregulated winter streamflow. The comparison 

resulted in scaling up the Columbia River hydrograph by 

40-percent and scaling up the Willamette River and Lower 

Columbia River tributaries hydrographs by 20-percent. The 

downstream ocean boundary was based on a combination of 

sea-level change, high tide, and storm surge.

The models were calibrated for two historical periods: 

(1) from January 15 to February 28, 1996, and (2) from April 

12 to July 12, 1997. The two models compared well to the 

measured water-surface elevation over the historical periods 

and had good performance statistics, with root-mean square 

error ranging from 0.085 to 0.32 meters, Nash-Sutcliffe 

values greater than 0.96, and bias ranging from -0.03 to 0.28 

meters. The simulated peak stage in the Columbia River at 

Vancouver, Washington, for 1996 was 9.60 and 9.98 meters 

(31.5 and 32.7 feet) compared to the measured peak of 9.89 

meters (32.5 feet). Future peak stage then was simulated with 

boundary conditions representing extreme but plausible future 

conditions at the inflow sites and the ocean boundary.

The two calibrated models compared well in their 

simulations of extreme but plausible future conditions. For the 

0-meter sea-level change scenario, the simulated peak stage in 

the Columbia River at Vancouver was 11.15 and 11.39 meters 

(36.6 and 37.4 feet); and for the 1-meter sea-level change 

scenario, the simulated peak stage in the Columbia River was 

11.25 and 11.54 meters (36.9 and 37.9 feet). The total increase 

in stage as compared to the 1996 measured peak stage ranged 

from 1.26 to 1.65 meters (4.13 to 5.40 feet).

Significant Findings

1. Two 2-dimensional hydraulic models were calibrated 

to historical high-flow periods in 1996 and 1997. The 

models compared well in simulating the timing and 

magnitude of river stage in the Columbia and Willamette 

Rivers near Portland, Oregon.

2. Winter rain-on-snow periods were postulated to be a 

likely cause of future extreme flooding events in addition 

to the spring freshet, which the Columbia River system 

of dams best regulates. The 1996 flood period was 

selected as a historical, extreme, rain-on-snow winter 

period to scale up for simulating future climate.

• Extreme but plausible winter increases in flow were 

simulated as 40-percent on the Columbia River and 

20-percent on the Willamette River, based on the 

selection of a moderately wet and warm general 

circulation model, and a moderate scenario for future 

greenhouse gas emissions.

1U.S. Geological Survey.

2U.S. Army Corps of Engineers.
2 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

3. Storm surges could have a significant effect on tidal 

boundaries and upstream stage depending on the peak 

timing. Historical storm surges increased tidal stage by 

as much as 1.68 meters (5.51 feet), which is higher than 

the maximum potential relative sea-level rise attributable 

to climate change through the year 2100 at Astoria, 

Oregon, as provided by U.S. Army Corps of Engineers 

guidance.

4. The models using extreme but plausible future 

hydrographs simulated increases in stage of 1.26 to 

1.65 meters (4.13 to 5.40 feet) relative to the 1996 

measured peak stage in the Portland area. Additionally, 

most levees will be subject to prolonged exposure from 

water levels that exceed the safe levee height, which 

is defined by the U.S. Army Corps of Engineers as the 

highest flood level for which reasonable flood protection 

is provided.

Introduction

Levee Ready Columbia (LRC), a partnership of 

more than 20 organizations committed to collaborative 

and proactive flood risk reduction, is working to recertify 

the Columbia corridor levee system (CCLS) to ensure 

accreditation by meeting the Federal Emergency Management 

Agency (FEMA) and U.S. Army Corps of Engineers (USACE) 

Federal standards. LRC has taken a proactive approach to the 

recertification and accreditation process for these levees, and 

has requested assistance assessing the potential effects of a 

changing climate on the Columbia and Willamette River water 

levels near Portland and on sea level downstream at the mouth 

of the Columbia River (MCR). The U.S. Geological Survey 

(USGS) and USACE proposed to provide this assistance 

in the form of hydraulic model simulations of the lower 

Columbia River (LCR; fig. 1). This modeling incorporates the 

best available knowledge at the time of this study regarding 

peak flows in the Columbia and Willamette Rivers in a future 

climate, and projected sea-level change (SLC) at the MCR, 

both of which affect river stage at Portland.

This study focused on assessing future flood stage on the 

CCLS, which consists of 72 kilometers ([km] 45 miles [mi]) 

of levees near the fluvially dominated convergence of the 

Columbia and Willamette Rivers, and spans the southern shore 

of the Columbia River from North Portland near the Smith and 

Bybee Wetlands Natural Area to the Sandy River. The system 

is managed by three drainage districts and one drainage 

improvement company: Peninsula Drainage District #1 

(PEN 1), Peninsula Drainage District #2 (PEN 2), Multnomah 

County Drainage District #1 (MCDD), and Sandy Drainage 

Improvement Company (SDIC; fig. 2).

Throughout the report, variables are presented in the 

International System (SI) of Units with inch/pound units 

in parentheses to accommodate the wide range of readers 

interested in the CCLS. The only exceptions are the Columbia 

River mile demarcations, which are presented only in 

inch/ pound units, and the sea-level change increments used for 

the future simulations, which are only presented in SI units.

Hydrology and Morphology of the Lower 

Columbia River

The Columbia River flows into the Pacific Ocean 

at the boundary between Oregon and Washington after 

traversing 1,990 km (1,240 mi), dropping over 790 meters 

([m] 2,600 feet [ft]) from its Canadian headwaters in the 

Rocky Mountains, and draining an area of approximately 

668,000 square kilometers ([km2] 258,000 square miles 

[mi2]). The Columbia River is the second largest river in the 

United States in terms of annual river discharge; its drainage 

basin accounts for 60 percent of the total freshwater discharge 

into the Pacific Ocean between the Canadian border and San 

Francisco, California, during winter, and 90 percent during 

summer. The drainage area for the Lower Columbia River 

(LCR) downstream of Bonneville Dam (river mile [RM] 

145) is about 52,000 km2 (about 20,000 mi2), including the 

Willamette River Basin, and composes less than 10 percent 

of the overall Columbia River Basin. However, the LCR 

drainage area is an important part of the fluvial input to 

the lower river. Average runoff for the LCR drainage area 

is 0.0398 cubic meters per second per square kilometer 

([m3/s]/ km2) (3.62 [ft3/s]/mi2), whereas average run-off 

from the drainage area upstream of Bonneville Dam is only 

0.0089 (m3/s)/km2 (0.82 [ft3/s]/mi2) (Orem, 1968). The high 

runoff contribution for the LCR drainage is associated with 

west Cascades Range hydrology, which is dominated by the 

Willamette River Basin during autumn to spring, and explains 

the relevance of the Willamette River in terms of its effect on 

the combined flow for the LCR. The high runoff contribution 

produces flooding of non-leveed areas, and threatens levee 

systems along the LCR. The Willamette River flows into the 

LCR at Portland (RM 101). Other prominent LCR tributaries 

include the Cowlitz River (RM 68) and Lewis River (RM 87), 

Washington, Sandy River (RM 121), Oregon, and Washougal 

River (RM 121), Washington, which were included in the 

model boundaries to ensure completeness.
Introduction 3

tac18-1244_fig 01

McMinnville

Oregon

City

Portland

St. Helens

Salem

Sandy

The

Dalles

Aberdeen

Centralia

Longview

Olympia

Vancouver

Astoria

Quincy

Newberg

COLUMBIA

RIVER

Willamette River

Cowlitz River

Lewis River

Sandy River

Washougal

River

PA

CIFIC

O

C

E

A

N

Willapa

Bay

GRAYS HARBOR

PIERCE

THURSTON

YAKIMA

LEWIS PACIFIC

SKAMANIA

COWLITZ

WAHKIAKUM

CLATSOP

COLUMBIA

CLARK

KLICKITAT

TILLAMOOK WASHINGTON SHERMAN

MULTNOMAH HOOD

RIVER

WASCO CLACKAMAS

YAMHILL

MARION

POLK

LINCOLN JEFFERSON

LINN BENTON

CHELAN DOUGLAS

GRANT

KING

MASON

KITTITAS

BENTON

M

O

R

R

O

W

GILLIAM

WHEELER

CROOK

Bonneville

Dam

Willamette

Falls

14105700

14113000

14120000

14123500 14125500

14128500

 14128870 14113200

14143500

14191000

14194150

14202000

14210000

14142500 14137000

14222500

14220500

14243000

14246900

14238000

14245000

14241500

14242580

14144700

14211720

9439040

9440910

14207500

14211550

14197900

0 25 15

68

145

192

OREGON

WASHINGTON

Map

area

EXPLANATION

Stage site

Streamgage site

River mile

AdH

Delft3D-FM

145

Model domain

0 10 20 30 40 50 MILES

Base map from Esri, copyright 2018, and other digital data, various scales. 0 10 20 30 40 50 KILOMETERS

Coordinate system: USA Contiguous Albers Equal Area Conic USGS Version. 

Horizontal datum is North American Datum of 1983 

124° 123° 122° 121° 120°

47°

46°

45°

C

A

S

C

A

D E R

A

N

G

E

Figure 1. Locations of model domains and measurement sites along the Columbia and Willamette Rivers near Portland, Oregon. 

Site information is shown in table 2.

The Columbia River estuary is the largest fluvially 

dominated estuary in the Pacific Northwest (Fox and others, 

1984). It has a tidal prism, the difference in volume between 

low and high tide, of about 1.1 cubic kilometers (km3) 

(890,000 acre-ft; Jarrett, 1976). Freshwater inflows to the 

estuary primarily are from the Columbia and Willamette 

Rivers, and range from a late summer combined low of 

2,200 cubic meters per second (m3/s) (78,000 cubic feet 

per second [ft3/s]) to an annual spring freshet of 8,500 m3/s 

(300,000 ft3/s). The 0.01 annual exceedance probability (AEP) 

event for regulated river flow passing The Dalles Dam (RM 

192) is about 19,000 m3/s (670,000 ft3/s) with about 840 

m3/s (30,000 ft3/s) in tributary inflows entering the Columbia 

River between The Dalles and Bonneville Dam (U.S. Army 

Corps of Engineers, 1991). The 0.01 AEP regulated flow for 

the Willamette River at Willamette Falls (26 mi upstream of 

the confluence with the Columbia River) is about 11,000 m3/s 

(390,000 ft3/s; U.S. Army Corps of Engineers, 1991).
4 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig 02

Map from U.S. Army Corps of Engineers, 2018

Notes: Refer to table 6.

Equivalent site names:

Peninsula 1 Protected Area = Peninsula 1

Peninsula DD No. 2 Protected Area = Peninsula 2

Multnomah Protected Area-West = Multnomah County-West

Multnomah Protected Area-East = Multnomah County-East

Sandy Protected Area = Sandy Diking District

Figure 2. Columbia corridor levee system including locations of drainage district areas and drainage improvement company 

area near Portland, Oregon.

Downstream of RM 38, the LCR estuary consists of 

multiple deep channels meandering past shallow tidal flats, 

sandbars, and islands within a wide coastal plain (fig. 3). LCR 

tides in the estuary are of the mixed type with two high and 

two low water levels per day. The diurnal tide range at Astoria, 

Oregon (RM 15) is about 2.6 m (8.5 ft) and is 0.3 m (1.0 ft) 

larger than the MCR (RM 0) due to tidal amplification within 

the estuary. The upriver limit for the Columbia River estuary, 

defined in terms of salt water intrusion, varies between RMs 

28 and 38 and is a function of fluvial flow and timing of 

the tidal cycle (Simenstad and others, 2011). The hydraulic 

forcing for the lower estuary (downstream of RM 38) is 

correlated with tidal phase.

Depending on the discharge magnitude, fluvial discharge 

increasingly controls river hydraulics moving upstream 

from RM 38. During times of low river flow (less than about 

7,100 m3/s [251,000 ft3/s]), tidal propagation can cause 

reversal of the current throughout the water column in the 

Willamette River at locations more than 16 km (10 mi) 

upstream of the confluence with the Columbia River (RM 101; 

fig. 4). Tidal effects on water-surface elevation in the 

Columbia River extend upriver to Bonneville Dam (RM 145). 

During times of low river flow, a high tide entering the 

Columbia River from the Pacific Ocean takes about 5.5 hours 

to progress up the Columbia River from Astoria (RM 15) to 

the confluence of the Willamette River (RM 101).

Upstream of RM 38 (northern end of Puget Island; fig. 3), 

the LCR morphology becomes constrained by confining 

geology, leveed flood plain, and navigation improvements. 

This confining effect of the LCR produces a single river 

thalweg with a relatively steep profile gradient, compared to 

the lower estuary. Much of the expansive flood plain along 

RMs 80–124 has been leveed to decrease potential flood 

damage in low-lying areas during high river flow conditions, 

further confining the river and increasing river stage during 

extreme flow events (fig. 4). Upstream of the Sandy River 

(RM 121) the LCR is confined by the Columbia River Gorge 

through the Cascade Range (fig. 1).

Progressive improvement of the LCR for navigation has 

produced a navigation channel from the MCR to Vancouver, 

Washington (RM 105) about 183 m (600 ft) wide and 

maintained to an authorized depth of 13.1 m (43 ft) below 

Columbia River Datum (CRD), a datum based on river water 

level during minimum operating discharge from Bonneville 
Introduction 

5

tac18-1244_fig 03

Puget

Island

Skamokawa/Price Island

Little Island

Cathlamet

Channel

Clifton Channel

COLUMBIA RIVER

COLU M BIA

RIVER

Cathlamet

Skamokawa

Wauna

Woodson

Tenasillahe

Island

Mid al nd Levee

West Cr

25 26 27 28 29 30

31

32 33

34

35

36

37

38

39

40

41

42

43

44

45 46 47 48 49

50

51

52

EXPLANATION

Pile dike center lineLeveeRiver mileLevee name

2 to 40 to 2-2 to 0-4 to -2-6 to -4-8 to -6-10 to -8

-41.46 to -10

Elevation, in meters 

above NAVD 1988

32

East

123°15' 123°20' 123°25' 123°30' 123°35'

46°15'46°10'

0 1 2 3 4 MILES0 1 2 3 4 KILOMETERS

Base map from Esri, copyright 2018. Coordinate system: NAD 1983 UTM Zone 10N. Horizontal datum is North American Datum of 1983.

Figure 3. Land-surface elevations, levees, and pile dikes in the Columbia River for river miles 28 to 48, near Astoria, Oregon.
6 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac181244_fig 04

St. Helens

Woodland

Vancouver

Portland

Smith and Bybee 

wetlands

Steigerwald

Sandy

Diking

District

Multnomah

County-East

Multnomah

County-West

Peninsula 2

Clark County

DD 14-South

Lake River

Clark County

DD 14-North

Delta

Peninsula 1

Bachelor

Island

80

81

82

83

84

85 86

87

88

89

90

91 92

93

94

95

96

97

98

99

100

101

102

103 104

105

106

107 108 109

110

111 112

113

114 115 116

117 118 119 120 121 122123 124

125 126 127 128 130

129

131

132

133

134

135 136 137

138

139

COLUMBIA

RIVER

Willamette River

Multnomah Channel

Columbia Slough

Lewis River

Lewis River

Sandy River

Washougal River

Vancouver

Lake

DNAL SI EI VUAS

EXPLANATION

Pile dike center lineLeveeRiver mileLevee name

2 to 40 to 2-2 to 0-4 to -2-6 to -4-8 to -6-10 to -8

-45.8 to -10

Elevation, in meters 

above NAVD 1988

91

East

0 2 4 6 8 10 MILES0 2 4 6 8 10 KILOMETERS

Base map from Esri, copyright 2018. Coordinate system: NAD 1983 UTM Zone 10N. Horizontal datum is North American Datum of 1983.

122°5' 122°10' 122°15' 122°20' 122°25' 122°30' 122°35' 122°40' 122°45' 122°50' 122°55'

45°55'45°50'45°45'45°40'45°35'

Figure 4. Land-surface elevations, levees, and pile dikes near the confluence of the Columbia and Willamette Rivers and near Multnomah County Drainage District levees, 

Portland, Oregon.
Introduction 7

Dam. From RM 105 to Bonneville Dam (fig. 1), the navigation 

channel is 91 m (300 ft) wide and maintained at 5.2 m (17 ft) 

below CRD. Construction of 233 pile dikes (flow-control 

structures) along the LCR has improved navigation reliability 

by stabilizing river banks and islands and has further confined 

river flow to the channel thalweg. LCR pile dikes extend 

50–150 m (160–500 ft) from shore into the river and have a 

typical top elevation of 4 m (13 ft) above CRD. Pile dikes are 

composed of timber piles (0.3-m [1 ft] diameter) spaced 0.8 m 

(2.6 ft) apart, with a rock apron to prevent toe scour. These 

structures have 50–60 percent porosity and are intended to 

decrease flow near the riverbank by redirecting flow toward 

the thalweg. Due to structural-loading limitations, LCR pile 

dikes do not extend beyond 10–13 m (33–43 ft) water depth, 

keeping these structures out of the river thalweg.

The riverbed for much of the main stem LCR is 

composed of sand, which forms sand waves 1–2 m (3–7 ft) 

high and 50–100 m (60–330 ft) long. High-flow periods 

enhance bedload transport, resulting in sand waves 2–4 m 

(7–13 ft) high. Enhanced sand wave growth during high-flow 

periods can increase the equivalent roughness height of the 

river bottom, further increasing river stage.

Effects of Climate Change on Streamflow in the 

Pacific Northwest

The general circulation models (GCM) in the 

World Climate Research Programme Coupled Model 

Intercomparison Project (CMIP) (Taylor and others, 2012) 

generally indicated in the fourth (CMIP3) and fifth assessment 

(CMIP5) model ensembles that increased precipitation is 

likely to occur across Canada and the northern United States, 

with the largest increases occurring in winter (Climate Impacts 

Group, 2009), and decreased precipitation is likely to occur in 

the southern United States, particularly in the summer months 

(Intergovernmental Panel on Climate Change, 2007). There 

is, however, a large range among the GCMs in the magnitude 

of projected changes in precipitation for the Pacific Northwest 

(Mote and Salathé, 2010; Intergovernmental Panel on Climate 

Change 2014; Mote and others, 2014).

The effects of changing temperature and precipitation 

on the hydrologic cycle also have been investigated. Even 

when considering the uncertainties in future precipitation 

trends, significant changes in the magnitude and timing of 

streamflows are a likely outcome of climate change (Groisman 

and Easterling, 1994; Intergovernmental Panel on Climate 

Change, 2007). Climate change effects on hydrology have 

been studied extensively in the Pacific Northwest, including 

Cayan (1996), Hamlet and Lettenmaier (1999), Stewart and 

others (2005), and Tohver and others (2014). In these and 

other studies, a general trend was documented indicating 

earlier spring peak runoff, less summer runoff, and increased 

winter streamflows in basins where precipitation in the 

past has fallen predominantly as snow, but in the future, for 

transitional (lower elevation) basins, is more likely to fall 

as rain (Mote and others, 2014; Tohver and others, 2014). 

Increased winter runoff also implies higher peak flows 

associated with given recurrence frequencies, which is the 

basis for the interest in incorporating climate change into 

design criteria for flood risk reduction levees in Portland. 

Because higher peak flows are expected in the future, peakflow statistics derived from the historical period of streamflow 

record for the Columbia River at The Dalles (14105700; the 

nearest upstream streamgage on the Columbia River) or the 

Willamette River at Portland (14211720) or the Willamette 

River at Newberg (14197900) (the nearest upstream stage 

gages on the Willamette River) are not adequate for assessing 

the flood stage on the Columbia corridor levee system.

Previous Climate Change Studies

Future climate hydrographs were developed by first 

identifying a prototype flood from the historical record, and 

then projecting that prototype flood into the future to match 

the statistics of future hydrology. Because the purpose of 

the study was to investigate an extreme but plausible event, 

the focus was on one of the more extreme (as in higher 

temperatures and more precipitation and runoff) future climate 

scenarios projected by the suite of GCMs available. Previous 

studies by the USACE and others informed the selection of 

future climate scenarios.

The Climate Impacts Group (CIG) at the University 

of Washington has downscaled North Pacific hydroclimate 

scenarios from the forcing functions generated by six global 

scale GCMs that were included in the CMIP3 (Hamlet and 

others, 2013; Climate Impacts Group, 2018). The output 

of GCMs was statistically downscaled from approximately 

50-km2 to 6-km2 resolution. The CIG used these downscaled 

data to provide forcing functions for a hydrologic model 

(the Variable Infiltration Capacity model; Liang, 1994) that 

converts meteorological variables such as GCM-derived 

precipitation, soil moisture, and air temperature into daily 

values of streamflow. The hydrologic model simulations 

include three periods of 30 years: 2020s (between 2010 and 

2039), 2040s (between 2030 and 2059) and 2080s (2070–99).

Each simulation is additionally identified by the 

assumption regarding the greenhouse gas emissions scenario 

that went into the GCM simulation. These scenarios were 

defined for CMIP3 and described in the Synthesis Report 

(Intergovernmental Panel on Climate Change, 2007). The most 

recent climate CMIP5 GCM downscaled streamflow datasets 

were not available for analysis during this study; however, 

there were few differences in the two CMIP multimodal 

ensembles for the Pacific Northwest (Rupp and others, 2013).
8 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

For example, the A1B scenario assumes world-wide 

rapid economic growth and future energy sources to be 

balanced between fossil intensive and non-fossil sources. The 

B1 scenario assumes the same world-wide rapid economic 

growth as in A1B, but with far more reliance on clean and 

resource-efficient technologies. The A1B scenario is a more 

extreme scenario of future emissions than the B1 scenario 

but is moderate compared to the entire range of greenhouse 

gas emission scenarios defined in Intergovernmental Panel 

on Climate Change (2000) and those published between 2000 

and 2007 (Intergovernmental Panel on Climate Change, 2007; 

fig. 5, table 1).

The River Management Joint Operating Committee 

(RMJOC), in collaboration with CIG, assessed the sensitivity 

of Pacific Northwest hydroclimatology to potential future 

climate change. The goal of that study was to create 

hydroclimate streamflow datasets for use by regional planners 

and water resource modelers (Brekke and others, 2010). 

On the basis of an initial screening process, the RMJOC 

selected a subset of the 19 spatially downscaled datasets 

(each identified by a unique combination of 10 GCMs and 

2 CMIP-3 emissions scenarios) that were available from the 

CIG at the time for further study. The subset was selected to 

bracket the 10th and 90th percentile of the change in 30-year 

mean-annual temperature and precipitation, spatially averaged 

over the entire Columbia-Snake River Basin (Brekke and 

others, 2010). The scenarios at the extremes of temperature 

and precipitation change of the selected subset were identified 

as “more warming and wetter,” “less warming and wetter,” 

“more warming and drier,” and “less warming and drier.” 

For the purposes of the RMJOC planning study, the entire 

possible range in climate projections was of interest; for the 

purposes of this study, only the scenarios at the high end of 

the range in precipitation and water volume are of interest 

(fig. 6). The warmer and wetter combination of GCM and 

emissions scenario selected for this study was the MIROC 3.2 

global climate model, and the A1B carbon dioxide emissions 

scenario, which projects an average temperature increase 

of about 3 °C for the Columbia Basin in the 2040s, and a 

basin-aggregated precipitation increase of about 14 percent, 

compared to the 1971–2000 averages (Brekke and others, 

2010). This increase in runoff translates to an annual water 

year3 volume of 196 km3 (159 million acre-ft) at The Dalles, 

which is an increase of 20 percent over the baseline annual 

water year volume of 163 km3 (132.5 million acre-ft; 

Bonneville Power Administration, 2004). This combination 

was determined to be the “warmest and wettest” of the 19 

downscaled GCM and emissions scenario combinations that 

were initially screened. It should be noted, however, that only 

the A1B and B1 emissions scenarios were included in the 

CIG downscaled datasets, so the selection of the warmest and 

wettest scenario with respect to the RMJOC study was not 

necessarily the warmest or wettest climate change projection 

for the Pacific Northwest derived from the entire suite of 

CMIP3 models.

3The 12-month period from October 1, for any given year, through 

September 30 of the following year. The water year is designated by the 

calendar year in which it ends.

Global greenhouse gas emissions, in gigatonnes of equivalent carbon dioxide per year

Global surface warming, in degrees Celsius

Post-SRES (max)

Post-SRES (min)

2000 2100 2000 2100

Year Year

1900

200

180

160

140

120

100

80

60

40

20

0

6

5

4

3

2

1

0

-1

Scenarios for greenhouse gas emissions from 2000 to 2100 (in the absence of 

additional climate policies) and projections of surface temperatures

B1A1TB2A1BA2A1FI

EXPLANATION

Scenario

Post-SRES range (80 percent)

A1B

B1

A2

B2

Year 2000 constant concentrations

A1FI

A1T

20th century

Figure 5. Scenarios for global greenhouse gas emissions and surface warming projections from 2000 to 2100. 

Definitions of scenarios are shown in table 1; data from SRES (Intergovernmental Panel on Climate Change [2007]).
Introduction 9

Table 1. Definitions of greenhouse gas emissions scenarios.

[Source of definitions is Special Report on Emissions Scenarios (Intergovernmental Panel on Climate Change, 2000)]

Scenario 

family

Development 

pathway Scenario Technological change

A1 Rapid worldwide economic growth, a global population that 

peaks in mid-century, and rapid introduction of new and 

more efficient technologies.

A1F1

A1T

A1B

Fossil intensive energy sources

Non-fossil-intensive energy sources

Balance between fossil and non-fossil energy sources

B1 Same global population as A1, but with more rapid changes 

in economic structures toward a service and information 

economy.

A2 A very heterogeneous world with high population growth, 

slow economic development, and slow technological change.

B2 Intermediate population and economic growth worldwide, 

emphasizing local solutions to economic, social, and 

environmental sustainability.

Warmer and wetter 

scenario values

1.5 x interquartile

 range

1.5 x interquartile

range

75th percentile

Median

25th percentile

Outliers beyond 1.5 x 

interquartile range

EXPLANATION 

-15

-10

-5

0

5

10

15

20

25

Change relative to baseline, in percent

0.5

1.0

1.5

2.0

2.5

3.0

Temperature 

Change relative to baseline, in degrees Celsius

Mean annual

precipitation

Water-year

volume at

The Dalles

Figure 6. Change in mean annual precipitation and temperature in all future climate 

scenarios considered by the River Management Joint Operating Committee, and the 

changes in the warmer and wetter scenario considered in this study.

This study used results of the RMJOC work, which 

culled a large ensemble of GCMs and emissions scenarios 

into a regionally appropriate subset and included simulated 

streamflow data to be used to inform boundary conditions, 

which was not available for the CMIP5 model ensembles. This 

smaller selection effectively bracketed the range of possible 

hydrologic conditions of the ensemble of GCMs. Although 

the GCMs and emissions scenarios used by the current study 

may not be the most extreme in terms of wetter or drier, 

or warmer or cooler conditions, the selection used for the 

hydraulic modeling does meet the objective of selecting a set 

of conditions that likely would lead to an extreme but still 

plausible high-water event.

Selection of Prototype Flood 

By using a historical flood as the prototype on which to 

base future climate hydrographs for an extreme flood, a direct 

comparison of simulations to observations could be made, and 

thereby isolate the effects of future climate on the simulated 

water-surface elevation from flood-specific characteristics 

such as timing, duration, and total volume. The February 1996 

flood was selected as the prototype flood for this study. This 

flood produced the highest stages at Vancouver, Washington, 

and Portland, Oregon, in recent history, and was characterized 

by heavy rain falling on snowpack and frozen ground, and 
10 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

above-average winter Columbia River flow, resulting in high 

runoff, particularly in the Willamette Valley. The flood was 

caused by a concentrated inflow of warm and extremely moist 

air—an atmospheric river—which is expected to become more 

frequent and intense in the future (Warner and others, 2015). 

The high Willamette River flows resulting from the warm and 

heavy precipitation associated with atmospheric rivers, when 

coupled with moderately high winter Columbia River main 

stem flows, will be the most likely scenario for extreme highwater stages in the Portland/Vancouver area.

The campaign to construct dams to reduce flood risk 

on the Columbia River and its tributaries began in response 

to documented spring floods that devastated population 

centers in the 19th century. The highest stage of record in 

the Portland/Vancouver area of about 12.0 m (39 ft) above 

North American Vertical Datum of 1988 (NAVD 88), was the 

result of a flood that occurred in June 1894 from snowmelt 

(U.S. Army Corps of Engineers, 1948). With full Columbia 

River Basin regulation, a repeat of such a historical snowmelt 

freshet (typically peaking in May to middle of July) is not 

likely. Inspection of streamflow since 1970, which is after 

the Columbia River was regulated, indicates that most annual 

peak stages at CCLS near Portland occur in the winter 

(defined as November through March for this study). Roughly 

two-thirds of all annual peak stages at Vancouver occur 

during winter (65 percent based on the record from 1998 to 

2017 at USGS streamgage 14144700, Columbia River at 

Vancouver). The extreme high stages near Portland, under 

current conditions, are caused by the processes represented by 

a winter storm, which include concurrent high Willamette and 

Columbia River flows, and Willamette River flows sufficient 

to cause backwater-induced high stages in the Columbia 

River at Vancouver just upstream of their confluence. The 

February 1996 flood, which occurred with full regulation of 

the Columbia River in place, is just such an event. The peak 

stage at Columbia River at Vancouver streamgage (14144700) 

occurred on February 9, at approximately 9.89 m (32.5 ft) 

NAVD 88 (U.S. Army Corps of Engineers, 1997).

Methods

The LCR is a complex hydro-geomorphic system with 

natural and built features, where the interaction of tides with 

fluvial hydraulics produces spatially and temporally variable 

flow, which results in a temporally variable flow-stage 

relation throughout the river. To emulate the LCR within the 

framework of a hydraulic model, many features and processes 

must be properly simulated by the model to replicate river 

flow and stage. Relevant terrain features include: coastal 

bathymetry for the MCR, jetties at the MCR, estuary and 

riverine bathymetry and topography, pile dikes, levees, and 

interior flood plain areas (if levees are overtopped), and 

expression of hydraulic roughness for submerged terrain and 

features. Relevant hydraulic boundary conditions include 

ocean astronomical tide phasing and amplitude, non-tidal 

components of ocean water level, and time-varying river and 

tributary flow. Successful hydraulic modeling of the LCR 

is predicated on the ability of a model to properly integrate 

the terrain features and hydraulic processes and replicate the 

physics within the focused study area.

The scope for this study focused on evaluating river stage 

within the fluvial-dominated Lower Columbia River (upstream 

of RM 38), and specifically for the Portland-Vancouver 

area (RM 90 to 110; fig. 4). Although salinity and related 

baroclinic circulation affects the hydraulics of the lower 

estuary of the Columbia River (RM 0 to 25), salinity effects of 

the lower estuary have minor influence on river stage within 

the Portland-Vancouver area, especially during high fluvial 

discharge periods. For this reason, the study did not include 

salinity-induced or 3-dimensional circulation effects within the 

hydrodynamic evaluation. Instead a 2-dimensional approach 

was used to evaluate LCR hydrodynamics, with the limitation 

that results may be unreliable downstream of RM 25.

To explore multiple methods of estimating peak stage and 

understand the uncertainty in simulations, two 2-dimensional 

hydraulic models of the LCR were developed using Delft3DFlexible Mesh (Delft3D-FM) and the USACE Adaptive 

Hydraulics (AdH) frameworks. The models were calibrated 

to historical high-flows measured in the Willamette River at 

Portland (14211720) and the Columbia River at Vancouver 

(14144700) in 1996 and 1997. The 1996 flood produced 

the highest stage in the Portland area since full regulation 

was completed in the 1970s, and the high-flow periods in 

1996 and 1997 corresponded to the highest recorded daily 

average flows of 24,500 m3/s (865,000 ft3/s) and 19,600 

m3/s (692,000 ft3/s), respectively, measured at the Columbia 

River at Port Westward, near Quincy (14246900) from 1991 

to 2018. To bracket the uncertainty in Portland vicinity flood 

stage, the Delft3D-FM model was calibrated to Willamette 

River stage during the winter 1996 flood that was caused by 

large Willamette River flows, whereas the AdH model was 

calibrated to Columbia River stage during the spring 1997 

freshet, which was typically caused by high Columbia River 

flows. The calibrated models then were forced with various 

extreme but plausible future climate boundaries to simulate 

potential effects on river stage in the Portland area.

Datasets Used for Hydraulic Models

The data used to build the hydraulic models and 

validate simulations included stage and discharge data, tidal 

constituents, high-resolution bathymetry data, maps of levees 

and log pile dikes, and satellite imagery.
Methods 11

Model Terrain Data

Terrain refers to the topographic and bathymetric data 

that are required when constructing a model. The USACE 

obtained lidar topographic data for much of the Columbia 

River Basin covering an area equal to or greater than the 

FEMA 0.002 AEP flood plain (Watershed Sciences, 2010). The 

1-m lidar data were combined with bathymetric survey data 

collected in 2010 for the Columbia River and the Willamette 

River to develop a terrain model with a horizontal resolution 

of 1 m. For the off-shore bathymetry, the dataset provided by 

General Bathymetric Chart of the Oceans (GEBCO) was used 

(General Bathymetric Chart of the Oceans, 2018). It should 

be noted that parts of the Columbia River Federal Navigation 

Channel (FNC) were deepened by about 1 m during 2005–10, 

which is reflected in the lidar data used to generate the model 

mesh elevations for the simulation years of 1996 and 1997. 

The deepened terrain used for the model simulations was 

assumed to have a minimal effect on model performance due 

to the relatively small affected area.

Aerial Images

Satellite images from Landsat 5 were acquired and 

compared, when available, to understand inundation on 

dates with high-flows during the two calibration periods: 

(1) February 11, 1996, and (2) May 11, 1997 (https://

landsatlook.usgs.gov/viewer.html, accessed April 17, 2017). 

Visual comparison between the images and simulation maps 

helped to determine if the correct storage areas were being 

activated during high-flows.

Historical Flood Boundary Conditions

Each hydraulic model has six boundaries requiring data 

inputs: five upstream river boundaries and one downstream 

ocean tidal boundary. Hourly hydrographs were applied at the 

upstream river boundaries, and hourly water-surface elevations 

were applied at the ocean boundary.

Hourly Flow Hydrographs at the Upstream Boundaries

The five river boundaries include: Columbia River at 

Bonneville, Willamette River at Willamette Falls, and inflows 

from the Sandy, Lewis, and Cowlitz Rivers. Washougal 

River inflow is included by adding one-half its discharge to 

the Sandy River time series and one-half to the Bonneville 

time series. Hourly discharge data were applied at the 

river boundaries for the two historical calibration periods: 

(1) January 15 to February 28, 1996, and (2) April 12 to 

July 12, 1997.

Hydraulic model inflow data were obtained from 

recorded streamflow when possible. The USGS Streamflow 

Record Extension Facilitator (SREF) computer program 

(Granato, 2009) was used to fill gaps in the streamflow record 

and to estimate streamflow outside the period of record or for 

ungaged sites when streamflow records were incomplete. This 

program uses the Maintenance Of Variance-Extension, type 1 

(MOVE .1) methodology for estimating missing daily-mean 

streamflow. MOVE.1 produces a regression equation, based 

on concurrent records between hydrologically similar basins, 

and then the regression equation coefficients are adjusted to 

reflect differences in statistics between the concurrent records. 

After the daily mean streamflow records were extended they 

were later disaggregated smoothly into hourly or sub-hourly 

streamflow for model boundary input.

Columbia River at Bonneville Dam—The streamflow 

input for the Columbia River at Bonneville Dam boundary 

is a composite of streamflow recorded at The Dalles on the 

Columbia River (14105700), and tributaries that enter the river 

between The Dalles and Bonneville Dam, including Klickitat, 

Hood, White Salmon, Little White Salmon, Wind, Mosier 

(creek), Eagle (creek) and Kalama Rivers, and includes onehalf of the flow measured in the Washougal River (table 2). 

The Washougal River time series was filled and extended 

using SREF and recorded data from the East Fork Lewis River 

streamgage in Washington (14222500).

Sandy River—The streamflow input for the Sandy River 

boundary was derived by combining recorded data from the 

Sandy River and one-half of the flow from the SREF-modified 

Washougal River time series (table 2). The Sandy River 

streamflow time series was filled and extended using SREF 

and data recorded farther upstream on the Sandy River near 

Marmot, Oregon (14137000).

Willamette River at Willamette Falls—The Willamette 

River boundary is just downstream of the Willamette Falls 

near Oregon City. The 1996 and 1997 streamflow for this 

boundary is based on a flow routing procedure used to 

estimate Willamette River streamflow at the Morrison Bridge 

(14211720) in Portland, Oregon using recorded data from 

the Willamette River at Salem (14191000), and the South 

Yamhill, Pudding, Tualatin, Clackamas Rivers, and Johnson 

Creek (table 2). The streamflow determined from the flow 

routing procedure is then applied at the model boundary near 

the Willamette Falls, circumventing the need to add separate 

inflow boundaries for all contributing tributaries.

Lewis River—The streamflow input for the Lewis River 

boundary is a combination of the Lewis and East Fork Lewis 

Rivers, Washington (table 2). The East Fork Lewis River time 

series was filled and extended with SREF using recorded data 

from the Lewis River at Ariel streamgage (14220500).

Cowlitz River—The Cowlitz River boundary corresponds 

to the confluence and is the combination of the Cowlitz and 

Coweeman Rivers, which are both gaged. The SREF software 

was used to fill and extend the Cowlitz River time series using 

upstream data, and the Coweeman River time series was 

similarly modified using data from the Toutle River (table 2).
12 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Table 2. Sources and types of data from measurement sites in the Columbia and Willamette River Basins, Oregon and Washington. 

[Locations of sites are shown in figure 1. Managing agency: NOAA, National Oceanic and Atmospheric Agency; NWS, National Weather Service; USGS, U.S. 

Geological Survey. Abbreviations: OR, Oregon; NA, not applicable; WA, Washington]

Boundary Data 

type

Contributing 

sites

Adjustments and 

factors

Site 

No.

Managing 

agency

Columbia River at 

Bonneville Dam

Streamflow Columbia River at The 

Dalles, OR

NA 14105700 USGS

Klickitat River near 

Pitt, WA

NA 14113000 USGS

Hood River at Tucker 

Bridge, near Hood 

River, OR

NA 14120000 USGS

White Salmon River 

near Underwood, WA

NA 14123500 USGS

Little White Salmon 

River near Cook, WA

NA 14125500 USGS

Wind River near Carson, 

WA

NA 14128500 USGS

Mosier Creek near 

Mosier, OR

NA 14113200 USGS

Washougal River near 

Washougal, WA

0.5 times flow 14143500 USGS

Lewis River at Ariel, WA MOVE.1 to fill/extend 14143500 14220500 USGS

Sandy River Streamflow Sandy River below 

Bull Run River, OR

NA 14142500 USGS

Sandy River near 

Marmot, OR

MOVE.1 factor 1.15 to fill/extend 14142500 14137000 USGS

Washougal River near 

Washougal, WA

0.5 times flow 14143500 USGS

Lewis River at Ariel, WA MOVE.1 to fill/extend 14143500 14220500 USGS

Willamette River 

at Willamette 

Falls

Streamflow Willamette River at 

Salem, OR

NA 14191000 USGS

South Yamhill River at 

McMinnville, OR

NA 14194150 USGS

Willamette River at 

Newberg, OR

NA 14197900 USGS

Pudding River at 

Aurora, OR

NA 14202000 USGS

Tualatin River at 

West Linn, OR

NA 14207500 USGS

Clackamas River at 

Estacada, OR

NA 14210000 USGS

Johnson Creek at 

Milwaukie, OR

NA 14211550 USGS

Lewis River Streamflow East Fork Lewis near 

Heisson, WA

MOVE.1 factor 1.94 to fill/extend 14143500 14222500 USGS

Lewis River at Ariel, WA MOVE.1 factor 1.70 to fill/extend 14222500 14220500 USGS
Methods 13

Table 2. Sources and types of data from measurement sites in the Columbia and Willamette River Basins, Oregon and Washington.—

Continued 

Boundary Data 

type

Contributing 

sites

Adjustments and 

factors

Site 

No.

Managing 

agency

Cowlitz River Streamflow Cowlitz River at Castle 

Rock, WA

NA 14243000 USGS

Cowlitz River below 

Mayfield Dam, WA

MOVE.1 to fill/extend 14243000 14238000 USGS

Coweeman River near 

Kelso, WA

NA 14245000 USGS

South Fork Toutle River 

at Toutle, WA

MOVE.1 to fill/extend 14245000 14241500 USGS

Toutle River at Tower 

Road near Silver 

Lake, WA

MOVE.1 to fill/extend 14245000 14242580 USGS

Validation data

River Data 

type Site name Purpose Site No.

Managing 

agency

NA Stage Toke Point, WA Evaluate storm surge from non-tidal residual 9440910 NOAA

Columbia River Streamflow Columbia River at Port 

Westward near 

Quincy, OR

Evaluate annual peak flow statistics 14246900 USGS

Columbia River 

estuary

Stage Astoria/Tongue Point, 

OR

Validate simulated stage 9439040 NOAA

Willamette River Stage Willamette River at 

Portland, OR

Validate simulated stage 14211720 USGS

Columbia River Stage Columbia River at 

Vancouver, WA

Validate simulated stage 14144700 Historical: NWS

Current: USGS

Columbia River Stage Columbia River below 

Bonneville Dam, OR

Validate simulated stage 14128870 USGS

Water-Surface Elevations Offshore of the Mouth of the 

Columbia River

Water levels recorded by the National Oceanic and 

Atmospheric Administration (NOAA) at Astoria, Oregon 

(9439040) were used to determine the ocean boundary 

conditions, which was accomplished differently in the two 

models. The methods used for each model are described in 

section, “Two-Dimensional River Stage Modeling.”

Historical Events Calibration Data

Both models were calibrated to water levels at three 

sites within the model reach. Water levels recorded at the 

NOAA stage gage at Astoria were used for calibrating to tidal 

elevations in the lower estuary. Water levels recorded on the 

Willamette River at Portland (USGS 14211720) and on the 

Columbia River at Vancouver (USGS 14144700) were used 

to establish a good calibration to the fluvially dominated river 

stage near Portland.

Future Climate Boundary Conditions

Boundary conditions representing extreme but plausible 

future conditions were developed in the form of hydrographs 

at the upstream inflow boundaries and water-surface elevation 

time series at the ocean boundary. The development of 

those future boundary conditions for a high-flow event was 

patterned on the February 1996 winter storm.

Hydrology and Streamflows

Several steps were required to convert the results 

from a GCM to streamflow at the locations represented by 

the models’ upstream boundaries. First, future runoff was 

simulated with the Variable Infiltration Capacity hydrologic 

model, using downscaled meteorological boundary conditions 

as simulated by the MIROC 3.2 GCM assuming an aggressive 

carbon dioxide emissions scenario (SRES A1) for 2030–59. 

This step was done by the Climate Impacts Group at the 

University of Washington, and the datasets produced are 

available for download (Climate Impacts Group, 2018). 
14 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Using this Variable Infiltration Capacitysimulated runoff, a future unregulated 

2040s streamflow at Bonneville Dam on 

the Columbia River and Willamette Falls 

on the Willamette River was simulated. 

This was done by running the USACE 

Hydrologic Engineering Center (HEC) 

Reservoir System Simulation software 

for the Columbia River Basin through 

the 2040s to simulate natural conditions 

within the basin, but assuming that 

downstream dams had not yet been 

constructed.

Because a direct comparison of 

statistics between historical streamflows 

and future streamflows was required, 

historical streamflows were converted 

to an unregulated condition to match 

the unregulated condition of the future 

streamflows. This was done by running 

the Reservoir System Simulation 

software through water years 1928–98, 

again simulating the effect of large 

natural lakes before dams had been 

constructed.

The HEC Statistical Software 

Package, version 2.1, was used to 

generate peak annual winter (November–

March) unregulated flow rankings for 

the historical and future datasets. The 

resulting estimated flow ranges and 

rankings were based on the unregulated 

datasets of 1928–98 and 2030–59 

for the historical and future periods, 

respectively, which enabled ranking of 

peak winter flows (table 3). Comparing 

the rankings of historical, winter, 

unregulated peak-flow periods to future, 

winter, unregulated peak-flow periods provided scaling factors 

that were applied to historical period hydrographs to create 

extreme but plausible future condition hydrographs.

The historical hydrograph, representing an extreme 

high-flow, was the 0.005 AEP flood that occurred in winter 

1996. The USACE computed an unregulated peak flow 

of approximately 14,100 m3/s (500,000 ft3/s) for this 

flood on the Columbia River at The Dalles (14105700; 

U.S. Army Corps of Engineers, 1997) and interpolation 

between the first and second ranked peak flows indicated 

that the corresponding future peak flow was approximately 

40 percent greater (table 3). Similarly, the computed historical 

peak flow at Willamette River below Willamette Falls in 

winter 1996 was 12,200 m3/s (432,000 ft3/s) (U.S. Army 

Corps of Engineers, 1997), about 20 percent less than the 

corresponding future unregulated peak flow for the same 

Table 3. Peak-flow rankings for historical winter unregulated flow and future winter 

unregulated flow, Columbia and Willamette Rivers, Oregon, winter 1996.

[Flows based on Bulletin 17B flood-frequency analysis (Interagency Advisory Committee on Water 

Data [1981]) using the U.S. Army Corps of Engineers Hydrologic Engineering Cener statistical software 

package. Flows are in thousands of cubic meters per second (1,000 m3/s) and thousands of cubic feet 

per second (1,000 ft3/s)]

Rank of low 

to high 

probability

Historical unregulated 

flow

Future unregulated 

flow (2040s) Difference

(percent) (1,000 m3/s) (1,000 ft3/s) (1,000 m3/s) (1,000 ft3/s)

Columbia River at Bonneville Dam

1 15.89 561 21.38 755 34.6

2 14.05 496 19.77 698 40.8

3 12.69 448 18.49 653 45.8

4 11.35 401 17.16 606 51.0

5 9.66 341 15.26 539 58.3

6 8.35 295 13.71 484 64.1

7 7.02 248 11.98 423 70.3

8 5.07 179 9.06 320 78.7

9 3.68 130 6.71 237 82.1

10 3.14 111 5.69 201 81.7

11 2.74 96.8 4.93 174 80.2

12 2.14 75.5 3.74 132 74.8

Willamette River below Willamette Falls

1 12.23 432 14.98 529 22.3

2 10.96 387 13.82 488 26.2

3 9.99 353 12.88 455 29.1

4 9.03 319 11.92 421 32.0

5 7.73 273 10.50 371 35.8

6 6.74 238 9.32 329 38.6

7 5.69 201 8.01 283 40.9

8 4.08 144 5.80 205 42.4

9 2.89 102 4.02 142 39.4

10 2.40 84.9 3.28 116 36.1

11 2.06 72.9 2.73 96.6 32.5

12 1.54 54.4 1.91 67.4 23.9

ranking (table 3). Therefore, the 1996 historical hydrographs 

at the inflow boundary locations were perturbed to a 2040’s 

level by applying a scaling factor of 1.4 and 1.2 at Bonneville 

Dam on the Columbia River and the Willamette River 

below Willamette Falls, respectively (fig. 7). Future flood 

hydrographs for the lower Columbia River tributaries—

Washougal, Sandy, Lewis, and Cowlitz Rivers—were 

determined by using a scaling factor of 1.2 to correspond with 

the Willamette River, because insufficient data were available 

for the smaller lower Columbia River tributary basins to 

make river-specific scale factor estimates. For modeling 

purposes, these basins were scaled with the same factor as the 

Willamette River Basin because it seemed likely they would 

respond similarly to future atmospheric river events. These 

perturbed hydrographs were used as the inflow hydrographs in 

the future conditions hydraulic simulations.
Methods 15

tac18-1244_fig 07

EXPLANATION

0

5,000

10,000

15,000

20,000

Willamette River below Willamette Falls

Discharge in cubic meters per second

0

5,000

10,000

15,000

20,000

Columbia River below Bonneville Dam

Measured

Scaled measurement

January February

20 30 101 20 1

January February

20 30 101 20 1

Figure 7. Future inflow flood hydrographs for the Columbia River at Bonneville Dam 

and the Willamette River below Willamette Falls, Oregon.

Water-Surface Elevations Offshore of the Mouth of the 

Columbia River

The water-surface elevation imposed at the Pacific Ocean 

Boundary comprises three parts: (1) mean sea level, (2) storm 

surge deviations from mean sea level, and (3) deviations from 

mean sea level because of astronomical tides.

Mean Sea Level—The projections of future changes in 

mean sea level (MSL) depend on the assumptions made about 

greenhouse gas emissions in the future, the rate of warming of 

the climate, and future rate of terrestrial ice-sheet melting and 

collapse. At a given coastal location, relative changes in local 

MSL reflect the integrated effects of global MSL change plus 

changes of regional geologic, oceanographic, or atmospheric 

origin. The locally affected potential for future sea level is 

referred to as relative SLC and its effects should be considered 

as far inland as the extent of estimated tidal influence. In this 

study, a range of SLC realizations was considered because it 

is problematic to assign a specific value to future SLC (Hinkel 

and others, 2015).

The scenario-based approach bounds the range of 

potential SLC realizations using three equally plausible 

scenarios: low, intermediate, and high. Each of the three 

USACE scenarios is based on the latest science from 

Intergovernmental Panel on Climate Change (IPCC), NOAA 

and National Research Council (NRC) and is specific 

to individual NOAA tide stations (U.S. Army Corps of 

Engineers, 2018). The three SLC scenarios applicable for 

Astoria, Oregon (NOAA stage-measurement site 9439040) 

are shown in figure 8. In this study, three values for SLC 

were used that provided a wide range over which to evaluate 

the sensitivity of flood stage at Portland to a climate changeaffected ocean boundary. These three values can be placed into 

the context of the USACE scenarios as follows:

1. SLC 0 m: The USACE low scenario for future SLC 

is an extrapolation from the measured historical rate 

derived from NOAA tide gages. For 2040, the USACE 

projection for Astoria is -0.015 m (due to local tectonic 

uplift of the coast) using a base year of 1992, so the 

lowest value of SLC considered in this study was 0, 

representing no change from baseline conditions.

2. SLC 0.25 m: The USACE “intermediate” future SLC 

scenario accounts for the thermal expansion of the 

oceans and loss of ice from Antarctica and Greenland. 

The SLC of 0.25 m corresponds to a high USACE 

scenario in 2040 or an intermediate USACE scenario in 

2094.

3. SLC 1 m: To provide a context for assessing how an 

accelerating SLC in years beyond 2040 might affect the 

results shown, a third value of 1.0 m SLC was simulated. 

This value corresponds to the USACE “high” scenario in 

the year 2088.
16 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig 08

Polynomial (High SLC scenario)

Polynomial (Intermediate SLC scenario)

Polynomial (Historical trend, low SLC scenario)

EXPLANATION

Estimated relative sea-level change (SLC) scenarios for Astoria, 

Oregon—Based on USACE Engineer Regulation 1110-2-8162 

(NOAA CO-OPS/NOS, 9439040-Astoria/Tongue Point, Oregon) 

-0.1

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090

Year

Relative sea-level change, in tmeters (relative to local mean sea level)

Figure 8. Estimated sea-level change scenarios at Astoria, Oregon. Projections based on 

U.S. Army Corps of Engineers (2018).

Non-Tidal Residual Associated with Maritime Storms—

Based on its close proximity to the coastal ocean, the NOAA 

tide gage at Toke Point, Washington (9440910; fig. 1) was 

used to define the non-tidal residual due to maritime storms 

affecting the region of northwest Oregon and southwest 

Washington coast. The Toke Point tide gage is located at 

the mouth of Willapa Bay 8 km from the open coast and 50 

km north of the MCR. The Willapa Bay inlet has not been 

altered, and remains as a broad unobstructed tidal interchange 

from estuary to ocean. Because of this, the storm-induced 

non-tidal residual (storm surge) signal observed at Toke 

Point is unaltered, unlike tidal gages that are located within 

estuaries like the LCR where the inlet has been engineered/

confined. Storm surge (non-tidal residual) was determined 

by subtracting the astronomical tide reconstructed from 

tidal harmonics at Toke Point from the total water level 

recorded at Toke Point. Based on these considerations, storm 

surge computed for Toke Point is assumed to be a close 

approximation for open coast storm surge applicable for the 

coastal realm of the MCR.

The 0.5 AEP non-tidal residual associated with storm 

surge at Toke Point is 1.05 m (3.4 ft), based on a 43-year 

period of record. Non-tidal residual during storms frequently 

exceeds 0.6 m (2.0 ft), during average annual conditions. 

Three significant storms were identified, with peak water 

levels between 1.4 and 1.6 m (4.6 and 5.2 ft; fig. 9). The 

highest and broadest peak of non-tidal residuals associated 

with storm surge occurred in December 2007, with peak levels 

greater than 1.4 m that persisted for 14 hours. Therefore, the 

storm surge of December 2–6, 2007, was used as the prototype 

for the storm surge in future climate simulations. The 

calculated storm surge at Toke Point was scaled by a factor 

of 0.91 to convert the storm surge at Toke Point from an AEP 

recurrence of 0.02 to 0.05. This reduction in AEP intensity 

was implemented to develop a plausible total water level and 

to avoid imposing an excessively extreme ocean boundary 

condition of maximum spring tide sequence combined with 

maximum storm-induced non-tidal residual. The resulting 

time series of storm surge was added to the mean sea level 

projection and to the reconstructed tides (see section, 

“Astronomical Tidal Signal”).

Astronomical Tidal Signal—Tidal estimates at the 

location of the Astoria stage gage (9439040) were used 

to develop the astronomical tidal component of the future 

climate ocean boundary condition. In this study, no changes to 

sedimentation or accretion that might affect the tidal signal at 

the MCR were assumed. These “estimates” are reconstructions 

of the tides from the component tidal harmonics, the amplitude 

and phases of which are determined for individual locations 

based on the historical record of tides measured at that 

location. These estimates remove the non-tidal effects that are 

embedded in the records and can be compiled and downloaded 
Methods 17

tac18-1244_fig 09

December 2007

February 2006

March 1999

EXPLANATION

Non-tidal residual component of 

water level observed during 

three significant storms

-0.25

0

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

Non-tidal residual, in meters

Days

Figure 9. Storm surge peak water levels at Toke Point, Washington, March 1999, February 2006, and December 2007. Non-tidal 

residual component of water levels based on tidal gage at Toke Point (NOAA 9440910) for a 45-year period of record. The time 

series were aligned so the maximum value for each is coincident (at 4.5 days) to enable a unified comparison of each time series.

from the NOAA website: https://tidesandcurrents.noaa.gov/

tide_predictions.html. For the purpose of this study, tidal 

estimates at the Astoria stage gage through 11 water years 

(October 1, 1995—September 30, 2006) were analyzed. The 

5-day running mean of the daily maximum tidal water level 

was computed. The maximum of this 5-day running mean, 

during the 11 water years considered, occurred on February 9, 

2003. The time series of predicted tide centered on this date 

was used as the prototype for the astronomical tide in the 

future climate simulations by centering the high tide that 

occurred February 9, 2003, at 26 days and 12 hours in the 

future climate simulations and centering the peak in the time 

series of the non-tidal residual representing storm surge at 26 

days and 0 hours, which aligned semi-diurnal tidal peaks with 

the maximum in the storm surge (table 4; fig. 10).

Two-Dimensional River Stage Modeling

The approach of this study was to use two independently 

developed 2-dimensional hydraulic models to simulate watersurface elevation in the LCR and compare the output of the 

two models as an additional constraint on the precision of 

the results. The first model uses the Delft3D-Flexible Mesh 

(FM) platform; the second model uses the USACE Adaptive 

Hydraulics (AdH) platform. Both models were calibrated and 

Table 4. Timeline of peak stage and discharge in future climate 

prototype flood along the Columbia and Willamette Rivers, Oregon 

and Washington.

Event description Day Hour

Start of simulation 0 0

Maximum discharge at Bonneville on the 

Columbia River

24 0

Maximum discharge at Willamette Falls 

on the Willamette River, Oregon

25 0

Higher high water at Astoria, Oregon 25 12

Maximum stage at Vancouver, Washington 25 18

Maximum stage at Portland, Oregon 25 18.5

Maximum peak in storm surge at Astoria, 

Oregon

26 0

Lower high water at Astoria, Oregon 26 1

Higher high water at Astoria, Oregon 26 12

End of simulation 44 0
18 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig 10

Astronomical tide

Storm surge

Future boundary condition

EXPLANATION

0

1

2

3

4

5

Days since start of simulation

Water-surface elevation, in meters

20 25 30

Figure 10. Simulated astronomical tide, storm surge, and future tidal conditions at the 

mouth of the Columbia River, Oregon and Washington.

validated with historical flows and historical sea level during 

high-flows occurring during January and February 1996 

and April through July 1997. Both models then were used 

to simulate an extreme but plausible future climate scenario 

based on the February 1996 period, while considering three 

values for SLC at the MCR, resulting in three future climate 

simulations from each model. Important aspects of both 

models include the progression of LCR model development, 

model-specific aspects of how the ocean boundaries are 

handled, and the different way physical structures are 

embedded into the model mesh.

Hydraulic Model Comparison

This study compared the simulated outputs of the two 

models that were individually calibrated but used similar 

geometries, parameters, and boundary conditions. The domain 

of the LCR in both models extends from the Bonneville Dam 

on the Columbia River and the Willamette Falls, to 30–40 km 

offshore into the Pacific Ocean (fig. 1).

The models differed in their mesh resolution and the 

approach of representing physical structures. The Delft3D-FM 

model was coarser (fig. 11A), with 26,086 nodes and 39,382 

flow elements, than the AdH mesh, which included about 

268,000 nodes and about 518,000 elements (fig. 11B). 

For the Delft3D-FM model, the weir tool was used to draw 

the levee and pile dike features onto the model mesh and 

assign top elevations (figs. 12A and B). Alternatively, the 

AdH model, with its fine mesh, was able to resolve levees 

and represent nominal spatial attributes of pile dikes within 

the mesh and then assign appropriate heights, Manning’s n 

roughness coefficients, and vegetation classes to those mesh 

cells (figs. 12C and D). Additionally, the two models used 

different friction formulations, with Delft3D-FM using the 

Chézy formula and roughness coefficients, and AdH using the 

Manning formula and Manning’s n values (table 5).

Despite these differences, many model specifics were the 

same. The number, location, and height of levees included in 

the models were the same in size and crest elevation. Levee 

elevations were assigned based on lidar and as-built surveys 

(table 6). The two models also used the same terrain data, 

a composite of lidar and bathymetric surveys compiled in 

2010 (described in section, “Model Terrain Data,”) to assign 

ground elevation to mesh cells. Lastly, the riverine boundary 

conditions were developed from the same hydrographs, with 

the Delft3D-FM model applying discharge values at an hourly 

time step and the AdH model applying discharge values at a 

daily time step.
Methods 19

tac18-1244_fig 11

Sauvie

RM 101

RM 105

Vancouver

Bybee Lake

Smith Lake

Pile dike

PEN 1

PEN 2

Portland

Vancouver

Lake

Kelly

Point

Industrial

Area

Island

Pearcy Island

Hayden Island

Columbia

River

Columbia

Slough

Willamette

Multnomah

River

Channel

13.0

10.7

8.4

6.1

3.8

1.5

-0.8

-3.1

-5.4

-7.7

-10.0

EXPLANATION

Elevation, in meters above 

North American Vertical 

Datum of 1988 

EXPLANATION

13.0

-10.0

Elevation, in meters above 

North American Vertical 

Datum of 1988 

A. Delft3D-FM

B. AdH

0 1 2 MILES

0 1 2 KILOMETERS

0 1 2 MILES

0 1 2 KILOMETERS

Base from U.S. Army Corps of Engineers

Figure 11. Comparison of Delft3D-Flexible Mesh (Delft3D-FM) (A) and Adaptive Hydraulics (AdH) (B) model meshes with 

assignments of elevation along the Columbia and Willamette Rivers, Oregon.
20 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig12

EXPLANATION

6.03.40.9-1.7-4.2-6.8-9.3-11.9-14.4-17.0

Elevation, in meters 

above North American Vertical Datum of 1988 

Elevation, in meters 

above North American Vertical Datum of 1988 

Vegetation, 

emergent and upland

Off-channel 

bathymetry

Thalweg 

bathymetry

Pile dike

Finite element mesh 

material types

EXPLANATION EXPLANATION

253760

Grid cell 

boundary

EXPLANATION

Levee and pile 

dike

Grid cell 

boundary

Levee and pile 

dike

-17.0

Chezy value

A

B

C

D

0 1,000 FEET

0 200 METERS

Columbia

River Downstream

Upstream

Map from U.S. Army Corps of Engineers, 2018

Columbia

River Downstream

Upstream

RM 85.5

RM 85.5

RM 86RM 86

RM 86

RM 85.5

Figure 12. Comparison of Delft3D-Flexible Mesh (Delft3D-FM) mesh with assignments of bathymetry (

A) and roughness coefficients (

B), to Adaptive Hydraulics (AdH) 

mesh with assignments of bathymetry (

C) and mesh material types (

D) along the Columbia and Willamette Rivers, Oregon.
Methods 21

Table 5. Model roughness values for Delft3D-Flexible Mesh 

(Delft3D-FM) and Adaptive Hydraulics (AdH) along the Columbia 

and Willamette Rivers, Oregon.

[–, no data]

Model 

domain

Friction coefficient value

Delft3D-FM 

Chézy

AdH 

Manning’s n

Ocean 86 0.015

Estuary

Main channel 54–86 0.015

Tidal flood plain 5–56 0.025

Above estuary

Main channel 37–56 0.0265

Secondary channel 25 0.0275

Flood plain 5–25 0.05

Channel island 5 0.08

Jetty/pile dike – 0.05–0.08

Table 6. Elevation data compiled from light detection and radar surveys along the Columbia corridor levee system, Oregon and 

Washington.

[Values determined from U.S. Army Corps of Engineers lidar dataset. River miles shown in figures 2–4. Abbreviations: ft, foot; m, meter; MCDD, 

Multnomah County Drainage District #1; RM, river mile; NAVD 88, North American Vertical Datum of 1988; NA, not applicable]

Levee 

name

Diking 

district

Columbia River 

(RM)

Top of levee crest elevation above NAVD 88

Upstream Downstream

(m) (ft) (m) (ft)

Skamokawa/Price Island Wakiakum 4 34.2–38.9 4.8 15.7 4.8 15.7

Tenasillahe Island Clatsop 6 (inactive) 34.8–36.5 4.3 14.1 5.0 16.4

Puget Island/Little Island Wakiakum 39–46 5.1 16.7 4.7 15.4

Web, Westland, Woodson NA 44.5–49 5.5 18.0 5.2 17.0

Midland NA 49–50 5.5 18.0 5.5 18.0

Cowlitz 15 NA 57–59 6.6 21.7 6.6 21.7

Deer Island NA 77–82.5 9.8 32.2 9.7 31.8

Woodland Cowlitz 2 81.25–86 11.5 37.6 9.2 30.2

Lake River Delta NA 88–90 8.5 27.8 8.5 27.8

Bachelor Island - North NA 89–90.5 8.5 27.8 6.0 20.0

Bachelor Island - South NA 88.5–90 7.7 25.3 7.7 25.3

Scappoose NA 90–99.25 10.7 35.1 10.3 33.8

Clark County DD 14 - North Ridgefield 94–95.5 8.5 27.9 8.0 26.3

Clark County DD 14 - South Ridgefield 95.5–102.5 9.1 29.8 8.1 26.3

Sauvie Island Columbia 1 (inactive) 93–98 9.0 29.5 9.0 29.5

Sauvie Island Sauvie Diking District 98.3–101.5 10.9 35.8 10.9 35.8

Peninsula 1 MCDD 105.5–106.5 11.7 38.4 11.1 36.4

Peninsula 2 MCDD 106.5–108.5 11.6 38.1 11.5 37.7

Multnomah County - West NA 108.5–115 13.0 42.0 12.5 41.0

Multnomah County - East NA 115–118.5 13.7 44.0 13.0 42.0

Sandy Diking District NA 118.5–123 14.5 46.0 13.7 44.0

Steigerwald NA 123.9–128 14.1 46.3 13.1 42.9
22 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Delft3D-Flexible Mesh

The Delft3D-FM Suite is an open-source hydrodynamic 

model, capable of calculating combinations of 1D, 2D, 

and 3D unsteady flow over unstructured meshes in riverine 

and estuarine systems. It was developed by Deltares in the 

Netherlands, a research institute with a long history of hydrodynamical simulation throughout the world (Deltares, 2015). 

Delft3D-FM is the successor to the structured Delft3D Suite 

which was developed in the late 1980s. The unstructured 

mesh used in Delft3D-FM pairs rectangular, curvilinear 

cells, for main channel flow, with triangular cells for offchannel flow. This approach provides greater flexibility than 

structured meshes in adapting the resolution of the mesh to 

the underlying bathymetric and topographic gradients, and 

in aligning mesh boundaries to complex, difficult-to-follow 

boundaries on the ground. Delft3D-FM then solves the 

unsteady shallow water equations using the finite volume 

method on the unstructured mesh.

Delft3D-FM solves the Navier-Stokes equations for an 

incompressible fluid in two dimensions by depth averaging, 

which is the approach used in this study, and under the shallow 

water and Boussinesq assumptions. Under these assumptions, 

the vertical momentum equation is reduced to the hydrostatic 

pressure equation and vertical accelerations due to buoyancy 

effects and changes in topography are not considered. Because 

of mesh coarseness, the Navier-Stokes equations were 

Reynolds averaged to describe turbulent flow at the mesh 

scale; this process introduces Reynolds stresses. A k-epsilon 

turbulence closure model was then used to relate the Reynolds 

stresses to the Reynolds-averaged flow quantities. The 

equations are formulated in orthogonal curvilinear coordinates 

and the free surface level and bathymetry are related to a flat 

horizontal plane of reference, which, in this study, was the 

North American Vertical Datum of 1988 (NAVD 88).

Lower Columbia River Model Development

In 2012, the USGS Coastal and Marine Geology Program 

and Deltares collaborated to develop a coupled Delft3DSimulating Waves Nearshore structured model system, 

including hydrodynamic, wave, and sediment transport 

components, for the mouth of the Columbia River with the 

purpose of state-of-the-art simulation of sediment transport 

in the dynamic estuary entrance (Elias and others, 2012). 

Continuing with this research collaboration, a second study 

was developed to explore the effect of discharge on tidal 

hydrodynamics for a range of discharge classes (Van der 

Steeg, 2016). In the second study, the modeling suite was 

updated to the unstructured Delft3D-FM system and the study 

domain was expanded to include the entire LCR.

The first iteration Delft3D-FM LCR model developed 

in Van der Steeg (2016) extends from the Columbia River at 

Bonneville Dam and Willamette River at Willamette Falls in 

Oregon City to about 137 km offshore from the MCR into the 

Pacific Ocean. The large model domain allowed simulation 

of ocean tide propagation into the Columbia River estuary 

and LCR, replication of fluvial flow from LCR main stem and 

tributaries, and tides interacting with riverine flow. The initial 

model domain had spatial resolution that varied from 100 to 

2000 m, and was represented by approximately 25,375 nodes. 

Nodal point elevations within the Delft3D-FM model mesh 

were interpolated from the 2010 Lower Columbia Terrain 

Model developed from lidar and multibeam bathymetric 

survey data by the USACE Portland District in support of 

the Columbia River Treaty. With its focus on the estuary 

and effects of discharge and tides, this Delft3D-FM LCR 

model was fully 3-dimensional and accounted for salinity 

propagation.

Lower Columbia River Model for Climate Change Study

Prior to this study, the Delft3D models developed by 

USGS Coastal and Marine Geology Program were focused 

studies of the LCR estuary, which did not require the same 

level of upstream flood plain coverage in the model mesh 

that was required for this study. Because this study explored 

the effects of extreme but plausible high flows on the 

Columbia Corridor Levee System, it was critical to include 

flood plains in the LCR that might be inundated during high 

flow. Greater detail was added to Van der Steeg’s (2016) 

first-iteration unstructured mesh to include more LCR flood 

plain, and inflow was added from appropriate tributaries. 

Mesh and model modification tasks were required to create a 

Delft3D-FM model that would be appropriate to use for this 

Levee Ready Columbia (LRC) study:

1. Increase the mesh coverage to include relevant flood 

plain with the potential for inundation during peak flow 

conditions, specifically around North Portland peninsula, 

Multnomah Channel, and the Columbia River slough.

2. Expand mesh coverage to include interior areas behind 

levees, specifically the North Portland peninsula and 

Sauvie Island, to model the effect of interior area storage 

(and hydrograph effects) should the levees become 

overtopped.

3. Expand the mesh to include inflow from relevant 

tributaries, specifically the Sandy, Lewis, and Cowlitz 

Rivers. The lowest 1–2 km of these tributaries was 

incorporated into the model mesh in order to accurately 

convey the inflows into the main river channel.

4. Include weir structures to portray levees and pile dikes 

with appropriate crest elevations.
Methods 23

When the enhancements to the model mesh were 

complete, it was composed of 39,382 elements, 26,086 nodes, 

122 weir structures to represent off-channel levees, and 137 

weir structures to represent in-channel pile dikes.

Physical Parameters—Flow characteristics were 

assigned to the mesh cells using triangulation from values 

specified at discrete point locations. Each cell was assigned 

an average elevation value (figs. 12A and 12C) based on 

high-resolution bathymetry data provided by the USACE and 

GEBCO. Chézy roughness values also were mapped onto 

the mesh using Helaire (2016) and Elias and others (2012) 

initially and refined to optimize calibration to the historical 

events. Generally, Chézy values were 86 in the ocean, ranged 

from 54 to 86 in the estuary, were 50 along the main channel 

and flow paths, and were 5 to 25 over vegetated flood plain 

areas (table 5; figs. 12B and 12D).

Hydraulic Structures—The last step of model 

construction was to map flow structures, such as pile dikes 

and levees, that were not fully captured at the mesh resolution. 

In Delft3D-FM, the “weir” tool was used to represent these 

features and their maximum height information in the model. 

Pile dike locations were determined using maps and aerial 

images (Google Earth) and represented by weirs at the nearest 

cell edges in the model (white lines in figures 12A and 12B). 

The Delft3D-FM weir structure was used to simulate levees 

throughout the lower Columbia River. Levees were placed at 

their correct locations, crest, and height with maps and lidar 

data (U.S. Army Corps of Engineers, 2010).

Boundary Conditions—Boundary conditions for river 

inflow are applied in the model at each of the five upstream 

tributary locations using a time-varying flow boundary 

condition at a 1-hour time step. Inflow boundary conditions 

used USGS data for the Columbia River at Bonneville Dam, 

Sandy River, Washougal River, Willamette River, Lewis 

River, and Cowlitz River as described in section, “Hourly 

Flow Hydrographs at the Upstream Boundaries.” The head 

of tides for the Washougal River was not implemented in 

the Delft3D-FM model, because the tributary flow from this 

drainage was not deemed relevant in comparison to the other 

four tributaries. Instead, flow from the Washougal River was 

split and applied to the Sandy River and Bonneville Dam 

inflows.

The offshore area of the MCR in the Delft-FM model 

domain is roughly rectangular, about 54 km in latitude and 42 

km in longitude (fig. 1). The ocean boundary condition was a 

specified water elevation at the upper and lower left corners 

of this rectangle (fig. 1) in several steps. First, the amplitude 

and phase of 13 tidal constituents (M2, S2, N2, K2, K1, O1, 

P1, Q1, Mf, Mm, M4, MS4, and MN4; Talley and others, 

2011) were determined at the location of the upper and lower 

left corners of the ocean boundary using tidal prediction 

software developed by Oregon State University (Egbert and 

Erofeeva, 2002). The model was run through the period of the 

1996 and 1997 historical floods with these tidal constituents 

specified as boundary conditions (amplitude and phase) at 

the upper and lower left corners of the ocean boundary. The 

amplitude and phase of the same 13 tidal constituents were 

extracted from the simulated time series at Astoria using the 

ftide function of the TideHarmonics package in R version 

3.3.2 (R Core Team, 2016; Stephenson, 2016). The simulated 

amplitudes and phases were compared with the published 

amplitudes and phases of the tidal constituents at Astoria 

(https://tidesandcurrents.noaa.gov/harcon.html?id=9439040, 

accessed February 28, 2017) to calculate a correction to the 

amplitude and phase at the boundary locations. The model was 

run again with these corrections, and the simulated time series 

at Astoria was again compared to the recorded elevation. This 

time, the comparison was done by subtracting the recorded 

time series from the simulated time series to obtain a nontidal residual, and then smoothing that residual with a 5-day 

moving average. The smoothed residual was added into the 

hourly tidal time series at the upper and lower left corners of 

the ocean boundary to provide the next iteration of the ocean 

boundary condition. The model was run again, and a 3-day 

moving average of the residual at Astoria was calculated and 

added into the boundary conditions time series to provide the 

final ocean boundary condition.

To obtain ocean boundary conditions for the future 

climate simulations, the model simulated the historically high 

tide period from November 23, 2003, to January 12, 2004, 

with the amplitude and phase of eight tidal constituents from 

the Oregon State University tidal prediction software specified 

at the upper and lower left corners of the ocean boundary, 

and using the corrections to amplitude and phase for the 1996 

historical period. The NOAA predicted tide at Astoria during 

the same period was subtracted from the simulated time series 

at Astoria, and the residual was smoothed with a 5-day running 

average. This provided a small correction (average about 

9 cm) to the tidal boundaries to account for unresolved minor 

tidal harmonics and effects of the geometry of the estuary on 

the propagation of the tides. The ocean boundary conditions 

were converted to an hourly time series of elevations, and the 

smoothed residual was added into those time series, as well 

as the projected change in mean sea level and the storm surge 

based on the winter 2007 prototype, to provide the final ocean 

boundary condition for the future climate simulations.
24 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Adaptive Hydraulics (AdH) Model

Adaptive Hydraulics (AdH) is a multi-physics computer 

model developed by the USACE, Engineer Research and 

Development, and Coastal and Hydraulics Laboratory to 

evaluate hydrodynamics and related transport processes 

(https://chl.erdc.dren.mil/adh/main/index.html, accessed 

February 23, 2018). AdH incorporates capabilities for 

the numerical simulation of saturated and unsaturated 

groundwater flow, the full Navier-Stokes equation, as well as 

2- and 3-dimensional (2- and 3-D) shallow-water equations. 

The AdH 2D shallow-water equations are based on the 

vertical integration of the equations of mass and momentum 

conservation for incompressible flow under the hydrostatic 

pressure assumption. Reynolds stresses are evaluated using 

the Boussinesq approach based on the gradient in the currents, 

fluid density, and kinematic eddy viscosity. The AdH shallowwater equations conserve local and global mass, and balance 

momentum with pressure across an interface (Berger and 

Howington, 2002).

The domain is represented by an unstructured triangle 

mesh where an implicit finite element method (FEM) 

solves for variables of interest, in this case water depth and 

velocity. An unstructured mesh allows element size to vary 

throughout the model domain. The shallow-water equations 

are discretized using the Petrov-Galerkin FEM approach, with 

primary variables being represented as linear polynomials 

across each element (Berger and Stockstill, 1995). Material 

properties affecting fluid flow due to friction, eddy-viscosity, 

or other local considerations are assigned for each element 

based on morphology, vegetation, and if present, relevant 

physical aspects of structures.

The adaptive feature of AdH consists of its ability 

to dynamically refine and relax the model mesh and vary 

temporal resolution such that both model accuracy and model 

performance are optimized. The ability of AdH to allow the 

domain to be wet and dry as flow conditions or water depths 

change is suitable for solving fluid flow problems in shallow 

marsh environments, beach slopes, flood plains, and other 

terrain features of interest. For the simulations discussed in 

this report, the adaptive mesh option was not activated (the 

AdH mesh remained static through each simulation).

Lower Columbia River Model Development

The AdH model was first developed for the LCR in 

2011–12, under a collaborative framework between the 

USACE-Portland District and the Engineering and Research 

Development Center-Coastal and Hydraulics Laboratory 

(Pevey and others, 2012; Savant and McAlpin, 2014) to 

evaluate the effect of sea-level change on the water-surface 

profile and sediment transport within the Federal navigation 

channel, to optimize dredged material management practices 

within the LCR, and to evaluate hydraulic attributes of several 

habitat restoration projects.

The LCR AdH model domain extends from Bonneville 

Dam to 33 km offshore into the Pacific Ocean (fig. 1). The 

large domain allowed simulation of ocean tide propagation 

into the Columbia River estuary and LCR, fluvial flow from 

LCR main stem and tributaries, and tides interacting with 

riverine flow. The initial model domain had spatial resolution 

that varied from 10 to 1,000 m, and was represented by 

approximately 433,300 elements and 226,100 nodes. Nodal 

point elevations within the AdH model FEM mesh were 

interpolated from a digital elevation model developed from 

lidar (Watershed Sciences, 2010) and bathymetric survey data 

collected by the USACE Portland District. The LCR AdH 

model uses the 2D shallow water flow module to simulate 

time-varying depth-averaged currents and time-varying river 

stage in a horizontally variable framework. The scope for 

this study focused on evaluating river stage for the PortlandVancouver area (RM 90–110; fig. 4). Although salinity and 

related baroclinic (3D) circulation in the Columbia River 

affects the hydraulics of the lower estuary (RM 0 to 25), 

salinity effects of the lower estuary have minor effect on river 

stage in the Portland-Vancouver area, especially during high 

fluvial discharge periods. For this reason, salinity propagation 

was not considered relevant for this work, so a 3D analysis 

to evaluate saline and fresh water mixing was not required. 

Consequently, model results may be unreliable downstream of 

RM 25.

Lower Columbia River Model for Climate Change Study

Prior to this study, the LCR AdH model had been used 

by the USACE for evaluating fluvial flow scenarios equal to 

or less than the 0.5 AEP. Initial development of the LCR AdH 

model did not include areas that would be inundated by flows 

significantly greater than 0.5 AEP. Because the LRC project 

was focused on evaluating Columbia River flows for future 

scenarios greater than the current 0.01 AEP in combination 

with effects of relative SLC, the LCR AdH model was 

modified and recalibrated for the LRC project. The following 

model modification tasks were required to improve the AdH 

model for use on the LRC project:
Methods 25

1. Increase mesh resolution in the lower reaches of inflow 

tributaries to ensure physically accurate flow conveyance 

and model stability during extreme high flow conditions.

2. Expand the model mesh coverage to include flood plains 

that have the potential of being inundated during peak 

flow conditions evaluated for this project.

3. Expand the mesh coverage to include areas behind 

levees in order to accurately simulate the effect of 

interior area storage on the river profile should the levees 

become overtopped. (The interior areas for several “very 

high” levees in the Portland metro area, east of PEN 2 

along RM 108–120 (fig. 2), were not implemented 

within the AdH model because it was deemed highly 

unlikely that these levees would be overtopped in the 

model simulations. The model accurately defined the 

crest elevation for these levees (MCDD and SDIC); 

however, if the simulated river stage exceeded the 

crest elevation of these levees, the levees would not be 

overtopped and river stage would continue to increase as 

if the levee were an infinitely high wall.) Consequently, 

these levees were not overtopped during model runs for 

this study. If they had been overtopped, the mesh would 

have been revised to correctly emulate the levee interior 

area aspects.

4. Increase mesh resolution to ensure accurate portrayal of 

levee crest elevation and width.

5. Increase mesh resolution near confluence areas, where 

multiple channels meet or rejoin, to ensure physically 

accurate flow conveyance and model stability during 

extreme high flow conditions. For example, it was 

essential that Multnomah Channel (fig. 4) be accurately 

portrayed within the model domain, due to the complex 

hydraulic connectivity that Multnomah Channel has with 

the Willamette and Columbia Rivers, and with the flood 

plain of Sauvie Island during high water conditions.

6. Fully resolve backchannel areas behind diking 

districts—Smith and Bybee Lakes and the Columbia 

Slough (fig. 4), for example to ensure physically 

accurate flow conveyance and model stability during 

extreme high flow conditions.

After the modifications were imposed on the model, the 

mesh had increased to 518,000 elements and 268,000 nodes; 

an increase of 84,700 elements and 41,900 nodes from the 

inception of the model.

Physical Parameters—Each polygon within the AdH 

LCR mesh was assigned a material type based on river 

morphology, such as emergent and upland vegetation, channel 

thalweg, off-channel flood plain, or pile dike. Hydraulic 

friction of the terrain was defined in terms of Manning’s n 

values, which were converted to an equivalent bed-roughness 

height based on water depth and material type. Manning’s n 

varied from a low of 0.015 in the ocean to a high of 0.08 on 

channel islands (table 5). Turbulent shear stress was defined 

in term of a constant eddy viscosity, which varied from a low 

value of 2 in the main channel, to a high of 20 in pile dikes.

Hydraulic Structures—The AdH model included most 

of the 233 pile dikes in the LCR and numerous levee systems 

within the model mesh. Rather than emulate each individual 

piling, the pile dikes were represented within the AdH mesh 

in terms of average pile density (piles per unit area) applied 

over the effective area (figs. 12C and 12D). Pile dikes were 

expressed as unsubmerged vegetation with a Manning’s 

roughness coefficient of 0.05, pile density equal to 1.5 piles 

per square meter, and pile diameter of 0.3 m. Pevey and others 

(2012) documents that this approach successfully emulated 

pile dikes as compared to expressing each timber element 

within a pile dike. A disadvantage of emulating pile dikes 

as unsubmerged vegetation is that top elevation for timber 

piles is unbounded, regardless of river stage and the pile 

dike effect may be overestimated for conditions when river 

stage is significantly higher than the actual pile top elevation; 

however, this effect is assumed to be small for the LCR due to 

the high porosity of the simulated pile dikes. The LCR levees 

also were represented within the AdH mesh with a width of 

two mesh elements to avoid any numerical “leakage” across 

unsubmerged levees, and levee height was determined from 

lidar and construction documentation (table 6).

External Boundary Conditions—The LCR AdH model 

has two types of hydraulic boundary conditions: (1) a 

downstream ocean boundary simulated with time-varying 

water-surface elevation and (2) upstream tributary inflow 

boundaries for the five main riverine systems simulated with 

time-varying flow. The farthest downstream ocean boundary 

of the AdH model is a semi-circular arc extending 33 km 

offshore from the mouth of the Columbia River. The upstream 

boundaries of the AdH model are defined by the head of tides 

for each of the five main riverine systems affecting the model 

domain.
26 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Time-varying water-surface elevation, based on tides 

measured by NOAA at the tide gage at Astoria (9439040; 

RM 17.5), was applied to the ocean boundary of the AdH 

model at a 1-hour time step for the calibration simulations 

that used historical data and the climate change scenario 

evaluations. Because the Astoria tide gage is located 24 km 

inland and 57 km from the ocean boundary of the model, it 

was necessary to adjust the measured tide elevations before 

applying them at the ocean boundary. The tidal adjustment 

had three parts: vertical shift, amplitude reduction, and time 

lag. The mean of the measured tidal data at Astoria required 

a vertical shift of -0.027 m and a scaling factor of 0.95 due to 

the tidal wave amplification within the estuary. The scaling 

factor essentially decreases the amplitude of the tidal signal, 

whereas the vertical shift adjusts the mean of the signal. Due 

to the distance between the AdH ocean tidal boundary and 

the Astoria tidal gage, a time lag of 1.1 hours was applied to 

the Astoria tide data. The resulting simulated water-surface 

elevation at Astoria closely matched the data reported by 

NOAA. The tidal adjustment factors were developed as part 

of the LCR AdH model development (U.S. Army Corps 

of Engineers, 2016) and followed a similar approach and 

associated values produced to support the 2014 Columbia 

River Treaty Study (WEST Consultants, written commun., 

November 11, 2011).

Boundary conditions for river inflow were applied at 

each of the five upstream tributary locations using a timevarying flow boundary condition at a 1-day time step. Inflow 

boundary conditions used USGS data for the Columbia River 

at Bonneville Dam, Sandy River, Washougal River, Willamette 

River, Lewis River, and Cowlitz River as described in section, 

“Hourly Flow Hydrographs at Upstream Boundaries.”

Historical Simulations

The calibration of the LCR hydraulic models focused on 

adjusting the roughness parameters (table 5) to simulate river 

stage accurately during high-flow periods in 1996 and 1997. 

The simulated stage near the mouth of the LCR was compared 

to NOAA-predicted tidal stage at Astoria, and simulated 

stage near Portland was compared to measured water-surface 

elevations in the Columbia River at Vancouver (14144700) 

and in the Willamette River at Portland (14211720). There 

were differences in the calibration and validation procedure 

used for the two models. The Delft3D-FM model was 

calibrated to Willamette River stage during the winter 1996 

flood, whereas the AdH model was calibrated to Columbia 

River stage during the spring 1997 freshet event in order to 

bracket the uncertainty in Portland-vicinity flood stage.

The Delft3D-FM model was calibrated to the 1996 

flood, with an emphasis on adjusting friction parameters 

(Chézy coefficients) to accurately simulate the overall flood 

hydrograph and, in particular, peak stage at the Willamette 

River stage gage at Portland (14211720). This decision was 

based on the higher peak stage on the Willamette River at 

Portland than the stage on the Columbia River at Vancouver, 

and because this type of flood was exceptional mostly because 

of the high flows in the Willamette River that coincided with 

moderately high flows on the Columbia. The Delft3D-FM 

model was then validated to the 1997 flood, with no change in 

friction parameters.

In contrast, the AdH model was calibrated to the 1997 

flood, with an emphasis on accurately simulating the peak 

stage on the Columbia River at Vancouver. This decision was 

made because the Columbia Corridor Levee System is located 

on the Columbia River and within several miles of Vancouver; 

therefore, it was more important to match the higher stage 

at Vancouver on the Columbia River than to match stage at 

Portland on the Willamette River. Model calibration for the 

AdH model was achieved by adjusting the hydraulic friction 

parameters (Manning’s n). Calibration for the AdH model was 

achieved for the 1997 freshet by increasing the Manning’s-n 

value for three mesh material types: Material 1 (off-channel 

area) was increased from 0.025 to 0.0265, Material 3 (river 

thalweg) was increased from 0.025 to 0.0275, and Material 7 

(shore attached riparian/upland) was increased from 0.025 to 

0.050. These Manning’s-n adjustments are reasonable because 

the initial values were based on flows for a 0.5 AEP flood. 

The higher Manning’s n values used in the current study were 

necessary because simulated higher flows result in enhanced 

bedforms and increased riverbed friction (U.S. Army Corps of 

Engineers, 2014). The AdH model then was validated to the 

1996 flood, with no further changes.

Simulations for 1996

This extraordinary high-water event (during January 15–

February 28, 1996) was the result of an atmospheric river 

rain period and the associated rapid increase in temperature, 

following prolonged snow accumulation at high elevations. 

The resulting regional (westside of the Cascade Mountains) 

run-off was characterized by high flow conditions for all 

LCR tributaries. The flood had an estimated AEP of 0.01 for 

Willamette River flow and an AEP of 0.05 for the combined 

flow in the Columbia and Willamette Rivers. Near the mouth 

of the Columbia River during February 5–10, the combination 

of a spring phase ocean tide and a coastal storm surge of 

0.6 m (2.0 ft) resulted in a sea level at the MCR exceeding 

3 m (10 ft) above NAVD 88. Thus, the February 1996 flood 

affected the LCR water levels from both the ocean and 

upstream boundaries.
Historical Simulations 27

Flow in the Willamette River at Portland (14211720) 

peaked at 11,800 m3/s (417,000 ft3/s) on February 9, 1996, 

12–24 hours after the Columbia River peaked at 13,200 m3/s 

(466,000 ft3/s) at Bonneville Dam on February 8, 1996. 

Considerable effort was expended by the USACE to manage 

Columbia and Willamette River flood control reservoirs to 

avert flooding in the Portland-Vancouver metro area. The 

Willamette River is constrained through urbanized Portland 

and has a fraction of the hydraulic radius of the Columbia 

River, and unlike the 1997 freshet in which the Willamette 

River was essentially a backwater for Columbia River high 

flow, the Willamette River peak flow during February 1996 

was 85-percent of the combined peak flow in the Columbia 

River downstream of the confluence. 

Both models were run for the period between January 15 

and February 28, 1996, to capture the hydrograph build-up to 

the February 8–9 flood and then simulate the slow ramp-down 

period, and both models captured the trends in Columbia River 

and Willamette River water-surface elevations at Astoria, 

Portland, and Vancouver (figs. 13, 14, and 15). Throughout 

the 1.5-month simulation, AdH model results tended to be 

0.05 to 0.1 m higher than the measurements made at the 

Columbia River at Vancouver. Delft3D-FM model results over 

the entire simulation were less biased than AdH model results 

(-0.022 m [-0.07 ft] as opposed to 0.11 m [0.37 ft], table 7) 

but the peak stage simulated by the Delft3D-FM model was 

about 0.3 m (1 ft) lower than measurements, whereas the 

peak stage simulated by the AdH model was about 0.1 m 

(0.3 ft) higher (table 8, fig. 15). The comparison between the 

two models was similar at the Willamette River at Morrison 

Bridge streamgage—AdH model results were biased high 

over the entire simulation (0.28 m [0.93 ft]), Delft3D-FM 

model had a lower bias (0.10 m [0.33 ft]), and the peak stage 

simulated by the AdH and Delft3D-FM models was 0.39 m 

(1.29 ft) and 0.11 m (0.37 ft) higher, respectively, compared 

to the streamgage measurements (table 8). The performance 

statistics for both models were very good—Nash-Sutcliffe 

statistics ranged from 0.96 to 0.99 (table 7). Root mean 

squared error (RMSE) was 0.11 m (0.37 ft) (at Columbia 

River at Vancouver) and 0.18 m (0.59 ft) (at Willamette River 

at Morrison Bridge) in Delft3D-FM model simulation results, 

RMSE was 0.16 m (0.52 ft) (at Columbia River at Vancouver) 

and 0.32 m (1.06 ft) (at Willamette River at Morrison 

Bridge) in the AdH model simulation results. Some deviation 

from measurements at the streamgages is expected and a 

consequence of simplifying assumptions used in the models. 

For example, the boundary condition at Bonneville Dam is 

based on daily-averaged flow and therefore will smooth out 

some real fluctuations, which could broaden the simulated 

peak in water-surface elevation downstream. Much of the 

difference between the model simulation results, however, 

can be explained by the selections made during the calibration 

process. The AdH model was calibrated to Columbia River 

at Vancouver stage during 1997; the Delft3D-FM model was 

calibrated to Willamette River at Morrison Bridge stage during 

1996. It is notable that both models simulated a peak stage 

during the 1996 flood that was higher at Morrison Bridge than 

at Vancouver by similar amounts—0.37 m (1.21 ft) in the 

AdH model, and 0.46 m (1.50 ft) in the Delft model (table 8). 

The measurements indicated Morrison Bridge peak stage was 

higher by only 0.059 m. Because both models were calibrated 

separately but resulted in a similar difference in stage between 

Portland and Vancouver, the difference is likely due to an 

incomplete understanding of the hydraulics of the Portlandvicinity system during the 1996 flood or uncertainties in the 

Willamette River boundary.

The maximum water-surface elevation profiles for the 

AdH and Delft3D-FM models along the Columbia River 

were in good agreement from RM 0 to about RM 38 but 

diverged upstream from there (fig. 16). Upstream of this 

transition point, the maximum stage simulated by the AdH 

model was consistently higher than that simulated by the 

Delft3D-FM model, by an average of 0.45 m (1.48 ft), with 

the maximum difference of 0.74 m (2.43 ft) occurring about 

RM 87. The gradient in water-surface elevation in both models 

also increased upstream of about RM 38. The increase in 

the gradient of the water-surface profile is consistent with 

geologic and morphologic confinement of the Columbia River 

upstream of RM 38, especially under high flow conditions. 

The AdH maximum water-surface elevation profile was higher 

than the Delft3D-FM maximum water-surface elevation 

profile along the entire reach of the Columbia River upstream 

from RM 38, and the 0.38 m (1.22 ft) difference in maximum 

water-surface elevation between the two models is evident at 

RM 105 (Vancouver; fig. 2); however, both models reasonably 

bound the 1996 high-water marks collected from RM 39 to 

114 (table 9; fig. 16).

Several levee systems downstream of the PortlandVancouver area were overtopped during the 1996 model 

run in both models. These included Tenasillahe Dike, Lake 

River Dike, and parts of the Clark County diking district 

near Ridgefield, Washington. These same levees are thought 

to have been overtopped during the 1996 flood, based on 

anecdotal information. The overtopping of these levees and 

filling of the areas behind them had little or no effect on the 

water-surface elevation hydrograph at Vancouver because the 

rate of overtopping was slow and because the storage volume 

in the flooded interior areas was small compared to the volume 

of flood water in the LCR.
28 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig 13

EXPLANATION

Measurement

AdH simulation

Delft3D-FM simulation

1996

1997

-1

0

1

2

3

4

Water-surface elevation, in meters

31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

-1

0

1

2

3

4

Water-surface elevation, in meters January February 1996

31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

May June 1997

Figure 13. Measured and simulated time series on the Columbia River at Astoria, Oregon, 1996 and 1997.
Historical Simulations 29

tac18-1244_fig 14

EXPLANATION

Measurement

AdH simulation

Delft3D-FM simulation

1996

1997

4

6

8

10

11

3

5

7

9

Water-surface elevation, in meters 4

6

8

10

11

3

5

7

9

Water-surface elevation, in meters

January February

April May June July

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

15 20 25 30 5 10 15 20 25 30 5 10 15 20 25 30 5 10

Figure 14. Measured and simulated water-surface elevations at the Willamette River at Morrison Bridge, Oregon, 

1996 and 1997.
30 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig 15

EXPLANATION

Measurement

AdH simulation

Delft3D-FM simulation

1996

1997

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

15 20 25 30 5 10 15 20 25 30 5 10 15 20 25 30 5 10

January February

April May June July

4

6

8

10

11

3

5

7

9

Water-surface elevation, in meters

4

6

8

10

11

3

5

7

9

Water-surface elevation, in meters

Figure 15. Measured and simulated water-surface elevations at the Columbia River at Vancouver, Washington, 1996 

and 1997.

Table 7. Hydraulic model performance statistics, Willamette and Columbia Rivers, Oregon and Washington, 1996 and 1997.

[Model: AdH, Adaptive Hydraulics model. Delft3D-FM, Delft3D-Flexible Mesh model. Abbreviations: ft, foot; m, meter]

Model Year Root mean square error Nash-Sutcliffe 

statistic

Bias Number data 

points (m) (ft) (m) (ft)

Willamette River at Morrison Bridge, Portland, Oregon (14211720) hourly values

Delft3D-FM 1996 0.18 0.59 0.99 0.100 0.33 1,057

AdH 1996 0.32 1.06 0.96 0.280 0.93 1,057

Delft3D-FM 1997 0.09 0.28 0.99 0.002 0.01 2,185

AdH 1997 0.13 0.41 0.99 0.065 0.21 2,185

Columbia River at Vancouver, Washington (14144700) hourly values

Delft3D-FM 1996 0.11 0.37 0.99 -0.022 -0.07 1,057

AdH 1996 0.16 0.52 0.99 0.110 0.37 1,057

Delft3D-FM 1997 0.09 0.29 0.99 0.016 0.05 2,185

AdH 1997 0.13 0.43 0.99 -0.031 -0.10 2,185
Historical Simulations 31

Table 8. Comparison of peak stage for historical simulations, Willamette and Columbia Rivers, Oregon and 

Washington, 1996 and 1997.

[Model: AdH, Adaptive Hydraulics model. Delft3D-FM, Delft3D-Flexible Mesh model. Abbreviations: ft, foot; m, meter; NAVD, North 

American Vertical Datum of 1988]

Model Year

Peak stage above 

NAVD 88

Deviation of simulated peak stage from 

measured peak stage

(m) (ft) (m) (ft)

Mouth of Columbia River at Tongue Point, Astoria, Oregon (9439040)

Measured 1996 3.53 11.58 NA NA

Delft3D-FM 1996 3.76 12.32 0.23 0.74

AdH 1996 3.74 12.26 0.21 0.68

Measured 1997 3.34 10.95 NA NA

Delft3D-FM 1997 3.60 11.82 0.27 0.87

AdH 1997 3.57 11.70 0.23 0.75

Willamette River at Morrison Bridge, Portland, Oregon (14211720)

Measured 1996 9.95 32.64 NA NA

Delft3D-FM 1996 10.06 33.01 0.11 0.37

AdH 1996 10.34 33.94 0.39 1.29

Measured 1997 7.17 23.52 NA NA

Delft3D-FM 1997 7.11 23.32 -0.062 -0.20

AdH 1997 7.19 23.58 0.016 0.05

Columbia River at Vancouver, Washington (14144700)

Measured 1996 9.89 32.45 NA NA

Delft3D-FM 1996 9.60 31.51 -0.29 -0.94

AdH 1996 9.98 32.73 0.085 0.28

Measured 1997 7.43 24.37 NA NA

Delft3D-FM 1997 7.36 24.14 -0.069 -0.23

AdH 1997 7.30 23.93 -0.13 -0.44

Difference in peak stage between Willamette River at Portland and Columbia River at Vancouver

Measured 1996 0.059 0.19 NA NA

Delft3D-FM 1996 0.46 1.50 NA NA

AdH 1996 0.37 1.21 NA NA

Measured 1997 -0.26 -0.85 NA NA

Delft3D-FM 1997 -0.25 -0.82 NA NA

AdH 1997 -0.11 -0.36 NA NA
32 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig 16

EXPLANATION

AdH maximum

AdH mean

Measurement

Delft3D-FM maximum

Delft3D-FM mean

High-water marks

0 50 100 150

0

5

10

15

0 50 100 150

Distance upstream from mouth of Columbia River, in river miles

Water-surface elevation, in meters

1996

0

5

10

15

Water-surface elevation, in meters

1997

Figure 16. Stream profile showing simulated water-surface elevation, river miles 0–150, 

Columbia River, Oregon and Washington.
Historical Simulations 33

Table 9. High-water marks measured by CH2MHILL for the U.S. Army Corps of Engineers along the Columbia River, Oregon and 

Washington, February 1996.

[Elevations are in meters above North American Vertical Datum of 1988. Latitude/longitude referenced to North American Datum of 1927. Abbreviations: ft, 

foot; HWM, high-water mark; mi, mile; NA, not applicable; NGVD 29, National Geodetic Vertical Datum of 1929; PGE, Portland General Electric; RM, river 

mile; USACE, U.S. Army Corps of Engineers; USWB, U.S. Weather Bureau]

River 

mile Elevation Latitude Longitude Comment

39.0 4.24 46.190 -123.425 Puget Island; on right bank on northwest side of island, on Ostervold Road, 

about 1,700 ft from intersection with Crossdike Road and North Welcome 

Slough Road.

41.1 4.24 46.171 -123.402 Puget Island; on right bank on southwest side of island, at 

327 West Sunny Sands Road (near west end of Sunny Sands Road).

43.9 4.52 46.150 -123.365 Puget Island; on right bank at south end of island, off East Sunny Sands Road 

about 0.8 mi from intersection with Highway 409 (Ferry Road).

47.1 4.82 46.138 -123.296 On left bank on north side of Webb Drainage District Dike Road about 0.85 mi 

east of Woodson Road.

48.8 5.53 46.135 -123.252 NA

50.5 5.88 46.150 -123.220 NA

52.6 5.43 46.174 -123.190 NA

54.8 5.82 46.172 -123.156 From PGE Beaver Power Plant staff gage, HWM form, and photograph.

55.1 5.62 46.170 -123.149 NA

57.8 5.98 46.168 -123.104 Vicinity of Mayger RM 57.7.

60.5 6.49 46.163 -123.044 Elevation by Cowlitz County Consolidated Diking Improvement District #1.

62.4 6.64 46.141 -123.015 Elevation by Cowlitz County Consolidated Diking Improvement District #1; 

river staff gage at Reynolds pump station outfall.

66.0 6.69 46.101 -122.965 NA

66.1 6.64 46.108 -122.959 Elevation by Cowlitz County Consolidated Diking Improvement District #1; 

staff gage on port dock.

67.7 7.05 46.090 -122.933 NA

72.5 7.57 46.040 -122.870 Could be exposed to wave action from Columbia River.

72.6 7.07 46.040 -122.865 Within leveed area north side Kalama River.

73.1 7.18 46.029 -122.887 NA

75.4 7.76 46.007 -122.845 Local ponding east of Interstate 5 in city of Kalama.

75.4 7.90 46.004 -122.847 NA

75.6 7.64 45.996 -122.872 NA

77.2 7.89 45.982 -122.830 NA

83.7 8.46 45.890 -122.806 At Columbia City, Oregon.

85.6 8.64 45.867 -122.799 St. Helens; located north side of St. Helens Marina on side street to right and 

behind 135 North River Street.

87.4 8.85 45.846 -122.803 HWM established by Boise Cascade Corporation at their St. Helens paper mill 

plant.

92.4 9.64 45.779 -122.779 Sauvie Island, at north end of Columbia Diking District, HWM on east side of 

Reeder Road.

94.2 9.50 45.758 -122.771 Sauvie Island, south of Willow Point at Columbia Diking District; HWM on 

telephone pole on Reeder Road across from Fish and Wildlife grey building.

103.0 9.73 45.646 -122.735 Elevation by Vanalco: staff gage at their dock on Columbia River.

103.0 9.38 45.652 -122.726 Elevation by Vanalco: on south side New River Road; Bonneville Power 

Administration substation, slough.

103.0 9.25 45.652 -122.725 Elevation by Vanalco: on north side New Lower River Road; that is, 

Vancouver Lake.

106.5 9.93 45.621 -122.674 At Interstate 5 bridge: USWB and USACE recording gage; stage 

= 27.15 at 1800, February 9, 1996; datum = 1.82 ft above NGVD 29.

114.0 10.18 45.593 -122.523 HWM (double headed nail on carport/shop wall) set by property owner
34 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Simulations for 1997

During the freshet simulation (April 12–July 12, 1997), 

the Columbia River main stem was the dominant contributor 

of flow to the LCR. Streamflow at Bonneville Dam peaked 

at 16,000 m3/s (565,000 ft3/s), which was more than 10 

times the peak flow in the Willamette River. Columbia River 

flow at Bonneville Dam was greater than the 0.3 AEP for 9 

continuous weeks and greater than the 0.10 AEP for 6 weeks. 

For most of the 1997 freshet, the Willamette River at Portland 

(14211720) was essentially a backwater due to the high flow 

in the Columbia River. The 1997 freshet tested the AdH and 

Delft3D-FM models in terms of a long duration and variable 

high-flow condition with intermittent contributions from 

LCR tributaries and spring-neap ocean tidal forcing. The 

maximum water-surface elevation profile along the Columbia 

River as simulated by both models was in good agreement 

(fig. 16). The maximum water-surface elevation gradient 

tended to increase upstream of RM 38 in both models, with 

an average difference of 0.04 m (0.13 ft) between the two, as 

the Columbia River estuary narrows and the river becomes 

fluvially dominated. At the mouth of the Columbia River, the 

AdH and Delft3D-FM models matched well the measured 

tidal time series at Astoria (fig. 13). The AdH and Delft3D-FM 

models also matched the Willamette and Columbia River 

stage at Portland and Vancouver, respectively, reasonably 

well through multiple peaks between April and June (figs. 14

and 15). Peak flood stage in both models was lower than 

measurements at Vancouver by about 0.1 m (0.2 to 0.4 ft), 

and for the Willamette River at Portland, the AdH model 

matched the peak flood stage whereas the Delft3D-FM model 

was lower by about 0.1 m (0.2 ft) (table 8). The performance 

statistics for both models were very good—Nash-Sutcliffe 

statistics were consistently 0.99 (table 7). Root mean squared 

error (RMSE) was 0.09 m (0.3 ft) at Vancouver and Morrison 

Bridge in Delft model results, RMSE was 0.13 m (0.4 ft) at 

Vancouver and Morrison Bridge in the AdH model results.

Future Climate Scenarios

Simulations considered three extreme but plausible 

future boundary conditions which paired scaled-up 1996 

inflow hydrographs with an ocean boundary constructed from 

record high tides, storm surge, and 0-, 0.25-, and 1-m sea-level 

change (SLC).

The future climate simulations showed similar maximum 

stage profiles between models along the main channel of 

the LCR (fig. 17). For all three scenarios, the water-surface 

elevations in the estuary match well between models and start 

to diverge upstream. In the 0- and 0.25-m SLC simulations, 

the divergence between models occurs at around RM 50, 

similar to the 1996 simulated profile; however, in the 1-meter 

SLC simulation the divergence occurs at around RM 30. 

Upstream of RM 50, the AdH simulations were 0.32 to 

0.39 m (1.05 to 1.28 ft) higher on average as compared to 

Delft3D-FM. At the upstream boundary, the difference in 

maximum stage between the models was consistent across all 

future simulations, and was consistent with the difference in 

maximum stage simulated by the two models in 1996 (fig. 16).

The future simulations also were consistent between 

models at the mouth of the LCR and near Portland. At Astoria, 

the model simulation results were nearly identical for all 

future scenarios and simulated peak stages were similar, with 

the greatest difference between models being 0.07 m (0.23 ft) 

for the 0-m SLC (fig. 18; table 10). The increase in stage at 

Astoria from the historical (1996) peak ranged from 1.13 to 

2.11 m (3.71 to 6.93 ft) (table 10), reflecting the cumulative 

effects of higher SLC at the ocean boundary. In both the 

Willamette and Columbia Rivers, the future simulations had 

good agreement between the AdH and Delft3D-FM models 

with respect to the timing and magnitude of floods (figs. 

19 and 20). In the Willamette River, the difference in peak 

stage between the two models ranged from 0.06 to 0.07 m 

(0.17 to 0.24 ft) for the three future climate simulations, and 

increases from the historical (1996) peak ranged from 1.69 

m (5.56 ft) seen in the 0-m SLC scenario to 1.90 m (6.24 ft) 

in the 1-m SLC scenario (table 10). Therefore, the increase 

in stage simulated for future climate scenarios compared to 

the measured 1996 peak stage is significantly larger than the 

differences between the two models. The difference in peak 

stage between the two models was greater in the Columbia 

River at Vancouver, ranging from 0.24 to 0.29 m (0.80 to 

0.93 ft) across the three future climate simulations, which 

was similar in magnitude to the difference between peak 

stage simulated at Vancouver by the two models in the 1996 

simulations. The increase in stage from the historical peak in 

the Columbia River ranged from 1.26 m (4.13 ft) in the 0-m 

SLC scenario to 1.65 m (5.40 ft) in the 1-m SLC scenario; 

again, larger than the difference between the two models (fig. 

20; table 10).

The peak stage information was compared to known 

levee elevations to determine if overtopping occurred in any 

of the future scenario simulations. The PEN 1 levee along the 

Columbia River was designed to a top elevation of 11.80 m 

(38.71 ft) upstream and 11.73 m (38.48 ft) downstream; 

however, USACE lidar data indicated that the low point 

actually is 11.07 m (36.32 ft) above NAVD 88. Therefore, the 

levee is overtopped by at least 0.08 m (0.26 ft) for the 0-m 

SLC scenario (Delft3D-FM model simulation results) and by 

as much as 0.47 m (1.54 ft) for the 1-m SLC scenario (AdH 

model simulation results; fig. 20). The PEN 2 levee along the 

Columbia River was designed to a top elevation of 11.86 m 

(38.91 ft) upstream and 11.73 m (38.49 ft) downstream, above 

NAVD 88; however, USACE lidar data indicated the low point 

actually is 11.48 m (37.67 ft) above NAVD 88. Therefore, the 

levee is at incipient overtopping (table 10; fig. 20). Neither the 

MCDD nor SDIC levee systems overtopped during the future 

climate simulations.
Future Climate Scenarios 35

tac18-1244_fig 17

EXPLANATION

1.00

AdH model

Flow increase with sea-level change, in meters

0.25

0

1.00

Delft3D-FM model

0.25

0

0 50 100 150

4

6

8

10

12

14

Distance upstream from mouth of Columbia River, in miles

Water-surface elevation, in meters

Figure 17. Stream profile showing future simulated maximum river stage from AdH and Delft3D-FM models along 

the Columbia River, Oregon and Washington.

Additionally, the duration of high water levels on levees 

is expected to increase. In the 1-m SLC scenario, the AdHmodeled river stage exceeding 11.5 m (37.7 ft) at the location 

of MCDD levees is estimated to have a duration of 6–9 hours, 

whereas water levels exceeding 11 m (36 ft) may be sustained 

for 2 days through the course of the rise and fall of water 

levels. The 1996 measured peak stage was 9.89 m (32.45 ft) at 

the Columbia River at Vancouver (14144700; table 10) with 

stage exceeding 8 m (26 ft) for 5 days, and the high sustained 

stage after the 1996 peak was a little less than 8 m (26 ft) for 

11 days. In the future climate scenarios, river stage is expected 

to be greater than 8 m (26 ft) for 21 days (fig. 20). This type 

of flood will test the Columbia Corridor Levee System both 

in terms of the capacity of levees to prevent overtopping and 

their ability to resist failure due to seepage.

To create the future boundary conditions hydrographs 

on which these simulations are based, historical 1996 flows 

were scaled up by a factor of 1.4 at Bonneville Dam, and by a 

factor of 1.2 on the Willamette River and all other tributaries. 

Even though the prototype flow selected was a historical 

rain-on-snow event in which the Willamette River flows had a 

lower AEP than the Columbia River, it was not a certainty that, 

when the boundary conditions were scaled in this way, the 

water-surface elevation gradient would be downward between 

Portland and Vancouver. Based on our simulations, the 

resulting water-surface elevation was higher in the Willamette 

River at Portland by 0.3 m (1 ft) (AdH model simulation 

results) to 0.5 m (1.6 ft) (Delft model simulation results), than 

on the Columbia River at Vancouver. Therefore, in terms of 

the boundary conditions and hydraulics near the confluence, 

the future extreme flood simulated bears more resemblance 

to the atmospheric river rain-on-snow period in 1996, than 

to the spring freshet of 1997 in which the Willamette River 

was essentially a backwater to the Columbia River. This 

contributes to significant hydraulic complexity around 

the North Portland Peninsula between the Columbia and 

Willamette Rivers, and the Multnomah Channel. Simulations 

indicated that the Multnomah Channel conveyed much flow 

and contributed to significant flooding at Sauvie Island.
36 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig 18

EXPLANATION

AdH simulation

Delft3D-FM simulation

0

2

4

6

20 25 30 35

Flow increases and 0-meter sea-level change

0

2

4

6

Water-surface elevation, in meters

20 25 30 35

Flow increases and 0.25-meter sea-level change

0

2

4

6

Days since start of simulation

20 25 30 35

Flow increases and 1-meter sea-level change

Figure 18. Simulated future water-surface elevations from AdH and Delft3D-FM models, Columbia River at Astoria, 

Oregon.
Future Climate Scenarios 37

Table 10. Measured historical and simulated future peak stage and 

projected sea-level change for selected areas in the Willamette and 

Columbia Rivers, Oregon and Washington.

[Model: AdH, Adaptive Hydraulics model. Delft3D-FM, Delft3D-Flexible Mesh 

model. Abbreviations: ft, foot; m, meter; NA, not applicable; NAVD 88, North 

American Vertical Datum of 1988]

Model

Sea-level 

change 

(m)

Peak stage in 

NAVD 88

Increase in peak 

stage from historical 

measurement

(m) (ft) (m) (ft)

Columbia River at Astoria, Oregon (9439040)

Measured in 1996 NA 3.53 11.58 NA NA

Delft3D-FM 0.00 4.73 15.52 1.20 3.94

AdH 0.00 4.66 15.29 1.13 3.71

Delft3D-FM 0.25 4.97 16.30 1.44 4.72

AdH 0.25 4.92 16.13 1.39 4.55

Delft3D-FM 1.00 5.64 18.51 2.11 6.93

AdH 1.00 5.64 18.51 2.11 6.93

Willamette River at Morrison Bridge, Portland, Oregon (14211720)

Measured in 1996 NA 9.95 32.64 NA NA

Delft3D-FM 0.00 11.64 38.20 1.69 5.56

AdH 0.00 11.70 38.37 1.75 5.73

Delft3D-FM 0.25 11.68 38.32 1.73 5.68

AdH 0.25 11.74 38.50 1.79 5.86

Delft3D-FM 1.00 11.78 38.65 1.83 6.00

AdH 1.00 11.85 38.89 1.90 6.24

Columbia River at Vancouver, Washington (14144700)

Measured in 1996 NA 9.89 32.45 NA NA

Delft3D-FM 0.00 11.15 36.58 1.26 4.13

AdH 0.00 11.39 37.38 1.50 4.93

Delft3D-FM 0.25 11.18 36.67 1.29 4.22

AdH 0.25 11.43 37.50 1.54 5.05

Delft3D-FM 1.00 11.25 36.92 1.36 4.47

AdH 1.00 11.54 37.85 1.65 5.40
38 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

tac18-1244_fig 19

EXPLANATION

1996 measurement

AdH simulation

Delft3D-FM simulation

Flow increases and 0-meter sea-level change

Water-surface elevation, in meters

Flow increases and 0.25-meter sea-level change

Days since start of simulation

Flow increases and 1-meter sea-level change

4

2

2

6

8

10

12

0 5 10 15 20 25 30 35 40

0 5 10 15 20 25 30 35 40

0 5 10 15 20 25 30 35 40

4

6

8

10

12

12

4

2

6

8

10

Figure 19. Measured historical and simulated future water-surface elevations from AdH and Delft3D-FM models, 

Willamette River at Morrison Bridge, Oregon.
Future Climate Scenarios 39

tac18-1244_fig 20

PEN1 levee low point

PEN2 levee low point

PEN1 levee low point

PEN2 levee low point

PEN1 levee low point

PEN2 levee low point

EXPLANATION

1996 measurement

AdH simulation

Delft3D-FM simulation

Flow increases and 0-meter sea-level change

Water-surface elevation, in meters

Flow increases and 0.25-meter sea-level change

Days since start of simulation

Flow increases and 1-meter sea-level change

4

2

2

6

8

10

12

0 5 10 15 20 25 30 35 40

0 5 10 15 20 25 30 35 40

0 5 10 15 20 25 30 35 40

4

6

8

10

12

12

4

2

6

8

10

Figure 20. Measured historical and simulated future water-surface elevations from AdH and Delft3D-FM models, 

Columbia River at Vancouver, Washington.
40 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Summary and Conclusions

This study provided important information for the Levee 

Ready Columbia project and the Columbia Corridor Levee 

System in the Portland, Oregon, area regarding the potential 

effect of a future climate on extreme but plausible floods. 

The lower estuary of the Columbia downstream of river 

mile 40 is the most affected by ocean conditions, including 

a change in mean sea level. Under even some relatively 

extreme assumptions, the change in mean sea level will not 

have a large effect on the flood stage in Portland; an increase 

of 0.25 meters in mean sea level changed the simulated peak 

stage at Portland by only 3–4 centimeters (1–2 inches). A 

large storm surge, however, can have a larger effect on the 

flood stage at Portland because the storm surge can add up to 

1.4 meters (4.6 feet) of water-surface elevation at the ocean 

boundary. A large storm surge in combination with high flows 

associated with a winter storm is not a remote possibility as 

the atmospheric rivers that cause rain-on-snow winter floods 

in the Willamette River Basin often are associated with storm 

surges at the coastline. If circumstances are particularly 

adverse, high storm surge can be associated with a high spring 

tide, which can add another few meters to ocean watersurface elevation. Therefore, when considering an extreme 

but plausible high flow in Portland, it is prudent to consider a 

storm surge and high tide at the ocean occurring in concert.

Nonetheless, the reach of the Columbia River along 

Peninsula Drainage District No. 1 and No. 2 in Portland is 

fluvially dominated. Under the assumptions made in this study 

about future Columbia Basin hydrology, based on the best 

available scientific data and professional judgment, extreme 

high-flow boundary conditions were imposed in the models. 

The selected critical events were a winter streamflow in the 

Columbia River that was modeled as 40-percent greater than 

current conditions and an extreme winter streamflow in the 

Willamette River resulting from a rain-on-snow type of flow 

could be about 20-percent greater than current conditions. 

Under the selected future climate scenarios, most levees in the 

LCR will be subject to prolonged exposure from water levels 

that exceed the authorized levee height making the Columbia 

Corridor Levee System vulnerable to such high flood stage 

from increased flows on the Columbia and Willamette Rivers.

There is significant hydraulic complexity in the area near 

the confluence of the Columbia and the Willamette Rivers, 

and where the Multnomah Channel leaves the Willamette 

River. The Multnomah Channel conveys much flow from 

the Willamette River under the assumed future climate 

scenarios. This complexity warrants additional study in order 

to understand the effects of flooding, particularly on Sauvie 

Island. The conveyance of the Multnomah Channel also affects 

the water-surface profile in the main channel of the Columbia 

River between Portland and St. Helens, Oregon.

It is important, to correctly account for flood plain 

storage, that levees be overtopped in the simulations in a 

realistic manner. This requires that levee-crest elevations be 

defined as accurately as possible, not just in the Portland area, 

but in the entire lower Columbia River. There may still be 

unresolved uncertainty in some levee heights along this reach.

There is a benefit to using different models developed 

by independent teams to investigate such a complex 

simulated flood stage on the Columbia from Bonneville Dam 

to the Pacific Ocean. This approach provides independent 

verification of results and provides clarity about whether the 

results are robust enough to be well outside any differences 

that can be ascribed to the particular model selected. The range 

in results also provides an estimate of uncertainty.

Two state-of-the-art hydraulic models—Adaptive 

Hydraulics (AdH) and Delft3D-Flexible Mesh 

(Delft3D-FM)—were used to simulate the same extreme but 

plausible peak flood in the future, to assess the sensitivity 

of the results and conclusions. The models differed in 

how physical structures such as levees and pile dikes were 

embedded into the numerical mesh, in the mesh resolution, 

in how friction was parameterized, and the measurements 

given the most weight in the calibration phase. Great care 

was taken, however, to assure that bed elevation in the two 

model meshes was based on the same terrain model, that levee 

heights and access to interior storage were the same, and that 

the models were run with the same boundary conditions. The 

domain of both models included the Columbia River between 

Bonneville Dam and the Pacific Ocean, and the Willamette 

River between Willamette Falls and the confluence with the 

Columbia River, as well as the lowest reaches of three small 

tributaries. Although the domain included the ocean boundary 

and estuary, the models were run in two dimensions and did 

not consider salinity and three-dimensional circulation in the 

estuary because the effects on stage at the Columbia Corridor 

Levee System were negligible during high flows in the 

fluvially dominated study reach.

Both models simulated the 1996 winter rain-on-snow 

storm, and the 1997 spring freshet, and accurately matched 

the timing of floods in the fluvially dominated reach of the 

rivers and the tidal effects on the water-surface elevation 

in the estuary, during both historical periods. The AdH 

model was calibrated with an emphasis on simulating the 

water-surface elevation of the Columbia River at Vancouver 

(14144700; RM 105) during the 1997 spring freshet. The 

Delft3D-FM model was calibrated with an emphasis on 

simulating the water-surface elevation of the Willamette River 

at Portland (14211720) during the 1996 winter flood. Based 

on comparison to water-surface elevations at Columbia and 

Willamette River streamgages at Vancouver and Portland, 

the models had comparable and good performance statistics 

over the two historical periods. For the AdH model, the 

Nash-Sutcliffe statistic ranged from 0.96 to 0.99, the RMSE 

from 0.13 to 0.32 m (0.41 to 1.06 ft), and the bias from -0.03 

to 0.28 m (-0.10 to 0.93 ft). For the Delft3D-FM model, the 

Nash-Sutcliffe statistic was 0.99, the RMSE ranged from 

0.09 to 0.18 m (0.28 to 0.59 ft), and the bias from -0.02 to 

0.10 m (-0.07 to 0.33 ft). Considering only the highest peakflood stage simulated in 1996, the AdH model simulated 
Summary and Conclusions 41

9.98 m (32.73 ft), the Delft3D-FM model simulated 9.60 m 

(31.51 ft), and the measured peak stage was 9.89 m (32.45 ft) 

at the Columbia River at Vancouver (U.S. Geological Survey 

streamgage 14144700). At the Willamette River at Portland 

(14211720), the AdH model simulated a peak stage of 10.34 

m (33.94 ft), the Delft3D-FM model simulated 10.06 m 

(33.01 ft), and the measured peak stage was 9.95 m.

In the 1996 simulations, the peak stage simulated 

by the AdH model was higher than that simulated by the 

Delft3D-FM model throughout the main channel upstream 

of the estuary. At about RM 38 an inflection point indicated a 

transition in the Columbia River from being tidally dominated 

to being fluvially dominated. Upstream of this transition 

point, the maximum stage simulated by the AdH model was 

consistently higher than that simulated by the Delft3D-FM 

model, by an average of 0.45 meters, with the maximum 

difference of 0.74 meters occurring about RM 87. In the 

1997 simulations, the average difference in maximum stage 

between the two models along the reach upstream of RM 38 

was only 0.04 meters. This difference in simulated peak 

stage along the channel is likely explained by a combination 

of factors including the effect of differences in meshes in 

how off-channel storage is simulated, differences in friction 

properties resulting from how friction is parameterized in the 

two models, differences in sites used in model calibration, and 

differences in how the two models simulate pile dikes. The 

Delft3D-FM model simulates pile dikes as impermeable weirs 

with a fixed height that can be overtopped, whereas the AdH 

model simulates pile dikes within the mesh cells as porous 

regions with higher roughness that cannot be overtopped.

The calibrated models were used to simulate extreme but 

plausible high water in the near future—2030 to 2059—which 

is identified as the 2040s. Both models were applied using a 

scenario-based approach, consistent with U.S. Army Corps of 

Engineers and U.S. Geological Survey practice for evaluating 

future conditions affected by climate change. The analyses 

are based on the best available scientific data and professional 

judgment, but there is inherent uncertainty in hydrologic 

and coastal conditions when simulating future water-surface 

profiles in the Columbia River.

The future scenarios represent simulated large-scale 

climate trends which are extreme but plausible at the regional 

scale, assumptions about what type of event will be most 

important in the future, and appropriate coincident tidal and 

storm surge conditions. The use of scenarios informs adaptive 

management by placing management actions in a context of 

future uncertainty and by bounding the envelope of potential 

climate effects.

This study used projected future climate results, and 

uncertainties documented in reports on future climate 

published in 2010 through present by regional agencies. 

These studies focused on the 2040s timeframe and developed 

streamflow datasets in collaboration with University of 

Washington Climate Impacts Group. The forecasted climate 

change datasets were used to develop boundary conditions for 

three future scenarios incorporating increases in river flow and 

relative sea-level rise.

The literature also points to changing Columbia River 

basin hydrology on time scales relevant to infrastructure 

planning. Projected future trends indicate an earlier peak in the 

spring freshet is likely on the main stem, shifted on average by 

about 1 month, from a May to June peak in current conditions 

to a late April to early May peak in the 2040s. Concurrently, 

increases in winter (November–March) runoff volume in the 

Willamette Valley are plausible as well. Although the future 

spring Columbia River peak stage would not coincide with 

the stage of Willamette River winter flows, the rise on the 

Columbia River would begin earlier, effectively increasing 

2040s winter discharges in the Columbia River at the time 

of the peak flow on the Willamette River. This pointed to a 

February 1996 type winter rain-on-snow event as being more 

likely to cause plausible extreme future floods than the spring 

freshet.

The 2040s relative change in sea level at Astoria, Oregon, 

was estimated to vary between -0.015 to 0.25 meter above 

North American Vertical Datum of 1988 (NAVD 88) based 

on U.S. Army Corps of Engineers guidance. Storm surge 

and high-tide conditions based on regional observations 

were aligned so that the timing of sea-level peaks were 

appropriately shifted from the timing of water-level peaks near 

Portland, and added to future sea level. Storm surge and tidal 

conditions were determined to have a more significant effect 

on the coastal boundaries than projected sea-level change.

The future 2040 condition hydraulic model inflows were 

amplified compared to the baseline measured historical flows. 

For modeling purposes, it was estimated that a winter peak 

on the Columbia River could be as much as 40-percent higher 

and on the Willamette River could be as much as 20-percent 

higher than the February 1996 historical winter flood that was 

used as a prototype.

Forcing the hydraulic models with plausible extreme 

future inflows at the upstream boundaries and a combination 

of 0.25 meter of sea-level change, extreme storm surge and 

high tides at the ocean boundary resulted in a 2040s stage 

of 11.4 meters (37.5 feet) and 11.2 meters (36.7 feet) on the 

Columbia River at Vancouver (14144700) for the AdH and 

Delft3D-FM models, respectively. The two models generally 

agreed well, and both showed peak stages more than 1 meter 

higher than the peak stage measured in 1996. Under the 

selected future climate scenarios, it was also evident that 

levees generally will be subject to more prolonged exposure to 

high water levels.

The hydraulic analyses revealed that the lower Columbia 

River estuary, from the mouth to approximately river mile 

38, was the reach most affected by the tidal and storm surge 

conditions and change in mean sea level. From Columbia 

River mile 38 and upstream, fluvial discharges, as expected, 

had a dominant influence on the water-surface elevations 

adjacent to the Columbia Corridor Levee System between 

river miles 105 and 145.
42 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Results from this study indicate that a 1996-type flood, 

perturbed by the selected future climate-change scenario, can 

subject Multnomah County Drainage District (MCDD) levees 

to a peak water level exceeding 11 meters (36 feet) above 

NAVD 88 and a long-duration river level of 8 meters (26 feet) 

above NAVD 88. The AdH- and Delft3D-FM-modeled 2040s 

peak stage, with flow increases and a sea-level change of 

1.00 meter, is 11.5 and 11.25 meters (37.9 and 36.9 feet) on 

the Columbia River at Vancouver (14144700), respectively. 

In this scenario, the peak AdH-modeled river stage exceeding 

11.5 meters (37.9 feet) at the location of MCDD levees is 

estimated to have a duration of 6–9 hours, whereas river levels 

exceeding 11 meters above NAVD 88 may be sustained for 2 

days through the course of the rising and falling water levels. 

The 1996 measured peak stage was 9.9 meters (32.5 feet) 

above NAVD 88 at the Columbia River at Vancouver 

(14144700), and the high sustained stage after the 1996 

peak was just under 8 meters (26 feet). In the future climate 

scenarios, river stage is expected to be more than 8 meters 

(26 feet) above NAVD 88 for 21 days. This type of flow will 

test the Columbia Corridor Levee System both in terms of the 

capacity of levees to prevent overtopping and their ability to 

resist failure due to seepage.

Acknowledgments

This study supported efforts by Levee Ready Columbia 

and was funded by the following partners: Peninsula 

Drainage District No. 1, Peninsula Drainage District No. 2, 

Multnomah County Drainage District No. 1, Sandy Drainage 

Improvement Company, Cities of Portland, Gresham, 

Fairview, and Troutdale, Multnomah County, Metro, and 

the Port of Portland. This project was funded in part with 

a financial award from the Special Public Works Fund and 

Regional Solutions, funded by the Oregon State Lottery and 

administered by the Oregon Infrastructure Finance Authority.

References Cited

Berger, R.C., and Howington, S.E., 2002, Discrete fluxes 

and mass balance in finite elements: Journal of Hydraulic 

Engineering, v. 128, no. 1, p. 87–92, https://doi.org/10.1061/

(ASCE)0733-9429(2002)128:1(87).

Berger, R.C., and Stockstill, R.L., 1995, Finite-element 

model for high-velocity channels: Journal of Hydraulic 

Engineering, v. 121, no. 10, p. 710–716, https://doi.

org/10.1061/(ASCE)0733-9429(1995)121:10(710).

Bonneville Power Administration, 2004, 2000 Level Modified 

Streamflow 1928–1999—Diversion and Return Flow 

Patterns, Summation of Depletion Adjustments, Evaporation 

Adjustments, 2000 Level Modified Streamflow—Columbia 

and Coastal Basins: Portland, Oregon, Bonneville Power 

Administration report.

Brekke, L., Keupper, B., and Vaddey, S., 2010, Climate 

and Hydrology Datasets for use in the RMJOC agencies’ 

longer-term planning studies—Part I, Future climate and 

hydrology datasets, Bureau of Reclamation report, accessed 

September 28, 2018, https://www.usbr.gov/pn/climate/

planning/reports/index.html.

Cayan, D.R., 1996, Interannual climate variability and 

snowpack in the western United States: Journal Climate, 

v. 9, p. 928–948.

Climate Impacts Group, 2009, The Washington Climate 

Change Impacts Assessment, in McGuire Elsner, M., 

Littell, J., and Whitely Binder, L., eds., Center for Science 

in the Earth System, Joint Institute for the Study of the 

Atmosphere and Oceans: Seattle, Washington, University 

of Washington, http://www.cses.washington.edu/db/pdf/

wacciareport681.pdf.

Climate Impacts Group, 2018, Resources—Climate Impacts 

Group datasets: University of Washington database, 

accessed March 9, 2018, at https://cig.uw.edu/resources/

data/cig-datasets/.

Deltares, 2015, D-Flow Flexible Mesh—D-Flow FM in 

Delta Shell user manual (ver. 1.1.148, rev. 43108): The 

Netherlands, Deltares, 402 p.

Egbert, G.D., and Erofeeva, S.Y., 2002, Efficient inverse 

modeling of barotropic ocean tides: Journal of Atmospheric 

and Oceanic Technology, v. 19, no. 2, p. 183–204, https://

doi.org/10.1175/1520-0426(2002)019<0183:EIMOBO>2.0

.CO;2.

Elias, E.P.L., Gelfenbaum, G., and Van der Westhuysen, A.J., 

2012, Validation of a coupled wave-flow model in a highenergy setting—The mouth of the Columbia River: Journal 

of Geophysical Research—Oceans, v. 117, C09011, 21 p., 

doi:10.1029/2012JC008105.

Fox, D.S., Bell, S., Nehlsen, W., and Damron, J., 1984, The 

Columbia River Estuary atlas of physical and biological 

characteristics: Astoria, Oregon, Columbia River Estuary 

Data Development Program, 87 p.

General Bathymetric Chart of the Oceans, 2018, Gridded 

bathymetry data: International Hydrographic Organization 

(IHO) and the Intergovernmental Oceanographic 

Commission database, accessed March 13, 2018, at https://

www.gebco.net/data_and_products/gridded_bathymetry_

data/.
References Cited 43

Granato, G.E., 2009, Computer programs for obtaining 

and analyzing daily mean streamflow data from the U.S. 

Geological Survey National Water Information System 

website: U.S. Geological Survey Open-File Report 

2008– 1362, 123 p. on CD-ROM, 5 appendixes.

Groisman, P.Y., and Easterling, D.R., 1994, Variability 

and trends of total precipitation and snowfall over 

the United States and Canada: Journal of Climate, 

v. 7, no. 1, p. 184–205, https://doi.org/10.1175/1520-

0442(1994)007<0184:VATOTP>2.0.CO;2.

Hamlet, A.F., Elsner, M.M., Mauger, G.S., Lee, S.Y., 

Tohver, I., and Norheim, R.A., 2013, An overview of the 

Columbia Basin Climate Change Scenarios Project—

Approach, methods, and summary of key results: 

Atmosphere-ocean, v. 51, no. 4, p. 392–415, https://doi.org/

10.1080/07055900.2013.819555.

Hamlet, A.F., and Lettenmaier, D.P., 1999, Effects of climate 

change on hydrology and water resources in the Columbia 

River Basin: Journal of the American Water Resources 

Association, v. 35, no. 6, p. 1597–1623, https://doi.

org/10.1111/j.1752-1688.1999.tb04240.x.

Helaire, L.T., 2016, Modeling of historic Columbia River 

flood impacts based on Delft 3D simulations: Portland 

State University, Master of Science thesis, 165 p., accessed 

January 2018 at https://pdxscholar.library.pdx.edu/open_

access_etds/3206/, doi:10.15760/etd.3197.

Hinkel, J., Jaeger, C., Nicholls, R.J., Lowe, J., Renn, O., 

and Peijun, S., 2015, Sea-level rise scenarios and coastal 

risk management: Nature Climate Change, v. 5, no. 3, 

p. 188– 190, https://doi.org/10.1038/nclimate2505.

Interagency Advisory Committee on Water Data, 1981, 

Guidelines for determining flood flow frequency: U.S. 

Geological Survey Bulletin 17B of the Hydrology 

Subcommittee, 28 p. plus 14 apps.

Intergovernmental Panel on Climate Change, 2000, Emissions 

scenarios—A special report of working group III of the 

Intergovernmental Panel on Climate Change: New York, 

Cambridge University Press, 608 p.

 Intergovernmental Panel on Climate Change, 2007: Climate 

change 2007—Synthesis report—Contribution of working 

groups I, II and III to the Fourth Assessment Report of 

the Intergovernmental Panel on Climate Change: Geneva, 

Switzerland, Intergovernmental Panel on Climate Change, 

104 p.

Intergovernmental Panel on Climate Change, 2014, Climate 

change 2014—Synthesis report—Contribution of working 

groups I, II and III to the Fifth Assessment Report of the 

Intergovernmental Panel on Climate Change: Geneva, 

Switzerland, Intergovernmental Panel on Climate Change, 

151 p.

Jarrett, J.T., 1976, Tidal Prism-Inlet relationships, general 

investigation of tidal inlets—Report 3: Vicksburg, 

Mississippi, U.S. Army Engineer Research Center and U.S. 

Army Engineer Waterways Experiment Station, 55 p.

Liang, X., 1994, A two-layer variable infiltration capacity 

land surface representation for general circulation models: 

Seattle, University of Washington, Water Resources Series, 

TR140, 208 p.

Mote, P.W., and Salathé, E.P., Jr., 2010, Future climate in 

the Pacific Northwest: Climatic Change, v. 102, no. 1–2, 

p. 29–50, https://doi.org/10.1007/s10584-010-9848-z.

Mote, P.W., Snover, A.K., Capalbo, S.M., Eigenbrode, S., 

Glick, P., Littell, J.S., Raymondi, R., and Reeder, S., 2014, 

Northwest, Chap. 21 in Melillo, J., Terese, Richmond, T.C., 

and Yohe, G.W., eds., Climate change impacts in the United 

States, The Third U.S. National Climate Assessment: U.S. 

Global Change Research Program, 16-1-nn.

Orem, H.M., 1968, Discharge in the Lower Columbia River 

basin, 1928–65: Geological Survey Circular 550, 24 p.

Pevey, K., Savant, G., Moritz, H., and Childs, E., 2012, Lower 

Columbia River Adaptive Hydraulics (AdH) model—

Development, water surfaces elevation validation and sea 

level rise analysis: Portland, Oregon, U.S. Army Corps of 

Engineers, Northwest Division, 81 p.

R Core Team, 2016, R—A language and environment for 

statistical computing: Vienna, Austria, R Foundation for 

Statistical Computing, https://www.R-project.org/.

Rupp, D.E., Abatzoglou, J.T., Hegewisch, K.C., and 

Mote, P.W., 2013, Evaluation of CMIP5 20th century 

climate simulations for the Pacific Northwest USA: Journal 

of Geophysical Research, D, Atmospheres, v. 118, no. 19, 

p. 10884–10906, https://doi.org/10.1002/jgrd.50843.

Savant, G., and McAlpin, T.O., 2014, Tidal hydrodynamics in 

the lower Columbia River estuary through depth averaged 

adaptive hydraulics modeling: Journal of Engineering, 

v. 2014, Hindawi Publishing Corporation, article ID 

416914, 12 p., http://dx.doi.org/10.1155/2014/416914.

Simenstad, C.A., Burke, J.L., O’Connor, J.E., Cannon, 

C., Heatwole, D.W., Ramirez, M.F., Waite, I.R., 

Counihan, T.D., and Jones, K.L., 2011, Columbia 

River Estuary Ecosystem Classification—Concept and 

application: U.S. Geological Survey Open-File Report 

2011-1228, 54 p., https://doi.org/10.3133/ofr20111228.

Stephenson, A.G., 2016, Harmonic analysis of tides using tide 

harmonics: The R Foundation, https://CRAN.R-project.org/

package=TideHarmonics.
44 Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate

Stewart, I.T., Cayan, D.R., and Dettinger, M.D., 2005, 

Changes toward earlier streamflow timing across 

Western North America: Journal of Climate, v. 18, no. 8, 

p. 1136– 1155, https://doi.org/10.1175/JCLI3321.1.

Talley, L.D., Pickard, G.L., Emery, W.J., and Swift, J.H., 2011, 

Gravity waves, tides, and coastal oceanography, chap. S8 of

Descriptive physical oceanography—An introduction 6th 

ed.: Boston, Academic Press, p. 223–244.

Taylor, K.E., Stouffer, R.J., and Meehl, G.A., 2012, An 

overview of CMIP5 and the experiment design: Bulletin 

of the American Meteorological Society, v. 93, no. 4, 

p. 485– 498, https://doi.org/10.1175/BAMS-D-11-00094.1.

Tohver, I., Hamlet, A.F., and Lee, S.-Y., 2014, Impacts of 

21st century climate change on hydrologic extremes in 

the Pacific Northwest region of North America: Journal 

of American Water Resources Association, v. 50, no. 6, 

p. 1461–1476, doi:10.1111/jawr.12199.

 U.S. Army Corps of Engineers, 1948, Review report on 

Columbia River and tributaries, appendix L—Columbia 

River below Yakima River: U.S. Army Corps of Engineers, 

Portland District, 340 p., https://www.streamnetlibrary.

org/?page_id=895.

 U.S. Army Corps of Engineers, 1991, Review of flood control 

Columbia River Basin—Columbia River and Tributaries 

Study, CRT-63, Final Report: U.S. Army Corps of 

Engineers, North Pacific Division.

 U.S. Army Corps of Engineers, 1997, February 1996 post 

flood report—Hydrometeorlogical evaluation: U.S. Army 

Corps of Engineers, Portland District, Hydrologic, Coastal, 

and River Engineering Section.

 U.S. Army Corps of Engineers, 2010, Lower Columbia 

River digital terrain model: Prepared by David Smith and 

Associates, Inc., David Evans and Associates, Inc., and CC 

Patterson and Associates for U.S. Army Corps of Engineers, 

Portland District, Contract No W9127N-09-D-009, Task 

Order No. 0005, available at http://www.estuarypartnership.

org/lower-columbia-digital-terrain-model.

 U.S. Army Corps of Engineers, 2014, Columbia River Treaty 

2014/2024 review program: U.S. Army Corps of Engineers, 

Northwestern Division.

 U.S. Army Corps of Engineers, 2016, Investigation of 

impacts associated with modifying east Sand Island 

to prevent nesting of double-crested cormorants: 

Vicksburg, Mississippi, U.S. Army Engineer Research and 

Development Center-Coastal and Hydraulics Laboratory, 

Technical Report ERDC/CHL TR-15-16.

U.S. Army Corps of Engineers, 2018, Climate preparedness 

and resilience: U.S. Army Corps of Engineers website, 

accessed February 27, 2018, at https://www.usace.army.mil/

corpsclimate/.

Van der Steeg, S., 2016, Investigations of tidal hydrodynamics 

in the lower Columbia River and estuary: The Netherlands, 

Delft University of Technology, Master’s thesis, 130 p.

Warner, M.D., Mass, C.F., and Salathé, E.P., Jr., 2015, 

Changes in winter atmospheric rivers along the North 

American west coast in CMIP5 climate models: Journal 

of Hydrometeorology, v. 16, no. 1, p. 118–128, https://doi.

org/10.1175/JHM-D-14-0080.1.

Watershed Sciences, 2010, Lidar remote sensing data 

collection—Columbia River Survey—Final delivery, 

September 22, 2010: Submitted to Jacob Macdonald, U.S. 

Army Corps of Engineers, Portland District, by Watershed 

Sciences, 70 p.
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Wherry and others—Columbia and Willamette River Flood Stage, Columbia Corridor Levee System at Portland, Oregon, in a Future Climate—Scientific Investigations Report 2018–5161

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20185161