NOAA Technical Memorandum OAR PMEL

NOAA TIME Eastern Strait of Juan de Fuca,

Washington, Mapping Project: Procedures, Data

Sources, and Products

Angie J. Venturato1, Vasily V. Titov1, Harold Mofjeld2, and Frank I. Gonz ́alez2

1Joint Institute for the Study of the Atmosphere and Ocean (JISAO)

University of Washington

Box 354235

Seattle, WA 98195-4235

2NOAA/Pacific Marine Environmental Laboratory

7600 Sand Point Way NE

Seattle, WA 98115-6349

September 2004

Contribution 2713 from NOAA/Pacific Marine Environmental Laboratory
NOTICE

Mention of a commercial company or product does not constitute an endorsement by

NOAA/OAR. Use of information from this publication concerning proprietary products

or the tests of such products for publicity or advertising purposes is not authorized.

Contribution No. 2713 from NOAA/Pacific Marine Environmental Laboratory

Contribution 1064 from the Joint Institute for the Study of the Atmosphere and Ocean

For sale by the National Technical Information Service, 5285 Port Royal Road

Springfield, VA 22161

ii
Contents iii

Contents

1. Introduction ............................ 1

2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

3. Tsunami Source .......................... 3

4. Tsunami Model .......................... 4

5. Discussion of Modeling Results ................. 5

5.1 Offshore dynamics . . . . . . . . . . . . . . . . . . . . . . . . 5

5.2 Inundation details . . . . . . . . . . . . . . . . . . . . . . . . 10

5.3 Bellingham Area . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.4 Anacortes Area . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.5 Whidbey Island . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 15

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Appendix A: Bathymetry Data and Computational Grids .... 18

Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Appendix B: Modeling Products ................... 22

List of Figures

1 Study areas of the Eastern Strait of Juan de Fuca Tsunami Mapping

Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Distribution of computed vertical deformation used as a tsunami

source for the inundation study ..................... 3

3 Snapshots of model offshore tsunami propagation in the Strait of

Juan de Fuca, Rosario Strait, and Admiralty Inlet .......... 5

4 Snapshots of local tsunami propagation in Bellingham and Lummi

Bays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5 Time series of Anacortes and northwest Whidbey Island tsunami

wave propagation. Figure 1b shows the location of each gage. .... 7

6 Time series of Bellingham tsunami wave propagation. Figure 1a

shows the location of each gage. ..................... 8

7 Water-level sites with associated tides hindcast around the time of

1700 Cascadia Subduction Zone Earthquake (0500 UTC 27 January

1700) .................................... 9

8 Maximum computed inundation depths (depth of water over land)

for the Bellingham area at a resolution of 1 arc-second. . . . . . . . . 11

9 Maximum computed flow speed (m/s) for the Bellingham area at a

resolution of 1 arc-second. . . . . . . . . . . . . . . . . . . . . . . . . 11

10 Maximum computed inundation depths (depth of water over land) for

the Anacortes and Whidbey Island area at a resolution of 1 arc-second. 13

11 Maximum computed flow speed (m/s) for the Anacortes and Whidbey Island area at a resolution of 1 arc-second. . . . . . . . . . . . . 13

A1 Tidal datum distribution of Bellingham, Anacortes, and Whidbey

Island areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

A2 Digital Elevation Models for modeling propagation in the Strait of

Juan de Fuca and inundation in the Bellingham, Anacortes, and

Whidbey Island areas. . . . . . . . . . . . . . . . . . . . . . . . . . . 20
iv Contents

List of Tables

A1 Vertical control for grid development. . . . . . . . . . . . . . . . . . 18

A2 Grid summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

A3 Data sources used for grid development. . . . . . . . . . . . . . . . . 21

B1 Product summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
NOAA TIME Eastern Strait of Juan de Fuca, Washington,

Mapping Project: Procedures, Data Sources, and Products

Angie J. Venturato1, Vasily V. Titov1, Harold Mofjeld2, and Frank I. Gonz ́alez2

1. Introduction

This report describes a project conducted by the NOAA Center for Tsunami

Inundation Mapping Efforts (TIME) to model potential tsunami inundation

along the shores of Bellingham, Anacortes, and northwest Whidbey Island,

Washington (Fig. 1). This work provides data for the creation of tsunami

hazard maps covering these areas. The maps are prepared through National

Tsunami Hazard Mitigation Program funds to assist local governments in

the development of evacuation plans in areas at risk of potentially dangerous

tsunamis. The source of the tsunami scenario is a major (magnitude 9.1)

earthquake along the Cascadia Subduction Zone. Previous tsunami mapping

studies for sites along open coasts of the Pacific Northwest used the same

source scenario that is discussed in detail by Priest et al. (1997) and Myers

et al. (1999). A high-resolution inundation model is applied to estimate wave

propagation and runup on land within the region of interest.

2. Background

The Cascadia Subduction Zone (CSZ) is a significant seismic and tsunami

hazard for the Pacific Northwest. Geologic evidence from stratigraphic studies suggest that great earthquakes (magnitude > 8) have occurred along

the CSZ (Atwater et al., 1995). Estimates of the recurrence interval for a

large event on the CSZ are between 500–540 years (Atwater and HemphillHaley, 1997). Numerous geological studies of the CSZ have found evidence

of tsunami deposits at 60 sites in the Pacific Northwest region, including

one within the region of interest at Swantown Marsh on Whidbey Island

(Peters et al., 2003). Native American oral tradition suggests a significant

earthquake and subsequent tsunami from the CSZ at the entrance to the

Strait of Juan de Fuca (Swan, 1868).

Inundation studies for the Cascadia-generated tsunami have been done

for several sites at the open coast of Oregon and Washington, where highresolution modeling of tsunami inundation has been completed (Priest et al.,

1997; Myers et al., 1999). The studies also included a low-resolution tsunami

propagation model for a larger area of the coast and some internal waterways.

This modeling has shown that simulated tsunami waves propagated through

the Strait of Juan de Fuca (SJDF) without much attenuation and generated

1Joint Institute for the Study of the Atmosphere and Ocean (JISAO), University of

Washington, Box 354235, Seattle, WA 98195-4235 2NOAA/Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle,

WA 98115-6349
2 A.J. Venturato et al.

Figure 1: Study areas of the Eastern Strait of Juan de Fuca Tsunami Mapping Project. (a) The highresolution modeling area of Bellingham and Lummi Nation. (b) The high-resolution modeling area of Anacortes and northwest Whidbey Island. (c) The study area with respect to Washington State. Triangles

represent locations of wave height time series. Green lines represent the location of levees (Skagit County

GIS, personal communication).
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 3

Figure 2: Distribution of computed vertical deformation used as a tsunami source

for the inundation study. The dashed line represents the axis of the Cascadia

Subduction Zone. The blue rectangle outlines the area of high resolution tsunami

inundation modeling.

significant amplitudes at the coasts of eastern SJDF. These preliminary results prompted focused study of the potential impact of a tsunami within

the eastern SJDF and the local waters surrounding Bellingham, Anacortes,

and Whidbey Island (Fig. 1) presented here.

3. Tsunami Source

The geometry of the CSZ (Fig. 2) suggests that the megathrust earthquake

would generate vast areas of coastal subsidence and offshore uplift that will

displace tremendous amounts of water. The displaced water will result in a

tsunami propagating along the outer Washington coast and into the SJDF.

The impact of the tsunami within the eastern SJDF and the local waters surrounding Bellingham, Anacortes, and Whidbey Island (Fig. 1) is estimated

here using high-resolution numerical modeling.

The tsunami source for this study assumes wave generation by a rupture

along the CSZ. Six scenarios, defined by Priest et al. (1997) and Myers et al.

(1999), were obtained from the Oregon Department of Geology and Mineral

Industries. We chose Scenario 1A as the maximum credible event for this

study. Scenario 1A consists of a magnitude (Mw) 9.1 CSZ earthquake with a

rupture length of approximately 1,050 km, average rupture width of 70 km,
4 A.J. Venturato et al.

and average slip of 17.5 m (Fig. 2). See Priest et al. (1997) for a complete

discussion.

4. Tsunami Model

Tsunami propagation within the northern straits of Washington and wave

inundation on dry land were simulated with the MOST numerical model

(Titov and Gonz ́alez, 1997; Titov, 1997; Titov and Synolakis, 1995, 1997).

The MOST model has been extensively tested against various laboratory

experiments (Titov and Synolakis, 1995, 1998) and verified by successfully

reproducing field data for many historical tsunamis (Yeh et al., 1995; Titov

and Synolakis, 1997, 1998; Titov and Gonz ́alez, 2001; Titov et al., 2004).

Titov et al. (2003) described the details of the MOST model application for

a tsunami inundation mapping project. The following briefly describes the

use of the MOST model for modeling the Cascadia tsunami in the SJDF.

The MOST model is designed to use several nested computational grids

to telescope into the high-resolution inundation area. Three levels of computational grids were used for this project to properly simulate the tsunami

generation in deeper ocean, wave propagation through the relatively narrow

SJDF, and inundation at impact areas. To reproduce the correct wave dynamic during the inundation computations, high-resolution grids were used

for areas around Bellingham, Anacortes, and Whidbey Island. These highresolution computations require high-quality bathymetry and topography

data merged into one computational grid.

The tsunami simulations did not include tidal dynamics in the modeled

area. The tides were assumed to interact linearly with a propagating tsunami

wave, and Mean High Water level was assumed for all computational areas

to simulate credible worst case scenario of tsunami inundation during high

tide. Appendix A describes the tidal datum distribution.

As in previous tsunami inundation studies, the topography used for the

simulation does not include buildings, trees, and smaller vegetation—i.e., a

so-called “bald earth” digital elevation model (DEM). These obstacles may

change and decrease inundation estimates, especially for large flat areas.

One way of accounting for that increased dissipation in the long-wave model

is the use of a greater bottom friction parameter (Fujima, 2001). However,

there are not enough data and scientific studies to choose the proper friction

coefficients to account for large structures. In the absence of proven scientific estimates, we have chosen to use a standard engineering value for the

Manning parameter corresponding to mildly rough surfaces (n = 0.025).

Appendix A describes details of the grid development procedure and lists

the bathymetric and topographic sources used to create the computational

grids.
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 5

Figure 3: Snapshots of model offshore tsunami propagation in the Strait of Juan de Fuca, Rosario Strait,

and Admiralty Inlet. Frames are shown from left-to-right, top-to-bottom at 30-minute intervals from 30

minutes to 4 hours after generation. Red color indicates positive wave amplitudes in meters above Mean

High Water (MHW), blue is negative (below MHW). Wave amplitudes range from –1 to 2 meters.

5. Discussion of Modeling Results

5.1 Offshore dynamics

The Cascadia tsunami source (Scenario 1A) creates significant subsidence

near the coast with the area of larger uplift further offshore (Fig. 2), causing

the waters to initially recede and form a leading-depression wave propagating

into the SJDF (Walsh et al., 2002). This leading depression wave is followed

by a positive wave of about 2 m amplitude. The tsunami propagates through

the SJDF for more than 2 hours before reaching the eastern shores of the

Strait (Fig. 3). The maximum amplitude of the propagating wave stays

virtually constant inside the SJDF at around 2 m, since the Strait forms a

near perfect one-dimensional channel where wave energy is not dissipating.

Upon reaching the western shore of Whidbey Island, the tsunami wave

splits north into Rosario Strait and south into Admiralty Inlet. The wave

crest reaches Anacortes with amplitudes above 1.4 m 2:09 (2 hours, 9 min)

after generation. The amplitudes increase above 2.8 m before reaching the

Bellingham shores 2:43 after generation (Fig. 4). Figures 5 and 6 show time

series of amplitudes within the high-resolution computational area.

The considered model source (Fig. 2) is associated with a Cascadia event

that is believed to have occurred at 0500 UTC, on 27 January 1700 (Satake

et al., 1996). Our high-resolution model provides travel time and amplitude

estimates for this event. Tidal hindcasts were calculated around the Cascadia

event using established techniques (Mofjeld et al., 1997) at specific locations

of the inundation modeling study (Fig. 7). Assuming modeled propagation

times, the tsunami reached all of these sites at the low water phase of the

predicted tides. The model results are obtained for the Mean High Water

level, suggesting smaller amplitudes if an event occurred at a lower tide.
6 A.J. Venturato et al.

Figure 4: Snapshots of local tsunami propagation in Bellingham and Lummi Bays. Frames are shown

from left-to-right, top-to-bottom at 15-minute intervals from 2 hours to 4 hours after generation. Red color

indicates positive wave amplitudes in centimeters above Mean High Water (MHW), blue is negative (below

MHW). Vectors represent current speeds in centimeters per second.
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 7

Figure 5: Time series of Anacortes and northwest Whidbey Island tsunami wave propagation. Figure 1b

shows the location of each gage.
8 A.J. Venturato et al.

Figure 6: Time series of Bellingham tsunami wave propagation. Figure 1a shows the location of each gage.
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 9

Anacortes Predicted Tides

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 6 12 18 24

January 27, 1700

Water Level (m) above MLLW

Sandy Point Predicted Tides

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 6 12 18 24

January 27, 1700

Water Level (m) above MLLW

Bellingham Predicted Tides

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 6 12 18 24

January 27, 1700

Water Level (m) above MLLW

Sunset Beach Predicted Tides

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 6 12 18 24

January 27, 1700

Water Level (m) above MLLW

Figure 7: Water-level sites with associated tides hindcast around the time of 1700 Cascadia Subduction

Zone Earthquake (0500 UTC 27 January 1700). The period is 0000-2354 UTC 27 January 1700 with sampling

every 6 minutes. The observed tidal harmonic constants (O1, K1, N2, M2, S2) were obtained from Parker

(1977); the remaining 37 harmonic constants are inferred based on amplitude ratios and phase differences

from the reference water-level station for the eastern Strait of Juan de Fuca and Strait of Georgia (Port

Townsend).
10 A.J. Venturato et al.

5.2 Inundation details

The model predicts extensive inundation along the low-lying shores of Lummi

Bay, Bellingham Bay, Samish Bay, Padilla Bay, Swinomish Channel, and

northwestern Whidbey Island. Though not part of the study area, inundation is also predicted along the Skagit River delta, also known as Fir Island

(Fig. 1). The results are explained below.

5.3 Bellingham Area

The simulation shows that most of the tsunami flooding in the Bellingham

vicinity occurs on and near river deltas, where large areas are not more than

3 m above Mean High Water.

The tsunami arrives in the vicinity of Bellingham Bay after about 2

hours of propagation from the source at the Cascadia margin. The wave

approaches Lummi Bay earlier but with smaller offshore amplitudes (1 to

2 m) than at Bellingham Bay (2 to 4 m). Nevertheless, these relatively

small amplitudes are enough to inundate the low-lying area of Lummi river

delta and propagate deep inland along the river valley. The waves start to

inundate the delta of Lummi river at around 2:15 after generation. By 2:30

the crest of the wave arrives and completely overtops the Sandy Point spit

at the mouth of Lummi Bay.

The modeled tsunami starts to inundate the shores of Bellingham Bay

at around 2:30 after generation. The crest of the wave reaches the shores

near the delta of Nooksack River about 15 minutes later and water starts

inundating the river valley. The tsunami flooding propagates simultaneously

along Lummi and Nooksack River deltas, and about 3:15 after tsunami generation the two floods meet and completely surround the Lummi Peninsula,

transforming it into an island for some period of time.

Again, simulations of tsunami inundation dynamics, especially for such

extensive on-land penetrations, depend on the choice of bottom friction

model and the bottom roughness coefficient. Our low bottom roughness

with Manning formulation gives conservative estimates of the tsunami penetration distances (Fig. 8) and flow speeds (Fig. 9). Without site-specific

data, our generic formulation and the roughness coefficients have not been

fine-tuned for the details of the area (vegetation type, buildings, etc.). Different bottom roughness may produce different inundation area. Our choice

of roughness coefficient leads to conservative estimates of potential hazard

zones.

Figure 8 shows maximum computed inundation for this area. It illustrates the large inundation distances along river deltas with highest vertical

runup above 3.4 m in the Nooksack River delta. The highest vertical runup

in the Bellingham area (above 5 m) is computed on the northern tip of

Portage Island. The model does not show significant inundation at the port

of Bellingham. However, tsunami amplitudes near the port facilities are virtually the same as the seawall height, which makes the port a potentially

hazardous zone during the tsunami.
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 11

Figure 8: Maximum computed inundation depths (depth of water over land) for the Bellingham area at a

resolution of 1 arc-second.

Figure 9: Maximum computed flow speed (m/s) for the Bellingham area at a resolution of 1 arc-second.
12 A.J. Venturato et al.

5.4 Anacortes Area

The maximum amplitudes of the first and second waves approaching Anacortes and western Fidalgo Island are similar, ranging from 1.5 to 1.8 m.

Fidalgo Bay and Padilla Bay experience an initial water withdrawal, as the

leading depression wave comes in, followed by the tsunami elevation wave

with amplitudes from 1 to 1.6 m (Fig. 5). Little to no inundation occurs in

downtown Anacortes (Fig. 10).

The Skyline Marina at the north end of Burrows Bay experiences higher

levels of inundation (above 2 m) and high flow speed magnitudes (>1.5 m/s).

High currents also occur around the Anacortes Ferry terminal, Guemes

Channel, and Fidalgo Bay (Fig. 11).

Large areas of inundation occur in areas of low topography surrounding

Samish Bay, Padilla Bay, and the Swinomish Channel. Though not part of

the modeling study, inundation also occurs within the vicinity of Fir Island.

The coastal areas of Samish Bay, Padilla Bay, Swinomish Channel, and Fir

Island all lie within the historic Skagit River delta region (U.S. Army Corps of

Engineers, 2002). This region contains a network of levees and coastal dikes

to protect farmland from tidal inundation and river flooding (Fig. 1). These

features are not resolved in the model; however, an analysis of coastal dike

heights along the shores of Samish Bay, Padilla Bay, Swinomish Channel,

and Fir Island suggest that tsunami waves will overtop the dikes and cause

inundation as suggested by the model.

The average heights of the dikes along the shores of Padilla Bay, Swinomish Channel, and Fir Island range from 1.1 to 1.2 m above Mean High

Water (Riggs, personal communication; National Geodetic Survey, 2004).

Photos of the Samish Bay coastal dikes suggest a similar height (U.S. Army

Corps of Engineers, 2002; Bloch et al., 2002). Maximum wave heights along

the coastal dikes range from 1.5 to 1.8 m for Samish Bay, 2.0 to 2.5 m for

Padilla Bay, 1.0 to 2.5 m for Swinomish Channel, and 1.0 to 1.5 m for Fir

Island.

High flow speeds (>1.5 m/s) may also breach many of these coastal dikes

and levees. Levees along the Swinomish Channel have not been maintained

(U.S. Army Corps of Engineers, 2002), and some of the coastal dikes along

Samish Bay are in poor condition (Bloch et al., 2002). Damage of dikes

and levees within the Fir Island region have occurred due to flooding in

1990 and 2003 (U.S. Army Corps of Engineers, online source; Washington

Military Department Emergency Management Division, 2004).

5.5 Whidbey Island

The initial wave approaching Whidbey Island has the largest maximum amplitude, ranging from 1.5 to 2.5 m (Fig. 5). The second and third waves

approach 1.1 m. The simulated tsunami wave floods areas of low topography on Whidbey Island at Deception Pass State Park, Joseph Whidbey

State Park, and the Keystone Ferry terminal (Fig. 10).

Deception Pass State Park has areas of inundation in low topographic

elevations, with inundation values above 1.5 m overtopping the West Beach
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 13

Figure 10: Maximum computed inundation depths (depth of water over land) for the Anacortes and

Whidbey Island area at a resolution of 1 arc-second.

Figure 11: Maximum computed flow speed (m/s) for the Anacortes and Whidbey Island area at a resolution

of 1 arc-second.
14 A.J. Venturato et al.

barrier of Cranberry Marsh. Flow speeds above 2 m/s occur within the

shallow depths around West Point and into Deception Pass.

High inundation amplitudes (>2 m) with a landward extent ranging from

150 m to 850 m are also found at Swantown Marsh in Joseph Whidbey

State Park, where flow speed above 4 m/s occur along the narrow beach

barrier. Inundation covers the entire marsh area, which is approximately

0.4 sq km in size (Island County Public Works, 2002). Evidence of prehistoric tsunami, presumably from a Cascadia earthquake, has been found

at these marshes by Williams and Hutchinson (2000). The locations of

the discovered tsunami-transported sediments are within the area of the

computed tsunami inundation. The sediments from the presumed Cascadia

tsunami were found in several cores within 100 m from the shoreline. The

landward extent of the modeled inundation is larger; this discrepancy may

be attributed to several factors, including topographic data resolution and

quality, and tidal level during the event. Also, lack of sediments in a limited

amount of cores does not necessarily exclude the inundation of this area.

In general, the model results for this location support the hypothesis of a

Cascadia tsunami as the source of the Swantown Marsh sediments.

The same study at Swantown Marsh found no evidence of tsunami deposits corresponding to the 1700 Cascadia event (Williams and Hutchinson,

2000), which should have been comparable in size with the modeled event.

Estimates from tide models for the time of the 1700 event at the Sunset

Beach water-level station (a location just north of Swantown Marsh) show

tides about 1 m below Mean High Water at the time of tsunami arrival (assuming the modeled 2-hour propagation time before the tsunami hits this

area, Fig. 7). Hence, the computed amplitudes become only 1 m at this

location, which make it too small to overcome the beach ridge.

The modeled tsunami also floods areas within the Keystone Harbor. Inundation amplitudes there reach 1.4 m above Mean High Water. High flow

speeds (>3 m/s) occur in the immediate vicinity of the Keystone Ferry terminal (Fig. 11).

6. Summary

The described tsunami modeling project studied local inundation and propagation effects at the eastern Strait of Juan de Fuca for a tsunami originated

on the Cascadia margin. The results of the study were used for the development of tsunami inundation maps for the area.

The main surprising result of the study is the extensive tsunami flooding

at some areas of the eastern SJDF for a tsunami originated at the open ocean.

A relatively narrow and long straight with numerous islands across its main

body seemingly protect the inner shores of Washington from a tsunami wave

propagating from the open ocean. Yet, the simulation results show that the

tsunami wave not only preserved the amplitude during its propagation but

also was additionally amplified at some east coast locations, especially at

Bellingham Bay.

Given the surprisingly high amplitudes of the approaching waves, the in-
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 15

undation pattern of tsunamis with such amplitudes is expected. Long waves

like tsunamis tend to flood the entire area below its shoreline amplitude.

Over flat topography, such waves lose their energy via bottom friction and

the inundation depths then slowly decrease over long penetration distances.

Many historical tsunamis demonstrated similar inundation patterns. The

recent example of the 2001 Peru tsunami demonstrated up to 1 mile inland

flooding over flat agricultural fields near Cam ́ana (Okal et al., 2002). Similar settings at the deltas of the Nooksack and Lummi Rivers resulted in

comparable model predictions of extensive tsunami flooding. Figures 8 and

9 show maximum computed inundation depths that illustrate those inundation patterns. It demonstrates the decrease of flow depths away from a

shoreline for inundation at large flat areas such as the Nooksack and Lummi

River deltas. Coastal dikes within the historic Skagit River delta region may

slow inundation along the coastal areas of Samish Bay, Padilla Bay, and the

Swinomish Channel; however, a height analysis of these manmade structures

suggest that tsunami waves will overtop and/or breach many of the coastal

dikes.

These modeling results are intended for development of the tsunami inundation maps and associated products for the regions of Bellingham, Anacortes, and northwest Whidbey Island. The numerical data provided to the

Washington State officials were used in the creation of official inundation

maps (Walsh et al., 2004a,b). Appendix B lists all modeling products prepared as a result of this study.

7. Acknowledgments

This research is funded by the National Tsunami Hazard Mitigation Program

via a grant from the Washington State Emergency Management Division.

We thank George Crawford, Timothy Walsh, George Priest, Ed Myers, and

others for assistance with the Cascadia Subduction Zone source. We also

thank Sharon Riggs, Skagit County GIS, City of Bellingham Planning Department, and City of Anacortes Public Works for assistance with GIS data

and point elevations.

This publication is partially funded by the Joint Institute for the Study of

the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement

No. NA17RJ1232, Contribution #1064.

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18 A.J. Venturato et al.

Appendix A: Bathymetry Data and

Computational Grids

Procedure

The TIME Center has developed data grids for the Eastern Strait of Juan

de Fuca inundation mapping project using the following five-step process:

1. Data Collection

2. Data Assessment

3. Grid Computation

4. Grid Assessment

5. Product Delivery

The best available bathymetric and topographic data were obtained from

government agencies. These sources are listed in the next section. The

data were reformatted and then analyzed for quality using ESRI© ArcGIS

software. Datasets were converted to geographic coordinates and the North

American Datum of 1927 at the modeler’s request. Bathymetric data were

then corrected from a vertical datum of Mean Lower Low Water (MLLW)

to Mean High Water (MHW) using an averaged value of tidal data from

National Ocean Service tertiary and secondary water level stations located

within the region of interest (Fig. A1). These data are controlled by the

Friday Harbor, San Juan Channel National Ocean Service primary water

level station (station number 944-9880). The mean values were calculated

by the National Ocean Service using the 1960–1978 tidal epoch throughout

the grid region. This approximation is accurate to within ±0.057 m along the

region’s shoreline (Table A1). Since the grids were built, the National Ocean

Service has updated values to the 1983–2001 tidal epoch. The difference of

mean values from the 1960–1978 epoch to the 1983–2001 epoch for this region

is +0.022 m.

A coastline file was generated based on governmental data sources. The

coastline represents the Mean High Water line as defined by the U.S. Geological Survey. Piers with open pile foundations were eliminated from the

coastline data for inundation modeling purposes. Tsunami waves can freely

propagate under open pile piers; therefore, the inundation is better modeled

without those piers than as part of the reflective shoreline.

A combined bathymetric and topographic data grid was then generated

using ArcGIS. Various datasets were combined using Triangulated Irregular

Table A1: Vertical control for grid development.

Datum Value (meters) Error (meters)

MHW 2.202 ±0.057

NGVD29 0.810 ±0.010

MLLW 0.000
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 19

Figure A1: Tidal datum distribution of Bellingham, Anacortes, and Whidbey

Island areas.

Network modeling. The results were converted into rectangular grids of 1-,

6-, and 36-arcsecond resolution (Table A2, Fig. A2).

The computed grids were analyzed for quality. Comparisons were made

between the original datasets and the grids. Datums were verified, point

errors were removed, and the grids were checked for logical consistency.

Data Sources

The data sources for the grids are described in Table A3. The resolution of

each data source varied; data sources for the highest resolution grid ranged

from approximately 1–30 m. Many sources were in different formats, which

may lead to a small conversion error. The vertical accuracy of the data is

based on the root mean square error, approximately 5% of depth for bathymetry and one-half of the contour interval for topography. Grid accuracy is
20 A.J. Venturato et al.

Figure A2: Digital Elevation Models for modeling propagation in the Strait of

Juan de Fuca and inundation in the Bellingham, Anacortes, and Whidbey Island

areas.

Table A2: Grid summary.

Region Name Resolution Extents (SW and NE corners)

Cascadia Subduction

Zone

sjdf36 36 arc-seconds SW: −132.00, 43.00

NE: −122.00, 53.00

Eastern Strait of Juan

de Fuca

sjdf6 6 arc-seconds SW: −125.00, 47.75

NE: −122.10, 49.25

Bellingham, Anacortes,

and Whidbey Island

sjdf1 1 arc-second SW: −122.81, 48.14

NE: −122.40, 48.87

based on the level of detail of the source and the grid interval used to sample

the source.

The data sources used for the grids are credited to the following groups:

• National Oceanic and Atmospheric Administration, National Geodetic

Database Centers. Hydrographic Surveys, GEODAS Version 4.1 Software. Boulder, Colorado. Website reference: http://www.ngdc.noaa.

gov/mgg/bathymetry/relief.html

• National Oceanic and Atmospheric Administration, National Ocean

Service. NOS Estuarine Bathymetry. Silver Spring, Maryland. Website reference: http://mapfinder.nos.noaa.gov/
NOAA TIME Eastern Strait of Juan de Fuca Mapping Project 21

Table A3: Data sources used for grid development.

Media Source Media Data Description

National Ocean

Service (NOS)

Digital Elevation

Model

30-meter NOS

bathymetric digital

elevation model

Quality-controlled bathymetric

data grid based on 1934–1982

NOS hydrographic surveys

National Geophysical

Data Center (NGDC)

CD-ROM (GEODAS

Version 4.1)

NOS Hydrographic

Surveys

Bathymetric data from

1982–1998 NOS hydrographic

survey

Canadian

Hydrographic Service

Point Data Hydrographic Surveys Bathymetric data from 1999

hydrographic surveys

USGS Open File

Report OF99-369

ArcInfo Grid 250K digital elevation

model

Bathymetric and topographic

data from various sources

University of

Washington PRISM

Project

ArcInfo Grid 10-meter topographic

digital elevation model

Topographic data obtained

from the U.S. Geological Survey

City of Bellingham ArcView shapefiles 5-foot topographic

contours of Bellingham

Topographic data obtained

from aerial photography

collected in 1988

City of Anacortes CAD drawing 10-foot topographic

contours of Anacortes

Topographic data obtained

from aerial photography

collected in 2001

• U.S. Geological Society, Western Region Geology. Open File Report

OF99-369 Cascadia DEM. Seattle, Washington. Website reference:

http://geopubs.wr.usgs.gov/open-file/of99-369/

• Washington State Geospatial Data Archive, University of Washington. U.S. Geological Survey 10-meter Digital Elevation Model. Seattle,

Washington. Website reference: http://duff.geology.washington.

edu/data/raster/tenmeter/

• City of Bellingham, Planning Department. City of Bellingham Topographic Contours. Anacortes, Washington. Website reference: http:

//www.cob.org/planning/

• City of Anacortes, Public Works. City of Anacortes Topographic

Contours. Anacortes, Washington. Website reference: http://www.

cityofanacortes.org/

• National Oceanic and Atmospheric Administration, Center for Operational Oceanographic Products and Services, Water Level Station Information for Seattle, Washington. Silver Spring, Maryland. Website

reference: http://www.co-ops.nos.noaa.gov/

• Information about ESRI ArcGIS software can be found on the Internet

at http://www.esri.com/
22 A.J. Venturato et al.

Appendix B: Modeling Products

Animations, screenshots, time series, GIS files, metadata, and user documentation were developed for distribution to the Washington State Division

of Geology and Earth Resources and the Washington State Military Department Emergency Management Division. The Washington State Military Department Emergency Management Division is responsible for redistribution

of these products.

An overview of products are listed in Table B1. All vector files and raster

grids are in the ESRI ArcGIS 3.2 format and have the following parameters:

• Horizontal Datum: North American Datum of 1983

• Vertical Datum: Mean High Water

• Projection: State Plane Coordinate System, Zone 5626

• XY Units: feet

• Z Units: meters (meters/second for current speeds)

The vector files and raster grids have an associated jpeg image and are

displayed in an ArcGIS 3.2a project for easy access and distribution. The

animations are in QuickTime format.

Table B1: Product summary.

Item Name Filename Type Image

1 Time Series bell timeseries ASCII bell timeseries.jpg

wdb timeseries wdb timeseries.jpg

2 Animations bell qt1, bell qt2, whidb qt QT bell screenshots

sjdf screenshots

3 User Documentation Bellingham presentation,

Product Report, Grid Report

4 Grid Limits limits vector sjdfgrids.jpg

5 Shoreline shoreline vector sjdfgrids.jpg

6 Elevation Grids (36-, 6-, 1-arcsecond) sjdf1, sjdf6, sjdf36 raster sjdfgrids.jpg

7 Source Deformation (Scenario 1A) src1a raster sjdfdef.jpg

8 Water Level Stations for Tidal Datums tides vector sjdfvdatum.jpg

9 Maximum Inundation Lines ainun, binun vector ainun.jpg, binun.jpg

10 Maximum Inundation Depths and Zones amaxd, bmaxd raster amaxd.jpg, amaxdz.jpg

bmaxd.jpg, bmaxdz.jpg

11 Maximum Current Speeds and Zones amaxu, bmaxu raster amaxu.jpg, amaxuz.jpg

bmaxu.jpg, bmaxuz.jpg

12 Maximum Wave Heights amaxh, bmaxh raster amaxh.jpg, bmaxh.jpg

13 Time Series Gages agages, bgages vector agages.jpg, bgages.jpg