Argus Eyes on Benson Beach Mouth of the Columbia River - North Head Lighthouse

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Argus Eyes on Benson BeachMouth of the Columbia River - North Head Lighthouse

Sponsored by: USACE Portland District

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Proving Argus Quantitative Accuracy: Where are the White Rocks?

• After installation, USACE Portland District asked,– “where are these two

rock fall in State Plane coordinates”

– (We want to verify your claim that Argus provides quantitative information)

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Proving Argus Accuracy: Comparing MHW

Alongshore (m)

Cro

ss-s

hore

(m)

Jul. 28, 2004

1000 1500 2000 2500 3000

300

350

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BuggyArgus

Argus/AREand

WA DOE “Buggy Surveys” (RTK GPS)

Special processing:1) Collect

shorelines during flood tide only

2) Recalculate shoreline Z using foreshore slope from a first pass

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200m

500m

Submerged sandbars

N

630m

MHW Shoreline

Meso-tidal beach

Hsig: 1m – 13m

Foreshore slopes: 0.01 – 0.06

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Background: Argus at Benson Beach since Feb 2004

• Severe winter of 2005/2006– Erosion of grass dunes behind beach– Weakened offshore bar system

• Followed with two years of erosion– Extreme shoreward shift of MHW shoreline– North Jetty foot weakened

• 125k yd3 placed along jetty in 2008• 367k yd3 placed on beach in 2010

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Benson Beach Sediment SystemInterpreted from 7+ years of Argus Eyes

• Observed seasonal changes:– MHW shorelines, sandbar movement, and

foreshore slopes suggest -• interdependency between offshore sandbar

morphodynamics and foreshore change• Differences in foreshore change from one

year to the next are a result of difference in the:– strength and intensity of the winter waves– morphology and health of the offshore

sandbars

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Argus Eyes• Imagery

– Snaps, timex, variance, brightness - hourly– Sandbar location tracking maps – 2x/month

• MHW (2.0 NAVD88) Shorelines– Shoreline location maps – 2x/month– Dry-beach acreage graphs – 2x/month

• Foreshore (1.5-2.5m NAVD88) Bathymetry– Foreshore volume graphs – 2x/month

• A proxy for foreshore beach slopes

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200m

500m

Middle bar

N

630mDry-Beach Acreage

Inner bar

MHW

Foreshore sand volume

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Sandbar Maps – bars moving shoreward

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Thu.Mar.03.18.20.00.GMT.2005

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-200

0

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outer sand barmiddle sand bar

MHW shoreline

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Mon.May.16.23.20.00.GMT.2005

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The middle bar attaches to the shoreface, moving the 2.0m

shoreline seaward

N

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Tue.Jul.26.19.00.00.GMT.2005

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-200

0

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The summer intertidal terrace incorporates the middle bar

Middle bar moving onshore

March 2006 April 2006

May 2006 July 2006

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Sept 2010

Oct 2006

(bold lines mark early March MHW shorelines)

N

OCEAN

BEACH

630m

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Man-made salientSW WA LDR dredge material

placement – Sept 2010

Natural salientSummer following severe 2005/2006

winter

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200m

500m

Middle bar

N

630mDry-Beach Acreage

Inner bar

MHW

Foreshore sand volume

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4/1/200410/1/2004

4/1/200510/1/2005

4/1/200610/1/2006

4/1/200710/1/2007

4/1/200810/1/2008

4/1/200910/1/2009

4/1/201010/1/2010

350000

400000

450000

500000

550000

600000

sum

mer

sum

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sum

mer

sum

mer

sum

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win

ter e

rosi

on

extre

me

win

ter

win

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win

ter

win

ter

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sum

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acc

retio

n

Dry-Beach Acreage (m2)

12.3 acres

144/1/2004

10/1/20044/1/2005

10/1/20054/1/2006

10/1/20064/1/2007

10/1/20074/1/2008

10/1/20084/1/2009

10/1/20094/1/2010

10/1/2010 700,000

750,000

800,000

850,000

900,000

950,000

1,000,000 2004-2011 Foreshore (1.5-2.5m NAVD88) Volumes (m3)

sum

mer

sum

mer

sum

mer

win

ter

win

-te

r

win

ter

sum

mer

sum

mer

sum

-m

er

win

-te

r win

-te

r

win

ter

sum

mer

sha

llow

slo

pe

win

ter

stee

p sl

ope

Stee

per

(a proxy for beach shape - steep, shallow, plane, concave, convex)

154/1/200410/1/2004

4/1/200510/1/2005

4/1/200610/1/2006

4/1/200710/1/2007

4/1/200810/1/2008

4/1/200910/1/2009

4/1/201010/1/2010

350000

400000

450000

500000

550000

600000

win

ter e

rosi

on

win

ter

win

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win

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acr

etio

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Dry-Beach Acreage (m2)

Extreme 05-06 Win-ter

North Jetty berm repair – 125k yds3

Healthy 3-bar system

Greatest north & south shore-

line retreat

SW WA LDR 367k yd3

First 4-bar system observed

Weak 2-bar system

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Argus Eyes on the SW WA LDRDredge Material Beach Placement

• 1 Aug - 22 Sept 2010– 367k yd3 (281 m3) placed on Benson Beach– First storm in the last week of Sept

• Argus foreshore (1.5-2.5m NAVD88) volume measurements– capture the material placement & movement

(reshaping of the foreshore)• Argus sandbar maps reveal the creation of

a fourth sand bar by Spring 2011

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NN of

DS

N of DS

N DS

S DS

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160,000

180,000

200,000

220,000

240,000

260,000

280,000

South Disposal Site

North Disposal Site

North of DS

North North of DS

AlongshoreRange

Volume (m3)Jetty

Lighthouse

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First observed 4-bar system

Dec 2010

March 2011

Oct 2010

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Benson Beach Sediment SystemInterpreted from 7+ years of Argus Eyes

• Interdependency of offshore sandbar morphodynamics and foreshore change– Winter storms >> swash bar pulled offshore

>> steep foreshores– Summer calm >> swash bar attaches to

shoreface >> shallow foreshores– Health of sandbars affect how much sand is

pulled from the foreshore during storms• Feed the bars, save the beach

– OR! starved bars feed on beaches

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What’s Next?• Quantifying the “health” of a sandbar

– The volume/linear-meter of sand in the bar may be a metric of health and behavior (Russeinik et al, 2009)

– Kaminsky’s and Ruggiero’s jet ski bathymetry surveys of Benson Beach can provide volume information!

• Imagine! We may be able to identify the presence of a “weak” bar system – before a winter of extreme erosion and jetty

damage

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Argus at North Head Lighthouse would not have been possible without funding from USACE and the joint cooperation of Washington State

Parks, Coast Guard, and USACE/Portland District

A collaborative effort with WA DOE (Kamininsky), OSU (Ruggiero, Ozkan-Haller, Haller), USGS (Gelfenbaum), Golder (Osborne)

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NorthWest Research Associates (NWRA)

Redmond, WA

NWRA is a scientific

research group, owned

and operated by its

Principal Investigators,

with expertise in the

geophysical and related

sciences.