Upload
zelig
View
45
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Argus Eyes on Benson Beach Mouth of the Columbia River - North Head Lighthouse. Sponsored by: USACE Portland District. Proving Argus Quantitative Accuracy: Where are the White Rocks?. After installation, USACE Portland District asked, - PowerPoint PPT Presentation
Citation preview
1
Argus Eyes on Benson BeachMouth of the Columbia River - North Head Lighthouse
Sponsored by: USACE Portland District
2
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)
3
Proving Argus Accuracy: Comparing MHW
Alongshore (m)
Cro
ss-s
hore
(m)
Jul. 28, 2004
1000 1500 2000 2500 3000
300
350
400
450
500
550
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
4
200m
500m
Submerged sandbars
N
630m
MHW Shoreline
Meso-tidal beach
Hsig: 1m – 13m
Foreshore slopes: 0.01 – 0.06
5
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
6
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
7
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
8
200m
500m
Middle bar
N
630mDry-Beach Acreage
Inner bar
MHW
Foreshore sand volume
9
Sandbar Maps – bars moving shoreward
15
Thu.Mar.03.18.20.00.GMT.2005
1000 1500 2000 2500 3000 3500 4000 4500
-200
0
200
400
600
800
1000
1200
1400
1600
outer sand barmiddle sand bar
MHW shoreline
17
Mon.May.16.23.20.00.GMT.2005
1000 1500 2000 2500 3000 3500 4000 4500
-200
0
200
400
600
800
1000
1200
1400
1600
The middle bar attaches to the shoreface, moving the 2.0m
shoreline seaward
N
18
Tue.Jul.26.19.00.00.GMT.2005
1000 1500 2000 2500 3000 3500 4000 4500
-200
0
200
400
600
800
1000
1200
1400
1600
The summer intertidal terrace incorporates the middle bar
Middle bar moving onshore
March 2006 April 2006
May 2006 July 2006
10
Sept 2010
Oct 2006
(bold lines mark early March MHW shorelines)
N
OCEAN
BEACH
630m
11
Man-made salientSW WA LDR dredge material
placement – Sept 2010
Natural salientSummer following severe 2005/2006
winter
12
200m
500m
Middle bar
N
630mDry-Beach Acreage
Inner bar
MHW
Foreshore sand volume
13
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
mer
sum
mer
sum
mer
sum
mer
sum
mer
win
ter e
rosi
on
extre
me
win
ter
win
ter
win
ter
win
ter
win
ter
win
ter
sum
mer
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
ter
win
ter
win
ter
win
ter
win
ter
sum
mer
acr
etio
n
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
16
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
17
NN of
DS
N of DS
N DS
S DS
18
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
19
First observed 4-bar system
Dec 2010
March 2011
Oct 2010
20
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
21
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
22
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)
23
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.