argus as an coastal engineering tool - validation through comparisons with traditional methods

Argus as an Coastal Engineering Tool -

Validation through Comparisons with Traditional Methods

Joan Oltman-Shay,Matt Pruis, and Dave Berliner

Sponsored (Requested) by: USACE Portland District

Background: Argus Monitoring at North Head

• Sponsor: US Army Corps of Engineers – Portland District

• Project Objectives:

• Survey the intertidal zone of Benson Beach, north of the Mouth of the Columbia River

• Develop a process understanding of sediment transport on Benson Beach

• Provide an “informed” opinion of best location(s) for dredge material disposal within the littoral cell (beneficial use of dredged sands)

Eight cameras looking south

50mm lenses

Jetties, MCR, and the great state of Oregon in the distance

Site E

2 miles; 3.22 km

1km

4km

MCR

North HeadLighthouse

USACE District Experience with Argus• The bosses of Corps project engineers do not “know”

Argus from Adam

• Proof of Argus methods is therefore needed

– e.g., comparison with “traditional” survey methods like RTK GPS

• Comparison #1: Where is the painted rock?

• Comparison #2: Intertidal bathmetry comparision with RTK GPS

– Result: Identification of “best-use” images and parameters for intertidal bathymetry mapping

• Only use images collected during flood tides

• “Measure” foreshore beach slope for each survey day

Comparison #1:GPS vs Argus: Location of the White Rocks

2005 Request: Location ofPainted Stones ?

Argus Answer:

A creative X,Y, Z solution

Results:

The contract has continued.

Comparison #2: Traditional vs ArgusIntertidal Bathymetry Surveys

• RTK GPS “Traditional” Surveys– Peter Ruggiero and George

Kaminsky • USACE Portand District funding

– Bi-annual surveys of Benson Beach and the larger Columbia River Littoral Cell

• 6 surveys between Feb 2004 and Nov 2005 coincide with Argus acquisition of good images– No fog, Hrms < 2m, large tidal

range

Argus intertidal bathymetry surveys:• Tools from Delft’s ARE

Shoreline Detection: Pixel Intensity Clustering Method of Aarninkof and Roelvink (1999)

Shoreline Elevation:

Zwl = Ztide + Zwvsetup + (Kosc)Zswash(Battjes&Jannsen, 1978; Svendsen, 1984; Stive and DeVriend, 1994; Aarninkof&Roelvink, 1999)

Note: Zwvsetup and Zswash are a function of Hrms, Tpk, and foreshore beach slope) Contours span 4m elevation

Sept 2005

Sept 2006

Warning: Foreshore beach slope can changea lot…and often

Date Intertidal Beach Slope Comments

20 February 2004 0.044 0.053 slope for 1.5-2.5m elev

30 July 2004 0.016 0.042 slope for 1.5-2.5m elev

20 September 2004 0.026 0.028 slope for 1.5-2.5m elev

20 February 2005 0.022 0.026 slope for 1.5-2.5m elev

23 August 2005 0.01 0.015 slope for 1.5-2.5m elev

15 November 2005 0.042 0.042 slope for 1.5-2.5m elev

The alongshore average (2km) intertidal (0.5-1.5m NAVD88) beach slope determined from an initial (beach slope fixed at 0.025) Argus intertidal bathymetry

Argus and RTK GPS Comparisons: Flood vs Flood & Ebb Tide Images

Flood & ebb images

Flood only images

Argus contour elevations compared with the average elevation of the interpolated GPS-Buggy data along each of the Argus x,y contours (Aarninkhof method).

Argus and RTK GPS Comparisons: Flood vs Flood & Ebb Tide Images

DATE FLOOD TIDE ONLY FLOOD & EBB TIDE

Mean Error (cm)

RMS Error (cm)

Mean Error (cm)

RMS Error (cm)

20 Feb 2004 -1.4 10.6 11.7 30.6

30 July 2004 -3.4 8.9 -10 18.8

20Sep 2004 -5.2 9.3 -21.2 26.7

20 Feb 2005 8.9 11.5 10.1 14

23Aug 2005 0.2 9.3 -11.3 20

15Nov 2005 -7.3 10.9 -10.2 30.6

Argus and RTK GPS Comparisons: Fixed vs “Measured” Foreshore Slope

DATE MEASURED BEACH SLOPE FIXED 0.025 BEACH SLOPE

Mean Error (cm)

RMS Error (cm)

Mean Error (cm)

RMS Error (cm)

20 Feb 2004 -1.4 10.6 25.2 26.5

30 July 2004 -3.4 8.9 -20.6 22

20 Sep 2004 -5.2 9.3 -4.1 8.6

20 Feb 2005 8.9 11.5 5.3 8.9

23 Aug 2005 0.2 9.3 -24.8 26.4

15 Nov 2005 -7.3 10.9 -6.3 10.8

A Picture is Worth A Thousand Words

Alongshore (m)

Cro

ss-s

hore

(m)

Feb. 21, 2004

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550

BuggyArgus

MHW Shoreline

Alongshore (m)

Cro

ss-s

hore

(m)

Jul. 28, 2004

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300

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450

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550

BuggyArgus

Alongshore (m)

Cro

ss-s

hore

(m)

Feb. 20, 2004

1000 1500 2000 2500 3000

300

350

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550

BuggyArgus

Alongshore (m)

Cro

ss-s

hore

(m)

Aug. 23, 2005

1000 1500 2000 2500 3000

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BuggyArgus

Summary• RMS errors of O(10cm) between RTK GPS and

Argus surveys at North Head can be achieved if:– Argus uses only images acquired during flood tides

• rms errors reduced by as much as 20cm

– the Argus waterline elevation model uses a timely “measured” foreshore slope

• An one-step, iterative method of first estimating foreshore slope from Argus contour elevations estimated with a fixed beach slope and then corrected with the “measured” foreshore slope improved comparisons

– rms errors reduced by as much as 15cm– you don’t have to re-pick contours to do this

Reprocessing North Head Contour Data

• We’re going back through 30+ months of Argus images and constraining (“filtering”) our contour for:– Flood tide images– Flood tidal ranges spanning nominally 1 to 3m NAVD88– Hrms < nominally 2m*– Tpk < nominally 15sec*

• We use autogeom to also help us identify and filter good quality images (good geometry solutions = good images … no fog at North Head)– This is a critically important time saver

* Minimizing Hrms and Tpk reduces the magnitude of wave setup and swash (model error); we presently use Hrms < 1m in summer, < 2.5m in winter and do not constrainTpk.

This exercise has given us great confidence in the ARE waterline elevation model

NorthWest Research Associates (NWRA)

Bellevue, WA

NWRA is a scientific

research group, owned

and operated by its

Principal Investigators,

with expertise in the

geophysical and related

sciences.