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 Head Lighthouse

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 of Painted Stones ? Argus Answer: A creative X,Y, Z solution Results: The contract has continued.

Comparison #2: Traditional vs Argus Intertidal 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 change a lot…and often DateIntertidal Beach SlopeComments 20 February slope for m elev 30 July slope for m elev 20 September slope for m elev 20 February slope for m elev 23 August slope for m elev 15 November slope for m elev The alongshore average (2km) intertidal ( m 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 DATEFLOOD TIDE ONLYFLOOD & EBB TIDE Mean Error (cm) RMS Error (cm) Mean Error (cm) RMS Error (cm) 20 Feb July Sep Feb Aug Nov

Argus and RTK GPS Comparisons: Fixed vs “Measured” Foreshore Slope DATEMEASURED BEACH SLOPEFIXED BEACH SLOPE Mean Error (cm) RMS Error (cm) Mean Error (cm) RMS Error (cm) 20 Feb July Sep Feb Aug Nov

A Picture is Worth A Thousand Words MHW Shoreline

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.