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Title
Cobble cam: grain-size measurements of sand to boulder from digital photographs and autocorrelation analyses
Alternative Title
Earth Surf. Process. Landforms 34, 1811-1821
Creator
Amy E. Draut
Daniel Buscombe
David M. Rubin
Jodi N. Harney
Jonathan A. Warrick
Peter Ruggiero
Date Created and/or Issued
2009
Publication Information
John Wiley & Sons, Ltd.
Contributing Institution
UC Riverside, Library, Water Resources Collections and Archives
Collection
Clearinghouse for Dam Removal Information (CDRI)
Rights Information
Copyrighted
Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user.
Description
Scope/Content: Abstract: A new application of the autocorrelation grain size analysis technique for mixed to coarse sediment settings has been investigated. Photographs of sand- to boulder-sized sediment along the Elwha River delta beach were taken from approximately 1·2 m above the ground surface, and detailed grain size measurements were made from 32 of these sites for calibration and validation. Digital photographs were found to provide accurate estimates of the long and intermediate axes of the surface sediment (r2 > 0·98), but poor estimates of the short axes (r2 = 0·68), suggesting that these short axes were naturally oriented in the vertical dimension. The autocorrelation method was successfully applied resulting in total irreducible error of 14% over a range of mean grain sizes of 1 to 200 mm. Compared with reported edge and object-detection results, it is noted that the autocorrelation method presented here has lower error and can be applied to a much broader range of mean grain sizes without altering the physical set-up of the camera (~200-fold versus ~6-fold). The approach is considerably less sensitive to lighting conditions than object-detection methods, although autocorrelation estimates do improve when measures are taken to shade sediments from direct sunlight. The effects of wet and dry conditions are also evaluated and discussed. The technique provides an estimate of grain size sorting from the easily calculated autocorrelation standard error, which is correlated with the graphical standard deviation at an r2 of 0·69. The technique is transferable to other sites when calibrated with linear corrections based on photo-based measurements, as shown by excellent grain-size analysis results (r2 = 0·97, irreducible error = 16%) from samples from the mixed grain size beaches of Kachemak Bay, Alaska. Thus, a method has been developed to measure mean grain size and sorting properties of coarse sediments.
Scope/Content: Author affiliation: USGS
Scope/Content: Author affiliation: Oregon State University
Scope/Content: Author affiliation: Coastal & Ocean Resources, Inc.
Type
text
Identifier
ark:/86086/n2833rn7
1130
Subject
Sediment and channel dynamics
Dams
Dam retirement
Place
Elwha River, WA
Elwha Dam
Glines Canyon Dam

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