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Title: Understanding mass fluvial erosion along a bank profile: using PEEP technology for quantifying retreat lengths and identifying event timing

Author
item PAPANICOLAOU, ATHANASIOS - University Of Tennessee
item WILSON, CHRISTOPHER - University Of Tennessee
item TSAKARIS, ACHILLES - University Of Tennessee
item SUTARTO, TOMMY - Samarinda Polytechnic State University
item BERTRAND, FABIENNE - United Nations Children Fund
item RINALDI, MASSIMO - University Of Florence
item DEY, SUBHASISH - Indian Institute Of Technology
item Langendoen, Eddy

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2017
Publication Date: 9/5/2017
Citation: Papanicolaou, A.N., Wilson, C.G., Tsakaris, A.G., Sutarto, T.E., Bertrand, F., Rinaldi, M., Dey, S., Langendoen, E.J. 2017. Understanding mass fluvial erosion along a bank profile: using PEEP technology for quantifying retreat lengths and identifying event timing. Earth Surface Processes and Landforms. 42(11): 1717-1732. https://doi.org/10.1002/esp.4138.
DOI: https://doi.org/10.1002/esp.4138

Interpretive Summary: Bank erosion occurs through different modes, namely mass failure, fluvial erosion of individual particles or aggregates, and mass erosion of larger clods, all of which vary in terms of magnitude, frequency of occurrence, and spatial extent along the channel. Unfortunately, quantitative studies of the parameters describing mass erosion, which occurs at higher shear stresses exerted by the flow, are lacking. In a collaborative study researchers at the USDA, ARS, Watershed Physical Processes Research Unit, University of Iowa, University of Florence (Italy), and the Indian Institute of Technology Kharagpur (India) conducted a field study in Clear Creek, IA to quantify the mass erosion parameters and used the USDA, ARS channel evolution computer model CONCEPTS to quantify the contribution of mass erosion to total bank erosion. The shear stresses needed to induce mass erosion were about 3 to 6 times larger than those needed to induce fluvial erosion. The rate of mass erosion was about twice that of fluvial erosion. CONCEPTS showed that fluvial erosion and mass erosion provided about 80% of the total sediment mass from streambanks. These findings can be used to further enhance computer models, such as CONCEPTS, that are needed by watershed managers and governmental agencies to identify sediment sources and quantify sediment loads and yield at the watershed scale.

Technical Abstract: This study is designed to promote fundamental understanding of mass erosion using Photo-Electronic Erosion Pins (PEEPs) to quantify stream bank retreat lengths and identify event timing along a bank profile. Mass erosion is considered as the detachment of soil clods or thin layers from the bank face due to hydraulic shear with retreat lengths of the centimeter scale. This is in comparison to hydraulically driven fluvial erosion, which is the entrainment of individual grains with retreat lengths at the millimeter scale. PEEPs were placed in a representative U.S. Midwestern stream with mostly cohesive, loess-derived banks, namely Clear Creek, IA. A unique and systematic data processing routine (e.g., filtering, correcting, and smoothing) was developed for the PEEPs to remove the effects of ambient light changes from solar orientation, vegetation, and turbidity. Additionally, a statistical treatment of the retreat length time series was applied consisting of moving averages and Shewhart diagrams to identify key mass erosion events in terms of magnitude and frequency of occurrence. The PEEP measurements compared well (errors less than 28%) with conventional erosion pins; however, the pins provided time-integrated retreat lengths over the monitoring period, whereas the PEEPs measurements were semi-continuously and identified the timing of mass erosion event. This study also provided the construction of the spectrum of hydraulic conditions within which fluvial and mass erosion occur. The mass erosion strength was found to be at least 3 to 6 times higher in magnitude than the fluvial erosion strength, and mass erosion proceeded at a higher erodibility. The mass erosion strength and erodibility values were supplied to the CONCEPTS 1D channel evolution model to quantify retreat rates for different hydrologic events. The simulation data suggest that fluvial and mass erosion can produce ~80% of channel-derived sediments to the suspended load, thus supporting the need for considering both erosion processes in a bank stability analysis.