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Title: Site-scale variability of streambank fluvial erodibility parameters as measured with a jet erosion test

Author
item DALY, ERIN - Oklahoma State University
item FOX, GAREY - Oklahoma State University
item ENLOW, HOLLY - Oklahoma State University
item STORM, DANIEL - Oklahoma State University
item Hunt, Sherry

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2015
Publication Date: 12/30/2015
Citation: Daly, E.R., Fox, G.A., Enlow, H.K., Storm, D.E., Hunt, S.L. 2015. Site-scale variability of streambank fluvial erodibility parameters as measured with a jet erosion test. Hydrological Processes. 29(16):5451-5464.

Interpretive Summary: Sediment and nutrients are a significant source of pollution in streams, rivers, lakes, and other water bodies worldwide. The erosion rate of streambanks is dependent on the erosion resistance of the soil. A test method known as the JET is commonly used to characterize soil erodibility in the field whether it is in the streambank, streambed, spillway, dam, or some other site of interest. The objective of this study was to determine the number of JETs needed to accurately characterize the erosion resistance of a given streambank. Equations that predict erosion properties based on soil characteristics will likely contain high uncertainty and thus should be used with caution. This study highlights the need to conduct field measurements using the JET in order to properly characterize erosion rates encountered along a streambank.

Technical Abstract: The erosion rate of cohesive streambanks is typically modeled using the excess shear stress equation, dependent on two erodibility parameters: critical shear stress and erodibility coefficient. The Jet Erosion Test (JET) has become the most common method for estimating these erodibility parameters in situ. Typically, results from a few JETs are averaged to acquire a single set of parameters for characterizing a streambank layer; however, this may be inadequate for accurately characterizing erodibility. The research objectives were to investigate the variability of JET results from assumed homogeneous streambank layers and to estimate the number of JETs required to accurately characterize erodibility for use in predictive models. On three unique streambanks in Oklahoma and across a range of erodibility, 20 to 30 JETs were conducted over the span of three days. Each JET was analyzed using the Blaisdell, scour depth, and iterative solutions. The required sample size to accurately estimate the erodibility parameters depended on the JET solution technique, the parameter being estimated, and the degrees of precision and confidence. Conducting three to five JETs per soil layer on a streambank typically provided an order of magnitude estimate of the erodibility parameters. Because the parameters were log-normally distributed, using empirical equations to predict erosion properties based on soil characteristics will likely contain high uncertainty and thus should be used with caution. This study exemplifies the need to conduct in situ measurements using the JET in order to accurately characterize streambank resistance to fluvial erosion.