Improved analysis procedures of soil erosion resistance measurement methods

Authors: Langendoen, Eddy; Ursic, Michael - Mick

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2023
Publication Date: 8/21/2023
Citation: Langendoen, E.J., Ursic, M.E. 2023. Improved analysis procedures of soil erosion resistance measurement methods. In Abstract Book of 40th IAHR World Congress, Vienna, Austria, August 21-25, 2023.

Interpretive Summary: Abstract only.

Technical Abstract: Fine-grained, suspended sediments are a leading pollutant of water bodies in the United States. Farmland and stream banks are the main sources of the fine-grained sediments. The erosion rate of fine-grained sediments is typically calculated using a linear excess-shear stress equation, which is a function of two soil erosion-resistance parameters: a critical shear stress that needs to be exceeded for erosion to commence and a detachment coefficient that indicates the rate at which particles or aggregates are entrained. Measured soil erosion-resistance parameters exhibit large variability not only between different soil types, but also for same soil types. This variability is caused by the inherent, spatial variability in soil properties and the different instrumentation and post-processing techniques employed to quantify soil erosion-resistance. Two widely used measurement methods are the Jet Erosion Test (JET) and Erosion Function Apparatus (EFA). Both JET and EFA measurements have shown that the erosion function is often non-linear, which generally indicates differing erosion mechanics along the erosion function. For example, at higher applied shear stresses, aggregates or chunks of soils are detached, which are much larger than the detached particles at small excess shear stresses, resulting in magnitude differences in the rate of detachment. Post-processing techniques that fit a linear excess shear stress equation to the measured non-linear erosion function can introduce significant variability in the measured soil erosion resistance parameters. In addition to the systemic post-processing discrepancies, the JET and EFA use different hydraulics to erode soil samples and different techniques to determine the applied shear stresses. The inherent differences between devices and methods typically leads to dissimilarities in their respective erosion functions. We conducted JET and EFA tests on silt and silty sand bank soils. Using their standard post-processing techniques, distributions of JET and EFA soil erosion-resistance values for each soil type differed significantly. However, accounting for sources of variability during the post-processing stage resulted in distributions of JET- and EFA-derived soil erosion-resistance values that were statistically similar. Further, we used these soil erosion-resistance distributions to conduct a stochastic analysis with the Bank Stability and Toe Erosion Model (BSTEM) of bank erosion along the Lower American River, CA. Calibration of model erosion-resistance values against observed bank erosion showed the distribution of calibrated values for the silt soil type was similar as that measured. However, for the silty sand soil type the distribution of calibrated erodibility values significantly differed from that measured. We recommend that erosion calculations of fine-grained, cohesive soils should be based on measured data that are carefully analyzed to account for variability introduced by instrumentation and soil heterogeneity and match the expected, study erosion regime. Erosion estimation reliability can further be improved by employing a thorough calibration process.