Improving the reliability of soil erosion estimates

Authors: Langendoen, Eddy; Ursic, Michael - Mick; BRIAUD, JEAN-LOUIS - Texas A&M University; AUBUCHON, JONATHAN - Us Army Corp Of Engineers (USACE); RIVAS, TODD - Us Army Corp Of Engineers (USACE)

Submitted to: Joint Federal Interagency Sedimentation and Hydrologic Modeling
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2023
Publication Date: 5/8/2023
Citation: Langendoen, E.J., Ursic, M.E., Briaud, J., Aubuchon, J.S., Rivas, T.M. 2023. Improving the reliability of soil erosion estimates. Joint Federal Interagency Sedimentation and Hydrologic Modeling. 7 pp. In Proceedings of SEDHYD 2023, St. Louis, MO, May 8-12, 2023.

Interpretive Summary: The Jet Erosion Test (JET) and Erosion Function Apparatus (EFA) methods are most commonly used to characterize soil erosion resistance. Unfortunately, erosion-resistance values derived with these measurement methods generally differ widely for the same soil. ARS scientists in Oxford, MS, collaborated with the US Army Corps of Engineers (USACE), Sacramento District, and Texas A&M University to compare the soil erosion-resistance parameters derived by the JET and EFA methods for silt and silty sand soil samples collected from stream banks on the American and Sacramento Rivers adjacent to the City of Sacramento. It was found that the discrepancies between JET and EFA methods are primarily caused by (1) derived erosion-resistance parameters representing different erosion regimes and (2) not accounting for surface roughness. After adjusting measured erosion-resistance parameters for these differences, the distributions of erosion-resistance parameters quantified by the EFA and JET methods compared well for both soil types. The study's findings are used by the US Army Corps of Engineers to derive distributions of erosion-resistance parameters for probabilistic simulations with the ARS Bank Stability and Toe Erosion Model (BSTEM). Model results are used to prioritize bank stabilization measures along reaches of the American and Sacramento Rivers to protect the City of Sacramento as authorized by the Water Resources Development Act of 2016.

Technical Abstract: Measured soil erosion-resistance parameters exhibit large variability (up to several orders of magnitude) not only between different soil types, but also for same or similar soil types. This variability is not only caused by the inherent, spatial variability in soil properties (e.g., texture, density, moisture, and organic content), but also by the different instrumentation and post-processing techniques employed to quantify soil erosion-resistance. We conducted JET and EFA tests on silt and silty sand Unified Soil Classification System soil types obtained from the banks along the Lower American and Sacramento Rivers, CA. We showed that using modified post-processing techniques of JET and EFA tests, which use applied shear stress at the grain/aggregate scale, mass surface erosion regime, and uncertainty in estimated shear stress and measured erosion rate, results in similar distributions of soil erosion-resistance parameters. 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 differed slightly 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, erosion regime. Erosion estimation reliability can further be improved by employing a thorough calibration process.