Soil Moisture Impacts Linear and Nonlinear Erodibility Parameters from Jet Erosion Tests

Abstract

HighlightsThe jet erosion test (JET) remains the most commonly used instrument for measuring in situ erodibility.This research investigated the impact of soil moisture content below saturation on erodibility parameters.Erodibility parameters were derived for both linear and nonlinear detachment models.Higher soil moisture increased initial resistance to erosion but also increased erosion rate.Abstract. The jet erosion test (JET) is a commonly employed technique to measure the erodibility of soils in situ by estimating the parameters of linear and nonlinear cohesive sediment detachment models. However, additional research is needed to understand the effect of soil moisture, a critical in situ test condition, on the derived erodibility parameters. This study compared the erodibility parameters, i.e., critical shear stress (tc) and the erodibility coefficient (kd) for the linear excess shear stress equation and two parameters (b0 and b1) for a nonlinear detachment model, from laboratory JETs across two soil types with contrasting texture and moisture contents. The general pattern was that higher soil moisture content increased the soil’s initial resistance to erosion (i.e., higher tc and b1), but once erosion was initiated the rate of erosion was greater (i.e., higher kd and b0). The magnitude of the changes in the erodibility parameters across the three soil moisture profiles investigated in this research were statistically significant, with kd and b0 varying by as much as a factor of 3. This research also confirmed the greater impact of soil moisture content on kd and b0 as compared to tc and b1. For the range of shear stress applied during these JETs, a linear detachment model was more appropriate for the sandy loam soil but less so for the more cohesive clay loam soil, but results were limited to a narrow range in applied shear stress. The results further support existing research conclusions that in situ erodibility measurements obtained under one set of soil moisture conditions may need to be adjusted to better predict soil detachment during storm events. Keywords: Cohesive soil, Critical shear stress, Detachment model, Erodibility, Jet erosion test, Shear stress, Soil moisture.

Guidance on Applied Pressure Heads for Quantifying Cohesive Soil Erodibility with a Jet Erosion Test (JET)

“…To calculate the minimum applied h, the total scour depths were analyzed from 187 previous "mini"-JET experiments. Those studies included raw data from JETs performed by Al-Madhhachi (2013a), Daly et al (2015), Daly et al (2016), McNichol et al (2017, Khanal et al (2020), and Swanson and Castro-Bolinaga (2022). We used the 25 th percentile from these previous JETs (fig.…”

“…Additionally, the standard practice remains the selection and use of a single, constant h (table 1). Next, the test should ideally be performed until a quasi-equilibrium scour depth is obtained, but this is not always practical; therefore, a total test duration of approximately 1 to 2 hr is typically used for in situ tests (Al-Madhhachi, 2013a;Daly et al, 2015;Daly et al, 2016;McNichol et al, 2017;Khanal et al, 2020;Swanson and Castro-Bolinaga, 2022), although shorter times are also common under more controlled conditions. Collected data can be analyzed to estimate erodibility parameters for cohesive soils in either linear or nonlinear detachment models for predicting erosion rates across a range of applied shear stress (Fox, 2019;Khanal et al, 2020;Wahl, 2021;Fox et al, 2022).…”

“…It should also be noted that soil moisture content can significantly influence erodibility parameters for cohesive soils. Khanal et al (2020) suggested that higher soil moisture increased initial resistance to erosion but also increased the erosion rate. Therefore, even resistant soils can become more erodible once the applied shear stress exceeds the critical shear stress due to changes in soil moisture content.…”

Perspective: Lessons Learned, Challenges, and Opportunities in Quantifying Cohesive Soil Erodibility with the Jet Erosion Test (JET)

“…However, as noted earlier, when JETs are conducted in situ, significant variability is commonly reported in the measurements due to the multitude of factors that influence soil erodibility. For example, higher soil moisture within a specific soil type increased the initial resistance to erosion but also increased the overall erosion rate (Khanal et al, 2020). For this reason, the workshop encouraged the use of probabilistic modeling approaches, as opposed to direct modeling applications that use single averaged values of erodibility parameters to generate a single model prediction.…”

Infiltration-Based Variability of Soil Erodibility Parameters Evaluated with the Jet Erosion Test

“…Lisenbee et al [17] compared the results of JET experiments for soils of tallgrass prairie and red ceder woodlands with the estimates from the WEPP model under varying soil conditions and found out that the WEPP-based k d were smaller that JET-derived values, while the values of τ c were within the same order of magnitude. In addition, laboratory and field studies have shown that these parameters may vary with the changes in soil moisture content and pore pressure gradients that occur during rainfall, surface runoff, and/or soil infiltration events [3,13,[18][19][20][21][22][23].…”