Sediment detachment in piping‐prone soils: Cohesion sources and potential weakening mechanisms

Abstract

Soil piping is a widespread land degradation process that may lead to gully formation. However, the processes involved in sediment detachment from soil pipe walls have not been well studied, although their recognition is a crucial step to protect soils from piping erosion. This study aims to recognize the factors affecting cohesion and to identify the mechanisms which are likely to be responsible for the disintegration of soil. The study has been conducted in mid-altitude mountains under a temperate climate (the Bieszczady Mountains, the Carpathians, SE Poland). The research was based on the detailed field and laboratory analyses of morphology, and the physical and chemical properties of soil profiles with and without soil pipes. Moreover, experiments with flooding the undisturbed soil samples using different solutions (deionized water, ammonium oxalate, dithionate citrate, 35% hydrochloric acid and 30% hydrogen peroxide) were conducted in order to check the role of air slaking, the removal of soil organic carbon (SOC), and Fe and Al oxides on sediment detachment. The obtained results have confirmed that soil pipes develop in quite cohesive soils (silt loams), which allow the formation and maintenance of pipes with a diameter up to 30cm. Soil cohesion, and thus susceptibility to piping, are impacted by the content of major oxides, soil particle size distribution, biological activity and porosity. The tested soils affected by piping erosion have a lower content of Al 2 O 3 and Fe 2 O 3 , and free Fe (Fe (DCB)), lower clay content, higher biological activity (more roots and animal burrows), higher porosity, and more and larger pores than the profile without soil pipes. The experiments have indicated that especially SOC along with Fe and Al oxides are an important cohesion source in the study area. This suggests that the removal of SOC, and Fe and Al oxides may weaken and disintegrate aggregates in soil pipes. Further study of soil leaching and tensile strength will broaden understanding of which chemical processes control where pipes will develop in other cohesive piping-prone soils.

Detection of soil pipe network by geophysical approach: Electromagnetic induction (EMI) and electrical resistivity tomography (ERT)

“…The lower values of ER and higher values of EC a in deeper layers may be connected to higher water and clays content that increases down the undisturbed soil profile (not affected by piping). These trends in soil profiles have been recently presented by Bernatek‐Jakiel et al (2020) in the vicinity of the plot analyzed in this study. This is connected with the water table which occurs at the depth of 1–1.1 m.…”

“…They observed that the highest measurement accuracy was obtained at the highest tested soil moisture (i.e., 24.5%). In the study area, the soil moisture is generally above 30% (Bernatek‐Jakiel et al, 2020), which may suggest sufficient measurement accuracy.…”

Achieving change through gully erosion research

“…For example, a recent study quantified rainfall thresholds for gully initiation (Zhao et al, 2021), which could inform prevention activities such as drainage design. Underscoring the importance of hydrology and soil erodibility, recent research has identified soil saturation as a cause of piping erosion through loss of soil cohesion (Bernatek‐Jakiel et al, 2020). Consistent with that finding, soil pipe sediment yields have been found to be dependent on detachment rather than on runoff rate; and on supply rather than transport capacity (Wilson et al, 2020).…”

Internal erosion of soil pipes: Sediment rating curves for soil pipes

“…The result of these extreme flow conditions is not only high sediment detachment and transport capacity, but also frequent mass failures of aggregates from pipe sidewalls and roofs. However, limited research has been conducted on particle and aggregate detachment (Bernatek-Jakiel et al, 2020) within soil pipes. Bernatek-Jakiel et al (2020) conducted the most detailed study to date on the effects of fluid chemistry on particle and aggregate detachment in soil pipes formed in cohesive soils.…”

“…However, limited research has been conducted on particle and aggregate detachment (Bernatek-Jakiel et al, 2020) within soil pipes. Bernatek-Jakiel et al (2020) conducted the most detailed study to date on the effects of fluid chemistry on particle and aggregate detachment in soil pipes formed in cohesive soils. Their experiments involved flooding undisturbed soil samples with different solutions to determine the role of fluid properties on soil cohesion losses as well as air slaking.…”