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

Abstract

The collapse of soil pipes due to internal erosion can result in fully mature gullies. Few studies have measured the rates of sediment detachment and transport through soil pipes in situ. The objectives of this work were to determine suspended sediment concentration (SSC) in soil pipes as a function of pipeflow rate to develop sediment rating curves (SRC) and measure the bedload transport as a function of cumulative flow per storm event. H‐flumes were installed in seven discontinuous gullies formed by pipe collapse and instrumented for pipe discharge measurements and suspended sediment sampling. The typical response to pipeflow was an initial flush of high concentration of suspended sediment followed by a decrease as pipeflow increased (rising limb of hydrograph). Pipeflows were often so dynamic that it was difficult to consistently capture the initial flush of sediment, resulting in weak to non‐existent SRCs. The falling limb of the hydrograph tended to have a relatively low SSC. Thus, soil pipe SRCs tended to be better represented by hysteretic SRCs, although relationships between SSC and flow rate were poorly represented by SRCs. A power law equation given by SSC = aQb was adopted to represent the SRC relationships. Fitting this equation to data showed a correlation between the offset, a, and the slope, b, with the slope decreasing as the offset increases. Both SRC parameters (a and b) were correlated to the contributing area of the individual pipe. Bedload appeared to be an important contributor to sediment transport, with bedload – expressed as an average event sediment concentration (mg l−1) – decreasing as the volume of the event discharge (m3) increased. A significant portion (11–31%) of the bedload material was gravel and aggregates (>2 mm diameter material). While this work was the first to determine SRCs for soil pipes, refined sampling and measurement techniques are needed. © 2020 John Wiley & Sons, Ltd.

Achieving change through gully erosion research

“…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). The erodibility of some soils means that rain splash can be a significant contributor to gully sediment yields (Crouch & Blong, 1989;Daley et al, 2023).…”

Loess susceptibility to erosion: Interaction of cohesion sources, air slaking and confinement

“…There have been few attempts to identify the sources of cohesion in the soil (Wilson et al 2020). Xue et al (2019) and Bernatek-Jakiel et al ( 2020) identified soil organic carbon as the major cohesion source, with some contribution from Fe and Al oxides and hydroxides.…”

“…The remaining 3–30% of cohesion after 10% HCl leaching is most likely caused by organic matter as the only remaining major source of cohesion (c. f. Le Bissonnais, 1996; Xue et al, 2019). There have been few attempts to identify the sources of cohesion in the soil (Wilson et al 2020). Xue et al (2019) and Bernatek‐Jakiel et al (2020) identified soil organic carbon as the major cohesion source, with some contribution from Fe and Al oxides and hydroxides.…”