Rill erosion on an oxisol influenced by a thin compacted layer

Abstract

SUMMARYThe presence of compacted layers in soils can induce subprocesses (e.g., discontinuity of water flow) and induces soil erosion and rill development. This study assesses how rill erosion in Oxisols is affected by a plow pan. The study shows that changes in hydraulic properties occur when the topsoil is eroded because the compacted layer lies close below the surface. The hydraulic properties that induce sediment transport and rill formation (i.e., hydraulic thresholds at which these processes occur) are not the same. Because of the resistance of the compacted layer, the hydraulic conditions leading to rill incision on the soil surface differed from the conditions inducing rill deepening. The Reynolds number was the best hydraulic predictor for both processes. The formed rills were shallow and could easily be removed by tillage between crops. However, during rill development, large amounts of soil and contaminants could also be transferred.

Experimental determination of sediment transport capacity of concentrated water flow over saturated soil slope

“…Firstly, when the soil becomes saturated, the soil surface runoff is also altered due to reduced soil infiltration capability under the saturation status compared with that under non‐saturated soil (Defersha, Quraishi, & Melesse, 2011; Zegeye et al, 2010; Zegeye et al, 2016). Then, a large flow velocity over the saturated soil slope can transport more sediments than that over the non‐saturated soil slope, as previously discussed (Gabbard, Huang, Norton, & Steinhardt, 1998; Lin, Brooks, McDaniel, & Boll, 2008; Thomaz, 2013). Soil erosion over saturated soil slopes usually produces a relatively smooth rill bed without abrupt headcuts (Y. H. Huang et al, 2018), decreasing the energy consumption of water flow, and results in the transportation of additional sediments.…”

“…However, the STC value of the saturated loess slope was approximately 25% larger than that of the non‐saturated soil slope (Figure 7). This finding indicates that a saturated loess slope could transport more sediments than a non‐saturated one (Rockwell, 2002; Thomaz, 2013; Wilson et al, 2007), and the occurrence of rill erosion on a saturated loess slope is possible.…”

“…Thus, the hydrodynamics on saturated slopes is significantly altered compared with that on non‐saturated soil slopes. Therefore, additional sediments could be transported under the same slope gradient and unit‐width flow rate (Rockwell, 2002; Thomaz, 2013; Wilson et al, 2007). Meanwhile, the occurrence of headcuts over saturated soil slopes is unlikely during the erosion process, thus avoiding waterfalls that slow down flow velocity and kinetic energy (Y. H. Huang et al, 2018).…”

“…The saturated condition may change the boundary layer status of the rill bed and reduce its frictional resistance (Zhang et al, 2017). All these factors resulted in an easily erodible soil and a larger STC over the saturated soil slope than over the non‐saturated one under the same slope gradient and unit‐width flow rate (Rockwell, 2002; Thomaz, 2013; Wilson et al, 2007).…”

Rill length and plot‐scale effects on the hydrogeomorphologic response of gravelly roadbeds

“…However, rill erosion processes on the roadbed differ substantially from rill erosion on agricultural lands (Foltz et al , ). Therefore, our common understanding of the importance of rills on surface erosion might not be applicable to our experiments on roads where a highly compacted layer prevents rill deepening and avoids sediment detachment (Thomaz, ). Rainfall rates during our simulation experiments were not sufficient to expand the existing rill network; thus, erosion from our micro‐catchments represents the integration of interill erosion and sediment transport through the rill network.…”