Rill erosion processes on a constantly saturated slope

Abstract

Rill erosion processes on saturated soil slopes are important for understanding erosion hydrodynamics and determining the parameters of rill erosion models. Saturated soil slopes were innovatively created to investigate the rill erosion processes. Rill erosion processes on saturated soil slopes were modelled by using the sediment concentrations determined by sediment transport capacities (STCs) measurement and the sediment concentrations at different rill lengths. Laboratory experiments were performed under varying slope gradients (5°, 10°, 15°, and 20°) and unit‐width flow rates (0.33, 0.67, and 1.33 × 10−3 m3 s−1 m−1) to measure sediment concentrations at different rill lengths (1, 2, 4, and 8 m) on saturated soil slopes. The measured sediment concentrations along saturated rills ranged from 134.54 to 1,064.47 kg/m3, and also increased exponentially with rill length similar to non‐saturated rills. The model of the rill erosion process in non‐saturated soil rills was applicable to that in saturated soil rills. However, the sediment concentration of the rill flow increased much faster, with the increase in rill length, to considerably higher levels at STCs. The saturated soil rills produced 120–560% more sediments than the non‐saturated ones. Moreover, the former eroded remarkably faster in the beginning section of the rills, as compared with that on the non‐saturated soil slopes. This dataset serves as the basis for determining the erosion parameters in the process‐based erosion models on saturated soil slopes.

Saturation effect on the distribution of rill detachment rate

“…Numerically computed rill detachment rates can also be related to sediment concentrations due to the good correlation of sediment concentration with rill length (Huang, Li, Wang, et al, 2020). The computed rill detachment rates on saturated soil slopes show effective linearly decreasing relationships with sediment concentration (Figure 3).…”

“…The first aspect is that the saturated state changes the physical properties of the soil. Saturated states of the soil reduced soil cohesion and broke down soil aggregates to single‐grained particles (Bertolino et al, 2010; Huang et al, 2018; Huang, Li, Liu, et al, 2020; Huang, Li, Wang, et al, 2020; Osman & Barakbah, 2011). Thus, the soil strength of saturated soil is considerably weakened compared with that of non‐saturated soil (Auerswald, Muchler, & Mcgregor, 1994; Rudoloph, Helming, & Diestel, 1997).…”

“…Experimental device of seepage tubes wrapped with geotextiles (a), seepage units (b) and saturated soil slope (c) (Huang, Li, Wang, et al, 2020)…”

“…Huang, Li, Wang, et al (2020) measured and reported sediment concentrations of rill erosion on saturated soil slopes at different rill lengths. The measured results distributed with rill lengths under designed hydraulic conditions are presented in Table 1.…”

“…Little attention has been paid to the study of soil erosion from saturated soil slopes. However, great differences in hydrology, soil detachment and sediment transportation exist between saturated and non‐saturated soils (Huang et al, 2018; Huang, Li, Wang, and Li 2020; Huang, Li, Liu, Li, & Gao, 2020). Some situations can result in soil slope saturation, which causes serious soil erosion because of changes in soil erodibility and hydrodynamics of overland water flow.…”