The impact of flow discharge on the hydraulic characteristics of headcut erosion processes in the gully region of the Loess Plateau

Abstract

Headcut erosion is associated with major hydraulic changes induced by the gully head of concentrated flow. However, the variation in the hydraulic characteristics of the headcut erosion process is still not clear in the gully region of the Loess Plateau.A series of rainfall combined scouring experiments (flow discharges ranging from 3.6 to 7.2 m 3 hr −1 , with 0.8 mm min −1 rainfall intensity) were conducted on experimental plots to clarify the variation in the hydraulic parameters induced by gully head and erosion processes under different flow discharges. The results showed that concentrated flows in the catchment area and gully bed were turbulent (Reynolds number ranging from 1,876 to 6,693) and transformed between supercritical and subcritical (Froude number ranging from 0.96 to 3.73). The hydraulic parameters, such as the flow velocity, Reynolds number, shear stress, stream power, Darcy-Weisbach friction factor, and unit stream power in the catchment area were 0.45-0.59 m s −1 , 2086-6693, 1.96-5.33 Pa, 0.89-2.86 W m −2 , 0.08-0.16, and 0.023-0.031 m s −1 ,respectively. When the concentrated flows dropped from the gully head, the hydraulic parameters in the gully bed decreased by 3., respectively, which contributed to the flow energy consumption at the gully head. As flow discharge increased, Reynolds number, shear stress, and stream power increased, while flow velocity, Froude number, unit stream power, and Darcy-Weisbach friction factor did not. The flow energy consumption at the gully head was 9. 66-10.13, 13.25-13.74, 15.68-16.41, and 19.28-20.25 J s −1 , respectively, under different flow discharges and accounted for 60.58-68.50% of the flow energy consumption of the experimental plots. Generally, the sediment discharges increased rapidly at the initial stage, then increased slowly, and finally reached a steady state condition, which showed a significant declining logarithmic trend with experimental duration (P<.01) and increased with increasing flow discharge. Accordingly, the flow energy consumption was significantly correlated with the sediment yield. These findings could improve our understanding of the hydraulic properties and flow energy characteristics of headcut erosion.

Predicting the sediment transport capacity from flow condition and particle size in the presence of vegetation cover

“…Thus, hydraulic variables alone are able to predict the sediment transport capacity without considering the vegetation stem cover as an independent variable. The results were similar to those of Govers (1992) and Shi et al (2020) who had shown that a hydraulic variable such as unit stream power which accounts for the effect of bed roughness can alone be used to determine the transport capacity. Abrahams et al (1998) also argued that flow depth in combination with the excess stream power could capture the impact of surface roughness on the sediment transport capacity.…”

“…One possible reason for this is that the effect of the roughness due to vegetation stem on the sediment transport capacity cannot be completely explained by the sheer stress, and the rate of sediment transport is mainly controlled by the grain shear stress (Carson, 1987; Einstein, 1950; Meyer‐Peter & Müller, 1948; Singhal, Mohan, & Agrawal, 1980). Yang et al (2017) and Shi et al (2020) also found that the shear stress is not closely related to the surface roughness, because the linear relationship between the mean shear stress and Darcy–Weisbach friction factor is weak based on their experiment results. However, as flow depth was measured under the clear flow condition in this study, the calculated shear stress based on the depth measurement may not represent the shear stress acting on the sediment particles.…”

Variations in Soil Erosion Resistance of Gully Head Along a 25-Year Revegetation Age on the Loess Plateau

“…Notably, in the gully region of the Loess Plateau, about 63% of total runoff is generated from the loess tableland with a gentle slope of 1-5 • , which can initiate gully headcut erosion and contribute 86.3% of total sediment [32]. The gully headcut erosion by concentrated flow became the main sediment resource.…”

Ephemeral gully erosion in concentrated flow channels induced by rainfall and upslope inflow on steep loessial slopes

“…Among those flow types, the headcut flow dominated due to the predominant headcut erosion during EG formation in our study. Headcut flows refer to hydraulic drops, vortices, and jumps (Figure 10), which have a negative effect on slope runoff velocity (Shi et al, 2020). Headcuts and scour holes formed and developed much better along the concentrated flow channel under higher S, I, and Q due to the higher flow stress and power (Table 3, shear stress, stream power, and unit stream power increased when S, I, and Q were increased) (He et al, 2013;Xu, Zheng, Qin, & Han, 2019).…”