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

Abstract

Ephemeral gullies (EGs) play a crucial role in hydrological connectivity, soil erosion, and land degradation. However, little research has focused on flow hydraulics in concentrated flow channels and their effects on EG erosion on steep loessial slopes. A simulated experiment of rainfall (60-120 mm hr À1 ) and upslope inflow (0.45-2.25 m 2 hr À1 ) were conducted on concentrated flow channels with loess at 15 -25 slope gradients. The concentrated flow was turbulent and subcritical in most cases.The flow shear stress, stream power, and unit stream power in the concentrated flow channels varied from 32.65 to 109.40 N m À2 , 10.85 to 38.66 N m À1 s À1 , and 0.08 to 0.16 m s À1 , respectively. The EG depth, width, and width-depth ratio varied within 14.8-24.6 cm, 18.5-33.8 cm, and 1.13-1.83, respectively. Moreover, the EG depth and width increased in a power function with the runoff rate (R 2 = 0.82-0.83; p < 0.01). The sediment yield rate (Ys) varied within 15.94-94.44 g m À2 s À1 under the different treatments and had a good linear relationship with the runoff rate (R 2 = 0.78; p < 0.01). Furthermore, the flow shear stress and stream power can be used to predict Ys by linear functions. The critical runoff rate and shear stress to initiate EG erosion were determined to be 0.09 m 3 hr À1 and 2.66 N m À2 . However, the coefficient of determination for the linear relationship between Ys and shear stress was low (0.58). The results indicate that the flow shear stress mechanism might not be enough to explain sediment load variation for EG erosion, and headcut erosion mechanism should be taken into account.

Gully erosion on alluvial fans can be mitigated by altering the hydrological connectivity between an alluvial fan and the contributing catchment: a study in the Lhasa River basin

“…Therefore, more attention should be paid to bank erosion of gullies on AF in the Lhasa River basin than in other regions. Kang, Guo, & Wang (2021) concluded that toe scour freed the hanging soil material on the sidewall, which accelerated gully bank collapse. Chaplot (2013) proposed that lateral seepage may be the main factor for bank expansion.…”

“…All these researches verified the off‐site effect of the hydrological connectivity in catchment on gully erosion. Meanwhile, several works evidence that gullies also provide access to runoff, improve hydrological connectivity, and accelerate runoff generation in catchment (Bracken & Croke, 2007; Kang, Guo, & Wang, 2021; Molina et al, 2009; Monsieurs et al, 2015). For example, Croke et al (2005) found that the maximum distance of runoff transport in the gullies was 2–3‐times longer than that in the dispersive pathways.…”

“…Gully erosion aggravates the loss of soil and water, reduces soil quality and grain yield (Xu et al, 2016), even leads to the fragmentation and abandonment of farming, and limits economic development (Frankl et al, 2016). In addition, the development of gullies can increase catchment hydrological connectivity, shorten confluence time, and increase flow peak and runoff (Costa & Bacellar, 2007; Kang, Guo, & Wang, 2021; Poesen, 2018; Poesen et al, 2003), thus increasing off‐site risks such as downstream flood and reservoir sedimentation (Pulley et al, 2018; Vanmaercke et al, 2021). In order to select relevant measures for gully erosion prevention and control, it is very important to identify the key influencing factors and reveal the mechanisms (Frankl et al, 2021; Vanmaercke et al, 2021).…”

Monitoring soil erosion on field slopes by terrestrial laser scanning and structure‐from‐motion

“…Runoff scouring experiments have been widely employed to study slope erosion processes (Kang et al, 2021; Sun et al, 2022). During the experiments, water is released into a slope to reproduce the initiation and development of erosion processes (Bai et al, 2021).…”

Morphodynamics of Gully Development on the Platform–Slope System of Spoil Dumps under Platform Concentrated Flow

“…Gully length development has been systematically studied in terms of its correlation with average daily rainfall, flow discharge, and catchment area [15][16][17]. Gully depth and width increase with flow discharge [18]. A dynamic model of gully erosion, established by Sidorchuk et al, is used to predict the development of gully depth and width, and involves longitudinal profile, flow velocity, water shear stress, and coefficient of flow resistance [6].…”