Soil detachment by overland flow on steep cropland in the subtropical region of China

Abstract

Accurate prediction of soil detachment capacity is fundamental to establish processbased erosion models and improve soil loss assessment. Few studies were conducted to reveal the mechanism of detachment process for yellow soil on steep cropland in the subtropical region of China using field experiments. This study was performed to determine soil detachment characteristics and explore the relationships between soil detachment capacity (D c ) and flow rate, slope gradient, mean velocity, shear stress, stream power and unit stream power. Field experiments were conducted on intact soil with flow rates ranging from 0.2 × 10 −3 to 0.5 × 10 −3 m −3 s −1 and slope gradients varying from 8.8 to 42.4%. The results showed the following. (a) D c of yellow soil was smaller than other soils because of its high clay content. (b) D c was more susceptible to flow than to slope gradient. Power functions were derived to depict the relationship between D c and the flow rate and slope gradient (R 2 = 0.91). (c) D c was better simulated by power functions of the stream power (R 2 = 0.83) than functions of the shear stress or the unit stream power. (d) Considering its accuracy, simplicity and accessibility, the power function based on flow rate and slope gradient is recommended to predict D c of yellow soil in the field. The results of this study provide useful support for revealing soil detachment mechanism and developing processbased soil erosion models for the subtropical region of China. K E Y W O R D S detachment capacity, erosion prediction, hydraulic parameters, karst regions, soil erosion, steep slopes Over the past several decades, two main experimental procedures, filed plot experiment and laboratory flume experiment, were generally used to determine soil detachment rate or capacity (Knapen, Poesen, Govers, Gyssels, & Nachtergaele, 2007). Laboratory flume experiments were widely used to understand fundamental erosion processes. Small sample area and flexible setups allow laboratory tests easy to control and replicate. Numerous results from laboratory flume experiments have been reported to relate the D r or D c to hydraulic parameters, such as the flow regime, flow rate, slope gradient, flow depth, velocity, shear stress, stream power and unit stream power, under different conditions. Lyle and Smerdon (1965) conducted flume experiments and indicated a linear relationship between soil erosion and shear stress for Texas soils, but the conclusion was obtained from a constant gentle slope (0.2%). Subsequently, Nearing et al. (1991) used a hydraulic flume to study the process of soil detachment. The results showed a logarithmic relationship between detachment capacity and flow depth, slope gradient, and mean weight diameter of the aggregates. The results also indicated that soil detachment was greatly influenced by flow depth while weakly affected by slope. Nearing's experiments were well-conducted, but the test slopes were very low, ranging only from 0.5 to 2.0%. Due to the fact that much of the cultivated farmland in China lies ...

The vertical heterogeneity of soil detachment by overland flow on the water‐level fluctuation zone slope in the Three Gorges Reservoir, China

“…The slope gradient and flow rate strongly affect D c . In particular, increases in the slope gradient and flow rate generally increase D c (Li, Xiao, et al, 2019;Ma et al, 2020;Xiao et al, 2017). Accordingly, the power function of either the slope gradient or the flow rate has been shown to be feasible for forecasting D c (Nearing et al, 1991;Zhang et al, 2002;Zhu et al, 2020).…”

“…Shear stress is the most common hydraulic parameter for estimating D c and has been adopted in the Water Erosion Prediction Project (WEPP) (Nearing et al, 1989). As an alternative, stream power has performed better than other parameters in many simulation studies of D c (Ma et al, 2020;Zhang et al, 2002;Zhu et al, 2020) and is used as the hydraulic parameter for estimating D c in the Griffith University Erosion System Template (GUEST) (Misra & Rose, 1996). In contrast, unit stream power has been regarded as the most appropriate parameter to describe D c in some studies (Nazari et al, 2016;Yang et al, 2018) and is used to calculate D c in the European Soil Erosion Model (EUROSEM).…”

Spatiotemporal changes in flow hydraulic characteristics and soil loss during gully headcut erosion under controlled conditions

“…Land use change is recognized as having the strongest effect on processes related to gully erosion (Poesen et al, 2003;Chaplot et al, 2005;Descroix et al, 2008), and it also significantly affects the activation of gully headcut erosion (e.g., Torri and Poesen, 2014). In this aspect, the vegetation coverage is a parameter that is often used to clarify its effect on gully erosion (e.g., De Baets et al, 2007;Martínez-Casasnovas et al, 2009); however, in fact, the vegetation effect mainly depends on the root characteristics and its distribution at gully head (e.g., Vannoppen et al, 2015;Guo et al, 2019). Nevertheless, at present, most studies on gully erosion focus on the changes in gully morphology between different periods at a watershed or regional scale (Vanmaercke et al, 2016), which is why the previous studies fail to address the effects of root systems on gully headcut retreat.…”