Ephemeral gully (EG) erosion represents the early stage of large-scale gully (locally named as “Benggang”) development on Ultisols in the granite hilly area. However, the EG erosion process and the mechanism underlying sediment production have not been fully elucidated. In this study, a series of field scouring experiments were conducted under different flow discharge levels (10, 15, 20, 25, and 30 L·min), and the primary EGs in three typical soil layers with different weathering degrees (red soil layer (RL), transition layer (TL), and sandy layer (SL)) was dynamically monitored. The results indicated that the ratio of width to depth of the EGs rapidly decreased as the flow discharge increased. At 30 L·min, the average sediment yield and transport rate (Sr) of the SL were 4.85 and 5.39 times, greater than those of the RL, respectively. The sediment particles were concentrated within the 1–2 mm particle size range, accounting for over 35 %. In addition, the mean weight diameter of the sediment particles in the RL was the largest. The sediment distribution characteristics did not respond to flow changes but were affected by EG morphological changes. With increasing flow discharge, the flow shear stress and stream power increased. Further analysis revealed that the coupling effect of flow hydraulic characteristics and EG morphological evolution drove the EG erosion sediment production process, and the Sr of the SL was highly sensitive to flow discharge changes. The soil disintegration rate was an internal factor that directly affected soil loss in the EGs, with a path coefficient of 0.71. The bulk density, organic matter content, and sand content were all indirect influencing factors. The RL exhibited greater anti-erodibility than the other layers and could serve as an effective protective layerfor granite hilly areas. These findings provide a theoretical basis for improving soil loss management systems.

中文翻译：

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花岗岩丘陵区短暂沟蚀产沙过程及水力特征

短暂沟壑（EG）侵蚀代表花岗岩丘陵区腐土上大规模沟壑（当地称为“崩岗”）发育的早期阶段。然而，EG侵蚀过程和沉积物产生的机制尚未完全阐明。本研究通过不同流量水平（10、15、20、25和30 L·min）进行了一系列田间冲刷实验，对不同风化程度的3个典型土层（红土层）进行了原生EG的测定。动态监测层（RL）、过渡层（TL）和沙层（SL）。结果表明，随着流量的增加，EG的宽深比迅速减小。在30 L·min时，SL的平均产沙量和输运速率（Sr）分别是RL的4.85和5.39倍。沉积物颗粒集中在1~2 mm粒径范围内，占35%以上。此外，RL中沉积物颗粒的平均重量直径最大。沉积物分布特征对流量变化不产生响应，但受EG形态变化的影响。随着流量的增加，水流剪切应力和水流功率增加。进一步分析发现，水流水力特征与EG形态演化的耦合作用驱动了EG侵蚀沉积物的生成过程，并且SL的Sr对流量变化高度敏感。土壤崩解速率是直接影响EGs土壤流失的内部因素，其通径系数为0.71。容重、有机质含量、含砂量均为间接影响因素。 RL比其他层表现出更强的抗侵蚀性，可以作为花岗岩丘陵地区的有效保护层。这些发现为改进水土流失管理系统提供了理论基础。