Shallow water flows over rough natural hillslopes contribute to interrill erosion and floods. The friction factor, that describes the hydraulic resistance, is particularly important for modeling soil erosion and transport processes. The present review focuses on the Darcy-Weisbach friction factor f for both large and small-scale roughness conditions and addresses the effects of rainfall intensity, vegetation cover, and sediment transport on overland flow resistance. All the studies on rainfall effect agree regarding the increase of the friction factor with rainfall intensity for the laminar flow regime and their independence for flows characterized by Reynolds number higher than a threshold varying between 800 and 2000. The analysis of the literature allows for concluding that f always increases with vegetation cover. Moreover, f (or its component due to sediment transport) increases with sediment concentration, slope, and Reynolds number, while it decreases with increasing values of Froude number and dimensionless sediment diameter. Finally, the focus areas for future research are highlighted.

中文翻译：

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陆上流动阻力：综述


崎岖不平的天然山坡上的浅水流会导致 Interrill 侵蚀和洪水。描述水力阻力的摩擦系数对于模拟土壤侵蚀和传输过程尤为重要。本综述侧重于大尺度和小尺度粗糙度条件下的 Darcy-Weisbach 摩擦系数 f，并讨论了降雨强度、植被覆盖和沉积物输送对陆上流动阻力的影响。所有关于降雨效应的研究都同意层流状态中摩擦因子随降雨强度的增加，以及它们对雷诺数高于 800 到 2000 之间变化的阈值的流动的独立性。对文献的分析可以得出结论，f 总是随着植被覆盖率的增加而增加。此外，f （或其由于沉积物迁移引起的成分） 随着沉积物浓度、斜率和雷诺数的增加而增加，而 f （或其成分） 随着 Froude 数和无量纲沉积物直径值的增加而减小。最后，强调了未来研究的重点领域。