Effects of different tillage practices on the hydraulic resistance of concentrated flow on the Loess Plateau in China.

• Roughness tends to decrease on the tilled surface, which increasing the velocity. • Friction factors' evolving over time varies from one tillage practice to another. • Friction factors in MD and CD conditions increase with slope. • f-Re relation shows a power function influenced by time and tillage practice type. • f-Fr relation shows a power function with slope parameter included. Numerous fixed or movable flume experiments have been conducted to characterize the hydraulic resistance of concentrated flow on natural and tilled surfaces. However, few studies have elucidated how the friction factor of flow resistance evolves over time on tilled surfaces. Since hydraulic resistance and concentrated flow interact with each other, it is critical to explore the underlying principles controlling their equilibrium under tillage practices. The objective of this paper is to study how during erosion, roughness and the relationship between the hydraulic characteristics and friction factor changed under different soil surface condition and tillage practices. We performed a series of flume experiments on rough soil surfaces under three treatments (manual dibbling, manual hoeing, and contour drilling). We then analyzed the changes in the Darcy-Weisbach friction factor based on surface roughness, hydraulic characteristics (slope gradient and unit discharge), Reynolds number, and Froude number. The results show that the temporal changes in surface roughness are associated with the tillage practices applied, and initial roughness cannot predict the surface responses adequately. Time plays a key role in the relationship between friction factor and hydraulic characteristics; therefore, different tilled surfaces exhibit inconsistent initial roughness values in addition to their varying evolution trends over time. There is a power function relationship between Reynolds number and friction factor, so that the effects of roughness and time should not be disregarded. The friction faction–Froude number relationship can also be expressed as a power function. However, the friction factor varies from one tillage practice to another and time remains a key factor in an erosion event. In addition, the Froude number is close to 1 in all cases, which may be an underlying principle controlling the dynamic equilibrium between flow hydraulics and surface roughness under tillage practices. [ABSTRACT FROM AUTHOR]