Abstract Accurate measurements of the overland flow velocity along the flow depth are critical to understanding hydraulic and soil erosion processes on hillslopes; however, this topic has not been investigated in detail to date. This study used a high-resolution particle image velocimetry method to capture the flow fields of overland flow on a fixed smooth bed. Experiments were conducted under eight shallow flow conditions at flow depths ranging from 0.49 to 1.1 ×10-2 m. A fully developed open-channel flow condition was the control group. The Reynolds stress values indicated the presence of two regions, namely the inner and outer regions. The inner region was affected by viscous stress and Reynolds stress, whereas the outer region was affected only by Reynolds stress. The boundary between the two regions was variable, whereas the open-channel flow had a fixed boundary. Three subregions were observed in the inner region, and two sublayers were detected in the outer region. The free surface was primarily affected by surface tension, which weakened as the flow depth H and the Weber number We increased. At We > 6, the surface tension effect was buffered, and no free surface region was observed in the velocity profile. Our results indicated that the division of the velocity region for overland flow differed from that of the open-channel flow, and the expressions of the subregions were also different in terms of the empirical constant A and integration constant C. Overland flow occurred when the dimensionless flow depth ( H + = H u ∗ / ν ) was less than 550. This study provides an approach to improve the measurement accuracy and theoretical understanding of overland flow processes and hydrodynamic mechanisms on hillslopes.

中文翻译：

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使用高分辨率粒子图像测速系统测量的地表流速

摘要 沿水流深度准确测量地表流速对于理解山坡上的水力和土壤侵蚀过程至关重要。然而，迄今为止，尚未对该主题进行详细调查。本研究使用高分辨率粒子图像测速方法来捕捉固定光滑床上的地表流流场。实验在八种浅流条件下进行，流深范围为 0.49 至 1.1 ×10-2 m。完全发展的明渠流动条件是对照组。雷诺应力值表明存在两个区域，即内部区域和外部区域。内部区域受粘性应力和雷诺应力的影响，而外部区域仅受雷诺应力的影响。两个区域之间的界限是可变的，而明渠流有一个固定的边界。在内部区域中观察到三个子区域，在外部区域中检测到两个子层。自由表面主要受表面张力的影响，随着流动深度 H 和韦伯数 We 的增加而减弱。在 We > 6 时，表面张力效应得到缓冲，在速度剖面中没有观察到自由表面区域。我们的结果表明，地表流速度区域的划分与明渠流的速度区域划分不同，并且子区域在经验常数 A 和积分常数 C 方面的表达式也不同。流深 ( H + = H u ∗ / ν ) 小于 550。