Abstract
The effect of vegetation density on overland flow dynamics has been extensively studied, yet fewer investigations have focused on vegetation arrangements with different densities and position features. Flume experiments were conducted to investigate the hydrodynamics of flow through rigid emergent vegetation arranged in combinations with three densities (Dense, Middle, and Sparse) and three positions (summit, backslope, and footslope). This study focused on how spatial variations regulated hydrodynamic parameters from two dimensions: direction along the slope and water depth. The total hydrodynamic parameters of bare slopes were significantly different from those of vegetated slopes. The relationship between Re and f illustrated that Re was not a unique predictor of hydraulic roughness on vegetated slopes. In the slope direction, all hydrodynamic parameters on vegetated slopes exhibited fluctuating downward/upward trends due to the clocking effect before the vegetated area and the rapid conveyance effect in the vegetated area, whereas constant values were observed on bare slopes. The performance of hydrodynamics parameters suggested that the dense rearward arrangement (SMD) was the optimal vegetation pattern to regulate flow conditions. Specifically, the vertical profiles of the velocity and turbulence features of the SMD arrangement at different sections demonstrated the significant role of vegetation density in identifying the velocity layers along the water depth. The maximum velocity and Reynolds Stress Number (RSN) indicated the position where local scour was most likely to occur, which would improve our basic understanding of the mechanisms underlying hydraulic and soil erosion processes.
Highlights
Indicated the position where local scour was most likely to occur, which would improve our basic understanding of the mechanisms underlying hydraulic and soil erosion processes
Overland flow passing through vegetation on hillslopes has been extensively studied, both experimentally and numerically, due to its remarkable roles in the transportation of nutrients, contaminants, and sediment loads [1,2,3]; this factor is widely used in soil erosion control and stream ecological restoration [4]
To understand the mechanisms underlying the hydraulic and soil erosion processes on vegetated hillslopes, hydrodynamic characteristics, which were mainly quantified by hydraulic parameters, e.g., water depth, mean velocity, flow pattern and resistance, kinetic energy and momentum distributions were considered as fundamental variables [6,7]
Summary
Overland flow passing through vegetation on hillslopes has been extensively studied, both experimentally and numerically, due to its remarkable roles in the transportation of nutrients, contaminants, and sediment loads [1,2,3]; this factor is widely used in soil erosion control and stream ecological restoration [4]. In terms of altering flow hydrodynamic characteristics, such as by increasing local roughness, modifying flow pattern, providing additional resistance and decreasing bed shear stress, etc. The existence of such rigid and emergent (usually discontinued and uneven planted) vegetation alters the velocity distribution and flow dynamics. Determining the optimum conditions for flow within vegetated slopes is vital for water and soil conservation and control. To understand the mechanisms underlying the hydraulic and soil erosion processes on vegetated hillslopes, hydrodynamic characteristics, which were mainly quantified by hydraulic parameters, e.g., water depth, mean velocity, flow pattern and resistance, kinetic energy and momentum distributions were considered as fundamental variables [6,7]. Dunkerley et al [16] pointed out that plants could stabilize the flow state as laminar flow, whereas Hamilton et al [17] stated that mixed flow states occurred on vegetated slopes
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