Effect of vegetative bed on flow structure through a pool-riffle morphology |
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Affiliation: | 1. Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, 16765/1719, Iran;2. Department of Water Engineering, College of Agriculture, Isfahan University of Technology, Isfahan, 84156-83111, Iran |
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Abstract: | Natural habitats are created and developed through pool-riffle sequences in rivers, while vegetation cover could play a critical role in the sediment transfer and its quantity and quality. In this study, the effect of vegetation cover on the flow structure in a pool-riffle sequence is investigated in a laboratory flume under bed formation to compare with non-vegetated cover. In this context, instantaneous point velocities were measured by ADV to determine averaged velocity, shear velocity, root mean square velocity, friction factor, Reynolds shear stress and turbulence intensities. Results showed that the vegetation cover increases the thickness of the wall law. Meanwhile, the length of the flow separation zone in the vegetated bedform is more than in the non-vegetated bedform. Variation in roughness coefficients may cause a new boundary layer in which local flow velocities decrease. In both cases (vegetated and non-vegetated bedforms), the momentum is mostly transferred by ejection and sweep phenomena between flow and bedform. |
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Keywords: | Pool-riffle Vegetation cover Spatially average method Turbulence intensities Quadrant analysis Reynolds shear stress distribution |
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