Evaluation of Flow Resistance in Alluvial Streams with Ripples in Various Hydraulic Conditions

Document Type : Research Paper

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Abstract

Sediment transport and bedforms in alluvial streams, significantly affect the flow resistance. In the present research to discuss the effect of ripple bedform on the flow shear stress, a series of experiments were done and the influences of ripples on flow roughness coefficient were investigated. These experiments were carried out in a laboratory flume with changing discharge, slope and flow depth alternatively to create different hydraulic conditions. In flow surfaces having bedforms, shear stress includes two parts. The first part is the , which is imposed on each particle of the sediment and the second part is the , which is the stress created by bedforms. The results showed that the shear stress and roughness coefficient increased with formation of bedforms. Also, with intensifying the flow parameters the turbulences were grown in the downstream of the bedform crest and the studied factors increased accordingly. In a certain limit of discharge (10 to 14 lit/s) and slope (0 to 0.015), results showed that with increasing flow velocity, the height of ripple increased and the number of them increased too. The most variation area was at the last 70 cm length from the end of the channel. With ripple height increasing, sediment transportation was increased more and there was a 40 percent growth of dimensionless sediment discharge, when the  (bedfrom height to the length) increased about 35 percent. Studying the shear stress caused by bedform in relation with bedform height, it was obvious when the ripple height increased about 45 percent, the bedform shear stress increased about 58 percent.

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References

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Water and Soil Science
Volume 26, 3-2
December 2016
Pages 63-73

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