When does bedload transport begin in steep boulder‐bed streams?

When does bedload transport begin in steep boulder‐bed streams? The paper presents the results of field measurements of critical conditions for bedload motion conducted in the Rio Cordon, a steep boulder‐bed stream in the Italian Alps, under conditions of high Reynolds numbers and low relative submergence poorly explored before. Two methods have been used to determine threshold of motion: the displacement of marked clasts and the flow competence approach, which uses the largest grain size diameter transported by each flood event. The high values of $\tau_{\rm {c}i}^{*}$ confirm the great relevance of non‐bedload effective shear stresses in step–pool streams given by the additional form drag associated with this morphology. Relative submergence effects on the dimensionless critical shear stress $\tau_{\rm {c}i}^{*}$ have been quantified by considering the relative submergence ratio Rh/D84, and the major effect of relative size on the mobility of each particle in steep, widely graded bed mixtures has been evaluated. Finally, the dimensionless critical unit discharge $q_{\rm {c}i}^{*}$ has also been adopted in the regression equations as the critical hydraulic parameter, because it may represent an easier parameter to use than the critical shear stress for steep, rough mountain rivers. Copyright © 2006 John Wiley & Sons, Ltd. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Hydrological Processes Wiley

When does bedload transport begin in steep boulder‐bed streams?

Hydrological Processes, Volume 20 (16) – Oct 30, 2006
17 pages

Publisher
Wiley
ISSN
0885-6087
eISSN
1099-1085
DOI
10.1002/hyp.6168
Publisher site
See Article on Publisher Site

Abstract

The paper presents the results of field measurements of critical conditions for bedload motion conducted in the Rio Cordon, a steep boulder‐bed stream in the Italian Alps, under conditions of high Reynolds numbers and low relative submergence poorly explored before. Two methods have been used to determine threshold of motion: the displacement of marked clasts and the flow competence approach, which uses the largest grain size diameter transported by each flood event. The high values of $\tau_{\rm {c}i}^{*}$ confirm the great relevance of non‐bedload effective shear stresses in step–pool streams given by the additional form drag associated with this morphology. Relative submergence effects on the dimensionless critical shear stress $\tau_{\rm {c}i}^{*}$ have been quantified by considering the relative submergence ratio Rh/D84, and the major effect of relative size on the mobility of each particle in steep, widely graded bed mixtures has been evaluated. Finally, the dimensionless critical unit discharge $q_{\rm {c}i}^{*}$ has also been adopted in the regression equations as the critical hydraulic parameter, because it may represent an easier parameter to use than the critical shear stress for steep, rough mountain rivers. Copyright © 2006 John Wiley & Sons, Ltd.

Journal

Hydrological ProcessesWiley

Published: Oct 30, 2006

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