The Experts below are selected from a list of 195915 Experts worldwide ranked by ideXlab platform
Dieter Rickenmann - One of the best experts on this subject based on the ideXlab platform.
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a one dimensional bedload transport model for steep slopes
Journal of Hydraulic Research, 2010Co-Authors: Michael Chiari, Kurt Friedl, Dieter RickenmannAbstract:A sediment routing model called SETRAC has been developed to simulate bedload transport in torrents and mountain streams. SETRAC is the acronym for Sediment Transport in Alpine Catchments. Flow Resistance is modelled using an approach proposed by Smart and Jaggi, and bedload transport is predicted with an equation by Rickenmann. Form roughness losses are accounted for by an empirical approach which is based on flow Resistance observations in mountain streams. It is possible to compute fractional bedload transport taking grain sorting effects into account. Flow hydrographs are routed through the channel network by using the kinematic wave approach. An application of the model is discussed for an extreme flood event of August 2005 in the Chiene catchment, Switzerland, which mobilized 120,000 m3 of bedload along the mountain stream. The simulation results underline the importance of Form Resistance when modelling bedload transport in steep and rough channels.
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the impact of exceptional events on erosion bedload transport and channel stability in a step pool channel
Earth Surface Processes and Landforms, 2009Co-Authors: Jens M Turowski, Dieter Rickenmann, Elowyn M Yager, Alexandre Badoux, Peter MolnarAbstract:Sediment transport in the Erlenbach, a small stream with step-pool morphology in the canton of Schwyz, Switzerland, has been monitored for more than 20 years. During this time three exceptional events (events with high sediment yield and long return times that have a large effect on channel morphology) have impacted the stream and partly or completely rearranged the existing step-pool morphology. In the aftermath of the events, sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer. For the last event, dated on the 20 June 2007, observations of boulder mobility and step destruction were used to interpret channel stability. Boulders with median diameters of up to 135 cm and estimated weights of more than 2·5 tons have moved during the 2007 event. Using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions, even if Form Resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account. For two of the events, estimated peak shear stresses at the bed exceeded 1000 Pa, calculated both from observations of the flow hydraulics and from boulder mobility. This suggests that highly energetic flows occur relatively frequently in small, steep streams and that large boulders can be transported by fluvial processes in such streams. The observations have potential significance for hazard risk mitigation, stream engineering and restoration. Copyright © 2009 John Wiley & Sons, Ltd.
Ellen Wohl - One of the best experts on this subject based on the ideXlab platform.
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large woody debris and flow Resistance in step pool channels cascade range washington
Geomorphology, 2003Co-Authors: Janet H Curran, Ellen WohlAbstract:Abstract Total flow Resistance, measured as Darcy–Weisbach f, in 20 step-pool channels with large woody debris (LWD) in Washington, ranged from 5 to 380 during summer low flows. Step risers in the study streams consist of either (1) large and relatively immobile woody debris, bedrock, or roots that Form fixed, or “forced,” steps, or (2) smaller and relatively mobile wood or clasts, or a mixture of both, arranged across the channel by the stream. Flow Resistance in step-pool channels may be partitioned into grain, Form, and spill Resistance. Grain Resistance is calculated as a function of particle size, and Form Resistance is calculated as large woody debris drag. Combined, grain and Form Resistance account for less than 10% of the total flow Resistance. We initially assumed that the substantial remaining portion is spill Resistance attributable to steps. However, measured step characteristics could not explain between-reach variations in flow Resistance. This suggests that other factors may be significant; the coefficient of variation of the hydraulic radius explained 43% of the variation in friction factors between streams, for example. Large woody debris generates Form Resistance on step treads and spill Resistance at step risers. Because the Form Resistance of step-pool channels is relatively minor compared to spill Resistance and because wood in steps accentuates spill Resistance by increasing step height, we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel. Hence, the distribution and function, not just abundance, of large woody debris is critical in steep, step-pool channels.
Peter Molnar - One of the best experts on this subject based on the ideXlab platform.
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the impact of exceptional events on erosion bedload transport and channel stability in a step pool channel
Earth Surface Processes and Landforms, 2009Co-Authors: Jens M Turowski, Dieter Rickenmann, Elowyn M Yager, Alexandre Badoux, Peter MolnarAbstract:Sediment transport in the Erlenbach, a small stream with step-pool morphology in the canton of Schwyz, Switzerland, has been monitored for more than 20 years. During this time three exceptional events (events with high sediment yield and long return times that have a large effect on channel morphology) have impacted the stream and partly or completely rearranged the existing step-pool morphology. In the aftermath of the events, sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer. For the last event, dated on the 20 June 2007, observations of boulder mobility and step destruction were used to interpret channel stability. Boulders with median diameters of up to 135 cm and estimated weights of more than 2·5 tons have moved during the 2007 event. Using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions, even if Form Resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account. For two of the events, estimated peak shear stresses at the bed exceeded 1000 Pa, calculated both from observations of the flow hydraulics and from boulder mobility. This suggests that highly energetic flows occur relatively frequently in small, steep streams and that large boulders can be transported by fluvial processes in such streams. The observations have potential significance for hazard risk mitigation, stream engineering and restoration. Copyright © 2009 John Wiley & Sons, Ltd.
Peter M Atkinson - One of the best experts on this subject based on the ideXlab platform.
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criticality in the planForm behavior of the ganges river meanders
Geology, 2016Co-Authors: Paul A Carling, Niladri Gupta, Peter M AtkinsonAbstract:The critical point of planForm transition from straight to meandering in the wandering Ganges River is identifiable. Recent remote-sensing data indicate that four similar meanders cut off, or attempted to cut off, after ∼31–35 yr, primarily due to channel aggradation. As main channels aggrade, sinuosity is maximized for broad channel widths and small radii of curvature and relaxes for bends of greater radii. Maximized Form Resistance occurs close to self-organized criticality and promotes cutoffs. Avulsions lead to main channel narrowing and prevent further bend tightening, relaxing the system by reducing sinuosity. Thus, the wandering river oscillates in space and time across the transition from a more ordered to a more chaotic state. PlanForm behavior is described by the Jerolmack-Mohrig mobility number and the Parker stability criterion, which well define meanders behavior as they approach criticality and then relax via partial or completed avulsions. The results have significance for river engineering and river network and stratigraphic modeling. Such an approach could be of practical value when predicting the behaviors of other major wandering rivers.
Janet H Curran - One of the best experts on this subject based on the ideXlab platform.
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large woody debris and flow Resistance in step pool channels cascade range washington
Geomorphology, 2003Co-Authors: Janet H Curran, Ellen WohlAbstract:Abstract Total flow Resistance, measured as Darcy–Weisbach f, in 20 step-pool channels with large woody debris (LWD) in Washington, ranged from 5 to 380 during summer low flows. Step risers in the study streams consist of either (1) large and relatively immobile woody debris, bedrock, or roots that Form fixed, or “forced,” steps, or (2) smaller and relatively mobile wood or clasts, or a mixture of both, arranged across the channel by the stream. Flow Resistance in step-pool channels may be partitioned into grain, Form, and spill Resistance. Grain Resistance is calculated as a function of particle size, and Form Resistance is calculated as large woody debris drag. Combined, grain and Form Resistance account for less than 10% of the total flow Resistance. We initially assumed that the substantial remaining portion is spill Resistance attributable to steps. However, measured step characteristics could not explain between-reach variations in flow Resistance. This suggests that other factors may be significant; the coefficient of variation of the hydraulic radius explained 43% of the variation in friction factors between streams, for example. Large woody debris generates Form Resistance on step treads and spill Resistance at step risers. Because the Form Resistance of step-pool channels is relatively minor compared to spill Resistance and because wood in steps accentuates spill Resistance by increasing step height, we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel. Hence, the distribution and function, not just abundance, of large woody debris is critical in steep, step-pool channels.