Influence of Bed‐Load Transport on Flow Resistance of Step‐Pool Channels

Hohermuth, Benjamin; Weitbrecht, Volker

doi:10.1029/2017wr021523

Cited by 25 publications

(27 citation statements)

References 52 publications

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“…Step-pool stability is reported to be closely related to discharge magnitude, sediment transport and local scour (Comiti et al, 2009;Zimmermann, 2009;Curran, 2012;Waters and Curran, 2012;Zhang et al, 2016Zhang et al, , 2018Hohermuth and Weitbrecht, 2018) and all of these influencing factors are intensified during the rising limb. Therefore, the rising limb was focused on in our experiment.…”

Section: Hydrograph Designmentioning

confidence: 99%

“…> 0.5) indicates that most of the potential energy at the step entrance is dissipated and thus, the flow velocity increase is largely limited and even negative sometimes. If the kinetic energy of the flow is well controlled, the capability of the flow to mobilize and transport grains will be limited (Hohermuth and Weitbrecht, 2018). Therefore, the energy dissipation ratio is related to bed stability and is a crucial parameter for effective riverbed consolidation by stabilization structures like step-pools (Wang et al, 2012).…”

Section: Energy Dissipationmentioning

confidence: 99%

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Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

Chendi

Hassan

et al. 2019

Earth Surf Processes Landf

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Exceptional flood events with a return period of about 50 years can be destructive to step‐pool channel segments. However, field investigations and flume experiments have not examined the hydraulic and morphological feedbacks of step‐pool morphology during unsteady hydrographs of exceptional flood events. We performed a series of flume experiments with a manually constructed step model, perturbed with three hydrographs that varied in the rate of water supply change. The bed texture, topography, flow regimes, surface flow field and water depth were characterized and measured as the flow rate was increased during the experiments. A distinct pool feature emerged downstream of the manually constructed step when the flow rate exceeded the threshold scaled to the peaks of ordinary flood events in well‐graded mountain streams. The pool feature was modified in several different ways with flow rate increase. The bed surface steadily coarsened, micro‐bedforms developed and became more pronounced, the bed topography became more spatially complex based on analysis using the Hurst exponent, and last, pool depth steadily increased. Pool modification was also linked to the flow regime: the impinging jet regime led to grain size segmentation in the pool while the jump regime contributed to decelerating flow velocity. The steeper rising limb of hydrograph led to a less developed pool feature, with smaller sized micro‐bedforms in the pool bottom to outlet, and higher discharge threshold for distinct coarsening and scouring in the pool. The estimated energy dissipation within the step‐pool unit decreased as a power function from low to high flow, quantified as the ratio hc/HS, where hc is the critical water depth and HS is scour depth. Our results highlight the interaction between morphology, hydraulics, and energy dissipation of step‐pool unit and the crucial role of hydrograph shape on the interaction during flow increase © 2019 John Wiley & Sons, Ltd.

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Section: Hydrograph Designmentioning

confidence: 99%

Section: Energy Dissipationmentioning

confidence: 99%

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

Chendi

Hassan

et al. 2019

Earth Surf Processes Landf

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“…Several studies in the last decades have increased our knowledge on how step-pool systems function, especially with regard to the step-forming mechanisms (Chin, 1999;Curran, 2007;Golly et al, 2019;Saletti et al, 2016;Zimmermann et al, 2010), the stability of steps (Waters and Curran, 2012;Zhang et al, 2019Zhang et al, , 2018Zimmermann et al, 2010), the links between channel and hillslope dynamics (Golly et al, 2017;Molnar et al, 2010), and the relations between flow magnitude, flow resistance, and sediment transport (Comiti et al, 2009a;Hohermuth and Weitbrecht, 2018;Saletti et al, 2015;Turowski et al, 2009;Zimmermann, 2010). Field studies and flume experiments highlighted how boulder protrusion (Yager et al, 2018(Yager et al, , 2007, grain clustering (Johnson, 2017), and the supply of fine sediment (Johnson et al, 2015) impact flow resistance and therefore channel stability and sediment transport in step-pool channels. Furthermore, the importance of granular interactions for step formation and stability has been previously recognized (Church and Zimmermann, 2007;Saletti et al, 2016) and it has been suggested that steps are more stable than predicted because of the emergence of force chains in the transversal direction that keep them in place even when subjected to higher shear stress (Bouchard et al, 2001;Church and Zimmermann, 2007;Saletti and Hassan, 2020a).…”

Section: Introductionmentioning

confidence: 99%

Experimental study of sediment supply control on step formation, evolution, and stability

Saletti¹,

Hassan²

2020

Earth Surf. Dynam.

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Abstract. We present results from an experimental campaign conducted in a steep flume subject to longitudinal width variations and different sediment feed rates. The experiments were designed to study how sediment supply influences step formation, step location, and step stability. Our results show that steps are more likely to form in segments of the channel where the width narrows because of particle jamming, and these steps are also more stable. Sediment feed increases particle activity which generates a dynamic channel morphology with steps forming and collapsing. A comparison with experiments without sediment feed shows that sediment supply does not inhibit step formation. Time series of step formation, evolution, and destruction show that the maximum number of steps is achieved when the sediment feed is larger than zero but smaller than the transport capacity. We summarize this outcome in a conceptual model where the dependence of step frequency on sediment supply is expressed by a bell curve. Sediment yield measured at the channel outlet followed the sediment feed at the inlet closely, even when we fed 50 % more and 50 % less than the calculated transport capacity. This outcome challenges the applicability of the concept of transport capacity to steep channels and highlights the key role played by sediment feed in dictating sediment yield and channel response. Finally, we detected a positive correlation between sediment concentration and step destruction, which stresses the importance of particle interactions for step formation and stability.

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“…In addition to the experiments conducted for this study, we obtained topographic and hydraulic data for 86 step-pool experiments published by Hohermuth and Weitbrecht (2018). The experiments were conducted in a 1:20 Froude-scaled model of a mountain stream, utilizing a range of bed slopes (8 -11 percent), channel widths (15 -35 cm), and discharges.…”

Section: Additional Experimentsmentioning

confidence: 99%

Short communication: Multiscalar drag decomposition in fluvial systems using a transform-roughness correlation (TRC) approach

Adams

Zampiron

2020

Preprint

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Abstract. In natural open-channel flows over complex surfaces, a wide range of superimposed roughness elements may contribute to flow resistance. Gravel-bed rivers present a particularly interesting example of this kind of multiscalar flow resistance problem, as both individual grains and bedforms can potentially be important roughness elements. In this paper, we propose a novel method of estimating the relative contribution of different physical scales of river bed topography to the total drag, using a transform-roughness correlation (TRC) approach. The technique, which requires only a single longitudinal profile, consists of (1) a wavelet transform which decomposes the surface into roughness elements occurring at different wavelengths, and (2) a `roughness correlation' that estimates the drag associated with each wavelength based on its geometry alone, expressed as ks. We apply the TRC approach to original and published laboratory experiments and show that the multiscalar drag decomposition yields estimates of grain- and form-drag that are consistent with estimates in channels with similar morphologies. Also, we demonstrate that the roughness correlation may be used to estimate total flow resistance via a conventional equation, suggesting that it could replace representative roughness values such as median grain size or the standard deviation of elevations. An improved understanding of how various scales contribute to total flow resistance may lead to advances in hydraulics as well as channel morphodynamics.

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Influence of Bed‐Load Transport on Flow Resistance of Step‐Pool Channels

Cited by 25 publications

References 52 publications

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

Experimental study of sediment supply control on step formation, evolution, and stability

Short communication: Multiscalar drag decomposition in fluvial systems using a transform-roughness correlation (TRC) approach

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