Highest natural bed forms

Giménez‐Curto, Luis A.; Corniero, Miguel A.

doi:10.1029/2002jc001474

Cited by 14 publications

(13 citation statements)

References 24 publications

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“…Sequences with larger step spacing were predominantly observed as more stable, reflecting the importance of pool development during sequence existence, which has been shown to dissipate energy through turbulence [ Gimenez‐Curto and Corniero , 2003, 2006; Wilcox et al , 2011]. By definition, the same sequence showed little changes in step spacing, so increases in either H / L or H / L / S were a result of increases in step height and scour related to pool development.…”

Section: Discussionmentioning

confidence: 99%

“…Step‐pool sequences best fit this relation when the distance between steps was equal to the length of the downstream pool [ Abrahams et al , 1995]. More recent data from flume experiments have shown steps form with a minimum spacing set by the exclusion zone, which is larger than the length of the associated pool [ Curran and Wilcock , 2005; Gimenez‐Curto and Corniero , 2003]. Many steps were spaced farther apart than the minimum spacing set by the exclusion zone, and thus did not fit the Abrahams relation, despite the wide parameter range possible.…”

Section: Introductionmentioning

confidence: 99%

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Investigating step‐pool sequence stability

Waters¹,

Curran²

2012

Water Resources Research

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[1] Step-pool units, common features in steep, narrow streams, are highly dynamic systems that adjust during high flows and active sediment transport conditions. Consecutive step pools in a reach form a step-pool sequence, and though these features are prevalent in nature, quantifying the stability of such systems is challenging. This study focuses on the statistical relationships between 445 stable sequences of three or more steps and nine geometric and resistance-based parameters.Step sequence stability is parameterized through a sequence stability parameter, a metric of how long a given step-pool sequence exists relative to the total run time. Despite variability in the strength of the statistical relationships, the results allow identification of dominant trends between sequence stability and both roughness and geometric parameters. The sediment concentration ratio provides a means for comparing the relative strength of these statistical relationships. As sediment concentration ratios increase, the relations between flow resistance parameters and step stability change from dominantly inverse to dominantly direct. Thus, at higher sediment concentration ratios, sequence stability is more likely to increase with flow resistance, but the reverse is more likely at low sediment concentration ratios. A connection exists between bed morphology, flow resistance, and stability. For the majority of stable step sequences, resistance parameters increase over time, indicating some sequences adjust their geometry to increase stability during flood events. The influence of sediment concentration over the stability-geometric and stability-resistance parameter relationships may enable the use of the sediment concentration ratio as a predictor of step sequence stability during a flow event.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigating step‐pool sequence stability

Waters¹,

Curran²

2012

Water Resources Research

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“… Giménez‐Curto and Corniero [2006] point out that the minimum pool length, in effect the exclusion zone in the observations of Curran and Wilcock [2005], is the direct consequence of energy dissipation, or flow resistance, in very rough flows dominated by form resistance. Giménez‐Curto and Corniero [2003] show that L min (the exclusion zone) is given by in which 〈 H 〉 is the obstacle height, that is, the step height, and 〈 H 〉/ d is normalized mean drop height. Reversing the argument, when L = L min for given H (determined by available grain size), f is a maximum.…”

Section: Step Geometry Revisitedmentioning

confidence: 99%

Form and stability of step‐pool channels: Research progress

Church

Zimmermann

2007

Water Resources Research

205

267

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[1] Research examining the hydraulics, morphology, and stability of step-pool mountain streams has blossomed in the last decade, resulting in more than a dozen dissertations. These, along with other research projects, have transformed our understanding of step-pool channels. Contributions have been made toward understanding depositional step formation and destruction, scour downstream of steps, step-pool hydraulics, and the effect of sediment transport on step stability. We propose that depositional steps exist in a jammed state whereby the boulders are structurally arranged within the channel and thereby stabilize it. Once a step has formed, a scour pool with a characteristic length and depth develops downstream, creating a zone where additional steps are unlikely to occur. Downstream of the scour hole, steps are more likely to occur as the high energy associated with the plunge pool has dissipated. Data suggest that the presence of cobbles or boulders limits pool scour as well as the degree to which well-defined, channelspanning step-pools form. We propose a state-space for step-pools in which conditions for a step to form include (1) the ratio between width and boulder diameter (the jamming ratio), (2) the ratio between applied shear stress and the stress needed to mobilize the bed (relative Shields number), and (3) the ratio between bed material supply and discharge (bed sediment concentration). Available data suggest this model is plausible. Emerging critical research questions are discussed.

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“…Nikora (2009) extended the use of the double-averaging methodology to develop a theoretical expression that explicitly showed that the friction factor can be accounted for by six additive components, of which only three are present in two-dimensional uniform spatially-averaged flow without secondary currents: viscous stress, turbulent stress and forminduced stress. The contribution of the form-induced stress, ũw , has recently attracted substantial attention as it has been shown to play an important role in the overall streamwise momentum balance in the near-bed region (Aberle, Koll, & Dittrich, 2008;Dey & Das, 2012;Ferreira et al, 2010;GimenezCurto and Corniero, 1996;Gimenez-Curto and Corniero Lera, 2003;Manes, Pokrajac, Coceal, & McEwan, 2008;Manes, Pokrajac, & McEwan, 2007;Manes, Pokrajac, McEwan, & Nikora, 2009;Mignot, Barthelemy, & Hurther, 2009a,b;Nikora et al, 2007b;Sarkar & Dey, 2010). Indeed, Gimenez-Curto and Corniero (1996) and Gimenez-Curto and Corniero Lera (2003) suggested that at very low submergences the form-induced stress could become the dominant component in the streamwise momentum balance.…”

Section: Introductionmentioning

confidence: 99%

“…The contribution of the form-induced stress, ũw , has recently attracted substantial attention as it has been shown to play an important role in the overall streamwise momentum balance in the near-bed region (Aberle, Koll, & Dittrich, 2008;Dey & Das, 2012;Ferreira et al, 2010;GimenezCurto and Corniero, 1996;Gimenez-Curto and Corniero Lera, 2003;Manes, Pokrajac, Coceal, & McEwan, 2008;Manes, Pokrajac, & McEwan, 2007;Manes, Pokrajac, McEwan, & Nikora, 2009;Mignot, Barthelemy, & Hurther, 2009a,b;Nikora et al, 2007b;Sarkar & Dey, 2010). Indeed, Gimenez-Curto and Corniero (1996) and Gimenez-Curto and Corniero Lera (2003) suggested that at very low submergences the form-induced stress could become the dominant component in the streamwise momentum balance. Interestingly Manes et al (2007) found that the relative contribution of form-induced stress increased as submergence decreased in their experiments on open channel flow over closely-packed spheres.…”

Section: Introductionmentioning

confidence: 99%

Free surface flow over square bars at intermediate relative submergence

McSherry

Chua

Stoesser

et al. 2018

Journal of Hydraulic Research

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Results from large-eddy simulations and complementary flume experiments of turbulent open channel flows over bed-mounted square bars at intermediate submergence are presented. Scenarios with two bar spacings, corresponding to transitional and k-type roughness, and three flow rates, are investigated. Good agreement is observed between the simulations and the experiments in terms of mean free surface elevations and mean streamwise velocities. Contours of simulated time-averaged streamwise, streamfunction and turbulent kinetic energy are presented and these reveal the effect of the roughness geometry on the water surface response. The analysis of the vertical distribution of the streamwise velocity shows that in the lowest submergence cases no logarithmic layer is present, whereas in the higher submergence cases some evidence of such a layer is observed. For several of the flows moderate to significant water surface deformations are observed, including weak and/or undular hydraulic jumps which affect significantly to the overall streamwise momentum balance. Reynolds shear stress, form-induced stress and form drag are analysed with reference to the momentum balance to assess their contributions to the total hydraulic resistance of these flows. The results show that form-induced stresses are dominant at the water surface and can contribute significantly to the overall drag, but the total resistance in all cases is dominated by form drag due to the presence of the bars.

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Highest natural bed forms

Cited by 14 publications

References 24 publications

Investigating step‐pool sequence stability

Investigating step‐pool sequence stability

Form and stability of step‐pool channels: Research progress

Free surface flow over square bars at intermediate relative submergence

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