A flume experiment on the effect of constriction shape on the formation of forced pools

Thompson, Douglas; McCarrick, C. R.

doi:10.5194/hessd-7-1945-2010

Cited by 5 publications

(5 citation statements)

References 33 publications

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“…Further experiments with different bend geometries would be required to physically verify these relationships. Width variations have been shown to influence the spontaneous formation of morphologic features such as pool and riffles by affecting the local acceleration and deceleration of flow in flume experiments (e.g., Chartrand, Jellinek, Hassan, & Ferrer‐Boix, 2018; Thompson & McCarrick, 2010), field observations (e.g., Thompson & Wohl, 2009), and numerical models (e.g., MacWilliams, Wheaton, Pasternack, Street, & Kitanidis, 2006). Therefore, channel width variation can be expected to also play a role in the spatial distribution of cover formation in semi‐alluvial channels through similar hydraulic mechanisms.…”

Section: Discussionmentioning

confidence: 99%

Experiments on restoring alluvial cover in straight and meandering rivers using gravel augmentation

Welber

Papangelakis

Ashmore

et al. 2020

River Research & Apps

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Successful management of natural and engineered channels with discontinuous alluvial cover requires knowledge of how the cover develops and evolves. We report on physical model experiments designed to compare alluvial cover dynamics in straight and sinuous fixed-bed channels at a range of gravel-bed material supply rates and constant discharge conditions. Experiments investigated the formation of alluvial

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Section: Discussionmentioning

confidence: 99%

Experiments on restoring alluvial cover in straight and meandering rivers using gravel augmentation

Welber

Papangelakis

Ashmore

et al. 2020

River Research & Apps

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“…This resulted in a maximum channel width of 1.21 m, a minimum channel width of 0.52 m, a dimensional amplitude of A = 0.69 m ( A = 2 A c B 0 ), and a wavelength of width variations equaling λ c = 3.42 m ( L c = 2 πB 0 / λ c ). The minimum width was 60% of the average width, and this 40% constriction is in line with extensive field and experimental work suggesting riffles and pools emerge with constrictions ranging from 30% to 50% of the mean width (e.g., Caamano et al ., 2009; de Almeida & Rodriguez, 2011, 2012; Lisle, 1986; MacVicar & Roy, 2007a, 2007b; Nelson et al ., 2015; Thompson & Fixler, 2017; Thompson & McCarrick, 2010). The wavelength of width variations in our flume corresponds to a pool spacing of approximately four channel widths.…”

Section: Methodsmentioning

confidence: 99%

Experimental investigation of the morphodynamic response of riffles and pools to unsteady flow and increased sediment supply

Morgan

Nelson

2021

Earth Surf Processes Landf

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Gravel‐bed rivers characteristically exhibit shallow riffles in wide sections and deeper pools where the channel becomes constricted and narrow. While rivers can adjust to changing flow and sediment supply through some combination of adjustments of channel slope, bed‐surface sorting, and channel shape, the degree to which riffle‐pools may adopt these changes in response to changing flows and sediment supplies remains unclear. This article presents results from a flume experiment investigating how constant‐ and variable‐width channels adjust their morphology in response to changing flow and increased sediment supply. Two flume geometries were used: (1) constant‐width and (2) variable‐width, characterized by a sinusoidal pattern with a mean width equal to that of the first channel. The variable‐width channel developed bed undulations in phase with the width, representing riffle‐pools. The experiment consisted of three phases for each flume geometry: (1) steady flow, constant sediment supply; (2) unsteady flow, constant sediment supply; and (3) unsteady flow, doubled sediment supply. Unsteady flow was implemented in the form of repeated symmetrical stepped hydrographs, with a mean discharge equal to that in the steady flow phase. In all phases the bed and sediment supply were composed of a sand/gravel mixture ranging from 1 to 8 mm. In both the straight and variable‐width channels, transitioning from steady flow to repeated hydrographs did not result in significant changes in bed morphology. The two channel geometries had different responses to increased sediment supply: the slope of the straight channel increased nearly 40%, while the variable‐width channel reduced the relief between bars and pools and decreased the variability in cross‐sectional elevation with a slight slope increase. Bar‐pool relief varied with repeat discharge hydrographs. Pool elevation changed twice the distance of bar elevations, emphasizing the relevance of pool scour for riffle‐pool self‐maintenance in channels with width variations.

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“…; MacWilliams et al. ; MacVicar and Roy, ; Thompson and McCarrick, ; MacVicar and Rennie, ; MacVicar and Best, ; Chartrand et al. ).…”

Section: Morphodynamic Evolution Metrics At the Scale Of A Channel Widthmentioning

confidence: 99%

What controls the disequilibrium state of gravel‐bed rivers?

Chartrand

Jellinek

Hassan

et al. 2019

Earth Surf Processes Landf

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A river at equilibrium is described by a statistically‐stationary mean bed elevation profile that arises in response to steady supplies of relief, water and sediment. Outside of the profile shape, how is the equilibrium state of a river most reliably identified and rigorously defined? Motivated by a proposed link between equilibrium and physical processes, we use scaling theory to develop the dimensionless channel response number ξ=KUb/Up. ξ is a metric for the local disequilibrium state of gravel‐bed mountain streams, which reflects a balance between the rate of topographic adjustment Ub, and the rate of bed sediment texture adjustment Up. The coefficient K can take one of two forms depending on choice of length scale for topographic adjustment. We hypothesize that equilibrium occurs where and when ξ≈O(1), and consequently, disequilibrium is the more general state captured by conditions of ξ≉O(1). The rates Ub and Up are controlled by the mechanics of sediment deposition and entrainment at the local scale of the channel width. The extent to which either process regulates disequilibrium depends on the bed strength, which is set by the time‐varying grain size distribution and packing. We use flume experiments to understand ξ and find that in the limit ξ>>1, the time‐varying response of an experimental channel depends sensitively on the spatially‐averaged bed shear stress ratio τ/τref. When τ/τref≈1.5, Ub was the dominant control on disequilibrium. However, when τ/τref≈2.0, Up contributed more significantly to disequilibrium. These results suggest that after an upstream supply perturbation, the equilibrium timescale is governed by Up, which we show is consistent with expectations from linear damping theory. Our experimental test of ξ is promising, but inconclusive with respect to our hypothesis. This uncertainty can be readily addressed with numerical or additional physical experiments. © 2019 John Wiley & Sons, Ltd.

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A flume experiment on the effect of constriction shape on the formation of forced pools

Cited by 5 publications

References 33 publications

Experiments on restoring alluvial cover in straight and meandering rivers using gravel augmentation

Experiments on restoring alluvial cover in straight and meandering rivers using gravel augmentation

Experimental investigation of the morphodynamic response of riffles and pools to unsteady flow and increased sediment supply

What controls the disequilibrium state of gravel‐bed rivers?

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