Experimental analysis of braided channel pattern response to increased discharge

Egozi, Roey; Ashmore, Peter

doi:10.1029/2008jf001099

Cited by 114 publications

(127 citation statements)

References 58 publications

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“…However, other studies have shown that discharge variation has a large effect on river morphology (e.g., Kiss and Sipos, 2007;Crosato and Saleh, 2010) due, among other things, to vegetation colonization on exposed bar sections (Gordon and Meentemeyer, 2006;Tealdi et al, 2011). Also, Egozi and Ashmore (2009) demonstrated that braiding intensity increased with increasing discharge, although this was temporary and braiding intensity decreased after the channel adapted to the new discharge. In the context of both river training and morphological studies, the effects of discharge variation on the braided river network are still largely unknown.…”

Section: Disturbances In Braiding Riversmentioning

confidence: 70%

Network response to disturbances in large sand-bed braided rivers

2016

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Abstract. The reach-scale effects of human-induced disturbances on the channel network in large braided rivers are a challenge to understand and to predict. In this study, we simulated different types of disturbances in a large braided river to get insight into the propagation of disturbances through a braided channel network. The results showed that the disturbances initiate an instability that propagates in the downstream direction by means of alteration of water and sediment division at bifurcations. These adjustments of the bifurcations change the migration and shape of bars, with a feedback to the upstream bifurcation and alteration of the approaching flow to the downstream bifurcation. This way, the morphological effect of a disturbance amplifies in the downstream direction. Thus, the interplay of bifurcation instability and asymmetrical reshaping of bars was found to be essential for propagation of the effects of a disturbance. The study also demonstrated that the large-scale bar statistics are hardly affected.

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Section: Disturbances In Braiding Riversmentioning

confidence: 70%

Network response to disturbances in large sand-bed braided rivers

2016

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“…During the period of analysis, a large proportion of the bed area was reworked by processes typical of braided rivers, i.e., channel avulsions, bar migration, bedload transport, confluence and bifurcation evolution, and active and non-active anabranches (e.g., Egozi and Ashmore, 2009). Natural grain sorting is observed over the entire bed surface; fine and coarse sediments are organized in relation to local topography, flow bifurcation, bed roughness or flow constriction, which lead to a complex pattern of different surface grain size (e.g., Carson and Griffiths, 1987).…”

Section: Natural and Modeled Surface Grain Sortingmentioning

confidence: 99%

Grain sorting in the morphological active layer of a braided river physical model

2015

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Abstract.A physical scale model of a gravel-bed braided river was used to measure vertical grain size sorting in the morphological active layer aggregated over the width of the river. This vertical sorting is important for analyzing braided river sedimentology, for numerical modeling of braided river morphodynamics, and for measuring and predicting bedload transport rate. We define the morphological active layer as the bed material between the maximum and minimum bed elevations at a point over extended time periods sufficient for braiding processes to rework the river bed. The vertical extent of the active layer was measured using 40 hourly high-resolution DEMs (digital elevation models) of the model river bed. An image texture algorithm was used to map bed material grain size of each DEM. Analysis of the 40 DEMs and texture maps provides data on the geometry of the morphological active layer and variation in grain size in three dimensions. By normalizing active layer thickness and dividing into 10 sublayers, we show that all grain sizes occur with almost equal frequency in all sublayers. Occurrence of patches and strings of coarser (or finer) material relates to preservation of particular morpho-textural features within the active layer. For numerical modeling and bedload prediction, a morphological active layer that is fully mixed with respect to grain size is a reliable approximation.

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“…It can be observed that the development of a braided pattern in the predicted river shares many common properties with the experimental river ( Figure 5, activity number identified with Figure 4). Most of the morphologic elements and activities observed in the experimental river [31] have been found in the predicted river.…”

Section: River Evolution Processes and Phenomenamentioning

confidence: 97%

“…The model was applied to a laboratory experiment conducted by Egozi and Ashmore [31], in which a braided river pattern was generally developed. The river was originally designed to be a generic Froude-scaled model with the prototype being the Sunwapta River in Canada.…”

Section: Model Setupmentioning

confidence: 99%

“…Nevertheless, non-uniform sediments exist in natural rivers, and different size fractions of sediment particles are transported at different rates [29]. Sediment gradation plays an essential role in the bed deformation process, which is especially important for the evolution of local units in natural [30] and laboratory braided rivers [31]. In addition, laboratory experiments [32] also show the influence of vertical grain sorting in the active layer, indicating that it is necessary to divide the riverbed into multiple bed layers in river simulation.…”

Section: Introductionmentioning

confidence: 99%

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Simulating Laboratory Braided Rivers with Bed-Load Sediment Transport

Yang

Lin

Sun

et al. 2017

Water

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Numerical models provide considerable assistance in the investigation of complicated processes in natural rivers. In the present study, a physics-based two-dimensional model has been developed to simulate the braiding processes and morphodynamic changes in braided rivers. The model applies the basic hydrodynamic and sediment transport principles with bed morphology deformation and a TVD (Total Variation Diminishing) scheme to predict trans-critical flows and bed morphology deformation. The non-equilibrium transport process of graded bed load sediment is simulated, with non-uniform sediments, secondary flows, and sheltering effects being included. A multiple bed layer technique is adopted to represent the vertical sediment sorting process. The model has been applied to simulate the bed evolution process in an experimental river with bed load transport. Comparisons between the experimental river and predicted river are analysed, including their pattern evolution processes, important braiding phenomena, and statistical characteristics. Avulsion activities have been found in the braiding evolution process, representing the primary ways in which channels form and disappear in braided rivers. The increases in the active braiding intensity and total braiding intensity show similar trends to those observed in the experimental river. Statistical methods are applied to assess the scale-invariant topographic properties of the simulated river and real rivers. The model demonstrated its potential to predict the morphodynamics in natural rivers.

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Experimental analysis of braided channel pattern response to increased discharge

Cited by 114 publications

References 58 publications

Network response to disturbances in large sand-bed braided rivers

Network response to disturbances in large sand-bed braided rivers

Grain sorting in the morphological active layer of a braided river physical model

Simulating Laboratory Braided Rivers with Bed-Load Sediment Transport

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