The equilibrium alluvial river under variable flow and its channel‐forming discharge

Blom, Astrid; Arkesteijn, Liselot; Chavarrías, Víctor; Viparelli, E.

doi:10.1002/2017jf004213

Cited by 123 publications

(168 citation statements)

References 107 publications

(220 reference statements)

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“…Once the flow inundates the floodplain, the thread of high velocity of the flow no longer needs to follow the channel (Shiono & Muto, ). Furthermore, added resistance due to the complexity at the channel‐floodplain transition acts to suppress the increase of bed shear stress as the flow goes overbank (Blom et al, ; Knight & Demetriou, ). Thus, we assume that the Shields number remains at the bankfull value during overbank flow:

τ^{*} = ({, \begin{array}{c} \frac{{italicHS}_{normalc}}{{italicRD}_{BM}} & when Q < Q_{bf}; \\ \frac{H_{bf} S_{c}}{{italicRD}_{BM}} & when Q \geq Q_{bf} . \end{array})

…”

Section: Modeling Frameworkmentioning

confidence: 99%

Can Bankfull Discharge and Bankfull Channel Characteristics of an Alluvial Meandering River be Cospecified From a Flow Duration Curve?

Naito

Parker

2019

JGR Earth Surface

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We present a simple modeling framework for the codetermination of bankfull discharge and corresponding bankfull channel geometry (width, depth, and longitudinal channel slope) of an alluvial meandering river. We specifically consider a sand‐bed river whose floodplain is capped by a mud‐rich layer. We inquire as to how the wide spectrum of flows to which the river is subjected leads to the establishment of specific values for bankfull discharge and associated bankfull geometry. Here we provide a physically based predictor of bankfull discharge that goes beyond the simple assumption of the 1.5‐year flood discharge. We do this using physics‐based submodels for channel and floodplain processes. We show that bankfull discharge and bankfull geometry are established as a result of (i) floodplain vertical accretion due to overbank deposition, (ii) migration of the inner bank and outer cut bank, (iii) net removal of floodplain sediment and reduction in average floodplain height due to lateral channel shift, and (iv) in‐channel downstream bed material transport. The flow duration curve is employed to quantify the effect of these processes, as well as to account for flow variability. Our model captures the spatiotemporal evolution of bankfull discharge, depth, width, and down‐channel slope toward equilibrium for specified flow duration curve and watershed characteristics. Our new framework can be used for assessing long‐term river response to change in sediment supply or flow duration curve. A model implementation is presented for the case of the Trinity River, TX, USA, to demonstrate the use of the model and its behavior.

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τ^{*} = ({, \begin{array}{c} \frac{{italicHS}_{normalc}}{{italicRD}_{BM}} & when Q < Q_{bf}; \\ \frac{H_{bf} S_{c}}{{italicRD}_{BM}} & when Q \geq Q_{bf} . \end{array})

…”

Section: Modeling Frameworkmentioning

confidence: 99%

Can Bankfull Discharge and Bankfull Channel Characteristics of an Alluvial Meandering River be Cospecified From a Flow Duration Curve?

Naito

Parker

2019

JGR Earth Surface

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“…The backwater-Hirano model runs are made using the one-dimensional numerical research code Elv (Blom et al, 2017). The time step is 2 days and the spatial step is 500 m. The active layer thickness and the vertical grid cell size for keeping track of the substrate texture are equal to 1 m. The depositional flux to the substrate is defined according to equation (A10) with = 0.3.…”

Section: Appendix C: Specifications Of Validationmentioning

confidence: 99%

Advance, Retreat, and Halt of Abrupt Gravel‐Sand Transitions in Alluvial Rivers

Blom

Chavarrías

Ferguson

et al. 2017

Geophysical Research Letters

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Downstream fining of bed sediment in alluvial rivers is usually gradual, but often an abrupt decrease in characteristic grain size occurs from about 10 to 1 mm, i.e., a gravel‐sand transition (GST) or gravel front. Here we present an analytical model of GST migration that explicitly accounts for gravel and sand transport and deposition in the gravel reach, sea level change, subsidence, and delta progradation. The model shows that even a limited gravel supply to a sand bed reach induces progradation of a gravel wedge and predicts the circumstances required for the gravel front to advance, retreat, and halt. Predicted modern GST migration rates agree well with measured data at Allt Dubhaig and the Fraser River, and the model qualitatively captures the behavior of other documented gravel fronts. The analysis shows that sea level change, subsidence, and delta progradation have a significant impact on the GST position in lowland rivers.

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“…A dynamic equilibrium is achieved when the time‐averaged sediment flux supplied from upstream is equal to the time‐averaged sediment transport capacity, for each of the grain size fractions (e.g., Blom et al, ; Blom, Arkesteijn, et al, ; Mackin, ). This condition can be adjusted to account for particle abrasion (Blom et al, ), but the current analysis assumes unisize sediment and omits mixed‐grain size and abrasion effects.…”

Section: Introductionmentioning

confidence: 99%

“…The notion of quasi‐equilibrium has motivated development of models for quasi‐equilibrium river geometry (see Blom, Arkesteijn, et al, , for an overview). These models provide tools for rapid assessment of the quasi‐equilibrium river geometry and the long‐term river response to natural changes in controls and river training works (e.g., De Vriend, ).…”

Section: Introductionmentioning

confidence: 99%

“…These models provide tools for rapid assessment of the quasi‐equilibrium river geometry and the long‐term river response to natural changes in controls and river training works (e.g., De Vriend, ). A limitation of these models is that they typically only apply to quasi‐normal flow segments (e.g., Blom et al, ; Blom, Arkesteijn, et al, ; Blom, Chavarrías, et al, ; De Vries, ) or conditions with a spatially variable channel width and a steady water discharge (Bolla Pittaluga et al, ; Li et al, ). As such, these models cannot be applied to backwater reaches, for example, upstream of a river mouth.…”

Section: Introductionmentioning

confidence: 99%

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The Quasi‐Equilibrium Longitudinal Profile in Backwater Reaches of the Engineered Alluvial River: A Space‐Marching Method

et al. 2019

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An engineered alluvial river (i.e., a fixed‐width channel) has constrained planform but is free to adjust channel slope and bed surface texture. These features are subject to controls: the hydrograph, sediment flux, and downstream base level. If the controls are sustained (or change slowly relative to the timescale of channel response), the channel ultimately achieves an equilibrium (or quasi‐equilibrium) state. For brevity, we use the term “quasi‐equilibrium” as a shorthand for both states. This quasi‐equilibrium state is characterized by quasi‐static and dynamic components, which define the characteristic timescale at which the dynamics of bed level average out. Although analytical models of quasi‐equilibrium channel geometry in quasi‐normal flow segments exist, rapid methods for determining the quasi‐equilibrium geometry in backwater‐dominated segments are still lacking. We show that, irrespective of its dynamics, the bed slope of a backwater or quasi‐normal flow segment can be approximated as quasi‐static (i.e., the static slope approximation). This approximation enables us to derive a rapid numerical space‐marching solution of the quasi‐static component for quasi‐equilibrium channel geometry in both backwater and quasi‐normal flow segments. A space‐marching method means that the solution is found by stepping through space without the necessity of computing the transient phase. An additional numerical time stepping model describes the dynamic component of the quasi‐equilibrium channel geometry. Tests of the two models against a backwater‐Exner model confirm their validity. Our analysis validates previous studies in showing that the flow duration curve determines the quasi‐static equilibrium profile, whereas the flow rate sequence governs the dynamic fluctuations.

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The equilibrium alluvial river under variable flow and its channel‐forming discharge

Cited by 123 publications

References 107 publications

Can Bankfull Discharge and Bankfull Channel Characteristics of an Alluvial Meandering River be Cospecified From a Flow Duration Curve?

Can Bankfull Discharge and Bankfull Channel Characteristics of an Alluvial Meandering River be Cospecified From a Flow Duration Curve?

Advance, Retreat, and Halt of Abrupt Gravel‐Sand Transitions in Alluvial Rivers

The Quasi‐Equilibrium Longitudinal Profile in Backwater Reaches of the Engineered Alluvial River: A Space‐Marching Method

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