Low relative-submergence effects in a rough-bed open-channel flow

Rouzes, Maxime; Moulin, F.; Florens, Emma; Eiff, Olivier

doi:10.1080/00221686.2018.1478894

Cited by 21 publications

(36 citation statements)

References 45 publications

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“…All agree on the necessity to use the double-averaging methodology proposed by Nikora et al (2007) [4] in order to describe the flow inside the roughness sublayer, but few experiments achieve enough spatial convergence to obtain correct estimates of double-average quantities, as discussed in Florens et al (2013) [5]. Surprisingly, it was found that profiles above the canopy (z>h) still exhibit log-law behaviours for values of h/D as large as 0.66, see Rouzès et al (2016) [6].…”

Section: Dvn /Derudwru\ H[shulphqwvmentioning

confidence: 86%

“…Measurements in the centre of the rough bed S1 for completely developed flow conditions (at position X5) were used to investigate the turbulent boundary layer structure above the canopy for high values of h/D, focusing in particular on the roughness sublayer extent and the log law parameters. These measurements and results are analysed in a separate publication (see Rouzès et al (2016) [6]). …”

Section: Experiments At Imftmentioning

confidence: 99%

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Predicting the flow in the floodplains with evolving land occupations during extreme flood events (FlowRes ANR project)

Proust¹,

Berni²,

Boudou³

et al. 2016

E3S Web Conf.

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Abstract. Flood hazards (flow depth and velocity) must be accurately assessed in high-risk areas during extreme flood events. However, the prediction of the very high flows is not an easy task due to the lack of field data and to the strong link between flow resistance and the land occupation of the floodplain. Confinement and inhomogeneity in lateral and longitudinal directions of hydraulic roughness strongly vary with return period T. The physical processes are complex, some still largely unexplored, and the assumptions linked to numerical modelling cannot be validated without field data. The FlowRes project (2015)(2016)(2017)(2018), funded by the French National Research Agency (ANR), aims at improving the flood hazard assessment in floodplains in: 1) investigating in laboratory the hydrodynamic structure associated with extreme flood flows for various land occupations and flow discharge magnitudes; 2) assessing if the existing numerical modelling practices used for T ~ 100 years are still valid for extreme events with T > 1000 years, relying on the experimental data and on one field case. This paper reports some results obtained during the first year of the project.

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Section: Dvn /Derudwru\ H[shulphqwvmentioning

confidence: 86%

Section: Experiments At Imftmentioning

confidence: 99%

Predicting the flow in the floodplains with evolving land occupations during extreme flood events (FlowRes ANR project)

Proust¹,

Berni²,

Boudou³

et al. 2016

E3S Web Conf.

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“…The radius R of the hemispheres was chosen to keep the relative submergence D / k for the highest protrusion ( P =80%) high enough to avoid low submergence effects. In Rouzes et al (), low submergence effects are observed in the log law parameters with an array of cubes for D / k below 6.7, with values of the hydraulic roughness k s diverging from values found in highly submerged flow conditions. With R =2 cm chosen here, the lowest D / k was equal to 7.8 so that all protrusions can be considered highly submerged.…”

Section: Methodsmentioning

confidence: 91%

“…Thus, in the double‐averaged framework, τ xz ( z ) is given by

τ_{x z} false(z false) = - ρ_{f} ⟨ \overset{u^{'} w^{'}}{true} ⟩ - ρ_{f} ⟨ ũ \overset{w}{true} ⟩ + μ \frac{\partial ⟨ ū ⟩}{\partial z},

that is, the sum of the spatially averaged Reynolds shear stress, the dispersive shear stress, and the double‐averaged viscous shear stress. More detail on the estimation of the dispersive stress is given in Florens et al () and Rouzes et al ().…”

Section: Flow Structurementioning

confidence: 99%

The Impact of Coarse‐Grain Protrusion on Near‐Bed Hydrodynamics

2019

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In steep rivers, sediment is often transported over immobile cobbles and boulders. Previous studies of such conditions have observed that the entrainment rate of the mobile sediment strongly depends on the level of protrusion of the immobile grains. Here experiments are conducted in a laboratory flume in order to quantify how different levels of protrusion of large aggregates above a fixed fine-sediment bed, modeled as a patch of hemispheres, modify the local hydrodynamics near the fine-sediment bed. Five protrusion levels defined by P = k∕R = {0%, 20%, 40%, 60%, 80%} were investigated, where k is the protrusion height and R the radius. For small protrusion (P = 20%), enhanced shear stress and turbulence intensity on the fine-sediment bed is observed as the mixing layer generated at the hemisphere top impacts the fine-sediment bed. Moreover, sweep events generated near the top of the hemispheres reach the fine-sediment bed. For large protrusions (P ≥ 60%), the mixing layer generated near the top of the hemispheres does not reach the fine grains with the consequence that the shear stress drops. The remaining turbulence near the fine-sediment bed, although enhanced by the wakes generated by the hemispherical caps, is quasi-isotropic. The transition between these two distinct near-bed flow regimes is found to be around P = 40%, corresponding to the protrusion levels observed by Grams and Wilcock (2014, https://doi.org/10.1002/2013JF002925) above which the erosion of fine sediment ceases.

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“…Rare are the experiments that deal with solute transport in channels under well‐controlled conditions and unsteady state flow events. In the literature, some studies were carried on real‐scale channels (e.g., Errico et al, ; Newson, ; Rudi, Bailly, Belaud, & Vinatier, ) and on laboratory channels (Vinatier, Bailly, & Belaud, ) for various purposes according to project features: impact of land use change on floods (Jung, Kang, Hong, & Yeo, ), impact of dikes on inundation (Ettema & Muste, ), impact of vegetation on hydraulic resistance (Defina & Peruzzo, ; Errico et al, ), role of flow conditions in hydraulic properties (Rouzes, Moulin, Florens, & Eiff, ) and in biofilm colonization (Coundoul et al, ), and so on. The experiment size should verify hydraulic laws of similitude (Chanson, ).…”

Section: Introductionmentioning

confidence: 99%

A novel platform to evaluate the dampening of water and solute transport in an experimental channel under unsteady flow conditions

Majdalani

Moussa

Chazarin

2020

Hydrological Processes

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This paper presents a novel platform to study the dampening of water and solute transport in an experimental channel under unsteady flow conditions, where literature data are scarce. We address the question about what could be the smallest size of experimental platform that is useful for research, project studies, and teaching activities and that allows to do rational experiments characterized by small space occupation, short experimental duration, high measurement precision, high quality and reproducible experimental curves, low water and energy consumption, and the possibility to test a large variety of hydrograph scenarios. Whereas large scale hydraulic laboratories have focused their studies on sediment transport, our platform deals with solute transport. The objectives of our study are (a) building a platform that allows to do rational experiments, (b) enriching the lack of experimental data concerning water and solute transport under unsteady state conditions, and (c) studying the dampening of water and solute transport. We studied solute transport in a channel with lateral gain and lateral loss under different experimental configurations, and we show how the same lateral loss flow event can lead to different lateral loss mass repartitions under different configurations. In order to characterize water and solute dampening between the input and the output of the channel, we calculate dampening ratios based on peak coordinates of time flow curves and time mass curves and that express the decrease of peak amplitude and the increase of peak occurrence time between the input and output curves. Finally, we use a solute transport model coupling the diffusive wave equation for water transfer and the advection-diffusion equation for solute transport in order to simulate the experimental data. The simulations are quite good with a Nash-Sutcliffe efficiency NSE > 0.98 for water transfer and 0.84 < NSE < 0.97 for solute transport. This platform could serve hydrological modellers because it offers a variety of measured parameters (flow, water height, and solute concentration), at a fine time step under unsteady flow conditions. KEYWORDS diffusive wave equation, solute transport dampening, unsteady flow event, water height measurement, water and solute transport

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Low relative-submergence effects in a rough-bed open-channel flow

Abstract: OATAO is an open access repository that collects the work of some Toulouse researchers and makes it freely available over the web where possible.

Cited by 21 publications

References 45 publications

Predicting the flow in the floodplains with evolving land occupations during extreme flood events (FlowRes ANR project)

Predicting the flow in the floodplains with evolving land occupations during extreme flood events (FlowRes ANR project)

The Impact of Coarse‐Grain Protrusion on Near‐Bed Hydrodynamics

A novel platform to evaluate the dampening of water and solute transport in an experimental channel under unsteady flow conditions

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