References of "Pirotton, Michel"
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See detailPhysical modeling of lateral dike breaching due to overtopping
Rifai, Ismail; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in River, Coastal and Estuarine Morphodynamics, RCEM 2015 (2015, August)

Dikes are commonly used as defense structures for river flow channelization, protecting population and property from floods and against lateral riverbed migration. However, the aging of these structures ... [more ▼]

Dikes are commonly used as defense structures for river flow channelization, protecting population and property from floods and against lateral riverbed migration. However, the aging of these structures, combined with their increased vulnerability to extreme hydrological events may cause the dikes to breach, and subsequently to break. Furthermore, statistics show that flow overtopping is the main cause of dike failure, which emphasizes the need to understand thoroughly the process of breaching. Indeed, from a risk management perspective it is particularly important to have a detailed understanding of the mechanisms (e.g. internal erosion, overtopping erosion) underlying the formation of breaches due to overtopping and reliable information on flows passing through them. Conversely, the current knowledge of breaching mechanisms remains fragmented, especially because dike failure involves complex interactions between flows, materials of the structure, soil and foundations. The existing studies have addressed partially these interactions as the considered idealized dikes were generally homogenous, the piping erosion unaccounted for and the overtopping replicated in a dam-break like configuration. Yet, river embankments are subjected to high flow velocities parallel to the direction of the dike and to flow in the floodplain, which highly influence the shape of the breach and its evolution. The objective of the present work is to fill this gap. A laboratory experimental investigation is planned in the National Laboratory for Hydraulics and Environment (LNHE) of EDF R&D (France) and in the research group Hydraulics in Environmental and Civil Engineering (HECE) of the University of Liege (Belgium), reproducing realistic configurations of river dikes, accounting for the tangential flow in both main channel and floodplain. It enables thus the assessment of, on the one hand, the effect of the increase of the water level, and on the other hand, the influence of waves. The laboratory tests also consider the effect of a surface layer and composition of the dike core by testing different material mixtures. Geometry and composition of the idealized dikes are representative of typical field dikes, based on the similarity theory. [less ▲]

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See detailComposite hydraulic modeling to design a complex dam spillway
Erpicum, Sébastien ULg; Dewals, Benjamin ULg; Archambeau, Pierre ULg et al

Conference (2015, July 01)

The paper presents the application of a composite hydraulic modeling approach to the rehabilitation studies of a complex dam spillway. First, a physical scale model of the existing works has been built ... [more ▼]

The paper presents the application of a composite hydraulic modeling approach to the rehabilitation studies of a complex dam spillway. First, a physical scale model of the existing works has been built and operated. It enabled to define very accurately the actual discharge capacity and to validate a numerical model of the system. Second, the numerical model has been used to rapidly test several rehabilitation solutions. Finally, the final design has been validated and optimized using the physical model. The paper shows how composite hydraulic modeling enables to combine the inherent advantages of physical and numerical modeling approaches, which are complementary, while being beneficial to the delay as well as the quality of the analysis. [less ▲]

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See detailImpacts of climate change on future flood damage on the river Meuse, with a distributed uncertainty analysis
Detrembleur, Sylvain; Stilmant, Frédéric ULg; Dewals, Benjamin ULg et al

in Natural Hazards (2015), 77(3), 1533-1549

Flood-risk assessments are an objective and quantitative basis for implementing harmonized flood mitigation policies at the basin scale. However, the generated results are subject to different sources of ... [more ▼]

Flood-risk assessments are an objective and quantitative basis for implementing harmonized flood mitigation policies at the basin scale. However, the generated results are subject to different sources of uncertainty arising from underlying assumptions, data availability and the random nature of the phenomenon. These sources of uncertainty are likely to bias conclusions because they are irregularly distributed in space. Therefore, this paper addresses the question of the influence of local features on the expected annual damage in different municipalities. Based on results generated in the frame of a transnational flood-risk-assessment project for the river Meuse (Western Europe) taking climate change into account, the paper presents an analysis of the relative contributions of different sources of uncertainty within one single administrative region (the Walloon region in Belgium, i.e. a river reach of approximately 150 km). The main sources of uncertainty are not only found to vary both from one municipality to the other and in time, but also to induce opposite effects on the computed damage. Nevertheless, practical conclusions for policy-makers can still be drawn. [less ▲]

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See detailModélisation mathématique des risques d’inondation dans le bassin liégeois suivant différents scénarios de changements climatiques et d’aménagement du territoire
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

Conference (2015, June 03)

Dans une ancienne région minière, affectée par des affaissements significatifs de surface, la ville de Liège est actuellement efficacement protégée contre les crues par débordement de la Meuse grâce ... [more ▼]

Dans une ancienne région minière, affectée par des affaissements significatifs de surface, la ville de Liège est actuellement efficacement protégée contre les crues par débordement de la Meuse grâce essentiellement à une canalisation du fleuve. Une analyse prospective a été entamée, visant à évaluer la pérennité de la protection actuelle de la ville sous différents scénarios d’évolutions climatiques et d’aménagement du territoire. Prenant sa source en France et traversant la Belgique pour rejoindre son embouchure aux Pays-Bas, la Meuse ne peut être étudiée qu’en tenant compte de ce contexte transnational. C’est pourquoi, l’analyse prospective menée a été concertée à toutes les étapes non seulement avec les acteurs scientifiques et les gestionnaires de l’eau dans les régions limitrophes concernées, mais également avec des organisations représentatives de la société civile. En particulier, les scénarios climatiques retenus ainsi que les modélisations hydrauliques et hydro-économiques effectuées ont systématiquement été coordonnés, voire harmonisés, à l’échelle du bassin versant international du fleuve. Les résultats de l’analyse mettent en évidence un accroissement significatif de l’aléa inondation dans la ville de Liège à l’échéance de la fin du siècle. Ils permettent également de circonscrire le potentiel d’adaptation de la ville pour atténuer l’impact d’inondations, tant par des mesures techniques locales qu’à plus grande échelle. La portée de diverses politiques d’aménagement du territoire à Liège et au-delà a également pu être évaluée et l’analyse révèle un degré d’efficacité très contrasté selon les communes concernées. [less ▲]

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See detailA shallow-water model with depth-dependent porosity for urban flood modeling
Bruwier, Martin ULg; Archambeau, Pierre ULg; Erpicum, Sébastien ULg et al

in E-proceedings of the 36th IAHR World Congress (2015, June)

The availability of high-resolution topographic data enables the modeling of urban floods with a high level of accuracy. However, such a modelling has a poor computational efficiency. Subgrid models ... [more ▼]

The availability of high-resolution topographic data enables the modeling of urban floods with a high level of accuracy. However, such a modelling has a poor computational efficiency. Subgrid models enable to decrease the computational time by using coarse cells while preserving information from the detailed topographic data to some degree. In particular, shallow-water models with porosity constitute a subgrid model well-adapted for urban flood modeling. In this article, a new set of fully dynamic shallow-water equations with depth-dependent porosities is presented. Then, the implementation of the model is detailed and preliminary results obtained for a theoretical two-dimensional urban area are analyzed. Unlike recent works, the new model solves the fully dynamic shallow-water equations with depth-dependent and anisotropic porosities, a divergent formulation of the bed slope term, a non-staggered grid with quadrilateral cells and an efficient use of look-up tables to store the porosity relations. [less ▲]

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See detailApplication of the morphological acceleration factor in fluvial hydraulics
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in E-proceedings of the 36th IAHR World Congress (2015, June)

The morphological acceleration factor (Morfac) has been widely used to speed-up morphodynamic simulations, mostly in coastal applications. The value of Morfac was generally set by trial and error and ... [more ▼]

The morphological acceleration factor (Morfac) has been widely used to speed-up morphodynamic simulations, mostly in coastal applications. The value of Morfac was generally set by trial and error and little theoretical background is available to identify an optimal value of Morfac for a given application and a target level of accuracy. In the present research, we generalize the few previous theoretical analyses regarding two main aspects. First, the range of the considered parameters (Froude number, relative roughness, transport rate …) has been considerably extended to cover typical values characterizing fluvial applications and not only coastal settings. Second, we show that the optimal value of Morfac depends greatly on the specific mathematical formulation of the flow model and on the flow regime. [less ▲]

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See detailLanduse change and future flood risk: an integrated and multi-scale approach
Dewals, Benjamin ULg; Bruwier, Martin ULg; Mohamed El Saeid Mustafa, Ahmed ULg et al

in E-proceedings of the 36th IAHR World Congress (2015, June)

The goal of this research is a better understanding of the complex interactions between landuse change and future flood risk. Landuse change is mainly driven by population growth and socio-economic ... [more ▼]

The goal of this research is a better understanding of the complex interactions between landuse change and future flood risk. Landuse change is mainly driven by population growth and socio-economic factors. It affects future flood risk by altering catchment hydrology and vulnerability in the floodplains, as well as through the feedback effect that changes in flood hazard may have on landuse evolution. The research is based on a chain of modelling tools, including: stochastic landuse change modelling, traffic modelling as well as Land-Use and Transport Interactions models, continuous hydrological modelling and efficient hydraulic modelling of floodplains inundation. The coupling of these modelling tools will allow assessing direct and indirect impacts of land use change on future flood risk, while considering the uncertainties related to each of these processes and their combinations at a 2100 time horizon. [less ▲]

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See detailDoes the soil’s effective hydraulic conductivity adapt in order to obey the Maximum Entropy Production principle? A lab experiment
Westhoff, Martijn ULg; Zehe, Erwin; Erpicum, Sébastien ULg et al

Conference (2015, April)

The Maximum Entropy Production (MEP) principle is a conjecture assuming that a medium is organized in such a way that maximum power is subtracted from a gradient driving a flux (with power being a flux ... [more ▼]

The Maximum Entropy Production (MEP) principle is a conjecture assuming that a medium is organized in such a way that maximum power is subtracted from a gradient driving a flux (with power being a flux times its driving gradient). This maximum power is also known as the Carnot limit. It has already been shown that the atmosphere operates close to this Carnot limit when it comes to heat transport from the Equator to the poles, or vertically, from the surface to the atmospheric boundary layer. To reach this state close to the Carnot limit, the effective thermal conductivity of the atmosphere is adapted by the creation of convection cells (e.g. wind). The aim of this study is to test if the soil’s effective hydraulic conductivity also adapts itself in such a way that it operates close to the Carnot limit. The big difference between atmosphere and soil is the way of adaptation of its resistance. The soil’s hydraulic conductivity is either changed by weathering processes, which is a very slow process, or by creation of preferential flow paths. In this study the latter process is simulated in a lab experiment, where we focus on the preferential flow paths created by piping. Piping is the process of backwards erosion of sand particles subject to a large pressure gradient. Since this is a relatively fast process, it is suitable for being tested in the lab. In the lab setup a horizontal sand bed connects two reservoirs that both drain freely at a level high enough to keep the sand bed always saturated. By adding water to only one reservoir, a horizontal pressure gradient is maintained. If the flow resistance is small, a large gradient develops, leading to the effect of piping. When pipes are being formed, the effective flow resistance decreases; the flow through the sand bed increases and the pressure gradient decreases. At a certain point, the flow velocity is small enough to stop the pipes from growing any further. In this steady state, the effective flow resistance of the sand bed will be compared with the theoretical optimal flow resistance obtained with the MEP principle. For this study, different magnitudes of the forcing will be tested, while also the effect of dry spells will be explored. [less ▲]

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See detailFormulations of the bed slope term in the shallow water equations: implication for energy balance
Bruwier, Martin ULg; Archambeau, Pierre ULg; Erpicum, Sébastien ULg et al

in Workshop on Advances in Numerical Modelling of Hydrodynamics (2015, March 24)

For an incompressible, isothermal, continuous and frictionless flow, the exact resolution of the equation of conservation of mechanical energy is equivalent to the exact resolution of the equation of ... [more ▼]

For an incompressible, isothermal, continuous and frictionless flow, the exact resolution of the equation of conservation of mechanical energy is equivalent to the exact resolution of the equation of momentum conservation. However, the discrete solution of the equation of momentum conservation does not verify the equation of energy conservation. This is particularly the case as a result of the presence of a non-conservative bed slope term in the equation of momentum conservation. In this research, the influence of (i) the formulation and (ii) the discretization scheme of the non-conservative bed slope term on the energy conservation is analysed in the case of a 1D horizontal and frictionless channel with a topographic step. The results for two different formulations of the bed slope term are firstly compared: the standard formulation of the bed slope source term and a divergence formulation of the bed slope term. Then, different discretization schemes of the divergence formulation of the bed slope term are analyzed to determine the one minimizing the numerical variation of energy. [less ▲]

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See detailAssessing the operation rules of a reservoir system based on a detailed modelling chain
Bruwier, Martin ULg; Erpicum, Sébastien ULg; Pirotton, Michel ULg et al

in Natural Hazards & Earth System Sciences (2015), 15

The current operation rules of two muti-purpose reservoirs are analysed based on an integrated model including a hydrological model, a hydraulic model, a model of the reservoir system and a flood damage ... [more ▼]

The current operation rules of two muti-purpose reservoirs are analysed based on an integrated model including a hydrological model, a hydraulic model, a model of the reservoir system and a flood damage model. Five performance indicators have been defined, reflecting the ability to provide drinking water, to control floods, to produce hydropower and to reduce low-flow conditions. Then, impacts of two climate change scenarios are assessed and enhanced operation rules are proposed for mitigation. [less ▲]

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See detailStochastic modelling of reservoir sedimentation in a semi-arid watershed
Adam, Nicolas; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Water Resources Management (2015), 29(3), 785-800

Sedimentation in large reservoirs is a major concern in semi-arid regions characterized by severe seasonal water scarcity. As a contribution to improved sediment management, this study analyses the real ... [more ▼]

Sedimentation in large reservoirs is a major concern in semi-arid regions characterized by severe seasonal water scarcity. As a contribution to improved sediment management, this study analyses the real case of the reservoir of Sidi Yacoub in the north of Algeria. First, a dynamic model of the reservoir was set up and used to estimate past water and sediment inflows (period 1990-2010) based on data recorded by the dam operator and measurements at a gauging station located downstream of the reservoir. Second, in a stochastic framework using the statistical characteristics of inflow and outflow discharges, a projection of future sedimentation was performed until 2030, assuming stationarity of the statistical distributions. Third, the model was used to investigate the influence of possible climate change and to quantify the positive effects of soil conservation measures upstream. [less ▲]

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See detailErosion and sedimentation issues in a hydropower project: assessing impacts and opportunities
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Schüttrumpf, Holger (Ed.) Offene Gewässer: Strahlwirkung, Fischaufstieg, Fischabstieg, Sedimente, Schadstoffe (2015, January 09)

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See detailCan the collapse of a fly ash heap develop into an air-fluidized flow? - Reanalysis of the Jupille accident (1961)
Stilmant, Frédéric ULg; Pirotton, Michel ULg; Archambeau, Pierre ULg et al

in Geomorphology (2015), 228

A fly ash heap collapse occurred in Jupille (Liege, Belgium) in 1961. The subsequent flow of fly ash reached a surprisingly long runout and had catastrophic consequences. Its unprecedented degree of ... [more ▼]

A fly ash heap collapse occurred in Jupille (Liege, Belgium) in 1961. The subsequent flow of fly ash reached a surprisingly long runout and had catastrophic consequences. Its unprecedented degree of fluidization attracted scientific attention. As drillings and direct observations revealed no water-saturated zone at the base of the deposits, scientists assumed an air-fluidization mechanism, which appeared consistent with the properties of the material. In this paper, the air-fluidization assumption is tested based on two-dimensional numerical simulations. The numerical model has been developed so as to focus on the most prominent processes governing the flow, with parameters constrained by their physical interpretation. Results are compared to accurate field observations and are presented for different stages in the model enhancement, so as to provide a base for a discussion of the relative influence of pore pressure dissipation and pore pressure generation. These results show that the apparently high diffusion coefficient that characterizes the dissipation of air pore pressures is in fact sufficiently low for an important degree of fluidization to be maintained during a flow of hundreds of meters. [less ▲]

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See detailClosure to “Parapet Wall Effect on Piano Key Weir Efficiency”
Erpicum, Sébastien ULg; Machiels, Olivier; Pirotton, Michel ULg et al

in Journal of Irrigation & Drainage Engineering (2015), 141(1), 07014033

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See detailPressure and velocity on an ogee spillway crest operating at high head ratio: experimental measurements and instrumentation
Peltier, Yann ULg; Dewals, Benjamin ULg; Archambeau, Pierre ULg et al

in Carvalho, Rita; Pagliara, Stefano (Eds.) 2nd International workshop on hydraulic structures: data validation (2015)

This paper aims at validating pressure and velocity measurements conducted in two physical scale models of an ogee spillway crest operating at heads largely greater than the design head. The design head ... [more ▼]

This paper aims at validating pressure and velocity measurements conducted in two physical scale models of an ogee spillway crest operating at heads largely greater than the design head. The design head of the second model is 50% smaller than the one of the first model. No piles effect or air entrance is considered in the study. The velocity field is measured by Large Scale Particle Image Velocimetry. The relative pressure along the spillway crest is measured using pressure sensors. Comparisons of measured velocities between both spillways indicate low scale effects, the scaled-profiles collapsing in most parts of the flow. By contrast, measurements of relative pressure along the spillway crest differ for large heads. A theoretical velocity profile based on potential flow theory and expressed in a curvilinear reference frame is then fitted to the velocity measurements, considered as reference, for extrapolating the velocity at the spillway crest. Comparing the extrapolated velocity at the spillway crest and the velocity expressed from the relative pressure finally emphasizes that bottom pressure amplitudes are overestimated for the large spillway, while an averaging effect might operate for the pressure measurements on the small spillway. [less ▲]

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See detailA modular approach dedicated to dam-break and dam-breaching modelling
Stilmant, Frédéric ULg; Dewals, Benjamin ULg; Erpicum, Sébastien ULg et al

in Advances in Hydroinformatics (2015)

The paper presents an integrated tool for dam-break hazard modelling. It is based on a two-dimensional, depth-averaged hydraulic model that uses a conservative and shock-capturing finite volume scheme on ... [more ▼]

The paper presents an integrated tool for dam-break hazard modelling. It is based on a two-dimensional, depth-averaged hydraulic model that uses a conservative and shock-capturing finite volume scheme on a Cartesian grid. The hydraulic model is designed so that different zones within the computation domain can be modelled with different spatial resolutions and/or different model enhancements (e.g. pressurised flows, sediment transport, etc.). The two-dimensional model can be coupled with lumped models that compute the water stage in reservoirs and the outflow discharge through hydraulic structures, in case of normal operating, failure of a valve or breaching processes. These features make hydraulic modelling versatile and computationally efficient. They enable the definition of different failure scenarios, which is of prominent importance given the uncertainty of such a phenomenon. If several hydraulic structures are involved, the procedure takes the behaviour of each structure into account. The sensitivity of the results with respect to the interactions between the flow and the terrain (roughness coefficient, collapse of buildings, breaching process) can be analysed. The results of the hydraulic model are handled thanks to a graphical user interface that provides one-, two- and three-dimensional views and animations of the unsteady flow-field and enables the understanding and verification of the results. Danger maps are generated based on the results of one or more ‘worst-case’ scenarios. In case of a complete risk analysis, the danger maps are combined with data on the exposure and vulnerability of elements at risk for the computation of the corresponding damage. [less ▲]

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See detailCan meandering flows in shallow rectangular reservoir be modelled with the 2D shallow water equations?
Peltier, Yann ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Journal of Hydraulic Engineering (2015)

In this article, the ability of the 2D shallow water equations to model meandering flows in shallow rectangular reservoirs is discussed. Four meandering flows, of various shallowness, were modelled using ... [more ▼]

In this article, the ability of the 2D shallow water equations to model meandering flows in shallow rectangular reservoirs is discussed. Four meandering flows, of various shallowness, were modelled using the academic flow model WOLF 2D, which includes a depth-averaged k- model accounting for the horizontal and vertical turbulent length-scales. The bottom friction was modelled with the Colebrook-White formula and different roughness heights were considered. A Proper Orthogonal Decomposition (POD) was applied to the simulation results to extract the behaviour of the main structures responsible for the meandering flow. The same POD analysis was also performed for the reference experimental flow fields, obtained by Large-Scale Particle Image Velocimetry. The first two POD modes obtained from the numerical simulations assuming a smooth bottom are in good agreement with the experimental modes in terms of energy, as well as temporal and spatial variations, whatever the shallowness. In contrast, the remaining simulated modes are not well rendered. The effect of an increased roughness height in the simulations is finally discussed. It leads to an improved reproduction of the first two modes and of the following modes, except when significant viscous effects govern in the flow. [less ▲]

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