Some selected publications by Benjamin Dewals
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See detailDoes the Budyko curve reflect a maximum power state of hydrological systems? A backward analysis
Westhoff, Martijn ULg; Zehe, Erwin; Archambeau, Pierre ULg et al

in Hydrology and Earth System Sciences (2016), 20

Almost all catchments plot within a small envelope around the Budyko curve. This apparent behaviour suggests that organizing principles may play a role in the evolution of catchments. In this paper we ... [more ▼]

Almost all catchments plot within a small envelope around the Budyko curve. This apparent behaviour suggests that organizing principles may play a role in the evolution of catchments. In this paper we applied the thermodynamic principle of maximum power as the organizing principle. In a top-down approach we derived mathematical formulations of the relation between relative wetness and gradients driving runoff and evaporation for a simple one-box model. We did this in an inverse manner such that when the conductances are optimized with the maximum power principle, the steady state behaviour of the model leads exactly to a point on the asymptotes of the Budyko curve. Subsequently, we added dynamics in forcing and actual evaporations, causing the Budyko curve to deviate from the asymptotes. Despite the simplicity of the model, catchment observations compare reasonably well with the Budyko curves subject to observed dynamics in rainfall and actual evaporation. Thus by constraining the model with the asymptotes of the Budyko curve we were able to derive more realistic values of the aridity and evaporation index without any calibration parameter. Future work should focus on better representing the boundary conditions of real catchments and eventually adding more complexity to the model. [less ▲]

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See detailEnergy conservation properties of Ritter solution for idealized dam break flow
Dewals, Benjamin ULg; Bruwier, Martin ULg; Erpicum, Sébastien ULg et al

in Journal of Hydraulic Research (2016), 54(5), 581-585

We examine different aspects of energy conservation in the case of the analytical solution of Ritter for idealized dam break flow in a horizontal frictionless and dry channel. We detail the application of ... [more ▼]

We examine different aspects of energy conservation in the case of the analytical solution of Ritter for idealized dam break flow in a horizontal frictionless and dry channel. We detail the application of the unsteady Bernoulli equation in this case and highlight that the inertial effects cancel out when averaged over the whole flow region. We also show that the potential and kinetic contributions to the total mechanical energy in the flow region have a distinct and constant relative importance: potential energy accounts for 60 %, and kinetic energy for 40 % of the total mechanical energy. These properties of Ritter solution are rarely emphasized while they may be of practical relevance, particularly for the verification of numerical schemes with respect to their ability to ensure energy conservation. [less ▲]

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See detailDiscretization of the divergence formulation of the bed slope term in the shallow-water equations and consequences in terms of energy balance
Bruwier, Martin ULg; Archambeau, Pierre ULg; Erpicum, Sébastien ULg et al

in Applied Mathematical Modelling (2016)

In this research, the influence on energy balance of the discretization scheme of the divergence formulation of the bed slope term in the shallow-water equations is analysed theoretically (for a single ... [more ▼]

In this research, the influence on energy balance of the discretization scheme of the divergence formulation of the bed slope term in the shallow-water equations is analysed theoretically (for a single topographic step) and based on two numerical tests. Different values of the main parameter controlling the discretization scheme of the divergence formulation are analysed to identify the formulation which minimizes the energy variation resulting from the discretization. For a wide range of ambient Froude numbers and relative step heights, the theoretical value of the control parameter minimizing the energy variation falls within a very narrow range, which can reasonably be approximated by a single “optimal” value. This is a result of high practical relevance for the design of accurate numerical schemes, as confirmed by the results of the numerical tests. [less ▲]

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See detailScale effects in physical piano key weirs models
Erpicum, Sébastien ULg; Tullis, Blake; Lodomez, Maurine ULg et al

in Journal of Hydraulic Research (2016)

With inertia and gravity representing the dominant forces for most open channel flow applications (e.g. weir flow), Froude similitude is commonly used for scaling hydraulic performance data from the model ... [more ▼]

With inertia and gravity representing the dominant forces for most open channel flow applications (e.g. weir flow), Froude similitude is commonly used for scaling hydraulic performance data from the model to prototype structures. With weir flow, as the upstream head decreases, however, the relevance of surface tension and viscosity forces can increase to the point when the model and prototype similitude is not fully achieved through Froude scaling. Such discrepancies are referred as size-scale effects, and among other things, can result in variations in the head–discharge relationship, nappe trajectory, and air entrainment. Published criteria for avoiding significant size-scale effects for free flow over linear weirs have suggested that minimal heads of ∼0.02 to 0.07m be respected, independently of the model size. In this study, the size-scale effect, minimum upstream head, and Weber number limits are investigated for four piano key weirs with geometric model scales of 1:1, 1:7, 1:15, and 1:25. [less ▲]

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See detailHydrodynamics of long-duration urban floods: experiments and numerical modelling
Arrault; Finaud-Guyot, Pascal; Archambeau, Pierre ULg et al

in Natural Hazards & Earth System Sciences (2016), 16

Flood risk in urbanized areas raises increasing concerns as a result of demographic and climate changes. Hydraulic modelling is a key component of urban flood risk analysis. Yet, detailed validation data ... [more ▼]

Flood risk in urbanized areas raises increasing concerns as a result of demographic and climate changes. Hydraulic modelling is a key component of urban flood risk analysis. Yet, detailed validation data are still lacking for comprehensively validating hydraulic modelling of inundation flow in urbanized floodplains. ln this study, we present an experimental model of inundation flow in a typical European urban district and we compare the experimental observations with predictions by a shallow-water numerical model. The setup is 5 ll\X Sm and involves seven streets along each direction, leading to 49 intersections. Different inflow discharges and flow partitions were tested. The performance ofthe numerical model is assessed and the upscaling ofthe experimental observations to the field is discussed. [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 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 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 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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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 detailPrediction of mean and turbulent kinetic energy in rectangular shallow reservoirs
Camnasio, Erica; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Engineering Applications of Computational Fluid Mechanics (2014), 8(4),

Shallow rectangular reservoirs are common structures in urban hydraulics and river engineering. Despite their simple geometry, complex symmetric and asymmetric flow fields develop in such reservoirs ... [more ▼]

Shallow rectangular reservoirs are common structures in urban hydraulics and river engineering. Despite their simple geometry, complex symmetric and asymmetric flow fields develop in such reservoirs, depending on their expansion ratio and length-to-width ratio. The original contribution of this study is the analysis of the kinetic energy content of the mean flow, based on UVP velocity measurements carried throughout the reservoir in eleven different geometric configurations. A new relationship is derived between the specific mean kinetic energy and the reservoir shape factor. For most considered geometric configurations, leading to four different flow patterns, the experimentally observed flow fields and mean kinetic energy contents are successfully reproduced by an operational numerical model based on the depth-averaged flow equations and a two-length-scale k-e turbulence closure. The analysis also highlights the better performance of this depth-averaged k-e model compared to an algebraic turbulence model. Finally, the turbulent kinetic energy in the reservoir is derived from the experimental measurements and the corresponding numerical predictions based on the k-e model agree satisfactorily in the main jet but not in the recirculation zones. [less ▲]

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See detailMeandering jets in shallow rectangular reservoirs: POD analysis and identification of coherent structures
Peltier, Yann ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Experiments in Fluids (2014), 55

The effect of the shallowness on meandering jets in a shallow rectangular reservoir is investigated. Four meandering flows were investigated in an experimental shallow rectangular reservoir. Their ... [more ▼]

The effect of the shallowness on meandering jets in a shallow rectangular reservoir is investigated. Four meandering flows were investigated in an experimental shallow rectangular reservoir. Their boundary conditions were chosen to cover a large range of friction numbers (defined with the sudden expansion width). Due to the unsteady characteristics of the flows, a Proper Orthogonal Decomposition of the fluctu-ating part of the surface velocity fields measured using LSPIV was used for discriminating the flow struc-tures responsible for the meandering of the jet. Less than 1 % of the calculated POD modes significantly contribute to the meandering of the jet and two types of instability are in competition in such a flow con-figuration. The sinuous mode is the dominant mode in the flow and it induces the meandering of the flow, while the varicose mode is a source of local mixing and weakly participates to the flow. The fluctuating velocity fields were then reconstructed using the POD modes corresponding to 80% of the total mean fluctuating kinetic energy and the coherent structures were identified using the residual vorticity, their centres being localised using a topology algorithm. The trajectories of the structures centres emphasize that at high friction number the coherent structures are small and laterally paired in the near, middle and far fields of the jet, while with decreasing friction number the structures merge into large horizontal vortices in the far-field of the jet, their trajectories showing more variability in space and time. The analysis of the stability regime finally reveals that the sinuous mode is convectively unstable and may become absolutely unstable at the end of the reservoir when the friction number is small. [less ▲]

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See detailExperimental investigation of meandering jets in shallow reservoirs
Peltier, Yann ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Environmental Fluid Mechanics (2014)

Meandering flows in rectangular shallow reservoirs were experimentally investi- gated. The characteristic frequency, the longitudinal wave length and the mean lateral exten- sion of the meandering jet ... [more ▼]

Meandering flows in rectangular shallow reservoirs were experimentally investi- gated. The characteristic frequency, the longitudinal wave length and the mean lateral exten- sion of the meandering jet were extracted from the first paired modes, obtained by a proper orthogonal decomposition of the surface velocity field measured by large scale PIV. The depth-normalised characteristic lengths and the Strouhal number were then compared to the main dimensionless numbers characterizing the experiments: Froude number, friction num- ber and reservoir shape factor. The normalised wave length and mean lateral extension of the meandering jet are neither correlated with the Froude number nor with the reservoir shape factor; but a clear relationship is found with the friction number. Similarly, the Strouhal num- ber is found proportional to a negative power of the friction number. In contrast, the Froude number and the reservoir shape factor enable to predict the occurrence of a meandering flow pattern: meandering jets occur for Froude number greater than 0.21 and for a shape factor smaller than 6.2. [less ▲]

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See detailHybride Modellierung deichbruchinduzierter Strömungen
Roger, Sebastian; Dewals, Benjamin ULg; Schüttrumpf, Holger

in Heimerl, S.; Meyer, H. (Eds.) Vorsorgender und nachsorgender Hochwasserschutz (2014)

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See detailDiscussion of "Two-dimensional depth-averaged finite volume model for unsteady turbulent flows"
Erpicum, Sébastien ULg; Pirotton, Michel ULg; Archambeau, Pierre ULg et al

in Journal of Hydraulic Research (2014), 52(1), 148-150

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See detailExperimental parametric study and design of Piano Key Weirs
Machiels, Olivier; Pirotton, Michel ULg; Archambeau, Pierre ULg et al

in Journal of Hydraulic Research (2014), 52(3), 326-335

Piano Key Weirs are an effective solution for dam rehabilitation as well as new dam projects with a high level of hydraulic constraints. In order to improve the efficiency of their design, an experimental ... [more ▼]

Piano Key Weirs are an effective solution for dam rehabilitation as well as new dam projects with a high level of hydraulic constraints. In order to improve the efficiency of their design, an experimental study of the influence of the main geometric parameters has been performed. Thirty one configurations were tested for a wide range of discharges. The results of the study show the influence of the weir height, the keys widths and the overhangs lengths on the discharge capacity and flow characteristics. Based on hydraulic considerations, optimum values of the main geometric ratios are provided. An analytical formulation is developed to predict the discharge capacity of the weir as a function of its geometry. It shows an accuracy of 10% compared to the experimental results of this study and from other sources. [less ▲]

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See detailLocal head-loss coefficient at the rectangular transition from a free-surface channel to a conduit
Van Nam, Nguyen; Archambeau, Pierre ULg; Dewals, Benjamin ULg et al

in Journal of Hydraulic Engineering (2013), 139(12), 1318-1323

Experimental tests have been performed to observe and determine, in stationary flow conditions, the local head loss at the transition from a free surface channel to a conduit. These investigations ... [more ▼]

Experimental tests have been performed to observe and determine, in stationary flow conditions, the local head loss at the transition from a free surface channel to a conduit. These investigations considered a wide range of discharge and varied dimensions and positions of a rectangular cross section conduit connected to the downstream extremity of a rectangular free surface channel. From the head loss evaluation results, simple analytical expressions to predict the local head loss coefficient value at the rectangular transition from a channel to a conduit are proposed and validated. [less ▲]

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See detailContribution of land use changes to future flood damage along the river Meuse in the Walloon region
Beckers, Arnaud ULg; Dewals, Benjamin ULg; Erpicum, Sébastien ULg et al

in Natural Hazards & Earth System Sciences (2013), 13

Managing flood risk in Europe is a critical issue because climate change is expected to increase flood hazard in many european countries. Beside climate change, land use evolution is also a key factor ... [more ▼]

Managing flood risk in Europe is a critical issue because climate change is expected to increase flood hazard in many european countries. Beside climate change, land use evolution is also a key factor influencing future flood risk. The core contribution of this paper is a new methodology to model residential land use evolution. Based on two climate scenarios (“dry” and “wet”), the method is applied to study the evolution of flood damage by 2100 along the river Meuse. Nine urbanization scenarios were developed: three of them assume a “current trend” land use evolution, leading to a significant urban sprawl, while six others assume a dense urban development, characterized by a higher density and a higher diversity of urban functions in the urbanized areas. Using damage curves, the damage estimation was performed by combining inundation maps for the present and future 100 yr flood with present and future land use maps and specific prices. According to the dry scenario, the flood discharge is expected not to increase. In this case, land use changes increase flood damages by 1–40 %, to EUR 334–462 million in 2100. In the wet scenario, the relative increase in flood damage is 540–630 %, corresponding to total damages of EUR 2.1–2.4 billion. In this extreme scenario, the influence of climate on the overall damage is 3–8 times higher than the effect of land use change. However, for seven municipalities along the river Meuse, these two factors have a comparable influence. Consequently, in the “wet” scenario and at the level of the whole Meuse valley in the Walloon region, careful spatial planning would reduce the increase in flood damage by no more than 11–23 %; but, at the level of several municipalities, more sustainable spatial planning would reduce future flood damage to a much greater degree. [less ▲]

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