Some selected publications by Benjamin Dewals
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See detailMaximum energy dissipation to explain velocity fields in shallow reservoirs
Westhoff, Martijn; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

in Journal of Hydraulic Research (in press)

Shallow reservoirs are often used as sediment traps or storage basins, in which sedimentation depends on the flow pattern: Short rectangular reservoirs reveal a straight jet from inlet to outlet with on ... [more ▼]

Shallow reservoirs are often used as sediment traps or storage basins, in which sedimentation depends on the flow pattern: Short rectangular reservoirs reveal a straight jet from inlet to outlet with on both sides identical recirculation zones. In longer reservoirs, the main jet reattaches to the side of the reservoir leading to a small and a large recirculation zone. Previous studies found an empirical geometric relation describing the switch between these two flow patterns. In this study, we demonstrate, with a simple analytical model, that this switch coincides with a maximization of energy dissipation in the shear layer between the main jet and recirculation zones: Short reservoirs dissipate more energy when the flow pattern is symmetric, while longer reservoirs dissipate more energy with an asymmetric pattern. This approach enables to predict the flow patterns without detailed knowledge of small scale processes, potentially useful in the early phase of reservoir design. [less ▲]

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See detailFlow field in shallow reservoir with varying inlet and outlet position
Ferrara, Velia; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

in Journal of Hydraulic Research (in press)

Shallow reservoirs are used for multiple purposes, such as storm water retention and trapping of sediments. Reliable predictions of the flow fields are necessary to inform the design and operation of ... [more ▼]

Shallow reservoirs are used for multiple purposes, such as storm water retention and trapping of sediments. Reliable predictions of the flow fields are necessary to inform the design and operation of these structures. Using numerical simulations, we performed a systematic analysis of the influence of the location of the inlet and outlet on the flow fields developing in rectangular shallow reservoirs of various sizes. Depending on the relative location of the inlet and outlet with respect to the reservoir centreline, contrasting flow patterns are obtained, involving either no flow reattachment, or a jet reattached on either of the reservoir sidewalls. The results reveal also the occurrence of bi-stable flow configurations, i.e. different steady state flow fields are reached depending on the flow history. This is of high relevance for the design of shallow reservoirs as such configurations should certainly be avoided to achieve a robust hydraulic sizing of the reservoir. [less ▲]

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

in Journal of Hydro-Environment Research (in press)

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 pier effect or air venting is considered in the study. The velocity field is measured by Bubbles Image Velocimetry. The relative pressure along the spillway crest is measured using pressure sensors. Comparison of measured velocities between both spillways indicates 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 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 calculated from the relative pressure considering a potential flow finally emphasizes that bottom pressure amplitudes seem overestimated for the larger spillway, while an averaging effect might operate for the pressure measurements on the smaller spillway. [less ▲]

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See detailHydraulic determination of dam releases to generate warning waves in a mountain stream: performance of an analytical kinematic wave model
Stilmant, Frédéric; Pirotton, Michel ULiege; Archambeau, Pierre ULiege et al

in Journal of Hydraulic Engineering (in press)

In this case study, we study the generation of warning waves with prescribed characteristics in a mountain stream. We determine which dam release will generate the desired warning wave. We solve this ... [more ▼]

In this case study, we study the generation of warning waves with prescribed characteristics in a mountain stream. We determine which dam release will generate the desired warning wave. We solve this inverse problem following a two-model approach. An analytical kinematic model is used for a preliminary design of the dam release and a detailed two-dimensional (2D) fully dynamic model is used to converge to the final solution. Although the presented case study is far from an idealized academic case, the analytical model performs well and, beyond its role for preliminary design, turns out to be of prime interest for both understanding and discussing the results of the detailed 2D model. The complex interactions between the release hydrograph, the geometry of the river and the friction formula are brought to light by the analytical model, which highlights the complementarity of both models and the usefulness of such a two-model approach. [less ▲]

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See detailEditorial
Dewals, Benjamin ULiege

in Proceedings of ICE : Water Management (2017), 170(WM3), 109-110

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See detailOvertopping induced failure of non-cohesive, homogenous fluvial dikes
Rifai, Ismail ULiege; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

in Water Resources Research (2017), 53(4), 33733386

Accurate predictions of breach characteristics are necessary to reliably estimate the outflow hydrograph and the resulting inundation close to fluvial dikes. Laboratory experiments on the breaching of ... [more ▼]

Accurate predictions of breach characteristics are necessary to reliably estimate the outflow hydrograph and the resulting inundation close to fluvial dikes. Laboratory experiments on the breaching of sand-filled fluvial dikes were performed, considering a flow parallel to the dike axis. The breach was triggered by overtopping of the dike crest. A detailed monitoring of the transient evolution of the breach geometry was conducted, providing key insights into the gradual and complex processes involved in fluvial dike failure. The breach develops in two phases: (1) the breach becomes gradually wider and deeper eroding on the downstream side along the main channel, and (2) breach widening controlled by side slope failures, continuing in the downstream direction only. Increasing the inflow discharge in the main channel, the breach formation time decreases significantly and the erosion occurs preferentially on the downstream side. The downstream boundary condition has a strong influence on the breach geometry and the resulting outflow hydrograph. [less ▲]

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See detailComputing flooding of crossroads with obstacles using a 2D numerical model (Discussion)
Bruwier, Martin ULiege; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

in Journal of Hydraulic Research (2017), 55(5), 737-741

Based on an operational 2D shallow-water model, the Authors computed subcritical dividing flow at a three-branch crossroad, considering obstacles located at different positions. The numerical predictions ... [more ▼]

Based on an operational 2D shallow-water model, the Authors computed subcritical dividing flow at a three-branch crossroad, considering obstacles located at different positions. The numerical predictions were compared to observations from Mignot et al. (2013). Two issues are addressed here, related respectively to the efficiency and relevance of the turbulence model, and to the representation of the obstacles in operational flood models. [less ▲]

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See detailShallow-water models with anisotropic porosity and merging for flood modelling on Cartesian grids
Bruwier, Martin ULiege; Archambeau, Pierre ULiege; Erpicum, Sébastien ULiege et al

in Journal of Hydrology (2017)

Shallow-water models with porosity are used to compute floods at a relatively coarse resolution while accounting indirectly for detailed topographic data through porosity parameters. In many practical ... [more ▼]

Shallow-water models with porosity are used to compute floods at a relatively coarse resolution while accounting indirectly for detailed topographic data through porosity parameters. In many practical applications, these models enable a significant reduction of the computational time while maintaining an acceptable level of accuracy. In this paper, we improve the use of porosity models on Cartesian grids by three original contributions. First, a merging technique is used to handle cells with low porosity values which tend otherwise to seriously hamper computational efficiency. Next, we show that the optimal method for the determination of the porosity parameters depends on the modelling scale, i.e. the grid resolution compared to the characteristic size of obstacles and flow ways. Finally, we investigate the potential benefit of using a different porosity parameter in each term of the shallow-water equations. Five test cases, two of them being original, are used to validate the model and assess each contribution. In particular, we obtained speedup values between 10 and 100 while the errors on water depths remain around few percent. [less ▲]

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See detailDiscussion of: Laboratory Study on 3D Flow Structures Induced by Zero-Height Side Weir and Implications for 1D Modeling
Rifai, Ismail ULiege; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

in Journal of Hydraulic Engineering (2017), 143(3), 07016010

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See detailLooking beyond general metrics for model comparison – lessons from an international model intercomparison study
de Boer-Euser, Tanja; Bouaziz, Laurène; De Niel, Jan et al

in Hydrology and Earth System Sciences (2017), 21

International collaboration between research institutes and universities is a promising way to reach consensus on hydrological model development. Although comparative studies are very valuable for ... [more ▼]

International collaboration between research institutes and universities is a promising way to reach consensus on hydrological model development. Although comparative studies are very valuable for international cooperation, they do often not lead to very clear new insights regarding the relevance of the modelled processes. We hypothesise that this is partly caused by model complexity and the comparison methods used, which focus too much on a good overall performance instead of focusing on specific events. In this study, we use an approach that focuses on the evaluation of specific events and characteristics. Eight international research groups calibrated their hourly model on the Ourthe catchment in Belgium and carried out a validation in time for the Ourthe catchment and a validation in space for nested and neighbouring catchments. The same protocol was followed for each model and an ensemble of best performing parameter sets was selected. Although the models showed similar performances based on general metrics (i.e. Nash–Sutcliffe Efficiency), clear differences could be observed for specific events. The results illustrate the relevance of including a very quick flow reservoir preceding the root zone storage to model peaks during low flows and including a slow reservoir in parallel with the fast reservoir to model the recession for the Ourthe catchment. This intercomparison enhanced the understanding of the hydrological functioning of the catchment and, above all, helped to evaluate each model against a set of alternative models. [less ▲]

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See detailDoes the Budyko curve reflect a maximum power state of hydrological systems? A backward analysis
Westhoff, Martijn ULiege; Zehe, Erwin; Archambeau, Pierre ULiege 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 detailDiscretization of the divergence formulation of the bed slope term in the shallow-water equations and consequences in terms of energy balance
Bruwier, Martin ULiege; Archambeau, Pierre ULiege; Erpicum, Sébastien ULiege et al

in Applied Mathematical Modelling (2016), 40(17-18), 75327544

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 detailEnergy conservation properties of Ritter solution for idealized dam break flow
Dewals, Benjamin ULiege; Bruwier, Martin ULiege; Erpicum, Sébastien ULiege 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 detailScale effects in physical piano key weirs models
Erpicum, Sébastien ULiege; Tullis, Blake; Lodomez, Maurine ULiege 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 ULiege 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 detailDevelopment trajectory of an integrated framework for the mitigation of future flood risk: results from the FloodLand project
Saadi, Ismaïl ULiege; Bruwier, Martin ULiege; El Saeid Mustafa, Ahmed Mohamed ULiege et al

in Transportation Letters: The International Journal of Transportation Research (2016)

In this paper, the development trajectory of an integrated framework for the mitigation of future flood risk of the Ourthe river basin in Belgium is discussed. The paper contributes to the state-of-the ... [more ▼]

In this paper, the development trajectory of an integrated framework for the mitigation of future flood risk of the Ourthe river basin in Belgium is discussed. The paper contributes to the state-of-the-art by presenting an integrated multidisciplinary framework capable of making long-term projections (time horizon 2050 and 2100) with the objective of mitigating future flood risk by proposing alternative land-use scenarios. It bridges numerous different fields, including urban planning, transport engineering, hydrology, geology, environmental engineering, and economics. The overall design and validation results of the different sub-modules of the framework are presented, and ongoing and future enhancements are highlighted. [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 ULiege; Dewals, Benjamin ULiege 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 ULiege; Erpicum, Sébastien ULiege; Pirotton, Michel ULiege 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 ULiege; Archambeau, Pierre ULiege 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 ULiege; Pirotton, Michel ULiege; Archambeau, Pierre ULiege 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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