References of "Dewals, Benjamin"
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See detailApparent cohesion effects on overtopping-induced fluvial dike breaching
Rifai, Ismail; El Kadi Abderrezzak, Kamal; Hager, Willi et al

in Journal of Hydraulic Research (in press)

Flow overtopping can lead to the initiation of breaching and failure of fluvial dikes, causing severe inundations and damage in the protected areas. For flood risk management and prevention, the accurate ... [more ▼]

Flow overtopping can lead to the initiation of breaching and failure of fluvial dikes, causing severe inundations and damage in the protected areas. For flood risk management and prevention, the accurate estimate of flow discharge across the fluvial dike breach is paramount, requiring the precise understanding of the breach expansion. Laboratory experiments were conducted to analyse the effects of fine sand, inducing apparent cohesion in the dike material, on the breach development and outflow. Tests were conducted under controlled inflow discharge and dike material composed of either homogeneous non-cohesive coarse sand or heterogeneous fine sand/coarse sand mixtures. Based on the non-intrusive Laser Profilometry technique, high temporal and spatial resolution of the three-dimensional breach geometry evolution was measured, indicating a small effect of the fine material on the overall breach dynamics. A detailed analysis revealed, however, that fine sand induces less frequent slope collapses but larger sliding/failing lumps compared to homogenous non-cohesive coarse sand. [less ▲]

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See detailExperimental test bench for performance-assessment of large submersible and dry-action pumps used in waterways
Hardy, Joris ULiege; Erpicum, Sébastien ULiege; Pirotton, Michel ULiege et al

Conference (2021, April 13)

Pumping in waterways, particularly in artificial canals, is energy-intensive, costly and may be responsible for the emission of large quantities of CO2. Innovative pumping technologies have the potential ... [more ▼]

Pumping in waterways, particularly in artificial canals, is energy-intensive, costly and may be responsible for the emission of large quantities of CO2. Innovative pumping technologies have the potential to reduce energy consumption; but their performance needs to be thoroughly as-sessed. This communication presents the design, sizing and construction of an experimental test bench for evaluating the performance of large submersible and dry-action centrifugal pumps typically used in waterways. It enables testing prototype-scale pumps and was designed in close collaboration with stakeholders such as canal operators. This experimental facility is challeng-ing on many aspects given its size, as well as requirements for power supply and for measure-ment of system efficiency. [less ▲]

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See detailEnvironmental Inequalities in Flood Exposure: A Matter of Scale
Poussard, Clémence; Dewals, Benjamin ULiege; Archambeau, Pierre ULiege et al

in Frontiers in Water (2021), 3(633046), 1-14

Studies on inequalities in exposure to flood risk have explored whether population of a lower socio-economic status are more exposed to flood hazard. While evidence exist for coastal flooding, little is ... [more ▼]

Studies on inequalities in exposure to flood risk have explored whether population of a lower socio-economic status are more exposed to flood hazard. While evidence exist for coastal flooding, little is known on inequalities for riverine floods. This paper addresses two issues: (1) is the weakest population, in socio-economic terms, more exposed to flood hazard, considering different levels of exposure to hazard? (2) Is the exposure to flood risk homogeneous across the territory, considering different scales of analysis? An analysis of the exposure of inhabitants of Liège province to flood risk was conducted at different scales (province, districts, and municipalities), considering three levels of exposure to flood hazard (level 1- low hazard, level 3- high hazard), and five socio-economic classes (class 1-poorest, class 5-wealthiest households). Our analysis confirms that weaker populations (classes 2 and 3) are usually more exposed to flood hazards than the wealthiest (classes 4 and 5). Still it should be stressed that the most precarious households (class 1) are less exposed than low to medium-range ones (classes 2 and 3). Further on the relation between socio-economic status and exposure to flood hazard varies along the spatial scale considered. At the district level, it appears that classes 4 and 5 are most exposed to flood risk in some peripheral areas. In municipalities located around the center of the city, differences of exposure to risk are not significant. [less ▲]

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See detailOccurrence and characteristic frequencies of nappe oscillations at free-overfall structures
Kitsikoudis, Vasileios ULiege; Lodomez, Maurine; Dewals, Benjamin ULiege et al

in Journal of Hydraulic Engineering (2021), 147(2),

The present study investigated the occurrence and characteristic frequency of nappe oscillations on weirs by re-analysing data from 52 experimental configurations. The considered configurations include ... [more ▼]

The present study investigated the occurrence and characteristic frequency of nappe oscillations on weirs by re-analysing data from 52 experimental configurations. The considered configurations include various shapes of the weir crest and a range of weir geometric and hydraulic characteristics with two different scales. Nappes were either confined with lateral and back walls forming a non-vented air pocket between the nappe and the weir or unconfined with atmospheric pressure everywhere around the nappe. Oscillations occurred at nappes with uniformly distributed approaching flow of low velocity and unit discharge between 0.01 and 0.06 m2/s, regardless of the model scale. Weir crests that favoured nappe oscillations had an upstream profile without geometric discontinuities. A dimensionless frequency of nappe oscillations was expressed as a power function of the ratio of fall height to the water depth at the point of detachment at the crest, separately for quarter-round and truncated half-round weir crests. The exponents of the two obtained power functions were very close to each other, which allows the usage of their average so that different weir crests exhibit solely offsetting curves. [less ▲]

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See detailPorosity Models for Large-Scale Urban Flood Modelling: a Review
Dewals, Benjamin ULiege; Bruwier, Martin ULiege; Pirotton, Michel ULiege et al

in Water (2021)

In the context of large-scale urban flood modelling, porosity shallow-water models enable a con-siderable speed-up in computations, while preserving information on subgrid topography. Over the last two ... [more ▼]

In the context of large-scale urban flood modelling, porosity shallow-water models enable a con-siderable speed-up in computations, while preserving information on subgrid topography. Over the last two decades, major improvements have been brought to these models; but a single gen-erally accepted model formulation has not yet been reached. Instead, existing models vary in many respects. Some studies define porosity parameters at the scale of the computational cells or cell interfaces, while others treat the urban area as a continuum and introduce statistical-ly-defined porosity parameters. The porosity parameters are considered either isotropic or aniso-tropic, and depth-independent or depth-dependent. The underlying flow models are based either on the full shallow-water equations, or on approximations thereof, with various parametrizations of flow resistance. Here, we provide a review of the spectrum of porosity models developed so far for large scale urban flood modelling. [less ▲]

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See detailBehind the scenes of streamflow model performance
Bouaziz, Laurène J. E.; Fenicia, Fabrizio; Thirel, Guillaume et al

in Hydrology and Earth System Sciences (2021), 25(2), 10691095

Streamflow is often the only variable used to evaluate hydrological models. In a previous international comparison study, eight research groups followed an identical protocol to calibrate twelve ... [more ▼]

Streamflow is often the only variable used to evaluate hydrological models. In a previous international comparison study, eight research groups followed an identical protocol to calibrate twelve hydrological models using observed streamflow of catchments within the Meuse basin. In the current study, we quantify the differences in five states and fluxes of these twelve process-based models with similar streamflow performance, in a systematic and comprehensive way. Next, we assess model behavior plausibility by ranking 5 the models for a set of criteria using streamflow and remote sensing data of evaporation, snow cover, soil moisture and total storage anomalies. We found substantial dissimilarities between models for annual interception and seasonal evaporation rates, the annual number of days with water stored as snow, the mean annual maximum snow storage and the size of the root-zone storage capacity. These differences in internal process representation imply that these models cannot all simultaneously be close to reality. Modeled annual evaporation rates are consistent with GLEAM estimates. However, there is a large uncertainty in modeled and remote sensing annual interception. Substantial differences are also found between MODIS and modeled number of days with snow storage. Models with relatively small root-zone storage capacities and without root water uptake reduction under dry conditions tend to have an empty root-zone storage for several days each summer, while this is not suggested by remote sensing data of evaporation, soil moisture and vegetation indices. On the other hand, models with relatively large root-zone storage capacities tend to overestimate very dry total storage anomalies of GRACE. None of the models is systematically consistent with the information available from all different (remote sensing) data sources. Yet, we did not reject models given the uncertainties in these data sources and their changing relevance for the system under investigation. [less ▲]

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See detailAssessment of lumped physically-based numerical models of dyke breaching
Schmitz, Vincent ULiege; Wylock, Grégoire; El Kadi Abderrezzak, Kamal et al

in Geophysical Research Abstracts (2021)

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See detailThermodynamic optimality principles in Earth sciences
Schymanski, Stanislaus J.; Dewals, Benjamin ULiege; Dijkstra, Henk A. et al

in Geophysical Research Abstracts (2021)

Ecohydrological systems are a result of long-term co-evolution of soils, biota and atmospheric conditions, and often respond to perturbations in non-intuitive ways. Their short-term responses can be ... [more ▼]

Ecohydrological systems are a result of long-term co-evolution of soils, biota and atmospheric conditions, and often respond to perturbations in non-intuitive ways. Their short-term responses can be explained and sometimes predicted if we understand the underlying dynamic processes and if we can observe the initial state precisely enough. However, how do they co-evolve in the long-term after a change in the boundary conditions? In 1922, Alfred Lotka hypothesised that the natural selection governing the evolution of biota and composition of ecosystems may be obeying some thermodynamic principles related to maximising energy flow through these systems. Similar thoughts have been formulated for various components of the Earth system and individual processes, such as heat transport in the atmosphere and oceans, erosion and sediment transport in river systems and estuaries, the formation of vegetation patterns, and many others. Different thermodynamic optimality principles have been applied to predict or explain a given system property or behaviour, of which the maximum entropy production and the maximum power principles are most widespread. However, the different studies did not use a common systematic approach for the formulation of the relevant system boundaries, state variables and exchange fluxes, resulting in considerable ambiguity about the application of thermodynamic optimality principles in the scientific community. Such a systematic framework has been developed recently and can be tested online at: https://renkulab.io/projects/stanislaus.schymanski/thermodynamic_optimality_blueprint In the present study, we illustrate how such a common framework can be used to classify and compare different applications of thermodynamic optimality principles in the literature, and discuss the insights gained and key criteria for a more rigorous testing of such principles. [less ▲]

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See detailModélisation hydraulique 2D pour la détermination des zones inondables
Archambeau, Pierre ULiege; Erpicum, Sébastien ULiege; Dewals, Benjamin ULiege et al

Scientific conference (2020, November 09)

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See detailAge of Water Particles as a Diagnosis of Steady-state Flows in Shallow Rectangular Reservoirs
Dewals, Benjamin ULiege; Archambeau, Pierre ULiege; Bruwier, Martin ULiege et al

in Water (2020), (12), 2819

The age of a water particle in a shallow man-made reservoir is defined as the time elapsed since it entered it. Analyzing this diagnostic timescale provides valuable information for optimally sizing and ... [more ▼]

The age of a water particle in a shallow man-made reservoir is defined as the time elapsed since it entered it. Analyzing this diagnostic timescale provides valuable information for optimally sizing and operating such structures. Here, the constituent-oriented age and residence time theory (CART) is used to obtain not only the mean age, but also the water age distribution function at each location. The method is applied to 10 different shallow reservoirs of simple geometry (rectangular), in a steady-state framework. The results show that complex, multimodal water age distributions are found, implying that focusing solely on simple statistics (e.g., mean or median age) fails to reflect the complexity of the actual distribution of water age. The latter relates to the fast or slow pathways that water particles may take for traveling from the inlet to the outlet of the reservoirs. [less ▲]

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See detailInfluence of model formulation on the critical morphological acceleration factor: an analytical study
Dewals, Benjamin ULiege; Archambeau, Pierre ULiege; Pirotton, Michel ULiege et al

E-print/Working paper (2020)

The morphological acceleration factor (Morfac) has been used for over two decades to speed-up long term morphodynamic simulations. However, the Morfac values are usually set heuristically and hardly any ... [more ▼]

The morphological acceleration factor (Morfac) has been used for over two decades to speed-up long term morphodynamic simulations. However, the Morfac values are usually set heuristically and hardly any study investigated theoretically the critical Morfac value leading to a predefined level of accuracy. In this research, we evaluated theoretically the critical Morfac value from the analysis of the amplitude and phase errors induced by the use of Morfac. While the few existing studies focused only on relatively low Froude numbers and a single mathematical formulation of the morphodynamic model, we consider here a significantly wider range of Froude numbers, including supercritical flow, and we compare four different model formulations. We show that the model formulation leading to the highest critical Morfac values for subcritical flow is not the same as for supercritical flow. [less ▲]

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See detailA combined experimental and numerical strategy to assess the influence of model geometric distortion in laboratory scale modelling of urban flooding
Li, Xuefang ULiege; Erpicum, Sébastien ULiege; Mignot, Emmanuel et al

Conference (2020, July)

Accurate modelling of urban flood hazard remains hampered by a lack of suitable validation data. In contrast with water marks and inundation extent, discharge partition in-between streets and flow fields ... [more ▼]

Accurate modelling of urban flood hazard remains hampered by a lack of suitable validation data. In contrast with water marks and inundation extent, discharge partition in-between streets and flow fields are generally unknown, while they have a strong influence on flood risk (human destabilization, scour, contaminant transport). Laboratory experiments may provide a valuable complement to field data to achieve robust validation of flood hazard models. However, urban flooding is a multiscale phenomenon, with horizontal length scales (~ 103 m) are considerably larger than the vertical ones (~ 1 m). Therefore, recent experimental studies of urban flooding used geometrically distorted scale models, with a vertical scale factor smaller than the horizontal one. Though, little is known so far on the bias induced by model geometric distortion in the case of urban flooding. To address this issue, we have combined computational modelling with laboratory experiments. Based on 100+ numerical simulations, the bias induced by model geometric distortion on flow depth and discharge partition was found of the order of 10 %, which is not negligible compared to other uncertainties involved in urban flood hazard modelling. Moreover, when the geometric distortion is varied, the induced bias shows an intriguing non-monotonous evolution, which we could relate to a competition between frictional and secondary head losses. New tailored laboratory experiments are on-going on a “series” of laboratory scale models, i.e. several laboratory models representing the same urban layout at various scales. The outcomes of these experiments will make more robust the conclusions drawn from computational modelling. [less ▲]

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See detailNumerical insights into the effects of model geometric distortion in laboratory experiments of urban flooding
Li, Xuefang ULiege; Erpicum, Sébastien ULiege; Mignot, Emmanuel et al

in Water Resources Research (2020)

Geometrically distorted scale models have been a valuable tool for physical modelling of urban flooding in a network of streets. However, little is known so far about the bias induced in such cases by the ... [more ▼]

Geometrically distorted scale models have been a valuable tool for physical modelling of urban flooding in a network of streets. However, little is known so far about the bias induced in such cases by the model geometric distortion. Here, we use 2D computational modelling to provide a first systematic quantification of this bias in the case of a synthetic urban layout. The bias is found to be generally small, with the maximum deviations of the upscaled flow depth and discharge partition from the corresponding values of the undistorted model being around 10 % in the case of relatively rapid and shallow flow conditions. When the geometric distortion is increased, the computations reveal a non-monotonous pattern of the flow variables (depth, discharge partition, size of flow separation zones), which results from a competition between declining frictional losses and growing local losses in the model. These findings may guide the design of distorted scale models of urban flooding and assist the interpretation of laboratory observations for assessing flood protection measures, for process understanding or for validating computational modelling. [less ▲]

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See detailProcedural generation of flood-sensitive urban layouts
Mustafa, Ahmed Mohamed El Saeid ULiege; Zhang, Xiao Wei; Aliaga et al

in Environment and Planning B: Urban Analytics and City Science (2020), 47(5), 889-911

Aside from modeling geometric shape, three-dimensional (3D) urban procedural modeling has shown its value in understanding, predicting and/or controlling effects of shape on design and urban planning. In ... [more ▼]

Aside from modeling geometric shape, three-dimensional (3D) urban procedural modeling has shown its value in understanding, predicting and/or controlling effects of shape on design and urban planning. In this paper, instead of the construction of flood resistant measures, we create a procedural generation system for designing urban layouts that passively reduce water depth during a flooding scenario. Our tool enables exploring designs that passively lower flood depth everywhere or mostly in chosen key areas. Our approach tightly integrates a hydraulic model and a parameterized urban generation system with an optimization engine so as to find the least cost modification to an initial urban layout design. Further, due to the computational cost of a fluid simulation, we train neural networks to assist with accelerating the design process. We have applied our system to several real-world locations and have obtained improved 3D urban models in just a few seconds. [less ▲]

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See detailDiscussion of "modeling and Prototype Testing of Flows over Flip-Bucket Aerators" by Penghua Teng and James Yang
Erpicum, Sébastien ULiege; Dewals, Benjamin ULiege; Archambeau, Pierre ULiege et al

in Journal of Hydraulic Engineering (2020), 146(5),

The Authors propose an interesting comparison between physical scale modeling, CFD modeling and field observations related to a unique spillway with flip buckets and built-in aerators. Despite the field ... [more ▼]

The Authors propose an interesting comparison between physical scale modeling, CFD modeling and field observations related to a unique spillway with flip buckets and built-in aerators. Despite the field observations are mainly qualitative, the Discussers would like to thank the Authors for sharing with the scientific community these results. Indeed, such analysis are very valuable but are too rare. Physical models and CFD are both modeling tools. They both suffer limitations and, consequently, their results need to be carefully and objectively discussed and validated. Comparison to quantitative prototype data is the only way to proof the validity of a modeling technique for real projects. However, such validation data remain sparse and rare, in particular considering large hydraulic structures. In the following, the Discussers aim to raise one issue in the Authors’ research and to highlight recent contributions and existing datasets, which are of direct relevance for the interpretation and discussion of the Authors’ results. [less ▲]

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See detailInfluence of urban forms on surface flow in urban pluvial flooding
Bruwier, Martin ULiege; Maravat, Claire; Mustafa, Ahmed et al

in Journal of Hydrology (2020), 582

This paper presents a systematic analysis of the influence of nine urban characteristics (distance be-tween buildings, mean building size, building coverage, etc.) on surface flow in case of pluvial ... [more ▼]

This paper presents a systematic analysis of the influence of nine urban characteristics (distance be-tween buildings, mean building size, building coverage, etc.) on surface flow in case of pluvial flooding. Time dependent stored volumes, outflow discharges and mean water depths were comput-ed for a set of 2,000 synthetic urban forms, considering various terrain slopes and return periods of the rainfall. An efficient porosity-based surface flow model was used to compute the 2D flow varia-bles. Statistical analysis of the relationship between the flow and urban variables highlights that the flooding severity is mostly influenced by the building coverage. [less ▲]

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See detailThe need to integrate flood and drought disaster risk reduction strategies
Ward, Philip; de Ruiter, Marleen; Mård, Johanna et al

in Water Security (2020)

Most research on hydrological risks focuses either on flood risk or drought risk, whilst floods and droughts are two extremes of the same hydrological cycle. To better design disaster risk reduction (DRR ... [more ▼]

Most research on hydrological risks focuses either on flood risk or drought risk, whilst floods and droughts are two extremes of the same hydrological cycle. To better design disaster risk reduction (DRR) measures and strategies, it is important to consider interactions between these closely linked phenomena. We show examples of: how flood or drought DRR measures can have (unintentional) positive or negative impacts on risk of the opposite hazard; and (b) how flood or drought DRR measures can be negatively impacted by the opposite hazard. We focus on dikes and levees, dams, stormwater control and upstream measures, subsurface storage, migration, agricultural practices, and vulnerability and preparedness. We identify key challenges for moving towards a more holistic risk management approach. [less ▲]

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