References of "Dewals, Benjamin"
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See detailInfluence of urban patterns on flooding
Bruwier, Martin ULiege; Mustafa, Ahmed; Aliaga, Daniel et al

in E-proceedings of the 37th IAHR World Congress (2017, August)

The goal of this paper is to identify the respective influence of different characteristics of urban patterns on urban flooding. A set of 2,290 alternate urban patterns was generated randomly using an ... [more ▼]

The goal of this paper is to identify the respective influence of different characteristics of urban patterns on urban flooding. A set of 2,290 alternate urban patterns was generated randomly using an urban generator tool providing the geometry of buildings and their relative location to the ground, over a square area of 1 km². Steady 2-D hydraulic computations were performed for these 2,290 different urban patterns with identical hydraulic boundary conditions. The computational time was reduced by using an anisotropic porosity model. This model uses relatively coarse computational cells; but preserves information from the detailed topographic data through the use of porosity parameters. Based on the computed maps of waterdepths for the 2,290 urban patterns, a sensitivity analysis based on a multiple linear regression was performed to outline the most influential urban characteristics. [less ▲]

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See detailModèles de porosité pour les inondations urbaines
Dewals, Benjamin ULiege; Bruwier, Martin ULiege; El Saeid Mustafa, Ahmed Mohamed ULiege et al

Scientific conference (2017, July 25)

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See detailOn the transition between symmetric and asymmetric flow in rectangular shallow reservoirs - a case of maximum energy dissipation?
Westhoff, Martijn; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

Conference (2017, June 28)

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 ... [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 identical recirculation zones on both sides. In longer reservoirs, the main jet reattaches to the side of the reservoir leading to small and large recirculation zones. Previous studies have 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 the prediction of 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 detailOn the transition between symmetric ans asymmetric flow in rectangular shallow reservoirs - a case of maximum energy dissipation?
Westhoff, M.C.; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

Conference (2017, June)

Shallow reservoirs are often used in hydraulic engineering as sediment traps or storage basins. For short rectangular reservoirs, the main jet flows straight from the inlet to the outlet with on both sides ... [more ▼]

Shallow reservoirs are often used in hydraulic engineering as sediment traps or storage basins. For short rectangular reservoirs, the main jet flows straight from the inlet to the outlet with on both sides symmetric recirculation zones. In longer reservoirs, however, the main jet reattaches to the side of the reservoir leading to a small and a large recirculation zone. Previous studies have found an empirical geometric relation describing the switch between these two flow pattems. In this study, we demonstrate with a simple analytical model, that this switch in flow pattem coincides with a maximization of energy dissipation in the shear layer between the main jet and the recirculation zones. We show that for short reservoir lengths, energy dissipation is higher in the case of a symmetric fiow pattern, while for longer reservoir the energy dissipation is higher for asymmetric flow pattems. The simulated switch between the two flow patterns appears to be very close to the empirical relation. The strength of this approach lies in the fact that no detailed knowledge of small scale processes is needed, which may prove useful at an early stage of reservoir design. [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 detailShallow water model with anisotropic porosity for flood modelling on Cartesian grids
Bruwier, Martin ULiege; Archambeau, Pierre ULiege; Erpicum, Sébastien ULiege et al

Conference (2017, June)

Detailed topographic data have become widely available for inundation mapping. While the use of such high-resolution data enables the computation of flow variables at a fine scale, the computation time ... [more ▼]

Detailed topographic data have become widely available for inundation mapping. While the use of such high-resolution data enables the computation of flow variables at a fine scale, the computation time remains too high for many practical applications. In contrast, models solving the shallow-water equations with porosity provide a useful tool to improve the computational efficiency, while preserving to some extent the detailed topographic information through porosity parameters. In this study, we present a new model solving the fully dynamic shallow water equations with anisotropic porosity based on Cartesian grids. Using a Cartesian grid leads to specific challenges, particularly as regards the definition of the conveyance porosities at the cell edges. Moreover, the presented model is further improved by a merging method so as to increase the computational efficiency without affecting the overall accuracy. The performance of the model has been evaluated based on a wide range of test cases, which confirm the validity of the model and the benefits of such a modelling framework. [less ▲]

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See detailA laser profilometry technique for monitoring fluvial dike breaching in laboratory experiments
Dewals, Benjamin ULiege; Rifai, Ismail; Erpicum, Sébastien ULiege et al

Conference (2017, April)

A challenging aspect for experimental modelling of fluvial dike breaching is the continuous monitoring of the transient breach geometry. In dam breaching cases induced by flow overtopping over the whole ... [more ▼]

A challenging aspect for experimental modelling of fluvial dike breaching is the continuous monitoring of the transient breach geometry. In dam breaching cases induced by flow overtopping over the whole breach crest (plane erosion), a side view through a glass wall is sufficient to monitor the breach formation. This approach can be ex- tended for 3D dam breach tests (spatial erosion) ifthe glass wall is located along the breach centreline. In contrast using a side view does not apply for monitoring fluvial dike breaching, because the breach is not symmetric in this case. We present a non-intrusive, high resolution technique to record the breach development in experimental models of fluvial dikes by means of a laser profilometry (Rifai et al. 2016). Most methods used for monitoring dam and dike breaching involve the projection of a pattern (fringes, grid) on the dam or dike body and the analysis of its deformation on images recorded during the breaching (e.g., Pickett et al. 201 1, Frank and Hager 2014). A major limitation of these methods stems from reflection on the water surface, particularly in the vicinity of the breach where the free surface is irregular and rippled. This issue was addressed by Spinewine et al. (2004), who used a single laser sheet so that reflections on the water surface were strongly limited and did not hamper the accurate processing of each image. We have developed a similar laser profilometry technique tailored for laboratory experiments on fluvial dike breaching. The setup is simple and relatively low cost. It consists of a digital video camera (resolution of 1920 >< 1080 pixels at 60 frames per second) and a swiping red diode 30 mW laser that enables the projection of a laser sheet over the dike body. The 2D image coordinates of each defomied laser profile incident on the dike are transformed into 3D object coordinates using the Direct Linear Transformation (DLT) algorithm. All 3D object coordinates computed over a swiping cycle of the laser are merged to generate a cloud of points. The DLT-based image processing method uses control points and reference axes, so that no prior knowledge is needed on the position, orientation and intrinsic characteristics of the camera, nor on the laser position. Refraction of the light and laser rays across the water surface needs to be taken into account, because the dike is partially submerged during the experiments. An ad hoc correction is therefore applied using the Snell-Descartes law. For dtis purpose, planar approximations are used to describe the shape of the water surface. In the presen- tation, we will discuss the resulting uncertainty and will detail the validation of the developed method based on configurations of known geometry with various complexity. The presented laser profilometry technique allows for a rapid non-intrusive measurement of the dike geometry evolution. It is readily available for laboratory experiments and has proven its performance (Rifai et al. 2017). Further adjustments are needed for its application to cohesive dike material due to the reduced visibility resulting from the higher turbidity of water. [less ▲]

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See detailTransition between symmetric and asymmetric flow in rectangular shallow reservoirs — a case of maximum dissipation?
westhoff, Martijn; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

Conference (2017, April)

Shallow reservoirs are often used in hydraulic engineering as sediment traps or storage basins, Sedimentation within these reservoirs depends on the flow pattern, which in turn depends on the shape of the ... [more ▼]

Shallow reservoirs are often used in hydraulic engineering as sediment traps or storage basins, Sedimentation within these reservoirs depends on the flow pattern, which in turn depends on the shape of the reservoir. For short rectangular reservoirs, the main jet flows straight from the inlet to the outlet with on both sides identical recirculation zones. In longer reservoirs, however, the main jet reattaches to the side of the reservoir leading to a small and a large recirculation zone. Previous studies have found an empirical geometric relation describing the switch between these two different flow patterns. In this study, we demonstrate that this switch in flow pattern coincides with a maximization of energy dissipation in the shear layer between the main jet and the recirculation zones. To show this we described the power received from the jet by the recirculation zone as the product of a fluid-fluid friction coefficient and the square of the velocity difference times the shear velocity of the recirculation zone. This power is balanced by the bottom friction of the recirculation zone. Energy dissipation in the shear layer is then determined as the difference between the power performed by the jet and the power received by the recirculation zone. In this setup, energy dissipation is maximized by optimizing the friction coefficient. We show that for short reservoir lengths, energy dissipation is higher in the case of a symmetric flow pattern, while for longer reservoir the energy dissipation is higher for asymmetric flow patterns. The simulated switch between the two flow patterns appears to be very close to the empirical relation. This suggests that the flow pattem adapts in order to maximize energy dissipation between the jet and recirculation zones. The strength of this approach lies in the fact that no detailed knowledge of small scale processes is needed, while large scale structure formation can still be predicted. [less ▲]

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See detailLessons learned from combined experimental and numerical modelling of urban floods
Archambeau, Pierre ULiege; Bruwier, Martin ULiege; Finaud-Guyot, Pascal et al

Conference (2017, April)

Field data for validating hydraulic models remain scarce, They are often limited to inundation extents and water marks, which provide little insights into the dynamic features of the flow in urbanized ... [more ▼]

Field data for validating hydraulic models remain scarce, They are often limited to inundation extents and water marks, which provide little insights into the dynamic features of the flow in urbanized floodplains, such as the discharge partition in-between the streets and the velocity fields. To address this issue, a unique experimental setup representing a whole urban district was built in the laboratory ICube in Strasbourg and the state-of-the-art shallow- water model Wolf 2D was tested against the experimental measurements (An'ault et al, 2016), The numerical model was also used to extend and refine the analysis of the laboratory observations. The experimental model (5 m >< 5 m) represents a square urban district with a total of l4 streets of different Widths and 49 intersections (crossroads). The inflow discharge can be controlled in each street individually and the outflow discharges were measured downstream of each street. The numerical model Wolf was developed at the University of Liege and has been extensively used in flood risk research (Beckers et al, 2013, Bruwier et al. 2015, Detrembleur et al. 2015). Several lessons could be learned from this combined experimental and numerical analysis. First, we found that the discharge partition in—between the streets is primarily controlled by the street widths. Second, although the standard shallow-water equations reproduce satisfactorily tnost of the flow characteristics, adding a turbulence model improves the prediction of the shape and length of the flow recirculations in the streets. Yet, this has little influence on the discharge partition because the computed recirculation widths are hardly affected by the turbulence model. The experiments and the numerical model also show that the water depths in the streets remain fairly constant in~between two intersections, while they drop suddenly downstream of each intersection as a result of complex flow interactions at the intersections. This hints that friction has little influence on the water depths obtained in the experiments. However, tailored numerical tests demonstrate that this is a direct consequence of the distorted nature of the experimental setup. Indeed, the ratio between the water depth and the street width is close to 1 in the experiments, while it would be at least one order of magnitude lower in real-world conditions, even for extreme floods. Finally, remote sensing data, such as digital elevation models, are generally available on a regular grid, which makes it convenient to use also a Cartesian grid for hydraulic modelling, We show here that the discretization of the geometry of the buildings on such a Cartesian grid has a major influence on the modelling accuracy (overestimation of the overall flow resistance). An extended shallow-water model based on non-isotropic porosity parameters is shown to improve substantially the prediction of the discharge partition in-between the streets. It is therefore considered as a valuable tool to advance urban flood modelling in practice. From the lessons learned here, we recommend that future research focuses on the design and exploitation of a less distorted experimental model, as well as on the analysis of extra flow processes such as transient conditions and interactions between overland flow and pressurized flow in underground passages. [less ▲]

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See detailFluvial dike breaching due to overtopping: how different is it from dam breaching?
Rifai, Ismail; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

Conference (2017, April)

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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 detailSystematic flood modelling to support flood-proof urban design
Bruwier, Martin ULiege; Mustafa, Ahmed; Aliaga, Daniel et al

Poster (2017, April)

Urban flood risk is influenced by many factors such as hydro-meteorological drivers, existing drainage systems as well as vulnerability of population and assets. The urban fabric itself has also a complex ... [more ▼]

Urban flood risk is influenced by many factors such as hydro-meteorological drivers, existing drainage systems as well as vulnerability of population and assets. The urban fabric itself has also a complex influence on inundation flows. In this research, we performed a systematic analysis on how various characteristics of urban patterns control inundation flow within the urban area and upstream of it. An urban generator tool was used to generate over 2,250 synthetic urban networks of 1 km². This tool is based on the procedural modelling presented by Parish and Müller (2001) which was adapted to generate a broader variety of urban networks. Nine input parameters were used to control the urban geometry. Three of them define the average length, orientation and curvature of the streets. Two orthogonal major roads, for which the width constitutes the fourth input parameter, work as constraints to generate the urban network. The width of secondary streets is given by the fifth input parameter. Each parcel generated by the street network based on a parcel mean area parameter can be either a park or a building parcel depending on the park ratio parameter. Three setback parameters constraint the exact location of the building whithin a building parcel. For each of synthetic urban network, detailed two-dimensional inundation maps were computed with a hydraulic model. The computational efficiency was enhanced by means of a porosity model. This enables the use of a coarser computational grid , while preserving information on the detailed geometry of the urban network (Sanders et al. 2008). These porosity parameters reflect not only the void fraction, which influences the storage capacity of the urban area, but also the influence of buildings on flow conveyance (dynamic effects). A sensitivity analysis was performed based on the inundation maps to highlight the respective impact of each input parameter characteristizing the urban networks. The findings of the study pinpoint which properties of urban networks have a major influence on urban inundation flow, enabling better informed flood-proof urban design. [less ▲]

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See detailUrbanization and changing flood risk: a multi-level analysis
Dewals, Benjamin ULiege; Bruwier, Martin ULiege; El Saeid Mustafa, Ahmed Mohamed ULiege et al

in Bronstert, Axel; Thieken, Annegret; Petrow, Theresia (Eds.) et al The Effects of Global Change on Floods, Fluvial Geomorphology and Related Hazards in Mountainous Rivers (2017, March 06)

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See detailLanduse change and future flood risk: the influence of micro-scale spatial patterns (FloodLand) - 5th progress report
Dewals, Benjamin ULiege; Bruwier, Martin ULiege; El Saeid Mustafa, Ahmed Mohamed ULiege et al

Report (2017)

The goal of the project FloodLand is to investigate the complex interactions between landuse change and future flood risk. Landuse change is assumed to be mainly driven by population growth and socio ... [more ▼]

The goal of the project FloodLand is to investigate the complex interactions between landuse change and future flood risk. Landuse change is assumed to be mainly driven by population growth and socio-economic factors. It affects future flood risk by altering catchment hydrology as well as vulnerability in the floodplains; but the feedback effect of (the perception of) changes in flood hazard on landuse evolution is also considered. The research is based on a chain of modelling tools, which represent parts of the natural and human systems, including: landuse change modelling, transportation modelling as an onset for the estimation of indirect flood damage, continuous hydrological modelling (forced by precipitation and temperature data disturbed according to climate change scenarios), as well as efficient hydraulic modelling of inundation flow in the floodplains. Besides reproducing a broad spectrum of processes, the modelling approach spans over multiple scales, from the regional or catchment level down to the floodplain and building levels. This distinctive feature is reflected both within the individual models and through their combination involving fine-scale detailed analyses (or data) embedded within coarser models at a broader level. [less ▲]

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See detailUnderground pumped hydro-energy storage in Wallonia (Belgium) using old mines – Potential and challenges
Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege; Dewals, Benjamin ULiege et al

in Shaping the future of hydropower (2017)

Pumped Storage Hydroelectricity (PSH) is a well-known and efficient technology to store various amounts of electricity. In most parts of Europe, appropriate sites for new classical PSH plants are getting ... [more ▼]

Pumped Storage Hydroelectricity (PSH) is a well-known and efficient technology to store various amounts of electricity. In most parts of Europe, appropriate sites for new classical PSH plants are getting scarce. An alternative consists in using underground volumes as lower reservoirs to build so-called Underground Pumping Storage Hydroelectricity (UPSH) plants. The paper presents the main results of a research project currently investigating the potential and feasibility of such innovative plants in the context of Wallonia, where numerous abandoned mines and quarries are located all over the territory. After a description of the main types of reservoir configurations existing in the considered region and the evaluation of their expected energy storage potential, the tools and methodology developed in the scope of the project are presented. Their application to the case of an underground slates quarry and an open pit chalk mine helps in identifying the remaining challenges [less ▲]

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See detailA Piano Key Weir to improve the discharge capacity of the Oule Dam spillway (France)
Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege; Dewals, Benjamin ULiege et al

in Erpicum, Sébastien; Laugier, Frédéric; Ho Ta Khanh, Michel (Eds.) et al Labyrinth and Piano key weirs III - PKW 2017 (2017)

The Oule dam spillway (France) is made of a lateral weir on the right bank of the reservoir, a collecting channel, a macro-steps channel and a downstream lateral weir for water release in the natural ... [more ▼]

The Oule dam spillway (France) is made of a lateral weir on the right bank of the reservoir, a collecting channel, a macro-steps channel and a downstream lateral weir for water release in the natural river bed. This spillway presents a deficit in discharge capacity. In order to solve this problem, several rehabilitation solutions have been analyzed. From this process, a piano key weir solution to improve the discharge capacity of the lateral upstream weir has been selected. This piano key weir will replace the existing ogee crest while keeping weir level and thus normal reservoir elevation constant. The piano key weir, 1 m high, has been designed with steel and is made of 22.5 units for a total width of 33 m. Its main advantage is to drastically increase the discharge capacity at low heads, enabling the release of the design flood peak discharge just below the reservoir maximum elevation by optimizing the reservoir temporary storage. [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), 554(C), 693-709

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 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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