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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 detailAssessing the vulnerability of sites in the East African Rift Valley to natural hazards: case study of Bujumbura, Burundi
Nibigira, Léonidas ULg; Havenith, Hans-Balder ULg; Dewals, Benjamin ULg et al

Conference (2013, November 13)

Due to the geomorphologic, structural and climatic context, the East African Rift Valley is prone to many natural hazards. The locally high density of the population contributes to related risk. As a ... [more ▼]

Due to the geomorphologic, structural and climatic context, the East African Rift Valley is prone to many natural hazards. The locally high density of the population contributes to related risk. As a result, the impacts on the habitat and infrastructures are constantly increasing. This work is based on a case study near the city of Bujumbura, which, for decades, has been affected by severe floods. Based on a study focusing on one of its rivers, the river Ntahangwa, this work tries to answer some questions related to the potential causes and ways of prevention and management of flood risk. The analysis is based on hydrological considerations while having a look at the possible mutual influences between these hydrological risks and geodynamic hazards. The methodology uses rainfall, geographic, demographic, topographic, and elevation data. Hydraulic modeling reveals the extent of the flood hazard according to its likelihood of occurrence and its sensitivity to geodynamic disturbances. This led us to propose solutions and related prevention/remediation measures. Considering the vulnerability of the population, it is clear that a change of people’s behavior is needed to reduce the total risk they’re exposed to, both with respect to the choice of construction areas and to all kinds of activities related to rivers exploitation. [less ▲]

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See detailLa facture salée des inondations - Construire en zone inondable : un risque chiffré par l'Université de Liège
de Muelenaere, Michel; Dewals, Benjamin ULg; Pirotton, Michel ULg

Article for general public (2013)

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See detailA fundamental study of the inception of motion of coarse sediments
Duma, Diana ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Proceedings of 2013 IAHR World Congress (2013, September)

This research aims to provide new knowledge about the inception of motion in rivers with coarse sediments and, possibly, macro-roughness flow regime, for which, so far, civil and environmental engineers ... [more ▼]

This research aims to provide new knowledge about the inception of motion in rivers with coarse sediments and, possibly, macro-roughness flow regime, for which, so far, civil and environmental engineers face much uncertainty in the determination of threshold hydraulic conditions for sediment transport. The threshold conditions have to be clearly defined, at the theoretical level, and well identified, in experimental tests. Therefore, a specific program of laboratory experiments has been designed. It relies on two complementary laboratory flumes of, respectively, 6m and 20m in length (discharge up to 100 l/s, slope between 0 and 4%). Three different thresholds have been defined to distinguish between the following four states: no motion, vibration of stone, local motion, and large scale motion. Based on experimental tests conducted so far in the smaller flume, velocity profile and turbulence intensity measured in quasi-uniform and non-uniform flow conditions have been correlated with the inception of motion. Flow velocity was measured using UVP transducers. In this paper, the results of a first phase of the study are presented, with the aim of validating the experimental setup, procedure and instrumentation. They focus particularly on the feasibility of collecting the relevant flow variables (shear velocity, turbulence) from a limited number of pointwise velocity measurements. [less ▲]

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See detailHydraulic modelling of the river Meuse
Dewals, Benjamin ULg; Huismans; Stilmant, Frédéric ULg et al

Conference (2013, September)

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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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See detailDam break flow modelling with uncertainty analysis
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Pirotton, Michel ULg et al

in Gourbesville, Philippe; Cunge, Jean; Caignaert, Guy (Eds.) Advances in Hydroinformatics (2013)

Handling uncertainties in dam break flow modelling is of primary interest. Therefore, a procedure is presented here to conduct systematic analysis of the uncertainties resulting from the roughness ... [more ▼]

Handling uncertainties in dam break flow modelling is of primary interest. Therefore, a procedure is presented here to conduct systematic analysis of the uncertainties resulting from the roughness coefficient, the breaching hydrograph and topographic data. The flow simulations have been conducted with the model WOLF 2D developed at the University of Liege. This two-dimensional flow model is computationally too costly to perform a high number of repeated runs, as needed for Monte Carlo simulations. Therefore, a “reduced complexity model” has been set up, in the form of multidimensional Hermite polynomials. This method, developed by Isukapalli et al. (2004) and first applied to dam break flow by Niemeyer (2007), involves a reduced number of runs of the complete model to calibrate the polynomials. This paper shows the applicability and efficiency of the methodology, but it also discusses previously unreported shortcomings of the approach, together with hints to overcome them. Results of such uncertainty analysis for dam break flow modelling disclose crucial information for practical risk management. In particular, they reveal that the uncertainty ranges on maximum water depth and time of arrival of the front are not symmetric (overestimation vs. underestimation) and very unevenly distributed in space. [less ▲]

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See detailExperimental analysis of the stability of coarse sediments
Duma, Diana ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Symposium on Two-phase Modelling for Sediment Dynamics in Geophysical Flows (2013, June 12)

To predict the inception of sediment motion, Shields diagram remains the most widely used criterion in engineering practice so far. However, this approach faces several limitations and a number of gaps in ... [more ▼]

To predict the inception of sediment motion, Shields diagram remains the most widely used criterion in engineering practice so far. However, this approach faces several limitations and a number of gaps in knowledge still remain. The present research aims to provide new knowledge about the inception of motion in rivers with coarse sediments. A series of experiments was conducted in a flume horizontal 6 m long and 15 cm wide. The bottom was paved, either entirely or partly, with gravels of approximately 12 mm in diameter. Ultrasonic sensors were used to measure the water depth, a flowmeter for the discharge, an ultrasonic velocity profiler (UVP) transducer for the flow velocity. Three different thresholds were defined to distinguish between the following states: no motion, vibration of stones, local motion, and large scale motion. The overwhelming influence of turbulence was emphasized by the conducted tests. This paper details the results of these experiments and demonstrates the need for further research in order to better quantify these effects. [less ▲]

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See detailParapet wall effect on Piano Key Weirs efficiency
Machiels, Olivier; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Journal of Irrigation & Drainage Engineering (2013), 139(6), 506-511

Piano Key Weir is a cost effective solution for rehabilitation as well as for new dam projects with a high level of constraints (limited space, high specific flood discharge, small reservoir level ... [more ▼]

Piano Key Weir is a cost effective solution for rehabilitation as well as for new dam projects with a high level of constraints (limited space, high specific flood discharge, small reservoir level variation). While the higher efficiency of the Piano Key Weir compared to standard linear weirs has already been demonstrated, its optimal geometry is still poorly defined. In order to improve the design of the complex geometry of this structure, the use of parapet walls has been tested. They consist of vertical extensions placed over the weir crest. Following a former study of the influence of the weir height on its discharge capacity, this paper presents the results of an experimental campaign dedicated to investigating the effect of parapet walls to increase weir height while reducing bottom slopes and keeping the weir height constant. These results indicate the relative influences of the alveoli bottom slopes and of the weir height on the Piano Key Weir release capacity. Comparisons with former experimental results as well as design guidelines are also provided. [less ▲]

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See detailHydraulic modelling in civil and environmental engineering
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

Scientific conference (2013, May 08)

Detailed reference viewed: 25 (3 ULg)