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See detailFlood risk analysis in Wallonia: micro (and meso-)scale approaches
Dewals, Benjamin ULiege; Detrembleur, Sylvain ULiege; Archambeau, Pierre ULiege et al

Conference (2010, October 25)

Flood risk analysis has been undertaken in Wallonia in the framework of several national and international research projects. The analysis relies on a micro-scale procedure, which involves • hazard ... [more ▼]

Flood risk analysis has been undertaken in Wallonia in the framework of several national and international research projects. The analysis relies on a micro-scale procedure, which involves • hazard modelling by means of detailed 2D inundation modelling • as well as processing of high resolution topographic and land use database for vulnerability modelling. The inundation modelling is conducted using the fully dynamic flow model WOLF 2D, entirely developed at the University of Liege. The model is run on a highly accurate DEM resulting from the combination of laser altimetry and, when available, sonar bathymetry. The typical grid spacing for the simulations is kept as low as 2m, which is definitely fine enough to represent the complex flows occurring at the scale of individual buildings and streets in urbanized floodplains. In this way, both the static and dynamic impacts of the flow may be characterized for all affected assets. This approach has been extensively applied since 2003 to issue inundation maps throughout the Walloon region based on detailed 2D flow modelling. Consequently, the outcomes of such detailed inundation modelling constitute suitable inputs for the subsequent exposure analysis, performed at a micro-scale using detailed land use maps and geographic database. Eventually, based on a multidisciplinary work, the procedure may incorporate social flood impact analysis and evaluation of direct economic damage to different categories of buildings and land types. Besides detailing the characteristics and performance of the hazard modelling, the presentation will describe the flow of data within the overall risk analysis procedure and will demonstrate its applicability by means of a case study, for which three different flood protection measures have been evaluated. These include rehabilitation of an old canal, recalibration of a floodplain as well as heightening of a protection wall by means of mobile dikes. The risk-oriented analysis of these flood protection measures has lead to findings which would not have arisen from a more standard hydraulic study such as based on a design flood. The flood risk analysis procedure is now readily available for large scale applications throughout the hydrographic basins in Wallonia and, in the near future, it will be combined with catchment modelling (accounting for climate change projections) to evaluate upstream flood mitigation measures as well as for the fine tuning of reservoir management rules in the framework of adaptation strategies to climate change. [less ▲]

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See detailExperimental investigation of flow pattern and sediment deposition in rectangular shallow reservoirs
Dufresne, Matthieu; Dewals, Benjamin ULiege; Erpicum, Sébastien ULiege et al

in International Journal of Sediment Research (2010), 25(3), 258-270

This work involved the experimental investigation of flow pattern, preferential regions of deposition and trap efficiency as a function of the length of rectangular shallow reservoirs. Four flow patterns ... [more ▼]

This work involved the experimental investigation of flow pattern, preferential regions of deposition and trap efficiency as a function of the length of rectangular shallow reservoirs. Four flow patterns were identified (from longer to shorter reservoirs): an asymmetric flow with two reattachment points, an asymmetric flow with one reattachment point, an unstable flow, and a symmetric flow without any reattachment point. Using dye visualizations, the median value and the temporal variability of the reattachment lengths were precisely measured for the asymmetric flows. For each stable flow, sediment tests with plastic particles were carried out. The regions of deposition on the bed of the reservoir were clearly a function of the flow pattern. The transition from an asymmetric flow pattern to a symmetric flow pattern was responsible for an abrupt decrease of the trap efficiency; a number of regression laws were discussed to take it into account. [less ▲]

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See detailDam-break flow computation based on an efficient flux-vector splitting
Erpicum, Sébastien ULiege; Dewals, Benjamin ULiege; Archambeau, Pierre ULiege et al

in Journal of Computational & Applied Mathematics (2010), 234

Dam-break flow computation is a task of prime interest in the scope of risk analysis processes related to dams and reservoirs. In this paper, a 2D finite volume multiblock flow solver, able to deal with ... [more ▼]

Dam-break flow computation is a task of prime interest in the scope of risk analysis processes related to dams and reservoirs. In this paper, a 2D finite volume multiblock flow solver, able to deal with natural topography variation, is presented in details. The model is based on an efficient Flux Vector Splitting method developed by the authors. A number of validation examples are comprehensively described. [less ▲]

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See detailRiver modelling and flood mitigation in a Belgian catchment
Khuat Duy, Bruno; Archambeau, Pierre ULiege; Dewals, Benjamin ULiege et al

in Proceedings of ICE : Water Management (2010), 163(8), 417-423

This paper describes the steps followed to propose solutions to recurring flooding problems in a Belgian catchment. Firstly, the hydraulic capacity (maximum discharge before bank overflow) of the cross ... [more ▼]

This paper describes the steps followed to propose solutions to recurring flooding problems in a Belgian catchment. Firstly, the hydraulic capacity (maximum discharge before bank overflow) of the cross sections was computed all along the river by an iterative 1D steady-state approach. In order to carry out these simulations, cross sections from on-site surveys of the river were integrated into the model, as well as hydraulic structures such as culverts, footbridges, and pipes. Secondly, the flooding problem was analysed with a time-dependant approach consisting of simulating floods following extreme rainfall events. The hydrological aspect was studied in a spatially distributed way using a multi-layer hydrological model. The available data on the basin such as the digital elevation model (DEM), the landuse, and the pedology were exploited to identify the basic modelling parameters. The hydrological contribution was routed by a 1D network resulting from the merging of the DEM-based and the cross section-based river networks. According to the results of the aforementioned steps, various local and catchment-wide solutions against flooding were proposed and analyzed. The comparison of simulated situations before and after these improvements allowed checking the effectiveness of the proposed solutions. [less ▲]

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See detailMicro-scale flood risk analysis based on detailed 2D hydraulic modelling and high resolution geographic data
Ernst, Julien ULiege; Dewals, Benjamin ULiege; Detrembleur, Sylvain ULiege et al

in Natural Hazards (2010), 55(2), 181-209

The paper presents a consistent micro-scale flood risk analysis procedure, relying on detailed 2D inundation modelling as well as on high resolution topographic and land use database. The flow model is ... [more ▼]

The paper presents a consistent micro-scale flood risk analysis procedure, relying on detailed 2D inundation modelling as well as on high resolution topographic and land use database. The flow model is based on the shallow-water equations, solved by means of a finite volume scheme on multiblock structured grids. Using highly accurate laser altimetry, the simulations are performed with a typical grid spacing of 2m, which is fine enough to represent the flow at the scale of individual buildings. Consequently, the outcomes of hydraulic modelling constitute suitable inputs for the subsequent exposure analysis, performed at a micro-scale using detailed land use maps and geographic database. Eventually, the procedure incorporates social flood impact analysis and evaluation of direct economic damage to residential buildings. Besides detailing the characteristics and performance of the hydraulic model, the paper describes the flow of data within the overall flood risk analysis procedure and demonstrates its applicability by means of a case study, for which two different flood protection measures were evaluated. [less ▲]

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See detailIntegrated flood risk analysis for assessing flood protection strategies
Ernst, Julien ULiege; Dewals, Benjamin ULiege; Detrembleur, Sylvain ULiege et al

in Tagelsir, Gasmelseid (Ed.) Handbook of Research on Hydroinformatics: Technologies Theories and Applications (2010)

The present chapter describes an end-to-end methodology for assessing flood protection strategies, including the whole methodological process from hydrological statistics to detailed 2D hydraulic ... [more ▼]

The present chapter describes an end-to-end methodology for assessing flood protection strategies, including the whole methodological process from hydrological statistics to detailed 2D hydraulic modelling, damage calculation and flood risk evaluation. This risk-based approach serves as a component of a decision-support system (DSS) developed in Belgium for identifying cost-effective flood management strategies in the context of climate change. The DSS accounts for both hydraulic and socio-economic parameters to quantify the benefits (in terms of avoided risk) and the cost of each strategy. Besides reviewing fundamentals of flood risk assessment, including the inundation model and main concepts related to flood risk, a consistent methodology for micro-scale flood risk analysis is presented in detail, combining complementary sources of GIS information such as high resolution and high accuracy land use database as well as socio-economic datasets. Finally a case study on a main tributary of river Meuse in Belgium is described. [less ▲]

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See detailHydraulic behavior of Piano Key Weirs: experimental approach
Machiels, Olivier ULiege; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

in Janssen, Robert; Chanson, Hubert (Eds.) 3rd Int. Junior Researcher and Engineer Worjshop on Hydraulic Structures (2010, May)

The Piano Key Weir (PKW) is a particular geometry of weir similar to a labyrinth shape that features overhanging cycle ends to reduce the base length. Together with its high discharge capacity for low ... [more ▼]

The Piano Key Weir (PKW) is a particular geometry of weir similar to a labyrinth shape that features overhanging cycle ends to reduce the base length. Together with its high discharge capacity for low heads, this geometric feature makes the PKW an interesting solution for dam rehabilitation, permitting the placement of the weir directly on dam crest. However, PKW stays a new type of weir, firstly designed in 2001 and built for the first time in 2006 by Electricité de France (EDF). Even if the first experimental studies confirmed its discharge capacities, lacks persist in the understanding of the flow behaviour upstream, along and downstream of this complex structure. This paper presents the mean results and observations obtained from experiments on a large scale model of PKW. The hydraulics of the structure is clarified based on measurements of water depths, pressures, velocities and discharges on each part of the weir. These observations explain the effect of geometric improvements proposed in former studies. [less ▲]

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See detailFlood Protection Design Based on Micro-scale Risk Modelling
Ernst, Julien ULiege; Dewals, Benjamin ULiege; Detrembleur, Sylvain ULiege et al

Poster (2010, April 22)

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See detailCaractérisation micro-échelle du risque d’inondation : modélisation hydraulique détaillée et impacts socio-économiques
Ernst, Julien ULiege; Dewals, Benjamin ULiege; Detrembleur, Sylvain ULiege et al

in Risque d'Inondation en Ile de France, 100 ans après les crues de 1910 (2010, March)

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See detailClassification of flow patterns in rectangular shallow reservoirs
Dufresne, Matthieu; Dewals, Benjamin ULiege; Erpicum, Sébastien ULiege et al

in Journal of Hydraulic Research (2010), 48(2), 197-204

This work focuses on the experimental classification of flow patterns in rectangular shallow reservoirs, including symmetric flows without any reattachment point to asymmetric flows with one reattachment ... [more ▼]

This work focuses on the experimental classification of flow patterns in rectangular shallow reservoirs, including symmetric flows without any reattachment point to asymmetric flows with one reattachment point, two reattachment points, or two reattachment points and one detachment point. The median position and the natural variability of the reattachment lengths of asymmetric flows were measured for forty geometric and hydraulic conditions. The effects of dimensionless flow depth, Froude number, lateral expansion ratio and dimensionless length on the median reattachment lengths were analyzed. A number of regression equations were proposed. For “high” dimensionless flow depths and a Froude number of 0.20, a shape parameter was proposed for predicting the transition between symmetric and asymmetric flows. The results of this study are useful knowledge for improving current methods to predict the trapping efficiency and the preferential regions of deposition in reservoirs. [less ▲]

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See detailAnalyse expérimentale de l'influence des largeurs d'alvéoles sur la débitance des déversoirs en touches de piano
Machiels, Olivier ULiege; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

in Houille Blanche (2010), (2), 22-28

Within the framework of updating the release and storage capacities of existing reservoirs, the use of piano keys weirs (PKW) can be an interesting alternative either to increase the discharge of a free ... [more ▼]

Within the framework of updating the release and storage capacities of existing reservoirs, the use of piano keys weirs (PKW) can be an interesting alternative either to increase the discharge of a free weir without changing the weir layout or the reservoir level, or increase the reservoir level before discharge while keeping the weir layout and the level of safety. In order to help to the understanding of the behavior of this new type of weirs and to characterize their hydraulic potential, the results of an experimental study with for objectives to study the influence of the relative width of the inlets and outlets on the hydrodynamic characteristics of the structure are presented. A process oriented analytical formulation for the evaluation of the discharge coefficient of the PKW tested on scale models is proposed. It is in satisfactory agreement with the experimental results and leads to an objective evaluation of the optimal ratio of the alveoli widths. [less ▲]

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