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Energy conservation properties of Ritter solution for idealized dam break flow Dewals, Benjamin ; Bruwier, Martin ; Erpicum, Sébastien et al in Journal of Hydraulic Research (in press) 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 ▲] Detailed reference viewed: 46 (25 ULg)Monitoring topography of laboratory fluvial dike models subjected to breaching based on a laser profilometry technique Rifai, Ismail ; Erpicum, Sébastien ; Archambeau, Pierre et al in International Symposium on River Sedimentation: Stuttgart 19th-22d september 2016 (2016, September) Detailed reference viewed: 25 (9 ULg)Failure of fluvial dikes: how does the flow in the main channel influence the breach development? Rifai, Ismail ; Erpicum, Sébastien ; Archambeau, Pierre et al in 4th IAHR Europe Congress (2016, July) Detailed reference viewed: 14 (5 ULg)Sensitivity of the breaching process in the case of overtopping induced fluvial dike failure Rifai, Ismail ; Erpicum, Sébastien ; Archambeau, Pierre et al in River Flow 2016 Proceedings (2016, July) Fluvial dikes are common structures constructed for flow channelization, prevention of river bed lateral migration and for flood protection purposes. Their aging increases their vulnerability to extreme ... [more ▼] Fluvial dikes are common structures constructed for flow channelization, prevention of river bed lateral migration and for flood protection purposes. Their aging increases their vulnerability to extreme hydro-logical events, and subsequently may cause their failure. Many laboratory studies of overtopping induced dike failure were conducted, dealing mainly on normal configurations (i.e. dam break configuration) without ac-counting for the influence of a parallel flow. The fluvial dike breaching process remains, therefore, insuffi-ciently studied. A simplified model assuming a parameterized evolution of the breach geometry has been de-veloped to evaluate the fluvial breaching process. Results showed a sensitivity of the breaching process to the main channel configuration and to the flow conditions. Also, the evolution mode that was prescribed for the breach cross-section strongly influences the breaching duration and the sediment discharge [less ▲] Detailed reference viewed: 12 (3 ULg)Distribution of uncertainties at the municipality level for ﬂood risk modelling along the river Meuse: implications for policy-making Pirotton, Michel ; ; Erpicum, Sébastien et al Conference (2016, April) Flood risk modelling has been conducted for the whole course of the river Meuse in Belgium. Major cities, such as Liege (200,000 inh.) and Namur (l 10,000 inh.), are located in the ﬂoodplains of river ... [more ▼] Flood risk modelling has been conducted for the whole course of the river Meuse in Belgium. Major cities, such as Liege (200,000 inh.) and Namur (l 10,000 inh.), are located in the ﬂoodplains of river Meuse. Particular attention has been paid to uncertainty analysis and its implications for decision-making. The modelling chain contains ﬂood frequency analysis, detailed 2D hydraulic computations, damage modelling and risk calculation. The relative importance of each source of uncertainty to the overall results uncertainty has been estimated by considering several alternate options for each step of the analysis; different distributions were considered in the ﬂood frequency analysis; the inﬂuence of modelling assumptions and boundary conditions (e.g., steady vs. unsteady) were taken into account for the hydraulic computation; two different landuse classiﬁcations and two sets ofdamage functions were used; the number of exceedance probabilities involved in the risk calculation (by integration of the risk-curves) was varied. In addition, the sensitivity of the results with respect to increases in ﬂood discharges \vas assessed. The considered increases are consistent with a "wet" climate change scenario for the time horizons 202l~2050 and 2071-2100 (Detrembleur et al., 2015). The results of hazard computation differ signiﬁcantly between the upper and lower parts of the course of river Meuse in Belgium. In the former, inundation extents grow gradually as the considered ﬂood discharge is increased (i.e. the exceedance probability is reduced), while in the downstream part, protection structures (mainly concrete walls) prevent inundation for ﬂood discharges corresponding to exccedance probabilities of 0.01 and above (in the present climate). For higher discharges, large inundation extents are obtained in the ﬂoodplains. The highest values of risk (mean annual damage) are obtained in the municipalities which undergo relatively frequent flooding (upper part of the river), as well as in those of the downstream part of the Meuse in which ﬂow depths in the urbanized floodplains are particularly high when inundation occurs. This is the case of the city of Liege, as a result of a subsidence process following former mining activities. For a given climate scenario, the uncertainty ranges affecting ﬂood risk estimates are significant; but not so much that the results for the different municipalities would overlap substantially. Therefore, these uncertainties do not hamper prioritization in terms of allocation of risk reduction measures at the municipality level. In the present climate, the uncertainties arising from ﬂood frequency analysis have a negligible inﬂuence in the upper part of the river, while they have a considerable impact on risk modelling in the lower part, where a threshold effect was observed due to the ﬂood protection structures (sudden transition from no inundation to massive ﬂooding when a threshold discharge is exceeded). Varying the number of exceedance probabilities in the integration of the risk curve has different effects for different municipalities; but it does not change the ranking of the municipalities in terms of ﬂood risk. For the other scenarios, damage estimation contributes most to the overall uncertainties. As shown by this study, the magnitude of the uncertainty and its main origin vary in space and in time. This emphasizes the paramount importance of conducting distributed uncertainty analyses. In the considered study area, prioritization of risk reduction means can be reliably performed despite the modelling uncertainties. [less ▲] Detailed reference viewed: 19 (2 ULg)The contribution of air-ﬂuidization to the mobility of rapid ﬂowslides ; Dewals, Benjamin ; Archambeau, Pierre et al Conference (2016, April) Air-fluidization can be the origin of the long runout of gravitational ﬂows involving ﬁne particles such as ash. An excessive air pore pressure dramatically reduces the friction angle of the material as ... [more ▼] Air-fluidization can be the origin of the long runout of gravitational ﬂows involving ﬁne particles such as ash. An excessive air pore pressure dramatically reduces the friction angle of the material as long as this pressure has not been dissipated, which occurs during the ﬂow. This phenomenon can be modelled thanks to the 2D depth-averaged equations of mass and momentum conservation and an additional transport equation for basal pore pressure evolu- tion (Iverson and Denlinger, 2001). ln this contribution, we discuss the application of this model in relation to recent experimental results on air- fluidized ﬂows by Roche et al. (2008) and Roche (2012). The experimental results were used to set a priori the value of the diffusion coefficient in the model, taking into account the diference of scale between the experiments and real-world applications. We also compare the model predictions against detailed observations of a well-documented historical event, the collapse of a fly-ash heap in Belgium (Stilmant et al., 2015). In particular, we analyse the inﬂuence of the different components of the model on the results (pore pressure dissipation vs. pore pressure generation). The diffusion coefﬁcient which characterizes the dissipation of air pore pressure is found sufficiently low for maintaining a ﬂuidized ﬂow over hundreds of meters. The study concludes that an air-tluidization theory is consistent with the ﬁeld observations. These ﬁndings are particularly interesting as they seem not in line with the mainstream acceptation in landslide modelling that air generally plays a secondary role (e.g., Legros, 2002). [less ▲] Detailed reference viewed: 18 (1 ULg)Contribution of future urbanisation expansion to ﬂood risk changes Bruwier, Martin ; ; Archambeau, Pierre et al Conference (2016, April) The ﬂood risk is expected to increase in the future due to climate change and urban development. Climate change modiﬁes ﬂood hazard and urban development inﬂuences exposure and vulnerability to ﬂoods ... [more ▼] The ﬂood risk is expected to increase in the future due to climate change and urban development. Climate change modiﬁes ﬂood hazard and urban development inﬂuences exposure and vulnerability to ﬂoods. While the inﬂuence of climate change on flood risk has been studied widely, the impact of urban development also needs to be considered in a sustainable ﬂood risk management approach. The main goal of this study is the determination of the sensitivity of future ﬂood risk to different urban devel~ opment scenarios at a relatively short-time horizon in the River Meuse basin in Wallonia (Belgium). From the different scenarios, the expected impact of urban development on ﬂood risk is assessed. Three urban expansion scenarios are developed up to 2030 based on a coupled cellular automata (CA) and agent-based (AB) urban expansion model: (i) business-as-usual, (ii) restrictive and (m) extreme expansion scenarios. The main factor controlling these scenarios is the future urban land demand. Each urban expansion scenario is developed by considering or not high and/or medium flood hazard zones as a constraint for urban development. To assess the model's performance, it is calibrated for the Meuse River valley (Belgium) to simulate urban expansion between i990 and 2000. Calibration results are then assessed by comparing the 2000 simulated land-use map and the actual 2000 land-use map. The ﬂood damage estimation for each urban expansion scenario is determined for ﬁve ﬂood discharges by overlaying the inundation map resulting from a hydraulic computation and tlte urban expansion map and by using damage curves and speciﬁc prices. The hydraulic model Wolt‘2D has been extensively validated by comparisons between observations and computational results during ﬂood event .This study focuses only on mobile and immobile prices for urban lands, which are associated to the most severe damages caused by ﬂoods along the River Meuse. These ﬁndings of this study offers tools to drive urban expansion based on numerous policies visions to mitigate future ﬂood risk along the Meuse River. In particular, we assess the impacts on future ﬂood risk of the prohibition of urban development in high and/or medium ﬂood hazard zones. [less ▲] Detailed reference viewed: 46 (9 ULg)When the same hydraulics conditions lead to different depositional patterns: case of an idealised delta ; Erpicum, Sébastien ; Archambeau, Pierre et al in Geophysical Research Abstracts (2016, April) Deltas are complex hydrosystems and ecosystems resulting from the interactions of a river system with a water body almost at rest. Anthropogenic factors (hydropower, ﬂood management, development in the ... [more ▼] Deltas are complex hydrosystems and ecosystems resulting from the interactions of a river system with a water body almost at rest. Anthropogenic factors (hydropower, ﬂood management, development in the ﬂoodplains) lead to dramatic changes in sediment transport in the rivers and in sediment management practice. From continuous, the sediment transport becomes increasingly intermittent, with long periods of deﬁcit in the sediment supply and short periods characterized by large supplies. Understanding how these intermittencies in the sediment supply affect the delta morphodynamics is of paramount importance for predicting the possible evolution and functioning of deltas. Deltas can reasonably be idealised as a reservoir, with an inlet channel representing the river and the sud- den enlargement of the reservoir representing the water body at rest. Using such an ideal conﬁguration enables the assessment of the inﬂuence of individual geometric and hydraulic parameters on the depositional patterns responsible for the morphodynamic evolution of the delta. Recent literature has shown that for very similar hydraulic boundary conditions, two very different types of ﬂow ﬁelds may develop (“straight jet” vs. “meandering jet”), leading to totally different depositional patterns. In turn, these distinct depositional patterns affect the ﬂow itself through a two-way coupling between the hydrodynamics and the morphodynamics of the deposits. These complex processes will be discussed in the proposed presentation, based on the results of over 160 experimental tests and corresponding numerical simulations. [less ▲] Detailed reference viewed: 20 (2 ULg)Does the Budyko curve reflect a maximum power state of hydrological systems? A backward analysis Westhoff, Martijn ; ; Archambeau, Pierre et al Conference (2016, April) 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 – with the maximum power principle optimized – model with the asymptotes of the Budyko curve we were able to derive more realistic values of the aridity and evaporation index without any parameter calibration. [less ▲] Detailed reference viewed: 16 (3 ULg)Effective soil hydraulic conductivity predicted with the maximum power principle Westhoff, Martijn ; Erpicum, Sébastien ; Archambeau, Pierre et al Conference (2016, April) Drainage of water in soils happens for a large extent through preferential flowpaths, but these subsurface flowpaths are extremely difficult to observe or parameterize in hydrological models. To ... [more ▼] Drainage of water in soils happens for a large extent through preferential flowpaths, but these subsurface flowpaths are extremely difficult to observe or parameterize in hydrological models. To potentially overcome this problem, thermodynamic optimality principles have been suggested to predict effective parametrization of these (sub-grid) structures, such as the maximum entropy production principle or the equivalent maximum power principle. These principles have been successfully applied to predict heat transfer from the Equator to the Poles, or turbulent heat fluxes between the surface and the atmosphere. In these examples, the effective flux adapts itself to its boundary condition by adapting its effective conductance through the creation of e.g. convection cells. However, flow through porous media, such as soils, can only quickly adapt its effective flow conductance by creation of preferential flowpaths, but it is unknown if this is guided by the aim to create maximum power. Here we show experimentally that this is indeed the case: In the lab, we created a hydrological analogue to the atmospheric model dealing with heat transport between Equator and poles. The experimental setup consists of two freely draining reservoirs connected with each other by a confined aquifer. By adding water to only one reservoir, a potential difference will build up until a steady state is reached. From the steady state potential difference and the observed flow through the aquifer, and effective hydraulic conductance can be determined. This observed conductance does correspond to the one maximizing power of the flux through the confined aquifer. Although this experiment is done in an idealized setting, it opens doors for better parameterizing hydrological models. Furthermore, it shows that hydraulic properties of soils are not static, but they change with changing boundary conditions. A potential limitation to the principle is that it only applies to steady state conditions. Therefore the rate of adaptation of hydraulic properties should be faster than the rate of change in boundary conditions. [less ▲] Detailed reference viewed: 16 (6 ULg)Hydrodynamics of long-duration urban ﬂoods: experiments and numerical modelling ; ; Archambeau, Pierre et al in Natural Hazards & Earth System Sciences (2016) 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 ▲] Detailed reference viewed: 37 (8 ULg)Does the Budyko curve reflect a maximum power state of hydrological systems? A backward analysis Westhoff, Martijn ; ; Archambeau, Pierre 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 ▲] Detailed reference viewed: 36 (14 ULg)Towards a New Design Equation for Piano Key Weirs Discharge Capacity Bashiri Atrabi, Hamid ; Dewals, Benjamin ; Pirotton, Michel et al in Proc. of the 6th International Symposium on Hydraulic Structures (2016) Piano Key weirs are Labyrinth like weirs which can be placed on the top of gravity dams. They represent a powerful solution to increase the discharge capacity of existing dam spillways. For proper design ... [more ▼] Piano Key weirs are Labyrinth like weirs which can be placed on the top of gravity dams. They represent a powerful solution to increase the discharge capacity of existing dam spillways. For proper design it is necessary to accurately predict this discharge capacity. In this research, artificial neural network, multiple linear and nonlinear regressions are used to set up a new design equation for the discharge capacity of Piano Key weirs. The effect of each parameter on the discharge capacity of Piano Key weirs is tested in these models. Several non-dimensional parameters are used to define a functional relationship between the inputs and output. These parameters are built from the geometric dimensions of the structure such as weir height, inlet and outlet keys width, overhangs length, water head and side crest length. Previous experimental data, which were collected at the experimental laboratory of the research group Hydraulics in Environmental and Civil Engineering (HECE), University of Liege, are used for training and testing patterns of the models. Root mean square errors (RMSE) and coefficient of determination (R2) are used as comparing criteria for the evaluation of the models. The models’ results are compared with experimental results and other existing equations. [less ▲] Detailed reference viewed: 16 (1 ULg)Non-linear optimization of a 1-D shallow water model and integration into Simulink for operational use Goffin, Louis ; Dewals, Benjamin ; Erpicum, Sébastien et al in 4th IAHR Europe Congress (2016) Detailed reference viewed: 15 (4 ULg)Erosion and sedimentation in a hydropower project: assessing impacts and opportunities Dewals, Benjamin ; Erpicum, Sébastien ; Archambeau, Pierre et al in Schüttrumpf, Holger (Ed.) Offene Gewässer: Strahlwirkung, Fischaufstieg, Fischabstieg, Sedimente, Schadstoffe (2016) Detailed reference viewed: 21 (2 ULg)Hydrodynamic instabilities in shallow reservoirs: implications for sediment management ; ; Erpicum, Sébastien et al Conference (2016) Detailed reference viewed: 21 (1 ULg)Numerical investigation of the pressure on a spillway crest Goffin, Louis ; Erpicum, Sébastien ; Archambeau, Pierre et al Conference (2016) Detailed reference viewed: 17 (5 ULg)Discretization of the divergence formulation of the bed slope term in the shallow-water equations and consequences in terms of energy balance Bruwier, Martin ; Archambeau, Pierre ; Erpicum, Sébastien et al in Applied Mathematical Modelling (2016) 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 ▲] Detailed reference viewed: 33 (11 ULg)Can the maximum power principle predict effective conductivities of a confined aquifer? A lab experiment Westhoff, Martijn ; Erpicum, Sébastien ; Archambeau, Pierre et al Conference (2015, December 14) Power can be performed by a system driven by a potential difference. From a given potential difference, the power that can be subtracted is constraint by the Carnot limit, which follows from the first and ... [more ▼] Power can be performed by a system driven by a potential difference. From a given potential difference, the power that can be subtracted is constraint by the Carnot limit, which follows from the first and second laws of thermodynamics. If the system is such that the flux producing power (with power being the flux times its driving potential difference) also influences the potential difference, a maximum in power can be obtained as a result of the trade-off between the flux and the potential difference. This is referred to as the maximum power principle. It has already been shown that the atmosphere operates close to this maximum power limit when it comes to heat transport from the Equator to the poles, or vertically, from the surface to the atmospheric boundary layer. To reach this state of maximum power, the effective thermal conductivity of the atmosphere is adapted by the creation of convection cells. The aim of this study is to test if the soil’s effective hydraulic conductivity also adapts in such a way that it produces maximum power. However, the soil’s hydraulic conductivity adapts differently; for example by the creation of preferential flow paths. Here, this process is simulated in a lab experiment, which focuses on preferential flow paths created by piping. In the lab, we created a hydrological analogue to the atmospheric model dealing with heat transport between Equator and poles, with the aim to test if the effective hydraulic conductivity of the sand bed can be predicted with the maximum power principle. The experimental setup consists of two freely draining reservoir connected with each other by a confined aquifer. By adding water to only one reservoir, a potential difference will build up until a steady state is reached. The results will indicate whether the maximum power principle does apply for groundwater flow and how it should be applied. Because of the different way of adaptation of flow conductivity, the results differ from that of the atmosphere. [less ▲] Detailed reference viewed: 37 (13 ULg)Développement d'un module Simulink pour la modélisation d'écoulements transitoires sur la Romanche sous WOLF1D Goffin, Louis ; Pirotton, Michel ; Dewals, Benjamin et al Report (2015) Detailed reference viewed: 12 (2 ULg) |
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