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See detailEffective soil hydraulic conductivity predicted with the maximum power principle
Westhoff, Martijn ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg 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 ▲]

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See detailDoes the Budyko curve reflect a maximum power state of hydrological systems? A backward analysis
Westhoff, Martijn ULg; Zehe, Erwin; Archambeau, Pierre ULg 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 ▲]

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See detailNumerical modelling of meandering jets in shallow rectangular reservoir using two different turbulent closures
Peltier, Y.; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Erpicum, Sébastien; Dewals, Benjamin; Archambeau, Pierre (Eds.) et al Sustainable Hydraulics in the Era of Global Change (2016)

In this article, the shallow water equations are used to model meandering flows in shallow rectangular reservoir.Two distinct meandering flows in termof friction regimewere modelled (frictional and ... [more ▼]

In this article, the shallow water equations are used to model meandering flows in shallow rectangular reservoir.Two distinct meandering flows in termof friction regimewere modelled (frictional and nonfrictional) and two turbulent closures were tested with various values for their tuning parameters. One turbulent closure accounts for both the 2D horizontal (k-ε) and 3D vertical (algebraic model) turbulent mixing, while the second turbulent closure accounts for the unresolved scales of the shallow water equations through a subgridscale model (Smagorinsky). The purpose here is to give advices on which turbulent closure is the most likely appropriate for modelling meandering flows. A Proper Orthogonal Decomposition (POD) is performed on the simulation results for extracting objective parameters accounting for transient behaviors and to be compared with experiments. Comparisons between models and with experiments indicate a great dependence of the simulation results to the modelling of the small scales of the turbulence. © 2016 Taylor & Francis Group, London. [less ▲]

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See detailLimitation of self-organization within a confined aquifer
Westhoff, M. C.; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Dewals, Benjamin; Archambeau, Pierre; Pirotton, Michel (Eds.) et al Sustainable Hydraulics in the Era of Global Change (2016)

Preferential flow paths are omnipresent in the subsurface, but very hard to observe or parameterize. Often they are even sub-grid processes requiring effective parametrization. In an ongoing study ... [more ▼]

Preferential flow paths are omnipresent in the subsurface, but very hard to observe or parameterize. Often they are even sub-grid processes requiring effective parametrization. In an ongoing study,Westhoff et al. (2016) show within a lab experiment that the steady state effective hydraulic conductance evolves (under certain circumstances) to the conductance that maximizes power by the flux through the confined aquifer. Here we explore why in one setup the effective conductance did obey this maximum power principle, while the same setup with slightly different boundary conditions did not lead to this.We suggest here, with a detailed numerical setup of the experiment, that the degrees of freedom to create a long enough preferential flowpathwas too limited in the latter case: a foam rubber layer, placed between the sand and the plate covering the sand (to pressurize the sand layer) prevented further development of the preferential flow path. While this preferential flow path was long enough to result in an effective conductance leading to maximum power in the first setup, it needed to be longer in the second setup. © 2016 Taylor & Francis Group, London. [less ▲]

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See detailNon-linear optimization of a 1-D shallow water model and integration into Simulink for operational use
Goffin, Louis ULg; Dewals, Benjamin ULg; Erpicum, Sébastien ULg et al

in Sustainable Hydraulics in the Era of Global Change - Proceedings of the 4th European Congress of the International Association of Hydroenvironment engineering and Research, IAHR 2016 (2016)

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See detailImpacts of urban expansion on future flood damage: A case study in the River Meuse basin, Belgium
Mustafa, Ahmed; Bruwier, Martin ULg; Teller, Jacques ULg et al

in Erpicum, Sébastien; Dewals, Benjamin; Archambeau, Pierre (Eds.) et al Sustainable Hydraulics in the Era of Global Change: Advances in Water Engineering and Research (2016)

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See detailCharacterization of Nappe Vibration on a Weir
Lodomez, Maurine ULg; Pirotton, Michel ULg; Dewals, Benjamin ULg et al

in Sustainable Hydraulics in the Era of Global Change (2016)

The nappe vibration phenomenon may affect numerous prototype structures, such as gates and spillways, when they operate under low head conditions. This phenomenon, which is far not well understood and ... [more ▼]

The nappe vibration phenomenon may affect numerous prototype structures, such as gates and spillways, when they operate under low head conditions. This phenomenon, which is far not well understood and poorly controlled, produces frequency oscillations in the thin flow nappe cascading downstream of the weir. These oscillations result in a disturbing noise production that increases the environmental and societal impacts of the hydraulic structure. Given limited information available regarding the physical processes of this phenomenon, a detailed investigation has been undertaken to characterize the flow for free-overfall structures where nappe vibration may be of concern. The research conducted on a prototype-scale linear weir model (weir length of 3.5 m and a fall height of 3 m) at the Engineering Hydraulics laboratory of the University of Liège enable to describe the flow and nappe vibration by using image and sound analysis. The paper presents the first quantitative results of the study. [less ▲]

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See detailDiscretization of the divergence formulation of the bed slope term in the shallow-water equations and consequences in terms of energy balance
Bruwier, Martin ULg; Archambeau, Pierre ULg; Erpicum, Sébastien ULg et al

in Applied Mathematical Modelling (2016), 40(17-18), 75327544

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 ▲]

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See detailFrequencies of Nappe Vibration for Free-overfall Structures
Lodomez, Maurine ULg; Pirotton, Michel ULg; Dewals, Benjamin ULg et al

in 6th IAHR IJREWHS (2016)

Under relatively low-head discharges, the occurrence of nappe oscillation, otherwise known as nappe vibration, may be observed on hydraulic structures with a free overfall, such as weirs, crest gates and ... [more ▼]

Under relatively low-head discharges, the occurrence of nappe oscillation, otherwise known as nappe vibration, may be observed on hydraulic structures with a free overfall, such as weirs, crest gates and fountains. This phenomenon, which has been early identified as undesirable and potentially dangerous on gates, is characterized by oscillations in the thin flow nappe cascading downstream of the crest. In addition, these oscillations produce a significant level of noise and acoustic pressure waves that increase the environmental and societal impacts of the structure. A review of the scientific literature shows a lack of consensus regarding the causes and source of the oscillations development. In this context of relatively poor understanding of the dominant processes, a detailed investigation has been undertaken to identify and quantify the nappe vibration mechanism. The research is being performed with a prototype-scale linear weir located at the Engineering Hydraulics laboratory of the University of Liège. The study employs high-speed cameras and audio equipment to characterize the nappe vibration. This paper presents first characteristics of the nappe vibrations gained from images and sound analysis, especially in terms of vibration frequency, for a quarter round and a half round weir crest. This study shows that frequencies measured by sound and image analyses are identical and depend on the crest shape, the fall height and the unit discharge. [less ▲]

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See detailEnergy conservation properties of Ritter solution for idealized dam break flow
Dewals, Benjamin ULg; Bruwier, Martin ULg; Erpicum, Sébastien ULg et al

in Journal of Hydraulic Research (2016), 54(5), 581-585

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 ▲]

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See detailPhysical modeling of an aerating stepped spillway
Erpicum, Sébastien ULg; Lodomez, Maurine ULg; Savatier, Jérémy et al

in Crookston, Brian; Tullis, Blake (Eds.) Hydraulic Structures and Water System Management (2016)

To mitigate the negative effects on the water quality in the downstream river of a projected large dam, and in particular to increase the dissolved oxygen concentration during low flow periods within the ... [more ▼]

To mitigate the negative effects on the water quality in the downstream river of a projected large dam, and in particular to increase the dissolved oxygen concentration during low flow periods within the first 10 years of dam operation, an aerating weir has been designed and tested on a physical model at the Laboratory of Engineering Hydraulics (HECE) of the Liege University. The design of the structure has been done considering data from the literature. The selected solution is a 3 m high stepped spillway designed to operate in nappe flow conditions within the range of design discharges (25 – 100 m³/s). To validate the design, a physical model representing a section of the weir at a 1:1 scale has been built and operated in the laboratory. Chemical dissolved oxygen removal technique has been applied upstream of the model to be able to measure the weir aerating efficiency. The physical model results show that the proposed structure is able to maintain, in the range of discharge in the river from 25 to 100 m³/s, a minimum 5 mg/l oxygen concentration downstream, whatever the upstream oxygen concentration. The paper presents the design process of the weir, the scale model features and the results of the validation tests on the physical model. The prototype construction will take place in 2017 and the water quality will be monitored. [less ▲]

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See detailTowards a New Design Equation for Piano Key Weirs Discharge Capacity
Bashiri Atrabi, Hamid ULg; Dewals, Benjamin ULg; Pirotton, Michel ULg 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 ▲]

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See detailSustainable hydraulics in the era of global change - Advances in water engineering and research
Erpicum, Sébastien ULg; Dewals, Benjamin ULg; Archambeau, Pierre ULg et al

Book published by CRC Press (2016)

In an increasingly urbanized world, water systems must be designed and operated according to innovative standards in terms of climate adaptation, resource efficiency, sustainability and resilience. This ... [more ▼]

In an increasingly urbanized world, water systems must be designed and operated according to innovative standards in terms of climate adaptation, resource efficiency, sustainability and resilience. This grand challenge triggers unprecedented questions for hydro-environment research and engineering. Addressing these issues requires a deep understanding of basic processes in fluid mechanics, heat and mass transfer, surface and groundwater flow, among others. This book unveils latest research achievements and innovations which were presented at the 4th European Congress of IAHR in Liege (Belgium). These new developments rely on state-of-the-art modelling technologies, supported by the exponentially growing availability of data and computation power. The book will serve as a reference for professionals and decision-makers involved in various water-related sectors, such as hydraulic engineering, fluvial hydraulics, coastal engineering, water resources management and many more. [less ▲]

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See detailScale effects in physical piano key weirs models
Erpicum, Sébastien ULg; Tullis, Blake; Lodomez, Maurine ULg et al

in Journal of Hydraulic Research (2016)

With inertia and gravity representing the dominant forces for most open channel flow applications (e.g. weir flow), Froude similitude is commonly used for scaling hydraulic performance data from the model ... [more ▼]

With inertia and gravity representing the dominant forces for most open channel flow applications (e.g. weir flow), Froude similitude is commonly used for scaling hydraulic performance data from the model to prototype structures. With weir flow, as the upstream head decreases, however, the relevance of surface tension and viscosity forces can increase to the point when the model and prototype similitude is not fully achieved through Froude scaling. Such discrepancies are referred as size-scale effects, and among other things, can result in variations in the head–discharge relationship, nappe trajectory, and air entrainment. Published criteria for avoiding significant size-scale effects for free flow over linear weirs have suggested that minimal heads of ∼0.02 to 0.07m be respected, independently of the model size. In this study, the size-scale effect, minimum upstream head, and Weber number limits are investigated for four piano key weirs with geometric model scales of 1:1, 1:7, 1:15, and 1:25. [less ▲]

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See detailHydrodynamics of long-duration urban floods: experiments and numerical modelling
Arrault; Finaud-Guyot, Pascal; Archambeau, Pierre ULg et al

in Natural Hazards & Earth System Sciences (2016), 16

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 ▲]

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See detailErosion and sedimentation in a hydropower project: assessing impacts and opportunities
Dewals, Benjamin ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg et al

in Schüttrumpf, Holger (Ed.) Offene Gewässer: Strahlwirkung, Fischaufstieg, Fischabstieg, Sedimente, Schadstoffe (2016)

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See detailHydrodynamic instabilities in shallow reservoirs: implications for sediment management
Peltier, Yann; de Cuyper, Anaïs; Erpicum, Sébastien ULg et al

Conference (2016)

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See detailCan the maximum power principle predict effective conductivities of a confined aquifer? A lab experiment
Westhoff, Martijn ULg; Erpicum, Sébastien ULg; Archambeau, Pierre ULg 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 ▲]

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