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Mitigation measures for downstream-migrating Atlantic salmon smolts (Salmo salar L.) are commonly insufficiently attractive to enable safe entrance and passage with no delay. Combining 2D telemetry with hydrodynamic modelling has been shown to be a good tool to better understand the influence of hydrodynamic factors on the migration route choice of fishes. In this study, we investigated the smolt downstream migration at a hydropower plant in Belgium that offers five migration routes, including two Archimedes screws and one nature-like fishway. At the hydropower plant, the Archimedes screws were the most used migration routes, due to higher discharges and more important water depths at their entrance. The weir and the canal intake were less used by the smolts. The nature-like fishway turned out to be less used, with 23% of the smolts. Its associated crossing time was significantly longer, probably due to shallow water depths and high flow velocities. The nature-like fishway had the potential to become a good migration route for salmon smolts after improvements to increase attractiveness and passage efficiency. Moreover, the Archimedes screws were not detrimental to the smolts and did not cause any significant delays to the crossing time.

Extreme events as the ones which occurred in July 2021 mostly in Belgium, Germany and the south of the Netherlands are causing important human and material losses. This event broke many records in a meteorological point of view as well as in the behaviour of the rivers, hence it urges several procedures of water and flood management to be revisited or better understood. However, hydrological modelling of such phenomena is challenging as it should cope with historical rain and discharge flow intensities never recorded before in the region but also deal with human construction and behaviour such as dams. Furthermore, most of the measurement devices in the Vesdre river were swept away or damaged during this flood engendering a paucity of reliable data for this catchment.This presentation will focus on the hydrological simulation and a model comparison in the Vesdre and Amblève catchments in Belgium during the episode of July 2021. Both neighbour catchments were among the most damaged and displays anthropogenic characteristics. The former lacks accurate data along the watercourse but chronicles of the water depths and the manoeuvres of the sluice gates in the dams are exploitable to reconstruct the inputs and outputs. While the latter contains a rich database of flow measurements during that period and spatially well distributed to capture all main tributaries in the Amblève.The Amblève river was favoured to perform a calibration of the models and analysis of the evolution of the flow properties along its stream. With this aim in mind, the modular structure of the hydrology package in the WOLF software, developed by the HECE team at the University of Liège, was employed to carry out distributed event hydrology simulations. Semi-distributed optimisations were performed, considering the functioning of the dams. The impact of an increasing complexity of the models and a comparison with celebrated models such as GR4H and VHM was investigated, as well as the effect of the source of rain data and their quality on the results.This study emphasised that, for all models, most of the flow in the surface drained by the dams in the Vesdre was mainly caused by runoff/overland flows. This effect was observed in some subbasins in the Amblève displaying the same types of land uses, but also in more urban areas. Nonetheless, head catchments in the Ambève were mostly composed of groundwater flow. Moreover, it shows the importance of accurately distributed rain and confirms the local character of the phenomenon and its effect on the hydrological properties evolution

The multiple flow paths existing in urban environments lead to complex flow fields during urban flooding. Modelling these flow processes with three-dimensional numerical models may be scientifically sound; however, such numerical models are computationally demanding. To ascertain whether urban floods can be modelled with faster tools, this study investigated for the first time the capacity of the 2D shallow water equations (SWE) in modelling the flow patterns within and around urban blocks with openings, i.e., involving flow exchanges between the flows in the streets and within the urban blocks (e.g., through alleys leading to courtyards or through broken windows or doors). Laboratory experiments of idealized urban floods were simulated with two academic 2D SWE models, with their most notable difference being the parameterization of the eddy viscosity. Specifically, the first model had a turbulence closure based on flow depth and friction velocity while the second model had a depth-averaged k-ε turbulence closure. Thirteen urban layouts were considered with steady flow and five with unsteady flow. Both models simulated the flow depths accurately for the steady cases. The discharge distribution in the streets and the flow velocities were predicted with lower accuracy, particularly in layouts with large open spaces. The average deviation of the modelled discharge distribution at the outlets was 2.5% and 7.3% for the first and second model, respectively. For the unsteady cases, only the first model was tested. It predicted well the velocity pattern during the falling limb of a flood wave, while it did not reproduce all recirculation zones in the rising limb. The peak flow depths in the streets and the peak discharges at the outlets were predicted with an average deviation of 6.7% and 8.6%, respectively. Even though some aspects of the flow in an urban setup are 3D, the findings of this study support the modelling of such processes with 2D SWE models.

Damage modelling generally remains less mature than other components of the flood risk modelling chain. Existing damage models were calibrated for particular regions and flood types, but their transferability to other contexts is scientifically challenging. The calibration of damage models is currently hampered by a lack of reliable empirical data.In July 2021, devastating floods occurred in several catchments in North-West Europe. Germany and Belgium were particularly hit. This communication presents ongoing initiatives to collect consistent hazard, vulnerability and impact data in the catchment of river Vesdre, Belgium, where up to 30% of annual precipitation was measured in just 48 h. During the night of July 14-15, 2021, the peak discharge in river Vesdre exceeded by a factor 2 to 4 the 100-year flood. At most stations, the observed flow was the highest on record. This led to tremendous tangible and intangible impacts, including 100+ buildings washed out by the flow. Considerable surprise effects also played a part.A large-scale field survey is being designed to collect, structure and analyse data on flow variables, building characteristics and experienced damage in the housing sector. For the sake of ensuring the quality of data, particularly on technical aspects such as type of building material or level of ground flood compared to street level, a field survey was preferred to an online questionnaire or phone-based interviews.As an onset for the large-scale flood damage survey, a pilot study was undertaken in November 2021. With the help of a group of students, about 400 buildings were visited to interview the inhabitants. For only 30 % of them, it was possible to get in contact with the inhabitants, as many buildings were still not inhabited due to the extent of the damages. Only for four buildings out of ten, the respondent was willing to conduct the interview, primarily due to lack of time or lack of interest. Other invoked reasons include trauma, language difficulties, or Covid quarantine. It was noticed that building characteristics are easier to obtain when the inhabitant owns the building and that respondents express a strong expectation on receiving feedback on the study outcomes.Based on collected data, the mean damage per building is 55 k€. However, although the interviews were conducted four months after the event, only half of the participants were able to provide monetary estimates of the damages. The heating system was by far the most affected component due to its usual positioning in the building basements.The upcoming large-scale survey will enable calibrating suitable flood damage models and provide new insights into damage mechanisms to contribute to improved cost-effectiveness analyses for risk reduction measures.

Hydraulic engineering is the application of hydraulic science to problems dealing with water management and use. In this discipline, dams and reservoirs and their appurtenant (or ancillary) structu...

Flood modelling in transnational rivers requires efficient cross-border collaboration among the riparian countries. Currently, each country/region usually uses a different hydraulic modelling approach, which may hinder the modelling of the entire river. For the sake of accurate and consistent river modelling there is a necessity for the establishment of a framework that fosters international collaborations. This study investigates the current hydraulic modelling approach across the whole length of the River Meuse, the main course of which crosses three north-western European countries. The numerical models used by French, Belgian, and Dutch agencies and authorities were interconnected by exchanging boundary conditions at the borders. At the central part of the river, the Belgian hydraulic model assumed steady flow conditions, while the rest of the river was modelled in unsteady mode. Results for various flood scenarios revealed a distinctive pattern of water depths at the Belgian-Dutch border. To clarify whether this is a bias induced by the change in modelling approach at the border (steady vs. unsteady), we remodelled a stretch of the river across the Belgian-Dutch border using a consistent unsteady modelling approach. The steady and unsteady approaches led to similar patterns across the border, hence discarding the hypothesis of a bias resulting from a change in the employed model. Instead, the pattern in water depths was attributed to a change in the topography of the Meuse Valley, where there is a transition from a narrow steep corridor with limited water storing capacity in Ardennes massif to wide floodplains in the Dutch lowlands. The associated flood damping for the 100-year discharge is less than 1% in the Ardennes and exceeds 15% in the Dutch lowlands. It can be inferred that the current differences in regional hydraulic modelling approaches for the River Meuse are generally well-grounded and not just a legacy of the past.

Air-water flows occur commonly in stepped spillways including the nappe flow regime for low flow rates. The present laboratory experiments researched the nappe flow regime in a stepped chute with prototype-scale steps height providing unique insights into the evolution of nappe flows along a stepped chute. Detailed visual observations highlighted the varying flow features along the stepped chute including the evolution of flow aeration, of jet properties and of instationarities in form of jump waves and cavity fluctuations with typical frequencies of around 1 Hz. These instationarities were caused by complex flow interactions at the impingement of the jet on the horizontal step face. Detailed air-water flow measurements revealed the complexity of the flows highlighting both S-shape and jet-like void fraction distributions and jet-like interfacial velocity distributions downstream of the jet impact and at step edges. This resulted in a downwards shift of the bubble count rate distributions closer to the step face. The nappe flows showed strong energy dissipation and reaeration performances along the stepped chute. The present study provided a robust and extensive characterisation of nappe flows and due to the large scale of the experiments, the results should provide confidence for the design of stepped chutes with embankment dam slope.

This paper presents two datasets obtained from laboratory experiments of urban flooding in a street network performed at the University of Liège. The experimental model represents a part of a synthetic urban district that consists of three inlets, three outlets and several three- and four- branches crossroads. The following experimental data was produced: (i) dataset 1: time-series of flow depths at model inlets and time-series of discharges at model outlets for a two-branch junction model, a two-branch bifurcation model and a district model. The datasets were generated by varying the upstream and downstream boundary conditions, i.e. flooding conditions; (ii) dataset 2 includes the same data type as dataset 1 complemented by 2D surface velocity measured using the non-intrusive LSPIV technique for eight urban form configurations in the district model. The collected data enable improving the understanding of the effect of urban forms on the urban flood processes. These two datasets are valuable for validating and improving numerical or analytical models of urban flooding and may contribute to flood risk management and flood-resilient urban design.

Laboratory studies of urban flooding often use geometrically distorted scale models due to the multi-scale nature of these specific flows. The possible bias induced by geometric distortion has never been thoroughly investigated with dedicated laboratory experiments. In this study, we combine experimental and computational modeling to systematically assess the influence of the distortion ratio, that is, the ratio of horizontal to vertical scale factors, on upscaled flow depths and discharge partition between streets. Three flow configurations were considered: a street junction, a street bifurcation, and a small synthetic urban district. When the distortion ratio is varied up to a value of about 5, the upscaled flow depths at the model inlets decrease monotonously and the flow discharge in the branch that conveys the largest portion of the flow is greatly enhanced. For equal flow depths at the model outlets and depending on the configuration, the distortion effect induces a variation of the upstream flow depth approximately from ∼4% to ∼17% and a change in outlet discharge partition up to 24 percentage points. For a distortion ratio above 5, both upscaled upstream flow depths and outlet discharge partition tend to stabilize asymptotically. Our study indicates the direction and magnitude of the bias induced by geometric distortion for a broad range of flow cases, which is valuable for offsetting these effects in practical laboratory studies of urban flooding.

Afin d’étudier l’évolution du comportement hydraulique des seuils standard pour des charges supérieures à la charge de dimensionnement, plusieurs profils ont été testés sur une plateforme d’essais spécifiquement dimensionnée et instrumentée. Ces profils ont été définis en regard des profils réels des seuils des barrages exploités par EDF et de la géométrie de la littérature la plus utilisée en pratique. Les essais expérimentaux ont été complétés par des modélisations numériques qui ont fourni des résultats généralement semblables. L’analyse permet de démontrer que le coefficient de débit augmente avec la charge jusque pour des rapports de charge de l’ordre de 5.5. Cette évolution peut être valablement approximée par les relations en puissance de la littérature. Pour des rapports de charge supérieurs à 5.5, le coefficient de débit subit une diminution brutale en passant d’une valeur de l’ordre de 0.6 à une valeur de l’ordre de 0.55 matérialisée au sein de l’écoulement par l’apparition d’une zone de faible vitesse à proximité du radier du seuil (la lame décroche du seuil). L’analyse permet également de démontrer une nette diminution du coefficient de débit lorsque le quadrant amont du seuil présente une charge de dimensionnement apparente supérieure à deux fois celle du quadrant aval (diminution de l’ordre de 10%). En revanche, aucun effet n’est perceptible sur l’évolution du coefficient de débit lorsque le quadrant amont présente une charge de dimensionnement apparente inférieure à celle du quadrant aval.

Flood damage modelling is a key component of flood risk modelling, assessment and management. Reliable empirical data of flood damage are essential to support the development and validation of flood damage models. However, such datasets remain scarce and incomplete, particularly those combining a large spatial coverage (e.g., regional, national) over a long time period (e.g., several decades) with a detailed resolution (e.g., address-level data).In this research, we analysed a database of 27,000 compensation claims submitted to a Belgian state agency (Disaster Fund). It covers 104 natural disasters of various types (incl. floods, storms, rockslides …) which occurred in the Walloon region in Belgium between 1993 and 2019. The region extends over parts of the Meuse and of the Scheldt river basins. The registered amounts of damage at the building level were estimated by state-designated experts. They are classified in six categories. While roughly half of the registered disasters are pluvial flooding events, they account for less than a quarter of the total claimed damage. In contrast, riverine floods correspond to about one third of the registered events, but they lead to one half of the claimed damage.A detailed analysis of the data was undertaken for a limited number of major riverine flood events (1993, 1995, 2002), which have caused a very large portion of the total damage. By geo-referencing the postal address of each individual building, it was possible to assign each claim to a specific river reach. This enabled pointing at the most flood prone river stretches in an objective way. Then, using cadastral data, each type and amount of damage could be attributed to a specific building.To explore the value of the database for elaborating and validating damage models, the claimed damage data at the building level were related to estimates of hydraulic variables for the corresponding flood events. To do so, we used an existing database of results of 2D hydrodynamic modelling, covering 1,200+ km of river reaches and providing raster files at a spatial resolution ranging from 2 m to 5 m for computed flow depth and velocity in the floodplains. The attribution of flow depth to individual buildings was performed either by averaging the computed flow depths around the building footprint or by considering the maximum value.The correlation between claimed damage at the building level and attributed flow depth is relatively low, irrespective of the flow depth attribution method. This may result from the high uncertainty affecting each of these variables. It also hints at the necessity of using multivariable damage models which account for a broader range of explanatory variables than the sole flow depth (flow velocity, characteristics of building material and equipment, building age, etc.). This will be discussed in the presentation and further explored in the next steps of this research.Data for this analysis were provided by the Belgian regional agency SPW-IAS in July 2020. Due to privacy reasons, data at the address-level may not be disseminated in the scientific community; but results of data processing may be shared at an aggregated level.

Failure of fluvial dykes often leads to devastating consequences in the protected areas. Overtopping flow is, by far, the most frequent cause of failure of fluvial dykes. Numerical modeling of the breaching mechanisms and induced flow is crucial to assess the risk and guide emergency plans.Various types of numerical models have been developed for dam and dyke breach simulations, including 2D and 3D morphodynamic models (e.g., Voltz et al., 2017 ; Dazzi et al., 2019 ; Onda et al., 2019). Nevertheless, simpler models are a valuable complement to the detailed models, since they enable fast multiple model runs to test, e.g. a broad range of possible breach locations or to perform uncertainty analysis. Moreover, unlike statistical formulae, physically-based lumped models are reasonably accurate and remain interesting in terms of process-understanding (Wu, 2013 ; Zhong et al., 2017 ; Yanlong, 2020).Nonetheless, existing lumped physically-based models were developed and tested mostly in frontal configurations, i.e. for the case of breaching of an embankment dam and not a fluvial dyke. Despite similarities in the processes, the breaching mechanisms involved in the case of fluvial dykes differ due to several factors such as a loss of symmetry and flow momentum parallel to the breach (Rifai et al., 2017). Therefore, there is a need to assess the transfer of existing lumped physically-based models to configurations involving fluvial dyke breaching.Here, we have developed a modular computational modeling framework, in which we are able to implement various physically-based lumped models of dyke breaching. In this framework, we started with our own implementation of the model presented by Wu (2013) and we incorporated a number of changes to the model. Next, we evaluated the model performance for a number of laboratory and field tests covering both frontal (Frank, 2016; Hassan and Morris, 2008) and fluvial (Rifai et al., 2017; 2018; Kakinuma and Shimizu, 2014) configurations. The modular framework we have developed proves also particularly suitable for testing the sensitivity and uncertainties arising from assumptions in the model structure and parameters.

In the context of large-scale urban flood modeling, porosity shallow-water models enable a considerable speed-up in computations while preserving information on subgrid topography. Over the last two decades, major improvements have been brought to these models, but a single generally accepted model formulation has not yet been reached. Instead, existing models vary in many respects. Some studies define porosity parameters at the scale of the computational cells or cell interfaces, while others treat the urban area as a continuum and introduce statistically defined porosity parameters. The porosity parameters are considered either isotropic or anisotropic and depth-independent or depth-dependent. The underlying flow models are based either on the full shallow-water equations or approximations thereof, with various flow resistance parameterizations. Here, we provide a review of the spectrum of porosity models developed so far for large-scale urban flood modeling.

The present study investigated the occurrence and characteristic frequency of nappe oscillations on weirs by reanalyzing data from 52 experimental configurations. The considered configurati...

The age of a water particle in a shallow man-made reservoir is defined as the time elapsed since it entered it. Analyzing this diagnostic timescale provides valuable information for optimally sizing and operating such structures. Here, the constituent-oriented age and residence time theory (CART) is used to obtain not only the mean age, but also the water age distribution function at each location. The method is applied to 10 different shallow reservoirs of simple geometry (rectangular), in a steady-state framework. The results show that complex, multimodal water age distributions are found, implying that focusing solely on simple statistics (e.g., mean or median age) fails to reflect the complexity of the actual distribution of water age. The latter relates to the fast or slow pathways that water particles may take for traveling from the inlet to the outlet of the reservoirs.

International audience; no abstract

In the research project Iot.H2O, which is funded under the Water JPI Joint Call 2017 IC4WATER, the potential of the Internet of Things concept is investigated for monitoring and controlling water distribution systems. Smart sensors are used which send data via LoraWAN to gateways which are connected to the Internet. The aim of the project is to use low-cost sensors and open-source software.In the presentation, a prototype on a laboratory scale will be shown. The design of the monitoring system will be explained in detail and compared to the design of standard SCADA systems. Results on a pump test rig based on a laboratory scale will be shown as well as first results of field tests in a real water distribution system in Germany.The presentation will also detail how data gathered through the smart sensors will be integrated into software modelling and optimization of water distribution systems. Combined with the new data, such tools offer a range of applications of practical relevance, such as the identification of optimal locations of micro-turbines for energy recovery in water distribution networks and the estimation of water demand throughout the network.

Overtopping of fluvial dikes occurs frequently during major floods and may lead to dike failure, with severe consequences in the protected areas. Mechanisms of fluvial dike breaching remain incompletely understood, while predicting the breach hydrograph is of paramount importance for the flood risk management.Here, we present a new series of laboratory experiments, in which the evolving 3D fluvial dike geometry was monitored in detail using the laser profilometry technique. The experimental setup extends over about 20 m by 7 m and accommodates a 15 m long main channel and a 7 m-long dike section. The facility is located at LNHE of EDF-R&D (France). The present study extends former experiments by Rifai et al. (2017, 2018), which were conducted with uniform coarse sand (d50 = 1.03 mm). In the new tests, various mixtures of coarse (d50 = 1.03 mm) and fine (d50 = 0.24 mm) sands were used as dike material (Rifai et al., 2020). The fraction of fine sand was varied systematically to assess its influence on the breaching process, specifically as regards the apparent cohesion.The experimental observations reveal that the frequency of breach slope collapse tends to decrease as the fraction of fine sand is increased; but the collapsing volumes become larger. Consequently, in the tested configurations, the addition of fine sand to the dike material has virtually no effect on the overall breaching dynamics, due to compensation between less frequent but larger collapsing material volumes. In the presentation, the relative importance of the effects will be discussed in comparison with other influencing parameters such as the main channel discharge, floodplain backwater effects and the dike geometry.All experimental data, including high resolution 3D dynamic models of the breach geometry, are publicly available online (Rifai et al., 2019).ReferencesRifai, I., Erpicum, S., Archambeau, P., Violeau, D., Pirotton, M., El kadi Abderrezzak, K., & Dewals, B. (2017). Overtopping induced failure of noncohesive, homogeneous fluvial dikes. Water Resources Research, 53(4), 3373-3386.Rifai, I., El kadi Abderrezzak, K., Erpicum, S., Archambeau, P., Violeau, D., Pirotton, M., & Dewals, B. (2018). Floodplain backwater effect on overtopping induced fluvial dike failure. Water Resources Research, 54(11), 9060-9073.Rifai, I., El kadi Abderrezzak, K., Erpicum, S., Archambeau, P., Violeau, D., Pirotton, M., & Dewals, B. (2019). Flow and detailed 3D morphodynamic data from laboratory experiments of fluvial dike breaching. Scientific data, 6(1), 53.Rifai, I., El kadi Abderrezzak, K., Hager, W.H., Erpicum, S., Archambeau, P., Violeau, D., Pirotton, M., & Dewals, B. (2020). Apparent cohesion effects on overtopping-induced fluvial dike breaching. Journal of Hydraulic Research. In press. https://doi.org/10.1080/00221686.2020.1714760.

Flow overtopping can lead to the initiation of breaching and failure of fluvial dikes, causing severe inundations and damage in the protected areas. For flood risk management and prevention, the ac...

Scale physical modeling is widely used for large hydraulic structures design. It is recognized as a reliable method to characterize detailed flow conditions at prototype scale. However, similar to numerical models, scale physical models are simplifications of real size flow conditions. That’s why, when possible, comparison of scale model data to prototype data has to be done and shared among the scientific and practitioners’ community. In this paper, data gained from a large dam bottom outlet operation are compared at prototype and physical model scale (1:35). The structure includes a bottom step aerator, specific downstream channel sidewalls and a complex flip bucket to control the jet impact location in the narrow downstream valley. Prototype tests cover a large range of upstream head with varied gate openings. The comparison shows that, while main flow features have been properly predicted by the scale model, significant differences exist. For instance, flow aeration is much more important on the prototype than on the scale model. Transients have also been properly capture during the experimental tests.

Shallow-water models are standard for simulating flow in river systems during floods, including in the nearfield of sudden changes in the topography, where vertical flow contraction occurs such as in case of channel overbanking, side spillways or levee overtopping. In the case of stagnant inundation and for frontal flow, the flow configurations are close to the flow over a broad-crested weir with the trapezoidal profile in the flow direction (i.e. inclined upstream and downstream slopes). In this study, results of shallow-water numerical modelling were compared with seven sets of previous experimental observations of flow over a frontal broad-crested weir, to assess the effect of vertical contraction and surface roughness on the accuracy of the computational results. Three different upstream slopes of the broad-crested weir (V:H = 1:Z(1) = 1:1, 1:2, 1:3) and three roughness scenarios were tested. The results indicate that, for smooth surface, numerical simulations overestimate by about 2 to 5% the weir discharge coefficient. In case of a rough surface, the difference between computations and observations reach up to 10%, for high relative roughness. When taking into account mentioned the differences, the shallow-water model may be applied for a range of engineering purposes. Modely mělké vody jsou standardem pro simulaci toku v říčních systémech během povodní, a to i v blízkém poli náhlých změn v topografii, kde dochází ke svislé kontrakci toku, jako například v případě přetížení kanálu, postranních přelivů nebo přetížení hrází. V případě stagnujícího inundace a pro čelní tok jsou konfigurace toku blízké toku přes široko-chocholatý jez s lichoběžníkovým profilem ve směru toku (tj. Nakloněné před a za svahem). V této studii byly výsledky numerického modelování mělké vody porovnány se sedmi sadami předchozích experimentálních pozorování toku přes čelní široko-chocholatý jez, aby se vyhodnotil vliv vertikální kontrakce a drsnosti povrchu na přesnost výpočtových výsledků. Byly testovány tři různé svahy proti proudu širokého hřebenu (V: H = 1: Z (1) = 1: 1, 1: 2, 1: 3) a tři scénáře drsnosti. Výsledky ukazují, že pro hladký povrch numerické simulace přeceňují asi o 2 až 5% koeficient propouštění jezu. V případě drsného povrchu dosahuje rozdíl mezi výpočty a pozorováním až 10% pro vysokou relativní drsnost. Při zohlednění uvedených rozdílů lze model mělké vody použít pro řadu inženýrských účelů.

This paper aims at validating pressure and velocity measurements conducted in two physical scale models of an ogee spillway crest operating at heads largely greater than the design head. The design head of the second model is 50% smaller than the one of the first model. No pier effect or air venting is considered in the study. The velocity field is measured by Bubbles Image Velocimetry. The relative pressure along the spillway crest is measured using pressure sensors. Comparison of measured velocities between both spillways indicates low scale effects, the scaled-profiles collapsing in most parts of the flow. By contrast, measurements of relative pressure along the spillway crest differ for large heads. A theoretical velocity profile based on potential flow theory and expressed in a curvilinear reference frame is fitted to the velocity measurements, considered as reference, for extrapolating the velocity at the spillway crest. Comparing the extrapolated velocity at the spillway crest and the velocity calculated from the relative pressure considering a potential flow finally emphasizes that bottom pressure amplitudes seem overestimated for the larger spillway, while an averaging effect might operate for the pressure measurements on the smaller spillway.

An Acoustic Doppler Velocimeter (ADV) system, with digital signal processing has been used to measure the longitudinal, transverse, and vertical velocity components in three‐dimensional, fully deve...

Water-sensitive urban design is an integral part of flood risk management. Based on computational modelling, we investigated the influence of various urban forms on flooding severity at the level of an urban block and for the case of long-duration urban flooding. The upstream flow depths, downstream discharge partition and flow exchange through the urban forms were examined. The results indicate that one urban characteristic has an overwhelming influence on the flow variables: the conveyance porosity in the main flow direction is by far more influential than the conveyance porosity in the normal direction or the number of streets. Such anisotropic effect was not pointed in recent similar studies, and it hints at practical guidelines for sustainable urban planning in practice. Moreover, the computational model was verified against laboratory observations, which constitute a novel valuable dataset for the validation of other urban flooding models.

Contrary to small- and medium-sized rivers, little attention has been paid to the downstream migration of Atlantic salmon smolts in large-sized rivers and the size-related impact of hydropower stations. From 2014 to 2016, we investigated the downstream migration of n = 72 acoustic-tagged smolts in the Meuse river at a bifurcation zone between a hydropower station equipped with three Kaplan turbines and a navigation canal. A hydrodynamic model that solves the depth-integrated shallow water equations on a Cartesian grid using a finite volume technique was used to infer the influence of water discharge and flow velocity on the smolts' behaviour upstream of the hydroelectric complex. Of the migrating smolts, 41.5% performed back and forth movements before approaching the complex for the first time, sometimes over long distances and at a slow pace, leading to significant delays (3–298 h). Beyond about 250 m3 s−1, the water flow direction changes towards the hydropower station with a gradual acceleration. A median water discharge of 161 m3 s−1 and associated median flow velocity of 0.14 m s−1 tended to favour a more direct and downstream movement towards the hydropower station. On the other hand, the navigation canal was mainly approached at low water discharge (median 132 m3 s−1), due to a higher flow velocity (median 0.11 m s−1) at the entrance. Of the released smolts, only 38.6% passed through the complex, of which 36.4% migrated by the navigation canal and 63.6% by the hydropower station, with a median research time of 04:44. Among all the released individuals, the escapement rate at the end of the study site was 2.9% by the canal and 8.3% by the Meuse river. This site, which offers two non-optimal, unattractive and unsafe migration routes, turns out to be problematic for successful downstream smolt migration.

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.

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 fluvial sand dikes were performed, considering a flow parallel to the dike axis. The breach was triggered by overtopping 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.

Underground Pumped Storage Hydropower (UPSH) is a potential alternative to manage electricity production in flat regions. UPSH plants will interact with the surrounding porous medium through exchanges of groundwater. These exchanges may impact the surrounding aquifers, but they may also influence the efficiency of the pumps and turbines because affecting the head difference between the reservoirs. Despite the relevance for an accurate efficiency assessment, the influence of the groundwater exchanges has not been previously addressed. A numerical study of a synthetic case is presented to highlight the importance of considering the groundwater exchanges with the surrounding porous medium. The general methodology is designed in order to be further applied in the decision making of future UPSH plants introducing each case specific complexity. The underground reservoir of a hypothetical UPSH plant, which consists in an open pit mine, is considered and modelled together with the surrounding porous medium. Several scenarios with different characteristics are simulated and their results are compared in terms of (1) head difference between the upper and lower reservoirs and (2) efficiency by considering the theoretical performance curves of a pump and a turbine. The results show that the efficiency is improved when the groundwater exchanges increase. Thus, the highest efficiencies will be reached when (1) the underground reservoir is located in a transmissive porous medium and (2) the walls of the open pit mine do not constrain the groundwater exchanges (they are not waterproofed). However, a compromise must be found because the characteristics that increase the efficiency also increase the environmental impacts. Meaningful and reliable results are computed in relation to the characteristics of the intermittent and expected stops of UPSH plants. The frequency of pumping and injection must be considered to properly configure the pumps and turbines of future UPSH plants. If not, pumps and turbines could operate far from their best efficiency conditions.

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.

Nappe oscillation and its potentially undesirable impact associated with significant noise production can be an issue for free-overfall hydraulic structures. Although nappe oscillation has ...

In this paper, the development trajectory of an integrated framework for the mitigation of future flood risk of the Ourthe river basin in Belgium is discussed. The paper contributes to the state-of-the-art by presenting an integrated multidisciplinary framework capable of making long-term projections (time horizon 2050 and 2100) with the objective of mitigating future flood risk by proposing alternative land-use scenarios. It bridges numerous different fields, including urban planning, transport engineering, hydrology, geology, environmental engineering, and economics. The overall design and validation results of the different sub-modules of the framework are presented, and ongoing and future enhancements are highlighted.