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International audience; In order to optimize ship navigation in the macrotidal Gironde Estuary, a recent project funded by the port of Bordeaux aims at better understand and forecast hydrodynamic and fine sediment transport within the estuary. In the framework of this project, a two-dimensional hydro-sedimentary model is built. The model includes hydrodynamic forcings, mixed-sediment transport, and consolidation processes. The harmonic analysis of the astronomical tides reveals a strong distortion of the tidal wave inducing the growth of overtide constituents and the non-significant effect of tide-surge interactions in annual-scale prediction. Depending on hydrological conditions, river discharge can considerably alter the model accuracy due to the migration of the turbidity maximum zone modifying the bottom roughness. Comparison with measurements shows the ability of the model to reproduce suspended-sediment concentrations in the central Estuary. Sensitivity of the model to sediment features has also been discussed in regard of suspended-sediment concentrations and fluid mud deposits. The model will be further coupled with ship squat predictions and a morphodynamic model.p { margin-bottom: 0.25 cm; line-height: 115%; }

Every year, in the Vietnam Mekong Delta Coastal Zone (VMDCZ), erosions cause approximately 300 ha of agricultural land loss. Therefore, measures for shoreline protection are urgently needed. This paper discusses the impacts of protection measures in the Go-Cong Coastal Zone to prevent erosion/accretion processes, predicted by two numerical models, MIKE21-FM and TELEMAC-2D. Hard and soft measures have been proposed using breakwaters and sandbars, respectively. The simulations show that the erosion/accretion trends provided by both models are similar. For breakwaters, MIKE21-FM provides less accretion than TELEMAC-2D in areas extending over 300 m and 500 m from shorelines. However, for sandbars, MIKE21-FM shows higher accretion within areas extending over 500 m but less than 300 m. Sandbars cause higher accretion in a larger area, extending over 1000 m offshore. The simulation results allow us to propose two alternative measures: (1) a row of several breakwater units will be implanted at 300 m offshore. The length of each unit is 600 m, with a gap between two neighbouring units of 70 m and a crest elevation of 2.2 m above mean sea level (MSL). (2) A row of sandbar units will be posed at 500 m offshore, with a unit length of 1000 m and a gap between the two neighbouring units of 200 m. The crest elevation is fixed at MSL.

This paper presents experimental and numerical studies on the erosion of a horizontal granular bed by a two-dimensional plane vertical impinging jet to predict the eroded craters’ size scaling (depth and width). The simulations help understand the microscopic processes that govern erosion in this complex flow. A modified jet-bed distance, accounting for the plane jet virtual origin, is successfully used to obtain a unique relationship between the crater size and a local Shields parameter. This work develops a two-phase flow numerical model to reproduce the experimental results. The numerical techniques are based on a finite volume formulation to approximate spatial derivatives, a projection technique to calculate the pressure and velocity for each phase, and a staggered grid to avoid spurious oscillations. Different options for the sediment’s solid-to-liquid transition during erosion are proposed, tested, and discussed. One model is based on unified equations of continuum mechanics, others on modified closure equations for viscosity or momentum transfer. A good agreement between the numerical solutions and the experimental measurements is obtained.

In this study, scour-based vibrations of bridge piers are investigated using a bridge model in a water flume: first, the eigenmode corresponding to the measured frequencies of pier-like structures is identified. Secondly, the effect of the pier-deck interaction is studied. Finally, a theoretical model is proposed to characterize the pier vibration, and identify its input parameters.To this end, experimental campaigns were conducted and a laboratory scale model pier was tested in two configurations: single piers and two piers in bridge configuration. The experimental results enable the identification of the modal shape and indicate that the deck decreases significantly the pier's frequency. Parallely, a theoretical model was proposed to model the pier, where the soil was modeled with both lateral springs along the pier and a rotational spring at the base. These springs stiffness were then identified using a 3D-finite element model. These results, obtained with the theoretical and numerical models, are in good agreement with the experimental results with the bridge pier in the two tested configurations. Moreover the obtained theoretical, numerical and experimental results were compared to experimental data found in the literature, for further validation.

A Large Eddy Simulation model is developed to simulate the hydrodynamics and scour process around a circular cylinder. The Navier-Stokes solver is based on the projection method and a second-order unstructured finite-volume method. A sigma-coordinate system is used to obtain an accurate representation of the evolution of the sediment-water interface. Bed erosion is simulated by solving the sediment continuity equation using a mass-conservating sand-slide algorithm and a bedload transport rate, which is based on a description of physical processes (Engelund & Fredsoe, 1976). Simulations of flow around a vertical cylinder for free-slip bed, rigid bed, and live-bed cases are done. The mean velocity profile and shear stress validate the accuracy of this model. Horseshoe vortex and lee-wake vortex shedding structure are simulated, and the results are thoroughly discussed in depth. The formation and the temporal development of the scour hole and other topographic bed features are successfully reproduced. The current paper reports the first known investigation of both scour evolution and coherent structure using large-eddy simulation.

Non-staggered triangular grids have many advantages in performing river or ocean modeling with the finite-volume method. However, horizontal divergence errors may occur, especially in large-scale hydrostatic calculations with centrifugal acceleration. This paper proposes an unstructured finite-volume method with a filtered scheme to mitigate the divergence noise and avoid further influencing the velocities and water elevation. In hydrostatic pressure calculations, we apply the proposed method to three-dimensional curved channel flows. Approximations reduce the numerical errors after filtering the horizontal divergence operator, and the approximation is second-order accurate. Numerical results for the channel flow accurately calculate the velocity profile and surface elevation at different Froude numbers. Moreover, secondary flow features such as the vortex pattern and its movement along the channel sections are also well captured.

In this paper, we introduce a second-order time- and space-accurate technique, developed to solve in parallel free-surface flows in arbitrary three-dimensional geometries. The discretization is based on a second-order finite-volume technique on prisms elements, consisting of triangular grids on the horizontal and bounded by a free surface and an irregular bottom on the vertical. The equations are transformed vertically to the σ-coordinate system in order to obtain an accurate representation of top and bottom topography. The reconstruction of three presure/velocity decoupling methods using a Crank-Nicolson scheme formulation is proposed. The Momentum Interpolation Method (MIM) is combined with Local Extremum Diminishing (LED) second-order upstream scheme for convective terms is developed. The parallelization is designed by a block domain decomposition technique. The discretization results in non-symmetric variable-coefficient linear systems which are solved using a parallel multi-color Successive Over-Relaxation algorithm. Several test cases of surface wave motion are used to demonstrate the capabilities, numerical stability and performance of the model.

Bars are large sediment deposits alternating with deeper areas that arise from alluvial river bed instability and forcing. The present study aimed at investigating the combined influence of flow and longitudinal width variations on the co-evolution between bar pattern and sediment sorting in a sandy-gravel river reach. To this goal, a fully non-linear 2D numerical model was developed to reproduce the morphodynamic behavior of bars in a reach of the Loire River consisting in a typical channel expansion/contraction. Numerical results showed that varying water discharge promoted a competition between low and high bar modes: i.e., from alternate to multiple bar patterns. Low bar modes were associated with coarse sediment over bar tops and fine sediment in pools, and this sorting pattern was inverted for higher bar modes. Surface sediment was coarser and the degree of sediment sorting was greater after periods of low than high flow. Due to high sediment mobility, sediment sorting did not significantly modify bar morphodynamics.

Scour is a hydraulic risk threatening the stability of bridges in fluvial and coastal areas. Therefore, developing permanent and real-time monitoring techniques is crucial. Recent advances in strain measurements using fiber optic sensors allow new opportunities for scour monitoring. In this study, the innovative optical frequency domain reflectometry (OFDR) was used to evaluate the effect of scour by performing distributed strain measurements along a rod under static lateral loads. An analytical analysis based on the Winkler model of the soil was carefully established and used to evaluate the accuracy of the fiber optic sensors and helped interpret the measurements results. Dynamic tests were also performed and results from static and dynamic tests were compared using an equivalent cantilever model.

The effect of the consolidation process on the morphodynamics and fine sediment dynamics of the Rio de la Plata estuary is explored through a circulation-wave-sediment transport model. The consolidation model is calibrated based on settling column experimental data. Different simulations are done in order to initialize the mud layer distribution and to investigate the impact of different erosion parameter assumptions on the modeled sediment dynamics. Finally a two-year simulation is done with and without the consolidation process and realistic hydrodynamic forcings. Considering the consolidation process, the model correctly reproduces measured vertical density profiles in the Montevideo Bay access channel. The simulated suspended sediment dynamics behavior in Montevideo Bay with the consolidation process provides a more realistic deposition pattern in regard to the dredging activities.

Rivers inherently show heterogeneous sediment sizes and can also show a strong sediment supply variability in time because of natural episodic events or as a consequence of human activities, which alter the characteristics and dynamics of alluvial bars at the macro-scale. The impact of the combination between sediment size heterogeneity and sediment supply variation, or even with other forcings (i.e. hydrology, channel geometry) remains poorly documented. In this work, a physics-based numerical model is applied on a trained reach of a sandy-gravel bed river to investigate the combination of these parameters on bar morphodynamics. The morphodynamic computations are performed with a two-dimensional depth-averaged hydrodynamic solver, internally coupled to a sediment transport and bed evolution module, which estimate the transport of graded sediment and model bed stratigraphy, respectively. A 1 km long reach of the Loire River at Bréhémont (France) is selected to conduct the numerical investigations. The interaction between several forcing mechanisms induces highly complex bar morphodynamic processes in this area.A comprehensive set of high-definition data is available, which allows to study the river morphodynamics for a succession of three flooding events and a period of low flows. Based on this model, a variety of scenarios is presented with the aim of exploring the implications of sediment gradation, geometrical and boundary forcing effects on in situ bars morphodynamics.

Modelling the hydrodynamics and fine-sediment dynamics in estuarine environments is important for coastal engineering design and environmental assessment. This paper presents the application of a coupled wave–current–sediment transport model to a complex estuarine system with high spatial resolution in a harbour area. The case study was the Rio de la Plata, with a focus on the Montevideo Bay area. We used a bidimensional depth-averaged approach, and the sediment transport modelling focused on fine cohesive sediments. The model considers realistic forcings, allows for the simulation of complex geometries such as those present in harbour basins and is capable of providing long-term environmental simulations (on the order of several years) within reasonable computational times. The model results are in good agreement with the measured data and satisfactorily represent the main features of the flow and sediment dynamics of the Rio de la Plata. The effect of the internal coupling on the hydrodynamic results is analysed, and the computational times with various coupling alternatives are discussed. The dynamics of fine sediment in Montevideo Bay were analysed based on the model results. The current-induced bottom shear stress results are relevant for representing the permanent suspended sediment concentrations, whereas the wave-induced bottom shear stress is fundamental for reproducing the main resuspension events during storm conditions. The suspended fine-sediment dynamics in the estuary are strongly controlled by the sediment exchange between the bed and water column, whereas inside Montevideo Bay, the dynamics are controlled mainly by advection of sediment originating from the nearby coastal area.

SUMMARY We present a solver for a three-dimensional Poisson equation issued from the Navier‐Stokes equations applied to model rivers, estuaries, and coastal flows. The three-dimensional physical domain is composed of an arbitrary domain in the horizontal direction and is bounded by an irregular free surface and bottom in the vertical direction. The equations are transformed vertically to the � -coordinate system to obtain an accurate representation of top and bottom topographies. The method is based on a second-orderfinite volume technique on prisms consisting of triangular grids in the horizontal direction. The algorithm is accompanied by an analysis of different linear system solvers in order to achieve fast solutions. Numerical experiments are conducted to test the numerical accuracy and the computational efficiency of the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.

Mixtures of non-cohesive and cohesive sediment are frequently encountered in natural environments such as estuaries. Depending on the concentration of both species, mixed sediment can record segregation effect or not, behaves like a non-cohesive sediment or like a cohesive sediment. The present study deals with the segregation effect between mud flocs and sand grains during hindered settling. Simulations of this process under various conditions of mixture are proposed by using two coupled mass conservation equations which are solved by a high order numerical model. Specific closure equations are proposed herein for the hindered settling of sand–mud mixed sediment. Comparisons between simulations and experiments are presented on vertical concentration profiles during the segregation process. Obviously, the model enables the description of hindered settling for pure non-cohesive (or pure cohesive) case and the segregation for bi-disperse suspensions.

This paper presents some on-going developments made jointly at Saint-Venant Laboratory for Hydraulics, in order to improve the numerical schemes, physical processes and accuracy of a 2D morphodynam...

Sea-level rise and changes in storm frequency and intensity will undoubtedly modify beach morphology. To reduce shoreline retreat, many structural solutions have been proposed by coastal engineers. Among them, Submerged BreakWaters (SBW) are becoming a preferred solution owing to their aesthetical and environmental advantages. Here, a reduced scale physical model is used to study the reduction of storm-induced erosion for different shapes and locations of SBW's. The originality of the set-up is: (1) the 1/10 scale model beach and SBW under irregular waves; and (2) respecting sediment transport similarity. Starting with an equilibrium beach profile, a synthetic storm is tested with and without the SBW. Preliminary results show a promising reduction of erosion rates and shoreline retreat for the selected SBW geometry and

Le transport sedimentaire induit par les vagues est simule avec un sable de silice de 700 µm de diametre. La morphologie des fonds est suivie grâce a un procede optique non intrusif de photogrammetrie. Les tests comparatifs effectues avec et sans la maquette du dispositif mettent en evidence l’impact des filets sur la dynamique hydro-sedimentaire en zone cotiere. Mots-cles : Modele physique, Modele reduit, Environnement littoral, Sable, Erosion, Filets, Turbulence.

International audience; A one-dimensional vertical two-phase flow model for sedimentation-consolidation process is presented. The model is based on solving the continuity and momentum equations for both fluid and solid phases. In the non-cohesive case, the momentum transfer between the two phases is reduced to the drag force around a single particle modified to take the hindrance effects into account. In the cohesive case, Darcy-Gersevanov's law is used for the closure of the momentum transfer between the two phases and the concept of "effective stress" is introduced to take into account the bed structuring. These closure laws are validated against high resolution experimental data in terms of settling curves and concentration profiles. The reliability of the model is illustrated from an analysis of the momentum balances at different stages during the process. Finally, the proposed closure laws and numerical algorithms are shown to be able to quantitatively reproduce sedimentation of non-cohesive and sedimentation- consolidation of cohesive sediments, including mud.

Mots-cles : Sedimentation - Consolidation - Two-phase flow - Numerical model Abstract: A two-phase flow model for sedimentation-consolidation process is presented. The model is based on solving the continuity and momentum equations for both fluid and solid phases. Darcy-Gersevanov's law is used for the closure of the momentum transfer between the two phases and the concept of "effective stress" is introduced to account for the bed structuring. These closure laws are validated against high resolution experimental data in terms of settling curves and concentration profiles. The good agreement obtained between numerical results and experimental data shows the predictive capability of the two-phase model.

Dredging operations of navigation channels and harbours are regularly planned in order to maintain the nautical depth and to ensure the navigation safety. Depending on the quality of the dredged material (fixed by the Oslo convention, 1972), dredged sediments can be released into the sea or stored at the Earth’s surface to be cleaned up. The present study deals with release operations. We simulate the complete process (generation and settling of a sediment plume, propagation of a density current on the bottom) using a two-phase flow model. We show that in this case, the sediment (or solid) phase strongly differs from the motion of the water (or fluid) phase. Comparisons between numerical results and experiments are carried out in order to illustrate the effects of sediment diameter, initial concentration, and ambient current on the plume dynamics and on the density current. We obtain a correct agreement with experiments for the specific release case.

Fluvial transport in inland waterways is used in France and Europe since millennia. It was the most effective transport mode for goods and merchandizes before the development of the terrestrial alternatives. As an illustration, the French network of the inland waterways counted 12800 km of both, rivers and channels, at the beginning of the twentieth century. The huge development of highways and railways encountered in France has progressively decreased the use of fluvial transport. By considering the duration for the transport, the terrestrial mode looks more attractive than the fluvial one. But, the actual context of climate change and the international or European commitments to strongly diminish CO2 emissions are pleading for the reverse modal transfer, i.e. from highways and/or railways to waterways. Rebalancing the different transport modes are indeed compatible with the sustainable development concepts facing against road saturation, CO2 emissions, visual or noise pollutions while ensuring a better safety. Even through the shared awareness and the common efforts to increase the river traffic, this transport mode is still considered "under-developed" in the white paper of the European commission of 2001. For example, the fluvial transport in France has increased by 30% in ten years (1997− 2007), but it only represents 3% of the means of transport. And the recent recommendations in "Grenelle de l’environnement" initiated by the Frenchministry of ecology may accelerate the rebalance between rails, roads and rivers, carrying the ambition of a 25% report from the road down to the river by 2020. However, the development of this transport mode will certainly have economical and ecological consequences on the river management. The intensification of the river traffic by increasing the size and/or the frequency of passing boats will impact the actual management plan of the river. The waves induced by navigation could become stronger and bank erosion more frequent. The induced currents may be more intense and the resulting sediment transport more problematic. Indeed, it is accepted in aquatic environment that erosion Numerical Modelling of the Sediment Re-Suspension Induced by Boat Traffic 3

This paper deals with the sedimentation of highly concentrated sediment suspensions (cohesive as well as non-cohesive) and the beginning of the consolidation of cohesive sediments. Based on a comparison of existing empirical formulas and experimental data, the particle Reynolds number was shown to be of importance for the behaviour of particularly non-cohesive sediments. In addition it plays a role in determining whether one or two interfaces develop during the sedimentation phase. In the case of cohesive sediments, the estimation of the gelling concentration, although difficult, seems to be fundamental. Some suggestions on the estimation of the permeability coefficient and total settling function are then given in order to improve the modelling of the sedimentation and consolidation behaviour for concentrations close to the gelling concentration.

International audience; La maintenance des chenaux de navigation et des zones portuaires implique laréalisation d’opérations de dragage. Les produits de dragages sont souvent déposés enmer (opération de clapage) pouvant induire des nuisances sur l’environnement. Lephénomène de clapage comporte principalement trois phases (BOUTIN, 2000) : laphase de chute (soumise aux courants) ; l’impact sur le fond et la génération d’uncourant de densité ; la propagation des courants de densité et la décantation dessédiments. Nous simulons ce phénomène à l’aide d’un modèle à deux phases adapté auxmilieux denses en différentiant les deux constituants. Les études sur le clapage avec cemodèle ont démarré dans un cas sans courant (GUILLOU et al., 2011). Les travauxprésentés ici portent sur une étude systématique de la dynamique de chute et detransport en fonction du courant relative à la configuration expérimentale utilisée parVILLARET et al. (1998).

This paper presents two non-intrusive techniques to measure the time evolution of the vertical profile of concentration during batch settling test. The first one is a Magnetic Resonant Imaging (MRI) vertical prototype used on Gironde estuary. The second is an X-ray ‘home-made’ prototype used on Seine estuary. Both are used to observe the sedimentation and the consolidation processes of natural cohesive sediments. They provide the movement of the supernatant/suspension interface and the isoconcentration lines of the process. A space-time based method is proposed to close the governing equation.Copyright © 2011 by JSME

Hafenanlagen werden oft in Gebieten errichtet,wo die Wassertiefen gering sind, insbesondere inÄstuaren. Es ist dann notwendig, Ausbaggerungsarbeitendurchzuführen, um Schiffen die Zufahrtzu ermöglichen. Das ausgebaggerte Sedimentwird in einer vorher definierten Deponierungszonefreigesetzt. Wegen der Konzentration derSedimentwolke, die sich während der Freisetzungbildet (zu Beginn mehr als 350g/l) entsteht einEinfluss auf die Umwelt. Die chemische Zusammensetzungdes Wassers wird direkt beeinflusst.Nach der Freisetzung schlagen sich die Sedimenteunter einer sehr hoch konzentrierten Wolkenieder. Auf diesen Schritt des Niederschlags folgtein Einfluss auf die Sohle durch Bildung einesSuspensionsstroms.Der Zweck dieses Beitrags ist das Studium diesesPhänomens mittels numerischer Simulationenunter Verwendung eines Zwei-Phasen-Modellsfür den Sedimenttransport (Barbry et al., 2000 ;Chauchat et al., 2008 ; Nguyen et al., 2009). Esbasiert auf der Lösung der Erhaltungs- und Impuls-Gleichungen für jede Phase (Wasser undPartikel) und integriert dann die Interaktion zwischenPartikeln und Wasser. Ein Vergleich mitden experimentellen Konfigurationen von Villaretet al. (1997, 1998), ohne Strömung, zeigt, dassdie verschiedenen Schritte des Phänomens rechtgut ohne Modellierung, The port structures are often established in areaswhere water levels are fairly low, especially in estuaries.It is then necessary to perform dredging toallow ships accessing to the docks. The dredgedsediment is released over a predefined depositzone. Because of the concentration of the sedimentcloud appearing during the release, morethan 350 g/l at the beginning, there is an impacton the environment. The chemical composition ofwater is affected directly.After the release, the sediments settle under acloud of very high concentration. This settling stepis followed after impact on the bed by the formationof turbidity current. The purpose of this work is tostudy the phenomenon via numerical simulationsby using a two-phase model of sediment transport[Barbry et al., 2000 ; Chauchat et al., 2008 ;Nguyen et al., 2009]. It is based on the solving ofconservation and momentum equations for eachphase (water and particles) and then integratesthe interaction between the particles and the water.A comparison with the experimental configurationof Villaret et al. (1997, 1998), without current,shows that the different steps of the phenomenonare quite reproduce without turbulence modelling., La gestion des clapages (ou rejets en mer des produits de dragage) constitue une problématique environnementale et économique importante pour les estionnaires des voies navigables et des infrastructures portuaires. Moins coûteuses qu’un stockage à terre, ces opérations peuvent induire des nuisances sur l’environnement notamment en provoquant un accroissement local de la turbidité et en ensevelissant les habitats de la faune aquatique. Le phénomène de clapage comporte principale ment trois phases [Boutin, 2000]: la phase de chute (soumise aux courants) ; l’impact sur le fond et la génération d’un courant de densité ; la propagation des courants de densité et la décantation des sédiments.

Settling and consolidation of colloidal and non-colloidal suspensions are investigated from a nuclear Magnetic Resonance Imaging (MRI) vertical prototype. The mathematical model of Gibson with a 1D...

A field experiment to measure the impact of passing boats on the maintenance of waterways is presented. The bottom and the banks of an artificial channel and a navigated river are instrumented by currentmeters, turbidimeters and water level sensors. Sediment resuspension induced by passing boats are measured at the bottom and behind the boats. The waves generated by boats are obtained close to the banks by a three point device.

Settling and consolidation of colloidal and non-colloidal suspensions are investigated from a nuclear Magnetic Resonance Imaging (MRI) vertical prototype. The mathematical model of Gibson with a 1D numerical modeling based on the Finite Element Method (FEM) are presented. A time ‘Lax Wendroff’ discretization with a shock capturing technique (Flux Corrected Transport, FCT) is used for the propagation of concentration fronts. Finally comparisons between experiment and simulation are proposed and discussed for the case of noncolloidal and colloidal suspension.

Rivers often present a wavy bed topography due to the presence of bars, corresponding to large sediment deposits alternating with deeper areas (pools). Intense and continual river engineering works altering the river geometry, flow regime and sediment supply can impact bar morphodynamics at the reach scale. A deep knowledge of bar processes is important for river managers, because bars actively control the river bed topography and influence bank erosion, with consequences for navigation, water intakes, infrastructure and the quality of their habitats. Although the origin of bar formation and propagation is well understood, the understanding of bar morphodynamics in rivers remains limited due to the non-linearity of combined natural and anthropogenic effects. Sediment non-uniformity is an inherent characteristic of rivers, but its impact on bar properties, even considering simple configurations, is still unclear. This Ph.D. thesis aims at investigating the impact of sediment size heterogeneity on bars in rivers with non-erodible banks, using a two-dimensional morphodynamic model implemented in the Telemac-Mascaret system. The necessary model developments are brought to comply with the state of the art on the modelling of heterogeneous sediment with bars. Then, the model is used to study bar morphodynamics in a straight channel on the basis of laboratory experiments. Eventually, the analysis is transferred in a 1 km reach of the Loire river characterized by a relatively complex geometry. General outcomes validate the modelling approach and demonstrate the application portability for other study cases, shed more light on the relationship between non-uniform sediment and bars, and can be later used as recommendations for river managers., Les rivières présentent généralement un lit ondulé dû à la présence de bancs, qui correspondent à des larges dépôts sédimentaires alternant avec des zones profondes (mouilles). Des travaux d'ingénierie importants et répétés modifiant la géométrie du cours d'eau, le régime hydraulique et l'apport sédimentaire peuvent à terme modifier la dynamique des bancs à l'échelle de la rivière. Une meilleure compréhension des processus liés aux bancs est importante pour les gestionnaires des rivières, car les bancs contrôlent activement la morphologie du lit et érodent les berges, impactant la navigation, les prises d'eaux, les ouvrages et la qualité des habitats. Même si les mécanismes régissant la formation et le développement des bancs sont bien compris, la compréhension de la morphodynamique des bancs en milieu fluvial reste limitée, en raison de la non-linéarité induite par la combinaison de facteurs naturels en atrophiques. La non-uniformité des sédiments est une caractéristique inhérente des rivières, mais son impact sur la propriété des bancs, même dans des cas simplifiés, reste obscure. Ce travail de thèse vise à étudier l'impact de l'hétérogénéité granulométrique sur des bancs dans des chenaux endigués, via l'utilisation d'un modèle morphodynamique bi-dimensionnel implémenté dans le système Telemac-Mascaret. Les développements numériques nécessaires sont apportés afin d'être en accord avec l'état de l'art sur la modélisation de bancs avec un sédiment-non-uniforme. Par la suite, ce modèle est utilisé pour l'étude de la morphodynamique des bancs dans un chenal rectiligne sur la base d'expériences réalisées en laboratoire. Finalement, l'analyse est transférée sur un tronçon de 1 km de la Loire, caractérisé par sa géométrie relativement complexe. Les résultats permettent de valider l'approche de modélisation et démontrent la portabilité pour d'autres études, apportent plus d'éléments sur la relation entre sédiment non-uniforme et les bancs, et pourront être utilisés pour préconiser les gestionnaires des rivières

L'affouillement est l'arrachement et le transport des sédiments du lit d'un cours d'eau sous l'action érosive d'un écoulement hydraulique. Ce phénomène est accentué par la présence d'obstacles à l'écoulement, tels que les piles et culées de ponts, ou également les quais, les éoliennes et les oléoducs offshores dans un contexte maritime. La présence de fosses d'affouillement engendre une perte de la capacité portante de la structure et menace sa stabilité. Face à ce risque hydraulique, il est crucial de suivre en continu l'évolution de la profondeur d'affouillement au droit des ouvrages d'art et d'évaluer sa conséquence sur le comportement de la structure. Cette thèse est une contribution à l'utilisation de l'analyse vibratoire pour le suivi de l'affouillement, et à la compréhension des phénomènes d'interaction sol-structure mis en jeu. La démarche scientifique retenue intègre deux approches distinctes du suivi d'affouillement : indirecte et directe. L'approche indirecte a pour objectif le développement d'un capteur de profondeur d'affouillement (scour depth sensor SDS). Des études expérimentale et numérique ont été menées afin d'évaluer l'influence de l'affouillement, d'une part sur la réponse dynamique du capteur (fréquences, déformées modales et amortissement), d'autre part sur sa réponse statique sous chargement latéral. Sur la base des résultats obtenus, un modèle théorique de poutre équivalente a été proposé afin de lier la variation de la fréquence du capteur à la profondeur d'affouillement. L'approche directe s'intéresse à l'effet de l'affouillement sur la réponse dynamique de la structure elle-même. Des campagnes d'essais ont été menées sur des modèles réduits en canal hydraulique. Un intérêt particulier a été porté aux effets de la géométrie de la pile et de l'interaction pile-tablier. Un modèle analytique a été proposé pour prédire l'évolution de la fréquence des piles avec l'affouillement. Afin de valider ce modèle, ses résultats ont été comparés aux résultats des essais expérimentaux. Scour is the removal of riverbed sediments by the erosive action of flowing water. Scour depth is greater near structures as a result of the obstruction to the flow by bridge piers and abutments, or docks, wind turbines and offshore pipelines in a marine environment. The existence of scour holes may decrease the bearing capacity of the structure and threaten its stability. Therefore, it is crucial to develop monitoring techniques to track the evolution of scour depth in real-time and evaluate its consequences on the behaviour of the structure. This thesis is a contribution to the use of vibration based techniques for scour monitoring and provides an insight to the soil-structure interactions involved. Two proposed approaches can be distinguished in this study : indirect and direct. The indirect approach aims to develop a scour depth sensor (SDS). Experimental and numerical studies have been conducted to evaluate the effect of scour, on the one hand, on the dynamic response of the sensor (frequencies, modal shapes, damping), on the other hand, on its static response under lateral loading. Based on the findings, a theoretical model of an equivalent cantilever beam was proposed to predict the variation of the sensor frequency as a function of scour depth. The direct approach focuses on the effect of scour on the structure itself. To this end, experimental campaigns were conducted on laboratory scale models tested in a flume. Particular attention was paid to the effect of the pile geometry and the pile-deck interaction. An analytical model was proposed to correlate the variation of the pier frequency to scour depth. Experimental and numerical results were compared to assess the model validity.

Rivers often present a wavy bed topography due to the presence of bars, corresponding to large sediment deposits alternating with deeper areas (pools). Intense and continual river engineering works altering the river geometry, flow regime and sediment supply can impact bar morphodynamics at the reach scale. A deep knowledge of bar processes is important for river managers, because bars actively control the river bed topography and influence bank erosion, with consequences for navigation, water intakes, infrastructure and the quality of their habitats. Although the origin of bar formation and propagation is well understood, the understanding of bar morphodynamics in rivers remains limited due to the non-linearity of combined natural and anthropogenic effects. Sediment non-uniformity is an inherent characteristic of rivers, but its impact on bar properties, even considering simple configurations, is still unclear. This Ph.D. thesis aims at investigating the impact of sediment size heterogeneity on bars in rivers with non-erodible banks, using a two-dimensional morphodynamic model implemented in the Telemac-Mascaret system. The necessary model developments are brought to comply with the state of the art on the modelling of heterogeneous sediment with bars. Then, the model is used to study bar morphodynamics in a straight channel on the basis of laboratory experiments. Eventually, the analysis is transferred in a 1 km reach of the Loire river characterized by a relatively complex geometry. General outcomes validate the modelling approach and demonstrate the application portability for other study cases, shed more light on the relationship between non-uniform sediment and bars, and can be later used as recommendations for river managers., Les rivières présentent généralement un lit ondulé dû à la présence de bancs, qui correspondent à des larges dépôts sédimentaires alternant avec des zones profondes (mouilles). Des travaux d'ingénierie importants et répétés modifiant la géométrie du cours d'eau, le régime hydraulique et l'apport sédimentaire peuvent à terme modifier la dynamique des bancs à l'échelle de la rivière. Une meilleure compréhension des processus liés aux bancs est importante pour les gestionnaires des rivières, car les bancs contrôlent activement la morphologie du lit et érodent les berges, impactant la navigation, les prises d'eaux, les ouvrages et la qualité des habitats. Même si les mécanismes régissant la formation et le développement des bancs sont bien compris, la compréhension de la morphodynamique des bancs en milieu fluvial reste limitée, en raison de la non-linéarité induite par la combinaison de facteurs naturels en atrophiques. La non-uniformité des sédiments est une caractéristique inhérente des rivières, mais son impact sur la propriété des bancs, même dans des cas simplifiés, reste obscure. Ce travail de thèse vise à étudier l'impact de l'hétérogénéité granulométrique sur des bancs dans des chenaux endigués, via l'utilisation d'un modèle morphodynamique bi-dimensionnel implémenté dans le système Telemac-Mascaret. Les développements numériques nécessaires sont apportés afin d'être en accord avec l'état de l'art sur la modélisation de bancs avec un sédiment-non-uniforme. Par la suite, ce modèle est utilisé pour l'étude de la morphodynamique des bancs dans un chenal rectiligne sur la base d'expériences réalisées en laboratoire. Finalement, l'analyse est transférée sur un tronçon de 1 km de la Loire, caractérisé par sa géométrie relativement complexe. Les résultats permettent de valider l'approche de modélisation et démontrent la portabilité pour d'autres études, apportent plus d'éléments sur la relation entre sédiment non-uniforme et les bancs, et pourront être utilisés pour préconiser les gestionnaires des rivières

Scour is the removal of riverbed sediments by the erosive action of flowing water. Scour depth is greater near structures as a result of the obstruction to the flow by bridge piers and abutments, or docks, wind turbines and offshore pipelines in a marine environment. The existence of scour holes may decrease the bearing capacity of the structure and threaten its stability. Therefore, it is crucial to develop monitoring techniques to track the evolution of scour depth in real-time and evaluate its consequences on the behaviour of the structure. This thesis is a contribution to the use of vibration based techniques for scour monitoring and provides an insight to the soil-structure interactions involved. Two proposed approaches can be distinguished in this study: indirect and direct. The indirect approach aims to develop a scour depth sensor (SDS). Experimental and numerical studies have been conducted to evaluate the effect of scour, on the one hand, on the dynamic response of the sensor (frequencies, modal shapes, damping), on the other hand, on its static response under lateral loading. Based on the findings, a theoretical model of an equivalent cantilever beam was proposed to predict the variation of the sensor frequency as a function of scour depth. The direct approach focuses on the effect of scour on the structure itself. To this end, experimental campaigns were conducted on laboratory scale models tested in a flume. Particular attention was paid to the effect of the pile geometry and the pile-deck interaction. An analytical model was proposed to correlate the variation of the pier frequency to scour depth. Experimental and numerical results were compared to assess the model validity, L'affouillement est l'arrachement et le transport des sédiments du lit d'un cours d'eau sous l'action érosive d'un écoulement hydraulique. Ce phénomène est accentué par la présence d'obstacles à l'écoulement, tels que les piles et culées de ponts, ou également les quais, les éoliennes et les oléoducs offshores dans un contexte maritime. La présence de fosses d'affouillement engendre une perte de la capacité portante de la structure et menace sa stabilité. Face à ce risque hydraulique, il est crucial de suivre en continu l'évolution de la profondeur d'affouillement au droit des ouvrages d'art et d'évaluer sa conséquence sur le comportement de la structure. Cette thèse est une contribution à l'utilisation de l'analyse vibratoire pour le suivi de l'affouillement, et à la compréhension des phénomènes d'interaction sol-structure mis en jeu. La démarche scientifique retenue intègre deux approches distinctes du suivi d'affouillement: indirecte et directe. L’approche indirecte a pour objectif le développement d'un capteur de profondeur d'affouillement (scour depth sensor SDS). Des études expérimentale et numérique ont été menées afin d'évaluer l'influence de l'affouillement, d'une part sur la réponse dynamique du capteur (fréquences, déformées modales et amortissement), d'autre part sur sa réponse statique sous chargement latéral. Sur la base des résultats obtenus, un modèle théorique de poutre équivalente a été proposé afin de lier la variation de la fréquence du capteur à la profondeur d'affouillement. L’approche directe s'intéresse à l'effet de l'affouillement sur la réponse dynamique de la structure elle-même. Des campagnes d'essais ont été menées sur des modèles réduits en canal hydraulique. Un intérêt particulier a été porté aux effets de la géométrie de la pile et de l'interaction pile-tablier. Un modèle analytique a été proposé pour prédire l'évolution de la fréquence des piles avec l'affouillement. Afin de valider ce modèle, ses résultats ont été comparés aux résultats des essais expérimentaux