The presence of man-made levees along the Lower Mississippi River (MR) has significantly reduced the River sediment input to the wetlands and much of the River's sediment is now lost to the Gulf of Mexico. The sediment load in the River has also been decreased by dams and river revetments along the Upper MR. Freshwater and sediment diversions are possible options to help combat land loss. Numerical modeling of hydrodynamics and sediment transport of the MR is a useful tool to evaluate restoration projects and to improve our understanding of the resulting River response. The emphasis of this study is on the fate of sand in the river and the distributaries. A 3-D unsteady flow mobile-bed model (ECOMSED; HydroQual 2002) of the Lower MR reach between Belle Chasse (RM 76) and downstream of Main Pass (RM 3) was calibrated using field sediment data from 2008 – 2010 (Nittrouer et al. 2008; Allison, 2010). The model was used to simulate River currents, diversion sand capture efficiency, erosional and depositional patterns with and without diversions over a short period of time (weeks). The introduction of new diversions at different locations, e.g., Myrtle Grove (RM 59) and Belair (RM 65), with different geometries and with different outflows was studied. A 1-D unsteady flow mobile-bed model (CHARIMA; Holly et al. 1990) was used to model the same Lower MR reach. This model was used for longer term simulations (months). The simulated diversions varied from 28 m3/s (1, 000 cfs) to 5, 700 m3/s (200, 000 cfs) for river flows up to 35, 000 m3/s (1.2x106 cfs). The model showed that the smaller diversions had little impact on the downstream sand transport. However, the larger diversions had the following effects: 1) reduction in the slope of the hydraulic grade line downstream of the diversion; 2) reduction in the available energy for transport of sand along distributary channels; 3) reduced sand transport capacity in the main channel downstream of the diversion; 4) increased shoaling downstream of the diversion; and 5) a tendency for erosion and possible head-cutting upstream of the diversion.

L'étude de l'écoulement à l'aval d'une ride a un intérêt primordial dans la dynamique et l'évolution des rivières, des milieux côtiers ou des estuaires. Une des questions au coeur de ces écoulements est liée aux mécanismes d'interaction entre les particules et l'écoulement. Cette interaction donne souvent lieu à la formation de structures ondulées (rides ou dunes). Ce couplage est engendré au niveau de l'écoulement moyen, de la forme de la dune mais aussi au niveau de la macro turbulence et des structures tourbillonnaires instationnaires générées par la présence même des formes sédimentaires. L'identification des différents mécanismes et processus hydrodynamiques générés par la présence de dunes ou rides est exposée en détail par l'examen de l'écoulement laminaire à l'aval d'une ride fixe et isolée. Des techniques de mesure optiques 2D (PIV, visualisations) et 3D (Stéréo-PIV, tomographie laser) couplées à une étude numérique avec un code industriel, permettent de mettre en évidence l'instationarité, la tridimensionnalité de l'écoulement ainsi que la dynamique tourbillonnaire de la zone de recirculation à l'aval de la ride. L'impact de l'écoulement turbulent sur la naissance de dunes isolées est analysé au moyen d'une étude détaillée sur le transport de particules à partir d'essais menés en canal hydro-sédimentaire. Le rôle particulier de la zone de recirculation à l'aval de la dune est mis en évidence à l'aide d'un suivi spatio-temporel du transport des particules entre sa crête et sa face d'avalanche. Finalement, l'analyse et l'influence des conditions hydrauliques sur le seuil critique de mise en mouvement d'un lit de particules ainsi que la formation et la migration d / The aim of this study is to examine the processes leading to development a bed river, estuary or coastal environments morphology. The ability to investigate the complex nature of the interaction between fluids and sediments mechanisms and its role in bed transport and river stability is important to understand river evolution. Dunes or ripples are in frequent interaction with the bed. Hence, the topology of dune is related to the macroturbulence of the flow, mean flow field and the instantaneous structures of the vortices generated by these forms. Details of different mechanisms and hydrodynamic process generated behind a fixed single ripple are exposed by examining a laminar flow over the dune itself. Measurements with two-component Particle Image Velocimetry, three-component Stereo-PIV and flow visualization coupled with a numerical studies are performed to acquire and to obtain a detailed knowledge of the flow over the dune concerning the three-dimensionality, the instantaneous behavior of the flow and the large dynamic of vortex in the recirculation zone along the ripple. A set experiment generating turbulent flow is conducted in a hydro-sedimentary channel to detail the quantitative measurement of bedload transport processes in order to determine the effects of the turbulent flow on dune creation. A spatio-temporal monitoring of particles transport from crest to dune slip face is conducted to point the particular role of the recirculation region. Finally, the analyze and the effect of hydraulics conditions on the critical shear stresses for incipient particle motion as well as the formation and the migration of the mobile dune are emphasized by a geomorphological st

Une étude de l'impact des mascarets sur le transport des sédiments à l'aide de la simulation numérique a été réalisée dans ce travail. En utilisant le logiciel OpenFOAM CFD, nous avons généré 17 simulations numériques de mascaret avec divers nombres de Froude Fr, allant de 0,99 à 1,66. Deux types de mascarets, ondulant et déferlant, ont été couverts dans ces 17 simulations numériques. Pour les particules sédimentaires non cohésives, nous avons utilisé les équations de Maxey et Riley pour déterminer la trajectoire des particules sédimentaires non cohésives sous l’influence d’un mascaret ondulant. En utilisant le schéma Runge-Kutta du quatrième ordre, une méthode tracker résout les équations de Maxey et Riley qui nécessitent l’information des champs de vitesse au temps t. Pour les particules sédimentaires cohésives, nous avons calculé la distribution des particules sédimentaires cohésives en utilisant un modèle de transport de flocs, présenté par Winterwerp (2001). Dans ce modèle, la concentration volumique solide des sédiments et le diamètre des flocs D sont estimés. Les équations de transport de et D sont résolues en utilisant la méthode des moments présentée par Beaudoin et al. (2002 et 2004). La méthode des moments permet de réduire le temps CPU rendant possible une étude paramétrique. De ce travail, nous avons trouvé une classification du mascaret en fonction du nombre de Froude Fr. Cette classification est également basée sur l’étude menée par Furgerot (2014). Pour un nombre de Froude 1,04 < Fr < 1,43, le mascaret est ondulant. Pour un nombre de Froude 1,43 < Fr < 1,57, le mascaret est partiellement déferlant, similaire à la transition de mascaret définie par Furgerot (2014). Pour un nombre de Froude Fr > 1,57, le mascaret est totalement déferlant. Une analyse de la distribution de la pression a été effectuée par Baddour et Song (1990). Nous avons trouvé que les pressions totales et hydrostatiques d’un mascaret ondulant ont de grandes valeurs sous la crête et le creux. Dans le cas d’un mascaret ondulant, les pressions totales ne sont pas égales à les pressions hydrostatiques. Cela provoque la présence de pressions dynamiques. Dans le cas de mascaret déferlant, les pressions totales deviennent égales aux pressions hydrostatiques. La turbulence réduit les pressions dynamiques. L'impact des mascarets sur le transport de particules sédimentaires non cohésives et cohésives a été étudié dans ce travail. Pour les particules sédimentaires non cohésives, nous avons observé que la trajectoire utilisant l’écoulement généré par OpenFOAM est similaire à la trajectoire de type e proposée par Chen et al. (2010). Des modifications du modèle de Chen ont été faites en incluant les effets de la gravité, l’élévation et l’atténuation pour reproduire des trajectoires de particules non cohésives sous un mascaret ondulant. Nous avons obtenu des relations linéaires entre les paramètres du modèle de Chen modifié (β1 , β2 et β3) et le nombre de Froude Fr. C’est parce que le niveau de la turbulence du mascaret ondulant est faible. L’écoulement induit par mascaret ondulant n’est pas complexe. Ce phénomène physique est quasi linéaire. Le paramètre β1, lié à la célérité avant du mascaret ondulant, diminue lorsque le nombre de Froude Fr augmente. Les paramètres β2 et β3, liés respectivement à l’élévation et à l’atténuation du mascaret déferlant, augmentent lorsque le nombre de Froude Fr augmente. Enfin, pour les particules sédimentaires cohésives, nous avons calculé la distribution de la taille des flocs D sous deux types de mascaret, ondulant et déferlant. Nous avons utilisé le diamètre initial de la particule sédimentaire cohésive d = 4 μm. La taille du floc initial D est égale à 10 μm avec la concentration du floc c = 0,5 kg/m3 . Et nous avons limité la taille maximale du floc à 2000 μm. Nous avons observé que la valeur maximal de la taille des flocs Dmax augmente de façon exponentielle par rapport au nombre de Froude Fr. / A study of the impact of tidal bores on sediment transport by using the numerical simulation has been done in this work. Using OpenFOAM CFD software, we have generated 17 numerical simulations of tidal bores with various values of Froude number Fr, ranging from 0.99 to 1.66. Two types of tidal bores, undular and breaking, have been covered in these 17 numerical simulations. We have studied the behavior of two types of sediment particles, non-cohesive and cohesive sediment particles. For the non-cohesive sediment particles, we have resolved the Maxey and Riley equations to study the influence of undular tidal bores on the trajectory of non cohesive sediment particles. Using the fourth order Runge-Kutta scheme, the method tracker can solve the Maxey and Riley equations that requires the information of velocity fields at time t. For the cohesive sediment particles, we have calculated the distribution of cohesive sediment particles using a floc model that allows to estimate the sediment solid volume concentrationand the diameter of flocs D, presented by Winterwerp (2001). The transport equations of and D are solved using the moment method presented by Beaudoin et al. (2002 and 2004). The moment method has been used because it allows to reduce the CPU time, making feasible a parametric study. From this work, we have found a classification of tidal bores as a function of Froude number Fr. This classification is also based on the study conducted by Furgerot (2014). We have obtained that for a Froude number 1.04 < Fr < 1.43, the tidal bore is undular. For 1.43 < Fr < 1.57, the tidal bore is partially breaking that is similar with the tidal bore transtition defined by Furgerot (2014). For Fr > 1.57, the tidal bore is totally breaking. An analysis of pressure distributions has been performed by Baddour and Song (1990). We found that the total and hydrostatic pressures of undular tidal bores have great values under the crest and the trough wave. In the case of undular tidal bores, the total pressures are not equal to the hydrostatic pressures. In the case of breaking tidal bores, the total pressures become equal to the hydrostatic pressures when the tidal bores are totally breaking. The turbulence reduces the dynamic pressures. The impact of tidal bores on the transport of non-cohesive and cohesive sediment particles have been studied in this work. For the non-cohesive sediment particles, we have observed that the trajectory using the flow generated by OpenFOAM is similar with the type e trajectory proposed by Chen et al. (2010). The modifications of Chen’s model have been done by including the effects of gravity, elevation and attenuation to reproduce non-cohesive particle trajectories under an undular tidal bore. We have obtained that the relationship between the Chen’s parameters (β1 , β2 and β3) and the Froude number Fr are linear. This is because the level of turbulence for undular tidal bores is low. The flow induced by an undular tidal bore is not complex. This physical phenomenon is quasi linear. The parameter β1 , related to the front celerity of tidal bores, decreases when the Froude number Fr increases. The parameters, β2 and β3, related to the elevation and attenuation of tidal bores respectively, increase when the Froude number Fr increases. Finally, for the cohesive sediment particles, we have calculated the distribution of floc size D under two types of tidal bore, undular and breaking. We have used the initial diameter of cohesive sediment particles d = 4 μm. The initial floc size D is equal to 10 μm with the consentration of floc c = 0.5 kg/m3. And we have limited the maximum floc size equal to 2000 μm. We have obtained that the maximum value of floc size Dmax increases exponentially with the Froude number Fr.

Cette thèse porte sur le développement d’un modèle numérique de l’affouillement causée par des obstacles montes sur le lit, combinant les processus hydrodynamiques et morphologiques. Le modèle numérique est basé sur le solveur de champ d’écoulement polyphasique de l’outil CFD open-source OpenFOAMR qui est distribue par OpenCFD Ltd. Le module hydrodynamique du modèle résout les équations de Navier-Stokes avec moyennes de Reynolds (RANS) et les modèles des turbulences k-ε ou k-ω. Il existe deux interfaces dans le domaine de simulation: la surface libre entre l’eau et l’air, qui est suivi par la méthode de Volume de Fluide (VOF); et l’interface entre l’eau et le lit du sédiment, qui est représentée par un maillage de surface finie déformable construit à partir de la limite en bas du maillage de volume fini. En outre, un module morphologique qui a été développé dans le cadre du projet se compose de trois composantes: un modèle de transport de sédiments comprenant la charge suspendue et le charriage; l’équation d’Exner pour mesurer la déformation du lit; et un mécanisme de glissement du sable pour limiter la pente du lit à être plus petite que l’angle de repos du sédiment. Le changement morphologique est incorporé dans le modèle hydrodynamique par la déformation du maillage. Des conditions limites spéciales et des corrections nécessaires pour le calcul en parallèle sont également ajoutées au modèle. Chaque partie du modèle est validée séparément avec les tests préliminaires correspondants, y compris les fonctions de paroi rugueuse, les performances de la méthode VOF, le modèle de transport de charge suspendu et le mécanisme de glissement de sable. Le modèle numérique est ensuite appliqué pour étudier un affouillent bidimensionnelle cause par un jet immerge provenant d’une ouverture sous écluse. Comparaison des résultats de la simulation avec des données expérimentales prouve la capacité du modèle. Et les limites du modèle sont également discutées. Enfin, le modèle est appliqué à l’étude du champ d’écoulement tridimensionnel et de la formation d’affouillement autour d’un obstacle dans l’écoulement. Tout d’abord, la déformation du lit n’est pas activée. Le tourbillon en fer à cheval devant un obstacle et le champ d’écoulement turbulent autour d’un cylindre sur un lit lisse ou rugueux sont simulés. Deux types de simulation pour le module hydrodynamique sont effectués: une simulation qui utilise une surface fixe et rigide pour représenter l’interface air-eau, et une simulation incluant à la fois les domaines de l’eau et de l’air avec la surface libre suivie par la méthode VOF. Les influences de la surface libre sur le champ d’écoulement sont identifiées et discutées. La comparaison avec les données expérimentales confirme l’importance de la déformation de la surface libre sur le champ d’écoulement. Ensuite, le lit est autorisé à se déformer et le développement temporel de l’affouillement tridimensionnelle autour d’un cylindre sur le lit est simule. Le développement temporel d’affouillement et la profondeur maximale du trou calcule devant et derrière le cylindre conviennent assez bien avec les mesures expérimentales. Les influences de l’affouillement sur le champ d’écoulement sont aussi étudiées et la performance du modèle numérique développé est discutée. / This thesis describes the development of a numerical model for local scour caused by bed-mounted obstacles, combining the hydrodynamic and morphological processes. The basis of the numerical model is the multiphase flow field solver in the open-source CFD toolbox OpenFOAMR which is released by OpenCFD Ltd. The hydrodynamic module of the model solves the Reynolds Averaged Navier-Stokes (RANS) equations with either a k-ε or a k-ω model. There are two interfaces in the simulation domain: the free surface between water and air, which is tracked using the Volume of Fluid (VOF) method, and the interface between the water and the sediment, which is represented by a finite area mesh constructed from the bottom boundary of the finite volume mesh. A morphological module which has been developed as part of the project consists of three components: a sediment transport model which includes suspended load and bed load transport; the Exner equation to compute the bed deformation, and a sand-sliding mechanism to restrict the bed slope angle to be smaller than the angle of repose. The morphological changes are incorporated into the hydrodynamic field through deformation of the computational mesh. Additional boundary conditions and parallel computing corrections are also added into the model. Each individual part of the model has been validated separately with corresponding preliminary test cases including the rough wall functions, the performance of the VOF method, the suspended load transport model and the sand-sliding mechanism. The numerical model is then applied to study two-dimensional scour caused by a submerged jet issuing from an opening under sluice gate. Comparison of the simulation results with the experimental measurements proves the ability of the model for conducting two-dimensional simulations and the limitations of the model are also discussed. Finally, the model is applied to study the three-dimensional flow field and scour formation around an obstacle in flow. Initially, the bed deformation is not activated in the model. The horseshoe vortex formed in front of an obstacle in water and the turbulent flow field around a cylinder on smooth and rough beds are simulated. Two types of simulations for the hydrodynamic module are used: a rigid lid simulation with a slip boundary condition to represent the air-water interface, and a free surface simulation including both the water and air domains with the free surface tracked by the VOF method. The influences of the variation of the water depth on the flow field are identified and discussed. Comparison with the experimental data also confirms the importance of the water surface variation on the flow field. Next, the bed is allowed to deform in the model. The temporal development of three-dimensional scour around a cylinder on live-bed in a steady current is simulated. The development of the scour with time and the computed maximum scour depths in front of and behind the cylinder agree quite well with the experimental measurements. The influences of the scour process on the flow field are also studied and the performance of the numerical model is discussed.

Este estudo teve por objetivo analisar as possíveis correlações entre as taxas de recomposição do fundo, pluviometria e marés para a região do Terminal Marítimo de Ponta da Madeira, Maranhão, Brasil. Foram analisados os dados de levantamentos batimétricos, pluviometria e marés, realizados na região do Terminal, além de dados de chuvas e vazões líquidas e sólidas provenientes do sistema fluvial da sub-bacia do rio Mearim, ligado ao estuário em que se localiza o Terminal. O período analisado compreende os anos de 2010 a 2013. Observou-se que há boa correlação entre vazões sólidas e líquidas no sistema fluvial, sendo que há variação sazonal de vazão líquida, relacionada aos períodos chuvoso e seco, com maiores vazões no período chuvoso. Foram observadas influências desta sazonalidade nas áreas de dragagem mais a sul no Terminal, com boa correlação entre taxas de recomposição do fundo e pluviometria. Em relação às marés, as influências foram melhor observadas nas áreas mais a norte, com boa correlação entre taxas de recomposição do fundo e marés nestas áreas. Os períodos com maiores intensidades de movimentação de fundo estão, de maneira geral, relacionados ao período de intensificação das chuvas e aos solstícios e equinócios, principalmente o equinócio de primavera. O método utilizado provou ser uma boa ferramenta de auxílio à previsão de movimentação e deposição de sedimentos. / The objective of this is study was to analyze possible correlations between bed recovery rates, rainfall and tides for Ponta da Madeira maritime terminal, located in Maranhão, Brazil. Bathymetries, rain and tidal data from the terminal area were analyzed, besides rain and river solid and liquid flow from Mearim river, which flows into the estuary. The data analyzed was collected from 2010 to 2013. There was good correlation between solid and liquid Mearim river flow, related directly to rainy and dry seasons. Seasonal influence was more important at dredging areas located at the terminal south region, which presented good relations between bed recovery rates and rain. North dredging areas bed recovery rates were more subjected to tidal variations. Generally, periods with high bed recovery rates were associated with rainy periods or either solstice and equinox, mainly in the spring. Such a methodology was considered to be successful as an auxiliary tool to predict bed behavior.

O presente trabalho visa caracterizar, através de experimentos numéricos, a hidrodinâmica e o transporte de sedimentos em suspensão no sistema estuarino de Caravelas e Peruípe sob diferentes condições forçantes. O sistema é formado por canais que estabelecem a conexão entre os rios Caravelas e Peruípe. Dados de nível de água e velocidade de correntes, obtidos em coletas de campo foram utilizados para aplicar e calibrar o modelo numérico MOHID. Diferentes experimentos numéricos, simulando condições de maré de sizígia e de quadratura com diferentes condições de descarga fluvial, foram realizados. A partir destas simulações foram obtidas distribuições espaciais e pontuais da concentração de sedimentos em suspensão e das correntes forçadas pela maré integradas verticalmente. Em condições de sizígia o estuário é caracterizado por correntes mais intensas e assimétricas, com dominância de vazante. As maiores concentrações médias de sedimento em suspensão ocorreram em condições de sizígia e o transporte de sedimentos resultante foi em direção ao oceano, em função do domínio das correntes de maré vazante. Os experimentos numéricos mostram que os canais que conectam os dois estuários têm papel relevante na dinâmica local. Eles possuem influência na dinâmica sedimentar do sistema estuarino. A hidrodinâmica e o balanço sedimentar do sistema são principalmente modulados pela altura da maré, com pouca contribuição do aporte de água doce. / The aim of this work is to characterize, through numerical modeling experiments, the hydrodynamics and suspended sediment transport dynamics in the Caravelas ? Peruípe estuarine system under different forcing conditions. The system comprises channels that connect the Caravelas and Peruípe rivers. Water level and current velocity data obtained through field campaigns were used to apply and calibrate the MOHID numerical model. Different numerical experiments simulating spring and neap tides with different river discharge conditions have been conducted. Based on these simulations, the hydrodynamics and spatial and temporal distributions of suspended sediment concentrations have been analyzed. During spring tide the estuary is characterized by intense and asymmetric currents (ebb dominated). The highest average suspended sediment concentration occurred during spring tide conditions, with net sediment transport being seaward. The numerical experiments show that the connecting channels play a relevant role in the local suspended sediment dynamics. The hydrodynamic and sediment balance in the system are modulated mainly by the tidal range, with little influence from the freshwater supply.

Este trabalho teve como objetivo analisar o transporte de sedimentos na região central da Baixada Santista (SP) através do uso do modelo numérico ROMS (Regional Ocean Modeling System) acoplado ao modelo numérico SWAN (Simulating WAves Nearshore) em simulações representativas dos meses de agosto de 2009 e janeiro de 2010. Os resultados indicaram haver picos no transporte de sedimentos, principalmente na plataforma continental e na Baía de Santos, durante a passagem de sistemas frontais, chegando a atingir 4,2 kg m2 s1 na região costeira. As menores taxas de concentração de sedimentos em suspensão na coluna d\'água ocorreram durante os períodos de quadratura, sem a presença de ventos fortes e incidência de ondas com grande energia. O transporte por carga de fundo encontrado na área costeira de Praia Grande foi predominantemente para sudoeste, em ambos os meses simulados, onde, as maiores taxas de transporte foram observadas no mês de agosto com valores em torno de 1 x 10 kg m2 para o mês. A taxa de sedimentação na região do alto estuário foi da ordem de 1 cm ano1, concordando com os dados disponíveis na literatura. O modelo numérico representou de forma satisfatória os padrões de transporte de sedimentos encontrados na região. / This study aimed to analyze the sediment transport in the central region of Baixada Santista (SP) using the numerical model ROMS (Regional Ocean Modeling System) coupled to the numerical model SWAN (Simulating Waves Nearshore) in simulations representing the months of August 2009 and January 2010. The results suggested peaks in sediment transport, especially on the continental shelf and the Bay of Santos, during the passage of frontal systems, achieving values of 4,2 kg m2 s1 nearshore. The lowest rates of concentration of suspended sediment in the water column occurred during periods of neap tides, without the presence of strong winds and incidence of waves with high energy. In both simulated months, the bedload transport found in the coastal area of Praia Grande was predominantly to the southwest, with the highest rates of transport observed in the month of August, with values of 1 x 10 kg m2. The rate of sedimentation in the upper estuary has been on the order of 1 cm year1, in agreement with the data available in the literature. The numerical model represented the transport patterns of sediments found in the region in a satisfactory way.

A previsão hidrológica é um processo estocástico dependente de fatores aleatórios, e, por si só, possui incertezas, porém, como a descarga sólida de um rio se correlaciona com a vazão por uma relação do tipo potência, na previsão do assoreamento de reservatório estas incertezas são maximizadas. Métodos empíricos e semi-empíricos de previsão de assoreamento negligenciam importantes fenômenos hidráulicos que regem o comportamento instantâneo do transporte de sedimentos. Incertezas e erros na estimativa da vida útil de reservatórios na fase de estudo de viabilidade é prejudicial ao processo decisório de qual reservatório e/ou se o reservatório deve ser construído. A pesquisa identificou os mecanismos de como a variabilidade hidrológica influencia a previsão do assoreamento de reservatórios por meio de casos idealizados e validação das hipóteses em estudo de caso, também foi proposto um fluxograma de atividades para a previsão de assoreamento capaz de reduzir incertezas inerentes a estes estudos, pautado na modelagem hidrodinâmica de transporte de sedimentos, ferramentas de hidrologia estatística e uso de múltiplos cenários, o Procedimento Metodológico para Redução de Incertezas na Previsão do Assoreamento de Reservatórios (PRIPAR - NH). Identificou-se que: séries de vazões com maior variabilidade resultam em um aporte de sedimento maior quando comparado à somatório de seu valor médio, e quanto maior a variabilidade maior o aporte resultante; séries com mesmo aporte de sedimentos e maior parte nos primeiros anos do reservatório resultam em assoreamento mais rápido devido a relativa alta Eficiência de Retenção de sedimentos nos primeiros anos e sua redução com a evolução do assoreamento; e, comprovou-se que modelos estocásticos para geração de séries sintéticas produzirão séries ligeiramente diferentes caso aplicados mais de uma vez, mesmo quando utilizando parâmetros de calibração iguais, causando significativa diferença na previsão do assoreamento. O PRIPAR - NH foi aplicado no estudo de caso do reservatório da PCH Mogi-Guaçu. Os 50 cenários analisados suportam a hipótese, apresentando amplitude de 12,4% do volume assoreado calculado, com média de 48,1% de seu volume em 50 anos. / The hydrologic forecast is a stochastic process that relays on a random factor. It present uncertainties by itself, but when used for reservoir sedimentation studies this uncertain are maximized due the fact that sediment load relates with flow discharge by a power type function. Empirical and semi-empirical methods for reservoir sedimentation forecast, widely used in Brazil, neglects important hydraulic phenomena that governs the instantaneous sediment transport behavior. Uncertainties and errors in reservoirs useful life estimation during feasibility studies are detrimental for the process of choosing which reservoir should be build and/or if the reservoir should be build. This study identified how hydrologic forecast and flow variability affects reservoir sedimentation studies, by means of hypothetical ideal scenarios and validations of the hypothesis in a study case. It also proposed a process flowchart for reservoir sedimentation studies able reduces uncertainty by the use of sediment transport modelling, statistical tools applied in hydrology and multiple scenarios, the PRIPAR-NH. It was identified that: as the degree of variability in flow data series increases, sediment loads also increase in comparison with the value calculated by the average flow; for the same sediment income, data series that presents most part of the sediment loads in the early years of the reservoir operation presents a faster sedimentation, it is explained by the fact the sediment Trap Efficiency reduces along the time due the reservoir storage capacity loss; and, it was proved that stochastic model will produce different data series if applied more than once, even when using the same calibration parameters, and it affects significantly the sedimentation forecast results. The PRIPAR-NH was applied to assess the sedimentation in Mogi-Guaçu Hydropower reservoir. The 50 analyzed scenarios support the study main hypotheses, presenting results for sedimentation volume ranging in 12.4%. The average sedimentation volume found was 48.1% for a 50 years scenario.

A modelagem unidimensional tem sido adotada desde os anos 1980, com sucesso nas práticas de engenharia, para a caracterização do regime de transporte de sedimentos de longo termo. É também uma importante ferramenta para o entendimento da dinâmica sedimentar de bacias e gestão de sedimentos em reservatórios. Esta pesquisa teve como objetivo aplicar a modelagem unidimensional de transporte de sedimentos na bacia do reservatório Taiaçupeba, São Paulo, Brasil, a partir do sistema computacional HEC-RAS, orientada à estimativa das descargas sólidas afluentes ao reservatório. O período de coleta de dados coincidiu com a estiagem de 2013-2015 na Região Sudeste, o que contribuiu com a análise crítica do método e dos resultados, cuja discussão ressalta o uso da modelagem unidimensional como instrumento eficaz de validação das curvas de sedimento para caracterização do regime de transporte. As funções de capacidade de transporte de Laursen-Copeland e Toffaleti mostraram-se aplicáveis a esse sistema fluvial, bem como os métodos de encouraçamento de fundo de Hirano e Thomas-Copeland. Os coeficientes de Manning ajustados foram considerados preliminares e dados de campo adicionais são encorajados para refinar seu ajuste e incorporar maior acurácia na estimativa do perfil da linha d\'água em trabalhos futuros. Além disso, são apresentadas recomendações metodológicas ao monitoramento fluvissedimentométrico que contribuem com a sistematização das técnicas e tecnologias disponíveis à pesquisa hidrossedimentológica. / One-dimensional modeling has been successfully adopted since the 1980s in engineering practices to assess long-term sediment transport regimes. It is also an important tool for the understanding of sediment dynamics in watersheds and sediment management in reservoirs. The objective of this research was to apply the one-dimensional sediment transport modeling in the Taiacupeba reservoir basin, located in Sao Paulo, Brazil, implemented on HEC-RAS, aiming to estimate longterm loads into the reservoir. The data collection period coincided with the drought of 2013-2015 in Southeastern Brazil, which contributed to the critical analysis of the method and results, whose discussion highlights the use of one-dimensional modeling as an effective instrument for validating sediment curves. The transport capacity functions of Laursen-Copeland and Toffaleti have been shown to be applicable to this river system, as well as the bed sorting and armoring methods of Hirano and Thomas-Copeland. The Manning coefficients were considered preliminary and additional field data are encouraged to enhance its adjustment and incorporate greater accuracy in estimating the water surface profile in future work. Besides, methodological recommendations for sediment monitoring are presented, contributing to the systematization of available techniques and technologies applied to sediment research.

O estudo do transporte de sedimentos, partindo da estimativa de estruturas turbulentas relevantes, constituiu o principal foco deste trabalho. Assim, a equação de transporte de massa (advecção-difusão) foi aplicada em conjunto com as equações de Navier-Stokes e da continuidade filtradas. Neste contexto, houve a necessidade de uma descrição conveniente da turbulência, o que ocorreu mediante a aplicação da simulação de grandes escalas acoplada a modelos de viscosidade turbulenta sub-malha. O método de fronteira imersa foi utilizado na modelação da interface sólido/fluido, representada pela geometria de fundo dos canais. As equações de Navier-Stokes filtradas e da continuidade foram resolvidas numericamente pelo método de passos fracionados, o qual estabeleceu o almejado acoplamento entre ambas. Na discretização das equações governantes foi utilizado o método de diferenças finitas, aplicado sobre malhas deslocadas. Os esquemas explícitos de Adams-Bashforth (de segunda e quarta ordens) foram utilizados no avanço temporal das velocidades do escoamento e das concentrações de sedimentos. Uma nova formulação para a velocidade de sedimentação foi desenvolvida analiticamente, enquanto que eventuais fluxos de ressuspensão foram impostos como condição de contorno no fundo do canal. Todos os códigos computacionais, que estabeleceram as diretrizes e a lógica de cálculo, foram criados no contexto deste trabalho. Os resultados obtidos indicam que a simulação de grandes escalas, associada ao método de fronteira imersa, considerando velocidade de sedimentação conforme aqui modelada, e ainda utilizando a equação de advecção-difusão para o transporte de massa, constituem ferramentas altamente adequadas à estimativa do transporte de sedimentos pela água. / The goal of this work is the research of sediment transport phenomena, deriving from outstanding turbulent eddies estimative. Thus, the mass transport equation (advection-diffusion) was connected with the filtered Navier-Stokes and continuity equations. In this context, the large-eddy simulation and sub-grid viscosity modeling established a convenient description of turbulence effects. The immersed boundary method was applied to model solid/fluid interface, represented here by the shapes of channel bottom. The filtered Navier-Stokes and continuity equations were solved by the fractional step method. The equations were discretized with the finite difference method, applied over staggered grids, whereas explicit Adams-Bashforth schemes (second and forth orders) were used in temporal advancement of velocities and sediment concentration fields. A new analytical formulation for settling velocity was obtained, while fortuitous re-suspension flux was applied like a boundary condition in the channel bottom. The computational code was totally developed in this work. The results of present simulations show that large-eddy simulation coupled to the immersed boundary method, considering, yet, the settling velocity of particles and the advection-diffusion equation for mass transport, constitute potential tools for sediment transport evaluation in water flows.