Cette recherche porte sur les mécanismes de ségrégation dans le transport de sédiments par charriage. Des expériences simplifiées consistant à introduire un débit de particules fines sur un lit plus grossier, mobile, en équilibre, ont été entreprises dans un canal particulaire étroit en utilisant des billes de verre sphériques. Les expériences montrent des réponses différenciées en fonction du rapport de taille entre les particules grossières du lit (Dc) et les fines (Df). Des rapports de taille (Dc/Df) entre 7,14 et 1,25 ont été testés, pour différents débits solides de particules fines, tout en maintenant le débit solide des particules grossières constant. Des travaux antérieurs ont mis en évidence une augmentation des débits solides suite à l’introduction de grains fins. Les expériences présentées ici identifient les frontières au sein de ce comportement.Le tamisage cinétique a lieu à la surface du lit mobile, avec des sédiments plus fins se déplaçant vers le bas de la couche de charriage à l'interface du lit grossier quasi-statique. Le comportement à cette interface dicte comment le système répond à l’introduction de sédiments fins. Si, par percolation spontanée, le sédiment fin est capable de s’infiltrer dans le lit quasi-statique sous-jacent, le débit solide total augmente et le lit s’incise (diminution de pente). Toutefois, si les fines ne peuvent géométriquement s’infiltrer ou dépassent la capacité de transport, elles forment une couche quasi-statique sous la couche de charriage, qui empêche l'entraînement du lit sous-jacent, résultant en un exhaussement (augmentation de pente).Un essai formel de la reproductibilité des résultats ci-dessus a été effectué dans un autre laboratoire avec le même mode opératoire expérimental. La comparaison des résultats qualitatifs révèle les mêmes processus dominants. Cependant, des différences sont notées dans les résultats quantitatifs, du fait de la quasi-impossibilité de reproduire exactement la même expérience.Une dernière série d'expériences évalue les différences et les similitudes entre les expériences menées avec des billes de verre sphériques et des matériaux naturels ce qui permet d’étudier l’influence de la forme. Alors que les expériences avec des matériaux idéaux révèlent des mécanismes fondamentaux associés au transport granulaire et à la ségrégation, plusieurs nouveaux phénomènes sont observés avec des matériaux naturels, notamment une modification du potentiel d’infiltration et l’émergence de formes du lit. / This research focuses upon size segregation mechanisms in bedload sediment transport. Simplified experiments with fine grain inputs to a mobile coarse bed in equilibrium were undertaken in a small, narrow flume using spherical glass beads. The experiments demonstrate the influence of the size ratio between the bed (Dc) and the input (Df) upon the channel response. Size ratios (Dc/Df) between 7.14 and 1.25 were tested, with a constant coarse feed rate, and a variety of fine feed rates. Previous work has documented an increase in sediment transport rates as a result of a fine grain input; the experiments presented herein identify boundaries within this behaviour.Kinetic sieving takes place in the mobile bed surface, with the finer sediment moving to the bottom of the bedload transport layer at the interface to the underlying quasi-static coarse bed. The behavior at this interface dictates how a channel responds to a fine sediment input. If, by spontaneous percolation, the fine sediment is able to infiltrate into the underlying quasi-static bed, the total transport increases and the bed degrades causing a reduction in the slope. However, if the fine sediment input rate exceeds the transport capacity or is geometrically unable to infiltrate into the underlying bed, it forms a quasi-static layer underneath the transport layer that inhibits entrainment from the underlying bed, resulting in aggradation and an increase in bed slope.A formal test of the reproducibility of the aforementioned results was undertaken in a different laboratory, with the same experimental procedure. Comparison of the qualitative results reveals that the same dominant processes occur. Consistent differences, however, were present between the quantitative results; likely a result of differences in the experimental arrangement.A final set of experiments assesses the differences and similarities between experiments undertaken with spherical glass beads and natural materials to examine the complexities introduced due to particle shape. While the experiments with ideal materials reveal fundamental mechanisms associated with granular transport of mixed sizes, several key new phenomena are apparent in the experiments with natural materials, including changes in the infiltration potential and the emergence of bed structures.

Cette thèse, à dominante expérimentale, tente de décrire, de comprendre et de quantifier le transport sédimentaire pour un système torrentiel caractérisé par une forte pente et des conditions hydrauliques faibles. Une plateforme expérimentale a été mise en place et instrumentée. Elle permet de contrôler quatre paramètres du système : la pente du canal, le débit hydraulique, le débit solide et la granulométrie. La durée des expériences est suffisamment longue pour couvrir l'ensemble des fluctuations gouvernant le transport. L'étude de l'évolution d'un même mélange granulaire soumis à un forçage hydraulique fort, (Shield = 1.37 Shield critique) ou à un forçage hydraulique faible (Shield = 0.94 Shield critique) a permis de mettre en évidence, au sein des structures sédimentaires observées, deux classes de comportement différentes. Pour l'expérience à Faible Transport, le lit est globalement pavé au cours de la durée de l'expérience qui est de 110 heures. Des structures de type step-pools sont présentes et très stables, et contrôlent la dynamique de transport du système à court terme et à long terme. A court terme, le transport solide n'est pas uniforme mais s'effectue à travers des processus transitoires d'érosion et de dépôt « de proche en proche », associés respectivement à la destruction et à la formation de step-pools dans le système. A long terme, les step-pools conduisent à un pavage uniforme sur l'ensemble du canal. Des destructions périodiques de ce pavage de surface sont également observées et sont associées à une capacité de transport pour le système pouvant atteindre jusqu'à 15 fois le débit solide moyen. Pour l'expérience à Fort Transport, d'une durée de 92 heures, la morphologie du lit fluctue entre deux états extrêmes. Un lit plat dont la surface est formée de particules fines, à forte capacité de transport et un lit pavé à forte pente et à faible capacité de transport. Les step-pools ne sont, ici, que des états éphémères associés à la phase de transition du système qui sont rapidement détruits par les nappes de charriage. Ces dernières sont le mode principal de transport pour le système et expliquent les évolutions cycliques mesurées à court et à long terme. Enfin, nous avons étudié les conséquences des phénomènes décrits ci-dessus en conditions hors équilibre à forte pente. Nous avons pour cela réalisé deux expériences : une première expérience où nous étudions le cas d'un système en phase d'aggradation et une seconde où nous prenons le cas d'un système contrôlé par deux seuils de correction torrentielle. La première a nécessité une longue période afin que le système atteigne une condition d'équilibre dynamique : plus que 210 heures. L'équilibre local du système est atteint progressivement de l'amont vers l'aval, les parties les plus proches de l'alimentation atteignant en premiers l'état d'équilibre. De plus, pendant l'aggradation les fluctuations du système autour de la moyenne sont inférieures à celles mesurées pour un système à l'équilibre. La seconde expérience a montré que l'aménagement d'un système torrentiel avec des seuils peut avoir un impact non négligeable sur la quantité maximum de matériau transporté au cours d'un seul événement. Néanmoins, l'intensité maximale instantanée du transport et le comportement global du système à long terme ne sont en rien affectés par la présence de seuils. / This experimental thesis aims to describe, understand and quantify the sediment dynamics of a torrential system, characterized by steep slope and low hydraulic conditions. An experimental platform has been developed and instrumented for monitoring the channel slope, the water discharge, the feed solid discharge and the bed grain size distribution. The duration of the experiments were sufficiently long to cover all the fluctuations governing the bedload transport phenomenon. Two flow conditions were considered, in order to observe the bed dynamic under different forcing. A strong hydraulic forcing capable to move the bed pavement (Shield parameter = 1.37 Critical Shield parameter) was compared to a low hydraulic forcing supposed to not disturb the bed pavement (Shield Parameter = 0.94 Critical Shield Parameter). We measured for each case the sediment dynamic and associated bedforms. For the “Low Transport” experiment the bed was generally paved over all the duration of the experiment (110 hours). Bedforms similar to step-pools developed and were present for all the duration of the run. These macroforms seems to control the transport dynamic of the system in the short and long term. In the short term, bedload transport was not uniform. Instead, transient processes of erosion / deposition associated with the formation / destruction of step-pools were observed. In the long term, step-pools lead to the formation of a uniform paved bed on the whole channel length. Periodic destruction of bed pavement was also observed and associated with a transport capacity that could reach 15 times the value of average measured bedload transport. For the “High Transport” experiment (92 hours) the channel morphology fluctuates between two extremes. A flat bed characterised by highly mobile fine sediments and high transport capacity, and a steep paved bed corresponding to a low transport capacity. For this experiment step-pools were just a transitory state associated with the transition between the two extremes and they are quickly destroyed by the bedload sheets propagation. Bedload sheets were the main transport mode for the system. Their formation and propagation can explain the cyclical evolution of the system in the short and long term. We finally studied the consequences of the observed phenomena for non-equilibrium systems on steep slopes. We conducted two experiments: one in order to reproduce an aggradational system and the second to reproduce the dynamic of a system controlled by two check dams. A very long duration was necessary for reaching the dynamic equilibrium condition with the aggradational system (more than 210 hours). The local equilibrium was achieved gradually from upstream to downstream, with the flume sections closest to the feeding device attaining first the dynamic equilibrium. Experiments with check dams showed that this kind of slope correction can have a significant impact on the maximum amount of material transported during a single event. However, the maximum instantaneous transport and the long term sediment behaviour of the system are not affected by the presence of the check dams.

abstract: Worldwide, rivers and streams make up dense, interconnected conveyor belts of sediment– removing carved away earth and transporting it downstream. The propensity of alluvial river beds to self-organize into complex trains of bedforms (i.e. ripples and dunes) suggests that the associated fluid and sediment dynamics over individual bedforms are an integral component of bedload transport (sediment rolled or bounced along the river bed) over larger scales. Generally speaking, asymmetric bedforms (such as alluvial ripples and dunes) migrate downstream via erosion on the stoss side of the bedform and deposition on the lee side of the bedform. Thus, the migration of bedforms is intrinsically linked to the downstream flux of bedload sediment. Accurate quantification of bedload transport is important for the management of waters, civil engineering, and river restoration efforts. Although important, accurate qualification of bedload transport is a difficult task that continues t elude researchers. This dissertation focuses on improving our understanding and quantification of bedload transport on the two spatial scales: the bedform scale and the reach (~100m) scale. Despite a breadth of work investigating the spatiotemporal details of fluid dynamics over bedforms and bedload transport dynamics over flat beds, there remains a relative dearth of investigations into the spatiotemporal details of bedload transport over bedforms and on a sub-bedform scale. To address this, we conducted two sets of flume experiments focused on the two fundamental regions of flow associated with bedforms: flow separation/reattachment on the lee side of the bedform (Chapter 1; backward facing-step) and flow reacceleration up the stoss side of the next bedform (Chapter 2; two-dimensional bedform). Using Laser and Acoustic Doppler Velocimetry to record fluid turbulent events and manual particle tracking of high-speed imagery to record bedload transport dynamics, we identified the existence and importance of “permeable splat events” in the region proximal to flow reattachment. These coupled turbulent and sediment transport events are integral to the spatiotemporal pattern of bedload transport over bedforms. Splat events are localized, high magnitude, intermittent flow features in which fluid impinges on the bed, infiltrates the top portion of bed, and then exfiltrates in all directions surrounding the point of impingement. This initiates bedload transport in a radial pattern. These turbulent structures are primarily associated with quadrant 1 and 4 turbulent structures (i.e. instantaneous fluid fluctuations in the streamwise direction that bring fluid down into the bed in the case of quadrant 1 events, or up away from the bed in the case of quadrant 4 events) and generate a distinct pattern of bedload transport compared to transport dynamics distal to flow reattachment. Distal to flow reattachment, bedload transport is characterized by relatively unidirectional transport. The dynamics of splat events, specifically their potential for inducing significant magnitudes of cross-stream transport, has important implications for the evolution of bedforms from simple, two dimensional features to complex, three-dimensional features. New advancements in sonar technology have enabled more detailed quantification of bedload transport on the reach scale, a process paramount to the effective management of rivers with sand or gravel-dominated bed material. However, a practical and scalable field methodology for reliably estimating bedload remains elusive. A popular approach involves calculating transport from the geometry and celerity of migrating bedforms, extracted from time-series of bed elevation profiles (BEPs) acquired using echosounders. Using two sets of repeat multibeam sonar surveys from the Diamond Creek USGS gage station in Grand Canyon National Park with large spatio-temporal resolution and coverage, we compute bedload using three field techniques for acquiring BEPs: repeat multi-, single-, and multiple single-beam sonar. Significant differences in flux arise between repeat multibeam and single beam sonar. Mulitbeam and multiple single beam sonar systems can potentially yield comparable results, but the latter relies on knowledge of bedform geometries and flow that collectively inform optimal beam spacing and sampling rate. These results serve to guide design of optimal sampling, and for comparing transport estimates from different sonar configurations. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2018

Orientador: Evaldo Miranda Coiado / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-12T09:09:22Z (GMT). No. of bitstreams: 1 Paiva_LuizEvaristoDiasde_D.pdf: 35394414 bytes, checksum: 213e131fa220c1a9965c1c327156d87f (MD5) Previous issue date: 2007 / Resumo: Nesta tese apresenta-se uma alternativa à definição do diâmetro de cículo a ser usado nas equações de estimativa da descarga de sedimentos na camada do leito, em escoamento com superfície livre. Foram empregadas quatorze equações de estimativa da descarga de sedimentos, a partir das quais foram determinados os diâmetros que poderiam ser empregados em substituição áqueles definidos pelos respectivos autores das equações. Para o desenvolvimento deste trabalho, foram empregados dados coletados no Rio Atibaia em Sousas, no município de Campinas (SP). No decorrer dos estudos, verificou-se que a vazão e a declividade da linha de água foram as variáveis mais significativas na definição do diâmetro. Para validar a alternativa à definição do diâmetro de círculo a ser usado nas equações de estimativa da descarga de sedimentos na camada do leito, foram utilizados dados de dois outros rios, de porte menor e maior que o rio Atibaia. Para os dois rios, a aplicação da metodologia produziu resultados mais satisfatários, se comparados àqueles obtidos pelos métodos na sua forma original. A aplicaçã da metodologia proposta nesta tese apresenta; além de ter demonstrado reduções nas diferenças percentuais relativas entre os valores das descargas calculadas e medidas, a vantagem de poder ser empregada para cursos de água com granulometria uniforme ou não e dispensa o levantamento de dados granulométricos. / Abstract: This thesis presents an alternative proposal to evaluate the sediment size to be used in the methods to estimate its discharge from bedload when occurring under open flow water. Fourteen different equations were employed in this work. From this equations different diameters were obtained that could replace respectively those suggested for each equation. Also, in order to undetake this work, data were collected from Atibaia River, Campinas-SP. Analises of these data showed that the discharge and slope of free surface of water were the most important variable to define de sediment dimension. To validate the alternative proposal to the calculated diameter, dates were used of the two other rivers one smaller and the other larger than Atibaia. Metodology apllied to those data produced sactisfactory results compared with the original methodology. The proposed methodology applied during this studies, besides having demonstrated decreased relative differences between calculated discharges and the measured ones also showed that it can be used in rivers whit uniform or non uniform grain sizes eliminating the necessity of collecting granulometric data. / Doutorado / Recursos Hidricos / Doutor em Engenharia Civil

No description available.

yes / A two dimensional (2D) RNG k-ε sediment model including the effects of secondary currents is developed to simulate sediment transport and bed deformation in rivers with continuous bends. Nonuniform suspended and bedload sediment transports and variation of effective bed material size distribution are included in the model. A semi-coupled scheme for sediment model is proposed, which can be used for simulating both the long- and short-term sediment transport whenever riverbed changes. The model is applied to simulate the flow and sediment transport in the Shapotou reservoir in the upper reach of the Yellow River which is a typical natural river reach with continuous bends. River bed deformations caused by suspended and bedload sediment transport are investigated. Good agreement between the numerically simulated results and the field measurements is obtained, indicating that the model is capable of simulating the sediment transport and predicting the bed deformation of rivers having continuous bends with reasonable accuracy. / the Major Research Plan Project, National Natural Science Foundation of China(Grant No.: 91230111 and 51279071); National Key BasicResearch Development Program of China (973 Program, Grant No.: 2010CB429002);Project of Science and Technology of Colleges in Ningxia, China (Grant No.:NGY2012097)

Sediment, an integral part of rivers and watersheds, is eroded from, stored in, and transported through various watershed components. Rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes, this sediment can be transported downstream along the bed or suspended in the water column. Most sediment measurements are focused on the component suspended in the water column. Recent advances in data collection techniques have substantially increased both the resolution and spatial scale of data on suspended sediment dynamics, which is helpful in linking small, site-scale measurements of transport processes in the field with large-scale modeling efforts. Part of this research evaluates the accuracy of the latest laser diffraction instrument for suspended-sediment measurement in rivers, LISST-SL2 for measuring suspended sediment concentration (SSC), particle size distribution (PSD), and velocity by comparing to concurrent physical samples analyzed in a lab for SSC and PSD, and velocity measured using an acoustic Doppler current profiler (ADCP) at 11 sites in Washington and Virginia during 2018-2020. Another part of this work employs a 1-D river network, bed material transport model to investigate the magnitude, timing, and persistence of downstream changes due to the introduction of sediment pulses in a linear river network. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. Then the model capability is utilized to explore the control of hydrograph structure on debris flow sediment transport through a more complex river network at different time horizons. Another part of this work investigates the effect of differences in spatial distribution of debris flow sediment input to the network by analyzing corresponding tributary and mainstem characteristics. Based on an extensive dataset, our results highlight the need for a correction of the raw LISST-SL2 measurements to improve the estimation of effective density and particle size distribution with the help of a physical sample. Simulation results from the river network model show that bed response is primarily influenced by the sediment-pulse grain size and distribution. Intermediate mixed-size pulses are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed-size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform-size pulse. While investigating the hydrologic control on debris flow simulation, this study finds that differences between transport by a 30-year daily hydrograph and simplified hydrographs were greatest in the first few years, but errors decreased to around 10% after 10 years. Our simulation results highlight that the sequence of flows (initial high/low flow) is less important for transport of finer sediment. We show that such network-scale modeling can quantitatively identify geomorphically significant network characteristics for efficient transport from tributaries to the mainstem, and eventually to the outlet. Results suggest that watershed area and slope characteristics are important to predict aggradation hotspots in a network. However, to predict aggradation and fluvial geomorphic responses to variations in sediment supply from river network characteristics more confidently, more widespread (in several other river networks) model applications with field validation would be useful. This work has important implications for river management, as it allows us to better predict geomorphically significant tributaries and potential impact on downstream locations, which are important for river biodiversity. Model results lead the way to use of simplified flow hydrographs for different timescales, which is crucial in large-scale modeling as it is often restricted by computational capacity. Finally, given the ability for reliable quantification of a high-resolution time-series of different suspended-sediment characteristics, in-stream laser diffraction offers great potential to advance our understanding of suspended-sediment transport. / Doctor of Philosophy / Rivers receive sediment from different natural and human sources, and water moves this sediment in various ways. These ways include along the bottom of the stream or suspended in the water. Quantifying suspended sediment in streams is an important step to estimate the threat to riverine environments as suspended sediments not only carry chemicals and pollutants, but also interact with the river bottom to affect the characteristics of streams. Measurement of suspended-sediment concentration and particle-size is critical for many engineering, ecological, and river-structure issues, but obtaining an accurate measurement of sediment quantity in a river is challenging. The recent advancement of a laser diffraction instrument allows us to obtain frequent measurements of suspended-sediment concentration and particle size by volume. We applied the most recent such instrument at 11 sites in Washington and Virginia during 2018-2020, along with concurrent water samples to measure suspended-sediment concentration and particle size by mass in a laboratory. Our analysis suggests that at least one supporting physical mass measurement be obtained to improve the estimation from laser measurement. Beside this site-scale measurement, we apply a large-scale river network model to estimate how sediment moves along the bed of rivers at large spatial extents. We simulate how this added sediment results in downstream changes in the amount of sediment in the river channel. We compare observed changes in the elevation of the stream bottom and sediment accumulation rates in a downstream lake to model results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of added sediment by comparing the changes against a baseline condition (without the added sediment). We find that the added sediment that is half as large as on the river bottom and with a range of sizes are likely to affect the largest downstream changes because smaller sizes move quickly and larger sizes move slowly. Furthermore, added sediment that is smaller than on the river bottom and with a range of sizes help more sediment on the river bottom move than if that sediment addition all had the same particle size. We also employ this model to explore the effect of flow variation and river characteristics on sediment movement. Comparing between a 30-year flow record and simplified flow records, we show that results from simplified flow records vary initially, but errors decrease after 10 years. That is, both flow records result in similar sediment movement in the long-term. In terms of aggradation from added sediment, results show that the characteristics of elevation change of the river bottom play a vital role along with the contributing landscape area. This work has important implications for river management, as it not only allows us to accurately measure suspended sediment with an advanced instrument, but also better understand how rivers and aquatic habitat are affected by variations in added sediment.

New analytical and numerical solutions are developed to both the kinematic approximation to the St Venant equations and the Hairsine-Rose (HR) soil erosion model in order to gain a better physical understanding of soil erosion and sediment transport in shallow overland flow. The HR model is unique amongst physically based erosion models in that it is the only one that: considers the entire distribution of the soil s sediment size classes, considers the development of a layer of deposited non-cohesive sediment having different characteristics to the original underlying cohesive soil and considers separately the erosion processes of rainfall detachment, runoff entrainment and gravitational deposition. The method of characteristics and the method of lines were used to develop both the analytical and numerical solutions respectively. These solutions were obtained for boundary and initial conditions typical of those used in laboratory flume experiments along with physically realistic constant and time dependent excess rainfall rates. Depending on the boundary and initial conditions, interesting new solutions of the kinematic wave equation containing expansion waves, travelling shocks as well as solutions which split into an upslope and downslope drying profiles were found. Numerical solutions of the HR model were applied to the experimental flume data of Polyakov and Nearing (2003) obtained under flow conditions which periodically cycled between net erosion and net deposition conditions. While excellent agreement was found with suspended sediment data, the analysis suggested that an additional transport mechanisms, traditionally not included in soil erosion models, was occurring. While the inclusion of bed-load transport improved the ii overall model prediction, it was still not sufficient. Subsequent asymptotic analysis then showed that the interaction of the flow with an evolving bed morphology was in fact far more important than bed load transport. A very interesting finding from this work showed that the traditional criterion of validating sediment transport model based solely on suspended sediment data was not sufficient as reliable predictions could be obtained even when important transport mechanisms were neglected. Experimental plots of sediment discharge or suspended sediment concentration against water discharge in overland flow have been shown to contain significant hysteresis between the falling and rising limbs of the discharge hydrograph. In the final Chapter, the numerical solution developed for the complete system of soil erosion and kinematic flow was used to show that it was possible for the HR model to simulate three of the four hysteresis loops identified in the literature. Counter clock-wise loops, clock-wise loops and figure 8 loops could all be produced as a result of starting with different initial conditions, being mi(x; 0) = 0, mi(x; 0) = pimt and mi(x; 0) = 0:5pimt respectively. This is the first time that these types of hysteresis loops have been produced by any erosion model. The generation of these hysteresis loops are physically explainable in terms of sediment availability and is consistent with data obtained on the field scale.

Made available in DSpace on 2016-12-23T14:04:34Z (GMT). No. of bitstreams: 1 Livia Meneghel de Almeida.pdf: 3825098 bytes, checksum: 99ed41a80ff85db844fb2553aee7b6b3 (MD5) Previous issue date: 2012-08-17 / Knowledge of bedload transport is of primary importance in a number of aspects in watershed management, including fluvial geomorphology and ecology, stability of engineered structures and navigation condition. Despite the fundamental importance of bedload measurement, the amount of variables involved in the bedload transport mechanics, as well the complexity of the interactions among the physical processes, makes it difficult to establish a fully satisfactory criteria to determine the solid transport, thus there is not an accepted universal method. With recent advances, new methods have been proposed for measuring the bedload transport. Therewith, the aim of this study was to evaluate the suitability of methodologies for bedload measurement on a reach of the Doce River, ES, Brazil. For this were used traditional direct sampling method, with Helley Smith s sampler; formulas proposed by Einstein & Brown (1950), Engelund & Hansen (1967), Ackers & White (1973), Yang (1973) e Van Rijn (1984); bedform movement methods, considering velocity of bedform displacement and the difference between bed surfaces; and bedload velocity using an ADCP. Results indicated an unstable flow, with a bed composed primarily of fine and medium-sized sand, and bedforms in transition. Bedload values obtained by different methods showed variation of different orders of magnitude, and the highest estimates were provided by the equation of Yang (1973). The application of the bedform movement methods has been complicated by the bed condition at the site. However, the bedload measured from the velocity of bedform displacement has been quite consistent with the hydraulic conditions. The equations of Engelund & Hansen (1967) and Van Rijn (1984), and the bedload velocity method showed excellent performance, and the latter being a very promising alternative for the measurement of the bedload. To confirm the suitability of these methods in the Doce river (ES) is suggested to be carried out more measurements, in a uniform stretch, primarily using the bedload velocity and the bedform displacement methods / O conhecimento da descarga de sedimentos de fundo é de primordial importância em vários aspectos da gestão de uma bacia hidrográfica, incluindo, a geomorfologia e a ecologia fluvial, a estabilidade das estruturas de engenharia e condições de navegação. Apesar da sua fundamental importância, a quantidade de variáveis envolvidas na mecânica de transporte de sólidos de fundo, bem como a complexidade das interações entre os processos físicos, torna difícil estabelecer um critério totalmente satisfatório para determinar o transporte sólido de fundo, assim, não há ainda um método universalmente aceito. Com os avanços recentes, novos métodos têm sido propostos para a medição da descarga de fundo. Com isso, o objetivo deste trabalho foi avaliar a adequação de metodologias para o cálculo da descarga de fundo em um trecho do rio Doce, ES. Foram aplicados os métodos da amostragem direta, com um amostrador Helley Smith; as fórmulas propostas por Einstein & Brown (1950), Engelund & Hansen (1967), Ackers & White (1973), Yang (1973) e Van Rijn (1984); métodos do deslocamento de formas de fundo, considerando a velocidade de deslocamento, e a diferença de superfícies do leito; e o método da velocidade do leito medida com um ADCP. Os resultados indicaram um fluxo instável, com leito composto principalmente de areias finas e médias, e formas de fundo em transição. As descargas de fundo estimadas pelos diferentes métodos apresentaram variação de diferentes ordens de magnitude, e as maiores estimativas foram fornecidas pela equação de Yang (1973). A aplicação dos métodos de deslocamento das formas de fundo foi dificultada pelas condições de leito em transição encontradas no local, entretanto, a descarga do leito a partir da velocidade de deslocamento das formas de fundo foi bastante coerente com as condições hidráulicas. As fórmulas de Engelund & Hansen (1967) e Van Rijn (1984), e o método de velocidade do leito apresentaram ótimo desempenho, sendo este último uma alternativa muito promissora para a medição da descarga de fundo. Para confirmar a adequação desses métodos ao rio Doce (ES) sugere-se que sejam realizadas mais medições, em um trecho uniforme, utilizando principalmente os métodos de velocidade do leito e de deslocamento das formas de fundo

Dans les bassins versants abrupts de montagne, de larges quantités de sédiments provenant des pentes escarpées viennent se déposer dans la partie supérieure des torrents et sont remobilisées par les laves torrentielles ou par charriage. Le but de ce travail était d'étudier le transport des sédiments grossiers dans les petits bassins versants torrentiels et d’analyser l’influence du stockage de ces sédiments dans le chenal sur les laves torrentielles. Cela a requis sur le terrain une intense surveillance géomorphologique des événements d'écoulement dans les bassins versants des torrents du Manival et du Réal, susceptibles de produire des laves torrentielles et du transport solide par charriage chaque année.Le bilan sédimentaire du Manival a été réalisé grâce à des mesures topographiques répétées entre les événements importants d’écoulements (sections transversales et relevés au scan laser terrestre). Deux évènements de laves torrentielles et plusieurs évènements de charriage ont été observés. La reconstitution de leur budget sédimentaire a révélé que la majeure partie de leurs volumes a été apportée par l'érosion du chenal. Les évènements de charriage de l’automne ont contribué à la recharge sédimentaire du chenal principal par le dépôt de grands bancs de gravier. Ce processus est fondamental au déclenchement de laves torrentielles lors des printemps et été suivants. Un décalage dans le temps des séquences érosion /dépôt a été observé entre les parties supérieure et inférieure du chenal, révélant un transfert discontinu de sédiments dans le bassin versant. Un modèle conceptuel de transfert des sédiments est proposé pour les différentes magnitudes d’écoulement.Dans le Réal, le volume de sédiment transporté est similaire à celui du Manival avec une augmentation importante du volume dans le chenal. La plus importante lave torrentielle observée a révélé une diminution en aval des hauteurs d'écoulement maximales, des contraintes de cisaillement, de la vitesse et de la résistance à l'écoulement. Cela suggère que le front de la lave torrentielle érode et déstabilise le chenal, mais qu’il ne peut pas transporter les matériaux en raison de sa concentration élevée en sédiments. La vague hyperconcentrée qui suit se charge des matériaux restants, croît en volume et fusionne avec la lave torrentielle en décélération. Le front et les vagues suivantes jouent un rôle essentiel pour l'érosion lors d'un événement de lave torrentielle.Les laves torrentielles ont créé une érosion significative à la variabilité spatiale importante alors que les déformations du lit induites par le charriage sont en équilibre. L’érosion du chenal par les laves torrentielles est contrôlée étroitement par la pente en amont et les conditions de stockage des sédiments et peut être prédite par une relation logarithmique. Les matériaux les plus sensibles à l'érosion dans le Manival sont les bancs de gravier non consolidés formés par le charriage. Ils constituent une surface lisse au sein du chenal rugueux qui peut être automatiquement cartographiée à partir de données de laser scan terrestre ou aérien. Ceci fournit une évaluation des zones sensibles à l'érosion dans un chenal au moment du relevé au scan laser.Cette étude a permis d’alimenter le domaine des laves torrentielles en observations quantitatives sur le terrain. Des bases de données détaillées ont été obtenues par l'intégration de multiples relevés des différentes sections transversales, des nombreux balayages laser et des données des stations de mesure à haute fréquence. Les mesures de transfert de sédiments, des interactions/contrôles dans le chenal, de la dynamique des laves torrentielles. La caractérisation des stockages dans ces bassins différents fournit une base solide pour le développement de modèles conceptuels et statistiques. Ces observations ont également mis en évidence les paramètres importants à mesurer sur le terrain qui ont une influence sur les laves torrentielles. / Steep mountain catchments typically experience large sediment pulses from hillslopes which are stored in headwater channels and remobilized by debris-flows or bedload transport. The purpose of this research was to investigate the coarse sediment transport through steep catchments and how channel storage can influence debris-flows. This required intensive field-based geomorphic monitoring of flow events in the Manival and Réal torrent catchments which can experience debris-flows and bedload transport every year.In the Manival Torrent, the sediment transfers were characterized at a seasonal time scale by a complete sediment budget of the catchment derived from multi-date topographic measurements between important flow events (cross-section surveying and terrestrial laser scanning). Sediment budget reconstitution of two debris-flows revealed that most of their volumes were supplied by channel scouring (more than 92%). Bedload transport during autumn contributed to the sediment recharge of high-order channels by the deposition of large gravel wedges. This process is recognized as being fundamental for debris-flow occurrence during the subsequent spring and summer. A time shift of scour-and-fill sequences was observed between low- and high-order channels, revealing the discontinuous sediment transfer in the catchment during common flow events. A conceptual model of sediment routing for different event magnitudes is proposed.In the Réal Torrent, post-event surveying and high-frequency monitoring stations were used to compare and compile measurements of flow events. Three debris-flow events and three periods of bedload transport with small headwater debris-flows were observed. Sediment transport volumes for debris-flows were very similar to the Manival with important volume growth in the channel. The largest observed debris-flow revealed a downstream decrease of maximum flow heights, shear stress, velocity, and flow resistance. We hypothesize that the debris-flow front scours and destabilizes the channel, but it cannot transport the material because of its high sediment concentration. Therefore, the trailing hyperconcentrated surge picks up the remaining material, grows in volume, and coalesces with the decelerating debris-flow. Both the front and following surges play an integral role for net erosion during a debris-flow event.Multi-date cross-sections in the Manival and Réal have shown that debris-flows have significant scouring with large spatial variability. Bedload transport was observed to be at equilibrium with little variability. Field observations of channel deformations show that debris-flow scouring is strongly controlled by upstream slope and storage conditions. A logarithmic relationship is proposed as an empirical fit for the prediction of channel erosion. The most susceptible materials for erosion in the Manival are the unconsolidated gravel wedges developed from bedload transport. This material has a smooth surface within the rugged channel which can be automatically mapped with a 20 cm digital elevation model from either terrestrial or airborne laser scans by calculating roughness with a one meter window. This provides an automatic assessment of erodible areas in a channel at the time of the laser scan survey.This study has contributed to the need of quantitative field observations in the realm of debris-flow research. Complete and thorough databases were obtained by integrating multi-date cross-section surveys, multi-date laser scans, and high-frequency monitoring stations. Quantified evidence revealing sediment transfers, channel interactions/controls, debris-flow dynamics, and storage characterizations in two different catchments provides a strong basis in the development of conceptual and statistical models. These observations also highlighted the significant field parameters that have an influence on debris-flows and steep catchment systems.