No description available.

To further understand bank undercutting processes that occur in the Petitcodiac River estuary (New Brunswick, Canada), the erosion of sediment cores obtained at the base of the estuary banks was studied by testing for the critical shear stress and erosion rates in a laboratory flume. It was found that there is variation in the erodibility of the sediment with depth horizontally into the bank over the depths tested. The bank cores were shown to erode in distinct layers, with the erosion of extremely weak layers occurring at rates that were an order of magnitude higher than the rates of adjacent resistant layers. Bed cores obtained at the toe of the bank were also tested and similar variability in sediment erodibility was found with vertical depth into the bed. Sediment properties of the cores, including particle size distribution, bulk density, water content, and organic content were compared to the erodibility of the sediment. Additional investigations included observations of the Petitcodiac River estuary bank movement through GPS surveys and erosion pin monitoring, as well as testing for the presence of biological sediment-stabilization factors, and changes in particle size and mineralogy on the river bank.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22049号 / 工博第4630号 / 新制||工||1722(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中川 一, 教授 藤田 正治, 准教授 川池 健司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Rivers in the U.S. Midwest are dynamic systems that can be natural laboratories for understanding the different modes of bank erosion, namely fluvial erosion, mass erosion, and mass failure. Fluvial and mass erosion are hydraulically driven and semicontinuous, whereas mass failure is episodic and often catastrophic. Being catastrophic, mass failure and its driving mechanisms have received considerable attention comparatively to mass and fluvial erosion. However, the linkage between hydraulically driven erosion and mass failure has not been examined fully. We hypothesize that fluvial and mass erosion affect the memory and response of the system by creating favorable hydrogeomorphic conditions for mass failure. This dissertation addresses three major shortcomings in the bank erosion literature, including the confusion surrounding critical erosional strength values for mass and fluvial erosion (τc,m and τc,f, respectively). The herein results clearly show that these two parameters are different, with τc,m being three to five times greater than τc,m. Therefore, excluding mass erosion estimates from sediment budgets or stability analyses can lead to significant errors in quantifying or predicting bank retreat and channel geometry. In addition, this study offered a methodological improvement for measuring the τc,m in-situ using Photo-Electric Erosion Pins, which semi-automatically measure mass erosion to generate erosional strength and erodibility values that are currently missing in the literature. This study also addressed the preconceived notion in morphodynamic modeling that bank soil profiles are homogeneous and universal strength/ cohesion parameters adequately represent the bank soil profile. This study shows that bank soil heterogeneity is present and significantly affects bank stability. Therefore, heterogeneity along a bank face must be assessed in at least three locations to provide adequate input data for bank erosion models. Finally, this study suggests that Factors of Safety for mass failure must be complemented with those for fluvial and mass erosion to avoid underestimating mass failure by as much as 30%. Hence, this study provides agencies like the U.S. Department of Agriculture key data regarding the total contributions from the different modes of bank erosion and channel, itself, to the stream sediment load for strategic targeting of Best Management Practices and in-streams stabilization structures.

No description available.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The lower San Francisco river had changed their hidrossedimentological behavior by changes in river channel through the impoundment of water reservoirs for the implementation of large hydropower projects. These direct impact on the stability of river banks, demands actions to mitigate the erosion resulting from soil mass movements. Soil bioengineering, which is a correct technique from the standpoint of ecological and aesthetic, makes use of biological knowledge for slope stabilization and banks of watercourses. The objective of this study was to evaluate the behavior of slope of São Francisco river throught physical parameters and development of vetiver grass composing the technique of soil bioengineering. Before the deployment of this biotechnique undisturbed samples of soil were collected and deformed to run the auger boreholes down to the water being removed layers representing the slope. Subsequent to sampling laboratory tests were performed allowing the characterization and identification of physical and mechanical properties of the soil. The experimental site studied was located on the Sergipe side of the lower course of the São Francisco river, has vertical slope, a decrease of margin collapse mass of soil and undermining the base with no riparian vegetation. For deployment of the biotechnique, at the experimental base of the slope technique was used to vegetated riprap with live cuttings of thrush (Mimosa caesalpiniaefolia Benth) and planting of vetiver grass (Chrysopogon zizanioides L (Roberty) with different levels of phosphorus and on top of slope sediment retainers were placed Bermalonga ®. The soil texture of the slope is closely related to susceptibility to erosion and the mechanical behavior of the same. The performance of the ongoing struggles of the water flow at its base promotes different values of moisture in the soil causing different levels of densities that change their mechanical properties by developing a dynamic behavior in the soil. The levels of phosphorus and developmental stages morphological parameters interact in shoot dry weight, root dry weight, fresh air, fresh root, root density, density of root length, root number, external surface, shoot length, root length. / O baixo curso do rio São Francisco teve seu comportamento hidrossedimentológico alterado pelas modificações no canal fluvial, através do represamento das águas para implantação de reservatórios de grandes projetos hidrelétricos. Estes impactaram diretamente na estabilidade das margens do rio, demandando ações de mitigação dos processos erosivos resultantes dos movimentos de massa de solo. A bioengenharia de solo, que é uma técnica correta do ponto de vista ecológico e estético, utiliza-se de conhecimentos biológicos para estabilização de encostas de terrenos e margens de cursos de água. O objetivo neste trabalho foi avaliar o comportamento de talude da margem do rio São Francisco por meio de atributos físicos e desenvolvimento do capim vetiver compondo à técnica de bioengenharia de solos. Antes da implantação da biotécnica foram realizadas coletas de amostras indeformadas e deformadas de solo com execução de furos de sondagem a trado até o nível d água sendo retiradas camadas representativas do talude. Posteriormente, a coleta de amostras foram realizados ensaios laboratoriais possibilitando a caracterização e identificação das propriedades físicas e mecânicas do solo. O sítio experimental estudado está localizado na margem sergipana do baixo curso do Rio São Francisco, apresenta talude verticalizado, recuo de margem, desmoronamento de massa de solo e solapamento da base com ausência de vegetação ripária. Para implantação da biotécnica, na área experimental base do talude foi utilizada a técnica do enrocamento vegetado, com estacas vivas de sabiá (Mimosa caesalpiniaefolia Benth) e plantio da gramínea vetiver (Chrysopogon zizanioides L (Roberty) com diferentes doses de fósforo e no topo do talude foram colocados retentores de sedimento Bermalonga®. A granulometria do material do talude se mostrou intimamente relacionada com a suscetibilidade ao processo erosivo e com o comportamento mecânico do mesmo. A atuação dos embates da corrente fluvial permanente em sua base promove diferentes valores de umidade no solo provocando níveis diferentes de densidades que modificam suas propriedades mecânicas desenvolvendo um comportamento dinâmico no solo. Doses de fósforo aplicadas ao capim vetiver e os períodos de desenvolvimento morfológico interagiram nos parâmetros massa seca parte aérea, massa seca raíz, massa fresca aérea, massa fresca raiz, densidade de raíz, densidade de comprimento da raiz, numero de raíz, superficie externa, comprimento parte aérea, comprimento raíz.

Sediment is a major source of water quality impairment in streams, rivers and lakes in the US. However, sediment fate and transport in small streams is poorly understood. Previous attempts to characterize sediment transport often insufficiently represented the physical and chemical sediment properties and lacked spatial and/or temporal resolution. Therefore, there is a need to develop better sediment tracers, for which rare earth element (REE)-labeled sediment is examined as an alternative. The objectives of this study were to: 1) assess the adsorption of REEs to natural soils and ensure their reliability as a tracer in a fluvial environment; and 2) evaluate the efficacy of utilizing REE-labeled sediment to quantify fate and transport in a second-order stream during a series of storm events. Two natural stream bank soils from Stroubles Creek in Virginia were labeled with the REEs lanthanum and ytterbium. The REEs adsorbed equally to both soils and had minimal desorption after several washes with stream water. This suggests that REEs form a dependable natural sediment tracer and sufficiently label natural soils for use in a sediment tracing study. During two storm events, two unique REE tracers were injected into Stroubles Creek. These tracers were detected at varying discharges and sediment loads in bed and suspended sediment samples up to 875 m downstream. REE tracers proved to be an ideal tracer for detecting sediment fate and transport in a small stream during a series of storm events and hold great potential for evaluating best management practices and sediment transport models. / Master of Science

L’érosion et la redistribution des particules détachées représentent un enjeu environnemental, sociétal et économique majeur. Afin de mettre en place des mesures de protection, il est nécessaire d’identifier et quantifier les sources et puits de sédiments ainsi que leur dynamique spatiale et temporelle. L’objectif de cette thèse est donc de dresser le bilan sédimentaire d’un large bassin versant (Loire Bretagne, 155 000 km2) aux paysages contrastés. Sur les versants, les particules détachées issues des différentes sources (érosion diffuse, concentrée, mouvements de masse) représentent un apport de 1.5 * 107 t.an−1 (contribution respective au stock : 82.4%, 12.9%, 4.7%). La prise en compte de la distribution spatiale des processus mis en jeu dans le transfert particulaire et des caractéristiques du site d’étude (ruissellement par saturation en zone de plaine et présence de haies) dans un indice qualitatif permet d’évaluer la connectivité des versants. L’érosion de berge contribue également au stock sédimentaire à hauteur de 6.9 * 105 t.an−1. Au final, seuls 5% des particules détachées, toutes sources confondues, sont transportées jusqu’à l’exutoire du bassin versant et témoignent du fort taux de dépôt au sein du bassin. En parallèle, une valorisation de la base de données des éléments dissous permet de montrer l’importance des flux sédimentaires exportés sous forme dissoute (~ 90% des exports totaux). La représentation de l’ensemble de ces résultats à différentes résolutions spatiales permet de développer une approche qualitative du transfert particulaire et d'identifier les zones à risque. / Erosion and particles redistribution represent major environmental, societal and economic issues. To adopt protection measures, it is essential to identify and quantify sources and sinks of sediment and their spatial and temporal dynamic. The aim of this work is thus to establish a sediment budget for a large river basin (Loire and Brittany river basin 155,000 km2) with contrasted landscapes. On hillslopes, detached particles from the miscellaneous form of erosion (sheet and rill erosion, gullies and mass movements) represent a supply of 1.5 * 107 t.yr−1 (contribution to the stock of 82.4%, 12.9%, and 4.7% respectively). The consideration of the spatial distribution of processes involved in sediment transport and the characteristics of the study site (soil saturation and presence of hedgerows) in a qualitative landscape-based index allows us to assess the hillslope connectivity. Bank erosion also participates in the sediment budget with 6.9 * 105 t.yr−1 of material provided to the river network. In the end, only 5% of detached particles, from all sources of sediment, reach the basin outlet indicating a substantial deposition on the way from source to outlet. In parallel, the use of the database of dissolved elements allows us to highlight the importance of the dissolved sediment fluxes ( 90% of the total exports of the Loire river). The presentation of all results at different spatial scales permits to provide a qualitative approach of sediment source-to-sink transfers and to identify hotspots of erosion and transfers.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-12-03T07:36:31Z No. of bitstreams: 2 Dissertação - Wallas de Souza Castro - 2015.pdf: 6091228 bytes, checksum: 3a8c31295dc00c579cd64b79adafcefb (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-12-03T07:39:02Z (GMT) No. of bitstreams: 2 Dissertação - Wallas de Souza Castro - 2015.pdf: 6091228 bytes, checksum: 3a8c31295dc00c579cd64b79adafcefb (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-12-03T07:39:02Z (GMT). No. of bitstreams: 2 Dissertação - Wallas de Souza Castro - 2015.pdf: 6091228 bytes, checksum: 3a8c31295dc00c579cd64b79adafcefb (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-06-24 / Meanders rivers have sinuous channel with singular dynamic of lateral migration by eroding its concave bank and depositing on its convex bank. This dynamic is able to expand and restore fluvial environments when creates a sedimentary environments complex linked to development of floodplain. The nature of preexistent deposits on floodplain, which are remobilized by lateral migration, is important to interpret deposicional dynamics, being central to the identification evolution of meanders. Heterogeneity of the facies is formed by several cycles of sedimentary evolution through channel migration, generating a succession of deposits with different degree cohesion. These depositional environments affect the continuity migration and the evolution of meanders. It was researched the current evolution of meander and riparian vegetation influence and theirs deposit about lateral migration process on downstream Claro river. It was used aerial photographs, satellite images, facies analysis and pin set on the banks to identify the influences of vegetation and material in the migration processes of meanders. The channel showed high mobility verified by the high amount of migration process in 47 years, due to the planforms diffusion and oxbow lakes and by deposits and paleochannel sedimentary facies. The vegetation has not shown attenuating effect against the bank erosion in the two curves analyzed meanders, erosion rates for the segments with vegetation cover were up to 1,3m ahead of the environments of floodplain. It was found that the intensity of channel migration differs between the curves. Migration advances with little resistance from unconsolidated deposits of the current floodplain, whereas in older deposits, pedogenesis and consistent terraces have hindered lateral advance, due to theirs material. / Rios meandrantes possuem canais fluviais sinuosos com dinâmica particular de migração lateral ao erodir suas margens côncavas e depositar nas margens convexas. Esta dinâmica é capaz de ampliar e renovar os ambientes fluviais ao criar um complexo ambiente sedimentar ligado ao desenvolvimento das planícies fluviais. A natureza dos depósitos preexistentes na planície, que são remobilizados pela migração lateral, é importante para a interpretação da dinâmica deposicional, sendo fundamental para identificação da evolução dos meandros. A heterogeneidade das fácies é formada por vários ciclos de evolução sedimentar pela migração do canal fluvial, gerando uma sucessão de depósitos com grau de coesão diferentes. Os próprios ambientes deposicionais afetam a continuidade da migração lateral e a evolução dos meandros. Investigou-se a evolução atual dos meandros e a influência da vegetação ripária ou ciliar e os seus antigos depósitos sobre os processos de migração lateral do baixo curso do rio Claro. Utilizou-se de fotografias aéreas, imagens orbitais, análise faciológica e pinos fixados nas margens para identificar as influências da vegetação e material nos processos de migração dos meandros. O canal fluvial apresentou alta mobilidade, verificada pela a elevada quantidade de processos de migração em 47 anos, em virtude da difusão de feições marginais e lagoas de meandros (oxbow lakes) e pelos depósitos e fácies sedimentares do paleocanal. A vegetação não apresentou efeito atenuador diante da erosão marginal nas duas curvas de meandros analisadas, as taxas de erosão para os segmentos com cobertura vegetal foram de até 1,3m de avanço sobre os ambientes da planície. Atestou que a intensidade da migração do canal apresenta diferenças entre as curvas. A migração avança com pouca resistência entre depósitos inconsolidados da planície fluvial atual, enquanto que nos depósitos mais antigos, pedogeneizados e consistentes dos terraços, tem avanço lateral dificultado, em função dos seus materiais.

Reservoir release patterns are determined by a number of purposes, the most fundamental of which is to manage water resources for human use. Managing our water resources means not only controlling the water in reservoirs but also determining the optimum release rate taking into account factors such as reservoir stability, power generation, water supply for domestic, industrial, and agricultural uses, and the river ecosystem. However, riverbank stability has generally not been considered as a factor, even though release rates may have a significant effect on downstream riverbank stability. Riverbank retreat not only impacts land properties but also damages structures along the river such as roads, bridges and even buildings. Thus, reservoir releases need to also take into account the downstream riverbank stability and erosion issues. The study presented here investigates the riverbank stability and erosion at five study sites representing straight as well as inside and outside channel meander bends located on the lower Roanoke River near Scotland Neck, North Carolina. Extensive laboratory and field experiments were performed to define the hydraulic and geotechnical properties of the riverbank soils at each site. Specifically, soil water characteristic curves were determined using six different techniques and the results compared to existing mathematical models. Hydraulic conductivity was estimated using both laboratory and in situ tests. Due to the wide range of experimentally obtained values, the values determined by each of the methods was used for transient seepage modeling and the modeling results compared to the actual ground water table measured in the field. The results indicate that although the hydraulic conductivities determined by in situ tests were much larger than those typically reported for the soils by lab tests, numerical predictions of the ground water table using the in situ values provided a good fit for the measured ground water table elevation. Shear strengths of unsaturated soils were determined using multistage suction controlled direct shear tests. The test method was validated, and saturated and unsaturated shear strength parameters determined. These parameters, which were determined on the basis of results from both laboratory and field measurements, and the associated boundary conditions, which took into account representative flow rates and patterns including peaking, drawdown and step-down scenarios, were then utilized for transient seepage analyses and slope stability analyses performed using SLIDE, a software package developed by Rocscience. The analyses confirmed that the riverbanks are stable for all flow conditions, although the presence of lower permeability soils in some areas may create excess pore water pressures, especially during drawdown and step-down events, that result in the slope becoming unstable in those locations. These findings indicate that overall, the current reservoir release patterns do not cause adverse impacts on the downstream riverbanks, although a gradual drawdown after a prolonged high flow event during the wet season would reduce unfavorable conditions that threaten riverbank stability. / Ph. D.