Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1985. / "June 1985." Bibliography p. 262-272.

Parks Canada focuses its tourism and conservation efforts in Kouchibouguac National Park along the park's diverse coastline made up of a variety of sensitive ecosystems including salt marshes, stream estuaries and a shifting barrier island lagoon system. The dynamic sediment processes in the park are not fully understood, making it difficult for Parks Canada to make informed decisions as sea-level rise in the region accelerates. In this study, extensive field data were collected in two sediment zones bordering the Kouchibouguac Lagoon. Stream data were collected and used to estimate the monthly average sediment load entering the lagoon. The maximum and minimum monthly average sediment loads were 130 g/s and 11 g/s in April and September, respectively. These freshwater sediments pass through estuaries to deposit at the coastline of the park. Changes in the barrier system surrounding the tidal inlet Little Gully were also monitored over 15 months using modern surveying techniques. The surveys showed a general southward shift in the study area and a landward migration of sediments within the flood tidal delta of the inlet. Dune surface area, volume, and vegetation cover were also examined, and the critical shear stress and velocity of the sediments were calculated. The field investigations revealed that the Kouchibouguac Lagoon was gradually filling in with sediments during the study. It is recommended that a permanent hydrometric station be installed in one of the major streams in the park and that future research along the coastline of the park complement Parks Canada's current monitoring program for the barrier island system.

Understanding of the processes of sediment transfer within, and from, glaciated catchments is of fundamental importance in order to establish rates of sediment transfer and resultant landscape evolution. Rates of glacio-fluvial sediment transfer are strongly controlled by glacier meltwater runoff and the availability of sediments for entrainment. However, it is becoming apparent that recently deglaciated forefields can modify the patterns of suspended sediment transfer. Glacier shrinkage exposes areas of unstable glacigenic sediments that can be subject to reworking and redistribution, and, as these environments become ice-free, heightened levels of geomorphological activity (so-called 'paraglacial' activity) are also likely to have a significant impact on both sediment and water yields from deglaciating catchments. Consequently, questions are raised as to the impacts of deglaciation upon contemporary and future rates of suspended sediment transfer, and the resultant fluvial sediments loads and rates of landscape adjustment. Therefore, the aim of this research was to present an integrated study of how sediment transfer in a glaciated catchment functions during, and is responding to, deglaciation. A variety of techniques were employed to examine the hydrological functioning of an Alpine glacier, the Feegletscher Nord, Switzerland, and the resultant temporal and spatial patterns of sediment transfer in light of catchment hydrology, ablation processes and forefield geomorphology. Data was collected over two field campaigns in 2010 and 2012 to capture the inputs, throughputs and outputs of meltwater and sediment. This research found that patterns of sediment transfer were modified within the proglacial zone, reinforcing previous findings that the location of proglacial monitoring is important in determining the observed patterns of sediment transfer. These patterns of sediment transfer were attributed to variations in forefield sediment availability, which appeared to demonstrate marked spatial variability. This variability was hypothesised to be influenced by the geomorphological characteristics of the forefield, including rock fall debris that appeared to limit sediment availability, and glacigenic sediment deposits that enhanced the availability of in-channel and channel-marginal sediments. These findings suggest that the investigation of rates of sediment transfer and paraglacial sedimentation may be complicated in catchments that have experienced complex geomorphological responses to deglaciation. In addition, the investigation of sediment transfer processes and the development of a glacier runoff model enabled the exploration of future suspended sediment loads with progressive deglaciation and a changing climate. Suspended sediment loads were predicted to experience rapid declines until the end of the 21st Century due to reductions in meltwater runoff as glacier extent is reduced. However, it is suggested that uncertainties in future sediment availability limit the usefulness of such forecasts. Consequently, this research highlights how the understanding of both sedimentary and hydrological processes in glaciated catchments may be enhanced by consideration of the changes that can occur in these environments associated with glacier shrinkage and a changing climate.

Dans certains petits bassins versants de montagne, des évènements de pluie extrême peuvent engendrer de forts exports sédimentaires. Ce volume important de sédiment peut avoir un impact sur la gestion des ouvrages hydrauliques à l’aval de ces bassins. Aujourd’hui, pour représenter les processus d’érosion à l’échelle du bassin versant, des modèles conceptuels distribués sont majoritairement utilisés (CASC2D, SHETRAN, DWSM). Ces modèles sont basés sur des formules d’érosion globales et sont validés pour des maillages grossiers (> 30 m). D’un autre côté, il existe des modèles capables de représenter finement des processus d’érosion gravitaire, par des écoulements multiphasiques, principalement utilisés sur des cas à petite échelle. Ce travail de thèse propose le développement d’un modèle à base physique capable de représenter à la fois les transferts hydrauliques et l’hydrologie des bassins versants, les processus d’érosion gravitaire et de reprise/dépôt des sédiments dans le réseau hydraulique. Cela permettra de quantifier l’export sédimentaire à l’exutoire d’un bassin pour des tempêtes extrêmes, d’identifier des zones de fortes productions sédimentaires et des dynamiques de stockage des sédiments dans le réseau hydraulique afin d’aider à la gestion des bassins versants. Il s’agit dans un premier temps d’évaluer la résolution des équations de Saint-Venant pour du ruissellement avec des faibles hauteurs d’eau sur des fortes pentes. Pour diagnostiquer les différents schémas numériques que l’on peut trouver dans la littérature, un cas test, disposant d’une solution analytique des équations de Saint-Venant, représentant, un canal rectiligne sur lequel tombe une pluie constante est utilisé. Ce cas test comporte une zone sèche à l’amont et permet d’évaluer les propriétés clés qu’un schéma doit comporter pour représenter le ruissellement sur un bassin versant, à savoir la positivité des hauteurs d’eau, la transition entre zones sèches et mouillées, l’équilibre du lac au repos et la non limitation de la pente. Le schéma de Chen et Noelle (2017) est finalement choisi. Ensuite, avec l’ajout d’une loi d’infiltration de type Green-Ampt (1911), le modèle sera évalué dans sa capacité à représenter les hydrogrammes en sortie, mais surtout les vitesses locales d’écoulement sur des bassins versants réels. Pour cela, on évalue la part d’erreur provenant de la résolution numérique et de la modélisation physique du frottement de l’eau sur le fond au travers de quatre cas expérimentaux de l’échelle du laboratoire à un bassin de 1 km².Un modèle d’érosion gravitaire, basé sur les critères de détachement et de dépôt de Takahashi (2009), est couplé au modèle d’hydraulique global par une équation d’évolution du fond. L’évolution du stock de sédiment dans le réseau hydraulique est modélisée à l’aide d’une équation d’advection représentant les sédiments en suspension dans l’écoulement. Les lois classiques de dépôts de d’érosion de Krone et Parthéniades sont utilisées pour la reprise dépôt des sédiments dans le réseau.Le modèle d’érosion est ensuite validé sur le bassin versant du Laval (86 ha), instrumenté et surveillé par l’ORE Draix-Bléone, sur plusieurs évènements très érosifs. Le modèle est enfin appliqué à deux bassins non instrumentés mais à enjeu pour EDF, pour une étude de dimensionnement d’ovoïdes dans la vallée de la Durance / In some small mountain catchments, extreme rainfall events can lead to strong sediment exports. This large volume of sediment can have an impact on the management of hydraulic structures downstream these basins. Today, to represent erosion processes on a watershed scale, distributed conceptual models are mainly used (CASC2D, SHETRAN, DWSM). These models are based on global erosion formulas and are validated for coarse mesh sizes (> 30 m). On the other hand, there are models capable of finely representing gravity erosion processes, by multiphase flows, mainly used on small-scale cases. This thesis work proposes the development of a physics-based model capable of representing both hydraulic transfers and watershed hydrology, gravity-driven erosion processes and sediment erosion/deposition in the hydraulic network. This will quantify sediment export at the outlet of a basin for extreme events, identify areas of high sediment production and sediment storage dynamics in the hydraulic network to facilitate watershed management. The first step is to evaluate the resolution of the Saint-Venant equations for run off with low water depths on steep slopes. To diagnose the different numerical schemes that can be found in the literature, a test case, with an analytical solution of the Saint-Venant equations, representing a straight channel on which a constant rain falls is used. This test case includes a dry zone upstream and allows the evaluation of the key properties that a scheme must include to represent runoff over a watershed, such as positive water depths, the transition between dry and wet zones, the balance of the lake at rest and the non-limitation of the slope. The Chen and Noelle (2017) scheme is finally chosen.Then, with the addition of a Green-Ampt infiltration law (1911), the model will be evaluated in its ability to represent output hydrographs, but especially local flow velocities over real watersheds. For this, we evaluate the part of error coming from the numerical resolution and the physical modeling of the friction of the water on the bottom through four experimental cases from the laboratory scale to a basin of 1 km².A gravity erosion model, based on Takahashi's (2009) detachment and deposition criteria, is coupled to the global hydraulic model by a bottom evolution equation. The evolution of the sediment stock in the hydraulic network is modeled using an advection equation representing suspended sediments in the flow. The classic laws of Krone and Parthenades erosion and deposition are used for the recovery sediment deposition in the network.The erosion model is then validated on the Laval watershed (86 ha), instrumented and monitored by the ORE Draix-Bléone, on several very erosive events. Finally, the model is applied to two basins that are not instrumented but are of interest to EDF, for an ovoid dimensioning study in the Durance valley. Translated with www.DeepL.com/Translator

No description available.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The growing demand for modeling tools able represent erosive processes in catchments, and their connections, requires that mathematical modelling be associated with monitoring. This doctoral thesis sought to contribute to a description of the erosive processes at catchment scale, by combining monitoring and modeling techniques to reduce the impacts of agricultural activities in a large agricultural catchment through scenarios that simulate the impact of different conservation measures. Two studies were carried out in the Conceição River Catchment (800km2), a region characterized by the grain production system in the northwest of Rio Grande do Sul - Brazil. The first study sought to quantify the impact of different conservation measures on erosion and hydrosedimentological dynamics in a no-till agricultural catchment to simulate scenarios using the WATEM SEDEM model. Conservation measures reduced erosion and sediment yield in all scenarios. Crop leveling and terracing were the measures with greater impact in the reduction of the erosive process. The results demonstrate that soil losses due to erosion processes are significant and unsustainable in agricultural catchments in southern Brazil, and that soil erosion is exacerbated by the lack of information provided to the farmers and the use of isolated conservation measures without coordination at the catchment scale. The second study aimed to propose an efficient way to determine the current P factor through modeling, besides proposing conservation measures to better meet current practices. Four areas totaling 25 km2 were selected, representing the various properties present in the site. The efficiency of the current farming was determined by relating the angle between the sowing lines and the terrain level curves. In this study, values of P above 0.8 were obtained in over 60% of the area. This technique proved to be an important tool for determining factor P in a fast and spatialized way with potential for use in large areas, since an efficient determination of the P factor can result in a reduction of the erosion potential. In view of these results it is possible to affirm that conservation measures should not be isolated actions, but rather associated with other practices suitable for each type of land use. The use of mathematical models of erosion can be an important support tool in environmental management decision making and the methodology developed to determine the factor P in GIS can aid mathematical models to better simulate the impacts of conservation practices on erosive processes. Catchment scale modeling should be more widespread in Brazil in order to promote sustainable agricultural practices, reducing the anthropic impact on soil and water degradation. Farmers’ and local communities’ awareness should be raised to reduce soil degradation and sediment transfer to river systems. / A demanda por ferramentas de modelagem, com capacidade de representar os processos erosivos em bacias hidrográficas e suas conexões com os corpos hídricos, exige que o monitoramento esteja associado à modelagem. Este trabalho buscou contribuir para descrição dos processos erosivos em escala de grandes bacias agrícolas, a partir da combinação de técnicas de monitoramento e modelagem para reduzir os impactos das atividades agrícolas de uma grande bacia agrícola por meio de cenários que simulam o impacto de diferentes medidas conservacionistas. Para tanto, dois estudos foram conduzidos na bacia hidrográfica do Rio Conceição (800km2), região característica pelo sistema de produção de grãos no noroeste do Rio Grande do Sul. O primeiro estudo buscou quantificar o impacto de diferentes medidas conservacionistas na erosão e dinâmica hidrosedimentologica em uma bacia agrícola sob plantio direto para simular cenários utilizando o modelo WATEM SEDEM. Todos os cenários com medidas de conservação reduziram erosão e produção de sedimento. A implementação de plantio em nível e terraceamento foram as medidas com maior impacto na redução do processo erosivo. Os resultados demonstram que perdas de solo devido a processos erosivos são significantes e insustentáveis em bacias agrícolas no sul do Brasil e que a erosão é exacerbada pela falta de informação dos produtores e uso isolado de medidas conservacionistas sem que haja um esforço coordenado em escala de bacia. O segundo estudo teve como objetivo propor uma forma eficiente de determinar o atual fator P por meio da modelagem, além de alvitrar medidas conservacionistas para melhor atender as práticas atuais. Dessa maneira, cumpre expor que foram selecionadas quatro áreas totalizando 25 km2, representativa das diversas propriedades presentes no local. A eficiência da semeadura atual foi determinada relacionando o ângulo entre as linhas de semeadura e as curvas de nível do terreno. No segundo estudo, foram obtidos valores de P acima de 0,8 em 60% da área, indicando semeadura em desnível em grande parte das lavouras. Essa técnica mostrou ser uma ferramenta importante para a determinação do fator P de forma rápida e espacializada, com potencial de uso em grandes áreas, pois uma determinação eficaz do fator P pode resultar em redução do potencial de erosão. Diante desses resultados, é possível afirmar que medidas de conservação não devem ser tomadas como ações isoladas, mas sim associadas a outras práticas adequadas para cada tipo de uso do solo. A utilização de modelos matemáticos de erosão pode ser uma importante ferramenta de suporte na tomada de decisões de gestão ambiental e a metodologia desenvolvida para a determinação do fator P em SIG pode auxiliar modelos matemáticos a simular os impactos das práticas conservacionistas sobre os processos erosivos de maneira mais representativa. Sendo assim, a modelagem em escala de bacia deve ser mais difundida no Brasil a fim de promover práticas agrícolas sustentáveis, reduzindo o impacto antrópico na degradação do solo e da água.

Cette thèse se propose de définir les temps caractéristiques des processus d’altération à l'échelle de profil d'altération (bassin versant de Rio Icacos à Porto Rico) et de transfert sédimentaire subséquent dans les plaines alluviales (bassins du Gange et du Brahmapoutre). Cette problématique est abordée par l’analyse des nucléides des séries de désintégration radioactives de l’uranium-238. L’étude du système d’altération sphéroïdale développée sur le site de Porto Rico a permis de développer une méthode numérique de type quasi-Newton afin de résoudre le système d'équations qui rend compte du comportement des nucléides et du taux de formation de la saprolite et des couronnes d’altération.Pour les bassins du Gange et du Brahmapoutre, les sédiments ont été collectés sur différents affluents et à son exutoire. La variation des déséquilibres 238U-234U-230Th dans les sédiments, différente pour les sédiments en suspension et les sédiments à grains grossiers d’amont en aval, semble être une caractéristique générale des rivières himalayennes coulant dans la plaine Indo-gangétique. Par ce travail de thèse, nous avons montré l’utilité d’inclure l’analyse du 226Ra à l’analyse des autres nucléides de la chaîne de décroissance radioactive de l’238U (l’238U -234U-230Th 230Th) pour déterminer un taux d’altération dans un système bien défini. Néanmoins, l’étude du système du Brahmapoutre montre que la méthode proposée demande à être affinée car le transfert sédimentaire est un processus plus complexe dû à la variabilité minéralogique, granulométrique et à la dynamique sédimentaire (locale) des échantillons récoltés. / This thesis proposes to define the time-scales of weathering processes on a spheroidal weathering profile, (Rio Icacos watershed, Puerto Rico ) and the transfer time of sediments within alluvial plains (Ganges and Brahmaputra basins). This issue is addressed through the analysis of the nuclides of the 238U decay chain. The study of a spheroidal weathering system developed on the site of Puerto Rico permit to develop a limited memory quasi-Newton algorithm in order to solve the system of equations that reflects the behavior of nuclides and the rate of formation of the saprolite and the rindlet zone. For the Ganges and Brahmaputra basins, sediments were collected from different tributaries and their outlets. The variation of 238U - 234U - 230Th disequilibria in the sediments, with different variation trends for suspended and coarse-grained sediments, is probably a general feature of all Himalayan rivers flowing across the Indo-Gangetic plain. For this work, we have shown the usefulness of including the analysis of 226Ra analysis of other nuclides in the chain of radioactive decay of 238U (238U - 234U - 230Th) to determine the weathering rate in a well-defined system. Nevertheless, the study of the Brahmaputra system shows that proposed method needs to be refined as the sediment transfer is a complex process due to the mineralogical variability, size and (local) dynamics of sediments samples collected.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The impact of agriculture on water resources has been a focus for problems associated with reservoir siltation, depletion of water quality, reduced infiltration and soil water storage, formation of floods and low water availability during drought periods. In this sense the estimation of gross erosion and sediment yield monitoring reflect the dynamic that occurs in catchments and the processes observed in the rivers. Studies of erosion in grain crop agricultural areas using no-tillage systems are scarce at catchment scale. Thus, this study estimated gross erosion and sediment yield in a large catchment representative of grain crop cultivation and its potential impacts on land degradation and consequent impacts on water resources. The catchment is located on the Riograndense plateau characterized by deep and weathered soils and landscape is gently sloping. Gross erosion estimation was performed with the RUSLE model along with a Geographic Information System where the attributes of soil, climate, landscape, and land use and management were spatialized for the entire drainage area of the catchment (800 km2). The catchment is drained by the Conceição River, which includes towns such as Cruz Alta and Ijuí, among others. The hydrossedimentometric monitoring was carried out for twenty months with automatic instruments, daily sample collection and sampling during rainfall-runoff events. The variables monitored were rainfall, flow, turbidity and suspended sediment concentration. From this data set sediment yield was estimated for the period and a sediment discharge rating curve was established to extrapolate sediment yield for the last decade. The average results of gross erosion for the catchment are in the order of 8 t ha-1 year-1 and average sediment yield was 140 mg km-2 year-1, generating sediment delivery ratio values of 17.5 %. From the temporal and spatial variability of the results, this study seeks to highlight the erosion processes operating at this scale and the implications for management and water and soil conservation programs for similar regions. / O impacto da agricultura nos recursos hídricos tem sido enfoque para problemas associados ao assoreamento de reservatórios, depauperamento da qualidade da água, reduzida infiltração e armazenamento de água no solo, formação de enxurradas e baixa disponibilidade hídrica em períodos de estiagem. Neste sentido a estimativa da erosão bruta e o monitoramento da produção de sedimentos refletem a dinâmica que ocorre nas bacias vertentes e os processos observados nos rios. Estudos de processos erosivos em áreas agrícolas sob produção de grãos em sistema plantio direto são incipientes na escala de bacia hidrográfica. Este estudo estimou a erosão bruta e a produção de sedimentos em uma grande bacia agrícola que representa o processo de produção de grãos e o seu potencial reflexo sobre a degradação dos solos e o impacto nos recursos hídricos. A bacia se localiza no planalto Riograndense caracterizada por solos profundos e intemperizados e relevo suave ondulado. A estimativa da erosão bruta foi realizada com o modelo RUSLE acoplado a um Sistema de Informação Geográfica, onde os atributos de solo, clima, relevo, uso e manejo foram espacializados para toda a área de drenagem da bacia (800 km2). A bacia em questão é drenada pelo rio Conceição que engloba os municípios de Cruz Alta e Boa Vista do Cadeado, dentre outros. O monitoramento hidrossedimentométrico foi realizado durante vinte meses com instrumentos automáticos, coletas de amostras diárias e amostras durante eventos de chuva-vazão. As variáveis monitoradas foram precipitação, vazão, turbidez e concentração de sedimentos em suspensão. A partir desse conjunto de dados foi estimada a produção de sedimentos no período, bem como estabelecida uma curva-chave de sedimentos utilizada para a extrapolação da PS para a última década. Os resultados médios da erosão bruta da bacia estão na ordem de 8 t ha-1 ano-1 e a produção de sedimentos média foi de 140 t km-2 ano-1, gerando valores de razão de entrega de sedimentos de 17,5%. A partir da variabilidade temporal e espacial dos resultados, o trabalho procura salientar os processos erosivos operantes nessa escala e as implicações para os programas de manejo e conservação de água e solo para regiões semelhantes.