Turbulent structures are known to be important physical processes in gravel-bed rivers. A number of limitations exist that prohibit the advancement and prediction of turbulence structures for optimization of civil infrastructure, biological habitats and sediment transport in gravel-bed rivers. This includes measurement limitations that prohibit characterization of size and strength of turbulent structures in the riverine environment for different case studies as well as traditional numerical modeling limitations that prohibit modeling and prediction of turbulent structure for heterogeneous beds under high Reynolds number flows using the Navier-Stokes equations. While these limitations exist, researchers have developed various theories for the structure of turbulence in boundary layer flows including large eddies in gravel-bed rivers. While these theories have varied in details and applicable conditions, a common hypothesis has been a structural organization in the fluid which links eddies formed at the wall to coherent turbulent structures such as large eddies which may be observed vertically across the entire flow depth in an open channel. Recently physics has also seen the advancement of topological fluid mechanical ideas concerned with the study of vortex structures, braids, links and knots in velocity vector fields. In the present study the structural organization hypothesis is investigated with topological fluid mechanics and experimental results which are used to derive a vortex model for gravel-bed flows. Velocity field measurements in gravel-bed flow conditions in the laboratory were used to characterize temporal and spatial structures which may be attributed to vortex motions and reconnection phenomena. Turbulent velocity time series data were measured with ADV and decomposed using statistical decompositions to measure turbulent length scales. PIV was used to measure spatial velocity vector fields which were decomposed with filtering techniques for flow visualization. Under the specific conditions of a turbulent burst the fluid domain is organized as a braided flow of vortices connected by prime knot patterns of thin-cored flux tubes embedded on an abstract vortex surface itself having topology of a Klein bottle. This model explains observed streamline patterns in the vicinity of a strong turbulent burst in a gravel-bed river as a coherent structure in the turbulent velocity field.

Dans cette étude, nous examinons la trajectoire d’un migrant canadien-français au XIXe siècle, Sam Gravel, ainsi que les changements identitaires qu’il subit en fonction des lieux de migration qu’il atteint. Sam se rend en Nouvelle-Angleterre en 1882 pendant quelques mois. Il revient brièvement au Québec puis immigre dans l’Ouest canadien en 1883 et y demeurera jusqu’en 1891. Il s’établira ensuite dans le Midwest américain jusqu’en 1897. Il rentrera finalement au Québec et s’installera dans le village de Somerset en 1897. Il décède en 1899 d’une noyade à Québec. C’est en analysant son parcours migratoire, son mode d’établissement et son discours que nous pouvons déterminer comment s’insère sa migration dans les courants de migration du XIXe siècle. Est-ce que ses choix sont représentatifs de la majorité des migrants de l’époque ? Comment ces choix influencent-ils sa perception des autres groupes ethniques ainsi que ses valeurs religieuses et familiales? Sam tient un discours qui se rapproche beaucoup de celui des Canadiens français de l’époque alors qu’il se trouve dans l’Ouest canadien et tend à s’en dégager alors qu’il atteint le Midwest américain.

Signal crayfish are an internationally widespread invasive species that can have important detrimental ecological impacts. This thesis aims to determine whether signal crayfish have the potential to also impact the physical environment in rivers. A series of experiments were undertaken in purpose-built still-water aquaria using a laser scanner to obtain Digital Elevation Models (DEMs) of narrowly-graded gravel surfaces before and after exposure to crayfish. The difference between DEMs was used to quantify volumetric changes in surface topography due to crayfish activity. Two distinct types of topographic change were identified. The first was the construction of pits and mounds which resulted in an increase in surface roughness and grain exposure. The second was the rearrangement of surface material caused by crayfish brushing past grains when walking and foraging, reorientating grains and altering friction angles. A series of 80 flume runs were undertaken to quantify alterations made by crayfish to water-worked, as well as loose, gravel substrates at low velocity flows. Crayfish significantly altered the structure of water-worked substrates, reversing the imbrication of surface grains to a more random arrangement. Surfaces were entrained at a relatively high velocity flow subsequent to crayfish activity in order to directly link topographic and structural alterations to substrate stability. Nearly twice as many grains were mobilised from surfaces which had been disturbed by crayfish in comparison to control surfaces that were not exposed to crayfish. A field investigation aimed to determine the potential significance of the geomorphic impact of crayfish in rivers. Signal crayfish were tracked through a 20 m reach of a small, lowland alluvial river for 150 days using a Passive Integrated Transponder (PIT) system. Crayfish were active throughout the channel, although their activity became limited as water temperature dropped and flow stage increased. Substrate was not an important determinant of crayfish activity at this scale. Instead, crayfish tended to be found along the inner bank of a meander bend where there was a substantial cover of macrophytes. Consequently, signal crayfish were active for extended periods on substrates of a similar size to those that they could disturb in flume experiments. These results suggest that signal crayfish could have important geomorphic effects in rivers, disturbing bed structures and increasing the mobility of coarse material. This may have important implications for both the management of some rivers and benthic organisms that reside on the river bed.

Numerical modelling currently cannot accurately reproduce the onshore-offshore transport asymmetry observed on gravel beaches. The role of the impulsive pressure response generated by plunging waves has been hypothesised to aid mobilisation of sediment, and thus may contribute to transport asymmetry. This process is not currently included in models. Laboratory tests were conducted across a range of wave conditions to investigate the role of plunging wave-breaker impacts on the mobilisation of sediment of gravel beaches. Pressure records were obtained at positions close to the plunging impact locations, to monitor the localised pressures that lead to sediment mobilisation. The correction of the recorded pressure to the bed surface, for further analysis, was achieved through a two stage approach. Adoption of a new technique for separating the pressure records into two components, each determined by different processes is presented. Each component is then corrected to the bed surface with the application of a pragmatic prediction of the experienced attenuation. Data covering a wide range of Iribarren values was assessed, and the impact pressure was parameterised against the wave-breaker type. This procedure identified a potential peak in the impact pressure-Iribarren space in the plunging breaker region, consistent with the previous hypothesis. Comparison of cross-shore profile records provides further limited evidence that morphological prediction fails to reproduce specific characteristics associated with profiles generated under plunging breaker action. Finally, a brief discussion is provided on how the role of the additional pressure generated under plunging impacts can be incorporated into future numerical models.

Roads alter the ecological landscape and affect the function and composition of nearby soil chemistry and plant communities in an area of impact termed the “edge-effect zone”. While the 6.3 million kilometers of roads in the US cover only about 1% of the land, the edge effect zone around these roads has been estimated to occupy nearly 20% of the total land area in the US (Forman 2000). The objective of this study was to examine the spatial extent of transported materials and impacts on forest soil and vegetative communities immediately surrounding roadways based on road types classified as “Highway,” “Two-Lane Paved,” and “Gravel.” This research was located within two watersheds in the state of Vermont, in areas where a substantial area of forest existed adjacent the roadway. Using GIS mapping, transects were constructed at right angles to the road, and samples were gathered at the Shoulder, Ditch, Backslope, 10m from the edge of the forest, and 50m from road center during the summer of May 2009 to August 2009. Soil samples were analyzed for a suite of nutrients and physical characteristics, as well as heavy metals. The forest composition and percent area coverage by species of herbaceous flora and woody shrubs were also recorded. The main effects from roads were dependent on the extent of clearing and topography modification required for a roadway. The spatial extent of these modifications was correlated positively with road use intensity. Highways have the greatest ecological impact and gravel roads the least impact. The cleared area defines how much sunlight is available to plant communities and the distance that road pollutants will travel. Some heavy metals (such as Pb, Cd, Ni and Zn) were correlated positively with road use intensity. Gravel roads have higher calcium content in nearby soil when compared to other road types. This is most likely due to mobilized dust from the road base. Proximity to all road types had neutralizing effects on the soil pH relative to the acidic native forest soil. Changes in microtopography next to the road have marked effects on the composition of plant communities through maintenance and direction of water flow. Ditch areas support wetland plants, and have greater soil moisture and sulfur content, while plant communities closer to the road are characteristic of drier upland zones. The area past the edge of the forest does not appear to be affected chemically or physically by any of the road types, possibly due to the dense vegetation that develops outside of the right-of-way. To reduce the ecological footprint of future road development, road corridors should be narrowed, traffic consolidated to mass transit systems such as busses or railroad, and buffer zones of vegetation next to the right-ofway should be encouraged to contain the spread of pollutants.

Gravel bed braided rivers are distinctive natural environments that provide a wide range of key environmental, economic and recreational services. There is, however, a growing concern that over the twentieth century, an increasing number of braided rivers have metamorphosed into wandering or single thread channels, representing a loss of key habitats, geodiversity and amenity. While in some situations, shifts in channel pattern may be unambiguously linked to abrupt changes in flow or sediment supply, the lack of a theoretical basis underpinning the development and maintenance of braiding makes identification of the cause and effect of channel metamorphosis hazardous. A growing body of research has suggested that the transition between channel patterns may depend on the poorly understood interaction between the flow regime, sediment supply and vegetation colonisation. Such interactions are governed by critical thresholds, due to changes in flow resistance and bank strength associated with the distribution, form and intensity of vegetation colonisation. Subtle changes in flow or sediment supply that promote vegetation growth or indeed remove it through inundation or attrition. This can lead to complex non-linear shifts in the balance of forces that govern sediment transport and bedform morphodynamics, ultimately resulting in one-way changes in channel morphology. There is, therefore, a critical need to develop a quantitative understanding of these feedbacks in order to design sustainable river management programmes that seek to optimize the ecological and socio-economic benefits these rivers offer. During the last three decades, significant advances in the understanding of the morphodynamics of braided rivers have been made through a combination of field and physical experimentation. More recently, the emerging field of numerical modelling has created a new avenue to investigate the processes that govern channel dynamics. While this methodology offers significant promise through the construction of virtual experiments that examine the spectrum of drivers and responses of river systems, such models require careful and critical evaluation before they can be used to guide management practice. The wider goal of this research is to explore the application of a numerical modelling to investigate the feedbacks associated with the development and maintenance of braiding. Specifically, the state-of-the-art numerical model, BASEMENT, was used to examine channel responses to steady, and unsteady flow regimes, with and without the representation of vegetation. The research focuses on four main contributions: 1. The development of a systematic framework to quantify the evolving form and processes of braided rivers that can be used as part of a comprehensive approach to model validation. 2. Simulation of braiding development and maintenance using BASEMENT under steady flow conditions. Model simulations based on the natural prototype of the braided River Feshie were used to examine the sensitivity of emergent channel morphologies to the model parameterisation, focusing in particular on the representation of bank erosion and gravity-driven sediment transport. A novel multi6metric framework for model validation is presented and the results demonstrate the critical importance of lateral bank migration processes in order to maintain braided morphologies under steady flow. 3. A critical evaluation of the simulation of braiding under different form of steady and unsteady flow regimes is presented. These experiments investigate how the morphodynamics of braiding vary under energetically-normalised flow regimes characterized by differences in hydrograph form (peak discharge and duration). This experiment provides a novel insight into the role of flow variation in the maintenance of braiding. 4. Finally, the feedback between flow regimes, sediment transport and vegetation growth are examined using a novel model of vegetation colonisation and die- back. Four scenarios are presented, a no-vegetation model, one based on low growth rate, one based on an intermediate growth rate, and finally a high growth rate parameterisation. These simulations provide a clear insight into the non-linear processes driving channel evolution and demonstrate how subtle changes in the balance between flow frequency and vegetation growth can lead to divergent channel patterns. In summary, this thesis aims to advance our understanding of the morphodynamics of braided rivers and the role numerical models may have in helping to interrogate their behaviour and governing controls. It is hoped that this work may contribute, albeit in a small way, to advancing the science that promotes the sustainability of these fascinating and valuable environments.

As rodovias com revestimento primário constituem a imensa maioria da extensão da malha viária do Brasil e de muitos países. Sua manutenção em um nível mínimo aceitável de serventia consome parcelas importantes de orçamentos governamentais. Contudo, na maioria das vezes, as atividades de implantação e manutenção têm escasso sucesso, porque os agentes encarregados desconhecem a tecnologia específica. Visando contribuir para práticas mais efetivas, esta tese analisa os resultados de uma pesquisa realizada com o objetivo de identificar e discutir os mecanismos de degradação de rodovias com revestimento primário, à luz das Mecânicas dos Solos e dos Pavimentos. O projeto experimental incluiu ensaios laboratoriais, bem como a construção e monitoramento de desempenho, ao longo de 30 meses, de um pavimento experimental, em projeto de assentamento da Reforma Agrária, no Rio Grande do Sul. O revestimento primário foi construído em duas camadas (a superior constituída por 7 cm de saibro e a inferior por 17 cm de argila laterítica) assentes sobre um subleito estratificado, com camada superior arenosa. As formações geológicas são constituídas por depósitos aluvionares (subleito) e por siltito (jazida de argila) e gnaisse (jazida do saibro). A compactação das camadas foi verificada por meio de ensaios clássicos e com emprego do cone de penetração dinâmica (DCP). As deflexões foram medidas no topo do subleito e sobre cada camada de revestimento, com utilização de viga Benkelman. Amostras deformadas dos materiais do revestimento primário e da camada superior do subleito foram coletadas. Em laboratório realizaram-se ensaios de caracterização, bem como da classificação MCT; foram avaliadas a resistência ao desgaste e a durabilidade da fração graúda do saibro (abrasão Los Angeles e alteração de rochas água-estufa). Realizaram-se ensaios de compactação, Índice de Suporte Califórnia, Inderbitzen (erodibilidade), cisalhamento direto e triaxiais de carga repetida, para obtenção de módulos de resiliência e avaliação do comportamento quanto à deformação permanente. Complementarmente, foram obtidas curvas de retenção de água. Com base nos resultados laboratoriais foram realizadas previsões de desempenho do pavimento experimental, fundamentadas em conceitos, prescrições e em modelos matemáticos e estatísticos encontrados na literatura e no emprego do programa HDM 4. Durante o período de monitoramento do pavimento experimental foram realizados 3 levantamentos para a obtenção da Irregularidade Longitudinal (IRI), com o emprego de um perfilômetro inercial e 4 inspeções para a avaliação da evolução dos principais defeitos típicos de pavimento com revestimento primário. Os defeitos observados foram: afundamento de trilha de roda, buracos, perda de abaulamento, perda de espessura de revestimento e sulcos de erosão; identificando-se e discutindo-se os mecanismos de degradação a eles associados. Também foram comparadas as previsões de desempenho com a evolução da serventia do pavimento experimental, constatando-se que os modelos apresentados na literatura internacional nem sempre apresentam acurácia satisfatória. Isto mostra a necessidade de se desenvolverem novos modelos e calibrar os existentes, como condição indispensável para otimizar as atividades de manutenção das rodovias com revestimento primário. / Most of Brazilian and other countries’ roads networks mainly comprise unsurfaced gravel roads. The maintenance of such roads at a minimum acceptable level of serviceability consumes large percentages of governs budgets. In spite of that, the construction and maintenance activities are scarcely well-succeeded, since the personnel involved do not know the specific technology. Aiming at contributing for more effective practices, this thesis analyses the results of a research carried out with the objective of identifying and discussing distress mechanisms of unsurfaced gravel roads, based on Soil and Pavement Mechanics. Experimental procedures included laboratory tests, as well as the construction and performance monitoring, along 30 months, of a test section, in an agrarian reform settlement, in Rio Grande do Sul state, southern Brazil. The wearing course of the unsurfaced pavement consisted of two different layers (a 7-cm-thick upper layer, made of genuine residual soil and a lower one with 17 cm of lateritic clay), built over a stratified subgrade, with a sandy upper layer. Geological formations consisted of alluvial fans (the subgrade), siltstone (the clay site) and gneiss (genuine residual soil site). Layers compaction was quantified by means of classic tests and also using the dynamic cone penetrometer (DCP). Using a Benkelman beam, surface deflections were measured on the top of the subgrade and every layer. Samples were taken from the subgrade and from both materials that constitute the wearing course, in order to perform laboratory tests of characterization and those of a Brazilian soils classification system, known as MCT (miniature, compacted, tropical). Los Angeles abrasion and rock alteration by wetting and drying tests were done on samples of the genuine residual soil coarse fraction. Every material was subjected to compaction, CBR, Inderbitzen (erodibility), direct shear and repeated loading triaxial tests (these latter to compute resilient moduli and to evaluate the permanent deformation behaviour). Besides, water-retention curves were obtained. Based on laboratory results, the performance of the experimental pavement was predicted, founded on concepts, materials prescriptions and mathematical and statistical models and using HDM 4 program. During the monitoring period three roughness (IRI) surveys were carried out, using an inertial profilometer. Four distresses surveys were carried out to evaluate the evolution of the most important distresses typical of unsurfaced gravel roads. Distresses as rutting, potholes, cross-section deformation and thickness reduction and erosion channels were observed and the associated distress mechanisms were discussed. Pavement performance predictions were compared to the measured serviceability evolution. It was found out that the models available in the literature not always yield accurate results. Because of that, developing new models and calibrating the existing ones is mandatory to optimize maintenance activities in unsurfaced gravel roads.

This study is aimed at understanding the physical and chemical effects that changes in water content have on uranium leaching in sediment containing gravel. It was hypothesized that leaching will be more efficient under unsaturated conditions because flow will be restricted to the smallest pores and will have the most contact with the uranium contaminated sediment. Under saturated conditions, a large portion of the flow will bypass the < 2 mm material, and in turn not come into contact with uranium contaminated material. Batch adsorption and desorption experiments were performed on < 2 mm ERDF sediment to determine the linearity and reversibility of sorption processes and to aid in the interpretation of the leaching experiments. Results of the desorption experiments on aged, contaminated sediments show that the mass percent of sorbed U(VI) released to solution decreased as the sorbed concentration of U(VI) decreased. The opposite trend was observed on freshly contaminated sediments. This indicated that aging increased U(VI) affinity for the solid phase and was attributed to either the crystallization of calcite, which incorporated a portion of the sorbed U(VI) as it crystallized, or the presence of voids in basaltic lithic fragments accessed by diffusion. Column leaching experiments were performed at two water contents on artificially contaminated sediment collected from the Department of Energy’s (DOE) Hanford Site, Washington state. The sediment contained 81.3% gravel (> 2 mm) by mass. Non-reactive tracers were well fit with the convection-dispersion equation (CDE) at both high and low water contents indicating physical equilibrium. The column experimental data were fitted to an analytical solution to the CDE; the results of the modeling show an increase in the distribution coefficient (Kdeffective) with decreasing water content. Several potential explanations for this trend were proposed; one is based on a physical effect in which solute exposure to reactive surfaces changes as a function of water content and the others are based on results of the batch desorption experiments. This work has important implications for the Hanford Site where there is ongoing research regarding the persistence of U(VI) in the vadose zone and underlying aquifer.

This thesis presents a novel three dimensional (3D) image-analysis method for characterizing the physical characteristics of coarse particles in the field, and introduces new methodology for the total analysis of glacial till samples. The novel image analysis method, called the GID method, is capable of determining the size, shape and surface texture of each individual clast analysed. Images of particles are taken in the field and analysis is done in the laboratory. Therefore the GID method makes it feasible to analyse statistically representative large sample in short period; for poorly sorted sediments, such as till, one-tonne is required if the analysis includes cobble size. The capability of the GID method was demonstrated by studying coarse clasts (20-200 mm) from till. There is excellent agreement in the results of the size distribution obtained from the GID method and sieve analysis. The GID method results for size and shape parameters show high and very high repeatability. The particle angularity in the GID method has not been measured to acceptable level; the repeatability test shows some variability. The new methodology for total analysis of till applied the GID method at four different locations in Sweden. The total analysis included 3D size and shape distribution of coarse particles coupled to electrical resistivity, lithological distribution and magnetic susceptibility of the clasts. The results show clear difference in the till samples from the different sites. / <p>QC 20120828</p>

Dans cette étude, nous examinons la trajectoire d’un migrant canadien-français au XIXe siècle, Sam Gravel, ainsi que les changements identitaires qu’il subit en fonction des lieux de migration qu’il atteint. Sam se rend en Nouvelle-Angleterre en 1882 pendant quelques mois. Il revient brièvement au Québec puis immigre dans l’Ouest canadien en 1883 et y demeurera jusqu’en 1891. Il s’établira ensuite dans le Midwest américain jusqu’en 1897. Il rentrera finalement au Québec et s’installera dans le village de Somerset en 1897. Il décède en 1899 d’une noyade à Québec. C’est en analysant son parcours migratoire, son mode d’établissement et son discours que nous pouvons déterminer comment s’insère sa migration dans les courants de migration du XIXe siècle. Est-ce que ses choix sont représentatifs de la majorité des migrants de l’époque ? Comment ces choix influencent-ils sa perception des autres groupes ethniques ainsi que ses valeurs religieuses et familiales? Sam tient un discours qui se rapproche beaucoup de celui des Canadiens français de l’époque alors qu’il se trouve dans l’Ouest canadien et tend à s’en dégager alors qu’il atteint le Midwest américain.