The delivery of suspended sediment from drainage basins has frequently been quantified in mass terms by use of the suspended sediment budget approach, which identifies sources, storage and output of mobilised sediment. This thesis investigates the particle size characteristics of the sediment associated with the key components of the suspended sediment budgets of four drainage basins in Devon, U. K. to determine whether particle size selectivity occurs in the delivery of suspended sediment from the hillslopes to the basin outlet. Attention focused on pasture land because previous studies had indicated that this was the dominant source of suspended sediment and that arable fields and channel banks were relatively insignificant in these catchments. Samples of sediment were mobilised from pasture hillslopes using a field-portable rainfall simulator; samples of suspended sediment were collected from the river channel during storm events either manually, by automatic pump samplers or by using rising limb siphon samplers; suspended sediment deposited on the channel bed was sampled using bed traps and by resuspending sediment deposited on the river bed during low flows; and sediment deposited on the floodplain during overbank flooding was collected using Astroturf mat traps or by sampling surface material. Samples were collected to investigate both temporal and spatial variability in grain size behaviour. All sediment samples were pretreated to remove organic matter and their chemically dispersed (absolute) particle size composition was measured using a Coulter LS 130 laser granulometer. The particle size composition of transported/deposited sediment was compared with that of the samples from potential sources to determine whether particle size selectivity had occurred. Where possible, measurements of the natural in situ particle size distribution (effective particle size) were also undertaken by quick return of samples to the laboratory for immediate measurement without pre-treatment using the laser granulometer. Particle size selectivity was found to have occurred in the mobilisation of sediment from the hillslope pasture land sources. Seasonal variations were identified in the particle size characteristics of both sediment mobilised from the hillslopes and suspended sediment samples. Spatial variations were identified in the particle size composition of sediment deposited on the floodplain. These seasonal and spatial variations reflect the particle size selectivity of detachment, transport and deposition processes which is in turn influenced by the aggregation or flocculation (effective particle size) of the sediment.

Thesis advisor: Noah P. Snyder / Thesis advisor: Gabrielle C. David / The Reservoir Sedimentation Database (ResSed), a catalogue of reservoirs and depositional data that has recently become publicly available, allows for rapid calculation of sedimentation and capacity-loss rates over short (annual to decadal) timescales. This study is a statistical investigation of factors controlling average sediment yield (Y) in eastern United States watersheds. I develop an ArcGIS-based model that delineates watersheds upstream of ResSed dams and calculate drainage areas to determine Y for 191 eastern US watersheds. Geomorphic, geologic, regional, climatic, and land use variables are quantified within study watersheds using GIS. Sediment yield exhibits a large amount of scatter, ranging from 4.7 to 3336 tonnes1km 2year-1. A weak inverse power law relationship between drainage area (A) and Y (R2 = 0.09) is evident, similar to other studies (e.g., Koppes and Montgomery, 2009). Linear regressions reveal no relationship between mean watershed slope (S) and Y, possibly due to the relatively low relief of the region (mean S for all watersheds is 6°). Analysis of variance shows that watersheds in formerly glaciated regions exhibit a statistically significant lower mean Y (159 tonnes1km-2year-1) than watersheds in unglaciated regions (318 tonnes1km-2year-1), while watersheds with different dam purposes show no significant differences in mean Y. Linear regressions reveal no relationships between land use parameters like percent agricultural, and percent impervious surfaces (I) and Y, but classification and regression trees indicate a threshold in highly developed regions (I > 34%) above which the mean Y (965 tonnes1km-2year-1) is four times higher than watersheds in less developed (I < 34%) regions (237 tonnes1km 2year-1). Further, interactions between land use variables emerge in formerly glaciated regions, where increased agricultural land results in higher rates of annual capacity loss in reservoirs (R2 = 0.56). Plots of Y versus timescale of measurement (e.g., Sadler and Jerolmack, 2014) show that nearly the full range of observed Y, including the highest values, are seen over short survey intervals (< 20 years), suggesting that whether or not large sedimentation events (such as floods) occur between two surveys may explain the high degree of variability in measured rates. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Fuel inventory and generation of carbon and metal dust in a tokamak are perceived to be serious safety and economy issues for the steady-state operation of a fusion reactor, e.g. ITER. These topics have been explored in this thesis in order to contribute to a better understanding and the development of methods for controlling and curtailing fuel accumulation and dust formation in controlled fusion devices. The work was carried out with material facing fusion plasmas in three tokamaks: TEXTOR in Forschungszentrum Jülich (Germany), Tore Supra in the Nuclear Research Center Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom). Following issues were addressed: (a) properties of material migration products, i.e. co-deposited layers and dust particles; (b) impact of fuel removal methods on dust generation and on modification of plasma-facing components; (c) efficiency of fuel and deposit removal techniques; (d) degradation mechanism of diagnostic components - mirrors - and methods of their regeneration. / <p>QC 20121116</p>

Bien que répandus dans l'environnement et dans l'industrie, les écoulements granulaires possèdent des caractéristiques particulières qui sont différentes de celles des écoulements de liquides ordinaires comme l'eau (fluides newtoniens). L'une de ces caractéristiques est de présenter un seuil d'écoulement, il est donc fréquent qu'une des frontières de l'écoulement soit constituée de grains au repos (frontière érodable). L'échange entre les deux états solide et liquide d'un écoulement granulaire est à l'origine du phénomène d'érosion et de déposition et constitue le cœur de cette thèse. Nous y effectuons à la fois des études expérimentales et des études théoriques en nous basant sur les modèles phénoménologiques concernant le taux d'échange proposés par Bouchaud, Cates, Ravi Prakash et Edwards et modifiés par Boutreux et de Gennes. A l'aide d'un dispositif expérimental permettant de lâcher sans vitesse initiale une colonne de grains sur une pente granulaire, nous avons quantifié l'importance relative des phénomènes d'érosion et de déposition notamment en déterminant l'angle neutre qui définit la pente critique pour laquelle ces deux processus s'équilibrent. Dans un deuxième temps nous avons appliqué le modèle proposé par Boutreux et de Gennes au cas de l'étalement d'une « marche » granulaire (marche du Sinaï). / Granular flows, which are common in nature and industry, have particular characteristics that are different from the ordinary flow of liquid (eg. water, oil, etc.) and are not yet well understood in the literature. This case underlines the lack of knowledge on the exchange rate between solid and liquid states of granular flows which is the origin of the erosion - deposition phenomenon and constitutes the core of this thesis. To address the issue of the exchange rate solid - liquid, this work is based mainly in two subjects. The first subject is to study the processes of erosion and deposition of a flow generated by the grains stocked in a reservoir. By releasing naturally with zero-velocity the grains to generate the granular flow, we quantified the relation between the erosion and deposition for determining the neutral angle which defines the slope where these two processes balance. The second subject is to analyze the fall of grains in Sinai step problem by studying the spread of the march. For both works, we conduct not only the experimental but also theoretical studies based on the phenomenological models of the exchange rate proposed by BCRE (Bouchaud, Cates, Ravi Prakash and Edwards) and BDG (Boutreux and de Gennes) with some modifications.

This dissertation focused on developing a numerical model of spatial and temporal changes in bed morphology of ridge and slough features in wetlands with respect to hydrology and sediment transport when a sudden change in hydrologic condition occurs. The specific objectives of this research were: (1) developing a two-dimensional hydrology model to simulate the spatial distribution of flow depth and velocity over time when a pulsed flow condition is applied, (2) developing a process-based numerical model of sediment transport coupled with flow depth and velocity in wetland ecosystems, and (3) use the developed model to explore how sediment transport may affect the changes in bed elevation of ridge and slough landscape patterns observed in wetlands when a conditional pulsed flow was applied. The results revealed the areas within deep sloughs where flow velocities and directions change continuously. This caused enhanced mixing areas within the deep slough. These mixing areas may have had the potential to affect processes such as sediment redistribution and nutrient transport. The simulation results of solute/sediment transport model also supported the existence of areas within the domain where the mixing processes happened. These areas may have caused that nutrients and suspended particles stay longer time rather than entraining toward downstream and exiting the system. The results of bed simulation have shown very small magnitude of change in bed elevation inside deep slough and no changes on the ridge portion of the study area, when a conditional pulsed flow is applied. These findings may suggest that implementing pulsed flow condition did not increase suspended sediment concentration, which results in insignificant changes in bed morphology of a ridge and slough landscape. Therefore sediment transport may not play an important role in wetland bed morphology and ridge and slough stability. Results from the model development and numerical simulations from this research will provide an improved understanding of how wetland features such as ridge may have formed and degraded by changes in water management that resulted from increasing human activity in wetlands such as The Florida Everglades, over the past decades.