Browsing by Subject "Sediment Transport"

Now showing 1 - 4 of 4
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    Investigating the Roles of Wind Speed and Sediment Supply on Continental Shelf Formation
    (2017-04) Harrington, Stephen; Paola, Chris
    Continental shelves represent an environment in which it is unclear whether the geometry has been affected by modern wave and wind interactions, or are the relict results of fluvial processes that have been drowned by rising sea levels since the Last Glacial Maximum. There are some modern examples of constructional shelves forming, but the sediment composition is primarily silty and muddy, not sandy. However, stratigraphic records show that sand is a major component of the continental shelf. This unique project investigated the use of silica sand to create a shelf with a steady-state transport system which is driven by waves and currents.
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    Local and Non-local Geomorphic Effects of Hydrokinetic Turbines: Bridging Renewable Energy and River Morphodynamics
    (2019-06) Musa, Mirko
    Marine and Hydrokinetic (MHK) energy is an emerging renewable and sustainable technology which harnesses kinetic energy of natural water flows such as tides, rivers and ocean currents. In particular, rivers are currently an overlooked source of local and continuous kinetic energy that can be exploited using the available in-stream converters technology. The uncertainties regarding the interaction between these devices and the surrounding environment complicate the regulatory permitting processes, slowing down the expansion of MHK industry. A crucial issue that needs further attention is the interaction between these devices and the physical fluvial environment such as the bathymetry, sediment transport, and the associated morphodynamic processes. Analytical and experimental research conducted at Saint Anthony Falls Laboratory (SAFL) addressed this topic, unveiling the local and non-local (far from the device location) effects of hydrokinetic turbines on channel bathymetry and morphology. A theoretical model framework based on the phenomenology of turbulence was derived to predict the scour at the base of MHK device. Asymmetric installations of turbine array models within multi-scale laboratory channels were observed to trigger river instabilities known as forced-bars. Results suggest that the amplitude of these instabilities might be reduced by limiting the power plant lateral obstruction within the channel cross-section. A 12-turbine staggered array also proved to be resilient to intense flooding conditions, encouraging the expansion of this technology to large sandy rivers. Current research is investigating how hydrokinetic technology can be synergistically integrated in rivers, not only minimizing the environmental costs but also providing a positive feedback on the channel. Experiments suggest that turbines strategically installed in the river (i.e. at the side bank in yawed condition or in a vane-shaped array) could be used as stream bank protection systems and, eventually, be integrated in stream restoration projects.
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    A Network-Based Framework for Hydro-Geomorphic Modeling and Decision Support with Application to Space-Time Sediment Dynamics, Identifying Vulnerabilities, and Hotspots of Change
    (2016-05) Czuba, Jonathan
    Increasing pressure to meet the food, water, and energy demands of our growing society in a changing climate has strained the physical, chemical, and biological functioning of watersheds to maintain ecosystem services, such as providing clean water, and to sustain a productive and diverse ecosystem. Confronted with multifaceted environmental issues, watershed managers could use a simple first-order approach for understanding how physical, chemical, and biological processes operate within a watershed to guide watershed-management decisions. This research advances a network-based modeling framework for guiding effective landscape management decisions towards sustainability focusing on understanding large-scale system functioning and predicting the emergence of vulnerabilities, “hotspots” of change, and unexpected system behavior. Based on a combination of mathematical theory, field-data analysis, and numerical simulations applied to the dynamics of bed-material sediment (i.e., the sediment composing the riverbed) on river networks, we (1) identify a resonant frequency of sediment supply from network topology and sediment-transport dynamics that could lead to an unexpected downstream amplification of sedimentological response in the Minnesota River Basin; (2) identify hotspots of likely sediment-driven fluvial geomorphic change where sediment has a tendency to persist and exacerbate channel migration on the Greater Blue Earth River Network; and (3) elucidate the hierarchical role of river-network structure on bed-material sediment dynamics in propagating, altering, and amalgamating the emergent large temporal fluctuations and periodicities of bed-sediment thickness. By embedding small-scale bed-material sediment dynamics on a river network, this research shows that it is possible to gain a better understanding of the large-scale system functioning whereby management actions that target the identified critical times, places, and processes in the landscape will be most effective at improving water quality and the health of the aquatic ecosystem.
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    Statistical mechanics of sediment transport.
    (2011-12) Singh, Arvind
    Accurate prediction of the evolution of rivers and landforms under varying climatic and human-induced conditions requires quantification of the total sediment transported by a river. Based on a series of controlled laboratory experiments conducted at the St. Anthony Falls laboratory, University of Minnesota, we demonstrated that (a) bedload sediment transport at very small time scales can be an order of magnitude larger or smaller than the long-time average; (b) bed morphodynamics can be inferred from the spectral properties of turbulent velocity fluctuations above the bed; and (c) the nature of scaling and the degree of complexity and non-linearity in bed elevation fluctuations and sediment transport rates depend on the bed shear stress. These results are discussed in the context of understanding and exploring the dependence of sediment transport scaling on near-bed turbulence, bed topography, and particle-size distribution, and deriving stochastic transport models which give rise to the observed scaling. They also form the foundation of relating microscale dynamics of particle movement to the macroscale statistics of sediment transport via minimum complexity stochastic models.