Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 37 for “"bedform"”.
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Hydrodynamic variability and bedform dynamics at an inner shelf artificial reef
… stressors (e.g. Trembanis et al., 2004), sorted bedforms (e.g. Green et al., 2004) and object scour (e.g. Quinn, 2006), but our understanding of bedform morphodynamics is still incomplete. Consequently, this study examines the specific hydrodynamic and bedform morphodynamics occurring over an …
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Bedform and Flow Relationships, Little Missouri River Near Medora, North Dakota
<p>Data concerning flow conditions over known bedforms in the Little Missouri River were used to seek relationships between the two. The flow parameters that were measured included: current velocity, depth, water temperature, and suspended-load concentration. A bedload sample was also taken at each …
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Burial of Short Cylinders Induced by Local Scour and Bedform Migration Under Waves Plus Currents
… presence of ripples and sandwaves. The role of bedform evolution on the burial of short cylinders was studied. For this purpose, a series of detailed measurements of geometric and migrating characteristics of bedforms under combined flows was conducted. Under certain hydraulic conditions, …
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Flow, sediment transport and bedforms under combined flows
… in natural environments and generates a range of bedforms on sandy beds. Combined-flow bedforms are abundant in coastal and lacustrine environments, as well as in their ancient counterparts in the rock record. However, few experimental studies have focused on the relationship between the …
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Modeling the dynamics and depositional patterns of sandy rivers
… Mars. At the smallest scale, ripples and dunes (bedforms) arise spontaneously under most natural flow conditions, acting as the primary agents of sediment transport and flow resistance in sandy rivers. I use physical modeling in a laboratory flume to explore the feedbacks among bedform geometry, …
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Measurements and dynamics of multiple scale bedforms in tidally energetic environments
The presence of superimposed bedforms, where smaller bedforms exist on larger bedforms, is ubiquitous to energetic tidal environments. Due to their wide range in scale, it is difficult to simultaneously observe these features over tidal timescales. This thesis examines the morphological response of …
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Measurements and dynamics of multiple scale bedforms in tidally energetic environments
The presence of superimposed bedforms, where smaller bedforms exist on larger bedforms, is ubiquitous to energetic tidal environments. Due to their wide range in scale, it is difficult to simultaneously observe these features over tidal timescales. This thesis examines the morphological response of …
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Architecture and origin of fluvial cross-bedding based on flume experiments and geological examples field case studies: Rillo de Gallo, Spain and Northumberland, UK
… of, and processes on, the original formative bedforms, and processes that truncate, deform or bury the cross-strata. This thesis reports an investigation of cross-bedded sandstones and their internal sedimentary structures formed in fluvial environments within different depositional settings …
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A Generalized Log-Law Formulation For a Wide Range of Boundary Roughness Conditions Encountered in Streams
… roughness elements comprised of mobile bedforms. The method resulted in similar values of normalized zero-plane displacement for all roughness types considered. The ratios of zero-plane displacement, dh, to roughness height, ks, were 0.20 and 0.26 for the sediment- and vegetation-scale …
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Developing GPS river flow tracers (GRiFTers) to investigate large scale river flow phenomena
… understanding of these fundamentally important bedform structures. Within the study of riffle-pool sequences the most prominent debates concern the precise means of sequence development and maintenance, the existence / operation of the velocity reversal hypothesis and the spatial compositions …
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Bedforms and Gravity Underflows in Marine Environments
… can develop long-wavelength, upstream-migrating bedforms is presented for the first time. Additional experimental evidence of the coexistence of upstream-migrating antidunes and small-scale downstream-migrating ripples created by both supercritical saline density currents and turbidity currents …
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Bed Morphology and Sediment Transport Under Oscillatory Flow
… restrict the three-dimensional development of bedforms. For the case of the long water excursion experiments, the ripple size was found to initially decrease as the maximum orbital velocity was increased, as it has been reported by other authors. However, as the maximum orbital velocity was …
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Modelling fine sediment transport over an immobile gravel bed
… that, in its turns, controls the sand bedform development. A limited volume of bedload sediment leads either to smaller dimensions, the sediment starved bedform or fewer isolated bedforms. Bedform types that are typically associated with partial mobility condition are: sand ribbons, …
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The marine geology of Walker Bay, off Hermanus, SW Cape, South Africa
… to sediment-covered areas displaying different bedform types. Facies 3 is dominated by well-defined patches of megarippled gravelly sand, whereas Facies 4 consists of small-scale rippled sand. The characteristics of the Facies 3 megarippled patches are discussed in detail and their relationships …
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Assessing Dynamic Seabed Change on the Scottish Continental Shelf
The dynamics of sediment bedforms mobilised by modern day coastal fluid mechanics can reduce the lifespan of offshore construction by modifying the foundational stability for offshore projects such as wind turbines and subsea cables. Dunes represent wave-like bedforms that range in size and …
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A 2-D Time-Dependent Ripple Prediction Model for Wave Dominated Flows
… spectral width provide an indication of the bedform irregularity.</p>
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Sedimentology and Regional Implications of Fluvial Quartzose Sandstones of the Lee Formation, Central Appalachian Basin
… 20 meters thick, contain a complex hierarchy of bedform deposits. The principal internal component of channels were downstream-accreting (mid-channel?) macroforms; channel elements frequently contain deposits of more than one macroform. Reconstruction of the macroforms reveals accretion primarily …
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Distinguishing flood frequency and magnitude in the morphodynamics and sedimentology of rivers: insights from the South Saskatchewan River, Canada
… and further research on the relationship between bedform geometry and flow depth in natural rivers. The results have wider applications to other sand bed braided rivers and may aid interpretation and modelling of such deposits on a wider scale.
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Experimental Evaluation of Three Backward Transit Time Distributions (bTTD) for Solute Storage and Release During Hyporheic Exchange
… of flow conditions, sediment grain sizes, and bedform sizes and types. Based on measures of model fit and parsimony (AICc), in all 47 experiments hyporheic exchange was best represented by either the Gamma or exponential distributions. Further, values for key process variables, including …
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The effects of groundwater seepage on stream regimen : a laboratory study
… and monitored. </p><p> In the absence of bedforms, upward (positive) seepage has little effect on stream competence or transport rate, even when quicksand conditions are reached. The decrease in effective grain density brought about by uptward seepage might possibly be compensated entirely …
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