Bryan, Karin
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Bryan, Karin
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Bryan, Karin
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Item-typ:Veröffentlichung, Morphodynamics of single-barred embayed beaches : Shoreline and barline morphodynamics at the scale of the embayment(2016-06-01); ; ; Seven years of shore and sandbar positions extracted from hourly time-averaged images collected at Tairua Beach (New Zealand) are used to study the morphodynamics of the shoreline and the nearshore parallel sandbar of single-barred embayed beaches. First, a semi-empirical model is proposed, that validates the concept of sandbar rotation and relates it to the wave energy gradient along the embayment. Then, a statistical study confirms the role of the alongshore wave energy flux in the rotation of embayed beach shorelines. Finally, principal component analyses and semi-empirical models are used together to characterize the dominant dynamic patterns of the shoreline and sandbar at the scale of the embayment. Dominant, simultaneous cross-shore migrations relate to beach state transitions and to variations in beach planform curvature (breathing). Rotations are largely asynchronous, confirming that different drivers are likely to be involved in shoreline and sandbar rotations.Dissertation276 138 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Micro Scale Sediment - Fluid Interactions(2013-07-23); ; ; This thesis was inspired by the inherent limitations in the quantification of the physical parameters (e.g. flow speed, grain size and density) controlling sediment-fluid interactions in the direct vicinity of the sediment water interface of a seabed. For this, the transport behaviour of layered - and mixed sediment beds consisting of a simplified two-grain fraction distribution (silt and sand) was tested in an analogue laboratory-based annular flume. The results showed that the sediment bed stabilized with increasing silt composition. To investigate this effect in more detail, a high resolution 3D numerical model was designed for the simulation of sediment transport by a fluid by coupling two numerical techniques i.e., Finite Difference Method (FDM) and the Distinct Element Method (DEM). It verified that in the case of the deposition of fine particles on top of, or mixed into, a coarse matrix, the bed stability increased significantly. The model was also used to examine the role of grain density variations on the threshold conditions and erosion behavior of sediment beds. The experiments showed that bed stability increased when the heavy mineral concentrations were increased, which validated the process of heavy mineral enrichment.Dissertation276 271 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, On the Enrichment of Magnetic Heavy Minerals in a Coastal Environment : Exploration, Examination, Explanation(2016-11-10); ; ; In this thesis, an approach for the detailed assessment of magnetic heavy mineral enrichments in a coastal environment using integrated geophysical and sedimentological data is developed, the observed enrichment patterns are interpreted, and their formation mechanisms discussed. Used methods are electromagnetic profiling of the subsurface, close-up seafloor photography, various laboratory techniques to analyze bulk and magnetic grain sizes and mineralogy, and numerical modelling of bi-fractional sediment transport. The studies take place in an exemplary study area in the western Bay of Plenty (New Zealand) with dimensions of 60 km x 7 km in water depths from 2-35 m. Primary instrument is the benthic profiler MARUM NERIDIS III. Overall, the findings of this thesis demonstrate an innovative, effective way to approach an unmapped area and reach detailed results with conclusive interpretations in a relatively short time. It shows the conditions under which natural sorting patterns due to size and density develop along the coast. The basic formation mechanisms are applicable to other areas in similar coastal settings and for a diverse range of heavy minerals.Dissertation351 163 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Morphodynamic Equilibria of Embayed Beach Systems(2013-11-15); ; ; Embayed beaches are well-known for the prominent curvature of their shorelines and are often observed in states of dynamic or static equilibrium. These equilibrium states are typically assumed to be influenced by headland geometry, cellular circulation patterns, wave obliquity at the shoreline and diffraction in and around the shadow zone. One of the main aims of this study is to gain a comprehensive understanding of the role of (i) wave forcing, (ii) environmental conditions and (iii) the geological setting in long-term embayed beach evolution. In doing so, a state-of-the-art morphodynamic model was used to simulate the evolution of a schematic embayment under idealized wave forcing conditions. Wave forcing is varied between a mixture of time-invariant and time-varying cases. Environmental conditions are varied by changing sediment size, tidal amplitude and mean wave height. The geological setting is varied by changing the angle of obliquity of the waves and the bay width. Several wave climate variables influence the distribution of wave energy throughout the bay and in the shadow zone: wave direction, directional spreading and wave height. Diffraction is shown to be dominant only when the incoming wave conditions are both directionally narrow-banded and highly oblique. Nevertheless, time varying wave directions (as little as 6%) can account for shoreline curvature in the shadow zone. Changes in environmental conditions and geological setting generally affect the rate of development of the bay as well as the equilibrium size of the bay. For example: increased tidal amplitude enhances the size of the shadow zone due to modulation of the wave energy in this area, and wider bays require an exponentially larger period of time to attain equilibrium. Progressive weakening of the residual long-shore current and sediment transport as the bay develops is shown to be consistently related to long-term, non-uniform shoreline cutback (beach rotation). Hence, the curvature of the shoreline planform is primarily due to weakened shoreline erosion processes resulting from beach rotation. The research aims are extended to investigate seasonal and event-driven changes based on real-world cases. In doing so, the model has been used to reconstruct the medium-term, quasi-equilibrium morphology of a bay by discretising the measured wave climate variability in terms of wave heights and directions into several representative wave conditions. The effect of extreme events appeared to be balanced by average forcing conditions occurring over a longer period of time. Additionally, the equilibrium bathymetry is largely determined by wave direction variability; therefore it is necessary to have a high level of directional resolution in order to obtain accurate results. A nine-month field campaign was conducted at embayed beaches of Tairua and Pauanui, Coromandel Peninsula, New Zealand. During this period the beaches exhibited highly dynamic behaviour in response to storm events characterised by non-uniform cross-shore sediment movement within the bay. The residual sediment transport pathways between the surf zone and the adjacent beach and shoaling zones will be determined in future.Dissertation274 123 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Magnetic mineral enrichment and transport in coastal environments: Tauranga Harbour, Northeastern, New Zealand(2012-12-13); ; ; The present PhD thesis was written at the Faculty of Geosciences, Universität Bremen, and Department of Earth and Ocean Sciences, University of Waikato, New Zealand. The major aim of this thesis is to develop the potential of environmental magnetic methods, i.e. the application of rock magnetic measurements in a sedimentological context, for coastal zone research. We combined a range of laboratory based magnetic and non-magnetic methods with hydrodynamic modelling in the aim to identify and explain heavy mineral rich zones in and around a meso-tidal estuarine lagoon of Tauranga Harbour and in the nearshore Bay of Plenty located on the northeast coast of New Zealand. This thesis presents a comprehensive study on the distribution pattern and formation mechanisms of magnetite rich zones in estuary and near-shore environments and explores the responsible hydrodynamic conditions.Dissertation476 131