Die Inhalte dieser Seite sind leider nicht auf Deutsch verfügbar.
Seitenpfad:
PhD projects
Cohesive sediment transport in complex coastal environments
The intermittent nature of suspended transport is commonly associated with the occurrence of coherent flow structures generated in the bottom boundary layer. Coherent Flow Structures are irregular, but repetitive turbulent events believed to be caused by the deformation and evolution of vortices in the seabed region. They are characterised by rapid in- and outrush of fluid from the near-bed region, interspersed with quiescent inter-event periods.
High frequency hydro-acoustic and optical sensors have been deployed to derive time series of velocity fluctuations and suspended sediment concentration throughout the water column over several tidal cycles. This will enable the determination of inter-event period of the flow structures and suspension events close to the seabed and possibly scaling to dune or flow variables. Furthermore, it is aimed at a better understanding of the processes causing the confined upward transport of material and sustainment of the clouds at the water surface.
High frequency hydro-acoustic and optical sensors have been deployed to derive time series of velocity fluctuations and suspended sediment concentration throughout the water column over several tidal cycles. This will enable the determination of inter-event period of the flow structures and suspension events close to the seabed and possibly scaling to dune or flow variables. Furthermore, it is aimed at a better understanding of the processes causing the confined upward transport of material and sustainment of the clouds at the water surface.
Sediment dynamics in tidal inlet systems
Christian Svenson
The main goal of this PhD project is to approach the spatial and temporal behaviour and interplay of the surface sediment composition, the hydrodynamics and bedform geometry in unsteady flow regimes. Therefore extensive bed sampling campaigns have been conducted during two cruises in 2008. They were supported by a multibeam echo sounder system (MBES) and an Acoustic Doppler current profiler (ADCP) for high resolution bathymetry measurements and current velocity profiling respectively.
The main investigation areas are the Jade tidal inlet at the German North Sea coast and the Knudedyb tidal inlet in the Esbjerg region in the Danish Wadden Sea. The Jade represents an extensively used and dredged tidal inlet whereas the Danish inlet stands for a completely natural system.
So far it was shown that the surficial sediment varies in grain size and sediment composition spatially in the dune-profiles and temporarily in the course of a tidal cycle. The bed sediment on the investigated dunes displays a clear coarsening up crest trend, triggered by the local hydrodynamics (cp. Svenson et al. 2009).
Recently the findings are substantiated and expanded to the third dimension. On the most recent cruise to the Knudedyb channel in 2009 box cores have been taken from the sampled dunes. The box cores were meant to recover small scale sedimentary structures such as second and third order discontinuities in the bedforms. Internal structures enable conclusions with regard to the sediment dynamics in the course of more than one tidal cycle. Further the question of which part of the grain size spectrum is really being conserved in the dunes can be approached.
One method to explore larger scale internal stuctures (first order discontinuities) within the sandy bedforms is a parametric echosounding system. In the Jade and the Knudedyb channel sweeping sediment echo sounder surveys (SES by INNOMAR Technologie GmbH) were conducted. It is anticipated that the geometry of those discontinuities shed light on the long term impact of dredging activities onto the bedform structure.
Literature:
Svenson C., Ernstsen V.B., Winter C., Bartholomä A., Hebbeln D. (2009): Tide-driven sediment variations on a large compound dune in the Jade tidal inlet channel, Southeastern North Sea. Journal of Coastal Research, SI 56: 361-365.
The main goal of this PhD project is to approach the spatial and temporal behaviour and interplay of the surface sediment composition, the hydrodynamics and bedform geometry in unsteady flow regimes. Therefore extensive bed sampling campaigns have been conducted during two cruises in 2008. They were supported by a multibeam echo sounder system (MBES) and an Acoustic Doppler current profiler (ADCP) for high resolution bathymetry measurements and current velocity profiling respectively.
The main investigation areas are the Jade tidal inlet at the German North Sea coast and the Knudedyb tidal inlet in the Esbjerg region in the Danish Wadden Sea. The Jade represents an extensively used and dredged tidal inlet whereas the Danish inlet stands for a completely natural system.
So far it was shown that the surficial sediment varies in grain size and sediment composition spatially in the dune-profiles and temporarily in the course of a tidal cycle. The bed sediment on the investigated dunes displays a clear coarsening up crest trend, triggered by the local hydrodynamics (cp. Svenson et al. 2009).
Recently the findings are substantiated and expanded to the third dimension. On the most recent cruise to the Knudedyb channel in 2009 box cores have been taken from the sampled dunes. The box cores were meant to recover small scale sedimentary structures such as second and third order discontinuities in the bedforms. Internal structures enable conclusions with regard to the sediment dynamics in the course of more than one tidal cycle. Further the question of which part of the grain size spectrum is really being conserved in the dunes can be approached.
One method to explore larger scale internal stuctures (first order discontinuities) within the sandy bedforms is a parametric echosounding system. In the Jade and the Knudedyb channel sweeping sediment echo sounder surveys (SES by INNOMAR Technologie GmbH) were conducted. It is anticipated that the geometry of those discontinuities shed light on the long term impact of dredging activities onto the bedform structure.
Literature:
Svenson C., Ernstsen V.B., Winter C., Bartholomä A., Hebbeln D. (2009): Tide-driven sediment variations on a large compound dune in the Jade tidal inlet channel, Southeastern North Sea. Journal of Coastal Research, SI 56: 361-365.
Fluid Mud dynamics
Li Wang
Fluid mud is a highly concentrated suspension of fine-grained cohesive sediment, which often occurs in tidal estuaries. The Weser estuary is a partially mixed mesotidal estuary located at the southern coast of the North Sea, where the occurrence of fluid mud is highly variable on time and spatial scales. Temporally and spatially highly resolved field measurements have revealed the built-up and and remobilisation of Fluid Mud bodies in the troughs of large subaquatic dunes. Here dedicated high resolution field data and hydrodynamic numerical models are used to measure and simulate the fluid mud dynamics in the turbidity maximum zone (TMZ).
Fluid mud is a highly concentrated suspension of fine-grained cohesive sediment, which often occurs in tidal estuaries. The Weser estuary is a partially mixed mesotidal estuary located at the southern coast of the North Sea, where the occurrence of fluid mud is highly variable on time and spatial scales. Temporally and spatially highly resolved field measurements have revealed the built-up and and remobilisation of Fluid Mud bodies in the troughs of large subaquatic dunes. Here dedicated high resolution field data and hydrodynamic numerical models are used to measure and simulate the fluid mud dynamics in the turbidity maximum zone (TMZ).
