2 results
Now showing1 - 2 of 2
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Zur Beschreibung der vertikalen Bodenaustauschprozesse von kohäsiven Sedimenten am Beispiel des Weserästuars(2025); This thesis deals with the processes of erosion, deposition and consolidation that determine the accumulation of cohesive sediments in the navigational channel within the estuarine turbidity maximum in estuaries. The overall objective is to better understand the vertical sediment exchange processes and the properties of sediments based on experimental investigations in the field and in the laboratory using cohesive sediments from the turbidity zone of the Weser estuary as an example, and to describe them using mathematical formulations. In order to achieve the set objectives, the first step was to develop new methods and equipment that enable the transport properties of cohesive sediments to be recorded in both the field and the laboratory in a repeatable and systematic manner. This includes the development of a gravity core sampler for sediment sampling, the development of a methodology for recording density depth profiles, the development of a methodology for determining concentration-dependent effective settling velocities, and the development of the C-GEMS, a mobile erosion test rig based on the Gust microcosm. In a second step, the developed methods and equipment have been applied in systematic test series in the field and in the laboratory, using natural sediments from the turbidity zone of the Weser estuary as the object of investigation. Within the scope of the experimental investigations carried out, at least one adequate model approach could be identified, parameterised and developed for each of the processes erosion, deposition and consolidation. The present work thus enables a consistent description of the vertical soil exchange of cohesive Weser sediments based on measurements of the total density and water density.Publicationtype: Doctoral Thesis84 58 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A contribution to understanding the recently enhanced coastal siltation in the German Wadden SeaThe Wadden Sea on the Northwestern European Shelf is world's largest channel-shoal system that comprises broad coherent intertidal flats, islands, shoals, and several estuaries. Coastal management has shaped the Wadden Sea's coastline and its estuaries for centuries which is why navigational channel dredging and coastline maintenance have become routine coastal engineering tasks. Since the 2010s, German coastal stakeholders reported further enhanced coastal siltation. My research objectives were (1) to identify whether there was quantifiable evidence of enhanced coastal siltation and (2) to find the driving processes behind this development. An analysis of bathymetry data confirmed that intertidal flats accreted and that lateral expansion and subtidal deepening occurred. Balanced subtidal and intertidal sediment budgets suggested a redistribution of local subtidal sediments to intertidal flats. In addition, surface sediment data indicated a gradually increasing mudflat coverage over time. Based on this information, numerical modeling and observational data were used to quantify changes in tidal and non-tidal forcing: I found near-constant wind-wave and storm surge conditions which indicated that event-driven phenomena were an unlikely driver. Spatial tidal analysis and observational data revealed amplitude and phase shifts of principle and shallow water tidal constituents which reflected in increased tidal amplitude, and reduced flood dominance. Furthermore, diminishing flood flow velocity and increased slack duration were noted. These phenomena were related to increased relative intertidal storage and to subtidal deepening from bathymetry evolution. Hence, the reduction in channel volume and the intertidal accretion likely decreased tidal and wave energy on the tidal flats and enabled the deposition of more fines. Longer flood and ebb slack duration should add to this effect. The import of sand into the coastal zone was likely reduced as flood dominance diminished at the entire study site.Publicationtype: Doctoral Thesis435 182