Bedforms, macroturbulence, and sediment transport at the fluid-bed interface

Small scale morphodynamic processes at the fluid-bed interface in coastal environments are still not fully understood. Deformation of the seabed by hydrodynamic forces results in the occurrence of complex bedforms on a variety of scales. Owing to their interaction with the water column and turbulence production, large bedforms, such as dunes, significantly influence sediment transport and hydraulic roughness. Turbulence production above bedforms is predominately associated with large-scale coherent flow structures (macroturbulence). It has been suggested that macroturbulence is the principle mechanism behind the entrainment and transport of sediment in suspension. The objective of this thesis was to investigate the formation and occurrence of macroturbulent structures and their coupling to suspended sediment transport forming downstream of natural bedforms. Specifically, the effect of flow unsteadiness and bedform geometry was examined. The research is based on multiple research approaches including two field campaigns into the German Elbe Estuary and Danish tidal inlet Knudedyb. Ship-based observations and lander-based moorings deploying acoustic Doppler current profilers and optical measurement probes were conducted. The field research was complemented by laboratory experiments and a 2DV numerical model study. Results show that flow unsteadiness has significant implications on the production of macroturbulence. In both, the Elbe Estuary and the tidal inlet Knudedyb, very large compound bedforms occur in water depths of < 20 m. The primary bedforms remain ebb-oriented during a tidal cycle while smaller superimposed bedforms reverse direction with each tidal phase. Water-depth scale macroturbulence develops when flow direction and primary bedform orientation are aligned (ebb phase), once the accelerating ebb flow overcomes a velocity threshold. The frequency of macroturbulent structures falls into the Strouhal range of macroturbulence associated with flow separation zones downstream of bedforms. The flow structures originate in the region of high velocity gradients in the bedform lee and are traceable over the downstream bedform stoss-side. The magnitude of turbulence production decreases with the slope of the bedform lee-side. Our laboratory and model results show that the velocity gradient downstream of bedforms decreases with lower lee-slopes. Low turbulence intensities above lower lee-slopes are attributed to a smaller scale of macroturbulent structures though this has yet to be verified. In the field, water-depth scale macroturbulence is absent when bedform orientation and flow direction are opposed (flood phase). The former gentle-sloping ebb stoss-side now serves temporally as the hydraulic lee-side. High velocity and pressure gradients are absent preventing the generation of macroturbulence of this scale. Macroturbulent structures are responsible for the rapid upward transport and mixing of suspended sediment. In the Elbe Estuary, sediment within flow structures forms distinct clouds of sediment with cohesive properties. Confined clouds can be observed for up to one hour after their first occurrence, even after they merge to form larger structures. In the Knudedyb, such cohesive properties are absent. Sediment disperses more rapidly under the high flow velocities of the upper water column. During the flood tide, due to the absence of water-depth scale macroturbulence, suspended sediment transport is smaller in magnitude and believed to be associated with turbulence generated at the secondary bedforms. Transport distances are limited by the steep flow-facing flank of the primary bedforms. The complexity of these processes currently lacks adequate description and might result in under- or overestimation of regional sedimentary budgets. The variability of macroturbulence production due to flow unsteadiness causes a change in hydraulic roughness between tidal phases. Hydraulic roughness is also shown to vary for bedforms with equal height and length, based on the lee-slope. Our results demonstrate that there is a need for current generations of morphodynamic models to take into account the variability of hydraulic roughness induced by flow unsteadiness, the relative orientation of flow to bedforms, and lee-slope characteristics

The impact of non-equilibrium flow on the structure of turbulence over river dunes

This piece of research expands our description of how rivers flow over dunes on a river bed. Most of the scientific communities' research to date has used unnaturally steady conditions to measure how water moves over dunes. Yet these flow conditions are not strictly true to the variety of conditions nature produces, most importantly during floods. This research is the first detailed description of a wide range of flow states over dunes, and changes our present understanding of the structure of flow over dunes in rivers. Consequently, the scientific community will be able to use this new information to better model and simulate how rivers work, how they flood, and how they transport sediment towards the worlds deltas

Wissenschaftliche Monitoringkonzepte für die Deutsche Bucht (WIMO) - Abschlussbericht

The state and development of coastal marine systems and an understanding of the interaction of organisms, sea floor, water column, and biochemical and physical processes can only be obtained by a combination of long-term monitoring and modelling approaches of different complexity. A need for the development and evaluation of monitoring strategies is driven by a framework of different European and German regulations. The research project WIMO (Scientific Monitoring Concepts for the German Bight) has developed concepts and methods that aim at a fundamental scientific understanding of marine systems and also meet monitoring requirements of European legislation and regulations like the EU Marine Strategy Framework Directive. In this final report examples of common descriptors of ecosystem state like seabed integrity, eutrophication, and biodiversity are discussed. It has been assessed to what extent established measuring procedures used to survey the characteristics of the sea floor, and newly developed technologies are eligible for governmental monitoring. The significance of integrative modelling for linking and visualising results of measurements and models is illustrated. It is shown how new concepts have been implemented into governmental monitoring in the form of web based data sheets. These insights enable continuous analyses and developments in the future

Bodenformen, Makroturbulenz und Sedimenttransport an der Sohle

Small scale morphodynamic processes at the fluid-bed interface in coastal environments are still not fully understood. Deformation of the seabed by hydrodynamic forces results in the occurrence of complex bedforms on a variety of scales. Owing to their interaction with the water column and turbulence production, large bedforms, such as dunes, significantly influence sediment transport and hydraulic roughness. Turbulence production above bedforms is predominately associated with large-scale coherent flow structures (macroturbulence). It has been suggested that macroturbulence is the principle mechanism behind the entrainment and transport of sediment in suspension. The objective of this thesis was to investigate the formation and occurrence of macroturbulent structures and their coupling to suspended sediment transport forming downstream of natural bedforms. Specifically, the effect of flow unsteadiness and bedform geometry was examined. The research is based on multiple research approaches including two field campaigns into the German Elbe Estuary and Danish tidal inlet Knudedyb. Ship-based observations and lander-based moorings deploying acoustic Doppler current profilers and optical measurement probes were conducted. The field research was complemented by laboratory experiments and a 2DV numerical model study. Results show that flow unsteadiness has significant implications on the production of macroturbulence. In both, the Elbe Estuary and the tidal inlet Knudedyb, very large compound bedforms occur in water depths of < 20 m. The primary bedforms remain ebb-oriented during a tidal cycle while smaller superimposed bedforms reverse direction with each tidal phase. Water-depth scale macroturbulence develops when flow direction and primary bedform orientation are aligned (ebb phase), once the accelerating ebb flow overcomes a velocity threshold. The frequency of macroturbulent structures falls into the Strouhal range of macroturbulence associated with flow separation zones downstream of bedforms. The flow structures originate in the region of high velocity gradients in the bedform lee and are traceable over the downstream bedform stoss-side. The magnitude of turbulence production decreases with the slope of the bedform lee-side. Our laboratory and model results show that the velocity gradient downstream of bedforms decreases with lower lee-slopes. Low turbulence intensities above lower lee-slopes are attributed to a smaller scale of macroturbulent structures though this has yet to be verified. In the field, water-depth scale macroturbulence is absent when bedform orientation and flow direction are opposed (flood phase). The former gentle-sloping ebb stoss-side now serves temporally as the hydraulic lee-side. High velocity and pressure gradients are absent preventing the generation of macroturbulence of this scale. Macroturbulent structures are responsible for the rapid upward transport and mixing of suspended sediment. In the Elbe Estuary, sediment within flow structures forms distinct clouds of sediment with cohesive properties. Confined clouds can be observed for up to one hour after their first occurrence, even after they merge to form larger structures. In the Knudedyb, such cohesive properties are absent. Sediment disperses more rapidly under the high flow velocities of the upper water column. During the flood tide, due to the absence of water-depth scale macroturbulence, suspended sediment transport is smaller in magnitude and believed to be associated with turbulence generated at the secondary bedforms. Transport distances are limited by the steep flow-facing flank of the primary bedforms. The complexity of these processes currently lacks adequate description and might result in under- or overestimation of regional sedimentary budgets. The variability of macroturbulence production due to flow unsteadiness causes a change in hydraulic roughness between tidal phases. Hydraulic roughness is also shown to vary for bedforms with equal height and length, based on the lee-slope. Our results demonstrate that there is a need for current generations of morphodynamic models to take into account the variability of hydraulic roughness induced by flow unsteadiness, the relative orientation of flow to bedforms, and lee-slope characteristics

Fetal-neonatale Risiken bei untergewichtigen Schwangeren (BMI < 18,50 kg/m²) unter Berücksichtigung des Rauchens: Analyse eines Schwangerenkollektivs mit 508.926 Einlingsgeburten der Jahre 1998 - 2000 der Bundesrepublik Deutschland

Rauchen gilt als fetaler Wachstumskiller Nr.1. Nach wie vor rauchen rund 20 % der Schwangeren auch nach Bekanntwerden ihrer Schwangerschaft weiter. In der vorliegenden Untersuchung bestätigt sich anhand einer umfangreichen retrospektiven Populationsstudie der Deutschen Perinatalerhebung, dass mütterliches Rauchen während der Schwangerschaft einen entscheidenden Faktor in der Ätiopathogenese der small-for-gestational-age (SGA) neonates darstellt. Bei untergewichtigen Schwangeren (BMI unter 18,50) liegt die Hypotrophierate bei 29,5 %. Bei normalgewichtigen Nichtraucherinnen sind es 9,0%