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Item type:Publication, Access status: with files , Concentration-dependent settling velocities of cohesive sediments from the Port of Hamburg based on ultrasound velocity profilingThe settling behavior of cohesive sediments plays a key role in estuarine sediment dynamics and harbor maintenance. This study aimed to assess the applicability of Ultrasound Velocity Profiling (UVP) to capture the spatial and temporal evolution of the settling process and to derive concentration-dependent settling velocities. Laboratory experiments were conducted in a settling column with initial sediment concentrations (C0[jls-end-space/]) of 0.3-80 g/L, using cohesive sediments from the Port of Hamburg. A 4 MHz transducer was utilized to measure the vertical particle velocities with a resolution of 0.08 mm/s and a sampling volume height of 1 mm. Effective settling velocities were derived from the UVP measurements and compared to the settling velocities obtained from the lutocline evolution. Subsequently, common mathematical models were fitted to the data. The results demonstrate that UVP is a suitable, non-intrusive method for high-resolution imaging of settling processes, revealing concentration-dependent characteristics in particle movement in unprecedented detail. The calculated effective settling velocities increased approximately linearly in the flocculation settling range until a maximum of ws,max = 2 mm/s was reached at C0 = 3.5 g/L, followed by an asymptotic decline in the hindered settling range. The associated deposition flux showed a broad maximum of approximately 0.01 kg/(m2s) for C0 in the range of 5-15 g/L. The results provide previously unavailable, site-specific data on the settling behavior of the studied cohesive sediments. Potential application areas of UVP include the execution of field experiments and the automated high-resolution tracking of the lutocline or bed level.Publicationtype: Journal Article21 21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Near-field dynamics of discrete dredged material discharge events in the Elbe estuary: Quantifying deposition fraction and plume evolutionDredging and relocation of sediments are essential to maintain navigable waterways and port access in many estuaries. The relocated volumes can significantly influence long-term morphological evolution and thus need to be represented in relevant numerical models. In morphodynamic simulations, relocation processes require parameterization, typically based on limited empirical data, as dedicated field measurements of near-field processes during discharge at relocation sites are scarce. Therefore, this study aims to quantify (i) the spatiotemporal evolution of the suspended sediment plume, (ii) the deposition fraction and resulting changes in bed morphology, and (iii) the sediment mass balance for individual discharge events.Publicationtype: Conference Poster41 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Erosion threshold of cohesive sediments in the German Wadden Sea: temporal variability and comparison of in-situ and laboratory experimentsA newly developed in-situ setup of the Closed Gust Erosion Microcosm System (C-GEMS) was utilized for erosion experiments in a tidal mudflat in the mouth of the Elbe in the German Wadden Sea to investigate the temporal variability of the erosion threshold τc of cohesive sediments. In addition, erosion experiments with extracted sediment cores from the same site were conducted in the field and in the laboratory with the identical device to analyze the influence of sample extraction and transport on the derived erosion threshold. A total of 21 erosion experiments were carried out in four measuring campaigns between April and September 2024. The erosion thresholds derived from the in-situ experiments exhibit considerable temporal variability across campaigns, with values of τc = 0.1–0.27 N/m²>, while repeated experiments within the individual campaigns demonstrate a high degree of reproducibility. Accompanying analyses of surface sediment particle size distribution and bulk density revealed that mud concentration (clay and silt) varied with wind conditions and the associated hydrodynamic load prior to the measurement campaigns. The observed temporal variability in τc is reasonably well captured by a mathematical model based on mud concentration and particle size, suggesting that τc can be plausibly estimated from these parameters. For campaigns with a cohesive surface sediment layer, erosion thresholds derived in the ex-situ experiments are consistently lower than those obtained in the in-situ experiments. This is attributed to the disturbance of the surface sediments due to mechanical extraction and liquefaction during transport. The findings offer insights into the transport dynamics of cohesive sediments and help guide decisions on whether future erosion experiments should be conducted in situ, despite the significant effort involved, or whether extracted sediment cores are a suitable alternative.Publicationtype: Journal Article65 30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Deriving erosion thresholds of freshly deposited cohesive sediments from the port of Hamburg using a closed microcosm systemThe quantification of the erodibility of cohesive sediments is fundamental for an advanced understanding of estuarine sediment transport processes. In this study, the surface erosion threshold τc for cohesive sediments collected from two sites in the area of the Port of Hamburg in the River Elbe is investigated in laboratory experiments. An improved closed microcosm system (C-GEMS) is used for the erosion experiments, which allows the accumulation of suspended sediment concentration (SSC) over an experimental run. A total of 34 erosion experiments has been conducted with homogenized samples and bulk densities between 1050 kg/m³ and 1250 kg/m³. The covered range of bulk densities is seen to represent the values commonly exhibited by freshly deposited cohesive sediments. Two approaches to derive τc based on the erosion rate (ε-method) and the SSC (SSC-method) were elaborated and compared. For both approaches, only one parameter has to be set in order to facilitate transferability to other devices. The results show a better performance of the SSC-method in terms of lower uncertainties, especially at the upper application limits of the utilized C-GEMS. The application of the SSC method yields values for τc between 0.037 N/m² and 0.305 N/m², continuously increasing with bulk density. Repetition tests proved the repeatability of the experimental procedure and utilized methods to derive τc. The derived data for τc is used to fit two mathematical models: i) a highly empirical model relating τc to dry bulk density and ii) a recently proposed model relating τc to the physical properties of the sediment-mixture. While the derived parameters for the first model vary widely for the two sampling sites, the fit-parameter for the latter model is virtually independent of the investigated site, suggesting the superiority of this approach.Publicationtype: Journal Article49 153 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Measuring detailed vertical density profiles in cohesive sediment layers : a comparison of techniques(Markus Witt@Intercoh2023, Inha University, Incheon, Korea, 2023-09-18); ; ; The representation of the complex behavior of cohesive sediments in numerical models is a major challenge. To tackle this situation and deepen the understanding of estuarine sediment transport in general, the joint project ELMOD is conducted. Involved partners are the Federal Waterways Engineering and Research Institute (BAW, model application), the University of the Bundeswehr Munich (UniBW, development of model approaches) and the Hamburg University of Technology (TUHH, field measurements and laboratory investigations). This contribution outlines the conception of the first ship-based measurement campaign in the research project ELMOD which was conducted in the port area of Hamburg. It puts a focus on the in-situ measurements of vertical density- and SSC-profiles with different methods. Additionally, the agreement of the in-situ measured density profiles with the vertical density distribution of sediment cores collected during the same campaign is checked. The utilized devices and techniques deliver very consistent results. The bed-density profiles and especially their gradient are in good agreement for the subsamples of the extracted cores, Admodus USP pro, Rheotune and sediment echosounder, which shows that the extracted sediment cores reflect the natural density profiles to a high degree. The slightly different elevations of the associated densities are seen to be due to small changes in Ship positions. Hach Solitax sc and peristaltic pump (+vacuum filtration) deliver comparable SSC-values in the water column. In the relatively thin bottom layer with rapidly rising sediment concentrations both techniques reach their limits.Publicationtype: Conference Poster130 103 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Measurement and comparison of settling velocities of cohesive sediments from the German estuaries Weser and Ems(Justus Patzke@Intercoh2023, Inha University, Incheon, Korea, 2023-09-18); ; ; ; Settling and sedimentation of fine-grained sediments is a physical phenomenon influenced by bio-geochemical processes that occurs in natural water bodies such as rivers, channels and estuaries. Of particular concern are estuaries maintained for navigation. The deepening of waterways to improve the navigability for ever larger container ships has the potential to intensify sedimentation and the accumulation of cohesive sediments, particularly within the estuarine turbidity maximum (ETM). For example, significant net sedimentation and accumulation are observed in the ETM of the Weser estuary even in the centre of the navigational channel, where high flow velocities favour sediment transport and erosion. Dredging is the main method of maintaining a channel, which requires large financial investment and also has potential negative environmental impacts. In engineering practice, numerical modelling of the ETM and accumulation zones is an important tool to improve channel maintenance. Knowledge of site-specific information on settling velocities is therefore essential, as underlying processes cannot be simulated universally valid yet and require sufficient local parametrisation. The research project FAUST (For An improved Understanding of estuarine Sediment Transport) addressed the challenge of net sedimentation and accumulation in the navigational channel by investigating the transport properties of cohesive sediments (mainly from the Weser estuary) in field and in laboratory studies. The conceptual design of the project FAUST has been presented in Patzke et al. (2019). Research on sediment erodibility, sediment fractions and density profiles has been published recently (Patzke et al. 2021; Patzke et al. 2022). The follow-up project ELMOD (Simulation and analysis of the hydrological and morphological development of the Tidal Elbe for the period from 2013 to 2018) focuses on sediment transport processes in the Elbe estuary. The findings and derived model parameterisations of the projects contribute to the development of large-scale 3D morphodynamical-numerical models. In this submission, laboratory-derived effective settling velocities of natural cohesive sediments from two German estuaries are examined.Publicationtype: Conference Poster131 87 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , ELMOD - Simulation und Analyse der hydrologischen und morphologischen Entwicklung der Tideelbe für den Zeitraum 2013 bis 2018(Markus Witt@Intercoh2023, Inha University, Incheon, Korea, 2023-05-24); ; ; Between 2013 and 2018, striking hydrological and morphological changes were observed in the Tidal Elbe, in particular an unusually strong increase in tidal range, turbidity and sedimentation rates. The latter led to increased maintenance dredging, which, however, represents a major economic and ecological burden. Reasons for the described changes are seen in morphological changes in the mouth of the estuary, persistently low headwater discharges and insufficiently adapted sediment management (Weilbeer et al. 2021). The numerical models currently used cannot adequately represent these developments. In particular, the complex behaviour of cohesive sediments in the heavily anthropogenically influenced river sections such as the port of Hamburg poses a major challenge. The joint project ELMOD is conducted to improve the predictive capability of numerical models and to improve the understanding of estuarine sediment transport in general. For this purpose, the changes observed in the Tidal Elbe in the period 2013-2018 are analysed by means of hindcast studies and the model approaches used are extended on the basis of natural measurements and laboratory investigations. The partners involved are the Federal Waterways Engineering and Research Institute (BAW, model application), the University of the Bundeswehr Munich (UniBW, development of model approaches) and the Hamburg University of Technology (TUHH, field measurements and laboratory investigations).Publicationtype: Conference Poster67 66