AUTHOR=Witt M. , Patzke J. , Nehlsen E. , FrΓΆhle P. TITLE=Deriving erosion thresholds of freshly deposited cohesive sediments from the port of Hamburg using a closed microcosm system JOURNAL=Frontiers in Marine Science VOLUME=Volume 11 - 2024 YEAR=2024 URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1386081 DOI=10.3389/fmars.2024.1386081 ISSN=2296-7745 ABSTRACT=The 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 𝜏 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/mΒ³ and 1250 kg/mΒ³. The covered range of bulk densities is seen to represent the values commonly exhibited by freshly deposited cohesive sediments. Two approaches to derive 𝜏 based on the erosion rate (πœ€-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 𝜏 between 0.037 N/mΒ² and 0.305 N/mΒ², continuously increasing with bulk density. Repetition tests proved the repeatability of the experimental procedure and utilized methods to derive 𝜏 . The derived data for 𝜏 is used to fit two mathematical models: i) a highly empirical model relating 𝜏 to dry bulk density and ii) a recently proposed model relating 𝜏 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.