Uncertainty analysis of settling, consolidation and resuspension of cohesive sediments in the Upper Rhine

ABSTRACT

Understanding the dynamics of settling, consolidation and remobilization of cohesive and contaminated sediment is an important requirement to assess the risk of erosion and to manage mud-dominated ecosystems. Here, we present data on the erodibility of cohesive sediments from the impounded Upper Rhine River and develop a modelling concept to understand the suspended sediment dynamics along the impounded Upper Rhine. The conceptual framework includes 10 reservoirs of the Upper Rhine between Basel and Iffezheim, which serve as long-term sinks of cohesive sediment. Each reservoir is represented by a 1D sediment budget model, which is coupled to its upstream and downstream neighbour. In this paper, we focus on the uncertainty associated with the measurement of the erodibility of cohesive sediments and on the implications to model the risk of erosion. The statistical analysis showed a large uncertainty of the estimated critical shear stresses and erosion rates. Root mean square errors are in the order of 50% and 100% of the average critical shear stresses and average erosion rates, respectively. Preliminary model results are in good agreement with bed changes of the Iffezheim reservoir, which were measured using approximately quarterly echo-soundings of the reservoir. The probabilistic approach that is based on Monte-Carlo simulations allows assessing the uncertainty related to our limited knowledge (i) of the dynamics of contaminated sediments and (ii) of the environmental conditions in the reservoir that control the risk of erosion of contaminated sediments.

KEYWORDS:

• Cohesive sediment
• erosion
• sediment settling
• consolidation
• probabilistic modelling
• uncertainty analysis
• Upper Rhine reservoirs

Acknowledgements

All field data are provided by the German Federal Institute of Hydrology (BfG), the Federal Waterways and Shipping Authority (Office Freiburg), and by the Institute for Modelling Hydraulic and Environmental Systems of the University of Stuttgart. The study is supported in the framework of the project ‘Estimating long-term evolution of fine sediment budget in the Upper Rhine’. The authors appreciate the support by BfG.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Thomas Hoffmann http://orcid.org/0000-0002-3853-1830