Laboratory experiments to understand mix-size sediments dynamics that typically occur in rivers (Source: Left image: TUDelft).
Insight into the origin and possible solution to the limited predictive capabilities of morphodynamic models that account for mixed-size sediment.
Rivers carry sediment of different sizes. Modelling this characteristic is essential for properly predicting the effect of interventions (e.g., sediment nourishments). The current modelling approach sometimes catastrophically fails when accounting for mixed-size sediment, as the model is mathematically ill-posed. Currently, river managers do not have a reliable tool for predicting river morphodynamic changes accounting for mixed-size sediment. We conducted laboratory experiments aimed at gaining insight into the origin of the problem and in search of a possible solution. We used two sediment size fractions: fine (blue) and coarse (red). Degradational conditions were imposed, causing the entrainment of fine sediment. The current model cannot predict this situation.
Key goals: Fundamental understanding
The current model (top) fails when modelling the experiments. Our strategy to regularize the current model (bottom) is stable and captures the behavior averaged with time reasonably well.
We have analyzed the conditions under which the current model becomes useless in practice (see top Figure): A large spurious oscillations develops that mixes the substrate sediment in an unrealistic manner. We have developed a tool to predict when will this happen in numerical simulations. We have conducted a set of laboratory experiments to gain insight into the physical reasons that cause failure of the current model. Using the results of the analysis and the laboratory data, we have developed a strategy that prevents the current model from failing (see bottom Figure). We have also developed a new model that describes the physical processes observed in the experiment that are not included in the current model.
Form whom and where?
Our results are of special interest for modellers. In particular, for people dealing with morphodynamic changes including mixed-size sediment. Our results are applicable at both laboratory and field scale without restriction. The problem of ill-posedness is independent of the numerical solver. For this reason, the results apply to all modellers independently of the software they use (e.g., Delft3D, FM, Telemac, Basement,…).
Data-collection methods: Numerical modeling Physical and laboratory experiments
Temporal scale: 1-10years
Application and findings
- Mathematical analysis of the typical model for mixed-sediment river morphodynamics.
- Development of a tool into the software pachake Delft3D to numerically assess the results of simulations and their representation of the natural phenomena.
- Laboratory experiments to gain insight on the mechanisms that are important under those conditions where the typical model fail to reproduce the natural phenomena.
Status for day-to-day practice
A tool to analyze well-posedness of numerical simulations is available. A research numerical model describing river morphodynamics with mixed-size sediment is available that includes the current modelling approach as well as the strategy to regularize the current model when this becomes ill-posed and our new model. This type of tools are specially useful when looking at parts of the river where mixed-sediment properties are relevant such as the Pannerdensch Kannal (see map) but also in other rivers around the world.
Example location in The Netherlands where this project outputs are specially relevant.
Spatial scale: River section
Key locations: Abroad Netherlands (NL)
While we have analyzed the problem of ill-posedness under one and two-dimensional conditions, our solutions have focused on one-dimensional conditions only. We are currently extending our work to two-dimensional conditions.
Last updated: 10/02/2020
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Delft University of Technology - RiverCare
As soon as available, explore the storyline to get to know more about the main methods or prototype tools that were developed within this project.
Explore the output details for available publications to get a glance of the innovative components and implications to practice as well as the links to supporting datasets.
Ill-posedness in modeling mixed sediment river morphodynamics
Take a look to the dissemination efforts and application experiences which are available in the news items and blogs.
The rivers of the future initiative is taken up
30/01/2018 by dr. Ralph Schielen
RiverCare is now well on its course and is delivering great results. Rijkswaterstaat is involved in all user committees and tries to incorporate the...
Sharing knowledge with HKV, one of the project partners.
For RiverCare, it is very important to have face to face meetings to exchange the knowledge, and make sure to discuss with interested parties the results of the researchers.
Knowledge sharing meeting in Witteveen+Bos, Rotterdam
How can we apply the researchers’ findings to improve our designs and environmental impact assessments? How can we share lessons learned from RiverCare within our team of engineers and consultants?
Anything to ask or share?About us
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