Innovative components
The most common mathematical model to predict the downstream movement of mixed-size sediment in the river bed (i.e., the active layer model) can lose its prediction capabilities under certain circumstances. Thereby, negligible perturbations in the initial or boundary conditions produce significant differences in the solution. We propose a method that regularizes the traditional model to recover its prediction capabilities and compared the improved model results with data from four new laboratory experiments. Via the below experimental setup, we observed the mixed-size sediment movement (see figure below) for conditions in which the traditional model does not provide a unique solution. We measured water and bed elevation using laser sensors and a camera that was mounted on the carriage to measure the grain size distribution of the bed surface. We used two sediment size fractions (fine sediment painted in blue and coarse sediment painted in red).
Sketch of downstream movement (from a to d) of mix-size sediment under conditions in which the traditional active model loses its prediction capabilities. (Source: Figure 5, Chavarrias et al 2019).
Findings and Implications to practice
The regularized active layer model captures the change of bed elevation and surface texture reproduced with the laboratory experiments. The physical meaning of our regularization approach is that the mixing processes are slowed down or the time scale of the mixing processes is increased. Thereby, the improved model can be applied to a wider range of physical problems (i.e., also those characterized by a fairly small time scale of mixing) than the traditional active layer model.
Elements a), b), d), e), f) and g) are placed to control the conditions of the experiments. The river bed is represented by the mixture of red and blue sediment layers. h) and i) are the measurement sensors. (Source: Figure 3, Chavarrias et al. 2019)
Related Content
Dataset access
Chavarrías, V., Stecca, G., Siviglia, A., Blom, A., 2019. A regularization strategy for modeling mixed-sediment river morphodynamics. Adv. Water Resour. 127, 291–309. https://doi.org/10.1016/j.advwatres.2019.04.001
Related outputs
Ill posedness in modelling two-dimensional morphodynamic problems
We reveal the existence of two additional mechanisms under which the 2D system of equations does not provide a unique solution.
11/04/2019 by Victor Chavarrias et al.
Contains: Publication open access
Ill-posedness in modeling mixed sediment river morphodynamics
Our aim is to provide modelers of river morphodynamics with the mathematical tools to detect the occurrence of ill-posedness in their results.
13/02/2018 by Victor Chavarrias et al.
Contains: Publication open access
Last modified: 03/06/2019