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).
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.
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
Ill-posedness in modeling mixed sediment river morphodynamics
Last modified: 03/06/2019