D1) Mixed-Size Sediment Morphodynamics

Victor Chavarrias

"When a morphodynamic model accounts for mixed-size sediment it can lose its predictive capabilities. We conduct laboratory experiments to understand the origin of the problem and search for a possible solution"

Practical motivation

Rijkswaterstaat has started a large scale nourishment field experiment in the German-Dutch border area, a part of the Rhine River specially relevant for its mixed-sediment properties. The mixed character of the sediment is a property necessary to explain physical phenomena as downstream fining of rivers, the gravel sand transition zone, the formation of bedload sheets, the evolution of bars, or bed surface armoring. When a morphodynamic model accounts for mixed-size sediment it can lose its predictive capabilities. We conduct laboratory experiments aimed at gaining insight into the origin of the problem and in search of a possible solution.

Median bed surface grain size in the Pannerdensch Kanaal, c. 5 km downstream from the nourishment place (adapted from Frings, 2007).

Management phase: Problem identification |

Management goals: Morphological understanding |

Research aim

In order to predict the evolution of rivers with multiple grain sizes, we use mathematical models in which we impose the conservation of water mass and momentum and the mass of sediment of different size fractions. The conservation of sediment mass of different grain sizes poses a challenge:

  • the model needs to be simple as modelling the behavior of every single particle is de facto impossible;
  • the model needs to be complete enough to be physically realistic.

Our objective is to find the limits where the typical model describing mixed-sediment river morphodynamics is physically realistic (and thus usable). We aim at providing a model that is usable outside these limits.

Temporal scale: Model run |


  • 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.

Data-collection methods: Numerical modeling | Physical and laboratory experiments |

Main progress and next steps

  • Our results show that the current approach to model river morphodynamics with mixed-sediment is not appropriate over a wide domain.
  • Laboratory experiments are being carried out to assess whether the solutions we propose to improve the modelling approaches is also physically realistic.
  • Eventually, we aim at providing a model that improves the description of the prevailing physics of mixed sediment river morphodynamics.

Study areas

Key study areas: Rhine river (The Netherlands) |

Last modified: 17/06/2018

Main researcher

Victor Chavarrias

Supervisory team

dr. ir. Astrid Blom


dr. Ralph Schielen


Prof. dr. ir. Wim Uijttewaal


Contributing partners

Rijkswaterstaat Ministry of Infrastructure and Water Management

LievenseCSO Infrastructure & Environment

Witteveen+Bos Engineering and Consulting

HKV Consultants

University of Twente

Delft University of Technology

NWO Applied and Engineering Sciences

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Featured Outputs

Ill-posedness in modeling mixed sediment river morphodynamics

13/02/2018 by Victor Chavarrias et al.

Contains: Data repository access Journal publication

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Other outputs

Jump to: Conference abstract | Report




  • Chavarrias Borras, V., Stecca, G., Labeur, R. J. & Blom, A. (2017). A strategy to avoid ill-posedness in mixed sediment morphodynamics. RCEM 2017 – Back to Italy: The 10th Symposium on River, Coastal and Estuarine Morphodynamics, Trento-Padova, 15-22 September 2017, Book of Abstracts. Lanzoni, S., Redolfi, M. & Zolezzi, G. (eds.). p. 166.
  • Chavarrias Borras, V., Ottevanger, W., Labeur, R. J. & Blom, A. (2017).  Ill-posedness in modelling 2D river morphodynamics. NCR days 2017: Book of abstracts. Hoitink, A. J. F., de Ruijsscher, T. V., Geertsema, T. J., Makaske, B., Wallinga, J., Candel, J. H. J. & Poelman, J. (eds.). Vol. NCR publication 41-2017p. 74-76.


  • Chavarrias Borras, V., Blom, A. & Stecca, G. (2016). Ill-posedness of the Saint-Venant-Hirano Model. Abstract 90221, 31st IUGG Conference on Mathematical Geophysics, Paris, 6-10 June.
  • Chavarrias Borras, V., Stecca, G., Siviglia, A. & Blom, A. (2016). Ellipticity in modelling mixed-sediment river morphodynamics. Abstract presented at the 9th Symposium of the RCEM, Iquitos, Perú, 30 Aug – 3 Sep.


  • Chavarrias Borras, V., Stecca, G., Siviglia, A., Labeur, R. J. & Blom, A. (2015). Limitations when modelling mixed-sediment river morphodynamics. In: H.J.R. Lenders, F.P.L. Collas, G.W. Geerling, R.S.E.W. Leuven (Eds.). Bridging gaps between river science, governance and management. Book of abstracts NCR-days 2015, NCR Publication 39-2015, 1-2 October 2015, Radboud University, Nijmegen, pp. 97-100.




  • Chavarrias Borras, V. and Ottevanger, W. (2016) Mathematical analysis of the well-posedness of the Hirano active layer concept in 2D models. Tech. Rep. 1230044, Deltares.


Follow the pretty pebbles

01/06/2017 by Victor Chavarrias

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The rivers of the future initiative is taken up

30/01/2018 by dr. Ralph Schielen

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Symposium on River, Coastal and Estuarine Morphodynamics 2017 in Padova (Italy)

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DeltaLinks Magazine | oktober 2016: Rivieren

01/10/2016 by dr. ir. Astrid Blom

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Project group
Project D

Contact details

Victor Chavarrias

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