Stochastic Modeling of Bedload Transport and Bar Development in Shallow Flow: Linear Stability Analysis and Numerical Simulation

Mehrdad Kiani Oshtorjani
2023
Discussion par affiche

Field surveys and laboratory experiments show that bedload transport rates may vary to within one order of magnitude for a given water discharge. One of today's major challenges is to account for these large transport rate fluctuations in computational hydraulics models. To that end, we developed a two-dimensional stochastic bedload model computing the random time variations in particle activity (i.e., the number of moving particles per streambed area). This model differs from most current bedload transport model, in which mean bedload transport rates are related to flow rate deterministically. The stochastic model was coupled to the two-dimensional Saint-Venant--Exner equations. The one-dimensional version of this model was successfully tested by Bohorquez and Ancey [1]. In this study, we focused on the development of two-dimensional bedforms under varied flow conditions. We conducted linear stability analysis to determine the flow conditions for which these bedforms develop, and then compare the resulting criteria with experimental evidence. We implemented a numerical algorithm based on the finite-volume method [2]. We used it to study gravel bar development in a long flume under steady state conditions, and compared the numerical simulations with experimental data [3]. The bed surface was initially flat at t=0, and one small perturbation was imposed. Figure 1 shows an example of alternate bars simulated by our code. The numerical simulations captured the stages of bar formation, from inception and migration, consistently with experimental data. [1] Bohorquez, P. and Ancey, C., 2015. Stochastic-deterministic modeling of bed load transport in shallow water flow over erodible slope: Linear stability analysis and numerical simulation. Advances in water resources, 83, pp.36-54. [2] LeVeque, R.J., 2011. A well-balanced path-integral f-wave method for hyperbolic problems with source terms. Journal of scientific computing, 48, pp.209-226. [3] Dhont, B.E.M., 2017. Sediment pulses in a gravel-bed flume with alternate bars (No. THESIS). EPFL.

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Mehrdad Kiani Oshtorjani
2023
Discussion par affiche

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https://infoscience.epfl.ch/record/308644?ln=fr

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Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural systems where the particles are clastic rocks (sand, gravel, boulders, etc.), mud, or clay; the fluid is air, water, or ice; and the force of gravity acts to move the particles along the sloping surface on which they are resting.

thumb|Roche abrasée par un glacier en Norvège près du glacier de Jostedalsbreen. thumb|Côte polonaise de la mer Baltique. L'abrasion est l'érosion par frottement d'une surface rocheuse par frottement entre les roches et des éléments mobiles transportés par le vent, les glaciers, les vagues, la gravité ou le charriage des cours d'eau. Après le frottement les éléments mobiles emportent les débris de la roche érodée. Arrondi (géologie) Catégorie:Glaciologie Catégorie:Phénomène d'érosion Catégorie:Phénomène géo

vignette|300x300px| Charge de fond dans le thalweg de en Alaska . Le terme charge de fond ou charriage de fond ou les sédiments charriés sur le fond (en bed load ou bedload) décrit les particules dans un fluide en écoulement (généralement de l'eau) qui sont transportées sur le fond de la rivière (sur le lit). La charge de fond est complémentaire de la charge en suspension et de la . La charge de fond se déplace en roulant, en glissant et/ou par saltation (en sautillant).