• Contaminant transfers in freshwater environments: prediction and modelling.
  
  • Context et stakes
    When a metallic contaminant is introduced into water, chemical reaction occurs with electrolytes and suspended matters (adsorption-desorption, ionoic exchanges or precipitation-dissolution). By this way, a release of contaminant affects both the water - whose export toward the sea is ensured by advection and diffusion in a few days - and the sediment - that can constitute a stock in settling areas (banks, upstream of hydraulic works...): the residence time of the contaminant is considerably increased.
    Remobilization processes of the contaminant at medium and long terms are different. In the deposition zones, the export is ensured punctually during flood events. Other remobilization processes can also be mentionned at this time scale, such as diffusion of contaminant from the bottom sediment toward the water column.
  
  
  • Modelling presentation
    Simulate such scenarios requires the elaboration of the modelling for each process. To describe an abiotic freshwater ecosystem, we need a chemical model of exchanges between the contaminants and the surrounding reactive entities (in case of radioactivity, a radiological model may be needed). Then a transport modelling of the water flow and a transport modelling for each passive scalar (concentration of chemical entities, temperature...). After modelling of the suspended matter transport is needed, with the need of taking into account the fluid/particle interactions. Finally, the two last boxes are the hydrographical modelling and the bottom sediment modelling.
    The system of equation is quiet complex and can be simplified under some hypothesis. The main difficulty remains in the coupling between those equations to close the system and allow its resolution. Most of the time, these closure equations are the aim of a lot of investigation works.
    In my case, there was a need to finding an equation for the critical erosion shear stress of the sediment. This is what I expose in dedicated part...
  
  

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