Executive Summary : | River systems are responsible for transporting almost 80 % of the plastic that ends up in the oceans. Microplastics (mean particle size more than 5 mm), both primary and secondary form a major portion of these derbies. The growing concentration of microplastics (MP) in fluvial systems has become a major environmental concern. Most of the research on MP dynamics is focused on submarine environments, however, mechanism of MP threshold and movement in river systems is not sufficiently explored. For modelling the fate of microplastics in rivers at macro-scales, key parameters such critical bed shear stress of Microplastic-sediment mix, fall velocities etc. are essential. significant gaps are identified in the current literature, on the horizontal transport of MP. The Incipient motion criteria for Microplastic-sediment mix in channel flows cannot be found in the literature. The role of turbulence in the near MP-sediment bed, in the resuspension and transport of MP is still not clear. Also, the efficiency of instream vegetation in trapping MP has not been sufficiently explored. On these lines, an experimental study is proposed to investigate transport of MP-sediment mix in fluvial systems. steady flow experiments shall be carried out in a rectangular flume laid with MP-sediment mix (50 % MP + 50% sediment by volume). Artificial MP particles of 4 types, i.e. polypropylene (PP), polystyrene (Ps), polyamide 6, and polyethylene terephthalate (PET) shall be tested. The incipient motion condition shall be established using under-water cameras and 3-D instantaneous velocities shall be recorded across the depth at this condition. Also, experiments will be conducted on MP-sediment mix bed with submerged instream vegetation, to study its efficiency in retention of MP. The proposed research will deliver improved understanding of the Hydrodynamics and movement of Microplastic in Fluvial systems. High quality and more realistic experimental data generated from the research will provide better estimates of critical bed shear stress and turbulence parameters causing the motion of MP-sediment mix. These data sets will be helpful for more accurate numerical modelling of fate of MP transport in fluvial systems at macro-scales in the future. |