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A Stability Approach to the Patchy Behaviour of Aquatic Plants in Rivers
  • Giulio Calvani,
  • Costanza Carbonari,
  • Luca Solari
Giulio Calvani
University of Florence

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Costanza Carbonari
University of Genoa
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Luca Solari
University of Florence
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The presence of vegetation in riverine habitats gathered the attention of scientific community during the last decades. Aquatic and riparian plants interact with sediment and affect transport of bed material, besides the additional drag provided by stems and foliage. At the same time, water flows and bed erosion have an impact on the growth and survival of vegetation species. While the interactions of fluvial vegetation with river hydro- and morpho-dynamics are conceptually known, their modelling and the quantification of their effects are still object of research. Particularly, it is widely documented in literature that the mutual interactions between the presence of aquatic plants and the morphodynamic equilibrium of a river reach result in an organised disposition (patches of different size and geometry) of vegetation within the channel itself. In this work, we investigated the critical conditions for the formation of such organised arrangements in a straight channel of constant width characterised by an erodible bed of uniform sediment with uniform vegetation density. A 2D stability analysis was performed on shallow water equations (SWE) for the water flow, 2D Exner equation for bed elevation dynamics and sediment continuity and an additional equation for vegetation dynamics. Closure relations for drag and sediment transport in vegetated conditions were involved, as well. Results reveal the particular conditions of dimensionless parameters leading either to the suppression of vegetation or to the survival of aquatic plants. In the latter, the analysis suggests that multiple patches (order higher than 1) of vegetation may exist as aa result of instability, which is contrast to the findings prenset in literature.