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A new morphodynamic instability associated to the cross-shore transport in the nearshore
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  • Albert Falqués,
  • Francesca Ribas,
  • Anna Mujal-Colilles,
  • Càrol Puig-Polo
Albert Falqués
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Francesca Ribas
Universitat Politecnica de Catalunya, Physics Department

Corresponding Author:francesca.ribas@upc.edu

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Anna Mujal-Colilles
Universitat Politècnica de Catalunya, Department of Nautical Sciences and Engineering
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Càrol Puig-Polo
Division of Geotechnical Engineering and Geosciences, Department of Civil and Environmental Engineering, UPC BarcelonaTECH
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The existing theory for alongshore rhythmic bars relies on morphodynamic instabilities involving the wave-driven longshore current and rip currents. Transverse finger bars are common on coasts with a beach profile above the equilibrium profile (something not related to those currents). Here we show that under these conditions, the cross-shore transport can induce an instability which is triggered by the onshore transport together with wave refraction by the emerging bars. It is a finite amplitude instability, something not previously found in coastal geomorphology. We use a numerical model that filters out the dynamics associated to those currents. The alongshore spacing scales with the wavelength of the incident waves and the cross-shore extent is about the distance from shore to the depth of closure. The modelled bars compare qualitatively well with observations at El Trabucador back-barrier beach (Ebro delta, Western Mediterranean Sea).