Morphodynamics of a microtidal protected beach during low wave-energy conditions

This paper presents detailed hydrodynamic and morphological data from a field experiment spanning 5 days (10 tidal cycles, starting at Spring Tide conditions) undertaken in Lido di Dante, a microtidal protected beach in the Northern Adriatic Sea. This microtidal beach experienced intense erosion in the recent past and therefore it has been protected by groins, nourishments and a semi-submerged breakwater (Low-Crested Structures). During the fieldwork, an intertidal swash bar formed at spring tide under very low wave-energy conditions. The swash bar migrated 3.5 m landwards during two consecutive tides when the measured maximum significant wave height at the upper beach was around 0.2 m. This migration was associated with an onshore sediment transport, resulting from the erosion of the bar’s seaward slope. Once the tidal range decreased during the last tides and wave action ceased, the swash bar became static and only some non-significant changes were observed on both seaside slope and bar slip-face. The net volumetric change of this beach during the fieldwork was non-significant, in spite of the swash bar landward migration (cross-shore redistribution of the initial beach sediment budget). The wave attenuation generated by the beach protection structures was highlighted through comparison between wave measurements inside and outside the barrier. This had a significant role on swash processes and tide controlled duration of swash action, which controlled the cross-shore bar’s morphodynamics in the absence of significant longshore processes