Morphodynamic evolution of a microtidal barrier, the role of overwash: Bevano, Northern Adriatic Sea

Abstract : This study discusses the morphological changes of the Bevano "microtidal barrier" and the washover dynamics and evolution in response to several storm surges recorded during one year between September 2008 and September 2009. This barrier corresponds to the old Bevano river spit (characterised by a northward migration) which was abandoned after the relocation of the river mouth some 600 m to the south of the previous inlet position. The first overwash event was recorded in this barrier just after one of the highest surges recorded in the last 100 years (01 December 2008) with a high a surge level of 0.97 m, combined with an offshore significant wave height of 1.45 m (measured at Cesenatico). Seven separate washover fans were identified together with severe damages to fences and dune vegetation. The washover fans had different dimensions, the most important one being around 18 m wide, and generating a ~ 9 m landward migration of the back-barrier limit. The study area was therefore subjected to a series of storm-surges during the study period with surge values fluctuating between 0.6 m and 0.8 m. The overwash processes and particularly the exceptional surge of 01 December 2008 was the instigator of initial morphological changes which then facilitated successive morphological changes caused by the subsequent storm surges and, as a result, generating the complete change of the morphologic configuration of the microtidal setting.