Tidal Meander Migration: a Case Study from the Venice Lagoon

Abstract:

Meandering patterns are universal features of tidal landscapes which exert a great influence on the dynamics of tidal channel networks and on the stratigraphy of intertidal platforms. Despite their importance in landscape evolution and their ubiquity, tidal meanders have received less attention when compared to their fluvial counterparts. Quite a few studies, in fact, have focused on the morphodynamic evolution of tidal meanders, together with their planimetric shape and morphometric characteristics. To improve current understanding of tidal meander migration and its possible stratigraphic implications, we have analyzed a sequence of aerial photographs (from 1938 to present day) for a 20 m in diameter, abandoned tidal meander in the Venice Lagoon, and have carried out high-resolution sedimentological and chronostratigraphical analyses of channel deposits. Aerial photographs before and after the cutoff event have been used to infer a minimum velocity of migration. Well-cores have also been collected along a transect crossing through the neck zone in order to evaluate changes in grain size, sedimentation rates across the cutoff event, and gain further insight into the velocity of migration of meander bends. Spatial distribution of sedimentary facies (pointbar sand, oxbowlake and saltmarsh mud), grain size analyses, and ²¹⁰ Pb and ¹³⁷Cs chronometers highlighted that meander cutoff occurred progressively around 60 years ago with a velocity of migration of about 0.5m/year. The effectiveness of the methods and the high spatial and temporal resolution of the data call for further investigations and analyses of the type proposed herein, furthermore highlighting the potentiality of the study area as modern analogue for ancient tidal deposits.