Tidal meander migration and dynamics: A case study from the Venice Lagoon

Meandering patterns are universal features of tidal landscapes, and exert a critical influence on the dynamics of tidal channel networks and on the stratigraphy of the intertidal platforms they dissect. Despite their importance in landscape evolution and their ubiquity, tidal meanders have received less attention when compared to their fluvial counterparts. To improve current understanding of tidal meander migration and its possible stratigraphic implications, we analysed a sequence of aerial photographs and satellite images (from 1938 to present) of a meandering tidal channel in the Venice Lagoon, which experienced multiple cutoff events during its evolution. Migration rates of the considered bends are in the range of 0.06-0.17 m/y, whereas migration rates per unit width vary between 0.6 and 2.5% yr(-1). Detailed high-resolution geomorphological, sedimentological, and geochronological analyses were carried out for an abandoned meander bend, which experienced one of these cutoffs. Aerial photographs before and after the cutoff event (1938 and 1955, respectively) were used to infer a minimum velocity of migration (about 0.10 milt). Sediment cores were also collected along a transect crossing through the meander neck in order to evaluate changes in grain size, sedimentation rates during the cutoff event, and gain further insight into the velocity of migration of meander bends. The spatial distribution of sedimentary facies (point-bar sand, oxbow lake, and salt-marsh mud), grain-size analyses, and 210 Pb and Cs-137 chronologies highlighted that meander cutoff occurred progressively around 70 years before present with an average migration rate of 0.25 m/year. Such a procedure to estimate meander migration rates from stratigraphic data reveals to be particularly useful in the absence of high-temporal resolution remotely sensed-images. The effectiveness of the methods used and the high spatial and temporal resolution of the data call for further investigations and analyses of the type proposed herein, furthermore highlighting the potential of the study area as modern analogue for ancient tidal deposits. (C) 2017 Elsevier Ltd. All rights reserved.