Use of aerial photograph interpretation and Geographic Information Systems to study tidal channel changes: an example from the Venice Lagoon (Italy)

The geomorphological transformations of modern tidal channels were examined to identify the effects of sea-level fluctuations on wetlands. The present study was carried out in a salt marsh area not significantly modified by human interventions and located in the northern Venice Lagoon (Italy). The two-dimensional planform changes of channel morphology, occurred since the 1930s, were analyzed through the interpretation of a chronological sequence of ultra-high resolution aerial photographs and satellite images, using Geographic Information Systems. First, the modifications were identified and quantified. Then, they were compared to the yearly data of both relative sea-level rise and tides to highlight the control of water-level oscillations on channel evolution and the results were interpreted in the light of sediment availability, vegetation density, and anthropogenic factors. This approach allowed distinguishing the effects of long- and short-term sea-level variations on channel changes and identifying details on the possible human impact on their modifications. Moreover, the roles of sediment input and vegetation cover on salt marsh preservation were distinguished.