Morphological changes and human impact in the Entella River floodplain (Northern Italy) from the 17th century

In this article the morphological changes undergone by the Entella River (Northern Italy) over the last four centuries has been investigated. The historical analysis has allowed reconstruction of fluvial evolution and shoreline dynamics and demonstrated their relationship to human disturbance over a very long period compared to most previous studies in Italy and Europe. A set of 12 historical and current maps and aerial photos, ranging from the 17th century to the present, were entered into a Geographic Information System (GIS) in order to calculate four morphological parameters (i.e., channel length, width, sinuosity and centreline shifting) and the distance of the shoreline. Modification of the Entella River over the 360-years period 1656–2016 include: i) a reduction in channel length by 128m (3%); ii) a mean narrowing of 56m (46%); iii) a decrease in total sinuosity from 1.10 to 1.05, with a variation in river pattern, from sinuous to straight; iv) a total shifting of the centreline of 30 m. This evolutionary trend is consistent with most of the previous studies on Italian and European rivers. Conversely, the total channel shortening and the recent phase of substantial morphological stability, with a slight increase in channel width and length, seems to be in contrast with the results of other studies. We correlated the channel planform changes and the regression of the shoreline, at least until the latter 20th century, to the reduction in sediment supply produced by the morphological modifications due to human intervention. At the beginning of the 19th century and, later, from the 1950s to the end of the 20th century, channelization, channel diversion, land-use changes and coastal defences accounted for this supply change to the Entella River and its floodplain. Furthermore, our findings reveal that human disturbance has contributed to increased flood risk in the plain, through the progressive reduction in width of the riverbed and the increasing urbanization along its riverbanks. At the same time, channelization seems to have a negative effect not only on the morphological evolution of the river, but also in terms of prevention and flood risk reduction within the floodplain