Geomorphological changing of the Calore River near Benevento (Southern Italy) in modern times: flood hazard implications

The aim of this paper is to define the morphodynamic evolution of a sector of the Calore River, located in Campania (Southern Italy), from 1825 to nowadays. The studied fluvial sector is between the towns of Benevento and Ponte. The channel morphological changing has been highlighted by an overlay process of topographic maps and aerial photographs (scale 1:25.000), performed using GIS softwares. Further data have been obtained by field survey. In the studied sector, the Calore River shows a sinuosity of 1,25 and is characterized by alternated lateral and longitudinal bars, migrating downstream: such features allow to classify it as wandering river. It flows on a substratum mainly consisting of calcarenite with marly interbeddings (“Flysch Rosso” Formation, Upper Cretaceous to Miocene in age) and of Pliocene clastic deposits. In proximity of Benevento and Ponte, Middle Pleistocene alluvial deposits of Calore River unconformably overlie on such substratum. Holocene and present alluvial deposits complete the lithological framework. The study of the Calore River channel between 1870 and 1936 has been performed overlaying the 1870, 1909 and 1936 topographic maps. In such period, no remarkable morphological changes of the channel have been detected. The channel was characterized by a width ranging from ~30 meters to ~450 meters. The overlay of 1936 and 1957 topographic maps highlighted a strong width reduction of the Calore River channel. In such a period, three catastrophic floodings occurred in 1949, 1952 and 1954; the sediments transported by the water completely filled the 1936 wide channel. Such depositional processes were followed by severe downcutting, probably increased by human activities. From 1957 to nowadays, the Calore River shows an overall increase of straightness and remarkable morphological changes at the confluence of tributary streams. It must be stressed that, since 1958, the Calore River discharge dramatically reduced from several tens of m3/s to less than 10 m3/s, due to the construction of the Apulia Aqueduct. Thus, an almost complete lack of water occurs into the Calore River channel during the summer. Notwithstanding this, even ordinary floodings cause damages to the poor local agriculture and, in some cases, human victims too. The fluvial morphodynamics of the Calore River, inferred from historical dataset, highlighted a notable channel instability, which is not adequately countered by anthropic defences. Such instability, coupled with the intense anthropization of most of the landsurfaces, induces a high flood hazard in the study area, especially near the most densely populated towns.