Recent geomorphological changes of the Middle and Lower Calore River (Campania, Italy)

In recent years, many studies focused on both the recent geomorphological changes of river channels and the role played by human interventions in inducing them. In general, these studies converged in pointing out a tendency to narrowing and incision of the examined rivers, even if, very recently, some exceptions were highlighted locally. In Italy, most part of the existing studies were carried out on rivers located in Northern and Central regions, while a general lack of information about Southern Italy seems to arise from literature. Filling this gap could unquestionably help in understanding the scale at which these phenomena occur. In this study, the geomorphological changes experienced by the Middle and Lower Calore River (Campania region, Southern Italy) between 1957 and 1998 were investigated. This study is part of a wider research aimed to detect and interpret the geomorphological changes experienced by such watercourse in a wider time span. The Calore River starts from Accellica Mount and flows down for some 110 km before joining the Volturno River. As a first step of this study, both 1:25000-scale topographic maps, dated back to 1957 and previously rasterised, and 1:10.000 nominal-scale orthophotos, dated back to 1998, were georeferenced and introduced into a GIS. The river channel and the centerline were, then, manually digitized. Using GIS, the channel width was measured along more than 2500 transects. Fluvial bars were also mapped and classified. To calculate the sinuosity index, the channel was subdivided into 11 reaches, according to the dominant direction of the valley axis. Finally, bridges and quarries were also mapped. The results showed that, in the considered time span, the Calore River underwent a shortening of its length of about 2.8 km. The overall sinuosity also decreased (1.37 in 1957 versus 1.33 in 1998), even if a very slight increase was detected in the uppermost reaches where human interventions are negligible or absent. The maximum, minimum and mean width of the channel also significantly reduced. In particular, mean width decreased from 30.2 m in 1957 to 21.8 m in 1998. The overall extension of fluvial bars reduced by more than 83%, while their number increased from 151 to 381. Particularly, the reduction of the number of point-bars was a consequence of 37 meander cut-offs, these latter also responsible of the decrease of the channel sinuosity. It was also noted that 13 mid-channel bars were dissected by the watercourse and their remnants joined the surrounding floodplain. Both the meander cut-offs and the dissection of the mid-channel bars witnesses a tendency to incision of the river and an increase of its erosive power. These evidence are particularly clear both in proximity of quarries, currently inactive, and downstream to bridges built before than 1957. In particular, where these bridges are present, a sudden changes in planform geometry is clearly observable in the field. In fact, upstream to the bridges, the river is wider and no sedimentary bodies are evident, while downstream the channel is narrower, straighter, characterized by several kinds of fluvial bars and the flow is more turbulent. The increase of erosive power due to bridges could also have played a role in favoring the relatively fast migration of the meander formed by Calore River in 1957 just upstream to its former confluence into Volturno River, which led to the shifting of the confluence itself of some 1 km north-westward. In fact, immediately upstream to the former meander, two bridges very close each other and built before and after 1957, respectively, are present. In conclusion, notwithstanding the short duration of observation, the Calore River displayed remarkable changes in its planform geometry. The results are coherent with the data reported in the pre-existing literature. Finally, the role of human interventions looks evident, as the most clear changes were detected in proximity of bridges and/or quarries.