The impact of anthropogenic activities on the geomorphological evolution of the Taro River over the last 70 years

Abstract

Human pressures, in response to economic development and population growth, have been one of the main drivers of river systems changes especially since the second half of the last century. In the European context, anthropogenic impacts mainly concern with catchment land use changes, in-stream gravel mining, and in-channel works construction. The reconstruction of the past evolutionary trajectories and the temporal analysis of driving factors is considered fundamental to understand present river conditions, to support channel network management and to anticipate future changes. The aim of this study is to investigate the anthropogenic factors that have impacted the geomorphological evolution of the Taro River (Northern Apennines, Italy) over the last 70 years. Traditional methods based on multi-temporal orthophoto (1954, 1976, 1988, 1994 and 2020) analysis in GIS environment were used for studying historical channel changes along a channel segment 90 km long. Analyses of anthropogenic factors that may have influenced changes in the active channel included: (i) analysis of land use changes at the catchment scale, (ii) quantification of gravel mining activities, and (iii) analysis of in-channel work constructions. Results showed that between 1954 and 1976 the Taro River channel width decreased by 39% on average, mainly in response to gravel mining activities, and subsequently to the increase of works into the channel. To the contrary, as a result of mining activities abandonment in the early 1980s, and of the occurrence of an extreme flood event in 1982, an increase of 18% in the active channel width was observed in 1988. The decreases in active channel width in the last 30 years (since the end of the 1980s) were correlated with the increase in forested areas in the catchment and with the increasing degree of stabilization of channel banks. These studies are fundamental to identify management solutions in degraded rivers and to anticipate impacts in such rivers still featuring poorly impacted channel morphologies.