Geomorphological analysis of the Serio River aimed at its sustainable management

Abstract

The study of the historical evolution of rivers is a requirement for their sustainable management.  This work aims to investigate the historical geomorphological evolution and the present evolutionary trends of the valley portion of the Serio River (Lombardia, Italy) in order to propose a sustainable management of its river corridor. In particular, we focus on the planimetric evolution of the active channel from 1954 until today through the analysis of: (i) channel morphological configuration, (ii) variation of channel width, and (iii) bank erosion rates. Analyses were based on multi-temporal orthophoto mapping in GIS environment (with the highest temporal resolution over the last 25 years) along a valley segment of about 80 km. Results show that in 1954 the Serio River was characterised by a braided pattern in the segment flowing through the high plain and by a sinuous-meandering in the segment flowing through the lower plain. In the sinuous and meandering segment, where the morphology configuration did not change over time, the active channel width decreased from a maximum of about 80 m in 1954 to a minimum of about 35 m until the 1970s-80s and then it remained stable due to the construction of anthropogenic works along the banks. The braided reach narrowed from a maximum of about 350 m in 1954 to a minimum of about 130 m in 1988, with decreases in the braiding index. By the 1990s, active channel width alternated phases of widening and narrowing (between about 10 m and 40 m). Correspondence between the widening and the occurrence of flood events was observed. Moreover, the high river dynamic, with a continuous lateral migration of the active channel, resulted in bank erosions that locally reaches up to 100 metres in a time interval of 1-5 years. The final outcome of this study was to propose integrated management solution aiming at the mitigation of geomorphic hazards and at the improvement of the morphological status of the river, through the delineation of areas of potential future lateral erosion.