GIARDINO M., AUDISIO C.
Analisi storica e geomorfologica di fenomeni alluvionali in ambiente montano: casi di studio in Val Soana (Alpi Graie, Piemonte) – Historical and geomorphological analysis of alluvial phenomena in the mountain environment: casestudies in the Soana Valley, (Graie Alps, Piemonte)
Pages 183-191
Abstract
The mountain environment is often interested by alluvial phenomena affecting both the main fluvial river and the tributary alluvial fans. In both cases, the consequences of paroxysmal events can be very dangerous for peopl e and anthropic structures. Th is study shows applications of an integr ated methodology to support the geomo rphological hazard assessment in a mount ain environment . Th e meth odology is based both on an historical and a geomor phological analysis of alluvial ph enomena. Th e analysis of historical information defines the «historic al/s teady-state time» evolut ion of a phenomenon. The field analysis establishes the steps of the «geomorphological/dynamic time» and the spatial distribution of a phenomenon. So, the integrated analysis allows to get spatial/ temporal information concerning processes and landform evolution of alluvial fans or mountain rivers. The study area is in the Soana Valley (Turin province), in the Graie Alps, a typical alpine region of the North -Western Piemont e, near the Aosta Valley. The historical information and geomorphological data collection put in evidence a lot of paroxysmal alluvial events in the past (1654 and 1845 A.D.) and in recent times (1993 and 2000). In particular, the ancient events data allowed to establish the reactivation time of the alluvial fans; also allowed a compa rison between morphodynamic processes along the Soana mountain river and damage typology for man-made structures during the last two alluvial events . In a first case-study, the integrated methodology allowed to reconstruct the geomorphological evolution of the Soana river , pointing out that the river’s abrupt changes towards a br aided pa tte rn is not an exception linked to the stronger alluvial events , b ut the natura l tend ency of the Soana river. In the second case this methodology enables the spatial and temporal analysis of geomo rphological activity along tr ibutary torrents: this leaded to the definition of frequency, intensity and spatia l distribution of paroxysmal phenomena of debris flows in the Soana Valley. Th e integrated methodology resulted as a very import ant tool for a better definition of alluvial hazards and for a future evolut ion outlook on morphogenetic processes of the mountain environment.