Unraveling the Response of a Mountain basin to a Large Disturbance

This work studies the effects of a severe and rare natural disturbance named Vaia (27-30 October 2018) on a mountain basin. It unravels the hydrological, geomorphological and sedimentological responses of the Rio Cordon Basin (Dolomites, Italy) by integrating the findings obtained from three past studies with different spatial scales and focuses of analyses. It combines information about three main topics: (i) identification of geomorphic changes along the channel network, (ii) evolution of the step-pool morphology and (iii) changes in sediment flux and yields. The geomorphic changes registered intense streambed remobilization, boulder mobility, incision and lateral erosion. The step-pool morphology featured a complete disruption, but a fast recovery to the stable condition in just two years. The suspended sediment dynamics, instead, surprisingly showed fluxes and yields (42 t km-2 years-1) that were in line with those registered before the Vaia event (40 t km-2 years-1). Thus, the integration of such findings, obtained through pre- and post-event remote and field-based data, proved to be a valuable approach to comprehend the hydrological and sedimentological responses of a mountain basin affected by an extreme event. Therefore, based on the current morphological and sedimentological condition, it can be concluded that the Rio Cordon is now heading back to the pristine state but with a new dynamic equilibrium since (i) the morphology of the system changed during the Vaia event and (ii) the sediment fluxes and stability of the step-pool configuration resulted in line with the prior event conditions.