On the assessment of the management priority of sediment source areas in a debris-flow catchment

In many Alpine catchments the monitoring and hazard mitigation of debris-flow events require enormous economic and social resources. To confront these problems, a subjective estimation of the most hazardous zones of the basin could be useful in the best, sustainable planning of protective measures. In this paper, a new methodology is proposed that develops a Management Priority Index (MPI) to rank sediment source areas by their quantitative capability to deliver debris-flow volumes to a point of interest within the catchment. The MPI sets the intervention priority based on a combination of three sub-indicators: a susceptibility indicator evaluating the overall catchment predisposition to generate debris flow, a triggering indicator and a volume budget indicator assessing the rate of deliverable volume to a selected outlet. MPI was applied to the basin of the Rio Gadria catchment (Venosta Valley, Bolzano, Italy), an alpine basin with an unlimited sediment supply that is characterized by multiple, very active, shallow landslides and bare soil zones. The proposed ranking method was successfully verified using post-event surveys and through evidence from consolidation check dams built over many years in the basin.