Rischio da frana indotto dagli eventi di pioggia in Avigliano (Basilicata)

The urban area of Avigliano is widely affected by a conspicuous proneness to landslides which results in heavy damage to buildings and facilities. Some ancient, recent and current mass movements can be recognized which undergo periodica1 total or partial reactivation due mainly to the unstabilizing influence of repeated rainfalls. Landslides are also caused by earthquakes and by unwary human activities. This paper aims at ascertaining the true incidence of rainfall on the landslides occurring in the urban area of Avigliano, by means of rigorous hydrological and statistica1 methods. Five major landslides were selected based on the following criteria: good knowledge of the corresponding geometrical, geomorphological and evolutionary features, availability of an accurate database on landsliding, triggering causes, reactivations occurred in the last decades following heavy rains, availability of hydrological, geognostic, aerial photography and historical data. The role played by rainfalls in the reactivation of the investigated landslides was studied by applying hydrological and statistical empirical models previously used and checked by the authors. The probability grades of the daily cumulative amounts of rain were also determined broadening the concept of rainfall threshold. These grades may also account for hazard thresholds beyond which landslides may be individully reactivated.