RAINFALL AND LANDSLIDES IN AVIGLIANO URBAN AREA (BASILICATA, SOUTHERN ITALY)

Polemio, M. (CNR CERIST, c\o Istituto di Geologia Applicata e Geotecnica, Politecnico di Bari, Via Orabona 4, 70125 Bari, Italy) & Sdao, F. (DISGG, Basilicata University, Potenza, Italy)

In Basilicata (Southern Italy) in the last decades there has been periodically a widespread and severe susceptibility to landslides, often involving urban areas with consequent serious damage, caused and/or intensified by even unexceptional rainfall events. A times this susceptibility to landslides has been so widespread and visible as to create a form of geomorphological crisis on the slopes. In particular, reference is made to that which occurred following the rainfall events of the November 1959, March 1973, November 1976, April 1985 and December 1990.

Studies have shown that the many landslides produced following these rainfall events were for the most part in the form of rototranslational or translational slides, often evolving into earthflows. Although there were first - time landslides, the major part of the mass movements can be attributed to the total or partial mobilization of already existing slide bodies. While some large mass movements were also produced, the greater part of the landslides were in the form of superficial slides, often with a depth of only a few metres. It has been the aim of this work to highlight the existence and intensity of the influence exerted by rains in triggering selected landslides occurring in Avigliano urban areas, with reference to their main geomorphological and morphoevolutive features.

Landslides are developed in a sandy-conglomerate succession, lying on a structurally complex marly clay. Landslides are rototranslational or translational slide. In particular, the Gianturco and Lagariello landslides are relevant: they are frequently remoulded by rainfall. The first one was remoulded many times in the last forty years, especially on November, 1976 and April, 1985. The Lagariello landslide was particularly remoulded on April, 1978 and 1985.

The complex of rainfall - landslide events is studies by means of a hydrological - statistical method which employs as primary data the totals of the daily rainfall by time periods of between 1 and 180 days. These hydrological variables are associated with each rainfall-landslide event and compared statistically with the almost 100 year historical series of rainfall data which is available. In this way the critical rainfall period is determined for a specific landslide and the return time is quantified of the hydrological event associated with the landslide. The calculation of suitable statistical coefficients allows the comparison between the different rainfall-landslide events.