Successes and failures in fighting landslides: some experiences from Italy and elsewhere

When is an action taken to cope with a hazardous mass movement considered a success ? When is it necessary to admit failure ? This paper attempts to give an answer to these questions by examining the three main aspects of a landslide risk management programme: prediction, prevention (or mitigation) and emergency planning. Examples of successes and failures are given with reference to some of the best known case histories that have occurred, more or less recently, in Italy and elsewhere in the world. The recent developments of scientific research regarding the different aspects of landslide risk management are briefly outlined. As far as the prediction phase is concerned, the state-of-the-art on landslide risk assessment and the basic differences between spatial and temporal prediction are briefly summarized and discussed. The GIS database of the Emilia-Romagna region, containing over 30 000 individual landslides, is presented as a successful example of a spatial prediction containing elements for temporal forecasting. The exceptional 1996 Versilia rainstorm that triggered more than 450 debris flows, causing 13 casualties, is described as a representative case of an unpredictable event. A general framework for the main strategies and techniques employed for landslide risk prevention is proposed. A successful case history, the urban transformation accomplished in the second half of the 19th century on the San Miniato hill of Florence is presented: the architectonic transformation, of high artistic and landscape value, was combined with an effective stabilization of the hill, the instability of which was documented in a number of historic documents starting from the 11th century. The 1998 Sarno disaster is illustrated as an example of prevention failure: a series of debris flows caused 161 casualties in the suburbs of Sarno and Quindici, where uncontrolled urban development took place on areas historically exposed to high hazard. The basic requirements of a successful emergency plan are therefore discussed, such as monitoring and warning systems and simulation techniques for risk scenario analyses. The emergency plan devised and implemented after the occurrence of the 1993 La Josefina landslide in Ecuador is presented as a success: the landslide produced a dam on the Rio Paute and the successive emergency measures managed to reduce the losses caused by the dam breaching and overtopping to a minimum. Finally, the well-known 1963 Vaiont disaster is proposed as a representative example of unsuccessful emergency planning: more than 1 700 casualties were caused by the catastrophic flood wave generated by the sudden failure of a huge mass of rock into a reservoir.