Rockfall Hazard and Risk Assessment Along a Transportation Corridor in the Nera Valley, Central Italy FAUSTO GUZZETTI* PAOLA REICHENBACH IRPI CNR via della Madonna Alta 126, 06128 Perugia Italy SILVIA GHIGI Cousultant via del Polacchino 21, 06012 Citt di Castello Italy ABSTRACT / Rockfalls are a common type of fast-moving slope failures, and in many countries they represent the pri- mary cause of landslide fatalities. We present a methodology to ascertain rockfall hazard and to determine the associated risk along transportation networks. The proposed methodol- ogy is based on the combined analysis of the recurrence of rockfall events, determined from historical information, the fre- quency-volume statistics of rockfalls, obtained from invento- ries of recent rockfall triggering events, and the results of a physically based, spatially distributed rockfall simulation model used to determine rockfall hazard. The available information on rockfall hazard is combined in a Geographic Information System with a map of the transportation network to identify the road sections potentially subject to rockfalls. Information on the location and type of rockfall defensive measures, in- cluding revetment nets, elastic fences, concrete walls, and artificial tunnels, is used to estimate the efficacy of the defen- sive structures and to determine the level of the residual rock- fall risk along the roads. To illustrate the methodology, we dis- cuss an application in a 48-km 2 area in the Nera River valley, in the Umbria Region of central Italy, where rockfalls are abun- dant, and where considerable investments were recently made to mitigate rockfall risk. Rockfalls are a common type of fast-moving land- slide and represent a major hazard in mountain areas worldwide (Whalley 1984, Flageollet and Weber 1996). According to Varnes (1978), a rockfall is a fragment of rock (a block) detached by sliding, toppling, or falling, that falls along a vertical or subvertical cliff, and pro- ceeds downslope by bouncing and flying along para- bolic trajectories or by rolling on talus or debris slopes. Rockfalls range from small cobbles to large boulders hundreds of cubic meters in size, and travel at speeds ranging from a few to tens of meters per second. De- spite their small size compared to other landslide types, rockfalls are among the most destructive mass move- ments (Whalley 1984, Rochet 1987, Evans and Hungr 1993, Evans 1997). In Italy, rockfalls represent a pri- mary cause of landslide fatalities (Guzzetti 2000). A rockfall was the cause of the largest historical landslide catastrophe in the Umbria Region of central Italy, when six people were killed near Stifone, along the railway connecting Terni to Rome, on May 10, 1939 (Guzzetti and others 2003a). Although rockfalls are widespread and highly de- structive, only a few attempts have been made to estab- lish hazards and the associated risk in large mountain areas or along transportation corridors (Pierson and others 1990, van Dijke and van Westen 1990, Evans and Hungr 1993, Brunce and others 1997, Hungr and oth- ers 1999, Guzzetti and others 2003b). We present a methodology to ascertain the rockfall hazards and de- termine the associated risk along transportation net- works. The methodology is based on the combined analysis of a) the recurrence of rockfall events, deter- mined from the available historical information on rockfall occurrence; b) the frequency volume statistics of rockfalls, obtained from detailed inventories of re- cent rockfalls; and c) the results of a physically based, spatially distributed rockfall simulation model, which are used to identify the road sections most subject to rockfall hazard. Comparison of the results of the hazard model with the position of rockfall defensive structures, including revetment nets, elastic fences, concrete walls, and artificial tunnels, is used to estimate the efficacy of the defensive measures and to determine the level of the residual rockfall risk for vehicles traveling along the roads. To illustrate the methodology, we discuss a case KEY WORDS: Rockfall; Hazard; Risk; Defensive measures; Transporta- tion network Published online July 13, 2004. *Author to whom correspondence should be addressed, email: fausto.guzzetti@irpi.cnr.it DOI: 10.1007/s00267-003-0021-6 Environmental Management Vol. 34, No. 2, pp. 191–208 © 2004 Springer Science+Business Media, Inc.