Hazard Zoning for Landslides Connected to Torrential Floods in the Jerte Valley (Spain) by using GIS Techniques

Abstract

The Jerte Valley is a northeast-southwest tending graben located in the mountainous region of west central Spain (Spanish Central System). Mass movements have been a predominant shaping process on the Valley slopes during the Quaternary. Present day activity is characterized as either ‘first-time failure’ (shallow debris slides and debris flows) or ‘reactivations’ of pre-existing landslides deposits. A delineation of landslide hazard zoning within the Valley has been carried out by using the detailed documentation of a particular event (a debris slide and a sequel torrential flood, which occurred on the Jubaguerra stream gorge), and GIS techniques. The procedure has had four stages, which are: (1) the elaboration of a susceptibility map (spatial prediction) of landslides; (2) the elaboration of a map of ‘restricted susceptibility’ in the particular case of slopes that are connected to streams and torrents (gorges); (3) the elaboration of a digital model which relates the altitude to the occurrence probability of those particular precipitation conditions which characterized the Jubaguerra event and (4) the combination of the probability model with the ‘restricted susceptibility map’, to establish ‘critical zones’ or areas which are more prone to the occurrence of phenomena that have same typology as this one.