Data collection and geodatabase

Leader: Prof. Paolo Frattini (Università di Milano Bicocca)

Mapping Of Past Landslide Events

Why? Shallow landslides are recognized as highly unpredictable phenomena due to their multiple triggering factors. The occurrence of shallow landslides is controlled by the morphological characteristics of the slope and by the distribution of rainfalls. The knowledge of the exact position and the exact time at which a landslide takes place is fundamental to detect the rainfall threshold and the instability critical conditions of the soil. For this reason, the implementation of a complete database is essential to define all factors involved in the phenomenon.

What? Database of rapid flow-like landslides in Regione Lombardia, inclusive of event date and triggering factors.

How? The creation of the database is performed starting from the union of landslides classified in the IFFI catalog and previous works of landslide mapping carried out by the University of Milan Bicocca. The database is completed by the mapping of landslides through digital aerial photos in ArcGis, which allowed the multiscale and multitemporal analysis of the territory. The use of digital aerial photos permits to locate and know with certainty the source areas of the landslides and to integrate information from other maps (land use, lithology).

Results

The database has been implemented in a GIS environment and is composed of 2450 landslides. Major events are triggered by high intensity short duration rainfall or low intensity long duration rainfall and are located in areas ranging from one hundred to thousands of square kilometers. For each event in the last 30 years the terrain variables were studied by comparing the landslide density with the elevation, the slope, the aspect, the curvature, the Topographic Wetness Index, the lithology and the land use. The analysis has shown correlation between these factors and the landslide density in some cases, especially for the land use, the aspect, the slope and the elevation. These relations differ for every analyzed event suggesting that the interaction of the triggering factors varies in time and space.

The 2000 event

On November 2000 Valtellina was characterized by a rainfall event that caused landslides, for a total of at least 200 collapses. The meteorological event goes from November 13th to November 18th with a maximum intensity of 6.8 mm/h. The affected areas involved the quaternary deposit and in particular the terraced soils, which constitute the 75% of the areas where the instabilities took place. The collapses in terraced slope were caused by the degradation of the dry stone walls due to the insufficient maintenance and to the poor development of the drainage network. The majority of instabilities occurred from the afternoon until the evening of November 17th and the worst consequences were recorded in the Dubino’s area, where two landslides had damaged different buildings.

Ongoing Research

  • Analysis of the return period of triggering events
  • Analysis of the runout of debris flows triggered by rainfall events

Researchers involved in this project

Giovanni B. Crosta, Fabio De Blasio, Paolo Frattini, Agostino Meroni, Claudia Pasquero, Luca Piciullo, Giulia Rusconi, Marco Zangari