O. Terranova

Landslide inventory map for the Briga and the Giampilieri catchments, NE Sicily, Italy

On 1 October 2009, a high intensity storm hit the Ionian coast of Sicily, SW of Messina, Italy. The Santo Stefano di Briga rain gauge, located 2 km W of the Ionian coast, recorded 225 mm of rain in seven hours. The intense rainfall event triggered abundant slope failures, and resulted in widespread erosion and deposition of debris along ephemeral drainage channels, extensive inundation, and local modifications of the coastline. Landslides occurred in a territory prone to slope failures, due to the local geological and geomorphological settings. Many landslides were related to the presence of roads lacking adequate drainage. Abandoned terraced slopes lacking proper drainage, and unmaintained dry walls were also related to slope failures. Damage was particularly severe in small villages and at several sites along the transportation network. The shallow landslides and the inundation resulted in 37 fatalities, including 31 deaths and six missing persons, and innumerable injured people. After the event, an accurate landslide inventory map was prepared for the Briga and the Giampilieri catchments. The map shows: (i) the distribution of the event landslides triggered by the 1 October 2009 rainfall event; (ii) the distribution of the pre-existing slope failures; and (iii) other geomorphological features related to fluvial processes and slope movements. The landslide inventory map was prepared at 1:10,000 scale through a combination of field surveys and photo-interpretation of pre-event and post-event, stereoscopic and pseudo-stereoscopic, aerial photography. Different types of aerial photographs were analysed visually to prepare the landslide inventory map. The event landslides were mapped through the interpretation of pseudo-stereoscopic colour photographs taken shortly after the event at 1:3500 scale, combined with digital stereoscopic photographs at approximately 1:4500 scale, taken in November 2009. The pre-event landslides and the associated geomorphological features were mapped using 1:33,000 scale aerial photographs flown in 1954, 1955, and 2005. The event and pre-existing landslides were checked in the field in the period October–November 2009.

Landslide-risk scenario of the Costa Viola mountain ridge (Calabria, Southern Italy)

ABSTRACT The study area of the Costa Viola mountain ridge is strongly exposed to shallow landslides triggered by rainfall. Starting from a susceptibility map, recently published by the same team, the related risk has been assessed, limitedly to landslide sources. The hazard has first been evaluated by considering the recurrence periods of triggering events. Economic value and physical vulnerability of the types of elements at risk have been assumed by considering land-use and the effects of similar events in Southern Italy, respectively. The 1:30,000-scale risk map (Main Map) has been produced by combining the above-mentioned layers. Low risk prevails in the study area, whilst the highest values are concentrated along the coast, where villages and the main infrastructure are located. The expected annual damage exceeds 570 million € (about 68% pertaining to low-risk cells). Risk maps produced through similar simplified geographic information system-based procedures may play a crucial role in accurate land-use planning and effective decision-making.

CM SAKe: A Hydrological Model to Forecasting Landslide Activations

Worldwide, most landslides are generally triggered by rainfalls. In this paper, the hydrological model CM SAKe to forecast the timing of activation of slope movements is described.

Shallow-Landslide Susceptibility in the Costa Viola Mountain Ridge (Italia)

The “Costa Viola” mountain ridge (Calabria) is exposed to severe geo-hydrological risk conditions, especially in the sector between Bagnara Calabra and Scilla. This sector has repeatedly been affected by slope instability events in the past, mainly related to debris slides, rock falls and debris flows.

Hydrological characterisation of possible triggering scenarios in slope instability.

One of the most frequent landslide triggering causes are rainfalls which can determine such variation in pore pressures to reduce the shear strength and to determine slope instabilities. To realize failure mechanisms, surveys, investigations and analysis are expensive indispensable conditions. Then hydrological models are very useful to define scenarios that could trigger landslides generally classifiable and connected to homogeneous geoenvironmental contexts. Three classes of instabilities are considered: shallow (SH), medium deep (MD) and deep (DD) landslides. The hydrological analysis has been carried out referring to geo-environmental contexts in which landslides, referable to the considered classes, are traceable. For SH the employed procedure consists of analysing the heaviest rainy events. The analysis of rainfalls cumulated at the daily scale on prolonged periods or an indirect analysis of the soil moisture content, through the AR(1) autoregressive model, are used to study MD. For the DD, temporal periods longer than one rainy season are considered. A monthly temporal scale is then adopted with reference to cumulated rainfall and to the AR(1) model. Results allow us to define possible triggering scenarios for the considered instability classes and in the ambit of the geo-environmental contexts chosen as references. The scenarios we found may allow us to calibrate the instability mechanisms referring to simplified geotechnical schemes individuated as representative of homogeneous geo-environmental contexts.

Probabilistic Definition And Analysis Of Severe Rainy Events

Human activities are often subject to damages resulting flom exceptional rainy events. The character of exceptionality of a rainy event may be due only to one or to many factors. In particular the total rainfall amount the maximum intensity, the average intensity and the total duration affect the natural catastrophic phenomena. Based on this concept, a methodology to identi~ severe rainy events is proposed, with the aim to select and characterize those events potentially more dangerous to human activities. The single normal rainy event is simply defined by being preceded and followed by at least one not rainy day; the events are considered severe according to the overcoming of one or more threshold values of the aforesaid factors. The study refers to the method of peaks over threshold (P.O.T.), based on the theory of the rare events and on the extreme values theory. The fust theory was introduced by Poisson and aims exclusively to define the relations between the number of events and their low probability of occurrence; the second theory is usually adopted for the annual maximum analysis and deals just with the size of the events, with no account for their number. Actually the reduction law of the number of events when the threshold values are increasing is illustrated by simple correlative relationships. An application to rainfall data of the North area of Stretta di Catanzaro (Calabria, Southern Italy) is proposed, comparing the results with those of an hktorical investigation regarding landslides and flooding. The analysis allows to assess the temporal and spatial distribution of the most severe events and to evaluate their hazard for forecasting and/or real-time alert system identification. Particular sites and year periods that are more frequently subject to severe events are identified, in this way we can identi~ homogeneous regions keeping constant values of parameters.

Geomorphic effects caused by heavy rainfall in southern Calabria (Italy) on 30 October–1 November 2015

ABSTRACT A severe rainfall event occurred in southern Calabria between 29 October and 2 November 2015, causing two deaths and serious damage to transport infrastructure. Widespread slope erosion and thousands of shallow landslides were triggered on the slopes, combined with flooding and transport of debris along the streams. Rains recorded by the regional gauge network and the national radar monitoring system were analysed by means of Kriging techniques. Ground effects were surveyed in the field, and mapped using post-event air photos taken along the coastal sector. Shallow landslides, soil erosion (including sheet, rill, and gully erosion), flooding, lateral erosion, and debris deposition along streambeds, overflow on lateral slopes, and fan deposition at the mouths of the streams were mapped at 1:60,000 scale. Isohyets of the rainfall event – in terms of cumulative maxima over 24 h – are also shown on the Main Map. In Annex A, a list of notices of processes and/or damage, arranged by municipalities, with coordinates, types of ground effect, and synthetic descriptions, is also provided.