Laura Turconi

Catalogue of Rainfall Events with Shallow Landslides and New Rainfall Thresholds in Italy

In Italy, rainfall-induced shallow landslides are frequent and harmful phenomena. The prediction of their occurrence is of social significance for civil protection purposes. For the operational prediction of rainfall-induced shallow landslides empirical rainfall thresholds based on the statistical analysis of past rainfall conditions that triggered slope failures are commonly used. The paper describes a catalogue of 1981 rainfall events, which caused 2408 shallow landslides in Italy in the period 1996–2012. Information on rainfall-induced landslides was collected searching chiefly online newspaper archives, blogs, and fire brigade reports. For each documented failure, we reconstructed the triggering rainfall conditions (rainfall duration D and cumulated rainfall E) using national and regional rain gauge networks. We analysed the rainfall conditions to determine new ED rainfall thresholds for Italy. The calculated thresholds can be implemented in a landslide forecasting system to mitigate landslide hazard and risk.

Detecting torrential processes from a distance with a seismic monitoring network

The detection of debris flows through seismic devices occurs at a certain distance from the channel bed. Ground vibration detectors are installed outside of the flow path, usually along the banks of the torrent or on the surrounding valley slopes, in order to avoid damage or even complete destruction. Seismic networks, however, are also prone to detect other earth surface processes that can be confused with the passage of a debris flow. Recognizing these other processes is important, particularly when the seismic network is used for warning purposes and not only for monitoring. To this aim, two seismic networks were installed in two instrumented basins located in the Italian Alps. Both networks were designed for debris flow monitoring purposes and for testing warning algorithms. In this paper, the seismic recordings of torrential processes that occurred at different distance from the monitoring networks, within and outside the monitored channels, are presented and discussed. It was found that knowledge of the waveform that these different processes produce is critical to the successful design and implementation of seismic networks for debris flow warning.

Yet another disaster flood of the Bisagno stream in Genoa (Liguria, Italy): October the 9th -10th 2014 event

On 2014, 9th October, short and heavy rainfall hit the Bisagno Valley. The Bisagno stream overflowed again and flooded the center of Genoa, causing severe economic damage and a victim. This is the fourth serious flooding of the stream in the last fifty years, which shows similarities with the previous catastrophic ones in 1970, 1992 and 2011, both because of the trigger conditions, determined by the orography of the city of Genoa, and for the weather situations marked by an anticyclonic block converging over the Liguria Gulf.Between 06:00 a.m. on October the 9th and 12:00 a.m. on October the 10th in the Bisagno catchment were recorded some peaks of rain up to almost 140 mm/h and heaps of more than 550 mm/24hrs, which resulted in a rapid increase in the level of all streams of the Bisagno basin and subsequent flooding in the final stretch of the Bisagno stream, where the watercourse underflows covered by a long manhole for the last 1.4 kilometres.Interventions for risk mitigation through more careful weather-hydrology monitoring in nowcasting, the improvement of the civil protection activities, structural works on the watercourse, maintenance of the territory of the Bisagno catchment, a correct information and a timely communication to the population living in high risk areas are all urgently needed.

Monitoring Mud-Flows for Investigative and Warning Purposes: The Instrumented Catchment of Rio Marderello (North-Western Italy)

Mud-flows are natural phenomena that may occasionally occur in mountain torrents. They appear as waves with a steep front and a shape resembling that of debris-flows, but consisting of a muddy slurry that contains much less boulders and granular material than these latter. Nevertheless, mud-flows can cause severe damages to human settlements and infrastructures and may produce many casualties, as much as debris-flows do. The reduced boulder and debris content of mudflows may have an important influence on the results of the monitoring, which might be significantly different than those of debris-flows. This might be particularly true if seismic devices were employed as detecting tools, since the lack of huge boulders and large particles might impede the generation of strong ground vibrations. The ground vibration signals produced by mud-flows might also have different frequency ranges and different peak frequencies. These different behaviors should be investigated, not only for scientific purposes but also because they might lead to the choice of different parameters and algorithms in case seismic sensors were used for warning. For these reasons the Marderello basin, an alpine catchment prone to mud-flows located in North-western Italy, has been equipped with a micro-seismic network. The new monitoring system has been installed in the spring of 2013 and in July a mud-flow occurred that has allowed the collection of the first field data. These latter are presented in this paper together with a characterization of the catchment, a detailed description of the monitoring installations and an outline of future investigation plans.

Flash Flood Events and Urban Development in Genoa (Italy): Lost in Translation

Coastal locations in the Mediterranean area experienced several geo-hydrological events from the beginning of the 3rd Millennium. Among the most flooded areas featuring the Ligurian coastal environment, Genoa is sorrowfully at international level, for the flash flood characteristics and consequent damage: the last event of 4 November 2011, once again, caused the loss of human lives. Genoa, in fact, can be considered an interesting case study for geo-hydrological risks: it can be said that to a general trend of increasing hazard, due to global and particular climate changes of the Mediterranean area, corresponds an increase of the vulnerability due to the urban growth on the flood plains. In this paper are analyzed the unusual meteorological characteristics of the Gulf of Genoa, the changes in the rate of daily precipitation using the recorded data at the station of Genoa, in use since 1833. The most significant periods of the land urban development are also briefly described. They have determined important changes of the territory, modifying the water balance of the basins in a considerable way.

Influence of geological, morphological and climatic factors in the initiation of shallow landslides in North Western Italy

Landslides are recurrent geomorphic processes in Italy and represent a serious economic and societal problem. Historical catalogues report thousands of landslide casualties since the 9th Century. The importance to predict landslide occurrence is particularly evident to prevent the effects of rapid mass movements. The mitigation of landslide-related risk needs the improvement of prediction skills, obtained with a better understanding of triggering mechanisms, which are peculiar of the specific geological and environmental settings. The prominent role of rainfall in mass movement activations is widely recognised in the scientific community and several authors all over the world have long attempted to define the critical values responsible for landslide initiation. In Italy, the National Department for Civil Protection (DPC) is funding a CNR-IRPI (National Research Council-Research Institute for Hydro-geological Protection) research, aiming at the definition of regional rainfall thresholds for shallow landslides for the entire national territory. In this study, we investigated the role of geological, morphological and climatic factors on the initiation of rainfall-induced slope failures in the Piedmont, the Aosta Valley and the Lombardy regions (NW Italy).

Rainfall events with shallow landslides in the Entella catchment (Liguria, Northern Italy)

In recent decades, the Entella River basin, in the Liguria Apennines, northern Italy, was hit by numerous intense rainfall events that triggered shallow landslides and earth flows, causing casualties and extensive damage. We analyzed landslide information obtained from different sources and rainfall data recorded in the period 2002–2016 by rain gauges scattered throughout the catchment, to identify the event rainfall duration, D (in h), and rainfall intensity, I (in mm h−1), that presumably caused the landslide events. Rainfall-induced landslides affected the whole catchment area, but were most frequent and abundant in the central part, where the three most severe events hit on 23–24 November 2002, 21–22 October 2013 and 10–11 November 2014. Examining the timing and location of the slope failures, we found that the rainfall-induced landslides occurred primarily at the same time or within 6 h from the maximum peak rainfall intensity, and at or near the geographical location where the rainfall intensity was largest. Failures involved mainly forested and natural surfaces, and secondarily cultivated and terraced slopes, with different levels of maintenance. Man-made structures frequently characterize the landslide source areas. Adopting a frequentist approach, we define the event rainfall intensity–event duration (ID) threshold for the possible initiation of shallow landslides and hyperconcentrated flows in the Entella River basin. The threshold is lower than most of the curves proposed in the literature for similar mountain catchments, local areas and single regions in Italy. The result suggests a high susceptibility to rainfallinduced shallow landslides of the Entella catchment due to its high-relief topography, geological and geomorphological settings, meteorological and rainfall conditions, and human interference. Analysis of the antecedent rainfall conditions for different periods, from 3 to 15 days, revealed that the antecedent rainfall did not play a significant role in the initiation of landslides in the Entella catchment. We expect that our findings will be useful in regional to local landslides early warning systems, and for land planning aimed at reducing landslide risk in the study area.

Scouring in the Po river basin at the upper plain (Italy)

The Po River basin, the largest in Italy (about 70,000 km2), highlights channel network adjustment at the populated alluvial plain of the upper basin (35,000 km2) related to the geological uplift and hydrological changes. Changes in the upper network result by channel straightening and deepening. Shorter channel length allows faster flood propagation as in 1994 and 2000 floods, the major floods since 1940s in the Po River basin, when peak flow values attained 13,000 m3s−1 at 325 km from the source. Sediment supply is decreasing along the channels and pre–Holocene bedrock is exposed at the channel bottoms that is subject to the surface scratching due to bed-load sediment transfer from the coarse alluvial river banks. Fluvial processes enhance erosion at the river system and scouring at the channel bottom. Scouring effects include water loss from the surface water bed. Hydraulic instability induces bridge hazard.

3D Video Simulation of a Debris Flow

In 2011 a consortium of different institutions leaded by the Civil Protection Department of the Turin Province and including the CNR IRPI, the University of Turin and Thales Alenia, realized a 3D video simulation of a debris flow in motion. The 3D video, which is part of a larger installation that includes also the representation of a landslide and of a snow avalanche, allows a direct interaction with the process through a joystick. This latter, in fact, allows to change the viewpoint of the user, choosing an aerial view, a lateral one or a view that is closer to the ground permitting a more detailed observation of the phenomenon in its progress. The video has primarily instructional and educational purposes, enabling the user to acquire a personal reality of a debris flow and to become aware of its different aspects. It is also an example of the precious support that monitoring data may provide, since the virtual simulation was strictly based on real data recorded in field installations. The 3D video was created as a tool to support the communication activities devoted to explain to the general public the basic principles of civil protection through a direct involvement in a situation of danger. This involvement can be an important stimulus to better understand the natural phenomenon under investigation and to assimilate the basic behaviors needed for self defense. The video was realized with the funds of the European RiskNat project.