Giuseppe Spilotro

Assessing landslide exposure in areas with limited landslide information

Landslide risk assessment is often a difficult task due to the lack of temporal data on landslides and triggering events (frequency), run-out distance, landslide magnitude and vulnerability. The probability of occurrence of landslides is often very difficult to predict, as well as the expected magnitude of events, due to the limited data availability on past landslide activity. In this paper, a qualitative procedure for assessing the exposure of elements at risk is presented for an area of the Apulia region (Italy) where no temporal information on landslide occurrence is available. Given these limitations in data availability, it was not possible to produce a reliable landslide hazard map and, consequently, a risk map. The qualitative analysis was carried out using the spatial multi-criteria evaluation method in a global information system. A landslide susceptibility composite index map and four asset index maps (physical, social, economic and environmental) were generated separately through a hierarchical procedure of standardising and weighting. The four asset index maps were combined in order to obtain a qualitative weighted assets map, which, combined with the landslide susceptibility composite index map, has provided the final qualitative landslide exposure map. The resulting map represents the spatial distribution of the exposure level in the study area; this information could be used in a preliminary stage of regional planning. In order to demonstrate how such an exposure map could be used in a basic risk assessment, a quantification of the economic losses at municipal level was carried out, and the temporal probability of landslides was estimated, on the basis of the expert knowledge. Although the proposed methodology for the exposure assessment did not consider the landslide run-out and vulnerability quantification, the results obtained allow to rank the municipalities in terms of increasing exposure and risk level and, consequently, to identify the priorities for designing appropriate landslide risk mitigation plans.

Landslide susceptibility assessment in Apulian Southern Apennine: heuristic vs. statistical methods

In this paper, a bivariate-heuristic model (modified Stevenson’s method) and two multivariate statistical procedures (discriminant analysis and logistic regression) were used in order to assess and map landslide susceptibility in the north-western side of Daunia region (Apulia, Southern Italy). The whole Daunia region is characterized by complex and composite landslides, which are located on clayey slopes, near urban centers, affecting structures and infrastructures. The high predisposition to landsliding of the Daunia hillslopes is related to the very poor strength properties of clayey formations. The comparative analysis of landslide susceptibility using different methods, on the same test site and with the same inventory map allowed understanding the dependence of the results from the dataset and the capability of models under different levels of use, from expert to simple operator. By comparing the performance of the three models through the success rate curves, it emerges that the simple modified Stevenson’s method produces reliable outcomes, comparable with those deriving from more complex multivariate statistical models. This result is related to the characteristics of clayey slopes, in which the landslide occurrence is so much controlled by the poor strength properties of the clayey formations that the multivariate analysis of a large set of morphometric, geological and land-use variables results to be somehow superfluous. This suggests that, for clayey slopes, a simple, easy-to-manage bivariate-heuristic model based on expert opinion can be used with reliable results.

Evaluating the quality of landslide inventory maps: comparison between archive and surveyed inventories for the Daunia region (Apulia, Southern Italy)

A landslide inventory map, which shows the location of landslide phenomena and contains information about movement type, activity, etc., is a basic element for landslide susceptibility and risk assessment. For this reason, the evaluation of the quality, in terms of accuracy and completeness, of landslide inventory maps is an important issue. In this paper, two landslide inventory maps are compared, in order to determine the corresponding quality, through a direct comparison, aimed to evaluate the degree of cartographic matching between the maps, and the determination of the statistical properties of landslide areas and the comparison between the frequency-area statistics of landslides contained in the two inventories. The two landslide inventory maps at 1:25,000 scale, used for these analyses, have been produced for Daunia region (Apulia, Southern Italy), by the Apulia River Basin Authority; the first, “archive inventory”, by unifying the existing archive inventories; the second, “surveyed inventory”, through aerial-photo interpretation and field investigations.

Rockfall trajectory modeling combined with heuristic analysis for assessing the rockfall hazard along the Maratea SS18 coastal road (Basilicata, Southern Italy)

In this paper, a study aimed to assess the rockfall hazard along a portion of the SS18 coastal road, located in the coastal area of Maratea (Basilicata Region, Southern Italy), is presented. The relevance of this study derives from the location of the study area, because the SS18 is a strategic roads in a touristic area, and, since the hazard assessment was performed in 2004 within a project financed by the Viability Regional Department of Autonomous National Company of Roads (ANAS), from the possibility to validate the results by using real rockfall events occurred after 2004. The procedure for assessing the rockfall hazard was composed of four sequential analyses: (i) geomechanical and kinematic characterization of rock mass, (ii) implementation of Romana’s (1985) Slope Mass Rating (SMR) method for identifying the potential boulder release areas (rockfall initiation areas), (iii) determination of rockfall trajectories by using a 3D numerical model (ROTOMAP), (iv) calculation and mapping of the hazard index by combining three factors, i.e., (a) lithological features of outcropping materials on rock faces, (b) kinematic compatibility defined by simulating the rockfall trajectories, and (c) spatial distribution of occurred rockfall events. Finally, the proposed methodology was validated by combining the distribution of the hazard levels along the road with the location on the SS18 of the rockfall events occurred from 2004 to 2014.

GIS-based predictive models for regional-scale landslide susceptibility assessment and risk mapping along road corridors

ABSTRACT In this paper, a study aimed to assess the landslide susceptibility at a regional scale for the wide provincial territory of Matera (Basilicata region, southern Italy) and the relative risk along the main road corridors distributed in this area is presented. A heuristic-bivariate statistical predictive model was performed to assess and map the landslide susceptibility in the study area by using a polynomial function of eight predisposing factors, weighted according to their influence on the instability process. The resulting susceptibility map was successively used for assessing the landslide risk along the provincial road network. The importance of these roads, representing the main network connecting the urban centres, derives from the absence of an efficient integrated transportation system through the entire regional territory. The landslide risk was evaluated through a matricial approach, which has allowed to define the risk levels (low, medium and high) along road stretches by overlapping the consequences and hazard maps, by combining their corresponding classes in a matrix and by associating to each combination a risk level. The resulting landslide risk map provides support information for decision-making and for identifying the priorities for the design of appropriate mitigation plans.

The 20,000-years-long sedimentary record of the Lesina coastal system (southern Italy): From alluvial, to tidal, to wave process regime change

The present-day Lesina area (Adriatic coast of southern Italy) preserves in the subsurface the stratigraphic signature of a recent sedimentary process regime change, which was responsible for the conversion of a former alluvial plain into a back-barrier tidal flat and, finally, into the modern barrier island. Facies-based analyses of the first 55 m of the upper Pleistocene–Holocene stratigraphic record, integrated with biostratigraphic sampling, radiocarbon data, and aerial observations of some diagnostic relict morphologies, allowed us to reconstruct the history of the last 20,000 years of this area. The succession investigated is adjacent to a salt dome, which uplifted in recent times, forming the easternmost boundary of the present-day Lesina lagoon. Three main stratigraphic intervals were detected in the subsurface: the lowermost unit is made up of conglomerates, sandstones, and mudstones of terrestrial origin, belonging to a complex system of alluvial plain filling a pre-existing Last Glacial Maximum (LGM) topography. The second interval consists of sands and muds, with subordinate conglomerates of brackish and marine origin, and lies on the previous one through a wide ravinement. Its composing lithofacies exhibit a strong tidal signature preserved in tidal rhythmites belonging to a net of tidal channels, associated with marshes, mud flat, and lagoonal deposits. These sediments record the emplacement of a back-barrier tidal flat, which developed under the strong influence of a tidal influx enhanced by the late post-LGM transgression. The third uppermost interval resulted from the deposition of coastal-marine sands and gravels accumulated during the ensuing modern normal regression, under the dominance of a wave-dominated coastal dynamics, which was responsible for the progradation of the present-day beach barrier and the closure of the Lesina lagoon. The paleogeography of the back-barrier tidal flat preceding the onset of the modern barrier island is thus reconstructed based on the results of our facies analysis, biostratigraphy, and AMS dating. Many of the elements composing this mid-Holocene tide-influenced system were also interpreted from the aerial-photograph observation of several relict morphologies, which are still preserved in many parts of the modern Lesina barrier island. We propose some new interpretation on the origin some of these elements, which possibly developed under sedimentary process regimes different from the modern ones, including some flood-tidal deltas, previously interpreted as tsunami-derived washover fans.

Mass transport triggered by heavy rainfall: the role of endorheic basins and epikarst in a regional karst aquifer

This study aims at recognizing the mechanisms of mass transport between the karst surface and the saturated zone in a morpho-structural relief of the Mesozoic karst carbonate platform of Murgia (Puglia, Southern Italy). The large dimension of the karst aquifer, the regional scale of the flow system, the boundary condition constituted by the sea, and the lack of freshwater springs constrain to the use of wells as monitoring points and limit the study area to the recharge area comprising 986 endorheic basins. The concentrations of non-reactive tracers (nitrates) in the waters of autogenic recharge (from endorheic basins) have been modelled through the evaluation of effective infiltration, land use, and nitrogen surplus, with reference to a time window, which includes a low precipitation period followed by significant rainfall events. The comparison between the modelled nitrate concentrations and the nitrate concentrations measured in ground waters, coupled with the analysis of groundwater chemograms and records of hydraulic heads (all referred to the same time window), allows inferring the mechanism of mass transport between the karst surface and the groundwater table. The mass transport conceptual model requires the presence of the epikarst. The infiltration of significant rainfall in the endorheic basins after a low precipitation period displaces waters stored in the epikarst towards the saturated zone. Ground waters in the post-evet period show higher concentrations of nitrates, lower concentrations of Total Organic Carbon and higher Mg/Ca ratios than both those of the pre-event period and the autumn-winter recharge period. The post-event recharge from epikarst storage determines a transient hazard of groundwater pollution with a time lag from the occurrence of the heavy rainfall.

Dynamic response of a rocky cliff under the sea wave pulse: a study along the Adriatic coast of Polignano (Apulia, Italy)

The dynamic behavior of a rocky cliff under severe sea waves has been analyzed in the location of Polignano, facing on the Adriatic coast of Apulia, Southern Italy. In this area, the classical and, at the same time, complex problem of the stability of a cliff in calcareous rocks is burdened by the presence on the top of the cliff of the ancient town. To analyze the behavior of the cliff under the impulsive transfer of energy generated by the sea waves, two types of measures were carried out on the rocky mass: (1) ambient noise and (2) strong-motion records. The first type of measures, which may be executed in a short time with a high spatial density, has provided a recognition of the intrinsic and anisotropic dynamic behavior of the coastal cliff. The accelerometric records, carried out during heavy storms in December 2009 and January 2010, allowed to evaluate the energy transfer from waves to cliff, in terms of maximum values and temporal and directional distribution. To facilitate a correct interpretation of the measures, also a geomechanical characterization of the rocky mass has been carried out through the Rock Mass Rating system Bieniawski (The Geomechanics Classification in Rock Engineering Applications. Proceedings of the 4th ISRM Cong., Montreux, pp 51–58, 1979), Bieniawski (Engineering Rock Mass Classifications. Wiley, New York, p 251,1989) and the Markland’s test (A useful technique for estimating the stability of rock slopes when the rigid wedge sliding type of failure is expected, pp 10,1972). The first allowed to classify the rocky masses in terms of quality, the second one to individuate the potential failure mechanisms of the cliff.

La Piccola Età Glaciale nell'area di Taranto (Puglia, Italia)

Little Ice Age in the Taranto Area (Apulia, Southern Italy).The present study focuses on the key role that the interactions between sea level changes and standing and hydrogeological mechanisms played on the evolution of the interconnected dynamics of the actual geomorphological and hydrogeological system of the Taranto area, from the Quaternary to nowadays. Moreover the retrieval of historical maps and files allowed us to recognize clear tracks of the Little Ice Age in the area of interest.

Geomorphological Complexity in Landslide Susceptibility Modelling

In this work, the role of the geomorphological complexity factor on landslide susceptibility models is analyzed. The landslide susceptibility is generally modeled by evaluating the relationship between the spatial distribution of instability factors (environmental and triggering factors) and the distribution of the existing instability phenomena (landslide inventory). The geomorphological features of slopes can be considered as predisposing factors of instability. The geomorphological complexity can be defined as the descriptive feature which synthesizes and classifies the multiplicity of effects which determine the topographical surface and which are determined by the sequence and overlapping in time of the morphogenetic factors. Moreover, the geomorphological complexity is an important factor for the prediction of landslides, as it reveals the hillslope evolution, i.e. the effects induced by mass movements and by surface drainage conditions. In this paper, the Authors attempt to develop a preliminary procedure for generating a thematic map, representing the spatial distribution of complexity factor in a determined study area.