Francesco M. Guadagno

Long karst spring discharge time series and droughts occurrence in Southern Italy

A series of long karst spring discharges have been analysed to determine trends, fluctuations and relationship to rainfall. Data come from aquifers in southern Italy, and in some cases cover more than one hundred years of records. Based on yearly discharge data, hydrological series show the drop of the discharge after 1986, which has been interrupted by the recent wet years of 2009 and 2010. This drop is connected to the decrease in annual rainfall, but other factors also seem to contribute to this phenomenon. Based on monthly scale data series, the relationship between meteorological and hydrological droughts has been analyzed, using the standard precipitation index (SPI). As karst systems are large reservoirs, only longer meteorological droughts induce groundwater droughts, and the start, duration and time-lag of the hydrological droughts have been evaluated.

Multi-temporal Maps of the Montaguto Earth Flow in Southern Italy from 1954 to 2010

Historical movement of the Montaguto earth flow in southern Italy has periodically destroyed residences and farmland, and damaged the Italian National Road SS90 and the Benevento-Foggia National Railway. This paper provides maps from an investigation into the evolution of the Montaguto earth flow from 1954 to 2010. We used aerial photos, topographic maps, LiDAR data, satellite images, and field observations to produce multi-temporal maps. The maps show the spatial and temporal distribution of back-tilted surfaces, flank ridges, and normal, thrust, and strike-slip faults. Springs, creeks, and ponds are also shown on the maps. The maps provide a basis for interpreting how basal and lateral boundary geometries influence earth-flow behavior and surface-water hydrology.

Storminess and geo-hydrological events affecting small coastal basins in a terraced Mediterranean environment

This study was prompted by the occurrence of an extreme Damaging geo-Hydrological Event (DHE) which occurred on October 25th 2011 and which affected a wide area of the northern Mediterranean region. After analysing the storm by means of the precipitation time series, the study attempts to relate the October 25th 2011 DHE with a series of other DHEs that occurred in the period 1954-2012, assessed via the use of historical data and classified according to severity, with a Storm Erosivity Indicator (Ra). The annual mean of the Ra value (2582 MJ mm ha(-1) h(-1) y(-1)) confirmed that the study area is one of the European regions with the highest rainfall erosivity level. A shift in storminess during 1991-2012 with respect to 1954-1990 was observed. A return period of 1000 years was calculated for the single storm erosivity of October 25th, which contributed to 84% of the total annual storm erosivity of 2011 A quite good agreement was found comparing DHE distribution and severity with Ra anomalies over time. As a matter of fact, most of the low severity DHEs (62.5%) occurred in years in which the Ra was below the average value. Moreover, almost all DHEs (93%) ranging from medium- to very high-severity occurred in years for which the Ra exceeded the average value. With regard to the occurrence of the most severe DHE classes, a threshold of the Ra and a recurrence time of approximately 3300 MJ mm ha(-1) h(-1) y(-1) and 12 years, respectively, were identified. Finally, some evidences suggest that an increasing frequency of DHEs is expected in the forthcoming years. It is argued that understanding these issues is a major priority for future research in order to improve land and urban planning strategies for preserving people and the environment, leading ultimately to an effective risk reduction.

Predicting Monthly Spring Discharges Using a Simple Statistical Model

Current precipitation and past climate variability induce considerable intermonthly fluctuations in spring discharges. This study presents the DISHMET model (Discharge Hydro-Climatological Model) developed to perform historical spring reconstructions in the lack of physical assumptions. We analyzed discharge data of the Caraventa spring, located on the southern side of Mount La Montagna in Southern Italy, which has been monitored since the 1996s. The La Montagna aquifer is tectonically and litologically complex and deformed bedding controls the groundwater flow. Due to this aspect a parsimonious model should be more suitable than a complex model in spring discharge estimation. Thus, the DISHMET model incorporates monthly and annual precipitation only. The model is able to estimate sufficiently well the monthly fluctuations of groundwater discharge. DISHMET can be easily used to assess historical discharge, even when hydrological data is discontinuously available. The magnitude of this discharge is linked to the frequency and type of weather patterns transiting over the central Mediterranean area during the autumn and winter seasons. It is mainly related to the local precipitation that recharges the Mt. La Montagna aquifer. An analysis of antecedent rainfall and spring discharge reveal moderate to strong relationships.

Reconstruction of long-term earth-flow activity using a hydroclimatological model

This study presents a new proxy for the reconstruction of the historical activity of large earth flows. A simple relationship between rainfall, temperature and groundwater levels was established using available monthly time series and subsequently utilized to develop the Landslide Hydrological Climatological (LHC) indicator to simulate the effects of hydroclimatic influence on slope stability for the Montaguto earth flow in Southern Italy. In order to identify phases of earth-flow activity, an empirical threshold was assigned. Our result indicates a different response of the earth flow to hydroclimatic stress with both ordinary and extraordinary reactivations over the historic period. Additional information suggests that earth-flow reactivations are clustered in the spring and an extraordinary earth-flow activity follows periods with a LHC below the average. A modeling result shows that the LHC is able to realistically reconstruct the long-term activity of a complex earth flow with only a few false-positives in a very long period of application. Thus, it can be considered as a tool for long-term earth-flow activity reconstruction and assessment.

Space–time prediction of rainfall-induced shallow landslides through a combined probabilistic/deterministic approach, optimized for initial water table conditions

In landslide-prone areas the magnitude of events is related to recurring rainfall intensity. In a large sector of the Sannio Apennines (Southern Italy), predictive mapping of recurrent shallow landslides was undertaken by combining deterministic and probabilistic predictive approaches. This, with the aim to minimize the negative influence of the uniform distribution of the initial water table depth in steady condition that usually influence the theoretical instability resulting from the application of methods for large-scale estimation. The deterministic approach was performed by means of the Transient Rainfall Infiltration and Grid-based Regional Slope-stability model to obtain triggering maps in multi-temporal transient pore-water pressures. The optimized physical modeling was validated by back-analysis on large-magnitude landslide events which occurred in 2003 by means of the introduction of two cross-mapping correlation indexes. Subsequently, different predictive scenarios were proposed for different probabilistic return periods of the rainstorm events. The output data permitted the definition of a linear log regression curve to estimate the theoretical instability of the study area. This curve is defined as a function of cumulative precipitation, duration and return periods of the possible rainfall events.

Initiation and propagation of the 2005 debris avalanche at Nocera Inferiore (Southern Italy)

Pyroclastic deposits covering most of the carbonate relief of the Campania Apennines are prone to develop frequent high-velocity flow instabilities. The present study investigates the debris avalanche that occurred at Nocera Inferiore (Campania Region, Southern Italy) on March 4, 2005 which claimed three casualties. The landslide involved the 1.5 to 2 m thick layered pyroclastic mantle which overlies the carbonate hill slopes. The slope movement initiated as adebris slide, then producing a debris avalanche on the 40°-dipping open slope, which had never been affected by a landslide of the same type as the one that occurred. Landslide initiation is linked to a morphological change of the slope due to the building of a carriage path to be used as access for the nearby open quarry. Reconstructionscarried out on aerial and ground photographs of different dates highlighted that the road construction likely took place around 1998, increasing the landslide susceptibility at this location. The propagation characteristics of the landslide were modelled by using 2D and 3D dynamic codes (DAN-W and DAN 3D, respectively), in order to investigate the applicability of the 3D model with the rheological parameters of previous calibration of DAN-W in Campania Region.Although, these analyses are well comparable with those implemented in the past, they highlight that it is unlikely to derive a unique set of values for the rheological parameters to be used on similar landslides over the entire region. Accuracy of back-analysis results strongly depends on the quality and availably of comparative input data, suggesting the need to improve calibration for each site within the region, enlarging information from similar cases and using statistical treatments.

The Mount Pizzuto earth flow: deformational pattern and recent thrusting evolution

ABSTRACT The Mount Pizzuto earth flow has been periodically active in recent decades. Early in 2006, it surged and created a dam across the Ginestra torrent. Episodic floods induced by the earth-flow dam periodically damaged a section of a local road and power and telephone service lines. This paper presents a map showing deformational structures along the flow and a geometric reconstruction of thrust faults at the earth-flow toe from 2006 to 2014. The map, produced on the basis of field observations, shows the spatial distribution of back-tilted surfaces, flank ridges and normal, thrust, and strike-slip faults. Springs, creeks, and ponds are also shown on the map. The map indicates that the earth flow is composed of five kinematic zones. Cartographic data and the spatial–temporal reconstruction of the thrusting evolution offer the basis for interpreting the (mid-term) kinematics of the flow and its controlling factors, and for assessing the influence of earth-flow movement on torrent channel capacity.

Regression analysis for seismic slope instability based on a double phase viscoplastic sliding model of the rigid block

Semi-empirical models based on Newmark’s sliding block permit the estimation of expected co-seismic displacements in relation to one or more parameters which characterize the ground motion that theoretically caused them. Taking this into consideration, a regression analysis, based on a double-phase viscoplastic (DPV) model, was developed using 96 Italian ground motion accelerograms for a total of 1,448 combinations obtained for different parametric conditions of the indefinite slope model. Repeated stability analysis, performed by means of the DPV model, allows for the assessment of the seismic instability of a slope in relation to different reached behaviour levels, as well as seismically induced permanent displacements. At these behaviour levels, co-seismic increases and possible subsequent decreases of viscoplastic shear strengths are associated. This implies that the post-seismic persistent mobility (collapse) of the slope can be obtained from the computation. On the other hand, coherently with the increasing of shear resistances during fast sliding displacements in clay soils, the seismic-forced displacements result substantially lower than corresponding values obtained by means of the rigorous Newmark’s sliding block. In addition, in relation to some seismic ground motion parameters, regression and functional border and separation curves were obtained with the aim of providing an expeditious seismic slope stability evaluation in reference to the co-seismic and post-seismic behaviour of clayey slopes. Regarding this, the real behaviour of two historical landslide events is discussed in the light of the results of the regression analysis outlined in this work.

Structural and lithostratigraphic controls of earth-flow evolution, Montaguto earth flow, Southern Italy

This paper aims to define the control exerted by geological setting on the evolution and segmentation of the Montaguto earth flow in Southern Italy. A detailed geological survey and multi-temporal maps were used to reconstruct the geological model of La Montagna Mt. and to quantify the evolution of the flow in terms of sediment pulse formation, movement direction and spatial change in earth-flow area. The spatial distribution of structural fabric of the mountainside was compared with (1) planar geometry of earth-flow source area, (2) orientation of strike-slip faults bounding the earth-flow moving core (i.e. movement direction) and (3) kinematic-zone position and extent. We infer that the evolution of the earth flow is controlled by geological structures and lithology. Moreover, the entire basal-slip surface is composed of newly formed basal-slip surface in the source area, and corresponds to pre-earth-flow topography downslope from the neck. Implications of our work are that (1) a detailed geological model of an unstable mountainside, combined with information about earth-flow spatial evolution, might be considered as a tool that allows the localization of areas of possible earth-flow enlargement and (2) geological structures constrain earth-flow movement, inducing a predictable seasonal behaviour in terms of movement direction.