Francesco Fiorillo

Introductory editorial thematic issue: Mediterranean karst hydrogeology

This Special Thematic Issue of Environmental Earth Sciences (EES) is a collection of contributions from authors of the Mediterranean region in the specific field of karst hydrogeology. The editors invited well known researchers from Mediterranean countries, some of whom are members of the International Association of Hydrogeologists (IAH) Karst Commission, and encouraged them to provide a general or case history paper. Apologies are made to authors who were not invited with the hope to involve them in future projects. The idea to have such an issue originated during a meeting organised by the IAH-Italian Chapter in preparation for the 42nd Congress of IAH to be held in Rome in September 2015 (AQUA 2015). This opportunity is taken to thank the President of the Organising Committee of the IAH Congress, Marco Petitta, (University of Rome ‘‘La Sapienza’’) and Jo de Waele (University of Bologna) who have supported the idea and facilitated arrangements for this Special Thematic Issue. Support of the Editor in Chief of EES, James LaMoreaux, who approved the idea and followed up the publication process, is gratefully acknowledged. Thanks are also given to the Italian IAH Chapter, University of Rome ‘‘La Sapienza’’ and University of Sannio, which supported this issue. Finally, papers in this issue provide material that complements the Guides for several of the excursions organised on the occasion of this congress. Interest in karst aquifers continues to increase worldwide mainly because groundwater resources in these environments are generally more abundant than those in other environments which have been greatly exploited. In Mediterranean countries research in the field of karst hydrogeology has a long history and most methods have been applied and/or developed in various case studies in this region. The importance of karst aquifers in the Mediterranean area also relates to locally specific climatic conditions, characterised by long, dry and hot summers. Especially in the southern and eastern parts of the Mediterranean, the dry period could extend more than 6 months while in contrast the wet period could be reduced to 1–2 months. In such a climatic context variation of groundwater reserves in karst aquifers and the deficit of water in waterworks during dry periods (summer–autumn) is more the rule than the exception. Many engineering master works have been constructed in the past with the aim of regulating karst aquifer regimes; protecting fresh ground water from sea water intrusion; or keeping vulnerable karstic waters from uncontrolled pollution. These attempts have had great importance in the historical and economic development of the Mediterranean area as well as its civilization. The most powerful karst springs were easily tapped, and gravity channels allowed water to be supplied to high concentrations of people. Most large towns along the shoreline built up in the vicinity of large karstic springs. Ancient Rome and its empire are probably the most significant example: powerful karst springs fed ancient aqueducts, supplying large quantities of water for towns, villages, harbours, thermes and pools. More than 13 m/s of water flowed during that time & Francesco Fiorillo francescofiorillo@libero.it; francesco.fiorillo@unisannio.it

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.

The Recession of Spring Hydrographs, Focused on Karst Aquifers

This study constitutes a review of spring hydrograph recession analysis, and it is focused on karst aquifers. The different literature models have been separated into empirical and physically-based models; in the last ones, only analytical models have been considered, as they provide the discharge equation during recession. Under constant geometrical and hydraulic aquifer characteristics, it has been found that the “exponential form” appears to be the most recurrent theoretical type, at least during the long-term flow recession. During this stage, any deviation from the exponential form, may suggest hydraulic anisotropy of actual aquifers, as well as aquifer geometry has a fundamental role in controlling the shape of spring hydrographs. The hydrodynamics of karst aquifer under recession has been described, associating any segment of the hydrograph to a specific hydrologic condition of the aquifer, and also to a specific physical law which control the water flow.

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.

Geological features and landslide mechanisms of an unstable coastal slope (Petacciato, Italy)☆

Abstract On the basis of geological and geomorphological surveys, landslide phenomena are analysed on a slope along a stretch of the Adriatic coast, near Petacciato (Molise, Italy). Locally, a blue clay sequence of Pleistocene outcrops, stratified with silty-sandy layers; bedding dips 3–8°NE and the slope has a similar attitude. This sequence evolves upwards to sands and conglomerates, with thickness of up to 40 m, on which the built-up area is located. Several episodes of landslide reactivation occurred in the past century, involving the zone between the built-up area and the sea, along a coastal slope of over 2000 m long and 200 m high. Important roads and railway lines have been heavily damaged as well as the town itself. The typology of the movement is a rotational–translational slide; the displacement reaches tens of centimetres at each reactivation episode along the entire coastal slope, extending well beyond the shore line. Detailed studies already exists, but different mechanism failures have been proposed to explain the landslide phenomena. In this study, a new failure mechanism is proposed, (sudden spreading of Terzaghi, K., Peck, R.B., 1948. Soil Mechanics in Engineering Practice. Wiley and Sons New York) and analytical approaches have been adopted to evaluate the slope stability, based on the geotechnical and monitoring data and the geometrical and geological features of the slope.

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.

KARST AQUIFER DRAINING DURING DRY PERIODS

2 Abstract: We analyzed hydrographs of five karst springs in southern Italy during the recession period using ten continuous years of daily discharge measurements and provided conclusions on the aquifer behavior under dry periods and droughts. A straight line was fitted to a semilogarithmic plot (log-discharge versus time), and the recession coefficient (the slope of the line generated from the equation) was calculated for each spring and for each year considered. A deviation from the straight line produced by a simple exponential decay of discharge through time provides information on the actual emptying rate of the aquifer compared to a simple exponential decline. If the recession coefficient decreases or increases, the aquifer is empting more slowly or more quickly than expected, respectively. Water level of a monitored well inside the karst catchment was also assessed and provided information on the water distribution into aquifers. The results describe the hydraulic behavior of karst aquifers during their emptying and provide information for better management of karst springs.

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.