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Torri D.,CNR Research Institute for Geo-hydrological Protection
Earth-Science Reviews

Gully head development represents a significant geomorphic process in a wide range of environments. Several studies investigated the critical topographic conditions, expressed by local slope gradient (s) and drainage area (A), controlling the development and position of gully heads in various landscapes. This review examines over 39 publications. After critically analysing the reported threshold data and after standardisation of the procedure to determine the critical topographic conditions for gully head development, i.e., sAb>k or s>kA-b some data sets were discarded because they were not compatible with the standard presentation of data as reported by the majority of studies. Hence, a detailed analysis was made of 63 reported s-A relationships for overland-flow induced gully-heads extracted from data sets collected in various parts of the world. A first examination of the behaviour of both the exponent b and the threshold coefficient k, which reflects the resistance of the site to gully head development, shows clear effects of land use on the value of k whereas the value of b does not seem to be affected. Further analyses are conducted of the recalculated threshold coefficients k, for two predefined constant values of the exponent b. The lowest k-values were observed for cropland followed by values for rangeland, pasture and forest. Effects of climate, rock fragment cover at the soil surface and water storage capacity of the gully catchment on k-values were also shown. The most interesting result is that for a given and constant b-value, the threshold coefficient k can be predicted using soil and vegetation characteristics, based on the NRCS Runoff Curve Number values and on surface rock fragment cover.Furthermore, the underlying physical processes explaining the value of the exponent b were analysed. Finally, a physically-based model, well anchored in the established theories, is proposed as a first step to predict gully head development in various landscapes and under changing environmental conditions. The results of this review clearly show that better and more reliable models can be built, including effects of land use, climate changes and natural disasters. © 2013 Elsevier B.V. Source

Wasowski J.,CNR Research Institute for Geo-hydrological Protection | Bovenga F.,CNR Institute of Intelligent Systems for Automation
Engineering Geology

Multi Temporal Interferometry (MTI) stands for advanced synthetic aperture radar differential interferometry (DInSAR) techniques, which include Permanent/Persistent Scatterers Interferometry - PSInSAR™/PSI and similar methods, as well as Small Baseline Subset - SBAS and related/hybrid approaches. These techniques are capable to provide wide-area coverage (thousands of km2) and precise (mm-cm resolution), spatially dense information (from hundreds to thousands of measurement points/km2) on ground surface deformations. New MTI application opportunities are emerging thanks to i) greater data availability from radar satellites, and ii) improved capabilities of the new space radar sensors (X-band Cosmo-SkyMed, C-band RADARSAT-2, TerraSAR-X) in terms of resolution (from 3 to 1m) and revisit time (from 11 to 4days for X-band acquisitions). This implies greater quantity and quality information about ground surface displacements and hence improved landslide detection and monitoring capabilities. Even though the applicability of MTI to regional and local-scale investigations of slow landslides has already been demonstrated, the awareness of the MTI utility and its technical limitations among landslide scientists and practitioners is still rather low. By referring to recent works on radar remote sensing, many regional and local scale MTI application examples from the geoscience literature and our own studies, we present an up-to-date overview of current opportunities and challenges in this field. We discuss relevant technical constraints and data interpretation issues that hamper the use of MTI in landslide assessment. Then guidelines on how to mitigate MTI technical limitations and avoid erroneous interpretations of radar-derived slope surface deformations are presented for the benefit of users lacking advanced knowledge in SAR applications. Finally, in view of the upcoming radar satellite launches, future perspectives on MTI applications are outlined and recommendations for applied research priorities are suggested. We foresee that with regular globe-scale coverage, improved temporal resolution (weekly or better) and freely available imagery, new radar satellite background missions such as the European Space Agency's Sentinel-1 will guarantee ever increasing and more efficient use of MTI in landslide investigations. Furthermore, thanks to the improved temporal and spatial resolutions of the new generation radar sensors, significant breakthroughs are expected in detailed slope instability process modeling (e.g. kinematic and geotechnical models), as well as in the understanding of spatial and temporal patterns of landslide movement/activity and their relationships to causative or triggering factors (e.g. precipitation, seismic loading). © 2014 Elsevier B.V. Source

Manconi A.,CNR Research Institute for Geo-hydrological Protection | Casu F.,CNR Institute for Electromagnetic Sensing of the Environment
Geophysical Research Letters

We study the impact of jointly analyzing the phase and amplitude information of a SAR dataset on the interpretation of the surface displacement over time in areas characterized by large dynamics. In particular, we compute the ground displacement time series over Fernandina and Sierra Negra calderas (Galápagos islands), by applying the Small BAseline Subset (SBAS) and the Pixel Offset (PO)-SBAS techniques to 25 ENVISAT SAR images acquired between 2003 and 2007, when both volcanoes experienced catastrophic eruptions. By merging the SBAS and PO-SBAS time series results the spatial density of measurements increased substantially. In addition, the joint analysis of the time series allows us to better constrain the temporal evolution of the magmatic source volume changes. Our results show that the joint use of the SBAS and PO-SBAS approaches may help for a more correct evaluation of large deformation affecting the Earth's surface caused by eruptions, earthquakes, and landslide phenomena. © 2012. American Geophysical Union. Source

The Murge (Apulia, southern Italy) is the main karst area in the central part of the region, extending from the inland plateau to the Adriatic coastline. Along this transect, a relief energy of a few hundred meters is reached. Even though such relief may seem small when compared to mountain karst areas, actually it is not for Apulia, a very flat carbonate region that acted as the foreland during the building up of the Apenninic Chain in Miocene time. Murge can be subdivided into two sectors: High Murge, the inland plateau, where remnants of an ancient tropical karst are still recognizable; and Low Murge, closer to the sea, with smoother karst morphologies and landforms. Here, some of the most remarkable underground karst systems of Apulia are located: the Castellana caves, a show cave that has been opened since 1939 to tourists (only a few months after the discovery), and the Pozzo Cucù karst system. Overall, the two systems (that are located few hundreds of meters apart) are more than 5,5 km long. In addition, many other karst caves are widespread in the territory, showing different typologies, from percolation shafts, to intrastratal caves, to tectonically-controlled caves, down to marine caves along the coastline. At the surface, other interesting morphological features related to karst may be observed, the main one being the Canale di Pirro polje, which cuts the SE Murge with an E-w strike, until its easternmost reach against the Murge fault line scarp. This latter is the main morphological feature intervening between the Murge plateau and the Adriatic plain. In this article the karst morphological features of Murge are depicted, putting together surface and underground data, in the effort to contribute to the recognition of the main phases of development of karst processes in the region. Source

Maccherini S.,University of Siena | Santi E.,CNR Research Institute for Geo-hydrological Protection
Biological Conservation

Calcareous grasslands are among the most diverse habitats, supporting species-rich vegetation. Propagule limitation and availability of microsites for germination represent major constraints to the successful restoration of these grasslands. To date, little information is available on the effectiveness of seed addition and soil disturbance on the restoration success of encroached semi-natural calcareous grasslands. Here, we conducted a 1year before - 9year after control-impact (BACI) study aimed at testing the effect of the addition of seeds of native species and livestock grazing on calcareous grasslands. Each restoration measure and their combination differed in their impact on these communities and varied over time. Grazing had a significant, beneficial, impact on these communities, although the impact was species-specific. On average, grazed plots were characterized by a higher number of species and a lower vegetation cover. Nine years after treatment application, grazed site were dominated by Trifolium incarnatum subsp. molinerii, Xeranthemum cylindraceum, Orlaya grandiflora, Teucrium chamaedrys and Bromus erectus while ungrazed sites were dominated by B. erectus, X. cylindraceum, O. grandiflora and Prunus spinosa. Only 8 out of 34 species responded significantly to disturbance or/and disturbance and seed addition while 22 species were significantly affected by the sampling year and 18 by a blocking factor. The low recruitment from added seeds and the fact that seed addition is a time-and labor-consuming activity suggests that an adequate level of disturbance and natural regeneration represent the most cost-effective approach to the restoration of these calcareous grasslands. © 2011 Elsevier Ltd. Source

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