A GIS-based approach for gully erosion susceptibility modelling: a test in Sicily, Italy

Abstract

The aim of this study is to analyze the susceptibility conditions to gully erosion phenomena in the Magazzolo River basin and to test a method that allows for driving the factors selection. The study area is one of the largest (225 km2) watershed of southern Sicily and it is mostly characterized by gentle slopes carved into clayey and evaporitic sediments, except for the northern sector where carbonatic rocks give rise to steep slopes. In order to obtain a quantitative evaluation of gully erosion susceptibility, statistical relationships between the spatial distributions of gullies affecting the area and a set of twelve environmental variables were analyzed. Stereoscopic analysis of aerial photographs dated 2000, and field surveys carried out in 2006, allowed us to map about a thousand landforms produced by linear water erosion processes, classifiable as ephemeral and permanent gullies. The linear density of the gullies, computed on each of the factors classes, was assumed as the function expressing the susceptibility level of the latter. A 40-m digital elevation model (DEM) prepared from 1:10,000-scale topographic maps was used to compute the values of nine topographic attributes (primary: slope, aspect, plan curvature, profile curvature, general curvature, tangential curvature; secondary: stream power index; topographic wetness index; LS-USLE factor); from available thematic maps and field checks three other physical attributes (lithology, soil texture, land use) were derived. For each of these variables, a 40-m grid layer was generated, reclassifying the topographic variables according to their standard deviation values. In order to evaluate the controlling role of the selected predictive variables, one-variable susceptibility models, based on the spatial relationships between each single factor and gullies, were produced and submitted to a validation procedure. The latter was carried out by evaluating the predictive performance of models trained on one half of the landform archive and tested on the other. Large differences of accuracy were verified by computing geometric indexes of the validation curves (prediction and success rate curves; ROC curves) drawn for each one-variable model; in particular, soil texture, general curvature and aspect demonstrated a weak or a null influence on the spatial distribution of gullies within the studied area, while, on the contrary, tangential curvature, stream power index and plan curvature showed high predictive skills. Hence, predictive models were produced on a multi-variable basis, by variously combining the one-variable models. The validation of the multi-variables models, which generally indicated quite satisfactory results, were used as a sensitivity analysis tool to evaluate differences in the prediction results produced by changing the set of combined physical attributes. The sensitivity analysis pointed out that by increasing the number of combined environmental variables, an improvement of the susceptibility assessment is produced; this is true with the exceptio...

Gully erosion susceptibility assessment by means of GIS-based logistic regression: A case of Sicily (Italy)

“…Rainfall temporal distribution influences runoff hydraulics and soil moisture: the former regulates flow erosivity while the latter before rainfall events influences both generation of runoff (Descroix et al, 2002;Castillo et al, 2003;Capra et al, 2012) and soil resistance to erosion (Bocco, 1991;Nachtergaele et al, 2002;Poesen et al, 2003;Torri et al, 2006;Bou Kheir et al, 2007;Magliulo, 2012;Torri et al, 2012b). Volume and velocity of concentrated flow are controlled by topographic attributes such as contributing drainage area, slope curvature and slope steepness (Moore et al, 1988;Vandekerckhove et al, 1998Vandekerckhove et al, , 2000aPoesen et al, 2003;Valentin et al, 2005;Zucca et al, 2006;Gómez Gutiérrez et al, 2009a, b;Kakembo et al, 2009;Nazari Samani et al, 2009;Capra et al, 2012;Svoray et al, 2012;Chaplot, 2013;Conoscenti et al, 2013). Depth and cross-sectional morphology of gullies are regulated by erodibility of soil horizons (Ireland et al, 1939;Imeson and Kwaad, 1980;Poesen et al, 2003) and characteristics of geological substrata (Vandekerckhove et al, 2000a;Zucca et al, 2006;Conoscenti et al, 2008;Conforti et al, 2010;Lucà et al, 2011;Marzolff et al, 2011;El Maaoui et al, 2012).…”

“…Hence, the calculated probability values can be used to generate maps of gully erosion susceptibility, showing how proneness to this phenomenon changes spatially. Different statistical methods have been recently adopted to predict spatial distribution of gully erosion on various spatial scales (see Table 1), from the field scale to the continental scale (Meyer and Martínez-Casasnovas, 1999;Hughes et al, 2001;Chaplot et al, 2005;Bou Kheir et al, 2007;Geissen et al, 2007;Conoscenti et al, 2008;Gómez Gutiérrez et al, 2009a;Conforti et al, 2010;Magliulo, 2010;Akgün and Türk, 2011;Lucà et al, 2011;Märker et al, 2011;Magliulo, 2012;Conoscenti et al, 2013).…”

Estimation of intrinsic aquifer vulnerability with index-overlay and statistical methods: the case of eastern Kopaida, central Greece

“…Despite the limited adoption of statistical methods for aquifer vulnerability studies, other branches of the earth sciences have extensively used these approaches in a wide range of applications (e.g., Conoscenti et al 2013;Lombardo et al 2014;Sahragard and Chahouki 2015). The procedure involves the identification of a dependent variable that a given algorithm, among the several available in literature, multivariately explains through a set of covariates.…”

Physiography of the Sicilian region (1:250,000 scale)

“…The final map was checked and validated through field surveys and matched with several published geomorphological maps at a local scale (Agnesi, Di Maggio, & Macaluso, 1995;Agnesi, Di Maggio, Macaluso, Madonna, & Messana, 2000;Agnesi, Cappadonia, & Conoscenti, 2007;Ciampalini et al, 2013;Conoscenti et al, 2013;Daina et al, 1979;Giorgianni, Giunta, & Pipitone, 1997;Monteleone, Pipitone, & Sabatino, 2000Monteleone, Sabatino, & Bambina, 2006;Pulice et al, 2012).…”