Assessing the susceptibility to water-induced soil erosion using a geomorphological, bivariate statistics-based approach

The aim of this study was the assessment, at basin scale, of the susceptibility to water-induced soil erosion processes(i.e. gully erosion and sheet/rill erosion)using geomorphological analysis, Geographical Information Systems(GIS)and bivariate statistics. The study was carried out in awatershed located in Southern Italy. A detailed analysis of thepre-existing literature led to select lithology, land-use, slopeangle and slope aspect as soil-erosion determining factors(DFs), as they are ‘‘non-redundant’’ and affect both the soil-formingprocesses that control soil erodibility and the erosivepower of running waters. Water-produced erosional landforms,such as gullies and areas severely affected by sheet/rillerosion, were surveyed andmapped using classical techniquesof geomorphological analysis. The GIS processing of thegeomorphological data allowed calculating the areal density ofthese landforms in each DF class. Weighting values (Wi),corresponding to the susceptibility level of each DF class,werecalculated using bivariate statistics. Finally, GIS overlay proceduresof the thematic maps, previously reclassified on thebasis of the calculated Wi, allowed to produce two SusceptibilityMaps (i.e. Gully Erosion and Sheet and/or Rill ErosionSusceptibility Map). The soil-geomorphological coherence ofthe produced results has been checked and widely discussed inthe framework of the pre-existing literature. Both the geomorphologicalcoherence of the calculated Wi and the results ofthe validation procedure suggested a good reliability of themethod, which is also relatively easy to apply and update.