Produzione di sedimenti e tassi di erosione a medio termine nei "gullies" della Fossa Bradanica, Basilicata

Marco Piccarreta (*), Mario Bentivenga (**) & Domenico Capolongo (*)
(*) Dipartimento di Geologia e Geofisica, Università degli Studi di Bari, Via Orabona 4, 70125 Bari. E-mail: marcopiccarreta@geo.uniba.it; capolongo@geo.uniba.it (**) Dipartimento di Scienze Geologiche, Università degli Studi della Basilicata, Via Ateneo Lucano 10, 85100 Potenza. E-mail: mario.bentivenga@unibas.it

Medium-term Sediment Production and Erosion Rate in Gullies of Fossa Bradanica, Basilicata. Gully erosion is an important soil degradation process in a range of environments, causing considerable soil loss and producing large volumes of sediment and it has a very significant contribution to total soil loss in Mediterranean areas. Nothwistanding its importance in the soil erosion processes, gully erosion has been long neglected because it is difficult to study and to predict. Consequently, there is a need for monitoring, experimental and modelling studies of gully erosion as a basis for predicting the effects of environmental change (climatic and land use changes) on gully erosion rates. A key issue to be addressed, as the basis for predicting the effects of global changes such as land use and climate changes, is the mapping and quantification of gully erosion and sediment production rates. At present no standardized procedures are available for measuring gully erosion rates and controlling factors. At the medium-time scale (10-70 years) aerial photographs have been analysed to measure temporal changes in length, area or volume of various gully tipes. In this respect, contribution has been the use of multi-temporal DEMs to map active gully areas and compute sediment production and deposition within gullies. In Basilicata (Southern Italy), agricultural soils underwent continuous degradation during the last century due to the highly erodible nature of outcropping terrains and to the anthropic pressure favoured by the introduction of Common Agricultural Policy (CAP) measures, which, especially in the last 30 years, has led to the reclamation of scrub lands and badlands for durum wheat cultivation. All these practices have accelerated the natural soil erosion processes, leading to the depletion of soil organic matter (i.e. reduction of soil structure stability) and favouring crusting, runoff production, gully erosion and shallow mass movements. On the basis of these considerations, some research questions remain open, the most importance one in Basilicata is: what is the contribution of gully erosion to overall soil loss and sediment production at different temporal and spatial scales and under different climatic and land use conditions? In this paper we attempt to answer to this question adopting the consolidate procedure in GIS to determine medium-term sediment production and deposition rates in a large gullies of Fossa Bradanica, Basilicata, Southern Italy. This method, which is based on the subtraction of multi-date elevation values from digital elevation model, does not produce significant errors in the estimetes and has been considered as a valide technique in the estimating net erosion in gully areas. Infact, in comparison with other methods, it also includes sediment produced by processes other than only overland flow, i.e. downcutting, headcutting, and mass movements and bank erosion.

gully erosion, erosion rates, aerial photo interpretations, GIS, digital elevation model, Basilicata