Sediment yield for erosion evaluation in a small Apennine watershed, and location of sediment sources through the use of the USLE model and of air photo interpretation.

Sediment yield for erosion evaluation in a small Apennine watershed, and location of sediment sources through the use of the USLE model and of air photo interpretation. D. Pavanelli, A. Bigi, M. Rigotti Corresponding Author: D. Pavanelli, Dipartimento di Economia ed Ingegneria Agrarie, Università di Bologna, V.le G. Fanin 50, 40127 Bologna, Italy. Tel:+39 051 2096168, Fax:+39 051 2096171, E-mail: donatella.pavanelli@unibo.it Soil erosion in the Apennines is quite a relevant issue, being a cause of land degradation and reducing the land available to farming. Mountain areas abandonment worsened landscape situation, because of the lack of erosion direct and indirect control. Estimates of soil erosion activity in a mountain basin are usually made with a significant degree of uncertainty, because usually few data are available to calibrate erosion models or to directly estimate eroded soil amount, thus leading to inability of taking decision in conservation policies. In order to evaluate the suspended sediment yield (SSY) carried by the Gaiana torrent, a ~9 km2 basin in the Bologna Apennines, we applied a very simple linear model previously built on a geomorphologically similar watershed nearby, which has a very large SSY dataset. This model estimates average SSY from the maximum rainfall intensity on a storm event basis: the simplicity of the model allowed its application on scarcely gauged basins, where precipitation is the main erosive agent, giving reasonable estimates of soil loss. According to the philosophy behind this approach, we applied the USLE model to the Gaiana catchment, in order to have a further estimate of the order of magnitude of the sediment yield and to test our methodology. We also realized a chart of geomorphology and soil erosion by air photo interpretation, in order to be able to locate the source areas of sediment production. Furthermore, a river monitoring station along with a water samples has been installed at the Gaiana basin outlet. The few collected data since December 2004 have been employed to further verify the linear model efficiency. GIS analysis has been fundamental for extracting USLE factor from the digital elevation model of the basin, and to analyse vegetation cover and geomorphology of the Gaiana basin, as well as for air photo elaboration.