PRELIMINARY-STUDY OF THE EROSION MECHANISMS IN A BIANCANA BADLAND (TUSCANY, ITALY)

Italian badlands are present along the Appennini mountains, with an annual precipitation which ranges from 400 to 1200 mm. The genesis of these badlands has often been studied, whereas current processes and erosion rates have only rarely been examined and measured. This paper describes a preliminary study on a badland developed in temperature mediterranean climate and located in SW Tuscany (Italy). The selected site is characterized by biancane, dome-shaped features a few meters in height, generally having a vegetated NNE aspect and severely eroded SSW slope, with a sub-horizontal basal pediment. Field rainfall and runoff experiments were carried out. Field results were substantiated by data collected in specially devised laboratory tests. It was concluded that near-surface pipes - which develop at the point of contact between a surficial layer of weathered and severely fractured regolith and the less fractured and weathered regolith underneath - are the main drainage channels, while rills play a secondary role. Soil detachment is largely due to mechanical and chemical slaking of the regolith during infiltration. The role of runoff is almost solely transport. In particular, it was found that the runoff detachment rate is limited by the rate at which the water front penetrates into the regolith.