Sviluppo di metodi per la valutazione quantitativa dell'intensità della denudazione e della relativa pericolosità in bacini idrografici italiani.

During the years 2002-2004, geomorphological studies focused on the quantitative evaluation of denudation processes within dilferent drainage basins. These studies, started in some cases since long ago, were further deepened, and extended to a wider number of basins, representative of varied morphostructural conditions. The study areas are located in Southern Central Italy and belong to the Fiume Ombrone drainage basin (Toscana), the middle Fiume Tronto valley (Marche), the drainage basins of Fiume Paglia, Fiume Mignone and Torrente della Mola (Lazio), some catchments belonging to the main basin of rivers Cavone (Basilicata) and Trionto (Calabria). Preliminary quantitative geomorphic analyses allowed the indirect evaluation of denudation entity through the elaboration of morphometric parameters and the hypsometric analysis; results obtained helped the identification of drainage basins and subbasins affectcd by the very intense denudation. The complex cause/effect relationships among factors influencing both the morphogenesis and the plano-altimetric configurations of drainage basins resulted in the wide variability of denudation index (Tu) values ranging from 183 t/km2/year (T. della Mola drainage basin, Lazio) to 5700 t/km2/year ( T. Bretta drainage basin, Marche). Very high values (Tu> 6000 t/km2/year) were calculated for small catchments belonging to the wider basins of rivers Ombrane, Paglia, Tevere, Cavone, where quick morphological modifications occur due to the action of surface running waters and gravity. Drainage basins affected by the most intense dcnudational processes were equipped with several observation stations which recorded the punctual modifications of topographic surfaces with time. Some of these stations have been working continuously since 1993 (MARINI1,1995; DEL MONTE & alii, 1998: DEL MONTE, 2003, whereas some others have been monitored for shorter time intervals between 1993 and nowadays. Briefly, direct measurements relevant to periods longer than a decade, indicated mcan annual values of denudation ranging between 1 and 2,5 cm/year for slopes affected by sharp-edged and/or rounded edged badlands. Higher denudation rates were obtained for shorter observation periods (3 up to 4 cm/year); still higher cares were recorded for short periods at the gully bottom or in coincidence mirh mass movements before bench mark were torn up or damaged. Finally, direct and indirect evaluation of denudation rates for one of the study areas with long term records at a dense monitoring network, coupled with detailed long term geomorphological field surveys, were used as informative bases to evaluate accelerate erosion hazards. Thus, a map of accelerate erosion hazard was drown, that has the merit of being based on numerical data and easy readable. This map can evidence the probability of the different areas to overcame o mean denudation rare of 1 cm/year; starting from the available database, it is possible to elaborate the hazard map relevant a chosen denudation rate showing the desired number of classes