Stream recovery in protected areas: planning with a geomorphological approach

San Lucano Valley (Belluno, Italy) is included in the UNESCO System n.3: award of "World Heritage" area. The land use in the valley is not intensive and there has not been interference to the riparian zone, since the flood of 1966, during which the majority of the existing trees (conifer) were uprooted. After 1966, an exceptional riparian forests of Alnus incana and Fraxinus excelsior with some Mountain Maple and Spruce, took over. These forests are of high natural interest for the E. C.: (site BL28 from Natura 2000 network), and constantly under observation and carefully preserved. For these reasons, the lower Tegnas River has become an open-laboratory to study the stream and how it adjusts from past periods to recent morphodynamic events, and to verify the applicability of the methodology referred as Watershed Assessment of River Stability and Sediment Supply (Rosgen, 2006) in the morphological context of the Alps and in their hydroclimatic environment. The stream geomorphology shows the evidence of channel changes during over 50 years. Quaternary fluvial deposits, postglacial landslides and debris flows are filling the valley bottom with a 200m thick covering. The gravel of this flat area must be periodically quarried to ensure the hydraulic protection of the sideway road, but the newly rebuilt banks are quickly eroded due to the floods and the streambed becomes impracticable and unsuitable for spontaneous fish habitats and for forest growth. The monitoring of streams over time, modeling their geomorphologic trends, gives some contribution to understand the erosion-transport-deposition process in order to reset a more stable, long-lived, riverbed with natural solutions. This may be a useful approach in restoration plans, in order to make the riverbed renaturalization more stable and improving the accessibility to the riparian zone, without disregarding the preservation of the natural environment quality.