Soil loss and landslide susceptibility evaluations at the Hills of Freisa Vineyards (Central Piedmont, Northwestern Italy)

In the paper, the potential soil loss and the landslides susceptibility have been evaluated means of empirical models at one of the hilly sites candidate as “Typical Piedmont Vineyard Landscapes: Langhe, Monferrato, Roero” to the World Heritage List of UNESCO. The study area is defined as “Core 1 – Freisa” and its territory is included within the municipalities of Albugnano, Castelnuovo Don Bosco, Moncucco Torinese and Pino d’Asti all in the Asti district. It is located along the north-western boundary of the Piedmont central hill system, outlined by a wide ridge crown converging towards the Chieri Plain, near the administrative border of the Turin district. The territory possess a historical viticulture tradition, characterized by the culture of the autochthon vines of Freisa and Malvasia. The viticulture is diffused on the sunny slopes, with high quality production and increasing extension; an intricate shrub and wood vegetation grows on the steeper slopes and the lateral watershed. The rich culture mosaic presents parcels of small size also with seminative cultures, separated by tree fruit rows. The historical settlements are located on the height sites (characteristic is the Albugnano borough), while the rural settlements occurs in isolated or aggregated buildings, disposed on the better exposed slopes. Among the significant historical sites, excels the Vezzolano Abbey, low medieval complex of regional relevance. The USLE method has been applied in the study for evaluating sheet water erosion. For that scope, the main factors causing erosive processes have been computed from experimental or literature data: rainfall erosivity, soil erodibility, topography of the slopes (length and slope), cropping factor, conservation practice factor. In particular the difference of potential erosion at the vineyard slopes has been evidenced in presence or not of a grass cover among the vine rows. A simplified method for the assessment of the shallow landslide susceptivity has been applied in the study area. The model takes in account both the rainfall infiltration in the soil and her influence on the slope stability. For the infiltration analysis the model uses the Green-Ampt method that considers the downwards advancement of a saturation front from the ground surface in consequence of a project rainfall. The thickness value of saturated soil is used as input information for the stability analysis according to the infinite slope method. The utilization of the Safety Factor equation permits to relate the project rainfall with the landslides trigger, through the h value, assuming very low values for cohesion and friction angle. At last, the slope exposure and the layer arrangements (dip direction, dip angle) are elaborated in a simplify model for the evaluation of the susceptivity of the examined territory to the translational landslides.