Studio geoambientale dei Biotopi “Foci dell’Avisio”, “La Rupe” e “La Rocchetta” finalizzato alla Valutazione di Impatto Ambientale

Abstract

Thematic cartography in a GIS (Geographic Information System) have been employed to assess the direct impact produced on geological, geomorphologic and vegetation settings by the construction of a new motorway between the town of Mezzolombardo (TN) and the snout of the Non Valley (Rocchetta area). geological, geomorphologic and vegetation maps have been created at a 1:5,000 scale and implemented in a GIS. The geological map concerns not only the Mesozoic substratum and the size of the rocky outcrops, but also the complex Quaternary deposits occurring in the area. Similarly, by adopting the polygonal units of the geomorphologic map, the main goal was a complete and continuous definition of the study area. Slope classification has been achieved through the use of the available DTMs (digital terrain model). Rock-fall hazard zoning has been performed by the combination of the previous maps and the shadow cone method, which has been modified for the purposes of this study. Vegetation maps have been obtained through physionomic-structural criteria, by means of the phytosociologic method of Zurich-Montpellier. The synthetic units for the subsequent indicisation of the environmental quality, have been obtained by the crossing-over of geological and geomorphologic maps. In this way a synthetic map was performed, where each unit was characterised by the following attributes: geology, geomorphologic specific origin, and slope value. These units have been gathered into homogeneous groups, depending on the dominant geomorphologic processes. The method proposed by Rivas et al. (1995), slightly modified and normalised, has been adopted for the environmental quality assessment. The vegetation map has been directly transformed into a numerical index map. An attempt to estimate the environmental value of plant communities hase been carried out, basing on the evaluation of their soil stabilisation capability, structural stability, and omeostatic range. A final thematic map showing the environmental value of each unit has was performed by crossing the two specific geological-geomorphologic and vegetation value maps. In order to assess the environmental impact, a buffer has been created along two alternative layouts of the designed morotway. The buffer area (60 m wide) has been overlaid to the environmental value and hazard maps, in order to evaluate the direct loss of land with a certain environmental value and the direct exposition to rock-fall hazard for each of the two analysed solutions. The described methods, besides their use in the definition of a clear EIA procedure, form a well-structured database which can be used in multicriteria analyses and multidecision systems.