Valutazione dei rischi ambientali con particolare riferimento alle zone colpite da problemi di dissesto idrogeologico e dal ripetuto passaggio di incendi boschivi.

摘要

Wildfires are one of the most widespread factors of ecosystem degradation around theudworld. The degree of change in both chemical and biological properties of soil inductedudby forest fires depends on the temperature and the persistence of the fire as well as onudthe soil moisture content of fuel.udThis research, in a first step, deals the study of the stability variation of a hill slopeudcrossed by a forest fire. The first site of investigation is located at western boundary ofudthe rift of Campidano, south-western Sardinia, Italy, to the North-West of the urbanudarea of Villacidro. The geological features are constituted by metamorphic rocksud(Hercynian basement) overlying granitoid rocks with a sub-horizontal and weakly wavyudcontact surface. In order to perform the stability analysis, two geotechnical modelsudwere derived by the integration of the results of geotechnical surveys (NSPTudmeasurements and direct shear tests) with electrical resistivity tomographies. Classicaludapproach based on Limit Equilibrium Method is used to determine the safetyudcoefficient. Furthermore, the effects of the forest fire on the slope stability have beenuddiscussed modifying the 2D models and introducing an ultra-shallow thin layer with theudshear strength parameters determined on burned soil samples, collected after the fireudcrossing. In particular, this analysis has shown a marked reduction of safety factor atudthe interface between the burned soil layer and the underlying material for bothudgeotechnical models, considering the infinite slope method with several saturationudconditions of the shallow layer.udIn this study also were determined the concentrations of geochemical components inudthe soils affected by forest fires. The fire-burn severity was medium, but the effect ofudgeochemical variation on soil is evident. We observe the variation of total content ofudMn that increase in soils affected by a forest fires, respect the control soils. Moreoverudthe C,N and P contents of soil decrease in the time, according with most of theudinternational bibliography. Mapping the values of the geochemical components it wasudpossible to see their mobilization after the rains. With these data we will try in theudfuture to build a model of mobilization of contaminants that is able to predict theuddecrease in the concentration of the element considering the time elapsed from theudfire, the intensity of rainfall and slope.udIn a third step the study aim is to develop methods for the analysis and the collectionudof field data, by means of a multidisciplinary approach, to evaluate land erosion hazard. The second experimental area is located also in Mediterranean basin, on audsteep slope in a hilly area of north-western Sardinia (Municipality of Ittiri, province ofudSassari, Italy),where a human caused fire occurred in august 2013. The area is mainlyudcovered by the typical Mediterranean vegetation.udPrecipitations were recorded using tipping bucket rain gauge installed at the site.udSoil erosion rates from experimental plots were measured and estimated with siltudfences technique taking into account different slopes and vegetation distribution. Theudstudy aims to compare the results obtained by ERMiT (Erosion Risk ManagementudTool) model application and post-fire sediment yields measured in the study area.udThe application of the model shows that the area experienced most of erosion after theudfirst rain events after fire occurring. Comparing experimental and model estimateduddata, there is evidence of ERMiT model overestimating in respect of sampled data forudthe first year. Future experimental data are needed to confirm this assumption and toudcontribute to calibrate ERMiT in a Mediterranean typical vegetation and climateudenvironment.