Remote sensing and GIS related to the water and soil evaluation and protection in Mediterranean region

摘要

This contribution highlights the advantages of using a multidisciplinary modelling approach to the characterisation of the environmental dynamics of a typical semi-arid Mediterranean region, the Flumendosa river basin located in central Sardinia (Italy). Here, the widespread presence of gcomorphological active techniques as support tools. Radiometric enhancement and supervised classification processing of multitemporal Landsat TM images were used to derive land cover information, allowing to understand the seasonal evolution of the area and to monitor the presence and movement of organic materials These data were then combined with those derived from ground truth and ground survey campaigns concerning not only geology and geomorphology, but also pedology, land use and vegetation coverage. At the same tune, rainfall simulations were carried out in order to evaluate the principal parameters involved in the soil erosion processes. On these data a hydro-geomorphological model based on the spatial prevalence of the different erosion processes, In drought-prone semi-arid Mediterranean regions characterised by an ancient geomorphologic evolution such as the area under examination, erosion processes are mainly controlled by the relative contribution of soil properties, land use and morphologic parameters. The different combinations of these induce the spatial prevalence of either erosion by overland flow or erosion by subsurface flow, which, together with other processes less important in the studied area, contribute to the existence of a given erosion hazard for each portion of the basin. A model for the prediction of the relative soil loss hazard should hence take into account both phenomena. Generally speaking erosion by overland flow is the prevalent process in the Flumendosa basin but in hillslopes where appropriate conditions are met pipe and seepage flow can greatly contribute to the overall sediment production and transport. These conditions are mainly: i) a highly variable rainfall between seasons; ii) the presence of an underlying impermeable layer in the soil; iii) rcgolith materials prone to shrinking-swelling phenomena; iv) human or naturally induced reduction of the vegetation cover and, v) the presence of at least one dispersible processes interacts with the consequences of intense human activities on crop cultivation and forest management to produce a fragile environment the equilibrium of which must be carefully surveyed and maintained. To this end, an hydro-geomorphological soil erosion hazard model was devised and applied on the slope basin, using remote sensing and G.l.S. was applied. Six main parameters (i.e. soil erosivity, land use, hillslope gradient and curvature, contributing area and soil infiltration capacity) were used and combined with a matrix linear combination. At the last, the results were tested and validated using the following gcomorphological and soil parameters of the soil database: slope, drainage, surface texture.