MULTITEMPORAL ANALYSIS OF LAND COVERING AND VEGETATION AREAS UNDER QUATERNARY SUPERFICIAL FORMATION – A STUDY OF THE HYDROGRAPHIC BASIN STREAM PUIT , RIO GRANDE DO SUL – BRAZIL

The hydrographic basin of stream Puit , located in the southwest of the state of Rio Grande do Sul – Brazil, is characterized by quaternary superficial formation. These formations are dominated by erosive features and sand strands located in the geological compartment of hills as well by bushes located on the hillside and ciliary’s bushes located along the course of the water together with the campestre vegetation. The use of the land stands out with plots of land used to agriculture, intensified in the last decades. Theagricultural activities left the soil fragile, causing erosive features. This study aims to identify the existent relationship between the type of vegetation and the soil degradation in the regionof the hydrographic basin. The methodology is based on digital classification of Landsat-TM satellite images, data acquired between 1984 e 2004, on the correlation analysis between degraded areas, classes of land use and vegetation’s types.The results showed thematic maps that allowed identifying the different fragilities and susceptible areas to the sandification process. The multitemporal approach allowed to evaluate the modifications of the mapping classes and to identify the expansion or retracting of sand strands and erosive processes. It was detected that the agricultural use is the responsible agent for the amplification of the soil fragility.