The model SWAT (Soil and Water Assessment Tool) was used to simulate alternative scenarios of land use in Ribeirão dos Marins watershed, in Piracicaba, State of São Paulo, Brazil, for the biennial period 1999/2000. Two scenarios were simulated. The first one (scenario 1) was based on the current land use except for the introduction of a continuous riparian buffer of 30 m along the drainage network and of 50 m around the springs, in accordance to Brazil's environmental legislation. In the second (scenario 2) the steepest slopes (30.9 % of the watershed area) with high erosive potential, covered by pasture, were substituted by native forest. The two simulated scenarios were compared to the current one in relation to sediment yield. The scenarios brought forth different spatial patterns of sediment yield. A reduction of 94,0 % in sediment yield was obtained by the substitution of pasture with native vegetation (scenario 2), and of 10.8 % in scenario 1. These results showed that it is necessary to manage landscape aspects of watersheds comprehensively, identifying the environmentally most sensitive areas, mainly in relation to erosion, instead of protecting only the riparian areas.
simulation models; non-point source pollution; sediment; GIS; SWAT
