Use of the swat Model for hydro-sediMentologic siMUlation in a sMall... sUMMaryMathematical models have great potential to support land use planning, with the goal of improving water and land quality. Before using a model, however, the model must demonstrate that it can correctly simulate the hydrological and erosive processes of a given site. the swat model (soil and water assessment tool) was developed in the United states to evaluate the effects of conservation agriculture on hydrological processes and water quality at the watershed scale. this model was initially proposed for use without calibration, which would eliminate the need for measured hydro-sedimentologic data. in this study, the swat model was evaluated in a small rural watershed (1.19 km²) located on the basalt slopes of the state of rio grande do sul in southern Brazil, where farmers have been using cover crops associated with minimum tillage to control soil erosion. Values simulated by the model were compared with measured hydrosedimentological data. results for surface and total runoff on a daily basis were considered unsatisfactory (nash-sutcliffe efficiency coefficient -nse < 0.5). however simulation results on monthly and annual scales were significantly better. with regard to the erosion process, the simulated sediment yields for all years of the study were unsatisfactory in comparison with the observed values on a daily and monthly basis (nse values < -6), and overestimated the annual sediment yield by more than 100 %. index terms: soil and management, water erosion, sediment yield, hydrologic modeling.(1) received for publication in May 3, 2011 and approved in december 1, 2011.(2) civil engineer, Master in water resources and environmental sanitation by the institute of hydraulic research at the federal University of rio grande do sul -Ufrgs. av. Bento gonçalves