Land use changes most of the time increases the hydric erosion leading to loss of water, nutrients and organic matter in agricultural systems. Thus, aiming to estimate the soil loss in the watershed of Colonia River, in Bahia, in the last twenty-seven years, the software SWAT (Soil and Water Assessment Tool) was used. For the purpose, a digitalization thematic map (Arc View), interpretation of aerial photographs from 1975, supervised classification of 2002 satellite images and a land use map generation were developed. The SWAT software was used for obtaining a digital thematic map for every sub-basin of Colonia River Watershed, soil loss quantification in every sub-basin and in the forms of uses obtained by theoretical concept, simulating the inclusions of areas of permanent preservation (APP), as well as, forest in all surface of the sub-basins. Between 1975 and 2002 the average of soil loss in Colonia River Watershed was estimated as 47 t ha-1 year-1, in 2002 the estimate of soil loss was 46.64 t ha-1 year-1. In the simulation of a theoretical scenery of APP and forests, there was a decrease in the average of soil loss in all watershed of Colonia River, respectively, 9.09 t ha-1 year-1 and 20.91 t ha-1 year-1.
soil erosion; soil modeling; SWAT
