Identification of erosion susceptible areas in Grande river basin (Brazil)

Since the 1970s, there is a increasing occupation of the Brazilian "cerrados" by agriculture, with important soil and erosion impacts. The present paper has the purpose to the model morphologic features estimating erosion to subsidize the agricultural planning of the Great river basin (Barreiras, state of Bahia - Brazil), by means of geoprocessing tools. Thus, the topographical factor of Universal Soil Loss Equation (USLE) was used. It was modeled from the Digital Elevation Model (DEM), created by Topogrid module of the ArcInfo software, focusing on hydrology. The slope length of the USLE presents difficulty to be modeled in computational environs. To supply that deficiency methodologies have been proposed in order to obtain automated values with better results. This way, it was developed a program in ArcInfo Macro Language (AML) to optimize the factor slope length map construction from the mathematical formulation proposed before. The input of the developed program it just DEM. A proposition to estimate this variable uses a mathematical formulation from the contribution area. The results maps were: aspect, slope, length exponent of the USLE-factor (m), coefficient X and slope length map. The slope length factor map enables to identify the largest susceptible areas for erosion, improper to agriculture: the results attest that areas prone to erosive process take place at high flow concentration of water.