The runoff-erosion process is modeled for a typical Brazilian semiarid area with a kinematic model. The data are analyzed and the model is optimized by the SP method. The scale effects of the basin elements on the model coefficients are discussed by dividing the basin in three different configurations. Predicting runoff using a kinematic model has become a useful tool, but to model this process special care must be taken when the infiltration for a given event is estimated. Thus, hydrographs

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... to runoff with different initial infiltration capacity of soil and various types of rainfall are also discussed and the moisture-tension parameter, which is one of the optimized parailieters, is studied separately.