Overland flow generation mechanisms in the Concórdia River basin, in southern Brazil

ABSTRACT Overland flow in watersheds is responsible for the occurrence of various environmental problems, including flood formation, erosion and the transportation of sediment, and the addition of pollutants to the soil. Additionally, understanding this hydrological process is fundamental to improving knowledge regarding individual interest factors in a region, since it interferes with agricultural productivity and water supply for both the population and industry, among other contributions. Two principal theorists have described the overland flow generation processes: Horton (1933) and Dunne (1978). The TOPMODEL (a topography-based hydrological model) approach represents the overland flow by variable contribution areas, which develop along the watercourses following the concept of Dunne’s overland flow. Thus, this study aimed to evaluate the mechanisms of overland flow generated in the Concórdia River basin based on the application of the TOPMODEL, using measured hydrological data obtained from a high frequency installed monitoring network. Discharge data series were performed for three sub-basins: SF3 (29.74 km2), SF2 (5.81 km2), and SF1 (2.36 km2). In these sub-basins, the flood hydrograph were separated and its response conditions were verified in the TOPMODEL. Rainfall, discharge, and potential evapotranspiration data were used in an hourly scale for the three sub-basins. In general, the model showed adequate efficiency for the SF3 sub-basin; however, the SF2 and SF1 sub-basins showed distortion in its parameters, thereby delaying the simulated hydrograph in terms of time. Accordingly, the results corroborate the more frequent appearance of Dunnian overland flow in the SF3 sub-basin, where the topography is smoother and features large areas with a low slope, which serve as variable saturation areas. The SF2 and SF1 sub-basins present characteristics that strongly reflect Hortonian overland flow, with slopes in the topography that do not allow the frequent formation of variable contribution areas.