Estradas rurais não pavimentadas como fonte de sedimentos em bacia hidrográfica do semiárido

• Ano de defesa: 2016
• Autor(a) principal: Farias, Teresa Raquel Lima
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Hidrologia; Produção de sedimentos; Manutenção de estradas; Caatinga; Conectividade sedimentológica; Sediment yield; Road maintenance; Caatinga vegetation; Sedimentological connectivity
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/18957

Approximately 80% of the road network in Brazil is unpaved. Studies have reported high erosion rates and runoff produced by the road infrastructure in various parts of the world and report that unpaved roads are significant sources of sediment in river basins. For two years (2013-2014), monitoring in the field under natural rainfall conditions was conducted to characterize runoff and sediment yield of unpaved rural road segments and the respective slopes in semiarid area of the Caatinga biome of northeastern Brazil, vulnerable to desertification. It was assessed the application of modelling in the yield of sediments from road surface. The sediment yield values measured in the years 2013-2014 ranged from 0.30 Mg.ha-1.year-1 to 0.92 Mg.ha-1.year-1, higher than those recorded in the preserved area, but generally lower than those reported in the literature for unpaved roads. However, it is a semiarid area with low rainfall and characterized by low runoff coefficients, which limits the sediment yield and the hydrological connectivity in the area, additionally the two monitoring years coincided with drought in the region. In the monitored road slope segments, sediment yield from the non-vegetated slope was about ten times that of the slope with vegetation. On the road surfaces, the annual sediment yield (normalized by the slope) in a segment with traffic was three times higher than that without traffic, in addition, events occurring after maintenance activities generated sediment concentration peaks as high as 5,000 mg.L-1 in these areas. In the road segment scale, among the models tested for the predicting of sediment yield, the USLE associated with the Maner equation, proved to be a suitable approach, the best results being obtained for the road without traffic due to no interference from external factors, such as traffic and maintenance activities, which are not explained by the model. In the scale of the Benguê catchment (933 km²), where the roads occupy only 0.7% of the surface, the modelling indicated that these areas contributed with approximately 7% of the total soil loss. The results of this study suggest that the sediment yield from roads and slopes with bare surface is at least one order of magnitude higher than those recorded in the preserved areas of the basin. Maintenance activities on roads and traffic of vehicles contribute to the increased availability of sediments and impacting the sediment concentrations, but produce lower impact on the sediment loads, which depend on runoff and the its occurrence after reprofiling of roads. It was also found that the natural vegetation of the semiarid region has potential in capturing sediments in road slopes, with an important role in breaking down connectivity between sediment flows from unpaved roads and the natural drainage system of the catchment.