Análise da produção de sedimentos e associação do uso e ocupação do solo com a impermeabilização da microbacia do Rio Granjeiro, Crato - CE

Abstract

The watershed of the Granjeiro river has geological risks of mass landslides and floods due to geological, geomorphological and climatic factors linked to soil loss by erosion and combined with densification problems of the urban core and occupation in risk areas. This scenario provided the development of this research that evaluates the use and occupation, impermeabilization, soil erosion and sediment yield in the area. The approach to territorial analysis, were related to the use and occupancy patterns with the impermeabilization conditions of the watershed and evaluate the spatial distribution of sectors in permeability levels and your changes in two years (2006 and 2014). The criteria for use and occupancy patterns were the density of buildings and coating free areas (urban) and type of vegetation and exposure of soil (rural or unemployed). Thus, they were attributed impermeabilization levels for each class. The main change occurred in urbanization, which generated growth of more impermeable portions advancing south of the area. There was growth of 4% and 0.8% of the urban sectors of high and medium density and low-density areas, respectively. The use class corresponding to high infiltration retreated 4.3%, while the level of maximum infiltration remained virtually unchanged. There is perspective arise of the low to moderate infiltration upstream, along roads, from the urban center. In water erosion analysis, it was estimated sediment yield of the watershed and correlated to soil erodibility. For erosion in non-urban areas (rural) was applied to USLE, being calculated erodibility values nomogram Wischmeier et al. (1971) and equation of the Denardin (1990). The sediments of urban origin were quantified by the contribution of the population of the area. Erosion results were adjusted to the morphology characteristics calculated by diffuse transport index (SDR). Therefore, it was possible to obtain a production of sediments per year 6.02 ton.ha-1, where 29% of the erosion produced for exutório carried sediments. About 4% of the sediments is of urban origin. The model showed a strong correlation to the erodibility data measured by the two mentioned procedures, with the observation that the values of Denardin equation are overestimated in relation to the nomogram. The production of pellets also showed significant sensitivity with respect to variation of erodibility also demonstrating that the presence of urban areas reduces the influence of the K-factor in the model.