Modelagem chuva-vazão: correlação entre coeficiente CN e abstração inicial do Método Curva Número

Abstract

Surface runoff is one of the main components of the hydrological cycle. Using the Number Curve Method, the correlation equation of estimated CN values and the ANA metadata base referring to CN values based on specific characteristics, the analyzes of this research were discussed. Thus, the proposals in the present study were (1) to determine the best flow separation method for the analyzed events; (2) correlate CN value, maximum flow coefficient and initial abstraction coefficient and compare with CN metadata values; (3) compare three stations with different flows and drainage areas and validate the influence of the drainage area on runoff. The central hypothesis of this study is that the influence of the drainage area of the river basins significantly affects the precision of the parameters used in the Number Curve Method (CN) to estimate surface runoff. And the main scientific contribution of this work is the validation and improvement of the Number Curve Method (CN) based on empirical data and detailed drainage area analysis. For this, 10 river basins were used, obtained from the database of the National Water and Basic Sanitation Agency (ANA). The results indicated that the graphical separation method was more effective for separating surface and underground flows. Related to the comparisons between the initial abstraction coefficient, 0.200 from the literature and 0.138 (Barbosa, 2021), 60% of the values estimated using the coefficient of 0.138 were closer to the values calculated by the Number Curve Method, proving to be more effective for river basins studied. When comparing medium CN metadata values, provided to the ANA Metadata Catalog, 80% of the estimated average values were below, as estimated average values were compared with medium CN metadata values, which justifies the variation. This CN variation was 21% on average. Regarding influences, the comparison between the São Martinho, Pirai and Itaú de Minas river basins shows the great relevance of specific characteristics when checking the surface runoff values for each study area. Furthermore, to verify the influence of the drainage area, the comparison between the Piracicaba and Pirassununga river basins, which have drainage areas in the same order of magnitude, 9000 km², the variations in CN values estimated with CN metadata values, were 30% and 23%, consequently generating large impacts on surface runoff. In this way, it shows that the other parameters influence is more relevant than the drainage area.