Modelagem chuva-vazão: uma proposta metodológica à análise do coeficiente de abstração inicial do Método Curva Número

Abstract

The Curve Number Method (CN) is one of the most used to prediction direct runoff from the conversion of storm rainfall in a hydrographic basin. However, it presents uncertainties regarding its use, as it depends on physiographic parameters, characteristic of each area, in addition to the assumption that the constant 0.200 can define the initial abstraction ratio. The proposals of this study were: (1) to contribute with a methodological proposal to analyze the initial abstraction ratio based on rain-flow data; (2) characterize the rain-flow events and the separation of quickflow and baseflows by different methods; (3) characterize the initial abstraction ration (λ) and the Number Curve (CN); (4) correlate the observed quickflow runoff with those estimated by different initial abstraction ratios (λ). 43 events were used for the Santana River Basin, obtained through the portal of the Agência Nacional de Águas e Saneamento Básico (ANA). The results indicated that the graphic separation method, for this study basin, generated the best data for analysis of the parameters obtained through the curve number method. The initial abstraction ratio varied between 0.006 and 0.376, presenting an average of 0.138, lower than that originally proposed by the method. The analysis of the runoff data in blocks, made possible by the confirmation of the normal distribution of the initial abstraction ratio data, generated greater correlations between the estimated and observed runoffs, which may characterize a lesser influence of the physiographic parameters and a greater concentration on the hydrological behavior of the data set. For maximum flow data, the block analyzes were not satisfactory, however, for values less than 50 m³. s -1, we obtained a correlation between estimated and observed flows. A new methodological proposal is beneficial to obtain results in non-studied basins, given its ease and simplicity of application.