Análise do processo chuva-vazão utilizando o hidrograma unitário conceitual de Nash na bacia hidrográfica do rio Santana

Abstract

The process of modeling the flow from precipitation is one of the challenges that hydrology proposes to solve. Because they are complex systems, with several variables involved, the flow is often treated as a model response that is a function of a specific variable. Nash’s model (1957) considers the basin as a linear system that is a function of two parameters: number of reservoir (n) and decay rate (k). Through the series of precipitation and flow data, it is possible to find, for each event, numerical values for these parameters that can be used to model future events. In this work, the objective was to find a representative average unit hydrograph for the Santana river basin, through 42 precipitation events, and to analyze the influence that the parameters have mainly on the peak flow and peak time. For the separation of the underground flow, graphic analysis was used; to determine the parameters n and k, the method of moments and convolution of unitary surface flow vector was used to model the hydrograph. Values of n equal to 4.37 and k equal to 22,91 were found for the mean of the 42 events. These events presented the best results for modeling, even when compared with the events selected according to the considerations of Phillip (2002). There was a strong correlation between parameters n and k withs Pearson’s coefficient equal to -0,73. It was also possible to observe a strong correlation between k and peak flow, with Pearson equal to 0,63 for the selected events and a Pearson of 0,42 indicating the correlation between n and peak time. It was concluded that the representative average unit hydrograph can be used for modeling future events for this basin, as it reaches a satisfactory level of accuracy, with R² equal to 0,797, despite finding that it underestimates the peak flow and overestimates the time of discharge peak.