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The time of concentration for a watershed is an essential parameter to the design of any hydrological project. In this study, a time of concentration estimation-model that uses variables obtained by monitoring rainfall-runoff events in a rural watershed of a tropical climate is proposed. In developing the model, the relationship between the time of concentration and independent variables was verified using a linear correlation matrix. Two variables with the highest correlation coefficient were selected to derive a model that can estimate the time of concentration. The Harmony Search (HS) optimization algorithm was employed to optimize the model parameters. The performance of the model was evaluated based on the Nash-Sutcliffe (NS) coefficient, which yielded a value greater than 0.80. The proposed model allows one to estimate the time of concentration using only the hydrograph of an event at the base level of a watershed, without the use of rainfall data.

The time of concentration (T c ) is a fundamental parameter in the design of hydrological projects for watersheds. In this study a graphical methodology is described for estimating T c in a watershed, and this is applied to 17 rainfall-runoff events from a rural watershed located near the capital city of Mato Grosso do Sul State, in the Brazilian Cerrado. The T c values obtained through the graphical method were compared to T c values estimated using 20 equations from various references. The equations were selected by considering those that were not developed using data for urban watersheds, and the results of the graphical method were compared to those derived by applying the equations to sub-basin data. The graphical method was reliable in determining T c , and Ventura's equation was found to present the best performance for a rural watershed in a tropical climate region.