Performance of methods for estimating the time of concentration in a watershed of a tropical region

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.