Time of Concentration Model for Non-Urban Tropical Basins Based on Physiographic Characteristics and Observed Rainfall Responses

The time of concentration (Tc), which represents the steady-state hydraulic conditions of a watershed, is an essential parameter for understanding precipitation and runoff dynamics in a hydrographic basin. Precise Tc estimates are required in many hydrological models and for the correct scaling of hydraulic structures. In Brazil, common empirical or semi-empirical methods for estimating Tc have not been developed and verified using local data, studies are needed in the area of hydrological modeling, which provide knowledge of the flow dynamics in tropical regions. In this study, we develop a model for estimating Tc for non-urban tropical basins, which are characterized by soils with high to very high runoff potential. The model employs the following input variables: basin area, main thalweg length, and average rainfall intensity, and an unprecedented methodology that applies: the Harmony Search algorithm to optimize parameters, data from 15 basins with areas less than 2,000 km 2 , 1,002 hydrological events, 46 equations for estimating Tc, and six different statistical techniques. The model is effective for estimating Tc in non-urban basins in a tropical climate region that mostly present soils with a high to very high runoff potential.