Comparative study between empirical equations and the velocity method for estimating time of concentration

Abstract

ABSTRACT: So important for hydrological projects, the estimation of the time of concentration (tc), is realized by the use of empirical equations obtained in international studies. The limits of applicability to which they have been proposed are often disregarded. Nevertheless, the use of the NRCS (Natural Resources Conservation Service) velocity method, the most recommended for the estimation of “tc” in urban basins, is not observed. Thus, the present paper aims to analyze the estimate of tc using empirical equations versus the adoption of the velocity method. For this, the values ??obtained between the methods were compared by means of the construction of 168 hypothetical scenarios resulting from the combination of parameters such as slope, the extension of the sheet flow; the extension of the flow in shallow concentrated flow and open-channel flow. After this stage, the flow by the Rational Method was calculated for all scenarios. By the discrepancy of the values ??obtained for the times of concentration and flow between the equations and the speed method; we highlight the importance of the field survey of the basin under study, as well as the knowledge of the application ranges of empirical equations. As observed, the influence of the extensions of flows in natural or defined stretches will greatly influence peak flows; showing the importance of the definition of the most appropriate method by designer.