Sensitivity analysis of some equations for estimating of time of concentration in watersheds

Estimation of time of concentration has considerable role in physiographic and hydrologic studies of watersheds. Especially, it affects on estimation of peak discharge in hydrological studies. However, there are many various equations for computating of time of concentration, which have not been analyzed by sensitivity analysis. So, in this study, beside of introducing of new straightforward method for sensitivity analysis of simple equations, four common applicable equation of time of concentration in Iran (e.g. Kirpich, California, Bransly Williams and SCS) have been analysed by sensitivity analysis. Results show that very low amount of changes in the slope, especially in low slope reaches, have considerable effects on time of concentration. While, increase in slope of stream, the effects of stream length or curve number (CN) parameters on time of concentration increases. In the other hand, the effect of circularity coefficient on time of concentration is not so considerable. Generally, results show that the measuring or estimating of stream slope, length and curve number need to more attention and correction.