Comparison of salt experiments and empirical time of concentration equations

The time of concentration (Tc) is one of the most contributing parameters for assessing the response of a catchment to rainfall events and estimating the peak flood in many hydrological models. The aim of this work was to evaluate 36 time of concentration equations based on Tc values obtained based on the salt dilution tracing approach. In addition, hierarchical cluster analysis (CA) was applied to identify the degree of similarity between all the Tc formulas and categorise them into several groups. The findings, based on seven sub-watersheds of the Meime river basin in Iran, demonstrate that the Picking, Pickering, DNOS, California and Kirpich-Ten equations provide reliable estimation of Tc; the average bias of these formulas was found to be in the range 2·6–15 min while, for all 36 equations, the bias was 2·6–132·8 min. Furthermore, based on CA, all Tc equations were categorised into four overall groups with the maximum similarity within the members of each group.