A Novel Method for Estimating Time of Concentration in Ungauged Catchments

Abstract

Time of Concentration (TC) is one of the most frequently used time parameters in many hydrological studies. A good estimation of TC value results in a more precise design of expensive hydraulic structures, as well as a better estimation of ood discharge. There are the three available approaches to determine TC: physical, empirical, and graphical methods. Among these, graphical method is a widely accepted and popular among researchers for estimating TC. It is also considered as benchmark in TC studies. However, this method faces problems due to the lack of recorded data in many catchments. In this study, two-dimensional (2D) hydraulic simulation is studied and suggested as a novel technique for calculation of TC. The required input for 2D simulation can be obtained by using free satellite data. Some empirical formulas were also considered for calculating TC as well. The graphical method was used as a benchmark to evaluate the outputs of hydraulic simulation, and empirical formulas. To do this, four different watersheds were considered, with 28 rainfall-runoff events. In hydraulic simulation, TC was calculated as the time taken by a water parcel to travel from the upstream (headwater) to the downstream (outlet) of a watershed. The TC values obtained from the hydraulic simulation, and empirical formulas were compared with graphical method. It was observed that the maximum difference between the graphical method and the 2D simulation was less than 10% in all watersheds. Therefore, hydraulic simulation is a reliable method for calculating TC, especially in ungauged catchments where graphical method is not applicable.