Assessment and Uncertainty Analysis of Different Time of Concentration Methods

There are many uncertainty sources initiated from dependency of time of concentration equations (Tc) upon different parameters, which generally include rainfall intensity, topographic and land use map scale, DEM resolution and stream's delineation threshold. Throughout the present research the uncertainty and the performance of twenty Tc equations were investigated in the Kasilian and Amameh catchments. Results indicate that in either of the catchments, BransbyWilliams and Morgali-Linsley equations show good agreement with the observed values, with a relative error of less than 10%. Also, the uncertainty analysis of different Tc equations by use of delta method illustrates that McCuen, ASCE, Eagleson and FAA, Johnstone-Cross equations are of the highest vs. lowest uncertainties, respectively. In the geomorphological-based equations, the uncertainty that is caused by streams delineation threshold is approximately 3-4 times that of DEM and data resolution's uncertainties. This indicates that streams delineation threshold is the most important factor and should be more consideration, especially in ungagged catchments.