J. Bio. Env. Sci.3(12), 150-159, December 2013
Temporal parameters are used in most of hydrological and hydraulic models. The most common temporal parameter in hydrology is time of concentration which is required for spillway design, flood volume estimation, producing flood hydrograph and much other hydrological analysis. Therefore, in this research, 10 estimation methods have been calculated for each sub-basin of both studied watersheds. Ultimately, equations of estimating the time of concentration were evaluated using mean deviation, mean difference, relative error percentage and mean square error tests and comparison method of mean by Tukey method and their categorization in Minitab software. The results of analysis of variance table showed that, there is a significant difference at the level of 1% between the equations. The results of analysis of variance by Tukey method for Banadak Sadat watershed showed that, Passini Model (which has the minimum amount of MD, BIAS, RE, RMSE by 0.001, 0.0031, 0.0043, 1.892 respectively) is the best approach, and after this model, Ventura model and Rational Hydrograph were respectively the best equations to estimate the time of concentration in the considered watershed. For Siazakh Watershed also, results showed that, the best method for concentration method estimation which has the minimum difference with observed values, is logistic hydrograph (also it has the minimum amount of MD, BIAS, RE and RMSE by 0.085, 0.0092, 0.068 and 5.83 respectively) and after this model, Kirpich and Chow models were respectively the best equations to estimate the time of concentration. Overall results demonstrated that, Rational Hydrograph equation is the most appropriate equation and Bransly-Williams equation is not recommended because of very much difference with observed data.
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