Volume 29, Issue 3 (Fall 2025)
jwss 2025, 29(3): 171-186 |
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Tahvilian M, Eslamian S, Gohari A, Jamali M. Comparison and Analysis of Empirical Equations for Estimating Time of Concentration (A Case Study in Khuzestan Province). jwss 2025; 29 (3) :171-186
URL: http://jstnar.iut.ac.ir/article-1-4494-en.html
URL: http://jstnar.iut.ac.ir/article-1-4494-en.html
Department of Water Science and Engineering, College of Agriculture, Isfahan University of Technology, Isfahan, Iran. , saeid@iut.ac.ir
Abstract: (109 Views)
Time of concentration (Tc) is one of the key parameters in hydrological studies, playing a critical role in flood control structure design, runoff simulation, and water resource management. This study evaluates the performance of seven empirical equations—Bransby-Williams, California, Giandotti, Kirpich, Pilgrim, Rational Hydrograph (SCS), and Carter—in estimating Tc across 35 sub-watersheds in Khuzestan Province, Iran. To assess the accuracy, six sub-watersheds with reliable rainfall-runoff data were selected, and observational Tc values were calculated. The estimated results from the empirical formulas were then compared with observed data using statistical indices such as RMSE, ME, and the Nash–Sutcliffe Efficiency (NSE). The findings revealed that the Kirpich equation provided the most accurate and reliable estimates, with RMSE = 2 hours, ME = 0.44 hours, and NSE = 0.91. Subsequently, all seven models were applied to estimate Tc for the remaining sub-watersheds. Finally, a concentration time zoning map was generated, which can serve as a practical tool for hydraulic design, flood risk analysis, and optimal water resource planning in Khuzestan Province.
Keywords: Time of Concentration, Empirical Equations, Khuzestan Sub-watersheds, Kirpich method, Statistical analysis, Flood design
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