Title: Evaluation of some probability distribution functions for derivation of unit hydrograph in the Bar Watershed, Iran

Authors: Seyed Amir Naghibi; Mehdi Vafakhah; Alireza Moghaddam Nia; Saeid Eslamian

Addresses: Department of Watershed Management Engineering, Faculty of Natural Resources, Tarbiat Modares University, Noor, Iran ' Department of Watershed Management Engineering, Faculty of Natural Resources, Tarbiat Modares University, Noor, Iran ' Department of Arid and Mountainous Regions Reclamation, University of Tehran, Tehran, Iran ' Water Engineering Department, College of Agriculture, Isfahan University of Technology, Isfahan, Iran

Abstract: Considering the ever increasing financial damages of floods and the need to manage the surface water, the use of new and more sufficient methods seems to be necessary. Therefore, the present study aims to investigate capability of the Gamma, Beta, Chi-square, and Weibull probability distribution functions (PDFs) for flood hydrograph derivation. The present study was conducted in the Bar watershed, Iran using 14 suitable rainfall-runoff events. After base-flow separation and direct runoff determination, the three hour unit hydrograph of the watershed was computed to determine the coefficients and parameters of the mentioned PDFs. Finally, Nash-Sutcliffe (NS), relative error (RE), and root mean square error (RMSE) indices were used for evaluation. According to the results, Gamma, Chi-square, and Weibull PDFs had satisfying results for predicting the peak flow with RE values of 11.87%, 25.34% and 37.67% respectively. In the case of time to peak, Gamma, Chi-square and beta PDFs showed acceptable results with RE values of 26.66%, 39.17%, and 34.17% respectively. Totally, considering the high importance of peak discharge and time to peak in flood control projects, Gamma PDF is recommended to be used in flood control projects.

Keywords: probability distribution function; PDF; flood hydrograph; time to peak; peak discharge; Iran.

DOI: 10.1504/IJHST.2018.090880

International Journal of Hydrology Science and Technology, 2018 Vol.8 No.2, pp.134 - 147

Received: 18 Dec 2015
Accepted: 07 May 2016
Published online: 03 Apr 2018 *

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