Abstract—A simple procedure is suggested to compute direct runoff hydrograph (DRH) using an improved two-parameter gamma distribution (2PGD) based synthetic unit hydrograph (SUH) and it is tested on several storm events recorded in 3 different hydrometeorological catchments. When compared, the computed hydrographs were more accurate than those due to popular Gray, SCS, and Snyder methods, because of avoidance of manual, subjective, and tiresome fitting of hydrograph through few data points for their adjustments for unit runoff volume. The improved 2PGD incorporates the available approximate, but accurate, empirical relations for estimation of β and factors governing the shape of the dimensionless unit hydrograph (UH) from the Nash parameter number of reservoirs (n). The SUH peak discharge per unit area per unit effective rainfall (qp) and time to peak (tp) have been derived from hydrologic and geomorphologic characteristics of the watershed, which is advantageous for field use. The objective of this paper is to propose a 2PGD-based method, test it on the data of 3 watersheds, and finally carry out a sensitivity analysis for model parameters. Model results during calibration and validation are very promising with average efficiency of each watershed exceeding 92% and 72%, respectively.

Index Terms—Direct runoff hydrograph, Gamma distribution, Synthetic unit hydrograph, Unit hydrograph.

P. R. Patil, S. K. Mishra, and Nayan Sharma are with the Dept. of WRD&M, Indian Institute of Technology, Roorkee, Roorkee- 247 667, U.K., India (e-mail: prpatil25@gmail.com; skm61fwt@iitr.ernet.in; nayanfwt@iitr.ernet.in).
A. K. Swar is with the State Pollution Control Board, Odisha, Bhubaneswar- 751 012, Orissa, India (e-mail: swarakhila@gmail.com).

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Cite:P. R. Patil, S. K. Mishra, Nayan Sharma, and A. K. Swar, "Two-Parameter Gamma-Based SUH Derivation," International Journal of Environmental Science and Development vol. 3, no. 5, pp. 427-432, 2012.