American Society of Civil Engineers


Empirical Determination of Rational Method Runoff Coefficients


by C. Bryan Young, (corresponding author), (Associate Professor, Dept. of Civil, Environmental, and Architectural Engineering, Univ. of Kansas, 1530 W. 15th St., Rm. 2150, Lawrence, KS 66045 E-mail: cbyoung@ku.edu), Bruce M. McEnroe, (Professor, Dept. of Civil, Environmental, and Architectural Engineering, Univ. of Kansas, 1530 W. 15th St., Rm. 2150, Lawrence, KS 66045. E-mail: mcenroe@ku.edu), and Anthony C. Rome, (Design Engineer, Wilson & Company, Inc., 8735 Rosehill Rd., Suite 200, Lenexa, KS 66215.)

Journal of Hydrologic Engineering, Vol. 14, No. 12, December 2009, pp. 1283-1289, (doi:  http://dx.doi.org/10.1061/(ASCE)HE.1943-5584.0000114)

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Document type: Journal Paper
Discussion: by S. David Graber, P.E. E-mail: sdavidgraber@cs.com    (See full record)
Abstract: The rational method for determining peak flood discharges has been used for the design of hydraulic structures for decades. Despite the popularity of the method, little attention has been paid to improving guidance for selection of the runoff coefficient. This study determined rational runoff coefficients (the rational C) for 72 gauged rural watersheds in Kansas ranging in size from 0.45 to 76.6 km2 using a frequency-based approach. The median rational C values for Kansas ranged from 0.17 for the 2-year recurrence interval in western Kansas up to 0.97 for the 100-year recurrence interval in eastern Kansas. This paper investigates the spatial variation in runoff coefficients and documents the dependence of the rational C on recurrence interval. The rational C values determined in this study do not exhibit dependence on drainage area, indicating that the method is acceptable for use on much larger basins than is typically assumed.


ASCE Subject Headings:
Runoff
Coefficients
Floods
Hydrology
Storm sewers
Design