Rational Equation Calculator |
Compute peak discharge from a drainage basin using the Rational Equation Method |
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Rational Equation: Q=ciA Note that our calculation allows you to use a variety of units. The Rational method runoff coefficient (c) is a function of the soil type and drainage basin slope. A simplified table is shown below. See the references at the bottom of the page for more complete tables including impact of slope. The Rainfall intensity (i) is typically found from Intensity/Duration/Frequency curves for rainfall events in the geographical region of interest. The duration is usually equivalent to the time of concentration of the drainage area. The storm frequency is typically stated by local authorities depending on the impact of the development. A 10-yr, 25-yr, 50-yr, or even 100-yr storm frequency may be specified.
Chow, Ven Te, David R. Maidment, and Larry W. Mays. 1988. Applied Hydrology. McGraw-Hill. Corbitt, Robert A. 1999. Standard Handbook of Environmental Engineering. McGraw-Hill. 2ed. Lindsley, Ray K., Joseph B. Franzini, David L. Freyberg, and George Tchobanoglous. 1992. Water-Resources Engineering. McGraw-Hill. 4ed. McCuen, Richard H. 1998. Hydrology Analysis and Design. Prentice-Hall. 2ed. Singh, Vijay P. 1992. Elementary Hydrology. Prentice-Hall.
LMNO Engineering, Research, and Software, Ltd. August 25, 2015: Made text fields show 8 significant figures rather than 16. Calculation still uses double precision internally. |
To: LMNO Engineering home page (more calculations) Related calculations: Time of Concentration |