Calculation of peak storm water runoff rate from a drainage area is often done with the Rational Method equation (Q = CiA). Calculations with the Rational Method equation often involve determination of the design rainfall intensity and the time of concentration of the watershed as well. Example calculations and examples using an Excel spreadsheet for Rational Method equation calculations and for determination of the design rainfall intensity and the time of concentration of the drainage area, are presented and discussed in this course. The parameters in the equations are defined with typical units for both U.S. and S.I. units.
This 1 hour course is intended primarily for civil engineers, hydraulic engineers, highway engineers, and environmental engineers. After completing this course you will be able to calculate peak storm water runoff rate using the Rational Method equation in either U.S. or S.I. units, including determination of runoff coefficient, calculation of time of concentration, and determination of design rainfall intensity. You will also be prepared to use Excel spreadsheets to efficiently make the calculations.