Which of the following parameters is not required in the Rational method to calculate the peak flow?

• A. A) drainage area
• B. B) curve number
• C. C) time of concentration
• D. D) runoff coefficient

Answer: (B)

The Rational Method is a widely used approach for estimating peak discharge from a drainage area, particularly in urban settings. It is based on a few key parameters that are essential for making accurate calculations. The parameters required typically include the drainage area, runoff coefficient, and time of concentration.

The drainage area represents the total area that contributes runoff to a specific point. The runoff coefficient quantifies the portion of rainfall that will convert to runoff, reflecting the land use, soil type, and moisture conditions. The time of concentration is the time it takes for water to travel from the most distant point in the drainage area to the outlet.

While the curve number is an important parameter in other hydrologic methods, particularly the SCS method, it is not a necessary component of the Rational Method. Instead, the Rational Method directly utilizes the runoff coefficient, which captures the information that the curve number would represent. Thus, the correct answer pertains to the curve number not being a required parameter in the Rational Method for calculating peak flow.