Question

Select the parameter(s) required for determining peak rates of runoff using the Rational formula.

• A. Intensity of rainfall
• B. Coefficient of runoff
• C. Velocity of flow
• D. Hydraulic mean depth of flow

Hint:

Rational formula = C × I × A. Remember: Only rainfall intensity, runoff coefficient, and area are needed.

Answer 1

The Correct Option is A, B

Step 1: Recall the Rational Formula.
\nThe Rational formula for peak runoff is stated as: \n\[\nQ = C \cdot I \cdot A\n\] \nwhere: \n- \(Q\) = Peak runoff rate (m\(^3\)/s)
\n- \(C\) = Runoff coefficient (dimensionless)
\n- \(I\) = Rainfall intensity (mm/hr)
\n- \(A\) = Catchment area (ha or km\(^2\)) \n\n \n

Step 2: Examine Parameters.
\n- (A) Rainfall intensity → Directly incorporated into the formula. ✓
\n- (B) Runoff coefficient → Reflects surface permeability and land use. ✓
\n- (C) Flow velocity → Not used in the Rational formula; pertains to hydraulic design, not peak runoff. ✗
\n- (D) Hydraulic mean depth of flow → Associated with open channel hydraulics, not the Rational formula. ✗ \n\n \n

Step 3: Conclusion.
\nTherefore, only parameters (A) and (B) are necessary. \n\n \n

Final Answer: \n\[\n\boxed{\text{(A) and (B)}}\n\]