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.
The Rational formula for peak runoff is stated as: \[Q = C \cdot I \cdot A\] where: - \(Q\) = Peak runoff rate (m\(^3\)/s)
- \(C\) = Runoff coefficient (dimensionless)
- \(I\) = Rainfall intensity (mm/hr)
- \(A\) = Catchment area (ha or km\(^2\))

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

Step 3: Conclusion.
Therefore, only parameters (A) and (B) are necessary.

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