The information needed for estimating the design flood using Rational formula is:
Show Hint
- cumulative infiltration
- antecedent moisture condition of soil
- shape factor of the catchment
- time of concentration of the catchment
The Correct Option is D
Solution and Explanation
Step 1: Rational Formula. The Rational formula for peak flood discharge is: \[ Q = C \cdot i \cdot A \] where - \(Q\) = Peak discharge, - \(C\) = Runoff coefficient, - \(i\) = Rainfall intensity corresponding to the time of concentration, - \(A\) = Area of catchment.
Step 2: Role of time of concentration. Rainfall intensity \(i\) is taken as the intensity corresponding to the time of concentration of the catchment. This ensures that the entire catchment contributes simultaneously to runoff.
Step 3: Eliminate other options.
- (A) Cumulative infiltration → Not required in Rational formula.
- (B) Antecedent moisture condition → Affects runoff coefficient but not directly in Rational formula.
- (C) Shape factor of the catchment → Not a direct parameter in Rational formula.
Hence, the critical factor is (D).
\[
\boxed{\text{Time of concentration of the catchment}}
\]
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