Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Analysis of precipitation data
Question Statement:
The information needed for estimating the design flood using Rational formula is
Options:
(A) cumulative infiltration
(B) antecedent moisture condition of soil
(C) shape factor of the catchment
(D) time of concentration of the catchment
Official Answer Key:
D
Step-by-Step Solution & Explanation
The Rational formula, Q_p = C×i×A (runoff coefficient × rainfall intensity × catchment area), assumes peak flow occurs when the entire catchment is contributing, which happens at a rainfall duration equal to the catchment's time of concentration (t_c) — the rainfall intensity i used in the formula is specifically the intensity for a duration = t_c. Hence time of concentration is essential input data. Cumulative infiltration (A), antecedent moisture condition (B), and catchment shape factor (C) are not direct inputs to the basic Rational method (infiltration/AMC effects are lumped into the empirical runoff coefficient C, not measured separately; shape factor is used in other methods like the SCS or Snyder's synthetic unit hydrograph, not the Rational formula). Answer: (D).
Practice This in Real CBT Exam Interface
Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.