Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Hydrograph analysis, unit hydrograph theory and application
Question Statement:
Which of the following assumptions form the core foundation of Sherman's Unit Hydrograph (UH) theory?
Options:
(A) Linear response: The ordinates of direct runoff are directly proportional to the effective rainfall depth
(B) Time invariance: The direct runoff response from a given effective rainfall is independent of the time of occurrence
(C) Uniform spatial distribution of effective rainfall over the entire watershed area
(D) Nonlinear storage effect where peak discharge increases quadratically with storm depth
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. Principle of proportionality (linear response): Doubling the effective rainfall doubles every direct runoff ordinate. (Statement A True)
2. Principle of superposition / time invariance: A rainfall event produces the same hydrograph regardless of when it occurs. (Statement B True)
3. Constant duration and spatial uniformity: Effective rainfall is assumed to be distributed uniformly across the entire watershed. (Statement C True)
4. UH theory is strictly a linear lumped system model; it deliberately excludes nonlinear storage interactions. (Statement D False)