Which of the following is/are the assumptions of the unit hydrograph theory? i. The effective rainfall is uniformly distributed within its duration ii. For a given drainage basin, the hydrograph of runoff due to a given period of rainfall reflects the unchanging characteristics of the basin
- AOnly (i)
- BOnly (ii)
- CBoth (i) and (ii)Correct
- DNeither (i) nor (ii)
Solution
Concept
Assumptions of unit hydrograph theory
Formula
NONE
Step-by-step solution
1. Unit hydrograph theory relies on linearity and time-invariance assumptions for a given drainage basin. 2. The principle of time invariance states that unchanging basin characteristics produce identical runoff hydrographs for equal rainfall durations. Answer: C
Explanation
Unit hydrograph theory relies on key simplifying assumptions including time invariance and linear response. It assumes effective rainfall is uniformly distributed over both time and space across the watershed, and that catchment characteristics remain constant for specified durations. Consequently, both listed statements are core assumptions, making option C correct.
Why the other options are wrong
D) Statement (ii) is a valid assumption of unit hydrograph theory regarding basin runoff characteristics.
Shortcut
Unit hydrograph theory assumes uniform rainfall distribution and linear time-invariance (unchanging basin characteristics).
Common mistake
Selecting option A or B by assuming either uniform spatial/temporal rainfall distribution or basin time-invariance is not an underlying assumption of unit hydrograph theory.
Correct answer: C) Both (i) and (ii)