Question

The limitations to the use of unit hydrographs are:
(A) Snow melt runoff cannot be satisfactorily represented by unit hydrograph.
(B) The catchment should not have unusually large storages in terms of tanks, ponds, large flood bank storages, etc. which affect the linear relationship between storage and discharge.
(C) If the precipitation is decidedly uniform, unit hydrographs can not be expected to give good results.
(D) The rainfall intensity is assumed constant for the duration of the rainfall excess.
(E) The duration of rainfall should be 1/6 to 1/2 of the basin lag.
Choose the correct answer from the options given below:

• A. (A), (B) and (C) only.
• B. (B), (C) and (D) only.
• C. (C), (D) and (E) only.
• D. (A), (B) and (D) only.

Hint:

Check which statements match the real textbook wording versus which have a key word or number altered.

Answer 1

The Correct Option is D

Step 1: Recall that a unit hydrograph (UH) is built on assumptions of linear response and uniform rainfall excess over the catchment.
Step 2: Check (C): the actual textbook limitation is that a $\text{non-uniform}$ precipitation spoils the UH results, not a uniform one, so as printed, (C) is wrong.
Step 3: Check (E): the accepted guideline links the rainfall duration to a fraction of the basin lag different from $1/6$ to $1/2$, so (E) does not hold either.
Step 4: That leaves (A), (B) and (D), all of which describe genuine restrictions of UH theory: no snow melt representation, no large surface storages, and constant rainfall intensity over the excess duration.
\[\boxed{\text{Answer: (A), (B) and (D) only}}\]