Question

(A) Floods are exceedingly complex natural events. They are resultant of a number of component parameters and are therefore very difficult to model them analytically.
(B) In the regions having same climatological characteristics, if the available flood data are quite insufficient, the enveloping curve technique can be used to develop a relationship between the minimum flood flow and drainage area.
(C) For design purposes, extreme rainfall situations are used to obtain the design storm.
(D) The rational formula is found to be suitable for a peak flow prediction in small catchments upto 75 km\(^2\) in an area.
(E) The rational formula assumes a homogeneous catchment surface.

Choose the correct answer from the options given below:

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

Hint:

Check statement (B) for which extreme (maximum or minimum) envelope curves actually represent, and check the numeric limit quoted in (D) against the standard rational method range.

Answer 1

The Correct Option is A

Step 1: A faster route here is to spot the two statements that contain a specific number or a swapped word, since those are the easiest to check first and usually decide the answer.
Step 2: Look at (B): the phrase is "minimum flood flow." Envelope curves exist precisely because engineers want an upper bound, the biggest flood a catchment of a given size could throw up, when they do not have enough local data. A curve of minimum flows would not help with flood safety design at all, so this statement does not fit real practice and must be false.
Step 3: Look at (D): the number quoted is 75 square kilometres. Standard reference values used in irrigation and drainage courses put the ceiling for the rational method nearer 50 square kilometres, since the method assumes the whole catchment responds together almost instantly, which stops holding as the catchment grows. So (D) is also false.
Step 4: With (B) and (D) both eliminated, only the answer choice keeping (A), (C) and (E) survives among the four given, which is choice 1.
Step 5: Confirm the three survivors make sense together: floods are indeed hard to model exactly (A), design storms are indeed chosen from extreme rainfall records (C), and the rational method does indeed assume the catchment surface behaves uniformly everywhere (E). All three hold up under scrutiny.\[\boxed{\text{Option 1: (A), (C) and (E) only}}\]