Q.42 Select the correct option for the given statements. Statement 1: Direction of the movement of a storm over the catchment area has a definite effect on the runoff. Statement 2: If the storm moves against the flow direction, then the base period will be comparatively more and less peak flow may be expected.
- AStatement 1 is true and statement 2 is false
- BBoth statement 1 and statement 2 are true, and statement 2 is the correct explanation of statement 1Correct
- CStatement 1 is false and statement 2 is true
- DBoth statement 1 and statement 2 are true, but statement 2 is not the correct explanation of statement 1
Solution
Concept
A storm moving upstream (against the flow) gives a lower peak and a longer base period. A storm moving downstream gives a higher peak.
Step-by-step solution
1. Storm direction changes the timing of runoff from different parts of the catchment. 2. So statement 1 is true. 3. If the storm moves upstream (against flow), runoff from the lower area reaches the outlet first and leaves before runoff from the upper area arrives. 4. Contributions spread out in time, so the peak is lower and the base period is longer. Statement 2 is true. 5. Statement 2 shows how direction affects runoff, so it explains statement 1.
Explanation
When the storm moves downstream with the flow, runoff from all parts reaches the outlet together and gives a high, sharp peak. When it moves upstream, the runoff is spread out, giving a low peak and a long base. This is why storm direction affects runoff.
Why the other options are wrong
A: Statement 2 is true, not false. C: Statement 1 is true; storm direction does affect runoff. D: Statement 2 directly explains the effect described in statement 1.
Shortcut
Storm with the flow gives a high peak and short base. Storm against the flow gives a low peak and long base.
Common mistake
Thinking a storm moving against the flow gives a higher peak.
Correct answer: B) Both statement 1 and statement 2 are true, and statement 2 is the correct explanation of statement 1