Question

Given below are two statements:

Statement (I): In small catchments the overland flow phase is predominant over the channel flow. Hence the land use and the intensity of rainfall have an important role on the peak flood.

Statement (II): On large catchments the effects of land use and intensity of rainfall are suppressed as the channel flow phase is more predominant.

In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Think about which flow phase, overland or channel, dominates the travel time in small versus large catchments.

Answer 1

The Correct Option is A

Step 1: Compare each statement with how runoff behaves in small versus large catchments.

Step 2: Statement (I) is correct. In a small catchment, water spends most of its travel time moving as a thin sheet over the land surface before it reaches a defined channel. Because this overland flow phase dominates the total time of concentration, the type of land cover and how intense the rainfall is over that short travel path directly control how sharp and how high the resulting peak flood is. This is also why simple methods such as the Rational Method, which lean heavily on rainfall intensity and land use, are used for small catchments.

Step 3: Statement (II) is correct. In a large catchment, water spends most of its travel time inside stream channels rather than as overland sheet flow. The channel network stores and routes the flow over a long distance, smoothing out short bursts of high intensity rainfall and averaging out local differences in land use, so their influence on the peak flood becomes far less pronounced than in a small catchment.

Step 4: Since both statements correctly describe the shift from overland flow dominance in small catchments to channel flow dominance in large catchments, option 1 is correct.