Runoff and Hydrographs MCQ with answer and solution

Concept

The rising limb of a hydrograph indicates the increasing rate of flow as direct runoff enters the stream network after a rainfall event.

Step-by-step solution

1. Understand the components of a hydrograph: rising limb, crest/peak, and falling/recession limb. 2. Identify that the rising limb corresponds to the initial phase where rainfall intensity exceeds infiltration, generating direct surface runoff that quickly accumulates in the channels. 3. Conclude that quick runoff from rainfall causes the discharge to rise.

Explanation

A storm hydrograph represents the surface runoff resulting from a storm event. The rising limb shows the increase in discharge over time, which is primarily caused by quick surface runoff and interflow reaching the stream following rainfall.

Why the other options are wrong

A: Baseflow increase contributes to the overall streamflow slowly over a long period, not the rapid rise of a storm hydrograph. B: Evaporation removes water from the system and does not cause a rise in stream discharge. D: Groundwater recharge decreases surface runoff rather than causing a rapid rise in a storm hydrograph.

Shortcut

Rising limb = Quick response to rainfall (surface runoff).

Common mistake

Confusing the rising limb due to surface runoff with long-term baseflow increases.