Runoff and Hydrographs MCQ with answer and solution

Concept

Components of runoff include direct runoff (surface runoff and prompt subsurface runoff), interflow, and baseflow. Direct runoff reaches the stream the fastest and forms the bulk of the peak flood.

Step-by-step solution

1. Identify the components of runoff: Baseflow, Interflow, and Direct Runoff. 2. Understand their relative speeds: Baseflow is very slow, interflow is moderate, and direct runoff is extremely rapid. 3. Relate speed to peak flood: The component that reaches the outlet quickest with the highest volume per unit time causes the highest peak discharge. 4. Conclude that Direct Runoff contributes most to the peak flood.

Explanation

Direct runoff travels quickly over the ground surface and through channels to the watershed outlet, resulting in a rapid and high discharge response. Therefore, it is the primary contributor to the peak flood of a hydrograph.

Why the other options are wrong

A: Baseflow contributes to long-term sustained flow, not the sharp peak of a flood. B: Interflow moves much slower than surface runoff and arrives after the peak. D: Evaporation is a water loss mechanism, not a runoff component.

Shortcut

Remember: Direct runoff = Surface runoff = Fastest response = Main cause of peak flood.

Common mistake

Confusing baseflow (which contributes to sustained dry-weather flow) with direct runoff (which causes floods).