Runoff and Hydrographs MCQ with answer and solution

Concept

A unit hydrograph represents the lumped response of a catchment to a unit volume (1 cm) of excess rainfall occurring in a specified duration.

Step-by-step solution

1. Recall the definition of a unit hydrograph (UH). 2. A UH represents the surface runoff resulting from 1 cm of effective rainfall (excess rainfall). 3. Match with the given options to find option (B).

Explanation

A unit hydrograph is defined as the surface runoff hydrograph resulting from 1 cm (or 1 unit) of direct runoff generated by a unit storm of specified duration uniformly distributed over the catchment area.

Why the other options are wrong

A: Continuous rainfall leads to complex runoff, not a single unit hydrograph duration. C: Total rainfall includes losses like infiltration, not just the excess rainfall. D: Constant discharge does not define a unit hydrograph.

Shortcut

Remember 'Unit' in Unit Hydrograph stands for 1 cm of excess rainfall.

Common mistake

Confusing total rainfall with excess rainfall (effective rainfall).