A Unit Hydrograph has one unit of
- APeak Discharge
- BRainfall Duration
- CDirect RunoffCorrect
- DNone of the above
Solution
Concept
Unit hydrograph direct runoff depth
Formula
NONE
Step-by-step solution
1. A unit hydrograph is a direct runoff hydrograph resulting from a unit depth of rainfall excess. 2. By definition, the total area under the unit hydrograph represents 1 unit (e.g., 1 cm or 1 mm) of direct runoff depth over the basin. 3. Thus, a unit hydrograph represents one unit of direct runoff. Answer: C
Explanation
A unit hydrograph is a direct runoff hydrograph resulting from one unit depth of direct runoff generated uniformly over a drainage basin at a constant rate for a specified duration. It isolates the basin runoff response to a unit input of effective rainfall. While peak discharge and duration vary with storm characteristics, the total runoff volume represented always equals one unit.
Why the other options are wrong
A) Peak discharge varies based on storm duration and watershed characteristics, rather than being fixed at one unit. B) The duration of rainfall excess is specified as D hours, not required to be one unit of duration. D) Option C is correct because a unit hydrograph is defined by one unit of direct runoff.
Shortcut
Unit Hydrograph represents 1 unit (1 cm) of Direct Runoff.
Common mistake
Assuming the "one unit" in a unit hydrograph refers to unit duration of rainfall rather than 1 cm depth of direct runoff.
Correct answer: C) Direct Runoff