The word unit in the unit hydrograph refers to the
- AUnit area of the basin
- BUnit duration of the storm
- CUnit base period of the hydrograph
- DUnit depth of runoffCorrect
Solution
Concept
Definition of unit in unit hydrograph
Formula
NONE
Step-by-step solution
1. A unit hydrograph is a direct runoff hydrograph resulting from a specified depth of direct runoff. 2. The term unit specifically refers to a unit depth, typically 1 cm, of direct runoff produced uniformly over the entire catchment area. 3. Thus, the word unit denotes the unit depth of runoff. Answer: D
Explanation
A unit hydrograph represents the direct runoff hydrograph resulting from a storm that produces a unit depth of direct runoff, usually 1 cm or 1 inch, uniformly over a drainage basin. The term unit specifically refers to this depth of surface runoff rather than the basin area or storm duration. Therefore, unit depth of runoff is the correct meaning.
Why the other options are wrong
A) The catchment basin area can be any size and is not required to be a single unit of area. B) The storm duration can vary and does not need to be restricted to a single unit of time. C) The hydrograph base period depends on catchment parameters rather than a unit time period.
Shortcut
Unit in Unit Hydrograph stands for 1 unit (cm/inch) depth of direct runoff.
Common mistake
Assuming the term unit refers to unit duration or basin area rather than unit depth of direct runoff.
Correct answer: D) Unit depth of runoff