Which one of the following terms refers to the time between the end of the net rainfall and the end of the direct runoff hydrograph ?
- ARecession timeCorrect
- BTime-to-peak
- CLag time
- DConcentration time
Solution
Concept
Recession time
Step-by-step solution
1. Time to peak: from the start of rise to the peak. 2. Lag time: from the centre of rainfall to the peak. 3. Concentration time: time for the farthest drop to reach the outlet. 4. Recession time: from the end of net rainfall to the end of direct runoff.
Explanation
The recession (falling) limb extends from the end of net rainfall until the direct runoff ends; this duration is the recession time.
Why the other options are wrong
The other options are defined with respect to the peak or to the catchment.
Shortcut
Recession = falling limb duration.
Common mistake
Choosing the concentration time.
Correct answer: A) Recession time