In hydrology, what does 'time of recession' indicate?

The term 'time of recession' in hydrology refers to the period from the peak flow of a hydrograph to the point when the flow returns to baseline or normal conditions. This is critical for understanding how river systems respond to precipitation events and how long it takes for water levels to recede after a flood event.

During the recession phase, water that has accumulated due to rainfall or snowmelt begins to drain away, and the flow within the river or stream decreases gradually. Understanding this time frame helps in flood management and designing drainage systems, as it allows engineers and planners to anticipate how long a water body will remain elevated and potentially hazardous.

The other options do not accurately capture the definition of 'time of recession'. The duration from the beginning flow rate to the peak flow rate describes the rising limb of a hydrograph, while the travel time between two points in a drainage area refers to the time it takes for water to move through the landscape. The total time taken for rainfall to affect surface runoff deals with the entire process from precipitation to runoff, which is different from the specific period of decrease following peak flow.