Hydrologic Cycle: Maximum Water Residence Time
Residence time refers to the average duration water molecules spend within a specific reservoir in the Earth's hydrologic cycle. Different reservoirs hold water for vastly different lengths of time.
Comparing the residence times in various components:
- Atmosphere: Very short (days).
- Rivers: Short (weeks to months).
- Soils: Relatively short (months to a few years).
- Groundwater: Can be very long (months to tens of thousands of years).
- Ice sheets and glaciers: Extremely long (thousands to millions of years).
The largest reservoirs with the slowest turnover rates exhibit the maximum residence time. Therefore, groundwater, stored deep beneath the surface, and ice sheets, massive frozen bodies, hold water for the longest periods compared to the atmosphere, rivers, or soils.
Important Questions from Hydrology And Water Resources
- A river with $2\text{ km}$ wide flood plain and $10\text{ m}$ channel depth flows with a velocity of $2\text{ ms}^{-1}$. What will be flow condition in the river?
Read the following statements and choose the CORRECT answer.
I. The suspended sediment concentration in rivers is supply-limited rather than hydraulically-limited, when
II. Much suspended material is contributed by overland flow from hillslope erosion
III. Suspended material is entirely derived by turbulent diffusion from the channel bed
Match the basin types A, B and C with the hydrograph patterns P, Q and R
Basin types Hydrograph pattern A. 
P. 
B. 
Q. 
C. 
R. 
Hydraulic gradient beneath A and B during rainy and dry seasons will
Identify the correct sequence of freshwate abundance on the Earth.(GP = Glaciers and Polar ice; A = Atmosphere; LR = Lakes and Rivers; UW = Underground Water)
