Groundwater basics: Identify the incorrect statement about the water table and free-surface groundwater conditions.
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AFree surface groundwater is subjected to atmospheric pressure
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BWater table position rises and falls with seasons
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CDepth of the water table is directly proportional to the rate of drawal of water
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DLevel of the water table remains stationary
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ENone of these.
Answer
Correct Answer: Level of the water table remains stationary
Explanation
Introduction / Context:Understanding the behavior of the water table is essential for well design, yield prediction, and sustainable groundwater management. Several statements about groundwater dynamics are presented; the task is to identify the incorrect one based on hydrogeologic principles.
Given Data / Assumptions:
- Unconfined aquifer with a true free surface (water table).
- Seasonal recharge and pumping may influence levels.
- Heterogeneity and boundary conditions affect responses.
Concept / Approach:
The water table is an equipotential surface at approximately atmospheric pressure. It fluctuates due to recharge (rainfall, infiltration) and discharge (pumping, baseflow). While pumping rate affects drawdown near wells, a simple direct proportionality between water-table depth and withdrawal rate is not universally valid; it depends on transmissivity, storativity, and boundary effects. The claim that the water table remains stationary is clearly incorrect because natural systems are dynamic.
Step-by-Step Solution:
Evaluate (a): Free surface equals atmospheric pressure — correct.Evaluate (b): Seasonal rise/fall occurs with recharge/evapotranspiration — correct.Evaluate (c): “Directly proportional” is an oversimplification; response depends on aquifer parameters — not reliably correct but not as blatantly false as (d).Evaluate (d): “Remains stationary” — unequivocally false in natural settings.Verification / Alternative check:
Observed hydrographs show clear seasonal and event-driven water-level fluctuations, disproving the notion of a stationary water table.
Why Other Options Are Wrong:
- (a) and (b) are standard hydrogeologic facts.
- (c) can be conditionally false; however, the clearly incorrect statement is (d), which contradicts observed behavior.
- (e) “None of these” is not correct because (d) is incorrect.
Common Pitfalls:
- Treating complex aquifer responses as linear proportionalities without considering transmissivity and storativity.
- Ignoring boundary conditions that control regional water-table gradients.
Final Answer:
Level of the water table remains stationary.